Abstract
Palladium(II) acetate reacts with proline and proline homologs in acetone/water to yield square planar bis-chelated palladium amino acid complexes. These compounds are all catalytically active with respect to oxidative coupling of olefins and phenylboronic acids. Some enantioselectivity is observed and formation of products not reported in other Pd(II) oxidative couplings is seen. The crystal structures of nine catalyst complexes were obtained. Extended lattice structures arise from N-H••O or O••(HOH)••O hydrogen bonding. NMR, HRMS, and single-crystal XRD data obtained on all are evaluated.
Highlights
Oxidative coupling reactions are some of the most utilized reactions in modern synthetic chemistry, and transition metal catalyzed oxidations are well known [1]
This paper describes the synthesis and catalytic activity of palladium(II)-amino acid chelates acid complexes of rhodium and iridium piano stools were useful for asymmetric hydrogenation where proline, N-methylproline, 4-fluoroproline, 4-hydroxyproline, 2-benzylproline, azetidine-2We have previously reported on the simpler glycine complexes [69], and these proline and proline carboxylicrepresent acid, andanother pipecolinic acidsubset were of used as the chelating ligands
Nine palladium(II) bis-amino acid chelates with aliphatic ring structures for their R-group have been synthesized, characterized, and tested for catalytic activity for the oxidative coupling of phenylboronic acid with olefins
Summary
Oxidative coupling reactions are some of the most utilized reactions in modern synthetic chemistry, and transition metal catalyzed oxidations are well known [1]. Palladium catalysts are known for their functional group tolerance, mild reaction conditions, and low sensitivity to air and water Pairing these advantages with an abundant and accessible oxidant source shows the great utility and economic benefit that these systems can provide. The formation of biaryl products from palladium-catalyzed cross-couplings is well known, and there of biaryls is an unwanted side reaction and catalyst systems of this type where the biaryl formation is are examples from the literature [21,50,63,64,65,66,67]. Thisreaction paper describes theorsynthesis and catalytic activity ofFor palladium(II)-amino where product is desired, the formation of biaryls is an unwanted side reaction and catalyst systems of this proline, N-methylproline, 4-fluoroproline, 4-hydroxyproline, 2-benzylproline, azetidine-2-carboxylic type where the biarylacid formation is minimized or eliminated are preferred. Results and Discussion amino acid complexes and amino acids where the R-group is a linear substituent
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