Stannylenes preparation

Tin amidinates display a rich coordination chemistry with the metal in both the di- and tetravalent oxidation states. The first results in this area were mainly obtained with N-silylated benzamidinate ligands. Typical reactions are summarized in Scheme 48. A stannylene containing unsymmetrically substituted amidinate ligands, [o-MeC6H4C(NSiMe3)(NPh)]2Sn, has been prepared accordingly and isolated in the form of colorless crystals in 75% yield. ... 

The first landmark syntheses of persistent radicals of the heavier group 14 elements were reported nearly 30 years ago by Lappert s group. ° The first radical of this series, [(Me3Si)2CH]3Sn , was prepared by photolysis of the stable stannylene [(Me3Si)2CH]2Sn with visible light in benzene (Scheme 2.26). ° =... 

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). 

A remarkably stable, deep red Ni° stannylene complex, [Ni(1068)4l, has been prepared by the reaction of [Ni(l,5-cyclooctadiene)2] with (1068) in toluene at —78 °C. 70 In spite of the bulkiness of (1068) and the known tendency of analogous Ni° phosphine complexes to dissociate in solution, [Ni(1068)4] remains intact in solution and, moreover, melts at 178-180 °C without decomposition. X-ray crystallography shows tetrahedral geometry about the nickel atom, with Ni—Sn bond lengths of 2.3898(2)-2.399(2) A. 

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). 

Actually, 64 is known to be dimeric in the solid state but monomeric in dilute solution or in the gas phase. The first monomeric dialkyl- and diarylstannylenes are 2-pyridylbis[(tri-methylsilyl)methyl]-substituted stannylenes and bis[2,4,6-tris(tiifluoromethyl)phenyl]stan-nylene it should be stressed, however, that the coordination number around Sn in the solid state is not 2 in these compounds. The first actual monomer with coordination number 2 in the solid state was found to be 2,2,5,5-tetrakis(trimethylsilyl)cyclopentane-l-stannylene, 65, prepared by the following reaction141 ... 

SnX2 (X = Cl, Br), the polymeric species (SnR2) and the stannylenes SnR2 can be used for the preparation of organotin halides319 ... 

Srivastava and Schuerch [255] and Desinges et al. [256] demonstrated the potential utility of glycosyl 1,2-O-stannylene acetals, and Hodosi and Kovac [257] established this method involving alkylation of a 1,2-O-stannylene acetal with a triflate derivative as an aglycon (Scheme 5.97). This glycosyl donor was prepared by the... 

Unsubstituted or 2,3-disubstituted stannoles can be prepared from the palladium-catalyzed reaction of an alkyne with the stable stannylenes [(Me3Si)2CH]2Sn and CH2C(SiMe3)2 2Sn . The mechanism has been traced by the isolation of intermediates,235 and by ab initio calculations (Equation (78)).236... 

Stannenes, R2Sn=CR2, are usually prepared either by coupling of a stable stannylene with a stable carbene, or by an elimination reaction (Equation (185)). 

The stannane-thiones, -selenones, and -tellurones are usually prepared by addition of the element, or a source of the element such as a thiirane, to a stannylene, or by dechalcogenation of a tetrachalcogenostannolane with triphenylphosphine (Equation (192)). 

Hodosi, G. Kovac, P., Manipulation of free carbohydrates via stannylene acetals. Preparation of beta-per-O-acyl derivatives of D-mannose, L-rhamnose, 6-0-trityl-D-talose, andD-lyxose. Carbohydr. Res. 1997,303, 239-243. 

Stannanorbornadienes prepared from stannole (137) and benzyne or tetrafluoroben-zyne are too unstable to be isolated. They decompose to the naphthalene and stannylene, which can be trapped. With tetracyanoethylene, however, the [4 + 2] cycloadduct does result but decomposes above -20 °C by what is believed to be a concerted rather than a two-step mechanism, in sharp contrast to that of 7-sila- and 7-germa-norbornadienes (Scheme 214) <79AG(E)543). 

Stannylenes have been prepared efficiently from some fairly dilute (20-40 mM) solutions of nucleotides in methanol, by refluxing for 30 min in the presence of an equimolar amount of BUjSnO, without removal of water [9]. In these conditions, the soluble methyl ether CHj-O-SnBu -O-SnBu -OCHj may be the reactive species. This is a useful technique for compounds insoluble in benzene or toluene, provided die stannylene is stable in methanol, which is not always so. Problems may arise with rnmr-diequatorial 1,2-diols. 

Experiment G [see Eq. (16)] shows that a stannylene may be prepared from a molecule protected by acetylation. 

Monoetherification of polyols.12 Monobenzylation and monoallylation of polyols can be conducted conveniently under mild conditions by conversion to the stannylene derivative (dimeric) by di-n-butyltin oxide (5, 189 9, 141). The stannylene is then treated with benzyl bromide or allyl bromide and tetra-n-butylammonium iodide (1 equiv.) in benzene. The same conditions can be used to prepare monomethoxymethyl ethers. Quaternary ammonium bromides are less efficient catalysts than the iodides. These salts also accelerate reaction of stannylenes with acid anhydrides. The mechanism for this activation is not clear it may involve coordination of I" to tin. 

Substitution of a six-membered stannylene derivative involving the primary position always occurs at that position. Various 6-0-benzyl derivatives of d-gluco and d-galacto configuration have been prepared by this method in good yields [54, 135]. Treatment of allyl 2-acetamido-3-0-benzyl-2-deoxy-4,6-0-dibutylstannylene-a-D-galactopyranoside with benzyl bromide in the presence of tetrabutylammonium iodide furnished 75 % of the 6-benzyl ether [141]. 

Novel, monomeric heteroleptic derivatives of divalent Ge 40 and divalent Sn 41 have been prepared and characterized by single crystal X-ray diffraction <19990M389>. Heteroatoms in these germylene and stannylene species are not formally part of a four-membered ring however, crystal structures point to the azametallacyclobutane structures formed due to the N —> M coordination. The heteroleptic nature of 40 and 41 gives rise to an interesting reactivity in their coupling with transition metal clusters. 

A triaminostannyl lithium, prepared by oxidative addition of the corresponding amide to the stannylene bearing the same substituents (equation 56)73, was characterized by methylation (Mel, 71% yield) and halogenation (I2, 62% yield). 

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