Giambattista Consiglio

Asymmetric hydroformylation of unsaturated esters with PtCl(SnCl3)[(R,R)-Diop] catalyst

Dimethyl 2-(formylmethyl)butanedioate (2e) has been synthesized regioselectively with an enantiomeric excess of more than 82% by the homogeneous catalytic hydroformylation of dimethyl itaconate (1e) with PtCl(SnCl3)[(R,R)-DIOP] as the catalyst precursor. Under the conditions used a competitive hydrogenation to dimethyl 2-methylsuccinate (3e) takes place. This reaction occurs with an optical yield of up to 51%. For other vinylidene esters 1 the asymmetric induction was lower both in the hydroformylation and in the competitive hydrogenation. The relationship between the absolute configuration of the predominant antipodes and the possible transition states responsible for the enantioface discrimination is discussed in terms of a model developed and successfully used for olefinic hydrocarbons as substrates.

Rhodium- and platinum-catalyzed asymmetric hydroformylation with (2S,3S )-2,3-bis(diphenylphosphino)butane as the chiral ligand

Abstract Some mono- and disubstituted ethenes have been asymmetrically hydroformylated with rhodium and platinum catalysts using (2 S ,3 S )-2,3-bis(diphenylphosphino)butane (Chiraphos) as the chiral ligand (maximum optical yield ∼ 45%). The results are compared with those obtained when the chiral ligand is (4 R ,5 R )-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane (Diop). The Chiraphos ligand causes a decrease of the catalytic activity with respect to Diop. Optical yields for rhodium catalysts are always higher with Chiraphos, whereas scattered results were obtained with platinum catalysts. Since for the catalytic systems examined asymmetric induction takes place before or during the formation of the intermediate diastereomeric metal alkyl complexes, the results are tentatively rationalized on the basis of a stereochemical model for the transition state leading to the above metal alkyl complexes intermediate.

Asymmetric hydroformylation of the linear butenes by [(R,R)-Diop]Pt(SnCl3)Cl

The asymmetric hydroformylation of the three isomeric straight chain butenes catalyzed by [(R,R)-Diop]Pt(SnCl3)CI (Diop is 2,2-dimethyl-4, 5-bis(diphenylphos- phinomethyl)-l,3-dioxolane) has been reinvestigated. Depending on the conditions, hydroformylation can be accompanied by extensive isomerization and hydrogenation of the substrate. Enantiomeric excess and regioselectivity depend on the extent of conversion. At least two pathways must be responsible for the formation of the straight chain aldehyde from the 2-butenes. The chirality of the 2-methylbutanal arising from 1-butene (best e.e 46.7%) is opposite to that arising from (Z)- and (E )-2-butene. Under the conditions used asymmetric induction is determined during or before the formation of the alkyl complexes which are generally postulated as intermediates in the catalytic cycle. The assumption of the existence of different catalytic species responsible for hydroformylation and hydrogenation/isomerization accounts satisfactorily for the results.

Asymmetric nickel-catalyzed cross-coupling reaction of allylic substrates with grignard reagents

Two possible routes for the synthesis of optically active olefinic compounds through cross-coupling reaction between allylic electrophiles and Grignard reagents catalyzed by nickel complexes containing chiral diphosphine ligands were investigated: i) the reaction of chiral racemic (or prochiral) allylic compounds with achiral Grignard reagents and ii) the reaction of chiral Grignard reagents with allyl electrophiles. Optical yields higher than 90% were obtained for the first reaction route (compound 11) and up to 58% (compound 34) were obtained for the second route, using a C2 chiral ligand, namely (S,S)-1,2-dimethyl-1,2-ethanediylbis(diphenylphosphine).

P∧N versus N∧N ligands for the palladium-catalyzed alternating copolymerization of styrene and carbon monoxide

Cationic palladium(II) complexes, modified by C1-symmetric chelate ligands containing the 3-phenyl-4-methoxymethyl-4,5-dihydrooxazole chiral moiety and either 2-pyridyl or 2-diphenylphosphinophenyl substituents, catalyze the copolymerization of styrene with carbon monoxide with either a prevailingly syndiotactic or isotactic microstructure, respectively. This and other results obtained with several ligands are interpreted on the basis of a site-selective coordination of the olefin before migratory insertion to cause chain growing.

Platinum-promoted cyclization reactions of amino olefins : II. Regio- and stereoselectivity in the cyclization reactions of C-methyl substituted pent-4-enylamines

Abstract The compounds 1-, 2- and 3-methylpent-4 enylamine cyclize, in a reaction medium containing [PtCl4]2-, to the corresponding cis- and trans-dimethylpyrrolidines showing marked regio and stereoselectivity effects. The following cyclization reactions are also reported: a) that of hex-4-enylamine which gives a mixture of 2-ethylpyrrolidine and 2-methylpiperidine, b) that of 2,2-dimethylpent-4-enylamine which produces 2,4,4-trimethylpyrrolidine and c) that of 2,2-dimethylhex-4-enylamine which results in the formation of 2-ethyl-4,4-dimethylpyrrolidine and 2-methyl-5,5-dimethylpiperidine. The X-ray crystal structures of trans-[PtCl2(amine)(Et3P)] (amine = cis-2, 4-dimethylpyrrolidine and cis-2,3-dimethylpyrrolidine) are reported.

Platinum dichloride complexes with (R,R)-[(bicyclo[2.2.2]-octane-2,3-diyl)bis(methylene)]bis[diphenylphosphine]- or bis[5H-benzo[b]phosphinindole]: new catalyst precursors for enantioselective hydroformylation

Abstract The preparation of the platinum dichloride complexes with ( R,R )-[(bicyclo [2.2.2]octane-2,3-diyl)bis(methylene)]bis[diphenylphosphine]- or bis[5H-benzo[b]-phosphinindole] is reported. The complexes have been tested as catalyst precursors for enantioselective hydroformylation of some aromatic olefins. Asymmetric inductions up to 85% have been obtained.

Carbonylation (hydroformylation and hydrocarbalkoxylation) and enantioselective carbonylation of some methacrylic acid derivatives

The hydroformylation of methyl methacrylate (1) or t-butyl methacrylate (2) takes place with fair to good chemoselectivity, the regioselectivity depending on the catalyst precursor used. By contrast, methacrylonitrile (3), methacrylamide (4), and N-benzyl-methacrylamide (5) undergo hydroformylation followed by subsequent reactions. The formyl product formed is reduced to the corresponding 2-cyano-2-methylpropan-1-ol in the case of 3, and undergoes cyclization to 2-methyl-2,3-dehydrobutyrolactames for 4 and 5. Under conditions of hydrocarbalkoxylation in the presence of palladium catalysts, 4 gives 3-methylsuccinimide. In the enantioselective reactions, extents of asymmetric induction of about 20–50% have been obtained.

Asymmetric hydrocarboxylation of olefins : IV. Influence of PPh3 in the asymmetric hydrocarboxylation catalyzed by [(—)-DIOP]PdCl2

In the palladium-catalyzed hydrocarboxylation of α-methylstyrene using PPh3 and (—)-DIOP as ligands, with a constant ratio of phosphorus to palladium atoms of 2, the optical yield depends on the proportions of PPh3 and (—)-DIOP, showing a maximum for a molar ratio of 2.

Cationic palladium(II)–diphosphine complexes as catalysts for the carbonylation of alkenes to ketones

Cation palladium complexes of the type [(dppp)Pd(solvent)2][X]22[X = non or weakly coordinating anion; dppp = 1,3-bis(diphenylphosphino)propane] are active catalysts for the carbonylaion to ketones, e.g., for the seletive formation of E-1,5-diphenylpent-l-en-3-one from styrene; in the presence of water and depending on the acidity conditions dimerisation to the much less catalytically active [(dppp)Pd(µ-OH)2 Pd(dppp)]X23 takes place, the structure of which was determined by X-ray crystallography.