Transition metal dihydrogen complexes: isotope effects on reactivity and structure

Complexation of dihydrogen to transition metal centers was discovered by Kubas and coworkers in 1984. The notion that the simplest molecule in chemistry can act as a ligand to form relatively stable transition metal complexes has led to a paradigm shift in coordination chemistry. Crucial to the exploration of this intriguing new chemistry has been the use of isotope substitution. Several aspects of the coordination chemistry of dihydrogen have revealed fascinating isotope effects on reactivity, spectroscopy and in some cases structure. Complexation of HD has been used to diagnose bond distances from measurements of JHD and isotope effects for D2 versus H2 binding have been evaluated. Examples of quantum mechanical exchange coupling in H2 complexes have been described. These effects disappear when one of the H atoms is replaced by D. In molecules with bound hydrogen adjacent to a hydride ligand, non‐statistical occupancy of hydrogen versus hydride sites by deuterons has been observed. In some cases, isotope‐dependent structures have been established by the study of HD, HT and DT complexes using NMR spectroscopy.