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1. Comparison of two Mn ^IV Mn ^IV -bis-μ-oxo complexes {[Mn ^IV (N ₄ (6-Me-DPEN))] ₂ (μ-O) ₂ } ²⁺ and {[Mn ^IV (N ₄ (6-Me-DPPN))] ₂ (μ-O) ₂ } ²⁺

   https://doi.org/10.1107/S2056989020004557  

   Coggins, Michael K.; Downing, Alexandra N.; Kaminsky, Werner; Kovacs, Julie A. (July 2020, Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   The addition of tert -butyl hydroperoxide ( t BuOOH) to two structurally related Mn II complexes containing N,N -bis(6-methyl-2-pyridylmethyl)ethane-1,2-diamine (6-Me-DPEN) and N,N -bis(6-methyl-2-pyridylmethyl)propane-1,2-diamine (6-Me-DPPN) results in the formation of high-valent bis-oxo complexes, namely di-μ-oxido-bis{[ N , N -bis(6-methyl-2-pyridylmethyl)ethane-1,2-diamine]manganese(II)}( Mn — Mn ) bis(tetraphenylborate) dihydrate, [Mn(C 16 H 22 N 4 ) 2 O 2 ](C 24 H 20 B) 2 ·2H 2 O or {[Mn IV (N 4 (6-Me-DPEN))] 2 ( μ -O) 2 }(2BPh 4 )(2H 2 O) ( 1 ) and di-μ-oxido-bis{[ N , N -bis(6-methyl-2-pyridylmethyl)propane-1,3-diamine]manganese(II)}( Mn — Mn ) bis(tetraphenylborate) diethyl ether disolvate, [Mn(C 17 H 24 N 4 ) 2 O 2 ](C 24 H 20 B) 2 ·2C 4 H 10 O or {[Mn IV (N 4 (6-MeDPPN))] 2 ( μ -O) 2 }(2BPh 4 )(2Et 2 O) ( 2 ). Complexes 1 and 2 both contain the `diamond core' motif found previously in a number of iron, copper, and manganese high-valent bis-oxo compounds. The flexibility in the propyl linker in the ligand scaffold of 2 , as compared to that of the ethyl linker in 1 , results in more elongated Mn—N bonds, as one would expect. The Mn—Mn distances and Mn—O bond lengths support an Mn IV oxidation state assignment for the Mn ions in both 1 and 2 . The angles around the Mn centers are consistent with the local pseudo-octahedral geometry. 

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2. 1,2-Addition and cycloaddition reactions of niobium bis(imido) and oxo imido complexes

   https://doi.org/10.1039/D0SC03489D  

   Fostvedt, Jade I.; Grant, Lauren N.; Kriegel, Benjamin M.; Obenhuber, Andreas H.; Lohrey, Trevor D.; Bergman, Robert G.; Arnold, John (November 2020, Chemical Science)

   null (Ed.)

   The bis(imido) complexes (BDI)Nb(N t Bu) 2 and (BDI)Nb(N t Bu)(NAr) (BDI = N , N ′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate; Ar = 2,6-diisopropylphenyl) were shown to engage in 1,2-addition and [2 + 2] cycloaddition reactions with a wide variety of substrates. Reaction of the bis(imido) complexes with dihydrogen, silanes, and boranes yielded hydrido-amido-imido complexes via 1,2-addition across Nb-imido π-bonds; some of these complexes were shown to further react via insertion of carbon dioxide to give formate-amido-imido products. Similarly, reaction of (BDI)Nb(N t Bu) 2 with tert -butylacetylene yielded an acetylide-amido-imido complex. In contrast to these results, many related mono(imido) Nb BDI complexes do not exhibit 1,2-addition reactivity, suggesting that π-loading plays an important role in activating the Nb–N π-bonds toward addition. The same bis(imido) complexes were also shown to engage in [2 + 2] cycloaddition reactions with oxygen- and sulfur-containing heteroallenes to give carbamate- and thiocarbamate-imido complexes: some of these complexes readily dimerized to give bis-μ-sulfido, bis-μ-iminodicarboxylate, and bis-μ-carbonate complexes. The mononuclear carbamate imido complex (BDI)Nb(NAr)(N( t Bu)CO 2 ) ( 12 ) could be induced to eject tert -butylisocyanate to generate a four-coordinate terminal oxo imido intermediate, which could be trapped as the five-coordinate pyridine or DMAP adduct. The DMAP adducted oxo imido complex (BDI)NbO(NAr)(DMAP) ( 16 ) was shown to engage in 1,2-addition of silanes across the Nb-oxo π-bond; this represents a new reaction pathway in group 5 chemistry. 

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3. A Diiron(I/II) μ-1,2-Carbonyl Complex Relevant to CO Binding on Fe(111)

   https://doi.org/10.1021/acs.inorgchem.5c00759  

   John, Titto Sunil; Singh, Devender; Maurel, Vincent; García-Serres, Ricardo; Murray, Leslie J (June 2025, Inorganic Chemistry)

   Fischer–Tropsch conversion of syngas to hydrocarbons is proposed to begin with CO binding to the iron surface of the catalyst. CO adsorption on various iron facets of relevance to the Fischer–Tropsch process suggest that the Fe(111) surface is the most active for catalysis, and that CO bound to the penultimate layer of Fe atoms or the b-state is the resting state during catalysis. Notably, a μ-1,2 mode was discarded for the b-state due to a lack of exemplar molecular species and expectation that such a mode would have a higher energy infrared (IR) absorption than observed experimentally (viz. 1735–1860 cm–1). Here, we report the synthesis of a diiron(I/II) complex in which CO binds μ-1,2: (Fe(OTf))(Fe(THF)(μ-1,2-CO))L where L2– is a bis(β-diketiminate) cyclophane (1). Surprisingly, the observed νCO at 1763 cm–1 for 1 compares well with that reported for b-state. Electron paramagnetic resonance (EPR), Mössbauer, and density functional theory (DFT) results support a weakly coupled s = 3/2 iron(I) and s = 2 iron(II) pair. Reduction of 1 results in C–O cleavage and C–C bond formation to yield a ketenylidene (CCO) complex as a major product observed spectroscopically. 

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4. The Scandium(II) Carbonyl Complex (C ₅ H ₂ ^t Bu ₃ ) ₂ Sc(CO) and Its Isocyanide Analog (C ₅ H ₂ ^t Bu ₃ ) ₂ Sc(CNC ₆ H ₃ Me ₂ -2,6)

   https://doi.org/10.1021/jacs.4c09021  

   Queen, Joshua D; Goudzwaard, Quinn E; Rajabi, Ahmadreza; Ziller, Joseph W; Furche, Filipp; Evans, William J (September 2024, Journal of the American Chemical Society)

   Treatment of the scandium(II) metallocene Cpttt2Sc (Cpttt = C5H2tBu3) with CO or the isocyanide CNXyl (Xyl = C6H3Me2-2,6) yields the carbonyl complex Cpttt2Sc(CO), 1, or the isocyanide complex Cpttt2Sc(CNXyl), 2, which were identified by X-ray crystallography. Isotopic labeling with 13CO shows the CO stretch of 1 at 1875 cm−1 shifts to 1838 cm−1 in 1-13CO. The CN stretch in 2 is shifted to 1939 cm−1 compared to 2118 cm−1 for the free isocyanide. The 80.1 MHz (28.7 G) 45Sc hyperfine coupling in 1 and 74.7 MHz (26.8 G) in 2 are similar to the 82.6 MHz (29.6 G) coupling constant in Cpttt2Sc and indicate that 1 and 2 are Sc(II) complexes. A comprehensive analysis of the electronic structures of 1 and 2 using DFT calculations is reported. 

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5. 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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