Silsesquioxane Chemistry, 5. Retention of the Cu4O4 core upon formation of the first copper(I) silsesquioxane from tetrameric copper(I)-t-butoxide

The first copper(I) silsesquioxane derivative, Cu₄O₄[Cy₇Si₇O₉(OSiMe₃)]₂ (4) was prepared by reacting tetrameric copper(I)-t-butoxide, (CuOtBu)₄ (3), with the monosilylated silsesquioxane precursor Cy₇Si₇O₉(OH)₂(OSiMe₃) (2) in a 1:2 molar ratio. An X-ray diffraction study revealed the presence of a centrosymmetric dimer. A slightly puckered Cu₄O₄ ring forms the central part of a complex structure comprising nine eight-membered inorganic ring systems.     

Silsesquioxane chemistry, 6 : The first beryllium silsesquioxane: synthesis and structure of [Cy7Si7O12BeLi]2·2THF

The compound [Cy₇Si₇O₁₂BeLi]₂·2THF (3) was prepared in high yield by reacting in situ prepared Cy₇Si₇O₉(OLi)₃ (2) with anhydrous BeCl₂ in THF at 20°C. The molecular structure of 3 has been determined by X-ray diffraction and is the first structurally characterized silsesquioxane derivative of beryllium. In the solid state, self-assembly leads to the formation of a dimeric molecule.     

A linear bifunctionalized organoimido derivative of hexamolybdate: Convenient synthesis and crystal structure

A new disubstituted imido derivative [Bu₄N]₂[Mo₆O₁₇(NAr)₂] (1) (Ar = 2,4-(CH₃)₂C₆H₃), has been synthesized under a mild and convenient reflux reaction of [Bu₄N]₂[Mo₆O₁₉], 2,4-dimethylaniline, and DCC, and characterized by IR spectroscopy, elemental analysis, UV–vis absorption spectroscopy, and single-crystal X-ray diffraction. The most interesting characteristic of 1 is that its anion segment is linear and centrosymmetric with two imido groups occupying two terminal positions of hexamolybdate in an unusual trans fashion. This is the first trans-bis(imido)hexamolybdate prepared via a convenient synthetic route.     

Organic–inorganic hybrid material as zwitterion: Synthesis and structure of terminal ammonium ions-containing organosilyl species supported on mono-lacunary Dawson polyoxometalate

The title compound 1 with a formula of (Bu₄N)₄[α₂-P₂W₁₇O₆₁{Me₃N⁺(CH₂)₃Si}₂O] · CH₃CN was obtained in 77.1% (4.21 g scale) yield by a 1:2 molar-ratio reaction of the mono-lacunary Dawson polyoxometalate (POM) [P₂W₁₇O₆₁]¹⁰⁻ with N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride ([Me₃N(CH₂)₃Si(OMe)₃]Cl) in mixed water/acetonitrile solution under acidic conditions and unequivocally characterized with complete elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, solution (³¹P, ¹H, ¹³C and ²⁹Si) NMR and X-ray crystallography. Compound 1 contained two types of the ammonium cations, i.e., the counterions Bu₄N⁺ (free cations) and the terminal quaternary ammonium ions (bound cations) which are connected to the POM through the organosilyl groups.     

A new family of dimolybdenum compounds with cyanide and phosphine ligands

Reaction of Mo₂Cl₄(dppm)₂ with excess [n-Bu₄N][CN] produces [Bu₄N]₂[Mo₂^II,II(CN)₆(dppm)₂]·2(CH₃CN)·2(C₆H₆) (1) the first example of an edge-sharing bioctahedral compound of Mo(II), that upon exposure to air oxidizes to the mixed valence analog [Bu₄N][Mo₂^II,III(CN)₆(dppm)₂]·2(H₂O)·2(CH₃CN) (2).     

Star-shaped poly(?-caprolactone) with polyhedral oligomeric silsesquioxane core

A readily available octa(3-chloropropyl) polyhedral oligomeric silsesquioxane (POSS) [(ClCH₂CH₂CH₂)₈Si₈O₁₂] framework was used to prepare octa(3-hydroxypropyl) POSS [(HOCH₂CH₂CH₂)₈Si₈O₁₂], which was further used as an initiator to synthesize star poly(?-caprolactone) with POSS core via ring-opening polymerization catalyzed by Stannous (II) octanoate [Sn(Oct)₂]. The organic-inorganic star PCLs were characterized by means of gel permeation chromatograph (GPC), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The wide-angle X-ray diffraction (WAXRD) experiments indicate that the presence of POSS cores did not alter the crystal structure of PCL. The star PCLs exhibited enhanced melting temperatures in comparison with the linear counterpart. The isothermal crystallization kinetics shows that both the overall crystallization rate and the spherulitic growth rate of the star PCLs increased with increasing the concentration of POSS (or with decreasing the arm lengths of the stars). The fold surface free energy of the star PCLs decreased with increasing the concentration of POSS. These results could be interpreted based on the effect of the heterogeneous nucleation of POSS cores, which accelerates the process of crystallization.     

Synthesis and structural characterization of two complex tantalum(V) siloxides

The reaction of tantalum(V) ethoxide, Ta(OEt)₅, with 1 equiv. of 1,1,3,3-tetraphenyl-disiloxane-1,3-diol, (HO)SiPh₂OSi-Ph₂(OH) (1), afforded the dinuclear tantalum(V) disiloxanediolate complex [{μ-(Ph₂OSiO)₂O}Ta(OEt)₂(μ-OEt)]₂ (3). Similarly, Ta(OEt)₅ reacted with the incompletely condensed silsesquioxane precursor Cy₇Si₇O₉(OH)₃ (2, Cy = cyclohexyl) in a 1:1 molar ratio to afford the dinuclear tantalasilsesquioxane derivative [Cy₇Si₇O₁₂Ta(OEt)(μ-OEt)]₂ (4) in 80% yield. Both new complexes were structurally characterized by single-crystal X-ray diffraction studies.     

Models of intermediates in metallocene-catalyzed alkene polymerizations: observation of a d0 cationic titanium–alkyl-alkene complex and decomposition by β-allyl elimination

Low temperature activation of Cp^*₂Ti[η¹,η¹- CH₂CH(CH₂CHCH₂)CH₂] (3) with [HN(CH₃)(C₆H₅)₂] [B(C₆F₅)₄] led to the formation of Cp^*₂Ti[η¹,η²-CH₂CH(CH₃)CH₂CHCH₂][B(C₆F₅)₄] (6) as determined by ¹H NMR spectroscopy. Cp^*₂Ti[η¹,η²-CH₂CH(CH₃)CH₂CHCH₂][B(C₆F₅)₄] undergoes rapid quantitative β-allyl elimination at temperatures as low as −140 °C. The resulting cationic titanium allyl complex [Cp^*₂Ti(η³-CH₂CHCH₂)][B(C₆F₅)₄] (4) exhibits a static structure at low temperatures, but interconversion of η³–η¹ binding modes can be observed at higher temperatures. Lineshape analysis of this process yielded ΔG³(−10 °C)= 13.7 ± 0.6 kcal mol⁻¹, ΔH³=9.8 ± 0.6 kcal mol⁻¹, and ΔS³=−15 ± 3 eu. The use of neutral borane B(C₆F₅)₃ also resulted in β-allyl elimination with the formation of [Cp^*₂Ti(η³-CH₂CHCH₂)][CH₂=CHCH₂B(C₆F₅)₃] (8).     

pH-dependent assembly of 1D–2D structures based on both {V10O28} and [NiMo6O24H6]4 − units: Synthesis,structure and magnetic properties

Two novel complexes [H₂N(CH₂CH₂)₂O]₄[Na(H₂O)₂{O(CH₂CH₂)₂NH₂}]₂[Na(H₂O)₄]₂[V₁₀O₂₈][NiMo₆O₂₄H₆]·8H₂O (1) and [H₂N(CH₂CH₂)₂O]₆[Na(H₂O)₃]₂[V₁₀O₂₈H₂][NiMo₆O₂₄H₆]·4H₂O (2) containing both isopolyvanadate {V₁₀O₂₈} and [NiMo₆O₂₄H₆]^4 − units have been synthesized and structurally characterized for the first time, showing that the pH value of the reaction plays a key role in structure control of self-assembled processes. Compound 1 exhibits a novel one-dimensional (1-D) chain-like structure consisting of Anderson-type [NiMo₆O₂₄H₆]^4 − and isopolyvanadate [V₁₀O₂₈]^6 − anions linked by Na⁺ ions. In compound 2 with the lower pH value, [NiMo₆O₂₄H₆]^4 − and [V₁₀O₂₈H₂]^4 − anions are bridged by [Na₂O₁₀] units to form the 2D extended layer. The magnetic properties of 1 and 2 are presented.     

Synthesis,structures, and magnetic properties of tetranuclear nickel and cobalt complexes with 2-mercaptobenzoxazole

The synthesis and magnetic properties of two tetranuclear Ni complex Ni₄(L)₄(CH₃CN)₄(OCH₃)₄ 1 and Co complex Co₄(L)₄(CH₃CN)₄(OCH₃)₄ 2 (HL = 2-mercaptobenzoxazole) are reported. The X-ray structures reveal that 1 and 2 are isostructural with [Ni₄O₄] 1 and [Co₄O₄] 2 cubane-like cores. Analysis of the temperature dependent magnetic measurements data shows that both complexes are paramagnetic with weak antiferromagnetic coupling. One-J model and two-J model are both applied to fit the experimental magnetic data of 1 and the results indicate the exchange coupling between the type A Ni(II) ions affected by NCS three atoms bridge in 2-mercaptobenzoxazole ligand.     

Two novel lanthanide (Nd, Gd) coordination polymers with chromate anion as building block of the 2D metal oxide

Two novel lanthanide coordination polymers, [Nd(IN)CrO₄]_n (1) and [Gd(IN)CrO₄]_n (2) (HIN = isonicotinic acid), were obtained from the reaction of Ln₂O₃, HIN and K₂Cr₂O₇ under hydrothermal conditions. The single-crystal X-ray diffraction studies reveal that 1 and 2 are isostructural. Compounds 1 and 2 are three-dimensional frameworks consisting of inorganic layers of Ln and pillared by the organic IN. Each anion in the structure binds four Nd(III) ions in an η³,μ₄-pentadentate coordination mode. Measurements of magnetic susceptibilities for Compounds 1 and 2 indicate the presence of antiferromagnetic interactions.     

Ionic Liquid-Supported Bis-(salicylaldimine) Nickel Complexes: Robust and Recyclable Catalysts for Ethylene Oligomerization in Biphasic Solvent System

Two new ionic liquid-supported bis-(salicylaldimine) Ni(II) complexes Ni[2-(O)C₆H₄CH=N(CH₂)₃(methylimidazole)Br]₂ (1) and Ni[3, 5-^tBu₂-2-(O)C₆H₂CH=N(CH₂)₃(methylimidazole)Br]₂ (2) have been synthesized and characterized. Ethylene oligomerizations were carried out with these two complexes in biphasic solvent systems consisting of chloroaluminate ionic liquid and n-heptane or toluene under mild reaction conditions. In the presence of diethylaluminum chloride, both complexes 1 and 2 are highly active for ethylene oligomerization. The olefinic products can be easily separated from the catalytic ionic liquid phase by simple decantation, and the nickel catalysts can be reused in successive ethylene oligomerization cycles. GC-MS analyzes showed that the obtained oligomers contained mainly C4, C6, and C8 olefins.     

A one-step synthesis of protected functionalised titanocene dichlorides

We report a novel, high yield one-step synthesis of water stable and soluble titanocene dichloride dihydrochloride salts from the direct reaction of the neutral amino-substituted cyclopentadienes with TiCl₄. The following novel complexes have been synthesised: C₅H₄(CH₂)₂N(CH₂)₅]₂TiCl₂ (5), [C₅H₄CH(CH₂)₄NMe]₂TiCl₂ (6), [C₅H₄(CH₂)₂N(CH₂)₅]₂TiCl₂·2HCl (7), [C₅H₄CH(CH₂)₄]₂NMeTiCl₂·2HCl (8), [C₅H₄(CH₂)₂N(CH₂)₅]₂TiMe₂ (9).     

Monocarbaborane anion chemistry: use of an anilinyl residue as an anchor group for the construction of rod-like monocarbaboranyl diazo and imino compounds

Reaction of the [1-(4-H₂N–C₆H₄)-closo-1-CB₉H₉]⁻ anion 1 with Me₂CHCH₂CH₂ONO and dilute HCl gives neutral [1-(4-N₂–C₆H₄)-closo-1-CB₉H₉] 3, which reacts with PhNH₂ to form the 19.5 Å [1-{4-(4-H₂N–C₆H₄–NN)–C₆H₄}-closo-1-CB₉H₉]⁻ azo anion 2. Anion 1 with ketones and aldehydes gives imino compounds: with (CH₃)₂CO it gives neutral [1-{4-(Me₂CNH)–C₆H₄}-closo-1-CB₉H₉] 6 and with the para-dialdehyde C₆H₄-1,4-(CHO)₂ it gives the 30.5 Å extended rod-like neutral species [C₆H₄-1,4-{1-(CHNH–C₆H₄)-closo-1-CB₉H₉}₂] 8.     

Single molecule magnet of 2D Salen-type dysprosium coordination polymer

A new flexible Salen-type dysprosium coordination polymer, [Dy₂(H₂L)₂(NO₃)₄(CH₃O)₂]_n (1) (H₂L = N,N′-bis(salicylidene)-1,4-butane-diamine), has been synthesized by a solvothermal method. The single-crystal X-ray diffraction studies reveal that complex 1 features a two dimension (2D) network structure with rare dinuclear units. Each Dy(III) ion is eight-coordinated where the μ₂-(OCH₃)₂ bridged Dy₂O₂ cores are linked by four Salen-type ligands in bidentate fashion. Magnetic studies reveal that complex 1 presents antiferromagnetic interactions between Dy(III) centers and exhibits the frequency dependent peaks, a behavior characteristic of a single-molecule magnet.     

Preparation of high-temperature stable SiBCN fibers from tailored single source polyborosilazanes

Bulk SiBCN ceramics derived from polyborosilazanes of the type [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H; C₂H₄ = CHCH₃, CH₂CH₂) exhibit an exceptional structural stability at high temperature. Therefore, such quaternary systems are of great scientific and technical interest as fibrous reinforcements intended for high-temperature applications. In this context, the design of novel polyborosilazanes, which display properties tailored for the preparation of SiBCN fibers, is studied. Boron-modified polysilazanes of the type [B(C₂H₄SiRNCH₃)₃]_n (1b, R = CH₃; 2b, R = H) are prepared via aminolysis of the tris(dichlorosilylethyl)boranes B(C₂H₄SiRCl₂)₃ (1, R = CH₃; 2, R = H). It is shown that the functionalisation of the precursors with NCH₃ units improves their processability (i.e. solubility) compared to that of their ammonolysed analogs [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H). In addition to the influence of the NCH₃ units, the presence of the SiCH₃ functions in such polymers offers the best potential for the preparation of fibers by melt-spinning. As-spun fibers are then converted under controlled atmosphere into high-temperature stable SiBCN fibers according to the polymer-derived ceramic route.     

Three new polyoxometalate-based hybrids prepared from choline chloride/urea deep eutectic mixture at room temperature

Three new polyoxometalate-based hybrids {[(CH₃)₃N(CH₂)₂OH]₂(H₃O)}[Na₂(H₂O)₆][IMo₆O₂₄]·H₂O 1 , {Na₂[(CH₃)₃N(CH₂)₂OH]₄}[Al(OH)₆Mo₆O₁₈]₂·8NH₂CONH₂·4H₂O 2 and {Na₆(H₂O)₁₈[(CH₃)₃N(CH₂)₂OH]₂(CON₂H₅)₂}[NaMo₇O₂₄]₂·4NH₂CONH₂·H₂O 3 were successfully synthesized in the choline chloride/urea deep eutectic mixture at room temperature. Reactant quantities of water presents in the nonaqueous eutectic mixture solvent may influence the structure of the products. The three compounds are fully characterized by elemental analyses, IR, UV–vis, TG analyses, power X-ray diffraction and single-crystal X-ray diffraction. The photocatalytic properties of 1 and 2 are investigated.     

Synthesis and characterizations of a layered antimony (III) phosphonate: [NH2CH2CH2NH2][Sb2(O3PCH(OH)CO2)2]

In the presence of ethylenediamine template agents, a layered antimony (III) phosphonate, [NH₂CH₂CH₂NH₂][Sb₂{O₃PCH(OH)CO₂}₂] (1) has been synthesized by hydrothermal reaction at 140 °C and characterized by single-crystal X-ray diffraction as well as by infrared spectroscopy, elemental and thermogravimetric analysis. The structure of compound 1 comprises [SbO₄E] trigonal bipyramids (E is the lone pair electrons occupying an axial position) and [O₃PC] tetrahedra connected by [O₃PCH(OH)CO₂]³⁻ to form a 2D layered structure with a one-dimensional channel system, and the ethylenediamine template agent is located inside the channels.     

Single‐Pot Ethane Carboxylation Catalyzed by New Oxorhenium(V) Complexes with N,O Ligands

The oxorhenium(V) chelates [ReOCl(N,O‐L)(PPh₃)] [N,O‐L=(OCH₂CH₂)N(CH₂CH₂OH)(CH₂COO) ( 2 ), (OCH₂CH₂)N(CH₂COO)(CH₂COOCH₃) ( 3 )] and [ReOCl₂(N,O‐L)(PPh₃)] [N,O‐L=C₅H₄N(COO‐2) ( 4 ) C₅H₃N(COOCH₃‐2)(COO‐6) ( 5 )] have been prepared by reaction of [ReOCl₃(PPh₃)₂] ( 1 ), in refluxing methanol, with N,N‐bis(2‐hydroxyethyl)glycine [bicine; N(CH₂CH₂OH)₂(CH₂COOH)], N‐(2‐hydroxyethyl)iminodiacetic acid [N(CH₂CH₂OH)(CH₂COOH)₂], picolinic acid [NC₅H₄(COOH‐2)] or 2,6‐pyridinedicarboxylic acid [NC₅H₃(COOH‐2,6)₂], respectively, with ligand esterification in the cases of 3 and 5 . All these complexes have been characterized by IR and multinuclear NMR spectroscopy, FAB⁺‐MS, elemental and X‐ray diffraction structural analyses. They act as catalysts, in a single‐pot process, for the carboxylation of ethane by CO, in the presence of potassium peroxodisulfate K₂S₂O₈, in trifluoroacetic acid (TFA), to give propionic and acetic acids, in a remarkable yield (up to ca. 30%) and under relatively mild conditions, with some advantages over the industrial processes. The picolinate complex 4 provides the most active catalyst and the carboxylation also occurs, although much less efficiently, by the TFA solvent in the absence of CO. The selectivity can be controlled by the ethane and CO pressures, propionic acid being the dominant product for pressures about ca. 7 and 4 atm, respectively (catalyst 4 ), whereas lower pressures lead mainly to acetic acid in lower yields. These reactions constitute an unprecedented use of Re complexes as catalysts in alkane functionalization.     

A novel organic/inorganic hybrid nanoporous material incorporating Keggin-type polyoxometalates

Tree novel nanoporous compounds, [Cu₃(TMA)₂(H₂O)₃]₄[{(CH₃)₄N}₂(H₂SiMo₁₂O₄₀)] ·≈40H₂O (1), [Cu₃(TMA)₂(H₂O)₃]₄[{(CH₃)₄N}₂(HPW₁₂O₄₀)] ·≈40H₂O (2), and [Cu₃(TMA)₂(H₂O)₃]₄[{(CH₃)₄N}₂(HPMo₆W₆O₄₀)] ·≈40H₂O (3) (TMA=acidtrimesic acid=1,3,5-benzentricaboxylate) have been synthesized via hydrothermal process, and characterized by X-ray structure analysis, IR and NMR spectroscopy, and thermogravimetry. All the compounds crystallize isostructurally consisting of a nanoporous coordination polymer framework [Cu₃(TMA)₂(H₂O)₃]_n accommodating α-Keggin polyoxomolybdate and -tungstate anions. Results of the IR and ²⁹Si and ³¹P MAS NMR spectra reveal the existence of α-Keggin species with no other impurity.