Construction of Three Coordination Compounds Formed by in‐situ Ligand Reaction of 1‐Cyanobenzoimidazole

Solvothermal reactions of 1‐cyanobenzoimidazole, NaN₃, and hydrated M^IICl₂ (M = Mn, Zn, Cu) in a mixture of EtOH/H₂O in the presence of NH₄Cl afforded a mononuclear complex [Mn(L¹)₂(H₂O)₄] ( 1 ), a 3D polymer [Zn(L¹)(OH)]_n ( 2 ), and a linear polymer {[Cu(Bim)]}_n ( 3 ), respectively, where the ligand L¹ is formed in‐situ from [3+2] dipolar cycloaddition of N₃^– with nitrile and the ligand Bim is in‐situ formed from C–N bond cleavage of 1‐cyanobenzoimidazole. (L¹ = 5‐benzoimidazoyltetrazolate, Bim = benzoimidazole). All the compounds were characterized by IR spectroscopy, elemental analysis, and thermo‐gravimetric analysis (TGA), and their structures were determined by X‐ray crystallography. The solid state luminescent properties of 2 and 3 were also investigated at room temperature.     

Synthesis,Crystal Structures,and Luminescent Properties of a Series of Coordination Compounds bearing Quinoline‐2‐tetrazolato Ligands

Four new coordination compounds, [Cd(L¹)₂]_n ( 1 ), [Mn(L¹)₂]_n ( 2 ), [Zn(L¹)(NA)] ( 3 ), and [Pb(L¹)₂(H₂O)] ( 4 ) were obtained on the basis of the in‐situ ligand reactions of quinoline‐2‐carbonitrile (QCN) and NaN₃ under solvothermal conditions. 1 and 2 are 1D isostructural chains, where the central metal atoms are six‐coordinate by six nitrogen atoms in a distorted octahedron. The cycloaddition reaction of QCN and NaN₃ in the presence of hydrated ZnCl₂ occur with the aid of the ancillary ligand nicotinic acid (NA), where NA not only provides an acidic environment but also serves as an ancillary ligand. The extended structure of 3 is a 1D ladder‐like polymer. Compound 4 is a mononuclear Pb²⁺ compound. All the compounds were structurally characterized by X‐ray crystallography and their luminescent properties were investigated in detail.     

Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N1,N2‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

The hexadentate ligand all‐cis‐N¹,N²‐bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine (L^e) was synthesized in five steps with an overall yield of 39 % by using [Ni(taci)₂]SO₄?4 H₂O as starting material (taci=1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol). Crystal structures of [Na_0.5(H₆L^e)](BiCl₆)₂Cl_0.5?4 H₂O ( 1 ), [Ni(L^e)]‐ Cl₂?5 H₂O ( 2 ), [Cu(L^e)](ClO₄)₂?H₂O ( 3 ), [Zn(L^e)]CO₃?7 H₂O ( 4 ), [Co(L^e)](ClO₄)₃ ( 5 c ), and [Ga(H_?2L^e)]‐ NO₃?2 H₂O ( 6 ) are reported. The Na complex 1 exhibited a chain structure with the Na⁺ cations bonded to three hydroxy groups of one taci subunit of the fully protonated H₆(L^e)⁶⁺ ligand. In 2 , 3 , 4 , and 5 c , a mononuclear hexaamine coordination was found. In the Ga complex 6 , a mononuclear hexadentate coordination was also observed, but the metal binding occurred through four amino groups and two alkoxo groups of the doubly deprotonated H_?2(L^e)^2?. The steric strain within the molecular framework of various M(L^e) isomers was analyzed by means of molecular mechanics calculations. The formation of complexes of L^e with Mn^II, Cu^II, Zn^II, and Cd^II was investigated in aqueous solution by using potentiometric and spectrophotometric titration experiments. Extended equilibrium systems comprising a large number of species were observed, such as [M(L^e)]²⁺, protonated complexes [MH_z(L^e)]^2+z and oligonuclear aggregates. The pK_a values of H₆(L^e)⁶⁺ (25 °C, μ=0.10 m ) were found to be 2.99, 5.63, 6.72, 7.38, 8.37, and 9.07, and the determined formation constants (log β) of [M(L^e)]²⁺ were 6.13(3) (Mn^II), 20.11(2) (Cu^II), 13.60(2) (Zn^II), and 10.43(2) (Cd^II). The redox potentials (vs. NHE) of the [M(L^e)]^3+/2+ couples were elucidated for Co (?0.38 V) and Ni (+0.90 V) by cyclic voltammetry.     

Influence of Ligand Architecture on Oxidation Reactions by High‐Valent Nonheme Manganese Oxo Complexes Using Water as a Source of Oxygen

Mononuclear nonheme Mn^IV?O complexes with two isomers of a bispidine ligand have been synthesized and characterized by various spectroscopies and density functional theory (DFT). The Mn^IV?O complexes show reactivity in oxidation reactions (hydrogen‐atom abstraction and sulfoxidation). Interestingly, one of the isomers (L¹) is significantly more reactive than the other (L²), while in the corresponding Fe^IV?O based oxidation reactions the L²‐based system was previously found to be more reactive than the L¹‐based catalyst. This inversion of reactivities is discussed on the basis of DFT and molecular mechanics (MM) model calculations, which indicate that the order of reactivities are primarily due to a switch of reaction channels (σ versus π) and concomitant steric effects.     

A comparative kinetic study for the oxidation of 2‐mercaptoethanol by di‐μ‐oxo‐bis(1,4,7,10‐tetraazacyclododecane)‐dimanganese(III,IV) and di‐μ‐oxo‐bis(1,4,8,11‐tetraazacyclotetradecane)‐dimanganese(III,IV) complexes: Influence of copper(II)

A comparative kinetic study of the reactions of two mixed valence manganese(III,IV) complexes with macrocyclic ligands, [L¹Mn^IV(O)₂Mn^IIIL¹], 1 (L¹ = 1,4,7,10‐tetraazacyclododecane) and [L²Mn^IV(O)₂Mn^IIIL²], 2 (L² = 1,4,8,11‐tetraazacyclotetradecane) with 2‐mercaptoethanol (RSH) has been carried out by spectrophotometry in aqueous buffer at (30 ± 0.1)°C. Rate of the reactions between the oxidants and the reductant was found to be negligibly slow with no systematic dependence on either redox partners. Externally added copper(II) (usually 5 × 10^?7 mol dm^?3), however, increases the rate of the reduction of 1 and 2 significantly. In the presence of catalytic amount of copper(II), the rate of the reaction is nearly proportional to [RSH] at lower concentration of the reductant but follows a saturation kinetics at higher concentration of the latter for the reaction between 1 and the thiol. Reaction rate was found to be strongly influenced by the variation of acidity of the medium and the observed kinetics suggests that the two reductant species ([Cu(RSH)]²⁺ and [Cu(RS)]⁺) are significant for the reaction between 1 and the thiol. The dependence of the rate on [RSH] for the reduction of 2 by the thiol was complex and rationalized considering two equilibria involving the catalyst (Cu²⁺) and the reductant. The pH rate profile suggests that both the μ‐O protonated [Mn^III(O)(OH)Mn^IV] and the deprotonated [Mn^III(O)₂Mn^IV] forms of the oxidant 2 become important. The kinetic results presented in this study indicate the domination of outer‐sphere path. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 129–137, 2004     

catena‐Poly­[[[1,8‐bis(2‐hydroxy­ethyl)‐1,3,6,8,10,13‐hexa­aza­cyclo­tetra­decane]copper(II)]‐μ‐cyano‐[tri­cyano­nitro­soiron(III)]‐μ‐cyano]

The bimetallic title complex, [CuFe(CN)₅(C₁₂H₃₀N₆O₂)(NO)] or [Cu(L)Fe(CN)₅(NO)] [where L is 1,8‐bis(2‐hydroxy­ethyl)‐1,3,6,8,10,13‐hexa­aza­cyclo­tetra­decane], has a one‐dimensional zigzag polymeric –Cu(L)–NC–Fe(NO)(CN)₃–CN–Cu(L)– chain, in which the Cu^II and Fe^II centres are linked by two CN groups. In the complex, the Cu^II ion is coordinated by four N atoms from the L ligand [Cu—N(L) = 1.999 (2)–2.016 (2) Å] and two cyanide N atoms [Cu—N = 2.383 (2) and 2.902 (3) Å], and has an elongated octahedral geometry. The Fe^II centre is in a distorted octahedral environment, with Fe—N(nitroso) = 1.656 (2) Å and Fe—C(CN) = 1.938 (3)–1.948 (3) Å. The one‐dimensional zigzag chains are linked to form a three‐dimensional network via N—H⋯N and O—H⋯N hydrogen bonds.     

A one‐dimensional coordination polymer of 5‐[(imidazol‐1‐yl)methyl]benzene‐1,3‐dicarboxylic acid with CuII cations

5‐[(Imidazol‐1‐yl)methyl]benzene‐1,3‐dicarboxylic acid (H₂L) was synthesized and the dimethylformamide‐ and dimethylacetamide‐solvated structures of its adducts with Cu^II, namely catena‐poly[[copper(II)‐bis[μ‐3‐carboxy‐5‐[(imidazol‐1‐yl)methyl]benzoato]] dimethylformamide disolvate], {[Cu(C₁₂H₉N₂O₄)₂]·2C₃H₇NO}_n, (I), and catena‐poly[[copper(II)‐bis[μ‐3‐carboxy‐5‐[(imidazol‐1‐yl)methyl]benzoato]] dimethylacetamide disolvate], {[Cu(C₁₂H₉N₂O₄)₂]·2C₄H₉NO}_n, (II), the formation of which are associated with mono‐deprotonation of H₂L. The two structures are isomorphous and isometric. They consist of one‐dimensional coordination polymers of the organic ligand with Cu^II in a 2:1 ratio, [Cu(μ‐HL)₂]_n, crystallizing as the dimethylformamide (DMF) or dimethylacetamide (DMA) disolvates. The Cu^II cations are characterized by a coordination number of six, being located on centres of crystallographic inversion. In the polymeric chains, each Cu^II cation is linked to four neighbouring HL⁻ ligands, and the organic ligand is coordinated via Cu—O and Cu—N bonds to two Cu^II cations. In the corresponding crystal structures of (I) and (II), the coordination chains, aligned parallel to the c axis, are further interlinked by strong hydrogen bonds between the noncoordinated carboxy groups in one array and the coordinated carboxylate groups of neighbouring chains. Molecules of DMF and DMA (disordered) are accommodated at the interface between adjacent polymeric assemblies. This report provides the first structural evidence for the formation of coordination polymers with H₂Lvia multiple metal–ligand bonds through both carboxylate and imidazole groups.     

Synthesis,Crystal Structure and Spectroscopic Properties of [2,13‐Bis(1‐naphthalenylmethyl)‐5,16‐dimethyl‐2,6,13,17‐tetraazatricyclo(14,4,01.18,07.12)docosane]copper(II) Diperchlorate Acetonitrile Disolvate

The N‐functionalized macrocyclic ligand 2,13‐bis(1‐naphthalenylmethyl)‐5,16‐dimethyl‐2,6,13,17‐tetraazatricyclo(14,4,0^1.18,0^7.12)docosane (L³) and its copper(II) complex were prepared. The crystal structure of [Cu(L³)](ClO₄)₂·2CH₃CN was determined by single‐crystal X‐ray diffraction at 150 K. The copper atom, which lies on an inversion centre, has a square planar arrangement and the complex adopts a stable trans‐III configuration. The longer distance [2.081(2) Å] for Cu–N(tertiary) compared to 2.030(3) Å for Cu–N(secondary) may be due to the steric effect of the attached naphthalenylmethyl group on the tertiary nitrogen atom. Two perchlorate ions are weakly attached to copper in axial sites and are further connected to the ligand of the cation through NH ··· O hydrogen bonds [N ··· O 3.098 Å]. IR and UV/Vis spectroscopic properties are also described.     

Poly[aqua[μ3‐(pyridin‐1‐ium‐3,5‐diyl)diphosphonato‐κ3O:O′:O′′][μ2‐(pyridin‐1‐ium‐3,5‐diyl)diphosphonato‐κ2O:O′]calcium(II)]

The rigid organic ligand (pyridine‐3,5‐diyl)diphosphonic acid has been used to create the title novel three‐dimensional coordination polymer, [Ca(C₅H₆NO₆P₂)₂(H₂O)]_n. The six‐coordinate calcium ion is in a distorted octahedral environment, formed by five phosphonate O atoms from five different (pyridin‐1‐ium‐3,5‐diyl)diphosphonate ligands, two of which are unique, and one water O atom. Two crystallographically independent acid monoanions, L1 and L2, serve to link metal centres using two different coordination modes, viz.η²μ₂ and η³μ₃, respectively. The latter ligand, L2, forms a strongly undulated two‐dimensional framework parallel to the crystallographic bc plane, whereas the former ligand, L1, is utilized in the formation of one‐dimensional helical chains in the [010] direction. The two sublattices of L1 and L2 interweave at the Ca²⁺ ions to form a three‐dimensional framework. In addition, multiple O—H...O and N—H...O hydrogen bonds stabilize the three‐dimensional coordination network. Topologically, the three‐dimensional framework can be simplified as a very unusual (2,3,5)‐connected three‐nodal net represented by the Schläfli symbol (4·8²)(4·8⁸·10)(8).     

New CuII and CdII Metal‐organic Coordination Polymers with 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazole Ligands: Syntheses,Structures and Luminescent Properties

Three new complexes {[Cu( L¹ )₂(NO₃)₂]?H₂O}_oo ( 1 ), {[Cu₄( L² )₂(OAc)₈]‐CH₃CH₂OH}_oo ( 2 ) and [Cd₂( L³ )₃(NO₃)₄(H₂O)₂]_oo ( 3 ) ( L¹= 4‐phenyl‐7‐(pyridine‐3‐yl)‐1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazole, L²= 4‐(pyridine‐3‐yl)‐7‐phenyl‐1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazole, and L³= 4‐(pyridine‐4‐yl)‐7‐phenyl‐1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazole) have been synthesized and characterized by elemental analyses, IR spectra and single crystal X‐ray diffraction. The structural analyses reveal that complex 1 is a neutral 2‐D network structure with a 4⁴ topology, 2 has a 1‐D neutral coordination chain with a [Cu₂(CH₃COO)₄] dinuclear structural unit bridged by four acetate ions, and 3 is a neutral rhombohedral grid structure. All the complexes are air stable at room temperature. Furthermore, the fluorescent properties of complex 3 and corresponding ligand L³ have been investigated and discussed.     

Self‐Assembly of Water‐Soluble Platinum(II)‐Based Metallacalixarenes and Tuning Their Conformational Interconversion via Synergistic Effects between Solvents and Anions

The aqueous self‐assembly of the flexible ligand L bis(1H‐benz[d]imidazole‐1‐yl)methane and cis‐coordinated Pt^II precursors [(en)Pt²⁺, (tmeda)Pt²⁺, en=ethylenediamine, tmeda=N,N,N′,N′‐tetramethylethylenediamine)] led to the formation of the metallacalixarenes with full alternative conformations (e.g., two novel water‐soluble metallacalixarenes [M₂L₂]⁴⁺ and [M₃L₃]⁶⁺ with D₂ and D₃ symmetry, respectively). Their molecular structures were determined by single crystal X‐ray analyses in solid state. The two metallacalixarenes present different cavity sizes and the [M₃L₃]⁶⁺ cavity encapsulates one NO₃⁻. NOESY NMR revealed that the conformational interconversion between 1,3‐alternate conformer in methanol and cone conformer in DMSO was tuned via the synergistic effect between solvent and anion. Guest encapsulation is also discussed.     

Solvent‐Dependent Self‐Assembly Behaviour and Speciation Control of Pd6L8 Metallo‐supramolecular Cages

The C₃‐symmetric chiral propylated host‐type ligands (±)‐tris(isonicotinoyl)‐tris(propyl)‐cyclotricatechylene ( L1 ) and (±)‐tris(4‐pyridyl‐4‐benzoxy)‐tris(propyl)‐cyclotricatechylene ( L2 ) self‐assemble with Pd^II into [Pd₆L₈]¹²⁺ metallo‐cages that resemble a stella octangula. The self‐assembly of the [Pd₆( L1 )₈]¹²⁺ cage is solvent‐dependent; broad NMR resonances and a disordered crystal structure indicate no chiral self‐sorting of the ligand enantiomers in DMSO solution, but sharp NMR resonances occur in MeCN or MeNO₂. The [Pd₆( L1 )₈]¹²⁺ cage is observed to be less favourable in the presence of additional ligand, than is its counterpart, where L=(±)‐tris(isonicotinoyl)cyclotriguaiacylene ( L1 a ). The stoichiometry of reactant mixtures and chemical triggers can be used to control formation of mixtures of homoleptic or heteroleptic [Pd₆L₈]¹²⁺ metallo‐cages where L= L1 and L1 a .     

Copper(II) and Cadmium(II) Complexes Based on N,N‐Bis(3, 5‐dimethyl‐2‐hydroxybenzyl)‐N‐(2‐pyridylmethyl)amine Ligand: Syntheses,Structures, Magnetic,and Luminescent Properties

The reaction of the aryl‐oxide ligand H₂L [H₂L = N,N‐bis(3, 5‐dimethyl‐2‐hydroxybenzyl)‐N‐(2‐pyridylmethyl)amine] with CuSO₄ · 5H₂O, CuCl₂ · 2H₂O, CuBr₂, CdCl₂ · 2.5H₂O, and Cd(OAc)₂ · 2H₂O, respectively, under hydrothermal conditions gave the complexes [Cu(H₂L¹)₂] · SO₄ · 3CH₃OH ( 1 ), [Cu₂(H₂L²)₂Cl₄] ( 2 ), [Cu₂(H₂L²)₂Br₄] ( 3 ), [Cd₂(HL)₂Cl₂] ( 4 ), and [Cd₂(L)₂(CH₃COOH)₂] · H₂L ( 5 ), where H₂L¹ [H₂L¹ = 2, 4‐dimethyl‐6‐((pyridin‐2‐ylmethylamino)methyl)phenol] and H₂L² [H₂L² = 2‐(2, 4‐dimethyl‐6‐((pyridin‐2‐ylmethylamino)methyl)phenoxy)‐4, 6‐dimethylphenol] were derived from the solvothermal in situ metal/ligand reactions. These complexes were characterized by IR spectroscopy, elementary analysis, and X‐ray diffraction. A low‐temperature magnetic susceptibility measurement for the solid sample of 2 revealed antiferromagnetic interactions between two central copper(II) atoms. The emission property studies for complexes 4 and 5 indicated strong luminescence emission.     

Phenylimidorhenium(V) Complexes with 1,3‐Diethyl‐4,5‐dimethylimidazole‐2‐ ylidene Ligands

The phenylimidorhenium(V) complexes [Re(NPh)X₃(PPh₃)₂] (X = Cl, Br) react with the N‐heterocyclic carbene (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐2‐ylidene (L^Et) under formation of the stable rhenium(V) complex cations [Re(NPh)X(L^Et)₄]²⁺ (X = Cl, Br), which can be isolated as their chloride or [PF₆]^? salts. The compounds are remarkably stable against air, moisture and ligand exchange. The hydroxo species [Re(NPh)(OH)(L^Et)₄]²⁺ is formed when moist solvents are used during the synthesis. The rhenium atoms in all three complexes are coordinated in a distorted octahedral fashion with the four NHC ligands in equatorial planes of the molecules. The Re–C(carbene) bond lengths between 2.171(8) and 2.221(3) Å indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atoms. Attempts to prepare analogous phenylimido complexes from [Re(NPh)Cl₃(PPh₃)₂] and 1,3‐diisopropyl‐4,5‐dimethylimidazole‐2‐ylidene (L^i?Pr) led to a cleavage of the rhenium‐nitrogen multiple bond and the formation of the dioxo complex [ReO₂(L^i?Pr)₄]⁺.     

Complex Formation of 2, 6‐Bis‐(2′‐hydroxyphenyl)pyridine with AlIII,FeIII and CuII

Complex formation of 2, 6‐bis(2′‐hydroxyphenyl)pyridine (H₂Lⁱ) with Fe³⁺ and Cu²⁺ was investigated in a H₂O/DMSO medium (mole fraction x_DMSO = 0.2) by potentiometric and spectrophotometric methods. The pK_a values of [H₃Lⁱ]⁺ are 2.25, 10.51 and 14.0 (25 °C, 0.1 M KCl). The formation constants of [Fe^III(Lⁱ)]⁺ and [Cu^II(Lⁱ)] (25 °C, 0.1 M KCl) are log β₁ = 21.5 for Fe³⁺ and log β₁ = 18.5 for Cu²⁺. The crystal structures of [Al(Lⁱ)₂Na(EtOH)₃], [Fe(Lⁱ)₂Na(EtOH)₃], and [Cu(Lⁱ)(py)]₂ were investigated by single‐crystal X‐ray diffraction analyses. The Fe^III and the Al^III compound are isotypic and crystallize in the monoclinic space group P2₁/n. Al‐compound (215 K): a = 12.599(3) Å, b = 16.653(3) Å, c = 17.525(4) Å, β = 100.27(3)°, Z = 4 for C₄₀H₄₀AlN₂NaO₇; Fe‐compound (293 K): a = 12.753(3) Å, b = 16.715(3) Å, c = 17.493(3) Å, β = 99.68(3)°, Z = 4 for C₄₀H₄₀FeN₂NaO₇. Both compounds contain a homoleptic, anionic bis‐complex [M(Lⁱ)₂]^‐ of approximate D₂ symmetry. The Cu compound crystallized as an uncharged, dinuclear and centrosymmetric [Cu(Lⁱ)(py)]₂ complex in the monoclinic space group P2₁/n with (293 K) a = 13.386(3) Å, b = 9.368(2) Å, c = 14.656(3) Å, β = 100.65(3)°, Z = 2 for C₄₄H₃₂Cu₂N₄O₄. The structural properties and in particular the possible influence of the ligand geometry on the stability of the metal complexes is discussed.     

Di‐μ‐hydroxido‐bis{[bis(6‐methyl‐2‐pyridylmethyl)(2‐phenylethyl)amine‐κ3N′,N′′,N′′′]copper(II)} bis(perchlorate)

The title compund, [Cu₂(OH)₂(C₂₂H₂₅N₃)₂](ClO₄)₂, is a copper(II) dimer, with two [CuL]²⁺ units [L is bis(6‐methyl‐2‐pyridylmethyl)(2‐phenylethyl)amine] bridged by hydroxide groups to define the {[CuL](μ‐OH)₂[CuL]}²⁺ cation. Charge balance is provided by perchlorate counter‐anions. The cation has a crystallographic inversion centre halfway between the Cu^II ions, which are separated by 3.0161 (8) Å. The central core of the cation is an almost regular Cu₂O₂ parallelogram of sides 1.931 (2) and 1.935 (2) Å, with a Cu—O—Cu angle of 102.55 (11)°. The coordination geometry around each Cu^II centre can be best described as a square‐based pyramid, with three N atoms from L ligands and two hydroxide O atoms completing the coordination environment. Each cationic unit is hydrogen bonded to two perchlorate anions by means of hydroxide–perchlorate O—H...O interactions.     

Enantioselective Construction of 2,3‐Dihydrofuro[2,3‐b]quinolines through Supramolecular Hydrogen Bonding Interactions

The first asymmetric synthesis of 2,3‐dihydrofuro[2,3‐b]quinolines has been achieved by a cascade asymmetric aziridination/intramolecular ring‐opening process of differently substituted 3‐alkenylquinolones. Good yields and high enantioselectivities (up to 78 % yield and 95 % ee) were recorded when employing 2,2,2‐trichloroethoxysulfonamide as the nitrene source, PhI(OCOtBu)₂ as the oxidant, and a chiral C₂‐symmetric Rh^II complex as the catalyst (1 mol %). The catalyst bears two lactam motifs, which serve as binding sites for substrate coordination through supramolecular hydrogen‐bonding interactions.     

Copper‐Catalyzed C(sp3)−H Amidation: Sterically Driven Primary and Secondary C−H Site‐Selectivity

Undirected C(sp³)?H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C?H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C?H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C?H bonds over tertiary and benzylic C?H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C?H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N₃. Mechanistic and DFT studies indicate that C?H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ²‐N,O‐NC(O)Ar) to provide carbon‐based radicals R^. and copper(II)amide intermediates [Cu^II]‐NHC(O)Ar that subsequently capture radicals R^. to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C?H amidation selectivity in the absence of directing groups.     

Metallkomplexe mit biologisch wichtigen Liganden. CLXVI Metallkomplexe mit Ferrocenylmethyl‐L‐cysteinat und 1,1′‐Ferrocenylbis‐(methyl‐L‐cysteinat) als Liganden

Metal Complexes of Biologically Important Ligands. CLXVI Metal Complexes with Ferrocenylmethylcysteinate and 1,1′‐Ferrocenylbis‐(methylcysteinate) as Ligands A series of complexes of transition metal ions ( Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ ) and of lanthanide ions ( La³⁺, Nd³⁺, Gd³⁺, Dy³⁺, Lu³⁺ ) with the anions of ferrocenylmethyl‐L‐cysteine [(C₅H₅)Fe(C₅H₄CH(R)SCH₂CH(NH₃⁺)CO₂^?] (L¹) and with the dianions of 1,1′‐ferrocenylbis(methyl‐L‐cysteine) [Fe(C₅H₄CH(R)SCH₂CH(NH₃⁺) CO₂^?)₂] (R = H, Me, Ph) (L²) as N,O,S‐donors were prepared. With the monocysteine ferrocene derivative L¹ as ligands complexes [M^IIL¹₂] or [Cr^IIIL¹₂]Cl type complexes are formed whereas the bis(cysteine) ligand L² yields insoluble complexes of type [ML²]_n, presumably as coordination polymers. The magnetic moments of [Mn^IIL²]_n, [Pr^IIIL²]_n(OH)_n and [Dy^IIIL²]_n(OH)_n exhibit “normal” paramagnetism.     

Redox‐Induced Spin‐State Switching and Mixed Valency in Quinonoid‐Bridged Dicobalt Complexes

The complexes [{(tmpa)Co^II}₂(μ‐L¹)^2?]²⁺ ( 1²⁺ ) and [{(tmpa)Co^II}₂(μ‐L²)^2?]²⁺ ( 2²⁺ ), with tmpa=tris(2‐pyridylmethyl)amine, H₂L¹=2,5‐di‐[2‐(methoxy)‐anilino]‐1,4‐benzoquinone, and H₂L²=2,5‐di‐[2‐(trifluoromethyl)‐anilino]‐1,4‐benzoquinone, were synthesized and characterized. Structural analysis of 2²⁺ revealed a distorted octahedral coordination around the cobalt centers, and cobalt–ligand bond lengths that match with high‐spin Co^II centers. Superconducting quantum interference device (SQUID) magnetometric studies on 1²⁺ and 2²⁺ are consistent with the presence of two weakly exchange‐coupled high‐spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 1²⁺ and ferromagnetic for 2²⁺ . Both complexes exhibit several one‐electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near‐IR spectroelectrochemistry. For 1²⁺ , it was possible to chemically isolate the pure forms of both the one‐electron oxidized mixed‐valent 1³⁺ and the two‐electron oxidized isovalent 1⁴⁺ forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin‐state of the molecule. In contrast to 2²⁺ , for 1⁴⁺ the metal–ligand distances and the distances within the quinonoid ligand point to the existence of two low‐spin Co^III centers, thus showing the innocence of the quintessential non‐innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two‐electron oxidation, which confirms the change in spin state associated with the electron‐transfer steps.