Highly functionalizable penta-coordinate iron hydrogen production catalysts with low overpotentials

Abstract

Penta-coordinate iron carbonyl complexes that are built around the rigid Fe(PNP) motif (PNP = (C6H5)2PN(R)P(C6H5)2) are synthesized and structurally and spectroscopically characterized. These complexes allow for facile customization of the secondary ligand sphere with various types of linkers and functional groups. The new [Fe(S2C6H4)(PNP)(CO)] complexes show dihydrogen production electrocatalysis at overpotentials of 0.09-0.21 V vs. Pt under mildly acidic conditions (and activities from 0.28 to 3.51 s(-1)). The most active compound exhibits a turnover frequency (TOF) of 3.51 s(-1) at an overpotential of only 0.15 V vs. Pt. Trends in activity are further analyzed. It is found that (a) a decrease in overpotential correlates strongly with the electron withdrawing strength of the PNP amine substituent, and (b) aliphatic substituents give comparatively higher TOFs than aromatic ones. An EC-type mechanism is shown to proceed by initial reduction of the Fe(II) metal center and proposed formation of an Fe(III) hydride intermediate. Analogous cobalt compounds were synthesized and characterized, but were found to have low stability in acidic media under turnover conditions, and hence, are unsuitable as catalysts for proton reduction.

Role of the ligand and activator in selective Cr–PNP ethene tri- and tetramerization catalysts – a spectroscopic study

“…((C 6 H 5 ) 2 P) 2 N iPr and ((o-C 6 H 4 OMe) 2 P) 2 N Me (Scheme 1) were prepared following earlier reported literature procedures. 17,18 ((C 6 H 5 ) 2 P) 2 N iPr CrCl 3 (THF) (complex 1, Scheme 2a) and ((o-C 6 -H 4 OMe) 2 P) 2 N Me CrCl 3 (complex 2, Scheme 2b) were also prepared following literatures procedures. 7,15 Catalytic performance of complex 1 and 2…”

Investigations on the PNP‐chelated diiron dithiolato complexes Fe2(μ‐edt)(CO)4{κ2‐(Ph2P)2NC6H4R} related to the [FeFe]‐hydrogenase active site

“…The aminodiphosphine ligands (Ph 2 P) 2 NC 6 H 4 R (R =À 3-CCH, 4-CCH) were prepared according to literature procedures. [43][44]…”

“…Fe 3 (CO) 12 , Me 3 SiSCH 2 CH 2 SSiMe 3 , Et 3 N and some other materials were available commercially and used as received. The aminodiphosphine ligands (Ph 2 P) 2 NC 6 H 4 R (R=−3‐CCH, 4‐CCH) were prepared according to literature procedures [43–44] . Preparative TLC was carried out on glass plates (26 × 20 × 0.25 cm) coated with silica gel H (10–40 μ m).…”

Synthesis of Mono- and Diiron Dithiolene Complexes as Hydrogenase Models by Dithiolene Transfer Reactions, Including the Crystal Structure of [{Ni(S2C2Ph2)}6]

“…This is particularly the case for 5-coordinate complexes of the type [Fe(bdt)(CO)(L 2 )] where L 2 is a diphosphine ligand (Figure 2). [32][33][34][35][36][37][38][39] It should also be mentioned that bdt complexes of other metals, notably cobalt, nickel and molybdenum, have also shown activity for proton reduction. [40][41][42][43][44][45] Over fifty years after the initial breakthroughs of the 1960s, the efficient synthesis of transition metal dithiolene complexes continues to be an important objective in inorganic chemistry.…”