Silica Supported Organometallic IrI Complexes Enable Efficient Catalytic Methane Borylation.

Catalytic C-H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH4), to a mild nucleophilic building block. However, existing CH4 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)CH3], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH4 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 (H3CBpin) 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 IrI 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 IrI fragment onto amorphous silica represents a unique and simple strategy to improve the TON and longevity of a CH4 borylation catalyst.

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R3 Si+ Species.

The silylium-like surface species [i Pr3 Si][(RF O)3 Al-OSi≡)] activates (N^N)Pd(CH3 )Cl (N^N=Ar-N=CMeMeC=N-Ar, Ar=2,6-bis(diphenylmethyl)-4-methylbenzene) by chloride ion abstraction to form [(N^N)Pd-CH3 ][(RF O)3 Al-OSi≡)] (1). A combination of FTIR, solid-state NMR spectroscopy, and reactions with CO or vinyl chloride establish that 1 shows similar reactivity patterns as (N^N)Pd(CH3 )Cl activated with Na[B(ArF )4 ]. Multinuclear 13 C{27 Al} RESPDOR and 1 H{19 F} S-REDOR experiments are consistent with a weakly coordinated ion-pair between (N^N)Pd-CH3 + and [(RF O)3 Al-OSi≡)]. 1 catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd-CH3 ]+ in solution and incorporates up to 0.4 % methyl acrylate in copolymerization reactions. 1 produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

Unveiling the Interstitial Pressure between Growing Ice Crystals during Ice-Templating Using a Lipid Lamellar Probe.

What is the pressure generated by ice crystals during ice-templating? This work addresses this crucial question by estimating the pressure exerted by oriented ice columns on a supramolecular probe composed of a lipid lamellar hydrogel during directional freezing. This process, also known as freeze-casting, has emerged as a unique processing technique for a broad class of organic, inorganic, soft, and biological materials. Nonetheless, the pressure exerted during and after crystallization between two ice columns is not known, despite its importance with respect to the fragility of the frozen material, especially for biological samples. By using the lamellar period of a glycolipid lamellar hydrogel as a common probe, we couple data obtained from ice-templated-resolved in situ synchrotron small-angle X-ray scattering (SAXS) with data obtained from controlled adiabatic desiccation experiments. We estimate the pressure to vary between 1 ± 10% kbar at -15 °C and 3.5 ± 20% kbar at -60 °C.