Aryl sulfonates, homocoupling

Apart from aryl halides, other very easily available substrates for nickel-catalysed biaryl (II) synthesis are aryl sulfonates (XII). Method D is very efficient in the homocoupling reactions of substituted aryl sulfonates in good to excellent yields [15], Table 6. Substituted aryl sulfonates are readily obtained from phenols and trifluoromethanesulfonic anhydride, benzenesulfonyl-, tosyl- or methanesulfonyl chloride in pyridine, or in a suitable inert solvent such as dichloromethane in the presence of triethylamine or Hiinig s base. Among other nickel complexes, Ni(dppe)Cl2 and Ni(dppf)Cl2 have been used (10 mo1%) as slightly less versatile catalysts for the homo-couplings of naphthyl sulfonates in refluxing THF, DMF or their mixtures [42]. 

Aryl sulfonates undergo homocoupling in high yield in the presence of Ni(0) catalysts generated in situ [22]. 

Polymer Forming Homocoupling Reactions. The high yield homocoupling of aryl halides and sulfonates has been extensively applied to the synthesis of aromatic polymers. Two types of aromatic polymers are prepared by this method. TTie first type contains heteroatom linkages between aromatic groups and the second type contains only aromatic groups in the backbone. 

In the first example of the application of the homocoupling reaction of aryl chlorides to polymer synthesis, high molecular weight polyarylether sulfones were prepared by the Ni(0) catalyzed homocoupling reaction of 4,4 -bis(p-chlorophenoxy)diphenylsulfone [equations 50 (178) and 51 (779)]. 

The Ni(0) catalyzed homocoupling reaction of aryl halides and sulfonates is also an excellent method for the preparation of high molecular weight soluble poly(p-phenylene)s and poly(arylene)s. The development of this methodology began with the synthesis of soluble functionalized PPP and polyarenes from substituted dichlorobenzene (28,29,31) and the triflates (28-31,182) of hydroquinones and bisphenols (equations 54 and 55). 

---