New synthesis and thermal studies of palladacycloalkanes and their precursors

A series of new palladacycloalkanes of formula cis-[PdL2(CH2)n] (9. n = 6, L = PPh3; 10. n = 6, L2 = dppe; 11. n = 8, L = PPh3; 12. n = 8, L2 = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-[PdL2((CH2)nCHdouble bond; length as m-dashCH2)2] (1. n = 2, L = PPh3, 2. n = 2, L2 = dppe, 3. n = 3, L = PPh3, 4. n = 3, L2 = dppe) were allowed to react with Grubb’s 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL2(CH2)nCHdouble bond; length as m-dashCH(CH2)n] (5. n = 2, L = PPh3, 6. n = 2, L2 = dppe, 7. n = 3, L = PPh3, 8. n = 3, L2 = dppe), which were then hydrogenated to the palladacycloalkanes, 9–12. In the second route, the di-Grignard reagents BrMg(CH2)nMgBr (n = 6, 8) were reacted with the palladium complex [PdCl2(COD)] followed by immediate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9–12 and the main organic products shown to be 1-alkenes and 2-alkenes.