Synthesis, structure, and 15N NMR studies of paramagnetic lanthanide complexes obtained by reduction of dinitrogen

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