Coordination and organometallic diamido-donor iron and cobalt complexes

The structures, reactivity and magnetic properties of high-spin iron and cobalt complexes of diamido donor ligands were investigated. Unusual multinuclear Fe(II) and Co(II) complexes with the basic dinuclear unit M2X2[tBuNON] (X= Br, M= Fe (1), Co (2); X= Cl, M= Fe (3), Co (4)), ([tBuNON]2−= [Me3CN(SiMe2)]2O2−) were synthesized and characterized. The reduction reaction of 3 with KC8 and addition of CO and dmpe (Me2P(CH2)2PMe2) generated {Fe2[tBuNON]}2 and, with dmpe also FeCl2(dmpe)2. However, the addition of 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (NHC) carbene to 3 resulted in the new {[NHC]FeCl2}2. Alkyl for halide metathesis via the reaction of LiCH2SiMe3 in 1-4 generated rare high-spin alkyl/halide {[tBuNON]M2X(CH2SiMe3)2}2 (8-11) complexes and unusual high-spin dialkyl iron and cobalt complexes of the form {M2(CH2SiMe3)2[tBuNON]} (M = Fe (6) and Co (7)); reaction with MeLi to form the dimethyl analogue was not successful, while addition of one equivalent of methyl reagent per dinuclear unit in 3 and 4 resulted in {Fe2Br(Me)[tBuNON]}2 and {Co2Cl(Me)[tBuNON]}2. Neither 6 nor 7 act as polymerization catalysts for ethylene; addition of B(C6F5)3 as a cocatalyst was found to further hinder any activity of 6 and 7 by the formation of {Co2(C6F5)2[tBuNON]} and {Fe2Cl(C6F5)[tBuNON]}2. Upon exposing 6 to excess CO, a rare dicarbamoyl trinuclear iron complex was obtained, which results from CO binding, isocarbonyl binding and Fe-C and Fe-N CO insertions. Attempts towards obtaining high oxidation state iron and cobalt complexes showed that the [NON] ligand did not support such systems. Addition of benzyl bromide to {Fe[Me3PhNON]}2 resulted in {FeBr[Me3PhNON]}2 and reaction of {FeCl[tBuNON]}2 with dmpe led to a rare tetrahedral iron(III) complex {FeCl[tBuNON]}2(µ-Me2PCH2CH2PMe2). To overcome potential difficulties with limited Si-N bond stabilities, carbon-backbone diamido {M[iPrNN′N]}2 and {M[iPrNO′N]}2 (M= Fe, Co) [MeN((CH2)2N−iPr)2] ([iPrNO′N]2−) and [O((CH2)2N−iPr)2] ([iPrNN′N]2−) were synthesized, characterized and compared with similar diamido complexes.