Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols

Abstract

Ruthenium complexes [Ru(CO) 2 (PPh 3 ) 2 (O 2 CR) 2 ] -3a (R = CH 2 OCH 3 ), 3b (R = iPr), 3c (R = tBu), 3d (R = 2-c C 4 H 3 O), and 3e (R = Ph) -were synthesized by treatment of Ru(CO) 3 -(PPh 3 ) 2 with the corresponding carboxylic acids. The molecular structures of the newly synthesized complexes in the solid state are discussed. Compounds 3a-e were successfully applied as catalysts in the addition of carboxylic acids to propargylic alcohols to give the corresponding β-oxo esters in good to excellent yields even in air. The different carboxylate ligands do not have an influence on the productivities, because the carboxylates exchange rapidly under the applied [a]2939 reaction conditions, as was confirmed by 31 P{ 1 H} NMR spectroscopic studies. The addition of catalytic amounts of Na 2 CO 3 resulted in an increase in β-oxo ester formation. The reaction is tolerant to the use of versatile functional groups on the propargylic alcohols and carboxylic acids, revealing a broad substrate generality. In contrast to most other known catalytic systems, even sterically hindered substrates, including 2,4,6-trimethylbenzoic acid, 1,1-diphenylprop-2-yn-1-ol, or the biologically active steroid ethisterone, were successfully converted.

Chemical vapor deposition of ruthenium-based layers by a single-source approach

“…Unique to the 13 C{ 1 H} NMR spectra is the splitting of the aand b-CH 2 groups of the P(n-Bu) 3 ligand into triplets (Experimental section), which is a common phenomenon for complexes containing trans-phosphine ligands. 26,27 This finding is confirmed by the calculations of Metzinger 28 and Harris. 29 In the IR spectra of ruthenium complexes 4a-g, two strong stretching vibrations for the terminal carbonyl groups are observed between 1969 and 2057 cm À1 (Experimental section).…”

Ruthenium‐Catalyzed Hydrocarboxylation of Internal Alkynes

“…[34] In cases 2f-j (Scheme 2), when carboxylic acids other than benzoic acid were applied, the formation of up to 2 % of the benzoate product 2a was observed, presumably arising from conversion of the benzoate ligands on initial catalyst 1. [40][41][42] Compared to previously reported results on the formation of (E)-isomers, the current conditions employing 1 and B(C 6 F 5 ) 3 led to higher selectivities while using both lower catalyst loadings and similar or even reduced reaction times. [32][33][34] Having demonstrated that, with catalyst 1, a broad range of symmetrically substituted internal alkynes could be successfully converted to isomerically pure (E)-enol esters, we were encouraged to study the reaction with unsymmetrically substituted internal alkynes.…”

“…Toluene was chosen as solvent since it had proven to be the best solvent for this catalytic system. [40][41][42] By applying 1.0 mol-% of catalyst 1, a conversion of 70 % was reached after 6 h at 140°C (Table 1, Entry 1). Interestingly, this reaction led to the formation of (E)-2a as the exclusive product.…”

“…[40][41][42] In continuing these studies, we have investigated the catalytic activity of 1 for hydrocarboxylation of challenging internal alkynes. [40][41][42] In continuing these studies, we have investigated the catalytic activity of 1 for hydrocarboxylation of challenging internal alkynes.…”

“…Recently, we demonstrated that the mononuclear ruthenium complex [Ru(CO) 2 {P(p-CF 3 -C 6 H 4 ) 3 } 2 (O 2 CPh) 2 ] (1) is a highly efficient and selective catalyst for the addition of carboxylic acids to terminal alkynes and propargylic alcohols under mild reaction conditions. [40][41][42] In continuing these studies, we have investigated the catalytic activity of 1 for hydrocarboxylation of challenging internal alkynes. Herein, the effect of catalytic amounts of various additives on reaction efficiency and selectivity as well as substrate scope is explored and discussed.…”