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Insights in the Mechanism of Selective Olefin Oligomerisation Catalysis using Stopped-Flow Freeze-Quench Techniques: a Mo K edge QEXAFS Study

DOI: 10.1016/j.jcat.2011.10.015 DOI Help

Authors: Stuart Bartlett (University of Southampton) , Peter Wells (University College London; R-C Harwell) , Maarten Nachtegaal (Paul Scherrer Institute) , Andrew Dent (Diamond Light Source Ltd) , Giannantonio Cibin (Diamond Light Source) , Gill Reid (University of Southampton) , John Evans (University of Southampton) , Moniek Tromp (Technical University Munich)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Catalysis

State: Published (Approved)
Published: November 2011
Diamond Proposal Number(s): 7046

Abstract: The activation of [MoX3(L)] (with X = Cl, Br; L = tridentate ligands with S3 and SNS donor sets) by AlMe3, analogous to the industrially important [CrCl3(L)] catalysts for selective oligomerisation of alkenes, has been investigated by Mo K-edge X-ray absorption (XAS) and UV–visible spectroscopies. Time-resolved stopped-flow XAS, in combination with a newly developed anaerobic freeze-quench approach, have established the complete alkylation of the Mo centres and a slower, stepwise sequence for [MoBr3(L)]. No evidence for directly bonded or bridged Mo–Mo dimers was observed at the high Mo:AlMe3 ratios used in this study. Decomposition of the complexes is in competition with the activation and resulted in precipitation of particulate Mo over time and explains the deactivation as observed in catalytic tests. The novel freeze-quench approach, which can trap reaction solutions within 1 s of mixing, opens up a large field of homogeneous catalysis and liquid chemistry to be studied, being able to quench this rapidly, whilst characterisation techniques with long data acquisition can be performed.

Journal Keywords: Oligomerisation; Catalysis; Xas; Mechanism; Mo; Stopped-Flow; Freeze-Quench; Homogeneous

Subject Areas: Chemistry, Technique Development

Instruments: B18-Core EXAFS