Structurally Characterized Transition-Metal Phosphine Complexes of Relevance to Catalytic Reactions

Abstract

A catalytic reaction that occurs under homogeneous conditions can be probed by spectroscopic and kinetic methods, but hardly by crystallographic techniques. Why then include in a book concerned with homogeneous catalysis a chapter on the structures of isolable transition-metal phosphine complexes? There are several answers. One is that such structures provide details, albeit indirectly, on the substrate-metal interaction that occurs in such a reaction. How this interaction is affected by the nature of the metal and its ligands can be probed macroscopically by kinetic measurements; it can also be probed at the molecular level in a qualitative way by spectroscopic methods. But if one seeks metrical details about the interaction, then one must turn to diffraction studies on stable, isolable analogues of the original system. Of course, one must employ spectroscopic methods to establish that the analogue is indeed a good model for the temporal species in the catalytic reaction. A second answer is that such structural information is an aid to the formulation of reaction schemes, some of which are based on minimal data. In such schemes there frequently are proposed intermediates of new or unusual structures. Known structures may serve as a basis for such speculation. Sometimes, of course, a scheme may precede the isolation and characterization of a new structural type. In such instances the ensuing characterization of a useful analogue supports the credibility (or perhaps minimizes the incredibility) of the scheme.