Marta Martínez Belmonte

Simple, stable, and easily accessible well-defined CuCF3 aromatic trifluoromethylating agents.

matic building blocks are made by a Swarts-type process involving exhaustive chlorination of a methyl group on the ring and subsequent Cl/F exchange on the resultant ArCCl3 with HF. This process deals with hazardous materials and generates large quantities of chlorine waste. An ecologically friendly alternative to the Swarts reaction is the direct introduction of a CF3 group into the desired position on the ring. This has been achieved by coppermediated or -catalyzed and palladium-mediated or -catalyzed trifluoromethylation of aromatic substrates. The most widely utilized are the Cu CF3 reagents, originally discovered by McLoughlin and Thrower and further developed by Kobayashi and Kumadaki for stoichiometric trifluoromethylation of haloarenes. These reagents, which have been known for over 40 years, are still poorly defined, and their structure and composition remain unknown. In their classic report on the F NMR spectroscopy studies of “CuCF3”, Wiemers and Burton [9] identified these compounds as “elusive and complex species”. Understanding mechanisms of trifluoromethylation reactions with Cu reagents is important for further progress in the area. This understanding, however, is hardly conceivable without studies on well-defined CF3 Cu I complexes that can trifluoromethylate aromatic electrophiles. Such complexes are extremely rare, being limited to a few derivatives of only one type of ligand, N-heterocyclic carbenes (NHCs). Vicic and co-workers have recently prepared a handful of air-sensitive complexes of the type [(NHC)Cu(CF3)] and demonstrated their ability to trifluoromethylate iodoarenes. Air-stable well-defined Cu trifluoromethylating reagents that are easy to make and handle are still unknown. Herein we report a highyielding simple preparation, full characterization, and aromatic trifluoromethylation reactions of [(Ph3P)3Cu(CF3)] (1), a remarkably airstable Cu trifluoromethyl complex. Complex 1 has been previously prepared by Komiya et al. by a multistep route requiring an organocopper reagent. Although microanalytical data and room-temperature NMR (H, F, P) and IR spectroscopic data for 1 have been provided, structural data, solution behavior, and reactivity studies for 1 have not been reported. We have developed the first organocopper-free, exceedingly simple and efficient synthesis of 1 (Scheme 2). It was found that [(Ph3P)3Cu(F)]·2MeOH [13] (2) smoothly reacted

Shape-persistent octanuclear zinc salen clusters: synthesis, characterization, and catalysis.

We describe a selective and template-controlled synthesis of a series of Zn(8) metal complexes based on a bis-nucleating salen ligand scaffold. Our results, a combination of X-ray analysis and solution studies, show that discrete, shape-persistent metal clusters can be prepared in high yield. Their activity in organic carbonate catalysis is a function of the metal-connecting fragment present in the exterior of the cluster complex. The high stability of the clusters has been confirmed by (1)H, (13)C (DEPTQ) and DOSY NMR, gel permeation chromatography, high-performance liquid chromatography, and mass spectrometry.

A Recyclable Trinuclear Bifunctional Catalyst Derived from a Tetraoxo Bis-Zn(salphen) Metalloligand

A tetraoxo bis-Zn(salphen) supramolecular host can bind various divalent metal salts, thereby providing access to trinuclear bifunctional systems that incorporate both Lewis acid sites and dynamically bound nucleophilic anions. The formation of these trinuclear species was investigated and their stability features were also determined. The application of these trinuclear complexes as bifunctional catalysts was evaluated in the formation of cyclic organic carbonates from epoxides and CO(2). The catalytic data, in combination with control experiments, clearly demonstrate that these trinuclear compounds show much higher recycling potential compared to various control compounds and they can be used in up to five cycles without an observable loss in activity. Furthermore, this new recyclable catalytic system does not require any additives and can be applied under solvent-free conditions.

[6]Saddlequat: a [6]helquat captured on its racemization pathway

A dicationic [6]helicene congener captured on the racemization pathway in its saddle-shaped geometry is introduced. Synthesis, structure, resolution, and dynamic properties of this chiral [6]saddlequat in-between and its highly stereocontrolled transformation into enantiopure [6]helquat are discussed and demonstrated. The dynamic aspects established by experiment and supported by detailed DFT-D calculations are presented visually in the form of a movie (electronic table-of-contents and electronic supplementary information). The title [6]saddlequat was found to be an isolable chiral species on the entirely chiral enantiomerization pathway of a [6]helquat that is discussed as an example of Mislows “rubber glove” molecule.

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. Considering the challenging nature of these coupling reactions, the isolated yields of the targeted bio-carbonates are reasonable and in most cases in the range 50-60 %. The first crystal structures of tri-substituted terpene based cyclic carbonates are reported and their stereoconnectivity suggests that their formation proceeds through a double inversion pathway.

Practical Approach to Structurally Diverse Monoimine Salts and Nonsymmetrical Metallosalphen Complexes

A practical approach toward the synthesis of monoimine NBu(4) salts derived from Zn(salphen) complexes is described. The method involves nucleophilic addition of the hydroxide anion to the imine bond followed by hydrolysis. These monoimines provide accessible and useful reagents for the synthesis of (chiral) metallosalens with fine-tunable properties.

Versatile Switching in Substrate Topicity: Supramolecular Chirality Induction in Di‐ and Trinuclear Host Complexes

Supramolecular chirality effects have been achieved both for ditopic and monotopic substrates by using a programmable bis-salphen scaffold that incorporates either two or three Zn nuclei. The dinuclear host shows preferential chirogenesis in the presence of ditopic systems, whereas effective chirality transfer to the trinuclear complex is realized through monotopic binding. The mode of binding in the trinuclear host has been investigated through X-ray crystallography, CD measurements, UV/Vis spectroscopy, and DFT analysis. The bis-salphen scaffold holds promise for the development of substrate-specific host systems useful for determination of the absolute configuration of various types of organic molecules.

Well-Defined CuC2F5 Complexes and Pentafluoroethylation of Acid Chlorides†

Four new well-defined Cu(I) complexes bearing a C2 F5 ligand have been prepared and fully characterized: [(Ph3 P)2 CuC2 F5 ] (2), [(bpy)CuC2 F5 ] (3), [(Ph3 P)Cu(phen)C2 F5 ] (4), and [(IPr*)CuC2 F5 ] (5). X-ray structures of all four have been determined, showing that the C2 F5 -ligated Cu atom can be di- (5), tri- (2 and 3), and tetracoordinate (4). The mixed phen-PPh3 complex 4 is a highly efficient fluoroalkylating agent for a broad variety of acid chlorides. This high-yielding transformation represents the first general method for the synthesis of RCOC2 F5 from the corresponding RCOCl.

A Short Desymmetrization Protocol for the Coordination Environment in Bis-salphen Scaffolds

A remarkable short preparation of desymmetrized bis-salphen scaffolds is presented. The protocol consists of an hydroxide-mediated hydrolysis of Lewis acidic bis-Zn(salphen) complexes yielding C(s)-symmetric diimine/amine salts that can be selectively transformed into bis-salphens with dissymmetric substitution patterns within each salphen unit under mild conditions. These isolated nonsymmetrical bis-salphen derivatives do not show signs of imine scrambling or decomposition due to a metal template effect. A possible rationale is provided for the formation and isolation of one of the intermediate bis-phenolate salts, and the hypothesis involves H-bond directed hydrolysis of the nearest located imine bond across the bis-salphen scaffold.

Strong asymmetric hydrogen bonding in 2-(oxamoylamino)ethylammonium oxamate-oxamic acid (1/1)

The title compound, C(4)H(10)N(3)O(2)(+) x C(2)H(2)NO(3)(-) x C(2)H(3)NO(3), contains at least 11 distinct hydrogen-bond interactions showing a great variety of bond strengths. The shortest and strongest hydrogen bond [O...O = 2.5004 (12) A] is found between the uncharged oxamic acid molecule and the oxamate monoanion. The grouping formed by such a strong hydrogen bond can thus be considered as a hydrogen bis(oxamate) monoanion. It lacks crystallographic symmetry and the two oxamate groups have different conformations, showing an asymmetric hydrogen-bond interaction. Significantly, the asymmetry allows us to draw a direct comparison of site basicity for the two inequivalent carboxylate O atoms in the planar oxamate anion. The constituent molecular ions of (I) form ribbons, where all amide and carboxylate groups are coplanar. Graph-set analysis of the hydrogen-bonded networks reveals the R(2)(2)(10) and R(2)(2)(9) homodromic nets as important structure-directing motifs, which appear to be a common feature of many oxamate-containing compounds.