Design of non-ionic carbon superbases: second generation carbodiphosphoranes

The edge-cutting design, synthesis and characterization of the so far strongest non-ionic carbon superbases is presented.

The 31 P{ 1 H} NMR spectra of the titration experiment in THF-d 8 are given in Figures S30-S32. In case of (tmg)P 1 -tBu as reference base, 4 deprotonated the used (tmg)P 1 -tBu•HBF 4 quantitatively, indicating a pK BH + value at least one order of magnitude higher than 29.1.
In case of (dma)P 4 -tBu only the reference base was protonated by HTFSI with 4 remaining quantitativly in its free base form, indicating a pK BH + value one order of magnitude lower than 33.9. The pK BH + value of 4 can therefore be assigned between 30.1 and 32.9.
The 31 P{ 1 H} NMR spectra of the titration experiment in THF-d 8 are given in Figures S33-S35. In case of (dma)P 4 -tBu as reference base, only 1 was protonated by HTFSI with (dma)P 4 -tBu remaining quantitativly in its free base form, indicating a pK BH + value of 1 at least one order of magnitude higher than 33.9. In case of (pyrr)P 4 -tBu as reference base, signals for 1, 1•HTFSI, (pyrr)P 4 -tBu and (pyrr)P 4 -tBu•HTFSI were detected in the 31 P{ 1 H} NMR spectrum. Results of thermal dynamic basicity determination are shown in Table S1. Thus, the pK BH + of 1 was determined to be 35.8±1 in THF.

Crystallographic Section
Data were collected with a Bruker D8 Quest area detector diffractometer equipped with MoK α radiation, a graded multilayer mirror monochromator (λ = 0.71073 Å) and a Photon-100 CMOS detector or with a Stoe Stadivari diffractometer equipped with CuK α radiation, a graded multilayer mirror monochromator (λ = 1.54178 Å) and a Dectris Pilatus 300K detector, both using an oil-coated shock-cooled crystal at 100(2) K. Data collection, reduction, cell refinement and semi-empirical absorption correction (multi-scan) were performed within Bruker Apex3 3 or Stoe X-Area. 4 Structures were solved with dual-space methods using ShelXT 5 and refined against F 2 with ShelXL, 6 all within the user interface of WinGX 7 and ShelXLe. 8

PA and GB calculation
Calculations in the gas phase are performed at the M06-2X/6-311+G(2df,p)//M06-2X/6-31+G(d) level of theory. All structures were optimized without any geometry constraints and To calculate the pK BH + in THF we have used the isodesmic reaction approach (Scheme S1).
Scheme S1: Isodesmic reaction where proton exchange between an acidic species and a reference acid molecule.
The charge of the acids and the conjugate bases are represented by q/q' and q−1/q'−1, respectively.

Deprotonation/decomposition reaction
Reaction profile for deprotonation/decomposition reaction of 2•H + in THF under the action of NH 2 is presented on Figure S36.