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

Abstract

Abstract A series of new and known Rh(I) complexes [Rh(R 2 P(CH 2 ) n PR 2 ) 2 ]Y and [Rh(diene)(R 2 P(CH 2 ) n PR 2 )]Y (R = Me, Et, Ph, C 6 F 5 , C 6 H 4 CF 3 ; Y = Cl, ClO 4 , PF 4 , BF 4 , OSO 2 CF 3 ; diene = norbornadiene, cyclooctadiene) were prepared and their 103 Rh NMR spectra were recorded on a 100‐MHz spectrometer by using inverse two‐dimensional 31 P, 103 Rh{ 1 H} NMR. This technique provides quick access to 103 Rh NMR data (2–8 h for ca. 0.1 M samples) when dealing with Rh‐phosphine complexes. The 103 Rh NMR data are discussed. All δ( 103 Rh) 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 σ p and with a large Δ E in square‐planar d 8 complexes. The relative change in Δ E between complexes is not large and the changes in paramagnetic shift for these complexes are essentially determined by their relative σ‐donor capacities. δ( 103 Rh) shows an inverse correlation with δ( 31 P), which was rationalized by invoking the chelate ring size containing the Rh centre and the bidentate phosphine ligands.