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

The reaction of the syn-bimetallic bis(pentalene)dititanium complex Ti(2)(μ:η(5),η(5)-Pn(†))(2) (Pn(†) = C(8)H(4)(1,4-Si(i)Pr(3))(2)) 1 with carbon suboxide (O[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]O, C(3)O(2)) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti(2)(μ:η(5),η(5)-Pn(†))(2)}{μ-C(9)O(6)}]. The trimeric bridging C(9)O(6) 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 C(3)O(2) 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 C(3)O(2). Indeed, the carefully controlled reaction of 1 with C(3)O(2) affords [Ti(2)(μ:η(5),η(5)-Pn(†))(2) (η(2)-C(3)O(2))], as the first structurally authenticated complex of carbon suboxide.