Lanthanide borate complexation

Scheme 42 Reactivity of lanthanide amide complexes with organoaluminum or borate reagents...

The NIR emission intensity of the lanthanide porphyrinate complexes follows the trend Yb > Nd > Er. This agrees with observations on other luminescent lanthanide complexes and reflects the fact that the efficiency of nonradiative decay increases as the energy of the luminescent state decreases. The emission yields of the ternary lan-thanide(III) monoporphyrinate complexes with hydridotris(pyrazol-l-yl)borate or (cyclopen-tadienyl)tris(diethylphosphito)cobaltate as a co-ligand are generally higher than those of other Yb(III), Nd(III), and Er(III) complexes because the coordination environment provided by the porphyrinate in combination with the tripodal anion effectively shields the Ln + ion from interacting with solvent (C-H) vibrational modes that enhance the rate of nonradiative decay. 

The parent ligand tris(pyrazolyl)borate, [L4]-, forms 1 1 and 1 2 metakligand complexes [Ln(L4)(N03)2] and [Ln(L4)2]+ the molecular structure of the latter is shown in Fig. 6. In solution, dissociation of the nitrate anions in the former complex leave the lanthanide ion open to coordination by solvent molecules (47). Photophysical studies in water and methanol (48) confirm this use of the Horrocks equation... 

Reeves, Z. R. Mann, K. L. V. Jeffery, J. C. McCleverty, J. A. Ward, M. D. Barigelletti, F. Armaroli, N. Lanthanide complexes of a new sterically hindered potentially hexadentate podand ligand based on a tris(pyrazolyl)borate core crystal structures, solution structures and luminescence properties. J. Chem. Soc., Dalton Trans. 1999, 349-355. 

These complexes are the first examples of multifunctional catalysts and demonstrate impressively the opportunities that can reside with the as yet hardly investigated bimetallic catalysis. The concept described here is not limited to lanthanides but has been further extended to main group metals such as gallium [31] or aluminum [32]. In addition, this work should be an incentive for the investigation of other metal-binaphthyl complexes to find out whether polynuclear species play a role in catalytic processes there as well. For example, the preparation of ti-tanium-BINOL complexes takes place in the presence of alkali metals [molecular sieve ( )]. A leading contribution in this direction has been made by Kaufmann et al, as early as 1990 [33], It was proven that the reaction of (5)-la with monobromoborane dimethyl sulfide leads exclusively to a binuclear, propeller-like borate compound. This compound was found to catalyze the Diels-Alder reaction of cyclopentadiene and methacrolein with excellent exo-stereoselectivity and enantioselectivity in accordance with the empirical rule for carbonyl compounds which has been presented earlier. 

The lanthanide halides are usually bi(cyclopentadienyl) and related lanthanide complexes M is an alkali metal or silver, and A is an anionic transition metal carbonyl compound or tetraphenyl borate. The formation of the insoluble salt MX is a driving force for this reaction. 

Davies, G.M., Aarons, R. J., Motson, GR., et al. (2004) Structural and near-IR photophysical smdies on ternary lanthanide complexes containing poly(pyrazolyl)borate and 1,3-diketonate Ugands. Dalton Transactions, 1136. 

Lanthanide complexes with dihydrobis(benzimidazolyl)borate for which a seven-coordinate polymeric structure was proposed have been described by Khan and co-workers.171... 

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