Synthesis of 5,5-Bicyclic Amidines as Ligands for Thermally Stable Vapor Deposition Precursors

Abstract

We describe the syntheses of three fully aliphatic 5,5-bicyclic amidines. The syntheses are facile and scalable and can be easily modified to produce other 5,5-bicyclic amidine ligands with other substitution patterns. Treatment of one of the ligands with KHMDS and subsequent transmetalation with CuCl resulted in a dimeric copper­(I) bicyclic amidinate complex in 55% yield after recrystallization. This modestly air stable complex exhibits good volatility and thermal decomposition rates 1 order of magnitude lower than those of a similar, but acyclic, copper­(I) amidinate. Together, the ligands enable a general method for producing a library of thermally stable metal amidinate precursors with a wide variety of metals for use in vapor deposition.

Synthesis of volatile, reactive coinage metal 5,5-bicyclic amidinates with enhanced thermal stability for chemical vapor deposition

“…Thermogravimetric analysis (TGA) was performed in a nitrogen-filled glovebox to study the thermal stability and evaporation rate of 2-4 ( Figure 3). As reported previously, 32 2 sublimes cleanly under a linear temperature ramp, with 50 % mass loss at 270 °C and < 0.2 wt. % of residue.…”

“…Amidinates lacking β-hydrogens and having cyclic backbones have been employed to suppress this decomposition pathway. 25,31,32 Barry and coworkers prepared silver(I) and gold(I) tert-butylimino-2,2-dimethylpyrrolidinates, combining these strategies and improving thermal stability to 170 °C. 25 Silver and gold films can be grown with these singlesource CVD precursors via thermolysis; 25 however, the gold films are carbon-contaminated and poorly conductive (ρ = 5580 μΩ·cm, cf.…”

“…We have recently reported the synthesis of the purposedesigned, fully β-substituted 5,5-bicyclic amidine ligand 1, and its copper (I) complex (Scheme 1). 32 The lack of β-hydrogens prevents β-hydride elimination, and the bicyclic system constrains bond rotations to make β-methyl migration reactions unlikely. 32 Consistent with this goal, the solution thermal decomposition rate of 2, 32 a dimeric copper(I) complex of 1, is 10× slower than that of a previously reported 11 acyclic copper(I) amidinate.…”

“…32 The lack of β-hydrogens prevents β-hydride elimination, and the bicyclic system constrains bond rotations to make β-methyl migration reactions unlikely. 32 Consistent with this goal, the solution thermal decomposition rate of 2, 32 a dimeric copper(I) complex of 1, is 10× slower than that of a previously reported 11 acyclic copper(I) amidinate. Encouraged by this result, we investigated the ability of bicyclic 1 to form volatile gold and silver CVD compounds.…”

“…The synthesis of the gold(I) complex 3 is analogous to the synthesis of the copper(I) complex 2 (Scheme 1). 32 Although AuCl can be used to prepare 3, its more soluble dimethylsulfide adduct, AuCl(SMe2), 33 provides improved yields. Treatment of a THF solution of 1 with KHMDS, followed by transmetalation with AuCl(SMe2), affords the gold(I) amidinate complex 3.…”