Electronic spectra and photoreactivity of cyclopentadienyl complexes

The cyclopentadienyl (Cp) ligand coordinates to high- and low-oxidation sta te transition metals as well as main group metals. Consequently, a variety of different excited states and photoreactions is possible, This diversity is illustrated by selected examples. Recent observations are emphasized. Sp ectral and photochemical properties are related to the following electronic transitions: metal-centered (e.g, Cp2NbCl2, TlCp), intraligand, ligand-to- metal charge transfer (e.g. CpReO3, CpTiCl3, Cp2TiS5, TlCp), metal-to-ligan d charge transfer, ligand-to-ligand charge transfer (e.g. Cp2Zr-2,2'-biquin oline(2+)), metal-to-metal charge transfer (e.g. Cp2Ti[NCRu(CN)(5)](2)(6-)) , outer sphere charge transfer (e.g. CoCp2+Mn(CO)(5)(-), CpWH2 x 9,10-phena nthrenequinone) and charge-transfer-to-solvent. The Cp ligand may be direct ly involved in these electronic transitions or act as a spectator ligand. ( C) 2001 Elsevier Science B.V. All rights reserved.