Catalyst Activity and Selectivity in the Isomerising Alkoxycarbonylation of Methyl Oleate

Abstract

The synthesis of unsymmetrical diphosphine ligands (3a-g) with an o-tolyl backbone and tert-butyl, adamantyl, cyclohexyl and isopropyl substituents on the phosphorus moiety is described (1,2-(CH2PR2)(PR'2)C6H4; 3a: R=tBu, R'=tBu, 3b: R=tBu, R'=Cy, 3c: R=tBu, R'=iPr, 3d: R=Ad, R'=tBu, 3e: R=Ad, R'=Cy, 3f: R=Cy, R'=Cy, 3g: R=Ad, R'=Ad). The corresponding diphosphine-Pd(II) ditriflate complexes [(P^P)Pd(OTf)2] (5a-g) 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 (L) with 70-80% selectivity. The products of this catalytic reaction with the known [{1,2-(tBu2PCH2)2C6H4}Pd(OTf)2] complex (5h) were fully analysed, and revealed the formation of the linear α,ω-diester (L, 89.0%), the methyl-branched diester B1 (4.3%), the ethyl-branched diester B2 (1.0%), the propyl-branched diester B3 (0.6%) and all diesters from butyl- to hexadecyl-branched diesters B4-B16 (overall 4.8%) at 90 °C and 20 bar CO. The productivity of the catalytic conversion of methyl oleate with complexes 5a-g varied with the steric bulk of the alkyl substituent on the phosphorus. Ligands with more bulky groups, like tert-butyl or adamantyl (e.g., 5a, 5d, 5g), were more productive systems. The formation of the catalytically active hydride species [(P^P)Pd(H)(MeOH)](+) (6-MeOH) was investigated and observed directly for complexes 5a-e and 5g, respectively. These hydride species were isolated as the corresponding triphenylphosphine complexes (6-PPh3) and fully characterised, including by X-ray crystallography. The catalytic productivity of 6a-PPh3 was virtually identical to that of 5a, thereby confirming the efficient hydride formation of 5a under catalytic conditions.

Mid-chain carboxylic acids by catalytic refining of microalgae oil

“…These selectivities are in accordance with the literature values for the isomerizing alkoxycarbonylation of a neat linear mono-unsaturated substrate. 24 The selectivity of the alkoxycarbonylation of 2,5-heptadiene (61%) is also comparable to the observed selectivity on the isolated EPA as a starting material. The isomerizing alkoxycarbonylation catalyst was compatible with the remaining components in algae oil, and was also not disturbed by the quenched metathesis catalyst.…”

“…S14 †) were observed in 10% selectivity which is typical of this catalyst for mono-unsaturated substrates. 24 For the largest part (7%) these are composed of dimethyl 2-methyloctanedioate. Furthermore, three different ketones (2-heptanone, 3-heptanone and 4-heptanone, Fig.…”

Isomerizing Hydroformylation of Cashew Nut Shell Liquid

“…Therefore, establishing the coordination behavior of L4 around the Rh center and identification of the resultant catalyst resting state might shed light on the observed selectivity. The coordination behavior of L4 has been extensively studied in Pd‐catalyzed isomerizing alkoxycarbonylation …”

“…Very few attempts have been made in this regard (Scheme ) . The most successful example is isomerizing alkoxycarbonylation (>95 % terminal selectivity) of methyl oleate (from edible plant oils) . Metathesis has gained significant attention; however, it does not allow complete utilization of the carbon chains obtained from plant oils .…”

The mission of addition and fission – catalytic functionalization of oleochemicals

“…This developed protocol for isomerizing alkoxycarbonylation proved in many succeeding publications to be a useful tool for the synthesis of linear diesters of different chain length, depending on the applied substrate, as platform chemicals for the production of different polycondensates . As a result of that, subsequent work has been performed towards natural oils as starting material , mechanistic elucidations , and expanding the reaction scope to related transformations, such as alkoxycarbonylation with formates , terpenes as substrates , and aminocarbonylations .…”