Synthesis and crystal structures of copper complexes with N,N,N-tridentate chelating ligands containing o-phenanthroline-appended benz-fused polyazoles and their catalytic application in A3 coupling reaction

Design of a Copper(II) Complex with Tetradentate Bis‐Benzotriazole‐Appended Bipyridine Ligand and its Catalytic Application in A3 Coupling Reaction

“…Treatment of benzotriazole and 6,6'-dibromo-2,2'-bipyridine in the presence of CuI and K 2 CO 3 in DMSO resulted in the desired ligand in good yield (77 %). [20] The air-stable Cu(II) complex [Cu(L4)(ClO 4 )(H 2 O)](ClO 4 ) (Cu-L4) was isolated in good yield (90 %) by reacting the ligand L4 with Cu(ClO 4 ) 2 .6H 2 O in nitromethane (Scheme 1). The complex was first analyzed by electron-spray ionization mass spectrometry (ESI-MS) to get insight into its probable structural formulation in solution.…”

“…[10][11][12][13][14][15][16][17][18] In this regard, the importance of chelating N-donor heterocyclic ligands in such multicomponent reaction is noteworthy since these are found to be good π-accepting as well as good σ-donating, and therefore are highly effective to stabilize the Cu(I) intermediates, which are the key species in the catalytic cycle of A 3 coupling reactions. [16][17][18][19][20] Recently nitrogen-enriched benzotriazole-based ligands have gained significant interest in different catalytic processes. [21][22][23][24][25] Interestingly, as these ligands qualify in terms of excellent σ-donation/π-acceptance property, they could be obvious choice for A 3 coupling reactions which, as explained above, benefit from stabilization of low-valent Cu(I) intermediates in the catalytic cycle.…”

“…[16] Recently, we became interested to design and study the electronic and chelating effect of several benzotriazole-based N-enriched ligands in their transition metal complexes. [19][20][26][27][28][29] Inspired by these studies, we rationally employed benzotriazole-appended N,N-bidentate and N,N,N-tridentate suitable chelating ligands for ready access and effective utilization of air-stable, structurally well-defined and discrete Cu(II) complexes as precatalysts for A 3 coupling reactions (Figure 1, B-C). [18][19][20] The results showed that the multidentate chelate binding of these ligands to the Cu centre facilitated the catalytic processes, most probably via efficient stereo-electronic effect exerted to the catalytically active low-valent Cu(I) centre.…”

“…[19][20][26][27][28][29] Inspired by these studies, we rationally employed benzotriazole-appended N,N-bidentate and N,N,N-tridentate suitable chelating ligands for ready access and effective utilization of air-stable, structurally well-defined and discrete Cu(II) complexes as precatalysts for A 3 coupling reactions (Figure 1, B-C). [18][19][20] The results showed that the multidentate chelate binding of these ligands to the Cu centre facilitated the catalytic processes, most probably via efficient stereo-electronic effect exerted to the catalytically active low-valent Cu(I) centre. Encouraged by these findings, in the present study, we examined a new N,N,N,Ntetradentate chelating ligand with bis-benzotriazole-appended bipyridine backbone, in accessing its Cu(II) complex Cu-L4 (Figure 1D), and exploring it as a easily handleable, air-stable catalyst precursor toward A 3 coupling reaction.…”

“…Among others, Cu‐complexes have been mostly used catalysts for such reactions because of the versatility of Cu‐chemistry, mainly the accessibility of different oxidation states of Cu by tuning the surrounding ligand backbone [10–18] . In this regard, the importance of chelating N‐donor heterocyclic ligands in such multicomponent reaction is noteworthy since these are found to be good π‐accepting as well as good σ‐donating, and therefore are highly effective to stabilize the Cu(I) intermediates, which are the key species in the catalytic cycle of A 3 coupling reactions [16–20] …”