Stannylenes cyclic

A redox process also occurs in the reaction of selenium diimides with bis(amino)stannylenes. Eor example, the cyclic stannylene McaSi)//-N Bu)2Su reacts in a 1 1 molar ratio with BuN=Sc=N Bu to give a spirocyclic tin complex, which reacts with a second equivalent of the stannylene to generate a Sn-Sn bond [d(Sn-Sn) = 2.85 A, /( Sn- Sn) = 13,865 Hz)] (Scheme 10.6). ... 

The use of the second type of compound, in which the cyclic stannylene 1 can be considered as trihapto-coordinating, results in the same reaction 47. We have studied the mechanism of this reaction and found that the primary step is an acid-base interaction between the stannylene and the amine (Eq. (50)). It is very difficult to prove that the adduct 83 is formed in solution because of very rapid exchange of base molecules at the tin atom. We succeeded in preparing the adduct at low temperature (—70 °C)177). 

The first organophosphorus betaines ( + )E15-C-E14( ) (31) with the negative charge on the atom of the Group 14 element were prepared by Veith and Huch69 in the reaction of cyclic stannylene (30) with phosphorus ylides (Scheme 15). 

The following set of oxides provides a useful series of six-rings for comparison of substituent effects. Where R = R and is bulky, six-membered rings are planar (6a) as in (f-Bu2GeO)3 formed above65 and the Sn analogues66 with R = f-Bu or r-amyl. The stannylene Ar(f)2Sn, discussed later, readily forms a similar cyclic oxide67 and use of a... 

Compound 64, after reaction with 2,3-dimethylbutadiene, produces a cyclic stannylene 66 in an oxidative addition step104. 

Cyclic stannanes can be generated by reaction of stannylenes with alkynes112. For example, bis[bis(trimethylsilyl)methyl]tin reacts with cyclooctyne to provide A1,18-9,10-(distanna-9,9,10,10-tetrakis[bis(trimethylsilyl)methyl])bicyclo[6,2,0]-decene, 69. This reaction is a typical oxidative addition on stannylenes. 

Cyclic stannylenes formed from activated tin and a-dicarbonyl compounds undergo a specific addition reaction (Scheme 34) with aldehydes to give ketodiols in high yields <83CL1825). 

The other important type of reaction leading to the formation of two bonds between a metal and four-atom fragment is addition of carbenoids, i.e. germylenes and stannylenes, to a-dicarbonyl and related compounds. The process can be classified as redox (4 + 1) cycloaddition since the dicarbonyl fragment is reduced while the carbenoid is oxidized. Formally the simplest example of such reactions is the interaction of methylglyoxal with activated tin metal to give a cyclic stannylene, Sn(II) enediolate (see Scheme 34) <83CL1825>. 

In 1974, David18 reported that cyclic stannylenes (97), formed by reaction of 1,2-diols (96) with dibutyltin oxide— -Bu2SnO—in refluxing benzene with azeotropic elimination of water, reacted with Br2 in solution at room temperature at titrating speed, leading to a-hydroxyketones (98). 

In this tetrol, a single secondary alcohol is oxidized with 88% yield thanks to the formation of the most stable cyclic stannylene intermediate by the regioselective reaction of BU2S11O with one of the 1,2-diol moieties in the molecule. 

Cyclic diazastannylenes, Sn(NBu-f)2SiMe2, afford a series of interesting stannylene complexes. They insert into the Fe—Me bond of Cp(CO)2FeMe, to form the corresponding stannylene complex 101101. 

A reaction of the four-membered cyclic stannylene with nickelocene gave compound 102 with a Sn—Ni—Sn fragment313. 

With toluene solvated nickel atoms, the stannylenes Sn[CH(SiMe3)2]2 and Sn(CgH-2-f-Bu-3,4, 5-Me3)2 at —78 °C form homoleptic stannylene analogs of nickel tetracarbonyl, Ni(SnR2)4 with R = CH(SiMe3)2 and 2,3,4-Me3-6-f-BuCgH318. The four membered cyclic stannylene Sn(NBu-f)2SiMe2 can also form a similar homoleptic complex319. 

The four-membered cyclic stannylene Sn(NBu-f)2SiMe2 reacts with nickelocene to give an 87% yield of insertion product containing a CpNi moiety bridging two tin atoms. The structure was established by single crystal X-ray diffraction313. 

A limited number of thermal redistribution reactions are reported, involving redistribution at both the tin and metal centers of the Sn-M complex (equations 136 and 137)329-331. The product in equation 137 contains a cyclic Os3Sn3 skeleton. A similar multimetal product 109 was obtained by the pyrolysis of the stannylene complex [/71-Cp2SnFe(CO)4]2332. 

While the inorganic chemistry of divalent tin and lead is well established, there are few well-characterized divalent organotin and organo-lead compounds. The R2Sn formulation seen in the older literature has proved to be an empirical formula, the formally divalent stannylene actually being an oligomeric linear or cyclic organostannane. Neumann has commented on this point several times (1-3). 

As mentioned in the introduction, the simple alkyl find aryl stannylenes originally formulated as R2Sn are actually linear, branched, or cyclic poly-stannanes. One isomer of the compound diphenyltin is the cyclic hex-amer dodecaphenyl cyclohexastannane as shown by its X-ray crystallographic structure determination (62). 

Reactivity of the highly crowded silicon-substituted cyclic stannylene 70 was investigated in detail <20020M2430>. Upon treatment with iodoalkanes, enones, and diones, the derivatives 71, 72, and 73 were obtained (Figure 3) and their structure was confirmed by H, 13C, z9Si, and 119Sn NMR spectroscopy as well as X-ray crystallographic studies. 

Starting from new bivalent germylenes and stannylenes 282, various stable cyclic organometallic compounds 283-285 were obtained as shown in Scheme 47 <1997MGM791>. 

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