Diiron Dithiolate Hydrides Complemented with Proton‐Responsive Phosphine–Amine Ligands

The reaction of Fe 2 (pdt)(CO) 6 with two equivalents of Ph 2 PC 6 H 4 NH 2 (PNH 2 ) affords the amido hydride HFe 2 (pdt)(CO) 2 (PNH 2 )(PNH) {[H 1 H] 0 , pdt 2– = CH 2 (CH 2 S – ) 2 }. Isolated intermediates in this conversion include Fe 2 (pdt)(CO) 5 (κ 1 ‐PNH 2 ) and Fe 2 (pdt)(CO) 4 (κ 2 ‐PNH 2 ). X‐ray crystallographic analysis of [H 1 H] 0 shows that the chelating amino/amido–phosphine ligands occupy trans ‐dibasal positions. The 31 P NMR spectrum indicates that [H 1 H] 0 undergoes rapid proton exchange between the amido and amine centers. No exchange was observed for the hydride. Protonation of [H 1 H] 0 gives [HFe 2 (pdt)(CO) 2 (PNH 2 ) 2 ] + ([H 2 1 H] + ), which contains two equivalent amino–phosphine ligands. Single‐crystal X‐ray crystallographic analysis of [H 2 1 H] + also reveals hydrogen bonds between the exo amine protons with a THF molecule and BF 4 . Deprotonation of [H 1 H] 0 with potassium tert ‐butoxide gave [HFe 2 (pdt)(CO) 2 (PNH) 2 ] – ([ 1 H] – ), which was characterized spectroscopically. The complex has time‐averaged C 2 symmetry with two amido–phosphine ligands. FTIR spectroscopic measurements show that υ CO shifts by approximately 20 cm –1 in the series [ 1 H] – , [H 1 H] 0 , and [H 2 1 H] + . These shifts are comparable to those seen for the S‐protonation of the (NC) 2 (CO)Fe(µ‐Scys) 2 Ni(Scys) 2 site in the [NiFe]‐hydrogenases.[1][C. Fichtner, 2006]