Direct Observation of ¹⁰³Rh‐Chemical Shifts in Mono‐ and Dinuclear Olefin Complexes

Abstract

SummaryThe Io3Rh-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 signallnoise ratio is improved by the factor (T2/T;)"2 by this steady-state method in comparison with the usual freeinduction technique. The '03Rh-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 &scale, which extends over 10 000 ppm. For cyclic 173-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,Ccoupling constants in (diene)RhCp-complexes increase, for the terminal diene C-atom, with increasing ring size of the 1,3-diene, 'J(Rh,C)= 11.7 to 17.4 Hz.

Redox‐Responsive Rhodocenium [O,O]‐, [N,O]‐, [N,N]‐, and [N,C,N]‐Metalloligands

“…Due to the presence of the spin 1/2 and 100 % abundant 103 Rh nucleus, diagnostic 1 J( 13 C-103 Rh) couplings were observed in their 13 C NMR spectra. The single-crystal structure analyses of the three representatives showed more or less regular metallocenes with strongly tilted acyl/imidoyl substituents.…”

“…The acyl and imidoyl functionalities are evident from their 13 In addition to these diagnostic NMR properties, the various alkyl/aryl substituents of 5a-8b gave rise to their expected signals and coupling patterns (see Experimental Section). Whereas the NMR spectra of the non-fluorinated rhodocenium/iridocenium salts are well resolved, less clean and slightly broadened spectra are observed for the trifluoromethylated compounds 6c, 8a, and 8b.…”

“…This observed chemical shift is extremely deshielded in comparison to the unsubstituted, parent rhodocenium salt, Cp 2 Rh + Cl -(δ = -10147 ppm). [13,14] A certain degree of deshielding for 5a was expected due to its two benzoyl acceptor substituents, but such a large difference (over 10000 ppm) cannot be explained by simple substituent effects. At present we are unable to explain this behavior, but it would seem that 103 Rh NMR spectroscopy is of limited value for simple structure-related correlations based on the limited data available.…”

“…[5] In general, the importance of the metallocenes (predominantly ferrocenes) stems from their useful properties as the steering ligands in (stereoselective) catalysis, in redox sensing, in supramolecular chemistry, as components of NLO materials, and in biochemical or medicinal applications. These ap-erties of these novel metallocene metalloligands in solution and in the solid state were studied by NMR spectroscopy ( 1 H, 13 C, 103 Rh) and by single-crystal structure analysis. The electrochemical investigations on complexes 5a, 6b, and 7a showed the effect of the appended functional groups on the potential and on the reversibility of the rhodocenium/rhodocene reduction and provided evidence for the dimerization that followed the reduction.…”

Dimetallic Complexes with Bridging Seven‐membered Cycloolefins. Synthesis, Multinuclear NMR.‐Spectroscopic Properties and Structure

“…A closed-shell configuration for both metal centres is formally achieved either via a donor (metal, metal)-bond or an unsymmetrical bonding mode of the bridging cyclooctatetraene. Structural arguments were obtained by spectroscopic as well as X-ray data [2] [4]. Curiously, the Io3Rh-NMR.…”