Some acetylene and hydride chemistry of group 8 metal complexes with cyclopentadienyls and their analogous ligands

The reactivities of several ruthenium complexes with closely related ligands Cp, Cp*, PCP (2,6-(PPh2CH2)(2)C6H3) and Tp (hydrotris(pyrazolyl)borate) towards terminal acetylenes are compared. While reactions of terminal acetylenes with ruthenium complexes such as CpRuCl(PR3)(2), Cp*RuCl(PR3)(2) and TpRuCl(PR3)(2) usually give vinylidene, allenylidene, hydroxyvinylidene or vinylvinylidene complexes, unusual coupling products are produced in the reactions of terminal acetylenes with analogous Ru(PCP) complexes. The structures of group 8 metal hydride complexes of the formula LRuH3(L') (L = Cp, Cp*, Tp; L' = PPh3) and [LMH2(L')(2)](+) (L = Cp, Cp*, Tp; L' = tertiary phosphine) have also been compared in terms of the relative stability of dihydrogen vs, dihydride forms and cia vs. trans-dihydride isomers. Although both Cp and Tp are isoelectronic and both facially coordinate to metal centers, they have different abilities to stabilize the dihydrogen ligand. The difference is reflected in the fact that CpRuH3(PPh3) and [CpRuH2(PPh3)(2)](+) are classic metal hydride complexes but TpRuH(H-2)(PPh3) and [TpRu(H-2)(PPh3)(2)](+) are dihydrogen complexes. Complexes of the formula [C5R5)MH2(PP)](+) (M = Fe, Ru, Os; PP = chelating diphosphine) can adopt either the pure dihydrogen form, or a mixture of dihydrogen and trans-dihydride forms, or pure trans-dihydride form, or a mixture of cis- and trans-dihydride forms, depending on metals, C5R5 and the chelating ring sizes of diphosphines. (C) 1998 Elsevier Science S.A. All rights reserved.