Tris 2-pyridylmethyl Amine Ligands Research Articles

Russian Nesting Doll Complexes of Molecular Baskets and Zinc Containing TPA Ligands.

In this study, we examined the structural and electronic complementarities of convex 1-Zn(II), comprising functionalized tris(2-pyridylmethyl)amine (TPA) ligand, and concave baskets 2 and 3, having glycine and (S)-alanine amino acids at the rim. With the assistance of (1)H NMR spectroscopy and mass spectrometry, we found that basket 2 would entrap 1-Zn(II) in water to give equimolar 1-Zn⊂2in complex (K = (2.0 ± 0.2) × 10(3) M(-1)) resembling Russian nesting dolls. Moreover, C3 symmetric and enantiopure basket 3, containing (S)-alanine groups at the rim, was found to transfer its static chirality to entrapped 1-Zn(II) and, via intermolecular ionic contacts, twist the ligand's pyridine rings into a left-handed (M) propeller (circular dichroism spectroscopy). With molecular baskets embodying the second coordination sphere about metal-containing TPAs, the here described findings should be useful for extending the catalytic function and chiral discrimination capability of TPAs.

Redox-Noninnocent Behavior of Tris(2-pyridylmethyl)amine Bound to a Lewis Acidic Rh(III) Ion Induced by C-H Deprotonation.

Rh(III) complexes having tris(2-pyridylmethyl)amine (TPA) and its derivative as tetradentate ligands showed reversible deprotonation at a methylene moiety of the TPA ligands upon addition of a strong base as confirmed by spectroscopic measurements and X-ray crystallography. Deprotonation selectively occurred at the axial methylene moiety rather than equatorial counterparts because of the thermodynamic stability of corresponding deprotonated complexes. One-electron oxidation of the deprotonated Rh(III)-TPA complex afforded a unique TPA radical bound to the Rh(III) center by a ligand-centered oxidation. This is the first example to demonstrate emergence of the redox-noninnocent character of the TPA ligand.

Lanthanide(II) Complexes Supported by N,O-Donor Tripodal Ligands: Synthesis, Structure, and Ligand-Dependent Redox Behavior.

The preparation and characterization of a series of complexes of the Yb and Eu cations in the oxidation state II and III with the tetradentate N,O-donor tripodal ligands (tris(2-pyridylmethyl)amine (TPA), BPA(-) (HBPA=bis(2-pyridylmethyl)(2-hydroxybenzyl)amine), BPPA(-) (HBPPA=bis(2-pyridylmethyl)(3.5-di-tert-butyl-2-hydroxybenzyl)amine), and MPA(2-) (H2 MPA=(2-pyridylmethyl)bis(3.5-di-tert-butyl-2-hydroxybenzyl)amine) is reported. The X-ray crystal structures of the heteroleptic Ln(2+) complexes [Ln(TPA)I2 ] (Ln=Eu, Yb) and [Yb(BPA)I(CH3 CN)]2 , of the Ln(2+) homoleptic [Ln(TPA)2 ]I2 (Ln=Sm, Eu, Yb) and [Eu(BPA)2 ] complexes, and of the Ln(3+) [Eu(BPPA)2 ]OTf and [Yb(MPA)2 K(dme)2 ] (dme=dimethoxyethane) complexes have been determined. Cyclic voltammetry studies carried out on the bis-ligand complexes of Eu(3+) and Yb(3+) show that the metal center reduction occurs at significantly lower potentials for the BPA(-) ligand as compared with the TPA ligand. This suggests that the more electron-rich character of the BPA(-) ligand results in a higher reducing character of the lanthanide complexes of BPA(-) compared with those of TPA. The important differences in the stability and reactivity of the investigated complexes are probably due to the observed difference in redox potential. Preliminary reactivity studies show that whereas the bis-TPA complexes of Eu(2+) and Yb(2+) do not show any reactivity with heteroallenes, the [Eu(BPA)2 ] complex reduces CS2 to afford the first example of a lanthanide trithiocarbonate complex.

Kinetic and Mechanistic Aspects of Atom Transfer Radical Addition (ATRA) Catalyzed by Copper Complexes with Tris(2-pyridylmethyl)amine

Kinetic and mechanistic studies of atom transfer radical addition (ATRA) catalyzed by copper complexes with tris(2-pyridylmethyl)amine (TPMA) ligand were reported. In solution, the halide anions were found to strongly coordinate to [Cu(I)(TPMA)](+) cations, as confirmed by kinetic, cyclic voltammetry, and conductivity measurements. The equilibrium constant for atom transfer (K(ATRA) = k(a)/k(d)) utilizing benzyl thiocyanate was determined to be approximately 6 times larger for Cu(I)(TPMA)BPh(4) ((1.6 ± 0.2) × 10(-7)) than Cu(I)(TPMA)Cl ((2.8 ± 0.2) × 10(-8)) complex. This difference in reactivity between Cu(I)(TPMA)Cl and Cu(I)(TPMA)BPh(4) was reflected in the activation rate constants ((3.4 ± 0.4) × 10(-4) M(-1) s(-1) and (2.2 ± 0.2) × 10(-3) M(-1) s(-1), respectively). The fluxionality of Cu(I)(TPMA)X (X = Cl or Br) in solution was mainly the result of TPMA ligand exchange, which for the bromide complex was found to be very fast at ambient temperature (ΔH(‡) = 29.7 kJ mol(-1), ΔS(‡) = -60.0 J K(-1) mol(-1), ΔG(‡)(298) = 47.6 kJ mol(-1), and k(obs,298) = 2.9 × 10(4) s(-1)). Relatively strong coordination of halide anions in Cu(I)(TPMA)X prompted the possibility of activation in ATRA through partial TPMA dissociation. Indeed, no visible differences in the ATRA activity of Cu(I)(TPMA)BPh(4) were observed in the presence of as many as 5 equiv of strongly coordinating triphenylphosphine. The possibility for arm dissociation in Cu(I)(TPMA)X was further confirmed by synthesizing tris(2-(dimethylamino)phenyl)amine (TDAPA), a ligand that was structurally similar to currently most active TPMA and Me(6)TREN (tris(2-dimethylaminoethyl)amine), but had limited arm mobility due to the rigid backbone. Indeed, Cu(I)(TDAPA)Cl complex was found to be inactive in ATRA, and the activity increased only by opening the coordination site around the copper(I) center by replacing chloride anion with less coordinating counterions such as BF(4)(-) and BPh(4)(-). The results presented in this Article are significant from the mechanistic point of view because they indicate that coordinatively saturated Cu(I)(TPMA)X complexes catalyze the homolytic cleavage of carbon-halogen bond during the activation step in ATRA by prior dissociation of either halide anion or TPMA arm.

Substituted Tris(2-pyridylmethyl)amine Ligands for Highly Active ATRP Catalysts.

The synthesis and application of a very active catalyst for copper-catalyzed atom transfer radical polymerizations (ATRP) with tris([(4-methoxy-2,5-dimethyl)-2-pyridyl] methyl)amine (TPMA*) ligand is reported. Catalysts with TPMA* ligands are approximately 3 orders of magnitude more active than those with tris(2-pyridylmethyl)amine (TPMA). Catalyst activity was evaluated by cyclic voltammetry, stopped-flow, and ATRP kinetics. Catalysts with TPMA* ligands perform better than those with TPMA ligands, especially at low catalyst concentrations.

Synthesis, Structure and Magnetic Properties of a Cyano‐bridged Dinuclear Compound fac‐{[FeIII(pzTp)(CN)2(μ‐CN)] CuII(TPyA)}·Et2O·ClO4 (pzTp = tetrakis(pyrazolyl)borate)

AbstractThe reaction of tricyanometallate precursor, (Bu4N)[(pzTp)Fe(CN)3] with Cu(ClO4)2·6H2O in the presence of the tetradentate ligand tris(2‐pyridylmethyl)amine (TPyA) afford the dinuclear compound fac‐{[FeIII(pzTp)(CN)2(μ‐CN)]CuII(TPA)}·Et2O·ClO4 (1) (pzTp = tetrakis(pyrazolyl)borate). The molecular structure was determined by single‐crystal X‐ray diffraction. In compound 1, the FeIII ion is coordinated by three cyanide carbon atoms and three nitrogen atoms of pzTp anions. Whereas, the CuII ion is surrounded by one cyanide nitrogen atom and four nitrogen atoms from the TPyA ligand. Magnetic measurements indicate the intramolecular ferromagnetic coupling is observed for compound 1, and it has S = 1 ground states.

ルテニウム-トリス（２-ピリジルメチル）アミン錯体の化学

This account describes a current summary of our research on ruthenium complexes having tris(2-pyridylmethyl)amine (TPA) and its derivatives as ligands. Topics include their characteristics, catalytic oxygenations of organic compounds including alkanes, alkenes, and alcohols by peroxide activation and proton-coupled electron transfer to generate Ru(IV)=O complexes as reactive species, Ru-TPA complexes with redox-active heteroaromatic coenzymes such as pterins and flavin analogues to elucidate their characteristics, construction of specific coordination spheres by introducing functional moieties to the TPA ligand via amide linkage to develop non-covalent interactions in the first and second coordination spheres, and bistability in photochromic structural change. The important features of the Ru-TPA complexes are following: (1) Reliable stability due to the π-back bonding from 4dπ orbitals of the ruthenium center to π* orbitals of heteroaromatic ligands, (2) Very clear reversible redox behaviour, (3) Availability of a wide range of oxidation states and a variety of reactivity at the ruthenium center, (4) Feasibility of derivatization of TPA toward the construction of unique coordination environments, and (5) Accessibility to bistability in photochemical and thermal processes.

Synthesis and Characterization of Mononuclear Ruthenium(III) Pyridylamine Complexes and Mechanistic Insights into Their Catalytic Alkane Functionalization with m‐Chloroperbenzoic Acid

A series of mononuclear RuIII complexes [RuCl2(L)]+, where L is tris(2-pyridylmethyl)amine (TPA) or one of four TPA derivatives as tetradentate ligand, were prepared and characterized by spectroscopic methods, X-ray crystallography, and electrochemical measurements. The geometry of a RuIII complex having a non-threefold-symmetric TPA ligand bearing one dimethylnicotinamide moiety was determined to show that the nicotine moiety resides trans to a pyridine group, but not to the chlorido ligand. The substituents of the TPA ligands were shown to regulate the redox potential of the ruthenium center, as indicated by a linear Hammett plot in the range of 200 mV for RuIII/RuIV couples with a relatively large rho value (+0.150). These complexes act as effective catalysts for alkane functionalization in acetonitrile with m-chloroperbenzoic acid (mCPBA) as terminal oxidant at room temperature. They exhibited fairly good reactivity for oxidation of cyclohexane (C--H bond energy 94 kcal mol(-1)), and the reactivity can be altered significantly by the electronic effects of substituents on TPA ligands in terms of initial rates and turnover numbers. Catalytic oxygenation of cyclohexane by a RuIII complex with 16O-mCPBA in the presence of H2 18O gave 18O-labeled cyclohexanol with 100% inclusion of the 18O atom from the water molecule. Resonance Raman spectra under catalytic conditions without the substrate indicate formation of a RuIV==O intermediate with lower bonding energy. Kinetic isotope effects (KIEs) in the oxidation of cyclohexane suggest that hydrogen abstraction is the rate-determining step and the KIE values depend on the substituents of the TPA ligands. Thus, the reaction mechanism of catalytic cyclohexane oxygenation depends on the electronic effects of the ligands.

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO 4 ( 1), [Co(TPA)Br]ClO 4 ( 2), [Co(TPA)(H 2O)]Cl(ClO 4) ( 3) and [Co 2(TPA) 2(μ-tp)](ClO 4) 2 · 2H 2O ( 4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV–vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2–300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl − ion in 1, Br − ion in 2, coordinated oxygen atom from H 2O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1– 3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO −) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣ D∣ = 7.3 cm −1, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm −1. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique – the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.

Synthesis of poly(vinyl acetate)‐graft‐polystyrene by a combination of cobalt‐mediated radical polymerization and atom transfer radical polymerization

AbstractVinyl acetate and vinyl chloroacetate were copolymerized in the presence of a bis(trifluoro‐2,4‐pentanedionato)cobalt(II) complex and 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) at 30 °C, forming a cobalt‐capped poly(vinyl acetate‐co‐vinyl chloroacetate). The addition of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy after a certain degree of copolymerization was reached afforded 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐terminated poly(vinyl acetate‐co‐vinyl chloroacetate) (PVOAc–MI; number‐average molecular weight = 31,000, weight‐average molecular weight/number‐average molecular weight = 1.24). A 1H NMR study of the resulting PVOAc–MI revealed quantitative terminal 2,2,6,6‐tetramethyl‐1‐piperidinyloxy functionality and the presence of 5.5 mol % vinyl chloroacetate in the copolymer. The atom transfer radical polymerization (ATRP) of styrene (St) was studied with ethyl chloroacetate as a model initiator and five different Cu‐based catalysts. Catalysts with bis(2‐pyridylmethyl)octadecylamine (BPMODA) or tris(2‐pyridylmethyl)amine (TPMA) ligands provided the highest initiation efficiency and best control over the polymerization of St. The grafting‐from ATRP of St from PVOAc–MI catalyzed by copper complexes with BPMODA or TPMA ligands provided poly(vinyl acetate)‐graft‐polystyrene copolymers with relatively high polydispersity (>1.5) because of intermolecular coupling between growing polystyrene (PSt) grafts. After the hydrolysis of the graft copolymers, the cleaved PSt side chains had a monomodal molecular weight distribution with some tailing toward the lower number‐average molecular weight region because of termination. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 447–459, 2007

Unexpected assembly of a (μ-oxo)(μ-formato)diiron(III) complex from an aerobic methanolic solution of Fe(III) and the TPA ligand

Crystals of a (μ-oxo)(μ-formato)diiron(III) complex [Fe 2(μ-O)(TPA) 2(O 2CH)](ClO 4) 3 ( 1) formed from a methanolic solution of Fe(ClO 4) 3 and the tetradentate tripodal ligand tris(2-pyridylmethyl)amine (TPA) in methanol when left standing for days under aerobic conditions, despite the fact that no formate ion had been added to the solution. Complex 1 was found to have UV—Vis and 1H NMR properties very similar to those of [Fe 2(μ-O)(TPA) 2(O 2CCH 3)](ClO 4) 3 ( 2), and its formula weight was corroborated by fast atom bombardment mass spectrometry. Complex 1 crystallized in the monoclinic space group P2 1 (No. 4) with a = 11.693(3), b = 10.414(4), c = 18.144(6) Å, and β = 93.98(3)°. The structure was determined at −84°C from 4464 out of a total of 6753 reflections with R = 0.058 and R w = 0.068. The crystal structure confirmed the presence of a (μ-oxo)(μ-carboxylato)diiron(III) unit with distinct iron sites as found for 2. The formate bridge was shown to derive from the aerobic oxidation of methanol: 1 was not formed in the absence of air, and 2 was formed from the reaction carried out in ethanol solvent. Manometric measurements showed that the amount of dioxygen consumed was approximately stoichiometric to the combined amounts of formate found in 1 (80%) and formaldehyde (20%) found in the reaction mixture.

Cu(II)-α-keto acid complexes as structural models of α-keto acid-dependent enzymes: syntheses, crystal structure and properties of [Cu(L) (benzoylformate)

Three [Cu II(L)(BF)] + complexes, where L is tris(2-pyridylmethyl)amine (TPA) ( 1), bis(2-pyridylmethyl)amine (BPA) ( 2) or bis(2-benzimidazolymethyl)amine (BBA) ( 3), and BF is benzoylformate, have been synthesized as structural models for the active site of α-keto acid-dependent enzymes. Single crystals of 1 P2 1/n, a = 11.3332(1), b = 9.0159(1), c = 40.2883(1) A ̊ , Z = 4, V = 4114.62(6) A ̊ 3) were obtained and subjected to X-ray diffraction analysis. Complex 1 has a mononuclear trigonal bipyramidal Cu(II) center with a monodentate BF occupying an axial position. The solid structure of 1 appears to be maintained in solution as probed by IR, Vis, NMR and EPR spectroscopy. Spectroscopic studies of 2 and 3 with tridentate ligands replacing the tetradentate TPA ligand suggest a square pyramidal Cu(II) center in these two complexes, and the BF is proposed to bind in a bidentate manner via its two carboxylate oxygen atoms. The fact that the α-keto carbonyl is not involved in binding to the Cu(II) center suggests that it is not crucial for the formation of Cu(II)-BF complexes. This conclusion supports the working model proposed for the metal site in Cu-TfdA (Cu-substituted 2,4-dichlorophenoxyacetate/α-ketoglutarate dioxygenase) and its interaction with the cofactor α-ketoglutarate.

Synthesis, crystal structure and spectroscopic characterization of the complex of palladium(II) with tris(2-pyridylmethyl)amine

A complex of palladium(II) chloride with tris(2-pyridylmethyl)amine (TPA) has been synthesized and characterized. The single-crystal structure has been determined by X-ray diffraction analysis. The palladium(II) atom in the title complex is in a square planar environment surrounded by three nitrogen atoms of TPA and one chlorine atom, with bond lengths in the range of 2.004–2.012 Å for PdN and 2.296 Å for PdCl. The properties of [Pd((TPA)Cll)]·ClO 4 have been further studied with IR and UV-vis techniques. IR spectra show that most of the bands of [Pd((TPA)Cl)]·ClO 4 are shifted to lower wavenumbers in comparison with those of the TPA ligand.

Electrospray mass spectrometry and X-ray crystallography studies of divalent metal ion complexes of tris (2-pyridylmethyl) amine

Coordination complexes of tris(2-pyridylmethyl)amine (TPA) were prepared and characterized including [Zn(TPA)X]ClO 4 (X = Cl, Br, I), [Cu(TPA)Br]ClO 4, [Cd(TPA)Br 2], [Cd(TPA) (H 2O) (NO 3]NO 3, [Cd(TPA)I 2], [Co9TPA)Cl 2], [Fe(TPA)Cl 2] and [Mn(TPA) Cl 2] The solid-state structures of Zn(TPA)ClClO 4 (monoclinic space group, P2 1/c; a = 14.733(3), b = 9.408(2), c = 29.722(4) A ̊ , β=90.65(1)°; V=4119(1) A ̊ 3 ; Z=8, Zn(TPA)IClO 4 (triclinic space group, P1; a = 14.435(3), b = 17.69(4), c = 9.745(2) A ̊ , α=100.36(2), β=91.40(2), γ=114.62(1)°; V=2134(2) A ̊ 3 ; Z=4) and Cu(TPA)BrClO 4 (monoclinic space group, P2 1/ c; a=14.555(3), b=9.519(2), c=30.024(3) A ̊ , β=91.66(1)°; V=4158(1) A ̊ 3 ; Z=8), contain trigonal bypyramidal metal ions with halide coordinated in an apical position. The X-ray structure of [Cd(TPA)(H 2O)(NO 3)]NO 3 (monoclinic space group, P2 1/ n; a=15.415(4), b=9.333(2), c=17.429(4) a ̊ , β=99.39(2)° ; V=2474(2) A ̊ 3 ; Z=4) contains a seven-coordinate cadmium ion including a bidentate nitrate anion and a water molecule as ligands. The X-ray structure of [Cd(TPA)I 2] (monoclinic space group, P2 1/ n; a=10.383(2), b=13.813(2), c=15.391(1) A ̊ , β=106.07(1)° ; V=2121.1(5) A ̊ 3 ; Z=4) contains a cadmium ion with an approximately octahedral geometry. In this structure, the TPA ligand is conformationally distorted in order to accomodate the octahedral coordination geometry. The convenient new technique, electrospray mass spectrometry (ESI-MS), provided mass spectra consistent with X-ray and spectroscopic data. Mass analysis of solutions containing added competing anions was also consistent with solution data.