Staples Orion, Ferrandon Magali S, Laurent Guillaume P, Kanbur Uddhav, Kropf A Jeremy, Gau Michael R, Carroll Patrick J, McCullough Katherine, Sorsche Dieter, Perras Frédéric A, Delferro Massimiliano, Kaphan David M, Mindiola Daniel J
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Chemical Sciences and Engineering, Argonne National Laboratory Division, Lemont, Illinois 60439, United States.
J Am Chem Soc. 2023 Apr 12;145(14):7992-8000. doi: 10.1021/jacs.2c13612. Epub 2023 Mar 30.
Catalytic C-H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH), to a mild nucleophilic building block. However, existing CH 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], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH 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 (HCBpin) 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 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 fragment onto amorphous silica represents a unique and simple strategy to improve the TON and longevity of a CH borylation catalyst.
催化C-H硼化是一种将最丰富的碳氢化合物甲烷（CH）转化为温和亲核构件的有吸引力的方法。然而，现有的CH硼化催化剂往往存在低周转数和转化率的问题，据推测这是由无活性的金属氢化物团聚体导致的。在此，我们报告双膦分子前催化剂[(dmpe)Ir(cod)CH]负载于无定形二氧化硅上后，其性能显著增强，得到一种比当前CH硼化标准催化剂效率高12倍的催化剂。该催化剂在150℃下16小时内实现了超过2000次周转，单硼化与双硼化的选择性为91.5%。更高的催化剂负载量提高了单硼化产物（HCBpin）的产率和选择性，在1255次周转时产率达到82.8%，选择性大于99%。X射线吸收和动态核极化增强固态核磁共振光谱研究确定负载的前催化剂为Ir物种，并表明催化完成后，多核Ir多氢化物未形成。这与有机金属Ir物种固定在表面可防止双分子分解途径的假设一致。将均相Ir片段固定在无定形二氧化硅上是提高CH硼化催化剂周转数和寿命的一种独特而简单的策略。
