Chemistry of highly electrophilic binuclear cations. 6. Synthesis of the alkyne-bridged complexes [Mo2(η5-C5H5)2{μ-η2:η2-HC2(p-tol)}(CO)2(μ-L2)][B{3,5-C6H3(CF3)2}4]2 and their isocyanide derivatives (L2=Ph2PCH2PPh2, Me2PCH2PMe2)

Chemistry of Unsaturated Group 6 Metal Complexes with Bridging Hydroxy and Methoxycarbyne Ligands. 3. Formation and Cleavage of C−C and C−O Bonds in the Reactions of the Complexes [Mo2Cp2(µ-COMe)(µ-COR)(µ-PCy2)]BF4(R = Me, Et)

“…In particular, the coupling process leading to the alkyne ligand is clearly denoted by the disappearance of the characteristic highly deshielded 13 C NMR resonances of the methoxycarbyne groups (366.0 ppm in 1a ), to render a quite shielded resonance instead (147.4 ppm). The chemical shifts of these C atoms are similar to those previously reported by us for the isoelectronic alkyne-bridged cations [Mo 2 Cp 2 {µ-η 2 :η 2 -HC 2 ( p -tol)}(L) 2 (µ-L′ 2 )] +2 (L = CO, CN t Bu; L′ 2 = dppm, dmpm); however, we have to point out that all these values are slightly higher than those found for the neutral and electron-precise complexes [M 2 Cp 2 (CO) 4 (µ-η 2 :η 2 -C 2 R 2 )] mentioned above . This possibly reflects not only the higher charge and oxidation state of the molybdenum atoms in our complexes, but also the difference in the total electron count for these molecules (32-electron vs 34-electron species).…”