MULTINUCLEAR NMR-STUDIES ON SUBSTITUTED DERIVATIVES OF RH-6(CO)(16) IN SOLUTION

Multinuclear NMR data (C-13, P-31, C-13-{P-31}, C-13-{Rh-103} and P-31 -{Rh-103}) for a series of mono- and di-substituted derivatives of Rh- 6(CO)(16) containing neutral two electron donor ligands [Rh-6(CO)(15)L , (L = NCMe, py, cyclooctene, PPh3, P(OPh)(3),1/2(mu(2),eta(1):eta(1)- dppe)); Rh-6(CO)(14)(LL), (LL = cis-CH2=CMe-CMe=CH2, dppm, dppe, (P(OP h)(3))(2))] are reported; these data show that the solid state structu re is maintained in solution. Detailed assignments of the (CO)-C-13 NM R spectra of Rh-6(CO)(15)(PPh3) and Rh-6(CO)(14)(dppm) clusters have b een made on the basis C-13-{Rh-103} double resonance measurements and the specific stereochemical features of the observed long range coupli ngs in these clusters have been studied. The stereochemical dependence of (3)J(P-C) for terminal carbonyl ligands is discussed and the value s of (3)J(P-C) are found to be mainly dependent on the bond angles in the P-Rh-Rh-C fragment; these data enable the fine structure of the co mplex multiplets in the C-13-{H-1} and P-31-{H-1} NMR spectra of Rh-6( CO)(14) (dppm) to be simulated. Variable temperature C-13-{H-1} NMR me asurements on Rh-6(CO)(15)(PPh3) reveal the carbonyl ligands in this c omplex to be fluxional. The fluxional process involves exchange of all the CO Ligands except the two terminal CO's associated with the rhodi um trans to the substituted rhodium and can be explained by a simple o scillation of the PPh3 on the substituted rhodium atom aided by concom itant exchange of the unique terminal CO on this rhodium with adjacent mu(3)-CO's. (C) 1998 Elsevier Science S.A.