Synthesis and characterization of mono- and di-cyclometallated compounds of symmetric and asymmetric azines with palladium(II) and manganese(I). X-Ray crystal structure of [Mn(C6H4CHN–NCHPh)(CO)4]

Abstract

The reaction of symmetric benzalazines, (p-RC₆H₄CHN–)₂(R = NO₂, Cl, H, or NMe₂), with Pd(O₂CMe)₂ gives mono- or di-metallated compounds, [{[graphic omitted]–NCHC₆H₄R-p)(O₂CMe)}₂](R = Cl or H) or [{[graphic omitted]–)(O₂CMe)}_n](R = NO₂, Cl, H, or NMe₂), depending on the amounts of reactants used. The analogous reactions with [MnMe(CO)₅] lead also to the formation of mono- or di-metallated compounds, [[graphic omitted]–NCHC₆H₄R-p)(CO)₄] or [{M[graphic omitted]–)(CO)₄}₂](R = H or NMe₂). Equimolar amounts of asymmetric benzalazines, p-R¹C₆H₄CHN–NCHC₆H₄R²-p(R¹= H, R²= NO₂; R¹= H, R²= Cl; R¹= NMe₂, R²= NO₂), and Pd(O₂CMe)₂ yield monometallated compounds in which the electron-rich ring has been preferably metallated. With PdCl₂, only the dimetallated compound [{ClP[graphic omitted]–[graphic omitted]dCl}_n] is obtained. No cyclomanganated compound is obtained by reaction of p-O₂NC₆H₄CHN–NCHPh and [MnMe(CO)₅]. The mixed-metal cyclometallated compounds [{Cl[graphic omitted]–[graphic omitted]tCl}_n](R = H or Cl) are obtained from monocyclopalladated [{[graphic omitted]–NCHC₆H₄R-p)(O₂CMe)}₂] and PtCl₄^2–. These comparative studies of palladation and manganation show that the mechanisms proposed for the metallation of azobenzenes are not entirely applicable to benzalazines. The polymeric and dimeric cyclopalladated compounds were converted into mononuclear species by action of PEt₃ for an easy characterization. Structures for the new compounds are assigned on the basis of i.r. and n.m.r. (¹H, ¹³C, ³¹P) spectra. The molecular structure of [M[graphic omitted]–NCHPh)(CO)₄] has been determined by a single-crystal X-ray structural analysis. The crystals are monoclinic, space group C2/c, with a= 20.591 (3), b= 20.517(3), c= 12.466(2)Å, β= 140.78(2)°, Z= 8; R= 0.059 for 1 896 observed reflections. The manganese atom is co-ordinated in a distorted octahedral configuration, to four carbonyl groups and to the chelating ligand.