Transfer Hydrogenation and Hydrogenation of Commercial‐Grade Aldehydes to Primary Alcohols Catalyzed by 2‐(Aminomethyl)pyridine and Pincer Benzo[h]quinoline Ruthenium Complexes

Abstract

The chemoselective reduction of commercial‐grade aldehydes (97–99 %) to primary alcohols is achieved with cis‐[RuCl2(ampy)(PP)] [ampy=2‐(aminomethyl)pyridine; PP=1,4‐bis(diphenylphosphino)butane, 1,1′‐ferrocenediyl‐bis(diphenylphosphine)] and pincer [RuCl(CNNR)(PP)] [PP=1,3‐bis(diphenylphosphino)propane, 1,4‐bis(diphenylphosphino)butane, 1,1′‐ferrocenediyl‐bis(diphenylphosphine); HCNNR=4‐substituted‐2‐aminomethyl‐benzo[h]quinoline; R=Me, Ph] complexes by transfer hydrogenation and hydrogenation reactions. Aromatic, conjugated, and aliphatic aldehydes are converted quantitatively to the corresponding alcohols using 2‐propanol with potassium carbonate at substrate/catalyst ratios up to 100 000 by transfer hydrogenation, whereas aldehyde hydrogenation (5–20 atm of H2) is achieved efficiently in MeOH in the presence of KOtBu at substrate/catalyst ratios up to 40 000.

Hydrogenation and Reductive Amination of Aldehydes using Triphos Ruthenium Catalysts

“…Full conversion was observed in most cases and, pleasingly, improved selectivity was observed, up to 98:2 in favour of cinnamyl alcohol (entries 11–17). The low catalyst loading and high selectivity for the allylic alcohol compare favourably with the best homogenous catalysts under hydrogenation conditions, for example: (Ir) S/C=500:1, (Ru) S/C=500:1, (Ru) S/C=200:1, (Ru) S/C=200:1, (Ru) SC=500:1, (Ru) S/C=1000:1, (Fe) S/C=200:1, (Fe) S/C=500:1, (Fe) S/C=20 000:1, (Ru) S/C=10 000:1 …”

“…The low catalyst loading and high selectivity for the allylic alcohol comparef avourably with the best homogenous catalysts under hydrogenation conditions, for example: (Ir) S/C = 500:1, [41] (Ru) S/C = 500:1, [8] (Ru) S/C = 200:1, [42] (Ru) S/ C = 200:1, [43] (Ru) SC = 500:1, [44] (Ru) S/C = 1000:1, [45] (Fe) S/C = 200:1, [46] (Fe) S/C = 500:1, [47] (Fe) S/C = 20 000:1, [48] (Ru) S/C = 10 000:1. [49] The substrate scope was then investigated using 1 ( Table 2). In most cases al oading of S/C = 10 000:1 was achievable without the need for the significant optimisationo ft he reaction conditions.…”

Chemoselective Transfer Hydrogenation of Aldehydes with HCOONH4 Catalyzed by RuCl(CNNPh)(PP) Pincer Complexes

“…[23] Given that the catalytically active metal-hydride species [24] are generated under basic conditions, under which aldehydes,m ore than ketones, may undergo several side reactions (Claisen-Tishchenko, [25] Cannizzaro, [26] and aldol condensation reactions [27] ), selective aldehyde reductionr emains ad elicate point. Recently,w edescribed the preparation of benzo[h]quinoline pincer complexes RuCl(CNN Ph )(PP) 1-3 that are active catalysts in the hydrogenation and TH with 2-propanol of ketones [28] and aldehydes [29] (Figure 1).In the TH of aldehydes in 2-propanol, the reaction was performed atalow substrate concentration (0.1 m)a nd under weaklyb asic conditions to inhibit the condensation reaction with the formed acetone, aside reaction that strongly depends on the typeoft he aldehyde. [29] We report herein the straightforward and chemoselective TH of aldehydes of commercial-grade purity to alcohols by using ammonium formate as the hydrogen donor in aw ater/toluene biphasic system catalyzedb yp incer complexes 1-3 at S/C 2000-20000.…”

“…Recently,w edescribed the preparation of benzo[h]quinoline pincer complexes RuCl(CNN Ph )(PP) 1-3 that are active catalysts in the hydrogenation and TH with 2-propanol of ketones [28] and aldehydes [29] (Figure 1).In the TH of aldehydes in 2-propanol, the reaction was performed atalow substrate concentration (0.1 m)a nd under weaklyb asic conditions to inhibit the condensation reaction with the formed acetone, aside reaction that strongly depends on the typeoft he aldehyde. [29] We report herein the straightforward and chemoselective TH of aldehydes of commercial-grade purity to alcohols by using ammonium formate as the hydrogen donor in aw ater/toluene biphasic system catalyzedb yp incer complexes 1-3 at S/C 2000-20000. Employment of HCOONH 4 with 1-3 allowed the clean reduction of aliphatic, conjugated, and functionalized aromatic and heteroaromatic aldehydes, without the formation of condensation and amination side products.Reaction of benzaldehyde (a)o fc ommercial-grade purity (assay 99 %) in toluene (0.5 m)w ith HCOONH 4 (2 equiv.)…”

“…[23] Given that the catalytically active metal-hydride species [24] are generated under basic conditions, under which aldehydes,m ore than ketones, may undergo several side reactions (Claisen-Tishchenko, [25] Cannizzaro, [26] and aldol condensation reactions [27] ), selective aldehyde reductionr emains ad elicate point. Recently,w edescribed the preparation of benzo[h]quinoline pincer complexes RuCl(CNN Ph )(PP) 1-3 that are active catalysts in the hydrogenation and TH with 2-propanol of ketones [28] and aldehydes [29] (Figure 1).…”