The photochemistry of [CpMo(CO)(3)(eta(1)-C3H5)] in frozen gas matrices at10K and the behaviour of [CpMo(CO)(2) (eta(3)-C3H5)] isomers in different media

On photolysis of [CpMo(CO)(3)(eta (1)-C3H5)] in solid inert matrices at low temperature, one CO molecule is eliminated yielding the exo and endo isome rs of [CpMo(CO)(2)(eta (3)-C3H5)] in almost 1:1 proportions, although the f raction of the exo conformer is increased by prolonged broad-band UV irradi ation. If gaseous [CpMo(CO)(2)(eta (3)-C3H5)] is isolated in an Ar matrix t he proportions of the two conformers are again about 1:1, indicating that t hey possess almost equal energies, as confirmed by DFT calculations (B3LYP/ SDD). This situation changes in a solvent environment, where increasing the polarity of the solvent favours the exo isomer, as indicated by the ratios exo/endo = 1.7:1 (pentane or cyclohexane), 3.0:1 (benzene) and 3.3:1 (CH2C l2) determined by IR and NMR measurements. Such a finding is consistent wit h the results of DFT calculations, which reveal that the exo isomer is more polar.