Generation of nickel(0)aryne and nickel(II)biphenyldiyl complexes via in situ dehydrohalogenation of arenes. Molecular structures of [Ni(2,2′-C6H4C6H4)(dcpe)] and C2-hexabenzotriphenylene

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.