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 beta-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV-vis, H-1 NMR and IR spectroscopy, magnetic measurements, and X-ray crystallography. Reaction of the beta-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (DiPP(2)N<^>NH; Dipp = C6H3-2,6-Pr-2(i)) with M{N(SiMe3)(2)}(2) (M = Mn or Co) gave Dipp(2)N<^>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-Me-2, or C6H3-2,6-Cl-2) afforded the series of iron complexes Ar2N<^>NFe{N(SiMe3)(2)} (Ar = Dipp, 2a; C6F5, 2b; Mes, 2c; C6H3-2,6-Me-2, 2d; C6H3-2,6-Cl-2, 2e). This represents a new synthetic route to beta-diketiminate complexes of these metals. The four-coordinate bis-beta-diketiminate complex Fe{N<^>N(C6F5)(2)}(2), 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the Dipp(2)N<^>NLi with CoCl2 gave the "ate" salt Dipp(2)N<^>NCoCl2Li(THF)(2), 5, in which the lithium chloride has formed a complex with Dipp(2)N<^>NCoCl through chloride bridging. The Fe(III) species Dipp(2)N<^>NFeCl2, 6, was obtained cleanly from the reaction of FeCl3 with Dipp(2)N<^>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 H-1 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.