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 triphenylphosp hine (PPh(3)) and gamma-alumina. The metal loading was determined by R utherford backscattering spectrometry (RBS) and the generated species were analysed by Fourier transform IR spectroscopy (FT-IR) and C-13 NM R spectroscopy. The metal loading on the alumina surface was seen to i ncrease 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 i n the case of Cr, where only the trans disubstituted species was found on the alumina surface. However, it is less important for the two oth er metals, where the cis compound was formed preferentially and the el ectronic cis-labilization factor seems more important. After grafting, only the disubstituted species was seen to remain on alumina evidenci ng a stronger interaction with the support than in the case of the mon osubstituted and the hexacarbonyl compounds. (C) 1997 Elsevier Science Ltd.