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Disproportionation of aldehydes through Cannizzaro, Tishchenko, and Meerwein–Ponndorf–Verley reactions often requires the application of high temperatures, equimolar or excess quantities of strong bases, and is mostly limited to the aldehydes with no CH2 or CH3 adjacent to the carbonyl group. Herein, we developed an efficient, mild, and multifunctional catalytic system consisting AlCl3/Et3N in CH2Cl2, that can selectively convert a wide range of not only aliphatic, but also aromatic aldehydes to the corresponding alcohols, acids, and dimerized esters at room temperature, and in high yields, without formation of the side products that are generally observed. We have also shown that higher AlCl3 content favors the reaction towards Cannizzaro reaction, yet lower content favors Tishchenko reaction. Moreover, the presence of hydride donor alcohols in the reaction mixture completely directs the reaction towards the Meerwein–Ponndorf–Verley reaction.

Strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4 − salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the R1,R2BDI ligand (R1,R2BDI=HC[C(R1)N(R2)]2) influence sterics and Lewis acidity. Ligand bulk increases along the row Me,DIPPBDI, A series of strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4 − salts. Their catalytic activity in imine hydrogenation depends strongly on the substituents in the BDI ligand. DFT calculations on the mechanism reveal two interconnected catalytic cycles. Hydrogen is activated either by Al⋅⋅⋅imine or Al⋅⋅⋅amine Frustrated‐Lewis‐Pairs.

In the last decade, major conceptual advances in the chemistry of actinide molecules and materials have been made to demonstrate their distinct reactivity profiles as compared to lanthanide and transition metal compounds, but some difficult questions remain concerning the intriguing stability of low-valent actinide complexes, and the importance of the 5f-orbitals in reactivity and bonding. The imidazolin-2-iminato moiety has been extensively used in ligands for the advancement of actinide chemistry owing to its unique capability of stabilizing the reactive and highly electrophilic metal ions by virtue of its strong electron donation and steric tunability. The current review article describes recent developments in the chemistry of light actinide metal ions (thorium and uranium) bearing these N-heterocyclic iminato moieties as supporting ligands. In addition, the effect of ring expansion of the N-heterocycle on the catalytic aptitude of the organoactinides is also described herein. The synthesis and reactivity of actinide complexes bearing N-heterocyclic iminato ligands are presented, and promising apposite applications are also presented. The current review focuses on addressing the catalytic behavior of actinide complexes with oxygen-containing substrates such as in the Tishchenko reaction, hydroelementation processes, and polymerization reactions. Actinide complexes have also found new catalytic applications, as demonstrated by the potent chemoselective carbonyl hydroboration and tandem proton-transfer esterification (TPTE) reaction, featuring coupling between an aldehyde and alcohol.

The first successful example of a catalytic enantioselective intramolecular Tishchenko reaction of a meso-dialdehyde in the presence of a chiral iridium complex is described. Chiral lactones were obtained in good yields with up to 91% ee. The obtained enantioenriched lactones were utilized for the first synthesis of (S)-cedarmycins A and B.

The synthesis of rhodium complexes with weakly binding highly fluorinated benzene ligands is described: 1,2,3‐F3C6H3, 1,2,3,4‐F4C6H2 and 1,2,3,4,5‐F5C6H are shown to bind with cationic [Rh(Cy2P(CH2)xPCy2)]+ fragments (x=1, 2). Their structures and reactivity with alkenes, and use in catalysis for promoting the Tishchenko reaction of a simple aldehyde, are demonstrated. Key to the synthesis of these complexes is the highly concentrated reaction conditions and use of the [Al{OC(CF3)3}4]− anion., Weakly binding highly fluorinated benzene ligands 1,2,3‐F3C6H3, 1,2,3,4‐F4C6H2 and 1,2,3,4,5‐F5C6H are shown to bind with cationic [Rh(Cy2P(CH2)xPCy2)]+ fragments (x=1, 2), and the resulting complexes have been used in synthesis and catalysis.

Pincer-type complexes [OsH2(CO){PyCH2NHCH2CH2NHPtBu2}] and [OsH2(CO){HN(CH2CH2PiPr2)2}] catalyze the disproportionation reaction of aldehydes via an outer-sphere bifunctional mechanism achieving turnover frequencies up to 14 000 h−1. The N−H group of the catalysts is a key player in this process, elucidated with the help of DFT calculations.

Zinc oxide has been developed as a catalyst for the dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The reaction is performed in mesitylene solution in the presence of potassium hydroxide, followed by workup with hydrochloric acid. The transformation can be applied to both benzylic and aliphatic primary alcohols and the catalytically active species was shown to be a homogeneous compound by a hot filtration test. Dialkylzinc and strongly basic zinc salts also catalyze the dehydrogenation with similar results. The mechanism is believed to involve the formation of a zinc alkoxide which degrades into the aldehyde and a zinc hydride. The latter reacts with the alcohol to form hydrogen gas and regenerate the zinc alkoxide. The degradation of a zinc alkoxide into the aldehyde upon heating was confirmed experimentally. The aldehyde can then undergo a Cannizzaro reaction or a Tishchenko reaction, which in the presence of hydroxide leads to the carboxylic acid.

The synthesis of the mono(imidazolin-2-iminato) actinide(IV) complexes [(Im(R)N)An(N{SiMe3)2}3] (3-8) was accomplished by the protonolysis reaction between the respective imidazolin-2-imine (Im(R)NH, R = tBu, Mes, Dipp) and the actinide metallacycles [{(Me3Si)N}2An{κ(2)C,N-CH2SiMe2N(SiMe3)}] (1, An = U; 2, M = Th). The thorium and uranium complexes were obtained in high yields, and their structures were established by single-crystal X-ray diffraction analysis. The mono(imidazolin-2-iminato) actinide complexes 3-8 display short An-N bonds together with large An-N-C angles, indicating strong electron donation from the imidazolin-2-iminato moiety to the metal, corroborating a substantial π-character to the An-N bond. The reactivity of complexes 3-8 toward benzaldehyde was studied in the catalytic dimerization of aldehydes (Tishchenko reaction), displaying low to moderate catalytic activities for the uranium complexes 3-5 and moderate to high catalytic activities for the thorium analogues 6-8, among which 8 exhibited the highest catalytic activity. In addition, actinide coordination compounds showed unprecedented reactivity toward cyclic and branched aliphatic aldehydes in the catalytic Tishchenko reaction mediated by the thorium complex [(Im(Dipp)N)Th{N(SiMe3)2}3] (8), exhibiting high activity even at room temperature. Moreover, complex 8 was successfully applied in the crossed Tishchenko reaction between an aromatic or polyaromatic and an aliphatic cyclic and branched aldehyde, yielding selectively the asymmetrically substituted ester in high yields (80-100%).

Photocatalytic homolysis of dry methyl formate (MF) to dry formaldehyde readily takes place in high selectivity (≥80%) upon irradiation of MF vapour on PdO/TiO2 in the 385–1050 nm region. The Pd(I)Pd(0) nanoparticles supported on Ti(III)-bearing TiO2 produced during the reaction are proposed to be the active form of the catalyst for this novel reaction.

Mechanistic studies have been performed for the recently developed, Ni-catalysed selective cross-coupling reaction between aryl and alkyl aldehydes. A mono-carbonyl activation (MCA) mechanism (in which one of the carbonyl groups is activated by oxidative addition) was found to be the most favourable pathway, and the rate-determining step is oxidative addition. Analysing the origin of the observed cross-coupling selectivity, we found the most favourable carbonyl activation step requires both coordination of the aryl aldehyde and oxidative addition of the alkyl aldehyde. Therefore, the stronger π-accepting ability of the aryl aldehyde (relative to alkyl aldehyde) and the ease of oxidative addition of the alkyl aldehyde (relative to aryl aldehyde) are responsible for the cross-coupling selectivity.

A samarium-mediated novel synthesis of enantiopure 4-amino-1,3-diols is carried out through a samarium-promoted aldol–Tishchenko reaction starting from chiral α′-amino-α-chloro ketones (derived from natural α-amino acids) and aldehydes. The process takes place with moderate levels of stereoselectivity and in high yields. A mechanism is proposed to explain these results while the absolute configuration and structure of the aldol–Tishchenko adducts were established by X-ray analysis. This method has also been utilized for the synthesis of enigmols, 1-deoxysphingoid base analogues.

The ‘Tishchenko reaction’ (discovered by Claisen in 1887) is the disproportionation of two aldehyde molecules to furnish an ester product (Scheme 1). Aluminium alkoxides and boric acid, were the first classes of synthetically relevant homogeneous catalysts for this reaction, these were then followed by a range of transition metal complexes of low-high catalytic activity but often limited practical utility. More recently, lanthanide, actinide and calcium 11 ] complexes capable of promoting aldehyde dimerization with excellent activity have been reported. A generalized mechanistic outline of the process is given in Scheme 1 – reaction of the transition metal complex 1 with the aldehyde generates the metal-alkoxide 2, which acts as the hydride transfer agent in a metal-mediated redox process (i.e. 3) leading to ester 4.

A simple and efficient catalytic system for the selective dimerization of aldehydes, the Tishchenko reaction, is described. High yields of symmetrical esters were generally achieved using an in situ generated ruthenium catalyst in association with the electron-rich and hindered cyclohexyl-(diphenyl)phosphane (CyPPh 2 ) ligand.

Potentially useful 17-, and 22÷25-membered macrolides containing azine or hydrazide groups were synthesized from tetrahydropyran via [1+1]-condensation at room temperature of 7-oxooctyl-7-oxooctanoate, which was obtained via Tishchenko reaction from 7-oxooctanal, with hydrazine hydrate and hydrazides of several dicarboxylic acids.

Potentially useful 15- and 20-membered macrolides containing azine or hydrazide groups were synthesized from L-menthol via [1+1]-condensation at room temperature of 3R,7-dimethyl-6-oxooctyl-3R,7-dimethyl-6-oxooctanoate, which was obtained from 3R,7-dimethyl-6-oxooctanal via a Tishchenko reaction, with hydrazine hydrate or malonic acid dihydrazide.

Kinetic regularities of joint obtaining of 2,5- diethyl-3,4-dihydro-2H-pyran-2-methanol and sodium salt of 2,5-diethyl-3 ,4-dihydro-2H-pyran-2-carboxylic acid have been investigated. Optimal synthesis conditions have been established and physico-chemical characteristics of the main products have been determined. carbaldehyde by molecular oxygen. The main identified products are acetonylacetone (~30 %), acetic acid (25 %), and formic acid (15 %). As regards the pyranic alcohols, 2,5-dimethyl-3,4- dihydro-2H-pyran-2-methanol is obtained by catalytic hydrogenation of 2,5-dimethyl-3,4-dihydro-2-formyl-2H- pyran with the yield of 62 % (3). The yield of 3,4-dihydro- 2H-pyran-2-methanol obtained by reduction of 3,4- dihydro-2-formyl-2H-pyran with lithiumaluminumhydride is 61 % (7) and 20 % - when it is obtained by Tishchenko reaction (8). Sodium salt of 3,4-dihydro-2H-pyran-2-carboxylic acid is obtained by saponificatio n of 2-(3,4-dihydro-1,2- pyranyl)-methyl-3,4-dihydro-2H-pyran-2-carboxilate at the heating with small excess of NaOH 20 %-aqueous solution (9). The yield is 70 %. Sodium salt of 2,5-dimethyl-3,4- dihydro-2H-pyran-2-carboxylic acid is obtained in a similar way by saponificatio n of 2-carboxy-2,5-dimethyl-3,4- dihydro-2H-pyran (10). The yield is 40 %. However the best results (yield by all products is nearly 80 %) are obtained at joint synthesis of 2,5- dimethyl-3,4-dihydro-2H-pyran-2-methanol and sodium salt of 2,5-dimethyl- 3,4-dihydro-2H-pyran-2-carboxylic acid from metacrolein dimer via Cannizzaro reaction (11). Data concerning sodium salts of pyranic acids of the following terms of acrolein homologous series are absent. Therefore the aim of the present work is the investigation of kinetic regularities of joint obtaining of 2,5-diethyl-3,4- dihydro-2H-pyran-2-methanol and sodium salt of 2,5- diethyl-3,4-dihydro-2H-pyran-2-carboxylic acid via Cannizzaro reaction with the following choice of optimal synthesis conditions.

The heterometal alkoxide clusters of Group 3 metal and lanthanides with sodium Ln2Na8(OCH2CH2NMe2)12(OH)2 (Ln=Y, lanthanide) were found to serve as highly active catalysts for the Tishchenko reaction of various aldehydes to form the corresponding esters. The reaction scope and the influence of lanthanide and sodium metal on the catalytic activity were investigated, and the proposed mechanism of the reaction was discussed.

The development of solid strong base catalysts utilizable in green but acidic medium of scCO2 is reviewed. The strong base sites on mesoporous alumina and sulfated mesoporous alumina that had been generated by severe treatment at 773 K under vacuum (10−4 Torr) were not neutralized by the compressed Lewis acidic molecules of CO2, promoting a representative strong base-catalyzed reaction of the Tishchenko reaction as well as a typical base-catalyzed reaction of the Knoevenagel reaction in scCO2. Infrared spectroscopy of the adsorbed pyrrole, temperature-programmed desorption of CO2, and the poisoning by a very weak Bronsted acid of methanol have revealed that the average strengths of the base sites on mesoporous alumina and sulfated mesoporous alumina are weaker than that on conventional γ-alumina like JRC-ALO-4, but that they have a small number of strong base sites which function even in scCO2 medium. It was found that the addition of a slight amount of THF cosolvent into scCO2 remarkably accelerates the Tishchenko reaction over sulfated mesoporous alumina; the reaction rate in the scCO2–THF medium was 1.5-fold and 2-fold faster than those in ordinary organic solvents such as benzene and THF and that in pure scCO2, respectively. The unique structures of mesoporous alumina and sulfated mesoporous alumina have been fully characterized by N2 adsorption–desorption measurements and XRD analyses.

Tishchenko reaction of benzaldehyde was carried out over the MgO whose surface O atoms were enriched with 18 O to examine whether the surface O atoms of MgO are incorporated into the product and reactant. The surface lattice 18 O atoms were incorporated in both the product and reactant. The 18 O concentration was significantly higher for the product than for the reactant. In addition, the 18 O in the product ester was located not only in the carbonyl group (C O) but also in the bridging position (C O C); 18 O exchange between benzaldehyde and MgO surface occurred not only in the adsorption–desorption of benzaldehyde, but also in the dimerization process. The oxygen exchange results in the migration of active sites of coordinative unsaturated site (CUS) over the surface of MgO catalyst during the reaction.

A novel and highly diastereoselective samarium-catalyzed tandem rearrangement/reduction of secondary alpha-hydroxy epoxides, which involves a C1 to C3 carbon migration rearrangement and a very interesting hetero-Tishchenko reduction of the intermediate aldehyde and the reductant aldehyde, has been reported. This reaction could be developed to provide a facile and stereoselective construction of 2-quarternary 1,3-diol units with an hydroxymethyl moiety attached to the diastereogenic quaternary carbon center. Detailed investigations have been carried out concerning the screening of the aldehydes as a reductant, the optimization of reaction conditions, and the substrate scope of this tandem reaction. A catalytic cycle for this reaction, the electronic and steric effects of the reductant aldehydes, and the mechanism for the acyl migration of 1,3-diol monoesters are proposed.

The catalytic conversion of acyclic and cyclic esters into ketones was studied. Based on an analysis of data on the yields of the products of ester conversion, the conclusion was drawn that ketones result from a reaction between two ester molecules with the intermediate formation of a β-ketoester. This reaction is accompanied by the partial thermal decomposition of esters to aldehydes (reverse Tishchenko reaction) with the subsequent condensation.

Catalytic behavior of solid bases for mixed Tishchenko reaction in which an equimolar mixture of two different aldehydes is allowed to react was investigated employing the combinations of benzaldehyde and pivalaldehyde, pivalaldehyde and cyclopropanecarbaldehyde, and cyclopropanecarbaldehyde and benzaldehyde. The reactions were performed at 353 K for 4 h in vacuo without solvent using 5 mmol of each aldehyde and 100 mg of solid base catalyst. For all the combinations, the catalytic activity of alkaline earth oxides increased in the order of BaO≪MgO

We have synthesized a new nickel enolate [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] featuring fluorine atoms on the enolate moiety via B(C6F5)3-promoted C-F bond activation of α,α,α-trifluoroacetophenone. X-ray diffraction study of [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] revealed that the complex had adopted an η(3)-oxallyl coordination mode in the crystal lattice. The reaction of (t)BuNC with [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] resulted in the coordination of isocyanide to the nickel center to form a C-bound enolate complex. The reactions of [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] with aldehydes gave insertion products quantitatively which were fully characterized by NMR spectroscopy. Furthermore, we established unique catalytic applications for [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] toward a Tishchenko reaction, along with a highly selective crossed-esterification of α,α,α-trifluoroacetophenones with aldehydes.

International audience; The thiolate-catalyzed Tishchenko reaction has shown high chemoselectivity for the formation of double aromatic-substituted esters. In the present study, the detailed reaction mechanism and, in particular, the origin of the observed high chemoselectivity, have been studied with DFT calculations. The catalytic cycle mainly consisted of three steps: 1,2-addition, hydride transfer, and acyl transfer steps. The calculation results reproduce the experimental observations that 4-chlorobenzaldehyde acts as the hydrogen donor (carbonyl part in the ester product), while 2-methoxybenzaldehyde acts as the hydrogen acceptor (alcohol part in the product). The two main factors are responsible for such chemoselectivity: 1)in the rate-determining hydride transfer step, the para-chloride substituent facilitates the hydride-donating process by weakening the steric hindrance, and 2)the ortho-methoxy substituent facilitates the hydride-accepting process by stabilizing the magnesium center (by compensating for the electron deficiency).

Three contiguous stereocenters are constructed with high diastereoselectivity in a novel samarium-catalyzed tandem reaction of α-hydroxy epoxides 1 to give exclusively the C1,C2-anti isomers of 2 and 2'. This could lead to the development of a general procedure for the diastereoselective construction of 2-quaternary 1,3-diol units.

The homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides of the general type [Ln{N(SiMe3)2}3] (1) (Ln=Y, lanthanide) represent a new class of Tishchenko precatalysts and, to a limited extent, precatalysts for the hydroamination/cyclization of aminoalkynes. It is shown that 1 is the most active catalyst for the Tishchenko reaction. This contribution presents investigations on the scope of the reaction, substrate selectivity, lanthanide-ion size-effect, and kinetic/mechanistic aspects of the Tishchenko reaction catalyzed by 1. The turnover frequency is increased by the use of large-center metals and electron-withdrawing substrates. The reaction rate is second order with respect to the substrate. While donor atoms, such as nitrogen, oxygen, or sulfur, on the substrate decrease the turnover frequency, 1 shows a tolerance for a large number of functional groups. For the hydroamination/cyclization of aminoalkynes, 1 is less active than the well-known metallocene catalysts. On the other hand, 1 is much more readily accessible (one-step synthesis or commercially available), than the metallocenes and might therefore be an attractive alternative catalyst.

Shelf-available alkali metal tert-butoxides, hydrides and bis(trimethylsilyl)amides were shown to be highly efficient homogeneous precatalysts for the disproportionation of aldehydes to the corresponding carboxylic esters. Potassium compounds in combination with 18-crown-6 ether could drastically increase the rate of reaction in a few cases. Alternatively, efficient aldol condensations were found for aldehydes possessing an enolizable methylene group at the α-position to the aldehyde functionality. The active species involved in this esterification using any of these alkali metal catalysts is expected to be the metal alkoxide. Potassium compounds were found to be much more efficient when compared to analogous sodium compounds and kinetic studies revealed the rate-determining step to be a second order concerted hydride transfer from a potassium hemiacetal species to another molecule of aldehyde.

A synthetic route to magnesium guanidinate compounds that avoids ligand redistribution is reported; selected derivatives are active pre-catalysts in the dimerization of aldehydes.

In the presence of a Ni(0)/NHC catalyst, an equimolar mixture of aliphatic and aryl aldehydes can be employed to selectively yield a single cross-coupled ester. This reaction can be applied to a variety of aliphatic (1°, 2°, cyc-2°, and 3°) and aryl aldehyde combinations. The reaction represents 100% atom efficiency and generates no waste. Mechanistic studies have revealed that the striking feature of the reaction is the simultaneous coordination of two aldehydes to Ni(0).

No sooner said than done: A rhodi- um(III) hydride complex is an outstandingly effective and selective catalyst for the dimerization of aldehydes to the corresponding esters (see scheme). Evidence for an unusual mechanism in catalysis by rhodium is given., The generous financial support from MICINN/FEDER (Project CTQ2008-03860) and G.A. (Gobierno de Aragón, Project: PM 036/2007) is gratefully recognized. V.P. thanks C.S.I.C. for an I3P postdoctoral contract.

The oxidation of alcohols in the presence of methanol has been achieved using a ruthenium catalyst with crotononitrile as the hydrogen acceptor.

This article reviews the Tishchenko reaction: 2 RCHO → RCOOCH2R (R = hydrogen, alkyl, and aryl), describing the reaction mechanisms, homogeneous and heterogeneous catalysts developed for the reacti...

Sodium tert-butoxide promoted reaction between isobutyrophenone and excess (> 4 mol) benzaldehyde gives anti-1,3-dibenzoyloxy- 2,2-dimethyl-1,3-diphenylpropane, a product of sequential aldol–Tishchenko and Tishchenko reactions.

A direct catalytic asymmetric aldol reaction of propionate equivalent was achieved via the aldol-Tishchenko reaction. Coupling an irreversible Tishchenko reaction to a reversible aldol reaction overcame the retro-aldol reaction problem and thereby afforded the products in high enantio and diastereoselectivity using 10 mol % of the asymmetric catalyst. A variety of ketones and aldehydes, including propyl and butyl ketones, were coupled efficiently, yielding the corresponding aldol-Tishchenko products in up to 96% yield and 95% ee. Diastereoselectivity was generally below the detection limit of 1H NMR (>98:2). Preliminary studies performed to clarify the mechanism revealed that the aldol products were racemic with no diastereoselectivity. On the other hand, the Tishchenko products were obtained in a highly enantiocontrolled manner.

Using the catalytic transformation of isobutyl benzoate at 663 K in the presence of 12 % MnO2/γ-Al2O3 in a He atmosphere as an example, it has been shown that the inverse Tishchenko reaction can take place at a temperature above 600 K. Isobutyl benzoate gives isobutanal and benzaldehyde as well as products of their transformation,i.e., benzyl isobutyrate, isobutanol, benzyl alcohol, and toluene.

For many decades, compounds containing oxygen atoms were excluded from the actinide-catalysis field because of the high oxophilic nature of these complexes. Pursuing the conceptual question about the potential activity of actinide-oxo bonds we were surprised to find that the coupling of aromatic aldehydes catalyzed by Cp*2ThMe2 and Th(NEtMe)4 via thorium−alkoxide intermediates takes place in high yields to produce the corresponding esters. In this paper we present our breakthrough results including comprehensive mechanistic, deuterium labeling, kinetic, and thermodynamic studies. A plausible mechanism is presented taking into account as well the thermochemistry of the process.

Heterogeneous strong base catalysis for the Tishchenko reaction in acidic scCO2 solvent has been realized with mesoporous alumina modified with SO42−, while a conventional solid base like CaO showe...

The heterogeneous catalytic systems realized by alkaline earth oxides are successfully applicable to the highly efficient intramolecular Tishchenko lactonization of o-phthalaldehyde to phthalide.

RuH2(PPh3)4 and other hydridoruthenium complexes catalyze selective conversion of aldehydes into esters in high yields. The method is applicable to most aliphatic aldehydes as well as to aromatic aldehydes. The purity of aldehydes is critical for achieving high conversions, since the presence of carboxylic acid completely inhibits the reaction and alcohol and triphenylphosphine reduce the yields of esters. RuH2(PPh3)4 is converted into Ru(CO)3(PPh3)2 through the reaction indicating the occurrence of decarbonylation of aldehyde. A mechanism involving the acyl-H cleavage of aldehyde is proposed to account for the catalysis and formation of compounds accompanying the reaction. The mechanism is compared with an alternative one which comprises of consecutive insertions of two aldehyde molecules into Ru–H bond followed by β-hydrogen abstraction from an alkoxo intermediate formed. Addition of water changes the reaction course to give carboxylato carbonyl complexes Ru(OCOR)2(CO)m(PPh3)2 (m=1 and 2). Cross esterif...

Disodium tetracarbonylferrate (–II) is an efficient catalyst for the dismutation of aromatic aldehydes to esters, 2RCHO→RCOOCH2R. Aliphatic ones give aldol-condensation products upon treatment with the ferrate. A successive reaction of the ferrate with an aldehyde, RCHO, and then with alkyl iodide, R’I, gives an ester, R’COOCH2R, after protonation. The mechanisms of these reactions are discussed.

Reactions between diethylaluminum s-butoxide and n-butyraldehyde have been carried out at several temperatures from −65 to 40°C. The reaction mixtures were then treated with glacial acetic acid and subjected to vapor-phase chromatographic analysis (vpc). The products analyzed by vpc were methyl ethyl ketone, butanol-1, s-butyl n-butyrate, n-butyl n-butyrate, 2-ethyl-2-hexenal, and 2-ethyl-1, 3-hexanediol 1-n-butyrate. The last two compounds were formed only at reaction temperatures above 20°C, and methyl ethyl ketone was not formed below −40°C. The reaction of the ethylaluminum group with the aldehyde group was not observed. Finally, the interrelationship of the three reactions involving aluminum alkoxide and aldehyde, the Meerwein-Ponndorf-Verley reduction, the Tishchenko reaction, and the aldehyde polymerization, has been discussed.

The esterification of b6nzaldehyde has been studiedi over solid NaOH, NaOH-SiO2, A120s, SrO2, BaOz, SrO and CaO. The catalytic'activity was found not. only to closely relate with the basic properties, but also to relate, with the acidic proPerties (Fig., 6). lt was o. bserv. ed that two d-hYdrogens of benzyl groups of benzyl benzoate (major product) and benzyl alcohol (miner product) produced by the esterification of ibenzaldehyde-a-at were deuterat. ed. and t-hqt there The catalytic activity was was no hydrogen isotope effect(kH/kD=1, o, 2)(Figs, 1and 2), decreased by the addition of benzoic acid or phenol, but not by. the addition of benzene or cyclohexane' (Figs.3, 4 and 5). Thg amount of benzylE alcohol formed was increased by the addition of aliphatic alcohols (Fig.4).On the basi's of the observed results, it has been concluded that the aetive sites for the esterification are metal bezylates and those for the formation of metal benzylate consist of both basic sites (surface OZ) and Lewis acid sites (Ca2" etc. ). The mechanism of the esterification has been N@discussed in detail and 'c'ompared, with those of Cannizzaro and Tishchenko reaction in homogeneous system

Reactions of n-butyraldehyde caused by tris(trimethylsiloxy)aluminum were examined and compared with those caused by aluminum t-butoxide. In the Tishchenko reaction of aldehyde caused by aluminum t-butoxide, the t-butoxy group was first transferred from aluminum to the carbonyl group of n-butyraldehyde to produce t-butyl n-butyrate. On the other hand, we observed no formation of trimethylsilyl n-butyrate by the transfer of the trimethylsiloxy group to n-butyraldehyde. However, esters of the n-butyric acid of n-butanol and the glycol derived from the aldol of n-butyraldehyde were found in the system with tris(trimethylsiloxy)aluminum: their formation was ascribed to the aluminum alkoxide species which was first formed between tris(trimethylsiloxy)aluminum and the aldol of n-butyraldehyde. The above assumption has been supported by the finding that aluminum t-butoxide caused the Tishchenko reaction of benzaldehyde, producing benzyl benzoate almost quantitatively, whereas tris(trimethylsiloxy)aluminum did no...