Rapid screening of reactions of rare-earth metal complexes through MALDI-TOF mass spectrometry

摘要

This thesis describes investigations into the applicability of inert atmosphere: matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique for rapid screening of reactions. Complexation reactions of lanthanide amide reagents Ln{N(SiMe₃ )2}₃ (where Ln = Sm, Gd, Ho, Yb, Y or La) with amine-bis(phenol) ligands ([O₂N₂t -Bu,Me H2, [O₂ N₂t -Bu H₂ and [O₂ NN't-Am ]H₂ ) were probed using anthracene as the matrix. This technique rapidly confirmed ligand coordination by showing excellent agreement between the experimental and theoretical isotope patterns. Spectra of isolated lanthanide amine-bis(phenolate) amido complexes are similar to those seen from small scale parallel reactions of metal amides and protonated ligands. Although in all cases molecular ion peaks were not observed, peaks for lanthanide arene complexes, [M + arene] + , formed in situ , were seen. The absence of these molecular ion peaks was due to difficulties in ionizing Ln³⁺ complexes by charge-transfer, and the low coordination number of the lanthanide ions led to laser-assisted arene complex formation. The mechanism of ionization in this study is proposed to involve adduct formation. -- The screening of the hydroamination-cyclization reaction of 5-phenyl-4-pentyne-1-amine potentially catalyzed by various lanthanide amine bis(phenolate) complexes was also studied. Characterization of the reaction mixtures from in situ hydroamination reactions showed changes in mass spectral patterns from the starting materials. Also, significant differences in the spectra of the mixtures containing lanthanide [O₂N₂] and [O₂N₂] complexes were observed. The aminoalkyne substrate is proposed to coordinate to the metal center of the lanthanide bearing [O₂N₂] complexes indicating potential precatalysts for hydroamination of aminoalkynes. These results demonstrate the utility of MALDI-TOF MS as a potential technique for rapid screening of reactions of paramagnetic and extremely moisture-sensitive metal complexes. Aspects of this work have been accepted for publication: Nduka Ikpo, Samantha M. Butt, Kayla L. Collins and Francesca M. Kerton*, Organometallics , om 2008-00453b, accepted for publication August 2008.