Selective Dimerization of Arylalkynes to (E)-1,4-Diaryl Enynes Catalyzed by the [Ru(p-cymene)Cl₂]₂/Acetic Acid System under Phosphine-Free Conditions

Abstract

The commercially available di-mu-chlorobis[(p-cymene)chlororuthenium(II)] complex catalyzes the dimerization of aromatic alkynes in acetic acid at room temperature to form the corresponding (E)-1,4-diarylbut-1-ene-3-yne derivatives, with high stereoselectivity. The procedure does not require the use of additives and can be carried out in the presence of water or aprotic cosolvents, under homogeneous conditions.

Symmetrical Bis(acetylido)ruthenium(II) Complexes

“…Scheme 2. The complexes were characterised by multinuclear NMR and IR spectroscopy, mass spectrometry and, in some cases, by X-ray crystallography. Complexes 1 and 2 have previously been prepared by the addition of the appropriate terminal alkyne to [RuH 2 (dmpe) 2 ] [7] and the reaction of [trans-RuCl 2 (dmpe) 2 ] with phenylacetylene in the presence of Zn/Hg amalgam (complex 1 only), [2f] although characterisation of 2 was limited to 31 P and 1 H NMR spectroscopy. Complexes 3-6 have not been previously reported.…”

Regio- and Stereoselective Homodimerization of Monosubstituted Acetylenes in the Presence of the Second Generation Grubbs Catalyst

“…Many examples of effective run of the process in the presence of transition metal complexes have been described. Catalytic activity in the process has been reported to be shown by complexes of such metals as palladium [4,[7][8][9][10][11][12][13], rhodium [14][15][16][17][18][19], ruthenium [20][21][22][23][24][25][26][27][28][29], nickel [30], iridium [31][32][33], osmium [34,35], iron [36] and the f-block metals [37][38][39]. However, a highly selective synthesis of conjugated enynes by dimerization is still a challenging process.…”

One‐Pot Desilylation/Dimerization of Terminal Alkynes by Ruthenium and Acid‐Promoted (RAP) Catalysis

“…[7] We reported recently that a catalytic system composed of the commercially available ruthenium com-plex [RuCl 2 A C H T U N G T R E N N U N G (p-cymene)] 2 (I) and acetic acid promotes the dimerization of arylalkynes and affords 1,4-diaryl-1-buten-3-ynes with high (E)-stereoselectivity under mild reaction conditions (Scheme 1). [8] The catalytic species is formed upon interactions of the three components: complex, acetic acid and alkyne. This methodology was then extended to diynic starting materials, thus affording phenyleneethynylene-vinylene oligomers and polymers via a stepwise polyaddition process.…”

“…The yield of the enyne product 1,4-diphenyl-1-buten-3-yne (1a, 60%, E:Z, 99:1, determined by 1 H NMR and GC) after 6 h was higher than that observed from the catalytic dimerization of 1 in neat AcOH after 45 h (55%). [8] This onepot protocol was then tested employing n-Bu 4 NF/ AcOH (1 equiv.) in THF (method B), [11,12] as alternative to the desilylation step by NaOH.…”

“…The dimerization processes proceed in the presence of tetrabutylammonium or sodium acetate, which form as the by-product of the desilylation by the fluoride source (method B), or upon addition of I/AcOH (method A), respectively. In attempts to rationalize the observed faster conversion of the free alkynes with respect to the reactions catalyzed by complex I in neat acetic acid, [8] the reactivity of PhC CH was checked upon addition of equimolar NaOAc, in order to simulate the one-pot conditions, other factors such as the precise medium composition remaining different. The rates of consumption of the alkyne 1 and formation of the enyne (E)-1a, as followed by 1 H NMR in the presence or absence of NaOAc, are shown in the plot of Figure 1.…”