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Introduction of ionic or nonionic hydrophilic terminal groups into the hydrophobic dendritic backbone Si(CH2CH2Sn)4 led to a variety of first-generation water-soluble tin-based dendrimers. Functionalization of the hydridotin dendrimer Si(CH2CH2SnH3)4 (1) via 12-fold hydrostannation reaction of acrylic acid derivatives served as the key step. 1 reacts with methyl acrylate to give Si[CH2CH2Sn(CH2CH2COOCH3)3]4 (2), which by means of alkaline hydrolysis was converted into the water-soluble carboxylate-terminated dendrimers Si[CH2CH2Sn(CH2CH2COOM)3]4 [M = Na (3), K (4)]. Reduction of 2 afforded the dendritic polyalcohol Si[CH2CH2Sn(CH2CH2CH2OH)3]4 (5). A clearly enhanced water solubility due to nonionic surface functionalization of 2 was obtained by its reaction with 2-aminoethanol, formally yielding Si[CH2CH2Sn(CH2CH2CONHCH2CH2OH)2.5(CH2CH2COOCH3)0.5]4 (6). The hydrostannation of O-protected N-(2-hydroxyethyl)acrylamides by 1, however, gave the monodisperse derivatives Si[CH2CH2Sn(CH2CH2CONHCH2CH2OR)3]4 [R = CO2^tBu (7), SiMe2^tBu (8)]; deprotection of 8 with tetra-n-butylammonium fluoride yielded the water-soluble Si[CH2CH2Sn(CH2CH2CONHCH2CH2OH)3]4 (9). Also via hydrostannation reaction by 1, the ester-substituted analogue Si[CH2CH2Sn(CH2CH2COOCH2CH2OH)3]4 (10), showing a clearly lower hydrolytic stability, and the homologous amide-substituted dendrimer Si[CH2CH2Sn(CH2CH2CONHCH2CH2OCH2CH2OH)3]4 (11) were synthesized. The new organotin dendrimers were characterized by elemental analysis, multinuclear NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn), and mass spectrometry (MALDI-TOF, ESI). With respect to the potential use of water-soluble tin-based metallodendrimers as X-ray contrast agents, 6 was studied in vivo in mice, roughly estimating its LD50 to 3 mmol Sn/kg body weight.

The hydroalumination of the allyl ethers CH2&dbd;CHCH2OR with ⁱBu2AlH yields the (3-alkoxypropyl)diisobutylaluminum complexes ⁱBu2Al(CH2)3OR (R = Me (1), Et (2), Bu (3)). Et2AlCl and ⁱBu2AlCl react with (2-(methoxymethyl)phenyl)lithium and (2-methoxybenzyl)magnesium chloride, yielding (2-(methoxymethyl)phenyl)diethylaluminum (4), (2-(methoxymethyl)phenyl)diisobutylaluminum (5), and (2-methoxybenzyl)diisobutylaluminum (7), respectively. The reaction of ⁱBu2AlCl with (2-methoxyphenyl)lithium affords the dimeric bis((2-methoxyphenyl)diisobutylaluminum) (6). Et2AlCl and (8-ethoxynaphthyl)lithium form (8-ethoxynaphthyl)diethylaluminum (10) along with a few crystals of bis(8-ethoxynaphthyl)aluminum chloride (13). AlCl3 reacts with 2 equiv of (2-methoxybenzyl)magnesium chloride, yielding bis(2-methoxybenzyl)aluminum chloride (9). Ligand redistribution followed by metathesis was observed for the reactions of Me2AlCl and Et2AlCl with (2-methoxybenzyl)magnesium and (8-methoxynaphthyl)lithium, yielding bis(2-methoxybenzyl)methylaluminum (8), bis(8-methoxynaphthyl)methylaluminum (11), and bis(8-methoxynaphthyl)ethylaluminum (12), respectively. The new compounds have been characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. The solid-state structures of 6, 8, 9, and 11−13 were determined by single-crystal X-ray diffraction. The new aluminum alkyls are very active cocatalysts in the TiCl4-catalyzed ethylene polymerization. 7 and 10 cause a higher productivity compared to the common cocatalyst Al2Et6. The activity depends strongly on the structure of the oxygen-stabilized aluminum alkyls and is also influenced by the Al/Ti ratio.