Organotin alkoxides

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. 

The 119Sn chemical shifts have been used extensively to study inter-molecular association in various organotin alkoxides, RnSn(OR )4 , where n = 1-3. 

Simple organotin alkoxides as well as the cyclic dioxastannolanes are also suggested to associate in solution and in the solid state83,214. The degree of association depends on... 

A considerable amount of effort has already been devoted to producing dimethyl carbonate (DMC) from methanol and CO2, and some of the reactions have been catalyzed by organotin alkoxides. However, the catalytic activities so far obtained have been very low due to the decomposition of the catalysts by water generated during the reaction. The supercritical C02 reaction with trimethyl orthoacetate leads to the desired reaction and gives DMC and methyl acetate. Although di- -butyltin dimethoxide is less effective, the addition of tetrabutylphosphonium iodide substantially enhances the catalytic activity of the system (Equation (96)).261 262... 

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). 

With di- or triisocyanates, insoluble polymers are obtained. Reaction (a) illustrates the use of amides in catalysis. In commercial practice, organotin alkoxides or carboxylates are preferred, being used for catalytic trimerization of isocyanates to cyanurates and addition of diols to diisocyanates to yield polyurethanes . ... 

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 alkoxides and phenoxides can be prepared from the reaction of an alkali metal alkoxide or phenoxide with the appropriate organotin halide. Triorganotin alkoxides and phenoxides are available from the reaction of bis(triorganotin) oxides with alcohols or phenols or the corresponding carbonates, and the amides R Sn(NR"2)4 react with alcohols to give the corresponding alkoxides. 

The 1,3,2-dioxastannacycloalkanes can be prepared by the usual routes to organotin alkoxides, but whereas simple alcohols react with diorganotin oxides only to the stage of the distannoxanes (R 0)R2Sn0SnR2(0R ), 1,2-diols react further to give the dioxastannolanes (equation 14-41).61 62 The reactions proceed much more quickly (typically in 4 to 9 min) if the reactants are heated in a microwave oven.63 Similar reactions can be carried out with dialkyltin dihalides64 and, under milder conditions, with dialkyltin dialkoxides.65-67... 

Borane is an effective reducing agent for organotin alkoxides and amides,11 and this has been exploited in the preparation of diorganotin dihydrides from the dioxastan-nolanes which can readily be obtained by azeotropic dehydration of a mixture of diorganotin oxide and 1,2-diol (e.g. equation 15-9).12... 

---