Axial Ligand Substitution Reactions Research Articles

Reaction of dirhodium and diruthenium paddlewheel tetraacetate complexes with nucleophilic protein sites: A computational study

The biomolecular affinity of three paddlewheel dinuclear complexes Rh2(µ-O2CCH3)4(H2O)2, Ru2(µ-O2CCH3)4(H2O)Cl, [Ru2(µ-O2CCH3)4(H2O)2]+ for the binding at cancer-specific protein targets was determined by means of DFT approaches. Thermodynamics of axial ligand substitution reaction by models of suitable protein sites was investigated in order to assess the binding selectivity displayed by the paddlewheel complexes. Both Rh2(µ-O2CCH3)4(H2O)2 and Ru2(µ-O2CCH3)4(H2O)Cl resulted to react favorably with most of the examined models of the protein side chains, with higher exergodicity demonstrated in the reaction of Arg, Cys, His, Lys, Sec, thus showing a limited selectivity. On the other hand, we identified Sec and His as the most suitable targets of the examined paddlewheel complexes, while Arg and Lys are expected to be also targetable at higher pH. Therefore, our calculations showed how both dirhodium and, majorly, diruthenium examined complexes undergo to a certain degree of destabilization upon the binding at nucleophilic protein sites. The presented computational results allowed us to shed light onto the protein sites’ affinity and on the therapeutic potential of both Rh2(µ-O2CCH3)4(H2O)2 and Ru2(µ-O2CCH3)4(H2O)Cl, and provided for a structural basis for the development of newly designed paddlewheel complexes.

Communication—Semi-Rigid Ru(II)Porphyrinate-Based Macrocyclic Receptor as Endotopic Catalyst for Carbene Transfer Reactions

A 5,15-bis(1,1′-biphenyl)porphyrin-based macrocyclic receptor with a well-defined cavity is suitable for coordination of Ru(II) ions with carbonyl axial ligands. Axial ligand substitution reaction using diphenyldiazomethane as reactant affords a macrocyclic Ru(II)porphyrinate with a diphenylcarbene moiety that functions as an excellent endotopic catalysts for the dimerization reaction of ethyldiazoacetate. The extraordinary stability of the diphenylcarbene axial ligand in conjunction with the high reactivity of the Ru(II)porphyrinate moiety towards diazoderivatives render the macrocyclic complex a promising candidate for the active metal template synthesis of interlocked molecules.

Facile Axial Ligand Substitution in Linear Mo≣Mo-Ni Complexes.

Clean axial ligand substitution reactions of heterometallic extended metal atom chains (HEMACs) supported by the dpa ligand (dpa = 2,2'-dipyridylamine) have been synthetically challenging due to side reactions that alter the trimetallic core. Following the hypothesis that a heterometallic core containing second-row transition metals would be more robust toward ligand substitution, we report the synthesis of three new heterotrimetallic compounds, Mo2Ni(dpa)4(OTf)2 (1), Mo2Ni(dpa)4(NCS)2 (2), and Mo2Ni(dpa)4(NCSe)2 (3) that are obtained cleanly and in good yield. Compound 1 may be synthesized either directly by reaction of Ni(OTf)2 with Mo2(dpa)4 (4) or indirectly, by reaction of Mo2Ni(dpa)4Cl2 (5) with 2 equiv of TlOTf. Axial ligand substitution on 1 via solutions containing NaNCS or KNCSe afford 2 or 3, respectively. X-ray crystal structures of 1, 2, and 3 present short Mo-Ni distances of 2.458(8)Å /2.47(1) Å, 2.548(1), and 2.546(1), respectively. Density functional theory (DFT) calculations indicate a 3-center 3-electron σ bonding interaction between the Mo2 quadruply bonded core and the Ni in both 1 and 2. These complexes were analyzed by SQUID magnetometry, supporting the presence of a high spin Ni2+ center with S = 1.

Axial ligand substitution reactions of head-to-head α-pyridonato-bridged Pt(III) binuclear complexes bearing various equatorial ligands with chloride ion and olefin

In this study, axial ligand-substitution reactions of head-to-head (HH) α-pyridonato-bridged platinum(III) binuclear complexes bearing equatorial amine ligands (L = MeNH2, EtNH2, and L–L = ethylenediamine (en), and N,N′-dimethylethylenediamine (Me2en)) [(Cl)(NH3)2Pt(μ-α-pyridonato)2Pt(L)2(Cl)]2+ are synthesized, and the axial ligand substitution on these complexes with chloride ions are kinetically investigated in acidic aqueous solution. For these complexes, the formation reactions of the dichloro complexes from the monochloro complexes proceeded through three parallel reaction pathways, in contrast to those for the HH tetraammine amidato-bridged platinum (III) binuclear complexes. The effects of equatorial amine ligands as well as the bridging ligands on the axial ligand substitution are discussed. The reaction of [(H2O)(NH3)2Pt(μ-α-pyridonato)2Pt(en)(OH2)]2+ with p-styrenesulfonate is also kinetically investigated.

Axial-ligand substitution reactions of a head-to-head pivalamidato-bridged Pt(III) binuclear complex bearing equatorial bromide ligands: A mechanistic study

Axial ligand-substitution reactions of head-to-head (HH) a binuclear pivalamidato-bridged platinum(III) complex bearing equatorial bromide ligands, [(H2O)(NH3)2Pt(μ-pivalamidato)2Pt(Br)2(OH2)]2+ (1), with chloride and bromide ions were thermodynamically and kinetically investigated in acidic aqueous solutions. Reactions of 1 with p-styrenesulfonate and 4-penten-1-ol were also kinetically investigated in order to clarify the reaction mechanisms involving olefins. In contrast to the reactions of the HH tetraammine pivalamidato-bridged platinum(III) binuclear complex, [(H2O)(NH3)2Pt(μ-pivalamidato)2Pt(NH3)2(OH2)]4+ (2′), all substitution processes on 1 involve single-step reactions. The effect of the equatorial halide ligands on the axial ligand substitution reactions of 1 is discussed in relation to 2′; the rate-determining first substitution of H2O by X− at the Pt(Br2O2) site in 1 is followed by a fast second substitution of H2O by X− at Pt(N4). In contrast, axial ligand substitution on 2′ by X− proceeds in two consecutive steps. Reactions of 1 with p-styrenesulfonate or 4-penten-1-ol proceed in one step to form only mono-π complexes that are in rapid equilibrium with σ complexes, whereas reactions of 2′ with these olefins proceed in three consecutive steps via di-π complexes. These mechanistic differences are interpreted in terms of enhanced charge localization in the mono-π complexes of 1 ([PtII(NH3)2(μ-pivalamidato)2PtIV(Br)2(p-styrenesulfonate or 4-penten-1-ol)]2+).

Synthesis, Characterization And Electrolytic Behavior Of Cadmium(II) Complexes Of 5,7,7,12,14,14- Hexamethyl-1,4,8,11-Tetraazacyclotetradeca-4,11- Diene And Isomers Of Its Saturated Analogue

Condensation of ethylendiamine with acetone in the presence of quantitative amount of perchloric acid, yielded the ligand 5,7,7,12,14,14- hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene dihydroperchlorate (denoted by L.2HClO4). The ligand L.2HClO4 on reduction with NaBH4, yielded an isomeric mixture of saturated macrocycles, the Me6[14]anes, which were resolved into two distinct C-chiral isomers (denoted by ‘tet-a’ and ‘tet-b’). Interaction of ligands L.2HClO4, ‘tet-a’ and ‘tet-b’ with salts CdI2, Cd(NO3)2.4H2O, CdCl2.2H2O and Cd(ClO4)2.6H2O produced different five coordinated square pyramidal and six coordinated octahedral cdmium(II) complexes. Among them the complexes, cis-[Cd(teta)( NO3)](NO3) and cis-[Cd(tet-b)(NO3)](NO3) underwent axial ligand substitution reaction with KCNS; whereas complex [Cd(tet-a)I2] underwent axial ligand substitution reaction and complex [CdLI](ClO4) underwent simultaneous ligand substitution and addition reaction with NaNO2. Characterization of all the complexes were carried out on the basis of elemental analysis; FT-IR, UV-Vis. and 1H-NMR spectroscopy; melting point determination as well as by magnetic moment and conductivity measurements. Molar conductivity measurment of the complexes reavealed that they show different electrolytic behavior in different solvents.

Axial ligand effect on the reaction mechanism of head-to-head pivalamidato-bridged Pt(III) binuclear complex containing an equatorial bromide ligand with acetone

The axial ligand substitution reactions of head-to-head (HH) pivalamidato-bridged platinum(III) binuclear complexes containing equatorial Br− ligands, ([(H2O)(NH3)2Pt(μ-pivalamidato)2Pt(Br)2(OH2)]2+ (complex 1) and [(Br)(NH3)2Pt(μ-pivalamidato)2Pt(Br)2(Br)] (complex 2)) with acetone were kinetically investigated in acidic aqueous solutions. Both the complexes reacted with acetone slowly and acetonyl PtIII binuclear complexes were formed in two steps (1 and 2). The observed pseudo first-order rate constants (kobs1) for step 1 of the reactions of complexes 1 and 2 were linearly and quadratically dependent on the excess ligand concentration (CL) at a given [H+], respectively. The rate constants for step 2 in both the reactions were independent of both CL and [H+]. A reaction mechanism involving an intermediate with one π-coordinated acetone molecule was proposed for complex 1, which is similar to those proposed previously for the reactions of HH tetraammine amidato-bridged diplatinum(III) complexes with acetone. In contrast, a reaction mechanism involving an intermediate with two π-coordinated acetone molecules on the axial sites was proposed for complex 2.

Thermodynamics of Axial Substitution and Kinetics of Reactions with Amino Acids for the Paddlewheel Complex Tetrakis(acetato)chloridodiruthenium(II,III)

The known paddlewheel, tetrakis(acetato)chloridodiruthenium(II,III), offers a versatile synthetic route to a novel class of antitumor diruthenium(II,III) metallo drugs, where the equatorial ligands are nonsteroidal anti-inflammatory carboxylates. This complex was studied here as a soluble starting prototype model for antitumor analogues to elucidate the reactivity of the [Ru(2)(CH(3)COO)(4)](+) framework. Thermodynamic studies on equilibration reactions for axial substitution of water by chloride and kinetic studies on reactions of the diaqua complexes with the amino acids glycine, cysteine, histidine, and tryptophan were performed. The standard thermodynamic reaction parameters ΔH°, ΔS°, and ΔV° were determined and showed that both of the sequential axial substitution reactions are enthalpy driven. Kinetic rate laws and rate constants were determined for the axial substitution reactions of coordinated water by the amino acids that gave the corresponding aqua(amino acid)-Ru(2) substituted species. The results revealed that the [Ru(2)(CH(3)COO)(4)](+) paddlewheel framework remained stable during the axial ligand substitution reactions and was also mostly preserved in the presence of the amino acids.

Effect of the axial halogen ligand on the substitution reactions of chromium(III) porphyrin complex

The thermodynamics and kinetics of the substitution reaction of the chromium(III) complex of 5,10,15,20-tetraphenylporphyrin, [Cr(TPP)(X)(L)] (X=F, Cl, Br), where L represents a non-charged ligand such as H2O, pyridine, or 1-methylimidazole, was investigated. The present study aimed to elucidate the effect of the axial halogen ligand, X on the substitution reaction of the ligand trans to X. The substitution reaction of the axial pyridine ligand of [Cr(TPP)(X)(Py)] by 1-methylimidazole was studied spectrophotometrically in dichloromethane, and it was found that the reaction proceeds via a limiting dissociative mechanism and the activation enthalpy of the dissociation of pyridine is much smaller for the fluorine complex, [Cr(TPP)(F)(Py)], than for the chlorine complex, [Cr(TPP)(Cl)(Py)], i.e., ΔH‡=57.5±1.1 and 97.2±1.4kJmol−1, respectively. These results are discussed in terms of the trans effect of the halogen ligand on the axial ligand substitution reaction of [Cr(TPP)(X)(L)], and it is concluded that the strength of the bond shows the tendency of Cr–F>Cr–Cl>Cr–Br, leading to the strong trans effect of the F− ligand.

Interconversion between Molecular Polyhedra and Metal−Organic Frameworks

The construction of a metal-organic framework (MOF) with a pcu-a topology using a preassembled soluble molecular octahedron has been realized experimentally. The resulting MOF can also be reversibly converted to the molecular octahedron. All such conversions are based on axial-ligand substitution reactions on the molecular octahedron.

Synthesis, electrolytic behaviour and antimicrobial activities of cadmium complexes of isomers of 3,10-C- meso -3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane

Reactions of two diastereoisomers of 3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecanes, Me8[14]ane (LA and LB) with Cd(NO3)2 in methanol produced trans-[CdL(NO3)2] (L = LA or LB). However, the third diastereoisomer, Me8[14]ane (LC) did not react with Cd(NO3)2. Trans-[CdLB(NO3)2] undergoes axial ligand substitution reactions with KSCN, KNO2, KCl, KBr and KI, in the ratio of 1 : 2 to yield white solid products corresponding to molecular formula [CdLBX2] where X = NCS−, , Cl−, Br− or I−. Characterization has been carried out on the basis of elemental analysis, IR, UV-visible and 1H-, 13C- and 113Cd-NMR spectroscopy, as well as by magnetic moment and conductivity measurement. These complexes show different electrolytic behaviours in different solvents. In chloroform, they are noneletrolytic indicating that both anions coordinate to cadmium(II) with retention of original molecular formula [CdLBX2]; their 1 : 2 electrolytic nature in water reveals the formation of diaquo complexes [CdLB(H2O)2]X2. On the other hand, conductance values corresponding to 1 : 2 electrolyte in DMF indicate the formation of square pyramidal complexes [CdLB(DMF)]X2. The antimicrobial activities of these ligands and their complexes have been tested against some selected fungi and bacteria.

195Pt NMR Spectra of Head‐to‐Head and Head‐to‐Tail Amidato‐Bridged Platinum(III) Dinuclear Complexes

Abstract195Pt chemical shifts and 1JPt–Pt coupling constants were measured for a series of head‐to‐head (HH) and head‐to‐tail (HT) amidato‐bridged cis‐diammineplatinum(III) dinuclear complexes involved in the axial water substitution reactions with halide ions (X– = Cl–, Br–): HH‐[Pt2(NH3)4(μ‐amidato)2L1L2]n+ ≡ [L1–Pt(N2O2)–Pt(N4)–L2]n+ (amidato = α‐pyridonato, α‐pyrrolidonato, and pivalamidato) and HT‐[Pt2(NH3)4(μ‐α‐pyridonato)2L1L2]n+ ≡ [L1–Pt(N3O)–Pt(N3O)–L2]n+; the diaqua (L1, L2 = H2O, n = 4), the aquahalo (L1 = X–, L2 = H2O, n = 3), and the dihalo complexes (L1, L2 = X–, n = 2). The 195Pt NMR spectroscopic data were considered in relation to the lability in the axial ligand substitution reaction and the electron distribution along the Pt–Pt bond. The NMR spectroscopic data suggested different electron distributions along the Pt–Pt bonds in all the HH dimers and in the HT aquahalo dimers, such as [L1–PtIV(N2O2)–PtII(N4)–L2]n+ and [X–PtIV(N3O)–PtII(N3O)–OH2]3+, respectively. Relative shifts of the 195Pt NMR signals for each substitution step indicate that the replacement of the axial water ligand by X– affects more effectively the electron density of the opposite Pt atom than that of the substituted one. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Kinetics and mechanisms of the axial ligand substitution reactions of platinum(III) binuclear complexes with halide ions

The axial water ligand substitution reaction on the head-to-head (HH) and head-to-tail (HT) amidato-bridged cis-diammineplatinum(III) binuclear complexes, HH- and HT-[Pt2(NH3)4(m-amidato)2(OH2)2]4+ (amidato = α-pyridonato, a-pyrrolidonato, or pivalamidato), with halide ions (X = Cl ,Br ) in acidic aqueous solution reveals a consecutive 2-step kinetics under the pseudo first-order conditions of a large excess concentration of halide ion relative to that of the complex (Cx bCpt), corresponding to formation of the monohalo (step 1) and the dihalo complexes (step 2). The first substitution step of all the HH and HT diaqua dimers consists of two parallel reaction pathways: one is the simple substituion path of one of the coordinated aqua ligands with X, and the other is the replacement in the aquahydroxo complex which is the conjugate base of the diaqua dimer. In step 2, there are three reaction pathway patterns: the direct substitution path, the path via a coordinatively unsaturated intermediate, and the unusual path of OH replacement. Step 2 proceeds via either one or two paths of the three depending on the nature of the halide ion as well as the bridging ligand. On the other hand, the substitution reaction of the hydrogenphosphato-bridged lantern-type complex, [Pt2(m-HPO4)4(OH2)2]2 proceeds in 1-step at Cx bCpt, in which the first aqua ligand substitution to form the monohalo species is rate-determining and the monohalo species is in rapid equilibrium with the dihalo complex. The rate-determining step consists of parallel pathways similar to step 1 in the amidato-bridged complex systems.

Precise Investigation of the Axial Ligand Substitution Mechanism on a Hydrogenphosphato-Bridged Lantern-Type Platinum(III) Binuclear Complex in Acidic Aqueous Solution

Detailed equilibrium and kinetic studies on axial water ligand substitution reactions of the "lantern-type" platinum(III) binuclear complex, [Pt(2)(mu-HPO(4))(4)(H(2)O)(2)](2)(-), with halide and pseudo-halide ions (X(-) = Cl(-), Br(-), and SCN(-)) were carried out in acidic aqueous solution at 25 degrees C with I = 1.0 M. The diaqua Pt(III) dimer complex is in acid dissociation equilibrium in aqueous solution with -log K(h1) = 2.69 +/- 0.04. The consecutive formation constants of the aquahalo complex () and the dihalo complex () were determined spectrophotometrically to be log = 2.36 +/- 0.01 and log = 1.47 +/- 0.01 for the reaction with Cl(-) and log = 2.90 +/- 0.04 and log = 2.28 +/- 0.01 for the reaction with Br(-), respectively. In the kinetic measurements carried out under the pseudo-first-order conditions with a large excess concentration of halide ion compared to that of Pt(III) dimer (C(X)()- >> C(Pt)), all of the reactions proceeded via a one-step first-order reaction, which is a contrast to the consecutive two-step reaction for the amidato-bridged platinum(III) binuclear complexes. The conditional first-order rate constant (k(obs)) depended on C(X)()- as well as the acidity of the solution. From kinetic analyses, the rate-limiting step was determined to be the first substitution process that forms the monohalo species, which is in rapid equilibrium with the dihalo complex. The reaction with 4-penten-1-ol was also kinetically investigated to examine the reactivity of the lantern complex with olefin compounds.

Laser Photolysis Studies of the Reaction of Chromium(III) Octaethylporphyrin Complex with Triphenylphosphine and Triphenylphosphine Oxide

The photoreaction of the chromium(III) octaethylpoprhyrin complex, [Cr(OEP)(Cl)(L)] (L = H2O, Py, OPPh3), in dichloromethane was studied using laser flash photolysis technique. Laser irradiation causes the generation of a coordinately unsaturated intermediate [Cr(OEP)(Cl)], which reacts with ligands in solution to give the parent complex, [Cr(OEP)(Cl)(L)], or a transient species, [Cr(OEP)(Cl)(H2O)], when L = Py or OPPh3. Once produced [Cr(OEP)(Cl)(H2O)] eventually exchanges the axial H2O ligand with L to regenerate [Cr(OEP)(Cl)(L)]. The kinetics of the axial ligand substitution reaction was followed spectrophotometrically, and the ligand-concentration dependence of the ligand exchange rate revealed that the reaction occurs via a limited dissociative mechanism. The photoreaction of [Cr(OEP)(Cl)(OPPh3)] containing excess PPh3 in the bulk solution leads to the unfavorable coordination of the PPh3 molecule to the chromium ion to give a transient complex, [Cr(OEP)(Cl)(PPh3)]. The dynamic and thermodynamic properties of [Cr(OEP)(Cl)(PPh3)] in solution are discussed on the basis of the kinetic parameters of the dissociation and association reactions of the PPh3 ligand together with the steric aspect of the molecular structure of the related complexes.

Mechanism of the axial ligand substitution reactions on the head-to-tail alpha-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex with olefins.

Reactions of the head-to-tail alpha-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex having equivalent two platinum atoms, Pt(N(3)O), with p-styrenesulfonate and 4-penten-1-ol were studied kinetically. Under the pseudo first-order reaction conditions in which the concentration of the Pt(III) dinuclear complex is much smaller than that of olefin, a consecutive basically four-step reaction was observed for the reaction with p-styrenesulfonate, but for the reaction with 4-penten-1-ol, the reaction was three step. The olefin pi-coordinates to one of the two equivalent Pt atoms in the first step (step 1), followed by the second pi-coordination of another olefin molecule to the other Pt atom (step 2). In the next step (step 3), the nucleophilic attack of water to the first pi-coordinated olefin initiates its pi-sigma bond conversion on the Pt atom, and the second pi-bonding olefin molecule on the other Pt atom is released. Finally, dissociation of the alkyl group on the Pt(N(3)O) and reduction of the Pt(III) dinuclear complex to the Pt(II) dinuclear complex occur (step 4). The first water substitution with olefin (step 1) consists of two paths, the reaction of the diaqua dimer complex (path a) and the reaction of the aquahydroxo dimer complex (path b), whereas the second substitution (step 2) proceeds through three reaction paths: the normal path of the direct substitution of H(2)O (path c), the path of the coordinated OH(-) substitution (path d), and the path via the coordinatively unsaturated five-coordinate intermediate (path e). The reaction with p-styrenesulfonate proceeds through paths c, d, and e, whereas the reaction with 4-penten-1-ol proceeds through paths c and d. The third step (step 3) for the reaction with p-styrenesulfonate involves the coordinatively unsaturated intermediate, but that for the 4-pentene reaction does not. The reactivities of the HH dimer and HT dimer with olefins are compared and discussed.

Kinetic and Equilibrium Study on the Axial-Ligand Substitution Reaction of the Head-to-Tail α-Pyridonate-Bridged cis-Diammineplatinum(III) Dinuclear Complex: trans Effect of the Axial Ligand through the Pt−Pt Bond to the Opposite Axial Ligand

Acid dissociation constant of the axial aqua ligand in the Head-to-Tail (HT) α-pyridonate-bridged cis-diammineplatinum(III) dimer complex {[(H2O)Pt(NH3)2(μ-C5H4NO)2Pt(NH3)2(H2O)]4+} was determined spectrophotometrically to be −log(Kh1/M) = 1.98±0.01 at 25 °C and I = 2.00 M. Successive substitution reaction of the HT dimer with halide ions X− (X− = Cl− and Br−) at the two axial sites to give monohalo and dihalo complexes was studied kinetically: [(H2O)Pt(NH3)2(µ-C5H4NO)2Pt(NH3)2(H2O)]4+ + X− ←→ [(H2O)Pt(NH3)2(µ-C5H4NO)2Pt(NH3)2(X)]3+ + H2O (kobs1) [(H2O)Pt(NH3)2(µ-C5H4NO)2Pt(NH3)2(X)]3+ + X− ←→ [(X)Pt(NH3)2(µ-C5H4NO)2Pt(NH3)2(X)]2+ + H2O (kobs2) Formation constants of the monohalo and dihalo complexes were determined spectrophotometrically to be log(K1Cl/M−1) = 5.27±0.02 and log(K2Cl/M−1) = 3.83±0.01 for the reaction with Cl−, and log(K1Br/M−1) = 5.33±0.03 and log(K2Br/M−1) = 4.44±0.02 for the reaction with Br−. In the HT dimer having two equivalent platinum atoms, the deprotonation occurs to the water molecule on one of the two Pt atoms, whereas the first nucleophilic substitution with X− occurs to the other Pt atom. Substitution of the second water ligand with Cl− proceeds by a simple substitution path, whereas the second substitution with Br− proceeds by two parallel paths: one includes the dissociation of the axially coordinated water molecule followed by the Br− coordination, and the other is the simple one-step substitution path. The difference of the reaction paths is reasonably explained by the different trans effect of the halide ions exerted through the Pt−Pt bond to the other terminal Pt atom in the monohalo complexes.

Axial ligand substitution and photoisomerization reactions in ruthenium(II) trans mixed-chelate complexes containing the ligands 1,2-phenylenebis(dimethylarsine) and 2,2′-bipyridine or 1,10-phenanthroline

The nitrosyl complex in trans-[RuCl(pdma)(bpy)(NO)][PF 6] 2 (pdma=1,2-phenylenebis(dimethylarsine), bpy=2,2′-bipyridine) reacts at room temperature with stoichiometric NaN 3, followed by an excess of a neutral ligand L 1 in 2-butanone under reflux, to afford high yields of the mono-substituted derivatives trans-[RuCl(pdma)(bpy)L 1]PF 6 (L 1=pyridine (py) 1, triphenylphosphine (PPh 3) 2, N-methylimidazole (mim) 3, acetonitrile (MeCN) 4, dimethylsulfoxide (dmso) 5 or pyrazine (pyz) 6). The related compound trans-[RuCl(pdma)(phen)(NO)][PF 6] 2 (phen=1,10-phenanthroline) reacts similarly to yield trans-[RuCl(pdma)(phen)L 1]PF 6 (L 1=py 8, PPh 3 9, mim 10 or pyz 11). The pyrazine complexes in 6 and 11 react with MeI at room temperature in acetone to afford trans-[RuCl(pdma)(L–L)(mpyz +)][PF 6] 2 (mpyz += N-methylpyrazinium, L–L=bpy 7 or phen 12, respectively). 3 reacts with an excess of a neutral ligand L 2 in the presence of stoichiometric AgCF 3CO 2 in water/acetone under reflux to afford high yields of the di-substituted derivatives trans-[Ru(pdma)(bpy)mim(L 2)][PF 6] 2 (L 2=mim 13, py 14 or MeCN 15) and 2 reacts similarly with AgCF 3CO 2 in water/MeCN to give trans-[RuCl(pdma)(bpy)PPh 3(MeCN)][PF 6] 2 ( 16). The complexes in 1– 16 exhibit intense d π(Ru II)→π*(L–L) and d π(Ru II)→π*(L 1/L 2) (L 1/L 2=py, pyz or mpyz +) metal-to-ligand charge-transfer absorption bands in the near-UV–visible region and are mildly photosensitive in solution. Solar irradiation leads to isomerization; for example 3 is converted into cis-[RuCl(pdma)(bpy)mim]PF 6 ( 17) over a period of ca. 100 h exposure to diffuse sunlight in acetone. Single crystal X-ray structures have been determined for 1, 2·DMF, 3, 12·3MeCN, 14·DMF and 17.

Synthesis, Characterisation and Anti-Fungal Activities of Some New Copper(II) Complexes of Octamethyl Tetraaza-Cyclotetradecadiene

The ligand Me8[14]diene, L, in its free state as well as in the dihydroperchlorate form, L.2HClO4, coordinates copper(ll) in different salts to yield a series of [CuLXx] Xy(H2O)z complexes where X = NO3, ClO4, NCS, Cl and Br; x and y may have values of 0 or 2 and z = 0, 1 or 2. The complex, [CuL(ClO4)2].2H2O is found to undergo axial ligand substitution reactions with SCN-, NO3 and Cl- to give a variety of substitution derivatives: [CuL(ClO4)m Xn] where X = NCS, NO3 and Cl; m = 0 or 1, and n = 1 or 2. The complexes .have been characterised on the basis of analytical, spectroscopic, magnetic and conductance data. The anti-fungal activities of the ligand and its complexes have been investigated against a range of phytopathogenic fungi.

Effect of a Sterically Hindered Imidazole Ligand on the Molecular Structure and Axial Ligand Substitution Reaction of the Chromium(III) Porphyrin Complex

Abstract A structural, thermodynamic, and kinetic study of a chromium(III) complex of 5,10,15,20-tetraphenylporphyrin, [Cr(tpp)(Cl)(L)], where L represents an imidazole ligand, is presented. The present study is aimed at elucidating the effect of a steric strain induced by the 2-methyl substituent of the imidazole ligand on the molecular structure and the dynamics of an axial ligand-substitution reaction. Crystals of the 1-methylimidazole complex [Cr(tpp)(Cl)(1-Meim)] (1) and 1,2-dimethylimidazole complex [Cr(tpp)(Cl)(1,2-Me2im)] (2) were obtained from a dichloroethane–toluene mixture containing a slight excess of imidazole ligand in the monoclinic space group Cc, Z = 4, a = 18.306(2), b = 13.311(2), c = 21.391(5) Å, β = 120.05(1)°, V = 4512(1) Å3, and in the orthorhombic space group P212121, Z = 4, a = 9.926(1), b = 17.902(3), c = 25.247(4) Å, V = 4486(1) Å3, respectively. The axial Cr–Nim bond lengths for 1 and 2 are 2.103(4) and 2.139(5) Å, respectively. A steric hindrance has been demonstrated by a 0.036 Å increase in the Cr–Nim bond length and a tilting and tipping of the imidazole ligand of 2 from the symmetrical position observed in 1. The substitution reaction of the axial pyridine ligand of [Cr(tpp)(Cl)(py)] by various imidazole ligands was studied spectrophotometrically in dichloromethane or in toluene. A steric effect due to the 2-methyl substituent of the imidazole ligand was observed along with an increase in the ligand-dissociation rate and a decrease in the binding constant of the imidazole ligand to the metalloporphyrin. These results were examined in terms of steric interactions between the axial ligand and the porphyrin core.