Correlation of metal spin-state in alpha-diimine iron catalysts with polymerization mechanism

Laura E. N. Allan, Michael P. Shaver, Andrew J. P. White, Vernon C. Gibson

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The alpha-diimine iron complexes, (R',R '')[N,N]FeCl2 ((R',R '')[N,N] = 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 paradimethylaminophenyl (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, sigma, with polymerization rate and polymer molecular weight, respectively.

Original languageEnglish
Pages (from-to)8963-8970
Number of pages8
JournalInorganic Chemistry
Issue number21
Publication statusPublished - 15 Oct 2007

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