Direct Conversion of a Si–C(aryl) Bond to Si–Heteroatom Bonds in the Reactions of η³‑α-Silabenzyl Molybdenum and Tungsten Complexes with 2‑Substituted Pyridines

η³-α-Silabenzyl complexes Cp*M­(CO)₂{η³(<i>Si,C,C</i>)-Si­(<i>p</i>-Tol)₃} (M = Mo (<b>1-Mo</b>), W (<b>1-W</b>)) reacted with 2-substituted pyridines NC₅H₄(2-EH_<i>n</i>) (E = O, S (<i>n</i> = 1); N (<i>n</i> = 2)) under mild conditions to give M–Si–E–C–N (E = O, N), W–Si–N–C–S, and M–E–C–N (E = S, N) metallacycles depending on the metal M or heteroatom E. These three kinds of metallacycles were characterized by spectroscopy, elemental analysis, and X-ray crystallography. The first two silametallacycles take on some silylene complex character and are considered to form via (aryl)­silylene complex intermediates generated by cleavage of the Si–C­(aryl) bond in the η³-α-silabenzyl ligand of <b>1-Mo</b> and <b>1-W</b>

Direct Conversion of a Si–C(aryl) Bond to Si–Heteroatom Bonds in the Reactions of η³‑α-Silabenzyl Molybdenum and Tungsten Complexes with 2‑Substituted Pyridines

η³-α-Silabenzyl complexes Cp*M­(CO)₂{η³(<i>Si,C,C</i>)-Si­(<i>p</i>-Tol)₃} (M = Mo (<b>1-Mo</b>), W (<b>1-W</b>)) reacted with 2-substituted pyridines NC₅H₄(2-EH_<i>n</i>) (E = O, S (<i>n</i> = 1); N (<i>n</i> = 2)) under mild conditions to give M–Si–E–C–N (E = O, N), W–Si–N–C–S, and M–E–C–N (E = S, N) metallacycles depending on the metal M or heteroatom E. These three kinds of metallacycles were characterized by spectroscopy, elemental analysis, and X-ray crystallography. The first two silametallacycles take on some silylene complex character and are considered to form via (aryl)­silylene complex intermediates generated by cleavage of the Si–C­(aryl) bond in the η³-α-silabenzyl ligand of <b>1-Mo</b> and <b>1-W</b>

Tandem Hydrosilylation/<i>o</i>‑C–H Silylation of Arylalkynes Catalyzed by Ruthenium Bis(silyl) Aminophosphine Complexes

An unprecedented reaction via consecutive trans-selective hydrosilylation and <i>o</i>-C–H silylation of arylalkynes with hydrosilanes was developed by use of ruthenium complex catalysts Ru­{κ³(<i>Si</i>,<i>O</i>,<i>Si</i>)-xantsil}­(CO)­(PR₃) (R = NC₄H₈ (<b>1-Pyrr</b>), NC₅H₁₀ (<b>1-Pip</b>); xantsil = (9,9-dimethylxanthene-4,5-diyl)­bis­(dimethylsilyl)). This reaction proceeded with gentle heating at 40–60 °C and afforded novel 2,α-bis-silylated (<i>Z</i>)-stilbene or (<i>Z</i>)-styrene derivatives <b>2</b> together with an equimolar amount of (<i>E</i>)-/(<i>Z</i>)-arylalkenes as byproducts. The selectivity of the formation of <b>2</b> reached a maximum by employing catalyst <b>1-Pyrr</b> ligated by the less bulky triaminophosphine P­(NC₄H₈)₃ and hydrosilane HSiMe­(OSiMe₃)₂ having moderately bulky and electron withdrawing substituents

Synthesis of Ruthenium Complexes with a Nonspectator <i>Si,O,P</i>-Chelate Ligand: Interconversion between a Hydrido(η²‑silane) Complex and a Silyl Complex Leading to Catalytic Alkene Hydrogenation

A ruthenium complex bearing a new phosphine­(η²-silane) chelate ligand connected by a xanthene backbone, Ru­{κ⁴(<i>Si,H,O,P</i>)-^<i>t</i>Bu₂xantSiP­(H)}­(H)­Cl­(PPh₃) (<b>2</b>), was synthesized by a ligand substitution reaction of Ru­(H)­Cl­(PPh₃)₃ with 2,7-di-<i>tert</i>-butyl-4-dimethylsilyl-5-diphenylphosphino-9,9-dimethylxanthene (<b>1</b>, ^<i>t</i>Bu₂xantSiP­(H)). Dehydrogenation reaction of <b>2</b> with styrene, a hydrogen acceptor, gave a 16-electron phosphine­(silyl) complex Ru­{κ³(<i>Si,O,P</i>)-^<i>t</i>Bu₂xantSiP}­Cl­(PPh₃) (<b>3</b>) together with ethylbenzene. Complex <b>2</b> was reproduced quantitatively by exposure of <b>3</b> to H₂ (1 atm) at room temperature. Thus, hydrido­(η²-silane) complex <b>2</b> and silyl complex <b>3</b> are interconvertible through alkene hydrogenation (from <b>2</b> to <b>3</b>) and dihydrogen addition to the Ru–Si bond (from <b>3</b> to <b>2</b>) in which ^<i>t</i>Bu₂xantSiP functions as a nonspectator ligand by reversibly releasing and accommodating a hydrogen atom. Complex <b>2</b> was also found to catalyze hydrogenation of alkenes via this interconversion

(η³‑α-Silabenzyl)tungsten Complexes: An Isolable Intermediate for Interconversion between a Silylene Complex and a Silyl Complex through 1,2-Aryl Migration

η³-α-Silabenzyl complexes Cp*W­(CO)₂{η³(<i>Si,C,C</i>)-Si­(<i>p</i>-Tol)₂R} (<b>1a</b>, R = Me; <b>1b</b>, R = <i>p</i>-Tol; Cp* = η⁵-C₅Me₅, <i>p</i>-Tol = <i>p</i>-tolyl), the first silicon analogues of η³-benzyl complexes, were synthesized by abstraction of DMAP (4-(dimethylamino)­pyridine) with BPh₃ either from (aryl)­(DMAP·silylene)tungsten complexes <b>2a</b>,<b>b</b> at room temperature or from (arylsilyl)­(DMAP)­tungsten complexes <b>3a</b>,<b>b</b> under irradiation. Complex <b>1</b> was demonstrated to be a key intermediate for the interconversion between <b>2</b> and <b>3</b> and to serve as a synthetic equivalent for both base-free silylene complexes and coordinatively unsaturated silyl complexes

Directed <i>ortho</i>-C–H Silylation Coupled with <i>trans</i>-Selective Hydrogenation of Arylalkynes Catalyzed by Ruthenium Complexes of a Xanthene-Based <i>Si,O,Si</i>-Chelate Ligand, “Xantsil”

Ruthenium complexes bearing a xanthene-based bis­(silyl) chelate ligand, “xantsil” ((9,9-dimethylxanthene-4,5-diyl)­bis­(dimethylsilyl)), Ru­{κ³(<i>Si,O,Si</i>)-xantsil}­(CO)­(PR₃) (<b>1-Cy</b>: R = Cy (cyclohexyl), <b>1-Cyp</b>: R = Cyp (cyclopentyl)), were found to catalyze the reactions of internal arylalkynes with tertiary silanes (1–1.3 equiv) at a moderate temperature (room temperature to 70 °C) to give (<i>E</i>)-alkenes having an <i>ortho</i>-silylated aryl group, i.e., (<i>E</i>)-R¹C­(H)C­(H)­(C₆H₃-<i>o</i>-SiR³₃-<i>p</i>-R²). These catalytic reactions involve a unique <i>ortho</i>-selective C–H silylation of an aryl group in arylalkynes accompanied by hydrogenation of their C–C triple bonds (<i>ortho</i>-C–H silylation/hydrogenation). Importantly, in these reactions, the alkynyl moiety of arylalkynes serves as both a directing group and a hydrogen acceptor. The substrate scope of this <i>ortho</i>-C–H silylation/hydrogenation was explored by use of eight combinations of arylalkynes and tertiary silanes. In cases using bulky substrates, the catalytic performance of <b>1-Cyp</b> with a relatively less bulky phosphine ligand (PCyp₃) was shown to be superior to that of the PCy₃ analogue <b>1-Cy</b>

Directed <i>ortho</i>-C–H Silylation Coupled with <i>trans</i>-Selective Hydrogenation of Arylalkynes Catalyzed by Ruthenium Complexes of a Xanthene-Based <i>Si,O,Si</i>-Chelate Ligand, “Xantsil”

Ruthenium complexes bearing a xanthene-based bis­(silyl) chelate ligand, “xantsil” ((9,9-dimethylxanthene-4,5-diyl)­bis­(dimethylsilyl)), Ru­{κ³(<i>Si,O,Si</i>)-xantsil}­(CO)­(PR₃) (<b>1-Cy</b>: R = Cy (cyclohexyl), <b>1-Cyp</b>: R = Cyp (cyclopentyl)), were found to catalyze the reactions of internal arylalkynes with tertiary silanes (1–1.3 equiv) at a moderate temperature (room temperature to 70 °C) to give (<i>E</i>)-alkenes having an <i>ortho</i>-silylated aryl group, i.e., (<i>E</i>)-R¹C­(H)C­(H)­(C₆H₃-<i>o</i>-SiR³₃-<i>p</i>-R²). These catalytic reactions involve a unique <i>ortho</i>-selective C–H silylation of an aryl group in arylalkynes accompanied by hydrogenation of their C–C triple bonds (<i>ortho</i>-C–H silylation/hydrogenation). Importantly, in these reactions, the alkynyl moiety of arylalkynes serves as both a directing group and a hydrogen acceptor. The substrate scope of this <i>ortho</i>-C–H silylation/hydrogenation was explored by use of eight combinations of arylalkynes and tertiary silanes. In cases using bulky substrates, the catalytic performance of <b>1-Cyp</b> with a relatively less bulky phosphine ligand (PCyp₃) was shown to be superior to that of the PCy₃ analogue <b>1-Cy</b>

Iridium and Platinum Complexes of Li⁺@C₆₀

Iridium and platinum complexes of the lithium cation encapsulated fullerene Li⁺@C₆₀ were synthesized and structurally determined. The encapsulated Li⁺ strengthens the π back-bonding from the transition-metal center to the fullerene cage and is attracted toward the two negatively charged carbon atoms bound to the transition metal in the solid state