25878-73-3Relevant academic research and scientific papers
Solution equilibrium between classical and nonclassical polyhydride tautomers [ReH4(CO)L3]+ and [ReH2(η2-H2)(CO)L3]+ (L = PMe2Ph). Equilibrium isotope effects and an intermediate trihydrogen complex in intramolecular site exchange of dihydrogen and hydride ligands
Luo, Xiao-Liang,Crabtree, Robert H.
, p. 6912 - 6918 (2007/10/02)
Treatment of ReCl3(CO)(PMe2Ph)3 with LiAlH4 in refluxing Et2O gives ReH3(CO)(PMe2Ph)3 (1). Protonation of 1 with HBF4·OEt2 in CD2Cl2 at -78 °C results in an equilibrium mixture of [ReH4(CO)(PMe2Ph)3]+ (2a) and its nonclassical tautomer [ReH2(η2-H2)(CO)(PMe2Ph) 3]+ (2b). The site exchange of dihydrogen and hydride ligands in 2b and the interconversion of 2a and 2b lead to an unusual temperature dependence of the T1 values. 2b-d3 shows a 1JHD value of 34 Hz. An isotope effect is observed for the equilibrium between 2a and 2b; deuteration shifts the equilibrium toward the nonclassical form. In addition, an isotope fractionation is found in partially deuterated 2b, with a substantial preference for deuterium to occupy the nonclassical site. These two processes can lead to isotopic perturbation of resonance (IPR) effects of opposite sign and constitute a new case in which expected IPR shifts are not observed. The hydride site exchange in 2b is much faster than the interconversion of 2b and 2a, indicating that 2a is not an intermediate in the former process. The intermediacy of a trihydrogen complex is therefore proposed for the site exchange in 2b.
