Role of Ligand in the Selective Production of Hydrogen from Formic Acid Catalysed by the Mononuclear Cationic Zinc Complexes [(L)Zn(H)]⁺ (L=tpy, phen, and bpy)

Abstract

As eries of zinc-based catalysts wase valuated for their efficiency in decomposing formic acid into molecular hydrogen and carbon dioxide in the gas phase using quadrupole ion trap mass spectrometry experiments.T he effectiveness of the catalysts in the series [(L)Zn(H)] + ,w here L = 2,2':6',2''-terpyridine (tpy), 1,10-phenanthroline (phen) or 2,2'-bipyrydine( bpy), wasf ound to dependo nt he ligand used, whicht urned out to be fundamental in tuning the catalytic properties of the zinc complex. Specifically, [(tpy)Zn(H)] + displayed the fastest reaction with formic acid proceedingb yd ehydrogenation to produce the zinc formate complex [(tpy)Zn(O 2 CH)] + and H 2 .T he catalysts [(L)Zn(H)] + are reformed by decarboxylating the zinc formate complexes [(L)Zn(O 2 CH)] + by collision-induced dissociation, which is the only reactionc hannel for each of the ligands used. The decarboxylation reactionw as found to be reversible, since the zinc hydride complexes [(L)Zn(H)] + react with carbon dioxide yielding the zinc formate complex. This reactionw as again substantially faster for L = tpy than L = phen or bpy.T he energetics and mechanisms of these processes were modelled using severall evelso fd ensity functional theory (DFT) calculations. Experimental results are fully supported by the computational predictions.

Near thermal, selective liberation of hydrogen from formic acid catalysed by copper hydride ate complexes

“…Here we show that mononuclear cuprates [(L)Cu(H)] − (where L = H − , O 2 CH − , BH 4 − and CN − ), 12,13 are potent catalysts for the liberation of hydrogen from formic acid. While they follow a similar two-step catalytic cycle (Scheme 2) with similar mechanistic features to other metal hydride complexes previously reported, 15 a key unique feature is that step 2 occurs spontaneously making these catalysts capable of the near thermal activation of formic acid.…”

Gas‐Phase Models for the Nickel‐ and Palladium‐Catalyzed Deoxygenation of Fatty Acids

“…17 (mass spectra shown in Figure 7C and 7D for propionic acid; reaction of 4‐Ni with acetic acid is shown in Figure S8B, data for 4‐Pd shown in Figure S8E). This is not surprising considering the fact that numerous metal hydride complex ions have been shown to react with carboxylic acids via acid‐base hydrogen recombination [39,40] …”

Molecular Main Group Metal Hydrides

“…Venugopal and coworkers also found that a 1:1 catalytic mixture of the terminal hydridozinc complex [(Me 6 tren)­ZnH]­[BAr F 4 ] ( 393 ) and BPh 3 promoted the reaction between CO 2 (1.5 atm) and PhSiH 3 to yield the tris­(formate) insertion product PhSi­(OC­(O)­H) 3 at 50 °C in acetonitrile (98% yield, TOF = 29 h –1 ) . Interesting examples of catalytic gas phase formic acid to H 2 and CO 2 decomposition were noted with the cationic zinc hydride complexes [(tpy)­ZnH] + ( 429 ) (tpy = 2,2′:6′,2″-terpyridine), [(bipy)­ZnH] + ( 430 ), and [(phen)­ZnH] + ( 431 ) (phen = 1,10-phenanthroline) . Quite recently, Xu and coworkers noted that the phosphine-substituted NHC complexes [{ArN­(CH) 2 N­(CH 2 CH 2 PPh 2 )­C}­Zn­(μ-H)] 2 (Ar = Mes or Dipp, 432 or 433 ) (Figure ) instigated the reaction between HBpin and CO 2 (10 atm of CO 2 ; C 6 D 6 , 25 °C, TOF = ca.…”

“…504 Interesting examples of catalytic gas phase formic acid to H 2 and CO 2 decomposition were noted with the cationic zinc hydride complexes [(tpy)ZnH] + (429) (tpy = 2,2′:6′,2″-terpyridine), [(bipy)ZnH] + (430), and [(phen)-ZnH] + (431) (phen = 1,10-phenanthroline). 543 Quite recently, Xu and coworkers noted that the phosphine-substituted NHC complexes [{ArN(CH) 2 N(CH 2 CH 2 PPh 2 )C}Zn(μ-H)] 2 (Ar = Mes or Dipp, 432 or 433) (Figure 42) instigated the reaction between HBpin and CO 2 (10 atm of CO 2 ; C 6 D 6 , 25 °C, TOF = ca. 3 h −1 ) to give the monohydroborated product HC(O)OBpin; Okuda's complex [IMes•HZn(μ-H) 2 ZnH• IMes] (312) was also explored in this reaction, and gave a slightly lower yield of HC(O)OBpin (31% vs. 68% with 432).…”