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.