SiMe3 Group Research Articles

Selective Silylation of Nitriles with an NHC-Stabilized Silylene to 1,2-Disilylimines and Subsequent Synthesis of Silaaziridines

The highly regioselective synthesis of trans-1,2-disilylimines have been achieved by the bis-silylation of nitriles with the NHC-stabilized silylene NHC-Si(NArSiMe3)Cl (1; Ar = 2,6-iPr2C6H3, NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The bis-silylation involves the migration of the SiMe3 group on the nitrogen atom in the silylene to the carbon atom of the nitrile functionality. The 1,2-disilylimine products feature an NHC-stabilized silaimine moiety and could undergo nucleophilic attack by phenyllithium reagents to yield novel silaaziridines with an NHC-stabilized exocyclic Si═N double bond.

The Nature of Secondary Interactions at Electrophilic Metal Sites of Molecular and Silica-Supported Organolutetium Complexes from Solid-State NMR Spectroscopy.

Lu[CH(SiMe3)2]3 reacts with [SiO2-700] to give [(≡SiO)Lu[CH(SiMe3)2]2] and CH2(SiMe3)2. [(≡SiO)Lu[CH(SiMe3)2]2] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH3 and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 0-2) also have secondary Lu···C interactions. The (1)H NMR spectrum of Lu[CH(SiMe3)2]3 shows that the -SiMe3 groups are equivalent to -125 °C and inequivalent below that temperature, ΔG(⧧)(Tc=148K) = 7.1 kcal mol(-1). Both -SiMe3 groups in Lu[CH(SiMe3)2]3 have (1)JCH = 117 ± 1 Hz at -140 °C. The solid-state (13)C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give (1)JCH = 117 ± 2 Hz. The (29)Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ-Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling's electroneutrality concept.

Aminosilanes derived from 1H-benzimidazole-2(3H)-thione.

Two new molecular structures, namely 1,3-bis(trimethylsilyl)-1H-benzimidazole-2(3H)-thione, C13H22N2SSi2, (2), and 1-trimethylsilyl-1H-benzimidazole-2(3H)-thione, C10H14N2SSi, (3), are reported. Both systems were derived from 1H-benzimidazole-2(3H)-thione. Noncovalent C-H···π interactions between the centroid of the benzmidazole system and the SiMe3 groups form helicoidal arrangements in (2). Dimerization of (3) results in the formation of R2(2)(8) rings via N-H···S interactions, along with parallel π-π interactions between imidazole and benzene rings.

Thermal Isomerization of the Buchwald Seven-Membered Zirconacyclocumulene and Its Interaction with Acetylenes. Synthesis and Structures of Novel Seven-Membered Zirconacyclocumulene Complexes

On prolonged heating of the Buchwald seven-membered zirconacyclocumulene Cp2Zr[η4-Me3SiC4(SiMe3)–C(C2SiMe3)═CSiMe3] (1) in toluene at 100 °C, the isomerization of 1 takes place with the formation of a seven-membered zirconacyclocumulene complex, Cp2Zr[η4-Me3SiC4(SiMe3)–C(SiMe3)═C(C2SiMe3)] (8), containing the Me3SiC≡C group in α-position and the SiMe3 group in β-position with respect to the Zr atom. A remarkable peculiarity of complex 8 is its ability to undergo a rapid degenerate rearrangement at room temperature in toluene solution, as a result of which only two rather than four singlets of the Me3Si groups are observed in the 1H NMR spectrum of 8 under such conditions. At temperatures below 200 K, the rate of this rearrangement decreases and, as a consequence, the 1H NMR spectrum of 8 acquires the normal view. If 1 is heated at 100 °C in the presence of acetylenes such as 1,4-bis(tert-butyl)butadiyne (tBuC≡C–C≡CtBu) and tolane, the corresponding seven-membered zirconacyclocumulenes, viz., Cp2Zr[η4-tBuC4(tBu)–C(C2SiMe3)═CSiMe3] (7) and Cp2Zr[η4-Me3SiC4(SiMe3)–C(Ph)═CPh] (14), are formed along with free Me3SiC≡C–C≡CSiMe3. The interaction of 1 with 1,4-diphenylbutadiyne (PhC≡C–C≡CPh) at 100 °C leads to the formation of a mixture of products, from which a zirconacyclopentadiene metallacycle, Cp2Zr[η2-PhC═C(C2Ph)–C(C2Ph)═CPh] (10), as well as seven-membered zirconacyclocumulenes Cp2Zr[η4-PhC4(Ph)–C(C2SiMe3)═CSiMe3] (11), Cp2Zr[η4-Me3SiC4(SiMe3)–C(C2Ph)═CPh] (12), and Cp2Zr[η4-PhC4(Ph)–C(C2Ph)═CPh] (13) were isolated. The structures of 8, 9, 10, 12, and 14 have been established by X-ray crystallography. The mechanism of the reactions found is discussed.

Quantum Chemical Study of the Reaction of 3-(Trimethylsilyl)cyclohexa-1,4-dienes with B(C6F5)3

The reaction of 3-(trimethylsilyl)cyclohexa-1,4-diene with tris(pentafluorophenyl)borane, B(C6F5)3, has been investigated by using the M06-2X DFT method with the PCM model. The Lewis acid B(C6F5)3 is most likely to abstract a hydrogen at the C6 position in 3-(trimethylsilyl)cyclohexa-1,4-diene from the face opposite to the SiMe3 group. The product complex of the abstraction easily dissociates into [SiMe3(C6H6)]+ and [HB(C6F5)3]− or a loosely bound ion pair in dichloromethane. The dissociated ions give the complex in another structure from which the reagent, Me3Si–H–B(C6F5)3, for the following hydrosilylation reaction is generated. The calculations suggest that the transformation to the complex structure that leads to the key reagent is more difficult in toluene and in benzene and is very difficult in n-pentane. The mechanism of hydrosilylation of alkenes is discussed, estimating the Lewis acidity of the silicon center in Me3Si–H–B(C6F5)3, Me3SiH, and SiMe3+.

Conjugation in and optical properties of 1-R-1,2-diphospholes and 1-R-phospholes.

The strength of conjugation between the diene moieties of 1-R-1,2-diphospholes and 1-R-phospholes and exocyclic phenyl groups of these P-heteroles has been quantitatively characterized by the use of Raman activities of the bands of the phenyl substituents. It is shown that conjugation in both types of phospholes is very similar to the conjugation of phenyl groups with the diene system of cyclopentadiene. Introduction of substituents (-OMe, -C(═O)H, -NO2, -NMe2, and -CH═CH2) in the para-position of the phenyl groups of 1-R-1,2-diphospholes extends π-delocalization of exocyclic groups into the electronic system of the 1,2-diphosphole ring, producing bathochromic shifts of the absorption bands up to 63 nm. In contrast, hypsochromic shifts up to 40 nm can be achieved by introduction of SnMe3 or SiMe3 groups at the phosphorus(III) atom of the 1,2-diphosphole and concomitant increase of aromaticity of the P-heterole. Conjugation shifts the "centre of gravity" of the whole electronic absorption spectrum, whereas positions of separate absorption bands are not simply dependent on conjugation lengths.

Zirconocene Complexes as Catalysts for the Cycloaddition of CO2 to Propylene Oxide

AbstractSix zirconocene derivatives were systematically designed; one of the cyclopentadienyl (Cp) ligands of zirconocene dichloride [Cp2ZrCl2] was silylated and this group was then incrementally increased in size; furthermore, one derivative with a 4,4′‐disilylbiphenyl bridge between the two zirconocene fragments was prepared. One zirconium complex was characterized by single‐crystal X‐ray analysis. All zirconium complexes were effective catalysts for the cycloaddition of CO2 to propylene oxide. Two complexes containing a biphenyl group attached to a SiMe2 group showed higher activity than the other complexes. In addition, the dinuclear complex containing the biphenylenebis(dimethylsilyl) bridge showed the highest activity among all the zirconium complexes reported. Furthermore, these complexes are the first examples of zirconocene catalytic systems for the cycloaddition reaction of CO2 to propylene oxide.

Synthesis and Reactivity of Novel Mesityl Boratabenzene Ligands and Their Coordination to Transition Metals

The synthesis and characterization of novel bulky mesitylboratabenzene ligands have been achieved. The isolated boracyclohexadienes 6a,b were found to be extremely stable and could be selectively desilylated by hydrolysis. These ligands have been successfully coordinated to Fe(II) and Cr(II). The selective desilylation of the boratabenzene ring was also observed in the iron complexes, thus furnishing three ironboratabenzene sandwich complexes without a SiMe3 group (11) and with one (10) and two (12) SiMe3 groups. Interestingly, species 11 represents the first structurally characterized bis(boratabenzene) metallic species not exhibiting the expected trans geometry.

Inverting the Diastereoselectivity of the Mukaiyama–Michael Addition with Graphite-Based Catalysts

Here, we show that graphite-based catalysts, mainly graphite oxide (GO) and exfoliated GO, are effective recyclable catalysts for a relevant stereoselective Mukaiyama–Michael addition, outperforming currently available catalysts. Moreover, the graphite-based catalysts described here invert the diastereoselectivity relative to that observed with known catalysts, with the unprecedented large prevalence of the anti diastereoisomer. This inverted diastereoselectivity is increased when the catalyst concentration is reduced and after catalyst recycling. Density functional theory calculations suggest that the selectivity is determined by two types of supramolecular interactions operating between the catalyst and the substrates at the diastereoselectivity-determining transition state, specifically, the π-stacking of β-nitrostyrene with graphite and the van der Waals interaction between the SiMe3 group of the silyl ether and the graphite.

Si(SiMe3)2SiPh3 - a ligand for novel sub-valent tin cluster compounds.

For the synthesis of metalloid tin cluster compounds applying the disproportionation reaction of a Sn(i) halide, silyl ligands, especially the symmetric Si(SiMe3)3 has proven to be extremely useful. Silyl ligands of lower symmetry where e.g. one SiMe3 group is substituted with SiPh3 are thereby unexplored, although the synthesis of the anionic silyl precursors is quite easy, referring to previously described methods. Here the synthesis of the silanide [Si(SiMe3)2(SiPh3)](-) as its potassium () as well as its lithium salt () in excellent yield is presented. proved to be a suitable starting material for the synthesis of subvalent tin compounds as shown by the reaction with tin halides in oxidation state +2 (SnCl2) and +1 (SnCl); i.e. on the one hand the anticipated stannide [Sn(Si(SiMe3)2SiPh3)2Cl](-) could be isolated and on the other hand the unexpectedly partly substituted ring compound Cl4Sn4[Si(SiMe3)2SiPh3]4 is obtained. As no elemental tin is formed during the reaction with SnCl, metalloid tin clusters may be present in solution too, which is supported by the nearly black color of the reaction mixture, showing that might be a suitable ligand for the synthesis of such cluster compounds.

Reactions of (SiMe2)(SiRR′) doubly-bridged biscyclopentadienes (RR′ = MePh, Ph2) with iron and molybdenum carbonyls

In the reaction of the doubly-bridged biscyclopentadiene (C5H4(SiMe2))(C5H4(SiMePh)) (1b) with Fe(CO)5, migration of the bridging SiMe2 or SiMePh group from the ligand to an iron atom gives the corresponding compound (SiMePh)(η5-C5H3)(η5:η1-C5H3)[(SiMe2)Fe(CO)2][Fe(CO)2] (4) or (SiMe2)(η5-C5H3)(η5:η1-C5H3)[(SiMePh)Fe(CO)2][Fe(CO)2] (5), containing one Fe–Si bond. The reaction also affords the product [(η5-C5H4)2(SiMePh)]Fe2(CO)2(μ-CO)2 (6), in which the SiMe2 group is totally cleaved, and the corresponding doubly-bridged Fe–Fe bonded products [(η5-C5H3(SiMe2))(η5-C5H3(SiMePh))]Fe2(CO)4 (2 and 3) as a pair of isomers. A similar reaction of 1b with Mo(CO)6 only results in the SiMe2 cleaved product [(η5-C5H4)2(SiMePh)]Mo2(CO)6 (9), as well as the normal doubly-bridged Mo–Mo bonded complexes [(η5-C5H3(SiMe2))(η5-C5H3(SiMePh))]Mo2(CO)6 (7 and 8) as a pair of isomers. Reaction of the doubly-bridged biscyclopentadiene (C5H4(SiMe2))(C5H4(SiPh2)) (1c) with Fe(CO)5 or Mo(CO)6, similarly, yields the corresponding SiMe2 removed product (11 or 13) and the doubly-bridged dinuclear complex (10 or 12). The molecular structures of complexes 2, 4, 5 and 7 were determined by X-ray diffraction.

Siloxane-bridged [n]troticenophanes: Syntheses, structures and ring-opening reactions

Salt elimination reactions between dilithiotroticene [(η7–C7H6Li)Ti(η5–C5H4Li)]∙pmdta (1) (pmdta = N,N′,N′,N″,N″-pentamethyldiethylenetriamine) and siloxane dichlorides ClMe2Si-(OSiMe2)m-Cl (m = 1–3) at low temperature allowed the synthesis and isolation of the siloxane-bridged [n]troticenophanes [(η7–C7H6)Ti(η5–C5H4)](OSiMe2)m(SiMe2) (2, m = 1; 3, m = 2; 4, m = 3) as blue crystalline solids in moderate yield. The compounds were characterized by 1H, 13C and 29Si NMR spectroscopy, elemental and single-crystal X-ray diffraction analyses. The molecular structures of 2 and 3 showed a low degree of strain indicated by the dihedral (α = 4.8° for 2; 4.9/3.7° for 3) and distortion (δ = 176.2° for 2; 174.3/176.3° for 3) angles between the two rings. The structure of 4 was severely disordered. Compounds 2–4 are thermally resistant to ring-opening polymerization, as revealed by differential scanning calorimetry studies, with 2 exhibiting the higher melting temperature. Moreover, the observation of two endotherms in the DSC spectrum of 2 suggests a solid state transition as a result of polymorphism. The reactions of 2–4 with basic initiators such as potassium siloxanolate, ammonium siloxanolate or n-BuLi and analysis of the product distribution by electron ionization mass spectrometry revealed the formation of oligotroticenylsiloxanes incorporating one or more troticenyl units, ring-opened troticenes and ring-expanded troticenophanes [(η7–C7H6)Ti(η5–C5H4)](OSiMe2)r(SiMe2) (r > m). Similar cleavage and extension of the ring were observed by treatment of 2–4 with the acidic initiator Purolite CT-175, and ring-opened troticenes having mixed terminal –OH and –SiMe3 groups were detected. Attempts to copolymerize 2–4 and cyclotrisiloxane with n-BuLi afforded essentially the monomeric and polymeric siloxanes [Me2SiO]w (w = 7, 8), Me2(nBu)Si[OSiMe2]yOSiMe2 (y = 3–6) and Me2(n-Bu)Si[OSiMe2]zOH (z = 1–7), together with the ring-opened and ring-expanded products mentioned above.

Synthesis of new organosilicon compounds by CS2: Mercapto-silyl-thiones

A new type of chemistry of carbon disulfide proceeding by way of nucleophilic attack of tris(trimethylsilyl)methyllithium (TsiLi) at carbon of carbon disulfide is reported. The treatment of TsiLi and CS2 with some symmetrical and unsymmetrical benzyl halides has yielded novel multifunctional compounds with SiMe3, SH and CS groups. The obtained compounds (mercapto-silyl-thiones) have been produced with unusual rearrangement that is apparently the first example of such migration of sulphur to carbon atom. These reactions have high selectivity and the yields are quantitative.

Synthesis, Molecular Structure, and Electrochemistry of 1‐Ferrocenyl‐1,2‐dicarba‐closo‐dodecaboranes

AbstractBis(dimethylsulfido)decaborane, 6,9‐(Me2S)2‐arachno‐B10H12, reacts smoothly with ferrocenyl alkynes FcC≡CR [1a–h; Fc = ferrocenyl, R = H (1a), CH3 (1b), Ph (1c), 4‐MeO2CC6H4 (1d), Fc (1e), C≡CFc (1f), C(O)CH3 (1g), and CO2CH2CH3 (1h)] to afford the corresponding 1‐ferrocenyl‐1,2‐dicarba‐closo‐dodecaboranes 2a–h in good yields. Ester 2h was further reduced to the respective hydroxymethyl derivative, 1‐Fc‐2‐CH2OH‐1,2‐closo‐C2B10H10 (3). The reaction of 6,9‐(Me2S)2‐B10H12 with FcC≡CSiMe3 proceeded in a different manner to produce (among other products) an SMe2 adduct of an opened decaborane substituted with a 2‐ferrocenyl‐2‐(trimethylsilyl)ethen‐1‐yl group (4). This compound probably results through hydroboration of the starting alkyne and migration of the SiMe3 group. All prepared compounds were characterized by spectroscopic methods (1H, 13C, and 11B NMR spectroscopy, IR spectroscopy, and mass spectrometry), and their molecular structures were determined by single‐crystal X‐ray diffraction analysis. In addition, the compounds were studied by cyclic and differential pulse voltammetry on a platinum disc electrode to reveal simple ferrocenyl‐centered oxidations for the singly ferrocenylated carboranes and two consecutive oxidation waves for compounds 2e and 2f, which possess two ferrocenyl substituents.

Synthesis of silyl-disubstituted poly(p-phenylenevinylene) membranes and their gas permeability

p-Bis(bromomethyl)benzene with two silyl groups [SiMe2-n-C8H17, SiMe3 (1a), SiMe2-n-C8H17, SiEt3 (1b), SiMe2-n-C8H17, SiMe2-n-C8H17 (1c), SiMe2-n-C8H17, SiMe2-n-C18H37 (1d), SiMe2-n-C18H37, SiMe2-n-C18H37 (1e)] were polymerized by Gilch method to afford silyl-disubstituted poly(p-phenylenevinylene)s (2a–e). The polymers containing SiMe3 groups (2a) showed poor solubility and dissolved in only CHCl3. On the other hand, the other polymers (2b–e) exhibited good solubility in common organic solvents. According to thermogravimetric analysis (TGA), the silyl-disubstituted poly(p-phenylenevinylene)s showed high thermal stability (thermal decomposition temperature: Td ≥ 310 °C). Polymers 2a–e had relatively high molecular weight over 7.6 × 104, and gave free-standing membranes by solution casting method. Except 2e, the oxygen permeability coefficients (PO2) of membranes of the silyl-disubstituted poly(p-phenylenevinylene)s increased as increasing alkyl length of silyl groups (2a: 5.4, 2b: 6.0, 2c: 15.0, 2d: 20.4 barrers). The membrane of 2e having two dimethyl-n-octadecylsilyl groups in the repeating unit exhibited the lowest gas permeability among the present polymers, and its PO2 was 1.8 barrers. This is because polymers 2a–d were amorphous while 2e was crystalline. The PO2 values for amorphous poly(p-phenylenevinylene)s increase in direct proportion to the number of carbon in the side chains.

Efficient Tertiary Amine/Weak Acid Bifunctional Mesoporous Silica Catalysts for Michael Addition Reactions

AbstractWe describe the development and application of efficient bifunctional acid–base mesoporous silica catalysts, denoted hereafter as Ext‐SBA‐15‐NMe2, comprising tertiary amine and silanol (weak acid) groups for the Michael addition reaction. The catalysts were synthesized by grafting tertiary amine containing organosilane into the mesoporous channel pores of SBA‐15 mesoporous silica in polar protic solvent (isopropyl alcohol) or nonpolar solvent (toluene). The resulting materials, Ext‐SBA‐15‐NMe2‐IPA or Ext‐SBA‐15‐NMe2‐Tol, respectively, were used as catalysts for the Michael addition reactions between trans‐β‐nitrostyrene(s) and active methylene compounds, such as malononitrile, acetylacetone, and diethylmalonate, at different temperatures. A variable‐temperature NMR‐array technique was used to monitor the reactant conversion and the reaction progress. Among the active methylene compounds tested with trans‐β‐nitrostyrene, malononitrile gave the highest conversion of 90 % in 0.3 h at 0 °C if catalyzed by the catalyst Ext‐SBA‐15‐NMe2‐IPA, the silanol groups of which were not passivated by trimethysilyl (SiMe3) groups. Compared with Ext‐SBA‐15‐NMe2‐Tol, the Ext‐SBA‐15‐NMe2‐IPA material (whose the amine groups were grafted in polar‐protic solvents), in particular, demonstrated an effective cooperative bifunctional catalysis because of its optimized proportions of tertiary amine groups and a significant number of surface silanol groups that were judiciously left behind on the material with this optimized synthetic strategy. The catalytic activity of this material was found to be significantly higher than that of the corresponding material that was grafted in toluene and that contained less optimized proportions of these two catalytic groups (i.e., amine and silanol groups). The bifunctional catalysts also showed good recyclability upon washing with acetone, which offered an effective way of regenerating the catalyst free from any undesired product/substrate bound on the surface of the catalysts.

Co-complexation Syntheses, Structural Characterization, and DFT Studies of a Novel Series of Polymeric Alkali-Metal Tetraorganogallates

Exploring the co-complexation reactions between the gallium alkyl Ga(CH2SiMe3)3 and alkali-metal alkyl MCH2SiMe3 (M = Li, Na, or K) using an arene/hexane solvent mixture has allowed the isolation of solvent-free alkali-metal tetraorganogallates [{MGa(CH2SiMe3)4}∞] (M = Li, 1; Na, 2) and related benzene adduct [{(C6H6)2KGa(CH2SiMe3)4}∞] (3). By combining X-ray crystallography, NMR spectroscopy, and DFT calculations, this study sheds new light on the constitution of these mixed-metal species. X-ray crystallographic studies reveal that all gallates exhibit novel polymeric arrangements, with 1 and 2 sharing the same linear chain structure, made up exclusively of M–C and Ga–C bonds, whereas 3 displays a significantly more open structural motif, where the K and Ga atoms are connected by a single alkyl bridge and propagation occurs via weaker K···Me electrostatic interactions of a methyl from a SiMe3 group of an alkyl ligand from one monomer to the potassium from a neighboring monomeric unit. Multinuclear NMR sp...

Ruthenocenes and Half‐Open Ruthenocenes: Synthesis, Characterization, and Their Use as CVD Precursors for Ruthenium Thin Film Deposition

AbstractConsecutive synthesis methodologies for the preparation of a series of trimethylsilyl and tert‐butyl‐substituted ruthenocenes of the type Ru(η5‐C5H3R1R2)(η5‐C5H3R3R4) (2, R1 = SiMe3, R2 = R3 = R4 = H; 3, R1 = R3 = SiMe3, R2 = R4 = H; 4, R1 = R2 = R3 = SiMe3, R4 = H; 5, R1 = R2 = R3 = R4 = SiMe3; 6, R1 = R3 = tBu, R2 = R4 = H; 7, R1 = R3 = tBu, R2 = SiMe3, R4 = H; 8, R1 = R3 = tBu, R2 = R4 = SiMe3) and Ru(η5‐2,3‐Me2C5H5)(η5‐C5H4R) (10, R = tBu; 12, R = SiMe3) are discussed and their use as a MOCVD precursor for the deposition of ruthenium is reported. The molecular structures of 3, 5–8, 10, and 12 in the solid state are reported. The half‐open ruthenocenes 10 and 12, which are liquids at ambient temperature, exhibit significantly shorter Ru–centroid (η5‐2,3‐Me2C5H5) bond lengths in contrast to ruthenocenes 3 and 5–8. The thermal behavior of all ruthenocenes was studied by thermogravimetric analysis showing that they evaporate without decomposition at atmospheric pressure. In addition, vapor pressure measurements were carried out to obtain profound information about the volatility of the synthesized sandwich compounds. The highest vapor pressures were found for 10 and 12. It was observed that the higher the number of SiMe3 groups, the higher the deposition temperature. All compounds were applied as precursors in MOCVD. The depositions on Si/SiO2 targets were carried out in a vertical cold‐wall CVD reactor between 633 and 688 K with a flow rate of 50 mL min–1 using nitrogen as the carrier gas and oxygen as the coreactant (50 mL min–1). With the tBu‐functionalized ruthenocenes 6 and 10 ruthenium thin films were obtained, while mixed ruthenium/SiO2 layers were formed with 2, 7, 8, and 12. The appropriate layers possess thicknesses between 75–135 nm and are conformal and dense as proven by SEM, EDX spectroscopy, and XPS studies.

Asymmetric Hydroalkynylation of Norbornadienes Promoted by Chiral Iridium Catalysts

Across bonds: The first successful iridium-catalyzed asymmetric hydroalkynylation of nonpolar alkenes with good to excellent enantioselectivity is described (see scheme; cod = 1,5-cyclooctadiene, DCE = 1,2-dichloroethane). This catalytic system exhibits good functional group compatibility as NH(2), OH, Br, F, and SiMe(3) groups remain intact during the reaction.

Substituent Effects in Thermal Reactions of a Silene with Silyl-Substituted Alkynes: A Theoretical Study

Thermal reactions of a silene derivative (Me3Si)2Si═C(OSiMe3)(t-Bu) (1) with silyl-substituted acetylenes, bis(trimethylsilyl)butadiyne, tert-butyldimethylsilylacetylene, and bis(trimethylsilyl)acetylene have been investigated with density functional theory calculations for the understanding of substituent effects in the reactivity of the silene. The first critical reaction step for determining the final product is the formation of a biradical intermediate from 1 and the acetylenes. A stepwise [2 + 2] cycloaddition via the biradical intermediate gives a silacyclobutene derivative, which is the precursor of the final product. The activation energy for this reaction step as well as thermodynamic stability of the biradical intermediate is governed by an interplay between geometric and electronic factors. The biradical intermediate is destabilized by steric hindrance between bulky substituents on 1 and acetylene, while it can be stabilized by delocalization of an unpaired electron in the acetylene moiety. Silacyclobutene derivatives undergo Si–C bond cleavage to give silabutadiene derivatives. The second critical reaction step is the attack of the OSiMe3 group on the silene Si atom in the silabutadienes. If the substituent on one of the acetylene C atoms does not easily migrate, the SiMe3 group of the OSiMe3 group rebounds to the silene C atom to form an oxasilacyclopentene derivative. If this substituent migrates easily, on the other hand, it migrates to the silene C atom with a simultaneous migration of the OSiMe3 group, resulting in the formation of an allene derivative.