The reaction of hexaphenyl-carbodiphosphorane C(PPh₃)₂ (CDP, 1) with BF₃·OEt₂ provides the corresponding difluoroborenium cation [CDP–BF₂]⁺ (2⁺) through fluoride abstraction. Advanced NMR spectroscopy methods, including ¹⁹F,³¹P HMQC; ³¹P,¹³C HMQC; ¹⁹F,¹H HOESY; ¹⁹F NOESY; ³¹P,¹³C INEPT; and ¹H, ³¹P, ¹⁹F, and ¹¹B diffusion NMR measurements, were performed, and they revealed strong ion pairing of 2⁺ with the [BF₄]^– counterion in chloroform solution. Structural and computational studies showed strong donor–acceptor interactions, in which the σ and π lone pairs of electrons of C(PPh₃)₂ donate into the vacant orbitals of the [BF₂]⁺ fragment. The C–B bond shows the highest interaction energy of 242.9 kcal mol^–1 found for the corresponding carbodiphosphorane adducts.

Depending on the temperature, the twofold deprotonation of 1,1′-methylenebis(3-methylimidazole-2-thione) (1) and the subsequent reaction with 2 equiv. of trimethylsilyl chloride (TMSCl) gives two different bis-TMS-functionalized isomers, namely, 1,1′-methylenebis(3-methyl-4-trimethylsilylimidazole-2-thione) (2) and 1,1′-methylenebis(3-methyl-5-trimethylsilylimidazole-2-thione) (3). The cyclic dimethylsilyl-bridged derivative 1,1′-methylene-5,5′-dimethylsilylenebis(3-methylimidazole-2-thione) (4) can also be obtained, corroborating the 5/5′ addition under certain conditions. All compounds have been examined by multinuclear 1D and 2D NMR experiments (1–4) together with single-crystal X-ray diffraction (3 and 4). Additionally, the dilithiated species 5 was synthesized by reacting 1 with 2 equiv. of nBuLi at ambient temperature in solution (THF). ¹H and ⁷Li pulsed field-gradient spin-echo (PGSE) NMR, ⁷Li–¹H heteronuclear Overhauser spectroscopy (HOESY), gradient heteronuclear multiple quantum correlation (gHMQC) and gradient heteronuclear multiple bond correlation (gHMBC) experiments showed that 5 exists as a monomeric contact ion pair (CIP) in THF solution. On the contrary, the X-ray diffraction analysis of 5 revealed a polymeric chain, which can be described as [{5(thf)₂}₂]_∞. Quantum chemical DFT and MP2 calculations were also conducted to determine the energies required for the deprotonation of 1. These results explain the regioselective deprotonation of 1 by CIP formation depending on the temperature and fully support the results of the synthetic and spectroscopic experiments.

How many rare gas atoms can be placed into a fullerene cage until the pressure becomes large enough to break the C₆₀ framework? The answer given by density functional and ab initio computations is surprising and underlines the high stability of this unique carbon structure.