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.

Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac‐1,3‐diphenylprop‐2‐enyl acetate (rac‐5) with the anion of dimethyl malonate (Scheme 1). Using enantiomerically pure (S,E)‐1‐(4‐tolyl)‐3‐phenylprop‐2‐enyl acatete ((S)‐25) as substrate, the reaction was shown to proceed by a clean ‘syn’ displacement of acetate by dimethyl malonate (Scheme 6). The [Pd11(η3‐allyl)] complex 18 and the analogous [Pd(η3‐1,3‐diphenylallyl)] complex 20, both containing the same bis(dihydrooxazole) ligand, were characterized by X‐ray structure analysis and by NMR spectroscopy in solution. The structural data reveal that steric interactions of the allyl system with the chiral ligand result in selective electronic activation of one of the allylic termini. The higher reactivity of one allylic terminus toward nucleophilic attack is reflected in a significantly longer PdC bond and a shift of the corresponding 13C‐NMR resonance to higher frequency.

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

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.

With personal pleasure, we dedicate this Perspective to the memory of Luigi M. Venanzi, who, apart from his many scientific contributions, was a major promotor of NMR spectroscopy within the Swiss and international Inorganic Chemistry communities.Diffusion data from pulsed-field gradient spin-echo (PGSE) methods are shown to be qualitatively useful in the investigation of problems involving unknown molecular aggregation and/or the nature of inter-ionic interactions in metal complexes. For charged species possessing anions such as PF À 6 , BF À 4 , CF 3 SO À 3 or BArF À , both 19 F-and 1 H-PGSE methods offer a valid alternative and, sometimes, unique view of gross and subtle solution molecular structure and dynamics. Problems associated with solvents, concentration, and reproducibility are discussed.1. Introduction. ± Although organometallic chemistry (and especially homogeneous catalysis) continues to move from strength to strength [1 ± 5], the applications of modern NMR methods in these areas have lagged somewhat behind. Slowly, but surely, three-dimensional structures are being solved with NOE-and ROE-NMR methods [6 ± 9]; nevertheless, there are areas, e.g., determining molecular size, aggregation, and/ or the nature of interionic interactions, where NMR spectroscopic possibilities have not been sufficiently explored.A promising NMR method involves the use of pulsed-field gradient spin-echo (PGSE) experiments [10], which can measure the diffusion coefficients of molecules and thus provide information on particle size. PGSE Methods were introduced in 1965 by Stejskal and co-workers [11] [12] and, since then, have been widely used. In the 1970s, this approach was used to determine diffusion coefficients of organic molecules [13]. In the following decade, variants of this technique have been applied to problems in polymer chemistry [14]. Recently, diffusion data on dendrimers [15 ± 20] and peptides [21 ± 24] as well as on molecules in various environments, e.g., in porous silica [25], and zeolites [26], have been obtained. However, there are very few applications of PGSE methods in coordination and/or organometallic chemistry [27 ± 35].In an interesting and recent application, Beck et al. [27] have studied the polymerization catalyst precursors 1 ± 5. Their results prompted the authors to suggest that these zirconium complexes can exist as ion-quadruples in the presence of a boronbased cocatalyst. In their construction of novel Pt-molecules, Olenyuk et al. [28] employed diffusion data to support a self-assembled dodecahedron structure of the product of the reaction shown in the Scheme. In a bio-inorganic application, Gorman et al.[15] estimated the hydrodynamic radii of the iron-sulphur based dendrimers, abbreviated below, using PGSE studies. These three examples are impressive as much for their scarcity as for their elegance.

Pulsed field gradient spin-echo (PGSE) measurements on (a) four arsine complexes of Pd(II), PdCl 2 L 2 (L ) AsMe x Ph 3-x (x ) 3-0)), (b) three different ferrocene phosphine dendrimers, and (c) a selection of other organometallic complexes of differing molecular weight, are demonstrated to provide a practical alternative to classical methods used in organometallic chemistry for estimating molecular size. PGSE measurements make use of translational and not rotational properties of molecules and will be especially valuable where one cannot isolate an unknown complex and/or where a side product is of especial interest, since one can measure several components of the mixture simultaneously.

Bioactivity-guided fractionation of a CH2Cl2 extract from the leaves of Piper aduncum afforded three new dihydrochalcones, piperaduncins A [3], B [4], and C [5], as well as two known dihydrochalcones, 2',6'-dihydroxy-4'-methoxydihydrochalcone [1] and 2',6',4-trihydroxy-4'-methoxydihydrochalcone [2] (asebogenin), together with sakuranetin, anodendroic acid methyl ester, and the carotenoid lutein. The structures of the isolates were elucidated by spectroscopic methods, mainly 1D- and 2D nmr spectroscopy. The proposed stereochemistry for compound 4 was deduced by NOESY spectroscopy and the corresponding energy minimum was established by molecular modelling calculations and translated into a 3D structure.

Iridium complexes relevant to the catalytic enantioselective hydrogenation of 2-methyl-6-ethylphenyl-1'-methyl-2'-methoxyethylimine (MEA-imine, 1) in the Syngenta Metolachlor (3) process were prepared and characterized. Reaction of the diphosphane (S)-1-[(R)-2-(diphenylphosphanyl)ferrocenyl]ethyldi(3,5-xylyl)phosphane ((S)-(R)-Xyliphos, (S)-(R)-4) with [Ir(2)(micro-Cl)(2)(cod)(2)] (cod=1,5-cyclooctadiene) afforded [Ir(Cl)(cod)[(S)-(R)-4]] (7), which reacted with AgBF(4) to form [Ir(cod)[(S)-(R)-4]]BF(4) (8). Complexes 7 and 8 reacted with iodide to yield [Ir(I)(cod)[(S)-(R)-4]] (9). When 9 was treated with one and two equivalents of HBF(4), two isomers of the cationic Ir(III) iodo hydrido complex [Ir(I)(H)(cod)[(S)-(R)-4]]BF(4) were solated (10 and 11, respectively). Complex 9 was oxidized with one equivalent of I(2) to give the iodo-bridged dinuclear species [Ir(2)I(2)(micro-I)(3)[(S)-(R)-4](2))]I (12). [Ir(2)(micro-Cl)(2)(coe)(4)] (coe=cyclooctene) reacted with (S)-(R)-4 to yield the chloro-bridged dinuclear complex [Ir(2)(micro-Cl)(2)[(S)-(R)-4](2)] (13). Complexes 7-12 were structurally characterized by single-crystal X-ray diffraction and tested as single-component catalyst precursors for enantioselective hydrogenation of MEA-imine. Complex 10 and dinuclear complex 12 gave the best catalytic results. Efforts were also directed at isolating substrate- or product-catalyst adducts: Treatment of 8 with 2,6-dimethylphenyl-1'-methyl-2'-methoxyethylimine (DMA-imine, 14, a model for 1) under H(2) allowed four isomers of [Ir(H)(2)[(S)-(R)-4](14)]BF(4) (18-21) to be isolated. These analytically pure isomers were fully characterized by 2D NMR techniques. X-ray structural analysis of an Ir(I)-imine adduct, namely, [Ir(C(2)H(4))(2)(14)]BF(4) (25), which was prepared by reacting [IrCl(C(2)H(4))(4)] with [Ag(14)(2)]BF(4) (16), confirmed the kappa(2) coordination mode of imine 14.