Communication pubs.acs.org/JACS
Volatile and Thermally Stable Mid to Late Transition Metal Complexes Containing α‑Imino Alkoxide Ligands, a New Strongly Reducing Coreagent, and Thermal Atomic Layer Deposition of Ni, Co, Fe, and Cr Metal Films Lakmal C. Kalutarage, Philip D. Martin, Mary Jane Heeg, and Charles H. Winter* Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States S Supporting Information *
used precursors for the growth of Cu and Ni films by ALD and chemical vapor deposition (CVD).3,9 However, volatile βamino alkoxide complexes are unknown for the other first row transition metals, presumably because these ligands cannot saturate the coordination spheres of the larger metal(II) ions. Moreover, there is a lack of volatile, strong reducing agents that can transform first row transition metal(II) ions to the metals at low temperatures.1 Herein, we describe the synthesis, structure, volatility, and thermal stability of a series of Cu(II), Ni(II), Co(II), Fe(II), Mn(II), and Cr(II) complexes that contain α-imino alkoxide ligands (Chart 1B). These complexes exhibit good volatilities, high thermal stabilities, and high reactivities toward reducing agents and, thus, have excellent properties for use as ALD precursors. Additionally, we demonstrate that BH3(NHMe2) is a reducing coreagent in the ALD growth of Ni, Co, Fe, and Cr films from the α-imino alkoxide precursors. The present work therefore demonstrates a general new class of ALD precursors as well as a strong reducing agent that can be used for the ALD growth of metal films from metal ions with negative E° values. The α-imino alcohols were prepared as described in the Supporting Information.10 Treatment of the alcohols with KH in tetrahydrofuran, followed by addition of anhydrous MCl2, afforded 1−15 after workup by sublimation (Scheme 1). These complexes were characterized by spectral and analytical methods and by X-ray crystallography.10 The Ni complexes 2, 5, and 11 are diamagnetic, and the 1H NMR spectrum of 11 showed the expected two singlets in a 2:1 ratio for the ligand tBu groups. The 1H NMR spectra of 2 and 5, by contrast, revealed sets of resonances for two diastereomers in 1:1 ratios, due to the presence of a chiral center in each ligand. The remaining complexes are paramagnetic and exhibited very broad resonances in their 1H NMR spectra. Solid state and solution magnetic moment data suggested that 1, 4, 9, 10, and 15 are square planar in both media, which was corroborated by X-ray structural data for 1, 10, and 15. Magnetic data showed that 3, 7, 13, and 14 are tetrahedral in the solid state and in solution, which fit the crystal structures of 3 and 14. Magnetic data suggest that 6 and 12 are square planar in the solid state, but are tetrahedral in solution. Among 1−9, only low resolution X-ray crystal structures could be obtained for 1−3 and 8, due to the diastereomeric
ABSTRACT: Treatment of MCl2 (M = Cu, Ni, Co, Fe, Mn, Cr) with 2 equiv of α-imino alkoxide salts K(RR′COCNtBu) (R = Me, tBu; R′ = iPr, tBu) afforded M(RR′COCNtBu)2 or [Mn(RR′COCNtBu)2]2 in 9−75% yields. These complexes combine volatility and high thermal stability and have useful atomic layer deposition (ALD) precursor properties. Solution reactions between Ni, Co, and Mn complexes showed that BH3(NHMe2) can reduce all to metal powders. ALD growth of Ni, Co, Fe, and Cr films is demonstrated. Mn film growth may be possible, but the films oxidize completely upon exposure to air. here is considerable interest in the growth of metallic first row transition metal thin films by atomic layer deposition (ALD), in view of their applications in microelectronics and other devices.1 ALD of these metals requires precursors that combine volatility, thermal stability at the deposition temperature, and high reactivity toward a second reagent to afford the metallic film.2 Moreover, the films need to be grown at
