Controlled Pd(0)/ t -Bu₃P-catalyzed suzuki cross-coupling polymerization of AB-Type monomers with ArPd(t -Bu₃P)X or Pd₂(dba)₃/ t -Bu₃P/ArX as the initiator

Controlled Pd(0)/t-Bu₃P-catalyzed Suzuki cross-coupling polymerizations of AB-type monomers via the chain-growth mechanism with a series of ArPd(t-Bu₃P)X (X = I, Br, Cl) complexes as initiators were described. Both isolated PhPd(t-Bu₃P)X (X = I, Br) complexes and ArPd(t-Bu₃P)X (X = I, Br, Cl) complexes in situ generated from Pd₂(dba)₃/t-Bu₃P/ArX (X = I, Br, Cl) were employed as initiators for the controlled Pd(0)/t-Bu₃P-catalyzed Suzuki cross-coupling polymerization. The in situ generated ArPd(t-Bu₃P)X complexes were found to be better initiators in general. Among them, the combinations of p-BrC₆H₄I, p-HOCH₂C₆H₄Br and p-PhCOC₆H₄Br with Pd₂(dba)₃/t-Bu₃P were identified as highly robust initiator systems, resulted in polymers with narrow PDIs (1.13-1.20). In addition, the Pd₂(dba)₃/t-Bu₃P/p-HOCH₂C₆H₄Br and Pd₂(dba)₃/t-Bu₃P/p-PhCOC₆H₄Br initiator systems also offered heterobifunctional chain ends with high fidelity. Our study showed that an additional amount of t-Bu₃P in the initiator system helped to achieve the narrow PDIs, likely by stabilizing Pd(0) species in the initiator system via coordination to form more stable Pd(t-Bu₃P)_n (n ≥ 2) complexes. Our study opens a new avenue toward well-defined conjugated polymers.