NMR INVESTIGATIONS OF DI-RHODIUM-TETRAACETATE COMPLEXES WITH CYCLIC PHOSPHITES

The formation of adducts in the system containing Rh-2(OAc)(4), cyclic amidophosphite [Et2NPO(CH2)(3)O] and bicyclic phosphite [P(OCH2)(3)CE t] have been studied using low temperature P-31 NMR. Varying the conce ntration of Rh-2(OAc)(4) made the signals due to a mono-adduct, a homo ligated bis-adduct and a mixed bis-adduct observable in the P-31 spect ra. Iterational optimisation of the parameters of the spectra of symme tric bis-adducts showed a very strong correlation between the values o f the coupling constants (1)J(RhRh') and (3)J(PP'). The spectrum of th e asymmetric adduct (amidophosphite-Rh-Rh-phosphite) yielded a well de fined estimate of (3)J(PP'). This value (793 Hz) is found to be betwee n the values of the coupling constants for phosphite-phosphite and pho sphite-phosphine interactions found by Boyar and Robinson. The integra ls of the lines in the P-31 spectra of the samples derived from differ ent starting concentrations of Rh-2(OAc)(4) yielded values for the sta bility constants of the detected adducts. The mono-adduct of amidophos phite was found to be significantly more stable than that of phosphite . (C) 1998 Elsevier Science S.A.