Recent Developments in the Chemistry of Fluorinated Isopropoxides and Tertiary Butoxides

Abstract

Studies on OCH(CF 3 ) 2 , OCMe(CF3) 2 , OCMe 2 (CF 3 ), and OC(CF3)3 derivatives of the alkali metals, alkaline earth metals, transition metals, and the lanthanide elements are reviewed, with emphasis on work reported since 1988. Alkali and alkaline earth fluoroalkoxides are generally made from reaction between the alcohol and the metal, its hydride, or organometallics. Most syntheses of transition metal derivatives involve reaction between metal halides and alkali or alkaline earth salts, or the alcoholysis of metal alkyls, alkoxides and amides. Coordination between organic fluorine and electropositive metals (ie. Na, Ba, Τl, Pr) is often observed in the crystal structures of these fluoroalkoxides and may be related to their use as chemical vapor deposition precursors for metal fluorides.Fluorinated metal alkoxides are of interest for a number of reasons. Complexes with bulky fluorinated alkoxy ligands usually have substantially greater volatility and solubility than their unfluorinated counterparts, primarily as a result of low polarizability of the C-F bond(7,2). In addition, the high electronegativity of Rp reduces the basicity of the alkoxy oxygen, which renders extended alkoxy bridged polymers less favorable than those with unfluorinated alkoxy groups (2). These properties are of interest in the design of new precursors for CVD (chemical vapor deposition) and sol-gel types of ceramic synthesis. Of note here is the ability of fluorinated metal complexes to serve as precursors for metal fluorides (3). The high electronegativity and oxidation resistance of fluorinated alkoxy groups can help to stabilize the higher oxidation states of some metals and also finds application in the design of new olefin metathesis catalysts.Although many types of fluoro-alkoxy ligands are known, this chapter is primarily concerned with the alkoxy derivatives of 1,1,1,3,3,3-hexafluoroisopropanol (HOCH(CF3)2, H[HFIP]), 1,1,1-trifluoro-im-butanol (HOCMe2CF3, HfTFTB]) 1,1,1,3,3,3-hexafluoro-fô/t-butanol (HOCMe(CF3)2, HfHFTB]), and perfluoro-terf-butanol (HOC(CF3)3, H[PFTB]). Emphasis is placed on compounds reported after 1988, as an excellent review by Willis details work prior to that time (2). Discussion will focus on the synthesis of these This chapter not subject to U.S.

Highly Volatile Alkaline Earth Metal Fluoroalkoxides

“…The Ba−O distances in 2d [Ba−O(PFTB), 2.544(3) Å; Ba−O(DME), 2.86(3) Å (av)] compare favorably with the average Ba−O(PFTB) bond lengths given above, as well as to Ba−O distances of other simple fluoroalkoxides. For example Ba 5 (μ 5 −OH)[μ 3 -OCH(CF 3 ) 2 ] 4 [μ 2 -OCH(CF 3 ) 2 ] 4 [OCH(CF 3 ) 2 ](THF) 4 (H 2 O)·THF displays Ba−O bonds between 2.53(3)−2.86(3) Å, and the related BaAg(PFTB) 3 (thf) 4 , has a terminal Ba−O distance of 2.448(12) Å . Not surprisingly and in contrast to 2b − c , the increase in coordinative saturation through additional DME coordination and trans ligand configuration in 2d does not allow for steric flexibility resulting in the absence of long distance Ba−F contacts.…”

Metal–Organic Derivatives with Fluorinated Ligands as Precursors for Inorganic Nanomaterials

“…Metal–organic precursors with a fluorinated ligand have several advantages such as enhanced thermal and hydrolytic stability, better solubility, low melting and boiling points, and improved mass-transport properties, over nonfluorinated analogues. Researchers have exploited the strong electron-withdrawing property of a fluoro group as a means to enhance the volatility of metal–organic precursors. − The presence of electron-withdrawing fluoro-groups increases intra- and intermolecular repulsions and generates a less basic O-donor atom of an alkoxide, carboxylate, or β-diketonate ligand. This results in a much lower bridging tendency of these ligands, leading very often to the selective formation of mono- (or low) nuclear complexes.…”

“…Three classes of metal compounds, metal alkoxides M­(OR) n , carboxylates M­(O 2 CR) n , and β-diketonates M­(β-dik) n , are the most commonly used precursors for the synthesis of metal oxide nanomaterials. − Modifications are often needed in these complexes for tailoring properties at a molecular level. The strategy to use fluorinated ligands helps in achieving many of the above-mentioned properties of the precursors. − The hydrophobic nature of the fluoro groups can be exploited to control the hydrolysis rates of many moisture-sensitive complexes, for example, alkoxides derivatives, and thereby design more hydrolytically stable and hence easy to handle precursors. − Also, the enhanced strength of the carbon–fluorine bond over the carbon–hydrogen bond leads to greater thermal stability. The presence of strongly electron-withdrawing CF 3 groups (or perfluorinated alkyl chains) in alpha positions generates a less basic O donor site, making these ligands far less π donating than conventional ligands.…”

Synthesis and stabilization—advances in organoalkaline earth metal chemistry

“…Few organofluorine alkaline earth compounds have been previously reported, but this number is steadily growing. 134,[149][150][151][152][153][154][155][156][157][158][159][160][161] With expanded knowledge about how fluorinated impact the metal centers, M-F interactions are beginning to reveal their potential. Recently, a series of monometallic and heterobimetallic compounds based on perfluoro-tert-butanoxide (PFTB) have been prepared.…”