Structural and theoretical studies of the methoxycarbonylation of higher olefins catalysed by (Pyrazolyl‐ethyl)pyridine palladium (II) complexes

Abstract

Reactions of 2-[1-(3,5-dimethylpyrazol-1-yl)ethyl]pyridine (L1) and 2-[1-(3,5diphenylpyrazol-1-yl)ethyl]pyridine (L2) with the [Pd (COD)Cl 2 ] or [Pd (COD)MeCl] produced palladium (II) complexes [Pd(L1)ClMe] (1), [Pd(L1) Cl 2 ] (C2), [Pd(L2)ClMe] (3), and [Pd(L2)Cl 2 ] (4) in quantitative yields. Solid state structures of complexes 1, 3 and 4 established the formation of mononuclear compounds, containing one bidentate ligand unit per metal atom, to give square planar complexes. All the other spectroscopic characterization data and elemental analyses were consistent with the observed structures. All the palladium (II) complexes 1-4 gave active catalysts in the methoxycarbonylation of 1-octenes. The catalysts demonstrated 100% chemoselectivities towards esters and favored the formation of linear isomers. Reaction conditions such as the type of phosphine derivative, acid promoter, solvent system, time, pressure and temperature have been investigated and shown to affect both the catalytic activity and regio-selectivity of the catalysts. Solid-angle modelling established the comparable steric contributions from the ligands, consistent with the similar regioselectivities of the resultant catalysts.

Sterically hindered (pyridyl)benzamidine palladium(II) complexes: Syntheses, structural studies, and applications as catalysts in the methoxycarbonylation of olefins

“…For example, palladium(II) catalysts based on mixed N^N^O(S) (TON of 264) in the methoxycarbonylation reaction. [29,32] While the catalytic activities of the current are comparable with our previous systems, [21,25,30,51] complexes Pd1-Pd5 registered significant improvement with respect to regioselectivity. For instance, while most of our previous reports produced linear and branched products in almost equal quantities, the current complexes afforded up to 75% of the linear esters in the methoxycarbonylation of 1-hexene.…”

“…These results are in good agreements with previous reports and have been associated with steric and electronic contributions from various alkenes. [ 22,25,30,51 ] The superior percentage yields recorded for styrene (>99%) is normal and is attributed to the resultant benzylic palladium(II) intermediate, which is a more active as compared to alkyl palladium(II) species, in aliphatic alkenes. [ 56 ] The identity of the olefin substrate also controlled the type of the ester products yielded.…”

“…Pursuant to these limitations, significant efforts are being channeled toward the invention of alternative donor ligands, which are cheaper and amenable to synthetic manipulations such as N^N, [21][22][23][24][25][26][27] N^P, [28,29] and N^O [30,31] among others. [32] In addition, the design, isolation, and structural characterization of discrete palladium(II) catalysts is attractive as it allows for better understanding of the catalytic process in terms of kinetics, mechanistic, and deactivation profiles.…”

Cytotoxic Effects of New Palladium(II) Complexes with Thiazine or Thiazoline Derivative Ligands in Tumor Cell Lines

“…It is noted that 1 H NMR signals of thiazine and thiazoline of all complexes are in general shifted to higher frequencies with respect to their free ligands. This also occurs for pyrazole ring signals for PdPzTn, PdPzTz, and PdDMPzTn, while the signals of complexes with phenyl substituents are slightly shifted to lower frequencies, probably due to the presence of aromatic groups which help with the redistribution of electronic density loss [ 26 , 27 ]. Therefore, it can be concluded that the ligands are coordinated to palladium in DMF solution for PdPzTn, PdPzTz, PdDPhPzTn, and PdDPhPzTz and in DMSO solution for PdDMPzTn.…”