Bidentate Nitrogen Donor Ligands Research Articles

Calix[4]arene-Analogous Technetium Supramolecules.

Calix[4]arene-analogous technetium supramolecules (1 and 2) were assembled using (NBu4)[Tc2(μ-Cl)3(CO)6] and neutral flexible bidentate nitrogen-donor ligands (L1 and L2) consisting of four arene units covalently joined via methylene units. The neutral homoleptic technetium macrocycles adopt a partial cone/cone-shaped conformation in the solid state. These supramolecules are the first example of fac-[Tc(CO)3]+ core-based metallocalix[4]arenes and second example of fac-[Tc(CO)3]+ core-based metallomacrocycles. Structurally similar fac-[Re(CO)3]+ core-based macrocycles (3 and 4) were also prepared using [Re(CO)5X] (where X = Cl or Br) and L1 or L2. The products were characterized spectroscopically and by X-ray analysis.

New Complexes of organotin(IV) and organosilicon(IV) with 2-{(3,4-dimethoxybenzylidene)amino}-benzenethiol: Synthesis, spectral, theoretical, antibacterial, docking studies

New series of dimethyl-, dibutyltin(IV), trimethylsilicon(IV), and phenylsilicon(IV) compounds with bidentate nitrogen and sulphur donor ligands have been synthesized with the 2-{(3,4-dimethoxybenzylidene)amino}-benzenethiol (LH), in molar ratios of 1:1 and 1:2. For structure elucidation, all produced compounds were characterized using IR, UV–vis, elemental analysis, conductance measurements, NMR (1H, 13C, 29Si, 119Sn) spectroscopy techniques. The 2-{(3,4-dimethoxybenzylidene)amino}-benzenethiol behaves as monofunctional bidentates, interacting with the tin and silicon atom via the thiolic-sulphur and azomethine-nitrogen atoms. Compound 1, 3, and 5 have a five-coordinated trigonal bipyramidal geometry surrounding the metal atoms, whereas Compound 2, 4, and 6 have deformed octahedral structures. The optimum geometrical parameters, including bond length, bond angles, HOMO, LUMO, electrophilicity index, chemical hardness, global softness, and mulliken atomic charges, were determined using density functional theory-based methods (DFT). The studied compounds and their ligands were simultaneously evaluated for antibacterial activity in-vitro and compared to streptomycin. The binding affinity of compound with bulky group and hydrogen bond acceptor groups is more in comparision of other compounds. The structure activity relationship revealed that compounds with bulky and hydrogen bond acceptor group will enhance the antibacterial activity agaisnt Staphylococcus aureus.

Crystal structures, proton conductivities and luminescence of two organic-inorganic hybrid materials based on Keggin-type clusters and Cu(II)/Cu(I)-bis(hydroxymethyl)-2,2′-bipyridine complexes

Two proton-conductive and luminescent organic-inorganic hybrid materials, {[Cu(II)(bhmbpy)(H2O)(Cl)0.5(CH3CN)]2[PW(VI) 10W(V) 2O39]}·4H2O(1) and {H2[Cu(I)(bhmbpy)2(Cl)Cu(I)(bhmbpy)2][PW12O40]}·7H2O (2) (where bhmbpy is bis(hydroxymethyl)-2,2′-bipyridine), were synthesized at room temperature. The two products were characterized by infrared spectroscopy, X-ray single-crystal diffraction, X-ray powder diffraction, elemental and thermogravimetric analyses. The proton conductivities and luminescence of 1 and 2 were studied by using alternating-current impedance spectroscopy and luminescence spectroscopy, respectively. X-ray diffraction analysis revealed that 1 includes a decorated polyanion chain {[Cu(II)(bhmbpy)(H2O)(Cl)0.5(CH3CN)]2[PW(VI) 10W(V) 2O39]}n and forms a three-dimensional network structure depending on short Cl…Cl contacts and hydrogen-bonding interactions. X-ray diffraction analysis revealed that 2 includes a butterfly-like bi-nuclear copper cluster unit with a Cl-bridge, [Cu(I)(bhmbpy)2(Cl)Cu(I)(bhmbpy)2]+, and forms a three-dimensional network structure depending on hydrogen-bonding interactions. [PW12O40]3– anions fill in the network based on hydrogen-bonding and electrostatic interactions. In them, the bhmbpy acts as a bidentate nitrogen donor ligand in the chelating fashion to coordinate with the Cu(II) center in 1 and the Cu(I) center in 2. The bhmbpy in 2 successfully constrains the Cu(I) within a rigid environment in a tetragonal-pyramidal geometry. The two compounds exhibit good proton conductivity (10−4 S·cm−1) at 100 °C in the relative humidity range 35–98%. Their luminescence behaviors in the solid state at room temperature have also been investigated. Upon excitation at 384 nm, 1 exhibits three emission peaks centered at 439, 507 and 566 nm. When excited at 364 nm, 2 displays three emission peaks centered at 443, 501 and 553 nm.

Reversible Photo- and Thermo-Induced Spin-State Switching in a Heterometallic {5d-3d} W2Fe2 Molecular Square Complex.

Following the complex-as-a-ligand strategy, self-assembly of [W(CN)8]3- and iron(II) with bidentate nitrogen donor ligand bik (bik = bis(1-methyl-1H-imidazol-2-yl)ketone) ligand affords a cyanide-bridged [W2Fe2] molecular square complex [HNBu3]2{[W(CN)8]2[Fe(bik)2]2}·6H2O·CH3OH (1). The complex was characterized by single-crystal X-ray diffraction analyses, (photo)magnetic studies, optical reflectivity, electrochemical studies, and spectroscopic studies. Structural analyses revealed that in the [W2Fe2] square motif tungsten(V) and iron(II) centers reside in an alternate corner of the square and are bridged by the cyanide ligands. Complex 1 exhibits thermo-induced spin crossover (SCO) between {WV (S = 1/2) - FeIILS (S = 0)} and {WV (S = 1/2) - FeIIHS (S = 2)} pairs near room temperature and photoinduced spin-state switching with TLIESST = 70 K under light irradiation at low temperature. To the best of our knowledge, 1 represents the first complex containing iron(II) and [WV(CN)8]3- units exhibiting both SCO and photomagnetic effect.

1,1'-Biisoquinolines-Neglected Ligands in the Heterocyclic Diimine Family That Provoke Stereochemical Reflections.

1,1′-Biisoquinolines are a class of bidentate nitrogen donor ligands in the heterocyclic diimine family. This review briefly discusses their properties and the key synthetic pathways available and then concentrates upon their coordination behaviour. The ligands are of interest as they exhibit the phenomenon of atropisomerism (hindered rotation about the C1–C1′ bond). A notation for depicting the stereochemistry in coordination compounds containing multiple stereogenic centers is developed. The consequences of the chirality within the ligand on the coordination behaviour is discussed in detail.

Crystal structures and properties of two Cu(I) complexes based on Keggin-type clusters and diethyl 4,4′-dicarboxy-2,2′-biquinoline acid

Two proton-conductive Cu(I) complexes based on Keggin-type clusters, [Cu(debqdc)2]2[HPW12O40]·4H2O (1), and [Cu(debqdc)2]2[HPW12O40]·debqdc·4H2O (2), where debqdc is diethyl 4,4′-dicarboxy-2,2′-biquinoline, were simply synthesized at room temperature. The products were structurally characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray diffraction analyses. Single-crystal X-ray diffraction analyses revealed that both complexes crystallized in the triclinic space group P−1 and presented two three-dimensional supramolecular networks with one-dimensional hydrophilic channels via hydrogen-bonding interactions and π–π stacking interactions between the aromatic rings. In the [Cu(debqdc)2]+ ion, debqdc acts as a bidentate nitrogen donor ligand in the chelating fashion. The bulky debqdc ligand constrains the Cu(I) metal center within such a rigid environment in a tetrahedral geometry. The two complexes exhibit good proton conductivities (10−5 ~ 10−4 S cm−1) at 100 °C in the relative humidity range 35 ~ 98%. The luminescence behaviors of these complexes in the solid state at room temperature have also been investigated. Upon excitation at 285 nm, both 1 and 2 display three main emission peaks centered at 470, 520, and 568 nm, respectively.

Assessment of the interaction procedure between Pt(IV) prodrug [Pt(5,5′-dmbpy)Cl4 and human serum albumin: Combination of spectroscopic and molecular modeling technique

In this study, a cytotoxic Pt(IV) complex [Pt(5,5′-dmbpy)Cl4 (5,5′-dmbpy is 5,5′-dimethyl-2,2′-bipyridine) was selected to investigate its affinity to human serum albumin (HSA) by spectroscopy and molecular docking methods. This complex has a bidentate nitrogen donor ligand with four chloride anions attached to a Pt(IV) metal in a distorted octahedral environment. The fluorescence data showed this complex quench the intrinsic fluorescence of HSA through a static quenching mechanism. The binding constant (Kb) and the number of binding sites (n) were obtained based on the results of fluorescence measurements. UV–vis, circular dichroism spectroscopy, and three-dimensional fluorescence spectroscopy proved that the Pt(IV) complex could slightly change the secondary structure of protein. Thermodynamic parameters show that the Pt(IV) complex binds to HSA through electrostatic and Vander Waals interactions with one binding site. The molecular docking results confirmed the spectroscopic results and showed that Pt(IV) complex is embedded into subdomain IIA of protein. The aim of this study is to describe the performance of effective anti-cancer drugs when faced with proteins such as HSA.

Electrophilic RhI catalysts for arene H/D exchange in acidic media: Evidence for an electrophilic aromatic substitution mechanism

A series of new rhodium (I) complexes supported by bidentate nitrogen-donor ligands with varying electronic and steric properties were synthesized in situ and evaluated for catalytic arene C–H/D activation. In trifluoroacetic acid (HTFA), these complexes are proposed to mediate H/D exchange of arene C–H/D bonds by an electrophilic aromatic substitution mechanism that involves Rh-mediated activation of HTFA (or DTFA). DFT calculations support the proposed pathway for the H/D exchange reactions.

Abstract P6-02-09: Structure-activity relationship of ruthenium (Ru) complexes to inhibit breast cancer growth and metastasis

Abstract Previous studies demonstrated that transition metal complexes inhibit cancer cell growth. We have examined a series of ruthenium (Ru (II)) complexes for their ability to inhibit growth of breast cancer cells. Among three complexes with the general formula [Ru(η6-p-cym)(N-N)Cl]+ tested for their abilities to inhibit MDA-MB-231 cell growth, the complex with o-phenalyenediamine (o-pda) as the bidentate nitrogen donor (N-N) ligand, [Ru(η6-p-cym)(o-pda)Cl]+, showed significant inhibitory activity in both a concentration- and a time-dependent manners. Although [Ru(η6-p-cym)(o-pda)Cl]+ inhibited growth of various human cancer types such as MCF-7 (breast), SK-Br3 (breast), B-cell lymphoma (Raji), osteosarcoma (HT1080), and melanoma (Bowes) cells, two TN breast cancer cells, HCC1806 and HCC38, were resistant to this treatment, suggesting cell-type specific functions of [Ru(η6-p-cym)(o-pda)Cl]+ for inhibiting cell growth. When MDA-MB-231 cells were treated with [Ru(η6-p-cym)(o-pda)Cl]+, both cleavage of caspase-3 and release of HMGB-1 into conditioned medium increased in a concentration dependent manner, suggesting [Ru(η6-p-cym)(o-pda)Cl]+ induced both apoptosis and necrosis processes. Importantly, [Ru(η6-p-cym)(o-pda)Cl]+ synergistically inhibited MDA-MB-231 cell growth with cyclophosphamide but not doxorubicin and paclitaxel. These results suggest that [Ru(η6-p-cym)(o-pda)Cl]+ is a potent tumor growth inhibitor per se and enhances tumoricidal activity of chemotherapeutic agents such as cyclophosphamide. Thus, Ru (II) complexes are promising anti-cancer drugs which could be used alone and/or in combination with chemotherapeutic agents for breast cancer patients. The opinion and assertions contained herein are the private views of the authors and are not to be construed as official or as representing the views of the Department of the Army or the Department of Defense. Citation Format: Joji Iida, Marc L Prazo, Yifeng Lu, Elisabeth T Bell-Loncella, Craig D Shriver. Structure-activity relationship of ruthenium (Ru) complexes to inhibit breast cancer growth and metastasis [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-02-09.

Oxidation of dimethylplatinum(II) complexes with malonyl peroxide derivatives

The reaction of the cyclic peroxides cyclobutane malonoyl peroxide and cyclopentane malonoyl peroxide to dimethylplatinum(II) complexes with the bidentate nitrogen donor ligand 4,4′-di-t-butyl-2,2′-bipyridine (bubpy) gave a mixture of the products of cis and trans oxidative addition, [PtMe2{(O2C)2C(C3H6)}(bubpy)] and [PtMe2{(O2C)2C(C4H8)}(bubpy)], respectively. The cis isomers exist with a chelating dicarboxylate ligand, forming a six-membered ring, while the trans isomers are thought to exist as oligomers, which may react with water or solvent to give complexes containing a monodentate dicarboxylate ligand. Equilibration of the product of cis oxidative addition, cis-[PtMe2{(O2C)2C(C3H6)}(bubpy)], with oxalic or phthalic acid to give equilibria with the oxalate cis-[PtMe2(O4C2)(bubpy)] or phthalate cis-[PtMe2{(O2C)2C6H4}(bubpy)] derivative, respectively, indicated the expected sequence of chelate stability oxalate > cyclobutane malonate > phthalate.

In Situ Catalysts for the Intramolecular Hydroamination of Aminoalkynes – What Ligand Properties Determine Catalyst Activity?

AbstractInsight into the iridium(I)/rhodium(I)‐catalyzed hydroamination of 4‐pentyn‐1‐amine was established through comparison of catalysts formed in situ from metal precursors and selected ligands with analogous catalysts which had been synthesized and isolated as pure complexes. The isolated metal complexes used were [Rh(bim)(CO)2]BPh4 (1) and [M(bpm)(CO)2]BPh4 (2 M = Rh, 3 M = Ir), which contain the bidentate nitrogen donor ligands bis(1‐methylimidazol‐2‐yl)methane (bim, 4) and bis(1‐pyrazolyl)methane (bpm, 5). The metal precursors used for formation of in situ catalysts included [Rh(μ‐Cl)(CO)2]2, [Ir(μ‐Cl)(CO)2]n, [Ir(μ‐Cl)(C2H4)2]2, [Ir(μ‐Cl)(COE)2]2, and [Ir(μ‐Cl)(COD)]2. The sp2‐hybridised N‐donor ligands investigated included heterocyclic bim (4) and bpm (5); and the diimines glyoxal bis(4‐methylphenylimine) (p‐tol‐DAD, 8), bis(2,4,6‐trimethylphenylimino)acenapthene (Mes‐BIAN, 9) and bis(4‐methylphenylimino)acenapthene (p‐tol‐BIAN, 10). The weakly coordinating p‐tol‐DAD (8) ligand was found to yield the most active RhI catalyst which opens up a new, and synthetically very facile, ligand class for the hydroamination reaction. The most active catalysts were formed from a combination of N‐donor ligand, co‐ligand and counterion that resulted in the most electron‐deficient metal centre. This indicated that the most likely mechanism of action of the catalysts was via alkyne binding and activation as a first step.

Insight into the Photoinduced Ligand Exchange Reaction Pathway of cis-[Rh2(μ-O2CCH3)2(CH3CN)6]2+ with a DNA Model Chelate

We previously showed that [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+) binds to dsDNA only upon irradiation with visible light and that photolysis results in a 34-fold enhancement of its cytotoxicity toward Hs-27 human skin fibroblasts, making it potentially useful for photodynamic therapy (PDT). With the goal of gaining further insight on the photoinduced binding of DNA to the complex, we investigated by NMR spectroscopy the mechanism by which 2,2'-bipyridine (bpy), a model for biologically relevant bidentate nitrogen donor ligands, binds to [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+) upon irradiation in D(2)O. The photochemical results are compared to the reactivity in the dark in D(2)O and CD(3)CN. The photolysis of [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+) with equimolar bpy solutions in D(2)O with visible light affords [Rh(2)(O(2)CCH(3))(2)(eq/eq-bpy)(CH(3)CN)(2)(D(2)O(ax))(2)](2+) (eq/eq) with the reaction reaching completion in ~8 h. Only vestiges of eq/eq are observed at the same time in the dark, however, and the reaction is ~20 times slower. Conversely, the dark reaction of [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+) with an equimolar amount of bpy in CD(3)CN affords [Rh(2)(O(2)CCH(3))(2)(η(1)-bpy(ax))(CH(3)CN)(5)](2+) (η(1)-bpy(ax)), which remains present even after 5 days of reaction. The photolysis results in D(2)O are consistent with the exchange of one equiv CH(3)CNeq for solvent, and the resulting species quickly reacting with bpy to generate eq/eq; the initial eq ligand dissociation is assisted by absorption of a photon, thus greatly enhancing the reaction rate. The photolytic reaction of [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+):bpy in a 1:2 ratio in D(2)O affords the eq/eq and (eq/eq)(2) adducts. The observed differences in the reactivity in D(2)O vs CD(3)CN are explained by the relative ease of substitution of eq D(2)O vs CD(3)CN by the incoming bpy molecule. These results clearly highlight the importance of dissociation of an eq CH(3)CN molecule from the dirhodium core to attain high reactivity and underscore the importance of light for the reactivity of these compounds, which is essential for PDT agents.

Thermodynamic and Kinetic Studies on Novel Dinuclear Platinum(II) Complexes Containing BidentateN,N-donor ligands

A series of novel dinuclear platinum(II) complexes were synthesized with bidentate nitrogen donor ligands. The two platinum centers are connected by an aliphatic chain of variable length. The selected chelating ligand system should stabilize the complex toward decomposition. The pK(a) values and reactivity of four synthesized complexes, viz. [Pt(2)(N(1),N(4)-bis(2-pyridylmethyl)-1,4-butanediamine)(OH(2))(4)](4+) (4NNpy), [Pt(2)(N(1),N(6)-bis(2-pyridylmethyl)-1,6-hexanediamine)(OH(2))(4)](4+) (6NNpy), [Pt(2)(N(1),N(8)-bis(2-pyridylmethyl)-1,8-octanediamine)(OH(2))(4)](4+) (8NNpy), and [Pt(2)(N(1),N(10)-bis(2-pyridylmethyl)-1,10-decanediamine)(OH(2))(4)](4+) (10NNpy), were investigated. This system is of special interest because only little is known about the substitution behavior of dinuclear platinum complexes that contain a bidentate chelate that forms part of the aliphatic bridging ligand. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of the coordinated water ligands. The substitution of coordinated water by thiourea was studied under pseudofirst-order conditions as a function of nucleophile concentration, temperature, and pressure, using stopped-flow techniques and UV-vis spectroscopy. The results for the dinuclear complexes were compared to those for the corresponding mononuclear reference complex [Pt(aminomethylpyridine)(OH(2))(2)](2+) (monoNNpy), by which the effect of increasing the aliphatic chain length on the bridged complexes could be investigated. The results indicated that there is a clear interaction between the two platinum centers, which becomes weaker as the chain length between the metal centers increases. In addition, quantum chemical calculations were performed to support the interpretation and discussion of the experimental data.

Highly soluble dichloro, dibromo and dimethyl dioxomolybdenum(VI)-bipyridine complexes as catalysts for the epoxidation of olefins

The reaction of solvent substituted MoO 2X 2(S) 2 (X = Cl, S = THF; X = Br, S = DMF) complexes with one equivalent of bidentate nitrogen donor ligands at room temperature leads within a few minutes to the quantitative formation of complexes of the type [MoO 2X 2L 2] (L = 4,4′-bis-methoxycarbonyl-2,2′-bipyridine, 5,5′-bis-methoxycarbonyl-2,2′-bipyridine, 4,4′-bis-ethoxycarbonyl-2,2′-bipyridine, 5,5′-bis-ethoxycarbonyl-2,2′-bipyridine). Treatment of the complexes [MoO 2Cl 2L 2] with Grignard reagents at low temperatures yields dimethylated complexes of the formula [MoO 2(CH 3) 2L 2]. [MoO 2Br 2(4,4′-bis-ethoxycarbonyl-2,2′-bipyridine)], [MoO 2Br 2(5,5′-bis-methoxycarbonyl-2,2′-bipyridine)] and [MoO 2Br 2(5,5′-bis-ethoxycarbonyl-2,2′-bipyridine)] have been exemplary examined by single crystal X-ray analysis. The complexes were applied as homogenous catalysts for the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) as oxidising agent under solvent-free conditions. The complexes containing L = Cl have been additionally investigated with room temperature ionic liquids (RTILs) as solvents. The catalytic activity of the [MoO 2X 2L 2] complexes in olefin epoxidation with tert-butyl hydroperoxide is on average very good. The main advantage of the synthesised complexes in comparison to previously reported complexes is their high solubility. This good solubility is apparently the reason that the catalytic potential of the compounds can unfold. The turnover frequencies (TOFs) in RTILs are even higher, showing the performance of the catalysts under optimised conditions.

Bidentate Lewis base adducts of molybdenum(VI): Ligand impact on catalytic performance and stability

The reaction of solvent substituted [MoO 2Cl 2] (THF) 2 complexes with 1 equiv. of bidentate nitrogen donor ligands leads to complexes of the type [MoO 2Cl 2L 2] (L 2 = 4,5-diazafluorene-9-one; 1,10-phenanthroline-5,6-dione; 2,2′-biquinoline-4,4′-dicarboxylic acid, diethyl ester; 3,6′-bis-2-pyridyl-pyridazine; 4,4′-di-ethoxycarbonyl-2,2′-bipyridine) in quantitative yields at room temperature under inert gas atmosphere within a few minutes. The catalytic activity of the [MoO 2Cl 2L 2] complexes in olefin epoxidation with t-butyl hydroperoxide as oxidizing agent is strongly influenced by the nature of the ligand L and its steric demand. The complexes, with the sole exception of compound 9 [MoO 2Cl 2(1,10-phenanthroline-5,6-dione)], are very active and highly selective epoxidation catalysts. The influence of the terminal oxo ligands together with the Lewis base ligands on the Mo center obviously keeps the compounds on a quite stable level of electron density.

Syntheses, structures and spectroscopy of uni- and bi-dentate nitrogen base complexes of silver(i) trifluoromethanesulfonate

In extension of recent synthetic and crystallographic studies of adducts of silver(I) oxyanion salts with uni- and bi-dentate nitrogen-donor ligands, AgX : L (1 : n), a parallel series of complexes formed with silver(I) trifluoromethanesulfonate ('tfs', 'triflate') has been similarly defined, showing rather more divergence from tendencies established with the previous ClO(4), NO(3), F(3)CCO(2) core arrays than might be expected from basicity arguments. Thus, while silver triflate crystallised from neat base forms 1 : 2 mononuclear adducts with 2,4,6-trimethylpyridine and quinoline which comprise essentially linear two-coordinate [LAgL](+) cations, perturbed by approaches of the anions, 1 : 2 adducts obtained similarly from pyridine and 2-methylpyridine are [L(2)Ag(mu-tfs)(2)AgL(2)] dimers, with central four- and eight-membered rings arising from mu-OSO(2)CF(3) and extended mu-(O,O'SOCF(3)) anion bridging modes, respectively. With piperidine, a single-stranded polymer reminiscent of the arrays [(pip)(2)AgX](infinity/infinity), X = Cl, NCS, is formed, the triflate bridging through two of its oxygen atoms, rather than via a single atom bridge. With 2- and 4-cyanopyridine, the former a 1 : 1 adduct (being an acetonitrile solvate (MeCN coordinated)), and the latter 1 : 2, both are more complex structures in which the nitrile functionalities now coordinate weakly. The 1 : 2 adduct with 2-acetylpyridine parallels its perchlorate analogue, the ligands being bidentate in a mononuclear complex [L(2)AgOSO(2)CF(3)], while adducts of 2,9-dimethylphenanthroline and 2,2'-biquinolyl, both acetonitrile monosolvates, take the form [LAg(NCMe)]tfs. Agtfs : dpk (8 : 8)(infinity/infinity).EtOH ('dpk' = bis(2-pyridyl)ketone) is a complex polymer. The nature of the interactions is explored by way of spectroscopy (IR, NMR and ESI MS) and a density functional theory approach.

Application of Chiral Amine-Imine Ligands in Palladium-Catalyzed Polyketone Synthesis: Effect of Ligand Backbone on the Polymer Stereochemistry

Two pairs of enantiomerically pure chiral bidentate nitrogen-donor ligands (N*-N) featuring one sp3 and one sp2 nitrogen atom have been applied to the CO/vinyl arene copolymerization reaction catalyzed by the corresponding monocationic palladium(II) complexes [Pd(CH3)(CH3CN)(N*-N)][PF6]. The ligand fragment containing the sp2 nitrogen atom is a 2-pyridinyl or an 8-quinolinyl building block, while the chiral framework of the ligand derives from (S)-(+)-2,2′-(2-azapropane-1,3-diyl)-1,1′-binaphthalene or from trans-2,5-dimethylpyrrolidinyl. Ligands with the binaphthyl moiety generate catalysts showing a moderate activity, while ligands having the pyrrolidinyl fragment result in very low activity species. The stereochemistry of the synthesized polyketones depends on the sp2 nitrogen-containing fragment: ligands with the 2-pyridinyl group lead to atactic copolymers, whereas those with the quinolinyl moiety give an isotactic polyketone. The effect of the nature of the quinone, added to the reaction mixture as oxidant, has been investigated. MALDI-TOF analysis reveals the formation of several polymeric chains, differing in the presence of various end-groups.

Well‐Defined Regioselective Iminopyridine Rhodium Catalysts for Anti‐Markovnikov Addition of Aromatic Primary Amines to 1‐Octyne

Abstractmagnified imageA series of cationic rhodium(I) complexes of the type [Rh(N‐N)(COD)][BPh4], containing the following iminopyridine‐based bidentate nitrogen donor ligands (N‐N): 2,6‐diisopropyl‐N‐[1‐(pyridin‐2‐yl)ethylidene]aniline (dipea, 1), 2,6‐dimethyl‐N‐[1‐(pyridin‐2‐yl)ethylidene]aniline (dmpea, 2), 2,4,6‐trimethyl‐N‐[1‐(pyridin‐2‐yl)ethylidene]aniline (tmpea, 3) and 2,6‐diisopropyl‐N‐[1‐(4‐methylpyridin‐2‐yl)ethylidene]aniline] (dipmpea, 4), were synthesized and fully characterized. The intermolecular hydroamination of a terminal alkyne, such as 1‐octyne, with primary aromatic amines in the presence of these cationic rhodium(I) catalysts occurred in an anti‐Markovnikov fashion. The rhodium complexes catalyzed the regioselective formation of the E‐isomer of the corresponding imine, without the formation of the Z‐isomer or the Markovnikov product. These compounds are also presented as efficient regioselective catalysts for the hydroamination of anilines in the presence of air and/or water.

Adduct Formation of Dichloridodioxidomolybdenum(VI) and Methyltrioxidorhenium(VII) with a Series of Bidentate Nitrogen Donor Ligands

AbstractThe stability of a variety of bidentate N‐base adducts of MoO2Cl2 and (CH3)ReO3 (MTO) was investigated in thf and CH2Cl2 as solvents. The formation constants were determined from the spectrophotometric data based on 1:1 adduct formation. The adduct formation constants for [MoO2Cl2L2] (L2 = bidentate nitrogen ligand) are 104–106 times higher than those for [(CH3)ReO3L2] with the same ligands under the same conditions. The adduct stability of both systems is very sensitive to the electronic nature of the ligands and increases with their donor ability. Hammett correlations of the formation constants against σ give relatively large negative values for the reaction constants (ρRe = –5.9, ρMo = –6.6). The stability is also governed by steric and strain factors. Thus, sterically hindered 6,6′‐disubstituted‐2,2′‐bipyridines do not form adducts with MTO, and only 6,6′‐dimethyl‐ and 6,6′‐diphenyl‐2,2′‐bipyridines form adducts with MoO2Cl2. However, these adducts are much less stable than other methyl derivatives of 2,2′‐bipridine adducts. The steric strain between the two methyl groups in 3,3‐dimethyl‐2,2′‐bipyridine influences the bipyridine planarity upon complexation and reduces the adduct stability. The thermodynamic parameters (enthalpy and entropy) were determined from temperature‐dependence studies. The adduct stability is mainly due to the strongly exothermic binding of the nitrogen‐bidentate ligand. The entropy change is small and has little effect on adduct stability.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Application of UV-Vis spectroscopy to high throughput screening of hydroamination catalysts

Potential catalysts for the hydroamination of 2-(2-phenylethynyl)aniline 2 which have been identified through high throughput screening methods were investigated. Two complexes were shown to be highly active hydroamination catalysts in acetone: the in situ combinations of [Rh(CO)2Cl]2–mesBIAN–NaBF4 (mesBIAN = bis(2,4,6-trimethylphenylimino)acenapthene) and [Ir(COD)Cl]2–NaBF4 (COD = 1,5-cyclooctadiene). The isolated complexes [M(N–N)XCl]BF4 (M = Rh, Ir; N–N = bidentate nitrogen donor ligand; X = CO or Cp*) were found to be inactive as catalysts for the conversion of 2 to 3. However, chloride abstraction from these complexes through the addition of AgBF4 was found to generate extremely active catalysts. Particularly active was the complex [Rh(CO)ClmesBIAN]–AgBF4 (5 mol%) which achieved complete conversion of 2 to 3 in 12 minutes at 50 °C. Also identified was the formation of the unusual product, N-(2-methylvinyl)-2-phenylindole 5, catalysed by [IrCp*Cl2]2–NaBF4 from starting material 2via the incorporation of one molecule of acetone.