Hybrids of [FeFe]- and [NiFe]-Hase Active Site Models.

Complexes of the type (diphosphine)Ni(-SR)Fe(CO) are investigated with azadithiolate (adt, HN(CHS)) as the dithiolate. The resulting complexes are hybrid models for the active sites of the [NiFe]- and [FeFe]-hydrogenases. The key complex (dppv)Ni(-adt)Fe(CO) was prepared from the complex Ni[(SCH)NCbz](dppv), which contains a Cbz-protected adt ligand (Cbz = C()OCHPh, dppv = -1,2-(PhP)CH). This complex combines with Fe(CO) to give (dppv)Ni[(-SCH)NCbz]Fe(CO), which is readily deprotected to give . Complex undergoes protonation at both Fe and N to give successively [(dppv)Ni(-adt)FeH(CO)] ([H]) and [(dppv)Ni(-adtH)FeH(CO)] ([H3H]). The redox properties and dynamics of these complexes resemble previously reported analogues with propanedithiolate. Solutions of [H] readily degrade to [(dppv)Ni[(-SCH)NCH]Fe(CO)] ([]), which features a methylene group linking N and Fe. Complex [] can be made in high yield by reaction of [H] with CHO, and this conversion was also demonstrated with CHO. Complex [] undergoes hydrogenolysis by photochemical reaction with H to give [(dppv)Ni[(-SCH)NMe]FeH(CO)], the -methylated analogue of []. Upon treatment ith MeO, [] undergoes quaternization, giving [(dppv)Ni[(-SCH)N(Me)CH]Fe(CO)]. In contrast with the lability of [H], the phosphine-substituted derivative [(dppv)Ni(-adt)FeH(CO)(PPh)] did not degrade. Most complexes were characterized by X-ray crystallography.