Tricarbon monoxide

Abstract In this chapter, aspects related to the synthesis, structure, and reactivity of metallacumulenes [M]=C(=C) =CR R ( = 1, 3, 5) in which one or both substituents R /R are heteroatomic 7t-donor groups (NR2, OR, SR, SeR) are discussed. The coordination chemistry of related heteroatom-cumulated ligands, i.e., phosphonioacetylides and tricarbon monoxide, is also presented. 

Keywords Allenylidene ligands Carbene complexes Cumulenylidene ligands Phosphonioacetylide ligands Tricarbon monoxide... 

Fig. 3 Mesomeric forms of metal complexes derived from phosphonioacetylides and tricarbon monoxide...

Carbon monoxide carbo-mers [5-7], i.e., monoxides of linear odd carbon chains longer than one C 0 n = 3, 5, 7, 9...), are highly reactive molecules suggested as potential constituents of interstellar and circumstellar gas clouds. Considerations based on MO theory and quantum chemical calculations indicate that, similar to pure odd carbon chains, all these heterocumulenes are singlet carbenes in the ground state [93]. Since its matrix isolation in 1971 [94] and its synthesis in gas phase in 1983 [95], the simplest member of this family, i.e., tricarbon monoxide C3O, has been extensively studied both experimentally and theoretically [96-102], and its interstellar presence fully confirmed [103]. In particular, on the basis of... 

On the basis of the above-mentioned calculations it seems that coordination chemistry is a viable alternative to stabilize this heterocumulene. However, the experimental access to metal complexes containing the tricarbon monoxide ligand remains a challenge. Thus, to date, the coordination chemistry of C3O is confined to [Cr(=C=C=C=0)(C0)s] (89), obtained by treatment of [n-Bu4N] [CrI(CO)5] with the silver acetylide derived of sodium propiolate in the presence of Ag" (Scheme 28) [105]. Reaction of the presumed Tt-alkyne intermediate complex 88 with thiophosgene generates the heterocumulene 89. Neither structural nor reactivity studies were undertaken with this complex. 

Aspects related to the chemistry of the heteroatom-terminated -carbon ligands R3P C=C and C3O have also been discussed. Thus, upon coordination, the former seem to present a partial cumulenic character [M]=C=C=PR3, but little is known about the chemical behavior of this coordinated unit. In the case of the tricarbon monoxide ligand, recent theoretical calculations have shown that coordination chemistry could be an alternative to stabilize this highly unstable heterocumulene. However, the access to metal complexes containing the C3O unit represents an exciting experimental challenge for the near future. 

Neutralization of the ionic products of these reactions, by proton transfer or recombination with electrons, can establish tricarbon monoxide, C=C=C=0, and tricarbon monosulphide C=0=C=S (24). 

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