Synthesis and Characterization of (^DIPPCCC)Fe Complexes: A Zwitterionic Metalation Method and CO₂ Reactivity

Abstract

The synthesis and characterization of a series of novel iron complexes has been accomplished using a monoanionic pincer bis­(carbene) ligand framework. Metalation first proceeded through an isolated Fe­(II) zwitterionic intermediate that was subsequently reduced in situ to Fe(0) to facilitate oxidative addition of the aryl C–H bond, generating the FeII–H complexes. Varying the L-type ligand on these complexes exhibited profound effects, as observed by IR and 1H NMR spectroscopy. Higher oxidation states of Fe could also be supported in this ligand framework, as evidenced by the isolation of two Fe­(III) complexes. Treating an FeII–H complex with CO2 generated an Fe–formate complex (κ2-OOCH) from insertion into the FeII–H bond. The independent synthesis of this molecule was accomplished by treating FeII–Cl with excess NaOOCH.

Bis(tridentate) Iron(II) Complexes with a Cyclometalating Unit: Photophysical Property Enhancement with Combinatorial Strong Ligand Field Effect

“…In comparison to the aforementioned extensive applications of NHC ligands, the development of cyclometalating carbanion-type donors, which are also strongly σ donating, for similar studies has lagged behind . The scarcity of reported cyclometalated Fe complexes is in stark contrast to the numerous reports of high-performance cyclometalated complexes of 4d and 5d TMs (e.g., Ru, Au, Ir, and Pt) in the context of photophysical studies. ,− These cyclometalating C donors usually take the form of an sp 2 phenyl carbanion, with the phenyl group usually incorporated with N-heterocycle, e.g. pyridine, units to construct coordinatively more robust multidentate ligands.…”

Transition Metal Complexes Supported by N‐Heterocyclic Carbene‐Based Pincer Platforms: Synthesis, Reactivity and Applications

“…They made use of a pincer proligand 67 and prepared a series of CCC‐pincer iron complexes 69 a/b/c (Scheme 23). [35] Treating 67 with FeCl 2 and LiN(SiMe 3 ) 2 produced a zwitterionic Fe II complex 68 . Reducing with KC 8 in situ generated the Fe 0 intermediate, which underwent further oxidative addition to give Fe II hydrido complexes 69 a/b/c .…”

“…The combination of an X-type central N donor and two flanking NHC arms makes the pincer ligand monoanionic. In this regard, Guisado-Barrios, Bezuidenhout and others described the preparation and reactivity of a series of carbazolide-bridged CNC pincer complexes (32)(33)(34)(35) bearing mesoionic triazolin-5ylidenes (Scheme 13). [24] Two different Ru precursors [Ru(NBD) Cl 2 ] n and [RuHCl(CO)(AsPh 3 ) 3 ] were used producing two carbonyl pincer complexes 33 and 34.…”

Well-Defined Aryl-FeII Complexes in Cross-Coupling and C–H Activation Processes

“…With regard to well-defined systems featuring aryl-halide oxidative addition processes, Nishiyama reported a low-spin aryl-Fe II complex using a bisoxazoline aryl-Br pincer ligand and Fe 0 2 (CO) 9 . Recently, Fout described the synthesis of an aryl-Fe II -hydride stabilized within a bis­(carbene) pincer CCC ligand, but no reactivity of the aryl-Fe II was reported . An alternative strategy to get access to well-defined aryl-Fe II species consists of the use of macrocyclic aryl-X and aryl-H model substrates capable of stabilizing otherwise very reactive species.…”