Abstract: The reaction steps for the selective conversion of a transition metal carbonyl complex to a hydroxymethyl complex that releases methanol upon irradiation with visible light have been successfully quantified in acetonitrile solution with dihydrobenzimidazole organic hydride reductants. Dihydrobenzimidazole reductants have been shown to be inactive toward H2 generation in the presence of a wide range of proton sources and have been regenerated electrochemically or photochemically. Specifically, the reaction of cis-[Ru(bpy)2(CO)2]2+ (bpy = 2,2′-bipyridine) with one equivalent of a dihydrobenzimidazole quantitatively yields a formyl complex, cis-[Ru(bpy)2(CO)(CHO)]+, and the corresponding benzimidazolium on a seconds time scale. Kinetic experiments revealed a first-order dependence on the benzimidazole hydride concentration and an unusually large kinetic isotope effect, inconsistent with direct hydride transfer and more likely to occur by an electron transfer-proton-coupled electron transfer (EΤ?PCET) or related mechanism. Further reduction/protonation of cis-[Ru(bpy)2(CO)(CHO)]+ with two equivalents of the organic hydride yields the hydroxymethyl complex cis-[Ru(bpy)2(CO)(CH2OH)]+. Visible light excitation of cis-[Ru(bpy)2(CO)(CH2OH)]+ in the presence of excess organic hydride was shown to yield free methanol. Identification and quantification of methanol as the sole CO reduction product was confirmed by 1H NMR spectroscopy and gas chromatography. The high selectivity and mild reaction conditions suggest a viable approach for methanol production from CO, and from CO2 through cascade catalysis, with renewable organic hydrides that bear similarities to Nature’s NADPH/NADP+.
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1,2-Diamino-4,6-dimethylbenzene. A mixture of 4,6-dimethyl-2-nitroaniline (1.66 g, 10.0 mmole) and 10% Pd/C (200 mg) in ethanol (35 mL) was hydrogenated for 2 h at room temperature under 25 psi H2. The catalyst was removed by filtration with celite and the solvent was removed by rota-evaporation to give 1.300 g (96%) of 1,2-diamino-4,5-dimethylbenzene as a brown solid. 1 H NMR (CDCl3): 6.449 (s, 1H), 6.469 (s, 1H), 3.327 (br, 2H), 3.259 (br, 2H), 2.190 (s, 3H), 2.159 (s, 3H).
2-(4-fluoro-2-(trifluoromethyl)phenyl)-5,6-dimethyl-1H-benzo[d]imidazole[ No CAS ]
Yield
Reaction Conditions
Operation in experiment
90%
In ethanol; at 80℃; for 1h;
General procedure: ZrO2-Al2O3 solid acid catalytic material was added to the stirred solution of O-phenylenediamines and different substituted aromatic aldehydes in a suitable solvent, and the resulting mixture was heated at a particular temperature and monitored by TLC. After the completion of the reaction, the reaction mixture was cooled and filtered and the residue was washed with ethanol to recover the solid acid catalyst. Filtrate was evaporated in vacuum to get the crude reaction product, which was then purified by silica-gel column chromatography using a suitable mobile phase to separate the desired product. The reaction products were characterized by melting point, 1H NMR and 13C NMR spectroscopy (Bruker, 400 MHz), LC-MS (Varian), and HPLC (Waters) techniques
With ammonium bromide; In dimethyl sulfoxide; at 20℃; for 24h;
General procedure: A solution of o-diaminobenzene 2 (1 mmol) in anhydrousDMSO (2 ml) was slowly added to a solution of the correspondingaldehyde 1 (1 mmol) in DMSO (2 ml). Then, NH4Br (39 mg, 0.4 mmol)was added and the resulting mixture was stirred in the contact with dryair at room temperature for 24 h
3-bromo-5,9,10-trimethylbenzo[4,5]imidazo[1,2-c]quinazolin-6(5H)-one[ No CAS ]
Yield
Reaction Conditions
Operation in experiment
With tert.-butylhydroperoxide; In dimethyl sulfoxide; at 90℃; for 0.5h;
N-methyl indole (0.5 mmol), DMSO (5 ml) were added into reaction tube and stirred at 90 C. Then the I2 (0.6 mmol) and TBHP (2.5 mmol) were added into the reaction tube. After 24 h the o-benzenediamine (0.34 mmol) was added into the mixture. The reaction was stopped until the o-benzenediamine was completely consumed as monitored by TLC analysis. After the completion of reaction, 5% Na2S2O3 solution (30 mL) was added to the mixture. The mixture was extracted with EtOAc (3 * 20 ml) and the organic layer was dried by Na2SO4. Then the crude product was purified by silica gel chromatography (petroleum ether/ethyl acetate/dichloromethane 3/1/1).
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