Cut-and-pasting ligands: The structure/function relationships of a thermally robust Mo(VI) precursor

The bis(tert-butylimido)-molybdenum(VI) framework has previously been used for the successful atomic layer deposition (ALD) and chemical vapor deposition of many molybdenum-containing thin films. Here, we have prepared and fully characterized a new thermally robust bis(tert-butylimido)molybdenum(VI) complex, bis(tert-butylimido)-bis(N-2-(tert-butyliminomethyl)pyrrolato)-molybdenum(VI), (^tBuN)₂Mo(PyrIm)₂ (1), that incorporates two N,N’-κ₂-monoanionic ligands. The volatility and thermal stability of 1 were measured using thermogravimetric analysis and differential scanning calorimetry, where it was found to achieve a vapor pressure of 1 Torr at 212 °C and had an onset of thermal decomposition at 273 °C. A comparison of its thermal properties with those of the known ALD precursor (^tBuN)₂Mo(dpamd)₂ (dpamd = N,N’-diisopropyl-acetamidinato) showed that 1 had similar volatility but a 78 °C improvement in thermal stability. Preliminary deposition experiments indicated that 1 should be a good ALD precursor; it exhibited self-limiting adsorption and did not decompose on the surface until at least 500 °C, features that will enable its use in the development of new high-temperature ALD processes.