Yttrium–Benzyl Complexes Bearing Chiral Iminophosphonamide Ligands: Synthesis and Application in Catalytic Asymmetric Amine‐Silane Dehydrocoupling Reactions

Abstract

A series of novel iminophosphonamide ligands with chiral diamine moieties were designed and synthesized. Yttrium-benzyl compounds bearing these chiral iminophosphonamide ligands showed high reactivity and selectivity on the first catalytic asymmetric cross-dehydrogenative coupling of amines with prochiral silanes under mild conditions. A stable silylamine-boron derivative was synthesized in up to 23% ee, as determined by chiral HPLC analysis. By employing this catalyst system, catalytic kinetic resolution of an axially chiral silane and further in situ allylation were achieved in good yields and enantioselectivities.The past decades have witnessed the development of organosilane compounds, which have been widely used in organic functional materials and bioactive drugs. [1] Optically active silicon stereogenic compounds, however, are not available in nature, probably due to the Berry pseudorotation (BPR) of the highercoordinate silicon atom. [2] Significant progress has been made in creating silicon stereocenters utilizing chiral resolution and asymmetric induction. [3] However, the development of catalytic asymmetric methods using transition-metal catalysts has rarely been explored. Inventive catalytic desymmetrization reactions of prochiral silicon compounds have been developed, such as hydrosilylation of ketones, [4] alkenes [5] and alkynes, [6] carbon silylation of alkynes, [7] and [2 + 2 + 2] cycloaddition. [8] Additionally, enantioselective carbene insertion, [9] alcoholysis, [10] SiÀC cross-coupling, [11] and other desymmetrization reactions [12] have also been established.Silylamines, serving as bases, ligands, silylation agents and polymer precursors, play an important role in synthetic chemistry. [13] In contrast with traditional silylamine synthesis from chlorosilanes and amines, catalytic cross-dehydrogenative coupling of amines and silanes presents an atom-economic approach, with the generation of hydrogen as the only byproduct. Extensive studies have been carried out using metal catalysts, including metal carbonyls, [14] alkali metal complexes, [15] alkaline-earth complexes, [16] rare-earth complexes, [17] group IV metal complexes [18] and other catalysts. [19] However, an asymmetric version has not been introduced into the catalytic cross-dehydrogenative coupling of amines and silanes so far. Herein, we synthesized a series of novel rare-earth and alkalineearth alkyl complexes bearing non-C 2 -symmetric chiral iminophosphonamide ligands, among which yttrium complexes showed good reactivity and selectivity on the first catalytic asymmetric amine À silane dehydrogenative coupling reactions.The iminophosphonamide ligands, being versatile in tuning steric and electronic properties around rareearth metal centers, [20] have found their applications in catalytic polymerization and hydroamination reactions. In order to further explore the catalytic asymmetric potentiality, a chiral diamine moiety (1R, 2R)diaminocyclohexane or (1R,2R)-diphenylethylenediamine was introduced into the iminophosphonamide struct...

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N‐Silylation

“…Many catalysts either enhance the nucleophilicity of the amine or the electrophilicity of silane, which allows significant variability in catalyst design. The production of chiral silylamines has recently emerged through catalysis [56] …”

“…Guan and Li used the yttrium‐benzyl complex ( 31 ) bearing a chiral iminophosphoamide for the rapid coupling of mixed aryl‐ and alkyl‐secondary silanes and simple amine substrates under ambient conditions to high conversions of 91–100 % (Figure 10). [56] …”

Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence

“…However, the chemistry with chiral iminophosphonamide ligands is still nearly dormant. In 2007, racemic trans -1,2-diaminocyclohexyl-linked N -aryl bis(iminophosphonamines) and subsequent complexes with group 3 and group 13 elements were reported by Hill et al 13 More recently, Li and Guan reported on yttrium and alkaline earth metal complexes of chiral iminophosphonamides and their application as catalysts in cross-dehydrogenative coupling reactions of amines 14. In both reports, the chiral center was solely introduced at one nitrogen atom of the NPN ligand.…”

Enantiopure Calcium Iminophosphonamide Complexes: Synthesis, Photoluminescence, and Catalysis

“…Note that for the whole ligand class of iminophosphonamides only a few examples of alkaline earth metal complexes are known [7] . Moreover, only one heteroleptic calcium complex based on a chiral iminophosphonamide has been reported, with the chirality solely introduced at one nitrogen center [8] . None of these reported alkaline earth metal complexes based on iminophosphonamides showed PL.…”