Asymmetric Magnesium‐Catalyzed Hydroboration by Metal‐Ligand Cooperative Catalysis

Abstract

Asymmetric catalysis with readily available,c heap, and non-toxic alkaline earth metal catalysts represents as ustainable alternative to conventional synthesis methodologies. In this context, we describe the development of af irst Mg IIcatalyzede nantioselective hydroboration providing the products with excellent yields and enantioselectivities.N MR spectroscopys tudies and DFT calculations provide insights into the reaction mechanism and the origin of the enantioselectivity which can be explained by ametal-ligand cooperative catalysis pathwayinvolving anon-innocent ligand. Scheme 1. Magnesium-catalyzed asymmetric hydroboration of ketones.

Magnesium‐Catalyzed Tandem Dehydrogenation‐Dehydrocoupling: An Atom Economical Access to Alkynylboranes

“…Within few minutes, conversion reached a maximum leading to a mixture of 4 products: (1) diisopropylaminophenyl borane ( 5 , 11 B NMR δ =39 ppm, (d)) resulting from the addition of remaining PhMgBr onto DIPOB; (2) the expected diisopropylaminohex‐1‐yn‐1‐ylborane ( 2 a , 11 B NMR δ =42 ppm, (d)), (3) magnesium diisopropylaminohex‐1‐yn‐1‐ylborohydride ( 4 a , 11 B NMR δ =−13 ppm, (t)), albeit in very low quantity with respect to the other compounds and finally (4) magnesium diisopropylamino borohydride ( 6 , 11 B NMR δ =−22 ppm, (t)) (See NMR in the Supporting Information). This product could result from the direct hydride transfer from 4 a to DIPOB without the formation of Mg−H as observed in the C=O Mg‐catalyzed hydroboration …”

“…This product could result from the direct hydride transfer from 4a to DIPOB without the formation of MgÀHa s observed in the C=OM g-catalyzed hydroboration. [29] Alternatively, it can intermediately go through HMgBr loss which was proven to occur after addition of PhMgBr to HBpin for example. [30] To evaluatei ts potentiali mplication in the catalytic process, HMgBr was separately prepared by reaction between magnesium hydride and magnesium bromide.…”

Strategies of In Situ Generated Magnesium Catalysis in Asymmetric Reactions

“…In 2019, one enantioselective hydroboration of ketones was successfully achieved using simple binolate-Mg(II) catalysts by Rueping and co-workers as a breakthrough work (Scheme 3). 7,8 The reaction is highly interesting because it first identified binolate-Mg(II) complexes were effective catalyst for activation of HBpin, given the fact that in previous works only monoanionic ligands, such as β-diketiminato stabilized magnesium complexes, worked well in the hydroboration of unsaturated bonds via a Mg-H species as the key intermediate. 9 However, under this binolate-Mg(II) catalytic method, there was no Mg-alkyl bond remained after sequential neutralization processes to generate the Mg-H bond (Scheme 3, A).…”

Hydrosilylation and hydroboration in a sustainable manner: from Earth-abundant catalysts to catalyst-free solutions

“…The group of Rueping reported a series of examples that involve hydroboration of ketones, carbonates, and alkynes (Scheme 21). [130][131][132][133] In these processes, a commercially available, non-toxic, and quite inexpensive di-n-butylmagnesium solution has been applied as the catalyst. An enantioselective version provides products with excellent yields (up to 99%) and enantioselectivities (er up to 99 : 1).…”