Mild and Selective H/D Exchange at the β Position of Aromatic α‐Olefins by N‐Heterocyclic Carbene–Hydride–Rhodium Catalysts

Hydride‐Rhodium(III)‐N‐Heterocyclic Carbene Catalysts for Vinyl‐Selective H/D Exchange: A Structure–Activity Study

“…Thus, reactions of [Rh(μ‐Cl)(η 2 ‐coe) 2 ] 2 ( 1 ) with the corresponding free NHC ligands gave the dinuclear complexes [Rh(μ‐Cl)(IPr)(η 2 ‐coe)] 2 ( 2 a ) and [Rh(μ‐Cl)(IMes)(η 2 ‐coe)] 2 ( 3 ). Following the previously reported synthetic scheme,7j treatment of the dimers 2 a and 3 with 8‐hydroxyquinoline in toluene at room temperature led to the diastereoselective synthesis of the 16‐electron complexes [RhClH(κ 2 ‐O,N‐C 9 H 6 NO)(NHC)] ( 4 , IPr; 5 , IMes; Scheme ). Complexes 4 and 5 were isolated as orange solids in yields of 767j and 79 %, respectively.…”

“…Following the previously reported synthetic scheme,7j treatment of the dimers 2 a and 3 with 8‐hydroxyquinoline in toluene at room temperature led to the diastereoselective synthesis of the 16‐electron complexes [RhClH(κ 2 ‐O,N‐C 9 H 6 NO)(NHC)] ( 4 , IPr; 5 , IMes; Scheme ). Complexes 4 and 5 were isolated as orange solids in yields of 767j and 79 %, respectively. The related mononuclear hydride/8‐quinolinolate derivatives bearing carbenes SIPr and SPXyl were synthesized according to a one‐pot procedure (Scheme ).…”

“…An efficient strategy for selective deuterium‐labeling of alkenes is to use a metal hydride species that gives rise to an alternative insertion–elimination mechanism, which is not operative for aromatic protons (Scheme b) 4d. 6g, 7a,e,i,j, 11 In addition, a high oxidation state of the metal center may reduce the competitive olefin CH activation pathway and thereby prevent hydrogenation of the double bond of the target olefin. Moreover, a bulky and strongly electron‐donating ancillary ligand should provide additional stability to the hydride‐metal species in a high oxidation state, while exerting a significant steric effect in the vicinity of the coordination site, which may dramatically influence the selectivity of the reaction.…”

“…The results of this study have allowed us to disclose highly efficient catalysts and to establish a relationship between the structure of the complex and its catalytic activity. A part of this work has been previously communicated 7j…”

Impact of Protic Ligands in the Ir-Catalyzed Dehydrogenation of Formic Acid in Water

“…To the best of our knowledge Ir-IPr or Ir-IMes complexes (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) have not been used hitherto as FA dehydrogenation catalysts in spite of the many successful catalysts that feature these ligands. [47][48][49][50][51][52][53][54][55] Building on our previous research on the Ir-IPr scaffold, 51 in this work we report on the activity of Ir-complexes that contain the IPr ligand (together with other additional ancillary ligands) as catalysts for formic acid dehydrogenation. The effect of the ligands that complete the coordination sphere of the Ir-IPr complexes on the catalytic performance was studied in order to identify reactivity patterns.…”