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Rock around the Ring: An Experimental and Theoretical Study of the Molecular Dynamics of Stannyltriphospholes with Chiral Tin Substituents
Author(s) -
Hofmann Martin,
Clark Tim,
Heinemann Frank W.,
Zenneck Ulrich
Publication year - 2008
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200701321
Subject(s) - chemistry , enantiopure drug , stereocenter , diastereomer , tin , stereochemistry , moiety , enantiomer , ring (chemistry) , crystallography , organic chemistry , enantioselective synthesis , catalysis
Abstract The reaction of diphenyltin dichloride with enantiopure Grignard reagents prepared in situ leads to diphenyltin chlorides 7a – e , which contain chiral organyl substituents. The 2‐bornyl derivative 7a forms a mixture of exo and endo isomers and the (–)‐menthyl derivative 7b yields a mixture of epimers, whereas the cis ‐ and trans ‐myrtanyl complexes 7c and 7d and the m ‐(2‐bornyl‐2‐ene)phenyl species 7e form only one enantiomer as the tin atom is separated from the next stereogenic centre by a methylene or m ‐phenylene group. The target chirally modified 1‐(triorganylstannyl)‐1,2,4‐triphospholes 2a – e are accessible from 7a – e by treatment of the latter with the salt (3,5‐di‐ tert ‐butyl‐1,2,4‐triphospholyl)sodium (Na 5 ) in good yield. As for 7c – e , complexes 2c – e exhibit enantiopure organyl tin substituents that combine with the planar chiral 1,2,4‐triphosphole moiety to form diastereomers. X‐ray diffraction studies on crystalline phases of 2a , b , d and 7b , c confirm the stereochemical interpretations of their spectroscopic data with the help of absolute structure parameter determinations. Dynamic NMR spectroscopy experiments with these compounds demonstrate for the first time a facile stannyl group shift between the two adjacent P atoms (P1 and P2) of the heterocycles that includes ring inversion through a planar transition state ( T i ). In line with the NMR spectroscopic results for 2a – e , density functional calculations with the simplified model compound (trimethylstannyl)‐1,2,4‐triphosphole ( 9 ) point to 1‐(trimethylstannyl)‐1,2,4‐triphosphole ( 9a ) as the global energetic minimum for 9 and an almost isoenergetic 1,2‐shift and ring inversion as the main epimerisation processes of the two enantiomers of 9a .(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)