Catalyst-free room-temperature iClick reaction of molybdenum(II) and tungsten(II) azide complexes with electron-poor alkynes: Structural preferences and kinetic studies

Article abstract of DOI:10.1039/c7dt03096g

Two isostructural and isoelectronic group VI azide complexes of the general formula [M(η³-allyl)(N₃)(bpy)(CO)₂] with M = Mo, W and bpy = 2,2′-bipyridine were prepared and fully characterized, including X-ray structure analysis. Both reacted smoothly with electron-poor alkynes such as dimethyl acetylenedicarboxylate (DMAD) and 4,4,4-trifluoro-2-butynoic acid ethyl ester in a catalyst-free room-temperature iClick [3 + 2] cycloaddition reaction. Reaction with phenyl(trifluoromethyl)acetylene, on the other hand, did not lead to any product formation. X-ray structures of the four triazolate complexes isolated showed the monodentate ligand to be N2-coordinated in all cases, which requires a 1,2-shift of the nitrogen from the terminal azide to the triazolate cycloaddition product. On the other hand, a ¹⁹F NMR spectroscopic study of the reaction of the fluorinated alkyne with the tungsten azide complex at 27 °C allowed detection of the N1-coordinated intermediate. With this method, the second-order rate constant was determined as (7.3 ± 0.1) × 10^-2 M^-1 s^-1, which compares favorably with that of first-generation compounds such as difluorocyclooctyne (DIFO) used in the strain-promoted azide-alkyne cycloaddition (SPAAC). In contrast, the reaction of the molybdenum analogue was too fast to be studied with NMR methods. Alternatively, solution IR studies revealed pseudo-first order rate constants of 0.4 to 6.5 × 10^-3 s^-1, which increased in the order of Mo > W and F₃C-CC-COOEt > DMAD.

Full text of DOI:10.1039/c7dt03096g

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: P. Schmid, M.
Maier, H. Pfeiffer, A. Belz, L. Henry, A. Friedrich, F. Schönfeld, K. Edkins and U. Schatzschneider, Dalton
Trans., 2017, DOI: 10.1039/C7DT03096G.
This is an Accepted Manuscript, which has been through the
Volume 45 Number
1 7 January 2016 Pages 1–398
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
Accepted Manuscripts are published online shortly after
An international journal of inorganic chemistry
www.rsc.org/dalton
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
rsc.li/dalton

Please do not adjust margins
Dalton Transactions
Page 1 of 12
View Article Online
DOI: 10.1039/C7DT03096G
Journal Name
ARTICLE
Catalyst-free room-temperature iClick reaction of molybdenum(II)
and tungsten(II) azide complexes with electron-poor alkynes:
Structural preferences and kinetic studies
Received 00th January 20xx,
Accepted 00th January 20xx
Paul Schmid,a Matthias Maier, a Hendrik Pfeiffer,a Anja Belz,a Lucas Henry,a Alexandra Friedrich,a
Fabian Schönfeld,a Katharina Edkinsa,b and Ulrich Schatzschneidera*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Two isostructural and isoelectronic group VI azide complexes of the general formula [M(η3-allyl)(N3)(bpy)(CO)2] with M =
Mo, W and bpy = 2,2'-bipyridine were prepared and fully characterized, including X-ray structure analysis. Both reacted
smoothly with electron-poor alkynes such as dimethyl acetylenedicarboxylate (DMAD) and 4,4,4-trifluoro-2-butynoic acid
ethyl ester in
a catalyst-free room-temperature iClick [3+2] cycloaddition reaction. Reaction with phenyl-
trifluoromethylacetylene, on the other hand, did not lead to any product formation. X-ray structures of the four triazolate
complexes isolated showed the monodentate ligand to be N2-coordinated in all cases, which requires a 1,2-shift of the
nitrogen from the terminal azide to the triazolate cycloaddition product. On the other hand, a 19F NMR spectroscopic study
of the reaction of the fluorinated alkyne with the tungsten azide complex at 27 °C allowed detection of the N1-coordinated
intermediate. With this method, the second-order rate constant was determined as (7.3±0.1) × 10-2 M-1 s-1, which
compares favorably with that of first-generation compounds such as difluorocyclooctyne (DIFO) used in the strain-
promoted azide-alkyne cycloaddition (SPAAC). In contrast, the reaction of the molybdenum analogue was too fast to be
studied with NMR methods. Alternatively, solution IR studies revealed pseudo-first order rate constants of 0.4 to 6.5 × 10-3
s-1, which increased in the order of Mo > W and F3C-C≡C-COOEt > DMAD.
triazolates, however under addition of copper(II) acetate as a
catalyst.17 While initial kinetic studies by Veige et al. were
focused on linear gold(I) azide compounds,18 we have recently
Introduction
Since their introduction about 15 years ago,1 "click" reactions
have been an indispensable tool for drug development2-4 and
also attracted considerable attention in bioorthogonal
labelling.5-8 Careful optimization of the reactants has led to
systems with very fast coupling kinetics (k up to 105 M-1 s-1),9, 10
which has enabled the study of cellular processes on a
timescale of minutes.11 In recent years, interest has also been
directed at the development of inorganic "click" (iClick)
shown for
a
series of Cp*Rh(III) azide complexes with
substituted 2,2'-bipyridine (bpy) coligands that the rate of the
reaction is accelerated by introduction of electron-donating
groups in the 4- and 4'-position of the bpy.19 However, the
effect of variation of metal center and alkyne on the speed of
the iClick reaction has not been investigated so far. Herein, we
report on the synthesis and structural characterization of two
isoelectronic molybdenum(II) and tungsten(II) azide complexes
[M(η3-allyl)(N3)(bpy)(CO)2] and their iClick cycloaddition
reaction with two different electron-deficient alkynes,
dimethyl acetylenedicarboxylate (DMAD) and 4,4,4-trifluoro-2-
butynoic acid ethyl ester, which are formally related to each
other by substitution of a methyl ester by a trifluoromethyl
group. In particular, 19F NMR studies involving the latter
coupling partner were aimed at identifying the initial N1-
bound triazolate species which should form from the terminal
azide ligand in the starting material, while essentially all iClick
products with substituents in the 4- and 5-position of the
triazolate ring structurally characterized so far are N2-
coordinated,20-28 with some rare N1-bound structures possibly
enforced by increased steric bulk on the substituents.29
reactions which involve small ligands directly coordinated to a
metal center.12,
13
In particular, the [3+2] cycloaddition
reaction of metal-azide complexes with terminal and internal
alkynes as well as nitriles gives rise to metal-triazolate and
metal-tetrazolate complexes, respectively.14-16 Very recently,
dual-functional platinum(II) complexes incorporating both a
metal-coordinated alkyne and a peripheral organoazide moiety
have also been sucessfully polymerized to metallopoly-
a.Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg,
Am Hubland, D-97074 Würzburg, Germany, +49 931 31 83636
ulrich.schatzschneider@uni-wuerzburg.de.
b.School of Pharmacy, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7BL,
United Kingdom
Electronic Supplementary Information (ESI) available: Synthesis of ligand and metal
complex precursors; molecular structures of
parameters for all X-ray structures; IR spectra of precursors and kinetic traces; DFT- Results and discussion
calculated conformational energy diagramm of . See DOI: 10.1039/x0xx00000x
2, 5, 6, and 11; crystallographic
6
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 12
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
Journal Name
Synthesis
cycloaddition reaction with electron-poor alkynes dimethyl
acetylenedicarboxylate (DMAD, 3) and 4,4,4-trifluoro-2-butynoic
acid ethyl ester (4). Using these coupling partners, the [3+2]
cycloaddition reaction proceeded smoothly at room temperature in
dichloromethane, from which the triazolate complexes 5, 6, 11, and
12 were easily isolated by precipitation with diethyl ether or
n-hexane in moderate to good yield (36–85%). Alternatively, a
"masked" alkyne in the form of dimethyl-7-oxa-bicyclo[2.2.1]hepta-
2,5-diene-2,3-dicarboxylate (ONBCOOCH3,COOCH3) was also utilized in
the cycloaddition with 2,33 which gave an even higher yield of
triazolate 5 compared to the reaction with DMAD (3). To further
evaluate the scope of dipolarophiles, phenyltrifluoromethyl-
acetylene (15) was prepared in a three-step published procedure
with the pyrolysis of triphenylphosphonium-α-(trifluoroacetyl)-
benzylide (14) as the key step (Scheme S1).34-40 However, no
product could be isolated from a mixture of molybdenum azide
complex 2 and alkyne 15 upon reaction in dichloromethane at room
temperature for 24 h. A change of the solvent to acetone and
increase of the reaction temperature to reflux did not improve the
outcome and in both cases, the precipitated red solid turned out to
be the molybdenum azide starting material 2 based on 1H and 19F
NMR analysis. Either the presence of only one electron-withdrawing
group is insufficient for a proper match of frontier orbitals or the
phenyl group is sterically too demanding to allow approach to the
azide reaction partner.
The azide complexes [M(η3-allyl)(N3)(bpy)(CO)2] with M = Mo
(
2
) and W (10) were prepared from the corresponding halides
and , respectively. In the case of the molybdenum
compound, a one-pot reaction of [Mo(CO)6] with allyl chloride
and 2,2'-bipyridine in tetrahydrofuran afforded in 76%
1
9
1
yield.30 However, the corresponding tungsten complex was not
accessible via this route due to considerably slower ligand
exchange on the 5d vs. 4d metal center. Therefore, a
consecutive reaction sequence had to be employed. Starting
from [W(CO)6], two carbonyl ligands were oxidized to carbon
dioxide by addition of 2 eq. of trimethylamine N-oxide
(TMAO),31 which facilitates the introduction of the 2,2'-
bipyridine ligand under mild conditions, leading to
[W(bpy)(CO)4] (
7), although only in a low efficiency of 31%. An
additional carbonyl ligand was then replaced by pyridine upon
reflux in xylene for 18 h, leading to [W(bpy)(CO)3(py)] (8) in
76% yield.32 The mixed-ligand bipyridine/pyridine complex
then underwent oxidative addition of allyl chloride to give
[W(η3-allyl)Cl(bpy)(CO)2] (
9
) in a yield of 86%. Introduction of
the azide ligands also required different procedures. In the
case of molybdenum, the chlorido complex was first treated
1
with silver triflate to precipitate the halide as insoluble silver
chloride, followed by reaction with a 2-fold excess of sodium
azide in acetonitrile at room temperature overnight, to give
2
in 58% yield. The analogous tungsten compound, on the other Spectroscopy and X-ray structure analysis
hand, was obtained by refluxing chlorido complex
9 in a
The strong and well-separated vibrational bands of the azide,
carbonyl, and triazolate ester groups provide an easy handle
for the identification of the reaction products with IR
spectroscopy. In particular, the successful substitution of the
chlorido by azide ligand is evident from the strong azide
mixture of acetone/methanol in the presence of 5 eq. of
sodium azide for 6 h, which allowed isolation of 10 in 62%
yield.
antisymmetric stretch present in
cm-1, respectively (Table 1).41 In the course of the iClick
cycloaddition reaction with alkynes, asym(N3) disappears and
2 and 10 at 2036 and 2046
ν
instead, the C=O stretches of the ester carbonyl groups on the
triazolate ring formed are observed at about 1710 to 1725
cm-1.
Table
1 Comparison of azide, carbonyl, and triazolate ester group vibrations for
molybdenum and tungsten complexes [M(η3-allyl)X(bpy)(CO)2] 1, 2, 5, and 6 as well as
9–12 (in cm-1).
X
molybdenum
tungsten
difference
ν(W) - ν(Mo)
1925 (C≡O)
1832(C≡O)
2036 (N3)
1915 (C≡O)
1819 (C≡O)
2046 (N3)
-10
-13
+10
-8
Cl
N3
1928 (C≡O)
1836 (C≡O)
1931 (C≡O)
1856 (C≡O)
1723 (C=O)
1938 (C≡O)
1920 (C≡O)
1821 (C≡O)
1921 (C≡O)
1841 (C≡O)
1724 (C=O)
1929 (C≡O)
-15
-10
-15
+1
triazolateCOOCH3,COOCH3
Scheme 1 Synthesis of molybdenum and tungsten triazolate complexes 5, 6, 11, and 12
by catalyst-free room temperature "iClick" reaction of the corresponding azide
compounds with electron poor alkynes dimethyl acetylenedicarboxylate (DMAD, 3) and
4,4,4-trifluoro-2-butynoic acid ethyl ester (4) or "masked" alkyne dimethyl-7-oxa-
bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (ONBCOOCH3,COOCH3).
-9
triazolateCF3,COOEt
1864, 1854 (C≡O) 1850 (C≡O)
1713 (C=O) 1723 (C=O)
-9
+10
The symmetric and antisymmetric stretches of the cis-M(CO)2
The molybdenum and tungsten azide compounds 2 and 10 were
moiety, on the other hand, are much less responsive to the
then tested for their efficiency in the catalyst-free "iClick"
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 3 of 12
View Article Online
DOI: 10.1039/C7DT03096G
Journal Name
ARTICLE
Fig. 1 Molecular structure of [W(η3-allyl)(N3)(bpy)(CO)2] 10 with thermal ellipsoids
displayed at the 50% probability level. The asymmetric unit contains only one half of
the molecule with the other one related to it by a mirror plane. Selected bond lengths
[Å] and angles [°] for 10: W1–C1 1.959(4), W1–N1 2.169(5), W1–N4 2.227(3), W1–(allyl
centroid) 2.032(4), C1–O1 1.161(4), C7–C8 1.413(5), N1–N2 1.199(6), N2–N3 1.160(7),
C1–W1–C1a 82.2(2), N4–W1–N4a 72.5(2), C1–W1–N4 102.0(2), N1–W1–(allyl centroid)
172.8(2), C7–C8–C7a 114.5(5), W1–N1–N2 124.3(3), N1–N2–N3 175.4(5).
exchange of the axial ligand. The replacement of chloride by
azide results in changes < 5 cm-1 in both bands. Rather small
shifts are also observed upon generation of the coordinated
triazolate ligand in the course of the cycloaddition reaction
and seem to depend on the further substitution pattern on the
newly generated five-membered ring, with the antisymmetric
stretch somewhat more responsive than the symmetric one.
All other parameters, in particular long N1–N2 (1.199(6) Å) and
short N2–N3 (1.160(7) Å) bond distances in the azide ligand,41 as
well as C1–O1 bond lengths of 1.161(4) Å, are as expected.46 There
Replacement of the methyl ester group in the triazolates
5 and
11 by trifluoromethyl in 6 and 12 leads to somewhat larger
shifts in the band positions but generally, these do not exceed
about 20 cm-1.
1
The assignment of the H NMR spectra is complicated by the
are about
a dozen tungsten azide complexes structurally
characterized so far,47-55 but only one of them features a mixed-
ligand carbonyl/azide coordination sphere related to 10. However,
in [W(η3-allyl)(N3)(CO)2(en)], the azide ligand is trans to one of the
two carbonyl groups,53 while in 10, it is trans to the allyl moiety. The
presence of a mixture of exo and endo conformers due to two
alternative orientations of the allyl group relative to the bpy
ligand, with some of the signals overlapping.42-45 In addition,
the triazolate ligand can assume two different coordination
modes (N1 vs. N2) when carrying identical substituents in 4-
metrical parameters of molybdenum azide complex
2 are
essentially identical to those of the tungsten congener 10, with
differences in bond lengths and angles below 0.01 Å and 0.5°,
respectively (Fig. S1). Most closely related structurally characterized
compounds include [Mo(η3-allyl)(N3)(CO)2(en)],53 also isostructural
to the tungsten complex mentioned above, two molybdenum
dicarbonyl complexes with chelating diphosphane ligands of general
formula [Mo(η3-allyl)(N3)(CO)2(R2P(CH2)nPR2)], which vary in the
linker length and substituent on the phosphorous center (n = 2, R =
C6H5 vs. n = 1, R = CH3),22, 56 and [Mo(N3)(NO)(bpmCH3,CH3)(CO)2] with
bpmCH3,CH3 = bis(3,5-dimethyl-pyrazol-1-yl)methane.57 However, in
all these compounds, the azide ligand is oriented trans to one of the
diatomic ligands, either CO or NO, not the allyl.
and 5-position, as in
are possible for the unsymmetrically substituted compounds
and 12. However, the trifluoromethyl group in alkyne as well
as triazolate complexes and 12 is a sensitive and diagnostic
marker for 19F NMR spectroscopy. In 4,4,4-trifluoro-2-butynoic
acid ethyl ester ( ), its resonance is observed at -50.9 ppm
5 and 11, while three different isomers
6
4
6
4
while in the resulting triazolate complexes, it is shifted upfield
by about -6 to -8 ppm to approx. -58 ppm. In the case of
molybdenum compound 6, three signals are observed in that
range with an intensity ratio of 80:14:6, while the tungsten
analogue 12 shows only two species in 88:12 ratio. However,
since the differences in chemical shift are very small, it is not All four triazolate complexes 5, 6, 11, and 12 obtained by iClick
possible to assign the different species to either exo/endo reaction with the electron-poor alkynes dimethyl acetylene-
isomers or the different coordination modes of the triazolate dicarboxylate (DMAD, 3) or 4,4,4-trifluoro-2-butynoic acid ethyl
ligand.
ester (4) exhibit N2-coordination of the five-membered ring (Fig. 2
Both azide complexes 2 and 10 as well as the four triazolate and Fig. S2–S4), similar to the other compounds prepared this way
28
compounds 5, 6, 11, and 12 were characterized by single-crystal we have characterized so far.19, Since the azide ligand is N1-
X-ray structure analysis with the molecular structures shown in coordinated in 2 and 10, apparently a 1,2-shift has to take place
Fig. 1 and 2 as well as Fig. S1–S4. Relevant crystallographic during or after the cycloaddition reaction. The bond lengths and
parameters are listed in Table S1. The tungsten center in 10 is in a angles of all four triazolate complexes 5, 6, 11, and 12 are
pseudooctahedral coordination environment with the bpy ligand essentially identical, with deviations below 0.02
Å and 0.3°,
and the cis-W(CO)2 moiety in the central plane (Fig. 1). The azide respectively. Apparently, the influence of the metal center (Mo vs.
group points away from the bpy with a W1–N1–N2 angle of W) and substituent in the 4- and 5-position on the triazolate ring
124.3(3)° and is located on a mirror plane which intersects the two (methyl ester vs. trifluoromethyl/ethyl ester) on these parameters
carbonyl ligands and the central bpy C6–C6a axis, with the two is negligible.
halves of the molecule symmetry-related to each other.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 12
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
Journal Name
Fig. 2 Molecular structure of [W(η3-allyl)(triazolateCF3,COOCH3)(bpy)(CO)2] 12 with thermal
ellipsoids displayed at the 50% probability level. Selected bond lengths [Å] and angles
[°] for 12: W1–C1 1.957(2), W1–C2 1.965(2), W1–N2 2.206(2), W1–N4 2.213(2), W1–N5
2.224(2), W1–(allyl centroid) 2.031(2), C1–O1 1.163(3), C2–O2 1.158(2), C15–C16
1.415(4), C16–C17 1.413(4), C1–W1–C2 78.0(1), N4–W1–N5 73.02(7), C1–W1–N4
105.22(9), C2–W1–N5 101.89(9), N2–W1–(allyl centroid) 176.27(7), C15–C16–C17
115.1(2), (N2–W1–C16)–(triazolate) 49.5(3).
azide complex-to-alkyne ratio adjusted to 1:1. A series of
19F NMR spectra were recorded at 27 °C in 40–50 s intervals
over 30 min, with a time lag of about 1 min between the
mixing and the first spectrum obtained due to experimental
limitations. In addition to the signal of the alkyne at -50.9 ppm
and the doublet of the hexafluorophosphate anion at -70.1
1
ppm with a JF,P coupling of 711 Hz, already the first spectrum
The same is also true when comparing the azide vs. triazolate
complexes, where differences of key parameters are below 0.02 Å
and 0.8°, respectively. One notable exception, however, is the
orientation of the triazolate ring plane relative to the central C–C
axis of the bpy ligand. In the trifluoromethyl-substituted
molybdenum compound 6, these two are essentially parallel to
each other and the triazolate assumes a staggered orientation
relative to the two bipyridine N–metal–CO angles. In contrast, in
the other three complexes 5, 11, and 12, the triazolate ring plane is
significantly rotated around the M–N2 axis relative to the central
bpy C–C vector and assumes a more or less eclipsed orientation
relative to one of the M-CO moieties. In the absence of any notable
intramolecular interactions, the twist around the metal–triazolate
N2 bond is apparently governed by subtle packing effects in the
solid state. A detailed analysis of the energy barrier between the
different conformations based on DFT calculations is presented
below.
recorded shows two additional signals at -58.7 and -59.0 ppm
(Fig. 3 top). With increasing reaction time, these two signals
assigned to the isomeric N1- and N2-coordinated triazolate
complexes increased in intensity, while the alkyne CF3 peak
at -50.9 ppm decreased continuously with similar time profiles
(Fig. 4). In contrast, the intensity of the signal of the
hexafluorophosphate additive remained constant during the
whole time of the measurement.
1.0
0.8
0.6
0.4
0.2
0.0
19F NMR kinetic measurements
The rate constant of the cycloaddition reaction is a very
important parameter when this method is to be applied to
bioconjugation, since it has to be faster than the biological
process of interest. With 4,4,4-trifluoro-2-butynoic acid ethyl
0
500
1000
1500
2000
Time [s]
ester (4
) as the alkyne component, the use of 19F NMR
spectroscopy is a facile way to follow the course of the
reaction, since there is a shift of about -8 ppm between the
alkyne CF3 signal,28 which is observed at -50.9 ppm in DMSO-
d6, and that of the trifluoromethyl group in the 4-position of
Fig. 4 Change of the 19F NMR peak intensity of the signals of the tungsten triazolate
complex 12 at around -58 ppm (red circles) and of 4,4,4-trifluoro-2-butynoic acid ethyl
ester (4) at -50.9 ppm (blue squares) with reaction time (1–30 min) at 27 °C. Due to an
experimental lag time no data could be obtained for the initial phase of the reaction < 1
the molybdenum- and tungsten-coordinated triazolates min.
resulting from the cycloaddition, where the peaks are found at
Assuming a second-order rate law and equal concentrations of
around -58 ppm, with very little variance between the two
metals.
azide complex and alkyne at the start of the reaction as well as
negligible side-reactions, the kinetics can be modelled up to
50% conversion by eq. 1.
ꢀ
ꢀ
ꢋ ꢌ ꢁ
ꢋ ꢍ ꢎꢏꢐ
(eq. 1)
ꢁ
ꢂꢃꢄꢅꢆꢇꢈꢉꢊ
ꢂꢃꢄꢅꢆꢇꢈ
With an initial concentration of the alkyne of 35 mmol L-1, the
second-order rate constant k2 was determined by a linear fit
from the slope of a plot of 1/[alkynet=0]-1/[alkynet] over t as
(7.3±0.1) ×
magnitude faster than the value of k = 7.6
10-2 M-1 s-1 at 27 °C. This is about one order of
10-3 M-1 s-1
×
reported by Veige and coworkers for the iClick reaction of
[Au(N3)(PPh3)] with [Au(C≡C-C6H5)(PPh3)].18 The rate constant
determined for the iClick reaction of the tungsten azide
complex is comparable to those reported, for example, for the
strain-promoted azide-alkyne cycloaddition (SPAAC) of first-
generation compounds such as difluorocyclooctyne (DIFO), but
Fig. 3 Changes in the 19F NMR spectra (470.59 MHz, DMSO-d6) of a mixture of tungsten
azide complex 10 (35 mM), 4,4,4-trifluoro-2-butynoic acid ethyl ester (4, 35 mM) and
ammonium hexafluorophoshate (17 mM) at 27 °C over 1–15 min. Due to an
experimental lag time no data could be obtained for the initial phase of the reaction < 1
min.
Thus, the tungsten azide complex 10 was dissolved in DMSO-d6 about 1–2 orders of magnitude slower than values obtained
and mixed with ammonium hexafluorophosphate serving as an for the latest reagents such as aza-dibenzocyclooctyne
internal standard. Then, alkyne
4
was added with the metal (DIBAC), biarylazacyclooctynone (BARAC), and 3,3,6,6-
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 5 of 12
View Article Online
DOI: 10.1039/C7DT03096G
Journal Name
tetramethyl-thiacycloheptyne (TMTH).9 Other bioorthogonal The molybdenum azide complex
ARTICLE
2
reacts about 3–4 times
coupling reactions such as the tetrazine ligation show even faster than the tungsten analogue 10, while the cycloaddition
faster kinetics with rate constants up to 104 M-1 s-1.10 The same reaction with 4,4,4-trifluoro-2-butynoic acid ethyl ester (
) is
method was also attempted to study the kinetics of the iClick 4–7 times more rapid than the one with DMAD ( ).
reaction of the related molybdenum azide complex with
alkyne . However, the reaction proceeded very fast at room
4
3
2
4
temperature and after 2–3 min, no signal for the
trifluoromethyl-substituted alkyne was detectable at -50.9
ppm. This is a strong indication that the type of metal center
(Mo vs. W) has a significant influence on the rate constant, but
apparently the NMR spectroscopic method successfully
applied to the tungsten complex has too long a time lag
between mixing and recording of the first spectrum as well as
too long delay times between the individual measurements to
follow the process in the case of the molybdenum compound.
Solution IR kinetic measurements
Since the iClick reaction was too fast to be monitored by NMR
in the case of the molybdenum complex
the cycloaddition reactions of the azide complexes with DMAD
) was not possible using this method, since it lacks the
fluorine label as in 4,4,4-trifluoro-2-butynoic acid ethyl ester
), solution IR measurements were explored as an alternative
method to obtain the rate constants for the iClick reaction of
and 10 with the two alkynes and , as previously used
successfully to study the cycloaddition reaction of
[Rh(Cp*)(N3)(bpyR,R)]CF3SO3 with alkyne 4 19
Thus, the azide
complex ( or 10, 8 mM) dissolved in dimethylsulfoxide was
mixed with alkyne ( or 40 mM) and then quickly
2 and comparison of
(
3
(
4
2
3
4
.
2
3
4,
transferred to a liquid IR cell, with a maximum time lag of
about 1.5 min between mixing and start of the measurement.
Measurements in the 1800–2100 cm-1 spectral range were
carried out in 20 s intervals until the azide band at 2050–2060
cm-1 had completely disappeared. No spectral overlap was
observed in that region with bands assigned to alkynes
3 and 4
(Fig. S5). In contrast to the azide band, the two signals due to
the antisymmetric and symmetric C≡O stretching vibrations
between 1835 and 1935 cm-1 remained essentially unchanged
during the course of the reaction (Fig. 5 and Fig. S6). A minor
intermediate decrease in the intensity of the symmetric C≡O
band might be due to subtle differences in the extinction
coefficients of this vibration in the azide vs. triazolate species.
Significant differences in the time required for the reaction to
reach completion are clearly evident in a plot of the intensity
of the azide stretch vs. reaction time (Fig. 6). The reaction of
Fig. 5 Changes in the 1800–2100 cm-1 spectral range of the IR spectrum of a mixture of
2 (top) or 10 (bottom) in dimethylsulfoxide (8 mM) upon reaction with alkyne 4 (40
mM) at 26 °C in 20 s intervals for up to 40 min.
the azide complexes
2
and 10 with 4,4,4-trifluoro-2-butynoic
) regardless
acid ethyl ester (4) is faster than that with DMAD (
3
of the metal complex, while the molybdenum azide complex
reacts faster than the tungsten analogue irrespective of the
alkyne. The data was fit to a monoexponential decay according
to eq. 2 with a correlation coefficient of better than 0.9990 for
all four reactions and gave pseudo-first order rate constants k
in the range of 0.4 to 6.5
×
10-3 s-1 (Table 2).
ꢕꢈꢈ
ꢖ
Fig. 6 Changes in the intensity of the azide stretch of complexes 2 or 10 (8 mM) upon
reaction with alkynes 3 or 4 (40 mM) in dimethylsulfoxide at 26 °C for up to 180 min.
ꢒ
ꢓ
ꢑ N3 ꢌ ꢑꢀ ∙ ꢔ ꢍ ꢗꢘ
(eq. 2)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 6 of 12
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
Journal Name
While the latter trend corresponds well with an increase in the degrees of freedom, the additional effect of rotation of the
rate constant with increasing electron density on one of the methyl ester groups around the triazolate-C4/C5–COOCH3 axis
organic
reactants,
as
observed
previously
for and variation of the H3C-O-C=O torsion angle was not further
[Rh(Cp*)(N3)(bpyR,R)]CF3SO3,19 and reflected in the Hammett investigated.
constants for COOCH3 vs. CF3 of 0.45 and 0.54, respectively,58
the influence of the metal on the speed of the iClick reaction
has not been studied so far and thus there is no data available
for comparison. Unfortunately, the isostructural chromium
azide complex was not accessible for comparison due to low
stability of the starting materials.
Table 2 Pseudo-first order rate constants k and half-lives t1/2 for the cycloaddition
reaction of azide complexes 2 or 10 with alkynes 3 or 4 in dimethylsulfoxide at 26 °C.
reactants
10 + 3
2 + 3
metal
W
alkyne
DMAD
k (in 10-3 s-1)
0.4 ± 0.1
1.6 ± 0.1
2.5 ± 0.1
6.5 ± 0.1
t1/2 (in s)
1896
448
Mo
W
DMAD
10 + 4
2 + 4
F3C-C≡C-COOEt
F3C-C≡C-COOEt
274
Mo
107
Overall, however, the rate constants compare well with those
of the abovementioned RhCp* complexes19 of 2.4 to 3.8
×
10-3
s-1 and the ones reported by Veige et al. for the iClick reaction
Fig. 8 Conformational energy diagram of 5 for variation of the torsion angle between
the triazolate mean plane and the bpy C2–C2' axis calculated with DFT (ORCA 2.8, BP86,
RI, TZVP, COSMO in DMSO).
of [Au(N3)(PPh3)] with gold(I) phenylacetylides.59
DFT calculations
A relaxed surface scan of the N2-coordinated endo isomer
In order to obtain some insight into the energy hypersurface of with rotation of the triazolate around the Mo-N2 bond in 15°
the triazolate complexes, in particular with regard to the steps showed the "parallel" orientation of the triazolate mean
orientation of the allyl ligand (exo vs. endo), the coordination plane and the central bpy C–C axis as well as the
mode of the five-membered ring (N1 vs. N2), and the rotation "perpendicular" conformation with the triazolate at 90°
of the triazolate around the metal-N axis, DFT calculations relative to the bipyridine central axis to be minimum
were carried out on one of the molybdenum complexes structures, with the latter slightly lower in energy by about 0.2
serving as a model system, using the BP86 functional, a TZVP kcal mol-1, while the eclipsed orientations are transition states
basis set, and the COSMO solvation model using between the four minimum structures (Fig. 8). However, with
dimethylsulfoxide, as also employed in the NMR studies.
a maximum difference in energy of only 0.9 kcal mol-1, the
barrier is extremely low, even less than the 1.3 kcal mol-1
determined for a [Mn(triazolate)(bpy)(CO)3] derivative in a
previous study28 and only about one-third of the energy
difference between the staggered and eclipsed conformations
of ethane of about 2.9 kcal mol-1.62 In the case of the
unsymmetrically substituted molybdenum complex
6, a
different energy profile was observed (Fig. S7), since the
"perpendicular" conformer with the trifluoromethyl group
pointing towards the bpy ring is significantly more stable than
the one turned by 180°, with the ethyl ester group towards the
bipyridine. Furthermore, the eclipse conformations now also
become inequivalent. Still, even in this case, the maximum
barrier height does not exceed 1.3 kcal mol-1. Thus, the
triazolate ligand can rotate freely around the Mo-N2 axis at
ambient temperature and there is only a very minor influence
of the substituents in 4- and 5-position on the barrier height.
Fig. 7 DFT-optimized structures (ORCA 2.8, BP86, RI, TZVP, COSMO in DMSO) of (left)
the N2-coordinated endo isomer, (center) the N1-coordinated exo isomer, and (right)
the N2-coordinated endo isomer of 5. Relative energies are reported in kcal mol-1
.
A full geometry optimization without constraints showed the
N2-coordinated endo isomer of
to be 6.2 kcal mol-1 more
5
stable than the exo one. Retaining the endo orientation of the
allyl ligand, the corresponding N1 species was destabilized by
6.9 kcal mol-1 relative to the reference isomer (Fig. 7), which is
also confirmed by other recent structural studies.60, 61 Thus,
the triazolate coordination mode and allyl ligand orientation
Conclusions
Two group VI azide complexes of the general formula [M(η3
allyl)(N3)(bpy)(CO)2] with M = Mo, W were prepared and fully
characterized, including X-ray structure analysis, which
revealed little differences between the two compounds. While
-
observed in the X-ray structure of
5 is indeed the most stable
of the three isomers studied. However, due to the many
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 7 of 12
Journal Name
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
the molybdenum(II) complex was accessible in two steps, the
one-pot reaction of [Mo(CO)6] with allyl chloride and 2,2'-
bipyridine followed by exchange of the chloride to the azide
ligand, the tungsten(II) analogue required a different synthetic
strategy due to significantly slower ligand exchange. Initially,
two of the CO ligands in tungsten(0) hexacarbonyl were
removed with TMAO and then replaced by bpy. This was
Experimental section
Materials and instruments
Reactions were carried out in oven-dried Schlenk glassware under
an atmosphere of pure argon or dinitrogen and reaction vessels
were protected from light by wrapping with aluminium foil if
necessary, in particular for the carbonyl complexes. Molybdenum
followed by exchange of a third carbonyl ligand by pyridine in and tungsten hexacarbonyl were supplied by Strem. All other
refluxing xylene. The resulting [W(bpy)(CO)3(py)] was then
employed in a further reaction sequence similar to the one
employed for the molybdenum complex. The two azide
complexes underwent smooth [3+2] cycloaddition iClick
reactions with electron-poor alkynes such as dimethyl
acetylenedicarboxylate (DMAD) and 4,4,4-trifluoro-2-butynoic
acid ethyl ester, while phenyltrifluoromethylacetylene did not
react. However, at present it is unclear whether this is due to
electronic or steric factors. The four triazolate compounds
obtained were characterized by X-ray structure analysis, which
revealed the five-membered ring to be coordinated to the
metal center via the N2 nitrogen atom in all cases. In contrast,
19F NMR spectra of the trifluoromethyl-substituted products
gave hints of a mixture of the N1- and N2-coordinated species
in solution, although the assignment is complicated by the
additional exo/endo isomerism of the ally ligand. Still, the
method allowed facile study of the reaction kinetics in the case
of the tungsten azide complex, which gave a second-order rate
chemicals were purchased from commercial sources and used as
received. 4,4,4-Trifluoro-2-butynoic acid ethyl ester and dimethyl-7-
oxa-bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate were prepared
by published procedures.33, 35
IR spectra of pure solid samples were obtained using a Nicolet 380
FT-IR spectrometer fitted with a smart iTR ATR accessory. The
solution IR kinetic measurements were carried out with a JASCO FT-
IR 4100 instrument in an Omni-Cell 31800 liquid sample holder
composed of calcium fluoride windows (width: 4 mm) with a Teflon
spacer (d = 200 µm).
NMR spectra were recorded on Bruker Avance 200 (1H: 200.13
MHz, 13C: 50.32 MHz, 19F: 188.12 MHz), Avance 400 (1H: 400.40
Mhz, 13C: 100.68 MHz, 19F: 376.76 MHz), and Avance 500 (1H:
500.13 MHz, 13C: 125.76 MHz, 19F: 470.59 MHz, 31P: 202.46 Hz)
spectrometers. In the case of the 1H and 13C NMR, they were
referenced relative to the residual signal of the solvent63 while they
are given relative to CFCl3 in the case of the 19F NMR. Peak
multiplicities are marked as singlet (s), doublet (d), doublet of
doublet (dd), doublet of doublet of doublet (ddd), doublet of triplet
(dt), triplet (t), and multiplet (m), respectively and coupling
constants J are given in Hertz (Hz). The elemental composition of
the compounds was determined with an Elementar Vario MICRO
cube CHN analyzer. Addition of V2O5 was usually required to obtain
proper results in the case of the metal complexes.
constant of (7.3±0.1)
×
10-2 M-1 s-1, comparable to that
observed for some first-generation cyclic alkynes used in the
strain-promoted azide-alkyne cycloaddtion (SPAAC). The
analogous molybdenum complex reacted too fast for study
with NMR methods and attempts to also prepare the similar
chromium compound did not succeed due to very low stability
of the precursors. On the other hand, solution IR
measurements allowed the determination of pseudo-first
order rate constants for all four combinations of metal-azide
complexes and alkynes, which were found to be in a range of
Synthesis
[Mo(η3-allyl)Cl(bpy)(CO)2] (1). To a degassed mixture of
anhydrous tetrahydrofuran (20 mL) and allyl chloride (1.6 mL,
1.5 g, 19.7 mmol), molybdenum hexacarbonyl (500 mg, 1.9
mmol) and 2,2’-bipyridine (265 mg, 1.7 mmol) were added
under a dinitrogen atmosphere and the mixture heated to
reflux for 18 h. The resulting red precipitate was filtered from
0.4 to 6.5
×
10-3 s-1 and increased in the order of Mo > W and
F3C-C≡C-COOEt > DMAD. Thus, for the first time, there has
been a systematic evaluation of the effect of the metal center
on the kinetics of the iClick cycloaddition reaction of metal-
coordinated azides with electron-poor alkynes. In otherwise
isostructural and isoelectronic compounds, the 4d complex
was consistently found to react faster than the 5d analog. This
demonstrates that the kinetics of the iClick reaction of metal-
coordinated small ligands can be tuned not only by variation of
electron-withdrawing vs. electron-donating groups in the
periphery of the alkyne18 or the coligands,19 but also by
exchange of the metal itself. Thus, it is expected that this
reaction can be extended to additional transition metal azide
complexes and such experiments are currently under way. In
contrast, the choice of the alkyne seems to be much more
limited, as demonstrated by the failure of phenyl-
trifluoromethylacetylene to give any cycloaddition product,
even at elevated temperatures. More work will be required to
dissect the electronic and steric factors which govern the
reactivity of this component and establish a general building
block approach to metal-triazolate complexes.13
the purple solution, washed with n-hexane (4×25 mL) and
dried under vacuum to give a bright red solid. Yield: 76% (486
mg, 1.3 mmol). Elemental analysis (%): calc. C15H13ClMoN2O2: C
46.84, H 3.41, N 7.28, found: C 46.55, H 3.48, N 7.15; IR (ATR,
cm-1): 3064 (w), 2985 (w), 1925 (s, C
≡O), 1832 (s, C≡O), 1600
(m), 1469 (m), 1442 (m), 1310 (w), 1152 (w), 1024 (w), 769
(m); 1H NMR (DMSO-d6, 200.13 MHz, ppm):
δ major isomer:
8.77 (d, 2H, JH6,H5 = 4.9 Hz, bpy-H6), 8.56 (d, 2H, JH3,H4 = 8.0
3
3
3
Hz, bpy-H3), 8.17 (dt, 2H, JH4,H3/H5 = 8.0 Hz, JH4,H6 = 1.0 Hz,
4
3
bpy-H4), 7.63 (t, 2H, JH5-H4/H6 = 6.3 Hz, bpy-H5), 3.12–3.27 (m,
1H, allyl-Hmeso), 3.07 (d, 2H, 3JHsyn,Hmeso = 6.2 Hz, allyl-Hsyn), 1.23
3
(d, 2H, JHanti,Hmeso = 8.7 Hz, allyl-Hanti); minor isomer: 9.06 (d,
3
2H, JH6,H5 = 3.8 Hz, bpy-H6), 8.65 (d, 2H, JH3,H4 = 8.3 Hz, bpy-
3
3
H3), 8.26 (d, 2H, JH4,H3 = 8.3 Hz, bpy-H4), 7.79 (t, 2H, JH5 H4/H6
3
-
= 6.3 Hz, bpy-H5), 3.79–3.91 (m, 1H, allyl-Hmeso), 3.51 (d, 2H,
3
3JHsyn,Hmeso = 6.2 Hz, allyl-Hsyn), 1.36 (d, 2H, JHanti,Hmeso = 9.4 Hz,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 8 of 12
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
Journal Name
allyl-Hanti); 13C NMR (DMSO-d6, 50.32 MHz, ppm):
δ
major 13.13, found: C 47.03, H 3.58, N 13.14; IR (ATR, cm-1): 3071
O), 1856 (s, C O), 1723 (s, C=O),
139.18 (bpy-C4), 126.27 (bpy-C5), 122.98 (bpy-C3), 70.76 (CH- 1600 (w), 1439 (m), 1292 (w), 1220 (m), 1163 (m), 1090 (m),
allyl), 54.00 (CH2-allyl); minor isomer: the signal intensity was 764 (m); 1H NMR (DMSO-d6, 200.13 MHz, ppm):
major
isomer: 8.97 (dd, 2H, JH6,H5 = 5.5 Hz, JH6,H4 = 1.6 Hz, bpy-H6),
isomer: 227.13 (C
≡
O), 153.30 (bpy-C2), 151.85 (bpy-C6), (w), 2957 (w), 1931 (s, C
≡
≡
δ
3
4
below the detection limit.
[Mo(η3-allyl)(N3)(bpy)(CO)2] (2). To a suspension of [Mo(η3
3
3
-
8.54 (d, 2H, JH3,H4 = 8.0 Hz, bpy-H3), 8.16 (dt, 2H, JH4,H3/H5 =
4
3
allyl)Cl(bpy)(CO)2]
acetonitrile (50 mL) was added silver triflate (301 mg, 1.2 3JH5,H6 = 5.5 Hz, JH5,H3 = 1.6 Hz, bpy-H5), 3.63 (s, 6H, COOCH3),
mmol). white precipitate appeared and the resulting 3.31–3.33 (m, 2H, allyl-Hsyn, overlapping with water signal),
(1, 450 mg, 1.2 mmol) in degassed 8.0 Hz, JH4,H6 = 1.6 Hz, bpy-H4), 7.58 (ddd, 2H, JH5,H4 = 8.0 Hz,
4
A
3
suspension was stirred for 2 h under a dinitrogen atmosphere 3.06–3.21 (m, 1H, allyl-Hmeso), 1.49 (d, 2H, JHanti,Hmeso = 9.0 Hz,
under exclusion of light. The clear red solution was then allyl-Hanti); minor isomer: 9.19 (s, 2H, bpy-H6), 8.52–8.57 (m,
transferred with a teflon cannula into another flask containing 2H, bpy-H3), 8.18–8.25 (m, 2H, bpy-H4), 7.77–7.84 (m, 2H,
sodium azide (152 mg, 2.3 mmol) and stirred at room bpy-H5), 4.05–4.14 (m, 1H, allyl-Hmeso), 3.62 (s, 6H, COOCH3),
3
temperature for 19 h while protected from light. The resulting 3.45 (d, 2H, JHsyn,Hanti = 6.3 Hz, allyl-Hsyn), 1.47–1.54 (m, 2H,
red precipitate was filtered off, first washed with plenty of allyl-Hanti); 13C NMR (DMSO-d6, 50.32 MHz, ppm):
δ
major
O), 162.38 (C=O), 154.49 (bpy-C2), 152.24
×10 mL) and subsequently (bpy-C6), 139.55 (bpy-C4), 138.34 (triazolate-C4/C5), 126.36
water to remove excess sodium azide, and then with ethanol isomer: 226.31 (C
≡
(2×5 mL) followed by diethylether (2
dried under vacuum to give the product as a bright red solid. (bpy-C5), 122.76 (bpy-C3), 81.58 (CH-allyl), 57.56 (CH2-allyl),
Yield: 58% (258 mg, 0.7 mmol). Elemental analysis (%): calc. 51.64 (COOCH3); minor isomer: the signal intensity was below
C15H13MoN5O2: C 46.05, H 3.35, N 17.90, found: C 44.99, the detection limit.
H 3.38, N 18.04; IR (ATR, cm-1): 3083 (w), 2036 (s, azide), 1928 [Mo(η3-allyl)(triazolateCF3,COOEt)(bpy)(CO)2]
(6).
(s, C O), 1836 (s, C , 44 mg, 0.11 mmol) and 4,4,4-
≡
≡
O), 1600 (m), 1469 (m), 1440 (m), 1311 [Mo(η3-allyl)(N3)(bpy)(CO)2] (
2
(w), 1172 (w), 757 (m), 733 (w); 1H NMR (DMSO-d6, 200.13 trifluoro-2-butynoic acid ethyl ester (23 mg, 0.14 mmol) were
MHz, ppm): δ
= 0.9 Hz, bpy-H6), 8.57 (d, 2H, JH3,H4 = 8.2 Hz, bpy-H3), 8.20 temperature under exclusion of light for 4 d. Then, the solvent
major isomer: 8.80 (dd, 2H, 3JH6,H5 = 5.3 Hz, 4JH6,H4 dissolved in dichloromethane (15 mL) and stirred at room
3
3
(dt, 2H, JH4,H3/H5 = 7.9 Hz, JH4,H6 = 1.2 Hz, bpy-H4), 7.66 (ddd, was removed under vacuum and the red residue washed with
4
3
3
4
2H, JH5,H4 = 7.9 Hz, JH5,H6 = 5.4 Hz, JH5,H3 = 1.1 Hz, bpy-H5), n-hexane (3×5 mL). After drying under vacuum, the product
3.18–3.23 (m, 1H, allyl-Hmeso), 3.14 (d, 2H, JHsyn,Hmeso = 6.7 Hz, was obtained as a red solid. Yield: 55% (35 mg, 0.06 mmol).
3
3
allyl-Hsyn), 1.29 (d, 2H, JHanti,Hmeso = 8.9 Hz, allyl-Hanti); minor Elemental analysis (%): calc. C21H18F3MoN5O4: C 45.26, H 3.26,
isomer: 9.05 (m, 2H, bpy-H6), 8.69 (m, 2H, bpy-H3), 8.26 (m, N 12.57, found: C 45.26, H 3.34, N 12.38; IR (ATR, cm-1): 1938
2H, bpy-H4), 7.83 (m, 2H, bpy-H5), 3.71–3.89 (m, 1H, allyl- (s, C
≡
O), 1864 (s, C
Hmeso), 3.20 (d, 2H, JHsyn,Hmeso = 8.1 Hz, allyl-Hsyn), 1.36 (d, 2H, (m), 1472 (w), 1441 (m), 1310 (m), 1161 (m), 1132 (m), 1049
3JHanti,Hmeso = 9.0 Hz, allyl-Hanti); 13C NMR (DMSO-d6, 50.32 MHz, (m), 763 (w), 734 (m); 1H NMR (DMSO-d6, 199.93 MHz, ppm):
≡O), 1854 (s, C≡O), 1713 (m, C=O), 1604
3
δ
3
4
ppm):
δ major isomer: 227.20 (C≡O), 153.27 (bpy-C2), 151.85 major isomer: 8.79 (dd, 2H, JH6,H5 = 5.3 Hz, JH6,H4 = 0.9 Hz,
3
(bpy-C6), 139.48 (bpy-C4), 126.56 (bpy-C5), 123.04 (bpy-C3), bpy-H6), 8.56 (d, 2H, JH3,H4 = 8.2 Hz, bpy-H3), 8.18 (dt, 2H,
72.54 (CH-allyl), 55.78 (CH2-allyl); minor isomer: the signal 3JH4,H3/H5 = 7.9 Hz, 4JH4,H6 = 1.5 Hz, bpy-H4), 7.58 (ddd, 2H, 3JH5,H4
intensity was below the detection limit.
= 7.6 Hz, 3JH5,H6 = 5.5 Hz, 4JH5,H3 = 1.1 Hz, bpy-H5), 4.14 (q, 2H, 3J
[Mo(η3-allyl)(triazolateCOOCH3,COOCH3)(bpy)(CO)2] (5). Method A: = 7.2 Hz, COOCH2CH3), 1.52 (d, 2H, JHanti,Hmeso = 9.0 Hz, allyl-
3
[Mo(η3-allyl)(N3)(bpy)(CO)2]
dimethyl acetylenedicarboxylate (DMAD, 17 µL, 20 mg, 0.14 Hsyn, overlapping with solvent water signal; minor isomer not
(2,
44 mg, 0.11 mmol) and Hanti), 1.18 (t, 3H, 3J = 7.1 Hz, COOCH2CH3), allyl-Hmeso and allyl-
mmol) were dissolved in dichloromethane (15 mL) and stirred observed due to low signal intensity; 13C NMR (DMSO-d6, 50.27
for 36 h at room temperature under exclusion of light. The MHz, ppm):
δ major isomer: 154.71 (bpy-C2), 152.18 (bpy-C6),
resulting red solution was filtered through Celite. After 139.62 (bpy-C4), 126.33 (bpy-C5), 122.72 (bpy-C3), 60.23
concentration under vacuum, it was layered with n-hexane for (COOCH2CH3), 57.61 (CH2-allyl), 13.88 (COOCH2CH3), CO and
crystallization. After 3 d in the dark, the red needles obtained CH-allyl signals not observed due to low signal intensity; minor
were filtered off, washed with n-hexane and dried under isomer: the signal intensity was below the detection limit; 19F
vacuum. Yield: 45% (28 mg, 0.05 mmol). Method B: [Mo(η3
-
NMR (DMSO-d6, 188.12 MHz, ppm): δ -58.76 (CF3, major
allyl)(N3)(bpy)(CO)2] (62 mg, 0.16 mmol) and dimethyl-7-oxa- species, 80%), -58.56 (CF3, minor species, 14%), -57.53 (CF3,
bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (50 mg, 0.24 minor species, 6%).
mmol) were dissolved in dichloromethane (20 mL) and stirred [W(η3-allyl)Cl(bpy)(CO)2] (9). To
a
degassed mixture of
for 48 h at room temperature under exclusion of light. The anhydrous tetrahydrofuran (35 mL) and allyl chloride (4.98 mL,
solvent was removed under vacuum and the red residue 4.68 g, 61.2 mmol), solid [W(bpy)(CO)3(py)] ( , 1.03 g, 2.05
washed with ethyl acetate (3 5 mL) followed by n-hexane (3 mmol) was added and the reaction mixture heated to reflux
8
×
×5
mL) and subsequently dried under vacuum to give a red for 4.5 h. The resulting dark brown precipitate was filtered
powder. Yield: 75% (65 mg, 0.12 mmol). Experimental data is from the dark violet solution, washed with n-hexane (50 mL),
reported for the material obtained following procedure B: and dried under vacuum. Yield: 86% (836 mg, 1.77 mmol).
Elemental analysis (%): calc. C21H19MoN5O6: C 47.29, H 3.59, N Elemental analysis (%): calc. C15H13ClN2O2W⋅H2O: C 38.12, H
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 9 of 12
Journal Name
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
3
4
2.77, N 5.93, found: C 36.02, H 3.09, N 5.84; IR (ATR, cm-1): major isomer: 8.82 (dd, 2H, JH6,H5 = 5.5 Hz, JH6,H4 = 0.9 Hz,
3
2976 (m), 1915 (s), 1819 (s), 1601 (m), 1466 (m), 1445 (m), 773 bpy-H6), 8.61 (d, 2H, JH3,H4 = 8.2 Hz, bpy-H3), 8.24 (dt, 2H,
(s); 1H NMR (DMSO-d6, 500.13 MHz, ppm):
δ
8.81 (ddd, 2H, JH6,H5 = 5.5 Hz, JH6,H4 = 1.5 Hz, JH6,H3 = 0.6 Hz, = 7.5 Hz, JH5,H6 = 5.5 Hz, JH5,H3 = 1.1 Hz, bpy-H5), 3.63 (s, 6H,
major isomer: 3JH4,H3/H5 = 7.9 Hz, 4JH4,H6 = 1.5 Hz, bpy-H4), 7.61 (ddd, 2H, 3JH5,H4
3
4
5
3
4
bpy-H6), 8.64 (d, 2H, JH3,H4 = 8.2 Hz, bpy-H3), 8.24 (dt, 2H, COOCH3), 3.10 (d, 2H, 3JHsyn,Hmeso = 6.2 Hz, allyl-Hsyn), 2.29–2.37
3
3JH4,H3/H5 = 7.9 Hz, 4JH4,H6 = 1.6 Hz, bpy-H4), 7.67 (ddd, 2H, 3JH5,H4 (m, 1H, allyl-Hmeso), 1.68 (d, 2H, 3JHanti,Hmeso = 8.8 Hz, allyl-Hanti);
3
= 7.6 Hz, JH5,H6 = 5.5 Hz, JH5,H3 = 1.2 Hz, bpy-H5), 2.85 (d, 2H, minor isomer: 3.59 (s, COOCH3), the other signals were too
4
3JHsyn,Hmeso = 6.0 Hz, allyl-Hsyn), 2.29–2.37 (m, 1H, allyl-Hmeso), weak for clear identification; 13C NMR (DMSO-d6, 125.76 MHz,
3
1.45 (d, 2H, JHanti,Hmeso = 8.3 Hz, allyl-Hanti); minor isomer: 9.07 ppm):
δ 220.04 (C≡O), 162.12 (COOCH3), 155.53 (bpy-C2),
(m, 2H, bpy-H6), 8.72 (d, 2H, 3JH3,H4 = 8.1 Hz, bpy-H3), 8.28 (dt, 152.50 (bpy-C6), 139.83 (bpy-C4), 138.83 (triazolate-C4/C5),
3
4
2H, JH4,H3/H5 = 7.8 Hz, JH4,H6 = 1.3 Hz, bpy-H4), 7.82 (t, 2H, 127.19 (bpy-C5), 123.15 (bpy-C3), 65.48 (CH-allyl), 51.79
3JH5,H4/H6 = 6.4 Hz, bpy-H5), 3.30 (m, 2H, allyl-Hsyn), 3.05–3.14 (COOCH3), 49.45 (CH2-allyl); minor isomer: the signal intensity
3
(m, 1H, allyl-Hmeso), 1.50 (d, 2H, JHanti,Hmeso = 8.0 Hz, allyl-Hanti); was below the detection limit.
13C NMR (DMSO-d6, 125.76 MHz, ppm):
δ
major isomer: 220.52 [W(η3-allyl)(triazolateCF3,COOEt)(bpy)(CO)2]
(12).
25 mg, 0.05 mmol) was
in dichloromethane (5 mL). 4,4,4-Trifluoro-2-
allyl); minor isomer: the signal intensity was below the butynoic acid ethyl ester (17 mg, 0.10 mmol) was added and
detection limit. the reaction mixture stirred at room temperature for 6 d.
[W(η3-allyl)(N3)(bpy)(CO)2] (10). In a degassed mixture of Then, diethyl ether (30 mL) was added to precipitate the
methanol (100 mL) and acetone (25 mL), solid [W(η3
product from the dark red solution. The resulting red-brown
allyl)Cl(bpy)(CO)2] ( , 300 mg, 0.63 mmol) and sodium azide crystalline solid was filtered off, washed with diethyl ether (10
(C
≡ (10,
O), 154.17 (bpy-C2), 152.02 (bpy-C6), 139.36 (bpy-C4), [W(η3-allyl)(N3)(bpy)(CO)2]
127.03 (bpy-C5), 123.44 (bpy-C3), 62.96 (CH-allyl), 45.91 (CH2- dissolved
-
9
(207 mg, 3.18 mmol) were dissolved under argon and the mL), and dried under vacuum. Yield: 40% (12 mg, 0.02 mmol).
reaction mixture heated to reflux for 6 h. The resulting Elemental analysis (%): calc. C21H18F3N5O4W: C 39.09, H 2.81, N
precipitate was filtered off from the dark red solution, washed 10.85, found: 39.09, H 2.86, N 10.56; IR (ATR, cm-1): 1929 (s),
with water (80 mL) and methanol (40 mL), and dried under 1850 (s), 1723 (s); 1H NMR (DMSO-d6, 500.13 MHz, ppm):
δ
vacuum to result in a red-brown solid. Yield: 62% (189 mg, 0.39 major isomer: 8.83 (dd, 2H, JH6,H5 = 5.4 Hz, JH6,H4 = 0.8 Hz,
3
4
3
mmol). Elemental analysis (%): calc. C15H13N5O2W: C 37.60, H bpy-H6), 8.64 (d, 2H, JH3,H4 = 8.2 Hz, bpy-H3), 8.25 (dt, 2H,
2.73, N 14.62, found: C 37.57, H 2.70, N 14.57; IR (ATR, cm-1): 3JH4,H3/H5 = 7.9 Hz, 4JH4,H6 = 1.6 Hz, bpy-H4), 7.61 (ddd, 2H, 3JH5,H4
2046 (vs), 1920 (s), 1821 (vs), 1602 (m), 1471 (m), 1442 (m), = 7.5 Hz, 3JH5,H6 = 5.5 Hz, 4JH5,H3 = 1.1 Hz, bpy-H5), 4.14 (q, 2H, 3J
3
756 (m); 1H NMR (DMSO-d6, 500.13 MHz, ppm):
δ
isomer: 8.84 (ddd, 2H, JH6,H5 = 5.4 Hz, JH6,H4 = 1.4 Hz, JH6,H3
major = 7.1 Hz, COOCH2CH3), 3.13 (d, 2H, JHsyn,Hmeso = 6.2 Hz, allyl-
3
Hsyn), 2.37–2.44 (m, 1H, allyl-Hmeso), 1.71 (d, 2H, JHanti,Hmeso =
3
4
5
=
3
0.5 Hz, bpy-H6), 8.64 (d, 2H, JH3,H4 = 8.2 Hz, bpy-H3), 8.27 (dt, 8.8 Hz, allyl-Hanti), 1.17 (t, 3H, J = 7.1 Hz, COOCH2CH3); minor
2H, JH4,H3/H5 = 7.9 Hz, JH4,H6 = 1.6 Hz, bpy-H4), 7.70 (ddd, 2H, isomer: signals were too weak for clear identification; 13C NMR
3
3
4
3JH5,H4 = 7.6 Hz, 3JH5,H6 = 5.5 Hz, 4JH5,H3 = 1.2 Hz, bpy-H5), 2.95 (d, (DMSO-d6, 125.76 MHz, ppm):
δ major isomer: 219.88 (C≡O),
2H, JHsyn,Hmeso = 6.2 Hz, allyl-Hsyn), 2.35–2.43 (m, 1H, allyl- 159.69 (COOCH2CH3), 155.70 (bpy-C2), 152.45 (bpy-C6), 139.85
3
3
2
Hmeso), 1.48 (d, 2H, JHanti,Hmeso = 8.7 Hz, allyl-Hanti); minor (bpy-C4), 137.07 (q, JC,F = 37.1 Hz, triazolate-C4), 136.18 (m,
isomer: 9.07 (m, 2H, bpy-H6), 8.75 (d, 2H, 3JH3,H4 = 8.0 Hz, bpy- 3JC,F < 0.6 Hz, triazolate-C5), 127.13 (bpy-C5), 123.09 (bpy-C3),
3
H3), 8.32 (dt, 2H, JH4,H3/H5 = 7.7 Hz, JH4,H6 = 1.2 Hz, bpy- 121.09 (q, JC,F
4
1
= 268 Hz, CF3), 65.39 (CH-allyl), 60.39
3
H4), 7.86 (t, 2H, JH5,H4/H6 = 6.2 Hz, bpy-H5), 3.18 (d, 2H, (COOCH2CH3), 49.50 (CH2-allyl), 13.85 (COOCH2CH3); minor
3JHsyn,Hmeso = 6.1 Hz, allyl-Hsyn), 3.02–3.13 (m, 1H, allyl-Hmeso), isomer: the signal intensity was below the detection limit; 19F
1.51 (d, 2H, 3JHanti,Hmeso = 9.0 Hz, allyl-Hanti); 13C NMR (DMSO-d6, NMR (DMSO-d6, 470.59 MHz, ppm):
δ
-58.95 (CF3, major
125.76 MHz, ppm): δ major isomer: 220.57 (C≡O), 154.14 (bpy- species, 88%), -58.70 (CF3, minor species, 12%).
C2), 152.06 (bpy-C6), 139.70 (bpy-C4), 127.30 (bpy-C5), 123.44 X-ray diffraction analysis
(bpy-C3), 65.12 (CH-allyl), 47.91 (CH2-allyl); minor isomer: the
Single crystals suitable for X-ray structure determination of 2,
signal intensity was below the detection limit.
[W(η3-allyl)(triazolateCOOCH3,COOCH3)(bpy)(CO)2]
5, 6, 11, and 12 were obtained by slow diffusion of n-hexane
(11).
into a solution of the compound in dichloromethane while 10
[W(η3-allyl)(N3)(bpy)(CO)2]
(10, 30 mg, 0.06 mmol) was
was recrystallized from a mixture of acetone and methanol.
dissolved in dichloromethane (3 mL). Dimethyl acetylene-
dicarboxylate (DMAD, 31 µL, 35.6 mg, 0.25 mmol) was added
and the reaction mixture stirred at room temperature for 5 d.
Then, diethyl ether (50 mL) was added to precipitate the
product from the red-brown solution. The resulting brown
crystalline solid was filtered off, washed with diethyl ether (10
mL), and dried under vacuum. Yield: 83% (33 mg, 0.05 mmol).
Elemental analysis (%): calc. C21H19N5O6W: C 40.60, H 3.08, N
11.27, found: 39.87, H 3.29, N 10.82; IR (ATR, cm-1): 1921 (s),
Selected crystals were immersed in
a
film of
perfluoropolyether oil, mounted on a polyimide microloop
(MicroMounts, MiTeGen) or glass fiber, and transferred to a
stream of cold dinitrogen (Bruker Kryoflex2). Crystal data for
10 11 and 12 were obtained on a BRUKER X8-APEX II while
data for was collected on BRUKER SMART-APEX
diffractometer. Both instruments were equipped with a CCD
area detector and used graphite monochromated MoK
2,
6,
,
5
a
α
radiation. The structures were solved using the intrinsic
1841 (s), 1724 (s); 1H NMR (DMSO-d6, 500.13 MHz, ppm):
δ
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 10 of 12
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
Journal Name
phasing method,64 refined with the SHELXL program65 and
expanded using Fourier techniques. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included in
structure factors calculations. All hydrogen atoms, except
those of the allyl moiety in some cases, were assigned to
idealised positions. The coordinates of the hydrogen atoms of
the allyl moiety were refined freely. The C–H distances in the
allyl moiety were restrained to a values of 0.950(5) Å during
the refinement. Crystallographic data has been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publications no. CCDC-1562700–1562705. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
8
M. Grammel and H. C. Hang, Nature Chem. Biol., 2013, 9,
475.
C. P. Ramil and Q. Lin, Chem. Commun., 2013, 49, 11007.
K. Lang and J. W. Chin, Chem. Rev., 2014, 114, 4764.
N. K. Devaraj and R. Weissleder, Acc. Chem. Res., 2011,
44, 816.
T. J. Del Castillo, S. Sarkar, K. A. Abboud and A. S. Veige,
Dalton Trans., 2011, 40, 8140.
L. Cararrubios, M. C. de la Torre and M. A. Sierra, Chem.
Eur. J., 2013, 19, 3534.
9
10
11
12
13
14
15
16
H.-W. Frühauf, Chem. Rev., 1997, 97, 523.
H.-W. Frühauf, Coord. Chem. Rev., 2002, 230, 79.
W. P. Fehlhammer and W. Beck, Z. Anorg. Allg. Chem.,
2015, 641, 1599.
17
18
19
20
21
22
23
24
25
26
C. C. Beto, E. D. Holt, Y. Yang, I. Ghiviriga, K. S. Schanze
and A. S. Veige, Chem. Commun., 2017, 53, 9934.
A. R. Powers, I. Ghiviriga, K. A. Abboud and A. S. Veige,
Dalton Trans., 2015, 44, 14747.
L. Waag-Hiersch, J. Mößeler and U. Schatzschneider, Eur.
J. Inorg. Chem., 2017, 3024.
J. A. Krause-Bauer, T. M. Becker and M. Orchin, J. Chem.
Cryst., 2004, 34, 843.
K. Pachhunga, B. Therrien and M. R. Kollipara, Inorg.
Chim. Acta, 2008, 361, 3294.
F.-C. Liu, Y.-L. Lin, P.-S. Yang, G.-H. Lee and S.-M. Peng,
Organometallics, 2010, 29, 4282.
K. Agapiou, R. A. Jones and X. Yang, Main Group Chem.,
2010, 9, 41.
Y.-H. Lo, T.-H. Wang, C.-Y. Lee and Y.-H. Feng,
Organometallics, 2012, 31, 6887.
DFT calculations
DFT calculations were carried out on the Linux cluster of the
Leibniz-Rechenzentrum (LRZ) in Munich with ORCA version
2.8,66 using the BP86 functional with the resolution-of-the-
identity (RI) approximation, a def2-TZVP/def2-TZVP/J basis set,
the tightscf and grid4 options, and the COSMO solvation
model with dimethylsulfoxide as the solvent for geometry
optimization and subsequent calculation of vibrational
frequencies to characterize the structure obtained as a
minimum by inspection for absence of imaginary modes. Then,
a relaxed surface scan was carried out in 15° steps for the full
360° rotation of the triazolate ring relative to the central C–C2
axis of the 2,2'-bipyridine ligand while allowing all other
variables to relax. The maxima located on the resulting
potential energy curve where then further characterized as
transition states using the optTS keyword in separate runs.
S. Miguel-Fernandez, S. M. de Salinas, J. Diez, M. P.
Gamasa and E. Lastra, Inorg. Chem., 2013, 52, 4293.
F.-C. Liu, J.-E. Liang, J.-Y. Jin, Y.-L. Lin, Y.-J. Chu, P.-S. Yang,
G.-H. Lee and S.-M. Peng, J. Organomet. Chem., 2013,
735, 1.
27
28
T. Cruchter, K. Harms and E. Meggers, Chem. Eur. J., 2013,
19, 16682.
L. Henry, C. Schneider, B. Mützel, P. V. Simpson, C. Nagel,
K. Fucke and U. Schatzschneider, Chem. Commun., 2014,
50, 15692.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
29
30
31
K. S. Singh, K. A. Kreisel, G. P. A. Yap and M. R. Kollipara, J.
Organomet. Chem., 2006, 691, 3509.
H. Pfeiffer, M. Dragoun, A. Prokop and U.
Schatzschneider, Z. Anorg. Allg. Chem., 2013, 639, 1568.
T. S. A. Hor and S.-M. Chee, J. Organomet. Chem., 1987,
331, 23.
This
work
was
supported
by
the
Deutsche
Forschungsgemeinschaft (DFG) with grants no. SCHA962/3-1
and SCHA962/8-1 to U.S.
32
33
H. Behrens and N. Harder, Chem. Ber., 1964, 97, 433.
S. S. van Berkel, T. J. Dirks, M. F. Debets, F. L. van Delft, J.
J. L. M. Cornelissen, R. J. M. Nolte and F. P. J. T. Rutjes,
ChemBioChem, 2007, 8, 1504.
J. E. Bunch and C. L. Bumgardner, J. Fluorine Chem., 1987,
36, 313.
B. C. Hamper, Org. Synth., 1992, 70, 246.
Y. Kobayashi, T. Yamashita, K. Takahashi, H. Kuroda and I.
Kumadaki, Tetrahedron Lett., 1982, 23, 343.
G. Meazza and G. Zanardi, J. Fluorine Chem., 1991, 55,
199.
S. T. D. Gough and S. Trippett, J. Chem. Soc., 1962, 2333.
Y. Kobayashi, T. Yamashita, K. Takahashi, H. Kuroda and I.
Kumadaki, Chem. Pharm. Bull., 1984, 32, 4402.
F. Eymery, B. Iorga and P. Savignac, Synthesis, 2000, 185.
Z. Dori and R. F. Ziolo, Chem. Rev., 1973, 73, 247.
References
1
2
3
4
5
6
7
H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem.
Int. Ed., 2001, 40, 2004.
H. C. Kolb and K. B. Sharpless, Drug Discovery Today,
2003, 8, 1128.
J. E. Moses and A. D. Moorhouse, Chem. Soc. Rev., 2007,
36, 1249.
P. Thirumurugan, D. Matosiuk and K. Jozwiak, Chem. Rev.,
2013, 113, 4905.
J. A. Prescher and C. R. Bertozzi, Nature Chem. Biol., 2005,
1, 13.
C. R. Bertozzi and E. M. Sletten, Angew. Chem. Int. Ed.,
2009, 48, 6974.
34
35
36
37
38
39
40
41
R. K. V. Lim and Q. Lin, Chem. Commun., 2010, 46, 1589.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 11 of 12
Journal Name
View Article Online
DOI: 10.1039/C7DT03096G
ARTICLE
42
43
44
45
46
47
J. W. Faller, D. A. Haitko, R. D. Adams and D. F. Chodosh, J.
Am. Chem. Soc., 1979, 101, 865.
J. W. Faller and B. C. Whitmore, Organometallics, 1986, 5,
752.
M. J. Calhorda and P. J. Costa, Coord. Chem. Rev., 2017,
344, 83.
D. E. Ryan, D. J. Cardin and F. Hartl, Coord. Chem. Rev.,
2017, 335, 103.
A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G.
Watson and R. Taylor, Dalton Trans., 1989, S1.
E. O. Fischer, D. Wittmann, D. Himmelreich, R. Cai, K.
Ackermann and D. Neugebauer, Chem. Ber., 1982, 115,
3152.
48
49
50
51
52
53
54
55
56
D. Sellmann, W. Weber, G. Liehr and H. P. Beck, J.
Organomet. Chem., 1984, 269, 155.
H. Wadle, E. Conradi, U. Müller and K. Dehnicke, Z.
Naturforsch. B, 1985, 40, 1626.
D. Fenske, A. Frankenau and K. Dehnicke, Z. Anorg. Allg.
Chem., 1989, 579, 27.
H.-W. Lam, G. Wilkinson, B. Hussian-Bates and M. B.
Hursthouse, Dalton Trans., 1993, 781.
D. Rische, A. Baunemann, M. Winter and R. A. Fischer,
Inorg. Chem., 2006, 45, 269.
F.-C. Liu, T.-C. Tsai, Y.-L. Lin, C.-S. Lee, P.-S. Yang and J.-C.
Wang, J. Organomet. Chem., 2010, 695, 423.
R. Haiges, J. Skotnitzki, Z. Fang, D. A. Dixon and K. O.
Christe, Angew. Chem. Int. Ed., 2015, 54, 9581.
R. Haiges, J. Skotnitzki, Z. Fang, D. A. Dixon and K. O.
Christe, Angew. Chem. Int. Ed., 2015, 54, 15550.
J. Pérez, V. Riera, A. Rodríguez, R. López, T. L. Sordo, S.
García-Granda, E. García-Rodríguez and A. Galindo,
Organometallics, 2003, 22, 1540.
57
58
59
60
61
K.-B. Shiu, S.-T. Lin, D.-W. Fung, T.-J. Chan, S.-M. Peng, M.-
C. Cheng and J. L. Chou, Inorg. Chem., 1995, 34, 854.
C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91,
165.
A. R. Powers, X. Yang, T. J. Del Castillo, I. Ghiviriga, K. A.
Abboud and A. S. Veige, Dalton Trans., 2013, 42, 14963.
E. Evangelino, N. P. Rath and L. M. Mirica, Dalton Trans.,
2012, 41, 8010.
E. A. Giner, M. Gomez-Gallego, L. Casarrubios, M. C. de la
Torre, C. R. de Arellano and M. A. Sierra, Inorg. Chem.,
2017, 56, 2801.
62
63
E. Hirota, S. Saito and Y. Endo, J. Chem. Phys., 1979, 71,
1183.
G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb,
A. Nudelman, B. M. Stoltz, J. E. Bercaw and K. I. Goldberg,
Organometallics, 2010, 29, 2176.
64
65
66
G. M. Sheldrick, Acta Cryst. A, 2015, A71, 3.
G. M. Sheldrick, Acta Cryst. A, 2008, A64, 112.
F. Neese, WIREs Comput. Mol. Sci., 2011, 2, 73.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Dalton Transactions
Page 12 of 12
View Article Online
DOI: 10.1039/C7DT03096G
254x190mm (96 x 96 DPI)