Gas-phase intramolecular anion rearrangements of some trimethylsilyl-containing systems revisited. A theoretical approach

Ab initio calculations at the CCSD(T)/6-311++G(2d,p)//B3LYP/6-311++G(d,p) level of theory have been carried out for three prototypical rearrangement processes of organosilicon anion systems. The first two are reactions of enolate ions which involve oxygen–silicon bond formation via three- and four-membered states, respectively. The overall reactions are: CH2 = C(O-)Si(CH3)3 → (CH3)3SiO- + CH2H, and (CH3)3SiCH = CHO- → (CH3)3SiO- = C2H2.The ΔG (reaction) values for the two processes are +175 and +51 kJ mol−1, with maximum barriers (to the highest transition state) of +55 and +159 kJ mol−1, respectively. The third studied process is the following: (CH3O)C(CH2)Si(CH3)2CH → (CH3)2(C2H5)Si− + CH2CO, a process involving an Sni reaction between -CH and CH3O- followed by silicon–carbon bond cleavage. The reaction is favourable [ΔG(reaction) = −39 kJ mol−1] with the barrier for the Sni process being 175 kJ mol−1. The previous experimental and the current theoretical data are complementary and in agreement. Copyright © 2009 John Wiley & Sons, Ltd