Trialkyltin, reactivity

Trialkylstannyl enolates can be prepared from enol acetates by reaction with trialkyltin alkoxides and are sufficiently reactive to add to aldehydes. Uncatalyzed addition of trialkylstannyl enolates to benzaldehyde shows anti stereoselectivity.31... 

Indirect electrosynthesis of reactive formyl transition metal compounds involves an initial step of reduction of metal carbonyls to radicals followed by transfer of a hydrogen atom from trialkyltin hydrides190. Electroreduction of metal carbonyls yields products of dimerization and loss of CO from the radical anion. Electroreduction in the presence of R3SnH yields the formylmetalcarbonyls ... 

Trialkyltin hydrides represent an important class of reagents in organic chemistry because of their utility in radical reactions. However, problems of toxicity and the difficulty of product purification made trialkyltin hydrides less than ideal reagents. Several workup procedures and structurally modified trialkyltin hydrides have been developed to facilitate the separation of tin residues from the reaction mixture. Tris(trimethylsilyl)silicon hydride has also been synthesized and is often used successfully in radical reactions. However, its reactivity is different from that of trialkyltin hydrides in a number of important respects. Other tin hydride surrogates are also available. ... 

Besides new insight into the reactivity of free radicals, methods for die production of carbon-centered free radicals have also seen major improvements in die last several years. One very common new mediod is to use tin-based reagents as radical chain carriers. Trialkyltin radicals readily abstract bromine or iodine from carbon to produce a carbon-centered free radical. Placement of a bromide or iodide substituent on a substrate dius permits formation of a carbon-centered free radical at diat position using tin-based mediodology. This process was initially developed for die reduction of alkyl halides, and it remains an excellent synthetic method for diat purpose. The complete chain mechanism for die reduction is shown. 

Not only trialkyltin halides, but also tetraalkyltins themselves act in this way as perturbers . Evidence for this effect was obtained47 by determination of the relative reactivities of alkyl groups in unsymmetrical tetraalkyltins. The following data are typical. 

In complete analogy to silicon, trialkyltin chlorides react with the lithiated ferrocenylalkyl amines to give the corresponding tin derivatives (Fig. 4-26, bottom) trimethyltin [129] and tributyltin substituents [106] have been introduced by this method. The tin compounds are more reactive towards transmetalation than the silicon analogues and are therefore useful intermediates in the preparation of other derivatives [129], e.g., by C —C coupling to give chiral biferrocenes [106]. Several racemic planar chiral derivatives of ferrocenyltriethylstannane have been prepared via lithiated N,lV-dimethyl-ferrocenylmethylamine and similar compounds [150]. 

Trialkyltin chlorides, R3SnCl (R = butyl, octyl, heptyl, and decyl), can also be prepared by the reaction between tin and the alkyl halide in a molten quaternary ammonium halide, R 4NX.67 The reactivity of the alkyl halides RX follows the usual sequence for their reaction with nucleophiles, and the Sn-C bonds are thought to be formed by reaction of the tin(II) nucleophiles RHSnBr4 with the RX.68... 

Aldehydes, and certain more reactive ketones, react to form distannyl acetals or ketals, and with an excess of chloral, repetition of this process leads to the formation of polychloral. If an attempt is made to distil the 1 1 adduct, elimination occurs to give the trialkyltrichloromethyltin and trialkyltin formate. 

Selectivity can be an overriding commodity in cases where reactivity is dictated by logic and accepted concepts. Such is the case with stannylene acetals of diols and trialkyl-staimyl ethers of alcohols. Enhanced nucleopbilicity of oxygen attached to tin and well-documented stereoelectronic effects associated with metbine carbon atoms of trialkyltin ethers lead to remarkably selective reactions of 0-substitution and oxidation in polyhydroxy compounds. 

RCl, with similar rates for primary, secondary, and tertiary halides. em-Dibro-mocyclopropanes are reduced rapidly to monobromocyclopropanes, which are then inert to further reduction at 25°. Acyl and benzyl halides are reduced very rapidly. The reactivity of 1 is similar to that of trialkyltin hydrides, and reductions with 1 probably also proceed by a radical chain mechanism. ... 

The preference of the tin radical for the olefin can be due to the low solubility of oxygen in organic solvents. The oxygen concentration is probably kept to a constant and sufficient level by the improved contact between the gas and the sonicated solution (nebulization effect). The carbon radical which reacts with oxygen gives a peroxyl radical. From alkynes, the vinyl radical formed by addition of the trialkyltin group is more reactive towards the tin hydride, and preferential reduction occurs without any hydroxystannylation. 

The study of the reactivity of trialkylsilyl radicals in solution has been placed on a firmer foundation by the measurement of absolute rate constants for some reactions of triethylsilyl radicals (generated by the reactions of tert-butoxyl radicals with triethylsilane), with some organic halides and benzil/ These data show for example, the greater reactivity of Et3Si in halogen abstraction than that of trialkyltin radicals. Kinetic isotope effects (kn/fco) for the insertion of photochemically generated dimethylsilylene and methylphenylsilylene into Si-H and 0-H single bonds are about 1.3 and 2.1 - 2.3, respectively. The preferred mechanism for insertion of silylenes into O-H bonds is shown in equation (1). Other workers haye shown that dimethylsilylene inserts preferentially into O-H bonds of alcohols compared with S-H bonds in silanes or Si-O bonds in alkoxy-silanes. ... 

The relative reactivities of the carbonyls M3(CO)i2, where M = Os, Ru, or Fe, towards trialkylsilicon or trialkyltin hydrides can be related to the relative strengths of the respective metal-silicon or metal-tin bonds, The compounds Ma(PF8)8, where M = Rh or Ir, react with silanes and germanes RH, where R = Ph3Si, (EtO)3Si, ClaSi, or PhaGe, according to the equations ... 

A ready route to phenylpropynenitrile involves refluxing copper phenylacetylide and cyanogen bromide in ether-acetonitrile. The yield was 60 % but some diphenyl-butadiyne is formed as a by-product. Nitroacetylenes are reactive compounds, and two routes to these compounds have been described starting from trialkyltin acetylides via electrophilic cleavage of the Sn bond-C bond. - ... 

The driving force for this reaction is the greater strength of the aluminum-oxygen bond relative to the aluminum-nitrogen bond. Trialkyltin amides and tetrakis(dimethylamino)titanium show similar reactivity. 

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