An Integrated Organic and Organometallic Synthesis Experiment for an Advanced Undergraduate Synthesis Course

An integrated organic/organometallic experiment suitable for an advanced synthesis laboratory course is presented. The synthesis and characterization of an organic chelating ligand, bis(pyrazole)methane (bpm), is accomplished by the reaction of pyrazole with dibromomethane in a refluxing biphasic mixture of water and toluene. This compound is purified by column chromatography. Reaction of the bis(pyrazole)methane with Mo(CO)6 or W(CO)6 in refluxing toluene leads to the formation of a metal tetracarbonyl complex containing the coordinated bis(pyrazole)methane ligand. The tetracarbonyl compounds readily undergo oxidative addition with elemental iodine to form examples of diamagnetic, seven-coordinate metal complexes, (bpm)M(CO)3I2, At each step, IR and NMR spectroscopy assist in characterizing the products. These three procedures together constitute a viable, integrated synthesis laboratory that may be conducted over three or four three-hour laboratory periods; however, the experiment is modular so that instructors wishing to only do the organometallic syntheses can prepare the organic ligand in advance (on a large scale) for student use.