Dimetalated Crown Ether Schiff Base Palladacycles. Influence of the Carbon Chain Length on the Coordination Mode of Bidentate Phosphines. Crystal and Molecular Structure of the Novel Complex [Pd₂{1,4-[C(H)N{9,10-(C₈H₁₆O₅)C₆H₃}]<sub>

Reaction of the Schiff base ligand 1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H4 (a), derived from terephthalaldehyde and 4′-aminobenzo-15-crown-5, with Pd(OAc)2 in chloroform at 50 °C for 96 h, gave the polymeric compound [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5,N,N′}(μ-O2CMe)2]n (1a) after double C−H activation at the C2 and C5 phenyl carbons. The metathesis reaction of 1a with saturated solutions of NtBu4Cl or NtBu4Br gave [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5,N,N′}(μ-Cl)2]n (2a) and [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5,N,N′}(μ-Br)2]n (3a), respectively, with exchange of the acetate group by a chloride or bromine ligand, also respectively, which likewise adopt polymeric arrangements. Further reaction of 2a with thallium acetylacetonate gave the dinuclear complex [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5,N,N′}{MeC(O)CH-C(O)Me-O,O′}2] (4a), whereas treatment of 2a with monophosphines in a 1:1 molar ratio resulted in splitting of the polymer and yielded the dinuclear complexes [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5,N,N′}(Cl)2(L)2] (5a, L = PPh3; 6a, L = P(p-MeOC6H4)3). The reactions of 2a with diphosphines were influenced by the length of the alkyl chain binding the two phosphorus atoms and the relative palladium atom/diphosphine molar ratio. Reaction of 2a with dppm in a 2:1 ratio gave the tetranuclear compound [{Pd2[1,4-{C(H)N[9,10-(C8H16O5)C6H3]}2C6H2-C2,C5,N,N′](Cl)2}2(μ-Ph2PCH2P-Ph2)2] (7a) with the diphosphine in a bridging mode. However, treatment of 2a with dppm or dppe in a 1:1 ratio gave the dinuclear complexes [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5,N,N′}(Ph2PRPh2-P,P′)2][Cl]2 (8a, R = CH2; 9a, R = (CH2)2, respectively) with two chelating phosphines. With the longer chain diphosphines Ph2P(CH2)nPPh2 (n = 4, dppb; n = 5, dpppe; n = 6, dpph) in a 1:1 palladium/diphosphine molar ratio the dinuclear compounds [Pd2{1,4-[C(H)N{9,10-(C8H16O5)C6H3}]2C6H2-C2,C5}(Cl)2{μ-Ph2P(CH2)nPPh2}2] (10a, n = 4; 11a, n = 5; 12a, n = 6) were obtained, with two diphosphines intramolecularly bridging both palladium atoms. The molecular structures of compounds 5a, and 11a have been determined by X-ray diffraction analysis.