Search

103Rh NMR chemical shiftshave been computed at theGIAO-B3LYP level of density functional theory (DFT) for a number of[Rh(COD)(P∩P)]+complexes [COD = 1,5-cyclooctadiene,P∩P = chelating bis(phosphine) including bis(dimethylphosphino)ethane(dmpe), bis(diphenylphosphino)ethane (dmpe), MeDUPHOS, DIOP, BINAP,and others]. Structures have been optimized using PBE0 and M06 functionalsin the gas phase, in a continuum modeling the solvent, and with [PF6]−counteranion included explicitly. Observedtrends in δ(103Rh) are well reproduced for pristinePBE0-optimized cations in the gas phase or for ion pairs optimizedin a continuum with M06. While there is no overall trend between computedδ(103Rh) values and complex stabilities (evaluatedthrough isodesmic ligand exchange reactions), there is a linear relationshipbetween the 103Rh chemical shifts and the mean Rh–Pbond distances. This relationship appears to be remarkably general,encompassing various chelating ring sizes and substituents at P, includingremote electron-donating and -withdrawing substituents that are characterizedthrough their Hammett constants. The combination of 103Rh NMR and DFT computations emerges as a useful tool for structureelucidation of Rh–phosphine complexes. [ABSTRACT FROM AUTHOR]

The experimental reaction of [1,2,4-(Me3C)3C5H2]2CeH, Cp′2CeH, and CH3OSO2CH3beginsby α-C–Hactivation of the SCH3group, forming Cp′2CeCH2SO2(OCH3), which evolves intoCp′2CeOCH3with elimination of CH2(and presumably SO2). Prolonged heating of thismixture (days at 60 °C) forms Cp′2CeOSO2CH3and CH3OCH3. The metallacycle[1,2,4-(Me3C)3C5H2][1,2-(Me3C)2-4-(Me2CCH2)C5H2]Ce, when presented with the choice of C–H bondsin CH3S and CH3O groups, deprotonates both withcomparable rates, ultimately forming Cp′2CeOCH3and Cp′2CeOSO2CH3at 20 °C. The experimental studies are illuminated by DFT calculationson the experimental systems, which show that the hydride selects themore acidic CH3S bond, whereas the metallacycle reactswith C–H bonds of both the CH3S and CH3O groups of CH3OSO2CH3. In the metallacyclereaction, the initially formed regioisomers, Cp′2CeCH2SO2(OCH3) and Cp′2CeCH2OSO2CH3, rearrange tothe observed products, Cp′2CeOCH3andCp′2CeOSO2CH3, respectively.Furthermore, C–H activation at the SCH3group formstwo isomers of Cp′2CeCH2SO2(OCH3) in the reaction of CH3OSO2CH3with the metallacycle and only one in the reactionwith the hydride. The lack of selectivity in the reactions of themetallacycle relative to the hydride is due to the metallacycle’sgreater thermodynamic advantage and lower energy barriers, which arelinked to the higher bond energy of Ce–H relative to Ce–Cin the metallacycle. [ABSTRACT FROM AUTHOR]