Addition reactions of alkenes catalysed by dinuclear complexes
This work has been concerned with the role and behaviour of dinuclear transition metal complexes in promoting addition reactions between halocarbons and alkenes. Detailed studies have been made of the following catalysts:- [Fe2(CO)4(~-C5H5)2J, [Ru2(CO)4(1-C5HS)2J, [Mo2(CO)4(1~C5Me5)2J, [Mo2(CO)(i(7l.-CSHIj)2J,. C~2L(1[-C5H4)Mo(CO)3J2 ana [CH2[(1-C5H4)FetCO)2J2 The [Fe2(CO)4(1-C5H5)2J system had been studied previously and a non-radical mechanism proposed for addition reactions in the presence of this complex. This would make it unique in this type of reaction. For this reason the reaction has been re-examined in detail. A complete kinetic study and CCI4/CBr4 cross-over reactions show that the mechanism is in fact of the non-chain free radical type catalysed, rather than initiated, by a metal complex. Cross-over reactions involving a mixture of [Fe2(CO)4(1J-C5H )2J and [Fe2(CO)4(~-C5Me5)2J have provided evidence that indicates t6e presence of a dinculear active species and CO inhibition suggests that this is [Fe2(CO) (~-C H5)2J. It seems therefore likely that the mechanism involves a dinuclear active species with radical pair intermediates. The ruthenium dimer proved to be an efficient catalyst at high temperature but gave poor yields at temperatures appropriate to mechanistic studies. For this reason a detailed kinetic study could not be carried out on this system, however cross-over reactions suggest a free radical mechanism. [Mo2(CO)4(1-C5Me5) J was found to be the most effective dinuclear catalyst so far examined. A detailed kinetic study and CCI4/CBr4 cross-over reactions again indicate a free radical mechanism. Metal-metal cross-over studies also indicated the involvement of binuclear active species. Reactions in the presence of [Mo2(CO)6(~-C5H5)J2 have been reinvestigated since a previous study suggested that this complex followed a mechanism different to all other well characterised examples. However, the present findings have confirmed a similar mechanism to those outlined above. Reactions in the presence of the ligand bridged complexes [(OC)iMO(CsH4CH2C5H4)MO(CO)3J and [(OC)2Fe(C5H4CH2C5H4)Fe(CO)2J were carried out. A brief kinetic study of Ehe reaction involving the molybdenum complex has shown a similar order of reaction to previous examples. Cross-over studies have again indicated the presence of free radicals. Thus, the study of these six systems suggests a common mechanism for all which involves binuclear active catalytic species and radical pair intermediates.