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.

Graphical abstractSchiff 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 full-size imageDownload as PowerPoint slide