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(η6‐1,3,5‐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(η4:2‐7,8‐bis(trimethylsilyl)bicyclo[4.2.1]nona‐2,4,7‐triene} (2, 60% yield, Φ=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.