Redox-dependent isomerization of organometallic RuII/Ru III compounds containing the hydrotris(methimazolyl)borate ligand: An electrochemical square scheme mechanism

Abstract

[Cp*RuIII{HB(mt)3}]X (1A(X); X = Cl, PF 6) and [Cp*RuII{HB(mt)3}] (2A) (Cp* = η5-C5-Me5, mt = N-methyl-2- mercaptoimidazol-1-yl) were synthesized by the reactions of K[HB(mt) 3] with [Cp*RuIIICl2]2 and [Cp*RuII(OMe)]2, respectively. 1A and 2A exist in the solid state in k3-S,S′,S″ coordination, so that the sulfur atom in each mt group coordinates to the central Ru ion, producing the normal tripodal geometry of the [HB(mt)3] ligand. However, both compounds undergo an isomerization reaction in solution, where the sulfur on one mt group is displaced in favor of coordination to the hydrogen bonded to the boron (an agostic B-H-Ru interaction), resulting in k3-H,S,S′ coordination about the Ru (K3-H,S,S′ forms of [Cp*Ru III{HB(mt)3}] and [Cp*RuII{HB(mt) 3}] are designated 1B and 2B, respectively). The rate and equilibrium constants associated with the reactions 1A ⇄ 2A ⇄ 2B ⇄ 1B ⇄ 1A have been determined by theoretical digital simulation comparisons of experimental 1H NMR spectroscopic and cyclic voltammetric data over a range of temperatures. © 2005 American Chemical Society.