The reaction of 1a  with [Ru]Cl ([Ru]=CpRu(PPh3)2) yields 2a  and the dinuclear bisvinylidene complex 3a  . The structural assignment of 3a   is based on a single crystal X-ray diffraction analysis confirming formation of the dinuclear bisvinylidene complex by an intermolecular dehydration. Presumably, the alkyne moiety is activated by [Ru]Cl electrophilically to give the monosubstituted vinylidene complex. Direct coupling of the aldehyde carbonyl group with C� of the vinylidene moiety leads to 2a  , which undergoes a further intermolecular dehydration to afford 3a . The dehydration is accelerated upon heating to 40�C.Treatment of 1b  with [Ru]Cl affords two mononuclear complexes 2b  and 5b . No dinuclear vinylidene complex is obtained. An intramolecular dehydration step takes place in the case of 2b  . Presence of the characteristic resonance for the vinylidene Ca in the 13C NMR spectrum and the FAB mass spectrum are both consistent with complex 2b  . In the 1H NMR spectrum of 5b  , two singlet resonances at d 5.70 and 4.93 are assigned to two olefinic protons in 5b  . The solid state structure of 5b  is also determined by a single crystal X-ray diffraction analysis. The intramolecular dehydration is revealed by the double bond with a distance of 1.328(6)�.

Intermolecular dehydration reactions in ruthenium vinylidene complexes

248th National Meeting (2014)

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