The ruthenium(II) cation, [Cp*Ru(NCMe)
3]OTf (
4), triggers the Bergman cycloaromatization of acyclic endiynes at room temperature in THF solvent. Treatment of 1,2-di(1-alkynynyl)cyclopentenes (
13-Me, alkynyl = propynyl;
13-Pr
n, alkynyl = pentynyl;
13-Bu
i, alkynyl = 4-methyl-pent-1-ynyl) with
4 in THF solvent at room temperature gives rise to the ruthenium arene complexes: [Cp*Ru{(3a,4,5,6,7,7a-
![](/images/gifchars/eta.gif)
)-2,3-dihydro-5,6-dialkyl-1H-indene}]OTf (
15-Me, alkyl = methyl, 64% yield;
15-Pr
n, alkyl =
n-propyl, 73% yield;
15-Bu
i, alkyl = 4-methyl-1-pentynyl, 88% yield). In a similar fashion, the room-temperature reaction of
4 with 1-ethynyl-2-(1-propynyl)cyclopentene (
11) and [2-(1-propynyl)-1-cyclopenten-1-yl]trimethylsilane (
14) leads to the formation of [Cp*Ru{(3a,4,5,6,7,7a-
![](/images/gifchars/eta.gif)
)-2,3-dihydro-5-methyl-1H-indene}]OTf (
12, 92% yield) and [Cp*Ru{(3a,4,5,6,7,7a-
![](/images/gifchars/eta.gif)
)-2,3-dihydro-6-methyl-1H-inden-5-yl)trimethylsilane}]OTf (
16, 77% yield), respectively. The bis(TMS)-substituted enediyne (1-cyclopentene-1,2-diyldi-2,1-ethynediyl)bis(trimethylsilane) (
9-TMS) and
4 underwent reaction at 100
![](/images/entities/deg.gif)
C to give [Cp*Ru{(3a,4,5,6,7,7a-
![](/images/gifchars/eta.gif)
)-2,3-dihydro-1H-inden-5-yl)trimethylsilane}]OTf (
10, 69% yield). Deuterium-labeling studies rule out a mechanism that involves a ruthenium-vinylidene intermediate, and provide support for the involvement of a
p-benzyne intermediate. In a similar fashion, complex
4 is shown to trigger the cycloaromatization of the conjugated dienyne, 1-ethenyl-2-(1-pentynyl)cyclopentene (
19), at room temperature in chloroform-
d1 solvent to give [Cp*Ru{(3a,4,5,6,7,7a-
![](/images/gifchars/eta.gif)
)-2,3-dihydro-5-(1-propyl)-1H-indene}]OTf (
20, 96% yield), with no deuterium enrichment. In the absence of ruthenium the thermal cyclization reactions of unsubstituted acyclic enediynes (Bergman cycloaromatization) and acyclic conjugated dienynes (Hopf cyclization) typically require elevated temperatures (150-250
![](/images/entities/deg.gif)
C). Complexes
10 and
15-Pr
n were characterized structurally by X-ray crystallography.