Hybrids of [FeFe]- and [NiFe]-H 2 ase Active Site Models.

Complexes of the type (diphosphine)Ni( μ -SR) 2 Fe(CO) 3 are investigated with azadithiolate (adt, HN(CH 2 S - ) 2 ) as the dithiolate. The resulting complexes are hybrid models for the active sites of the [NiFe]- and [FeFe]-hydrogenases. The key complex (dppv)Ni( μ -adt)Fe(CO) 3 (3) was prepared from the complex Ni[(SCH 2 ) 2 NCbz](dppv), which contains a Cbz-protected adt ligand (Cbz = C( O )OCH 2 Ph, dppv = cis -1,2-(Ph 2 P) 2 C 2 H 2 ). This complex combines with Fe 2 (CO) 9 to give (dppv)Ni[( μ -SCH 2 ) 2 NCbz]Fe(CO) 3 , which is readily deprotected to give 3 . Complex 3 undergoes protonation at both Fe and N to give successively [(dppv)Ni( μ -adt)FeH(CO) 3 ] + ([H 3 ] + ) and [(dppv)Ni( μ -adtH)FeH(CO) 3 ] 2+ ([H3H] 2+ ). The redox properties and dynamics of these complexes resemble previously reported analogues with propanedithiolate. Solutions of [H 3 ] + readily degrade to [(dppv)Ni[( μ -SCH 2 ) 2 NCH 2 ]Fe(CO) 3 ] + ([ 4 ] + ), which features a methylene group linking N and Fe. Complex [ 4 ] + can be made in high yield by reaction of [H 3 ] + with CH 2 O, and this conversion was also demonstrated with 13 CH 2 O. Complex [ 4 ] + undergoes hydrogenolysis by photochemical reaction with H 2 to give [(dppv)Ni[( μ -SCH 2 ) 2 NMe]FeH(CO) 3 ] + , the N -methylated analogue of [ H3 ] + . Upon treatment ith Me 3 O + , [ 4 ] + undergoes quaternization, giving [(dppv)Ni[( μ -SCH 2 ) 2 N(Me)CH 2 ]Fe(CO) 3 ] 2+ . In contrast with the lability of [H 3 ] + , the phosphine-substituted derivative [(dppv)Ni( μ -adt)FeH(CO) 2 (PPh 3 )] + did not degrade. Most complexes were characterized by X-ray crystallography.