ABSTRACT
The site-selective reaction of substrates with multiple reactive sites has been a focus of the current synthetic chemistry. The use of attractive noncovalent interactions between the catalyst and substrate is emerging as a versatile approach to address site-selectivity challenges. Herein, we designed and synthesized a series of palladacycles, to control meta-selective Suzuki coupling of 3,4-dichlorophenol and 3,4-dichlorobenzyl alcohol. Noncovalent interactions directed zwitterionic aqua palladacycles catalyzed meta-selective Suzuki couplings of 3,4-dichloroarenes bearing hydroxyl in water have been developed. Experiments and density functional theory (DFT) calculations demonstrated that the electrostatic interactions play a critical role in meta-selective coupling of 3,4-dichlorophenol, while meta-selective coupling of 3,4-dichlorobenzyl alcohol arises due to the hydrogen-bonding interactions.
ABSTRACT
Triggering C-N bond formation with nitroaromatics and boronic acids at mild conditions is highly desirable, since most prior works were carried out under harsh conditions and sometimes suffered from poor chemo- or regioselectivity. Herein, a low-valent-tungsten-catalyzed reaction that enables the ambient temperature amination of boronic acids with nitroaromatics is disclosed. With readily available W(CO)6 as a precatalyst under external-photosensitizer-free conditions, nitroaromatics smoothly undergo C-N coupling reactions with their boronic acid partners, delivering structurally diverse secondary amines in good yields (>50 examples, yields up to 96%). This methodology is both scalable and highly chemoselective and engages both aliphatic and aromatic boronic acid partners. The catalysis is initiated by the deoxygenation of nitroaromatics by a trans-[W(CO)4(PPh3)2] (trans-W, PPh3 = triphenylphosphine) complex, which forms in situ via ligand replacement.
