Iron complexes supported by silyl-NHC chelate ligands: synthesis and use for double hydroboration of nitriles.

Iron complexes bearing new silyl-NHC bidentate ligands were synthesised by treating Fe3(CO)12 with a mixture of N-(hydrosilyl)methyl imidazolium salts and a base. These complexes showed high performance in the catalytic double hydroboration of nitrile with pinacolborane (HBpin) to produce N,N-bis(boryl)amine by a combination of UV irradiation and mild heating (60 °C). The product yields for the hydroboration of aromatic and aliphatic nitriles reached 85%-95% (NMR) using an iron complex (5 mol%). Reducing the loading amount of the iron complex to 0.5 mol% still afforded the products in high yields. An analogous ruthenium complex, which was similarly synthesised using Ru3(CO)12, showed lower activity. Stoichiometric reactions of the iron complex with nitriles afforded Fe(0)-N-silylimine complexes, which may be dormant states in nitrile hydroboration. A catalytic mechanism including Fe(0) N-silylimine species is proposed.

Neutral Chromium Complex with a Cr≡Si Triple Bond: Synthesis and Photoinduced H-H and Benzene C-H Bond Activation.

A neutral silylyne complex with a Cr≡Si triple bond was prepared by dehydrogenation of a chromium silylene complex with Cr-H and Si-H bonds, and was isolated as monomeric crystals, unlike dimeric forms of its tungsten and molybdenum congeners. The strong Cr(δ-)-Si(δ+) bond polarity was revealed by the reaction with MeOH and DFT calculations. The chromium silylyne complex reacted with H2 under LED (365 nm) irradiation to reproduce the precursor silylene complex with a (H)Cr=Si(H) moiety, as a result of 1,2-H-H addition across the Cr≡Si triple bond. Similarly, the chromium silylyne complex reacted with benzene under irradiation to afford an 1,2-addition product with a (H)Cr=Si(Ph) moiety, via benzene C-H bond activation accompanied by Si-C bond forming.

Neutral Silylyne Complex of Molybdenum: Synthesis, Properties, and Access to Silaiminoacyl Complexes via [2+3] Cycloaddition.

A neutral silylyne complex of molybdenum was synthesized by the stepwise dehydrogenation method and its properties were compared with those of the tungsten analog. The complex takes a dimeric form as crystals but afford a monomer-dimer equilibrium in solution. The replacement of the central metal from W to Mo led to a monomer dominant (~98 %) solution at room temperature. The monomer-dimer dynamics was investigated based on thermodynamic parameters. The molybdenum silylyne complex underwent [2+2] cycloaddition with alkynes much faster than the tungsten analog. The reactions with organic azides led to the formation of the first example of silaiminoacyl complexes through [2+3] cycloaddition. The structures and bonding aspects of the products were clarified by multiple measurements and DFT calculations.

Iridium and rhodium complexes bearing a silyl-bipyridine pincer ligand: synthesis, structures and catalytic activity for C-H borylation of arenes.

Unsaturated 16-electron iridium and rhodium complexes bearing a silyl-bipyridine-based SiNN-pincer ligand (BpySiNN) were synthesised and characterised by X-ray crystallography and NMR spectroscopy. The iridium-BpySiNN complex facilitated the catalytic C(sp2)-H borylation of arenes to give arylboronate esters in high yields (≥93%) under mild conditions (∼40 °C).

A Nickel Complex Containing a Pyramidalized, Ambiphilic Pincer Germylene Ligand.

Reaction of N-heterocyclic carbene (NHC)-stabilized PGeP-type germylene Ge{o-(PiPr2 )C6 H4 }2 ⋅Me IiPr (1) (Me IiPr=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with Ni(cod)2 gave pincer germylene complex Ni[Ge{o-(PiPr2 )C6 H4 }2 ](Me IiPr) (2), in which the Ge center of 2 is significantly pyramidalized. Theoretical calculation on 2 predicted the ambiphilicity of the germanium center, which was confirmed by reactivity studies. Thus, complex 2 reacted with both Lewis base Me IMe (Me IMe=1,3,4,5-tetramethylimidazol-2-ylidene) and Lewis acid BH3 ⋅SMe2 at the germanium center to afford the adducts Ni[Ge{o-(PiPr2 )C6 H4 }2 ⋅Me IMe](Me IiPr) (3) and Ni[Ge{o-(PiPr2 )C6 H4 }2 ⋅BH3 ](Me IiPr) (4), respectively. Furthermore, the former was slowly converted to dinuclear complex Ni2 [Ge{o-(PiPr2 )C6 H4 }2 ]2 (Me IMe)2 (5) at room temperature. Complex 5 can be regarded as a dimer of the Me IMe analog of 2 with a Ni-Ge-Ge-Ni linkage.

Reactions of a Silylyne Complex with Aldehydes: Formation of W-Si-O-C Four-Membered Metallacycles and Their Metathesis-Like Fragmentation.

A tungsten silylyne complex having a W≡Si triple bond reacted with two molecules of aldehydes at room temperature to give W-Si-O-C four-membered metallacycles by [2+2] cycloaddition and subsequent formyl hydrogen transfer from one aldehyde molecule to another. Upon heating to 70 °C, the four-membered metallacycles underwent metathesis-like fragmentation cleanly to afford carbyne complexes and "silanoic esters," in a manner similar to that of metallacyclobutadiene, an intermediate of alkyne metathesis reactions, and dimerization of the latter products gave 1,3-cyclodisiloxanes. The "silanoic ester" was also trapped by pivalaldehyde to give a [2+2] cycloaddition product in high yield.

Silyl-pyridine-amine pincer-ligated iridium complexes for catalytic silane deuteration via room temperature C-D bond activation of benzene-d6.

Iridium-hydrido complexes bearing a hemilabile silyl-pyridine-amine pincer ligand were synthesised. They were found to catalyse Si-H deuteration of trialkylsilanes with excess benzene-d6 in 99-94% conversion at room temperature through C-D bond activation and H/D exchange.

An iron germylene complex having Fe-H and Ge-H bonds: synthesis, structure and reactivity.

A base-free iron germylene complex Cp*(CO)(H)Fe[double bond, length as m-dash]GeH{C(SiMe3)3} (1) was synthesised by abstraction of pyridine from a germyl complex Cp*(CO)(py)FeGeH2{C(SiMe3)3} (2), which was prepared by treatment of Cp*Fe(CO)(py)(Me) with H3GeC(SiMe3)3. X-ray crystallographic analysis revealed that 1 has an Fe-Ge bond that is the shortest among those ever reported. Reactivity of 1 toward several polar unsaturated organic compounds was investigated. Complex 1 underwent stoichiometric hydrogermylation of carbonyl compounds such as ketones, aldehydes and isocyanates (RNCO) at room temperature. In contrast, the reactions of 1 with isothiocyanates (RNCS) resulted in clean cleavage of the C[double bond, length as m-dash]S double bonds.

Hydrogen-bridged bis(silylene) complexes of ruthenium and iron: synthesis, structures and multi-centre bonding interactions at the M-Si-H-Si four-membered ring.

Hydrogen-bridged bis(silylene) complexes of ruthenium and iron were synthesized as the first examples of this type containing Group 8 metals and their rare four-membered ring structures and multi-center bonding interactions at the M-Si-H-Si moiety were clarified by NMR spectroscopy, X-ray crystallography and theoretical calculations.

Stabilization of a Silaaldehyde by its η(2) Coordination to Tungsten.

Treatment of pyridine-stabilized silylene complexes [(η(5)-C5 Me4R)(CO)2(H)W=SiH(py)(Tsi)] (R = Me, Et; py = pyridine; Tsi = C(SiMe3)3) with an N-heterocyclic carbene (Me)I(i)Pr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) caused deprotonation to afford anionic silylene complexes [(η(5)-C5Me4 R)(CO)2W=SiH(Tsi)][H(Me)I(i)Pr] (R = Me (1-Me); R = Et (1-Et)). Subsequent oxidation of 1-Me and 1-Et with pyridine-N-oxide (1 equiv) gave anionic η(2)-silaaldehydetungsten complexes [(η(5)-C5Me4R)(CO)2W{η(2)-O=SiH(Tsi)}][H(Me)I(i)Pr] (R = Me (2-Me); R = Et (2-Et)). The formation of an unprecedented W-Si-O three-membered ring was confirmed by X-ray crystal structure analysis.

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.

Unexpected Formation of NHC-Stabilized Hydrosilylyne Complexes via Alkane Elimination from NHC-Stabilized Hydrido(alkylsilylene) Complexes.

N-heterocyclic carbene (NHC)-stabilized hydrosilylyne complex Cp*(CO)2WSiH((Me)IMe)2 (3a) ((Me)IMe = 1,3,4,5-tetramethylimidazole-2-ylidene) was formed by the reaction of an NHC-stabilized silylene complex Cp*(CO)2(H)WSiH((Me)IMe){C(SiMe3)3} (2a) with 1 equiv of (Me)IMe at 70 °C. In this reaction, HC(SiMe3)3 was unexpectedly eliminated from 2a. A C5Me4Et analogue of 3a, (C5Me4Et)(CO)2WSiH((Me)IMe)2 (3b), was also synthesized by the same method, and the structure of 3b was confirmed by X-ray crystallography. Although the silicon center of 3b is coordinated by two NHCs, the length of the W-Si bond of 3b [2.363(4) Å] is as short as that of the shortest W═Si double bond (∼2.36 Å). These complexes, 3a and 3b, are the first examples of a base-stabilized silylyne complex having only a hydrogen on the silicon atom.

Isolation of a hydrogen-bridged bis(silylene) tungsten complex: a snapshot of a transition state for 1,3-hydrogen migration.

A hydrogen-bridged bis(silylene) complex, which can be viewed as a snapshot of a transition state for 1,3-hydrogen migration, was isolated, and its unprecedented WSi2H four-membered-ring structure with a short diagonal Si-Si distance was revealed by X-ray crystallography. NMR studies including determination of the W-Si, Si-Si, and Si-H coupling constants and theoretical calculations suggest that a novel multicenter bond is formed in the WSi2H system, in which the bridging hydrogen takes on a hydridic nature.

Cationic metallogermylene and dicationic dimetallodigermenes: synthesis by chloride abstraction from N-heterocyclic carbene-stabilized chlorometallogermylenes.

Reaction of NHC-stabilized dichlorogermylenes (NHC = N-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.

Reactions of a tungsten-germylyne complex with α,ß-unsaturated ketones: complete cleavage of the W≡Ge bond and formation of two types of η3-germoxyallyl tungsten complexes.

Germylyne complex Cp*(CO)2W≡Ge{C(SiMe3)3} (1) reacted with two molecules of RC(O)CH═CH2 (R = Me, Et) to give η(3)-allyl complexes, in which an oxagermacyclopentene framework was bound to an η(3)-allyl ligand through an oxygen atom. In the reaction with α-Me-substituted MeC(O)C(Me)═CH2, 1 reacted with only one molecule of the substrate to give another type of η(3)-allyl complex, in which a five-membered oxagermacyclopentenyl ring was coordinated to the W center in an η(3) fashion. Both reactions resulted in unprecedented complete cleavage of a W≡Ge triple bond.

Reactions of a tungsten-germylyne complex with alcohols and arylaldehydes.

A germylyne complex Cp*(CO)2W≡GeC(SiMe3)3 (1) reacted with alcohols to give simple nucleophilic addition products, while 1 reacted with two molecules of arylaldehydes consecutively to give base-stabilised alkoxy(germylene) complexes via C-H bond activation and hydrogermylation.

Covalently chemical modification of lithium ion-encapsulated fullerene: synthesis and characterization of [Li+@PCBM]PF6(-).

Covalently organic derivatization of [Li(+)@C60]PF6(-) to obtain Li(+)-encapsulated PCBM, [Li(+)@PCBM]PF6(-), is described. Synthetic procedures, electrochemical properties, light absorption properties, details of isomerization from [5,6]- to [6,6]-isomer, and X-ray crystal structure of [Li(+)@PCBM]PF6(-) are discussed.

Rock-salt-type crystal of thermally contracted C60 with encapsulated lithium cation.

Rock solid: fullerene-encapsulated Li(+) (Li(+)@C(60)) is an alkaline cation owing to the spherical shape and positive charge. Li(+)@C(60) crystallizes as a rock-salt-type crystal in the presence of PF(6)(-). The orientations of C(60) and PF(6)(-) (orange) are perfectly ordered below 370 K, and Li(+) (purple) hops within the cage. At temperatures below 100 K two Li(+) units are localized at two polar positions within each C(60) .

Hydrido(hydrosilylene)tungsten complexes: dynamic behavior and reactivity toward acetone.

Reaction of a labile tungsten nitrile complex, [(Cp*)W(CO)(2)(NCMe)Me] (Cp*=η(5)-C(5)Me(5)), with H(3)SiC(SiMe(3))(3) gave the hydrido(hydrosilylene) complex [(Cp*)(CO)(2)(H)W=Si(H){C(SiMe(3))(3)}] (1a). The hydrido(silylene) complex [(η(5)-C(5)Me(4)Et)(CO)(2)(H)W=SiMes(2)] (2) (Mes=2,4,6-Me-C(6)H(2)) was synthesized by a similar reaction with H(2)SiMes(2). There is a strong interligand interaction between the hydrido and silylene ligands of these complexes; this was confirmed by a neutron diffraction study of [D(2)]1b, that is, the deuterido and η(5)-C(5)Me(4)Et derivative of 1a. The exchange between the W-H and the Si-D groups was observed in the deuterido complex [D]1a. This H/D exchange proceeded slowly at room temperature, but very rapidly under UV irradiation. Variable-temperature NMR spectroscopy measurements show the dynamic behavior of carbonyl ligands in 1a. Complex 1a reacted with acetone at room temperature to give mainly a hydrosilylation product, [(Cp*)(CO)(2)(H)W=Si(OiPr){C(SiMe(3))(3)}] (3a), along with a siloxy complex, [(Cp*)(CO)(2)WO(Si(H)iPr{C(SiMe(3))(3)})] (4a). At low temperature, a different reaction, namely, α-H abstraction, proceeded to give an equilibrium mixture of 1a and a dihydrido(silyl) complex, [(Cp*)(CO)(2)(H)(2)W(Si(H){OC(=CH(2))Me}{C(SiMe(3))(3)})] (5).