Frustrated lewis pair modification by 1,1-Carboboration: Disclosure of a phosphine oxide triggered nitrogen monoxide addition to an intramolecular P/B frustrated lewis pair

Article abstract of DOI:10.1021/ja5028293

The vicinal frustrated Lewis pair (FLP) mes₂P-CH ₂CH₂-B(C₆F₅)₂ (3) reacts with phenyl(trimethylsilyl)acetylene by 1,1-carboboration to give the extended C₃-bridged FLP 6 featuring a substituted vinylborane subunit. The FLP 6 actively cleaves dihydrogen. The FLP 3 also undergoes a 1,1-carboboration reaction with diphenylphosphino(trimethylsilyl)acetylene to give the P/B/P FLP 11 that features a central unsaturated four-membered heterocyclic P/B FLP and a pendant CH₂CH₂-Pmes₂ functional group. Compound 11 reacts with nitric oxide (NO) by oxidation of the pendant Pmes₂ unit to the P(O)mes₂ phosphine oxide and N,N-addition of the P/B FLP unit to NO to yield the persistent P/B/PO FLPNO aminoxyl radical 14. This reaction is initiated by P(O)mes₂ formation and opening of the central Ph₂P···B(C₆F ₅)₂ linkage triggered by the pendant CH₂CH ₂-P(O)mes₂ group.

Full text of DOI:10.1021/ja5028293

Article
pubs.acs.org/JACS
Frustrated Lewis Pair Modification by 1,1-Carboboration: Disclosure
of a Phosphine Oxide Triggered Nitrogen Monoxide Addition to an
Intramolecular P/B Frustrated Lewis Pair
Rene Liedtke,† Felix Scheidt,† Jinjun Ren,‡ Birgitta Schirmer,† Allan Jay P. Cardenas,§
́
Constantin G. Daniliuc,† Hellmut Eckert,*,‡ Timothy H. Warren,*,§ Stefan Grimme,*,∥ Gerald Kehr,†
and Gerhard Erker*,†
†Organisch-Chemisches Institut, Universitat Munster, Corrensstrasse 40, Munster 48149, Germany
̈
̈
̈
‡Institut fur Physikalische Chemie, Universitat Munster, Corrensstrasse 30, Munster 48149, Germany
̈
̈
̈
̈
§Department of Chemistry, Georgetown University, 37th and O Streets NW, Washington, DC 20057-1227, United States
∥Mulliken Center for Theoretical Chemistry, Institut fur Physikalische und Theoretische Chemie, Universitat Bonn, Beringstrasse 4,
̈
̈
Bonn 53115, Germany
S
* Supporting Information
ABSTRACT: The vicinal frustrated Lewis pair (FLP) mes2P−
CH2CH2−B(C6F5)2 (3) reacts with phenyl(trimethylsilyl)-
acetylene by 1,1-carboboration to give the extended C3-
bridged FLP 6 featuring a substituted vinylborane subunit. The
FLP 6 actively cleaves dihydrogen. The FLP 3 also undergoes
a 1,1-carboboration reaction with diphenylphosphino-
(trimethylsilyl)acetylene to give the P/B/P FLP 11 that features a central unsaturated four-membered heterocyclic P/B FLP
and a pendant CH2CH2−Pmes2 functional group. Compound 11 reacts with nitric oxide (NO) by oxidation of the pendant
Pmes2 unit to the P(O)mes2 phosphine oxide and N,N-addition of the P/B FLP unit to NO to yield the persistent P/B/PO
FLPNO aminoxyl radical 14. This reaction is initiated by P(O)mes2 formation and opening of the central Ph2P···B(C6F5)2
linkage triggered by the pendant CH2CH2−P(O)mes2 group.
described by the Dewar−Chatt−Duncanson model.4 Of course,
INTRODUCTION
■
in contrast to the d-metal situation, the donor and acceptor
functions are separated from each other in a FLP and residing
on different atoms. A similar situation has been encountered
upon treatment of the saturated ethylene-bridged vicinal P/B
FLP 35 with nitric oxide (NO). In this case, the cooperative
addition of the boron acceptor and the phosphane donor to the
nitrogen atom of nitrogen monoxide has resulted in the
formation of the persistent heterocyclic FLPNO radical 4 (see
Scheme 1).6c
Intramolecular frustrated Lewis pairs (FLPs) can undergo quite
some remarkable reactions.1 Some of such main group element
Lewis acid/Lewis base combinations show a transition-metal-
reminiscent coordination behavior with selected small-molecule
ligands.2 Typical examples are the formation of the isonitrile-
bridged addition products 2 derived from a small series of the
unsaturated intramolecular vicinal P/B FLPs 13 (see Scheme
1). Binding of the isonitrile donor to the boron Lewis acid of 1
in these cases is strongly amended by a backbonding interaction
from the adjacent phosphane donor to the isonitrile π* orbital,
resulting in an overall bonding situation that is remotely
reminiscent of the bonding/backbonding combination of
ligands at single transition-metal centers as it is commonly
Various substituted derivatives of 3 have been shown to also
undergo this reaction under mild conditions to yield the
respective substituted FLPNO systems.6 Examples of the
compound 1 so far have been resistant to NO addition.
However, we have now prepared a variety of analogues of 1
featuring an additional pendant Pmes2 group at the periphery of
the FLP core. In contrast to 1, these new systems showed a
remarkable reactivity toward nitrogen monoxide as will be
described and discussed in this account. Moreover, we found
out that the 1,1-carboboration reaction turned out to be an
ideally suited tool for the modification and functionalization of
FLPs.
Scheme 1
Received: March 27, 2014
Published: May 21, 2014
© 2014 American Chemical Society
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RESULTS AND DISCUSSION
■
Frustrated Lewis Pair Modification by the 1,1-
Carboboration Reaction. Silyl substituents have long been
known to serve as good migrating groups in classical 1,1-
carboboration reactions (“Wrackmeyer reaction”).7 We and
others have more recently shown which the use of strongly
electrophilic R-B(C6F5)2 boranes greatly facilitated 1,1-
carboboration reactions, extending their application potential
significantly.3,8−12 Therefore, we treated the P/B FLP 3
(bearing the strongly electrophilic B(C6F5)2 functionality)
with trimethylsilylphenylacetylene (5). Not unexpectedly,
these two reagents underwent a clean 1,1-carboboration
reaction at 60 °C to give the extended and alkylidene
functionalized new FLP 6 in good yield (see Scheme 2). The
Scheme 2
Figure 1. Molecular structure of the FLP−isonitrile adduct 7 (thermal
ellipsoids are shown with 30% probability). Selected bond lengths (Å)
and angles (deg): P1−C4:1.861(3), C4−C3:1.537(4), C3−
C2:1.518(4), C2−C1:1.362(4), C2−B1:1.639(4), B1−C5:1.612(5),
C5−N1:1.136(4), C3−C2−C1:119.0(2), C3−C2−B1:115.2(2), C1−
C2−B1:125.8(3), C21−C1−Si1:109.0(2), C2−B1−C5:104.9(2), B1−
C5−N1:177.0(3), C5−N1−C6:173.6(3), P1−C4−C3-C2:161.56,
ΣP1CCC = 313.9.
NMR signals of the substituted exomethylene group at δ 157.3
(C[B]) and δ 149.4 (C[Si]), respectively.
The new C3-bridged P/B FLP 6 reacts with dihydrogen
under mild reaction conditions.16 Treatment of in situ
generated 6 with H2 (rt, 1.5 bar, overnight) resulted in
heterolytic cleavage of the dihydrogen molecule with formation
of the C3-bridged phosphonium/hydridoborate product 8 (49%
isolated). The composition of 8 was confirmed by X-ray
diffraction (see the Supporting Information). Compound 8
shows typical doublets in the 11B (δ −19.6, 1JBH ∼ 85 Hz) and
31P (δ −11.6, 1JPH = 468 Hz) NMR spectra with corresponding
NMR characterization revealed that 6 features a B−P
interaction as expected. This has become evident by the typical
NMR chemical shifts of the pair of core heteronuclei (31P: δ
26.5; 11B: δ 4.7). Consistently, the 19F NMR spectrum of 6
shows three signals (o, p, m) of the pair of symmetry-equivalent
C6F5 groups at boron with a relatively small Δδ19F(m, p)
separation of 7.2 ppm (for further details see the Experimental
Section and the Supporting Information). The ring-expanded
C3-bridged P/B FLP 6 reacted rapidly with one molar
equivalent of n-butylisocyanide13 to give the adduct 7 (78%
isolated). It was characterized by C,H,N elemental analysis, by
spectroscopy and by X-ray diffraction (single crystals were
obtained from pentane at −40 °C).
The X-ray crystal structure analysis of compound 7 (see
Figure 1) shows that the (Me3Si)PhCC vinylidene isomer of
514 has formally become inserted into the [B]CH2 linkage of
3. Of course, this has taken place by the typical mechanistic 1,1-
carboboration sequence, probably with the SiMe3 substituent
serving as one migrating group11a,15 and the CH2CH2−Pmes2
moiety as the other. This has resulted in the formation of the
C3-bridge between phosphorus and boron including the Me3Si/
Ph-substituted exomethylene group at its α position. The
isonitrile donor has added to the boron Lewis acid, thereby
cleaving the B−P bond of the starting material 6. Consequently,
the boron atom shows a pseudotetrahedral coordination
geometry, and the phosphorus atom shows a trigonal-pyramidal
coordination geometry.
1H NMR resonances at δ 3.51 (br, [B]H) and δ 6.73 (dt, 1JPH
=
3
468 Hz, JHH = 7.0 Hz, [P]H), respectively (for further details
and the depicted NMR spectra see the Supporting
Information).
Compound 6 reacts with nitric oxide, but it apparently shows
only the typical reaction behavior of the phosphane to nitrogen
monoxide. It is well known that many phosphanes react with
NO to give the corresponding phosphine oxides with
concomitant formation of N2O.17 Compound 6 is no exception.
We treated the FLP 6 with excess NO (1.5 bar) for 2 h at room
temperature (rt) and isolated the phosphine oxide 9 in 61%
yield. The X-ray crystal structure analysis revealed that the
Pmes2 moiety had been converted to P(O)mes2 and the newly
introduced oxygen atom had coordinated to the boron atom
forming a [P]O Lewis base/RB(C6F5)2 Lewis acid adduct.
The resulting six-membered heterocycle is nonplanar (θ P1−
C1−C2−C3: 73.9(2)°). The sp2-carbon atom C3 is part of the
exocyclic CC double bond (see Figure 2). Both the
phosphorus and the boron atoms show pseudotetrahedral
coordination geometries (ΣPCCC = 333.6°; ΣBCCC = 342.6°).
1
In solution, compound 9 shows H NMR signals of the
CH2CH2 moiety at δ 2.65 and 2.76 with corresponding 13C
NMR resonances at δ 29.0 (2JPC = 6.3 Hz) and δ 29.7 (1JPC
=
57.0 Hz), respectively. The Ph[Si]CC 13C NMR signals
occur at δ 160.1 (C[B]) and δ 144.2 (C[Si]), respectively, and
we have monitored the core heteroatom magnetic resonance
signals at δ 0.0 (11B) and δ 62.4 (31P), respectively (29Si: δ
−10.4).
In solution, compound 7 shows NMR signals at δ −18.9
1
(10B), δ −21.6 (31P), and δ −11.4 (29Si). It features H NMR
resonances of the CH2CH2 unit at δ 2.50 and δ 2.14 and 13C
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Figure 2. Molecular structure of compound 9 (thermal ellipsoids are
shown with 30% probability). Selected bond lengths (Å) and angles
(deg): P1−O1:1.544(1), B1−O1:1.591(2), B1−C2:1.637(3), C1−
C2:1.353(3), C3−C2:1.520(3), C3−C4:1.535(3), C4−P1:1.801(2),
C4−P1−O1:103.5(1), P1−O1−B1:124.7(1), O1−B1−C2:107.3(2),
B1−C2−C1:128.1(2), Si1−C1−C11:110.3(1), C1−C2−C3:119.2(2),
C4−C3−C2:111.6(2).
Figure 3. View of the molecular structure of the P/B/P FLP 11a
(thermal ellipsoids are shown with 30% probability).
Table 1. Selected Structural Parameters of the P/B/P FLPs
11a (PPh2) and 11b (P(o-tol)2) and the Intermolecular H2
a
Activation Product 13
Formation and Characterization of the New P/B/P
Frustrated Lewis Pairs. We treated diphenylphosphino-
(trimethylsilyl)acetylene (10a) with the ethylene-bridged FLP
3. It apparently formed a B/P Lewis acid/base adduct upon
mixing of the two components in d6-benzene at rt (NMR: δ
−7.0 (11B), δ −2.4, −16.3 (31P), for further details see the
Supporting Information). Heating of the sample at 60 °C
overnight eventually resulted in the 1,1-carboboration reaction
with a practically complete conversion to the new ring enlarged
FLP 11a (see Scheme 3). We prepared compound 11a on a
compd
P1−B1
P1−C1
C1−C2
C2−B1
B1−P1−C2
C2−B1−P1
P1−C1−C2−B1
C2−C3−C4−P2
11a
11b
13
2.028(3)
1.790(3)
1.367(3)
1.647(4)
78.9(1)
2.057(4)
1.792(3)
1.356(5)
1.635(5)
77.8(2)
42.9(1)
3.5(3)
2.025(4)
1.786(3)
1.370(4)
1.640(5)
79.0(1)
43.4(1)
43.4(1)
−1.6(2)
−179.0(2)
−5.9(3)
−170.7(2)
173.9(2)
a
Bond lengths in Å; angles and dihedral angles in deg.
membered P/B containing heterocycle.3 The more bulky
pendant Pmes2 group contains a tricoordinate phosphorus
center with a typical trigonal-pyramidal coordination geometry
(ΣP2CCC = 314.7°).
Scheme 3
The intramolecular Ph2P/B(C6F5)2 coordination of 11a is
retained in solution. This has become evident from the typical
NMR features (31P: δ 14.0 (PPh2) and δ −21.0 (Pmes2); 10B: δ
−6.3; 19F: δ −129.6 (o), −157.7 (p), −163.9 (m) of C6F5,
Δδ19F(m, p) = 6.2 ppm). The bridging CC unit gives rise to
13C NMR resonances at δ 209.4 (C[B]) and δ 136.6 (
1
C[P], JPC = 27.3 Hz), respectively, and we have observed the
1
typical H NMR signals of the pendant CH2CH2−[P] moiety
at δ 3.05 and 2.76.
The markedly more bulky di(o-tolyl)phosphino-(trimethyl-
silyl)acetylene reagent 10b reacts analogously with the FLP 3
to directly give the extended P/B/P FLP 11b that was isolated
in 81% yield. It shows similar spectroscopic data (see the
Supporting Information for details) and structural parameters
(see Table 1; the structure of compound 11b is depicted in the
Supporting Information).
preparative scale from 10a and 3 in toluene (70 °C, overnight)
and isolated the P/B/P FLP 11a in 75% yield. It was
characterized by X-ray diffraction (see Figure 3 and Table 1).
The X-ray crystal structure analysis has shown that a 1,1-
carboboration reaction has occurred with migration of the
CH2CH2−Pmes2 group to an acetylenic carbon atom. The
newly formed (“inserted”) substituted exomethylene group
(C1C2) is formed stereoselectively with the Ph2P substituent
and the remaining B(C6F5)2 functionality oriented cis to each
other. Consequently, compound 11a features a marked P1−B1
interaction resulting in a central monounsaturated four-
The unsaturated vicinal P/B FLPs 1 are not very reactive.2,3
They usually only show a small spectrum of the typical FLP
reactivity among that being the 1,2-addition of an aldehyde18 or
the above-mentioned cooperative P/B addition to isonitriles.2
The new unsaturated P/B/P FLP 11a is no exception, but as
expected, it cleanly reacted with n-butylisocyanide to give the
five-membered heterocyclic product 12 (see Scheme 3) that we
isolated as colorless crystals in 40% yield. The X-ray crystal
structure analysis shows that a pair of new bonds (P1−C5 and
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B1−C5) have been formed to the carbon atom of the incoming
isonitrile reagent (see Figure 4 and Table 2). This has resulted
In contrast to the C3-bridged P/B FLP 6 (see above), the P/
B/P FLP 11a does not react with dihydrogen under similar
conditions. This is probably due to deactivation of the boron
Lewis acid by internal interaction with the adjacent relatively
small PPh2 phosphanyl Lewis base. However, addition of one
molar equivalent of the strong boron Lewis acid B(C6F5)3 gave
an intermolecular FLP.19 Exposure of the 11a/B(C6F5)3
mixture to H2 at ambient conditions gave the respective
phosphonium/hydridoborate salt 13 (isolated in 87% yield)
(see Scheme 3).
The NMR spectra show the typical [P]-H and [B]-H signals:
δ −25.4 (11B, 1JBH ∼ 90 Hz) and δ −12.2 (31P, 1JPH = 476 Hz).
The spectra also show that the Ph2P···B(C6F5)2 unit of the
central four-membered core structure has remained largely
unaffected by the reaction. Consequently, we have monitored
the typical 31P (δ 13.1, PPh2) and 11B (δ −7.4, B(C6F5)2) NMR
signals of this unit of compound 13 [cf. starting material 11a:
31P: δ 14.0 (PPh2) and 11B: δ −6.3 (B(C6F5)2)].
The intact four-membered core structure of compound 13
has been confirmed by X-ray crystal structure analysis (see
Figure 5). The core structural features of 13 are very similar to
Figure 4. Molecular structure of the isonitrile addition product 12
(thermal ellipsoids are shown with 30% probability).
Table 2. Selected Structural Parameters of the Isonitrile
a
Addition Products 12 and 18 (see Schemes 3 and 5)
compd
C1−P1
C1−C2
C2−B1
B1−C5
12
18
1.777(3)
1.362(4)
1.649(4)
1.664(4)
1.840(3)
1.266(3)
97.5(1)
1.776(2)
1.362(3)
1.654(3)
1.651(3)
1.838(2)
1.270(3)
97.3(1)
C5−P1
C5−N1
C1−P1−C5
C2−B1−C5
P1−C5−B1
B1−C5−N1
P1−C5−N1
C5−N1−C6
P1−C5−N1−C6
B1−C5−N1−C6
C2−C3−C4−P2
ΣP2CCC
100.1(2)
102.7(2)
142.4(3)
114.8(2)
120.8(2)
−177.4(2)
−1.1(6)
172.5(2)
314.4
100.0(2)
103.1(1)
142.7(2)
114.1(2)
121.6(2)
−175.8(2)
−1.0(4)
−178.1(2)
−
Figure 5. Molecular structure of the cation of the phosphonium/
hydridoborate salt 13 (thermal ellipsoids are shown with 30%
probability).
b
a
b
those of the parent compounds 11a (see Table 1). The pendant
Bond lengths in Å; angles and dihedral angles in deg. C2−C3−C4−
+
C41.
CH2CH2−PHmes2 substituent of 13 contains a pseudote-
trahedral phosphonium center (ΣP2CCC = 341.3°). The
structure contains the [HB(C6F5)3]− counteranion with a
pseudotetrahedral boron center (ΣB2CCC = 333.2°). We note
that, in the crystal, there seems to be a rather short distance
between the phosphonium proton [P]−H and the borate
hydride H−[B] (d P2−H···H−B2 = 2.244 Å).
Reactions of the P/B/P-Frustrated Lewis Pairs 11 with
Nitrogen Monoxide. The unsaturated vicinal P/B FLPs 1 so
far have not been shown to be able to add to NO. This is
surprisingly different with the P/B/P FLPs 11 although they
contain the same type of a central P/B FLP core. The
compounds 11 react cleanly with nitrogen monoxide. As a
typical example, we have exposed a benzene solution of the P/
B/P FLP 11a to an atmosphere of NO (1.5 bar) overnight at rt.
Workup with pentane eventually gave the persistent FLPNO
aminoxyl radical 14a as a pale blue-green solid that was isolated
in 81% yield (Scheme 4).
in the formation of the central five-membered heterocyclic core
of compound 12 that contains a total of three sp2-hybridized
carbon atoms (C1, C2, C5). The resulting C(5)N(1) double
bond is oriented slightly unsymmetrically at the central core,
leaning over toward the phosphorus side. It appears as if the μ-
(RCN) group was experiencing a “memory effect”, having
been attacked by the phosphorus nucleophile after being
activated by coordination to the boron Lewis acid. We have
observed the E isomer of the resulting imine-like structure.
In solution we can also only identify one isomer of 12. It is
characterized by a 13C NMR (R-CN) resonance at δ 193.6.
The core heteroatom NMR features occur at δ −14.6 (11B) and
δ 22.1 (31P (1:1:1:1 quartet)). The 31P NMR signal of the
pendant Pmes2 group was located at δ −21.1 and compound 12
exhibits a 29Si NMR resonance at δ −9.3.
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to the excess NO. Also, the central B/P Lewis acid/Lewis base
pair has undergone a N,N-addition to one equivalent of NO to
give the five-membered heterocyclic central core of the FLPNO
aminoxyl radical 14a. A close inspection of the characteristic
bonding features of 14a reveals that the NO unit has become
rather symmetrically bonded inside this framework. Free NO
has a short nitrogen−oxygen bond of 1.15 Å.20a In 14a, this has
become elongated to 1.292(2) Å (4: 1.296(2) Å;6b TEMPO:
1.284(8) Å20c), which is still a reasonably short bond distance,
indicating quite substantial π interaction between these atoms.
Compound 14a was characterized by electron paramagnetic
resonance (EPR) spectroscopy (see Figure 7). The X-band
Scheme 4
The persistent aminoxyl radical 14a was characterized by X-
ray diffraction (see Figure 6 and Table 3). The X-ray crystal
Figure 7. X-band EPR spectrum and simulation for 14a
(fluorobenzene, 10 mM, rt). The sample seems to contain some
minor unknown paramagnetic admixture.
EPR spectra of compound 14a in fluorobenzene at rt shows a
signal at giso = 2.0075 with a distinct hyperfine coupling pattern.
Simulation gave A(14N) = 20.5 MHz (4: 18.5 MHz;6c TEMPO:
43.5 MHz20b), A(31P) = 47.0 MHz (4: 48.5 MHz),6b and
A(11B) = 9.5 MHz (4: 9.1 MHz).6c This is rather different from
some often used organic aminoxyl radicals such as TEMPO but
close to typical values observed for the FLPNO radical 4 and
closely related phosphane/borane FLPNO derivatives.6 The
Mulliken spin density populations of 14a were density
functional theory (DFT) calculated. Similar to other
phosphane/borane FLPNO species,6 14a is a rather oxygen-
centered radical with spin densities at O of 55% and at N of
32% and some rather low contributions at P (ca. 5%) and B (ca.
4%) (for details see the Supporting Information).
The P/B/P system 11b (Ar = o-tolyl) reacts analogously
with NO. We have isolated the persistent P/B/PO FLPNO
aminoxyl radical 14b, bearing the more bulky P(o-tolyl)2
moiety, as a green solid in 87% yield (see Scheme 4).
Compound 14b was also characterized by X-ray diffraction.
Selected structural parameters of 14b are listed in Table 3. For
a view of the molecular structure and further details see the
Supporting Information.
Figure 6. Molecular structure of the persistent P/B/PO FLPNO
aminoxyl radical 14a (thermal ellipsoids are shown with 30%
probability).
Table 3. Selected Structural Parameters of the P/B/PO
FLPNO Aminoxyl Radicals 14a (Ar = PPh2) and 14b (Ar =
P(o-tolyl)2) and Their Corresponding FLPNOH Products
a
15a, b
compd
N1−O1
P1−N1
B1−N1
C1−P1
C1−C2
C2−B1
P2−O2
14a
15a
14b
15b
1.292(2)
1.694(2)
1.570(2)
1.774(2)
1.368(2)
1.637(2)
1.489(1)
114.3(1)
126.2(1)
119.3(1)
170.7(2)
323.2
1.431(3)
1.647(2)
1.557(4)
1.789(3)
1.353(4)
1.635(4)
1.491(2)
109.9(2)
121.2(2)
111.2(2)
−165.7(2)
320.8
1.299(5)
1.676(4)
1.571(7)
1.790(5)
1.379(6)
1.630(8)
1.482(3)
110.5(3)
126.8(4)
122.1(3)
170.1(3)
323.8
1.436(2)
1.642(2)
1.560(3)
1.790(2)
1.362(3)
1.635(3)
1.479(2)
111.0(1)
121.2(2)
114.5(1)
168.5(2)
323.2
The FLPNO radicals 4 (see Scheme 1) behave as typical
persistent organic aminoxides (such as e.g. TEMPO or
PINO).21 They undergo typical radical reactions such as
hydrogen atom abstraction from suitable H· donors. The P/B/
PO FLPNO radicals 14 behave similarly. In situ generated
compound 14a reacted rapidly with the H atom donor 1,4-
cyclohexadiene (30 min, rt) to give the diamagnetic FLPNOH
product 15a that we have isolated as a colorless solid in 69%
yield (see Scheme 4). Compound 15a was characterized by C,
H, and N elemental analysis, by spectroscopy, and by X-ray
diffraction (see Table 3).
B1−N1−P1
B1−N1−O1
P1−N1−O1
C2−C3−C4−P2
ΣP2CCC
ΣN1POB
359.9
342.4
359.4
346.7
a
Bond lengths in Å; angles and dihedral angles in deg.
structure analysis has shown that the pendant CH2CH2−Pmes2
moiety of the starting material 11a had been oxidized to the
respective CH2CH2−P(O)mes2 phosphine oxide by exposure
Compound 15a shows the [N]OH 1H NMR signal at δ 4.31
(d with a 3JPH = 5.1 Hz coupling constant). It shows 19F NMR
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signals of the pair of symmetry equivalent C6F5 groups typical
for a tetracoordinated boron geometry (δ −130.8 (o), −160.4
(p), −164.8 (m, Δδ19F(m, p) = 4.4 ppm)) and a corresponding
10B NMR feature at δ −5.6. Two 31P NMR signals were located
at δ 52.0 (PPh2) and 38.9 (P(O)mes2), and a 29Si NMR
resonance was at δ −9.5.
In the crystal, the structures of the FLPNO radical 14a and
the FLPNOH product 15a look superficially similar. However,
there are a number of significant differences in detail. First, and
most importantly, the N1−O1 bond in 15a is much longer than
that in 14a.6 The difference is ∼0.14 Å, indicating the loss of
the electron delocalization between N and O by using the odd
electron of 14a to make the new [N]O−H bond. The P1−N1
bond in 15a is slightly shorter as compared to 14a (see Table
3) that may indicate some participation of the phosphinimine
resonance structure (15′, see Scheme 4). In contrast,
compound 14a seems to be adequately described by the σ-
bonded core structure. In 15a, the B1−N1 bond has largely
been unaffected by the change of the bonding situation at the
adjacent P−N−OH unit. We also note that, in 15a, the
nitrogen atom N1 exhibits a slightly pyramidalized coordination
geometry different from the trigonal-planar situation encoun-
tered for nitrogen in 14a (see Table 3 and Figure 8). The
Figure 9. 11B{1H} (left) and 31P{1H} (right) MAS NMR spectra of
compounds 11a (top), 25a (middle), and 15a (bottom). Impurities
are indicated by asterisks.
typical spectroscopic behavior of a four-coordinate boron
compound.
While neither the 11B nor the 31P NMR spectra give any
indication of indirect 11B−31P spin−spin interactions in 11a,
15a, and 25a, the corresponding coupling constants
1J(31P−11B) can be easily extracted from 11B observed two-
dimensional J-resolved spectra (see Figure 10). Values near 50
Hz measured for 11a and 25a are typical for similar
intramolecular FLPs,22 and for the NO cycloaddition product
15a, a 2J(11B−31P) value of 27.7 Hz is measured. In addition, J-
based 31P/11B heteronuclear correlation spectroscopy
(HQMC) can be used for the selective detection of those P
species interacting covalently with the Lewis acid center,
providing an unambiguous assignment of the two 31P signals
(see Figures S78−S80 in the Supporting Information). The
latter method is particularly useful for compound 15a, (see
Figure S80 in the Supporting Information) where the
assignment of the two closely spaced 31P signals is not obvious.
Figure 11 shows the 31P{11B} REAPDOR (left) and the
11B{31P} REDOR (right) curves of 11a, 15a, and 25a. The
experimental REAPDOR data of 11a and 25a show good
agreement with simulated curves based on two rather different
P···B distances as indicated also by the crystal structure (2.1
and 5.0 Å; dashed and solid curves, respectively). In the case of
the 31P{11B} REAPDOR measurement of 15a, the data
obtained for the remote P atom (40.3 ppm) are best modeled
by a 31P (11B)2 three-spin system based on an intramolecular
distance of 5.24 Å, an intermolecular distance of 5.93 Å, and an
angle of 119.8° between the two internuclear vectors as
deduced from the crystal structure. In contrast, the REAPDOR
curve observed for the 47.3 ppm resonance is satisfactorily
modeled just by a two-spin system (2.68 Å), which completely
dominates the interaction.
Figure 8. View of the molecular structure of the FLPNOH product
15a (thermal ellipsoids are shown with 30% probability).
persistent P/B/PO FLPNO aminoxyl radical 14b, bearing the
markedly more bulky P(o-tolyl)2 moiety, reacts analogously
with 1,4-cyclohexadiene by H atom abstraction to yield the
corresponding diamagnetic FLPNOH product 15b. Compound
15b was characterized by NMR spectroscopy (10B: δ −5.3; 31P:
δ 53.3 (P-(o-tolyl)2), 38.6 (P(O)mes2)) and by X-ray
diffraction (see Table 3 and the Supporting Information for
details).
The 11B{31P} REDOR curves (right parts of Figure 11) also
agree well with those predicted from the molecular distance
geometry (see Table 4). In all three cases, the simulations are
based on the full intramolecular 11B31P2 three-spin systems. The
angles between the dipolar vectors are given as 127.6°, 129.1°,
and 105.6° for 11a, 15a, and 25a, respectively. For compound
17, for which no crystal structure was available, the REDOR
data are consistent with a B−P distance of 2.10 Å (see the
Supporting Information).
Altogether, all the solid-state NMR results, both on the FLPs
11a and 25a as well as on the NO cycloaddition product 15a,
indicate the absence of any covalent interactions between the
boron Lewis acid center and the more remote pendant
phosphorus Lewis base center in the solid state.
1
Solid-State NMR. Figure 9 shows the H decoupled 11B
and the 31P MAS NMR spectra of compounds 11a, 15a, and
25a. The 11B MAS NMR spectra were influenced by second-
order nuclear electric quadrupolar coupling perturbations. The
corresponding line shape fit parameters, namely, the quad-
rupolar coupling constants CQ, the asymmetry parameters ηQ,
and the isotropic chemical shifts δiso, are summarized in Table
4. The values for 11a and 25a are typical for those measured in
FLPs with weak intramolecular interactions between vicinal
Lewis centers. The 11B CQ values follow closely the previously
established correlations of CQ and δiso with the internuclear
distance d(B···P) for such systems.2 Compound 15a shows the
Mechanistic Studies. Since the P/B FLPs 1 that we had
previously described were inert toward NO in contrast to our
new P/B/P FLPs 11, it appeared that the pendant CH2CH2−
Pmes2 group played a vital role in the formation of the P/B/PO
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Table 4. 11B−31P Distances (Å) from the Crystal Structure (dcryst) and from 31P{11B} REAPDOR (dNMR), Isotropic Indirect
Dipolar-Coupling Constants J(11B−31P) (Solid) and J(31P−31P) (Solution/Solid) ( 0.5 Hz), Isotropic Chemical Shifts δiso31P
a
b
(solution ; solid ) and δiso10B/11B (Solution/Solid) ( 0.5 ppm), 11B Nuclear Electric Quadrupolar Coupling Constant Cq
( 0.10 MHz), and Electric Field Gradient Asymmetry Parameter ηQ ( 0.10)
a
b
dcryst
dNMR
J
11B31P
48.7
J
31P31P
δiso 10B/11B
δiso 31P
δiso 31P
Cq
ηQ
c
11a
25a
15a
17
2.03
5.03
2.02
4.96
2.62
2.10
6.3/7.8
−6.3/
−7.5
−6.5/
−7.4
−5.6/
−6.2
−6.2/
−7.1
14.0
13.4
1.34
0.3
d
5.0
−21.0
37.4
13.4
52.0
38.9
14.4
−21.4
37.0
13.5
47.3
40.3
13.1
c
2.10
49.6
27.7
50.3
0/0
1.31
0.71
1.31
0.32
0.82
0.41
d
5.0
c
2.70
1.9/0
−
d
5.24
e
5.2
c
2.10
a
b
c
d
e
Solution. Solid. 0.05 Å. 0.1 Å. No single-crystal structure available.
Figure 11. 31P{11B} REAPDOR (left) and 11B{31P} REDOR (right)
experimental data points and simulated curves, for compounds 11a
(first row), 25a (middle row), and 15a (bottom row). See text for
further details.
14.4; 10B: δ −6.2; for further characterization see the
Supporting Information). Since we did not get single crystals
suitable for characterizing 17 by X-ray diffraction, we prepared
its n-butylisocyanide addition product 18 (see Scheme 5) (13C
Figure 10. 11B/31P heteronuclear J-resolved spectra of compounds 11a
(top), 25a (middle), and 15a (bottom). The J-coupling doublets
extracted from these data are shown in the figure.
Scheme 5
FLPNO product. This became supported by a series of
additional reactions. We first prepared the unsaturated vicinal
P/B FLP 17. This compound is in many details similar to the
P/B/P FLP 11, only that it contains a nonfunctionalized
pendant CH2CH2−Ph substituent instead of the CH2CH2−
Pmes2 functional group.
Compound 17 was prepared by 1,1-carboboration of the
borane 16 (i.e., the HB(C6F5)2 hydroboration product of
styrene)23,24 with diphenylphosphino(trimethylsilyl)acetylene
(10a) (70 °C, 26 h). It was isolated in 82% yield (31P NMR: δ
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NMR: δ 194.2 (CN); 10B: δ −14.4 (2J31P10B ∼ 16 Hz); 31P: δ
Scheme 7
2
22.7 (1:1:1:1 q, J31P11B ∼ 51 Hz)). Compound 18 was
characterized by X-ray diffraction (see Table 2 and the
Supporting Information for details). This derivatization
reaction further confirmed the formation of the P/B FLP 17
by 1,1-carboboration (see Scheme 5). It turned out that the P/
B FLP 17 was indeed inert toward nitrogen monoxide under
our typical reaction conditions.
Free phosphanes react readily with NO to form phosphine
oxides and N2O. The mechanistic course of this phosphane
oxidation reaction had been carefully examined.17 We had
recently shown that the alkenyl phosphane 19 (see Scheme 6)
reacts with NO to give the phosphine oxide 20 (and probably
N2O).6f
Scheme 6
Figure 12. Molecular structure of the P/B/PO FLP 25a (thermal
ellipsoids are shown with 30% probability).
Table 5. Selected Structural Data of the P/B/PO FLPs 25a
It was shown that this was kinetically a third-order reaction,
first order in the phosphane and second order in nitric oxide.
Treatment of the phosphane 19 with Piers’ borane [HB-
(C6F5)2] gave the saturated vicinal FLP 21, which reacted with
NO following a second-order rate law (first order in the FLP
and first order in NO) to give the persistent FLPNO radical
22.6f We were able to detect the coproduct N2O in the reaction
(Ar = PPh2) and 25b (Ar = P(o-tolyl)2) and the Related P/
a
B/PS FLP 28a (Ar = PPh2)
compd
P1−B1
C1−P1
C2−B1
C1−C2
P2−O1
C4−P2
C1−P1−B1
P1−B1−C2
ΣP2CCC
25a
25b
28a
2.024(4)
1.793(4)
1.643(6)
1.368(5)
1.481(3)
1.816(4)
78.9(2)
78.8(2)
322.1
2.061(3)
1.796(2)
1.629(4)
1.358(3)
1.484(2)
1.822(2)
77.3(1)
78.5(1)
319.9
2.023(3)
1.788(3)
1.651(4)
1.368(4)
1.955(1)
1.835(3)
79.1(1)
78.7(2)
318.2
t
of the intermolecular FLP Bu3P/B(C6F5)3 (23) with excess
6b
t
b
NO to give the phosphine oxide Bu3PO and the known
FLP−N2O trapping product 24.6c
Therefore, it was tempting to assume that oxidation of the
free pendant CH2CH2−Pmes2 phosphane to the CH2CH2−
P(O)mes2 phosphine oxide might be the initial step in the
overall reaction of the P/B/P FLPs 11 with nitric oxide. We
were able to confirm that experimentally. We exposed the FLP
11a to 2.2 molar equiv of NO gas at −78 °C. The mixture was
slowly warmed to rt and stirred for some time to give a
practically quantitative conversion to the P/B/PO FLP product
25a (see Scheme 7). From the reaction mixture, we isolated
compound 25a in 82% yield. Single crystals of 25a were
obtained from dichloromethane/pentane by the diffusion
method.
B1−C2−C1−P1
C2−C1−P1−B1
C2−C3−C4−P2
−3.7(3)
3.0(2)
−7.9(2)
6.1(2)
−1.4(2)
1.1(2)
−173.0(3)
171.5(2)
−175.8(2)
a
b
Angles and dihedral angles in deg; bond lengths in Å. PS.
13.4 of the central PPh2−B(C6F5)2 unit with a 10B NMR signal
at δ −6.5 (11a: δ 14.0 (PPh2), δ −6.3 B(C6F5)2). The terminal
P(O)mes2 group gives rise to a 31P NMR signal at δ 37.4.
However, compound 25a shows temperature-dependent 31P
NMR spectra (see Figure 13). Below −10 °C, we see a 1:1
intensity pair of new 31P NMR signals appear along with the
PPh2/P(O)mes2 pair of 25a that rapidly increase with
decreasing temperature. At −80 °C, the new equilibrium
component (26a) is the major product (25a/26a ∼ 1:3.5 at
−80 °C). From a van’t Hoff plot, we have determined the
thermodynamic parameters ΔH = −4.5 kcal mol−1 and ΔS0 =
−21.0 cal K−1 mol−1 for the 25a ⇄ 26a equilibrium.
In the crystal, compound 25a shows an intact central four-
membered heterocyclic FLP structure (similar to the starting
material 11a), with a marked P···B interaction. A pendant
−CH2CH2− unit is attached at the unsaturated C1C2 unit of
the FLP core that has the P(O)mes2 phosphine oxide
functional group at its end (see Figure 12 and Table 5).
In solution, the NMR features of the four-membered core
structure of compound 25a are quite similar to those of its
precursor 11a. Compound 25a shows a 31P NMR signal at δ
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Scheme 8. Gibbs Free Energies (ΔG, kcal mol−1) at 298 K,
in Benzene, DFT Calculated
Figure 13. Temperature-dependent 31P NMR spectra of the 25a ⇄
26a equilibrium (in d8-toluene).
elemental sulfur. We isolated the P(S)mes2-substituted FLP
28a as a colorless solid in 73% yield. It was shown by X-ray
diffraction to contain the usual four-membered core structure
with a rather long P1−B1 linkage (see Scheme 9, Table 5, and
We assume that compound 26a is the B−O−P bonded
isomer of 25a.25 This is supported by the characteristic 31P
NMR signal of the P(O)mes2 resonance of 26a at 62.9 that is
similar to the corresponding B−O−Pmes2 signal of the model
compound 9 (31P: δ 62.4 (P(O)mes2); see Scheme 2). The 25a
⇄ 26a situation was modeled by DFT calculation. This
revealed that the formation of the B−O isomer 26a is only
slightly endothermic in solution (benzene) at ambient
temperature (ΔΔG (25a/26a) calcd. (298 K) = 5.8 kcal
mol−1, for further details of the DFT analysis see ref 26 and the
Supporting Information).
Scheme 9
The P(o-tolyl)2-containing P/B/P FLP 11b reacted analo-
gously with NO (2.2 molar equiv) under our carefully
controlled reaction conditions. The product 25b (see Scheme
7) was isolated in 85% yield as a colorless solid. It was also
characterized by X-ray diffraction (for details see Table 5 and
the Supporting Information). In solution, compound 25b also
equilibrates with its isomer 26b. However, in this case, the 25b
⇄ 26b equilibrium lies markedly on the 25b side. At −80 °C,
we have monitored compound 25b as the major component by
31P NMR spectroscopy (δ 18.3 (P(o-tolyl)2), δ 37.8 (P(O)-
mes2)) and the minor compound 26a (δ −12.2 (P(o-tolyl)2), δ
+62.4 (P(O)mes2)) in a 25b/26b ratio of approximately 7:1.
These results show that Pmes2 oxidation by the typical reaction
of a free phosphane with two molar equivalents of NO
(probably with formation of N2O) is initiating the overall
reaction sequence of the formation of the P/B/PO FLPNO
radicals 14 from the P/B/P FLPs 11. The presence of the
pendant phosphine oxide donor seems essential for activating
the FLP Ar2P···B(C6F5)2 unit. We see this in our experiment of
the formation of 26 from 25 (see Schemes 7 and 8).
Figure 14. View of the molecular structure of compound 28a (thermal
ellipsoids are shown with 30% probability).
The possible subsequent reaction course has been studied by
DFT calculation (see Scheme 8 and the Supporting
Information).26 The B−O−Pmes2 coordination generates a
free PPh2 functionality available for the phosphane reaction
with NO. Formation of the respective Ph2P−NO product
27a is energetically slightly “uphill”, but the subsequent
trapping of the coordinated NO by the adjacent borane is
strongly exergonic (see Scheme 8). This final step in the
formation may take place by a SNi-type mechanism, as it is
schematically depicted in Scheme 7, or stepwise with reversible
opening of the phosphine oxide borane coordination.
Figure 14). In solution, compound 28a shows heteronuclear
magnetic resonance signals at δ −7.0 (10B), δ 42.8 (31P:
P(S)mes2), δ 13.6 (31P: PPh2), and δ −10.8 (29Si). The
corresponding P(O)mes2 FLPs 25a, b ⇄ 26a, b react readily
with NO to form the corresponding FLPNO radical systems
14a, b. In contrast, the P(S)mes2-substituted analogue 28a did
not react with nitrogen monoxide under our typical reaction
conditions.
Eventually, we have also prepared the respective phosphane
sulfide product 28a by treatment of the P/B/P FLP 11a with
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slightly yellow solution was stirred at 70 °C for overnight. 31P NMR
experiments indicated complete conversion on the next day. After all
volatiles were removed in vacuo, the obtained residue was suspended
in n-pentane (ca. 5 mL) and sonicated for 10 min. Then, the
supernatant was taken off, and the remaining solid was washed with n-
pentane (2 × 5 mL).
CONCLUSIONS
■
Our study has shown that the 1,1-carboboration reaction has
probably become a versatile tool for modification of FLPs. We
have seen that the reaction of the simple parent C2-bridged
FLP mes2P-CH2CH2−B(C6F5)2 (3) with the trimethylsilyl-
substituted alkyne 5 gave the ring enlarged C3-bridged new FLP
6. Formally, the substituted exomethylene containing system 6
contains the vinylidene isomer of the acetylene inserted into
the B−C bond;14 however, this reaction is likely to be
mechanistically different, featuring an established pathway of
the 1,1-carboboration reaction.7,8 The easy synthetic availability
of systems like 6 might eventually become significant, since
some alkenylborane derivatives were recently shown to be
susceptible to nucleophilic attack at an activated carbon
position to give borata-alkenes,27 which might eventually add
new aspects to FLP chemistry in suitably designed examples.
We have shown that the 1,1-carboboration reaction of 3 with
phosphanyl-substituted silylacetylenes readily takes place. The
CH2CH2−Pmes2 group becomes transferred to carbon in this
reaction, and we have achieved an easy entry to P/B/P FLPs
11. In contrast to the simpler C3-bridged P/B FLPs 6 that
proved to be active, for example, in H2 cleavage, the P/B/P
FLPs are much less reactive. However, they undergo a
remarkable reaction sequence with nitrogen monoxide, using
the pendant CH2CH2−Pmes2 functionality for generating an
activation principle for the adjacent dormant P/B FLP in situ.
This weakening of the deactivating P···B interaction by a
pendant activator group is quite a unique feature. This
indicated to us that remote activation of FLP systems might
become a useful tool in FLP chemistry.
Compound 11a. Drying of the remaining solid in vacuo gave 11a
(690 mg, 0.75 mmol, 75%) as a colorless solid. mp: 121 °C. Anal.
Calcd for C49H45BF10P2Si: C, 63.64; H, 4.91. Found: C, 64.09; H, 5.07.
1H NMR (500 MHz, C6D6, 299 K): δ = 7.25 (4H), 6.90 (2H), 6.83
4
(4H)(Ph), 6.65 (dm, JPH = 2.7 Hz, 4H, m-mes), 3.05 (m, 2H, 
CH2), 2.76 (m, 2H, PCH2), 2.32 (s, 12H, o-CH3mes), 2.06 (s, 6H, p-
2
CH3mes), 0.02 (s, JSiH = 6.6 Hz, 9H, SiCH3). 13C{1H} NMR (126
2
MHz): δ = 209.4 (br, CB), 142.0 (d, JPC = 13.5 Hz, o-mes) 137.7
(p-mes), 136.6 (d, 1JPC = 27.3 Hz, CSi), 133.1 (d, 1JPC = 23.0 Hz, i-
2
4
mes), 132.0 (d, JPC = 9.1 Hz, o-Ph), 131.5 (d, JPC = 2.8 Hz, p-Ph),
4
3
130.5 (d, JPC = 2.8 Hz, m-mes), 128.8 (d, JPC = 10.2 Hz, m-Ph),
1
3
2
127.4 (d, JPC = 37.9 Hz, i-Ph), 37.9 (dd, JPC = 52.1 Hz, JPC = 23.1
Hz, CH2), 27.4 (d, 1JPC = 17.0 Hz, PCH2), 23.0 (d, 3JPC = 13.6 Hz,
o-CH3), 20.8 (p-CH3), −0.1 (d, 3JPC = 2.0 Hz, 1JSiC = 52.6 Hz, SiCH3).
19F NMR (470 MHz): δ = −129.6 (o), −157.7 (p), −163.9 (m),
[Δδ19Fm,p = 6.2].10B{1H} NMR (54 MHz): δ = −6.3. 31P{1H} NMR
5
(202 MHz): δ = 14.0 (PPh2), −21.0 (d, JPP = 6.3 Hz, Pmes2).
29Si{1H} DEPT (99 MHz): δ = −11.4 (d, JPSi = 6.5 Hz).
2
Compound 11b. The combined washing solutions were kept at
−40 °C for overnight, and the obtained precipitate was collected. Both
the dried precipitate and the previously isolated solid gave compound
11b (773 mg, 0.8 mmol, 81%) as a colorless solid. mp: 81 °C. Anal.
Calcd for C51H49BF10P2Si: C, 64.29; H, 5.18. Found: C, 64.26; H, 5.18.
1H NMR (600 MHz, tol-d8, 299 K): δ = 7.14 (2H), 6.84 (2H), 6.69
4
(2H), 6.68 (2H)(otol), 6.61 (d, JPH = 2.6 Hz, 4H, m-mes), 2.91 (br,
2H, CH2), 2.78 (br, 2H, PCH2), 2.29 (s, 12H, o-CH3mes), 2.20 (br,
6H, o-CH3o‑tol), 2.01 (s, 6H, p-CH3mes), −0.11 (s, JSiH = 6.6 Hz, 9H,
2
SiCH3). 13C{1H} NMR (151 MHz): δ = 206.2 (br, CB), 142.2 (d,
2
2JPC = 11.9 Hz, o-otol), 141.9 (d, JPC = 13.4 Hz, o-mes), 137.7 (p-
EXPERIMENTAL SECTION
■
1
2
mes), 137.2 (d, JPC = 29.0 Hz, CSi), 133.9 (br d, JPC = 5.6 Hz,
1,1-Carboboration Reactions: Preparation of Compounds 6,
11a, b, and 17. In Situ Generation of Compound 3. HB(C6F5)2 (1
equiv) and dimesityl(vinyl)phosphane (1 equiv) were both dissolved
in the respective solvent, and then the solutions were combined at rt
and stirred for ∼15 min at this temperature. Subsequently, the solution
was used for further reactions.
o′-otol), 133.3 (d, JPC = 23.1 Hz, i-mes), 131.6 (br d, JPC = 8.0 Hz,
m-otol), 131.5 (br d, 4JPC = 2.6 Hz, p-otol), 130.6 (d, 3JPC = 2.6 Hz, m-
mes), 126.5 (d, 1JPC = 35.7 Hz, i-otol), 126.1 (d, 3JPC = 8.4 Hz, m′-otol),
118.3 (br, i-C6F5), 38.0 (dd, JPC = 50.5 Hz, JPC = 23.3 Hz, CH2), 27.0
(d, 1JPC = 18.7 Hz, PCH2), 23.3 (d, 3JPC = 13.4 Hz, o-CH3mes), 22.2 (br
1
3
d, JPC = 5.2 Hz, o-CH3o‑tol), 20.8 (p-CH3mes), −0.1 (d, JPC = 1.8 Hz,
1JSiC = 53.1 Hz, SiCH3). 19F NMR (564 MHz): δ = −128.7 (o),
−157.5 (p), −163.6 (m), [Δδ19Fm,p = 6.1]. 31P{1H} NMR (243 MHz):
3
3
Synthesis of Compound 6. Compound 3 was generated in situ as
described above (HB(C6F5)2: 34.6 mg, 0.1 mmol; dimesityl(vinyl)-
phosphane: 29.6 mg, 0.1 mmol; solvent: C6D6) and combined with
trimethyl(phenylethynyl)silane (5, 17.3 mg, 0.1 mmol, 1 equiv) at
room temperature. The resulting solution was heated to 60 °C
overnight and then investigated by NMR spectroscopic experiments.
Then, all volatiles were removed in vacuo, and the residue dried in
vacuo that gave compound 6 as a yellow solid (60.0 mg, 0.07 mmol,
73%). Anal. Calcd for C43H40BF10PSi: C, 63.24; H, 4.94. Found: C,
δ = 18.5 (P(otol)), −19.5 (d, 5JPP = 6.8 Hz, Pmes). 10B{1H} NMR (64
MHz,): δ = −2.3. 29Si{1H} DEPT (119 MHz): δ = −11.4 (d, JPSi
=
2
6.1 Hz).
X-ray Crystal Structure Analysis of Compounds 11a, b.
Compound 3 was generated in situ as described above (HB(C6F5)2:
69.2 mg, 0.2 mmol; dimesityl(vinyl)phosphane: 59.3 mg, 0.2 mmol;
solvent: n-pentane). Then, a solution of the respective diaryl-
((trimethylsilyl)ethynyl)phosphane (10a: 56.5 mg, 0.2 mmol, 1
equiv; 10b: 62.0 mg, 0.2 mmol, 1 equiv) in n-pentane (∼2 mL) was
added, and the resulting slightly yellow solution was stirred in an
autoclave at 70 °C for overnight. After the solution was cooled to rt, it
was stored at −40 °C for 2 h, resulting in a colorless precipitate. The
supernatant was taken off and stored at −40 °C for 2 days, giving 120
mg (0.13 mmol, 65%) of crystalline material, which was identified as
pure 11a by NMR experiments (11b: 105 mg, 0.14 mmol, 71%). The
obtained crystals were suitable for the X-ray crystal structure analysis.
Synthesis of Compound 17. Compound 10a (113 mg, 0.4 mmol, 1
equiv) and PhCH2CH2B(C6F5)2 (16, 180 mg, 0.4 mmol, 1 equiv)
were dissolved separately in toluene (each ca. 2 mL). The solutions
were combined at rt and then heated to 70 °C for 2 days. After the
solution was cooled to rt, all volatiles were removed in vacuo to give
compound 17 (240 mg, 0.33 mmol, 82%) as a yellow solid. Anal.
Calcd for C37H28BF10PSi: C, 60.67; H, 3.85. Found: C, 60.26; H, 3.96.
NMR characterization of compound 17: An analogous reaction (0.1
mmol reaction size) was carried out in C6D6. After heating the sample
1
63.27; H, 5.34. H NMR (500 MHz, C6D6, 299 K): δ = 7.22 (2H),
4
7.06 (1H), 6.90 (2H)(Ph), 6.40 (d, JPH = 3.1 Hz, 4H, m-mes), 2.61
(m, 2H, CH2), 2.43 (m, 2H, PCH2), 1.90 (s, 6H, p-CH3mes), 1.89 (s,
12H, o-CH3mes), −0.14 (s, 2JSiH = 6.4 Hz, SiCH3). 13C{1H} NMR (126
MHz): δ = 161.4 (br, CB), 149.1 (d, 5JPC = 0.9 Hz, i-Ph), 148.3 (d,
4JPC = 14.9 Hz, CSi), 142.1 (d, 1JPC = 8.4 Hz, o-mes), 140.3 (d, 4JPC
3
1
= 2.3 Hz, p-mes), 130.8 (d, JPC = 8.0 Hz, m-mes), 128.7 (d, JPC
=
34.2 Hz, i-mes)1, 128.6, 127.7, 125.3 (Ph), 36.4 (d, 2JPC = 11.9 Hz, 
1
3
CH2), 26.9 (d, JPC = 26.1 Hz, PCH2), 23.8 (d, JPC = 5.7 Hz, o-
CH3mes), 20.4 (d, JPC = 1.0 Hz, p-CH3mes), 1.1 (SiCH3). 19F NMR
5
(470 MHz): δ = −123.3 (o), −156.9 (p), −164.1 (m), [Δδ19Fm,p
=
7.2]. 11B{1H} NMR (160 MHz): δ = 4.7. 31P{1H} NMR (202 MHz):
δ = 26.5. 29Si{DEPT} NMR (99 MHz): δ = −9.5.
Synthesis of Compound 11a, b. General Procedure. Compound 3
was generated in situ as described above (HB(C6F5)2: 346 mg, 1.0
mmol; dimesityl(vinyl)phosphane: 296 mg, 1.0 mmol; solvent:
toluene). Then, a solution of the respective diaryl((trimethylsilyl)-
ethynyl)phosphane (10a: 282 mg, 1.0 mmol, 1 equiv; 10b: 310 mg,
1.0 mmol, 1 equiv) in toluene (ca. 2 mL) was added, and the resulting
9023
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Article
1
3
for 2 days at 70 °C and subsequent cooling to rt, the solution was
PhP), 122.3 (d, JPC = 47.5 Hz, CSi), 59.0 (d, JPC = 37.8 Hz, C1),
characterized by NMR experiments, which showed complete
44.1 (d, 3JPC = 23.7 Hz, CH2), 35.0 (PhCH2), 32.9 (d, 4JPC = 2.0 Hz,
3
1
1
C2), 20.9 (C3), 14.1 (C4), 1.5 (d, JPC = 2.0 Hz, JSiC = 53.7 Hz,
SiCH3). 19F NMR (470 MHz): δ = −128.5 (br m, 2F, o), −160.5 (t,
3JFF = 20.2 Hz, 1F, p), −165.3 (m, 2F, m) (C6F5), [Δδ19Fm,p = 4.8].
10B{1H} NMR (54 MHz): δ = −14.4 (d, 2J31P10B = 15.9 Hz). 31P{1H}
conversion of the starting materials to compound 17. H NMR (500
MHz, C6D6, 299 K): δ = 7.34 (4H), 6.94 (2H), 6.88 (4H)(PhP), 7.26
(2H), 7.16 (2H), 7.06 (1H)(Ph), 3.37 (m, 2H, CH2), 2.88 (m, 2H,
PhCH2), 0.02 (s, 2JSiH = 6.7 Hz, SiCH3). 13C{1H} NMR (126 MHz): δ
1
2
= 208.6 (br, CB), 141.8 (i-Ph), 137.9 (d, JPC = 27.7 Hz, CSi),
NMR (202 MHz): δ = 22.7 (q 1:1:1:1, J31P11B = 50.6 Hz). 29Si{1H}
2
132.1 (d, 2JPC = 9.1 Hz, o-PhP), 131.5 (d, 4JPC = 3.0 Hz, p-PhP), 129.0
(m-Ph), 128.8 (d, 3JPC = 10.2 Hz, m-PhP), 128.4 (o-Ph), 126.9 (d, 1JPC
= 38.9 Hz, i-PhP), 126.5 (p-Ph), 43.0 (d, 3JPC = 49.3 Hz, CH2), 36.1
DEPT (99 MHz): δ = −9.1 (d, JPSi = 17.7 Hz).
Reactions of Compounds 6 and 11a with Dihydrogen.
Synthesis of Compound 8. Compounds 3 and 6 were generated in
situ as described above (HB(C6F5)2: 69.2 mg, 0.2 mmol; dimesityl-
(vinyl)phosphane: 59.2 mg, 0.2 mmol; compound 5: 34.9 mg, 0.2
mmol; solvent: benzene). Then, the evacuated flask was filled with H2
gas (1.5 bar). Subsequently, the solution was stirred overnight at an H2
atmosphere. Then, all volatiles were removed in vacuo, and the
resulting solid was washed with n-pentane (5 × 5 mL). After drying in
vacuo, compound 8 was isolated as a colorless solid (80 mg, 0.1 mmol,
49%). Slow diffusion of n-pentane into a solution of compound 8 in
dichloromethane at −40 °C gave crystals that were suitable for the X-
ray crystal structure analysis. mp: 146 °C. Anal. Calcd for
C43H42BF10PSi: C, 63.09; H, 5.17. Found: C, 62.12; H, 5.13. 1H
NMR (500 MHz, CD2Cl2, 299 K): δ = 7.14 (2H), 6.99 (1H), 6.92
4
1
(d, JPC = 1.9 Hz, PhCH2), 0.2 (d, J = 2.3 Hz, JSiC = 53.0 Hz,
SiCH3).19F NMR (470 MHz): δ = −129.6 (o), −157.3 (p), −163.8
(m), [Δδ19Fm,p = 6.5].10B{1H} NMR (54 MHz): δ = −6.2. 31P{1H}
NMR (202 MHz,): δ = 14.4. 29Si{1H} DEPT (99 MHz): δ = −11.3 (d,
2JPSi = 6.5 Hz).
Reactions of Compounds 11a and 17 with Isocyanide.
Caution! Many isocyanides are toxic compounds that need to be
handled with due care.
Synthesis of Compound 12. Compound 3 and compound 11a
were generated in situ as described above (HB(C6F5)2: 69.2 mg, 0.2
mmol; dimesityl(vinyl)phosphane: 59.3 mg, 0.2 mmol; compound
10a: 56.2 mg, 0.2 mmol; solvent: toluene). Then, n-butylisocyanide
(21.0 μL, 0.2 mmol, 1 equiv) was added, and the solution was stirred
for 1 h at rt. Subsequently, all volatiles were removed in vacuo. The
obtained solid was taken up in n-pentane (∼2 mL) and stored at −40
°C for 2 days. The white precipitate was collected and taken up in n-
pentane (∼2 mL). Slow evaporation of the solvent at −40 °C gave
compound 12 (80 mg, 0.08 mmol, 40%) as colorless crystals. Crystals
obtained in this way were suitable for the X-ray crystal structure
analysis. Anal. Calcd for C54H54BF10NP2Si: C, 64.35; H, 5.40; N, 1.39.
Found: C, 63.87; H, 5.34; N, 1.23. 1H NMR (600 MHz, CD2Cl2, 299
K): δ = 7.60 (2H), 7.49 (4H), 7.48 (4H)(Ph), 6.71 (d, 4JPH = 2.4 Hz,
4H, m-mes), 3.28 (m, 2H, 1-H), 2.60 (m, 2H, PCH2), 2.48 (m, 2H, 
CH2), 2.20 (s, 6H, p-CH3mes), 2.11 (s, 12H, o-CH3mes), 1.35 (m, 2H,
4
1
(2H)(Ph), 6.96 (d, JPH = 4.3 Hz, 4H, m-mes), 6.73 (dt, JPH = 468.1
3
Hz, JHH = 7.0 Hz, PH), 3.51 (br, 1H, BH), 2.35 (m, 2H, CH2),
2.33 (m, 2H, PCH2), 2.31 (s, 6H, p-CH3mes), 2.11 (s, 12H, o-CH3mes),
−0.12 (s, JSiH = 6.6 Hz, SiCH3). 13C{1H} NMR (126 MHz): δ =
2
165.0 (br, CB), 149.3 (i-Ph), 147.3 (br, CSi), 146.4 (d, 4JPC = 3.0
Hz, p-mes), 143.1 (d, 2JPC = 10.3 Hz, o-mes), 132.2 (d, 3JPC = 11.2 Hz,
1
m-mes), 128.3, 128.2, 124.5 (Ph), 111.7 (d, JPC = 80.6 Hz, i-mes),
31.5 (br, CH2), 25.0 (d, 1JPC = 37.8 Hz, PCH2), 22.1 (d, 3JPC = 7.0
Hz, o-CH3mes), 21.4 (d, 5JPC = 1.2 Hz, p-CH3mes), 1.3 (1JSiC = 52.0 Hz,
SiCH3). 19F NMR (470 MHz): δ = −132.1 (o), −164.4 (p), −166.7
(m), [Δδ19Fm,p = 2.3]. 11B NMR (160 MHz): δ = −19.6 (d, 1JBH ∼ 85
Hz). 31P NMR (202 MHz): δ = −11.6 (d, JPH ∼ 468 Hz). 29Si{1H}
1
DEPT (99 MHz): δ = −9.9.
3
2-H), 1.11 (m, 2H, 3-H), 0.74 (t, JHH = 7.5 Hz, 3H, 4-H), 0.03 (s,
Synthesis of Compound 13. Compounds 3 and 11a were
generated in situ as described above (HB(C6F5)2: 69.2 mg, 0.2
mmol; dimesityl(vinyl)phosphane: 59.3 mg, 0.2 mmol; compound
10a: 56.2 mg, 0.2 mmol; solvent: toluene). Then, B(C6F5)3 (102.4 mg,
0.2 mmol, 1 equiv) in toluene (∼5 mL) was added, and the evacuated
flask was filled with H2 gas (1.5 bar). After the reaction solution was
stirred at rt for overnight, all volatiles were removed in vacuo. The
obtained residue was washed with n-pentane (2 × ca. 5 mL) and dried
in vacuo to give compound 13 as a colorless solid (251 mg, 0.17
mmol, 87%). Single crystals suitable for the X-ray crystal structure
analysis were obtained by diffusion of n-pentane into a saturated
solution of 13 in dichloromethane at −40 °C. Anal. Calcd for
2JSiH = 6.6 Hz, SiCH3). 13C{1H} NMR (151 MHz): δ = 219.1 (br, 
CB), 193.6 (br t (1:1:1), J ∼ 45 Hz, CN), 142.0 (d, 2JPC = 13.3 Hz,
o-mes), 138.0 (p-mes), 133.4 (d, 2JPC = 9.0 Hz, o-Ph), 133.3 (d, 4JPC
=
3.1 Hz, p-Ph), 132.7 (d, 1JPC = 22.4 Hz, i-mes), 130.1 (d, 3JPC = 3.0 Hz,
3
1
m-mes), 129.3 (d, JPC = 11.7 Hz, m-Ph), 124.0 (d, JPC = 73.8 Hz, i-
Ph), 58.6 (d, 3JPC = 37.2 Hz, C1), 39.4 (dd, JPC = 24.6 Hz, JPC = 23.0
Hz, CH2), 32.8 (d, JPC = 2.0 Hz, C2), 26.3 (d, JPC = 15.5 Hz,
4
1
PCH2), 22.9 (d, JPC = 13.3 Hz, o-CH3mes), 20.9 (C3), 20.8 (p-
3
CH3mes), 14.0 (C4), 1.0 (d, 3JPC = 2.0 Hz, 1JSiC = 53.1 Hz, SiCH3). 19
F
NMR (564 MHz): δ = −129.0 (o), −160.3 (p), −165.3 (m), [Δδ19Fm,p
= 5.0]. 11B{1H} NMR (192 MHz): δ = −14.6 (d, 2J31P11B = 49.4 Hz).
31P{1H} NMR (243 MHz): δ = 22.1 (q 1:1:1:1, J31P11B = 49.4 Hz,
PPh2), −21.1 (d, 5JPP = 4.7 Hz, Pmes2).29Si{1H} DEPT (119 MHz): δ
1
C67H47B2F25P2Si: C, 55.93; H, 3.29. Found: C, 56.14; H, 3.26. H
NMR (500 MHz, CD2Cl2, 299 K): δ = 7.74 (dt, 1JPH = 475.0 Hz, 3JHH
= 7.1 Hz, 1H, PH), 7.53 (2H), 7.39 (4H), 7.20 (4H)(Ph), 7.10 (d,
4JPH = 4.8 Hz, m-mes), 3.58 (br q 1:1:1:1, 1JBH ∼ 90 Hz, 1H, BH), 3.05
(m, 2H, CH2), 2.88 (m, 2H, PCH2), 2.36 (s, 6H, p-CH3mes), 2.29 (s,
2
= −9.3 (d, JPSi = 17.4 Hz).
Synthesis of Compound 18. Compound 17 was generated in situ
as described above (compound 10a: 28.4 mg, 0.1 mmol;
PhCH2CH2B(C6F5)2 (16): 45.1 mg, 0.1 mmol). Then, n-butylisocya-
nide (11 μL, 0.1 mmol, 1 equiv) was added. The solution was stirred
overnight at rt, and all volatiles were removed in vacuo. The obtained
solid was taken up in n-pentane (∼5 mL) and stored at −40 °C
overnight. The precipitate was collected and identified as compound
18 (50 mg, 0.06 mmol, 1 equiv). Single crystals suitable for the X-ray
crystal structure analysis were obtained by slow evaporation of a
saturated solution of 18 in n-pentane at −40 °C. Anal. Calcd for
C42H37BF10NPSi: C, 61.85; H, 4.57; N, 1.72. Found: C, 61.27; H,
4.74; N, 1.77. 1H NMR (500 MHz, CD2Cl2, 299 K): δ = 7.64 (m, 2H,
p-PhP), 7.60 (m, 4H, o-PhP), 7.53 (m, 4H, m-PhP), 7.23 (m, 2H, m-
Ph), 7.15 (m, 1H, p-Ph), 6.97 (m, 2H, o-Ph), 3.41 (m, 2H, 1-H), 2.92
(br m, 2H, CH2), 2.65 (m, 2H, PhCH2), 1.41 (m, 2H, 2-H), 1.17
(m, 2H, 3-H), 0.78 (t, 3JHH = 7.4 Hz, 3H, 4-H), 0.17 (s, 2JSiH = 6.6 Hz,
9H, SiCH3). 13C{1H} NMR (126 MHz): δ = 218.0 (br, CB), 194.2
(br m, CN), 142.5 (d, J = 0.7 Hz, i-Ph), 133.6 (d, 2JPC = 8.9 Hz, o-
PhP), 133.4 (d, 4JPC = 3.0 Hz, p-PhP), 129.3 (d, 3JPC = 11.6 Hz, m-PhP),
128.9 (m-Ph), 128.3 (o-Ph), 126.3 (p-Ph), 124.2 (d, 1JPC = 73.8 Hz, i-
12H, o-CH3mes), 0.06 (s, JSiH = 6.6 Hz, 9H, SiCH3). 13C{1H} NMR
2
4
(126 MHz): δ = 199.7 (br, CB), 147.7 (d, JPC = 3.0 Hz, p-mes),
2
1
143.4 (d, JPC = 10.4 Hz, o-mes), 142.4 (d, JPC = 27.6 Hz, CSi),
132.7 (d, 3JPC = 11.6 Hz, m-mes), 132.5 (d, 4JPC = 3.0 Hz, p-Ph), 132.2
2
3
(d, JPC = 9.3 Hz, o-Ph), 129.4 (d, JPC = 10.6 Hz, m-Ph), 125.6 (d,
1JPC = 41.6 Hz, i-Ph), 109.9 (d, JPC = 82.3 Hz, i-mes), 33.5 (d, JPC
=
1
1
3
56.0 Hz, CH2), 23.6 (d, JPC = 56.0 Hz, PCH2), 22.1 (d, JPC = 7.5
Hz, o-CH3mes), 21.4 (d, JPC = 1.3 Hz, p-CH3mes), −0.2 (d, JPC = 2.0
4
3
Hz, JSiC = 53.1 Hz, SiCH3). 19F NMR (470 MHz): δ = −130.5 (o),
1
−156.5 (p), −163.6 (m) (B(C6F5)2), [Δδ19Fm,p = 7.1] −134.0 (o),
−164.8 (p), −167.6 (m) (B(C6F5)3), [Δδ19F = 2.8]. 11B NMR (160
MHz): δ = −7.4 (B(C6F5)2), −25.4 (d, JBH ∼ 90 Hz, B(C6F5)3). 31P
1
1
NMR (202 MHz): δ = 13.1 (PPh2), −12.2 (br d, JPH ∼ 476 Hz,
Pmes2). 29Si{1H} DEPT (99 MHz): δ = −10.2 (d, JPSi = 5.1 Hz).
2
Reactions of Compounds 6 and 11a, b with Nitric Oxide.
Caution! NO is a toxic gas that must to be handled with due care.
Synthesis of Compound 9. Compounds 3 and 6 were generated in
situ as described above (HB(C6F5)2: 69.2 mg, 0.2 mmol; dimesityl-
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Journal of the American Chemical Society
Article
(vinyl)phosphane: 59.2 mg, 0.2 mmol; compound 5: 34.9 mg, 0.2
mmol; solvent: benzene). Then, the evacuated flask was filled with NO
gas (1.5 bar). After 2 h stirring at rt, all volatiles were removed in
vacuo. The resulting solid was washed with n-pentane (3 × 5 mL) to
give compound 9 (102 mg, 0.12 mmol, 61%) as a slightly yellow solid.
Single crystals suitable for the X-ray crystal structure analysis were
obtained by diffusion of n-pentane into a solution of compound 9 at
−40 °C. mp: 252 °C. Anal. Calcd for C43H40BF10OPSi: C, 62.03; H,
4.84. Found: C, 61.97; H, 5.06. 1H NMR (500 MHz, CD2Cl2, 299 K):
137.8 (d, 1JPC = 24.8 Hz, CSi)1 132.0 (d, 2JPC = 9.8 Hz, o-Ph), 131.4
(m, m-mes), 131.4 (m, p-Ph), 130.7 (br d, 1JPC ∼ 90 Hz, i-mes), 128.8
1
(m-Ph), 127.7 (i-Ph), 35.1 (d, JPC = 62.0 Hz, PCH2), 33.3 (d, JPC
=
51.3 Hz, CH2), 22.7 (br d, JPC = 3.2 Hz, o-CH3mes), 20.7 (br, p-
CH3mes), 0.2 (br, SiCH3). 19F NMR (564 MHz,): δ = −129.5 (o),
−157.7 (p), −163.8 (m), [Δδ19Fm,p = 6.1]. 10B{1H} NMR (64 MHz,):
δ = −6.5. 31P{1H} NMR (243 MHz): δ = 37.4 (Pmes2), 13.4 (PPh2).
29Si{1H} DEPT (119 MHz): δ = −10.8.
3
Compound 25b. Mp: 203 °C Anal. Calcd for C51H49BF10NOP2Si:
C, 63.23; H, 5.10 Found: C, 63.53; H, 5.27. 1H NMR (500 MHz, tol-
d8, 299 K): δ = 7.17 (2H), 6.85 (2H), 6.71 (2H), 6.69 (2H)(otol), 6.55
4
δ = 7.37 (2H), 7.20 (1H), 7.04 (2H)(Ph), 6.89 (br d, JPH = 4.3 Hz,
4H, m-mes), 2.76 (br m, 2H, PCH2), 2.65 (br dm, 3JPH = 25.8 Hz, 2H,
CH2), 2.38 (br, 12H, o-CH3mes), 2.33 (m, 6H, p-CH3mes), −0.36 (s,
2JSiH = 6.5 Hz, SiCH3). 13C{1H} NMR (126 MHz): δ = 160.1 (br, 
CB), 149.0 (i-Ph), 144.2 (br, CSi), 144.0 (d, 4JPC = 2.9 Hz, p-mes),
4
(d, JPH = 3.2 Hz, 4H, m-mes), 3.29 (br, 2H, CH2), 2.66 (m, 2H,
PCH2), 2.39 (s, 12H, o-CH3mes), 2.20 (br, 6H, o-CH3o‑tol), 1.94 (s, 6H,
p-CH3mes), 0.14 (s, JSiH = 6.6 Hz, 9H, SiCH3). 13C{1H} NMR (126
2
3
2
MHz): δ = 204.5 (br, CB), 142.1 (d, JPC = 11.4 Hz, o-otol), 141.4
142.7 (br, o-mes), 132.1 (d, JPC = 12.0 Hz, m-mes), 128.5, 128.3,
1
1
(d, 2JPC = 10.3 Hz, o-mes), 140.7 (p-mes), 139.1 (m, CSi), 133.9 (d,
2JPC = 5.6 Hz, o′-otol), 131.5 (m, m,p-otol), 131.5 (m, m-mes), 130.8
124.8 (Ph), 123.0 (br d, JPC = 103.2 Hz, i-mes), 29.7 (d, JPC = 57.0
Hz, PCH2), 29.0 (d, 2JPC = 6.3 Hz, CH2), 22.5 (br, o-CH3mes), 21.0
(p-CH3mes), 0.2 (1JSiC = 51.8 Hz, SiCH3). 19F NMR (470 MHz): δ =
−126.7 (o), −159.6 (p), −165.9 (m), [Δδ19Fm,p = 6.3]. 11B{1H} NMR
(160 MHz): δ = 0.0. 31P{1H} NMR (202 MHz): δ = 62.4. 29Si{1H}
DEPT (99 MHz): δ = −10.4.
1
3
(br d, JPC ∼ 90 Hz, i-mes), 126.6 (i-otol), 126.1 (d, JPC = 8.3 Hz,
m′-otol), 34.8 (d, JPC = 63.6 Hz, PCH2), 32.9 (d, JPC = 51.4 Hz, 
1
CH2), 22.9 (d, JPC = 3.9 Hz, o-CH3mes), 22.1 (br d, JPC = 5.8 Hz, o-
CH3o‑tol), 20.8 (d, 5JPC = 1.2 Hz, p-CH3mes), 0.1 (br, SiCH3). 19F NMR
3
3
(470 MHz,): δ = −128.6 (o), −157.4 (p), −163.6 (m), [Δδ19Fm,p
=
Synthesis of Compounds 14a, b. Compound 14a. Compounds 3
and 11a were generated in situ as described above (HB(C6F5)2: 208
mg, 0.6 mmol; dimesityl(vinyl)phosphane: 178 mg, 0.6 mmol;
compound 10a: 169 mg, 0.6 mmol; solvent: benzene). Then, the
evacuated flask was filled with NO gas (1.5 bar), and the solution was
stirred overnight. All volatiles were removed in vacuo, and the crude
product was washed with n-pentane (3 × 5 mL) and dried in vacuo to
give compound 14a (470 mg, 0.48 mmol, 81%) as a slightly green-blue
solid. Single crystals suitable for the X-ray crystal structure analysis
were obtained by slow evaporation of the solvent of a solution of 14a
in a mixture of benzene and n-pentane at room temperature. mp: 131
°C. Anal. Calcd for C49H45BF10NO2P2Si: C, 60.63; H, 4.67; N, 1.44.
Found: C, 60.28; H, 5.03; N, 1.33.
Compound 14b. Compound 11b (286 mg, 0.3 mmol, 1 equiv) was
dissolved in benzene (∼2 mL), and the evacuated flask was filled with
NO gas (1.5 bar). The reaction solution was stirred for overnight, and
then, all volatiles were removed in vacuo. The resulting solid was
washed with n-pentane (3 × 5 mL) and dried in vacuo to give
compound 14b (260 mg, 0.26 mmol, 87%) as a green solid. Single
crystals suitable for the X-ray crystal structure analysis were obtained
by diffusion of n-pentane into a saturated solution of 14b at −40 °C.
Anal. Calcd for C51H49BF10NO2P2Si: C, 61.33; H, 4.94; N, 1.08.
Found: C, 61.36; H, 5.11; N, 0.95.
Synthesis of Compounds 25a, b. General Procedure. Compound
11a (555 mg, 0.6 mmol, 1 equiv; 11b: 270 mg, 0.28 mmol, 1 equiv)
was dissolved in toluene (∼5 mL), and the solution was cooled to −78
°C. At this temperature, NO (30 mL, 1.3 mmol, 2.2 equiv; 11b: 14.0
mL, 2.2 equiv) was added slowly via a syringe directly into the solution
within ∼2 min. After that, the resulting solution was stirred for 30 min
at −78 °C, warmed to rt, and stirred at rt for 1 h (25b: the solution
was stirred at rt for overnight). The reaction process was controlled by
31P NMR experiments to indicate complete conversion to 25a (25b).
Then, all volatiles were removed in vacuo, n-pentane (∼10 mL) was
added to the residue, and the obtained suspension was sonicated for 5
min. The supernatant was taken off, and the solid was dried in vacuo
to give compound 25a (460 mg, 0.49 mmol, 82%; 25b: 180 mg, 0.24
mmol, 85%) as a colorless solid. Single crystals suitable for the X-ray
crystal structure analysis were obtained by diffusion of n-pentane into a
solution of compound 25a in dichloromethane at −40 °C. Single
crystals suitable for the X-ray crystal structure analysis of compound
25b were obtained by slow evaporation of a saturated solution of 25b
in C6D6 at rt.
6.2]. 31P{1H} NMR (202 MHz): δ = 37.4 (Pmes2), 18.3 (Potol2).
10B{1H} NMR (54 MHz): δ = −1.6. 29Si{1H} DEPT (99 MHz): δ =
2
−10.5 (d, JPSi = 7.5 Hz).
Synthesis of Compounds 15a, b. Compound 15a. Compound
25a (47.0 mg, 0.05 mmol, 1 equiv) was dissolved in toluene (∼2 mL),
NO gas (1.5 bar) was added to the evacuated flask, and it was stirred at
rt for overnight. At the next day, the gas phase was removed in vacuo,
and 1,4-cyclohexadiene (5 μL, 0.05 mmol, 1 equiv) was added. After
stirring for 2 h at rt, all volatiles were removed in vacuo. The residue
was washed with n-pentane (1 × ∼5 mL) and dried in vacuo to give
compound 15a (36.0 mg, 0.04 mmol, 74%) as a colorless solid. Single
crystals suitable for X-ray crystal structure analysis were obtained from
a saturated solution of compound 15a (stored in a flame-sealed NMR
tube) in CD2Cl2 after 3 days at rt. Decomp: 239 °C. Anal. Calcd for
C49H46BF10NO2P2Si: C, 60.57; H, 4.77; N, 1.44. Found: C, 60.58; H,
1
4.88; N, 1.16. H NMR (500 MHz, CD2Cl2, 299 K): δ = 7.72 (4H),
4
7.68 (2H), 7.55 (4H)(Ph), 6.78 (d, JPH = 3.2 Hz, 4H, m-mes), 4.31
(d, 3JPH = 5.1 Hz, NOH), 2.77 (m, 2H, CH2), 2.42 (m, 2H, PCH2),
2.24 (s, 6H, p-CH3mes), 2.21 (s, 12H, o-CH3mes), 0.06 (s, 9H, JSiH
=
2
6.5 Hz, SiCH3). 13C{1H} NMR (126 MHz): δ = 207.8 (br, CB),
2
4
141.2 (d, JPC = 9.9 Hz, o-mes), 141.1 (d, JPC = 2.3 Hz, p-mes),
134.12 (d, 2JPC = 10.1 Hz, o-Ph), 134.08 (d, 4JPC = 2.8 Hz, p-Ph), 131.3
(d, 3JPC = 10.9 Hz, m-mes), 130.1 (d, 1JPC = 92.8 Hz, i-mes), 129.2 (d,
3JPC = 12.1 Hz, m-Ph), 124.3 (d, 1JPC = 92.5 Hz, i-Ph), 122.7 (d, 1JPC
=
1
56.6 Hz, CSi), 34.9 (d, JPC = 65.7 Hz, PCH2), 31.8 (d, JPC = 26.1
Hz, CH2), 22.7 (d, 3JPC = 4.0 Hz, o-CH3mes), 20.9 (d, 5JPC = 1.1 Hz,
p-CH3mes), 0.8 (d, JPC = 2.7 Hz, JSiC = 53.6 Hz, SiCH3). 19F NMR
3
1
(470 MHz): δ = −130.8 (o), −160.4 (p), −164.8 (m), [Δδ19Fm,p
=
4.4]. 10B{1H} NMR (54 MHz): δ = −5.6. 31P{1H} NMR (202 MHz):
5
δ = 52.0 (PPh2), 38.9 (d, JPP = 1.9 Hz, Pmes2). 29Si{1H} DEPT (99
2
MHz): δ = −9.5 (d, JPSi = 24.2 Hz).
Compound 15b. Compound 14b (100 mg, 0.1 mmol, 1 equiv) was
dissolved in toluene (∼3 mL), and 1,4-cyclohexadiene (10 μL, 0.11
mmol, 1.1 equiv) was added at rt. The resulting solution was stirred for
2 h at rt, all volatiles were removed in vacuo, and n-pentane (∼5 mL)
was added to the residue. The solvent was immediately removed again
in vacuo, and the crude product was washed with n-pentane (∼5 mL)
to give 15b (70.0 mg, 0.9 mmol, 89%) as a colorless solid. Single
crystals suitable for X-ray crystal structure analysis were obtained by
slow evaporation of a saturated solution of 15b in CD2Cl2 at rt.
Decomp: 231 °C. Anal. Calcd for C51H50BF10NO2P2Si: C, 61.27; H,
5.04; N, 1.08. Found: C, 60.76; H, 5.01; N, 1.17. 1H NMR (600 MHz,
CD2Cl2, 299 K): δ = 7.67 (o′), 7.50 (p), 7.33 (m′), 7.32 (m) (each m,
each 1H, otol2), 7.56 (p), 7.42 (o′), 7.39 (m), 7.24 (m′) (each m, each
Compound 25a. Decomp: 171 °C. Anal. Calcd for
1
C49H45BF10NOP2Si: C, 62.56; H, 4.82 Found: C, 63.09; H, 5.20. H
NMR (600 MHz, tol-d8, 299 K): δ = 7.20 (4H), 6.87 (2H), 6.81
(4H)(Ph), 6.51 (d, 4JPH = 3.1 Hz, 4H, m-mes), 3.35 (m, 2H, CH2),
2.53 (m, 2H, PCH2), 2.31 (s, 12H, o-CH3mes), 1.95 (s, 6H, p-CH3mes),
o
4
3
1H, tol1), 6.80 (d, JPH = 3.0 Hz, 4H, m-mes1,2), 4.57 (d, JPH = 5.2
Hz, NOH), 3.11, 3.02 (each m, each 1H, CH2), 2.62 (s, 3H, o-
CH3o‑tol1), 2.43 (s, 3H, o-CH3 o‑tol2), 2.25 (s, 3H, p-CH3mes2), 2.24 (s,
2
0.09 (s, JSiH = 6.6 Hz, 9H, SiCH3). 13C{1H} NMR (151 MHz): δ =
2
207.7 (br, CB), 141.4 (br d, JPC = 9.5 Hz, o-mes), 140.6 (p-mes),
9025
dx.doi.org/10.1021/ja5028293 | J. Am. Chem. Soc. 2014, 136, 9014−9027

Journal of the American Chemical Society
Article
3H, p-CH3mes1), 2.20 (s, 6H, o-CH3mes1), 2.18 (m, 2H, PCH2), 2.16 (s,
B.S. is member of the Center for Multiscale Theory and
2
6H, o-CH3mes2), 0.07 (s, JSiH = 6.6 Hz, 9H, SiCH3). 13C{1H} NMR
Computation (CMTC), Universitat Munster, Corrensstr. 40,
̈
̈
2
(151 MHz): δ = 207.5 (br, CB), 145.4 (d, JPC = 8.9 Hz, o), 137.1
48149 Munster, Germany.
̈
2
4
3
(d, JPC = 14.9 Hz, o′), 134.4 (d, JPC = 3.0 Hz, p), 133.1 (d, JPC
=
10.8 Hz, m), 126.4 (d, 3JPC = 13.7 Hz, m′), 122.5 (d, 1JPC = 92.3 Hz, i)
(otol1), 143.7 (d, 2JPC = 6.2 Hz, o), 134.7 (d, 2JPC = 14.3 Hz, o′), 133.3
ACKNOWLEDGMENTS
■
4
3
3
(d, JPC = 2.7 Hz, p), 132.7 (d, JPC = 10.3 Hz, m), 125.8 (d, JPC
=
Finanical support from SusChemSys, the European Research
Council, and the Deutsche Forschungsgemeinschaft (DFG) is
gratefully acknowledged. The project “Sustainable Chemical
Synthesis (SusChemSys)” is cofinanced by the European
Regional Development Fund (ERDF) and the state of North
Rhine-Westphalia, Germany, under the Operational Pro-
gramme “Regional Competitiveness and Employment” 2007−
2013. T.H.W. thanks the U.S. National Science Foundation for
an EPR spectrometer (CHE-0840453) as well as the Petroleum
Research Fund (51971-ND3).
12.9 Hz, m′), 124.6 (d, 1JPC = 81.9 Hz, i) (otol2), 141.22, 141.17 (each
d, JPC = 2.7 Hz, p-mes1,2), 141.08 (d, JPC = 9.9 Hz, o-mes2), 141.04
4
2
(d, 2JPC = 9.9 Hz, o-mes1), 131.40, 131.39 (each d, 3JPC = 11.0 Hz, m-
mes1,2), 130.4 (d, JPC = 93.5 Hz, i-mes1),129.8 (d, JPC = 92.9 Hz, i-
1
1
mes2), 123.0 (d, JPC = 56.9 Hz, CSi), 36.7 (d, JPC = 62.9 Hz,
1
1
3
PCH2), 31.1 (d, JPC = 24.5 Hz, CH2), 24.3 (d, JPC = 1.9 Hz, o-
CH3o‑tol2), 22.9 (d, 3JPC = 4.0 Hz, o-CH3mes1), 22.7 (d, 3JPC = 4.0 Hz, o-
CH3mes2), 21.0, 21.0 (each d, JPC = 1.0 Hz, p-CH3mes1,2), 20.5 (m, o-
4
CH3o‑tol1), 0.9 (d, JPC = 2.8 Hz, JSiC = 53.1 Hz, SiCH3). 31P{1H}
NMR (243 MHz): δ = 53.3 (P(o-tol)2), 38.6 (d, 5JPP = 1.5 Hz, Pmes).
10B{1H} NMR (64 MHz): δ = −5.3. 29Si{1H} DEPT (119 MHz): δ =
−9.3 (d, 2JPSi = 23.6 Hz). 19F NMR (564 MHz): δ = −129.3 (br m, 2F,
3
1
3
REFERENCES
o), −161.0 (t, JFF = 20.0 Hz, 1F, p), −165.0 (m, 2F, m) (C6F5),
■
[Δδ19Fm,p = 4.0] −132.2 (br m, 2F, o), −159.9 (t, JFF = 20.4 Hz, 1F,
3
(1) Kehr, G.; Schwendemann, S.; Erker, G. Top. Curr. Chem. 2013,
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p), −163.7 (m, 2F, m) (C6F5), [Δδ19Fm,p = 3.8].
Synthesis of Compound 28a. Compounds 3 and 11a were
generated in situ as described above (HB(C6F5)2: 138 mg, 0.4 mmol;
dimesityl(vinyl)phosphane: 119 mg, 0.4 mmol; compound 10a: 113
mg, 0.4 mmol; solvent: toluene). Then, S8 (3.2 mg, 0.01 mmol, 0.13
equiv) was added to the solution, and the resulting solution was stirred
for 2 days at rt. All volatiles were removed in vacuo, and the resulting
solid was washed with n-pentane (4 × ∼5 mL) and dried in vacuo to
give compound 28a (280 mg, 0.29 mmol, 73%) as a colorless solid.
Single crystals suitable for the X-ray crystal structure analysis were
obtained by slow diffusion of n-pentane into a solution of 28a in
dichloromethane at −40 °C. mp: 254 °C. Anal. Calcd for
(2) Ekkert, O.; Miera, G. G.; Wiegand, T.; Eckert, H.; Schirmer, B.;
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Chem. Commun. 2013, 47, 10482. (c) See for a comparison: Sajid, M.;
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1
C49H45BF10P2SSi: C, 61.51; H, 4.74. Found: C, 62.48; H, 4.79. H
NMR (500 MHz, CD2Cl2, 299 K): δ = 7.48 (2H), 7.36 (4H), 7.24
(4H)(Ph), 6.81 (d,4JPH = 4.0 Hz, 4H, m-mes), 3.06 (m, 2H, CH2),
2.63 (m, 2H, PCH2), 2.24 (s, 6H, p-CH3mes), 2.24 (s, 12H, o-CH3mes),
(5) Spies, P.; Erker, G.; Kehr, G.; Bergander, K.; Frohlich, R.;
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2009, 131, 9918−9919. (c) Cardenas, A. J. P.; Culotta, B. J.; Warren,
2
0.10 (s, JSiH = 6.6 Hz, 9H, SiCH3). 13C{1H} NMR (126 MHz): δ =
206.7 (br, CB), 140.8 (d, 4JPC = 2.7 Hz, p-mes), 140.3 (d, 2JPC = 9.8
Hz, o-mes), 138.7 (d, 1JPC = 27.6 Hz, CSi), 132.3 (d, 2JPC = 9.2 Hz,
T. H.; Grimme, S.; Stute, A.; Frohlich, R.; Kehr, G.; Erker, G. Angew.
̈
3
4
o-Ph), 132.1 (d, JPC = 10.6 Hz, m-mes), 131.9 (d, JPC = 3.0 Hz, p-
Ph), 130.3 (d, 1JPC = 76.2 Hz, i-mes), 129.1 (d, 3JPC = 10.4 Hz, m-Ph),
Chem., Int. Ed. 2011, 50, 7567. (d) Sajid, M.; Stute, A.; Cardenas, A. J.
P.; Culotta, B. J.; Hepperle, J. A. M.; Warren, T. H.; Schirmer, B.;
1
1
127.1 (d, JPC = 39.2 Hz, i-Ph), 39.0 (d, JPC = 52.1 Hz, PCH2), 33.8
Grimme, S.; Studer, A.; Daniliuc, C. G.; Frohlich, R.; Petersen, J. L.;
̈
(d, JPC = 53.6 Hz, CH2), 23.3 (d, 3JPC = 4.9 Hz, o-CH3mes), 20.9 (d,
Kehr, G.; Erker, G. J. Am. Chem. Soc. 2012, 134, 10156. (e) Sajid, M.;
5JPC = 1.5 Hz, p-CH3mes), −0.1 (d, JPC = 2.3 Hz, JSiC = 52.9 Hz,
SiCH3).19F NMR (470 MHz): δ = −129.9 (o), −158.3 (p), −164.7
(m), [Δδ19Fm,p = 6.4]. 10B{1H} NMR (54 MHz): δ = −7.0. 31P{1H}
2
1
Kehr, G.; Wiegand, T.; Eckert, H.; Schwickert, C.; Pottgen, R.;
̈
Cardenas, A. J. P.; Warren, T. H.; Frohlich, R.; Daniliuc, C. G.; Erker,
̈
G. J. Am. Chem. Soc. 2013, 135, 8882. (f) Pereira, J. C. M.; Sajid, M.;
Kehr, G.; Wright, A. M.; Schirmer, B.; Qu, Z.-W.; Grimme, S.; Erker,
G.; Ford, P. C. J. Am. Chem. Soc. 2014, 136, 513−519.
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cited herein).
5
NMR (202 MHz): δ = 42.8 (d, JPP = 3.6 Hz, Pmes2), 13.6 (PPh2).
29Si{1H} DEPT (99 MHz): δ = −10.8 (d, JPSi = 5.8 Hz).
2
ASSOCIATED CONTENT
■
(8) Kehr, G.; Erker, G. Chem. Commun. 2012, 48, 1839 (see also
references cited herein).
S
* Supporting Information
Detailed description of experiments, characterization of all new
compounds, and crystal structure data as CIF files. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(9) (a) Chen, C.; Eweiner, F.; Wibbeling, B.; Frohlich, R.; Senda, S.;
̈
Ohki, Y.; Tatsumi, K.; Grimme, S.; Kehr, G.; Erker, G. Chem.Asian J.
2010, 5, 2199. (b) Chen, C.; Voss, T.; Frohlich, R.; Kehr, G.; Erker, G.
̈
Org. Lett. 2010, 13, 62.
(10) Chen, C.; Kehr, G.; Frohlich, R.; Erker, G. J. Am. Chem. Soc.
̈
2010, 132, 13594.
AUTHOR INFORMATION
■
(11) (a) Dierker, G.; Ugolotti, J.; Kehr, G.; Frohlich, R.; Erker, G.
Adv. Synth. Catal. 2009, 351, 1080. (b) Chen, C.; Frohlich, R.; Kehr,
G.; Erker, G. Chem. Commun. 2010, 46, 3580. (c) Mobus, J.; Bonnin,
Q.; Ueda, K.; Frohlich, R.; Itami, K.; Kehr, G.; Erker, G. Angew. Chem.,
̈
Corresponding Authors
eckerth@uni-muenster.de
thwarren@purdue.edu
grimme@thch.uni-bonn.de
erker@uni-muenster.de
̈
̈
̈
Int. Ed. 2012, 51, 1954. (d) Liedtke, R.; Harhausen, M.; Frohlich, R.;
̈
Kehr, G.; Erker, G. Org. Lett. 2012, 14, 1448.
(12) Jiang, C.; Blacque, O.; Berke, H. Organometallics 2010, 29, 125.
(b) Fan, C.; Piers, W. E.; Parvez, M.; McDonald, R. Organometallics
2010, 29, 5132.
Notes
The authors declare no competing financial interest.
9026
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G. Dalton Trans. 2010, 39, 7556.
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(26) Structures were calculated at the B2PLYP-D3/def2-TZVP level
of theory, thermal corrections with TPSS-D3/def2-TZVP and high
convergence criteria (see the Supporting Information for details),
solvent corrections with COSMO-RS; the general accuracy of the
resulting ΔGsolution data is assumed to be about 1−2 kcal mol−1.
(a) Grimme, S. J. Chem. Phys. 2006, 124, 034108. (b) Grimme, S.;
Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys. 2010, 132, 154104.
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01.11; COSMOlogic GmbH & Co. KG: Leverkusen, Germany, 2010.
(f) Ahlrichs, R. et al. TURBOMOLE, versions 6.3 and 6.4; Universitat
̈
Karlsruhe: Karlsruhe, Germany, 2011 and 2012; see www.turbomole.
com.
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Chem. 2013, 3312. (b) Mobus, J.; Kehr, G.; Daniliuc, C. G.; Frohlich,
̈
̈
R.; Erker, G. Dalton Trans. 2013, 43, 632.
9027
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