Redox-active Tris Research Articles

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn(2+) Coordination Framework.

An investigation of the redox-active tris[4-(pyridin-4-yl)phenyl]amine (NPy3) ligand in the solution state and upon its incorporation into the solid-state metal-organic framework (MOF) [Zn(NPy3)(NO2)2·xMeOH·xDMF]n (MeOH = methanol and DMF = N,N-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs.

Controlling Interpenetration in Electroactive Co(II) Frameworks Based on the Tris(4-(pyridin-4-yl)phenyl)amine Ligand

Control over the degree of interpenetration within metal–organic frameworks has important implications for the application of these materials in numerous areas ranging from gas storage to chemical separations. In this work, the degree of interpenetration was controlled in a series of three Co2+ frameworks with the redox-active tris(4-(pyridin-4-yl)phenyl)amine (NPy3) ligand, where the steric bulk of the dicarboxylate coligand (1,4-benzenedicarboxylate (bdc), 2,5-dimethyl-1,4-benzenedicarboxylate (dmbdc), or 2,3,5,6-tetramethyl-1,4-benzenedicarboxylate (tmbdc)) was increased by the addition of methyl groups to the phenyl core. The use of less sterically hindered carboxylates (bdc, dmbdc) resulted in 3-fold interpenetrated three-dimensional (3D) networks, while use of the tmbdc ligand resulted in a 3D non-interpenetrated structure. The redox activity of the NPy3 ligand was retained within the framework as elucidated from electrochemical and spectral measurements.

Redox-state investigation in a Co(II) framework with the redox-active tris(4-(pyridin-4-yl)phenyl)amine ligand

The synthesis, redox and spectral properties of a Co(II) 3D coordination framework, consisting of interpenetrated 2D (4,4′)-nets with the redox-active tris(4-(pyridine-4-yl)phenyl)amine (NPy3) ligand is reported. The accessible redox states in the framework were explored through solid state electrochemical and spectroelectrochemical experiments. The incorporation of a redox-active metal in conjunction with a redox-active ligand provides access to a greater number of accessible redox states within a solid state material. This strategy holds promise for the synthesis of multifunctional materials that are capable of changing their properties as a function of the electronic state.

Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes

The reaction of CoX2 (X = Cl, Br, NO3) with KTp(Ph2) in tetrahydrofuran (THF) yields the half-sandwich compounds [Tp(Ph2)CoX] (X = Cl 1, Br 2, NO3 3). The reaction of [Tp(Ph2)CoBr] with NaX (X = N3, NO2) or potassium thiocyanate (KNCS) permits isolation of [Tp(Ph2)CoX] (X = N3 4, NCS 5, NO2 6). In contrast, the reaction of cobalt(II) acetate with KTp(Ph2) yields [Tp(Ph2)CO(OAc)(Hpz(Ph2))] 7 as a result of B-N bond cleavage. Subsequent reaction of 7 with a range of beta-diketones in the presence of NaOMe produces the beta-diketonate complexes, [Tp(Ph2)Co(beta-diketonate)] (beta-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the Tp(Ph2) ligands are kappa3-coordinated and that the beta3-diketonate ligands adopt a bidentate coordination mode. Electronic spectra are consistent with four- or five-coordinate species in solution. X-Ray crystallographic studies of 7 reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9 and 10 show cobalt centres with square pyramidal coordination geometries and kappa2-coordinated beta-diketonate ligands. Cyclic voltammetric studies of 6 reveal irreversible one-electron reduction to Co(I). However, the beta-diketonate complexes, 8, 10 and 11 undergo irreversible one-electron oxidation. The redox potential and reversibility increases as the steric bulk of the substituent on the beta-diketonate ligand increases.

Thermodynamics and Kinetics of Adsorption of Poly(amido amine) Dendrimers Surface Functionalized with Ruthenium(II) Complexes

The thermodynamics and kinetics of adsorption of the redox-active tris(bipyridyl)ruthenium(II) pendant poly(amido amine) (PAMAM) dendrimers and bis(terpyridyl)ruthenium(II) pendant PAMAM dendrimers (generations 0, 1, 2, 3, and 4) have been studied using electrochemical methods. All of these metallodendrimers adsorb onto Pt electrodes at +0.8 V vs Ag/AgCl where the Ru sites of the dendrimers have 2+ charges and the adsorption thermodynamics are well characterized by the Langmuir adsorption isotherm. The kinetics of adsorption were found to be activation controlled with the rate constant decreasing with decreasing dendrimer generation. Electrochemically determined coverages were significantly larger than calculated values determined from the dimensions of the metallodenrimers obtained from molecular modeling. These comparisons suggest that upon adsorption, the dendrimers appear to compress to dimensions significantly smaller than those calculated.

Complexes containing redox-active fluorenone-based ligands linked to redox-active tris(pyrazolyl)boratomolybdenum fragments: assignment of ligand-centred and metal-centred redox processes by EPR and UV/VIS/NIR spectroelectrochemistry †

The dinuclear complex [{Mo(TpMe,Me)(NO)Cl}2(µ-L2)] 2 [L2 is the new bridging ligand 2,7-bis{2-(4-pyridyl)ethen-1-yl}fluorenone] contains two redox-active molybdenum(I) centres linked by a bridging ligand which is itself redox-active by virtue of the fluorenone spacer unit. The complex undergoes four one-electron reductions of which two are metal-centred Mo(0)/Mo(I) couples and two are reductions of the fluorenone unit. Also studied were the mononuclear analogue [Mo(TpMe,Me)(NO)Cl(L1)] [L1 is 2-bromo-7-{2-(4-pyridyl)ethen-1-yl}fluorenone], and the dinuclear complex [{Mo(TpMe,Me)(NO)Cl}2(µ-L3)] 3 [L3 is the bridging ligand 2,7-bis{2-(4-pyridyl)ethen-1-yl}fluorene] which lacks the ligand-centred redox activity. A combination of EPR and UV/VIS/NIR spectroelectrochemical techniques was used and showed how the separate metal-centred and ligand-centred reduction processes lead to quite distinct and characteristic spectroscopic signatures, such that it was possible to assign the sequence of reduction sites as ligand–metal–metal–ligand. The initial reduction of the bridging ligand in 2 results in a much larger separation between the two Mo(0)/Mo(I) couples (240 mV) than occurs in complexes where the bridging ligand is not redox-active.

Monometallic, homo- and heterobimetallic complexes based on redox active tris(3,5-dimethylpyrazolyl)borato-molybdenum and -tungsten nitrosyls—I. Meta substituent effects on the reduction potentials of monometallic arylamide complexes

The complexes [Mo(NO)LCl(NHC 6H 4-3-Z)] (L = HB(3,5-Me 2C 3N 2H) 3; Z = F, Cl, Br, Me, OMe, CF 3, NO 2), [W(NO)L(NHC 6H 4-3-Z)] (Z = F, Cl, Br, Me, OMe, COME, CF 3, NO 2) and [W(NO)L(NHC 6H 4-3-CF 3) 2] have been synthesized and characterized by spectroscopic methods. All of the monoarylamide complexes undergo one-electron reduction processes at potentials which vary according to the nature of Z. A linear correlation was found between the reduction potentials within each of the two series and the Hammett meta substituent parameters, σ m , for Z. The respective reaction constants, ϱ m , and intercepts, E f 0, are for [Mo(NO)LCl(NHC 6H 4-3-Z)], ϱ m = 5.50 (0.39), E f 0 = −0.848 (0.009) V and for [W(NO)L(NHC 6H 4-3-Z)], ϱ m = 4.75 (0.50), E f 0 1.291 (0.011) V.

ChemInform Abstract: Monometallic, Homo‐ and Hetero‐bimetallic Complexes Based on Redox Active Tris(3,5‐dimethylpyrazolyl)borato Molybdenum and Tungsten Nitrosyls. Part 6. Synthesis and Electrochemistry of Complexes Containing Saturated Heterocyclic Amide Ligands. X‐Ray Crystal and Molecular Structure of ((Mo(NO)(HB(Me2pz)3)Cl)2(NC4H8N)).

AbstractThe reaction of the appropriate dichloro complexes with an excess of the cyclic amines leads to the coordinatively unsaturated complexes (I).

Monometallic, homo- and hetero-bimetallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato molybdenum and tungsten nitrosyls. Part 8. Complexes exhibiting weak or intermediate interaction between two redox centres

The complexes [ML(NO)X(NHQNH2)][L = tris(3,5-dimethylpyrazolyl)borate; M = Mo, X = I, Q =(C6H4)2Y where Y = O, SO2, CH2, or CH2CH2; M = W, X = Cl, Q =(C6H4)2O], [MoL(NO)I(NHCH2CH2C6H4NH2)], [ML(NO)X(OQOH)][M = Mo, X = I, Q =(C6H4)2Y where Y = nothing or S; X = Cl, Q =(C6H4)2S], and [ML(NO)X(OCH2C6H4CH2OH)](M = Mo, X = I; M = W, X = Cl) have been prepared. The bimetallic complexes [{ML(NO)X}2(NHQNH)][M = Mo, X = I, Q =(C6H4)2Y where Y = O, SO2, CH2, or CH2CH2; M = W, X = Cl, Q =(C6H4)2O], [{MoL(NO)I}2(NHCH2CH2C6H4NH)], [{MoL(NO)X}2(OQO)][X = I, Q =(C6H4)2 Y where Y = nothing or S; X = Cl, Q =(C6H4)2 Y where Y = nothing, S, SO2, CO, or COC6H4C6H4CO], and [{ML(NO)X}2(OCH2C6H4CH2O)](M = Mo, X = I; M = W, X = Cl) were obtained either from the monometallics by reaction with [ML(NO)X2] or by direct reaction of the latter with the appropriate arylamine or phenol. The heterobimetallic [MoL(NO)I(NHC6H4OC6H4NH)WL(NO)Cl] was also prepared and all compounds were characterised spectroscopically. The monometallic species underwent a single, usually reversible, one-electron reduction determined by cyclic voltammetry (in CH3CN using a Pt electrode). Values of E½ were dependent on M, X, and the nature of the heteroatom ligand. The bimetallic species underwent two one-electron reductions, investigated by differential pulse polarography. The separation between the redox potentials (ΔE½) varied from 45 mV (negligible interaction between redox centres) to 138 mV (weak interaction), depending on the nature of the bridging ligand.

Monometallic, homo- and hetero-bimetallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato molybdenum and tungsten nitrosyls. Part 7. Compounds containing strongly interacting redox centres derived from para-substituted anilines and phenols

The compounds [ML(NO)X(NHC6H4ZH)][L = tris(3,5-dimethylpyrazolyl)borate; Z = NH; M = Mo, X = I; M = W, X = Cl; Z = O; M = Mo, X = I; M = W, X = Cl; Z = S, M = Mo, X = Cl], [{ML(NO)X}2(NHC6H4NH)](M = Mo, X = Cl or I; M = X = Cl), [{ML(NO)X}2(NHC6H4O)](M = Mo, X = Cl or I; M = W, X = Cl), [{MoL(NO)Cl}2(OC6H4O)], and [MoL(NO)I(YC6H4Z)WL(NO)Cl](Y = Z = NH; Y = O, Z = NH; Y = NH, Z = O) have been prepared. Cyclic voltammetric and coulometric studies established that the monometallic species undergo a one-electron reduction, whereas the bimetallic species are reduced in two one-electron steps. The electrochemical data suggest that the redox centres in the bimetallic complexes influence each other strongly.

ChemInform Abstract: Monometallic, Homo‐ and Hetero‐Bimetallic Complexes Based on Redox Active Tris(3,5‐dimethylpyrazolyl)borato‐molybdenum and ‐tungsten Nitrosyls. Part 4. Effects of Ligating Atom Type on the Reduction Potentials of Monometallic Complexes.

AbstractThe complexes (Ia)‐(Ic) are prepared by substitution reaction of their dichloro analogues (Id) with HY and characterized.

Monometallic, homo- and hetero-bimetallic complexes based on redox active tris(3,5-dimethylpyrazolyl)boratomolybdenum and tungsten nitrosyls. Part V.Para-substituent effects on the reduction potentials of arylamide complexes

Two series of complexes having the formula [M{HB(3,5-Me2C3N2H)3}(NO)Cl(NHC6H4Z-p)]; in which M=Mo and Z=F, Cl, Br, OMe, SMe, CN, CO2Me or NO2 and M=W and Z=Br, OMe, CN, CO2Me or NO2, have been prepared. The reduction potentials of these new complexes were measured by cyclic voltammetry and, in combination with previously reported data for related species and for [Mo{HB(3,5-Me2C3N2H)3} (NO)I-(NHC6H4Z-p], were used to determine reaction constants for the reduction of [M{HB(3,5-Me2C3N2H)3}(NO)X(NHC6H4Z)]M=Mo and X=I or Cl; M=W, X=Cl.

Monometallic, homo- and hetero-bimetallic complexes based on redox active tris(3,5-dimethylpyrazolyl)borato molybdenum and tungsten nitrosyls. Part 6. Synthesis and electrochemistry of complexes containing saturated heterocyclic amide ligands. X-Ray crystal and molecular structure of [{Mo(NO)[HB(Me2pz)3]Cl}2(NC4H8N)

The co-ordinatively unsaturated complexes [M(NO){HB(Me2pz)3}Cl(Y)][M = Mo or W; Y = NC3H6–, NC4H8–, or NC5H10–; HB(Me2pz)3= hydrotris(3,5-dimethylpyrazolyl)borate] have been prepared and characterised. All exhibit reversible one-electron reduction processes in their cyclic voltammograms. The bimetallic species [{M(NO)[HB(Me2pz)3]Cl}2(NC4H8N)](M = Mo or W) were also prepared, and the molybdenum complex structurally characterised by an X-ray diffraction study which revealed a chair conformation for the bridging piperazine-1,4-diyl ligand (NC4H8N). The molybdenum atoms are oriented essentially equatorially with Mo ⋯ Mo separation 6.773(2)A. These bimetallic species appear to behave as ‘strongly interacting’ redox systems. In the case of M = Mo two one-electron reduction processes, separated by 560 mV, were observed by cyclic voltammetry.

Monometallic, homo- and hetero-bimetallic complexes based on redox active tris(3,5-dimethylpyrazolyl)borato-molybdenum and -tungsten nitrosyls. Part 4. The effects of ligating atom type on the reduction potentials of monometallic complexes

The complexes [M(NO)(L)X(Y)][L = tris(3,5-dimethylpyrazolyl)borate; M = Mo, X = Cl, Y = OPh; M = W, X = Cl, Y = SPh; or M = W, X = Y = NC4H4, OPh, or SPh] have been prepared and characterised. The electrochemical properties of these compounds were investigated by cyclic voltammetry and compared with those of others in the series [M(NO)(L)X(Y)](M = Mo or W; X = Cl, Y = OPh, NHPh, or SPh; or X = Y = NC4H4, OPh, NHPh, or SPh). It was found that the thiophenolate complexes reduced at slightly more anodic potentials than their phenolate analogues while the arylamide complexes reduced at significantly more cathodic potentials. In general the tungsten complexes reduced at potentials ca. 0.45 V more cathodic than their molybdenum analogues.

Mono- and bi-metallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato-molybdenum nitrosyls, part III.(1) Complexes containing meta-substituted benzene- and naphthalenediols or -diamines

The complexes [MoL*(NO)Cl(YC6H4YH-m)] (Y = O or NH), [MoL*(NO)Cl(YC10H6YH-1,5)], (Y = O or NH), [MoL*(NO)Cl(OC10H6OH-2,7)], [{MoL*(NO)Cl}2(XC6H4Y-m)] (X=Y=O, NH or S; X=O, Y=NH), [{MoL*(NO)-C1}2(YC10H6Y-1,5)] (Y=O or NH) and [{MoL*(NO)Cl2-(OC10H6-2,7)] have been prepared and studied by cyclic voltammetry. The monometallic species undergo a reversible oneelectron reduction, whereas the bimetallics undergo two oneelectron reductions. A comparison of ΔE1/2 (E1/2(1)-E1/2(2)) values for those new species with those obtained frompara- substituted analogues and bimetallics containing extended bridges YC6H4ZC6H4Y (e.g. Z = S or CH2CH2) established that the interaction between the redox centres in these new species is intermediate (YC6H4Y-m; NHC10H6NH-1,5) or weak (OC10H6O).