Reactivity of Lewis basic platinum complexes towards fluoroboranes

Article abstract of DOI:10.1002/chem.201301056

We herein report detailed investigations into the interaction of Lewis acidic fluoroboranes, for example BF₂Pf (Pf=perfluorophenyl) and BF₂Ar^F (Ar^F=3,5-bis(trifluoromethyl)phenyl), with Lewis basic platinum complexes such as [Pt(PEt₃)₃] and [Pt(PCy₃)₂] (Cy=cyclohexyl). Two presumed Lewis adducts could be identified in solution and corresponding secondary products of these Lewis adducts were characterized in the solid state. Furthermore, the concept of frustrated Lewis pairs (FLP) was applied to the activation of ethene in the system [Pt(BPf₃)(CH₂CH₂)(dcpp)] (dcpp=1,3-bis(dicyclohexylphosphino)propane; Pf=perfluorophenyl). Finally, DFT calculations were performed to determine the interaction between the platinum-centered Lewis bases and the boron-centered Lewis acids. Additionally, several possible mechanisms for the oxidative addition of the boranes BF ₃, BCl_3, and BF₂Ar^F to the model complex [Pt(PMe₃)₂] are presented. Still elusive: Several attempts to yield the elusive, unsupported Lewis adduct between a Lewis basic transition-metal complex and a Lewis acidic borane are presented, including NMR spectroscopic characterization at low temperatures, isolation of secondary products and detailed DFT calculations (see figure). Copyright

Full text of DOI:10.1002/chem.201301056

FULL PAPER
DOI: 10.1002/chem.201301056
Reactivity of Lewis Basic Platinum Complexes Towards Fluoroboranes
Jꢀrgen Bauer, Holger Braunschweig,* Rian D. Dewhurst, and Krzysztof Radacki[a]
Abstract: We herein report detailed in-
vestigations into the interaction of
Lewis acidic fluoroboranes, for exam-
ple BF2Pf (Pf=perfluorophenyl) and
BF2ArF (ArF =3,5-bis(trifluoromethyl)-
phenyl), with Lewis basic platinum
were characterized in the solid state.
Furthermore, the concept of frustrated
Lewis pairs (FLP) was applied to the
activation of ethene in the system [Pt-
Pf=perfluorophenyl). Finally, DFT cal-
culations were performed to determine
the interaction between the platinum-
centered Lewis bases and the boron-
centered Lewis acids. Additionally, sev-
eral possible mechanisms for the oxida-
tive addition of the boranes BF3, BCl3,
and BF2ArF to the model complex [Pt-
A
N
(dcpp)]
(dcpp=1,3-
bis(dicyclohexylphosphino)propane;
complexes such as [Pt
ACHTUNGTREN(UNNG PEt3)3] and [Pt-
ACHTUNGTRENNUNG(PCy3)2] (Cy=cyclohexyl). Two pre-
Keywords: density functional calcu-
sumed Lewis adducts could be identi-
fied in solution and corresponding sec-
ondary products of these Lewis adducts
ACHTUNGTREN(NUNG PMe3)2] are presented.
lations
· fluoroboranes · Lewis
acids · transition metals
Introduction
In 1963, Shriver reported the reaction of the Lewis basic
transition-metal complex [Cp2W(H)2] (1; Cp=cyclopenta-
dienyl) with BF3,[1] presenting the first Lewis adduct of a
borane with a transition metal, the complex [Cp2(H)2W!
BF3] (Figure 1; 2). Until this finding, only Lewis adducts of
boranes with main-group Lewis bases, such as amines, were
known. After these preliminary results, several other related
borane adducts with BCl3 or B2H6 were presented by the
same group.[2] These results kick-started investigations
aimed at preparing complexes with dative interactions be-
tween Lewis basic metal complexes and Lewis acidic sub-
strates, leading to reports of a number of complexes with
BF3 in the coordination sphere of metals such as rhodium or
iridium.[3,4] The ability of early-transition-metal complexes
to form dative bonds with BH3 was also investigated.[5,6] Fi-
nally, the concept of metal-centered Lewis basicity was ap-
plied in the formation of so-called metal-only Lewis pairs
(MOLPs).[7,8]
Figure 1. Postulated (2) and isolated examples (4) of dative bonding be-
tween Lewis basic transition metals, and identified byproducts (3 and 7).
[Cp2W(H)3]ACTHNUTRGNEUNG
[BF4] (Figure 1, 3).[9–12] While these results ex-
perimentally disproved earlier claims of borane adducts of
1, it should be noted that subsequent theoretical investiga-
tions supported the early work of Shriver and suggest that
these complexes should be isolable.[13]
However, experimental proof for the existence of dative
bonds between boranes and Lewis basic transition-metal
complexes was disclosed several years later by Hill and co-
workers with the synthesis of a supported borane adduct of
ruthenium in which the Lewis acidic center is linked to the
metal base by a supporting covalent scaffold (Figure 1, 4),[14]
a concept that subsequently has been widely applied to
many other borane complexes.[15–30]
Eventually, the lack of structural data confirming the exis-
tence of the dative bond between the boron atom and the
Lewis basic metal led to renewed interest in the postulated
borane adducts. Thus, we reinvestigated the reactivity of 1
towards BF3 and several other boranes, which led exclusive-
ly to zwitterionic or salt-like compounds such as
[a] Dr. J. Bauer, Prof. Dr. H. Braunschweig, Dr. R. D. Dewhurst,
Dr. K. Radacki
Institut fꢀr Anorganische Chemie
Julius-Maximilians-Universitꢁt Wꢀrzburg, Am Hubland
97074 Wꢀrzburg (Germany)
Fax : (+49)931-888-4623
E-mail: h.braunschweig@mail.uni-wuerzburg.de
Nevertheless, we conducted further experiments in our
laboratory aimed at the structural characterization of a com-
plex with an unsupported bond between a borane and a
Lewis basic transition metal. To this end, we investigated
the well-established complex [Pt
of BF3. No signs of formation of the adduct trans-
ACHTUNGTREN(NNUG PCy3)2] (5) in the presence
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301056.
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[(Cy3P)2Pt!BF3] (6) could be observed even at low temper-
whereas the other signal is detected as a multiplet. In the
11B{1H} NMR spectra, a resonance is detected at d=
16.3 ppm, shifted towards higher field by 6 ppm relative to
that of the precursor (9=22.2 ppm). Finally, in the 19F{1H}
NMR spectra, four resonances are detected, as would be ex-
pected for such a Pt!B borane adduct. The signal at d=
ꢀ96.0 ppm could be assigned to the two fluorine atoms
bound to the boron, and the signals at d=ꢀ130.2, ꢀ149.6,
and ꢀ162.9 ppm belong to the C6F5 substituent. These spec-
troscopic parameters all indicate the formation of the unsup-
ported borane adduct [(Et3P)3Pt!BF2Pf] (13) in solution.
ꢀ
atures. Instead, oxidative addition of the very strong B F
bond was detected and the product trans-[(Cy3P)2Pt
N
ACHTUNGTRENNUNG
Results and Discussion
With these previous investigations and results in mind, we
attempted to envisage how the best candidate for an unsup-
ported borane–transition-metal interaction should look. Pri-
marily, the borane should possess high Lewis acidity, which
can be realized by s-electron-withdrawing substituents at
the boron center and by minimizing their p-donor ability.
Furthermore, all substituents should feature strong or inert
bonds that are not easily cleaved by transition metals. In our
opinion, fluoroboranes with fluorinated aryl rings fulfill
these requirements. One of the most widely used boranes is
the borane BPf3 (Pf=perfluorophenyl, 8),[32–34] but in the
presence of sterically encumbered Lewis bases, activation of
the para-position of the Pf group is commonplace.[35] There-
fore, we synthesized the fluoroborane BF2Pf (9) as it is ef-
fectively the smallest Pf-substituted haloborane.
ꢀ
However, another possibility would be a type of B C s co-
ordination similar to the complex [(Et3P)2Pt
(Mes)C
(Mes)C(Ph)})] (14).[37]
Unfortunately, after several hours these resonances gradu-
A
A
ACHTUNGTRENNUNG
ally diminished and a colorless microcrystalline solid formed
in the NMR tube. Dissolving the solid in a more polar sol-
vent and subjecting this to NMR spectroscopy indicated the
formation of a new product (Table 1). The resonances in the
31P{1H} NMR spectra were located at d=ꢀ0.6 (1JP–Pt
=
2633 Hz) and ꢀ1.4 ppm (1JP–Pt =1984 Hz), whereas the cou-
pling pattern of the more intense signal was still a doublet
(2JP–P =24 Hz). However, the resonance at d=ꢀ1.4 ppm
now consisted of a triplet (2JP–P =24 Hz) of doublets (J=
10 Hz) of doublets (J=4 Hz). In the 19F{1H} NMR spectra,
five signals were detected, whereby the resonance at d=
ꢀ134.8 ppm revealed an approximate threefold higher inten-
sity than the signals at d=ꢀ112.9, ꢀ134.1, ꢀ162.8, and
ꢀ164.9 ppm. Surprisingly, the resonance at d=ꢀ112.9 ppm
shows a characteristic platinum–fluorine coupling with a
coupling constant of 386 Hz. The coupling patterns could be
confirmed by the parameters derived from the 195Pt{1H}
NMR spectra; the resonance at d=ꢀ4757 ppm appeared as
a triplet (1JPt–P =2633 Hz) of doublets (1JPt–P =1984 Hz) of
doublets (3JPt–F =386 Hz). Based on the resonance at d=
2.8 ppm in the 11B{1H} NMR spectra, the activation of an ar-
The synthesis of 9 has been previously reported in the lit-
erature, usually involving halogen exchange from starting
materials such as BCl2Pf (10).[36] We used a commutation re-
action between BPf3 (8) and BF3, providing BF2Pf (9) in a
yield of 52%. Borane 9 was identified by its NMR spectro-
scopic parameters (Table 1), for example, its 11B{1H} (d=
Table 1. NMR parameters of compounds 9, 12, 13, and 15.
9
12
13
15
11B{1H}[a]
19F{1H}[a,b]
31P{1H}[a,c]
31P{1H}[a,d]
22.2
–
–
16.3
ꢀ96.0
0.3
ꢀ2.0
2441
2021
2.8
ꢀ134.8
ꢀ0.6
ꢀ73.8
–
–
–
–
41.8
ꢀ1.4
[c,e]
1JP–Pt
2633
1984
ꢀ
omatic C F bond leading to the zwitterionic compound
4206
[d,e]
1JP–Pt
[(Et3P)3Pt(C6F4-2-BF3)] (15) was postulated (Scheme 1).
In order to confirm the postulated constitution, X-ray dif-
fraction analysis of single crystals of 15 was performed
(Figure 2). The molecular structure exhibits a square-planar
[a] d in ppm. [b] Fluorine atoms attached to the boron center. [c] Phos-
phine ligands in the trans position. [d] Phosphine ligands in the cis posi-
tion. [e] Coupling constant in Hz.
ꢀ
arrangement at the platinum center with P Pt distances of
22.2 ppm) and 19F{1H} (d=ꢀ73.8 ppm for the fluorine atoms
attached to the boron) resonances. Remarkably, no sign of
the formation of BFPf2 (11) was detected; therefore the re-
maining solid after the vacuum transfer was pure 8, which
then was reacted with new BF3 to yield more 9.
233.2(2) to 236.8(2) pm and a C Pt distance of 208.7(6) pm.
ꢀ
The boron atom is coordinated in an almost ideal tetrahe-
dral geometry with angles between 107.7(6) and 108.6(5)8.
Given that the borane BF2Pf (9) appears to possess an ar-
ꢀ
omatic C F bond too reactive to allow isolation of the inter-
Reaction of the Lewis basic platinum complex [Pt
N
mediate, the related fluoroborane BF2ArF (16; ArF =3,5-
bis(trifluoromethyl)phenyl) was synthesized. Borane 16 can
be obtained by the reaction of Me3SnArF (17)[38] with BF3 in
a range of non-coordinating solvents like hexanes or tol-
uene.
(12) with equimolar amounts of 9 resulted in the formation
of only one product, as determined by multinuclear NMR
spectroscopy (Table 1). In the 31P{1H} NMR spectra, the res-
1
onance of the starting material (d=41.8 ppm, JP–Pt
=
4206 Hz) could no longer be observed. Instead, two new sig-
nals were detected, one at d=0.3 ppm with a JP–Pt coupling
The reaction of 16 with [Pt
nite products, therefore the complex [PtACTHUNGTRENNUNG
ACHTUNGTRENNUNG
1
constant of 2441 Hz, and a less intense resonance at d=
used. In an NMR tube charged with equimolar amounts of 5
and 16, immediate formation of a new compound could be
observed by the broad resonance at d=58 ppm in the
ꢀ2.0 ppm (1JP–Pt =2021 Hz). The signal at d=0.3 ppm ap-
2
pears as a doublet, due to a JP–P coupling constant of 23 Hz,
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Lewis Basic Platinum Complexes
FULL PAPER
Scheme 1. Reaction of the complex [Pt
tion of the zwitterionic complex [(Et3P)3Pt(C6F4-2-BF3)] (15).
G
the resonances in the 11B{1H}, 19F{1H} (for the fluorine
atoms attached to the boron), and 31P{1H} NMR spectra are
remarkably broadened. In order to favor 18 instead of 5 and
16, we performed NMR spectroscopic experiments at varia-
ble temperatures. As a result, we were able to characterize
18 at ꢀ808C by the recorded 31P{1H} NMR spectrum in
which a resonance of 18 was found at d=49.7 ppm (1JP–Pt
=
3760 Hz). Interestingly, the resonance appeared as a triplet
3
due to the JP–F coupling of 18 Hz due to the two fluorine
atoms attached to the Lewis acidic boron center (Table 2).
Table 2. NMR parameters of compounds 16, 5, 18, and 19.
Figure 2. Molecular structure of [(Et3P)3Pt(C6F4-2-BF3)] (15). Ellipsoids
drawn at the 50% probability level; ellipsoids of the ligands and hydro-
gen atoms omitted for clarity. Relevant bond lengths [pm] and angles [8]:
16
5
18
19
19F{1H}[a,b]
31P{1H}[a]
ꢀ87.8
–
ꢀ167
49.7[c]
3760[c]
ꢀ20.5
48.5
2631
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Pt P1 233.8(2), Pt P2 236.8(2), Pt P3 233.2(2), Pt C1 208.7(6), B C2
–
–
62.3
4164
ꢀ
ꢀ
ꢀ
162.7(9), B F5 142.9(8), B F6 140.8(8), B F7 140.1(8); P1-Pt-P2
166.8(1), P1-Pt-P3 96.6(1), P2-Pt-P3 94.8(1), P1-Pt-C1 86.1(1), P2-Pt-C1
82.8(2), P3-Pt-C1 176.7(1), C2-B-F5 108.6(5), F5-B-F6 107.7(6), F5-B-F7
108.1(5), F6-B-F7 107.8(5).
[d]
1JP–Pt
[a] d in ppm. [b] Fluorine atoms attached to the boron center. [c] Record-
ed at ꢀ808C. [d] Coupling constant in Hz.
1
31P{1H} NMR spectrum with a JPt–P coupling constant of
In further experiments, we tried to shift the equilibrium
towards 18 by adding additional equivalents of 16 to an
equimolar solution of 5 and 16. At a 5/16 ratio of 1:2, the
resonance detected in the 31P{1H} NMR spectrum was locat-
ed at about d=53 ppm (1JP–Pt =3770 Hz). At a ratio of 1:10,
4080 Hz (5; d=62.3 ppm, 4164 Hz) and a resonance at d=
12 ppm in the 11B{1H} NMR spectrum (16: d=23.5 ppm). In
addition, no signs of decomposition of the either the borane
or the complex 5 could be detected in the 19F{1H} and
1H NMR spectra. Therefore, we propose that this complex is
a Lewis adduct of the platinum-centered Lewis base 5 with
the borane 16, with the formula trans-[(Cy3P)2Pt!BF2ArF]
(18; Scheme 2).
the detected resonance was located at d=46 ppm (1JP–Pt
=
3230 Hz). In addition, in the 19F{1H} NMR spectrum an un-
expected resonance at d=ꢀ46 ppm was observed, together
with the expected resonances at d=ꢀ63.7 (CF3 groups) and
ꢀ102 ppm (BF2 moiety). Comparison of these 19F{1H} NMR
However, the information gained from the 31P{1H} NMR
spectrum indicates an equilibrium between complex 5 and
the formed 18, due to the fact that NMR spectroscopic pa-
rameters of 18 are quite similar to those of 5. Additionally,
resonances with those of the complex trans-[(Cy3P)2PtACHTUNGTRENNUNG(BF2)-
A
the assumption that, in the reaction between 5 and 16, an
oxidative addition also takes place, however, in this case it
seems to be reversible.
Using this Lewis base–Lewis acid system, we also ob-
served an irreversible reaction analogous to the synthesis of
T-shaped, cationic platinum–boryl complexes.[39,40] For this
purpose, one equivalent of a halide abstraction reagent, Na-
AHCTUNGTRENNUNG
[BArCl4] (ArCl =3,5-bis(trichloromethyl)phenyl), was added
to a mixture of one equivalent of 5 and two equivalents of
16, yielding the complex trans-[(Cy3P)2Pt
(BFArF)][BArCl
(19, Table 2, Scheme 3). In the 31P{1H} NMR spectrum the
Scheme 2. Postulated equilibrium between the Lewis basic complex [Pt-
ACHTUNGTRENNUNG
(PCy3)2] (5), the borane BF2ArF (16), and the Lewis adduct trans-
N
G
]
4
[(Cy3P)2Pt!BF2ArF] (18).
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H. Braunschweig et al.
and trans-[(Cy3P)2Pt!BF2ArF] (18), but were unable to iso-
late them. However, the formation of a FLP between [Pt-
AHCTUNGTRENNG(UN PCy2)3] (5) and BF2OtBu (21) could be an interesting ap-
proach to further investigate the properties of the herein
presented complexes. The activation of small, unreactive
molecules such as H2, CO2 or alkenes by FLPs[42] interested
us due to the fact that in our systems the Lewis base is a
transition-metal complex. We chose ethene for initial activa-
tion tests as it is not only a widely-used resource for indus-
trial processes, but also a well-established ligand in transi-
tion metal chemistry.
Scheme 3. Reaction of [Pt
(16) and one equivalent of Na
[(Cy3P)2Pt
(BFArF)][BArCl4] (19).
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
resonance of 19 was located at d=48.5 ppm (1JP–Pt
=
2631 Hz), whereas the resonance appears as a doublet due
After exchange of the argon atmosphere to an ethene at-
mosphere in a sealable NMR tube charged with a benzene
solution of equimolar amounts of 5 and 16, the complex
3
to the JP–F coupling of 9 Hz with the boron-bound fluorine
nucleus. In addition, the 19F{1H} NMR spectrum reveals a
2
resonance at d=ꢀ20.5 ppm with a JF–Pt coupling constant
trans-[(Cy3P)2Pt
(C2H4)] (23)[43] is exclusively formed, identi-
ACHTUNGTRENNUNG
1
of 637 Hz together with the resonance of the CF3 groups at
d=ꢀ63.3 ppm.
fied by 31P{1H} NMR spectroscopy (23; d=41.3 ppm, JP–Pt
=
3604 Hz). No signs of an activation process could be detect-
ed by NMR spectroscopy.
An alternative strategy for the synthesis of an unsupport-
ed metal-borane complex is the construction of the borane
ligand directly in the coordination sphere of a suitable plati-
num complex. To this end, we treated the compound trans-
We extended this study to the use of borane BPf3 (8), a
common Lewis acid in FLP chemistry.[44] In addition, we
used the compound [(dcpp)Pt
cyclohexylphosphino)propane) that could be synthesized by
reduction of cis-[PtCl2A(dcpp)] (25) under an atmosphere of
ACHTUGNRTEN(NUGN C2H4)] (24, dcpp=1,3-bis(di-
[(Cy3P)2Pt
KOtBu in a sealable NMR tube (Scheme 4).
ACHTUNGTRENNUNG
(BF2)Cl] (20)[31] with an equimolar amount of
CTHUNGTRENNUNG
ethene, as a Lewis base with a pre-coordinated small mole-
cule, the ethene ligand. After addition of 8 to a suspension
of 24 in benzene, immediate formation of a pale yellow solu-
tion was observed (Scheme 5). Analysis of the 31P{1H} NMR
Scheme 4. Reaction of trans-[(Cy3P)2PtACHTNUGTRENNUNG
KOtBu, yielding the free Lewis base [Pt
BF2OtBu (21).
ACHTUNGTRENNUNG
Directly after addition of the KOtBu, a new resonance
was detected in the 31P{1H} NMR spectrum at d=62.3 ppm
(1JP–Pt =4164 Hz), which was identified as the platinum(0)
complex [PtACHTUNGTRENNUNG(PCy3)2] (5). In addition, the resonance of 20
Scheme 5. Reaction of [(dcpp)Pt
ACHTUNGTRENNUNG
1
(d=30.7 ppm, JP–Pt =2604 Hz) remained for about five days
at room temperature. Thus the reaction takes place very
slowly and the other reaction product, borane BF2OtBu
(21), could be identified by its 19F{1H} (d=ꢀ139.4 ppm) and
11B{1H} (d=16.1 ppm) NMR spectra (Table 3). Interestingly,
neither the platinum complex 5 nor the borane 21 show any
sign of interaction or formation of the Lewis pair trans-
[(Cy3P)2Pt!BF2OtBu] (22) and therefore can be regarded
as a frustrated Lewis pair (FLP).[41]
the formation of the complex [(dcpp)Pt
G
ACHTUNGTRENNUNG
spectra revealed two resonances, one at d=26.5 ppm and
the other at d=16.8 ppm (24; d=25.7 ppm, JP–Pt =3270 Hz).
1
The resonance at d=26.5 ppm is a quartet of doublets due
2
to JP–P and JP–B coupling (both 7 Hz). Furthermore, the res-
onance is accompanied by 195Pt satellites with a JP–Pt cou-
1
pling of 4755 Hz. The second resonance at d=16.8 ppm is
split into a doublet (2JP–P =7 Hz) in addition to a JP–Pt cou-
1
To summarize, we were able to detect what appeared to
be platinum–borane Lewis adducts [(Et3P)3Pt!BF2Pf] (13)
pling constant of 2738 Hz. The 11B{1H} NMR spectra shows
only one resonance located at d=ꢀ13.5 ppm, which lies in
the established region for Lewis adducts of 5. Further proof
for the tetra-coordination at the boron atom is given by the
19F{1H} NMR spectra. Herein, three resonances are detected
at d=ꢀ131.0, ꢀ162.0, and ꢀ166.3 ppm. All resonances indi-
Table 3. NMR parameters of compounds 20, 5, and 21.
20
5
21
11B{1H}[a]
19F{1H}[a,b]
31P{1H}[a]
30
ꢀ24.8
30.7
–
–
62.3
4164
16.1
ꢀ139.4
1
cate JF–F coupling whereas the resonance at d=ꢀ131.0 ppm
–
–
[c]
1JP–Pt
2604
could be assigned to the ortho fluorine atoms and the reso-
nance at d=ꢀ166.3 ppm was assigned to the meta fluorine
atoms. Therefore, the resonance at d=ꢀ162.0 ppm repre-
[a] d in ppm. [b] Fluorine atoms attached to the boron center. [c] Cou-
pling constant in Hz.
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Lewis Basic Platinum Complexes
FULL PAPER
sents the fluorine atoms in para position. This pronounced
shift with respect to the starting material 8 (resonance of
the fluorine atoms in para postion: d=ꢀ143.0 ppm) pro-
vides further evidence for tetra-coordination of 8 (Table 4).
Table 4. NMR parameters of compounds 8, 24, and 26.
8
24
26
11B{1H}[a]
19F{1H}[a,b]
31P{1H}[a]
59.4
–
–
25.7
3270
ꢀ13.5
ꢀ130.1, ꢀ143.0, ꢀ164.4
ꢀ131.0, ꢀ162.0, ꢀ166.3
–
–
26.5, 16.8
4755, 2738
[c]
1JP–Pt
[a] d in ppm. [b] Fluorine atoms in ortho, para and meta positions.
[c] Coupling constant in Hz.
Figure 3. Molecular structure of [(dcpp)PtBPf3ACTHNUTRGEN(UNG CH2CH2)] (26). Ellipsoids
1
drawn at the 50% probability level; the hydrogen atoms of the ethylene
bridge are refined without constraints, and the ellipsoids of the ligands,
solvent molecules and all other hydrogen atoms are omitted for clarity.
Finally, the H NMR spectra reveals, in addition to the reso-
nances of the dcpp ligand, a doublet at d=ꢀ0.05 ppm with a
coupling constant of 33 Hz in addition to a characteristic
ꢀ
ꢀ
Relevant bond lengths [pm] and angles [8]: Pt P1 222.5(1), Pt P2
1JH–Pt coupling of 66 Hz. The origin of the smaller coupling
ꢀ
ꢀ
ꢀ
ꢀ
230.7(1), Pt C1 207.3(4), Pt H1 175(3), Pt C2 232.2(4), C1 C2 152.2(5),
1
ꢀ
ꢀ
ꢀ
ꢀ
B C2 167.4(5), B C3 165.6(5), B C4 166.2(5), B C5 165.5(5); P1-Pt-P2
99.2(1), P1-Pt-C1 99.7(1), P2-Pt-C1 160.1(1), P1-Pt-C2 138.5(1), P2-Pt-C2
121.6(1), C1-Pt-C2 39.0(2), Pt-C2-B 136.1(2), C1-C2-B 119.4(3), C2-B-C3
104.2(3), C2-B-C4 110.2(3), C2-B-C5 112.5(3), C3-B-C4 114.4(3), C3-B-
C5 113.2(3), C4-B-C5 102.4(3).
was determined by H
d=ꢀ0.05 ppm appeared as a singlet.
N
These spectroscopic data suggest an agostic interaction
between the ethene ligand and the platinum center. Howev-
er, in order to determine the chemical structure of the
newly formed complex, X-ray diffraction analysis of a suita-
ble single crystal was performed. On the basis of these re-
up to +57 kJmolꢀ1 for 22opt, therefore indicating endergonic
reactions for all investigated systems. This is in stark con-
trast to the DDGM05-2X values. Here, the complexes 13opt and
18opt indicate, with values for the DDGM05-2X of ꢀ32 kJmolꢀ1
and ꢀ40 kJmolꢀ1, respectively, an exergonic reaction. How-
ever, the DDGM05-2X value for the compound 22opt amounts
only to ꢀ3 kJmolꢀ1, being almost neutral. This is in good
agreement with the experimental results in which the Lewis
adducts 13 and 18 could be detected, whereas no evidence
for the Lewis adduct 22 could be observed. These overall
lower values for DDGM05-2X can be explained by the differ-
ence between the two functionals. Hereby, the functional
M05-2X takes weak interactions into account and therefore
predicts stronger bonds in Lewis pairs on the whole. This
functional seems, in this case, to be more adequate in repre-
senting the experimental results.
sults, the formula [(dcpp)Pt
assigned (Figure 3).
Due to the aforementioned agostic interaction in the trans
position to the P1 atom, the Pt P1 bonding distance
(222.5(1) pm) is about 8 pm shorter than the Pt P2 distance
(230.7(1) pm). This pronounced difference in the bonding
distances is also reflected in the smaller coupling constants
between platinum and P2 (1JP2–Pt =2738 Hz) and in contrast
ACHTUTGNRENUNG(BPf3)ACHUTGNTREN(NUGN CH2CH2)] (26) could be
ꢀ
ꢀ
1
to the large JP1–Pt coupling (4755 Hz). However, the overall
coordination at the platinum center is square-planar with an
angular sum of 395.5(5)8. Hereby, the P2-Pt-C2 (121.6(1)8)
and the C1-Pt-C2 (39.0(2)8) angles reveal the most pro-
nounced deviance from ideal square-planarity (908). The
boron is coordinated in a tetrahedral geometry with C-B-C
angles between 102.4(3) and 114.3(3)8.
In order to further examine the interactions between plat-
inum complexes and fluoroboranes, theoretical calculations
were performed using the functionals B3LYP and M05-2X.
The first functional was chosen due to its frequent applica-
tion in the calculation of bond dissociation enthalpies
(BDE) in Lewis pairs with transition metals,[45–48] the second
was chosen due to its ability to reproduce weak interactions
in Lewis pairs, as demonstrated for example in the calcula-
Furthermore, a possible mechanistic pathway for the oxi-
dative addition of BF2ArF (16opt) to the model complex [Pt-
AHCUTNERTG(GNNUN PMe3)2] (5mod) was investigated (Scheme 6). For compari-
son, mechanisms for the oxidative addition of BF3 and BCl3
to 5mod were determined. These calculations were exclusive-
ly performed with the functional M05-2X, due to the afore-
mentioned results. Initially, the pathway found for the oxida-
tive addition of BF3 at 5mod reveals formation of the Lewis
adduct trans-[(Me3P)2Pt!BF3] (6mod), which has a free
energy about ꢀ54 kJmolꢀ1 below the starting materials. The
actual transition state of the oxidative addition (6TS) is
+225 kJmolꢀ1 higher in energy than the starting materials
and can be described as a BF3 moiety coordinated side-on
tion of the FLP [(ItBu)ACTHNUTRGNEUNG(BPf3)] (ItBu=N,N’-bis(tert-butyl)-
imidazol-2-ylidene, 27opt).[49] The free formation energies
(DDG) of the complexes [(Et3P)3Pt!BF2Pf] (13opt), trans-
[(Cy3P)2Pt!BF2ArF]
(18opt
)
and
trans-[(Cy3P)2Pt!
BF2OtBu] (22opt) were determined by comparing the Gibbs
free energies (at 298.15 K) of the free Lewis acids and bases
with the associated Lewis pairs (Figure 4 and Table 5).
Interestingly, the DDGB3LYP values are all positive, in a
range from +21 kJmolꢀ1 for 13opt and +33 kJmolꢀ1 for 18opt
ꢀ
by one B F bond with the two phosphine ligands still in
trans position to each other. However, the product of the
oxidative addition, the complex trans-[(Me3P)2Pt
ACHTUNGTRENNUNG(BF2)F]
(28mod) is still about +42 kJmolꢀ1 higher in energy than the
Chem. Eur. J. 2013, 00, 0 – 0
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H. Braunschweig et al.
Table 5. Selected calculated parameters for complexes 13opt, 18opt, and
22opt
.
13opt
18opt
22opt
[a}
DDHB3LYP
ꢀ44
ꢀ104
+21
ꢀ32
ꢀ33
ꢀ99
+33
ꢀ40
0
ꢀ54
+57
ꢀ3
[a}
DDHM05-2X
DDGB3LYP
DDGM05-2X
[a}
[a}
[a] Enthalpies and Gibbs free energies (at 298.15 K) in kJmolꢀ1
.
materials and making the overall reaction exergonic. This is
in agreement with experiment, in which case only the com-
plex trans-[(Cy3P)2PtACTHUNRGTENNUG(BF2)ACHTUNGTRENN(GUN FBF3)] (7) was observed.
For comparison, calculation of the mechanistic pathway of
the oxidative addition of BCl3 to 5mod revealed similar steps.
At first, the Lewis adduct trans-[(Me3P)2Pt!BCl3] (29mod
)
was determined to have a free energy of ꢀ70 kJmolꢀ1 below
the starting materials, whereas the side-on coordinated tran-
sition state (29TS) is +31 kJmolꢀ1 higher in energy than the
starting materials. In contrast to the oxidative addition of
BF3, the product trans-[(Me3P)2PtACHTUNGTRNE(GNU BCl2)Cl] (30mod) is exer-
gonic by a free energy of ꢀ134 kJmolꢀ1 below the starting
materials. Additionally, the calculated geometry of a product
of the addition of two equivalents of BCl3, the complex
trans-[(Me3P)2PtACHTNUGTRENNG(U BCl2)CAHTUGNTERN(NUNG ClBCl3)] (31mod), has a free energy
only about ꢀ3 kJmolꢀ1 lower than 30mod. This again is in
agreement with the experimental investigations, wherein no
signs of addition of BCl3 to the complex trans-[Pt
(PCy3)2] (30) were observed.
To conclude the mechanistic studies herein, we deter-
mined a possible mechanism for the oxidative addition of
BF2ArF (16opt) to [Pt
(PMe3)2] (5mod). The first step, the for-
ACHTUNGRTEN(NUNG BCl2)Cl-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
mation of the Lewis adduct trans-[(Me3P)2Pt!BF2ArF]
(18mod) again is similar to the reaction of BF3 and BCl3. The
complex 18mod has a free energy of about ꢀ43 kJmolꢀ1 with
respect to its starting materials. The geometry in the transi-
tion state (18TS) again reveals a side-on coordination of one
ꢀ
B F bond, with
a
free energy of approximately
+114 kJmolꢀ1 with respect to the starting materials. Howev-
er, the two phosphine ligands are now mutually cis. This
stands in contrast to the transition states found for the other
two calculated pathways. Another difference is the complex
cis-[(Me3P)2PtACTHNUTRGNEUNG
(BFArF)F] (32mod) that is found as an inter-
mediate on the reaction path lying about +103 kJmolꢀ1
above the starting materials. As the next step, a cis–trans
isomerization could be identified, resulting in the complex
trans-[(Me3P)2PtACTHNUTRGNEUNG
(BFArF)F] (33mod). Complex 33mod has a
free energy of +60 kJmolꢀ1 above the starting materials. In-
terestingly, the geometry in the transition state (32TS) reveals
a mutually-cis arrangement of the fluorine and boryl ligands
with one phosphine ligand dissociated, overall with a free
energy +95 kJmolꢀ1 higher than the complex 32mod. This is
Figure 4. Optimized gas-phase structures of the Lewis adducts
[(Et3P)3Pt!BF2Pf] (13opt), trans-[(Cy3P)2Pt!BF2ArF] (18opt), and trans-
[(Cy3P)2Pt!BF2OtBu] (22opt).
ꢀ
in contrast to the findings for the oxidative addition of B H
bonds to platinum complexes, in which hexacoordinate tran-
sition states were identified.[50] However, as in the oxidative
addition of BF3, further addition of a second equivalent of
starting materials. Addition of another equivalent of BF3
furnishes the complex trans-[(Me3P)2Pt
G
G
the borane 16opt furnishes the complex trans-[Pt
ACHTUNGTRENNUNG
(BFArF)-
now having a free energy of ꢀ96 kJmolꢀ1 below the starting
A
ACHTUNGTRENNUNG
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Lewis Basic Platinum Complexes
FULL PAPER
Scheme 6. Possible mechanistic pathways for the oxidative addition of BF3, BCl3, and BF2ArF (16opt) to the model complex [Pt
ACHTNURTGNEUG(N PMe3)2] (5mod).
Experimental Section
ꢀ69 kJmolꢀ1 with respect to the starting materials. This
mechanism is in good agreement with the experimental re-
sults, in which a reversible oxidative addition of 16 to the
complex 5 was found. Thus the overall more shallow energy
barriers for the reaction of BF2ArF (16opt), in contrast to the
reaction of BF3, could be an explanation for the reversibility.
In addition, the cis configuration in the intermediate cis-
Theoretical calculations: The computations were performed using DFT
methods, applying the functionals B3LYP and M05-2X, using the 6-31G-
AHCTUNGERTG(NNUN d,p) basis set for H, B, C, F, Cl, O, P, and the Stuttgart RSC ECP basis
set for Pt. More detailed information concerning the calculations, includ-
ing Cartesian coordinates of the optimized geometries, can be found in
the Supporting Information.
[(Me3P)2PtACHTUNGTRENNUNG
(BFArF)F] (32mod) enables an easy reductive
General considerations: All manipulations were performed either under
dry argon or in vacuo using standard Schlenk line and glovebox techni-
ques.[51] Solvents were purified by standard procedures and stored under
elimination and therefore facilitates the reverse reaction of
the oxidative addition.
Argon over molecular sieves. BPf3 (8),[34] [Pt
(17),[38] [Pt(PCy3)2] (5),[53] and trans-[(Cy3P)2Pt
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
pared according to previously published procedures. NMR spectra in sol-
ution were acquired on a BrukerAvance 400 (1H: 400.1 MHz, 11B{1H}:
128.4 MHz, 13C{1H}: 100.6 MHz, 19F{1H}: 376.5 MHz, 31P{1H}: 162.0 MHz,
195Pt{1H}: 86.0 MHz) NMR spectrometer. NMR spectra were referenced
to external SiMe4 (1H, 13C), [BF3·Et2O] (11B), CFCl3 (19F), 85% H3PO4
Conclusion
We report herein detailed investigations into the interaction
of Lewis acidic fluoroboranes with Lewis basic platinum
complexes. Two presumed Lewis adducts were identified in
solution, but these were not able to be characterized in the
solid state. However, secondary products of these Lewis ad-
ducts were fully characterized.
Additionally, the concept of frustrated Lewis pairs (FLP)
was applied by the activation of ethene in the system
[(dcpp)PtACHTUNGTRENNUNG(CH2CH2)BPf3] (26). Furthermore, DFT calcula-
2ACTHNUTRGNEUNG
(31P), and Na [PtCl6] in D2O (195Pt). Microanalyses were performed on an
EuroEA3000 elemental analyzer.
Synthesis of BF2Pf (9): BPf3 (8, 0.300 g, 586 mmol) was dissolved in tol-
uene (10 mL) in a Schlenk flask equipped with a Teflon valve and the
Argon atmosphere was exchanged by an atmosphere of BF3. After stir-
ring at 808C for three days all volatiles were transferred from the remain-
ing 8 and the excess BF3 was removed by degassing of the colorless solu-
tion. The yield of 9 was determined by 19F{1H} NMR spectroscopy, by
adding 8 (5.1 mg, 10 mmol) to 0.1 mL of the yielded solution of 9. The
ratio hereby was 0.9 (9) to 1 (8), resulting in an overall yield of 52%
(0.198 g, 917 mmol). 11B{1H} NMR (128.4 MHz, C6D6): d=22.2 ppm (brs,
FWHMꢁ130 Hz); 19F{1H} NMR (376.5 MHz, C6D6): d=ꢀ73.8 (brs,
FWHMꢁ350 Hz, BF2), ꢀ128.2 (m, o-F), ꢀ144.5 (m, p-F), ꢀ161.5 ppm
(m, m-F).
tions were performed to determine the interaction between
the platinum-centered Lewis bases and the boron-centered
Lewis acids. Finally, possible mechanisms for the oxidative
addition of BF3, BCl3 and BF2ArF (16opt) to [Pt
(5mod) are presented.
ACHTUNGTRNE(NUNG PMe3)2]
Chem. Eur. J. 2013, 00, 0 – 0
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H. Braunschweig et al.
Synthesis of [(Et3P)3Pt!BF2Pf] (13): In a J. Young NMR tube, one
equivalent of PEt3 was removed in vacuo at 608C from the complex [Pt-
BFArF), ꢀ63.7 (s, CF3), ꢀ102 ppm (vbrs, FWHMꢁ1100 Hz, BF2ArF);
1
31P{1H} NMR (162.0 MHz, C6D6): d=46 ppm (vbr s, JP–Pt =3230 Hz).
Synthesis of trans-[PtACHTUNGTRENNGU ACHTUGNTRNE(NUGN PCy3)2]AHCTNUTGRENNUNG ] (19): [PtACHTNURGTEG(NNUN PCy3)2] (5,
(BFArF) [BArCl
ACHTUNGTRENNUNG(PEt3)4] (30.0 mg, 45 mmol). The resulting complex [PtAHCTUNGTREN(NUGN PEt3)3] (12,
4
24.7 mg, 45 mmol) was then dissolved in C6D6 (0.1 mL) and a solution of
BF2Pf (9, 0.50 mL, 0.09m in toluene, 45 mmol) was added. 11B{1H} NMR
(128.4 MHz, C6D6): d=16.3 ppm (brs, FWHMꢁ150 Hz); 19F{1H} NMR
(376.5 MHz, C6D6): d=ꢀ96.0 (vbrs, FWHMꢁ380 Hz, BF2), ꢀ130.2 (m,
69.5 mg, 92 mmol) was dissolved in fluorobenzene (3 mL) and a solution
of BF2ArF (16, 0.80 mL, 0.23m in hexanes, 0.18 mmol) was added at RT.
Then, NaACHTUNGTRNEUNG
[BArCl4] (48.8 mg, 92 mmol) was added and the reaction mixture
was stirred for 15 min at RT. After filtering and removing of all volatiles
in vacuo the crude product was washed with toluene (5 mL) and hexanes
(5 mL) to yield 19 as a yellow solid (55.9 mg, 35 mmol, 38%). 1H NMR
(400.1 MHz, CD2Cl2): d=8.46 (s, 2H, o-H), 8.19 (s, 1H, p-H), 7.06–7.00
(m, 12H, BArCl4), 2.24–1.15 ppm (m, 66H, Cy); 11B{1H} NMR
(128.4 MHz, CD2Cl2): d=ꢀ7.0 ppm (s, 1JB–C =49 Hz); 13C{1H} NMR
(100.6 MHz, CD2Cl2): d=165.1 (q, 1JC–B =49 Hz, BArCl4), 135.9 (m,
o-F), ꢀ149.6 (m, p-F), ꢀ162.9 ppm (m, m-F); 31P{1H} NMR (162.0 MHz,
1
C6D6): d=0.3 (d, 2JP–P =23 Hz, 1JP–Pt =2441 Hz), ꢀ2.0 ppm (brm, JP–Pt
=
2021 Hz).
Synthesis of [(Et3P)3Pt(C6F4-2-BF3)] (15): In a J. Young NMR tube, one
equivalent PEt3 was removed in vacuo at 608C from the complex [Pt-
ACHTUNGTRENNUNG(PEt3)4] (30.0 mg, 45 mmol). The resulting complex [PtAHCTUNGTREN(NUGN PEt3)3] (12,
24.7 mg, 45 mmol) was then dissolved in C6D6 (0.1 mL) and a solution of
BF2Pf (9, 0.50 mL, 0.09m in toluene, 45 mmol) was added. After 6 h at RT
colorless crystals started to grow in the NMR tube. After 18 h at RT the
solvent was decanted off and the residue was washed with hexanes
(1 mL) to yield 15 as a colorless, microcrystalline solid (13.0 mg, 17 mmol,
37%). Crystals suitable for X-ray diffraction were obtained by layering a
solution of 15 in dichloromethane with hexanes at RT. 1H NMR
2
3
BArF), 133.5 (q, JC–B =2 Hz, BArCl4), 133.3 (q, JC–B =4 Hz, BArCl4), 132.4
(q, 2JC–F =34 Hz, BArF), 127.4 (m, BArF), 123.4 (s), 123.3 (q, JC–F
=
1
273 Hz, CF3), 35.4 (vt, N=1JC–P +3JC–P =27 Hz, C1 Cy), 30.6 (s, C3,5 Cy),
27.4 (vt, N=2JC–P +4JC–P =12 Hz, C2,6 Cy), 26.1 ppm (s, C4 Cy); 19F{1H}
2
NMR (376.5 MHz, CD2Cl2): d=ꢀ20.5 (brs, FWHMꢁ70 Hz, JF–Pt
=
637 Hz, BFArF), ꢀ63.3 ppm (s, CF3); 31P{1H} NMR (162.0 MHz, CD2Cl2):
d=48.5 (d, 2JP–F =9 Hz, 1JP–Pt =2631 Hz); elemental analysis calcd (%)
for C68H81B2Cl8F7P2Pt·C6H6 (Mw = 1671.772): C 53.17, H 5.25; found: C
52.76, H 5.21.
(400.1 MHz, CD2Cl2): d=2.02–1.90 (m, 6H, P
12H, P(CH2CH3)3), 1.27–1.16 (m, 9H, P(CH2CH3)3), 1.11–0.99 ppm (m,
18H,
ACHTNUGTRENN(UGN CH2CH3)3), 1.80–1.52 (m,
A
ACHTUNGTRENNUNG
PACHTUNGTRENNUNG
(CH2CH3)3); 11B{1H} NMR (128.4 MHz, CD2Cl2): d=2.8 ppm
Synthesis of BF2OtBu (21): trans-[(Cy3P)2PtACHTNUGTRNEUNG(BF2)Cl] (20, 10.0 mg,
12 mmol) and KOtBu (1.3 mg, 12 mmol) were dissolved in C6D6 (0.6 mL)
in a J. Young NMR tube. After 5 days at RT the conversion to [Pt-
(brs, FWHMꢁ130 Hz); 13C{1H} NMR (100.6 MHz, CD2Cl2): d=17.4 (dt,
1JC–P =28 Hz, 3JC–P =4 Hz,
(CH2CH3)3), 16.9 (vtd, N=1JC–P +3JC–P
PACHTUNGRTNEGNU =
34 Hz, 3JC–P =2 Hz,
PACHTUNGTRENNUNG PACHTUNGTREN(NUGN CH2CH3)3),
(CH2CH3)3), 8.2 (d, 2JC–P =2 Hz,
AHCTUNTGREGUN(NN PCy3)2] (5), KCl and 21 was complete as determined by the absent reso-
(CH2CH3)3); 19F{1H} NMR (376.5 MHz, CD2Cl2): d=
nances of the starting materials. 1H NMR (400.1 MHz, C6D6): d=
1.39 ppm (s); 11B{1H} NMR (128.4 MHz, C6D6): d=16.1 ppm (brs,
FWHMꢁ180 Hz); 13C{1H} NMR (100.6 MHz, C6D6): d=72.4 (s, C-
8.1 ppm (bs, PACHTUNGTRENNUNG
ꢀ112.9 (m, 3JF–Pt =386 Hz, o-F), ꢀ134.1 (m, p-F), ꢀ134.8 (brs, FWHM
ꢁ140 Hz, BF3), ꢀ162.8 (m, m-F); ꢀ164.9 ppm (dd, 1JF–F =24 Hz, JF–F
=
=
1
24 Hz, m-F); 31P{1H} NMR (162.0 MHz, CD2Cl2): d=ꢀ0.6 (d, JP–P
2
A
(CH3)3); 19F{1H} NMR (376.5 MHz, C6D6): d=
ACHTUNGTRENNUNG
24 Hz, 1JP–Pt =2633 Hz,), ꢀ1.4 ppm (tdd, 2JP–P =24 Hz, 3JP–F =10 Hz, JP–
F =4 Hz, 1JP–Pt =1984 Hz,); 195Pt{1H} NMR (106.9 MHz, CD2Cl2): d=
ꢀ4757 ppm (tdd, 1JPt–P =2633 Hz, 1JPt–P =1984 Hz, 3JPt–F =386 Hz); ele-
mental analysis calcd (%) for C24H45BF7P3Pt (Mw = 765.430): C 37.66, H
5.93; found: C 38.08, H 6.02.
4
C
ACHTUNGTRENNUNG
pended in toluene (10 mL) and dcpp (1.0 mL of a 0.5m solution in ben-
zene, 500 mmol) was added. After stirring for 30 min at RT all volatiles
were removed in vacuo and the brownish residue was washed with pen-
tane (2ꢃ10 mL) to yield 25 as a colorless solid (0.334 g, 475 mmol, 95%).
1H NMR (400.1 MHz, CDCl3): d=2.48–1.04 ppm (m, 50H); 31P{1H}
NMR (162.0 MHz, CDCl3): d=8.1 ppm (s, 1JP–Pt =3458 Hz).
Synthesis of BF2ArF (16): Me3SnArF (17, 500 mg, 1.33 mmol) was dis-
solved in hexanes (5 mL) in a Schlenk flask equipped with a Teflon valve
and the Argon atmosphere was exchanged for an atmosphere of BF3.
After stirring at 608C for 18 h all volatiles were transferred and the spare
BF3 was removed by degassing of the yielded colorless solution. The
yield of 16 was determined by 1H and 19F{1H} NMR spectroscopy by
adding norbornene (4.7 mg, 50 mmol) and BPf3 (8, 5.1 mg, 10 mmol), re-
spectively, to a portion of the obtained solution of 16 (0.1 mL). The ratio
hereby was 1 (16) to 2.2 (norbornene) in the 1H NMR spectrum, or 2.3
(16) to 1 (8) in the 19F{1H} NMR spectrum, resulting in an overall yield
of 86% (0.299 g, 1.14 mmol). 1H NMR (400.1 MHz, C6D6): d=7.76 (s,
1H, p-H), 7.73 ppm (s, 2H, o-H); 11B{1H} NMR (128.4 MHz, C6D6): d=
23.5 ppm (brs, FWHMꢁ190 Hz); 13C{1H} NMR (100.6 MHz, C6D6): d=
Synthesis of [(dcpp)PtACHTUNRGTNE(UNG C2H4)] (24): [(dcpp)PtCl2] (25, 0.120 g, 171 mmol)
was suspended in THF (5 mL) and the argon atmosphere was exchanged
with an ethene atmosphere followed by slow addition of a sodium naph-
thalide solution (0.33m in THF, 1.04 mL, 0.34 mmol). After stirring for
10 min at RT all volatiles were removed in vacuo, the off-white residue
was extracted with dichloromethane (10 mL) and filtered. After again re-
moving all volatiles in vacuo the residue was washed with pentane (2ꢃ
1
5 mL) to yield 24 as a colorless solid (98.3 mg, 149 mmol, 87%). H NMR
3
2
(400.1 MHz, C6D6): d=2.33–0.91 (m, 50H), 2.25 ppm (d, JH–P =3 Hz, JH–
1
Pt =57 Hz, 4H); 31P{1H} NMR (162.0 MHz, C6D6): d=25.7 ppm (s, JP–Pt
=
2
3
135.7 (m), 131.7 (q, JC–F =34 Hz), 127.0 (sept, JC–F =4 Hz), 123.5 ppm (q,
1JC–F =272 Hz, CF3); 19F{1H} NMR (376.5 MHz, C6D6): d=ꢀ63.0 (s, CF3),
ꢀ87.8 ppm (brs, FWHMꢁ110 Hz, BF2).
3270 Hz).
Synthesis of [(dcpp)Pt(CH2CH2BPf3)] (26): In a J. Young NMR tube
[(dcpp)Pt(C2H4)] (24, 19.8 mg, 30 mmol) was suspended in C6D6 (0.6 mL)
AHCTUNGTRENNUNG
Synthesis of trans-[(Cy3P)2Pt!BF2ArF] (18): In a J. Young NMR tube,
and BPf3 (8, 15.4 mg, 30 mmol) was added, thus providing a pale yellow
solution. After removing all volatiles in vacuo and washing the residue
with hexanes (1 mL), 26 was obtained as a colorless solid (28.6 mg,
25 mmol, 83%). Crystals suitable for X-ray diffraction could be gained by
layering a solution of 26 in benzene with hexanes at RT. 1H NMR
(400.1 MHz, CD2Cl2): d=2.08–1.58 (m, 30H), 1.40–1.00 (m, 20H),
ꢀ0.05 ppm (vbr d, FWHMꢁ20 Hz, 2H, 2JH–P =31 Hz, 1JH–Pt =66 Hz),
11B{1H} NMR (128.4 MHz, CD2Cl2): d=ꢀ13.5 ppm (s, FWHMꢁ20 Hz);
13C{1H} NMR (100.6 MHz, CD2Cl2): d=148.7 (dm, 1JC–F =246 Hz), 138.9
(dm, 1JC–F =248 Hz), 137.1 (dm, 1JC–F =251 Hz), 37.8–18.7 ppm (dcpp and
[PtACHTUNGTRENNUNG(PCy3)2] (5, 34.7 mg, 46 mmol) was dissolved in C6D6 (0.4 mL) and a
solution of BF2ArF (16, 0.20 mL, 0.23m in hexanes, 46 mmol) was added.
1H NMR (400.1 MHz, C6D6, 300 K): d=8.54 (s, 2H, o-H), 7.85 (s, 1H, p-
H), 2.27–1.29 ppm (m, 66H, Cy); 11B{1H} NMR (160.5 MHz, C7D8,
300 K): d=11.5 ppm (vbrs, FWHMꢁ260 Hz); 19F{1H} NMR (376.5 MHz,
C6D6, 300 K): d=ꢀ62.7 (s, CF3), ꢀ167.0 ppm (vbrs, FWHMꢁ300 Hz,
BF2ArF); 31P{1H} NMR (202.5 MHz, C7D8, 300 K): d=58 (brs, FWHM
ꢁ60 Hz, 1JP–Pt =4080 Hz); 31P{1H} NMR (202.5 MHz, C7D8, 193 K): d=
3
1
49.7 ppm (t, JP–F =19 Hz, JP–Pt =3790 Hz).
Ratio of 5/16 of 1:2: 11B{1H} NMR (128.4 MHz, C6D6): d=16 ppm (vbrs,
FWHMꢁ490 Hz); 19F{1H} NMR (376.5 MHz, C6D6): d=ꢀ62.6 (s, CF3),
ꢀ101 ppm (vbrs, FWHMꢁ1600 Hz, BF2ArF); 31P{1H} NMR (162.0 MHz,
C6D6): d=53 ppm (vbrs, 1JP–Pt =3770 Hz).
C2H4); 19F{1H} NMR (376.5 MHz, CD2Cl2): d=ꢀ131.0 (d, 1JF–F =23 Hz,
1
o-F), ꢀ162.0 (t, 1JF–F =20 Hz, 1JF–F =23 Hz, p-F), ꢀ166.3 ppm (dd, JF–F
=
23 Hz, 1JF–F =20 Hz, m-F); 31P{1H} NMR (162.0 MHz, CD2Cl2): d=26.5
(dq, 2JP–P =7 Hz, 3JP–B =7 Hz, 1JP–Pt =4755 Hz), 16.8 ppm (d, 2JP–P =7 Hz,
Ratio of 5/16 of 1:10: 11B{1H} NMR (128.4 MHz, C6D6): d=18 ppm (vbrs,
1JP–Pt =2738 Hz); elemental analysis calcd (%) for C47H54BF15P2Pt·1=
2
FWHMꢁ680 Hz); 19F{1H} NMR (376.5 MHz, C6D6): d=ꢀ46 (vbrs,
C6H6 (Mw = 1210.824): C 49.60, H 4.74; found: C 49.92, H 4.85.
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Lewis Basic Platinum Complexes
FULL PAPER
Crystal structure determination: The crystal data of 15 and 26 were col-
lected on a Bruker x8apex diffractometer with a CCD area detector and
multi-layer mirror monochromated MoKa radiation. The structure was
solved using direct methods, refined with the Shelx software package[51]
and expanded using Fourier techniques. All non-hydrogen atoms were re-
fined anisotropically. Hydrogen atoms were included in structure factors
calculations. All hydrogen atoms were assigned to idealized geometric
positions, except the hydrogen atoms of the ethene ligand in 26, which
also were refined.
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Crystal data for 15: C24H45BF7P3Pt, Mr =765.41, colorless block, 0.610ꢃ
0.427ꢃ0.172 mm3, orthorhombic space group P212121, a=9.8891(4), b=
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c=18.3510(6) ꢄ,
V=2985.30(19) ꢄ3,
Z=4,
1calcd =
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Crystal data for 26: C109H123B2F30P4Pt2, Mr =2538.75, colorless block,
0.34ꢃ0.32ꢃ0.24 mm3, tetragonal space group I4, a=30.581(8), b=
¯
30.581(8), c=11.352(3) ꢄ, a=90.00, b=90.00, g=90.008, V=
10617(5) ꢄ3, Z=4, 1calcd =1.588 gcmꢀ3 m=2.793 mmꢀ1
, , FACHTUGNTRENN(UGN 000)=5092,
T=100(2) K, R1 =0.0267, wR2 =0.0496, 10792 independent reflections
[2qꢂ52.688] and 679 parameters.
CCDC929469 (15) and 929470 (26) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
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Received: March 19, 2013
Published online: && &&, 0000
Chem. Eur. J. 2013, 00, 0 – 0
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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H. Braunschweig et al.
Still elusive: Several attempts to yield
the elusive, unsupported Lewis adduct
between a Lewis basic transition-metal
complex and a Lewis acidic borane are
presented, including NMR spectro-
scopic characterization at low tempera-
tures, isolation of secondary products
and detailed DFT calculations (see
figure).
Acid–Base Interactions
J. Bauer, H. Braunschweig,*
R. D. Dewhurst, K. Radacki &&&& — &&&&
Reactivity of Lewis Basic Platinum
Complexes Towards Fluoroboranes
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ÝÝ
These are not the final page numbers!