Studies of tungsten-183 magnetic shielding by heteronuclear magnetic double and triple resonance

Abstract

¹ H-{¹⁸³W}, ¹H-{31P}, and ¹H-{¹⁸³W, ³¹P} nuclear magnetic double- and triple-resonance experiments have been used to determine tungsten-183 chemical shifts and other parameters in 35 tungsten(0) complexes with tertiary phosphine, η-cyclopentadienyl, and other ligands. The observed chemical shifts are several thousand p.p.m. to high field of those for derivatives of WF₆, and this is attributed to the occupancy of the d_xy, d_yz and d_xz valence orbitals in addition to the d_x²–y², and d_z², which reduces the delectron imbalance and gives a smaller paramagnetic term. π-Back bonding with ligands produces a high-field shift and the marked sensitivity of the shielding to temperature and isotopic substitution is attributed to changes in electronic excitation energies.