Synthesis and Properties of Ethyl, Propyl, and Butyl Hexa-alkyldisilanes and Tetrakis(tri-alkylsilyl)silanes

The preparation of (R3Si)4Si (R = ethyl, n‐propyl, iso‐propyl, n‐butyl, and iso‐butyl) was attempted using the procedure reported for [(CH3)3Si)]4Si.1 The type of alkyl group affected the resulting materials significantly. For R = ethyl, [(C2H5)3Si]2 [hexaethyldisilane (1)] was obtained phase pure if careful fractional distillation (under vacuum) was used, otherwise a mixture of 1, [(C2H5)2Si]4 (octaethyltetra‐cyclo‐silane), and other unidentified product(s) was obtained. For R = n‐propyl a mixture of [(CH3CH2CH)3Si]2 (hexa‐n‐propyldisilane), [(CH3CH2CH2)2Si]4, (octa‐n‐propyltetra‐cyclo‐silane), [(CH3CH2CH2)3Si]4Si {tetrakis(tri‐n‐propylsilyl)silane} (2)], and other unidentified product(s) was obtained. From this mixture only 2, a new and previously unreported compound, was purified. 2 is the second compound of this type to be reported and is characterized by mass spectrometry (MS), elemental analysis (EA), and thermogravimetry (TG). The crystal structure of 2 is also reported [space group R$\bar{3}$ (no.148), a = 17.9249(10) Å, c = 12.2752(7) Å, at 100 K]. For R = iso‐propyl pure [{(CH3)2CH2}3Si]2 [hexa‐iso‐propyldisilane (3)] was obtained in a good yield. For R = n‐butyl or iso‐butyl no phase pure compounds were synthesized. The pure compounds prepared have potential as precursors for the currently problematic atomic layer deposition of silicon, as demonstrated by their complete sublimation under thermal analysis. The sublimation temperature is dependent on the size of the molecule.