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

Whereas the reaction of alkali-metal salts of silyl−allyls E + [C 3 H 3 (SiMe 3 ) 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[C 3 H 3 (SiMe 3 ) 2 -1,3] to give Co{η 3 -C 3 H 3 (SiMe 3 ) 2 -1,3} 2 ( 1 ) and Ni{η 3 -C 3 H 3 (SiMe 3 ) 2 -1,3} 2 ( 2 ), respectively. The reaction of K[C 3 H 3 (SiMe 3 ) 2 -1,3] with Me 3 SnCl afforded Me 3 SiCH CHCH(SiMe 3 )(SnMe 3 ) ( 3 ), which reacted cleanly with TaCl 5 to give {η 3 -C 3 H 3 (SiMe 3 ) 2 -1,3}TaCl 4 ( 4 ). Treatment of this complex with tetramethylethylenediamine led to HCl abstraction, and the allyl complex was transformed into the vinyl−alkylidene compound Me 3 SiCH CHC(SiMe 3 ) TaCl 3 (TMEDA) ( 5 ). Whereas in the case of TaCl 5 dehalostannylation was facile, the reaction of 3 with ZrCl 4 and HfCl 4 took a different course, leading instead to the addition of Me 3 Sn + to 3 to give [HC{CH(SiMe 3 )(SnMe 3 )} 2 ] + [M 2 Cl 9 ] - ( 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 5 − 7 are reported.