Novel structures of cyclometallated complexes of palladium(II) derived from terdentate ligands. Crystal and molecular structure of [Pd{C6H4C(H)NCH2CH2CH2NMe2}(X)] (X=Cl, Br, I)

Treatment of N-(2-chlorobenzylidene)-N,N-dimethyl-1,3-propanediamine (1) and N-(2-bromo-3,4-(MeO)2-benzylidene)-N,N-dimethyl-1,3-propanediamine (20) with tris(dibenzylideneacetone)dipalladium(0) in toluene gave the mononuclear cyclometallated complexes [Pd{C6H4C(H)NCH2CH2CH2NMe2}(Cl)] (2) and [Pd{3,4-(MeO)2C6H2C(H)NCH2CH2CH2NMe2}(Br)] (21), respectively, via oxidative addition reaction with the ligand as a C,N,N terdentate ligand. Reaction of 2 with sodium bromide or iodide in an acetone–water mixture gave the cyclometallated analogues of 2, [Pd{C6H4C(H)NCH2CH2CH2NMe2}(Br)] (3) and [Pd{C6H4C(H)NCH2CH2CH2NMe2}(I)] (4), by halogen exchange. The X-ray crystal structures of 2, 3 and 4 were determined and discussed. Treatment of 2, 3, 4 and 21 with tertiary monophosphines in acetone gave the mononuclear cyclometallated complexes [Pd{C6H4C(H)NCH2CH2CH2NMe2}(L)(X)] (6: L=PPh3, X=Cl; 7: L=PPh3, X=Br; 8: L=PPh3, X=I; 9: L=PMePh2, X=Cl; 10: L=PMe2Ph, X=Cl) and [Pd{3,4-(MeO)2C6H2C(H)NCH2CH2CH2NMe2}(L)(Br)] (22: L=PPh3; 23: L=PMePh2; 24: L=PMe2Ph). A fluxional behaviour due to an uncoordinated CH2CH2CH2NMe2 could be determined by variable temperature NMR spectroscopy. Treatment of 2, 3 and 4 with silver trifluoromethanesulfonate followed by reaction with triphenylphosphine gave the mononuclear complex [Pd{C6H4C(H)NCH2CH2CH2NMe2}(PPh3)][F3CSO3] (11) where the Pd–NMe2 bond was retained. Reaction of 2, 3 and 4 with ditertiary diphosphines in a cyclometallated complex–diphosphine 2:1 molar ratio gave the binuclear complexes [{Pd[C6H4C(H)NCH2CH2CH2NMe2](X)}2(μ-L–L)][L–L=PPh2(CH2)4PPh2(dppb) (13, X=Cl; 14, X=Br; 15, X=I; L–L=PPh2(CH2)5PPh2(dpppe): 16, X=Cl; 17, X=Br; 18, X=I) with palladium–NMe2 bond cleavage. Treatment of 2, 3 and 4 with ditertiary diphosphines, in a cyclometallated complex–diphosphine 2:1, molar ratio and AgSO3CF3 gave the binuclear cyclometallated complexes [{Pd[C6H4C(H)NCH2CH2CH2NMe2]}2(μ-L–L)][F3CSO3]2 (11: L–L=PPh2(CH2)4PPh2(dppb), X=Cl; 12: L–L=PPh2(CH2)5PPh2 (dpppe), X=Cl). Reaction of 2 with the ditertiary diphosphine cis-dppe in a cyclometallated complex–diphosphine 1:1 molar ratio followed by treatment with sodium perchlorate gave the mononuclear cyclometallated complex [Pd{C6H4C(H)NCH2CH2CH2NMe2}(cis-PPh2CHCHPPh2–P,P)][ClO4] (19).