Contrasting photochemical and thermal reactivity of Ru(CO)2(PPh3)(dppe) towards hydrogen rationalised by parahydrogen NMR and DFT studies

Damir Blazina (1) , John P Dunne (1) , Stuart Aiken (1) , Simon B Duckett (1) , Charlotte Elkington (1) , John E Mcgrady (2) , Rinaldo Poli (3) , Sue J Walton (1) , M. Sabieh Sabieh Anwar (4) , Jonathan A Jones (4) , Hilary A Carteret (5)

1 Department of Chemistry [York, UK]
2 WestCHEM
3 LCC - Laboratoire de chimie de coordination
4 Clarendon Laboratory [Oxford]
5 Department of Combinatorics and Optimization

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)22 is formed. Photochemically, CO loss is the dominant process, leading to the alternative dihydride Ru(CO)(PPh3)(dppe)(H)23. 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 ΔH‡ = 95 ± 6 kJ mol−1 and ΔS‡ = 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 η2-coordinated H2 unit.

Domaines: Chimie de coordination; Chimie théorique et/ou physique

Damir Blazina, John P Dunne, Stuart Aiken, Simon B Duckett, Charlotte Elkington, et al.. Contrasting photochemical and thermal reactivity of Ru(CO)2(PPh3)(dppe) towards hydrogen rationalised by parahydrogen NMR and DFT studies. Dalton Transactions, 2006, 2006 (17), pp.2072-2080. ⟨10.1039/B510616H⟩. ⟨hal-03196074⟩