No abstract

Dihalomethanes react with Pd2(dpm)3 (dpm = bis(diphenylphosphino)methane) to form Pd2(dpm)2fii-CHR)X2

Di-µ-chloro-bis(η4-1,5-hexadiene)dirhodium(I) in a two-phase hexane–aqueous medium catalyzes the diastereoselective H2-hydrogenation of lignin degradation model compounds 4-propylphenol, 2-methoxy-4-propylphenol, and 2,6-dimethoxy-4-propylphenol. The all-cis diastereomer is obtained selectively when the phenolic hydroxy group is protected as a methyl ether or when a model compound possessing two methoxy substituents adjacent to the phenolic hydroxy group is used. The relative stereochemistries of the hydrogenated products are established by X-ray crystal structure analysis and (or) 1H NMR. Keywords: catalytic hydrogenation, diastereomer, lignin degradation model compounds, stereoselective, X-ray crystal structure.

. Can. J. Chcm. 70, 751 (1992). phosphine]palladium(II) complexes are prepared by metathesis of cis-PdC1,(PPh3-,,py,,), species (n = 1-3) using the appropriate sodium halide; py = 2-pyridyl. NMR spectroscopy, particularly ' 3~{ 1~} , is used to distinguish cis and trans isomers. The dinuclear complexes Pd2X2(k-PPh3-,,py,,),, X = halide, are synthesized via a conproportionation reaction using PdX, (PPh,-,,py,,), and Pd,(dba),; dba = dibenzylideneacetone. Both Pd211(k-PPh,py), and a dimethylacetylenedicarboxylate A-frame complex Pd,Cl2(k-Ppy3),(~-MeO?_C . C=C . C02Me) are characterized crystallographically as head-to-tail isomer:. ' The former crystallizes in the monoclinic space group C 2 / c with a = 30.992(3), b = 18.764(1), c = 13.100(1) A, P = 100.676(5)", and Z = 8; the dcta were refined to R = 0.035 for 5874 reflections withal 2 3u(I). The A-frame compound is triclinic of space group PI with a = 13.545(2), b = 15.064(2), c = 11.991(2) A, a = 1 l1.56(1), P = 95.36(1), y = 97.63(1)", and Z = 2; R = 0.033 from 7128 reflections with I ? 3u(I). The Pd,X2(k-PPhpy,)2 complexes exist as a mixture of diastereomers because of chirality induced at the phosphorus atoms. The Pd,X,(k-Ppy,)? complexes in water generate the [ P~~( H~O )~(~-P P~~) $ + dication, which is isolated as various salts. The mononuclear complexes in water generate aquo and hydroxo species.Key words: dimethylacetylenedicarboxylate adducts, palladium complexes (dinuclear), pyridylphosphines. que l'on a isole sous la forme du plusieurs sels. Dans l'eau, les complexes mononuclCaires fournissent des espkces aquo et hydroxo.Mots cle's : adduits de 1'acCtylknedicarboxylate de dimCthyle, complexes dinucleaires du palladium, pyridylphosphines.[Traduit par la rtdaction]

The complexes [Pd2X2(p-dppm)2] (1) [X = CI, Br, I; dppm = bis(diphenylphosphino)methane] abstract sulphur from H2S under ambient conditions to form [Pd2X2(p-S)(p-dppm)2] (2) and H 2 quantitatively; (2) can be oxidized in stages to p-SO and p-S02 derivatives, the latter losing SO2 spontaneously with regeneration of (1).