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

Room temperature stirring of THF solution of [Fe3Se2(CO)(9)] and P(C2R)(3) (R = Ph, Fc), in presence of Me3NO center dot 2H(2)O, 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)(7)P(C(2)Fc)(3)P(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 center dot center dot center dot pi 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