μ‐1,2‐Bis(4‐pyridyl)ethene‐κ2N:N′‐bis(tetraaqua­{4‐[2‐(4‐pyridinio)­ethenyl]pyridine‐κN}cobalt(II)) hexaaqua­cobalt(II) tetrakis(sulfate) octahydrate

The title compound, [Co₂(C₁₂H₁₁N₂)₂(C₁₂H₁₀N₂)(H₂O)₈][Co(H₂O)₆](SO₄)₄·8H₂O, consists of bis(4‐pyridyl)ethenedicobalt(II) cations, hexaaqua­cobalt cations, sulfate anions and water solvent molecules that are linked by hydrogen bonds into a network structure. In the hexaaquacobalt cation, the six water molecules are coordinated in an octahedral geometry to the Co atom, which lies on an inversion centre. The other cation is a 1,2‐bis(4‐pyridyl)ethene‐bridged centrosymmetric dimer, consisting of protonated 1,2‐bis(4‐pyridyl)­ethene cations, a bridging 1,2‐bis(4‐pyridyl)ethene ligand and tetraaqua­cobalt cations. Each Co atom is six‐coordinated by four water molecules and two N atoms from a protonated 1,2‐bis(4‐pyridyl)ethene cation and the bridging 1,2‐bis(4‐pyridyl)­ethene ligand, and the geometry around each Co atom is octahedral.     

Silyl Ligand Mediated Reversible β‐Hydrogen Elimination and Hydrometalation at Palladium

The mechanism and origin of the facile β‐hydrogen elimination and hydrometalation of a palladium complex bearing a phenylene‐bridged PSiP pincer ligand are clarified. Experimental and theoretical studies demonstrate a new mechanism for β‐hydrogen elimination and hydrometalation mediated by a silyl ligand at palladium, which enables direct interconversion between an ethylpalladium(II) complex and an η²‐(Si‐H)palladium(0) complex without formation of a square‐planar palladium(II) hydride intermediate. The flexibility of the PSiP pincer ligand enables it to act as an efficient scaffold to deliver the hydrogen atom as a hydride ligand.     

σ‐Alkylpalladium Intermediates in Intramolecular Heck Reactions:Isolation and Catalytic Activity

The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh₃)₄], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X‐ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five‐membered palladacycle with the metal center bearing a PPh₃ ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐hydride elimination. Subsequently, the thus obtained bridged five‐membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross‐coupling processes such as Suzuki and Stille reactions.     

Energy component analysis calculations on neutral atom …︁ base interactions

We present energy component analysis calculations on alkali atom (Li,Na) hydride (H₂O,NH₃,H₂S) interactions and compare these with corresponding (Li⁺ …? NH₃) cation …? hydride interactions. In contrast to cation hydride interactions, the neutral atom–hydride interactions are shown to involve considerable contributions from all energy components.     

Crystal Structure and Ethylene Oligomerization Catalytic Activity of {2-Carbethoxy-6-[1-[（2,6-diethylphenyl）imino]ethyl]pyridine}CoCl2

The unsymmetric precursor ethyl 6-acetylpyridine-2-carboxylate （4） was synthesized from 2,6-dimethylpyridine （1）. On the basis of this precursor, a new mono（imino）pyridine ligand （5） and the corresponding Co（Ⅱ） complex {2-carbethoxy-6-[1-[（2,6-diethylphenyl）imino]ethyl]pyridine}CoCl2 （6） were prepared. The crystal structure of complex indicates that the 2-carbethoxy-6-iminopyridine is coordinated to the cobalt as a tridentate ligand using [N, N, O] atoms, and the coordination geometry of the central cobalt is a distorted trigonal bipyramid, with the pyridyl nitrogen atom and the two chlorine atoms forming the equatorial plane. Being applied to the ethylene oligomedzation, this cobalt complex shows catalytic activity of 1.820× 10^4 g/mol-Cooh at 101325 Pa of ethylene at 15.5℃ for 1 h, when 1000 equiv, of methylaluminoxane （MAO） is employed as the cocatalyst.     

Peculiarities of intramolecular exchange and valence tautomerism in metal semiquinolates determined by high‐resolution NMR spectroscopy

The ¹H NMR spectra of semiquinalate cobalt complex have been analyzed in a wide range of temperatures. It has been established that the intramolecular exchange requires the obligatory presence of a paramagnetic structure containing non‐compensated electron spin localized on the carbon atom of the ligand aromatic ring, the cobalt atom being trivalent. The presence of such a structure leads to the appearance of satellite signals in the NMR spectra because of the superfine interactions. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel one‐dimensional metal–organic framework with a μ‐cyanido‐argentate group: catena‐poly[[(5,5′‐dimethyl‐2,2′‐bipyridyl‐κ2N,N′)silver(I)]‐μ‐cyanido‐κ2N:C]

The design and synthesis of metal coordination and supramolecular frameworks containing N‐donor ligands and dicyanidoargentate units is of interest due to their potential applications in the fields of molecular magnetism, catalysis, nonlinear optics and luminescence. In the design and synthesis of extended frameworks, supramolecular interactions, such as hydrogen bonding, π–π stacking and van der Waals interactions, have been exploited for molecular recognition associated with biological activity and for the engineering of molecular solids.The title compound, [Ag(CN)(C₁₂H₁₂N₂)]_n, crystallizes with the Ag^I cation on a twofold axis, half a cyanide ligand disordered about a centre of inversion and half a twofold‐symmetric 5,5′‐dimethyl‐2,2′‐bipyridine (5,5′‐dmbpy) ligand in the asymmetric unit. Each Ag^I cation exhibits a distorted tetrahedral geometry; the coordination environment comprises one C(N) atom and one N(C) atom from substitutionally disordered cyanide bridging ligands, and two N atoms from a bidentate chelating 5,5′‐dmbpy ligand. The cyanide ligand links adjacent Ag^I cations to generate a one‐dimensional zigzag chain. These chains are linked together via weak nonclassical intermolecular interactions, generating a two‐dimensional supramolecular network.     

Phosphine–Alkene Ligands as Mechanistic Probes in the Pauson–Khand Reaction

An alkyne tetracarbonyl dicobalt complex with a chelated phosphine–alkene ligand, in which the phosphorus atom and the alkene from the ligand are attached to the same cobalt atom has been prepared, isolated, and characterized by X‐ray crystallography. The complex serves as a mechanistic model for an intermediate of the Pauson–Khand (PK) reaction. Although the alkene fragment is located in an equatorial coordination site with an appropriate orientation, and, therefore, should undergo insertion, it failed to give the PK product upon either thermal or N‐methylmorpholine N‐oxide activation. However, a phosphine–alkene complex that contains a terminal alkene readily provided the corresponding PK product. We attribute this change in reactivity to the different ability of each olefin to undergo 1,2‐insertion. These results provide further insights into the factors that govern a crucial step in the PK reaction, the olefin insertion.     

An Alternative Mechanism for the Cobalt‐Catalyzed Isomerization of Terminal Alkenes to (Z)‐2‐Alkenes

The cobalt‐catalyzed selective isomerization of terminal alkenes to the thermodynamically less‐stable (Z)‐2‐alkenes at ambient temperatures takes place by a new mechanism involving the transfer of a hydrogen atom from a Ph₂PH ligand to the starting material and the formation of a phosphenium complex, which recycles the Ph₂PH complex through a 1,2‐H shift.     

Preparation of N‐(4′,6′‐difluoro‐2′‐hydroxybenzyl)‐monoaza‐15‐crown‐5 and x‐ray crystal structure of potassium thiocyanate complex: A molecular partition wall

Armed monoaza‐15‐crown‐5 having a 4′,6′‐difluoro‐2′‐hydroxybenzyl group as an additional binding site ( 2 ) has been prepared by the Mannich reaction of N‐methoxymethylmonoaza‐15‐crown‐5 with 3,5‐difluorophenol. The reactive site on 3,5‐difluorophenol for the Mannich reaction was predicted by an electrostatic potential calculation (density functional calculation, SVWN/DN* method). Ligand 2 is interesting, because it has two possible binding sites (phenolic OH group and fluorine atom) in the side arm. An X‐ray crystal structure of the potassium thiocyanate complex of ligand 2 revealed that the oxygen atom of the phenolic OH group binds to the potassium cation incorporated in the crown ether ring, and two water molecules are enclosed by two armed crown ethers with the crown ethers forming partition walls.     

Cobalt‐Catalyzed Asymmetric Hydrogenation of C=N Bonds Enabled by Assisted Coordination and Nonbonding Interactions

An efficient cobalt‐catalyzed asymmetric hydrogenation of C=N bonds has been realized. Chiral hydrazines were obtained in high yields and with excellent enantioselectivities (95–98 % ee). The hydrogenation went smoothly at up to 2000 substrate/catalyst and on a gram scale. The success of this reaction relies on the presence of an NHBz group in the substrates, with the reactivity and enantioselectivity improved by an assisted coordination to the cobalt atom and a nonbonding interaction with the ligand. Furthermore, this reaction has practical applications for the synthesis of several useful chiral nitrogen‐containing compounds.     

Self‐Assembly of Magnesium Hydride Clusters Driven by Chameleon‐Type Ligands

While magnesium hydride complexes are generally stabilized by hard, bulky N‐donor ligands, softer ligands with a broad variety of coordination modes are shown to efficiently adapt themselves to the large variety of Mg²⁺ centers in a growing magnesium hydride cluster. A P,N‐chelating ligand is introduced that displays coordination modes between that of enamide, aza‐allyl, and phosphinomethanide. Slight changes in the ligand bite angle have dramatic consequences for the structure type. The hitherto largest neutral magnesium hydride clusters are isolated either in a nonanuclear sheet‐structure (brucite‐type) or a dodecanuclear ring structure.     

Potassium bis­(carbonato‐O,O′)(ethylenedi­amine‐N,N′)­cobaltate(III) monohydrate at 173 K

The title salt, K[Co(C₂H₈N₂)(CO₃)₂]·H₂O, consists of a distorted octahedral cobalt complex anion and a seven‐coordinate potassium cation. Both metal atoms have crystallographic twofold symmetry, one C₂ axis passing through the Co atom and C—C bond, and another along a short K—O (water) bond of 2.600 Å (corrected for libration). The carbonate is bidentate to both cobalt and potassium and the water forms a hydrogen bond to a carbonate O atom.     

Poly[bis(μ3‐5′‐carboxy‐2,2′‐bipyridine‐5‐carboxylato‐κ4O:N,N′:O′)lead(II)]

The title compound, [Pb(C₁₂H₇N₂O₄)₂]_n, obtained by reaction of Pb(NO₃)₂ and 2,2′‐bipyridine‐5,5′‐dicarboxylic acid (H₂bptc) under hydrothermal conditions, has a structure in which the unique Pb^II cation sits on a twofold axis and is octa‐coordinated by four O‐atom donors from four Hbptc⁻ ligands and four N‐atom donors from two Hbptc⁻ ligands in a distorted dodecahedral geometry. With each Pb^II cation connected to six Hbptc⁻ ligands and each Hbptc⁻ ligand bridging three Pb^II cations, a three‐dimensional polymeric structure is formed. From a topological point of view, the three‐dimensional net is binodal, with six‐connected (the Pb^II cation) and three‐connected (the Hbptc⁻ ligand) nodes, resulting in a distorted rutile (4².8)₂(4⁴8⁹12²) topology.     

Poly[μ8‐4,4′‐bipyridine‐2,2′,6,6′‐tetracarboxylato‐dilead(II)]

The Pb^II cation in the title compound, [Pb₂(C₁₄H₄N₂O₈)]_n, is seven‐coordinated by one N atom and six O atoms from four 4,4′‐bipyridine‐2,2′,6,6′‐tetracarboxylate (BPTCA⁴⁻) ligands. The geometric centre of the BPTCA⁴⁻ anion lies on an inversion centre. Each pyridine‐2,6‐dicarboxylate moiety of the BPTCA⁴⁻ ligand links four Pb^II cations via its pyridyl N atom and two carboxylate groups to form two‐dimensional sheets. The centrosymmetric BPTCA⁴⁻ ligand then acts as a linker between the sheets, which results in a three‐dimensional metal–organic framework.     

[3+2] Fragmentation of a Pentaphosphido Ligand by Cyanide

The activation of white phosphorus (P₄) by transition‐metal complexes has been studied for several decades, but the functionalization and release of the resulting (organo)phosphorus ligands has rarely been achieved. Herein we describe the formation of rare diphosphan‐1‐ide anions from a P₅ ligand by treatment with cyanide. Cobalt diorganopentaphosphido complexes have been synthesized by a stepwise reaction sequence involving a low‐valent diimine cobalt complex, white phosphorus, and diorganochlorophosphanes. The reactions of the complexes with tetraalkylammonium or potassium cyanide afford a cyclotriphosphido cobaltate anion 5 and 1‐cyanodiphosphan‐1‐ide anions [R₂PPCN]^? ( 6‐R ). The molecular structure of a related product 7 suggests a novel reaction mechanism, where coordination of the cyanide anion to the cobalt center induces a ligand rearrangement. This is followed by nucleophilic attack of a second cyanide anion at a phosphorus atom and release of the P₂ fragment.     

Poly[[aqua(4,4′‐diazenediyldibenzoato‐κ4O,O′:O′′,O′′′)cadmium(II)]: a twofold interpenetrated three‐dimensional coordination polymer of PtS topology

In the title coordination compound, [Cd(C₁₄H₈N₂O₄)(H₂O)]_n, the Cd^II cation and the coordinated water molecule lie on a twofold axis, whereas the ligand lies on an inversion center. The Cd^II center is five‐coordinated in a distorted square‐pyramidal geometry by four carboxylate O atoms from four different 4,4′‐diazenediyldibenzoate (ddb) anions and one water O atom. The three‐dimensional frameworks thus formed by the bridging ddb anions interpenetrate to generate a three‐dimensional PtS‐type network. Additionally, the coordination water molecule and the carboxylate O atom form a hydrogen‐bonding interaction, stabilizing the three‐dimensional framework structure.     

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe2(CO)4(κ2‐PNPR)(μ‐S(CH2)3S] (PNPR={Ph2PCH2}2NR,R=Me,Ph)

The behavior of [Fe₂(CO)₄(κ²‐PNP^R)(μ‐pdt)] (PNP^R=(Ph₂PCH₂)₂NR, R=Me ( 1 ), Ph ( 2 ); pdt=S(CH₂)₃S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP^R appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF₃SO₃H or CH₃SO₃H; the cation with a bridging hydride ligand, 1 μH⁺ (R=Me) or 2 μH⁺ (R=Ph) is obtained rapidly. Only 1 μH⁺ can be protonated at the nitrogen atom of the PNP chelate by HBF₄?Et₂O or CF₃SO₃H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η²‐H₂ species in the Fe^IFe^II state. When R=Ph, the bridging hydride cation 2 μH⁺ cannot be protonated at the amine function by HBF₄?Et₂O or CF₃SO₃H, and protonation at the N atom of the one‐electron reduced analogue is also less favored than that of a S atom of the partially de‐coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH⁺ . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k_obs≈4–7 s^?1) because of the slow intramolecular proton migration and H₂ release steps identified by the theoretical study.     

Cobalt (II) and Copper (I) Complexes of Rigid Bidentate [N‐(2, 6‐Diisopropyl‐phenyl)imino]acenapthenone Ligand: Synthesis and Structural Studies

The cobalt(II) complex [CoCl₂(2, 6‐iPrC₆H₃‐BIAO)]₂ ( 1 ) of rigid unsymmetrical imine, carbonyl mixed ligand [N‐(2, 6‐diisopropylphenyl)‐imino]acenapthenone] (2, 6‐iPrC₆H₃‐BIAO) ( L1 ) can be achieved by the reaction of CoCl₂ and neutral [N‐(2, 6‐diisopropylphenyl)‐imino]acenapthenone] ligand. When ligand L1 reacted with CuCl in dichloromethane solution, only nitrogen coordinated copper complex [CuCl(2, 6‐iPrC₆H₃‐BIAO)] ( 2 ) was obtained. In the solid‐state structure, compound 1 is dimeric through the chelating two μ₂ chlorine atoms and each cobalt atom adopts either a distorted trigonal bipyramidal or a distorted square pyramidal arrangement. In contrast, the molecular structure of compound 2 reveals that copper is coordinated by imino nitrogen and adopts a linear arrangement around the central metal atom. The crystal structure of the rigid bidentate mixed nitrogen and oxygen ligand (2, 6‐iPrC₆H₃‐BIAO) ( L1 ) is also reported.     

Novel Dinuclear Redox‐isomeric Complexes with a Tetrapodal Pyridine‐based Ligand

Tris‐o‐semiquinonato cobalt complexes react with a tetrapodal pyridine‐derived ligand to form dinuclear cobalt compounds of general formula (OMP)[CoQ₂]₂, where OMP = 2,2′‐(pyridine‐2,6‐diyl)bis(N¹,N¹,N³,N³‐tetramethylpropane‐1,3‐diamine), Q = mono‐ or dianion of 3,6‐di‐tert‐butyl‐o‐benzoquinone (complex 1 ) and it derivatives: 3,6‐di‐tert‐butyl‐4,5‐N,N′‐piperazino‐o‐benzoquinone (complex 2 ), and 3,6‐di‐tert‐butyl‐4‐Cl‐o‐benzoquinone (complex 3 ). Single crystal X‐ray crystallography of 1 and 3 indicates two bis‐quinonato cobalt units bound by an OMP ligand, which acts as a bridge. Each central cobalt atom is chelated by one N¹,N¹,N³,N³‐tetramethylpropane‐1,3‐diamine and two o‐quinonato fragments. The nitrogen atom of the pyridine ring is uncoordinated. All complexes were characterized by NIR‐IR and EPR spectroscopy, precise adiabatic vacuum calorimetry, and by variable‐temperature magnetic susceptibility measurements. All data indicate a reversible thermally driven redox‐isomeric (valence tautomeric) transformation in the solid state for all complexes.