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Title: Chemistry of the lanthanides with pyrazolylborate ligands
Author: Maunder, Graham
ISNI:       0000 0001 3621 6768
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1996
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In the work presented in this thesis we have established the utility of the substituted tris-(pyrazolyl)borates as ancillary ligands for the lanthanides. Compounds of formula (TpME2)2LnOTf have been synthesized. For the larger lanthanides, the triflate group is coordinated to the metal, [(TpME2)2LnOTf] (Ln = La and Nd), whilst for the smaller elements ion pair complexes are formed, [(Tp ME2)2Ln]+[OTf]- (Ln = Y, Dy and Yb); the structures of the Nd and Yb complexes have been determined. For lanthanides of intermediate ionic radius (Ln = Sm), there are good indications that these two structural forms coexist in CDCI3. Attempts to derivatise these complexes were not successful. Reduction of (TpME2)2LnOTf (Ln = Sm, Eu and Yb) gave [(TpME2)2Ln]; 1 the related [(Tp ME2-4-Et)2Ln] complexes were also prepared. [(TpME2) 2Ln] (Ln = Eu and Yb) were characterised by X-ray crystallography and found to be isomorphous. Initial reactivity studies showed that [(Tp ME2)2Ln] and [(TpME2-4-Et)2Ln] were significantly less reactive than the decamethyllanthanocenes. They were found to react with TCNQ and TCNE and in the case of the Yb complexes, the products were simple charge transfer salts; the X-ray crystal structure of [(TpME2) 2Yb]+[TCNE]- was determined. The hydrolysis product [(TpME2)Sm{(pzMe2)2B(H)([μ-O)}]2.(THF)2 was also characterised crystallographically. Reaction of [(TpME2-4-Et)2Ln] with NO gave nitrito complexes and the structure of [(TpME2-4-Et)2Sm(η2-O2N)] was determined by X-ray crystallography. It was not possible to isolate stable half sandwich complexes of the divalent lanthanides with these 3-Me substituted tris-(pyrazolyl) borates. In contrast, the stable monomeric complexes [Tp3-t-Bu-5-MeSml(THF)2] .(Et2O)0.5 and [Tp3-t-Bu-5iMeYbl(THF)] were prepared and characterised crystallographically.3 These compounds could be desolvated, and pyridine and isonitrile adducts were prepared; the X-ray crystal structures of [Tp3-t-Bu-5-MeLnl(3,5-Me2py)2] and [Tp3-t-Bu-5-MeLnl(CNBut)] have been determined. [Tp3-t-Bu-5-MeYbBH4(THF)] was prepared by reaction of [Tp3-t-Bu-5-MeYbl(THF)] with NaBH4. This compound decomposes on heating to give at least two new products, the nature of which remains to be established.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic chemistry