Angew. Chem. 2015, http://dx.doi.org/10.1002/anie.201503345
Data from:
Basicity Limits of Neutral Organic Superbases. Ivo Leito,* Ilmar A. Koppel,* Ivar Koppel, Karl Kaupmees, Sofja
Tshepelevitsh, and Jaan Saame.
Number of phosphorus atoms
GB
P1
P0
P2
P3
P5
P4
P6
P7
kcal/mol
(imme)P3=N-C-N=P3(imme)
360
Guanidino Phosphorus
carbenes
359
(imme)P2=N-C-N=P2(imme)
350
Guanidino Phosphorus
ylides
348
t-BuCH=P7(imme)
340
338.5
t-Bu-N=P7(imme)
t-BuCH=P5(imme)
335.9
334.8
t-BuCH=P4(imme)
(imme)P1=N-C-N=P1(imme)
t-Bu-N=P5(imme)
327
327.2
Guanidino-phosphazenes
t-Bu-CH=P7(dma)
327.1
325.7
t-BuCH=P3(imme)
t-Bu-N=P4(imme)
320.3
320
t-Bu-CH=P5(dma)
318.4
Amino Phosporus ylides
318.1
t-BuCH=P2(imme)
t-Bu-N=P3(imme)
311.0
310
imme-C-N=P1(imme)
t-Bu-N=P7(dma)
306.8
t-Bu-CH=P4(dma)
305
300.0
300
t-Bu-N=P2(imme)
299.5
t-Bu-CH=P1(imme)
t-Bu-N=P5(dma)
t-Bu-CH=P3(dma)
296
Phosphazenes
294.9
t-Bu-N=P4(dma)
C(imme)2
289.0
287.7
t-Bu-CH=P2(dma)
286.7
t-Bu-N=P1(imme)
t-Bu-N=P3(dma)
282
282.9
280
t-Bu-N=P2(dma)
267.3
266.6
t-Bu-CH=P1(dma)3
260
Scheme 1. Trends of basicity changes in families of superbases. The Y-axis shows computational
gas-phase basicities. The X-axis shows the number of phosphorus atoms in molecular scaffolds. See
the article text for full details.
t-Bu-N=P1(dma)
252.0
240
1
Table 1. Results of model validation and superbase basicity limit predictions with eq 1.[a]
Base series
a
k[b]
Gas phase
RMSD[c]
GBmax
Validation
kcal mol
-1
kcal mol-1
HN=Pn(H)
0.32
1.78
268
1.6
HN=Pn(Me)
0.27
1.29
307
1.8
(iPr)2C=Pn(H)
0.18
1.43
290
1.8
H2C=Pn(Me)
0.26
1.34
325
1.9
R-NH2
0.05
1.61
214
0.5
R1R2R3N
0.15
1.40
231
0.6
tBu-N=Pn(dma)
0.28
1.30
320
1.6
tBu-CH=Pn(dma)
0.29
1.25
348
1.8
tBu-N=Pn(imme)
0.25
1.33
347
0.7
tBu-CH=Pn(imme)
0.21
1.38
355
0.9
(imme)Pn=N-C-N=Pm(imme)
0.22
1.37
372
0.8
Solution
pKa_max
RMSD
Prediction
–
–
Prediction
Ph-N=Pn(dma) in THF
0.79
1.45
32
0.4
tBu-N=Pn(dma) in MeCN
0.67
1.29
56
0.1
[a] See the article text and SI for full details. [b] k ≡ eb, see above. [c] Root mean square deviation of the computed/experimental GB values from those
predicted by eq 1.
Basicity changes in compound families are modelled with the following equation:
GB  GBmax (1  ae bn )
(1)
where n is the number of phosphorus atoms, GB is the gas-phase basicity, GBmax is the maximum GB obtainable with the
particular series and a and b are coefficients. In the case of pKa predictions in acetonitrile or tetrahydrofuran GB and GBmax are
substituted by pKa and pKa_max.
2