Suzuki Polycondensation toward High Molecular Weight Poly(m-phenylene)s: Mechanistic Insights and End-Functionalization

Synthesis of a poly(m-phenylene) by Suzuki polycondensation (SPC) using an AB-type m-phenylene monomer is reported (A and B refer to bromo and boron functional groups, respectively). Despite the attempted high molecular weight products, SPC under the conventional conditions using Pd[P(p-Tol)3]3 as catalyst gave rise to oligomeric products only. They comprise cycles and several series of open-chain poly(m-phenylene)s with various end group patterns. These patterns were caused by side reactions such as ligand scrambling. Buchwald’s SPhos ligand was therefore alternatively employed for high turnover catalysis to accelerate SPC over such detrimental side reactions. This modification indeed led to the formation of high molecular weight products ∼40 kDa (DP ∼ 210), while oligomeric cyclic products still remained prominent. Cycle formation could, however, drastically be reduced by slow monomer addition. SPC was also performed in the presence of an excess monofunctional compound, R–A or R–B. The molecular weights...