Correlation of Kondo effect and molecular conformation of the acceptor molecule in the TTF-TCNE charge transfer complex

A Kondo resonance has been observed on purely organic molecules in several combinations of charge transfer complexes on a metal surface. It has been regarded as a fingerprint of the transfer of one electron from the donor to the extended π orbital of the acceptor's LUMO. Here, we investigate the stoichiometric checkerboard structure of tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE) on a Au(1 1 1) surface using scanning tunneling and atomic force microscopy at 4.8 K. We find a bistable state of the TCNE molecules with distinct structural and electronic properties. The two states represent different conformations of the TCNE within the structure. One of them exhibits a Kondo resonance, whereas the other one does not, despite of both TCNE types being singly charged

Gating the charge state of a single molecule by local electric fields

The electron acceptor molecule TCNQ is found in either of two distinct integer charge states when embedded into a monolayer of a charge transfer-complex on a gold surface. Scanning tun- neling spectroscopy measurements identify these states through the presence/absence of a zero-bias Kondo resonance. Increasing the (tip-induced) electric field allows us to reversibly induce the ox- idation/reduction of TCNQ species from their anionic or neutral ground state, respectively. We show that the different ground states arise from slight variations in the underlying surface potential, pictured here as the gate of a three-terminal device.Comment: 5 pages, 4 figure

Synthesis of titanium and zirconium complexes with 2-pyridonate and 2, 6-pyridinedithiolate ligands

Special Issue: Dedicated to Professor F. Ekkehardt Hahn on the Occasion of His 60th Birthday with our most Sincere Congratulations for his Outstanding Contributions to Chemistry and Best Wishes.Treatment of complex [Cp2TiCl2] with the lithium salt of 2-hydroxypyridine afforded complex [Cp2Ti(Opy)2] (1), whereas the same synthetic strategy applied to the analogous zirconium compound [Cp2ZrCl2] did not worked. However, the use of the metallocene [Cptt 2ZrMe2] with protic ligands allowed directing the reactivity towards protonation of the methyl groups attached to zirconium. To check this approach we reacted [Cptt 2ZrMe2] with methanol affording complex [Cptt 2ZrMe(OMe)] (2), which was characterized in situ by NMR techniques. In the same line, the reaction of [Cptt 2ZrMe2] with 2-hydroxypyridine gave complex [Cptt 2Zr(Me)(Opy)] (3); forcing the conditions of this reaction did not lead to the expected complex [Cptt 2Zr(Opy)2], most probably due to the steric hindrance exerted by the bulky cyclopentadienyl ligands. Further reactions of complex 3 with ligands having acidic protons also led to the recovery of the starting complex. However, when shifting to the bifunctional ligand 2, 6-dimercaptopyridine [py(SH)2] a double protonation of the methyl ligands in [Cptt 2ZrMe2] occurred, allowing the isolation of mononuclear complex [Cptt 2Zr(κS,κS,κN-pyS2)] (4), upon evolution of methane. The molecular structure of complex 4 was determined by X-ray methods, showing the zirconium atom in a highly distorted trigonal bipyramidal arrangement; structural parameters indicate a conventional Zr-N bond, but rather weak Zr-S interactions.Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER, Projects CTQ2012-35665 and CTQ2013-42532-P), MICINN (Project Consolider Ingenio 2010, CSD2009-00050) and Diputación General de Aragón (DGA/ FSE-E07 and E70) is gratefully acknowledged.Peer Reviewe

The anions [Cptt2Zr(μ-S)2M(CO)2]- (M = Rh, Ir) as versatile precursors for the synthesis of sulfido-bridged early−late heterotrimetallic (ELHT) compounds

The reaction of [Cp2 ttZr(μ3-S) 2{Ir(CO)2}2] (Cptt = η5-1,3-di-tert-butylcyclopentadienyl) with dppe (1,2-bis-(diphenylphosphino)ethane) affords the ion-pair compound [Ir(CO)(dPPe)2][Cp2 ttZr(μ-S) 2Ir(CO)2] (2). The related compound [Rh(dPPe) 2][Cp2 ttZr(μ-S)2Rh(CO) 2] (5) has been obtained in solution under a carbon monoxide atmosphere by reaction of [Cp2 ttZr(μ3-S) 2{Rh(CO)2}2] with dppe through the intermediate heterotrinuclear compound [Cp2 ttZr(μ3-S) 2{Rh(dppe)}{Rh(CO)2}] (4). Reaction of the heterodinuclear anion [Cp2 ttZr(μ-S)2Ir(CO) 2]-, generated in situ, with [Rh(μ-Cl)(cod)] 2, [RhCl2(CO)2]- and [Pd(μ-Cl)-(η3-C3H5)]2 affords the d0-d8-d8 early-late compounds [Cp 2 ttZr(μ3-S)2{Ir(CO) 2}{Rh(cod)}] (6), [Cp2 tt-Zr(μ3-S) 2{Ir(CO)2}{Rh(CO)2}] (7), and [Cp 2 ttZr(μ3-S)2{Ir(CO) 2}{Pd(η3-C3H5)}] (8) each with a symmetrical trigonal-bipyramidal M3(μ3-S)2 heterotrimetallic metal-sulfur core. In the same way, the reaction of [Cp 2 ttZr(μ-S)2M(CO)2]- (M = Rh, Ir) with [AuCl(PPh3)] leads to the preparation of the d 0-d8-d10 early-late compounds [Cp 2 ttZr(μ-S)2(Ir(CO)2}{Au(PPh 3)}] (9) and [Cp2 ttZr(μ-S) 2{Rh(CO)2}{Au(PPh3)}] (10) with an open M 3(μ3-S)(μ2-S) heterotrimetallic metal-sulfur framework. On the other hand, treatment of the bis(hydrosulfido) zirconium compound [Cp2 ttZr(SH)2] with triethylamine followed by addition of [Pd(μ-Cl)(η3-C 3H5)]2 or [AuCl(PPh3)] affords the sulfido-bridged early-late heterobimetallic compounds [Cp2 ttZr(μ3-S)2{Pd(η3-C 3H5)}2] (11) and [Cp2 ttZr(μ-S)2(Au(PPh3)}2] (12). The molecular structure of complexes 9 and 12 determined by X-ray diffraction methods are also described.The financial support from Ministerio de Educación y Ciencia (MEC/FEDER) is gratefully acknowledged (Projects CTQ2006-03973/BQU and Factoría de Cristalización, CONSOLIDER INGENIO-2010).Peer Reviewe

Synthesis, reactivity, and catalytic activity of triangular ZrM2 (M = Rh, Ir) early-late heterobimetallic complexes

Reactions of the zirconium−sulfide metallocene anion [Cptt2ZrS2]2- (Cptt = η5-1,3-di-tert-butylcyclopentadienyl) with [{M(μ-Cl)(diolefin)}2 gave the d0−d8 complexes [Cptt2Zr(μ3-S)2{M(diolefin)}2] (M = Rh, diolefin = 2,5-norbornadiene (nbd) (1), 1,5-cyclooctadiene (cod); M = Ir, diolefin = cod) with a triangular ZrM2 core capped by two symmetrical μ3-sulfido ligands. The rhodium complexes [Cptt2Zr(μ3-S)2{Rh(diolefin)}2] (diolefin = tetrafluorobenzobarrelene (tfbb), nbd, cod) can also be prepared by the additive-deprotonation reactions of the mononuclear [Rh(acac)(diolefin)] (diolefin = nbd, tfbb) and the dinuclear [{Rh(μ-OH)(cod)}2] complexes with [Cptt2Zr(SH)2]. These compounds exist as two rotamers in solution due to a hindered rotation of the cyclopentadienyl rings and the relative disposition of the substituents of the Cptt groups in the sandwich moiety. The reaction of [Cptt2Zr(SH)2] with [Ir(acac)(cod)] gave the complex [Cptt(acac)Zr(μ3-S)2{Ir(cod)}2] (5) with release of HCptt and coordination of acetylacetonate to the zirconium center. Carbonylation of compounds 1 and 5 yielded [Cptt2Zr(μ3-S)2{Rh(CO)2}2] (6) and [Cptt(acac)Zr(μ3-S)2{Ir(CO)2}2], respectively, while the complexes [Cptt2Zr(μ3-S)2{M(CO)2}2] (M = Rh, Ir) resulted also from the reaction of [Cptt2Zr(SH)2] with (PPh3Bz)[MCl2(CO)2] in the presence of triethylamine. Reactions of the carbonyl complexes with 1 molar equiv of bis(diphenylphosphino)methane (dppm) gave the cisoid complexes [Cptt2Zr(μ3-S)2{M(CO)}2(μ-dppm)] (M = Rh (9), Ir) with evolution of carbon monoxide. Monodentate phosphites, P(OMe)3 and P(OPh)3, react with 6 to give mixtures of the transoid and cisoid isomers [Cptt2Zr(μ3-S)2{Rh(CO)(P(OR)3)}2], which also exhibit a restricted rotation of the Cptt rings. The molecular structures of complexes 6 and 9 have been determined by X-ray diffraction methods. Compound 6 in the presence of P-donor ligands, P(OMe)3, P(OPh)3, and PPh3, is a precursor of the catalyst for the hydroformylation of oct-1-ene under mild conditions of pressure and temperature. No Zr−Rh synergic effect is observed in this case, and the precursor breaks down after catalysis.We wish to thank Dirección General de Enseñanza Superior (DGES) and Diputación General de Aragón (DGA) for financial support (Projects PB88–0641 and P051/2000, respectively). Fellowships from the Ministerio de Educación y Cultura (M.A.F.H.-G.), Diputación General de Aragón (I.T.D.) and Programa CYTED (A.B.R.) are gratefully acknowledged.Peer Reviewe

Reversible opening of the triangular structure of a sulfido-bridged ZrRh2 early-late heterobimetallic complex induced by Bis-(diphenylphosphino)methane

Reaction of the early - late heterobimetallic complexes [Cp tt 2Zr(μ3-S)2{M(CO)} 2(μ-dppm)] (M = Rh, Ir) with dppm (bis-(diphenylphosphino)methane) yields the compounds [Cptt 2Zr(μ-S)2M(μ- CO)2(μ-dppm)M(η2-dppm)] (M = Rh (3), Ir (4)). The molecular structure of 3 shows a bent trimetallic ZrRhRh chain with tetrahedral, trigonal-bipyramidal, and square-pyramidal geometries, respectively. This trinuclear compound exhibits a mixed-valence Rh(II) - Rh(0) metal - metal bonded unit that results from the unusual chelating coordination of the metalloligand [Cptt 2Zr(S)2]2- and is further stabilized by the presence of two unsymmetrical bridging carbonyl ligands, which interact with the unsaturated Rh(II) metal. The formation of 3 is reversible, and the equilibrium 1 + dppm ⇄ 3 has been observed in solution (K ≈ 16 at 22 °C in C6D6). The opening of the triangular core in the heterotrimetallic compound [Cptt 2Zr(μ 3-S)2-{Rh(CO)}{Ir(CO)}(μ-dppm)] (5) is not selective and gives the compounds [Cptt 2Zr(μ-S) 2Rh(μ-CO)2(μ-dppm)Ir(η2-dppm)] (6) and [Cptt 2Zr(μ-S)2Ir(μ-CO) 2(μ-dppm)Rh(η2-dppm)] (7) in a 3:1 molar ratio.The generous financial support from Dirección General de Enseñanza Superior e Investigación (DGES) (Project BQU2003-05412-C02-01) is gratefully acknowledged.Peer Reviewe

Novel gem-dithiolato-bridged rhodium hydroformylation catalysts: Bridging the gap in dinuclear rhodium thiolate chemistry

The direct protonation of the bridging hydroxo ligands in [Rh(μ-OH)(cod)]2 by 1,1-dimercaptocyclohexane [Chxn(SH) 2] yields the gem-dithiolato-bridged compound [Rh2(μ- S2Chxn)-(cod)2] (1). The dinuclear framework in 1 is supported by a 1,1-cyclohexanedithiolato ligand exhibiting a 1:2κ2S,1:2κ2S′ coordination mode. Compound 1 is an active catalyst precursor in the presence of P-donor ligands for the hydroformylation of oct-1-ene under mild conditions of pressure and temperature (100 PSI, 353 K). The best results were obtained with phosphite ligands as modifying ligands. An aldehyde selectivity of 97 %, a regioselectivity towards the linear aldehyde of 81 %, and turnover frequencies of up to 198 h-1 were obtained with the catalytic system 1/P(OMe)3. The dinuclear compound [Rh2(μ-S 2Chxn)(CO)2(PPh3)2] (2) was isolated from the catalytic solutions resulting from the system 1/PPh3 and was characterized by spectroscopic means and by X-ray diffraction to be the frans isomer. The mixed-ligand dinuclear complexes 2 and [Rh2(μ- S2Chxn)(CO)2(PCy3)2] (3) (Cy = cyclohexyl) were independently prepared by reaction of Chxn(SH)2 with the mononuclear complexes [Rh(acac)(CO)-(PR3)] in the appropriate molar ratio.The financial support from Ministerio de Educación y Ciencia (MEC/FEDER) is gratefully acknowledged (Project CTQ2006-03973/BQU and Factoría de Cristalización, CONSOLIDER INGENIO-2010). A. B. R. thanks the Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (CYTED, Project V.9) for a fellowship. A. J. P. thanks to Fonacit-Venezuela (S1-2002000260) for financial support.Peer Reviewe