Acetyl dication

Tetrakis(dimethylamino)ethylene dication 224 Acetyl dication 224... 

Attempts were made to formylate and acetylate (230) but decomposition was extensive and no product could be isolated. Treatment of a solution of (230) in benzene with bromine vapor gave a stable blue cyclazine cation bromide, which was converted on further treatment with bromine into a greenish brown dication dibromide. 

Protonation and diprotonation of formic acid and acetic acid have also been studied theoretically (HF and MP2/6-312G levels).553,558 Both cations can be visualized as the donor-acceptor complex of H20 and diprotonated carbon monoxide (HCOH2+) and protonated acetyl cation (CHaCOH23"), respectively. Both dications 277 and 278 are characterized by a long C-OH2 bond and a shorter C-OH bond, suggesting that the latter retains substantial double-bond character. 

Cation radicals containing three electrons in the field of four atoms or anion radicals with five electrons retained by four atoms represent a special group of multicentered ion radicals. Thus, nonclassical, cyclically delocalized 3e/4C cation radicals and 2e/4C (dication) radicals of substituted cyclobutadienes are known (Allen and Tidwell 2001). The 3e/4N cation radical and the 5e/4N anion radical depicted in Scheme 3-27 have also been discovered (Exner et al. 1998, 1999, 2000). The reactions in Scheme 3-27 illustrate such species as well as the corresponding dianion and acetylated products of the latter. 

This is reasonably close to the experimentally determined value of AFF = 11.1 kcal/mol for the superelectrophilic cyclization of 62 (eq 12). Another computational study showed that the energy barriers dramatically decrease for the electrocyclization when the monocations are protonated to form superelectrophiles. In the case of 63, cyclization provides the acetyl-substituted fluorene in 70% yield from CF3SO3H (Scheme 5). At the B3LYP/6-31 level of theory, dication 64 is estimated to have a cyclization barrier to fluorene of 8.5 kcal/mol, compared to a value of 25 kcal/mol for the cyclization of monocation 65. 

The diprotonated species (179) is then observed slowly cleaving to the acetyl cation (181) in a process thought to involve dication (180). A number of /3-carbenium-acyl dications have also been studied by experiment and theory. Reaction of the 4-chloro-butanoyl cation (182) in superacidic HF-SbFs or HSOsF-SbFs leads to formation of the 2-butenoyl cation (185, eq 56).68... 

Vanadyl (acac) 2 is a square pyramidal complex of two molecules of the enolate of acac acetyl acetone, pentan-2,4-dione) and the vanadyl (V=0) dication. It can easily accept another ligand to form an octahedral complex so there is... 

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