Visible-Light-Driven Photocatalytic Coupling of Benzylamine over Titanium-Based MIL-125-NH₂ Metal–Organic Framework: A Mechanistic Study

Abstract

Imines are important building blocks in organic chemistry. Titanium-based metalorganic framework MIL-125-NH2(Ti) can photocatalyze, under visible light and at room temperature, the selective aerobic oxidation of benzylamine to N-benzylidenebenzylamine. We investigated the reaction mechanism using catalytic tests, ex situ infrared spectroscopy, and density functional calculations. In the dark, the presence of MIL-125-NH2(Ti) alone does not improve the reaction yield with respect to a blank experiment. This poor catalytic performance in the dark is associated to the absence of polarizing species on the MOF surface, as confirmed by acetonitrile adsorption. Excitation with different spectral regions evidenced the determinant role of the 450 < λ < 385 nm range for the catalyst photoactivation. The calculations show that the last step of the reaction would have an energy barrier of 206 kJ mol -1 in anhydrous conditions, while it decreases to 91 kJ mol -1 only if the mechanism is mediated by two water molecules.

Donor–Acceptor Pairs in Covalent Organic Frameworks Promoting Electron Transfer for Metal-Free Photocatalytic Organic Synthesis

“…The resultant imines are important fine chemicals. 42 Direct photocatalytic coupling of amines to form imines with O 2 as the oxidant is a promising alternative strategy for traditional reductive amination. 43 The catalytic reaction was initially carried out by the oxidation of benzylamine under 5 W white light-emitting diode (LED) irradiation (Figure S9).…”

“…The photocatalytic activity of Por-Ad-COF was examined in photocatalytic aerobic homocoupling of amines to imines. The resultant imines are important fine chemicals . Direct photocatalytic coupling of amines to form imines with O 2 as the oxidant is a promising alternative strategy for traditional reductive amination .…”

Structural and Morphological Engineering of Benzothiadiazole-Based Covalent Organic Frameworks for Visible Light-Driven Oxidative Coupling of Amines

“…Attenuated total reflection FT-IR (ATR−FT-IR) was further performed to identify key intermediates in the reaction process. 63 As displayed in Figure 9a, the band at 1644 cm −1 associated with the CN stretching vibration of the N-benzyl-1-phenylmethanimine product was observed and its intensity was gradually boosted with the reaction time. Additionally, after irradiation for 1 h, the adsorption peak at 1678 cm −1 gradually appeared, which can be attributed to the carbonyl group of benzaldehyde, indicating the formation of aldehyde in the oxidant.…”

“…Attenuated total reflection FT-IR (ATR–FT-IR) was further performed to identify key intermediates in the reaction process . As displayed in Figure a, the band at 1644 cm –1 associated with the CN stretching vibration of the N -benzyl-1-phenylmethanimine product was observed and its intensity was gradually boosted with the reaction time.…”

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

“…Finally, in selecting papers for highlighting we have necessarily omitted other clearly relevant papers, including papers by groups led by Rahul Banerjee, 425 Silvia Bordiga, 426 Avelino Corma, [427][428][429][430][431] Deanna M. D'Alessandro, 432 Zhengping Dong, 433 Mohamed Eddaoudi, 434 Roland A. Fischer, 277,435,436 Jorge Gascon, [437][438][439] Stefan Kaskel, 440,441 Hiroshi Kitagawa, 442,443 Susumu Kitagawa, 444 Jing Li, 445 Yangyang Liu, 446,447 Tian-fu Liu, 448 Jeffery Long, 449 Connie C. Lu, 450 Amanda J. Morris, 451 Ali Morsali, 254,452,453 Unni Olsbye, 454 W. L. Queen, 455 Matthew Rosseinsky, 456 Natalia B. Shustova, 457 Berend Smit, 458,459 Norbert Stock, [460][461][462][463] Shane G. Telfer, [464][465][466] Fernando Uribe-Romo, 467 Jenny G. Vitillo,…”