Arene Alkyne Linkage Isomerizations of Diphenylacetylene on Pentaammineosmium(II)

When 0s(NH3)3(CF3S03)3 is reduced in the presence of diphenylacetylene, four pentaammineosmium(II) complexes can be isolated

and characterized in which the alkyne remains intact. The kinetically favored mononuclear complex features a phenyl group

i;2-bound to the metal center. This species is observed to undergo a linkage isomerization in which the osmium migrates to the

alkyne. Through the use of pulse radiolysis, this isomerization was determined to be greatly accelerated by oxidizing the metal

to Os(III). The inherent stability of alkyne complexes for both di- and trivalent osmium provides the opportunity to assess the

ability of this ligand to act as a -donor as well as -acceptor.