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Measurement of Magnitude and Sign of Heteronuclear Coupling Constants in Transition Metal Complexes

✍ Scribed by Gottfried Otting; Linnea P. Soler; Barbara A. Messerle

Publisher
Elsevier Science
Year
1999
Tongue
English
Weight
301 KB
Volume
137
Category
Article
ISSN
1090-7807

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✦ Synopsis

Sets

of specifically tailored E.COSY-type correlation experiments and double-quantum/zero-quantum (DQ/ZQ) experiments are presented which enable the determination of sign and size of small heteronuclear coupling constants across the metal center of transition metal complexes. For the octahedrally coordinated complexes, [Ru(TPM)(H)(CO)(PPh 3 )] ؉ [BF 4 ] ؊ (1) and [Ir(TPM)(H)-(CO)(CO 2 CH 3 )] ؉ [BF 4 ] ؊ (2), 14 of 15 and 15 of 15 possible twobond scalar coupling constants across the metal center were measured, respectively, using 15 N and 15 N/ 13 C enriched samples (TPM ‫؍‬ tris(1-pyrazolyl)methane))

. The reduced coupling constants 2 K X-M-Y ‫؍‬ 4 2 2 J/(h␥ X ␥ Y ) were found to be positive when the coupled nuclei X and Y were trans with respect to the metal center, and negative when the coupled nuclei were in cis position. The validity of this sign rule was verified for J CC , J NN , J PN , J PC , J CN , J HP , J HC , and J HN couplings. Idiosyncracies associated with 2D NMR spectra for the sign determination of coupling constants with 15 N which lead to corrections for the signs of J HN , J PN , and J CN couplings reported previously are discussed.

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