Alessandro Caselli

[Silver(I)(Pyridine-Containing Ligand)] Complexes As Unusual Catalysts for A3-Coupling Reactions

Two original macrocyclic silver(I)(pyridine-containing ligand) complexes [Ag(I)(Pc-L)] were synthesized and characterized. Their ability to catalyze the coupling among aldehydes, terminal alkynes and amines (A(3)-coupling) was demonstrated. The reaction could be performed under conventional as well as dielectric heating. The catalysts were effective in both cases, but dielectric heating allowed a lower catalyst loading and reduced ratio among reaction partners in shorter reaction times. The reaction scope was broad, including aryl/alkyl aldehydes, aryl/alkyl acetylenes and secondary aliphatic amines. Some unprecedented propargylamines have been prepared. The new catalytic system was also tested with more challenging coupling partners such as aniline and ketones.

Mechanistic Study of the Palladium–Phenanthroline Catalyzed Carbonylation of Nitroarenes and Amines: Palladium–Carbonyl Intermediates and Bifunctional Effects

Palladium-phenanthroline complexes catalyze both the nitroarene carbonylation reaction and the amine oxidative carbonylation reaction to give, depending on the conditions, carbamates and ureas. There is evidence that the key step in both processes is the amine carbonylation. Here, we show that when the reaction is run in methanol key intermediate compounds have the general formula [Pd(RPhen)(COOMe)(2)] (1) (RPhen = 1,10-phenanthroline or one of its substituted derivatives). The kinetics of the reaction of 1 with toluidine in the presence of a carboxylic or phosphorus acid is first-order with respect to complex, acid, and toluidine. A CO atmosphere is also required for the reaction to proceed. Acid dimerization was shown not to be influential under the concentration conditions examined, but reaction between the acid and toluidine is not negligible and a correction has to be applied. Diphenylphosphinic acid is more effective than any carboxylic acid in promoting this reaction, as also observed under catalytic conditions. A series of equilibria and an irreversible acid-assisted proton transfer explain the observed data. Formation of an adduct between complexes of the kind 1 and CO was spectroscopically observed when RPhen = 2,9-Me(2)Phen. Several analogous complexes were also spectroscopically characterized and the X-ray structure of [Pd(2,9-Me(2)Phen)Cl(2)(CO)] was solved. This shows an asymmetric coordination of the nitrogen ligand. Kinetic measurements were also conducted under catalytic conditions. An Eyring plot shows that the effect of the acidic promoter is to decrease the DeltaS(double dagger) value, whereas no positive effect is observed on DeltaH(double dagger). A temperature-dependent correction for the reaction between the acid and aniline and phenanthroline present under the reaction conditions has to be applied. Comparison of the results obtained under stoichiometric and catalytic conditions strongly supports the view that 1 is involved even in the latter and that the acid is acting as a bifunctional promoter.

[Ru(TPP)CO]‐Catalysed Intramolecular Benzylic CH Bond Amination, Affording Phenanthridine and Dihydrophenanthridine Derivatives

Shedding light on azides: [Ru(TPP)CO] (TPP=tetraphenyl porphyrin dianion), white light and O(2) were found to be a suitable catalyst combination to perform the annulation of several biaryl azides. The high chemoselectivity of the process allows the synthesis of phenanthridines and dihydrophenanthridines in good yield and purity.

Rearrangement of N-aryl-2-vinylaziridines to benzoazepines and dihydropyrroles: a synthetic and theoretical study.

Herein we report the one-pot synthesis of several N-heterocyclic compounds by rearrangement reactions of N-aryl-2-vinylaziridines. The optimization of the synthetic methodology employed allowed us to obtain differently substituted 2,5-dihydro-1H-benzo[b]azepines in good yields and purities. The relationship between the nature of the starting N-aryl-2-vinylaziridine and the obtained N-heterocycle was also investigated. Finally, to rationalize all the experimental results reported in this paper a theoretical study was performed that casts light on the reaction mechanism.

Synthesis of C2-symmetrical diamine based on (1R)-(+)-camphor and application to oxidative aryl coupling of naphthols

Abstract The new C 2 -symmetrical 1,2-diamine { N , N ′-bis[(1 R ,2 R ,4 R )-1,7,7-trimethylbicyclo[2.2.1]hept-2-yl]-1,2-ethanediamine} 3 has been synthesized from commercial (1 R )-(+)-camphor 1 and scrutinized as ligand in the oxidative biaryl coupling of naphthol derivatives. Under the optimal conditions employing a Cu(I)- 3 triflate complex (10 mol%) in dichloroethane–MeCN and molecular sieves with air as the oxidant, aryl coupling of naphthol derivatives could be achieved in satisfactory yields (48–90% yield) and ees of up to 65%. The ester moiety at the 3-position of the substrate was found to be crucial for a satisfactory asymmetric induction in the present coupling reaction.

Synthesis of Heterocycles by Intramolecular Cyclization of Organic Azides

A review of synthetic methodologies reported in the last five years that yield N-heterocyclic products by intramolecular cyclization of organic azides with a particular emphasis on transformations catalyzed by metal complexes is presented. These reactions have been classified according to the ring size of the formed heterocycle.

Ruthenium porphyrins-catalyzed atom-efficient amination of C-H bonds by arylazides

Benzylic amines are synthesized in yield up to 90% by the Ru(TPP)CO-catalyzed amination of both exocyclic and endocyclic benzylic C-H bonds. The choice of arylazides as nitrogen sources confers to the methodology a good sustainability due to the formation of molecular nitrogen as the only stoichiometric by-product. A preliminary mechanistic investigation evidenced a critical role of the hydrocarbon concentration to drive the chemoselectivity of the reaction.

Catalytic Polymer Membranes under Forcing Conditions: Reduction of Nitrobenzene by CO/H2O Catalyzed by Ruthenium Bis(arylimino)acenaphthene Complexes

Polymeric membranes embedding a metal complex have been previously employed as reusable catalysts under relatively mild conditions. Herein, the first example of a polymeric catalytic membrane employed under very forcing conditions (160 °C and 5 MPa CO) is reported. The reaction investigated was the reduction of nitrobenzene to aniline by CO/H2O, catalyzed by ruthenium bis(arylimino)acenaphthene (Ar‐BIAN) complexes. To better retain the complex in the membrane, a modified ligand, with long alkyl chains in the para positions of the aryl rings, was prepared. Among several polymers tested as membranes, PEEK‐WC, a modified polyether ether ketone, gave the best results. Attempts to embed the ligand only in the membrane and functionalize it with the metal later, analogously to the in situ generation of the active species practiced for the homogeneous system, failed and it was necessary to synthesize new complexes that could be reduced under the reaction conditions. Best results were obtained using [Ru(Ar‐BIAN)(CO)2Cl2]+Et3N. During the reaction, the complex is transformed into a mixture of [Ru3(CO)12] and a reduced form of the ligand, Ar‐BIANH2. The latter was independently prepared and shown to be able to reduce nitrobenzene even in the absence of any metal. A new kind of support was designed to allow the placing of the membrane in a stirred autoclave. Using only water as solvent, no metal or ligand leaching was detected and several recycles were performed. All employed membranes were thoroughly characterized by different techniques.

Highly diastereoselective cyclopropanation of α-methylstyrene catalysed by a C2-symmetrical chiral iron porphyrin complex.

A new chiral iron porphyrin-based catalyst performed α-methylstyrene stereoselective cyclopropanation with excellent yields (up to 99%), enantio- and diastereoselectivities (ee(trans) up to 87%, trans/cis ratios up to 99 : 1) and outstanding TON and TOF values (up to 20,000 and 120,000 h(-1) respectively).

Continuous flow asymmetric cyclopropanation reactions using Cu(I) complexes of Pc-L* ligands supported on silica as catalysts with carbon dioxide as a carrier

Continuous flow heterogeneous asymmetric cyclopropanations catalysed by supported hydrogen-bonded (SHB) chiral copper(I) complexes of pyridine containing tetraazamacrocyclic ligands Pc-L* using CO2 as a transport vector are described. The catalytic system showed high stability and good recyclability without loss of activity for at least 24 h in CO2 and catalyst turnover numbers up to 440 were obtained with excellent conversion (up to 99%) and high selectivity (up to 88%). No leaching of copper was observed. Cyclopropane products from both aromatic and aliphatic olefins were obtained in good yields with enantiomeric excesses up to 72%.