Correlation of metal spin-state in alpha-diimine iron catalysts with polymerization mechanism.
The alpha-diimine iron complexes, (R',R'')[N,N]FeCl(2) ((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 para-dimethylaminophenyl (R' ' = NMe(2)-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.
Allan
Laura E N
LE
Contribution from the Department of Chemistry, Imperial College London, South Kensington, London, SW7 2AZ, UK.
Shaver
Michael P
MP
White
Andrew J P
AJ
Gibson
Vernon C
VC
D002384:Catalysis; D002621:Chemistry / Q000379:methods*; D018360:Crystallography, X-Ray / Q000379:methods; D005290:Ferric Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry*; D011522:Protons; D013343:Styrenes / Q000737:chemistry; D013997:Time Factors
D005290:Ferric Compounds; D008024:Ligands; D008670:Metals; D011108:Polymers; D011522:Protons; D013343:Styrenes; D007501:Iron