Synthesis and characterization of dinuclear rhodium complexes containing (benzylthiomethyl)diphenylphosphine as the bridging ligand. Structure of the novel rhodium(II) complex [Rh2Cl4(CO)2(µ-PhCH2SCH2PPh2)2]

Abstract

Treatment of [{RhCl(CO)₂}₂] with 5 equivalents of PhCH₂SCH₂PPh₂(btmp) gave the mononuclear Vaska-type complex trans-[RhCl(CO)(btmp-P)₂], whereas the reaction with 2 equivalents of btmp afforded not the expected face-to-face complex [Rh₂Cl₂(CO)₂(µ-btmp)₂] but the chloro-bridged complex [Rh₂(µ-Cl)(CO)₂(µ-btmp)₂][RhCl₂(CO)₂]. The tetraphenylborate salt analogue [Rh₂(µ-Cl)(CO)₂(µ-btmp)₂]BPh₄ was obtained from the reaction of an ethanolic solution of [RhCl₂(CO)₂]^– with 1 equivalent of btmp and NaBPh₄. Treatment of [NBuⁿ₄][RhCl₂(CO)₂] with 1 equivalent of btmp afforded the carbonyl-bridged dinuclear complex [Rh₂Cl₂(µ-CO)(µ-btmp)₂], while the above reaction performed in the presence of hydrochloric acid gave the novel dinuclear rhodium(II) complex [Rh₂Cl₄(CO)₂(µ-btmp)₂](5). Complex (5) was also obtained from the reaction of an ethanolic solution of [RhCl₂(CO)₂]^–and 1 equivalent of btmp. Crystals of (5) are monoclinic, space group C2/c, with a= 14.064(3), b= 19.364(4), c= 16.930(5)Å, β= 116.67(2)°, and Z= 4; final R= 0.036 for 3 529 observed reflections. The structure shows that there is a metal–metal bond [Rh–Rh 2.733(3)Å] and the two µ-btmp ligands are co-ordinated to rhodium atoms cis to each other with a head-to-tail arrangement. The relationships among the synthesized complexes are discussed.