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In comparison with (C6H6)Cr(CO)3, (C6H6)2Cr is relatively light stable. The major part of the light energy absorbed by (C6H6)2Cr leads neither to its decomposition or ligand exchange, nor can it be transferred to common low energy triplet acceptors. Internal dissipation of energy, either by rapid conversion to the ground state or by rapid reversible isomerization, must be an important process.In the case of (C6H6)Cr(CO)3, the main pathway to the previously reported lightinduced exchange of benzene involves an intermediate which is suggested to be (benzene)-dicarbonylchromium (1) and not a one-step dissociation of the excited molecule, to give Cr(CO)3 and benzene1b: 1 is also of major importance for the exchange of CO.

Dialkyl azodiformates form dihydrooxadiazines with indene, dihydro-1,4-dioxine, vinylene carbonate, cisand irons-1,2-dimethoxyethylene, and vinyl acetate by 1,4 addition; 1,2 addition yielding diazetidines is observed with vinyl ethers. Diazetidines also result from the addition of 4-phenyl-A'-1,2,4-triazoline-3,5-dione (PTD) to indene and dihydro-1,4-dioxine. Dihydrooxadiazines are formed in a concerted Diels-Alder reaction with inverse electron demand, the diazetidines via dipolar intermediates. The acceleration of azodiformate addition by illumination is due to the photochemical production of as azodiformates, which show increased thermal reaction rates compared with the irons isomers.

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