Controlling Thermal Stability and Volatility of Organogold(I) Compounds for Vapor Deposition with Complementary Ligand Design

Abstract

Atomic layer deposition (ALD) of gold is being studied by multiple research groups, but to date no process using non-energetic co-reactants has been demonstrated. In order to access milder co-reactants, precursors with higher thermal stability are required. We set out to uncover how structure and bonding affect the stability and volatility of a family of twelve organogold(I) compounds using a combination of techniques: X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and density functional theory (DFT). Small, unsubstituted phosphonium ylide ligands bind more strongly to Au(I) than their silyl-substituted analogues, but the utility of both these ligands suffers due to their poor volatility and substantial thermal decomposition. Pentafluoro- [a] 4927 Scheme 2. Decomposition pathways for (PMe 3 )AuMe as a neat liquid and in the presence of an active metal surface.

Ligand-Assisted Volatilization and Thermal Stability of Bis(imido)dichloromolybdenum(VI) ([(t-BuN═)2MoCl2]2) and Its Adducts

“…However, the TGA exhibits a high residual mass (8.6%), below the weight percent of molybdenum in 10 (19.5%). Finally, although this NHC has been shown to significantly stabilize gold(I) compounds, 36 the TD of the SIt-Bu adduct 10 was lower than that of the dimeric compound 2 (Table 2). This results in a negligible thermal range of 2 ºC.…”

“…Our group has also successfully used using N-heterocyclic carbenes to drastically increase the thermal stability of group 11 precursors, [36][37][38] so we decided to use the same NHC as a coordination ligand for molybdenum. Freshly distilled 1,3-bis(tert-butyl)imidazolin-2-ylidene (SIt-Bu) was added dropwise to a hexanes solution of 1.…”

“…The results of all these thermal analyses are tabulated below (Table 2). 9 for calculation; 36 the figure of merit is expressed in arbitrary units. b TV could not be estimated for 9 due to multiple mass-loss events in the TGA.…”

“…Our group has recently developed this statistic for comparing families of compounds (Figure 9). 36 The figure of merit is calculated according to the inset in Figure 9. The first term is the thermal range, which determines if a compound can achieve a 1 Torr vapor pressure before its onset of decomposition.…”