Masahiro Kamitani

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.

Phosphinoalkylidene and -alkylidyne Complexes of Titanium: Intermolecular C-H Bond Activation and Dehydrogenation Reactions.

The ethylene complex (PNP)Ti(η(2)-H2C═CH2)(CH2(t)Bu) or (PNP)Ti═CH(t)Bu(CH2(t)Bu) (PNP(-) = N[2-P(CHMe2)2-4-methylphenyl]2) reacts with H2CPPh3 to form the κ(2)-phosphinoalkylidene (PNP)Ti═CHPPh2(Ph) (1). Compound 1 activates benzene via the transient intermediate [(PNP)Ti≡CPPh2] (C). By treatment of (PNP)Ti═CH(t)Bu(OTf) with LiCH2PPh2, 1 or its isotopologue (PNP)Ti═CDPPh2(C6D5) (1-d6) can be produced by an independent route involving intermediate C, which activates benzene or benzene-d6 and dehydrogenates cyclohexane-d12. Addition of MeOTf to 1 results in elimination of benzene concomitant with the formation of the phosphonioalkylidyne complex, [(PNP)Ti≡CPPh2Me(OTf) (2). Theoretical studies of 2 suggest a resonance structure having dominant Ti-C triple-bond character with some contribution also from a C-P multiple bond.

Cyclo-P3 Complexes of Vanadium: Redox Properties and Origin of the 31P NMR Chemical Shift

The synthesis and characterization of two high-valent vanadium-cyclo-P3 complexes, (nacnac)V(cyclo-P3)(Ntolyl2) (1) and (nacnac)V(cyclo-P3)(OAr) (2), and an inverted sandwich derivative, [(nacnac)V(Ntolyl2)]2(μ2-η(3):η(2)-cyclo-P3) (3), are presented. These novel complexes are prepared by activating white phosphorus (P4) with three-coordinate vanadium(II) precursors. Structural metrics, redox behavior, and DFT electronic structure analysis indicate that a [cyclo-P3](3-) ligand is bound to a V(V) center in monomeric species 1 and 2. A salient feature of these new cyclo-P3 complexes is their significantly downfield shifted (by ∼300 ppm) (31)P NMR resonances, which is highly unusual compared to related complexes such as (Ar[(i)Pr]N)3Mo(cyclo-P3) (4) and other cyclo-P3 complexes that display significantly upfield shifted resonances. This NMR spectroscopic signature was thus far thought to be a diagnostic property for the cyclo-P3 ligand related to its acute endocyclic angle. Using DFT calculations, we scrutinized and conceptualized the origin of the unusual chemical shifts seen in this new class of complexes. Our analysis provides an intuitive rational paradigm for understanding the experimental (31)P NMR spectroscopic signature by relating the nuclear magnetic shielding with the electronic structure of the molecule, especially with the characteristics of metal-cyclo-P3 bonding.

Room-Temperature Ring-Opening of Quinoline, Isoquinoline, and Pyridine with Low-Valent Titanium

The complex (PNP)Ti═CHtBu(CH2tBu) (PNP = N[2-PiPr2-4-methylphenyl]2-) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti(CH2tBu)], which reacts with 2 equiv of quinoline (Q) at room temperature to form H3CtBu and a Ti(IV) species where the less hindered C2═N1 bond of Q is ruptured and coupled to another equivalent of Q. The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti═N[C18H13N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide moiety in 1 occurs to form 2, and thermolysis reverses this process. The reaction of 2 equiv of isoquinoline (Iq) with intermediate [(PNP)Ti(CH2tBu)] results in regioselective cleavage of the C1═N2 and C1-H bonds, which eventually couple to form complex 3, a constitutional isomer of 1. Akin to 1, the transient [(PNP)Ti(CH2tBu)] complex can ring-open and couple two pyridine molecules, to produce a close analogue of 1, complex (PNP)Ti═N[C10H9N] (4). Multinuclear and multidimensional NMR spectra confirm structures for complexes 1-4, whereas solid-state structural analysis reveals the structures of 2, 3, and 4. DFT calculations suggest an unprecedented mechanism for ring-opening of Q where the reactive intermediate in the low-spin manifold crosses over to the high-spin surface to access a low-energy transition state but returns to the low-spin surface immediately. This double spin-crossover constitutes a rare example of a two-state reactivity, which is key for enabling the reaction at room temperature. The regioselective behavior of Iq ring-opening is found to be due to electronic effects, where the aromatic resonance of the bicycle is maintained during the key C-C coupling event.

Synthesis, Characterization, and Crystal Structure of Germyl(phosphine)iron Complexes, Cp(CO)Fe(PPh3)(GeR3) (R = Et, n Bu, Ph), Prepared from Cp(CO)Fe(PPh3)(Me) and HGeR3

Photoreaction of Cp(CO)2Fe(Me) (Cp stands for η5-cyclopentadienyl) with PPh3 afforded Cp(CO)Fe(PPh3)(Me). Reaction of the methyl iron complex with HGeR3 (R = Et, nBu, Ph) produced Cp(CO)Fe(PPh3)(GeR3) (R = Et: 1, nBu: 2, Ph: 3). All new complexes were fully characterized using 1H, 13C{1H}, and 31P{1H} NMR measurements and elemental analyses. Furthermore, the structure of 3 was determined using single crystal X-ray analysis.

CCDC 1579927: Experimental Crystal Structure Determination

Related Article: Seung-yeol Baek, Takashi Kurogi, Dahye Kang, Masahiro Kamitani, Seongyeon Kwon, Douglas P. Solowey, Chun-Hsing Chen, Maren Pink, Patrick J. Carroll, Daniel J. Mindiola, and Mu-Hyun Baik|2017|J.Am.Chem.Soc.|139|12804|doi:10.1021/jacs.7b07433

CCDC 1579925: Experimental Crystal Structure Determination

Related Article: Seung-yeol Baek, Takashi Kurogi, Dahye Kang, Masahiro Kamitani, Seongyeon Kwon, Douglas P. Solowey, Chun-Hsing Chen, Maren Pink, Patrick J. Carroll, Daniel J. Mindiola, and Mu-Hyun Baik|2017|J.Am.Chem.Soc.|139|12804|doi:10.1021/jacs.7b07433

Carbon­yl(η5-cyclo­penta­dien­yl)(pyridine)(triethyl­stann­yl)iron(II)

In the title complex, [Fe(C5H5){Sn(C2H5)3}(C5H5N)(CO)], the Fe atom is coordinated by carbonyl, pyridine, triethylstannyl and cyclopentadienyl ligands in a typical three-legged piano-stool configuration. The Fe—Sn and Fe—N bond distances are 2.5455 (13) and 1.984 (6) Å, respectively.