TRANSIENT 1,1-DIMETHYL-1-GERMENE, (CH3)(2)GE=CH2 - GAS-PHASE PYROLYTIC GENERATION AND EIMS, MATRIX-ISOLATION FTIR, AND THEORETICAL-STUDIES

Vacuum pyrolyses of 1,1-dimethyl-1-germa-3-thietane (2) and 1,1,3,3-te tramethyl-1-germacyclobutane (3) most likely proceed with the formatio n of the same transient species, 1,1-dimethyl-1-germene (1), detected both in the gas phase by electron impact mass spectrometry (EIMS) and in argon solid matrixes at 12 K by Fourier transform infrared (FTIR) s pectroscopy. The production of methylgermylene (6) in the reactions st udied has also been suggested, probably as a result of secondary isome rization of 1 into methylethylgermylene (8) and subsequently to 1-meth yl-1-germacyclopropane (9), and further dissociation of 9 at higher te mperatures, in agreement with the theoretical consideration of the sug gested mechanism. Full vibrational assignments for the IR spectra of 1 and 6 have been proposed on the basis of ab initio and density functi onal theory calculations of the harmonic vibrational frequencies and i nfrared intensities, and of Literature data on related-molecules. The assignment of a high-intensity IR band at;847.3 cm(-1) to a Ge=C stret ching vibration coupled with the CH3 rocking mode in 1 has also been s upported by the calculation of potential energy distribution in the in ternal coordinates and by the observed splitting of this band due to n atural isotopic abundance. of germanium, being in accord with the B3LY P-calculated Ge-70/Ge-72/Ge-74/Ge-76 isotopic frequency shifts in 1. T he calculated force constant for the Ge=C bond in 1 confirms a pi natu re of this bond and yields an estimated bond order to be somewhat lowe r than the Si=C pi-bond order in 1,1-dimethyl-1-silene (4).