Cyclometallated complexes derived from pyrimidin- and pyridazinehydrazones: Structural evidence of intermolecular “chelate metal ring” π–π interactions

Reaction of 3,4-(Me)2C6H3C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2] (a) and 3,4-(Me)2C6H3C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2) (b) with palladium(II) acetate gave the mononuclear cyclometallated complexes [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2]}(OAc)] (1a) and [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2)}(OAc)] (1b) with the ligand as terdentate [C,N,N]. Treatment of a and b with Li2[PdCl4] and sodium acetate in methanol at room temperature yielded the mononuclear cyclometallated complexes [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2]}(Cl)] (2a) and [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2)}(Cl)] (2b), respectively. Recrystallization of 2b from a dimethylsulfoxide solution gave [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(4′-ClC4H2N2)}][(CH3)2Sdouble bond; length as m-dashO] after deprotonation of the hydrazine nitrogen. The reaction of 2a and 2b with silver trifluoromethanesulfonate and triphenylphosphine, yielded [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2]}-(PPh3)][CF3SO3] (3a) and [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2)}(PPh3)]-[CF3SO3] (3b) with the phosphine ligand occupying the vacant coordination position after chlorine abstraction; these were deprotonated at the hydrazine nitrogen after treatment with sodium acetate. Reaction of 2a with Ph2P(CH2)2AsPh2 (arphos), after AgCl removal gave mononuclear complex Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2]}(Ph2P(CH2)2AsPh2)][ClO4] (5a) with a non-coordinated As atom. Reaction of 2a and 2b with a Ag(I) salt and the tertiary diphosphine Ph2P(CH2)4PPh2 (dppb) in 2:1 molar ratio gave the dinuclear complexes [{Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2]}}2(μ-Ph2P(CH2)4PPh2)][CF3SO3]2 (6a) and [{Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2)}}2(μ-Ph2P(CH2)4PPh2)][ClO4]2 (6b) with the diphosphine as a bridging ligand. Similarly, treatment of 1b with silver triflate followed by reaction with the tertiary triphosphine (Ph2PCH2CH2)2PPh (triphos), in a 3:1 molar ratio, gave the new trinuclear complex [{Pd[3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2)]}3{μ3-(Ph2PCH2CH2)2PPh}][CF3SO3]3 (8b). However, reaction of 2a and 2b with (triphos), in 1:1 molar ratio gave the mononuclear complexes [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)[3′-(CF3)C4H2N2]}{(Ph2PCH2CH2)2PPh-P,P,P}][ClO4] (7a) and [Pd{3,4-(Me)2C6H2C(Me)double bond; length as m-dashNN(H)(4′-ClC4H2N2)}-{(Ph2PCH2CH2)2PPh-P,P,P}][ClO4] (7b) with a is five-coordinated palladium. The crystal structures of 2b, 3a, 3b, 7a and 7a have been determined by X-ray crystallography and they show π–π interactions between the metallacycle and the heterocyclic pyrimidine or pyridazine rings, which controls the crystal packing.