Frustrated Lewis pairs beyond the main group: transition metal-containing systems.

The concept of the "frustrated" Lewis pair (FLP) offers a valuable paradigm for transition metal complexes. This chapter describes recent developments in FLP chemistry where one or both of the Lewis acidic or Lewis basic components are based on a transition metal. At the forefront of these developments have been zirconocene-phosphinoaryloxide complexes; the activation of small molecules, including H2, CO2, ethers, olefins and alkyl chlorides or fluorides, with such zirconocene (or group 4 metallocene in general) phosphine pairs is described. Nascent catalytic applications for such complexes in dehydrogenation reactions and future possibilities for catalytic reactivity are also highlighted. A wider discussion of how the FLP concept may rationalise previous examples of cooperative reactivity in transition metal complexes, such as the heterolytic cleavage of hydrogen, suggests a strong and useful analogy.