ja0491432_si_002.pdf (984.07 kB)
Cooperative Bimetallic Reactivity: Hydrogen Activation in Two-Electron Mixed-Valence Compounds
journal contribution
posted on 2004-08-11, 00:00 authored by Thomas G. Gray, Adam S. Veige, Daniel G. NoceraReversible dihydrogen uptake by a two-electron mixed-valence di-iridium complex is examined
with nonlocal density-functional calculations. Optimized metrics compare favorably with crystal structures
of isolated species, and the calculated activation enthalpy of acetonitrile exchange is accurate within
experimental error. Dihydrogen attacks the Ir2 core at IrII; the Ir0 center is electronically saturated and of
incorrect orbital parity to interact with H2. Isomeric η2-H2 complexes have been located, and harmonic
frequency calculations confirm these to be potential energy minima. A transition state links one such complex
with the final dihydride; calculated atomic charges suggest a heterolytic H2 bond scission within the di-iridium coordination sphere. This investigation also establishes a ligand-design criterion for attaining
cooperative bimetallic reactivity, namely, that the supporting ligand framework has sufficient mechanical
flexibility so that the target complex can accommodate the nuclear reorganizations that accompany substrate
activation.