An Aerobic Synthetic Approach toward Bis-Alkynyl Cobalt(III) Compounds

Reported herein is an expanded investigation into a new method for the preparation of Co­(III) cyclam bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic, weak base conditions. Treatment of <i>trans</i>-[Co­(cyclam)­(C₂Ar)­Cl]­Cl-type complexes (Ar = C₆F₅ (<b>1a</b>), 4-C₆H₄NMe₂ (<b>1b</b>)) with AgOTf in MeCN resulted in the doubly charged complexes [Co­(cyclam)­(C₂Ar)­(NCMe)]­(OTf)₂ (Ar = C₆F₅ (<b>2a</b>), 4-C₆H₄NMe₂ (<b>2b</b>)). These solvento complexes <b>2a</b>,<b>b</b> undergo rapid alkynylation under aerobic conditions in the presence of an organic base and HC₂Ar′ to form the symmetrical or unsymmetrical bis-alkynyl complexes <i>trans</i>-[Co­(cyclam)­(C₂Ar)­(C₂Ar′)]­(OTf) (Ar/Ar′ = C₆F₅ (<b>3a</b>), 4-C₆H₄NMe₂ (<b>3b</b>); Ar = C₆F₅ and Ar′ = 4-C₆H₄NMe₂ (<b>3c</b>), C₂Ph (<b>3d</b>)) in good yields. Molecular structures of the new compounds were established using single-crystal X-ray diffraction. Structural studies revealed a notable <i>trans</i> influence for the Co–C_α bond lengths in the unsymmetrical complex <b>3c</b> with a bond length of 1.929(7) Å for the electron-withdrawing −C₂C₆F₅ ligand and 1.944(7) Å for −C₂-4-C₆H₄NMe₂. The optical HOMO–LUMO gaps for the bis-alkynyl complexes follow the trend <b>3a</b> (2.83 eV) > <b>3d</b> (2.77 eV) > <b>3c</b> (2.70 eV) > <b>3b</b> (2.64 eV). Although [Co­(cyclam)­(C₂R)₂]⁺ type complexes typically have irreversible electrochemical reductions, reversibility of the Co­(+3/+2) couple improves in Co­(III) cyclam complexes bearing more electron withdrawing substituents. Voltammetric analysis also revealed a modest NMe₂/NMe₂ coupling across the Co–alkynyl backbone in <b>3b</b>, while DFT calculations identified the HOMO in <b>3b</b> as the superexchange pathway for such coupling

Carbene Formation and Transfer at a Dinickel Active Site

The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [^{<i>i‑</i>Pr}NDI]­Ni₂(C₆H₆) complex (NDI = naphthyridine–diimine) reacts with Ph₂CN₂ to generate a metastable diazoalkane adduct, which eliminates N₂ at 60 °C to yield a paramagnetic Ni₂(μ-CPh₂) complex. The Ni₂(μ-CPh₂) complex undergoes carbene transfer to <i>t</i>-BuNC via an initial isonitrile adduct, which upon heating releases free <i>t</i>-BuNCCPh₂. On the basis of this sequence of stoichiometric reactions, a catalytic carbene transfer reaction is demonstrated

Synthesis and Characterizations of Macrocyclic Cr(III) and Co(III) 1‑Ethynyl Naphthalene and 9‑Ethynyl Anthracene Complexes: An Investigation of Structural and Spectroscopic Properties

Reported herein are the syntheses and structural and emission spectroscopic characterizations of new Cr^III(HMC) and Co^III(cyclam) complexes bearing fluorophore alkynyl ligands, where HMC and cyclam are 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane and 1,4,8,11-tetraazacyclotetradecane, respectively. Two Cr­(III) bis-1-ethynylnaphthalene (C₂Np) complexes, <i>trans</i>-[Cr­(HMC)­(C₂Np)₂]Cl ([<b>1</b>]­Cl) and <i>cis</i>-[Cr­(HMC)­(C₂Np)₂]Cl ([<b>2</b>]­Cl), were prepared from the reactions between <i>trans</i>/<i>cis</i>-[Cr­(HMC)­Cl₂]Cl and lithium 1-ethynylnaphthalene (LiC₂Np) in yields of 73 and 66%, respectively. Also investigated are Co^III(cyclam) complexes bearing both C₂Np and C₂ANT (ANT = 9-anthryl), namely [Co­(cyclam)­(C₂Ar)­Cl]Cl (Ar = ANT ([<b>3</b>]­Cl), Np ([<b>4</b>]­Cl)), [Co­(cyclam)­(C₂Np)­(NCCH₃)]­(OTf)₂ ([<b>5</b>]­(OTf)₂), and [Co­(cyclam)­(C₂Np)₂]­OTf ([<b>6</b>]­OTf). Complexes [<b>3</b>]Cl (72%) and [<b>4</b>]Cl (67%) were prepared from the reaction between [Co­(cyclam)­Cl₂]Cl and Me₃SiC₂ANT or Me₃SiC₂Np, respectively, in the presence of triethylamine. The reaction of [<b>4</b>]Cl with excess silver triflate in CH₃CN yielded complex [<b>5</b>]­(OTf)₂ (78%), which was reacted with HC₂Np in the presence of triethylamine to form complex [<b>6</b>]­OTf in 39% yield. Single crystal X-ray diffraction studies of [<b>1</b>]⁺, [<b>3</b>]⁺, [<b>4</b>]⁺, and [<b>6</b>]⁺ revealed a pseudo-octahedral geometry around the Cr­(III) or Co­(III) center with the tetraaza-macrocyclic ligand occupying the equatorial plane and the alkynyl- and/or chloro-ligand occupying the apical positions. The absorption spectra of complexes [<b>1</b>]⁺ and [<b>2</b>]⁺ display structured <i>d–d</i> bands between 400 and 550 nm, a feature that is absent in the <i>d–d</i> absorption of the Co­(III) complexes [<b>3</b>]⁺–[<b>6</b>]⁺. Contrasting emission behaviors were observed: the Cr­(III) complexes display metal-centered phosphorescence, while the Co­(III) species exhibit ligand-based fluorescence. Time-delayed phosphorescence measurements revealed lifetimes of 447 and 97 μs for [<b>1</b>]⁺ and [<b>2</b>]⁺ at 77 K, respectively, and a room temperature lifetime of 218 μs for [<b>1</b>]⁺

Stepwise Synthesis of Bis-Alkynyl Co^III(cyclam) Complexes under Ambient Conditions

Reported herein is a new synthetic method for the synthesis of Co^III(cyclam) bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic conditions. Upon the treatment of AgOTf in acetonitrile, complex <i>trans</i>-[Co­(cyclam)­(C₂C₆H₄NMe₂)­Cl]Cl (<b>1</b>) was converted to <i>trans</i>-[Co­(cyclam)­(C₂C₆H₄NMe₂) (NCMe)]­(OTf)₂ (<b>2</b>), and <b>2</b> was in turn reacted with HC₂Ar under weakly basic conditions to afford the novel bis-alkynyls <i>trans</i>-[Co­(cyclam)­(C₂C₆H₄NMe₂)­(C₂Ar)]­(OTf) (Ar = C₆H₄NMe₂ (<b>3</b>) and C₆F₅ (<b>4</b>)) in reasonable yields. Voltammetric analysis revealed a modest NMe₂/NMe₂ coupling across the Co-alkynyl backbone in <b>3</b>, while DFT calculations identified the HOMO in <b>3</b> as the superexchange pathway for such coupling

Catalytic Carbonylative Rearrangement of Norbornadiene via Dinuclear Carbon–Carbon Oxidative Addition

Single bonds between carbon atoms are inherently challenging to activate using transition metals; however, ring-strain release can provide the necessary thermodynamic driving force to make such processes favorable. In this report, we describe a strain-induced C–C oxidative addition of norbornadiene. The reaction is mediated by a dinuclear Ni complex, which also serves as a catalyst for the carbonylative rearrangement of norbornadiene to form a bicyclo[3.3.0] product

Dinuclear Pathways for the Activation of Strained Three-Membered Rings

Dinuclear, strain-induced ring-opening reactions of vinylaziridines and vinylcyclopropanes are described. The previously reported [NDI]­Ni₂(C₆H₆) complex (NDI = naphthyridine–diimine) reacts with <i>N</i>-tosyl-2-vinylaziridine via C–N oxidative addition to generate a dinickel metallacyclic product. On the basis of this stoichiometric reactivity, the [NDI]­Ni₂(C₆H₆) complex is shown to be a highly active catalyst for the rearrangement of vinylcyclopropane to cyclopentene. Notably, 2-phenyl-1-vinylcyclopropane undergoes regioselective activation at the less hindered C–C bond in contrast to the noncatalytic thermal rearrangement. DFT calculations provide insight into the ability of the Ni–Ni bond to stabilize key intermediates and transition states along the catalytic pathway

Catalytic Carbonylative Rearrangement of Norbornadiene via Dinuclear Carbon–Carbon Oxidative Addition

Single bonds between carbon atoms are inherently challenging to activate using transition metals; however, ring-strain release can provide the necessary thermodynamic driving force to make such processes favorable. In this report, we describe a strain-induced C–C oxidative addition of norbornadiene. The reaction is mediated by a dinuclear Ni complex, which also serves as a catalyst for the carbonylative rearrangement of norbornadiene to form a bicyclo[3.3.0] product

Ion-Directed Synthesis of Indium-Derived 2,5-Thiophenedicarboxylate Metal–Organic Frameworks: Tuning Framework Dimensionality

Template directed synthesis of metal–organic frameworks (MOFs) is of increasing interest. Herein we report the synthesis of six new MOFs synthesized from 2,5-thiophenedicarboxylic acid (TDC) and InCl₃. The new frameworks are formally two- (YCM-21) and one-dimensional (YCM-22) anionic, as well as three-dimensional neutral (YCM-23). YCM-22 contains an unprecedented dianionic [InCl₃(κ²-O₂CAr)₂]^2– node. The structural diversity represented by these materials is entirely controlled by addition of organic ammonium salts during the synthesis process. The role of the additives is briefly discussed with observed correlations of (1) hydrogen bonding and cation−π interactions influencing MOF dimensionality and (2) the presence of anionic chlorides creating a chlorine-rich metal center leading to a one-dimensional framework

Isomorphous but No Dead Ringer: Contrasting the Supramolecular Binding of Tetrafluoroberyllate and Sulfate Ions by Nanojars

An extensive single-crystal X-ray crystallographic study of 11 nanojar structures (of which seven are novel) of the formula [anion⊂{cis-CuII(μ-OH)(μ-pz)}n]2– (anion = BeF42–, n = 28, 31, 32, CunBeF4; anion = SO42–, n = 28, 31, CunSO4; pz = pyrazolate, C3H3N2–) has been carried out, providing a detailed description of isomorphism and pseudopolymorphism in nanojars. The results point to a remarkable variety in the shape of the constituent [cis-CuII(μ-OH)(μ-pz)]x (Cux; x = 6, 8, 9, 10, 12 and 14) metallamacrocycles, despite only small differences in the coordination environment of the individual Cu2+ centers. The flexibility of the Cux rings and, ultimately, of the nanojar framework allows for the incarceration of different anions with slightly different dimensions in a nanojar of a given size, resulting in the formation of isomorphous structures in the case of CunBeF4 and CunSO4. Selectivity studies monitored by electrospray-ionization mass spectrometry (ESI-MS) and proton nuclear magnetic resonance spectroscopy (1H NMR) reveal that despite the virtually identical H-bonding pattern around the two anions in nanojars of a given size, SO42– is strongly preferred over BeF42–. The origins of this selectivity are discussed, along with the nature of bonding in the two isosteric anions. Lastly, the crystal structure of (Bu4N)3Be2F7(H2O)3 documents the formation of the Be2F73– ion from BeF42–

Synthesis of indolo[4,3-<i>bc</i>]phenanthridine-6,11(2<i>H</i>,12<i>H</i>)-diones using the schiff base–homophthalic anhydride cyclization reaction

<p>A novel indolophenanthridine ring system has been synthesized via the Schiff base–homophthalic anhydride cyclization followed by thionyl chloride–mediated dehydrogenation and intramolecular Friedel–Crafts acylation. This adds to the array of heterocyclic systems that are available through the cycloaddition reaction of imines with cyclic dicarboxylic acid anhydrides. The cytotoxicities of the indolophenanthridines were investigated in human cancer cell cultures, and the results documented significant antitumor activity in a variety of human cancer cell lines. This provides a new heterocyclic scaffold for anticancer drug design.</p