Quinquedentate co-ordination of amino-substituted tetraazacycloalkanes to cobalt(III). Part 3. Synthesis of an unsymmetric ligand and crystal structure of its cis-chlorocobalt(III) complex

Lawrance, Geoffrey A.; Martı́nez, Manuel; Skelton, Brian W.; White, Allan H.

doi:10.1039/dt9920001649

Cited by 15 publications

(6 citation statements)

References 4 publications

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“…Synthesis and Structural Characterization. The preparation of the various complexes in this work as isomerically stable (non-interconverting) mixtures has been achieved with the standard procedures described in the literature; − , in all cases extensive slow chromatography workup at [HCl] = 1.5−2.0 M on Dowex 50W × 2 columns is needed for the separation of equally {2+}-charged chloro complexes. For the [CoClL 13 ] 2+ system, the cis-V isomer is obtained as a single product, as expected .…”

Section: Resultsmentioning

confidence: 99%

“…We have been involved in the chemistry of cobalt(III) complexes with pentadentate macrocyclic ligands containing a pendant primary amine arm (Scheme ). − The complexes have been prepared and characterized in pure isomeric forms in a neutral or acidic medium, and their cis/trans isomerism has been established by X-ray crystallography. , In these cases the relative disposition of the primary amine and the monodentate sixth ligand define the cis or trans geometric isomer. The preferred isomeric form under these conditions is found to depend on the size of the ring, for example, the smaller the ring the greater preference for the cis isomeric form.…”

Section: Introductionmentioning

confidence: 99%

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Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

et al. 2006

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We have investigated the isomeric distribution and rearrangement of complexes of the type [CoXLn]2+,3+ (where X = Cl-, OH-, H2O, and Ln represents a pentadentate 13-, 14-, and 15-membered tetra-aza or diaza-dithia (N4 or N2S2) macrocycle bearing a pendant primary amine). The preparative procedures for chloro complexes produced almost exclusively kinetically preferred cis isomers (where the pendant primary amine is cis to the chloro ligand) that can be separated by careful cation-exchange chromatography. For L13 and L14 the so-called cis-V isomer is isolated as the kinetic product, and for L15 the cis-VI form (an N-based diastereomer) is the preferred, while for the L14(S) complex both cis-V and trans-I forms are obtained. All these complexes rearrange to form stable trans isomers in which the pendent primary amine is trans to the monodentate aqua or hydroxo ligand, depending on pH and the workup procedure. In total 11 different complexes have been studied. From these, two different trans isomers of [CoClL14(S)]2+ have been characterized crystallographically for the first time in addition to a new structure of cis-V-[CoClL14(S)]2+; all were isolated as their chloride perchlorate salts. Two additional isomers have been identified and characterized by NMR as reaction intermediates. The remaining seven forms correspond to the complexes already known, produced in preparative procedures. The kinetic, thermal, and baric activation parameters for all the isomerization reactions have been determined and involve large activation enthalpies and positive volumes of activation. Activation entropies indicate a very important degree of hydrogen bonding in the reactivity of the complexes, confirmed by density functional theory studies on the stability of the different isomeric forms. The isomerization processes are not simple and even some unstable intermediates have been detected and characterized as part of the above-mentioned 11 forms of the complexes. A common reaction mechanism for the isomerization reactions has been proposed for all the complexes derived from the observed kinetic and solution behavior.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

et al. 2006

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“…The [CoL n Cl] 2+ complexes, as well as the dinuclear mixed-valence complexes [{L 14 Co III (μ-NC)}Fe II (CN) 5 ] - and [{L 15 Co III (μ-NC)}Fe II (CN) 5 ] - , have been prepared according to published procedures. ,,− , …”

Section: Methodsmentioning

confidence: 99%

“…In recent years, we have investigated a number of discrete dinuclear cyano-bridged mixed-valence compounds, and we have been successful in tuning the energy of the (visible) MMCT transition through deliberate structural changes made at each metal center. − These complexes comprise {Fe II (CN) 6 } 4- or {Ru II (CN) 6 } 4- moieties bound as monodentate ligands (through a single bridging cyano ligand) to the Co III complexes of known pentadentate macrocyclic ligands (see Chart ). − When coupled with hexacyanometalate(II) ions, the resulting dinuclear complexes exhibit different MMCT transition energies. These can be explained on the basis of the macrocyclic ring size (13, 14, or 15), the donor atoms (N 5 or N 3 S 2 ), and the conformation of the macrocyclic ring (either planar (trans) or folded (cis)).…”

Section: Introductionmentioning

confidence: 99%

Dinuclear Cyano-Bridged Co^III−Fe^II Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity

et al. 2005

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The preparation and characterization of a series of trinuclear mixed-valence cyano-bridged Co(III)-Fe(II)-Co(III) compounds derived from known dinuclear [[L(n)Co(III)(mu-NC)]Fe(II)(CN)(5)](-) complexes (L(n)() = N(5) or N(3)S(2) n-membered pendant amine macrocycle) are presented. All of the new trinuclear complexes were fully characterized spectroscopically (UV-vis, IR, and (13)C NMR). Complexes exhibiting a trans and cis arrangement of the Co-Fe-Co units around the [Fe(CN)(6)](4-) center are described (i.e., cis/trans-[{L(n)Co(III)(mu-NC)](2)Fe(II)(CN)(4)](2+)), and some of their structures are determined by X-ray crystallography. Electrochemical experiments revealed an expected anodic shift of the Fe(III/II) redox potential upon addition of a tripositively charged [Co(III)L(n)] moiety. The Co(III/II) redox potentials do not change greatly from the di- to the trinuclear complex, but rather behave in a fully independent and noncooperative way. In this respect, the energies and extinction coefficients of the MMCT bands agree with the formal existence of two mixed-valence Fe(II)-CN-Co(III) units per molecule. Solvatochromic experiments also indicated that the MMCT band of these compounds behaves as expected for a class II mixed-valence complex. Nevertheless, its extinction coefficient is dramatically increased upon increasing the solvent donor number.

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“…Compounds 1a , 1c , 1e , and 1f have been characterized via 1 H NMR spectra, in all cases very good agreement with previously reported values is obtained. For compound 1b the general synthetic procedure is the same as that described for the other complexes; imine b was prepared via condensation of the 2Br-benzaldehyde, and the corresponding amine which was prepared from the sodium reduction of mesitylnitrile21a obtained from the corresponding aldehyde using a published procedure 21b. Spectroscopic data agree with the proposed formulation ( 1 H NMR; δ/ppm( J /Hz): 1.08( 2 J (Pt−H) 71) 3H(Me), 1.30( 2 J (Pt−H) 68) 3H(Me), 2.10( 2 J (Pt−H) 14) 6H(SMe 2 ), 5.21/5.42 ( 2 J (H−H) 19) 2H(CH), 7.89( 3 J (Pt−H) 46) 1H(CH)).…”

Section: Methodsmentioning

confidence: 99%

Mechanisms of Substitution Reactions on Cyclometallated Platinum(IV) Complexes: “Quasi-labile” Systems

2000

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The substitution reactions of SMe 2 by phosphines (PMePh 2 , PEtPh 2 , PPh 3 , P(4-MeC 6 H 4 ) 3 , P(3-MeC 6 H 4 ) 3 , PCy 3 ) on Pt IV complexes having a cyclometalated imine ligand, two methyl groups in a cis-geometrical arrangement, a halogen, and a dimethyl sulfide as ligands, [Pt(CkN)(CH 3 ) 2 (X)(SMe 2 )], have been studied as a function of temperature, solvent, and electronic and steric characteristics of the phosphines and the X and CkN ligands. In all cases, a limiting dissociative mechanism has been found, where the dissociation of the SMe 2 ligand corresponds to the rate-determining step. The pentacoordinated species formed behaves as a true pentacoordinated Pt IV compound in a steady-state concentration, given the solvent independence of the rate constant. The X-ray crystal structures of two of the dimethyl sulfide complexes and a derivative of the pentacoordinate intermediate have been determined. Differences in the individual rate constants for the entrance of the phosphine ligand can only be estimated as reactivity ratios. In all cases an effect of the phosphine size is detected, indicating that an associative step takes place from the pentacoordinated intermediate. The nature of the CkN imine and X ligands produces differences in the dimethyl sulfide dissociation reactions rates, which can be quantified by the corresponding ∆S q values (72, 64, 48, 31, and 78 J K -1 mol -1 for CkN/X being C

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Quinquedentate co-ordination of amino-substituted tetraazacycloalkanes to cobalt(III). Part 3. Synthesis of an unsymmetric ligand and crystal structure of its cis-chlorocobalt(III) complex

Cited by 15 publications

References 4 publications

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

Dinuclear Cyano-Bridged Co^III−Fe^II Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity

Mechanisms of Substitution Reactions on Cyclometallated Platinum(IV) Complexes: “Quasi-labile” Systems

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Quinquedentate co-ordination of amino-substituted tetraazacycloalkanes to cobalt(III). Part 3. Synthesis of an unsymmetric ligand and crystal structure of its cis-chlorocobalt(III) complex

Cited by 15 publications

References 4 publications

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

Dinuclear Cyano-Bridged CoIII−FeII Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity

Mechanisms of Substitution Reactions on Cyclometallated Platinum(IV) Complexes: “Quasi-labile” Systems

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Dinuclear Cyano-Bridged Co^III−Fe^II Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity