Ketones heavy—

Reaction of cyclic tetrasulfido complexes of heavier group 14 elements bearing bulky substituents such as Tbt(Ar)MS4 (M=Si, Ar=Tip M=Ge, Ar=Tip M=Sn, Ar=Ditp) with 3 equivalents of phosphines afforded the successful isolation of the first stable double-bonded compounds between heavier group 14 elements and sulfur atom (heavy ketones), Tbt(Ar)M=S, accompanied by the quantitative formation of the corresponding phosphine sulfides (Scheme 40) [13, 15, 112, 113]. On the other hand, their lead an-... 

Although some review articles are now available on the synthesis of heavy ketones," they are restricted to dealing with some selected elements, especially silicon and germanium. We delineate here a more general account of the whole chemistry of stable double bonds between heavier Group 14 and Group 16 elements [i.e., RR M=X (M = Si, Ge, Sn, Pb X = O, S, Se, Te)]. 

B. Theoretical Calculation of the Bond Energies and Bond Lengths of Heavy Ketones... 

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... 

The results are shown in Table I, from which one can see the following points of interest pertinent to the intrinsic character of the heavy ketones. 

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. 

Thus, the synthetic route via dilithiosilane 62 should be noted as an alternative synthetic approach to the heavy ketones. To date, the isolation of silanetellone 60 as stable crystals has not been achieved yet, though 60 was found to be stable in solution at ambient temperature. 

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. 

In addition to the extensive studies on Ge-containing heavy ketones, there have been reported several examples of stable germanium-chalcogen double... 

It should be very important to reveal the structural features of heavy ketones and to make a systematic comparison with those of a carbonyl compound such as the bond shortening and the trigonal planar geometry which result from the sp2 hybridization between the carbon and oxygen atoms. 

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. 

Although the high reactivity of metal-chalcogen double bonds of isolated heavy ketones is somewhat suppressed by the steric protecting groups, Tbt-substituted heavy ketones allow the examination of their intermolecular reactions with relatively small substrates. The most important feature in the reactivity of a carbonyl functionality is reversibility in reactions across its carbon-oxygen double bond (addition-elimination mechanism via a tetracoordinate intermediate) as is observed, for example, in reactions with water and alcohols. The energetic basis... 

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

Remarkable progress in the chemistry of main group elements enabled us to synthesize and isolate heavy ketones which are capable of existence as stable species if their highly reactive M=X bond is adequately protected toward dimerization... 

The Compounds Between Si, Ge and Sn and Chalcogens (S, Se, and Te) Having Both a Single Bond and a Double Bond (Heavy Ketones)... 

Double-bond compounds between heavier group 14 and 16 elements (heavy ketones) undergo ready addition reactions with various reagents to give the corresponding single-bond compounds. The details of the reactivities are described in the next section (Schemes 20 and 21). 

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