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.

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As a further exploration of the asymmetrically substituted diiron models for the active site of [FeFe]hydrogenases, two new types of small bite-angle aminodiphosphine [(Ph 2 P) 2 NR; denoted as PNP in this study]chelated diiron N-phenyl-aza-and ethanedithioate complexes Fe 2 (μ-xdt)(CO) 4 {κ 2 -(Ph 2 P) 2 NR} (1a−1e) and (2a−2e), respectively, were successfully synthesized by the carbonyl substitution reactions of all-carbonyl diiron complexes Fe 2 (μxdt)(CO) 6 (xdt = SCH 2 N(Ph)CH 2 S (adt NPh ) and SCH 2 CH 2 S (edt)) with PNP (PNP = (Ph 2 P) 2 NR, R = CMe 3 , CH 2 CHMe 2 , (CH 2 ) 3 Me, (CH 2 ) 3 Si(OEt) 3 , and (CH 2 ) 3 NMe 2 ) in the presence of Me 3 NO•2H 2 O or UV irradiation.All the new complexes obtained above have been well characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1a, 1b, 2a, and 2d by single-crystal X-ray diffraction analysis. By comparison, 31 P{ 1 H} NMR and X-ray crystallographic studies have clearly revealed that the change of the dithiolate bridge from adt NPh to edt has a significant influence on the coordination geometry of the chelating PNP ligands in Fe 2 S 2 complexes, in which the basal−basal configuration in the adt NPh complexes 1a−1e is favorable whereas the apical−basal conformation in the edt complexes 2a−2e is main. In addition, the electrochemical properties of complexes 1b and 2b as a pair of representative counterparts are evaluated and compared by cyclic voltammetry in the absence and presence of HOAc as a proton source, indicating that they are found to be electrocatalytically active.

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The novel intumescent flame retardant rigid polyurethane foams ((PEPS‐RPUF) were prepared based on a P‐N containing intumescent flame retardant, poly ethanediamine spirocyclic pentaerythritol bisphosphonate (PEPS). The flammability, thermal, and mechanical properties of PEPS‐RPUF were discussed. Scanning electron microscopy (SEM) and compression strength tests showed PEPS exhibited favorable compatibility with polyurethane matrix and smaller negative influence on the mechanical properties of PEPS‐RPUF. Cone calorimeter, vertical burning test (UL‐94) and limiting oxygen index (LOI) showed when the content of PEPS was 25 pph, the peak heat release rate (PHRR) and total heat release (THR) decrease, respectively, from 75.2 to 52.2 kW m−2 and from 5.7 to 4.1 MJ m−2. The LOI of PEPS‐RPUF could reach 27%, and a UL‐94 V‐0 rating was achieved. The PEPS‐RPUF exhibited an outstanding water resistance that it could still obtain a V‐0 rating after water soaking. Thermogravimetric analysis (TGA) showed the charring ability of PEPS‐RPUF was improved greatly compared to RPUF. SEM and Fourier transform‐infrared spectroscopy (FT‐IR) were utilized to characterize the surface morphology and chemical structure of the intumescent chars formed from PEPS‐RPUF. The results indicated the chars were compact and smooth, which was a critical factor for protecting the substrate material from burning. POLYM. ENG. SCI., 53:2478–2485, 2013. © 2013 Society of Plastics Engineers

Diiron dithiolate complexes have received special attention because of their structural similarity to the active site of [FeFe]-hydrogenases, which are the most efficient and fastest catalysts for the generation of dihydrogen in nature. Recently, we established a novel and efficient way to prepare phosphinesubstituted diiron aza-and oxadithiolate complexes. Reaction of Fe 2 (μ-SCH 2 OH) 2 (CO) 6 and several phosphine ligands L (L = PPh 3 , PPh 2 (2-C 5 H 4 N), P(C 6 H 4 -4-CH 3 ) 3 ) affords the intermediate Fe 2 (μ-SCH 2 OH) 2 (CO) 5 L, while the intermediate in situ reacts with primary amines RNH 25 [PPh 2 (2-C 5 H 4 N)] (5), Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH 2 SCH 3 ](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] (6), Fe 2 [(μ-SCH 2 ) 2 N C 6 H 4 -4-CH 3 ](CO) 5 [PPh 2 (2-C 5 H 4 N)] (7), and Fe 2 [(μ-SCH 2 ) 2 N C 6 H 4 -4-CH 3 ](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] (8) in moderate yields. A novel complex Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 PPh 2 ](CO) 5 (9) can be obtained by reaction of Fe 2 (μ-SCH 2 OH) 2 (CO) 6 and Ph 2 PCH 2 CH 2 NH 2 . In addition, according to the same strategy, phosphine-substituted diiron oxadithiolate complexes Fe 2 [(μ-SCH 2 ) 2 O](CO) 5 [P(C 6 H 4 -4-F) 3 ] (10), Fe 2 [(μ-SCH 2 ) 2 O](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] (11), and Fe 2 [(μ-SCH 2 ) 2 O](CO) 5 (Ph 2 PCH 2 CH 3 ) ( 12) have been successfully synthesized. All of the new complexes 1−12 were fully characterized by elemental analysis, IR, and NMR spectroscopy, and particularly for 1−4, 6, 7, and 9−11 by X-ray single diffraction analysis. Moreover, complexes 1 and 10 were found to be catalysts for H 2 production under electrochemical conditions.

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