Reaction of [Os3(μ-H)2(CO)10] with 1,4-dipyridylbuta-1,3-diyne yields two clusters, [Os3(μ-H)(CO)10{μ-η1:η1-(C8H5N)–C–(C5H4N)}] 1 and [Os3(μ-H)(CO)10-{μ3-η1:η1:η1-(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 [Os3(μ-H)(CO)9{μ-η1:η2:η1-(C8H5N)–C–(C5H4N)}] 3. An analogous reaction involving [Os3(CO)10(MeCN)2] generates three products, [Os3(μ-H)(CO)10{μ-η1:η1-(NC5H3)–C2C2–(C5H5N)}] 4 and [{Os3(μ-H)(CO)10}2{μ-η1:η1-(NC5H3)–C2–}2] 5, both coordinated via orthometallated pyridyl rings, and a minor product [{Os3(CO)10}2{μ3-η1:η1:η1-C2-(NC5H4)}2] 6, coordinated via μ-carbene and σ-N interactions, the linking ligand retaining its central C![[triple bond, length as m-dash]](http://www.rsc.org/images/entities/char_e002.gif)
C bond. Complex 4 reacts with [Os3(μ-H)2(CO)10] to form the linked cluster [{Os3(μ-H)(CO)10}2{μ-η1:η1,μ-η1:η1-(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.
![Graphical abstract: Molecular rearrangements of diynes coordinated to triosmium carbonyl clusters: reactions of [Os3(μ-H)2(CO)10] and [Os3(CO)10(MeCN)2] with 1,4-dipyridylbuta-1,3-diyne](http://hg.y866.cn/compound/lib/scimg/usr/1/B412578A.jpg)
