UC Irvine

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 (N[double bond, length as m-dash]N)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 (N[double bond, length as m-dash]N)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.