Infrared spectra of M-η2-C2H2 and HMCCH produced in reactions of laser-ablated Fe and Os atoms with acetylene

M-η2-C2H2 and HMCCH are observed in reactions Fe and Os with acetylenes. While the vinylidene derivatives are energetically comparable, it is not produced enough to observe. The Fe insertion product owns a near linear structure in contrast to the more bent structures of the Os counterpart and the CC bonds the group 8 metal π-complexes are considerably shorter than those of the early transition-metal analogues, showing the general trend of decreasing back-donation to the π∗-orbitals of acetylene with moving right in the periodic table.