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Metal-Catalyzed Reduction of HCONR′2, R′ = Me (DMF), Et (DEF), by Silanes to Produce R′2NMe and Disiloxanes: A Mechanism Unraveled

Arias-Ugarte, Renzo, Sharma, Hemant K., Morris, Andrew L.C., Pannell, Keith H.
Journal of the American Chemical Society 2012 v.134 no.2 pp. 848-851
catalysts, germanium, hydrides, manganese, molybdenum, silane, tin, trimethylamine
We demonstrate that using Mo(CO)₆, Mo(CO)₅NMe₃, and (η⁵-C₅H₅)Mn(CO)₃ as catalysts for the silane, R₃SiH, reduction of N,N-dimethylformamide (DMF), and N,N-diethylformamide (DEF), we can observe, intercept, and isolate, the important siloxymethylamine intermediates, R₃SiOCH₂NR′₂, R′ = Me, Et, for the first time. In the presence of excess DMF such intermediates thermally react with a variety of silanes to form the corresponding disiloxanes in the absence of a metal catalyst. We also show that the germanium hydrides, Et₃GeH and Bu₃GeH, also reduce DMF to form trimethylamine and the corresponding digermoxane but observe no intermediates R₃GeOCH₂NMe₂. Bu₃SnH reduces DMF, but along with the low yields of Bu₃SnOSnBu₃ (but no Bu₃SnOCH₂NMe₂) significant side products are obtained including (Bu₃Sn)₂ and Bu₄Sn. In the absence of DMF the siloxymethylamines can undergo metal-catalyzed reactions with silanes, germanes and stannanes to form disiloxanes, and R₃SiOER₃ E = Ge, Sn, respectively. To date, the most efficient catalyst for this latter process is (η⁵-C₅H₅)Mo(CO)₃CH₃ via a photochemical reaction.