Synthesis and properties of two fold symmetric ruthenium and rhodium dihydrogen -hydride complexes

Complexes of the form (PCy3)2(L 2)RuH2 (L2 = bipyridine, phenanthroline or (CO) 2) have been prepared by reduction of the corresponding hydrido chloride complex with NaBH4 or LiAlH4. (PiPr 3)2(CO2)RuH2 was synthesized by reaction of (PiPr3)2RuH6 with CO. These dihydrides have been protonated to form (PR3)2(L 2)Ru(H2)H+ complexes which, along with Cp*(PMe 3)RhH3+, undergo rapid site exchange rendering the dihydrogen and hydride sites equivalent even at low temperatures. The dihydrogen-hydride complexes have been partially deuterated by exposure to D2(g) and show averaged JHD couplings of 5–12 Hz. Low temperature NMR spectra and interesting isotopic perturbation of resonance effects were observed in all five cases, but only in the case where L 2 = (CO)2 and R = Cy has decoalescence been observed. At 120K two carbonyl resonances were observed in the 13C NMR spectrum of 13CO enriched (PCy3)2(CO)2Ru(H 2)H+. This decoalescence allowed the barrier to exchange of the dihydrogen and hydride environments to be measured as approximately 5.5 kcal/mole. Tritium has been incorporated into Cp*(PMe3)RhH 3+ to further investigate the subtle effects of IPR with an even heavier isotope and therefore greater perturbation.