Palladium(0)-Alkene Bis(triarylphosphine) Complexes as Catalyst Precursors for the Methoxycarbonylation of Styrene

Abstract

The fluorous complex [Pd(0)(P{C 6 H 4 -p-SiMe 2 (CH 2 CH 2 C 6 F 13 )} 3 ) 2 (MA)] (MA ) maleic anhydride) was synthesized and characterized by its NMR spectra. Together with the nonfluorous complexes [Pd(0)(PPh 3 ) 2 (alkene)] (alkene ) C 2 H 4 , (NC) 2 CdC(CN) 2 , NCC(H)d C(H)CN, MA, or benzoquinone) these were evaluated as catalyst precursors in the methoxycarbonylation of styrene. The nonfluorous C 2 H 4 and MA complexes gave the highest conversions (the turnover number (TON) was 120; the (average) turnover frequency (TOF) amounted to 80 h -1 ). The fluorous complex gave a significantly lower conversion (TON about 38; TOF 26 h -1 ) than its nonfluorous counterpart, which is caused by a lower stability of the fluorous complex under the reaction conditions.

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

“…Since the C@C bond in the free olefin displays a length of about 1.25 Å it has been proposed that the change in the hybridization of the olefin carbon is almost always operative with the consequent formation of a metallacyclopropane structure. In this case, the out-of-plane bending of the carbon substituents confirms the hypothesis although, in at least the case of the complex [Pd(g 2 -fn)(t-BuDAB), the typical olefin sp 2 hybridisation is maintained [78]. Interestingly, when potentially ter-dentate nitrogen ligands are employed the usual trigonal arrangement around palladium is observed since one coordinating atom of the ligand itself remains uncoordinated.…”

“…X-ray diffractometric studies 10.1. Complexes bearing mono-bi-and ter-dentate nitrogen ligands A significant number of palladium(0) olefin compounds bearing the title ligands was synthesized by several authors [30,31,35,37,75,[78][79][80][81][82][83][84][85][86]. All the structures display the typical trigonal arrangement around the palladium centre with the Pd-N bond lengths being scarcely influenced by the olefin nature, spanning within 2.10 and 2.18 Å.…”

Protonation of palladium(II)-allyl and palladium(0)-olefin complexes containing 2-pyridyldiphenylphosphine

“…Owing to the chemical equivalence of the phosphorus atoms of the ligands, the 31 P{ 1 H} NMR spectrum of 4 consists of a singlet at d 27.6. In the 13 C{ 1 H} NMR spectrum the resonance of the olefin carbons appears as the A part of a AXX 0 spin system (the X nuclei are the two phosphorus atoms of Ph 2 PPy) centered at d 33.7 in keeping with the literature data for similar Pd(0)-fumaronitrile complexes [20,21].…”

“…The process is slow even at room temperature and in the early stages consists of a ''clean" deligation of the olefin from the metal centre which can be monitored recording the growth of the singlet due to uncoordinated fumaronitrile at d 6.35 in the 1 H NMR spectrum. Experiments aimed to highlight the fate of the metal fragment were unsuccessful and in particular it should be mentioned that no evidence supporting the formation of palladium-hydride species [21,28] was found. On standing the solutions of 4a darken, thus, it is likely that at the end the decomposition leads to colloidal palladium.…”

Multiphase Systems for the Recycling of Alkoxycarbonylation Catalysts

“…However, lightly fluorous catalysts have been successfully applied in biphasic solvent mixtures. [41] Hence more examples of catalyst recycling based on these new techniques can be expected in the near future.…”