Diastereoselective Synthesis of Sulfoxide-Functionalized N-Heterocyclic Carbene Ruthenium Complexes: An Experimental and Computational Study.

The synthesis of sulfoxide-functionalized NHC ligand precursors were carried out by direct and mild oxidation from corresponding thioether precursors with high selectivity. Using these salts, a series of cationic [Ru(II)(η-p-cymene)(NHC-SO)Cl] complexes were obtained in excellent yields by the classical AgO transmetallation route. NMR analyses suggested a chelate structure for the metal complexes, and X-ray diffractometry studies of complexes 4 b, 4 c, 4d and 4 e unambiguously confirmed the preference for the bidentate (κ-C,S) coordination mode of the NHC-SO ligands.

Polymerization/depolymerization of chiral metallo-supramolecular assembly induced by redox change.

We report on the polymerization/depolymerization of chiral metallo-supramolecular assembly by Cu /Cu redox change. By combining a monotopic enantiopure ligand with a ditopic ligand of opposite configuration, ML -type complexes are generated with chiral self-recognition or self-discrimination depending on the oxidation state of copper. In presence of Cu , the formation of heterochiral complexes is favored, thus generating dinuclear species whereas Cu advocates for the formation of homochiral species, namely, a mixture of mononuclear species and metallo-supramolecular polymeric species.

Hyperpositive non-linear effects: enantiodivergence and modelling.

The chiral ligand -methylephedrine (NME) was found to catalyse the addition of dimethylzinc to benzaldehyde in an enantiodivergent way, with a monomeric and a homochiral dimeric complex both catalysing the reaction at a steady state and giving opposite product enantiomers. A change in the sign of the enantiomeric product was thus possible by simply varying the catalyst loading or the ligand ee, giving rise to an enantiodivergent non-linear effect. Simulations using a mathematical model confirmed the possibility of such behaviour and showed that this can lead to situations where a reaction gives racemic products, although the system is composed only of highly enantioselective individual catalysts.

Observation of hyperpositive non-linear effect in catalytic asymmetric organozinc additions to aldehydes.

Asymmetric amplification is a phenomenon that is believed to play a key role in the emergence of homochirality in life. In asymmetric catalysis, theoretical and experimental models have been investigated to provide an understanding of how chiral amplification is possible, in particular based on non-linear effects. Interestingly, it has been proposed a quarter century ago that chiral catalysts, when not enantiopure might even be more enantioselective than their enantiopure counterparts.

Chiral stimuli-responsive metallo-supramolecular assembly induced by Cu/Cu redox change.

We investigated the selective formation of homoleptic and heteroleptic metal complexes controlled by means of the chiral molecular instruction of the ligand and the coordination geometry of the metal. Our results showed that chiral self-recognition or self-discrimination may be induced by the Cu/Cu redox transition using cyclic voltammetry. The further use of chiral ditopic ligands led to metallo-supramolecular copolymers with stimuli-responsive controlled arrangement.

Synthesis, characterization, catalytic and biological application of half-sandwich ruthenium complexes bearing hemilabile (κ2-C,S)-thioether-functionalised NHC ligands.

A series of cationic Ru(ii)(η-p-cymene) complexes with thioether-functionalised N-heterocyclic carbene ligands have been prepared and fully characterized. Steric and electronic influence of the R thioether substituent on the coordination of the sulfur atom was investigated. The molecular structure of three of them has been determined by means of X-ray diffractrometry and confirmed the bidentate (κ-C,S) coordination mode of the ligand.

Chiral Self-Sorting Process with Ditopic Ligands: Alternate or Block Metallopolymer Assembly as a Function of the Metal Ion.

We report an extensive study on the coordination behavior of chiral ditopic bridging ligands, which lead to metallosupramolecular polymers in the presence of Zn(II) and Cu(II) in solution. With the help of UV-vis and circular dichroism spectroscopies, we show that the metallopolymer sequence can be controlled by chirality and by the choice of the metal ion. Although the formation of a block metallopolymer proceeds through the assembly of homoleptic complexes, an alternate metallopolymer may be obtained only when heteroleptic complexes are formed.

Homo- and Heteropolymetallic Complexes of the Hybrid, Ambidentate N-Heterocyclic Carbene Ligand IMes-acac.

The anionic 5-acetylimidazol-2-ylidene-4-olate , named as "IMes-acac", is composed of fused diaminocarbene and acetylacetonato units in the same IMes-based imidazolyl ring. The bifunctional compound is shown to act as an effective, ditopic bridging ligand for transition metal centers. Several new complexes supported by this ligand were prepared, including the complex [RuCl(-Cym)(κ ,-·H)](BF) (), which can be regarded as a metallated imidazolium salt, the homobimetallic complex [((COD)Rh)(RhCl(COD))(μ-1κ ,:2κ -)] (), the heterobimetallic complexes [((-Cym)ClRu)(RhCl(COD))(μ-1κ ,:2κ -)] (), [((-Cym)ClRu)(RhCl(CO))(μ-1κ ,2κ -)] (), [((-Cym)ClRu)(Cu(IPr))(μ-1κ ,:2κ -)] (), the anionic homoleptic Cu(I) complexes [Cu(κ -)]K ([]K) and [Cu(κ -)](NEt) ([](NEt)), and the heterotrimetallic complex [((-Cym)RuCl)(Cu)(μ-1κ ,:3κ -)(μ-2κ ,:3κ -)](PF) ().

Synthesis of alternating metallocopolymers by chiral recognition.

We report the synthesis of chiral enantiopure polytopic bridging ligands, which may lead to the formation of metallosupramolecular polymers with zinc (II) as metal linker. We show that chiral C -symmetric bisoxazoline ligands are useful moieties to efficiently generate heterochiral complexes and thus polymeric entities. The corresponding metallopolymers were further characterized by powder X-ray diffraction (PXRD) to obtain information on the level of crystallinity of our different metallopolymers.

Easy Ruthenium-Catalysed Oxidation of Primary Amines to Nitriles under Oxidant-Free Conditions.

A dehydrogenation of primary amine to give the corresponding nitrile under oxidant- and base-free conditions catalysed by simple [Ru(p-cym)Cl ] with no extra ligand is reported. The system is highly selective for alkyl amines, whereas benzylamine derivatives gave the nitrile product together with the imine in a ratio ranging from 14:1 to 4:1 depending on the substrate. Preliminary mechanistic investigations have been performed to identify the key factors that govern the selectivity.

Well-defined cationic alkyl- and alkoxide-aluminum complexes and their reactivity with epsilon-caprolactone and lactides.

We describe the synthesis, structure, and reactivity of low-coordinate Al-alkyl and -alkoxide cationic complexes incorporating the sterically bulky aminophenolate bidentate ligand 6-(CH(2)NMe(2))-2-CPh(3)-4-Me-C(6)H(2)O- (N,O). These complexes are derived from the ionization of neutral dialkyl Al complexes (N,O)Al2) (1 a, R=Me; 1 b, R=iBu), readily obtained by alkane elimination between AlR3 and the corresponding aminophenol ligand, with the alkyl abstracting reagents B(C(6)F(5))3 and [Ph(3)C][B(C(6)F(5))4]. The reactions of 1 a,b with B(C(6)F(5))3 yield complicated mixtures or decomposition products, however the ionization of the Al-diisobutyl derivative 1 b with [Ph(3)C][B(C(6)F(5))4] affords a stable four-coordinate Al-PhBr cationic adduct [(N,O)Al(iBu)(PhBr)]+ (3+), as deduced from elemental analysis data.

Synthesis and structural characterization of an azatitanacyclobutene: the key intermediate in the catalytic anti-Markovnikov addition of primary amines to [small alpha]-alkynes.

Reaction of the imidotitanium complexes [Ti(N(t)Bu)(N(2)N(py))(py)](1) and [Ti(N-2,6-C(6)H(3)(i)Pr(2))(N(2)N(py))(py)](2) with phenyl acetylene and tolyl acetylene in toluene gave the corresponding [2+2] cycloaddition products [Ti(N(2)N(py))[kappa(2)-N((t)Bu)CH[double bond]CR]](R = Ph:3, Tol:4) and [Ti(N(2)N(py))[kappa(2)-N(2,6-C(6)H(3)(i)Pr(2))CH[double bond]CR]](R = Ph:5, Tol: 6). Complex 6 is the first example of a key intermediate in the anti-Markovnikov addition of a primary amine to a terminal acetylene which has been structurally characterized by X-ray diffraction.