Novel tridentate NNP preligands bearing 2,2′-bipyridine and secondary phosphine oxide (SPO) moieties (NNP(O)H and MeNNP(O)H preligands) were readily synthesized from 6-methyl-2,2′bipyridine or 6,6′-dimethyl-2,2′-bipyridine and ethyl phenylphosphinate, respectively. The reaction of the preligands with [PdMe(Cl)-(cod)] (cod = 1,5-cyclooctadiene) afforded [PdCl(NNP(O))] and [PdCl(MeNNP(O))], in which the NNP(O) ligands coordinated to Pd in a tridentate manner. The phosphorus moiety coordinated as a phosphoryl ligand with the loss of a proton from the SPO moiety in the original preligands. Cationic complexes [Pd(NNP(O))(MeCN)][OTf] and [Pd(MeNNP(O))(MeCN)][OTf] were prepared from the above complexes and AgOTf in MeCN. The reaction of [PdBn(Cl)(cod)] with AgOTf and MeNNP(O)H afforded the phosphinous acidphosphoryl-bridged dinuclear benzyl complex [{PdBn(MeNNP(O))} 2 H][OTf]. Oxygenation of benzyl ligands in the dinuclear complex was investigated under various reaction conditions. Ambient light or blue LED light promoted the reaction to afford oxygenated products, that is, BnOOH, BnOH, and PhCHO. Oxygenation mainly proceeded by the reaction of the excited triplet state(s) of the PdBn complex(es) with 3 O 2 , without involving a benzyl radical. The addition of PPh 3 to the reaction mixture after oxygenation afforded [Pd(MeNNP(O))(PPh 3 )][OTf]. [{PdBn(MeNNP(O))} 2 H][OTf] was converted into [{PdCl(MeNNP-(O))} 2 H][OTf] by exposure to ambient light or blue LED light in chloroform under N 2 via homolysis of a Pd−Bn bond.