Preparation of organogallium compounds from organolithium reagents and gallium chloride. Infrared, magnetic resonance, and mass spectral studies of alkylgallium compounds

Article abstract of DOI:10.1021/ic50153a042

Conditions for the preparation of a series of base-free trialkylgallium compounds in benzene solvent by the exchange reaction of alkyllithium compounds and gallium chloride are described. Optimum conditions which favor formation of the trialkyl involve mixing a benzene solution of an appropriate alkyllithium compound and a benzene solution of gallium chloride in exactly a 3:1 molar ratio, heating of the reaction mixture for 12 hr at 70°, filtration to remove by-product lithium chloride, removal of solvent under vacuum, and vacuum distillation of the product: 3RLi + GaCl₃ = 3LiCl + R₃Ga, where R = C₂H₅, n-C₃H₇, n-C₄H₉, i-C₄H₉, s-C₄H₉, and t-C₄H₉. Alkylgallium dichlorides and dialkylgallium chlorides are produced when lithium alkyls and gallium chloride are allowed to react in a 1:1 and 2:1 molar ratio, respectively: nRLi + GaCl₃ = nLiCl + R_nGaCl_3-n, where n = 1 and 2. Reaction of an alkyllithium compound and gallium chloride in a molar ratio in excess of 3:1 results in formation of the corresponding lithium tetraalkylgallate: 4n-C₃H₇Li + GaCl₃ = 3LiCl + LiGa(n-C₃H₇)₄. Trivinylgallium tetrahydrofuranate is produced by the reaction of vinyllithium and gallium chloride in 3:1 molar ratio in tetrahydrofuran solvent. Infrared, proton magnetic resonance, and mass spectra of R_nGaCl_3-n compounds where R = C₂H₅ to C₄H₉ isomers and n = 1-3 are reported and discussed. Proton magnetic resonance spectra reveal that the chemical shifts for protons on α-carbon atoms are sensitive to substitution on the gallium. An explanation for these chemical shift data along with molecular association data for R_nGaCl_3-n. compounds is given. Mass spectroscopy can be used as a convenient, diagnostic tool for the identification of organogallium compounds of this type. Ion abundance data for all compounds are presented and the fragmentation processes believed to give these ions are discussed.