pK_aMeasurements of P(RNCH₂CH₃)₃N

EtN=P(NMe2)N=P(NMe2)3: An efficient non-ionic base catalyst for the isomerization of allylic compounds and methylene-interrupted dienes

“…This observation may be attributed to the initial deprotonation of acetonitrile to form the CH 2 CN ion which functions as the active species for deprotonation of the substrate. This suggestion is made reasonable by the direct observation of the deprotonation of acetonitrile by pro-azaphosphatranes using 31 P NMR spectroscopy 14a and the fact that the pK a value of P 2 -Et in acetonitrile (32.74 18 ) is quite close to those of proazaphosphatranes in the same solvent (32.9-34.49 15 ). The poor performance of valeronitrile as a solvent for these reactions compared with acetonitrile could be due to the poorer ability of the former to lose a proton from the alpha methylene group owing to greater steric hindrance and/or to the inductive effect of the n-propyl moiety.…”

“…Alkoxide formation from alcohols in the presence of pro-azaphosphatranes has been directly observed by 31 P NMR spectroscopy. 15 cis,cis-18-Methoxy-6,9-octadecadiene was somewhat sluggish to conjugate under the same conditions, showing only 84.3 percent conversion after 72 hours (entry 4, Table 2). Complete conversion in 72 hours was realized by increasing the P 2 -Et concentration to 20 mol%.…”

A New Step Towards Solid Base Catalysis: Azidoproazaphosphatranes Immobilized in Nanopores of Mesoporous Silica

“…Tris-A C H T U N G T R E N N U N G (methyl)proazaphosphatrane (1a) was chosen because it combines the highest basicity (pK a = 32.90) [31] with the little steric effect, and has often proven to be the most efficient base, notably by Verkade. [21] Tris(neopentyl)proazaphosphatrane (1b) (pK a = 32.84) was included for its steric bulkiness.…”

“…Azidophosphatrane bases, whether they are homogeneous or immobilized on silica, gave rise to very high yields (85-98%) compared to NEt 3 catalyst (38%). Surprisingly, methylphosphatrane catalyst which exhibits the highest basicity [31] was the less active among the superbases. Using a much less reactive dienophile such as dimethyl fumarate gave cycloadduct 5 in good to high yield but in a noticeably slower reaction which required hours instead of minutes (Table 2).…”

“…Finally, the resulting solids were dried under vacuum at 50 8C. The organic-inorganic hybrid materials, denoted by 2a-c@SBA-15, have been characterized by several analytical, physical and spectroscopic techniques including small-angle X-ray powder diffraction, nitrogen sorption isotherms, and solid-state 31 d 25); ICP-AES analysis: 1% wt P. The organic content was found to be 0.43 and 0.47 mmol per gram of residual silica derived, respectively, from elemental and thermogravimetric analyses (see Supporting Information, Table S1-Table S3). …”