Efficient C-F and C-C activation by a novel N-heterocyclic carbene-nickel(0) complex

The NHC-stabilized complex [Ni-2(iPr(2)Im)(4)(cod)] (1) was isolated in good yield from the reaction of [Ni(cod)21 with 1,3-diisopropylimidazole-2ylidene (iPr(2)Im). Compound 1 is a source of the [Ni(iPr(2)IM)(2)] complex fragment in stoichiometric and catalytic transformations. The reactions of 1 with ethylene and CO under atmospheric pressure or with equimolar amounts of diphenyl acetylene lead to the compounds [Ni(iPr(2)IM)(2)(eta(C2H2)-C-2)] (2), [Ni(iPr(2)IM)(2)(eta(2)-C2Ph2)] (3), and [Ni(iPr(2)IM)(2)(CO)(2)] (4) in good yields. In all cases the [Ni(iPr2lM)21 complex fragment is readily transferred without decomposition or fragmentation. In the infrared spectrum of carbonyl complex 4, the CO stretching frequencies are observed at 1847 and 1921 cm(-1), and are significantly shifted to lower wave-numbers compared with other nickel(0) carbonyl complexes of the type [NiL2(CO)(2)]. Complex I activates the C-F bond of hexafluorobenzene very efficiently to give [Ni(iPr(2)IM)(2)(F)-(C6F5)] (5). Furthermore, [Ni-2(iPr(2)Im)(4)-(cod)] (1) is also an excellent catalyst for the catalytic insertion of diphenylacetylene into the 2,2' bond of biphenylene. The reaction of 1 with equimolar amounts of biphenylene at low temperature leads to [Ni(iPr(2)Im)(2)(2,2'-biphenyl)] (6), which is formed by insertion into the strained 2,2' bond. The reaction of diphenylacetylene and biphenylene at 80 degrees C in the presence of 2mol% of 1 as catalyst yields diphenylphenathrene quantitatively and is complete within 30 minutes.