Synthesis and Characterization of Paramagnetic Tungsten Imido Complexes Bearing α‑Diimine Ligands

Tungsten
imido complexes bearing a redox-active ligand, such as N,N′-bis­(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene
(L1), N,N′-bis­(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene
(L2), and 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene (L3),
were prepared by salt-free reduction of W­(NC6H3-2,6-iPr2)­Cl4 (1) using 1-methyl-3,6-bis­(trimethylsilyl)-1,4-cyclohexadiene
(MBTCD) followed by addition of the corresponding redox-active ligands.
In the initial stage, reaction of W­(NC6H3-2,6-iPr2)­Cl4 with
MBTCD afforded a tetranuclear W­(V) imido cluster, [W­(NC6H3-2,6-iPr2)­Cl3]4 (2), which served as a
unique precursor for introducing redox-active ligands to the tungsten
center to give the corresponding mononuclear complexes with a general
formula of W­(NC6H3-2,6-iPr2)­Cl3(L) (3,
L = L1; 4, L = L2; and 6, L = L3). X-ray
analyses of complexes 3 and 6 revealed a
neutral coordination mode of L1 and L3 to the tungsten in solid state,
while the electron paramagnetic resonance (EPR) spectra of 3 and 4 clarified that a radical was predominantly located
on the tungsten center supported by neutral L1 or L2, and the EPR
spectra of complex 6 indicated that a radical was delocalized
over both the tungsten center and the monoanionic redox-active ligand
L3.