Lanthanide complexes amides

Introducing a chiral center in the amide functionality renders all 32 potential isomers diastereomeric and thus discernable (in principle) by NMR spectroscopy. In practice, the lanthanide complexes formed (Eu, Gd and Tb) with macrocyclic monoamide tris(phosphinate) ligands bearing a chiral center on the amide group exist as only two non-interconverting diastereomers in a ratio of 2 1 and 4 1 for the a-phenylethyl and a-l-napthylethyl derivatives, respectively (DOTMP-MPMeA and DOTMP-MNaphMeA) [114]. The configuration at... 

Lanthanide complexes of mono- and tetra-amide /1-cyclodextrin derivatives of DOTA have been characterized [140]. The proton NMR spectra of the Eu3+ complexes in methanol-d, show that, while the tetra-amide complex occurs in solution exclusively as a C4-symmetry SAP structure, the mono-amide complex, with less than C4-symmetry, occurs predominantly as two SAP isomers (A/XXXX and Al8885), with the presence of a small amount of the twisted SAP isomer. Luminescence and relaxivity measurements confirm that the Eu3+, Tb3+ and Gd3+ complexes of the eight-coordinate mono-amide ligand possess one bound water molecule, while the tetra-amide complexes have q = 0. The relaxivity of the /LCD mono-amide Gd3+ complex is enhanced when non-covalently bound to a second Gd3+ complex bearing two phenyl moieties (MS-325, AngioMARK , EPIX/Mallinckrodt). 

Narita, H., Yaita, T., Tachimori, S. 1999. Extraction behavior for trivalent lanthanides with amides and EXAFS study of their complexes. In Solvent Extraction for the 21st Century. Proc ISEC 99, Barcelona, Spain, July 11-16, Cox, M., Hidalgo, M. Valiente,... 

It was shown that narrow-rim CMPO derivatives form stronger 1 1 lanthanide complexes than their wide-rim counterparts. However, lanthanide extraction results display a stronger extracting ability. This discrepancy can be explained by the fact that, contrary to the wide-rim CMPO calixarenes that form polymeric species, a part of less lipophilic monomeric narrow-rim CMPO calixarene piles up at the interface instead of being extracted, as predicted by Wipff for the extraction of strontium by mixed amide calixarenes (see Section 4.4.1.1). This assumption is all the more... 

Finally, 10 mol-% of the lanthanide perfluoroalkylsulfone amide complex Yb(N(S02C4F9)2)3 in QH5CF3 catalyzes both Friedel-Crafts acylation and the Diels-Alder reaction [26]. The high Lewis acidity of the metal complexes seems to be crucial. 

The central point in this consideration is the Ln-OH moiety, the preferred formation of which is considered to be a dilemma in organolanthanide chemistry. Organolanthanide compounds containing Ln-X a-bonds such as alkyls, amides and alkoxides readily hydrolyze when exposed to moist air, with the formation of the hydroxides. Lanthanide complexes with Ln-C linkages are considered to be oversensitive compounds [89]. Even ligands with lower pKa values than water, as exemplified by substituted phenol ligands, tend to hydrolyze in organic solvents because the insoluble hydroxides formed act as... 

Zhang, S., Kovacs, Z., Burgess, S., et al. (2001) DOTA-bis(amide) lanthanide complexes NMR evidence for differences in water-molecule exchange rates for coordination isomers. Chemistry - A European Journal, 1, 288-296. 

Synthetic routes for the preparation of lanthanide monoporphyrinate complexes with non-diketonate anionic axial ligands have been developed in recent years. Wong and coworkers developed a convenient synthetic route for the preparation of cationic lanthanide(III) monoporphyrinate complexes [Ln(porphyrin)(H20)3]Cl via the protonolysis of lanthanide(III) amide... 

A different mechanism again is involved in the hydroamination reaction catalyzed by lanthanide complexes, Cpff.nR which is applied to the cyclization of unsaturated amines. The mechanism involves the formation of a metal amide species from both the catalysts (by different routes), followed by the turnover —limiting intramolecular insertion of the alkene to give a cr-complex, from which the decomplexed cyclic amine is obtained after reaction with a second molecule of the unsaturated amine19,20,107. 

Phosphine Chalcogenides as Ligands. - The complexation of lanthanide and actinide ions by phosphine oxide ligands remains an active area, and a theoretical assessment of the coordination of phosphine oxides (and phosphate esters) by trivalent lanthanide ions has appeared." Trivalent lanthanide complexes of the functionalised enol phosphine oxide (265), (and a related phosphonate), have been describedComplexes of thorium(iv) with bis(di-phenylphosphino) ethane dioxide and bis(diphenylphosphinoyl)amide have also been characterised." Calixarene systems which bear phosphine oxide... 

---