Synthesis of Base-Stabilized Hydrido(hydroborylene)tungsten Complexes and Their Reactions with Terminal Alkynes To Give η³‑Boraallyl Complexes

Reaction of the methyl­(pyridine)­tungsten complex Cp*­(CO)₂W­(py)­Me with borane–NHC (NHC = N-heterocyclic carbene; ^MeIMe, ^MeI^<i>i</i>Pr) (^MeIMe = 1,3,4,5-tetramethylimidazol-2-ylidene, ^MeI^<i>i</i>Pr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) adducts gave the NHC-stabilized hydrido­(hydroborylene)tungsten complexes Cp*­(CO)₂W­(H)­(BH·NHC) (<b>1a</b>: NHC = ^MeIMe, <b>1b</b>: NHC = ^MeI^<i>i</i>Pr) as dark brown crystals in high yields accompanied by liberation of pyridine and methane. X-ray crystal structure analysis revealed that the W–B bond of <b>1b</b> is bridged by a hydrido ligand. Reactions of <b>1a</b>,<b>b</b> with phenylacetylene at room temperature afforded NHC-stabilized η³-boraallyl complexes <b>2a</b>,<b>b</b>, respectively, through a new type of hydroboration of the alkyne triple bond: i.e., addition of a hydrogen and a borylene. Reaction of <b>1a</b> with 3-butyn-2-one also led to hydroboration of the triple bond, not the CO double bond, to give η³-boraallyl complex <b>3</b>. In the reaction of <b>1a</b> with (trimethylsilyl)­acetylene, 1-oxo-4-borabutenyl complex <b>4</b> was formed as a primary product through carboboration of the alkyne triple bond. The subsequent slow reaction of <b>4</b> at ambient temperature resulted in the formation of η³-boraallyl complex <b>5</b> and carbyne complex <b>6</b> in the ratio of 5:4. In all of these reactions, regioselective boration of the terminal carbon of alkynes was observed

Cationic Metallogermylene and Dicationic Dimetallodigermenes: Synthesis by Chloride Abstraction from <i>N</i>‑Heterocyclic Carbene-Stabilized Chlorometallogermylenes

Reaction of NHC-stabilized dichlorogermylenes (NHC = <i>N</i>-heterocyclic carbene) with an anionic tungsten complex produced NHC-stabilized chlorometallogermylenes. Subsequent chloride abstraction from the products with NaBAr₄ (Ar = 3,5-(CF₃)₂C₆H₃) gave a cationic metallogermylene or dicationic dimetallodigermenes

Insertion of a Cationic Metallogermylene into E–H Bonds (E = H, B, Si)

A cationic germylene containing tungsten and N-heterocyclic carbene units reacted with H₂ in fluorobenzene at 60 °C, resulting in its insertion into the H–H bond. It also activated the Si–H bond of ethyldimethylsilane and the B–H bond of pinacolborane at ambient temperature to give the insertion products. The latter insertion reactions against hydrosilane and hydroborane were found to be reversible

Insertion of a Cationic Metallogermylene into E–H Bonds (E = H, B, Si)

A cationic germylene containing tungsten and N-heterocyclic carbene units reacted with H₂ in fluorobenzene at 60 °C, resulting in its insertion into the H–H bond. It also activated the Si–H bond of ethyldimethylsilane and the B–H bond of pinacolborane at ambient temperature to give the insertion products. The latter insertion reactions against hydrosilane and hydroborane were found to be reversible

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