The Preparation of Rhenium(I)-Amine and Rhenium(II) amine Dinitrogen Complexes and the Characterization of a Stretched Dihydrogen Species

A series of rhenium(I) dinitrogen complexes were prepared containing predominantly amine ligands. On the basis of infrared and electrochemical data, a system was selected that was anticipated to be a suitable precursor for an elongated dihydrogen complex. Upon oxidation by AgOTf, the dinitrogen ligand of fac-[Re(PPh₃)(PF₃)(dien)(N₂)]⁺ (3) is replaced with triflate to generate 13, fac-[Re(PPh₃)(PF₃)(dien)(OTf)]OTf, a convenient precursor to rhenium(II) and rhenium(I) amine complexes. Reduction of the rhenium(II) triflate 13 under 1 atm of hydrogen gas generates the complex fac-[Re(dien)(PPh₃)(PF₃)(dien)(H₂)]⁺ (fac-14). T₁ measurements indicate a dihydrogen species with a H−H distance of 1.38 ± 0.03 Å. The HD analog displays a J_HD of 6.7 Hz, corresponding to a H−H distance of 1.31 ± 0.03 Å, a value in good agreement with that determined from T₁ data and among the largest ever measured for an elongated dihydrogen system.