Dimethylalkoxygallanes: monomeric versus dimeric gas-phase structures.

The molecular structures of the vapors produced on heating dimethylalkoxygallanes of the type Me(2)Ga(OR) have been determined by gas electron diffraction and ab initio molecular orbital calculations. In the solid state Me(2)Ga(OCH(2)CH(2)NMe(2)) (1) and Me(2)Ga(OCH(2)CH(2)OMe) (2) adopt dimeric structures, although only the monomeric forms [Me(2)Ga(OCH(2)CH(2)NMe(2))] (1a) and [Me(2)Ga(OCH(2)CH(2)OMe)] (2a) were observed in the gas phase. For comparison the structure of the vapor produced on heating Me(2)Ga(O(t)Bu) (3) was also studied by gas electron diffraction. In contrast to 1 and 2, compound 3 is dimeric in the gas phase, as well as in the solid state. The gas-phase structures of 1a and 2a exhibit five-membered rings formed by a dative bond between Ga and the donor atom (N or O) from the donor-functionalized alkoxide. In 3 there is no possibility of a monomeric structure being stabilized by the formation of such a dative bond since only a monofunctional alkoxide is present in the molecule.