A Novel Catalytic Route to Polymerizable Bicyclic Cyclic Carbonate Monomers from Carbon Dioxide

A new catalytic route has been developed for the coupling of epoxides and CO(2) affording polymerizable six‐membered bicyclic carbonates. Cyclic epoxides equipped with a β‐positioned OH group can be transformed into structurally diverse bicyclic cyclic carbonates in good yields and with high selectivity. Key to the chemo‐selectivity is the difference between the reactivity of syn‐ and anti‐configured epoxy alcohols, with the latter leading to six‐membered ring carbonate formation in the presence of a binary Al(III) aminotriphenolate complex/DIPEA catalyst. X‐ray analyses show that the conversion of the syn‐configured substrate evolves via a standard double inversion pathway providing a five‐membered carbonate product, whereas the anti‐isomer allows for activation of the oxirane unit of the substrate opposite to the pendent alcohol. The potential use of these bicyclic products is shown in ring‐opening polymerization offering access to rigid polycarbonates with improved thermal resistance

Interplay between β-Diimino and β-Diketiminato Ligands in Nickel Complexes Active in the Proton Reduction Reaction

Acord transformatiu CRUE-CSICTwo Ni complexes are reported with κ4-P2N2 β-diimino (BDI) ligands with the general formula [Ni(XBDI)](BF4)2, where BDI is N-(2-(diphenylphosphaneyl)ethyl)-4-((2-(diphenylphosphaneyl)ethyl)imino)pent-2-en-2-amine and X indicates the substituent in the α-carbon intradiimine position, X = H for 1(BF4)2 and X = Ph for 2(BF4)2. Electrochemical analysis together with UV-vis and NMR spectroscopy in acetonitrile and dimethylformamide (DMF) indicates the conversion of the β-diimino complexes 12+ and 22+ to the negatively charged β-diketiminato (BDK) analogues (1-H)+ and (2-H)+ via deprotonation in DMF. Moreover, further electrochemical and spectroscopy evidence indicates that the one-electron-reduced derivatives 1+ and 2+ can also rapidly evolve to the BDK (1-H)+ and (2-H)+, respectively, via hydrogen gas evolution through a bimolecular homolytic pathway. Finally, both complexes are demonstrated to be active for the proton reduction reaction in DMF at Eapp = -1.8 V vs Fc+/0, being the active species the one-electron-reduced derivative 1-H and 2-H

Redox Metal-Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

Water oxidation catalysis stands out as one of the most important reactions to design practical devices for artificial photosynthesis. Use of late first-row transition metal (TM) complexes provides an excellent platform for the development of inexpensive catalysts with exquisite control on their electronic and structural features via ligand design. However, the difficult access to their high oxidation states and the general labile character of their metal–ligand bonds pose important challenges. Herein, we explore a copper complex (1²⁻) featuring an extended, π-delocalized, tetra-amidate macrocyclic ligand (TAML) as water oxidation catalyst and compare its activity to analogous systems with lower π-delocalization (2²⁻ and 3²⁻). Their characterization evidences a special metal–ligand cooperativity in accommodating the required oxidative equivalents using 1²⁻ that is absent in 2²⁻ and 3²⁻. This consists of charge delocalization promoted by easy access to different electronic states at a narrow energy range, corresponding to either metal-centered or ligand-centered oxidations, which we identify as an essential factor to stabilize the accumulated oxidative charges. This translates into a significant improvement in the catalytic performance of 1²⁻ compared to 2²⁻ and 3²⁻ and leads to one of the most active and robust molecular complexes for water oxidation at neutral pH with a k_(obs) of 140 s⁻¹ at an overpotential of only 200 mV. In contrast, 2²⁻ degrades under oxidative conditions, which we associate to the impossibility of efficiently stabilizing several oxidative equivalents via charge delocalization, resulting in a highly reactive oxidized ligand. Finally, the acyclic structure of 3²⁻ prevents its use at neutral pH due to acidic demetalation, highlighting the importance of the macrocyclic stabilization

The crystal and molecular structure of 2,7-di-tert-butyl-4,5,9,10-tetraphenylbenzo[1,2,:4,5]dicyclobutadiene: an exceptionally long C–C aromatic bond

The X-ray determined structure of the title compound is reported; it was found that the annelated bonds are the longest observed in a benzene derivative [1.540(5) Å]; ab initio calculations (at the B3LYP/6-31G* and MP2/6-31G* levels of theory) were used in order to understand the electronic and structural properties of the compound

Unravelling the Mechanistic Pathway of the Hydrogen Evolution Reaction Driven by a Cobalt Catalyst

Acord transformatiu CRUE-CSICA cobalt complex bearing a κ-NP ligand is presented (1 or Co(L), where L is (1E,1'E)-1,1'-(pyridine-2,6-diyl)bis(N-(3-(diphenylphosphanyl)propyl)ethan-1-imine). Complex 1 is stable under air at oxidation state Co thanks to the π-acceptor character of the phosphine groups. Electrochemical behavior of 1 reveals a two-electron Co/Co oxidation process and an additional one-electron reduction, which leads to an enhancement in the current due to hydrogen evolution reaction (HER) at E=−1.6 V vs Fc/Fc. In the presence of 1 equiv of bis(trifluoromethane)sulfonimide, 1 forms the cobalt hydride derivative Co(L)-H (2), which has been fully characterized. Further addition of 1 equiv of CoCp* (Cp* is pentamethylcyclopentadienyl) affords the reduced Co(L)-H (2) species, which rapidly forms hydrogen and regenerates the initial Co(L) (1). The spectroscopic characterization of catalytic intermediates together with DFT calculations support an unusual bimolecular homolytic mechanism in the catalytic HER with 1

Disseny d'un ànode molecular capaç de realitzar un milió de cicles en la catàlisi d'oxidació d'aigua

L'obtenció de H2 com a vector energètic a partir de l'aigua i l'energia solar és una alternativa interessant als combustibles fòssils. La seva obtenció a través de la dissociació de l'aigua (water splitting) requereix catalitzadors que disminueixin la barrera energètica de les dues semireaccions involucrades: l'oxidació de l'aigua a O2 i la reducció de protons a H2. El desenvolupament de nous catalitzadors permet millorar el coneixement dels mecanismes de reacció i dissenyar-ne de nous amb propietats catalítiques avançades. En aquest treball presentem la immobilització d'un complex molecular altament actiu en l'oxidació de l'aigua, el qual és capaç de fer un milió de cicles catalítics.Molecular hydrogen is a promising candidate for replacing fossil fuels. The production of this gas by water splitting requires catalysts to speed up the respective semi-reactions: oxidation of water to O2 and reduction of protons to H2. The development of these catalysts helps to provide a better understanding of the catalytic pathways, allowing the rational design of new active species. In this study the immobilization of a highly active water oxidation molecular catalyst is achieved, reaching over 1 million TONs under catalytic conditions. Keywords: Water oxidation, catalyst immobilization

Structural preferences in phosphanylthiolato platinum(II) complexes

The transition-metal complexes of heterotopic phosphanylthiolato ligands are useful in various reactions which depend on the stereochemistry of the complexes. Bis-chelate complex [Pt(SCH₂CH₂PPh₂-κ²P,S₂)] (1) was obtained in good yields by direct base-free substitution reaction of the corresponding phosphanylthiol (HSCH₂CH₂PPh₂) with K₂PtCl₄ or by oxidative addition of the same phosphanylthiol to Pt(PPh₃)₄. In agreement with the antisymbiosis rule, complex 1 shows a cis -P,P arrangement in solid state crystallizing in the monoclinic system (C2 /c). Density functional theory (DFT) calculations on 1 reveal the right characteristics for the preferred cis -P,P arrangement, rationalizing its formation. Direct base-free reaction of [PtCl₂(1,5-cyclooctadiene)] with one equivalent of the same phosphanylthiol produce the trinuclear complex [PtCl(μ-SCH₂CH₂PPh₂-κ²P,S)]₃ (2) instead of the binuclear structure common in palladium and nickel derivatives. Crystals of 2 are triclinic (P ) showing a sulfur-bridging edge-sharing cyclic trinuclear complex with square-planar coordination geometry around the platinum atoms and a Pt₃S₃ cycle in skew-boat conformation. This preference for the trinuclear structure was rationalized mechanistically and through conceptual DFT