Synthesis and Characterization of Three-Coordinate and Related β-Diketiminate Derivatives of Manganese, Iron, and Cobalt

Treatment of M{N(SiMe3)2}2 (M = Mn, Fe, Co) with various bulky β-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV−vis, 1H NMR and IR spectroscopy, magnetic measurements,
and X-ray crystallography. Reaction of the β-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (Dipp2N∧NH; Dipp = C6H3-2,6-Pri2) with M{N(SiMe3)2}2 (M = Mn or Co) gave Dipp2N∧NMN(SiMe3)2 (M = Mn, 1; Co, 3) while the reaction
of Fe{N(SiMe3)2}2 with Ar2N∧NH (Ar = Dipp, C6F5, Mes, C6H3-2,6-Me2, or C6H3-2,6-Cl2) afforded the series of iron
complexes Ar2N∧NFe{N(SiMe3)2} (Ar = Dipp, 2a; C6F5, 2b; Mes, 2c; C6H3-2,6-Me2, 2d; C6H3-2,6-Cl2, 2e). This
represents a new synthetic route to β-diketiminate complexes of these metals. The four-coordinate bis-β-diketiminate
complex Fe{N∧N(C6F5)2}2, 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the
Dipp2N∧NLi with CoCl2 gave the “ate” salt Dipp2N∧NCoCl2Li(THF)2, 5, in which the lithium chloride has formed a
complex with Dipp2N∧NCoCl through chloride bridging. The Fe(III) species Dipp2N∧NFeCl2, 6, was obtained cleanly
from the reaction of FeCl3 with Dipp2N∧NLi. Magnetic measurements showed that all the complexes have a high
spin configuration. The different substituents in the series of iron complexes 2a−e allowed assignment of their
paramagnetically shifted 1H NMR spectra. The X-ray crystal structures 1−2d and 3 showed that they have a
distorted three-coordinate planar configuration at the metals whereas complexes 4−6 have highly distorted four-coordinate geometries.