Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh3)(CH3CN)(2)](+) (E = P, As, Sb, Bi) and [RuCp(EPh3)(eta(3)-C3H5)Br](+) have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh3 either via a Ru-E or a eta(6)-arene bond, where the latter is favored when the former is weaker, that is in going down the series. Thus in the case of Bi, the starting material [RuCp(CH3CN)(3)](+) does not react with BiPh3 to give [RuCp(BiPh3)(CH3CN)(2)](+) but instead gives only the eta(6)-arene species [RuCp(eta(6)-PhBiPh2)](+) and [(RuCp)(2)(mu-eta(6),eta(6)-Ph2BiPh)](2+). Similarly, the EPh3 ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh3)(CH3CN)(2)](+) for the isomerization of allyl-phenyl ethers to the corresponding 1-propenyl ethers is best with E = P, while the conversion drops significantly using the As and Sb derivatives. By the same token, only [RuCp(PPh3)(CH3CN)(2)](+) is stable in a non-aromatic solvent, whereas both [RuCp(AsPh3)(CH3CN)(2)](+) and [RuCp(SbPh3)(CH3CN)(2)](+) rearrange upon warming to [RuCp(eta(6)-PhEPh2)](+) and related compounds. In addition, the potential of [RuCp(EPh3)(CH3CN)(2)](+) as precatalysts for the transfer hydrogenation of acetophenone and cyclohexanone has been investigated. Again aromatic substrates are clearly less suited than non-aromatic ones due to facile eta(6)-arene coordination leading to catalyst's deactivation. (C) 2002 Elsevier Science B.V. All rights reserved.