Metalloradical Reactivity, Charge Transfer, and Atom Abstractions in a T-Shaped Iron(I) Complex

Abstract

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,

Crystal structures of the gold NHC complex bis(4-bromo-1,3-diethylimidazol-2-ylidene)gold(I) iodide and its 1:1 adduct with trans-bis(4-bromo-1,3-diethyl-imidazol-2-ylidene)diiodidogold(III) iodide

“…Some of the existing therapeutics have reached the clinical trial stage as a result of drug repurposing efforts. Metal N-heterocyclic carbene (NHC) complexes in general have also proved to be biologically and medicinally active compounds (Ott, 2020); in particular, gold complexes with NHC ligands are often synthesized and investigated because of the high stability of the gold-carbon bonds and the convenient synthetic access to a broad variety of structurally diverse NHC structures (Nahra et al, 2021). We have reported on the synthesis, characterization and biological effects of [bis(4bromo-1,3-diethyl-imidazol-2-ylidene)gold(I)] iodide (3) (Schmidt et al, 2017a) (Fig.…”

Straightforward synthetic route to gold(i)-thiolato glycoconjugate complexes bearing NHC ligands (NHC = N-heterocyclic carbene) and their promising anticancer activity

“…It should be noted that NHC ligands represent an attractive alternative to phosphines as they possess a heightened ability to form strong bonds with most transition metals, rendering them promising ligands for metallodrug design. 17 The particular stability of gold-NHC complexes, even in a physiological environment, has been exploited for the design of promising anticancer agents. 4 Moreover, in the last decade numerous efforts have been devoted to the development of simple and sustainable synthetic strategies to metal-NHC complexes.…”

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

“…[ 3 , 4 ] At the same time, there is a growing interest in the detection and analysis of paramagnetic intermediates in catalytic reaction cycles, particularly for the first‐row transition metals, where the reactive molecular fragments tend to be either directly bonded, or otherwise in close proximity to the metal. [ 5 , 6 , 7 , 8 , 9 , 10 , 11 ] Other areas of current interest are single‐molecule magnets (SMMs),[ 12 , 13 , 14 , 15 ] contrast agents in magnetic resonance imaging (MRI),[ 16 , 17 , 18 ] and pseudocontact shift (PCS) probes in structural biology. [ 19 , 20 , 21 , 22 ] Several recent studies used magneto‐structural correlations derived by multireference ab initio methods to refine chemical structures using paramagnetic NMR shifts.…”