Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides

Abstract

The silica-supported transition metal hydrides (=Si-O-Si=)(=Si-O-)2Ta-H and (=Si-O-)xM-H (M, chromium or tungsten) catalyze the metathesis reaction of linear or branched alkanes into the next higher and lower alkanes at moderate temperature (25degrees to 200degreesC). With (=Si-O-Si=)(=Si-O-)2Ta-H, ethane was transformed at room temperature into an equimolar mixture of propane and methane. Higher and lower homologs were obtained from propane, butane, and pentane as well as from branched alkanes such as isobutane and isopentane. The mechanism of the step leading to carbon-carbon bond cleavage and formation likely involves a four-centered transition state between a tantalum-alkyl intermediate and a carbon-carbon final sigma-bond of a second molecule of alkane.

Silica‐Alumina‐Supported, Tungsten‐Based Heterogeneous Alkane Metathesis Catalyst: Is it Closer to a Silica‐ or an Alumina‐Supported System?

“…[1,2] Since the early 1990s, we have developed a series of oxidesupported metal hydrides [3][4][5][6] for the low temperature alkane transformation. [7][8][9] In contrast to hydrogenolysis, alkane metathesis allows both lower and higher homologues to be obtained, and we have shown recently through a combination of structure-reactivity [10] and kinetic [11] studies that the key carbon-carbon cleavage and formation process involves olefin metathesis. Other approaches have been investigated to carry out alkane metathesis.…”

The Impact of Nanoscience on Heterogeneous Catalysis

“…5, molecular precursors can also be used to anchor individual Fe atoms onto the surface of silica. This material is highly active and selective for the oxidation of organic compounds to the oxygenated products (19).…”

Novel mechanism for the formation of long-chain branching in polyethylene

“…There are reports in the literature of silica-supported, early-transition, metal hydride complexes which are capable of COH and COC bond activation. [33][34][35][36][37][38] It is tempting to speculate that a vanadium hydride is responsible for COH bond activation and therefore intermolecular COH bond activation predominates in producing LCB. However, more work is needed to support a vanadium hydride mechanism.…”