Stannyl structure

The development of sophisticated new experimental techniques during the last decade has made possible the isolation of stable representatives of the free radical species featuring an nnpaired electron on the heavier group 14 elements, that is, silyl, germyl, and stannyl radicals. This great progress in the isolation of the stable radicals opens unprecedented possibilities for their structural characterization in the crystalline form, which in tnrn enables the direct comparison of the fundamental differences and similarities between the solntion and solid state strnctnres of the free radical species. " ... 

The reduction of the stannyl radical (t-Bu2MeSi)3Sn with alkali metals produces a variety of structural modifications depending on the solvent used (Scheme 2.55). Thus, in nonpolar heptane, a dimeric stannyllithium species [58c Li ]2 (E = Sn) was formed, whereas in more polar benzene, the monomeric pyramidal structure 58c [Ti -Li (C6H5)] was produced. In the latter compound the Li+ ion was covalently bonded to the anionic Sn atom being at the same time n -coordinated to the benzene ring. A similar monomeric pyramidal CIP 58c [Li (thf)2] was prepared by reduction in polar THE the addition of [2.2.2]cryptand to this compound resulted in the isolation of the free stannyl anion 58c K+([2.2.2]cryptand), in which the ion lacked its bonding to the Sn atom. ... 

Previous syntheses An example of this point can be recognized by examination of one known synthesis of thienobenzazepines (Scheme 6.1). This synthetic route involves a key palladinm-catalyzed cross-conpling of stannyl intermediate 3, prepared by method of Gronowitz et al., with 2-nitrobenzyl bromide. Acetal deprotection and reductive cyclization afforded the desired thienobenzazepine tricycle 4. In support of structure activity relationship studies, this intermediate was conveniently acylated with varions acyl chlorides to yield several biologically active componnds of structure type 5. While this synthetic approach does access intermediate 4 in relatively few synthetic transformations for stractnre activity relationship studies, this route is seemingly nnattractive for preparative scale requiring stoichiometric amounts of potentially toxic metals that are generally difficult to remove and present costly purification problems at the end of the synthesis. 

Substitution of the dimethylsilyl group by bis(tert-butyl)-stannyl does not change the structure in solution, e.g. 33 is found to be monomeric. A very interesting dimer is 26. In contrast to the centrosymmetrical dimer of 1 (C-Symmetry), 26 has a twofold axis (C2, see Fig. 9). This special structure may be due to intramolecular Lewis acid-base interactions between the boron and nitrogen atoms 39). Nevertheless,... 

A bis(stannyl)bis(phosphine)palladium complex has a twisted square planar structure and shows facile unimolecular twist-rotation.170... 

Cross-coupling to form carbon heteroatom bonds occurs by oxidative addition of an organic halide, generation of an aryl- or vinylpalladium amido, alkoxo, tholato, phosphido, silyl, stannyl, germyl, or boryl complex, and reductive elimination (Scheme 2). The relative rates and thermodynamics of the individual steps and the precise structure of the intermediates depend on the substrate and catalyst. A full discussion of the mechanism for each type of substrate and each catalyst is beyond the scope of this review. However, a series of reviews and primary literature has begun to provide information on the overall catalytic process.18,19,22,23,77,186... 

Similarly, the (—)-menthyl substituted stannyl bromides 51 and 53, whose diastereomeric purity was confirmed by single crystal X-ray structure analysis, were found to slowly equilibrate to nearly 1 1 mixtures of diastereoisomers on standing in solution (equation 13)28. 

The structure of free radical 85 produced by dissociation of a stannyl benzopinacolate, was investigated by ESR spectroscopy and confirmed by ESR simulation. Free radical 85 is a good source for stannyl free radicals, as shown in reaction 10262. 

Hi. Pentacoordinated complexes. The structures of tris(stannyl)amines could not be determined exactly. On the one hand, IR spectroscopic investigations indicate a pyramidal... 

The heteroarylstannanes bear the same relation to the arylstannanes as do the heteroarenes to the arenes, with the extra factor that the Lewis acidity of the stannyl group may cause the heteroarylstannanes to have self-associated structures. 

The stannyl cation in zwitterion 80 is only stabilized by side-on coordination with the remote C = C triple bond. The crystal structure of 80 revealed a pyramidalized tin center with the sum of valence angles of 351.1° (see Table XIV). The coordination of the tin atom to the C = C triple bond is unsymmetrical and the SnC distances... 

Nitrile complexes of stannyl cations with a stoichiometry of staimyl cation/nitrile = 1 1 are described in the literature however no structural or spectroscopic data are given. 

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