Protonation reactions on the binuclear complexes [W2Cp2(CO)n(μ-L2)] [L2 = Ph2PCH2PPh2, Me2PCH2PMe2; n = 2, 4].: Chemical behavior of their hydrido and hydroxycarbyne derivatives

Reaction of the triply bonded dimers [W2Cp2(CO)(2)(mu-L-2)] (L-2 = Ph2PCH2PPh2, Me2PCH2PMe2) with HBF4. OEt2 and other strong acids leads to the unsaturated cationic hydrides [W2Cp2(mu-H)(CO)(2)(mu-L-2)](+). In contrast with this, reaction of HBF4. OEt2 with the singly bonded dimers [W2Cp2(CO)(4)(mu-L-2)] leads, depending on L-2 and reaction conditions, to either hydroxycarbyne cations [W-2(mu-COH)Cp-2(CO)(2)(mu-L-2)](+) or hydridoderivatives [W2Cp2(mu-H)(CO)(n)(mu-L-2)](+) (n = 2 or 4). The relative amounts of the above products in the reaction mixtures depend both on the nature of La and reaction conditions. From these data and the results of additional experiments it is concluded that, when L-2 = Ph2PCH2PPh2, protonation gives initially the hydroxycarbyne complex, which can experience afterward a solvent-assisted transformation into the corresponding hydride derivatives, possibly through an H-C(cyclopentadienyl) activation step. When L-2 = Me2PCH2PMe2, the above O-protonation competes with direct proton attack at the intermetallic bond, the latter process being dominant under most of the reaction conditions. The structure of the new complexes as well as the dynamic behavior of some of them is discussed with the aid of IR and variable-temperature NMR spectroscopy.