Amidine/Amidinate Cobalt Complexes: One-Pot Synthesis, Mechanism, and Photocatalytic Application for Hydrogen Production

Abstract

A new synthetic route was carried out via a one-pot reaction to prepare a novel series of amidine/amidinate cobalt complexes 8−10 by mixing ligand 2 (6-pyridin-2-yl-[1,3,5]triazine-2,4-diamine) with Co(II) in acetonitrile or benzonitrile. We observed that a change of solvent from methanol (used in complex 7, previously reported) to nitrile solvents (MeCN and PhCN) led to the in situ incorporation of the amidine group, ultimately forming 8−10. So far, this is a unique method reported to introduce amidine/amidinate groups into a pyridinyl-substituted diaminotriazine complex. Remarkably, the single crystal X-ray diffraction study (SCXRD) of these new compounds reveals associations involving Janus DATamidine and Janus DATamidinate. A mechanism is proposed to explain the formation of amidine/ amidinate groups by investigating the single crystal structures of the possible intermediates 11 and 12 where the cobalt ion acts as a template. These amidine/amidinate cobalt complexes were used as a model to assess the photocatalytic activity for the hydrogen evolution reaction (HER). Complexes 9 and 10 show a 74% and 86% enhancement, respectively, of the catalytic activity towards the HER compared to complex 7. This highlights the structure−property relationship. By examining the novel cobalt complexes described here, we discovered the following: (i) a method to introduce an amidine group into a pyridine DAT-based complex, (ii) the efficiency of amidine complexes to form multiple hydrogen bonds to direct the molecular organization, (iii) the plausible mechanism of formation of amidines based on the SCXRD study, (iv) the modification of the final structure and hence the final properties by varying the reaction conditions, and (v) the utility of amidine complexes towards photocatalytic HER activity.

Multifunctional Additives for High-Energy-Density Lithium-Ion Batteries: Improved Conductive Additive/Binder Networks and Enhanced Electrochemical Properties

“…61 In addition, crystal structures of the 1,3,5-trazine backbone with cobalt ions are frequently reported, indicating that the MF copolymers contribute to enhanced CNT/PVDF wrapping of LCO during cycling. 62,63 Recently, Yang et al reported the importance of coordination bonding formation between nitrile and LCO in the charging step. 63 Their findings imply that the MF copolymer-mediated contact enhancement between the HNBR-wrapped CNTs and LCO may result in the formation of additional chemical bonds between them during the charging step.…”

Amidines from cyclic amines and nitriles in the presence of zinc(ii): other nitriles in place of acetonitrile

“…1550 cm À1 . 41,62 On amidine protonation, the spectra undergo dramatic changes. With no exceptions, the spectra of all amidinium salts feature a broad band at 3000 cm À1 that masks the n(C-H) vibrations of methylene groups in amidinium cations.…”

“…Reactions of this type using ammonia or primary and secondary amines are well-documented. 6,9,28,29,[32][33][34][35][36][37] By analogy, nitroanilines, 38 diamines, triamines 39 and some rather complex amines, 23,40,41 (e.g., alkyldiamine-substituted 2,6-diaminopurines, 24 1H-indazole, 27 ) have also been reacted in this way. As well as acetonitrile, the other nitriles tested include propionitrile, 38,39 benzonitrile, 39,41,42 phenylacetonitrile 39 and 2-cyanopyridine.…”

Photocatalytic Carbon Dioxide Reduction and Density Functional Theory Investigation of 2,6-(Pyridin-2-yl)-1,3,5-triazine-2,4-diamine and Its Cobalt and Nickel Complexes

“…It is noteworthy that motif IV has already been reported for association of DAT groups in our previous work. 36,46 The network is reinforced by multiple hydrogen bonds involving ClO 4 − . Summaries of the crystallographic data and hydrogen bonds and angles are provided in Table S1 and Table S2.…”