PHOTOINDUCED REACTIONS OF CR(CO)3-COORDINATED 1,3,5-CYCLOHEPTATRIENE - (6+2) CYCLOADDITION WITH AN ALKYNE AND CATALYTIC 1,6-HYDROGENATION

Irradiation of Cr(CO)3(eta(6)-1,3,5-cycloheptatriene) (1) in the presence of bis(trimethylsilyl)ethyne results in [6 + 2] cycloaddition of the alkyne to the cycloheptatriene ligand, yielding Cr(CO)3{eta(4:2)-7,8-bis(trimethylsilyl)bicyclo[4.2.1]nona-2,4,7-triene} (2, 60% yield, PHI = 0.08), which upon oxidative decomposition with Ce(IV) releases the organic cycloadduct, 7,8-bis-(trimethylsilyl)bicyclo[4.2.1]-nona-2,4,7-triene (3). Photocatalytic hydrogenation of 1,3,5-cycloheptatriene in the presence of complex 1 affords 1,3-cycloheptadiene. This process involves 1,6-addition of hydrogen, as demonstrated by using D2.