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 Ti2(µ:?5,?5-Pn†)2 (Pn† = C8H4(1,4-SiiPr3)2) 1 with carbon suboxide (O=C=C=C=O, C3O2) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti2(µ:?5,?5-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:?5,?5-Pn†)2 (?2-C3O2)], as the first structurally authenticated complex of carbon suboxide.