All procedures were conducted with strict exclusion of oxygen and moisture, using Schlenk techniques with a vacuum-nitrogen manifold. Both precursors and products were stored and manipulated in a drybox (<1 ppm H2O / <1 ppm O2). All glass surfaces of reaction vessels and storage vials were silylated by an equimolar mixture of Me 3 SiCl and Et3N in CH2Cl2 prior to each use in order to eliminate surface -OH groups and thus prevent the production of HCl in contact with the Al-Cl functionality. The reaction vessels were sealed by PTFE sealing rings. All solvents were dried, deoxygenated and stored under nitrogen over activated 4Å molecular sieves. Starting compounds SnMe3Cl, AlMe3 (2M in toluene), AlCl3, [Me4N]OH (25 wt% in MeOH), Si(OEt)4, Me3SiCl, pyridine, Et3N, and TEPO were purchased from Merck and used without further purification. The building block (Me 3 Sn) 8 Si 8 O 20 was prepared according to a previously described procedure from SnMe3Cl, [Me4N]OH, and Si(OEt)4. The compounds py-AlMe3, Et3N-AlMe3, TEPO-AlMe 3 , and [Me 4 N] [AlCl 4 ] were synthesized according to the procedures described in the Supporting Information (Section S1) and stored in the drybox. The compounds THF-AlCl 3 , py-AlCl3, and TEPO-AlCl3 were generated in situ and never isolated to avoid the formation of complex ionic solids with the potential loss of the ligands. Caution! SnMe 3 Cl, SnMe 4 , and SnMe 3 Et are classified as GHS Category 1 acute toxicity (H300, H330, H310) and long-term aquatic toxicity (H400, H410) hazards.