Cu-Catalyzed Asymmetric Synthesis of γ-Amino Alcohols Featuring Tertiary Carbon Stereocenters.

Alkyne-functionalized oxetanes are presented as versatile substrates that in combination with amine reagents can be transformed into structurally diverse, chiral γ-amino alcohols featuring a tetrasubstituted tertiary stereocenter under Cu catalysis. Control experiments demonstrate the privileged nature of these oxetane precursors in terms of yield and asymmetric induction levels in the developed protocol, and postsynthetic modifications offer an easy way to access more advanced synthons.

An Expedient Radical Approach for the Decarboxylative Synthesis of Stereodefined All-Carbon Tetrasubstituted Olefins.

We report a user-friendly approach for the decarboxylative formation of stereodefined and complex tri- and tetra-substituted olefins from vinyl cyclic carbonates and amines as radical precursors. The protocol relies on easy photo-initiated α-amino-radical formation followed by addition onto the double bond of the substrate resulting in a sequence involving carbonate ring-opening, double bond relay, CO extrusion and finally O-protonation. The developed protocol is efficient for both mismatched and matched polarity substrate combinations, and the scope of elaborate stereodefined olefins that can be forged including drug-functionalized derivatives is wide, diverse and further extendable to other types of heterocyclic and radical precursors.

Catalytic Domino Three-Component Synthesis of Functionalized Heterocycles from Carbon Dioxide.

A catalytic domino, three-component reaction has been developed for the transformation of carbon dioxide into functionalized six-membered cyclic carbonates. The catalytic process combines an initial carboxylative cyclization of β-epoxy alcohols followed by an oxa-Michael reaction affording an unparalleled scope of heterocyclic structures. The wide range of functional groups, including free-alcohols, empowers the access to a range of products including C-oxo-based bicyclic heterocycles.

Ni-Catalyzed Regio- and Enantioselective Homoallylic Coupling: Synthesis of Chiral Branched 1,5-Dienes Featuring a Quaternary Stereogenic Center and Mechanistic Analysis.

Asymmetric synthesis of small molecules comprising quaternary stereogenic carbon centers represents a challenging objective. Here regio- and enantioselective synthesis of chiral 1,5-dienes featuring quaternary stereocenters is reported via nickel-promoted by reductive homoallylic coupling. The developed methodology features an atypical preference for the formation of unusual branched regioisomers (rr >20 : 1) in a sterically challenging allylic substitution event and furnishes the products with enantiomeric ratios of up to 98 : 2 and with high chemo- and E-selectivity.

Comprehensive Mechanistic Scenario for the Cu-Mediated Asymmetric Propargylic Sulfonylation Forging Tertiary Carbon Stereocenters.

Metal-catalyzed propargylic transformations represent a powerful tool in organic synthesis to achieve new carbon-carbon and carbon-heteroatom bonds. However, detailed knowledge about the mechanistic intricacies related to the asymmetric formation of propargylic products featuring challenging heteroatom-substituted tertiary stereocenters is scarce and therefore provides an inspiring challenge. Here, we present a meticulous mechanistic analysis of a propargylic sulfonylation reaction promoted by a chiral Cu catalyst through a combination of experimental techniques and computational studies.

Silver-Mediated Cascade Synthesis of Functionalized 1,4-Dihydro-2H-benzo-1,3-oxazin-2-ones from Carbon Dioxide.

A conceptually novel catalytic domino approach is presented for the synthesis of highly functional 1,4-dihydro-2H-1,3-benzoxazine-2-one derivatives. Key to the chemoselectivity is a proper design of the precursor to override thermodynamically favored parasitic cyclization processes and empower the formation of the desired product through Thorpe-Ingold effects. The synthetic diversity of these CO -based heterocycles is further demonstrated, and the isolation of a reaction intermediate supports an unusual ring-expansion sequence from an α-alkylidene, five-membered cyclic carbonate to a six-membered cyclic carbamate by N-induced isomerization.

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

Two Ni complexes are reported with κ-PN β-diimino (BDI) ligands with the general formula [Ni(XBDI)](BF), where BDI is -(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 (BF) and X = Ph for (BF). Electrochemical analysis together with UV-vis and NMR spectroscopy in acetonitrile and dimethylformamide (DMF) indicates the conversion of the β-diimino complexes and to the negatively charged β-diketiminato (BDK) analogues () and () via deprotonation in DMF. Moreover, further electrochemical and spectroscopy evidence indicates that the one-electron-reduced derivatives and can also rapidly evolve to the BDK () and (), respectively, via hydrogen gas evolution through a bimolecular homolytic pathway.

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

A cobalt complex bearing a κ-N P 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.

Room-Temperature-Stable Magnesium Electride via Ni(II) Reduction.

Herein, we report the synthesis of highly reduced bipyridyl magnesium complexes and the first example of a stable organic magnesium electride supported by quantum mechanical computations and X-ray diffraction. These complexes serve as unconventional homogeneous reductants due to their high solubility, modular redox potentials, and formation of insoluble, non-coordinating byproducts. The applicability of these reductants is showcased by accessing low-valent (bipy)Ni(0) species that are challenging to access otherwise.

Electrocatalytic water oxidation from a mixed linker MOF based on NU-1000 with an integrated ruthenium-based metallo-linker.

A novel tetratopic metallo-linker, [Ru(tda)(py(PhCOOH))], 1, (tda = 2,2':6',2''-terpyridine-6,6''-dicarboxylate; py(PhCOOH) = (4,4'-(pyridine-3,5-diyl)dibenzoic acid), that is structurally based on one of the most active molecular water oxidation catalysts has been prepared and fully characterized, including single crystal X-ray diffraction. 1 bears geometric similarities to HTBAPy (HTBAPy = 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetrabenzoic acid), the native linker in NU-1000, which offers the possibility to synthesize NU-1000-Ru mixed linker MOFs solvothermally. Mixed linker MOF formation was demonstrated by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM), and Ru linker incorporation confirmed by FT-IR, energy-dispersive X-ray (EDX) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES).

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 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 aminotriphenolate complex/DIPEA catalyst.

Synthesis, Structure, and Ammonia Oxidation Catalytic Activity of Ru-NH Complexes Containing Multidentate Polypyridyl Ligands.

Ammonia (electro)oxidation with molecular catalysts is a rapidly developing topic with wide practical applications ahead. We report here the catalytic ammonia oxidation reaction (AOR) activity using [Ru(tda-κ-NO)(py)], , (tda is 2,2':6',2''-terpyridine-6,6''-dicarboxylate; py is pyridine) as a catalyst precursor. Furthermore, we also describe the rich chemistry associated with the reaction of Ru-tda and Ru-tPa (tPa is 2,2':6',2''-terpyridine-6,6''-diphosphonate) complexes with NH and NH using [Ru(tda-κ-NO)(dmso)Cl] (dmso is dimethyl sulfoxide) and [Ru(tPa-κ-NO)(py)], , as synthetic intermediates, respectively.

Isolation of a Ru(IV) side-on peroxo intermediate in the water oxidation reaction.

The electrons that nature uses to reduce CO during photosynthesis come from water oxidation at the oxygen-evolving complex of photosystem II. Molecular catalysts have served as models to understand its mechanism, in particular the O-O bond-forming reaction, which is still not fully understood. Here we report a Ru(IV) side-on peroxo complex that serves as a 'missing link' for the species that form after the rate-determining O-O bond-forming step.

Consecutive Ligand-Based Electron Transfer in New Molecular Copper-Based Water Oxidation Catalysts.

Water oxidation to dioxygen is one of the key reactions that need to be mastered for the design of practical devices based on water splitting with sunlight. In this context, water oxidation catalysts based on first-row transition metal complexes are highly desirable due to their low cost and their synthetic versatility and tunability through rational ligand design. A new family of dianionic bpy-amidate ligands of general formula H LN (LN is [2,2'-bipyridine]-6,6'-dicarboxamide) substituted with phenyl or naphthyl redox non-innocent moieties is described.

Asymmetric Synthesis of Homoallylic Alcohols Featuring Vicinal Tetrasubstituted Carbon Centers via Dual Pd/Photoredox Catalysis.

Dual palladium/photoredox-catalysis provides an effective method for the decarboxylative asymmetric synthesis of vicinal α,β-tri/tetra- or α,β-tetrasubstituted homoallylic alcohols using Hantzsch-type esters as radical precursors. This mild methodology capitalizes on vinyl cyclic carbonates as accessible reagents providing the target molecules in appreciable to good yields, high branch selectivity, and enantiomeric ratios of up to 94:6, making it a rare example of using prochiral electrophiles for the creation of vicinal congested carbon centers.

Air-stable 18-electron adducts of Schrock catalysts with tuned stability constants for spontaneous release of the active species.

Schrock alkylidenes are highly versatile, very active olefin metathesis catalysts, but their pronounced sensitivity to air still hinders their applications. Converting them into more robust but inactive 18-electron adducts was suggested previously to facilitate their handling. Generating the active species from the inactive adducts, however, required a high-temperature Lewis acid treatment and resulted in an insoluble by-product, limiting the practicality of the methodology.

Pd/Cu Dual-Catalyzed Asymmetric Synthesis of Highly Functional All-Carbon Quaternary Stereocenters from Vinyl Carbonates.

The challenging metal-catalyzed asymmetric synthesis of highly functional quaternary carbon centers using decarboxylative C(sp )-C(sp ) bond formation reactions is reported. The key substrate, a vinyl cyclic carbonate, is activated to provide concomitantly both the requisite nucleophile (by formal umpolung) and electrophile reaction partner preceding the asymmetric cross-coupling process. A wide screening of reaction conditions, additives and catalyst precursors afforded a protocol that gave access to a series of compounds featuring densely functionalized, elusive quaternary carbon stereocenters in appreciable yield and with enantiomeric ratios (er's) of up to 90 : 10.

Synthesis, Characterization, and Water Oxidation Activity of Isomeric Ru Complexes.

The synthesis and characterization of the isomeric ruthenium complexes with the general formula and [Ru(trpy)(qc)X] (trpy is 2,2':6',2″-terpyridine, qc is 8-quinolinecarboxylate, and , X = Cl, = 0; and , X=OH, = 1) with respect to the relative disposition of the carboxylate and X ligands are reported. For comparison purposes, another set of ruthenium complexes with general formula and [Ru(trpy)(pic)(OH)] (pic is 2-picolinate (-, -)) have been prepared. The complexes with a qc ligand show a more distorted geometry compared to the complexes with a pic ligand.

A broad view on the complexity involved in water oxidation catalysis based on Ru-bpn complexes.

A new Ru complex with the formula [Ru(bpn)(pic)]Cl (where bpn is 2,2'-bi(1,10-phenanthroline) and pic stands for 4-picoline) (1Cl) is synthesized to investigate the true nature of active species involved in the electrochemical and chemical water oxidation mediated by a class of N4 tetradentate equatorial ligands. Comprehensive electrochemical (by using cyclic voltammetry, differential pulse voltammetry, and controlled potential electrolysis), structural (X-ray diffraction analysis), spectroscopic (UV-vis, NMR, and resonance Raman), and kinetic studies are performed. 1 undergoes a substitution reaction when it is chemically (by using NaIO) or electrochemically oxidized to Ru, in which picoline is replaced by an hydroxido ligand to produce [Ru(bpn)(pic)(OH)] (2).

Water oxidation electrocatalysis using ruthenium coordination oligomers adsorbed on multiwalled carbon nanotubes.

Photoelectrochemical cells that utilize water as a source of electrons are one of the most attractive solutions for the replacement of fossil fuels by clean and sustainable solar fuels. To achieve this, heterogeneous water oxidation catalysis needs to be mastered and properly understood. The search continues for a catalyst that is stable at the surface of electro(photo)anodes and can efficiently perform this reaction at the desired neutral pH.

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.

Synthesis, Electrochemical Characterization, and Water Oxidation Chemistry of Ru Complexes Containing the 2,6-Pyridinedicarboxylato Ligand.

The tridentate meridional ligand pyridyl-2,6-dicarboxylato (pdc) has been used to prepare complexes [Ru(pdc-κ-NO)(DMSO)Cl] (), [Ru(pdc-κ-NO)(bpy)(DMSO)] (), and {[Ru(pdc-κ-NO)(bpy)](μ-O)} (), where bpy = 2,2'-bipyridine. All complexes have been fully characterized through spectroscopic, electrochemical, and single-crystal X-ray diffraction techniques. Compounds and show S → O linkage isomerization of the DMSO ligand upon oxidation from Ru to Ru, and thermodynamic and kinetic data have been obtained from cyclic voltammetry experiments.

Analysis of the Active Species Responsible for Water Oxidation Using a Pentanuclear Fe Complex.

Water splitting with sunlight is today one of the most promising strategies that can be used to start the imperatively needed transition from fossil to solar fuels. To achieve this, one of the key reactions that need to be mastered is the electrocatalytic oxidation of water to dioxygen. Great developments have been achieved using transition metal complexes mainly based on Ru, but for technological applications it is highly desirable to be able to use earth-abundant transition metals.

Effect of Mechanochemical Recrystallization on the Thermal Hysteresis of 1D Fe-triazole Spin Crossover Polymers.

The thermal hysteresis in the cooperative spin crossover (SCO) polymer [Fe(trz)(Htrz)][BF] () has been tuned by a simple ball milling grinding process. Mechanical treatment affects the size and morphology of the crystallite domains, as confirmed by multiple complementary techniques, including ESEM, DLS, and PXRD data. Upon milling, the regular cubic shape particles recrystallize with slightly different unit cell parameters and preferential orientation.