Solid-state 115In and 31P NMR studies of triarylphosphine indium trihalide adducts

Article abstract of DOI:10.1021/ja100625p

Solid-state ¹¹⁵In and ³¹P NMR spectroscopy, relativistic density functional theory (DFT) calculations, and single-crystal X-ray diffraction were used to investigate a series of triarylphosphine indium(III) trihalide adducts, X₃In(PR₃) and X ₃In(PR₃)₂ (X = Cl, Br or I; PR₃ = triarylphosphine ligand). The electric field gradient tensors at indium as well as the indium and phosphorus magnetic shielding tensors and the direct and indirect ¹¹⁵In-³¹P spin-spin coupling were characterized; for complexes possessing a C₃ symmetry axis, the anisotropy in the indirect spin-spin coupling, δJ(¹¹⁵In,³¹P), was also determined. The ¹¹⁵In quadrupolar coupling constants, C _Q(¹¹⁵In), range from ±1.25 ± 0.10 to -166.0 ± 2.0 MHz. For any given phosphine ligand, the indium nuclei are most shielded for X = I and least shielded for X = Cl, a trend also observed for other group-13 nuclei in M(III) complexes. This experimental trend, attributed to spin-orbit effects of the halogen ligands, is reproduced by the DFT calculations. The spans of the indium magnetic shielding tensors for these complexes, Δ₁₁ - Δ₃₃, range from 40 ± 7 to 710 ± 60 ppm; those determined for phosphorus range from 28 ± 1.5 to 50 ± 3 ppm. Values of ¹J(¹¹⁵In, ³¹P) range from 550 ± 20 to 2500 ± 20 Hz. For any given halide, the ¹J(¹¹⁵In,³¹P) values generally increase with increasing basicity of the PR₃ ligand. Calculated values of ¹J(¹¹⁵In,³¹P) and δJ( ¹¹⁵In,³¹P) duplicate experimental trends and indicate that both the Fermi-contact and spin-dipolar Fermi-contact mechanisms make important contributions to the ¹J(¹¹⁵In,³¹P) tensors.