Thermal Stability and Decomposition Pathways in Volatile Molybdenum(VI) Bis-imides.

The vapor deposition of many molybdenum-containing films relies on the delivery of volatile compounds with the general bis( tert- butylimido)molybdenum(VI) framework, both in atomic layer deposition and chemical vapor deposition. We have prepared a series of ( t BuN) 2 MoCl 2 adducts using neutral N , N '-chelates and investigated their volatility, thermal stability, and decomposition pathways. Volatility has been determined by thermogravimetric analysis, with the 1,4-di- tert -butyl-1,3-diazabutadiene adduct ( 5 ) found to be the most volatile (1 Torr of vapor pressure at 135 °C). Thermal stability was measured primarily using differential scanning calorimetry, and the 1,10-phenanthroline adduct ( 4 ) was found to be the most stable with an onset of decomposition of 303 °C. We have also investigated molybdenum compounds with other alkyl-substituted imido groups: these compounds all follow a similar decomposition pathway, γ-H activation, with varying reaction barriers. The tert -pentyl, 1-adamantyl, and a cyclic imido (from 2,5-dimethylhexane-2,5-diamine) were systematically studied to probe the kinetics of this pathway. All of these compounds have been fully characterized, including via single-crystal X-ray diffraction, and a total of 19 new structures are reported.