Synthesis, structural characterization, and properties of chromium(iii) complexes containing amidinato ligands and η2-pyrazolato, η2-1,2,4-triazolato, or η1-tetrazolato ligands

Abstract

Treatment of anhydrous chromium(III) chloride with 2 or 3 equivalents of 1,3-di-tert-butylacetamidinatolithium or 1,3-diisopropylacetamidinatolithium in tetrahydrofuran at ambient temperature afforded Cr(tBuNC(CH₃)NtBu)₂(Cl)(THF) and Cr(iPrNC(CH₃)NiPr)₃ in 78% and 65% yields, respectively. Treatment of Cr(tBuNC(CH₃)NtBu)₂(Cl)(THF) with the potassium salts derived from pyrazoles and 1,2,4-triazoles afforded Cr(tBuNC(CH₃)NtBu)₂(X), where X = 3,5-disubstituted pyrazolato or 3,5-disubstituted 1,2,4-triazolato ligands, in 65–70% yields. X-Ray crystal structure analyses of Cr(tBuNC(CH₃)NtBu)₂(Me₂pz) (Me₂pz = 3,5-dimethylpyrazolato) and Cr(tBuNC(CH₃)NtBu)₂(Me₂trz) (Me₂trz = 3,5-dimethyl-1,2,4-triazolato) revealed η²-coordination of the Me₂pz and Me₂trz ligands. Treatment of Cr(tBuNC(CH₃)NtBu)₂(Cl)(THF) with trifluoromethyltetrazolatosodium (NaCF₃tetz) in the presence of 4-tert-butylpyridine afforded Cr(tBuNC(CH₃)NtBu)₂(CF₃tetz)(4-tBupy) in 30% yield. An X-ray crystal structure determination showed η¹-coordination of the tetrazolato ligand through the 2-nitrogen atom. The complexes Cr(iPrNC(CH₃)NiPr)₃ and Cr(tBuNC(CH₃)NtBu)₂(X) are volatile and sublime with <1% residue between 120 and 165 °C at 0.05 Torr. In addition, these complexes are thermally stable at >300 °C under an inert atmosphere such as nitrogen or argon. Due to the good volatility and high thermal stability, these new compounds are promising precursors for the growth of chromium-containing thin films using atomic layer deposition.