Phosphorus compounds Phosphines

Phosphorus is m the same group of the periodic table as nitrogen and tricoordi nate phosphorus compounds (phosphines) like amines are trigonal pyramidal Phos phmes however undergo pyramidal inversion much more slowly than amines and a number of optically active phosphines have been prepared... 

Phosphorus Compounds. Phosphine and phosphorus trioxide ignite on contact with chlorine ethylphosphine explodes.30... 

Boeing, I. A. Crutchfield, M. M. Heitsch, C. W. Phosphorus Compounds (Phosphines and Phosphine Derivatives), Kirk-Othmer Encycl. Chem. Technol. 3rd Ed. 17 [1982] 490/539. 

Organophosphorus compounds. Phosphorus-carbon bond fonnation takes place by the reaction of various phosphorus compounds containing a P—H bond with halides or tritlates. Alkylaryl- or alkenylalkylphosphinates are prepared from alkylphosphinate[638]. The optically active isopropyl alkenyl-methylphosphinate 778 is prepared from isopropyl methylphosphinate with retention[639]. The monoaryl and symmetrical and asymmetric diarylphosphi-nates 780, 781, and 782 are prepared by the reaction of the unstable methyl phosphinate 779 with different amounts of aryl iodides. Tnmethyl orthoformate is added to stabilize the methyl phosphinate[640]. 

Although unsynunetrically substituted amines are chiral, the configuration is not stable because of rapid inversion at nitrogen. The activation energy for pyramidal inversion at phosphorus is much higher than at nitrogen, and many optically active phosphines have been prepared. The barrier to inversion is usually in the range of 30-3S kcal/mol so that enantiomerically pure phosphines are stable at room temperature but racemize by inversion at elevated tempeiatuies. Asymmetrically substituted tetracoordinate phosphorus compounds such as phosphonium salts and phosphine oxides are also chiral. Scheme 2.1 includes some examples of chiral phosphorus compounds. 

Speziale and his co-workers have carried out comprehensive studies of the reactions of phosphorus compounds. It has been shown 108) that the reaction of N,N-dialkyl-a-trichloroacetamides (127) with phosphites and phosphines gives trichlorovinylamines (128). In general the trialkyl-phosphines gave somewhat higher yields (60 to 83%) and purer products... 

The recommended names for these compounds (phosphinic acid and phosphinates) have not yet gained wide acceptance for inorganic compounds but are generally used for organophosphorus derivatives. Hypophosphites can be made by healing white phosphorus in aqueous alkali ... 

A similar situation occurs in trivalent phosphorus compounds, or phosphines. It turns out, though, that inversion at phosphorus is substantially slower than Inversion at nitrogen, so stable chiral phosphines can be isolated. (R)- and (5)-metbylpropylphenylphosphine, for example, are configurationally stable for several hours at 100 °C. We ll see the Importance of phosphine chirality in Section 26.7 in connection with the synthesis of chiral amino adds. 

A comparison of bromine and phosphorus compounds on the flammability of PET fiber shows phosphorus (as phosphine oxide) to be 3.7 times more effective than bromine (Table 1). No synergy was observed. Nevertheless, phosphorus was shown to be more effective than antimony normally used as a synergist, resulting in a higher oxygen index at a lower concentration (Table 2). 

Two papers have appeared on the reactions of halogenophosphines with tervalent phosphorus compounds. In a detailed study of the reactions at 20 °C of a range of tertiary phosphines with phosphorus trichloride, dichlorophenylphosphine, and chlorodiphenylphosphine, it has been shown that, in general, 1 1 adducts are formed, provided that the tertiary phosphine is a good nucleophile. With diphenylchlorophosphine, for example, an adduct (18) is formed with dimethylphenylphosphine, but not with diphenylmethylphosphine, although the relative importance of steric and electronic factors remains to be established. The related reactions of phosphorus trichloride and of dichlorophenylphosphine are much more complex, and the initial crystalline products are not amenable to analysis. The reactions at 280 °C of a similar system have been shown to lead to halogen exchange, e.g. the conversion of (19) to (20). 

Many catalysts, both immobilized (on solid state supports) and heterogeneous, contain phosphines and other phosphorus compounds, so that solid state NMR has become an invaluable tool in the study of catalysis. 

Fluck, E. and Lorenz, J., Nuclear magnetic resonance of phosphorus compounds. XIV. Chemical shifts of phosphines, phosphonium salts, and diphos-phinonickel(II) chlorides, Z. Naturforsch., 22B, 1095, 1967. 

For propargyl phosphorus compounds, examples with cyclotriphosphazenes 135 [342] (Scheme 1.60), phosphinates 137 [343] (Scheme 1.61) and phosphonates 139 [344] (Scheme 1.62) have been published. 

It will be seen that the above system of nomenclature has the virtue of simplicity and is easy to memorize. All that one has to keep in mind is phosphon- for quinquivalent phosphorus compounds and phosphin- for tervalent phosphorus compounds. In fact, the above system was successfully used in Britain until 1950 and may be summarized thus ... 

Solvent and temperature effects have been especially studied in simple compounds—white phosphorus,(1969 180) PH3, (1967>43> PFS, (1968,51) phosphorus acid, phosphines, phosphonium compounds etc. (1965> 39 1967,169 1968,155 1969,53) phosphorus chemical shifts or line-widths,... 

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