Biomimetic oxidation of cyclic and linear alkanes: high alcohol selectivity promoted by a novel manganese porphyrin catalyst

A novel third-generation metalloporphyrin, chloro-5,10,15,20- tetrakis-(30 '-bromine- 40 '-methoxyphenyl)2,3,7,8,12,13,17,18- octabromoporphyrinatomanganese((III)), [ Mn(III)Br(12)T4(-OMe) PPCl], designated as MnBr(12)Por, was synthesized and characterized. The catalytic activity of the new manganese porphyrin was investigated in the oxidation of cyclohexane, adamantane and n-hexane by iodosylbenzene (PhIO) or iodobenzene diacetate (PhI(OAc)(2)) in comparison to the catalytic activity of the second- generation catalyst [ Mn(III)T4(-OMe) PPCl], designated as MnPor. All yields were based on oxidants. The MnBr(12)Por/PhIO system led to higher yields of cyclohexane oxidation products (45%) with high selectivity for cyclohexanol (80%) as compared to the MnPor/PhIO system (23% and 77%, respectively). Addition of imidazole to MnPor/ PhIO increased the total product yield from 23 to 43%; addition of imidazole to MnBr(12)Por/PhIO did not alter the total product yield at all. For the MnPor/ PhI(OAc)(2) and MnBr(12)Por/PhI(OAc)(2) systems, addition of imidazole increased the product yields from 19 to 45% and from 35 to 66%, respectively. Addition of water increased the total product yields during cyclohexane and adamantane oxidation for all the studied systems. In all cases, MnBr12Por performed better than MnPor.