SYNTHESIS, STEREOPHYSICAL-BONDING FEATURES, AND CHEMICAL ELECTROCHEMICAL REACTIVITY OF 2 DIMETAL-BRIDGING DIPHOSPHIDE COMPLEXES - CO2(ETA-5-C5ME5)2(MU-2-ETA-2-P2)2 AND FE2(ETA-5-C5ME5)2(MU-2-ETA-2-P2)2

Two dimetal-bridging diphosphido complexes, Co2Cp*2(mu-2-eta-2-P2)2 (1) and Fe2Cp*2(mu-2-eta-2-P2)2 (2) (Cp* = eta-5-C5Me5), were synthesized by cophotolysis of P4 with CoCp*(CO)2 and Fe2Cp*2(CO)2(mu-2-CO)2, respectively. 1 and 2 were characterized from X-ray diffraction, laser-desorption FT mass spectrometric, spectroscopic (H-1, P-31 NMR; IR), and electrochemical measurements. An X-ray diffraction study unambiguously showed that the 36-electron cobalt dimer (1) consists of two 14-electron CoCp* fragments linked at a nonbonding Co...Co distance of 3.10 angstrom by two four-electron-donating eta-2-coordinated P2 ligands. The X-ray crystallographic investigation of the corresponding 34-electron iron dimer (2) disclosed two FeCp* fragments separated by an electron-pair Fe-Fe distance of 2.59 angstrom; unfortunately, a rotational-type crystal disorder was encountered, which prevented a definitive determination of the number and bonding modes of the bridging phosphorus atoms from the crystallographic analysis per se. However, the X-ray data and a comparative analysis of mass spectral and P-31 NMR data for 1 and 2 provide persuasive evidence that the stoichiometry and connectivities of the phosphorus atoms in 2 are identical to those in 1. Cyclic voltammograms indicated that each dimer exhibits reversible oxidative behavior. Preliminary investigations of the potential chemical reactivities of these metal-bridged diphosphide ligands with H-2 and C2H4 revealed that they are relatively inert compared to the reactivities previously reported for metal-bridged disulfide ligands with these reagents.