Ruthenium vinylidene and sigma-acetylide complexes containing 1,4,7-trimethyl-1,4,7-triazacyclononane (Me(3)tacn): Synthesis and alkyne-coupling reactivity

The ruthenium(II) complexes [Ru(Me(3)tacn)(L)(2)X]PF6 (L = PMe3, X = O2CCF3 (la); L = PMe3, X = Cl (1b); L = 1/2 dmpe, X = O2CCF3 (1c)) are prepared. Only 1a reacts with 1 equiv of RC equivalent to CH (R = Ph and p-tolyl) to give the vinylidene complexes [Ru(Me(2)tacn)(PMe3)(O2CCF3){C=CH(R)}]PF6 (R = Ph (2a) and p-tolyl (2b)) in refluxing IB-dichloroethane. Reaction of 2a and 2b with PMe3 in methanolic KOH solution give the corresponding a-acetylide complexes [Ru(Me(3)tacn)(PMe3)(2)(C equivalent to CR)]PF6 (R Ph (3a) and p-tolyl (3b)). Similarly, treatment of 2a with P(OMe3)(3) affords [Ru(Me(3)tacn)(PMe3)(P(OMe)(3))(C equivalent to CPh)]PF6 (3c). Oxidative cleavage of the vinylidene ligand in 2a by oxygen gives [Ru(Me(3)taen)(PMe3)(O2CCF3)(CO)]PF6 (4) and benzaldehyde. Complex 1b reacts with 2.5 equiv of RC equivalent to CH (R = Ph, p-tolyl) and 1.5 equiv of KOH in methanol to yield the eta(3)-butenynyl species [Ru(Me(3)tacn)(PMe3){eta(3)-RC3=CH(R)}]PF6 (R = Ph (5a) and p-tolyl (5b)). In addition, 2a and 2b react with RC equivalent to CH (R = Ph, p-tolyl) and KOH in methanol to give 5a and 5b, respectively. Treatment of 2a with p-tolylC equivalent to CH and KOH in methanol gives [(Me(3)tacn)Ru(PMe3){eta(3)-PhC3=CH(p-tolyl)}]PF6 (5c) and [(Me(3)tacn)Ru(PMe3)(eta(3)-(p-tolyl)C-3=CH(Ph )]PF6 (5c') in a 1:1 ratio. Reacting 2b with PhC equivalent to CH similarly gives 5e and 5c' in equal amounts. :Structures of 3c, 5a, and 5c/5c' are established by X-ray crystallography. Mechanistic insights from the isolated complexes suggest that hydrogen shift between vinylidene and acetylide moieties is an important process in the coupling of alkynes.