A P-31 NMR-STUDY OF SOLID CARBONYLHYDRIDOTRIS(TRIPHENYLPHOSPHINE)RHODIUM(I) - UNUSUAL MAS SIDE-BAND INTENSITIES IN 2ND-ORDER NMR SPIN SYSTEMS

The CP/MAS P-31 NMR spectrum of carbonylhydridotris(triphenylphosphine)rhodium(1), RhH(CO)(PPh3)3 (1), can be described as a tightly coupled ABMX spin system (X = Rh-103). In contrast to the solution P-31 NMR spectrum, the three equatorial phosphorus nuclei are nonequivalent in the solid state and this structural feature allows us to measure the two-bond spin-spin couplings, 2J(P-31,P-31). A new method is proposed for extracting the principal components of the chemical shift tensor from slow MAS NMR spectra in a tightly J-coupled two-spin system. For compound 1, the principal components of the P-31 chemical shift tensors calculated using this method are in good agreement with those obtained from NMR spectra of a static sample. The principal components of the P-31 chemical shift tensors determined for 1 are compared with those reported previously for Wilkinson's catalyst, RhCl(PPh3)3. The delta-22 component of the P-31 chemical shift tensors in 1 shows the largest variation with structure. This is ascribed to differences in the orientation of the P-C(ipso) bond about the equatorial plane of the trigonal bipyramidal structure.