PD2-CATALYZED CYCLO-COPOLYMERIZATION OF 1,5-HEXADIENE AND CO - REGIOSELECTIVITY OF OLEFIN INSERTION()

The cyclocopolymerization of 1,5-hexadiene and CO with Shell-type cata lyst systems comprising palladium(II) complexes in the presence of che lating phosphines yields soluble cyclocopolymers containing 5- and 6-m embered cyclic ketones. Cyclocopolymerization of 1,5-hexadiene and CO in the presence of Pd(OAc)(2), 1,3-bis(diphenylphosphino)propane (Dppp ), 1,4-naphthaquinone, and Ni(ClO4)2 .-6H(2)O in chloroform/methanol ( 100-20/1) afforded a soluble cyclocopolymer 2 containing both 5- and 6 membered ring ketones in the polymer backbone Cyclocopolymerization u nder similar conditions in the presence of 1,3-bis(diisopropylphosphin o)propane (Dipp) gave a soluble cyclocopolymer 3 containing only 6-mem bered rings. Epimerization of the 6-membered ring cyclocopolymer 3 wit h 4-(dimethylamino)-pyridine provided evidence for an initial prevaili ngly cis microstructure (ca. 3/1 cis/trans) for the 2,5-disubstituted cyclohexanone repeating units of the cyclopolymer. The regioselectivit y for insertion of 1,5-hexadiene into the Pd-acyl bonds was inferred f rom the nature of the ring formed in the cyclocopolymerization. The fo rmation of 5-membered cyclopentanone repeating units was interpreted a s a signature for an initial 2,1-insertion of 1,5-hexadiene; the forma tion of 6-membered cyclohexnanone rings was interpreted in terms of an initial 1,2-insertion of the 1,5-hexadiene.