Triiron Complexes Featuring Azadiphosphine Related to the Active Site of [FeFe]-Hydrogenases: Their Redox Behavior and Protonation.

The design of iron clusters featuring a bimetallic core and several protonation sites in the second coordination sphere of the metal centers is important for modeling the activity of polymetallic active sites such as the H-cluster of [FeFe]-hydrogenases. For this purpose, the syntheses of complexes [Fe 3 (CO) 5 ( κ 2 -P Ph 2 N R 2 )( μ -pdt) 2 ] (R = Ph ( 1 ), Bn ( 2 )) and [Fe 3 (CO) 5 ( κ 2 -P Ph 2 N R 2 )( μ -adt Bn )( μ -pdt)] (R = Ph ( 3 ), Bn ( 4 )) were carried out by reacting hexacarbonyl precursors [Fe 2 (CO) 6 ( µ -xdt)] (xdt = pdt (propanedithiolate), adt Bn (azadithiolate) with mononuclear complexes [Fe( κ 2 -pdt)(CO) 2 ( κ 2 -P Ph 2 N R 2 )] (P Ph 2 N R 2 = (P Ph CH 2 N R CH 2 ) 2 , R = Ph, Bn) in order to introduce amine functions, through well-known P Ph 2 N R 2 diphosphine, into the vicinity of the triiron core. The investigation of the reactivity of these triiron species towards the proton (in the presence of CF 3 SO 3 H) and the influence of the pendant amines on the redox properties of these complexes were explored using spectroscopic and electrochemical methods. The protonation sites in such triiron clusters and their relationships were identified. The orientation of the first and second protonation processes depends on the arrangement of the second coordination sphere. The similarities and differences, due to the extended metal nuclearity, with their dinuclear counterparts [Fe 2 (CO) 4 ( κ 2 -P Ph 2 N R 2 )( μ -pdt)], were highlighted.