Masumi Itazaki

Fe–H Complexes in Catalysis

Organic syntheses catalyzed by iron complexes have attracted considerable attention because iron is an abundant, inexpensive, and environmentally benign metal. It has been documented that various iron hydride complexes play important roles in catalytic cycles such as hydrogenation, hydrosilylation, hydroboration, hydrogen generation, and element–element bond formation. This chapter summarizes the recent developments, mainly from 2000 to 2009, of iron catalysts involving hydride ligand(s) and the role of Fe–H species in catalytic cycles.

N−CN Bond Cleavage of Cyanamides by a Transition-Metal Complex

N-CN bond cleavage of cyanamides (R(2)N-CN) has been attained at room temperature in the reaction of R(2)N-CN with Cp(CO)(2)Fe(SiEt(3)). The mechanistic investigation revealed that silyl migration from Fe to CN nitrogen of cyanamide gave an N-silylated eta(2)-amidino iron complex, which was isolated and characterized by X-ray analysis. Catalytic N-CN bond cleavage was also attained using a methyl molybdenum complex under thermal conditions.

Selective Dehydrogenative Silylation–Hydrogenation Reaction of Divinyldisiloxane with Hydrosilane Catalyzed by an Iron Complex

A hydride and a silyl group of hydrosilane is introduced into 1,3-divinyldisiloxane in the presence of a catalytic amount of (η(5)-C(5)H(5))Fe(CO)(2)Me. Instead of the product expected from the well-known hydrosilylation reaction, the product obtained is that characteristic of dehydrogenative silylation at one vinyl group and hydrogenation at the other vinyl group of 1,3-divinyldisiloxane. Based on deuterium labeling experiments, a catalytic cycle for this new reaction has been proposed.

Regioselective Double Hydrophosphination of Terminal Arylacetylenes Catalyzed by an Iron Complex

The first catalytic double hydrophosphination of alkynes was achieved by reaction with diarylphosphines in the presence of an iron catalyst. The double hydrophosphination proceeded regioselectively and effectively for various secondary arylphosphines and terminal alkynes to give 1,2-bisphosphinoethane derivatives.

Iron‐Catalyzed Dehydrogenative Coupling of Tertiary Silanes

A variety of tertiary silanes, even those with functional substituents, undergo an unprecedented iron-catalyzed dehydrogenative coupling (see scheme) in a convenient approach to disilanes, including unsymmetrical disilanes and polymers with Si-Si bonds in the backbone. Consideration of the catalytic reaction pathway revealed the intermediacy of a hydrido(disilyl)iron(IV) complex.

A Chemical Device That Exhibits Dual Mode Motions: Dynamic Coupling of Amide Coordination Isomerism and Metal-Centered Helicity Inversion in a Chiral Cobalt(II) Complex

Dynamic and consecutive molecular motions such as stretching, winding, and rotation are observed in nature. The ATP-driven F1 part of ATP synthase and the bacterial flagellar motor are typical examples, in which some external stimuli kick-off such events through conformational changes of biopolymers. Several molecular machines such as molecular rotors, gears, and shuttles have recently been developed, in which metal-coordination linkage isomerizes dynamically to offer single mode motion. Since the planar amide linkage (-CO-NH-) has two preferred structures (cis– trans isomers) and two different metal coordination modes (O-coordination and N-coordination), its isomerism is often used to alter the three-dimensional structures of biological proteins. Herein, we develop a chemical device based on a chiral Co complex that exhibits dual mode motions. The ligand employed here (H2L1) includes 2,5-dimethoxy benzene moieties attached through amide linkages to both terminals of a helical tetradentate ligand. The acid– base reaction of the corresponding cobalt complex triggered the interconversion of coordinating atoms between amide nitrogen atoms and amide oxygen atoms, giving rise to a stretching (extension/contraction) molecular motion. Since we previously demonstrated that the helicity of the Co complex with H2L2 was dynamically inverted from the L cis-a form to the D cis-a form by adding achiral NO3 ions, the employed H2L1-Co II complex was designed to work as a novel type of molecular machine that exhibits coupled stretching and inverting motions. Several types of helical ligands have shown extension/contraction molecular motion on metal complexation/decomplexation and/or protonation/deprotonation, but the present type of kinetically labile Co complex allows a dual molecular motion in a highly dynamic fashion, as would be required for a sophisticated supramolecular switching device. As established for the H2L2-CoACHTUNGTRENNUNG(ClO4)2 complex, [4] X-ray analysis of the pink-colored H2L1-Co ACHTUNGTRENNUNG(CF3SO3)2 complex [9,10] and its solid-state CD studies revealed that the complex had a L cis-a coordinated structure, in which two amine nitrogen atoms, two amide oxygen atoms, and two donors from solvent molecules and/or counter anions coordinated (see extended L-form in Figure 1, middle). F NMR and IR studies in acetonitrile/chloroform (1/9) indicated that one CF3SO3 ion coordinated to the Co center, and one CF3SO3 ion remained noncoordinated, as observed in the solid state. Its diastereomeric excess (de) value in the solution was determined to be above 95% on the basis of paramagnetic H NMR spectra. A green-colored Co complex was isolated by mixing H2L1 and Co ACHTUNGTRENNUNG(ClO4)2·6H2O in the presence of two equivalents of (C2H5)3N, and showed a characteristic CD spectrum in CH3CN (see contracted L-form in Figure 1, left). Two amine nitrogen, two amido nitrogen, and two methoxy oxygen atoms from the ligand coordinated to the Co center, to give overall a distorted octahedral geometry with contracted left-handed helical structure (L4D2 absolute configuration between the skew chelate pairs). In the H NMR spectrum recorded in CD3CN/CDCl3 (1/9), all signals appeared in the region d= 70 to 110 ppm with C2-symmetric patterns (see Figure S5 in the Supporting Information). Since no significant signals for the minor diastereomeric isomer were observed, it appears that this complex retains the contracted helical structure in the solution. The [Co(L1)] complex exhibited positive CD signals at 433 and 918 nm and negative signals at 474, 607, and 1100 nm in CH3CN/CHCl3 (1/9; Figure 2, *), which has a pattern similar to that observed in the solid-state CD spectrum (see Fig[a] Prof. H. Miyake, M. Hikita, Dr. M. Itazaki, Prof. H. Nakazawa, Dr. H. Sugimoto, Prof. H. Tsukube Department of Chemistry, Graduate School of Science Osaka City University, 3-3-138, Sumiyoshi-ku Osaka 558-8585 (Japan) Fax: (+81)6-6605-2522 E-mail : miyake@sci.osaka-cu.ac.jp Supporting information for this article is available on the WWW under http://www.chemistry.org or from the author.

Iron-Catalyzed Cross-Dehydrogenative-Coupling Reactions

Cross-dehydrogenative-coupling (CDC) reactions involving C–H bond activation are powerful tools for C–C bond formation and are highly significant from the perspective of atom economy. A variety of carbon–carbon bond-forming reactions utilizing various coupling partners are known today. Iron-catalyzed organic syntheses have attracted considerable attention because iron is an abundant, inexpensive, and environmentally benign metal. This chapter summarizes the development of iron-catalyzed CDC reactions, the reaction mechanism, and the role of the Fe species in the catalytic cycle in the period from 2007 to 2014.

Selective Boryl Silyl Ether Formation in the Photoreaction of Bisboryloxide/Boroxine with Hydrosilane Catalyzed by a Transition-Metal Carbonyl Complex

Selective B-O-Si bond formation was achieved in the reaction of bisboryloxide O(Bpin)2 (pin = (OCMe2)2)/boroxine (MeBO)3 system with tertiary silane R3SiH in the presence of stoichiometric water and a catalytic amount of [M](CO)5 ([M] = Mo(CO), W(CO), Fe) to give boryl silyl ethers. Moreover, this reaction can be applied to various hydrosilanes (disilyl compounds and secondary silanes) and hydrogermane. Some of the boryl silyl ethers thus formed were confirmed by X-ray analysis.

Catalytic C–C bond cleavage and C–Si bond formation in the reaction of RCN with Et3SiH promoted by an iron complex

Catalytic C-C bond cleavage of acetonitrile and C-Si bond formation have been attained in the photoreaction of MeCN with Et3SiH in the presence of an iron complex, Cp(CO)2FeMe. This catalytic system can be applied for arylnitrile C-C bond cleavage.

Selective Double Hydrosilylation of Nitriles Catalyzed by an Iron Complex Containing Indium Trihalide

Selective double hydrosilylation was achieved by using tertiary and secondary silanes with an excess amount of an organonitrile (RC≡N; R=alkyl, aryl) in the presence of a catalytic amount of triirondodecacarbonyl [Fe3(CO)12] and indium trichloride (InCl3). This reaction was also catalyzed by an iron complex containing indium trihalide [Fe(MeCN)6][Fe(CO)4(InX3)2], prepared by the reaction of Fe3(CO)12 with InX3 (X=Cl, Br, I). This is a novel report of the combination of a transition‐metal complex and an indium source in organic synthesis.