Preparation of visible-light-activated metal complexes and their use in photoredox/nickel dual catalysis

• Published in: Nature protocols Vol. 12; no. 3; pp. 472 - 492
• Main Authors: Kelly, Christopher B, Patel, Niki R, Primer, David N, Jouffroy, Matthieu, Tellis, John C, Molander, Gary A
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-03-2017; Nature Publishing Group
• Subjects: 639/638/403/933; 639/638/439/890; 639/638/549/884; Analytical Chemistry; Biological Techniques; Catalysis; Chemical properties; Chemistry Techniques, Synthetic - methods; Chemists; Computational Biology/Bioinformatics; Electrons; Iridium; Life Sciences; Ligands; Light; Metal complexes; Methods; Microarrays; Nickel; Nickel - chemistry; Optical properties; Organic Chemistry; Organometallic Compounds - chemistry; Oxidation; Oxidation-Reduction; Oxidation-reduction reactions; Photocatalysis; Photochemical Processes; Polymers; Properties; Protocol; Ruthenium; Transition metal compounds
• ISSN: 1754-2189; 1750-2799
• DOI: 10.1038/nprot.2016.176

This protocol describes the synthesis of two photoredox catalysts, [Ir{dF(CF
3
)
2
ppy}
2
(bpy)]PF
6
and [Ru(bpy)
3
](PF
6
)
2
, that are activated by visible light. These single-electron transfer agents are used to facilitate diverse synthetic transformations.
Visible-light-activated photoredox catalysts provide synthetic chemists with the unprecedented capability to harness reactive radicals through discrete, single-electron transfer (SET) events. This protocol describes the synthesis of two transition metal complexes, [Ir{dF(CF
3
)
2
ppy}
2
(bpy)]PF
6
(
1a
) and [Ru(bpy)
3
](PF
6
)
2
(
2a
), that are activated by visible light. These photoredox catalysts are SET agents that can be used to facilitate transformations ranging from proton-coupled electron-transfer-mediated cyclizations to C–C bond constructions, dehalogenations, and H-atom abstractions. These photocatalysts have been used in the synthesis of medicinally relevant compounds for drug discovery, as well as the degradation of biological polymers to access fine chemicals. These catalysts are prepared from IrCl
3
and RuCl
3
, respectively, in three chemical steps. These steps can be described as a series of two ligand modifications followed by an anion metathesis. Using the cost-effective, scalable procedures described here, the ruthenium-based photocatalyst
2a
can be synthesized in a 78% overall yield (∼8.1 g), and the iridium-based photocatalyst
1a
can be prepared in a 56% overall yield (∼4.4 g). The total time necessary for the complete protocols ranges from ∼2 d for
2a
to 5–7 d for
1a
. Procedures for applying each catalyst in representative photoredox/Ni cross-coupling to form C
sp
3–C
sp
2 bonds using the appropriate radical precursor—organotrifluoroborates with
1a
and bis(catecholato)alkylsilicates with
2a
—are described. In addition, more traditional photoredox-mediated transformations are included as diagnostic tests for catalytic activity.