Generation of nickel(0)-aryne and nickel(II)-biphenyldiyl complexes via in situ dehydrohalogenation of arenes. Molecular structures of

Reactions of the aromatic halides chlorobenzene, 9-bromophenanthrene and chloro-p-xylene with lithium 2,2,6,6-tetramethylpiperidide (LiTMP) in the presence of [Ni(η²-C₂H₄)(dcpe)] (1) generated the corresponding η²-aryne complexes [Ni(η²-aryne)(dcpe)] [aryne = C₆H₄ (2), 9,10η-C₁₄H₈ (4) and 2,3η-1,4-Me₂C₆H₂ (9)], which could not be isolated as pure compounds but were identified tentatively on the basis of spectroscopic data. In the case of 2, further insertion of free benzyne formed the biphenyldiyl complex [Ni(2,2′ -C₆H₄C₆H₄)(dcpe)] (3). In addition to forming 4, 9,10-phenanthryne also underwent cyclotrimerisation under the reaction conditions to give hexabenzotriphenylene (6), having C₂-symmetry. Compounds 3 and 6 were structurally characterised by X-ray diffraction analyses.