Bifunctional nickel precatalysts of amido-functionalized N-heterocyclic carbenes for base-free Michael reaction under ambient conditions

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) …”

“…Michael addition under base-free conditions as catalyzed by bifunctionalNi−NHC complexes.Significantly enough, the following N-heterocyclic carbene based bifunctional catalysts of nickel namely, the (610−613),[187] (614−618)[188] and (619−621)[189] complexes carried out the base-free Michael addition reactions with cyclic and acyclic compounds containing an acidic hydrogen with activated olefins at ambient temperature. A DFT study investigating the mechanistic cycle showed that an amido-functionalized side arm of the N−heterocyclic carbene ligand chelated to the metal center was involved in the deprotonation of the dicarbonyl substrate containing an acidic hydrogen while the metal center in the bifunctional catalyst behaved as an acidic site in facilitating the 1,4−conjugate addition of the dicarbonyl compound to the activated olefinic substrate[264].…”

Ruthenium complexes of chelating amido-functionalized N-heterocyclic carbene ligands: Synthesis, structure and DFT studies

“…RuCl 3 •xH 2 O was purchased from SD-fine Chemicals (India) and used without any further purification. The 1a, 15 (2-3)b Cl 2 ] 2…”

Nickel(II) and Iron(II) Complexes with Tetradentate NHC/Amide Hybrid Ligands

“…3); selected bond lengths and angles are given in Table 1. The short Ni-C NHC (1.85Å) and slightly longer Ni-N amido (1.90 and 1.89Å) bonds resemble those of the known nickel(II) complexes I (d = 1.85/1.92Å) [14] and II (d = 1.89/1.94Å) [15]. Bond angles C NHC -Ni-C NHC generally depend on whether the two NHC subunits are linked and, if so, on the length of the spacer.…”

“…In view of their prevalence in catalytic applications, NHC complexes of late transition metals such as Rh and Pd are particularly abundant [10 -13]. Recently, several group 10 metal complexes with ligands containing one or two NHC moieties and appended amide side arms have been reported (I [14], II [15], III [16] in Fig. 1).…”