Tris- and pentakis-dialkyldithiocarbamates of ruthenium, [Ru(S2CNR2)3]n and [Ru2(S2CNR2)5]n (n = +1, 0, and –1): chemical and electrochemical interrelations

Abstract

The electron-transfer characteristics of many ruthenium(III) dithiocarbamates have been studied in acetone at a platinum electrode. The tris complexes undergo a relatively facile, reversible, one-electron reduction step to yield the ruthenium(II) complexes [Ru(S₂CNRR′)₃]^–(R,R′= Me, Et, Prⁱ, Buⁱ, Ph, PhCH₂, C₆H₁₁; RR′= piperidinyl, 2,6-dimethylpiperidinyl, pyrrolrdinyl, or morpholinyl). The corresponding one-electron oxidation step to the formally ruthenium(IV) complex [Ru(S₂CNRR′)₃]^– is not reversible, the degree of irreversibility being markedly dependent on the substituents R and R′. Substituent effects on the redox potentials parallel those reported previously for many first-row transition-metal dithiacarbamates. Chemical and electrolytic oxidation of [Ru(S₂CNR₂)₃] yield the dimeric ruthenium(III) cations [Ru₂(S₂CNR₂)₅]⁺ which are obtained in two structural isomeric forms, α and β. Both series (α and β) undergo successive one-electron reductions to the corresponding [Ru₂(S₂CNR₂)₅] and [Ru₂(S₂CNR₂)₅]^– complexes. The rates of isomerisations (i) and (ii) have been measured. β-[Ru₂(S₂CNMe₂)₅]^–→α-[Ru₂(S₂CNMe₂)₅]^–(i), α-[Ru₂(S₂CNMe₂)₅]⁺→β-[Ru₂(S₂CNMe₂)₅]⁺(ii) The combined redox-potential data and equilibrium measurements afford the relative thermodynamic stabilities of the six dimeric species. Many of the new complexes have been characterised by spectroscopic techniques including i.r., visible–u.v., and ¹H n.m.r. Paramagnetic shift reagents have been employed and, in the case of β-[Ru₂(S₂CNMe₂)₅]⁺, enantiomers have been distinguished with an optically active shift reagent.