Manganese-Catalyzed Asymmetric Hydrosilylation of Aryl Ketones

Abstract

We disclose the synthesis of a series of manganese complexes of chiral iminopyridine oxazoline ligands and their application in the first manganese-catalyzed asymmetric ketone hydrosilylations. The most sterically hindered manganese catalyst bearing two CH(Ph) 2 groups at the 2,6-ortho positions of the imino aryl ring and a t Bu group on the oxazoline ring furnishes the secondary alcohols in high enantioselectivities and yields.

Manganese‐Catalyzed Hydrosilylation Reactions

“…Very recently, the group of Huang achieved an elegant manganese‐catalyzed asymmetric hydrosilylation reaction of ketones for the first time (Scheme a) . By activation with NaBEt 3 H, the Mn II catalyst 43 bearing a chiral iminopyridine oxazoline ligand with sterically hindered groups gave the best results.…”

“…Very recently,t he group of Huang achieved an elegant manganese-catalyzed asymmetrich ydrosilylationr eactiono fk etones for the first time (Scheme9a). [22] By activation with NaBEt 3 H, the Mn II catalyst 43 bearing ac hiral iminopyridine oxazoline ligand with sterically hindered groupsgave the best results. Aw ide range of chiral secondary alcohols 44 were obtained in good to excellent yields and enantioselectivities after hydrolysiso ft he hydrosilylation products.L ater on, the Gade group developedm anganese complexes bearingp incer ligands 45 and 46,w hich showed am oderate enantioselectivity in the reduction of acetophenone (Scheme 9b).…”

“…In the 1990s, manganese carbonyl acyl catalysts were widely utilized in the works reported by the group of Cutler, and exhibited high reactivities in the hydrosilylationo f ketones, [14] esters, [15] and organoiron complexes. [11][12][13] In addition, many manganese catalysts covered in this review,i ncluding carbonyl-Mn complexes, half-sandwich manganese complexes, [16,18] Salen-Mn complexes, [17] bis-NHC-Mn complexes, [20] pincerm anganese complexes, [21][22][23] as well as manganeseamide complexes, [26] also presented their features on carbonyl hydrosilylation reactions. Of particular note is that the catalytic system reported by Trovitchh ad the highest TOF (4950 min À1 ) among all the base-metal catalysts, [21d] which might provide potentialf or large-scale applications of manganese catalysts in the hydrosilylation industry.…”

Reduction of carbonyl compounds via hydrosilylation catalyzed by well-defined PNP-Mn(I) hydride complexes

“…An attractive alternative to that is the use of hydrogen donors such as silanes [19,20]. Since the first report on manganese-catalyzed hydrosilylation reactions by Yates and coworkers in 1982 [21], several protocols for the hydrosilylation of polarized double bonds such as ketones [22][23][24][25][26][27], esters [28,29], amides [30][31][32] and acids [33] as well as alkenes [34][35][36] and alkynes [37] were developed.…”

Manganese‐Catalyzed Hydrofunctionalization of Alkenes

“…The manganese-catalysed hydrosilylation of polar double bonds such as aldehydes and ketones is well established. [15][16][17][18][19][20][21][22] Examples also exist for the hydrosilylation of esters, 21,23 amides 21 and carboxylic acids 24 (Scheme 1, A). Recently, Wang and co-workers reported the first manganese-catalysed hydrosilylation of alkynes.…”