Ruthenium vinylidene and σ-acetylide complexes containing 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn): Synthesis and alkyne-coupling reactivity

Abstract

The ruthenium(II) complexes [Ru(Me3tacn)(L)2X]PF6 (L = PMe3, X = O2CCF3 (1a); L = PMe3, X = Cl (1b); L = 1/2 dmpe, X = O2CCF3 (1c)) are prepared. Only 1a reacts with 1 equiv of RC≡CH (R = Ph and p-tolyl) to give the vinylidene complexes [Ru(Me3tacn)-(PMe3)(O2CCF 3){C=CH(R)}]PF6 (R=Ph (2a) and p-tolyl (2b)) in refluxing 1,2-dichloroethane. Reaction of 2a and 2b with PMe3 in methanolic KOH solution give the corresponding σ-acetylide complexes [Ru(Me3tacn)(PMe3)2(C≡CR)]PF6 (R=Ph (3a) and p-tolyl (3b)). Similarly, treatment of 2a with P(OMe3)3 affords [Ru(Me3tacn)(PMe3)(P(OMe) 3)(C≡CPh)]-PF6 (3c). Oxidative cleavage of the vinylidene ligand in 2a by oxygen gives [Ru(Me3tacn)-(PMe3)(O2CCF 3)(CO)]PF6 (4) and benzaldehyde. Complex 1b reacts with 2.5 equiv of RC≡CH (R=Ph, p-tolyl) and 1.5 equiv of KOH in methanol to yield the η3-butenynyl species [Ru(Me3-tacn)(PMe3){η3-RC 3=CH(R)}]PF6 (R = Ph (5a) and p-tolyl (5b)). In addition, 2a and 2b react with RC≡CH (R = Ph, p-tolyl) and KOH in methanol to give 5a and 5b, respectively. Treatment of 2a with p-tolylC≡CH and KOH in methanol gives [(Me3tacn)Ru(PMe3){/73-PhC 3=CH(p-tolyl)}]PF6 (5c) and [(Me3tacn)Ru(PMe3){η 3-(p-tolyl)C3=CH(Ph)}]PF6 (5c′) in a 1:1 ratio. Reacting 2b with PhC≡CH similarly gives 5c 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.