Experimental and theoretical methods have been employed to investigate the influenceof the chelating phosphine ligand on the
103Rh chemical shift in complexes containing the[(P
2)Rh] fragment (P
2 = chelating bidentate phosphine). The
![](/images/gifchars/delta.gif)
(
103Rh) values obtained by2D(
31P,
103Rh{
1H}) NMR spectroscopy for a series of neutral rhodium complexes [{R
2P(CH
2)
nPR
2}Rh(hfacac)] (R = Ar, Ph, Cy, Me,
n = 1-4, hfacac = hexafluoroacetylacetonate) havebeen compared. Systematic variation of the phosphine ligand has allowed separation ofelectronic and geometrical effects. The purely electronic influence of
para substituents incomplexes [{(
p-XC
6H
4)
2P(CH
2)
4P(
p-XC
6H
4)
2}Rh(hfacac)] correlates directly with the Hammett
P constants of X, but leads to variations in the chemical shift of less than 80 ppm betweenX = CF
3 and X = OMe. In contrast, geometrical changes in complexes [(P
2)Rh(hfacac)] leadto variations in the chemical shift over a range of approximately 800 ppm. The individualcontributions of various structural parameters on the
![](/images/gifchars/delta.gif)
(
103Rh) values have been assessedby density-functional-based calculations for suitable model compounds. The same approachhas been extended to the rationalization of the trends in
103Rh chemical shifts of cationiccomplexes with four P donor ligands around a Rh(+I) center and selected anionic Rh(-I)complexes [(P
2)
2Rh]
-. This analysis allows for the first time a direct corroboration ofgeometrical variations and their effect on
103Rh chemical shifts, demonstrating thatcorrelations of reactivity with
103Rh chemical shifts can give valuable information onstructure/reactivity relationships.