Towards Naked Zinc(II) in the Condensed Phase: A Highly Lewis Acidic ZnII Dication Stabilized by Weakly Coordinating Carborate Anions

Article abstract of DOI:10.1002/anie.202012287

The employment of the hexyl-substituted anion [HexCB₁₁Cl₁₁]^? allowed the synthesis of a Zn^II species, Zn[HexCB₁₁Cl₁₁]₂, 3, in which the Zn²⁺ cation is only weakly coordinated to two carborate counterions and that is soluble in low polarity organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of at least one of the counterions, and this near nakedness of the cation results in high catalytic activity in the hydrosilylation of 1-hexene and 1-methyl-1cyclohexene. Fluoride ion affinity (FIA) calculations reveal a solution Lewis acidity of 3 (FIA=262.1 kJ mol^?1) that is higher than that of the landmark Lewis acid B(C₆F₅)₃ (FIA=220.5 kJ mol^?1). This high Lewis acidity leads to a high activity in catalytic CO₂ and Ph₂CO reduction by Et₃SiH and hydrogenation of 1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, and DFT studies.

Full text of DOI:10.1002/anie.202012287

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Towards “naked” Zn2+ in the condensed phase: synthesis,
structure and reactivity of a highly Lewis acidic Zn(II) dication
stabilized by weakly coordinating carborate anions
Authors: Samuel Dagorne and Rudolf J. Wehmschulte
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10.1002/anie.202012287
Angewandte Chemie International Edition
Table of Contents Only
A salt compound containing a formal Zn2+ dication only stabilized by weakly coordinated
carborate anions was first structurally characterized and shown to be soluble in low polarity
solvents. Based on its reactivity with alkene, alkyne and in hydrosilylation catalysis, it is a
strong Lewis acid, possibly the strongest Zn-based Lewis acid to date.
Keywords: Zinc – Lewis acid – cation – hydrosilylation – carborate
1
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Towards “naked” Zn2+ in the condensed phase: synthesis, structure and reactivity of a
highly Lewis acidic Zn(II) dication stabilized by weakly coordinating carborate anions
Nicolas Adet,a David Specklin,a Christophe Gourlaouen,a Thibault Damiens,a Béatrice
Jacques,a Rudolf J. Wehmschulteb,* and Samuel Dagornea,*
a Institut de Chimie de Strasbourg, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67000
Strasbourg, France.
b
Chemistry Program, Florida Institute of Technology, 150 West University Boulevard,
Melbourne, Florida 32901-6975, United States
Abstract. The employment of the hexyl-substituted anion [HexCB11Cl11]- allowed for
the first time the synthesis of a Zn(II) species, Zn[HexCB11Cl11]2, 3, in which the Zn2+ cation
is only weakly coordinated to two carborate counterions and that is soluble in low polarity
organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of
at least one of the counterions, and this near “nakedness” of the cation results in high catalytic
activity in the hydrosilylation of 1-hexene and 1-methyl-1cyclohexene. Fluoride Ion Affinity
(FIA) calculations reveal a solution Lewis acidity of 3 (FIA = 262.1 kJ·mol-1) that is higher
than that of the landmark Lewis acid B(C6F5)3 (FIA = 220.5 kJ·mol-1). This high Lewis acidity
leads to a high activity in catalytic CO2 and Ph2CO reduction by Et3SiH and hydrogenation of
1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was
characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray
diffraction and DFT studies.
* Email: rwehmsch@fit.edu, dagorne@unistra.fr
2
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Metal-centered Lewis acids are widespread powerful and versatile reagents in all areas
of chemistry, ranging from synthetic chemistry to material science, due to the utility of various
Lewis acidic metal ions for substrate activation/functionalization.1 In that regard, low-
coordinate ligand-supported metal cations have attracted attention over the years to access
electrophilic/reactive species for enhanced reactivity.2 Ideally though, the simplest of all metal
Lewis acids, i.e. ligand-free (“naked”) or weakly coordinated metal cations, should be most
reactive for chemical functionalization since direct “naked” metal cation/substrate activation
should maximize electrophilic activation. However, access to stable ligand-free metal ions in
the condensed phase has thus far remained a major challenge, which is due to their high
electrophilicity, their instability and/or insolubility in common organic media. Over the past
years, the use of modern weakly coordinating anions (WCAs) such as [B(C6F5)4]-, [Al(ORF)4]-
and halogenated carborate ions (most notably [CH6B6X6]- and [CHB11X11]-; X = Cl, I) for
minimal cation-anion interactions,3 has led to the characterization of several mono-valent and
M+ Lewis acids only stabilized by a low basicity solvent and a WCA, including Li+, Ag+ and
M+ (M = group 13 metal) salts.4,5,6,7,8,9,10 Such salts display enhanced reactivity due to weaker
cation-anion interactions, including the acceleration of Diels-Alder reactions with
Li[B{C6H3(CF3)2-3,5}4],4 carbonyl-ene reactions catalyzed by Li[B(C6F5)4],5 and the
polymerization of isobutene catalyzed by [Ga(arene)3][Al{OC(CF3)3}4].6 Also noteworthy, an
Ag(I) complex with two P4 molecules coordinated to one Ag+ cation was characterized.11
To date, weakly coordinated or “naked” M2+ divalent cations that are stable at room temperature
and soluble in low basicity/polarity solvents are unknown, despite their interest as strong Lewis
acids/electrophiles. Compounds such as M[BF4]2 or M[EF6]2 (M = +2 cation, E = As, Sb),
prepared by the reaction of MF2 with BF3 or EF5 in anhydrous HF, are known but insoluble in
most organic solvents.12 Species Hg[B12H12]13 and Ni[B12H12],14 were obtained from
dehydration of hydrate salts Hg(H2O)x[B12H12] and Ni(H2O)6[B12H12], respectively. The
3
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10.1002/anie.202012287
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solvent-free zinc salt Zn[Al{OCH(CF3)2}4]2 was also recently characterized, but the rather short
Zn···O contacts (1.986 Å avg.) significantly quench the Lewis acidity of the Zn2+ center as
deduced from solid state and solution data.15 Zn(II) complexes of electron-rich arenes
Zn(SbF6)2·C6Me6 and Zn(SbF6)2·C6HMe5 have only been characterized by NMR spectroscopy
in SO2 solution.16 Only very recently, the structure of Sr[Al{OC(CF3)3}4]2 was reported, which
features a partially “naked” large and therefore less Lewis acidic Sr2+ cation.17
Zn(II) salts, considered as borderline Lewis acids in Pearson’s HSAB classification, are
commonly used as Lewis acids for the mediation of various stoichiometric and catalytic
transformations. Well-defined Zn organometallics such as arylzinc species Zn(C6F5)2 are well-
established Lewis acid catalysts, especially for the polymerization of various monomers.18 Of
particular interest, ligand-supported Zn(II)-based organocations are well-established
electrophilic species but have attracted recent attention since Zn is an Earth-abundant and
inexpensive metal source.2a,19 Recent developments, including from our labs, have shown that
a number of reactive low-coordinate (two- and three-coordinate) Zn(II) cations, all consisting
of ligand-stabilized [Zn–R]+ mono-cations (R = alkyl, aryl), may behave as Lewis acids for the
mediation of various catalytic reactions ranging from alkyne hydroamination to alkyne, alkene
and CO2 hydrosilylation.20 We herein report on the synthesis and structural characterization of
the first weakly coordinated Zn2+ cation (isolated as Zn[WCA]2) that is stable and soluble in
low polarity organic solvents. We also provide preliminary reactivity studies indicating an
unprecedentedly strong Lewis acidity for a Zn(II) species.
As an entry to Zn[WCA]2, the fully chlorinated carborate anion [CHB11Cl11]-, which is one of
the least coordinating and least reactive anions known thus far,21 was initially tested to access
stable and characterizable Zn[WCA]2 salts. To generate a formal Zn2+ di-cation in a low (Lewis)
basicity medium, Et- abstraction from [EtZn(C6H6)][CHB11Cl11] (1),20a a formal source of the
4
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[Zn–Et]+ mono-cation, with [Ph3C][CHB11Cl11] was first attempted. The reaction of a 1/1
1/[Ph3C][CHB11Cl11] mixture (C6D5Br, 24 h at RT and then 24 h at 95 °C) led to complete
consumption of both reactants, the formation of Ph3CH and ethylene (as deduced from NMR
data) in line with Et- abstraction from the [Zn–Et]+ fragment, along with the precipitation of
colorless solid, possibly Zn[CHB11Cl11]2. However, poor solubility precluded structural
identification whether in solution or in the solid state, prompting us towards the synthesis of a
more soluble WCA as a Zn2+ counterion.22 To this end, anion [CHB11Cl11]- was C-
functionalized by a hexyl group to access the more soluble carborate anion [HexCB11Cl11]-.23
The C–H deprotonation of Cs[CHB11Cl11] and subsequent hexyl functionalization afforded
Cs[HexCB11Cl11], isolated in 74% yield (Scheme 1). Salt metathesis between Cs[HexCB11Cl11]
and Ph3CCl led to the corresponding trityl salt [Ph3C][HexCB11Cl11] (2, 73% yield), as
confirmed by X-ray crystallographic analysis (see SI). IR data for salt [HNOct3][HexCB11Cl11]
(see SI for its preparation) agree with a slightly more Lewis basic [HexCB11Cl11]- anion
compared to [CHB11Cl11]- (nNH = 3176 and 3180 cm-1, respectively) due to the better electron
donor ability of the hexyl group (vs. hydrogen).21
1) nBuLi
2) Hex-I
Cs[HexCB11Cl11]
Cs[CHB11Cl11]
- nBuH
- LiI
Ph3CCl
Hex
- CsCl
C
B
Cl
Cl
Cl
Cl
B
B
B
Cl
Cl
B
B
B
B
Ph3C
B
B
B
Cl
Cl
Cl
Cl
[Ph3C][HexCB11Cl11] (2)
Scheme 1. Synthesis of trityl salt [Ph3C][HexCB11Cl11] (2)
5
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The synthesis of Zn[HexCB11Cl11]2 (3, Scheme 2) was achieved directly from ZnEt2 and
trityl salt 2. Thus, the double ionization reaction of ZnEt2 with 2 equiv of 2 (PhBr, 60 °C, 6 h)
led to the quantitative formation of 3 along with Ph3CH and ethylene, as deduced from NMR
data. Species 3, isolated in 71% yield, is soluble and stable for days in PhBr (RT) but
decomposes within minutes in CH2Cl2 (RT) to unknown species.
2 ( 2 equiv)
60 °C, PhBr
Zn[HexCB11Cl11]2 (3)
ZnEt2
- 2 Ph3CH
- 2 C2H4
Scheme 2. Synthesis of Zn[HexCB11Cl11]2 (3)
The solid state molecular structure of 3 was determined through XRD studies (Figure 1). It
crystallizes as an ion pair with a central Zn2+ cation in a slightly distorted octahedral
environment since surrounded by two [HexCB11Cl11]- anions coordinated in a k3-Cl3 fashion.
The Zn…Cl contacts (2.495 Å average) are shorter than those in compound
[EtZn(C6H6)][CHB11Cl11] (2.613 Å average), reflecting the higher charge at Zn in 3 and thus
stronger electrostatic interactions. As has been observed previously,20a, 31b the coordination to
the Zn2+ cation results in a slight elongation of the involved B-Cl bonds (1.801 Å average versus
1.763 Å average).
6
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10.1002/anie.202012287
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Figure 1. Molecular structure (ORTEP view, 50% probability) of Zn[HexCB11Cl11]2 (3). H
atoms have been omitted for clarity. Selected distances (Å) and angles (°): Zn(1)···Cl(1)
2.4544(7), Zn(1)···Cl(2) 2.4905(7), Zn(1)···Cl(3) 2.5456(7), B-Cl(···Zn) 1.810(avg.), B-Cl
1.763(avg.), Cl(1)-Zn-Cl(1A) 180, Cl(1)-Zn-Cl(2) 90.85(2), Cl(1)-Zn-Cl(3) 86.94(2).
Figure 2. DFT-estimated (B3LYP/6-31+G**) Non-Covalent Interaction (NCI) analysis of a
model species for 3. Attractive electrostatic interactions appear in blue areas and attractive
dispersion forces appear in green areas.
Computations on the electronic structure of species 3 using Electron Localization Function
(ELF, see SI) and Non-Covalent Interactions (NCI, Figure 2) analysis agree with purely
electrostatic interactions (and no covalence) between the central Zn2+ cation and the
surrounding chlorines. Importantly, species 3 is clearly dynamic in solution as deduced by
7
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NMR data indicating a ready cation/anion dissociation at room temperature in C6D5Br. Thus,
DOSY NMR measurements for 3 led to an estimated hydrodynamic volume of 1100 Å, i.e.
lying between those of free [HexCB11Cl11]- anion (around 850 Å) and solid-state characterized
3 (around 1650 Å). This is consistent with fast cation/anion dissociation in 3 on the NMR
timescale with stabilization of the Zn2+ by PhBr coordination.24 This is corroborated by DFT
calculations (B3LYP/6-31+G**, PhBr as solvent, modelled in the presence of one PhBr
molecule) with the dissociation of 3 to [Zn(HexCB11Cl11)(PhBr)]+ and free [HexCB11Cl11]-
anion computed to occur at little energy cost (DG = 28.4 kJ·mol-1).25 Furthermore, to assess the
Lewis acidity of species 3, its Fluoride Ion Affinity (FIA) was DFT-estimated (B3LYP/6-
31+G**, PhBr, see SI).26,27 In agreement with a highly electrophilic Zn(II) center, FIA
calculations are consistent with 3 (FIA = 262.1 kJ·mol-1) being significantly more Lewis acidic
than the ion-pair [EtZn(C6H6)][CHB11Cl11] (FIA = 224.3 kJ·mol-1), the two-coordinate
+
(NHC)Zn–C6F5 cation (NHC = IDipp, FIA = 185.5 kJ·mol-1) and the landmark Lewis acid
B(C6F5)3 (FIA = 220.5 kJ·mol-1).
To substantiate the electrophilicity of the Zn(II) center in 3, it was first reacted with
unsaturated substrates such as 1-hexene and 1-octyne, as well as H2. 1H NMR data of a 1/1 3/1-
hexene mixture (RT, C6D5Br) agree with immediate reaction, but a ready polymerization of 1-
hexene precluded any adduct characterization. This was further confirmed by the reaction of a
1/100 3/1-hexene mixture (RT, C6D5Br) leading to a 61% conversion of 1-hexene to poorly
defined poly(1-hexene) oligomers within 3 h, as deduced from GPC data (Mn = 924 g. mol-1, Ð
= 1.76). DFT (B3LYP/6-31+G**, PhBr) calculations predict that the formation of p-adduct
[(HexCB11Cl11)Zn(propene)]+ (along with free carborate) from 3 and propene should occur
under the reaction conditions (DG = 5.9 kJ·mol-1), reflecting the strong Lewis acidity of Zn(II)
center.28 Alkene oligo-/poly-merization mediated by Lewis acidic metal complexes is well-
established.2a Likewise, 1-octyne immediately reacts with 1 equiv of 3 (RT, C6D5Br) according
8
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10.1002/anie.202012287
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to 1H NMR data, provoking a significant downfield of the alkynyl proton 1H NMR shift (s, br,
d = 4.40 ppm) vs. that of free 1-octyne (t, d = 1.92 ppm), in line with an enhanced vinylic
character. Though the latter suggests the formation of a Zn–alkyne adduct, further
characterization was precluded due its decomposition within a couple of hours to unknown
species. According to DFT (B3LYP/6-31+G**, PhBr) calculations with propyne as the
modelled alkyne, the formation of p-adduct [(HexCB11Cl11)Zn(propyne)]+ (along with free
carborate) from 3 and propyne also occurs at little energy cost (DG = 7.9 kJ·mol-1), in agreement
with a labile Zn–alkyne adduct at RT. The reactivity of salt 3 with H2 was also probed: no
apparent reaction was observed between 3 under H2 (3 bar) at RT or 90 °C in C6D5Br for 2 h.
Next, species 3 was evaluated in hydrosilylation catalysis (alkene and CO2) to probe
the ability of 3 for Si-H activation.29 In the presence of HSiEt3, species 3 (1 mol%) catalyzes
fast 1-hexene hydrosilylation at room temperature (C6D5Br) with a quantitative conversion to
4 within 15 min (Scheme 3). As a comparison, [EtZn(C6H6)][CHB11Cl11] is an inactive catalyst
at room temperature while cation [(IDipp)Zn–C6F5]+ and B(C6F5)3 proceed much more
slowly.20a,20c,30 A similar high activity was observed for the hydrosilylation of 1-
methylcyclohexene catalyzed by 3 (1 mol%, C6D5Br, RT, 15 min) and selectively led to the
cis-hydrosilylated product 5, consistent with a selective anti-1,2-addition of Si–H to the C=C
bond. Though species 3 remains intact after olefin hydrosilylation catalysis, an NMR control
experiment of a HSiEt3/3 mixture showed that species 3 interacts with HSiEt3 (2 equiv, PhBr,
RT) with an immediate broadening of the Si-H 1H NMR resonance, in line with Si-H activation
by the Zn(II) cationic center (see SI).
Et3Si
4
5
C4H9
3 (1% mol.)
C4H9
SiEt3
+
HSiEt3
RT, PhBr, 15 min
Scheme 3. Olefin hydrosilylation catalyzed by Zn(II) species 3.
9
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Consistent with 3/HSiEt3 interactions, HSiEt3 redistribution was observed over time in the
presence of a catalytic amount of 3 (1 mol% vs. HSiEt3), with the formation of a mixture of
SiEt4 (38% conv. of initial HSiEt3), HSiEt3, H2SiEt2 and H3SiEt after 16 h at room temperature,
1
13
29
as indicated by H, C, Si and 2D NMR analysis (see SI). Interestingly, according to DFT
computation (B3LYP/6-31+G**, PhBr), the formation of the [Et3Si….H….SiEt3]+ silylium
cation and the Zn–H species [(HexCB11Cl11)Zn–H] from strong Lewis acid 3 and 2 equiv of
HSiEt3 is possible at low energy cost (DG = 25.9 kJ·mol-1), though such products were not
experimentally observed.31,32 Besides, as DFT-computed, HSiEt3 cleavage mediated by 3 is
even more accessible in the presence of an alkene (propene as model) to afford
[(HexCB11Cl11)Zn–H] and cation [(propyl)SiEt3]+ (DG = 9.2 kJ·mol-1). In view of the latter and
for comparison with 3, hydrosilylation of methylcyclohexene catalyzed by
[Ph3C][HexCB11Cl11] (1% mol vs. HSiEt3, RT, C6D5Br),33 was studied: it was found to proceed
with a similar rate (quantitative within 15 min) and selectivity with the formation of the cis-
product 5, as typically observed in silylium-catalyzed alkene hydrosilylation.30,34,35 Altogether,
though no clear-cut mechanism may be proposed at this stage, DFT and experimental data
strongly suggest the involvement of a transient silylium cation, generated from the reaction of
3 with HSiEt3, to account for the observed catalytic activity and selectivity in alkene
hydrosilylation.
3 (0.5% mol. vs. HSiEt3)
2/1 HSiEt3/Ph2C=O ratio
O
Ph
Ph
RT, PhBr, 1 h
Ph
Ph
- Et3Si-O-SiEt3
3 (1% mol. vs. HSiEt3)
CO2
HSiEt3
+
CH4
90 °C, PhBr, 4 h
- 2 Et3Si-O-SiEt3
97% conv.
Scheme 4. Hydrosilylation of C=O substrates catalyzed by species 3.
10
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Species 3 was also tested in hydrosilylation/deoxygenation catalysis of C=O substrates
(Scheme 4). In the presence of 3 (1 mol%), a 1/1 mixture of benzophenone/HSiEt3 (C6D5Br,
RT, 5 h, not optimized) led to the formation of doubly reduced product Ph2CH2 (50 % conv)
along with side-product Et3SiOSiEt3 and 50% of unreacted Ph2C=O, based on 1H NMR data.
Starting from a 1/100/200 3/Ph2C=O/HSiEt3 mixture led to an 80% conversion of Ph2C=O to
reduction products PhCH-OSiEt3/Ph2CH2 in a 1/15 ratio within 15 min at RT. A complete
formation of PhCH2Ph (along with equimolar amount of Et3SiOSiEt3) occurred within 1 h at
room temperature in C6D5Br. Interestingly, CO2, a more challenging C=O substrate, may also
be reduced by HSiEt3 in the presence of 3 as catalyst. An initial run at room temperature (10
mol% of 3, 1.5 atm CO2, C6D5Br) showed slow CO2 hydrosilylation (15% silane conversion
after 60 h) with the observation of reduction products Et3SiOCH2OSiEt3, MeOSiEt3 and
eventually CH4 as the reduction reaction proceeds.36 However, satisfyingly, species 3 (1 mol%
vs. HSiEt3) efficiently and selectively catalyzed CO2 hydrosilylation upon heating (1.5 atm
CO2, C6D5Br, 90 °C) with a nearly quantitative conversion of HSiEt3 (97%) to methane and
SiEt4/siloxanes by-products within 4 h, as deduced from NMR and GC-MS data (SI).
Remarkably, as a Lewis acid catalyst in CO2 hydrosilylation, species 3 is considerably more
active than any other Zn(II) cations such as [EtZn(C6H6)][CHB11Cl11], two-coordinate
[(NHC)Zn–R]+ systems and even group 13 metal cations of the type [MR2]+ (M = Al, Ga) thus
far reported.20a,20c,37 No adduct formation was observed between 3 and CO2 at various
13
temperatures (1.5 atm CO2, C6D5Br) according to C data recorded from -20 °C to 90 °C.
Under the studies’ conditions and given the reactivity of 3 with HSiEt3 (vide supra), CO2
hydrosilylation catalysis by 3 is likely to proceed through the initial involvement of cation
[Et3Si….H….SiEt3]+ cation and/or [(HexCB11Cl11)Zn–H]. To gain additional insight, the relative
performances of 3 vs. [Et3Si….H….SiEt3]+ were contrasted. Thus, CO2 hydrosilylation initiated
11
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by [Ph3C][HexCB11Cl11] (1% mol vs. HSiEt3, 70 °C, 2.5 h, C6D5Br) proceeded twice as fast as
that mediated by 3 (1% mol) under identical conditions (61% vs. 30% conversion of HSiEt3,
respectively), both catalysis yielding methane as the only reduction product.38 The latter could
be consistent with cation [Et3Si….H….SiEt3]+ being the catalytically active component upon
associating 3 and HSiEt3, with a lower activity due to a smaller concentration in silylium as the
catalysis proceeds. Though a few ligand-supported Zn–H+ cations are known to effectively
reduce CO2 under similar reaction conditions to ours,39 the possible inactivity of a nearly
“naked” Zn–H moiety such as [(HexCB11Cl11)Zn–H] could be due to its decomposition under
such conditions.
Finally, in preliminary studies, highly Lewis acidic species 3 was also tested in transfer
hydrogenation of alkenes using 1,4-cyclohexadiene (CHD) as hydrogen source, a very
convenient and safe H2 surrogate. Such hydrogenations may be catalyzed by gallium or boron
Lewis acidic complexes, though heating and long reaction times are frequently required.40 A
Zn(II) cation was also recently reported to catalyze hydrogenation transfer of 1,1-
diphenylethylene at 80 °C with 24 h using 10 mol% of catalyst.41 Satisfyingly, species 3 (2
mol% vs. substrates) performed much better and efficiently catalyzed 1,1-diphenylethylene
hydrogenation to Ph2CH-CH3 at room temperature in the presence of CHD within 3 h (Scheme
5), further illustrating the strong Lewis acidity of the Zn2+ center of 3.
H
H
H
3 (2% mol.)
H
+
RT, PhBr, 3 h
- C6H6
Ph
Ph
Ph
Ph
H
H
86% conv.
Scheme 5. Transfer hydrogenation of 1,1-diphenylethylene catalyzed by species 3.
In conclusion, we synthesized and characterized the first example of a compound
incorporating a formal Zn2+ cation only stabilized by weakly coordinating anions, that is stable
12
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at room temperature and soluble in low polarity organic solvents. Based on its reactivity with
various substrates, it stands as a strong (perhaps the strongest) Zn-based Lewis acid in solution
thanks to ready anion dissociation even in a low-basicity solvent such as PhBr. It constitutes an
important step forward towards a “naked” Zn(II) dication in the condensed phase, i.e. a
compound in which cation···anion interactions are minimized as far as possible. Further
reactivity studies of such Zn(II) dications for the activation of various small molecules as well
as access to other “naked” metal cations are currently underway in our labs.
Acknowledgments. The CNRS and the University of Strasbourg are gratefully thanked
for financial support. Part of this work was also supported by the Agence Nationale de la
Recherche (ANR): ANR project Tu-Zin-Cat (ANR-19-CE07-0020-01). N. A. thanks the icFRC
(Chemistry Research Foundation of the University of Strasbourg) for a PhD fellowship.
13
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