4.3 Materials Chemistry
127
More recent examples of this chemistry have capitalised on the rediscovered
reactivity of NIs with carboxylic acids [93]. The use of a smaller, less sophisticated
reaction partner such as a carboxylate means that it can be more readily incorporated
into the polymer backbone, meaning only the tetrazole moiety must be introduced
following polymerisation. This method of SCNP synthesis has also been shown to
furnish the nanoparticle when visible light is employed, through the application of a
2-pyrenyltetrazole [94].
One further report on SCNP synthesis using NIs sought to quantify the rate of collapse of the polymer as a function of N 2 gas emission, an often underexploited characteristic of 2,5-tetrazole photolysis [95]. The tandem application of mass spectrometry
and size exclusion chromatography facilitated a correlation between gas release and
SCNP size to be established in the case of a polystyrene species (Scheme 4.32).
4.3.3 Reactions with Carbon Allotropes
Due to the propensity with which NIs are known to react with carbon-carbon double
bonds, their application in the modification of carbon nanoparticles containing this
functionality has been extensively reported. The majority of activity in this area has
centred around the synthesis of pyrazolino [60]fullerenes through the cycloaddition
of NIs with C 60 spheres [96]. In the context of cycloaddition chemistry, [60]fullerene
may be considered an electron deficient alkene owing to the significant degree of
conjugation present within its π-electron system. The species is therefore able to
undergo facile 1,3-dipolar cycloaddition with a number of dipoles, including NIs, as
was first shown in 1994 by Matthews (Scheme 4.33) [97].
Two further reports on the subject from Yoshida expanded the scope and also
enabled the isolation of the mono-cycloadduct by shortening the reaction time [98,
99]. Again, hydrazonyl chlorides were employed as the NI precursor, with both alkyl
and aryl substituents investigated. In contrast to bioorthogonal and polymer chemistry, hydrazonyl halides have remained the most common source of the NI dipole in
the modification of carbon allotropes. While [60]fullerene is in most instances a competent dipolarophile, a large excess of NI or forcing conditions such as microwave
irradiation are often necessary to deliver high yields of product [100]. 2,5-Tetrazoles
remain applicable within this manifold, with NI generation through thermolysis [101]
and photolysis [102] first exemplified in 2003 and 2015, respectively. The pyrazoline that this procedure forms is normally used as a linking moiety, meaning that this
process typically involves the use of NIs with easily modifiable functional handles
such as amines or aldehydes for further attachment of an additional chemical species
(Scheme 4.34) [103, 104]. [70]fullerene and [80]fullerene have also been shown to
be amenable to modification, although these examples are more limited [105, 106].
[60]Fullerenes are known to act as powerful electron accepting agents, and as such
have found widespread application in materials science due to their high reduction
potential [107]. The augmentation of C 60 with electron-rich moieties has received
particular attention as a method of generating donor-acceptor, or push-pull, electron
127
More recent examples of this chemistry have capitalised on the rediscovered
reactivity of NIs with carboxylic acids [93]. The use of a smaller, less sophisticated
reaction partner such as a carboxylate means that it can be more readily incorporated
into the polymer backbone, meaning only the tetrazole moiety must be introduced
following polymerisation. This method of SCNP synthesis has also been shown to
furnish the nanoparticle when visible light is employed, through the application of a
2-pyrenyltetrazole [94].
One further report on SCNP synthesis using NIs sought to quantify the rate of collapse of the polymer as a function of N 2 gas emission, an often underexploited characteristic of 2,5-tetrazole photolysis [95]. The tandem application of mass spectrometry
and size exclusion chromatography facilitated a correlation between gas release and
SCNP size to be established in the case of a polystyrene species (Scheme 4.32).
4.3.3 Reactions with Carbon Allotropes
Due to the propensity with which NIs are known to react with carbon-carbon double
bonds, their application in the modification of carbon nanoparticles containing this
functionality has been extensively reported. The majority of activity in this area has
centred around the synthesis of pyrazolino [60]fullerenes through the cycloaddition
of NIs with C 60 spheres [96]. In the context of cycloaddition chemistry, [60]fullerene
may be considered an electron deficient alkene owing to the significant degree of
conjugation present within its π-electron system. The species is therefore able to
undergo facile 1,3-dipolar cycloaddition with a number of dipoles, including NIs, as
was first shown in 1994 by Matthews (Scheme 4.33) [97].
Two further reports on the subject from Yoshida expanded the scope and also
enabled the isolation of the mono-cycloadduct by shortening the reaction time [98,
99]. Again, hydrazonyl chlorides were employed as the NI precursor, with both alkyl
and aryl substituents investigated. In contrast to bioorthogonal and polymer chemistry, hydrazonyl halides have remained the most common source of the NI dipole in
the modification of carbon allotropes. While [60]fullerene is in most instances a competent dipolarophile, a large excess of NI or forcing conditions such as microwave
irradiation are often necessary to deliver high yields of product [100]. 2,5-Tetrazoles
remain applicable within this manifold, with NI generation through thermolysis [101]
and photolysis [102] first exemplified in 2003 and 2015, respectively. The pyrazoline that this procedure forms is normally used as a linking moiety, meaning that this
process typically involves the use of NIs with easily modifiable functional handles
such as amines or aldehydes for further attachment of an additional chemical species
(Scheme 4.34) [103, 104]. [70]fullerene and [80]fullerene have also been shown to
be amenable to modification, although these examples are more limited [105, 106].
[60]Fullerenes are known to act as powerful electron accepting agents, and as such
have found widespread application in materials science due to their high reduction
potential [107]. The augmentation of C 60 with electron-rich moieties has received
particular attention as a method of generating donor-acceptor, or push-pull, electron