Structural and electronic effects of mono- and bidentate perfluorinated alkoxide ligands in late first-row transition metal complexes

Abstract

Seven homoleptic first-row transition metal complexes were prepared with the perfluoro-t-butoxide ligand with three- and four-coordinate geometry. The compounds were prepared via metathesis reactions with the form [M(OC4F9)3]-, M = Mn (1), Fe (2), Co (5), and Zn (7); [M(OC4F9)4]n-, M = Fe (4), Co (6); and the THF adducts [M(THF)(OC4F9)3]- M = Co (5-TBF), and Zn (7-THF). The complexes were synthesized and structurally characterized. Spectroscopic characterization with UV-vis, NMR, and IR will be discussed. Cyclic voltammetry studies of 5 and 6 in conjunction with UV-vis data show the presence of an equilibrium between the three- and four-coordinate complexes with ligand association and dissociation. Using the bidentate perfluorinated pinacolate ligand, ddfp, three complexes were prepared as [M(ddfp)2]2-, in which M =Fe (8), Co (9), and Zn (10). Complexes 8 and 9 have square-planar geometry and are high-spin. The magnetism was studied both in solution and the solid state. The combination of geometry and spin-state is rare for {M04} complexes and 9 is the first example of {C0O4} with this combination, and 8 is the second example of this combination in an {FeO4} system. A five-coordinate Co complex was also structurally characterized (9-OH2). A family of heteroleptic complexes of the form [Fe(X)(OC4F9)3]- in which X = Cl (11), Br (12), or pyridine (13), and [M(py)(ddfp)2]2- for M= Co (14), and Fe (15), were prepared and some were structurally characterized. Analytical data suggests the formation of an iron-amide complex, [Fe(HN(C6H5)(ddfp)2]3-, (16), capable of further reactivity. The synthesis, characterization, and preliminary reactivity studies will be discussed. Two iron aryloxide complexes were synthesized with the pentafluorophenolate ligand, [Fe(OArF)4]2-, (17) and [(OArF)3Fe(μ2-OArF)2Fe(OArF)3]2-, (18). The FeIII complex was formed as a result of presumed ligand oxidation and dissociation, highlighting the vulnerability of aryloxide ligands. A series of isotopically labeled compounds containing a short, strong hydrogen bond were prepared and characterized for neutron diffraction experiments. The compounds, [Cp2Co][D(OAr5)], (19) and d10-[Cp2Co][H(OAr')], (20), were prepared with the partially fluorinated OAr' ligand, bis-(3,5-trifluoromethyl)phenoxide. The synthesis and characterization of these compounds will be discussed.