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

Rhodium-103 chemical shifts are reported for 62 compounds, namely [Rh(X)(PPh3)(3)] [X = Cl, N-3, NCO, NCS, N(CN)(2), NCBPh3, CNBPh3, 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)(PPh3)(2)(CO)] (delta in the range -816 to -368 ppm) trans-[Rh(X)(PPh3)(2)(XNC)] (delta -817 to -250 ppm), cis-[Rh(X)(PPh3)(2)(py)] (the trans isomer is formed with X = CN, CNBPh3) (delta -233 to 170 ppm), [Rh(X)(H)(2)(PPh3)(3)] (delta - 611 to 119), trans-[Rh(X)(H)(2)(PPh3)(2)(py)] (delta -30 to 566 ppm), [Rh(X)(O-2)(PPh3)(3)] (delta 1393 to 3273 ppm) and cis-[Rh(X)(O-2)(PPh3)(2)(py)] (8 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)(PPh3)(3)] (delta -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 delta(Rh-103) with decreasing temperature (vibrational shielding) is observed for the dichloromethane data, but data from solutions (of [Rh(X)(PPh3)(3)]} in chloroform and toluene show a number of features which diverge from this pattern, i.e. shifts to higher delta 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 delta(Rh-103) 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 (O2CCF3) that is only weakly polarizable the solvent dependence of delta(Rh-103) is minimal. Copyright (C) 2004 John Wiley Sons, Ltd.