103Rh Chemical Shifts in Complexes Bearing Chelating Bidentate Phosphine Ligands
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- 作者：Walter Leitner ; Michael Bü ; hl ; Roland Fornika ; Christian Six ; Wolfgang Baumann ; Eckhard Dinjus ; Magnus Kessler ; Carl Krü ; ger ; and Anna Rufi
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- 刊名：Organometallics
- 出版年：1999
- 出版时间：March 29, 1999
- 年：1999
- 卷：18
- 期：7
- 页码：1196 - 1206
- 全文大小：264K
- 年卷期：v.18,no.7(March 29, 1999)
- ISSN：1520-6041
文摘
Experimental and theoretical methods have been employed to investigate the influenceof the chelating phosphine ligand on the 103Rh chemical shift in complexes containing the[(P2)Rh] fragment (P2 = chelating bidentate phosphine). The 
(103Rh) values obtained by2D(31P,103Rh{1H}) NMR spectroscopy for a series of neutral rhodium complexes [{R2P(CH2)nPR2}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-XC6H4)2P(CH2)4P(p-XC6H4)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 = CF3 and X = OMe. In contrast, geometrical changes in complexes [(P2)Rh(hfacac)] leadto variations in the chemical shift over a range of approximately 800 ppm. The individualcontributions of various structural parameters on the (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 [(P2)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.
(103Rh) values obtained by2D(31P,103Rh{1H}) NMR spectroscopy for a series of neutral rhodium complexes [{R2P(CH2)nPR2}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-XC6H4)2P(CH2)4P(p-XC6H4)2}Rh(hfacac)] correlates directly with the HammettP constants of X, but leads to variations in the chemical shift of less than 80 ppm betweenX = CF3 and X = OMe. In contrast, geometrical changes in complexes [(P2)Rh(hfacac)] leadto variations in the chemical shift over a range of approximately 800 ppm. The individualcontributions of various structural parameters on the (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 [(P2)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.