Dynamic interaction of theory and experiment: total determination of the gas-phase molecular structure of tri-tert-butylphosphine oxide (OPBu^t₃)

Abstract

A new method to aid the determination of structures of sterically crowded molecules in the gas phase by dynamically linking the gas-phase electron diffraction (GED) refinement process with computational methods has been developed. The procedure involves refining the heavy-atom skeleton of the molecule using the GED data while continually updating the light-atom positions during the refinement using computational methods, in this case molecular mechanics. This removes errors associated with the assumption of local symmetry for the light-atom groups, which can affect the final values of the heavy-atom parameters. The refinement of the molecular structure of tri-tert-butyl phosphine oxide has been used to illustrate this new technique, which we call the DYNAMITE (DYNAMic Interaction of Theory and Experiment) method. Re-examination of the structure using this method has resulted in a shorter P-O distance than was found in a less sophisticated anaylsis, and is consistent with the molecule being regarded as O=PBut3, rather than O(-)-P+But3.

Structure and Bonding Nature of the Strained Lewis Acid 3‐Methyl‐1‐boraadamantane: A Case Study Employing a New Data‐Analysis Procedure in Gas Electron Diffraction

“…[5] These obtained data are of course of rather limited use in the discussion of properties and reactivity on the basis of the geometrical features of free 1-boraadamantane molecules, because the influence of Abstract: Base-free 3-methyl-1-boraadamantane was synthesized by starting from its known THF adduct, transforming it to a butylate-complex with n-butyllithium, cleaving the cage with acetyl chloride to give 3-n-butyl-5methyl-7-methylene-3-borabicyclo-A C H T U N G T R E N N U N G [3.3.1]nonane and closing the cage again by reacting the latter with dicyclohexylborane. The identity of 3methyl-1-boraadamantane was proven by 1 H, 11 B and 13 C NMR spectroscopy and elemental analysis. The experimental equilibrium structure of the free 3methyl-1-boraadamantane molecules has been determined at 100 8C by using gas-phase electron diffraction.…”

“…There were studies in which the comparisons of results, produced with usage of rigid and flexible restraints, have been performed by using refined values of parameters and their standard deviations. [10,13] However, a reliable comparison of structural methods can only be based on total errors. For this study of 3-methyl-1-boraadamantane we needed to elaborate an even more advanced approach of structure refinement and its assessment.…”

Gas-phase structures of 1-adamantylphosphines, PH n (1-Ad)3−n (n = 1–3)

“…C(3) 0 C(2) 0 PZ and C(4) 0 C(2) 0 PZ were found to be -140.4°a nd 106.4°, indicating that the absolute twist of each adamantyl group is 17°. This is a typical value for a compound containing a moiety of the type X(YZ 3 ) 3 , including t-butylphosphine derivatives [10,21,22], and sterically hindered disilane molecules, such as 1,1,2-tri-t-butyl disilane [23].…”

Structure by theory and experiment: One nationality, two languages

“…I total ϭI atomic ϩI molecular ϩI background (1) The total scattering reveals little information. The top diagram in Figure 2 is a favourable example, and even in this case very little pertinent information can be seen.…”

“…A new method to deal with this problem has recently been developed by the Edinburgh group. The technique involves the dynamic interaction of theory and experiment (DYNAMITE) [1], whereby molecular mechanics methods are used to constantly update the light atom positions, whilst the heavy atom positions refine using the experimental data. This allows a more realistic molecular structure to be determined, free from symmetry constraints that may have been imposed upon the light atoms due to lack of information.…”