Osmium Models of Intermediates Involved in Catalytic Reactions of Alkylidenecyclopropanes

The complex [OsCp­{κ3-P,C,C-PiPr2[C­(CH3)CH2]}­(CH3CN)]­PF6 (1) reacts with (2-pyridyl)­methylenecyclopropane, at room temperature, to give initially the cyclobutylidene derivative [Os­(η5-C5H5)­(CCH2CH2CH-o-C5H4N)­{PiPr2[C­(Me)CH2]}]­PF6 (2), as a result of the ring expansion of the alkylidenecyclopropane unit. Over time complex 2 rearranges into the cyclobutene derivative [Os­(η5-C5H5)­{η2-C­(CHCH2CH2)-o-C5H4N}­{PiPr2[C­(Me)CH2]}]­PF6 (3). The reaction of 1 with (2-pyridyl)­methylenecyclopropane at room temperature also 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 reaction at 45 °C. This osmacyclopentane results from the C–C coupling of the isopropenyl substituent of the phosphine ligand and the organic substrate. In acetone at 75 °C, the reaction of 1 with (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 of one of the C­(sp2)–C­(sp3) bonds of the cyclopropane unit of the substrate to the osmium atom, along with 6, a diastereomer of 4. Complexes 3–5 have been characterized by X-ray diffraction analysis. DFT calculations suggest that all of the reaction products are derived from a common key 1-osma-2-azacyclopent-3-ene intermediate (D).