Arab K. El-Qisairi

Oxidation of olefins by palladium(II): Part 17. An asymmetric chlorohydrin synthesis catalyzed by a bimetallic palladium(II) complex

Abstract Previous studies showed that oxidation of α-olefins with monometallic catalysts containing chiral diphosphines and diamines gave chlorohydrins with poor to good enantioselectivites (28–82% ee). The present studies demonstrate that bimetallic catalysts containing a β-triketone and bridging chiral diphosphine and diamines are excellent catalysts for this reaction giving enantioselectivites considerably higher than the monometallic catalysts. Enantioselectivities were more than 50% for most olefins tested. The highest optical purities were 94% ee for propene and 93% ee for allylphenyl ether. A useful feature of this asymmetric synthesis is the fact it is a net air oxidation.

Oxidation of ketone by palladium(II). α-Hydroxyketone synthesis catalyzed by a bimetallic palladium(II) complex

Abstract A bimetallic palladium(II) complex containing a triketone ligand and a bridging dinitrogen ligand oxidizes ketones in aqueous THF to α-hydroxyketone by a direct air oxidation. While the normal synthesis of α-hydroxyketones involves a series of reactions, this synthesis performs the transformation in one step in a catalytic air oxidation. This synthesis does not involve an olefin and is almost unprecedented in transition metal catalysis. Its main virtue is its simplicity and actually it is an enolization reaction. Methanesulfonic acid is used to accelerate the enolization of ketones. The reaction is carried out in the presence of CuCl 2 and/or dioxygen only. In particular, it is found that the hydroxyketone formation does not require the presence of CuCl 2 . Matrix assisted laser desorption ionization (MALDI) and time-of-flight mass spectrometry (TOFMS) are used to record the mass spectra of α-hydroxyketones products. α-Cyano-4-hydroxycinnamic acid (CHCA) matrix promoted the molecular ion detection when 180 pmol of α-hydroxyketones is introduced into the TOFMS.

Oxidation of olefins by palladium(II). 18. Effect of reaction conditions, substrate structure and chiral ligand on the bimetallic palladium(II) catalyzed asymmetric chlorohydrin synthesis

The effect of electronic factors, solvent composition, identity of the chiral bidentate, and olefin structure on the yields and enantioselectivities of the asymmetric chlorohydrin synthesis were investigated. Electronic effects on the chlorohydrin reaction were tested by oxidation of phenyl allyl ether p -substituted by H, Cl, CH3O and CN. All species gave same similar yields and enantioselectivities indicating that electronic effects are not important. Varying the solvent composition of the THF � /H2O mixtures indicated that the optimal solvent mixture contains more than 85% THF. Variation of added [Cl � ] indicated that the added chloride had to be greater than 0.2 M for high yields and %ee’s. Under ideal conditions the enantioselectivities of the chlorohydrins from the phenyl allyl ethers were more than 90%ee. Vinylacetic acid, methyl acrylate and trans -cinnamaldehyde were unreactive under the usual reaction conditions while 2-hydroxy-3-butene and allyl acetate give lower %ee’s than did the phenyl allyl ethers. Styrene and amethylstyrene gives comparable rates of reactions but the %ee’s were lower with the latter. (2,6-Diisopropyl)phenyl allyl ether and 2hydroxy-3-butene give high %ee’s indicating that steric hindrance was not a major factor. All of the chiral bridging ligands tested gave satisfactory results except for DACH. A strange case was BZOX which did not give any induction at all. Structural studies showed the ligands are not large enough to bridge both Pd(II) in the bimetallic catalyst so one Pd(II) contained both ligand groups of the bidentate ligand and was thus unreactive. The other Pd(II) of the dimer was reactive but did not contain any chiral ligands to induce optical activity. # 2002 Elsevier Science B.V. All rights reserved.

Palladium(II) catalyzed carbonylation of ketones

Abstract Cyclic ketones react with PdCl2 in methanol under a CO atmosphere to give mainly diesters by a ring cleavage reaction along with some chloro-substituted monoester. 13CO labeling experiments indicate the major product is formed by a mechanism involving Pd(II)-CO2CH3 insertion across the double bond of the enol form of the ketone. Pd(II) elimination and acid-catalyzed ring cleavage form a second methyl ester group.

Synthesis, characterization and semiempirical calculations of mercury(II) complexes of 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine

The reactions of 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine (bptz) with HgX2 (X = Cl, Br, I) have been investigated. The isolated complexes have been characterized by elemental analysis, conductivity measurements, IR, 1H, and 13C NMR spectroscopy. PM3 calculations show that the trans-conformation is preferred. Thermodynamic calculations and orbital energies are reported.

Substituted dipyridylpyridazine rhodium(III) complexes

Abstract3,6-Bis(2′-pyridyl)pyridazine derivatives (n-dppn) react with hydrated rhodium(III) chloride and bromide (prepared in situ) to give cis-[Rh(n-dppn)2Cl2]PF6·xH2O (n = 5, 6, 7, 8) and cis-[Rh(n-dppn)2Br2]Br·xH2O (n = 5, 7) complexes, which have been characterized by elemental analyses, conductivity measurements, i.r., electronic and 1H- and 13C-n.m.r. spectra.

Complexes of substituted dipyridylpyridazines with palladium(II) and platinum(II)

Reactions of 3,6-bis(2′-pyridyl)pyridazine derivatives (n-dppn)¶ with MX2(PhCN)2 (M = Pd, Pt; X = Cl, Br) have been investigated. The new complexes cis-[PdCl2(n-dppn)] (n = 5, 6, 8, 12), cis-[PtCl2(n-dppn)] · H2O (n = 5, 6), cis-[PtCl2(8-dppn)] and cis-[PtBr2(5-dppn)] have been characterized by elemental analyses, conductivity measurements, infrared, electronic and 1H-NMR spectra. ¶For the n-dppn ligands, n stands for the size of the cyclic aliphatic ring on positions 4 and 5 of the pyridazine ring, n = 5, 6, 8, and 12.