Search

Metal-based catalysts and initiators have played a pivotal role in the ring-opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis-stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal-based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts-primarily metal-based catalysts, but also organocatalysts-that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted.

Reaction of methyl 1-bromocyclobutanecarboxylate with zinc and 1-aryl-2-(arylimino)ethanones leads to 4,6a-diaryl-3,3:6,6-dipropano- tetrahydro-2H-furo[3,2-b]pyrrole-2,5(3H)-diones. Structure of one of these compounds is confirmed by X-ray analysis.

Treatment of methyl 1-(2-bromo-4-methoxy-1,4-dioxobutyl)cyclohexanecarboxylate with zinc followed by aromatic aldehydes affords methyl 1-(2-aryl-5-oxotetrahydrofuran-3-carbonyl)cyclohexanecarboxylates.

Reactions of (E)-10-aryl-8-(2-arylethenyl)-7-oxaspiro[4.5]dec-8-en-6-ones with maleic anhydride result in the formation of 4,9-diaryl-3a,4,9,9a-tetrahydrospiro[furo[3,4-f]chromene-8,1′-cyclopentane]-1,3,7(9bH)-triones whose structure was established by XRD analysis.

The reaction of dienones (I) with cyclopentane derivative (II) gives rise to the formation of a mixture of regioisomeric spiro compounds (III) and (IV).

Reformatsky reaction of methyl 1-bromocyclobutane-, 1-bromocyclopentane-, 1-bromocyclohexane-, and 1-bromocycloheptanecarboxylates with 2,5-bis(arylmethylidene)cyclopentanones gave the corresponding 4′-aryl-7′-arylmethylidene-4′,5′,6′,7′-tetrahydro-2′H-spiro[cycloalkane-1,3-cyclopenta[b]pyran]-2′-ones.

Allyl complexes based on group IIIb metals (Sc, Y, La) and lanthanides are reviewed. The diversity, synthesis, and main structural and reactivity features of discrete, well-defined homoleptic and pseudo-homoleptic neutral, anionic and cationic bis-, tris- and tetra(allyl)-lanthanide complexes, as well as heteroleptic allyl-lanthanidocenes and allyl-lanthanide complexes supported by non-Cp ligands are covered. Brief comments on the catalytic performances of some key compounds in polymerization processes are also provided.

Reactions of new bis(α-diketones) with 1,3-diphenylacetone resulted in new bis(tetraarylcyclopentadienones).

The Diels-Alder reactions of 4,4′-bis(2,4,5-triphenylcyclopentadienon-3-yl)benzophenone with carboxylic anhydrides containing multiple carbon-carbon bonds afforded novel tetracarboxylic dianhydrides.

A convenient and clean route to transform, in aqueous medium, various alkanes to carboxylic acidsvia single-pot carboxylation with CO and water, under mild conditions, has been achieved, proceeding efficiently and selectively even without any metal catalyst and any acid additive, at low temperatures; the relevant hydroxylating role of H2O and radical mechanisms are disclosed by radical-trap, H218O and DFT studies.

Methyl 3-(1-bromocycloheptyl)-2,2-dimethyl-3-oxopropanoate and methyl 1-(2-bromo-2-methylpropanoyl)cycloheptanecarboxylates react with zinc and arylcarbaldehydes yielding 5-aryl-2,2-dimethyl-4-oxaspiro[5.6]dodecan-1.3-diones and 3-aryl-4,4-dimethyl-2-oxaspiro[5.6]dodecan-1.5-diones respectively.

Methyl 1-bromocyclohexanecarboxylate reacts with zinc and substituted chalcones yielding the corresponding spiro-3,4-dihydropyran-2-one derivatives, 3-aryl-5-aryl-2-oxaspiro[5.5]undec-3-en-1-ones.

A series of novel β-hydroxy-β-bis(trifluoromethyl)-imines (2a–j) and di(β-hydroxy-β-bis(trifluoromethyl))-diimines (3a–f) were prepared in moderate to good yields via a simple two-step approach: first, β-hydroxy-β-bis(trifluoromethyl)-ketones (1a–c) were obtained by a catalyst-free aldol reaction between liquid hexafluoroacetone sesquihydrate and ketones (acetone, acetophenone, and pinacolone, respectively); then, condensation of the latter fluorinated β-ketols 1a–c with primary amines or diamines was achieved in the presence of Lewis (montmorillonite, InBr3, La(OTf)3) or Bronsted (PTSA) acid catalysts. The molecular structures of mono- and di-β-hydroxy-β-bis(trifluoromethyl)-(di)imines 2e,h and 3a,f were determined and found to exhibit strong intramolecular (R)N⋯H–O hydrogen bonding.

Methyl 1-(2-bromo-2-methyl-1-oxopropyl)-, 1-(1-bromocyclopentylcarbonyl)-, and 1-(1-bromocyclohexylcarbonyl) cyclobutanecarboxylates reacted with zinc and aromatic aldehydes to give, respectively, 7-aryl-2,2-dimethyl-6-oxaspiro[3.5]nonane-5,9-diones, 11-aryl-12-oxadispiro[3.1.4.3]tridecane-5,13-diones, and 12-aryl-13-oxadispiro[3.1.5.3]tetradecane-5,14-diones.

Reformatsky reagents derived from methyl 1-bromocyclobutane- and 1-bromocycloheptanecarboxylates reacted with Schiff bases to give 2,3-diaryl-2-azaspiro[3.3]heptane-1-ones and 2,3-diaryl-2-azaspiro-[3.6]decan-1-ones, respectively.

Reformatsky reagent prepared from methyl 1-bromocyclopentanecarboxylate and zinc reacted with 2-oxochromen-and 6-bromo-2-oxochromen-3-carboxylic acids N-arylamides yielding 3-aryl-1,1-tetramethylene-and 3-aryl-9-bromo-1,1-tetramethylene-2,3,4,4a,5,10b-hexahydro-1H-chromeno[3,4-c]pyridine-2,4,5-triones as single diastereomers.

The results of my latest research into molten halides of alkali and alkaline-earth metals by a method of Raman spectroscopy are reviewed. A dynamic criterion for the formation of complexes in melts is considered. The results that testify to the existence of instantaneous and short-lived autocomplexes in these liquids are analyzed in the light of an autocomplex model for the structure of melts.

Cette mini-revue decrit une serie de complexes neutres et ioniques de metaux du groupe 3 et de lanthanides a base de deux types de ligands fluorenyle pontes, [Cp-CMe 2 -Flu] 2 et [Me 2 Si(3,6- t Bu 2 C 13 H 7 )(N t Bu)] 2- , qui ont ete prepares dans notre groupe a l'aide de diverses methodologies synthetiques. Les aspects structuraux, en particulier les differents modes de coordination du ligand fluorenyle dans ces complexes, sont discutes, suivis par des applications en catalyse de chimie fine, et principalement de polymerisation. Pour citer cet article : E. Kirillov et al., C. R. Chimie 9 (2006).

Reformatsky reagents obtained from methyl 1-bromocyclohexane-and 1-bromocyclopentane-1-carboxylates reacted with aromatic aldehyde phenyl-and benzoylhydrazones to give 3-aryl-2-phenylamino-2-azaspiro[3.5]nonan-, 3-aryl-2-phenylamino-2-azaspiro[3.4]octan-, 3-aryl-2-benzoylamino-2-azaspiro[3.5]-nonan-, and 3-aryl-2-benzoylamino-2-azaspiro[3.4]octan-1-ones, respectively. The reaction of furan-2-carbaldehyde phenylhydrazone with methyl 1-bromocyclohexane-1-carboxylate and zinc led to the formation of 4-(2-furyl)-2-phenyl-2,3-diazaspiro[4.5]decan-1-one.

Reformatsky reactions of methyl 1-bromocyclohexanecarboxylate and methyl 1-bromocyclo-pentanecarboxylate with 2-aryl-2-oxoacetaldehydes involve both carbonyl groups of the latter and result in formation of 3a-aryl-3,3 : 6,6-bis(pentamethylene)- and 3a-aryl-3,3 : 6,6-bis(tetramethylene)tetrahydrofuro-[3,2-b]furan-2,5-diones. The reaction with 2-(2,4-dimethylphenyl)-2-oxoacetaldehyde gives acyclic products, methyl 1-[1-hydroxy-2-(2,4-dimethylphenyl)-2-oxoethyl]cyclohexanecarboxylate and methyl 1-[1-hydroxy-2-(2,4-dimethylphenyl)-2-oxoethyl]cyclopentanecarboxylate, while with benzil methyl 1-(4-hydroxy-1-oxo-3,4-diphenyl-2-oxaspiro[4.5]dec-3-yl)cyclohexanecarboxylate and methyl 1-(4-hydroxy-1-oxo-3,4-diphenyl-2-oxaspiro[4.4]non-3-yl)cyclopentanecarboxylate are obtained.

A short review of results obtained in latest infrared and Raman studies, with special reference to in situ measurements and first-principles quantum-mechanical investigations of adsorption and oxidation of alcohol molecules over different (metallic, semiconductor and oxide) surfaces and metal/oxide interfaces is presented, and differences and similarities in the behaviour of methanol and ethanol are discussed.

Hexakis[bis(2-aminoethoxy)methylsilylethyl]benzene and hexakis[bis(N,N-dimethyl-2-aminoethoxy)methylsilylethyl]benzene C6[(NR2CH2CH2O)2SiMeCH2CH2]6 (4, R = H; 5, R = Me) were prepared from hexakis(methyldichlorosilylethyl)benzene C6(Cl2MeSiCH2CH2)6 and 2-aminoethanol or N,N-dimethyl-2-aminoethanol, respectively. Compounds 4 and 5 react with anhydrous cobalt (ii) chloride to give poorly soluble dodecachloro{hexakis[bis(2-aminoethoxy)methylsilylethyl]benzene}hexacobalt and dodecachloro{hexakis[bis(N,N-dimethyl-2-aminoethoxy)methylsilylethyl]benzene}hexacobalt {Co6[(NR2CH2CH2O)2SiMeCH2CH2]6C6}Cl12 (R = H or Me), respectively. Polyfunctional amine 4 reacts with dicobalt octacarbonyl to produce hexakis[bis(2-aminoethoxy)methylsilylethyl]benzenedicobalt(ii) tetrakis(tetracarbonylcobaltate) {Co2[(NH2CH2CH2O)2SiMeCH2CH2]6C6}[Co(CO)4]4. N,N-Dimethyl-substituted polyfunctional amine 5 is lowly reactive in the reaction with Co2(CO)8, whereas the simplest model of this compound, viz., bis(N,N-dimethyl-2-aminoethoxy)dimethylsilane (NMe2CH2CH2O)2SiMe2, slowly reacts with Co2(CO)8 to give tris[bis(N,N-dimethyl-2-aminoethoxy)dimethylsilane]cobalt(ii) bis(tetracarbonylcobaltate) {Co[(NMe2CH2CH2O)2SiMe2]3}[Co(CO)4]2. Thermal decomposition and transformations of the resulting complexes under the action of oxygen and water were studied.