Phosphoryl trihalides

Zyk et al. <2000RJ0794> reported the synthesis of fused-ring thietanes by the reaction of the bis-morpholine sulfide-phosphoryl trihalide complex 85 with norbornadiene. The formation of 4-thiatricyclo[3.2.1.03,6]octane 86 was demonstrated and yields varied slightly depending on the phosphoryl trihalide used. When phosphoryl trichloride was used, the yield was 69% in the case of phosphoryl tribromide, it was 72%. The complex 84 was obtained by the reaction of the bis-morpholine sulfide with phosphoryl trihalide in dichloromethane at —40°C (Scheme 15). The same authors <1996RCB2393> performed a similar reaction of norbornadiene with bis-morpholine disulfide-phos-phoryl tribromide complex 87, which led to the formation of the same thietane 86 in 63% yield (Scheme 15). These reactions have also been described by Robin and Rousseau in a review <2002EJ03099>. 

Most assuredly the conversion of phosphoryl halides to tertiary phosphine oxides in ether does not consistently provide good yields. In contrast to the situation with phosphorus trihalide, however, the displacement sequence with phosphoryl trihalides can be of preparative value for the intermediate phosphinic halides. 

In Eig. 20.11 we compare the structures of PF3 and PCI3 with the sfructures of the corresponding phosphoryl trihalides, OPX3. Both the PO bond distances and the thermochemical bond energies calculated by transfer of the P-X bond energies from the trihalides, indicate that the PO bonds are best described as double. 

Fig. 20.11. The molecular structures and bond energies in phosphorus trihalides and phosphoryl trihalides.

All the phosphoryl halides, POX3, have now been characterised (4.307), as well as mixed species such as POF2CI, POFCI2, POBrCl2, etc. The phosphoryl halides are all toxic and reactive. They may be formed by oxidation of the appropriate trihalide and all are hydrolysed by water. The iodide has also been prepared (4.322) below. 

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