Synthesis and application of novel ionic phosphine ligands with a cobaltocenium backbone

Six novel ionic phosphine ligands with a cobaltocenium backbone, 1,1′-bis(dicyclohexylphosphino) cobaltocenium hexafluorophosphate () (1a), 1,1′-bis(di-iso-propylphosphino) cobaltocenium hexafluorophosphate () (2a), 1,1′-bis(di-tert-butylphosphino) cobaltocenium hexafluorophosphate () (3a), and the monophosphine ligand (Cc⁺ = cobaltocenium; R = Cy, 1b; R = i-Pr, 2b; R = t-Bu, 3b) were synthesized and characterized by elemental analysis, spectroscopy, and X-ray diffraction techniques. These ligands are air-stable and useful for Suzuki coupling reactions in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (), enabling high catalytic activity.     

Ruthenium (II) complexes of the chelating phosphine borane H2ClB · dppm

Reaction of H₂ClB · PPh₂CH₂PPh₂ (H₂ClB · dppm) with results in displacement of all three acetonitrile ligands and the formation of (1), which has been characterised crystallographically. Reaction with carbon monoxide results in a change from η² to η¹ of the borane ligand to afford (2). Compound 1 undergoes H/D exchange under a D₂ atmosphere to afford , while 2 does not.     

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.     

Synthesis and characterization of new thorium and uranium phenolate complexes

The reaction between the chelating amino bisphenole ligand (ONOO)H₂ (1) and (ONNO)H₂ (2) with an excess of NaH gives the corresponding bis-sodium salts 3 and 4 quantitatively.The salts were reacted with thorium tetrachloride at room temperature to obtain the corresponding (ONOO)ThCl₂ (5) and (ONNO)ThCl₂ (6) complexes.However, ThCl₄ and UCl₄ react with (3) at higher temperatures to give the corresponding isomorphous homoleptic complexes (ONOO)₂Th (7) and (ONOO)₂U (8).We have also synthesized and characterized a thorium salicylaldiminato complex L₃ThCl (11) , in order to study the effect of the bridged ligand on the molecular structure.     

Synthesis and characterization of new, modified terphenyl ligands: Increasing the rotational barrier for flanking rings

The synthesis and characterization of some new terphenyl ligands, modified by meta alkyl substitution on the central ring are described. The new ligands were designed for potential applications in the stabilization of novel low valent main group species or transition metal heteronuclear multiply bonded compounds. Compounds (1), (3) (Mes = 2,4,6-trimethylphenyl), (5) (Trip = 2,4,6-triisopropylphenyl) and (6) (Dipp = 2,6-diisopropylphenyl) were obtained by addition of two equivalents of the corresponding aryl Grignard reagent to the benzyne intermediate generated by lithiation with BuⁿLi of the starting material 2,4-dichloro-5-isopropylcumene, followed by quenching with iodine. The lithium salts of 2 and 4 were obtained treatment of the parent terphenyl iodides with one equivalent of nBuLi. All compounds were isolated as either colorless crystals or as white powders. They were characterized by ¹H and ¹³C NMR spectroscopy and (in the case of 1 and 3) by X-ray crystallography. DFT calculations were performed on model terphenyl molecules in an attempt to estimate how much the rotation barriers of the flanking aryls can be influenced by substitution by alkyl groups of the two meta positions on central ring.     

An anionic chromogenic sensor based on the competition between the anion and a merocyanine solvatochromic dye for calix[4]pyrrole as a receptor site

The interaction of Brooker’s merocyanine (BM), a merocyanine dye, with calix[4]pyrrole (CP) was studied in acetonitrile. BM is violet in solution, but its interaction with CP changes the color of the solution due to the formation of CP-BM species associated through hydrogen bonding. A displacement assay was then carried out in the presence of different anions (F⁻, Cl⁻, Br⁻, I⁻, , , and ). It was verified that F⁻, and to a lesser extent Cl⁻ and , displace BM through the formation of a complex with CP, coloring the solution. Addition of makes the solution almost colorless because it is sufficiently acidic to transfer a proton to BM, removing it from the receptor site in CP and protonating the dye, thereby allowing the visual detection of the anion in relation to the other anions.     

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.     

The importance of cluster fragmentation in the catalytic hydrogenation of phenylacetylene by PtRu5 carbonyl cluster complexes

has been shown to be a catalyst precursor for the hydrogenation of PhC₂H to styrene and ethylbenzene. Three new organometallic products have been found in the catalyst solutions. These are , , and Ru₅(CO)₁₁(μ₄-CCHCPh)(μ₄-HC₂Ph)(μ₃-HC₂Ph) (6). Compounds 4-6 have been synthesized independently and structurally characterized and each one has been tested independently for its ability to produce hydrogenation of PhC₂H catalytically. Compound 4 contains an open square-pyramidal cluster of five ruthenium atoms with one platinum atom bridging an edge of the cluster. It is structurally related to 2 but contains one less CO ligand and two hydrido ligands formed by the addition of one equivalent of hydrogen to the metal cluster. It can be obtained directly from 2 by reaction with hydrogen in the presence of trimethylamine oxide. Compound 5 is a tricoordinated mononuclear platinum complex containing one ligand, one CO ligand and one μ₂-PhC₂H ligand. Compound 5 can be obtained directly from by reaction with PhC₂H under an atmosphere of CO. Compound 6 was obtained from the reaction of Ru₅(CO)₁₅(μ₅-C) with PhC₂H in the presence of UV-Vis irradiation. Compound 6 contains three equivalents of PhC₂H; one is present as triply bridging PhC₂H ligand; one is a quadruply bridging ligand; the third one has formed a bond to the carbido ligand in the center of the metal cluster to form a novel tetra-metallated allyl ligand. Compound 5 has the highest catalytic activity of all three compounds and is believed to be responsible for the vast majority of the catalytic hydrogenation produced from the solutions of 2. Compound 4 is transformed into 5 under the conditions of catalysis.     

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).     

Tris(trimethylsilyl)silyl versus tris(trimethylsilyl)germyl: Radical reactivity and oxidation ability

A comparison of the tris(trimethylsilyl)silyl I and tris(trimethylsilyl)germyl II radical reactivity is provided. Their formation as well as their reactivity encountered in a large variety of chemical processes (addition to double bond, halogen abstraction, peroxyl radical formation…) is examined by laser flash photolysis, quantum mechanical calculations and electron spin resonance (ESR) experiments. The starting compound (TMS)₃GeH is more reactive than (TMS)₃SiH toward the t-butoxyl, the t-butylperoxyl and the phosphinoyl radicals. A similar behavior is noted for an aromatic ketone triplet state. II exhibits a lower absolute electronegativity: accordingly, the addition to electron rich alkenes is less efficient than for I. Radical II is also found less reactive for both the peroxylation and the halogen abstraction reactions. The rearrangement of is slower than for ; this is related to the respective exothermicity of the processes.     

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.     

Adamantane-dipyrromethanes: novel anion receptors

New adamantane-dipyrromethanes (AdD 1-4) were synthesized and their anion binding properties investigated. AdD 1-3 form 2:1 complexes with F⁻ (AdD:F = 2:1) characterized by high association constants, and 1:1 complexes with Cl⁻, Br⁻, and . The binding of Cl⁻, Br⁻, and by AdD 1-3 is 2-3 times stronger than for the reference compound, meso-phenyldipyrromethane (5). However, AdD 4 forms complexes with F⁻ characterized by 1:1 and 1:2 stoichiometry (AdD:F = 1:2).     

Transition metal carbene chemistry 2: kinetic studies on the nucleophilic substitution reactions of (CO)5MC(SCH3)CH3 (M = Cr and W) with morpholine in aqueous acetonitrile

Kinetic studies of the aminolysis of [methyl(thiomethyl)carbene]pentacarbonyl chromium(0),(CO)₅CrC(CH₃)(SCH₃) (1-Cr(S)) and [methyl(thiomethyl)carbene]pentacarbonyltungsten(0), (CO)₅WC(CH₃)(SCH₃) (1-W(S)), with morpholine, a secondary amine, in 50% acetonitrile-50% H₂O (v/v at 25 °C) is reported. The second-order rate constant (k_A in m⁻¹ s⁻¹) increases with amine concentration, giving a linear dependence with an intercept on the rate axis and a tendency towards leveling off at higher amine concentration. The reaction was found to undergo general base catalysis. The mechanism proposed is very similar to those for ester reactions, involving a nucleophilic addition of amine to the substrate to yield a zwitterionic tetrahedral intermediate in the first step, followed by deprotonation to form in the second step, which, in the third step, converted to product by H₂O and/or conjugate acid of the base (BH⁺), assisted MeS⁻ expulsion. The reactivity (k₁) of 1-W(S) was found to be higher than that of 1-Cr(S), whereas, comparable , water catalyzed and , BH⁺ catalyzed, leaving group departure were found for both the carbenes complexes. All these observations have been explained successfully.     

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.     

[{(C5Me5)2Nb}2PdTe4], a heterometallic palladium telluride cluster with a planar PdTe4 fragment

The reaction of (Cp^∗ = η⁵-C₅Me₅) with [Pd(DBA)₂] (DBA = dibenzylidenacetone) and dppm (bis(diphenylphosphanyl)methane) gave the new tetratelluropalladate cluster (1), which has been characterised by means of elemental analysis, FD-MS and X-ray crystallography. The structure of compound 1 contains a planar PdTe₄ rectangle to which two niobocene groups are coordinated. DFT calculations on the hypothetical [PdTe₄]²⁻ anion and comparison of the results with those of the W and Ni homologues show that the planar arrangement of Te ligands in 1 is due to the intrinsic property of the central Pd atom.     

Bimetallic nickel complexes of macrocyclic tetraiminodiphenols and their ethylene polymerization

Schiff’s base condensation of 2,6-diformyl-4-R-phenol and affords 34-membered macrocyclic tetraiminodiphenol compounds, (R = H and R′ = iPr, 1; R = Me and R′ = iPr, 2; R = F and R′ = iPr, 3; R = Me and R′ = Et, 4; R = F and R′ = Et, 5) in good yields (47-62%), from which dinuclear nickel complexes, (R = H and R′ =  iPr, 6; R = Me and R′ = iPr, 7; R = F and R′ = iPr, 8) are prepared. Molecular structures of 2, dipotassium salt of 1, and 7 were confirmed by X-ray crystallography. Addition of B(C₆F₅)₃ to a toluene solution of 6-8 gives insoluble precipitates which show good activity for ethylene polymerization.     

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.     

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⁻.