Chemoselective nickel-catalyzed coupling through substrate photoexcitation

Abstract

Metallaphotoredox catalysis combines the well-established mechanisms of transition-metal-catalyzed cross-coupling reactions with one-electron redox manipulations enabled by light. In most cases, a transition metal or organic dye serves as the photoredox catalyst while a ground-state Pd or Ni catalyst performs the organometallic steps. Cross-coupling mechanisms that rely on direct photoexcitation of a light-absorbing substrate have the potential to access distinct mechanisms and deliver unique selectivity based on the substrate’s excited-state properties. In this report, we describe a photoinduced, Ni-catalyzed Suzuki–Miyaura cross coupling reaction that selectively functionalizes BODIPY chromophores, a versatile class of tunable, bright, photostable fluorophores. Using a bis-iodo BODIPY substrate, the selectivity for mono- vs. bis-arylation was found to be governed by a remote substituent that subtly alters the excited-state properties of the substrate. Consistent with a substrate photoexcitation mechanism, high chemoselectivity is also observed in mixtures of chromophores with distinct excited-state properties. This reaction is compatible with a variety of substituted BODIPY chromophores and boronic acids and esters, enabling the rapid synthesis of unsymmetrically-substituted chromophores.