Electronic absorption and magnetic circular dichroism (MCD) spectra are reported for the chloro-bridged dimers [RhCl(CO)2]2, [RhCl(COD)]2, [RhCl(NBD)]2, and [IrCl(COD)]2 (COD = 1,5-cyclooctadiene; NBD = norbornadiene) in dichloromethane solution. Absorption spectra are also reported for the less stable [RhCl(C2H4)2]2, [RhCl(COT)2]2, and [IrCl(COT)2]2 (COT = cyclooctene) complexes. Spectra at 77 K were also obtained for [RhCl(CO)2]2 and several of the olefin complexes in glassy EPA or methylcyclohexane/pentane solution. Dissolution of [RhCl(CO)2]2, [RhCl(COD)]2, [RhCl(NBD)]2, and [IrCl(COD)]2 in acetonitrile gives a bridge-cleavage reaction, and spectral data are reported for the monomeric products [RhCl(CO)2(CH3CN)], [RhCl(COD)(CH3CN)], [RhCl(NBD)(CH3CN)], and [IrCl(COD)(CH3CN)]. The intense bands observed in the visible and near-ultraviolet regions of the spectra of all these complexes are assigned as metal-to-ligand charge-transfer (MLCT) transitions from occupied metal d orbitals to low-energy ligand * orbitals. Detailed spectral assignments are presented, and comparisons are made between the chloro-bridged complexes and related monomeric complexes.
Irradiation of solutions of HCCo3(CO)9 under an H2 atmosphere with visible or UV light leads to quantitative formation of Co4(CO)12 and production of methane. Under a 3:1 H2/CO atmosphere irradiation produces Co2(CO)8 with a 366-nm quantum yield of 0.03. Photolysis in the presence of D2 has shown that the methane derives from the apical CH group and not from CO. Irradiation of HCCo3(CO)9 in the presence of H2 and 1-hexene leads to catalytic isomerization to errand í/ww-2-hexene. The photochemical properties of CH3CCo3(CO)9 parallel those of HCCo3(CO)9, except that no reaction is observed under an H2/CO atmosphere. Irradiation of HFeCo3(CO)u and HFeCo3(CO)10(PPh3)2 in degassed solutions also leads to declusterification with subsequent formation of.Co4(CO)i2 and Co2(CO)6(PPh3)2, respectively.
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