Palladium complexes of (Benzoimidazol-2-ylmethyl) amine ligands : synthesis and applications as catalysts in methoxycarbonylation of olefins.
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Date
2014
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Abstract
Compounds N-(1H-benzoimidazol-2-ylmethyl)-2-aniline(L1), N-(1H-benzoimidazol-
2-ylmethyl)-2-methoxyaniline (L2), N-(1H-benzoimidazol-2-ylmethyl)-2-thioaniline
(L3) and N-(1H-benzoimidazol-2-ylmethyl)-2-bromoaniline (L4) were prepared by
reaction of 2-(chloromethyl) benzimidazole with the appropriate aniline. Ligands
L1– L4 were reacted with either [PdCl2(COD)] or [PdClMe(COD)] to form palladium
complexes [PdCl2(L1)], [PdClMe(L1)], [PdCl2(L2)],[PdClMe(L2)], [PdCl2(L4)] and
[PdClMe(L4)].
Treatment of the neutral complexes C1 – C6 with one equivalent of PPh3 in the
presence of the halide abstractor NaBAr4 (Ar = 3,5-(CF3)2C6H3) led to the formation
of the cationic species [(PdCl(L1)]Bar4, [(PdMe(L1)]Bar4, [(PdCl(L2)]BAr4,
[(PdMe(L2)]BAr4 and [(PdMe(L4)]BAr4. All the new compounds were characterized
by combination of 1H and 31P NMR spectroscopy, mass spectrometry, X-ray
crystallography of complexes C8, C9 and C11 and elemental analysis (for
complexes).
The palladium complexes were investigated as catalyst in methoxycarbonylation of
olefins. Methoxycarbonylation of 1-hexene using C2, C4, C6, C8-C11 was studied in
order to investigate the effect of catalyst structure and PPh3 ligand on activity and
selectivity. Complex C10 bearing electron donating OCH3 substituent on phenyl
group was the most active, while the corresponding analogue containing the Br
substituent on phenyl group was the least active. Complex C9 with Pd-Cl showed
lower catalytic activity, compared complex C10 with Pd-Me. Addition of PPh3 to the
palladium complexes resulted in higher catalytic activities and high regioselectivity
towards the linear esters. The activity also dependent in the identity of acid
promoter where HCl gave highest active system while no activity was observed with
p-TsOH. The effects of pressure, temperature, catalysts concentration, identity of the
olefin and time was also investigated. Increasing the catalysts concentration, chain
length and time resulted in higher catalytic activities and higher regioselectivity
towards the branched ester.
Description
M. Sc. Eng. University of KwaZulu-Natal, Pietermaritzburg 2014.
Keywords
Palladium compounds., Catalysts., Alkenes., Amine oxidase., Theses -- Chemistry.