Full Paper
compound 2 in solution DART experiments. This further con-
firmed that SuFEx with IBZ had indeed taken place and
strengthened our hypothesis that SꢀN bond cleavage product
could be used as an “internal tag” for reaction kinetics determi-
nation.
the o-quinone, which is necessary to allow the SPOCQ reaction
to proceed (near-)quantitatively; see Scheme 3]. A subsequent
SPOCQ reaction with a fluorinated BCN MS tag (5) provided
M11 surfaces as substantiated by a strong F1s signal in wide
After thus showing that the surface-bound SuFEx reaction
can be made quantitative, we next focused our attention on
demonstrating the orthogonal nature of the SuFEx reaction at
a surface, with two other transformations that have previously
been shown to proceed in a quantitative manner, also at a sur-
[
29a]
face.
To this aim, we chose two routes: Br-terminated sur-
faces (M ) were reacted with propargylamine to yield alkyne-
4
terminated surfaces (M ), or with 3,4-dihydroxybenzylamine to
5
yield quinone-terminated surfaces (M ) upon oxidation. The
9
formation of M surfaces was evidenced by the disappearance
5
of Br3d signal (69.0 eV) in the narrow scan spectra of M and
5
M (see for example, Figure 2c and S4.13). Further confirmation
6
of propargyl attachment was obtained by the slight lowering
of static water contact angle (from 103ꢁ28 to 92ꢁ28; Fig-
ure S4.14). Following this, the M surfaces were reacted with
5
ESF for 16 h to provide dual CuAAC–SuFEx-ready functionali-
ties (M ). The quantitative conversion to M was confirmed by
Scheme 3. Surface M might undergo equilibration with aziridine surface
6
6
9
M
13, although the Michael addition and subsequently the SPOCQ reaction
the appearance of a F1s signal in the XPS wide and narrow
spectrum (Figure 2a and S4.15) and an eventual F/P ratio of
will pull the equilibrium to the left.
1
:4 in the XPS wide spectrum (Figure S4.16). Upon performing
SuFEx with IBZ, we found that M surfaces achieved quantita-
6
tive reaction within 6 h to yield the IBZ-alkyne-terminated sur-
scan XPS spectra (Figure 2a). Furthermore, SPOCQ reaction on
this platform occurred with excellent surface yield (95ꢁ2%) as
quantified using the F/P ratio (10:4) in XPS wide scan (Fig-
ure S4.25) within 5 h further displaying the modularity of our
design. XPS C1s narrow scan analysis of M11 surfaces showed
the different fluorinated carbons attributable to the C F - chain
faces (M ), as evidenced by the complete disappearance of F1s
7
signal and N/P ratios (2:4) in XPS wide spectra (Figure 2a and
S4.18). C1s narrow scan analysis of M surfaces (Figure S4.19)
7
also showed the presence of carbons in distinct chemical envi-
ronments, arising from CꢀS, CꢀN and CꢀI linkages, the latter
attributable to the iodobenzyl motif.
4
9
distinctly (Figure S4.26). Presence of the expected fluorinated
MS fragment (m/z 339.0072) in negative mode DART-HRMS
analysis of SPOCQ-modified M11 surfaces provided further
proof of the reaction (Figure S4.27). In a previous paper the
100% efficiency of this SPOCQ reaction at a surface has been
displayed—the high, but non-perfect yield (95%) obtained in
the current reaction may be due to the intermittent Michael
addition, where the quinones might undergo some slight reac-
tion with for example, methanol.
To test the dual click nature of our strategy, we also per-
formed CuAAC on M surfaces using a fluorinated azide tag 4
6
[
29b]
that is labile under DART conditions.
Upon stirring M sur-
6
faces with a 5 mm solution of 4 in DMF for 16 h, we observed
a 80ꢁ2% surface conversion to M as confirmed by the F/P
8
(4:4) ratios in XPS wide scan spectra (Figure S4.20). Although
the reaction occurred in excellent yield, we did not achieve a
quantitative conversion for surface bound CuAAC under our
[
11]
conditions as has been reported in literature before. Further-
more, DART-HRMS analysis of M8 surfaces also showed the
presence of the fluorinated mass tag (m/z 189.0169) in the EIC
In the spirit of further application of the dual click strategy
for orthogonal functionalization, we performed a SuFEx micro-
stamping experiment using aminoferrocene on M8 surfaces
(Figure 3a). As already stated, these surfaces were CuAAC
clicked with a fluorinated tag. Interestingly, after 16 h we ob-
served a quantitative SuFEx reaction even on this sterically hin-
dered substrate as confirmed by the N/P (5:4) and F/N (2.4:5)
ratios in XPS wide scans upon aminoferrocene immobilization
(Figure S4.28). The patterned surface could be easily visualized
using scanning electron microscopy (SEM). SEM images (Fig-
ure 3b and S4.29) clearly showed regular patterns with a width
of 5 mm. Moreover, XPS Fe2p narrow scan (705–725 eV) analy-
sis clearly showed emergence of Fe2p signals (710.0 eV and
723.0 eV) characteristic of the ferrocene moiety (Figure S4.30).
Having established the reaction efficiency, orthogonality and
applicability of SuFEx, we finally embarked on determination
(Figure S4.21).
The dual SPOCQ–SuFEx platform was prepared by reacting
the Br-terminated surfaces (M ) with 3,4-dihydroxybenzylamine
4
followed by oxidation to quinone (M ) as evidenced by the N/
9
P ratios in XPS wide scan spectrum (Figure S4.22). Directly after
preparation, the o-quinone-terminated surfaces (M ) were re-
9
acted with ESF to install the SO F moiety (M ). The appear-
2
10
ance of an F1s signal in the XPS spectra with the correspond-
ing F/P ratio (1:4) confirmed quantitative attachment (Fig-
ure S4.24) [The o-quinone surface M may be in equilibrium
9
with the hydroquinone surface obtained after internal nucleo-
philic attack of the amine N-atom to yield an aziridine surface
M , but upon reaction with ESF, the equilibrium should favor
13
Chem. Eur. J. 2018, 24, 1 – 8
5
ꢀ 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ
Gahtory, Digvijay
