Diiron Azadithiolate Complexes with Bridging Phosphine Ligand dppf: Synthesis and Characterization

Reaction of complex [(μ-SCH₂)₂NCH₂CO₂Me]Fe₂(CO)₆ (A) with 1,1^′-bis(diphenylphosphino)ferrocene (dppf) in the presence of the decarbonylating agent Me₃NO?2H₂O gave complex [(μ-SCH₂)₂NCH₂CO₂MeFe₂(CO)₅]₂[(η ⁵-Ph₂PC₅H₄)₂Fe] (1) in 72 % yields, whereas complex [(μ-SCH₂)₂NPhFe₂(CO)₅]₂[(η ⁵-Ph₂PC₅H₄)₂Fe] (2) was produced by reaction of [(μ-SCH₂)₂NPh]Fe₂(CO)₆ (B) with dppf in toluene at reflux in 41 % yield. The new complexes 1 and 2 were characterized by elemental analysis, IR, and ¹H (³¹P, ¹³C) NMR spectroscopy as well as by single crystal X-ray diffraction analysis. In the crystal structures of 1 and 2, the dppf ligand resides in an apical position of the square-pyramidal geometry of the neighbouring Fe atoms and the crystal structures were stabilized by the intermolecular C–H···O hydrogen bonds.     

Synthesis and Crystal Structures of Diiron Dithiolate Complexes Containing Diphosphine Ligands

As the active site model of [FeFe]-hydrogenases, complexes [(μ-PDT)Fe₂(CO)₅]₂(dppb) (PDT = SCH₂CH₂CH₂S, dppb = Ph₂PCH₂CH₂CH₂CH₂PPh₂) (1) and [(μ-SCH₂)₂NCH₂CO₂Me]Fe₂(CO)₅(dppm) (dppm = Ph₂PCH₂PPh₂) (2) were prepared by reactions of (μ-PDT)Fe₂(CO)₆ (A) or [(μ-SCH₂)₂NCH₂CO₂Me]Fe₂(CO)₆ (B) with dppb or dppm in the presence of the decarbonylating agent Me₃NO?2H₂O in MeCN at room temperature. Complex 1 was characterized by elemental analysis, IR, and ¹H (³¹P, ¹³C) NMR spectroscopic techniques. In addition, the molecular structures of 1 and 2 have been confirmed by single crystal X-ray diffraction analysis. In the crystal structure of 1, two phosphorus atoms of dppb reside in a basal position of the square-pyramidal coordination sphere of the Fe2 and Fe3 atoms. However, in the crystal structure of 2, P1 atom of dppm resides in an apical position of the square-pyramidal coordination sphere of the Fe2 atom.     

Phenyl-functionalized Diiron Propanedithiolate Complexes with 1,3-Bis(diphenylphosphine)propane Ligand: Chelated and Bridged Isomers as Proton-reduction Catalysts

Reaction of the diiron propanedithiolate complex [μ-(SCH₂)₂CHC₆H₅]Fe₂(CO)₆ (A) with 1,3-bis(diphenylphosphine)propane (dppp) in refluxing xylene yielded a chelated complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(κ²-dppp) (1) and a bridged isomer [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(μ-dppp) (2), while in refluxing toluene or in hot MeCN in the presence of Me₃NO·2H₂O gave the chelated isomer 1 as the major or sole product. Protonation of complex 1 upon addition of HBF₄·Et₂O gave a bridging hydride (μ-H)[(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(κ²-dppp)(BF₄) (3). The structures of all complexes were fully characterized by spectroscopic methods and for complexes 1 and 2 by X-ray crystallography. In the solid state, the chelated complex adopts an apical–basal diphosphine arrangement and exhibits a six-membered ring in approximate chair conformation. The bridged isomer presents an expected cisoid dibasal geometry and the bond length of Fe–Fe is longer than that in chelated isomer, reaching to 2.61 ?. The electrochemical investigation of both isomers in MeCN-[NBu₄][PF₆] in the presence of HBF₄ showed that the catalytic efficiency of the bridged isomer is no less than that of the chelated isomer but better than that of the analogue [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(μ-dppm). Interestingly, isomer 1 was converted to isomer 2 in refluxing xylene. An electron-transfer-catalyzed isomerization between one isomer and the other was not observed.     

Synthesis,structures and electrochemical properties of hydroxyl- and pyridyl-functionalized diiron azadithiolate complexes

The hydroxyl- and pyridyl-functionalized diiron azadithiolate complexes [{(μ-SCH₂)₂N(CH₂CH₂OH)}Fe₂(CO)₆] (1) and [{(μ-SCH₂)₂N(CH₂CH₂OOCPy)}Fe₂(CO)₆] (Py = pyridyl) (2) were prepared as biomimetic models of the active site of Fe-only hydrogenases. Both complexes were characterized by MS, IR, ¹H NMR spectra and elemental analysis. The molecular structures of 1 and 2 were determined by single crystal X-ray analysis. A network is constructed by intermolecular H-bonds in the crystals of 1. An S?O intermolecular contact was found in the crystals of 2, which is scarcely found for organometallic complexes. Cyclic voltammograms of 1 and 2 were studied to evaluate their redox properties.     

Unexpected Carbon–Carbon Bond Cleavage in the Reactions of the Pentagonal Bipyramidal Cluster Fe3(CO)6(μ-CO)2[μ3-η4-{RCC(Et)C(Et)CR}] with Styrene. Synthesis and X-ray Structure of Fe3(CO)6[μ3-η4-{EtC2CR}]2 (R = CH3(=CH2))

The thermal reactions of 2-methyl-1-hexen-3-yne [CH₃CH₂C≡CC(=CH₂)CH₃, metey] with Fe₃(CO)₁₂ have been studied: cluster opening or fragmentation and alkyne dimerization occur. Main products are the open triangular isomers [Fe₃(CO)₆(μ-CO)₂{CH₃(=CH₂)CC(Et)C(Et)C(=CH₂)CH₃}] (complex 3a) and [Fe₃(CO)₆(μ-CO)₂{C(Et)CCH₃(=CH₂)C(Et)CCH₃(=CH₂)}] (complex 3b). The structure and isomerism of the complexes has been confirmed by X-ray studies. The minor products of the reaction have been characterized by spectroscopic techniques. An attempt at exploiting the reactivity of the “free” C=C bonds of the coordinated ene-yne was made: complex 3a was reacted with styrene under thermal conditions. Unexpectedly considerable yields of the closed triangular cluster [Fe₃(CO)₆{EtC₂C(=CH₂)CH₃}₂] (complex 5) have been obtained. This behaviour had not been previously observed. The unprecedented structure of complex 5 has been confirmed with an X-ray study.     

Synthesis, characterization and electrochemical behavior of some N-heterocyclic carbene-containing active site models of [FeFe]-hydrogenases

Treatment of parent compounds [(μ-SCH₂)₂X]Fe₂(CO)₆ (A, X = O; B, X = NBu-t; C, X = NC₆H₄OMe-p) with N-heterocyclic carbene I_Mes (I_Mes = 1,3-bis(mesityl)imidazol-2-ylidene) generated in situ through reaction of imidazolium salt I_Mes ·HCl with n-BuLi or t-BuOK afforded the monocarbene-substituted complexes [(μ-SCH₂)₂X]Fe₂(CO)₅(I_Mes) (1, X = O; 2, X = NBu-t; 3, X = NC₆H₄OMe-p). Similarly, the monocarbene and dicarbene-substituted complexes [(μ-SCH₂)₂NBu-t]Fe₂(CO)₅[I^∗_Mes(CH₂)₃I^∗_Mes]·HBr (4) and [(μ-SCH₂)₂CH₂Fe₂(CO)₅]₂[μ-I^∗_Mes(CH₂)₃I^∗_Mes] (5, I^∗_Mes = 1-(mesityl)imidazol-2-ylidene) could be prepared by reactions of parent compound B with the mono-NHC ligand-containing imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · HBr and parent compound [(μ-SCH₂)₂CH₂]Fe₂(CO)₆ (D) with di-NHC ligand I^∗_Mes(CH₂)₃I^∗_Mes (both NHC ligands were generated in situ from reaction of n-BuLi with imidazolium salt [I^∗_MesI^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr), respectively. The imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr was prepared by reaction of 1-(mesityl)imidazole with Br(CH₂)₃Br. All the new model compounds 1-5 and imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr were fully characterized by elemental analysis, spectroscopy, and X-ray crystallography. On the basis of electrochemical studies of 1 and 2, compound 2 was found to be a catalyst for proton reduction to hydrogen. In addition, an EECC mechanism for this electrocatalytic reaction is preliminarily suggested.     

Reactivity study of a hydroxyl coordinated osmium vinyl complex OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)]

We studied the reactivity of an osmium vinyl complex containing a coordinated hydroxyl group OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)] (1) toward bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB),acid ligand (CO),base (Cs2CO3) and heat.Two osmium vinyl complexes OsCl2(dppb)[CH=C(PPh3)CHPh(OH)](2) and OsCl2(CO)2(PPh3)[CH=C(PPh 3)CHPh(OH)] (3),as well as two relatively rare phosphonium-containing osmafuran complexes Os(2-OCOO)(PPh3)2[CHC(PPh3)CPhO](4) and OsCl2 (PPh3)2[CHC(PPh3)CPhO](5),were obtained in high yields from these reactions.All products were characterized by NMR spectroscopy,elemental analysis,and their structures were further confirmed by single crystal X-ray diffraction.     

Synthetic and structural studies of tolyl-dithiolate diiron carbonyl complexes with tris(aryl)phosphine co-ligands

Reaction of [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₆ (1) with 2 equivalents of PPh₃ gave the monosubstituted complex [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅(PPh₃) (2) plus the disubstituted [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₄(PPh₃)₂ (3), while the complexes [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(3-C₆H₄CH₃)₃] (4) and [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄F)₃] (5) were prepared by the reactions of 1 with P(3-C₆H₄CH₃)₃ or P(4-C₆H₄F)₃ in the presence of Me₃NO. Complexes 3–5 were characterized by IR, NMR spectroscopy and single-crystal X-ray diffraction analysis. The molecular structures of 3–5 reveal that in each case, the phosphine ligand occupies the apical position in an overall distorted square pyramidal iron(I) complex geometry.     

Synthesis and characterization of carboxy-functionalized diiron model complexes of [FeFe]-hydrogenases: Decarboxylation of Ph2PCH2COOH promoted by a diiron azadithiolate complex

Two carboxy-functionalized diiron complexes [{(μ-SCH₂)₂X}{Fe(CO)₃}{Fe(CO)₂L}] (X = NC₃H₇, L = Ph₂PCH₂CH₂COOH, 4; X = CH₂, L = Ph₂PCH₂COOH, 5) were prepared, as biomimetic models of the [FeFe] hydrogenase active site, from the CO-replacement of [{(μ-SCH₂)₂NC₃H₇}Fe₂(CO)₆] (1) and (μ-pdt)Fe₂(CO)₆ (2) by phosphine ligands in CH₃CN at 40 °C, respectively. In contrast, the reaction of 1 with Ph₂PCH₂COOH under the same condition afforded complex [{(μ-SCH₂)₂NC₃H₇}{Fe(CO)₃}{Fe(CO)₂(Ph₂PCH₃)}] (3) with a decarboxylated phosphine ligand. The molecular structures of complexes 3-5 were determined by X-ray crystallographic analyses, which show that they have similar frameworks with the phosphine ligand on the apical position. The interesting C-H···S contacts between the methylene hydrogen atoms of the PhCH₂COOH ligand and the μ-S atoms of the pdt-bridge are found in the crystal of 5. According to the experimental evidence, a plausible mechanism, via sequential phosphine coordination, N-protonation, and decarboxylation steps, is proposed for the formation of 3 and for explanation of the contrastive reactivities of the adt- (2-aza-1,3-propanedithiolato) and the pdt- (1,3-propanedithiolato) bridged diiron complexes toward decarboxylation of the Ph₂PCH₂COOH ligand.     

Branched and dendritic metallo-carbosiloxanes with OCH2PPh2MLn end-grafted units

A straightforward method for the preparation of metallo carbosiloxanes of type Si(OCH₂CH₂CH₂SiMe₂[OCH₂PPh₂M(CO)_n])₄ (n = 3, M = Ni, 7a; n = 4, M = Fe, 7b; n = 5: M = Mo, 7c; M = W, 7d), Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₄ (8) and Me₂Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₂ (11) is described. The reaction of Si(OCH₂CH₂CH₂SiMeXCl)₄ (1: X = Me, 2: X = Cl) or Me₂Si(OCH₂CH₂CH₂SiMeCl₂)₂ (9) with HOCH₂PPh₂ (3) produces Si(OCH₂CH₂CH₂SiMe₂(OCH₂PPh₂))₄ (4), Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₄ (5) or Me₂Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₂ (10) in presence of DABCO. Treatment of the latter molecules with Ni(CO)₄ (6a), Fe₂(CO)₉ (6b), M(CO)₅(Thf) (6c: M = Mo; 6d: M = W), respectively, gives the title compounds 7a-7d, 8 and 11 in which the PPh₂ groups are datively bound to a 16-valence-electron metal carbonyl fragment.The formation of analytical pure and uniform branched and dendritic metallo carbosiloxanes is based on elemental analysis, and IR, ¹H, ¹³C{¹H}, ²⁹Si{¹H} and ³¹P{¹H} NMR spectroscopic studies. In addition, ESI-TOF mass spectrometric studies were carried out.     

Synthesis, structure and electrochemical properties of N-substituted diiron azadithiolates as active site models of Fe-only hydrogenases

As biomimetic models for the active site of Fe-only hydrogenases,six new N-substituted diiron azadithiolates (ADT) were prepared.Treatment of CH₂Cl₂ solutions of primary amines RNH₂ with paraformaldehyde followed by an excess of SOCl₂ gave N,N-bis(chloromethyl)amines RN(CH₂Cl)₂ (1,R = CH₂CO₂Et;2,C₆H₄C(O)Me-p;3,C₆H₄CO₂Me-p;4,C₆H₄SCN-p) in 30-90% yields.Further treatment of the chloromethylated amines 1-4 with (μ-LiS)₂Fe₂(CO)₆ in THF resulted in formation of the corresponding N-substituted ADT-type models [(μ-SCH₂)₂NR]Fe₂(CO)₆ (5,R = CH₂CO₂Et;6,C₆H₄C(O)Me-p;7,C₆H₄CO₂Me-p;8,C₆H₄SCN-p) in 24-75% yields.Also prepared were the N-substituted models [(μ-SCH₂)₂NC(O)CH₂C₁₀H₇-α]Fe₂(CO)₆ (9) and 1,4-[Fe₂(CO)₆(μ- SCH₂)₂NC(O)]₂C₆H₄ (10) by reaction of CH₂Cl₂ solutions of [(μ-SCH₂)₂NH]Fe₂(CO)₆ with α-C₁₀H₇CH₂COCl and 1,4-C₆H₄(COCl)₂ in 81% and 28% yields, respectively. All the new compounds 1-10 were characterized by elemental analysis and spectroscopy, as well as for 5-7 and 9 by X-ray crystallography. The crystallographic studies indicated that the functionality of 5 attached to the bridged N atom lies in an equatorial position, whereas those of functionalities of 6, 7, and 9 are located in an axial position. This is presumably due to different electronic and steric effects between the N-substituted aliphatic and aromatic functionalities. More interestingly, model 7 has been found to be a catalyst for proton reduction in the presence of either strong acid CF₃CO₂H or weak acid HOAc under electrochemical conditions. In addition, two mechanisms ECCE and EECC are preliminarily suggested for such two electrocatalytic H₂ production processes, respectively.     

Synthesis,Characterization, and Crystal Structure of Tertiary Phosphine-Substituted Diiron Propanedithiolate Complexes

As the active site models of [FeFe]-hydrogenase, two new tertiary phosphine-substituted diiron propanedithiolate complexes [(μ-PDT)Fe₂(CO)₅L] (PDT = SCH₂CH₂CH₂S, L = P(PhMe-m)₃, 1; PPh₂(CH₂CH₂CH₃), 2) have been prepared through carbonyl substitution reactions of parent complex [(μ-PDT)Fe₂(CO)₆] (A) with P(PhMe-m)₃ or PPh₂(CH₂CH₂CH₃) in the presence of the decarbonylating agent Me₃NO·2H₂O in MeCN at room temperature. The new complexes 1 and 2 were fully characterized by elemental analysis, FT-IR, ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, as well as for 1 by X-ray crystallography. In addition, the crystal structure of 1 has indicated that the phosphorus atom of the P(PhMe-m)₃ ligand resides in an apical position of the pseudo-square-pyramidal geometry of the tertiary phosphine-coordinated Fe₂ atom.     

Carbon-nitrogen bond formation in the reaction of the reaction of diphenyl diazomethane Ph2 CN2 with diiron-carbene complexes (Fe2(CO)7x03BD;-C(R)C(NEt2)x03BD;-C(R)C(NEtx03BC;-C(R)C(NEt2)N(NCPh2)x03BC;-C(R)C(NEtx03BC;-C(R)C(NEt2)NN(CPh2)x03BC;-C(R)C(NEt)]

The diiron ynamine complex [Fe₂(CO)₇{μ-CR)C(NEt₂)}] (1:R=Me,2:R = C₃H₅.3:R=SiMe₃.4:R = Ph) reacts at room temperature with diphenyldiazomethane Ph₂CN₂, in hexane to yield complexes [Fe₂(CO)₆{C(R)C(NEt₂)N (NCPh₂)] (5a:R=Me,6a:R=C₃H₅.7a R=SiMe₃.8a:R=Ph) resulting from the insertion of the terminal nitrogen atom into the Fe=C carbene bond. Insertion the second nitrogen atom and formation of compounds [Fe₂(CO)₆zμ-C(R)C(NEt₂)NN(CPh₂)}] (5b:R=Me,6b:R=C₃H₅,7b:R=SiMe₃,8b:R=Ph) is observed when compounds5a-5a are treated in refluxing hexane. Transformation of compoundsa tob is also obtained at room temperature within a few days. All compounds were identified by their¹H NMR spectra. Compounds6a, 7a, 8a, and8b were characterized by single crystal X-ray diffraction analyses. Crystal data: for6a: space group = P2₁/n,a=12.853(1) A,b=24.800(7) A,c=8.947(6) A,β=99.29(3)°,Z=4, 2227 rellectionsR=0,038; for7a: space group=Pl,a=ll.483(4) A,b=14.975(4) A,c = 17.890(8) A,α = 82.80(3)°,β=94.29(7)°,γ=85.42(2),Z = 4, 5888 reflectionR = 0.035: for8a: space group = Pcab.a = 31.023(8) A.b=20.137(1) A.c=9.686(2) A.Z=8. 1651 reflections,R=0.071; for8b: space group=P2₁/n,a=21.459(4),b=10,100(3) A,c=28,439(8) A,ß=103.86(4)°,Z=8. 2431 reflections.R=0.057.     

Reactions of Co2(CO)8 and of Co2(CO)6L (L = 3-pentyn-1-ol, 1,4-butyn-diol or 2-methyl-3-butyn-2-ol) with 2(diphenylphosphino)ethyl-trietoxysilane and tris(hydroxymethyl)phosphine for applications to new sol-gel materials

The complex Co₂(CO)₆[μ-η²-(H₃CCCCH₂CH₂OH)] (1) with the ligand 3-pentyn-1-ol (pol) has been synthesized following established procedures. Its structure has been determined by X-ray analysis. The complex Co₂(CO)₆(mbo) (mbo = 2-methyl-3-butyn-2-ol, HCCC(CH₃)₂OH), (3), along with the already known Co₂(CO)₆(bud) (bud = 1,4-butyn-diol, HOCH₂CCCH₂OH) (2), and Co₂(CO)₈ were reacted with 2(diphenylphosphino)ethyl-triethoxysilane [Ph₂PCH₂CH₂Si(OCH₂CH₃)₃] (dpts) and tris(hydroxymethyl)phosphine [P(CH₂OH)₃] (thp). With dpts, mono- and di-substituted complexes were obtained: these were characterized by analytical and spectroscopic techniques. The structures of Co₂(CO)₆(dpts)₂ (5) and of Co₂(CO)₄(pol)(dpts)₂ (8) have been determined by X-ray analysis.Complex (1) was reacted with 3-(triethoxysilyl)propyl isocyanate [(H₃CCH₂O)₃Si(CH₂)₃NCO] (tsi): the new complex Co₂(CO)₆[H₃CCCCH₂CH₂OC(O)NH(CH₂)₃Si(OCH₂CH₃)₃] (9) was obtained and spectroscopically characterized. The complex has also been reacted with tetraethyl orthosilicate (teos); a new inorganic-organometallic material was obtained. Complex (5) has been grafted on the mesoporous material SBA-15. The hybrid inorganic-organometallic materials obtained have been characterized by inductively coupled plasma-mass spectrometry (ICP-MS), infrared spectroscopy (FT-IR) under vacuum conditions, X-ray diffraction (XRD) and scanning electron microscopy coupled to EDS probe (SEM-EDS).     

The structures of the dicationic tetranitrosyl iron complex with cysteamine [Fe2S2(CH2CH2NH3)2(NO)4]2+ and its decomposition products in protic media: an experimental and theoretical study

Decomposition products of [Fe₂S₂(CH₂CH₂NH₃)₂(NO)₄]SO₄·2.5H₂O (1??) were studied by electrochemistry and mass spectrometry. The structures of the dicationic tetranitrosyl iron complex with cysteamine of the composition [Fe₂S₂(CH₂CH₂NH₃)₂(NO)₄]²⁺ (1) and possible products of its decomposition and NO replacement by an aqua ligand were studied by quantum chemical methods at the density functional theory level. Taking into account the solvation effects, the replacement of the nitrosyl ligand in dication 1 by an aqua ligand was found to be less favorable in aqueous solution than in the gas phase. The pK value was calculated for the proton abstraction from the NH₃ group of compound 1 (7.2), and the removal of NO from the deprotonated form of the complex was found to be much easier. This result is consistent with the experimental data on an increase in the rate of NO formation in aqueous solutions of 1 with increasing pH from 6 to 8 assuming that the increase in pH is accompanied by an increase in the percentage of the less stable deprotonated form of the complex and that OH^? does not participate in the elementary step of NO formation. The kinetic curves of NO formation are well described by a two-step scheme of consecutive first-order reactions of the NO formation and consumption. In the gas phase, dication 1 was found to be unstable to decomposition into two mononuclear cationic dinitrosyl iron complexes with cysteamine. This result is consistent with the fact that these cations are observed in the electrospray ionization mass spectrometric experiment. The major peak in the mass spectra is associated with the [Fe₂S₂(CH₂CH₂NH₃)₂(NO)₄ ? H]⁺ ion. As follows from the calculations, this is due to the deprotonation of the dication as it gets rid of the hydration shell, because even the dimer of water molecules is more basic than dication 1.     

Reactions of nitrosoarenes containing electron-withdrawing substituents with coordinated CO. Synthesis and structure of complexes Pd2(OAc)2(p-ClC6H4N[p-ClC6H3NO])2 and Pd2(OAc)2(o-ClC6H4N[o-ClC6H3NO])2

The reaction of tetranuclear Pd₄(μ-COOCH₃)₄(μ-CO)₄ cluster (1a) with p- and o-chloronitrosobenzenes was found to give dinuclear nitrosoamide complexes, Pd₂(OAc)₂(p-ClC₆H₄N[p-ClC₆H₃NO])₂ (4) and Pd₂(OAc)₂(o-ClC₆H₄N[o-ClC₆H₃NO])₂ (5), respectively. The formation of complexes 4 and 5 is accompanied by evolution of CO₂, resulting from oxidation of CO coordinated in cluster 1. Complexes 4 and 5 were characterized by elemental analysis and IR and ¹H NMR spectroscopy; their structures were studied by EXAFS. The reactions of dinuclear complex 4 with molecular hydrogen and CO were studied. The major products of reduction of 4 with hydrogen include metallic palladium, acetic acid, cyclohexanone, and molecular nitrogen. Treatment of complex 4 with CO under mild conditions (1 atm, 20 °C) affords p-chlorophenyl isocyanate.     

Azadithiolates cofactor of the iron-only hydrogenase and its PR3-monosubstituted derivatives: Synthesis, structure, electrochemistry and protonation

The core structure (μ-SCH₂)₂NH[Fe₂(CO)₆] (5) of Fe-only hydrogenases active site model has been synthesized by the condensation of iron carbonyl sulfides, formaldehyde and silyl protected amine. Its monosubstituted complexes (μ-SCH₂)₂NH[Fe₂(CO)₅PR₃] (R = Ph (6), Me (7)) were accordingly prepared. The coordination configurations of 5 and 6 were characterized by X-ray crystallography. Protonation of complex 7 to form the N-protonated product occurs in an acetonitrile solution upon addition of triflic acid. The redox properties of these model complexes were studied by cyclic voltammetry.     

The first bidentate phosphanylborohydride: Synthesis, structure, and reactivity towards [CpFe(CO)2I]

Deprotonation of the phosphane-borane adduct rac/meso-(HP(BH₃)(Ph)CH₂)₂ (2) with KH provides facile access to the bidentate phosphanylborohydride rac/meso-K₂[(P(BH₃)(Ph)CH₂)₂] (3). Treatment of 3 with two equivalents of [CpFe(CO)₂I] gives the dinuclear complex rac/meso-[(CpFe(CO)₂)₂-μ-(P(BH₃)(Ph)CH₂)₂] (4). Single crystals of the pure diastereomers meso-2, meso-3(thf)₄, and rac-4 have been grown from toluene/pentane, diethyl ether/thf, and benzene/pentane, respectively. The molecular structures of all three compounds have been determined by X-ray crystallography.     

Synthesis and structural characterization of iron–sulfur complexes with hydrophilic nitrogen–phosphorus ligands

Reaction of the parent complex (μ-PDT)Fe₂-(CO)₆ (A) (PDT = 1,3-SCH₂CH₂CH₂S^2?) with the bidentate N/P ligand [(Ph₂P)₂N(C₆H₄Cl-p)] in the presence of Me₃NO as decarbonylating agent produced an unexpected iron–sulfur complex [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄Cl-1,4)}] (1). Extending this chemistry further, two similar complexes [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄NO₂-1,4)}] (2) and [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄CO₂Et-1,4)}] (3) could be prepared from the simple substitution reactions of the precursor A with the monodentate N/P ligands Ph₂P(NHC₆H₄NO₂-1,4) and Ph₂P(NHC₆H₄CO₂Et-1,4), respectively. These new complexes, which can be considered as active site models of [FeFe] hydrogenases, have been characterized by elemental analysis, FTIR, and NMR (¹H, ¹³C, ³¹P) spectroscopies, as well as by X-ray crystallography for complex 1.     

Iron carbonyl cluster complexes with monophosphine ligands: synthesis,characterization, and crystal structure

Three new monophosphine-substituted iron carbonyl cluster complexes [(μ-PDT)Fe₂(CO)₅L] [(PDT = SCH₂CH₂CH₂S, L = P(CH₂Ph)₃, 1; P(C₆H₁₁)₃, 2; PPh₂(PhMe-p), 3)], which can be regarded as active site mimics for [FeFe]-hydrogenase, have been prepared in 40–70 % yields by reactions of the parent complex (μ-PDT)Fe₂(CO)₆ (A) with monophosphine ligands in the presence of the decarbonylating agent Me₃NO·2H₂O. All three complexes were characterized by elemental analysis and spectroscopic techniques, as well as by X-ray crystallography for complex 1. The IR spectra of the complexes reveal that the electron-donating abilities of the different monophosphine ligands follow the order PPh₂(PhMe-p) > P(C₆H₁₁)₃ > P(CH₂Ph)₃.