Tervalent Phosphorus Amides

The reaction of tervalent phosphorus amides containing a NH with activated olefins predictably gives phosphine imines, e.g. (24), through addition and proton transfer. 

Once again, the drive for improved performance in transition metal ion-catalysed processes has continued to stimulate the synthesis of new types of organophosphine and tervalent phosphorus-ester and -amide ligands. Activity in the chemistry of heteroaromatic phosphorus ring systems and low-coordination number p -bonded systems has also remained at a high level. New mechanistic insights into the Mitsunobu reaction have been reported, and interest in synthetic applications of Staudinger/Mitsunobu procedures has continued to develop. 

As this chapter covers two years of the literature relating to the above area, it has been necessary to be somewhat selective in the choice of publications cited. Nevertheless, it is hoped that most significant developments have been noted. As in previous reports, attempts have been made to minimise the extent of overlap with other chapters, in particular those concerned with the synthesis of nucleic acids and nucleotides to which the chemistry of tervalent phosphorus esters and amides contributes significantly, the use of known halogen-ophosphines as reagents for the synthesis of phosphines (see Chapter 1), and the reactions of dialkyl- and diaryl-phosphite esters in which the contribution of the phosphonate tautomer, (R0)2P(0)H), is the dominant aspect, which are usually covered elsewhere in these volumes. 

As in recent years, the synthesis of new chiral phosphines and related chiral tervalent phosphorus esters and amides continues to be a major preoccupation, being driven by the need for improved performance in metal-catalysed processes. It is very pleasing to note that two of the recipients of the 2001 Nobel Prize for Chemistry, William S. Knowles, and Ryoji Noyori, are honoured for their work in the synthesis and application in catalysis of chiral phosphine ligands. Interest in the structures of metallo-organophosphide systems, noted in the previous volume, has continued to develop. The chemistry of heteroaromatic ring systems, notably that of phospholes, and of low coordination number p -bonded compounds, also remain active areas. 

Oxaphospholans.—Full details have appeared of the reactions of the lactone and dione dimers of dimethylketen with a series of tervalent phosphorus esters and amides, and the postulated quinquecovalent intermediate (49) from the lactone dimer has been isolated in one case. Of potential mechanistic significance is the preferred migration of exocyclic substituents in the steps corresponding to (49) (50). 

The hydrolysis of tervalent phosphorus acid derivatives with two P—C bonds leads to secondary phosphine oxides (50) and with one P—C bond to phosphonus acid derivatives (51). Chlorophosphines react rapidly with water, but aminophosphines, phosphinites and phosphonites often survive a short wash with aqueous NaHC03, an effective way to remove contaminating ammonium salts in the crude products. However, aminophosphines with small substituents, e.g. dimethylaminodimethylphosphine, aryl phosphinites and phosphonites and trimethylsilyl phosphinites and phosphonites are hydrolysed too quickly for such a treatment. The hydrolyses are catalysed by acids (the hydrolyses of phosphinites and phosphonites are also catalysed by OH ) and are much faster than hydrolyses of the corresponding phosphoryl compounds [up to a factor of 10 for acid-catalysed hydrolysis of (MeO)3P compared with (MeO)3P=0 ]. Dialkyl phosphonites are rapidly hydrolysed to the monoalkyl esters (51, X = OR) in weakly acidic water, whereas hydrolyses to phosphonous acids require reflux with strong acid or base, e.g. equation 131 Bis-(dialkylamino) phosphines may also be partially hydrolysed to phosphonous acid amides (51, X = NR2). Tervalent phosphorus acid derivatives with hydrogen sulphide give secondary phosphine sulphides or phosphonodithious acids, e.g. equation 156 . ... 

---