Examination of the reduction chemistry of Nd-(NR 2 ) 3 (R = SiMe 3 ) under N 2 has provided connections between the in situ Ln(III)-based Ln III (NR 2 ) 3 /K reductions of N 2 that form side-on bound neutral (N=N) 2− complexes, [(R 2 N) 2 (THF)-Ln] 2 [μ-η 2 :η 2 -N 2 ], and the Ln(II)-based [Ln II (NR 2 ) 3 ] 1− reductions by Sc, Gd, and Tb that form end-on bound (N=N) 2− complexes, {[(R 2 N) 3 Ln] 2 [μ-η 1 :η 1 -N 2 ]} 2− , which are dianions. The reduction of Nd(NR 2 ) 3 by KC 8 under dinitrogen in Et 2 O in the presence of 18-crown-6 (18-c-6) forms dark yellow solutions of [K 2 (18-c-6) 3 ]{[(R 2 N) 3 Nd] 2 N 2 } at low temperatures that become green as they warm up to −35 °C in a glovebox freezer. Green crystals obtained from the solution turn yellow-brown when cooled below −100 °C, and the yellow-brown compound has an end-on Nd 2 (μ-η 1 :η 1 -N 2 ) structure. The yellow-brown crystals isomerize in the solid state on the diffractometer upon warming, and at −25 °C, the crystals are green and have a side-on Nd 2 (μ-η 2 :η 2 -N 2 ) structure.Collection of X-ray diffraction data at 10 °C intervals from −50 to −90 °C revealed that the isomerization occurs at temperatures below −100 °C. In the presence of tetrahydrofuran (THF), the dianionic {[(R 2 N) 3 Nd] 2 N 2 } 2− system can lose an amide ligand to provide the monoanionic [(R 2 N) 3 Nd III (μ-η 2 :η 2 -N 2 )Nd III (NR 2 ) 2 (THF)] 1− , characterized by X-ray crystallography. These data suggest a connection between the in situ Ln(III)/K reductions and Ln(II) reductions that depends on solvent, temperature, the presence of a chelate, and the specific rare-earth metal.

Crystal structures demonstrate that 2.2.2-cryptand can function as a κ2-O,O′ bidentate ligand to rare-earth metal ions.

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