Weak intramolecular proton-hydride and proton-fluoride interactions: Experimental (NMR, X-ray) and DFT studies of the bis(NBH3) and bis(NBF3) adductsof 1,3-dimethyl-1,3-diazolidine

Citation
M. Guizado-rodriguez et al., Weak intramolecular proton-hydride and proton-fluoride interactions: Experimental (NMR, X-ray) and DFT studies of the bis(NBH3) and bis(NBF3) adductsof 1,3-dimethyl-1,3-diazolidine, J AM CHEM S, 123(37), 2001, pp. 9144-9152
Citations number
45
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry & Analysis",Chemistry
Journal title
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
ISSN journal
0002-7863 → ACNP
Volume
123
Issue
37
Year of publication
2001
Pages
9144 - 9152
Database
ISI
SICI code
0002-7863(20010919)123:37<9144:WIPAPI>2.0.ZU;2-O
Abstract
Bis(NBH3), bis(NBF3), and NBF3/NBH3 adducts 1-3 were prepared from 1,3-dime thyl-1,3-diazolidine and characterized by the H-1, C-13, B-11, F-19, 2D H-1 -C-13 HETCOR and NOESY NMR spectra. The structures and conformations of the adducts were established by the variable-temperature H-1 NMR spectra, the X-ray diffraction method (adduct 2A), and density functional calculations a t different theoretical levels. The experimental and theoretical data have revealed that bis adducts 1-3 prefer trans orientations of the borane group s (1A, 2A, 3A) in solution, the solid state, and the gas phase. The studies have shown that the energetic preference of trans adducts with respect to cis compounds, decreasing as 2A (2.9 kcal/mol) > 3A (2.7 kcal/ mol) > 1A (1 .4 kcal/mol), is dictated by spatially repulsive interactions between the C H3, BH3, and BF3 groups. The results of DFT calculations agree well with an experimental trans/cis isomeric ratio of 9:1 determined in solutions of ad duct 1. The calculated geometry and energy, as well as the topological anal ysis of electronic densities, show that trans adducts 1-3 should exist in g as phase as twist conformations T-2 stabilized by the intramolecular C-Hdel ta+. . . H-delta-B or C-Hdelta+. . . F-delta-B interactions. These interact ions are characterized as closed-shell. The energy of one proton-hydride an d proton-fluoride intramolecular contact, estimated as 1.9 1A-T-2) and 0.7 (2A-T-2) kcal/mol, respectively, classifies the "elongated" intramolecular interactions CHdelta+. . . -deltaHB and CHdelta+. . . -deltaFB as weak ones . It has been established that, on going from gas phase to a condensed phas e (solution and solid), the twist-conformations T-2 transform to conformati ons T-1, probably by intermolecular dipole-dipole interactions. The data pr esented in this work show that despite a weakness of the "elongated" proton -hydride and proton-fluoride interactions, they can play a significant role in the stabilization of conformational molecular states, especially when c ooperativity is in action.