Synthesis, Structure, and Reactivity of an Imido- and an Oxo(imido)pliosphorane R-P(=X)=NR (X = NH, O; R = tBu_3C_6H_2)

摘要

Bis(imino)phosphoranes are versatile synthetic building blocks for phosphorus-nitrogen heterocycles and moreover have gained significance as ligands for homogeneous catalytic processes. The possibility of extending the synthetic potential of these compounds by functionalization of an inline nitrogen atom was the stimulus for the investigations described. We report here on the synthesis and structure of the first imido(immo)phosphorane (I) and on the structure of the oxygen thermally stable crystals.In solution, 2 decomposes above 40 °C with the elimination of nitrogen. The initially formed phosphi-nonitrene intermediate 3 is stabilized by a 1,3-H shift to give the imido(imino)phosphorane 4. The iminophosphorane 5 iso-rneric to 4 is a by-product ofthe reaction, which can be obtained quantitatively by heating the reaction mixture for several days under reflux. The conversion 4 -> 5 involves the CH activation of an ortho-positioned tert-butyl group on the phosphorus sub-stituent by the highly etectrophilic phosphorus center. One insertion reaction corresponding to this isomerization is also documented for the analogous arykdithioxophosphorane and is thought to be responsible for the unsuccessful attempts at the synthesis of a kinetically stabilized aryldioxophosphorane. The oxgen derivative 6 isoelectronic to 4 can be obtained by ozonization of 1 in CH_2Cl_2.