Detrimental Ni(0) transfer in Kumada catalyst transfer polycondensation of benzo[2,1‐b:3,4‐b']dithiophene

Abstract

This article deals with the Kumada Catalyst Transfer Polycondensation (KCTP) of 4,7-dioctylbenzo[2,1-b:3,4-b']dithiophene (BDP-Oct) using Ni(II) catalyst or In/cat combination. A combination of MALDI MS, GPC, and 31 P NMR spectroscopy is used to reveal the failure of the KCTP of this particular monomer. Intermolecular transfer reactions to monomer appeared to prevent the formation of polymer. This result is remarkable, since isomeric benzo [1,2-b:4,5-b']dithiophene polymerizes in a controlled way. The presence of a "non-aromatic double bond" in annulated monomers is discussed.

Advances in the controlled polymerization of conjugated polymers

“…Later, the polymerization of benzodithiophene was attempted, but the presence of the 'non-aromatic' double bond introduced transfer reactions, leading to loss of control over the polymerization. 125 Normally the double bond is considered as a part of the aromatic system, but due to the almost equal energy of the total aromatic system and the system with the double bond not being part of the aromatic system, this double bond can behave as a 'normal' double bond. A final problem that was encountered for KCTP was the incomplete conversion of the Grignard metathesis reaction necessary to convert the precursor monomer, leaving unreacted metalation reagents in the reaction mixture, which can act as termination reagents.…”

Diversifying Cross‐Coupling Strategies, Catalysts and Monomers for the Controlled Synthesis of Conjugated Polymers

“…At first thought, these features may suggest nickel catalysts will be more effective for polymerization; however, the situation is more complicated if the conjugated building block has certain features. For example, monomers which are electron deficient or have fused aromatic rings can strengthen π‐complexation with the metal, particularly with nickel, and increase the activation barrier for oxidative addition . Ultimately, both group 10 metals have advantages; further work is necessary to compare the two under identical conditions …”

“…For example, monomers which are electron deficient or have fused aromaticr ings can strengthen p-complexation with the metal, particularly with nickel, and increaset he activation barrierf or oxidative addition. [34][35][36] Ultimately,b oth group 10 metals have advantages;f urther work is necessary to compare the two under identical conditions. [62,76,77] The ancillary ligand (L, Figure 2) is absolutely critical for CTP and is used to tune the electronic and sterice nvironment aroundt he metal center.S ignificant advances in ligand design, particularly for Pd, have produced aw ide range of catalysts that promote efficient small molecule cross-coupling.…”

“…It has yet to be directly observed in situ, since the catalyst resting state normally involves the M 2+ species . Direct observation of metal π‐binding with certain monomers has been noted, but the metal catalyst was trapped in these cases and polymerization did not proceed in the desired chain‐growth fashion . There is a significant body of evidence to support this proposed mechanism including; end group analysis, competitions, and computation .…”

“…[31][32][33] Direct observation of metal p-binding with certain monomers has been noted, but the metal catalyst was trapped in these cases and polymerization did not proceed in the desired chain-growth fashion. [34][35][36] Therei sasignificant body of evidencet os upport this proposed mechanism including;e nd group analysis, [29] competitions, [26,[37][38][39][40][41] and computation. [42,43] While this p-complexr emains elusive, the degree of control in these reactions can be quite high, and near al iving polymerization.…”