Ylide-substituted phosphines (YPhos) have been shown to be excellent ligands for several transition metal catalyzed reactions. Investigations of the coordination behavior of the YPhos ligand Y-s PPh2 (1) [with Y-s = (Ph3P)(SO(2)Tol)C] toward group 9 and 10 metals revealed a surprisingly diverse coordination chemistry of the ligand. With Ni(CO)(4), the formation of a di- as well as tricarbonyl complex is observed depending on the reaction conditions. In [(kappa P,eta(2)-benzene-1)Ni(CO)(2) ] the phosphine ligand also coordinates via a phosphonium bound phenyl group to the metal leading to a unique nickel eta(2)-arene interaction, which can be viewed as an intermediate state toward P-C bond activation. Full cleavage of the P-C bond takes place with [Rh(COD)Cl](2) leading to a complex salt with [(kappa P,kappa O-1)Rh(COD)](+) as cation and a dirhodium trichloride complex anion. Here, Y-S PPh2 underwent P-C bond cleavage to thus act as an anionic diphosphine ligand. In contrast, in [(kappa P,kappa O-1)Rh(COD)](+) as well as [(kappa P,kappa O-1)Rh(CO)Cl](+), formed from the reaction of 1 with [Rh(CO)(2)Cl](2), the YPhos ligand acts as bidentate ligand complexing the metal via the phosphine and sulfonyl moiety with an intact PPh3 unit. A further type of coordination is observed with [Ir(COD)Cl](2). Here, phosphine coordination is accompanied by C-H activation at one of the phosphonium bound phenyl groups leading to a cyclometalated complex.