Structure and nitrite reduction reactivity study of bio-inspired copper(i)–nitro complexes in steric and electronic considerations of tridentate nitrogen ligands

Abstract

Two copper(i)-nitro complexes [Tpm3-tBuCu(NO2)] (1) and [(Ph3P)2N][Tp3-tBuCu(NO2)] (2), containing steric bulky neutral tris(3-tert-butylpyrazolyl)methane and anionic hydrotris(3-tert-butylpyrazolyl)borate ligands, have been synthesized and characterized. Complex 2 adopts a unique κ2-binding mode of Tp3-tBu around the copper(i)-nitro environment in the solid state and shows a four-coordinated tetrahedral geometry surrounded by a nitro and three pz3-tBu groups in solution. Both complexes 1 and 2 allow for the stoichiometric reduction of NO2- to NO with H+ addition. The results of this effort show that increasing steric bulk and electron donation properties on the nitrogen ancillary ligand will improve the nitrite reduction ability of the copper(i)-nitro model complexes.

Nitric oxide generation study of unsymmetrical β-diketiminato copper(ii) nitrite complexes

“…S1a and S1b †). 19,29,40,41 The complexes L 1 CuCl-L The geometries and bond parameters of the two independent molecules of L 1 CuCl in the unit cell are very similar, so only one of the structures is presented in Fig. 1(a).…”

“…Previous reports illustrating the copper(I)-nitrito complexes could be a good model system for bio-relevant nitrite reduction despite their instability issue. [29][30][31] On the other hand, Cu(II)metal scaffolds (Scheme 1) such as the N 2 S ligand 24,25 and the hydrotris(triazolyl)borate ligand have been used for the reduction of nitrite to nitric oxide in the presence of an acid source using a cyclic voltametric reduction process. 31 Apart from them, triphenylphosphine (PPh 3 ) has also been used but under higher temperature conditions (60 °C) (Scheme 1).…”

“…19,27 However, lacking in the literature is a thorough study of copper complexes supported by unsymmetrical N-aryl-N′-alkyl-substituted β-diketiminato ligands in comparison with N,N′aryl-substituted analogues. 32 Based on previous studies of symmetric N-aryl-N′-aryl-substituted type of β-diketiminato copper (I) and copper(II) nitrite 19,28 and our work on biomimetic copper(I)-nitrito complexes, 29,30,33 we decided to introduce unsymmetrical N-aryl-N′-alkyl-substituted β-diketiminato ligands 32,34,35 into copper-nitrite chemistry. Herein, we describe the synthesis and structural characterization of unsymmetrical N,N′-aryl-substituted β-diketiminato L 1 CuCl-L 4 CuCl complexes (Scheme 2) and their nitrite complexes L 1 Cu(O 2 N) and L 2 Cu(O 2 N).…”

“…In a similar manner, using 1 : 3 equivalents of L 1 Cu(O 2 N) : PPh 3 will afford OvPPh 3 (25.25 ppm), L 1 CuPPh 3 (3.24 ppm), and unreacted PPh 3 (−4.75 ppm) in a 1 : 1 : 1 ratio, respectively (Fig.S11 †). To identify and quantify the gaseous product, vial-to-vial gas trapping experiments (Fig.S14and S15 †) were performed using a similar reported experimental set up 19,28,29,54. Trapping of the evolved gas with (TPP)Co(II) (TPP = tetraphenylporphyrin) leads to the formation of the corresponding (TPP)Co(NO) indicating a clear stoichiometric reduction of nitrite to NO.…”

A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

“…Structurally characterized copper(II)-nitrite complexes typically exhibit k 2 -O,O' or k 1 -O binding modes of nitrite, whereas copper(I)-nitrite favors the k 1 -N binding mode (Figure 1). [17][18][19][20] Chemical and electrochemical reductions of isolated [Cu II ](k 2 -O,O'-nitrite) complexes have been demonstrated to flip the nitrite binding mode to k 1 -N. [21,22] Moreover, electrocatalytic reduction of nitrite to NO at copper(II) sites have been demonstrated in the recent past. [23,24] Examples of NO release from [Cu I ]-nitrite are well known under acidic conditions.…”