So far, isolable mononuclear Pd(I) complexes are exceedingly rare. Figure lists the known examples. The P t Bu3supported two-coordinate Pd(I) complexes [Pd(P t Bu3)2][X] (I, X = CB11H12, PF6) reported independently by Chaplin's and Ozerov's groups in 2016 were prepared by single-electron oxidation of the Pd(0) complex [Pd(P t Bu3)2] with ferrocenium or triphenylmethyl cation. In similar way, the twocoordinate Pd(I) complexes with PAd3 and N-heterocyclic carbene as supporting ligands [Pd(PAd3)2][BAr (II, Ar F = 3,5-(CF3)2C6H3) and [Pd(IPr)2][PF6] (III, IPr = 1,3-bis(2',6'diisopropylphenyl)imidazole-2-ylidene) were prepared by oxidizing the corresponding Pd(0) precursors. The reactivity of the homoleptic Pd(I) complexes I-III remains poorly understood. Ozerov's study noted that [Pd(P t Bu3)2] + can coordinate MeCN to form the T-shaped complex [Pd(P t Bu3)2(NCMe)][CB11H12] (IV). Chaplin found that the cation [Pd(P t Bu3)2] + can react with organic iodides to yield the Pd(I) dimer [Pd(P t Bu3)(I)]2 and phosphonium salts. The heteroleptic Pd(I) complexes V reported by Mirica's group can be prepared by reducing Pd(II) species supported by cyclic tetra-and tri-dentate ligands with Cp2Co or by ligand-exchange reaction between[Pd(P t Bu3)2] + and the cyclic ligands. Among them, the Pd(I) complex featuring a tridentate NS2 ligand proved effective catalyst for the crosscoupling reaction of aryl bromides with alkyl Grignard reagents. A Pd(I)-Pd(III)-Pd(I) catalytic cycle was proposed for this Pd(I)-catalyzed cross-coupling reaction. While, based on the Covalent-Bond-Classification method, the Pd(I) complexes I-V are unanimously the ones supported by ) is unique for the X-type amido ligand. Complex VI was prepared from the reaction of the Pd(II) complex (BINAP)PdCl2 with two equiv. of LiNHAr Trip . It is heat-and light-sensitive and can readily fragment into Pd(0) species and aminyl radical at ambient conditions. Very recently, Gade and his coworkers reported the preparation of the mononuclear Pd(I) pincer VII by the reduction of the corresponding Pd(II) chloride complex or by thermolysis of the corresponding Pd(II) neopentyl complex. Under high CO pressure (5 atm.), VII coordinates reversibly with CO to form the Pd(I) carbonyl complex VIII that slowly reacts with di(tert-butyl) disulfide to give palladathioester. The limited knowledge on mononuclear Pd(I) complexes, particularly those bearing X-type ligands, urges further exploration on them. Herein, we wish to report the isolation and characterization of the first mononuclear Pd(I) aryl complexes [(IPr)Pd(Ar)], as well as their reactions with organic halides, which produce C-C cross-coupling products.