Zerovalent Iron Complex Research Articles

Zero valent iron complexes as base partners in frustrated Lewis pair chemistry.

The prototypical iron(0) complex [Fe(CO)3(PMe3)2] (1) forms a frustrated Lewis pair (FLP) with B(C6F5)3 (BCF). In this FLP, the iron complex acts as the Lewis base partner, and the borane as the Lewis acid partner. This FLP is able to cleave H-H, H-Cl, H-O and H-S bonds in H2, HCl, H2O and HSPh. The FLP 1/BCF is shown to catalyze the hydrogenation of alkenes under mild conditions, where terminal alkenes are preferentially reduced. Mechanistic studies using D2 gas suggest that a branched intermediate in an alkene insertion cycle or an ionic cycle is favored for this catalytic reaction.

Synthesis, Reactivity, and Electronic Structure of a Bioinspired Heterobimetallic [Ni(μ-S2)Fe] Complex with Disulfur Monoradical character

The first synthesis of a monoradical Ni(μ-S2)Fe core in the [(Nacnac)Ni(μ-S2)Fe(dmpe)2] complex 3 could be accomplished in good yields by PMe3 elimination from the zerovalent iron complex [(dmpe)2(PMe3)Fe] (2; dmpe =1,2-bis(dimethylphosphine)ethane) upon reaction with the supersulfido nickel(II) complex [(Nacnac)Ni(S2)] (1; Nacnac = CH{(CMe)(2,6-iPr2C6H3N)}2). Complex 3 bears Ni(II) and Fe(II) centers, both of which are in a low-spin state. A single electron is located in the HOMO and is somewhat delocalized over the Ni(μ-S2)Fe core, so that the bridging disulfur subunit exhibits some “subsulfide” S23– character. Compound 3 represents a bioinspired example of a monoradical with a Ni(μ-S2)Fe structural motif, reminiscent of the Ni(μ-S2)Fe core structure of the active site in [NiFe] hydrogenases. Its oxidation with [Fe(η5-C5H5)2][B(C6H3(CF3)2)4] affords the product [(Nacnac)Ni(μ-S)2Fe(dmpe)2][B(C6H3(CF3)2)4] (4), and complex 3 can alternatively be prepared via a reductive route upon reaction of [Co(η5-C5Me5)2][(Nacnac)NiS2] (6) with the Fe(0) precursor 2. All synthesized complexes were fully characterized, including in some cases single-crystal X-ray diffraction analysis, magnetometry, EPR, NMR, and 57Fe Mössbauer spectroscopy. DFT calculations were used to compute the spectroscopic parameters and to establish the electronic structure of 3 and its oxidized and reduced forms and related complexes.

Synthesis and Characterization of Pentaphosphino Zero-Valent Iron Complexes and Their Corresponding Iron(II)-Chloride and -Hydride Complexes

A pentaphosphino iron(II)-chloride species [(t)SiP(3)(dmpm)FeCl][Cl] (1-Cl) ((t)SiP(3) = (t)BuSi(CH(2)PMe(2))(3), dmpm = Me(2)PCH(2)PMe(2)) was prepared from [((t)SiP(3)Fe)(2)(mu-Cl)(3)][Cl] and dmpm. This species was reduced to give the corresponding iron(0) complex, (t)SiP(3)(dmpm)Fe (3), in near quantitative yield. Analogous complexes [SiP(3)(dmpe)FeCl][Cl] (2-Cl) and SiP(3)(dmpe)Fe (4) (SiP(3) = MeSi(CH(2)PMe(2))(3), dmpe = Me(2)PCH(2)CH(2)PMe(2)) were prepared in the same manner as 1 and 3 but with lower yields because of competitive ligand rearrangement reactions that gave byproduct of trans-(dmpe)(2)FeCl(2) and (dmpe)(5)Fe(2) (5). [(t)SiP(3)(dmpm)FeH][A] (6) was prepared from the reaction of 3 with weak acids (HA), and the pK(a) of 6 was established to be approximately 25. Attempts to prepare pentaphosphino-iron(0) complexes of the form SiP(3)(PR(3))(2)Fe using PPh(3) and PMe(3) resulted in cyclometalated products, SiP(3)FeH((o-C(6)H(4))PPh(2)) (7) and SiP(3)FeH(CH(2)PMe(2)) (8). Synthesis and characterization of these complexes, including crystal structures of 1-5, are reported.

Kinetics and mechanism of dealkylation of coordinated isocyanide in Fe(PMe3)2(t-BuNC)3

The zerovalent iron complex Fe(PMe3)2(t-BuNC)3 undergoes thermal cleavage of the C—N bond to give Fe(PMe3)2(t-BuNC)2(H)(CN) and isobutylene. The reaction follows first order kinetics, and addition of the hydrogen-atom donor 1,4-cyclohexadiene leads to the preferential formation of isobutane rather than isobutylene. Mechanistic studies are consistent with a rate determining homolysis of the C—N bond, giving rise to tert-butyl radicals.Key words: iron, isocyanide, elimination, C—N cleavage.

Experimental and theoretical investigations on the synthesis, structure, reactivity, and bonding of the stannylene-iron complex Bis bis(2-tert-butyl-4,5,6-trimethyl-phenyl)SnFe (eta6-toluene) (Sn-Fe-Sn)

The pi-(arene)bis(stannylene) complex bis(bis(2-tert-butyl-4,5,6-trimethylphenyl)SnFe(eta6-toluene) (Sn-Fe-Sn, 15) is accessible in high yields by a metal-atom-mediated synthesis between iron atoms, toluene, and the stannylene [bis(2-tert-butyl-4,5,6-trimethylphenyl)Sn](3). Complex 15 has a half-sandwich structure with short Fe -Sn bonds (2.432(1) A) and a trigonal-planar coordination at both the Fe and Sn atoms. The distance between the two Sn centers is 3.56 A. Complex 15 is stable under ambient conditions and displays a pi-arene lability, so far rarely observed for (arene)iron complexes; this leads to an irreversible substitution of the arene and formation of fivefold-coordinated zerovalent iron complexes. The pi-arene lability of the title compound is a result of the Fe-Sn bonding situation, which can be interpreted, on the basis of an extended Huckel molecular orbital calculation, as being solely a donation of the 5sigma lone-pair of Sn into empty or half-filled acceptor d orbitals on Fe. As the calculations reveal, there is little backbonding from the iron to the tin, and the strong sigma donation leads to an increased occupation of the pi-antibonding orbitals of the eta6-arene, which are mainly responsible for the experimentally observed arene lability. Fe and Sn Mossbauer spectra support the polar character of Sn(sigma+)-->Fe(sigma-) with strong sigma donation from tin to iron, but significantly low iron-to-tin pi backdonation.

C–S, C–H, and N–H bond cleavage of heterocycles by a zero-valent iron complex, Fe(N 2)(depe) 2 [depe=1,2-bis(diethylphosphino)ethane

Treatment of Fe(N 2)(depe) 2 [depe=1,2-bis(diethylphosphino)ethane] ( 1) with benzo[ b]thiophene at room temperature results in the regioselective C–S and C–H bond cleavages giving Fe(SC 6H 4CHC H)(depe) 2 ( 2a) and trans-FeH( CCHC 6H 4S )(depe) 2 ( 3a) in 72 and 19% yields, respectively. Complex 1 also reacts with thiophene, 2- and 3-acetylthiophenes and 2- and 3-methylthiophenes to give both C–S and C–H bond oxidative addition products: Fe(SCHCHCHC H)(depe) 2 ( 2b) and trans-FeH( CCHCHCHS )(depe) 2 ( 3b), Fe[SC(COMe)CHCHC H](depe) 2 ( 2c) and trans-FeH[ CCHCHC(COMe)S ](depe) 2 ( 3c), Fe[SC(Me)CHCHC H](depe) 2 ( 2d) and trans-FeH[ CCHCHC(Me)S ](depe) 2 ( 3d), and Fe[SCHC(Me)CHC H](depe) 2 ( 2e) and trans-FeH[ CCHC(Me)CHS ](depe) 2 ( 3e), respectively. On the other hand, only C–H bond cleavage takes place in the reactions of 1 with furans such as furan, benzo[ b]furan, and 2,3-dihydrofuran to give trans-FeH( CCHCHCHO )(depe) 2 ( 4a), FeH( CCHC 6H 4O )(depe) 2 ( 4b) and trans-FeH( CCHOCH 2C H 2)(depe) 2 ( 4c) and N–H bond is exclusively cleaved by the reaction of 1 with pyrroles such as pyrrole, indole and 2-acetylpyrrole to give trans-FeH( NCHCHCHC H)(depe) 2 ( 5a), trans- and cis-FeH( NCHCHC 6H 4)(depe) 2 ( 5b) and FeH[ NC(COMe)CHCHC H](η 2-depe)(η 1-depe) ( 6). Treatment of 2a with MeI results in the Fe–S bond cleavage of the thiaferracycle giving trans-FeI[( E)-CHCHC 6H 4-2-SMe](depe) 2 ( 7) whose structure is unequivocally characterized by X-ray analysis. In contrast, hydrogenolysis of 2a with H 2 (50 atm) leads to the cleavage of the Fe–C bond of the thiaferracycle to yield cis- and trans-FeH(SC 6H 4-2-Et)(depe) 2 ( 8).

Synthesis, structure and reactivity of an ( η6-naphthalene)iron(0) complex having a 1,2-bis(dicyclohexylphosphino)ethane ligand

A zerovalent iron complex having an η 6-naphthalene ligand, Fe( η 6-C 10H 8)(dcype) ( 3) [dcype=1,2-bis(dicyclohexylphosphino)ethane] has been prepared by the reduction of high spin 14 electron dichloroiron(II) complex, FeCl 2(dcype) ( 1) with sodium-naphthalene. In refluxing benzene solution of 3, the coordinated naphthalene can be replaced by benzene giving Fe( η 6-C 6H 6)(dcype) ( 4). Exposure of 3 to CO results in the formation of Fe(CO) 3(dcype) ( 5). Protonation of 3 with HBF 4 yields cationic complex, [FeH( η 6-C 10H 8)(dcype)][BF 4] ( 6), which can be deprotonated by lithium diisopropylamide.

ChemInform Abstract: CHEMISTRY OF PENTAKIS(TRIMETHYL PHOSPHITE)IRON(0), (FE(P(OME)3)5)

AbstractDurch Reduktion des Eisen(II)‐chlorid‐Trimethylphosphit‐Komplexes (I) mit Natriumamalgam in Gegenwart von überschüssigem Trimethylphosphit erhält man ien Eisen(0)‐Komplex (II), der mit Sauerstoff, Ammoniumhexafluorophosphat oder Trifluoressigsäure die Verbindungen (III), (IV) bzw. (V) ergibt.

Chemistry of pentakis(trimethyl phosphite)iron(0), [Fe{P(OMe)3}5

A new zerovalent iron complex,[Fe{P(OMe)3}5], has been prepared; this volatile molecule has a relatively basic iron atom that is readily protonated and alkylated.

Stereospecific Synthesis of 1,4-Dienes. IV. The Catalytic Behavior of the Ethylenebis(diphenylphosphine) Complex of Iron(0)

Abstract A zerovalent iron complex, Fe(Ph2P·CH2CH2·PPh2)2· C2H2, catalyzes addition of ethylene to butadiene to afford 1 : 1 adducts consisting of 1,cis-4-hexadiene, 1,3-hexadiene, 2,4-hexadiene and 1,5-hexadiene, and 2 : 1 adducts. The combination of the iron complex and a Lewis acid (triethylaluminum, diethylaluminum chloride, ethylaluminum dichloride and boron trifluoride etherate) gives 1,cis-4-hexadiene much more selectively. The most efficient Lewis acid component for the synthesis of 1,cis-4-hexadiene is diethylaluminum chloride.