M.P. Hogerheide

Intramolecular Coordination in Group 3 and lanthanide Chemistry: An overview

Abstract The presence of potentially intramolecularly coordinating substituents in ligands can be an attractive alternative to steric bulk as an approach to stabilizing monomeric, solvent-free complexes of Lewis-acidic metal complexes. In addition, intramolecular coordination has proven to be a useful tool for the preparation of well-defined mixed-metal complexes. This paper gives an overview of the various types of ligands containing intramolecularly coordinating substituents that have been used in complexes with Group 3 and lanthanide metals. Emphasis is put on the synthesis of such complexes and on an analysis of the intramolecular coordination present. Their (potential) applications as catalysts in organic transformations and as precursors for lanthanide-oxide-containing ceramics are described.

Synthesis and structural studies of phenyl(iodo)- and methyl(phenyl)palladium(II) complexes of bidentate nitrogen donor ligands

Phenylpalladium(I1) complexes of the type PdIPh(N-N), with N-N = N,N,N’,N’-tetramethylethylenediamine (tmeda) or 2,2’-bipyridyl (bpy), can be conveniently prepared in 70-95% yield by oxidative addition of iodobenxene to bis(dibenzylideneacetone)palladium(0) in the presence of the appropriate nitrogen donor ligand. The bromo analogues were obtained in only S-12% yield in this way. The complex PdIPh(tmeda) (la) reacts readily with MeLi to give PdMePh(tmeda) (3) in 88% yield, whereas PdIPh(bpy) (la) gives PdMePh(bpy) (4) and PdMe,(bpy) in varying ratios. The formation of PdMe,(bpy) was found to result from the synergistic action of lithium iodide and methyllithium. Pure PdMePh(bpy) (4) was obtained in 82% yield via ligand-exchange from PdMePh(tmeda) (3). The crystal structures of PdIPh(N-N) (la, 2a) and PdMePh(N-N) (3, 4) complexes were determined by X-ray diffraction studies. The results show that the phenyl group is always oriented perpendicular to the coordination plane aroutd palladium, with the largest deviation found for 3 (14.3(2)“). The Pd-N bond distances in the tmeda complexes (2.127(6)-2.210(3) A) are larger than those in the bpy-coordinated complexes (2.870(8)-2.144f8) A). Similarly, the Pd-CfMe) bond distances (2.5703(8) and 2.575(l) & are larger than the Pd-C(Ph) bond distances (1.985(3)-1.996tlO) A)>.

BISPHENOLATE IRON(II) COMPLEXES WITH INTRAMOLECULARLY COORDINATING NITROGEN LEWIS BASES

The synthesis and characterisation of a novel Fe(II) bisphenolate complex [Fe(OC6H4CH2NMe2-2)2]2 (1) from [Na(OC6H4CH2NMe2-2)] and anhydrous FeCl2 is reported. The solid state structure has been elucidated by single crystal X-ray analysis and shows a dimeric structure with two bridging and two terminal phenolate ligands. Compound 1 reacts with pyridine to form the adduct [Fe(OC6H4CH2NMe2-2)2(py)2 ]( 2). Similarly, 2 equiv. of [Na(OC6H2(CH2NMe2)2-2,6-Me-4)] were reacted with FeCl2 and the thus in situ prepared ‘[Fe(OC6H2(CH2NMe2)2-2,6-Me-4)2]n ’( 3) was reacted with pyridine to form the adduct [Fe(OC6H2(CH2NMe2)2-2,6-Me-4)2(pyr)2 ]( 4). Compound 4 was characterised by single crystal X-ray analysis. Attempts to use these compounds as catalysts in the oxidation of cyclohexane with t-butylhydroperoxide (cat.:C6H12:t-BuOOH 1:1000:100) resulted in the direct formation of brown coloured products, probably as a result of irreversible oxidation of 1, 2, 3 and 4, respectively. No cyclohexanol or cyclohexanone was formed.

The first lithium phenolate with a trinuclear structure and the tetranuclear product of 1 : 1 addition of lithium iodide; X-ray structures of [LiOAr]3 and [Li2(OAr)I]2[OAr = OC6H2(CH2NMe2)2-2,6-Me-4]

Reaction of 2,6-bis[(dimethylamino)methyl]-4-methylphenol with n-butyllithium affords quantitatively [LiOAr]3[OAr = OC6H2(CH2NMe2)2-2,6-Me-4]1, which has an unprecedented trinuclear structure both in solution (cryoscopy in C6H6) and in the solid state (X-ray); 1 reacts selectively with Lil to form the adduct [Li2(OAr)l]22 which has a tetranuclear structure (X-ray).