Di(µ-acetato)dialkyldigallium as starting compound for the facile syntheses of digallium derivatives containing bridged or terminally co-ordinated Ga–Ga single bonds

Abstract

Di(µ-acetato)dialkyldigallium Ga₂R₂(µ-O₂CCH₃-O,O′)₂ [R = CH(SiMe₃)₂] 2 was easily obtained in an almost quantitative yield by the reaction of R₂Ga–GaR₂1 with acetic acid. As shown by a crystal structure determination, the short Ga–Ga bond of 2 [237.85(3) pm] is bridged by two acetato groups. This compound appeared to be a very suitable starting material for the facile syntheses of further derivatives containing Ga–Ga bonds, when treated with appropriate lithium compounds. Thus 1 was re-formed in a high yield by the reaction of 2 with two equivalents of LiCH(SiMe₃)₂ and the precipitation of lithium acetate. Treatment with two equivalents of lithium diphenyltriazenide yielded the bis(triazenido)digallium derivative 3, which before was obtained in our group only in an inseparable mixture with a monogallium product. The reaction with lithium diphenyltriazenide in an equimolar ratio gave a product 4 in which the Ga–Ga bond [236.75(4) pm] was unsymmetrically bridged by one triazenido and one acetato group and in which the gallium atoms adopted a chiral co-ordination sphere. A similar compound 5 was obtained with lithiated diphenylbenzamidine. Furthermore, the reaction of 1 with pentafluorophenol was reinvestigated, which did not yield the dimeric dialkylgallium fluoride, as recently reported by our group, but a dialkylgallium phenolato derivative. The latter is monomeric even in the solid state and has short Ga–O bonds (184.3 pm on average). The dialkylgallium fluoride was obtained by treatment of 1 with the hydrogen fluoride–pyridine complex.