Perspectives on Ligand Properties of N-Heterocyclic Carbenes in Iron Porphyrin Complexes

Abstract

There has been considerable research interest in the ligand nature of N-heterocyclic carbenes (NHCs). In this work, two six-coordinate NHC iron porphyrin complexes [FeII(TTP)­(1,3-Me2Imd)2] (TTP = tetratolylporphyrin, 1,3-Me2Imd = 1,3-dimethylimidazol-2-ylidene) and [FeIII(TDCPP)­(1,3-Me2Imd)2]­ClO4 (TDCPP = 5,10,15,20-tetrakis­(2,6-dichlorophenyl)­porphyrin) are reported. Single-crystal X-ray characterizations demonstrate that both complexes have strongly ruffled conformations and relatively perpendicular ligand orientations which are forced by the sterically bulky 1,3-Me2Imd NHC ligands. Multitemperature (4.2–300 K) and high magnetic field (0–9 T) Mössbauer and low-temperature (4.0 K) EPR spectroscopies definitely confirmed the low-spin states of [FeII(TTP)­(1,3-Me2Imd)2] (S = 0) and [FeIII(TDCPP)­(1,3-Me2Imd)2]­ClO4 (S = 1/2). The similarity of 1,3-Me2Imd and imidazole, as well as the well-established correlations between the ligand nature and spectroscopic characteristics of [FeII,III(Porph)­(L)2]0,+ (Porph: porphyrin; L: planar base ligand) species, allowed direct comparisons between the pair of ligands which revealed for the first time that NHC has a stronger π-acceptor ability than imidazoles, in addition to its very strong σ-donation.

Synthesis and Structure Elucidation of Two Essential Metal Complexes: In-Vitro Studies of Their BSA/HSA-Binding Properties, Docking Simulations, and Anticancer Activities

“…The percentage of hydrogen deviates from the experimental value. In addition, the reported Fe(III) complexes produced by light-colored ligands were very dark (such as red, dark red, brown, or black) [ 45 , 46 , 47 , 48 , 49 , 50 ]. We took a closer look at the color of complex 2 —light yellowish green is a good description.…”

Coexistence of Three Different Spin States in a Cyanido‐Bridged Trinuclear Iron(III) Complex with an Unusual FeIII to Ligand Charge Transfer

“…The different charge transfer mechanisms were also validated by the subsequent IR spectra. Remarkably, the average bond length of Fe 2 III ‐N L (1.924(2) Å) in complex 2[PF 6 ] 4 is significantly shorter than the bond length of high‐spin Fe III −N L (about 2.03 Å) in six coordinated iron porphyrin complexes, [11] but close to that of low‐spin Fe III −N L bond length (about 1.92 Å–1.96 Å) in similar position [12] . These suggest the low‐spin character of the central Fe of complex 2[PF 6 ] 4 .…”

“…Remarkably, the average bond length of Fe 2 III -N L (1.924(2) Å) in complex 2[PF 6 ] 4 is significantly shorter than the bond length of high-spin Fe III À N L (about 2.03 Å) in six coordinated iron porphyrin complexes, [11] but close to that of low-spin Fe III À N L bond length (about 1.92 Å-1.96 Å) in similar position. [12] These suggest the low-spin character of the central Fe of complex 2[PF 6 ] 4 . Furthermore, it should be noted that the crystal structural data of 2[PF 6 ] 4 at 100, 200 and 300 K show that its space group keeps unchanged and the metal related bond lengths are almost same within the experimental error (Table S3), suggesting the absence of SCO, consistent with the variable-temperature Mössbauer spectral results (see below).…”

Inducing ring distortions in unsubstituted metallophthalocyanines using axial N-heterocyclic carbenes

“…Given their wide utility as ligands, it is surprising that no PcM (NHC) x complexes have been reported, although several analogous PorM(NHC) complexes are known. [49][50][51][52][53][54][55][56][57][58] Herein, we explore the preparation and physical properties of four new PcM(NHC) x complexes. The NHC ligands increase the solubility of the ring-unsubstituted PcM complexes in general and also illustrate the ability of an axially bound NHC to induce distortions to the PcM ring.…”