Activity of Mo(II) allylic complexes supported in MCM-41 as oxidation catalysts precursors

[Mo(η³-C₃H₅)X(CO)₂(NCCH₃)₂] (X = Br, 1a; X = Cl, 1b) complexes reacted with the bidentate ligand RNC(Ph)–C(Ph)NR, R = (CH₂)₂CH₃ (DAB, 2) affording [Mo(η³-C₃H₅)X(CO)₂(DAB)] (X = Br, 4a; X = Cl, 4b), which were characterized by elemental analysis, FTIR and ¹H and ¹³C NMR spectroscopy. The modified silylated ligand RNC(Ph)C(Ph)NR, R = (CH₂)₃Si(OCH₂CH₃)₃ (DAB–Si, 3), was used to immobilize the two complexes in MCM-41 (MCM) mesoporous silica. The new materials were characterized by powder X-ray diffraction, N₂ adsorption analysis, FTIR and ²⁹Si and ¹³C CPMAS solid state NMR spectroscopy. Both the materials and the complexes were tested in the oxidation of cyclooctene and styrene and behaved as active catalyst precursors for cyclooctene and styrene epoxidation with TBHP (t-butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs. Although the homogeneous systems reach 100% conversion of cyclooctene and slightly less for styrene, the loss of catalytic activity in the heterogeneous systems is small, with a 98% conversion of styrene achieved by the chloride containing material.     

Linked macrocyclic systems. Interaction of copper(I) with tris-ring N2S2-donor macrocycles and their single-ring analogues

The interaction of two tri-linked N₂S₂-donor macrocyclic ligands, 1 (R = H) and 2 (R = H), and their related single ring derivatives, 3 (R = H) and 4 (R = CH₂C₆H₅), with copper(I) is reported. Solid 3:1 (metal:ligand) complexes of type [Cu₃L](PF₆)₃ (L = 1 and 2, R = H) and single ring derivatives of type [CuL]PF₆ (L = 3, R = H; L = 4, R = CH₂C₆H₅) were isolated; the X-ray structure of [CuL]PF₆ (L = 3, R = H) showed that the four macrocyclic donor atoms coordinate to the copper(I) in a quasi-tetrahedral manner (Cu–N 2.089, 2.096(4); Cu–S 2.239, 2.264(2) Å, X–Cu–Y 104.5(1)–115.4(1))°.     

Synthesis,luminescence, and structural characterization of Zn and Cd coordination polymers of flexible bis(imidazolyl) derivatives

Coordination polymers [Zn(imc)(L¹)] · H₂O, (1, imc = iminodiacetate, L¹ = bis(N-imidazolyl)methane) [Zn(hba)₂(L²)]₂ · EtOH · 3H₂O, (2, hba = p-hydroxybenzoate, L² = bis(N-benzimidazolyl)methane), [Cd(mal)(H₂O)(L³)](3, L³ = 1,4-bis(N-imidazolyl)butane, mal = maleate) have been prepared and structurally characterized. Complex 1 consists of hexa-coordinated central Zn ions and exhibits 2D network structure. The Zn atoms in 2 have tetrahedral coordination geometry, and are linked by bis(imidazolyl) ligands into 1D chain structure. The cadmium ions in 3 are hepta-coordinated with pentagonal bipyramidal geometry. Complex 3 displays 2D grid structure. The TGA showed that the coordination polymers are stable up to 200 °C. All the three complexes are emissive at room temperature in their solid state.     

Tetra- and hexanuclear cage molecules based on diruthenium tetracarbonyl sawhorse units: Synthesis and molecular structure of [{Ru2(CO)4(PPh3)2}2(O2CCH2CO2)2] and [{Ru2(CO)4(PMe3)2}3(O2CC6H4CO2)3]

The thermal reaction of Ru₃(CO)₁₂ with malonic acid, followed by the addition of the corresponding ligand, yields the tetranuclear ruthenium complexes [{Ru₂(CO)₄L₂}₂(O₂CCH₂CO₂)₂] (L = PPh₃: 1, L = 3,5-Me₂NC₅H₃: 2), while the reaction of Ru₃(CO)₁₂ with terephthalic acid, followed by the addition of the corresponding ligand, gives rise to the formation of the hexanuclear ruthenium complexes [{Ru₂(CO)₄L₂}₃(O₂CC₆H₄CO₂)₃] (L = PMe₃: 3, L = 3,5-Me₂NC₅H₃: 4). The single-crystal X-ray structure analyses for 1 and 3, reveal both cages to consist of Ru₂(CO)₄ sawhorse units, 1 being a molecular loop, while 3 is a molecular triangle.     

Synthesis,characterization and compared reactivity of asymmetrical ansa-metallocenes

Rac and meso ansa-zirconocenes [Zr{1-Me₂Si(3-R-(η⁵-C₉H₅))(3-R′-(η⁵-C₉H₅))}Cl₂] (R = Et, R′ = H; R = Pr, R′ = H; and R = Et, R′ = Pr) 4–9 have been prepared by the reaction of ZrCl₄ with the corresponding dilithiated derivatives from the ligands {1-Me₂Si(3-R-(η⁵-C₉H₅))(3-R′-(η⁵-C₉H₅))} (R = Et, R′ = H 1; R = Pr, R′ = H 2; and R = Et, R′ = Pr 3) in diethyl ether/toluene at ?78 °C. The molecular structure of rac [Zr{1-Me₂Si(3-Et-(η⁵-C₉H₅))(3-Pr-(η⁵-C₉H₅))}Cl₂] 8 has been determined by single crystal X-ray diffraction studies, which show a pseudotetrahedral environment formed by the two chlorine ligands and two η⁵-coordinated indenyl ligands. The activity in homogeneous and heterogeneous polymerization is compared and discussed.     

Hetero-trinuclear near-infrared (NIR) luminescent ZnLn2 (Ln = Nd,Yb or Er) complexes based on monomer ZnL Schiff-base precursor and o-vanillin

With the monomer [Zn(L¹)(H₂O)] (1) complex in situ formed by the deprotonated hexadentate Salen-type Schiff-base ligand H₂L¹ (H₂L¹ = N,N′-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) and Zn(NO₃)₂ as the precursor, series of the hetero-trinuclear ZnLn₂ complexes [ZnLn₂(L¹)₂(L²)(NO₃)₂Cl] (Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) were obtained from the further reaction with LnCl₃ (Ln = Nd, Yb Er or Gd) and the second o-vanillin (HL²) ligand, respectively. The photophysical properties of complexes 2–4 showed that the characteristic near-infrared (NIR) luminescence of Ln^3 + ions with two emission centers and emissive lifetimes in microsecond ranges, was sensitized from the excited state (both ¹LC and ³LC) of mixed H₂L¹–HL² ligands.     

Synthesis,characterization and photoluminescence properties of copper(II)–azido/thiocyanato complexes with thiazolylazo dye and1,2-bis(diphenylphosphino)ethane

A series of copper(II) complexes of the formula [Cu(L)(dppe)(N₃)₂] (1a–3a) and [Cu(L)(dppe)(NCS)₂] (1b–3b) (where L = 4-(2′-thiazolylazo)chlorobenzene (L₁); 4-(2′-thiazolylazo)bromobenzene (L₂) and 4-(2′-thiazolylazo)iodobenzene (L₃); dppe = cis-1,2-bis(diphenylphosphino)ethane) has been prepared and characterized on the basis of their elemental analysis, molar conductance, magnetic moment, IR, UV–vis and ¹H NMR spectral studies. The electrochemical behaviour of the complexes showed that the redox responses of copper(II) complexes shifted to more negative potential in order of decrease in electron withdrawing nature of the substituent on the azo ligands. All the complexes exhibit intraligand (π→π*) fluorescence in blue-green region with high quantum yield in DMF solution.     

Thermally stable pseudo-third-generation Grubbs ruthenium catalysts with pyridine–phosphinimine ligand

The ligand precursors 2-(R₃PN)CH₂Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl₂(CHPh)(Py)₂(H₂IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl₂(CHPh)(PyCH₂(NPR₃))(H₂IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.     

Formation of extended 1D coordination polymers in tetrathioether complexes of mercury(II): Effect of the organic substituents on the crystal structures of {Si(CH2SR)4}HgBr2 (R = Me,Ph)

Two novel one-dimensional (1D) coordination polymers of stoichiometry [{Si(CH₂SR)₄}HgBr₂]_n (R = Me, 2a; R = Ph, 2b) have been prepared by treatment of HgBr₂ with the functionalized silanes Si(CH₂SR)₄ (R = Me, 1a; R = Ph, 1b) acting as tetradentate thioether ligands. The extended structures result from intermolecular Hg–S interactions linking the monomeric {Si(CH₂SR)₄}HgBr₂ units, as established for 2a, b using single-crystal X-ray diffraction. The effective coordination around the Hg atoms in both compounds is best described as distorted octahedral.     

New hetero-dilanthanide complexes containing Ln1(fod)3 and Ln2(fod)3 fragments (Ln=Pr–Nd; Nd–Sm; Eu–Tb and Ho–Er) linked by bis-diimine bridging ligand

New hetero-dilanthanide β-diketonate complexes of the type [Ln¹Ln²(fod)₆(μ-bpm)] {fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione; bpm = 2,2′-bipyrimidine; Ln¹ = Pr and Ln² = Nd (1); Ln¹ = Nd and Ln² = Sm (2); Ln¹ = Eu and Ln² = Tb (3) and Ln¹ = Ho and Ln² = Er (4)} have been isolated by reacting sequentially, the coordinatively unsaturated Ln(fod)₃ chelates of two different lanthanides and 2,2′-bipyrimidine bridging ligand in 1:1:1 molar ratio, in ethanol. The purity and hetero-dilanthanide nature of the complexes has been confirmed by NMR, 4f–4f absorption spectroscopies and electrospray mass spectrometry. The oscillator strength of the hypersensitive transitions confirms the presence of the two different lanthanides in the complexes in 1:1 ratio. The complexes 2 and 3 display strong pink and red luminescences, respectively. The intramolecular Tb(III) → Eu(III) energy transfer has been observed in complex 3.     

A new stable Cd(II)-framework for sensitive and selective detection of Cu2 + ions

A new water-stable 3D metal–organic framework (MOF), [Cd₂L₂]·NMP·MeOH (1, H₂L = 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,3-dioxoisoindoline-5,6-dicarboxylic acid, NMP = 1-methyl-2-pyrrolidinone) has been solvothermally synthesized and structurally characterized. 1 exhibits a 3D open-framework with a 2D metallic plane pillared by L^2 − fragments. Meanwhile, luminescent studies indicate that the luminescence intensity of 1 was strongly dependent on different metal ions. Most interestingly, 1 exhibited significantly quenching effect toward Cu^2 +, which implies that it may be used as a luminescent probe for the detection of Cu^2 +.     

Novel W(II) complexes for reversible addition-fragmentation chain transfer (RAFT) polymerizations

Alkylation of the phosphorus coordination of the diphenyl(dithioformato)phosphine ligand in [W(CO)₅(PPh₂CS₂)]NEt₄ (1) at the S atom results in the formation of the novel RAFT agent S═C[W(CO)₅PPh₂]S–R (2a, R = CH₂Ph; 2b, R = CH₂CH═CH₂). These compounds have been shown to be highly effective in reversible addition-fragmentation chain transfer (RAFT) polymerization to produce polymers (homopolymer and diblock copolymer) of predetermined molecular weight and narrow polydispersity (< 1.3). Electron-withdrawing organometallic substituents can increase the activity of RAFT agents. To the best of our knowledge, this is the first report of their use as RAFT agents in polymerization.     

Syntheses,crystal structures and properties of dinuclear hydrido-tris(3,5-diphenylpyrazol-1-yl)borate complexes with the S―S coupled and dimerized quinoxaline-2,3-dithiolate ligand

New dinuclear complexes with the bridging S―S coupled and dimerized quinoxaline-2,3-dithiolate (dsqdt) ligand, [Tp^Ph2M(dsqdt)MTp^Ph2] (Tp^Ph2 = hydro-tris(3,5-diphenylpyrazol-1-yl)borate; M = Co, 1; M = Ni, 2; M = Mn, 3), were prepared. X-ray crystal structure studies for complexes 1–3 indicate that the dsqdt ligand forms the unique κ²-coordinated mode through S and N atoms from the same qdt unit. The absorption spectra, redox behavior and magnetic properties of the compounds are reported.     

Single-nodal linking for Zn2 +-Nd3 +-containing metallopolymer with efficient near-infrared (NIR) luminescence

Through the single-nodal copolymerization of MMA (methyl methacrylate) and a vinyl-containing complex monomer [Zn(L)(4-vinyl-Py)Nd(NO₃)₃] (2; H₂L = N,N′-bis(3-methoxy-salicylidene)ethylene-1,2-diamine; 4-vinyl-Py = 4-vinyl-pyridine) with the both ¹π-π* and ³π-π* sensitizing approach to Nd^3 + ion, the Zn^2 +-Nd^3 +-containing metallopolymer Poly(MMA-co-2) exhibits good physical properties including an attractive Nd^3 +-centered NIR sensitization efficiency (Φ^L_Nd = 1.22% and η = Φ^L_Nd/Φ^Nd_Nd = 82%).     

Synthesis,structure and near-infrared (NIR) luminescence of three solvent-induced pseudo-polymorphic complexes from a bimetallic Zn–Nd Schiff-base molecular unit

Three solvent-induced pseudo-polymorphic bimetallic Zn–Nd complexes [ZnNdL(OAc)(NO₃)₂(DMF)] · solvate (solvate: MeCN (1), THF (2), EtOH (3); H₂L = N,N′-bis(3-methoxy-salicylidene)phenylene-1,2-diamine) were obtained, and their solid NIR luminescence related to the packing structure from the intermolecular π–π interactions was discussed.     

The novel example of organotin(IV) metallacrowns: Syntheses,characterizations and crystal structures of [12-MC[RSn(IV)]N(shi)-4] complexes (R = Et,Bu, Ph; Shi = salicylhydroxamic acid)

Three 12-metallacrown-4(12-MC-4) organotin(IV) complexes [12-MC_{[RSn(IV)]N(shi)}-4] (R = Et(1), Bu(2), Ph(3); Shi = salicylhydroxamic acid) have been synthesized and characterized by elemental analyses, IR, TGA and X-ray diffraction. Single-crystal X-ray analyses reveal that all the complexes 1–3 contain a neutral 12-membered metallacrown ring which is formed by the succession of four repeating units of –[Sn–N–O]–. The metallacrown molecules of complexes 1 and 2 are further linked by intermolecular C–H···O interactions to form a 2D supramolecular networks, while the molecules of complex 3 are linked by intermolecular C–H···O and C–H···π interactions to form a 3D framework.     

Structural differences of half-sandwich complexes of scandium and yttrium containing bulky substituents

Scandium and yttrium half-sandwich chloride complexes (η⁵-C₅Me₄R)ScCl₂(THF)₂ R = CH₂Ph (3) or SiMe₂CH₂CH₂Ph (5) and (η⁵-C₅Me₄R)YCl₂(THF)₂ R = CH₂Ph (4) or SiMe₂CH₂CH₂Ph (6) were prepared by metathetic reactions of the corresponding substituted lithium or potassium cyclopentadienides with scandium or yttrium trichloride. A mutual comparison of the determined solid state structures of 4 and 5 revealed the tetranuclear character in the case of scandium complex containing C₅Me₄SiMe₂CH₂CH₂Ph ligand, while a formation of the trinuclear ate-complex 4 incorporating lithium was observed for the combination of yttrium and the benzyl substituted tetramethyl cyclopentadienyl. Moreover, the steric effect of addition of another differently substituted cyclopentadienyl ring into the molecule was evaluated.     

Co-existence of heterometallic Zn2Er and ZnEr arrayed chromophores for the sensitization of near-infrared (NIR) luminescence

With the Zn-Schiff-base [ZnL(Py)] from the simple Salen-type Schiff-base ligand H₂L (H₂L = N,N′-bis(salicylidene)ethylene-1,2-diamine) as the precursor, two co-crystallized heterometallic (Zn₂Ln and ZnLn array) complexes [Zn₂Ln(L)₂(Py)₂(NO₃)₂]·[ZnLn(L)(Py)(NO₃)₃(H₂O)]·NO₃·mMeOH·nS (Ln = Er(1), S = CH₃CN, m = 2, n = 1 or Gd(2), S = H₂O, m = 1, n = 3) were obtained by the further reaction with Ln(NO₃)₃·6H₂O, respectively. The result of their photophysical properties shows the intramolecular effective energy transfer has been demonstrated in the Zn₂Er and ZnEr arrayed complex 1, and the co-existence of different chromophores should be a potentially new way to the fine-tuning properties of NIR luminescence from Er³⁺ ions.     

Construction of isostructural Ln–Ag (Ln = Eu; Tb; Dy) nano-channel heterometallic coordination frameworks based on pyrazine-2-carboxylate and oxalate ligands

The self-assembly of pyrazine-2-carboxylate and oxalate with mixed-metal salts under hydrothermal conditions gave three isostructural 3D 4d-4f coordination polymers, LnAg(ox)(2-pzc)₂ · H₂O [Ln = Eu (1); Tb (2); Dy (3)] [ox = oxalate, 2-pzc = pyrazine-2-carboxylate]. All three structures exhibit same unusual 3D nanoporous heterometallic coordination frameworks constructed by zigzag lanthanide–oxalate chains and Ag(2-pzc)₂ units. Furthermore, the luminescent properties of complexes 1 and 2 are discussed.     

Synthesis,crystal structures and NIR luminescence properties of binuclear lanthanide Schiff Base complexes

Three binuclear lanthanide complexes [Nd₂(L¹)₃(MeOH)]·MeOH·H₂O (1) and [Ln₂(H₂L²)₂(OAc)₄]·2(CF₃SO₃)·MeOH·EtOH (Ln = Nd (2) and Ho (3)) were prepared using two Schiff base ligands. Interestingly, 1 has a triple-decker structure with two lanthanide ions enclosed by three rigid conjugated Schiff base ligands (H₂L¹), while 2 and 3 show nanoscale ring structures (8 × 12 × 12 Å) formed by flexible long-chain Schiff base ligands (H₂L², ~ 23 Å) with the lanthanide ions located in the center. Upon excitation of the ligand-centered absorption bands, 1–2 and 3 show typical NIR emission spectra for Nd^3 + and Ho^3 + ions, respectively. In 1, the Nd(III) centers are shielded within the decker-like structure and surrounded by chromogenic Schiff base ligands (energy transfer donors). Luminescence studies show that the NIR emission lifetime of 1 is longer than that of 2 in solution.