Copper(I)/S(8) reversible reactions leading to an end-on bound dicopper(II) disulfide complex: nucleophilic reactivity and analogies to copper-dioxygen chemistry

Elemental sulfur (S8) reacts reversibly with the copper(I) complex [(TMPA')CuI](+) (1), where TMPA' is a TMPA (tris(2-pyridylmethyl)amine) analogue with a 6-CH2OCH3 substituent on one pyridyl ligand arm, affording a spectroscopically pure end-on bound disulfido-dicopper(II) complex [{(TMPA')Cu(II)}2(mu-1,2-S2(2-))](2+) (2) {nu(S-S) = 492 cm(-1); nu(Cu-S)sym = 309 cm(-1)}; by contrast, [(TMPA)Cu(I)(CH3CN)](+) (3)/S8 chemistry produces an equilibrium mixture of at least three complexes. The reaction of excess PPh3 with 2 leads to formal "release" of zerovalent sulfur and reduction of copper ion to give the corresponding complex [(TMPA')Cu(I)(PPh3)](+) (11) along with S=PPh3 as products. Dioxygen displaces the disulfur moiety from 2 to produce the end-on Cu2O2 complex, [{(TMPA')Cu(II)}2(mu-1,2-O2(2-)](2+) (9). Addition of the tetradentate ligand TMPA to 2 generates the apparently more thermodynamically stable [{(TMPA)Cu(II)}2(mu-1,2-S2(2-))](2+) (4) and expected mixture of other species. Bubbling 2 with CO leads to the formation of the carbonyl adduct [(TMPA')CuI(CO)](+) (8). Carbonylation/sulfur-release/CO-removal cycles can be repeated several times. Sulfur atom transfer from 2 also occurs in a near quantitative manner when it is treated with 2,6-dimethylphenyl isocyanide (ArNC), leading to the corresponding isothiocyanate (ArNCS) and [(TMPA')Cu(I)(CNAr)](+) (12). Complex 2 readily reacts with PhCH2Br: [{(TMPA')Cu(II)}2(mu-1,2-S(2)(2-)](2+) (2) + 2 PhCH2Br --> [{(TMPA')Cu(II)(Br)}2](2+) (6) + PhCH2SSCH2Ph. The unprecedented substrate reactivity studies reveal that end-on bound mu-1,2-disulfide-dicopper(II) complex 2 provides a nucleophilic S2(2-) moiety, in striking contrast to the electrophilic behavior of a recently described side-on bound mu-eta(2):eta(2)-disulfido-dicopper(II) complex, [{(N3)Cu(II)}(2)(mu-eta(2):eta(2)-S2(2-))](2+) (5) with tridentate N3 ligand. The investigation thus reveals striking analogies of copper/sulfur and copper/dioxygen chemistries, with regard to structure type formation and specific substrate reactivity patterns.     

H2O2-reactivity of copper(II) complexes supported by tris[(pyridin-2-yl)methyl]amine ligands with 6-phenyl substituents

The structure and H(2)O(2)-reactivity of a series of copper(II) complexes supported by tris[(pyridin-2-yl)methyl]amine (TPA) derivatives having a phenyl group at the 6-position of pyridine donor group(s) [(6-phenylpyridin-2-yl)methyl]bis[(pyridin-2-yl)methyl]amine (Ph(1)TPA), bis[(6-phenylpyridin-2-yl)methyl][(pyridin-2-yl)methyl]amine (Ph(2)TPA), and tris[(6-phenylpyridin-2-yl)methyl]amine (Ph(3)TPA) have systematically been examined to get insights into the aromatic substituent (6-Ph) effects on the coordination chemistry of TPA ligand system. The X-ray crystallographic analyses have revealed that [Cu(II)(TPA)(CH(3)CN)](ClO(4))(2) (CuTPA) and [Cu(II)(Ph(3)TPA)(CH(3)CN)](ClO(4))(2) (3) exhibit a trigonal bipyramidal structure, whereas [Cu(II)(Ph(1)TPA)(CH(3)CN)](ClO(4))(2) (1) shows a slightly distorted square pyramidal structure and [Cu(II)(Ph(2)TPA)(CH(3)CN)](ClO(4))(2) (2) has an intermediate structure between trigonal bipyramidal and square pyramidal. On the other hand, the UV-vis and ESR data have suggested that all the copper(II) complexes have a similar trigonal bipyramidal structure in solution. The redox potentials of CuTPA, 1, 2, and 3 have been determined as E(1/2) = -0.34, -0.28, -0.16, and -0.04 mV vs Ag/AgNO(3), respectively, demonstrating that introduction of each 6-Ph group causes positive shift of E(1/2) about 0.1 V. Notable difference in H(2)O(2)-reactivity has been found among the copper(II) complexes. Namely, CuTPA and 1 afforded mononuclear copper(II)-hydroperoxo complexes CuTPA-OOH and 1-OOH, respectively, whereas complex 2 provided bis(mu-oxo)dicopper(III) complex 2-oxo. On the other hand, copper(II) complex 3 was reduced to the corresponding copper(I) complex 3(red). On the basis of the H(2)O(2)-reactivity together with the X-ray structures and the redox potentials of the copper(II) complexes, the substituent effects of 6-Ph are discussed in detail.     

Spectroscopic and computational characterization of CuII-OOR (R = H or cumyl) complexes bearing a Me6-tren ligand

A copper(II)-hydroperoxo complex, [Cu(Me(6)-tren)(OOH)](+) (2), and a copper(ii)-cumylperoxo complex, [Cu(Me(6)-tren)(OOC(CH(3))(2)Ph)](+) (3), were synthesized by reacting [Cu(Me(6)-tren)(CH(3)CN)](2+) (1) with H(2)O(2) and cumyl-OOH, respectively, in the presence of triethylamine. These intermediates, 2 and 3, were successfully characterized by various physicochemical methods such as UV-vis, ESI-MS, resonance Raman and EPR spectroscopies, leading us to propose structures of the Cu(II)-OOR species with a trigonal-bipyramidal geometry. Density functional theory (DFT) calculations provided geometric and electronic configurations of 2 and 3, showing trigonal bipyramidal copper(II)-OOR geometries. These copper(II)-hydroperoxo and -cumylperoxo complexes were inactive in electrophilic and nucleophilic oxidation reactions.     

Density functional study on the mechanism of the vanadium-catalyzed oxidation of sulfides by hydrogen peroxide

A computational study with the Becke3LYP method is carried out on the mechanism of the reaction of complexes V(O)(L)(OOH) and V(O)(LH)(OO) (L = O(CH)(3)N(CH(2))(2)O) with CH(3)S-SCH(3), a system that stands as a model for experimental systems where the metal complex contains larger chelating Schiff bases and the substrate is bis(tert-butyl) disulfide. The different possible isomers of both the hydroperoxo V(O)(L)(OOH) and the peroxo V(O)(LH)(OO) forms of the catalyst are explored, and the reactivity of the most stable among them with the dimethyl disulfide substrate is studied through location of the corresponding transition states. A large variety of reactive paths happen to exist, though in all cases the reaction takes place through a direct transfer process, with the simultaneous formation of the S-O bond and breaking of the O-O bond being the rate-limiting step.     

An unusual mixed-valence Cu(I)-Cu(II) 3-D framework

The reaction of Cu(CH(3)CN)(4)ClO(4) with 2-pyridylacrylic acid (2-HPYA) affords an unusual mixed-valence Cu(I)-Cu(II) 3-D framework ([Cu(II)(2-PYA)(2)](3).[Cu(I)(2-PYA)](2).(H2O)(2))n (1) with a novel topology which features Cu(II) dimeric units (or paddle-wheel unit). The almost perpendicular coordinating direction between the N atom of pyridyl and the O atom of carboxylate groups may be responsible for the formation of such a novel network.     

Reactivity study of a hydroperoxodicopper(II) complex: hydroxylation, dehydrogenation, and ligand cross-link reactions

Employing a binucleating phenol-containing ligand PD'OH, a mu-phenoxo-mu-hydroperoxo dicopper(II) complex [Cu(II)2(PD'O-)(-OOH)(RCN)2](ClO4)2 (1, R = CH3, CH3CH2 or C6H5CH2; lambda(max) = 407 nm; nu(O-O) = 870 cm(-1); J. Am. Chem. Soc. 2005, 127, 15360) is generated by reacting a precursor dicopper(I) complex [Cu(I)2(PD'OH)(CH3CN)2](ClO4)2 (2) with O2 in nitrile solvents at -80 degrees C. Species 1 is unable to oxidize externally added substrates, for instance, PPh3, 2,4-tert-butylphenol, or 9,10-dihydroanthracene. However, upon thermal decay, it hydroxylates copper-bound organocyanides (e.g., benzylcyanide), leading to the corresponding aldehyde while releasing cyanide. This chemistry mimics that known for the copper enzyme dopamine-beta-monooxygenase. The thermal decay of 1 also leads to a product [Cu(II)3(L")2(Cl-)2](PF6)2 (6); its X-ray structure reveals that L" is a Schiff base-containing ligand which apparently derives from both oxidative N-dealkylation and then oxidative dehydrogenation of PD'OH; the chloride presumably derives from the CH2Cl2 solvent. With an excess of PPh3 added to 1, a binuclear Cu(I) complex [Cu(I)2(L')(PPh3)2](ClO4)2 (5) with a cross-linked PD'OH ligand L' has also been identified and crystallographically and chemically characterized. The newly formed C-O bond and an apparent k(H)/k(D) = 2.9 +/- 0.2 isotope effect in the benzylcyanide oxidation reaction suggest a common ligand-based radical forms during compound 1 thermal decay reactions. A di-mu-hydroxide-bridged tetranuclear copper(II) cluster compound [{Cu(II)2(PD'O-)(OH-)}2](ClO4)4 (8) has also been isolated following warming of 1. Its formation is consistent with the generation of [Cu(II)2(PD'O-)(OH-)]2+, with dimerization a reflection of the large Cu...Cu distance and thus the preference for not having a second bridging ligand atom (in addition to the phenolate O) for dicopper(II) ligation within the PD'O- ligand framework.     

Galactose oxidase models: solution chemistry, and phenoxyl radical generation mediated by the copper status

Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu(II)-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N(3)O ligands first chelate Cu(II), leading, in the presence of base, to [Cu(II)(ligand)(CH(3)CN)](+) complexes (ortho-tert-butylated ligands) or [(Cu(II))(2)(ligand)(2)](2+) complexes (ortho-methoxylated ligands). Excess copper(II) then oxidizes the complex to the corresponding mononuclear Cu(II)-phenoxyl radical species. N(2)O(2) tripodal ligands, in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper(II) affords a Cu(II)-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N(3)O donor set, while disproportionation is observed for ligands possessing an N(2)O(2) donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the cross-linked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme.     

Alkane hydroperoxidation with peroxides catalysed by copper complexes

Various copper(I) and copper(II) derivatives, both "simple" ones (copper acetate, perchlorate and a complex with CH3CN) and compounds containing N,O-chelating ligands, catalyse very efficient (turnover numbers attain 2200) oxidation of saturated hydrocarbons with peroxyacetic acid (PAA) or tert-butyl hydroperoxide (TBHP) in acetonitrile solution at 60 degrees C. Alkyl hydroperoxide, alcohol and ketone are formed, the main product being an alkyl hydroperoxide in the oxidation with PAA and an alcohol for the case of TBHP. It has been proposed that the oxidation with PAA is induced via the attack of species r* [HO* or CH3C(=O)O*] on the alkane, RH. A competitive attack of r* on the solvent, CH3CN, also occurs. It has been assumed that in the case of the reaction catalysed by complex Cu(CH3CN)4BF4, copper is present mainly in the form of Cu+ cation, and the rate-limiting step of the oxidation process is the formation of r* via reaction (1): CH3C(=O)OOH + Cu+ --> CH3C(=O)O* + HO- + Cu2+ or/and CH3C(=O)OOH + Cu+ --> CH3C(=O)O- + HO* + Cu2+ with initial rate W1 = k1[PAA][Cu(CH3CN)4BF4] and k1 = 1.7 mol(-1) dm3 s(-1) at 60 degrees C. The activity of the Cu-catalyst is dramatically changed on a small modification of N,O-chelating ligands in the catalyst.     

Heterobimetallic activation of dioxygen: characterization and reactivity of novel Cu(I)-Ge(II) complexes

Reaction of the known germylene Ge[N(SiMe3)2]2 and a new heterocyclic variant Ge[(NMes)2(CH)2] with [L(Me2)Cu]2 (L(Me2) = the beta-diketiminate derived from 2-(2,6-dimethylphenyl)amino-4-(2,6-dimethylphenyl)imino-2-pentene) yielded novel Cu(I)-Ge(II) complexes L(Me2)Cu-Ge[(NMes)2(CH)2] (1a) and L(Me2)Cu-Ge[N(SiMe3)2]2 (1b), which were characterized by spectroscopy and X-ray crystallography. The lability of the Cu(I)-Ge(II) bond in 1a and b was probed by studies of their reactivity with benzil, PPh3, and a N-heterocyclic carbene (NHC). Notably, both complexes are cleaved rapidly by PPh3 and the NHC to yield stable Cu(I) adducts (characterized by X-ray diffraction) and the free germylene. In addition, the complexes are highly reactive with O2 and exhibit chemistry which depends on the bound germylene. Thus, oxygenation of 1a results in scission and formation of thermally unstable L(Me2)CuO2, which subsequently decays to [(L(Me2)Cu)2(mu-O)2], while 1b yields L(Me2)Cu(mu-O)2Ge[N(SiMe3)2]2, a novel heterobimetallic intermediate having a [Cu(III)(mu-O)2Ge(IV)]3+ core. The isolation of the latter species by direct oxygenation of a Cu(I)-Ge(II) precursor represents a new route to heterobimetallic oxidants comprising copper.     

Catalytic transesterification of dialkyl phosphates by a bioinspired dicopper(II) macrocyclic complex

For a number of phosphoryltransfer enzymes, including the exonuclease subunit of DNA polymerase I, a mechanism involving two-metal ions and double Lewis-acid activation of the substrate, combined with leaving group stabilization, has been proposed. Inspired by the active site structure of this enzyme, we have designed as a synthetic phosphoryl transfer catalyst the dicopper(II) macrocyclic complex LCu(2). Crystal structures of complexes [(L)Cu(2)(mu-NO(3))(NO(3))](NO(3))(2) (1), [(L)Cu(2)(mu-CO(3))(CH(3)OH)](BF(4))(2) (2), and [(L)Cu(2)(mu-O(2)P(OCH(3))(2))(NO(3))](NO(3))(2) (3) illustrate various possibilities for the interaction of oxoanions with the dicopper(II) site. 1 efficiently promotes the transesterification of dimethyl phosphate (DMP) in CD(3)OD, k(cat) = 2 x 10(-)(4) s(-)(1) at 55 degrees C. 1 is the only available catalyst for the smooth transesterification of highly inert simple dialkyl phosphates. From photometric titrations and the pH dependence of reactivity, we conclude that a complex [(L)Cu(2)(DMP)(OCH(3))](2+) is the reactive species. Steric bulk at the -OR substituents of phosphodiester substrates O(2)P(OR)(2)(-) drastically reduces the reactivity of 1. This is explained with -OR leaving group stabilization by Cu coordination, an interaction which is sensitive to steric crowding at the alpha-C-atom of substituent R. A proposed reaction mechanism related to that of the exonuclease unit of DNA polymerase I is supported by DFT calculations on reaction intermediates. The complex [(L)Cu(3)(mu(3)-OH)(mu-CH(3)O)(2)(CH(3)CN)(2)](ClO(4))(3) (4) incorporates a [Cu(OH)(OCH(3))(2)(CH(3)CN)(2)](-) complex anion, which might be considered as an analogue of the [PO(2)(OCH(3))(2)(OCD(3))](2)(-) transition state (or intermediate) of DMP transesterification catalyzed by LCu(2).     

Combined experimental and theoretical approach to understand the reactivity of a mononuclear Cu(II)-hydroperoxo complex in oxygenation reactions

A copper(II) complex bearing a pentadentate ligand, [Cu(II)(N4Py)(CF(3)SO(3))(2)] (1) (N4Py = N,N-bis(2-pyridylmethyl)bis(2-pyridyl)methylamine), was synthesized and characterized with various spectroscopic techniques and X-ray crystallography. A mononuclear Cu(II)-hydroperoxo complex, [Cu(II)(N4Py)(OOH)](+) (2), was then generated in the reaction of 1 and H(2)O(2) in the presence of base, and the reactivity of the intermediate was investigated in the oxidation of various substrates at -40 degrees C. In the reactivity studies, 2 showed a low oxidizing power such that 2 reacted only with triethylphosphine but not with other substrates such as thioanisole, benzyl alcohol, 1,4-cyclohexadiene, cyclohexene, and cyclohexane. In theoretical work, we have conducted density functional theory (DFT) calculations on the epoxidation of ethylene by 2 and a [Cu(III)(N4Py)(O)](+) intermediate (3) at the B3LYP level. The activation barrier is calculated to be 39.7 and 26.3 kcal/mol for distal and proximal oxygen attacks by 2, respectively. This result indicates that the direct ethylene epoxidation by 2 is not a plausible pathway, as we have observed in the experimental work. In contrast, the ethylene epoxidation by 3 is a downhill and low-barrier process. We also found that 2 cannot be a precursor to 3, since the homolytic cleavage of the O-O bond of 2 is very endothermic (i.e., 42 kcal/mol). On the basis of the experimental and theoretical results, we conclude that a mononuclear Cu(II)-hydroperoxo species bearing a pentadentate N5 ligand is a sluggish oxidant in oxygenation reactions.     

Dioxygen activation of a trinuclear Cu(I)Cu(I)Cu(I) cluster capable of mediating facile oxidation of organic substrates: competition between O-atom transfer and abortive intercomplex reduction

The dioxygen activation of a series of Cu(I)Cu(I)Cu(I) complexes based on the ligands (L) 3,3'-(1,4-diazepane- 1,4-diyl)bis(1-{[2-(dimethylamino)ethyl](methyl)amino}propan-2-ol)(7-Me) or 3,3'-(1,4-diazepane-1,4-diyl)bis(1-{[2-(diethylamino)ethyl](ethyl)amino}propan-2-ol)(7-Et) forms an intermediate capable of mediating facile O-atom transfer to simple organic substrates at room temperature. To elucidate the dioxygen chemistry, we have examined the reactions of 7-Me, 7-Et, and 3,3'-(1,4-diazepane-1,4-diyl)bis[1-(4-methylpiperazin-1-yl)propan-2-ol] (7-N-Meppz) with dioxygen at -80, -55, and -35?°C in propionitrile (EtCN) by UV-visible, 77?K EPR, and X-ray absorption spectroscopy, and 7-N-Meppz and 7-Me with dioxygen at room temperature in acetonitrile (MeCN) by diode array spectrophotometry. At both -80 and -55?°C, the mixing of the starting [Cu(I)Cu(I)Cu(I)(L)](1+) complex (1) with O(2)-saturated propionitrile (EtCN) led to a bright green solution consisting of two paramagnetic species: the green dioxygen adduct [Cu(II)Cu(II)(μ-η(2):η(2)-peroxo)Cu(II)(L)](2+) (2) and the blue [Cu(II)Cu(II)(μ-O)Cu(II)(L)](2+) species (3). These observations are consistent with the initial formation of [Cu(II)Cu(II)(μ-O)(2)Cu(III)(L)](1+)(4), followed by rapid abortion of this highly reactive species by intercluster electron transfer from a second molecule of complex 1 to give the blue species 3 and subsequent oxygenation of the partially oxidized [Cu(II)Cu(I)Cu(I)(L)](2+)(5) to form the green dioxygen adduct 2. Assignment of 2 to [Cu(II)Cu(II)(μ-η(2):η(2)-peroxo)Cu(II)(L)](2+) is consistent with its reactivity with water to give H(2)O(2) and the blue species 3, as well as its propensity to be photoreduced in the X-ray beam during X-ray absorption experiments at room temperature. In light of these observations, the development of an oxidation catalyst based on the tricopper system requires consideration of the following design criteria: 1)?rapid dioxygen chemistry; 2)?facile O-atom transfer from the activated cluster to substrate; and 3)?a suitable reductant to rapidly regenerate complex 1 to accomplish efficient catalytic turnover.     

Iron-catalyzed olefin epoxidation in the presence of acetic acid: insights into the nature of the metal-based oxidant

The iron complexes [(BPMEN)Fe(OTf)2] (1) and [(TPA)Fe(OTf)2] (2) [BPMEN = N,N'-bis-(2-pyridylmethyl)-N,N'-dimethyl-1,2-ethylenediamine; TPA = tris-(2-pyridylmethyl)amine] catalyze the oxidation of olefins by H2O2 to yield epoxides and cis-diols. The addition of acetic acid inhibits olefin cis-dihydroxylation and enhances epoxidation for both 1 and 2. Reactions carried out at 0 degrees C with 0.5 mol % catalyst and a 1:1.5 olefin/H2O2 ratio in a 1:2 CH3CN/CH3COOH solvent mixture result in nearly quantitative conversions of cyclooctene to epoxide within 1 min. The nature of the active species formed in the presence of acetic acid has been probed at low temperature. For 2, in the absence of substrate, [(TPA)FeIII(OOH)(CH3COOH)]2+ and [(TPA)FeIVO(NCCH3)]2+ intermediates can be observed. However, neither is the active epoxidizing species. In fact, [(TPA)FeIVO(NCCH3)]2+ is shown to form in competition with substrate oxidation. Consequently, it is proposed that epoxidation is mediated by [(TPA)FeV(O)(OOCCH3)]2+, generated from O-O bond heterolysis of the [(TPA)FeIII(OOH)(CH3COOH)]2+ intermediate, which is promoted by the protonation of the terminal oxygen atom of the hydroperoxide by the coordinated carboxylic acid.     

Modeling Tyrosinase Monooxygenase Activity. Spectroscopic and Magnetic Investigations of Products Due to Reactions between Copper(I) Complexes of Xylyl-Based Dinucleating Ligands and Dioxygen: Aromatic Ring Hydroxylation and Irreversible Oxidation Products

A full account of a chemical system possessing features that mimic the reactivity aspects of tyrosinase is presented. Using dinucleating ligands with a m-xylyl spacer three new dicopper(I) complexes have been synthesized and their reactivity with dioxygen investigated. The six-membered chelate ring forming ligands provide only two nitrogen coordinations to each copper. The complexes [Cu(I)(2)L(CH(3)CN)(2)]X(2) (X = ClO(4)(-) (1a), SbF(6)(-) (1b)) and [Cu(I)(2)(L-NO(2))(CH(3)CN)(2)][SbF(6)](2) (1c) [L = alpha,alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; L-NO(2) = para-nitro derivative of L] have been characterized by IR and (1)H NMR spectroscopy. The reaction of O(2) with 1a-c in CH(2)Cl(2) or THF is instantaneous and causes stoichiometric xylyl hydroxylation reactions producing phenol products. Thus 1a produces phenoxo-/hydroxo-bridged product [Cu(II)(2)(L-O)(OH)][ClO(4)](2) (2a). The existence of putative peroxo-dicopper(II) species could not be detected even at -80 degrees C. A trend is observed for the extent of aromatic ring hydroxylation (298 K): CH(3)CN approximately DMF > CH(3)OH > CH(2)Cl(2). Cyclic voltammetric experiment of 1a in DMF reveals an appreciably low redox potential (E(1/2) = -0.26 V vs SCE) for the Cu(II)(2)/Cu(I)(2) redox process. Variable-temperature (25-300 K) magnetic susceptibility measurements establish that the copper(II) centers in 2a and the dihydroxo-bridged complex [Cu(II)(2)L'(OH)(2)][ClO(4)](2) (2b) [formed due to an impurity (L') present during the synthesis of L following Method A; L' = bis[alpha,alpha'-bis(N-methyl-N-(2-pyridylethyl)amino)-m-xylene]methylamine] are antiferromagnetically coupled, with 2a considerably more coupled than 2b. Reaction of 1a with O(2) in CH(2)Cl(2) (298 K) produces an additional unhydroxylated product of composition [Cu(II)(2)L(OH)(OH(2))][ClO(4)](3).2H(2)O.0.5HCl (3a). In agreement with its proposed hydroxo-/aquo-bridged structure, 3a is weakly antiferromagnetically coupled. In CH(3)CN solution, 3a rearranges to generate a doubly hydroxo-bridged species [Cu(II)(2)L(OH)(2)](2+). Using a solution-generated dicopper(I) complex of a closely similar ligand (L' ') providing five-membered chelate ring, the reactivity toward dioxygen was also investigated. It produces only an irreversibly oxidized product of composition Cu(II)(2)L' '(OH)(ClO(4))(3)(H(2)O)(2) (3b) (L' ' = alpha,alpha'-bis[N-methyl-N-(2-pyridylmethyl)amino]-m-xylene). For 3b the copper(II) centers are almost uncoupled.     

Heterolytic addition of E-H bonds across Pt-P bonds in Pt N-heterocyclic phosphenium/phosphido complexes

The reactivity of E-H bonds (E = S, O, Cl) with Pt(II) complexes ligated by an N-heterocyclic phosphido-containing diphosphine ligand have been investigated. Addition of PhSH to [(PPP)Pt(PPh(3))][PF(6)] (1) results in clean formation of [(PP(H)P)Pt(SPh)][PF(6)] (3), in which the substrate has added across the Pt-P(NHP) bond. Similar reactivity occurs when 1 is treated with ROH (R = Ph, Me), but in this case the O-H bond adds across the Pt-P bond in the opposite direction producing [(PP(OR)P)Pt(H)(PPh(3))][PF(6)] (R = Ph (4), Me (5)). HCl addition to 1 cleanly generates [(PP(H)P)PtCl][PF(6)] (6(PF6)). The neutral Pt-NHP complex (PPP)PtCl (2) exhibits similar reactivity; however, in the presence of the nucleophilic Cl(-) anion, the (PP(OR)P)Pt(H)Cl species presumably generated via addition of ROH (R = Me, Et) undergoes an Arbuzov-like dealkylation reaction to exclusively form the N-heterocylic phosphinito species (PP(O)P)Pt(H) (7).     

Modular approach to tridentate N,O,N' ligands using pyrazolylborate chemistry

Two anionic tridentate N,O,N' chelators, [pz(Ph)B(mu-pz)(mu-O)B(Ph)pz](-) (3(-)) and [pz(Ph)(Ph)B(mu-pz)(mu-O)B(Ph)pz(Ph)](-) (4(-)), as well as the corresponding complexes [Fe(3)(py)Cl], [Fe(3)Cl(2)] and [Cu(3)Cl], have been synthesised and structurally characterised by X-ray crystallography (pz: pyrazolyl, pz(Ph): 3-phenylpyrazolyl, py: pyridine). Since our synthesis approach takes advantage of the highly modular pyrazolylborate chemistry, inexpensive and relatively resistant N,O,N' ligands of varying steric demand are readily accessible. The complexes [Fe(3)(py)Cl] and [Fe(3)Cl(2)] possess a distorted trigonal-bipyramidal configuration with the pyrazolyl rings occupying equatorial positions and the oxygen donor being located at an apical position. The complex [Cu(3)Cl] crystallises as chloro-bridged dimers featuring Cu(II) ions with ligand environments that are intermediate between a square-planar and a trigonal-bipyramidal geometry.     

Ni(P(Ph)2N(C6H4X)2)2]2+ complexes as electrocatalysts for H2 production: effect of substituents, acids, and water on catalytic rates

A series of mononuclear nickel(II) bis(diphosphine) complexes [Ni(P(Ph)(2)N(C6H4X)(2))(2)](BF(4))(2) (P(Ph)(2)N(C6H4X)(2) = 1,5-di(para-X-phenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; X = OMe, Me, CH(2)P(O)(OEt)(2), Br, and CF(3)) have been synthesized and characterized. X-ray diffraction studies reveal that [Ni(P(Ph)(2)N(C6H4Me)(2))(2)](BF(4))(2) and [Ni(P(Ph)(2)N(C6H4OMe)(2))(2)](BF(4))(2) are tetracoordinate with distorted square planar geometries. The Ni(II/I) and Ni(I/0) redox couples of each complex are electrochemically reversible in acetonitrile with potentials that are increasingly cathodic as the electron-donating character of X is increased. Each of these complexes is an efficient electrocatalyst for hydrogen production at the potential of the Ni(II/I) couple. The catalytic rates generally increase as the electron-donating character of X is decreased, and this electronic effect results in the favorable but unusual situation of obtaining higher catalytic rates as overpotentials are decreased. Catalytic studies using acids with a range of pK(a) values reveal that turnover frequencies do not correlate with substrate acid pK(a) values but are highly dependent on the acid structure, with this effect being related to substrate size. Addition of water is shown to dramatically increase catalytic rates for all catalysts. With [Ni(P(Ph)(2)N(C6H4CH2P(O)(OEt)2)(2))(2)](BF(4))(2) using [(DMF)H](+)OTf(-) as the acid and with added water, a turnover frequency of 1850 s(-1) was obtained.     

醋酸乙烯酯基桥连铁硫配合物(σ,π-μ-CH3CO2C=CH2)(μ-RS)Fe2CO)6的制备及结构鉴定

本文报道乙酰氯同[μ-CO)(μ-RS)Fe2(CO]Et3NH相作用生成了标题化合物, 除用碳氢分析, IR, 'HNMR及X衍射技术表征这类配合物的结构和构象外, 还对形成此类产物的过程进行了初步讨论。     

Selective DNA strand scission with binuclear copper complexes: implications for an active Cu2-O2 species

A homologous series of binuclear copper(II) complexes [Cu(II)(2)(Nn)(Y)(2)](2+) (1-3) (n = 3-5 and Y = (ClO(4))(-) or (NO(3))(-)) were studied to investigate the intermediate(s) responsible for selective DNA strand scission in the presence of MPA/O(2) (MPA = 3-mercaptopropanoic acid). While the N3 complex does not react, the N4 and N5 analogues show comparable activity with strand scission occurring at a single-strand/double-strand junction. Identical reactivity is also observed in the alternate presence of H(2)O(2). Spectroscopic and reactivity studies with [Cu(II)(2)(N4)(Y)(2)](2+) (2) and H(2)O(2) are consistent with DNA oxidation mediated by formation of a side-on peroxodicopper(II) (Cu(2)-O(2)) complex.     

Selective C-C coupling of Ir-ethene and Ir-carbenoid radicals

The reactivity of the paramagnetic iridium(II) complex [Ir(II)(ethene)(Me(3)tpa)](2+) (1) (Me(3)tpa=N,N,N-tris(6-methyl-2-pyridylmethyl) amine) towards the diazo compounds ethyl diazoacetate (EDA) and trimethylsilyldiazomethane (TMSDM) was investigated. The reaction with EDA gave rise to selective C--C bond formation, most likely through radical coupling of the Ir-carbenoid radical species [Ir(III){CH(.)(COOEt)}(MeCN)(Me(3)tpa)](2+) (7) and (the MeCN adduct of) 1, to give the tetracationic dinuclear complex [(MeCN)(Me(3)tpa)Ir(III){CH(COOEt)CH(2)CH(2)}Ir(III)(MeCN)(Me(3)tpa)](2+) (4). The analogous reaction with TMSDM leads to the mononuclear dicationic species [Ir(III){CH(2)(SiMe(3))}(MeCN)(Me(3)tpa)](2+) (11). This reaction probably involves a hydrogen-atom abstraction from TMSDM by the intermediate Ir-carbenoid radical species [Ir(III){CH(.)(SiMe(3))}(MeCN)(Me(3)tpa)](2+) (10). DFT calculations support pathways proceeding via these Ir-carbenoid radicals. The carbenoid-radical species are actually carbon-centered ligand radicals, with an electronic structure best described as one-electron-reduced Fischer-type carbenes. To our knowledge, this paper represents the first reactivity study of a mononuclear Ir(II) species towards diazo compounds.