Hypervalent Sulfur-Functionalized Diphosphagermylene and Diphosphastannylene Compounds
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The reaction between either GeCl2(1,4-dioxane) or SnCl2 and 2 equiv of the lithium phosphide [{(Me3Si)2CH}P(C6H4-2-SMe)]Li(tmeda) gives the corresponding diphosphatetrylenes [{(Me3Si)2CH}P(C6H4-2-SMe)]2E [E = Ge (10), Sn (11)] in good yields. Both 10 and 11 crystallize as discrete monomers in which the Ge and Sn atoms are coordinated by both P and S atoms. Although 10 and 11 crystallize as racemic mixtures of the RR and SS diastereomers, variable-temperature NMR experiments suggest that, in solution, these compounds are in dynamic equilibrium with small amounts of the corresponding RS and SR diastereomers. DFT calculations reveal that the lowest-energy minima for both 10 and 11 possess rac stereochemistry; two higher-energy minima were located for each of 10 and 11, both of which have meso stereochemistry. The two calculated meso diastereomers differ in the location of the sulfur and phosphorus substituents within the pseudo-trigonal-bipyramidal structures. Both 10 and 11 decompose on exposure to light, generating the diphosphine {(Me3Si)2CH}(C6H4-2-SMe)P-P(C6H4-2-SMe){CH(SiMe3)2} (14) as the major product.
