Cyclometallated complexes of palladium(II) with 1-methyl-2-phenylimidazole and tertiary diphosphines. Crystal and molecular structure of [{Pd[o-C6H4C=NC(H)=C(H) NMe]}(Ph2PCH(Me)PPh2-P,P)][PF6]

Article abstract of DOI:10.1016/S0022-328X(97)00387-2

Treatment of Pd(AcO)₂ with 1-methyl-2-phenylimidazole, and subsequent treatment with sodium chloride or sodium bromide gave the corresponding halide-bridged cyclometallated complexes [Pd{o-C₆H₄C=NC(H)=C(H)NMe}(μ-X)]₂ (2, X = Cl; 3, X = Br). Complexes 2 and 3 react with tertiary diphosphines in a 1:1 molar ratio to give dinuclear cyclometallated compounds with bridging diphosphine and halogen ligands [Pd{o-C₆H₄C=NC(H)=C(H)NMe}(μ-L-L)(μ-X)]X (4-9) or with only bridging diphosphine ligands [Pd{o-C₆H₄C=NC(H)=C(H)NMe}(μ-L-L)(X)₂] (10-17), [X = Cl, Br; L-L = Ph₂PCH₂PPh₂ (dppm), Ph₂PC(=CH₂)PPh₂ (vdpp), Ph₂PCH(CH₃)PPh₂ (1,1-dppe), trans-Ph₂P(CH=CH)PPh₂ (trans-dppe), Ph₂P(CH₂)₂PPh₂ (dppe), Ph₂P(CH₂)₃PPh₂ (dppp), Ph₂P(CH₂)₄PPh₂ (dppb), as appropriate]. When the reaction is carried out in a 1:2 molar ratio and in the presence of NH₄PF₆ or NaClO₄, mononuclear cyclometallated compounds with a chelating diphosphine ligand are obtained [Pd{o-C₆H₄C=NC(H)=C(H)NMe}(L-L-P,P)][Y] (18-27) [Y = PF₆, ClO₄; L-L = Ph₂PCH₂PPh₂ (dppm), Ph₂PC(=CH₂)PPh₂ (vdpp), Ph₂PCH(CH₃)PPh₂ (1,1-dppe), Ph₂PN(CH₃)PPh₂ (dppma), cis-Ph₂P(CH=CH)PPh₂ (cis-dppe), Ph₂P(CH₂)₂PPh₂ (dppe), Ph₂P(CH₂)PPh₂ (dppp), Ph₂P(CH₂)₄PPh₂ (dppb)]. Compounds 18-22 and 25-27 could also be obtained by reaction of complexes 4-17 with the appropriate diphosphine and NH₄PF₆ or NaClO₄. The diphosphines dppma and cis-dppe failed to behave as bridging ligands and only gave mononuclear compounds. The complexes were characterized by their elemental analysis (C, H, N) and by IR and ³¹P-{¹H} and ¹H NMR data. The X-ray crystal structure of complex 22 is described.