Introduction - New Synthetic Routes to Polyoxometalate Containing Ionic Liquids - page 14

1.4.2 The merits of POM-ILs exemplified by state-of-the-art
research
Until recently, POMs have rarely been connected to the field of soft materials.
Pioneering work on soft polyoxometalate materials started at the end of the 20 th
century and has quickly developed into a thriving field. Research has been focused on
the development of novel materials which synergistically combine "hard" POMs with a
range of "soft", mostly organic materials to form novel compounds. [45-47] Their usage as
catalysts, sensors and electrochemically active materials is shortly discussed in this
chapter, with three literature examples to give insight into the current frontiers of POM-
IL research.
1.4.2.1 POM-ILs as self separating catalysts
In a landmark paper, the use of POM-ILs as self-separating catalysts for esterification
has been reported. [48] The authors synthesized three POM-ILs based on different organic
cations and the plenary Keggin- cluster anion [PW 12 O 40 ] 3˗ . It should however be noted
that these compounds are not truly ionic liquids but should rather be considered molten
salts, as their melting points are higher than 100 ˚C. [48-50] In their report, the authors
focused on the use of [MIMPS] 3 [PW 12 O 40 ] (POM-IL-3; see Figure 9 on previous page) and
demonstrated that the material effectively catalyzes the esterification of a range of
carboxylic acids and alcohols with almost quantitative yields and selectivities of more
than 90 %. Further, the material can easily be separated: POM-IL-3 is readily dissolved
in the polar starting materials (carboxylic acid, alcohol) but is immiscible with the less
polar reaction product (ester) so that after the reaction, a biphasic system is obtained
where the liquid product can easily be separated from the solid catalyst. Thus, the
advantages of homogeneous and heterogeneous catalysis can be combined, facilitating
recovery and recycling of the POM-IL catalyst.
A true room-temperature POM-IL was recently reported as an excellent liquid
epoxidation catalyst. The compound, POM-IL-4 , is based on n-dodecylimidazolium
cations and the dinuclear peroxotungstate cluster [W 2 O 11 ] 2˗ . [51] POM-IL-4 has been
shown to be active for the epoxidation of olefins and allylic alcohols with almost