Pergamon PII: S0040-4020(97)0097 3-3 Tetrahedron, Vol.53, No. 45, pp. 15459-15467,1997 © 1997Published by Elsevier Science Ltd All rightsreserved.Printed in GreatBritain 0040-4020/97$17.00+ 0.00 Suzuki Polycondensation: On Catalyst Derived Phosphorus Incorporation and Reproducibility of Molecular Weights J6rg Frahn, Birol Karakaya, Andreas Sch~fer, A.-Dieter Schltiter* Freie Universitat Berlin,Institut fllrOrganische Chemic Takustr. 3, D-14195Berlin, Germany Fax: 0049-(0)30838 3357,e-mail: adschlue@chemie.fu-berlin.de Abstract: This paper describes the quantification of the extent to which phosphorus is incorporatedinto polymer backbones during Suzuki polycondensation and gives details on how this step-growth polymerization is best performed to ensure reproducibleresults specificallyregarding the achievable molecular weights. © 1997 Published by ElsevierScienceLtd. The Suzuki polycondensation has been developed into an important tool for the synthesis of polyarylenes and related polymers.1 It is now one of the few established step-growth polymerizations which proceed with formation of carbon-carbon bonds and, thus, complements the wealth of polyreactions which lead to bond formation between carbon and hetero atoms. The great attraction of this polymerization originates from its regiospecific course, its high functional group compatibility, and the high molecular weights which can be achieved. It uses aryl boronic acids and aryl halides as coupling partners and Pd(0) complexes which typically carry stabilizing phosphine ligands as catalyst precursors. The catalytic cycle is believed to involve Pd(II) species, though an alternative suggestion has been made. 2 Recently, reports appeared in the literature which shed light on potential side reactions of this cross-coupling. For example, Cheng reported on a facile aryl-aryl exchange reaction between Pd center and phosphine ligands in Pd(II) complexes 3 and Marcuccio used this exchange to explain that a certain boronic acid not only coupled with the aryl halide provided but also to some extent with an aryl group of the phosphine ligand.4 Similar reactions have also been observed in the related Stille cross-coupling. 5 In low molecular weight chemistry scrambling of aryl groups is disadvantagous but may still be acceptable as long as the yields of side products are not too high and they can be separated off. In Suzuki polycondensations, however, aryl-aryl scrambling would be devastating. It was Novak who pointed out that phosphorus containing groups could not only by incorporated as terminator, but also as integral parts of the backbone.6 He in fact found evidence for phosporous incorporation in a polycondensation. In the first case, the rigid-rod character of the polyarylene backbone would be retained. In the second, however, phosphorus acts as kink or even net-point. This would considerably decrease the value of this method for the synthesis of structurally perfect rod-like polymers, which it was believed to be. We, therefore, decided to investigate the issue of phosphorus incorporation in some depth and devised experiments (a) to see whether the P-incorporation was a general phenomenon, (b) to quantify the degree of incorporation, and (e) to possibly determine the way P is incorporated into the polymer structure. We also contribute to another matter of importance in Suzuki polycondensationwhich is its reproducibility regarding the achievable molecular weights. 15459