Vinyltrimethylsilane Research Articles

A Multifunctional Additive Capable of Electrolyte Stabilization and Structure/Interphases Regulation of High‐Energy Li‐Ion Batteries

AbstractNi‐rich cathodes are regarded as the most suitable candidates for high‐energy‐density Li‐ion batteries (LIBs). However, the structural degradation of Ni‐rich cathodes and high reactivity of electrolytes at the high‐potential cathodes greatly affect the cycling stability. One of the prime reasons is that HF produced by the thermal decomposition and hydrolysis of the electrolyte salt LiPF6 can cause corrosion at the electrode/electrolyte interface, promote the transition‐metal dissolution from cathode, and aggravate the decomposition of the electrolyte. This work develops a multifunctional and promising silane‐based electrolyte additive, vinyltrimethylsilane (VTMS), which is generally applicable to Ni‐rich cathode‐based LIBs. Theoretical calculations and practical experiments reveal that VTMS is capable of eliminating HF, stabilizing PF5, and suppressing the hydrolysis of LiPF6. Besides, the additive VTMS undergoes redox reactions prior to other electrolyte components, mitigates the electrolyte decomposition, and constructs superior interphases at both cathode and anode. The electrochemical performance of LIBs is significantly improved at both room temperature (25 °C) and low temperature (0 °C), demonstrating that VTMS has broad application prospects in LIBs. The development of such a multifunctional additive is of great importance for simplifying the electrolyte composition.

Synthesis and Characterization of Phosphorus-Containing Sorbent for Basic Dye Removal.

A new phosphorus-containing sorbent was prepared by copolymerizing ethylene glycol dimethacrylate (EGDMA) and trimethylvinyl silane (TMVS) with diphenylvinylphoshine oxide (DPVO). It was characterized and applied in the removal of cationic dyes such as C.I. Basic Yellow 2 (BY2), C.I. Basic Blue 3 (BB3) and C.I. Basic Red 46 (BR46) using the batch method. Spectroscopic analysis indicated that the phosphinoyl group was introduced into the sorbent structure. Equilibrium adsorption data were fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The Freundlich model is the most suitable to describe the adsorption of BB3 (the Freundlich constant kF = 32.3 mg1-1/nL1/n/g) and BY2 on the sorbent (13.8 mg1-1/nL1/n/g), while the Langmuir model is the most adequate to describe the adsorption of BR46 (the monolayer capacity Q0 = 2.7 mg/g). The kinetics of the dye adsorption follows the assumptions of the pseudo-second-order (the rate constants k2 = 0.087 ÷ 0.738 g/mg min) model rather than pseudo-first-order or intraparticle diffusion. The presence of Na2SO4 and cationic surfactant in the aqueous solutions inhibited dye retention by the DPVO-EGDMA-TMVS. Adsorbent regeneration efficiency does not exceed 60% using 1 M NaCl and 1 M HCl solutions in the presence of 50% v/v methanol.

Mitigation of Physical Aging of Polymeric Membrane Materials for Gas Separation: A Review

The first commercial hollow fiber and flat sheet gas separation membranes were produced in the late 1970s from the glassy polymers polysulfone and poly(vinyltrimethyl silane), respectively, and the first industrial application was hydrogen recovery from ammonia purge gas in the ammonia synthesis loop. Membranes based on glassy polymers (polysulfone, cellulose acetate, polyimides, substituted polycarbonate, and poly(phenylene oxide)) are currently used in various industrial processes, such as hydrogen purification, nitrogen production, and natural gas treatment. However, the glassy polymers are in a non-equilibrium state; therefore, these polymers undergo a process of physical aging, which is accompanied by the spontaneous reduction of free volume and gas permeability over time. The high free volume glassy polymers, such as poly(1-trimethylgermyl-1-propyne), polymers of intrinsic microporosity PIMs, and fluoropolymers Teflon® AF and Hyflon® AD, undergo significant physical aging. Herein, we outline the latest progress in the field of increasing durability and mitigating the physical aging of glassy polymer membrane materials and thin-film composite membranes for gas separation. Special attention is paid to such approaches as the addition of porous nanoparticles (via mixed matrix membranes), polymer crosslinking, and a combination of crosslinking and addition of nanoparticles.

Eco-friendly Silane-Based Coating for Mitigation of Carbon Steel Corrosion in Marine Environments.

Losses from corrosion contribute roughly 3-5% of the gross domestic product of developed nations, and among the many methods used to avoid corrosion, using silane-based coatings is seen to be of the biggest importance due to their low toxicity and superior adhesive qualities. It is essential to develop an anti-corrosion coating that is efficient, economical, and eco-friendly. The corrosion resistance and durability of various silane-based coatings such as 1,2-bis(triethoxysilyl)ethane (BTSE), bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), and vinyltrimethylsilane (VTES) for carbon steel 1018 substrates were investigated in a high-salinity environment (4.5 wt % NaCl). The corrosion resistance performance was evaluated via potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. Results revealed that the TESPT film (pH ≈ 7) has the best corrosion resistance performance on the carbon steel surface in the aggressive chloride environment, that is, 99.6%. The high corrosion resistance of the TESPT film is due to the hydrophobic nature of this silane, which leads to the formation of a stable and dense film. These results were supported by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) analyses.

Surface and Structural Characterization of PVTMS Films Treated by Elemental Fluorine in Liquid Perfluorodecalin.

Poly(vinyl trimethylsilane) (PVTMS) films were subjected to direct surface fluorination in liquid medium (perfluorodecalin). The samples were investigated using several techniques: SEM-XEDS, XPS, ATR-IR, and contact angle measurement. The methods used allowed us to estimate chemical changes occurring because of the treatment. ATR-IR showed that most of the changes occurred in the Si(CH3)3 group. Monofluorinated Si(CH3)3 groups formed in the near-surface layer (Ge crystal, 0.66 µm penetration) after 30 min of fluorination, and then di- and trifluorinated groups appeared. Oxidation of the film with oxygen was also shown with the use of ZnSe crystal (2 µm penetration). The XPS method allowed an assessment of the ratio of the main elements at the surface of the fluorinated film. Two different exponential models were proposed to fit the experimental data of SEM-XEDS. Based on the model with the intercept, the depth of fluorination was estimated to be ≤1.1 µm, which is consistent with the result from the literature for the gas-phase fluorination. Contact angle measurements showed that oxidation of the PVTMS surface prevailed for the first 45 min of fluorination (surface hydrophilization) with a subsequent fluorine content increase and hydrophobization of the surface upon 60 min of fluorination.

Synthesis of vinyl trimethyl silane and acrylic acid modified silica nanoparticles as corrosion inhibition protocols in saline medium

Metal corrosion is one of the detrimental processes in many areas which can lead to induce tremendous economic losses and reduce industrial production. Therefore, metal protection is becoming a technical, economical, and environmentally important approach for delaying the corrosion process. Nanomaterials functionalization is gaining high interest due to its outstanding engineering performance of material for anti-corrosion. In an aggressive medium such as seawater and 3.5 wt% NaCl (stimulated seawater) environments, stainless steels are widely utilized where the polymeric inhibitor could easily be incorporated on the metal surface. In this report, the biodegradable polymeric inhibitor has been newly grafted on mesoporous silica nanoparticles (MSN). The silane agent was grafted with polyacrylic acid vinyltrimethoxysilane (Si-PAA-VTMS) by reacting MSN with polyacrylic acid (PAA) and vinyltrimethoxysilane (VTMS). Furthermore, FTIR, SEM/EDX, AFM, and WCA measurements were applied for material surface characterization, adsorbed polymeric film, and corrosion properties of the prepared inhibitor. FTIR spectra displayed the presence of the carboxylic groups on the prepared Si-PAA-VTMS inhibitor indicating the successful synthesis. From SEM/EDX and AFM results, low porosity and dense double-layer coating of the polymer inhibitor were found on the surface morphologies which could effectively delay the rust formation. Hydrophobicity behavior was also examined after inhibitor adsorption onto the steel surface producing a higher water contact angle that repels the aggressive water content. Additionally, by utilizing optimum inhibitor concentration at 100 ppm, low corrosion rate (∼4.0–9.0 × 10−3 mm/year) and high inhibition efficiency (>80 %) were achieved at higher temperatures up to 60 °C.

Percolation Effects in Mixed Matrix Membranes with Embedded Carbon Nanotubes.

Polymeric membranes with embedded nanoparticles, e.g., nanotubes, show a significant increase in permeability of the target component while maintaining selectivity. However, the question of the reasons for this behavior of the composite membrane has not been unequivocally answered to date. In the present work, based on experimental data on the permeability of polymer membranes based on Poly(vinyl trimethylsilane) (PVTMS) with embedded CNTs, an approach to explain the abnormal behavior of such composite membranes is proposed. The presented model considered the mass transfer of gases and liquids through polymeric membranes with embedded CNTs as a parallel transport of gases through the polymeric matrix and a "percolation" cluster-bound regions around the embedded CNTs. The proposed algorithm for modeling parameters of a percolation cluster of embedded tubular particles takes into account an agglomeration and makes it possible to describe the threshold increase and subsequent decrease permeability with increasing concentration of embedded particles. The numerical simulation of such structures showed: an increase in the particle length leads to a decrease in the percolation concentration in a matrix of finite size, the power of the percolation cluster decreases significantly, but the combination of these effects leads to a decrease in the influence of the introduced particles on the properties of the matrix in the vicinity of the percolation threshold; an increase in the concentration of embedded particles leads to an increase in the probability of the formation of agglomerates and the characteristic size of the elements that make up the percolation cluster, the influence of individual particles decreases and the characteristics of the percolation transition determine the ratio of the sizes of agglomerates and matrix; and an increase in the lateral linear dimensions of the matrix leads to a nonlinear decrease in the proportion of the matrix, which is affected by the introduced particles, and the transport characteristics of such MMMs deteriorate.

Preparation and anti-icing performance of cross-linked polysiloxane coatings containing silicone oil

In this work, a cross-linked polysiloxane coating containing silicone oil was prepared via a simple two-component mixing method and the anti-icing performance of the coating was investigated by detecting the ice adhesion force (τice) on the coating. The results of infrared spectroscopy and solvent swelling show that the polysiloxane coating with a certain cross-link density can be prepared by the reaction of methylhydrosiloxane and dimethylsiloxane copolymer and divinyl-terminated polysiloxane, and the cross-link density of the coating can be adjusted by the proportion of polymethylhydrosiloxane (PMHS) and vinyltrimethylsilane (VTMS). The results of ice adhesion force test show that the ice adhesion force on the coating is related to the cross-link density of the coating. With the increase of the cross-link density from 234 ± 43 mol/m3 to 1358 ± 31 mol/m3, the ice adhesion force decreases from 51.15 ± 4.7 kPa to 27.8 ± 3.9 kPa. The lower ice adhesion force corresponds to a higher anti-icing performance. With the addition of silicone oil, the ice adhesion force on the coating can be further reduced to 9.2 ± 1.2 kPa, indicating a further enhancement in the anti-icing performance. The results of icing/deicing cycle test show that, after icing/deicing for 30 cycles, the coating still exhibits efficient anti-icing performance.

Effective Approach to Render Stable Dynamic Omniphobicity and Icephobicity to Ultrasmooth Metal Surfaces.

Surface modifications for easy removal of liquids and solids from various metal surfaces are much less established than for silicon (Si) or glass substrates. Trimethylsiloxy-terminated polymethylhydrosiloxane (PMHS) is very promising because it can be directly immobilized covalently to a wide variety of metal surfaces by simply heating neat PMHS liquid, resulting in a film showing excellent dynamic omniphobicity. However, such PMHS films are easily degraded by hydrolytic attack in an aqueous environment. In this study, we have successfully improved the hydrolytic stability of the PMHS-covered ultrasmooth metal (Ti, Al, Cr, Ni, and Cu) surfaces by end-capping of the residual Si-H groups of the PMHS films with vinyl-terminated organosilanes, for example, trimethylvinylsilane (TMVS), through a platinum-catalyzed hydrosilylation reaction. The resulting TMVS-capped PMHS film surfaces showed significantly greater stability even after submersion in water for 6 days, with their excellent dynamic dewetting behavior toward water, toluene, n-hexadecane, and ethanol changing little. In addition, they also showed reasonable anti-icing (icephobic) properties with low ice-adhesion strength of less than 50 kPa even after 20 cycles of testing at -15 °C.

Bioinspired Electro-Responsive Multispectral Controllable Dye-Doped Liquid Crystal Yolk-Shell Microcapsules for Advanced Textiles.

Liquid crystal microcapsules have attracted increasing attention due to their sophisticated structures and adjustable multifunctional features. However, the synthesis of a microscale substrate with wide electromagnetic waveband modulation characteristics and good photoelectric stabilization is still limited and challenging. Herein, a new breed of microcapsules containing dye-doped liquid crystals in a yolk-shell configuration with VTES (vinyl-trim-ethyl-silane)-modified Fe3O4@SiO2 is created. It exhibits an unexpected color enhancement effect, reversible electrochromic performance, and excellent magnetically controllable characteristics. Additionally, a multispectral (visible light, near-infrared light, and high-frequency electromagnetic wave) electro-responsive fabric based on the proposed microcapsules was developed to explore its application in wearable sensors. The present work opens an avenue toward the fabrication of microscale microencapsulated soft materials with a continuous and stable yolk-shell structure. Moreover, it will expand the application regimes of liquid crystal materials in smart windows and advanced textiles.

Preparation and Evaluation of some polyaniline/ cycloadductcomposites for their biocidalactivity against some biofouling-causing organisms

Cycloadducts of 3-Hydroxy-1-phenacyl pyridinium bromide (1) and 3-Hydroxy-1-(4-nitrobenzyl) pyridinium chloride (2) with vinyl trimethylsilane, methyl sulfonyl chloride and vinyl triphenylphosphonium bromide were prepared. Six novel polyaniline/ cycloadduct (PANI/CY) composites were prepared by the polymerization of aniline in the presence of different weight percentages of cycloadduct were characterized using Fourier transform infrared (FTIR) spectroscopy, Mass spectrum (MS) and Nuclear magnetic resonance (NMR),Transmission electron microscopy (TEM). Their potential as antibiofouling agents was evaluated. Antimicrobial /macrobial fouling activity were conventional using inhibition zone, serial tube dilution methods and mortality tests respectively.

Characteristics of SiOx-containing hard film prepared by low temperature plasma enhanced chemical vapor deposition using hexamethyldisilazane or vinyltrimethylsilane and post oxygen plasma treatment

This study, monomers of hexamethyldisilazane (HMDSZ) and vinyltrimethylsilane (VTMS) were respectively used to deposit on the surface of polyethylene terephthalate (PET) substrate by plasma enhanced chemical vapor deposition. Oxygen plasma treatment follows the HMDSZ and VTMS deposition to produce a hydrophilic surface film on the deposited surface. Time for HMDSZ and VTMS plasma deposition was changed to investigate its influences on water contact angle, deposited film thickness, refractive index, and friction coefficient properties. The surface morphologies of the processed samples were observed by scanning electron microscope and their chemical compositions were measured by X-ray photoelectron spectroscopy. At 550 nm wavelength, the optical transmittance of PET after the HMDSZ treatment decreases from 89% to 83%, but increases from 89% to 95% for the VTMS treatment. With increase in HMDSZ and VTMS deposition times, the film thickness increases and the refractive index decreases. Result revealed by XPS, SiO2 film is formed on the sample surface after the O2 plasma treatment. The film adhesion capability by the HMDSZ+O2 and VTMS+O2 treatment was stronger than that by the HMDSZ and VTMS treatment only. The SiOx films produced by HMDSZ+O2 and VTMS+O2 treatment can increase the film hardness and improve light transmittance.

Formation of Copper Nanoparticles on ZnO Powder by a Surface-Limited Reaction

Formation of copper nanoparticles on zinc oxide (ZnO) powder is studied using a common chemical vapor deposition precursor, copper hexafluoroacetylacetonate vinyl trimethyl silane, Cu(hfac)(VTMS). This process is investigated by high-vacuum Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The growth was found to be promoted by exposing ZnO powder to the gas-phase water, and the intensity of the hydroxyl groups stretching signatures decreases after the powder is exposed to the copper deposition precursor. Vibrational spectroscopy results support the reaction on both polar and (1010) surfaces of the powder, and XPS confirms that the copper deposition takes place and identifies Cu(I) species as the main copper species on the surface of ZnO powder. The mechanism of the reaction includes the elimination of hfac ligand that reacts with surface hydrogen present in hydroxyl groups, and this surface-limited process stops when the surf...

Cp2TiCH2CHMe(SiMe3)]+, an Alkyl–Titanium Complex Which (a) Exists in Equilibrium between a β-Agostic and a Lower Energy γ-Agostic Isomer and (b) Undergoes Hydrogen Atom Exchange between α-, β-, and γ-Sites via a Combination of Conventional β-Hydrogen Elimination–Reinsertion and a Nonconventional CH Bond Activation Process Which Involves Proton Tunnelling

The compound [Cp2Ti(Me)(CD2Cl2)][B(C6F5)4] reacts with trimethylvinylsilane (TMVS) to form the 1,2-insertion product [Cp2TiCH2CHMe(SiMe3)](+) (III), which exists in solution as equilibrating β- and γ-agostic isomers. In addition, while free rotation of the β-methyl group results in a single, averaged γ-H atom resonance at higher temperatures, decoalescence occurs below ~200 K, and the resonance of the γ-agostic hydrogen atom at δ ~ -7.4 is observed. Reaction of [Cp2Ti(CD3)(CD2Cl2)](+) with TMVS results in the formation of [Cp2TiCH2CH(CD3)(SiMe3)](+), which converts, via reversible β-elimination, to an equilibrium mixture of specifically [Cp2TiCH2CH(CD3)(SiMe3)](+) and [Cp2TiCD2CD(CH3)(SiMe3)](+). Complementing this conventional process, exchange spectroscopy experiments show that the β-H atom of [Cp2TiCH2CHMe(SiMe3)](+) undergoes exchange with the three hydrogen atoms of the β-methyl group (β-H/γ-H exchange) but not with the two α-H atoms. This exchange process is completely shut down when [Cp2TiCH2CH(CD3)(SiMe3)](+) is used, suggesting an H/D kinetic isotope effect much larger (apparently >16,000) than the maximum possible for an over-the-barrier process. It is proposed that β-H/γ-H exchange is facilitated by quantum mechanical proton tunnelling in which a hydrogen atom of the 2-methyl group of the alkene-hydride deinsertion product [Cp2TiH{CH2═CMe(SiMe3)}](+) undergoes reversible exchange with the hydride ligand via the allyl dihydrogen species [Cp2TiH2{(η(3)-CH2C(SiMe3)CH2}](+). Complementing these findings, DFT calculations were carried out to obtain energies and NMR parameters for all relevant species and thence to obtain better insight into the agostic preference(s) of complex III and the observed exchange processes. In all cases where comparisons between experimental and calculated data were possible, agreement was excellent.

Modification of polyisoprene‐block‐poly(vinyl trimethylsilane) block copolymers via hydrosilylation and hydrogenation, and their gas transport properties

ABSTRACTPolyisoprene‐block‐poly(vinyl trimethylsilane) (PI‐b‐PVTMS) block copolymers having different isoprene contents are successfully chemically modified and characterized by proton nuclear magnetic resonance spectroscopy (1H‐NMR), Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. Gas transport properties of the initial block copolymers and their derivatives modified via hydrosilylation and hydrogenation are measured. The modified block copolymers show higher permeabilities for O2 and H2 than the unmodified block copolymers while maintaining similar O2/N2 and H2/N2 selectivities. Hydrosilylation and hydrogenation of block copolymers with a low isoprene content result in a permeability increase for O2 and H2 of 15 to 40%, respectively. Similarly, for block copolymers with high isoprene contents, increases in permeabilities up to 125% are observed compared to initial PI‐b‐PVTMS. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1252–1261

Charge Air Separation for the Reduction of Marine Diesel Engine Emissions by Means of Poly(Vinyl Trimethylsilane) Membranes

Charge Air Separation for the Reduction of Marine Diesel Engine Emissions by Means of Poly(Vinyl Trimethylsilane) Membranes

Poly(vinyl trimethylsilane) and block copolymers of vinyl trimethylsilane with isoprene: Anionic polymerization, morphology and gas transport properties

Poly(vinyl trimethylsilane) (PVTMS) and block copolymers of vinyl trimethylsilane with isoprene were synthesized by anionic polymerization and characterized. The synthesized pure PVTMS has properties similar to a reference material produced about two decades ago and can be used for thin film composite membrane formation. Even at low isoprene content the block copolymers have improved film forming properties compared to the pure PVTMS. However, the presence of the isoprene units in the block copolymers leads to a decrease of the gas permeability but does not affect the selectivity of the membranes (α(O2/N2)=3.9).

Cobalt-catalyzed regio- and stereoselective intermolecular enyne coupling: an efficient route to 1,3-diene derivatives

The reaction of alkynes with vinyl arenes or vinyl trimethyl silane in the presence of a cobalt(II) complex, Zn and ZnI(2) in CH(2)Cl(2) at rt to 50 degrees C provides 1,3-dienes in good to excellent yields.

Copolymerization of Ethylene with tert-Butylethylene Using Nonbridged Half-Titanocene-Cocatalyst Systems

The copolymerization of ethylene with tert-butylethylene (TBE, 3,3-dimethyl-1-butene) using various half-titanocene [Cp′TiCl2X (X = O-2,6-iPr2C6H3, N═CtBu2)]-cocatalyst systems has been carried out. The aryloxo-containing half-titanocenes, Cp′TiCl2(O-2,6-iPr2C6H3) (Cp′ = Cp*, tBuC5H4, 1,2,4-Me3C5H2), displayed the capability to bring about TBE incorporation in the presence of MAO as a cocatalyst, while their ketimide analogues, Cp′TiCl2(N═CtBu2) (Cp′ = Cp, Cp*, tBuC5H4), could not accomplish TBE enchainment in ethylene/TBE copolymerization. Among aryloxo derivatives, those carrying tert-butyl and trimethyl substituents on the cyclopentadienyl moiety, Cp′TiCl2(O-2,6-iPr2C6H3) (Cp′ = tBuC5H4, 1,2,4-Me3C5H2), exhibited efficient TBE incorporation and moderate catalytic activity in the presence of MAO, affording ethylene/TBE copolymers with relatively high molecular weight and uniform molecular weight distribution. However, the copolymerization conducted by employing constrained geometry catalyst (linked half-titanocene), [Me2Si(C5Me4)(NtBu)]TiCl2, and zirconocene [Cp2ZrCl2]−MAO catalyst systems resulted in polyethylene without TBE incorporation. Furthermore, the copolymerization of 1-hexene (1-Hex) with TBE and vinyltrimethylsilane (VTMS), by (tBuC5H4)TiCl2(O-2,6-iPr2C6H3) and CpTiCl2(N═CtBu2)−MAO catalyst systems, indicated a considerably higher reactivity of VTMS. The 1-Hex/VTMS copolymerization has been elucidated to proceed via 1,2-insertion as manifested by the remarkably efficient VTMS enchainment, hence revealing the difference in the reactivity of TBE and VTMS to arise from that in their electronic and/or steric nature.

Scope and Mechanism of the Intermolecular Addition of Aromatic Aldehydes to Olefins Catalyzed by Rh(I) Olefin Complexes

Rhodium (I) bis-olefin complexes Cp*Rh(VTMS)(2) and CpRh(VTMS)(2) (Cp* = C(5)Me(5), Cp = C(5)Me(4)CF(3), VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins to form ketones. Use of the more electron-deficient catalyst CpRh(VTMS)(2) results in faster reaction rates, better selectivity for linear ketone products from alpha-olefins, and broader reaction scope. NMR studies of the hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-olefin complexes and the corresponding Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that CpRh(VTMS)(2) displayed a faster turnover frequency (relative to Cp*Rh(VTMS)(2)) because of an increase in the rate of reductive elimination, the turnover-limiting step, from the more electron-deficient metal center of CpRh(VTMS)(2). Reaction of Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) with PMe(3) yields acyl complexes Cp*/Rh[C(O)CH(2)CH(2)SiMe(3)](PMe(3))(Ar); measured first-order rates of reductive elimination of ketone from these Rh(III) complexes established that the Cp ligand accelerates this process relative to the Cp* ligand.