Strong interfullerene electronic communication in a bisfullerene-hexarhodium sandwich complex

Reaction of Rh(6)(CO)(12)(dppm)(2) (dppm = 1,2-bis(diphenylphosphino)methane) with 1.4 equiv. of C(60) in chlorobenzene at 120 degrees C affords a face-capping C(60) derivative Rh(6)(CO)(9)(dppm)(2)(micro(3)-eta(2),eta(2),eta(2)-C(60)) (1) in 73% yield. Treatment of 1 with excess CNR (10 equiv., R = CH(2)C(6)H(5)) at 80 degrees C provides a bisbenzylisocyanide-substituted compound Rh(6)(CO)(7)(dppm)(2)(CNR)(2)(micro(3)-eta(2),eta(2),eta(2)-C(60)) (2) in 59% yield. Reaction of 1 with excess C(60) (4 equiv.) in refluxing chlorobenzene followed by treatment with 1 equiv. of CNR at room temperature gives a bisfullerene sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(micro(3)-eta(2),eta(2),eta(2)-C(60))(2) (3) in 31% yield. Compounds 1, 2, and 3 have been characterized by spectroscopic and microanalytical methods as well as by X-ray crystallographic studies. Electrochemical properties of 1, 2, and 3 have been examined by cyclic voltammetry. The cyclic voltammograms (CVs) of 1 and 2 show two reversible one-electron redox waves, a reversible one-step two-electron redox wave, and a reversible one-electron redox wave, respectively, within the solvent cutoff window. This observation suggests that compounds 1 and 2 undergo similar C(60)-localized electrochemical pathways up to 1(5)(-) and 2(5)(-). Each redox wave of 2 appears at more negative potentials compared to that of 1 because of the donor effect of the benzylisocyanide ligand. The CV of compound 3 reveals six reversible well-separated redox waves due to strong interfullerene electronic communication via the Rh(6) metal cluster bridge. The electrochemical properties of 1, 2, and 3 have been rationalized by molecular orbital calculations using the density functional theory (DFT) method. In particular, the molecular orbital (MO) calculation reveals significant contribution of the metal cluster center to the unoccupied molecular orbitals in 3, which is consistent with the experimental result of strong interfullerene electronic communication via the Rh(6) metal cluster spacer.     

Poly(trifluoromethyl)fullerene radical anions. An ESR/Vis-NIR Spectroelectrochemical Study of C60F2,4 and C60(CF3)2,10

Cyclic voltammograms are reported for C(60)(CF(3))(n) derivatives for the first time. The compounds studied were 1,9-C(60)(CF(3))(2) and 3 isomers of C(60)(CF(3))(10), including the structurally characterized derivative 1,3,7,10,14,17,23,28,31,40-C(60)(CF(3))(10) (C(60)(CF(3))(10)-3). The compound 1,9-C(60)(CF(3))(2) exhibited 3 reversible reductions; C(60)(CF(3))(10)-3 exhibited 2 reversible reductions; the other 2 isomers of C(60)(CF(3))(10) each exhibited 1 reversible reduction. ESR and near-IR spectroelectrochemical experiments were performed to characterize some of the C(60)(CF(3))(n)(-) and C(60)(CF(3))(n)(2-) species generated by cyclic voltammetry. The ESR spectrum of the C(60)(CF(3))(10)-3(-) radical anion consisted of an envelope of 25 lines centered at g = 2.0032 (the apparent a value is ca. 0.5 G), evidence of coupling between the unpaired electron and a significant number of the CF(3) fluorine atoms. The most significant finding is that this radical anion has a half-life in solution at 25 degrees C of about 7 min.     

New paramagnetic Re(II) compounds with nitrile and cyanide ligands prepared by homolytic scission of dirhenium complexes

The preparation and characterization of three new paramagnetic complexes of the 17-electron Re(II) ion are reported. The salts [Re(triphos)(CH(3)CN)(3))][X](2), X = [BF(4)](-) (1), [PF(6)](-) (2), and [Et(4)N][Re(triphos)(CN)(3)] (3) were prepared by homolytic cleavage of the Re-Re bond in [Re(2)(CH(3)CN)(10)][BF(4)](4) or by disruption of the chlorine bridges in [(triphos)Re(mu-Cl)(3)Re(triphos)]Cl (1) (triphos = 1,1,1-tris(diphenylphosphino-methyl)ethane) and characterized by single-crystal X-ray diffraction, infrared and (1)H NMR spectroscopies, cyclic voltammetry, and magnetic susceptibility measurements. Compound 2 undergoes reversible reduction and irreversible oxidation processes while 3 undergoes a reversible reduction, an irreversible oxidation, and a reversible oxidation. The magnetic susceptibility data for 2 and 3 exhibit a strong temperature independent paramagnetic component which is in accord with a highly anisotropic S = (1)/(2) magnetic ground state. The results of this study indicate that dinuclear Re(2)(II,II) starting materials are viable precursors for producing unusual mononuclear Re(II) complexes.     

Eilatin as a bridging ligand in ruthenium(II) complexes: synthesis,crystal structures,absorption spectra,and electrochemical properties

The potential of the heptacyclic aromatic alkaloid eilatin (1), that features two nonequivalent binding sites, to serve as a bridging ligand is reported. The nonequivalency of the binding sites allowed the selective synthesis of both mono- and dinuclear complexes. The mononuclear Ru(II) complexes [Ru(dmbpy)(2)(eilatin)](2+) (2) and [Ru(tmbpy)(2)(eilatin)](2+) (3) in which eilatin selectively binds "head-on" were synthesized and employed as building blocks in the synthesis of the dinuclear complexes [[Ru(dmbpy)(2)](2)(mu-eilatin)](4+) (4) and [[Ru(tmbpy)(2)](2)(mu-eilatin)](4+) (5). Complete structure elucidation of the complexes in solution was accomplished by 1D and 2D NMR techniques. The X-ray structures of the mononuclear complex 3 and of the two dinuclear complexes 4 and 5 were solved, and absorption spectra and electrochemical properties of the complexes were explored. Both dinuclear complexes formed as racemic mixtures in a 3:1 diastereoisomeric ratio, the major isomer being the heterochiral one (Delta Lambda/Lambda Delta) as revealed by crystallography. The mononuclear complexes feature an exceptionally low energy MLCT band around 600 nm that shifted to over 700 nm upon the binding of the second Ru(II) center. The mononuclear complexes show one reversible oxidation and several reversible reduction waves, the first two reductions being substantially anodically shifted in comparison with [Ru(bpy)(3)](2+), attributed to the reduction of eilatin, and consistent with its low lying pi* orbital. The dinuclear complexes follow the same reduction trend, exhibiting several reversible reduction waves, and two reversible well-resolved metal centered oxidations due to the nonequivalent binding sites and to a significant metal-metal interaction mediated by the bridging eilatin.     

An unprecedented, reversible coordination mode rearrangement: eta3(B-H) vs.eta1(Sn) stanna-closo-dodecaborate coordination

The synthesis of the ruthenium stanna-closo-dodecaborate complex [Bu(3)MeN](2)[Ru(dppb)(MeCN)(2)(SnB(11)H(11))(2)] by an unprecedented, reversible eta(3)(B-H) to eta(1)(Sn) rearrangement of [Bu(3)MeN](2)[Ru(dppb)(SnB(11)H(11))(2)] is described and the product is characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction.     

Redox-induced coordination isomerization of a phosphoniobenzophospholide

1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a,b were characterized by X-ray diffraction studies as well. The structural and (31)P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the eta(2)-bound Pdbond;C double bond moieties is dominated by the L-->M charge-transfer contribution; this hints at a very low back-donation ability of the central M(2)(CO)(6) fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF(6)]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF(6)] gave spectroscopic evidence for the formation of a Re analogue of 6 a. Electrochemical studies suggested that the oxidation 8 a-->2 6 a involves two consecutive single-electron-transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox-catalysis.     

The first fullerene-metal sandwich complex: an unusually strong electronic communication between two C(60) cages

Reaction of Rh(6)(CO)(9)(dppm)(2)(mu(3)-eta(2),eta(2),eta(2)-C(60)) (1) with C(60) in refluxing chlorobenzene followed by treatment with CNR (R = CH(2)C(6)H(5)) at room temperature affords the first fullerene-metal sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(mu(3)-eta(2),eta(2),eta(2)-C(60))(2) (2). Compound 2 has been characterized by an X-ray diffraction study. Electrochemical study of 2 reveals six well-separated reversible redox couples localized at C(60) cages due to a strong electronic communication between the two C(60) centers via the Rh(6) cluster spacer.     

Molecular motions in the solid state: the thermochromic nitro-nitrito Interconversion in nickel(II) bis(diamine) complexes

The NO(2)(-) ion, in the trans-octahedral [Ni(II)(N,N'-dimethylethylenediamine)(2)(NO(2))(2)](H(2)O) complex, coordinates the metal through the nitrogen atom (nitro form). On heating the solid complex, the anion rotates to give nitrito coordination (oxygen bound), according to a reversible process. The coordination mode of NO(2)(-) to Ni(II) is related to the steric interplay between the anion and the alkyl substituents on the diamine.     

An iridium-pyridylpyrrolide complex exhibiting reversible binding of H2

The synthesis and characterization of a series of iridium(I) and iridium(III) complexes supported by a 3,5-bis(trifluoromethyl)-2-(2'-pyridyl)pyrrole (L(-)) ligand are reported. Compound [Ir(L)(COD)] (COD = 1,5-cyclooctadiene) demonstrates reversible binding of hydrogen to form a dihydride complex [Ir(L)(H)(2)(COD)] with no hydrogenation of COD.     

Acquired pH-responsive and reversible enrichment of organic dyes by peroxide modified ultrathin TiO2 nanosheets

The acquired pH-responsive and reversible enrichment of organic dyes from aqueous solutions by peroxide modified ultrathin nanosheets of anatase and TiO(2)(B) is illustrated in comparison with P25 and TiO(2)(B) nanowires.     

Chemically induced cyclometalation of 2-(arylazo)phenols. Synthesis,characterization, and redox properties of a family of organoosmium complexes

Reaction of 2-(arylazo)phenols (H(2)ap-R; R = OCH(3), CH(3), H, Cl, and NO(2)) with [Os(PPh(3))(2)(CO)(2)(HCOO)(2)] affords a family of organometallic complexes of osmium(II) of type [Os(PPh(3))(2)(CO)(ap-R)] where the 2-(arylazo)phenolate ligand is coordinated to the metal center as a tridentate C,N,O-donor. Structure of the [Os(PPh(3))(2)(CO)(ap-H)] complex has been determined by X-ray crystallography. All the [Os(PPh(3))(2)(CO)(ap-R)] complexes are diamagnetic and show characteristic (1)H NMR signals and intense MLCT transitions in the visible region. They also show emission in the visible region at ambient temperature. Cyclic voltammetry on the [Os(PPh(3))(2)(CO)(ap-R)] complexes shows a reversible Os(II)-Os(III) oxidation within 0.39-0.73 V vs SCE, followed by a reversible Os(III)-Os(IV) oxidation within 1.06-1.61 V vs SCE. Coulometric oxidation of the [Os(PPh(3))(2)(CO)(ap-R)] complexes generates the [Os(III)(PPh(3))(2)(CO)(ap-R)](+) complexes, which have been isolated as the hexafluorophosphate salts. The [Os(III)(PPh(3))(2)(CO)(ap-R)]PF(6) complexes are one-electron paramagnetic and show axial ESR spectra. In solution they behave as 1:1 electrolytes and show intense LMCT transitions in the visible region. The [Os(III)(PPh(3))(2)(CO)(ap-R)]PF(6) complexes have been observed to serve as mild one-electron oxidants in a nonaqueous medium.     

Tetrarhena-heterocycle from the palladium-catalyzed dimerization of Re2(CO)8(μ-SbPh2)(μ-H) exhibits an unusual host-guest behavior

The six-membered heavy atom heterocycles [Re(2)(CO)(8)(μ-SbPh(2))(μ-H)](2), 5, and Pd[Re(2)(CO)(8)(μ-SbPh(2))(μ-H)](2), 7, have been prepared by the palladium-catalyzed ring-opening cyclo-dimerization of the three-membered heterocycle Re(2)(CO)(8)(μ-SbPh(2))(μ-H), 3. The palladium atom that lies in the center of the heterocycle 7 was removed to yield 5. The palladium removal was found to be partially reversible leading to an unusual example of host-guest behavior. A related dipalladium complex Pd(2)Re(4)(CO)(16)(μ(4)-SbPh)(μ(3)-SbPh(2))(μ-Ph)(μ-H)(2), 6, was also formed in these reactions of palladium with 3.     

Influence of fluoride on the reversible binding of NO by [Fe(II)(EDTA)(H2O)]2-. Inhibition of autoxidation of [Fe(II)(EDTA)(H2O)]2-

The promising BioDeNO(x) process for NO removal from gaseous effluents suffers from an unsolved problem that results from the oxygen sensitivity of the Fe(II)-aminopolycarboxylate complexes used in the absorber unit to bind NO(g). The utilized [Fe(II)(EDTA)(H2O)](2-) complex is extremely oxygen sensitive and easily oxidized to give a totally inactive [Fe(III)(EDTA)(H2O)](-) species toward the binding of NO(g). We found that an in situ formed, less-oxygen-sensitive mixed-ligand complex, [Fe(II)(EDTA)(F)](3-), still reacts quantitatively with NO(g). The formation constant for the mixed ligand complex was determined spectrophotometrically. For [Fe(III)(EDTA)(F)](2-) we found log K(MLF)(F) = 1.7 +/- 0.1. The [Fe(II)(EDTA)(F)](3-) complex has a smaller value of log K(MLF)(F) = 1.3 +/- 0.2. The presence of fluoride does not affect the reversible binding of NO(g). Even over extended periods of time and fluoride concentrations of up to 1.0 M, the nitrosyl complex does not undergo any significant decomposition. The [Fe(III)(EDTA)(NO(-))](2-) complex releases bound NO on passing nitrogen through the solution to form [Fe(II)(EDTA)(H2O)](2-) almost completely. A reaction cycle is feasible in which fluoride inhibits the autoxidation of [Fe(II)(EDTA)(H2O)](2-) during the reversible binding of NO(g).     

Bis-imine-cyclometalated macrocycles: synthesis, characterization and observation of solution behaviour

A novel class of cyclometalated macrocycles [(Cp*Ir)(2)(R-N=C-C(6)H(2)-C=N-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (4a), p-MeOC(6)H(4) (4b), p-MeC(6)H(4) (4c), p-ClC(6)H(4) (4d), Me (4e)]; [(Cp*Rh)(2)(R-N=C-C(6)H(2)-C=N-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (4a'), p-MeOC(6)H(4) (4b'), p-MeC(6)H(4) (4c')] and [(Cp*Ir)(2)(R-C=N-C(6)H(4)-N=C-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (5a), p-MeOC(6)H(4) (5b)] was stepwise constructed through the double-site C-H activation of aromatic bis-imine substrates. The structures of binuclear complexes and tetranuclear macrocycles were confirmed by single-crystal X-ray diffraction. Isomers were found both in binuclear species and macrocyclic complexes. Flexible substrates led to the existence of isomers for binuclear species, yet gave no isomers after macrocyclic constructions; rigid ones, in contrast, led to isomers only for macrocyclic species. The isomers of tetranuclear macrocycles were thermodynamically stable to reversible transformation on a scale of days. Robust bonding and a certain degree of rigidity were invoked to explain the existence of isomers. This is the first example, to our knowledge, in which coordinated macrocycles containing half-sandwich Cp*M (M = Ir, Rh) fragments have been constructed, without a dynamic reversible process.     

Mechanochromism of Ag(I) complexes with iPrNHC(S)NHP(S)(OiPr)2

Reaction of the potassium salt of iPrNHC(S)NHP(S)(OiPr)(2) (HL) with AgPF(6) leads to the hexanuclear [{Ag(3)(iPrNHC(S)NP(S)(OiPr)(2)-S,S')(3)}(2)] ([(Ag(3)L(3))(2)]) complex. The reversible conversion between yellow-emitting ([(Ag(3)L(3))(2)]) and blue-emitting ([Ag(3)L(3)]) materials on grinding and recrystallization was established. [Ag(3)L(3)] was also prepared by a mechanically induced solid-state reaction.     

Microporous vanadyl-arsenate with the template incorporated exhibiting sorption and catalytic properties

(C(5)H(14)N(2))[(VO)(3)(AsO(4))(HAsO(4))(2)(OH)].3H(2)O behaves as a microporous organically templated compound, with reversible adsorption and desorption of N(2) at 77 K, and as an extremely efficient catalyst that catalyzes selective sulfoxide formation from organic sulfides, under mild conditions.     

Reactions of the bis(dialkylphosphino)methane complexes Pd2X2(μ-R2PCH2PR2)2 (X = halogen, R = Me or Et) with H2S, S8, COS, and CS2; detection of reaction intermediates

The Pd(2)X(2)(dmpm)(2) complexes [X = Cl (1a), Br (1b), I (1c); dmpm = bis(dimethylphosphino)methane. In all the dipalladium complexes mentioned in this paper, the dmpm, depm, and dppm ligands (unless stated otherwise) are bridging, but for convenience the μ-symbol is omitted.] react with H(2)S to yield H(2) and the bridged-sulfido complexes Pd(2)X(2)(μ-S)(dmpm)(2) (2a-c), of which 2a and 2b are structurally characterized. With 1a, two rapid reversible equilibria are observed by NMR spectroscopy below -30 °C, and two reaction intermediates are detected; both are likely hydrido(mercapto) species. Reaction of 1a with 1 equiv of elemental sulfur also yields 2a. The reaction of 1a with COS results in the initial formation of Pd(2)Cl(2)(μ-COS)(dmpm)(2) (3) that undergoes decarbonylation to yield 2a and Pd(2)Cl(2)(μ-CO)(dmpm)(2) (4), which is also formed via reversible insertion of the CO into the Pd-Pd bond of 1a. The solid-state molecular structure of the previously reported complex Pd(2)Cl(2)(μ-CS(2))(dmpm)(2) (5), together with solution NMR data for 3 and 5, reveal that the bridging heterocumulene ligands coordinate in an η(2)-C,S fashion. Analogous findings were made for the corresponding Pd(2)X(2)(depm)(2) complexes [X = Cl (1a'), Br (1b'), I (1c'); depm = bis(diethylphosphino)methane], although no μ-COS species was detected. The Pd(2)X(2)(μ-S)(depm)(2) complex was structurally characterized. Differences in the chemistry of the previously studied, corresponding dppm systems (dppm = bis(diphenylphosphino)methane) are discussed.     

New supramolecular isomers with 2D 4(4) square-grid and 3D 6(5).8 frameworks in a one-pot synthesis; reversible solvent uptake and intriguing luminescence properties

Two supramolecular isomers of [Ni(4-bpd)(2)(NCS)(2)] (4-bpd = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) with 2D 4(4) square-grid and 3D 6(5).8 frameworks are co-crystallized in a one-pot reaction, both of which exhibit interesting luminescence properties and reversible adsorption-desorption with respect to guest solvents.     

A trinickel dipyridylamido complex with metal-metal bonding interaction: prelude to polynickel molecular wires and devices?

The molecule Ni(3)(dpa)(4)Cl(2) (1) can be oxidized by AgPF(6) to give crystalline Ni(3)(dpa)(4)(PF(6))(3) (2) (dpa is the anion of di(2-pyridyl)amine). This reversible oxidation occurs at a potential of 0.908 V vs Ag/AgCl electrochemically. The X-ray structure of 2 shows that the oxidation causes a major structural change (even though it is reversible), namely, a contraction of the Ni-Ni distances from ca. 2.43 A to 2.284[1] A. In addition, the electronic structure changes so that from four unpaired electrons in 1 there is only one in 2. From these remarkable results, it is inferred that while 1, and all higher homologues with 5, 7, 9,... nickel atoms are poor electronic conductors, the cations obtainable from them may be much better ones. This in turn means that by controlling the oxidation state electrochemically, these molecules may be able to function as nanoscale diodes.     

Dendritic arrays of [Re6(mu3-Se)8]2+ core-containing clusters: exploratory synthesis and electrochemical studies

The reaction between the previously reported site-differentiated cluster solvate [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(MeCN)](SbF(6))(2) (1) with pyridyl-based ditopic ligands 4,4'-trimethylenedipyridine (2), 1,2-bis(4-pyridyl)ethane (3), and (E)-1,2-bis(4-pyridyl)ethene (4) afforded cluster complexes of the general formula [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(L)](SbF(6))(2) (5-7), where L represents one of the pyridyl-based ligands. Reacting these cluster complex-based ligands with the fully solvated cluster complex [Re(6)(mu(3)-Se)(8)(MeCN)(6)](SbF(6))(2) (8) produced dendritic arrays of the general formula {Re(6)(mu(3)-Se)(8)[Re(6)(mu(3)-Se)(8)(PEt(3))(5)(L)](6)}(SbF(6))(14) (9-11), each featuring six circumjacent [Re(6)(mu(3)-Se)(8)(PEt(3))(5)](2+) units bridged to a [Re(6)(mu(3)-Se)(8)](2+) core cluster by the pyridyl-based ligands. Electrochemical studies using a thin-layer electrochemical cell revealed cluster-based redox events in these cluster arrays. For 9 (L = 2), one reversible oxidation event corresponding to the removal of 7 electrons was observed, indicating noninteraction or extremely weak interactions between the clusters. For 10 (L = 3), two poorly resolved oxidation waves were found. For 11 (L = 4), two reversible oxidation events, corresponding respectively to the removal of 1 and 6 electrons, were observed with the 1-electron oxidation event occurring at a potential 150 mV more positive than the 6-electron oxidation. These electrochemical studies suggest intercluster coupling in 11 via through-bond electronic delocalization, which is consistent with electronic spectroscopic studies of this same molecule.