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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.

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SummaryThe synthesis of dimetallic olefin complexes of the type L'M'C7H7M2L2 (M' = Fe, Co, Rh; M2= Rh, Ir, Pd; L' = CO, C5H5; L2= diene, allyl, P (OR),) is described. The fluxional structures were investigated by I3C-, 57Fe-and Io3Rh-NMR.-spectroscopy, and a cisoid dimetallic coordination, including a (metal, metal)-bond, can be deduced for the C,H,-ring. 57Fe-and Io3Rh-chemical shifts give indications for the charge distribution in the 34e-complexes. The homodimetallic complex (Cp) Rh (tropone) Rh (Cp) (13, Cp = cyclopentadienyl) and the corresponding 2-methoxytropone complex 14 were synthesized in addition to the above mentioned complexes. A fluxional bis (1-3-~-allyl)-coordination of the two Rh-atoms was derived from the temperature-dependent 13C-NMR.-spectra. A spin simulation of the (Cp)-multiplets of 12 and 13 yields information about (Rh,Rh)-spin-coupling which amounts to z 5 Hz at 30".