Catalysis in aromatic nucleophilic substitution. Note II. Piperidino substitution reactions of some 2-l-3-nitrothiophenes and 2-l-5-nitrothiophenes in methanol and benzene

The rates of piperidino substitution of some 2-L-3-nitrothiophenes (I) and 2-L-5-nitrothiophenes (II) (L = Cl, Br, I, OC₆H₄NO₂-p, and SO₂Ph) have been measured in methanol and in benzene at various piperidine concentrations. The reactivity of compounds (I) is not affected by the piperidine concentration in both methanol and benzene, except for the case of L = I (Ic). Probably due to association effects, the reactivity of Ic in benzene decreases as the piperidine concentration is increased. The reactions of compounds II follow overall second order kinetics in methanol while in benzene a different behaviour is observed as a function of the nature of the leaving group. In fact, the piperidino substitutions of IIa-c (L = Cl, Br, I) are mildly accelerated at high piperidine concentrations (a moderate solvent effect); on the contrary the reactivity of IId and e shows a strong dependence on the piperidine concentration, pointing out a genuine base catalysis.     

Nickel-catalyzed Asymmetric Alkylation of Some Chiral and Achiral Allylic Alcohols. Preliminary communication

[(?) (R)-1,2-bis (Diphenylphosphino)-1-phenylethane]nickel (II) chloride was found to catalyze the asymmetric alkylation of some chiral and achiral allylic alcohols with Grignard reagents, leading to the formation of optically active olefins. Enantiomer discrimination of the substrate takes place in the alkylation of chiral allylic alcohols.     

On hydrogen activation in the hydroformylation of olefins with Rh4(CO)12 or Co2(CO)8 as catalyst precursors

In the hydroformylation of ethylene with approximately equimolar H₂/D₂ mixtures and Rh₄(CO)₁₂ or Co₂(CO)₈ as the catalyst precursor about 50% of propionaldehyde-d₁ was formed. The propionaldehyde-d₀/d₂ ratio was ～ 3 for rhodium and ～ 2.6 for the cobalt catalyst. On the basis of the results and assuming that there is no rapid M(H)₂/M(D)₂ scrambling, activation of hydrogen through M(H)₂ or M(H)₂(olefin) complexes can be excluded.     

Crystal structure and reactivity of 2-chloro-3,5-dinitrothiophene and of 2-phenylsulphonyl-3,5-dinitrothiophene with nucleophiles

The geometry obtained by a crystal structure determination of the title compounds, as compared with that of the analogous benzene derivatives, along with results of ab initio calculations, is used to interpret the different S_NAr reactivities in some thiophene and benzene compounds. The smaller rotation of the nitro groups with respect to the aromatic rings observed in thiophene derivatives should be considered a relevant factor in the higher reactivity in the thiophene series.     

Enantioselective Alternating Terpolymerization of Styrene and Ethene with Carbon Monoxide. Preliminary communication

In spite of the higher reactivity of styrene with respect to ethene for the alternating copolymerization with carbon monoxide, catalyzed by chiral (dihydrooxazole)(phosphino)palladium complexes, ethene is preferentially (and randomly) enchained in terpolymerization experiments; enantioface selection for styrene is comparably high in both copolymerization and terpolymerization processes.     

PGSE diffusion, 1H-19F HOESY and NMR studies on several [Rh(1,5-COD)(Biphemp)]X complexes: detecting positional anion effects

Three new salts of Rh(I), [Rh(1,5-COD)(Biphemp)]X, Biphemp = (6,6'-dimethylbiphenyl-2,2'-diyl)bis(diphenylphosphine), X = BF4-, 2a, PF6-, 2b, and CF3SO3-, 2c, were prepared and studied using PGSE diffusion, 1H-19F HOESY and inverse 103Rh (amongst other) NMR methods. Although the immediate coordination sphere of the cation does not sense the change in the anion, the PGSE diffusion and 1H-19F HOESY data suggest that, in addition to some ion pairing, each of the anions in 2 demonstrates selectivity in its approach towards the cation.