Trimethylsilyl Phosphate Research Articles

Exploring the impact of synergistic dual-additive electrolytes on 5 V-class LiNi0·5Mn1·5O4 cathodes

Tris (trimethylsilyl) phosphate (TMSP) and tris(2,2,2-trifluoroethyl) phosphate (TTFP) was added to carbonate solvent-based electrolytes as dual-additives to enhance the performance of LiNi0·5Mn1·5O4 (LNMO). The X-ray photoelectron spectroscopy results revealed that both TMSP with high oxidation ability and TTFP with high oxidation resistance participated in the formation of cathode–electrolyte interphase (CEI) films. Electrochemical impedance spectroscopy confirmed that the constructed CEI films had excellent electronic insulation and ionic conductivity, reducing the interfacial impedance of the LNMO electrode, and improving the electrochemical performance of LNMO/Li half-cells and LNMO/Li4Ti5O12 full-cells. As measured by the nuclear magnetic resonance, the incorporation of TMSP and TTFP significantly reduced the HF content in the electrolytes. Therefore, both LNMO/Li half-cells (500 cycles with 95.7% capacity retention) and LNMO/Li4Ti5O12 full-cells (200 cycles with 79.9% capacity retention) displayed higher cycling stabilities at 5 C owing to the synergistic effect of TMSP and TTFP. In comparison, capacity retentions of ∼76.5% after 500 cycles and ∼37.2% after 200 cycles were respectively achieved for the LNMO/Li half-cells and LNMO/Li4Ti5O12 full-cells with the standard electrolyte at 5 C. This study provides strong evidence that additive combinations can improve the electrochemical performance of high-energy and high-voltage cathode materials.

Tailoring electrolyte enables high-voltage Ni-rich NCM cathode against aggressive cathode chemistries for Li-ion batteries

The LiNi0.8Co0.1Mn0.1O2 (Ni-rich NCM) cathode materials suffer from electrochemical performance degradation upon cycling due to detrimental cathode interface reactions and irreversible surface phase transition when operating at a high voltage (≥4.5 V). Herein, a traditional carbonate electrolyte with lithium difluoro(oxalato)borate (LiDFOB) and tris(trimethylsilyl)phosphate (TMSP) as dual additives that can preferentially oxidize and decompose to form a stable F, B and Si-rich cathode-electrolyte interphase (CEI) that effectively inhibits continual electrolyte decomposition, transition metal dissolves, surface phase transition and gas generation. In addition, TMSP also removes trace H2O/HF in the electrolyte to increase the electrolyte stability. Owing to the synergistic effect of LiDFOB and TMSP, the Li/LiNi0.8Co0.1Mn0.1O2 half cells exhibit the capacity retention 76.3% after 500 cycles at a super high voltage of 4.7 V, the graphite/LiNi0.8Co0.1Mn0.1O2 full cells exhibit high capacity retention of 82.8% after 500 cycles at 4.5 V, and Li/LiNi0.8Co0.1Mn0.1O2 pouch cells exhibit high capacity retention 94% after 200 cycles at 4.5 V. This work is expected to provide an effective electrolyte optimizing strategy compatible with high energy density lithium-ion battery manufacturing systems.

Silyl-Functionalized Electrolyte Additives and Their Reactivity toward Lewis Bases in Li-Ion Cells

Silyl groups are included in a wide range of electrolyte additives to enhance the performance of state-of-the-art Li-ion batteries. A recognized representative thereof is tris-(trimethylsilyl)phosphate (TMSPa) which, along with the similarly structured phosphite, has been at the center of numerous electrolyte studies. Even though the silyl group has already been widely reported to be specifically reactive towards fluorides, herein, a reactivity towards several Lewis bases typically found in Li-ion cells is postulated and investigated with the aim to establish a more simplified and generally applicable reaction mechanism thereof. Both gaseous and electrolyte soluble reactants and products are monitored by combining nuclear magnetic resonance and injection cell-coupled mass spectrometry. Experimental observations are supported by computational models. The results clearly demonstrate that the silyl groups react with water, hydroxide, and methoxide and thereby detach in a stepwise fashion from the central phosphate in TMSPa. Intermolecular interaction between TMSPa and the reactants likely facilitates dissolution and lowers the free energy of reaction. Lewis bases are well known to trigger side reactions involving both the Li-ion electrode and electrolyte. By effectively scavenging these, the silyl group can be explained to lower cell impedance and prolong the lifetime of modern Li-ion batteries.

In Situ Construction of Uniform and Robust Cathode–Electrolyte Interphase for Li‐Rich Layered Oxides

AbstractHigh‐energy‐density Li‐rich layered oxides (LLOs) as promising cathodes for Li‐ion batteries suffer from the dissolution of transition metals (especially manganese) and severe side reactions in conventional electrolytes, which greatly deteriorate their electrochemical performance. Herein, an in situ “anchoring + pouring” synergistic cathode–electrolyte interphase (CEI) construction is realized by using 1,3,6‐hexanetricarbonitrile (HTCN) and tris(trimethylsilyl) phosphate (TMSP) electrolyte additives to alleviate the challenges of an LLO (Li1.13Mn0.517Ni0.256Co0.097O2). HTCN with three nitrile groups can tightly anchor transition metals by coordinative interaction to form the CEI framework, and TMSP will electrochemically decompose to reshape the CEI layer. The uniform and robust in situ constructed CEI layer can suppress the transition metal dissolution, shield the cathode against diverse side reactions, and significantly improve the overall electrochemical performance of the cathod with a discharge voltage decay of only 0.5 mV cycle−1. Further investigations based on a series of experimental techniques and theoretical calculations have revealed the composition of in situ constructed CEI layers and their distribution, including the enhanced HTCN anchoring effect after lattice densification of LLOs. This study provides insights into the in situ CEI construction for enhancing the performance of high‐energy and high‐voltage cathode materials through effective, convenient, and economical electrolyte approaches.

Elucidating the Reactivity of Tris(trimethylsilyl)phosphite and Tris(trimethylsilyl)phosphate Additives in Carbonate Electrolytes—A Comparative Online Electrochemical Mass Spectrometry Study

The electrolyte additives tris(trimethylsilyl)phosphite (TMPSi) and tris(trimethylsilyl)phosphate (TMSPa) have shown their potential to improve lifetime and decrease impedance build-up in lithium i...

S-containing and Si-containing compounds as highly effective electrolyte additives for SiOx -based anodes/NCM 811 cathodes in lithium ion cells

Recently, high-energy density cells containing nickel-rich cathodes and silicon-based anodes have become a practical solution for increasing the driving range of electric vehicles. However, their long-term durability and storage performance is comparatively poor because of the unstable cathode-electrolyte-interphase (CEI) of the high-reactivity cathode and the continuous solid-electrolyte-interphase (SEI) growth. In this work, we study several electrolyte systems consisting of various additives, such as S-containing (1,3,2-dioxathiolane 2,2-dioxide (DTD), DTD + prop-1-ene-1,3-sultone (PES), methylene methanedisulfonate (MMDS)) and Si-containing (tris(trimethylsilyl) phosphate (TTSP) and tris(trimethylsilyl) borate (TMSB)) compounds, in comparison to the baseline electrolyte (BL = 1.0 M LiPF6 + 3:5:2 w-w:w EC: EMC: DEC + 0.5 wt% lithium difluoro(oxalato)borate (LiDFOB) + 2 wt% lithium bis(fluorosulfonyl)imide (LiFSI) + 2 wt% fluoroethylene carbonate (FEC) + 1 wt% 1,3-propane sultone (PS)). Generally, electrolytes with Si-containing additives, particularly BL + 0.5% TTSP, show a lower impedance increase in the full cell, better beginning-of-life (BOL) performance, less reversible capacity loss through long-term cycles and better storage at elevated temperatures than do electrolytes with S-containing additives. On the contrary, electrolytes with S-containing additives exhibit the advantage of low SEI impedance but yield a worse performance in the full cell than do those with Si-containing additives. The difference between two types of additives is attributed to the distinct function of the electrodes, which is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS), which was performed on full cells and half cells with fresh and harvested electrodes.

Operando Monitoring of F– Formation in Lithium Ion Batteries

Online electrochemical mass spectrometry (OEMS) was applied to study the influence of tris(trimethylsilyl)phosphate (TMSPa) as an additive in 1 M LiPF6 (fluoroethylene carbonate/diethylene carbonate (DEC)) electrolyte on the gas evolution in Li-rich/NCM full cells during cycling. The results indicate that TMSPa neither influences the solid electrolyte interphase (SEI) formation on the anode nor the surface reconstruction on the cathode but acts as a chemical scavenger for HF and LiF. TMSPa thus lowers the electrolyte acidity and suppresses further LiPF6 decomposition, resulting in lower impedance and higher lithium ion battery (LIB) performance. Furthermore, the selective reactivity of TMSPa toward fluorides leads to the formation of Me3SiF enabling the additive to act as a chemical probe and to study HF/LiF formation operando by OEMS. By this methodology, we were able to identify contributions from SEI formation, proton and reactive oxygen formation >4.2 V, cross-talk between the anode and cathode, and t...

Electrochemical performance of lithium-ion capacitors evaluated under high temperature and high voltage stress using redox stable electrolytes and additives

Lithium-ion capacitors (LICs) were investigated for high power, moderate energy density applications for operation in extreme environments with prolonged cycle-life performance. The LICs were assembled as three-layered pouch cells in an asymmetric configuration employing Faradaic pre-lithiated hard carbon anodes and non-Faradaic ion adsorption-desorption activated carbon (AC) cathodes. The capacity retention was measured under high stress conditions, while the design factor explored was electrolyte formulation using a set of carbonates and electrolyte additives, with a focus on their stability. The LIC cells were evaluated using critical performance tests under the following high stress conditions: long-term voltage floating-cycling stability at room temperature (2.2–3.8 V), high temperature storage at 3.8 V, and charge voltages up to 4.4 V. The rate performance of different electrolytes and additives was measured after the initial LIC cell formation for a 1C–10C rate. The presence of vinylene carbonate (VC) and tris (trimethylsilyl) phosphate (TMSP) were found to be essential to the improved electrochemical performance of the LIC cells under all testing conditions.

Effect of Phosphorus-Based Additives on Cathode-Electrolyte Interface of Charged Ncm Surface through Potentiostatic Holds

Nickel-rich layered oxide cathode materials have seen widespread deployment due to their high gravimetric capacity and high average discharge voltage. However, achieving this high capacity requires charging voltages above the potential at which the electrolytes decompose at the cathode surface (>4.5 V vs. Li/Li+). This interfacial instability leads to impedance rise and capacity loss. One strategy to stabilize this interface is by the addition of additives to the electrolyte, in which small amounts of a new component change the interactions of the interface. Potentiostatic holds with LiNi0.5Mn0.3 Co0.2O2 (NMC) as the working electrode and Li4Ti5O12 (LTO) as the counter/reference allow a quantitative measurement of the oxidation reactions occurring at cathode. A 60 hour hold allows for concentration polarizations to relax and oxidative side reactions to dominate the current. A more stable electrolyte at the cathode/electrolyte interface would lead to a lower current during the potentiostatic hold. In this work, the performance of five phosphorus-based additive electrolyte formulations (1% wt. ratio) is evaluated against a baseline organic carbonate electrolyte in NMC (LiNi0.5Mn0.3 Co0.2O2 ) / LTO (Li4Ti5O12) full cells. These additives include triethylphosphite (TEPi), tris(2,2,2-trifluoroethyl)phosphite (TTFPi), tris(trimethylsilyl) phosphite (TMSPi), and tris(trimethyl silyl) phosphate (TMSPa). The electrochemical protocol used to evaluate these additives comprises multiple cycles up to 4.4 V vs. Li+/Li, a potentiostatic hold at 4.6 V vs. Li+/Li, followed by AC impedance spectroscopy and extended cycling. Of the formulations surveyed, only electrolytes containing TMSPa and TMSPi (aged for one week) increased the coulombic efficiency during the initial cycling. For the potentiostatic hold, only the aged TMSPi electrolyte lowered the terminal oxidation current compared to the baseline electrolyte, indicating increased stability of the cathode/electrolyte interface. AC impedance spectra indicated the aged TMSPi electrolyte had a slightly elevated high-frequency semicircle (traditionally associated with phenomena at the solid-electrolyte interphase) and a vastly decreased mid-frequency semicircle (traditionally associated with charge-transfer phenomena), compared with all other electrolytes tested. Characterization of cycled electrodes was performed with XPS and SEM will be presented. Acknowledgements The work at Argonne National Laboratory was performed under the auspices of the U.S. Department of Energy (DOE), Office of Vehicle Technologies, under Contract No. DE-AC02-06CH11357. The submitted issue has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W-31-109-Eng-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, non-exclusive, irrevocable, worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

A comparative study of Si-containing electrolyte additives for lithium ion battery: Which one is better and why is it better

Abstract Influence of two Si-containing electrolyte additives, tris(trimethylsilyl)borate (TMSB) and tris(trimethylsilyl)phosphate (TMSP), on the cyclic stability of high voltage LiNi0.5Mn1.5O4 electrode has been systematically studied in this work. The capacity retention of LiNi0.5Mn1.5O4 cycling in STD (1M LiPF6/EC: EMC = 3:7), TMSB- and TMSP-containing electrolytes is 23%, 85% and 71% after 600 cycles at 1C rate, respectively, revealing that the ability of TMSB on improving the cyclic performance of LiNi0.5Mn1.5O4 is superior to that of TMSP. Experimental and theoretical characterizations show that the preferential reaction of both TMSB and TMSP generates thin and uniform film on LiNi0.5Mn1.5O4 surface, which effectively suppress the continuous oxidation reaction of electrolyte. While the film generated from TMSB, which contains B and Si-rich compounds, shows better ability on restraining the growth of interfacial resistance during cycling, resulting in better cyclic stability of LiNi0.5Mn1.5O4 than that of TMSP.

Tris(trimethylsilyl)phosphate as electrolyte additive for self-discharge suppression of layered nickel cobalt manganese oxide

Application of layered nickel cobalt manganese oxide as cathode under higher potential than conventional 4.2V yields a significant improvement in energy density of lithium ion battery. However, the cathode fully charged under high potential suffers serious self-discharge, in which the interaction between the cathode and electrolyte proceeds without potential limitation. In this work, we use tris(trimethylsilyl)phosphate (TMSP) as an electrolyte additive to solve this problem. A representative layered nickel cobalt manganese oxide, LiNi1/3Co1/3Mn1/3O2, is considered. The effect of TMSP on self-discharge behavior of LiNi1/3Co1/3Mn1/3O2 is evaluated by physical and electrochemical methods. It is found that the self-discharge of charged LiNi1/3Co1/3Mn1/3O2 can be suppressed significantly by using TMSP. TMSP is oxidized preferentially in comparison with the standard electrolyte during initial charging process forming a protective cathode interface film, which avoids the interaction between cathode and electrolyte at any potential and thus prevents electrolyte decomposition and protects LiNi1/3Co1/3Mn1/3O2 from structure destruction.

Importance of Reduction and Oxidation Stability of High Voltage Electrolytes and Additives

The electrolyte is a critical component for rechargeable Li-ion batteries, especially batteries containing high voltage cathodes. A series of electrolyte salts, solvents and additives was investigated via cyclic voltammetry (CV) on glassy carbon (GC) electrodes. Quantum chemistry (QC) calculations were used for prediction of oxidation and reduction stability of electrolyte components such as ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), tris(trimethylsilyl) phosphate (TMSP), 1,3-propane sultone (PS), tris(hexafluoroisopropyl) phosphate (HFiPP) and lithium salts such as LiPF6, LiBF4, lithium difluoro(oxalato)borate (LiDFOB), lithium 4,5-dicyano-2-trifluoromethyl-imidazolide (LiTDI), and lithium bis(trifluoromethanesulfonimide) (LiTFSI). QC calculations predicted that defluorination of LiPF6 and LiTFSI aggregates coupled with electron transfer significantly increased their reduction potential, while H-transfer upon oxidation lowered oxidation potential for many solvents. The composition of the Li+ cation solvation shell was estimated from the binding energies for the Li+–solvent complexes using cluster-continuum calculations and was used to provide insight into the experimental data on electrolyte reduction. Full coin cell data was acquired using LiNi0.5Mn1.5O4 (LNMO) cathodes with graphite anodes at 25°C and 55°C. Differential capacity plots (dQ/dE vs. E) and electrochemical impedance spectroscopy (EIS) results. The electrolyte with the most desirable performance was 1M LiPF6 in 3:7 EC:EMC (wt%) with 1wt% TMSP. Oxidative CV experiments show that the TMSP containing electrolyte has a slightly lower oxidation stability compared to the baseline, which is consistent with the order of oxidation stability of electrolyte components from QC calculations. The EIS measurements showed that the TMSP containing electrolyte had the lowest impedance after cycling and the dQ/dE plots show that the redox reactions retained their peak shape and area more so than an electrolyte without TMSP, indicating a greater capacity retention. Density functional theory calculations of TMSP oxidation on the LNMO surface were performed in order to provide insight into the additive role in improving cell performance.

Enhanced cyclability of LiNi0.5Mn1.5O4 cathode in carbonate based electrolyte with incorporation of tris(trimethylsilyl)phosphate (TMSP)

In this work, tris (trimethylsilyl) phosphate (TMSP) is used as an electrolyte additive to improve the cycling performance of Li/LiNi0.5Mn1.5O4 cell upon cycling at high voltage, 4.9 V vs. Li/Li+ at room temperature and elevated temperature (55 °C). The effects of TMSP on the cathode interface and the cycling performance of Li/LiNi0.5Mn1.5O4 cell were investigated via the combination of electrochemical methods, including cycling test, cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). It is found that cells with electrolyte containing TMSP have better capacity retention than that of the cells without TMSP upon cycling at high voltage at room temperature and elevated temperature. The functional mechanism of incorporation of TMSP to the electrolyte to improve the cycling performance is conducted with ex-situ analysis approaches, including X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and ICP-MS. The surface analysis results reveal that more stable and more conductive surface layer is formed on the LiNi0.5Mn1.5O4 electrode with TMSP containing electrolyte, which is a leading factor for the enhanced the cycling performance of Li/LiNi0.5Mn1.5O4 cells upon cycling at high voltage at room temperature and elevated temperature.

A High Precision Study of Electrolyte Additive Combinations Containing Vinylene Carbonate, Ethylene Sulfate, Tris(trimethylsilyl) Phosphate and Tris(trimethylsilyl) Phosphite in Li[Ni1/3Mn1/3Co1/3]O2/Graphite Pouch Cells

The effects of electrolyte additive combinations containing vinylene carbonate (VC), ethylene sulfate (DTD), tris(trimethylsilyl) phosphate (TTSP) and tris(trimethylsilyl) phosphite (TTSPi) in Li[Ni1/3Mn1/3Co1/3]O2/graphite pouch cells have been investigated using the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS), gas evolution measurements and long term cycling. The results show that combinations of electrolyte additives that act synergistically can be more effective than a single electrolyte additive (2%VC). These additive mixtures: reduce parasitic reactions at the positive electrode above 4.1 V compared to VC alone; improve coulombic efficiency, reduce charge end-point capacity slippage and also reduce impedance of the cells. A particularly useful additive combination is 2% VC + 1% DTD + 0.5% TTSP + 0.5% TTSPi.

Ternary and Quaternary Electrolyte Additive Mixtures for Li-Ion Cells That Promote Long Lifetime, High Discharge Rate and Better Safety

Combinations of vinylene carbonate (VC), a sulfur-containing additive like methylene methane disulfonate (MMDS), and tris(-trimethyl-silyl)-phosphite (TTSPi) and/or tris(-trimethyl-silyl)- phosphate (TTSP) used as electrolyte additives in Li(Ni1/3Mn1/3Co1/3)O2 (NMC111)/graphite Li-ion cells are shown to impart exceptional properties to those cells. These ternary or quaternary additive mixtures: apparently reduce parasitic reactions, such as electrolyte decomposition, at the positive electrode above 4.1 V compared to VC alone; increase the thermal stability of the charged graphite electrode at elevated temperature; improve coulombic efficiency and also reduce impedance of the cells. These factors all suggest longer lived, safer, higher power Li-ion cells with better tolerance to high voltages which will improve energy density.

Artificial Interface Deriving from Sacrificial Tris(trimethylsilyl)phosphate Additive for Lithium Rich Cathode Materials

Tris(trimethylsilyl)phosphate (TMSP) has been investigated as an additive to form a modified solid electrolyte interface (SEI) on lithium rich cathode material Li[Li0.2Ni0.13Mn0.54Co0.13]O2 and improve its electrochemical performances. Linear sweep voltammetry (LSV) results show that TMSP additive decomposes at the potential ca. 4.1V, lower than that of electrolyte solvent decomposition. The morphology images via TEM clearly demonstrate a continuous interfacial layer formed on the cathode surface after initial cycles. XPS results prove that the components of SEI are mainly derived from the decomposition of TMSP. The Li[Li0.2Ni0.13Mn0.54Co0.13]O2 cathode materials cycled in 1.0 wt% TMSP-containing electrolyte demonstrate obvious enhancement in its cycling stability and capacity retention reaches 91.1% after 50 cycles. The improved performances are ascribed to modified SEI which tightly covers on cathode particle, and effectively avoids a direct contact between cathode active material and electrolyte, leading to the stabilized interfacial structures.

Tris(trimethylsilyl)phosphate: A film-forming additive for high voltage cathode material in lithium-ion batteries

Tris(trimethylsilyl)phosphate (TMSP) is investigated as a novel film-forming additive for LiNi0.5Co0.2Mn0.3O2 cycling at high cut-off potential in LiPF6-based electrolyte. Linear sweep voltammetry (LSV) results reveal that TMSP oxidizes prior to the decomposition of carbonate solvents in electrolyte. When TMSP is incorporated into the electrolyte, the electrochemical performance of LiNi0.5Co0.2Mn0.3O2 is enhanced significantly. The initial discharge capacity of LiNi0.5Co0.2Mn0.3O2 cathode material cycling in the electrolyte with 1% TMSP is increased from 173.4 to 191.0 mAh g−1 compared with that without TMSP between 3.0 and 4.5 V (vs. Li/Li+) at 0.1 C (1 C = 170 mA g−1). In addition, it exhibits a capacity-retention of 90.9% at 1 C after 100 cycles, while that without TMSP is 77.0%. TEM, XPS, and EIS analyses confirm that the film derived from TMSP protects LiNi0.5Co0.2Mn0.3O2 material from eroding by HF effectively, and reduces the interface impedance.

Regioselective oxygenations of s-trans dienes, silyl dienol ethers (SDEs), by triphenyl phosphite ozonide (TPPO) and its mechanistic study.

The direct oxygenation of s-trans dienes, silyl dienol ethers (SDEs) 2, by triphenyl phosphite ozonide (TPPO) has been examined in detail. The regioselective oxygenation was found to give hydroperoxide 3, alcohol 4, ketone 5, dimer 6, and peroxy phosphate 7 with concomitant formation of triphenyl phosphate 8 and diphenyl trimethylsilyl phosphate 10. The formation of peroxy phosphate 7 was found for the first time in TPPO oxygenation reactions. The low temperature (31)P and (1)H NMR spectroscopic analyses proved the direct reaction of SDEs with TPPO without generation of singlet oxygen. The formation of the oxygenated products 3-7 is reasonably explained by the intervention of the zwitterion ZI, which can be formed by the nucleophilic attack of SDE to the central oxygen of the ozonide. The regioselective attack of SDE to the central oxygen of the ozonide was supported by the quantum chemical calculation (B3LYP/6-31G).

The synthesis and reactions of dialkyl fluoroalkyl phosphates

Dimethyl and diethyl fluoroalkyl phosphates were prepared from (1) a dialkyl phosphite with a fluoroalcohol, triethylamine and carbon tetrachloride, (2) a dialkyl chlorophosphate with a fluoroalcohol and triethylamine, and (3) a dialkyl chlorophosphate with the sodium salt of a fluoroalcohol. Dimethyl and diethyl (2,2,2-trifluoroethyl) phosphates reacted with bromotrimethylsilane (TMSBr) in chloroform to give two products with loss of alkyl bromide. The major product was an alkyl (trifluoroethyl) trimethylsilyl phosphate, RO(TMSO)P(O)OCH 2CF 3 and the minor product was a bis(trimethylsilyl) trifluoroethyl phosphate, (TMSO) 2P(O)OCH 2CF 3. The mechanism presumably involves initial attack of an alkoxy oxygen atom on the silicon atom of bromotrimethylsilane. Diethyl (2,2,2-trifluoroethyl) phosphate is resistant to chlorination. It did not react with oxalyl or thionyl chloride in chloroform under prolonged reflux. Unlike triethyl phosphate, it did not react with phosphorus oxychloride in chloroform under reflux.

FORMATION OF PHOSPHORUS YLIDE VIA 1,3-SILYL MIGRATION OF DIMETHYL TRIMETHYLSILYLMETHYLPHOSPHONATE. APPLICATION OF THE PHOSPHONATE TO A WITTIG REACTION

Abstract The reactions of carbonyl compounds with dimethyl trimethylsilylmethylphosphonate gave terminal olefins, dimethyl methylphosphonate, methyl trimethylsilyl methylphosphonate, and dimethyl trimethylsilyl phosphate. Terminal olefins may be formed by a Wittig type reaction of carbonyl compounds with a phosphorus ylide produced via 1,3-silyl migration of dimethyl trimethylsilylmethylphosphonate.