A Family of Heteroleptic Titanium Guanidinates: Synthesis, Thermolysis, and Surface Reactivity

A family of new mixed-ligand titanium guanidinate compounds was synthesized as potential atomic layer deposition precursors, and the surface chemistry on silica of a promising candidate (Cp2Ti[(NiPr)2CN(H)iPr]) was explored. Generally, these compounds have very good thermal stability with onsets of volatility between 127 and 168 °C, with melting points generally ranging from 147 to 165 °C. The reactivity of [iPrN(H)C(NiPr)2]TiCp2 was studied with high surface area silica between 180 and 330 °C. The surface reactivity was found to differ if the silica was preheated to 350 or 900 °C; this was attributed to the hydroxyl nucleation site density of the silica, which is known to vary with the temperature. The surface reaction products were characterized by solid-state NMR, and these agreed well with a calculated model. When the silica was pretreated to 350 °C, the precursor appeared to chemisorb primarily through the loss of a Cp ligand, while with a 900 °C pretreatment, the chemisorption occurred primarily through a loss of the guanidinate ligand. The adsorption enthalpies to silica were calculated for the different surface species.