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Direct Observation of 103 Rh‐Chemical Shifts in Mono‐ and Dinuclear Olefin Complexes
Author(s) -
Maurer Ellen,
Rieker Susanne,
Schollbach Michael,
Schwenk Andreas,
Egolf Thomas,
von Philipsborn Wolfgang
Publication year - 1982
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19820650105
Subject(s) - chemistry , diene , olefin fiber , coupling constant , chemical shift , resonance (particle physics) , ring (chemistry) , stereochemistry , coupling (piping) , analytical chemistry (journal) , atomic physics , catalysis , organic chemistry , mechanical engineering , natural rubber , physics , engineering , particle physics
The 103 Rh‐resonance has been investigated at 2.8 MHz in mono‐ and dinuclear olefin complexes by steady‐state NMR.‐pulse techniques. For dirhodium complexes with scalar Rh, Rh‐coupling, a selective rf‐irradiation was applied to improve sensitivity. Within the same measuring time the signal/noise ratio is improved by the factor (T 2 /T 2 * ) 1/2 by this steady‐state method in comparison with the usual free‐induction technique. (T 1 /T 2 )‐ratios, as obtained from the dependence of signal in tensity on the pulse‐flip angle are discussed in terms of relaxation mechanisms and chemical exchange phenomena. From (T 1 /T 2 )‐ and (T 1 + T 2 )‐experiments, individual T 1 and T 2 values have been determined for C 5 H 5 RhC 8 H 12 and Rh(acac) 3 . The 103Rh‐chemical shifts of 39 olefin complexes are reported. Shielding depends upon the (formal) oxidation state of Rh whereby resonances of pure olefin complexes appear at the low‐frequency end of the δ‐scale, which extends over 10000 ppm. For cyclic 1,3‐diene ligands Rh‐shielding increases with decreasing ring size and decreases with further conjugation of the diene systems. In the dirhodium complexes, Rh, Rh spin‐coupling constants are < 10 Hz. Rh, C‐coupling constants in (diene)RhCp‐complexes increase, for the terminal diene C‐at om, with increasing ring size of the 1,3‐diene, 1 J (Rh, C) = 11.7 to 17.4 Hz.