ChemInform Abstract: Phosphorotropic Tautomerism in Amidine Systems

Abstract

367ChemInform Abstract (4 refs.).

Neutral Six-Coordinate Phosphorus

“…Kal'chenko and co-workers 13,58,59 analyzed the isomerization of similar six-coordinate compounds, PCl 4 [(NR) 2 CCX 3 ] (10), in which intramolecular chlorine atom migration occurs to give the five-coordinate phosphorus(V) derivatives, PCl 3 [(NR) 2 CCX 3 (Cl)], where X ) Cl or F, R pairs are Me and Me, Me and Et, Me and i-Pr, or Me and t-Bu (Figure 6). Dynamic multinuclear ( 1 H, 13 C, and 31 P) NMR studies were used to follow the shift in equilibrium between the two isomers. Also the tetrachloroamidinate systems, PCl 4 (NMe) 2 CX (X ) CCl 3 ) 60 and (X ) Ph, CCl 3 , and CF 3 ) 61 were investigated with 35 Cl NQR spectroscopy.…”

“…62 A mechanism for the isomerism was proposed based on the migration of an axial chlorine atom to form a contact ion pair in the transition state and the phosphorus adopts first a square-pyramidal geometry which is then easily rearranged to the final trigonal-bipyramidal configuration (Figure 7). 13,14 Aspects of this amidine chemistry 13 and the more…”

“…Kal'chenko and co-workers ,, analyzed the isomerization of similar six-coordinate compounds, PCl 4 [(NR) 2 CCX 3 ] ( 10 ), in which intramolecular chlorine atom migration occurs to give the five-coordinate phosphorus(V) derivatives, PCl 3 [(NR) 2 CCX 3 (Cl)], where X = Cl or F, R pairs are Me and Me, Me and Et, Me and i -Pr, or Me and t -Bu (Figure ). Dynamic multinuclear ( 1 H, 13 C, and 31 P) NMR studies were used to follow the shift in equilibrium between the two isomers.…”

“…The IR data suggested that PCl 4 (NMe) 2 CCCl 3 is stable in the solid state without signs of chlorotropism but that the process occurs in solution, shifting to the predominance of the six-coordinate form as the polarity of the solvent increases . A mechanism for the isomerism was proposed based on the migration of an axial chlorine atom to form a contact ion pair in the transition state and the phosphorus adopts first a square-pyramidal geometry which is then easily rearranged to the final trigonal-bipyramidal configuration (Figure ). , Aspects of this amidine chemistry 13 and the more general coordination isomerism behavior of phosphorus compounds 14 have been reviewed.

6 Halogen tautomers of 10 due to intramolecular chlorine atom migration.

7 Proposed contact ion pair intermediate for axial chlorine atom migration mechanism in 10 .

…”

“…That review covered both adduct and ionized species of phosphorus(V) pentahalides. In 1987, Cherkasov and Polezhaeva 12 and more recently Markovskii et al 13,14 have reviewed some aspects of their work on hexacoordinate phosphorus(V) chemistry. These reports will provide an additional guide to some aspects of the work described in the present review.…”