Transition metal benzyne complexes are organometallic complexes that contain benzyne ligands (C<sub>6</sub>H<sub>4</sub>). Unlike benzyne itself, these complexes are less reactive although they undergo a number of insertion reactions.
The studies of metal-benzyne complexes were initiated with the preparation of zirconocene complex by reaction diphenylzirconocene with trimethylphosphine.
The preparation of Ta(÷<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(C<sub>6</sub>H<sub>4</sub>)Me<sub>2</sub> proceeds similarly, requiring the phenyl complex Ta(÷<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(C<sub>6</sub>H<sub>5</sub>)Me<sub>3</sub>. This complex is prepared by treatment of Ta(÷<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)Me<sub>3</sub>Cl with phenyllithium. Upon heating, this complex eliminates methane, leaving the benzyne complex:
The second example of a benzyne complex is Ni(÷<sup>2</sup>-C<sub>6</sub>H<sub>4</sub>)(dcpe) (dcpe = Cy<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>PCy<sub>2</sub>). It is produced by dehalogenation of the bromophenyl complex NiCl(C<sub>6</sub>H<sub>4</sub>Br-2)(dcpe) with sodium amalgam. Its coordination geometry is close to trigonal planar.
Benzyne complexes react with a variety of electrophiles, resulting in insertion into one M-C bond. With trifluoroacetic acid, benzene is lost to give the trifluoroacetate Ni(O<sub>2</sub>CF<sub>3</sub>)<sub>2</sub>(dcpe).
Several benzyne complexes have been examined by X-ray crystallography.
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