Evaluation of the Stereoelectronic Parameters of Fluorinated Phosphorus(III) Ligands. The Quantitative Analysis of Ligand Effects (QALE)

Abstract

Using the QALE model, we determined the QALE stereoelectronic parameters for the following ligands:In addition, we evaluated the parameters for P. Revised parameters for PF 3 are also presented: χ d ) 33 ( 2, θ ) 110 ( 24°, E ar ) 0, π p ) 13.2 ( 0.5. The absence of an indicated error means that these values were assigned initially to the particular parameters in the analyses or that the parameters are statistically indistinguishable from zero. Where a comparison can be made, we find that our calculated values of θ are indistinguishable from those of Tolman; therefore, we suggest the continued use of Tolman's values. It is observed that the perfluoroalkyl groups are highly π acidifying and that this effect is transmitted through intervening CH 2 groups.

Tuning the Electronic Properties of N‐Heterocyclic Carbenes

“…For the other anilines, the normal sequence of diimine formation (products 1-6) and ring closure leads to the respective imidazolium salts (13 u·H + -18 u·H + ) with a Cl À counter ion. The sequence of diimine formation and LiAlH 4 reduction of the imines results in the formation of the related diamines (7)(8)(9)(10)(11)(12) and ring closure leads to the analogous imidazolinium salts ( 2 with the respective free carbene (Scheme 3) according to a general procedure by Herrmann. [38] Bubbling of CO through solutions of these complexes generated the respective [IrCl(CO) 2 A C H T U N G T R E N N U N G (NHC)] complexes in virtually quantitative conversions.…”

“…[1] Subtle variations of steric bulk and electron density at the active site may have drastic effects on the catalytic efficiency. [2][3][4][5][6] Consequently, the quantification of the steric and electronic effects of ligands, [7][8][9][10] such as through the classic approach by Tolman, [11] is essential. N-Heterocyclic carbenes (NHCs) are rivaling the leading status of phosphines as ligands in homogeneous catalysis.…”

SambVca: A Web Application for the Calculation of the Buried Volume of N‐Heterocyclic Carbene Ligands

“…In the case of the electronic parameter E, which represents the result of changes in molecular properties arising from transmission along chemical bonds, [1] the procedure originally suggested by Tolman was to relate it to the frequency of the A l carbonyl mode of Ni(CO) 3 L complexes. Other electronic parameters have been proposed and used, [2][3][4][5][6][7][8] but because this paper is focused on the steric parameter S we do not discuss the electronic parameter E any further.…”

“…[61] The fairly large and consistent set of DFT binding energies (E DFT ) was fitted by use of Equation (2), (2) in which E ST , the singlet-triplet splitting of the isolated NHC, was assumed as the electronic parameter E of 1.…”

“…[ [62][63][64] As in the case of the % V Bur values, we decided to use an aseptic estimate from NHC geometries in prototype (NHC)-Ir(CO) 2 Cl complexes, which in the case of the Tolman cone angle calculations should in principle mimic the (PR 3 )-Ni(CO) 3 prototype complex. For the atomic radii we used the Bondi radii of Table 1, a well accepted set commonly used in the literature, [65] and we found that the DFT dimerization energies were better reproduced (R 2 = 0.93) if the radius of the sphere (R) was set equal to 4.0 Å.…”