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.     

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.     

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.     

Structure and reactivity of mono- and dinuclear diiminate zinc alkyl complexes

The synthesis, structure and reactivity of several diiminate ligands are presented. The syntheses of five representative β-diiminate (BDI) zinc alkyl complexes and one β-oxo-δ-diiminate (BODDI) zinc alkyl are described. BDI ligands with varying backbone and N-aryl substituents display different solid state structures. [(BDI)ZnR] are synthesized by the reaction of (BDI)H with ZnR₂ in quantitative yield. Previously reported (BDI-1)ZnEt is a three-coordinate monomer in the solid state whereas [(BDI-3)ZnEt]_∞ [(BDI-3)=2-((2,6-diisopropylphenyl)amido)-3-cyano-4-((2,6-diisopropylphenyl)imino-2-pentene] and [(BDI-4)ZnEt]_∞ [(BDI-4)=2-((2,6-diethylphenyl)amido)-3-cyano-4-((2,6-diethylphenyl)imino-2-pentene] form one dimensional coordination polymers. The bimetallic complex [(BODDI-1)(ZnEt)₂] [(BODDI-1)=2,6-bis((2,6-diisopropylphenyl)amido)-2,5-heptadien-4-one] is prepared through the reaction of (BODDI-1)H₂ with two equivalents ZnEt₂. Both [(BDI)ZnEt] and [(BODDI)ZnEt] complexes react with acetic acid to give the acetate complexes in moderate to high yields, offering a superior synthetic route to these complexes. [(BDI)ZnR] [BDI=(BDI-3) or 1,1,1-trifluoro-2-((2,6-diisopropylphenyl)amido)-4-((2,6-diethylphenyl)imino-2-pentene), (BDI-5)] complexes react with MeOH to produce [{(BDI)Zn(μ-OMe)}₂Zn(μ-OMe)₂] in moderate yields. The molecular structures of [(BDI-3)ZnEt], [(BDI-4)ZnEt], [(BODDI-1)(ZnEt)₂], [(BODDI-1)Zn₂(μ-OAc)₂], [{(BDI-3)Zn(μ-OMe)}₂Zn(μ-OMe)₂] and [{(BDI-5)Zn(μ-OMe)}₂Zn(μ-OMe)₂] have been determined by X-ray diffraction.     

Synthetic and Structural Studies on Some New Butterfly Fe/S Cluster Complexes Containing 2,6-(CH2)2C5H3N or (CH2)2 Groups

Four new butterfly Fe/S cluster complexes bearing 2,6-(CH₂)₂C₅H₃N or (CH₂)₂ groups, as the active site models of [FeFe]-hydrogenase, have been prepared by condensation reaction and structurally characterized. Treatments of the parent complex Fe₂(CO)₆[(μ-SCH₂)₂CHCO₂H] (A) with 2,6-(HOCH₂)₂C₅H₃N or HOCH₂CH₂OH in the presence of 4-dimethylaminopyridine and dicyclohexylcarbodiimide afforded the single-butterfly Fe/S complexes Fe₂(CO)₆[(μ-SCH₂)₂CHC(O)OCH₂(2,6-C₅H₃N)CH₂OH] (1) and Fe₂(CO)₆[(μ-SCH₂)₂CHC(O)OCH₂CH₂OH] (3) and the double-butterfly Fe/S complexes [Fe₂(CO)₆(μ-SCH₂)₂CHC(O)OCH₂]₂(2,6-C₅H₃N) (2) and [Fe₂(CO)₆(μ-SCH₂)₂CHC(O)OCH₂]₂ (4). The new complexes 1–4 were fully characterized by elemental analysis, ESI-MS, IR, and ¹H (¹³C) NMR spectroscopy.     

Substituted cyclopentadienylchromium(III) complexes containing neutral donor ligands. Synthesis, crystal structures and reactivity in ethylene polymerization

Lithium derivatives of substituted cyclopentadiene ligands reacted with CrCl₃(THF)₃ in THF solution to afford homodinuclear complexes of the type [{(η⁵-RCp)CrCl(μ-Cl) }₂] [R=SiMe₃ (1), CH₂C(Me)CH₂ (2)]. Complex 1 reacts with pyrazole (C₃H₄N₂) to yield the mononuclear half-sandwich complex [(η⁵-Me₃SiCp)CrCl₂(pyrazole)] (3). The similar complex [Cp*CrCl₂(pyrazole)] (4) was synthesised by reaction of [{Cp*CrCl(μ-Cl)}₂] with pyrazole. Complex 2 reacts with bidentate ligands to give binuclear complexes of the type [{(η⁵-CH₂C(Me)CH₂Cp)CrCl₂ }₂(μ-L-L)] [L-L=Ph₂PCH₂CH₂PPh₂ (5), trans-Ph₂P(O)CHCHP(O)Ph₂ (6)]. All complexes were structurally characterised by X-ray diffraction. After reaction with methylaluminoxane these complexes are active in the polymerization of ethylene. At 25 °C and 4 bar of ethylene, complex 3 yields polyethylene with a bimodal molecular weight distribution centred at 155,000 and 2000 g/mol. Complex 4 shows similar activity, yielding only the low molecular weight fraction. On the other hand, the binuclear complexes 5 and 6 under the same conditions were three times more active than mononuclear complexes. The melting point of the polymers indicates the formation of linear polyethylene.     

Syntheses and characterization of [(η-C6Me6)Ru(μ-N3)(X)]2 (X = N3 and Cl) complexes and their reactions towards mono- and bidentate ligands

The reaction of the complex [{(η⁶-C₆Me₆)Ru(μ-Cl)Cl}₂] 1 with sodium azide ligand gave two new dimers of the composition [{(η⁶-C₆Me₆)Ru(μ-N₃)(N₃)}₂] 2 and [{(η⁶-C₆Me₆)Ru(μ-N₃)Cl}₂] 3, depending upon the reaction conditions. Complex 3 with excess of sodium azide in ethanol yielded complex 2. These complexes undergo substitution reactions with monodentate ligands to yield monomeric complexes of the type [(η⁶-C₆Me₆)Ru(X)(N₃)(L)] {X = N₃, Cl, L = PPh₃ (4a, 9a); PMe₂Ph (4b, 9b); AsPh₃ (4c, 9c); X = N₃, L = pyrazole (Hpz) (5a); 3-methylpyrazole (3-Hmpz) (5b) and 3,5-dimethyl-pyrazole (3,5-Hdmpz) (5c)}. Complexes 2 and 3 also react with bidentate ligands to give bridging complexes of the type [{(η⁶-C₆Me₆)Ru(N₃)(X)]₂(μ-L)} {X = N₃, Cl, L = 1,2-bis(diphenylphosphino)methane (dppm) (6, 10); 1,2-bis(diphenylphosphino)ethane (dppe) (7, 11); 1,2-bis(diphenylphosphino)propane (dppp) (8, 12); X = Cl, L = 4,4-bipyridine (4,4′-bipy) (13)}. These complexes were characterized by FT-IR and FT-NMR spectroscopy as well as by analytical data.The molecular structures of the representative complexes [{(η⁶-C₆Me₆)Ru(μ-N₃)(N₃)}₂] 2, [{(η⁶-C₆Me₆)Ru(μ-N₃)Cl}₂] 3,[(η⁶-C₆Me₆)Ru(N₃)₂(PPh₃)] 4a and [{(η⁶-C₆Me₆)Ru(N₃)₂}₂ (μ-dppm)] 6 were established by single crystal X-ray diffraction studies.     

The synthesis and reactivity of some indenyl and bis-indenyl ruthenium carbonyl complexes

The reaction of [Ru₃(CO)₁₂] (1), with indene in refluxing xylene affords [{(η⁵-C₉H₇)Ru(CO)₂}₂] (2), in high yield. An analogous reaction of 1 with 2-phenylindene affords the expected dinuclear complex [{(η⁵-C₉H₆Ph)Ru(CO)₂}₂] (5), and a heptaruthenium cluster [(C₉H₄Ph)Ru₇(μ-H)(μ-CO)₂(CO)₁₆] (6). The indenyl ligand in compound 6 exhibits a novel bonding mode in which the benzenoid ring is μ₄,η¹:η¹:η²:η² bound to the cluster. Refluxing 1 with bis-indenyl methane affords the dinuclear complex [Ru₂(CO)₄{μ-(η⁵-C₉H₆)₂CH₂}] (7), which reacts with iodine via Ru-Ru bond cleavage to give [Ru₂I₂(CO)₄{(η⁵-C₉H₆)₂CH₂}] (8).     

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.     

Ethynylferrocene insertion into Fe-C bond in bridging aminocarbyne diiron complexes: New triiron vinyliminium complexes

The μ-aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCMe)(Cp)₂][SO₃CF₃] (R = Me, 1a; Xyl, 1b; Xyl = 2,6-Me₂C₆H₃) react with ethynylferrocene to give the corresponding bridging vinyliminium complexes [Fe₂{μ-η¹:η³-CN(Me)(R)CHC(Fc)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = Me, 2a; R = Xyl, 2b). Insertion of the ethynylferrocene in the metal-carbyne bond is regiospecific, and leads to the formation of only one isomer.Complexes 2a and 2b undergo hydride addition (by NaBH₄) affording the enaminoalkylidene complex [Fe₂{μ-η¹:η³-C(H)(N(Me)₂)CHC(Fc)}(μ-CO)(CO)(Cp)₂] (3a) and the bis-alkylidene [Fe₂{μ-η¹:η²-C(N(Me)(Xyl))CH₂C(Fc)}(μ-CO)(CO)(Cp)₂] (3b), respectively. Upon treatment with NaH, compounds 2a and 2b undergo fragmentation, affording the 1-metalla-2-aminocyclopenta-1,3-dien-5-one complexes [Fe(CO)(Cp){C(N(Me)(R))}CHC(Fc)C(O)}] (R = Me, 4a; R = Xyl, 4b).The molecular structures of 2b, 3b and 4b have been determined by X-ray diffraction studies.     

Stereochemistry of the insertion of disubstituted alkynes into the metal aminocarbyne bond in diiron complexes

Terminal alkynes (HCCR^′) (R^′=COOMe, CH₂OH) insert into the metal-carbyne bond of the diiron complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCMe)(Cp)₂][SO₃CF₃] (R=Xyl, 1a; CH₂Ph, 1b; Me, 1c; Xyl=2,6-Me₂C₆H₃), affording the corresponding μ-vinyliminium complexes [Fe₂{μ-σ:η³-C(R^′)CHCN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Xyl, R^′=COOMe, 2; R=CH₂Ph, R^′=COOMe, 3; R=Me, R^′=COOMe, 4; R=Xyl, R^′=CH₂OH, 5; R=Me, R^′=CH₂OH, 6). The insertion is regiospecific and C-C bond formation selectively occurs between the carbyne carbon and the CH moiety of the alkyne. Disubstituted alkynes (R^′CCR^′) also insert into the metal-carbyne bond leading to the formation of [Fe₂{μ-σ:η³-C(R^′)C(R^′)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R^′=Me, R=Xyl, 8; R^′=Et, R=Xyl, 9; R^′=COOMe, R=Xyl, 10; R^′=COOMe, R=CH₂Ph, 11; R^′=COOMe, R=Me, 12). Complexes 2, 3, 5, 8, 9 and 11, in which the iminium nitrogen is unsymmetrically substituted, give rise to E and/or Z isomers. When iminium substituents are Me and Xyl, the NMR and structural investigations (X-ray structure analysis of 2 and 8) indicate that complexes obtained from terminal alkynes preferentially adopt the E configuration, whereas those derived from internal alkynes are exclusively Z. In complexes 8 and 9, trans and cis isomers have been observed, by NMR spectroscopy, and the structures of trans-8 and cis-8 have been determined by X-ray diffraction studies. Trans to cis isomerization occurs upon heating in THF at reflux temperature. In contrast to the case of HCCR^′, the insertion of 2-hexyne is not regiospecific: both [Fe₂{μ-σ:η³-C(CH₂CH₂CH₃)C(Me)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Xyl, 13; R=Me, 15) and [Fe₂{μ-σ:η³-C(Me)C(CH₂CH₂CH₃)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Xyl, 14, R=Me, 16) are obtained and these compounds are present in solution as a mixture of cis and trans isomers, with predominance of the former.     

Models of the iron-only hydrogenase: Reactions of [Fe2(CO)6(μ-pdt)] with small bite-angle diphosphines yielding bridge and chelate diphosphine complexes [Fe2(CO)4(diphosphine)(μ-pdt)]

Reactions of [Fe₂(CO)₆(μ-pdt)] (1) (pdt = SCH₂CH₂CH₂S) and small bite-angle diphosphines have been studied. A range of products can be formed being dependent upon the nature of the diphosphine and reaction conditions. With bis(diphenylphosphino)methane (dppm), thermolysis in toluene leads to the formation of a mixture of bridge and chelate isomers [Fe₂(CO)₄(μ-dppm)(μ-pdt)] (2) and [Fe₂(CO)₄(κ²-dppm)(μ-pdt)] (3), respectively. Both have been crystallographically characterised, 3 being a rare example of a chelating dppm ligand in a first row binuclear system. At room temperature in MeCN with added Me₃NO · 2H₂O, the monodentate complex [Fe₂(CO)₅(κ¹-dppm)(μ-pdt)] (4) is initially formed. Warming 4 to 100 °C leads the slow conversion to 2, while oxidation (on alumina) gives [Fe₂(CO)₅(κ¹-dppmO)(μ-pdt)] (5). With bis(dicyclohexylphosphino)methane (dcpm), heating in toluene cleanly affords [Fe₂(CO)₄(μ-dcpm)(μ-pdt)] (6). With Me₃NO · 2H₂O in MeCN the reaction is not clean as the phosphine is oxidised but monodentate [Fe₂(CO)₅(κ¹-dcpm)(μ-pdt)] (7) can be seen spectroscopically. With 1,2-bis(diphenylphosphino)benzene (dppb) and cis-1,2-bis(diphenylphosphino)ethene (dppv) the chelate complexes [Fe₂(CO)₄(κ²-dppb)(μ-pdt)] (8) and [Fe₂(CO)₄(κ²-dppv)(μ-pdt)] (9), respectively are the final products under all conditions, although a small amount of [Fe₂(CO)₅(κ²-dppvO)(μ-pdt)] (10) was also isolated. Protonation of 2 with HBF₄ affords a cation with poor stability while with the more basic diiron centre in 6 readily forms the stable bridging-hydride complex [(μ-H)Fe₂(CO)₄(μ-dcpm)(μ-pdt)][BF₄] (11) which has been crystallographically characterised.     

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.     

Synthesis and characterization of new oxazoline-based palladacycles with bridging or terminal imidate ligands. Crystal structures of [{Pd(μ-dibromomaleimidate)(Phox)}2], [Pd(dibromomaleimidate)(Phox)(PPh3)] and [Pd(glutarimidate)(Phox)(PPh3)] (Phox = 2-(2-oxazolinyl)phenyl))

The dinuclear hydroxo complex [{Pd(μ-OH)(Phox)}₂] (I) (Phox = 2-(2-oxazolinyl)phenyl) reacts in a 1:2 molar ratio with several imidate ligands to yield new cyclometallated palladium complexes [{Pd(μ-NCO)(Phox)}₂] containing asymmetric imidate –NCO– bridging units. [–NCO– = succinimidate (succ) (1), phtalimidate (phtal) (2), maleimidate (mal) (3), 2,3-dibromomaleimidate (2,3-diBrmal) (4) and glutarimidate (glut) (5)]. The reaction of these complexes with tertiary phosphines provides novel mononuclear N-bonded imidate derivatives of the general formula [Pd(imidate)(Phox)(PR₃)] [R = Ph (a), 4-F–C₆H₄ (b) or CH₂CH₂CN (c)]. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, ¹H, ¹³C and ³¹P). The single-crystal structures of compounds 4, 4a and 5a have been established.     

C-C bond formation by cyanide addition to dinuclear vinyliminium complexes

The diiron vinyliminium complexes [Fe₂{μ-η¹:η³-C(R′)C(H)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Me, R′ = SiMe₃ (1a); R = Me, R′ = CH₂OH (1b); R = CH₂Ph, R′ = Tol (1c), Tol = 4-MeC₆H₄; R = CH₂Ph, R′ = COOMe (1d); R = CH₂Ph, R′ = SiMe₃ (1e)) undergo regio- and stereo-selective addition by cyanide ion (from ), affording the corresponding bridging cyano-functionalized allylidene compounds [Fe₂{μ-η¹:η³-C(R′)C(H)C(CN)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (3a-e), in good yields. Similarly, the diiron vinyliminium complexes [Fe₂{μ-η¹:η³-C(R′)C(R′)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = R′ = Me (2a); R = Me, R′ = Ph (2b); R = CH₂Ph, R′ = Me (2c); R = CH₂Ph, R′ = COOMe (2d)) react with cyanide and yield [Fe₂{μ-η¹:η³-C(R′)C(R′)C(CN)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (9a-d). The reactions of the vinyliminium complex [Fe₂{μ-η¹:η³-C(Tol)CHCN(Me)(4-C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4) with NaBH₄ and afford the allylidene [Fe₂{μ-C(Tol)C(H)C(H)N(Me)(C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂] (5) and the cyanoallylidene [Fe₂{μ-C(Tol)C(H)C(CN)N(Me)(C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂] (6), respectively. Analogously, the diruthenium vinyliminium complex [Ru₂{μ-η¹:η³-C(SiMe₃)CHCN(Me)(CH₂Ph)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (7) reacts with to give [Ru₂{μ-η¹:η³-C(SiMe₃)CHC(CN)N(Me)(CH₂Ph)}(μ-CO)(CO)(Cp)₂] (8).Finally, cyanide addition to [Fe₂{μ-η¹:η³-C(COOMe)C(COOMe)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2e) (Xyl = 2,6-Me₂C₆H₃), yields the cyano-functionalized bis-alkylidene complex [Fe₂{μ-η¹:η²-C(COOMe)C(COOMe)(CN)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (10). The molecular structures of 3a and 9a have been elucidated by X-ray diffraction.     

Modeling [FeFe] hydrogenase: Synthesis and protonation of a diiron dithiolate complex containing a phosphine-N-heterocyclic-carbene ligand

The ligand exchange reaction of I_Me-(CH₂)₂-PPh₂ (I_Me = 1-methyimidazol-2-ylidene) and the hexacarbonyl complex [{Fe₂{μ-S(CH₂)₃S}(CO)₆] (1) resulted in the formation of the chelated complex [{Fe₂{μ-S(CH₂)₃S}(CO)₄(I_Me-(CH₂)₂-PPh₂)] (2). The molecular structure of 2 was confirmed by spectroscopic and X-ray analyses. This complex catalyzes proton reduction. Low temperature NMR studies on the protonation of 2 revealed the formation of a terminal hydride intermediate.     

Reactions of a phosphido-bridged unsymmetrical diiron complex (η-C5Me5)Fe2(CO)4(μ-CO)(μ-PPh2) with various alkynes

A phosphido-bridged unsymmetrical diiron complex (η⁵-C₅Me₅)Fe₂(CO)₄(μ-CO)(μ-PPh₂) (1) was synthesized by a new convenient method; photo-dissociation of a CO ligand from (η⁵-C₅Me₅)Fe₂(CO)₆(μ-PPh₂) (2) that was prepared by the reaction of Li[Fe(CO)₄PPh₂] with (η⁵-C₅Me₅)Fe(CO)₂I. The reactivity of 1 toward various alkynes was studied. The reaction of 1 with ^tBuCCH gave a 1:1 mixture of two isomeric complexes (η⁵-C₅Me₅)Fe₂(CO)₃(μ-PPh₂)[μ-CHC(^tBu)C(O)] (3) containing a ketoalkenyl ligand. The reactions of 1 with other terminal alkynes RCCH (R=H, CO₂Me, Ph) afforded complexes incorporating one or two molecules of alkynes and a carbonyl group. The principal products were dinuclear complexes bridged by a new phosphinoketoalkenyl ligand, (η⁵-C₅Me₅)Fe₂(CO)₃(μ-CO)[μ-CR¹CR²C(O)PPh₂] (4a: R¹=H, R²=H; 4b: R¹=CO₂Me, R²=H; 4c: R¹=H, R²=Ph). In the cases of alkynes RCCH (R=H, CO₂Me), dinuclear complexes having a new ligand composed of two molecules of alkynes, a carbonyl group, and a phosphido group; i.e. (η⁵-C₅Me₅)Fe₂(CO)₃[μ-CRCHCHCRC(O)PPh₂] (5a: R=H; 5b: R=CO₂Me), were also obtained. In all cases, mononuclear complexes, (η⁵-C₅Me₅)Fe(CO)[CR¹CR²C(O)PPh₂] (6a: R¹=H, R²=H; 6b: R¹=H, R²=CO₂Me; 6c: R¹=H, R²=Ph) were isolated in low yields. The structures of 1, 4c, 5b, and 6a were confirmed by X-ray crystallography. The detailed structures of the products and plausible reaction mechanisms are discussed.     

Diruthenium(I,I) saccharinate complexes: Synthesis, molecular structure, and evaluation as catalysts for carbenoid reactions of diazoacetates

The dinuclear ruthenium complexes [Ru₂(μ-sac)₂(CO)₆] (1), [Ru₂(μ-sac)₂(CH₃CN)₂(CO)₄] (3), [Ru₂(μ-sac)₂(CO)₅(PPh₃)] (4) and [Ru₂(μ-sac)₂(CO)₄(PPh₃)₂] (5) as well as the tetranuclear ruthenium complex [Ru₂(μ-sac)₂(CO)₅]₂ (2) (sac = saccharinate, C₇H₄NO₃S⁻) were synthesized starting from Ru₃(CO)₁₂ and saccharin. X-ray crystal structure analysis of 1, 3A × p-xylene, 4 × CH₂Cl₂ and 5 × 3CH₂Cl₂ showed that the core is bridged through the amidate moieties of the two saccharinate ligands, with a head-tail arrangement in complexes 1, 3A and 5, and a head-head arrangement in 4. For complex 3, an equilibrium mixture of the head-head regioisomer 3A and a second species 3b exists in solution. Complexes 1 and 2 are suitable catalysts for the cyclopropanation of nucleophilic alkenes (styrene, cyclohexene and 2-methyl-2-butene) with methyl diazoacetate.     

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.