METALATION REACTIONS OF DIPHOSPHIRANES - NEW ACCESS TO SIGMA-DIPHOSPHAALLYL AND PI-DIPHOSPHAALLYL COMPLEXES

The metallation reactions of the functionalized diphosphiranes la,b wi th the anionic metal transition complexes Na[(Cp)nM(CO)m] (M = Mo, W, or Co) afford sigma- or pi-diphosphaally] complexes depending on the s ubstituents of the intracyclic carbon atom. The same complexes are als o obtained from their photochemical isomers, the 1,3-diphosphapropenes 2a,b. The complexes are thermally labile as shown by variable-tempera ture NMR spectroscopy. Upon heating, the sigma-diphosphaallyl cobalt c omplex 3aC is irreversibly transformed into the pi-complex 4aC. In con trast, with M = Fe and in toluene solution at reflux, reduced 1,3-diph osphapropenes 5a,b are obtained. Further, the gem-dihalogenated diphos phiranes 1c,d and their isomers 2c,d lead quantitatively to 1.3-diphos phaallene 6 under the same metallation conditions. The mechanism of th e coordination reactions is discussed.