Reactivity of Silica-Supported Hafnium Tris-neopentyl with Dihydrogen: Formation and Characterization of Silica Surface Hafnium Hydrides and Alkyl Hydride

Abstract

Surface organometallic chemistry represents an approach to the preparation of well-defined single sites for catalysis, the possibility of observing some elementary reaction steps, and the development of a fundamental basis for the synthesis of tailor-made catalysts. Silica-supported metal hydrides are an important class of new catalysts for alkane metathesis, methanolysis of alkanes, Ziegler−Natta depolymerization, alkane hydrogenolysis, etc. Understanding their mechanism of formation and aging is crucial. In the work presented here, the reaction of the well-defined silica surface organometallic complex [(⋮SiO)Hf(CH2tBu)3], 1, ((⋮SiO) = silica surface ligand) with dihydrogen has been performed at different temperatures (θ). At θ ≤ 100 °C, there is formation of a stable hafnium neopentyl dihydride, [(⋮SiO)Hf(CH2tBu)(H)2], 2. For 100 ≤ θ ≤ 200 °C, 2 affords, via a succession of β-methyl transfer and subsequent hydrogenolysis of the resulting Hf−alkyl bonds, the formation of [(⋮SiO)2Hf(H)2], 3, and [(⋮SiO)3S...