Transition metal benzyne complex

 ( Organometallic Chemistry ) 

Transition metal benzyne complexes are organometallic complexes that contain benzyne ligands (C₆H₄). Unlike benzyne itself, these complexes are less reactive although they undergo a number of insertion reactions.Buchwald, S. L.; Nielsen, R. B. "Group 4 Metal Complexes of Benzynes, Cycloalkynes, Acyclic Alkynes, and Alkenes" Chem. Rev. 1988, volume 88, 1047-1058

---

Examples The studies of metal-benzyne complexes were initiated with the preparation of zirconocene complex by reaction diphenylzirconocene with trimethylphosphine.Buchwald, S. L.; Watson, B. T. The Trimethylphosphine Adduct of the Zirconocene-Benzyne Complex: Synthesis, Reactions, and X-ray Crystal Structure. J. Am. Chem. Soc. 1986, 108, 7411-7413

Cp₂ZrPh₂ + PMe₃ → Cp₂Zr(C₆H₄)(PMe₃) + PhH

The preparation of Ta(η⁵-C₅Me₅)(C₆H₄)Me₂ proceeds similarly, requiring the phenyl complex Ta(η⁵-C₅Me₅)(C₆H₅)Me₃. This complex is prepared by treatment of Ta(η⁵-C₅Me₅)Me₃Cl with phenyllithium.McLain, S. J.; Schrock, R. R.; Sharp, P. R.; Churchill, M. R.; Youngs, W. J. Synthesis of Monomeric Niobium- and Tantalum-Benzyne Complexes and Molecular Structure of Ta(η⁵-C₅Me₅)(C₆H₄)Me₂" J. Am. Chem. Soc. 1979, volume 101, 263-265 Upon heating, this complex eliminates methane, leaving the benzyne complex:

Ta(η⁵-C₅Me₅)(C₆H₅)Me₃ → Ta(η⁵-C₅Me₅)(C₆H₄)Me₂ + CH₄

The second example of a benzyne complex is Ni(η²-C₆H₄)(dcpe) (dcpe = Cy₂PCH₂CH₂PCy₂). It is produced by dehalogenation of the bromophenyl complex NiCl(C₆H₄Br-2)(dcpe) with sodium amalgam. Its coordination geometry is close to trigonal planar.

---

Reactivity 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(O₂CF₃)₂(dcpe).

---

Structural trends

Several benzyne complexes have been examined by X-ray crystallography.

+ Bond lengths (Å) in Ta, Ni and Zr benzyne complexes
2.267
2.228
1.364
1.389
1.383
1.380
1.377
1.406

+ Bond angles (degrees) in Ni and Zr benzyne complexes
35.3
70.8
73.9
120.2
122.1
(n/a)
(n/a)
(n/a)
(n/a)

Categories: Organometallic Chemistry, Coordination Chemistry, Transition Metals

Post Comment