Hypervalent phosphorus heterocycles

Figure 7 Typical structural types of hypervalent phosphorus heterocycles.

In a more recent work, Kornev and coworkers reported the preparation and structural studies of a series of phenylpyrazole-based hypervalent phosphorus compounds 34 and 35 (Figure 8), which represent another example of low-coordinate hypervalent phosphorus heterocycles (2015EJIC2057). According to X-ray structural data, the phosphorus atom in molecule 34 has overall trigonal bipyramidal geometry with chlorine atoms at the apical position, while the N- and C-substituents and the lone electronic pair are occupying the equatorial positions with P—N and P—C bond distances of 1.771 and 1.831 A, respectively. 

Figure 8 Phenylpyrazole-based hypervalent phosphorus heterocycles.

Numerous stmctural types of hypervalent phosphorus compounds are known (1999MI1). Representative examples of stable hypervalent phos-phoms heterocycles include lO-P-3 compounds 29 (1994CR1215), anionic lO-P-4 species 30 (1983CB3301), pentacovalent lO-P-5 compounds 31... 

H. H. Karsch, R. Richter, E. Witt, "Novel Sila-Phospha-Heterocycles and Hypervalent Silicon Compounds with Phosphorus Donors", in Organosilicon Chemistry III From Molecules to Materials (Eds. N. Auner, J Weis), VCH, Weinheim, 1997, p. 460. 

Novel Sila-Phospha-Heterocycles and Hypervalent Silicon Compounds with Phosphorus Donors... 

Summary The reaction of two equivalents of lithium phosphinomethanides with di- or trifunctional chlorosilanes yields novel five- and six-membered heterocycles by multistep rearrangements or transmetallation reactions. Silaethene intermediates and hypervalent intermediates are likely to be involved. The reaction of one or two equivalents of lithium phosphinomethanide Li[C(PMe2)2(SiMe2Ph)] TMEDA with pTolSiCb and ci QHbcii iCb yields novel penta- and hexacoordinated silicon complexes. Both are the first examples of truly hypervalent organosilicon species with phosphorus donors characterized by X-ray structure determination. 

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