2.4.6- Triphenyl-phosphabenzene

The reactions of the phosphabenzene system [124] confirm these conclusions. Phosphabenzenes have low basicity towards hard acids. They are not protonated by CF3CO2H nor alkylated by trialkyloxonium salts. However, soft acids attack at phosphorus. For instance, 2,4,6-triphenyl-phosphabenzene forms compounds 4 with the hexacarbonyl derivatives of Cr, W and Mo in which the phosphorus coordinates to the metal, possibly with metal-P back-donation. The complexes 4 rearrange photochemically or thermally affording the 67i-heteroarene complexes 5. Although 2,4,6-triphenyl-pyridine is protonated on nitrogen, it undergoes complex formation with chromium hexacarbonyl exclusively on the phenyl moieties yielding the ri -arene complexes 6 [125]. 

Dash KC, Eberlein J, Schmidbaur H (1973) Gold(I) halide complexes of 2,4,6-triphenyl-phosphabenzene. Synth Inorg Metalorg Chem 3 375-380... 

The aromatic heterocycle phosphabenzene C5H5P (analogous to pyridine) was reported in 1971, some years after its triphenyl derivative 2,4,6-Ph3C5H2P. See also HP=CH2 29) nd [P(CN)2] ° (p. 484). The burgeoning field of heterocyclic phosphorus compounds featuring... 

Interestingly, the bond distances and angles of l,l-dimethyl-2,4,6-triphenyl-/l -phosphorin determined by X-ray diffraction are similar to those of /( -derivatives (Figure 18), yet the physical and chemical properties show that the 2 -phosphorins with electron-donor substituents (H, Me, SiHs) at the P heteroatom are not aromatic, and that the tetracoordinated phosphorus atom interrupts the ring current in such compounds. Flowever, when the P-substituents of /l -phosphorins have higher electronegativities (F, OFl, Cl, Br) the NlCS(l) values indicate aromaticity, but somewhat less than phosphabenzene (01HCA1578). 

The aromatic heterocycle phosphabenzene C5H5P (analogous to pyridine) was reported in 1971, some years after its triphenyl derivative... 

At least three names are available for the compound H3P=CH2. These are phosphine methylene, methylene phosphonium ylid and phosphonium methylide moreover, the compound can be classed as a phosphorane The compound PhjP Rj may be called triphenylphosphonium methylide, tri-phenylphosphonium methanide or triphenyl-methylenephosphorane. The pyridine analogue, C5H5P, has been known variously as phosphobenzene, phosphabenzene, phosphorin, and most recently, phosphinine. The term phosphane for (1) in Table 1.4 and its derivatives is the most recent and the most systematic, but it is difficult to see how the more widespread and firmly rooted term phosphine will ever be replaced. In addition, adoption of the term phosphane would put it in line with such little-used terms as carborane for CH4, nitrane for NH3 and oxane for HjO. 

Phosphabenzene Complexes.—Photolysis of [CpMn(CO)2(L)j (L=P-bonded 2,4,6-triphenyl- and 2-phenyl-4,5-dimethyl-phosphabenzene) affords the sandwich complexes [CpMn( -L)]. ... 

Nucleophilic attack on phosphorus is not restricted to phosphonium salts, phosphines, and phosphoranes as Gottfried Markl has brilliantly demonstrated. Phenyllithium binds readily to the heteroelement of the faintly yellow 2,4,6-triphenyl-1-phosphabenzene (2,4,6-triphenylphosphorine). The resulting ate complex (69, Scheme 1-48) gives with methyl iodide the crystalline deep red 1-methyl-1,2,4,6-tetraphenyl-1 -phosphabenzene (76%). ... 

Scheme 1-48. Nucleophilic addition of phenyllithium onto 2,4,6-triphenyl-1- phosphabenzene and condensation of the resulting ate complex 69with iodomethane.

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