Indicator Chelate-Forming Chemical Structures

This group demonstrated that both dinuclear complexes 38 and 40 exhibit a remarkably better activity than the mononuclear complexes 39 and 41 at equivalent metal-catalyst concentrations (Table 22.19). The reaction was evaluated/tested against the Monsanto catalyst [Rhl2(CO)2l used in industrial processes, which is formed in situ from [ RhCl(CO)2 2]. In the carbonylation of methanol, 38 outperformed the Monsanto catalyst, whereas 40 demonstrated a similar turnover number. The exceptionally good reactivity could be explained by the formation of thermally stable metal chelate complexes, due to the ort/ o-carborane(12) backbone. NMR spectra of the residue at the end of the reaction showed a high content of phosphine bound to rhodium with a retained bimetallic structure, indicated by the chemical shifts and coupling constants. 

Comparison of the properties of metal alkoxides with their structures permits a conclusion that the polymeric nature does not always lead to chemical inertness. The major role appears to be played by the nature of the M-OR bonding. Solubility in alcohols and liquid ammonia of the methoxides of alkaline and alkaline earth metals and that in hydrocarbons ofthe isopropoxides of K, Rb, Cs (isostructural with the corresponding methoxides), and also M(OC2H4OMe)n, M = Pb, Bi indicates the easy oligomerization due to solvation or chelation. At the same time the methoxides and ethoxides of Al, Cr, Fe, and so on, forming the strongest covalent bonds in the [MOs/6] octahedra (and not prone to solvation in alcohols), appear almost inert. They can be dissolved only due to complexation or partial destruction with formation ofoxobridges. 

The structure of the adsorbate systems formed by mercaptobenzothiazole and analogue molecules on CdS (1010) surface was studied quantum chemically using density functional theory [57]. Preliminary calculations of the free adsorptive molecules indicate an energetic preference of their thione form compared to the thiol form. For the anions of the adsorptive molecules, the role of the endocyclic nitrogen and the exocychc sulfur as possible donor atoms was examined by means of known chelate complexes. Geometry optimizations showed that the structure of the adsorbate systems is dominated by the formation of two coordinative bonds from the donor atoms of the adsorptive anions to two adjacent Cd atoms of the surface. It showed that the molecular plane of the adsorptives is tilted with respect to the normal of the crystal face. They have shown that the tilt angle is mainly determined by the tendency of the surface Cd atoms to continue the tetrahedral coordination from the bulk [57]. 

Tautomerism of benzothiazoles continues to attract attention. 2-Phenacyl-benzothiazole (13), for example, has been shown by i.r., n.m.r., and chemical evidence to exist in three tautomeric forms. The spectroscopic properties (u.v., i.r.) of compounds (12 Ar = Ph, p-MeC H4, or P-CIC6H4) indicate that they exist as chelate ring structures. N.m.r. spectroscopy has been used to study... 

---