Naphthyl homo-couplings

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]. 

In similar manner, hexaalkyldistannanes allow the homo-coupling reactions of aryl iodides, bromides [104] and triflates [105] to the symmetrical biaryls. First, the aryltrialkylstannane is generated by reaction of the aryl halides with Me6Sn2 or -BugSn2, followed by the in situ Stille reaction with an excess of electrophilic reactant, since both reactions are catalysted by the same complexes and proceed at comparable reaction rates. For instance, 2-naphthyl triflate (165) was coupled to 2,2 -binaphthalene (166) in 69% yield [105], respectively, Scheme 22. 

In agreement with data [3], our calculations predict a very small CT between /V,/V -diphenyl-7V,7V -bis(/-naphthyl)-l-l -biphenyl-4,4 "-diamine (a-NPD) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecules in spite of the large difference in electronegativity. The small value of the VLS in this system is primarily explained by the weak coupling between HOMO of a-NPD and the LUMO of PTCDA. 

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