Synthesis and Characterization of Sterically Encumbered β-Ketoiminate Complexes of Iron(ii) and Zinc(ii)

Abstract

The synthesis, structure, and spectroscopic signatures of a series of four-coordinate iron(II) complexes of β-ketoiminates and their zinc(II) analogues are presented. An unusual five-coordinate iron(II) triflate with three oxygen bound protonated β-ketoimines is also synthesized and structurally characterized. Single-crystal X-ray crystallographic analysis reveals that the deprotonated bis(chelate)metal complexes are four-coordinate with various degrees of distortion depending on the degree of steric bulk and the electronics of the metal center. Each of the high-spin iron(II) centers exhibits multiple electronic transitions including ligand π to π*, metal-to-ligand charge transfer, and spin-forbidden d-d bands. The (1)H NMR spectra of the paramagnetic high-spin iron(II) centers are assigned on the basis of chemical shifts, longitudinal relaxation times (T(1)), relative integrations, and substitution of the ligands. The electrochemical studies support variations in the ligand strength. Parallel mode EPR measurements for the isopropyl substituted ligand complex of iron(II) show low-field resonances (g > 9.5) indicative of complex aggregation or crystallite formation. No suitable solvent system or glassing mixture was found to remedy this phenomenon. However, the bulkier diisopropylphenyl substituted ligand exhibits an integer spin signal consistent with an isolated iron(ii) center [S = 2; D = -7.1 ± 0.8 cm(-1); E/D = 0.1]. A tentative molecular orbital diagram is assembled.

Nanostructured Fe2O3 Processing via Water‐Assisted ALD and Low‐Temperature CVD from a Versatile Iron Ketoiminate Precursor

“…The synthesis procedure for [Fe( i pki) 2 ] of Granum et al based on a salt metathesis reaction of [Fe(OTf) 2 (CH 3 CN) 2 ] (OTf = Trifluoromethanesulfonate) with in situ synthesized [Na( i pki)] was modified, as the reported yields were not reproducible in large scale reactions . This is most likely due to the very low solubility of the iron complex in common organic solvents.…”

Redox Non‐Innocence and Isomer‐Specific Oxidative Functionalization of Ruthenium‐Coordinated β‐Ketoiminate

“…Substituted β‐ketoimines (R‐AcNacH=LH, R=H, Cl, OMe) were prepared from acetylacetone and corresponding para ‐substituted aniline in refluxing ethanol and in presence of catalytic amount of trifluoroacetic acid . Though three tautomeric forms of LH (ketamine, ketimine and enimine) are feasible, the observed sharp and D 2 O exchangeable broad 1 H NMR peaks at δ , 5.2 ppm and 12 ppm corresponding to methine (β‐CH) and hydrogen bonded NH protons, respectively, suggested its ketamine form (Scheme ).…”

“…The precursor complex cis-[Ru(acac) 2 (CH 3 CN) 2 ] [19] and b-ketoamines (R-AcNacH = LH, R = H, Cl, OMe) were prepared according to the literature procedures. [7] Other reagents and chemicals were obtained from Aldrich and used as received. HPLC grade solvents were employed for spectroscopic and other electrochemical studies.…”

Backbone-Substituted β-Ketoimines and Ketoiminate Clusters: Transoid Li2O2 Squares and D2-Symmetric Li4O4 Cubanes. Synthesis, Crystallography and DFT Calculations

“…A similar Li2O2 cluster (refcode: SEKVIK) of a close analogue of ligand 1b (2,6-xylyl rather than Mes group) has two neutral ligands filling the coordination sphere of the lithium ions [21]. An iron(II) triflate complex derived from 1a (refcode: ISEXUA) has recently been structurally characterised [22]. Titanium chloride and chloromethyltin complexes (refcodes: LIRCAQ and DULREI) of 1b have also been structurally confirmed [23,24].…”