Formation of rhodium carbonyl thiolate dimers via elimination of dihydrogen;: crystal and molecular structure of [Rh2(CO)4(μ-SC6H4CH3)2]

Reaction of [Rh-6(CO)(15)(NCMe)] with p-thiocresol [(4-Me)C6H4SH] leads to the formation of [Rh-2(CO)(4)(mu -SC6H4CH3)(2)] as the main product along with a small amount of [Rh-6(CO)(16)]. An approximately 30-fold excess of the thiol is required in order to obtain a good yield of the thiolate-bridged dimer while reaction of [Rh-4(CO)(12)] with an excess of p-thiocresol leads to an apparently clean conversion to the dimeric Rh(I) complex. Mass spectrometric measurements show that the latter reaction involves evolution of H-2, and CO evolution is indicated by the retardation of the reaction in CO saturated solution; these results suggest the following reaction stoichiometry: [Rh-4(CO)(12)] + 4RSH --> 2[Rh-2(CO)(4)(mu -SR)(2)] + 2H(2) + 4CO. Kinetic measurements show that the reaction proceeds in three stages which are proposed to involve two rapid pre-equilibria and a final irreversible and relatively slow conversion to the products. The crystal and molecular structure of [Rh-2(CO)(4)(mu (2)-SC6H4CH3)(2)] is reported. (C) 2001 Elsevier Science B.V. All rights reserved.