Tricoordinated phosphorus compounds, reactivity

The most direct synthesis is performed by reaction of a dihalo compound with a tricoordinated phosphorus compound including a reactive P—Y bond (reaction 101). This synthesis, first used with secondary phosphines, the corresponding phosphides or diphosphines (Y = H, Na, K, PPh2)2b,38°, has subsequently been developed also with silylphosphines (Y = SiMe3),132,381-383 which are easier to handle (reaction 102). The same kind of cyclization by intramolecular alkylation can be achieved using a functional phosphine prepared in a multi-step synthesis380,384,385 (reaction 103). 

Tricoordinate phosphorus >P-X compounds containing a suitable leaving group are indispensable in the synthesis of biophosphates and their structural analogues. In contrast to phosphoryl >P(0)-X and thiophosphoryl >P(S)-X, compounds they are spectacularly more reactive in nucleophilic displacements at the phosphorus centre. Westheimer has compared reactions of P compounds with nucleophiles to enzymatic reactions regarding their reactivity [1]. The essential feature of P compounds is their free electron pair with all the structural, stereochemical and mechanistic consequences that follow. P compounds have the structure of a trigonal pyra-... 

Black phosphorus may be either amorphous or crystalline. It exhibits quite low reactivity, both with oxygen and other reagents, compared to white or red phosphorus, and is stable in air. Because it has a puckered shape, the phosphorus remains tricoordinated in black phosphorus and crystallizes in sheets in a way similar to the behavior of graphite. Black phosphorus is generated from white phosphorus either by heating under pressure or in the presence of mercury. It is of relatively little value for the synthesis of organophosphorus compounds. 

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