Metal-only Lewis pairs between group 10 metals and Tl(i) or Ag(i): Insights into the electronic consequences of Z-type ligand binding

Article abstract of DOI:10.1039/c5sc03104d

Complexes bearing electron rich transition metal centers, especially those displaying coordinative unsaturation, are well-suited to form reverse-dative σ-interactions with Lewis acids. Herein we demonstrate the generality of zerovalent, group 10 m-terphen

Full text of DOI:10.1039/c5sc03104d

View Article Online
View Journal
Chemical
Science
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: B. R. Barnett, C. E.
Moore, P. Chandrasekaran, S. Sproules, A. L. Rheingold, S. DeBeer and J. S. Figueroa, Chem. Sci., 2015,
DOI: 10.1039/C5SC03104D.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
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
Information for Authors.
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 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.
www.rsc.org/chemicalscience

Please do not adjust margins
Chemical Science
Page 1 of 10
View Article Online
DOI: 10.1039/C5SC03104D
Journal Name
ARTICLE
Metal-Only Lewis Pairs Between Group 10 Metals
and Tl(I) or Ag(I): Insights into the Electronic
Consequences of Z-Type Ligand Binding
Received 00th January 20xx,
Accepted 00th January 20xx
Brandon R. Barnetta, Curtis E. Moorea, Perumalreddy Chandrasekaranb, Stephen Sproulesc, Arnold
DOI: 10.1039/x0xx00000x
L. Rheingolda, Serena DeBeerd,e and Joshua S. Figueroa*a
www.rsc.org/
Complexes bearing electron rich transition metal centers, especially those displaying coordinative unsaturation, are well-
suited to form reverse-dative σ-interactions with Lewis acids. Herein we demonstrate the generality of zerovalent, Group
10 m-terphenyl isocyanide complexes to form reverse-dative σ-interactions to Tl(I) and Ag(I) centers. Structural and
spectroscopic investigations of these Metal-only Lewis Pairs (MOLPs) has allowed insight into the electronic consequences
of Lewis-acid ligation within the primary coordination sphere of a transition metal center. Treatment of the bis-isocyanide
complex, Pt(CNArDipp2
)
(ArDipp2 [O3SCF3]–) yields the Pt/Tl MOLP
= 2,6-(2,6-(i-Pr)2C6H3)2C6H3) with TlOTf (OTf =
2
[TlPt(CNArDipp2)2]OTf (1). 1H NMR and IR spectroscopic studies on 1, and its Pd congener [TlPd(CNArDipp2)2]OTf (2),
demonstrate that the M→Tl interaction is labile in solution. However, treatment of complexes 1 and 2 with Na[BArF4] (ArF
= 3,5-(CF3)2C6H3) produces [TlPt(CNArDipp2)2]BArF4 (3) and [TlPd(CNArDipp2)2]BArF4 (4), in which Tl(I) binding is shown to be
static by IR spectrosocopy and, in the case of 3, 195Pt NMR spectroscopy as well. This result provides strong evidence that
the M→Tl linkages can be attributed primarily to σ-donation from the group 10 metal to Tl, as loss of ionic stabilization of
Tl by the triflate anion is compensated for by increasing the degree of M→Tl σ-donation. In addition, X-ray Absorption
Near-Edge Spectroscopy (XANES) on the Pd/Tl and Ni/Tl MOLPs, [TlPd(CNArDipp2)2]OTf (2) and [TlNi(CNArMes2)3]OTf,
respectively, is used to illustrate that the formation of a reverse-dative σ-interaction with Tl(I) does not alter the
spectroscopic oxidation state of the Group 10 metal. Also reported is the ability of M(CNArDipp2)2 (M = Pt, Pd) to form
MOLPs with Ag(I), yielding the complexes [AgM(CNArDipp2)2]OTf (5, M = Pt; 6, M = Pd). As was determined for the Tl-
containing MOLPs 1-4, it is shown that the spectroscopic oxidation states of the group 10 metal in 5-6 are essentially
unchanged compared to the zerovalent precursors M(CNArDipp2)2. However, in the case of 5 and 6, the formation of a
dative M→Ag σ-bonding interaction facilitates the binding of Lewis bases to the group 10 metal trans to Ag, illustrating
the potential of acceptor fragments to open up new coordination sites on transition metal complexes without formal, two-
electron oxidation.
rich complexes, the transition metal center may also be capable of
exhibiting Lewis basic behavior.1 Although this phenomenon was
initially invoked for the case of carbonyl metallates acting as
Introduction
On account of their relatively electropositive nature and
Brønstead bases,2-4 it is now recognized as a central tenet of
transition-metal bonding to π-acidic ligands5-7 as well as an essential
component of many oxidative addition mechanisms.8-12 More
recently, the extension of this concept to the binding of various
main-group acceptor fragments (Z-type ligands)13 in a σ-fashion by
electron-rich transition metals has been realized, and the study of
such complexes continues to be of intense interest.14-27
ability to act as formal acceptors toward Lewis bases, the transition
metals in coordination complexes are traditionally viewed as Lewis
acids. Classical “Werner-type” complexes utilize their empty nd, as
well as (n+1)s and (n+1)p, orbitals to form dative bonds with
electron-donor ligands. In the case of highly reduced and electron-
a. Department of Chemistry and Biochemistry, University of California, San Diego,
9500 Gilman Drive, Mail Code 0358, La Jolla, CA 92093, United States
b. Department of Chemistry and Biochemistry, Lamar University, Beaumont, TX
77710.
In addition to these examples, a related topic concerning
transition metal Lewis basicity is the ability to form dative
interactions to another metal center. Judicious ligand design
strategies that constrain an electron-rich metal center in close
proximity to a coordinatively unsaturated metal fragment has
proven to be a reliable approach for engendering metal-metal
dative bonding.28-34 Furthermore, in certain instances, unsupported
c. School of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK.
d Max-Planck-Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470
Mülheim an der Ruhr, Germany
e Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York
14853, United States
† Electronic Supplementary Information (ESI) available: Synthetic and spectroscopic
details, crystallographic structure determinations and CSD search results. See
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
Chemical Science
Page 2 of 10
ARTICLE
Journal Name
Metal-only Lewis Pairs (MOLPs), which do not rely on a ligand the Pt variant 5, further aggregation with additional AgOTf leads to
View Article Online
buttress, can be generated.2,35-39 The formation of such
unsupported metal-metal interactions, while sometimes labile in
solution, offers an interesting approach toward tuning the reactivity
profiles of low-valent complexes, as the addition of metallic Lewis
acids has been shown to enhance the rates of certain catalytic
processes.40-43
While synthetic methods leading to MOLPs and their
structural chemistry has advanced, a detailed understanding of how
the presence of a metal-metal dative bond affects the electronic
properties of the constituent fragments remains of significant
dimeric {[Ag2Pt(CNArDipp2)2(η1-C6H6)]2(µ-OTfD)2O}(IO: 1T0f.)1203(97/)C5cSoCn0ta3i1n0i4nDg
triangulo-PtAg2 cores. It is shown that binding of one (Compounds
5-6) and two (Compound 7) equivalents of Ag(I) results in a
sequential increase in the Lewis acidity of the group 10 metal
center, thus illustrating how σ-acceptor fragments can be used to
rationally tune the properties of electron-rich transition metal
complexes.
interest. It is generally accepted that protonation of a transition Scheme 1.
metal complex is best viewed as involving a two-electron oxidation
of the metal center to give a hydride ligand.44 As the electrons
involved in the M-H bond have necessarily come from the metal, an
increase of its valence by two units is required.45 In the case of
other main group Lewis acids (e.g. boranes), the degree of charge
transfer is often not as clear. As such, the adoption and assignment
of formalisms to adequately describe the electronic structure of
such adducts has been a point of debate in the community.46,47
Similar ambiguities in the electronic structures of MOLPs exist,
although considerably less effort has been put toward uncovering
satisfactory electronic descriptors for such compounds.39 Despite
the fact that X-ray Absorption Near-Edge Spectroscopy (XANES)
holds promise in this regard,30,34 its thus-far limited use in this
capacity has not yet led to the development of general principles
for properly describing the electronic structures of complexes
containing metal-metal dative interactions.
Work from our research group has demonstrated the utility of
encumbering m-terphenyl isocyanides in stabilizing low-valent and
coordinatively unsaturated complexes of late transition metals.27,48-
55
Such electron-rich metal centers are prime candidates for acting
as Lewis bases toward appropriate Lewis acidic substrates, a
concept that has been demonstrated by the heterobimetallics
[TlNi(η4-COD)(CNArMes2)2]X (X = OTf, BArF ),49 [TlNi(CNArMes2)3]OTf,49
4
and [TlPd(CNArDipp2)2]OTf (2),50 as well as by the recently-reported
platinum
(boryl)iminomethane
complex
Pt(κ2-N,B-
Cy2BIM)(CNArDipp2).27 In addition, the response of the isocyanide
υ(C≡N) IR bands to the electron density on the Lewis-basic metal
center renders them a convenient spectroscopic reporter on the
degree of formal charge transfer upon binding a σ-acceptor
fragment.25 In this work, we demonstrate the ability of the two-
coordinate complexes M(CNArDipp2
)
(M = Pt, Pd)27,50 to form
2
unsupported metal-metal linkages with Tl(I). Two Tl-containing
MOLPs have also been examined by X-ray Absorption Near-Edge
Spectroscopy (XANES), illustrating that the spectroscopic oxidation
state of the group 10 metal is not affected by its interaction with
Tl(I). We also show that the zero-valent platforms M(CNArDipp2)2 (M
= Pt, Pd) can form Metal-only Lewis Pairs with Ag(I), yielding the
heterobimetallic salts [AgM(CNArDipp2)2]OTf (5, M = Pt; 6, M = Pd).
Spectroscopic and structural investigations provide insight into the
nature of the M-Ag interactions in these compounds, and give
strong evidence that formation of the M→Ag linkage results in only
a marginal degree of metal-to-metal charge transfer. In the case of
Figure 1. Molecular structure of [TlPt(CNArDipp2)2]OTf (1).
Table 1. Selected bond distances (X-ray structure) of Pt(CNArDipp2)2,
Pd(CNArDipp2)2, and their Tl-containing MOLPs.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 10
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
corresponding to Pd(CNArDipp2)2 are readily observable as a minor
View Article Online
component in the IR spectrum of [TlPd(CNDAOrDI:ip1p02).120]O39T/fC(52S)Ci0n31C064DD6
solution, thereby suggesting the presence of an equilibrium
between bound and unbound Tl(I) (Figure 2). In addition, extended
scanning failed to locate the 195Pt NMR62 resonance for the
platinum analogue [TlPt(CNArDipp2)2]OTf (1). We suggest that this
observation is indicative of lability in the Pt-Tl interaction on the
NMR timescale, resulting in a broadening of this resonance that
obviates its detection at room temperature.
Complex
d(M-Ciso)
1.906(3) Å
1.930(4) Å
1.918(5) Å
1.951(7) Å
1.922(4) Å
1.958(4) Å
1.933(8) Å
1.965(3) Å
d(M-Tl)
a
Pt(CNArDipp2
)
)
–
–
2
Pd(CNArDipp2
b
2
1
2.8617(3) Å
2.855(1) Å
2.7710(4) Å
2.7481(5) Å
2.7659(5) Å
2.7770(2) Å
2b
3(Et2O)c
4(Et2O)c
3
4(Tol)2
aData from Ref. 27. bData from Ref. 50. cOne of the two crystallographically
independent molecules in the Xray structures of 3(Et2O) and 4(Et2O) contain
two-site disorder of the Tl atom. We have used the major component of this
disorder to calculate the average d(M-Tl).
Results and Discussion
Similar to the zero-valent Pd congener, Pd(CNArDipp2)2,50 the
addition of TlOTf to a solution of Pt(CNArDipp2)2 in Et2O yields the
unsupported heterobimetallic compound [TlPt(CNArDipp2)2]OTf (1)
as a yellow microcrystalline solid. Structural characterization of 1
(Scheme 1 and Figure 1) reveals a T-shaped coordination geometry
about Pt, while the Tl center makes long, but non-negligible
contacts with the [OTf]– anion (d(Tl-O3) = 2.799(5) Å) and the Caryl
atoms of the Dipp rings (shortest d(Tl-Caryl) = 3.355 Å). The presence
of a Pt-Tl bonding interaction is apparent given their interatomic
separation of 2.8617(3) Å. Importantly, this value is comparable to
the most reasonable range for the sum of the covalent radii
between Pt and Tl (2.67–2.84 Å),56 thereby suggesting that the
solid-state structure of 1 does not simply arise from the co-
crystallization of Pt(CNArDipp2)2 with TlOTf. While the role of closed-
shell metallophilic interactions57 cannot be completely discounted,
spectroscopic evidence indicates that this interaction is formed by a
reverse-dative σ-bond, whereby Pt donates two electrons to an
empty 6p orbital on Tl. Analysis of these solutions by FTIR
spectroscopy shows a strong υ(C≡N) band at 2112 cm–1, which is
shifted to higher energy relative to those of Pt(CNArDipp2)2 (2065,
Figure 2. FTIR spectrum (υ(C≡N) region) of [TlPd(CNArDipp2)2]OTf (2) showing
the presence of Pd(CNArDipp2)2. Conditions: C6D6, 20 ˚C, KBr windows.
2020 cm–1),27 consistent with
a decrease in π-backbonding
interactions to the isocyanides as a result of the formation of a
Pt→Tl retrodative σ-bonding interaction. A similar blue-shift of this
band for the palladium analogue [TlPd(CNArDipp2)2]OTf (2) with
respect to Pd(CNArDipp2)2 was observed previously.50 Surprisingly,
bonds between electron-rich, late transition metals (especially
third-row metals) and Tl(I) have often been rationalized largely
based on metallophilic interactions.58-61 However, the FTIR spectra
Figure 3. Molecular structure of [(Et2O)TlPt(CNArDipp2)2]BArF4 (3(Et2O)).
Isopropyl groups and BArF4 counterion have been omitted for clarity. The Pd
congener 4(Et2O) is isostructural.
of 1 and 2 compared with those of M(CNArDipp2
) (M = Pt, Pd)
2
provide strong experimental evidence that late-metal-Tl(I) bonds
likely contain a substantial dative-bonding component in a manner
analogous to that seen for complexes bearing main-group Z-type
ligands.23-25
Although [TlPt(CNArDipp2)2]OTf (1) gives rise to a sharp set of 1H
and 13C{1H} NMR resonances in benzene-d6, other spectroscopic
data suggest that the metal-metal interaction is labile in solution.
While the IR absorption bands of Pt(CNArDipp2)2 are not apparent in
the IR spectrum of 1, it is important to note that υ(C≡N) bands
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
Chemical Science
Page 4 of 10
ARTICLE
Journal Name
In the case of 4, cooling a saturated toluene solutVioienw Atroticl–e3O5nli˚nCe
yields [(η6-Tol)2TlPd(CNArDipp2)2]BArF (4(TDolO)2I,: 10F.i1g0u3r9e/C55S)C, 0w31h0i4cDh
4
displays two toluene molecules bound in an η6-fashion to Tl (d(Tl-C)
= 3.192–3.589 Å). Although the Tl-Carene distances in 3 and 4(Tol)2
are seemingly long, they are well in line with other structurally
characterized examples of Tl-arene π-complexes.60,64-67
Examination of the solid-state and solution-phase behaviour of
1-4 reveals that replacement of the triflate anion with [BArF ]– has
4
important ramifications for the lability of the M→Tl linkage. In both
solvates of 3 and 4, the M-Tl distance is significantly contracted
relative to 1 and 2 (Table 1), consistent with an increase in the
degree of M→Tl donation. As the triflate anion likely stabilizes the
Tl center through contact ion pairing, replacement of [OTf]– with
neutral Et2O or arene donors appears to only partially compensate
for the loss of this ionic association. Accordingly, in an attempt to
recoup some of this stabilization, we contend that the degree of
M→Tl σ-donation is increased. This notion is supported by the
progression of the υ(C≡N) bands in 3 (2121 cm–1) and 4 (2116 cm–1)
to higher energies relative to 1-2, as the increased withdrawal of
electron density from the group 10 metal by Tl serves to attenuate
backbonding interactions with the isocyanide ligands. Importantly,
and in contrast to the triflate salt [TlPd(CNArDipp2)2]OTf (2), the
solution FTIR spectra of 3 and 4 in benzene-d6 are devoid of υ(C≡N)
features corresponding to M(CNArDipp2)2, signalling that Tl(I)
dissociation in benzene can be significantly inhibited by the use of
Figure 4. Molecular structure of [TlPt(CNArDipp2)2]BArF4 (3). BArF4 counterion
has been omitted for clarity.
the weakly coordinating [BArF ]– anion. Interestingly, this
4
replacement also allows for detection of the 195Pt NMR resonance
of [TlPt(CNArDipp2)2]BArF4 (3), which appears as a doublet with well-
1
resolved coupling to 205Tl (δ = –3802 ppm, JPt,Tl = 11.2 kHz).68 This
resonance is shifted significantly downfield respective to that of
Figure 5. Molecular structure of [(η6-Tol)2TlPd(CNArDipp2)2]BArF4 (4(Tol)2).
Pt(CNArDipp2
) (δ = –5993 ppm (s), C6D6), further suggestive of
2
BArF4 counterion has been omitted for clarity.
decreased electron density at the Pt center upon coordination of
Tl(I).69,70 However, it is also important to note that dissolution of 1-4
in THF results in complete dissociation of the Tl(I) center and
formation of M(CNArDipp2)2, according to FTIR spectroscopy. This
result, which was similarly observed in the case of
As the lability of unsupported M-Tl linkages have been
observed to display a dependence on counteranion identity,58 we
sought to explore the behavior of [TlM(CNArDipp2)2]+ (M = Pt, Pd)
when accompanied by a traditionally non-coordinating anion.
Addition of an Et2O solution of NaBArF4 (BArF4 = [B(3,5-(CF3)2C6H3)4]–
) to 1 or 2 results in precipitation of NaOTf and smooth formation of
[TlNi(CNArDipp2)3]OTf,54 serves as
a reminder of the weak
dissociation energies inherent in most unsupported metal-metal
dative bonds, as dissolution in solvents of moderate coordinating
strength is sufficient to completely disrupt this interaction.
[(Et2O)TlM(CNArDipp2)2]BArF (M
= Pt (3(Et2O)), Pd (4(Et2O)))
4
following crystallization from Et2O (Figure 3). Structural
determinations of 3(Et2O) and 4(Et2O) reveal discreet cation-anion
pairs (two independent pairs per asymmetric unit). While no
contact between the Tl center and the [BArF4 ]– anion is evident in
the solid state, the Tl center is bound to a molecule of Et2O in both
complexes (average d(Tl-O) = 2.760(3) Å (3) and 2.729(3) Å (4)).
Furthermore, as noted for 1, long-range contacts (ca. 3.4 Å)
between Tl and several Caryl atoms of the flanking Dipp rings are
apparent. The Tl-bound ether molecules are easily liberated from
crystalline samples upon prolonged exposure to vacuum (~100
mTorr) as assayed by 1H NMR spectroscopy. Subsequent
Although limited experimental techniques are capable of
probing metal-metal dative interactions, X-ray Absorption Near-
Edge Spectroscopy (XANES)71 has begun to find an important use in
this regard.30,34 Importantly, its utility lies in its ability to decipher
the spectroscopic oxidation states of the metals involved in a given
bonding interaction. In order to assess the degree of charge
transfer inherent in the formation of a reverse-dative σ-interaction
to Tl(I), Pd K-edge XANES was carried out on the palladium-thallium
adduct [TlPd(CNArDipp2)2]OTf (2, Figure 6). While neither the Pd K-
edge spectra of 2 nor that of Pd(CNArDipp2)2 display a discernable
pre-edge feature, both exhibit nearly identical energies for the
rising edge of the XANES region. In comparison, the rising edge
crystallization of
3
from toluene produces solvent-free
[TlPt(CNArDipp2)2]BArF (3, Figure 4), which contains Tl-(η2-arene)
energy of the Pd(II) peroxo complex50,72 Pd(η2-O2)(CNArDipp2
) is
2
4
interactions with the flanking Dipp rings (d(Tl-C) = 3.188–3.616 Å).63
shifted to higher energy by ca. 4.0 eV relative to that of
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 10
Chemical Science
Please do not adjust margins
Journal Name
Pd(CNArDipp2)2 and 2. Despite their differing geometries, the rising
ARTICLE
For an additional comparison, XANES measurements were
View Article Online
DOI: 10.1039/C5SC03104D
edge transition for each of these three Pd complexes should involve carried out on the binary nickel tris-isocyanide complex
the promotion of a core 1s electron to a 5p orbital that is relatively Ni(CNArMes2
)
and its adduct with Tl(I), [TlNi(CNArMes2)3]OTf.49
3
unperturbed by ligand field effects. Accordingly, the marked shift of Despite the unambiguous d10 configuration of Ni(CNArMes2)3, its Ni
the rising edge to higher energy for Pd(η2-O2)(CNArDipp2)2 can be
K-edge absorption spectrum (Figure 7) displays a prominent pre-
edge feature, which is likely the result of a 1s to isocyanide π*
transition. The analogous absorption band for [TlNi(CNArMes2)3]OTf
occurs at an identical energy, again signalling that the formation of
reasonably attributed to the presence of an oxidized Pd center
relative to that found in Pd(CNArDipp2)2 or 2. However, the near-
identical rising edge energies observed for Pd(CNArDipp2
) and 2
2
strongly reflect that Tl(I) binding to an electron rich Pd center does
not result in a formal oxidative event.
Figure 6. Comparative Pd K-edge XANES spectra of Pd(CNArDipp2)2 (red), [TlPd(CNArDipp2)2]OTf (2, blue), and Pd(η2-O2)(CNArDipp2)2 (black).
Figure 7. Comparative Ni K-edge XANES spectra of Ni(CNArMes2)3 (red) and [TlNi(CNArMes2)3]OTf (blue).
extraordinary conditions,73 the stabilization of its 6s2 “inert pair”
a reverse-dative M→Tl σ-interaction does not result in significant
due to relativistic effects74 should render it a very weak 2e– donor.
formal charge transfer from the Group 10 metal.
The fact that neither Pd(CNArDipp2)2 nor Ni(CNArMes2)3 undergo
As such, the electrons involved in a covalent interaction between an
electron-rich transition metal and Tl(I) center will most plausibly be
supplied by the former, meaning that the valence count of the
transition metal must necessarily increase by two units. However,
this interaction should not be described as effecting a two-unit
significant charge transfer via the formation of a reverse-dative σ-
interaction to Tl(I) suggests some important guidelines regarding
the proper formalisms that should be used to describe such MOLPs.
Although Tl(I) can exhibit Lewis basic properties under
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
Chemical Science
Page 6 of 10
ARTICLE
Journal Name
increase in the formal oxidation state of the transition metal, as
such an event would be readily apparent in the comparative XANES
spectra of M(CNR)n and [TlM(CNR)n]+ complexes. This conclusion is
further supported by the modest changes in the FTIR υ(C≡N)
energies between the neutral parent compounds and their Tl(I)
adducts (ca. 50 cm–1). For comparison, the Pd(II) and Ni(II)
complexes trans-PdCl2(CNArDipp2)2 and trans-NiCl2(CNArMes2)2 display
IR υ(C≡N) bands that are blue-shifted by ca. 200 cm–1 relative to
Pd(CNArDipp2)2 and Ni(CNArMes2)3.49,75
View Article Online
DOI: 10.1039/C5SC03104D
The abilities of M(CNArDipp2)2 (M = Pt, Pd) to act as the basic
components of Metal-Only Lewis Pairs can also be extended to
Lewis acidic Ag(I) centers.76 Treatment of Pt(CNArDipp2)2 with AgOTf
in Et2O results in precipitation of the heterobimetallic salt
[AgPt(CNArDipp2)2]OTf (5) as
a yellow powder. Attempts to
Figure 8. Molecular structure of [AgPt(CNArDipp2)2(THF)]OTf (5(THF)). The Pd
congener 6(THF) is isostructural. Triflate counterion has been omitted for
clarity.
synthesize the palladium analogue [AgPd(CNArDipp2)2]OTf (6) in the
same fashion results in the formation of metallic mirrors and free
CNArDipp2
.
However, performing the synthesis at reduced
temperatures (ca. –100 ˚C) allows for 6 to be precipitated from
solution as a pale yellow powder in modest yields. Crystallization of
5
or
6
from THF/(TMS)2O at –35 ˚C yields trans-
[AgM(CNArDipp2)2(THF)]OTf (5(THF), M = Pt; 6(THF), M = Pd), where a
molecule of THF is bound to the Group 10 metal trans to the
coordinated Ag center (Figure 8). The M-OTHF distances in 5(THF)
(2.366(5) Å) and 6(THF) (2.326(7) Å) are long relative to Pd and Pt
etherate complexes reported in the Cambridge Structural
Database,77 thereby suggesting an attenuated interaction of THF
with the Group 10 metal center. Indeed, the 1H NMR spectra
obtained from crystalline 5(THF) and 6(THF) in C6D6 show sharp
peaks occurring at the expected chemical shift values for free THF.78
Further, prolonged exposure of crystalline samples to vacuum (~100
mTorr) successfully liberates all THF as analyzed by 1H NMR
spectroscopy. Subsequent recrystallization of these samples from
Et2O/C6H6 (5) or n-hexane/toluene (6) yields 5(C6H6) and 6(C7H8)
(Figure 9 and 10), which display η1-Carene interactions between the
Group 10 metal and arene solvent in the position trans to Ag (for 5,
d(Pt-C63 = 2.885(7) Å); for 6, d(Pd-C64) = 2.496(3)). These
interactions are notable given the likely intermediacy of transient π-
complexes79 in the C-H activation of arenes by electrophilic group
10 complexes.80,81
Figure 9. Molecular structure of [AgPt(CNArDipp2)2(η1-C6H6)]OTf (5(C6H6)).
Flanking isopropyl groups and the triflate counter ion have been omitted for
clarity.
Scheme 2.
Figure 10. Molecular structure of [AgPd(CNArDipp2)2(η1-C7H8)]OTf (6(C7H8)).
Triflate counterion has been omitted for clarity.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 10
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Table 2. Selected bond distances (X-ray structure) of Ag-containing
heterobimetallic complexes.
View Article Online
DOI: 10.1039/C5SC03104D
Complex
5(THF)
6(THF)
5(C6H6)
6(C7H8)
d(M-Ciso)
1.926(8) Å
1.941(9) Å
1.916(4) Å
1.950(3) Å
d(M-Ag)
2.6299(6) Å
2.6303(9) Å
2.6463(5) Å
2.6112(4) Å
The M-Ag bond lengths in both solvates of 5 and 6 are among
the shortest reported in the Cambridge Structural Database (see
Table 2 and Supporting Information S1). As was seen for the M-Tl
adducts above, the metal-metal interactions in 5-6 can be
rationalized via M→Ag σ-donation, a notion that is supported by
the increase in isocyanide υ(C≡N) stretching frequencies relative to
M(CNArDipp2
) (M = Pt, Pd) upon coordination of Ag(I) (υ(C≡N) =
2
Figure 11. Molecular orbital diagram for a transition metal (M) bound to a σ-
acceptor fragment (Z), showing how the LUMO of the resulting adduct can
be stabilized with respect to the acceptor-free complex.
2094 cm–1 (5); 2082 cm–1 (6)). An examination of the solid state
structures of 5 and 6 also implicates a role of the flanking Dipp aryl
rings in buttressing the M-Ag linkage through π-type interactions.
Interestingly, these contacts are reflected in the room temperature
1H NMR spectra of 5 and 6 (measured in C6D6), for which the
resonances corresponding to the Dipp aryl protons are broadened
and shifted downfield by ca. 0.2 ppm relative to those typically
observed for diamagnetic mononuclear complexes containing the
CNArDipp2 ligand. It is also notable that the different solvates of both
5 and 6 both display a square-planar coordination environment
around the Group 10 metal. While these geometries are certainly
reminiscent of Pt(II) and Pd(II), it is critical to note that the
progression of the IR υ(C≡N) stretching frequencies to higher
energies upon binding of Ag(I) is quite modest and actually less than
that seen for Tl(I). This observation serves to suggest that similar
bonding descriptions laid out above for Tl-containing 1-4 can be
extended to 5 and 6. While the use of electrons from the Group 10
metal to form a covalent interaction with Ag requires an increase of
two valence units, minimal charge transfer to Ag occurs. As such,
these M/Ag MOLPs should not be described as containing formal
M(II) centers (M = Pt, Pd).
Despite the fact that formation of a M-Ag bonding interaction
does not result in a formal oxidative event at Pt/Pd, it is remarkable
that the Ag-containing heterobimetallics 5-6 will bind THF and arene
molecules at the group 10 metal center in the solid state, whereas
the zero-valent precursors M(CNArDipp2
) (M = Pt, Pd) do not.
2
Furthermore, Pt(CNArDipp2)2 and Pd(CNArDipp2)2 do not participate in
addition reactions with stronger σ-donors (e.g. phosphines) to form
species of the type ML(CNArDipp2)2, as the attempted syntheses of
such compounds has led invariably to isocyanide dissociation
and/or decomposition. While the ability of 5 and 6 to bind an
additional Lewis base may be partly attributable to increased
positive charge on the complexes, molecular orbital considerations
provide a basis for enhanced Lewis acidity at the Group 10 metal
center of these MOLPs specifically. It has been suggested previously
that coordination of a Z-type acceptor ligand to a square-planar d8
complex should result in enhanced affinity for Lewis bases at the
open coordination site trans to the acceptor.82 Similarly, formation
of a reverse-dative σ-interaction by M(CNArDipp2)2 (nominally from
the ndZ2 orbital) to an acceptor may have a stabilizing effect on the
coaxial empty (n+1)pz orbital of the Group 10 metal (Figure 11).
While such stabilization may not be drastic, it is plausible that such
effects could promote the binding of Lewis bases at a coordination
site trans to the acceptor, resulting in square-planar [AgML2L’]+-type
species. Similar behavior was observed by Peters in the trigonal-
pyramidal Pt salt [(SiPPh3)Pt]BArF ,83 (SiPPh = (2-Ph2PC6H4)3Si) for
4
3
which the crystal structure shows a molecule of toluene bound in
the apical position trans to the silyl group. As silyl ligands can be
viewed in certain systems as silylium Lewis acids,84 the binding of an
arene molecule may be a result of Pt-to-Si σ-donation, thereby in
effect enhancing the Lewis acidic nature of the Pt complex. In
addition, similar phenomena have been observed by Gabbaï for a
Hg(II) complex85 and by Berry for a bimetallic Mo2 system.86 In these
examples, association of a Z-type fragment was shown to increase
Lewis acidity at the coordination site trans to the acceptor ligand.
However, to our knowledge, the MOLPs derived from M(CNArDipp2
)
2
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
Chemical Science
Page 8 of 10
ARTICLE
Journal Name
(M = Pt, Pd) represent unique cases where Z-ligand-promoted Lewis 2.7684(8) Å) bridged by two triflate groups. ConsisVtieenwtArwticiltehOntlhinee
acidity has been unambiguously observed for mononuclear coordination of an additional Lewis acid toDthOeI: P10t-.1A0g39u/nCi5tSiCn0531,0t4hDe
transition metal complexes. Importantly, these observations isocyanide stretching frequencies of 7 are shifted to higher energies
(2132, 2169 cm–1, KBr pellet) compared to 5. In the solid state, the
highlight the ability of σ-acceptor ligands to open up a previously
unavailable coordination site on a transition metal center without platinum centers in 7 also feature η1-C-bound benzene molecules
effecting a formal oxidative event. Furthermore, the observation trans to one of the silver atoms as seen in 5(C6H6). Interestingly
that the Ag-containing complexes 5 and 6 bind solvent molecules at however, the Pt-Cbenzene distance in 7 (d(Pt-C1) = 2.529(7) Å) is
the Group-10 metal center, while the Tl-containing complexes 1 and significantly contracted relative to that in 5(C6H6), a further
2 exhibit binding at the Tl center, is likely attributable to the greater indication of an increase in the Lewis acidity in the Pt center in 7
electronegativity of Ag relative to Tl.87 As stabilization of the empty promoted by the presence of a second Ag center. It is also
pz orbital on the Group 10 metal by a bound Lewis acid is expected important to note that relative to complex 5, the second Ag atom in
to be marginal at best, Lewis acids possessing greater group 7 (i.e. Ag(2), Figure 12) can best be described as occupying the axial
electronegativity may be expected to more effectively stabilize this position of a nominally square-planar Pt center. As the binding of
orbital and render it accessible to an exogenous Lewis base.
Lewis acids to the axial position square planar Pt(II) centers is
known,88-92 complex 7 provides additional evidence that the
presence of one Z-type ligand effectively results in the formation of
a divalent Pt center capable of binding a second Z-type ligand.
However, this electronic modulation occurs without formal
oxidation of the Pt center.
Conclusions
Zero-valent binary m-terphenyl isocyanide complexes of Pt and
Pd are excellent candidates for acting as the Lewis basic component
of Metal-only Lewis Pairs (MOLPs). In addition to stabilizing low
oxidation states, the steric encumbrance of the m-terphenyl
isocyanide ligand promotes coordinative unsaturation, yielding
electron-rich metal centers that can accommodate an exogenous
Lewis acid in the primary coordination sphere. Furthermore, the IR
υ(C≡N) resonances provide a convenient handle to assess the
degree of Group 10 metal σ-donation in these complexes. In this
work, it has been demonstrated that Pt(CNArDipp2
)
and
) can form discreet and unsupported adducts with
2
2
Pd(CNArDipp2
Tl(I). Although these bonding interactions are not particularly
robust, use of the weakly coordinating anion BArF – diminishes the
4
lability of the M-Tl bond in non-coordinating solvents. Analysis of
two M→Tl adducts by XANES spectroscopy provides compelling
evidence that any degree of formal charge transfer inherent in
these metal-metal interactions is minimal, and that therefore no
formal oxidative event takes place upon binding of Tl(I). The ability
of Pt(CNArDipp2)2 and Pd(CNArDipp2)2 to form Lewis Pairs with Ag(I)
has also been demonstrated, with FTIR spectroscopy and X-ray
crystallography suggesting, again, that no significant charge transfer
to Ag occurs in the adducts. Despite this fact, the binding of Ag(I)
activates the Group 10 metal toward the ligation of Lewis bases
trans to the Ag acceptor, thus highlighting how σ-acceptor ligands
can be utilized to tune the reactivity profiles of electron-rich
transition metal complexes. The Pt/Ag MOLP [AgPt(CNArDipp2)2]OTf
(5) can also accommodate an additional equivalent of AgOTf to
form dimeric 7, which further increases the Lewis acidity of the Pt
center. These results indicate that the presence of a reverse-dative
σ-interaction can activate the coordination site trans to it for
binding of Lewis bases despite the high trans influence exhibited by
Figure 12. Molecular structure of the cationic portion of
{[Ag2Pt(CNArDipp2)2(η1-C6H6)]2(µ-OTf)2}(OTf)2 (7). Top: Full view of the centro-
symmetric dication. Bottom: Truncated view of one triangulo-Ag2Pt core. In
both views, isopropyl groups and non-coordinating triflate anions have been
removed for clarity.
Although [AgPt(CNArDipp2)2]OTf (5) contains one acceptor
fragment bound to platinum, its Pt-Ag unit can accommodate
another equivalent of Ag(I). Stirring [AgPt(CNArDipp2)2]OTf (5) and
equimolar AgOTf in THF followed by crystallization from
benzene/THF (20:1) yields
{[Ag2Pt(CNArDipp2)2(η1-C6H6)]2(µ-
OTf)2}(OTf)2 (7) as determined by X-ray diffraction. Attempts to
synthesize a palladium analogue from [AgPd(CNArDipp2)2]OTf (6)
resulted only in decomposition. The solid-state structure of 7
(Figure 12) revealed a centro-symmetric dimer composed of
triangulo-PtAg2 cores (average d(Pt-Ag) = 2.6843(6) Å; d(Ag-Ag) =
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 10
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Z-type ligands.24,25 Such modulation can be thought of as a novel
type of cooperative effect between a Lewis acid and Lewis base,
whereby the former alters the reactivity profile of the electron rich
metal without directly participating in the reaction with an incoming
substrate. A more detailed understanding of the possibilities
afforded by such cooperative effects are currently being pursued in
our laboratory.
22.
23.
W. H. Harman and J. C. Peters, J. Am. Chem. Soc., 2V0i1e2w,A1r3tic4l,e5O0n8li0n–e
5082.
H. Braunschweig, R. D. Dewhurst, and A. Schneider, Chem. Rev.,
2010, 110, 3924–3957.
H. Braunschweig and R. D. Dewhurst, Dalton Trans., 2010, 40, 549.
A. Amgoune and D. Bourissou, Chem. Commun., 2010, 47, 859.
M. Devillard, G. Bouhadir, and D. Bourissou, Angew. Chem., Int.
Ed., 2014, 54, 730–732.
DOI: 10.1039/C5SC03104D
24.
25.
26.
27.
28.
B. R. Barnett, C. E. Moore, A. L. Rheingold, and J. S. Figueroa, J. Am.
Chem. Soc., 2014, 136, 10262–10265.
Acknowledgements
P. Gualco, T.-P. Lin, M. Sircoglou, M. Mercy, S. Ladeira, G.
Bouhadir, L. M. Pérez, A. Amgoune, L. Maron, F. P. Gabbaï, and D.
Bourissou, Angew. Chem., Int. Ed., 2009, 48, 9892–9895.
T.-P. Lin, C. R. Wade, L. M. Pérez, and F. P. Gabbaï, Angew. Chem.,
Int. Ed., 2010, 49, 6357–6360.
C. R. Wade, T.-P. Lin, R. C. Nelson, E. A. Mader, J. T. Miller, and F. P.
Gabbaï, J. Am. Chem. Soc., 2011, 133, 8948–8955.
C. R. Wade and F. P. Gabbaï, Angew. Chem., Int. Ed., 2011, 50,
7369–7372.
We are grateful to the U.S. National Science Foundation for
support of this work (CHE-0954710, CHE-1464978 and a
Graduate Research Fellowship to B.R.B.). J.S.F is a Camille
Dreyfus Teacher-Scholar (2012-2017). S.D. acknowledges the
Max Planck Foundation for funding. Portions of the data in this
manuscript were obtained at SSRL. SSRL is supported by the
U.S. Department of Energy, Office of Science, Office of Basic
29.
30.
31.
Energy Sciences under Contract No. DE-AC02-76SF00515. The 32.
SSRL Structural Molecular Biology Program is supported by the
T.-P. Lin, I.-S. Ke, and F. P. Gabbaï, Angew. Chem., Int. Ed., 2012,
51, 4985–4988.
J. S. Jones, C. R. Wade, and F. P. Gabbaï, Angew. Chem., Int. Ed.,
2014, 53, 8876–8879.
J. P. Krogman, J. R. Gallagher, G. Zhang, A. S. Hock, J. T. Miller, and
Christine M. Thomas, Dalton Trans., 2014, 43, 13852–13857.
G. M. Sheldrick and R. N. F. Simpson, J. Chem. Soc., A, 1968, 1005.
W. Clegg and P. J. Wheatley, J. Chem. Soc., A, 1971, 3572.
B. A. Sosinsky, R. G. Shong, B. J. Fitzgerald, N. Norem, and C.
O'Rourke, Inorg. Chem., 1983, 22, 3124–3129.
33.
DOE Office of Biological and Environmental Research, and by
the National Institutes of Health, National Institute of General
Medical Sciences (including P41GM103393).
34.
35.
36.
37.
Notes and References
1.
2.
D. F. Shriver, Acc. Chem. Res., 1970, 3, 231–238.
W. Hieber, in Advances in Organometallic Chemistry; F. G. A. Stone
and R. West, Ed.; Academic Press, 1970; Vol. 8, pp. 1–28.
W. Hieber and F. Leutert, Naturwissenschaften, 1931, 19, 360–361.
W. Hieber, Angew. Chem., 1936, 49, 463–464.
D. M. P. Mingos, J. Organomet. Chem. 2001, 635, 1–8.
Chatt, J.; Duncanson, L. A. J. Chem. Soc. 1953, 2939.
D. M. P. Mingos, in Advances in Organometallic Chemistry; F. G. A.
Stone and R. West, Ed.; Academic Press, 1977; Vol. 15, pp. 1–51.
L. Vaska, Acc. Chem. Res., 1968, 1, 335–344.
L. M. Rendina and R. J. Puddephatt, Chem. Rev., 1997, 97, 1735–
1754.
J. K. Stille and K. S. Y. Lau, Acc. Chem. Res., 1977, 10, 434–442.
C. E. Johnson and R. Eisenberg, J. Am. Chem. Soc., 1985, 107,
3148–3160.
J. P. Collman and W. R. Roper, in Advances in Organometallic
Chemistry; F. G. A. Stone and R. West, Ed.; Academic Press, 1969,
Vol 7, pp. 53–94.
M. L. H. Green, J. Organomet. Chem., 1995, 500, 127–148.
J. M. Burlitch, M. E. Leonowicz, R. B. Petersen, and R. E. Hughes,
Inorg. Chem., 1979, 18, 1097–1105.
S. J. La Placa and J. A. Ibers, Inorg. Chem., 1966, 5, 405–410.
K. W. Muir and J. A. Ibers, Inorg. Chem., 1969, 8, 1921–1928.
R. A. Fischer and J. Weiss, Angew. Chem., Int. Ed., 1999, 38, 2830–
2850.
A. F. Hill, G. R. Owen, A. J. P. White, and D. J. Williams, Angew.
Chem., Int. Ed., 1999, 38, 2759–2761.
38.
39.
40.
41.
T. Tanase, Y. Yamamoto, and R. J. Puddephatt, Organometallics,
1996, 15, 1502–1504.
J. Bauer, H. Braunschweig, and R. D. Dewhurst, Chem. Rev., 2012,
112, 4329–4346.
R. Grigg, V. Loganathan, V. Santhakumar, and A. Teasdale,
Tetrahedron Lett., 1991, 32, 687–690.
R. Grigg, P. Kennewell, and A. J. Teasdale, Tetrahedron Lett., 1992,
33, 7789–7792.
R. Grigg and V. Sridharan, Tetrahedron Lett., 1993, 34, 7471–7474.
C. C. Roberts, D. M. Matias, M. J. Goldfogel, and S. J. Meek, J. Am.
Chem. Soc., 2015, 137, 6488–6491.
R. G. Pearson, Chem. Rev., 1985, 85, 41–49.
G. Parkin, J. Chem. Educ., 2006, 83, 791.
G. Parkin, Organometallics, 2006, 25, 4744–4747.
A. F. Hill, Organometallics, 2006, 25, 4741–4743.
B. J. Fox, Q. Y. Sun, A. G. DiPasquale, A. R. Fox, A. L. Rheingold, and
J. S. Figueroa, Inorg. Chem., 2008, 47, 9010–9020.
B. J. Fox, M. D. Millard, A. G. DiPasquale, A. L. Rheingold, and J. S.
Figueroa, Angew. Chem., Int. Ed., 2009, 48, 3473–3477.
L. A. Labios, M. D. Millard, A. L. Rheingold, and J. S. Figueroa, J. Am.
Chem. Soc., 2009, 131, 11318–11319.
G. W. Margulieux, N. Weidemann, D. C. Lacy, C. E. Moore, A. L.
Rheingold, and J. S. Figueroa, J. Am. Chem. Soc., 2010, 132, 5033–
5035.
A. E. Carpenter, G. W. Margulieux, M. D. Millard, C. E. Moore, N.
Weidemann, A. L. Rheingold, and J. S. Figueroa, Angew. Chem., Int.
Ed., 2012, 51, 9412–9416.
3.
4.
5.
6.
7.
42.
43.
8.
9.
44.
45.
46.
47.
48.
10.
11.
12.
49.
50.
51.
13.
14.
15.
16.
17.
52.
18.
19.
J. S. Figueroa, J. G. Melnick, and G. Parkin, Inorg. Chem., 2006, 45,
7056–7058.
K. Pang, J. M. Tanski, and G. Parkin, Chem. Commun., 2008, 1008.
M.-E. Moret and J. C. Peters, J. Am. Chem. Soc., 2011, 133, 18118–
18121.
53.
54.
55.
A. E. Carpenter, I. Wen, C. E. Moore, A. L. Rheingold, and J. S.
Figueroa, Chem. Eur. J., 2013, 10452–10457.
B. M. Emerich, C. E. Moore, B. J. Fox, A. L. Rheingold, and J. S.
Figueroa, Organometallics, 2011, 30, 2598–2608.
C. C. Mokhtarzadeh, G. W. Margulieux, A. E. Carpenter, N.
20.
21.
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
Chemical Science
Page 10 of 10
ARTICLE
Journal Name
Weidemann, C. E. Moore, A. L. Rheingold, and J. S. Figueroa, Inorg.
Chem., 2015, 54, 5579–5587.
2000, 200-202, 831–873.
S. S. Stahl, J. A. Labinger, and J. E. Bercaw, J. Am. Chem. Soc., 1996,
View Article Online
DOI: 10.1039/C5SC03104D
80.
56.
Given the uncertainty in values for the covalent radii of transition
118, 5961–5976.
metals and heavy main-group elements, we present a range for 81.
the sum of the covalent radii of Pt and Tl based on several
commonly used tabulations (in Å): rcov(Pt) 1.36 + rcov(Tl) 1.45 = 82.
2.81, a): B. Cordero, V. Gómez, A. E. Platero-Prats, M. Revés, J. 83.
Echeverría, E. Cremades, F. Barragán, and S. Alvarez, Dalton Trans.
2008, 2832. rcov(Pt) 1.30 + rcov(Tl) 1.44 = 2.74, b): L. Pauling, The 84.
Nature of the Chemical Bond, 3rd Ed.; Cornell University Press:
Cornell, NY, 1960; Chapter 11, p 403. rcov(Pt) 1.23 + rcov(Tl) 1.44 = 85.
2.67, c): P. Pyykkö and M. Atsumi, Chem.–Eur. J. 2009, 15, 186.
D. D. Wick and K. I. Goldberg, J. Am. Chem. Soc., 1997, 119, 10235–
10236.
G. Aullón and S. Alvarez, Inorg. Chem., 1996, 35, 3137–3144.
C. Tsay, N. P. Mankad, and J. C. Peters, J. Am. Chem. Soc., 2010,
132, 13975–13977.
V. K. Dioumaev and J. F. Harrod, Organometallics, 1996, 15, 3859–
3867.
T.-P. Lin, R. C. Nelson, T. Wu, J. T. Miller, and F. Gabbai, Chem. Sci.,
2012, 3, 1128–1136.
57.
58.
P. Pyykkö, Chem. Rev., 1997, 97, 597–636.
V. J. Catalano, B. L. Bennett, S. Muratidis, and B. C. Noll, J. Am. 87.
Chem. Soc., 2001, 123, 173–174.
86.
B. S. Dolinar and J. F. Berry, Inorg. Chem. 2013, 52, 4658–4667.
C. H. Suresh and N. Koga, J. Am. Chem. Soc., 2002, 124, 1790–
1797.
59.
60.
61.
S. Wang, J. P. Fackler, C. King, and J. C. Wang, J. Am. Chem. Soc., 88.
1988, 110, 3308–3310.
E. J. Fernández, A. Laguna, J. M. A. Lopez-de-Luzuriaga, M. Elena 89.
Olmos, and J. Perez, Chem. Commun., 2003, 1760.
S. Jamali, M. M. Ashtiani, Z. Jamshidi, E. Lalinde, M. T. Moreno, H. 90.
Samouei, E. Escudero-Adán, J. Benet-Buchholz, Inorg. Chem., 2013,
M.-E. Moret and P. Chan, J. Am. Chem. Soc., 2009, 131, 5675–
5690.
T. Yamaguchi, F. Yamazaki, and T. Ito, J. Am. Chem. Soc., 2001, 123,
743–744.
R. Uson, J. Fornies, M. Tomas, I. Ara, J. M. Casas, and A. Martin, J.
Chem. Soc., Dalton Trans., 1991, 2253–2264.
T. Yamaguchi, F. Yamazaki, and T. Ito, J. Am. Chem. Soc., 1999, 121,
7405–7406.
L. R. Falvello, J. Fornies, A. Martin, R. Navarro, V. Sicilia, and P.
Villarroya, Inorg. Chem., 1997, 36, 6166–6171.
52, 10729–10731.
91.
62.
63.
B. M. Still, P. G. A. Kumar, J. R. Aldrich-Wright, and W. S. Price,
Chem. Soc. Rev., 2007, 36, 665–686.
92.
For each arene ring seen to be interacting with Tl in 3 (two per
molecule, two independent molecules per asymmetric unit), there
are two Tl-C bond lengths that are appreciably shorter than the
others for that given arene ring. As such, we believe this
interaction is best characterized as having η2 hapticity.
E. J. Fernández, A. Laguna, J. M. López-de-Luzuriaga, M. Monge, M.
Montiel, and M. E. Olmos, Inorg. Chem., 2007, 46, 2953–2955.
S. H. Strauss, M. D. Noirot, and O. P. Anderson, Inorg. Chem., 1986,
25, 3850–3851.
64.
65.
66.
67.
68.
M. D. Noirot, O. P. Anderson, and S. H. Strauss, Inorg. Chem., 1987,
26, 2216–2223.
Y. Sarazin, N. Kaltsoyannis, J. A. Wright, and M. Bochmann,
Organometallics, 2007, 26, 1811–1815.
While naturally-occuring thallium also consists of 29.5% 203Tl (I =
1/2), complexes containing Pt-Tl bonds typically only resolve
coupling to 205Tl in their 195Pt NMR spectra. For example, see Ref.
58.
69.
70.
S. Fuertes, C. H. Woodall, P. R. Raithby, and V. Sicilia,
Organometallics, 2012, 31, 4228–4240.
U. Belío, S. Fuertes, and A. Martín, Dalton Trans., 2014, 43, 10828–
10843.
71.
72.
F. de Groot, Chem. Rev., 2001, 101, 1779–1808.
N. C. Tomson, L. A. Labios, T. Weyhermüller, J. S. Figueroa, and K.
Wieghardt, Inorg. Chem., 2011, 50, 5763–5776.
73.
R. J. Wright, A. D. Phillips, S. Hino, and P. P. Power, J. Am. Chem.
Soc., 2005, 127, 4794–4799.
74.
75.
P. Pyykkö, Chem. Rev., 1988, 88, 563–594.
A. E. Carpenter, A. J. McNeece, B. R. Barnett, A. L. Estrada, C. C.
Mokhtarzadeh, C. E. Moore, A. L. Rheingold, C. L. Perrin, and J. S.
Figueroa, J. Am. Chem. Soc., 2014, 136, 15481–15484.
For other examples of Metal-only Lewis Pairs with Ag as the Lewis
acidic component, see Ref. 39 and references cited therein.
See the Supporting Information, section S1.
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, 2176–2179.
76.
77.
78.
79.
S. M. Hubig, S. V. Lindeman, and J. K. Kochi, Coord. Chem. Rev.,
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins