Nickel bis(phosphinite) pincer complexes [2,6-(R 2 PO) 2 C 6 H 3 ]NiCl (R = Ph, 1a; R = Me, 1b; R = i Pr, 1c; R = t Bu, 1d) show catalytic activity in cross-coupling of aryl iodides and aryl thiols. The optimal catalytic conditions involve 1 mol % of 1a and 2 equiv of KOH (with respect to aryl thiols) in DMF at 80 °C and tolerate a variety of functional groups in the substrates. The potential intermediates in these catalytic reactions, such as nickel thiolate complexes [2,6-(Ph 2 PO) 2 C 6 H 3 ]-NiSAr (Ar = Ph, 2a; Ar = p-MeC 6 H 4 , 3a; Ar = p-MeOC 6 H 4 , 4a), have been synthesized and spectroscopically characterized. The reaction between 2a and PhI in DMF-d 7 is slow enough to argue against 2a being directly involved in the C-S bond-forming step. NMR studies suggest that the pincer ligand framework in complexes 1a, 3a, and 4a is destroyed by KOH via the cleavage of P-O bonds to release Ph 2 POK, and further decomposition leads to Ph 3 P and other phosphorus-containing products. The cross-coupling reactions are more effectively catalyzed by Ni(COD) 2 /Ph 2 P(O)H. The structures of 1b, 2a, 4a, and [2,6-(Ph 2 PO) 2 C 6 H 3 ]NiP(O)Ph 2 (5a), which is relevant to the decomposition process, have been studied by X-ray crystallography.
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