Synthesis and Characterization of New Dicationic Dihydrogen Complexes of Ruthenium

Abstract

A series of new dicationic dihydrogen complexes of the type trans‐[Ru(η²‐H₂)(L)(dppm)₂][X]₂ (L=CH₃CN, CH₂˭CHCN, C₆H₅CN, C₆H₅NC, CO; X=BF₄, OTf; dppm=Ph₂PCH₂PPh₂) have been prepared by protonating the precursor hydrides using either HBF₄ · Et₂O or HOTf. The variable temperature spin‐lattice relaxation times (T ₁, ms) and the H, D coupling constants of the η²‐HD isotopomers indicate the intact nature of the H‐H bond in these derivatives. The H‐H distances of the dihydrogen complexes bearing trans‐nitrile ligands are not significantly affected by the sterics and the electronics of the nitrile. On the other hand, the H‐H distances of the dihydrogen complexes bearing either isonitrile or CO ligand are comparable to those possessing chelating diphosphine ligands of greater bite angle. Also, the thermal stabilities of these complexes are significantly less than those bearing diphosphines of greater bite angle. The trans‐[Ru(H)(CH₃CN)(dppm)₂][BF₄] complex has been characterized by X‐ray crystallography.

Keywords:

• Hydride complex
• dihydrogen complex
• dihydrogen activation
• sigma complex
• ruthenium
• bite angle

Acknowledgments

We are grateful to the Department of Science & Technology, India for financial support and also for funding the procurement of a 400 MHz NMR spectrometer under the “FIST” program and an X‐ray diffractometer.