Solid-State End-On to Side-On Isomerization of (N═N) 2- in {[(R 2 N) 3 Nd] 2 N 2 } 2- (R = SiMe 3 ) Connects In Situ Ln III (NR 2 ) 3 /K and Isolated [Ln II (NR 2 ) 3 ] 1- Dinitrogen Reduction.

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.