Phosphite Bearing [(μ-ADT)RFe2(CO)6] (ADT = Azadithiolate) Moieties: A Tool for the Building of Multimetallic [FeFe]-Hydrogenase Mimics

Abstract

A new phosphite ligand having three [(μ-ADT)RFe2(CO)6] (R= p-HOC6H4) moieties (2) has been prepared in good yield by the reaction of complex [(μ-ADT)RFe2(CO)6] (R= p-HOC6H4) 1a with PCl3. Coordination of this phosphite to [PdCl2(MeCN)2] or [PtCl2(DMSO)2] forms heterometallic square planar complexes 5 (C84H48Cl2Fe12N6O42P2MS12) (M = Pt, Pd) in excellent yields. Three-legged piano stool complexes 6 (C52H39Cl2Fe6N3O21PMS6) (M = Rh, Ir) were obtained by the reaction of phosphite 2 with [MCl2Cp*]2 (M = Rh, Ir) in good yields. The formation of complexes 5 and 6 demonstrates the versatility of this new ligand for forming different heteropolymetallic complexes under mild reaction conditions. Moreover, the open-chain derivatives [(μ-ADT)RFe2(CO)6] (R= HOCH2CH2, o-HOC6H4) (1b and 1c, respectively) form cyclic complexes 4 by spontaneous intramolecular CO substitution by the P atom in one of the three [FeFe] fragments. The electrocatalytic behavior of complexes 2 and 4 upon the addition of AcOH is similar to that of related [(μ-ADT)Fe2(CO)6] derivatives. The successive additions of AcOH cause an increase in the current intensity in the wave at about −1.80 V for heteropolymetallic complexes 5 and 6. However, the appearance of a new wave around −1.40 V in complexes 5 points to an acid-promoted side reaction in the electrochemical process.