Catalyst Activity and Selectivity in the Isomerising Alkoxycarbonylation of Methyl Oleate. Issue 50 (20th November 2013)

• Record Type: Journal Article
• Authors: Christl, Josefine T.; Roesle, Philipp; Stempfle, Florian; Wucher, Philipp; Göttker‐Schnetmann, Inigo; Müller, Gerhard; Mecking, Stefan
• Is Part Of: Chemistry. Volume 19:Issue 50(2013)
• Page Start: 17131
• Page End: 17140
• Publication Date: 2013-11-20
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201301124
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The synthesis of unsymmetrical diphosphine ligands (<bold>3 a</bold>–<bold>g</bold>) with an <italic>o</italic>‐tolyl backbone and <italic>tert</italic>‐butyl, adamantyl, cyclohexyl and isopropyl substituents on the phosphorus moiety is described (1, 2‐(CH<sub>2</sub>PR<sub>2</sub>)(PR′<sub>2</sub>)C<sub>6</sub>H<sub>4</sub>; <bold>3 a</bold>: R=<italic>t</italic>Bu, R′=<italic>t</italic>Bu, <bold>3 b</bold>: R=<italic>t</italic>Bu, R′=Cy, <bold>3 c</bold>: R=<italic>t</italic>Bu, R′=<italic>i</italic>Pr, <bold>3 d</bold>: R=Ad, R′=<italic>t</italic>Bu, <bold>3 e</bold>: R=Ad, R′=Cy, <bold>3 f</bold>: R=Cy, R′=Cy, <bold>3 g</bold>: R=Ad, R′=Ad). The corresponding diphosphine–Pd<sup>II</sup> ditriflate complexes [(P^P)Pd(OTf)<sub>2</sub>] (<bold>5 a</bold>–<bold>g</bold>) were prepared and structurally characterised by X‐ray crystallography. These new complexes were studied as catalyst precursors in the isomerising methoxycarbonylation of methyl oleate, and were found to convert methyl oleate into the corresponding linear α, ω‐diester (<bold>L</bold>) with 70–80 % selectivity. The products of this catalytic reaction with the known [{1, 2‐(<italic>t</italic>Bu<sub>2</sub>PCH<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>}Pd(OTf)<sub>2</sub>] complex (<bold>5 h</bold>) were fully analysed, and revealed the formation of the linear α, ω‐diester (<bold>L</bold>, 89.0 %), the methyl‐branched diester <bold>B1</bold> (4.3 %), the ethyl‐branched diester <bold>B2</bold> (1.0 %), the propyl‐branched diester <bold>B3</bold> (0.6 %) and all diesters from butyl‐ to hexadecyl‐branched diesters <bold>B4</bold>–<bold>B16</bold> (overall 4.8 %) at 90 °C and 20 bar CO. The productivity of the catalytic conversion of methyl oleate with complexes <bold>5 a</bold>–<bold>g</bold> varied with the steric bulk of the alkyl substituent on the phosphorus. Ligands with more bulky groups, like <italic>tert</italic><bold>‐</bold>butyl or adamantyl (e.g., <bold>5 a</bold>, <bold>5 d</bold>, <bold>5 g</bold>), were more productive systems. The formation of the catalytically active hydride species [(P^P)Pd(H)(MeOH)]<sup>+</sup> (<bold>6‐MeOH</bold>) was investigated and observed directly for complexes <bold>5 a</bold>–<bold>e</bold> and <bold>5 g</bold>, respectively. These hydride species were isolated as the corresponding triphenylphosphine complexes (<bold>6‐PPh<sub>3</sub></bold>) and fully characterised, including by X‐ray crystallography. The catalytic productivity of <bold>6 a‐PPh<sub>3</sub></bold> was virtually identical to that of <bold>5 a</bold>, thereby confirming the efficient hydride formation of <bold>5 a</bold> under catalytic conditions.</p> </abstract>