P - N compounds

This section deals with the binary compounds that nitrogen forms with metals, and then describes the extensive chemistry of the hydrides, halides, pseudohalides, oxides and oxoacids of the element. The chemistry of P-N compounds is deferred until Chapter 12 (p. 531) and S-N... 

There has been a HO study of the stereoelectronic effects in methy1phosphines (90). Steric effects were found to concentrate in the HOHO and accounted for half the substituent effects on the pK values, whilst electronic effects on the HOHO was minimal.242 The relative basicities of polymethoxytriarylphosphines have been measured. Tris(2,4,6-trimethoxyphenyl)phosphine was considerably more basic than piperidine.243 The basicities of P-N compounds have been reviewed and their correlation with P-N bond lengths invest igated.2 4 4... 

Among other solid P-N compounds examined, the title compound ignited immediately on contact with nitric acid, hydrogen peroxide or dinitrogen trioxide. 

Infrared spectroscopy (continued) of phosphazotrihalides, ionic P-N compounds, 14 19... 

X -Phosphorins as well as X -phosphorins have five characteristic bands between 1400 and 1600 cm . 1.1-Dialkoxy- and 1. l-diaryloxy-X -phosphorins have additional intense bands in the region 1180—1220 cm and at 1008 cm and 1040 cm , as well as a weak band at 1160cm which can be attributed to the P—0 vibration. In P—N compounds the band at 718 cm is probably due to the P—N vibration. With increasing P—N band strength it shifts to 785 cm ... 

In the large and important class of compounds called phosphazenes we are formally dealing with Pv and Nra. There are other P—N compounds that are formally Pm—Nm types. In these the P—N bonds are all nominally single, but, of course, partial double-bond character arises by Npir—Pdir donor bonding, indicated as follows in resonance terms ... 

Finally, there are polycyclic P—N compounds such as those shown in Fig. 10-14. Note that (a) which has an adamantane-type structure and (c) are isomers when R = Me, the adamantane structure is thermally stable, but when R = Me C, the (a) structure converts to the (c) structure on heating for 12 days at 157°C. 

In the reaction of bis(trimethylsilyl)carbodiimide with the P=N compound 45 the cycloadduct 46 is obtained, which rearranges to give the linear carbodiimide 47. ... 

A175. M. F. Lappert and G. J. Leigh, eds., Developments in Inorganic Polymer Chemistry. Elsevier, Amsterdam, 1962. 285 pp. Contains articles on B—N, P—N compounds, silicones, and polymetallosiloxanes. 

These reactions are highly chemoselective as indicated by NMR analysis of the crude reaction mixture which showed that only a single product was produced in each case. The reactions with the P=N compound were completed at room... 

A great many compounds are known with P—N and P=N bonds.47 R2N—P bonds are particularly stable and occur widely in combination with bonds to other univalent groups, such as P—R, P—Ar and P—halogen. The entire subject of P—N compounds cannot be properly outlined in the space available. Hence, only one part of it, the chemistry of phosphazenes (also called phosphonitrilic compounds), will be described in detail. 

Restricted Rotation.—Several studies have been reported on P—N compounds. " Restricted rotation about the P—N bond in the dimethyl-aminophosphines (48) is observed with a variety of phosphorus substituents the barrier was largest for (48 Y = Cl, Z = Ph). However, in the (methoxymethylamino)phosphines (49) slow rotation was not detected... 

The magnetic rotations of the pyrophosphates (153 Y = alkyl or OR, X = O) show that the linking oxygen atom interrupts the delocalization of TT-electrons. A comparison of observed and calculated magnetic rotations of the monothiopyrophosphates shows that they have the thiono-structure (153 X = S). The Faraday effect and diamagnetic susceptibilities of a number of P" -N compounds reflect a large variation... 

The less stable -P=C compounds tend to dimerise or form higher polymers (3.21), and the same considerations apply to -P=N- compounds (3.22), (3.23). 

Similar sideways bonding arrangements occur with phosphaalkenes -P=C, phosphaalkynes (3.29a), P=C-, Ji-bonded ring systems (3.29b) and -P=N compounds. The discovery of P=C double bonds, has, like P=P double bonds, led to the synthesis of a whole series of P analogues of the classical carbon n complexes. 

Cyclic P=N compounds, such as phosphonitrilic chlorides, phosphonitrilic esters, and salts of phosphonitrilic acids, absorb strongly " at 1320-1100 cm due to the stretching of the P=N bond. Compounds of the type... 

Compounds containing the P=0 group absorb in the region 1300-1140 cm", the exact position depending on the sum of the electronegativities of the substituents. Trialkyl phosphates for example abosrb near 1290 cm , and trialkyl phosphine oxides absorb near 1150 cm Cyclic P—N compounds also absorb in this region. 

The reaction of 159 with a second equivalent of isocyanate results in complete conversion of the C=0 to C=NR bonds after 20 days at 120 The reaction of P=N compounds with isocyanates to give carbodiimides is a general reaction, and it is referred to as the aza-Wittig reaction This reaction is used to synthesize... 

Across other double bonds The reaction of phenyl thiocyanate with P N compounds was first investigated by Staudinger and Meyer in 1919 . The reaction proceeds across the C=S bond of the isothiocyanate to give fragmentation products. For example, from ethyliminotriphenylphosphorane 67 and ethyl isothiocyanate a good yield of diethylcar-bodiimide and triphenylphosphine sulfide is obtained. The reaction most likely proceeds via the four-membered ring intermediate 68 formed in a [2+2] cycloaddition reaction. 

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