Anion Receptors Containing ‐NH Binding Sites: Hydrogen‐Bond Formation or Neat Proton Transfer?

When the amide‐containing receptor 1 ⁺ is in a solution of dimethyl sulfoxide (DMSO) in the presence of basic anions (CH₃COO^?, F^?, H₂PO₄^?), it undergoes deprotonation of the ‐NH fragment to give the corresponding zwitterion, which can be isolated as a crystalline solid. In the presence of less basic anions (Cl^?, Br^?, NO₃^?), 1 ⁺ establishes true hydrogen‐bond interactions of decreasing intensity. The less acidic receptor 2 ⁺ undergoes neat proton transfer with only the more basic anions CH₃COO^? and F^?, and establishes hydrogen‐bond interactions with H₂PO₄^?. An empirical criterion for discerning neutralisation and hydrogen bonding, based on UV/Vis and ¹H NMR spectra, is proposed.     

Janus‐Like Squaramide‐Based Hosts: Dual Mode of Binding and Conformational Transitions Driven by Ion‐Pair Recognition

New tripodal squaramide‐based hosts have been synthesised and structurally characterised by spectroscopic methods. In 2.5 % (v/v) [D₆]DMSO in CDCl₃, compound 4 formed dimeric assemblies [log K_dim=3.68(8)] as demonstrated by ¹H NMR spectroscopy and UV dilution experiments. AFM and SEM analyses revealed the formation of a network of bundled fibres, which indicates a preferential mechanism for aggregation. These C₃‐symmetric tripodal hosts exhibited two different and mutually exclusive modes of binding, each one easily accessible by simultaneous reorientation of the squaramide groups. In the first, a convergent disposition of the NH squaramide protons allowed the formation of an array of N? H???X^? hydrogen bonds with anions. In the second mode, reorientation of carbonyl squaramide groups allowed multiple C?O???H interactions with ammonium cations. The titration of 4 with different tetraalkylammonium iodides persistently showed the formation of 1:1 complexes, as well as 1:2 and 1:3 complexes. The corresponding stoichiometries and binding affinities of the complexes were evaluated by multi‐regression analysis. The formation of high‐order complexes, supported by ROESY, NOESY and mass spectrometry experiments, has been attributed to the insertion of NR₄I ion pairs between the carbonyl and NH protons of the squaramide groups located in adjacent arms of 4 . The observed effects reflect the induction of significant conformational changes in the hosts, mainly in relation to the relative orientation of the squaramide groups adapting their geometries to incoming ion‐pair complementary substrates. The results presented herein identify and fully describe two different modes of ion‐pair recognition aimed at directing conformational transitions in the host, therefore establishing a base for controlling more elaborate movements of molecular devices through ion‐pair recognition.     

Ligand‐Centred Reactivity of Bis(picolyl)amine Iridium: Sequential Deprotonation,Oxidation and Oxygenation of a “Non‐Innocent” Ligand

Treatment of [Ir(bpa)(cod)]⁺ complex [ 1 ]⁺ with a strong base (e.g., tBuO^?) led to unexpected double deprotonation to form the anionic [Ir(bpa?2H)(cod)]^? species [ 3 ]^?, via the mono‐deprotonated neutral amido complex [Ir(bpa?H)(cod)] as an isolable intermediate. A certain degree of aromaticity of the obtained metal–chelate ring may explain the favourable double deprotonation. The rhodium analogue [ 4 ]^? was prepared in situ. The new species [M(bpa?2H)(cod)]^? (M=Rh, Ir) are best described as two‐electron reduced analogues of the cationic imine complexes [M^I(cod)(Py‐CH₂‐N?CH‐Py)]⁺. One‐electron oxidation of [ 3 ]^? and [ 4 ]^? produced the ligand radical complexes [ 3 ]^. and [ 4 ]^.. Oxygenation of [ 3 ]^? with O₂ gave the neutral carboxamido complex [Ir(cod)(py‐CH₂‐N‐CO‐py)] via the ligand radical complex [ 3 ]^. as a detectable intermediate.     

Synthesis of novel zirconium complexes bearing mono‐Cp and tridentate Schiff base [ONO] ligands and their catalytic activities for olefin polymerization

A series of novel zirconium complexes {R²Cp[2‐R¹‐6‐(2‐CH₃OC₆H₄N?CH)C₆H₃O]ZrCl₂ ( 1 , R¹ = H, R² = H, 2 : R¹ = CH₃, R² = H; 3 , R¹ = ^tBu, R² = H; 4 , R¹ = H, R² = CH₃; 5 , R¹ = H, R² = n‐Bu)} bearing mono‐Cp and tridentate Schiff base [ONO] ligands are prepared by the reaction of corresponding lithium salt of Schiff base ligands with R²CpZrCl₃·DME. All complexes were well characterized by ¹H NMR, MS, IR and elemental analysis. The molecular structure of complex 1 was further confirmed by X‐ray diffraction study, where the bond angle of Cl? Zr? Cl is extremely wide [151.71(3)°]. A nine‐membered zirconoxacycle complex Cp(O? 2? C₆H₄N?CHC₆H₄‐2? O)ZrCl₂ ( 6 ) can be obtained by an intramolecular elimination of CH₃Cl from complex 1 or by the reaction of CpZrCl₃·DME with dilithium salt of ligand. When activated by excess methylaluminoxane (MAO), complexes 1–6 exhibit high catalytic activities for ethylene polymerization. The influence of polymerization temperature on the activities of ethylene polymerization is investigated, and these complexes show high thermal stability. Complex 6 is also active for the copolymerization of ethylene and 1‐hexene with low 1‐hexene incorporation ability (1.10%). Copyright © 2006 John Wiley & Sons, Ltd.     

Umsetzung von N-Trimethylmetall(IVb)-trialkylphosphiniminen mit Halogenwasserstoffen

Reaction of N-Trimethylmetal(IVb) Trialkylphosphine Imines with Hydrogen Halides Investigations of the reaction of N-trimethylmetal(IVb)-substituted phosphine imines with hydrogen have been carried out. With one mole of HX phosphonium halides of the general formula [R₃P? NH? MMe₃]^⊕X^? (R = CH₃, C₂H₅; M = Si, Ge, Sn; X = Cl, Br, J) are obtained. A second mole of HX causes M? N bond cleavage, yielding aminophosphonium halides, [R₃P? NH₂]^⊕X^?.     

Relationships between the acidity of the Z and E isomers of N-Nitroso-N-alkyl-α-amino acids and their conformations

The acidity constants of both Z and E conformational isomers of five N-nitroso-N-alkyl-α-amino acids, ON? N(R₁)? CH(R₂)? COOH, are determined by the observation of selected pH titrated ¹H NMR signals. For two glycine derivatives (1, R₁?CH₃, R₂?H, ON? Sar; 2, R₁?C₂H₅, R₂?H, ON? EtGly) and two alanine derivatives (3, R₁?CH₃, R₂?CH₃, ON? MeAla; 4, R₁?C₂H₅, R₂?CH₃, ON? EtAla) the E isomers appear to be stronger acids than the Z while for the third alanine derivative (5, R₁?n-C₃H₇, R₂?CH₃, ON? PrAla) the opposite is observed. These results, also including anisotropy effects associated with the N? NO group, are discussed in terms of conformations. A 7-membered ring conformation with an ? NO…HOOC? intramolecular hydrogen bond is proposed to be statistically important in the Z isomers of 1, 2, 3 and, to a lesser extent, 4.     

Head‐to‐Tail Intermolecular Hydrogen Bonding of OH and NH Groups with Fluoride

To explore the anion‐recognition ability of the phenolic hydroxyl group and the amino hydrogen, we synthesized three different acridinedione (ADD) based anion receptors, 1 , 2 and 3 , having OH, NH, and combination of OH and NH groups, respectively. Absorption, emission and ¹H NMR spectral studies revealed that receptor 1 , having only a phenolic OH group, shows selective deprotonation of the hydroxyl proton towards F^?, which results in an “ON–OFF”‐type signal in the fluorescence spectral studies. Receptor 2 , which only has an amino hydrogen, also shows deprotonation of the amino hydrogen with F^?, whereas receptor 3 (having both OH and NH groups) shows head‐to‐tail intermolecular hydrogen bonding of OH and NH groups with F^? prior to deprotonation. The observation of hydrogen bonding of the OH and NH groups in a combined solution of 1 and 2 with F^? in a head‐to‐tail hetero‐intermolecular fashion, and the absence of head‐to‐head and tail‐to‐tail intermolecular hydrogen bonding in 1 and 2 with F^?, prove that the difference in the acidity of the OH and NH protons leads to the formation of an intermolecular hydrogen‐bonding complex with F^? prior to deprotonation. The presence of this hydrogen‐bonding complex was confirmed by absorption spectroscopy, 3D emission contour studies, and ¹H NMR titration.     

New anticancer zinc(II) complexes comprising thiosemicarbazones of saturated ring: structure,DNA/protein binding,DNA cleavage,topoisomerase‐1 inhibition and anti‐proliferation studies

The reaction of the thiosemicarbazones (CH₂)₄C?NN(H)C(?S)NHR (R = H, Me) with zinc(II) acetate in methanolic solution proceeds readily under mild conditions to form stable mononuclear complexes Zn[(CH₂)₄C?NN?C(S)NHR]₂. DNA interaction studies show that the zinc(II) complexes bind to DNA via groove mode and exhibit efficient DNA cleavage activity in the presence of hydrogen peroxide. Also, the complexes display a binding affinity to bovine serum albumin protein with K_BSA values of ca 10⁵ M^?1. Topoisomerase catalytic inhibition studies suggest that both complexes are efficient topoisomerase‐I impeders. Furthermore, the anti‐proliferative effects of the two complexes on five human tumor cell lines (Caki‐2, MCF‐7, CaSki, NCI‐H322M and Co‐115) indicate that both complexes have the potential to act as effective anticancer drugs. Copyright © 2016 John Wiley & Sons, Ltd.     

Dual Role of the 1,2,3‐Triazolium Ring as a Hydrogen‐Bond Donor and Anion–π Receptor in Anion‐Recognition Processes

Several bis(triazolium)‐based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side‐arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen‐bond donor, the other as an anion–π receptor. Receptors 9²⁺?2BF₄ ^? (C₆H₅), 11²⁺?2BF₄ ^? (4‐NO₂?C₆H₄), and 13²⁺?2BF^4? (ferrocenyl) bind HP₂O₇^3? anions in a mixed‐binding mode that features a combination of hydrogen‐bonding and anion–π interactions and results in strong binding. On the other hand, receptor 10²⁺?2 BF₄ ^? (4‐CH₃O?C₆H₄) only displays combined Csp₂?H/anion–π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)⁺???anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H₂PO₄^? anions. That suggests that only hydrogen‐bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) C?H donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum‐energy conformation for all the complexes that explains their measured properties.     

DFT/TDDFT studies of the ancillary ligand effects on structures and photophysical properties of rhenium (I) tricarbonyl complexes with the imidazo[4,5‐f]‐1,10‐phenanthroline ligand

The seven rhenium (I) tricarbonyl complexes having a general formula fac‐[ReBr(CO)₃(R₁,R₂,R₃‐N^{^}N)] (N^{^}N = imidazo[4,5‐f]‐1,10‐phenanthroline; R₁ = ? ^tBu, R₂ = R₃ = ? H, 1 ; R₁ = ? C?CH, R₂ = R₃ = ? H, 2 ; R₁ = ? ^tBu, R₂ = ? C?CH, R₃ = ? H, 3 ; R₁ = ? ^tBu, R₂ = R₃ = ? C?CH, 4 ; R₁ = ? ^tBu, R₂ = ? CH₃, R₃ = ? H, 5 ; R₁ = ? ^tBu, R₂ = R₃ = ? CH₃, 6 ; R₁ = ? ^tBu, R₂ = ? OCH₃, R₃ = ? H, 7 ) have been investigated theoretically by density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods. The different substituted groups on N^{^}N ligand induce changes on the electronic structures and photophysical properties for these complexes. It is found that the introduction of ? C?C decreases the energy level of lowest unoccupied molecular orbital (LUMO) while the introduction of ? CH₃ or ? OCH₃ lead to increase the energy level of LUMO. The order of LUMO energy level rising is in line with the increasing of donating abilities of substituted groups; and the influence of R₂ position is greater than that of R₁ position on LUMO energy level. The lowest energy absorption bands have changes in the order of 7 < 6 < 5 < 1 < 2 < 3 < 4 . These results of electronic affinity (EA), ionization potential (IP), and reorganization energy (λ) indicate that all of these complexes can be used as electron transporting materials. Moreover, the smallest difference between λ_electron and λ_hole of 4 indicates that it is better to be used as an emitter in the organic light‐emitting diodes. © 2015 Wiley Periodicals, Inc.     

Reactivity in the gas phase. Behaviour of isoxazoles under negative ion chemical ionization conditions

[M ? H⁺]^? ions of isoxazole (la), 3-methylisoxazole (1b), 5-methylisoxazole (1c), 5-phenylisoxazole (1d) and benzoylacetonitrile (2a) are generated using NICI/OH^? or NICI/NH₂^? techniques. Their fragmentation pathways are rationalized on the basis of collision-induced dissociation and mass-analysed ion kinetic energy spectra and by deuterium labelling studies. 5-Substituted isoxazoles 1c and 1d, after selective deprotonation at position 3, mainly undergo N ? O bond cleavage to the stable α-cyanoenolate NC ? CH ? CR ? O^? (R = Me, Ph) that fragments by loss of R? CN, or R? H, or H₂O. The same α-cyanoenolate anion (R = Ph) is obtained from 2a with OH^?, or NH₂^?, confirming the structure assigned to the [M ? H⁺]^? ion of 1d, On the contrary, 1b is deprotonated mainly at position 5 leading, via N? O and C(3)? C(4) bond cleavages, to H? C ≡ C? O ^? and CH₃CN. Isoxazole (1a) undergoes deprotonation at either position and subsequent fragmentations. Deuterium labelling revealed an extensive exchange between the hydrogen atoms in the ortho position of the phenyl group and the deuterium atom in the α-cyanenolate NC ? CD = CPh ? O^?.     

The role of ion–neutral complexes in the reactions of onium ions and related species

An account is given of the development of the proposal that ion–neutral complexes are involved in the unimolecular reactions of onium ions (R¹R²C?Z⁺R³; Z = O, S, NR⁴; R¹, R², R³, R⁴ = H, C_nH_{2n + 1}), with particular emphasis on the informative C₄H₉O⁺ oxonium ion system (Z = O; R¹, R² = H; R³ = C₃H₇). Current ideas on the role of ion-neutral complexes in cation rearrangements, hydrogen transfer processes and more complex isomerizations are illustrated by considering the behaviour of isomeric CH₃CH₂CH₂X⁺ and (CH₃)₂CHX⁺ species [X = CH₂O, CH₃CHO, H₂O, CH₃OH, NH₃, NH₂CH₃, NH(CH₃)₂, CH₂?NH, CH₂?NCH₃, CO, CH₃˙, Br˙ and I˙]. Attention is focused on the importance of four energetic factors (the stabilization energy of the ion–neutral complex, the energy released by rearrangement of the cationic component, the enthalpy change for proton transfer between the partners of the ion neutral complex and the ergicity of recombination of the components) which influence the reactivity of the complexes. The nature and extent of the chemistry involving ion-neutral complexes depend on the relative magnitudes of these parameters. Thus, when the magnitude of the stabilization energy exceeds the energy released by cation rearrangement, the ergicity of proton transfer is small, and recombination of the components in a new way is energetically favourable, extensive complex-mediated isomerizations tend to occur. Loss of H₂O from metastable CH₂?O⁺C₃H₇ ions is an example of such a reaction. Conversely, if the stabilization energy is small compared with the magnitude of the energy released by eation rearrangement, the opportunities for complex-mediated processes to become manifest are decreased, especially if proton transfer is endoergic. Thus, CH₃CH₂CH₂CO⁺ expels CO, with an increased kinetic energy release, after rate-limiting isomerization of CH₃CH₂CH₂⁺? CO to (CH₃)₂CH⁺? CO has taken place. When proton transfer between the components of the complex is strongly exoergic, fragmentation corresponding to single hydrogen transfer occurs readily. The proton-transfer step is often preceded by cation rearrangement for CH₃CH₂CH₂X⁺ species. In such circumstances, the involvement of ion–neutral complexes can be detected by the observation of unusual site selectivity in the hydrogen-transfer step. Thus, C₃H₆ loss from CH₂?N⁺(R¹)CH₂CH₂CH₃ (R¹ = H, CH₃, C₃H₇) immonium ions is found by ²H-labelling experiments to proceed via preferential α-and γ-hydrogen transfer; this finding is explained if the incipient ⁺CH₂CH₂CH₃ ion isomerizes to CH₃CH⁺CH₃ prior to proton abstraction. In contrast, the isomeric CH₂?N⁺(R¹)CH(CH₃)₂ species undergo specific β-hydrogen transfer because the developing CH₃CH⁺CH₃ cation is stable with respect to rearrangements involving a 1,2-H shift.     

Binuclear copper(II) and oxovanadium(IV) complexes with 2,6-diformyl-4- tert -butylphenol- bis -(1′-phthalazinylhydrazone). Synthesis,properties and quantum chemical study

Four binuclear transition metal complexes: [Cu₂L(μ-OCH₃)]?·?CH₃OH, [Cu₂H₂L(μ-Cl)Cl₂]?·?(CH₃OH), [Cu₂H₂L(μ-Br)Br₂]?·?(CH₃OH), [(VO)₂H₂L(μ-Cl)]Cl₂?·?(CH₃OH) were synthesized by reaction of the Robson-type binucleating ligand H₃L (2,6-diformyl-4-tert-butylphenol-bis-(1′-phthalazinylhydrazone)) with Cu(II) acetate, CuCl₂, CuBr₂ and VOCl₂, correspondingly. IR and ESR spectra, elemental analysis, conductivity measurements, magnetochemical study and DFT calculations were used to characterize the ligand and isolated complexes. The ligand is a NNONN donor and its degree of deprotonation varies with the metal salt used for reaction (triply deprotonated form L^?3 is observed in reaction with copper(II) acetate, while monodeprotonated form H₂L^? is found in complexes obtained from metal halides). All complexes contain an endogenous phenoxide bridge and an exogenous methoxide, chloride or bromide bridge. Magnetic data reveal existence of antiferromagnetic interactions between the metal ions (experimental 2J values are ?700, ?73, ?50 and ?190?cm^?1, correspondingly). Broken symmetry approach at the UB3LYP/6-31G(d) level was used to theoretically calculate spin-spin coupling between metal centers. Obtained values ?570, ?62, ?53 and ?214?cm^?1 are rather close to experimental ones and reproduce their counterrelation. Spin density distribution in the singlet and triplet states of the complexes is discussed.     

Phosphoniumsalze mit Hydrogendihalogenidanionen HCl2−, HBr2− Hl2− oder HBrCl−

Phosphonium Salts with Hydrogen Dihalide Anions HCl₂^?, HBr₂^?, HI₂^?, or HBrCl^? Phosphonium hydrogen dihalides [R₃PR′][XHY] (X = Y = Cl, Br, I; X = Br, Y = Cl) resp. [R₃PH]HBr₂ are obtained as extremely hydrolyzable crystals by reaction of phosphonium halides or tertiary phosphanes with hydrogen halide. According to IR spectroscopic results the solid compounds mostly contain anions [XHX]^? with symmetric hydrogen bonds. In solution ¹H NMR measurements show a slight (X = Cl, Br) or considerable (X = I) dissociation according to HX₂^? ? X^? + HX. On heating the solid compounds decompose with formation of hydrogen halide and [R₃PR′]X or [R₃PH]X. In this process the hydrogen bromidechlorides [R₃PR′][BrHCl] exclusively eliminate HCl. NMR studies (¹H und ³¹P) with solutions containing [R₃PH]HBr₂ (R = phenyl, 1-naphtyl) or HBr and Ph₃P in varying molar ratios show that a fast proton exchange between the competing Lewis bases R₃P and Br^? exists.     

CH⋅⋅⋅N Hydrogen‐Bonding Interaction in 7‐Azaindole:CHX3 (X=F,Cl) Complexes

The C?H???Y (Y=hydrogen‐bond acceptor) interactions are somewhat unconventional in the context of hydrogen‐bonding interactions. Typical C?H stretching frequency shifts in the hydrogen‐bond donor C?H group are not only small, that is, of the order of a few tens of cm^?1, but also bidirectional, that is, they can be red or blue shifted depending on the hydrogen‐bond acceptor. In this work we examine the C?H???N interaction in complexes of 7‐azaindole with CHCl₃ and CHF₃ that are prepared in the gas phase through supersonic jet expansion using the fluorescence depletion by infra‐red (FDIR) method. Although the hydrogen‐bond acceptor, 7‐azaindole, has multiple sites of interaction, it is found that the C?H???N hydrogen‐bonding interaction prevails over the others. The electronic excitation spectra suggest that both complexes are more stabilized in the S₁ state than in the S₀ state. The C?H stretching frequency is found to be red shifted by 82 cm^?1 in the CHCl₃ complex, which is the largest redshift reported so far in gas‐phase investigations of 1:1 haloform complexes with various substrates. In the CHF₃ complex the observed C?H frequency is blue shifted by 4 cm^?1. This is at variance with the frequency shifts that are predicted using several computational methods; these predict at best a redshift of 8.5 cm^?1. This discrepancy is analogous to that reported for the pyridine‐CHF₃ complex [W. A. Herrebout, S. M. Melikova, S. N. Delanoye, K. S. Rutkowski, D. N. Shchepkin, B. J. van der Veken, J. Phys. Chem. A­ 2005 , 109, 3038], in which the blueshift is termed a pseudo blueshift and is shown to be due to the shifting of levels caused by Fermi resonance between the overtones of the C?H bending and stretching modes. The dissociation energies, (D₀), of the CHCl₃ and CHF₃ complexes are computed (MP2/aug‐cc‐pVDZ level) as 6.46 and 5.06 kcal mol^?1, respectively.     

Solid‐State Form Screen of Cardiosulfa and Its Analogues

Cardiosulfa is a biologically active sulfonamide molecule that was recently shown to induce abnormal heart development in zebrafish embryos through activation of the aryl hydrocarbon receptor (AhR). The present report is a systematic study of solid‐state forms of cardiosulfa and its biologically active analogues that belong to the N‐(9‐ethyl‐9H‐carbazol‐3‐yl)benzene sulfonamide skeleton. Cardiosulfa (molecule 1 ; R¹=NO₂, R²=H, R³=CF₃), molecule 2 (H, H, CF₃), molecule 3 (CF₃, H, H), molecule 4 (NO₂, H, H), molecule 5 (H, CF₃, H), and molecule 6 (H, H, H) were synthesized and subjected to a polymorph search and solid‐state form characterization by X‐ray diffraction, differential scanning calorimetry (DSC), variable‐temperature powder X‐ray diffraction (VT‐PXRD), FTIR, and solid‐state (ss) NMR spectroscopy. Molecule 1 was obtained in a single‐crystalline modification that is sustained by N? H???π and C? H???O interactions but devoid of strong intermolecular N? H???O hydrogen bonds. Molecule 2 displayed a N? H???O catemer C(4) chain in form I, whereas a second polymorph was characterized by PXRD. The dimorphs of molecule 3 contain N? H???π and C? H???O interactions but no N? H???O bonds. Molecule 4 is trimorphic with N? H???O catemer in form I, and N? H???π and C? H???O interactions in form II, and a third polymorph was characterized by PXRD. Both polymorphs of molecule 5 contain the N? H???O catemer C(4) chain, whereas the sulfonamide N? H???O dimer synthon R₂²(8) was observed in polymorphs of 6 . Differences in the strong and weak hydrogen‐bond motifs were correlated with the substituent groups, and the solubility and dissolution rates were correlated with the conformation in the crystal structure of 1 , 2 , 3 , 4 , 5 , 6 . Higher solubility compounds, such as 2 (10.5 mg mL^?1) and 5 (4.4 mg mL^?1), adopt a twisted confirmation, whereas less‐soluble 1 (0.9 mg mL^?1) is nearly planar. This study provides practical guides for functional‐group modification of drug lead compounds for solubility optimization.     

Dicarbonylrhodium(I) complexes of aminophenols and their catalytic carbonylation reaction

The complexes [Rh(CO)₂ClL]( 1 ), where L = 2‐aminophenol ( a ), 3‐aminophenol ( b ) and 4‐aminophenol ( c ), have been synthesized and characterized. The ligands are coordinated to the metal centre through an N‐donor site. The complexes 1 undergo oxidative addition ( OA ) reactions with various alkyl halides ( RX ) like CH₃I, C₂H₅I and C₆H₅CH₂Cl to produce Rh(III) complexes of the type [Rh(CO)(COR)XClL], where R = ? CH₃( 2 ), ? C₂H₅( 3 ), X = I; R = C₆H₅CH₂? and X = Cl ( 4 ). The OA reaction with CH₃I follows a two‐stage kinetics and shows the order of reactivity as 1b > 1c > 1a . The minimum energy structure and Fukui function values of the complexes 1a–1c were calculated theoretically using a DND basis set with the help of Dmol³ program to substantiate the observed local reactivity trend. The catalytic activity of the complexes 1 in carbonylation of methanol, in general, is higher (TON 1189–1456) than the species [Rh(CO)₂I₂]^? (TON 1159). Copyright © 2007 John Wiley & Sons, Ltd.     

Synthetic,spectral, thermal and antimicrobial studies on some bis(N,N′‐dialkyldithiocarbamato) antimony(III) alkylenedithiophosphates

Bis(N, N′‐dialkyldithiocarbamato)antimony(III) alkylenedithiophosphates of the type [R₂NCS₂]₂ SbS(S)POGO [where NR₂ = N(CH₃)₂, N(C₂H₅)₂ and N(CH₂)₄; G = ? CH₂? C(C₂H₅)₂? CH₂? , ? CH₂? C(CH₃)₂? CH₂? , ? CH(CH₃)? CH(CH₃)? and ? C(CH₃)₂? C(CH₃)₂? ] were synthesized and characterized by physico‐chemical, spectral [UV, IR and NMR (¹H, ¹³C and ³¹P)] and thermal (TG, DTA and DSC) analysis. The TG decomposition analysis step of the complex indicated the formation of Sb₂S₃ as the final product. The first endothermic peak in DSC indicated the melting point of the complexes. These complexes were screened for their antimicrobial activities using the disk diffusion method. All the complexes showed good activity as antibacterial and antifungal agents on some selected bacterial and fungal strains, which increased on increasing the concentration. Chloroamphenicol and terbinafin were used as standards for comparison. Copyright © 2007 John Wiley & Sons, Ltd.     

Versatile Reactivity of Scorpionate‐Anchored Yttrium?Dialkyl Complexes towards Unsaturated Substrates

A series of unusual chemical‐bond transformations were observed in the reactions of high active yttrium? dialkyl complexes with unsaturated small molecules. The reaction of scorpionate‐anchored yttrium? dibenzyl complex [Tp^Me2Y(CH₂Ph)₂(thf)] ( 1 , Tp^Me2=tri(3,5‐dimethylpyrazolyl)borate) with phenyl isothiocyanate led to C?S bond cleavage to give a cubane‐type yttrium–sulfur cluster, {Tp^Me2Y(μ₃‐S)}₄ ( 2 ), accompanied by the elimination of PhN?C(CH₂Ph)₂. However, compound 1 reacted with phenyl isocyanate to afford a C(sp³)? H activation product, [Tp^Me2Y(thf){μ‐η¹:η³‐OC(CHPh)NPh}{μ‐η³:η²‐OC(CHPh)NPh}YTp^Me2] ( 3 ). Moreover, compound 1 reacted with phenylacetonitrile at room temperature to produce γ‐deprotonation product [(Tp^Me2)₂Y]⁺[Tp^Me2Y(N=C?CHPh)₃]^? ( 6 ), in which the newly formed N?C?CHPh ligands bound to the metal through the terminal nitrogen atoms. When this reaction was carried out in toluene at 120 °C, it gave a tandem γ‐deprotonation/insertion/partial‐Tp^Me2‐degradation product, [(Tp^Me2Y)₂(μ‐Pz)₂{μ‐η¹:η³‐NC(CH₂Ph)CHPh}] ( 7 , Pz=3,5‐dimethylpyrazolyl).     

Tuning a Single Ligand System to Stabilize Multiple Spin States of Manganese: A First Example of a Hydrazone‐Based Manganese(III) Spin‐Crossover Complex

A series of bis‐chelate pseudo‐octahedral mononuclear coordination complexes of manganese with the chromophore [MnN₄O₂]ⁿ⁺ (n=0, 1) have been generated in all three principal oxidation states of this transition‐metal center under ambient conditions by utilizing a readily tunable, versatile phenolic pyridylhydrazone ligand system (i.e., H₂(3,5‐R¹,R²)‐L; L=ligand). Strategic combinations of the nature and position of a variety of substituent groups afforded selective, spontaneous stabilization of multiple spin states of the manganese center, which, upon close crystallographic scrutiny, appears to be in part due to the occurrence or absence of hydrogen‐bonding interactions that involve the phenolate/phenolic oxygen atom. The divalent complexes are isolable in two forms, namely, molecular [Mn^II{H(3,5‐R¹,R²)‐L}₂] and ionic [Mn^II{H₂(3,5‐R¹,R²)‐L}{H(3,5‐R¹,R²)‐L}]ClO₄, with the latter complex converting easily into the former complex on deprotonation. Accessibility of the higher‐valent states is achievable only when the phenolate oxygen atom is sterically hindered from participation in hydrogen bonding. The [Mn^III{H(3,5‐tBu₂)‐L}₂]ClO₄ complex is the first example of a hydrazone‐based Mn^III complex to exhibit spin crossover. Formation of the tetravalent complexes [Mn^IV{(3,5‐R¹,R²)‐L}₂] (R¹=tBu, R²=H; R¹=R²=tBu) necessitates base‐assisted abstraction of the hydrazinic proton.