The first isolable molecular thorium nitride, [(NR2)3Th(μ-N)Th(NR2)3]−, was synthesized by reaction of [Th{N(R)(SiMe2)CH2}(NR2)2] with NaNH2 and characterized by X-ray crystallography, 15N NMR spectroscopy, and DFT calculations.

The solid-state 15 N NMR powder spectra of the thorium nitride complex, [K(18-crown-6)(THF) 2 ][(R 2 N) 3 Th(μ-15 N)Th(NR 2 ) 3 ] ([K][1-15 N], R = SiMe 3 ), and the thorium amide complex, [Th(NR 2 ) 3 ( 15 NH 2 )] (2-15 N), were recorded. The spectrum for [K][1-15 N] represents the first reported solid-state 15 N NMR data for an actinide complex. The experimentally measured tensor spans are Ω = 847 ppm for [K][1-15 N] and Ω = 237 ppm for 2-15 N. Both shielding tensors exhibit axial symmetry, which for [K][1-15 N] is consistent with a local rotational symmetry of its 15 N-labeled nitride ligand. For 2-15 N, the axial asymmetry can be rationalized by a quasi-free Th-NH 2 bond rotation in the solid-state. Density functional theory calculations overestimate the tensor span somewhat for [K][1-15 N], but provide isotropic shifts in good agreement with both the solid-state and solution values for both complexes. Natural localized molecular orbital analyses of the nuclear shielding reveal that the larger tensor span in [K][1-15 N] vs 2-15 N is primarily a consequence of more pronounced covalency of the σ(N−Th) bonds and large spin−orbit coupling due to significant Th 5f orbital contribution to those bonds, impacting the principal components of the shielding tensor perpendicular to the Th−N−Th axis. Overall, our analysis confirms the involvement of the 5f orbitals in Th−N multiple bonds and further demonstrates the value of solid-state NMR spectroscopy for interrogating actinide-ligand bonding.