Heinz Rüegger

Silver–Ethene Complexes [Ag(η2‐C2H4)n][Al(ORF)4] with n=1, 2, 3 (RF=Fluorine‐Substituted Group)

Compounds including the free or coordinated gas-phase cations [Ag(eta(2)-C(2)H(4))(n)](+) (n = 1-3) were stabilized with very weakly coordinating anions [A](-) (A = Al{OC(CH(3))(CF(3))(2)}(4), n = 1 (1); Al{OC(H)(CF(3))(2)}(4), n = 2 (3); Al{OC(CF(3))(3)}(4), n = 3 (5); {(F(3)C)(3)CO}(3)Al-F-Al{OC(CF(3))(3)}(3), n = 3 (6)). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH(2)Cl(2) solution. As a reference we also prepared the isobutene complex [(Me(2)C=CH(2))Ag(Al{OC(CH(3))(CF(3))(2)}(4))] (2). The compounds were characterized by multinuclear solution-NMR, solid-state MAS-NMR, IR and Raman spectroscopy as well as by their single crystal X-ray structures. MAS-NMR spectroscopy shows that the [Ag(eta(2)-C(2)H(4))(3)](+) cation in its [Al{OC(CF(3))(3)}(4)](-) salt exhibits time-averaged D(3h)-symmetry and freely rotates around its principal z-axis in the solid state. All routine X-ray structures (2theta(max.) < 55 degrees) converged within the 3sigma limit at C=C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C=C stretching modes indicated red-shifts of 38 to 45 cm(-1), suggesting a slight C=C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C=C distance in [M(C(2)H(4))] complexes from experimental Raman data was developed and meaningful C=C distances were obtained. These spectroscopic C=C distances compare well to newly collected X-ray data obtained at high resolution (2theta(max.) = 100 degrees) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG-cc-pVTZ methods. In most cases several isomers were considered. Additionally, [M(C(2)H(4))(3)] (M = Cu(+), Ag(+), Au(+), Ni(0), Pd(0), Pt(0), Na(+)) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of sigma donation and pi back donation. Comparing the group 10 and 11 analogues, we find that the lack of pi back bonding in the group 11 cations is almost compensated by increased sigma donation.

Conformational Behavior of Cinchonidine Revisited: A Combined Theoretical and Experimental Study

Conformational space of cinchonidine has been explored by means of ab initio potential and free energy surfaces, and the temperature-induced changes of conformational populations were studied by a combined NOESY-DFT analysis. The DFT-derived potential energy surface investigation identified four new conformers. Among them, Closed(7) is substantially relevant to fully understand the conformational behavior. The energy surfaces gave access to the favored transformation pathways at different temperatures (280-320 K). They also revealed the reasons for the negligible presence of energetically stable conformers and explained the experimentally observed temperature dependence of the populations.

Vesicles as Soft Templates for the Enzymatic Polymerization of Aniline

The feasibility of using surfactant vesicles as soft templates for the peroxidase-triggered polymerization of aniline was investigated. It was found that mixed anionic vesicles (diameter approximately 80 nm) composed of sodium dodecylbenzenesulfonate (SDBS) and decanoic acid (1:1, molar ratio) are promising templates. In the presence of the vesicles and horseradish peroxidase/hydrogen peroxide (H2O2) as initiator system, aniline polymerizes under optimized conditions at pH=4.3 to the desired conductive emeraldine form of polyaniline (PANI). The optimal polymerization conditions were elaborated, and some of the chemical and physicochemical aspects of the reaction system were investigated. After addition of aniline and peroxidase to the vesicles, aniline is only loosely associated with the vesicles, as shown by NOESY-NMR and zeta potential measurements. In contrast, the peroxidase strongly binds to the vesicle surface, as shown by fluorescence measurements using TNS (2-(p-toluidino)naphthalene-6-sulfonate) as vesicle membrane probe. This binding of the enzyme to the vesicle surface indicates that the polymerization reaction is initiated predominantly on the surface of the vesicles. Cryo-transmission electron microscopy indicates that the polymerization product remains associated with the vesicles on their surface. For short reaction times (30 s<t<60 s), it is shown that oligoanilines containing an excess of oxidized units are obtained, as shown by VIS/NIR spectroscopy and MALDI-TOF mass spectrometry. For longer reaction times (1 min<t<30 min), the relative amount of over oxidized units in PANI decreases until polymers are obtained which have a VIS/NIR spectrum that is typical for the emeraldine salt form of PANI (lambdamax approximately 1000 nm). The appearance of stable unpaired electrons during the reaction was demonstrated by EPR measurements, in full support of the in situ formation of the conductive emeraldine salt form of PANI. At the end of the reaction (after 1 h), the PANI formed remains homogenously dispersed in the aqueous solution thanks to the presence of the vesicles. No precipitation occurs on a time scale of at least several weeks. FTIR and 13C NMR measurements of the product isolated from the reaction mixture confirm the formation of the emeraldine form of PANI. If the polymerization reaction is carried out in the absence of vesicles but under otherwise identical reaction conditions, the outcome of the reaction is very different, i.e., no indication at all for the formation of the conductive form of PANI.

Coinage metal complexes of tris(pyrazolyl)methanide [C(3,5-Me2pz)3]−: κ3-coordination vs. backbone functionalisation

Tris(pyrazolyl)methanides, [C(3,5-R2pz)3]-, contain an unassociated tetrahedral carbanionic centre in the bridgehead position. In addition to nitrogen donor centres for transition metal coordination, an accessible reactive site for further manipulations is available in the backbone of the ligand. The coordination variability of the ambidental C-/N ligand [C(3,5-Me2pz)3]- was elucidated by investigating its coinage metal complexes. Two principle coordination modes were found for complexes of general formula [LMPR3] (with M = Cu(I), Ag(I), Au(I); L =[C(3,5-Me2pz)3]-; R = Ph, OMe). While for Cu(I) (2,3) and Ag(I) (4) complexes the anionic ligand acts as a face-capping, six electron N3-donor, gold(I) (5) is coordinated by the bridging carbanion yielding a two coordinate Au(I) complex comprising a covalent Au-C bond. The complexes featuring the kappa3-coordinated N3-donor ligand were investigated by 31P CP (MAS) NMR in the solid state.

Synthesis, 119Sn, 13C and 195Pt NMR studies of five-coordinate rhodium(I), iridium(I) and platinum(II) complexes containing three trichlorostannate ligands

Abstract The synthesis and 119 Sn NMR characteristics of new five-coordinate tris(trichlorostannato) complexes of Rh I , Ir I and Pt II are reported. The Rh I and Ir I complexes are complex dianions of the form (PPN) 2 [M(SnCl 3 ) 3 L 2 ] where L can be CO, CN (cyclohexyl) or L 2 , a diolefin such as 1,5-COD or NBD (norbornadiene). The anionic platinum complexes (PPN)[Pt(SnCl 3 ) 3 L 2 ] contain similar L ligands. A number of neutral monotrichlorostannato complexes of type [M(SnCl 3 )L 4 ] including [Ir(SnCl 3 )(NBD)(1,5-COD)] have been prepared and characterized. Their δ( 119 Sn), δ( 13 C), δ( 195 Pt) as well as 1 J ( 103 Rh, 119 Sn), 1 J ( 195 Pt, 119 Sn), 2 J ( 119 Sn, 117 Sn) and 2 J ( 119 Sn, 13 C) data are given. A trans influence series, based on 1 J ( 195 Pt, 119 Sn), reveals the following sequence: H − > PR 3 > AsR 3 > SnCl 3 − > olefin > Cl − .

Rhodium(I) complexes of the type [Tp3R,5RRh(LL)] (LL = 2 CO, NBD, COD) with trifluoromethyl substituted tris (pyrazolyl) borate ligands and their dynamic behaviour in solution. The X-ray crystal structure of TpCF3MeRh(CO)2☆

Three seriesof Rh(I) complexes of the type Tp3R,5RRh(LL), with LL = 2 CO (1), norbornadiene (NBD) (2) and 1,5-cyclooctadiene (COD) (3) and the tris (pyrazolyl)borate (Tp) ligands 3R=5R=Me (a), 3R=CF35R=Me (b); and 3R=5R=CF3 (c) were synthesized and fully characterized by IR and multinuclear NMR spectroscopy. Three isomeric forms were identified in solutions of these complexes: two square-planar isomers with a κ2-Tp3R,5R ligand, the uncoordinated pyrazolyl ring occupying either an equatorial position (type A), or an axial position (type B), and a five-coordinate species with a κ3, Tp3R,5R ligand (type C). In the carbonyl complexes 1 the dynamic equilibria between these isomers are solvent dependent. Interestingly, solutions of complex 1c contained all three isomers simultaneously. 103Rh and 13C NMR spectral studies indicate that the NBD compounds, 2, preferentially form square-planar complexes when TpCF3,Me and TpCF3,CF3 are present, while for the COD complexes, 3, square-planar complexes are preferred for all three Tp-type ligands. The X-ray structure of TpCF3,MeRh(CO)2 (1b) was determined (spacce group C2/ c,a = 21.271(9), b = 11.004(3), c = 21.563(9) A, β = 114.93(3)°, V=4577(3) A3, Z = 8, R = 3.41, Rw = 4.70). Its structure is of type B, with the third pyrazolyl ring axially placed, the N(4) being almost directly above the Rh atom but exerting only a weak Rh-N interaction.

The reactivity of complexes containing the [Mo3(μ3S)(μS2)3]4+ core. Ligand substitution, sulfur elimination and sulfide binding

The reactivity of complexes, containing the [Mo 3 (μ 3 S)(μS 2 ) 3 ] 4+ core, was investigated in solution. Three types of electrophilic centers, (i) the three Mo atoms, (ii) the three equatorial (in plane) and (iii) the three axial (out of plane) sulfur atoms of the disulfido bridges, interact distinctly different with nucleophilic agents. The selective reactivity enabled the specific synthesis of new complexes containing either the [Mo 3 (μ 3 S)(μS 2 ) 3 ] 4+ or the [Mo 3 (μ 3 S)(μS) 3 ] 4+ cores by using (NEt 4 ) 2 [Mo 3 S(S 2 ) 3 Br 6 ] as starting material. A combination of sulfur abstraction and ligand substitution resulted in the formation of complexes of the composition [Mo 3 S 4 L 3 ] 4+ , where L represents the tridentate N,O donors 1,3,5-triamino-1,3,5-trideoxy- cis -inositol and 1,3,5-trideoxy-1,3,5-tris(dimethylamino)- cis -inositol. The complexes were characterized by one- and two-dimensional NMR spectroscopy and FAB mass spectrometry. In the presence of a weak base and 6-mercaptopurine (Hmp) or 8-hydroxyquinoline (Hoxq), the six Br atoms were replaced by these bidentate ligands forming [Mo 3 S(S 2 ) 3 (oxq) 3 ] + and [Mo 3 S(S 2 ) 3 (mp) 3 ] + . In addition, the three oxq ligands could be quantitatively replaced by diethyldithiocarbamate (dtc − ) in the presence of a slight excess of Na(dtc). The [Mo 3 S(S 2 ) 3 ] 4+ core was not affected under the harsh reaction conditions, but S 2− was liberated by hydrolysis of dtc − . The formed S 2− anion was bound selectively to the three S ax atoms of the [Mo 3 S(S eq S ax ) 3 ] 4+ core, resulting in the formation of the dimer [Mo 3 S(S 2 ) 3 (dtc) 3 ] 2 S. The dimeric structure was established by X-ray analysis, exhibiting a hexacoordinated S 2− atom with a rather short average S ax S 2− distance of 2.71 A and an elongated S eq S ax distance of 2.11 A. Space group Aba 2, a =17.48(1), b =26.13(2), c =16.489(8) A, Z =4, R =0.051.

Chemistry of PdII complexes containing both BINAP (2′2′-bis(diphenylphosphino)binaphthyl) and a η3-pinene or -allyl ligand. NMR studies on [Pd(η3-C10H15){S(−)BINAP}] (CF3SO3). The crystal structure of [Pd(η3-C10H15)(4,4′-dimethylbipyridine)](CF3SO3)

Abstract One and two-dimensional 1H, 13C and 31P NMR studies on palladium(II) complexes containing η3-C10H15 or η3-C4H7 allyl and S(−)BINAP ligands are reported. Details of the three-dimensional solution structure for [Pd(η3C10H15) {S(−)BINAP}(CF3SO3) based on 1H-2D NOESY and molecular modelling calculations are presented. The structure for the model β-pinene allyl complex [Pd(η3-C10H15)(4,4′-dimethylbipyridine)]CF3SO3) has been determined by an X-ray diffraction study, which reveals that the CH2 terminal allyl carbon is significantly displaced from the N-Pd-N plane.

Electron transfer reactions involving trans-[PtH2(PCy3)2] and fluorinated benzonitriles

Abstract The complex trans-[PtH2(PCy3)2] reacts with activated benzonitriles such as 4-R-C6F4CN (R = F, H, CN, OCH3) bearing electron-withdrawing substituents to give the new platinum(II) aryl complexes trans-[PtHRC6F3CN(PCy3)2], which have been isolated and fully characterized, and a hydridofluoride trans-[PtH(“F”)(PCy3)2], where “F” is either F or HF2, which has been detected in solution. These complexes and related by-products from the reaction have been characterized by one- and two-dimensional multinuclear NMR spectroscopy. A reaction mechanism involving rate-determining electron transfer from the dihydride complex to the organic substrate is postulated on the basis of (i) the relative reaction rates for the nitriles (p-C6F4(CN)2 > C6F5CN > p-C6HF4CN > p-C6F4(OCH3)CN > o,o-C6H3F2CN), which parallel their electron affinities, and (ii) the observation of a radical by ESR spectroscopy after “spin-trapping” with PBN.

Novel Type of Bicellar Disks from a Mixture of DMPC and DMPE-DTPA with Complexed Lanthanides

We report on the formation of bicelles from a mixture of dimyristoylphosphatidylcholine (DMPC) and the chelator-lipid dimyristoylphosphatidylethanolamine-diethylenetriaminepentaacetate (DMPE-DTPA) with complexed lanthanides, either thulium (Tm(3+)) or lanthanum (La(3+)). The two phospholipids used have the same acyl-chain length but differ in headgroup size and chemical structure. The total lipid concentration was 15 mM, and the molar ratio of DMPC to DMPE-DTPA was 4:1. The system was studied with small angle neutron scattering (SANS) in a magnetic field, cryo-transmission electron microscopy (cryo-TEM), and (31)P NMR spectroscopy. We found that, after appropriate preparation steps, that is, extrusion through a polycarbonate membrane followed by a cooling step, monodisperse small unilamellar disks (flat cylinders called bicelles) are formed. They have a radius of 20 nm and a bilayer thickness of about 4 nm and are stable in the investigated temperature range of 2.5-30 degrees C. Fitting of SANS data with a form factor for partly aligned flat cylinders shows that the bicelles are slightly orientable in a magnetic field of 8 T if DMPE-DTPA is complexed with Tm(3+).