Electrospray mass spectrometry of highly moisture-sensitive metal alkoxides

Abstract

Electrospray mass spectra of the metal alkoxides Zr(OEt) ₄ , Ti(OEt) ₄ , Al(OEt) ₃ and Si(OEt) ₄ and of Zr(OEt) ₄ after reaction with chelating agents have been recorded in dry ethanol. By adding sodium ethoxide to enhance the formation of ions, well resolved isotope patterns were obtained for each major peak, allowing identification of species. The dominant ions detected in the spectra of Zr(OEt) ₄ were [Zr _n (OEt) _4n+1 ] ^- (n=1–5). Minimal fragmentation was observed at low cone voltages, and the molecular complexity n of the dominant species agreed with the previously established polymeric nature of the alkoxides. Fragmentation of the polymeric Ti and Zr species at high cone voltages occurred by loss of neutral Ti(OEt) ₄ and Zr(OEt) ₄ . Complexation of Zr(OEt) ₄ with acetylacetone [CH ₃ COCH ₂ COCH ₃ ] (Hacac) yields the monomeric ions [Zr(OEt) _4-n (acac) _n ] ^- (n=1–3) as the dominant species. Hydrolysis and condensation products were observed for 3-sulfanylpropyltrimethoxysilane [HS(CH ₂ ) ₃ Si(OC ₂ H ₅ ) ₃ ] reacted with water. The reaction of Zr(OEt) ₄ with 3-sulfanylpropyltrimethoxysilane resulted in the detection of zirconium alkoxide–silane complexes containing Zr–O–Si links. ESMS is applicable to the study of transition-metal alkoxide compounds and solution species formed in reactions of these with chelating ligands. The results reveal further opportunities for development of metal alkoxide chemistry.