Synthesis, Structure, and ¹⁵N NMR Studies of Paramagnetic Lanthanide Complexes Obtained by Reduction of Dinitrogen

The recently discovered LnZ3/M and LnZ2Z‘/M methods of reduction (Ln = lanthanide; M = alkali metal; Z, Z‘ = monoanionic ligands that allow these combinantions to generate “LnZ2” reactivity) have been applied to provide the first crystallographically characterized dinitrogen complexes of cerium, [(C5Me5)2(THF)Ce]2(μ-η2:η2-N2) and [(C5Me4H)2(THF)Ce]2(μ-η2:η2-N2), so that the utility of 15N NMR spectroscopy with paramagnetic lanthanides could be determined. [(C5Me5)2(THF)Pr]2(μ-η2:η2-N2) and [(C5Me4H)2(THF)Pr]2(μ-η2:η2-N2) were also synthesized, crystallographically characterized, and studied by 15N NMR methods. The data were compared to those of [(C5Me5)2Sm]2(μ-η2:η2-N2). [(C5Me5)2(THF)Ce]2(μ-η2:η2-N2) and [(C5Me5)2(THF)Pr]2(μ-η2:η2-N2) are unlike their (C5Me4H)1- analogs in that the solvating THF molecules are cis rather than trans. Structural information on precursors, (C5Me4H)3Ce, (C5Me4H)3Pr, and the oxidation product [(C5Me5)2Ce]2(μ-O) is also presented.