Cp₂Ni-KOt-Bu-BEt₃ (or PPh₃) Catalyst System for Direct C−H Arylation of Benzene, Naphthalene, and Pyridine

Abstract

Ni-catalyzed direct C-H arylation of benzene and naphthalene using aryl halides was investigated. For the first time, the arylation was successfully catalyzed by Cp(2)Ni (5 mol %) in the presence of KOt-Bu and BEt(3). This Ni catalyst system was also applied to direct C-H arylation of pyridine, an electron-deficient heteroarene; PPh(3) was used instead of BEt(3) in this case.

Cross‐Coupling of Heteroarenes by CH Functionalization: Recent Progress towards Direct Arylation and Heteroarylation Reactions Involving Heteroarenes Containing One Heteroatom

“…[170] Li and Hua found that mixtures of 2-, 3-and 4-arylpyridines were also efficiently obtained by the reaction of a large molar excess of pyridine (242) aryl bromides in the presence of t-BuOK using Cy 3 PAuCl (5 mol%) as the catalyst.…”

Transition Metal‐Mediated Direct CH Arylation of Heteroarenes Involving Aryl Radicals

“…[26] The transition metal-mediated radical C À H arylation of (hetero)arenes has the advantage of requiring only a catalytic amount of radical initiator, but it usually requires several equivalents of a strong base and a very large excess of (hetero)arene. Iridium, [27] cobalt, [28] nickel [29] and iron [30] catalysts have been used to carry out the direct C À H arylation of unactivated arenes with good to excellent yields, starting from aryl iodides, bromides and even chlorides, although with lower yields in the latter case. [29] Li and Hua described the first transition metalmediated radical arylation of electron-poor pyridine using an Au(I) catalyst.…”

“…Iridium, [27] cobalt, [28] nickel [29] and iron [30] catalysts have been used to carry out the direct C À H arylation of unactivated arenes with good to excellent yields, starting from aryl iodides, bromides and even chlorides, although with lower yields in the latter case. [29] Li and Hua described the first transition metalmediated radical arylation of electron-poor pyridine using an Au(I) catalyst. [31] The reaction was examined with pyrazine as well, but mechanistic investigations using 1,2-dihydroxybenzene as radical inhibitor showed that a radical pathway was probably not involved with this substrate.…”

“…[29] The optimized reaction conditions used a combination of 5 mol% of bis(cyclopentadienyl)-nickel and PPh 3 , with one equivalent of t-BuOK, in pyridine (60 equiv.) at 100 8C for 12 h. The reaction temperature was higher than that required for the arylation of benzene and naphthalene with the corresponding aryl bromides.…”

Iron‐Catalyzed Direct Arylation of Unactivated Arenes with Aryl Halides

“…[2,3] Various transition metals have been reported as efficient catalysts for this transformation, for example, Pd, [4][5][6][7][8][9][10][11] Rh, [12][13][14][15] Ru, [16][17][18] Ir, [19,20] Cu, [21][22][23][24][25][26][27] and other transition metals. [28][29][30] The application of inexpensive, non-toxic, commercially available, and environmentally benign iron complexes as catalysts in chemical syntheses has attracted much attention. [31,32] Recently, iron has been utilized extensively as a catalyst to promote the "traditional" cross-coupling between R 1 X and R 2 M. [33][34][35][36][37][38][39][40][41] Iron catalysts are also involved in many important transformations, such as Friedel-Crafts benzylation, [42,43] carbonylation, [44] oxidation [45,46] and other processes.…”