Browsing by Author "Mullik, Sanam U."

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Thermal reactions of methyl and acetyl manganese pentacarbonyls. Part 1.—Initiation of free-radical polymerization and formation of methyl(2-methyl 4-oxopentanoate)
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Bamford, Clement H.; Mullik, Sanam U.
The manganese pentacarbonyl derivatives CH3Mn(CO)5 and CH3COMn(CO)5 are low-molecular-weight analogues of macroinitiators which carry terminal Mn(CO)5 groups and their thermal reactions in methyl methacrylate at 100°C have been studied from this aspect. Under these conditions isomerization reactions are rapid and the two compounds behave similarly. The derivatives initiate free-radical polymerization above 60°C but give rise to marked retardation except at very low concentrations. The rate of polymerization ω is increased by the presence of “halide” or “non-halide” additives and at the same time retardation is greatly reduced. The dependence of ω upon additive concentration is of the familiar form showing a plateau value at high concentrations. The rate of polymerization is depressed by the presence of carbon monoxide. However, initiation of polymerization is only a minor component of the overall reaction at 100°C, the major process (∼90%) being formation of methyl(2-methyl 4-oxopentanoate), CH3COCH2CH (CH3)COOCH3. This reaction follows a non-radical route. A mechanism is suggested involving intramolecular interaction between an acetyl anion and the coordinated monomer (M) in CH3COMn(CO)4M; the process is completed by proton transfer from water present in the system in trace quantities. This mechanism is strongly supported by investigations with D2O. Spectral (u.v.-visible) changes accompanying these transformations are recorded. Thermal decomposition of CH3Mn(CO)5 and CH3COMn(CO)5 in benzene yields Mn2(CO)10; in methyl methacrylate an additional peak develops at 385 nm which we attribute to Mn(CO)5OH. This peak is not much affected by the presence of CCl4 or CO.
Thermal reactions of perfluoromethyl and perfluoroacetyl manganese pentacarbonyls. Part 2.—Initiation of free-radical polymerization and formation of methyl(2-methyl 4-oxo-5,5,5-trifluoropentanoate)
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Bamford, Clement H.; Mullik, Sanam U.
This paper continues the study of the thermal reactions of low-molecular-weight analogues of macroinitiators carrying terminal Mn(CO)5 groups e.g. [graphic omitted]CF2 CF2 Mn(CO)5. The reactions of CF3Mn(CO)5 and CF3COMn(CO)5 in methylmethacrylate solution at 100°C have been examined. Both derivatives initiate free-radical polymerization; retardation is less marked than with the unfluorinated analogues, especially in the case of CF3Mn(CO)5. Rates of polymerization ω are increased by the presence of “halide” and “non-halide” type additives; with CF3Mn(CO)5 the increase corresponds to a factor of 2 in the rate of initiation. The dependence of ω on [CCl4] is very sharp and a plateau value is reached for [CCl4] > 5 × 10–3 mol dm–3. The reaction of CF3COMn(CO)5 yields methyl(2-methyl-4-oxo-5,5,5-trifluoropentanoate), CF3COCH2CH(CH3)COOCH3. Reaction in the presence of D2O yields CF3COCH2CD(CH3)COOCH3, indicating that the mechanism is of a polar type involving intramolecular attack by a CF3CO anion on a coordinated monomer molecule, with subsequent acquisition of a proton from water present in trace quantities. No corresponding reaction with CF3Mn(CO)5 has been observed under similar conditions. On heating these derivatives in methyl methacrylate at 100°C a peak with λmax= 342 nm slowly develops in the u.v.-visible spectrum and represents the formation of Mn2(CO)10. In the presence of added water a peak near 385 nm appears, attributable to Mn(CO)5OH. The bearing of these results on the use of macroinitiators for block-copolymer synthesis is discussed.