CO-59 NMR-STUDY OF CLUSTER REACTIONS - SOLVENT AND LIGAND EFFECTS IN MIXED-METAL, TETRAHEDRAL MCO3 (M = FE, RU) CARBONYL CLUSTERS - CRYSTAL-STRUCTURE OF FECO3(MU-3-H)(MU-CO)3(CO)8(PPH2H)

Co-59 NMR spectroscopy is used to study the site selectivity of reactions between tetrahedral mixed-metal clusters HMCo3(CO)12 (M = Fe (1a), M = Ru (1b) and various 2e donor ligands. In the monosubstituted clusters HMCo3(CO)11L [M = Fe, L = PPh2H (2a), PCy2H (4a), PPh3 (5a), NMe3 (6a), SEt2 (7a); M = Ru, L = PPh2H (2b), PCy2H (4b), PPh3 (5b)] the ligand L is bound to a basal Co atom, generally giving rise to two Co-59 NMR resonances in a 2:1 ratio. The variation in chemical shift is examined throughout the series. The reaction of 2a with a slight excess of Me3NO in CH2Cl2 was monitored by Co-59 NMR spectroscopy and gave HFeCo3(CO)10(NMe3)(PPh2H) (8a), in which each of the three chemically different Co atoms gives rise to a different resonance. This labile cluster transforms first to 2a and then to the anion [FeCo3(CO)11(PPh2H)-, owing to decoordination of the amine. Deprotonation of cluster 2a also occurs in solvents like THF or acetone, which deprotonate the more acidic clusters 1a or 1b even more readily. Comparisons are made between disubstituted FeCo3 clusters containing (P,P), (P,N), or (P,S) monodentate donor ligands, which illustrate the sensitivity of Co-59 NMR spectroscopy and its diagnostic value for the study of metallosite selectivity in cluster reactions. The structure of 2a has been determined by X-ray diffraction: space group P1BAR with a = 14.615 (5) angstrom, b = 17.087 (2) angstrom, c = 11.136 (3) angstrom, alpha = 99.20 (1)-degrees, beta = 105.94 (2)-degrees, gamma = 87.49 (2)-degrees, and Z = 4. The structure was refined to R = 0.029 and R(w) = 0.041 on the basis of 5764 reflections having F(o)2 > 3-sigma(F(o)2). There are two independent, almost identical molecules in the asymmetric unit. The cluster has a tetrahedral structure and the phosphine is axially bonded to a basal cobalt atom. The triply bridging hydride ligand was found to be closer to the cobalt atom bearing the PPh2H ligand.