Phosphorus multiple bond formation

A common theme in the speculated polymerization reactions discussed in this section is that the polymers were generally uncharacterized or were composed of small cyclic oligomers. No evidence for high molecular weight polymers from low-coordinate phosphorus compounds was obtained. Of course, multiple bond formation, not polymerization, was the focus of these studies. 

The chemistry of trivalent phosphorus compounds in which phosphorus is one or two coordinate is rapidly developing. These systems contain sp or sp2 hybridized phosphorus and multiple TT-bonds between P and other elements and until 1964 it was believed that bond formation involving ptr-pir overlap was unfavourable. Subsequently certain -P=C systems resulted from the use of charged ( 1, 2, 3) and or delocalized systems (4J but it is only in the past few years that successful syntheses of phospha-alkenes, R2C=PR , and phospha-alkynes, RC=P, have been reported. These novel compounds are the subject of this paper. 

The phosphorus activation of alcohols to substitution with inversion of configuration. The reactions are based on the high heat of formation of the P-O bond and the tendency for phosphorus to form multiple bonds with oxygen. For example, treatment of an alcohol with triphenyl phosphite and methyl iodide leads to the corresponding iodo compound (Scheme 2.17). 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

Essentially all the reactions reported which result in the stereoselective formation of a C - I> bond involve (formally) trivalent phosphorus compounds. The reactions consist mainly of the addition of trivalent phosphorus compounds to C-C and C-heteroatom multiple bonds1. 

---