Synthesis, Structures, and Reactivities of Pincer‐Type Ruthenium Complexes Bearing Two Proton‐Responsive Pyrazole Arms

Abstract

A new metal-ligand bifunctional, pincer-type ruthenium complex [RuCl(L1-H(2))(PPh(3))(2)]Cl (1; L1-H(2)=2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine) featuring two proton-delivering pyrazole arms has been synthesized. Complex 1, derived from [RuCl(2)(PPh(3))(3)] with L1-H(2), underwent reversible deprotonation with potassium carbonate to afford the pyrazolato-pyrazole complex [RuCl(L1-H)(PPh(3))(2)] (2). Further deprotonation of 1 and 2 with potassium hexamethyldisilazide in methanol resulted in the formation of the bis(pyrazolato) complex [Ru(L1)(MeOH)(PPh(3))(2)] (3). Complex 3 smoothly reacted with dioxygen and dinitrogen to give the side-on peroxo complex [Ru(L1)(O(2))(PPh(3))(2)] (4) and end-on dinitrogen complex [Ru(L1)(N(2))(PPh(3))(2)] (5), respectively. On the other hand, the reaction of [RuCl(2)(PPh(3))(3)] with less hindered 2,6-di(1H-pyrazol-3-yl)pyridine (L3-H(2)) led to the formation of the dinuclear complex [{RuCl(2)(PPh(3))(2)}(2)(μ(2)-L3-H(2))(2)] (6), in which the pyrazole-based ligand adopted a tautomeric form different from L1-H(2) in 1 and the central pyridine remained uncoordinated. The detailed structures of 1-6 were determined by X-ray crystallography.