Enabling Valence Delocalization in Iron(III) Macrocyclic Complexes through Ring Unsaturation

Clendening, Reese A.; Delancey, Stephanie S.; Poore, Andrew T.; Xue, Shan; Guo, Yisong; Tian, Shiliang; Ren, Tong

doi:10.1021/acs.inorgchem.3c01179

Cited by 1 publication

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“…Electronic absorption spectra and voltammetric data indicate that TIM is a more electron-rich macrocycle than HMTI, which results in higher energy dπ orbitals in Fe(TIM) than those in Fe(HMTI). Similar to the previously reported [Fe(HMTI)(C 2 Y) 2 ] + , both [Fe(TIM)Cl 2 ] + and [Fe(TIM)(C 2 R) 2 ] + are low spin d 5 species based on their EPR characteristics. Among many interesting features revealed by SEC analysis is the emergence of the low-energy MLCT band(s) with the concurrent disappearance of the LMCT band(s) upon the first one-electron reduction of both [ 1 ] + and [ 2 ] + .…”

Section: Discussionsupporting

confidence: 88%

“…Although the yields are not impressive, the synthesis of [Fe(TIM)(C 2 R) 2 ] + is based on a one-step reaction of [ 1 ]PF 6 with the appropriate LiC 2 R, a significant improvement over that of Fe(HMTI) alkynyl species. − For the latter, the oxidative dehydrogenation of the saturated macrocycle in the Fe(HMC) precursor complex is required and is achieved in situ by the addition of excess n -butyllithium/HC 2 R followed by the subsequent exposure of the reaction mixture to air. However, the tetra-imine nature of the TIM ligand in [ 1 ]PF 6 eliminates the need for both the oxidative dehydrogenation step and the ensuing purification to remove the byproducts.…”

Section: Resultsmentioning

confidence: 99%

“…Access to the spectrum of [Fe(HMTI)(CN) 2 ] −1 helped to ascertain the MLCT absorption in the transient spectra of Fe(HMTI)(CN) 2 . The extraction of the [Fe(HMTI)(C 2 Y) 2 ] +2 spectrum allowed the establishment of an IVCT band associated with the [Y–Y] + pair that is consistent with a highly delocalized class II mixed valency …”

Section: Resultsmentioning

confidence: 99%

“…EPR simulation of [ 1 ] + –[ 4 ] + shows that all complexes are axial low-spin S = 1/2 Fe III species (Figure ), with the exception of complex [ 1 ] + displaying a slightly more rhombic signal (Figure S9). According to the Griffith theory, first developed for low-spin ferric porphyrin complexes, a large g max ( g ≈ 3) and a Σ g 2 = 16 are typical for a (d xy ) 2 (d xz ,d yz ) 3 ground state, whereas a (d xz ,d yz ) 4 (d xy ) 1 ground state usually has an axial EPR spectrum with a g max < 2.6 and Σ g 2 < 16. − The g values for the alkynyl complexes [ 2 ] + –[ 4 ] + were found to be in the same range as seen for the previously reported Fe(HMTI) complexes, with a slightly higher Σ g 2 values ranging from 14.40 to 14.46 (Table ). This suggests that the alkynyl complexes [ 2 ] + –[ 4 ] + have a (d xz ,d yz ) 4 (d xy ) 1 ground state.…”

Section: Resultsmentioning

confidence: 99%

“…Our laboratory has studied a number of 3d metal alkynyl complexes supported by both cyclam (1,4,8,11-tetraazacyclotetradecane) and its C-substituted derivatives during the past decade. , While interesting structural features were observed, the conjugation along the metal–alkynyl backbone was weak at best . The investigation of the [Fe III (HMTI)(C 2 R) 2 ] + -type complexes revealed that the dπ(Fe) → π*(α-diimine) interaction is substantial due to the enhanced π-acidity of the unsaturated HMTI. , Subsequent study of the [Y–Y] + mixed valency in the [Fe III (HMTI)(C 2 Y) 2 ] + -type complexes (Y = DMAP and Fc) revealed facile hole delocalization across the –C 2 –Fe III –C 2 – backbone, further proving the significance of the π-acidity of HMTI in enabling metal–alkynyl conjugation . Nonetheless, further investigation of electronic and optical properties of Fe(HMTI) species is hindered by their low-yielding syntheses, which are generally based on aerobic dehydrogenation of the corresponding Fe(HMC) complexes (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) .…”

Section: Introductionmentioning

confidence: 99%

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Fe(III) Bis-Alkynyls Supported by the TIM Macrocycle: Molecular and Electronic Structures and Altering the Nature of Charge Transfer Transitions through Reduction

Gautam,

Clendening,

Poore

et al. 2024

Organometallics

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The bis-alkynyl complexes based on FeIII(TIM) (TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) are reported herein. A modified synthesis of trans-[Fe(TIM)Cl2]PF6 ([1]PF6) in a 90% yield was developed. The reaction between [1]PF6 and LiC2R (R = Ph, SiEt3, or SiiPr3) resulted in the bis-alkynyl complexes, trans-[Fe(TIM)(C2R)2]PF6, in good yields, 43% for 2 (R = Ph), 29% for 3 (R = SiEt3), and 18% for 4 (R = SiiPr3). X-ray diffraction studies yielded molecular structures of complexes 1–3, which feature a tightened Fe–N4 coordination in comparison with analogous Fe(cyclam) complexes. Electron paramagnetic resonance studies confirmed that the complex ions [Fe(TIM)Cl2]+ and [Fe(TIM)(C2R)2]+ are low-spin d5 species with S = 1/2 ground states. Electronic absorption spectra of bis-alkynyl complexes 2–4 all feature intense LMCT (π(C≡C) →dπ(Fe)) bands in the visible region, and the assignment was supported by the time-dependent density functional theory analysis. These complexes undergo multiple one-electron redox processes, and the first one-electron reduction is reversible in all four complexes and assigned as an Fe(+3/+2) couple. Spectroelectrochemical studies of 1 and 2 reveal that the first one-electron reduction leads to the emergence of intense metal-to-ligand charge transfer (dπ(Fe) → π*(α-diimine)) bands and the concurrent disappearance of the ligand-to-metal charge transfer bands.

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Section: Discussionsupporting

confidence: 88%