η6-Coordinated ruthenabenzenes from three-component assembly on a diruthenium μ-allenyl scaffold

Abstract

The room temperature reactions with internal alkynes, RCCR, of the μ-allenyl acetonitrile complex [Ru₂Cp₂(CO)₂(NCMe){μ–η¹:η²-C¹HC²C³Me₂}]BF₄ (1-NCMe), freshly prepared from the tricarbonyl precursor [Ru₂Cp₂(CO)₃{μ–η¹:η²-C¹HC²C³Me₂}]BF₄, 1, proceeded with alkyne insertion into ruthenium-allenyl bond and allenyl-CO coupling, affording compounds [Ru₂Cp₂(CO)₂{μ–η²:η⁵-C(R)C(R)C¹HC²(C³MeCH₂)C(OH)}]BF₄ (R = Ph, 2; R = CO₂Me, 3; R = CO₂Et, 4) in 83–94% yields. Deprotonation of 2–4 by triethylamine gave [Ru₂Cp₂(CO)₂{μ–η²:η⁵-C(R)C(R)CHC(CMeCH₂)C(O)}] (R = Ph, 5; R = CO₂Me, 6; R = CO₂Et, 7) in 75–88% yields, and 2–4 could be recovered upon HBF₄·Et₂O 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.