Remarkable, Sterically Induced Rate Enhancement in the Insertion of Allenes into Palladium−Methyl Bonds

Abstract

The rate of insertion of methyl-substituted allenes into the Pd-Me bond in chelate pyridinethioether complexes [PdCl(Me)derivatives is remarkably enhanced by the presence of a methyl group in position 6 of the pyridine ring, which induces distortion on the main coordination plane, resulting in a metal substrate more prone to allene insertion. The flexibility of the sulfur-donor chelate ligand appears to be a paramount requisite.

Kinetic Studies of the Oxidative Addition and Transmetallation Steps Involved in the Cross‐Coupling of Alkynyl Stannanes with Aryl Iodides Catalysed by η2‐(Dimethyl fumarate)(iminophosphane)palladium(0) Complexes

“…The much greater stability of complex 1b is largely due to the greater π-accepting properties of fumaronitrile which increase the strength of the palladium-olefin bond as already observed for the olefin exchange equilibria in similar zero-valent complexes [Pd(η 2 -ol)(LϪLЈ)] {LϪLЈ ϭ 2-(iminomethyl)pyridine [16] or 2-(methylthio)pyridine [17] }. A reduced electron density on the metal in 1b will render the complex less susceptible to oxi- ].…”

Synthesis, stability and reactivity of palladium(0) olefin complexes bearing labile or hemi-labile ancillary ligands and electron-poor olefins

“…The precursor is a palladium allyl derivative bearing a bidentate ligand which is reacted with BPh 4 À or amines. The elimination of the phenyl-allyl or amino-allyl moieties yields the palladium(0) species which is stabilized by fn, dmfu or ma [28,29].…”

Oxidative addition of organic halides on palladium(0) complexes stabilized by dimethylfumarate and quinoline-based N–P or N–S spectator ligands

“…Moreover, complex 5 reacts faster than its non methylated analog 2. Since such a difference in reactivity is essentially due to the distortion imposed to the main coordinative plane of complex 5 by the methyl group in position 2 of the quinoline ring [15], we may advance the hypothesis that in this case In 2 is the most probable intermediate. Such a conclusion was also confirmed by a computational approach based on theoretical calculations carried out with the GAUSSIAN 09 package [16] (see Section 3 for computational details).…”

“…The Pd1-I1 of 2.5902(4) Å displays a shortening with respect to the same distances, in the range 2.63-2.64 Å, as found in other similar Pd(II) structures where I is in trans position to a S atoms of a thioether group [9a,18,19]. In these compounds the I À anion exerts a significant trans influence on the Pd-S bonds because their distances (in the range 2.31-2.33 Å) are rather longer than those reported in analogous structures where S is in trans position to a Cl À anion (in the range 2.26-2.28 Å) [12,15,20,21]. An ORTEP [17] view of the neutral complex 5c is shown in Fig 2. A selection of bond distances and angles is given in the caption of the figure.…”