Reactions of Silicon Atoms with Methanol: A Combined Matrix‐Spectroscopic and Density Functional Theory Study

The reaction of silicon atoms with methanol ( 4 ) has been studied in an argon matrix at 10 K. In the initial step a triplet n‐adduct T‐5 between a silicon atom and 4 is formed. It cannot be detected directly as long as a low concentration of 4 is used. But T‐5 must be generated since upon simultaneous irradiation during cocondensation methylsilanone ( 15 ) is found. Without irradiation T‐5 undergoes immediately O,H insertion and methoxysilylene ( S‐7‐c ) is isolated, which establishes a photoequilibrium between the s,trans ( S‐7‐t ) and s,cis form ( S‐7‐c ). If a high concentration of 4 is applied the silylenes exist as complexes S‐17 . The next step needs photochemical activation. Products are dimethoxysilane ( 3 ) and (hydroxy)(methoxy)methylsilane ( 19 ). The picture becomes even more complicated when deuteromethanol ( [D]4 ) is treated with silicon atoms. In this case the primarily formed n‐adduct ( [D]T‐5 ) is stable under matrix conditions. As long as a low concentration is applied, the subsequent step has to be induced by long wavelength irradiation and leads – different from the undeuterated case – to O,CH₃ insertion, giving (hydroxy)methylsilylenes ( [D]S‐11‐c ) and ( [D]S‐11‐t ). If a high concentration is used O,D insertion is preferred instead and even without irradiation the first observable products are methanol‐solvated methoxysilylenes ( [D₂]S‐17‐c ) and ( [D₂]S‐17‐t ). Subsequent irradiation of complexes [D₂]S‐17 gives in accordance with the protonated series a mixture of [D₂]3 and [D₂]19 . Our goal, to find a way to dimethylsilanediol ( [D₂]2 ), was finally reached by preparing silylenes [D]S‐11 in a diluted matrix, its specific solvation with [D]4 and final irradiation of complexes [D₂]S‐18 . The structural elucidation of all new species is based on the comparison of the experimental observations with density functional theory calculations. Upon cocondensation of silicon atoms with pure methanol at 77 K dimethoxysilane ( 3 ) and 1,1,2‐trimethoxydisilane ( 25 ) are produced. The also present methoxysilanes 22‐24 have to be regarded as secondary products of 3 .