高橋 慎太郎

The hydrosilylation reactions of dihydrosilylium ion, stabilized by coordination of a σ‐donating Ni(0) fragment, has been investigated. This complex with two reactive sites, dihydrosilylium and Ni(0) centers, readily reacts with diphenylacetylene via a selective mono‐hydrosilylation reaction to afford the corresponding Ni(0)‐stabilized (hydro)(vinyl)silylium ion. In the case of ethylene, three equivalents of olefin are consumed to give a cationic Ni(II)‐complex featuring a Bu‐Si+‐NiII‐Et moiety with a NHC‐supported Si atom. DFT calculations indicate that the hydrosilylation proceeds by a classical (Chalk‐Harrod type) mechanism with the assistance of NHC ligand moving between Si and Ni centers according to their stabilization requirements.

Abstract A silyliumylidene ion 2 stabilized by two σ‐donating Ni(0)‐ and Pd(0)‐fragments was successfully synthesized. Due to the σ‐donation of M→Si interactions, 2 presents a pyramidalized cationic silicon center with a localized lone pair. The additional coordination of basic Pd(0) fragment to the mono‐Ni(0)‐stabilized silyliumylidene 1 results in a higher HOMO level and an unchanged HOMO‐LUMO gap and thus, 2 remains highly reactive. Interestingly, the coordination mode at the Si center is closely related to the nature of M‐ligands. Indeed, the donor/donor‐stabilized silyliumylidene ion 2 has been transformed into a donor/acceptor‐stabilized ion 13, featuring a trigonal planar Si center with a vacant orbital, just via a ligand exchange reaction from PCy₃/NHC toward PMe₃.

Three‐coordinated chlorogermylenes of the type [Ph2P(RN)2]GeCl (3: R = tBu; 4: R = Dip = 2,6‐iPr2C6H3), which bear an N,N‐substituted iminophosphonamide ligand, were synthesized. The coordination behavior of 3 and 4 toward rhodium(I) complex was investigated. When 3 was treated with 1/2 of an equivalent of [RhCl(cod)]2 (cod = 1,5‐cyclooctadiene), the corresponding chlorogermylene‐Rh(I) complex 5 was obtained as orange crystals. In contrast, the reaction of 4 with a half equivalent of [RhCl(cod)]2 under a CO atmosphere resulted in the formation of a five‐membered germarhodacycle 7. Compounds 3, 4, 5, and 7 were characterized using NMR spectroscopies and single‐crystal X‐ray diffraction. Complex 5 can be employed as a catalyst for the hydrosilylation and hydroboration reactions of diphenylacetylene, thus demonstrating the utility of germylene ligands comparable to those of NHCs in the major transition metal catalytic processes.

The title complex {[Ph2P(tBuN)2](Cl)Si:->Fe(CO)4} (2) was synthesized via the reaction of chlorosilylene [Ph2P(tBuN)2]SiCl (1), supported by an iminophosphonamide ligand with Fe(CO)5 in THF. The molecular structure of 2 was fully characterized by NMR (1H, 13C, 29Si, and 31P) and IR spectroscopies, as well as single-crystal X-ray diffraction (SCXRD) analysis. In the SCXRD analysis of 2, the silylene ligand was located in the axial positions of the coordination sphere of the central iron atom and other sites were occupied by carbonyl ligands.

Halogen-substituted silylenes are an important building block for synthesizing silicon-based low-valent and multiple-bond species. However, the number of reports on heavier halosilylenes that contain bromine and iodine is still limited. Here, we present a convenient synthesis for bromo- and iodosilylenes supported by an iminophosphonamide ligand. The heavier halosilylenes [Ph2P(tBuN)2]SiX (2: X = Br, 3: X = I) were successfully synthesized via the halogen-exchange reaction of chlorosilylene 1 with alkali halides in THF. As a demonstration of the reactivity of 2 and 3, oxidative addition reactions of 2 and 3 with elemental selenium in C6D6 afforded the corresponding bromo- (5) or iodosilylene-selone (6) as colorless crystals. The molecular structures of 2, 3, 5, and 6 were fully characterized by spectroscopic means and single-crystal X-ray diffraction analysis. Furthermore, the effects of the halogen atom on the electronic state of halosilylenes 1-3 and halosilylene-selones 4-6 were investigated using density functional theory (DFT) calculations.

<jats:p>A novel three-coordinated tin(II) chloride [Ph<jats:sub>2</jats:sub>P(N<jats:italic><jats:sup>t</jats:sup></jats:italic>Bu)<jats:sub>2</jats:sub>]SnCl (<jats:bold>1</jats:bold>) supported by an <jats:italic>N</jats:italic>,<jats:italic>N</jats:italic>’-di-<jats:italic>tert</jats:italic>-butyliminophosphonamide having two phenyl groups on the phosphorus atom was synthesized by the reaction of the starting lithium iminophosphonamide [Ph<jats:sub>2</jats:sub>P(N<jats:italic><jats:sup>t</jats:sup></jats:italic>Bu)<jats:sub>2</jats:sub>]Li...</jats:p>

<p>The sterically demanding iminophosphonamido chlorosilylene [Ph2P(DipN)2]SiCl (Dip = 2,6-diisopropylphenyl) was synthesized and fully characterized using NMR spectroscopy and X-ray crystallography. Substitution reactions of [Ph2P(DipN)2]SiCl with N- and Fe-nucleophiles led to...</p>

The reaction of a chlorosilylene, supported by an iminophosphonamide ligand, with KN(SiMe3)(2) resulted in the formation of a silaimine instead of the expected aminosilylene. However, this silaimine exists in equilibrium with the corresponding aminosilylene, which was experimentally demonstrated using variable-temperature NMR spectroscopy and a trapping reaction with elemental selenium to give a silaselenourea.

A hydrido(dihydrosilyl) platinum(II) complex having PMe(3)ligands, [cis-PtH(SiH(2)Trip)(PMe3)(2)] (2) (Trip = 9-triptycyl) was prepared by the ligand-exchange reaction of [PtH(SiH2 Trip)-(PMe3)(PPh3)] (1) with an excess amount of free PMe3 in hexane. X-ray crystallographic analysis of 2 revealed that the platinum center adopts a twisted square-planar geometry; the dihedral angle between the P-Pt-P and Si-Pt-H planes is 10.43 degrees. The complex displayed a fluxional NMR behavior in solution on the NMR time scale, where a eta(1) -Si-H structure was suggested as a transition state of the rate-controlling step by DFT calculation.

A novel N-hetero-Rh-I-metallacyclic silanone2has been synthesized. The silanone2, showing an extremely large dimerization energy (Delta G=+86.2 kcal mol(-1)), displays considerable stability and persists in solution up to 60 degrees C. Above 120 degrees C, an intramolecular C-sp3-H insertion occurs slowly over a period of two weeks leading to the bicyclic silanol5. The exceptional stability of2, related to the unusual electronic and steric effects of Rh-I-substituent, should allow for a more profound study and understanding of these new species. Furthermore, the metallacyclic silanone2presents two reactive centers (Si=O and Rh), which can be involved depending upon the nature of reagents. Of particular interest, the reaction with H(2)starts with the hydrogenation of Rh(I)center leading to the corresponding Rh-III-dihydride complex7and it undergoes acis/trans-isomerization via a particular mechanism, demonstrating that addition-elimination processes can also happen for silanones just like for their carbon analogues!

The N-heterocyclic silylene (NHSi) [Ph2P((BuN)-Bu-t)(2)]SiCl (1), supported by an iminophosphonamide ligand, was obtained from the dehydrochlorination of [Ph2P((BuN)-Bu-t)(2)]SiHCl2 (2) with LiN(SiMe3)(2). NHSi 1 contains an extremely high-energy HOMO level and consequently displays unique coordination behavior toward Rh-I complexes. When 1 was treated with 1/4 of an equivalent of [RhCl(cod)](2) (cod=1,5-cyclooctadiene), the 14-electron Y-shaped bis(chlorosilylene) Rh-I complex 5 was obtained as dark purple crystals. The reaction of 1 with 1/6 of an equivalent of [RhCl(cod)](2) yielded the cationic tris(silylene)-Rh-I complex [6](+).Cl- as red crystals, wherein a two-coordinated silylene ligand engages in a Si=Rh double bond. A structural analysis of 5 and [6](+).Cl- revealed that the central rhodium atoms adopt trigonal and square-planar coordination geometries, respectively, with considerably shortened Si-Rh bonds [5: 2.1605(5) angstrom; [6](+): 2.133(1) angstrom].

A cyclic (amino)metal-substituted dicoordinated silylene derivative has been synthesized and fully characterized. Of particular interest is that the N-hetero-Rh-I-metallacyclic silylene exhibits a distorted tetrahedral geometry around the rhodium atom and a considerably shortened Si-Rh bond (2.138 angstrom) compared to classical Si-Rh single bonds (ca. 2.30-2.35 angstrom). A theoretical investigation reveals that the geometrical deviation around the rhodium center from the classical square-planar to a tetrahedral geometry increases the pi-donating and sigma-accepting character of the rhodium atom, thereby efficiently stabilizing the silylene moiety.

Treatment of 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-tellone 1 with Tf2O in CH2Cl2 resulted in the formation of dicationic ditelluride salt 2(2+) 2 (OTf)(-) as air-stable green crystals in 88% yield. The anion exchange reaction of 2(2+) 2 (OTf)(-) with Na[B(C6F5)(4)] proceeded in CH3CN at room temperature giving the corresponding borate salt 2(2+) 2 [B(C6F5)(4)](-) as blue crystals in 40% yield. The structures of these dicationic ditelluride derivatives were fully characterized on the basis of their NMR spectroscopic data and X-ray crystallography. In the crystalline state of 2(2+) 2 (OTf)(-), two NHC ligands are entirely perpendicular to the central Te-Te bond with a Te-Te-C-N torsion angle of 89.93(19)degrees. In sharp contrast, X-ray analysis of 2(2+) 2 [B(C6F5)(4)](-) revealed that two NHC ligands and the central Te-Te moiety are essentially coplanar with a Te-Te-C-N torsion angle of 7.99(17)degrees. In the DFT calculation for the model compound 3(2+), NBO orbitals around the Te-Te moiety in C-i symmetry consist of a Te-Te sigma-bonding orbital, a Te-C sigma-bonding orbital, a lone pair orbital on the Te atom (mainly s-character), and a lone pair orbital on the Te atom (pure p-character).

The reaction of the lithium salt of N, N'-di-tert-butyldiimidosulfinate ([PhS((NBu)-Bu-t)(2)] Li) having a phenyl group on the sulphur atom with ECl2 center dot(dioxane) (E = Ge, Sn) afforded the corresponding chlorogermylene [PhS((NBu)-Bu-t)(2)] GeCl 1 and -stannylene [PhS((NBu)-Bu-t)(2)]SnCl 2, respectively. In contrast, treatment of the N, N'bis( trimethylsilyl) diimidosulfinate ion ([PhS(NSiMe3)(2)](-)) with ECl2 center dot(dioxane) resulted in the unexpected formations of six-membered 1,3-bis(chlorogermylene) [PhS(NSiMe3)(2)(eta(1)-eta(1)-GeCl)(2)[mu-NSPh(NHSiMe3)] 7 and -stannylene [PhS(NSiMe3)(2)(eta(1)-eta(1)-SnCl)(2)[mu-NSPh(NHSiMe3)]8. The structures of these chlorometallylene derivatives were fully characterized on the basis of their NMR spectroscopic data and X-ray diffraction. In the crystalline states of 1 and 2, the diimidosulfinate ligands chelate to the metal centre to form slightly hinged four-membered EN2S rings. On the other hand, X-ray analyses of 7 and 8 revealed that the central six-membered E2N3S rings adopt a distorted boat-conformation, and one diimidosulfinate ligand coordinates to the metal centre in a bridging monodentate mu-eta(1)-eta(1)-fashion. As the reactivity of 1 and 2, the oxidation of 1 with elemental chalcogen (S8 or Se) afforded the corresponding tetra-coordinated germanium compounds [PhS((NBu)-Bu-t)(2)] Ge(=Ch) Cl 3 (Ch=S) and 4 (Ch=Se). In sharp contrast, the reactions of 2 with elemental chalcogen resulted in the formation of four-membered Sn(2)Ch(2) ring compounds, 1,3,2,4dichalcogenadistannetanes {(PhS((NBu)-Bu-t) 2) SnCl(mu-Ch)}(2) 5 (Ch=S) and 6 (Ch=Se).