Inverse two‐dimensional 31P, 103Rh{1H}NMR of cationic rhodium(I) complexes containing chelating diphosphines

A series of new and known Rh(I) complexes [Rh(R2P(CH2)nPR2)2]Y and [Rh(diene)(R2P(CH2)nPR2)]Y (R = Me, Et, Ph, C6F5, C6H4CF3; Y = Cl, ClO4, PF4, BF4, OSO2CF3; diene = norbornadiene, cyclooctadiene) were prepared and their 103Rh NMR spectra were recorded on a 100‐MHz spectrometer by using inverse two‐dimensional 31P, 103Rh{1H} NMR. This technique provides quick access to 103Rh NMR data (2–8 h for ca. 0.1 M samples) when dealing with Rh‐phosphine complexes. The 103Rh NMR data are discussed. All δ(103Rh) of the cationic Rh(I) complexes appear at the lower frequency end of the Rh(I) range, i.e. between −1350 and + 200 ppm, which is in agreement with the fact that the Rh shift is determined by σp and with a large ΔE in square‐planar d8 complexes. The relative change in ΔE between complexes is not large and the changes in paramagnetic shift for these complexes are essentially determined by their relative σ‐donor capacities. δ(103Rh) shows an inverse correlation with δ(31P), which was rationalized by invoking the chelate ring size containing the Rh centre and the bidentate phosphine ligands.