The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.

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1) in which the imine acts as a bidentate [N,NЈ] 2) has been obtained by refluxing a methanol solution of complex 1 in the presence of base; both complexes 1 and 2 have been characterized crystallographically. The cyclometallation process has been studied kinetically at variable temperature and pressure as a function of the base added in methanol and ethanol solutions. In all cases, the actual C-H bond activation is preceded by the Z to E isomerization of the imine; detection of this species by proton NMR has also been achieved. The kinetic, thermal and baric activation parameters associated with the two processes are indicative of a different reaction mechanism operating for the reactions when the "external" base added (NaCH 3 CO 2 ) can, in fact, react with the starting material to form a new acetato complex which allows for the reactions to be intramolecular.

The cyclometalation reactions of benzylidenebenzylamines, -anilines, and -propylamine with palladium acetate have been studied in toluene solution. The cyclometalated compounds are formed via C−H electrophilic bond activation to produce different types of metallacycles, depending upon the polyfunctional nature of the ligand selected. If a five-membered endo metallacycle is possible, it is formed via aromatic C−H bond activation. Formation of a five-membered exo metallacycle only takes place when endo cyclometalation requires the formation of a six-membered compound via aliphatic C−H bond activation or when the steric hindrance affects the planarity of the imine in an important way. The activation of aliphatic C−H bonds has been achieved for endo six-membered metallacycles only when the alternative aromatic C−H bond activation would produce a four-membered exo compound; no activation of aliphatic C−H bonds to form exo five-membered complexes has been observed. The reactions have been monitored kinetically at different temperatures and pressures in order to establish the mechanism through which these spontaneous reactions occur. Three different sets of activation parameters are apparent from the results obtained:  those related to the benzylamines and propylamine (ΔH ⧧ = +45/+67 kJ mol-1, ΔS ⧧ = −100/−180 J K-1 mol-1, ΔV ⧧ = −11/−17 cm3 mol-1), those related to the aniline derivatives (ΔH ⧧ = +66/+75 kJ mol-1, ΔS ⧧ = −96/−123 J K-1 mol-1, ΔV ⧧ = −21/−25 cm3 mol-1), and finally those related to the imines producing aliphatic bond activation (ΔH ⧧ = +48/+49 kJ mol-1, ΔS ⧧ = −167/−177 J K-1 mol-1, ΔV ⧧ = −20/−24 cm3 mol-1). The results are interpreted as the formation of a highly ordered four-center transition state, involving the C−H and Pd−O(acetato) bonds, which is found to be very sensitive to the flexibility and steric hindrance of the imine ligands and very insensitive to electronic changes of the C−H bonds.

shows a strong bias to 6-membered lactams over the 5-membered analogues, which can be explained by a greater reactivity of the six-membered palladacycles.3