Protonation (CF3SO3H) of WH(2)Cl(2)L(4) (L = PMe(2)Ph) below -70 degrees C in CD2Cl2 gives A as the kinetic product. This shows two hydride signals at -85 degrees C, and inequivalent (A(2)M(2)) P-31 nuclei. By -70 degrees C, the kinetic product converts completely to the thermodynamic product W-VI(H)(3)Cl(2)L(4)(+), B, which has fluxional hydrides but inequivalent (A(2)M(2)) P-31 nuclei. The W-P coupling constants, the W/H T-1 value of B, and the green color of A support metal oxidation state IV for A and VI for B. By -30 degrees C, B reacts further to dissociate one phosphine, to produce stereochemically-rigid, C-3-symmetric W-VI(H)(3)Cl(2)L(3)(+), C Both the H-1 and P-31 NMR spectral patterns and the W-P coupling constant support the claimed oxidation state of W(VI) in C. Above 10 degrees C, C decomposes both in solution (CH2Cl2 or toluene) and also as a pure solid to a variety of uncharacterized products. Comparison to the result of protonation of W(H)(2)XYL(4) (XY = Br-2, I-2, CII, ClBr) support certain structural proposals for A-C and indicate how the diminished X-->W pi-donation by the heavier halides influences these oxidative and phosphine dissociation processes.