Emanuela Pitzalis

Hydrosilylation of aromatic nitriles promoted by solvated rhodium atom-derived catalysts

Abstract Rhodium metal particles, isolated as supported or unsupported powder starting from mesitylene solvated rhodium atoms, catalyse the hydrosilylation of aromatic nitriles to N , N -disilylamines in high conversion at 100°C. Different hydrosilanes (HSiMe 3 , HSi(OEt) 3 ) can be employed. In the case of cinnamonitrile, the chemoselectivity of the reaction to 2-trimethylsilyl-3-phenylpropionitrile and ( E )- and ( Z )-1-di(trimethylsilyl)amino-3-phenyl-1-propene is strongly dependent on the reaction temperature. The commercial rhodium on γ-Al 2 O 3 catalyst is considerably less active and selective than the analogous catalyst prepared via Metal Vapour Synthesis (MVS) probably owing to the different dimension and distribution of the metal particles in the two samples as shown by HRTEM analysis.

Preparation and resolution of chiral areneruthenium(II) complexes

Abstract The synthesis of the chiral complexes [RuCl 2 (η n6 -C 6 H 5 CHMeR) 2 ], (R = Et, 1 , t Bu, 2 ), is reported. 1 was prepared from RuCl 3 ·3H 2 O and 1-(2-butyl)- 1,4-cyclohexadiene, whereas 2 was obtained starting from [Ru(η 6 -naphthalene)(η 4 -COD)] (COD = 1,5-cyclooctadiene) and 2,2-dimethyl-3-phenylbutane, which gives [Ru(η 6 -C 6 H 5 CHMe t Bu)(η 4 -COD)] and subsequent reaction with HCl. Complexes 1 and 2 react with (+)-neomenthyldiphenylphosphine (NMDPP) to give monomeric diastereomers [RuCl 2 (η 6 -C 6 H 5 CHMeEt)(NMDPP)] ( 3a , 3b ), and [RuCl 2 (η 6 C 6 H 5 CHMe t Bu)(NMDPP)], ( 4a , 4b ), which were separated by HPLC. The structure of compound 3a was solved by Patterson and Fourier techniques and refined by full-matrix least-squares analysis to R = 0.053, R w = 0.061. The arene is η 6 -bonded to the ruthenium with the phosphorus and the two chlorine atoms arranged as a three legs piano stool. The absolute configuration of the chiral centre of the aromatic ligand in 3a is R . The monomeric diastereomers 3a , 3b , 4a and 4b , were reconverted into their dimeric precursors ( R,R )- 1a , ( S,S )- 1b , ( R,R )- 2a and ( S,S )- 2b as pure enantiomers. The CD spectra of ( R,R )- 1a and ( S,S )- 2b are also reported.

Stoichiometric cyclotrimerisation of chiral alkynes at a ruthenium centre: preparation of optically active (η6-arene)(η4-cycloocta-1,5-diene)ruthenium(0) complexes

The chiral alkynes (S)-MeCH(R)CCH, 2 (R=Et, 3-methyl-1-pentyne, a; iPr, 3,4-dimethyl-1-pentyne, b; tBu, 3,4,4-trimethyl-1-pentyne, c), containing a stereogenic centre in α position to the triple bond, react at room temperature with the complex Ru(η6-naphthalene)(η4-COD), 1, to give the corresponding optically active complexes Ru{η6-(S)-1,3,5-C6H3[CH(Me)R]3}(η4-COD), 6, and Ru{η6-(S)-1,2,4-C6H3[CH(Me)R]3}(η4-COD), 7, the η6-1,3,5-arene regioisomer being the prevalent product. With (S)-2a, a mixture of 6a and 7a (6a/7a=90:10) is obtained and, with the more sterically demanding alkynes (S)-2b and (S)-2c, the regioselectivity to the corresponding complexes 6b and 6c is almost complete. This synthetic procedure does not involve the stereogenic centres on the alkynes and it proceeds with complete stereoselectivity.

On the difference in decomposition of taxifolin and luteolin vs. fisetin and quercetin in aqueous media

The decomposition of flavonols quercetin and fisetin, flavone luteolin and flavanone taxifolin was studied in slightly alkaline solution under ambient conditions. The study was based on spectrophotometry and high-pressure liquid chromatography. Products formed by atmospheric oxygen oxidation and hydrolysis were identified by HPLC–DAD and HPLC–ESI-MS/MS. Only small differences in the chemical structure of flavonoids resulted in extremely variable oxidation pathways and products. Oxidation of flavonols led to the formation of both a benzofuranone derivative and several open structures. On the contrary, the benzofuranone derivative was not found as a product of taxifolin and luteolin oxidative decomposition. These compounds were oxidized to their hydroxylated derivatives and typical open structures. Quercetin was not identified as a possible oxidation product of taxifolin.Graphical Abstract

Preparation via solvated metal atoms and surface reactivity of homo and heteronanostructured metal particles: supported and unsupported Rh nanoaggregates

Abstract Nanoscale Rh particles, (1.7–2.8 nm) have been easily generated by clustering of Rh atoms from mesitylene solvated Rh atoms, obtained by reaction of Rh vapour and mesitylene.