Paramagnetic amidometal chemistry: Iron, cobalt and chromium complexes containing diamidoether ligands

Several paramagnetic transition metal complexes incorporating diamidoether ligands are described. Reaction of {Li2[RN(SiMe2)] 2O} [R = tBu, 2,4,6-Me3Ph 2,6-iPr2Ph, 3,5-(CF3) 2Ph] and {Li2[RN(CH2CH2)]2O} (R = 2,4,6-Me3Ph, 2,6-iPr 2Ph) with MCl2 (M = Cr, Fe, Co) and FeX3 (X = Cl, Br) results in new paramagnetic amidometal complexes.;The structure and magnetism of dinuclear metal(II) complexes of the form {M[RN(SiMe2)]2O}2 are also reported. The metal atoms of the dimer are bridged by amido ligands, however an unusual 'serpentine' metal-ligand binding motif is found in dimeric complexes {Co[iPr2PhN(CH2CH 2)]2O}2 (26) and {Fe[ iPr2PhN(CH2CH2)]2O} 2 (28), where the metal atoms are bridged through the ether donors of the ligand backbone rather than the amido groups. Metal-metal banding may be present in the systems with short intermetallic distances and low magnetic moments. Finally, the oxidation of some metal(II) complexes with bromonium cation to generate the proposed metal(IV) species {CrBr[Me3PhN(SiMe 2)]2O}+ [BArf]- (36), {FeBr[tBuN(SiMe2)] 2O}+ [BArf]- (37) and {FeBr[Me3PhN(SiMe2)]2O} + [BArf]- (38) are also described.;The first multinuclear iron(III) systems {FeX[tBuN(SiMe 2)]2O}2 (1, X = Cl; 2, X = Br) exhibiting the rare magnetic phenomenon known as quantum mechanical spin admixture have been prepared. Magnetic and Mossbauer studies of these five coordinate, dinuclear iron(III) systems confirm the existence of this spin state (S = 5/2, 3/2). The analogous fluoride and iodide species have also been synthesized from {Fe[tBuN(SiMe 2)]2O}2 (3) by oxidation with AgPF 6 and I2 respectively. This halide series displays intramolecular antiferromagnetic coupling. A change to an aryl-based diamidoether ligand gives rise to unusual 'ate' complexes {FeX2Li[RN(SiMe 2)]2O}2 (13, X = Cl, R = 2,4,6-Me 3Ph; 14, X = Br, R = 2,4,6-Me3Ph; 15, X = Cl, R = 2,6-iPr2Ph), which are stabilized by Li-pi interactions. These pseudotetrahedral, dimeric iron(III) complexes exhibit magnetic behaviour characteristic of uncoupled high spin (S = 5/2) iron(III) centres. They also undergo halide metathesis, resulting in reduced iron(II) species. Similarly, {FeCl[tBuN(SiMe 2)]2O}2 (1) reacts with LiPPh 2 to yield the iron(II) dimer {Fe[tBuN(SiMe 2)]2O}2 (3) but reaction with LiNPh 2 gives the reduced iron(II) product {Fe2(NPh2) 2[tBuN(SiMe2)]2O} (6). Some redox chemistry is also observed as side reactions in the syntheses of the 'ate' complexes, yielding the 1-D chain [FeBr2(THF)2]n (17 ) and the cluster [Fe4Cl8(THF)6] ( 18).