Systematic synthesis of triply bridged binuclear copper(I) complexes containing bis(diphenylphosphino)methane (dppm) bridging ligands: X-ray crystal structures of [Cu2(µ-dppm)2(µ-mpyO)]BF4 and [Cu2(µ-dppm)(µ-mpyO)2](mpyO = 6-methylpyridin-2-olate)

Abstract

Triply bridged binuclear copper(I) complexes containing the moieties Cu₂(µ-dppm)(µ-L–L)₂[dppm = bis(diphenylphosphino)methane] and Cu₂(µ-dppm)₂(µ-L–L) have been prepared. The reaction in tetrahydrofuran (thf) at room temperature of [Cu₂(µ-dppm)₂(MeCN)₂][BF₄]₂ with the sodium salts of the bidentate ligands L–L in 1 : 1 or 1 : 2 molar ratio gives, respectively, [Cu₂(µ-dppm)₂(µ-L–L)]BF₄ and [Cu₂(µ-dppm)(µ-L–L)₂][L–L = 6-methylpyridin-2-olate (mpyO)(1a), (2a); 3,5-dimethylpyrazolate (dmpz)(1b), (2b); 1,3-di-p-tolyltriazenide (p-MeC₆H₄N₃C₆H₄Me-p)(1c), (2c); or acetate (1d), (2d)]. The complex [Cu₂(µ-mdppm)₂(µ-dmpz)]BF₄(1e)[mdppm = 1,1-bis(diphenylphosphino)ethane] has also been isolated. Complexes (2a) and (2d) have also been directly obtained by treatment of [Cu(MeCN)₄]BF₄ with dppm and Na(mpyO) or NaO₂CMe in 1 : 1 : 2 molar ratio, respectively, in thf. Crystal structures of the complexes (1a) and (2a) have been determined by X-ray diffraction methods. Crystals of (1a), containing dichloromethane molecules of crystallization, are triclinic, space group P with Z= 2 in a unit cell of dimensions a= 14.569(4), b= 15.299(5), c= 14.324(4)Å, α= 104.37(2), β= 115.84(2), and γ= 67.91 (2)°. Crystals of (2a), containing dichloromethane molecules of crystallization, are triclinic, space group P1, with Z= 1 in a unit cell of dimensions a= 9.595(4), b= 11.274(5), c= 9.414(4)Å, α= 66.44(2), β= 82.67(2), and γ= 81.70(2)°. The structures have been solved from diffractometer data by Patterson and Fourier methods and refined by block-matrix [(1a)] and full-matrix [(2a)] least squares to R= 0.0792 and 0.0386 for 1 670 [(1a)] and 3 006 [(2a)] observed reflections. In the cationic complex (1a) the two copper atoms, in a slightly distorted trigonal arrangement, are held in close proximity [2.679(6)Å] by three bridging ligands, two dppm through P atoms and one mpyO through one O and one N atom. The latter ligand is disordered and distributed in two positions (of equal occupancy) whereby the copper atoms are bridged either by the O and N or by the N and O atoms. In the neutral complex (2a) the separation of the two three-co-ordinate copper atoms, bridged by one dppm and two mpyO ligands, is 2.566(2)Å. Proton and ³¹P-{¹H} n.m.r. data are discussed.