Stannanorbornyl cation

The intramolecular n-electron donation from the remote double bond to the stannylium ion center in the stannanorbornyl cation, 62 (8 Sn = 336 in CeDg), also leads to a significant shielded tin nucleus compared to what is expected for a free trialkylstannylium ion. As already shown for the sila compounds 55-58, the coordination of the C = C double bond to the electron-deficient tin center in 62 is indicated by a low-field shift of the resonance of the vinylic carbon atoms by 11.1 ppm. Additionally, the small scalar Sn-C coupling constant J(SnC) = 26 Hz gives clear evidence for the intramolecular Ti-complexation." ... 

The bonding situation in the stannanorbornyl cation 62 is reminiscent of the intriguing zwitterions of the types 63 and 64 in which triorganotin cations are intramolecularly stabilized by side-on coordination with an alkynyl group. The zwitterions 63 with a [3-l-1] coordination for the tin atom are characterized by a significantly deshielded Sn NMR resonance and sizeable j(SnC) couplings to the alkynyl carbon atoms (for = alkyl and R = Et 5" Sn = 160-215 J(SnC ) = 41 8Hz, J(SnC ) = 60-80 Coordination with the amino... 

---