Synthesis, spectroscopy, and photochemistry of bis[bis(diphenylphosphino)methane]bis(2,5-di-isocyano-2,5-dimethylhexane)dirhodium(I)

Reaction between [Rh2L4]2+(L = 2,5-di-isocyano-2,5-dimethylhexane) and dppm [bis(diphenylphosphino)methane] in acetonitrile yielded [Rh2L2(dppm)2]2+. Its optical spectrum displays an intense absorption at 595 nm, which is assigned to the transition 1A1g[(dσ*)2]→1B1u[(dσ*)1(pσ)1]. Room-temperature fluorescence at 677 nm, from the 1B1u excited state, is observed in fluid solution. The 3B1u state of the rhodium complex is long-lived with a measured lifetime of 1.0 ± 0.1 µs. Studies on the quenching reactions with a series of pyridinium acceptors established that the excited reduction potential [E°(Rh23+–Rh22+*)] is –1.13 V vs. saturated calomel electrode. The mechanism of the photoreactions of the rhodium complex with halogenocarbons is discussed.