Synthesis of New N-Alkylphenanthrolinium Tetrafluoroborate Ionic Liquids by a New Anion Metathesis Procedure
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Date
2011-05
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Addis Ababa Universty
Abstract
Ionic liquids (ILs) are salts with melting points below 100oC and have remarkable and designer
flexible physicochemical properties that offer distinctive performance advantages in a variety of
synthetic, catalytic, and electrochemical applications. They are widely used as green alternatives
to conventional environment polluting volatile organic solvents (VOCs) due to their negligible
vapor pressure. However, their application in areas like catalysis is limited by the limited number
of cations on which the majority of ILs in common use is based and due to the low solubilities of
organometallic compounds in these groups of ILs. Their green credentials are also being put into
question as the interest in ILs increases. Hence designing new ILs for a given application should
also be accompanied by improvements in the methodology of their preparation with respect to
economics of preparation, environmental impact and cumulative energy demand (CED). In a
current work done in our laboratory, [CnPhen]X (X= Br-, PF6
-, Tf2N-) ILs have been synthesized
following a similar procedure to commonly used ILs and they exhibited good solubilities for
phenanthroline and phenanthroline - metal complexes. Tetrafluoroborate ILs normally exhibit
low melting points and low coordinating abilities that are desired for catalytic reactions. For this
study, we have synthesized a range of new [CnPhen]BF4 ILs with varying alkyl chains. Even
though, the new water miscible [CnPhen]BF4 ILs could be synthesized according to the
conventional procedure for the synthesis of other water miscible BF4
- containing ILs, we
developed a new simple anion metathesis procedure, which has cut down reaction times,
improved yields and bypassed the difficult by-product separation and product purification steps.
[CnPhen]BF4 ILs exhibited good solubilities for phenanthroline and a wide range of
phenanthroline based metal complexes. Their melting points were found to be relatively lower
than its halides, PF6
- and some of Tf2N- containing analogues and followed the same trend with
alkyl chain length of the cation as its [CnPhen]Br precursor. Furthermore, these ILs are found to
be soluble in a larger number of organic solvents than their analogous salts, which offer
flexibility for application in a number of reaction and catalysis schemes.
KEY WORDS: Ionic liquids, tetrafluoroborate, phenanthroline, phenanthrolinium ionic
liquids, metal complex solubility, homogeneous catalysis
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Keywords
Ionic liquids, Tetrafluoroborate, Phenanthroline, Phenanthrolinium ionic liquids, Metal complex solubility, Homogeneous catalysis