Water‐soluble ruthenium m‐triphenylphosphinetrisulfonate (TPPTS) complexes are excellent catalysts for formic acid dehydrogenation. Interestingly, the choice of metal catalyst precursor has a direct influence on initial activities. The reaction with hexaaquaruthenium(II) tosylate directly yields bisphosphine complexes in the presence of TPPTS and formic acid, whereas trisphosphine adducts are involved if the reaction starts with ruthenium(III) chloride. We present the results of a series of manometric and spectroscopic experiments that reveal the true nature of these highly active species, and subsequently propose a rational “fast” cycle mechanism explaining this peculiar activity profile.
Regioselective electrophilic substitution reactions of the iridabenzofurans [Ir(C 7 H 5 O{OMe-7})(CO)(PPh 3 ) 2 ]-[OTf] (1) and IrCl(C 7 H 5 O{OMe-7})(PPh 3 ) 2 (2) provide a convenient route to mononitro-, dinitro-, and mixed nitro-/halosubstituted derivatives. Treatment of cationic 1 with copper(II) nitrate in acetic anhydride ("Menke" nitration conditions) gives the mononitrated iridabenzofuran [Ir(C 7 H 4 O{NO 2 -2}{OMe-7})(CO)(PPh 3 ) 2 ][O 3 SCF 3 ] (3). Under the same conditions neutral 2 undergoes dinitration to form IrCl(C 7 H 3 O{NO 2 -2}{NO 2 -6}{OMe-7})(PPh 3 ) 2 (5). Simple substitution of the carbonyl ligand in 3 with chloride gives the neutral mononitro derivative IrCl(C 7 H 4 O{NO 2 -2}{OMe-7})(PPh 3 ) 2 (4). Depending on the conditions employed, treatment of the iridabenzofurans 1 and 2 with Cu(NO 3 ) 2 and either lithium chloride or lithium bromide in acetic anhydride gives either the mixed nitro-/halo-substituted iridabenzofurans IrCl(C 7 H 3 O{NO 2 -2}{Cl-6}{OMe-7})(PPh 3 ) 2 (6) and IrCl(C 7 H 2 O{NO 2 -2}{NO 2 -4}{Cl-6}{OMe-7})(PPh 3 ) 2 (7) or the simple halo-substituted iridabenzofurans [Ir(C 7 H 4 O-{Cl-6}{OMe-7})(CO)(PPh 3 ) 2 ][OTf] (8), [Ir(C 7 H 4 O{Br-6}{OMe-7})(CO)(PPh 3 ) 2 ][OTf] (9), and IrBr(C 7 H 3 O{Br-2}{Br-6}{OMe-7})(PPh 3 ) 2 (10). Bromination of 4 with pyridinium tribromide gives IrCl(C 7 H 3 O{NO 2 -2}{Br-6}{OMe-7})(PPh 3 ) 2 (11). The molecular structures of 3−7 and 11 have been obtained by X-ray crystallography.
A proof-of-concept prototype of a heterogeneous catalytic reactor has been developed for continuous production of hydrogen via formic acid (FA) dehydrogenation. A laboratory-type polymer electrolyte fuel cell (PEFC) fed with the resulting reformate gas stream (H 2 + CO 2 ) was applied to convert chemical energy to electricity. To implement an efficient coupling of the reactor and PEFC, research efforts in interrelated areas were undertaken: (1) solid catalyst development and testing for H 2 production; (2) computer modeling of heat and mass transfer to optimize the reactor design; (3) study of compatibility of the reformate gas fuel (H 2 + CO 2 ) with a PEFC; and (4) elimination of carbon monoxide impurities via preferential oxidation (PROX). During the catalyst development, immobilization of the ruthenium(II)−meta-trisulfonated triphenylphosphine, Ru-mTPPTS, catalyst on different supports was performed, and this complex, supported on phosphinated polystyrene beads, demonstrated the best results. A validated mathematical model of the catalytic reactor with coupled heat transfer, fluid flow, and chemical reactions was proposed for catalyst bed and reactor design. Measured reactor operating data and characteristics were used to refine modeling parameters. In turn, catalyst bed and reactor geometry were optimized during an iterative adaptation of the reactor and model parameters. PEFC operating conditions and fuel gas treatment/purification were optimized to provide the best PEFC efficiency and lifetime. The low CO concentration (below 5 ppm) in the reformate was ensured by a preferential oxidation (PROX) stage. Stable performance of a 100 W PEFC coupled with the developed reactor prototype was successfully demonstrated.
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