In this work, we prepared, isolated, and structurally characterized a zirconium complex having a terminally bound imide motif, (PN) 2 Zr≡NH (PN − = (N-(2-i Pr 2 P-4-methylphenyl)-2,4,6-trimethylanilide)), along with the zirconium nitride complex {(PN) 2 Zr≡N[μ 2 -Li(THF)]} 2 . (PN) 2 Zr≡NH was prepared by reduction of trans-(PN) 2 Zr(N 3 ) 2 with KC 8 . Isotopic labeling and spectroscopic studies were conducted using the respective 15 N enriched isotopologues, whereas solid-state structural studies confirmed some of the shortest Zr≡N distances known to date (Zr≡NH, 1.830(3) Å; Zr≡N − , 1.822(2) Å). It was found that the nitride in {(PN) 2 Zr≡N[μ 2 -Li(THF)]} 2 is super basic and in the range of −36 to −43 pK b units. Computational studies have been applied to probe the bonding and structure for this new class of zirconium−nitrogen multiple bonds.
The reaction of carbon dioxide with hydroxide to form carbonate in near neutral or alkaline medium severely limits the energy and carbon efficiency of CO2 electroreduction. Here we show that by suppressing the otherwise predominant hydrogen evolution using alkali cations, efficient CO2 electroreduction can be conducted in acidic medium, overcoming the carbonate problem. The cation effects are general for three typical catalysts including carbon supported tin oxide, gold, and copper, leading to Faradaic efficiency of as high as 90% for formic acid and CO formation. Our analysis suggests hydrated alkali cations physisorbed on the cathode modify the distribution of electric field in the double layer, which impedes hydrogen evolution by suppress the migration of hydronium ions while at the same time promotes CO2 reduction by stabilizing key intermediates.
An attractive, versatile, and operationally simple, visible-light-induced, transition-metal-free, photocatalyst-free, and oxidant-free trifluoromethylation has been demonstrated. Triflic anhydride (Tf 2 O), being inexpensive and readily available, was chosen as the radical trifluoromethyl source. Thianthrene was used as a recyclable Tf 2 O-activating reagent, and a high-yielding and scalable trifluoromethylation reaction was achieved. Density functional theory and mechanistic studies showed that a free radical homolytic process excited by visible light is involved in this reaction, generating a key trifluoromethyl radical intermediate.
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