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 (Cp(2)Ti[(N(i)Pr)(2)CN(H)(i)Pr]) was explored. Generally, these compounds have very good thermal stability with onsets of volatility between 127 and 168 degrees C, with melting points generally ranging from 147 to 165 degrees C. The reactivity of [(i)PrN(H)C(N(i)Pr)(2)]TiCp(2) was studied with high surface area silica between 180 and 330 degrees C. The surface reactivity was found to differ if the silica was preheated to 350 or 900 degrees 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 degrees C, the precursor appeared to chemisorb primarily through the loss of a Cp ligand, while with a 900 degrees 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.