Gold(i) alkoxide and thiolate complexes as potential atomic layer deposition precursors

Abstract

Reactions of AuCl(PR₃) with NaOC(CF₃)₃ in the presence of 1 equiv. of Ag[BF₄] or Ag[PF₆] afforded the gold(I) alkoxide complexes [(Au{OC(CF₃)₃}{PR₃})_n] (R = Me (1), Et (2), ⁱPr (3) and ^tBu (4)). In our hands, analogous reactions using NaO^tBu (for R = ⁱPr) did not yield a thermally robust product. However, the thiolate complexes [{Au(S^tBu)(PR₃)}_n] (R = Me (5) and ⁱPr (6)) were accessed by reaction of [{Au(S^tBu)}_n] with PR₃. Compound 1 is a trimer featuring linear Au{OC(CF₃)₃}(PMe₃) units connected through unsupported aurophilic interactions, whereas more sterically hindered 3 and 4 are monomers in the solid state. Compound 5 is a dimer connected via an aurophilic interaction, while 6 is a monomer. In solution, 1 and 3 reacted almost instantly with HBpin or H₃SiPh to afford metallic gold and volatile byproducts (free PR₃ and H₂ accompanied by {(F₃C)₃CO}Bpin or a mixture of {(F₃C)₃CO}SiH₂Ph and {(F₃C)₃CO}₂SiHPh). By contrast, analogous reactions with thiolate complex 5 required over 24 hours to reach completion. Complexes 1–4 melted at 105–106, 19–21, 59–61 and 181–183 °C, respectively, and sublimed cleanly between 50 and 80 °C at 5 mTorr. By contrast, 5–6 decomposed (completely or partially) during attempted sublimation at 5 mTorr; in the case of 5, decomposition was shown to occur via phosphine dissociation to re-form [{Au(S^tBu)}_n]. Of the complexes in this work, 3 offers the best combination of thermal stability and volatility, and the relatively low melting point is attractive. However, 3 was ∼4% decomposed after 72 h at 85 °C, and ∼10% decomposed after 96 h at 100 °C, forming soluble [Au(PⁱPr₃)₂][H{OC(CF₃)₃}₂] (7), gold metal, and other insoluble product(s). Preliminary ALD reactor experiments using 3 (with a delivery temperature of 85 °C) and HBpin showed gold deposition at 124 °C, and no deposition was observed at this temperature using 3 without HBpin.