Ultrasonic irradiation of liquids produces acoustic cavitation: the rapid formation, growth, and implosive collapse of vapor filled vacuoles. This generates short-lived “hot spots” with peak temperatures ~3000 K and nanosecond lifetimes. We have studied the effects of high intensity ultrasound on a variety of metal carbonyls and have observed the general phenomenon of sonochemical ligand dissociation, which often produces multiple CO substitution. Fe(CO)5, for example, upon sonolysis, yields Fe3(CO)12 in the absence of additional ligands and Fe(CO)3L2 and Fe(CO)4L (L = phosphine or phosphite) in their presence. Similar substitution patterns are observed for Fe3(CO)12, Mn2(CO)10, Cr(CO)6, Mo(CO)6, and W(CO)6. In all cases examined the rates of sonochemical ligand substitution are first order in metal carbonyl concentration and independent of L concentration. In addition, In Kobsd correlates well with solvent system vapor pressure. These results are consistent with a dissociative mechanism in which coordinatively unsaturated species are produced by the cavitation process. Further use of these transient intermediates is made as alkene isomerization catalysts. Sonocatalysis by a wide range of metal carbonyls shows many similarities to photocatalysis, but different relative efficiencies and selectivities have also been observed.
ASJC Scopus subject areas
- Colloid and Surface Chemistry