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1. 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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2. Tuning a phosphine-substituted diimine ligand to afford an iron monocarbonyl complex

   https://doi.org/10.1016/j.poly.2024.116910  

   Ghosh, Chandrani; Slater, Gavin C; Groy, Thomas L; Trovitch, Ryan J (May 2024, Polyhedron)

   A series of low-valent iron complexes that feature a phosphine-substituted α-diimine (DI) ligand have been synthesized. Reduction of (Ph2PPrDI)FeBr2 with an excess of Na/Hg in the presence of carbon monoxide afforded the corresponding dicarbonyl complex, (Ph2PPrDI)Fe(CO)2. Through multinuclear NMR and single crystal X-ray diffraction analysis, this complex was found to possess a 3-coordinate DI ligand. Upon heating for 10 days at 110 °C while applying intermittent vacuum, (Ph2PPrDI)Fe(CO)2 was successfully converted to the corresponding monocarbonyl complex, (Ph2PPrDI)Fe(CO), which was found to feature a tetradentate chelate. Similar reactivity was explored using the analogous bis(tert-butyl)phosphine-substituted ligand, tBu2PPrDI. Addition of this chelate to FeBr2 afforded (tBu2PPrDI)FeBr2, and subsequent reduction yielded (tBu2PPrDI)FeBr, which was found to possess a tridentate DI ligand by single crystal X-ray diffraction. Performing the reduction of (tBu2PPrDI)FeBr2 in the presence of CO afforded the corresponding dicarbonyl complex, (tBu2PPrDI)Fe(CO)2. Like aryl-substituted (Ph2PPrDI)Fe(CO)2, alkyl-substituted (tBu2PPrDI)Fe(CO)2 was found to feature a pendant phosphine arm. However, heating (tBu2PPrDI)Fe(CO)2 under vacuum did not allow for phosphine substitution and conversion to the corresponding monocarbonyl complex, highlighting the importance of phosphine π-acidity for substitution and the stabilization of low-valent iron. 

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3. Bis(iminoxolene)iridium Anion and Alkyls: How Does Ligand Redox Noninnocence Interface with Oxidative Addition?

   https://doi.org/10.1021/acs.organomet.4c00514  

   Meißner, Maximilian; Nugraha, Kahargyan; Grandstaff, Kristin D; Do, Thomas H; Jiménez, Carolina A; Chin, William Y; Farrell, Lauren E; Nguyen, Peter D; Brown, Seth N (March 2025, Organometallics)

   The bis(iminoxolene) complex (Diso)2IrCl (Diso = N-(2,6-diisopropylphenyl)-4,6-di-tert-butyl-2-imino-o-benzoquinone) is reduced by two equivalents of sodium naphthalenide to give square planar, diamagnetic Na[(Diso)2Ir]. The anionic iridium center acts as a nucleophile to primary and secondary alkyl and allyl halides to give square pyramidal iridium alkyls. Benzoyl chloride reacts to give an iridium benzoyl complex. Organoiridium complexes are also formed by reaction of (Diso)2IrCl with Grignard reagents, and treatment with acetone in the presence of base gives the 1 carbon-bonded enolate complex (Diso)2IrCH2COCH3. The solid-state structures of the primary alkyls show significant inclinations of the iridium-carbon bond away from the twofold axis of the square pyramid, apparently for steric reasons. The relative reactivity of substrates and exclusive formation of (Diso)2Ir(5-hexenyl) from 1-bromo-5-hexene indicates that primary alkyl halides react by an SN2 mechanism. Structural data suggest that the oxidative addition is about 70% metal centered, consistent with nucleophilic behavior that is analogous to that of other square planar group 9 anions. 

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4. Panoply of P: An Array of Rhenium–Phosphorus Complexes Generated from a Transition Metal Anion

   https://doi.org/10.1021/acs.inorgchem.4c01085  

   Hales, David P; Rajeshkumar, Thayalan; Shiau, Angela A; Rao, Guodong; Ouellette, Erik T; Bergman, Robert G; Britt, R David; Maron, Laurent; Arnold, John (June 2024, Inorganic Chemistry)

   We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (1, BDI = N,N’-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) to generate several rhenium–phosphorus complexes. Complex 1 reacts in a metathetical manner with chlorophosphines Ph2PCl, MeNHP-Cl, and OHP-Cl to generate XL-type phosphido complexes 2, 3, and 4, respectively (MeNHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad 2, 3, and 4 reveal that increasing the electronegativity of the phosphorus substituent (C < N < O) results in a shortening and strengthening of the rhenium–phosphorus bond. Complex 1 reacts with iminophosphane Mes*NPCl (Mes* = 2,4,6-tritert-butylphenyl) to generate linear iminophosphanyl complex 5. In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine iPr2NPCl2 to afford cationic phosphinidene complex 6+. Complex 6+ may be reduced by one electron to form 6•, a rare example of a stable, paramagnetic phosphinidene complex. Spectroscopic and structural investigations, as well as computational analyses, are employed to elucidate the influence of the phosphorus substituent on the nature of the rhenium–phosphorus bond in 2 through 6. Furthermore, we examine several common analogies employed to understand metal phosphido, phosphinidene, and iminophosphanyl complexes. 

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5. Requirements for Late-Stage Hydroboration of Pyridine N-Heterocyclic Carbene Iron(0) Complexes: The Role of Ancillary Ligands

   https://doi.org/10.1021/acs.organomet.1c00307  

   Kiernicki, John J.; Zeller, Matthias; Szymczak, Nathaniel K. (January 2021, Organometallics)

   null (Ed.)

   A series of zerovalent iron complexes were synthesized that contain allylic substituents attached to a 2,6-bis(imidazol-2-ylidene)pyridine pincer ligand. These species varied in the identity of their ancillary ligands and were used to study the requirements and limitations of late-stage hydroboration. While late-stage ligand functionalization can facilitate the incorporation of Lewis acidic boranes into a ligand scaffold, thereby alleviating Lewis acid/base incompatibilities of the free ligand, we identify and discuss complicating factors that arise from complexes containing labile M–L bonds. 

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