Cyclometallation of phenylhydrazones: Synthesis, reactivity, crystal structure analysis and novel trinuclear palladium(II) cyclometallated compounds with [C, N, N′] terdentate ligands

Abstract

Reaction of the ligand C 6H 5N(H)N CMe(C 5H 4N) ( a) with palladium(II) acetate in toluene gave the mononuclear cyclometallated complex [Pd{C 6H 4N(H)N CMe(C 5H 4N)}(AcO)] ( 1a). Reaction of 1a with sodium chloride gave the analogous chlorine compound [Pd{C 6H 4N(H)N CMe(C 5H 4N)}(Cl)] ( 3a) which could also be prepared by reaction of a with lithium tetrachloropalladate and sodium acetate in methanol for 48 h; whereas shorter reaction times afforded the non-cyclometallated complex [Pd{C 6H 5N(H)N CMe(C 5H 4N)}(Cl) 2] ( 2a). Reaction of the ligand 2-ClC 6H 4N(H)N CMe(C 5H 4N) · HCl ( b), with palladium(II) acetate, or with lithium tetrachloropalladate and sodium acetate, yielded the cyclometallated complex [Pd2-ClC 6H 3N(H)N CMe(C 5H 4N)(Cl)] ( 1b). Treatment of 3a and 1b with silver trifluoromethanesulphonate (triflate) and triphenylphosphine in acetone gave the mononuclear complexes [Pd{2-RC 6H n N(H)N CMe(C 5H 4N)}(PPh 3)][CF 3SO 3], (R = H, n = 4, 4a; R = Cl, n = 3, 2b) with the ligand as C,N,N′ terdentate and substitution of chlorine by triphenylphosphine. Reaction of 3a and 1b with silver triflate and the tertiary diphosphine Ph 2P(CH 2) 4PPh 2 (dppb) in a 2:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-RC 6H 3N(H)N CMe(C 5H 4N)]} 2(μ-Ph 2P(CH 2) 4PPh 2)][CF 3SO 3] 2 (R = H, 5a; R = Cl, 3b) with a μ 2-diphosphine bridging ligand. Similarly, treatment of 3a and 1b with silver triflate and the tertiary triphosphines MeC(CH 2PPh 2) 3 (tripod) and (Ph 2PCH 2CH 2) 2PPh (triphos), in 3:1 molar ratio, gave the novel trinuclear complexes [{Pd[C 6H 4N(H)N CMe(C 5H 4N)]} 3{μ 3-MeC(CH 2Ph 2) 3}][CF 3SO 3] 3 ( 6a) and [{Pd[2-ClC 6H 3N(H)N CMe(C 5H 4N)]} 3{μ 3-(PPh 2CH 2CH 2) 2PPh}][CF 3SO 3] 3 ( 4b) regioselectively, with the phosphine as a μ 3-bridging ligand. When the reaction between 3a and triphos was carried out in 1:1 molar ratio the mononuclear complex [Pd{C 6H 4N(H)N CMe(C 5H 4N)}{(PPh 2CH 2CH 2) 2PPh-P,P,P}][ClO 4] ( 7a) was obtained. The crystal structures of 2b, 3a and 4a have been determined by X-ray crystallography.