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.
Carlton
Laurence
L
Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, PO Wits, 2050, Republic of South Africa. carlton@aurum.chem.wits.ac.za
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