Reversible coordination of N2 and H2 to a homoleptic S = 1/2 Fe(i) diphosphine complex in solution and the solid state

A 15 valence-electron Fe(i) species rapidly and reversibly binds N2 and H2, the latter producing a rare paramagnetic dihydrogen complex.


General considerations
All chemical manipulations were performed under a N 2 or Ar atmosphere either using standard Schlenk-line techniques or a MBraun Labmaster DP glovebox, unless stated otherwise. H 2 (BOC, 5.5 Research Grade) was dried by passage through a NANOCHEM ® WA-500 OMX™ purifying column.

UV-vis: See
[Fe(depe) 2             °C; the concentration of N 2 in THF was taken to be 6.4 mM using solubility data from ref. [8]. The presence of clearly defined isosbestic points corroborates a completely reversible equilibrium solely involving two Fe-containing complexes and N 2 .

Computational data
Density functional calculations were carried out using the ADF program suite version 2014.1. [13] The Slater-type orbital (STO) basis sets were of triple-ζ quality augmented with a one polarization function (ADF basis TZP). Core electrons were frozen (C, N 1s; Fe 2p) in our model of the electronic configuration for each atom. The local density approximation (LDA) by Vosko, Wilk and Nusair (VWN) [14] was used together with the exchange correlation corrections of Becke and Perdew (BP86). [15] Optimized geometries were ascertained as local mimima via frequency calculations. Timedependent DFT (TDDFT) calculations for calculating electronic absorption spectra used a SAOP functional and a QZ4P all-electron basis set.   were found to sit on independent -4 positions. With the exception of the Fe centre, the cation was found to be disordered due to a mismatch between the lower symmetry of the cation (D 2 ) and the site symmetry of its location in the crystal (S 4 ), hence only the Fe atom (which sits directly on the latter) is strictly ordered. This disorder was modelled by using one complete unique 50% occupancy orientation for the depe ligand.
The geometry of the unique orientation was optimised, the thermal parameters of the phosphorus atoms were restrained to be similar, and all of the non-hydrogen atoms were refined anisotropically.
Two of the CH 3 groups of each depe ligand orientate themselves above and below the FeP 4 moiety, which might suggest weak C-H···Fe agostic or anagostic interactions. While the inherent crystallographic disorder precludes a definitive assignment, it should be noted that computational calculations suggest the absence of such features.