Synthesis of a Stabilized 1λ⁵,3λ⁵‐Diphosphacyclobutadiene

Abstract

warming to -15°C the reaction mixture evolves CO and slowly changes color from dark red to yellow. After 30min methanol is added (5ml) at -100°C. The orange reaction mixture is then evaporated to dryness at -30°C; the residue is taken up in the minimum amount of CHZC12 necessary (-50°C) and chromatographed on silica gel (column: I= 15, d=2.5cm). After concentration of the yellow zone to 2m1, addition of pentane (50ml) at -78°C leads to deposition of a finely crystalline precipitate. The mother liquor is decanted off and the precipitate recrystallized five times at -78°C from CHzClz/pentane (1 :40) and dried for 2d at -30°C in vacuo. Ivory crystals, dec. >ca. 65°C; yield 1.5 g (93 %).(3): An excess of NaCsHs['] is added to a stirred solution of (2) (2.25 g, 3.5 mmol) in tetrahydrofuran (30ml) at -78"C, the reaction mixture evolving CO and turning orange-brown. Removal of solvent and chromatography of the residue at -30°C on silica gel (column: 1=25, d=2.5cm) in pentane/CHzCl* (1 : 1) gives an orange zone which is evaporated to 2 ml at -30°C. After addition of pentane (50 mi) at -78 "C fine crystals of (3) precipitate. They are recrystallized three times at -78 "C from ether/pentane and dried for 2 d at -20°C in uacuo. Orange crystals, m.p. 103-104°C; yield 1.1 g (55 %).

Geminal Dianions Stabilized by Main Group Elements

“…Deprotonation of [167] On the continuation of his research program dealing with the synthesis of P-chlorinated and P-amino substituted CDPs made from phosphines and CCl 4 , Appel and Wihler described the unsymmetrical carbodiphosphorane Ph 3 P=C=PPh 2 Cl (178 in Scheme 147). [291][292][293] Careful temperature control has to be done in the synthesis and isolation of 178 due to its thermal sensibility vs the formation of its dimer structure 1 5 ,3 5 -diphosphacyclobutadiene [179][Cl] 2 , that is also obtained in high yield (79%) from precursor [Ph 3 P-C(Cl)-PPh 2 Cl][Cl] by reduction with (Me 2 N) 3 P. 292 The structure of the P-chlorinated CDP 178 was confirmed by 31 In a later report, Shevchenko, Röschenthaler and co-workers used a similar approach to prepare the CDPs 218b,c from diphosphines 215b,c and the hexafluorothioacetone dimer (HFTA; Scheme 153). 304 Carbodiphosphorane 218b was fully characterized by EA, 1 H, 31 In spite of the high stability of 228b in both solid state and in solution, when heated at 80°C in C 6 H 6 for 60 h 228b rearranged into the 1,2λ 5 -azaphosphete 229b and allowed for its isolation as white crystals in 76% yield (Scheme 156).…”

“…On the continuation of his research program dealing with the synthesis of P-chlorinated and P-amino substituted CDPs made from phosphines and CCl 4 , Appel and Wihler described the unsymmetrical carbodiphosphorane Ph 3 PCPPh 2 Cl (178 in Scheme 147). 291−293 Careful temperature control has to be done in the synthesis and isolation of 178 due to its thermal sensibility vs the formation of its dimer structure 1λ 5 ,3λ 5 diphosphacyclobutadiene [179] [Cl] 2 that is also obtained in high yield (79%) from precursor [Ph 3 P-C(Cl)-PPh 2 Cl][Cl] by reduction with (Me 2 N) 3 P. 292 The structure of the P-chlorinated CDP 178 was confirmed by 31 P NMR, EA, and its chemical reactivity toward HCl and H 2 O that led to the isolation of chloride salts [180][Cl] and [178-H] [Cl] in excellent yields (92% and quantitative respectively; see Scheme 147). 291 The synthetic utility of the P-chlorinated CDP 178 was demonstrated by the same group by reacting it with a variety of secondary amines [HNR 2 (181a−e), with R groups being Me, Et, nPr, nBu, and −(CH 2 ) 5 −].…”

“…377 Later, Burk et al revisited this chemistry and proved the intermediacy of compounds of the type XIX (kinetic product) that underwent the phosphine-group migration upon thermal treatment to afford the thermodynamic zwitterion XX. 378 The comparative studies carried out by Appel pursued with the reactivity studies of P-amino substituted CDPs 185c, 173 and 189a-d. [290][291][292][293] The results are summarized in Schemes 186-188.…”

Aromaticity and Antiaromaticity of Four-Membered P-Heterocycles

“…All prepared 1 5 ,3 5 -diphosphete, however, contains C substituents, which decrease further the antiaromaticity and stabilize the ring structure. From the reaction of (trichloromethyl)triphenylphosphonium chloride (56) and chlorodiphenylphosphane (57) ylide 58 could be isolated, which underwent a thermal elimination (58 59) and dimerization to give compound 60 with stable 1 5 ,3 5 -diphosphete ring structure (Scheme 21) [107], in which the C substituents, bearing positive charge, decreased the antiaromaticity.…”

Ylidische viergliedrige Vier-π-Elektronen-λ5-Phosphorheterocyclen: elektronische Heterocyclobutadien-Isomere

“…Kopf-Schwanz-Dimerisierungen kurzlebiger l 5 -Phosphaalkine 15 zu den 1l 5 ,3l 5 -Diphospheten 4 wurden von Appel et al, [28] Fluck et al [29] sowie Regitz et al [30] beobachtet (Schema 4). Beachtenswert ist, daû das Diphosphet 4 e nicht aus der Dimerisierung des anfangs gebildeten l 5 -Phosphaalkins 15 d entsteht, sondern aus der isomeren Form 15 e, die durch eine 1 33-Wanderung des Sauerstoffatoms von einem Phosphoratom zum anderen entsteht.…”