The surface organometallic chemistry of organolanthanum species is limited in comparison to related late lanthanides, yttrium, scandium, and early transition metal systems. As the largest trivalent lanthanide, lanthanum is targeted for potentially high activity in catalytic applications. We recently reported lanthanum analogue of a new class of organolanthanide compounds, namely La{C(SiHMe2)3}3, for applications in homogeneous and surface organometallic catalysis. In the present contribution, we report the reaction of La{C(SiHMe2)3}3 with mesoporous silica nanoparticles (MSN), a SBA-15 type material treated under vacuum at 550 °C (MSN550) with 91 Å pores, a surface area of 441 m2/g, and 0.745 mmol of surface silanols per g. The loading and local coordinate environment of surface supported species La{C(SiHMe2)3}1.5@MSN550 was characterized by quantitative solid state NMR spectroscopy, ICP-OES lanthanum analysis, and quantification of La{C(SiHMe2)3}3 consumed and HC(SiHMe2)3 produced during grafting experiments. Soluble La{C(SiHMe2)3}3 and grafted La{C(SiHMe2)3}1.5@MSN550 are catalysts for hydroboration of carbonyl compounds, including ketones and esters, as well as epoxides, with pinacolborane (HBpin) at room temperature. Both catalytic systems reduce esters containing halogens, alkoxides, nitro, and alkyl groups in high yield. Under otherwise equivalent conditions, aliphatic esters react more rapidly than aryl esters, and epoxides are slower than esters. Nonetheless, all reductions and C–O cleavage reactions occur at room temperature. Interestingly, the rate laws for supported and soluble catalytic hydroborations are comparable, suggesting that the mechanism of lanthanum-catalyzed hydroboration does not change between homogeneous and interfacial conditions.

Organolanthanides and their surface organometallic catalysis for hydroboration of esters and epoxides

255th National Meeting (2018)

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