Formation of Metallacyclobutene Complexes via the Addition of Hydrazines to Ruthenium Vinylidene Complexes

The reaction between monosubstituted hydrazines and Ru(II) vinylidene complexes [RuCl(P∩N)2(CCH(R))]BPh4 (where R = Ph, n-Bu and P∩N = 3,5-dimethyl[1-((2-diphenylphosphino)ethyl)]pyrazole (Me2PyP)) afforded metallacyclobutene derivatives of the general formula [RuCl(κ1P-Me2PyP)(κ2P,N-Me2PyP)(κ2N,C-NH2N′(R1)C(CH2R2))]BPh4 (where R1, R2 = Me, Ph, n-Bu). The new metallacyclic ruthenium complexes contain a four-membered ring (−RuC−N−N−) and one pendant P,N-donor ligand, Me2PyP, bound through the P-donor atom. The solid-state and solution-state structures of these complexes were confirmed through X-ray crystallographic analysis and extensive 2D NMR spectroscopic studies. The reactivity of [RuCl(Me2PyP)2(CCH(R))]BPh4 toward amines and disubstituted hydrazines was also investigated. The Me2PyP ligand exhibited hemilabile behavior on reaction of [RuCl(Me2PyP)2(CCH(R))]BPh4 with aniline. The mechanism of the formation of the four-membered metallacycle was investigated, and it was found that the formation of N−C bonds from hydrazines and vinylidene was only possible when facilitated by displacement of the N-donor atom of the P,N-donor ligand Me2PyP by the −NH2 group of the monosubstituted hydrazines.