Structural and electrochemical aspects of tris(ferrocenyl/phenyl-ethynyl)phosphine ligated chalcogen bridged iron carbonyl clusters

Abstract

Room temperature stirring of THF solution of [Fe₃Se₂(CO)₉] and P(C₂R)₃ (R = Ph, Fc), in presence of Me₃NO·2H₂O, yield monosubstituted [Fe₃Se₂(CO)₈{P(C₂R)₃}] (1, R = Ph; 2, R = Fc) and disubstituted [Fe₃Se₂(CO)₇{P(C₂R)₃}₂] (3, R = Ph; 4, R = Fc) clusters. Under similar conditions, reactions of [Fe₃Te₂(CO)₉] yield disubstituted [Fe₃Te₂(CO)₇{P(C₂R)₃}₂] (5, R = Ph; 6, R = Fc) and [Fe₃Te₂(CO)₈{P(C₂R)₃}₂] (7, R = Ph; 8, R = Fc), consisting of an adduct of Fe(CO)₂{P(C₂R)₃}₂ and Fe₂Te₂(CO)₆ butterfly moieties. Further substitution of 2 with P(C₂Ph)₃ forms a mixed disubstituted cluster, [Fe₃Se₂(CO)₇P(C₂Fc)₃P(C₂Ph)₃] (9). Crystal structures of disubstituted clusters 3–5 reveal a rare syn orientation of phosphinoalkyne ligands attached to the equatorial position of both basal irons, which is stabilised by an intramolecular CH⋯π interaction. DFT calculations also suggest that syn disubstituted products are thermodynamically most stable. Electrochemistry of tris(ferrocenylethynyl)phosphine containing clusters 2, 4, 8 and 9 has been studied by cyclic voltammetry, which shows cathodically shifted multielectron reversible oxidation of ferrocenyl groups.