Matrix isolation infrared and density functional theoretical studies of cryogenic reactions of silicon atoms with dimethyl ether and methanol: new route to generation and stabilization of transient silanones

Silicon atoms, produced by vaporization of silicon at temperatures 1450-1650 degrees C from a graphite cell, were co-condensed with dimethyl ether or methanol and a large excess of argon onto a polished copper substrate cooled down to 15 K. The deposited solid matrixes were studied by reflection-transmission IR spectroscopy. Structural identification of the reactive intermediates, formed during co-condensation and subsequent photoirradiation of the primary products, and vibrational analysis of their spectra have been accomplished by comparison with the previously reported IR features for silylene CH3OSiCH3 (2) (G. Maier, H.P. Reisenauer. K. Schottler. U. Wessolek-Kraus. J. Organomet. Chem. 366 (1989) 25), silanones (CH3)(2)Si=O (3) (V.N. Khabashesku, Z.A. Kerzina, A.K. Maltsev, O.M. Nefedov, J. Organomet. Chem. 347 (1988) 277) and CH3(H)Si=O (9) (R. Withnall, L. Andrews, J. Am. Chem. Sec. 108 (1986) 8118), and with the density functional theory B3LYP/6-311G(d,p) calculated harmonic frequencies and infrared intensities for complexes Si ... O(CH3)(2) (1) and Si ... O(CH3)H (7), silylenes (2), CH3OSiH (6), CH3SiOH (8), silanones (3) and (9), and 1-methyl-2-oxa-1-silirane (4) and oxasilirane (10). The step-wise mechanisms for the formation of the products 1-10 were suggested with the help of theoretical modeling based on DFT calculations of reaction dynamics of Si(D-1) atoms with CH3OCH3 and CH3OH. The directly observed formation of silanones (3) and (9) in the detectable by a standard IR spectrometer quantities suggests that the studied reactions can be utilized as a new route for generation and physical stabilization of transient silanones. (C) 2000 Elsevier Science S.A. All rights reserved.