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Dimerization of Terminal Arylalkynes in Aqueous Medium by Ruthenium and Acid Promoted (RAP) Catalysis: Acetate‐ Assisted ( sp )C( sp 2 )C Bond Formation
Author(s) -
Coniglio Alessandra,
Bassetti Mauro,
GarcíaGarrido Sergio E.,
Gimeno José
Publication year - 2012
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201100600
Subject(s) - chemistry , ruthenium , hexamethylbenzene , acetic acid , dimer , catalysis , aqueous solution , medicinal chemistry , alkyne , stereochemistry , phenylacetylene , organic chemistry , benzene
Abstract The hexamethylbenzene ruthenium(II) dimer [{RuCl(μ‐Cl)(η 6 ‐C 6 Me 6 )}] 2 (5 mol%), tested among a series of ruthenium(II) and ruthenium(IV) complexes, represents an efficient precatalyst source for the dimerization of terminal arylalkynes ArCCH [Ar=C 6 H 5 , 3,4,5‐(OMe) 3 C 6 H 2 , 4‐MeOC 6 H 4 , 2‐MeOC 6 H 4 , 4‐MeC 6 H 4 , 2,4,5‐Me 3 C 6 H 2 , 4‐BrC 6 H 4 , 4‐ClC 6 H 4 , 4‐FC 6 H 4 , 4‐HC(O)C 6 H 4 , 4‐CH 2 CHC 6 H 4 , 3‐NCC 6 H 4 , 4‐O 2 NC 6 H 4 , 4‐EtO 2 C‐(CH 2 ) 3 OC 6 H 4 , 4‐HO(CH 2 CH 2 O) 3 C 6 H 4 , 3‐HO(CH 2 CH 2 O) 3 ‐C 6 H 4 ] in acetic acid/water mixture (1:1, v/v). The reactions proceed for 24 h at room temperature under heterogeneous conditions and afford the dimeric enyne derivatives ( E )‐ArCHCHCCAr in high yields and stereoselectivity. The preformed acetato complex [RuCl(η 6 ‐C 6 Me 6 )(κ 2 ‐OAc)] catalyzes the dimerization of phenylacetylene under analogous conditions, with rapid substrate conversion. The presence of cosolvents of acetic acid different from water reduces dramatically the efficiency and selectivity of the reaction. The aqueous medium facilitates the activation stage of the precatalyst by assisting the splitting of the ruthenium dimer. The addition or generation in situ of acetate salts results in shorter reactions times (0.5–3 h) and excellent yields, due to the rapid formation of active acetato complexes. Circumstantial evidence indicates that the π‐bound alkyne molecule is activated by intramolecular proton abstraction. This is currently the most efficient, E ‐selective and wide‐scope catalytic system for the alkyne dimerization reaction in protic aqueous media.