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

Abstract

Metallaphotocatalytic cross‐coupling reactions are typically carried out by combining homogeneous or heterogeneous photocatalysts with a soluble nickel complex. Previous attempts to realize recyclable catalytic systems use immobilized iridium complexes to harvest light. We present bifunctional materials based on semiconductors for metallaphotocatalytic C−S cross‐coupling reactions that can be reused without losing their catalytic activity. Key to the success is the permanent immobilization of a nickel complex on the surface of a heterogeneous semiconductor through phosphonic acid anchors. The optimized catalyst harvests a broad range of the visible light spectrum and requires a nickel loading of only ∼0.1 mol %.

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.…”

“…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. Commonly applied homogeneous noble-metal based photocatalysts that are mainly applied are expensive, not easily recyclable and unsustainable.…”

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

“…A comparison of different aryl halides showed that an aryl iodide reacts significantly faster than the corresponding bromide (14). This is in contrast to dual nickel/photocatalytic protocols, where iodides and bromides exhibit similar reactivity.…”

“…Under optimized conditions, the light-mediated, nickel-catalyzed N-arylation of sulfonamides afforded 3 in 75% yield (entry 13). Light and the nickel salt were crucial for product formation (entry [13][14].…”

“…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. Commonly applied homogeneous noble-metal based photocatalysts that are mainly applied are expensive, not easily recyclable and unsustainable.…”