Adam Neuba

A Halide‐Induced Copper(I) Disulfide/Copper(II) Thiolate Interconversion

Shortly after their discovery as protein active sites, copper sulfur complexes entered the stage of modern synthetic coordination chemistry. In this respect, the combination of copper (II) and potentially reducing thiolate ligands appears especially attractive owing to its relevance to the CuA within cytochrome-c oxidase and N2O reductase. [2] Despite extensive research efforts, dinuclear copper(II) or mixed-valent copper(I/II) thiolate complexes with protein active site properties are rare. This situation can be traced back to the ligands under investigation, which are not capable of preventing Cu from being reduced to Cu along with the formation of organodisulfides. On the other hand, the selective and reversible oxidation of thiols/thiolates to organo-disulfides (e.g., cysteine to cystine) is one of the most important biological reactions resulting in the formation of disulfide bridges within peptides and proteins. In addition, the reaction system thiol– disulfide is an important electron source for a number of redox processes in biological systems, making it an indispensable component of basic regulatory processes during signal transduction and enzyme activity. Nevertheless, disulfide– thiolate redox processes are largely unexplored in an inorganic context, although they were investigated in terms of the participation of copper(II) ions in kinetic studies more than 50 years ago. Quite recently, further reports have been published on this subject, and in 2002 a unique model system was described which—under the influence of copper and controlled by halide ions—is able to shift the thiolate– disulfide equilibrium reversibly and completely from the one side to the other. This surprising discovery indicates an enormous but largely unrecognized potential for such reaction systems to act as novel electron sources and sinks, which has motivated us to explore this topic more deeply. We report herein a previously unknown chloride-induced disulfide–thiolate interconversion, leading from the copper(I) disulfide complex cation [Cu2{(NGuaS-)2}2] 2+ (1) to the electrically neutral copper(II) thiolate species [Cu2(NGuaS)2Cl2] (2 ; there is no longer an S S bond in the NGauS ligands, thus it is no longer written as (NGuaS )2). Both compounds (1 as 1[OTf]2) were characterized by X-ray crystallography. The proposed oxidation states of the Cu ions were confirmed by K-edge measurements. The reverse reaction can be initiated by removal of the chloride ligands from the corresponding thiolate complex (Scheme 1).

Density functional theory of the CuA -like Cu2 S2 diamond core in Cu 2II(NGuaS)2 Cl2.

Density functional theory (DFT) calculations with localized as well as plane‐wave basis functions are performed for the recently reported dicopper thiolate species Cu2(NGuaS)2Cl2 [NGuaS = 2‐(1,1,3,3‐tetramethylguanidino) benzenethiolate, C11H16N3S] and its bromo derivative [Neuba et al., Angew. Chem. Int. Ed. 2012, 51, 1714.]. For both hybrid and semilocal functionals, the neutral complexes are found to have broken symmetry (BS) character, with electron paramagnetic resonance silent, antiferromagnetically coupled [Cu2+…Cu2+] site in which the coupling is driven by super exchange interaction within the Cu2S2 diamond core. The accurate theoretical description of the geometric structure, however, provides a major challenge for DFT: (i) the multideterminant character of the ground state wave function has to be covered by the BS approach. It requires (ii) metageneralized gradient approximations, that is hybrid functionals with an explicit dependence on the kinetic energy of the individual orbitals: In combination with a dispersion correction, the metafunctional TPSSh results in a CuCu distance close to the experimentally observed value of 2.7 Å. For the negative charge state of the complex, a mixed‐valent [Cu1.5+…Cu1.5+] electronic structure with a smaller CuCu distance of 2.6 Å is predicted, similar to the value of the CuA site of cytochrome c oxidase.

Optical response of the Cu2S2 diamond core in Cu2II(NGuaS)2Cl2

Density functional theory (DFT) and time‐dependent DFT calculations are presented for the dicopper thiolate complex Cu2(NGuaS)2Cl2 [NGuaS=2‐(1,1,3,3‐tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu2S2Cl2 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 Cu2S2 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.

Synthesis of new copper(I) based linear 1-D-coordination polymers with neutral imidazolinium-dithiocarboxylate ligands

An imidazolinium-dithiocarboxylate betaine has been applied for the first time as a ligand in a coordination polymer with copper(I) halides. The resulting 1-D-coordination compounds show a linear double chain structure with trigonally coordinated copper(I). The potential of the material as a heterogeneous photocatalyst was explored.

Di-μ-oxido-bis{[1,3-bis(tetramethylguanidino)propane-κ2N,N′]bromidomanganese(III)}

The title compound, [Mn2Br2O2(C13H30N6)2], is the first crystallographically characterized MnIII2(μ-O)2 complex with a bidentate imine ligand . The molecule lies on a crystallographic inversion centre and shows distorted square-pyramidal coordination of the Mn atoms by two guanidine N atoms, the two bridging O atoms and a terminal Br ligand. The crystal structure involves an intermolecular C—H⋯Br hydrogen bond.

The mixed-valent copper thiol­ate complex hexa­kis­{μ3-2-[(1,3-dimethyl­imidazol­idene)amino]­benzene­thiol­ato}dicopper(II)tetra­copper(I) bis­(hexa­fluoridophosphate) acetonitrile disolvate dichloro­methane disolvate

The molecular structure of the title compound, [Cu4 ICu2 II(C11H14N3S)6](PF6)2·2CH3CN·2CH2Cl2, shows a mixed-valent copper(I/II) thiolate complex with a distorted tetrahedral coordination of the CuI and CuII 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-thiolate bridges and almost planar Cu2S2 units with a maximum deviation of 0.110 (1) Å from 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) Å and the non-bonding Cu⋯Cu distances from 2.5743 (7) to 2.5892 (6) Å. C—H⋯F hydrogen-bond interactions occur between the PF6 − anion and the complex molecule and between the PF6 − anion and the acetonitrile solvent molecule.

Rare examples of base pairing via a protonated pyridine N atom in two salts of N2,N6-bis(1,3-dimethylimidazolin-2-ylidene)pyridine-2,6-diamine.

The title compounds, namely 2,6-bis[(1,3-dimethylimidazolin-2-ylidene)amino]pyridinium perchlorate, C(15)H(24)N(7)(+) x ClO(4)(-), (I), and bis{2,6-bis[(1,3-dimethylimidazolin-2-ylidene)amino]pyridinium} mu-oxido-bis[trichloridoiron(III)], (C(15)H(24)N(7))(2)[Fe(2)Cl(6)O], (II), are structurally unusual examples of the organization of molecular units via base pairing. The cations in salts (I) and (II) are derived from the bisguanidine N(2),N(6)-bis(1,3-dimethylimidazolin-2-ylidene)pyridine-2,6-diamine, which associates in centrosymmetric pairs via two N-H...N hydrogen-bond interactions. N-H...N bridges are formed between the protonated pyridine N atom and one of the nonprotonated guanidine N atoms, with N...H distances of 2.01 (1)-2.10 (1) A. Compound (I) contains two crystallographically independent cations and anions per asymmetric unit. One of the perchlorate anions is disordered, while the [Fe(2)Cl(6)O](2-) anion lies on an inversion centre.

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

The title compound, C44H35NS, is a derivative of aminothiophenol and possesses a protected S-triphenylmethyl thioether and an N-triphenylmethylamine 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 intramolecular N—H⋯S hydrogen bond.

The diprotonated 2,2-(propane-1,3-diyl)bis(1,1,3,3-tetramethylguanidinium) cation: packing and conformational changes.

Subject to packing with different anions, the title cation undergoes various conformational changes with significantly different N-C-C-C torsion angles, as well as different angles between the NCN2 guanidine planes. The 2,2-(propane-1,3-diyl)bis(1,1,3,3-tetramethylguanidinium) salts reported here, viz. the dibromide, C13H32N6(2+).2Br-, the tetraphenylborate chloride, C13H32N62+.C24H20B-.Cl-, the tetrachloromercurate, (C13H32N6)[HgCl4], and the bis(trifluoromethanesulfonate), C13H32N6(2+).2CF3SO3-, are dominated by strong intermolecular N-H...X hydrogen bonds, which form different packing patterns.

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

The molecular 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) Å and 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)°. Intramolecular N—H⋯Se hydrogen bonds are noted. Intermolecular C—H⋯Se interactions give rise to supramolecular chains extended along [100]. One severely disordered acetonitrile solvent molecule per asymmetric unit was treated with SQUEEZE in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]; the crystal data take the presence of this molecule into account.