Single-crystal neutron diffraction: a valuable tool for probing bond activation in transition metal σ complexes

Abstract

Transition metal σ complexes are ubiquitous intermediates in metal-catalyzed reactions, including hydrogenations, activation and functionalization reactions of hydrocarbons, and hydroborations. For over 20 years, single-crystal neutron diffraction has been exploited to investigate bond activation in these systems. Topics investigated include H–H activation in H 2 complexes, C–H activation in agostic systems and, most recently, B–H activation in a catecholborane metal complex. These results are illustrated here drawing upon studies carried out at both pulsed neutron sources and steady-state reactors. Despite notable successes such as those that we highlight, however, single-crystal neutron diffraction has seen somewhat limited application here to date primarily due to the need for large crystals. Revolutionary improvements are anticipated with the advent of a new generation of sources including the Spallation Neutron Source (SNS) that is scheduled to become operational at Oak Ridge, TN in 2006. At the SNS, it will be possible to work with crystals approaching the size commonly used in X-ray studies employing laboratory sources and to greatly expand the range of materials that are open to investigation.