Rare example of structurally characterized mononuclear N-heterocyclic carbene containing zinc carboxylate

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Half-sandwich rhodium complexes containing both N-heterocyclic carbene and ortho-carborane-1,2-dithiolate ligands

A new route was used to synthesize half-sandwich rhodium complexes containing both N-heterocyclic carbenes (NHC) and carborane ligands. The rhodium carbene complexes Cp^∗Rh(L)[S₂C₂(B₁₀H₁₀)] (Cp^∗ = pentamethylcyclopentadienyl, L = 1,3-dimethylimidazolin-2-ylidene; 4) can be obtained from the reaction of Cp^∗Rh(L)Cl₂ (2) with Li₂S₂C₂(B₁₀H₁₀) or from the reaction of Cp^∗Rh[S₂C₂(B₁₀H₁₀)] (3) with silver-NHC complex prepared by direct reaction of an imidazolium precursor and Ag₂O. Complexes 2 and 4 were characterized by IR, NMR spectroscopy, element analysis and X-ray structure analyses.     

N-heterocyclic carbene complexes of Zn(II): synthesis, X-ray structures and reactivity

The synthesis of six novel zinc (II) mono(N-heterocyclic carbene) complexes is described. 1,3-Bis(mesityl)-imidazol-2-ylidene was reacted with the zinc salts ZnX₂ (X=Cl, CH₃COO, PhCOO, and PhCH₂COO) to yield the corresponding monomeric Zn-NHC complex ZnCl₂(NHC)(THF) (1) and dimeric [Zn(OOCCH₃)₂(NHC)]₂ (2), [Zn(OOCPh)₂(NHC)]₂ (3), [Zn(OOCCH₂Ph)₂(NHC)]₂ (4) (NHC=1,3-bis(mesityl)-imidazol-2-ylidene). Reaction of 1 with 2 equivalents of silver trifluoromethanesulfonate yielded monomeric Zn(O₃SCF₃)₂(NHC)(THF) (5), reaction of 1 with sodium {[R(+)-α-2-(1-phenyl-ethylimino)-methyl]-phenolate} yielded monomeric ZnCl(OC₆H₄-2-CHN(CHPhCH₃)(NHC) (6). Compounds 1, 4-6 were structurally characterized by X-ray analysis. Selected compounds were investigated for their activity in the copolymerization of carbon dioxide with cyclohexene oxide as well as in the ring-opening polymerization of cyclohexene oxide and ε-caprolactone.     

A Heterometallic FeII–DyIII Single‐Molecule Magnet with a Record Anisotropy Barrier

A record anisotropy barrier (319 cm^?1) for all d‐f complexes was observed for a unique Fe^II‐Dy^III‐Fe^II single‐molecule magnet (SMM), which possesses two asymmetric and distorted Fe^II ions and one quasi‐D_5h Dy^III ion. The frozen magnetization of the Dy^III ion leads to the decreased Fe^II relaxation rates evident in the Mössbauer spectrum. Ab initio calculations suggest that tunneling is interrupted effectively thanks to the exchange doublets.     

Investigation of structural and biological properties of N-heterocyclic carbene silver(I) and palladium(II) complexes

abstract

Computational investigations were done on bis(1-allyl-3-benzyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)silver(I), bis(1-benzyl-3-butyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)silver(I), bis(1-allyl-3-benzyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)dibromidepalladium(II), and bis(1-benzyl-3-butyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)dibromidepalladium(II) complexes. Related complexes were optimized at different six calculation levels which are HF/6-31G(LANL2DZ), HF/6-31G(d,p)(LANL2DZ), B3LYP/6-31G(LANL2DZ), B3LYP/6-31G(d,p)(LANL2DZ), M062X/6-31G(LANL2DZ) and M062X/6-31G(d,p)(LANL2DZ) levels in vacuo. IR and NMR spectrum are calculated and examined in detail. Energy diagram of molecular orbitals, contour diagram of frontier molecular orbitals, molecular electrostatic potential maps and the harmonic surface of related molecules are examined in detail. Finally, interactions between mentioned complexes and related proteins (1BNA, 1JNX, and 2ING) are investigated in detail. As a result, it is found that biological and anti-cancer properties of silver N-heterocyclic carbene complexes are higher than those of palladium complexes.     

Large Easy‐Plane Magnetic Anisotropy in a Three‐Coordinate Cobalt(II) Complex [Li(THF)4][Co(NPh2)3]

Magnetic anisotropy is the key element in the construction of single‐ion magnets, a kind of nanomagnets for high‐density information storage. This works describes an unusual large easy‐plane magnetic anisotropy (with a zero‐field splitting parameter D of +40.2 cm^?1), mainly arising from the second‐order spin‐orbit coupling effect in a trigonal‐planar Co^II complex [Li(THF)₄][Co(NPh₂)₃], revealed by combined studies of magnetism, high frequency/field electron paramagnetic resonance spectroscopy, and ab initio calculations. Meanwhile, the field‐induced slow magnetic relaxation in this complex was mainly attributed to the Raman process.     

Synthesis, structures, and magnetic properties of binuclear carboxylate complexes with NiII and NiIII atoms

The reaction of NiCl₂·6H₂O with Me₃CCOOH and KOH taken in a molar ratio of 1:2:2 in water afforded the nonanuclear antiferromagnetic complex Py₂Ni₂(Me₃CCOOH)₂(OOCCMe₃)₂(μ-OOCCMe₃)₂(μ-OH₂), which apparently contains Ni^II and Ni^III atoms. The complex was isolated by extraction with CH₂Cl₂, benzene, or hexane. The reactions of this complex with pyridine bases (pyridine (Py), 3,4-lutidine (Lut), and nicorandil (Nic)) gave the adducts L₄Ni₂(OOCCMe₃)₂(μ-OOCCMe₃)₂(μ-OH) (L=Py, Lut, or Nic, respectively). According to magnetic measurements, intramolecular ferromagnetic exchange interactions in these adducts are complemented by intermolecular antiferromagnetic interactions. Pyrolysis of the pyridine adduct in air or under an inert atmosphere in xylene yielded the antiferromagnetic complex Py₂Ni₂(Me₃CCOOH)₂(OOCCMe₃)₂(μ-OOCCMe₃)₂(μ-OH₂), which contains Ni^II atoms. The structures of all the complexes synthesized were established by X-ray diffraction analysis. The electronic absorption spectra of these compounds are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 725–738, April, 1998.     

Homo- and heterometallic trinuclear nickel(ii) and cobalt(ii) pivalate complexes

The reaction of the dinuclear complex Co₂(bpy)₂(OOCBu^t)₄ with the tetranuclear complex Ni₄(₃-OH)₂(OOCBu^t)₆(EtOH)₆ afforded the trinuclear heterometallic complex M₃(bpy)₂(₃-OH)(-OOCBu^t)₄(OOCBu^t) (6) (M = Ni, Co; Ni : Co = 1.2 : 1) in which two metal atoms are in an octahedral environment and one metal atom is in a tetrahedral environment. The reaction of 2,2"-bipyridine with Co₄(₃-OH)₂(OOCBu^t)₆(HOEt)₆ (reagent ratio was 2 : 1) or the reaction of bpy with Co₈(₄-O)₂( _n -OOCBu^t)₁₂ (reagent ratio was 4 : 1) produced a homometallic analog of 6, viz., the trinuclear cluster Co₃(bpy)₂(₃-OH)(-OOCBu^t)₄(OOCBu^t) (8). The reaction of 1,10-phenanthroline (phen) with the [Co(OH) _n (OOCBu^t)_2–n ] _x polymer gave the analogous trinuclear cluster (phen)₂Co₃(₃-OH)(₂-OOCBu^t)₄(¹-OOCBu^t). Compounds 6 and 8 exhibit antiferromagnetic spin-spin exchange interactions.     

Static and Dynamic Magnetic Properties of a Co(II)-Complex with N2O2 Donor Set – A Theoretical and Experimental Study

A representative Co(II) based single ion magnet (SIM) with N₂O₂ donor set and distorted pseudo-tetrahedral geometry has been synthesized and characterized to study the atomic and electronic structure. DC magnetometry results have been evaluated by means of a phenomenological Hamiltonian approach regarding zero field splitting (ZFS) parameters and compared with results from ab-initio multi-reference CASSCF (complete active space self-consistent field) calculations and qualitative ligand field theory (AILFT). Profound investigation of spin-lattice relaxation with the variation of temperature (from 1.8 to about 8 K) and magnetic field (at 14 different fields from zero up to 1 T) have been performed based on AC magnetometry. Under an applied dc magnetic field, spin-lattice relaxation occurs via a direct process with T² temperature dependence due to limited heat transfer at very low temperature and above 5 K relaxation by an Orbach process with an energy barrier of ≈80 K dominates.     

Pyrazole-3-carboxylates assisted N-heterocyclic carbene palladium complexes: synthesis,characterization, and catalytic activities towards arylation of azoles with arylsulfonyl hydrazides

Four mononuclear and dinuclear pyrazole-3-carboxylates assisted NHC–Pd complexes have been synthesized and characterized. Notably, the bridge-cleavage reactions of [Pd(μ-Cl)(Cl)(NHC)]₂ with 1H-pyrazole-3-carboxylic acid afforded dinuclear complexes [(NHC)Pd(μ-1H-pyrazolato-3-carboxylate)]₂, in which the 1H-pyrazolato-3-carboxylate was employed as a N^N^O dianionic chelating and bridging ligand. To further explore the structural features and catalytic properties of the complexes, 1-methyl-1H-pyrazole-3-carboxylic acid was introduced into the coordination with [Pd(μ-Cl)(Cl)(NHC)]₂ and the corresponding mononuclear complexes (NHC)PdCl(1-methyl-1H-pyrazole-3-carboxylate) were obtained. The catalytic properties of the complexes in desulfitative arylation of azoles with arylsulfonyl hydrazides were initially investigated.     

Rational Electrostatic Design of Easy‐Axis Magnetic Anisotropy in a ZnII–DyIII–ZnII Single‐Molecule Magnet with a High Energy Barrier

Two novel trinuclear complexes [ZnCl(μ‐L)Ln(μ‐L)ClZn][ZnCl₃(CH₃OH)]?3 CH₃OH (Ln^III=Dy ( 1 ) and Er ( 2 )) have been prepared from the compartmental ligand N,N′‐dimethyl‐N,N′‐bis(2‐hydroxy‐3‐formyl‐5‐bromo‐benzyl)ethylenediamine (H₂L). X‐ray studies reveal that Ln^III ions are coordinated by two [ZnCl(L)]^? units through the phenoxo and aldehyde groups, giving rise to a LnO₈ coordination sphere with square‐antiprism geometry and strong easy‐axis anisotropy of the ground state. Ab initio CASSCF+RASSI calculations carried out on 1 confirm that the ground state is an almost pure M_J=±15/2 Kramers doublet with a marked axial anisotropy, the magnetic moment is roughly collinear with the shortest Dy?O distances. This orientation of the local magnetic moment of the Dy^III ion in 1 is adopted to reduce the electronic repulsion between the oblate electron shape of the M_J=±15/2 Kramers doublet and the phenoxo‐oxygen donor atoms involved in the shortest Dy?O bonds. CASSCF+RASSI calculations also show that the ground and first excited states of the Dy^III ion are separated by 129 cm^?1. As expected for this large energy gap, compound 1 exhibits, in a zero direct‐current field, thermally activated slow relaxation of the magnetization with a large U_eff=140 K. The isostructural Zn–Er–Zn species does not present significant SMM behavior as expected for the prolate electron‐density distribution of the Er^III ion leading to an easy‐plane anisotropy of the ground doublet state.     

Mononuclear transition metal complexes with sterically hindered carboxylate ligands: Synthesis, structural and spectral properties

The metal coordination geometry in the active site of metalloproteins are very different from the one of small inorganic complexes, due to the inflexibility of the ligand set from amino acid side chains different from freely moving ligand set in synthesis. Using the sterically hindered 2,6-di-(p-fluorophenyl)benzoate(L) ligand, a series of mononuclear Co(II), Ni(II) and Cu(II) complexes of general formula [M(L)₂(Hdmpz)₂] (where, Hdmpz = 3,5-dimethyl pyrazole) have been synthesized and characterized by the variety of spectroscopic methods. A distorted octahedral geometry in case of nickel, tetrahedral geometry for cobalt and square pyramidal in copper was observed in the X-ray studies, which also revealed that the uncoordinated oxygen atom of the carboxylate group forms intramolecular hydrogen bonding with the N-H group of the coordinated 3,5-dimethylpyrazole in case of cobalt and copper.     

Experimental and theoretical studies on the magnetic properties of manganese(II) compounds with mixed isocyanate and carboxylate bridges

Two manganese(II) isocyanate complexes with different flexible zwitterionic dicarboxylate ligands, [Mn(2)(bcpp)(NCO)(4)](n) (1; bcpp=1,3-bis(N-carboxylatomethyl-4-pyridinio)propane) and [Mn(2)(bcp)(NCO)(4)](n) (2; bcp=bis(N-carboxylatomethyl)-4,4'-bipyridinium, have been synthesized and characterized by X-ray crystallography and magnetic measurements. Both compounds consist of two-dimensional coordination layers in which uniform anionic chains with mixed (NCO)(2)(COO) triple bridges are cross-linked by flexible cationic 4,4'-trimethylenedipyridinium spacers. Magnetic studies revealed antiferromagnetic interactions through the triple bridges (J=-8.0 cm(-1) (1) and J=-8.6 cm(-1) (2)), which are stronger than those in the isoelectronic analogue (N(3))(2)(COO). To complement the experimental data, periodic and finite-cluster DFT and CASPT2 calculations were performed on the dimeric units of the (NCO)(2)(COO) and (N(3))(2)(COO) mixed-bridged systems to support the Heisenberg picture and stress the relative efficiency of the magnetic couplers. It was found that the isocyanate ligand plays a greater role in the conveyance of antiferromagnetic behavior than the azide counterpart, and that both pseudohalide bridges function cooperatively with the carboxylate group.     

Genistein complexes with amines. Part II: ab initio study of the complexes with piperazine and triethylamine

The piperazine and triethylamine complexes of genistein, exhibiting high immunosuppressant activity, were ab initio modeled at RHF/6-31G^** level and results were compared with those obtained for genistein–morpholine complexes by X-ray, NMR, and theoretical methods. The most stable genistein–piperazine complex is formed due to hydrogen bonding of genistein's OH group at position C7 to piperazine's nitrogen atom. In the most stable genistein–triethylamine complex genistein's OH group at position C4′ (position para to phenyl substituent) and trimethylamine nitrogen atom are engaged in hydrogen bond formation. The calculations confirmed our previous NMR conclusion that piperazine is more strongly complexed by genistein than is morpholine or triethylamine. The theoretical ¹³C NMR spectra correlate fairly well with the experimental spectra.     

Syntheses,structures, and fluorescent properties of two helical complexes based on a long rigid N-heterocyclic ligand

A long N-heterocyclic ligand, 2,6-bis(3-(pyrid-3-yl)-1,2,4-triazolyl)pyridine (H₂bptp), and Zn(II)/Pb(II) yield {[Zn(bptp)(H₂O)]?·?2H₂O·CH₃CN} _n (1) and {[Pb(bptp)]?·?H₂O} _n (2). Single-crystal X-ray diffraction analysis reveals that 1 and 2 possess 2-D networks containing alternating left- and right-handed helical motifs. Topologically, 1 features a (4,4) topology, while 2 exhibits a (6,3) topology. The bptp^2? in 1 and 2 adopts syn-anti and syn-syn conformations, respectively. The results indicate that the long rigid N-heterocyclic ligand can adopt different conformations to coordinate with metals, beneficial to construction of helical structures with diverse topologies. The difference between the photoluminescence properties of the two complexes reveals that metal ions and coordination environment have significant influences on photoluminescence behavior.     

The first metal complexes of bis(diisopropylamino)carbene: synthesis, structure and ligand properties

The synthesis of rhodium(I) and iridium(I) complexes of the bis(diisopropylamino)carbene is described for the first time. The formamidinium chloride and the free bis(diisopropylamino)carbene (L) were used as consecutive precursor compounds to form the metal complexes. Spectroscopic and, for LRh(cod)Cl, crystallographic data are presented for the complexes LRh(cod)Cl and LIr(cod)Cl (L=bis(diisopropylamino)carbene). The ligand properties of the acyclic bis(diisopropylamino)carbene are compared with imidazolin-2-ylidenes and imidazolidin-2-ylidenes as ligands in related rhodium(I) carbonyl complexes. Bis(diisopropylamino)carbene is the most basic known carbene ligand to date.     

DFT description of the electronic structure and spectromagnetic properties of strongly correlated electronic systems: NiII, CuII and ZnII o-dioxolene complexes

The spectroscopic and magnetic properties of dioxolene complexes of zinc, copper and nickel were studied by DFT calculations on model complexes of formulas [(NH(3))(4)M(II)(SQ)](+) (M=Zn, Ni; SQ=semiquinonato) and [(NH(3))(2)Cu(II)(SQ)](+). Standard approaches such as time-dependent DFT (TDDFT), the Slater transition state (STS), and broken symmetry (BS) were found to be unable to completely account for the physical properties of the systems, and complete active space-configuration interaction (CAS-CI) calculations based on the Kohn-Sham (KS) orbitals was applied. The CAS-CI energies, properly corrected with multireference perturbation theory (MR-PT), were found to be in good agreement with experimental data. We present here a calculation protocol that has a low CPU cost/accuracy ratio and seems to be very promising for interpreting the properties of strongly correlated electronic systems in complexes of real chemical size.     

Construction of polymeric Cu(I) N-heterocyclic carbene complex utilizing terpyridine-Fe(II) as linkers: formation of an efficient and recyclable catalyst

A metal-coordination-driven self-assembly using the predesigned building block has been developed. Herein, the catalytic active NHC–Cu(I) units were introduced into the terpyridine metal coordination polymers. The self-assembled architecture, as a heterogeneous catalyst, was successfully used to catalyze the A³-coupling reaction of aldehyde, alkyne, and amine and Huisgen 1,3-dipolar cycloaddition reaction of azide and alkyne in high yields.     

Amending the Anisotropy Barrier and Luminescence Behavior of Heterometallic Trinuclear Linear [MIILnIIIMII] (LnIII=Gd,Tb, Dy; MII=Mg/Zn) Complexes by Change from Divalent Paramagnetic to Diamagnetic Metal Ions

The sequential reaction of a multisite coordinating compartmental ligand [2‐(2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylideneamino)‐2‐methylpropane‐1,3‐diol] (LH₄) with appropriate lanthanide salts followed by the addition of [Mg(NO₃)₂] ? 6 H₂O or [Zn(NO₃)₂] ? 6 H₂O in a 4:1:2 stoichiometric ratio in the presence of triethylamine affords a series of isostructural heterometallic trinuclear complexes containing [Mg₂Ln]³⁺ (Ln=Dy, Gd, and Tb) and [Zn₂Ln]³⁺ (Ln=Dy, Gd, and Tb) cores. The formation of these complexes is demonstrated by X‐ray crystallography as well as ESI‐MS spectra. All complexes are isostructural possessing a linear trimetallic core with a central lanthanide ion. The comprehensive studies discussed involve the synthesis, structure, magnetism, and photophysical properties on this family of trinuclear [Mg₂Ln]³⁺ and [Zn₂Ln]³⁺ heterometallic complexes. [Mg₂Dy]³⁺ and [Zn₂Dy]³⁺ show slow relaxation of the magnetization below 12 K under zero applied direct current (dc) field, but without reaching a neat maximum, which is due to the overlapping with a faster quantum tunneling relaxation mediated through dipole–dipole and hyperfine interactions. Under a small applied dc field of 1000 Oe, the quantum tunneling is almost suppressed and temperature and frequency dependent peaks are observed, thus confirming the single‐molecule magnet behavior of complexes [Mg₂Dy]³⁺ and [Zn₂Dy]³⁺.