Palladium(II) Complexes of the Hemilabile Pincer Ligand PPh(o-C6H4SMe)2 as Highly Active and Recyclable ­Mizoroki–Heck Catalysts

PdII complexes with PPh(o-C6H4SMe)2 acting as a pincer ligand in an S,S′,P- or S,P-coordination mode have been synthesized. The complexes include [PdCl2{PPh(o-C6H4SMe)2}] (1), [Pd(Me)Cl{PPh(o-C6H4SMe)2}] (2), and [Pd(X){PPh(o-C6H4SMe)2}]A [A = CF3SO3, X = Cl (3); A = CF3SO3, Me (4); A = PF6, X = Me (5)]. Insertion of CO into the Pd–Me bond of these complexes leads to [Pd(COMe)Cl{PPh(o-C6H4SMe)2}] (6) and [Pd(COMe){PPh(o-C6H4SMe)2}]A [A = CF3SO3 (7); A = PF6 (8)]. Some of these complexes are good Mizoroki–Heck catalysts (for the reactions between iodobenzene and methyl acrylate or styrene). The most active catalyst was found to be [Pd(Me)Cl{PPh(o-C6H4SMe)2}] (2). This catalyst could be retained on a silica gel column, recovered, and reused several times without losing activity.