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

Abstract

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh 3)(CH 3CN) 2] + (E=P, As, Sb, Bi) and [RuCp(EPh 3)(η 3-C 3H 5)Br] + have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh 3 either via a RuE or a η 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(CH 3CN) 3] + does not react with BiPh 3 to give [RuCp(BiPh 3)(CH 3CN) 2] + but instead gives only the η 6-arene species [RuCp(η 6-PhBiPh 2)] + and [(RuCp) 2(μ-η 6,η 6-Ph 2BiPh)] 2+. Similarly, the EPh 3 ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh 3)(CH 3CN) 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(PPh 3)(CH 3CN) 2] + is stable in a non-aromatic solvent, whereas both [RuCp(AsPh 3)(CH 3CN) 2] + and [RuCp(SbPh 3)(CH 3CN) 2] + rearrange upon warming to [RuCp(η 6-PhEPh 2)] + and related compounds. In addition, the potential of [RuCp(EPh 3)(CH 3CN) 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 η 6-arene coordination leading to catalyst's deactivation.