Organotin compounds alkoxides

Organotin compounds, R3S11X, R2SnX2, etc., react in the same way, again much more rapidly, to give the stannyl equivalents of the protic products (see Section 14.1.3).6 In the example shown here (equation 3-12), the addition of a tin alkoxide to an isocyanate can be part of a catalytic cycle by which polyurethanes are prepared commercially. 

Some examples are given in equations 4-71-4-75, and more are to be found in the sections dealing with the respective specific classes of organotin compounds which are formed. Cyclopentadiene can be both mono- and di-stannylated, and triphenylindenyltin has been obtained from indene (Section 9.3.1).116 Acetylene can be both mono-and di-stannylated,116-117 and the reaction of a diaminotin compound with acetylene gives a linear polymer.116-118 The acidity of sulphonylalkynes is sufficient to allow the reaction to be carried out with a tin alkoxide rather than a tin amide,119 and acetylenes can be stannylated with tributyltin oxide in benzene by dehydration with calcium hydride, or azeotropically.120... 

Various organotin compounds with tin-heteroatom bonds are synthesized by the reactions of halostannanes with the corresponding heteroatom nucleophiles. For example, trialkyltin alkoxides and trialkyltin amides are prepared by the treatments of halostannanes with sodium alkoxides (eq (139)) [134] and lithium amides (eq (140)) [135], respectively. Tin alkoxides are also formed by the reaction of alcohols with tin amides (eq (141)) [136]. 

In addition to the tin(IV) alkoxides mentioned above, there have been synthesized many organotin compounds in which tin-oxygen bonds are present, i . The organostannoxanes are mostly obtained by the hydrolysis of the requisite halides, as exemplified below. 

The organotin alkoxides RgSnOR and R2Sn(OR >2 can be prepared by treating the appropriate organotin chlorides with sodium alkoxides, and this procedure has been extended to the preparation of the monoal-kyltin trialkoxides, RSnCOR la (190), which serve as useful reagents for the synthesis of other monoalkyltin derivatives. Alternatively, the trialkoxides can be prepared by alcoholysis of the tris(amino) compounds RSn(NR )3 (191). 

Few X-ray diffraction data are available for the organotin alkoxides. Trimethyltin methoxide in the crystal is a five-coordinate linear polymer 47,380 and both tin atoms in the methanol solvate, CH2(SnPh2OMe)2-MeOH, are five coordinate, one by intramolecular coordination, and the other by solvation 48.381 Dimethyltin dimethoxide 49,382 dimethyltin diphenoxide 50,383 and isopropyltin triisopropoxide 51384 are five-coordinate oxygen-bridged dimers. All these compounds are monomers in solution. 

These compounds are most readily obtained by hydrolysis of organotin hahdes, especially under basic conditions, although hydrolysis of alkoxides and amides, etc., can also be used. Hydrolysis of di- and trihalides occurs in a stepwise fashion and various of the partial hydrolysis products have been characterized (Scheme 19). 

Simple organotin alkoxides or phenoxides are available from the halides on reaction with MOR or MOAr, as well as from the oxides and the alcohol or phenol on azeotropic dehydration. These compounds are generally sensitive to H2O and to CO2. Cyclic alkoxides, e.g. (51) and (52), and cyclic diaUcoxides from diols, e.g. (53), can also be prepared. These complexes are usually oligomeric. 

Two other methods involve reacting organotin halides with germyl-Hg compounds (see 5.7.5.3) and organotin alkoxides with silyl-Hg compounds (see 5.7.5.4). 

This early work is summarised in Krause and von Grosse s Organometallische Che-mie which was published first in 1937,11 and which described examples of tetraalkyl-and tetraaryl-stannanes, and of the organotin halides, hydrides, carboxylates, hydroxides, oxides, alkoxides, phenoxides, R2Sn(II) compounds (incorrectly), distannanes (R3SnSnR3), and oligostannanes (RiSn) . 

The opposite polarity in the organotin reagent R3Sn5+X5 can be exploited in, for example, the reaction of a tin alkoxide with an vinyl ester,83 the addition of an alkoxy- or amino-tin compound to a ketene,84 the reaction of a silyl enolate with a tin chloride,85 or the addition of an alkyltin hydride under non-radical conditions to an a,P-unsaturated carbonyl compound.86... 

Similar addition reactions occur with the Sn-0 bond of organotin alkoxides [e.g. Bu3SnOMe + PhN=CO —> Bu3SnNPhC(0)0Me], and, by recycling through the alkoxides, the bis(trialkyltin) oxides will catalyse the addition reactions of alcohols and similar compounds. These catalysed reactions are discussed in Section 14.1.2. 

Organotin esters of the oxy- and thio-acids of phosphorus can be prepared inter alia by azeotropic dehydration of a mixture of the organotin hydroxide or oxide and the acid, or by treating a tin alkoxide or tin amide with the acids, or an organotin halide with a salt of the phosphorus acid. By using different molecular ratios of the reactants, products of different compositions can be obtained. Attempts to prepare phosphites may result in an Arbuzov rearrangement to a phosphorus(V) compound (e.g. equation 13-11).47... 

Amidostannanes containing the groups Sn-NC(=0)R or Sn-NS(0)2R are easier to prepare and to handle than are the aminostannanes. The acidity of the proton on nitrogen in the parent amide is now sufficient for reaction to occur with organotin hydroxides, oxides, and alkoxides (and aminotin compounds), and, once formed, the amidostannanes are less sensitive to moisture. A variety of amidostannanes is also available from the addition of Sn-0 and Sn-N bonded compounds to nitrogen heterocumulenes. 

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