Sterically controlled reactivity of palladium(ii) tetranuclear cyclometallated complexes. Crystal and molecular structure of the novel tetranuclear compound [Pd2{1,3-[C(H)NCH2C4H7O]2C6H2}(μ-Cl)(Cl)(PPh3)]2

Abstract

The reaction of the Schiff base ligands 1,3-[CN(H)CH₂C₄H₇O]₂C₆H₄ (1) and 1,4-[CN(H)CH₂C₄H₇O]₂C₆H₄ (14) with palladium(II) acetate in toluene gave the acetato-bridged cyclometallated compounds [Pd₂{1,3-[C(H)NCH₂C₄H₇O]₂C₆H₂}(μ-AcO)₂]₂ (2) and [(μ-AcO)Pd{1,4-[C(H)NCH₂C₄H₇O]₂C₆H₂}Pd(μ-AcO)]_n (15). Reaction of 2 and 15 with aqueous sodium chloride gave the chloro-bridged cyclometallated compounds [Pd₂{1,3-[C(H)NCH₂C₄H₇O]₂C₆H₂}(μ-Cl)₂]₂ (3) and [(μ-Cl)Pd{1,4-[C(H)NCH₂C₄H₇O]₂C₆H₂}Pd(μ-Cl)]_n (16), respectively, after a metathesis reaction. Reaction of 3 with triphenylphosphine in a 1∶2 molar ratio gave the tetranuclear complex [Pd₂{1,3-[C(H)NCH₂C₄H₇O]₂C₆H₂}(μ-Cl)(Cl)(PPh₃)]₂ (4), where only one of the bridging PdCl₂Pd moieties was cleaved, and which was characterized by X-ray crystal structure analysis. However, reaction of 16 with PPh₃ gave the dinuclear complex [(PPh₃)(Cl)Pd{1,4-[C(H)NCH₂C₄H₇O]₂C₆H₂}Pd(PPh₃)(Cl)] (17) after a full bridge-splitting reaction. Similarly, treatment of 3 with PMe₂Ph, pyridine and thallium acetylacetonate produced the dinuclear complexes 5, 6 and 7, respectively. Treatment of 4 with pyridine in a 1∶2 molar ratio, and with 4,4′-dipyridyl in an 1∶1 molar ratio, gave the di- and tetranuclear complexes 12 and 13, respectively. Reaction of 3 with the tertiary diphosphine cis-Ph₂PCHCHPPh₂ in a 1∶2 molar ratio yielded the tetranuclear complex [Pd₂{1,3-[C(H)NCH₂C₄H₇O]₂C₆H₂}(μ-Cl)(Ph₂PCHCHPPh₂-P,P)][Cl]₂ (8) after selective splitting of one of the PdCl₂Pd bridging moieties. However, reaction of 3 with cis-Ph₂PCHCHPPh₂ and Ph₂P(CH₂)₂PPh₂ in 1∶4 molar ratios gave the dinuclear complexes 9 and 10, respectively. Reaction of 3 with the diphosphine Ph₂PC₅H₄FeC₅H₄PPh₂ in a 1∶2 molar ratio yielded the trinuclear complex [Pd₂{1,3-[C(H)NCH₂C₄H₇O]₂C₆H₂}(μ-Ph₂PC₅H₄FeC₅H₄PPh₂)] (11), with the diphosphine bridging the two palladium atoms of the dicyclometallated moiety.