The hydrogenation of CO2 to methanol using a recyclable molecular organometallic catalyst in the absence of an alcohol additive is demonstrated for the first time.

The complex [Ru(Triphos)(TMM)] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane, TMM = trimethylene methane) provides an efficient catalytic system for the hydrogenation of a broad range of challenging functionalities encompassing carboxylic esters, amides, carboxylic acids, carbonates, and urea derivatives. The key control factor for this unique substrate scope results from selective activation to generate either the neutral species [Ru(Triphos)(Solvent)H2] or the cationic intermediate [Ru(Triphos)(Solvent)(H)(H2)](+) in the presence of an acid additive. Multinuclear NMR spectroscopic studies demonstrated together with DFT investigations that the neutral species generally provides lower energy pathways for the multistep reduction cascades comprising hydrogen transfer to C═O groups and C-O bond cleavage. Carboxylic esters, lactones, anhydrides, secondary amides, and carboxylic acids were hydrogenated in good to excellent yields under these conditions. The formation of the catalytically inactive complexes [Ru(Triphos)(CO)H2] and [Ru(Triphos)(μ-H)]2 was identified as major deactivation pathways. The former complex results from substrate-dependent decarbonylation and constitutes a major limitation for the substrate scope under the neutral conditions. The deactivation via the carbonyl complex can be suppressed by addition of catalytic amounts of acids comprising non-coordinating anions such as HNTf2 (bis(trifluoromethane)sulfonimide). Although the corresponding cationic cycle shows higher overall barriers of activation, it provides a powerful hydrogenation pathway at elevated temperatures, enabling the selective reduction of primary amides, carbonates, and ureas in high yields. Thus, the complex [Ru(Triphos)(TMM)] provides a unique platform for the rational selection of reaction conditions for the selective hydrogenation of challenging functional groups and opens novel synthetic pathways for the utilization of renewable carbon sources.

The development of a tailored tridentate ligand enabled the synthesis of a molecular ruthenium-triphos catalyst, eliminating dimerization as the major deactivation pathway. The novel catalyst design showed strongly increased performance and facilitated the hydrogenation of highly challenging lactam substrates with unprecedented activity and selectivity.

Reported is the development of a novel catalytic cascade reaction facilitating the modular synthesis of cyclic tertiary amines from simple lactam substrates and secondary alcohols. Using a single molecular ruthenium-triphos catalyst in the presence of molecular hydrogen enabled the versatile formation of various amines in high yield with excellent selectivity. Extending the reaction system to using an alcohol as the hydrogen transfer reagent allowed the reduction of lactams without the need for molecular hydrogen.

The development of at ailored tridentate ligand enabled the synthesis of am olecular ruthenium-triphos catalyst, eliminating dimerization as the major deactivation pathway.T he novel catalyst design showed strongly increased performance and facilitated the hydrogenation of highly challenging lactam substrates with unprecedented activity and selectivity.Catalytic hydrogenation using molecular catalysts based on defined organometallic complexes has been advanced to be an essential tool for the chemical synthesis in research laboratories as well as on the industrial scale.[1] Very effective catalysts could be tailored for the addition of hydrogen to complex organic substrates,l argely based on fundamental mechanistic insight on am olecular level. Moreover,r ecent research efforts have illustrated that ruthenium complexes of the multidentate triphos (1,1,1-tri(diphenylphosphinomethyl)ethane) ligand demonstrate potential for the development of highly active and stable homogeneous species.[2] Especially for the reduction of challenging functionalities, the ruthenium-triphos systems could be established as important molecular catalyst, [2b,c] finding increasing application in numerous research groups.[3] This important advancement moved these molecular catalysts into the spotlight for novel transformations and in special cases closer to processing conditions of heterogeneous catalyst systems.[4] Nevertheless,t he hydrogenation of non-activated aliphatic amides remains an enormous challenge for molecular catalysts and especially the reductive cleavage of lactams requires novel dedicated catalysts.T he group of Bergens introduced the catalyst [Ru(Ph 2 P(CH 2 ) 2 NH 2 ) 2 (m 3 -C 3 H 5 )]BF 4 for the hydrogenation of N-phenylpyrrolidin-2-one,e nabling the formation of the respective amino alcohol with CÀNc leavage with high turnover number (TON).[5] Most recently the group of Milstein presented N,N,P-pincer ruthenium complexes for the conversion of glycine anhydride into ethanolamine in high yield.[6] Ther eduction of lactams to cyclic amines is still demanding,b ut the groups of Mashima and Saito could already use ab is-bidentate (P,N) 2 -Ru system to accomplish this transformation and obtained the cyclic products in low to moderate yield.[7] Therefore,effective homogeneous catalysts for the hydrogenolysis of lactams towards cyclic amines remain largely elusive and the development of novel transition-metal compounds for this challenging catalytic transformation needs to be established. Herein we describe arationally developed novel triphos-type ligand that enables this transformation in hitherto unprecedented efficacy.In our recent effort we could establish the highly versatile and stable ruthenium complex [Ru(triphos)(tmm)] (1a, tmm = trimethylenemethane)a sa ctive catalysts system. [2c,8] Initial mechanistic evaluation of the active hydride species 1b revealed two reaction pathways as important targets for tailoring an improved catalyst (Scheme 1).[ [2a] Them ajor pathway results in deactivation and is b...

Reported is the development of a novel catalytic cascade reaction facilitating the modular synthesis of cyclic tertiary amines from simple lactam substrates and secondary alcohols. Using a single molecular ruthenium‐triphos catalyst in the presence of molecular hydrogen enabled the versatile formation of various amines in high yield with excellent selectivity. Extending the reaction system to using an alcohol as the hydrogen transfer reagent allowed the reduction of lactams without the need for molecular hydrogen.

Scope. -(VOM STEIN, T.; MEURESCH, M.; LIMPER, D.; SCHMITZ, M.; HOELSCHER, M.; COETZEE, J.; COLE-HAMILTON, D. J.; KLANKERMAYER*, J.; LEITNER, W.; J. Am. Chem. Soc. 136 (2014) 38, 13217-13225, http://dx.doi.org/10.1021/ja506023f ; Inst. Tech. Makromol. Chem.,

Tailor-Made Ruthenium-Triphos Catalysts for the Selective Homogeneous Hydrogenation of Lactams. -The novel catalyst (RUT) shows increased activity and selectivity and facilitates the hydrogenation of challenging lactams. -(MEURESCH, M.; WESTHUES, S.; LEITNER, W.; KLANKERMAYER*, J.; Angew. Chem., Int. Ed. 55 (2016) 4, 1392-1395, http://dx.