Clusters containing compounds, oxidation

A nonstandard synthesis of the first uranium cluster containing an isopolyoxo-metalate core was reported recently [310b], Reduction of [Cp UCl2] (Cp7 — 1,2,4-/-Bu3C5H2) with two equivalents of KC8 in THF, followed by an addition of two equivalents of pyridine N-oxide, was conducted in an attempt to produce the organometallic dioxo species [Cp7U02]. However, the cluster compound [Cp (bipy)2][U6013] was isolated instead as the main product (54% yield) from this reaction. 

These functionalized clusters contain a maximum number of ferrocene units anchored to the molecular framework and may represent model compounds for the fixation of organometallic fragments on a lanthanide oxide surface (Baskar and Roesky, 2006). 

In 22, whose structure is illustrated in Figure 3-60, the Ti atoms are formally in the oxidation state +3 (d configuration) and the cluster contains 52 valence electrons, 8 electrons less than found in many other heterocubane clusters. [91] Admittedly, other compounds are known whose electron counts fall short of this normal value and still others which exceed it. Extended Huckel calculations predict a Ti4 tetrahedron having D2d symmetry with four longer and two shorter Ti-Ti bonds for this type of structure with 52 valence electrons. [92, 93] Indeed, 22 contains two shorter Ti-Ti distances of 268.6(2) pm and four longer distances of 277.2-278.5(2) pm. 

---