Synthesis, Structure, and Solution Reduction Reactions of Volatile and Thermally Stable Mid to Late First Row Transition Metal Complexes Containing Hydrazonate Ligands

Treatment of MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the hydrazonate salts K(tBuNNCHCtBuO), K(tBuNNCHCiPrO), or K(tBuNNCMeCMeO) afforded the complexes M(tBuNNCHCtBuO)2 (M = Ni, 65%; Co, 80%; Fe, 83%; Mn, 68%; Cr, 64%), M(tBuNNCHCiPrO)2 (M = Ni, 63%; Co, 86%; Fe, 75%), and M(tBuNNCMeCMeO)2 (M = Ni, 34%; Co, 29%; Fe, 27%). Crystal structure determinations of Co(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2 (M = Ni, Co), and M(tBuNNCMeCMeO)2 (M = Ni, Co, Fe) revealed monomeric complexes with tetrahedral geometries about the metal centers. To evaluate the potential of these new complexes as film growth precursors, preparative sublimations, thermogravimetric analyses, solid state decomposition studies, and solution reactions with reducing coreagents were carried out. M(tBuNNCHCtBuO)2 sublime between 120 and 135 °C at 0.05 Torr, whereas M(tBuNNCHCiPrO)2 and M(tBuNNCMeCMeO)2 sublime between 100 and 105 °C at the same pressure. All complexes afforded ≥96% recovery of sublimed material, with ≤3% of nonvolatile residues. The solid state decomposition temperatures were highest for M(tBuNNCHCiPrO)2 (273–308 °C), intermediate for M(tBuNNCHCtBuO)2 (241–278 °C), and lowest for M(tBuNNCMeCMeO)2 (235–250 °C). Treatment of Co(tBuNNCHCtBuO)2 in tetrahydrofuran with hydrazine, BH3(L) (L = NHMe2, SMe2, THF), pinacol borane, and LiAlH4 led to rapid formation of cobalt metal, while analogous reductions of Mn(tBuNNCHCtBuO)2 with BH3(THF), pinacol borane, and LiAlH4 appeared to afford manganese metal. The new complexes M(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2, and M(tBuNNCMeCMeO)2 have very promising properties for use as precursors for the growth of the respective metals in atomic layer deposition film growth processes.