Silyl- and Germyl-Substituted Boranes: Synthesis and Investigation as Potential Atomic Layer Deposition Precursors

• Published in: Inorganic chemistry 2024-11, Vol.63 (44), p.21143-21154
• Main Authors: Al Hareri, Majeda, Romero, Patricio, Britten, James F., Emslie, David J. H.
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X; 1520-510X
• DOI: 10.1021/acs.inorgchem.4c03416

Boranes featuring bulky hypersilyl or supersilyl groups and/or sterically unencumbered trimethylgermyl substituents were synthesized for investigation as potential precursors for atomic layer deposition (ALD) of elemental boron. The envisaged ALD process would employ a boron trihalide coreactant, exploiting the formation of strong silicon-halogen and germanium-halogen bonds as a driving force. The alkali metal silyl and germyl compounds hypersilyl lithium, {(Me3Si)3Si}­Li­(THF)3 (1), supersilyl sodium, ( t Bu3Si)­Na­(THF) n (2, n = 2–3), and trimethylgermyl lithium, {Me3GeLi­(THF)2}2 (3), were used for the synthesis of the silyl- and germyl-substituted boranes in this work. Compounds 1 and 2 were synthesized as previously reported, and compound 3 was isolated from the reaction of trimethylgermane with tert-butyl lithium. Compounds 2 and 3 were crystallographically characterized. Reaction of B­(NMe2)­Cl2 with 2 equiv of 1 afforded previously reported {(Me3Si)3Si}2B­(NMe2) (4), whereas reactions of B­(NMe2)­Cl2 or {B­(NMe2)­F2}2 with excess 2 only afforded the monosilyl boranes ( t Bu3Si)­B­(NMe2)­X {X = Cl (5) and F (6)}. Reaction of 5 with 0.5 equiv of {Me3GeLi­(THF)2}2 (3) provided the first example of a mixed silyl/germyl-substituted borane, ( t Bu3Si)­(Me3Ge)­B­(NMe2) (7). Attempts to synthesize (Me3Ge)2B­(NMe2) from the 1:1 reaction of B­(NMe2)­Cl2 with {Me3GeLi­(THF)2}2 afforded a mixture of two major products, one of which was identified as the tri­(germyl)­(amido)­borate {(Me3Ge)3B­(NMe2)}­Li­(THF)2 (8); compound 8 was isolated from the 1:1.5 reaction. Reaction of more sterically encumbered B­(TMP)­Cl2 with 1 equiv of {Me3GeLi­(THF)2}2 afforded the di­(germyl)­(amido)­borane (Me3Ge)2B­(TMP) (9). Boranes 4, 7, and 9 and borate 8 were crystallographically characterized. The thermal stability and volatility of boranes 4, 7, and 9 was evaluated, the solution reactivity of 4 and 7 with boron trihalides was assessed, and ALD was attempted using 4 in combination with BCl3 and BBr3 at 150 and 300 °C.