Phosphabenzene structure

A structural study of a molybdenum carbonyl complex of phosphabenzene has shown that the phosphorus is a-bonded to the... 

The orange, air-stable, homoleptic tetrakis( 71-phosphabenzene)nickel (1046) is tetrahedral (point symmetry 54) and can be obtained from phosphabenzene and [Ni(cod)2].2 25 It features a short Ni—P bond length of 2.1274(5) A with considerable N i P 7r-backbonding and a i/(Ni—P) stretch at 168 cm-1. In solution, partial dissociation of one phosphabenzene ligand is observed. 2-Diphenylphosphino-3-methylphosphinine forms with [Ni(cod)2] in the presence of the CO the dinuclear complex (1047) with a W-frame structure.2526... 

The syntheses, as well as physical and theoretical studies regarding the aromatic character of heterobenzenes, such as phosphabenzene " , arsabenzene and bismabenzene , have been extended also for stibabenzene . The benzenelike structure has been attributed to stibabenzene on the basis of experimental study and theoretical interpretation of the microwave spectra of SbCjH5, SbCjH5, ) -dideuterio SbC5H3D2 and 8-dideuterio SbC5H3D2 in the region 26.5-40.0GHz. 

UV and NMR spectra of phosphabenzenes 38a (89TL5245) and 38b (77TL3445), and 4-hydroxyarsabenzene (75AG(E)710) indicate their phenolic structure no evidence for a betaine form has been found in these cases. The dependence of the tautomeric equilibrium in phosphorinanes 39 (R = CN, COOMe) on the substituent R, solvent and temperature has been evaluated (77DOK858). For 39 (R = COOMe), the enol form 39b predominates independent of the solvent the keto fraction slightly increases with increase in the temperature. In contract, the keto form 39a predominates for 39 (R — CN) in all solvents studied with fraction of the enol form increasing in the polar solvents. 

Phosphabenzene has the geometry of an expanded planar hexagon, as shown by the X-ray structure of the 2,6-dimethyl-4-phenyl derivative (see Fig. 6.15). By its NMR data, phosphabenzene satisfies the criteria of a delocalized 6 i-heteroarene with a diamagnetic ring current. However, the electron distribution between P- and y-positions is the reverse of that of pyridine (see p 270) ... 

The unusual phosphole ring C FejP was synthesized by Huttner and co-workers (Scheme 12). In terms of Wade s rules (b) is an arachno system which can be converted into a nido cluster, (c), upon decarbonylation. The latter can form directly in the photochemical reaction of (a) with alkynes. The hve-membered organometallic heterocycle (c) is planar (deviation < 0.07 A) indicating delocalized bonding (structure 39). Signihcant developments may be expected from this new class of compounds. New types of heterocyclic phosphorus ligands are continuing to be synthesized, e.g. a 1,3,5-triphosphabenzene derivative, l,l,3,3-tetrakis(dimethylamino)-4-r-butyl-U 3x 5A -tri-phosphabenzene (40). 

In phosphinine (also called phosphorin or phosphabenzene) there is at least a formal resemblance to the situation in pyridine and benzene, and a planar ring system is to be expected. Crystal structure... 

Muller C, Lutz M, Spek AL, Vogt D (2006) 4-(p-Methylthio)phenyl-2,6-diphenyl phosphinine the first X-ray crystal structure of a 2 -triaryl-phosphabenzene. J Chem Crystallogr 36 869-874... 

Elschenbroich C, Nowotny M, Metz B, Graulich J, Massa W, Wocadlo S (1991) Bis(> -phosphabenzene)vanadium synthesis, structure, redox properties, and conformational flexibility. Angew Chem Int Ed 30 547-550... 

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