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Two Structurally Characterized Conformational Isomers with Different C−P Bonds
Author(s) -
Roy Sudipta,
Mondal Kartik Chandra,
Kundu Subrata,
Li Bin,
Schürmann Christian J.,
Dutta Sayan,
Koley Debasis,
HerbstIrmer Regine,
Stalke Dietmar,
Roesky Herbert W.
Publication year - 2017
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/chem.201702870
Subject(s) - carbene , chemistry , electronegativity , crystallography , crystal structure , nuclear magnetic resonance spectroscopy , alkyl , conjugated system , stereochemistry , organic chemistry , catalysis , polymer
The cyclic alkyl(amino) carbene (cAAC) bonded chlorophosphinidene (cAAC)P−Cl ( 2 / 2' ) was isolated from the direct reaction between cAAC and phosphorus trichloride (PCl 3 ). Compound 2 / 2' has been characterized by NMR spectroscopy and mass spectrometry. 31 P NMR investigations [ δ ≈160 ppm (major) and δ ≈130 ppm (minor)] reveal that there are two different P environments of the P−Cl unit. X‐ray single‐crystal determination suggests a co‐crystallization of two conformational isomers of (cAAC)P−Cl ( 2 / 2' ); the major compound possessing a cAAC−PCl unit with C cAAC −P 1.75 Å. This C−P bond length is very close to that of (NHC) 2 P 2 [NHC= N ‐heterocyclic carbene]. The residual density can be interpreted as a conformational isomer with a shorter C cAAC −P bond similar to a non‐conjugated phosphaalkene [R−P=CR 2 ]. Our study shows an unprecedented example of two conformational isomers with different C carbene −element bonds. Additionally, Br ( 3c / 3c' ), I ( 4c / 4c' ), and H ( 5c / 5c' ) analogues [(Me 2 ‐cAAC)P−X; X=Br ( 3 ), I ( 4 ), H ( 5 )] of 2c / 2c' [(Me 2 ‐cAAC)P−Cl] were also synthesized and characterized by NMR spectroscopy suggesting similar equilibrium in solution. The unique property of cAAC and the required electronegativity of the X (X=Cl, Br, I, and H) atom play a crucial role for the existence of the two isomers which were further studied by theoretical calculations.