PHOTOCHEMISTRY OF OS(ETA(6)-ARENE) COMPLEXES IN LOW-TEMPERATURE MATRICES - AN INFRARED SPECTROSCOPIC STUDY OF C-H BOND ACTIVATION

The photochemistry of a series of Os(eta(6)-arene) complexes has been investigated in argon, methane and dinitrogen matrices with IR and UV/ vis detection. The coordinatively unsaturated complex, Os(eta(6)-C(6)H (3)Me(3))(CO), may be formed by photolysis of either Os(eta(6)-C(6)H(3 )Me(3))(CO)(H)(2) or Os(eta(6)-C(6)H(3)Me(3))(CO)(CH3)(H) in argon mat rices. Irradiation of Os(eta(6)-C(6)H(3)Me(3))(CO)(H)(2) in nitrogen m atrices yields Os(eta(6)-C(6)H(3)Me(3))(CO)(N-2). Activation of methan e C-H bonds occurs on photolysis of either Os(eta(6)-C(6)H(3)Me(3))(CO )(H)(2) or Os(eta(6)-C(6)H(3)Me(3))(CO)(2) in methane matrices. The fo rmation of Os(eta(6)-C(6)H(3)Me(3))(CO)(CH3)(H) is established by comp arison of a complete IR spectrum with that of an authentic sample in t he matrix. These studies provide extremely strong evidence that insert ion into alkane C-H bonds is preceded by formation of the 16-electron intermediate Os(eta(6)-C(6)H(3)Me(3))(CO). Vinyl hydride complexes Os( eta(6)-C(6)H(3)Me(3))(L)(C2H3)(H) (L=CO, C2H4) and Os(eta(6)-C6H6)(CO) (C2H3)H are formed on photolysis of the ethene complexes, Os(eta(6)-C( 6)H(3)Me(3))(L)(C2H4) and Os(eta(6)-C6H6)(CO)(C2H4). The vinyl hydride products are established by comparison of the spectra from C2H4 and C 2D4 complexes, and observation of OsH(D) and vinyl vibrations, as well as characteristic nu(CO) modes. The photoproducts of Os(eta(6)-C(6)H( 3)Me(3))(CO)(CH2=CHMe) are probably cis and trans isomers of the prope nyl hydride Os(eta(6)-C(6)H(3)Me(3))(CO)(CH=CHMe)H.