| Autor: |
Prokopchuk DE; Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory , Richland , Washington 99352 , United States., Chambers GM; Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory , Richland , Washington 99352 , United States., Walter ED; Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland , Washington 99352 , United States., Mock MT; Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory , Richland , Washington 99352 , United States., Bullock RM; Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory , Richland , Washington 99352 , United States. |
| Abstrakt: |
While diamagnetic transition metal complexes that bind and split H 2 have been extensively studied, paramagnetic complexes that exhibit this behavior remain rare. The square planar S = 1/2 Fe I (P 4 N 2 ) + cation (Fe I+ ) reversibly binds H 2 /D 2 in solution, exhibiting an inverse equilibrium isotope effect of K H2 / K D2 = 0.58(4) at -5.0 °C. In the presence of excess H 2 , the dihydrogen complex Fe I (H 2 ) + cleaves H 2 at 25 °C in a net hydrogen atom transfer reaction, producing the dihydrogen-hydride trans-Fe II (H)(H 2 ) + . The proposed mechanism of H 2 splitting involves both intra- and intermolecular steps, resulting in a mixed first- and second-order rate law with respect to initial [Fe I+ ]. The key intermediate is a paramagnetic dihydride complex, trans-Fe III (H) 2 + , whose weak Fe III -H bond dissociation free energy (calculated BDFE = 44 kcal/mol) leads to bimetallic H-H homolysis, generating trans-Fe II (H)(H 2 ) + . Reaction kinetics, thermodynamics, electrochemistry, EPR spectroscopy, and DFT calculations support the proposed mechanism. |
