Tren Complexes Research Articles

Synthesis, characterization and cytotoxicity studies of Co(III)-flavonolato complexes

Hypoxia activated Co(III) complexes as prodrugs may provide with a selective delivery of cytotoxic or antibacterial compounds. Whithin this field sixteen novel Co(III) ternary complexes with the general formula [Co(4N)(flav)](ClO4)2, where 4N = tris(2-aminoethyl)amine (tren) or tris(2-pyridylmethyl)amine (tpa) and flav = deprotonated form of differently substituted flavonols have been synthesized, characterized, and their cytotoxicity assayed under both normoxic and hypoxic conditions. Molecular structures of two free flavonols and seven complexes are also reported. In all the complexes the bioligands exhibited the expected (O,O) coordination mode and the complexes showed a slightly distorted octahedral geometry. Cyclic voltammetric studies revealed that both the substituents of the flavonoles and the type of 4N donor ligands had an impact on the reduction potential of the complex. The ones containing tren demonstrated significantly higher stability than the tpa analogues, making these former compounds promising candidates for the development of hypoxia-activated prodrug complexes. Tpa complexes showed higher activity against both selected human cancer cell lines (A549, A431) than their free ligand flavonols, indicating that the anticancer activity of the bioligand can be enhanced upon complexation. However, slight hypoxia-selectivity was found only for a tren complex (11) with moderate cytotoxicity.

Electrocatalytic Water Oxidation by Mononuclear Cu(II) Aliphatic Tetraamine Complexes

AbstractWe report here electrocatalytic water oxidation by a series of mononuclear Cu(II) aliphatic tetraamine complexes at various pH. In phosphate buffer solution of pH 12, the Cu(II)‐Tren (Tren is tris‐(2‐aminoethyl)amine) complex is decomposed to generate a Cu oxide/hydroxide film with phosphate incorporated on the electrode surface which can catalyze water oxidation with a small onset overpotential of 420 mV and a low Tafel slope of 48 mV dec−1. By contrast, the other two Cu(II) complexes, Cu(II)‐Me3(Tren) (Me3(Tren) is (tris‐(2‐(methylamino)ethyl)amine)) and Cu(II)‐Me6(Tren) (Me6(Tren) is tris‐(3‐methyl‐3‐azabuty)amine), having the ligands that sharing the same molecular skeleton of Tren but with methyl group substituents, are noneffective to form the surface‐bound active species. The experimental results indicate that the Cu(II)‐Tren complex decomposes by intra‐complex proton‐coupled electron transfer (PCET) from the amine ligand to the higher‐oxidation‐state Cu with significant pH/buffer base effects. At pH 9, water oxidation with Cu(II)‐Tren transforms from heterogeneous to homogeneous featuring a single‐site catalysis mechanism. Moreover, the comparison of the three Cu(II) complexes at this pH also suggests a steric effect of methyl groups on the catalysis performance. As pH decreases further to 7, Tren, with pKb ∼5.9, becomes less coordinating and precipitation of a Cu3(PO4)2 film during electrolysis leads to electrode passivation, which inhibits the homogeneous water oxidation at this pH.

ChemInform Abstract: Uranium Triamidoamine Chemistry

AbstractReview: [57 refs.

Uranium triamidoamine chemistry.

Triamidoamine (Tren) complexes of the p- and d-block elements have been well-studied, and they display a diverse array of chemistry of academic, industrial and biological significance. Such in-depth investigations are not as widespread for Tren complexes of uranium, despite the general drive to better understand the chemical behaviour of uranium by virtue of its fundamental position within the nuclear sector. However, the chemistry of Tren-uranium complexes is characterised by the ability to stabilise otherwise reactive, multiply bonded main group donor atom ligands, construct uranium-metal bonds, promote small molecule activation, and support single molecule magnetism, all of which exploit the steric, electronic, thermodynamic and kinetic features of the Tren ligand system. This Feature Article presents a current account of the chemistry of Tren-uranium complexes.

A Photoreducible Copper(II)‐Tren Complex of Practical Value: Generation of a Highly Reactive Click Catalyst

A detailed study on the photoreduction of the copper(II) precatalyst 1 to generate a highly reactive cuprous species for the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction is presented. For the photoactive catalyst described herein, the activation is driven by a photoinduced electron transfer (PET) process harnessing a benzophenone-like ketoprofenate chromophore as a photosensitizer, which is equally the counterion. The solvent is shown to play a major role in the Cu(II) to Cu(I) reduction process as the final electron source, and the influence of the solvent nature on the photoreduction efficiency has been studied. Particular attention was paid to the use of water as a potential solvent, aqueous media being particularly appealing for CuAAC processes. The ability to solubilize the copper-tren complexes in water through the formation of inclusion complexes with β-CDs is demonstrated. Data is also provided on the fate of the copper(I)-tren catalytic species when reacting with O2, O2 being used to switch off the catalysis. These data show that partial oxidation of the secondary benzylamine groups of the ligand to benzylimines occurs. Preliminary results show that when prolonged irradiation times are employed a Cu(I) to Cu(0) over-reduction process takes place, leading to the formation of copper nanoparticles (NPs). Finally, the main objective of this work being the development of photoactivable catalysts of practical value for the CuAAC, the catalytic, photolatent, and recycling properties of 1 in water and organic solvents are reported.

The Efficient Copper(I) (Hexabenzyl)tren Catalyst and Dendritic Analogues for Green “Click” Reactions between Azides and Alkynes in Organic Solvent and in Water: Positive Dendritic Effects and Monometallic Mechanism

AbstractAn easily synthesized, copper(I) (hexabenzyl)tren complex 1 is an efficient catalyst for the copper(I)‐catalyzed Huisgen‐type 1,3‐cycloaddition between azides and alkynes (CuAAC) reaction in toluene. Alternatively, a convenient procedure involves mixing copper(I) bromide (CuBr) with hexabenzyltren and the substrates in toluene which gives, for instance, 100% yield of triazole in 10 min using 0.1 equiv. catalyst with phenylacetylene and benzyl azide at room temperature. The toluene‐soluble catalyst 1 is recyclable and is applied, for example, to the CuAAC synthesis of an 81‐branched dendrimer that previously required the use of a stoichiometric amount of copper(II) sulfate (CuSO4)+sodium ascorbate “catalyst”. Dendritic copper(I)‐centered analogues 2 and 3 of the first and second generations (G1 and G2, respectively) containing respectively 18 and 54 branch termini, including a 54‐branched water‐soluble metallodendrimer 5, are also very efficient catalysts for the CuAAC reaction. With the metallodendritic Cu(I) derivatives 2 and 3, the dendritic frame brings about steric protection against the well‐known inner‐sphere aerobic oxidation of Cu(I) to bis(μ‐oxo)‐bis‐Cu(II). The metallodendrimers 2 and 3 are also sometimes more efficient than the parent catalyst, as shown by kinetic studies. Catalysis in water without co‐solvent of the CuAAC reactions of water‐insoluble substrates was achieved under ambient conditions in good yields with the recyclable catalyst 5. Efficient catalysis of the CuAAC reaction by these bulky Cu(I) metallodendrimers emphasizes the monometallic mechanism. The difference of kinetic behavior between 1 and CuBr+hexabenzyltren suggests, however, that whereas a monometallic mechanism is working for 1, the mixture of CuBr+hexabenzyltren might involve the bimetallic mechanism proposed by Fokin and Finn.

Surface oxidation of Co 2+ and its dependence on ligand coordination number in silica polyamine composites

Coordination of CoCl 2 solutions to the silica polyamine composite, WP-1, made with the branched polymer polyethylenimine ( PEI) shows irreversible binding resulting from surface oxidation of the Co 2+–Co 3+. This is not the case for the silica polyamine composite BP-1 made with the linear polymer polyallylamine where reversible binding and no oxidation is observed. These observations suggested that oxidation of the cobalt was related to the greater coordination number available with the branched polyamine relative to the linear polyamine. A study of the kinetics of cobalt binding to WP-1 indicated initial loading of Co 2+ at relatively low coordination number followed by desorption of Co 2+ leading to oxidation and irreversible binding. Exclusion of oxygen from the composite-cobalt solution mixtures resulted in irreversible binding at a level that was 14% of the initial experiments. These observations prompted us to undertake a study to elucidate the coordination number around cobalt in the case of the branched polymer PEI. Towards this end, we have synthesized the model complexes [(tren)Co(H 2O) 2] 3+3Cl − (tren = tris(2,2′,2″aminoethyl)amine) and [(dien)Co(H 2O) 3] 3+3Cl − (dien = diethylenetriamine). The UV–Vis spectra of these model complexes were compared with Co 3+ coordinated to PEI in solution and it was concluded that the UV–Vis spectrum of the tren complex was closer to that observed for the solution UV–Vis spectrum of Co 3+–PEI. These data indicated that coordination of four amines was needed to drive surface oxidation under ambient conditions. In order to further elucidate the coordination number of a metal coordinated to the surfaces of WP-1 and BP-1, we reacted these composites with the probe molecule [Ru(CO) 3(TFA) 3] −K + (TFA = trifluoroacetate) (1) where the carbonyl stretching frequencies could be used as a measure of coordination number and geometry of the adsorbed complex. The IR of this complex on WP-1 indicated a monocarbonyl species while the IR of this complex on BP-1 indicated the presence of dicarbonyl species on the surface. These data are consistent with a coordination number of four amines in the case of WP-1 and the coordination of two amines in the case of BP-1 based on our previous studies of the solution coordination chemistry of the 1. Subsequent 13C CPMAS solid-state NMR on 13CO enriched samples of the 1 adsorbed onto BP-1 and WP-1 were consistent with the IR data.

Synthesis of linear and 4‐arm star block copolymers of poly(methyl acrylate‐b‐solketal acrylate) by SET‐LRP at 25 °C

AbstractThe new SET‐LRP (using Cu(0) powder for organic synthesis) was successfully used to produce well‐defined linear and star homo‐ and diblock‐copolymers of PMA, PSA, and P(MA‐b‐GA)n (where n = 1 or 4). The kinetic data showed that all SET‐LRP were first order and reached high conversions in a short period of time. The other advantage of using such a system is that the copper can easily be removed through filtration, allowing the production of highly pure polymer. The molecular weight distributions were well controlled with polydispersity indexes below 1.1 and the number‐average molecular weight close to theory, especially upon the addition of Cu(II)Br2/Me6‐TREN complex. The linear and star block copolymers were then hydrolyzed to produce the biocompatible amphiphilic P(MA‐b‐GA)n, where the glycerol side‐groups make the outer block hydrophilic. These blocks were micellized into water and found to have a Rg/RH equal to 0.8 and 1.59 for the liner and star blocks, respectively. This together with the TEM's supported that the linear blocks formed the classical core‐shell micelles, where as, the star blocks formed vesicles. We found direct support for the vesicle structure from a TEM where one vesicle squashed a second vesicle consistent with a hollow structure. Such vesicle structures have potential applications as delivery nanoscaled devices for drugs and other important biomolecules. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6346–6357, 2008

Synthesis, characterization, and structures of copper(II)-thiosulfate complexes incorporating tripodal tetraamine ligands.

The reaction of [Cu(L)(H(2)O)](2+) with an excess of thiosulfate in aqueous solution produces a blue to green color change indicative of thiosulfate coordination to Cu(II) [L = tren, Bz(3)tren, Me(6)tren, and Me(3)tren; tren = tris(2-aminoethyl)amine, Bz(3)tren = tris(2-benzylaminoethyl)amine, Me(6)tren = tris(2,2-dimethylaminoethyl)amine, and Me(3)tren = tris(2-methylaminoethyl)amine]. In excess thiosulfate, only [Cu(Me(6)tren)(H(2)O)](2+) promotes the oxidation of thiosulfate to polythionates. Products suitable for single-crystal X-ray diffraction analyses were obtained for three thiosulfate complexes, namely, [Cu(tren)(S(2)O(3))].H(2)O, [Cu(Bz(3)tren)(S(2)O(3))].MeOH, and (H(3)Me(3)tren)[Cu(Me(3)tren)(S(2)O(3))](2)(ClO(4))(3). Isolation of [Cu(Me(6)tren)(S(2)O(3))] was prevented by its reactivity. In each complex, the copper(II) center is found in a trigonal bipyramidal (TBP) geometry consisting of four amine nitrogen atoms, with the bridgehead nitrogen in an axial position and an S-bound thiosulfate in the other axial site. Each structure exhibits H bonding (involving the amine ligand, thiosulfate, and solvent molecule, if present), forming either 2D sheets or 1D chains. The structure of [Cu(Me(3)tren)(MeCN)](ClO(4))(2) was also determined for comparison since no structures of mononuclear Cu(II)-Me(3)tren complexes have been reported. The thiosulfate binding constant was determined spectrophotometrically for each Cu(II)-amine complex. Three complexes yielded the highest values reported to date [K(f) = (1.82 +/- 0.09) x 10(3) M(-1) for tren, (4.30 +/- 0.21) x 10(4) M(-1) for Bz(3)tren, and (2.13 +/- 0.05) x 10(3) M(-1) for Me(3)tren], while for Me(6)tren, the binding constant was much smaller (40 +/- 10 M(-1)).

Preparation and Stereochemistry of Cobalt(III) Complexes Containing 2,2′-Bipyridine 1,1′-Dioxide

Abstract New cobalt(III) complexes, [Co(N4)(bpdo)]3+ (N4 = (en)2, (tn)2, (NH3)4, and tren; bpdo = 2,2′-bipyridine 1,1′-dioxide) and [Co(en)2(rac-3,3′-Me2bpdo)]3+ (rac-3,3′-Me2bpdo = racemic3,3′-dimethyl-2,2′-bipyridine 1,1′-dioxide), were obtained, where tn and tren denote trimethylenediamine and 2,2′,2″-triaminotriethylamine, respectively. The [Co(en or tn)2(bpdo)]3+ and [Co(en)2(rac-3,3′-Me2bpdo)]3+ complexes form only one of two possible racemic pairs of diastereomers, which were resolved by SP-Sephadex column chromatography. Each pair of these complexes was assigned to have a lel(Δ(λ), Λ(δ)) structure on the basis of the 13C NMR and circular dichroism spectra, and the absolute configuration of optically active free 3,3′-Me2bpdo ligand recovered from the resolved complex. The tetraammine and tren complexes were resolved into a pair of enantiomers by a chemical method, but rapidly racemized in water with the rate of 7.33 × 10−3 s−1 and 1.16 × 10−3 s−1, respectively, at 10.0 °C. An intramolecular conformational inversion of the skew bpdo chelate ring (δ λ) was proposed for the racemization.

Kinetics of the acid dissociation of cyclic and open-chain tetramine complexes of cobalt(II): general acid catalysis with co-ordinating phosphate—citric acid buffers

The kinetics of dissociation of the cobalt(II) complexes of the quadridentate ligands 1.4.8.11-tetraazacyclotetradecane (cyclam), triethylenetetramine (trien) and 2,2′,2″-triaminotriethylamine (tren) was followed spectrophotometrically in the ranges 10 < T < 50 °C and 0.8 < pH < 4.0 in perchloric acid and Mcllvaine phosphate–citrate buffer system, an an ionic strength I= 1.0 mol dm–3, NaClO4. The complexes were prepared in situ in preaerated solutions under a nitrogen atmosphere, by the addition of a 10% excess of the ligand in the form of the free base to a solution of CoCl2·6H2O. The ligand dissociation reaction was then initiated by the addition of perchloric acid or Mcllvaine phosphate-citrate buffer. No dissociation was observed for the cyclam complex in perchloric acid media. It was, however, observed in the buffer and obeyed biphasic kinetics comprising two consecutive first-order steps. The action of the phosphate and/or citrate is attributed to their complexing ability and to their association through hydrogen bonding to the axial aqua ligand, thus bringin the proton closer to the dissociating nitrogen and hence catalysing the dissociation. The dissociation kinetics of the open-chain unbranched trien and the tripod tren was observed in perchloric acid as well as the Mcllvaine buffer system. Except when too fast to follow by conventional spectrophotometry, the reaction obeyed biphasic kinetics comprising two consecutive first-order steps. The tren complex dissociates at a rate 5–10 times faster than that of trien, the first step being too fast to follow except at 10 °C in the buffer system. The observed rate dependence is explained on the basis of mechanisms involving solvation, specific acid catalysis and general acid catalysis. The cyclam complex dissociates at a rate 5–30 times slower than those of the two open-chain complexes. This is attributed to the stabilization due to the hindered rotation of the dissociating nitrogen (entropic effect) and to the higher ligand-field stabilization of the macrocycle (enthalpic effect). Mechanisms covering the entire range of pH studied and conforming to the observed rate laws are given.

Substitution reactions of metallic complexes of 2,2′,2″-triaminotriethylamine. XVI. Kinetics of the (oxalato)(2,2′,2″-triaminotriethylamine) cobalt(III) cation in dilute and concentrated acid

The main emphasis in the study has been the investigation of the kinetics of the stepwise reactions of [Co(tren)C 2O 4] + ion [tren = 2,2’,2”-triaminotriethylamine, N(CH 2CH 2NH 2) 3] in both dilute and concentrated acids, as well as the characterization in solution of some new Co(III) tren complexes. The aquation reaction was conducted in 1.0 M HClO 4 solution under various conditions. Protonation of a carbonyl oxygen in the complex appeared to increase the lability of the Co—O moiety, leading to a unidentate oxalate ligand. The stepwise anation of [Co- (tren)C 2O 4]+ to [Co(tren)Cl 2]+ in concentrated HCl was also followed. Both systems react by a dissociative reaction mechanism.

Preparation and Circular Dichroism Spectra of Cobalt(III) Complexes Containing an Optically Active NH2CH2CH(CH3)X−-N,X (X=S or Se) Ligand

Abstract Several cobalt(III) complexes of the [Co(apS or apSe)(N4)]2+ type were prepared, where apS and apSe denote chiral 1-amino-2-propanethiolate-N,S and 1-amino-2-propaneselenolate-N,Se ligands, respectively, and N4 is (en=ethylenediamine)2, (R-chxn=(R,R)-1,2-cyclohexanediamine)2, or tren=tris(2-aminoethyl)amine. Their circular dichroism (CD) spectra were compared with one another and with those of complexes containing such ligands as achiral 2-aminoethanethiolate-N,S, 2-aminoethaneselenolate-N,Se or chiral 1-amino-2-propanolate-N,O (apO). The vicinal CD curves of S-apS obtained from CD spectra of the en and R-chxn complexes are similar and very large in magnitude in the d-d absorption band region. These curves are very similar to the CD spectrum of [Co(S-apO)(NH3)4]2+. The vicinal CD curve of S-apSe shows a similar pattern, but the magnitude is smaller than those of the S-apS and S-apO ligands. The vicinal effect of the protonated S-apSH ligand is much smaller compared with that of its conjugate base (S-apS) ligand. The tren complexes of S-apS and S-apSe exhibit CD spectra fairly different from the vicinal CD curves of the respective ligands in the d-d absorption band region.

Circular Dichroism Spectra and Racemization of Two Geometrical Isomers of the (2-Aminoethanesulfenato-S,N)[tris(2-aminoethyl)amine]cobalt(III) Ion

Abstract Optically active trans(t-N,S)(t) and cis(t-N,S)(p) isomers of [Co{S(O)CH2CH2NH2}(tren)]2+ (tren=tris(2-aminoethyl)amine; t-N= tertiary amine nitrogen) were prepared, and their circular dichroism spectra were compared with those of Δ(S or R)- and Λ(S or R)-[Co{S(O)CH2CH2NH2}(en)2]2+ and two geometrical isomers of [Co(R-pn)(tren)]3+ (R-pn=(R)-1,2-propanediamine) and [Co(S-dmbn)(tren)]3+ (S-dmbn=(S)-3,3-dimethyl-1,2-butanediamine). Racemization or epimerization of these sulfenato complexes was studied in aqueous solutions with ionic strength of 1.0 (NaClO4) in the pH and temperature ranges of 3.65–8.8 and 24.0–40.0 °C, respectively. The rates of p- and t-isomers of the tren complex are proportional to concentrations of the complex, but independent of pH, the latter isomer accompanying some decomposition during the course of racemization. The first-order rate constants of the p- and t-isomers are 9.92×10−5 and ca. 1.2×10−6 s−1 at 30.0 °C, respectively. No epimerization takes place in the en complexes under the same experimental conditions. The difference in rate of racemization or epimerization of these sulfenato complexes seems to be related closely to the crowding around the S=O group of the complex.

Oxygenation of Co(II) Complexes with Tripodal Ligands

AbstractThe kinetics of O2‐uptake of five‐coordinated Co2+/tren complexes (tren = 2,2′, 2″‐tris(2‐aminoethyl)amine) have been studied extensively. The kinetics of formation of (tren)Co(O2, OH)Co(tren)3+ exhibits two steps. The rate law of O2‐addition, the first step, was of the form: rate = (k[H+] + kKa)/([H+] + Ka) [Co(tren)2+][O2]. Second‐order rate constants k = 220 ± 19 M−1s−1 and k = 1.8 ± .035 · 103M−1s−1 agreed well from O2‐uptake and (stopped‐flow) spectrophotometric measurements. The protonation constant of the hydroxo complex obtained by equlibrium measurements (spectrophotometric and by pH‐titration) in anaerobic conditions (pKa = 10.03) agreed well with that derived from kinetic data (p Ka = 9.93); k and k are about a factor 100 smaller than those for the pseudooctahedral Co(trien) (H2O). This and the fact that several other Co(II) complexes with five‐coordinated geometry do not exhibit oxygen affinity led to the proposal that the oxygenation mechanism for Co2+/tren complexes involves fast preequilibria between Co(tren) (H2O)2+ and Co(tren) (H2O) and only the latter is assumed to be reactive. The enhanced rate at high pH is explained by rate determining H2O‐exchange in the O2‐addition step and the ability of coordinated OH− to labilize the neighbouring H2O. This mechanism is furthermore supported by the formation of one kinetically preferred isomer of the peroxo‐bridged dicobalt(III) complex (O2 cis to the tertiary N‐atom) and the large negative activation entropy (−30 eu). The second step is the intramolecular bridging reaction: equation image is independent of [Co(tren)2+] and [O2] but exhibits a pH‐dependence of the form k3 = k′3[H + ]/(Ka + [H+]); k−3 ( = 5 · 10−5 s−1) was determined independently and from the two rate constants the equilibrium constant was calculated as ≈ 105. The ligand combination as in Co(tren)2+ was shown to provide an excellent balance to form a reversible oxygen carrier; possible reasons for this are discussed.

OXYGEN COMPLEX FORMATION BY COBALT(II)-TRIS (2-AMINOETHYL) AMINE+

Abstract The reversible oxygenation of the Co(II) complex of tris(2-aminoethyl)amine (TREN, L) has been studied in some detail. The equilibrium constant K O2 =1026.92 M−2 atm−1, corresponding to the quotient [H+] [L2Co2(O2) (OH)3+]/[Co2+]2 [L]2 PO2 was determined by potentiometric equilibrium measurements of hydrogen ion concentration. Values for the thermodynamic constants, ΔH° =–63 ± 9 kcal/mole and ΔS° =–100 ± 15 cal/deg. mol, were calculated from the temperature dependence of the equilibrium constant. Oxygen stoichiometry, measured with a polarographic sensor, indicated the formation of a binuclear (peroxo bridged) complex, and the potentiometric equilibrium data indicated the presence of a second, μ-hydroxo, bridge. Measurement of the kinetics of the fast reaction between the cobalt(II)-TREN complex and dioxygen gave the value of the second order rate constant for the formation of the dioxygen complex as k 1 =2.8 × 10+3 sec−1 mol−1. The first order rate constant for the decomposition of the dioxygen complex measured by stopped-flow was found to be k −2 =0.7 sec−1. Kinetic and equilibrium data are discussed with respect to the probable structure and mechanism of formation of the dioxygen complex, and are compared with similar data previously reported for analogous complexes. The oxygen complex reported is unique with respect to its extremely slow rate of conversion to inert cobalt(III) complexes.

Synthesis and characterization of some octahedral cobalt(III) complexes with β, β′, β″-(triaminotriethylamine)

The preparation of several new octahedral cobalt(III) complexes of the type [Co(tren) X 2] A (tren = β, β′, β″-triaminotriethylamine; X = NO 2, NCS; N 3; A = anion) is reported, as well as those of several mixed complexes of the type [Co(tren) XY] A( X = NO 2, NCS; Y = F, Cl, Br; X = Cl, Y = Br). The chelating anion C 2O 4 2− forms a complex with the formula [Co(tren)C 2O 4] A. The visible spectra of some of the tren complexes in water, and as Nujol mull indicate that the average ligand field around the cobalt ion can be higher or lower than in the corresponding ethylenediamine complexes, depending upon the nature of the cis anionic ligands. The i.r. spectra of the complexes [Co(tren)BrClO 4]Br.H 2O and [Co(tren) XSO 4].H 2O ( X = Cl, Br) indicates that the perchlorate and sulfate ions are coordinated in the solid state.

Substitution reactions of metallic complexes of β,δ′,β″-triaminotriethylamine. VIII. Kinetics of acid hydrolysis reaction of the chlorobromo (β,β′,β″-triaminotriethylamine)cobalt(III) ion

The stoichiometry and kinetics of the acid hydrolysis reaction of Co(tren)ClBr − (tren = β,β′,β″-triaminotriethylamine) in 0.1 M HClO 4 have been investigated. In the acid hydrolysis process the data are consistent with two parallel reactions, probably due to the presence of two isomers in the reactant. One reaction is the release of Cl − in the α-isomer, and the other is the release of Br − in the β-isomer. The pseudo-first-order rate constants for these reactions in 0.1 M HClO 4 at 25.0°C were found to be 3.21 × 10 −3 sec −1 (k α) and 3.38 × 10 −2 (k β), respectively. Both rate constants were independent of the acid concentration below pH value 6, and independent of ionic strength from 0.10 to 0.15. Added sulfate ion accelerates the reaction rate. The activation enthalpies and entropies were calculated: ΔH α * = 18.3± 08 kcal mol −1, ΔH β * = 16.0±0.2 kcal mol −1; and ΔS α * = −13.5±2.7 cal mol −1 deg −i, ΔS β * = −9.0±0.7 cal mol −1 deg −1. The relative rate constants (k β/k α = 10) provide further evidence of the effect of steric strain and crowding on the reactivities of dihalo cobalt(III) tren complexes.

Deuterium isotope effect on the kinetics of aquation of dichloro(β,β′,β″-triaminotriethylamine)cobalt(III) ion

The kinetics of acid hydrolysis of Co(tren)Cl 2 + (tren = β,β′,β″-triaminotriethylamine) and Co(tren-d 6) 2 + have been studied in H 2O and D 2O at 25°. The solvent and β-deuterium isotope effects for these complexes are quite different from those observed for other Co III-amine complexes. These data indicate that the solvent isotope effect is dependent on the nature of the complex, and provide further support for the proposed distortion of tren complexes.