Oxidative Addition of Palladium(0) Complexes Generated from [Pd(dba)2] and P-N Ligands: A Kinetic Investigation

Abstract

The major complex formed in solution from [[Pd0(dba)2]+1P-N] mixtures is [Pd0(dba)(P-N)] (dba=trans,trans-dibenzylideneacetone; P-N=PhPN, 1-dimethylamino-2-diphenylphosphinobenzene; FcPN, N,N-dimethyl-1-[2-(diphenylphosphino)ferrocenyl]methylamine; OxaPN, 4,4'-dimethyl-2-(2-diphenylphosphinophenyl)-1,3-oxazoline). Each complex consists of a mixture of isomers involved in equilibria: two 16-electron rotamer complexes [Pd0(eta2-dba)(eta2-P-N)] and one 14-electron complex [Pd0(eta2-dba)(eta1-P-N)] observed for FcPN and OxaPN. [Pd0(dba)(PhPN)] and [SPd0(PhPN)] (S solvent) react with PhI in an oxidative addition: [SPd0(PhPN)] is intrinsically more reactive than [Pd0(dba)(PhPN)]. This behavior is similar to that of the bidentate bis-phosphane ligands. When the PhPN ligand is present in excess, it behaves as a monodentate phosphane ligand, since [Pd0(eta2-dba)(eta1-PhPN)2] is formed first by preferential cleavage of the Pd-N bond instead of the Pd olefin bond. [Pd0(eta1-PhPN)3] is also eventually formed. [Pd0(dba)(FcPN)] and [Pd0(dba)(OxaPN)] are formed whatever the excess of ligand used. [SPd0(FcPN)] and [SPd0)(OxaPN)] are not involved in the oxidative addition. The 16-electron complexes [Pd0(eta2-dba)(eta2-FcPN)] and [Pd0(eta2-dba)(eta2-OxaPN)] are found to react with PhI via a 14-electron complex as has been established for [Pd0(eta2-dba)(eta1-OxaPN)]. Once again, the cleavage of the Pd-N bond is favored over that of Pd-olefin bond. This work demonstrates the higher affinity for [Pd0(P-N)] of dba compared with the P-N ligand, and emphasizes once more the important role of dba, which either controls the concentration of the most reactive complex, [SPd0(PhPN)], or is present in the reactive complexes, [Pd0(dba)(FcPN)] or [Pd0(dba)(OxaPN)], and thus contributes to their intrinsic reactivity.

Di-t-butyl(ferrocenylmethyl)phosphine: air-stability, structural characterization, coordination chemistry, and application to palladium-catalyzed cross-coupling reactions

“…Based on these observations, we have tentatively identified this new species as a monophosphine palladium(0)(dba) complex, (1)Pd(dba) n (8). Although we cannot confirm coordination of dba by spectroscopic means, the trans-dibenzylideneacetone ligand provides an asymmetric coordination environment that is typically fluxional at room temperature [41,42]. L 2 Pd(dba) (L = tertiary phosphine) complexes have been previously reported [36,[43][44][45][46][47], but LPd(dba) n complexes of monodentate phosphines have not previously been reported to our knowledge.…”

Computational Study of a New Heck Reaction Mechanism Catalyzed by Palladium(II/IV) Species

“…The importance of ligand dissociation for the kinetics of this reaction step has been demonstrated by experimental studies by Amatore and Jutand on the oxidative addition of Ph À I to palladium(0) complexes with various ligands. [36,37] For the Pd II /Pd IV pathway the 14-electron complex 1 (II-IV) is assumed to be the active catalyst. This tricoordinate species can be described as a fragment of a square-planar complex (which is a stable ligand field for a d 8 transition metal atom) with a vacant coordination site cis to the iodo ligand: P-Pd-I angles of 88.38 and 175.58 are found.…”

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

“…As a matter of fact, Amatore and Jutand together or independently have published a great number of investigations on the oxidative addition of Pd(0) substrates in the presence of phosphine or phosphorus derivatives but, at the best of our knowledge, studies dealing with palladium(0) derivatives bearing olefins and ancillary ligands taken into consideration in this paper are very rare [69]. In one case the starting palladium(0) derivatives treated with phosphine were polyolefin macrocyclic substrates [70] which were recently reviewed [71].…”