An official website of the United States government
Abstract Three binuclear species [LCoIII2(μ‐Pz)2](ClO4)3(1), [LNiII2(CH3OH)2Cl2]ClO4(2), and [LZnII2Cl2]PF6(3) supported by the deprotonated form of the ligand 2,6‐bis[bis(2‐pyridylmethyl) amino‐methyl]‐4‐methylphenol were synthesized, structurally characterized as solids and in solution, and had their electrochemical and spectroscopic behavior established. Species1–3had their water reduction ability studied aiming to interrogate the possible cooperative catalytic activity between two neighboring metal centers. Species1and2reduced H2O to H2effectively at an applied potential of −1.6 VAg/AgCl, yielding turnover numbers of 2,820 and 2,290, respectively, after 30 minutes. Species3lacked activity and was used as a negative control to eliminate the possibility of ligand‐based catalysis. Pre‐ and post‐catalytic data gave evidence of the molecular nature of the process within the timeframe of the experiments. Species1showed structural, rather than electronic cooperativity, while species2displayed no obvious cooperativity. DFT methods complemented the experimental results determining plausible mechanisms.
more »
« less
Ag II ‐Mediated Electrocatalytic Ambient CH 4 Functionalization Inspired by HSAB Theory
Abstract Although most class (b) transition metals have been studied in regard to CH4activation, divalent silver (AgII), possibly owing to its reactive nature, is the only class (b) high‐valent transition metal center that is not yet reported to exhibit reactivities towards CH4activation. We now report that electrochemically generated AgIImetalloradical readily functionalizes CH4into methyl bisulfate (CH3OSO3H) at ambient conditions in 98 % H2SO4. Mechanistic investigation experimentally unveils a low activation energy of 13.1 kcal mol−1, a high pseudo‐first‐order rate constant of CH4activation up to 2.8×103 h−1at room temperature and a CH4pressure of 85 psi, and two competing reaction pathways preferable towards CH4activation over solvent oxidation. Reaction kinetic data suggest a Faradaic efficiency exceeding 99 % beyond 180 psi CH4at room temperature for potential chemical production from widely distributed natural gas resources with minimal infrastructure reliance.
more »
« less
- Award ID(s):
- 1955836
- PAR ID:
- 10273810
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 33
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 18152-18161
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Electrocatalytic Methane Functionalization with d 0 Early Transition Metals Under Ambient ConditionsAbstract The undesirable loss of methane (CH4) at remote locations welcomes approaches that ambiently functionalize CH4on‐site without intense infrastructure investment. Recently, we found that electrochemical oxidation of vanadium(V)‐oxo with bisulfate ligand leads to CH4activation at ambient conditions. The key question is whether such an observation is a one‐off coincidence or a general strategy for electrocatalyst design. Here, a general scheme of electrocatalytic CH4activation with d0early transition metals is established. The pre‐catalysts’ molecular structure, electrocatalytic kinetics, and mechanism were detailed for titanium (IV), vanadium (V), and chromium (VI) species as model systems. After a turnover‐limiting one‐electron electrochemical oxidation, the yielded ligand‐centered cation radicals activate CH4with low activation energy and high selectivity. The reactivities are universal among early transition metals from Period 4 to 6, and the reactivities trend for different early transition metals correlate with their d orbital energies across periodic table. Our results offer new chemical insights towards developing advanced ambient electrocatalysts of natural gas.more » « less
-
Abstract A new series of mono‐ and bis‐alkynyl CoIII(TIM) complexes (TIM=2,3,9,10‐tetramethyl‐1,4,8,11‐tetraazacyclotetradeca‐1,3,8,10‐tetraene) is reported herein. Thetrans‐[Co(TIM)(C2R)Cl]+complexes were prepared from the reaction betweentrans‐[Co(TIM)Cl2]PF6and HC2R (R=tri(isopropyl)silyl or TIPS (1), ‐C6H4‐4‐tBu (2), ‐C6H4‐4‐NO2(3 a), andN‐mesityl‐1,8‐naphthalimide or NAPMes(4 a)) in the presence of Et3N. The intermediate complexes of the typetrans‐[Co(TIM)(C2R)(NCMe)](PF6)(OTf),3 band4 b, were obtained by treating3 aand4 a, respectively, with AgOTf in CH3CN. Furthermore, bis‐alkynyltrans‐[Co(TIM)(C2R)2]PF6complexes,3 cand4 c, were generated following a second dehydrohalogenation reaction between3 band4 b, respectively, and the appropriate HC2R in the presence of Et3N. These new complexes have been characterized using X‐ray diffraction (2,3 a,4 a, and4 c), IR,1H NMR, UV/Vis spectroscopy, fluorescent spectroscopy (4 c), and cyclic voltammetry.more » « less
-
Abstract The silylium‐like surface species [iPr3Si][(RFO)3Al−OSi≡)] activates (N^N)Pd(CH3)Cl (N^N=Ar−N=CMeMeC=N−Ar, Ar=2,6‐bis(diphenylmethyl)‐4‐methylbenzene) by chloride ion abstraction to form [(N^N)Pd−CH3][(RFO)3Al−OSi≡)] (1). A combination of FTIR, solid‐state NMR spectroscopy, and reactions with CO or vinyl chloride establish that1shows similar reactivity patterns as (N^N)Pd(CH3)Cl activated with Na[B(ArF)4]. Multinuclear13C{27Al} RESPDOR and1H{19F} S‐REDOR experiments are consistent with a weakly coordinated ion‐pair between (N^N)Pd−CH3+and [(RFO)3Al−OSi≡)].1catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd−CH3]+in solution and incorporates up to 0.4 % methyl acrylate in copolymerization reactions.1produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.more » « less
-
Abstract Organofunctionalized tetranuclear clusters [(MIICl)2(VIVO)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2)}2] (1, M=Co,2: M=Zn) containing an unprecedented oxometallacyclic {M2V2Cl2N4O8} (M=Co, Zn) framework have been prepared by solvothermal reactions. The new oxo‐alkoxide compounds were fully characterized by spectroscopic methods, magnetic susceptibility measurement, DFT and ab initio computational methods, and complete single‐crystal X‐ray diffraction structure analysis. The isostructural clusters are formed of edge‐sharing octahedral {VO5N} and trigonal bipyramidal {MO3NCl} units. Diethanolamine ligates the bimetallic lacunary double cubane core of1and2in an unusual two‐mode fashion, unobserved previously. In the crystalline state, the clusters of1and2are joined by hydrogen bonds to form a three‐dimensional network structure. Magnetic susceptibility data indicate weakly antiferromagnetic interactions between the vanadium centers [Jiso(VIV−VIV)=−5.4(1); −3.9(2) cm−1], and inequivalent antiferromagnetic interactions between the cobalt and vanadium centers [Jiso(VIV−CoII)=−12.6 and −7.5 cm−1] contained in1.more » « less
