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13 C chemical shifts in the aryl complexes PdX( p ‐RC 6 H 4 )(TMEDA). Is the PdX(TMEDA) fragment a substantial π‐donor?
Author(s) -
Tschoerner Matthias,
Kunz Roland W.,
Pregosin Paul S.
Publication year - 1999
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199902)37:2<91::aid-mrc404>3.0.co;2-g
Subject(s) - chemistry , aryl , substituent , stereochemistry , chemical shift , phenyllithium , ring (chemistry) , linear correlation , carbon 13 nmr , medicinal chemistry , organic chemistry , alkyl , statistics , mathematics
A series of aryl complexes of the form PdX( p ‐RC 6 H 4 )(TMEDA)( 1 , R =OMe, Me, H, CO 2 Me, CN, NO 2 , TMEDA=tetramethylethylenediamine, X=Br, I) were prepared, together with the derivatives PdI(C 6 F 5 )(TMEDA) and PdI(2‐Me‐C 6 H 4 )(TMEDA). Their 13 C NMR spectra were recorded and showed that (i) the ipso carbon, C‐1, with δ=107.6–162.0, is always shifted to higher frequencies, relative to the model organic compound HC 6 H 4 R, (ii) C‐1 is markedly affected by the nature of the p ‐R substituent, with electron‐withdrawing groups producing high‐frequency shifts, (iii) there is a linear correlation between δC‐1 and the Hammett constant σ p + with a correlation coefficient R =0.998 and (iv) there is no compelling evidence for a large π−donor effect from palladium into the aryl ring. Screening constants for C‐1 in a series of phenyllithium compounds, p ‐RC 6 H 4 Li, were calculated. There is an excellent correlation ( R =0.972) of ΔδC‐1 for 1 with ΔσC‐1 for p ‐RC 6 H 4 Li. Copyright © 1999 John Wiley & Sons, Ltd.