Distannene

Disiloxane, tetramesityl-, 3,206 Disproportionation iridium catalysts, 4,1159 Dissolution nuclear fuels, 6, 927 Distannene, 3,217 Distannoxane, 1,3-dichloro-, 3,207 Distibine, tetraphenyl-, 2,1008 Distibines, 2,1008 Disulfido ligands metal complexes, 2,531-540, 553 bonding, 2, 539 electron transfer, 2, 537 intramolecular redox reactions, 2,537 reactions, 2, 537... 

The tin homolog of 49, distannene anion radical 50, was successfully prepared employing the same synthetic protocol the direct reduction of distannene (t-Bu2MeSi)2Sn=Sn(SiMer-Bu2)2 with potassium mirror in THF in the presence of [2.2.2]cryptand (Scheme 2.38). ... 

Compounds containing doubly bonded tin are highly colored due to a strong absorption in the visible spectrum (77-77 transition of the double bond). The extinction coefficients of the distannene [[(Me3Si)2CH]2Sn]2 (entry 3, Table VII) were found to depend on concentration and temperature5 that for the absorption at 332 nm increases with dilution while that for the 495 nm absorption decreases. This suggests that the absorptions arise from two different species, presumably the distannene and the stannylene. By comparison with the other absorption maxima of doubly bonded tin compounds, the absorption at 495 nm is probably that of the distannene. 

The low-temperature photolysis of hexakis(2,4,6-triisopropylphenyl) cyclotristannane leads quantitatively to the corresponding distannene (Eq. 30).90 The distannene was found to be in equilibrium with the cyclotristannane over a wide range of temperatures. The simplest explanation for this is that the stannylene is formed as an intermediate from either the cyclotristannane or the distannene, but quickly adds to the distannene or dimerizes. This equilibrium can be followed by ll9Sn NMR spectroscopy at elevated temperatures.96... 

The synthesis of doubly bonded tin compounds by the coupling of stannylenes, however useful, is limited by the need for a stable stannylene and often a second divalent species (for example, a carbene or isonitrile). The simplest example of this reaction is the formation of tetrakis[bis(tri-methylsilyl)methyl]distannene from two molecules of the corresponding stannylene,83 with which it is in equilibrium in solution as evidenced by NMR spectroscopy.91... 

Distannenes are in equilibrium with the corresponding stannylenes in solution therefore, reaction with alkynes can lead either to stannacyclo-propene or l,2-distannacyclobut-3-ene derivatives. Reaction of tetra-... 

Whereas several reports of doubly bonded tin compounds being sensitive to decomposition in air are to be found in the literature, there is only one instance of a controlled oxidation. Tetrakis[bis(trimethylsilyl)methyl]-distannene was treated with Me3NO to give the corresponding cyclo-1,3-distannoxane."2... 

Tin chemical shifts run broadly parallel to those of silicon tin can readily increase its coordination number to five or six. A few stable organostannyl-enes R2Sn and distannenes R2Sn=SnR2 are known. 

Similar reactions were performed earlier photochemically from 76, which can be converted into tetrakis(2,4,6-triisopropylphenyl)distannene. 

Similar to the Ge2H4, in Sn2H4 the four main structures are true minima while planar distannene is a saddle point. 

New distannenes linked through phenylene, biphenylene, or thiophene spacers have been prepared by reactions of the type shown in Equation (175) (Cp =pentamethylcyclopentadienyl),541 and the ansa-stannocene (Equation (176)) is formed in low yield when dimethylfulvene reacts with tin vapor.542... 

The NMR spectra of the two-coordinate stannylenes in solution show values of Sn ranging from about 1150 (e.g., in ArSnl) to 3750 (in (Ar3Sn)Sn ), with a large anisotropy. The stannylenes behave as Lewis acids, for example, in the three- or four-coordinate complexes (e.g., 78, 79, and 80), which are formed when the molecule carries an intramolecular ligand, and as Lewis bases, particularly in complexing to transition metals (e.g., 81, 82, and 83). The dimerization of stannylenes to give distannenes can be regarded as a result of this amphoteric character (Equation (179)). 

Most stannylenes, R2Sn , that are two coordinate in solution are in equilibrium with, and separate out as, the distannenes, R2Sn=SnR2. These are the distanna analogs of the alkenes, R2C=CR2, but the nature of the Sn=Sn bond is different from that of the C=C bond, and can be represented by the mutual coordination of the electron pair in the 5sp2 orbital of one stannylene unit into the vacant 5p orbital of the second stannylene unit, as illustrated in Equation (179). 5 The molecules are usually trans-bent (9 = 9 = ca. 40°, 0 = 0°), but are easily distorted, and the... 

A similar reaction62 between silylene 71 and stannylene [(Me3Si)2N]2Sn does not afford the distannene analogous to digermene 70, but a hydridodi-silystannane.62... 

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