Heavy ketones stability

Tetra- and penta-coordinate carbon-substituted heavy ketones stabilized by the coordination of nitrogen atoms... 

Table 4 shows the structural and spectral data of tetra- and pentacoordinate heavy ketones stabilized by the intramolecular coordination of nitrogen... 

The successful synthesis and isolation of a series of heavy ketones (r r2M = X M = Si, Ge, Sn, Pb X = S, Se, Te) using kinetic stabilization (vide infra) and the remarkable progress in the field of theoretical calculations prompted chemists to perform computational calculations on the a and it bond energies as well as on the single and double bond lengths of H2M=X at the higher level of theory.14... 

On the other hand, the calculation for the relative stabilities of H2Si=S shows that the silanethione form (H2Si=S, 0.0 kcal mol-1) is more stable than both s-cis-HSiSH (12.0 kcal moP1) and s-trans-HSiSH (9.3 kcal moP1) isomers.12 Thus, the relative stability of heavy ketones to their carbene type isomers is considerably influenced by the combination of the Group 14 and Group 16 elements. 

A variety of preparation methods are known for transient germanium-chalcogen double bond species some of them seemed to be useful also for the synthesis of kinetically stabilized systems. Indeed, the reaction of a germylene with an appropriate chalcogen source was found to be one of the most versatile and general methods for the synthesis of stable germanium-containing heavy ketones (Scheme 21). 

In view of these situations, synthesis and isolation of a kinetically stabilized germanetellone are significant not only for clarifying the character of the Ge-Te double bond by itself but also for elucidating the properties of germanium-containing heavy ketones systematically. 

Therefore, the elucidation of the intrinsic structural parameters of heavy ketones has to be done with kinetically stabilized systems. Most of the heavy ketones synthesized by steric protection with the Tbt group have provided single crystals suitable for X-ray structural analysis. The results for silanethione 38, germanethione 71b, germaneselones 75, 84, germanetellones 77,85, and stannaneselone 127, are summarized in Table III. 

In Table IV are listed characteristic visible absorptions observed for the heavy ketones kinetically stabilized by Tbt group. 

In contrast to the considerable thermal stability of the isolated heavy ketones of silicon, germanium, and tin, a plumbanethione behaves differently. When stable... 

The method (i) can be applied to the synthesis of almost all heavy ketones (Tables 3-5). Silanethiones and a silaneselone stabilized by the coordination of a nitrogen group have been synthesized by the method (ii) (Table 4). The method (iii) is effective to the synthesis of kinetically stabilized tricoordinate heavy ketones, although it cannot be applied to the synthesis of double-bond compounds between heavier group 14 elements and tellurium due to the instability of polytellurides (Table 3). The method (iv) can be used only when the unique dilithiometallanes can be generated (Table 3). The synthesis of heavy ketones by the method (v) demands the isolation of the corresponding heavy acyl chlorides as stable compounds (Table 5). 

On the other hand, an electronically stabilized heavy ketone by the coordination of the nitrogen atom shows extremely low reactivity. It does not react with phosphanes, phosphates, ketones, epoxides, Mel, HC1, etc., although it undergoes methanolysis and hydrolysis (Scheme 21).168... 

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