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A highly diastereo- and chemoselectiveintramolecular nickel-catalyzedcycloaddition of alkene- and alkyne-tethered alkynylidenecyclopropanesis reported. The method constitutes the first fully intramolecular[3 + 2 + 2] alkylidenecyclopropropane cycloaddition occurring viaa proximal cleavage of the cyclopropane and makes it possible to buildrelevant 6,7,5-tricyclic frameworks in a single-pot reaction. Importantly,the reaction outcome is highly dependent on the characteristics ofthe nickel ligands. [ABSTRACT FROM AUTHOR]

Thecomplex [OsCp{κ3-P,C,C-PiPr2[C(CH3)CH2]}(CH3CN)]PF6(1) reactswith (2-pyridyl)methylenecyclopropane, at room temperature, to giveinitially the cyclobutylidene derivative [Os(η5-C5H5)(CCH2CH2CH-o-C5H4N){PiPr2[C(Me)CH2]}]PF6(2), as a result of the ring expansionof the alkylidenecyclopropane unit. Over time complex 2rearranges into the cyclobutene derivative [Os(η5-C5H5){η2-C(CHCH2CH2)-o-C5H4N}{PiPr2[C(Me)CH2]}]PF6(3). The reaction of 1with (2-pyridyl)methylenecyclopropane at room temperaturealso affords the phosphinomethanide metallacycle [Os(η5-C5H5){κ4-P,Ca,Cb,N-PiPr2[Ca(Me)CH2CH)(CbCH2CH2-o-C5H4N]}]PF6(4) as a minor product, which becomes the major product of the reactionat 45 °C. This osmacyclopentane results from the C–C couplingof the isopropenyl substituent of the phosphine ligand and the organicsubstrate. In acetone at 75 °C, the reaction of 1with (2-pyridyl)methylenecyclopropane leads to the 2-alkylidene-1-osmacyclobutane[Os(η5-C5H5){κ3-N,Ca,Cb-Ca(CH2CbH2)(CH-o-C5H4N)}{PiPr2[C(Me)CH2]}]PF6(5), as a consequence of the oxidative addition ofone of the C(sp2)–C(sp3) bonds of thecyclopropane unit of the substrate to the osmium atom, along with 6, a diastereomer of 4. Complexes 3–5have been characterized by X-ray diffractionanalysis. DFT calculations suggest that all of the reaction productsare derived from a common key 1-osma-2-azacyclopent-3-ene intermediate(D). [ABSTRACT FROM AUTHOR]

The article focuses on the formation of cyclobutylidine complexes from osmium and ruthenium through the ring expansion of alkylidenecyclopropanes. It mentions that new reaction transition pattern of metal complexes and alkylidenecyclopropane formed the derivatives of cyclobutylidene. It concludes that alkalidenecyclopropanes that contains chelation assistant undergo ring expansion to afford cyclobutylidene derivatives.