Synthesis and reactivity of 1,8-bis(imino)carbazolide complexes of iron, cobalt and manganese

The synthesis and characterisation of a new family of monoanionic, tridentate bis(imino)carbazolide ligands (L) and their cobalt, iron and manganese complexes are described. The solid state structure of the five coordinate FeIII complex LFeCl2(9c) reveals a trigonal bipyramidal geometry with a short Fe-N(carbazolide) bond (1.959(3) (angstrom)), indicative of (pi)-donation from the carbazole nitrogen to the metal centre. The cationic derivatives LFeCl(MeCN)+(11), LFe(acac)+(12) and LCo(MeCN)+(14) have been prepared by chloride abstraction from the neutral precursors using AgSbF6 or Ag(acac). Treatment of LMCln(M = Fe, Co) complexes with MeLi affords metal -methyl species, tentatively formulated as LFeMe2(13), LFeMe (16a) and LCoMe (16b). All of the Mn, Fe and Co compounds are paramagnetic and generally exhibit magnetic moments consistent with high spin configurations. In certain cases, however, low spin as well as intermediate spin configurations are found, depending on the nature of the co-ligands around the metal centre. The LFeCl29c complex exhibits a room temperature magnetic moment of 4.8 (mu)B and is a rare example of a trigonal bipyramidal FeIII complex in which a spin admixture between a high spin and an intermediate spin state is present. None of the divalent or trivalent bis(imino) carbazolide metal complexes, using a variety of activators, showed activity for ethylene oligomerisation or polymerisation.