Preparation of the tricyclo[5.3.1.1^3,9]dodeca‐1,5‐diyl dication: attempts to prepare a novel µ‐H cation

Abstract

The tricyclo[5.3.1.1 3,9 ]dodeca-3,7-diyl dication (6) was prepared in situ and characterized by 1 H and 13 C NMR spectroscopy. Reaction of this dication with isopentane, NaBH 4 or H 2 , in an attempt to prepare the m-H cation 7, did result in hydride transfer, but to the 'outside' face of the dication, leading to the conventional monocation 8, or rearrangement products of this. This monocation was independently prepared, and is thermally less stable than the dication, rearranging to the 2-ethyl-2-adamantyl cation (19) at À60°C, DG ‡ = 16.0 AE 0.6 kcal mol À1 . The 2methyltricyclo[4.3.1.1 3,7 ]undec-2-yl cation (20), a likely intermediate in this rearrangement, was also independently prepared and shown to rearrange to 19, DG ‡ = 14.4 AE 0.3 kcal mol À1 , consistent with a stepwise rearrangement process for 8→[20]→19. The structures of dication 6 and monocation 8 were investigated by high-level ab initio calculations, and modeling studies were carried out to look at the factors that allow dications such as 6 to even be prepared.

Isolation and Low-Temperature X-ray Analysis of Intramolecular Triarylmethane−Triarylmethylium Complex: Preference for a C−H-Bridged Unsymmetric Structure Exhibiting a Facile 1,5-Hydride Shift and Charge-Transfer Interaction

“…A sharp C s -symmetric spectrum appeared with two distinct N -methyl resonances at 4.81 (acridinium) and 3.13 (acridan) ppm (−90 °C), showing that the bridging hydrogen is localized on one of the C9 carbons in solution and fluctuates between the two equivalent sites. The chemical shift of this hydrogen is 3.90 and 4.26 ppm at 0 and −90 °C, respectively, which is close to that of precursor 3b (4.36 ppm) but far different from the very high-field value characteristic of the delocalized 3c−2e bonding hydrogen. ,3b The 13 C NMR spectrum at −90 °C is also consistent with C s -symmetric Form A and exhibits two distinct resonances for C9: 163.63 and 42.33 ppm. The 13 C− 1 H coupling constant (126 Hz) is comparable to that of precursor 3b (128 Hz), indicating full bonding character between the bridging hydrogen and one of the C9 carbons.…”

“…The facile 1,5-hydride shift is the most characteristic process in 1 + , the energy barrier (Δ G ⧧ ) of which was determined to be 9.6 kcal mol -1 (at T c = −55 °C for N -methyl protons) for 1b + in CD 2 Cl 2 by VT-NMR analyses (300 MHz). This value is about 3-fold larger than that for the 1,5-shift in 3,7-dimethylbicyclo[3.3.1]nonan-3-yl cation 2b. In the more polar and Lewis basic acetone- d 6 , an even larger value of 10.1 kcal mol -1 was obtained ( T c = −43 °C), suggesting that the transition state is less polar than 1 + due to charge delocalization over the two Ar 2 C units.…”

“…A carbocation with a short C−H···C + contact has long attracted considerable attention since the first observation of the delocalized three-center two-electron (3c−2e) bond of (C···H···C) + by Sorensen and McMurry in superacidic media . From both experimental and theoretical perspectives, the most interesting point in studying these cations is to clarify what factors affect the preference of the localized or delocalized position of the bridging hydrogen, which should provide the key information for understanding the nature of the nontriangular 3c bond between carbon and hydrogen. Recently, the existence of a higher analogue of (C···H···C···H···C) + was theoretically predicted,3a and such bonding would not be stabilized in the alicyclic-bridged propellane studied before, but rather in a novel motif, triarylmethane−triarylmethylium complex, where the interacting parts are geometrically constrained by being located at the peri positions of the rigid arylene spacer.…”

“…The 13 C− 1 H coupling constant (126 Hz) is comparable to that of precursor 3b (128 Hz), indicating full bonding character between the bridging hydrogen and one of the C9 carbons. By measuring the 2 H NMR spectrum of 1b + -d OTf - , the Δδ test ( 1 H, 2 H) of Altman and Forsén was conducted, and the very small value (−0.02 ppm at −10 to −60 °C) clearly shows a deep double-minimum potential for the bridging hydrogen. , …”