On the Role of Disproportionation Energy in Kumada Catalyst-Transfer Polycondensation

Abstract

Kumada catalyst-transfer polycondensation (KCTP) is an effective method for the controlled polymerization of conjugated polymers. Nevertheless, side reactions leading to early termination and unwanted chain coupling cause deviations from the target molecular weight, along with increasing polydispersity and end group variation. The departure from the KCTP cycle stems from a disproportionation reaction that leads to experimentally observed side products. The disproportionation energies for a series of nickel-based initiators containing bidentate phosphino attendant ligands were computed using density functional theory at the B3LYP/DZP level. The initiator was found to be less favorable toward disproportionation by 0.5 kcal mol–1 when ligated by 1,3-bis(diphenylphosphino)propane (dppp) rather than 1,2-bis(diphenylphosphino)ethane (dppe). Trends in disproportionation energy (E disp) with a variety of bidentate phosphine ligands match experimental observations of decreased polymerization control. Theoretical E disp values can thus be used to predict the likelihood of disproportionation in cross-coupling reactions and, therefore, aid in catalyst design.

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

“…To gain insight into the extent of chain termination, end‐group analysis was conducted with MALDI‐TOF MS. A controlled polymerization would show P3HT with only Br/H chain ends. The presence of P3HT with Br/Br end‐groups indicates interchain termination or catalyst dissociation . Scheme illustrates the pathways that can result in P3HT containing H/Br or Br/Br end‐groups.…”

“…The presence of P3HT with Br/Br end-groups indicates interchain termination or catalyst dissociation. [41] Scheme 3 illustrates the pathways that can result in P3HT containing H/Br or Br/Br end-groups. The release of the catalyst through either dissociation or disproportionation can cause another initiated cycle of KCTP, resulting in the decrease in uniformity of polymer chains and higher dispersity.…”

The Influence of Substituents in the 3‐Position on the Polymerization of Metaphenylenes

“…Disproportionation occurs when two growing polymer chains meet after the oxidative addition. This can result in a ligand exchange in which Ni(L 2 )Cl 2 is formed together with two coupled polymer chains …”

“…This can result in a ligand exchange in which Ni(L 2 )Cl 2 is formed together with two coupled polymer chains. [25] Finally, Nojima et al were the first to notice intermolecular transfer of the catalyst induced by double bonds in the monomer unit during the polymerization of phenylene-vinylene with t-Bu 3 PPd. [18] The authors argue that sterical hindrance at the ortho-position is a necessity to achieve a living polymerization.…”

Catalyst‐Transfer Condensation Polymerization of Acceptor Aromatic Monomers and of Donor Carbon‐Carbon Double Bond‐Containing Monomers

“…In catalyst‐transfer Kumada‐Tamao coupling polymerization with a Ni catalyst, well‐defined poly(3‐alkylthiophene) s (P3ATs), poly( p ‐phenylene), poly( m ‐phenylene), poly( N ‐alkylpyrrole), polyfluorene, poly(cyclopentadithiophene), and poly(thiophene‐ alt ‐ p ‐phenylene) have been synthesized. Among these polymerizations, the catalyst‐transfer condensation polymerization (CTCP) leading to P3ATs has been extensively developed; many kinds of block copolymers and gradient copolymers containing the P3AT segment have been synthesized, and the mechanism, including the role of ligands on the catalyst, has been thoroughly investigated . Furthermore, isolable Ni‐initiators were formed and applied to the production of polythiophene brushes from a substrate surface and of star polymers .…”