NHC-Iridium-Catalyzed Deoxygenative Coupling of Primary Alcohols Producing Alkanes Directly: Synergistic Hydrogenation with Sodium Formate Generated in Situ

Abstract

The direct conversion of alcohols into long-chain alkanes is an attractive but extremely challenging approach for biomass upgrading. Here, we describe the highly selective deoxygenative coupling of aryl ethanols with primary alcohols to produce alkanes, using a bis-N-heterocyclic carbene iridium (bis-NHC-Ir) complex as the catalyst. Up to quantitative yields and selectivity with a broad substrate scope are attained in both homo- and cross-coupling reactions. Mechanistic studies reveal that the further synergistic hydrogenation of the alkene intermediates by the formate generated in situ in the presence of bis-NHC-Ir is crucial for alkane production.

Manganese‐Catalyzed Mono‐N‐Methylation of Aliphatic Primary Amines without the Requirement of External High‐Hydrogen Pressure

“…[13] However, the more nucleophilic aliphatic primary amines were not included in the substrate scope. Utilizing the same hydrogen-borrowing strategy, we have successfully synthesized alkanes, [14] β-methylated alcohols, [15] and mono-N-methylated aromatic amines [16] via CÀ C and CÀ N cross-coupling reactions. Inspired by these results, we envisioned that a pincer Mn catalyst could be utilized to achieve the selective mono-coupling of aliphatic primary amines and methanol.…”

Modular Access to Quaternary α-Hydroxyl Acetates by Catalytic Cross-Coupling of Alcohols

“…Acceptorless dehydrogenation of alcohol is a green and atom-economic alternative approach, which provides aldehyde (or ketone) without the use of sacrificial acceptor molecules, and the side product is molecular hydrogen. − By using an acceptorless dehydrogenation strategy, transition-metal-catalyzed C-alkylation of primary or secondary alcohols with other primary alcohols has received considerable attention, in which the primary alcohols are considered as environmentally friendly alkylating agents, and hydrogen and water are produced as clean byproducts. − Furthermore, the cross-coupling of alcohols may also constitute one of the most efficient protocols to access value-added compounds, such as upgraded alcohols, carboxylic acids, and even hydroxyl acids. − However, when 1,2-diols are utilized and coupled with primary alcohols, besides possible alkylation, other thermodynamically favorable products after dehydration, dehydrogenation, oxidization, esterification and even polymerization may also be generated . Even in the case of the alkylation, dehydrogenative cross-coupling of 1,2-propylene glycol and methanol may produce not only ethylene glycol, ethanol, and n - and iso -propanol, but also butane-1,2- and 2,3-diols, as well as other byproducts formed by the methylation of lactate (Figure c), − in which α-hydroxyl acetates may be generated by dehydrogenative oxidization of 1,2-propylene glycol .…”

Selective Modular Synthesis of ortho-Substituted Phenols via Pd-Catalyzed Dehydrogenation–Coupling–Aromatization of Alcohols

“…Recently, the acceptorless dehydrogenative cross-coupling between two different alcohols has drawn considerable attention due to its feasibility to access value-added chemicals. ,− On consideration that cyclohexanones are readily available from cyclohexanols via dehydrogenation, − and the aromatization process to access phenols also involves dehydrogenation, we conceived that ortho -substituted phenols may also be directly obtained from cyclohexanols and primary alcohols. This desired transformation mainly consists of the dehydrogenation of alcohols, aldol condensation, and aromatization, and is thus denoted as “dehydrogenation–coupling–aromatization”.…”

“…However, it would be extremely challenging to realize this multistep cascade transformation by a single catalyst. Besides ether formation under the base conditions, in the dehydrogenative cross-coupling of alcohols, after aldol condensation, hydrogenation usually occurs, leading to the formation of alkanes instead. ,− Therefore, the competition between rehydrogenation and aromatization is the key for the establishment of our protocol. Following our research interests in developing N-heterocyclic carbene (NHC) metal complexes and exploring their catalytic application in various challenging and practical reactions, herein, we accomplished ortho -substituted phenol synthesis from cyclohexanols with primary alcohols by using NHC-Pd complexes via a dehydrogenation–coupling–aromatization strategy (Figure c).…”

“…The dehydrogenative cross-coupling of tetralol with 1-hexanol proceeded smoothly and readily produced 1,3-dihexylnaphthalen-2-ol ( 34 ) in excellent yield (90%, Figure ). When benzyl alcohols, which are readily reduced to toluene derivatives ,,− or dehydrogenated to benzoic acids − by palladium catalysts, were utilized instead of cyclohexanols, disubstituted naphthalen-2-ols 35 – 53 were formed in moderate to excellent yields under otherwise identical reaction conditions (53–93%, Figure ). Delightedly, when benzyl alcohol was used as a substrate, the position, electronic properties, and steric hindrance of substitutes on benzyl rings barely hindered the dehydrogenation–coupling–aromatization process, even with heterocyclic benzyl type alcohols with furan and thiophene rings (53–88% for 35 – 44 , Figure ).…”