Palladium(II) Complexes with Phosphanylferrocenecarboxylate Ligands and Their Use as Catalyst Precursors for Semialternating CO–Ethylene Copolymerization
✍ Scribed by Claudio Bianchini; Andrea Meli; Werner Oberhauser; Anna Maria Segarra; Elisa Passaglia; Martin Lamač; Petr Štěpnička
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 455 KB
- Volume
- 2008
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Neutral [Pd(κ__P__,κ__O__‐P~O)(κ^3^C,C,C‐carbocycloenyl)] complexes, where P~O is a chiral or achiral chelating phosphanylferrocenecarboxylate ligand, were synthesized and characterized by multinuclear NMR spectroscopy. The crystalstructure of a representative complex was determined by single‐crystal X‐ray diffraction analysis. In all complexes, the palladium(II) ion is located at the centre of a square plane formed by the P and O donor atoms from an anionic P~O^–^ ligand, a σ‐carbon atom and a C–C double bond from a carbocycloenyl ligand. Neutral methyl complexes with the formulas [PdCl(Me)(κ__P__,κ__H__‐P~OH)] and [Pd(Me)(OTs)(κ__P__,κ__H__‐P~OH)] were also synthesized and characterized. On the basis of IR, NMR and MS–FAB data, the methyl complexes are proposed to be formulated with the fourth coordination position occupied by an agostic O–H···Pd interaction from a free carboxylic acid moiety [P~OH = 1′‐(diphenylphosphanyl)ferrocenecarboxylic acid] or a solvent molecule. Selected complexes were employed as catalyst precursors for CO–ethylene copolymerization in MeOH in the presence of an excess of p‐toluenesulfonic acid. In all cases, low molecular weight semialternating polyketones were produced. The catalytic activities were rather low and the extra‐ethylene insertion reached a maximum value of 4.3 %. An operando high‐pressure NMR experiment with [Pd(Me)(S)~2~(κ____P‐P~OH)]OTs (S = solvent, adventitious water) precursor showed that this monocationic Pd^II^ alkyl complex is readily converted into a catalytically inactive binuclear carbonyl‐bridged Pd^I^ compound, which, however, regenerates catalytically active Pd^II^–H species by reaction with TsOH and that β‐chelates of the formula [Pd(CH~2~CH~2~C(O)P)(S)(κP‐P~OH)]OTs (P = propagating polyketone chain) are catalyst resting states. For the first time, β‐chelate propagating species have been intercepted in a CO–olefin copolymerization assisted by catalysts devoid of a chelating ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)