The role of two-component catalysts containing chelating bisaryloxide ligands in controlling the stereochemistry of the metathesis polymerization of norbornene
“…One phenyl ring on the BINO ligand is pointing more or less straight up (away from the C(33)-N(1)-O(1) face), while the other phenyl ring in the BINO ligand lies more or less beneath the Mo=N bond. The C(1)−C(2)−C(22)−C(17) dihedral angle is 65°, which is approximately what has been found in several W(6+) complexes that contain the parent binaphtholate ligand. − 2 A Chem 3D view of Mo(N-2,6-C 6 H 3 Me 2 )(CHCMe 2 Ph)(3,3‘-diphenyl-2,2‘-diolate-1,1‘-dinaphthyl)(THF) ( 2b ‘).…”
Section: Resultsmentioning
confidence: 53%
“…A significant fact is that the neophylidene ligand has the anti configuration in which the Mo 17) dihedral angle is 65°, which is approximately what has been found in several W(6+) complexes that contain the parent binaphtholate ligand. [20][21][22] Proton NMR spectra of 2b′ in toluene-d 8 show two alkylidene H R resonances at low temperatures (Figure 3). The most downfield singlet (13.4 ppm) is assigned to anti-2b′ (J CH ) 144 Hz), while that at 13.2 ppm is assigned to syn-2b′.…”
Section: Synthesis Of Binaphtholate and Biphenolatementioning
Several racemic or enantiomerically pure complexes of the general
type Mo(CHR)(NR‘)(O2R‘‘) that contain binaphtholate or biphenolate
(O2R‘‘) ligands have been prepared and employed
to
ring open several achiral, racemic, or enantiomerically pure
norbornenes and norbornadienes. A bimodal
molecular weight distribution sometimes results from polymerization of
an enantiomerically pure monomer
with a racemic initiator as a consequence of a different rate of chain
growth from enantiomeric metal
centers. The analogous polymerization of an enantiomerically pure
monomer with an enantiomerically
pure initiator yields only a single polymer chain, as expected.
Evaluation of the cis content of the
resulting
polymers suggests that cis polymer results from
polymerization via syn alkylidene propagating
species
and that accessibility of the anti rotamer on the
polymerization time scale is determined by a subtle
combination of steric bulk in the biphenoxide and imido ligands.
All cis polymers were found to be highly
isotactic. The X-ray structures of two catalytically active
species are also described. One is a THF adduct
of 3,3‘-diphenyl-2,2‘-diolate-1,1‘-dinaphthyl (anti rotamer)
while the other is a base-free syn species that
contains the
6,6‘-dimethyl-3,3‘,5,5‘-tetra-tert-butyl-1,1‘-biphenyl-2,2‘-diolate
ligand.
“…One phenyl ring on the BINO ligand is pointing more or less straight up (away from the C(33)-N(1)-O(1) face), while the other phenyl ring in the BINO ligand lies more or less beneath the Mo=N bond. The C(1)−C(2)−C(22)−C(17) dihedral angle is 65°, which is approximately what has been found in several W(6+) complexes that contain the parent binaphtholate ligand. − 2 A Chem 3D view of Mo(N-2,6-C 6 H 3 Me 2 )(CHCMe 2 Ph)(3,3‘-diphenyl-2,2‘-diolate-1,1‘-dinaphthyl)(THF) ( 2b ‘).…”
Section: Resultsmentioning
confidence: 53%
“…A significant fact is that the neophylidene ligand has the anti configuration in which the Mo 17) dihedral angle is 65°, which is approximately what has been found in several W(6+) complexes that contain the parent binaphtholate ligand. [20][21][22] Proton NMR spectra of 2b′ in toluene-d 8 show two alkylidene H R resonances at low temperatures (Figure 3). The most downfield singlet (13.4 ppm) is assigned to anti-2b′ (J CH ) 144 Hz), while that at 13.2 ppm is assigned to syn-2b′.…”
Section: Synthesis Of Binaphtholate and Biphenolatementioning
Several racemic or enantiomerically pure complexes of the general
type Mo(CHR)(NR‘)(O2R‘‘) that contain binaphtholate or biphenolate
(O2R‘‘) ligands have been prepared and employed
to
ring open several achiral, racemic, or enantiomerically pure
norbornenes and norbornadienes. A bimodal
molecular weight distribution sometimes results from polymerization of
an enantiomerically pure monomer
with a racemic initiator as a consequence of a different rate of chain
growth from enantiomeric metal
centers. The analogous polymerization of an enantiomerically pure
monomer with an enantiomerically
pure initiator yields only a single polymer chain, as expected.
Evaluation of the cis content of the
resulting
polymers suggests that cis polymer results from
polymerization via syn alkylidene propagating
species
and that accessibility of the anti rotamer on the
polymerization time scale is determined by a subtle
combination of steric bulk in the biphenoxide and imido ligands.
All cis polymers were found to be highly
isotactic. The X-ray structures of two catalytically active
species are also described. One is a THF adduct
of 3,3‘-diphenyl-2,2‘-diolate-1,1‘-dinaphthyl (anti rotamer)
while the other is a base-free syn species that
contains the
6,6‘-dimethyl-3,3‘,5,5‘-tetra-tert-butyl-1,1‘-biphenyl-2,2‘-diolate
ligand.
“…Grubbs has reported the use of Schrock's tungsten-based carbene 103 for the cis -syndiospecific polymerization of 7-oxanorbornenes 99 and 100 . Basset and Hamilton have reported that complex 104 produces a high cis -content, regioregular, partially syndiotactic polymer from rac -1-methylnorbornene ( 101 ). , Heppert has reported that chiral tungsten complexes 105 − 107 can be activated by Et 2 AlCl to form active catalysts for the syndiospecific polymerization of rac -5,5-dimethylnorbornene ( 102 ). , The resulting polymers contained greater than 95% cis -olefins. 29 Monomers and Single-Site Tungsten Catalysts for Stereoselective ROMP…”
“…323,324 Heppert has reported that chiral tungsten complexes 105-107 can be activated by Et 2 AlCl to form active catalysts for the syndiospecific polymerization of rac-5,5-dimethylnorbornene (102). 325,326 The resulting polymers contained greater than 95% cis-olefins.…”
Geoffrey W. Coates was born in 1966 in Evansville, IN. He received a B.A. degree in chemistry from Wabash College in 1989 working with Roy G. Miller and a Ph.D. in organic chemistry from Stanford University in 1994 with Robert M. Waymouth. After postdoctoral research with Robert H. Grubbs at the California Institute of Technology, he joined the faculty at Cornell University in 1997, where he is now Assistant Professor of Chemistry and Chemical Biology. His research interests include the development of single-site catalysts for synthesis and the preparation and characterization of well-defined polymer architectures.
“…Schaverien has shown that binaphthoxide derivatives of Ti and Zr will produce isotactic poly(α-olefins) when activated with MAO . Heppert has also studied a number of molybdenum and tungsten complexes containing these ligands …”
Reaction of dimeric [(Et2N)2Cl2Ta(μ-Cl)2TaCl2(NEt2)2] with (R)-[H2O2C20H10(R)2-3,3‘]
(R = SiMe3, SiMe2Ph, SiMePh2, or SiPh3) produces the 3,3‘-dialkyl-1,1‘-bi-2,2‘-naphthoxido
complexes (R,R)-[H2NEt2][Ta(O2C20H10{R}2-3,3‘)2Cl2] (R = SiMe3, (R,R)-1; SiMe2Ph, (R,R)-2; SiMePh2, (R,R)-3; SiPh3, (R,R)-4). Structural studies of the SiMe3 derivative (R,R)-1 show
a pseudo-octahedral anion with mutually cis chloride ligands. Although NMR studies indicate
that the anion of (R,R)-1 is stable in DMSO-d
6, an equilibrium mixture is observed in C6D6
solution with the neutral complex (R,R)-[Ta{O2C20H10(SiMe3)2-3,3‘}2Cl], (R,R)-1a, and
[H2NEt2]Cl. The temperature dependence of the equilibrium has been studied. Addition of
[nBu4N]Cl to a mixture of (R,R)-1/(R,R)-1a in C6D6 is shown (1H NMR) to shift the equilibrium
toward (R,R)-1. Alkylation of (R,R)-1 with Grignard reagents RMgCl results in formation of
the five-coordinate (R,R)-[Ta(O2C20H10{SiMe3}2-3,3‘}2R‘] (R‘ = CH2SiMe3, (R,R)-5; CH2Ph,
(R,R)-6; c-C5H9, (R,R)-7).
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