title: Stereomutation of pentavalent compounds: validating the Berry pseudorotation, redressing Ugi's turnstile rotation, and revealing the two- and three-arm turnstiles.
abstract: A general reaction mechanism describes the qualitative change in chemical topology along the reaction pathway. On the basis of this principle, we present a method to characterize intramolecular substituent permutation in pentavalent compounds. A full description of the geometry around five-coordinate atoms using internal coordinates enables the analysis of the structural changes along the stereomutational intrinsic reaction coordinate. The fluxional behavior of experimentally known pentavalent phosphoranes, silicates, and transition-metal complexes has been investigated by density functional theory calculations, and three principal mechanisms have been identified: Berry pseudorotation, threefold cyclic permutation, and half-twist axial-equatorial interchange. The frequently cited turnstile rotation is shown to be equivalent to the Berry pseudorotation. In combination with graph theory, this approach provides a means to systematically investigate the stereomutation of pentavalent molecules and potentially identify hitherto-unknown mechanisms.
authors.affiliation: Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands. couzijn@org.chem.ethz.ch
authors.forename: Erik P A
authors.initials: EP
authors.lastname: Couzijn
authors.forename: J Chris
authors.initials: JC
authors.lastname: Slootweg
authors.forename: Andreas W
authors.initials: AW
authors.lastname: Ehlers
authors.forename: Koop
authors.initials: K
authors.lastname: Lammertsma