Structure and Dynamics of LRh“H4” (L = Cp, Tp) Systems. A Theoretical Study

A density functional theory study on the LRh“H 4 ” (L = Cp, Tp) systems has been carried out. When L = Cp, a piano-stool tetrahydride structure has been found to be the most stable, and a η 2 -H 2 structure has been found slightly higher in energy. Conversely, when L = Tp only an octahedral dihydrogen−dihydride structure has been determined. Rotational barriers corresponding to dihydrogen−dihydride structures when L = Cp and L = Tp are obtained and their differences are interpreted in terms of the dependence of π-back-donation along the librational motion of the dihydrogen unit. Finally, a value of 9.2 cm - 1 has been theoretically determined for the rotational tunneling splitting of the librational ground state of TpRh(η 2 -H 2 )H 2, in excellent accord with experimental measurements obtained by means of INS experiments.