Synthesis and characterization of new silicon-centred tin-dendrimers Si[CH2CH2SnR3]4. Single-crystal X-ray structure of the tetrahydrofuran adduct of tetrakis[2-(tribromostannyl)ethyl]silane

A series of novel first-generation silicon-centred tin dendrimers Si(CH2CH2SnR3)4 [R = CH3 (3), iBu (4), Ctriple bond; length of mdashCCH3 (5), C6H4CH3-4 (6), C6H4OCH3-4 (7), (CH2)4OCH2CH2OCH3 (8), CH2SiMe3 (9)] was prepared by the reaction of Si(CH2CH2SnBr3)4 (2) with the appropriate Grignard reagent or LiCH2SiMe3 in tetrahydrofuran. The new compounds were characterized by multinuclear NMR studies (1H, 13C, 119Sn), mass spectrometry (MALDI-TOF, EI) and elemental analyses. The molecular structure of Si[CH2CH2SnBr3(THF)2]2[CH2-CH2SnBr3(THF)]2 (2a) was determined by single-crystal X-ray diffraction.