A thermally stable, T-shaped, d 7 high-spin iron(I) complex was obtained by reduction of a PNP-supported ferrous chloride. Paramagnetic NMR spectroscopy combined with DFT modeling was used to analyze the electronic structure of the coordinatively highly unsaturated complex. The metalloradical character of the compound was demonstrated by the formation of a benzophenone ketyl radical complex upon addition of benzophenone. Furthermore, the compound displays a rich chemistry as an oxygen-atom abstractor from epoxides, yielding a dinuclear, diferrous [Fe 2 O] complex.

This study focused on the synthesis and characterization of a range of low-valent, high-spin iron(II) complexes supported by a carbazole-based PNP pincer-type ligand. The addition of the lithiated ligand (PNP)Li to FeCl(THF) yielded the chlorido complex (PNP)FeCl (1), which could be readily converted to the four-coordinate iron(II) alkyl complexes (PNP)FeR [R = CHSiMe (3a), Me (3b), CHPh (3c)]. These iron(II) complexes were fully characterized by X-ray analysis and a comprehensive, density-functional-theory-assisted study with complete assignment of their paramagnetic H andC NMR spectra. Treatment of 1 with KHBEt or the addition of molecular hydrogen to (PNP)FeR afforded a high-spin iron(II) PNP hydrido complex, which was identified as the dimer [(PNP)Fe(μ-H)] (4) with two bridging hydrido ligands between the iron centers. Exposing complexes 1 and 4 to carbon monoxide led to the corresponding six-coordinate, diamagnetic complexes (PNP)Fe(CO)Cl (2) and (PNP)Fe(CO)H (5), of which 2 was present as cis/trans isomers. Furthermore, 4 was found to be an active catalyst for the hydrogenation of alkenes.

Guided by DFT based modeling the chemical shift range of a hydride resonance in the proton nuclear magnetic resonance (NMR) spectrum of the intermediate-spin, square planar iron complex tBu (PNP)-Fe−H was predicted and detected as a broad resonance at −3560 ppm (295 K) with a temperature dependent shift of approximately 2000 ppm between 223 and 383 K. The first detection of a metal-bonded hydrogen atom by solution NMR in a complex with a paramagnetic ground state illustrates the interplay of theory and experiment for the characterization of key components in paramagnetic base metal catalysis.

A study of the reactivity of a T-shaped iron(I) complex supported by a carbazole-based PNP pincer ligand (1) has established its strongly reducing character and propensity to bind small molecules with concomitant transfer of charge and spin density. Metalloradical reactivity was observed in the reaction with the stable radical 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) yielding the corresponding Fe II hydroxylaminato complex 2. Complex 1 reacted rapidly and selectively with two molecules of carbon monoxide to give the corresponding low-spin dicarbonyl complex 3. When reacted with phenylacetylene, the alkyne complex 4 was isolated in which the alkyne was found to bind side-on as an η 2 -ligand, which adopts radical anion character as a result of charge transfer from the metal center. Reaction with diphenyl diazomethane generated an adduct 5 in which the diazoalkane also appears to be partially reduced and acquires radical character. Upon exposure to carbon dioxide, oxygen atom abstraction was observed, ultimately leading to the isolation of the monocarbonyl iron(I) complex 6 and a dinuclear carboxylato ferrous complex 7. Furthermore, reaction with chalcogen atom transfer reagents resulted in the formation of the corresponding dinuclear ferrous chalcogenido compounds (E = S (8), Se (9)), which were found to display strong antiferromagnetic coupling (8,

Atom Probe Tomography (APT) is currently a well-established technique to analyse the composition of solid materials including metals, semiconductors and ceramics with up to near-atomic resolution. Using an aqueous glucose solution, we now extended the technique to frozen solutions. While the mass signals of the common glucose fragments CxHy and CxOyHz overlap with (H2O)nH from water, we achieved stoichiometrically correct values via signal deconvolution. Density functional theory (DFT) calculations were performed to investigate the stability of the detected pyranose fragments. This paper demonstrates APT’s capabilities to achieve sub-nanometre resolution in tracing whole glucose molecules in a frozen solution by using cryogenic workflows. We use a solution of defined concentration to investigate the chemical resolution capabilities as a step toward the measurement of biological molecules. Due to the evaporation of nearly intact glucose molecules, their position within the measured 3D volume of the solution can be determined with sub-nanometre resolution. Our analyses take analytical techniques to a new level, since chemical characterization methods for cryogenically-frozen solutions or biological materials are limited.