186048-07-7Relevant academic research and scientific papers
Kinetics and mechanism of alkyl transfer from organocobalt(III) to nickel(I): Implications for the synthesis of acetyl coenzyme A by CO dehydrogenase
Ram,Riordan, Charles G.,Yap, Glenn P. A.,Liable-Sands, Louise,Rheingold, Arnold L.,Marchaj, Adam,Norton, Jack R.
, p. 1648 - 1655 (1997)
Reaction of CH3Co(dmgBF2)2L (dmgBF2 = (difluoroboryl)dimethylglyoximato); L = py, PEt3) with 2 equiv of [Ni(tmc)]OTf (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; OTf- = CF3SO3-) gave Co(dmgBF2)2py-, [Ni(tmc)]OTf2, and [Ni(tmc)CH3]OTf in 80% yield. The overall transformation provides the first model for the transfer of a CH3 group from methylcobalamin to the Ni-containing enzyme carbon monoxide dehydrogenase during acetyl coenzyme A synthesis. RRSS-[Ni(tmc)CH3](BAr'4) (BAr'4- = B(3,5-(CF3)2C6H3)4-) has been characterized by X-ray diffraction. The products and 1CH3Co(dmgBF2)2L:2[Ni(tmc)]OTf stoichiometry of the reaction are consistent with a three-step mechanism initiated by electron transfer from [Ni(tmc)]OTf to CH3Co(dmgBF2)2L. The second step is rapid CH3-Co- bond homolysis yielding Co(dmgBF2)2L- and CH3.; then the CH3 radical is captured by the second equivalent of [Ni(tmc)]OTf, yielding [Ni(tmc)CH3]OTf. Radical clock experiments have corroborated the production of free radicals. Reaction of (5-hexenyl)Co(dmgBF2)2L with [Ni(tmc)]OTf, followed by hydrolysis of the organonickel products, gave methylcyclopentane, consistent with the formation and cyclization of the 1-hexenyl radical. The second-order rate constants measured by stopped-flow experiments parallel the relative radical stabilities: R = CH3 (2.43 x 103 M-1 s-1) 2H5 (7.88 x 103 M-1 s-1) 3)2 (19.2 x 103 M-1 s-1), L = py (2.43 x 103 M-1 s-1) 3 (5.01 x 103 M-1 s-1). During the course of these studies the following molecules were also characterized by X-ray diffraction, CH3Co(dmgBF2)2L, L = PEt3, py, H2O.
