Vibrational Properties of [FeH(N2)(depe)2]+ and [FeCl(N2)(depe)2]+]: Dinitrogen Bonding in the Low Activation Limit

Abstract

The vibrational properties of the two octahedral Fe II dinitrogen complexes [FeH(N 2 )(depe) 2 ] ϩ (1) and [FeCl(N 2 )(depe) 2 ] ϩ (2, depe ϭ 1,2-bis(diethylphosphino)ethane) are investigated with the help of infrared and Raman spectroscopies.

Fe–H/D stretching and bending modes in nuclear resonant vibrational, Raman and infrared spectroscopies: Comparisons of density functional theory and experiment

“…This shift is well-matched int the DFT results in Fig. 6, and is similar to an Fe–H bending shift (from 783 to 573 cm −1 ) reported by Tuczek and co-workers for an FeHN 2 complex 14. The lower frequency feature (at 529 cm −1 in the DFT calculation on the H isotopomer) may be the same as a shoulder in the experimental spectrum at the about the same location.…”

The Iron Hydrido Complex [FeH(dppe)2]+: Solution and Solid‐State Reactivity with Dinitrogen

“…Figure 7 shows that there are four vibrations in the IR spectrum of 2a below 500 cm Ϫ1 ; i.e., at 472/454 cm Ϫ1 and 427/420 cm Ϫ1 , which shift in the 15 N spectrum to 467/451 cm Ϫ1 and 423/416 cm Ϫ1 , respectively. However, a definitive assignment of these vibrations to ν(FeN) and δ(FeNN), as achieved for [FeH(N 2 )(depe) 2 ]BPh 4 and [FeCl(N 2 )(depe) 2 ]BPh 4 [10], is problematic. In case of the latter compounds, the stretch could be distinguished from the bend by its much higher intensity in the Raman spectrum.…”

“…The bonding of N 2 in these systems pro-ceeds in a spin-forbidden process which could be shown to be the origin of the lability of the Fe-N 2 bond. The analogous Fe II -N 2 depe complex with a trans hydrido ligand is thermally more stable [10]. This also applies to the corresponding dppe system [FeH(N 2 )(dppe) 2 ] ϩ ; the five-coordinate precursor [FeH(dppe) 2 ]BPh 4 has even been described to bind dinitrogen in tetrahydrofuran (thf) solution from air [11].…”

“…Recently we reported a vibrational-spectroscopic comparison between [FeCl(N 2 )(depe) 2 ]BPh 4 and [FeH(N 2 )(depe) 2 ]-BPh 4 coupled to normal coordinate analysis [10]. In agreement with the high values found for ν(NN) (2086 and 2091 cm Ϫ1 , respectively), the N 2 ligands in both compounds are non-activated which corresponds to the observation that N 2 is not protonatable in Fe II systems (vide supra).…”

Can [M(H)2(H2)(PXP)] Pincer Complexes (M=Fe, Ru, Os; X=N, O, S) Serve as Catalyst Lead Structures for NH3 Synthesis from N2 and H2?

“…[2] Significant efforts, many of them driven by an attempt to understand biological nitrogen reduction, have been made to synthesize and characterize transition-metal complexes that bond with and activate the N 2 molecule. A wealth of metal complexes (for example, titanium, [3] zirconium, [4, 9c] vanadium, [5] molybdenum, [6] and iron complexes [7] ) were shown to bond with and activate the N 2 molecule to varying extents, some of them even breaking the N À N structure motif completely. Many of the theoretical and spectroscopic data available have been analyzed.…”