Hydrosilylation is widely conducted for the production of silicone coatings, adhesives, and cured rubbers. As resources have been devoted to the development of base metal replacements for common platinum hydrosilylation catalysts, manganese precatalysts have remained overlooked. Efforts in our laboratory have focused on the application of donor-substituted redox non-innocent ligands that can bind to manganese beyond their historically investigated core. This approach deters ligand dissociation while providing a handle to tune the electronic properties of the metal center. These properties have allowed for the preparation of a formally zero-valent manganese complex, (Ph2PPrPDI)Mn, that mediates carbonyl hydrosilylation with turnover frequencies of up to 4,950 min-1 in the absence of solvent. Under stoichiometric and catalytic conditions, addition of PhSiH3 to (Ph2PPrPDI)Mn was found to result in slow, partial conversion to the respective hydride complex. When 2,2,2-trifluoroacetophenone was added to (Ph2PPrPDI)Mn, radical transfer to the substrate was observed, leading to catalyst deactivation and intramolecular C-C formation. Varying precatalyst, substrate, and PhSiH3 concentrations revealed a first order dependence on each reagent. Kinetic isotope experiments suggest that Si-H(D) bond activation is or precludes the rate determining step. Considering our experimental observations, (Ph2PPrPDI)Mn-catalyzed hydrosilylation is proposed to proceed through a modified Ojima mechanism. A competing insertion pathway is also proposed along with an additive rate expression.

Mechanism of bis(imino)pyridine manganese-catalyzed carbonyl hydrosilylation

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.