A possible mechanism is proposed in Figure . The photoexcited *Ir can undergo single-electron transfer (SET) oxidation with Ph 3 P to form the triphenylphosphine radical cation 7, which could trigger the proposed radical deoxygenation. The resulting radical cation (7) reacts with carboxylate anion 6 to generate the phosphoryl radical (8). This is followed by β-selective C(acyl)-O bond cleavage of 8 with a thermodynamic impetus for the formation of Ph 3 P=O. The acyl radical (9) was generated in this way then regioselectively attacks gem-Ar,Bpin-or gem-diborylalkene 2, 2' to form the stabilized radical species (10), which is capable of undergoing a SET with reductive Ir II species to afford the corresponding ketone 3, 4 in the presence of water (from 8-I to 8, Figure ). Experimentally, ketone 3, 4 was not obtained in the absence of Light or PC. Also, the addition of TEMPO during the reaction did not lead to the desired product 3a (Figure ). These results support the radical mechanism of this reaction. When the photoredox reaction of gem-Ar,Bpin-and gemdiborylethene 2, 2' was carried out with 1a in the presence of D2O, the desired product 3a-D and 4a-D were obtained with 40% D-incorporation at apha carbonyl position and 98% D-incorporation at the geminated carbon, thus confirming the formation of gem-diborylanion xx (Figure ). The results of these deuterium labelling studies of geminated carbon may support the proposed singleelectron reduction of 10 to 11 (Figure ). Of note, a control experiment of the reaction of 3a and 4a with D2O under the reaction conditions gave the desired coupling product with deuterium labelling only at the alpha position of the carbonyl (for full details see the SI).