Synthesis, structural characterization, and volatility evaluation of zirconium and hafnium amidate complexes

Abstract

Treatment of tetrakis(dimethylamido)zirconium or tetrakis(dimethylamido)hafnium with four equivalents of N-tert-butylacetamide, N-isopropylisobutyramide, N-isopropylacetamide, N-methylacetamide, or N-tert-butylformamide in refluxing toluene, followed by sublimation of the crude products at 105–125 °C/0.05 Torr, afforded tetrakis(N-tert-butylacetamido)zirconium (81%), tetrakis(N-isopropylisobutyramido)zirconium (87%), tetrakis(N-isopropylacetamido)zirconium (51%), tetrakis(N-tert-butylacetamido)hafnium (83%), tetrakis(N-isopropyliso-butyramido)hafnium (79%), tetrakis(N-isopropylacetamido)hafnium (67%), tetrakis(N-methylacetamido)zirconium (5%), and tetrakis(N-tert-butylformamido)zirconium (1%) as colorless crystalline solids. The structural assignments for the new complexes were based upon spectral and analytical data and by X-ray crystal structure determinations for tetrakis(N-tert-butylacetamido)zirconium, tetrakis(N-isopropylacetamido)zirconium, tetrakis(N-isopropylacetamido)hafnium, tetrakis(N-methylacetamido)zirconium, and tetrakis(N-tert-butylformamido)zirconium. These complexes are monomeric in the solid state, with eight-coordinate metal centers surrounded by four κ2-N,O-amidate ligands. Six of the eight new complexes undergo sublimation on a preparative scale from 130 to 140 °C at 0.05 Torr, with 84.5–95.8% sublimed recoveries and 0.68–3.06% nonvolatile residues. Tetrakis(N-methylacetamido)zirconium and tetrakis(N-tert-butylformamido)zirconium decompose extensively upon attempted sublimation. Solid state decomposition temperatures for the zirconium complexes range between 218 and 335 °C and 290–360 °C for the hafnium complexes. Tetrakis(N-isopropylisobutyramido)zirconium, tetrakis(N-tert-butylacetamido)hafnium, and tetrakis(N-isopropylacetamido)hafnium exhibit the highest solid state decomposition temperatures in the series, possess good volatility, and have useful properties for chemical vapor deposition and atomic layer deposition precursors.