STERIC AND ELECTRONIC EFFECTS ON THE RH-103 NMR SHIFTS OF (COD)RH(PHOSPHINE) COMPLEXES

Rh-103 NMR data of several series of (COD)Rh(phosphine) complexes, (CO D)Rh(PR(3))Me, (COD)Rh(PR(3))Cl, {(COD)Rh(PR(3))(2))}Y, {(COD)Rh(PPh(3 ))(py)}PF6, (COD)Rh(PR(3))(2)Me, and of one NBD complex, {(NBD)Rh-(PPh (3))(2)}PF6, have been measured by inverse two-dimensional H-1, Rh-103 - or (31)p, Rh-103{H-1} NMR. Within the series, delta(Rh-103) extends from -332 for (COD)Rh(PMe(3))(2)Me to +557 ppm for (COD)Rh(P(NMe(2))3) Cl. Upon variations in the first coordination sphere, deshielding incr eases in the order PR(3) < CH3 < py similar to Cl. Going from P(OMe)(3 ) to trialkylphosphines to P(NMe(2))(3) the same trend for delta(Rh-10 3) is observed within different series of compounds, which allows an i nterpretation of the Rh shift which is based on the properties of the phosphorus ligand. A systematic variation of PR(3) reveals that parama gnetic shielding of the metal nucleus is caused by an increase in the basicity as well as the cone angle of the ligand. Within a subseries, delta(Rh-103) may quantitatively be described by invoking parameters t hat are a measure of the basicity and the cone angle of the phosphine ligand. There is no general correlation between delta(Rh-103) and P-31 NMR data. Explanations of the observed trends in delta(Rh-103) in ter ms of the paramagnetic shift are given.