Noel Angel Espinosa-Jalapa

Silicon‐based compounds with stereochemical information and convertible functional units are valuable building blocks in synthetic chemistry. Si‐stereogenic aminochlorosilanes are built up by Si−N bond formation between an achiral dichlorosilane and a chiral enantiomerically pure primary amine. Both diastereomers could be isolated as stereochemically pure single‐crystals by fractional crystallization and were analyzed by X‐ray crystallography. Defined intermolecular interaction patterns were identified illustrating the role of N−H⋅⋅⋅π, C−H⋅⋅⋅π, and N−H⋅⋅⋅Cl contacts in the molecular crystalline packing arrangements. Stepwise functionalization of the silicon−chlorine and silicon−amine functions was carried out, demonstrating their potential for use as a chiral synthesis precursors. Via optically pure aminomethoxysilanes, enantiomerically enriched methoxysilanols, chloromethoxysilanes, and methoxysilanethiols were synthesized. The stereospecificity of the transformations was monitored. The (R)‐BINOL‐PSSLi method for determining the enantiomeric purity was found to be the tool of choice for acid‐sensitive silanols and silanethiols.

Stereochemically pure phosphines with phosphorus‐heteroatom bonds andP‐centered chirality are a promising class of functional building blocks for the design of chiral ligands and organocatalysts. A route to enantiomerically pure primary aminophosphine sulfides was opened through stereospecific reductive C−N bond cleavage of phosphorus(V) precursors by lithium in liquid ammonia. The chemoselectivity of the reaction as a function of reaction time, substrate pattern, and chiral auxiliary was investigated. In the presence of exclusively aliphatic groups bound to the phosphorus atom, all competing reductive side reactions are totally prevented. The absolute configurations of allP‐stereogenic compounds were determined by single‐crystal X‐ray diffraction analysis. Their use as synthetic building blocks was demonstrated. The lithium salt of (R)‐BINOL‐dithiophosphoric acid proved to be a useful stereochemical probe to determine the enantiomeric purity. Insights into the coordination mode of the lithium‐based chiral complex formed in solution was provided by NMR spectroscopy and DFT calculations.

A new class of siloxane-based cations with hidden silylium-type reactivity is provided, which, in combination with an arylborate counteranion, initiates a highly selective para-C(sp²)–F defunctionalization of a perfluorinated aryl group. The hydrodefluorinated aryl borane is obtained as a crystalline solid via continuous sublimation during the reaction. The heterocyclic six-membered cation could be obtained single-crystalline after dehydrogenative anion exchange. DFT calculations give insight into the bonding within the siloxane-based cation and the mechanism of the ion pair reaction.

Phosphonium ions are widely used in preparative organic synthesis and catalysis. The provision of new types of cations that contain both functional and chiral information is a major synthetic challenge and can open up new horizons in asymmetric cation‐directed and Lewis acid catalysis. We discovered an efficient methodology towards new Si‐chiral four‐membered CPSSi* heterocyclic cations. Three synthetic approaches are presented. The stereochemical sequence of anchimerically assisted cation formation with B(C₆F₅)₃ and subsequent hydride addition was fully elucidated and proceeds with excellent preservation of the chiral information at the stereogenic silicon atom. Also the mechanism of dihydrogen release from a protonated hydrosilane was studied in detail by the help of Si‐centered chirality as stereochemical probe. Chemoselectivity switch (dihydrogen release vs. protodesilylation) can easily be achieved through slight modifications of the solvent. A matched/mismatched case was identified and the intermolecularity of this reaction supported by spectroscopic, kinetic, deuterium‐labeling experiments, and quantum chemical calculations.

Using a new bulky bidentate ligand and combining various structure elucidation methods, coordination modes of [ligand·LiX] (X = Cl, PF ₆ ) complexes both in solid-state and in solution have been revealed.

Functionalized disiloxane units with defined structures are interesting molecular models for investigating the reactivity and chemoselectivity in transformations that are of interest in synthesis, surface chemistry, and materials science. (Mes)PhSi(OMe)₂ (1) (Mes = mesityl) and (Mes)PhSiCl₂ (5) were chosen as starting compounds for the controlled synthesis of methoxy‐, amino‐, and chloro‐functionalized unsymmetric disiloxanes. Two synthesis routes towards (Mes)PhSi(OMe)(OSiPh₃) (3) were followed, one via the aminomethoxysilane (Mes)PhSi(OMe)(NC₄H₈) (2) and the other via the chlorodisiloxane (Mes)PhSiCl(OSiPh₃) (6). The amino‐substituted disiloxane (Mes)PhSi(NC₄H₈)(OSiPh₃) (4) was obtained from the chloro derivative 6 with N‐pyrrolidinyllithium, but the same reaction starting from compound 3 was not successful. All provided disiloxanes were structurally characterized by X‐ray crystallography.

Activation of CO₂ by manganese pincer complexes using two different modes of metal–ligand cooperativity (amido/amino mode and dearomatization/aromatization mode) is reported.

Amide synthesis is one of the most important transformations in chemistry and biology. The direct use of ammonia for the incorporation of nitrogen functionalities in organic molecules is an attractive and environmentally benign method. We present here a new synthesis of amides by acceptorless dehydrogenative coupling of benzyl alcohols and ammonia. The reaction is catalyzed by a pincer complex of earth-abundant manganese in the presence of a stoichiometric base, making the overall process economical, efficient, and sustainable. Interesting mechanistic insights based on detailed experimental observations, indicating the crucial role of the base, are provided.

The first example of a homogeneous catalyst based on an earth‐abundant metal for the hydrogenation of organic carbonates to methanol and alcohols is reported. Based on the mechanistic investigation, which indicates metal‐ligand cooperation between the manganese center and the N−H group of the pincer ligand, we propose that the hydrogenation of organic carbonates to methanol occurs via formate and aldehyde intermediates. The reaction offers an indirect route for the conversion of CO₂ to methanol, which coupled with the use of an earth abundant catalyst, makes the overall process environmentally benign and sustainable.