Alkene and Olefin Functionalization by Organoaluminum Compounds, Catalyzed with Zirconocenes: Mechanisms and Prospects

Alkene and olefin functionalization via addition of electro‐ or nucleophilic reagents is one of the convenient synthetic methods for the insertion of heteroatoms into organic molecules. The use of organometallic reagents in these reactions in combination with the specific catalysts provides high substrate conversion and process selectivity. The introduction of this approach into the chemistry of organoaluminum compounds leads to the development of chemo‐, regio‐ and stereoselective catalytic methods of alkene and olefin functionalization. The chapter focuses on the modern concepts of the alkene hydro‐, carbo‐ and cycloalumination mechanisms, that is, the experimental and theoretical data on the intermediate structures involved in the product formation, the effects of the catalyst and organoaluminum compound structure, reaction conditions on the activity and selectivity of the bimetallic systems. The prospects of the development of enantioselective methods using these catalytic systems for the alkene and olefin transformations are considered

Mechanistic aspects of chemo- and regioselectivity in Cp2ZrCl2 – catalyzed alkene cycloalumination by AlEt3

The reactions of styrene and 1-hexene with zirconacyclopropane and the bimetallic five-membered Zr,Al-complex [Cp2Zr(m-Cl)CH2CH2AlEt2] as catalytically active sites in Cp2ZrCl2-catalyzed cyclo- alumination of a-olefins with AlEt3 have been studied by DFT quantum chemical methods (PBE/3z, B3LYP/VDZ, B3LYP(GD3)/VDZ, M06-2X/VDZ, M06-2X/VTZ//VDZ). It was shown that key intermediates can exist in dynamic equilibrium with each other, and with ClAlEt2 adducts. Comparative analysis was carried out for the energy characteristics of alternative pathways in the reaction of styrene or 1-hexene with the intermediates, implying different orientations of the substrates towards the Zr-C bond. The obtained data were used to elucidate the reasons for the observed dependence of the reaction regio- selectivity on the substrate structure and the minor by-products formation. The applicability of M06-2X/ cc-pVTZ-PP//M06-2X/cc-pVDZ-PP and PBE/3z methods for the description of the available experimental data was shown

Enantioselectivity of chiral zirconocenes as catalysts in alkene hydro-, carbo- and cycloalumination reactions

Enantioselectivity of chiral Zr catalysts L1L2ZrCl2 (L1 = L2 = 1-neomenthylindenyl (Ind*), (1); L1 = Cp, L2 = Ind* (2); L1 = Cp, L2 = 1-neomenthylindenyl-4,5,6,7-tetrahydroindenyl (Cp*) (3)) in the hydro-, carbo- and cyclo-alumination of alkenes by organoaluminium compounds (OAC) (AlMe3, AlEt3, HAlBui2) has been studied. It was found that OAC type exhibits the most effect on the reactions chemo- and enantioselectivity. The reaction chemo- and enantio-selectivity depend on the catalyst structure and reaction conditions (solvent type, catalyst concentration, temperature) as well. It is shown that lack of asymmetric induction in the reaction of ?-methylstyrene hydroalumination by HAlBui2, catalyzed with complexes 1 or 3, is the result of the formation of Zr hydride complexes of different structure as reaction intermediates. MTPA was used as derivatization reagent for enantiomeric excess estimation and absolute configuration assignment of ?-chiral alcohols obtained after the oxidation and hydrolysis of reaction products. The applicability of MTPA for the assignment of chiral center absolute configuration in ?–ethyl substituted primary alcohols and ?–alkyl-1,4-butanediols was shown

Nontrivial Intramolecular Interaction in Ozonation of Dimethyl Ester of endo,cis-bicyclo[2,2,1]hept-5-en-2,3-dicarbonic acid in diethyl ether

The formation of the product of intramolecular interaction of a zwitterion and a methoxycarbonyl group was observed in the process of ozonating dimethyl ester of endo,cis-bicyclo [2,2,1]hept-5-en-2,3-dicarbonic acid in diethyl ether. The structure of racemic endo,cis-4-methoxy-5-methoxycarbonyl-6-formyl-1,4-epoxy-2,3-dioxacyclopenta[2,3-δ] cyclohexane was established by an X-ray structure analysis

Crystallization of SAPO-11 Molecular Sieves Prepared from Silicoaluminophosphate Gels Using Boehmites with Different Properties

In this article, we report the results of research the formation of silicoaluminophosphate gels under changing gel aging conditions and the influence of an aluminum source (boehmite), characterized by different properties. The samples of initial gels were characterized by XRF, X-ray diffraction, MAS NMR 27Al and 31P, and scanning electron microscopy (SEM). Products of crystallization were characterized by XRF, X-ray diffraction, MAS NMR 27Al and 31P, scanning electron microscopy (SEM), N2-physical adsorption, and IR spectroscopy with pyridine adsorption. It has been established that the chemical and phase composition of aging gels and the products of further crystallization is conditioned by the size of the crystals and the porous structure of boehmite. Methods of management the morphology and secondary porous structure of SAPO-11, including the hierarchical porous structure, are proposed based on the use of boehmits characterized by different properties and changing the aging conditions of the initial gels. SAPO—based catalyst with a hierarchical porous structure showed excellent catalytic performance in dimerization of α-methylstyrene with a high degree of conversion and selectivity for linear isomers

Crystallization of SAPO-11 Molecular Sieves Prepared from Silicoaluminophosphate Gels Using Boehmites with Different Properties

In this article, we report the results of research the formation of silicoaluminophosphate gels under changing gel aging conditions and the influence of an aluminum source (boehmite), characterized by different properties. The samples of initial gels were characterized by XRF, X-ray diffraction, MAS NMR 27Al and 31P, and scanning electron microscopy (SEM). Products of crystallization were characterized by XRF, X-ray diffraction, MAS NMR 27Al and 31P, scanning electron microscopy (SEM), N2-physical adsorption, and IR spectroscopy with pyridine adsorption. It has been established that the chemical and phase composition of aging gels and the products of further crystallization is conditioned by the size of the crystals and the porous structure of boehmite. Methods of management the morphology and secondary porous structure of SAPO-11, including the hierarchical porous structure, are proposed based on the use of boehmits characterized by different properties and changing the aging conditions of the initial gels. SAPO—based catalyst with a hierarchical porous structure showed excellent catalytic performance in dimerization of α-methylstyrene with a high degree of conversion and selectivity for linear isomers

Mechanism of Cp₂ZrCl₂‑Catalyzed Olefin Cycloalumination with AlEt₃: Quantum Chemical Approach

A mechanism of α-olefin cycloalumination by AlEt₃ in the presence of Cp₂ZrCl₂ catalyst was proposed, based on theoretical estimation of the thermodynamic and activation parameters of the possible reaction pathways calculated at the DFT level using the PBE/3ζ and M06-2X/cc-pVDZ quantum chemical methods. The reaction steps to bimetallic Zr,Al- and Zr,Zr-complexes, [Cp₂Zr­(μ-Cl)­CH₂CH₂­AlEt₂], [Cp₂Zr­(μ-H)­CH₂CH₂­AlEt₂], and [Cp₂Zr­(Cl)­CH₂CH₂­Zr­(Cl)­Cp₂], observable on the NMR time scale were considered. Among the possible intermediates, zirconacyclopropane was proposed as the catalyst species most active toward the alkenes, whose formation goes via two-step ligand exchange between Cp₂ZrCl₂ and AlEt₃, and subsequent ethane elimination from the Cp₂ZrEt₂. The reaction of zirconacyclopropane with the alkene gives the zirconacyclopentane intermediate, in which transmetalation by ClAlEt₂ and AlEt₃ gives 1-ethyl-3-alkyl­alumolanes via 2-substituted dialuminobutane

Mechanism of Cp₂ZrCl₂‑Catalyzed Olefin Cycloalumination with AlEt₃: Quantum Chemical Approach

A mechanism of α-olefin cycloalumination by AlEt₃ in the presence of Cp₂ZrCl₂ catalyst was proposed, based on theoretical estimation of the thermodynamic and activation parameters of the possible reaction pathways calculated at the DFT level using the PBE/3ζ and M06-2X/cc-pVDZ quantum chemical methods. The reaction steps to bimetallic Zr,Al- and Zr,Zr-complexes, [Cp₂Zr­(μ-Cl)­CH₂CH₂­AlEt₂], [Cp₂Zr­(μ-H)­CH₂CH₂­AlEt₂], and [Cp₂Zr­(Cl)­CH₂CH₂­Zr­(Cl)­Cp₂], observable on the NMR time scale were considered. Among the possible intermediates, zirconacyclopropane was proposed as the catalyst species most active toward the alkenes, whose formation goes via two-step ligand exchange between Cp₂ZrCl₂ and AlEt₃, and subsequent ethane elimination from the Cp₂ZrEt₂. The reaction of zirconacyclopropane with the alkene gives the zirconacyclopentane intermediate, in which transmetalation by ClAlEt₂ and AlEt₃ gives 1-ethyl-3-alkyl­alumolanes via 2-substituted dialuminobutane