Applications of Sonochemistry and Microwaves in Organometallic Chemistry

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Both low and high-intensity ultrasound have become useful energy sources in the synthesis and reactivity of organometallic compounds during the past 20 years. The principal mechanism of chemical activity lies in a process known as acoustic cavitation, that is, the creation, growth, and implosive collapse of microbubbles in solution as a consequence of the interaction of the acoustic field with the solvent. This process generates enormous local temperatures and pressures during the adiabatic collapse of the cavitation sites. It is primarily these physical extrema, coupled with rapid mixing and microjet formation at the surface of solid interfaces, that is largely responsible for the chemistry that is observed. The interior of the bubble during the collapse phase of cavitation typically produces a plasma state. Microwave dielectric heating provides a temperature profile which is quite different from that resulting from conventional resistive heating and specifically the efficient coupling between the microwave radiation and the solvent results in very fast heating rates and the occurrence of super-heating. Working in a pressure vessel magnifies these effects. The remote nature of the interaction and the specific coupling effect may be used to perform reactions in a unique fashion. The technique, when coupled with modern robotic technology, can increase the throughput of organic syntheses and has been taken up by the pharmaceutical industry. This chapter details the chemical applications of ultrasound and microwaves since the early 1990s in the synthesis of organometallic compounds in their own right, as precursors to advanced materials and in accelerating organic syntheses. It further describes the use of these energy sources in the facilitation of organometallic reactivity.