National Research Council of Canada. NRC Steacie Institute for Molecular Sciences
The structures of cationic rhodium carbonyl cluster compounds containing one to six Rh atoms are established by infrared multiple photon dissociation spectroscopy. Comparison with their well-known neutral analogues reveals that ionization of the neutral compounds destabilizes bridge bound CO ligands in Rh2(CO)8 and Rh4(CO)12, leading to cationic complexes with only terminally bound CO. The destabilization is associated with removal of charge from a highest occupied molecular orbital that is bonding with respect to bridge-bound CO. Density functional theory calculations support this conclusion. The results provide a possible insight into electronic promoter effects in catalysis.
Journal of the American Chemical Society130, no. 7 (29 January 2008): 2126–2127.