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, N3, 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 H2 or O2 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)(O2)(PPh3)3] (delta 1393 to 3273 ppm) and cis-[Rh(X)(O2)(PPh3)2(py)] (delta 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(103Rh) 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(103Rh) 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(103Rh) is minimal.
Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, PO Wits, 2050, Republic of South Africa. carlton@aurum.chem.wits.ac.za
Laurence
L
Carlton
D002248:Carbon Monoxide / Q000032:analysis / Q000737:chemistry*; D017606:Chlorine Compounds / Q000032:analysis / Q000737:chemistry*; D006859:Hydrogen / Q000032:analysis / Q000737:chemistry*; D017953:Isocyanates / Q000032:analysis / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D008968:Molecular Conformation; D010100:Oxygen / Q000032:analysis / Q000737:chemistry*; D011725:Pyridines / Q000032:analysis / Q000737:chemistry*; D012238:Rhodium / Q000032:analysis / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry
D017606:Chlorine Compounds; D017953:Isocyanates; D008024:Ligands; D011725:Pyridines; D012997:Solvents; D002248:Carbon Monoxide; D006859:Hydrogen; D012238:Rhodium; C023666:pyridine; D010100:Oxygen