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Electron correlation is the everlasting concern of people involved in ab initio Hartree-Fock calculations. If the investigation is restricted to the structure and properties of the ground state, the importance of correlation depends i) on the type of bonding in the molecule under scrutiny, and ii) on the level of accuracy requested for the calculation, that is, on the sensitivity of the investigated property. This sensitivity may be highly interrelated with the nature of the bonding: in the specific area of organometallic complexes, it has been recognized since more than a decade that no realistic description of multiple, direct metal-metal bonds can be obtained without an adequate treatment of the left-right correlation.1,2 Accidental near degeneracies connected for instance with the sd hybridization in complexes of Ni(0) should also be accounted for in a systematic way.3 Other cases where correlation is susceptible to qualitatively modify the description of the ground state can be detected from the occurrence of Hartree-Fock instability which makes the energy of the considered system symmetry-dependant.4,5 Introducing a systematic treatment of correlation for large systems in the frame of the Hartree-Fock methodology would lead to technical problems and to an intolerable computer cost. Our experience in the computation of the ground state electronic structure and properties of dimetallic complexes and of clusters with higher nuclearity argues for a flexible approach of the correlation problem.

Well-defined aryl-Cu(III) species undergo rapid reductive elimination upon reaction with phenolates (PhO(-)), to form aryl-OPh cross-coupling products. Kinetic studies show that the reaction follows a different mechanistic pathway compared to the reaction with phenols. The pH active cyclized pincer-like ligand undergoes an initial amine deprotonation that triggers a faster reactivity at room temperature. A mechanistic proposal for the enhanced reactivity and the role of EPR-detected Cu(II) species will be discussed in detail.

A series of aryl–copper(III)-halide complexes have been synthesized and characterized by NMR and UV-visible spectroscopy, cyclic voltammetry and X-ray crystallography. These complexes closely resemble elusive intermediates often invoked in catalytic reactions, such as Ullmann–Goldberg cross-coupling reactions, and their preparation has enabled direct observation and preliminary characterization of aryl halide reductive elimination from CuIII and oxidative addition to CuI centers. In situ spectroscopic studies (1H NMR, UV-visible) of a Cu-catalyzed C–N coupling reaction provides definitive evidence for the involvement of an aryl-copper(III)-halide intermediate in the catalytic mechanism. These results provide the first direct observation of the CuI/CuIII redox steps relevant to Ullmann-type coupling reactions.

Well-defined aryl-Cu(III)-halide species undergo reductive elimination upon acid addition resulting in the formation of strong aryl-halide bonds. The computationally studied mechanism points towards ligand protonation as the rate-determining step, in agreement with previous experimental data.

We demonstrate the application of infrared photodissocation spectroscopy for determination of the Fe═O stretching frequencies of high-valent iron(IV)–oxo complexes [(L)Fe(O)(X)]2+/+ (L = TMC, N4Py, PyTACN, and X = CH3CN, CF3SO3, ClO4, CF3COO, NO3, N3). We show that the values determined by resonance Raman spectroscopy in acetonitrile solutions are on average 9 cm–1 red-shifted with respect to unbiased gas-phase values. Furthermore, we show the assignment of the spin state of the complexes based on the vibrational modes of a coordinated anion and compare reactivities of various iron(IV)–oxo complexes generated as dications or monocations (bearing an anionic ligand). The coordinated anions can drastically affect the reactivity of the complex and should be taken into account when comparing reactivities of complexes bearing different ligands. Comparison of reactivities of [(PyTACN)Fe(O)(X)]+ generated in different spin states and bearing different anionic ligands X revealed that the nature of anion influences...

Efficient and highly stereoselective oxidation of olefins to cis-diols as the major product is obtained by using biomimetic non-heme FeII catalysts in combination with H2O2.

Aquest mateix article està publicat a l'edició alemanya d''Angewandte Chemie' (ISSN 0044-8249, EISSN 1521-3757), 2014, vol. 126, núm. 36, p. 9762-9766. DOI http://dx.doi.org/10.1002/ange.201405060 The bis(mu-oxo) dicopper(III) species [Cu-III 2(mu-O)(2)(m-XYLMeAN)](2+) (1) promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (eta(2) : eta(2)-O-2) dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(mu-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine Financial support for this work was provided by the European Commission (FP7-PEOPLE-2011-CIG-303522 to A. C.; ERC-2009-StG-239910 to M. C., and Marie Curie IOF to I. G.-B.), MINECO (CTQ2012-37420-C02-01/BQU and CSD2010-00065 to M. C.), Generalitat de Catalunya (ICREA Academia Award to M. C.), Spanish Ministry of Science (Ramon y Cajal contract to A. C.), and the INNPLANTA project INP-2011-0059-PCT-420000-ACT1 (Dr. X. Ribas). We also thank Dr. Laura Gomez (Serveis Tecnics de Recerca, Universitat de Girona) for helpful advice in setting up the HR-MS experiments, and for fruitful discussions

The geometry of a series of four [MLn“H2”] complexes (W(H2)(CO)3(PR3)2, IrH(H···H)Cl2(PR3)2, [Os(H···H)(NH2(CH2)2NH2)2(RCO2)]+, and OsH4(PR3)3) spanning a large range of H−H values is optimized at the B3LYP computational level, yielding satisfactory agreement with available neutron-diffraction data. The electron density resulting from these theoretical calculations is analyzed afterward within the “atoms in molecules” formalism, resulting in a positive assignment of the complexes W(H2)(CO)3(PR3)2 and IrH(H···H)Cl2(PR3)2 as dihydrogen complexes and of the complexes [Os(H···H)(NH2(CH2)2NH2)2(RCO2)]+ and OsH4(PR3)3 as dihydride complexes.

Peptide conjugates incorporating the red-ox active ligands Me2PyTACN or (S,S')-BPBP at the N- or the C-terminus of the cell-penetrating peptide BP16 were synthesized (PyTACN-BP16 (BP341), BP16-PyTACN (BP342), BPBP-BP16 (BP343), and BP16-BPBP (BP344)). Metal binding peptides bearing at the N-terminus the ligand, an additional Lys and a β-Ala were also prepared (PyTACN-βAK-BP16 (BP345) and BPBP-βAK-BP16 (BP346)). Moreover, taking into account the clathrin-dependent endocytic mechanism of BP16, the enzymatic cleavable tetrapeptide Gly-Phe-Leu-Gly was incorporated between the ligand and the N- or C-terminus of BP16 (BPBP-GFLG-BP16 (BP347) and BP16-GLFG-BPBP (BP348). Analysis of the cytotoxicity of all the peptide conjugates showed that: (i) the position of the ligand influenced the IC50 values, (ii) the incorporation of the βAla-Lys dipeptide rendered non active sequences, (iii) peptide conjugates derived from the (S,S')-BPBP ligand were more active than those bearing Me2PyTACN, and (iv) the introduction of the cleavable tetrapeptide significantly enhanced the activity of the BPBP conjugates (IC50 of 4.3 to 11.7 μM (BP347 and BP348) compared to 26.0 to >50 μM (BP343, BP344 and BP346)). The most active peptide was BPBP-GFLG-BP16 (BP347) (IC50 of 4.3 to 5.0 μM). This high activity was attributed to its high internalization in MCF-7 cells, as shown by flow cytometry, and to the subsequent release of the ligand by the intracellular cleavage of the enzyme-labile spacer, as observed in cathepsin B enzymatic assays. Therefore, these results pave the way for the design of novel peptide conjugates to be used in pro-oxidant anticancer therapies This work was supported by Consolider Ingenio CSD/CSD2010-00065 from MICINN of Spain. We also thank the Catalan DIUE of the Generalitat de Catalunya (2009SGR637). X.R. thanks financial support from INNPLANTA project INP-2011-0059-PCT-420000-ACT1

The complete chemoselective functionalization of aromatic C(sp(2))-H bonds of benzene and alkyl benzenes by carbene insertion from ethyl diazoacetate was unknown until the recent discovery of an iron-based catalytic system toward such transformation. A Fe(II) complex bearing the pytacn ligand (pytacn = L1 = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane) transferred the CHCO2Et unit exclusively to the C(sp(2))-H bond. The cycloheptatriene compound commonly observed through Buchner reaction or, when employing alkyl benzenes, the corresponding derivatives from C(sp(3))-H functionalization are not formed. We herein present a combined experimental and computational mechanistic study to explain this exceptional selectivity. Our computational study reveals that the key step is the formation of an enol-like substrate, which is the precursor of the final insertion products. Experimental evidences based on substrate probes and isotopic labeling experiments in favor of this mechanistic interpretation are provided., Support for this work was provided by the MINECO (Grants CTQ2014-62234-EXP, CTQ2014-52769-C3-R-1, CTQ2014-54306-P, CTQ2014-52525-P, and Grant BES-2012-052801 to V.P.), the Junta de Andalucia (Grant P10-FQM-06292) and the Generalitat de Catalunya (Grants 2017SGR39 and 2017SGR264, Xarxa de Referencia en Quimica Teorica i Computacional, ICREA Academia prizes 2013 to M.C. and 2014 to M.S.). The EU under the FEDER grant UNGI10-4E-801 (European Fund for Regional Development) has also funded this research.

Supramolecular systems resulting from the combination of peptides and a chiral iron coordination complex catalyze asymmetric epoxidation with aqueous hydrogen peroxide, providing good to excellent yields and high enantioselectivities in short reaction times. The peptide is shown to play a dual role; the terminal carboxylic acid assists the iron center in the efficient H 2 O 2 activation step, while its β-turn structure is crucial to induce high enantioselectivity in the oxygen delivering step. The high level of stereoselection (84-92% ee) obtained by these supramolecular catalysts in the epoxidation of 1,1′-alkyl ortho-substituted styrenes, a notoriously challenging class of substrates for asymmetric catalysis, is not attainable with any other epoxidation methodology described so far. The current work, combining an iron center ligated to N and O based ligands, and a peptide scaffold that shapes the second coordination sphere, may be seen as a bott om up approach towards the design of artificial oxygenases MC acknowledge nancial support from MINECO of Spain and Fondo Europeo de Desarrollo Regional (CTQ2015-70795-P/ BQU), and the Catalan Department for Innovation, Universities and Enterprise (DIUE) of the Generalitat de Catalunya (2009SGR637).