Photogeneration and characterization of Group 6 metal carbonyl derivatives on alumina

The photochemically-induced CO substitution reactions of [M(CO)(6)] (M = Cr, Mo, W) have been investigated in the presence of triphenylphosphine (PPh(3)) and gamma-alumina. The metal loading was determined by Rutherford backscattering spectrometry (RBS) and the generated species were analysed by Fourier transform IR spectroscopy (FT-IR) and C-13 NMR spectroscopy. The metal loading on the alumina surface was seen to increase with the irradiation time reaching 0.6, 0.8 and 3.4% for Cr, W and Mo, respectively. The ligand cone angle plays an important role in the case of Cr, where only the trans disubstituted species was found on the alumina surface. However, it is less important for the two other metals, where the cis compound was formed preferentially and the electronic cis-labilization factor seems more important. After grafting, only the disubstituted species was seen to remain on alumina evidencing a stronger interaction with the support than in the case of the monosubstituted and the hexacarbonyl compounds. (C) 1997 Elsevier Science Ltd.