Synthesis and Characterization of the First Examples of Dicationic Dihydrogen Complexes of Iron and Ruthenium with the PF 3 Ligand

New dicationic dihydrogen complexes of the type trans ‐[M(η 2 ‐H 2 )(PF 3 )(diphosphane) 2 ] 2+ [M = Ru, diphosphane = dppm (Ph 2 PCH 2 PPh 2 ); M = Fe, Ru, diphosphane = dppe (Ph 2 PCH 2 CH 2 PPh 2 )] have been prepared from the precursor hydrides trans ‐[M(H)(PF 3 )(diphosphane) 2 ] + upon reaction with HOTf. In the case of dppm, in addition to the trans ‐dihydrogen complex cis ‐[Ru(η 2 ‐H 2 )(PF 3 )(dppm) 2 ] 2+ was also obtained in the protonation reaction. The intact nature of the H−H bond in these derivatives has been established using the spin−lattice relaxation time measurements (short T 1 values) and the large J H,D coupling constant of the H−D isotopomers. The H−H bond lengths and the stabilities of the dihydrogen complexes are discussed in terms of the π‐acidity of the PF 3 ligand and compared with other systems possessing trans CO and CNH ligands. The trans ‐[Ru(η 2 ‐H 2 )(PF 3 )(dppe) 2 ] 2+ complex was found to be remarkably stable with respect to the loss of bound H 2 for a period of about 16 h. The H−D isotopomer of this complex exhibits small temperature variations in the J H,D coupling constant. The X‐ray crystal structure of trans ‐[Ru(H)(PF 3 )(dppm) 2 ][BF 4 ] has been determined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)