Back bonding without sigma-bonding: a unique pi-complex of dinitrogen withuranium

The synthesis, molecular structure, spectroscopic properties and bonding in a complex of dinitrogen with trivalent uranium are described. The molecule has a side-on U-N-2-U Core which is supported by U -->N-2 pi donation with no significant N-2 --> U bonding. Steric compression between the spectator triamidoamine ligands prevents the uranium atoms from approaching the N-2 ligand at the optimum distance for overlap, and thus the N-N distance is no t displaced significantly from that in gaseous dinitrogen. (C) 2001 Elsevie r Science BN. All rights reserved.