Syntheses and reactivity of novel unsaturated cyclic compounds containing phosphorus atoms

Synthesis and properties of air-stable 1,3-diphosphacyclobutane-2,4-diyls and the related compounds

“…The P 2 C 2 biradicals that we previously reported have a deformed lozenge structure to display shorter and phosphaalkene-like P-C distances together with longer and almost P-C single bond distances in the four-membered ring, which has been critically argued to characterize our compounds as biradical structures [8][9][10]. Therefore, an attempt was made to obtain novel biradicals, which are comparable with 1 by use of our synthetic strategy.…”

“…Reaction of 4 with 0.5 equivalents of t-butyllithium afforded the corresponding four-membered anionic intermediates 5 through a [2+2] cyclization of a 1,3-diphosphabuta-1,3-diene skeleton [8][9][10][11]. The roomtemperature stable P-heterocyclic anions 5 were allowed to react with alkyl or acyl halides to afford the unsymmetrically substituted 1,3-diphosphacyclobutane-2,4-diyls 3a-e through the P-alkylation pathway [8][9][10] (Scheme 1). The P-heterocyclic biradicals 3a-e can be handled in air at room temperature, indicating successful cooperation of kinetic protection by the Mes * group with thermodynamic perturbation by the phosphino group.…”

“…In the course of our research on such lowcoordinated phosphorus compounds, we have found a useful synthetic method for 2,4-bis(2,4,6-tri-t-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyls of biradical type (3) by use of a kinetically stabilized phosphaalkyne [Mes * C"P: 4] (Mes * = 2,4,6-tri-t-butylphenyl) [8][9][10]. Although Niecke's biradical 1 carries two sterically protecting Mes * groups, our biradical 3 demonstrates exceptional stability toward air at room temperature due to the effective stabilizing cooperation of an electronically perturbing phosphino group and the Mes * groups.…”

“…Although Niecke's biradical 1 carries two sterically protecting Mes * groups, our biradical 3 demonstrates exceptional stability toward air at room temperature due to the effective stabilizing cooperation of an electronically perturbing phosphino group and the Mes * groups. Furthermore, our synthetic protocol for 1,3-diphosphacyclobutane-2,4-diyls assures us of wide scope for preparation of varieties of P-heterocyclic biradical compounds simply by employing various nucleophiles and electrophiles [9,10]. We describe here preparation of several novel 1,3-diphosphacyclobutane-2,4-diyls carrying different or identical substituents on the phosphorus atoms, which leads to profound discussion of structural properties of the biradical compounds.…”

Unique molecular distortion in the 2,4,6-tri-t-butylphenyl group

“…The average torsion angles Θ(C skeletal -C ipso -C ortho -C tBu ) and Θ(C skeletal -C ipso -C ortho -C meta ) for 8 are 26.10° and 155.84°, 15 respectively, whereas 9 shows smaller degree of distortion…”