A new application of cerium(IV) ammonium nitrate [(NH4)2Ce(NO3)3] in fullerene chemistry—free-radical alkoxylation of C60 fullerene on reaction with primary alcohols

The reaction of [60]fullerene with primary aliphatic alcohols (ROH, R = Et, Me, Pr) mediated by cerium(IV) ammonium nitrate [(NH₄)₂Ce(NO₃)₃] affords the corresponding alkoxy-derivatives with a hydroxy group, C₆₀(OR)_x(OH) (x = 3, 4) in high yield. The reaction is characterized by a free radical mechanism confirmed by an EPR study of the alkoxy fullerenyl radical (g = 2.0023).     

Synthesis and structural characterization of (COT)Pr(C13H8CH2CH2OMe)(THF) containing the chelating 9-(2-methoxyethyl)fluorenyl ligand

Treatment of 9-(2-methoxyethyl)fluorene, C₁₃H₉CH₂CH₂OMe (1), with potassium hydride in THF/toluene in the presence of 18-crown-6 afforded orange-red crystalline K(18-crown-6)C₁₃H₈CH₂CH₂OMe (2) in 59% yield. A “constrained geometry”-type praseodymium complex containing the 9-(2-methoxyethyl)fluorenyl ligand, (COT)Pr(C₁₃H₈CH₂CH₂OMe)(THF) (3), was prepared by treatment of dimeric [(COT)Pr(μ-Cl)(THF)₂]₂ (COT = η⁸-cyclooctatetraenyl) with in situ prepared KC₁₃H₈CH₂CH₂OMe. The molecular structures of 1, 2, and 3 were determined by single-crystal X-ray diffraction.     

Synthesis and structure of chiral-at-metal complexes with the ligand (S)-2-[(Sp)-2-(diphenylphosphino)ferrocenyl]-4-isopropyloxazoline

Half-sandwich complexes of formula [(ηⁿ-ring)MClL]PF₆ [L = (S)-2-[(S_p)-2-(diphenylphosphino)ferrocenyl]-4-isopropyloxazoline; (ηⁿ-ring)M = (η⁵-C₅Me₅)Rh; (η⁵-C₅Me₅)Ir; (η⁶-p-MeC₆H₄iPr)Ru; (η⁶-p-MeC₆H₄iPr)Os] have been prepared and spectroscopically characterised. The molecular structures of the rhodium and iridium compounds have been determined by X-ray crystallography. The related solvate complexes [(η⁵-C₅Me₅)ML(Me₂CO)]²⁺ (M = Rh, Ir) are active catalysts for the Diels-Alder reaction between methacrolein and cyclopentadiene.     

Thermal low spin-high spin equilibrium of Fe(II) in thiospinels CuFe0.5(Sn(1−x)Tix)1.5S4 (0≤x≤1)

A series of spinel compounds with composition CuFe_0.5(Sn_(1−x)Ti_x)_1.5S₄ (0≤x≤1) is analysed by X-ray diffraction, measurements of magnetic susceptibilities and ⁵⁷Fe Mössbauer spectroscopy. All samples show a temperature-dependent equilibrium between an electronic low spin 3d(t_2g)⁶(e_g)⁰ and a high spin 3d(t_2g)⁴(e_g)² state of the Fe(II) ions. The spin crossover is of the continuous type and extends over several hundred degrees in all samples. The Sn/Ti ratio influences the thermal equilibrium between the two spin states. Substitution of Sn(IV) by the smaller Ti(IV) ions leads to a more compact crystal lattice, which, in contrast to many metal-organic Fe(II) complexes, does not stabilise the low spin state, but increases the residual high spin fraction for T→0 K. The role played by antiferromagnetic spin coupling in the stabilisation of the high spin state is discussed. The results are compared with model calculations treating the effect of magnetic interactions on spin state equilibria.     

Isolation and single crystal study of [Nb2(μ-OMe)2(OiPr)8]. Can alcohol interchange provide the homoleptic niobium isopropoxide?

Niobium isopropoxide, Nb(OⁱPr)₅, is an attractive precursor of simple and complex niobium oxides in sol-gel technology. This compound cannot, unfortunately, be obtained by alcohol interchange starting from linear chain homologues such as Nb(OMe)₅ or Nb(OEt)₅. The equilibrium in the latter reaction favours formation of mixed-ligand complexes, [Nb₂(OR)₂(OⁱPr)₈], R = Me, Et. In particular, [Nb₂(OMe)₂(OPrⁱ)₈] (1) has been isolated in high yield from repeated treatment of Nb₂(OMe)₁₀ with excess of isopropanol. The X-ray single crystal study reveals a dinuclear structure containing a pair of edge-sharing octahedra with methoxide ligands in the bridging position. Infrared (IR) and mass spectroscopy (MS) studies confirmed the incomplete ligand substitution. The ¹H-NMR spectra suggest equilibrium between different molecular forms in solution. Solvothermal interaction of 1 with La chips in toluene/isopropanol media results in formation of a mixture of LaNb₂(OⁱPr)₁₃ and La₂Nb₄(μ₄−O)₄(OH)₂(μ−OⁱPr)₈(OⁱPr)₈ (2). Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorised users.     

Syntheses of platinum(II) complexes of cyclo-octenyl group and isolation of a self-assembled oxo-bridged macrocyclic complex [Pt4(Spy)4(C8H12-O-C8H12)2]

Reactions of [Pt₂(μ-Cl)₂(C₈H₁₂OMe)₂] (1) (C₈H₁₂OMe = 8-methoxy-cyclooct-4-ene-1-yl) with various anionic chalcogenolate ligands have been investigated. The reaction of 1 with Pb(Spy)₂ (HSpy = pyridine-2-thiol) yielded a binuclear complex [Pt₂(Spy)₂(C₈H₁₂OMe)₂] (2). A trinuclear complex [Pt₃(Spy)₄(C₈H₁₂OMe)₂] (3) was isolated by a reaction between 2 and [Pt(Spy)₂]_n. The reaction of 1 with HSpy in the presence of NaOMe generated 2 and its demethylated oxo-bridged tetranuclear complex [Pt₄(Spy)₄(C₈H₁₂-O-C₈H₁₂)₂] (4). Treatment of 1 with ammonium diisopropyldithiophosphate completely replaced C₈H₁₂OMe resulting in [Pt(S₂P{OPrⁱ}₂)₂] (5), whereas non-rigid 5-membered chelating ligand, Me₂NCH₂CH₂E⁻, produced mononuclear complexes [Pt(ECH₂CH₂NMe₂)(C₈H₁₂OMe)] (E = S (6), Se (7)). These complexes have been characterized by elemental analyses, NMR (¹H, ¹³C{¹H}, ¹⁹⁵Pt{¹H}) and absorption spectroscopy. Molecular structures of 2, 3, 4, 5 and 7 were established by single crystal X-ray diffraction analyses. Thermolysis of 2, 6 and 7 in HDA gave platinum nanoparticles.     

Syntheses, structures and magnetic properties of heterometal hexanuclear [Mn2Ln4] complexes

Heterometal hexanuclear manganese-lanthanide complexes, [Mn^III₂Ln^III₄(μ₄-O)₂(Hbemp)₂(OMe)₂(OAc)₈]·nH₂O (Ln = Lu (1, n = 1) and Tm (2, n = 5), H₃bemp = 2,6-bis[N-(2-hydroxyethyl)iminomethyl]-4-methylphenol), were prepared and their magnetic properties were examined. The Mn₂Ln₄ units at the cluster cores consist of one central Mn^III₂Ln^III₂O₄ cubane unit and two lanthanide(III) ions bridged by μ₂-phenoxo groups of the ligands, and μ₂-methoxo and μ₄-oxo groups, forming the Mn₂Ln₄ hexanuclear cluster. Magnetic susceptibility measurements revealed that antiferromagnetic interactions were operative between metal centres.     

Titanium (IV) complexes based on substituted 2-[(2-hydroxyethyl)]aminophenols

Novel substituted 2-[(2-hydroxyethyl)]aminophenols, MeN(CHR¹CR²R³OH)(C₆H₄-o-OH) (2-5), were synthesized by the reaction of 2-methylaminophenol with corresponding oxiranes. Titano-spiro-bis(ocanes) [MeN(CHR¹CR²R³O)(C₆H₄-o-O)]₂Ti 6-9 (2, 6, R¹ = H, R² = R³ = Me; 3, 7, R¹ = R² = Ph (treo-), R³ = H; 4, 8, R¹ = Ph, R² = R³ = H; 5, 9, R¹ = R² = H, R³ = Ph) based on [ONO]-ligands have been synthesized. The obtained compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis data. The complex [Ti(μ²-O){O-o-C₆H₄}{μ²-CMe₂CH₂}NMe]₆ (10) was obtained by controlled hydrolysis of 6. Molecular structure of 10 was determined by X-ray structure analysis.     

Ruthenium(III) complexes of amine-bis(phenolate) ligands as catalysts for transfer hydrogenation of ketones

Twelve ruthenium(III) complexes bearing amine-bis(phenolate) tripodal ligands of general formula [Ru(L¹–L³)(X)(EPh₃)₂] (where L¹–L³ are dianionic tridentate chelator) have been synthesized by the reaction of ruthenium(III) precursors [RuX₃(EPh₃)₃] (where E = P, X = Cl; E = As, X = Cl or Br) and [RuBr₃(PPh₃)₂(CH₃OH)] with the tripodal tridentate ligands H₂L¹, H₂L² and H₂L³ in benzene in 1:1 molar ratio. The newly synthesized complexes have been characterized by analytical (elemental and magnetic susceptibility) and spectral methods. The complexes are one electron paramagnetic (low-spin, d⁵) in nature. The EPR spectra of the powdered samples at RT and the liquid samples at LNT shows the presence of three different ‘g’ values (g_x ≠ g_y ≠ g_z) indicate a rhombic distortion around the ruthenium ion. The redox potentials indicate that all the complexes undergo one electron transfer process. The catalytic activity of one of the complexes [Ru(pcr-chx)Br(AsPh₃)₂] was examined in the transfer hydrogenation of ketones and was found to be efficient with conversion up to 99% in the presence of isopropanol/KOH.     

Syntheses and crystal structures of binuclear ruthenium complexes bearing 1,8′-bis(diphenylphosphinomethyl)naphthalene

Treatment of [RuCl₂(η⁶-C₆H₆)]_x with bidentate phosphine ligand BDNA [1,8-bis(diphenylphosphinomethyl)naphthalene] in methanol at room temperature gave η⁶-benzene-ruthenium complexes Ru₂Cl₄(η⁶-C₆H₆)₂(μ-BDNA) (1). Complex 1 further reacted with AgBF₄ to form complex [Ru₂Cl₂(μ-Cl)(η⁶-C₆H₆)₂(μ-BDNA)](BF₄) (2). [RuCl₂(η⁶-C₆H₆)]_x reacted with BDNA in refluxing methanol and then the reaction solution was treated with AgBF₄ to generate complex [Ru₂Cl₂(η⁶-C₆H₆)₂(μ-BDNA)₂](BF₄)₂ (3). Their compositions and structures had been determined by elemental analyses, NMR spectra and single crystal X-ray diffractions. X-ray diffraction showed that complex 1 belonged to monoclinic crystal system, P2₁/c space group with Z = 4, a = 12.810 Å, b = 21.507 Å, c = 18.471 Å, β = 107.95°; complex 2 belonged monoclinic crystal system, P2₁/n space group with Z = 4, a = 14.498 Å, b = 15.644 Å, c = 20.788 Å, β = 103.404°, and complex 3 belonged to monoclinic crystal system, P2₁/n space group with Z = 2, a = 13.732 Å, b = 14.351 Å, c = 19.733 Å, β = 94.82°.     

Synthesis and structural characterization of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)C(Ph)], generated via an alkyne-Ti benzyne coupling reaction

The thermolysis of [(C₅H₄)SiMe₂(N-t-Bu)]TiPh₂ in the presence of diphenylacetylene proceeds at 80 °C in cyclohexane solution with the sole formation of the titanacyclic complex [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph)C(Ph)], which has been characterized by solution NMR measurements and X-ray crystallographic analysis. This reaction is accompanied by the elimination of benzene and presumably occurs via coupling of a titanium benzyne intermediate with diphenylacetylene. The two chemically inequivalent Ti-C bonds of 2.081(7) and 2.103(6) Å in [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph)C(Ph)] reflect the increased electrophilicity of the d⁰ Ti(IV) center arising from the presence of the bifunctional ansa-cyclopentadienyldimethylsilylamido ligand.     

Synthesis,structure and thermal properties of polynuclear complexes with a new multidentate ligand, N,N′-bis(5-ethyl-1,3,4-thiadiazol-2-yl)-2,6-pyridinedicarboxamide

Based on N,N′-bis(5-ethyl-1,3,4-thiadiazol-2-yl)-2,6-pyridinedicarboxamide (H₂L) and inorganic Zn^II and Cd^II salts, three polynuclear complexes [Zn₆(μ₄-O)₂(L)₄] (1), [Zn₃(μ₃-O)₂(L)₂(H₂L)] (2) and [Cd₅(μ₃-O)₂(L)₃(H₂L)(CH₃OH)(DMF)] (3) have been prepared and their crystal structures have been determined by single-crystal X-ray analysis. The thermal behaviors of these complexes in nitrogen and the thermal decomposition kinetics of complex 2 in the temperature range 350–540 °C have been studied, and kinetic parameters were also obtained. Kinetic results show that the decomposition of complex 2 is double-step reaction: a 1st-order reaction (F1) is followed by an nth-order reaction (Fn).     

Cu(II) and Pd(II) complexes of N-(2-hydroxybenzyl)aminopyridines

N-(2-Hydroxybenzyl)aminopyridines (Lⁱ) react with Cu(II) and Pd(II) ions to form complexes in the compositions Cu(Lⁱ)₂(CH₃COO)₂ · nH₂O (n = 0, 2, 4), Pd(Lⁱ)₂Cl₂ · nC₂H₅OH (n = 0, 2) and Pd(L²)₂Cl₂ · 2H₂O. In the complexes, the ligands are neutral and monodentate which coordinate through pyridinic nitrogen. Crystal data of the complexes obtained from 2-amino pyridine derivative have pointed such a coordinating route and comparison of the spectral data suggests the validity of similar complexation modes of other analog ligands. Cu(II) complex of N-(2-hydroxybenzyl)-2-aminopyridine (L¹), [Cu(L¹)₂(CH₃COO)₂] has slightly distorted square planar cis-mononuclear structure which is built by two oxygen atoms of two monodentate carboxylic groups disposed in cis-position and two nitrogen atoms of two pyridine rings. The remaining two oxygen atoms of two carboxylic groups form two Cu and H bridges containing cycles which joint at same four coordinated copper(II) ion. IR and electronic spectral data and the magnetic moments as well as the thermogravimetric analyses also specify on mononuclear octahedric structure of complexes [Cu(L²)₂(CH₃COO)₂ · 2H₂O] and [Cu(L³)₂(CH₃COO)₂ · 4H₂O] where L² and L³ are N-(2-hydroxybenzyl)-2- or 3-aminopyridines, respectively.     

Phospha(III)guanidinate complexes of titanium(IV) and zirconium(IV) amides

Two procedures for the synthesis of group 4 phosphaguanidine compounds M(R₂PC{NR′}₂)(NR″₂)₃ (M = Ti, Zr; R = Ph, Cy; R′ = ⁱPr, Cy; R″ = Me, Et) are described. Spectroscopic characterization indicated symmetrical bonding of the phosphaguanidinate ligand in solution for the P-diphenyl derivatives whereas the P-dicyclohexyl analogs adopt a more rigid geometry with inequivalent N_amidine substituents within the phosphaguanidinate ligand. X-ray diffraction studies show exclusively monomeric tbp metal centers for a series of derivatives, with a chelating phosphaguanidinate ligand that spans an axial and an equatorial position. Two different conformers have been identified in the solid-state that differ in the relative orientation of the phosphorus R₂P–C substituents with respect to the equatorial plane of the tbp metal. The synthetic protocol was extended to the bimetallic complex, [PhP(C{NⁱPr}₂Ti{NMe₂}₃)CH₂–]₂, which was characterized by crystallography as the meso-form.     

One-electron redox reactions involving chromium(0) and molybdenum(0) bis-1,3,5-trimethylbenzene derivatives

The reaction of M(η⁶-1,3,5-Me₃C₆H₃)₂, M = Cr, Mo, with the tetrahalides of Groups 4 and 5 elements proceeds with the monoelectronic oxidation of the metal bis-arene to the [M(η⁶-Me₃C₆H₃)₂]⁺ cation. In the case of MX₄, M = Ti, X = Cl, Br, M = V, X = Cl, and of Nb₂Cl₁₀ the reduction products are the titanium(III), vanadium(III) halides and the niobium(IV) chloride, isolated as the solvate anions [MCl₄(THF)₂]⁻ and [NbCl₄(CH₃CN)]⁻. The reaction of the tetrachloro complexes MCl₄(THF)₂, M = Zr, Hf, with Cr(η⁶-1,3,5-Me₃C₆H₃)₂ in THF produces the ionic [Cr(η⁶-1,3,5-Me₃C₆H₃)₂][MCl₅(THF)], which has been characterized by single-crystal X-ray diffraction in the case of hafnium.     

Mechanistic Studies on the Oxidation of Hydroquinone by an Oxo-bridged Diiron(III,III) Complex in Weakly Acidic Aqueous Media

The kinetics of oxidation of hydroquinone (H₂Q) by a μ-oxo-bridged diiron(III,III) complex, Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) has been investigated in aqueous media at 25.0 °C in presence of an excess of 1,10-phenanthroline (phen). The overall redox rate increases with increase in [H⁺]. The title complex (1) and its conjugate bases, [Fe₂(μ-O)(phen)₄(OH)₂]³⁺(2) and [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3), participate in the reaction with H₂Q as the only kinetically reactive reducing species. Rate constants (in dm³ mol⁻¹ s⁻¹) for the parallel reactions (1) + H₂Q → Products, (2) + H₂Q → Products and that for (3) + H₂Q → Products are, respectively, 500 ± 40, 100 ± 6 and 30 ± 2. Substantial rate retardation in D₂O media in comparison to that in H₂O media suggests that electron transfer is coupled with proton movements in the rate-determining step.     

Reversible oxidative addition of a diaryl diselenide to a diorganopalladium(II) complex, carbon-selenium bond formation at palladium(IV), and structural studies of palladium(II) and platinum(IV) selenolates

Methyl(4-methoxyphenyl)(2,2^′-bipyridine)palladium(II) (1) reacts with bis(4-chlorophenyl) diselenide in dichloromethane to form an equilibrium with the Pd(IV) complex Pd(SeC₆H₄Cl)₂Me(C₆H₄OMe)(bpy) (2) for which the forward reaction exhibits ΔH=−130±12 kJ mol⁻¹ and ΔS=−472±49 J K⁻¹ mol⁻¹, and with K=754±145 at −25 °C. The Pd(IV) complex is isolable at −40 °C, and when the equilibrium mixture is kept at −25 °C, a temperature at which the Pd(II) complex is stable, selective reductive elimination of Me-SeC₆H₄Cl occurs very slowly from the Pd(IV) complex to form Pd(SeC₆H₄Cl)(C₆H₄OMe)(bpy) (3). In contrast, (ClC₆H₄Se)₂ reacts with PdMe₂(dmpe) (4) [dmpe=1,2-bis(dimethylphosphino)ethane] to form Pd(SeC₆H₄Cl)Me(dmpe) (5) and Me-SeC₆H₄Cl. A second equivalent of (ClC₆H₄Se)₂ reacts with 5 to cleave the second Pd-Me bond to give Pd(SeC₆H₄Cl)₂(dmpe) (6) and Me-SeC₆H₄Cl. Similarly, PdMeTol(dmpe) (7) (Tol=4-tolyl) forms predominantly Pd(SeC₆H₄Cl)Tol(dmpe) (8) together with some Pd(SeC₆H₄Cl)Me(dmpe) (5), and 8 reacts with (ClC₆H₄Se)₂ to form Pd(SeC₆H₄Cl)₂(dmpe) (6) and Tol-SeC₆H₄Cl. Bis(4-chlorophenyl) diselenide reacts with PtTol₂(bpy) (9) (Tol=4-tolyl) to form Pt(SeC₆H₄Cl)₂Tol₂(bpy) (10) which, together with 2, has a trans-configuration for the selenolate ligands. X-ray structural studies of octahedral 10 as the solvate 10 · 3CHCl₃ and square planar 5 are reported.     

Trinuclear Schiff base complexes with uranium(V) and copper(II) or zinc(II) ions

Treatment of the uranium(IV) complexes [{ML¹(py)}₂U^IV] (M = Cu, Zn; L¹ = N,N′-bis(3-hydroxysalicylidene)-1,3-propanediamine) with silver nitrate in pyridine led to the formation of the corresponding cationic uranium(V) species which were found to be thermally unstable and were converted back into the parent U^IV complexes; no electron transfer was observed in solution between the U^IV and U^V compounds. In the crystals of [{ML¹(py)}₂U^IV][{ML¹(py)}₂U^V][NO₃], the neutral U^IV and cationic U^V species are clearly identified by the distinct U–O distances. Similar reaction of [{ZnL²(py)}₂U^IV] [L² = N,N′-bis(3-hydroxysalicylidene)-1,4-butanediamine] with AgNO₃ gave crystals of [{ZnL²(py)}U^V{ZnL²(py)₂}][NO₃] but the copper counterpart was not isolated. Crystals of [{ZnL¹(py)}₂U^V][OTf] · THF (OTf = OSO₂CF₃) were obtained fortuitously from the reaction of [Zn(H₂L¹)] and U(OTf)₃.     

A new [Ni4] distorted cubane assembly on four solvent derived μ3-OMe corners: Solvent dependent formation and cleavage of exogenous bridges

A new Ni₄ distorted cubane complex [Ni₄(μ₃-OMe)₄Q₄(MeOH)₄] (1) (where Q⁻ is the anion of 8-quinolinol) is obtained from the reaction of NaQ with Ni(OAc)₂ · 4H₂O in refluxing MeOH via solvent derived μ₃-OMe assisted self-assembly of four nickel(II) centres. The periphery of [Ni₄(OMe)₄] cubane is covered by four Q⁻ and four MeOH molecules. This methanol specific reaction is not supported in solvent glycinol (Hgl; NH₂(CH₂)₂OH), an amine substituted ethanol, producing monomeric [NiQ₂(Hgl)₂] · 2H₂O (2 · 2H₂O) instead and is able to cleave 1 to yield 2 · 2H₂O. The cryomagnetic susceptibility data of powdered 1 can be modeled by a two J equation yielding J₁ = −1.8(1) cm⁻¹, J₂ = 3.9(1) cm⁻¹ and g = 2.24.     

Catalytic ammonolytic sol-gel preparation of a mesoporous silicon aluminium nitride from a single-source precursor

A high-surface-area microporous silicon aluminum imide gel Al₃SiN₂(NH)_w(NH₂)_x(NMe₂)_y(NⁱPr)_z was prepared via catalytic ammonolysis of tetrakis(isopropylimino)bis[tris(dimethylamino)silylamino]alane H₆Al₆(NⁱPr)₄[NSi(NMe₂)₃]₂. Pyrolysis of the gel under NH₃ flow at 1000 °C gave an amorphous Si-Al-N ceramic composite in which silicon is tetrahedrally coordinated with nitrogen. Aluminum is mainly present as mixed AlN₄ species. The Si-Al-N ceramic composite exhibits a mesoporous structure with relatively high surface area (114 m² g⁻¹) and narrow pore size distribution (2-8 nm).