Molecular rearrangements of diynes coordinated to triosmium carbonyl clusters: reactions of [Os-3(mu-H)(2)(CO)(10)] and [Os-3(CO)(10)(MeCN)(2)] with 1,4-dipyridylbuta-1,3-diyne

Reaction of [Os-3(mu-H)(2)(CO)(10)] with 1,4-dipyridylbuta-1,3-diyne yields two clusters, [Os-3(mu-H)(CO)(10){mu-eta(1):eta(1)-(C8H5N)-C-(C5H4N)}] 1 and [Os-3(mu-H)(CO)(10)-{mu(3)-eta(1):eta(1):eta(1)-(C5H4N)-C-C(C8H6N)}] 2, in which the diyne has rearranged to form a substituted indolizine ring system. Complex 1 converts slowly to 2 at room temperature, and may be decarbonylated to yield [Os-3(mu-H)(CO)(9){mu-eta(1):eta(2):eta(1)-(C8H5N)-C-(C5H4N)}] 3. An analogous reaction involving [Os-3(CO)(10)(MeCN)(2)] generates three products, [Os-3(mu-eta)(CO)(10){mu-eta(1):eta(1)(NC5H3)-C2C2-(C5H5N)}] 4 and [{Os-3(mu-eta)(CO)(10)}(2){mu-eta(1):eta(1)-(NC5H3)-C-2-}(2)] 5, both coordinated via orthometallated pyridyl rings, and a minor product [{Os-3(CO)(10)}(2){mu(3)-eta(1):eta(1):eta(1)-C-2-(NC5H4)}(2)] 6, coordinated via mu-carbene and sigma-N interactions, the linking ligand retaining its central Cequivalent toC bond. Complex 4 reacts with [Os-3(mu-eta)(2)(CO)(10)] to form the linked cluster [{Os-3(mu-eta)(CO)(10)}(2){mu-eta(1):eta(1), mu-eta(1): eta(1)-(C8H5N)-C-(C5H3N)}] 7, also forming an indolizine ring system. The structures of 1-3, 6, 6.2[CH2Cl2] and 7 have been established by X-ray crystallography.