Reactions of a highly crowded cyclic stannylene with iodoalkanes, enones, and dienes. Inhibition of nucleophilic substitution at tin(IV) centers

The cyclic stannylene RSnR (2; RR = C(SiMe3)(2)SiMe2CH2CH2Me2Si(Me3Si)(2)C) reacted with alkyl iodides R'I (R' = Et, Tr) to give the Sn-IV compounds RSnR'IR (6b,c), which were converted by treatment with silver trifluoroacetate into RSnR'(OCOCF3)R (7b,c). Reactions of the stannylene 2 with appropriate enones or diones yielded the products RRSnOC(Et)= I CHCH2 (10), RRSnOCPh=CPhO (11), RRSnOC6H2-3,5-(Bu2O)-Bu-t (12), and RRSnOC14H8O (13) (OC14H8O = 9,10-phenanthrenediolato). The crystal structures of 6b, 7b,c, and 10-13 have been determined. Treatment of 2 with water, alcohols, or phenol led to ring opening. There is evidence from ESR spectroscopy that the oxidative additions of diones involve radical intermediates. The compound RSnMeIR (6a) reacted Nvith ICI to give the chloride RSnMeCIR (15) but, in contrast to the previously described crowded trialkyltin halides (Me3Si)(3)CSnMe2X (X = Cl, I), neither 6a nor 15 reacted with nucleophilic reagents.