Dinuclear Ti and Ti complexes supported by calix[4]arene ligands. Binding alkali-metal cations inside and outside the cavity of calix[4]arenes

New dinuclear Ti^IV and Ti^III complexes with the calix[4]arene ligand C₂₈H₂₀O₄H₄ (H₄L) have been isolated from the reaction of Ti(NMe₂)₄, H₄L, and Na (or KC₈) in THF. X-ray analyses revealed a similar core structure for the two complexes Na₄(THF)₈[Ti^IV ₂(μ-O)₂L₂] (1) and K₄(THF)₈[Ti^III ₂(μ-NMe₂)₂L₂] (2). Two titanium atoms are bridged by two oxygen atoms in 1 and by two dimethylamido groups in 2 and are also supported by two deprotonated calix[4]arene ligands in a cone conformation. This resulted in a similar Ti?Ti separation of about 3.29 Å in 1 and 3.28 Å in 2 and in a distorted octahedral environment for each Ti center in both complexes. In contrast, in a novel complex 3, Na₂(THF)₆[Ti^III ₂L₂], two Ti^III atoms are supported only by two deprotonated ligands. This results in a five-coordinate environment for both titanium(III) centers with the separation between them being 3.133(1) Å.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Template synthesis of N2S and N3S chelates via alkylation of bis(2-aminoethanethiolato)Ni: sulfur- and nitrogen-centered alkylations

Alkylation of bis(2-aminoethanethiolato)nickel(II) (1) with alkylating agents containing pendant donor groups has been investigated. Reaction with 2-bromoethylamine is strictly sulfur-centered yielding (2-[(2-aminoethyl)thio]ethaneamine)nickel(II)bromide, [(DAES)₂Ni]Br₂ (2), which was isolated as a lilac solid. Addition of chloroacetamide yields the sulfur- and nitrogen-alkylated product (2-[(2-aminoethyl)thio]acetamide)nickel(II)chloride, (AETA)NiCl₂ (3a), as a green solid. Recrystallization from water/acetone yields 3a as single crystals along with single crystals of [(AETA)NiCl(OH₂)]Cl (3b). The strictly S-alkylated product (2-[(2-amino-2-oxoethyl)thio]acetamide)nickel(II)iodide, [(AOTA)₂Ni]I₂ (4), is obtained upon reaction of 1 with iodoacetamide. A pathway is proposed consistent with the observed leaving group effect on the site of alkylation. The X-ray structures of 3a, 3b, and 4 are reported and the hydrogen-bonding network is described.     

Zinc complexes of a new N3O ligand and their biomimetic reactions

The new N₃O ligand 2-(pyridylmethylamino)-3-(3,5-dimethylpyrazol-1-yl)-propionic acid (L1H) was synthesized and converted to L1Zn-Cl and L1Zn-Br. These complexes are tetrameric in the solid state with bridging carboxylate functions. The reaction of deprotonated L1H with zinc nitrate or zinc perchlorate yielded the aqua complexes [L1Zn-OH₂] X with and , which crystallize as carboxylate-bridged dimers. Their deprotonation produced, in situ, the hydroxide complex L1Zn-OH, which acted as a base toward p-nitrophenol and bis(p-nitrophenyl)phosphoric acid resulting in L1Zn-ONit and L1Zn-OPO(ONit)₂. Tris(p-nitrophenyl)phosphate was cleaved hydrolytically by L1Zn-OH, releasing one p-nitrophenyl group. A kinetic investigation of this cleavage reaction under pseudo-first-order conditions has yielded second-order rate constants k″ of 0.9 s⁻¹ M⁻¹ in 50% aqueous DMSO and 4.0 s⁻¹ M⁻¹ in 75% aqueous DMSO.     

New aryl phosphinite ligands avoiding ortho-metallation: Synthesis and molecular structures of trans-[PdCl2(PPh2OR)2] and trans-[Rh(CO)Cl(PPh2OR)2] (R = 2,4,6-Me3C6H2; 2,6-Ph2C6H3)

The new aryl phosphinites PPh₂OR (R = 2,4,6-Me₃C₆H₂, 1; R = 2,6-Ph₂C₆H₃, 2) have been prepared from chlorodiphenylphosphine and the corresponding phenols. In these ligands, the ortho-positions of the aromatic phosphite function are blocked by methyl and phenyl substituents, which allows coordination to metal centres without ortho-metallation. Thus, reaction with [PdCl₂(cod)] leads to the complexes trans-[PdCl₂(PPh₂OR)₂] (R = 2,4,6-Me₃C₆H₂, 3; R = 2,6-Ph₂C₆H₃, 4), while the reaction with [Rh₂(CO)₄Cl₂] gives trans-[Rh(CO)Cl(PPh₂OR)₂] (R = 2,4,6-Me₃C₆H₂, 5; R = 2,6-Ph₂C₆H₃, 6). The single-crystal X-ray structure analyses of 3 and 5 confirm the trans-coordination of the new ligands in these square-planar complexes.     

Thiophenolate clusters as potential nanosized building blocks for zinc-based nanocomposite materials: synthesis and characterization

The synthesis, the spectroscopic and structural characterization of different thiophenolate-capped zinc clusters are reported and described. In particular, different reactions of 4-chlorobenzenethiol with zinc salts yield the clusters [Me₄N][Et₃NH][Zn₄(μ-S-C₆H₄-Cl)₆(S-C₆H₄-Cl)₄] (2a), [Et₃NH]₂[Zn₄(μ-S-C₆H₄-Cl)₆(S-C₆H₄-Cl)₄] (2b), and [Me₄N]₂[Zn₄(μ-S-C₆H₄-Cl)₆(S-C₆H₄-Cl)₄] (2c), and also the thiophenolate derivative [Et₃NH]₂[Zn₄(μ-S-C₆H₅)₆(S-C₆H₅)₄] (1b) was obtained.The nanosized thiophenolate-capped clusters were investigated by ¹H and ¹³C NMR, elemental analysis, and electrospray ionization (ESI) mass spectrometry. NMR experiments provided insights into the dynamic behaviour of the clusters. The thermal decomposition patterns of 2c were analyzed in air as well as in nitrogen, indicating the formation of zinc oxide and metallic zinc, respectively. The X-ray structure of 2a revealed that the cluster core consists of an adamantane-like framework analogous to those realized in many other M₄(SR)₁₀ metal complexes.     

Mechanism of reaction of peroxomethyl radicals with copper(II)(glycine)2 and copper(II)(glycylglycylglycine) in aqueous solutions

The reactions of O₂CH₃ radicals with Cu^II(glycine)₂ and Cu^II(GGG), GGG = glycylglycylglycine, in aqueous solutions were studied.The results demonstrate that the peroxyl radicals oxidize the copper complexes forming relatively stable intermediates of the type L_mCu^III-OOCH₃. These intermediates decompose via oxidation of the ligands glycine and GGG, respectively. Substituents on the alkyl of the peroxyl radical affect somewhat the kinetics of reaction but not the mechanism of oxidation. It is suggested that analogous reactions are probably contributing to the radical-induced deleterious biological processes.     

Solution and solid-state complexes of the potentially tetradentate pyridyl-thiazole ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine with Co, Ni, Cu, Cd, Hg, Cu and Ag

Reaction of the potentially tetradentate N-donor ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine (L¹) with the transition metal dications Co^II, Ni^II, Cu^II, Cd^II and Hg^II results in the formation of mononuclear [M(L¹)]²⁺ complexes, in which a planar ligand coordinates to the metals via all four N-donors. In contrast, reaction of L¹ with Cu^I and Ag^I monocations, affords dinuclear double stranded helicate species [M₂(L¹)₂]²⁺ (where M = Cu^I or Ag^I), in which partitioning of the ligand into two bis-bidentate pyridyl-thiazole chelating units allows each ligand to bridge both metal centres. X-Ray crystallography, electrospray mass spectroscopy and NMR spectroscopy reveal that the complexes [M_n(L¹)_m]^z+ (where n = 1, m = 1 and z = 2, when M = Co^II, Ni^II, Cu^II, Cd^II and Hg^II; n = 2, m = 2 and z = 2, when M = Cu^I), retain their solid-state structures in solution. Conversely, whilst ¹H NMR studies suggest that combination of equimolar amounts of Ag(X)(where ) and L¹ (in either nitromethane or acetonitrile) results in the formation of a helicate in solution, in the solid-state, an anion-templating effect gives rise to either mononuclear or dinuclear helicate structures [Ag_n(L¹)_n][X]_n (where n = 2 when X = OTf⁻; n = 1 when ).     

Diverse reactivity of stereoisomers containing quadruply bonded dimolybdenum with oxygen: formation of [{Mo(η-N,N′-diisopropylbenzamidinato)oxo}2(μ-acetato)2(μ-oxo)]

The reaction of quadruply bonded dimolybdenum complex, [Mo₂(μ-OAc)₄] (1), with lithiated amidinato, Li[(NⁱPr)₂CR] (R = ^tBu; 2a, Me; 2b, Ph; 2c), was investigated. The reaction of 1 with 2a afforded the dark-red solid, whereas the product was so highly unstable that the product was not able to be characterized. In the case of acetamidinato 2b, lantern-type mixed-ligand quadruply bonded dimolybdenum complex, [Mo₂(μ-OAc){μ-(NⁱPr)₂CMe}₃] (3), was obtained as a yellow solid. In the reaction with benzamidinato 2c, symmetrical lantern-type dimolybdenum complex, [Mo₂(μ-OAc)₂ {μ-(NⁱPr)₂CPh}₂] (4), was isolated as a yellow solid. In the latter reaction, intermediary red compound (5), which is considered to be stereoisomer of 4 possessing non-lantern-type skeleton, was formed. However, isolation of 5 as a single component was not successful due to isomerization to 4. Complex 5 readily reacted with dry oxygen to give dimolybdenum(V) complex, [{Mo(η-(NⁱPr)₂CPh)oxo}₂ (μ-OAc)₂(μ-oxo)] (6), as a red solid. These complexes were characterized spectroscopically as well as, in some cases, by X-ray analyses.     

The novel organolithium O,C,O-pincer compound

The preparation and characterization of organolithium O,C,O-pincer compound [2,6-(tBuOCH₂)₂C₆H₃]-Li (1) is described. The X-ray diffraction techniques revealed the dimeric structure of 1 consisting of two lithium atoms Li(1) and Li(2) and two monoanionic chelating aryl ligands in the solid state, where each lithium atom is coordinated by two oxygen atoms of two different ligands. The NMR spectroscopy and cryoscopy measurements established monomer-dimer equilibrium of 1 in concentrated solutions of non-coordinated solvents, while the diluted solutions of 1 consist of monomer only.