Activation of C–H and C–Br bonds in cyclopalladation reactions of Schiff base ligands: Influence of the benzylidene ring substituents

Reaction of Pd(AcO)2 with the Schiff base ligands 2-Br-4,5-(OCH2O)C6H2C(H)N(Cy) (a) and 4,5-(OCH2CH2)C6H3C(H)N(Cy) (b) leads to the cyclometallated compounds [Pd{2-Br-4,5-(OCH2O)C6HC(H)N(Cy)-C6,N}(μ-O2CMe)]2 (1a) and [Pd{4,5-(OCH2CH2)C6H2C(H)N(Cy)-C6,N}(μ-O2CMe)]2 (1b), respectively, via C–H activation. Treatment of a with Pd2(dba)3 gave [Pd{4,5-(OCH2O)C6H2C(H)N(Cy)-C2,N}(μ-Br)]2 (6a), via C–Br activation. The metathesis reaction of 1a and 1b with aqueous sodium chloride gave the corresponding cyclopalladated dimers with bridging chloride ligands, 2a and 2b, respectively. Treatment of the halogen-bridged compounds with tertiary tri- and diphosphines in the appropriate molar ratio gave the mono and dinuclear compounds 3a–5a, 7a–9a and 3b–5b. The structure of compounds 3a, 4a, 5a, 8a, 2b, 3b and 5b has been determined by X-ray diffraction analysis.

Graphical abstractCyclometallated compounds may be synthesized by activation of C–H or C–Br bonds as determined by the differing palladium reagents, to give acetato- or bromo-bridged dinuclear species.Figure optionsDownload full-size imageDownload as PowerPoint slide