SYNTHESIS AND CRYSTAL-STRUCTURE OF AMIDATO-BRIDGED DIRHENIUM(III,III) COMPOUNDS

Four amidato-bridged dirhenium(III,III) compounds (1-4) have been synthesized through reactions between Re2(O2CCH3)4Cl2 and four different molten amides and their structures determined by X-ray crystallography. In 1, 2 and 3, the nitrogen and oxygen atoms bonded to the same Re atom are cis to each other, and the virtual symmetry of the Re2(NCO)4 units is C2h. In 4, the trans arrangement of ligands yields a D2d virtual symmetry of the Re2(NCO)4 unit. All these compounds contain quadruple bonds between two rhenium atoms, with Re-Re distances 2.2304(6) angstrom, 2.2218(8) angstrom, 2.2181(6) angstrom, 2.2350(4) angstrom and 2.2364(5) angstrom for 1, 2a, 2b, 3 and 4, respectively. The electronic spectra and H-1 NMR were measured. Reaction chemistry and structures of these compounds are compared with those of carboxylato bridged and amidinato bridged compounds. It is concluded that the amidato compounds all have a sigma2pi4delta2 electron configuration, like their carboxylato analogs, but with larger delta-delta* orbital energy separations.