Copper(i) and silver(i) chemistry of vinyltrifluoroborate supported by a bis(pyrazolyl)methane ligand

Article abstract of DOI:10.1039/d1dt00974e

Although unsaturated organotrifluoroborates are common synthons in metal-organic chemistry, their transition metal complexes have received little attention. [CH₂(3,5-(CH₃)₂Pz)₂]Cu(CH₂CHBF₃), (SIPr)Cu(MeCN)(CH₂CHBF₃) and [CH₂(3,5-(CH₃)₂Pz)₂]Ag(CH₂CHBF₃) represent rare, isolable molecules featuring a vinyltrifluoroborate ligand on coinage metals. The X-ray crystal structures show the presence of three-coordinate metal sites in these complexes. The vinyltrifluoroborate group binds asymmetrically to the metal site in [CH₂(3,5-(CH₃)₂Pz)₂]M(CH₂CHBF₃) (M = Cu, Ag) with relatively closer M-C(H)₂distances. The computed structures of [CH₂(3,5-(CH₃)₂Pz)₂]M(CH₂CHBF₃) and M(CH₂CHBF₃), however, have shorter M-C(H)BF₃distances than M-C(H)₂. These molecules feature various inter- or intra-molecular contacts involving fluorine of the BF₃group, possibly affecting these M-C distances. The binding energies of [CH₂CHBF₃]^?to Cu⁺, Ag⁺and Au⁺have been calculated at the wB97XD/def2-TZVP level of theory, in the presence and absence of the supporting ligand CH₂(3,5-(CH₃)₂Pz)₂. The calculation shows that Au⁺has the strongest binding to the [CH₂CHBF₃]^?ligand, followed by Cu⁺and Ag⁺, irrespective of the presence of the supporting ligand. However, in all three metals, the supporting ligand weakens the binding of olefin to the metal. The same trends were also found from the analysis of the σ-donation and π-backbonding interactions between the metal fragment and the π and π* orbitals of [CH₂CHBF₃]^?

Full text of DOI:10.1039/d1dt00974e

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Copper(I) and silver(I) chemistry of vinyltrifluorobor
D
a
OI: 10.1039/D1DT00974E
t
e
supported by a bis(pyrazolyl)methane
Adway O. Zacharias, James Mao,* Kwangho Nam, H. V. Rasika Dias*
Department of Chemistry and Biochemistry, The University of Texas at Arlington,
Arlington, Texas 76019, USA
AUTHOR INFORMATION
Corresponding Authors
H. V. Rasika Dias, E-mail: dias@uta.edu; ORCID: 0000-0002-2362-1331
James Mao, E-mail: xiaojian@uta.edu
Key words:
Alkene chemistry, Organotrifluoroborate, Silver, Copper, Density functional
calculations
1

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Page 2 of 34
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DOI: 10.1039/D1DT00974E
Abstract: Although unsaturated organotrifluoroborates are common synthons in
metal-organic chemistry, their transition metal complexes have received scant
attention. The [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ), (SIPr)Cu(MeCN)(CH =CHBF )
2
3 2
2
2
3
2
3
and [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ) represent rare, isolable molecules
2
3 2
2
2
3
featuring a vinyltrifluoroborate ligand on coinage metals. X-ray crystal structures show
the presence of three coordinate metal sites in these complexes. The
vinyltrifluoroborate group binds asymmetrically to the metal site in [CH (3,5-
2
(
CH ) Pz) ]M(CH =CHBF ) (M = Cu, Ag) with relatively closer M-C(H) distances.
3 2 2 2 3 2
Computed structures of [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) and M(CH =CHBF )
2
3 2
2
2
3
2
3
however, have shorter M-C(H)BF than M-C(H) distances. These molecules feature
3
2
various inter- or intra-molecular contacts involving fluorine of the BF group, possibly
3

+
+
affecting these M-C distances. The binding energies of [CH =CHBF ] to Cu , Ag
2
3
+
and Au have been calculated at the wB97XD/def2-TZVP level of theory, in the
presence and absence of the supporting ligand CH (3,5-(CH ) Pz) . The calculation
2
3 2
2
+

+
shows that Au has strongest binding to the [CH =CHBF ] ligand, followed by Cu
2
3
+
and then Ag , irrespective of the presence of the supporting ligand. However, in all
three metals, the supporting ligand weakens the binding of olefin to the metal. The same
trends are also discovered from the analysis of the σ-donation and π-backbonding

interactions between the metal fragment and the π and π* orbitals of [CH =CHBF ] .
2
3
2

Page 3 of 34
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DOI: 10.1039/D1DT00974E
Introduction
Organotrifluoroborates such as alkenyl-, alkynyl- and aryl-trifluoroborates are
1
useful reagents in organic chemistry. They are employed most frequently in the metal
catalyzed, Suzuki-Miyaura cross-coupling reactions leading to new C-C bonds. Other
metals including copper also mediate important chemical processes involving
organotrifluoroborates.1a, 1d, 2 Interestingly, despite the wide utility of unsaturated
trifluoroborates as organic synthons in metal-organic chemistry, their -donor ligand
potential towards transition metal ions has received relatively less attention. For
3
example, a search of Cambridge Structural Database reveals that structurally
authenticated d-block complexes involving -bonded organotrifluoroborate ligands are
limited to several ferrocenyltrifluoroborates (i.e., iron complexes of cyclopentadienyl-
4
5
trifluoroborates, e.g., 1, Figure 1), a phenyltrifluoroborate adduct of ruthenium, 2, and
(
SIPr)Ag(CH =CHBF ) (3) and (IPr*)Ag(CH =CHBF ) (SIPr = 1,3-bis(2,6-
2
3
2
3
diisopropylphenyl)imidazolin-2-ylidene); IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-
methylphenyl)imidazol-2-ylidene) featuring a vinyltrifluoroborate ligand on silver(I)
supported by N-heterocyclic carbenes (NHCs).6
BF3
Fe
Ru
BF3
2
1
i-Pr
i-Pr
N
N
i-Pr
i-Pr
Ag
H
H
H
C
C
BF3
3
Figure 1. Organotrifluoroborate complexes of transition metal ions
3

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DOI: 10.1039/D1DT00974E
7
As a part of our ongoing activities involving metal-olefin complexes, we
became interested in the coordination chemistry of vinyltrifluoroborate ion

8
(
[CH =CHBF ] ) since it represents a virtually unexplored, formally negatively
2 3
charged, -donor ligand for metal ions. In addition, asymmetrically substituted olefins

1
such as [CH =CHBF ] could provide isolable molecules that feature pseudo  -
2
3
coordination mode, which is of interest as a model for olefin activation step towards
nucleophiles.9
Recently we reported the isolation of silver complexes (SIPr)Ag(CH =CHBF )
2
3
6
(
3) and (IPr*)Ag(CH =CHBF ) of this interesting ligand. Furthermore, calculated
2 3
–
metal-ligand binding energies show that [CH =CHBF ] is a significantly better ligand
2
3
for Ag(I) than CH =CH or isoelectronic CH =CHCF . Here we describe an expansion
2
2
2
3
of that effort to uncover the copper complexes, a comparison of copper and silver
chemistry, and a detailed computational study of vinyltrifluoroborates of Cu, Ag and
Au. We note that coinage metal complexes involving organoborates are also of interest
1
0
as reaction intermediates and for PET imaging work. In addition, reactions involving
vinylcuprates with BF3 additives11 as well as copper catalyzed reactions of
vinyltrifluoroborates are known,12 in which the formation of copper
vinyltrifluoroborates as intermediates is a possibility. To test this hypothesis, we have
also probed the utility of pre-formed copper-vinyltrifluoroborate as a catalyst for the
synthesis of functionalized 1,2-disubstituted cyclopropyltrifluoroborates, and as a
stoichiometric reagent to facilitate ring opening reactions of an unhindered epoxide.
4

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DOI: 10.1039/D1DT00974E
Results and discussion:
The NHC supported (SIPr)Cu(MeCN)(CH =CHBF ) (4) was synthesized by
2
3
treating (SIPr)CuNO with K(CH =CHBF ) in dichloromethane/acetonitrile and
3
2
3
isolated as a white, fairly air stable solid in 90% yield (Scheme 1). It shows good
solubility in halogenated solvents like CH Cl and CHCl but is insoluble in hexane or
2
2
3
Et O and has been characterized by multinuclear NMR spectroscopy and X-ray
2
1
3
1
crystallography. The C{ H} NMR signal of the copper bound CH =CHBF could be
2
3
observed as a singlet at  99.9 ppm for (SIPr)Cu(MeCN)(CH =CHBF ). It can be
2
3
2
compared to the corresponding resonance in (SIPr)Ag(CH =CHBF ) (that has an  -
2
3

bound [CH =CHBF ] moiety),
[(IPr) Ag][CH =CHBF ] (that has a free
2 2 3
2
3

6
13
[
CH =CHBF ] moiety) and K(CH =CHBF ) which is observed at  114.3, 120.1
2
3
2
3
and 121.6 ppm, respectively. Thus, the copper(I) coordination has a more significant

effect on [CH =CHBF ] group.
2
3
i-Pr
i-Pr
i-Pr
i-Pr
N
N
N
N
K(CH =CHBF )
MeCN
2
3
i-Pr
i-Pr
i-Pr
i-Pr
Cu
Cu
H
-
KNO3
NCMe
H
NO3
C
C
4
H
BF3
Scheme 1. Synthesis of (SIPr)Cu(MeCN)(CH =CHBF )
2
3
5

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DOI: 10.1039/D1DT00974E
Figure 2. Molecular structure of (SIPr)Cu(MeCN)(CH =CHBF ) (4). Selected bond
2
3
distances (Å) and angles (°): C28-C29 1.3682(18), Cu-C1 1.9756(10), Cu-N3
1
1
.9741(11), Cu-C28 2.1061(12), Cu-C29 2.0936(13), C28-B 1.6187(19), B-C28-Cu
09.52(8), C29-C28-B 122.87(12), C28-Cu-C29 38.03(5), C1-Cu-N3 112.78(4), Cu-
N3-C32 174.50(12)
The copper(I) complex (SIPr)Cu(MeCN)(CH =CHBF ) (4) has been
2
3
characterized by X-ray crystallography (Figures 2). In contrast to the related silver
analog (SIPr)Ag(CH =CHBF ) (3), (SIPr)Cu(MeCN)(CH =CHBF ) has an acetonitrile
2
3
2
3
molecule coordinated to the metal ion, which is not lost under reduced pressure. The
copper center is three-coordinate (which is a somewhat more common coordination
number for copper over two coordinate systems)14 and adopts a trigonal planar

geometry. The carbons of [CH =CHBF ] group are marginally twisted (~10.4°) with
2
3
respected to the N3-Cu-C1 plane. The Ag(CH =CHBF ) moiety of the directly related
2
3
(
SIPr)Ag(CH =CHBF ) shows positional disorder, and therefore is less useful for a
2 3
6
detailed analysis. However, the NHC-silver complex (IPr*)Ag(CH =CHBF ) is
2
3
6
known. A comparison of metal bound C=C bond distances in (IPr*)Ag(CH =CHBF )
2
3
and (SIPr)Cu(MeCN)(CH =CHBF ) shows that it is longer in the latter (1.323(5) vs
2
3
1
.3682(18) Å). In contrast to this silver complex, M-C(H ) and M-C(BF ) distances
2 3
6

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DOI: 10.1039/D1DT00974E
are marginally different in 4 (e.g., 2.0936(13) and 2.1061(12) Å for the copper complex
4
, while 2.316(3) and 2.328(3) Å for (IPr*)Ag(CH =CHBF )) pointing to slightly
2 3
2
asymmetric  -coordination. The Cu-C distances are shorter than Ag-C bond lengths
which is expected based on the relatively smaller copper atom.
To rationalize the formation of (SIPr)Cu(MeCN)(CH =CHBF ) instead of the
2
3
acetonitrile free (SIPr)Cu(CH =CHBF ), we calculated the free energy changes of
2
3
reaction:
(
SIPr)M(CH =CHBF ) + MeCN → (SIPr)M(MeCN)(CH =CHBF )
eq. 1
2
3
2
3
for M=Cu, Ag, and Au respectively, at the wB97XD/def2-TZVP level of DFT.
Although the calculations showed that for all three metal ions, the three coordinate
(
SIPr)M(CH =CHBF ) form is favored over (SIPr)M(MeCN)(CH =CHBF ) (by 2.6,
2 3 2 3
5
.8, and 6.1 kcal/mol, respectively), DFT correctly predicted that
(
SIPr)Cu(MeCN)(CH =CHBF ) is easier to form than (SIPr)Ag(MeCN)(CH =CHBF ).
2 3 2 3
Considering that the metal vinyltrifluoroborate complexes are rare and the NHC
complexes afforded complexes 3 and 4 with different coordination numbers at the
metal, we set out to uncover better examples that are more suitable for direct and
detailed comparison of metal ion effects. The bis(3,5-dimethylpyrazolyl)methane
1
5
(
CH (3,5-(CH ) Pz) ) was chosen as the supporting ligand for this purpose. The
2 3 2 2
treatment of (MeCN) M(CH =CHBF ) (M = Cu, Ag; generated in-situ from
3
2
3
K(CH =CHBF ) and (MeCN) Cu(BF ) or AgNO in acetonitrile) with CH (3,5-
2
3
4
4
3
2
(
CH ) Pz) gave [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) (5 and 6, Scheme 2) in over 90%
3 2 2 2 3 2 2 2 3
yield. The [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) was obtained as a pale green solid
2
3 2
2
2
3
while the silver analog is a white solid. Both are air stable and soluble in halogenated
solvents like CH Cl and CHCl and insoluble in hexane and Et O. X-Ray quality
2
2
3
2
7

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crystals of [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) (M = Cu, Ag) were grown in vials
DOI: 10.1039/D1DT00974E
2
3 2
2
2
3
open to air from a dichloromethane/hexane solution.
H
(
MeCN)4Cu(BF4)
K(CH2=CHBF3)
MeCN
H
C
C
CH3 CH3
N
H
CH3
CH3
N
H
or
N
N
N
N
N
H
N
H
AgNO3
K(CH2=CHBF3)
MeCN
M
C
CH3
CH3
CH3
C
CH3
H
CH (3,5-(CH ) Pz)
2
BF3
2
3 2
[
CH (3,5-(CH ) Pz) ]M(CH =CHBF )
2 3 2 2 2 3
M = Cu, 5; Ag, 6
Scheme 2. Synthesis of [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) (5) and [CH (3,5-
2
3 2
2
2
3
2
(
CH ) Pz) ]Ag(CH =CHBF ) (6)
3
2
2
2
3
1
The H NMR spectra of [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) display three
2
3 2
2
2
3
sets of broad resonances for the protons of CH =CHBF moiety. These signals of the
2
3
copper complex [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) (5) appear at a relatively
2
3 2
2
2
3
upfield regions compared to those of the silver analog 6, perhaps pointing to better
backbonding between the metal and vinyltrifluoroborate in 5.16 The C{ H} NMR
13
1
signal of the CH =CHBF was observed as a singlet at  87.3 and 102.2 ppm for
2
3
[
CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) and [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ),
2 3 2 2 2 3 2 3 2 2 2 3
respectively. They show notable upfield shifts from the corresponding resonance for
1
3
K(CH =CHBF ), which is detected at  121.6 ppm. Those values represent about
2
3
3
3.4 and 19.4 ppm upfield shifts as a result of metal ion coordination. This trend of
1
3
larger upfield shift of the olefinic C signal upon copper ion coordination relative to
that of silver is similar to those seen with previously reported ethylene complexes.7b, 16-
1
7
8

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Figure 3. Molecular structure of [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) (5).
2
3 2
2
2
3
Table 1. Selected bond distances (Å) and angles (°) of LM(CH =CHBF ); M = Cu,
2
3
Ag, Au; L = [CH (3,5-(CH ) Pz) ], and closest intra-molecular contacts (unless noted
2
3 2
2
otherwise, i.e., if inter-molecular contacts are closer)
Experiment (X-Ray)
Calculation (wB97xd/def2-tzvp)
LCu
LAg
LCu
LAg
LAu
Cu
Ag
Au
parameter
(CH =CHBF )
(CH =CHBF )
(CH =CHBF )
(CH =CHBF )
(CH =CHBF )
(CH =CHBF )
(CH =CHBF )
(CH =CHBF )
2
3
2
3
2
3
2
3
2
3
2
3
2
3
2
3
C=C
1.371(3) 1.3674(16)
1.620(3) 1.6300(17)
2.0279(17) 2.2562(11)
2.0488(16) 2.3022(11)
1.369
1.363
1.380
1.365
1.359
1.396
B-C
1.646
2.078
2.053
2.043
2.046
38.7
1.651
2.304
2.280
2.325
2.314
34.6
1.661
2.190
2.212
2.871
2.113
36.5
1.655
2.156
2.070
1.654
2.415
2.326
1.668
2.197
2.208
M-C(H)
2
M-CH(BF
M-N
3
)
1.9941(14)
1.9910(14)
39.31(7)
2.2768(9)
2.2454(9)
34.89(4)
M-N
C-M-C
C-C-B
M-C-B
N-M-N
37.6
125.0
85.1
33.3
124.8
86.9
37.0
124.6
98.8
122.27(17) 124.95(11)
124.3
96.1
125.4
96.6
124.9
106.3
73.7
110.16(11)
96.86(6)
110.74(7)
113.43(7)
101.5
108.64(7)
87.74(3)
115.61(4)
121.61(4)
99.7
92.1
83.0
bN-M-C(H)
119.5
109.4
84.8
129.5
108.0
86.5
160.2
88.6
2
bN-M-CH(BF
M-C-C-B
)
3
97.0
72.4
76.8
87.8
NMN/CMC
10.9
3.3
16.0
21.6
7.4
…
2.267a
2.384a
F H
2.202
2.542
137.5
2.248
2.769
143.9
2.225
2.937
173.2
…
F M
3.109
3.464
2.035
2.365
2.812
N-Au-Ccent
128.6
133.2
b
a
inter-molecular distances; pyrazolyl nitrogen atom on the same side as the olefinic
carbon; Ccent = C=C centroid
9

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DOI: 10.1039/D1DT00974E
Crystals of [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) (5) were investigated using
2
3 2
2
2
3
X-ray crystallography at 100 K (Figure 3). Selected bond distances and angles are
presented in Table 1.
The bis(prazolyl)methane group adopts a half-chair
2
conformation. The copper center has a trigonal planar geometry. The  -bound,
CH =CHBF moiety (CCuC plane) is slightly twisted (~10.9°) with respect to the
2
3
NCuN plane. This distortion appears to be a steric effect caused by -BF group on the
3
olefinic carbon interacting with a methyl at the pyrazolyl ring 3-position. Note that the
trigonal, in-plane conformation is the most stable geometry for ethylene-ML2
complexes.18 The C=C bond distance of CH =CHBF moiety in 5 (1.371(3) Å) is
2
3
essentially identical to that observed for 4 (1.3682(18) Å). The Cu-C distances are
slightly longer in the latter, which has a bulky NHC ligand support. Crystal packing
diagram of [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) shows intermolecular FH
2
3 2
2
2
3
interactions between the fluorine atoms of BF group and protons of methylene moiety
3
as well as 5-methyl groups of the pyrazolyl rings (with closest FH at 2.27 Å).
The molecular structure of the silver(I) complex [CH (3,5-
2
(
CH ) Pz) ]Ag(CH =CHBF ) (6) is illustrated in Figure 4. Basic features are similar
3 2 2 2 3
to those of the copper analog. As evident from the data presented in Table 1, the C=C
bond distance of CH =CHBF moiety is surprisingly similar between the two adducts.
2
3
The Ag-C distances are however significantly longer than Cu-C separations of the
copper adduct, which is expected due to the larger size of the silver atom. The metal-
N distances also show a similar trend. The olefinic moiety of CH =CHBF of 6 is
2
3
essentially coplanar with the NAgN plane, likely as a result of larger separation of the
two ligands on silver and therefore reduced steric interactions between the methyl and
BF groups. The metal-C(H) distance is shorter than the M-CH(BF ) in both
3
2
3
1
0

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DOI: 10.1039/D1DT00974E
2
complexes indicating asymmetric  -coordination of the olefin group to the metal atom.
1
Molecules that show such deformation towards  -coordination (i.e., slippage from
2
1
19
typical  to pseudo  - coordination) are of significant current interest, as they
represent models for key bond making and olefin activation steps during metal-olefin
chemistry.9a Investigation of crystal packing reveals that intermolecular FH
interactions between the fluorine atoms of BF group and protons of CH moiety as
3
2
well as 5-methyl groups of the pyrazolyl rings are also present in [CH (3,5-
2
(
CH ) Pz) ]Ag(CH =CHBF ) (with closest FH at 2.38 Å).
3
2
2
2
3
Figure 4. Molecular structure of [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ) (6).
2
3 2
2
2
3
The interactions between the metal center and the vinyl group were
characterized using the density functional theory (DFT) calculations. To establish the
level of theory used in the present study, we first compared the optimized geometries
and calculated dissociation energies between ethylene and three coinage metal ions
+
+
+
20
21
(
Cu , Ag , and Au ) between five widely used DFT functionals (B3LYP, M06-2X,
1
1

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wB97XD, PBE0, and BP8623a, 24). The results are presented in Tables S11 and S12.
2
2
23
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DOI: 10.1039/D1DT00974E
Among the tested DFT methods, the wB97XD results agree best with reported
experimental dissociation energies as well as with CCSD(T)/def2-
QZVPP//CCSD/def2-TZVP calculation results. Reported benchmark work25 also
supports that wB97XD performs well for olefin metathesis reactions. Accordingly, all
molecular geometry optimizations and interaction energies reported in this work are
2
6
based on the wB97XD/def2-TZVP level of theory.
The optimized structures of [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) (5),
2
3 2
2
2
3
[
CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ) (6), and the analogous complex involving Au
2 3 2 2 2 3
were calculated using the level of theory mentioned above. Several key distances and
angles are presented in Table 1 along with their corresponding values in the X-ray
structures for 5 and 6. Overall, the optimized structures agree well with the X-ray
crystal structures. However, some notable differences are also observed, which we
attribute to the change in the orientation of CH =CHBF relative to CH (3,5-
2
3
2
(
CH ) Pz) . For example, in crystal structures, the -BF group forms an intermolecular
3 2 2 3
HF bonds with a nearby unit. Since this symmetry-related intermolecular interaction
involving fluorides are not possible in the single molecule calculations, the
CH =CHBF moiety rotates slightly to form an intramolecular HF contact with the
2
3
CH (3,5-(CH ) Pz) fragment (Table 1). Furthermore, unlike the Cu and Ag analogs,
2
3 2
2
the gold complex is notably distorted from ideal trigonal planar geometry as evident
from the large N-Au-C angle of 160.2° (or N-Au-Ccent angle of 173.2°, Ccent = C=C
centroid) and very different Au-N separations of 2.113 and 2.871 Å. We do not have
experimental data of the gold complex thus far (synthesis of the gold adduct was
attempted briefly by treating [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ) with AuCl but
2
3 2
2
2
3
yielded only decomposed products) for a direct comparison.
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2

Page 13 of 34
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DOI: 10.1039/D1DT00974E
To characterize the intrinsic interactions between the coinage metal ion and π-
donor ligand, we calculated the structures and energies of metal-ethylene and metal-
vinyltrifluoroborate complexes, and analyzed the nature of the metal-ligand
2
7
interactions with the EDA (Energy Decomposition Analysis) partitioning scheme in
conjunction with the NOCV (Natural Orbitals for Chemical Valence) method.28 The
results of EDA are presented in Table 2. In a typical EDA partitioning scheme, the
overall interaction between fragments can be decomposed into two terms, the frozen
density component and the orbital interaction term:27
∆퐸푖푛푡 = ∆퐸푓푟푧 +∆퐸표푟푏
(1)
The frozen density term (i.e., ∆퐸푓푟푧) can be further decomposed into a quasiclassical
Coulomb electrostatic interaction and Pauli exchange repulsion.27 Since the sum of the
two terms corresponds to the interaction energy of the complex without any relaxation
of molecular orbitals on each fragment, we do not to separate them in this study.
Table 2. Results of the EDA-NOCV calculations. The LM were treated as one fragment
(
all energies in kcal/mol), L = [CH (3,5-(CH ) Pz) ], M = Cu, Ag, Au, L’ = C H BF
2
3 2
2
2
3
3
moiety.
∆
E(int)
∆E(frz) ∆E(orb)  donation
 backdonation
/E(orb)a
/E(orb)a
2 4
H
)]+
M
[M(C
-26.25
Cu
Ag
Au
-53.15
-35.91
-67.62
-4.56 -48.60
0.11 -36.02
13.31 -80.93
-10.54
-6.19
54.01%
21.70%
17.19%
21.81%
-21.45
-46.58
59.55%
57.56%
-17.65
M(CH
-23.48
-20.42
-48.79
LM(CH
-18.46
-17.26
-36.15
2 3
=CHBF )
Cu
Ag
Au
-170.95 -107.46 -63.49
-13.00
-6.13
36.99%
45.70%
56.31%
20.47%
13.71%
17.28%
-143.06
-172.58
-98.38 -44.69
-85.95 -86.63
-14.97
2
3
=CHBF )
Cu
Ag
Au
-123.00
-110.75
-139.49
-65.57 -57.43
-65.63 -45.12
-64.94 -74.55
-19.81
-10.19
-17.11
32.14%
38.26%
48.49%
34.49%
22.58%
22.95%
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3

Dalton Transactions
Page 14 of 34
aPercentage of the contribution of σ donation and π backdonation to ∆E(orb) term.
View Article Online
DOI: 10.1039/D1DT00974E
The orbital interaction term (i.e., ∆퐸표푟푏) is associated with the energy lowering
due to the orbital relaxation after the formation of a complex and can be identified as
covalent contribution to the chemical bond.28 With the NOCV method, we can further
decompose the orbital interaction term into pairwise orbital contributions of the
interacting fragments, which can provide an important insight into the nature of the
6
metal-ligand interactions. For example, in our recent study, we have shown that for
the system composed of a coinage metal ion and a π-donor ligand, the first two
dominant terms in ∆퐸표푟푏 can be viewed as the metal←ligand σ donation (i.e., the
donation of electrons from the occupied π orbital of the olefin ligand to the vacant
orbital of the metal ion) and metal→ligand π backdonation (from occupied d-orbital of
the metal ion to the vacant π* orbital of the olefin ligand) of the standard DCD (Dewar-
2
9
Chatt-Duncanson) model. The remaining orbital interactions are from weak δ bonding
and polarization of the fragments. Therefore, we only report the terms associated with
the metal←olefin ligand σ donation and the metal→olefin ligand π backdonation in
Table 2.
As shown in Table 2, the order of Au > Cu > Ag is well kept within the same

olefin ligand (CH =CH or [CH =CHBF ] ) with respect to the strengths of total
2
2
2
3
+
interaction, orbital interaction, σ donation, or π backdonation for [M(CH =CH )] and
2
2
M(CH =CHBF ) systems. This trend is also in good agreement with the previously
2
3
3
0

reported work. Since [CH =CHBF ] group is negatively charged, it is not surprising
2
3
that the total interactions (∆퐸 ) and the frozen density terms (∆퐸푓푟푧) of
푖푛푡
+
M(CH =CHBF ) have increased significantly relative to the [M(CH =CH )] system.
2
3
2
2
1
4

Page 15 of 34
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DOI: 10.1039/D1DT00974E
+

+

+

[
Cu ][C H BF ]
[Ag ][C H BF ]
[Au ][C H BF ]
2 3 3
2
3
3
2
3
3

EL’M = -23.5
EL’M = -20.4
EL’M = -48.8

EML’ = -13.0
EML’ = -6.1
EML’ = -15.0
Figure 5. Plot of the deformation densities of the two most important pairwise orbital
+
-
interactions associated with the orbital energies in the [M ][C H BF ] complexes, with
2
3
3
M = Cu, Ag, Au and L’ = C H BF . Top panel shows the deformation densities due to
2
3
3
the σ donation interactions with the NOCV pairwise orbital interaction energies, and
the bottom panel the deformation densities due to the π backdonation with
corresponding pairwise interaction energies. The energies are in unit of kcal/mol, and
the direction of the charge flow is red  blue.
6
+
Our previous work on silver(I) has shown that the Ag ←olefin σ donation and
+
Ag →olefin π backdonation exhibit a very similar strength between the
+
[
Ag(CH =CH )] and Ag(CH =CHBF ) systems. The same trend is also observed for
2
2
2
3
Cu and Au in the present calculations (Table 2). The shape of the deformation densities
for the M←L’ σ donation and M→L’ π backdonation interactions, respectively, are
illustrated in Figure 5 (L’ = C H BF ). For all three coinage metals (i.e., Cu, Ag, and
2
3
3
Au), the M← olefin ligand σ donation and M→ olefin ligand π backdonation are
different by less than 3 kcal/mol between CH =CH and CH =CHBF ; For the sum of
2
2
2
3
1
5

Dalton Transactions
Page 16 of 34
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DOI: 10.1039/D1DT00974E
the two interactions, their difference between the two systems is less than 1.1 kcal/mol
for each metal. In contrast, the total orbital interaction energy (∆퐸표푟푏) increases by 5.7
kcal/mol for Au, 8.7 kcal/mol for Ag, and 14.9 kcal/mol for Cu between the two
systems. This indicates that although each of the other orbital interactions contributes
little to the total orbital interaction, their cumulative contribution increases from
CH =CH to CH =CHBF .
2
2
2
3
+

+

+

[
L][Cu ][C H BF ] [L][Ag ][C H BF ] [L][Au ][C H BF ]
2
3
3
2
3
3
2
3
3

EL’M = -18.5
EL’M = -17.3
EL’M = -36.2

EML’ = -19.8
EML’ = -10.2
EML’ = -17.1
Figure 6. Plot of the deformation densities of the two most important pairwise orbital
+

interactions that are associated with the orbital energies in the [L][M ][C H BF ]
2
3
3
complexes, with L = CH (3,5-(CH ) Pz) , L’ = C H BF and M = Cu, Ag, Au. Top
2
3 2
2
2
3
3
panel shows the deformation densities due to the σ donation interactions with the
NOCV pairwise orbital interaction energies, and the bottom panel shows the
deformation densities due to the π backdonation with corresponding pairwise
interaction energies. The energies are in unit of kcal/mol, and the direction of the charge
flow is red  blue.
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6

Page 17 of 34
Dalton Transactions
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DOI: 10.1039/D1DT00974E
In Table 2, we also present the EDA-NOCV analysis data for [CH (3,5-
2
(
CH ) Pz) ]M(CH =CHBF ) systems, and in Figure 6, the shape of the deformation
3
2
2
2
3
densities for the M←L’ σ donation and M→L’ π backdonation interactions,
respectively (M = Cu, Ag, Au; L’ = C H BF ). It emerges from the figure the substantial
2
3
3
delocalization of the positive charge of M towards the CH (3,5-(CH ) Pz) ligand,
2
3 2
2
which is not possible in the M(CH =CHBF ) system. As a result, the electrostatic
2
3
interaction with the CH =CHBF (L’) fragment is decreased substantially, which is
2
3
evident from the decreased frozen density term (∆퐸푓푟푧) (Table 2). Interestingly, for this
CH (3,5-(CH ) Pz) ]M(CH =CHBF ) complex, the magnitudes of the frozen density
[
2
3 2
2
2
3
term are very close between the different metal ions. Thus, the order of the total
interactions is solely determined by the order of the orbital interactions, i.e., Au > Cu
>
Ag. We note that this order in the orbital interaction terms is the same for the
M(CH =CH ) and M(CH =CHBF ) systems, suggesting that this is an intrinsic
2
2
2
3
property of the interaction between the C=C bond and the metal ions. This order is also
reflected in the order of C=C double bond lengths of the CH =CHBF fragment in each
2
3
complex (Table 1). Namely, since both M←L’ σ donation (removal of electron density
from the C-C π orbital) and M→L’ π backdonation (increase of electron density in the
π* orbital) should lead to an elongation of the C=C double bond, stronger their
interactions results in longer C=C bond. The C=C double bond length therefore can be
viewed as a measurement of the strength of ∆퐸표푟푏 between metal and π-donor ligand.
As shown in Table 1, both experimental measurements and calculation results of the
C=C double bond lengths are in good agreement with the order of the calculated orbital
interactions.
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7

Dalton Transactions
Page 18 of 34
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DOI: 10.1039/D1DT00974E
Examining in more detail the σ donation and π backdonation terms, we find that
while the order of σ donation and that of the total orbital interactions remain the same,
i.e., Au > Cu > Ag, the order of π backdonation flips between Cu and Au in the
[
CH (3,5-(CH ) Pz) ]M(CH =CHBF ) system. However, given the relatively small
2 3 2 2 2 3
difference in their interaction energies (i.e., < 3 kcal/mol) and the difference in their
optimized) geometries (trigonal planar vs. approaching linear, Table 1), we believe
(
this change in the π backdonation order is possible. In addition, the magnitude of the π
backdonation is slightly larger than that of the σ donation in the metal-olefin fragment
of the [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) system, while the σ donation is
2
3 2
2
2
3
consistently larger in all other systems. In fact, this is the first time that we observed a
larger contribution of the π backdonation (albeit the difference is minor) to the total
orbital interaction energy than that of the σ donation in these types of metal-olefin
complexes, but it is not unusual in metal olefin complexes.31
Furthermore, the strength of the σ donation decreases going from the
M(CH =CHBF ) complex to the [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) complex,
2
3
2
3 2
2
2
3
while the π backdonation follows the opposite trend. This is perhaps because the
nitrogen donor CH (3,5-(CH ) Pz) ligand makes the metal sites less electrophilic
2
3 2
2
relative to the supporting ligand free systems. Interestingly, this trend is different,6
when different N-heterocyclic carbenes (NHCs) were used as the supporting ligand on
Ag(I). It was found upon coordination of two different NHCs (i.e., 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazolin-
2
-ylidene), both σ donation and π backdonation interactions decreased. It remains
interesting to further investigate the mechanism of how supporting ligand influences
the interactions between the metal and the π-donor ligand.
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8

Page 19 of 34
Dalton Transactions
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DOI: 10.1039/D1DT00974E
We have also examined M-C bond distances of vinyltrifluoroborate complexes
2
to see if they prefer  -symmetric or somewhat asymmetric bond formation to the metal
site. As noted earlier, X-ray data (Table 1) show that [CH (3,5-(CH ) ]M(CH =CHBF )
2
3 2
2
3
complexes (M = Cu, Ag) feature shorter M-C(H) distances (compared to M-CH(BF )
2
3
distances), but steric factors and intermolecular HF contacts could have an effect of
M-C distances. Computed structures of [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) and the
2
3 2
2
2
3
supporting ligand free M(CH =CHBF ) also show somewhat asymmetrically bound
2
3
CH =CHBF groups, but trend is opposite in which the M-CH(BF ) is the shorter
2
3
3
distance for each metal (Table 1, M = Cu, Ag). Unfortunately, BF moieties of these
3
molecules feature intramolecular HF and/or MF interactions, interfering with the
M-C bond-distance analysis. Although it is tempting to use data from M(CH =CHBF )
2
3
2
to indicate the preference for the  -(CH =CHBF ) to bind Cu(I) and Ag(I)
2
3
asymmetrically with a slightly shorter M-CH(BF ) distances, considering the
3
conflicting trends and inter- or intra-molecular contacts involving fluorine of BF group,
3
more data are useful before reaching a firm conclusion. It is noteworthy that a recent
study reveals such interactions involving fluorines play an important role in silver
phenyltrifluoroborate chemistry.10b
Finally, having synthesized (MeCN) Cu(CH =CHBF ) using a copper(I) salt
3
2
3
and K(CH =CHBF ), we also explored the synthetic/catalytic potential of the pre-
2
3
formed copper vinyltrifluoroborate, “Cu(CH =CHBF )”. The 1,2-disubstituted
2
3
3
2
cyclopropanes play a significant role as structural motifs in drug discovery. Motivated
by the work performed by Hryschuk and co-workers,12 we attempted to use
(
MeCN) Cu(CH =CHBF ) to access functionalized 1,2-disubstituted cyclopropane
3
2
3
boronic derivatives.
It was found that in acetone at 40 °C, preformed
(
MeCN) Cu(CH =CHBF ) catalyzed (10 mol% loading) the reaction of ethyl
3 2 3
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9

Dalton Transactions
Page 20 of 34
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diazoacetate with K(CH =CHBF ) at 1:1 molar ratio affording the diastereomers of
DOI: 10.1039/D1DT00974E
2
3
functionalized cyclopropyl trifluoroborate in 69% yield, which is comparable to yields
reported earlier using a copper catalyst CuPF6 with ethyl diazoacetate and
1
2
K(CH =CHBF ).
2
3
i) THF
BF3
o
O
-78 C, 4 hrs
Ph
+
(MeCN) Cu
3
Ph
ii) H O
2
OH
Scheme 3. Ring opening of 2-benzyloxirane with (MeCN) Cu(CH =CHBF )
3
2
3
Additionally, we also explored the utility of the pre-formed copper
vinyltrifluoroborate in a ring opening reaction of an unhindered epoxide, 2-
benzyloxirane, analogous to the lower order organocuprate work reported by Lipshutz
1
1b
et al using vinyllithium, BF Et O and CuI in THF (Scheme 3). The authors reported
3
2
that BF Et O not only activates substrate but also modifies the organocuprate itself.
3
2
We postulate that the identity of this lower order organocuprate in the presence of boron
trifluoride could be similar to the pre-formed copper vinyltrifluoroborate
“
Cu(CH =CHBF )”
described
in
this
manuscript.
A
reaction
of
2
3
(
MeCN) Cu(CH =CHBF ) with 2-benzyloxirane under reaction conditions similar to
3
2
3
described by these authors11b indeed led to 1-phenylpent-4-en-2-ol in 63% yield, as
confirmed by NMR spectroscopy. The vinyllithium, BF Et O and CuI mixture in
3
2
1
:1:1 molar ratio has reported to generate this product in 29% yield along with an
additional by product, 1-iodo-3-phenyl-propanol. Although we had to increase reaction
time to 4 hours for complete conversion, preformed (MeCN) Cu(CH =CHBF ) gave
3
2
3
the ring open product more cleanly in greater yield. Thus, it is possible that
2
0

Page 21 of 34
Dalton Transactions
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“
Cu(CH =CHBF )” species could play a role in copper-mediated transformation
2 3
DOI: 10.1039/D1DT00974E
involving vinyllithium, BF Et O and CuI in THF.
3
2
Summary and conclusions:
We have successfully isolated and completely characterized copper(I) and silver(I)
complexes [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ), (SIPr)Cu(MeCN)(CH =CHBF )
2
3 2
2
2
3
2
3
and [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ) featuring
a
vinyltrifluoroborate.
2
3 2
2
2
3
Spectroscopic data of (MeCN) M(CH =CHBF ) (M = Cu, Ag) are also presented. X-
3
2
3
ray crystal structures show vinyltrifluoroborate moieties bonded somewhat
asymmetrically to the metal site with relatively shorter M-C(H) distances. However,
2
DFT analysis of the M-C distances of [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) and
2
3 2
2
2
3
M(CH =CHBF ) predicts that M-C(H)BF distances are shorter than M-C(H) distances.
2
3
3
2
These variations appear to be a result of inter- and/or intra-molecular contacts involving
fluorine of BF group. Total interactions (∆퐸 ) and the frozen density terms (∆퐸푓푟푧)
3
푖푛푡
of M(CH =CHBF ) show significantly greater stabilization relative to the
2
3
+
corresponding [M(CH =CH )] systems (M = Cu, Ag, Au). The supporting ligand
2
2
CH (3,5-(CH ) Pz) on [CH (3,5-(CH ) Pz) ]M(CH =CHBF ) systems leads to notable
2
3 2
2
2
3 2
2
2
3
reduction in electrostatic interaction with the CH =CHBF fragment relative to that in
2
3
M(CH =CHBF ).
The
EDA-NOCV
analysis
of
[CH (3,5-
2
2
3
(
CH ) Pz) ]Cu(CH =CHBF ) with [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ) shows that
3 2 2 2 3 2 3 2 2 2 3
the copper center features a stronger  and interactions with CH =CHBF fragment.
2
3
The (MeCN) Cu(CH =CHBF ) serves as a catalyst for the carbene insertion to
3
2
3
K(CH =CHBF ) leading to 1,2-disubstituted cyclopropyltrifluoroborates, and as an
2
3
effective stoichiometric reagent to facilitate ring opening reactions of 2-benzyloxirane.
We are presently exploring new transition metal chemistry of unsaturated
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1

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DOI: 10.1039/D1DT00974E
organotrifluoroborate ligands.
2
2

Page 23 of 34
Dalton Transactions
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DOI: 10.1039/D1DT00974E
Experimental section
All experiments were performed in open atmosphere unless otherwise specified.
Solvents were procured from commercial sources and distilled from conventional
o
drying agents prior to use. Glassware was oven dried at 150 C overnight. The NMR
1
spectra were recorded at room temperature on a JEOL Eclipse 500 spectrometer ( H,
5
00.16 MHz; 13C, 125.77 MHz and 19F, 470.62 MHz) and a JEOL Eclipse 300
1
1
spectrometer ( B, 96.42 MHz). Proton and carbon chemical shifts are reported in ppm
and are referenced using the residual proton and carbon signals of the deuterated solvent
(1
H, CDCl , δ = 7.26 ppm; C, CDCl , δ = 77.16 ppm). F NMR chemical shifts were
13
19
3
3
1
1
referenced relative to external CFCl . B NMR was referenced to external BF •Et O.
3
3
2
IR spectra were collected at room temperature on a Shimadzu IRPrestige-21 FTIR
-1
instrument containing an ATR attachment at 2 cm resolution. Elemental analysis was
performed at Intertek USA, Whitehouse, NJ. Deuterated solvents were purchased from
1
3
Acros Organics and Cambridge Isotope Laboratories, respectively. K(CH =CHBF ),
2
3
3
3
and (SIPr)CuNO334 were prepared according to literature
CH (3,5-(CH ) Pz)
2
3 2
2
procedure.
(
SIPr)Cu(MeCN)(CH =CHBF ): (SIPr)CuNO (100 mg, 0.19 mmol) and
2 3 3
K(CH =CHBF ) (28 mg, 0.21 mmol) in 7 mL of dichloromethane and 3 mL of
2
3
acetonitrile were placed in a Schlenk tune and stirred overnight at room temperature.
The resulting mixture was filtered through Celite and the solvent was removed under
reduced pressure to give a white solid, (SIPr)Cu(MeCN)(CH =CHBF ). X-ray quality
2
3
crystals were obtained from dichloromethane/hexane at room temperature. Yield: 90 %.
1
H NMR (in CDCl ): δ (ppm) 7.43 (t, J = 8.0 Hz, 2H, CH ), 7.26 (d, J = 8.0 Hz, 4H,
3
Ar
CH ), 5.06 (br m, 1H, CH CHBF ), 4.66 (br d, J = 24.1 Hz, 1H, CH CHBF ), 4.36 (br
Ar
2
3
2
3
d, 1H, CH CHBF ), 4.07 (s, 4H, NCH ), 3.02 (sept, J = 6.8 Hz, 4H, CH(CH ) ), 2.24
2
3
2
3 2
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3

Dalton Transactions
Page 24 of 34
1
3
1 View Article Online
(
s, 3H, CH CN), 1.33 (d, J = 6.9 Hz, 12 H, CH ), 1.32 (d, J = 6.9 Hz, 12H, CH ). C{ H}
3 3 3 DOI: 10.1039/D1DT00974E
NMR (in CDCl ): δ (ppm) 201.7 (CCu), 146.7, 134.0, 130.1, 124.6, 118.1 (MeCN),
3
9
9.9 (CH =CHBF ), 53.8 (NCH ), 28.9 (CH(CH ) ), 25.1 (CH(CH ) ), 24.2
2 3 2 3 2 3 2
1
9
(
CH(CH ) ), 2.4 (MeCN). F NMR (in CDCl ,): δ (ppm) -149.5 (br s, CH CHBF ).
3 2 3 2 3
1
1
B NMR (in CDCl ): δ (ppm) -1.16 (q, J = 7.2 Hz, CH CHBF ) ppm. C H BCuF N
3
3
2
3
33 58
3
(628.19) Anal. calc.: C, 63.09%; H, 9.31%; N, 6.69%. Found: C, 63.28%; H, 9.48%;
N, 6.42%.
(
MeCN) Cu(CH =CHBF ): (MeCN) Cu(BF ) (350 mg, 1.11 mmol) and
3 2 3 4 4
K(CH =CHBF ) (148 mg, 1.11 mmol) were taken in 7 mL of acetonitrile under nitrogen
2
3
and the mixture was stirred overnight at room temperature. The mixture was filtered
with celite. A small aliquot was withdrawn from the filtrate and analysed. Prolonged
drying leads to sample decomposition. This product was used directly in the synthesis
1
of [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ) as noted below. H NMR (in CDCl ):
2
3 2
2
2
3
3

(ppm) 5.27 (m, 1H, CH CHBF ), 4.83 (dd, 1H, J = 2.9 Hz, J = 19.2 Hz CH CHBF ),
2 3 2 3
1
3
1
4
.63 (br d, 1H, J = 11.7 Hz, CH CHBF ), 2.14 (s, 9H, MeCN). C{ H} NMR (in
2 3
CDCl ): δ (ppm) 117.6 (NCCH ), 93.9 (CH CHBF ), 2.6 (NCCH ). 19F NMR (in
3
3
2
3
3
CDCl ): δ (ppm) -142.4 (br s, CH CHBF ).
3
2
3
[
CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ): CH (3,5-(CH ) Pz) (212 mg, 1.11 mmol)
2 3 2 2 2 3 2 3 2 2
dissolved in dichloromethane (7 mL) was added dropwise to the
MeCN) Cu(CH =CHBF ) obtained as noted above, and stirred overnight. The
(
3
2
3
resulting mixture was then filtered and the solvent was removed under reduced pressure
to give a slightly pale green solid, [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ). X-ray
2
3 2
2
2
3
quality crystals were grown from dichloromethane/hexane at room temperature. Yield:
2
4

Page 25 of 34
Dalton Transactions
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Dp zO I: 10.1039/D1DT00974E
1
9
2%. H NMR (in CDCl ):  (ppm) 6.08 (s, 2H, N(CH )N), 5.87 (s, 2H, CH ), 5.32
3
2
(
m, 1H, CH CHBF ), 4.83 (br d, 1H, J = 18.3 Hz, CH CHBF ), 4.61 (br d, 1H, J = 12.6
2 3 2 3
1
3
1
Hz, CH CHBF ), 2.35 (s, 6H, CH ), 2.31 (s, 6H, CH ). C{ H} NMR (in CDCl ): δ
2
3
3
3
3
(
ppm) 151.7 (s, C(CH )), 141.6 (s, C(CH )), 107.0 (s, CH Pz), 87.3 (s, CH CHBF ),
3 3 2 3
1
9
5
7.3 (s, NCH ), 31.1, 13.8 (s, CH ), 10.9 (s, CH ) ppm. F NMR (in CDCl ): δ (ppm)
2 3 3 3
1
1
-
140.1 (br s, CH CHBF ). B NMR (in CDCl ): δ(ppm) -0.91 (br s, CH CHBF ). IR
2 3 3 2 3
-1
(
cm ): 1600, 1558, 1467, 1420, 1390, 1284, 1044, 985, 982, 953, 856, 803.
C H N CuBF (362.67) Anal. calc.: C, 43.05%; H, 5.28%; N, 15.45%. Found: C,
1
3
19
4
3
4
3.37%; H, 5.59%; N,15.36%.
(
MeCN) Ag(CH =CHBF ): A mixture of AgNO (150 mg, 0.58 mmol) and
3 2 3 3
K(CH =CHBF ) (78 mg, 0.58 mmol) were taken in 7 mL of acetonitrile and allowed to
2
3
stir overnight at room temperature. The mixture was then filtered through celite. A
small aliquot was withdrawn from the filtrate and analysed. Prolonged drying leads to
sample decomposition. This product was used directly in the synthesis of [CH (3,5-
2
1
(
CH ) Pz) ]Ag(CH =CHBF ) as noted below. H NMR (in CDCl ):  ppm) 6.19 (br
3
2
2
2
3
3
m, 1H, CH CHBF ), 5.59 (dd, 1H, J = 4.9 Hz, J = 19.2 Hz CH CHBF ), 5.42 (br d, 1H,
2
3
2
3
1
3
1
J = 8.0 Hz, CH CHBF ), 2.15 (s, 9H, MeCN). C{ H} NMR (in CDCl ): δ (ppm) 118.4
2
3
3
1
9
(
s, NCCH ), 108.7 (s, CH CHBF ), 2.3 (s, NCCH ). F NMR (in CDCl ): δ (ppm) -
3
2
3
3
3
1
42.2 (br s, CH CHBF ).
2
3
[
CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ): CH (3,5-(CH ) Pz) (96 mg, 0.47 mmol)
2 3 2 2 2 3 2 3 2 2
dissolved in dichloromethane (7 mL) was added dropwise to the
MeCN) Ag(CH =CHBF ) obtained above, and stirred overnight. The resulting
(
3
2
3
mixture was filtered and the solvent was removed under reduced pressure to give a
2
5

Dalton Transactions
Page 26 of 34
View Article Online
white solid, [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ). X-ray quality crystals were grown
DOI: 10.1039/D1DT00974E
2
3 2
2
2
3
1
with dichloromethane/hexane at room temperature. Yield: 92%. H NMR (in CDCl ):
3

ppm) 6.15 (m, 1H, J = 3.2 Hz, CH CHBF ), 6.03 (s, 2H, N(CH )N), 5.88 (s, 2H,
2
3
2
CH ), 5.59 (dd, 1H, J = 4.7 Hz, J = 18.3 Hz, CH CHBF ), 5.31 (m, 1H, CH CHBF ),
pz
2
3
2
3
1
3
1
2
.41 (s, 6H, CH ), 2.27 (s, 6H, CH ) ppm. C{ H} NMR (in CDCl ): δ (ppm) 151.5 (s,
3 3 3
C(CH )), 141.2 (s, C(CH )), 107.0 (s, CH Pz), 102.2 (s, CH CHBF ), 58.1 (s, CH ),
3
3
2
3
2
1
9
11
1
4.1 (s, CH ), 11.2 (s, CH ). F NMR (in CDCl ): δ (ppm) -142.0 (s, CH CHBF ). B
3
3
3
2
3
-1
NMR (in CDCl ): δ (ppm) –1.24 (br s, CH CHBF ). IR (cm ): 3362, 2971, 2926, 1619,
3
2
3
1
9
1
557, 1464, 1420, 1383, 1376, 1353,1286, 1269, 1077, 1085, 1069, 1033, 1021, 1014,
97, 953, 930, 906. C H N CuBF (362.67) Anal. calc.: C, 38.36%; H, 4.71%; N,
1
3
19
4
3
3.77%. Found: C, 38.61%; H, 4.89%; N, 13.36%.
Synthesis of diasteromers of (ethoxycarbonyl)cyclopropyltrifluoroborates
Ethyl diazoacetate (0.54 mL, 1.5 mmol, 90% solution in dichloromethane) was added
dropwise to a solution of (MeCN) Cu(CH =CHBF ) (0.15 mmol, 10 mol%) and
3
2
3
K(CH =CHBF ) (200 mg, 1.5 mmol) in 5 mL of acetone over a period of two hours.
2
3
After the addition was completed, the reaction mixture was stirred for another two
o
hours at 40 C. After cooling, the mixture was reduced to half its original volume and
poured into 20 mL of hexane. A clayish brown precipitate was formed. The solvent
was decanted, and the precipitate was dissolved in 10 mL of ethanol by heating. After
a few minutes of heating, a white solid precipitated out and was immediately filtered
and
collected
to
obtain
the
trans-isomer,
potassium
trans-2-
(ethoxycarbonyl)cyclopropyltrifluoroborate. This product was identified by
1
2
1
comparing NMR data to those reported in the literature. Yield 52%. H NMR (in
DMSO-d ): δ (ppm) 3.96 (q, J = 7.6 Hz, 2H,), 1.11 (m, 4H,), 0.63 (d, J = 9.5 Hz, 1H,),
6
2
6

Page 27 of 34
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DOI: 10.1039/D1DT00974E
0
.47 (t, J = 7.2 Hz, 1H,), -0.11 (br. s, 1H). The filtrate was evaporated in vacuo to
give the cis-product, potassium cis-2-(ethoxycarbonylcyclopropyl)trifluoroborate.
This product was identified by comparing NMR to those reported in the literature.12
1
Yield 17%. H NMR (in DMSO-d ): δ (ppm) 3.92 (q, 2H, J = 7.1 Hz,), 1.26 (s, 1H),
6
1
.13 (m, 3H), 0.76 (s, 1H), 0.59 (m, 1H), -0.07 (br. s, 1H). The ratio of trans/cis-
isomers in the crude reaction mixture, 84:16. This ratio of trans/cis-isomers was
1
9
estimated using the F NMR spectrum as there are distinct peaks for trans- and cis-
1
2
19
isomers of the product and also for K(CH =CHBF ). F NMR (in DMSO-d ): δ
2
3
6
(
ppm) -141.6 (br m) potassium trans-2-(ethoxycarbonyl)cyclopropyl trifluoroborate,
135.2 (br m) potassium cis-2-(ethoxycarbonyl)cyclopropyl trifluoroborate, and -
-
1
39.6 (br m), unreacted K(CH =CHBF ).
2 3
Ring opening reaction of oxiranes using (MeCN) Cu(CH =CHBF )
3
2
3
Procedure was modified slightly from available literature.11b Briefly,
MeCN) Cu(CH =CHBF ) (89.25 mg, 0.317 mmol) was added dropwise to a solution
(
3
2
3
o
of allylbenzene oxide (42.53 mg, 0.317 mmol) in THF (4 mL) at -78 C. The reaction
was allowed to proceed at this temperature for 4 hours. The reaction was then
quenched with 4 mL of a 10% NH OH/90% saturated NH Cl solution. The crude
4
4
1
mixture was analyzed using H NMR to check for presence of 1-phenylpent-4-en-2-
ol.11b Percent yield was calculated from H NMR, using an internal standard of
1
1
dimethylformamide. Yield 63%. H NMR (in CDCl ): δ (ppm) 7.30 (m, 5H), 5.90
3
(dddd, 1H, J = 10.0, 5.1, 4.8, 2.4 Hz), 5.08 (m, 2H), 3.49 (m, 2H), 2.84 (dd, 1H, J =
1
5, 5 Hz), 2.53 (m, 2H).
2
7

Dalton Transactions
Page 28 of 34
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DOI: 10.1039/D1DT00974E
X-ray Data Collection and Structure Determinations
A suitable crystal covered with a layer of hydrocarbon/Paratone-N oil was selected and
mounted on a Cryo-loop, and immediately placed in the low temperature nitrogen
stream. The X-ray intensity data were measured at 100(2) K on a Bruker D8 Quest with
a Photon 100 CMOS detector equipped with an Oxford Cryosystems 700 series cooler,
a graphite monochromator, and a Mo K fine-focus sealed tube (λ = 0.71073 Å).
Intensity data were processed using the Bruker Apex program suite. Absorption
3
5
corrections were applied by using SADABS. Initial atomic positions were located by
SHELXT,36 and the structures of the compounds were refined by the least-squares
method using SHELXL37 within Olex2 GUI.38 All the non-hydrogen atoms were
refined anisotropically. The hydrogen atoms of CH CHBF moiety were located in
2
3
difference Fourier maps, included and refined freely with isotropic displacement
parameters. Remaining hydrogen atoms were included in their calculated positions
and refined as riding on the atoms to which they are joined. X-ray structural figures
were generated using Olex2.38 Compound (SIPr)Cu(MeCN)(CH =CHBF ) crystallizes
2
3
with two molecules of dichloromethane, one of which was disordered but modelled
satisfactorily. CCDC 2063572-2063574 files contain the supplementary
crystallographic data.
These data can be obtained free of charge via
or from the Cambridge
http://www.ccdc.cam.ac.uk/conts/retrieving.html
Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge, CB2 1EZ, UK).
Additional details are provided in supporting information section.
Crystal Data for (SIPr)Cu(MeCN)(CH =CHBF )2(CH Cl ): C H BCl CuF N
2
3
2
2
33 48
4
3
3
(
M =759.89 g/mol): monoclinic, space group P2 /n (no. 14), a = 10.7461(4) Å, b =
1
3
2
1
2.3203(8) Å, c = 16.4600(6) Å, β = 106.1390(10)°, V = 3792.4(2) Å , Z = 4, T =
-1
3
00.0 K, μ(MoKα) = 0.899 mm , Dcalc = 1.331 g/cm , 61121 reflections measured
2
8

Page 29 of 34
Dalton Transactions
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= 0.0207) which were
sigma
DOI: 10.1039/D1DT00974E
(
5.586° ≤ 2Θ ≤ 66.284°), 14453 unique (R = 0.0229, R
int
used in all calculations. The final R was 0.0386 (I > 2σ(I)) and wR was 0.1082 (all
1
2
data).
Crystal Data for [CH (3,5-(CH ) Pz) ]Cu(CH =CHBF ): C H BCuF N
4
2
3 2
2
2
3
13 19
3
(M =362.67 g/mol): monoclinic, space group C2/c (no. 15), a = 22.2814(7) Å, b =
3
7
1
.8139(3) Å, c = 20.3486(10) Å, β = 122.0380(10)°, V = 3003.2(2) Å , Z = 8, T =
-1
3
00.0 K, μ(MoKα) = 1.487 mm , Dcalc = 1.604 g/cm , 23153 reflections measured
(
6.544° ≤ 2Θ ≤ 66.278°), 5707 unique (R = 0.0387, R
= 0.0355) which were used
int
sigma
in all calculations. The final R was 0.0381 (I > 2σ(I)) and wR was 0.0892 (all data).
1
2
Crystal Data for [CH (3,5-(CH ) Pz) ]Ag(CH =CHBF ): C H AgBF N
4
2
3 2
2
2
3
13 19
3
(
M =407.00 g/mol): monoclinic, space group P2 /n (no. 14), a = 11.3966(6) Å, b =
1
3
1
9
2.1819(7) Å, c = 12.0151(7) Å, β = 114.8850(10)°, V = 1513.21(15) Å , Z = 4, T =
-1
3
9.98 K, μ(MoKα) = 1.364 mm , Dcalc = 1.787 g/cm , 30566 reflections measured
(
5.014° ≤ 2Θ ≤ 76.166°), 7962 unique (R = 0.0262, R
= 0.0253) which were used
int
sigma
in all calculations. The final R was 0.0243 (I > 2σ(I)) and wR was 0.0612 (all data).
1
2
Theoretical methods:
Optimization and frequency calculations were performed with the GAUSSIAN 09
3
9
software suites at the High Performance Computing Center North (HPC2N), Umeå,
2
2
Sweden. Optimized structures were obtained using wB97XD functional and def2-
TZVP26 basis sets. Energy minima of all optimized molecular geometries were
confirmed by the frequency analysis. The EDA-NOCV analysis were performed using
method implemented in ORCA40 software with wB97X-D341 functional and old-
2
9