The Suzuki-Miyaura cross-coupling is widely used in the synthesis of pharmaceuticals, agrochemicals, and organic light-emitting materials. Utilization of phenol derivatives in Suzuki-Miyaura coupling is economically, environmentally and synthetically desired. Nickel is less expensive, and more reactive than Pd in activation of inert C-Cl and C-O bonds. Replacing Pd catalysts with Ni in the borylation and cross-coupling of aryl halides and representative C-O based electrophiles provides inexpensive and efficient access to biaryl moieties.
In Chapter 2, the nickel catalyzed neopentylglycolborylation of ortho-substituted aryl halides was achieved by zero-valent metals accelerated NiCl2(dppp)/dppf mixed-ligand system. As a result of the fast borylation reaction, an enhancement of the yield of ortho- and para-substituted aryl halides catalyzed by nickel was achieved.
In Chapter 3, Ni(COD)2/PCy3 catalyzed cross-coupling of aryl and heteroaryl mesylates and sulfamates with aryl and heteroaryl neopentylglycolboronates in THF at room temperature was discussed. Meanwhile, the efficiencies of six different phenol derivatives, namely mesylates, sulfamates, pivalates, carbamates, carbonates and methyl ethers were compared in four different nickel-based cross-coupling reaction conditions. Aryl mesylates and sulfamates were the most reactive under Ni(COD)2/PCy3/K3PO4/THF catalytic condition, producing quantitative yields. The conditions developed for cross-coupling of aryl pivalates, sulfamates, carbamates and carbonates with arylboronic acids are not efficient for cross-coupling with aryl neopentylglycolboronates. The efficiencies of four aryl-boron nucleophiles in the Ni-catalyzed coupling of aryl halides, mesylates and sulfamates were compared. Aryl-boronic acids are much more reactive than aryl neopentylglycolboronates in nickel-catalyzed Suzuki-Miyaura cross-coupling in THF. Aryl neopentylglycolboronates were demonstrated to be more reactive and less expensive than currently used pinacol boronates and cross-couple quantitatively.
In Chapter 4, a bench stable and inexpensive NiIICl(1-naphthyl)(PPh3)2/PCy3 mixed-ligand catalytic system was developed as a more accessible alternative to the air-sensitive Ni(COD)2/PCy3 catalytic system. Further development of a library containing ten air-stable NiIIX(Aryl)(PCy3)2 precatalysts (X = Cl, Br, OTs, OMs, Aryl = 1-naphthyl, 2-naphthyl; X = Cl, Aryl = 1-acenaphthenyl, 1-(2-methoxynaphthyl), 9-phenanthrenyl, 9-anthracyl) has enabled quantitative cross-coupling of aryl sulfamates with aryl neopentylglycolboronates at 23 °C in less than 60 min.