Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C₂H₂)(CHCH-SPy)(SPy)] ( 4 ) and [W(CO)(C₂H₂)(CHCH-SPn)(SPn)] ( 5 ) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C₂H₂ molecule. Labelling experiments using C₂D₂ with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C₂H₂)(SPy)₂] ( 6 ) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C₂H₂)_n(MeCN)_3−nBr₂] (n=1 and 2; 7 ). All complexes represent rare examples in the field of W−C₂H₂ chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.     

New Palladium(II) Complexes with a Tridentate PNO Ligand

The synthesis of neutral and cationic palladium complexes containing the tridentate monoanionic ligand [2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O]^? is described. Deprotonation of the Schiff base formed by condensation of 2-(diphenylphosphino)benzaldehyde with 2-aminophenol in the presence of the appropriate palladium precursor ([Pd(AcO)₂] or [PdCl₂(PhCN)₂]) form the corresponding neutral complexes [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(AcO)] (1) or [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(Cl)] (2) in good yield. The first reacts smoothly with thiols and activated phenols to give complexes of general formula [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(X)] (X = OC₆F₅ (3), SEt (4), S^tBu (5), SC₆H₅ (6), SC₆H₄-4Me (7), SC₆H₄-4NO₂ (8)). When the chloro complex is treated with silver perchlorate and tertiary phosphines (L) the cationic derivatives [Pd{2-(2-Ph₂PC₆H₄-CH=N)C₆H₄O}(L)][ClO₄] (L = PPh₃ (9), PMePh₂ (10), PMe₂Ph (11), PEt₃ (12)) were obtained. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, ¹H, ¹⁹F and ³¹P NMR).     

Mixed Ligand Complexes of Oxovanadium (IV) Oxalate

The oxovanadium(IV) complexes VOC₂O₄ · 2DMF, VOC₂O₄ · 2 formamide, VOC₂O₄ · 2 ethylene urea, VOC₂O₄ · 2 urea and VOC₂O₄ · en have been prepared and characterized. The oxalato group functions as a bidentate ligand in all these complexes. Except ethylene diamine the remaining ligands – DMF. formamide, ethylene urea and urea – act as monodentate ligand coordinating through their carbonyl oxygen. Ethylene diamine is bound to the metal through nitrogen. In all the complexes vanadium is five coordinated in distorted tetragonal-pyramidal structures.     

Stable Mixed‐Valent Radicals from Platinum(II) Complexes of a Bis(dioxolene) Ligand

Three diplatinum(II) complexes [{PtL}₂(μ‐thea)] (H₄thea=2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene) have been prepared, with diphosphine or bipyridyl “L” co‐ligands. One‐electron oxidation of these complexes gave radical cations containing a mixed‐valent [thea]^3? ligand with discrete catecholate and semiquinonate centers separated by quaternary methylene spacers. The electronic character of these radicals is near the Robin–Day class II/III border determined by UV/Vis/NIR and EPR spectroscopies. Crystal‐structure determinations and a DFT calculation imply that oxidation of the thea^4? ligand may lead to an increased through‐space interaction between the dioxolene π systems.     

Selective Structural Transformation of Supramolecules to Multinuclear Heterosubstituted Pt Complexes via Ligand Exchange

Selective triflate to chlorine ligand exchange reaction between ditriflate and dichloride Pt complexes producing pure heterosubstituted complexes is demonstrated. We show that this reaction can be applied for selective chlorination of supramolecules leading to their structural transformation into multinuclear mono-chlorinated Pt(II) complexes. The X-ray structure of complex of 4,4′-bipyridine with two molecules of (Et₃P)₂Pt(Cl)OTf is reported.     

Syntheses of Molybdenum and Tungsten Imido Alkylidene Complexes that Contain a Bidentate Oxo/Thiolato Ligand

3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl[1,1′-biphenyl]-2-ol (H₂[^tBu₄OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H₂[^tBu₄OS] to Mo(NAr)(CHCMe₂Ph)(2,5-dimethylpyrrolide)₂ led to formation of Mo(NAr)(CHCMe₂Ph)[^tBu₄OS], which was trapped with PMe₃ to give Mo(NAr)(CHCMe₂Ph)[^tBu₄OS](PMe₃) ( 1 (PMe₃)). An X-ray crystallographic study of 1 (PMe₃) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1 (PMe₃)_A and 1 (PMe₃)_B are disordered. Mo(NAd)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 2 (PMe₃); Ad=1-adamantyl) and W(NAr)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 3 (PMe₃)) were prepared using analogous approaches. 1 (PMe₃) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(^tBu₄OS)(C₂H₄) ( 4 ) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for the ethylene ligand in 4 are like those found for bisalkoxide ethylene complexes of the same general type. Complex 1 (PMe₃) in the presence of one equivalent of B(C₆F₅)₃ catalyzes the homocoupling of 1-decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature. 1 (PMe₃), 2 (PMe₃), and 3 (PMe₃) all catalyze the ROMP of rac-endo,exo-5,6-dicarbomethoxynorbornene (rac-DCMNBE) in the presence of B(C₆F₅)₃, but the polyDCMNBE that is formed has a random structure.     

Dinuclear Copper(II) Complexes Incorporating a New Septadentate Polyimidazole Ligand

The dinuclear copper(II) complexes [Cu(2)(tmihpn)(prz)](ClO(4))(2).2CH(3)CN (6) and [Cu(2)(tmihpn)(O(2)CCH(3))](ClO(4))(2).CH(3)CN (7) were prepared, where tmihpn is the deprotonated form of N,N,N',N'-tetrakis[(1-methylimidazol-2-yl)methyl]-1,3-diaminopropan-2-ol and prz is the pyrazolate anion. The crystal structures of 6 and 7 were determined and revealed that both complexes contain bridging alkoxide ligands as well as bridging pyrazolate and acetate ions, respectively. Crystal data: compound 6, triclinic, P&onemacr;, a = 18.089(2) ?, b = 22.948(3) ?, c = 9.597(2) ?, alpha = 93.37(2) degrees, beta = 94.49(2) degrees, gamma = 81.69(2) degrees, V = 3925.1 ?(3), Z = 4; compound 7, triclinic, P&onemacr;, a = 12.417(2) ?, b = 15.012(3) ?, c = 10.699(2) ?, alpha = 104.76(2) degrees, beta = 102.63(2) degrees, gamma = 99.44(2) degrees, V = 1830.1 ?(3), Z = 2. In compound 6, the coordination geometry around both copper centers resembles a distorted square pyramid, while the stereochemistry around the copper centers in 7 is best described as trigonal bipyramidal. Both complexes display well-resolved isotropically shifted (1)H NMR spectra. Selective substitution studies and integration data have been used to definitively assign several signals to specific ligand protons. Results from the solution (1)H NMR studies suggest that the basal and apical imidazole groups do not exchange rapidly on the NMR time scale and the solid state structures of the complexes are retained in solution. In addition, the magnetochemical characteristics of 6 and 7 were determined and provide evidence for "magnetic orbital switching". Antiferromagnetic coupling in 6 (J = -130 cm(-)(1)) is strong, while the copper centers in compound 7 are ferromagnetically coupled (J = +16.4 cm(-1)). Differences in the magnetic behavior of the two copper centers have been rationalized using the "ligand orbital complementary" concept. The ground state magnetic orbitals involved in spin coupling in 6 (d(x)()()2(-)(y)()()2) are different from those in 7 (d(z)()()2).     

The complex of dicarbonyl(methylcyclopentadienyl)molybdenum with carbonyl(cyclopentadienyl)nitrosyl[tris(phenylacetylenide)stannyl]manganese: Synthesis and molecular formula

A reaction of CpMn(CO)(NO)Sn(C=CPh)₃ (I) with [Cp′Mo(CO)₂]₂ (Cp′ = MeC₅H₄) gave CpMn(CO)(NO)Sn(C=CPh)₃[Cp′Mo(CO)₂]₂ (II) as dark red prismatic crystals. The molecular structure of complex II was determined by X-ray diffraction study. Complex II contains the Mo-Mo bond (2.9799(5) Å), which is perpendicular to the coordinated C=C bond. The latter is longer (1.371(5) Å) than free acetylenide fragments (1.190(5) and 1.198(5) Å). In addition, the angle Sn-C=C for the coordinated C=C bond is smaller (134.1(3)°) than that in free fragments (173.5(4)° and 171.9(4)°). The Mn-Sn bond length in complex II (2.5662(7) Å) is close to that in complexI (2.5328(17) Å) and is much shorter than the sum of the corresponding covalent radii (2.78 Å). The Sn-C bond (2.108(4) Å) in the acetylenide fragment π-bound to two Mo atoms (average Mo-C, 2.19 Å), as well as the other Sn-C bonds (2.119(4) and 2.135(4) Å), remains virtually the same as in complex I (average 2.105 Å).     

含吡啶二脲配体汞(II)、镉(II)配合物的合成及其晶体结构

以2,2′-二氨基二苯醚和4-吡啶异氰酸酯反应合成了含吡啶二脲配体(L),并分别与HgCl_2和Cd(ClO_4)2进行了配位反应,得到2个配位聚合物{[Hg(L)Cl_2]·2DMF}_n(1)和{[Cd(L)_2(H_2O)_2](ClO_4)_2·4DMF·2H_2O·2CH_3OH}_n(2),采用1H NMR、MS、FTIR和元素分析等对化合物L进行了表征。通过X射线单晶衍射技术测定了配体及2个配合物的单晶结构,结构解析表明,2个配合物均为一维链状结构。进一步考察了2个配合物的热稳定性及其对甲醇蒸气的吸附性能。     

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

The synthesis and characterization of a biomimetic system that can reversibly bind acetylene (ethyne) is reported. The system has been designed to mimic catalytic intermediates of the tungstoenzyme acetylene hydratase. The thiophenyloxazoline ligand S‐Phoz (2‐(4′,4′‐dimethyloxazolin‐2′‐yl)thiophenolate) is used to generate a bioinspired donor environment around the W center, facilitating the stabilization of W–acetylene adducts. The featured complexes [W(C₂H₂)(CO)(S‐Phoz)₂] ( 2 ) and [WO(C₂H₂)(S‐Phoz)₂] ( 3 ) are extremely rare from a synthetic and structural point of view as very little is known about W–C₂H₂ adducts. Upon exposure to visible light, 3 can release C₂H₂ from its coordination sphere to yield the 14‐electron species [WO(S‐Phoz)₂] ( 4 ). Under light‐exclusion 4 re‐activates C₂H₂ making this the first fully characterized system for the reversible activation of acetylene.     

Mixed Ligand Complexes of Palladium (II) with Diethylenetriamine as Primary Ligand and Peptides as Secondary Ligand

Solution equilibria of the system palladium (II)-diethylenetriamine (dien) and peptides have been studied. The pH-metric titration of the reaction mixture containing equimolar solutions of palladium (II), dien and peptide have shown the formation of 1:1:1 mixed ligand complex. The pK_e of the peptides studied and formation constants of the resulting complexes have been determined at 25°C. The mode of chelation has been deduced from the conductivity measurements.     

Copper(II/I) Complexes of a Hexakis(bipyridyl)cyclotriveratrylene Ligand: A Redox-Induced Conformational Switch

A series of copper(II) and copper(I) complexes have been synthesized with ligands combining 6-methyl-2,2'-bipyridines with cyclotriveratrylene (CTV) (1) and with catechol (2). The electrochemical, (1)H NMR, and mass spectrometry characterizations of these complexes are described and discussed. The six pendant bipyridines of ligand 1 allow for the formation of two trinuclear copper(I) complexes [(1)Cu(3)](BF(4))(3) differing only in the conformation "vic" or "int" adopted by the ligand to fit the tetrahedral cuprous ions. Similarly, 1 generates two trinuclear copper(II) complexes in which the conformation of the ligand fits the square planar geometry of cupric ions. In both the cuprous and cupric complexes, a conformational equilibrium exists. Ligand 2 bearing two methylbipyridines has proven to be a useful model of the coordinating sites of ligand 1. In this case, two homologous copper(I) complexes are obtained, [(2)Cu]BF(4) and [(2)(2)Cu(2)](BF(4))(2), modeling respectively two possible coordination conformations of ligand 1. With copper(II), ligand 2 yields only one complex [(2)Cu](CF(3)SO(3))(2), which allows for the unambiguous identification of the conformations observed for ligand 1 complexes. The different coordinating modes of ligand 1 in the complexes mentioned are in exchange but exhibit different physical properties, thus representing a new bistable system based on conformational isomerism which exhibits an electrochemical potential hysteresis. An equilibrium constant and thermodynamic data were obtained for this system by variable-temperature cyclic voltammetry. The influence of coordinating vs noncoordinating solvents was also studied.     

DNA Cleavage of the Copper（II） Complexes with a Polyamine Ditopic Ligand

The investigations on simple and efficient reagents, which can cleave nucleic acids undermild conditions have been attracted considerable attentions1,2. Generally, in order toeliminate the possibility of significant cytotoxic side effect of reactive oxygen species,pathways that result in DNA cleavage by hydrolysis mechanisms are preferable3,4. Wehave reported two novel metal complexes magnesium (II)-diethylenetriamine (dien) andcopper (II)-L-histidine systems that both can effectively promo…     

Synthesis,Structure and Slow Magnetization Relaxation of Co(Ⅱ) Complexes from a Flexible Imidazole-based Ligand

The employment of a flexible imidazole-based ligand(H_2L), condensed from 1 Himidazole-2-carbaldehyde and 1,2-bis(aminooxy)ethane, and Co~(2+) salt has led to the formation of Co(Ⅱ) complexes [Co(H_2L)_2Cl]Cl·4CH_3OH(1) and [Co(H_2L)(NCS)_2]_2·2C_4H_(10)O(2), in the presence of different anions, i.e, Cl-and SCN-, respectively. Single-crystal X-ray analyses show that complex 1 with a square pyramid(C_(4v)) local environment exhibits a two-dimensional(2D)layered(4,4)-net framework and complex 2 displays a dinuclear molecule box with a T_d local environment. By comparison between complexes 1 and 2, the versatile configuration of ligand including cis-and trans-form isomer has a significant effect on the structures of the resulting complexes. The magnetic properties of 1 and 2 are also investigated. The ac magnetic susceptibility revealed that 2 exhibits the characteristic of slow magnetization relaxation.     

Unusual Oligonuclear Copper(II) Complexes based on a Bis( tridentate) Compartmental Pyrazolate Ligand

Some unusual oligonuclear copper(II) complexes with a bis(tridentate) pyrazolate‐based ligand that is composed of two diethylentriame‐type coordination compartments have been structurally characterized. In [(LCu₂)₂(CO₃)(H₂O)₂(ClO₄)](ClO₄)₃ ( 1 ), CO₂ has been taken up and two {LCu₂} subunits are spanned by both a μ₃‐μ₃‐κO:κO′:κO″‐bridging carbonate as well as by a μ₃‐κO:κO′:κO″‐bridging perchlorate. The latter is a rare structural motif in coordination chemistry. In one experiment, a different complex [(LCu₂(OH))₂Cu₂(OH)₄](BF₄)₄ ( 2 ) has been serendipitiously obtained. One Cu atom of each {LCu₂} subunit of 2 together with two further copper ions forms a pyrazolate‐appanded {Cu₄(OH)₄} cube.     

Excited State Properties of Lanthanide(III) Complexes with a Nonadentate Bispidine Ligand

Eu^III, Tb^III, Gd^III and Yb^III complexes of the nonadentate bispidine derivative L² (bispidine=3,7-diazabicyclo[3.3.1]nonane) were successfully synthesized and their emission properties studied. The X-ray crystallography reveals full encapsulation by the nonadentate ligand L² that enforces to all Ln^III cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C_4v symmetry). The well-resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long-lived excited states and high emission quantum yields ([Eu^IIIL²]⁺, H₂O, 298 K, τ=1.51 ms, ϕ=0.35; [Tb^IIIL²]⁺, H₂O, 298 K, τ=1.95 ms, ϕ=0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.     

Carbon‐Atom Extrusion from Halobenzenes and Its Coupling with a Methylene Ligand to Form Acetylene

Mechanistic aspects of an unusual gas‐phase reaction of [LaCH₂]⁺ with halobenzenes have been investigated using Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry combined with density functional theory (DFT) calculations. In this thermal process a carbon‐atom from the benzene ring, most likely the ipso‐position, and the carbene ligand are coupled to form C₂H₂.