Title Influence of alkyl substitution pattern on reactivity of thiophene-based monomers in kumada catalyst-transfer polycondensation
Date 15.08.2011
Number 26542
Abstract Transmetalation (TM) was found to be the key step defining the ability of alkyl-substituted thiophene-based ClMg-Th(R)-Br monomers to be polymerized under Ni-catalyzed Grignard metathesis/Kumada catalyst transfer polycondensation conditions. For both dppe- and dppp-supported catalysts (dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,2-bis(diphenylphosphino)propane), chain propagation is prohibited if the TM step would lead to sterically hindered head-to-head (HH) Th(R)-Ni-(R)Th intermediates in which alkyl substituents at both thienyl rings are in the “ortho” position relative to the Ni center. However, polymerization proceeds if no alkyl substituents are present at least at one “ortho” position relative to the Ni center. This rule is fulfilled for “regular” 2-bromo-5-chloromagnesio-3-hexylthiophene (2) which easily polymerize in the presence of various Ni initiators. However, “reversed” 5-bromo-2-chloromagnesio-3-hexylthiophene (1) has sterically hindered Grignard function and therefore the initiation step is hampered with Ni(dppe)Cl2 or Ni(dppp)Cl2 initiator precursors, but it proceeds with sterically nonhindered Ph-Ni(dppe)-Br and Ph-Ni(dppp)-Br initiators. “Disubstituted” 2-bromo-5-chloromagnesio-3,4-dihexylthiophene (3) does not polymerize by any initiators. “Unsubstituted” monomer 2-bromo-5-chloromagnesiothiophene (4) smoothly homopolymerizes and copolymerizes with 2-bromo-5-chloromagnesio-3-dodecylthiophene (2a) by various unsupported and surface-immobilized initiators via the chain-growth mechanism. This reflects the unimportance of the “ortho” stabilization of the chain-propagating Ni species for achieving a good polymerization control, if Ni catalysts are ligated by bidentante dppp and dppe ligands. The obtained results demonstrate that unsubstituted thiophene is a suitable building block for designing of new conjugated polymers via chain-growth Kumada catalyst-transfer polycondensation.
Publisher Macromolecules
Citation Macromolecules 44 (2011) 2006-2015
Authors Tkachov, R. ; Senkovsky, V. ; Komber, H. ; Kiriy, A.
Tags chain-growth polymerization structure-property relationships controlled molecular-weight grignard metathesis method low-bandgap polymer solar-cells conjugated polymers photovoltaic devices block-copolymers regioregular poly(3-alkoxythiophene)s

Back to list