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

Four amidato-bridged dirhenium(III,III) compounds (1-4) have been synt hesized through reactions between Re2(O2CCH3)4Cl2 and four different m olten amides and their structures determined by X-ray crystallography. In 1, 2 and 3, the nitrogen and oxygen atoms bonded to the same Re at om are cis to each other, and the virtual symmetry of the Re2(NCO)4 un its is C2h. In 4, the trans arrangement of ligands yields a D2d virtua l symmetry of the Re2(NCO)4 unit. All these compounds contain quadrupl e bonds between two rhenium atoms, with Re-Re distances 2.2304(6) angs trom, 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 compound s all have a sigma2pi4delta2 electron configuration, like their carbox ylato analogs, but with larger delta-delta orbital energy separations .