1,2- and 1,3-diphosphetanes from alkylidenephosphines

Scope and Limitations of the Base-Catalyzed Phospha-Peterson PC Bond-Forming Reaction

“…However, it has been proposed that phosphaalkenes bearing larger P than C substituents will favor head-to-head dimerization, because the long P-P bonds and short C-C bonds in the 1,2-diphosphetane will reduce intramolecular steric repulsions better than in a 1,3-diphosphetane containing four intermediate-length P-C bonds. 47 The observed head-to-head dimerization of 2a, which possesses bulkier P than C substituents (Ad vs Ph), is consistent with these arguments. 1,2-Diphosphetane 3a crystallizes with a molecule of THF in the unit cell; however, there is no close contact between THF and 3a.…”

“…The molecular structure of the 1,2-diphosphetane ( 3a ), formed from the dimerization of 2a , was confirmed using X-ray crystallography (Figure ). The [2+2] cycloaddition of phosphaalkenes is often observed when insufficient thermodynamic and/or kinetic stability is conferred to the PC bond, although formally, the dimerization is symmetry forbidden. 1h,1m,,,− Phosphaalkenes have been observed to dimerize with both head-to-tail (to 1,3-diphosphetanes) and head-to-head (to 1,2-diphosphetanes) regiochemistry, with head-to-tail cycloaddition being most common. However, it has been proposed that phosphaalkenes bearing larger P than C substituents will favor head-to-head dimerization, because the long P−P bonds and short C−C bonds in the 1,2-diphosphetane will reduce intramolecular steric repulsions better than in a 1,3-diphosphetane containing four intermediate-length P−C bonds .…”

PhP=CPh2 and Related Phosphaalkenes: A Solution Equilibrium between a Phosphaalkene and a 1,2‐Diphosphetane

“…This may be useful for future polymerization studies. Although a few cases of phosphaalkene‐diphosphetane equilibria have been reported previously for HP=C(OTMS) t Bu and PhP=C(R)H (R = NMe 2 , piperidyl), to our knowledge the present study represents the first time thermodynamic parameters have been determined experimentally. Moreover, the previous reports required weeks in solution or thermal distillation to reach equilibrium whereas the present equilibrium is established within a few hours in solution.…”

“…In the absence of a crystal structure, this compound had previously been assigned as the 1,3‐diphosphetane . The regioselective [2+2] cyclodimerization of phosphaalkenes is well‐established, and affords either the head‐to‐tail (i.e., 1,3‐diphosphetane) or the head‐to‐head product (i.e., 1,2‐diphosphetane) , , . Dimer 2a was fully characterized by using 31 P, 1 H and 13 C{ 1 H} NMR spectroscopy, mass spectrometry and elemental analysis.…”

“…[16] The regioselective [2+2] cyclodimerization of phosphaalkenes is well-established, and affords either the head-totail (i.e., 1,3-diphosphetane) or the head-to-head product (i.e., 1,2-diphosphetane). [16,20,[22][23][24][25][26][27][28][29][30][31][32][33][34] Dimer 2a was fully characterized by using 31 P, 1 H and 13 C{ 1 H} NMR spectroscopy, mass spectrometry and elemental analysis. The molecular structure of 2a, shown in Figure 3, reveals that the sterically favorable anti-configuration of the adjacent P-Ph moieties is adopted.…”