Abstract :
Full conformational analysis on some representative cycloalkyl carbocations and acyclic carbodications with μ-hydrido bridging has been performed at the RHF/6-31G∗∗ level of theory. The monocations involve bi- and tri-cyclic systems and the acyclic dications include the first example of a system containing two μ-hydrido bridges. For all cations examined, the most stable conformer is established as having a symmetric, bent C–Hμ–H three-centre two-electron bond (σ conjugation). By symmetry, only in the in-bicyclo[4.4.4]-1-tetradecyl cation is the μ-hydrido bridge linear. The 1H and 13C chemical shifts, calculated by the continuous-set-of-gauge-transformations formalism with the B3LYP hybrid density functional theory method and the 6-311+G(2d,p) basis set, are fairly consistent with NMR observation, in particular for the very high 1Hμ signal and the low-field 13C peak of the bridgehead carbon.
