Synthesis and structure of cyclic phosphate, phosphoramidate, phosphonates, and phosphonium salts. Phosphatrane formation

Reaction of tris(2-hydroxy-3,5-dimethylbenzyl)amine (6) with phosphorus reagents led to the formation of the phosphoramidate, NCH2(Me2C6H2)O]2PO (1), the phosphate NCH2(Me2C6H2)O]2CH2(Me2C6H2)OH]P(O)(OPh) (2), the phosphonium salts NCH2(Me2C6H2)O]3PMe+I- (3A) and NCH2(Me2C6H2)O]3PMe+I3- (3B), and the phosphonates NCH2(Me2C6H2)O]2CH2(Me2C6H2)OH]P(O)Me (4) and NCH2(Me2C6H2)O]2CH2(Me2C6H2)OSiMe3]P(O)Me (5). X-ray analysis provided molecular structures for all of the compounds. The solid-state structural representations were supported in solution by an analysis of the NCH2 proton NMR patterns. The structures of 3A and 3B show the presence of phosphatranes with weak P-N donor interactions. These represent the first phosphatranes containing all six-membered rings. Variable temperature analysis of the 1H NMR spectra of 3A indicates fluxional behavior whereby a racemic mixture of the chiral phosphonium salt rapidly intraconverts at room temperature. The activation energy for the enantiomeric conversion of the clockwise and anticlockwise orientations of the propeller-like phosphatrane is 11.2 kcal/mol, which is compared to that of the isoelectronic silatrane NCH2(Me2C6H2)O]3SiMe (E), 10.3 kcal/mol.