Oxidative Addition of Aryl Halides to a Ni(I)-Bipyridine Complex

The oxidative addition of aryl halides to bipyridine- or phenanthroline-ligated nickel(I) is a commonly proposed step in nickel catalysis. However, there is a scarcity of complexes of this type that both are well-defined and undergo oxidative addition with aryl halides, hampering organometallic studies of this process. We report the synthesis of a well-defined Ni(I) complex, [(CO2Etbpy)NiCl]4 (1). Its solution-phase speciation is characterized by a significant population of monomer and a redox equilibrium that can be perturbed by π-acceptors and σ-donors. 1 reacts readily with aryl bromides, and mechanistic studies are consistent with a mechanism proceeding through an initial Ni(I) → Ni(III) oxidative addition. Such a process was demonstrated stoichiometrically for the first time, affording a structurally characterized Ni(III) aryl complex.

Tertiary Alkylative Suzuki-Miyaura couplings

The Suzuki-Miyaura coupling is extremely useful to construct Csp2-Csp2 carbon bonds. On the other hand, Csp2-Csp3 coupling reactions are do not work well, and tert-alkylative Suzuki-Miyaura coupling is particularly challenging due to problematic oxidative addition and beta-hydride elimination side reactions. In this short review, we will introduce recent examples of tert-alkylative Suzuki-Miyaura couplings with tert-alkyl electrophiles or -boron reagents. The review will mainly focus on catalyst and product structures and the proposed mechanisms .

C(sp3)−H oxygenation via alkoxypalladium(II) species: an update for the mechanism

Pd-catalyzed C(sp3)−H oxygenation has emerged as an attractive strategy for organic synthesis. The most commonly proposed mechanism involves C(sp3)–H activation followed by oxidative addition of an oxygen electrophile to give...

Solvent coordination to palladium can invert the selectivity of oxidative addition

Reaction solvent was previously shown to influence the selectivity of Pd/PtBu3-catalyzed Suzuki-Miyaura cross-couplings of chloroaryl triflates. The role of solvents has been hypothesized to relate to their polarity, whereby polar...

Palladium Oxidative Addition Complexes Enabled Synthesis of Amino-Substituted Indolyl-4(3H)-quinazolinones and Their Antitumor Activity Evaluation

The indolyl-4(3H)-quinazolinone core is an important structural motif in functional molecules. However, few methods exist for the direct modification of which limit its potential application. Reported herein is a palladium-mediated...

Salt-Enhanced Oxidative Addition of Iodobenzene to Pd: an Inter-play Between Cation, Anion and Pd-Pd Cooperative Effects

Halide salts facilitate the oxidative addition of organic halides to Pd(0). This phenomenon originates from a combina-tion of anionic, cationic and Pd-Pd cooperative effects. Exhaustive computational exploration at the DFT level of the com-plexes obtained from [Pd0(PPh3)2] and a salt (NMe4Cl or LiCl) showed that chlorides promote phosphine release, leading to a mixture of mononuclear and dinuclear Pd(0) complexes. Anionic Pd(0) dinuclear complexes exhibit a cooperativity between Pd(0) centers which favors the oxidative addition of iodobenzene. The higher activity of Pd(0) dimers toward oxidative addition rationalizes the previously reported kinetic laws. In the presence of Li+, the oxidative addition to mon-onuclear [Pd0L(Li2Cl2)] is estimated barrierless. LiCl coordination polarizes Pd(0), enlarging both the electrophilicity and the nucleophilicity of the complex, which promotes both coordination of the substrate and the subsequent insertion into the C-I bond. These conclusions are paving the way to the rational use of salt effect in catalysis for the activation of more challenging bonds.