Pt(pop–BF2) as a Photosensitizer in Photocatalytic Carbon–Chlorine Bond Formation
Authors:Maraia E Ener, Megan N Jackson, Jeffrey J Warren
Mentor:Harry B Gray, Arnold O Beckman Professor of Chemistry, California Institute of Technology
A great many Pd complexes perform regioselective C-H functionalizations, which are essential in the synthesis of pharmaceuticals and agrochemicals. We are especially interested in halogenation reactions of unactivated C–H bonds. Using [(benzo[h]quinoline)PdII(μ–OAc)]2 complexes, we can employ bulk electrolysis (at 1.0 V vs. SCE) to catalytically chlorinate C–H bonds using chloride, thereby eliminating the need for chlorine gas or other harsh chemical oxidants. Our current efforts focus on performing the same reactions photochemically with the ultimate goal of improving the speed and energetic cost of these transformations. Fluoroborated tetrakis(μ–pyrophosphito)diplatinate(II) (Pt(pop–BF2)), is a potential photosensitizer in this system because of its long-lived electronically excited state that undergoes facile electron transfer reactions. Cyclic voltammetry was used to determine the PtII–PtII/PtI–PtII reduction potential (-1.3 V vs. SCE). We used this value along with fluorescence data to calculate the reduction potential of the electronically excited state (E°(*PtII–PtII/PtII–PtI) = 1.4 V vs. SCE). Thus, electronically excited Pt(pop–BF2) has sufficient driving force to oxidize our Pd catalysts. The absorbance spectra of the excited and singly reduced Pt complexes were recorded via transient absorption. Time-resolved laser experiments in the presence of Pd catalyst suggest that the electronically excited Pt(pop–BF2) can generate catalytically active Pd intermediates, making it a viable photosensitizer in photocatalyic C–H functionalization reactions.