Binuclear copper(I) complexes containing two or three 2-(diphenylphosphine) pyridine (dppy) bridging ligands: X-ray crystal structure of [Cu2(µ-dppy)3(MeCN)][BF4]2and variable-temperature1H and31P-{1H} nuclear magnetic resonance studies

Abstract

Treatment of [Cu(MeCN)4] BF4 with 2-(diphenylphosphino)pyridine (dppy) at room temperature in acetonitrile or dichloromethane gives [Cu2(µ-dppy)2(MeCN)x][BF4]2, x= 4 or 2, respectively. Reaction with an excess of dppy in refluxing acetone leads to the formation of [Cu2(µ-dppy)3]-[BF4]2, which gives [Cu(µ-dppy)3(MeCN)][BF4]2 upon recrystallization from acetonitrile. This complex can also be obtained from [Cu(MeCN)4]BF4 by reaction with an excess of dppy in refluxing acetonitrile. Substituted complexes [Cu2(µ-dppy)3Lx][BF4]2[x= 1, L = 2-methylpyridine, x= 2, L = 4-methylpyridine, P(OMe)3, or PMe3] are also described. Variable-temperature 1H and 31P-{1H} n.m.r. studies show that MeCN and dppy dissociation and rapid ligand-exchange processes take place in solution. The crystal structure of [Cu2(µ-dppy)3(MeCN)][BF4]2 has been determined by X-ray methods. Crystals are monoclinic, space group P21/c with Z= 4 in a unit cell of dimensions a= 21.424(7), b= 13.186(6), c= 18.232(6)A, and β= 99.77(2)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by blockmatrix least squares to R= 0.0657 for 6 539 observed reflections [I 2σ(I)]. The structure consists of [Cu2(µ-dppy)3(MeCN)]2+ cations and of BF4– anions. In the cations the two copper atoms are held in close proximity [2.721(3)A] by three dppy ligands acting as bridges through the P and N atoms. One copper atom is three-co-ordinate, being bonded to two N and one P atom from dppy ligands, the other is four-co-ordinate, being bonded to two P and one N atom from dppy ligands and to an additional N atom from an acetonitrile molecule. As expected, the Cu–P and Cu–N bonds for the three-co-ordinate copper are shorter than these of the four-co-ordinate copper.