Ni^II Complexes of C‐Substituted Cyclam as Efficient Catalysts for Reduction of CO₂ to CO

Abstract

Two new nickel(II) complexes of cyclams bearing C‐alkyl groups, Ni(MEC)OTf2 (1, MEC = 5,12‐diethyl‐7,14‐dimethyl‐1,4,8,11‐tetraazacyclotetradecane) and Ni(CTMC)OTf2 (2, CTMC = 5,7,12,14‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane), were prepared, and their similarity to NiII(MPC) (MPC = 5,12‐dimethyl‐7,14‐diphenyl‐1,4,8,11‐tetraazacyclotetradecane) in ring conformation was revealed through single‐crystal X‐ray diffraction studies. Solution electronic absorption spectroscopy indicates the retention of octahedral coordination mode for both 1 and 2 in 20 % aqueous acetonitrile. Cyclic voltammetry studies of 1 and 2 under CO2 in 20 % aqueous acetonitrile revealed significantly increased catalytic currents compared to previously studied NiII(cyclam) and NiII(MPC). Controlled potential electrolysis studies of 2 revealed a 250 % increase in CO turn over frequency from that of Ni(cyclam)OTf2 and a 40 % increase from that of Ni(MPC)OTf2. Such improvements establish the benefit of electronically donating substituents that minimize steric interference around the axial catalytic sites.

Synthesis and crystal structure of bis[μ-N,N-bis(2-aminoethyl)ethane-1,2-diamine]bis[N,N-bis(2-aminoethyl)ethane-1,2-diamine]-μ4-oxido-hexa-μ3-oxido-octa-μ2-oxido-tetraoxidotetranickel(II)hexatantalum(V) nonadecahydrate

“…The Ta-O bond lengths range from 1.786 (2) to 2.057 (2) A ˚, which is consistent with common values. Bond-valence-sum calculations (Brown & Altermatt, 1985;Liu & Thorp, 1993;O'Keefe & Brese, 1991) weiler et al, 2002;Niu et al, 2011;Kim et al, 2004;Mash et al, 2019;Junk & Steed, 2007). One tren ligand connects both Ni II cations via an Ni--N-Ni bond of 2.082 (3) A ˚.…”

Enhanced Ethylene Formation from Carbon Dioxide Reduction through Sequential Catalysis on Au Decorated Cubic Cu2O Electrocatalyst

“…[1][2][3][4][5][6] Great progress has been achieved for a variety of effective electrocatalysts, which can reduce CO 2 to C 1 products (such as CO, HCOOH) with high FEs at high current density. [7][8] However, due to the involvement of multiple proton-electron transfer steps and the difficulty in CÀ C coupling, [9][10] there is still a great challenge to selectively generate high energy-dense C 2 + products, such as ethylene (C 2 H 4 ), [11] ethanol (C 2 H 5 OH), [12] acetic acid (CH 3 COOH), [13] npropanol (C 3 H 7 OH) [9] or 1-butanol (C 4 H 9 OH). [14] Copper (Cu) has been proved to be the only active metal for electro-reduction of CO 2 to C 2 + products owing to its optimized binding energy with *CO, as the key intermediate to form > 2e À reduction products.…”

“…The electrochemical CO 2 reduction reaction (CO 2 RR) presents an attractive approach for the sustainable production of chemicals and fuels, and holds great potential for the effectively regulation of carbon loop [1–6] . Great progress has been achieved for a variety of effective electrocatalysts, which can reduce CO 2 to C 1 products (such as CO, HCOOH) with high FEs at high current density [7–8] . However, due to the involvement of multiple proton‐electron transfer steps and the difficulty in C−C coupling, [9–10] there is still a great challenge to selectively generate high energy‐dense C 2+ products, such as ethylene (C 2 H 4 ), [11] ethanol (C 2 H 5 OH), [12] acetic acid (CH 3 COOH), [13] n ‐propanol (C 3 H 7 OH) [9] or 1‐butanol (C 4 H 9 OH) [14] …”

Au(III) complexes with tetradentate-cyclam-based ligands

“…Cyclam is known as a tetraamino-macrocyclic ligand, which binds strongly to give complexes with many transition metal cations. While catalytic applications of square planar cyclam complexes are reported for metals, such as Ni [30][31][32][33], Cu [34], Fe [35], catalytic properties of cyclam coordinated gold(III) complexes are not known. Trigged by this knowledge gap, we wanted to develop new chiral cyclam coordinated gold(III) complexes.…”