Abstract
Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its 31P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this 31P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported.
Highlights
Transition metal organometallics are critically important in modern chemistry, regardless of whether it concerns novel reaction pathways or enhanced selectivity
The structure of organometallic compounds in solution can be highly dependent on competing solute–solvent interactions
Because the phosphorus atom of the P=O group is not directly involved in intermolecular interactions, its chemical shift is not strictly specific to a certain interaction, and different structures can result in similar chemical shift values [32]
Summary
Transition metal organometallics are critically important in modern chemistry, regardless of whether it concerns novel reaction pathways or enhanced selectivity. The exact chemical composition, structure and conformation of these catalysts may be very complex and dependent on their environment [1,2,3,4,5,6]. The structure of organometallic compounds in solution can be highly dependent on competing solute–solvent interactions. Because the phosphorus atom of the P=O group is not directly involved in intermolecular interactions, its chemical shift is not strictly specific to a certain interaction, and different structures can result in similar chemical shift values [32]. 31 P NMR chemical shift may depend on the conformation of the attached groups [25]. This effect is absent for rigid molecules, such as 1,3,5-triaza7-phosphaadamantane (PTA, Figure 1) and 2,8,9-trioxa-1-phosphadamantane [34]. PTA is especially useful as an NMR probe because its phosphorus atom is chemically inert
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