U.S. patent application number 15/099782 was filed with the patent office on 2016-08-25 for catalyst complex with carbene ligand.
The applicant listed for this patent is Jinkun HUANG, Steven P. NOLAN. Invention is credited to Jinkun HUANG, Steven P. NOLAN.
Application Number | 20160243535 15/099782 |
Document ID | / |
Family ID | 26796425 |
Filed Date | 2016-08-25 |
United States Patent
Application |
20160243535 |
Kind Code |
A1 |
NOLAN; Steven P. ; et
al. |
August 25, 2016 |
CATALYST COMPLEX WITH CARBENE LIGAND
Abstract
Catalytic complexes including a metal atom having anionic
ligands, at least one nucleophilic carbene ligand, and an
alkylidene, vinylidene, or allenylidene ligand. The complexes are
highly stable to air, moisture and thermal degradation. The
complexes are designed to efficiently carry out a variety of olefin
metathesis reactions.
Inventors: |
NOLAN; Steven P.; (St.
Andrews, GB) ; HUANG; Jinkun; (Thousand Oaks,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NOLAN; Steven P.
HUANG; Jinkun |
St. Andrews
Thousand Oaks |
CA |
GB
US |
|
|
Family ID: |
26796425 |
Appl. No.: |
15/099782 |
Filed: |
April 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14481401 |
Sep 9, 2014 |
9339805 |
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15099782 |
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13750265 |
Jan 25, 2013 |
8859779 |
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14481401 |
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13041573 |
Mar 7, 2011 |
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13750265 |
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12622225 |
Nov 19, 2009 |
7902389 |
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13041573 |
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09392869 |
Sep 9, 1999 |
7622590 |
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12622225 |
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60115358 |
Jan 8, 1999 |
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60099722 |
Sep 10, 1998 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 2231/54 20130101;
B01J 2531/825 20130101; B01J 31/2273 20130101; B01J 31/2295
20130101; C07D 207/46 20130101; B01J 2231/543 20130101; C07D 498/04
20130101; C07C 2531/22 20130101; B01J 31/2265 20130101; B01J
2231/10 20130101; B01J 2531/821 20130101; C07C 67/30 20130101; C07D
225/02 20130101; C07F 15/002 20130101; B01J 31/2404 20130101; C07D
223/04 20130101; B01J 31/2278 20130101; C07D 313/00 20130101; C07F
15/00 20130101; C07C 6/04 20130101; B01J 2231/4205 20130101; C07F
15/0046 20130101 |
International
Class: |
B01J 31/22 20060101
B01J031/22; C07C 6/04 20060101 C07C006/04 |
Goverment Interests
STATEMENT AS TO FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under Grant
No. CHE-963611 awarded by the National Science Foundation. The
Government has certain rights in this invention.
Claims
1. A method for performing an olefin metathesis reaction,
comprising the step of contacting an olefin with a catalytic
complex of the formula: ##STR00017## wherein M is ruthenium; R is
hydrogen; R.sup.1 is phenyl; X and X.sup.1 are independently
selected from the group consisting of anionic ligands; L is
selected from the group consisting of phosphines, phosphites,
phosphinites, phosphonites, and pyridines; and L.sup.1 is of the
formula: ##STR00018## wherein Y and Y.sup.1 are each independently
an aryl group substituted with halogen, C.sub.1-C.sub.5 alkyl
groups, or C.sub.1-C.sub.5 alkoxy groups; and Z and Z.sup.1 are
independently selected from the group consisting of hydrogen,
C.sub.1-C.sub.20 alkyl, C.sub.2-C.sub.20 alkenyl, C.sub.2-C.sub.20
alkynyl, C.sub.2-C.sub.20 alkoxycarbonyl, aryl, C.sub.1-C.sub.20
carboxylate, C.sub.1-C.sub.20 alkoxy, C.sub.2-C.sub.20 alkenyloxy,
C.sub.2-C.sub.20 alkynyloxy, and aryloxy, each Z and Z.sup.1
optionally being substituted with halogen, C.sub.1-C.sub.5 alkyl
groups, or C.sub.1-C.sub.5 alkoxy groups.
2. The method of claim 1, wherein Y and Y.sup.1 are each
independently an aryl group substituted with C.sub.1-C.sub.5 alkyl
groups; and Z and Z.sup.1 are independently selected from the group
consisting of hydrogen and C.sub.1-C.sub.20 alkyl.
3. The method of claim 1, wherein X and X.sup.1 are each halide,
CF.sub.3CO.sub.2, CH.sub.3CO.sub.2, CFH.sub.2CO.sub.2,
(CH.sub.3).sub.3CO, (CF.sub.3).sub.2(CH.sub.3)CO,
(CF.sub.3)(CH.sub.3).sub.2CO, PhO, MeO, EtO, tosylate, mesylate,
brosylate or trifluoromethanesulfonate; L is selected from the
group consisting of phosphines, phosphites, phosphinites, and
phosphonites; Y and Y.sup.1 are each independently an aryl group
substituted with C.sub.1-C.sub.5 alkyl groups; and Z and Z.sup.1
are independently selected from the group consisting of hydrogen,
methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, and
sec-butyl.
4. The method of claim 1, wherein X and X.sup.1 are chloride; Y and
Y.sup.1 are each 2,4,6-trimethylphenyl; L is selected from
phosphines; and Z and Z.sup.1 are independently selected from
hydrogen and methyl.
5. The method of claim 4, wherein L is selected from
trimethylphosphine, triphenylphosphine, triisopropylphosphine,
tricyclohexylphosphine, and tricyclopentylphosphine.
6. The method of claim 4, wherein L is tricyclohexylphosphine.
7. The method of claim 4, wherein L is triphenylphosphine.
8. The method of claim 4, wherein Z and Z.sup.1 are hydrogen.
9. The method of claim 8, wherein L is selected from
trimethylphosphine, triphenylphosphine, triisopropylphosphine,
tricyclohexylphosphine, and tricyclopentylphosphine.
10. The method of claim 8, wherein L is tricyclohexylphosphine.
11. The method of claim 8, wherein L is triphenylphosphine.
12. The method of claim 1, wherein X and X.sup.1 are chloride; Y
and Y.sup.1 are each 2,6-diisopropylphenyl; L is selected from
phosphines; and Z and Z.sup.1 are independently selected from
hydrogen and methyl.
13. The method of claim 12, wherein L is selected from
trimethylphosphine, triphenylphosphine, triisopropylphosphine,
tricyclohexylphosphine, and tricyclopentylphosphine.
14. The method of claim 12, wherein L is
tricyclohexylphosphine.
15. The method of claim 12, wherein L is triphenylphosphine.
16. The method of claim 12, wherein Z and Z.sup.1 are hydrogen.
17. The method of claim 16, wherein L is selected from
trimethylphosphine, triphenylphosphine, triisopropylphosphine,
tricyclohexylphosphine, and tricyclopentylphosphine.
18. The method of claim 16, wherein L is
tricyclohexylphosphine.
19. The method of claim 16, wherein L is triphenylphosphine.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/481,401, filed on Sep. 9, 2014, now
pending, which is a continuation of U.S. patent application Ser.
No. 13/750,265, filed Jan. 25, 2013, now U.S. Pat. No. 8,859,779,
which is a continuation of U.S. patent application Ser. No.
13/041,573, filed Mar. 7, 2011, now abandoned, which is a
continuation of U.S. patent application Ser. No. 12/622,225, filed
Nov. 19, 2009, now U.S. Pat. No. 7,902,389, which is a continuation
of U.S. patent application Ser. No. 09/392,869, filed Sep. 9, 1999,
now U.S. Pat. No. 7,622,590, which claims priority from U.S.
Provisional Application Ser. No. 60/115,358, filed Jan. 8, 1999 and
U.S. Provisional Application Ser. No. 60/099,722, filed Sep. 10,
1998. The disclosures of these applications are incorporated by
reference in their entirety.
BACKGROUND OF THE INVENTION
[0003] The invention relates to metal carbene complexes. More
particularly, it relates to catalyst systems comprising metal
carbene complexes.
[0004] Catalysts previously known in the art are described in, for
example, U.S. Pat. No. 5,312,940 to Grubbs et al. These catalysts
include bis(phosphine) complexes which involve the use of costly
phosphine (PR.sub.3) ligands. The stabilities of such systems, as
determined by, for example, P--C bond degradation at elevated
temperature, are limited. Also, the rates at which bis(phosphine)
catalysts carry out particular reactions are limited. Thus,
industrial applications involving large-scale syntheses are not as
efficient as they could be.
[0005] Previously available catalytic systems are also limited in
their ability to make highly substituted ring-closing metathesis
(RCM) products. Thus, bis(phosphine) catalysts cannot reliably
close dienes to make tri-substituted cyclic alkenes, and they fail
to make tetra-substituted cyclic alkenes in all but a few cases.
Although Schrock catalysts are available to carry out this type of
reaction, such systems are quite sensitive.
[0006] Thus there exists in the art a need for a generally air- and
moisture-sensitive catalyst system able to carry out RCM reactions
efficiently and reliably, and also without excessive thermal
sensitivity.
SUMMARY OF THE INVENTION
[0007] The invention provides catalysts including metal carbene
complexes which are useful for synthetic chemical reactions. The
catalysts include at least one bulky nucleophilic carbene ligated
to the metal center. Methods of making such catalysts, and ligands
useful for such catalysts are also provided in the present
invention.
[0008] The inventive catalytic complexes are thermally stable, have
high reaction rates, and are air- and moisture-stable. The
catalysts of the invention are easy to synthesize, have high
catalytic activity, and are relatively inexpensive, due to the
availability of the nucleophilic carbene ligand. The catalysts are
useful in the facilitation of chemical reactions, including
applications in the pharmaceutical industry, fine chemical
synthesis, and the synthesis of polymers.
[0009] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, suitable methods and materials are described below. In
case of conflict, the present specification, including definitions,
will control. In addition, the materials, methods, and examples are
illustrative only and not intended to be limiting.
[0010] Other features and advantages of the invention will be
apparent from the following detailed description, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a general structure of a first particular
embodiment of a catalytic complex, having a first ligation
pattern.
[0012] FIG. 1B is a general structure of a first particular
embodiment of a catalytic complex, having a second ligation
pattern.
[0013] FIG. 1C is a general structure of a first particular
embodiment of a catalytic complex, having a third ligation
pattern.
[0014] FIG. 2A is an example of a nucleophilic carbene ligand which
can be utilized in certain embodiments of the present
invention.
[0015] FIG. 2B is a particular nucleophilic carbene which can be
utilized in certain embodiments of the invention.
[0016] FIG. 2C is a particular nucleophilic carbene which can be
utilized in certain embodiments of the invention.
[0017] FIG. 3A is a general structure of a second particular
embodiment of a catalytic complex, having a first ligation
pattern.
[0018] FIG. 3B is a general structure of a second particular
embodiment of a catalytic complex, having a second ligation
pattern.
[0019] FIG. 3C is a general structure of a second particular
embodiment of a catalytic complex, having a third ligation
pattern.
[0020] FIG. 4 is an ORTEP diagram of the crystal structure of
Cp*Ru(IMes)Cl.
[0021] FIG. 5 is an ORTEP diagram of the crystal structure of
Cp*Ru(PCy.sub.3)Cl.
[0022] FIG. 6 is an ORTEP diagram of the crystal structure of
Cl.sub.2Ru(PCy.sub.3)(IMes) (.dbd.CHPh).
DETAILED DESCRIPTION
[0023] The invention includes a catalytic complex for the carrying
out of chemical reactions. The complex includes a metal atom and
various ligands. A particular embodiment of the catalytic complex
is depicted in FIGS. 1A, 1B and 1C.
[0024] Making reference to FIG. 1A, metal atom M can be a
transition metal generally having an electron count of from 14 to
18. Particular metals of this description which have been found
useful in the present invention include ruthenium and osmium.
[0025] Ligated to metal atom M are a number of ligands. At least
one of these ligands is a carbene ligand, which is functionally an
olefin metathesis active fragment, having a carbon atom C.sup.1
which can be further bonded up to two other groups. The bond from
metal atom M to carbon atom C.sup.1 can be formulated as the double
bonded M=C.sup.1, although other canonical forms are evidently
involved, as detailed in Cotton and Wilkinson's Advanced Inorganic
Chemistry, 5th Edition, John Wiley & Sons, New York (1980), pp.
1139-1140.
[0026] As noted, carbon atom C.sup.1 can further bonded to up to
two other groups, R and R.sup.1, and in this case the olefin
metathesis active fragment is referred to as an alkylidene. These R
and R.sup.1 groups are independently selected from a large number
of atoms and substituents. These include hydrogen, alkyl groups
having from 1 to 20 carbon atoms (such as methyl, ethyl, n-propyl,
iso-propyl, n-butyl, iso-butyl, sec-butyl, and the like). Also
possible as either R or R.sup.1 are alkenyl or alkynyl substituents
having from 2 to 20 carbon atoms. The groups R and R.sup.1 can also
include alkoxycarbonyl substituents having from 2 to 20 carbons
atoms, aryl groups, carboxylate substituents having from 1 to 20
carbon atoms, alkoxy substituents having from 1 to 20 carbon atoms,
alkenyloxy or alkynyloxy substituents having from 2 to 20 carbon
atoms, as well as aryloxy substituents. Also included are
alkylthio, alkylsulfonyl, and alkylsulfinyl substituents with from
1 to 20 carbon atoms. Each of the above classes of R or R'
substituent can be further optionally substituted with halogen, or
with alkyl or alkoxy groups of from 1 to 10 carbon atoms, or aryl
groups. Further substitution of R and R.sup.1 can include the
functional groups of hydroxyl, thiol, thioether, ketone, aldehyde,
ester, amide, amine, imine, nitro, carboxylic acid, disulfide,
carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and
halogen.
[0027] Any of the above R or R.sup.1 substituents can include
various structural isomers (n-, iso-, sec-, and tert-), cyclic or
polycyclic isomers, and multiply unsaturated variants.
[0028] Particularly useful R and R.sup.1 substituents are vinyl,
phenyl, hydrogen, wherein the vinyl and phenyl substituents are
optionally substituted with one or more moieties selected from
C.sub.1-C.sub.5 alkyl, C.sub.1-C.sub.5 alkoxy, phenyl or a
functional group, such as chloride, bromide, iodide, fluoride,
nitro, or dimethylamine.
[0029] When carbon atom C.sup.1 is not directly bonded to two
groups R and R.sup.1, it is further bonded to another carbon
C.sup.2, which is in turn bonded to previously described
substituents R and R.sup.1, and the olefin metathesis active
carbene ligand is referred to as a vinylidene. This is shown in
FIG. 1B. This ligation is generally achieved by means of a double
bond from C.sup.1 to C.sup.2.
[0030] Also, as shown in FIG. 1C, C.sup.2 can be further bonded to
another carbon C.sup.3. This type of olefin metathesis active
carbene ligand is referred to as an allenylidene. C.sup.3 is
further bonded to the above-described substituents R and R.sup.1.
Carbons C.sup.1, C.sup.2 and C.sup.3 are each sp.sup.2 hybridized
carbons, and the absence of one or two of such carbons in the
allenylidene structure of FIG. 1C gives the respective vinylidene
or alkylidene or FIG. 1B or 1A, respectively.
[0031] It has been found that when R or R.sup.1 are aryl, the
allenylidene ligand can undergo a rearrangement, forming a
different structure in which a ring is formed between C.sup.1 and
an aryl carbon of R or R.sup.1. For example, if
C.sup.1.dbd.C.sup.2.dbd.C.sup.3Ph.sub.2 is ligated to metal M in
the systems described herein, the olefin metathesis active carbene
ligand is not an allenylidene, but rather a cyclized vinyl carbene,
an "indenylidene" (in this case phenylindenylidene).
[0032] Also ligated to metal atom Mare ligands X and X.sup.1 which
are anionic ligands, shown in FIGS. 1A, 1B and 1C. Such anionic
ligands include those independently chosen from halogen, benzoate,
C.sub.1-C.sub.5 carboxylate, C.sub.1-C.sub.5 alkoxy, phenoxy, and
C.sub.1-C.sub.5 alkylthio groups. In other particular embodiments,
X and X.sup.1 are each halide, CF.sub.3CO.sub.2, CH.sub.3CO.sub.2,
CFH.sub.2CO.sub.2, (CH.sub.3).sub.3CO,
(CF.sub.3).sub.2(CH.sub.3)CO, (CF.sub.3)(CH.sub.3).sub.2CO, PhO,
MeO, EtO, tosylate, mesylate, brosylate, or
trifluoromethanesulfonate. In other particular embodiments, both X
and X.sup.1 are chloride. Ligands X and X.sup.1 can further be
bonded to each other, forming a bidentate anionic ligand. Examples
include diacid salts, such as dicarboxylate salts. As discussed
herein, such groups can alternatively be further bound to a solid
phase, for example a polymer support.
[0033] Also ligated to metal atom M are ligands L and L.sup.1.
These ligands are chosen from a number of different chemical
classes.
[0034] One of these classes of ligands L or L.sup.1 is the class of
nucleophilic carbenes. In the inventive catalytic complexes, at
least one of the ligands L or L.sup.1 is a member of this class.
Nucleophilic carbenes are those molecules having a carbon atom
which bears a lone pair of electrons, desirably also including
those molecules additionally having electron-withdrawing character
manifested in atoms or substituents in electronic communication
with, or bonded to, the carbon bearing the lone pair. Such electron
withdrawing atoms or substituents can include atoms which are more
electronegative than carbon, such as nitrogen, oxygen, and sulfur.
These atoms can either be bonded directly to the carbene carbon, or
in a conjugated or hyperconjugated position with respect to this
carbon. Substituents which have electron-withdrawing character
include nitro, halogen, sulfonate, carbonate, sulfide, thioether,
cyano, and other groups known to those in the art.
[0035] In particular embodiments, it has been found to be desirable
that not both of ligands L and L.sup.1 be nucleophilic carbenes,
although embodiments in which both L and L.sup.1 are nucleophilic
carbenes are also operative.
[0036] Particularly desirable are nucleophilic carbene ligands
further substituted with substituents which increase the steric
crowding around the carbon bearing the lone pair of electrons.
These groups can be bonded directly to the carbene carbon, within a
few atoms of the carbene carbon, or remotely from the carbene
carbon, as long as the bulky group is able to inhibit the approach
of agents which tend to react with, and destroy the carbene, and
consequently disable the catalytic complex as a whole. Thus the
stability of the nucleophilic carbene ligand, and the catalyst
itself are fostered by the presence of bulky groups which are able
to shield the nucleophilic carbene from reaction. It should be
noted that the olefin metathesis active carbene fragment is
sterically protected from bimolecular decomposition by the large
steric umbrella provided by the bulky nucleophilic carbene
ligand.
[0037] Although the invention is not limited by any particular
mechanistic theory, it is believed that such a substituent
arrangement can provide steric protection from carbene degradation
pathways, including thermally induced degradation. The steric bulk
of nucleophilic ligands as described herein can lead to more
thermally stable catalysts. Such bulky or sterically hindering
groups include branched alkyl groups, aryl groups, and aryl groups
having branched alkyl substituents, particularly at the ortho
positions of the aryl rings. For example, a nucleophilic carbene
ligand having bulky alkyl groups such as tert-butyl, iso-propyl or
aryl groups with bulky alkyl groups such as 2,4,6-trialkylphenyl or
2,6-dialkylphenyl interacting with the carbene, could be employed
in the present invention. The groups L and L.sup.1 can also be
further bonded to each other, forming a bidentate ligand wherein
either one or both of L and L.sup.1 are nucleophilic carbene
ligands.
[0038] Cyclic nucleophilic carbene ligands are also envisioned.
These may have heteroatoms either in the ring, or bonded to the
ring. Particularly desirable examples of this type of nucleophilic
carbene ligand are those ligands having a carbene carbon between
heteroatoms. Examples include dinitrogen rings such as imidazole,
disulfur rings such as 1,3-dithiolane, and dioxygen rings such as
2H, 4H-1,3-dioxine. The aromatic, non-aromatic, saturated or
unsaturated analogs can be used as well.
[0039] FIG. 2A depicts an example of a nucleophilic carbene ligand
which can be utilized in certain embodiments of the present
invention. Shown is an imidazol-2-ylidene having substituents Y and
Y.sup.1, and Z and Z.sup.1. Each substituent is independently
selected from a number of carbon-containing groups, or from
hydrogen. The carbon-containing groups which can comprise Y,
Y.sup.1, Z and Z.sup.1 include alkyl groups having from 1 to 20
carbon atoms (such as methyl, ethyl, n-propyl, iso-propyl, n-butyl,
iso-butyl, sec-butyl, and the like). Also possible are alkenyl or
alkynyl substituents having from 2 to 20 carbon atoms. The groups
can also include alkoxycarbonyl substituents having from 2 to 20
carbons atoms, aryl groups, carboxylate substituents having from 1
to 20 carbon atoms, alkoxy substituents having from 1 to 20 carbon
atoms, alkenyloxy or alkynyloxy substituents having from 2 to 20
carbon atoms, as well as aryloxy substituents. Each of the above
classes of substituent can be further optionally substituted with
halogen, or with alkyl or alkoxy groups of from 1 to 5 carbon
atoms.
[0040] Any of the above substituents can include all structural
isomers (n-, iso-, sec-, and tert-), cyclic or polycyclic isomers,
and multiply unsaturated variants. It should also be noted that the
presence of the double bond in the imidazole ring is not required
for catalytic activity in the present invention. In certain
embodiments, an imidazolidin-2-ylidene can be used as nucleophilic
carbene ligand L or L.sup.1.
[0041] The structure in FIG. 2B is a particular example of a useful
nucleophilic carbene ligand, having both Y and Y.sup.1 as
2,4,6-trimethylphenyl, and both Z and Z.sup.1 as hydrogen. This
particular ligand is referred to as 1,3-bis(2,4,6-trimethylphenyl)
imidazol-2-ylidene, or IMes. Another example of a useful
nucleophilic carbene is given in FIG. 2C, which shows a structure
having both Y and Y.sup.1 as 2,6-diisopropylphenyl, and both Z and
Z.sup.1 as hydrogen. This particular ligand is referred to as
1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, or IPr.
[0042] Another class of ligand which can serve as L or L.sup.1 is
the class of phosphines. Particularly useful are trialkyl- or
triarylphosphines, such as trimethylphosphine, triphenylphosphine,
triisopropylphosphine, and similar phosphines. The phosphines
tricyclohexylphosphine and tricyclopentylphosphine are also useful,
and are collectively referred to as PCy.sub.3.
[0043] Other classes of ligands which can serve as L or L.sup.1 are
sulfonated phosphines, phosphites, phosphinites, phosphonites,
arsine, stibine, 1 mmes, ethers, amines, amides, sulfoxides,
carbonyls, carboxyls, nitrosyls, pyridines, and thioethers.
[0044] Other embodiments of catalytic complexes useful in the
present invention are shown in FIGS. 3A (alkylidene), 3B
(vinylidene) and 3C (allenylidene), in which the analogy with the
series of FIGS. 1A, 1B and 1C is based on the identity of the
olefin metathesis active carbene ligand, alkylidene, vinylidene and
allenylidene, respectively. The elements M, X, C.sup.1, C.sup.2,
C.sup.3, R and R.sup.1 are as described above for the first
described embodiment of the inventive catalytic complex. In this
second particular embodiment, ligand L is a nucleophilic carbene
ligand, as described above. In addition, since the species depicted
in FIGS. 3A, 3B, and 3C are all cationic complexes, an anion
A.sup.- is required. This anion can be any inorganic anion, and can
also include some organic anions. Thus, A.sup.- can be, for
example, halide ion, SbF.sub.6.sup.-, PF.sub.6.sup.-,
BF.sub.4.sup.---, AsCl.sub.4.sup.---, O.sub.3SONO.sup.-,
SO.sup.2F.sup.-, NSO.sub.3.sup.-, azide, nitrite, nitrate, or
acetate, and many others known to those of skill in the art.
[0045] In this embodiment, another ligand of metal M is Ar, which
is an aromatic ring system, including the .eta..sup.6-bonded
system. The symbol .eta. is used to signify that all aromatic ring
atoms are bonded to the metal atom. Such systems include
C.sub.6H.sub.6 ring systems, and various alkyl substituted
C.sub.6H.sub.6 ring systems. Heterocyclic arene rings are also
suitable, and these include .eta..sup.6-C.sub.5H.sub.5N, and alkyl
substituted derivatives thereof. These rings can have substituents
chosen from a wide range of groups including alkyl groups having
from 1 to 20 carbon atoms (such as methyl, ethyl, n-propyl,
iso-propyl, n-butyl, iso-butyl, sec-butyl, and the like). Also
possible are alkenyl or alkynyl substituents having from 2 to 20
carbon atoms. The groups can also include alkoxycarbonyl
substituents having from 2 to 20 carbons atoms, aryl groups,
carboxylate substituents having from 1 to 20 carbon atoms, alkoxy
substituents having from 1 to 20 carbon atoms, alkenyloxy or
alkynyloxy substituents having from 2 to 20 carbon atoms, as well
as aryloxy substituents. Each of the above classes of substituent
can be further optionally substituted with halogen, or with alkyl
or alkoxy groups of from 1 to 5 carbon atoms. For example, useful
.eta..sup.6-bonded L or L.sup.1 ligands are p-cymene, fluorene and
indene.
[0046] The inventive catalytic complexes can be used as homogeneous
catalysts, or are equally well suited as heterogeneous catalysts.
The latter embodiment is realized by linking the catalytic
complexes to a suitable solid phase, such as a polymeric support.
The solid phase can be bound to the catalytic complex either
cleavably or non-cleavably. The solid phase can be a polymer which
can either be a solid-state resin such as a Wang resin, or a
soluble polymer such as non-crosslinked chloromethylated
polystyrene (NCPS). This polymer shows excellent properties, such
as solubility in tetrahydrofuran (THF), dichloromethane,
chloroform, and ethyl acetate, even at low temperatures
(-78.degree. C.). NCPS is insoluble in water and methanol. These
features allow traditional organic chemistry techniques such as
solvent extraction, and methanol precipitation. Suitable polymers
include hydroxyl-containing polymers such as Wang resin, or
poly(ethylene glycol) (PEG).
[0047] The method of attachment between solid phase and catalytic
complex can take the form of a link to the ligand L or L.sup.1
which is desirably the nucleophilic carbene ligand. This
arrangement is desirable since the catalytic complex is believed to
operate by first releasing the ligand which is not a nucleophilic
carbene, for example, by releasing a phosphine ligand. Thus,
linkage to the phosphine ligand would result in loss of the solid
phase-catalytic complex interaction, upon catalysis. Also
considered desirable is linkage of the catalytic complex to a solid
phase through the anionic ligands X and/or X.sup.1. Thus, any
linkage which involves a group serving as an anionic ligand as
described above can be used to attach the catalytic complex to a
solid support. For example, carboxylate resins can be employed for
this purpose.
[0048] The inventive catalytic complexes are air- and
moisture-stable, and thus can be used under atmospheric conditions,
and even in aqueous environments. The stability of the catalytic
substrates and products will be the limiting factors with respect
to use under such conditions. The inventive catalytic complexes are
soluble in typical organic solvents, such as tetrahydrofuran (THF),
benzene, toluene, xylene, diethyl ether, dioxane, alcohols,
acetonitrile, dimethylsulfoxide (DMSO), dimethylformamide (DMF),
and similar solvents, but not particularly soluble in water or
methanol.
[0049] The catalytic complexes need not be used in the presence of
any initiators or cocatalysts, although materials such as phosphine
sponges can optionally be used. Those of skill in the art will
recognize the identity of the members of this class, which includes
copper chloride, and Lewis acids generally, in concentrations up to
those stoichiometric with that of the catalytic complex.
Use of Catalytic Complexes in Ring-Closing Metathesis (RCM)
[0050] The catalytic complexes can be used for ring-closing
metathesis. This reaction converts a diterminal diene (a compound
having two --C.sup.a.dbd.C.sup.bH.sub.2 groups, the C.sup.a atoms
of which are able to link together to form a cyclic compound with a
--C.sup.a.dbd.C.sup.a-- linkage), to a cyclic alkene, with
H.sub.2C.sup.b.dbd.C.sup.bH.sub.2 as a side product. In some
instances, the diterminal diene (or an .alpha., .omega. diene) can
undergo a 1,3-hydrogen shift rearrangement (to give an .alpha.,
.omega.-1 diene), and the product will be a cyclic alkene with one
less methylene group in the ring, and propene as a side
product.
[0051] A pronounced solvent dependence of the reactivity of the
present catalytic complexes was noticed. As can be seen from the
results compiled in Scheme 1, reaction rates for
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) in toluene are substantially
higher than those in CH.sub.2Cl.sub.2 (the substituent E is
--CO.sub.2Et). Thus, the tetrasubstituted cyclohexene derivative of
Scheme 1 is formed in essentially quantitative yield after only 15
min if the reaction is carried out in toluene. The reaction
requires 2-3 hours in CH.sub.2Cl.sub.2 to reach completion. This
influence of the reaction medium has been observed for the
ruthenium carbene complexes bearing N-mesityl substituents on their
imidazol-2-ylidene ligands. However, the related complexes having
N-cyclohexyl or N-isopropyl groups do not show this effect.
##STR00001##
[0052] This reactivity of (IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) in
toluene is impaired by a tendency of the active species to promote
isomerization of the double bonds of the substrate. Thus, in Scheme
2, treatment of the pictured diene with as little as 1.2 mol % of
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) in toluene leads to complete
consumption of the starting material within 45 min, but delivers
significant amounts of the 20-membered ring in addition to the
desired 21-membered lactone. Although not wishing to be bound by
any particular theory, the cis-cyclic alkene is believed to result
from an initial isomerization of one of the double bonds in the
starting material, followed by elimination of propene instead of
ethylene during ring closure. This intrinsic bias for ring
contraction was not suppressed by lowering the reaction
temperature. In stark contrast, however, only minute amounts of the
cis-alkene are detected if the reaction is performed in
CH.sub.2Cl.sub.2.
##STR00002##
[0053] As can be seen from the results compiled in Table 1, the
reactivities of (IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) and
(IMes)(PCy.sub.3)Cl.sub.2Ru(phenylindenylidene) in CH.sub.2Cl.sub.2
are sufficiently high to allow the preparation of di-, tri- and
even tetrasubsituted cyclo-alkenes in good to excellent yields. All
ring sizes including medium and macrocyclic ones can be accessed.
The yield data given are the isolated yields. The reactions with
yields given with superscript b (entries 1-4) were carried out in
toluene at 80.degree. C. The compound 3a refers to
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh), and 3b to
(IMes)(PCy.sub.3)Cl.sub.2Ru(phenylindenylidene). E is
--CO.sub.2Et.
TABLE-US-00001 TABLE 1 RCM catalyzed by
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) and
(IMes)(PCy.sub.3)Cl.sub.2Ru(phenylindenylidene) in CH.sub.2Cl.sub.2
Catalyst Yield Entry Product (mol %) (%) 1 2 ##STR00003## 3a (2%)
3b (2%) 96.sup.b 97.sup.b 3 ##STR00004## 3a (5%) 77.sup.b (E =
CO.sub.2Et) 4 ##STR00005## 3b (2%) 89.sup.b 5 ##STR00006## 3a (5%)
98 6 ##STR00007## 3a (5%) 93 7 ##STR00008## 3b (5%) 71 8
##STR00009## 3a (1%) 64 9 10 ##STR00010## 3a (1%) 3a (5%) 62 (R =
H) 95 (R = Me) 11 ##STR00011## 3a (2%) 72 12 ##STR00012## 3a (3%)
82 13 ##STR00013## 3a (4%) 71
[0054] It must be noted that most of these cyclizations cannot be
carried out if the bis(phosphine) complex
(PCy.sub.3).sub.2Cl.sub.2Ru(.dbd.CHPh) is used as the catalyst.
This holds true for all tetrasubstituted cases (entries 1-4 and 7),
the trisubstituted 8-membered ring shown in entry 10, as well as
for annulation reactions depicted in entries 5 and 6. Although the
macrocyclic products (entries 11-13) can also be obtained with the
use of (PCy.sub.3).sub.2Cl.sub.2Ru(.dbd.CHPh), using
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) results in shorter reaction
times and allows lower catalyst loadings to be employed. This
aspect is particularly relevant with respect to pentadec-10-enolide
(entry 11) which is converted into the valuable, musk-odored
perfume ingredient EXALTOLIDE.RTM. (=pentadecanolide) upon simple
hydrogenation.
[0055] As can be deduced from the results in Table 1, complex
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) bearing a benzylidene
carbene moiety and complex
(IMes)(PCy.sub.3)Cl.sub.2Ru(phenylindenylidene) with a
phenylindenylidene unit are essentially equipotent
pre-catalysts.
Method of Making Catalytic Complexes
[0056] The inventive catalytic complexes can be made according to
the following general synthetic procedures, which are adapted from
known procedures.
[0057] To synthesize a catalytic complex according to a first
embodiment of the invention, one of the two phosphine ligands of a
diphosphine-ligated ruthenium or osmium catalyst is exchanged with
a nucleophilic carbene ligand. For example, starting material
diphosphine-ligated complexes (PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) and
(PPh.sub.3)Cl.sub.2Ru(.dbd.CHPh) can be synthesized according to
general procedures such as those given by Schwab et al., Angew.
Chem. Intl. Ed. Engl., (1995) 34, 2039-41.
[0058] Ligand-exchange reactions are carried out by exposing the
diphosphine-ligated complexes to nucleophilic carbene ligands, as
defined above, in suitable solvents such as THF, toluene, and the
like. Reactions are generally carried out at temperatures of from
about 0.degree. C. to about 50.degree. C., for about 15 minutes to
several hours. Subsequent recrystallization in inert solvents gives
the complexes in good yield and high purity.
[0059] The nucleophilic carbene ligands according to the invention
are synthesized according to the following general synthetic
procedure. Solutions of heteroatom-containing starting material
such as aniline, or substituted aniline, phenol or substituted
phenol, benzenethiol or substituted benezenethiol, primary- or
secondary-amines, alcohols and thiols can be prepared in solvents
such as tetrahydrofuran (THF), benzene, toluene, xylene, diethyl
ether, dioxane, alcohols, acetonitrile, dimethylsulfoxide (DMSO),
dimethylformamide (DMF), water, and similar solvents, under an
inert atmosphere. Substituents for the above groups include alkyl
groups having from 1 to 20 carbon atoms (such as methyl, ethyl,
n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, and the like).
Also possible are alkenyl or alkynyl substituents having from 2 to
20 carbon atoms. The groups can also include alkoxycarbonyl
substituents having from 2 to 20 carbons atoms, aryl groups,
carboxylate substituents having from 1 to 20 carbon atoms, alkoxy
substituents having from 1 to 20 carbon atoms, alkenyloxy or
alkynyloxy substituents having from 2 to 20 carbon atoms, as well
as aryloxy substituents. Each of the above classes of substituent
can be further optionally substituted with halogen, or with alkyl
or alkoxy groups of from 1 to 5 carbon atoms. Particularly useful
are those substituents such as methyl, ethyl, propyl, and butyl,
including branched isomers, and aryl substituents at the ortho- or
diortho-positions (for example, 2- or 2,6-substitution for benzyl
rings).
[0060] The solution is then contacted with an approximately one
half of equimolar amount (with respect to the heteroatom-containing
starting material) of paraformaldehyde. After heating to dissolve
paraformaldehyde, the contents of the flask are acidified with an
approximately one half of equimolar amount (with respect to the
heteroatom-containing starting material) of mineral acid (for
example, hydrochloric acid or nitric acid).
[0061] At this stage, if a nitrogen-containing starting material
(aniline-derivative or primary amine-derivative) is used, an
approximately one half of equimolar amount (with respect to the
heteroatoms-containing starting material) of a dialkoxyacetaldehyde
is added drop wise after a few minutes of stirring. The
dialkoxyacetaldehyde can be dimethoxy-, diethoxy-, dipropoxy-,
dibutoxy-, diphenoxy, or can be any of a number of combinations of
such alkoxy substituents such as for example methoxyethoxy, or
methoxyphenoxy. The procedure then continues as follows.
[0062] If, on the other hand, oxygen or sulfur
heteroatom-containing starting material is used, the above
paragraph is not followed, and the procedures from this point on
are common to all starting materials. After equipping the reaction
flask with a Dean-Stark trap, or similar device, the mixture is
heated to a temperature of from about 80.degree. C. to about
180.degree. C., preferably from about 100.degree. C. to about
150.degree. C. for several hours (from about 5 to about 30 hours).
During this time, a precipitate forms, as the side products of
water and methanol, as well as some solvent, are removed. The
reaction mixture is stirred at room temperature for a time ranging
from about 20 minutes to about 4 hours, preferably from 1 to 3
hours. Precipitate will have formed during this time.
[0063] The precipitate is filtered, washed with a suitable solvent,
such as THF to give the nucleophilic carbene product in the form of
a salt. For example, if aniline or substituted aniline is used, the
product will be a 1,3-diarylimidazole salt. If the starting
material is a primary amine, the product will be a 1,3-dialkyl
imidazole salt. Either of these products can be converted to the
saturated heterocyclic derivative (imidazo lidine) by conventional
hydrogenation techniques such as exposure to H.sub.2 over a
carbon-palladium or carbon-platinum catalyst. Such techniques will
be recognized and known to those of skill in the art. If the
starting material is a phenol- or thiobenzene-derived compound, the
product will be a dibenzoxymethane-, or dibenzthiomethane-product.
If the starting material is an alcohol or thiol, the product will
be a 1,1-bis(alkoxy)methane- or
1,1-bis(alkylthio)methane-product.
[0064] The second embodiments of the catalytic complexes of the
invention are easily made by combining a precursor species of the
catalytic complexes with an acetylene to give the allenylidene type
of catalytic complex (see FIG. 3C). An example of this precursor
species of the catalytic complex is shown below.
##STR00014##
[0065] In this structure, metal M, and ligands X, X.sup.1, L and Ar
are defined as above, with L being a nucleophilic carbene. This
precursor species is generally available in the form of a dimer
[ArRuCl.sub.2].sub.2, which is converted to the precursor species
when the dimer is exposed to a nucleophilic carbene in a suitable
solvent such as THF, hexanes and other non-protic solvents. For
example, the dimer [(p-cymene)-RuCl.sub.2].sub.2 is commercially
available from Strem Chemicals (Newburyport, Mass.).
[0066] The acetylenes with which precursor species of the inventive
catalytic complexes combine to form second embodiments of the
invention are terminal acetylenes, and can be substituted at the
y-position with alkyl or aryl groups, or optionally further
substituted with halogen, or with alkyl or alkoxy groups of from 1
to 10 carbon atoms, or aryl groups. Further substitution can
include the functional groups of hydroxyl, thiol, thioether,
ketone, aldehyde, ester, amide, amine, imine, nitro, carboxylic
acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy,
carbamate, and halogen. Particularly useful substituents are vinyl,
phenyl, or hydrogen, wherein the vinyl and phenyl substituents are
optionally substituted with one or more moieties selected from
C.sub.1-C.sub.5 alkyl, C.sub.1-C.sub.5 alkoxy, phenyl or a
functional group, such as chloride, bromide, iodide, fluoride,
nitro, or dimethylamine.
[0067] The invention will be further described in the following
examples, which do not limit the scope of the invention described
in the claims.
EXAMPLES
[0068] Illustrations of methods of making certain embodiments of
the inventive catalytic complexes, as well as properties thereof,
are provided by the following examples.
Example 1
Synthesis of IMes-HCl
[0069] A 300 mL Schlenk flask was charged with
2,4,6-trimethylaniline (10 g, 74 mmol), toluene (50 mL), and
paraformaldehyde (1.11 g, 37 mmol) under argon and heated to
110.degree. C. until all the paraformaldehyde was dissolved. The
flask was then cooled to 40.degree. C. and HCl (6.17 mL, 6N, 37
mmol) was added to the reaction mixture drop wise. The mixture was
stirred at that temperature for 10 minutes before
dimethoxyacetaldehyde (6.442 g, 60% wt. in water, 37 mmol) was
added in drop wise fashion. The flask was then equipped with a
Dean-Stark trap and heated to 120.degree. C. for 15 hours, during
which time a dark precipitate was formed and grew in volume by
removal of the side-products (H.sub.2O and methanol) and some of
the solvent through the Dean-Stark trap. The reaction mixture was
then allowed to cool to room temperature and stirred at that
temperature for two hours. Filtration of the precipitate through a
Schlenk frit, washing with tetrahydrofuran (three times, 20 mL each
wash), and drying yielded a white solid in 60% yield, which was
characterized spectroscopically as pure IMes-HCl. .sup.1H NMR:
.delta.=2.12 (s, 12H, o-CH3), 2.30 (s, 6H, p-CH.sub.3), 6.97 (s,
4H, mesityl), 7.67 (s, 2H, NCHCHN), 10.68 (s, 1H, HCl).
Example 2
Synthesis of iMes
[0070] In a glovebox, a 300 mL Schlenk flask equipped with a stir
bar was charged with 20.0 g (58.7 mmol) of IMes-HCl and 120 mL of
dry tetrahydrofuran. The resulting suspension was stirred for 10
minutes after which time 6.80 g (60.7 mmol) of solid potassium
tert-butoxide was added to the suspension at room temperature in a
single portion. A dark gray solution was obtained immediately. The
flask was taken out of the glovebox and connected to the Schlenk
line. The solution was stirred for 20 minutes before all volatiles
were removed under vacuum. The residue was extracted into warm
toluene (120 mL+60 mL+20 mL) and filtered through a medium porosity
frit (filtration was rather slow), and the solvent was removed
under vacuum to obtain crystals of IMes. The resulting product was
recovered in 90% yield, and had a dark tint but was sufficiently
pure for its use in further synthesis. Further purification could
be achieved by recrystallization from toluene or hexane, yielding
colorless crystals.
[0071] The synthesis of related carbenes
1,3-bis(4-methylphenyl)imidazol-2-ylidene (ITol) and
1,3-bis(4-chlorophenyl)imiadzol-2-ylidene (IpCl) was carried in an
analogous fashion.
Example 3
Synthesis of
(IMes)(PCy.sub.3)(Cl).sub.2Ru(.dbd.CHCH.dbd.CMe.sub.2)
[0072] The procedure was carried out under purified and dried argon
atmosphere and with dried and degassed solvents. IMes (2.1990 g,
7.221 mmol) was suspended in 250 mL hexanes, into which
(Cl).sub.2(PCy.sub.3).sub.2Ru(.dbd.CHCH.dbd.CMe.sub.2) (5.0718 g,
7.092 mmol) was added in one portion. The mixture was heated for
2.5 hours with stirring at 60.degree. C. During this period, the
formation of an orange-brown precipitate was observed. The volume
of the suspension was then reduced in vacuum to 50 mL and the
suspension was cooled to -78.degree. C. Following filtration and
cold pentane washing of the residue (2 washes, each 20 mL), the
product was isolated as a brown orange microcrystalline material in
72% yield (3.97 g).
Example 4
Synthesis of (IMes)(PC)13)CbRu(.dbd.CHPh)
[0073] The procedure of Example 3 was followed, except that
(Cl).sub.2(PCy.sub.3).sub.2Ru(.dbd.CHPh) was used. This complex was
soluble in a variety of organic solvents including hydrocarbon,
tetrahydrofuran, acetone, methylene chloride, and diethylether. The
identity of the complex was confirmed by X-ray crystallography.
Other embodiments will be readily synthesized by substituting the
IMes ligand with other nucleophilic carbene ligands.
Example 5
Thermodynamic Studies
[0074] The thermodynamics of the following reaction in
tetrahydrofuran (THF) at room temperature were studied.
[Cp*RuCl].sub.4+4IMes.fwdarw.4Cp*Ru(IMes)Cl
[0075] (Cp* is .eta..sup.5-C.sub.5Me.sub.5) The reaction proceeds
rapidly as indicated by the rapid development of a deep blue color
in the reaction solution. A deep blue crystalline solid was
isolated in 86% yield. Nuclear magnetic resonance data of the blue
solid indicated the isolation of a single species bearing a unique
Cp* and a single carbene ligand. X-ray crystallography confirmed
the formulation of Cp*Ru(IMes)Cl. An enthalpy of reaction of
-62.6.+-.0.2 kcal/mol was measured by anaerobic solution
calorimetry in THF at 30.degree. C. when 4 equivalents of carbene
were reacted with 1 equivalent of the tetramer, [Cp*RuCl].sub.4.
Table 2 compares the enthalpy of similar reactions where IMes is
replaced with other moieties.
TABLE-US-00002 TABLE 2 Comparison of Reaction Enthalpies Relative
stability Identity of L in .DELTA.H (kcal/mol) of reaction: of
Ru--L bond Cp * Ru(L)(Cl) [Cp * RuCl].sub.4 + 4L .fwdarw. 4Cp *
Ru(L)(Cl) (kcal/mol) IMes -62.6 .+-. 0.2 -15.6 P(isopropyl).sub.3
-37.4 .+-. 0.3 -9.4 P(cyclohexyl).sub.3 -41.9 .+-. 0.2 -10.5
[0076] The IMes ligand proves to be a stronger binder to the
Cp*RuCl fragment than PCy.sub.3, by 5 kcal/mol. The carbene ligand
is a fairly good binder but can be displaced if a better donor
ligand, such as a phosphite, is used. The phosphite reaction allows
for the construction of a thermochemical cycle which confirms the
internal consistency of the calorimetric data, as shown in Scheme
3.
##STR00015##
[0077] A further verification of the thermochemical results can be
made by examining the following hypothetical reaction.
##STR00016##
[0078] This reaction is calculated to be exothermic by 5 kcal/mol
and no entropic barrier is apparent, so the reaction should proceed
readily as written. Indeed, upon mixing of the reagents in
THF-d.sub.8, the characteristic .sup.31P signal of
Cp*Ru(PCy.sub.3)Cl disappears (at 11.3 ppm), and that of free
PCy.sub.3 appears (40.4 ppm), as observed by Campion et al., J
Chem. Soc. Chem. Commun., (1988)278-280.
Example 6
Structural Studies
[0079] In order to gauge the steric factor inherent in the
catalytic systems, structural studies were carried out on
CP*Ru(IMes)Cl (FIG. 4), Cp*Ru(PCy.sub.3)Cl (FIG. 5), and
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) (FIG. 6). Comparison was
made to another sterically demanding ligand in the complex
Cp*Ru(P.sup.iPr.sub.3)Cl. The following crystal data was obtained.
For Cp*Ru(IMes)Cl: monoclinic, space group P2.sub.l/c, dark blue
prism, 0.35.times.0.25.times.0.20, a=10.6715 (2), b=14.3501 (3),
c=19.2313 (4), .beta.-103.2670 (10) deg, Z=4, R.sub.f=0.0294,
GOF=0.888. For Cp*Ru(PCy.sub.3)Cl: orthorhombic, space group Pcba,
dark blue prism, 0.45.times.0.35.times.0.25, a=18.9915 (6),
b=15.6835 (5), c=19.0354 (6), Z=8, R.sub.f=0.0392, GOF=1.132. For
(IMes)(PCy.sub.3) ChRu(.dbd.CHPh): space group
P2.sub.12.sub.12.sub.1, yellow-orange prism, a=12.718 (1), b=14.549
(1), c=26.392 (2), R.sub.f=0.0616, z=4, GOF=1.038. The metrical
data of Cp*Ru(P.sup.iPr.sub.3)Cl (Campion et al., J Chem. Soc.
Chem. Commun., (1988) 278-280) can be used for comparison: Ru--P,
2.383 (1) .ANG.; Ru--Cl, 2.378 (1) .ANG.; Ru-Cp*(c), 1.771 (1)
.ANG.; Cl--Ru--P, 91.2 (1).degree.; Cl--Ru-Cp*(c), 129.9
(1).degree.; C(1)-Ru-Cp*(c), 139.9 (1).degree..
[0080] The three Cp*RuCl(L) structures are similar, with the
variation in Ru-L distances the only standout feature, but this is
explainable by the difference in covalent radii between P and C.
Only slight angle distortions are observed in Cp*Ru(IMes)Cl,
presumably to accommodate the bulkiness of IMes. The IMes ligand
displays non-coplanar rings with torsion angles of 78.46
(4).degree. between the arene ring bound to N(2) and the imidazole
ring and 78.78(5).degree. between the imidazole ring and the arene
ring bound to N(1). The two arene rings adopt a mutually staggered
configuration.
[0081] A direct comparison of the steric properties displayed by
IMes and PCy.sub.3 provides insight into the significant steric
congestion provided by the IMes ligation. The cone angle reported
for P.sup.iPr.sub.3 and PCy.sub.3 are 160.degree. and 170.degree.,
respectively (Tolman, Chem. Rev. (1977) 77, 313-348). Such a cone
angle measurement is not straightforward in the present system.
Instead, the crystallographic data can be used to determine closest
contact angles involving non-hydrogen atoms in Cp*Ru(IMes)Cl and
Cp*Ru(PCy.sub.3)Cl. For the Ru-PCy.sub.3 fragment, an angle of
96.3.degree. is measured using cyclohexyl methylene carbons on
adjacent cyclohexyl rings defining the largest angle. For the
Ru--P.sup.iPr.sub.3 fragment in Cp*Ru(P.sup.iPr.sub.3)Cl a similar
angle of 95.8.degree. is obtained. As for the IMes fragment, two
parameters can be obtained. Angles of 150.7.degree. and
115.3.degree. are measured for the <4-Me-Ru-4'-Me and
<6-Me-Ru-2'-Me angles, respectively. The steric coverage of the
IMes ligand can be considered as a fence rather than a cone. The
increased steric congestion provided by the IMes ligand compared to
PCy.sub.3 derives from the presence of bulky substituents on the
imidazole nitrogens and, to a greater extent, from the
significantly shorter metal-carbon bond distance which brings the
entire IMes ligand closer to the metal center.
[0082] The structural analysis of
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) shown in FIG. 6 reveals a
distorted square pyramidal coordination with a nearly linear
Cl(1)-Ru--Cl(2) angle (168.62.degree.). The carbene unit is
perpendicular to the C(1)-Ru--P plane, and the carbene aryl moiety
is only slightly twisted out of the Cl(1)-Ru--Cl(2)-C(40) plane.
The Ru--C(40) bond distance (1.841 (11) .ANG.) is the same as that
in RuCl.sub.2(.dbd.CH-p-C.sub.6H.sub.4Cl)(PCy.sub.3).sub.2 (1.838
(3) .ANG.) and shorter than that in
(PCy.sub.3).sub.2RuCl.sub.2(.dbd.CHCH.dbd.CPh.sub.2) (1.851 (21)
A). While two (formally) carbene fragments are present in
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh), they display different
Ru--C distances (Ru--C(40)=1.841 (11) and Ru--C(1)=2.069 (11)
.ANG.). These important metrical parameters clearly distinguish two
metal-carbene interactions: a metal benzylidene fragment with a
formal metal to carbon double bond and a metal imidazolium carbene
with a formal metal-carbon single bond. From FIG. 6, it is also
clear that the IMes ligand is sterically more demanding than
PCy.sub.3.
Example 7
Thermal Stability Studies
[0083] In the course of catalytic testing, the remarkable air
stability of the inventive catalytic complexes was observed. To
gauge the robust nature of these carbene complexes in solution,
their thermal stability under inert atmosphere was tested at
60.degree. C. The relative order of stability found was
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh)>>(IMes)(PPh.sub.3)Cl.sub.2Ru-
(.dbd.CHPh)>(PCy.sub.3).sub.2Cl.sub.2Ru(.dbd.CHPh). After 14
days of continuous heating of toluene solutions of
(IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) to 60.degree. C., no
decomposition was detected (as monitored by both .sup.1H and
.sup.31P NMR). In contrast, solutions of
(PCy.sub.3).sub.2Cl.sub.2Ru(.dbd.CHPh) showed signs of
decompositions after one hour, under the same conditions.
[0084] The catalyst (IMes)(PCy.sub.3)Cl.sub.2Ru(.dbd.CHPh) was
stable at 100.degree. C. for 36 hours before showing any indication
of decomposition. Similar thermal decomposition studies have been
conducted in refluxing methylene chloride, dichloromethane,
toluene, benzene and diglyme with similar results.
[0085] Except as may be expressly otherwise indicated, the article
"a" or "an" if and as used herein is not intended to limit, and
should not be construed as limiting, the description or a claim to
a single element to which the article refers. Rather, the article
"a" or "an" if and as used herein is intended to cover one or more
such elements, unless the text expressly indicates otherwise.
[0086] Each and every patent, patent application and printed
publication referred to above is incorporated herein by reference
in toto to the fullest extent permitted as a matter of law.
[0087] It is to be understood that while the invention has been
described in conjunction with the detailed description thereof, the
foregoing description is intended to illustrate and not limit the
scope of the invention, which is defined by the scope of the
appended claims. Other aspects, advantages, and modifications are
within the scope of the following claims.
* * * * *