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1. Investigating intermediates in the CCC–NHC pincer ligand metalation/transmetalation to Rh sequence, an improved stoichiometric synthesis of CCC–NHC pincer Rh complexes

   https://doi.org/10.1016/j.jorganchem.2022.122499  

   Amoateng, Enock D.; Zamora-Moreno, Julio; Kuchenbeiser, Glenn; Donnadieu, Bruno; Tham, Fook; Montiel-Palma, Virginia; Keith Hollis, T. (November 2022, Journal of Organometallic Chemistry)

   The metalation/transmetalation strategy using [Zr(NMe2)4] as initial metalating reagent offers an efficient approach to the synthesis of CCC–NHC pincer complexes. Many CCC–NHC pincer complexes have been prepared via this methodology. As efficient as this methodology is, many questions remained as to the mechanism for the process, particularly the requirement of two equivalents of Rh per proligand for good yields. Previously, no intermediates have been reported to shed light on the mechanism. In the process of investigating an intermediate and the mechanism of the metalation/transmetalation methodology, a new mixed valent bimetallic CCC–NHC pincer Rh complex with two chloro ligands bridged between a [(CCC–NHC)Rh(III)] and a [Rh(I)(COD)] fragment was isolated and fully characterized. The investigation of the Rh(III)/Rh(I) bimetallic intermediate in the CCC–NHC pincer metalation/transmetalation methodology led to an improved stoichiometric synthesis of CCC–NHC pincer Rh complexes. It was found that switching the proligand from iodide to chloride counterion obviated the need for an extra equivalent of Rh. The iodide bridged Rh(III)/Rh(I) intermediate was much more stable and prevented further reaction in comparison to the chloride congener. When it was switched to only chloride present the reaction quickly gave efficient, complete transmetalation with only a 1:1 ratio of proligand:Rh. 

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2. The synthesis and characterization of a bidentate complex of 1,1′-(1,3-phenylene)bis(3-butylimidazolium) pincer proligand with molybdenum – A non-pincer binding mode

   https://doi.org/10.1016/j.poly.2023.116714  

   Juárez-Escamilla, Samuel D.; Dey, Sriloy; Donnadieu, Bruno; Hollis, T. Keith (January 2024, Polyhedron)

   The synthesis of the bidentate Mo complex tetrachlorido[6-(3’-butylimidazolium-1’-yl)-2-(3’’-butylimidazol-1’’-yl-2’’-idene-κC2)phenyl-κC1]molybdenum(IV) 3 was carried out using the metalation followed by transmetalation methodology. The transmetallation process led to a bidentate complex after reaction of DCM with HNMe2 formed an acidic ammonium ion that protonated the bidentate complex. Optimization of the synthetic methodology provided the tetrachlorido[6-(3’-butylimidazolium-1’-yl)-2-(3’’-butylimidazol-1’’-yl-2’’-idene-κC2)phenyl-κC1]molybdenum(IV) complex in high yield. The crystal structure of the bidentate complex, 3, is reported herein. Attempts to avoid the acidic reaction conditions with different solvents or starting materials produced the bis-ligated Mo complex bis[2,6-bis(3’-butylimidazol-1’-yl-2’-idene-κC2)phenyl-κC1]molybdenum(IV) dichloride based on MS analysis. Electronic and coordinative unsaturation in the resulting bidentate complex, 3, open new possibilities for coordination of incoming substrates while also allowing access to the pincer-like motif via oxidative addition. Access to the interconversion of a NHC to/from imidazolium opens new avenues of non-innocent ligand pathways for proton shuttling in reactions such as nitrogen reduction to ammonia. 

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3. Synthesis of Crystallographically Characterizable Bis(cyclopentadienyl) Sc(II) Complexes: (C ₅ H ₂ ^t Bu ₃ ) ₂ Sc and {[C ₅ H ₃ (SiMe ₃ ) ₂ ] ₂ ScI} ^1–

   https://doi.org/10.1021/jacs.3c11922  

   Queen, Joshua D.; Anderson-Sanchez, Lauren M.; Stennett, Cary R.; Rajabi, Ahmadreza; Ziller, Joseph W.; Furche, Filipp; Evans, William J. (February 2024, Journal of the American Chemical Society)

   The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C5H2(tBu)3 (Cpttt), C5Me5 (Cp*), and C5H3(SiMe3)2 (Cp″) ligands. Cpttt 2ScI, 1, formed from ScI3 and KCpttt, can be reduced with potassium graphite (KC8) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, Cpttt 2Sc, 2. Complex 2 has a 170.6° (ring centroid)-Sc-(ring centroid) angle and exhibits an eight-line EPR spectrum characteristic of Sc(II) with Aiso = 82.6 MHz (29.6 G). It sublimes at 200 °C at 10−4 Torr and has a melting point of 268−271 °C. Reductions of Cp*2ScI and Cp″2ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp*2ScI in benzene formed the Sc(III) phenyl complex, Cp*2Sc(C6H5), 3, by C−H bond activation. However, in Et2O and toluene, reduction of Cp*2ScI at −78 °C gives a dark-red solution, 4, which displays an eight-line EPR pattern like that of 1, but it did not provide thermally stable crystals. Reduction of Cp″2ScI, in THF or Et2O at −35 °C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cp″2ScI], 5, which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp*2ScI with KC8 and 18-crown-6 in Et2O gave the ligand redistribution product, [Cp*2Sc(18- crown-6-κ2O,O′)][Cp*2ScI2], 6, as the only crystalline product. Density functional theory 

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4. Isocyanide Substituent Influences Reductive Elimination versus Migratory Insertion in Reaction with an [Fe ₂ (μ-H) ₂ ] ²⁺ Complex

   https://doi.org/10.1021/acs.inorgchem.4c03256  

   John, Titto Sunil; Dobrzycki, Łukasz; Catalano, Vincent J; Murray, Leslie J (November 2024, Inorganic Chemistry)

   Iron hydrides are proposed reactive intermediates for N2 and CO conversion in industrial and biological processes. Here, we report a reactivity study of a low-coordinate di(μ-hydrido)diiron(II) complex, Fe2(μ-H)2L, where L2– is a bis(β-diketiminate) cyclophane, with isocyanides, which have electronic structures related to N2 and CO. The reaction outcome is influenced by the isocyanide substituent, with 2,6-xylyl isocyanide leading to H2 loss, to form a bis(μ-1,1-isocyanide)diiron(I) complex, whereas all of the other tested isocyanides insert into the Fe–H bond to give (μ-1,2-iminoformyl) complexes. Steric bulk of the isocyanide substituent determines the extent of insertion (i.e., into one or both Fe–H–Fe units) with tert-butyl isocyanide reacting to yield the mono-(μ-1,2-iminoformyl)diiron(II) complex, exclusively, and isopropyl- and methyl isocyanides affording the bis(μ-1,2-iminoformyl)diiron(II) products. Treatment of Fe2(μ-1,2-CHNtBu)(μ-H)L with 2,6-xylyl isocyanide (or XylNC) yields Fe2(μ-XylNC)2L and tert-butylaldimine as one of the organic products. 

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5. Solvent‐Dependent Spin‐Crossover Behavior in Semiconducting Co–Crystals of [Fe(1‐bpp) ₂ ] ²⁺ Cations and TCNQ ^δ− Anions (0<δ<1)

   https://doi.org/10.1002/ejic.202100707  

   Üngör, Ökten; Choi, Eun_Sang; Shatruk, Michael (November 2021, European Journal of Inorganic Chemistry)

   Abstract Co‐crystallization of the spin‐crossover (SCO) cationic complex, [Fe(1‐bpp)₂]²⁺(1‐bpp=2,6‐bis(pyrazol‐1‐yl)pyridine) with fractionally charged organic anion TCNQ^δ−(0<δ<1) afforded hybrid materials [Fe(1‐bpp)₂](TCNQ)_3.5 ⋅ 3.5MeCN (1) and [Fe(1‐bpp)₂](TCNQ)₄ ⋅ 4DCE (2), where TCNQ=7,7,8,8‐tetracyanoquinodimethane, MeCN=acetonitrile, and DCE=1,2‐dichloroethane. Both materials exhibit semiconducting behavior, with the room‐temperature conductivity values of 1.1×10⁻⁴ S/cm and 1.7×10⁻³ S/cm, respectively. The magnetic behavior of both complexes exhibits strong dependence on the content of the interstitial solvent. Complex1undergoes a gradual temperature‐driven SCO, with the midpoint temperature ofT_1/2=234 K. The partial solvent loss by1leads to the increase in theT_1/2value while complete desolvation renders the material high‐spin (HS) in the entire studied temperature range. In the case of2, the solvated complex shows a gradual SCO withT_1/2=166 K only when covered with a mother liquid, while the facile loss of interstitial solvent, even at room temperature, leads to the HS‐only behavior. 

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