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Time-resolved infrared spectral studies of the photochemical transformation (quantum yield 0.41 for 366 nm photolysis in cyclohexane) of the 3,4-dirhenacyclobutene complex 1 to the 2,4-dirhena[1.1.0]bicyclobutane complex 2 demonstrate the prompt formation of the short-lived intermediate I proposed to be a bis(metallacarbene).
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Casey et al. (1996) studied this question.
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