884050-47-9Relevant academic research and scientific papers
Organometallic intermediates in the controlled radical polymerization of styrene by α-diimine iron catalysts
Shaver, Michael P.,Allan, Laura E. N.,Gibson, Vernon C.
, p. 4725 - 4730 (2007)
The α-diimine iron complexes R′,R″[N,N] FeCl2 (R′,R″[N,N] = R′-N=CR″- CR =N-R′) are efficient catalysts for the atom-transfer radical polymerization (ATRP) of styrene when R′ and R″ are electrondonating substituents and favor catalytic chain transfer (CCT) when electron-withdrawing substituents are employed. An organometallic pathway, alongside a halogen-atom-transfer equilibrium, is proposed to mediate the observed reactivity. The model alkyl complexes, R′,R″[N,N] FeCl2(R), where R = PhCH2 and Ph(Me)CH, were generated via treatment of R′,R″[N, N]FeCl3 with RMgCl. The alkyl derivatives obtained from intermediate spin-state R′,R″[N,N]FeCl3 complexes were found to be stable to ca. -30 °C and favor CCT, whereas the alkyl derivatives derived from high-spin-state trichloride precursors are unstable above -78 °C and favor ATRP. Azo-initiated polymerizations of styrene are moderately controlled by a-diimine iron catalysts. The role of organometallic-mediated radical polymerization (OMRP) in the controlled polymerization of styrene is discussed: an analysis of the radical concentrations generated by the competing OMRP and ATRP equilibria indicates that the halogenophilicity of the Fe(II) catalyst dominates the carbophilic alkyl radical-trapping capacity of the Fe(II) species in this a-diimine catalyst system.
Correlation of metal spin-state in α-diimine iron catalysts with polymerization mechanism
Allan, Laura E. N.,Shaver, Michael P.,White, Andrew J. P.,Gibson, Vernon C.
, p. 8963 - 8970 (2008/10/09)
The α-diimine iron complexes, R′,R″[N,M]FeCl2 (R′R″[N,M] = R′-N=CR″-CR″=N-R′, where R′ = tert-butyl (tBu), cyclohexyl (Cy) and R′ = phenyl (Ph), para-fluorophenyl (F-Ph), para-bromophenyl (Br-Ph), para-methylphenyl (Me-Ph), or para-methoxyphenyl (MeO-Ph)), are found to polymerize styrene through a catalytic chain transfer (CCT) mechanism. Magnetic moment measurements indicate that Fe(III) complexes containing these ligands possess intermediate (S = 3/2) spin-state iron centers. In contrast, Fe(III) complexes bearing proton (R″ = H) and para-dimethylaminophenyl (R″ = NMe2-Ph) substituents are high-spin and are efficient atom transfer radical polymerization (ATRP) catalysts. Hammett plots show a linear correlation of the substituent constant, σ, with polymerization rate and polymer molecular weight, respectively.
Correlation of metal spin state with catalytic reactivity: Polymerizations mediated by α-diimine-iron complexes
Shaver, Michael P.,Allan, Laura E. N.,Rzepa, Henry S.,Gibson, Vernon C.
, p. 1241 - 1244 (2007/10/03)
The mechanism of styrene polymerization by α-diimine iron complexes correlates with the metal spin state of the catalyst. Experimental and theoretical studies indicate that high-spin catalysts are halogenophilic, resulting in atom transfer radical polymerization (ATRP), while intermediate-spin complexes are carbophilic giving rise to catalytic chain transfer (CCT, see graph). (Graph Presented)
