Six-co-ordinate Species

The equilibrium shown in equation (2) is completely on the right-hand side, with two moles of methoxide in benzene or HMPT in the presence of 18-crown-6.  

The chirality of the six-co-ordinate anion in the salt (114) has been demonstrated by the diastereotopic nature of the methyl groups, as evidenced by their different chemical shifts. One form of the diethylammonium salt of the anion (115) has been 

Research in halogenophosphines during this year s coverage has in the main been directed at either new applications or a better understanding of known reactions. In the phosphorane field, structural studies continue to dominate, although a further decline is apparent in the number of papers devoted to M.O. calculations. The surprise of the year must be Becker s phospha-alkene (65). 

Preparation.— The importance of simple chlorophosphines to organophosphorus chemistry is reflected in the development of new routes to (1) and (2). For those requiring fairly large quantities of chlorodimethylphosphine (1), a one-pot preparation from red phosphorus is now available, The procedure involves a furnace, packed with red phosphorus, copper powder, glass wool, and active carbon, into which chloromethane is passed. Dichloro(methyl)phosphine (3) is also formed, and conditions can be adjusted to give (3) as the predominant product. 

One route to chlorodiphenylphosphine (2) involves the treatment of the silyl-phosphine (4) with chlorine. The disadvantages of this preparation are overcome largely by the use of hexachloroethane, from which (2) can be obtained in good yield.  

Hydroxamic acids and the cyclic phosphoramidite (64) in the presence of tri-ethylamine gave the salts (65). The first six-co-ordinate phosphate anions (66) containing three different bidentate oxygen ligands were obtained as shown.  

Details have appeared of the formation of six-co-ordinate species from o-phenylene phosphonites and catechol in the presence of triethylamine and of the remarkable properties of these salts. The formation of the phosphorane (68) in small yield from the reaction of the cyclic phosphoramidate (67) and 

Koizumi, Y. Watanabe, Y. Yoshida, and E. Yoshii, Tetrahedron Letters 1974,1075. 

The preparation of the salt (95) has been improved by using phosphorus trichloride at room temperature instead of the pentachloride at — 70 °C. The spirophosphorane (96) with ethylene glycol and sodium methoxide gave the tris(ethylenedioxy)phosphate (97). Attempts to prepare the six-membered-ring analogue failed, A -Ray analysis of the salt (98) confirmed the octahedral arrangement of oxygens around phosphorus. 

Bernard, P, Savignac, and R. Burgada, Bull. Soc. chim. France, 1972, 1657. 

The major absorption in the 31P n.m.r. spectrum of an equimolar solution of penta-phenoxyphosphorane and sodium phenoxide in DMF-acetonitrile is due to the hexaphenoxyphosphate anion, as predicted from the low equilibrium constant estimated for equation (2) (page 35).27 Catechol and phosphorus oxychloride in refluxing benzene gave the spirophosphorane(108), which with triethylamine gave the salt (109).45 On the basis of its 31P chemical shift in DMF solution, (108) was formulated86 as the free six-co-ordinate acid (110), but it seems probable that DMF is 

Pommeret-Chasle, A. Foucaud, M. Leduc, and M. Hassairi, Tetrahedron, 1975, 31, 2775. 68 J. Gloede and H. Gross, Tetrahedron Letters, 1976, 917. 

The phosphonamidite (111) and catechol, in the presence of base, gave initially the salt (112) and o-aminophenol.6 7 If the reaction mixture was allowed to stand at room temperature for a few days the final product was the spirophosphorane (113). 

Further six-co-ordinate anions incorporating an a-hydroxy-acid residue, e.g, (114), have been prepared, and the use of salicylic acid has given the anion (115), containing 

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The trifluorophosphorane (120) with caesium fluoride gave the salt (121) and with trimethylphosphine gave the six-co-ordinate species (122), whose configuration was shown by 19F n.m.r. spectroscopy.70... 

A remarkable demonstration of the ease of formation of six-co-ordinate species from four-co-ordinate precursors is the observation that both phenyl phosphorodichloridate and the cyclic ester (33) give the salt (34) when treated... 

Square-pyramidal metal carbonyls [M(CO)s] (M = Cr, Mo, or W) are generated on u.v. photolysis of metal hexacarbonyls and related compounds and appear as intermediates in photochemical replacement reactions of the six-co-ordinate species. The reaction step relevant in this context is an internal rearrangement of the square-pyramidal [M(CO)6] via a trigonal-bipyramidal intermediate, and back to the square-pyramidal ground state. This spy - tbp spy process represents an inverse Berry mechanism and also accounts for many other aspects of the photochemistry of these compounds. ... 

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