Highly Efficient D₂ Generation by Dehydrogenation of Formic Acid in D₂O through H⁺/D⁺ Exchange on an Iridium Catalyst: Application to the Synthesis of Deuterated Compounds by Transfer Deuterogenation

Abstract

Deuterated compounds have received increasing attention in both academia and industrial fields. However, preparations of these compounds are limited for both economic and practical reasons. Herein, convenient generation of deuterium gas (D(2)) and the preparation of deuterated compounds on a laboratory scale are demonstrated by using a half-sandwich iridium complex with 4,4'-dihydroxy-2,2'-bipyridine. The "umpolung" (i.e., reversal of polarity) of a hydrogen atom of water was achieved in consecutive reactions, that is, a cationic H(+)/D(+) exchange reaction and anionic hydride or deuteride transfer, under mild conditions. Selective D(2) evolution (purity up to 89 %) was achieved by using HCO(2)H as an electron source and D(2)O as a deuterium source; a rhodium analogue provided HD gas (98 %) under similar conditions. Furthermore, pressurized D(2) (98 %) without CO gas was generated by using DCO(2)D in D(2)O in a glass autoclave. Transfer deuterogenation of ketones gave α-deuterated alcohols with almost quantitative yields and high deuterium content by using HCO(2)H in D(2)O. Mechanistic studies show that the H(+)/D(+) exchange reaction in the iridium hydride complex was much faster than β-elimination and hydride (deuteride) transfer.

Development of Effective Catalysts for Hydrogen Storage Technology Using Formic Acid

“…[41] First, the pH dependency of catalytic activity greatly varies depending on the substitution positions of the OH groups. [41] First, the pH dependency of catalytic activity greatly varies depending on the substitution positions of the OH groups.…”

“…[41] First, the pH dependency of catalytic activity greatly varies depending on the substitution positions of the OH groups. [41] On the other hand, RDS of 3 was presumed to be (ii) by decrease of energy barrier of (iii) due to the pendant base effect of the OH group near the metal. On the other hand, the catalyst 3 showed the maximum TOF (entry 5, 5440 h −1 ) of the catalytic activity in a 1:1 mixed solution of FA/sodium formate (SF, pH 3.5).…”

Highly Robust Hydrogen Generation by Bioinspired Ir Complexes for Dehydrogenation of Formic Acid in Water: Experimental and Theoretical Mechanistic Investigations at Different pH

“…10,[50][51][52] We have previously investigated the mechanism of formic acid dehydrogenation with KIE studies, 50 and demonstrated a significant effect depending on the specific ligands with or without pendent OHs in the complexes. Complexes with 6,6′-dihydroxy- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 2,2′-bipyridine (OH substituents in ortho positions) exhibit a different pH dependence than those with 4,4′-dihydroxy-2,2′-bipyridine (OH substituents in para positions) owing to the two classes of complexes having different rate determining steps (RDS) in the catalytic cycle.…”

Iridium Catalysts with Diazole-containing Ligands for Hydrogen Generation by Formic Acid Dehydrogenation

“…2,2'-Biimidazole was purc h a s e d f r o m S a n t a C r u z B i o t e c h n o l o g y, I n c . 2-( P y r i d i n e -2-y l ) -i m i d a z o [1,2-a ] p y r i d i n e 37) , 1-(pyridine-2-yl)imidazo[1,5-a]pyridine 38) , 3-(pyridine-2-yl)-imidazo[1,5-a]pyridine 39) , 4,4'-biimidazole 40), 41) , 1,1'-dimethyl-2,2'-biimidazole 42) , and [IrCp (H2O)3] [SO4] 43) were synthesized according to the respective literature procedures . Complexes 1a-b, 3, 4, 6, 10, and 12 were synthesized according to the literature 34) .…”