Winter, Rainer F.

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Winter
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Rainer F.
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Vinyl-ruthenium entities as markers for intramolecular electron transfer processes

2011, Mücke, Philipp, Linseis, Michael, Zális, Stanislav, Winter, Rainer F.

The present account summarizes our work on mononuclear vinyl ruthenium complexes of the type RuCl(CHCHR′)(CO)(PR3)2L, divinyl-bridged diruthenium complexes {RuCl(CO)(PR3)2L}2(μ-CHCH-bridge-CHCH) and on heterobinuclear systems where only one of the two redox-active metal–organic moieties is of the vinyl ruthenium type. The favourable electrochemical properties of the {RuCl(CO)(PR3)2L(CHCH–) tag and the various spectroscopic handles offered by that unit provide detailed insights into the charge and spin delocalization over the {MCl(CO)(PR3)2L} and CHCHR′ constituents in their associated radical cations. They also offer a convenient means for measuring electronic coupling in the mixed-valent radical cations of the homo- and heterodinuclear vinyl-bridged complexes and, under favourable circumstances, on the rate of intramolecular electron transfer between the individual redox sites. Aspects of this work include examples of complexes showing time-dependent valence trapping, complexes aimed at delineating the efficiencies of through-space versus through-bond pathways for electron delocalization, complexes where electrostatic effects on the redox splitting ΔE1/2 dominate over those from the resonance contribution and systems that exhibit extensive charge and spin delocalization between two dislike endgroups despite their intrinsically different redox potentials.

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(Allenylidene)ruthenium complexes with redox-active substituents and ligands

2003, Hartmann, Stephan, Winter, Rainer F., Brunner, Birgit M., Sarkar, Biprajit, Knödler, Axel, Hartenbach, Ingo

We describe the allenylidene complexes [TpL2Ru=C=C=CPhR]+ SbF6− [Tp = HB(pz)3−, L2 = 2 PPh3 or 1,1′-bis(diphenylphosphanyl)ferrocene (dppf), R = Ph or ferrocenyl] and their spectroscopic and electrochemical characteristics. Three of these compounds possess redox-active, ferrocene-based substituents or ligands − that are oxidized at lower potentials than the ruthenium center itself − attached either to the terminal carbon atom of the allenylidene ligand or to the ruthenium atom. The Fc/Ph-substituted complexes 3a and 3b provide unique examples of hindered rotation of the allenylidene substituent around the M=C bond. For 3a (L2 = 2 PPh3), two isomers differing in the orientation of the vertically aligned, unsymmetrically substituted allenylidene ligand are discernible even at 388 K. The dppf-substituted congener 3b has the allenylidene ligand in a horizontal orientation and exhibits a rotational barrier, as determined by dynamic 31P NMR spectroscopy, of ΔG≠ = 47 kJ/mol at TC = 238 K. The changes in the spectroscopic and electrochemical properties upon replacement of the PPh3 by a dppf ligand and the Ph by an Fc moiety can be explained in terms of the bonding within these systems. These effects are attenuated when the ferrocene-based redox tags are oxidized, as shown by IR and UV/Vis spectroelectrochemistry. Thus, infrared spectroelectrochemistry reveals a blue shift of the allenylidene stretch upon oxidation of the dppf ligand, while oxidation of the ferrocene covalently linked to the unsaturated C3 ligand has the opposite effect. Oxidation of the ruthenium atom influences the bonding within the unsaturated ligand more profoundly. Results from IR spectroelectrochemistry point to a vinylidene structure in the RuIII state. Reduction enhances the contribution of alkynyl-type resonance forms to the overall bonding description, as also shown by IR spectroelectrochemistry. For the ferrocenyl-substituted allenylidene complexes, oxidation and reduction result in bleaching of the intense optical low-energy absorption band attributed to a ferrocenyl-to-allenylidene charge-transfer process. The EPR spectra of the paramagnetic reduced forms of these complexes also indicate spin delocalization into the aryl substituents attached to the allenylidene ligand. The complexes Tp(dppf)RuCl and [Tp(dppf)Ru=C=C=CPh2]+ SbF6− were also characterized by X-ray crystallography.

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Redox-Responsive Rhodocenium [O,O], [N,N] and [N,C,N]Metalloligands

2011, Pevny, Florian, Winter, Rainer F., Eisenstecken, Daniela, Kopacka, Holger, Enk, Barbara, Wurst, Klaus, Müller, Thomas, Bildstein, Benno

As we have recently shown, the doubly substituted [1,2-O,O]H, [1,2-O,N]H, [1,2-N,N]H, and [1,3-N,N]H pentafulvenes are convenient N/O-functionalized cyclopentadienide (Cp) precursors. Deprotonation of the pentafulvenes by potassium hydride followed by reaction with [Cp*RhCl2]2 or [Cp*IrCl2]2 gave access to the first functionalized rhodocenium and iridocenium salts that contain two acyl and/or imidoyl substituents. These air-stable compounds represent interesting bis(acyl/imidoyl) or mixed acyl/imidoyl metalloligand systems that combine an axially shielding, electrochemically active metallocene moiety with directly attached, conjugating oxygen and/or nitrogen donor sites. The structural properties of these novel metallocene metalloligands in solution and in the solid state were studied by NMR spectroscopy (1H, 13C, 103Rh) and by single-crystal structure analysis. The electrochemical investigations on complexes 5a, 6b, and 7a showed the effect of the appended functional groups on the potential and on the reversibility of the rhodocenium/rhodocene reduction and provided evidence for the dimerization that followed the reduction. Further redox processes that were due to the heteroatom functions included the stepwise reduction of the 1,2-diketo entity of 5a and the oxidation of the 1,2-diimino moiety of 7a.

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High-yield syntheses and electrochemistry of cis-[RuCl2(depe)2] and cis-[RuCl(CH3CN)(depe)2]+PF6 −

2000, Winter, Rainer F., Brunner, Birgit, Scheiring, Thomas

cis-[RuCl2(depe)2] (1) (depe=Et2PC2H4PEt2) is obtained in excellent yield and high isomeric purity by the reaction of [RuCl2(DMSO)4] with two equivalents of depe in acetone or ethyl acetate under reflux conditions. One of the chloride ligands is labile and readily displaced by CH3CN to afford the cationic monosubstitution product cis-[RuCl(CH3CN)(depe)2]+(2), which was isolated as the PF6 − salt. The X-ray crystal structure of 1 was determined. The redox properties of 1 and 2 as well as the chloride displacement from 1 by CH3CN were studied by cyclic and square wave voltammetry.

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Synthesis and electrochemical behavior of the ferrocenyl units assembled on imidoalane and carbaalane clusters

2005, Winter, Rainer F., Baldus, Marc, Andronesi, Ovidiu, Roesky, Herbert, Srisailam, Shravan Kumar

Hydroalumination reaction was effectively carried out on ferrocenylnitrile in the synthesis of imidoalane cluster [HAlNCH2C5H4FeCp]6 (3). Compound 3 exhibits a reversible electrochemical behavior. In the presence of ferrocenylmethanol, meta thesis reactions were carried out on [HAlNCH2(C4H3S)]6 (4) and [HAlNCH2Ph]6 (5) in the synthesis of [CpFeC5H4CH2OAlNCH2(C4H3S)]6 (6) and [CpFeC5H4CH2OAlNCH2Ph]6 (7). The ferrocenylmethoxide groups present in these two compounds show a single reversible oxidation wave, which suggests their electrochemical equivalence. Electrochemical studies were also carried out on the carbaalane [(AlH)2(FcCtriple bond; length of mdashCAl)4(AlNMe3)2(CCH2Ph)6] (9), which exhibited a considerably broadened wave with shoulders preceding the main anodic and cathodic peak, and it can be assigned to weak electronic interactions between the individual ferrocenyl sites.

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Synthesis, Structures, Ligand Substitution Reactions, and Electrochemistry of the Nitrile Complexes cis-[Ru(dppm)2Cl(NCR)]+ PF6– (dppm = Bis(diphenylphosphino)methane, R = CH3, C2H5, tBu, Ph)

2000, Winter, Rainer F., Scheiring, Thomas

Isomerically pure nitrile complexes cis-[Ru(dppm)2Cl(NCR)]+ (2 a–d) are formed upon chloride displacement from cis-[Ru(dppm)2Cl2] (1) or, alternatively, by ligand substitution from the acetonitrile complex 2 a. This latter approach does also allow for the introduction of pyridine (3 a,b), heptamethyldisilazane (4) or isonitrile ligands (5). All complexes are obtained as the configurationally stable cis-isomers. Only cis-[Ru(dppm)2Cl(CNtBu)]+ slowly isomerizes to the trans from. The solid state structures of the CH3CN, C2H5CN and the trans-tBuNC complexes were established by X-ray crystallography. Electrochemical investigations of the nitrile complexes 2 a–d show in addition to a chemically reversible one-electron oxidation an irrversible reduction step. In CH2Cl2 solution, cis- and trans-[Ru(dppm)2Cl2] have been identified as the final products of the electrochemically induced reaction sequence.