Early organotransition metal complexes often activate hydrocarbon CH bonds by reversible a-H abstraction/1,2-addition. The unsaturated ?2-cylopropene complex [TpMe2Nb(?2-c-C3H4)(MeCCMe)] A  generated by �-H abstraction of methane at ca room temperature from the a-CC agostic complex [TpMe2NbMe(c-C3H5)(MeCCMe)] is trapped by pyridine to give [TpMe2Nb(?2-c-C3H4)(MeCCMe)(pyridine)].1 Several unsaturated hydrocarbons RH, including other heteroaromatics, undergo CH bond activation via a 1,3-CH addition reaction across a Nb-C bond of A  to give [TpMe2NbR(c-C3H5)(MeCCMe)] (R = 1-cyclopentenyl, 1-thiophenyl, 1-furyl, 1-phenylacetylide). The cyclopentenyl complex reacts subsequently with benzene to give the phenyl cyclopropyl complex [TpMe2NbPh(c-C3H5)(MeCCMe)]. Pentafluorobenzene yields a pentafluorophenyl five-membered niobacycle [TpMe2Nb(C6F5)(CMeCMeCHCHMe)] resulting from (a) CH activation of C6F5H by A  followed by (b) cyclopropyl ring opening and alkyne coupling. Two regioisomers that do not interconvert on the NMR timescale are formed.1 Ouli� et al, J. Am. Chem. Soc. 2010  , 132, 14239.

CH bond activation of unsaturated hydrocarbons by a transient η<sup>2</sup>-cyclopropene niobium complex

245th National Meeting (2013)

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CH bond activation of unsaturated hydrocarbons by a transient η2-cyclopropene niobium complex

CH bond activation of unsaturated hydrocarbons by a transient η²-cyclopropene niobium complex