Ligands with 1,10-phenanthroline scaffold for highly regioselective iron-catalyzed alkene hydrosilylation

Abstract

Transition-metal-catalyzed alkene hydrosilylation is one of the most important homogeneous catalytic reactions, and the development of methods that use base metals, especially iron, as catalysts for this transformation is a growing area of research. However, the limited number of ligand scaffolds applicable for base-metal-catalyzed alkene hydrosilylation has seriously hindered advances in this area. Herein, we report the use of 1,10-phenanthroline ligands in base-metal catalysts for alkene hydrosilylation. In particular, iron catalysts with 2,9-diaryl-1,10-phenanthroline ligands exhibit unexpected reactivity and selectivity for hydrosilylation of alkenes, including unique benzylic selectivity with internal alkenes, Markovnikov selectivity with terminal styrenes and 1,3-dienes, and excellent activity toward aliphatic terminal alkenes. According to the mechanistic studies, the unusual benzylic selectivity of this hydrosilylation initiates from π–π interaction between the phenyl of the alkene and the phenanthroline of the ligand. This ligand scaffold and its unique catalytic model will open possibilities for base-metal-catalyzed hydrosilylation reactions.

In Situ Infrared Spectroscopic Study of Iron-Catalyzed Hydromagnesiation of Vinyl Arenes

“…However, recent advancements beginning in 2010 allowed for the use of Fe, Co, Mo, Cu, and Ni catalysts. Hydrosilylation, 95,104,[111][112][113][114][115][116][117][118][119][120][121][122][123][124] hydroboration, [116][117][118][125][126][127][128][129][130][131][132][133][134][135][136][137][138] hydroamination, [139][140][141][142] hydroformylation, [143][144][145][146][147][148][149] hydrocarboxylation, [150][151][152][153][154]…”

“…95,111,[113][114][115][116]120 Development of a well-defined ligand framework introduced a means of favoring hydrosilylation over the side reactions and in some cases increased 1,2-vs 2,1-insertion and α-(Markovnikov substitution) vs. β-(Anti-Markovnikov substitution) regioselectivity (Figure 1.8). 95,111,[113][114][115][116]120 Recently, regioselectivity of hydrosilylation has been determined for both aliphatic and aromatic olefins. For reagents containing aromatic olefins, α-silylation (Markovnikov substitution, Scheme 1.9A) is favored; whereas, aliphatic olefins favor β-silylation (Anti-Markovnikov substitution, Scheme 1.9B).…”

“…For reagents containing aromatic olefins, α-silylation (Markovnikov substitution, Scheme 1.9A) is favored; whereas, aliphatic olefins favor β-silylation (Anti-Markovnikov substitution, Scheme 1.9B). 95,111,[113][114][115][116]120,170 Based upon known limitations of iron-catalyzed hydrosilylation, future methodology development is a necessity to improve regioselectivity, reduce side product pathways, and provide catalyst control by using redox-active ligands. Iron-catalyzed hydrosilylation side reactions.…”

“…95,111,[113][114][115][116]120,169 Figure 1.8: Iron-catalyzed hydrosilylation catalysts. 95,111,[113][114][115][116]120 Scheme 1.9: Iron-catalyzed hydrosilylation. 95,111,[113][114][115][116]120 *Reproduced using ChemDraw Another class of hydrofunctionalization, hydroboration, adds a borane (B-H) across an unsaturated bond.…”

“…95,111,[113][114][115][116]120 Scheme 1.9: Iron-catalyzed hydrosilylation. 95,111,[113][114][115][116]120 *Reproduced using ChemDraw Another class of hydrofunctionalization, hydroboration, adds a borane (B-H) across an unsaturated bond. The hydroboration of C=C was first introduced by Brown and coworkers.…”