- Oxidative addition of silyl cyanides to rhodium porphyrin radical: Isocyanide or cyanide transfer mechanism
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Rhodium porphyrin radical, coordinated with pyridine, activated the carbon - silicon bond of silyl cyanides to yield rhodium porphyrin silyls and cyanide. The reaction with Me3SiCN exhibited second-order kinetics, rate - kabsd[Rh(tmp)][Me3SiCN], at a sufficiently high concentration of pyridine, and the mechanism was interpreted to involve a cyanide or isocyanide group transfer to rhodium radical.
- Chan, Kin Shing,Zhang, Lirong,Fung, Chun Wah
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- Metalloradical activations of aliphatic carbon-carbon bonds of nitriles: Scope and mechanism
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The C(sp3)-C(sp3) bonds of a series of α-alkylacetonitriles, 2-silylacetonitriles and 2-alkylbenzonitriles, have been activated by Rh(tmp) using Ph3P as the optimized promoter ligand at 130°C. Selective aliphatic-aliphatic carbon-carbon bond activation (CCA) occurred for α-alkylacetonitriles and 2-alkylbenzonitriles without aromatic-aliphatic or aromatic-cyanide bond activation. Competitive activations of C-Si and C-C bonds were observed for 2-silylacetonitriles. The yields of Rh(tmp) alkyls were affected by bond energy and steric hindrance of the nitriles. Kinetic studies for the carbon-carbon bond activation (CCA) of tBuCN at 130°C revealed the rate law: rate = k′K 1[Rh(tmp)]m[Ph3P]n + k 3K2(K1[Ph3P])/(1 + K 1[Ph3P])[Rh(tmp)][tBuCN]. The CCA is proposed to occur at the coordinated tBuCN with Rh(tmp) in a 1:1 ratio in the transition state.
- Chan, Kin Shing,Li, Xin Zhu,Zhang, Lirong,Fung, Chun Wan
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p. 2679 - 2687
(2008/10/09)
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- Mechanistic studies of Si-CN and C-NC bond activation of silylnitriles and alkyl isonitriles by rhodium porphyrin radical: Novel cyanide transfer
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The Si-CN and C-NC bonds of silylnitriles and alkyl isonitriles were activated by (tetramesitylpor-phyrinato)rhodium(II), Rh(tmp), to give rhodium porphyrin silyls or alkyls and rhodium porphyrin cyanide, respectively. Pyridine and triphenylphosphine promoted the rates and yields of the reactions with silylnitriles, but inhibited the rates and yields of the reactions with isonitriles. The reaction of Rh(tmp) with Me3SiCN exhibited second-order kinetics (rate = kobs[Rh(tmp)][Me3SiCN]) at a sufficiently high concentration of pyridine. The reaction with BuNC showed fourth-order kinetics, second-order in each of the reactants; rate = k obs[Rh(tmp)]2[BuNC]2. A novel cyanide transfer rate-determining step was proposed to account for the reaction mechanism.
- Zhang, Lirong,Fung, Chun Wah,Chan, Kin Shing
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p. 5381 - 5389
(2008/10/09)
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