Dimethylalkoxygallanes: monomeric versus dimeric gas-phase structures

The molecular structures of the vapors produced on heating dimethyl-alkoxygallanes of the type [Me₂Ga(OR)]₂ have been determined by gas electron diffraction and ab initio molecular orbital calculations. In the solid state [Me₂Ga(OCH₂CH₂NMe₂)]₂ (1) and [Me₂Ga(OCH₂CH₂OMe)]₂ (2) adopt dimeric structures, although only the monomeric forms [Me₂Ga(OCH₂CH₂NMe₂)] (1a) and [Me₂Ga(OCH₂CH₂OMe)] (2a) were observed in the gas phase. For comparison the structure of the vapor produced on heating [Me₂Ga(O^tBu)]₂ (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.