The photochemistry of [CpMo(CO)3(η1-C3H5)] in frozen gas matrices at 10K and the behaviour of [CpMo(CO)2 (η3-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 isomers of [CpMo(CO)(2)(eta (3)-C3H5)] in almost 1:1 proportions, although the fraction of the exo conformer is increased by prolonged broad-band UV irradiation. If gaseous [CpMo(CO)(2)(eta (3)-C3H5)] is isolated in an Ar matrix the proportions of the two conformers are again about 1:1, indicating that they 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 (CH2Cl2) determined by IR and NMR measurements. Such a finding is consistent with the results of DFT calculations, which reveal that the exo isomer is more polar.