Insights into the thermal fragmentation of intramolecularly coordinated gallanes. A matrix-isolation FTIR study.

Abstract

High-vacuum thermolyses (400-1000 degrees C) of the intramolecularly coordinated gallanes [Me(2)N(CH(2))(3)](2)GaX [X = Cl (1), Br (2)] and (Me(2)NCH(2)CD(2)CH(2))(2)GaBr (2D(4)) have been investigated with matrix-isolation FTIR techniques. Around 850 degrees C, the fragmentation of these compounds was completed, and their typical IR absorptions could no longer be detected in argon matrices. Products have been identified with IR spectroscopy with the help of ab initio and DFT calculations and known literature data. In the case of precursors 1 and 2, respectively, we identified GaH(3), XGaH(2), X(2)GaH, GaH, GaX, HX, HCN, CH(4), H(2)C=CH(2), H(2)C=CHCH(3), H(2)C=NMe, [H(2)CCHCH(2)]., and H(2)C=CHCH(2)NMe(2). In the case of the precursor 2D(4), we found GaH(3), GaH(2)D, BrGaH(2), BrGaDH, GaH, GaD, GaBr, HBr, HCN, CH(4), H(2)C=CD(2), H(2)C=CDCH(3), H(2)C=NMe, [H(2)CCDCH(2)]., and H(2)C=CDCH(2)NMe(2). Among the monomeric hydrides, BrGaH(2) and BrGaDH were isolated for the first time. These compounds have been characterized by their six normal modes, and the experimental frequencies have been compared to the results of MP2(fc)/6-311+G(2d,p) and B3LYP/6-311+G(2d,p) calculations. These results have been interpreted by assuming that the intramolecularly coordinated precursors 1, 2, and 2D(4) eliminate their ligands through Ga-C homolysis and beta-hydrogen elimination.