Reactions of pyridyl donors with halogens and interhalogens: an X-ray diffraction and FT-Raman investigation

Three different N-donors L, namely N-ethyl-N′-3-pyridyl-imidazolidine-4,5-dione-2-thione (1), N,N′-bis(3-pyridylmethyl)-imidazolidine-4,5-dione-2-thione (2), and tetra-2-pyridyl-pyrazine (3), bearing one, two and four pyridyl substituents, respectively, have been reacted with halogens X₂ (X = Br, I) or interhalogens XY (X = I; Y = Cl, Br). CT σ-adducts L · nXY, bearing linear N?XY moieties (L = 3; X = I; Y = Br, I; n = 2), and salts containing the protonated cationic donors H_nLⁿ⁺ (L = 1 − 3; n = 1, 2, 4), counterbalanced by Cl⁻, Br⁻, , , , , I₂Br⁻, , or anions, have been isolated. Among the reactions products, (H1⁺)Cl⁻, (H1⁺)Br⁻, , , and 3 · 2IBr have been characterised by single-crystal X-ray diffraction. The nature of the products has been elucidated based on elemental analysis and FT-Raman spectroscopy supported by MP2 and DFT calculations.     

Deprotonated diindolylmethanes as dianionic analogues of scorpionate bis(pyrazolyl)borate ligands: synthesis and structural characterization of representative titanocene and zirconocene complexes

Deprotonation of di(3-methylindol-2-yl)phenylmethane (L₂H₂) or with two equivalents of ⁿBuLi, followed by reactions with Cp₂TiCl₂ or Cp₂ZrCl₂ yielded complexes . Compounds 1-4 were characterized by NMR spectroscopy, and compounds 1, 3, and 4 were further analyzed by X-ray crystallography and elemental analysis. The molecular structures of 1, 3, and 4 illustrate that chelating di(3-methylindol-2-yl)methanes have a structural relationship to coordinated bis(pyrazolyl)borates.     

Tin(IV) complexes obtained by reacting 2-benzoylpyridine-derived thiosemicarbazones with SnCl4 and Ph2SnCl2

Reaction of 2-benzoylpyridine thiosemicarbazone (H2Bz4DH, HL1) and its N(4)-methyl (H2Bz4Me, HL2) and N(4)-phenyl (H2Bz4Ph, HL3) derivatives with SnCl₄ and diphenyltin dichloride (Ph₂SnCl₂) gave [Sn(L1)Cl₃] (1), [Sn(L1)PhCl₂] (2), [Sn(L2)Cl₃] (3), (4) [Sn(L3)PhCl₂] (5) and [Sn(L3)Ph₂Cl] (6). Infrared and ¹H, ¹³C and ¹¹⁹Sn NMR spectra of 1-3, 5 and 6 are compatible with the presence of an anionic ligand attached to the metal through the N_py-N-S chelating system and formation of hexacoordinated tin complexes. The crystal structures of 1-3, 5 and 6 show that the geometry around the metal is a distorted octahedron formed by the thiosemicarbazone and either chlorides or chlorides and phenyl groups. The crystal structure of 4 reveals the presence of and trans [Ph₂SnCl₄]²⁻.     

New divalent samarocenes for butadiene polymerisation: influence of the steric effect and the electron density on the catalytic activity

Two new divalent samarocenes, Cp^*′₂Sm(THF) (1) and (Cp^Ph3)₂Sm(THF) (2) (Cp^*′=C₅Me₄ⁿPr, Cp^Ph3=H₂C₅Ph₃-1,2,4), were synthesized and characterized by ¹H NMR and elemental analysis. The activity of 1 and 2 as butadiene polymerisation catalysts was studied, in the presence of MAO and MMAO, and compared to this of Cp^*₂Sm(THF)₂ (3) and (Cp⁴ⁱ)₂Sm (4) (Cp^*=C₅Me₅, Cp⁴ⁱ=C₅HⁱPr₄), in the same conditions. The 1/MAO system presents the highest activity. The less active 2/MAO system leads to a high cis-1,4 regular structure up to 97%. The MMAO cocatalyst is found very sensitive to the steric hindrance of the samarocenes: the activity decreases from 1/MAO to 1/MMAO, and no activity is observed in the case of complexes 2 and 4, associated to MMAO. Complexes 1 and 2 can be both oxidized with AlMe₃ to give the corresponding Sm/Al bimetallics and , respectively.     

Cyclopentadienyl ruthenium alkynyldithiocarboxylate complexes

Treatment of the ruthenium chloride, CpRu(PPh₃)₂Cl, with the alkynyldithiocarboxylate anions, , in refluxing THF affords the chelate complexes CpRu(PPh₃)(κ²S,S-S₂CCCR) (1) (R = Bu^t (a), Buⁿ (b), Ph (c), SiMe₃ (d)) in high yield. The room temperature reaction of the solvated species, [CpRu(PPh₃)₂(NCPh)]⁺, with the alkynyldithiocarboxylate anions, , produces the chelate complexes 1 and the mono-coordinated complexes CpRu(PPh₃)₂(κS-S₂CCCR) (2). Complexes 2 are converted to 1 in solution so that they were characterized spectroscopically.     

p-Cymene ruthenium thioether complexes

Thioethers PhC₂H₄SMe, PhC₃H₆SⁱPr and MeSAllyl form substitutionally labile monomeric adducts (p-cymene)RuCl₂(SRR′) (2a-c) upon treatment with the {(p-cymene)RuCl₂}₂ dimer (p-cymene = η⁶-MeC₆H₄ⁱPr-1,4). Pure adducts were obtained by crystallization from CH₂Cl₂/Et₂O, and 2a,c as well as the bis(thioether) complex (3) were studied by X-ray crystallography. The trichloro bridged diruthenium complex is formed as a byproduct in the preparation of 3 and was also crystallographically characterized. In solution, pure samples 2a-c equilibrate with free thioether and the dimeric starting complex 1. The amount of 1 present in these mixtures increases with increasing bulk of the thioether substituents. Attempts to thermally replace the cymene ligand by the dangling arene substituent of the thioether ligand of 2a,b failed. Complexes 2a-c as well as the dimethylsufide derivative 2d were studied by cyclic voltammetry and display a close to reversible (2a,c,d) or partially reversible (2b) oxidation near +0.85 V and an irreversible reduction at rather negative potential. New peaks observed after oxidation and reduction point to dissociation of the thioether ligand as the main decomposition pathway of the associated radical cations and anions.     

ipso-and para-Functionalization of meta-terphenyl ligands with substituted methyl groups: Unusual head-to-tail coupling of terphenyl moieties

The synthesis and characterization of several ipso-functionalized derivatives of the bulky terphenyl group are described. These include the primary alcohol Ar′CH₂OH (1), the bromo derivative Ar′CH₂Br (2), and the terphenyl formate Ar′CH₂OC(O)H (3). The alcohol 1 was obtained by treatment of LiAr′ with formaldehyde, and 1 was readily converted to the bromo derivative 2 using HBr. The reaction of 1 with formic acid afforded 3 in good yield. Attempts to form the Grignard derivative of 1, i.e., Ar′CH₂MgBr, resulted in a head-to-tail reaction of the terphenyl benzyl units to yield an unusual coupled product 4. An approach to the avoidance of this coupling involved the synthesis of the terphenyl derivatives and , bearing methyl groups in the para positions of the central aryl ring, which could be prepared in good yield, and converted to their respective lithium salts 7 and 8 without complication . The compounds were characterized by ¹H and ¹³C NMR spectroscopy, IR spectroscopy (1) and X-ray crystallography (2, 4, 5 and 6).     

Synthesis and characterization of aluminum complexes of 2-pyrazol-1-yl-ethenolate ligands

The synthesis and the characterization of some new aluminum complexes with bidentate 2-pyrazol-1-yl-ethenolate ligands are described. 2-(3,5-Disubstituted pyrazol-1-yl)-1-phenylethanones, 1-PhC(O)CH₂-3,5-R₂C₃HN₂ (1a, R = Me; 1b, R = Bu^t), were prepared by solventless reaction of 3,5-dimethyl pyrazole or 3,5-di-tert-butyl pyrazole with PhC(O)CH₂Br. Reaction of 1a or 1b with (R¹ = Me, Et) yielded N,O-chelate alkylaluminum complexes (2a, R = R¹ = Me; 2b, R = Bu^t, R¹ = Me; 2c, R = Me, R¹ = Et). Compound 1a was readily lithiated with LiBuⁿ in thf or toluene to give lithiated species 3. Treatment of 3 with 0.5 equiv of MeAlCl₂ or AlCl₃ yielded five-coordinated aluminum complexes [XAl(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₂] (4, X = Me; 5, X = Cl). Reaction of 5 with an equiv of LiHBEt₃ generated [Al(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₃] (6). Complex 6 was also obtained by reaction of 3 with 1/3 equiv of AlCl₃. Treatment of 5 with 2 equiv of AlMe₃ yielded complex 2a, whereas with an equiv of AlMe₃ afforded a mixture of 2a and [Me(Cl)AlOC(Ph)CH{(3,5-Me₂C₃HN₂)-1}] (7). Compounds 1a, 1b, 2a-2c and 4-6 were characterized by elemental analyses, NMR and IR (for 1a and 1b) spectroscopy. The structures of complexes 2a and 5 were determined by single crystal X-ray diffraction techniques. Both 2a and 5 are monomeric in the solid state. The coordination geometries of the aluminum atoms are a distorted tetrahedron for 2a or a distorted trigonal bipyramid for 5.     

Assembly of cyano-bridged Cu(II)/Cu(II) and Cu(I)/Cu(II) compounds obtained by controlled ration of cyanide

One reaction system of Cu²⁺, dipn, and CN⁻ with two different molar ratio sets of 1:1:5, and 2:1:8 produced two compounds 1 [Cu^II(dipn)][Cu^II(CN)₄], and 2, respectively (dipn = dipropylenetriamine). Their structures were determined by X-ray crystallography. Compound 2 is built from Cu(I) and Cu(II) centers, which are bridged by cyanide groups and metal-metal bonds. The magnetic properties of 1 and 2 were investigated in 2-300 K. Compound 1 exhibits an antiferromagnetic exchange interaction between copper(II) ions mediated by cyano-bridges.     

C2- and Cs-symmetric diamidodichlorotitanium complexes: Syntheses, structures and 1-hexene polymerization catalysis

The complexes l-[CMe₂{CHMeN(2-Prⁱ-C₆H₄)}₂TiCl₂] (2) and (3), C₂- and C_s-symmetric analogues, respectively, of McConville’s C_2v hexene polymerization precatalyst (1), were prepared by high-dilution salt-elimination from the lithium amides and characterized spectroscopically and crystallographically. Complex 2, though less active than 1, was a highly active catalyst of polymerization of 1-hexene when activated by MAO. Complex 3 was inactive under similar conditions. NMR analysis confirmed that there were more mmmm pentads in polymer produced by 2 than in the statistically atactic material produced by 1, though the isotacticity index was not high. The results are interpreted in terms of an isotactic/atactic block structure, caused by syn/anti fluxion of the two 2-isopropylphenyl rings in 2. Kinetic profiles and polydispersities were consistent with a slow initiation step involving monomer, followed by rapid propagation, with some chain transfer to aluminium and only a small extent of β-hydride elimination. The rubber-like polymers were indistinguishable by thermal analysis from those prepared by Ziegler-Natta catalyst systems.     

The A1−xUNbO6−x/2 compounds (x=0, A=Li, Na, K, Cs and x=0.5, A=Rb, Cs): from layered to tunneled structure

Attempts to prepare alkaline metal uranyl niobates of composition A_1−xUNbO_6−x/2 by high-temperature solid-state reactions of A₂CO₃, U₃O₈ and Nb₂O₅ led to pure compounds for x=0 and A=Li (1), Na (2), K (3), Cs (4) and for x=0.5 and A=Rb (5), Cs (6). Single crystals were grown for 1, 3, 4, 5, 6 and for the mixed Na_0.92Cs_0.08UNbO₆ (7) compound. Crystallographic data: 1, monoclinic, P2₁/c, a=10.3091(11), b=6.4414(10), c=7.5602(5) Å, β=100.65(1), Z=4, R₁=0.054 (wR₂=0.107); 3, 5 and 7 orthorhombic, Pnma, Z=8, with a=10.307(2), 10.272(4) and 10.432(3) Å, b=7.588(1), 7.628(3) and 7.681(2) Å, c=13.403(2), 13.451(5) and 13.853(4) Å, R₁=0.023, 0.046 and 0.036 (wR₂=0.058, 0.0106 and 0.088) for 3, 5 and 7, respectively; 6, orthorhombic, Cmcm, Z=8, and a=13.952(3), b=10.607(2) Å, c=7.748(2) Å, R₁=0.044 (wR₂=0.117).The crystal structure of 1 is characterized by layers of uranophane sheet anion topology parallel to the (100) plane. These layers are formed by the association by edge-sharing of chains of edge-shared UO₇ pentagonal bipyramids and chains of corner-shared NbO₅ square pyramids alternating along the [010] direction. The Li⁺ ions are located between two consecutive layers and hold them together; the Li⁺ ions and two layers constitute a neutral “sandwich” {(UNbO₆)⁻-(Li)₂²⁺-(UNbO₆)⁻}. In this unusual structure, the neutral sandwiches are stacked one above another with no formal chemical bonds between the neutral sandwiches.The homeotypic compounds 3, 5, 6, 7 have open-framework structures built from the association by edge-sharing in two directions of parallel chains of edge-shared UO₇ pentagonal bipyramids and ribbons of two edge-shared NbO₆ octahedra further linked by corners. In 3, 5 and 7, the mono-dimensional large tunnels created in the [001] direction by this arrangement can be considered as the association by rectangular faces of two columns of triangular face-shared trigonal prisms of uranyl oxygens. In 3 and 7, all the trigonal prisms are occupied by the alkaline metal, in 5, they are half-occupied. In 6, the polyhedral arrangement is more symmetric and the tunnels created in the [010] direction are built of face-sharing cubes of uranyl oxygens totally occupied by the Cs atoms. This last compound well illustrates the structure-directing effect of the conterion.     

Quaternary ammonium salt-based chromogenic and fluorescent chemosensors for fluoride ions

Chemosensors 5-7 possessing a quaternary ammonium cation (for electrostatic interactions) and an N-H group(s) (for H-bonding) as recognition sites and an anthracene-9,10-dione as both a chromogenic and fluorescent moiety exhibit absorption and emission changes with fluoride ions only. No significant response to other anions such as Cl⁻, Br⁻, I⁻, , CH₃COO⁻, , and is observed. The dual emission at λ_max 580 nm (free 5/6) and λ_max 510 and 540 nm (5/6 + F⁻) in chemosensors 5 and 6 enables ratiometric analysis of fluoride ions.