Nickel(II)‐Carbene Intermediates in Reactions of Geminal Dihaloalkanes with Nickel(0) Reagents and the Corresponding Carbene Capture as the Phosphonium Ylide
作者:John J. Eisch、Yun Qian、Arnold L. Rheingold
DOI:10.1002/ejic.200601106
日期:2007.4
in reactions with (Cod)2Ni. This finding compels one to conclude that the carbonyl reagent is capturing the Wittig reagent, R2C=PEt3, and not R2C=Ni0. Based upon all present data, the mechanism of such C=C bond dimerizations is best explicable in terms of nickel(II)-carbenes. The triethylphosphonium tetraphenylcyclopentadienide formed here has by single-crystal X-ray structure determination, complemented
在之前对 R2CE2 [E2 = X2, O, S, Li(SO2Ph)] 类型底物的孪晶键断裂的研究中,镍 (0) 试剂 [LnNi, Ln = (Cod)2, (Et4P)4],导致 R2C=CR2 作为产物,假设这种反应可能通过镍 (0)-卡宾中间体进行 (JJ Eisch, Y. Qian, M. Singh, J. Organomet. Chem.1996, 512, 207 )。由于此类提议的镍 (0)-卡宾不能令人满意地解释此类α-消除所遇到的反应,因此已对这些镍 (0) 试剂与孪晶二卤化物的反应进行了详细的重新检查。例如,这种假定的镍(0)-卡宾的两个反应仍然异常:(1)5,5-二溴四苯基环戊二烯未能形成其预期的二聚体,八苯基苯基富瓦烯,而不是在与 (Et3P)4Ni 反应中形成三乙基鏻四苯基环戊二烯化物;(2) 在捕集剂(苯甲醛或二苯甲酮)存在的情况下推测中间体 R2C=Ni0