PNP-Chelated and -Bridged Diiron Dithiolate Complexes Fe₂(μ-pdt)(CO)₄{(Ph₂P)₂NR} Together with Related Monophosphine Complexes for the [2Fe]_H Subsite of [FeFe]-Hydrogenases: Preparation, Structure, and Electrocatalysis

Abstract

As the [2Fe] H subsite models of [FeFe]-hydrogenases, a series of PNP-chelated and -bridged diiron dithiolate complexes 1a−f and 2a−f together with the three related monophosphine complexes 3a−c were prepared by the selective substitutions of the all-carbonyl complex Fe 2 (μpdt)(CO) 6 (A, pdt = SCH 2 CH 2 CH 2 S) with aminodiphosphines (Ph 2 P) 2 NR (denoted as PNP) under different reaction conditions. The first UV irradiation of the toluene solutions of A with different PNP ligands (PNP = (Ph 2 P) 2 NR; R = (CH 2 ) 3 Me, (CH 2 ) 3 NMe 2 , (CH 2 ) 3 Si(OEt) 3 , C 6 H 5 , C 6 H 4 OMe-p, C 6 H 4 CO 2 Me-p) readily afforded the target PNP-chelated complexes Fe 2 (μ-pdt)(CO) 4 {(κ 2 -Ph 2 P) 2 NR} (1a−f), while the reflux of xylene solutions of A with the aforementioned PNP ligands produced the PNP-bridged complexes Fe 2 (μ-pdt)(CO) 4 {(μ-Ph 2 P) 2 NR} (2a−f). Comparatively, treatments of A and one type of PNP ligand with N-aryl substituents R (R = C 6 H 5 , C 6 H 4 OMe-p, C 6 H 4 CO 2 Me-p) in MeCN at room temperature in the presence of the decarbonylating agent Me 3 NO•2H 2 O formed the unexpected monophosphine complexes Fe 2 (μ-pdt)(CO) 5 {κ 1 -Ph 2 P(NHR)} (3a−c) and the minor chelated complexes 1d−f. All of the complexes 1a−f, 2a−f, and 3a−c have been characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1a,b,d−f, 2b,d−f, and 3b by X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of complexes 1a and 2a as a pair of representative isomers have been evaluated and compared by cyclic voltammetry in MeCN as solvent in the absence and presence of HOAc as a proton source.

Synthesis, structures, and electrocatalytic properties of phosphine‐monodentate, −chelate, and ‐bridge diiron 2,2‐dimethylpropanedithiolate complexes related to [FeFe]‐hydrogenases

“…For the diphosphine‐chelate complexes 3a and 3b , their IR spectra show four absorption bands in the region of 2016–1911 cm −1 for their iron carbonyls (Table ), wherein the first ν C ≡ O value of approximately 2015 cm −1 is well accordant with those of the previously‐reported diiron chelate complexes Fe 2 ( μ ‐xdt)(CO) 4 ( k 2 ‐diphosphine) (xdt = pdt, edt, odt, adt NR ) . The average ν C ≡ O value (1955 cm −1 ) of 3a is slightly bigger than that (1952 cm −1 ) of 3b (Table ), clearly resulting from the electron‐donating effect of the N‐substituent (NR) with the following order of NPh ( 3a ) ˂ NBu n ( 3b ) in their (Ph 2 P) 2 NR ligands.…”

“…In contrast, the similar Me 3 NO‐assisted decarbonylations of A by 1.5 equiv. small bite‐angle diphosphines (Ph 2 P) 2 X (X = NPh and CH 2 ) resulted in the unexpected formation of the monodentate complexes Fe 2 ( μ ‐Me 2 pdt)(CO) 5 { κ 1 ‐Ph 2 PX'} [X' = NHPh ( 2a ) and CH 2 PPh 2 ( 2b )] in moderate yields (see route (ii) in Scheme ), as reported previously in several known diiiron pdt or adt NPh analogues . Furthermore, the UV‐irradiated toluene solutions of A and small bite‐angle PNP diphosphines (Ph 2 P) 2 NPh or (Ph 2 P) 2 NBu n resulted in the respective formation of the PNP‐chelate complexes Fe 2 ( μ ‐Me 2 pdt)(CO) 4 ( κ 2 ‐(Ph 2 P)X) [X = NPh ( 3a ) and NBu n ( 3b )] in moderate yields, whereas the similar reaction of A with one PCP diphosphine (Ph 2 P) 2 CH 2 (dppm) rarely produced a diphosphine‐bridge diiron complex Fe 2 ( μ ‐Me 2 pdt)(CO) 4 ( μ ‐dppm) ( 4b ) in low yield (see route (iii) in Scheme ) .…”

“…Inspired by these findings mentioned above and in comparison with the previous studies on the substitutions of diiron hexacarbonyl complexes bearing some dithiolate bridges such as pdt, edt and adt NR , little attention has been however paid to the reactions of all‐carbonyl diiron complexes with bulky dithiolate bridges such as Me 2 pdt [(SCH 2 ) 2 CMe 2 ], Et 2 pdt [(SCH 2 ) 2 CEt 2 ], etc . In this work, we carried out the treatments of parent complex Fe 2 ( μ ‐Me 2 pdt)(CO) 6 ( A ) with common monophosphines P(C 6 H 4 R‐ p ) 3 (R = Me, Cl) or small bite‐angle diphosphines (Ph 2 P) 2 X (X = CH 2 (dppm), NPh, NBu n ) in different conditions, mainly aiming to i) observe the potential influence of the diverse coordination modes (monodentate, chelate, bridge) of phosphine ligands in diiron complexes with bulky Me 2 pdt bridge on their formation, structures, and electrocatalytic behaviors, and to ii) further develop the biomimetic chemistry of [FeFe]‐hydrogenases for proton reduction.…”

“…In this context, in order to explore a class of cheap and efficient artificial catalysts for electrocatalytic proton reduction to H 2 , a great number of diiron dithiolate complexes that mimic the diiron subsite of [FeFe]‐hydrogenases were obtained over the decades . Among the preparation of diiron subsite models, the interesting substitutions of all‐carbonyl diiron complexes Fe 2 ( μ ‐xdt)(CO) 6 (xdt = pdt, (SCH 2 ) 2 CH 2 ; edt, (SCH 2 ) 2 ; adt NR , (SCH 2 ) 2 NR) by small bite‐angle diphosphines (Ph 2 P) 2 X (X = CR 2 named PCP and X = NR' labeled PNP in this study) have attracted much attentions since diverse diiron phosphine complexes can be afforded and have also shown different electrocatalytic properties of proton reduction to H 2 …”

Alloyed Tetranuclear Metal Chains of Pd4−nPtn (n=0–3) Scaffolded by a New Linear Tetraphosphine Containing a PNP Bridge

“…We have then intended to design Ph 2 PCH 2 P(Ph)N(R)P(Ph)CH 2 PPh 2 type linear tetraphosphines because the centralN Rg roup is easily varied by commercially availableprimary amines,and enablesb oth steric and electronic tuning of the central part of linear tetraphosphines.W hereas many phosphazane compounds formulated R 2 PN(R')PR 2 have been used to synthesize mono-, di-, andt rinuclearc omplexes with some functionalities concerning to the NR' substituents, [8][9][10][11][12][13][14][15][16][17][18] multidentate linear phosphine ligands with PNP bridgesa re no longer synthesized so far,e xcept some phosphazane macrocyclic ligands. [19] In the present study,anew linear tetraphosphine containing aP N(Ph)P phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan),w as synthesized and effectively utilized to stabilize as eries of Pd/Pt mixed metal tetranuclear chains, [Pd 4Àn Pt n (m-racdpmppan) 2 (XylNC) 2 ](PF 6 ) 2 (XylNC = xylyl isocyanide; n = 0: Pd 4 (1), 1: PtPd 3 (2), 2: PtPd 2 Pt (3), 2: Pt 2 Pd 2 (4), 3: Pt 2 PdPt (5)), in which the number and positionso fa dditional Pt atoms were remarkably controlled, and their electronic structures are finely tuned as alloyed metal chains by atomically precise Pt incorporation.…”