Multimetallic Catalysis Enabled Cross-Coupling of Aryl Bromides with Aryl Triflates

摘要

Transition metal-catalyzed strategies for the formation of new C-C bonds have revolutionized the field of organic chemistry, enabling the efficient synthesis of ligands, materials, and biologically active molecules.^– In cases where a single metal fails to promote a selective or efficient transformation, the synergistic cooperation of two distinct catalysts – multimetallic catalysis – can be employed instead. Many important reactions rely on multimetallic catalysis, including the Wacker oxidation of olefins^– and the Sonogashira coupling of alkynes with aryl halides.^– However, the application of this strategy, even in recently developed methods, has largely been limited to the use of metals with distinct reactivities, with only one metal catalyst undergoing an oxidative addition. In this manuscript, we demonstrate that cooperativity between two d10 metal catalysts, (bipyridine)nickel and (1,3-bis(diphenylphosphino)propane)palladium, enables a general cross-Ullman reaction.^– Our method couples aryl bromides with aryl triflates directly, eliminating the use of arylmetal reagents and avoiding the challenge of differentiating between multiple C–H bonds that is required for many C–H activation methods.^– The selectivity does not require an excess of either substrate and originates from the orthogonal activity of the two catalysts and the relative stability of the two arylmetal intermediates. While (dppp)Pd reacts preferentially with aryl triflates to afford a persistent intermediate, (bpy)Ni reacts preferentially with aryl bromides to form a transient, reactive intermediate. Although each catalyst forms less than 5% cross product in isolation, together they are able to achieve up to 94% yield. Our results reveal a new, general method for the synthesis of biaryls, heteroaryls, and dienes, as well as a new mechanism for selective transmetalation between two catalysts. We anticipate that this reaction will simplify the synthesis of pharmaceutical agents, many of which are currently made with pre-formed organometallic reagents,^– and lead to the discovery of new multimetallic reactions.