Ruthenium-Catalyzed Tandem Olefin Migration/Aldol and Mannich-Type Reactions in Water and Protic Solvents

Switchable catalysis offers opportunities to control the rate or selectivity of a reaction via a stimulus such as pH or light. However, few examples of switchable catalytic systems that can facilitate multiple processes exist. Here we report a rare example of such dual-functional, switchable catalysis. Featuring an easily prepared, bench-stable cobalt(I) hydride complex in conjunction with pinacolborane, we can completely alter the reaction outcome between two widely employed transformations – olefin migration and hydroboration – with visible light as the sole trigger. This dichotomy arises from ligand photodissociation which leads to metamorphosis of the active catalytic site, resulting in divergent mechanistic pathways.

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α-Ketophosphonates in the Synthesis of α-iminophosphonates

Current Green Chemistry ◽

10.2174/2213346107666200226095806 ◽

2020 ◽

Vol 7 (2) ◽

pp. 226-238

Author(s):

Petro P. Ony`sko ◽

Tetyana I. Chudakova ◽

Vladimir V. Pirozhenko ◽

Alexandr B. Rozhenko

Keyword(s):

Bond Cleavage ◽

Direct Synthesis ◽

Equilibrium Mixture ◽

Primary Amines ◽

Alkyl Amines ◽

Protic Solvents ◽

Metallic Salts ◽

Direct Preparation ◽

Stage Synthesis ◽

Aprotic Dipolar Solvent

The potentialities of condensation of α-ketophosphonates with primary amines for direct synthesis of α-iminophosphonates have been revealed. Diesters of α-ketophosphonic acids react with the primary amines by two competitive pathways: with a formation of α-iminophosphonates or a C-P bond cleavage resulting in a hydrogen phosphonate and an acylated amine. In many cases, the latter undesirable pathway is dominant, especially for more nucleophilic alkyl amines. Using metallic salts of α-ketophosphonates avoids the C-P bond cleavage, allowing direct preparation of α-phosphorylated imines by the reaction with primary amines. This strategy provides an atom economy single-stage synthesis of iminophosphonates – precursors of bio relevant phosphorus analogs of α-amino acids. Methyl sodium iminophosphonates, bearing aryl or heteryl substituents at the imino carbon atom exist in solutions at room temperature as an equilibrium mixture of Z- and E-isomers. A configuration of the C=N bond can be controlled by the solvent: changing the aprotic dipolar solvent DMSO-d6 by water or alcohols leads to the change from a predominant Z-isomer to almost an exclusive E-form. In contrast, diesters of the respective iminophosphonates exist in non-protic solvents predominantly in Econfiguration. The solvent effect on E-Z stereochemistry is demonstrated by DFT calculations.

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Anion effect on alkali ion-crown complex formation in a moderately concentrated solutions: A sensitive probe of hidden interionic interactions operating in dissociating protic solvents

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19901149 ◽

1990 ◽

Vol 55 (5) ◽

pp. 1149-1161

Author(s):

Jiří Závada ◽

Václav Pechanec ◽

Oldřich Kocián

Keyword(s):

Hydrogen Bond ◽

Complex Formation ◽

Charge Density ◽

Macrocyclic Ligand ◽

Simple Explanation ◽

Anion Effect ◽

Protic Solvents ◽

The Individual ◽

Alkali Salts ◽

Alkali Ion

A powerful anion effect destabilizing alkali ion-crown complex formation has been found to operate in moderately concentrated protic (H2O, CH3OH, C2H5OH) solution, following the order HO- > AcO- > Cl- > Br- > NO3- > I- > NCS-. Evidence is provided that the observed effect does not originate from ion-pairing. A simple explanation is provided in terms of concordant hydrogen bond bridges of exalted stability between the gegenions, M+···OR-H···(OR-H)n···OR-H···A-. It is proposed that encapsulation of alkali ion by the macrocyclic ligand leads to a dissipation of the cation charge density destroying its ability to participate in the hydrogen bond bridge. An opposition against the alkali ion-crown complex formation arises accordingly in the solution in dependence on strength of the hydrogen bridge; for a given cation, the hydrogen bond strength increases with increasing anion charge density from NCS- to HO-(RO-). It is pointed out, at the same time, that the observed anion effect does not correlate with the known values of activity coefficients of the individual alkali salts which are almost insensitive to anion variation under the investigated conditions. As a resolution of the apparent paradoxon it is proposed that, in absence of the macrocyclic ligand, the stabilizing (concordant) bonding between the gegenions is nearly balanced by a destabilizing (discordant) hydrogen bonding between the ions of same charge (co-ions). Intrinsic differences among the individual salts are thus submerged in protic solvents and become apparent only when the concordant bonding is suppressed in the alkali ion-crown complex formation.

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Evidence for general base catalysis by protic solvents in a kinetic study of alcoholyses and hydrolyses of 1-(phenoxycarbonyl)pyridinium ions under both solvolytic and non-solvolytic conditions

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc2008164 ◽

2009 ◽

Vol 74 (1) ◽

pp. 43-55 ◽

Cited By ~ 1

Author(s):

Dennis N. Kevill ◽

Byoung-Chun Park ◽

Jin Burm Kyong

Keyword(s):

Second Order ◽

Base Catalysis ◽

Substitution Reactions ◽

Third Order ◽

Methoxy Derivative ◽

First Order ◽

General Base ◽

Protic Solvents ◽

Kinetics Of ◽

Pyridinium Ions

The kinetics of nucleophilic substitution reactions of 1-(phenoxycarbonyl)pyridinium ions, prepared with the essentially non-nucleophilic/non-basic fluoroborate as the counterion, have been studied using up to 1.60 M methanol in acetonitrile as solvent and under solvolytic conditions in 2,2,2-trifluoroethan-1-ol (TFE) and its mixtures with water. Under the non- solvolytic conditions, the parent and three pyridine-ring-substituted derivatives were studied. Both second-order (first-order in methanol) and third-order (second-order in methanol) kinetic contributions were observed. In the solvolysis studies, since solvent ionizing power values were almost constant over the range of aqueous TFE studied, a Grunwald–Winstein equation treatment of the specific rates of solvolysis for the parent and the 4-methoxy derivative could be carried out in terms of variations in solvent nucleophilicity, and an appreciable sensitivity to changes in solvent nucleophilicity was found.

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