Visible-Light-Induced, Single-Metal-Catalyzed, Directed C-H Functionalization: Metal-Substrate-Bound Complexes as Light-Harvesting Agents

Abstract

C-H functionalization represents one of the most rapidly advancing areas in organic synthesis and is regarded as one of the key concepts to minimize the ecological and economic footprint of organic synthesis. The ubiquity and low reactivity of C-H bonds in organic molecules, however, poses several challenges, and often necessitates harsh reaction conditions to achieve this goal, although it is highly desirable to achieve C-H functionalization reactions under mild conditions. Recently, several reports uncovered a conceptually new approach towards C-H functionalization, where a single transition-metal complex can be used as both the photosensitizer and catalyst to promote C-H bond functionalization in the absence of an exogeneous photosensitizer. In this Minireview, we will provide an overview on recent achievements in C-H functionalization reactions, with an emphasis on the photochemical modulation of the reaction mechanism using such catalysts.

Keywords: Computational Chemistry; C−H Functionalization; Photocatalysis; Rhodium; Ruthenium.

Scheme 1

C−H functionalization strategies and opportunities for light‐mediated C−H functionalization via cyclometalated intermediates.

Scheme 2

Photoinduced rhodium‐catalyzed ortho‐C−H borylation reactions.

Scheme 3

a) Thermal alkylation reactions. b, c) Photoinduced ruthenium‐catalyzed meta‐C−H alkylation reactions with alkyl halides.

Scheme 4

Comparison of the proposed mechanisms for thermal and photocatalytic meta‐C−H alkylation reactions.

Scheme 5

Photoinduced ruthenium‐catalyzed ortho‐C−H alkylation reactions with benzyl or allyl halides.

Scheme 6

Photoinduced ruthenium‐catalyzed ortho‐arylation reactions with aryl halides. a) by Ackermann et al. and b) by Greaney et al.

Scheme 7

(TD‐)DFT calculated mechanism for the ruthenium‐catalyzed ortho‐C−H arylation.

Scheme 8

Photoinduced ruthenium‐catalyzed C(sp³)−C(sp³) coupling reaction.

Scheme 9

Photoinduced C−H alkylation or arylation reactions with a bimodular rhodium catalyst.