Trimerisation of carbon suboxide at a di-titanium centre to form a pyrone ring system

Abstract

The reaction of the syn-bimetallic bis(pentalene)dititanium complex Ti₂(μ:η⁵,η⁵-Pn^†)₂ (Pn^† = C₈H₄(1,4-SiⁱPr₃)₂) 1 with carbon suboxide (OCCCO, C₃O₂) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti₂(μ:η⁵,η⁵-Pn^†)₂}{μ-C₉O₆}]. The trimeric bridging C₉O₆ unit in the latter contains a 4-pyrone core, a key feature of both the hexamer and octamer of carbon suboxide which are formed in the body from trace amounts of C₃O₂ and are, for example, potent inhibitors of Na⁺/K⁺-ATP-ase. The mechanism of this reaction has been studied in detail by DFT computational studies, which also suggest that the reaction proceeds via the initial formation of a mono-adduct of 1 with C₃O₂. Indeed, the carefully controlled reaction of 1 with C₃O₂ affords [Ti₂(μ:η⁵,η⁵-Pn^†)₂ (η²-C₃O₂)], as the first structurally authenticated complex of carbon suboxide.