Synthesis of Novel Chelating Benzimidazole-Based Carbenes and Their Nickel(II) Complexes: Activity in the Kumada Coupling Reaction

Abstract

Nickel(II) halide complexes of novel chelating bidentate benzimidazole-based N-heterocyclic carbenes have been prepared from Ni(OAc)2 and bisbenzimidazolium salts. Single-crystal X-ray structure determination on four complexes revealed a cis-geometry on a square-planar nickel center. The complexes are active catalysts for the Kumada coupling of 4-chloroanisole and 4-bromoanisole with phenylmagnesium chloride. The most active catalyst gives a complete conversion of 4-bromoanisole within 75 min with a selectivity to 4-methoxybiphenyl of 82% and a complete conversion of 4-chloroanisole in less than 14 h with a selectivity to 4-methoxybiphenyl of 99%.

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…In particular, the (533−534), [163] (535), [164] (536), [165] (543−544), [166] (545−546), [167] (548 [168]−557), [169] (558), [51] (559), [71] (560), [161] (561), [170] (562−563), [141] (565), [171] (566−567), [172] (568), [173] (569), [126d] (570−573), [174] (574), [175] (575−576), [176] (577), [177] (578), [178] (579), [106] (580−581), [179] (582−583), [151] (584−585), [180] (586−588), [181] (595−596), [182] (597−599), [183] (600−603), [184] (604), [185] (605−608), [186] (609), [185] (610−613), [187] (614−618), [188] (619−621), [189] (622−623), [185] (624−630), [190] (631), [191] (633−635), [192] (636), [193] (637), [194] (647) [195] and (648) [196] complexes were obtained by this pathway from the treatment of the free or the in situ generated NHC The third route is the oxidation method (Scheme 15) using which the (589−590), [197] (638) …”

Synthesis of palladium(0) and -(ii) complexes with chelating bis(N-heterocyclic carbene) ligands and their application in semihydrogenation

“…Bis-NHCs have been coordinated to many transition metals: ruthenium, 4 rhodium, 3,5 iridium, 6 palladium, 7 platinum, 8,9 and more recently also the first row metals such as nickel [10][11][12] and iron. 13,14 We are interested in the properties and reactivity of low-valent late transition metal complexes, notably electron rich zero-valent palladium NHC complexes, as these often play a vital role in the catalytic cycles of many reactions.…”

Nickel N‐heterocyclic carbene complexes in the vinyl polymerization of norbornene

“…Unfortunately, a shorter reaction time was experimentally unattainable. In addition, it was attempted to perform the catalytic reaction in more diluted reaction mixtures (entries [27][28][29]. This way, the polymerization of norbornene using complex 4 was slowed down, giving only 45% yield in 5 min in a solution that was six times diluted, compared with 78% yield in 2 min (entry 23).…”

“…Methylaluminoxane (MAO, 10 wt% solution in toluene) was obtained from Aldrich and used as received. Complexes 2a,b, [29] 3a,b [31] and 4 [32] were synthesized following the procedures described in the literature and were added from a 3.0 mM stock solution in dichloromethane or 1,2-dichloroethane.…”

“…[28] A number of nickel complexes bearing chelating benzimidazole-based bisNHC ligands has been synthesized and applied as catalysts in the Kumada coupling reaction. [29] As nickel complexes bearing chelating phosphanes are active catalysts for the polymerization of norbornene, [19,30] it was decided to study the activity of the bisNHC complexes in this reaction. Given the successful use of N-donor ligands in the catalytic polymerization of norbornene, it was decided to investigate the catalytic properties of two nickel complexes with benzimidazolato-functionalized NHC ligands as well.…”