Casey Charles P, Bikzhanova Galina A, Cui Qiang, Guzei Ilia A
Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
J Am Chem Soc. 2005 Oct 12;127(40):14062-71. doi: 10.1021/ja053956o.
Reduction of imines by [2,5-Ph2-3,4-Tol2(eta(5)-C4COH)]Ru(CO)2H (2) produces kinetically stable ruthenium amine complexes. Reduction of an imine by 2 in the presence of an external amine trap gives only the complex of the newly generated amine. Reaction of 2 with H2N-p-C6H4N=CHPh (11), which contains an intramolecular amine trap, gave a 1:1 mixture of 2,5-Ph2-3,4-Tol2(eta(4)-C4CO)2RuNH(CH2Ph)(C6H4-p-NH2) (8), formed by coordination of the newly generated amine to the ruthenium center, and 2,5-Ph2-3,4-Tol2(eta(4)-C4CO)2RuNH2C6H4-p-NHCH2Ph (9), formed by coordination of the amine already present in the substrate. These results require transfer of hydrogen to the imine outside the coordination sphere of the metal to give a coordinatively unsaturated intermediate that can be trapped inside the initial solvent cage. Amine diffusion from the solvent cage must be much slower than coordination to the metal center. Mechanisms requiring prior coordination of the substrate to ruthenium would have led only to 8 and can be eliminated.
[2,5-二苯基-3,4-二甲基苯基(η⁵-C₄COH)]Ru(CO)₂H (2)对亚胺的还原反应生成动力学稳定的钌胺配合物。在外部胺捕获剂存在下，2对亚胺的还原反应仅生成新生成胺的配合物。2与含有分子内胺捕获剂的H₂N-p-C₆H₄N=CHPh (11)反应，得到2,5-二苯基-3,4-二甲基苯基(η⁴-C₄CO)₂RuNH(CH₂Ph)(C₆H₄-p-NH₂) (8)和2,5-二苯基-3,4-二甲基苯基(η⁴-C₄CO)₂RuNH₂C₆H₄-p-NHCH₂Ph (9)的1:1混合物，8是由新生成的胺与钌中心配位形成的，9是由底物中已存在的胺配位形成的。这些结果表明，氢转移到金属配位球外部的亚胺上，生成一个配位不饱和中间体，该中间体可被困在初始溶剂笼内。胺从溶剂笼中的扩散速度必须比其与金属中心的配位速度慢得多。需要底物先与钌配位的机理只会生成8，因此可以排除。
