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Oxidative Addition of Palladium(0) Complexes Generated from [Pd(dba) 2 ] and P‐N Ligands: A Kinetic Investigation
Author(s) -
Amatore Christian,
Fuxa Alain,
Jutand Anny
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/(sici)1521-3765(20000417)6:8<1474::aid-chem1474>3.0.co;2-o
Subject(s) - chemistry , oxidative addition , palladium , denticity , ligand (biochemistry) , stereochemistry , metal , catalysis , organic chemistry , biochemistry , receptor
The major complex formed in solution from {[Pd 0 (dba) 2 ]+1 PN} mixtures is [Pd 0 (dba)(PN)] (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 [Pd 0 ( η 2 ‐dba)( η 2 ‐PN)] and one 14‐electron complex [Pd 0 ( η 2 ‐dba)( η 1 ‐PN)] observed for FcPN and OxaPN. [Pd 0 (dba)(PhPN)] and [ S Pd 0 (PhPN)] ( S =solvent) react with PhI in an oxidative addition; [ S Pd 0 (PhPN)] is intrinsically more reactive than [Pd 0 (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 [Pd 0 ( η 2 ‐dba)( η 1 ‐PhPN) 2 ] is formed first by preferential cleavage of the Pd−N bond instead of the Pd−olefin bond. [Pd 0 ( η 1 ‐PhPN) 3 ] is also eventually formed. [Pd 0 (dba)(FcPN)] and [Pd 0 (dba)(OxaPN)] are formed whatever the excess of ligand used. [ S Pd 0 (FcPN)] and [ S Pd 0 (OxaPN)] are not involved in the oxidative addition. The 16‐electron complexes [Pd 0 ( η 2 ‐dba)( η 2 ‐FcPN)] and [Pd 0 ( η 2 ‐dba)( η 2 ‐OxaPN)] are found to react with PhI via a 14‐electron complex as has been established for [Pd 0 ( η 2 ‐dba)( η 1 ‐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 [Pd 0 (PN)] 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, [ S Pd 0 (PhPN)], or is present in the reactive complexes, [Pd 0 (dba)(FcPN)] or [Pd 0 (dba)(OxaPN)], and thus contributes to their intrinsic reactivity.