Bimetallic C–C Bond-Forming Reductive Elimination from Nickel

Abstract

Ni-catalyzed cross-coupling reactions have found important applications in organic synthesis. The fundamental characterization of the key steps in cross-coupling reactions, including C-C bond-forming reductive elimination, represents a significant challenge. Bimolecular pathways were invoked in early proposals, but the experimental evidence was limited. We present the preparation of well-defined (pyridine-pyrrolyl)Ni monomethyl and monophenyl complexes that allow the direct observation of bimolecular reductive elimination to generate ethane and biphenyl, respectively. The sp(3)-sp(3) and sp(2)-sp(2) couplings proceed via two distinct pathways. Oxidants promote the fast formation of Ni(III) from (pyridine-pyrrolyl)Ni-methyl, which dimerizes to afford a bimetallic Ni(III) intermediate. Our data are most consistent with the subsequent methyl coupling from the bimetallic Ni(III) to generate ethane as the rate-determining step. In contrast, the formation of biphenyl is facilitated by the coordination of a bidentate donor ligand.

Probing Redox Noninnocence of Copper and Zinc Bis‐pyridylpyrrolides

“…[8,9] A four-coordinate Ni II complex with a single pyridyl pyrrolide ligand and other ligands {[(py-Me pyrr)Ni(CH 3 )(lut)] and [(py-Me pyrr)Ni(Ph)(lut)], lut = 2,4-lutidine} has recently shown interesting reactivity. [10] Other transition metal complexes, with a variety of synthetic, catalytic, and energy transfer applications, which contain a single pyridyl pyrrolide ligand have been reported. Examples include metals such as Pd II , [11] Pt II , [6a,6c,12] Cu I , [13] and Au III .…”

Recent Progress in the Design of Monodisperse, Sequence-Defined Macromolecules

“…Recently catalyst. [42] The socalled photoinduced electron transfer (PET) RAFTSUMI was optimized in such a way that the conversion of the RAFT reagent could be driven to 97-99% in the absence of double addition of the monomer units. Therefore, 4cyanopentanoic acid dithiobenzoate (CPADB) was used as RAFT agent, allowing the selective monoaddi tion due to a significant change in the C-S bond stability upon addition of methyl acrylate (MA), styrene, dimeth ylacrylamide (DMA), or NiPAAm.…”

Exploring Mechanisms in Ni Terpyridine Catalyzed C–C Cross-Coupling Reactions—A Review

“…Palladium catalysts normally shuttle between two of the three even electron oxidation states (0, +II, and +IV) during C-C coupling reactions, and two-electron processes such as oxidative addition and reductive elimination are common mechanistic steps [14,15,24,25]. For nickel, single electron pathways between the oxidation states (0, +I, +II, +III, and +IV) often occur in addition to oxidative addition and reductive elimination [24][25][26]31,32].…”

“…For nickel, single electron pathways between the oxidation states (0, +I, +II, +III, and +IV) often occur in addition to oxidative addition and reductive elimination [24][25][26]31,32]. Out of the many applications of nickel(II) catalysts in C-C or C-E cross-coupling reactions, we will focus in this contribution on the Negishi-type reactions [15,18,19,25,26,33] using organometallic zinc reagents, and on electrochemically driven C-C cross-coupling reactions.…”