Dinitrogen reduction chemistry with scandium provides a complex with two side-on (NN)2− ligands bound to one metal: (C5Me5)Sc[(µ-η2:η2-N2)Sc(C5Me5)2]2

Abstract

Although there are few reduced dinitrogen complexes of scandium, this metal has revealed a new structural type in reductive dinitrogen chemistry by reduction of bis(pentamethylcyclopentadienyl) scandium halides under N₂. Reduction of (Cp* = C₅Me₅) with potassium graphite (KC₈) under dinitrogen generates the dark blue paramagnetic complex , 1. This end-on bridging (NN)²⁻ complex is a diradical with a magnetic moment of 2.8µ_B. Upon further reduction of 1 with KC₈, the orange diamagnetic trimetallic complex , 2, is obtained. This complex has an unprecedented structure in which two side-on bridging (NN)²⁻ ligands are bound to the central (Cp*Sc)²⁺ moiety. Complex 2 can also be obtained directly from reduction of or a mixture of and with KC₈. The reaction of with KC₈ in the presence of 18-crown-6 or 2.2.2-cryptand affords 2 along with small amounts of , 3, which is green at room temperature and purple at low temperature and displays a mixture of side-on and end-on bridging isomers in the crystal structure collected at −180 °C. Density functional theory (DFT) calculations are consistent with a triplet ground state for the end-on complex 1 and singlet ground states for the side-on complexes 2 and 3.