Reactions of (Diphenylphosphinomethyl)zirconocene chloride with B(C 6F5)3: Competition between P/B and P/Zr + frustrated lewis pair reactions

Article abstract of DOI:10.1021/om400769y

The title complex Cp₂ZrCl(CH₂PPh₂) reacts with B(C₆F₅)₃ under specific conditions by phosphinomethyl transfer to give the phosphane-stabilized salt [Cp ₂ZrCl⁺][Ph₂PCH₂B(C₆F ₅)₃^-]. X-ray crystal structure analysis showed the P-Zr coordination. This salt is trapped by phenyl isocyanate in an in situ three-component reaction to yield the respective P/Zr⁺ frustrated Lewis pair (FLP) addition product. In contrast, a mixture of Cp ₂ZrCl(CH₂PPh₂)/B(C₆F ₅)₃ and benzaldehyde under similar conditions gives the P/B FLP addition product. The Cp₂ZrCl(CH₂PPh ₂)/B(C₆F₅)₃ system may form a P/B adduct [Cp₂ZrCl(CH₂PPh₂)·B(C ₆F₅)₃] or a P/Zr⁺ adduct [Cp ₂ZrCl·PPh₂CH₂B(C₆F ₅)₃]. From the former it seems to show P/B FLP reaction and from the latter P/Zr⁺ FLP behavior; the outcome is dependent on the specific reagent and reaction conditions chosen.

Full text of DOI:10.1021/om400769y

Article
pubs.acs.org/Organometallics
Reactions of (Diphenylphosphinomethyl)zirconocene Chloride with
B(C6F5)3: Competition between P/B and P/Zr+ Frustrated Lewis Pair
Reactions
Xin Xu, Gerald Kehr, Constantin G. Daniliuc,† and Gerhard Erker*
Organisch-Chemisches Institut, Universitat Munster, Corrensstrasse 40, D-48149 Munster, Germany
̈
̈
̈
S
* Supporting Information
ABSTRACT: The title complex Cp2ZrCl(CH2PPh2) reacts
with B(C6F5)3 under specific conditions by phosphinomethyl
transfer to give the phosphane-stabilized salt [Cp2ZrCl+]-
−
[Ph2PCH2B(C6F5)3 ]. X-ray crystal structure analysis showed
the P−Zr coordination. This salt is trapped by phenyl
isocyanate in an in situ three-component reaction to yield the respective P/Zr+ frustrated Lewis pair (FLP) addition product.
In contrast, a mixture of Cp2ZrCl(CH2PPh2)/B(C6F5)3 and benzaldehyde under similar conditions gives the P/B FLP addition
product. The Cp2ZrCl(CH2PPh2)/B(C6F5)3 system may form a P/B adduct [Cp2ZrCl(CH2PPh2)·B(C6F5)3] or a P/Zr+ adduct
[Cp2ZrCl·PPh2CH2B(C6F5)3]. From the former it seems to show P/B FLP reaction and from the latter P/Zr+ FLP behavior; the
outcome is dependent on the specific reagent and reaction conditions chosen.
phosphonium borate product 3 (Scheme 2). We obtained
single crystals that allowed us to identify and characterize
INTRODUCTION
■
Frustrated Lewis pair (FLP) chemistry has seen the develop-
ment of a great variety of main-group element systems for
small-molecule binding and activation.1 Metal-free heterolytic
dihydrogen splitting2 by P/B or N/B systems (and a few
others)3 is a prominent example that has led to the
development of FLP-catalyzed hydrogenation reactions of a
variety of organic substrates.4,5 Whereas most FLP systems
contain Lewis acid/Lewis base components based on main-
group elements, there has been a beginning development of
using transition-metal-based Lewis acid components, most
notably zirconocene-derived cations.6,7 We here wish to
describe first experiments that we have carried out in this
direction using N. Shore’s (diphenylphosphinomethyl)-
zirconocene chloride complex 18 in conjunction with B(C6F5)3.
This results in the interesting situation that 1 may just serve as
a phosphane Lewis base (having a bulky organometallic
substituent) to form a conventional P/B FLP with the
tris(pentafluorophenyl)borane Lewis acid or undergo abstrac-
tion of the Ph2P−CH2− anion equivalent by the borane to then
give a P/Zr+ FLP (see Scheme 1). We shall see which pathway
will be followed in this system.
Scheme 2. Formation and Reactions of the P/Zr+ FLP 2
compound 3 by X-ray diffraction (Figure 1). The analysis
revealed that under these conditions the Ph2PCH2 group was
transferred from the zirconocene to the borane, followed by
trapping of the alleged product 2 by the CH2Cl2 solvent
(Scheme 2).7 Chloride abstraction by the cation gave
zirconocene dichloride. The remaining ClCH2 group was
found bonded to the phosphorus atom of the respective Ph2P−
CH2−B(C6F5)3 anion. In the product 3 the boron and
phosphorus atoms are bridged by a methylene group [B1−
C1 1.673(5) Å, P1−C1 1.789(3) Å] and the phosphonium
center bears the CH2Cl group [P1−C2 1.811(4) Å, C2−Cl1
1.773(4) Å]. The central core of compound 3 shows a gauche
conformation [B1−C1−P1−C2 −52.8(3)°].
RESULTS AND DISCUSSION
■
FLP Trapping Reactions. We treated compound 1 with
B(C6F5)3 in dichloromethane solution for 3 days at ambient
temperature. Workup then gave a mixture of Cp2ZrCl2 and the
Scheme 1. Synthesis of Compound 1
Received: August 1, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om400769y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 2. Molecular structure of compound 4 (thermal ellipsoids are
shown with 30% probability).
Figure 1. Molecular structure of the phosphonium borate zwitterion 3
(thermal ellipsoids are shown with 30% probability).
type to be favored when we treated the Cp2ZrCl(CH2PPh2)/
B(C6F5)3 mixture with benzaldehyde under similar reaction
conditions.10 Treatment of 1 with B(C6F5)3 and PhCHO in a
1:1:1 ratio for 2 days in CH2Cl2/pentane gave product 6
(Scheme 3), which was isolated as a white crystalline solid in ca.
75% yield.
In solution we monitored the heteronuclear magnetic
resonance signals of compound 3 [11B: δ −15.7; 31P: δ
+34.3; 19F: δ −131.9 (o), −160.5 (p), −164.9 (m)]. We
1
observed the H/13C NMR signals of a pair of methylene
groups. The [P]−CH2−[B] group gives rise to an overlapping
1
equal-intensity H NMR doublet of 1:1:1:1 quartets at δ 3.05
(2JPH = 16.9 Hz, 2JBH = 5.6 Hz; 13C NMR resonance at δ 15.4).
The [P]−CH2Cl moiety gives rise to a 13C NMR signal at δ
31.9 (d, 1JPC = 52.7 Hz) and a corresponding 1H NMR signal at
δ 4.36 (2JPH = 5.0 Hz).
Scheme 3. Formation of the P/B FLP 5 and Trapping of 5 to
Give 6
We were able to trap the P/Zr+ FLP 2 by a typical frustrated
pair 1,2-addition reaction to the carbonyl group of phenyl
isocyanate.9 Treatment of an equimolar mixture of 1, B(C6F5)3,
and OCNPh in dichloromethane/pentane gave the
addition product 4 (Scheme 2) as a colorless crystalline
precipitate that was isolated in >70% yield. In dichloromethane
X-ray crystal structure analysis of 6 (Figure 3) revealed that
the phosphane of the intact Cp2ZrCl(CH2PPh2) moiety added
1
solution 4 shows a single sharp Cp H NMR signal of the
[Cp2Zr] unit (δ 5.86, 10H; the corresponding 13C NMR
1
resonance is at δ 116.1) and the typical [P]−CH2−[B] H
2
NMR signal at δ 3.08 (1H, doublet of 1:1:1:1 quartets, JPH
=
18.4 Hz, JBH = 6.2 Hz; the corresponding 13C, 11B, and 31P
NMR signals are at δ 11.0, −15.8, and +23.9, respectively). The
13C NMR signal of the O−CN carbon was located at δ 157.6
(1JPC = 144.7 Hz).
2
Product 4 was also characterized by X-ray diffraction (Figure
2), which confirmed that P/Zr+ FLP 2 underwent 1,2-addition
to the carbonyl group. The zirconium atom added to the
carbonyl oxygen atom of the isocyanate reagent [bond lengths
Zr1−O1 2.042(2) Å, O1−C1 1.307(4) Å; angles Zr1−O1−C1
152.8(2)°, O1−Zr1−Cl1 95.7(1)°]. Carbon atom C1 is sp2-
hybridized and shows bond angles of N1−C1−O1 130.3(3)°,
N1−C1−P1 116.6(3)°, and O1−C1−P1 112.9(2)°. The C1−
N1 bond [1.273(4) Å] is in the typical CN double-bond
range. The phosphane added to C1 [P1−C1 1.852(3) Å]. The
phosphorus atom also has the CH2−B(C6F5)3 unit bonded to it
[bond lengths P1−C2 1.793(3) Å, C2−B1 1.666(5) Å; angle
P1−C2−B1 123.9(2)°], which makes product 4 overall neutral.
These results indicate that we generated the P/Zr+ FLP 2
upon treatment of 1 with B(C6F5)3. P/Zr+ FLP 2 was
subsequently scavenged by, for example, phenyl isocyanate to
yield product 4. However, this seems not to be the only
pathway that can be observed. We found a different reaction
Figure 3. A view of the molecular structure of complex 6 (thermal
ellipsoids are shown with 30% probability).
to the benzaldehyde carbonyl carbon atom [bond lengths P1−
C2 1.859(2) Å, C2−O1 1.399(3) Å; angle P1−C2−O1
104.7(1)°] and the B(C6F5)3 Lewis acid added to the carbonyl
oxygen atom [bond length O1−B1 1.484(3) Å; angle C2−O1−
B1 122.3(2)°; P1−C2−O1−B1 dihedral angle −154.7(2)].
B
dx.doi.org/10.1021/om400769y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
The Cp2ZrCl(CH2PPh2) unit in 6 shows the following bonding
parameters: bond lengths Zr1−Cl1 2.426(1) Å, Zr1−C1
2.357(2) Å, C1−P1 1.774(2) Å; angles Cl1−Zr1−C1
98.0(1)°, Zr1−C1−P1 129.3(1)°. It should be noted that
Shore’s complex 18 shows similar data (e.g., Zr−Cl 2.45 Å, Zr−
CH2 2.28 Å, Cl−Zr−CH2 90.4°, Zr−C−P 130.1°).
Complex 6 shows a 31P NMR resonance at δ 37.3 and a 11B
NMR signal at δ −2.2. The hydrogen atoms of the [Zr]−CH2−
[P] methylene group are diastereotopic. Their 1H NMR signals
occur at δ 1.64 (2JPH = 21.3 Hz) and 1.39 (2JPH = 18.8 Hz, 2JHH
= 13.0 Hz). The corresponding 13C NMR resonance is at δ
10.8 (1JPC = 30.5 Hz). The former aldehyde carbonyl carbon
atom gives rise to a 13C NMR signal at δ 78.1 (1JPC = 68.7 Hz).
The corresponding 1H NMR resonance occurs at δ 5.55 (2JPH
=
5.5 Hz).
We also treated the P/B FLP 5 with phenyl isocyanate.
However, in this case we observed the addition product 4
derived from the rearranged P/Zr+ FLP 2 (for details, see the
Supporting Information).
Figure 4. A projection of the molecular structure of complex 7
(thermal ellipsoids are shown with 30% probability).
Identification and Characterization of the P/B and P/
Zr+ FLP Isomers. It looks as if there are two different
frustrated Lewis pairs operative in the Cp2ZrCl(CH2PPh2)/
B(C6F5)3 system, namely, the P/B system [5 ⇄ 1 + B(C6F5)3]
and the P/Zr+ system 2 (see Schemes 2 to 4). Possibly, these
zirconium complex 1 was mixed with B(C6F5)3 in CD2Cl2
solution in a 1:1 molar ratio. The NMR spectra were measured
after ca. 30 min reaction time at r.t. Adduct 5 shows 31P and 11
B
heteronuclear magnetic resonance signals at δ 31.5 (1: −2.2)
and δ −8.4. The 19F NMR resonances of 5 are as expected for
tetracoordinate boron. The [Zr]−CH2−[P] methylene 1H
Scheme 4. Formation of the P/B Lewis pair 7
2
NMR resonance of 5 was located at δ 1.24. It features a JPH
coupling constant of 14.3 Hz. The 13C NMR CH2 resonance of
5 is at δ 25.3 (1JPC ≈ 24 Hz). The corresponding NMR data of
the starting material (i.e., Shore’s complex 1) are quite different,
namely, δ1H 1.71 (2JPH = 3.2 Hz), δ13C 46.5 (1JPC= 43.5 Hz).
The 1H/13C NMR Cp signals of 1 are at δ 6.19/113.8, and the
corresponding signals of adduct 5 were monitored at δ 6.02/
114.6 (all data were measured in CD2Cl2 solution).
interconverte under the specific conditions that we applied in
our trapping experiments. In order to get some more direct
information about the species involved, we reacted 1 with
electrophilic boranes under various reaction conditions.
We tried but could not get crystals of the phosphane/
B(C6F5)3 adduct 5. However, a related P/B adduct, 7, was
obtained as colorless crystals (ca. 71% isolated yield) from the
reaction mixture of 1 with Piers’ borane [HB(C6F5)2]11 in
CH2Cl2/pentane after several days at room temperature
(Scheme 4).
We were eventually able to isolate the new P/Zr+ FLP 2 by
adjusting the reaction conditions. The reaction between 1 and
B(C6F5)3 (1:1) was carried out in C6D6 for 4 days at r.t. Then
the solution was covered with pentane, and the resulting
product 2 slowly crystallized. It was isolated from the reaction
mixture as a white crystalline solid in ca. 49% yield.
1
In bromobenzene solution, the P/Zr+ FLP 2 shows a H
NMR Cp resonance at δ 5.98 that features a coupling constant
of JPH = 1.2 Hz. The [P]−CH2−[B] 1H NMR signal occurs at δ
2.93 (broad; the corresponding 13C NMR resonance is at δ
21.9). Compound 2 shows a 31P NMR signal at δ 32.8 and a
11B NMR resonance at δ −13.5.
In the crystal structure of compound 7 (Figure 4), we found
that the HB(C6F5)2 unit is bonded to the phosphane of the
Cp2ZrCl(CH2PPh2) unit [bond lengths P1−B1 1.972(4) Å,
C1−P1 1.789(3) Å; angle C1−P1−B1 109.2(2)°]. The
remaining bonding parameters of the metallocene unit are as
follows: C1−Zr1 2.365(3) Å, Zr1−Cl1 2.423(1) Å, C1−Zr1−
Cl1 104.9(1)°. Both the phosphorus and boron atoms show
pseudotetrahedral coordination geometries (∑P1CCC = 318.7°,
∑B1PCC = 339.9°). The complex shows a conformation in the
solid state that is characterized by Cl1−Zr1−C1−P1 and Zr1−
C1−P1−B1 dihedral angles of −21.7(2)° and 64.0(2)°,
respectively.
Single crystals of the P/Zr+ FLP 2 were obtained from a two-
layer toluene/cyclopentane mixture. The X-ray crystal structure
analysis of 2 (Figure 5) confirmed the abstraction of the
−CH2PPh2 σ ligand from zirconium by the B(C6F5)3 Lewis
acid. The remaining Cp2ZrCl+ cation has the resulting Ph2P−
−
CH2−B(C6F5)3 borate anion coordinated to the metal center
via the phosphane donor [bond lengths P1−Zr1 2.783(1) Å,
Zr1−Cl1 2.405(1) Å; angle P1−Zr1−Cl1 90.3(1)°]. The new
ligand has the following characteristic bonding features: bond
lengths P1−C1 1.831(3) Å, C1−B1 1.671(5) Å; angle P1−
C1−B1 130.6(2)°. Complex 2 features a conformation that is
characterized by Cl1−Zr1−P1−C1 and Zr1−P1−C1−B1
dihedral angles of 49.5(1)° and −179.8(3)°, respectively.
The in situ generated P/Zr+ FLP 2 was reacted with phenyl
isocyanate to give the 1,2-P/Zr+ adduct 4. Compound 2 was
also treated with benzaldehyde. This gave a major product
different from 6 (Scheme 3). We assume that it was probably
The 1/HB(C6F5)2 adduct 7 is characterized by a 31P NMR
signal at δ 18.4 and an 11B NMR resonance at δ −23.6. It
features 1JPB ≈ 1JBH coupling constants of ca. 77 Hz. The [B]H
1
resonance was located in the H NMR spectrum as a broad
1
signal at δ 4.08. The [Zr]−CH2−[P] H NMR resonance of 7
was found at δ 1.58 (2JPH = 16.0 Hz); the corresponding 13C
resonance is at δ 27.6 (1JPC = 22.6 Hz).
We generated the Cp2ZrCl(CH2PPh2)·B(C6F5)3 adduct 5 in
situ and characterized it by NMR spectroscopy.12 The
C
dx.doi.org/10.1021/om400769y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
MHz (Agilent), DD2 600 MHz (Agilent), Bruker AV400, and Bruker
DPX300 spectrometers. Chemical shifts are given in parts per million
relative to solvents [1H and 13C, δ(SiMe4) = 0] or an external standard
[δ(BF3·OEt2) = 0 for 11B NMR, δ(CFCl3) = 0 for 19F NMR].
Elemental analysis data were recorded on a Foss-Heraeus CHNO-
Rapid analyzer. For X-ray crystal structure analysis, data sets were
collected with a Nonius KappaCCD diffractometer. The following
programs were used: data collection, COLLECT;18 data reduction,
Denzo-SMN;19 absorption correction, Denzo;20 structure solution,
SHELXS-97;21 structure refinement, SHELXL-97;22 and graphics,
XP.23 Thermal ellipsoids are shown with 30% probability; R values are
given for observed reflections, and wR2 values are given for all
reflections. Exceptions and special features: For compounds 2 and 6,
one unidentified disordered solvent molecule was found in the
asymmetric unit. The program SQUEEZE24 was therefore used to
remove mathematically the effect of the disordered unidentified
solvent molecule. A cyclopentane group disordered over two positions
was found in the asymmetric unit of compound 4. Several restraints
(SAME, SIMU, and SADI) were used in order to improve the
refinement stability. In compound 7, the hydrogen on the B1 atom was
refined freely. For details of the X-ray crystal structure analyses, see the
Supporting Information.
Figure 5. Molecular structure of complex 2 (thermal ellipsoids are
shown with 30% probability).
Preparation of Complex 2. Complex 1 (18.2 mg, 40 μmol) and
B(C6F5)3 (20.5 mg, 40 μmol) were mixed in C6D6 (1 mL). After 4
days of standing at room temperature, the reaction mixture was
covered with pentane (3 mL). Complex 2 was obtained as a white
crystalline solid (18.8 mg, 49% yield). Crystals suitable for single-
crystal X-ray structure analysis were obtained from a two-layer
procedure using a toluene solution of 2 and cyclopentane at room
temperature. Anal. Calcd for C41H22BClF15PZr·C5H12: C, 53.11; H,
3.29. Found: C, 52.74; H, 2.75. 1H NMR (500 MHz, C6D5Br, 299 K):
δ 7.17 (m, 1H, p-Ph), 7.15 (m, 2H, o-Ph)*, 7.12 (m, 2H, m-Ph)*, 5.98
(d, 3JPH = 1.2 Hz, 5H, Cp), 2.93 (br, 1H, CH2P) [resonances marked
with * are from the ghsqc experiment]. 13C{1H} NMR (126 MHz): δ
formed by 1,2-carbonyl addition of the P/Zr+ FLP; however,
we could not isolate it in a pure form (for details, see the
Supporting Information).
CONCLUSIONS
Dimethylzirconocenes react with B(C6F5)3 by rapid methyl
■
+
anion equivalent abstraction to yield the salt [Cp2ZrCH3 ]
−
[H3CB(C6F5)3 ], usually isolated as a tight ion pair or in
ligand-stabilized form.13,14 Variants of this reaction have been
of great importance in homogeneous Ziegler−Natta olefin
polymerization catalysis.15 Alkyl anion abstraction from an
alkylzirconocene halide is much more difficult because the
resulting cation would be much less stabilized.16 In our case,
phosphane coordination is probably a decisive factor to see the
Ph2PCH2− transfer reaction from zirconocene to borane
proceed at all in the competition with simple phosphane/
borane coordination of the starting material.
1
1
148.2 (dm, JFC ≈ 241 Hz, C6F5), 138.5 (dm, JFC ≈ 245 Hz, C6F5),
1
2
136.5 (dm, JFC ≈ 250 Hz, C6F5), 133.3 (d, JPC = 10.3 Hz, o-Ph),
130.8 (p-Ph)*, 128.7 (d, 1JPC = 39.3 Hz, i-Ph)t, 128.4 (d, 3JPC = 9.9 Hz,
m-Ph), n.o. (i-C6F5), 115.6 (Cp), 21.9 (br, CH2P)t, [t tentatively
assigned, * from the ghsqc experiment]. 31P{1H} NMR (202 MHz): δ
32.8 (m). 19F NMR (470 MHz): δ −130.0 (br, 2F, o-C6F5), −160.5 (t,
3JFF = 19.9 Hz, 1F, p-C6F5), −164.0 (br m, 2F, m-C6F5), [Δδ19Fmp
3.5]. 11B{1H} NMR (160 MHz): δ −13.5 (ν1/2 ≈ 30 Hz).
=
Preparation of Compound 3 (Activation of CH2Cl2). Complex
1 (73.0 mg, 160 μmol) and B(C6F5)3 (82.0 mg, 160 μmol) were mixed
in CH2Cl2 (2 mL). After the reaction mixture was stored at room
temperature for 3 days, pentane (3 mL) was added to cover the
reaction mixture. A white crystalline solid (105.0 mg) was obtained
within 2 days. It was collected and analyzed as a mixture of Cp2ZrCl2
and complex 3 [61:39 (1H)]. Several crystals were suitable for the
single-crystal X-ray structure analysis of compound 3.
Under the various reaction conditions utilized in this study,
we therefore have a competing situation between the formation
of the adduct 5 and the product 2. Both probably represent the
FLP resting stages of the respective active (i.e., dissociated)
forms17 of the P/B and P/Zr+ systems. The transfer product 2
cleanly reacts in an FLP manner, giving for example the phenyl
isocyanate addition product. The P/B form can, however,
apparently be chemically addressed under very similar reaction
conditions. The respective product of P/B 1,2-addition to
benzaldehyde is an example. It is likely that the systems 2 and 5
(and their respective dissociated forms) interconverte (maybe
slowly) under the here-applied typical reaction conditions. It
will require a much more detailed study to unveil these rather
complicated equilibrating processes and to learn how they can
be controlled a priori, but the outcome of the here-described
reaction teaches us that metal-free and metal-containing FLPs
in a system like the one described here, where such a choice
exists, can actively compete for added substrates. This is an
interesting new facet of frustrated Lewis pair chemistry.
Data for Cp2ZrCl2: 1H NMR (500 MHz, CD2Cl2, 299 K): δ 6.49 (s,
Cp). 13C{1H} NMR (126 MHz): δ 116.5 (Cp).
1
Data for complex 3: H NMR (500 MHz, CD2Cl2, 299 K): δ 7.75
(m, 1H, p-Ph), 7.58 (m, 2H, m-Ph), 7.50 (m, 2H, o-Ph), 4.36 (d, 2JPH
2
2
= 5.0 Hz, 1H, ClCH2), 3.05 (dq (1:1:1:1), JPH = 16.9 Hz, JBH = 5.6
Hz, 1H, BCH2). 13C{1H} NMR (126 MHz): δ 148.4 (dm, 1JFC ≈ 235
Hz, C6F5), 139.4 (dm, JFC ≈ 249 Hz, C6F5), 137.3 (dm, JFC ≈ 242
1
1
4
2
Hz, C6F5), 134.7 (d, JPC = 3.0 Hz, p-Ph), 132.9 (d, JPC = 9.2 Hz, o-
Ph), 130.0 (d, 3JPC = 12.3 Hz, m-Ph), 122.5 (br, i-C6F5), 119.6 (d, 1JPC
= 86.0 Hz, i-Ph), 31.9 (br d, 1JPC = 52.7 Hz, ClCH2), 15.4 (m, BCH2).
31P{1H} NMR (202 MHz): δ 34.3 (ν1/2 ≈ 6 Hz). 19F NMR (470
3
MHz): δ −131.9 (m, 2F, o-C6F5), −160.5 (t, JFF = 20.4 Hz, 1F, p-
C6F5), −164.9 (m, 2F, m-C6F5), [Δδ19Fmp = 4.4]. 11B{1H} NMR (160
MHz): δ −15.7 (ν1/2 ≈ 20 Hz).
Preparation of Complex 4. (Caution: many isocyanates are toxic
and must be handled with due care.) Complex 1 (18.2 mg, 40 μmol)
and B(C6F5)3 (20.5 mg, 40 μmol) were mixed in CH2Cl2 (1 mL).
After the mixture was stored at room temperature for 5 min, PhNCO
(4.8 mg, 40 μmol) was added. Subsequently, the reaction mixture was
covered with pentane (3 mL). After 2 days, complex 4 was obtained as
EXPERIMENTAL SECTION
■
General Procedures. All experiments were carried out under a dry
argon atmosphere using standard Schlenk techniques or in a glovebox.
Solvents (including deuterated solvents used for NMR) were dried
and distilled prior to use. NMR spectra were recorded on VNMRS 500
D
dx.doi.org/10.1021/om400769y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
1
a white crystalline solid (31.0 mg, 71% yield). Crystals suitable for
single-crystal X-ray structure analysis were obtained from a two-layer
procedure using a CH2Cl2 solution of 4 and cyclopentane at room
temperature. Anal. Calcd for C48H27BClF15NOPZr: C, 53.03; H, 2.50;
Hz, C6F5), 139.8 (dm, JFC ≈ 248 Hz, C6F5), 137.4 (dm, JFC ≈ 250
Hz, C6F5), 133.4 (d, 2JPC = 8.1 Hz, o-Ph), 131.7 (d, 1JPC = 59.3 Hz, i-
4
3
Ph), 131.6 (d, JPC = 2.6 Hz, p-Ph), 128.7 (d, JPC = 9.9 Hz, m-Ph),
117.5 (br, i-C6F5), 114.5 (Cp), 27.6 (d, 1JPC = 22.6 Hz, CH2). 31P{1H}
NMR (243 MHz): δ 18.4 (m). 19F NMR (564 MHz): δ −128.3 (m,
2F, o-C6F5), −159.3 (t, 3JFF = 19.9 Hz, 1F, p-C6F5), −164.8 (m, 2F, m-
1
N, 1.29. Found: C, 52.73; H, 2.64; N, 1.12. H NMR (600 MHz,
CD2Cl2, 299 K): δ 7.69 (m, 2H, p-PhP), 7.64 (m, 4H, o-PhP), 7.51 (m,
4H, m-PhP), 7.50 (m, 2H, m-PhN), 7.27 (m, 1H, p-PhN), 6.97 (m, 2H,
C6F5), [Δδ19Fmp = 5.5]. 11B{1H} NMR (192 MHz): δ −23.6 (d, 1JPB
≈
o-PhN), 5.86 (s, 10H, Cp), 3.08 (dq (1:1:1:1), JPH = 18.4 Hz, JBH
=
=
=
77 Hz). 11B NMR: δ −23.6 (t, JPB ≈ JBH ≈ 77 Hz).
2
2
1
1
6.2 Hz, 2H, BCH2). 13C{1H} NMR (151 MHz): δ 157.6 (d, JPC
1
1
3
144.7 Hz, NC), 148.5 (dm, JFC ≈ 238 Hz, C6F5), 146.4 (d, JPC
ASSOCIATED CONTENT
* Supporting Information
Experimental details and physical characterization of the new
compounds, crystallographic data, and a CIF file. This material
is available free of charge via the Internet at http://pubs.acs.org.
■
18.6 Hz, i-PhN), 139.1 (dm, JFC ≈ 247 Hz, C6F5), 137.1 (dm, JFC
≈
1
1
S
255 Hz, C6F5), 134.2 (d, 2JPC = 9.4 Hz, o-PhP), 134.1 (d, 4JPC = 2.8 Hz,
p-PhP), 129.6 (m-PhN), 129.4 (d, JPC = 12.0 Hz, m-PhP), 125.1 (p-
3
PhN), 123.6 (br, i-C6F5), 121.5 (o-PhN), 121.2 (d, JPC = 79.9 Hz, i-
1
PhP), 116.1 (Cp), 11.0 (br m, BCH2). 31P{1H} NMR (243 MHz): δ
23.9 (ν1/2 ≈ 13 Hz). 19F NMR (564 MHz): δ −131.8 (m, 2F, o-C6F5),
3
−161.7 (t, JFF = 20.3 Hz, 1F, p-C6F5), −166.1 (m, 2F, m-C6F5),
AUTHOR INFORMATION
Corresponding Author
*E-mail: erker@uni-muenster.de.
■
[Δδ19Fmp = 4.4]. 11B{1H} NMR (192 MHz): δ −15.8 (ν1/2 ≈ 15 Hz).
Generation of Complex 5 (NMR Scale). Complex 1 (18.2 mg,
40 μmol) and B(C6F5)3 (20.5 mg, 40 μmol) were mixed in CD2Cl2
(0.6 mL). Then the reaction mixture was transferred to an NMR tube,
and after 30 min the reaction solution was characterized by NMR
experiments. 1H NMR (500 MHz, CD2Cl2, 299 K): δ 7.52 (m, 1H, p-
Ph), 7.45 (m, 2H, o-Ph), 7.37 (m, 2H, m-Ph), 6.02 (s, 5H, Cp), 1.24
Author Contributions
†C.G.D. performed the X-ray crystal structure analyses.
Notes
The authors declare no competing financial interest.
(d, JPH = 14.3 Hz, 1H, CH2P). 13C{1H} NMR (126 MHz): δ 148.9
2
1
1
(dm, JFC ≈ 242 Hz, o-C6F5), 140.0 (dm, JFC ≈ 256 Hz, p-C6F5),
1
2
ACKNOWLEDGMENTS
137.4 (dm, JFC ≈ 248 Hz, m-C6F5), 134.0 (d, JPC = 7.5 Hz, o-Ph),
■
4
1
131.7 (d, JPC = 2.7 Hz, p-Ph), 128.7 (d, JPC ≈ 51 Hz, i-Ph)*, 128.4
Financial support from the Deutsche Forschungsgemeinschaft
and the Alexander von Humboldt Stiftung (stipend to X.X.) is
gratefully acknowledged.
3
(d, JPC = 9.9 Hz, m-Ph), 117.5 (br, i-C6F5), 114.6 (Cp), 25.3 (dm,
1JPC ≈ 24 Hz, CH2P) [* from the ghmbc experiment]. 31P{1H} NMR
(202 MHz): δ 31.5 (ν1/2 ≈ 160 Hz). 19F NMR (470 MHz): δ −126.7
(br m, 2F, o-C6F5), −158.0 (br m, 1F, p-C6F5), −165.2 (br m, 2F, m-
REFERENCES
C6F5), [Δδ19Fmp = 7.2]. 11B{1H} NMR (160 MHz): δ −8.4 (ν1/2
≈
■
(1) (a) Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2010, 49,
46−76. (b) Frustrated Lewis Pairs I: Uncovering and Understanding;
Erker, G., Stephan, D. W., Eds.; Topics in Current Chemistry, Vol.
332; Springer: Berlin, 2013. (c) Frustrated Lewis Pairs II: Expanding the
Scope; Erker, G., Stephan, D. W., Eds.; Topics in Current Chemistry,
Vol. 334; Springer: Berlin, 2013.
200 Hz).
Preparation of Complex 6. Following the procedure described
for the preparation of compund 4, reaction of complex 1 (18.2 mg, 40
μmol), B(C6F5)3 (20.5 mg, 40 μmol), and PhCHO (4.2 mg, 40 μmol)
gave compound 6 as a white crystalline solid (32.0 mg, 75% yield).
Crystals suitable for single-crystal X-ray structure analysis were
obtained from a two-layer procedure using a CH2Cl2 solution of 6
and pentane at −35 °C. Anal. Calcd for C48H28BClF15OPZr: C, 53.67;
(2) (a) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124−1126. (b) Welch, G. C.; Stephan, D. W. J.
Am. Chem. Soc. 2007, 129, 1880−1881.
1
H, 2.63. Found: C, 53.12; H, 2.50. H NMR (500 MHz, CD2Cl2, 299
K): δ 7.76 (m, 1H, p-PhPA), 7.73 (m, 2H, o-PhPA), 7.61 (m, 1H, p-
PhPB), 7.54 (m, 2H, m-PhPA), 7.38 (m, 2H, m-PhPB), 7.32 (m, 1H, o-
PhPB), 7.09 (m, 1H, p-Ph), 6.97 (m, 2H, m-Ph), 6.68 (br m, 2H, o-
Ph), 6.30, 6.05 (each s, each 5H, Cp), 5.55 (d, 2JPH = 5.5 Hz, 1H, CH),
(3) (a) Stephan, D. W. Top. Curr. Chem. 2013, 332, 1−44. (b) Kehr,
G.; Schwendemann, S.; Erker, G. Top. Curr. Chem. 2013, 332, 45−84.
(4) Stephan, D. W.; Erker, G. Top. Curr. Chem. 2013, 332, 85−110.
(5) (a) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich,
̈
2
2
2
R.; Erker, G. Angew. Chem., Int. Ed. 2008, 47, 7543−7546. (b) Wang,
1.64 (dd, JPH = 21.3 Hz, JHH = 13.0 Hz, 1H, CH2), 1.39 (dd, JPH
=
2
18.8 Hz, JHH = 13.0 Hz, 1H, CH2). 13C{1H} NMR (126 MHz): δ
̈
H.; Frohlich, R.; Kehr, G.; Erker, G. Chem. Commun. 2008, 5966−
1
1
5968. (c) Xu, B.; Kehr, G.; Wibbeling, B.; Frohlich, R.; Schirmer, B.;
148.2 (dm, JFC ≈ 234 Hz, C6F5), 139.0 (dm, JFC ≈ 261 Hz, C6F5),
̈
1
2
137.0 (dm, JFC ≈ 250 Hz, C6F5), 136.8 (i-Ph), 134.9 (d, JPC = 8.1
Hz, o-PhPA), 134.2 (d, 4JPC = 2.9 Hz, p-PhPA), 133.9 (d, 4JPC = 2.9 Hz,
p-PhPB), 133.7 (d, 2JPC = 8.1 Hz, o-PhPB), 129.3 (d, 3JPC = 11.5 Hz, m-
PhPB), 129.1 (d, 3JPC = 11.5 Hz, m-PhPA), 128.5 (d, J = 3.5 Hz, p-Ph),
Grimme, S.; Erker, G. Angew. Chem., Int. Ed. 2011, 50, 7183−7186.
(d) Mahdi, T.; Heiden, Z. M.; Grimme, S.; Stephan, D. W. J. Am.
Chem. Soc. 2012, 134, 4088−4091. (e) Greb, L.; Ona-Burgos, P.;
Schirmer, B.; Grimme, S.; Stephan, D. W.; Paradies, J. Angew. Chem.,
̃
4
3
́
127.8 (d, JPC = 2.7 Hz, m-Ph), 127.6 (d, JPC = 5.3 Hz, o-Ph), 123.2
Int. Ed. 2012, 51, 10164−10168. (f) Chernichenko, K.; Madaras
Pap
723.
́
z, A.;
(br, i-C6F5), 122.4 (d, JPC = 80.0 Hz, i-PhPB), 121.7 (d, JPC = 79.1
Hz, i-PhPA), 115.5, 114.8 (Cp), 78.1 (d, 1JPC = 68.7 Hz, CH), 10.8 (d,
1JPC = 30.5 Hz, CH2). 31P{1H} NMR (202 MHz): δ 37.3 (ν1/2 ≈ 16
Hz). 19F NMR (470 MHz): δ −131.5 (m, 2F, o-C6F5), −162.3 (t, 3JFF
= 20.3 Hz, 1F, p-C6F5), −166.6 (m, 2F, m-C6F5), [Δδ19Fmp = 4.3].
11B{1H} NMR (160 MHz): δ −2.2 (ν1/2 ≈ 90 Hz).
1
1
́
ai, I.; Nieger, M.; Leskela, M.; Repo, T. Nat. Chem. 2013, 5, 718−
̈
(6) (a) Neu, R. C.; Otten, E.; Lough, A.; Stephan, D. W. Chem. Sci.
2011, 2, 170−176. (b) Chapman, A. M.; Haddow, M. F.; Wass, D. F. J.
Am. Chem. Soc. 2011, 133, 8826−8829. (c) Chapman, A. M.; Haddow,
M. F.; Wass, D. F. J. Am. Chem. Soc. 2011, 133, 18463−18478.
(d) Chapman, A. M.; Haddow, M. F.; Wass, D. F. Eur. J. Inorg. Chem.
2012, 1546−1554.
(7) (a) Xu, X.; Kehr, G.; Daniliuc, C. G.; Erker, G. J. Am. Chem. Soc.
2013, 135, 6465−6476. (b) Fromel, S.; Kehr, G.; Daniliuc, C. G.;
Erker, G. Dalton Trans. 2013, 42, 14531−14536.
Preparation of Complex 7. Complex 1 (27.4 mg, 60 μmol) and
HB(C6F5)2 (20.8 mg, 60 μmol) were mixed in CH2Cl2 (2 mL). Then
the reaction mixture was covered with pentane (3 mL). After several
days, complex 7 was obtained as colorless crystals (38.0 mg, 71%
yield), some of which were suitable for single-crystal X-ray structure
analysis of compound 7. Anal. Calcd for C36H23BClF10PZr·CH2Cl2: C,
49.44; H, 2.80. Found: C, 49.98; H, 2.83. 1H NMR (600 MHz,
CD2Cl2, 299 K): δ 7.55 (m, 2H, p-Ph), 7.49 (m, 4H, o-Ph), 7.44 (m,
4H, m-Ph), 6.07 (s, 10H, Cp), 4.08 (br, 1H, BH), 1.58 (d, 2JPH = 16.0
̈
(8) Schore, N. E.; Hope, H. J. Am. Chem. Soc. 1980, 102, 4251−4253.
(9) (a) Moebs-Sanchez, S.; Bouhadir, G.; Saffon, N.; Maron, L.;
Bourissou, D. Chem. Commun. 2008, 3435−3437. (b) Axenov, K. V.;
Momming, C. M.; Kehr, G.; Frohlich, R.; Erker, G. Chem.Eur. J.
̈
̈
1
Hz, 2H, CH2). 13C{1H} NMR (151 MHz): δ 148.5 (dm, JFC ≈ 239
2010, 16, 14069−14073.
E
dx.doi.org/10.1021/om400769y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(10) (a) Momming, C. M.; Kehr, G.; Wibbeling, B.; Frohlich, R.;
̈
̈
Erker, G. Dalton Trans. 2010, 39, 7556−7564. (b) Rosorius, C.; Kehr,
G.; Frohlich, R.; Grimme, S.; Erker, G. Organometallics 2011, 30,
̈
4211−4219. (c) Stute, A.; Kehr, G.; Daniliuc, C. G.; Frohlich, R.;
̈
Erker, G. Dalton Trans. 2013, 42, 4487−4499.
(11) Parks, D. J.; Piers, W. E.; Yap, G. P. A. Organometallics 1998, 17,
5492−5503.
(12) For related B(C6F5)3 adducts, see, for example: (a) Jacobsen,
H.; Berke, H.; Doring, S.; Kehr, G.; Erker, G.; Frohlich, R.; Meyer, O.
̈
̈
Organometallics 1999, 18, 1724−1735. (b) Spies, P.; Frohlich, R.;
̈
Kehr, G.; Erker, G.; Grimme, S. Chem.Eur. J. 2008, 14, 333−343.
(13) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113,
3623−3625.
(14) (a) Wu, Z.; Jordan, R. F. J. Am. Chem. Soc. 1995, 117, 5867−
5868. (b) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255−270.
(15) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
̈
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143−1170.
(16) (a) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994,
116, 10015−10031. (b) Chen, Y.-X.; Stern, C. L.; Yang, S.; Marks, T. J.
J. Am. Chem. Soc. 1996, 118, 12451−12452.
́ ́
(17) (a) Rokob, T. A.; Hamza, A.; Stirling, A.; Soos, T.; Papai, I.
Angew. Chem., Int. Ed. 2008, 47, 2435−2438. (b) Grimme, S.; Kruse,
H.; Goerigk, L.; Erker, G. Angew. Chem., Int. Ed. 2010, 49, 1402−1405.
(c) Gilbert, T. M. Dalton Trans. 2012, 41, 9046−9055. (d) Li, H.;
Wen, M.; Lu, G.; Wang, Z. Dalton Trans. 2012, 41, 9091−9100.
(e) Rokob, T. A.; Bako,
Chem. Soc. 2013, 135, 4425−4437.
(18) Hooft, R. W. W. COLLECT; Bruker AXS: Delft, The
Netherlands, 2008.
́ ́
I.; Stirling, A.; Hamza, A.; Papai, I. J. Am.
(19) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307−
326.
(20) Otwinowski, Z.; Borek, D.; Majewski, W.; Minor, W. Acta
Crystallogr. 2003, A59, 228−234.
(21) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467−473.
(22) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
(23) XP; Bruker AXS, 2000.
(24) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7−13.
F
dx.doi.org/10.1021/om400769y | Organometallics XXXX, XXX, XXX−XXX