Reactivity of the Carbyne complexes [W2(μ-COR)(η5-C5H5)2(CO)2(μPh2PCH2PPh2)]+ (R = H, Me) toward diazomethane

Reaction Of [W-2(mu-COH)CP2(CO)(2)(mu-dppm)]BF4 (Cp = eta(5)-C5H5; dppm = Ph2PCH2PPh2) with CH2N2 in the presence of CuCl at -75 degreesC leads to the methoxycarbyne cluster [CuW2Cl(mu(3)-CMe)CP2(CO)(2)(mu-dppm)]BF4- Copper(I) chloride can be cleanly removed from the latter upon addition of PPh3, thus giving the methoxycarbyne complex [W-2(mu-COMe)CP2(CO)(2)(mu-dppm)]BF4- In the absence of CuCl, either the hydroxy or the methoxycarbyne ditungsten cations react with CH2N2 to give a mixture of the mu-methylene,mu-alkenyl compound [W-2(mu-CH2)mu-eta(1) :eta(2)-C(OMe)=CH2}CP2(CO)(2)(mu-dppm)]BF4, which has been characterized through an X-ray study, and the mu-alkyne,mu-alkenyl species [W-2{mu-eta(1):eta(2)-C(OMe)CH}{mu-eta(1):eta(2)-C(OMe)(CH2}CP2(CO)(mu-dppm)]BF4, the latter being the result of the addition of four molecules of CH2N2 to the starting hydroxycarbyne compound. The influence of experimental conditions on the above reactions has been analyzed through separate experiments. For example, the use of tetrahydrofuran as solvent almost suppresses the formation of the alkyne product, whereas the use of a noncoordinating anion such us [B{3,5-C6H3(CF3)(2)}(4)]- instead of BF4- as counterion precludes the reaction to occur beyond the methoxycarbyne compound. The solution structures of the new compounds are analyzed in the light of the IR and NMR spectra, and plausible reaction pathways are proposed in order to explain the formation of the reaction products.