Mechanism of acetylene and olefin insertion into palladium-carbon .sigma. bonds

High‐Turnover Palladium Catalysts in Cross‐Coupling and Heck Chemistry: A Critical Overview

“…[127] The reluctance of 16e-Pd(II) intermediates bearing two phosphane ligands to undergo direct transmetalation has been clearly documented, and pre-dissociation of these complexes to yield a 14e-Pd(II) intermediate, where one of the phosphanes has been replaced by solvent or an agostic interaction, has been convincingly demonstrated to be a low free-energy pathway to transmetalation. [128] As a consequence of these studies, a useful paradigm in much cross-coupling chemistry has been to use ligands that have low s-donicity toward Pd(II), in such a way as to promote this pre-dissociation.…”

Synthesis of Homo‐ and Hetero‐Bimetallic Arsenic Complexes by Means of Regioselective Monoinsertion of Alkynylarsane into the Pd–C Bond of a Palladacycle

“…[19] We believe that a similar mechanism is involved in the current insertions of the alkynylarsane into the Pd-C bond of the ortho-palladated benzylamine. As illustrated in Scheme 4, upon coordination to the chiral cyclometallated template, the CϵC of the alkynylarsane coordinates in the η 2 mode to the Pd center of the ortho-palladated benzylamine to form a four-coordinate complex by means of a chloro bridge-splitting reaction on the ortho-palladated benzylamine template.…”

“…[18] The organometallic ring conformation of benzylamine, on the other hand, undergoes rapid interconversion between the λ and δ conformations in both the solution and the solid state. [19] In order to explore the subtle metal template effect that arises from the benzylamine and napththylamine auxiliaries, a series of insertion reactions that involved the cycloplatinated/palladated benzylamine templates were conducted.…”

“…As illustrated in Scheme 4, upon coordination to the chiral cyclometallated template, the CϵC of the alkynylarsane coordinates in the η 2 mode to the Pd center of the ortho-palladated benzylamine to form a four-coordinate complex by means of a chloro bridge-splitting reaction on the ortho-palladated benzylamine template. [19][20] Since the alkynylarsane is not symmetrical, the η 2 -coordination step may proceed by two different pathways, paths A and B (Scheme 4). The steric repulsion that arises from the phenyl group of the ortho-palladated benzylamine complex and the naphthyl/phenyl ring of the coordinated cyclometallated complex in pathway A is higher than that of the phenyl group of the ortho-palladated benzylamine and the Me group of the coordinated alkynylarsane in pathway B.…”

Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts

“…The olefin moiety is forced to coordinate to the fully occupied square planar Pd(II), generating a relatively unfavorable pentacoordinate intermediate (PC) as a neutral complex (Fig. 2) [73,74]. The higher catalytic activity under the polar conditions than that under the less polar conditions is well rationalized, in that the reaction proceeded via the preferred tetracoordinate intermediate TC.…”