The oxygen atom transfer (OAT) reactivity of Tp*MoO2Cl with PMe3, PEt3, and PPhMe2 (where Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) has been investigated. The OAT reactions proceed through a diamagnetic Mo(IV) phosphoryl intermediate complex of general formula Tp*MoOCl(OPR3) (OPR3 = OPMe3, OPEt3, OPPhMe2), which have been isolated and characterized by H-1 and P-31 NMR, UV-visible, and infrared spectroscopies and electrospray ionization mass spectrometry. Solid-state crystal structures of Tp*MoOCl(OPMe3) and Tp*MoOCl(OPPhMe2) are also reported, the oxygen-to-phosphorus distances agree with a double-bond formulation and a single bond between the metal and the phosphoryl oxygen atom. The stability of the phosphoryl intermediate complexes depends on the steric properties of the coordinated phosphine-oxides. These intermediate complexes have been converted to solventcoordinated species, Tp*MoOCI(solv) (solv = acetonitrile or dmf), and the coordinated solvents exchange with the bulk solvent.