Crystallographic and NMR studies on species intermediate between haloalkoxyphosphoranes and alkoxyphosphonium halides

Abstract

A series of the monocyclic organophosphorus compounds ([o‐OC(CH3)2C6H4]PPh(CH2 Ph)X) bearing a halogen (X = F, Cl, and Br) or a tetrafluoroborate (X = BF4) were synthesized. The solid‐state structures of the bromide, the tetrafluoroborate, and an analogous fluoride ([o‐OC(CF3)2C6H4]PPh(CH2 Ph)F) were determined by single crystal X‐ray crystallography. The geometry of the fluoride was almost an ideal trigonal bipyramid (TBP). On the other hand, the bromide and tetrafluoroborate were essentially phosphonium salts with phosphorane character to some extent for the former. In CD3 CN, the bromide, the chloride, and the tetrafluoroborate were found to exist as phosphonium salts. However, it was suggested that in CDCl3, the bromide and the chloride have structures rapidly equilibrating or averaged between the phosphorane and the phosphonium forms. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:523–530, 2011; View this article online at http://wileyonlinelibrary.com. DOI 10.1002/hc.20717

Synthesis and Characterization of Antiapicophilic Arsoranes and Related Compounds

“…Thus, the substituent effect upon changing from C 2 F 5 to n -C 3 F 7 was not as significant as that for the change from CF 3 to C 2 F 5 . This is understandable by considering the global maximum of the whole stereomutation process, which could be approximated as the highest energy intermediate where one of the bidentates occupies diequatorial sites, as shown in Figure . ,,− It would be easy to imagine that the terminal CF 3 groups of the C 3 F 7 groups are too far away to impose significant steric effects in the vicinity of the central As atom. A comparison with phosphoranes shows that the activation free energies for the arsoranes (Δ G ⧧ 363 ) are much lower than those for the corresponding t -Bu-substituted phosphoranes where the activation Gibbs free energy was calculated to be 31.1 kcal mol –1 for the CF 3 system and estimated to be ca.…”

“…As for 10-P-5 compounds, using the Martin ligand (Figure , A ), we succeeded in freezing the BPR enough to isolate a series of phosphoranes violating the apicophilicity concept with an oxygen-equatorial carbon-apical configuration (O-equatorial). − These phosphoranes are kinetically stabilized products and can still be converted into their corresponding more stable stereoisomers with a carbon-equatorial oxygen-apical configuration (O-apical). Furthermore, we recently developed a new bidentate ligand bearing two C 2 F 5 groups (Figure , B ), which was more effective for freezing the BPR of the phosphoranes than the Martin ligand. ,− More recently, we also developed an even more bulky bidentate ligand C bearing two n -C 3 F 7 groups, which had a larger capability to freeze the BPR of phosphoranes (Figure , C ) .…”

The SN2 reaction and its relationship with the Walden inversion, the Finkelstein and Menshutkin reactions together with theoretical calculations for the Finkelstein reaction

“…This was well known for silicon [12,13], but with P + , this situation has not been reported before (the Menshutkin examples stop at the quaternary salt [25][26][27]). The transformation of tetravalent phosphonium salts into pentavalent phosphoranes (right side, bottom equation) is a common reaction in phosphorus chemistry [62,63]. The barrier for the S N 2@C is 43.7 kJ•mol -1 [64] and for S N 2@N + is 33.4 kJ•mol -1 ; thus, a moderate decrease of the barrier was calculated (10.3 kJ•mol -1 ).…”

Chiral Hypervalent, Pentacoordinated Phosphoranes

“…Preparation of monocyclic halophosphoranes 31a,b and 31c was based on the reaction of the tricoordinate phosphinites 30a,b with benzyl chloride or benzyl bromide. The corresponding fluorophosphoranes 31d or 31e were isolated upon the chloride-fluoride or bromide-fluoride exchange reactions when the chloride 31a or bromide 31c were used as a substrate respectively (Scheme 14) [59]. The tricoordinate organophosphorus derivatives 26a-c were found to react with hexafluoroacetone to give chiral monocyclic phosphoranes 27a-c (Scheme 13) in which no ligand exchange processes were observed at room temperature.…”

“…Preparation of monocyclic halophosphoranes 31a,b and 31c was based on the reaction of the tricoordinate phosphinites 30a,b with benzyl chloride or benzyl bromide. The corresponding fluorophosphoranes 31d or 31e were isolated upon the chloride-fluoride or bromide-fluoride exchange reactions when the chloride 31a or bromide 31c were used as a substrate respectively (Scheme 14) [59]. Monocyclic (ethylthio)fluorophosphorane 34 was isolated in quantitative yield upon fluoride anion abstraction from BF4 counter anion of phosphonium salt 33 easily generated by the reaction of cyclic phosphinothionate 32 with triethyloxonium tetrafluoroborate.…”