Bridged acetals, preparation

The preparation of the compounds (2-RC3H4)(MeCOO)Pd2L2 was achieved by the reaction of the acetate-bridged palladium(II) complexes [(2-RC3H4)Pd]20t-MeCOO)2 with PdL (L = P-/-Pr3). The analogous binuclear /x-benzoate and /x-trifluoroacetate (Pd—Pd) compounds are accessible by the same route (26). 

While palladium carboxylates generally decompose in a CO atmoshere to give metal, the compounds [Pd(02CR)(C0)]-nRC02H (n = 0, 0.5 R = Me, CDs, Et or Ph) have been prepared from the corresponding Pd acetate in carboxylic acid-benzene solution. A crystallographic study on the acetate complex showed it to have the tetrameric structure (20). The compound consists of two dimeric palladium(I) units linked by acetate bridges. 

Much interesting work has been done in the last ten years on the bridging of pyrrole and piperidine rings. Early in their work on this subject Clemo and Metcalfe (1937) prepared quinuclidine (V) by the reduction of 3-ketoquinuclidine (IV), the latter resulting from the hydrolysis and decarboxylation of the product (III) of a Dieckmann internal alkylation, applied to ethyl piperidine-l-acetate-4-carboxylate (II), itself made by condensing ethyl piperidine-4-carboxylate (I) with ethyl chloroacetate. 

---