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.

Crystal structure of a new phen-yl(morpholino)methane-thione derivative: 4-[(morpholin-4-yl)carbothioyl]benzoic acid.

4-[(Morpholin-4-yl)carbothioyl]benzoic acid, CHNOS, a novel phen-yl(morpholino)methane-thione derivative, crystallizes in the monoclinic space group 2/. The morpholine ring adopts a chair conformation and the carb-oxy-lic acid group is bent out slightly from the benzene ring mean plane. The mol-ecular geometry of the carb-oxy-lic group is characterized by similar C-O bond lengths [1.

Capturing Elusive Cobaltacycle Intermediates: A Real-Time Snapshot of the Cp*Co -Catalyzed Oxidative Alkyne Annulation.

Despite Cp*Co catalysts having emerged as a very attractive alternative to noble transition metals for the construction of heterocyclic scaffolds through C-H activation, the structure of the reactive species remains uncertain. Herein, we report the identification and unambiguous characterization of two long-sought cyclometalated Cp*Co complexes that have been proposed as key intermediates in C-H functionalization reactions. The addition of MeCN as a stabilizing ligand plays a crucial role, allowing the access to otherwise highly reactive species.

Stereoselective and Versatile Preparation of Tri- and Tetrasubstituted Allylic Amine Scaffolds under Mild Conditions.

Significant progress has been observed in recent years in the synthesis of allylic amines, which are important building blocks in synthetic chemistry. Most of these processes are effective toward the preparation of allylic amines, with limited potential to introduce three or four different substituents on the olefinic unit in a stereocontrolled fashion. Therefore, the discovery of a mild and operationally simple protocol allowing such challenging stereoselective synthesis of multisubstituted allylic amines remains an inspiring target.

Highly Efficient Catalytic Formation of (Z)-1,4-But-2-ene Diols Using Water as a Nucleophile.

The first general catalytic and highly stereoselective formation of (Z)-1,4-but-2-ene diols is described from readily available and modular vinyl-substituted cyclic carbonate precursors using water as a nucleophilic reagent. These 1,4-diol scaffolds can be generally prepared in high yields and with ample scope in reaction partners using a simple synthetic method that does not require the presence of any additive or any special precaution unlike the stoichiometric approaches reported to date. Control experiments support the mechanistic view that hyperconjugation within the catalytic intermediate after decarboxylation plays an imperative role to control the stereoselective outcome of these reactions.

Catalytic Coupling of Carbon Dioxide with Terpene Scaffolds: Access to Challenging Bio-Based Organic Carbonates.

The challenging coupling of highly substituted terpene oxides and carbon dioxide into bio-based cyclic organic carbonates catalyzed by Al(aminotriphenolate) complexes is reported. Both acyclic as well as cyclic terpene oxides were used as coupling partners, showing distinct reactivity/selectivity behavior. Whereas cyclic terpene oxides showed excellent chemoselectivity towards the organic carbonate product, acyclic substrates exhibited poorer selectivities owing to concomitant epoxide rearrangement reactions and the formation of undesired oligo/polyether side products.

Substrate-Controlled Product Divergence: Conversion of CO2 into Heterocyclic Products.

Substituted epoxy alcohols and amines allow substrate-controlled conversion of CO2 into a wide range of heterocyclic structures through different mechanistic manifolds. This new approach results in an unusual scope of CO2-derived products by initial activation of CO2 through either the amine or alcohol unit, thus providing nucleophiles for intramolecular epoxy ring opening under mild reaction conditions. Control experiments support the crucial role of the amine/alcohol fragment in this process with the nucleophile-assisted ring-opening step following an SN i pathway, and a 5-exo-tet cyclization, thus leading to heterocyclic scaffolds.

Molecular Motion and Conformational Interconversion of Ir(I)·COD Included in Rebek's Self-Folding Octaamide Cavitand.

We report experimental and theoretical evidence of restrained axial rotation for heteroleptic L2·Ir(I)·1,5-cyclooctadiene (COD) complexes included in the aromatic cavity of Rebek's self-folding octaamide cavitand. At 298 K, the axial spinning motion of the included organometallic guests was slow on the (1)H NMR time scale and produced a proton spectrum for the bound host indicative of C2 symmetry. Signals corresponding to aromatic protons of the bound host coalesced at 323 K, indicating that the spinning process of the included guest became fast on the (1)H NMR time scale and that the complex approached C4 symmetry.

Stereodivergent Carbamate Synthesis by Selective in Situ Trapping of Organic Carbonate Intermediates.

Trans carbamates have been prepared in a diastereoselective approach by a judicious one-pot combination of organic carbonates, prepared in situ, and suitable amine reagents under appropriate reaction conditions. This unprecedented approach allows for stereodivergence from a single oxirane substrate with easy access to both cis and trans carbamate isomers with high stereoselectivity (>19:1 d.r.

Hypervalent Activation as a Key Step for Dehydrogenative ortho C-C Coupling of Iodoarenes.

Building on earlier results, a direct metal-free α-arylation of substituted cyclic 1,3-diones using ArI(O2CCF3)2 reagents has been developed; unlike other arylative approaches, the arylated products retain the iodine substituent ortho to the newly formed C-C bond. The mechanism is explored by using DFT calculations, which show a vanishingly small activation barrier for the C-C bond-forming step. In fact, taking advantage of an efficient in situ hypervalent activation, the iodoarenes are shown to undergo a cross-dehydrogenative C-C coupling at the C-H ortho to the iodine.

The Trifluoromethyl Anion.

First evidence for the existence of free trifluoromethyl anion CF3 (-) has been obtained. The 3D-caged potassium cation in [K(crypt-222)](+) is inaccessible to CF3 (-) , thus rendering it uncoordinated ("naked"). Ionic [K(crypt-222)](+) CF3 (-) has been characterized by single-crystal X-ray diffraction, solution NMR spectroscopy, DFT calculations, and reactivity toward electrophiles.

Easy Excited-State Trapping and Record High TTIESST in a Spin-Crossover Polyanionic Fe(II) Trimer.

Reaction of the polysulfonated triazole ligand L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) with iron(II) salts in water yields the trimeric species [Fe3(μ-L)6(H2O)6](6-). This polyanion, as the dimethylammonium salt, shows a thermally induced spin transition above room temperature for the central Fe position in the trimer with a large hysteresis cycle (>85 K) and remarkably slow dynamics. This allows easy quenching of the metastable high-spin (HS) state via gradual cooling (5 K min(-1)).

Highly Chemoselective Catalytic Coupling of Substituted Oxetanes and Carbon Dioxide.

The chemoselective coupling of oxetanes and carbon dioxide to afford functional, heterocyclic organic compounds known as six-membered cyclic carbonates remains a challenging topic. Here, an effective method for their synthesis relying on the use of Al catalysis is described. The catalytic reactions can be carried out with excellent selectivity for the cyclic carbonate product tolerating various (functional) groups present in the 2- and 3-position(s) of the oxetane ring.

Easy access to the copper(III) anion [Cu(CF3 )4 ](-).

CuCl or pre-generated CuCF3 reacts with CF3 SiMe3 /KF in DMF in air to give [Cu(CF3 )4 ](-) quantitatively. [PPN](+) , [Me4 N](+) , [Bu4 N](+) , [PhCH2 NEt3 ](+) , and [Ph4 P](+) salts of [Cu(CF3 )4 ](-) were prepared and isolated spectroscopically and analytically pure in 82-99% yield. X-ray structures of the [PPN](+) , [Me4 N](+) , [Bu4 N](+) , and [Ph4 P](+) salts were determined.

Synthesis and structural features of Co(II) and Co(III) complexes supported by aminotrisphenolate ligand scaffolds.

Co(II) complexes of aminotrisphenolate ((ArO)3N(3-)) ligands can be prepared straightforwardly in high yield. X-ray analysis reveals these complexes to comprise of two different hemispheres, one containing an anionic Co((ArO)3N)(-) and the other a cationic (ArO)3NH(+) unit, which are associated through hydrogen bonding. These Co(II) complexes can be easily converted into their Co(III) analogues in air in the presence of suitable bases such as dimethylaminopyridine and 2,2'-bipyridine, and the structural features and magnetic properties of these latter compounds are also reported.

An alternative to the classical α-arylation: the transfer of an intact 2-iodoaryl from ArI(O₂CCF₃)₂.

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes.

Carbon dioxide as a protecting group: highly efficient and selective catalytic access to cyclic cis-diol scaffolds.

The efficient and highly selective formation of a wide range of (hetero)cyclic cis-diol scaffolds using aminotriphenolate-based metal catalysts is reported. The key intermediates are cyclic carbonates, which are obtained in high yield and with high levels of diastereo- and chemoselectivity from the parent oxirane precursors and carbon dioxide. Deprotection of the carbonate structures affords synthetically useful cis-diol scaffolds with different ring sizes that incorporate various functional groups.

Hysteretic spin crossover above room temperature and magnetic coupling in trinuclear transition-metal complexes with anionic 1,2,4-triazole ligands.

The reaction of 4-(1,2,4-triazol-4-yl)ethanesulfonate (L) with Zn(2+), Cu(2+), Ni(2+), Co(2+), and Fe(2+) gave a series of analogous neutral trinuclear complexes with the formula [M3(μ-L)6(H2O)6] (1-5). These compounds were characterized by single-crystal X-ray diffraction, thermogravimetry, and elemental analysis. The magnetic properties of compounds 2-5 were studied.

Highly active aluminium catalysts for the formation of organic carbonates from CO2 and oxiranes.

Al(III) complexes of amino-tris(phenolate) ligand scaffolds have been prepared to attain highly Lewis acidic catalysts. Combination of the aforementioned systems with ammonium halides provides highly active catalysts for the synthesis of organic carbonates through addition of carbon dioxide to oxiranes with initial turnover frequencies among the highest reported to date within the context of cyclic carbonate formation. Density functional theory (DFT) studies combined with kinetic data provides a rational for the relative high activity found for these Al(III) complexes, and the data are consistent with a monometallic mechanism.

The critical effect of the countercation in the direct cupration of fluoroform with [Cu(OR)2 ](-).

Just a spectator or a key player? The alkali-metal counterion (K(+) ) plays a remarkable key role in the recently discovered cupration reaction of fluoroform with dialkoxycuprates. A total of eight Lewis acid and Lewis base centers synergistically interacting with one another arrange in a stable transition state, providing a low-energy pathway for this unique transformation.

Trifluoromethylation of aryl and heteroaryl halides with fluoroform-derived CuCF3: scope, limitations, and mechanistic features.

Fluoroform-derived CuCF3 recently discovered in our group exhibits remarkably high reactivity toward aryl and heteroaryl halides, performing best in the absence of extra ligands. A broad variety of iodoarenes undergo smooth trifluoromethylation with the "ligandless" CuCF3 at 23-50 °C to give the corresponding benzotrifluorides in nearly quantitative yield. A number of much less reactive aromatic bromides also have been trifluoromethylated, including pyridine, pyrimidine, pyrazine, and thiazole derivatives as well as aryl bromides bearing electron-withdrawing groups and/or ortho substituents.

Supramolecular bulky phosphines comprising 1,3,5-triaza-7-phosphaadamantane and Zn(salphen)s: structural features and application in hydrosilylation catalysis.

The use of the commercially available, bifunctional phosphine 1,3,5-triaza-7-phosphaadamantane (abbreviated as PN3) in conjunction with a series of Zn(salphen) complexes leads to sterically encumbered phosphine ligands as a result of (reversible) coordinative Zn-N interactions. The solid state and solution phase behaviour of these supramolecular ligand systems have been investigated in detail and revealed their stoichiometries in the solid state observed by X-ray crystallography, and those determined in solution by NMR and UV-Vis spectroscopy. Also, upon application of these supramolecular bulky phosphines in hydrosilylation catalysis employing 1-hexene as a substrate, the catalysis data infer the presence of an active Rh species with two coordinated, bulky PN3/Zn(salphen) assembly units having a maximum of three Zn(salphen)s associated per PN3 scaffold, with an excess of bulky phosphines hardly affecting the overall activity.

Merging catalysis and supramolecular aggregation features of triptycene based Zn(salphen)s.

A series of trinuclear, triptycene-based metallosalphen complexes (M = Zn, Ni) have been prepared incorporating various peripheral substituents. The introduction of Zn metal centres into these triptycene based salphen ligands gives rise to cross-linking between different triptycene molecules through μ-phenoxo bridges between the Zn metal centres, and variation in the peripheral groups allows the control of the self-assembling properties as shown by UV-Vis titration data. The strong association of these trinuclear Zn3 complexes under relatively apolar conditions has been exploited to recover the complex after its application as a catalyst in the cycloaddition of carbon dioxide to 1,2-epoxyhexane.

Aqueous synthesis of sulfonate-functionalized 1,2,4-triazole ligands and their 2D Cd2+ coordination networks: crystal structure and photoluminescent properties.

We have developed a water-based synthesis for the preparation of 4-substituted 1,2,4-triazole ligands with highly polar functional groups. This general synthetic approach has allowed us to prepare two sulfonate functionalized 4-substituted 1,2,4-triazole anions ( L1(-)= 4-(1,2,4-triazol-4-yl)benzenesulfonate; L2(-)= 4-(1,2,4-triazol-4-yl)ethanesulfonate). Reaction of these ligands with cadmium(II) salts leads to the formation of two novel two-dimensional coordination networks of formula [Cd(L)Cl]n (1, L1; and 2, L2), which were structurally characterized by X-ray diffraction.