Redox-Dependent Isomerization of Organometallic RuII/RuIIICompounds Containing the Hydrotris(methimazolyl)borate Ligand: An Electrochemical Square Scheme Mechanism

Abstract

[Cp*RuIII{HB(mt)3}]X (1A(X); X = Cl, PF6) and [Cp*RuII{HB(mt)3}] (2A) (Cp* = η5-C5Me5, 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 κ3-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 κ3-H,S,S‘ coordination about the Ru (κ3-H,S,S‘ forms of [Cp*RuIII{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.