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Dalton Trans., 2006, 2072 - 2080, DOI: 10.1039/b510616h
Contrasting photochemical and thermal reactivity of Ru(CO)2(PPh3)(dppe) towards hydrogen rationalised by parahydrogen NMR and DFT studies
Damir Blazina, John P. Dunne, Stuart Aiken, Simon B. Duckett, Charlotte Elkington, John E. McGrady, Rinaldo Poli, Sue J. Walton, M. Sabieh Anwar, Jonathan A. Jones and Hilary A. Carteret
The synthesis, characterisation and thermal and photochemical reactivity of Ru(CO)2(PPh3)(dppe) 1 towards hydrogen are described. Compound 1 proved to exist in both fac (major) and mer forms in solution. Under thermal conditions, PPh3 is lost from 1 in the major reaction pathway and the known complex Ru(CO)2(dppe)(H)2 2 is formed. Photochemically, CO loss is the dominant process, leading to the alternative dihydride Ru(CO)(PPh3)(dppe)(H)2 3. The major isomer of 3, viz. 3a, contains hydride ligands that are trans to CO and trans to one of the phosphorus atoms of the dppe ligand but a second isomer, 3b, where both hydride ligands are trans to distinct phosphines, is also formed. On the NMR timescale, no interconversion of 3a and 3b was observed, although hydride site interchange is evident with activation parameters of
H
= 95 ± 6 kJ mol–1 and S = 26 ± 17 J K–1 mol–1. Density functional theory confirms that the observed species are the most stable isomeric forms, and suggests that hydride exchange occurs via a transition state featuring an 
2-coordinated H2 unit.
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