REACTIONS OF DINUCLEAR AND POLYNUCLEAR COMPLEXES .11. THE ALKYNE INTERACTION - KINETIC AND ELECTROCHEMICAL STUDY ON THE PARALLEL MU-3-ETA(2) BONDING MODE IN TRINUCLEAR CARBONYL CLUSTERS OF IRON - INFLUENCE OF EXTERNAL LIGANDS ON THE ALKYNE ORIENTATION IN [FE3CP2(CO)5(CF3C2CF3)]

The parallel mu3-eta2 alkyne-cluster interaction in triiron compounds of the formula [Fe3-Cp2(CO)5(CF3C2CF3)] (1) has been investigated. Kin etics of the interconversion of asymmetrical (1a) and symmetrical (1b) conformers are reported. The influence of external ligands on the alk yne orientation is examined on treating 1 with tertiary phosphine and phosphite. The monosubstituted complexes [Fe3Cp2(CO)4(L) (CF3C2CF3)] ( L = PMe3 (2), P(OMe)3 (3)), in which the alkyne ligand is bonded in mu 3-eta2(parallel-to) mode, are obtained. The redox chemistry of triiron alkyne clusters 1-3 has been investigated by electrochemical techniqu es. One-electron reduction coupled with the decoordination of a ligand (CO or phosphorus ligand) induces alkyne reorientation over the trime tallic framework.