Mer Configuration Research Articles

Mechanochemical Synthesis of Chromium(III) Complexes Containing Bidentate PN and Tridentate P-NH-P and P-NH-P' Ligands.

Chromium(III) complexes bearing bidentate {NH2(CH2)2PPh2: PN, (S,S)-[NH2(CHPh)2PPh2]: P'N} and tridentate [Ph2P(CH2)2N(H)(CH2)2PPh2: P-NH-P, (S,S)-(iPr)2PCH2CH2N(H)CH(Ph)CH(Ph)PPh2: P-NH-P'] ligands have been synthesized using a mechanochemical approach. The complexes {cis-[Cr(PN)Cl2]Cl (1), cis-[Cr(P'N)Cl2]Cl (2), mer-Cr(P-NH-P)Cl3 (3), and mer-Cr(P-NH-P')Cl3 (4)} were obtained in high yield (95-97%) via the grinding of the respective ligands andthe solid Cr(III) ion precursor [CrCl3(THF)3] with the aid of a pestle and mortar, followed by recrystallization in acetonitrile. The isolated complexes are high spin. A single-crystal X-ray diffraction study of 2 revealed a cationic chromium complex with two P'N ligands in a cis configuration with P' trans to P' with chloride as the counteranion. The X-ray study of 4 shows a neutral Cr(III) complex with the P-NH-P' ligand in a mer configuration. The difference in molecular structures and bulkiness of the ligands influence the electronic, magnetic, and electrochemical properties of the complexes as exhibited by the bathochromic shifts in the electronic absorption peaks of the complexes and the relative increase in the magnetic moment of 3 (4.19 μβ) and 4 (4.15 μβ) above the spin only value (3.88 μβ) for a d3 electronic configuration. Complexes 1-4 were found to be inactive in the hydrogenation of an aldimine [(E)-1-(4-fluorophenyl)-N-phenylmethanimine] under a variety of activating conditions. The addition of magnesium and trimethylsilyl chloride in THF did cause hydrogenation at room temperature, but this occurred even in the absence of the chromium complex. The hydrogen in the amine product came from the THF solvent in this novel reaction, as determined by deuterium incorporation into the product when deuterated THF was used.

Solvothermal synthesis and selected properties of {[Ni(dien)2]3[V6As8O26]}2+·2 Cl– featuring the small [V6 IVAs8 IIIO26]4– cluster anion

Abstract A new arsenato-polyoxovanadate with the composition {[Ni(dien)2]3[V6As8O26]}2+·2 Cl– has been crystallized under solvothermal conditions as turquoise block-like crystals. The central structural feature is the [V6 IVAs8 IIIO26]4– cluster anion, which is composed of two trinuclear {V3O11} groups consisting of three edge-sharing VO5 polyhedra. Pairs of pyramidal AsO3 moieties share a common corner forming As2O5 units, which interconnect the {V3O11} groups. One of the [Ni(dien)2]2+ complexes adopts the s-fac (Ni1) and the second complex the mer configuration (Ni2). The Cl− anion is involved in strong hydrogen bonding interactions and links the [Ni(dien)2]2+ complexes to form twelve-membered rings which host the [V6As8O26]4– cluster anions. The Hirshfeld surface analysis yields a detailed picture of the intermolecular interactions revealing clear differences for the two unique [Ni(dien)2]2+ complexes. Intermolecular contacts also include As⋯H, O⋯H and H⋯H interactions. In the electronic spectrum the bands of d–d transitions of the vanadyl group and of the Ni2+ cations overlap, preventing a detailed analysis.

Electronic insights into aminoquinoline-based PNHN ligands: protonation state dictates geometry while coordination environment dictates N-H acidity and bond strength.

A variety of transition metal complexes bearing aminoquinoline PNHH'-R ligands R = Ph (L1H), Cy (L2H) and their amido analogues are reported for rhodium(I) ([Rh(L1H)(PPh3)]+1 and Rh(L1)(PPh3) 2), cobalt(II) (Co(L2)(Cl) 3), and iron(II) ([Fe(L1H)2]2+5, Fe(L1)26, and [Fe(C5Me5)(L1H)]PF67). The acid-base and redox properties of the amido complexes 2, 6, and their protio parent complexes 1, and 5 permit the determination of the pKa and bond dissociation free energy (BDFE) of their N-H bonds while the ligand scaffold is coordinated to metal centres of square planar and octahedral geometry, respectively. From relative concentrations obtained by the use of 31P{1H} NMR spectroscopy, a pKaTHF value of 14 is calculated for rhodium complex 1, 6.4 for iron complex 5, and 24 for iron complex 7. These data, when combined with elecrochemical potentials obtained via cyclic voltammetry, allow the calculations of BDFE values for the N-H bond of 69 kcal mol-1 for 1, and of 55 kcal mol-1 for 5.

Azido and thiocyanato bridged dinuclear Ni(II) complexes involving 8-aminoquinoline based Schiff base as blocking ligands: Crystal structures, ferromagnetic properties and magneto-structural correlations

The use of two 8-aminoquinoline-based tridentate N3-donor rigid Schiff base ligands (L1 and L2) with Ni(II) in the presence of the pseudohalides, NaN3 and NaSCN results in the crystallization of the two novel Ni(II) dimers: [Ni2(L1)2(µ1,1′-N3)2(N3)2] (1) and [Ni2(L2)2(µ1,3-NCS)2(NCS)2] (2). Both complexes are centrosymmetric Ni(II) dimers where the Schiff base ligands coordinate the octahedral Ni(II) centres in a mer configuration with one terminal and two bridging pseudohalide ligands in the remaining positions. Complex 1 shows Ni(II) ions connected by a double µ1,1′-N3− bridge whereas in complex 2 the Ni(II) ions are connected by a double µ1,3-NCS− bridge. The magnetic properties show the presence of a weak ferromagnetic coupling in both compounds that can be fit with g = 2.290(6), J = 6.1(2) cm−1, zJ′ = −0.32(1) cm−1 and |D| = 4.34(5) cm−1 for 1 and g = 2.096(2), J = 4.71(5) cm−1, zJ′ = −0.054(2) cm−1 and |D| = 1.52(2) cm−1 for 2 (the Hamiltonian is written as −2JS1S2). Both J values have been rationalized in terms of previous magneto structural correlations based on the Ni-N-Ni bridging angle in 1 and on the asymmetry of the Ni-S-C-N-Ni bridges in 2.

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al, Ga, In) and correlations with molecular electrostatic potential.

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λF ) values whereas the effect is moderate at the absorption maximum (λabs ) values. The molecular electrostatic potential (MESP) at the metal center (VM ) and the most electron rich region indicated by MESP minimum (Vmin ), located at the oxygen of phenoxide ring exhibit excellent correlations with the λF and Stokes shift (λF -λabs ) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the Vmin or VM emerge as theoretical quantities to measure the same.

Synthesis, structure and biological evaluation of ruthenium(III) complexes of triazolopyrimidines with anticancer properties.

Six novel ruthenium(III) complexes of general formula [RuCl3(L)3] (1,3,5) and [RuCl3(H2O)(L)2] (2,4,6), where L stands for three different triazolopyrimidine-derived ligands, are reported. The compounds have been structurally characterized (IR, EPR, SCXRD), and their magnetic moments have been determined. The single-crystal X-ray diffraction study revealed a slightly distorted octahedral geometry of the Ru(III) complexes with mer configuration in 1 and 5, and fac configuration in 3. In 2 and 4, three chloride ions are in mer configuration and the two triazolopyrimidines are oriented trans mutually with the water molecule playing the role of the sixth ligand. All complexes have been thoroughly screened for their in vitro cytotoxicity against human breast cancer cell line MCF-7, human cervical cancer cell line HeLa, and L929 murine fibroblast cells, uncovering among others that the most lipophilic complexes 5 and 6, containing the bulky ligand dptp (5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine), display high cytotoxic activity against MCF-7, and HeLa cells. Moreover, it was also revealed that during the interaction of the complexes 1-6 with the cancer MCF-7 cell line, reactive oxygen species are released intracellularly, which could indicate that they are involved in cell apoptosis. Furthermore, extensive studies have been carried out to reveal the mechanism by which complexes 1-6 interact with DNA, albumin, and apotransferrin. The biological studies were complemented by detailed kinetic studies of the hydrolysis of the complexes in the pH range 5-8, to determine the stability of the complexes in solution. Six novel ruthenium(III) complexes with triazolopyrimidine derivatives demonstrated the potential for use as anticancer agents by maintaining the toxic effect on MCF-7 and HeLa cells.

Chromium ethylene polymerization catalysts bearing sterically enhanced α,α′-bis(imino)-2,3:5,6-bis(pentamethylene)pyridines: Tuning activity and molecular weight

The ortho-benzhydryl-substituted α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridine-chromium(III) chlorides, [2,3:5,6-{C4H8C(N(2-R1-4-R2-6-(CHPh2)C6H2)}2C5HN]CrCl3 [R1 = R2 = Me Cr1, R1 = Me, R2 = CHPh2Cr2, R1 = Et, R2 = CHPh2Cr3, R1 = i-Pr, R2 = CHPh2Cr4, R1 = Cl, R2 = CHPh2Cr5, R1 = F, R2 = CHPh2Cr6], differing in the electronic and/or steric properties of their aryl-R1 and -R2 groups, have been prepared by a one-pot template approach involving α,α′-dioxo-2,3:5,6-bis(pentamethylene)pyridine, the corresponding aniline and CrCl3(THF)3 in acetic acid. The molecular structure of six-coordinate Cr1 reveals the carbocyclic-fused N,N,N-ligand to adopt a mer configuration with the puckered sections of the two fused rings arranged mutually cis. On activation with MAO or MMAO, Cr1 - Cr6 displayed high activities (up to 1.83 × 106 g (PE) mol−1 (Cr) h−1) for the polymerization of ethylene with the MAO-promoted polymerizations in most cases more productive than with MMAO. In general, the chromium complexes appended with ortho-halide substituents (Cr6 (F)) and (Cr5 (Cl)), proved the most active with the overall order being: Cr6 > Cr5 > Cr1 > Cr2 > Cr3 > Cr4. All catalysts formed linear polyethylene displaying a wide range of molecular weights (from 2.17 to 300.4 kg mol−1) that were highly dependent on the nature of the ortho-R1 substituent with fluoride Cr6 forming the lowest molecular weight and the most sterically demanding Cr4 (i-Pr) the highest.

A tetranuclear nickel(II) complex for water oxidation: Meeting new challenges

Ni complexes are promising catalysts for water splitting. Herein, a tetranuclear nickel(II) complex with bis-[(E)-N′-(1-(pyridin-2-yl)ethylidene)]carbohydrazide (HL), was synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. The complex is a tetranuclear complex and the ligands are coordinated to the metal ions in the mono-negative form, (L)- to form a tetranuclear [NiL]44+ unit. Each Ni(II) ion is six-coordinated by pyridine nitrogen, azomethine nitrogen and oxygen atoms of two perpendicular carbohydrazone ligands in the mer configuration. The complex was studied as a water-oxidizing catalyst. In the next step, the role of the Ni-based compound for water oxidation on the surface of fluorine doped tin oxide as one of the true catalysts was investigated by scanning transmission electron microscopy, scanning transmission electron microscopy, spectroelectrochemistry, and electrochemistry. The electrode after water oxidation by the complex was studied and a relation between the decomposition of the Ni complex and water-oxidation reaction was proposed. The experiments show that under water-oxidation condition in the presence of the complex, a Ni-based compound on the electrode is a candidate as a contributor to the observed catalysis.

Small Structural Variations Have Large Effects on the Assembly Properties and Spin State of Room Temperature High Spin Fe(II) Iminopyridine Cages.

Small changes in steric bulk at the terminus of bis-iminopyridine ligands can effect large changes in the spin state of self-assembled Fe(II)-iminopyridine cage complexes. If the added bulk is properly matched with ligands that are either sufficiently flexible to allow twisted octahedral geometries at the Fe centers or can assemble with unusual mer configurations at the metals, room temperature high spin Fe(II) cages can be synthesized. These complexes maintain their high spin state in solution at low temperatures and have been characterized by X-ray crystallographic and computational methods. The high spin M2L3 meso-helicate and M4L6 cage complexes display longer N-Fe bond distances and larger interligand N-Fe-N bond angles than their diamagnetic counterparts, and these structural changes invert the ligand selectivity in narcissistic self-sorting and accelerate subcomponent exchange rates. The paramagnetic cages can be easily converted to diamagnetic cages by subcomponent exchange under mild conditions, and the intermediates of the exchange process can be visualized in situ by NMR analysis.

Synthesis and Characterization of Self-Assembled Chiral FeII 2 L3 Cages.

We present here the synthesis of chiral BINOL‐derived (BINOL=1,1′‐bi‐2‐naphthol) bisamine and bispyridine‐aldehyde building blocks that can be used for the self‐assembly of novel chiral FeII 2L3 cages when mixed with an iron(II) precursor. The properties of a series of chiral cages were studied by NMR and circular dichroism (CD) spectroscopy, cold‐spray ionization MS, and molecular modeling. Upon formation of the M2L3 cages, the iron corners can adopt various isomeric forms: mer, fac‐Δ, or fac‐Λ. We found that the coordination geometry around the metal centers in R‐Cages 1 and 2 were influenced by the chiral BINOL backbone only to a limited extent, as a mixture of cages was formed with fac and mer configurations at the iron corners. However, single cage species (fac‐RR‐Cage and fac‐RS‐Cage) that are enantiopure and highly symmetric were obtained by generating these chiral M2L3 cages by using the bispyridine‐aldehyde building blocks in combination with chiral amine moieties to form pyridylimine ligands for coordination to iron. Next to consistent NMR spectra, the CD spectra confirm the configurations fac‐(Λ,Λ) and fac‐(Δ,Δ) corresponding to RR‐ and RS‐Cage, respectively.

Schiff Base Ligands Derived from l‐Histidine Methyl Ester: Characterization, Racemization, and Dimerization of Their Transition‐Metal Complexes

Reactions of methyl (S)‐2‐[(2‐hydroxybenzylidene)amino]‐3‐(1H‐imidazol‐4‐yl)propanoate (S‐H2LMe) and various transition‐metal(II) salts (MX2: M = Mn, Fe, Co, and Ni; X = ClO4, Cl, OAc, etc.) are examined. During the reactions with MnII and CoII salts, the MII ion is oxidized by air to form a cationic complex with two mono‐deprotonated ligands, [MIII(S‐HLMe)2]X [M, X = Mn, ClO4 (S‐1ClO4); Co, ClO4 (S‐3ClO4); and Co, Cl (S‐3Cl)], where (S‐HLMe)– is coordinated to a MIII center in a tridentate κ3O,N,N′ mode with a mer configuration. In contrast, the NiII ion is not oxidized; only one of the ligands is deprotonated to form a similar monocationic complex, [NiII(S‐HLMe)(S‐H2LMe)]PF6 (S‐6PF6), which forms a dimer structure by double hydrogen bonds between the coordinating phenoxide and phenol groups in the crystal. Interestingly, the above complexes show slow racemization of the ligand, as confirmed by circular dichroism spectroscopy. Racemic NiII complexes of [Ni(HLMe)(H2LMe)](PF6 or Cl) (rac‐6PF6 or rac‐6Cl) are isolated and their crystal structures are confirmed by X‐ray diffraction analysis. In the case where Co(OAc)2 is used as the metal(II) salt, a new ligand dimerization reaction takes place to afford a complex of [Co(H2LLMe)]Cl (7Cl, H4LLMe = methyl (E)‐3‐{[3‐(1H‐imidazol‐4‐yl)‐1‐methoxy‐1‐oxopropano‐2‐yl]amino}‐2‐[(1H‐imidazol‐4‐yl)methyl]‐2‐[(2‐hydroxybenzylidene)amino]‐3‐(2‐hydroxyphenyl)propanoate).

Vinyl‐Polyethylene Waxes with Narrow Dispersity Obtained by Using a Thermally Robust [Bis(imino)trihydroquinolyl]chromium Catalyst

Five structurally related chromium(III) complexes [2‐(ArNCMe)‐8‐(NAr)C9H8N]CrCl3 (Ar = 2,6‐Me2Ph: Cr1; 2,6‐Et2Ph: Cr2; 2,6‐iPr2Ph: Cr3; 2,4,6‐Me3Ph: Cr4; 2,6‐Et2‐4‐MePh: Cr5), each bearing an unsymmetrical bis(imino)trihydroquinoline ligand, were synthesized in good yield and fully characterized. The molecular structure of Cr2 reveals a distorted octahedral geometry at the metal center with the sterically bulky N,N,N ligand adopting a mer configuration. On activation with methylaluminoxane (MAO) or modified MAO, Cr1–Cr5 were highly active catalysts for ethylene polymerization operating most effectively at 80 °C [up to 15.96 × 106 g (PE)·mol–1 (Cr)·h–1]; even at 100 °C, the activity was still good [2.92 × 106 g (PE)·mol–1 (Cr)·h–1]. Highly linear polyethylene waxes of low molecular weight and narrow molecular weight distribution (polydispersity index: 1.1–1.8), incorporating predominantly vinyl/methyl and some methyl/methyl end groups were obtained. The influence of steric/electronic changes to the precatalyst and polymerization reaction parameters on the catalytic activity and the properties of the polymer product were the subject of a detailed investigation.

Solvothermal syntheses, crystal structures, and optical and thermal properties of transition metal selenidostannates

Four organic–inorganic hybrid selenidostannates, namely [H2en][H2dien][Fe(dien)2]2(Sn2Se6)2 (1), [Fe(dien)2]2Sn2Se6 (2), [Fe(dien)2]FeSnSe4 (3), and [Mn(dien)2]MnSnSe4 (4) (en = ethylenediamine; dien = diethylenetriamine), were prepared in different solvents under solvothermal conditions. Complexes 1 and 2 consist of discrete [Sn2Se6]4− and [Fe(dien)2]2+ ions, as well as organic cations [H2en]2+ and [H2dien]2+ in 1. The dimeric [Sn2Se6]4− anion is formed by two SnSe4 tetrahedra via edge-sharing. Complexes 3 and 4 are composed of one-dimensional polyanions [TMSnSe 4 2− ] n plus [TM(dien)2]2+ counter cations (TM = Fe, Mn). In the [TMSnSe 4 2− ] n anionic chain, the TM and Sn atoms are located at the same metal site with a ratio of 0.5/0.5. The TM1/2Sn1/2Se4 tetrahedra are interlinked via edge-sharing, forming the heterometallic [TMSnSe 4 2− ] n polymeric anion. The [TM(dien)2]2+ cations in 1–2 and 3–4 have u-fac and mer configurations, respectively. In all four crystal structures, the anions and cations are connected into extended structures via weak N–H···Se hydrogen bonds. The band gaps of complexes 1–4 calculated from the solid-state UV–vis diffuse reflectance spectra were at 2.58, 2.60, 2.21, and 2.25 eV, respectively. Thermogravimetric analyses show that complex 1 decomposes in three steps, while complexes 2–4 each decompose in one step.

Chromium(III) complexes bearing bis(benzotriazolyl)pyridine ligands: synthesis, characterization and ethylene polymerization behavior

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)3 in THF to form neutral complexes, [CrCl3{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV–Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH2 (complex 3) and from the fac configuration when the spacer is CO (complex 4).

Hydrogen-Bonded Supramolecular Structures of Cobalt(III) Complexes with Unsymmetrical Bidentate Ligands: mer/fac Interconversion Induced by Hydrogen-Bonding Interactions

Cobalt(III) complexes with three unsymmetrical bidentate ligands containing a noncoordinating N–H bond and a phenolate-O donor as hydrogen-bond donor and acceptor, respectively, were prepared and characterized. 1H NMR spectroscopy indicated that all the tris-chelate Co(III) complexes prepared favor the mer configuration in solution. [Co(Hthp)3] and [Co(Himn)3] also possess the mer configuration in the crystals (Hthp– = 2-(1,4,5,6-tetrahydropyrimidin-2-yl)phenolate, Himn– = 2-(2-imidazolinyl)phenolate). On the other hand, [Co(Himl)3] takes the fac configuration in the crystal (Himl– = 2-(2-imidazolyl)phenolate). These Co(III) complexes showed three types of characteristic supramolecular structures: ladder, distorted hexagonal sheet, and honeycomb sheet structure, constructed by intermolecular hydrogen bonds. Heating [Co(Himn)3] and [Co(Himl)3] in methanol selectively afforded precipitates of the fac isomer due to the low solubility of the hydrogen-bonded supramolecular structures. This mer to fac isomeriza...

Manganese(IV) complex with a polydentate Schiff base ligand: synthesis, crystal structure, TDDFT calculation, electronic absorption and EPR spectral study

A six-coordinate Mn(IV) complex, [Mn(H2L)2] (1) [H4L = 2-methoxy-6-(tris(hydroxymethyl)methyliminomethyl)phenol], was synthesized and characterized by elemental analysis, single-crystal X-ray crystallography, FTIR, UV–Vis electronic absorption, and EPR spectroscopy. The single-crystal structural determination reveals that the complex crystallizes in tetragonal space group P41212 and the tridentate Schiff base ligands are arranged in mer configuration chelating manganese, which exhibits as slightly distorted octahedral coordination sphere with a N2O4 chromophore. Weak hydrogen bonding interactions of uncoordinated hydroxyl groups result in a 2-D supramolecular structure. The UV–Vis electronic absorption and IR spectral data of 1 have been compared with the results obtained by employing DFT and time-dependent density functional theory calculation using B3LYP, B3PW91, and MPW1PW91 functionals, with 6-31G (d-p) and LanL2MB basis sets. The results of these calculations are functional-dependent and, among those used, B3PW91 proved to better reproduce the experimental results.

Active O,Npy,N-Titanium(IV) Fluoride Precatalysts for Ethylene Polymerization: Exploring “Fluoride Effects” on Polymer Properties and Catalytic Performance

Three examples of discrete six-coordinate O,Npy,N-bearing titanium(IV) trifluoride complexes, [{2-(C5H4N)-6-(CMe2O)C5H3N}TiF3] (1), [{2-(C6H4-2′-O),6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiF3] (2a), and [{2-(3-C12H8-2-O)-6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiF3] (3a), were prepared using a one-step HF elimination protocol from cis-[(THF)2TiF4] and the corresponding pincer ligand precursor (HL1, HL2H, and HL2Ph). A mer configuration of the three fluoride ligands is adopted in their solid-state structures, which is mirrored in solution, as shown by mutual two-bond F–F coupling in their 19F{1H} NMR spectra. For purposes of comparison, the chloride counterparts of 2a and 3a, [{2-(C6H4-2′-O),6-(CMe═N(2,6-i-Pr2C6H3)C5H3N}TiCl3] (2b) and [{2-(3-C12H8-2-O)-6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiCl3] (3b), are also reported. On treatment with excess MAO, 1 is scarcely active in ethylene polymerization, 2a is more active, and the most sterically protected system, 3a, represents the most active nonmetallocene metal-fluoride precatalyst r...

Solvothermal Syntheses and Characterizations of Selenidostannate Salts of Transition Metal Complex Cations: Conformational Flexibility of the Lamellar [Sn3Se72–]n Anion

AbstractThe selenidostannates [Mn(dien)2]Sn3Se7·0.5H2O (1), [Fe(tatda)]Sn3Se7 (2), and [Mn(dien)2]2Sn2Se6 (3) (dien = diethylenetriamine, tatda = 3, 6,9, 12‐tetraazatetradecane‐1, 14‐diamine) were prepared under solvothermal conditions. In compounds 1 and 2, the six Sn3Se4 semi‐cubes are bridged by double μ2‐Se atoms to form the [Sn3Se72–]n lamellar anion containing a elliptical 24‐membered Sn12Se12 ring, which show conformational flexibility of the 2D [Sn3Se72–]n anion influenced by the counter cation. The [Mn(dien)2]2+ complex ion in 1 is in mer configuration. The [Fe(tatda)]2+ complex ion possesses similar configuration to the [Mn(dien)2]2+ ion in 1. The [Mn(dien)2]2+ and [Fe(tatda)]2+ cations are located between the [Sn3Se72–]n layers. Compound 3 consists of dimeric [Sn2Se6]4– anions and octahedral [Mn(dien)2]2+ complex cations with u‐fac configuration. Compounds 1–3 have potential for uses as semiconductors with bandgaps in the range of 1.89–2.34 eV.

Unusual C–C Bond Cleavage in the Formation of Amine-Bis(phenoxy) Group 4 Benzyl Complexes: Mechanism of Formation and Application to Stereospecific Polymerization

Group 4 tetrabenzyl compounds MBn4 (M = Zr, Ti), upon protonolysis with an equimolar amount of the tetradentate amine-tris(phenol) ligand N[(2,4-tBu2C6H2(CH2)OH]3 in toluene from −30 to 25 °C, unexpectedly lead to amine-bis(phenoxy) dibenzyl complexes, BnCH2N[(2,4-tBu2C6H2(CH2)O]2MBn2 (M = Zr (1), Ti (2)) in 80% (1) and 75% (2) yields. This reaction involves an apparent cleavage of the >NCH2–ArOH bond (loss of the phenol in the ligand) and formation of the >NCH2–CH2Bn bond (gain of the benzyl group in the ligand). Structural characterization of 1 by X-ray diffraction analysis confirms that the complex formed is a bis(benzyl) complex of Zr coordinated by a newly derived tridentate amine-bis(phenoxy) ligand arranged in a mer configuration in the solid state. The abstractive activation of 1 and 2 with B(C6F5)3·THF in CD2Cl2 at room temperature generates the corresponding benzyl cations {BnCH2N[(2,4-tBu2C6H2(CH2)O]2MBn(THF)}+[BnB(C6F5)3]− (M = Zr (3), Ti, (4)). These cationic complexes, along with their analogues derived from (imino)phenoxy tri- and dibenzyl complexes, [(2,6-iPr2C6H3)N═C(3,5-tBu2C6H2)O]ZrBn3 (5) and [2,4-Br2C6H2(O)(6-CH2(NC5H9))CH2N═CH(2-adamantyl-4-MeC6H2O)]ZrBn2 (6), have been found to effectively polymerize the biomass-derived renewable β-methyl-α-methylene-γ-butyrolactone (βMMBL) at room temperature into the highly stereoregular polymer PβMMBL with an isotacticity up to 99% mm. A combined experimental and DFT study has yielded a mechanistic pathway for the observed unusual C–C bond cleavage in the present protonolysis reaction between ZrBn4 and N[(2,4-tBu2C6H2(CH2)OH]3 for the formation of complex 1, which involves the benzyl radical and the Zr(III) species, resulting from thermal and photochemical decomposition of ZrBn4, followed by a series of reaction sequences consisting of protonolysis, tautomerization, H-transfer, oxidation, elimination, and radical coupling.

Unusual cocrystals made of a Schiff base metal complex and an organic molecule – Close-packing vs. hydrogen bond interactions

The mononuclear complexes [ML2]0 (M=Co, Ni, Zn; HL – Schiff base ligand formed in situ from 2-pyridinecarbaldehyde and anthranilic acid, AA) can efficiently interact with unreacted AA molecules to produce CoL2·AA·H2O (1), NiL2·AA·H2O (2) and ZnL2·AA·0.25CH3OH·0.5H2O (3) cocrystals. Compounds 1–3 have been obtained as single crystals and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction techniques. The compounds crystallize in the triclinic space group P1‾, with 1 and 2 being isomorphous. Neutral ML2 molecules in 1–3 show no crystallographically imposed symmetry with the metal atoms octahedrally surrounded by two anionic ligands in a mer configuration. Of the two crystallographically distinct AA molecules, one molecule only is engaged in H-bonding N/OH⋯O interactions with ML2 units. The solid-state organization of the cocrystals is described as an insertion of the organic molecules between the layers of ML2 complexes as they occur in the reported native NiL2·H2O structure.