Microwave-Assisted Reflux in Organometallic Chemistry: Synthesis and Structural Determination of Molybdenum Carbonyl Complexes. An Intermediate-Level Organometallic-Inorganic Experiment

Simple modification of a household microwave oven leads to the acceleration of chemical reactions as a result of microwave-assisted reflux. This acceleration is illustrated in the reactions of metal–carbonyls where the M–CO bond is notoriously inert. Microwave-assisted reflux of Mo(CO) 6 and piperidine leads, under aerobic conditions, to the clean synthesis of cis -[Mo(CO) 4 (piperidine) 2 ] in 40 minutes rather than the four hours required by conventional reflux. Further, cis -[Mo(CO) 4 (piperidine) 2 ] is a well-known synthetic reagent as both amines can be easily displaced by phosphines and phosphites as illustrated by the reaction with PPh 3 . At lower temperatures cis -[Mo(CO) 4 (PPh 3 ) 2 ] can be prepared, which upon heating, leads to clean generation of the thermodynamically more stable trans isomer. Infrared spectroscopy can be easily used, in combination with group theory, to identify trans and cis isomers by their characteristic one and four bands respectively in the C–O region. Use of microwave-assisted synthesis allows the entire experiment to be carried out in a single laboratory class.