An Investigation of 1:1 Adducts of Gallium Trihalides with Triarylphosphines by Solid-State69/71Ga and31P NMR Spectroscopy

Abstract

Several 1:1 adducts of gallium trihalides with triarylphosphines, X(3)Ga(PR(3)) (X=Cl, Br, and I; PR(3)=triarylphosphine ligand), were investigated by using solid-state (69/71)Ga and (31)P NMR spectroscopy at different magnetic-field strengths. The (69/71)Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the (71)Ga quadrupolar coupling constants (C(Q)((71)Ga)) range from approximately 0.9 to 11.0 MHz. The spans of the gallium magnetic shielding tensors for these complexes, δ(11)-δ(33), range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In(III)-phosphine complexes. This experimental trend, attributed to spin-orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C(Q)((69/71)Ga) for some of the adducts were determined from the analysis of the (31)P NMR spectra acquired with magic angle spinning (MAS). The (1)J((69/71)Ga,(31)P) and ΔJ((69/71)Ga, (31)P) values, as well as their signs, were also determined; values of (1)J((71)Ga,(31)P) range from approximately 380 to 1590 Hz. Values of (1)J((69/71)Ga,(31)P) and ΔJ((69/71)Ga,(31)P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi-contact and spin-dipolar Fermi-contact mechanisms make important contributions to the (1)J((69/71)Ga,(31)P) tensors. The (31)P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single-crystal X-ray diffraction data for Br(3)Ga[P(p-Anis)(3)] and I(3)Ga[P(p-Anis)(3)] were obtained.