Comparison of Bonding in Isostructural Cerium and Thorium Parent Amide Complexes

A series of isostructural tetravalent cerium and thorium parent amide (NH2–) complexes were synthesized and characterized. The electronic structure of the M–N(amide) bond was investigated using 15N NMR spectroscopy and DFT calculations in a comparative study of the Na-capped complexes [Na(OEt2)2][M(NH2)(TriNOx)][BArF4], M = Ce (3-Ce), Th (3-Th). The 15N(amide) resonance in 3-Ce was observed at δ = 192 ppm, approximately 95 ppm downfield of the corresponding resonance in 3-Th (δ = 97 ppm). Computational analysis found that the spin–orbit (SO) heavy atom effect on the amide nitrogen NMR shift was relatively small, and comparable, at ΔSO = 12/16 ppm for 3-Ce/3-Th. The observed large difference in the 15N chemical shift for 3-Ce/3-Th is primarily due to differences in paramagnetic shielding generated by the amide lone pairs.