A Study of Ligand Coordination at Lanthanide and Group 4 Metal Centers by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Abstract

Reactions of lanthanide amide reagents Ln{N(SiMe3)2}3 (where Ln = Sm, Gd, Ho, or Yb) with amine-bis(phenol) ligands were probed using inert atmosphere matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) (anthracene matrix); the technique rapidly confirms ligand coordination, giving excellent agreement with theoretical isotope patterns for lanthanide(amine-phenolate) fragments. Spectra on 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 are not observed, peaks for lanthanide arene complexes, [M + arene]+•, formed in situ, are seen. The lack of molecular ion peak is due to difficulties in ionizing Ln3+ complexes by charge transfer. However, if Nujol is used to disperse the analyte and matrix prior to analysis rather than toluene, arene adducts are not observed. Similar phenol-derived ligands can be reacted with diamagnetic M(NMe2)4 (where M = Ti or Zr), and amine-phenolate complex formation is again confirmed easily by MALDI-TOF MS or LDI-TOF MS (no matrix). These complexes were also characterized by NMR spectroscopy and elemental analysis on isolated samples.