Stoichiometric and Catalytic H/D Incorporation by Cationic Iridium Complexes:  A Common Monohydrido-Iridium Intermediate

Abstract

A mechanistic study of the stoichiometric and catalytic H/D exchange reactions involving cationic iridium complexes is presented. Strong evidence suggests that both stoichiometric and catalytic reactions proceed via a monohydrido-iridium species. Stoichiometric deuterium incorporation reactions introduce multiple deuterium atoms into the organic products when aryliridium compounds CpPMe(3)Ir(C(6)H(4)X)(OTf) (X = H, o-CH(3), m-CH(3), p-CH(3)) react with D(2). Multiple deuteration occurs at the unhindered positions (para and meta) of toluene, when X = CH(3). The multiple-deuteration pathway is suppressed in the presence of an excess of the coordinating ligand, CH(3)CN. The compound CpPMe(3)IrH(OTf) (1-OTf) is observed in low-temperature, stoichiometric experiments to support a monohydrido-iridium intermediate that is responsible for catalyzing multiple deuteration in the stoichiometric system. When paired with acetone-d(6)(), [CpPMe(3)IrH(3)][OTf] (4) catalytically deuterates a wide range of substrates with a variety of functional groups. Catalyst 4 decomposes to [CpPMe(3)Ir(eta(3)-CH(2)C(OH)CH(2))][OTf] (19) in acetone and to [CpPMe(3)IrH(CO)][OTf] (1-CO) in CH(3)OH. The catalytic H/D exchange reaction is not catalyzed by simple H(+) transfer, but instead proceeds by a reversible C-H bond activation mechanism.

The neighboring group effect of fluorine in the tritium labeling of organic substrates with [Cp*(PMe3)IrMe(CH2Cl2)]+[BArf]−, a cationic iridium(III) complex

“…13,14 We found that 1 exchanges tritium most easily with the protons of aromatic rings. Exchange was also observed in simple alkyl groups that are activated by electron-withdrawing heteroatoms, such as nitrogen or oxygen, though to a lesser degree.…”

Die Renaissance des H/D‐Austausches

“…[59] Mit den N-heterocyclischen Iridium-Carben-Komplexen 77 (X = Cl, I) und 78 (R = H, Cl) und [D 4 ]Methanol beobachteten Peris et al ebenfalls einen effizienten H/D-Austausch unter anderem bei Diethylether, Ethylmethylketon, Isopropanol und Styrol. [60] Die stetige Weiterentwicklung homogener Iridiumkatalysatoren zur C-H-Aktivierung [61] dürfte in Zukunft immer mehr gut deuterierbare Verbindungen zugänglich machen.…”

Donor‐Functionalised N‐Heterocyclic Carbene Complexes of Group 9 and 10 Metals in Catalysis: Trends and Directions

“…[183] The ability of these complexes to undergo reversible metalation/solvolysis of the substituents on the NHC seem to make them very active in deuteration reactions. [184] Interesting selectivities were obtained (Scheme 23), and these complexes certainly deserve more investigation. The same group recently reported a chiral analogue of 105 and tested it in the chiral diboration of olefins.…”