Phosphines, nitrogen heterocycle adducts

Another arylation method, in the case of nitrogen heterocycles, does not need a halogenated derivative but a heterocycle activated by triflic anhydride260,261 (reaction 22). Simple aryl halides usually do not react with phosphines and special methods therefore have to be used for their arylation. The most widely used is the complex salt method , in which an aryl halide is heated with a phosphine in the presence of a transition metal such as nickel (II)2e (reaction 23). The catalytic cycle probably takes place by means of a reduced nickel(I) complex, generated in situ from the starting nickel(II) salt this nickel(I) species could undergo an oxidative addition of the aryl halide to yield a transient nickel(III) adduct, which after the reductive elimination of the aryphosphonium affords the recovery of the first active-nickel(I) complex (reaction 24). 

Adducts with Nitrogen Heterocycles, Amines, Imines, Phosphines, and Arsines. The addition of nitrogen heterocycles such as 2,2 -bipyridyl or 1,10-phenanthroline to bis[(trimethylsilyl) methyl]zinc leads to the quantitative formation of orange-red to red adducts which show remarkable stability towards oxygen. The complex with iV,iV,iV, Ai -tetramethylethylenediamine is less stable. ... 

Numerous adducts, mostly of type MX4L2 (X = Cl, Br, I), are known with nitrogen, phosphorus, arsenic, oxygen, and sulfur donors. They are synthesized by reaction of solid tetrahalides with the ligand or by reduction of pentahalides with the ligand, mainly bidentate or heterocyclic N-donors or phosphines. NbCLt(THF)2 (29) is of particular value since the lability of the THF molecules makes it a useful synthon in Nb chemistry. 

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