An imidazole-based P–N bridging ligand and its binuclear copper(I), silver(I) and palladium(I) complexes: synthesis, characterizations and X-ray structures

Abstract

Reaction of 1-methylimidazole with n-BuLi in tetrahydrofuran at −78°C followed by addition of chlorodiphenylphosphine afforded a P–N bridging ligand, 2-(diphenylphosphino)-1-methylimidazole (dpim) in good yield. The structure of the ligand was determined by single crystal X-ray analysis. Reaction of a stoichiometric amount of the ligand with [Cu(MeCN) 4]ClO 4 in acetonitrile led to the binuclear complex [Cu 2(μ-dpim) 3(MeCN)](ClO 4) 2·2CH 3CN ( 1·2CH 3CN), whose structure was determined by single crystal X-ray analysis. The solid state structure shows that the two copper ions are held by three dpim ligands and the coordination geometry around each metal atom is different, one being three- and the other being four-coordinated. One of the copper ions forms a distorted tetrahedral array with two P and one N atoms from the dpim ligand and an additional N atom from an acetonitrile ligand, whereas the other copper ion is three coordinated with two N and one P atoms from the dpim ligand. The nitrate-bridged polymeric silver(I) complex, {[Ag 2(μ-dpim) 2(NO 3)](NO 3)} n ( 2) was prepared by the reaction of equimolar amounts of the ligand and silver nitrate in methanol and was characterized by IR, NMR and X-ray analysis. The dimeric unit, [Ag 2(μ-dpim) 2], possesses an eight-membered annular core structure with two ligands bridging the two metal ions in a head-to-tail configuration. Two types of nitrate ions are present in 2: one makes an infinite one-dimensional chain by joining the dimeric units through its two oxygen atoms in an anti– anti bridging mode whereas the other is disordered with a half occupancy and is located at the left and right sides of the chain. The dynamic behavior of 2 in acetone was also studied by variable temperature 31P NMR. The binuclear palladium(I) complex [Pd 2Cl 2(dpim) 2] ( 4) was prepared by a conproportionation reaction between complex [PdCl 2(dpim) 2] ( 3) and [Pd(dba) 2] (dba=dibenzylideneaceton). Only one geometric isomer, probably head-to-tail (HT), was formed in this reaction. Complex 3 was prepared by treating [PdCl 2(PhCN) 2] with two moles of ligand in dichloromethane solution. In this complex the ligand acts as a P-monodentate. In solution it exists as a mixture of cis and trans isomers.