Combining 1,2-diketopyracene with bulky benzhydryl-substituted anilines to obtain highly active α-diimine nickel catalysts at elevated temperature

Effect of N‐Aryl Para‐Benzhydryl Substituent on the Thermal Stability of α‐Diimine Nickel Catalyst

“…2c: Ni1-N1 2.0306(18), Ni1-N2 2.0385(18), Ni1-Br1 2.3399(6), Ni1-Br2 2.3400 (6) not improve the thermal stability of the catalyst. [48] This seems to contradict previous conclusions. To further study the effect of N-aryl para-benzhydryl substitution on the thermal stability of 𝛼-diimine nickel catalyst, based on previous work, a series of catalysts with different N-aryl ortho-position size were selected, and benzhydryl was introduced at the N-aryl para-position, respectively.…”

“…1,2-Diketopyracene, 2,6-dimethylaniline (1a), 2,6-diisopropylaniline (3a) are commercially available, 2,6-dimethyl-4-benzhydrylaniline (2a) and 2,6-diisopropyl-4-benzhydrylaniline (4a) were synthesized according to our previous work. [48] The corresponding ligands (1b-4b) were synthesized in high yields using aniline (1a-4a) and 1,2-diketopyracene in ethanol at 80 °C with a catalytic amount of formic acid. Each ligand was characterized by 1 H NMR, 13 C NMR, and ESI-MS. Complexes 1c-4c can be obtained in high yields by stirring (DME)NiBr 2 and the corresponding ligands 1b-4b in CH 2 Cl 2 for 24 h at room temperature.…”

“…The molecular structures of the complexes 3c-4c were obtained in previous work. [48,54] (Figure 1. Right)…”

“…(That of 3c and 4c were presented in our previous work. [48,57] ) a) R1 is the complexation between the metal and the ligand is destroyed, that is, NiBr 2 falls off directly, which is the most likely decomposition method.…”

“…[11][12][13][14][15][16] Over the past three decades, the modification of the catalyst structure has been the main research direction, such as the change in the N-aryl structure [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] or the backbone structure, [34][35][36][37][38][39][40][41][42][43][44] even the introduction of strong combination strategy. [45][46][47][48][49] Improving the catalyst thermal stability is what researchers are passionate about, which is related to the industrial application of catalysts, but there are few related pieces of research about the inactivation mechanism. Now the discussion of the catalyst thermal stability mechanism mainly includes the following aspects, namely, the N-aryl bond rotation, stability of the five-membered coordination ring, the cocatalyst, and the non-activated additives.…”