Summary: In non‐polar solvents such as toluene, Cp‐Ni and ‐Pd complexes (Cp = η5‐C5H5) with appropriate activators have been found to induce the addition polymerization of norbornene in excellent yields, for example (Cp)Pd(allyl)/[Ph3C][B(C6F5)4] gave 105 120 kg‐polymer/cat‐mol · h at room temperature. While the Cp‐Pd system was not suitable in the presence of ester‐substituted norbornenes, the Cp‐Ni system, for example (Cp)Ni(Cl)(PPh3)/AlMe3/B(C6F5)3 can copolymerize norbornene with 5‐norbornene‐2‐carboxylic acid methyl ester in toluene to give high yields (up to 68% in 2 h at room temperature) of copolymer with variable contents of the methyl ester monomer unit (17.4–60.7 mol‐%). These copolymers have high molecular weights ($\overline M _{\rm n}$ = 234 100–109 500) and narrow molecular weight distributions ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.78–1.89). In addition, they are soluble in common organic solvents giving flexible and transparent films on casting, that show very high Tg in the range of 352.8 to 316.0 °C. The same Ni‐catalyst system can also copolymerize norbornene derivatives with bulky substituents, i.e., 2‐butyl‐5‐norbornene and 5‐norbornene‐2‐carboxylic acid butyl ester. The Tg of these copolymers are lower (294.9–267.3 °C) than the methyl ester‐based copolymers, demonstrating that the Tg of the polynorbornene copolymer film can be tailored simply by changing the alkyl group of the monomer to within the range of 352 to 267 °C.Figure showing the addition polymerization of norbornene using Cp‐Ni complex with appropriate activators.magnified imageFigure showing the addition polymerization of norbornene using Cp‐Ni complex with appropriate activators.
Reactions of the four alkenylruthenium(II) complexes Ru[C(R1)CH(R2)]Cl(CO)(PPh3)2 (R1
= H, R2 = Ph (1b); R1 = H, R2 = t-Bu (1c); R1 = Ph, R2 = Ph (1d); R1 = CHCH(SiMe3), R2
= SiMe2Ph (1e)) with HSiMe2Ph, which constitute the product-forming step of ruthenium-catalyzed hydrosilylation of alkynes, have been examined. Two reaction courses are
operative: one provides the C−Si coupling product PhMe2SiC(R1)CH(R2) and RuHCl(CO)(PPh3)3 (path A), and the other forms the C−H coupling product HC(R1)CH(R2) and
Ru(SiMe2Ph)Cl(CO)(PPh3)2 (path B). The ratio of the two courses significantly varies with
substituents on the alkenyl ligands, particularly with the α-substituent (R1). Thus, 1b and
1c, without an α-substituent, react mainly by path A. In contrast, 1d and 1e, bearing an
α-substituent, exclusively undergo path B. Kinetic studies using 1b and its para-substituted
styryl ligand derivatives have revealed that path A proceeds by direct interaction of the
five-coordinated complexes with hydrosilane, without dissociation of the PPh3 ligand. On
the other hand, path B involves dissociation of PPh3 prior to the reaction of 1d or 1e with
hydrosilane. Mechanisms of the C−Si and C−H bond formation are discussed with kinetic
data in detail.
Catalytic hydrosilation of
1-(trimethylsilyl)-1-buten-3-yne (1) with three kinds of
hydrosilanes
(HSiMePh2, HSiMe2Ph, and
HSiEt3) in CDCl3 at 30 °C in the presence of
a catalytic amount of RuHCl(CO)(PPh3)3 (2) gave five types of
reaction products:
(1E,3E)-CH(SiR3)CHCHCHSiMe3
(3), R3SiCH2CHCHCH2SiMe3 (4),
R3SiCHCCHCH2SiMe3
(5),
(1Z,3E)-CH(SiR3)CHCHCHSiMe3
(6), and
R3SiC⋮CCHCHSiMe3 (7).
Detailed investigations on the stoichiometric reactions of
intermediate ruthenium
species provided definitive evidence for the catalytic mechanism
comprised of two catalytic cycles, the Chalk−Harrod cycle A and the modified Chalk−Harrod cycle
C, and their interconnecting processes B and
D. Product
3 is formed by the insertion of 1 into the Ru−H
bond of 2 followed by the reaction of the resulting
terminal
dienyl complex
Ru(CHCHCHCHSiMe3)Cl(CO)(PPh3)2
(8) with hydrosilane. The latter process
regenerates
2 and the sequence of reactions proceeds catalytically
(cycle A). The reaction of 8 with
hydrosilane is
accompanied by a side reaction giving
Ru(SiR3)Cl(CO)(PPh3)2
(9) and CH2CHCHCHSiMe3
(10), and the
latter is further converted to 4 by hydrosilation (process
B). Silyl complex 9 thus generated in the
system is
the key intermediate for catalytic cycle C. Thus the
insertion of 1 into the Ru−SiR3 bond of
9 via a formal
trans-addition process forms an internal dienylruthenium
complex
Ru[C(CHSiR3)CHCHSiMe3]Cl(CO)(PPh3)2 (11), which reacts with
hydrosilane to give 5 and 6 and to regenerate
9. A part of 11 also undergoes
β-hydrogen elimination to give a dehydrogenative silation product
8 and hydride complex 2. Complex
2 thus
formed resumes catalytic cycle A (process D).
The catalytic intermediates 8, 9, and
11 were identified by
NMR spectroscopy and/or elemental analysis. Factors controlling
the catalytic cycles are discussed on the
basis of the experimental observations.
The reaction of a conjugated enyne, cis-(Me3Si)CH=CHC=CSiMe3, with [ R u C I ( C O ) H ( P P ~~) ~] gives a quantitative yield of a stable complex whose molecular structure is formally regarded as the result of either 1,2-addition of the H-Ru t o the double bond or 1,4-addition of the H-Ru t o the conjugated enyne; the former bonding scheme operates when the enyne is hydrogenated b y [Ru(CO)H2(PPh3)3] or [ R u H ~( P P ~~) ~] ,the sole product being Me3SiCH2CH2C-=CSiMe3.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.