Reactivity of tetranuclear complexes of Pd(II) with potentially homo- and heterobidentate ligands

Reaction of the cyclometallated compounds [Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)-5-RC6H3]}]4 (1a: R = H, 1b: R = tBu) with the phosphine PPh2[2-(COH)C6H4], in a complex/phosphine 1:4 molar ratio gave the mononuclear cyclometallated complexes [{Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)-5-RC6H3}}{PPh2[2-(HOC)C6H4]}] (2a: R = H; 2b: R = tBu), upon cleavage of the tetranuclear structure. Treatment of complex 1a with the diarsine AsPh2(CH2)2Ph2As (dppae) in a 1:2 or 1:4 molar ratio only yielded the dinuclear compound [{Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)C6H4]}}2{μ-AsPh2(CH2)2Ph2As}] (3a), regardless the molar ratio used. Reaction of the cyclometallated tetramers with Ph2P(CH2)2Ph2As (arphos) in a 1:4 molar ratio gave the mononuclear cyclometallated complexes [Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)C6H4]}{PPh2(CH2)2Ph2As-P}] (4a) and [Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)-5-tBuC6H3]}{PPh2(CH2)2Ph2As-P}] (4b), with the P, As ligand coordinated through the phosphorus atom, as air-stable solids. Treatment of 1a with arphos in a 1:2 molar ratio gave the dinuclear complex [{Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)C6H4]}}2{μ-PPh2(CH2)2Ph2As}] (5a). Reaction of 1b with the diphosphine Ph2P(C6H4)O(C6H4)PPh2 gave the dinuclear compound [{Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)-tBuC6H3]}}2{μ-PPh2(C6H4)O(C6H4)Ph2P}] (6b) for all the complex 1b/phosphine molar ratios tested. Reaction of the cyclometallated tetramer 1a with PPh2[4-(NMe2)C6H4] (in 1:2 or 1:4 molar ratio) produced the mononuclear cyclometallated complex [Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)C6H4]}{PPh2[4-(NMe2)C6H4]}] (7a) as an air-stable solid.

Schiff base ligands derived from 2-aminophenols bind tightly to the metal centre yielding cyclometallated palladium(II) species, and leaving only one coordination site available for further bonding to group 15 donor atom ligands.Figure optionsDownload as PowerPoint slide