Tetracation salt

Tetracation Salts as Novel Cyanine-Cyanine Hybrid System... 

The synthesized tetracations (254+, 284+, and 314+), did not show the presumed multiple color changes during electrochemical reduction. However, these tetracation salts are highly stable in spite of their tetracationic structure. They exhibit multiple-electron transfer as a function of the substitution of the di(l-azulenyl)methylium units and significant color change during electrochemical reduction. 

When the tetracation salt 33c was prepared by chemical oxidation with NOBF, it showed five signals reflecting an apparent Cj structure in its NMR chemical shifts. In addition, the chemical shifts of DT rings correspond to DT rings in the tetracationic species and are quite similar to those of 4,5-benzo-1,3-dithiolium salt 34e" -BF4 . Thus, the simultaneous four-electron transfer process in 33e is attributed to a particular stabilization of 33c, whose central five-membered ring strongly contributes to the aromatic cyclopentadienide characteristic (Figure 8.15). The same interpretation can be applied to the redox behavior of 33a and 33b. 

For the central violene rc-system, we chose benzene with acetylene spacers for decreasing steric hindrance between the large cationic centers. Therefore, the tetracation 254 salt was designed as a first example for a hybrid with a cyanine unit at the both termini (27). As illustrated in Figure 22, tetracation 254 exemplifies a new hybrid system, which produces another cyanine substructure 252 by two-electron transfer. In this case, overall, four electron transfer should afford a fully neutralized species such as a neutral diradical. 

Carbocations having more than four cationic centers are rare species, and very few have been isolated as isolable salts. A tetrahedrally-arrayed tetracation, which was stable only at low temperature was generated by G. A. Olah et al. in 1995 (22). Recently, R. Rathore et al. prepared isolable tetra- and hexatrityl cations utilizing tetraphenylmethane and hexaphenylbenzene as platforms (25). Tetracation 254 is one of the new multi-charged methylium compounds with considerable high stability. 

The eight-atom systems provide a compelling illustration of the structural diversity of tellurium polycations. There are examples of (a) structural isomers of the monomeric dication Tcg, (b) a polymeric (Teg ) cation and (c) a tetracation Teg" . Unlike cyclo-Sg and -Seg , the Teg dication cannot be made by oxidising tellurium with MF5 (M = As or Sb) in liquid SO2. However, the reactions of (a) the tellurium subhalide Te3Cl2 with ReC at 200 °C and (b) tellurium with WCl6 at 180°C produce the salts Teg[MCl6] (w=l, M = Re ... 

Recently Diederich et al. tried to overcome the solubility problems by using modifications where the linear stearyl side chains are exchanged by branched ones [76]. Dionium salt 53 turned out to be an effective transport catalyst at physiological pH for all investigated compounds [AMP, CTP, 2, 3 -dideoxy-TTP (ddTTP), and 3 -azido-dTTP (AZTTP)] and significantly improved the rates achieved with 52. A chloroform solution of 53 extracts half an equivalent of ATP -, which indicates the formation of a neutral 2 1 complex. Analogously, bis(DABCO) tetracation 54 binds to one ATP molecule. However, the transport acceleration is about one order of magnitude smaller than that of 53 [77]. 

The first example of a stable and isolable salt of a tetracation, composed of four directly bonded cyclopropenylium rings, was synthesized by the direct reaction of l,2-bis(diisopropyl-amino)-3-lithiocyclopropenylium perchlorate (10) with tetrachlorocyclopropene. Apparently this tetracation is stabilized by the resonance contribution from the structures containing both the triafulvene- and radialene-type -conjugated systems. ... 

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