Abstract
Two new dinuclear palladium complexes, [Pd2Me2Cl2(dmpm)2] (4) and [PdMe(Cl)(dmpm)2PdCl2] (5), have been prepared and their structures determined by single-crystal X-ray analysis. 5 is an interesting example of a complex with both a cis-PdCl2 center and a trans-MePdCl center, within the same molecule. The reactivity of 4, as well as the previously reported complexes [Pd2Me2Cl2(dppm)2] (1), [Pd2(μ-CH2)Cl2(dppm)2] (2), and [Pd2Me4(dmpm)2] (3), toward silica have been investigated. The complexes react readily with either dichloromethane or benzene suspensions of silica to give chemisorbed species, presumably by reaction of the Pd−Me group with the O−H bond of the surface silanol groups, in the case of 1, 3, and 4, and protonation of the methylene bridge, in the case of 2. The complexes containing the more basic phosphine, dmpm, gave much higher palladium loadings (wt % Pd 1.37−2.47) on silica, compared to the dppm complexes (wt % Pd 0.55−0.80). The molecular and grafted materials were initially tested as catalysts for the cyclization of 6-aminohex-1-yne to give 2-methyl-1,2-dehydropiperidine. The silica/dmpm complexes were found to be the most active catalysts for this reaction and were also tested for the cyclization of 5-phenyl-4-pentyn-1-amine.
Published Version
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