Homobimetallic Complexes Research Articles

Multistep Oxidation of Diethynyl Oligophenylamine-Bridged Diruthenium and Diiron Complexes.

Homo-dinuclear nonlinear complexes [{M(dppe)Cp*}2{μ-(-C≡C)2X}] (dppe = 1,2-bis(diphenylphosphino)ethane; Cp* = η5-C5Me5; X = triphenylamine (TPA), M = Ru (1a) and Fe (1b); X = N,N,N',N'-tetraphenylphenylene-1,4-diamine (TPPD), M = Ru (2a)) were prepared and characterized by 1H, 13C, and 31P NMR spectroscopy and single-crystal X-ray diffraction (1a, 2a). Attempts to prepare the diiron analogue of 2a were not successful. Experimental data obtained from cyclic voltammetry, square wave voltammetry, UV-vis-NIR (NIR = near-infrared) spectro-electrochemistry, and very informative IR spectro-electrochemistry in the C≡C stretching region, combined with density functional theory calculations, afford to make an emphasizing assessment of the close association between the metal-ethynyl termini and the oligophenylamine bridge core as well as their respective involvement in sequential one-electron oxidations of these complexes. The anodic behavior of the homo-bimetallic complexes depends strongly both on the metal center and the length of the oligophenylamine bridge core. The poorly separated first two oxidations of diiron complex 1b are localized on the electronically nearly independent Fe termini. In contrast, diruthenium complex 1a exhibits a significantly delocalized character and a marked electronic communication between the ruthenium centers through the diethynyl-TPA bridge. The ruthenium-ethynyl halves in 2a, separated by the doubly extended and more flexible TPPD bridge core, show a lower degree of electronic coupling, resulting in close-lying first two anodic waves and the NIR electronic absorption of [2a]+ with an indistinctive intervalence charge transfer character. Finally, the third anodic waves in the voltammetric responses of the homo-bimetallic complexes are associated with the concurrent exclusive oxidation of the TPA or TPPD bridge cores.

Enhancements in catalytic reactivity and selectivity of homobimetallic complexes containing heteroditopic ligands.

Rh(i) and Ir(i) homobimetallic complexes were synthesised using a heteroditopic ligand system on a xanthene scaffold containing a monodentate N-heterocyclic carbene ligand and a bidentate bis(pyrazol-1-yl)methane ligand. The complexes were tested as catalysts for the two-step dihydroalkoxylation and two-step hydroamination/hydrosilylation reactions. This is the first known report of an organometallic group 9 complex, Ir(i) bimetallic complex, 13, to selectively favour the opposite spirocyclisation product from that reported in the literature, 14cvs.14b. The Ir(i) homobimetallic complex catalyses the intramolecular hydroamination reaction of alkynamines efficiently and proved to be a highly active catalyst for promoting the subsequent hydrosilylation of the pyrrolines; completing the hydrosilylation reactions in less than 40 seconds. A chloro-bridged bimetallic species was observed in the solid state, revealing that the COD co-ligands present underwent an oxidation.

A base-free synthetic route to anti-bimetallic lanthanide pentalene complexes

We report the synthesis and structural characterisation of three homobimetallic complexes featuring divalent lanthanide metals (Ln = Yb, Eu and Sm) bridged by the silylated pentalene ligand [1,4-{SiiPr3}2C8H4]2- (= Pn†). Magnetic measurements and cyclic voltammetry have been used to investigate the extent of intermetallic communication in these systems, in the context of molecular models for organolanthanide based conducting materials.

Correction: Enhancements in catalytic reactivity and selectivity of homobimetallic complexes containing heteroditopic ligands.

Correction for 'Enhancements in catalytic reactivity and selectivity of homobimetallic complexes containing heteroditopic ligands' by Mark R. D. Gatus et al., Dalton Trans., 2017, 46, 7457-7466.

Synthesis, spectral characterization, X-ray crystal structure, electrochemical studies, and DNA interactions of a Schiff base pro-ligand and its homobimetallic complexes containing the cysteamine moiety

A Schiff base, N,N′-(3,4-dithiahexane-1,6-diyl)bis(5-methylsalicylideneimine), was synthesized and characterized by X-ray crystallography. Dimeric complexes of nickel(II), palladium(II), and vanadium(IV) were synthesized by the reactions of the Schiff base with nickel(II) acetate, palladium(II) acetate, and vanadyl acetylacetonate in 1:1 molar ratio. In all three complexes, the thiol group was deprotonated and coordinated to the metal. The X-ray structure of the Schiff base showed that in the crystalline form, the SH groups were oxidized to the corresponding disulfide. In the dimeric complexes, coordination took place through the azomethine nitrogen, enolic oxygen, and sulfur atoms. The metal-to-ligand ratio was 1:1, and molar conductance data revealed that the metal complexes were nonelectrolytes. The free Schiff base and its complexes showed photoluminescence in methanol at room temperature. The redox behavior of the compounds was studied by cyclic voltammetry in DMF, which showed both quasi-reversible and irreversible processes. The interaction of the complexes with DNA was investigated by electronic absorption spectroscopy.

Synthesis, characterization, X-ray crystal structure, luminescence, electrochemical and solvatochromism studies of new dimer of nickel and palladium complexes containing ferrocenyl imine ligand

The synthesis of a new Schiff base ligand was investigated by the reaction of ferrocenecarboxaldehyde, [(η5(C5H5) (η5(C5H4CHO)], with 2-aminoethanethiol at room temperature. For this product, ring closure was also observed in the crystalline form which thiazolidine was obtained. Furthermore, new homobimetallic complexes of nickel(II) and palladium(II) were synthesized by the reaction of the new Schiff base ligand with nickel chloride and palladium chloride in 1:1 M ratio. In nickel and also palladium complexes the ligands were coordinated to the metals via the imine N atoms and the chlorido-bridged unit for the reported complexes was suggested. The complexes have been found to possess 1:1 metals to ligands stoichiometry. The emission and absorption spectra of the ligand and its complexes were studied in methanol solvent. Electrochemical properties of the ligand and its metal complexes were investigated in CH3CN solvent at the 100 mVs−1 scan rate. The Schiff base ligand and its metal complexes showed both reversible and irreversible processes at this scan rate. These compounds have been characterized by IR, 1H NMR, UV/Vis and elemental analysis. The crystal structure of the thiazolidine has been determined by single crystal X-ray diffraction.

Synthesis and spectroscopic characterization of mononuclear/binuclear organotin(IV) complexes with 1H-1,2,4-triazole-3-thiol: Comparative studies of their antibacterial/antifungal potencies

A series of di and triorganotin(IV) complexes of the general formula, R2(Cl)SnL (R= Me: 1; Bu: 2) and R3SnL (R = Bu: 3; Ph: 4) have been synthesized by refluxing equivalent molar ratios of orgnotin(IV) chlorides (R2SnCl2/R3SnCl) with the 1H-1,2,4-Triazole-3-thiol (LH) in dry methanol. The synthesized complexes (1-4) were further treated with CS2 and R2SnCl2/R3SnCl in 1:1:1 molar ratio to yield the homobimetallic complexes of the types R2(Cl)SnLCS2Sn(Cl)R2 (R = Me: 5; Bu: 6) and R3SnLCS2SnR3 (R = Bu: 7; Ph: 8). The ligand and the complexes have been characterized by elemental microanalysis (CHNS), FT-IR and multinuclear NMR (1H&13C), and electron ionization mass spectrometry. IR data demonstrates that the dithiocarbamate donor site of the ligand acts in a bidentate manner and there isa trigonal bipyramidal geometry around Sn(IV) in solid state. 1H and 13C NMR data supports the tetrahedralgeometry with thiol donor sites of the ligand while tetra and penta coordinated environments around dithiocarboxylate bound tin(IV) in solution state. Mass spectrometric data supported well the structures of the synthesized complexes. The homobimetallic derivatives were found more active than mononuclear organotin(IV) compounds and free ligand against various strains of bacteria and fungus.

Photophysics of tungsten–benzylidyne complexes derived from s-indacene: synthesis, characterization and DFT studies

The photophysics of the mono- and homobimetallic complexes of tungsten benzylidyne has been examined by using absorption and emission. Theoretical calculations were carried out to gain further understanding of these novel molecular systems.

Metathesis reactions of rapeseed oil‐derived fatty acid methyl esters induced by monometallic and homobimetallic ruthenium complexes

In this study, homobimetallic ruthenium alkylidene complexes were used for the self‐metathesis and ethenolysis reactions of methyl oleate and rapeseed oil‐derived FAME mixtures. The activity and selectivity of homobimetallic ruthenium alkylidene complexes were also compared with their monometallic analogs. It has been determined that homobimetallic complexes bearing phosphine and N‐heterocyclic carbene ligands are more active and selective catalysts than their monometallic analogs for self‐metathesis and ethenolysis reactions of rapeseed FAME mixture. Homobimetallic ruthenium complexes showed superior selectivity at 25°C toward these reactions. Conversion values of 99% with 96% selectivity toward ethenolysis products were observed by using homobimetallic ruthenium complexes. In addition to these superiorities, relatively lower amounts of double bond isomerization side‐products were obtained by using homobimetallic complexes. This catalytic approach represents a unique example for metathesis transformation of FAME mixtures at relatively low temperature (25°C) and ethylene pressure (1 atm) with high selectivity using homobimetallic ruthenium alkylidene complexes.Practical applications: This study reports the selective transformation of rapeseed oil‐derived FAME by ethenolysis reactions catalyzed by homobimetallic ruthenium alkylidene complexes. Industrially important terminal olefins as well as new polymer precursors can be synthesized in a selective manner using these catalytic systems.Ethenolysis reactions of rapeseed oil‐derived fatty acid methyl ester mixture, catalyzed by homobimetallic ruthenium alkylidene complexes exhibit high selectivity at RT.

SYNTHESIS AND CHARACTERIZATION OF HOMO AND HETEROBIMETALLIC COMPLEXES WITH A DICOMPARTMENTAL MACROCYCLIC LIGAND CONTAINING PROPIONITRILE PENDENT ARMS

A binuclear macrocyclic ligand containing dissimilar N(amine)2O2 and N(imine)2O2 coordination sites sharing two phenolic oxygen atoms, was prepared by cyclic condensation of dialdehyde precursor L 1 H2 with 1,3-diaminopropane. The ligand includes two propionitrile pendant arms on the amine nitrogen atoms. The homobimetallic complex (ZnL 2 Zn(OAc))PF6 was synthesized by one step procedure. Heterobimetallic complexes (ZnL 2 M(OAc))PF6 that M= Cu(II) and Ni(II), were prepared by a trans-metallation reaction. The prepared complexes were characterized on the basis of molar conductance measurement, elemental analysis, IR, NMR and UV-Vis spectroscopy techniques. Characterization results showed that the nitrogen atoms of propionitrile pendant arms are not involved in the coordination to the metal center and also the two metal ions are bridged by two phenolic oxygen atoms and an acetate group.

Heterobimetallic porphyrin complexes displaying triple dynamics: coupled metal motions controlled by constitutional evolution.

A bis-strap porphyrin ligand (1), with an overhanging carboxylic acid group on each side of the macrocycle, has been investigated toward the formation of dynamic libraries of bimetallic complexes with Hg(II), Cd(II), and Pb(II). Highly heteroselective metalation processes occurred in the presence of Pb(II), with Hg(II) or Cd(II) bound out-of-plane to the N-core and "PbOAc" bound to a carboxylate group of a strap on the opposite side. The resulting complexes, 1(Hg)·PbOAc and 1(Cd)·PbOAc, display three levels of dynamics. The first is strap-level (interactional dynamics), where the PbOAc moiety swings between the left and right side of the strap owing to a second sphere of coordination with lateral amide functions. The second is ligand-level (motional dynamics), where 1(Hg)·PbOAc and 1(Cd)·PbOAc exist as two degenerate states in equilibrium controlled by a chemical effector (AcO(-)). The process corresponds to a double translocation of the metal ions according to an intramolecular migration of Hg(II) or Cd(II) through the N-core, oscillating between the two equivalent overhanging carbonyl groups, coupled to an intermolecular pathway for PbOAc exchanging between the two equivalent overhanging carboxylate groups (N-core(up) ⇆ N-core(down) coupled to strap(down) ⇆ strap(up), i.e., coupled motion #1 in the abstract graphic). The third is library-level (constitutional dynamics), where a dynamic constitutional evolution of the system was achieved by the successive addition of two chemical effectors (DMAP and then AcO(-)). It allowed shifting equilibrium forward and backward between 1(Hg)·PbOAc and the corresponding homobimetallic complexes 1(Hg2)·DMAP and 1(Pb)·PbOAc. The latter displays a different ligand-level dynamics, in the form of an intraligand coupled migration of the Pb(II) ions (N-core(up) ⇆ strap(up) coupled to strap(down) ⇆ N-core(down), i.e., coupled motion #2 in the abstract graphic). In addition, the neutral "bridged" complexes 1HgPb and 1CdPb, with the metal ions on opposite sides both bound to the N-core and to a carboxylate of a strap, were structurally characterized. These results establish an unprecedented approach in supramolecular coordination chemistry, by considering the reversible interaction of a metal ion with the porphyrin N-core as a new source of self-organization processes. This work should provide new inspirations for the design of innovative adaptative materials and devices.

Synthesis, Characterization and Reactivity of Group 4 Metallocene Bis(diphenylphosphino)acetylene Complexes—A Reactivity and Bonding Study

A study of the coordination chemistry of bis(diphenylphosphino)acetylene, Ph2P-C≡C-PPh2, with selected group 4 metallocenes is presented. By substitution of the alkyne in complexes of the type Cp'2M(L)(η(2)-Me3SiC2SiMe3) (M = Ti, no L; M = Zr, L = pyridine; Cp' = substituted or unsubstituted bridged or unbridged η(5)-cyclopentadienyl), the expected mononuclear complexes Cp*2Ti(η(2)-Ph2PC2PPh2) (4Ti), (rac-ebthi)Ti(η(2)-Ph2PC2PPh2) (5Ti), and (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp2Zr] was used in the reaction of Cp2Zr(py)(η(2)-Me3SiC2SiMe3) with Ph2P-C≡C-PPh2, the dinuclear complex [Cp2Zr(η(2)-Ph2PC2PPh2)]2 (6) was formed and isolated in the solid state. In solution, this complex is in equilibrium with the very spectacular structure of complex 7b as the first example of such a highly strained four-membered heterometallacycle of a group 4 metal, involving the rare R2PCCR' fragment in the cyclic unit. Both the stability and reactivity of heterodisubstituted alkynes X-C≡C-X (X = NR2, PR2, SR, SiR3, etc.) themselves and also of their complexes are of general interest. Complex 6 did not react with a second [Cp2Zr] fragment to form a homobimetallic complex. In contrast, for (rac-ebthi)Zr(η(2)-Ph2PC2PPh2) (5Zr) this reaction occurs. In the reaction of complex 4Ti with the Ni(0) complex (Cy3P)2Ni(η(2)-C2H4) (Cy = cyclohexyl), C-P bond cleavage of the alkyne ligand resulted in the formation of the isolated complex [(Cy3P)Ni(μ-PPh2)]2 (11). The structure and bonding of the complexes were investigated by DFT analysis to compare the different possible coordination modes of the R2P-C≡C-PR2 ligand. For compound 7b, a flip-flop coordination of the phosphorus atoms was proposed. Complexes 4Ti, 5Ti, 5Zr, 6, and 11 were characterized by X-ray crystallography.

Unsymmetrical Bimetallic Complexes with MII–(μ-OH)–MIII Cores (MIIMIII = FeIIFeIII, MnIIFeIII, MnIIMnIII): Structural, Magnetic, and Redox Properties

Heterobimetallic cores are important units within the active sites of metalloproteins but are often difficult to duplicate in synthetic systems. We have developed a synthetic approach for the preparation of a complex with a Mn(II)-(μ-OH)-Fe(III) core, in which the metal centers have different coordination environments. Structural and physical data support the assignment of this complex as a heterobimetallic system. A comparison with analogous homobimetallic complexes, Mn(II)-(μ-OH)-Mn(III) and Fe(II)-(μ-OH)-Fe(III) cores, further supports this assignment.

Photoinduced Electron and Energy Transfer and pH-Induced Modulation of the Photophysical Properties in Homo- and Heterobimetallic Complexes of Ruthenium(II) and Rhodium(III) Based on a Heteroditopic Phenanthroline–Terpyridine Bridge

Homo- and heterobimetallic complexes of compositions [(bpy)2Ru(II)(phen-Hbzim-tpy)Ru(II)(tpy/tpy-PhCH3/H2pbbzim)](4+) and [(bpy)2Ru(II)(phen-Hbzim-tpy)Rh(III)(tpy-PhCH3/H2pbbzim)](5+), where phen-Hbzim-tpy = 2-[4-(2,6-dipyridin-2-ylpyridin-4-yl)phenyl]-1H-imidazole[4,5-f][1,10]phenanthroline, bpy = 2,2'-bipyridine, tpy = 2,2':6',2"-terpyridine, tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2"-terpyridine, and H2pbbzim = 2,6-bis(benzimidazol-2-yl)pyridine, have been synthesized and characterized by elemental analyses, electrospray ionization mass spectrometry, and (1)H NMR spectroscopy. The absorption spectra, redox behavior, and luminescence properties of these bimetallic complexes have been thoroughly investigated and compared with those of monometallic [(bpy)2Ru(II)(phen-Hbzim-tpy)](2+) and [(tpy-PhCH3)Rh(III)(tpy-Hbzim-phen)](3+) model compounds. The electrochemistry of the complexes shows a reversible Ru(II/III) oxidation in the anodic region and an irreversible Rh(III/I) reduction and several ligand-based reductions in the cathodic region. Steady-state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer from the metal-to-ligand charge-transfer (MLCT) excited state of the [(bpy)2Ru(II)(phen-Hbzim-tpy)] chromophore to the MLCT state of the tpy-containing chromophore [(phen-Hbzim-tpy)Ru(II)(tpy/tpy-PhCH3/H2pbbzim)] occurs in all three unsymmetrical homobimetallic complexes. On the other hand, for both heterometallic dyads, an efficient intramolecular photoinduced electron transfer from the excited ruthenium moiety to the rhodium-based unit takes place. The rate constants for the energy- and electron-transfer processes have been determined by time-resolved emission spectroscopy. The influence of the pH on the absorption, steady-state, and time-resolved emission properties of complexes has been thoroughly investigated. The absorption titration data were used to determine the ground-state pK values, whereas the luminescence data were utilized for determination of the excited-state acid dissociation constants. In effect, deprotonation of the azole NH moieties of the complexes leads to a substantial lowering of the MLCT absorption and emission band energies.

Synthesis, Characterization and Biological Studies of Homobimetallic Schiff Base Cu(II) and Ni(II) Complexes

New bidentate ligands N 1 ,N 4 -bis(2-amino-5-nitrobenzylidene)benzene-1,4-diamine, L 1 and N 4 ,N 4' -bis(2-amino-5-nitrobenzylidene)biphenyl-4,4'-diamine, L 2 have been synthesized. The ligand L 1 and L 2 were treated with Cu(OCOCH 3)2.H 2O and Ni(OCOCH 3)2.4H 2O to afford the new homobi- metallic complexes (CuL 1 )2.4(OAc) ( 1), (NiL 1 )2.4(OAc) ( 2), (CuL 2 )2.4(OAc) ( 3) and (NiL 2 )2.4(OAc) ( 4) respectively. The four new homobimetallic complexes have been characterized by spectral techniques like elemental analysis, NMR, IR, UV Visible absorption, magnetic measurements, thermal, EPR, electrochemical studies and molar conductance. IR spectral data shows that the ligands are bidentate and the binding sites are azomethine nitrogen and free primary amine groups. Molar conductance measurements show that the complexes are electrolytes. EPR values and electronic spectral data suggest that it possesses square planar geometry. The Schiff base ligands and metal complexes were evaluated for antimicrobial activity against gram positive bacteria and gram negative bacteria. The ligands and its metal complexes were found to be biologically active. All the complexes show higher antimicrobial activity than the ligand and streptomycin.

Synthesis, characterization, semi-empirical study and biological activities of homobimetallic complexes of tranexamic acid with organotin(IV)

The Schiff base has been synthesized by reacting tranexamic acid with indol-3-carboxyaldehyde in the first step and then with carbon disulfide at room temperature in the second step. The homobimetallic complexes have been synthesized by reaction of Schiff base with R2SnCl2 and R3SnCl in 1 : 2 M ratio under stirring, where R = methyl, n-butyl and phenyl. The ligand and complexes have been characterized by elemental analysis, FT-IR, multinuclear NMR (1H, 13C and 119Sn) and semi-empirical study. IR data reveal the bidentate nature of the ligand. Five- or six-coordinate geometry was confirmed in solution by NMR spectroscopy. The homobimetallic complexes and ligand were tested in vitro against some pathogenic bacteria and fungi to assess their antimicrobial properties. The complexes show biological activities with few exceptions.

Synthesis and reactivity of a cyclopentadienyl-indenyl ligand ring-coupled by a chiral bridge derived from ethyl (S)-(−) lactate

In order to prepare a new unsymmetrical chiral ligand, C9H7CH(CH3)CH2C5H5, with an indenyl moiety connected to a cyclopentadienyl unit by a chiral ethylene bridge, we reacted the optically active tosylate 4, derived from ethyl (S)-(-) lactate, with LiCp. The only product resulting from this reaction was an optically active spirocyclopropane 6 obtained with a high diastereoselectivity (81.8% de). We also observed that, when the reduction of the ethyl indene lactate 2 was realized with an excess of LiAlH4 in Et2O under reflux, spirocyclopropane 6 was obtained in high yield with the same diastereoselectivity. When tosylate 4 was reacted with MgCp2, in place of LiCp, ligand 5 was obtained in good yield as a mixture of two double-bond isomers of the Cp unit. Ligand 5 was fully structurally characterized after conversion into transition monometallic complexes such as C9H7CH(CH3)CH2η(5)-C5H4Mo(CO)3Me 7 and C9H7CH(CH3)CH2η(5)-C5H4Rh(COD) 9, in which the indene moiety was kept intact due to the difference in reactivity of the indenyl moiety with respect to the cyclopentadienyl unit. An attempt to prepare a heterobimetallic complex from the sodium indenide salt of 7 and [RhCl(COD)]2, afforded a rhodium cyclopentadienyl complex 9, resulting from a metal exchange reaction with loss of the molybdenum part initially coordinated to the Cp unit, and conservation of the optical purity. An homobimetallic rhodium complex 10 could be prepared by deprotonation of ligand 5 with TlOEt, followed by quenching with [RhCl(COD)]2. The bis-rhodium complex 10 is obtained as a mixture of two diastereoisomers 10a and 10b with respect to the planar chirality of the indenyl ring system, with a good diastereoisomeric excess de = 70%. The structures of both complexes 9 and major (pS)-diastereoisomer 10a were determined by single crystal X-ray diffraction.

Dinitrosyl iron adducts of (N2S2)M(NO) complexes (M = Fe, Co) as metallodithiolate ligands

Adducts of the dinitrosyl iron unit and mono-nitrosyl bis-mercaptoethanediazacycloheptane (bme-dach) iron and cobalt are described in terms of the (bme-dach)M(NO) as metallodithiolate ligands. With M=Fe, a diamagnetic (N2S2)Fe(NO)·Fe(NO)2 diiron complex, in which the (N2S2)Fe(NO) unit serves as a bidentate ligand to the Fe(NO)2 unit is derived by use of a trinitrosyliron cation as precursor to the DNIC unit as well as a NO source to cleave the [(bme-dach)Fe]2 dimer (J. Am. Chem. Soc., 2010, 132, 14118). By a similar approach of [(bme-dach)Co]2 dimer cleavage, the Co–Fe bimetallic contains (N2S2)Co(NO) as a monodentate metallothiolate ligand to Fe(NO)2L, L=I-Mes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene. Characterization of this paramagnetic cation includes infrared and EPR spectroscopies, and X-ray diffraction analysis. The latter finds a Co⋯Fe distance of 3.697Å in contrast to the Fe–Fe bond distance of 2.7857(8)Å in the homobimetallic complex.

Metal Migration Processes in Homo- and Heterobimetallic Bismuth(III)–Lead(II) Porphyrin Complexes: Emergence of Allosteric Newton’s Cradle-like Devices

Metal ion migration in a bis-strapped porphyrin ligand with overhanging carboxylate groups has been investigated in solution. Two types of homobimetallic complexes are generated with Pb(II) and Bi(III) cations, which stand on both sides of the macrocycle: (i) a dissymmetric complex with one cation bound to the porphyrin N core and the other cation hung over the N core through bonding with a carboxylate of a strap; (ii) a C(2)-symmetric complex with both cations coordinated to the N core and to the carboxylate groups of the straps. Variable-temperature NMR studies and 2D rotational Overhauser effect spectroscopy NMR experiments have shown that in the former dissymmetric complexes, the two cations undergo a coupled intramolecular migration resulting in exchange of their coordination modes. Such complexes constitute active states of Newton's cradle-like devices (NCDs), with the ion migration rate depending on the lability of the metal-ligand interactions [Pb(II) faster than Bi(III) NCDs]. On the other hand, the C(2)-symmetric complexes constitute either an inactive state [with Pb(II)] or a resting state [with Bi(III)] of an NCD, since they correspond respectively to a precursor or an intermediate in the motion of the cations. The NCDs are under both allosteric and acid-base control: (i) with Pb(II), the addition of an allosteric effector such as an acetate anion to the medium allows the conversion of the symmetric form to the dissymmetric one, thus triggering the Newton's cradle-like motion of the cations; (ii) with Bi(III), a lifted state was converted to a resting one by the addition of protons and then restored by the addition of a base. As an extension to nondegenerate systems, a heterobimetallic Bi(III)-Pb(II) complex was selectively obtained, and it constitutes a frozen lifted state of a dissymmetric NCD. All of these homo- and hetero-NCDs could be successively formed by selective metal ion exchange. These unique findings open the way to novel tristable devices.

Di-Mesoionic Carbene-Bridged Complexes of Rh2, Ir2, and RhIr: A Stepwise Metalation Strategy for the Synthesis of di-MIC-Bridged Mixed-Metal Systems

A meta-substituted benzene-bridged ditriazolium salt has been prepared using copper-catalyzed azide–alkyne cycloaddition (CuAAC or “click” chemistry) and methylation protocols. Metalation of this dicationic species by basic-ligand-containing [Rh(μ-OMe)(COD)]2 and [Ir(μ-OMe)(COD)]2 precursors provides homobimetallic complexes of Rh and Ir bridged by a 1,2,3-triazol-5-ylidene-type di-mesoionic carbene (di-MIC) via an “internal-base” strategy. By using only 1/2 equiv of the internal-base precursor, mononuclear MIC-anchored/pendent-triazolium intermediates have been isolated, in which only one end of the ditriazolium salt has been deprotonated and attached to Rh or Ir. Reaction of these pendent intermediates with another 1/2 equiv of an internal-base precursor affords either the aforementioned homobimetallic products or an analogous di-MIC-bridged, mixed-metal Ir/Rh complex.