First dinuclear copper/gallium complexes: supporting Cu0 and Cu(I) centres by low-valent organogallium ligands.

The synthesis and structural characterisation of low-valent dinuclear copper(I) and copper(0) complexes supported by organogallium ligands has been accomplished for the first time by the reductive coordination reaction of [GaCp*] (Cp*=pentamethylcyclopentadienyl) and [Ga(ddp)] (ddp=HC(CMeNC(6)H(3)-2,6-iPr(2))(2) 2-diisopropylphenylamino-4-diisopropylphenylimino-2-pentene) with readily available copper(II) and copper(I) precursors. The treatment of CuBr(2) and Cu(OTf)(2) (OTf=CF(3)SO(3)) with [Ga(ddp)] under mild conditions resulted in elimination of [Ga(L)(2)(ddp)] (L=Br, OTf) and afforded the novel gallium(I)/copper(I) compounds [{(ddp)GaCu(L)}(2)] (L=Br (1), OTf (2)). The single-crystal X-ray structure determinations of 1 and 2 reveal that these molecules are composed of {(ddp)GaCu(L)} dimeric units, with planar Cu(I)-Ga(I) four-membered rings and short Cu(I)...Cu(I) distances, with 2 exhibiting the shortest Cu(I)Cu(I) contact reported to date of 2.277(3) A. The all-gallium coordinated dinuclear [Cu(2)(GaCp*)(mu-GaCp*)(3)Ga(OTf)(3)] (3) is formed when Cu(OTf)(2) is combined with [GaCp*] instead of [Ga(ddp)]. Notably, in the course of this redox reaction Lewis acidic Ga(OTf)(3) is formed, which coordinates to one of the electron-rich copper(0) centres. Compound 3 is suggested as the first case of a structurally characterised complex of copper(0). By changing the copper(II) to a copper(I) source, that is, [Cu(cod)(2)][OTf] (cod=1,5-cyclooctadiene), the salt [Cu(2)(GaCp*)(3)(mu-GaCp*)(2)][OTf](2) (4) is formed, the cationic part of which is related to previously described isoelectronic dinuclear d(10) complexes of the type [M(2)(GaCp*)(5)] (M=Pd, Pt).