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 eta2-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 eta1-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 degrees C at 0.05 Torr. In addition, these complexes are thermally stable at >300 degrees 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.