Conversion of tricoordinate to hexacoordinate phosphorus. Formation of a phosphorane-phosphatrane system

Reaction of RPCl(2) with tris(2-hydroxy-3-tert-butyl-5-methylbenzyl)amine (4) led to the formation of a tricoordinated phosphonite (1) when R = Ph and to a hexacoordinated phosphorane-phosphatrane (2) when R = Et. The X-ray structures showed that the unreacted hydroxyl group in 1 oxidatively added to phosphorus in 2 leading to the formation of three additional bonds, a P[bond]O, a P[bond]H, and a P[bond]N linkage. In solution, (31)P measurements assisted by solid-state (31)P measurements revealed that each of the compounds existed in both structural forms. VT (31)P established equilibria where the solid-state structures predominated in each case. This is the first example of a conversion of three-coordinate to six-coordinate phosphorus on going from the solid to the solution state and the existence of these two disparate geometries in equilibrium with one another in solution. In the absence of steric protection with the use of an analogous amine (5) without tert-butyl groups, a hydrolysis reaction occurred with PhPCl(2). X-ray analysis revealed an anionic phenylphosphinate structure (3) hydrogen bonded in a cage-like arrangement with the protonated amine. Similar hydrolysis reactions take place with 1 and 2 but much more slowly.