Rhodium-103 NMR of [Rh(X)(PPh3)3] [X = Cl, N3, NCO, NCS, N(CN)2, NCBPh3, CNBPh3, CN] and derivatives containing CO, isocyanide, pyridine, H2 and O2. Ligand, solvent and temperature effects

✍ Scribed by Laurence Carlton

• Book ID: 102530360
• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 162 KB
• Volume: 42
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1437

✦ Synopsis

Abstract

Rhodium‐103 chemical shifts are reported for 62 compounds, namely [Rh(X)(PPh~3~)~3~] [X = Cl, N~3~, NCO, NCS, N(CN)~2~, NCBPh~3~, CNBPh~3~, CN] and derivatives formed by replacement of a phosphine by CO, xylyl isocyanide (XNC) and pyridine and/or by oxidative addition of H~2~ or O~2~ to give trans‐[Rh(X)(PPh~3~)~2~(CO)] (δ in the range −816 to −368 ppm) trans‐[Rh(X)(PPh~3~)~2~(XNC)] (δ −817 to −250 ppm), cis‐[Rh(X)(PPh~3~)~2~(py)] (the trans isomer is formed with X = CN, CNBPh~3~) (δ −233 to 170 ppm), [Rh(X)(H)~2~(PPh~3~)~3~] (δ −611 to 119), trans‐[Rh(X)(H)~2~(PPh~3~)~2~(py)] (δ −30 to 566 ppm), [Rh(X)(O~2~)(PPh~3~)~3~] (δ 1393 to 3273 ppm) and cis‐[Rh(X)(O~2~)(PPh~3~)~2~(py)] (δ 1949 to 3374 ppm). For the majority of these compounds data were obtained from solutions in chloroform and in toluene at temperatures of 247 and 300 K; for [Rh(X)(PPh~3~)~3~] (δ −562 to −4 ppm) data are reported at a number of temperatures in the range 195–300 K for solutions in chloroform, toluene and dichloromethane and at 300 K for solutions in DMSO. The expected trend to lower δ(^103^Rh) with decreasing temperature (vibrational shielding) is observed for the dichloromethane data, but data from solutions {of [Rh(X)(PPh~3~)~3~]} in chloroform and toluene show a number of features which diverge from this pattern, i.e. shifts to higher δ are found to accompany a decrease in temperature, most noticeably where X = CN and Cl [on changing the solvent from dichloromethane to chloroform changes in δ(^103^Rh) of up to 172 ppm are observed]. These results are interpreted in terms of a hydrogen‐bonded interaction with the solvent that is enhanced by the presence of a polarizable ligand (CN, Cl). With a ligand (O~2~CCF~3~) that is only weakly polarizable the solvent dependence of δ(^103^Rh) is minimal. Copyright © 2004 John Wiley & Sons, Ltd.