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

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.