Experimental and Theoretical High Energy Resolution Hard X-ray Absorption and Emission Spectroscopy on Biomimetic Cu2S2 Complexes.

High energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and Valence-to-Core X-ray emission (VtC-XES) spectroscopy are established as hard X-ray methods to investigate complexes that might be relevant as mimics for the biologically important CuA site. By investigation of three carefully selected complexes of the type [Cu2(NGuaS)2X2], characterized by a cyclic Cu2S2 core portion and a varying adjunct ligand nature, it is proven that the HERFD-XANES and VtC-XES measurements in combination with extensive TD-DFT calculations can reveal details of the electronic states in such complexes, including HOMO and LUMO levels and spin states. By theoretical spectroscopy, the value of this methodic combination for future in situ studies is demonstrated.

Borane-Catalyzed Synthesis of Quinolines Bearing Tetrasubstituted Stereocenters by Hydride Abstraction-Induced Electrocyclization.

The borane-catalyzed synthesis of quinoline derivatives bearing tetrasubstituted stereocenters from vinyl anilines has been developed. Mechanistic studies and quantum-mechanical investigations support the hydride abstraction/electrocyclization/hydride addition mechanism. The products were obtained in up to 99 % yield with a diastereoselectivity of >99 % in favour for the 3a-5-cis isomer.

The Connection between NHC Ligand Count and Photophysical Properties in Fe(II) Photosensitizers: An Experimental Study.

Four homo- and heteroleptic complexes bearing both polypyridyl units and N-heterocyclic carbene (NHC) donor functions are studied as potential noble metal-free photosensitizers. The complexes [FeII(L1)(terpy)][PF6]2, [FeII(L2)2][PF6]2, [FeII(L1)(L3)][PF6]2, and [FeII(L3)2][PF6]2 (terpy = 2,2':6',2″ terpyridine, L1 = 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine, L2 = 2,6-bis[3-isopropylimidazol-2-ylidene]pyridine, L3 = 1-(2,2'-bipyridyl)-3-methylimidazol-2-ylidene) contain tridentate ligands of the C^N^C and N^N^C type, respectively, resulting in a Fe-NHC number between two and four. Thorough ground state characterization by single crystal diffraction, electrochemistry, valence-to-core X-ray emission spectroscopy (VtC-XES), and high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) in combination with ab initio calculations show a correlation between the geometric and electronic structure of these new compounds and the number of the NHC donor functions. These results serve as a basis for the investigation of the excited states by ultrafast transient absorption spectroscopy, where the lifetime of the 3MLCT states is found to increase with the NHC donor count. The results demonstrate for the first time the close interplay between the number of NHC functionalities in Fe(II) complexes and their photochemical properties, as revealed in a comparison of the activity as photosensitizers in photocatalytic proton reduction.

Heteroacene Synthesis through C-S Cross-Coupling/5-endo-dig Cyclization.

Highly efficient, one-step synthesis of sulfur-containing heteroacenes was achieved through palladium-catalyzed C-S cross-coupling of bis-alkynes with thioacetate as hydrogen sulfide surrogate. Heteroacenes consisting of three, five, and seven fused aromatic rings were obtained in a single catalytic step by four-, six-, and eightfold C-S bond formation.

A Comprehensive Study of Copper Guanidine Quinoline Complexes: Predicting the Activity of Catalysts in ATRP with DFT.

Copper complexes of the hybrid guanidine ligands 1,3-dimethyl-N-(quinolin-8-yl)-imidazolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)-guanidine (TMGqu) have been studied comprehensively with regard to their structural and electrochemical properties and their activity in atom transfer radical polymerization (ATRP). A simple analysis of the molecular structures of the complexes gives no indication about their activity in ATRP; however, with the help of DFT and NBO analysis the influence of particular coordinating donors on the electrochemical properties could be fully elucidated. With an adequate DFT methodology and newly applied theoretical isodesmic reactions it was possible to predict the relative position of the redox potentials of copper complexes containing DMEGqu and TMGqu ligands. In addition, predictions could be made as to whether the complexes of DMEGqu or TMGqu are more active in ATRP. Four new Cu(I) complexes were tested in standard ATRP reactions and kinetically investigated both in bulk and in solution. It could be proven that complexes featuring DMEGqu possess a lower redox potential and are more active in ATRP, although the tetramethylguanidine moiety represents the stronger donor.

Frustrated Lewis Pair-Catalyzed Cycloisomerization of 1,5-Enynes via a 5-endo-dig Cyclization/Protodeborylation Sequence.

The first frustrated Lewis pair-catalyzed cycloisomerization of a series of 1,5-enynes was developed. The reaction proceeds via the π-activation of the alkyne and subsequent 5-endo-dig cyclization with the adjacent alkene. The presence of PPh3 was of utmost importance on the one hand to prevent side reactions (for example, 1,1-carboboration) and on the other hand for the efficient protodeborylation to achieve the catalytic turnover. The mechanism is explained on the basis of quantum-chemical calculations, which are in full agreement with the experimental observations.

Frustrated Lewis Pair Catalyzed Dehydrogenative Oxidation of Indolines and Other Heterocycles.

An acceptorless dehydrogenation of heterocycles catalyzed by frustrated Lewis pairs (FLPs) was developed. Oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N-protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP-catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and X-ray crystal analysis, and by quantum-mechanical calculations. Hydrogen liberation from the ammonium hydridoborate intermediate is the rate-determining step of the oxidation. The addition of a weaker Lewis acid as a hydride shuttle increased the reaction rate by a factor of 2.28 through a second catalytic cycle.

Crystal structure of 2,2'-({[2-(trityl-sulfan-yl)benz-yl]azane-diyl}bis-(ethane-2,1-di-yl))bis-(isoindoline-1,3-dione).

In the structure of the title compound, C46H37N3O4S, the planes of the two isoindoline units make a dihedral angle of 77.86 (3)°. The dihedral angles between the benzyl plane and the isoindoline units are 79.56 (4) and 3.74 (9)°. The geometry at the S atom shows a short [1.7748 (17) Å] S-Cbenz-yl and a long [1.8820 (15) Å] S-Ctrit-yl bond and the C-S-C angle is 108.40 (7)°. N-C bond lengths around the azane N atom are in the range 1.454 (2)-1.463 (2) Å. he crystal packing exhibts two rather 'non-classical' C-H⋯O hydrogen bonds that result in stacking of the molecules along the a as well as the b axis and give rise to columnar sub-structures.

Bis{2-[(Tri-phenyl-meth-yl)amino]-phen-yl} diselenide aceto-nitrile monosolvate.

The mol-ecular structure of the title compound, C50H40N2Se2·C2H3N, shows a syn conformation of the benzene rings bound to the Se atoms, with an Se-Se bond length of 2.3529 (6) Šand a C-Se-Se-C torsion angle of 93.53 (14)°. The two Se-bonded aromatic ring planes make a dihedral angle of 18.42 (16)°. Intra-molecular N-H⋯Se hydrogen bonds are noted. Inter-molecular C-H⋯Se inter-actions give rise to supra-molecular chains extended along [100]. One severely disordered aceto-nitrile solvent mol-ecule per asymmetric unit was treated with SQUEEZE in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155]; the crystal data take the presence of this mol-ecule into account.

Crystal structure of bis-[1,3,4,5-tetra-methyl-1H-imidazole-2(3H)-thione-κS]chlorido-copper(I).

The mol-ecular structure of the title compound, [CuCl(C7H12N2S)2], shows a slightly distorted trigonal-planar coordination geometry of the Cu atom. The Cu-Cl bond measures 2.2287 (9) Å, and the two Cu-S bonds are significantly different from each other, with values of 2.2270 (10) and 2.2662 (10) Å. Also, the S-Cu-Cl angles differ, with values of 113.80 (4) and 124.42 (4)°, while the S-Cu-S angle is 121.51 (4)°. The two imidazole rings are almost parallel, making a dihedral angle of 2.1 (2)°. In the crystal, the shortest C-H⋯Cl interactions stabilize a three-dimensional network with molecules linked into centrosymmetric dimers that are stacked along the b-axis direction.

Crystal structure of di-chlorido-bis-(1,3-diisopropyl-4,5-dimethyl-2H-imidazole-2-thione-κS)zinc(II).

The mol-ecular structure of the title compound, [ZnCl2(C11H20N2S)2], shows tetra-hedral Zn coordination from two Cl ligands and two thione groups. The Zn-Cl bond lengths differ sligthly at 2.2310 (10) and 2.2396 (11) Šwhile the Zn-S bond lengths are equal at 2.3663 (9) and 2.3701 (10) Å. The Cl-Zn-Cl angle is 116.04 (4) and S-Zn-S is 101.98 (3)°. All other angles at the central Zn atom range from 108.108 (3) to 110.21 (4)°. The C-S-Zn angles are 100.75 (10) and 103.68 (11)°, the difference most probably resulting from packing effects, as both the C-S and both the S-Zn bonds are equal in each case. The two imidazole ring planes make a dihedral angle of 67.9 (1)°. The CH3 groups of one isopropyl moiety are disordered over two sets of sites with occupation factors of 0.567 (15) and 0.433 (15). It may be noteworthy that the isomolecular Cu complex shows a different crystal packing (group-subgroup relation) with the Cu atom lying on a twofold rotation axis. In the crystal, the shortest non-bonding contact is a C-H⋯Cl inter-action. This leads to the formation of centrosymmetric dimers that are stacked along the c-axis.

Catching an entatic state--a pair of copper complexes.

The structures of two types of guanidine-quinoline copper complexes have been investigated by single-crystal X-ray crystallography, K-edge X-ray absorption spectroscopy (XAS), resonance Raman and UV/Vis spectroscopy, cyclic voltammetry, and density functional theory (DFT). Independent of the oxidation state, the two structures, which are virtually identical for solids and complexes in solution, resemble each other strongly and are connected by a reversible electron transfer at 0.33 V. By resonant excitation of the two entatic copper complexes, the transition state of the electron transfer is accessible through vibrational modes, which are coupled to metal-ligand charge transfer (MLCT) and ligand-metal charge transfer (LMCT) states.

(2R,3R,4S,5R)-2-(4-Amino-5-iodo-7H-pyrrolo-[2,3-d]pyrimidin-7-yl)-5-methyl-tetra-hydro-furan-3,4-diol.

The mol-ecular structure of the title compound, C11H13IN4O3, shows a ribo-furanos-yl-pyrrolo O-C-N-C torsion angle of 59.1 (3)°, with the central C-N bond length being 1.446 (3) Å. The C-I bond length is 2.072 (2) Å. The amino group is coplanar with the attached aromatic ring [C-N-C-N torsion angle = -178.8 (2)°] and forms an intra-molecular N-H⋯I hydrogen bond. In the crystal, O-H⋯N and N-H⋯O hydrogen bonds link the mol-ecules into puckered layers parallel to (001). These layers are bound to each other by secondary I⋯O inter-actions [3.2250 (17) Å], forming a three-dimensional framework.

The mixed-valent copper thiol-ate complex hexa-kis-{µ3-2-[(1,3-dimethyl-imidazol-idene)amino]-benzene-thiol-ato}dicopper(II)tetra-copper(I) bis-(hexa-fluoridophosphate) acetonitrile disolvate dichloro-methane disolvate.

The mol-ecular structure of the title compound, [Cu4(I)Cu2(II)(C11H14N3S)6](PF6)2·2CH3CN·2CH2Cl2, shows a mixed-valent copper(I/II) thiol-ate complex with a distorted tetra-hedral coordination of the Cu(I) and Cu(II) cations by one guanidine N atom and three S atoms each. Characteristic features of the Cu6S6 skeleton are a total of six chemically identical µ3-thiol-ate bridges and almost planar Cu2S2 units with a maximum deviation of 0.110 (1) Šfrom the best plane. Each Cu2S2 unit then shares common Cu-S edges with a neighbouring unit; the enclosed dihedral angle is 60.14 (2)°. The geometric centre of the Cu6S6 cation lies on a crystallographic inversion centre. Cu-S bond lengths range from 2.294 (1) to 2.457 (1) Å, Cu-N bond lengths from 2.005 (3) to 2.018 (3) Šand the non-bonding Cu⋯Cu distances from 2.5743 (7) to 2.5892 (6) Å. C-H⋯F hydrogen-bond inter-actions occur between the PF6(-) anion and the complex mol-ecule and between the PF6(-) anion and the acetonitrile solvent mol-ecule.

2-Benzyl-sulfanyl-N-(1,3-dimethyl-imidazolidin-2-yl-idene)aniline.

The mol-ecular structure of the title compound, C18H21N3S, shows a twisted conformation with a dihedral angle of 67.45 (4)° between the aromatic ring planes and an N-C-C-S torsion angle of -5.01 (13)°. The imidazolidine ring and the aniline moiety make a dihedral angle of 56.03 (4)° and the asscociated C-N-C angle is 125.71 (10)°. The guanidine-like C=N double bond is clearly localized, with a bond length of 1.2879 (14) Å. The C-S-C angle is 102.12 (5)° and the S-C(aromatic) and S-C bond lengths are 1.7643 (11) and 1.8159 (12) Å.

Triethyl-ammonium 4-(3,5-dinitro-benzamido)-N-(3,5-dinitro-benzo-yl)benzene-sulfonamidate.

The mol-ecular structure of the title salt, C6H16N(+)·C20H11N6O12S(-), shows a planar geometry of the benzamido-phen-yl-sulfonyl moiety, with a dihedral angle of 1.59 (9)° between the aromatic ring planes. The central ring and the aromatic ring of the other dinitro-benzamide group are nearly perpendicular, making a dihedral angle of 89.55 (9)°. All nitro groups lie almost in plane with the associated aromatic rings, the O-N-C-C torsion angles ranging from 9.2 (2) to 24.3 (2)°. In the crystal, strong anion-anion N-H⋯O and anion-cation hydrogen bonds form inversion dimers stacked along the a axis. Less prominent anion-anion C-H⋯O inter-actions lead to the formation of a three-dimensional network including anion-anion dimers as well as anion-anion chains along [100?].

N,N'-Bis(4-bromo-phen-yl)pyridine-2,6-dicarboxamide.

The mol-ecule of the title compound, C19H13Br2N3O2, lies about a twofold rotation axis. The benzene ring makes dihedral angles of 8.9 (2) and 16.4 (2)° with the central pyridine ring and the second benzene ring, respectively. An intra-molecular N-H⋯N contact occurs. In the crystal, mol-ecules are connected by pairs of N-H⋯O hydrogen bonds into chains along the c axis.

N,N'-Bis(4-hy-droxy-phen-yl)pyridine-2,6-dicarboxamide di-methyl-formamide monosolvate.

The mol-ecular structure of the pyridine derivative, C19H15N3O4·C3H7NO, shows almost planar geometry with dihedral angles of 6.9 (1) and 13.4 (1)° between the pyridine ring and the two benzene rings. This conformation is stabilized by two intra-molecular N-H⋯N(pyridine) bonds. In the crystal, strong O-H⋯O(carboxamide) and N-H⋯O(hy-droxy-phen-yl) hydrogen bonds link the mol-ecules, forming a three-dimensional structure. The di-methyl-formamide solvent mol-ecules are not involved in the hydrogen bonding. The structure shows pseudosymmetry, but refinement in the space group Pbcn leads to significantly worse results and a disordered di-methyl-formamide mol-ecule.

Dichloridobis(1,3-diisopropyl-4,5-di-methyl-1H-imidazol-3-ium-2-thiol-ate-κS)copper(II).

The mol-ecular structure of the title compound, [CuCl2(C11H20N2S)2], shows the Cu(II) atom with a distorted tetra-hedral geometry from two Cl atoms [Cu-Cl = 2.2182 (6) Å] and two thione S atoms [Cu-S = 2.3199 (6) Å]. The angles at the copper cation, which lies on a twofold rotation axis, are Cl-Cu-Cl = 142.84 (4)°, Cl-Cu-S = 94.80 (2) and 99.97 (2)°, and S-Cu-S = 132.46 (4)°. The planes of the two imidazolium rings make a dihedral angle of 76.92 (8)°.

N-(4-Hy-droxy-phen-yl)-4-nitro-benzamide.

The mol-ecular structure of the title compound, C13H10N2O4, shows an almost planar conformation as the benzene rings make a dihedral angle of 2.31 (7)°. The nitro group lies in plane with the benzamide ring, with a C-C-N-O torsion angle of 0.6 (2)°. In the crystal, N-H⋯O and O-H⋯O hydrogen bonds link mol-ecules into sheets stacked along [10-1].