A Thioether-Ligated Cupric Superoxide Model with Hydrogen Atom Abstraction Reactivity.

The central role of cupric superoxide intermediates proposed in hormone and neurotransmitter biosynthesis by noncoupled binuclear copper monooxygenases like dopamine-ß-monooxygenase has drawn significant attention to the unusual methionine ligation of the CuM ("CuB") active site characteristic of this class of enzymes. The copper-sulfur interaction has proven critical for turnover, raising still-unresolved questions concerning Nature's selection of an oxidizable Met residue to facilitate C-H oxygenation. We describe herein a model for CuM, [(TMGN3S)CuI]+ ([1]+), and its O2-bound analog [(TMGN3S)CuII(O2•-)]+ ([1·O2]+). The latter is the first reported cupric superoxide with an experimentally proven Cu-S bond which also possesses demonstrated hydrogen atom abstraction (HAA) reactivity. Introduction of O2 to a precooled solution of the cuprous precursor [1]B(C6F5)4 (-135 °C, 2-methyltetrahydrofuran (2-MeTHF)) reversibly forms [1·O2]B(C6F5)4 (UV/vis spectroscopy: λmax 442, 642, 742 nm). Resonance Raman studies (413 nm) using 16O2 [18O2] corroborated the identity of [1·O2]+ by revealing Cu-O (446 [425] cm-1) and O-O (1105 [1042] cm-1) stretches, and extended X-ray absorption fine structure (EXAFS) spectroscopy showed a Cu-S interatomic distance of 2.55 Å. HAA reactivity between [1·O2]+ and TEMPO-H proceeds rapidly (1.28 × 10-1 M-1 s-1, -135 °C, 2-MeTHF) with a primary kinetic isotope effect of kH/kD = 5.4. Comparisons of the O2-binding behavior and redox activity of [1]+ vs [2]+, the latter a close analog of [1]+ but with all N atom ligation (i.e., N3S vs N4), are presented.

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.

Structural dynamics upon photoexcitation-induced charge transfer in a dicopper(i)-disulfide complex.

The structural dynamics of charge-transfer states of nitrogen-ligated copper complexes has been extensively investigated in recent years following the development of pump-probe X-ray techniques. In this study we extend this approach towards copper complexes with sulfur coordination and investigate the influence of charge transfer states on the structure of a dicopper(i) complex with coordination by bridging disulfide ligands and additionally tetramethylguanidine units [CuI2(NSSN)2]2+. In order to directly observe and refine the photoinduced structural changes in the solvated complex we applied picosecond pump-probe X-ray absorption spectroscopy (XAS) and wide-angle X-ray scattering (WAXS). Additionally, the ultrafast evolution of the electronic excited states was monitored by femtosecond transient absorption spectroscopy in the UV-Vis probe range. DFT calculations were used to predict molecular geometries and electronic structures of the ground and metal-to-ligand charge transfer states with singlet and triplet spin multiplicities, i.e. S0, 1MLCT and 3MLCT, respectively. Combining these techniques we elucidate the electronic and structural dynamics of the solvated complex upon photoexcitation to the MLCT states. In particular, femtosecond optical transient spectroscopy reveals three distinct timescales of 650 fs, 10 ps and >100 ps, which were assigned as internal conversion to the ground state (Sn → S0), intersystem crossing 1MLCT → 3MLCT, and subsequent relaxation of the triplet to the ground state, respectively. Experimental data collected using both X-ray techniques are in agreement with the DFT-predicted structure for the triplet state, where coordination bond lengths change and one of the S-S bridges is cleaved, causing the movement of two halves of the molecule relative to each other. Extended X-ray absorption fine structure spectroscopy resolves changes in Cu-ligand bond lengths with precision on the order of 0.01 Å, whereas WAXS is sensitive to changes in the global shape related to relative movement of parts of the molecule. The results presented herein widen the knowledge on the electronic and structural dynamics of photoexcited copper-sulfur complexes and demonstrate the potential of combining the pump-probe X-ray absorption and scattering for studies on photoinduced structural dynamics in copper-based coordination complexes.

[Cu6 (NGuaS)6 ]2+ and its oxidized and reduced derivatives: Confining electrons on a torus.

The hexanuclear thioguanidine mixed-valent copper complex cation [Cu6 (NGuaS)6 ]+2 (NGuaS = o-SC6 H4 NC(NMe2 )2 ) and its oxidized/reduced states are theoretically analyzed by means of density functional theory (DFT) (TPSSh + D3BJ/def2-TZV (p)). A detailed bonding analysis using overlap populations is performed. We find that a delocalized Cu-based ring orbital serves as an acceptor for donated S p electrons. The formed fully delocalized orbitals give rise to a confined electron cloud within the Cu6 S6 cage which becomes larger on reduction. The resulting strong electrostatic repulsion might prevent the fully reduced state. Experimental UV/Vis spectra are explained using time-dependent density functional theory (TD-DFT) and analyzed with a natural transition orbital analysis. The spectra are dominated by MLCTs within the Cu6 S6 core over a wide range but LMCTs are also found. The experimental redshift of the reduced low energy absorption band can be explained by the clustering of the frontier orbitals. © 2017 Wiley Periodicals, Inc.

Optical response of the Cu2 S2 diamond core in Cu2II(NGuaS)2 Cl2.

Density functional theory (DFT) and time-dependent DFT calculations are presented for the dicopper thiolate complex Cu2 (NGuaS)2 Cl2 [NGuaS=2-(1,1,3,3-tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu2 S2 Cl2 core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the CuA center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural CuA models. The spectrum can be roughly divided in the known regions of metal d-d absorptions and metal to ligand charge transfer regions. Nevertheless the chloride ions play an important role as electron donors, with the thiolate groups as electron acceptors. The bonding mechanism is dissected by means of charge decomposition analysis which reveals the large covalency of the Cu2 S2 diamond core mediated between Cu dz2 and S-S π and π* orbitals forming Cu-S σ bonds. Measured resonant Raman spectra are shown for 360- and 720-nm excitation wavelength and interpreted using the calculated vibrational eigenmodes and frequencies. The calculations help to rationalize the varying resonant behavior at different optical excitations. Especially the phenylene rings are only resonant for 720 nm. © 2016 Wiley Periodicals, Inc.

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 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.

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.

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.

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.

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)°.

Bis(2-{[bis-(dimethyl-amino)-methyl-idene]amino-κN}benzene-sulfonato-κN)copper(II).

The mol-ecular structure of the title compound, [Cu(C11H16N3O3S)2], shows the Cu(II) atom with a distorted square-planar coordination geometry from the N2O2 donor set of the two chelating 2-{[bis-(dimethyl-amino)-methyl-idene]amino}-benzene-sulfonate ligands. The Cu(II) atom lies 0.065 (1) Šabove the N2O2 plane and the Cu-O [2 × 1.945 (2) Å] and Cu-N bond lengths [1.968 (3) and 1.962 (3) Å] lie in expected ranges. The two aromatic ring planes make a dihedral angle of 85.48 (1)°.

Tricarbonyl-bis-(1,3-diisopropyl-4,5-dimethyl-imidazol-2-yl-idene)iron.

In the title compound, [Fe(C11H20N2)2(CO)3], the Fe atom shows a distorted trigonal-bipyramidal geometry with three carbonyl and two carbene ligands. The latter have a cis arrangement, with a C-Fe-C angle of 90.60 (7)°. The Fe atom lies 0.007 (1) Šabove the basal plane defined by two carbonyl and one carbene C atoms. The mol-ecular structure is closely related to that of the isomolecular but not isotypic Ru complex with an identical cis arrangement, so, in general, bond geometries lie in expected ranges. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into infinite zigzag chains extending along [010].

Bis{1-[2-(diphenyl-phosphan-yl)eth-yl]-3-ethyl-imidazol-2-yl-idene}nickel(II) diiodide acetonitrile disolvate.

The mol-ecular structure of the title compound, [Ni(C(19)H(21)N(2)P)(2)]I(2)·2CH(3)CN, shows two six-membered N-heterocyclic carbene/phosphane chelate rings that form a nearly square-planar coordination geometry around the Ni(II) atom, which lies 0.190 (1) Šabove the C(2)P(2) plane. The sum of the bond angles at the Ni(II) atom is 358.68 (6)°, with C-Ni-P bite angles of 82.89 (5) and 84.08 (6)°. The two carbene rings make a dihedral angle of 52.65 (8)°.

2-[2-(Benzyl-sulfan-yl)phen-yl]-1,1,3,3-tetra-methyl-guanidine.

The mol-ecular structure of the title compound, C(18)H(23)N(3)S, shows it to be a derivative of an amino-thio-phenol possessing a tetra-methyl-guanidine group with a localized C=N double bond of 1.304 (2) Šand a protected thiol functional group as an S-benzyl thio-ether. The two aromatic ring planes make a dihedral angle of 67.69 (6)°.

N-[Bis(dimethyl-amino)-methyl-idene]-2-[(triphenyl-meth-yl)sulfan-yl]ethanaminium hexa-fluoro-phosphate.

The mol-ecular structure of the title compound, C(26)H(32)N(3)S(+)·PF(6) (-), shows a protonated guanidyl group bridged by an ethyl-ene linker with a tritylsulfanyl unit. The guanidinium (gua) unit displays charge delocalization over the three N-C(gua) bonds. The N-C-C-S group shows a folded nonplanar conformation with a torsion angle of 158.4 (1)°. In the crystal, the cation and anion are linked by an N-H⋯F inter-action.

N-Trityl-2-(tritylsulfan-yl)aniline.

The title compound, C(44)H(35)NS, is a derivative of amino-thio-phenol and possesses a protected S-triphenyl-methyl thio-ether and an N-triphenyl-methyl-amine functional group. The trityl groups show an anti orientation, with C-C-N-C and C-C-S-C torsion angles of -151.0 (3) and -105.3 (2)°, respectively. There is an intra-molecular N-H⋯S hydrogen bond.

Bis{1-[2-(diphenyl-phosphino)-ethyl]-3-ethylimidazol-2-yl-idene}palladium(II) bis-(hexa-fluoridophosphate) acetonitrile 2.85-solvate.

In the structure of the title compound, [Pd(C(19)H(21)N(2)P)(2)](PF(6))(2)·2.85CH(3)CN, the two six-membered NHC-phosphane chelate rings form a distorted square-planar coordination geometry around the Pd(II) atom, which lies 0.212 (1) Šabove the coordination plane. The sum of the bond angles at Pd(II) is 358.3°, with C-Pd-P bite angles of 84.03 (10) and 83.54 (9)°. The structure includes three acetonitrile solvent mol-ecules, one with partial site occupation and one with severe disorder, which was eventually excluded from the refinement.

Phenolate hydroxylation in a bis(mu-oxo)dicopper(III) complex: lessons from the guanidine/amine series.

A new hybrid permethylated-amine-guanidine ligand based on a 1,3-propanediamine backbone (2L) and its Cu-O2 chemistry is reported. [(2L)CuI(MeCN)]1+ complex readily oxygenates at low temperatures in polar aprotic solvents to form a bis(mu-oxo)dicopper(III) (O) species (2b), similar to the parent bis-guanidine ligand complex (1b) and permethylated-diamine ligand complex (3b). UV-vis and X-ray absorption spectroscopy experiments confirm this assignment of 2b as an O species, and full formation of the 2:1 Cu-O2 complex is demonstrated by an optical titration with ferrocene-monocarboxylic acid (FcCOOH). The UV-vis spectra of 1b and 2b with guanidine ligation show low-intensity visible features assigned as guanidine pi --> Cu2O2 core transitions by time-dependent density functional theory (TD-DFT) calculations. Comparison of the reactivity among the three related complexes (1b-3b) with phenolate at 195 K is particularly insightful as only 2b hydroxylates 2,4-di-tert-butylphenolate to yield 3,5-di-tert-butylcatecholate (>95% yield) with the oxygen atom derived from O2, reminiscent of tyrosinase reactivity. 1b is unreactive, while 3b yields the C-C radical-coupled bis-phenol product. Attenuated outer-sphere oxidative strength of the O complexes and increased phenolate accessibility to the Cu2O2 core are attributes that correlate with phenolate hydroxylation reactivity observed in 2b. The comparative low-temperature reactivity of 1b-3b with FcCOOH (O-H BDE 71 kcal mol(-1)) to form the two-electron, two-proton reduced bis(mu-hydroxo)dicopper(II,II) complex is quantitative and presumably precedes through two sequential proton-coupled electron transfer (PCET) steps. Optical titrations along with DFT calculations support that the reduced complexes formed in the first step are more powerful oxidants than the parent O complexes. These mechanistic insights aid in understanding the phenol to bis-phenol reactivity exhibited by 2b and 3b.