Reactions of Manganese Silyl and Silylene Complexes with CO2 and C(NiPr)2: Synthesis of Mn(I) Formate and Amidinylsilyl Complexes

Reactions of the disilyl hydride complexes [(dmpe)2MnH­(SiH2R)2] (1Ph: R = Ph, 1Bu: R = nBu) or the silylene hydride complexes [(dmpe)2MnH­(SiR2)] (2Ph2: R = Ph, 2Et2: R = Et) with the heterocumulenes carbon dioxide (CO2) and diisopropylcarbodiimide {C­(NiPr)2} were investigated. With CO2, these reactions yielded the manganese­(I) formate complex trans-[(dmpe)2Mn­(CO)­(κ1-O2CH)] (3), with polysiloxane byproducts. Compound 3 was found to undergo reversible CO2 elimination at room temperature, and was only stable under an atmosphere of CO2. By contrast, reactions with C­(NiPr)2 afforded manganese­(I) amidinylsilyl complexes [(dmpe)2Mn­{κ2-SiRR′(NiPrCHNiPr)}] {5Ph,H: R = Ph, R′ = H, 5Bu,H: R = nBu, R′ = H, 5Ph2: R = R′ = Ph, 5Et2: R = R′ = Et}. Complexes 3, 5Ph,H, and 5Ph2 were crystallographically characterized. DFT calculations and analysis of XRD bond metrics suggest that the structure of 5 involves a contribution from a resonance structure featuring a neutral base-stabilized silylene and an anionic amido donor on manganese.