Silica Supported Organometallic Ir<sup>I</sup> Complexes Enable Efficient Catalytic Methane Borylation
Orion Staples, Magali Ferrandon, Guillaume Laurent, Uddhav Kanbur, A. Jeremy Kropf, Michael R. Gau, Patrick J. Carroll, Katherine McCullough, Dieter Sorsche, Frédéric A. Perras, Massimiliano Delferro, David M. Kaphan, Daniel J. Mindiola
Abstract
Catalytic C–H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH 4 ), to a mild nucleophilic building block. However, existing CH 4 borylation catalysts often suffer from low turnover numbers and conversions, which is hypothesized to result from inactive metal hydride agglomerates. Herein we report that the heterogenization of a bisphosphine molecular precatalyst, [(dmpe)Ir(cod)CH 3 ], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH 4 borylation. The catalyst affords over 2000 turnovers at 150 °C in 16 h with a selectivity of 91.5% for mono- vs diborylation. Higher catalyst loadings improve yield and selectivity for the monoborylated product (H 3 CBpin) with 82.8% yield and >99% selectivity being achieved with 1255 turnovers. X-ray absorption and dynamic nuclear polarization-enhanced solid-state NMR spectroscopic studies identify the supported precatalyst as an Ir I species, and indicate that upon completion of catalysis, multinuclear Ir polyhydrides are not formed. This is consistent with the hypothesis that immobilization of the organometallic Ir species on a surface prevents bimolecular decomposition pathways. Immobilization of the homogeneous Ir I fragment onto amorphous silica represents a unique and simple strategy to improve the TON and longevity of a CH 4 borylation catalyst.