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

A new metalligand bifunctional, pincer-type ruthenium complex [RuCl(L1-H2)(PPh3)2]Cl (1; L1-H2=2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine) featuring two proton-delivering pyrazole arms has been synthesized. Complex 1, derived from [RuCl2(PPh3)3] with L1-H2, underwent reversible deprotonation with potassium carbonate to afford the pyrazolatopyrazole complex [RuCl(L1-H)(PPh3)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)(PPh3)2] (3). Complex 3 smoothly reacted with dioxygen and dinitrogen to give the side-on peroxo complex [Ru(L1)(O2)(PPh3)2] (4) and end-on dinitrogen complex [Ru(L1)(N2)(PPh3)2] (5), respectively. On the other hand, the reaction of [RuCl2(PPh3)3] with less hindered 2,6-di(1H-pyrazol-3-yl)pyridine (L3-H2) led to the formation of the dinuclear complex [{RuCl2(PPh3)2}2(mu 2-L3-H2)2] (6), in which the pyrazole-based ligand adopted a tautomeric form different from L1-H2 in 1 and the central pyridine remained uncoordinated. The detailed structures of 16 were determined by X-ray crystallography.