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

The reaction of the Schiff base ligands 1,3-[C=N(H)CH2C4H7O](2)C6H4 (1) and 1,4-[C=N(H)CH2C4H7O](2)C6H4 (14) with palladium(II) acetate in toluene gave the acetato-bridged cyclometallated compounds [Pd-2{1,3-[C(H)=NCH2C4H7O](2)C6H2} (mu-AcO)(2)](2) (2) and [(mu-AcO)Pd{1,4-[C(H)=NCH2C4H7O](2)C6H2} Pd(mu-AcO)](n) (15). Reaction of 2 and 15 with aqueous sodium chloride gave the chloro-bridged cyclometallated compounds [Pd-2{1,3-[C(H)=NCH2C4H7O](2)C6H2} (mu-Cl)(2)](2) (3) and [(mu-Cl)Pd{1,4-[C(H)=NCH2C4H7O](2)C6H2}Pd(mu-Cl)](n) (16), respectively, after a metathesis reaction. Reaction of 3 with triphenylphosphine in a 1:2 molar ratio gave the tetranuclear complex [Pd-2{1,3-[C(H)=NCH2C4H7O](2)C6H2}(mu-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](2)C6H2}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-Ph2PCH=CHPPh2 in a 1:2 molar ratio yielded the tetranuclear complex [Pd-2{1,3-[C(H)=NCH2C4H7O](2)C6H2}(mu-Cl)(Ph2PCH=CHPPh2-P,P)] [Cl](2) (8) after selective splitting of one of the PdCl2Pd bridging moieties. However, reaction of 3 with cis-Ph2PCH=CHPPh2 and Ph2P(CH2)(2) PPh2 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 [Pd-2{1,3-[C(H)=NCH2C4H7O](2)C6H2} (mu-Ph2PC5H4FeC5H4PPh2)] (11), with the diphosphine bridging the two palladium atoms of the dicyclometallated moiety.