Latest News: Reactions of Group 4 Bis(trimethylsilyl)acetylene Metallocene Complexes and Applications of the Obtained Products

Recently published reactions of group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complexes from the last two years are reviewed. Complexes like Cp’₂Ti(η²-Me₃SiC₂SiMe₃) and Cp₂Zr(py)(η²-Me₃SiC₂SiMe₃) with Cp’ as Cp (cyclopentadienyl) and Cp* (pentamethylcyclopentadienyl) have been considered (py=pyridine). These complexes can liberate a reactive low-valent titanium or zirconium center by dissociation of the ligands and act as ‘‘masked’’ M^II complexes (M=Ti, Zr). They represent excellent sources for the clean generation of the reactive coordinatively and electronically unsaturated complex fragments [Cp’₂M]. This is the reason why they were used for many synthetic and catalytic reactions during the last years. As an update to several review articles on this topic, this contribution provides an update with recent examples of preparative organometallic and organic chemistry of these complexes, acting as reagents for a wide range of coordinating and coupling reactions. In addition, applications and investigations concerning reaction products derived from this chemistry are mentioned, too.     

Electrochemical preparation of polythiophene via 2,5-bis(trimethylsilyl)thiophene

Electrochemical polymerization of 2,5-bis(trimethylsilyl) thiophene produced highly conducting films which showed infrared spectra, visible-near infrared absorption spectra, and cyclic voltammograms identical to films prepared from thiophene. Elemental analysis indicated that almost all silicon atoms were eliminated during the electrochemical polymerization. However, scanning electron microscopy showed a morphological difference between the films from 2,5-bis(trimethylsilyl)thiophene and from thiophene. The electrochemical polymerization of bis(2-thienyl)dimethylsilane, 1,2-bis(2-thienyl)tetramethyldisilane, and bis(2-thienyl)diphenylsilane also produced polythiophene films having unique morphologies quite different from the conventional ones. These findings indicate that these electrochemical procedures must be useful for preparation of new conjugated polymers. © 1992 John Wiley & Sons, Inc.     

‘One-flask’ transformation of isocyanates and isothiocyanates to guanidines hydrochloride by using sodium bis(trimethylsilyl)amide

A ‘one-flask’ synthesis of guanidines was developed by reacting isocyanates and isothiocyanates with sodium bis(trimethylsilyl)amide followed by addition of primary or secondary amines with a catalytic amount of AlCl₃. The desired guanidines were obtained in good yields and the reaction was applicable to aliphatic and aromatic substrates. A plausible mechanism was proposed through the generation of cyanamide anion from isocyanates or isothiocyanates with sodium bis(trimethylsilyl)amide. Addition of amines and catalytic amount of AlCl₃ smoothly converted the cyanamides to the desired guanidines.     

Trimethylsilyl-group containing polyphenylacetylenes for oxygen and ethanol permselective membranes

Phenylacetylenes having one or two trimethylsilyl groups at their benzene ring were synthesized, and polymerized by [Rh(cyclooctadiene) (PPh₃)₂]PF₆, [Rh(norbornadiene)Cl]₂, or WCl₆ to afford high molecular-weight polymers in high yields. These poly(phenylacetylene)s were soluble in many kinds of solvents and were fabricated to tough membranes by the solvent casting method. The oxygen permselectivities of these membranes were very good. The oxygen permeability coefficients (P_o2) and oxygen separation factors (α = P_o2/P_N2) of poly[2,4-(o,p)-bis(trimethylsilyl)phenylacetylene] [poly ( o-1-p-1 )] and poly[(4(p)-trimethylsilyl)phenylacetylene] [poly( p-1 )] membranes were 4.73 × 10^?8 cc(STP) cm/cm² s cmHg and 2.65, and 1.52 × 10^?8 cc(STP) cm/cm² s cmHg and 3.39, respectively. In the case of poly( o-1-p-1 ), P_o2 was comparable to that of polydimethylsiloxane (PDMS) and α was higher than that of PDMS. However, the P_o2 value reduced to 48% of its initial value in about 1 year. In the case of poly( p-1 ), the P_o2 value did not change in about 1 year. Ethanol permeated preferentially through these membranes (α^EtOH > 1) in pervaporation of aqueous ethanol solution, whereas poly(phenylacetylene) [poly( PhA )] showed water permselectivity (α^EtOH < 1). These favorable effects of trimethylsilyl groups on the oxygen and ethanol permselectivities were discussed on the basis of comparison with those of poly( PhA ), other poly(substituted phenyl-acetylene)s, and trimethylsilyl-group containing polystyrenes. © 1994 John Wiley & Sons, Inc.     

Determining the vinyl alcohol distribution in poly(vinyl butyral) using normal-phase gradient polymer elution chromatography

The application of film-forming organic polymers, which are in common use in membrane technology, as chromatographic adsorbents for packed and capillary columns has been suggested. The chromatographic characteristics of poly[1-(trimethylsilyl)-1-propine] (PTMSP) as an adsorbent were studied. The film-forming properties of PTMSP simplify manufacturing of capillary and packed gas–solid columns. It was shown that separation of C₁–C₄ hydrocarbon gases on the columns with PTMSP is of practical interest. In the authors’ opinion, PTMSP is also promising for the separation of inorganic gases.     

The synthesis and structural characterization of silyl-substituted fluorenes

Three silyl-substituted fluorenes have been prepared by direct synthetic methods and structurally characterized by X-ray diffraction. The three silyl-substituted fluorenes studied were 9-trimethylsilylfluorene (1), 9-(tert-butyldimethyl)silylfluorene (2), and 2,7-di-tert-butyl-9-trimethylsilylfluorene (3). Complex 1 is orthorhombic, P2₁2₁2₁, a = 6.2681(14) Å, b = 14.329(3) Å, c = 15.231(4) Å, Z = 4. Complex 2 is monoclinic, P2₁/c, a = 12.1953(10) Å, b = 6.9977(6) Å, c = 19.6536(17) Å, = 93.818(2), Z = 4. Complex 3 is monoclinic, P2₁/c, a = 11.9954(9) Å, b = 9.8978(7) Å, c = 18.5464(13) Å, = 92.456(2), Z = 4. The long carbon–silicon bonds effectively remove any significant intramolecular interactions as little distortion is exhibited around the sp ³-carbon atom and the fluorenyl backbone demonstrates near planarity. The bulky silicon substituents also prevent intermolecular interactions, as only a few close contacts less than 4.0 Å exist in all three solid state structures.     

Electron‐deficient vanadium(IV) tetraphenylporphyrin: A new,highly efficient and reusable catalyst for chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane

In the present work, the application of electron‐deficient tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the trimethylsilylation of alcohols and phenols with hexamethydisilazane (HMDS) is reported. This new V(IV) catalyst was used as an efficient catalyst for silylation of not only primary alcohols but also sterically hindered secondary and tertiary alcohols with HMDS. Trimethylsilylation of phenols with HMDS was also performed to afford the desired Trimethylsilyl ethers (TMS) ethers. The chemoselectivity of this method was also investigated. This catalyst can be reused several times without loss of its activity. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and structure of isopropyldimethylsilyl-substituted octamethyltitanocene

Reduction of isopropyldimethylsilyl-substituted titanocene dichloride [TiCl₂(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (1) by excess magnesium in the presence of excess bis(trimethylsilyl)ethyne (btmse) in tetrahydrofuran at 60 °C yielded a mixture of products amongst them only the trinuclear Ti-Mg-Ti hydrido-bridged complex Mg[Ti(μ-H)₂(η⁵-C₅Me₄SiMe₂Prⁱ)]₂ (3) was isolated and characterized. The precursor of titanocene, [Ti(η⁵-C₅Me₄SiMe₂Prⁱ)₂(η²-btmse)] (6), was obtained from the identical system which, after initial formation of [TiCl(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (2), reacted at −18 °C overnight and then the solution was rapidly separated from the remaining magnesium. Titanocene [Ti(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (7) was obtained by thermolysis of 6 at 75 °C in vacuum. Crystal structures of 1, 2, 3, 6, and 7 were determined.     

Formation of a PIII−C(sp2) bond by addition of diphenyl(trimethylsilyl)phosphine to activated acetylenes

Diphenyl(trimethylsilyl)phosphine reacts with alkoxy(alkyl)acetylenes to give mixtures of addition products, (2-alkoxy-2-trimethylsilylalkenyl)diphenylphosphines and (2-alkoxyalkenyl)diphenylphosphines. The reaction is sensitive to the solvent; in MeCN, it gives only nonsilylated products. (1-Alkoxyethenyl)diphenylphosphines were obtained as the main products upon the reaction of Ph₂PSiMe₃ with terminal alkoxyalkynes, irrespective of the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1792–1796, September, 1998.