om0491692_si_001.cif (73.86 kB)

Reactivity of Silyl-Substituted Allyl Compounds with Group 4, 5, 9, and 10 Metals:  Routes to η3-Allyls, Alkylidenes, and sec-Alkyl Carbocations

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posted on 28.03.2005, 00:00 by Mark Schormann, Shaun Garratt, Manfred Bochmann
Whereas the reaction of alkali-metal salts of silyl−allyls E+[C3H3(SiMe3)2-1,3]- (E = Li, K) with group 4 and group 5 metal halides gave intractable reduction products, Co(acac)3 and Ni(acac)2 reacted with K[C3H3(SiMe3)2-1,3] to give Co{η3-C3H3(SiMe3)2-1,3}2 (1) and Ni{η3-C3H3(SiMe3)2-1,3}2 (2), respectively. The reaction of K[C3H3(SiMe3)2-1,3] with Me3SnCl afforded Me3SiCHCHCH(SiMe3)(SnMe3) (3), which reacted cleanly with TaCl5 to give {η3-C3H3(SiMe3)2-1,3}TaCl4 (4). Treatment of this complex with tetramethylethylenediamine led to HCl abstraction, and the allyl complex was transformed into the vinyl−alkylidene compound Me3SiCHCHC(SiMe3)TaCl3(TMEDA) (5). Whereas in the case of TaCl5 dehalostannylation was facile, the reaction of 3 with ZrCl4 and HfCl4 took a different course, leading instead to the addition of Me3Sn+ to 3 to give [HC{CH(SiMe3)(SnMe3)}2]+[M2Cl9]- (6, M = Zr; 7, M = Hf), the first examples of isolable sec-alkyl carbocations. These salts are surprisingly thermally stable and melt >100 °C; this stability is largely due to delocalization of the positive charge over the two tin atoms. The crystal structures of 1, 2, and 57 are reported.