Catalysis with Palladium Complexes Photoexcited by Visible Light

Abstract

Palladium catalysis induced by visible light is an emerging field of catalysis. In contrast to classical reactions catalyzed by Pd complexes in the ground state, which mostly proceed through two‐electron redox processes, the mechanisms of these new methods based on photoexcited Pd complexes usually operate through transfer of a single electron. Such processes lead to putative hybrid Pd/radical species, which exhibit both radical and classical Pd‐type reactivity. This Minireview highlights the recent progress in this rapidly growing area.

Catalytic radical generation of π-allylpalladium complexes

“…This could be the possible reason for higher selectivity when BINAP was employed in this system. Again, cyclic (19, 21, 23), heterocyclic (18,19) and acyclic (24)(25)(26)(27)(28)(29), difluorinated (20), indane (22) moieties smoothly participated in the cross-coupling reaction. A broad range of functional groups such as trifluoromethyl (5), amides (12, 16, 18), ethers (13,17) and esters (6,15) were found to be compatible.…”

“…18 However, recent breakthroughs in photoredox chemistry, [19][20][21] have shown that photoexcited palladium catalysts can be used to generate open-shell species from alkyl halide precursors. 22 Thus, we questioned whether -allylpalladium complexes could also be generated through a single-electron transfer (SET) mechanism to overcome the aforementioned limitations.…”

Visible-light-driven palladium-catalyzed Dowd–Beckwith ring expansion/C–C bond formation cascade

“…Inspired by the pioneering works on visible-light induced Pdcatalyzed alkyl-Heck coupling reactions, 11 we envisioned that photoirradiation might facilitate the SET event between Pd(0) complex and Dowd-Beckwith halides to initiate the ring expansion process. The interaction of the tertiary radical species and Pd(I) complex generated in situ would provide opportunities for further transformation (Scheme 1, eqn b).…”

A photoredox catalysed Heck reactionviahole transfer from a Ru(ii)-bis(terpyridine) complex to graphene oxide

“…[33][34][35][36] Recently, photocatalytic selective organic transformations [37][38][39][40][41] including homogenous photocatalyzed C-C cross-coupling reactions under visible-light have attracted much interest. [42][43][44][45][46][47][48][49][50][51][52][53] Heterogeneous catalytic systems 42,[54][55][56][57][58][59][60] for C-C cross-coupling reactions have been reported in smaller numbers. Ligand-free palladium catalysed cross-couplings in general require higher temperatures.…”