The reaction of M(CO)3(Ph2PCH2CH2PPh2) (M = Fe, Ru) with parahydrogen: probing the electronic structure of reaction intermediates and the internal rearrangement mechanism for the dihydride products

The photochem. reaction of Ru(CO)3(dppe) and Fe(CO)3(dppe) (dppe = bis-(1,2-diphenylphosphino)ethane; Ph2PCH2CH2PPh2) with parahydrogen has been studied by in situ-photochem. resulting in NMR spectra of Ru(CO)2(dppe)(H)2 that show significant enhancement of the hydride resonances while normal signals are seen in Fe(CO)2(dppe)(H)2. This effect is assocd. with a singlet electronic state for the key intermediate Ru(CO)2(dppe) while Fe(CO)2(dppe) is a triplet. DFT calcns. reveal electronic ground states consistent with this picture. The fluxionality of Ru(CO)2(dppe)(H)2 and Fe(CO)2(dppe)(H)2 has been examd. by NMR spectroscopy and rationalized by theor. methods which show that two pathways for ligand exchange exist. In the first, the phosphorus and carbonyl centers interchange positions while the two hydride ligands are unaffected. A second pathway involving interchange of all three ligand sets was found at slightly higher energy. The H-H distances in the transition states are consistent with metal-bonded dihydrogen ligands. However, no local min. (intermediate) was found along the rearrangement pathways. Electronic supplementary information (ESI) is available at http://www.rsc.org/suppdata/dt/b4/b407457b/ and contains Cartesian coordinates for all optimized geometries, synthesis and NMR parameters for Fe(CO)2(dppe)(H)2 and rate data for ligand interchange.