Silyl Hydride Research Articles

Neutral and Anionic Silyl Hydride Derivatives of the Tantalum Imido Fragment Cp*(DippN)Ta (Cp* = η5-C5Me5; Dipp = 2,6-iPr2C6H3). Reactive σ-Bonds and Intramolecular C−H Bond Activations Involving the Silyl Ligands

The syntheses and reactivities of alkyl, silyl, and hydride complexes of the type Cp*(DippN)TaRR‘ (Cp* = η5-C5Me5; Dipp = 2,6-iPr2C6H3; R = silyl, alkyl; R‘ = alkyl, hydride) are described. The compounds Cp*(DippN)Ta(SiR3)Cl (SiR3 = Si(SiMe3)3 (1), SiPh3 (2), SiHMes2 (3); Mes = 2,4,6-Me3C6H2), prepared from Cp*(DippN)TaCl2 and (THF)nLiSiR3, react with H2 to yield the dimeric hydride [Cp*(DippN)TaCl(μ-H)]2 (4). The reaction of 4 with (THF)3LiSi(SiMe3)3 (2 equiv) gave the 16-electron silyl hydride complex Cp*(DippN)Ta[Si(SiMe3)3]H (6), which is Lewis acidic and reversibly binds halide ions to afford anionic Ta(V) complexes of the type A+{Cp*(DippN)Ta(X)[Si(SiMe3)3]H}- (A = Li(THF)3, X = Cl (5); A = NBu4, X = Br (7) and I (8)). For complexes 5, 7, and 8, NMR and X-ray data suggest the presence of weak three-center interactions involving Ta, Si, and H. Silyl hydride 6 reacts with xylyl isocyanide (xylyl = 2,6-dimethylphenyl) and acetonitrile to give the corresponding η2-silaimine and azomethine insertion products, respectively, while treatment with acetone yields the stable isopropoxide product arising from insertion into the Ta−H bond. When complex 6 is treated with ethylene or diphenylacetylene, elimination of HSi(SiMe3)3 occurs, along with formation of a five-membered tantalacycle resulting from coupling of the unsaturated substrate at Ta. Hydrogenolysis of 6 yields HSi(SiMe3)3 and a dimeric dihydride [Cp*(DippN)TaH(μ-H)]2 (14). At room temperature, 6 rearranges (t1/2 = 8.5 h) to an unusual alkyl hydride species resulting from C−H bond activation, Cp*(DippN)Ta[CH2Si(SiMe3)2SiMe2H]H (15). This complex exhibits a γ-agostic Si−H interaction with the metal center. An attempt to prepare Cp*(DippN)Ta(SiHMes2)H produced the alkyl hydride product Cp*(DippN)Ta[η2-CH2(2-SiH2Mes-3,5-Me2C6H2)]H (20), which apparently results from decomposition of the expected silyl hydride. The alkyl hydride complex [Cp*(DippN)TaMe(μ-H)]2 (25) was prepared by the hydrogenolysis of Cp*(DippN)Ta[Si(SiMe3)3]Me (23), whereas Cp*(DippN)Ta(CH2CMe3)H (26) was obtained by treatment of 4 with NpMgCl. Complex 26 possesses an α-agostic C−H interaction, and the corresponding deuteride 26-d slowly scrambles deuterium into the methylene positions.

Site Selective Copper and Silver Electroless Metallization Facilitated by a Photolithographically Patterned Hydrogen Silsesquioxane Mediated Seed Layer

Patterned hydrogen silsesquioxane films have been used as templates for directed metallization of nonconductive discontinuous surfaces. Exposure of the surface to palladium(II) or silver(I) salt solutions results in silyl hydride site selective palladium or silver metal deposition on the HSQ exposed regions. This site-specific metal seed layer has been successfully used as a catalyst for the deposition of copper and silver films by electroless metallization processes.

Cross-coupling reactions of organosilicon compounds: new concepts and recent advances.

This review highlights the rapid evolution of the newly-developed class of palladium-catalyzed cross-coupling reactions of organosilicon compounds. A myriad of heteroatom-containing silicon moieties (silyl hydrides, siletanes, silanols, silyl ethers, orthosiliconates, di- and polysiloxanes and pyridylsilanes) undergo mild and stereospecific cross-coupling. The diversity of methods for introduction of silicon groups into organic molecules and the range of organic electrophiles that can be used are emphasized.

New types of non-classical interligand interactions involving silicon based ligands

This review summarises recent findings and ideas about new non-classical interligand interactions in which at least one of the ligands has a silicon atom as an interacting centre. For many years the field of non-classical interactions was dominated by agostic and σ-complexes, bonding in which is often described in terms of electron-deficient 3c–2e interactions. In the case of silyl hydride compounds these early works resulted in the observation of η 2-HSiR 3 co-ordination mode. However, several recently reported systems can be rationalised as having more extended SiH bonding, and ligands such as (η 3-H 2SiR 3) and even (η 4-H 3SiR 3) can be identified. Co-ordination of these complex ligands to the metal is still electron deficient. Another series of new discovered interligand interactions include donations from basic MH (or MSi) bond orbital onto suitable antibonding orbital of a neighbouring ligand ((SiX)*, (CO)*, etc). Different types of these hypervalent interactions are discussed and their relevance to migratory insertion reactions is traced.

C−H and Si−H Activation on Palladium(II) and Platinum(II) Complexes with a New Methoxyalkyl-Substituted Diimine Ligand

Electrophilic 1,4-bis(methoxypropyl)-2,3-dimethyl-1,4-diazabutadiene Pd(II) and Pt(II) cations 2a,b with a BArF counteranion have been prepared. Complex 2a undergoes intramolecular C−H activation to form tricyclic 5, and complex 2b adds to Et3SiH to form an octahedral diimine Pt(IV) silyl hydride complex, 7.

Mild and general cross-coupling of (alpha-Alkoxyvinyl)silanols and -silyl hydrides

(alpha-Alkoxyvinyl)silanols and (alpha-alkoxyvinyl)silyl hydrides are efficiently converted to aryl vinyl ethers by a palladium(0)-catalyzed cross-coupling reaction with aryl halides in the presence of tetrabutylammonium fluoride or hydroxide. Yields are generally high, and the reaction is compatible with a wide range of functional groups.

Copper Hydride- Catalyzed Tandem 1,4-Reduction/Alkylation Reactions

Exposure of an enone to a catalytic quantity of [CuH(PPh 3)] 6 in the presence of one of several silyl hydrides (PhMe 2SiH, PMHS, HMe 2SiOSiMe 2H) leads to conjugate reduction with concomitant formation of the corresponding silyl enol ether. Without isolation, treatment of these intermediates with a Lewis acid at low temperatures in the presence of an aldehyde, or with fluoride ion together with an activated halide, affords good yields of the product of 3-component coupling (3-CC) in a single reaction flask.

Femtosecond infrared studies of ligand rearrangement reactions: silyl hydride products from Group 6 carbonyls

The ultrafast dynamics of the SiH bond activation reaction by the Group 6 d 6 organometallic compounds M(CO) 5 (M=Cr, Mo, and W) have been studied in neat tri-substituted silanes under ambient conditions. The ultrafast spectral evolutions of the CO stretching bands were monitored following UV photolysis using femtosecond pump–probe spectroscopic methods. It was found that the coordinatively unsaturated species, which is formed following CO photolysis from the parent molecule, is quickly solvated (<2 ps) via the CH bonds of the solvent. These species then rearranged to the silyl hydride product on a timescale of a few nanoseconds. These results were augmented by rearrangement studies in neat ethanol, propanol and hexanol solutions in which the initially formed metal CH complex rearranged to the metal hydroxyl complex. The mechanism of this rearrangement was discussed by comparison of the data with various models in the literature. It was found that a mechanism that is primarily dissociative in nature provided the best description of the experimental data.

Photopatternable thin films from silyl hydride containing silicone resins and photobase generators

The photopatternability of various silyl hydride containing organosilicone resins containing the photobase generators N-methylnifedipine or O-(2-nitrobenzyl)-N-octyl carbamate have been examined, with the goal of identifying potential photopatternable compositions with high thermal stability after cure. Two different categories of silicone resins have been prepared from combinations of diphenylsiloxane and methyl and hydrogen silsesquioxane units and a combination of phenyl and hydrogen silsesquioxane monomer units. The photobase generators were incorporated into these resins at concentrations up to 10 weight percent. UV-irradiation of micrometer thick silicone resin-photobase films through a photomask, under an air atmosphere, yielded micrometer scale features after development. Photopatternable compositions have been identified with photosensitivities of less than 50 mJ/cm2. The photopatterning process is believed to proceed by base-catalyzed reaction of resin-based silanol groups with neighboring silyl hydride groups to yield thermally stable siloxane crosslinks. Copyright © 1999 John Wiley & Sons, Ltd.

Synthesis of an organosilicon hyperbranched oligomer containing alkenyl and silyl hydride groups

A new organosilicon hyperbranched oligomer has been prepared that contains both double bonds and silyl hydride groups. The monomer is prepared via the hydrosilylation of propargyl chloride with methyldichlorosilane in the presence of a platinum catalyst. The product is a mixture resulting from both α- and β-addition. Treatment of the monomer mixture with magnesium results in the formation of a hyperbranched oligomer, which is then treated with LiAlH4. Control of monomer addition speed to the magnesium is critical in order to keep head-head coupling low. The resulting oligomer is air- and water-stable, and has an average degree of polymerization of 8. This material gives a char yield of 24% but after crosslinking with platinum catalyst, the char yield increases to 69%. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3778–3784, 1999

Synthesis of an organosilicon hyperbranched oligomer containing alkenyl and silyl hydride groups

Synthesis of an organosilicon hyperbranched oligomer containing alkenyl and silyl hydride groups

Niobocene Silyl Hydride Complexes with Nonclassical Interligand Hypervalent Interactions

Niobocene mono- and bis(silyl) hydrides with dimethylhalosilyl groups exhibit a nonclassical interligand hypervalent interaction (IHI) between the hydride and silyl ligands. These interactions result in well-defined structural and reactivity trends and were found in two forms: three-centre, four-electron (A) and five-centre, six-electron (B), as shown schematically.

Demonstration of a Directly Photopatternable Spin-On-Glass Based on Hydrogen Silsesquioxane and Photobase Generators.

A commercially available spin-on-glass material, hydrogen silsesquioxane, has been rendered photopatternable to micrometer dimensions by the introduction of a photobase generator at concentrations of <5 wt %. The cure process proceeds via hydrolysis of the silyl hydride linkage by residual water in the film, as activated by a photogenerated base catalyst. Subsequent reaction of the generated silanol with neighboring silyl hydride groups yields a thermally stable siloxane cross-link. The photochemical cross-linking of hydrogen silsesquioxane shows high sensitivity (<40 mJ/cm2) and is not inhibited by molecular oxygen. The resultant oxide films can be further cured at elevated temperature either under an inert atmosphere to minimize the dielectric constant or heated in an air atmosphere to complete the conversion to silica glass. The oxidative nature of both the photo and thermal cure processes and the release of only traces of hydrogen as byproduct results in minimal weight loss in the film during processing.

A general synthesis of vinylic silyl hydrides using nickel catalysis. Applications to the syntheses of silylene-tethered conjugated polymers

Treatment of benzylic or allylic dithioacetals with Me 2( iPrO)SiCH 2MgCl in the presence of NiCl 2(PPh 3) 2 catalyst yielded the corresponding i-propoxy(vinyl)silanes which are reduced with LiAlH 4 to afford vinylic silyl hydrides. These hydrides serve as the precursors for the syntheses of silylene-tethered σ,π-conjugated copolymers.

Silyl-Komplexe des Molybdäns und Wolframs. Synthese, Reaktivität und Struktur

The photochemical reaction of Cp 2MH 2 (M=Mo, 1; W, 2) with several hydridosilanes HSiR 3 produces the corresponding silyl hydride complexes Cp 2M(H)(SiR 3) (M=Mo: SiR 3SiEt 3, 3; SiCl 3, 4; Si(OEt) 3, 5; SiH 2(C 5Me 5), 6; SiH 2(C 5Me 4H) 2, 7; SiH(C 5Me 4H) 2, 8; SiH 2[2-(Me 2NCH 2)C 6H 4], 9; M=W: SiR 3SiCl 3, 10) by a reductive elimination/oxidative addition process. Analogous photolysis of 1 in the presence of (C 5Me 5) 2SiHCl or (C 5Me 5) 2SiH 2 does not yield the corresponding complexes Cp 2Mo(H)(SiR 3) (SiR 3SiCl(C 5Me 5) 2; SiH(C 5Me 5) 2). Treatment of 4 and 6, respectively, with LiAlH 4 leads to the hydridosilyl complex Cp 2Mo(H)(SiH 3) 11. Compounds 6–8 and 11 are expected to be single-source precursors for generation of molybdenum silicides. The hydride complexes 4, 5, and 6 are readily converted to the chloro compounds Cp 2Mo(Cl)(SiR 3) (SiR 3SiCl 3, 12; Si(OEt) 3, 13; SiH 2(C 5Me 5), 14). The reaction of 11 with CCl 4 yields complex 12 under exchange of each non-C-bound hydrogen atom. Spectroscopic data of the metallosilanes are discussed and compared with the ones of the parent silanes. An intramolecular N-donor coordination of the functionalized aryl substituent is indicated for 9 by means of 29Si NMR spectroscopy. 6 undergoes fast sigmatropic rearrangements within the Si–(C 5Me 5) fragment as proved by a variable temperature 1H NMR investigation. The structures of 6, 7, 8, and 12 have been determined by single-crystal X-ray diffractometry. Bonding parameters of these typical bent–sandwich complexes are discussed taking account of electronic and steric influences.

Rh(I) and Rh(III) silyl PMe 3 complexes. Syntheses, reactions and 103Rh NMR spectroscopy

Synthetic approaches to Rh(I) silyls are described. The complexes L n RhSiR 3 (L=PMe 3; 6, n=4, R 3=(OEt) 3; 7, n=4, R 3=Me(OMe) 2; 21, n=3, R 3=Ph 3) resulted from the reactions of MeRhL 4 ( 1) with the corresponding silanes HSiR 3. Complex 21 was prepared alternatively from PhRhL 3 ( 2) and HSiPh 3, while analogous reactions of HSi(OEt) 3, HSiMe(OMe) 2 and HSi(OMe) 3 led to the bis(silyl)hydrides fac-L 3Rh(SiR 3) 2(H) ( 8, R 3=(OEt) 3; 9, R 3=Me(OMe) 2; 13, R 3=(OMe) 3). Like in analogous iridium-based systems, the outcome of these reactions largely depends on the nature of substituents at the silicon atom. Synthesis of Rh(I) silyls inaccessible by this route, namely those with alkyl substituents at the silicon, L n RhSiR 3 ( 19, n=3, R 3=PhMe 2; 22, n=4, R 3=Me 3), was achieved utilizing nucleophilic attack of the corresponding silyllithiums at [L 4Rh]Cl. The solid-state structure of 19 was determined by X-ray crystallography. C 17H 38P 3SiRh, Fw=466.38 monoclinic, C2/m, a=13.304(3) Å, b=13.814(2) Å, c=13.123(4) Å, β=110.66(3) deg, V=2257(1) Å 3, Z=4, d calcd=1.373 g cm −3, μ=1.019 mm −1. A series of di(hydrido)silyls fac-L 3Rh(H) 2(SiR 3) ( 10, R 3=(OEt) 3; 15, R 3=PhMe 2; 16, R 3=Ph 3) was synthesized using oxidative additions of HSiR 3 to HRhL 4 ( 3). Complexes 10, 15, 16 are thermodynamically stable with respect to H–H and Si–H reductive-elimination reactions at ambient conditions. Complex 8 reductively eliminates HSi(OEt) 3 reversibly at room temperature and complex 13 is capable upon heating of mediating dehydrogenative Si–Si coupling of HSi(OMe) 3 and redistribution of [(MeO) 3Si] 2. 103Rh NMR data obtained for MeRhL 4 ( 1), HRhL 4 ( 3), L 3RhSiPhMe 2 ( 19), L 3RhSiPh 3 ( 21) and for the di(hydrido) silyls ( 10, 15, 16) allowed to qualitatively evaluate steric and electronic effects of methyl, silyl, and hydride ligands on the 103Rh chemical shift.

Energy of adhesion of polydimethylsiloxane networks / glass and polycarbonate assemblies

The reversible energy of adhesion of polydimethylsiloxane (PDMS) networks/substrate assemblies evaluated from surface energy values obtained by wettability measurements is compared with that determined by Johnson, Kendall and Roberts' (JKR) approach. The role of the hydroxyl groups of the PDMS chains in the establishment of the interactions with the glass substrate is confirmed. Indeed, by using the hydrosilylation reaction between vinyl functional groups on PDMS chains on the one hand and silyl hydride functional groups carried by other PDMS chains on the other, polymer networks are obtained without any by-products. Moreover, no hydroxyl groups are present in the polymer network and only interactions of the van der Waals type should occur between the polymer and the glass substrate, even in the presence of ammonia vapor, which has a catalytic effect on the formation of the polymer-substrate interactions involving the hydroxyl groups, as already shown. The JKR approach indicates that the interactions are stronger with the glass substrate than with the polycarbonate substrate, although the calculated reversible energy of adhesion is of the same order of magnitude. This result is expected, considering the characteristics of the glass surface, especially its acid-base character compared with that of the polycarbonate.

Synthesis and Reactivity of d0Bis(imido) Silyl and Germyl Complexes of Molybdenum and Tungsten

The syntheses and reactivities of d0 bis(imido) molybdenum/tungsten silyl chloride complexes (2,6-iPr2C6H3N)2M[Si(SiMe3)3]Cl (1, M = Mo; 2, M = W) and the corresponding germyl complexes (2,6-iPr2C6H3N)2M[Ge(SiMe3)3]Cl (3, M = Mo; 4, M = W) are described. The complex (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]Cl (1), prepared by the reaction of (2,6-iPr2C6H3N)2MoCl2(dme) with (THF)3LiSi(SiMe3)3, has been structurally characterized. In general, these complexes are rather stable and do not react with CO, H2, or CH3CN. Complex 1 reacts with 2,6-Me2C6H3NC to provide the insertion product (2,6-iPr2C6H3N)2Mo[η2-C(N-2,6-Me2C6H3)Si(SiMe3)3](Cl) (5) and with AgOTf to give the silyl triflate complex (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]OSO2CF3 (6) in high yield. Complexes 1−6 react with neopentylmagnesium chloride to produce the silyl neopentyl complexes (2,6-iPr2C6H3N)2M[E(SiMe3)3](CH2CMe3) (7, M = Mo, E = Si; 8, M = W, E = Si; 9, M = Mo, E = Ge; 10, M = W, E = Ge). Complex 7, which was characterized by X-ray crystallography, contains an agostic interaction involving the α hydrogen of the neopentyl ligand (d(Mo−H) 2.55(4)Å). The neopentyl complexes 7−10 readily react with hydrogen (1 atm) to generate free neopentane and HSiMe3, probably via hydrogenation of the Mo−C bond to generate a highly unstable silyl hydride intermediate. The mechanism of HSiMe3 formation is unknown but may involve decomposition of the silyl hydride species via a four-membered transition state to generate a highly reactive silylene species. The corresponding tungsten analog 8 undergoes a similar reaction, but at a much slower rate. Attempts to trap the possible silylene intermediates (2,6-iPr2C6H3N)2MSi(SiMe3)2 (M = Mo, W) were unsuccessful.

Curing reactions and modeling of silicone-carbon resins

New silicone-carbon resins have been made, based on four- or five-membered cyclosiloxanes, cyclopentadiene dimer (DCPD), and cyclopentadiene trimer (TCPD). The monomers are first polymerized to a B-stage resin, and then heated at higher temperatures to cure. In this work, the curing reaction of this silicone-carbon resin (which leads to network formation) is simulated using two approaches. In the first approach (stochastic model), all the available functional groups (olefin and silyl hydride) are allowed to react with each other with equal probability. This gives the kinetically controlled, liquidlike, diffusion-free limit. Extrapolation of the model to reactions where diffusion may play a role can be made by including molecular weight dependence in the rates. This dependence on the molecular weight can be scaled to fit the experimental data. In the second approach a percolation model is used. In the extreme case, this model corresponds to the solid-state reaction between silicone-carbon resin molecules on 2-dimensional or 3-dimensional rigid lattices. Relaxation of this geometric constraint can be made by providing a larger reacting distance between the reactants. Computer programs have been written for 2- and 3-dimensional lattices. Illustrative examples are given for these approaches. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1557–1573, 1997

Synthesis and Reactivity of 16-Electron Hafnocene Silyl Hydride Complexes

The synthesis and reactivity of monomeric, 16-electron hafnocene silyl hydride complexes are described. The complex CpCp*Hf[Si(SiMe3)3]H (1; Cp* = η5-C5Me5), prepared by the reaction of CpCp*Hf(H)Cl with (THF)3LiSi(SiMe3)3, reacts rapidly with both ethylene and diphenylacetylene with elimination of HSi(SiMe3)3 to afford the corresponding hafnacyclopentane and tetraphenylhafnacyclopentadiene complexes. Complex 1 reacts with acetone to give the insertion product CpCp*Hf(OCHMe2)[Si(SiMe3)3] (4). Reaction of 1 with the secondary silane H2Si(SiMe3)2 proceeds smoothly to the new silyl hydride complex CpCp*Hf[SiH(SiMe3)2]H (5), which was characterized by X-ray crystallography. Deuterium labeling experiments indicate that the latter reaction occurs with significant scrambling of label between the SiH and HfH positions. The tertiary silane Ph3SiH does not react under comparable conditions. The silane H2Si(SiMe3)2 undergoes a similar σ-bond metathesis reaction with CpCp*Hf[Si(SiMe3)3]Cl, to give CpCp*Hf[SiH(SiMe3)2...