Eine einfache Synthese von 1,3‐Diphospha‐2,4‐disilabicyclo[1.1.0]butanen und Isomerisierung durch Silicium‐Inversion

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Abstract
A Facile Synthesis of 1,3‐Diphospha‐2,4‐disilabicyclo[1.1.0]butanes and Isomerization by Silicon InversionDilithiation of the PH positions of the P2Si2 cyclobutanes 2a—h with n‐BuLi and treatment with tBuHgCl leads to the 1,3‐bis(tert‐butylmercurio) compounds 3a—h. According to NMR spectroscopy and X‐ray structural analysis the tert‐butylmercurio groups at phosphours occupy trans configuration. Photolysis of solutions of 3a—d and 3f, g in toluene yields the corresponding 1,3‐diphospha‐2,4‐disilabicyclo[1.1.0]butanes 1a—d and 1f, g. Interestingly, the dimercury compound 3e (R = mesityl and tert‐butoxy) is quite stable in visible light, probably due to intramolecular donor (tBuO) acceptor (Hg) stabilization. Starting from 3b, the light‐induced elimination of the tBuHg groups gives the expected exo,endo‐P2Si2‐bicyclo[1.1.0]butane 1b only as intermediate. The final product of the latter photolysis is the CMe3/CMe3‐exo,exo isomer 1b′. The formation of 1b′ from 1b is an irreversible silicon inversion process caused by unfavourable interaction of the endo substituents in 1b. In comparison, the exo,endo isomer of 1g (R = isityl and CMe3 at silicon) does not rearrange to the Me3C/Me3C‐exo,exo derivative 1g′ under similar photolysis conditions or when heated at 140°C for several days. The route to 1,3‐diphospha‐2,4‐disilabicyclo[1.1.0]butanes 1 described herein allows the synthesis of new derivatives which cannot be prepared from disilenes and white phosphorus.