Studies of thermal- and photo-interconversions of manganese carbonyl halide species by ultraviolet spectroscopy

Abstract

Mn(CO)₅X and [Mn(CO)₄X]₂(X = Cl or Br) coexist in equilibrium in benzene solution, the position of equilibrium at a given temperature being determined by [CO]. Similarly, Mn(CO)₃L₂X and [Mn(CO)₃LX]₂[L = methyl methacrylate (mma) or acetonitrile (an)] are also easily interconverted. In mma (a weak donor) two substituted compounds are produced, Mn(CO)₃(mma)₂X and [Mn(CO)₃(mma)X]₂, the former predominating in mma solution. Irradiation of [Mn(CO)₃LX]₂(L = CO, an, or mma) with λ= 435·8 nm produces manganese carbonyl, the yield of which is dependent upon the nature of L. Mn(CO)₃L₂X also yields manganese carbonyl on photolysis, under conditions where the process Mn(CO)₃L₂X → Mn(CO)₃LX + L is not inhibited by the presence of excess L. Mn(CO)₃(mma)₂X is found to be an active photoinitiator of polymerization whereas Mn(CO)₅X alone is not.