Current advances on ruthenium(II) N-heterocyclic carbenes in hydrogenation reactions

Hey, Daniela A.; Reich, Robert M.; Baratta, Walter; Kühn, Fritz E.

doi:10.1016/j.ccr.2018.06.005

Cited by 87 publications

(57 citation statements)

References 130 publications

(61 reference statements)

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“…Subsequent optimization revealed the following facts and trends: (i) NHC's with an unsaturated backbone gave better results than their saturated cousins; (ii) the nature of the N‐substituent is also important even though its exact role remains to be elucidated: for the time being, [(IPr)(η 6 ‐cymene)RuCl 2 ] ( 3 c ) works best, followed by [(IMes)(η 6 ‐cymene)RuCl 2 ] ( 3 b ); the use of related NHC's ( 4 d – g ) as ancillary ligands resulted in failure; (iii) likewise, replacement of the NHC by R 3 P (R=Cy, Ph) brings hydrogenative metathesis to a hold; (iv) constant irradiation of the reaction mixture with a UV lamp is necessary; attempts to drive the reaction by thermal de‐coordination of the p ‐cymene ligand led to mixtures that contain only minute amounts of the desired product; (v) while the [Cp*Ru] catalysts previously used operate best in chlorinated media, the switch from 1,2‐dichloroethane to toluene resulted in a significant increase in yield; (vi) just like in our previous study on gem ‐hydrogenation, the substitution of the alkene strongly impacts on the outcome; enyne 1 b (R=Me) bearing a methyl cap on the olefinic site proved to be optimal. When the reaction of this substrate is carried out with 3 c (10 mol %) in toluene under H 2 atmosphere (balloon) and irradiation with a UV lamp ( λ =370±40 nm), the metathesis reaction is remarkably clean and essentially quantitative (see the SI), affording analytically pure 2 in 95 % yield after flash chromatography.…”

Section: Methodsmentioning

confidence: 99%

Grubbs Metathesis Enabled by a Light‐Driven gem‐Hydrogenation of Internal Alkynes

2020

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[(NHC)(cymene)RuCl 2 ] (NHC = N-heterocyclic carbene) complexes instigate a light-driven gem-hydrogenation of internal alkynes with concomitant formation of discrete Grubbs-type ruthenium carbene species. This unorthodox reactivity mode is harnessed in the form of a "hydrogenative metathesis" reaction, which converts an enyne substrate into a cyclic alkene. The intervention of ruthenium carbenes formed in the actual gem-hydrogenation step was proven by the isolation and crystallographic characterization of a rather unusual representative of this series carrying an unconfined alkyl group on a disubstituted carbene center.

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Section: Methodsmentioning

confidence: 99%

Grubbs Metathesis Enabled by a Light‐Driven gem‐Hydrogenation of Internal Alkynes

2020

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“…In light of N‐heterocyclic carbene‐metal (NHC‐M) complexes can act as robust and viable catalysts in a broad range of reactions, various strategies have been developed for their immobilization . Among them, self‐supporting strategy may represent one of the most practical and efficient approaches .…”

Section: Fabrication Of Pomp‐nhc‐m By Direct Knitting With Different mentioning

confidence: 99%

Hierarchical Porous Organometallic Polymers Fabricated by Direct Knitting: Recyclable Single‐Site Catalysts with Enhanced Activity

et al. 2019

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supported catalysts by simply knitting rigid aromatic ligands via hypercross-linking (Friedel-Crafts reactions) has recently been proposed. [13] After further postmodification/activation, several MCPPs have been successfully developed. [14][15][16][17] However, with postmodification, avoiding the problems, like low density of catalytic sites due to incomplete modification and random/ nonselective metal anchoring, can be difficult. These issues may still lead to low catalytic activity and selectivity, especially in some challenging transformations. [18] In light of N-heterocyclic carbene-metal (NHC-M) complexes can act as robust and viable catalysts in a broad range of reactions, [19][20][21][22][23][24][25][26][27][28] various strategies have been developed for their immobilization. [29,30] Among them, selfsupporting strategy may represent one of the most practical and efficient approaches. [31][32][33][34] It has to be noted that NHC ligands still have to be carefully designed and modified before selfsupporting. Alternatively, the high catalytic activities and robustness of NHC-M complexes make them perfect candidates for direct knitting. To the best of our knowledge, there are only two reported examples on MCPPs in which the NHC ligands are firstly knitted and then coordinated to active metal ions (postmodification approach). [14,15] Direct knitting of NHC-M complexes to fabricate porous organometallic polymers (POMPs) that do not require postmodification/activation is still unknown.Herein, we have designed and prepared a series of unprecedented porous organometallic polymers POMPs-NHC-M 1-3 via direct knitting three types of bis-chelating NHC-M complexes (M = Ir, Pd, and Ru, Figure 1a). Using this facile strategy, which does not require postmodification/activation, 1) the metal active sites are atomically dispersed in the hierarchical porous matrix, and 2) the intrinsic well-defined bis-chelating mode and their molecular catalytic properties are maximally retained, which allows 3) the precise design and control of the immobilized catalysts at the molecular level. The advantages of direct knitting allow the resulting POMPs-NHC-M 1-3 to behave as recyclable solid single-site catalysts and exhibit extremely high catalytic activities in both hydrogenation and dehydrogenation reactions.In light of their robustness toward Friedel-Crafts reaction conditions, bis-chelating NHC-M (Ir, Pd and Ru) complexes 4, 5 and 6, derived from corresponding benzimidazolium salts, [24,25,27] were selected to fabricate POMPs via direct knitting with benzene ( Figure 1a). Concerning the plausible impact Porous organometallic polymers (POMPs) with hierarchical pore structures, high specific surface areas, and atomically dispersed metal (Ir, Pd, Ru) centers are successfully fabricated by a facile one-pot method through direct knitting of diverse N-heterocyclic carbene metal (NHC-M) complexes. These polymers can function as recyclable solid single-site catalysts and exhibit excellent catalytic activity and selectivity in both dehydrogenat...

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“…Half-sandwich complexes of group 8 metals with a characteristic piano-stool architecture are privileged structures in organometallic and catalysis research, 1−5 and have found wide application in bioinorganic and medicinal chemistry. 3,6−9 In this context, 1-methyl-4-(propan-2-yl)benzene ( para -cymene, p -cym) plays a predominant role because it represents an easily accessible formally neutral η 6 -coordinating arene ligand and its ruthenium(II) complex [{Ru( p -cym)Cl 2 } 2 ] is commercially available.…”

Section: Introductionmentioning

confidence: 99%

Facile Arene Ligand Exchange in p-Cymene Ruthenium(II) Complexes of Tertiary P-Chiral Ferrocenyl Phosphines

2019

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Half-sandwich arene–metal complexes are commonly used for specific applications. Herein, we report facile arene ligand exchange reactions of two ruthenium(II) complexes of tertiary P-stereogenic ferrocenyl phosphines. By mild photochemical activation, the displacement of p-cymene and subsequent tethering by η6-coordination of the terminal phenyl ring of a biphenylyl-substituted ferrocenyl phosphine were enabled. Furthermore, the spontaneous p-cymene displacement in a 2-methoxyphenyl-containing ferrocenyl phosphine and ensuing coordination of the ligand as a P,O chelate were examined. For both reactions, theoretical calculations of the general course of the reaction confirmed the experimental findings. The ease of the controlled arene displacement reported here can offer new pathways for the synthesis and design of novel tailor-made catalysts.

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Current advances on ruthenium(II) N-heterocyclic carbenes in hydrogenation reactions

Cited by 87 publications

References 130 publications

Grubbs Metathesis Enabled by a Light‐Driven gem‐Hydrogenation of Internal Alkynes

Grubbs Metathesis Enabled by a Light‐Driven gem‐Hydrogenation of Internal Alkynes

Hierarchical Porous Organometallic Polymers Fabricated by Direct Knitting: Recyclable Single‐Site Catalysts with Enhanced Activity

Facile Arene Ligand Exchange in p-Cymene Ruthenium(II) Complexes of Tertiary P-Chiral Ferrocenyl Phosphines

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