Facile pyramidal inversion at phosphorus in [R3EP7W(CO)3]2− type complexes: An EXSY NMR study

Abstract A series of [R 3 EP 7 W(CO) 3 ] 2− complexes where (E = Si, Ge, Sn, Pb; R = alkyl, phenyl) were prepared from [P 7 W(CO) 3 ] 3− and R 3 EX reagents (X = Cl, Br) in dmf or CH 3 CN solutions. The Pb derivatives were prepared at −50 °C and are not thermally stable. The compounds were characterized by 31 P NMR spectroscopy and selected ESI-MS studies. All compounds undergo rapid inversion at the ER 3 -bound phosphorus atom. The barriers to inversion were measured by way of 2D 31 P EXSY experiments at various temperatures. The analysis showed very low barriers to pyramidal inversion (Δ G ‡ 10.3–13.5 kcal/mol) that were essentially enthalpic in origin. The activation barriers generally increased with increasing electronegativity of the E atom and the steric bulk of the ER 3 substituents. The latter was interpreted by way of a non-linear transition state.