Gold‐Catalyzed C−H Functionalization Polycondensation for the Synthesis of Aromatic Polymers

Abstract

Homogeneous gold (Au) complexes have demonstrated tremendous utility in modern organic chemistry; however, their application for the synthesis of polymers remains rare. Herein, we demonstrate the first catalytic application of Au complexes toward the polycondensation of alkyne-containing comonomers and heteroarene nucleophiles. Polymerization occurs through successive intermolecular hydroarylation reactions to produce high molecular weight aromatic copolymers with 1,1-disubstituted alkene backbone linkages. Clear correlations between the rate and degree of polymerization (DP) were established based on catalyst structure and counterion pairing, thus enabling polymerization reactions that proceeded with remarkable efficiency, high reactivity, and exceptional DPs. The reactivity is broad in scope, enabling the copolymerization of highly functionalized aromatic and aliphatic monomers. These results highlight the untapped utility of Au catalysis in providing access to new macromolecular constructs. A principal strategy to achieve materials with robust mechanical, chemical, electronic, and thermal properties involves the incorporation of planar, rigid aromatic, or pseudo-aromatic units within the polymer backbone. [1-3] These aromatic polymers form the basis for many highperformance materials applied in demanding applications. While these materials are primarily derived from traditional step-growth polymerizations, late transition metal (i.e., Ni, Pd, Ru, Rh) mediated polycondensations have matured to high levels in recent years, enabling the synthesis of novel aromatic polymers which impact an innumerable number of emerging technologies. [4-7] In order to broaden the scope of polymers that can be prepared, there remains an ongoing need for new catalytic approaches that overcome limitations that define these reactions such as multistep monomer syntheses, harsh reaction conditions, stoichiometric byproduct generation, and intolerance toward oxygen and water. Consequently, widespread efforts have focused on metal catalyzed C À H activation and functionalization processes, where C À C bond formation occurs directly between C(sp 2) À

Gold-Catalyzed Post-Polymerization Modification of Commodity Aromatic Polymers

“…N -Heterocyclic carbene (NHC) complexes with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) ligands were examined on account of their high reactivities. 17 , 32 , 33 Consistent with the low reactivity obtained using B , the direct use of I resulted in 0.8% functionalization (entry 10), while activation of J with AgSbF 6 resulted in 11.6% (entry 11).…”

“…We recently demonstrated the first catalytic application of homogeneous gold (Au) complexes toward the C–H functionalization polycondensation of alkyne-containing comonomers and aromatic nucleophiles resulting in high molecular weight aromatic copolymers. 17 We investigated whether this intermolecular reactivity in hydroarylations 18 , 19 could be applied to the challenging PPM of aromatic polymers as highlighted in Figure 1 c.…”

“…Modulation of ion pairing as a function of solvent dielectric (ε) demonstrated a profound effect on reactivity. 17 , 23 , 24 Reactions utilizing 2 equiv of 1 per repeat unit of PS (i.e., [ 1 ]/[PS] = 2) showed high reactivities but resulted in branching through a double hydroarylation ( Table S3 ). 25 Increasing [ 1 ]/[PS] to 10 equiv suppressed the double hydroarylation pathway and enabled the controlled functionalization of PS.…”