Reactions of Coordinated Ligands Exemplified by the Formation and Transformation of the Dithiocarbonate Ligand in the Rhodium(III) Complex [(triphos)Rh(S₂CO)]BPh₄

Abstract

The genesis and chemistry of the S,S-chelate dithiocarbonate ligand in the Rh(III) complex [(triphos)Rh(S₂CO)]BPh₄, (1), [triphos = MeC(CH₂PPh₂)₃] have been investigated by means of a variety of chemical and physical techniques. Compound 1 in CH₂Cl₂ or THF solutions thermically or photochemically decomposes affording, depending on the reaction conditions, CO and the bis(μ-S₂) complex [(triphos)Rh (μ-S₂)₂Rh(triphos)](BPh₄)₂ or COS and the bis(μ-S) complex [(triphos)Rh (μ-S)₂Rh(triphos)](BPh₄)₂. The latter, which can be also obtained by treatment of 1 with H⁺ or Me⁺, reacts with O₂ yielding the bis(μ-SO) derivative [(triphos)Rh(μ-SO)₂Rh(triphos)](BPh₄)₂. Nucleophiles such as halides, pseudohalides and H⁻, add to rhodium to form neutral, octahedral complexes of general formula (triphos)Rh(S₂CO)(Nu). Heteroallene molecules of the S[dbnd]C[dbnd]X type (X = S, O, NR) are metathesized by 1 to give the trithiocarbonate or dithiocarbimate derivatives [(triphos)Rh(S₂CS)]BPh₄ and [(triphos)Rh(S₂CNR)]BPh₄ (R = Ph, Et), which, together with 1, are able to heterolytically split dihydrogen under very mild conditions. As a result, the hydride (triphos)RhH(S₂CS), the hydrido(dithiocarbamate) (triphos)RhH(S₂CNHR) or the μ-SH dimeric hydride [(triphos)RhH(μ-SH)₂RhH(triphos)](BPh₄)₂ are obtained, respectively. Finally, 1 is chemically or electrochemically reduced to the Rh(II) congener (triphos)Rh(S₂CO) which represents one of the very few examples of mononuclear Rh(II) complexes stable both in the solid state and in solution.

Key Words:

• reactivity of coordinated ligands
• sulfur coordination chemistry
• dithiocarbonate metal complexes