Utility of Three-Coordinate Silver Complexes Toward
the Formation of Iodonium Ions
The work herein describes the synthesis of five three-coordinate silver(I) complexes comprising a bidentate ligand L1, either bpy (2,2′-bipyridyl) or bpyMe2 (4,4′-dimethyl-2,2′-dipyridyl), and a monodentate ligand L2, either mtz (1-methyl-1H-1,2,3-triazole), 4-Etpy (4-ethylpyridine), or 4-DMAP (N,N-dimethylpyridin-4-amine). Upon reaction of the three-coordinate silver(I) complexes with 0.5 equiv of I2, the reactions quantitatively produce a 1:1 pair of complexes of a four-coordinate silver(I) complex [Ag(L1)2]PF6 and a two-coordinate iodonium complex [I(L2)2]PF6. The combination of [Ag(bpyMe2)2]PF6 and [I(4-DMAP)2]PF6 gave rise to an I+···Ag+ interaction where the I+ acts as a nucleophile, only the second example of which, that was observed in both the solution (NMR) and solid (X-ray) states.
Introduction<!><!>Results
and Discussion<!><!>Results
and Discussion<!><!>Results
and Discussion<!><!>Results
and Discussion<!><!>Results
and Discussion<!><!>Results
and Discussion<!><!>Conclusions<!>General Considerations<!>Preparation of [Ag(bpyMe2)(mtz)]PF6 (2)<!>Preparation
of [Ag(bpy)(4-Etpy)]PF6 (3)<!>Preparation of [Ag(bpyMe2)(4-Etpy)]PF6 (4)<!>Preparation
of [Ag(bpy)(4-DMAP)]PF6 (5)<!>Preparation of [Ag(bpyMe2)(4-DMAP)]PF6 (6)<!>Formation of
the Ag+/I+ Pairs of Complexes
(8–12)<!>Pair
of Complexes 8<!>Pair of Complexes 9<!>Pair of Complexes 10<!>Pair of Complexes 11<!>Pair of Complexes 12<!>Preparation
of [Ag(bpyMe2)2]PF6 (13)<!><!>Accession Codes<!>Author Contributions<!>
<p>The pursuit of new
halonium ion motifs has been ongoing since their
popularization in the 1990s,1−4 three decades after first being described in the
literature,5,6 which was fueled by Barluenga using his reagent [I(pyridine)2]BF4 (Barluenga's
reagent) to demonstrate their great utility toward a myriad of organic
transformations such as the electrophilic iodonation of unactivated
arenes, the promotion of C–C and C–X bond formation,
and the selective direct iodonation of peptides.7−9 However, while
the reactivity of halonium ions is well explored territory, the properties
of these species in themselves are less well studied, undoubtedly
due to difficulties that arise from the aforementioned reactivity.</p><p>The formation of X+ halonium ions (X = Br, I) via a
cation exchange process is well established,4,10−13 where the respective two-coordinate silver(I) complex is first synthesized
and then reacted with elemental halogens X2 (X = Br, I)
to yield the desired two-coordinate halonium complex through loss
of AgX. This process can be extended to chlorine; however, the reactivity
increases (and stability decreases) in the order I > Br ≫
Cl,
which is reflected in the literature with very few examples of chloronium (Cl+) ions existing.2,14,15</p><p>While three-coordinate
silver(I) complexes are not as common as
their two- and four-coordinate counterparts, they are still well accounted
for in the literature.16−19 However, their use as precursors toward the synthesis of halonium
ions via cation exchange was only recently reported,20 opening up the possibility of a new pool of potential silver(I)
precursors that could be used to synthesize desirable halonium complexes.
The derivatives of this first example of a three-coordinate silver(I)
complex successfully reacting to a combination of a halonium ion and
a silver(I) complex, by what could be described as a partial cation exchange, demonstrated a highly interesting and previously
unknown interaction in which the I+ was acting as a nucleophile
toward the Ag+ (I+···Ag+ = 3.4608(3) Å; Figure 1). Utilizing the same strategy of performing a partial cation
exchange on a three-coordinate silver(I) complex, herein, the second
example of this "nucleophilic" I+ interaction
is reported between a pair of complexes synthesized directly from
a three-coordinate silver(I) precursor. The nature of the I+···Ag+ has been analyzed using DFT calculations
(M06-2X/def2-QZVP) combined with the quantum theory of "atoms-in-molecules"
(QTAIM), the noncovalent interaction plot (NCIPlot) index, and the
natural bond orbital (NBO) analyses.</p><!><p>Single-crystal X-ray structure of the
first I+—Ag+ interaction (3.4608(3) Å;
indicated with a red dotted
line) of an iodonium ion acting as a nucleophile (thermal ellipsoids
at 50% probability; PF6 anions and hydrogen atoms omitted
for clarity). Color key: purple = iodine, light gray = silver, blue
= nitrogen, dark gray = carbon.</p><!><p>The first examples of heteroleptic halonium
complexes highlighted
that halonium ions can,21−24 if suitable ligands are present, undergo ligand scrambling
in solution.25 It has also been reported
that silver(I) complexes bearing bidentate ligands such as [Ag(bpy)2]PF6 (bpy = 2,2′-bipyridyl) are resistant
to such processes and remained steadfastly coordinated to the Ag+ in solution when either I2 or iodonium ions were
added.20 Therefore, the pursuit of the
nucleophilic I+ interaction would be facilitated by testing bis(bidentate)silver(I) complexes as potential Lewis acid
acceptors. The partial cation exchange process of three-coordinate
silver(I) complexes adeptly yields the stoic bis(bidentate)silver(I)
complexes concomitantly with the iodonium ion in the desired 1:1 stoichiometry,
making them ideal to generate pairs of complexes in search for more
instances of nucleophilic halonium interactions. This strategy bypasses
the need to separately synthesize and, more challengingly, isolate
and quantify the often highly reactive halonium species. Instead generating
the reactive halonium ion in situ only when it is
required. The combination of a monodentate and a bidentate ligand
also brings the problem of ligand scrambling to heel, whereupon it
works with the strategy toward the desired outcome, rather than against
it.</p><p>The new three-coordinate silver(I) complexes 2–6 were synthesized straightforwardly in good
yields and show
no degradation over time as solids (Scheme 1), though some care must be taken due to
their mild light sensitivity while they are in solution. The 1H NMR spectra of complexes 2–6 were as expected and warrant no further comment. The 15N NMR shifts were determined by 1H–15N HMBC NMR experiments, and the bpy nitrogen atoms in complexes 1 (−111.5 ppm), 3 (−110.1 ppm),
and 5 (−108.7 ppm) were found not to deviate more
than 5 ppm from the bpy resonances of [Ag(bpy)2]PF6 (cf. – 106.5 ppm), with the largest
deviation found to be for the mtz (1-methyl-1H-1,2,3-triazole) derivative 1. A similar trend of the resonances for the bpyMe2 (4,4′-dimethyl-2,2′-dipyridyl) nitrogen atoms not
deviating more than 5 ppm from those of [Ag(bpyMe2)2]PF6 (cf. – 114.4 ppm)
was also observed for complexes 2 (−119.2 ppm), 4 (−117.9 ppm), and 6 (−116.5 ppm),
once again with the largest deviation observed for the mtz derivative 2.</p><p>All three-coordinate geometries for complexes 2–6 were confirmed in the solid state
by single-crystal X-ray
diffraction (Figure 2). Complexes 2 and 6 were observed as discrete
"monomeric" complexes, 3 and 5 were observed as argentophilic dimers with Ag+—Ag+ distances of 3.1664(5) and 3.231(3) Å, respectively,
and 4 was observed as an argentophilic polymer (Ag+—Ag+ distances of 3.3314(7) and 3.3526(8)
Å). The monodentate (mtz, 4-Etpy (4-ethylpyridine), 4-DMAP (N,N-dimethylpyridin-4-amine)), and bidentate
(bpy, bpyMe2) ligands were found to be effectively coplanar
in all complexes (2–6), with the
exception of one ring of a bpy ligand in 5 (of one of
the two crystallographically independent molecules present in the
asymmetric unit cell of 5) deviating significantly out
of the plane by 33.7°. The coordination geometries were predominantly
observed to be distorted trigonal planar for 2, 3, 6, and one of the two crystallographically
independent molecules of 4 and 5, with N(monodentate)–Ag+–N(bidentate) angles in the range of 129.2(1)–158.0(1)°.
However, one of the two crystallographically independent molecules
of 4 and 5 did display significant deviation
of this trigonal planar geometry with the example in 4 having N(monodentate)–Ag+–N(bidentate)
angles of 123.0(2) and 164.7(2)° and the example in 5 having the more divergent angles of 115.3(1) and 170.2(1)°
(it should be noted that in both of these instances, the AgN3 planes remain effectively planar, with the aforementioned deviations
occurring within the plane). These two examples can be viewed as a
distorted linear geometry between the monodentate ligand and one of
the two coordinating pyridyl groups of the bidentate ligand, with
the second pyridyl being only a pendant group that was only weakly
coordinating to the Ag+, evidenced by their much longer
Ag+–N bond lengths of 2.374(4) Å for 4 and 2.535(4) for 5 (cf. all
other Ag+–N(bidentate) bonds that are within the
range 2.249(4)–2.335(3) Å).</p><!><p>Single-crystal X-ray
structures of complexes 2–6, annotated
with the N(monodentate)–Ag+–N(bidentate)
angles in red (thermal ellipsoids at 50% probability;
PF6 anions omitted for clarity). Color key: light gray
= silver, blue = nitrogen, dark gray = carbon, white = hydrogen.</p><!><p>In the same manner as reported for the pair of
complexes 7, two equivalents of the three-coordinate
silver(I) complexes
(2–6) were reacted with 1 equiv of
elemental iodine to generate the pairs of complexes 8–12 (Scheme 2).</p><p>The partial cation exchanges proceeded rapidly
upon addition of
the I2, with immediate precipitation of AgI observed, and
all reactions were found to have gone to completion within 5 min by 1H NMR spectroscopy. The 1H NMR spectra had observable
shift changes of all resonances for the pairs of complexes (8–12) relative to their three-coordinate
silver(I) precursors (2–6) with modest,
but definitive, shifts (Figure 3) observed upon formation of the pairs of complexes, with
maximum shifts changes (ΔδH) observed for the
aromatic hydrogen atoms of 0.07 ppm (4 → 10),
0.08 ppm (3 → 9, 6 → 12),
0.09 ppm (2 → 8), and 0.14 ppm (5 →
11). The identity of all the pairs of complexes (8–12) as such was readily determined by 1H NMR spectroscopy by comparison to the spectra of their respective
individual pure I+ and Ag+ components, which
had all been described previously in the literature with the exception
of [Ag(bpyMe2)2]PF6 (13), that was subsequently synthesized and fully characterized for
that explicit purpose. Only very minor differences, that could be
considered within the error of the measurements and therefore negligible,
were observed in the 1H NMR spectra when comparing the
respective individual pure I+ and Ag+ components
to the pairs of complexes (8–12),
which was similarly observed in the effectively indistinguishable 15N NMR values for 8, 9, 10, and 11 (Tables S1 and S2). However, as was reported for the pair of complexes 7 which displayed a −2.9 ppm shift of the bpy nitrogen atoms
in [Ag(bpy)2]PF6 upon addition of 1 equiv of
[I(mtz)2]PF6, a similar divergence was observed
for the pair of complexes 12. A 15N NMR chemical
shift change of 2.3 ppm was observed between that of the individual
complex 13 (−114.4 ppm) and the [Ag(bpyMe2)2]PF6 component of the pair of complexes 12 (−112.1 ppm), indicating the presence of an I+···Ag+ interaction in solution.
It should be noted that no distinguishable 15N NMR chemical
shift change was observed for the [I(4-DMAP)2]PF6 component of 12 (−216.0 ppm) when compared to
the value of the individual spectrum of [I(4-DMAP)2]PF6 (−216.1 ppm), once again reminiscent of what was observed
for the pair of complexes 7.</p><!><p>Superimposed 1H NMR spectra (between 6 and 9 ppm) of
complex 6 (red) and the resulting pair of complexes 12 (cyan) that resulted after addition of 0.5 equiv of I2.</p><!><p>The pair of complexes 7 was reported to form a nucleophilic
iodonium interaction that was observed in both the solution and solid
states. Extensive attempts were made to generate similarly interacting
cocrystals of all pairs of complexes (8–12) generated in this study, varying conditions such as solvents,
antisolvents, and the crystallization method used, though for 8, 9, and 11 only crystals of their
respective pure Ag+ or I+ components were observed.
A noninteracting cocrystal 10 was successfully generated,
with the [I(4-Etpy)2]PF6 complex as a minor
solvate in the channels of polymerically packed [Ag(bpyMe2)2]PF6 complexes connected by argentophilic
interactions (Ag+—Ag+ distances of 3.444(1),
3.456(2), 3.590(2), 3.735(2), and 3.866(1) Å), with a crystallographic
Ag+:I+ ratio of 5:1. Serendipitously, this is
the first time [I(4-Etpy)2]+ has been observed
in the solid state as it proved unobtainable and defied crystallization
as the pure species, possibly due to decomposition when concentrated,
which is a necessary process of any solution-based crystallization
method. The I+–N bond distances were 2.25(1) and
2.26(1) Å, which are within the expected range based on other
previously reported examples of halonium ions,11,25 and therefore warrant no further comment.</p><p>In addition to the
first literature example in the pair of complexes 7,
a second example of an I+ ion acting as a nucleophile
was successfully observed for the pair of complexes 12 (Figure 4). It should
be noted that the success of 7 and 12 is
consistent with 15N NMR observations (vide supra), so the labor-intensive practice of testing the unit cells of a
statistically valid number of crystals in ultimately unsuccessful
combinations of potential cocrystals could possibly be replaced; instead,
the easier and more indicative process of 15N NMR screening
could be used to select combinations that have a higher chance of
success prior to attempts to more definitively confirm this interaction
in the solid state.</p><!><p>Single-crystal X-ray structure of the pair of complexes 12, showing the I+—Ag+ (3.4043(4)
Å)
interaction (thermal ellipsoids at 50% probability; PF6 anions and hydrogen atoms omitted for clarity). Color key: purple
= iodine, light gray = silver, blue = nitrogen, dark gray = carbon.</p><!><p>The solid-state structure of the pair of complexes 12 exhibits the second and shortest example of an iodonium
complex
acting as a nucleophile, with an I+···Ag+ distance of 3.4043(4) Å (cf. 3.4608(3)
Å for 7). Unlike in 7 where the structural
details closely resembled their individual I+ and Ag+ components, the structure of the [I(4-DMAP)2]+ component in 12 was observed to have significantly
changed to accommodate the I+···Ag+ interaction. This is most obviously apparent in the loss of coplanarity
of the two 4-DMAP ligands, with a 32.9° angle between the two
NC5 planes of the 4-DMAP aromatic rings (cf. the 3.6° angle between the two NC5 planes for pure
[I(4-DMAP)2]PF6). The pair of cations of 12, [I(4-DMAP)2]+ and [Ag(bpyMe2)2]+, pack in an alternating polymeric
fashion creating a second, but longer, I+···Ag+ distance of 3.8005(4) Å (Figure 5), which is noticeably longer than the van
der Waals radii of the respective atoms (cf. van
der Waals radii of silver + iodine = 3.70 Å). This polymeric
array of alternating I+/Ag+ units creates continuous
off-center π-stacking interactions between the 4-DMAP and bpyMe2 ligands, with centroid–centroid distances of the NC5 aromatic rings of 3.599 and 3.610 Å, similar to those
observed in 7 (centroid–centroid distances between
NC5 and N3C2 rings = 3.540, 3.675,
3.738, 3.771 Å). The I+–N (2.251(3) Å;
a crystallographic symmetry operation generates half of the cocrystal
structure) and Ag+–N (2.343(2) and 2.358(3) Å)
bond lengths of 12 showed no crystallographically distinguishable
difference from the solid-state structures of their pure individual
components [I(4-DMAP)2]PF6 (I+–N
= 2.236(3), 2.251(3) Å) and [Ag(bpyMe2)2]PF6 (13_1: Ag+–N range
= 2.265(2)–2.400(2) Å; 13_2: Ag+–N range = 2.251(8)–2.42(1) Å).</p><!><p>Packing of three molecules
of the pair of complexes 12, showing the second, longer
I+···Ag+ (3.8005(4) Å) spacing
observed between the pairs of
complexes in their solid-state packing (thermal ellipsoids at 50%
probability; PF6 anions and hydrogen atoms omitted for
clarity). Color key: purple = iodine, light gray = silver, blue =
nitrogen, dark gray = carbon.</p><!><p>While there is only one prior example of a halonium ion acting
as a nucleophile, there are examples of neutral iodine
atoms donating to silver(I). In the literature, six solid-state examples
were found of (R)I–Ag+ interactions, with bond lengths
ranging from 2.8354(8) to 3.2877(6) Å,26−29 though only two of those examples
contain comparable motifs: one based on a substituted iodophenyl group
as the donor of the neutral iodine (3.2877(6) Å)26 and the other with a substituted iodopyrimidine group as
the donor (3.1875(8) Å).27</p><p>The
intriguing solid-state structure of compound 12 has been
further analyzed by DFT calculations in order to shed light
on the nature of the I+···Ag+ interaction. The geometry of the fully optimized compound 12 is given in Figure S32, showing
a geometry that is similar to the one observed experimentally. It
also shows a marked loss of coplanarity of the two 4-DMAP ligands
and the counterintuitive I+···Ag+ interaction, which is maintained in the isolated dimer. The QTAIM
analysis combined with the NCIPlot is represented in Figure 6, where the X-ray geometry
has been used. The distribution of critical points (CPs) and bond
paths confirms the coexistence of the I+···Ag+ interaction and π-stacking forces. That is, a bond
CP (red sphere) and bond path interconnect the Ag and I atoms. Moreover,
the π-stacking is characterized by three bond CPs that interconnect
two C atoms and the exocyclic N atom of each 4-DMAP ligand to three
C atoms of the bpyMe2 ligands. Finally, the QTAIM analysis
also reveals a weak C–H···N contact between
one C–H bond of the methyl group of bpyMe2 ligand
and the N atom of the NMe2 group of 4-DMAP. Further analysis
of the π-stacking interaction and its contribution to the stabilization
of the assembly is given in the ESI (see Figure S33). It is interesting to highlight that the NCIPlot (Figure 6) shows a well-defined
blue isosurface located between the I and Ag atoms, thus confirming
the attractive nature of the I+···Ag+ interaction. The value of the charge density (ρ) at
the bond CP is 0.0149 au, which is slightly greater than that reported
recently for a similar complex (0.0130 au),20 thus suggesting a stronger interaction. Other parameters at the
bond CP are also useful to analyze the I+···Ag+ interaction. In particular, the positive value of the Laplacian
of ρ (∇2ρ = 0.0394 au) combined with
the negligible value of the total energy density (H = +0.0001 au)
indicates that the interaction has a marked noncovalent character.</p><!><p>Distribution
of bond, ring, and cage critical points (red, yellow,
and blue spheres, respectively) and bond paths (dashed ones correspond
to noncovalent interactions) for complex 12 at the M06-2X/def2-QZVP
level of theory. The NCIplot surface (isosurface = 0.5 au) is also
represented superimposed to the QTAIM. The color scale is −0.04
< sign(λ2)ρ < 0.04 au.</p><!><p>Finally, to investigate the I+···Ag+ from the perspective of a donor–acceptor interaction,
the NBO30 analysis which focused on the
second order perturbation analysis has been performed for compound 12. This method has been recently used to investigate the
energy stabilization associated with the donor–acceptor interactions
in a similar system.20 The energetic results
derived from the NBO calculations (Figure 7) reveal that in the dimer of compound 12, two relevant orbital donor–acceptor contributions
exist. In both, the electron donation comes from one of the free lone
pairs of I+ (located at atomic orbital 5pz) to (i) the empty 5s orbital of Ag(2) and (ii) the empty 5pz orbital of Ag+. The energy stabilization
of the system due to both donor–acceptor interactions is −32.6
kcal/mol. This result confirms the nucleophilic character of I+ and the electrophilic character of Ag+ and the
donor–acceptor nature of the interaction that largely contributes
to the stabilization of the system that compensates for the electrostatic
repulsion between the formal positive charges. Further support for
this explanation is provided by the analysis of the frontier molecular
orbitals of the isolated [I(4-DMAP)2]+ fragment,
which shows the significant participation of the pz atomic orbital of I in the HOMO (highest
occupied molecular orbital), as detailed in Figure S34. Finally, a bond order of 0.16 has been obtained for the
Ag···I contact using the Wiberg bond index (WBI),31 which confirms the existence and noncovalent
nature of this interaction. The WBI corresponding to the Ag···I
interaction in 12 is similar to those reported for argentophilic
interactions.32</p><!><p>Representation of the
orbital donor–acceptor interactions
in compound 12 obtained using the M06-2X/def2-QZVP wave
function.</p><!><p>The new three-coordinate
silver(I) complexes (2–6) were synthesized,
and their utility in the strategy of partial cation
exchange has been demonstrated to generate
a series of the related pairs of complexes (8–12). These partial cation exchanges upon reaction with 0.5
equiv of elemental iodine were monitored by 1H and 15N NMR studies and found to proceed quantitatively in all
cases. Closer inspection of the 15N NMR resonances revealed
that the silver(I) component in the pair of complexes 12 had shifted relative to its 15N NMR value of the pure
complex, indicating the observation for the second time of an I+···Ag+ interaction. This interaction
was further confirmed in the solid state by single-crystal X-ray diffraction
with an I+···Ag+ distance of
3.4043(4) Å, significantly shorter than the only other known
example of this "nucleophilic" iodonium interaction.</p><p>The interaction was interrogated computationally revealing the
nucleophilic nature of the I+ that uses one of its available
lone pairs to donate charge to the electrophilic Ag+, as
demonstrated by the second order perturbation analysis. The QTAIM
analysis confirmed the existence of the I+···Ag+ contact (bond CP and bond path connecting both atoms), and
the NCIplot revealed its attractive nature, in spite of the electrostatic
repulsion between the positive charges.</p><!><p>All reagents and solvents were
obtained from commercial suppliers and used without further purification.
For structural NMR assignments, 1H NMR spectra were recorded
on a Bruker Avance 300 MHz spectrometer at 25 °C in CD2Cl2. The 1H–15N NMR correlation
spectra were recorded on a Bruker Avance III 500 MHz spectrometer
at 25 °C in CD2Cl2, and in the instances
of complexes containing the mtz or 4-DMAP ligands which possess multiple
independent nitrogen environments, only the values for the nitrogen
atoms of interest (i.e., those that are directly bonded to the Ag+ or I+ ions) are reported. Chemical shifts are
reported on the Î´ scale in ppm using the residual solvent signal
as internal standard (CD2Cl2; δH 5.32) or, for 1H–15N NMR spectroscopy,
to an external d3-MeNO2 standard.
For 1H NMR spectroscopy, each resonance was assigned according
to the following conventions: chemical shift (Î´) measured in
ppm, observed multiplicity, number of hydrogens, observed coupling
constant (J Hz), and assignment. Multiplicities are denoted as s (singlet),
d (doublet), t (triplet), q (quartet), m (multiplet), and br (broad).</p><p>The single-crystal X-ray data for 2, 4, 6, and 7_2 were collected at 170 K using
a Bruker-Nonius Kappa CCD diffractometer with an APEX-II detector
with graphite-monochromatized Mo–Kα (λ = 0.71073
Å) radiation. The program COLLECT33 was used for the data collection, and the DENZO/SCALEPACK34 program was used for the data reduction. The
single-crystal X-ray data for 3, 7_1, 8, and 9 and for 5 were collected
at 120 K and 273 K, respectively, due to a catastrophic phase change
being observed at lower temperatures, using an Agilent SuperNova dual
wavelength diffractometer with an Atlas detector using mirror-monochromated
Cu–Kα (λ = 1.54184 Å) radiation. The program
CrysAlisPro35 was used for the data collection
and reduction on the SuperNova diffractometer, and the intensities
were absorption corrected using a Gaussian face index absorption correction
method. All structures were solved by intrinsic phasing (SHELXT)36 and refined by full-matrix least-squares on F2 using the OLEX2,37 utilizing the SHELXL-2015 module.38 Anisotropic
displacement parameters were assigned to non-H atoms and isotropic
displacement parameters for all H atoms and were constrained to multiples
of the equivalent displacement parameters of their parent atoms with Uiso(H) = 1.2Ueq (parent
atom). The X-ray single-crystal data and CCDC numbers of all new structures
are included below.</p><p>The 1H and 15N NMR
data of [Ag(bpy)2]PF6,20 [Ag(bpy)(mtz)]PF6 (1),20 [I(mtz)2]PF6,20 [I(4-Etpy)2]PF6,25 and [I(4-DMAP)2]PF625 have been previously
reported, and similarly, the solid-state structures (where applicable)
were also obtained from these same literature sources.</p><p>The preparation
of all three-coordinate silver(I) complexes was
performed in the absence of light sources, both natural and artificial,
to avoid accidental decomposition in solution.</p><!><p>An MeCN (acetonitrile)
(5 mL) suspension of bpyMe2 (73.7 mg, 0.4 mmol) was added
to a stirred MeCN (5 mL) solution
of AgPF6 (101.1 mg, 0.4 mmol), and after 5 min, mtz (28.4
Î¼L mg, 0.4 mmol) was added neat. The reaction was stirred for
30 min, and then all volatiles were removed under reduced pressure
to leave a white solid. Recovered yield = 183.2 mg (0.352 mmol, 88%).
Crystals suitable for single-crystal X-ray diffraction were obtained
from DCM (dichloromethane) vapor diffused with pentane. 1H NMR (300 MHz, CD2Cl2) Î´ 8.56 (d, J = 5.1 Hz, 2H), 8.04 (s, 2H), 7.95 (s, 2H), 7.43 (s, 1H),
7.41 (s, 1H), 4.24 (s, 3H), 2.56 (s, 6H). 15N NMR (500
MHz, CD2Cl2) δ −18.65, −81.26,
−119.22, −141.63. Analysis Found: C, 34.53; H, 3.03:
N, 12.89%. Calculated for C15H17AgF6N5P: C, 34.64; H, 3.29: N, 13.46%.</p><!><p>An MeCN
(5 mL) solution of bpy (62.5 mg, 0.4 mmol) was
added to a stirred MeCN (5 mL) solution of AgPF6 (101.1
mg, 0.4 mmol), and after 60 s, 4-Etpy (45.5 Î¼L mg, 0.4 mmol)
was added neat. The reaction was stirred for 30 min, and then all
volatiles were removed under reduced pressure to leave a pale yellow
solid. Recovered yield = 185.0 mg (0.358 mmol, 90%). Crystals suitable
for single-crystal X-ray diffraction were obtained from DCM vapor
diffused with pentane. 1H NMR (300 MHz, CD2Cl2) Î´ 8.72 (d, J = 4.3 Hz, 2H), 8.52
(d, J = 6.4 Hz, 2H), 8.27 (d, J =
8.1 Hz, 2H), 8.11 (td, J = 7.9, 1.6 Hz, 2H), 7.63
(ddd, J = 7.5, 5.1, 0.9 Hz, 2H), 7.45 (d, J = 6.3 Hz, 2H), 2.79 (q, J = 7.5 Hz, 2H),
1.32 (t, J = 7.6 Hz, 3H). 15N NMR (500
MHz, CD2Cl2) δ −110.10, −132.55.
Analysis Found: C, 38.73; H, 3.18: N, 8.34%. Calculated for C17H17AgF6N3P·0.3(H2O): C, 39.15; H, 3.40: N, 8.06%.</p><!><p>An MeCN
(5 mL) suspension of bpyMe2 (73.7 mg, 0.4 mmol) was added
to a stirred MeCN (5 mL) solution
of AgPF6 (101.1 mg, 0.4 mmol), and after 5 min, 4-Etpy
(45.5 Î¼L mg, 0.4 mmol) was added neat. The reaction was stirred
for 30 min, and then all volatiles were removed under reduced pressure
to leave a yellow crystalline solid. Recovered yield = 194.9 mg (0.358
mmol, 90%). Crystals suitable for single-crystal X-ray diffraction
were obtained from DCM vapor diffused with diisopropyl ether. 1H NMR (300 MHz, CD2Cl2) δ 8.60–8.45
(m, 4H), 8.06 (s, 2H), 7.49–7.38 (m, 4H), 2.79 (q, J = 7.0 Hz, 2H), 2.56 (s, 6H), 1.31 (t, J = 7.5 Hz, 3H). 15N NMR (500 MHz, CD2Cl2) δ −117.70, −130.76. Analysis Found:
C, 41.54; H, 3.87: N, 8.07%. Calculated for C19H21AgF6N3P: C, 41.93; H, 3.89: N, 7.72%.</p><!><p>An MeCN
(5 mL) solution of bpy (62.5 mg, 0.4 mmol) was
added to a stirred MeCN (5 mL) solution of AgPF6 (101.1
mg, 0.4 mmol), and after 60 s, a MeCN (1 mL) solution of 4-DMAP (48.9
mg, 0.4 mmol) was added. The reaction was stirred for 30 min, during
which time the colorless solution had become an orange/yellow color.
All volatiles were removed under reduced pressure to leave a khaki
solid. Recovered yield = 193.9 mg (0.365 mmol, 91%). Crystals suitable
for single-crystal X-ray diffraction were obtained from DCM vapor
diffused with pentane. 1H NMR (300 MHz, CD2Cl2) Î´ 8.70 (d, J = 4.8 Hz, 2H), 8.27
(d, J = 8.1 Hz, 2H), 8.15–8.06 (m, 4H), 7.61
(dd, J = 7.0, 5.4 Hz, 2H), 6.64 (d, J = 6.9 Hz, 2H), 3.09 (s, 6H). 15N NMR (500 MHz, CD2Cl2) δ −108.73, −169.62, −314.41.
Analysis Found: C, 38.21; H, 3.39: N, 10.76%. Calculated for C17H18AgF6N4P: C, 38.44; H,
3.42: N, 10.55%.</p><!><p>An MeCN (5 mL) suspension of bpyMe2 (73.7 mg, 0.4 mmol) was added to a stirred MeCN (5 mL) solution
of AgPF6 (101.1 mg, 0.4 mmol), and after 5 min, a MeCN
(1 mL) solution of 4-DMAP (48.9 mg, 0.4 mmol) was added. The reaction
was stirred for 30 min, during which time the colorless solution had
become an orange/yellow color. All volatiles were removed under reduced
pressure to leave a beige solid. Recovered yield = 189.3 mg (0.338
mmol, 85%). Crystals suitable for single-crystal X-ray diffraction
were obtained from DCM vapor diffused with pentane. 1H
NMR (300 MHz, CD2Cl2) Î´ 8.52 (d, J = 5.2
Hz, 2H), 8.08 (dd, J = 5.6, 1.4 Hz, 2H), 8.05 (s,
2H), 7.40 (d, J = 4.6 Hz, 2H), 6.64 (dd, J = 5.6, 1.5 Hz, 2H), 3.09 (s, 6H), 2.56 (s, 6H). 15N NMR (500 MHz, CD2Cl2) δ −116.49,
−169.95, −314.18. Analysis Found: C, 40.89; H, 3.92:
N, 10.26%. Calculated for C19H22AgF6N4P: C, 40.81 H, 3.97: N, 10.02%.</p><!><p>A general procedure
for the conversion of the three-coordinate silver(I) complexes (1–6) to iodonium ions (as the pairs of
complexes 8–12) was followed: a CD2Cl2 (0.5 mL) solution of the three-coordinate complexes
(1–6, 0.01 mmol) and a CD2Cl2 (0.5 mL) solution of I2 (1.3 mg, 0.005
mmol) were combined to immediately generate a yellow precipitate (AgI).
The reactions were stirred for 10 min and filtered, and their NMR
spectra were recorded. N.b.: 1H and 15N NMR data for the pair of complexes 7 matched
that previously reported for this combination in the literature.</p><!><p>1H NMR
(500 MHz, CD2Cl2) Î´ 8.47 (br. s, 4H),
8.08 (br. s, 4H), 7.98 (s, 2H), 7.92 (s, 2H), 7.40 (br. s, 4H), 4.25
(s, 6H), 2.56 (br. s, 12H). 15N NMR (500 MHz, CD2Cl2) δ −20.03, −137.97, −142.21
(a resonance for the bpyMe2 nitrogen atoms was not observed).</p><!><p>1H NMR
(300 MHz, CD2Cl2) Î´ 8.64 (d, J = 4.2 Hz, 4H), 8.58 (dd, J = 5.2, 1.4 Hz, 4H),
8.29 (d, J = 8.1 Hz, 4H), 8.09 (td, J = 7.9, 1.7 Hz, 4H), 7.58 (ddd, J = 7.6, 5.0, 1.1
Hz, 4H), 7.41 (d, J = 6.5 Hz, 4H), 2.83 (q, J = 7.6 Hz, 4H), 1.30 (t, J = 7.6 Hz, 6H). 15N NMR (500 MHz, CD2Cl2) δ −105.82,
−181.61.</p><!><p>1H NMR
(300 MHz, CD2Cl2) Î´ 8.58 (d, J = 6.6 Hz, 4H), 8.44 (d, J = 5.2 Hz, 4H), 8.06 (s,
4H), 7.39 (dd, J = 12.0, 5.5 Hz, 8H), 2.83 (q, J = 7.6 Hz, 4H), 2.56 (s, 12H), 1.30 (t, J = 7.6 Hz, 6H). 15N NMR (500 MHz, CD2Cl2) δ −114.10, −181.74.</p><!><p>1H NMR
(300 MHz, CD2Cl2) δ 8.64 (d, J = 4.9 Hz, 4H), 8.28 (d, J = 8.1 Hz, 4H), 8.13–8.03
(m, 8H), 7.58 (ddd, J = 7.3, 4.9, 0.8 Hz, 4H), 6.50
(d, J = 7.3 Hz, 4H), 3.11 (s, 12H). 15N NMR (500 MHz, CD2Cl2) δ −105.81,
−216.13.</p><!><p>1H NMR
(300 MHz, CD2Cl2) δ 8.44 (d, J = 5.1 Hz, 4H), 8.09–8.03 (m, 4H), 7.36 (d, J = 4.3 Hz, 4H), 6.50 (d, J = 7.3 Hz, 4H), 3.10 (s,
12H), 2.55 (s, 12H). 15N NMR (500 MHz, CD2Cl2) δ −112.14, −216.01.</p><!><p>A DCM (2 mL) solution of bpyMe2 (73.7 mg, 0.4
mmol) was added to a stirred MeCN (1 mL) solution
of AgPF6 (50.6 mg, 0.2 mmol) to give a pale yellow solution.
The solution was stirred for 30 min and then left to evaporate to
dryness to give the product as a yellow solid in quantitative yield.
Crystals suitable for single-crystal X-ray diffraction were obtained
from partial evaporation of a DCM/MeCN (3:1 ratio) solution (13_1) and from DCM vapor diffused with diisopropyl ether (13_2). 1H NMR (300 MHz, CD2Cl2) Î´ 8.43 (d, J = 5.2 Hz, 4H), 8.05 (s, 4H),
7.37 (d, J = 4.5 Hz, 4H), 2.55 (s, 12H).). 15N NMR (500 MHz, CD2Cl2) δ −114.35.
Analysis Found: C, 46.52; H, 3.96: N, 9.07%. Calculated for C24H24AgF6N4P: C, 46.40; H,
3.89: N, 9.02%.</p><!><p>Additional experimental
details, molecular structures,
crystallographic details, 15N NMR comparison tables, NMR
spectra, and details of quantum chemical calculations (PDF)</p><p>ic1c00409_si_001.pdf</p><!><p>CCDC 2062093–2062101 contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.</p><!><p>The manuscript
was written through contributions of all authors. All authors have
given approval to the final version of the manuscript.</p><!><p>J.S.W. gratefully
acknowledges the Finnish Cultural Foundation Central Fund (Grant Number
00201148) for funding. A.F. thanks the MICIU/AEI from Spain for financial
support (Project CTQ2017-85821-R, Feder funds).</p><p>The authors
declare no competing financial interest.</p>