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Polyphospha[ m ]cyclo[ n ]carbons ( m + n =15, 20, 25, 30, 40)
Author(s) -
Märkl Gottfried,
Zollitsch Thomas,
Kreitmeier Peter,
Prinzhorn Michael,
Reithinger Sabine,
Eibler Ernst
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20001016)6:20<3806::aid-chem3806>3.0.co;2-j
Subject(s) - intramolecular force , chemistry , intermolecular force , lone pair , molecular orbital , nitrogen inversion , ab initio , oxidative coupling of methane , stereochemistry , crystallography , molecule , organic chemistry , catalysis , nitrogen
The Eglinton reaction of diethynyl(2,4,6‐tri‐ tert ‐butylphenyl)phosphane ( 7 a ), that is, the oxidative coupling of 3, 4, 5, or 6 of these phosphane units, affords a mixture of the 15‐, 20‐, 25‐, and 30‐membered macrocycles 8, 9, 10 , and 11 . Pure triphosphacyclopentadecahexayne 8 and pentaphosphacyclopentacosadecayne 10 were isolated by HPLC, while the mixture of 9 and 11 could not be separated. Multistep syntheses of open‐chain polyphosphapolyynes are described, whose intra‐ or intermolecular coupling yields the phosphamacrocycles 8, 9 , and 11 . Eglinton coupling of bis(ethynylphosphanyl)butadiyne ( 17 ) gave a mixture of the 20‐membered tetraphosphacycloicosaoctayne 9 , the 30‐membered hexaphosphacyclotriacontadodecayne 11 , and the 40‐membered octaphosphacyclotetracontahexadecayne 23 as result of a di‐, tri‐, and tetramerization, respectively. Intramolecular coupling of bis[(ethynylphosphanyl)butadiynyl]phosphane 25 a gave 8 , while intermolecular coupling gave 11 ; these two compounds were isolated by chromatography to give yields of 70 and 5 %, respectively. The open‐chain tetraphosphaeikosaoctayne 28 couples intramolecularly to give 9 and intermolecularly to give the 40‐membered octaphosphacyclotetracontahexadecayne 23 , which was isolated in the pure form. Octaphosphatetracontahexadecayne 32 cyclized to give 23 , exclusively. The temperature‐dependent 1 H and 31 P NMR spectra of the open‐chain and cyclic ethynylphosphanes indicated a lowering of the inversion barrier of the tertiary phosphanes from the usual 130–140 kJ mol −1 to 65–75 kJ mol −1 . Ab initio calculations proved that the dramatic reduction of the inversion barriers results from the interaction of the lone pair on phosphorus with the π orbitals of the triple bonds in the planar transition state during inversion. The situation is comparable with the dramatic reduction of the P inversion barrier in phospholes, because of the planar, aromatic transition state. The polyphospha[ m ]cyclo[ n ]carbons may be considered as precursors to cyclic P m C n systems.