Deltate oxocarbons

As an illustrative example taken from the current literature, consider the variation of C-C and C-O bond lengths in the deltate species CsO2- held within a dinuclear organometallic uranium(IV) complex. In a remarkable synthesis, this cyclic aromatic oxocarbon dianion is generated by the metal-mediated reductive cyclotrimerization of carbon monoxide, as indicated in the reaction scheme... 

The rhodizonate dianion C60g (Fig. 20.4.19) is a member of a series of planar monocyclic oxocarbon dianions C 0 (n = 3, deltate n = 4, squarate n = 5, croconate n = 6 rhodizonate) which have been recognized as nonbenzenoid aromatic compounds. However, this six-membered ring species... 

The most dramatic synthetic achievement with cyclobutenediones is the synthesis of deltic acid derivatives. As illustrated below, photolysis43 of diethyl squarate (16 d) yielded, among other products, diethyl debate (21). The bis-trimethylsilyl ester (16 e) of squaric acid similarly furnished a deltate ester which was successfully hydrolysed to deltic acid itself (22), the lowest member of the series of oxocarbon acids48). 

Oxocarbons are organic compounds consisting only of carbon and oxygen in their neutral state, they exist as diacids, and their anions possess the general formula where n>2 and generally =3-6. Oxocarbons have been the focus of research since the nineteenth century, when the croconate (3, w = 5) and rhodi-zonate (4, n = 6) anions were first synthesized [1]. The squarate anion (2, w = 4) was later synthesized by Cohen et al. in 1959, and the oxocarbon deltate anion (1, K = 3) was synthesized by Eggerding and West in 1976 (Figure 5.1) [2]. 

Figure 53 The most common pseudo-oxocarbons derived from deltate 1 tris(cyanoimino)deltate 7, tris(dicyanomethylene)deltate 8, and tritiodeltate 9.

---