A Bridging Side-on Allenylidene Dimolybdenum Complex without Carbonyl Stabilization

The bis(nitrile) complex [Mo2Cp2(μ-SMe)3(NCCH3)2](BF4) (1) reacts with HC⋮CCPh2(OH) to give the μ-alkyne product [Mo2Cp2(μ-SMe)3{HC⋮CCPh2(OH)}](BF4) (2). Sequential treatment with triethylamine and tetrafluoroboric acid converts 2 almost quantitatively, via the μ-alkynyl derivative 3, into [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCCPh2)] (BF4) (4), the first example of a dinuclear μ-η1:η2-allenylidene species without carbonyl ligands.