Solvent stabilization of the edge inversion transition state in tetrahedral molecules

Abstract

The edge inversion process in phosphoric acid, PO(OH), has been studied by large scale ab initio molecular orbital theory. Edge inversion of the tetrahedral ground state via a square-planar transition state requires 69.5 kcal/mol (MP-2). Addition of two NH, solvent molecules to the vacant NLUMO stabilizes the transition state by 45 kcal/mol (MP-2). The value for AH(300K) for the reaction 2NH3 + PO(OH)3 + PO(OH), . (NH,), is 24.1 kcal/mol (MP-2). The complex with two NH, molecules is an intermediate. Addition of one NH, to PO(OH), leads to an energy lowering of the planar form of 31 kcal/mol. This structure is now a transition state. The value for AH(300K) for the reaction NH3 + PO(OH), + PO(OH)3 .NH, is 38.6 kcal/mol (MP-2). The complex of PF30 with two NH3 molecules was studied and is an intermediate. The value for AH(300K) for the reaction 2NH3 i WF3 -P POF, . (NH,), is only 3.3 kcal/mol (MP-2). Electron-donor solvents clearly will stabilize the edge inversion transition state for tetracoordinate main group compounds.

Non-classical structures of organic compounds: unusual stereochemistry and hypercoordination

“…The methonium ion is the parent compound for pentacoordinate carbon derivatives. Protonated methane (65) was first detected in the gas phase by mass spectroscopy by Talrose and Lubimova 134,135 and in superacid liquid media by Olah and coworkers. 136 ± 138 The methonium ion is important for astrophysics, as its microwave spectrum serves as an indicator of methane content in molecular galactic clouds.…”

“…) deformations are symmetry allowed. 15,63,64 The latter mechanism is also referred to as edge inversion 65,66 (as opposed to vertex inversion, characteristic of the stereoisomerisation of tricoordinated pyramidal structures). Detailed investigations 61,62 of the reaction pathway of methane stereoisomerisation using the method of intrinsic reaction coordinate (i.e., the trajectory obtained by moving down from the point on the PES corresponding to the transition state along the transition vector 67 ) showed that these trajectories are actually more intricate (Fig.…”

Periodicity in Structure, Bonding, and Reactivity for P-Block Complexes of a Geometry-Constraining Triamide Ligand

“…Together with the NMR spectroscopy data, we infer that 1 and 2 exist predominantly as bent monomeric molecules in their ground state in solution,a lthough duet ot he well-established facilityo fe dge-inversion in such speciesa low-lyingp lanar transitions tate is also expected (see below). [18] At 298 K, the spectra of 3 and 4 in pentanee xhibit two absorptions in the visible range, with values for the antimony analogue being hypsochromically shifted ( Figure 5c and d). The number of spectral features and their relative positions agree with TD-DFT predictionsb ased on the monomeric planar forms, but differ significantly from calculations performed on either the monomeric bent models or dimers 3 dim and hypothetical 4 dim .U pon cooling as olution of 3 in pentane to 193 K, the prominentb ands observed at 298 K( 525 and 443 nm) diminishs ubstantially whereas the bands at around3 85 nm decrease only marginally ( Figure S9, Supporting Information).…”

Dynamic aspects of hypervalent compounds effected by the formation of three center‐four electron bond in heteroatoms

“…Arduengo et al have already investigated the inversion at the germanium atom of 26 and concluded that the inversion proceeds by the edge inversion mechanism [30]. Thus, there is a good possibility for the edge inversion mechanism to be operative generally for heavier main group compounds even without lone-pair electrons.…”

“…Dixon and Arduengo predict that considerable stabilization of the TS should also be obtained by the second coordination of a nucleophile even after a large stabilization by the first one [30]. Then we prepared bismuth(III) (21 and 22) and antimony(III) compounds (23 and 24), each bearing one or two dimethylaminomethyl groups in the molecule that can coordinate to the central atom.…”