New functionalized bis(pyrazol-1-yl)methane ligands. Synthesis, spectroscopic characterization of early and late transition metal complexes containing a functionalized N,N or P,P-chelate bis(5-diphenylphosphinopyrazol-1-yl)methane ligand

Abstract

The multistep syntheses of the novel functionalized bis(pyrazol-1-yl)methane ligands, bis(5-diphenylphosphinopyrazol-1-yl)methane (bppzm) 1, bis(5-diphenylphosphinopyrazol-1-yl)trimethylsilylmethane (bppztm) 2 and bis(2-diphenylphosphinoimidazol-1-yl)methane (bpizm) 3, have been studied. The coordinative capacity of the bppzm ligand towards a variety of early and late metal fragments was evaluated and seven metallacycles were isolated. The complex [{NbCl₃(dme)}_n] (dme = 1,2-dimethoxyethane) reacted with an excess of bppzm to give the binuclear complex [{NbCl₃(bppzm)}₂] 4, and in the same way the reaction of the mononuclear species [NbCl₃(dme)(RCCR′)] with 1 gave the appropriate [NbCl₃(bppzm)(RCCR′)] complexes (R = R′ = Ph 5; R = R′ = SiMe₃ 6; R = Ph, R′ = Me 7; R = Ph, R′ = SiMe₃ 8). In all these niobium complexes, 1 behaves as an N,N chelate ligand. Compound 1 reacts with [MCl₂(PhCN)₂] (M = Pd, Pt) to yield the complexes [MCl₂(bppzm)] (M = Pd 9, Pt 10), where a P,P chelate behaviour for 1 was observed. A dynamic conformation of the six- and eight-membered metallacycles formed in the complexes was observed and variable-temperature NMR studies were carried out. Finally, the molecular structure of complex 10 was determined crystallographically and a distorted square-planar geometry was found in which a proton (H_endo) of the bridging methylene is in close proximity to the metal centre in the boat–boat conformation of the metallacycle.