Tridentate Ligand L1 Research Articles

Magnetic anisotropy and slow relaxation of magnetisation in double salts containing four- and six-coordinate cobalt(II) complex ions.

Four novel Co(II) coordination compounds 1-4 of the general formula [Co(Ln)2][Co(NCY)4]·mCH3CN (where Ln are tridentate ligands L1 = 2,6-bis(1-hexyl-1H-benzimidazol-2-yl)pyridine for 1 and 2; L2 = 2,6-bis(1-octyl-1H-benzimidazol-2-yl)pyridine for 3; L3 = 2,6-bis(1-dodecyl-1H-benzimidazol-2-yl)pyridine for 4, Y = O for 1, 3, and 4 and Y = S for 2; m = 0 for 1 and 3, m = 0.5 for 2 and m = 2 for 4) were prepared and characterised. The molecular structures of all four compounds consist of the hexacoordinate complex cation [Co(Ln)2]2+ and tetracoordinate complex anion [Co(NCY)4]2-, with distorted octahedral and tetrahedral symmetry of coordination polyhedra, respectively. The electronic structures of all compounds feature an orbitally non-degenerate ground state well-separated from the lowest excited state, which allows the analysis of the magnetic anisotropy by the spin Hamiltonian model. ZFS parameters, derived from both CASSCF-NEVPT2 calculations and magnetic data analysis, indicate that tetrahedral anions [Co(NCY)4]2- exhibit small axial parameters |D| spanning the range of 2.2 to 7.7 cm-1, while octahedral cations [Co(Ln)2]2+ display significantly larger |D| parameters in the range of 37 to 95 cm-1. For 1-3, the Fourier-transform infrared magnetic spectroscopy (FIRMS) revealed a reasonable transmission with a magnetic absorption around the expected value for the ZFS accompanied by features allowing to identify phonon frequencies and simulate spin-phonon couplings. Dynamic magnetic investigations unveiled the field-induced slow relaxation of magnetisation, with maximal relaxation times (τ) of 92(2) μs for 2 at 2 K and BDC = 0.3 T. The temperature evolution of τ was analysed using a combination of Orbach, direct and Raman relaxations (Ueff = 8(1) K (5.6 cm-1)) or Orbach, direct and spin-phonon induced relaxations (Ueff = 10.3(9) K (7.2 cm-1)). The rest of the complexes, namely 1, 3, and 4 show field-induced slow relaxation of magnetisation with τ smaller than 16 μs.

Electronic influence of pyrazole-appended pyridine/pyrazine based N,N,N-tridentate ligands on Ru complexes: Impact on selectivity of catalytic alkene oxidation with mild oxidant NaIO4

Three discrete Ru(II) complexes [Ru(L1)(bpy)Cl]Cl (1), [Ru(L1)(phen)Cl]Cl (2) and [Ru(L2)(bpy)Cl]Cl (3) have been prepared with two different pyridine/pyrazine based tridentate ligands L1 and L2, with one bipyridine/phenanthroline and one chloride as co-ligands. These complexes are characterized fully via spectroscopic and crystallographic techniques. The crystal structures of the complexes revealed the discrete monomeric structures. The Density Functional Theory (DFT) calculations showed that for complexes 1 and 3, the highest occupied molecular orbital (HOMO) is metal-centered whereas the lowest unoccupied molecular orbital (LUMO) is centered on the bpy ligand in 1, but interestingly it is based on the ligand L2 in case of the complex 3. Also, both the HOMO and LUMO are relatively more stabilized in 3 in comparison to 1. This fact implies very good π-acceptor nature of the ligand L2. This is reflected on the redox behavior of the complexes where around 200 mV anodic shift of the RuII/III redox potential was observed in 3 as compared to complex 1. This electronic influence of the ligands L1 and L2 impacted remarkably in the catalytic behavior of their Ru-complexes (1–3). Thus, the catalysts 1 and 2 were found to oxidize aryl alkenes to the corresponding acid products with high selectivity, whereas the catalyst 3 was selective toward the formation of aldehydes only, in the presence of only 2.5–3.0 equiv. of NaIO4 as the mild oxidant.

A Water‐Soluble Mn(CO)3‐Based and Non‐Toxic PhotoCORM for Administration of Carbon Monoxide Inside of Cells

The photoCORMs [Mn(CO)3(L)]Br with the tridentate ligands L1 = S[(CH2)2NH2]2 (1) (CORM‐EDE3) and L2 = cyclo‐S[(CH2)2NH(CH2‐)]2 (2) (CORM‐EDE4) are non‐toxic and release all CO ligands upon irradiation. Reduction of the hydrophilicity of the cation by L2 (thia‐4,7‐diazacyclononane) enables accumulation of the resulting water‐soluble CORM‐EDE4 as well as administration of CO inside of cells.

Ruthenium NNN complexes with a 2‐hydroxypyridylmethylene fragment for transfer hydrogenation of ketones

Four NNN tridentate ligands L1–L4 containing 2‐methoxypyridylmethene or 2‐hydroxypyridylmethene fragment were synthesized and introduced to ruthenium centers. When (HOC5H3NCH2C5H3NC5H7N2) (L2) and (HOC5H3NCH2C5H3NC6H6N3) (L4) reacted with RuCl2(PPh3)3, two ruthenium chloride products Ru(L2)(PPh3)Cl2 (1) and Ru(L4)(PPh3)Cl2 (2) were isolated, respectively. Reactions of (MeOC5H3NCH2C5H3NC5H7N2) (L1) and (MeOC5H3NCH2C5H3NC6H6N3) (L3) with RuCl2(PPh3)3 in the presence of NH4PF6 generated two dicationic complexes [Ru(L1)2][PF6]2 (3) and [Ru(L3)2][PF6]2 (4), respectively. Complex 1 reacted with CO to afford product [Ru(L2)(PPh3)(CO)Cl][Cl]. The catalytic activity for transfer hydrogenation of ketones was investigated. Complex 1 showed the highest activity, with a turnover frequency value of 1.44 × 103 h−1 for acetophenone, while complexes 3 and 4 were not active.

Synthesis, characterization, and biological evaluation of new biotinylated (99m) Tc/Re-tricarbonyl complexes.

The synthesis and biological evaluation of three new biotinylated fac-[(99m)Tc/Re(CO)3](+) complexes with the tridentate ligands L1, L2, and L3 are reported. L1-L3 contain the chelators 2-((5-aminopentyl)(pyridin-2-ylmethyl)amino)acetic acid, 2-(2-aminoethylthio)-3-(1H-imidazol-4-yl)propanoic acid, and 2-amino-3-(1-carboxy-2-(1H-imidazol-4-yl)ethylthio)propanoic acid, respectively, which are conjugated to biotin's carboxylate via their amine group. The fac-[Re(CO)3(L1-L3)] complexes were synthesized and characterized by NMR and IR, where the (N,N,O) coordination for ReL1 and the (N,S,O) coordination for ReL2 and ReL3 were confirmed. The tracer complexes fac-[(99m)Tc(CO)3(L1-L3)] were synthesized in high yield and were found highly stable in 10(-3) M L-histidine and L-cysteine over 24 h. Furthermore, they exhibited high binding affinity (>90%) for avidin. Rat plasma studies showed complete cleavage of biotin from (99m)TcL1 after 1 h and a low percentage of intact (99m)TcL2 and (99m)TcL3 with no biotin cleavage metabolites present, over 24 h. Similarly, rat urine analysis showed the presence of intact (99m)TcL2 and (99m)TcL3, while (99m)TcL1 was cleaved. Biodistribution studies of (99m)TcL2 and (99m)TcL3 revealed fast blood and tissue clearance.

Enantioselective syntheses of β-amino alcohols catalyzed by recyclable chiral Fe(iii) metal complex

An efficient asymmetric desymmetrization of meso-epoxides with anilines catalyzed by a series of simple and environmentally benign in situ generated Fe(iii) complexes based on chiral tridentate ligands L1–L7 was carried out at rt.

Synthesis, characterization, and X-ray crystal structures of copper(II) and nickel(II) complexes with Schiff base

New copper(II) complexes, [Cu2L1L2] · ClO4 (I) and [Ni(L3)2] (II), where L1 is the monoanionic form of 2-[1-(2-emthylaminoethylimino)ethyl]phenol, L2 is the dianionic form of N,N′-ethylene-bis(2-hydroxyacetophenonylideneimine), L3 is the mono-anionic form of 2-(1-iminoethyl)phenol, were prepared and characterized using elemental analysis, FT-IR spectroscopy, and X-ray single-crystal diffraction. In complex I, the Cu(1) atom is coordinated by the NNO tridentate ligand L1 and the two phenolate O atoms of L2, forming a square pyramidal geometry. The Cu(2) atom in complex I is coordinated by the NNOO tetradenate ligand L2, forming a square planar geometry. The Ni atom in complex II is coordinated by two phenolate O and two imine N atoms from two ligands L3, forming a square planar geometry. In the crystal structure of I, the perchlorate anions are linked to the dinuclear copper(II) complex cations through intermolecular N-H...O hydrogen bonds. In the crystal structure of II, the mononuclear nickel complex molecules are linked through intermolecular N-H...O hydrogen bonds, forming a trimer.

Synthesis, Characterization, and X-Ray Crystal Structures of Copper(II) and Nickel(II) Complexes with Schiff Bases

New copper(II) complexes, [Cu2L1L2] · ClO4 (I) and [Ni(L3)2] (II), where L1 is the mono-anionic form of 2-[1-(2-emthylaminoethylimino)ethyl]phenol, L2 is the dianionic form of N,N-ethylene-bis(2-hydroxyacetophenonylideneimine), L3 is the mono-anionic form of 2-(1-iminoethyl)phenol, were prepared and characterized using elemental analysis, FT-IR spectroscopy, and X-ray single-crystal diffraction. In complex I, the Cu(1) atom is coordinated by the NNO tridentate ligand L1 and the two phenolate O atoms of L2, forming a square pyramidal geometry. The Cu(2) atom in complex I is coordinated by the NNOO tetradenate ligand L2, forming a square planar geometry. The Ni atom in complex II is coordinated by two phenolate O and two imine N atoms from two ligands L3, forming a square planar geometry. In the crystal structure of I, the perchlorate anions are linked to the dinuclear copper(II) complex cations through intermolecular N–H···O hydrogen bonds. In the crystal structure of II, the mononuclear nickel complex molecules are linked through intermolecular N–H···O hydrogen bonds, forming a trimer.

Ruthenium hydride/nitrogen tridentate ligand-catalyzed α-alkylation of acetamides with primary alcohols

The α-alkylation reaction of acetamides with primary alcohols to afford the corresponding amides was accomplished effectively using RuHCl(CO)(PPh3)3 as a catalyst, nitrogen tridentate ligand L1 as an additive, and KOtBu as a base. While the addition of bpy was effective only for benzylic alcohols, L1 affected the alkylation reaction when both benzylic and non-benzylic type alcohols were used.

Mononuclear and Binuclear Copper(I) Complexes Ligated by Bis(3,5-diisopropyl-1-pyrazolyl)methane: Insight into the Fundamental Coordination Chemistry of Three-Coordinate Copper(I) Complexes with a Neutral Coligand

By using the neutral bidentate nitrogen-containing ligand, bis(3,5-diisopropyl-1-pyrazolyl)methane (L1' '), the copper(I) complexes [Cu(L1' ')2](CuCl2) (1CuCl2), [Cu(L1' ')2](ClO4) (1ClO4), [Cu(L1' ')]2(ClO4)2 (2ClO4), [Cu(L1' ')]2(BF4)2 (2BF4), [Cu(L1' ')(NCMe)](PF6) (3PF6), [Cu(L1' ')(PPh3)](ClO4) (4ClO4), [Cu(L1' ')(PPh3)](PF6) (4PF6), [{Cu(L1' ')(CO)}2(mu-ClO4)](ClO4) (5ClO4), and the copper(II) complexes [{Cu(L1' ')}2(mu-OH)2(mu-ClO4)2] (6), and [Cu(L1' ')Cl2] (7) were systematically synthesized and fully characterized by X-ray crystallography and by IR and 1H NMR spectroscopy. In the case of copper(II), ESR spectroscopy was also applied. In comparison with the related neutral tridentate ligand L1', bis-chelated copper(I) complexes and binuclear linear-coordinated copper(I) complexes are easy to obtain with L1' ', like 1CuCl2, 1ClO4, 2ClO4, and 2BF4. Importantly, stronger and bulkier ligands such as acetonitrile (3PF6) and especially triphenylphosphine (4ClO4 and 4PF6) generate three-coordinate structures with a trigonal-planar geometry. Surprisingly, for the smaller ligand carbon monoxide, a mononuclear three-coordinate structure is very unstable, leading to the formation of a binuclear complex (5ClO4) with one bridging perchlorate anion, such that the copper(I) centers are four-coordinate. The same tendency is observed for the copper(II) bis(mu-hydroxo) compounds 6, which is additionally bridged by two perchlorate anions. Both copper(II) complexes 6 and 7 were obtained by molecular O2 oxidation of the corresponding copper(I) complexes. A comparison of the new copper(I) triphenylphosphine complexes 4ClO4 and 4PF6 with corresponding species obtained with the related tridentate ligands L1' and L1 (8ClO4 and 9, respectively) reveals surprisingly small differences in their spectroscopic properties. Density functional theory (DFT) calculations are used to shed light on the differences in bonding in these compounds and the spectral assignments. Finally, the reactivity of the different bis(pyrazolyl)methane complexes obtained here toward PPh3, CO, and O2 is discussed.

Kinetics and DFT studies on the reaction of copper(II) complexes and H2O2

Copper(II) complexes supported by bulky tridentate ligands L1(H) (N,N-bis(2-quinolylmethyl)-2-phenylethylamine) and L1(Ph) (N,N-bis(2-quinolylmethyl)-2,2-diphenylethylamine) have been prepared and their crystal structures as well as some physicochemical properties have been explored. Each complex exhibits a square pyramidal structure containing a coordinated solvent molecule at an equatorial position and a weakly coordinated counter anion (or water) at an axial position. The copper(II) complexes reacted readily with H(2)O(2) at a low temperature to give mononuclear hydroperoxo copper(II) complexes. Kinetics and DFT studies have suggested that, in the initial stage of the reaction, deprotonated hydrogen peroxide attacks the cupric ion, presumably at the axial position, to give a hydroperoxo copper(II) complex retaining the coordinated solvent molecule (H(R).S). H(R).S then loses the solvent to give a tetragonal copper(II)-hydroperoxo complex (H(R)), in which the -OOH group may occupy an equatorial position. The copper(II)-hydroperoxo complex H(R) exhibits a relatively high O-O bond stretching vibration at 900 cm(-1) compared to other previously reported examples.

Structure and dioxygen-reactivity of copper(i) complexes supported by bis(6-methylpyridin-2-ylmethyl)amine tridentate ligands

The structure and dioxygen-reactivity of copper(I) complexes R supported by N,N-bis(6-methylpyridin-2-ylmethyl)amine tridentate ligands L2R[R (N-alkyl substituent)=-CH2Ph (Bn), -CH2CH2Ph (Phe) and -CH2CHPh2(PhePh)] have been examined and compared with those of copper(I) complex (Phe) of N,N-bis[2-(pyridin-2-yl)ethyl]amine tridentate ligand L1(Phe) and copper(I) complex (Phe) of N,N-bis(pyridin-2-ylmethyl)amine tridentate ligand L3(Phe). Copper(I) complexes (Phe) and (PhePh) exhibited a distorted trigonal pyramidal structure involving a d-pi interaction with an eta1-binding mode between the metal ion and one of the ortho-carbon atoms of the phenyl group of the N-alkyl substituent [-CH2CH2Ph (Phe) and -CH2CHPh2(PhePh)]. The strength of the d-pi interaction in (Phe) and (PhePh) was weaker than that of the d-pi interaction with an eta2-binding mode in (Phe) but stronger than that of the eta1 d-pi interaction in (Phe). Existence of a weak d-pi interaction in (Bn) in solution was also explored, but its binding mode was not clear. Redox potentials of the copper(I) complexes (E1/2) were also affected by the supporting ligand; the order of E1/2 was Phe>R>Phe. Thus, the order of electron-donor ability of the ligand is L1Phe<L2R<L3Phe. This was reflected in the copper(I)-dioxygen reactivity, where the reaction rate of copper(I) complex toward O2 dramatically increased in the order of R<R<R. The structure of the resulting Cu2/O2 intermediate was also altered by the supporting ligand. Namely, oxygenation of copper(I) complex R at a low temperature gave a (micro-eta2:eta2-peroxo)dicopper(II) complex as in the case of Phe, but its O-O bond was relatively weakened as compared to the peroxo complex derived from Phe, and a small amount of a bis(micro-oxo)dicopper(III) complex co-existed. These results can be attributed to the higher electron-donor ability of L2R as compared to that of L1Phe. On the other hand, the fact that Phe mainly afforded a bis(micro-oxo)dicopper(III) complex suggests that the electron-donor ability of L2R is not high enough to support the higher oxidation state of copper(III) of the bis(micro-oxo) complex.

Quantitative evaluation of d-pi interaction in copper(I) complexes and control of copper(I)-dioxygen reactivity.

Crystal structures of the copper(I) complexes 1(X), 2, and 3 of a series of tridentate ligands L1(X), L2, and L3, respectively (L1(X): p-substituted derivatives of N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=H, Me, OMe, Cl, NO(2); L2: N,N-bis[2-(2-pyridyl)ethyl]-2-methyl-2-phenylethylamine; L3: N,N-bis[2-(2-pyridyl)ethyl]-2,2-diphenylethylamine) were solved to demonstrate that all the copper(I) complexes involve an eta(2) copper-arene interaction with the phenyl ring of the ligand sidearm. The Cu(I) ion in each complex has a distorted tetrahedral geometry consisting of the three nitrogen atoms (one tertiary amine nitrogen atom and two pyridine nitrogen atoms) and C(1)-C(2) of the phenyl ring of ligand sidearm, whereby the Cu-C distances of the copper-arene interaction significantly depend on the para substituents. The existence of the copper-arene interaction in a nonpolar organic solvent (CH(2)Cl(2)) was demonstrated by the observation of an intense MLCT band around 290 nm, and the magnitude of the interaction was evaluated by detailed analysis of the (1)H and (13)C NMR spectra and the redox potentials E(1/2) of the copper ion, as well as by means of the ligand-exchange reaction between the phenyl ring and CH(3)CN as an external ligand. The thermodynamic parameters DeltaH(o) and DeltaS(o) for the ligand-exchange reaction with CH(3)CN afforded a quantitative measure for the energy difference of the copper-arene interaction in the series of copper(I) complexes. Density functional studies indicated that the copper(I)-arene interaction mainly consists of the interaction between the d(z(2) ) orbital of Cu(I) and a pi orbital of the phenyl ring. The copper(I) complexes 1(X) reacted with O(2) at -80 degrees C in CH(2)Cl(2) to give the corresponding (micro-eta(2):eta(2)-peroxo)dicopper(II) complexes 4, the formation rates k(obs) of which were significantly retarded by stronger d-pi interaction, while complexes 2 and 3, which exhibit the strongest d-pi interaction showed significantly lower reactivity toward O(2) under the same experimental conditions. Thus, the d-pi interaction has been demonstrated for the first time to affect the copper(I)-dioxygen reactivity, and represents a new aspect of ligand effects in copper(I)-dioxygen chemistry.

Modulation of coordination chemistry in copper(I) complexes supported by Bis[2-(2-pyridyl)ethyl]amine-based tridentate ligands.

Structure and physicochemical properties of copper(I) complexes of the tridentate ligands L(2) (N,N-bis[2-(6-methylpyridin-2-yl)ethyl]phenethylamine) and L(3) (N,N-bis[2-(2-pyridyl)ethyl]-beta-methylphenethylamine) have been examined to obtain deeper insights into modulation of the coordination chemistry of copper(I) complexes. [Cu(I)(L(2))(CH(3)CN)](ClO(4)) (2.CH(3)CN) has a distorted tetrahedral geometry, which consists of three nitrogen atoms of the ligand and one nitrogen atom of the bound CH(3)CN. Steric repulsion between the 6-methyl group on the pyridine nucleus of L(2) and the metal ion of the complex prevents the cuprous complex from adaptation to a three-coordinate geometry which must have a shorter Cu-N(pyridine) distance ( approximately 1.88 A). Thus, the four-coordinate copper(I) complex (2.CH(3)CN) with a longer Cu-N bond (1.98 approximately 2.13 A) becomes favorable, resulting in rather strong binding of CH(3)CN to the metal ion. In [Cu(I)(L(3))](ClO(4)) (3), there is a Cu(I)-pi interaction between the cuprous ion and the phenyl group of the ligand sidearm. Such a copper(I)-arene interaction is essentially weak, but is significantly stabilized in complex 3. The methyl group at the benzylic position of L(3)() reduces the degree of freedom of sidearm rotation to make the phenyl group stick on the cuprous ion. Thus, the reactivity of the copper(I) complexes of L(2) and L(3) toward dioxygen is significantly diminished, showing sharp contrast to the high reactivity of the copper(I) complex supported by a similar tridentate ligand L(1) (N,N-bis[2-(2-pyridiyl)ethyl]phenethylamine).

Synthesis and characterization of technetium(III) complexes with Schiff-base and phosphine ligands. Molecular structure of (diethylphenylphosphine)[N-(2-oxidophenyl)salicylideneiminato-NOO′](quinolin-8-olato-NO)technetium(III)

The complexes [TcL(L′)L″][L″= PEt2Ph, PMe2Ph, or PPh3; L =N-(2-oxidophenyl)salicylideneiminate (L1) or N-(2-sulphidophenyl)salicylideneiminate (L2); L′= quinolin-8-olate (quin) or salicylideneiminate (L3)] were synthesized starting from [TcO(L)(L′)] and characterized by means of physicochemical measurements and for [TcL1(quin)(PEt2Ph)] by means of X-ray analysis. The co-ordination around technetium is approximately octahedral with the phosphine ligand trans to the imino nitrogen of the ligand quin and the tridentate ligand L1 on a plane orthogonal to the line P–Tc–N. The complex crystallizes in the triclinic space group P with a= 14.196(6), b= 11.363(5), c= 9.742(4)A, α= 68.04(3), β= 101.09(3), γ= 106.68(3)°, and Z= 2. The structure has been refined to R= 0.070 for 1 743 independent reflections.