Boosting Photocatalytic Activities for Organic Transformations through Merging Photocatalyst and Transition-Metal Catalyst in Flexible Polymers

Abstract

The merger of photocatalysis and transition-metal catalysis is of particular interest to develop useful and challenging synthetic methodologies. The catalytic activities of conventional dual-catalytic systems, however, are limited by the low synergistic efficiency between discrete catalytic centers due to their long average distance in solution. Herein we carefully decorated Ir­(III) photosensitizers and Ni­(II) transition-metal catalyst into flexible polymers to afford two polymer-supported dual catalysts (P1–Ni and P2–Ni). These polyelectrolyte-type metallopolymers assembled into spherical polymer particles in some polar solvents. Their unique molecular and assembled structure contributed to shortening the distance between catalytic centers and increasing the local catalysts’ concentration within the catalyst, thereby greatly facilitating their electron, energy, and organic radical transfers during the catalytic cycles. The enhanced energy interaction and matched redox potential between two catalytic centers within the polymer were confirmed by steady- and transient-state luminescent spectra and cyclic voltammetry. These features enable them in catalyzing challenging organic transformations that involve efficiently incorporated photocatalytic and transition-metal catalytic cycles. We demonstrated that these two catalysts were highly effective in catalyzing C–S cross-coupling, C–O functionalized, C–N cross-coupling, and C–C cross-coupling reactions with broad substrate scopes and low catalyst loadings with turnover numbers of ∼3100, ∼1500, ∼1400, and ∼500, respectively. This work provides a general methodology to merge photosensitizer and transition-metal catalyst in a flexible polymer for significantly boosting the catalytic activity.

Photocatalyst-free, visible-light-mediated nickel catalyzed carbon–heteroatom cross-couplings

“…It is noteworthy that this substrate was earlier reported as a successful coupling partner when NiCl2•bpy was used in combination with tris(2,2'bipyridyl)dichlororuthenium(II) hexahydrate as exogenous photocatalyst. 30 With regard to the aryl iodide, the reaction affords the corresponding sulfones in presence of electron withdrawing groups such as trifluoromethyl (1), nitrile (8), ketone (9)(10)(11), amide (12), boron pinacolate ester (13), and methyl ester (14). Para-( 9) and ortho-( 11) substitution showed similar reactivity, whereas meta-substitution (10) required a longer reaction time for full conversion.…”

“…[5][6][7] Suitable photocatalysts for dual photo/nickel catalytic carbon-heteroatom cross-couplings range from ruthenium and iridium polypyridyl complexes and organic dyes to heterogeneous semiconductors. 6 Moreover, nickel complexes and visible-light photocatalysts were combined in bifunctional heterogeneous materials, such as metal-organic frameworks, 8,9 organic polymers, 10 or functionalized semiconductors. [11][12][13][14] Although dual photo/nickel catalysis is attractive, the need for a photocatalyst is a drawback.…”

Photoredox Heterobimetallic Dual Catalysis Using Engineered Covalent Organic Frameworks

“… 27 , 28 In addition, non-porous amorphous linear polymers designed with pending arms containing bipyridine fragments have also been used for these purposes. 29 Inspired by these precedents, this work is intended to design a bimetallated COF that requires simple synthetic procedures and to obtain a very stable and active material. In particular, we immobilize Ir and Ni fragments into phenanthroline units in a new imine-based COF (hereafter called Phen-COF ), allowing the interplay of both catalytic metal centers for the formation of Csp 3 –Csp 2 bonds (bottom, Figure 1 ).…”

Recyclable, Bifunctional Metallaphotocatalysts for C−S Cross‐Coupling Reactions

“…More recently, a bifunctional polymeric catalyst was prepared using building units that were functionalized with an iridium polypyridyl photocatalyst and a nickel complex [6] . Metal leaching during recycling experiments resulted in a gradual decrease of the yield.…”