The CO2 insertion into Sn−O bonds of a series of butyl(phenoxy)-, (alkoxy)-, and (oxo)stannanes has been investigated. The tributyl derivatives Bu3SnOR (2a, R = Me; 3a, R =
iPr; 4a, R = tBu; 5a, R = SnBu3)1 give quantitatively Bu3Sn(OCO2R), 2b−5b; the analogous
tributylphenoxystannane, 1, is less reactive. For the dibutyl series, Bu2Sn(OR)2, steric effects
of tBu groups in OR (8a) suppress carbonation under atmospheric pressure. With R = Me
(6a) or R = iPr (7a), only one Sn−OR bond reacts, resulting in Bu2Sn(OR)(OCO2R), 6b or
7b. Treating 6a with 2-propanol affords under CO2 the mixed compound Bu2Sn(OMe)(OCO2
iPr), selectively. Facile deinsertion of CO2 is a common property of all compounds,
occurring more readily in the dibutyl series. The stoichiometric transformation of the
carbonato ligand in 2b, 5b, or 6b to dimethyl carbonate (DMC) on reaction with MeI requires
nucleophilic assistance by F- to proceed. In the presence of MeOH, 2b and 5b
are almost
inactive forDMC formation, in contrast with 6b. The best yield is obtained under supercritical
CO2−methanol conditions.
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