Measuring and Leveraging Electrostatic Effects in a Charged Phosphine

<div>Local electric fields have recently been investigated for optimizing reactivity in synthetic systems. However, disentangling the relative contributions of inductive (through-bond) and electrostatic (through-space) effects in molecular systems has been a long-standing challenge. To understand the interplay of these effects and leverage electrostatic influences for enhanced reactivity, we have synthesized a distally charged phosphine, Ph₂PCH₂BF₃⁻, and studied the effect of the charged trifluoroborate group on its donor properties and reactivity. This charged phosphine displays solvent-dependent changes in donor strength as measured by the <i>J</i>_P-Se of the corresponding phosphine selenide. The variation with solvent dielectric illustrates a significant electrostatic component to the donor strength. Computations further support the importance of electrostatic contributions and highlight the effect of charge position and orientation. Finally, this charged group also greatly accelerates C–F oxidative addition reactivity in Ni complexes, experimentally</div><div>verifying recent theoretical predictions. These results show that covalently bound charged functionalities can exert a significant electrostatic influence even under common solution phase reaction conditions.</div>

Measuring and Leveraging Electrostatic Effects in a Charged Phosphine

<div>Local electric fields have recently been investigated for optimizing reactivity in synthetic systems. However, disentangling the relative contributions of inductive (through-bond) and electrostatic (through-space) effects in molecular systems has been a long-standing challenge. To understand the interplay of these effects and leverage electrostatic influences for enhanced reactivity, we have synthesized a distally charged phosphine, Ph₂PCH₂BF₃⁻, and studied the effect of the charged trifluoroborate group on its donor properties and reactivity. This charged phosphine displays solvent-dependent changes in donor strength as measured by the <i>J</i>_P-Se of the corresponding phosphine selenide. The variation with solvent dielectric illustrates a significant electrostatic component to the donor strength. Computations further support the importance of electrostatic contributions and highlight the effect of charge position and orientation. Finally, this charged group also greatly accelerates C–F oxidative addition reactivity in Ni complexes, experimentally</div><div>verifying recent theoretical predictions. These results show that covalently bound charged functionalities can exert a significant electrostatic influence even under common solution phase reaction conditions.</div>

Tris(2-methoxyphenyl)phosphine selenide

The title compound C21H21O3PSe, is comprised of a P atom in a distorted tetrahedral environment, attached to the selenium atom and three carbons from the phenyl rings. The phosphorus–selenium bond length is 2.1194 (11) Å. All three methoxy groups are nearly co-planar with their respective phenyl rings, with the angles between the phenyl ring and the C—O bond of the methoxy groups being 6.2 (2), 3.1 (2), and 5.7 (2)°. The torsion angles of the phenyl rings relative to the P=Se bond are 55.84 (19), 176.18 (16), and 63.9 (2)°. No strong interactions were observed, but in addition to van der Waals forces, there are close contacts between C—H...π and C—H...Se.

Tris(4-methoxyphenyl)phosphine selenide

The title compound, C21H21O3PSe, is comprised of a P atom in a distorted tetrahedral environment, attached to the Se atom and three C atoms of the phenyl rings. The P—Se bond length is 2.1214 (12) Å. All three methoxy groups are near coplanar with their respective phenyl rings, with the angles between the phenyl ring and the C—O bond of the methoxy groups being 5.7 (2), 1.5 (4), and 5.7 (3)°. The torsion angles of the phenyl rings relative to the P=Se bond are 35.62 (10), 35.07 (13), and 44.50 (11)°. No strong intermolecular interactions were observed, but that in addition to van der Waals forces, there are C—H...π and C—H...Se close contacts.