TRANSITION-METAL COMPLEXES OF DIAZENES .12. SYNTHESIS AND DYNAMIC PROPERTIES OF (CIS-DIAZENE)-M3(CO)9 CLUSTERS (M=FE,RU)

The ability of the NN group to coordinate to three metal atoms has been demonstrated by the synthesis of (cis-diazene)M3(CO)9 (M = Fe, Ru; cis-diazene = 2,3-diazanorbornene, 4-phenyl-3,3-bis(methoxycarbonyl)-1-pyrazoline). These new M3 clusters are prepared thermally from the free diazene and Fe(CO)5 or Ru3(CO)12, and photochemically from (cis-diazene)Fe2(CO)6 and Fe(CO)5. The complexes contain one seven-coordinated and two, equivalent, six-coordinated M(CO)3 groups. Dynamic 13C NMR spectroscopy over the range -130 to 40°.C reveals that these two sets of carbonyl groups do not undergo internuclear carbonyl exchange. Localized scrambling at the 7-coordinated metal is rapid even at -130°, resulting in one sharp signal over the whole temperature range. Localized exchange at the 6-coordinated metals is frozen out between -130°C and about -40°C, giving rise to three signals of equal intensity which coalesce into one broad signal at room temperature. In addition to the carbonyl resonances, the ligand carbon and hydrogen signals exhibit temperature dependence. A possible rotation of the diazene ligand around the M3-triangle is excluded because of the observation of chemically non equivalent M(CO)3 groups in the room temperature 13C NMR spectra and two isomers for the mono- and di-substituted trimethylphosphite derivatives (1H and 31P NMR). The same type of dynamic behaviour is found with the binuclear (2,3-diazanorbornene)Fe2(CO)6; here again only localized CO exchange was observed from -110 to +40°C. © 1979.