| 研究実績の概要 |
For the purpose to elucidate the dihydrogen activation process mediated by [NiFe] hydrogenase, I was engaged in the model study of plausible intermediates associated during catalysis by the enzyme. A series of new heterobimetallic dithiolate-bridged Ni-Fe(carbonyl/cyanide) complexes, [(18-Crown-6)K]2[(CO)(CN)2Fe(pdt)Ni(CO)(PPh3)] (1; pdt = propane-1,3-dithiolate), [(18-Crown-6)K]2[(CO)(CN)2Fe(ndt)- Ni(CO)(PPh3)] (2; ndt = norborane-exo-2,3-dithiolate), and the m-hydride complex [(18-Crown-6)K][(CN)(CO)2Fe(pdt)(mu-H)- Ni(CN)(PCy3)] (3), were synthesized as models of the different states named Ni-L and Ni-R states. The Fe(II)-Ni(0) complexes 1 and 2 were synthesized by the reaction of Ni(PPh3)4 with Fe(II) thiolato complexes [(CO)2(CN)2Fe(pdt)](2-) and [(CO)2(CN)2Fe(ndt)](2-), respectively. The mu-hydride complex 3 was obtained via a similar reaction of the Fe(II) thiolato complex with Ni(II)-hydride complex Ni(H)(Cl)(PCy3)2. Complexes 1 and 2 has Ni-Fe distances of ~2.5 A, and thus they serve as the novel synthetic model complexes native Ni-L state and Ni center retain tetrahedral geometry. The mu-hydride bimetallic complex 3 with Ni-Fe distance ~2.6 A represents the very important intermediate model complex in the catalytic cycle of [Ni-Fe] hydrogenase termed as Ni-R state where Fe is coordinated by CO/CN and the Ni possesses a distorted tetrahedral geometry. While a model complex having CN ligand protected with Lewis acid was reported by Rauchfuss, complex 3 is the first Ni-Fe (CO/CN) mu-hydride complex.
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