Access to Enantiomerically Pure P ‐Stereogenic Primary Aminophosphine Sulfides under Reductive Conditions

Stereochemically pure phosphines with phosphorus-heteroatom bonds and P-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 all P-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

Stereochemically Pure Si‐Chiral Aminochlorosilanes

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

Controlled Synthesis and Molecular Structures of Methoxy-, Amino-, and Chloro-Functionalized Disiloxane Building Blocks

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 derivative6withN-pyrrolidinyllithium, but the same reaction starting from compound3was not successful. All provided disiloxanes were structurally characterized by X-ray crystallography

Hidden silylium-type reactivity of a siloxane-based phosphonium–hydroborate ion pair

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(sp(2))-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

Functional Group Variation in tert ‐Butyldiphenylsilanes (TBDPS): Syntheses, Reactivities, and Effects on the Intermolecular Interaction Pattern in the Molecular Crystalline State

We present the preparation of tert-butyldiphenylsilanes differing in one functional group. The molecular structures of the phenyl (3), methoxy (4), and amino derivatives (5) were elucidated by single-crystal X-ray diffraction analysis and their crystal packing investigated by Hirshfeld surface analysis along with 2D fingerprint plots. In the all-C derivative 3, the high symmetry dependence of the crystal packing enables a multitude of directional C(methyl)−H⋅⋅⋅C(π) interactions between the tert-butyl and phenyl groups. The methoxy derivative 4 is characterized by considerably short H⋅⋅⋅H contacts possibly resulting from pre-orienting C(aryl)−H⋅⋅⋅O and C(aryl)−H⋅⋅⋅C(π) hydrogen bonds. In the amino derivative 5, the nitrogen atom is not involved in intermolecular interactions, instead dispersive H⋅⋅⋅H contacts might become more important for the crystal cohesion. These findings once again underline the pronounced lone electron pair density transfer from the nitrogen atom towards the silicon atom

Synthesis of Pyrazines and Quinoxalines via Acceptorless Dehydrogenative Coupling Routes Catalyzed by Manganese Pincer Complexes

Base-metal catalyzed dehydrogenative self-coupling of 2-amino alcohols to selectively form functionalized 2,5-substituted pyrazine derivatives is presented. Also, 2-substituted quinoxaline derivatives are synthesized by dehydrogenative coupling of 1,2-diaminobenzene and 1,2-diols. In both cases, water and hydrogen gas are formed as the sole byproducts. The reactions are catalyzed by acridine-based pincer complexes of earth-abundant manganese

Synthesis of Cyclic Imides by Acceptorless Dehydrogenative Coupling of Diols and Amines Catalyzed by a Manganese Pincer Complex

The first example of base-metal-catalyzed dehydrogenative coupling of diols and amines to form cyclic imides is reported. The reaction is catalyzed by a pincer complex of the earth abundant manganese and forms hydrogen gas as the sole byproduct, making the overall process atom economical and environmentally benign

Redox Noninnocent Nature of Acridine-Based Pincer Complexes of 3d Metals and C–C Bond Formation

Acridine-based PNP pincer complexes have been previously utilized for several environmentally benign catalytic processes. In light of the recent growth in interest in base-metal catalysis, we report here the synthesis of acridine-PNP pincer complexes of Ni, Co, Fe, and Mn. We also report here the noninnocent redox nature of these complexes that results in the dimerization of pincer complexes by forming a C-C bond at the C9 position of the acridine ring

Manganese-Catalyzed Environmentally Benign Dehydrogenative Coupling of Alcohols and Amines to Form Aldimines and H₂: A Catalytic and Mechanistic Study

The catalytic dehydrogenative coupling of alcohols and amines to form aldimines represents an environmentally benign methodology in organic chemistry. This has been accomplished in recent years mainly with precious-metal-based catalysts. We present the dehydrogenative coupling of alcohols and amines to form imines and H₂ that is catalyzed, for the first time, by a complex of the earth-abundant Mn. Detailed mechanistic study was carried out with the aid of NMR spectroscopy, intermediate isolation, and X-ray analysis