η 6 -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 [Ru 2 Cp 2 (CO) 2 (NCMe){μ-η 1 :η 2 -C 1 HC 2 C 3 Me 2 }]BF 4 (1-NCMe), freshly prepared from the tricarbonyl precursor [Ru 2 Cp 2 (CO) 3 {μ-η 1 :η 2 -C 1 HC 2 C 3 Me 2 }]BF 4 , 1, proceeded with alkyne insertion into ruthenium-allenyl bond and allenyl-CO coupling, affording compounds [Ru 2 Cp 2 (CO) 2 {μ-η 2 :η 5 -C(R)C(R)C 1 HC 2 (C 3 MeCH 2 )C(OH)}]BF 4 (R = Ph, 2; R = CO 2 Me, 3; R = CO 2 Et, 4) in 83-94% yields. Deprotonation of 2-4 by triethylamine gave [Ru 2 Cp 2 (CO) 2 {μ-η 2 :η 5 -C(R)C(R)CHC(CMeCH 2 )C(O)}] (R = Ph, 5; R = CO 2 Me, 6; R = CO 2 Et, 7) in 75-88% yields, and 2-4 could be recovered upon HBF 4 ·Et 2 O 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.