Unravelling the Photochemical Transformations of Chromium(I) 1,3 Bis(diphenylphosphino), [Cr(CO)(4)(dppp)](+), by EPR Spectroscopy

[Image: see text] UV-induced photochemical transformations of the paramagnetic [Cr(CO)(4)(Ph(2)PCH(2)CH(2)CH(2)PPh(2))](+) complex (abbreviated [Cr(CO)(4)(dppp)](+)) in dichloromethane was investigated by CW EPR spectroscopy. Room-temperature UV irradiation results in the rapid transformation of [Cr(CO)(4)(dppp)](+) into trans-[Cr(CO)(2)(dppp)(2)](+). However, low-temperature (77–120 K) UV irradiation reveals the presence of an intermediate mer-[Cr(CO)(3)(κ(1)-dppp)(κ(2)-dppp)](+) complex which photochemically transforms into trans-[Cr(CO)(2)(dppp)(2)](+). The derived spin Hamiltonian parameters for these complexes were confirmed by DFT calculations. The photoinduced reaction is shown to be concentration-dependent, leading to a distribution of the three complexes ([Cr(CO)(4)(dppp)](+), mer-[Cr(CO)(3)(κ(1)-dppp)(κ (2)-dppp)](+), and trans-[Cr(CO)(2)(dppp)(2)](+)). A bimolecular photoinduced mechanism is proposed to account for the formation of mer-[Cr(CO)(3)(κ(1)-dppp)(κ(2)-dppp)](+) and trans-[Cr(CO)(2)(dppp)(2)](+).