η-Coordinated ruthenabenzenes from three-component assembly on a diruthenium μ-allenyl scaffold.

The room temperature reactions with internal alkynes, RCCR, of the μ-allenyl acetonitrile complex [RuCp(CO)(NCMe){μ-η:η-CHCCMe}]BF (1-NCMe), freshly prepared from the tricarbonyl precursor [RuCp(CO){μ-η:η-CHCCMe}]BF, 1, proceeded with alkyne insertion into ruthenium-allenyl bond and allenyl-CO coupling, affording compounds [RuCp(CO){μ-η:η-C(R)C(R)CHC(CMeCH)C(OH)}]BF (R = Ph, 2; R = COMe, 3; R = COEt, 4) in 83-94% yields. Deprotonation of 2-4 by triethylamine gave [RuCp(CO){μ-η:η-C(R)C(R)CHC(CMeCH)C(O)}] (R = Ph, 5; R = COMe, 6; R = COEt, 7) in 75-88% yields, and 2-4 could be recovered upon HBF·EtO addition to 5-7. All the products, 2-7, were fully characterized by elemental analysis, IR and multinuclear NMR spectroscopy. The structure of 2 was ascertained by single crystal X-ray diffraction and investigated by DFT calculations, revealing a six-membered ruthenacycle with Shannon aromaticity index in line with related compounds. The formation of ruthenium-coordinated ruthenabenzenes from a preexistent diruthenium scaffold is a versatile but underdeveloped approach exploiting cooperative effects typical of a dimetallic core.