Mechanistic Aspects of Samarium-Mediated σ-Bond Activations of Arene C−H and Arylsilane Si−C Bonds
摘要:
To investigate the potential role of Sm-Ph species as intermediates in the samarium-catalyzed redistribution of PhSiH3 to Ph2SiH2 and SiH4, the samariurn phenyl complex [Cp*2SmPh](2) (1) was prepared by oxidation of Cp*Sm-2 (2) with HgPh2. Compound 1 thermally decomposes to yield benzene and the phenylene-bridged disamarium complex CP*Sm-2(mu -1,4-C6H4)SmCp*(2) (3). This decomposition reaction appears to proceed through dissociation of 1 into monomeric CP*2SmPh species which then react via unimolecular and bimolecular pathways, involving rate-limiting Cp* metalation and direct C-H activation, respectively. The observed rate law for this process is of the form: rate = k(1)[1] + k(2)[1](2) Complex I efficiently transfers its phenyl. group to PhSiH3, with formation of Ph2SiH2 and [Cp*Sm-2(mu -H)](2) (4). Quantitative Si-C bond cleavage Of C6F5SiH3 is effected by the samarium hydride complex 4, yielding silane and [Cp*Sm-2(mu -C6F5)](2) (5). In contrast, Si-H activation takes place upon reaction of 4 with o-MeOC6H4SiH3, affording the samarium. silyl species Cp*2SmSiH2(o-MeOC6H4) (7). Complex 7 rapidly decomposes to [Cp*Sm-2(mu -0-MeOC6H4)](2) (6) and other samarium-containing products. Compounds 5 and 6 were prepared independently by oxidation of 2 with Hg(C6F5)(2), and Hg(o-MeOC6H4)(2), respectively. The mechanism of samarium-mediated redistribution at silicon, and chemoselectivity in sigma -bond metathesis reactions, are discussed.
Mechanistic Aspects of Samarium-Mediated σ-Bond Activations of Arene C−H and Arylsilane Si−C Bonds
摘要:
To investigate the potential role of Sm-Ph species as intermediates in the samarium-catalyzed redistribution of PhSiH3 to Ph2SiH2 and SiH4, the samariurn phenyl complex [Cp*2SmPh](2) (1) was prepared by oxidation of Cp*Sm-2 (2) with HgPh2. Compound 1 thermally decomposes to yield benzene and the phenylene-bridged disamarium complex CP*Sm-2(mu -1,4-C6H4)SmCp*(2) (3). This decomposition reaction appears to proceed through dissociation of 1 into monomeric CP*2SmPh species which then react via unimolecular and bimolecular pathways, involving rate-limiting Cp* metalation and direct C-H activation, respectively. The observed rate law for this process is of the form: rate = k(1)[1] + k(2)[1](2) Complex I efficiently transfers its phenyl. group to PhSiH3, with formation of Ph2SiH2 and [Cp*Sm-2(mu -H)](2) (4). Quantitative Si-C bond cleavage Of C6F5SiH3 is effected by the samarium hydride complex 4, yielding silane and [Cp*Sm-2(mu -C6F5)](2) (5). In contrast, Si-H activation takes place upon reaction of 4 with o-MeOC6H4SiH3, affording the samarium. silyl species Cp*2SmSiH2(o-MeOC6H4) (7). Complex 7 rapidly decomposes to [Cp*Sm-2(mu -0-MeOC6H4)](2) (6) and other samarium-containing products. Compounds 5 and 6 were prepared independently by oxidation of 2 with Hg(C6F5)(2), and Hg(o-MeOC6H4)(2), respectively. The mechanism of samarium-mediated redistribution at silicon, and chemoselectivity in sigma -bond metathesis reactions, are discussed.