| Abstract
| - Several known and new dinuclear palladium complexes were chemisorbed onto silica and used as catalysts for the cyclization of aminoalkynes. The silica/dmpm−palladium complexes were the most effective catalysts.
- Two new dinuclear palladium complexes, [Pd2Me2Cl2(dmpm)2] (4) and [PdMe(Cl)(dmpm)2PdCl2] (5), have been prepared and their structures determined by single-crystalX-ray analysis. 5 is an interesting example of a complex with both a cis-PdCl2 center and atrans-MePdCl center, within the same molecule. The reactivity of 4, as well as the previouslyreported 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 byreaction of the Pd−Me group with the O−H bond of the surface silanol groups, in the caseof 1, 3, and 4, and protonation of the methylene bridge, in the case of 2. The complexescontaining 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 molecularand 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 bethe most active catalysts for this reaction and were also tested for the cyclization of 5-phenyl-4-pentyn-1-amine.
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