Primary alkyl bis-catecholato silicates in dual photoredox/nickel catalysis: aryl- and heteroaryl-alkyl cross coupling reactions

Abstract

International audiencePrimary alkyl bis-catecholato silicates have been successfully engaged with aryl and heteroaryl bromide substrates in photoredox/nickel dual catalysis to provide aryl- and heteroaryl-alkyl cross coupling products. The scope of the transformation is wide and the process appears to be tolerant of various functional groups present. Of note, most examples rely on the challenging use of highly reactive primary radicals which constitutes a significant advance in these cross coupling reactions

Photoredox Catalysis in Nickel-Catalyzed Cross-Coupling

“…Under the same set of conditions developed, the scope of this work was later expanded to a variety of aryl-and heteroaryl bromides containing electronwithdrawing and electron-donating groups, such as ketones, fluorides, hydroxyls, chlorides, and silyl and boronate esters, and the coupled products were obtained in moderate to good yields (Scheme 17) [31]. Benzylic, allylic, and primary alkylsilicates were also suitable partners for this transformation.…”

Photoredox Catalysis in Organic Chemistry

“…Interestingly, for benzylic trifluoroborate salts, only moderate levels of enantioselectivity were observed when a chiral ligand was employed and computational studies suggest that rapid dissociation of the benzylic radical from the Ni(III)–aryl species occurs, thereby rendering reductive elimination the enantiodetermining step. Recently, both the Molander group 114 and Fensterbank, Ollivier, and Goddard 115 demonstrated that alkylbis(catecholato)silicates could also be utilized as radical precursors in photoredox Ni-catalyzed cross-couplings. While preformation of the silicates from the corresponding trimethoxysilanes is required, a notable feature of this methodology is the ability to couple unstabilized primary and secondary radicals in excellent yield.…”

Mild, Redox-Neutral Alkylation of Imines Enabled by an Organic Photocatalyst

“…In the course of our investigations, our group and others have reported that alkyl bis(catecholato)silicates readily undergo SET oxidation under photoredox conditions and are viable radical precursors in photoredox/nickel dual catalysis. 3 Ultimately, it has been shown that alkyl bis(catecholato)silicates serve as progenitors for both primary and secondary alkyl radicals that can be engaged in numerous processes including: (1) Csp 2 –Csp 3 cross-couplings with aryl halides/(pseudo)halides and alkenyl halides, 3,4 (2) the functionalization of azaborine isosteres, 5 and (3) the synthesis of thioethers via H atom transfer. 6 When compared with other radical precursors, alkyl bis(catecholato)silicates pose a number of advantages, specifically the ability to undergo homolysis under neutral conditions as well as the ability to be oxidized at relatively low and uniform oxidation potentials ( E ox = 0.34 to 0.90 V).…”