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

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)(RC=CR')] with 1 gave the appropriate [NbCl3(bppzm)(RC=CR')] 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.