Organic Dye-Sensitized Nitrene Generation: Intermolecular Aziridination of Unactivated Alkenes.

Aziridines are important structural motifs and intermediates, and several synthetic strategies for the direct aziridination of alkenes have been introduced. However, many of these strategies require an excess of activated alkene, suffer from competing side-reactions, have limited functional group tolerance, or involve precious transition metal-based catalysts. Herein, we demonstrate the direct aziridination of alkenes by combining sulfonyl azides as a triplet nitrene source with a catalytic amount of an organic dye functioning as photosensitizer. We show how the nature of the sulfonyl azide, in combination with the triplet-excited state energy of the photosensitizer, affects the aziridination yield and provide a mechanistic rationale to account for the observed dependence of the reaction yield on the nature of the organic dye and sulfonyl azide reagents. The optimized reaction conditions enable the aziridination of structurally diverse and complex alkenes, carrying various functional groups, with the alkene as the limiting reagent.

Cleaner and stronger: how 8-quinolinolate facilitates formation of Co(III)-thiolate from Co(II)-disulfide complexes.

The formation of Co(III)-thiolate complexes from Co(II)-disulfide complexes using the anionic ligand 8-quinolinolate (quin-) has been studied experimentally and quantum chemically. Two Co(II)-disulfide complexes [Co2(LxSSLx)(Cl)4] (x = 1 or 2; L1SSL1 = 2,2'-disulfanediylbis(N,N-bis(pyridin-2-ylmethyl)ethan-1-amine; L2SSL2 = 2,2'-disulfanedylbis (N-((6-methylpyridin-2-yl)methyl)-N-(pyridin-2-ylmethyl) ethan-1-amine) have been successfully converted with high yield to their corresponding Co(III)-thiolate complexes upon addition of the ligand 8-quinolinolate. Using density functional theory (DFT) computations the d-orbital splitting energies of the cobalt-thiolate compounds [Co(L1S)(quin)]+ and [Co(L2S)(quin)]+ were estimated to be 3.10 eV and 3.07 eV, indicating a slightly smaller ligand-field strength of ligand L2SSL2 than of L1SSL1. Furthermore, the orientation of the quin- ligand in the thiolate compounds determines the stability of the thiolate complex. DFT computations show that the thiolate structure benefits from more electrostatic attraction when the oxygen atom of the quin- ligand is positioned trans to the sulfur atom of the [Co(L1S)]2+ fragment. Quin- is the first auxiliary ligand with which it appeared possible to induce the redox-conversion reaction in cobalt(II) compounds of the relatively weak-field ligand L2SSL2.

Probing the redox-conversion of Co(II)-disulfide to Co(III)-thiolate complexes: the effect of ligand-field strength.

The redox-conversion reaction of cobalt(II)-disulfide to cobalt(III)-thiolate complexes triggered by addition of the bidentate ligand 2,2'-bipyridine has been investigated. Reaction of the cobalt(II)-disulfide complex [Co2(L1SSL1)(X)4] (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyldisulfide; X = Cl or Br) [1X] with 2,2'-bipyridine (bpy) resulted in the formation of two different products, namely the cobalt(III)-thiolate complex [Co(L1S)(bpy)]X2 and the unexpected side product [Co2(L1SSL1)(bpy)2(X)2]X2. Crystals of [Co2(L1SSL1)(bpy)2(Cl)2](BPh4)2 [2Cl](BPh4)2 obtained after anion exchange showed the cobalt(II) ions to be in octahedral geometries with the nitrogen donors of the disulfide ligand arranged in a facial conformation and the chloride ion trans to the tertiary amine nitrogen. Remarkably, this side product cannot be converted to the cobalt(III)-thiolate compound [Co(L1S)(bpy)](SbF6)2 [3](SbF6)2 by removal of the chloride ion with use of a silver salt, as this causes scrambling of the ligands, resulting in the formation of [Co(bpy)3]n+. [Co(L1S)(bpy)](SbF6)2 was obtained in a pure form by addition of bpy to a solution in acetonitrile of the compound [Co(L1S)(MeCN)2]2+ [4]2+. Addition of NEt4Cl to [3](SbF6)2 regenerates the cobalt(II)-disulfide complex [1Cl] as confirmed spectroscopically. DFT studies revealed that the conversion from [1Cl] to [3]2+ most likely occurs via the hypothetical intermediate species [2Cl]2+mer, in which the nitrogen atoms of the disulfide ligand are arranged in a meridional conformation. Interestingly, the estimated d-orbital splitting energy of [3]2+ is lower than that of [4]2+, indicating that the ligand-field strength of bpy is lower than anticipated, which hampers clean conversion in the redox-conversion reaction. This study shows that the redox-conversion reaction between cobalt(II)-disulfide and cobalt(III)-thiolate complexes is intricate rather than straightforward.

Redox Interconversion between Cobalt(III) Thiolate and Cobalt(II) Disulfide Compounds.

The redox interconversion between Co(III) thiolate and Co(II) disulfide compounds has been investigated experimentally and computationally. Reactions of cobalt(II) salts with disulfide ligand L1SSL1 (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide) result in the formation of either the high-spin cobalt(II) disulfide compound [CoII2(L1SSL1)Cl4] or a low-spin, octahedral cobalt(III) thiolate compound, such as [CoIII(L1S)(MeCN)2](BF4)2. Addition of thiocyanate anions to a solution containing the latter compound yielded crystals of [CoIII(L1S)(NCS)2]. The addition of chloride ions to a solution of [CoIII(L1S)(MeCN)2](BF4)2 in acetonitrile results in conversion of the cobalt(III) thiolate compound to the cobalt(II) disulfide compound [CoII2(L1SSL1)Cl4], as monitored with UV-vis spectroscopy; subsequent addition of AgBF4 regenerates the Co(III) compound. Computational studies show that exchange by a chloride anion of the coordinated acetonitrile molecule or thiocyanate anion in compounds [CoIII(L1S)(MeCN)2]2+ and [CoIII(L1S)(NCS)2] induces a change in the character of the highest occupied molecular orbitals, showing a decrease of the contribution of the p orbital on sulfur and an increase of the d orbital on cobalt. As a comparison, the synthesis of iron compounds was undertaken. X-ray crystallography revealed that structure of the dinuclear iron(II) disulfide compound [FeII2(L1SSL1)Cl4] is different from that of cobalt(II) compound [CoII2(L1SSL1)Cl4]. In contrast to cobalt, reaction of ligand L1SSL1 with [Fe(MeCN)6](BF4)2 did not yield the expected Fe(III) thiolate compound. This work is an unprecedented example of redox interconversion between a high-spin Co(II) disulfide compound and a low-spin Co(III) thiolate compound triggered by the nature of the anion.

Dinuclear Nickel Complexes of Thiolate-Functionalized Carbene Ligands and Their Electrochemical Properties.

Four dimeric nickel(II) complexes [Ni2Cl2(BnC2S)2] [1], [Ni2Cl2(BnC3S)2] [2], [Ni2(PyC2S)2]Br2 [3]Br2, and [Ni2(PyC3S)2]Br2 [4]Br2 of four different thiolate-functionalized N-heterocyclic carbene (NHC) ligands were synthesized, and their structures have been determined by single-crystal X-ray crystallography. The four ligands differ by the alkyl chain length between the thiolate group and the benzimidazole nitrogen (two -C2- or three -C3- carbon atoms) and the second functionality at the NHC being a benzyl (Bn) or a pyridylmethyl (Py) group. The nickel(II) ions are coordinated to the NHC carbon atom and the pendent thiolate group, which bridges to the second nickel(II) ion creating the dinuclear structure. Additionally, in compounds [1] and [2], the fourth coordination position of the square-planar Ni(II) centers is occupied by the halide ions, whereas in [3]2+ and [4]2+, the additional pendant pyridylmethyl groups complete the coordination spheres of the nickel ions. The electrochemical properties of the four complexes were studied using cyclic voltammetry and controlled-potential coulometry methods. The thiolate-functionalized carbene complexes [1] and [2] appear to be poor electrocatalysts for the hydrogen evolution reaction; the complexes [3]Br2 and [4]Br2, bearing an extra pyridylmethyl group, show higher catalytic activity in proton reduction, indicating that the pyridine group plays an important role in the catalytic cycle.

Ultrasensitive Ethene Detector Based on a Graphene-Copper(I) Hybrid Material.

Ethene is a highly diffusive and relatively unreactive gas that induces aging responses in plants in concentrations as low as parts per billion. Monitoring concentrations of ethene is critically important for transport and storage of food crops, necessitating the development of a new generation of ultrasensitive detectors. Here we show that by functionalizing graphene with copper complexes biologically relevant concentrations of ethene and of the spoilage marker ethanol can be detected. Importantly, in addition these sensors provide us with important insights into the interactions between molecules, a key concept in chemistry. Chemically induced dipole fluctuations in molecules as they undergo a chemical reaction are harvested in an elegant way through subtle field effects in graphene. By exploiting changes in the dipole moments of molecules that occur upon a chemical reaction we are able to track the reaction and provide mechanistic insight that was, until now, out of reach.

Nickel-ruthenium-based complexes as biomimetic models of [NiFe] and [NiFeSe] hydrogenases for dihydrogen evolution.

The two heterodinuclear nickel-ruthenium complexes [Ni(xbSmS)RuCp(PPh3)]PF6 and [Ni(xbSmSe)RuCp(PPh3)]PF6 (H2xbSmS = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene, H2xbSmSe = 1,2,-bis(2-thiabutyl-3,3-dimethyl-4-selenol)benzene, Cp = cyclopentadienyl) were synthesized as biomimetic models of [NiFe] and [NiFeSe] hydrogenases. The X-ray structural analyses of the complexes show that the two NiRu complexes are isomorphous; in both NiRu complexes the nickel(ii) centers are coordinated in a square-planar environment with two thioether donor atoms and two thiolate or selenolate donors that are bridging to the ruthenium(ii) center. The Ru(ii) ion is further coordinated to a η5-cyclopentadienyl group and a triphenylphosphane ligand. These complexes catalyze hydrogen evolution in the presence of acetic acid in acetonitrile solution at around -2.20 V vs. Fc+/Fc with overpotentials of 810 and 830 mV, thus they can be regarded as functional models of the [NiFe] and [NiFeSe] hydrogenases.

Electrocatalytic proton reduction by a model for [NiFeSe] hydrogenases.

Two new heterodinuclear nickel-iron complexes [Ni(pbSmSe)FeCpCO]PF6 and [Ni(xbSmSe)FeCpCO]PF6 were synthesized as mimics of the [NiFeSe] hydrogenase active site (HCp = cyclopentadiene; H2pbSmSe = 1,9-diselenol-3,7-dithia-2,2,8,8-tetramethylnonane; H2xbSmSe = 1,2,-bis(2-thiabutyl-3,3-dimethyl-4-selenol)benzene). The compounds were characterized by single crystal X-ray diffraction and cyclic voltammetry. X-ray structure determinations showed that in both NiFe complexes the nickel(ii) center is in a square-planar S2Se2 environment; the two selenolate donors are bridging to the iron(ii) center that is further coordinated to an η5-cyclopentadienyl group and a carbon monoxide ligand. Electrochemical studies showed that the complex [Ni(pbSmSe)FeCpCO]PF6 is an electrocatalyst for the production of H2 in DMF in the presence of acetic acid at -2.1 V vs. Fc+/Fc; a foot-of-the-wave (FOWA) analysis of the catalytic currents yielded an estimation of kobs of 24 s-1.

Extremely bulky copper(i) complexes of [HB(3,5-{1-naphthyl}2pz)3]- and [HB(3,5-{2-naphthyl}2pz)3]- and their self-assembly on graphene.

The synthesis and characterization, using NMR (1H and 13C), infrared spectroscopy, and X-ray crystallography, of the ethene and carbon monoxide copper(i) complexes of hydridotris(3,5-diphenylpyrazol-1-yl)borate ([TpPh2]-) and the two new ligands hydridotris(3,5-bis(1-naphthyl)pyrazol-1-yl)borate ([Tp(1Nt)2]-) and hydridotris(3,5-bis-(2-naphthyl)pyrazol-1-yl)borate ([Tp(2Nt)2]-) are described. X-ray crystal structures are presented of [Cu(TpPh2)(C2H4)] and [Cu(Tp(2Nt)2)(C2H4)]. The compound [Cu(TpPh2)(C2H4)] features interactions between the protons of the ethene ligand and the π-electron clouds of the phenyl substituents that make up the binding pocket surrounding the copper(i) center. These dipolar interactions result in strongly upfield shifted signals of the ethene protons in 1H-NMR. [Cu(Tp(1Nt)2)(CO)] and [Cu(Tp(2Nt)2)(CO)] were examined using infrared spectroscopy and were found to have CO stretching vibrations at 2076 and 2080 cm-1 respectively. The copper(i) carbonyl complexes form self-assembled monolayers when drop cast onto HOPG and thin multilayers of a few nanometers thickness when dip coated onto graphene. General macroscopic trends such as the different tendencies to crystallize observed in the complexes of the two naphthyl-substituted ligands appear to extend well to the nanoscale where a well-organized monolayer could be observed of [Cu(Tp(2Nt)2)(CO)].

Catalytic Cracking of Lactide and Poly(Lactic Acid) to Acrylic Acid at Low Temperatures.

Despite being a simple dehydration reaction, the industrially relevant conversion of lactic acid to acrylic acid is particularly challenging. For the first time, the catalytic cracking of lactide and poly(lactic acid) to acrylic acid under mild conditions is reported with up to 58 % yield. This transformation is catalyzed by strong acids in the presence of bromide or chloride salts and proceeds through simple SN 2 and elimination reactions.

One-step growth of lanthanoid metal-organic framework (MOF) films under solvothermal conditions for temperature sensing.

A one-step direct solvothermal synthesis of an Ln metal-organic framework (MOF) film is reported. The LnHL (Ln = Tb and Gd) films that were deposited on a Gd2O3 subtrate are continuous and smooth. The Gd0.9Tb0.1HL film can be used as a ratiometric thermometer, showing good linear behaviour in the temperature range of 110-250 K with a sensitivity up to 0.8% K(-1).

Stabilization of the Low-Spin State in a Mononuclear Iron(II) Complex and High-Temperature Cooperative Spin Crossover Mediated by Hydrogen Bonding.

The tetrapyridyl ligand bbpya (bbpya=N,N-bis(2,2'-bipyrid-6-yl)amine) and its mononuclear coordination compound [Fe(bbpya)(NCS)2 ] (1) were prepared. According to magnetic susceptibility, differential scanning calorimetry fitted to Sorai's domain model, and powder X-ray diffraction measurements, 1 is low-spin at room temperature, and it exhibits spin crossover (SCO) at an exceptionally high transition temperature of T1/2 =418 K. Although the SCO of compound 1 spans a temperature range of more than 150 K, it is characterized by a wide (21 K) and dissymmetric hysteresis cycle, which suggests cooperativity. The crystal structure of the LS phase of compound 1 shows strong NH⋅⋅⋅S intermolecular H-bonding interactions that explain, at least in part, the cooperative SCO behavior observed for complex 1. DFT and CASPT2 calculations under vacuum demonstrate that the bbpya ligand generates a stronger ligand field around the iron(II) core than its analogue bapbpy (N,N'-di(pyrid-2-yl)-2,2'-bipyridine-6,6'-diamine); this stabilizes the LS state and destabilizes the HS state in 1 compared with [Fe(bapbpy)(NCS)2 ] (2). Periodic DFT calculations suggest that crystal-packing effects are significant for compound 2, in which they destabilize the HS state by about 1500 cm(-1) . The much lower transition temperature found for the SCO of 2 compared to 1 appears to be due to the combined effects of the different ligand field strengths and crystal packing.

Mixed-Lanthanoid Metal-Organic Framework for Ratiometric Cryogenic Temperature Sensing.

A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature. The sensing mechanism in the europium-doped compound Tb0.95Eu0.05HL (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) is based not only on phonon-assisted energy transfer from Tb(III) to Eu(III) centers, but also on phonon-assisted energy migration between neighboring Tb(III) ions. It shows good performance in a wide temperature range, especially in the range 4-50 K, reaching a sensitivity up to 31% K(-1) at 4 K.

Highly tunable fluorinated trispyrazolylborates [HB(3-CF3-5-{4-RPh}pz)3](-) (R = NO2, CF3, Cl, F, H, OMe and NMe2) and their copper(I) complexes.

The ethene and carbon monoxide adducts of copper(I) with seven trispyrazolylborate ligands ([HB(3-CF3-5-{4-RPh}pz)3](-); R = NO2 (4a), CF3 (4b), Cl (4c), F (4d), H (4e), OMe (4f) and NMe2 (4g)) were synthesized and characterized. The ligands were synthesized from their corresponding pyrazoles and sodium tetrahydridoborate and were obtained as solvent adducts of their sodium salts after workup. When the pyrazole with the most electron-withdrawing substituent (R = NO2) is used the asymmetric ligand [HB(3-CF3-5-{4-NO2Ph}pz)2(3-{4-NO2Ph}-5-CF3pz)](-) (4a') is formed as the major product. Copper(I) complexes with ethene or CO as a co-ligand were prepared in good yields and were structurally characterized using (1)H NMR, (13)C NMR and infrared spectroscopy. Single crystal X-ray crystallography analyses revealed the structures of Na4a', Na4b, four copper ethene complexes and four copper carbonyl complexes. The structures of the copper(I) complexes show Cu(I) ions in pseudo-tetrahedral coordination environments consisting of three nitrogen atoms of the trispyrazolylborate ligand and the carbonyl or η(2)-coordinated ethene ligands, with nearly identical coordination environments around the Cu(I) ion. The compound [Na(4a')(H2O)]n crystallizes as one-dimensional chains with intermolecular NaO2N interactions. The sodium ions were found in severely distorted octahedral geometries with three nitrogen atoms from the trispyrazolylborate ligand, one aqua ligand and two oxygen atoms from the nitro group of an adjacent molecule. The compound [Na2(4b)2(µ-H2O)2] crystallizes as a centrosymmetric water-bridged dimer: two five-coordinate square-pyramidal sodium ions each are coordinated facially by three nitrogen atoms from a trispyrazolylborate ligand and two bridging water ligands. Below the base of the pyramidal structure one intermolecular and two intramolecular NaF short contacts are present. The (1)H and (13)C NMR spectra of the copper-ethene complexes show signals for the ethene ligands in the range of 4.84-4.96 ppm and 84.9-86.8 ppm respectively. The infrared spectra of the carbonyl complexes show CO stretching frequencies in the range of 2096-2120 cm(-1). Both the NMR signals for the ethene ligands and infrared signals for the carbonyl ligands were found to show good correlations with the Hammett σp parameters of the substituents on the phenyl rings of the ligands.

Catalytic catechol oxidation by copper complexes: development of a structure-activity relationship.

A large library of Cu(II) complexes with mononucleating and dinucleating ligands was synthesized to investigate their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC). X-ray structure determination for a number of these complexes revealed relatively large Cu···Cu distances and the formation of polymeric species. Comparison of the 3,5-DTBC oxidation rates showed that ligands that stabilize the biomimetic dinuclear Cu(II) µ-thiolate complex also result in copper compounds that are much more active in the oxidation of 3,5-DTBC. This oxidation activity is however inhibited by the presence of chloride ions. The highest kcat that was observed was 6900 h(-1), which is one of the highest turnover frequencies reported so far for catechol oxidation in CH3CN.

Protonation of a biologically relevant Cu(II) µ-thiolate complex: ligand dissociation or formation of a protonated Cu(I) disulfide species?

The proton-induced electron-transfer reaction of a Cu(II) µ-thiolate complex to a Cu(I) -containing species has been investigated, both experimentally and computationally. The Cu(II) µ-thiolate complex [Cu(II) 2 (L(Me) S)2 ](2+) is isolated with the new pyridyl-containing ligand L(Me) SSL(Me) , which can form both Cu(II) thiolate and Cu(I) disulfide complexes, depending on the solvent. Both the Cu(II) and the Cu(I) complexes show reactivity upon addition of protons. The multivalent tetranuclear complex [Cu(I) 2 Cu(II) 2 (LS)2 (CH3 CN)6 ](4+) crystallizes after addition of two equivalents of strong acid to a solution containing the µ-thiolate complex [Cu(II) 2 (LS)2 ](2+) and is further analyzed in solution. This study shows that, upon addition of protons to the Cu(II) thiolate compound, the ligand dissociates from the copper centers, in contrast to an earlier report describing redox isomerization to a Cu(I) disulfide species that is protonated at the pyridyl moieties. Computational studies of the protonated Cu(II) µ-thiolate and Cu(I) disulfide species with LSSL show that already upon addition of two equivalents of protons, ligand dissociation forming [Cu(I) (CH3 CN)4 ](+) and protonated ligand is energetically favored over conversion to a protonated Cu(I) disulfide complex.

Thermodynamics of the Cu(II) µ-thiolate and Cu(I) disulfide equilibrium: a combined experimental and theoretical study.

The redox equilibrium between dinuclear Cu(II) µ-thiolate and Cu(I) disulfide structures has been analyzed experimentally and via DFT calculations. Two new ligands, L(2)SSL(2) and L(4)SSL(4), and their Cu(II) µ-thiolate and Cu(I) disulfide complexes were synthesized. For L(2)SSL(2), these two redox-isomeric copper species are shown to be in equilibrium, which depends on both temperature and solvent. For L(4)SSL(4) the µ-thiolate species forms as the kinetic product and further evolves into the disulfide complex under thermodynamic control, which creates the unprecedented possibility to compare both species under the same reaction conditions. The energies of the µ-thiolate and disulfide complexes for two series of related ligands have been calculated with DFT; the results rationalize the experimentally observed structures, and emphasize the important role that steric requirements play in the formation of the Cu(II) thiolate structure.

Enhanced photoinduced electron transfer at the surface of charged lipid bilayers.

Photocatalytic systems often suffer from poor quantum yields due to fast charge recombination: The energy-wasting annihilation of the photochemically created charge-separated state. In this report, we show that the efficiency of photoinduced electron transfer from a sacrificial electron donor to positively charged methyl viologen, or to negatively charged 5,5'-dithiobis(2-nitrobenzoate), increases dramatically upon addition of charged phospholipid vesicles if the charge of the lipids is of the same sign as that of the electron acceptor. Centrifugation and UV/Vis titration experiments showed that the charged photosensitizers adsorb at the liposome surface, that is, where the photocatalytic reaction takes place. The increased photoelectron transfer efficiency in the presence of charged liposomes has been ascribed to preferential electrostatic interactions between the photosensitizer and the membrane, which prevents the formation of photosensitizer-electron-acceptor complexes that are inactive towards photoreduction. Furthermore, it is shown that the addition of liposomes results in a decrease in photoproduct inhibition, which is caused by repulsion of the reduced electron acceptor by the photocatalytic site. Thus, liposomes can be used as a support to perform efficient photocatalysis; the charged photoproducts are pushed away from the liposomes and represent "soluble electrons" that can be physically separated from the place where they were generated.

Catalytic conversion of γ-valerolactone to ε-caprolactam: towards nylon from renewable feedstock.

The conversion of γ-valerolactone (GVL) in three atom-efficient steps to the important polymer precursor ε-caprolactam is reported. The bio-based GVL can be converted to a mixture of isomeric methyl pentenoates (MP) via trans-esterification with methanol with 94% yield (ratio of 3-MP/4-MP=3:1); subsequent aminolysis with ammonia leads to a mixture of pentenamides (PA) almost quantitatively (99% conversion). The resulting pentenamides are ultimately converted into ε-caprolactam via a rhodium-catalyzed intramolecular hydroamidomethylation reaction, comprising an initial hydroformylation of the alkene moiety of PA and subsequent ring-closing reductive amidation of the resulting aldehyde with the amide functionality. A promising yield of caprolactam of about 90% can be obtained with a Rh/xantphos catalyst system in a two-stage hydroformylation-reductive amidation using pure 4-PA as feedstock. The use of 3-PA as a substrate not only results in a significantly lower regioselectivity for the 7-membered lactam, but also in the formation of high amounts of valeramide (VA). Consequently, a best overall yield of caprolactam of nearly 40% could be demonstrated with a Rh/POP-xantphos [POP-xantphos=4,5-bis(2,8-dimethyl-10-phenoxaphosphino)-9,9,-dimethylxanthene] catalyst system based on the 3:1 mixture of 3-PA/4-PA directly obtainable from GVL.

Cu(I) thiolate reactivity with dioxygen: the formation of Cu(II) sulfinate and Cu(II) sulfonate species via a Cu(II) thiolate intermediate.

Cu(I)(Py2NS) (1) is formed by addition of Cu(I) to a solution of the pyridyl-thiol ligand N-(2-mercaptopropyl)-N,N-bis(2-pyridylmethyl)amine (Py2NSH). Oxidation of complex 1 by air leads to the formation of Cu(II) sulfinate and Cu(II) sulfonate complexes, providing a model for the oxidative degeneration of copper-sulfur enzymes. Crystal structures were obtained for two Cu(II) sulfinate complexes, [Cu(II)2(Py2NSO2)2](BF4)2·2(CH3)2CO (4a) and [Cu(II)2(Py2NSO2)2(OTf)2] (4b), which were further characterized by UV-vis and EPR spectroscopy and cyclic voltammetry. Furthermore, two Cu(II) sulfonate complexes with the proposed formulas Cu(II)2(Py2NSO3)2(BF4)2 (5a) and Cu(II)2(Py2NSO3)2(OTf)2 (5b) have been isolated and characterized. Monitoring the oxidation of 1 by UV-vis indicates that the oxidation proceeds via a dinuclear Cu(II) µ-thiolate complex (3); as an intermediate an octanuclear mixed-valent Cu(I)4Cu(II)4 cluster with formula [Cu(I)4Cu(II)4(Py2NS)4(µ-OH)2(CH3CN)6](ClO4)6·2CH3CN (2) was isolated and characterized by X-ray single crystal structure determination.