Pendant-arm Macrocycle Research Articles

Tuning of the flexibility in metal-organic frameworks based on pendant arm macrocycles.

An isostructural series of flexible metal-organic frameworks based on macrocycles having diverse pendant arms was developed to tune flexibility depending on functional groups. The pendant arms directing into the pores were found to play a key role in imparting different gate-opening behaviours in the threshold pressure and sorption capacity upon interaction with guest molecules.

Oxo-anion recognition by mono- and bisurea pendant-arm macrocyclic complexes.

The novel macrocyclic copper(II) complexes [2](2+) and [3](2+), carrying one or two (nitrophenyl)urea fragments appended to an azacyclam or diazacyclam framework, exploit the hydrogen-bond-forming abilities of the urea subunits, along with the metal-ligand interaction, in the recognition of anionic species. Equilibrium studies in acetonitrile performed on [2](2+) and [3](2+) show that (nitrophenyl)urea pendant arms strongly interact with anionic species such as carboxylates and phosphates, which display both coordinating tendencies toward copper(II) and good affinity toward urea subunits. Stability constants of the adducts are considerably higher than those determined for the interaction of the same anions with a "plain urea" reference compound, confirming the synergistic action of metallomacrocyclic and urea subunits. Complex [2](2+) forms 1:1 adducts with acetate, benzoate, hydrogendiphosphate, and dihydrogen phosphate, while complex [3](2+) interacts with the same anions according to both 1:1 and 1:2 stoichiometries, with the exception of hydrogendiphosphate, which forms only the 1:1 adduct with a distinctly high association constant (log K > 7). Spectrophotometric investigations suggest that oxoanionic species interact with the complexes according to a "bridged" mode, inducing the macrocyclic systems to adopt a scorpionate-like conformation, as confirmed by crystallographic studies on the [3](2+)/succinate adduct.

The stabilities and formation kinetics of some macrocycles with copper(II): crystal structures of some pendant arm macrocycles

Kinetics of complex formation and stability constants of tetra-(2-hydroxpropyl) substituted cyclam (L3) and cyclen (L4) with copper(II) have been studied in aqueous solution at room temperature. These data are compared to the corresponding parent compounds (cyclam L1 and cyclen L2) in an attempt to define the effect of pendant arm upon kinetics and stability constants of the complexes. The kinetics were observed by stopped-flow measurements followed at multiwavelengths. These ligands were chosen to furnish information concerning effect of pendant groups and cavity size on the kinetics and stability of the complexes. Stopped-flow and spectrophotometric titration techniques were used for evaluation of the kinetics and stability constants, respectively. The apparent rate constants increase as CuL3 > CuL4 > CuL1 > CuL2. Activation parameters and stability constants of the complexes were estimated. The effect of cavity size on the rate of reaction can be observed in CuL3 > CuL4 and CuL1 > CuL2 and the effect of pendant groups in CuL3 > CuL1 and CuL4 > CuL2. Mechanism of the complex formation reaction is proposed. The enhanced stability of the copper(II) complexes formed with L1 and L2 macrocyclic ligands is compared to those formed with analogous pendant arm species.

Kinetics and mechanism of complex formation of a pendant arm macrocycle reacting with copper(II) and mercury(II)

Stopped flow spectrophotometry was used to study the complexation kinetics of the N-pendant arm macrocycle: N,N′,N″,N‴-tetrakis (2-carbamoylethyl)-1,4,8,11-tetraazacyclotetradecane (TCEC=L) reacting with two metal ions Hg(II) and Cu(II) in aqueous solutions at 25°C and I=0.2M (Hg) and 0.5M (Cu), respectively. All the kinetic measurements were carried out under pseudo-first-order conditions in the pH ranges 4.0–5.2 and 5.0–6.6 for the Cu(II)/TCEC and Hg(II)/TCEC systems, respectively, with the total ligand concentration at least 10-fold excess of the total concentration of Cu(II) and the total concentration of Hg(II) at least 10-fold excess of the total concentration of the ligand. The complex formation is found to be a one step second order reaction (first order in both the metal ion and the ligand). The pH dependence was successfully analyzed in terms of the different reactivities for the different ligand species (kLxH):M+HxL→kHxLMHxL(M=Hg(II),Cu(II))The rate constants calculated for the mono- and diprotonated species of TCEC were lower than those for the parent cyclam ligand by a factor of 102(Cu). These results strongly indicate the noninvolvement of the pendant arms of TCEC in the complex formation reaction between the metal ion and the partially protonated ligand species and that the rate determining step is the first bound of the metal ion to the tertiary ring nitrogen for both ions.

Controlling the binding of dihydrogen using ruthenium complexes containing N-mono-functionalised 1,4,7-triazacyclononane ligand systems

Pendant arm macrocycles derived from 1,4,7-triazacyclononane were reacted with RuHCl(CO)(PPh(3))(3) and RuHCl(PPh(3))(3) to yield air-stable cationic ruthenium hydrides that were characterised by a variety of techniques, including X-ray crystallography. Protonation of the metal hydride complexes with a proton source yielded eta(2)-dihydrogen complexes. The lifetime of the dihydrogen ligand was effected by a judicious choice of ancillary ligands.

Aminoacid N-substituted 1,4,7-triazacyclononane and 1,4,7,10-tetraazacyclododecane Zn2+, Cd2+ and Cu2+ complexes. A preparative, potentiometric titration and NMR spectroscopic study.

The pK(a)s and Zn2+, Cd2+ and Cu2+ complexation constants (K) for 1,4,7-tris[(2''S)-acetamido-2''-(methyl-3''-phenylpropionate)]-1,4,7-triazacyclononane, 1, 1,4,7-tris[(2''S)-acetamido-2''-(1''-carboxy-3''-phenylpropane)]-1,4,7-triazacyclononane, H(3)2, 1,4,7-tris[(2''S)-acetamido-2''-(methyl-3''-(1H-3-indolyl)propionate)]-1,4,7-triazacyclononane, 3, and 1,4,7,10-tetrakis[(2''S)-acetamido-2''-(methyl-3''-phenylpropionate)]-1,4,7,10-tetraazacyclododecane, 4, 1,4,7,10-tetrakis[(2''S)-acetamido-2''-(1''-carboxy-3''-phenylpropane)]-1,4,7,10-tetraazacyclododecane, H(4)5, in 20 : 80 v/v water-methanol solution are reported. The pK(a)s within the potentiometric detection range for H(3)1(3+) = 8.69 and 3.59, for H(6)2(3+) = 9.06, 6.13, 4.93 and 4.52, H(3)3(3+) = 8.79 and 3.67, H(4)4(4+) = 8.50, 5.62 and 3.77 and for H(8)5(4+) = 9.89, 7.06, 5.53, 5.46, 4.44 and 4.26 where each tertiary amine nitrogen is protonated. The complexes of 1: [Zn(1)]2+(9.00), [Cd(1)]2+ (6.49), [Cd(H1)]3+ (4.54) and [Cu(1)]2+ (10.01) are characterized by the log(K/dm3 mol(-1)) values shown in parentheses. Analogous complexes are formed by 3 and 4: [Zn(3)]2+ (10.19), [Cd(3)]2+ (8.54), [Cu(3)]2+ (10.77), [Zn(4)]2+ (11.41) [Cd(4)]2+ (9.16), [Cd(H4)]3+ (6.16) and [Cu(4)]2+ (11.71). The tricarboxylic acid H(3)2 generates a greater variety of complexes as exemplified by: [Zn(2)-] (10.68) [Zn(H2)] (6.60) [Zn(H(2)2)+] (5.15), [Cd(2)](-) (4.99), [Cd(H2)] (4.64), [Cd(H2(2))]+ (3.99), [Cd(H(3)2)]2+ (3.55), [Cu(2)](-) (12.55) [Cu(H2)] (7.66), [Cu(H(2)2)]+ (5.54) and [Cu(2)2](4-) (3.23). The complexes of H(4)5 were insufficiently soluble to study in this way. The 1H and 13C NMR spectra of the ligands are consistent with formation of a predominant Zn2+ and Cd2+ Delta or Lambda diastereomer. The preparations of the new pendant arm macrocycles H(3)2, 3, 4 and H(4)5 are reported.

Structure and Kinetics of Oxidation of Amphiphilic Nickel(II) Pentaazamacrocycles by Peroxodisulfate and by a Nickel(III) Pendant-Arm Macrocycle

Three nickel(II) pentaazamacrocycles bearing pendant alkyl tails have been synthesized,and the crystal structure of one (bearing an octyl tail) is reported. The redox potentials of the complexes, for oxidation of the nickel(II) centre, is 0.72 V (versus S.H.E.) in all cases, indicating that the pendant alkyl tails have no effect on the redox site. The kinetics of oxidation of the complexes by peroxodisulfate, S2O8 2- and by aqua(5, 5, 7,12, 12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato)nickel(III),[Ni(hmca)(OH2)]2+ have been studied. Oxidation by S2O8 2- occursby ion-pairing of the reactants, followed by electron transfer with concomitant peroxo bond fissure. Oxidation by [Ni(hmca)(OH2)]2+ occurs by an outer sphere electron transfer process. Redox kinetics at the nickel centre provides a probe for supramolecular interactions at the pendant tails in such complexes.

Synthesis and X-ray Crystal Structure of Meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1,8-di-(1-methylnaphthalene)

The pendant-arm macrocycle, meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1,8-di-(1-methylnaphthalene) has been synthesized and its single crystal structure determined. The molecule crystallizes in a primitive monoclinic cell, with the space group P21/a (#14). The cell dimensions are a = 10.778(3)Å, b = 13.809(3) Å, c = 11.420(2) Å, ∃ = 102.49(2)°, volume = 1659.5(6) Å3.

Outer-sphere electron transfer reactions of aqua(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato) nickel(II) and (III).

The outer-sphere oxidation of the nickel(II) complex of the deprotonated pendant-arm macrocycle, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate, [NiL1(OH2)]+ by bis-(1,4,7-triazacyclononane)nickel(III), [Ni(tacn)2]3+ has been studied in aqueous perchlorate media. The reaction displays reversible second-order behaviour and the kinetic study reveals the forward and reverse rate constants for the reaction: [Formula: see text] The kinetics show the forward reaction to be acid dependent, a feature that is attributed to protonation of the acetato group of the nickel(II) complex. Using Marcus theory, the self-exchange rate for the [NiL1(OH2)]+/2+ couple has been calculated. The nickel(II/III) electron transfer is a reversible one electron process with E° = 1.04 V (vs. S.H.E.). The formation of the authentic nickel(III) product has been confirmed by esr spectroscopy. The kinetics of reduction of the [NiL1(OH2)]2+ species by Fe2+(aq) exhibits a second-order rate law, the reaction being independent of acid. Using the calculated self-exchange rate for the nickel complex, its reaction with Fe2+(aq) has been examined in terms of an inner- versus outer-sphere mechanism. Key words: nickel(III), pendant-arm macrocycles, hexaaquairon(II), outer sphere, kinetics, Marcus theory.

Applications for Polyaza Macrocycles with Nitrogen‐Attached Pendant Arms

AbstractFor Abstract see ChemInform Abstract in Full Text.

An unusual pendant-arm macrocycle formed by condensation of a cobalt(iii) tripodal complex with methanal

The reaction of [Co(ten)]3+ {ten = 4,4′,4″-ethylidynetris(3-thiabutan-1-amine)} with methanal and base in acetonitrile or water led to the synthesis of an unusual pendant-arm macrocyclic complex, 8-(4′-ammonio-2′-thiabutyl)-8-methyl-1-oxa-6,10-dithia-3,13-diazacyclo-tetradecane(chloro)cobalt(III) triperchlorate trihydrate. The structure of the complex has been established by X-ray crystallographic analysis and such molecules can readily be tied to polymers and proteins. The synthesis, chemical reactions, spectroscopy and electrochemical properties of the macrocyclic complex are described.

Coordination Chemistry of Lipoic Acid and Related Compounds V [1]. New Heteroditopic Ligands Derived from Monoazacrown Ethers and Lipoic Acid

Lipoyl imidazolide reacts with aza-15-crown-5 (1,4,7,10-tetraoxa-13-azacyclopentadecane) or aza-18-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) to afford new N-lipoylated azacrown compounds in good yields. These compounds can be transformed into 1,3-dithiols and amines by reduction with complex hydrides of the disulfide and/or amide group of the lipoyl chain. The new pendant-arm macrocycles react as heteroditopic ligands by forming dithiolate and disulfide complexes with the ‘soft’ metal ions Ni2+ and Pd2+, respectively, and an amine complex with the ‘hard’ Li+ ion. Semiempirical and DFT calculations on the complexation of a lithium ion give a most favourable structure in which the azacrown and two solvent molecules are in contact with the metal but not the pendant arm.

Synthesis and Complexation of a Chiral Sexidentate Pendant-Arm Macropolycyclic Polyamino Acid

The reaction of the acyclic complex ion (methyl (SS,SS)-3-[(2�-aminocyclohexyl)amino]-2-[(2�-aminocyclohexyl)-aminomethyl]propionate)copper(II) with formaldehyde and nitroethane in basic solution yields the pendant-arm macrocyclic complex (SS,SS)-(methyl-15-methyl-15-nitro-2,6,13,17-tetraazatricyclo[16.4.0.07,12]docosane-4-carboxylate)copper(ii) ion. Reduction with zinc in hydrochloric acid yields the hydrochloride salt of the pendant-arm macrocycle (SS,SS)-15-amino-15-methyl-2,6,13,17-tetraazatricyclo[16.4.0.07,12]docosane-4-carboxylic acid (1), separated into and isolated as the major trans (1a) and minor cis (1b) isomers. Co-ordination of (1) to several metal ions [CoIII, CrIII, NiII, ZnII, CuII] and comparison with a previously reported analogue without the cyclohexane rings, trans-13-amino-13-methyl-1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid (2a) salt, is described. The [Ni{(1a) – H+}](ClO4) crystallizes in the monoclinic space group P21, a 9.710(2), b 14.442(1), c 10.317(2) Å, β 96.02(2)°. The nickel displays a distorted octahedral geometry, with all four secondary amines coordinated (Ni–N range 2.044(7)–2.063(6) Å), in addition to pendant primary amine (Ni–N, 2.109(6) Å) and carboxylate (Ni–O, 2.100(6) Å) groups. Protonation constants for the trans (1a) and cis (1b) isomers and stability constants of these isomers with the labile metal ions ZnII, CdII, HgII, PbII, MnII, and CoII were determined by potentiometric titrations. The log K values for 1 : 1 complexes show small variations between geometric isomers.

Structure and redox kinetics of nickel(II) tetraazamacrocycles containing pendant carboxylate groups

The nickel(II) complex of the deprotonated pendant-arm macrocycle 5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetate (L2)2–has been structurally characterized by X-ray crystallography. The Ni(II)L2complex crystallizes in the monoclinic system, space group P21/c, with a = 12.981(8), b = 16.474(6), c = 14.262(7) Å and β = 98.81(4)°. The complex shows a distorted cis-geometry about the metal centre, the macrocyclic ligand being folded about a N-Ni-N axis, with the pendant arms coordinated cis to one another. The Ni(II)L1(where (L1)2–is meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetate) and Ni(II)L2complexes undergo reversible one-electron oxidation, with redox potentials of 0.717 and 0.766 V (vs. S.H.E.), respectively. Chemical oxidation of the complexes by peroxodisulfate obey overall second-order rate laws. Enthalpies and entropies of activation for Ni(II)L1are 38 ± 3 kJ mol–1and -106 ± 9 J K–1mol-1; and for Ni(II)L2the corresponding values are 41 ± 5 kJ mol–1and –126 ± 15 J K-1mol-1. Outer-sphere oxidation of Ni(II)L1by bis-(triazacyclononane)nickel(III) ([Ni(III)(tacn)2]3+) has been studied, and a self-exchange rate constant for the [Ni(II)L1]0/+system has been estimated at 55 mol–1dm3s–1.Key words: peroxodisulfate, nickel(II), dicarboxylato-pendant arm macrocycles, bis-(triazacyclononane)nickel(III), self-exchange rate.

Synthesis and characterization of magnesium and zinc complexes of 1,4,7-triazacyclononane- N-acetate. Potential models for the active site of RuBisCo

Reaction of the tetradentate pendant-arm macrocycle 1,4,7-triazacyclononane- N-acetate (L) with Zn(O 3SCF 3) 2 or Mg(O 3SCF 3) 2 in alcohol produces the six-coordinate complexes [ZnL(H 2O)]O 3SCF 3·C 2H 5OH ( 1) and [MgL(H 2O) 2]O 3SCF 3 ( 2). Compounds 1 and 2 were characterized by single-crystal X-ray crystallography. The complex cation of 1 forms a polymeric chain with zinc centers bridged in a syn, anti fashion by acetate pendant arms. The complex cation of 2 is mononuclear, with two adjacent coordination sites on magnesium occupied by water molecules. These labile coordination sites may provide a binding site for activation of substrates in functional modeling of magnesium enzymes such as RuBisCo. 1H and 13C NMR spectroscopy demonstrates that L remains bound to magnesium in methanol solution. Crystal data: 1, orthorhombic, space group P2 12 12 1, a=9.0536(7), b=14.3750(11), c=14.4741(11) Å, V=1883.7(2) Å 3, Z=4, R=0.041; 2, orthorhombic, space group P2 12 12 1, a=8.5949(3), b=13.9694(4), c=14.0076(5) Å, V=1681.83(10) Å 3, Z=4, R=0.0248.

Synthesis and Full Characterisation of the First Discrete Binuclear Complex Featuring a Two-Electron (σ)μ2-κC:κC Bridging Cyanide

Nitrile-functionalised pendant-arm macrocycles have been used as supporting ligands for the first binuclear complex containing a discrete two-electron (σ) μ2-κC:κC symmetrically bridged CN− ligand (see example depicted; N= hatched circle, COpen circle, S=shaded circle). A different coordination mode of the bridging CN− ligand is observed on changing the length of the aliphatic chain in the functionalised pendant arms of the macrocycle.

Pendant-Arm Macrocycles Derived from the Cyclocondensation Reaction of Sodium 2,6-Diformyl-4-substitutedphenolates and Tris-(2-aminoethyl)amine Derivatives. Preparation, Characterization and Properties of their Dinuclear Copper(II) Complexes

A series of pendant-arm Schiff base macrocycles have been obtained via the cyclocondensation reaction between sodium 2,6-diformyl-4-substitutedphenolates and tris-(2-aminoethyl)- amine derivatives followed by transmetallation with Cu(ClO4)2·6H2O. The resulting dinuclear copper(II) complexes have been characterized by elemental analysis, infrared and mass spectra as well as magnetic moments at room temperature. All complexes have been electrochemically investigated, and two typical compounds have been studied with ESR spectra as well.

Complexation of Pendant Arm Macrocycles with Cu(II) Hydroxo Complexes in Strongly Alkaline Solutions. Investigation of pH Dependences

The complexation kinetics of fully deprotonated pendent arm macrocyclic ligands with Cu(II) hydroxo species had been investigated in aqueous solution at high pH. The pH dependence of the initial second order reaction is explained by the different reactivities for the tris- and tetra-hydroxo species of Cu(II). In some instances, the pendent arms accelerate the rates of the complex formation reaction. An intermediate complex is observed which reacts in a first order reaction to the final complex. The pH dependence of this reaction is the result of the existence of different numbers of aquo and hydroxo ligands additionally coordinated to the metal. Spectral changes for this second step are small, suggesting an isomerisation reaction is taking place.

Outer-sphere complex formation and catalysis of adenosine 5′-triphosphate hydrolysis with polyammonium cations: kinetics employing an attenuated total reflectance infrared method

The outer-sphere complex formation constants between adenosine 5′-triphosphate (ATP) and the pendant arm macrocycles trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine ( 1) and 10-(3′-aminobenzyl)-1,4,8,12-tetraazacyclopentadec-10-ylamine ( 2) as well as the linear polyamine pentaethylenehexamine ( 4) are reported. For a given polyamine, the strength of the interaction with the ATP 4− anion increases with increasing degree of protonation and conversely the complex stability decreases as the charge on the anion decreases, as anticipated. The kinetics of ATP hydrolysis alone and in the presence of 1,2,4 and tetraethylenepentamine ( 3) have been followed by a recently-established attenuated total reflectance infrared (ATR-IR) method, illustrated here with complex systems for the first time. Results obtained for spontaneous hydrolysis and catalysis by protonated 3 and 4 agree well with determinations employing other techniques, indicating the general applicability of the new method. The presence of pendant protonated amine groups on macrocycles do not enhance catalysis compared with unsubstitutes macrocycles. Catalytic effects from the protonated acyclic polyamines are larger than those induced by the macrocycles. The dexibility of the polyammonium compound plays an important role towards optimising interaction with ATP in the precursor outer-sphere complex.

Molybdenum carbonyl complexes of pendant-arm polyazamacrocycles

Molybdenum hexacarbonyl reacted with the pendant-arm macrocycles 10-methyl-1,4,8,12-tetraazacyclopentadecane-10-amine (L1) and trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L2) in the absence of air to form complexes fac-[MoL1(CO)3] and [Mo2L2(CO)8] respectively. The mononuclear complex has the macrocycle bound in a tridentate manner, including the pendant primary amine, whereas the dinuclear complex exhibits a bridging bis(didentate) co-ordination mode, again involving the pendant primary amines. Structures have been defined by crystal structure analyses. The preferential binding of the pendant primary amines rather than additional secondary amines parallels similar behaviour observed earlier with some mercury(II) and rhodium(III) complexes, and points to the important general role of this pendant, despite being fused directly to the macrocyclic ring, in metal-ion binding.