Organoactinides Promote the Dimerization of Aldehydes: Scope, Kinetics, Thermodynamics, and Calculation Studies

Abstract

Surprising catalytic activities have been found for the actinide complexes Cp*(2)ThMe(2) (1), Th(NEtMe)(4) (2), and Me(2)SiCp''(2)Th(C(4)H(9))(2) (3) toward oxygenated substrates. During the catalytic dimerization of benzaldehydes to their corresponding esters, complexes 1 and 2 gave 65 and 85% yield in 48 h, respectively, while the geometry-constrained complex 3 gave 96% yield in 24 h. Exploring the effect of substituents on benzaldehyde, it has been found that, in general, electron-withdrawing groups facilitate the reaction. Kinetic study with complexes 1 and 3 reveals that the rate of the reaction is first order in catalyst and substrate, which suggests the rate equation "rate = k[catalyst](1)[aldehyde](1)". The activation energy of the reaction was found to be 7.16 ± 0.40 and 3.47 ± 0.40 kcal/mol for complexes 1 and 3 respectively, which clearly indicates the advantage of the geometry-constrained complex. Astonishing are the reactivity of the organoactinide complexes with oxygen-containing substrates, and especially the reactivity of complex 3, toward the dimerization of substrates like p-methoxybenzaldehyde, m/p-nitrobenzaldehyde, and furanaldehyde and the reactivity toward the polymerization of terephthalaldehyde. Density functional theory mechanistic study reveals that the catalytic cycle proceeds via an initially four-centered transition state (+6 kcal/mol), followed by the rate-determining six-centered transition state (+13.5 kcal/mol), to yield thermodynamically stable products.

Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

“…Moreover, a KIE measurement of 6.0 suggests that CÀH bond activation is ratedetermining (Scheme 5 b). [19] On the basis of these initial studies and literature reports, we propose the mechanism shown in Scheme 6. [20] Ketone 3 d binds to nickel to form complex 8 a, which can coordinate to an aldehyde (1) to give intermediate 8 b. Oxidative addition to the aldehyde CÀH bond generates 8 c, which reduces the hydrogen acceptor 3 d to yield acyl nickel alkoxide 8 d. [21] Ligand exchange with the nucleophile affords 8 e, and reductive elimination provides the final product.…”

Mechanistic Origin of Chemoselectivity in Thiolate‐Catalyzed Tishchenko Reactions

“…In recent decades, extensive studies have been carried out to improve the reaction yield and expand the substrate scope. [2] Various catalysts, including alkali metal, [1,3] boric acid, [4] actinides, [5] lanthanide [6] and transition-metal complexes [7,8] (such as Rh [7a] and Os complexes [7b] ), have been utilized in Tishchenko reactions. Nonetheless, traditional Tishchenko reactions are mainly limited to homocouplings between two molecules of the same substrate, whereas cross-coupling between two different substrates is relatively rare.…”

Selective Oligomerization and [2 + 2 + 2] Cycloaddition of Terminal Alkynes from Simple Actinide Precatalysts

“…27 The high yield of dimer generated from this substrate illustrates the lower energetic pathway of protolytic cleavage in comparison to migratory insertion into the actinide−vinyl bond. This is corroborated by the small quantities of product formed from the additional insertion into this intermediate, evident by the formation of only small amounts of trimer 6a (≤7%), similarly occurring from a headto-tail insertion.…”