Cyclopalladation of 1-tetralone (3,4-dihydronaphthalen-1-one) oximes

Abstract

Cyclopalladated complexes precipitate from methanolic Li₂[PdCl₄]–Na[O₂CMe] solutions containing 1-tetralone oxime, the 6-methoxy-analogue, and the 7-substituted derivatives, substituent R = CH₃–, CH₃CH₂–, MeO–, but reaction fails when R =(CH₃)₂CH–, (CH₃)₃C–, or –No₂. The oxime derivatives of methyl 12-methoxy-7-oxopodocarpa-8,11,13-trien-19-oate and methyl 7-oxopodocarpa-8,11,13-trien-19-oate readily metallate while the oxime of methyl 7-oxoabieta-8,11,13-trien-18-oate does not. Carbonylation of the cyclopalladated 1-tetralone oxime complexes in methanol gives the corresponding 8-methoxycarbonyl-1-tetralone oximes. Hydrogen-1 n.m.r. analysis of 1-tetralone oxime and Li₂[PdCl₄] solutions show [PdCl₂(oxime)₂] is not a reaction intermediate. At –76 °C co-ordinated oxime exhibits a downfield shift for H⁸, characteristic of above-plane geometry of the ligand, while at O °C an upfield shift relative to the free oxime suggests in-plane geometry. The intermediate is isolable in water giving cis-[PdCl₂(oxime)]·3H₂O which on redissolving gives the soluble cyclometallated species [PdCl-(CN-oxime)(S)](S = solvent) and HCl by an irreversible process. Dimerisation gives [{PdCl(CN-oxime)}₂] or the complex [PdCl(CN-oxime)L] in the presence of L (L = oxime or PPh₃).