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1. Synthesis of Chromium(II) Complexes with Chelating Bis(alkoxide) Ligand and Their Reactions with Organoazides and Diazoalkanes

   https://doi.org/10.3390/molecules25020273  

   Kurup, Sudheer S.; Staples, Richard J.; Lord, Richard L.; Groysman, Stanislav (January 2020, Molecules)

   Synthesis of new chromium(II) complexes with chelating bis(alkoxide) ligand [OO]Ph (H2[OO]Ph = [1,1′:4′,1′’-terphenyl]-2,2′’-diylbis(diphenylmethanol)) and their subsequent reactivity in the context of catalytic production of carbodiimides from azides and isocyanides are described. Two different Cr(II) complexes are obtained, as a function of the crystallization solvent: mononuclear Cr[OO]Ph(THF)2 (in toluene/THF, THF = tetrahydrofuran) and dinuclear Cr2([OO]Ph)2 (in CH2Cl2/THF). The electronic structure and bonding in Cr[OO]Ph(THF)2 were probed by density functional theory calculations. Isolated Cr2([OO]Ph)2 undergoes facile reaction with 4-MeC6H4N3, 4-MeOC6H4N3, or 3,5-Me2C6H3N3 to yield diamagnetic Cr(VI) bis(imido) complexes; a structure of Cr[OO]Ph(N(4-MeC6H4))2 was confirmed by X-ray crystallography. The reaction of Cr2([OO]Ph)2 with bulkier azides N3R (MesN3, AdN3) forms paramagnetic products, formulated as Cr[OO]Ph(NR). The attempted formation of a Cr–alkylidene complex (using N2CPh2) instead forms chromium(VI) bis(diphenylmethylenehydrazido) complex Cr[OO]Ph(NNCPh2)2. Catalytic formation of carbodiimides was investigated for the azide/isocyanide mixtures containing various aryl azides and isocyanides. The formation of carbodiimides was found to depend on the nature of organoazide: whereas bulky mesitylazide led to the formation of carbodiimides with all isocyanides, no carbodiimide formation was observed for 3,5-dimethylphenylazide or 4-methylphenylazide. Treatment of Cr2([OO]Ph)2 or H2[OO]Ph with NO+ leads to the formation of [1,2-b]-dihydroindenofluorene, likely obtained via carbocation-mediated cyclization of the ligand. 

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2. Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered

   https://doi.org/10.3390/molecules26040981  

   Hart, Mason D.; Meyers, John J.; Wood, Zachary A.; Nakakita, Toshinori; Applegate, Jason C.; Erickson, Nathan R.; Gerasimchuk, Nikolay N.; Barybin, Mikhail V. (February 2021, Molecules)

   null (Ed.)

   Isocyanoazulenes (CNAz) constitute a relatively new class of isocyanoarenes that offers rich structural and electronic diversification of the organic isocyanide ligand platform. This article considers a series of 2-isocyano-1,3-X2-azulene ligands (X = H, Me, CO2Et, Br, and CN) and the corresponding zero-valent complexes thereof, [(OC)5Cr(2-isocyano-1,3-X2-azulene)]. Air- and thermally stable, X-ray structurally characterized 2-isocyano-1,3-dimethylazulene may be viewed as a non-benzenoid aromatic congener of 2,6-dimethyphenyl isocyanide (2,6-xylyl isocyanide), a longtime “workhorse” aryl isocyanide ligand in coordination chemistry. Single crystal X-ray crystallographic {Cr–CNAz bond distances}, cyclic voltametric {E1/2(Cr0/1+)}, 13C NMR {δ(13CN), δ(13CO)}, UV-vis {dπ(Cr) → pπ*(CNAz) Metal-to-Ligand Charge Transfer}, and FTIR {νN≡C, νC≡O, kC≡O} analyses of the [(OC)5Cr(2-isocyano-1,3-X2-azulene)] complexes provided a multifaceted, quantitative assessment of the π-acceptor/σ-donor characteristics of the above five 2-isocyanoazulenes. In particular, the following inverse linear relationships were documented: δ(13COtrans) vs. δ(13CN), δ(13COcis) vs. δ(13CN), and δ(13COtrans) vs. kC≡O,trans force constant. Remarkably, the net electron withdrawing capability of the 2-isocyano-1,3-dicyanoazulene ligand rivals those of perfluorinated isocyanides CNC6F5 and CNC2F3. 

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3. Synthesis, characterization, and liquid injection field desorption ionization mass spectrometry analysis of pincer ligated group 6 (Cr, Mo, W) carbonyl complexes

   https://doi.org/10.1177/14690667221149498  

   Duletski, Olivia L.; Arulsamy, Navamoney; Mock, Michael T. (February 2023, European Journal of Mass Spectrometry)

   We report the synthesis of molybdenum and tungsten bromo dicarbonyl complexes (POCOP t Bu )M II Br(CO) 2 (M  =  Mo or W; POCOP t Bu   =  κ 3 -C 6 H 3 -1,3-[OP( tBu) 2 ] 2 ) supported by an anionic PCP pincer ligand, and the chromium complex (PNP t Bu )Cr 0 (CO) 3 (PNP t Bu   =  2,6-bis(di- tert-butyl-phosphinomethyl)pyridine) bearing a neutral PNP pincer scaffold. The three group six complexes described in this study have been characterized by Liquid Injection Field Desorption Ionization Mass Spectrometry (LIFDI-MS), NMR, and IR spectroscopy. Single crystal X-ray diffraction studies show the Mo II and W II complexes adopt a six-coordinate distorted trigonal prismatic geometry, whereas the Cr 0 complex exhibits a distorted octahedral geometry. 

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4. A five-coordinate Ni( i ) complex supported by 1,4,7-triisopropyl-1,4,7-triazacyclononane

   https://doi.org/10.1039/d2cc02516g  

   Griego, Leonel; Woods, Toby J.; Mirica, Liviu M. (June 2022, Chemical Communications)

   An isolated Ni( ii )-nitrosyl complex supported by the bulky tridentate 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPr 3 TACN) ligand was obtained from the reaction of a Ni( ii ) dimethyl complex with NOPF 6 , suggesting the in situ formation of a Ni( i ) species that reacts with the resulting NO product. Use of a π-acceptor ancillary isocyanide ligand led to the isolation and characterization of an uncommon 5-coordinate Ni( i ) complex supported by the iPr 3 TACN ligand and tert -butylisocyanide. 

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5. Porous Salts as Platforms for Heterogeneous Catalysis

   https://doi.org/10.1002/smll.202207507  

   Korman, Kyle J.; Dworzak, Michael R.; Yap, Glenn P.; Bloch, Eric D. (July 2023, Small)

   Abstract The preparation of a new class of reactive porous solids, prepared via straightforward salt metathesis reactions, is described here. Reaction of the dimethylammonium salt of a magnesium‐based porous coordination cage with the chloride salt of [Cr II Cl(Me 4 cyclam)] + affords a porous solid with concomitant removal of dimethylammonium chloride. The salt consists of the ions combined in the expected ratio based on their charge as confirmed by UV–vis and X‐ray photoelectron spectroscopies, ion chromatography (IC), and inductively coupled plasma mass spectrometry (ICP‐MS). The porous salt boasts a Brunauer‐Emmett‐Teller (BET) surface area of 213 m 2  g −1 . Single crystal X‐ray diffraction reveals the chromium(II) cations in the structure reside in the interstitial space between porous cages. Importantly, the chromium(II) centers, previously shown to react with O 2 to afford reactive chromium(III)‐superoxide adducts, are still accessible in the solid state as confirmed by UV–vis spectroscopy. The site‐isolated reactive centers have competence toward hydrogen atom abstraction chemistry and display significantly increased stability and reactivity as compared to dissolved ions. 

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