ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The 103Rh-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 (T2/T2*)1/2 by this steady-state method in comparison with the usual free-induction technique. (T1/T2)-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 (T1/T2)- and (T1 + T2)-experiments, individual T1 and T2 values have been determined for C5H5RhC8H12 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, 1J(Rh, C) = 11.7 to 17.4 Hz.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19820650105
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