Phosphine-Borane Frustrated Lewis Pairs Derived from a 1,1′-Disubstituted Ferrocene Scaffold: Synthesis and Hydrogenation Catalysis

Article abstract of DOI:10.1021/acs.organomet.7b00363

(Dimesitylphosphino)ferrocene (FcPMes₂) (1) reacted with HB(C₆F₅)₂ (2 equiv) by disproportionation to give adduct FcPMes₂·H₂B(C₆F₅) (4) plus B(C₆F₅)₃, whereas 1-(dimesitylphosphino)-1′-vinylferrocene (2) was cleanly hydroborated with HB(C₆F₅)₂ to afford [Fe(??⁵-C₅H₄PMes₂)(??⁵-C₅H₄CH₂CH₂B(C₆F₅)₂)] (7). Compound 7 adopted an open non-interacting P/B frustrated Lewis pair (FLP) structure in the crystal state as well as in a solution. This frustrated Lewis pair heterolytically cleaved dihydrogen under mild conditions to give the respective zwitterionic [P]H⁺/[B]H^- phosphonium/hydroborate product, [Fe(??⁵-C₅H₄PHMes₂){??⁵-C₅H₄CH₂CH₂BH(C₆F₅)₂}] (8), which served as a catalyst for the hydrogenation of the electron-rich ?€-systems (imine, enamine) as well as the electron-deficient carbon-carbon double and triple bonds in some enones and an ynone under more forcing conditions (50 bar H₂ pressure, 50 °C).

Full text of DOI:10.1021/acs.organomet.7b00363

Article
pubs.acs.org/Organometallics
Phosphine−Borane Frustrated Lewis Pairs Derived from a 1,1′-
Disubstituted Ferrocene Scaffold: Synthesis and Hydrogenation
Catalysis
†
†
‡
†
Zhongbao Jian, Sergei Krupski, Karel Skoch, Gerald Kehr, Constantin G. Daniliuc,† Ivana Císarova,‡
̌
̌
́
Petr Stepnicka,* and Gerhard Erker*,†
,‡
̌
̌
̌
†Organisch-Chemisches Institut, Westfalische Wilhelms-Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
̈
̈
̈
̈
‡Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague, Czech Republic
S
* Supporting Information
ABSTRACT: (Dimesitylphosphino)ferrocene (FcPMes2) (1) reacted with
HB(C6F5)2 (2 equiv) by disproportionation to give adduct FcPMes2·
H2B(C6F5) (4) plus B(C6F5)3, whereas 1-(dimesitylphosphino)-1′-vinyl-
ferrocene (2) was cleanly hydroborated with HB(C6F5)2 to afford [Fe(η5-
C5H4PMes2)(η5-C5H4CH2CH2B(C6F5)2)] (7). Compound 7 adopted an
open non-interacting P/B frustrated Lewis pair (FLP) structure in the crystal
state as well as in a solution. This frustrated Lewis pair heterolytically cleaved
dihydrogen under mild conditions to give the respective zwitterionic [P]H+/
[B]H− phosphonium/hydroborate product, [Fe(η5-C5H4PHMes2){η5-
C5H4CH2CH2BH(C6F5)2}] (8), which served as a catalyst for the
hydrogenation of the electron-rich π-systems (imine, enamine) as well as the electron-deficient carbon−carbon double and
triple bonds in some enones and an ynone under more forcing conditions (50 bar H2 pressure, 50 °C).
Chart 1. Representative Examples of Phosphinoferrocene
Boranes
INTRODUCTION
■
Phosphine−borane frustrated Lewis pairs (P/B FLPs) have
been the subject of recent interest, mainly due to their
unorthodox reactivity and an ability to react with and activate
small molecules such as H2, CO, and CO2.1 The chemical
properties of P/B FLPs strongly depend on the mutual
positioning of the phosphine and borane moieties in their
molecules and the substituents in the functional molecular parts
that are controlling their steric and electronic properties. The
majority of FLPs reported to date exploit simple organic
fragments as the molecular backbone. In contrast, the use of
organometallic fragments as molecular scaffolds for FLPs
remains still rather scarce. Indeed, there have been reported
examples of P/B FLPs derived from Group 4 metallocenes,2
but the otherwise ubiquitous ferrocene moiety3 has found only
a limited use in the design of FLP-type molecules.
a derivative activated molecular hydrogen and were used as
catalysts for asymmetric hydrogenation of imines, leading to the
corresponding amines with moderate enantioselectivity.11 The
promising reactivity of E-type compounds led us to extend our
studies toward the isomeric compounds derived from the 1,1′-
disubstituted ferrocene unit. The results of such investigations
are reported herein.
In the past few years, Bourissou,4 Cantat,5a Diaconescu,5b
and Hierso5c independently reported the synthesis of 1,1′-
disubstituted (R2B-/R2P-)ferrocenes, compounds A (Chart 1),
while Aldridge6 prepared the isomeric 1,2-disubstituted
(Mes2B-/Ph2P-)ferrocene, compound B (Chart 1). More
recently, the family of ferrocene-based P/B FLPs was extended
by the ring-fused bis-ferrocene derivative C.7
In order to increase molecular flexibility and thus possibly
allow for interactions between the Lewis acidic and basic sites
in the molecules of phosphinoferrocene boranes, some of us
have utilized the hydroboration of ferrocene phosphino-alkenes
D8 with Piers’ borane [HB(C6F5)2],9 that directly provides
planar-chiral FLPs of type E (see Chart 1).10 Compound E and
RESULTS AND DISCUSSION
■
As the starting materials for this study, we employed
(dimesitylphosphino)ferrocene (1) and 1-(dimesitylphosphi-
no)-1′-vinylferrocene (2; Note: the synthesis and character-
Received: May 11, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00363
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ization data of these two compounds are described in the
Supporting Information). The former compound was prepared
(Scheme 1) by lithiation of ferrocene with tert-butyl lithium in
through signal broadening and a shift to a lower field (compare
δP −34.3 for 1 with +5.7 for 4). The H NMR signal of the
equivalent BH2 protons was observed as a broad singlet at δH
2.95, while the corresponding 11B NMR resonance was found
at δB −24.2. The formulation of 4 was independently
corroborated by X-ray diffraction analysis (Figure 2).
1
Scheme 1. Synthesis of 1 and Its Reactions with HB(C6F5)2
the presence of potassium tert-butoxide,12 and subsequent
reaction of the in situ generated lithioferrocene with chloro-
dimesitylphosphine. Following chromatographic purification,
phosphine 1 was isolated as an orange solid and was
characterized by the standard spectroscopic methods and by
single-crystal X-ray diffraction analysis (Figure 1).
Figure 2. Molecular structure of compound 4 (thermal ellipsoids are
shown with 15% probability). Selected bond lengths (Å) and angles
(deg): P1−B1, 2.007(4); P1−C11, 1.798(3); P1−C21, 1.840(3); P1−
C31, 1.846(3); C21−P1−B1, 102.5(2); C41−B1−P1, 115.1(2).
Since the reaction of 1 with HB(C6F5)2 gave the unexpected
P/B adduct 4, we also investigated the interaction of 1 with
B(C6F5)3 (in situ). However, no similar reaction took place,
indicating the formation of an intermolecular P/B FLP. Indeed,
under 1.5 bar of H2 atmosphere, the 1/B(C6F5)3 system split
dihydrogen to afford [FcPHMes2][HB(C6F5)3] after 10 h,
confirmed by NMR analysis (for details, see the Supporting
Information).14
To avoid the formation of P/B adducts (such 3 and 4), we
introduced a vinyl substituent onto the ferrocene framework in
position 1′ and employed it for the introduction of a
−B(C6F5)2 moiety through hydroboration. To this end, 1-
(dimesitylphosphino)-1′-vinylferrocene (2) was synthesized by
Wittig vinylation of 1-bromoferrocene-1′-carbaldehyde (5)15
and lithiation/phosphinylation of the intermediate 1-bromo-1′-
vinylferrocene (6). Gratifyingly, the reaction of 2 with
HB(C6F5)2 in pentane proceeded cleanly and rapidly to
provide the anticipated hydroboration product 7, which was
isolated in a 90% yield (Scheme 2).
The NMR response of 7 suggested the presence of an intact
−PMes2 moiety (δP −34.8) and free terminal −B(C6F5)2 unit
(δB 72.9). The signals of the original vinyl moiety in 2 were
replaced upon hydroboration by a pair of triplets at δH 2.15 and
2.39 and by signals at δC 32.9 and 24.5 in the 1H and 13C NMR
spectra, respectively. The 19F NMR spectrum showed three
signals (o, m, p) with a relatively large Δδ19Fm,p = 13.9 ppm
chemical shift difference, as is typical of a trigonal planar boron
coordination geometry in such a situation.
Figure 1. View of the molecular structure of compound 1 (thermal
ellipsoids are shown with 15% probability). Selected bond lengths (Å)
and angles (deg): P1−C11, 1.817(5); P1−C21, 1.862(5); P1−C31,
1.844(5); ΣP1CCC = 314.9(2)°.
Piers reported that ferrocene reacts with HB(C6F5)2 to give
the bis(pentafluorophenyl)boryl ferrocene [Fe(η5-C5H5){η5-
C5H4B(C6F5)2}] with the releasing of dihydrogen.13 Intrigued
by this transformation, we performed the reaction of 1 with
Piers’ borane HB(C6F5)2 to possibly obtain compounds [Fe(η5-
C5H4PMes2){η5-C5H4B(C6F5)2}] (type A, Chart 1) or [Fe(η5-
C5H5){η5-C5H3(PMes2)B(C6F5)2}] (type B, Chart 1). How-
ever, the reaction of 1 with 1 molar equiv of HB(C6F5)2 in
toluene-d8 at room temperature led to a mixture containing the
Lewis adduct 1·HB(C6F5)2 (3) but also 1·H2B(C6F5) (4) and
B(C6F5)3 resulting from its redistribution reaction (Scheme 1).
When the amount of HB(C6F5)2 was increased to 2 equiv, the
formation of 3 was suppressed, and compound 4, the dominant
ferrocene species in the reaction mixture, was isolated by
crystallization as an orange solid in a 78% yield. The formation
of adduct 4 was clearly manifested in the 31P NMR spectrum
In addition to spectroscopic characterization, the structures
of the starting material 2 and its hydroboration product 7 were
determined by X-ray diffraction analysis (Figures 3 and 4). The
structure of compound 7 confirms the presence of an open,
non-interacting P/B FLP.16 It contains the unchanged bulky
B
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Scheme 2. Synthesis and Hydroboration of 2
Figure 4. Projection of the molecular structure of compound 7
(thermal ellipsoids are shown with 30% probability). Selected bond
lengths (Å) and angles (deg): C16−C1, 1.502(4); C1−C2, 1.542(4);
C2−B1, 1.556(4); C11−P1, 1.815(3); C16−C1−C2, 112.8(3); C1−
C2−B1, 119.2(3); ΣP1CCC = 314.4(1)°; ΣB1CCC = 359.9(3)°.
Scheme 3. Alternative Syntheses of the H2 Splitting Product
8
Figure 3. Molecular structure of compound 2 (thermal ellipsoids are
shown with 30% probability). Selected bond lengths (Å) and angles
(deg): P1−C11, 1.818(2); P1−C21, 1.856(2); P1−C31, 1.853(2);
C16−C1, 1.464(3); C1−C2, 1.301(3); C16−C1−C2, 125.6(2).
−PMes2 unit at the C11−C15 cyclopentadienyl (Cp) ring of
the central ferrocene unit. The substituents at the trigonal
pyramidal phosphorus atom (ΣP1CCC = 314.4(1)°) are
markedly rotated out of the parent Cp plane. The other Cp
ring bears the −CH2CH2B(C6F5)2 substituent formed by the
hydroboration reaction. It shows a gauche conformation (θ
C16−C1−C2−B1 = −62.5(4)°), which directs the borane
away from the center of the ferrocene unit. The vectors of the
pivotal C11−P1 and C16−C1 bonds at the eclipsed central
metallocene moiety assume a gauche-like orientation (see
Figure 4).
Alternatively, the phosphonium/hydroborate 8 was prepared
by introducing the proton at phosphorus and the hydride at
boron in two separate steps. This method was used previously
for the preparation of [P]H+/[B]H− products that were
sensitive to H2 liberation.19 In the present case, we first
added 1 molar equiv of triflic acid to the in situ generated
ferrocene P/B FLP 7 (see above). The addition reaction went
to completion within a short period of time, and the product 9
could be precipitated at −30 °C. It was isolated as a yellow
solid in 84% yield and fully characterized by elemental analysis
and by NMR spectroscopy. Aside from the typical ferrocene
signals and the resonances of the ethylene bridge, compound 9
showed the characteristic singlet of the triflate −CF3 group at
δF −79.2 and the o, m, p signals of the pair of −C6F5
substituents at the tetracoordinate boron [Δδ19Fm,p = 5.0
ppm, 11B: δB 6.3] in its 19F NMR spectrum. The 31P NMR
resonance of compound 9 occurred at δP −13.7 (d, 1JPH = 495.0
The P/B FLP 7 was next used for splitting dihydrogen.1,17
For that purpose a solution of this compound in CD2Cl2 placed
in a J. Young pressure NMR tube was exposed to H2 (1.5 bar)
at −5 °C (24 h). The formation of the [P]H+/[B]H− splitting
product 8 was nearly complete under these conditions (Scheme
3). We performed the reaction of 7 also with D2 under
analogous conditions and obtained the respective [P]D+/
[B]D− product 8-D2 (see the Supporting Information for a
comparison of the NMR spectra of compounds 8 and 8-D2).
The H2 splitting product 8 is stable in solution at low
temperature under the H2 atmosphere but slowly loses
dihydrogen at room temperature (see the Supporting
Information for the NMR spectra obtained under various
conditions that demonstrate reversible transformation of 7 into
8).18
1
Hz) with the corresponding H NMR signal (PH) at δH 8.52.
C
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Subsequent triflate for hydride exchange was effected by
treatment of 9 with excess (5-fold) of triethylsilane in
dichloromethane at −30 °C. After several days of crystallization
(pentane/CH2Cl2), orange yellow crystalline ferrocene phos-
phonium/hydroborate 8 was obtained. It was characterized by
elemental analysis, by NMR spectroscopy, and also by X-ray
Table 1. Results of Catalytic Hydrogenation Mediated by 7
or 1/B(C6F5)3
diffraction. It showed a 11B NMR resonance at δB −20.3 (d,
1
1JBH = 83.8 Hz) and a 31P NMR feature at δP −13.6 (d, JPH
=
1
492.0 Hz, with the associated H NMR signal at δH 8.37). A
1
single set of H NMR signals due to the pair of mesityl groups
at phosphorus and also the 19F NMR signals of the enantiotopic
−C6F5 substituents at boron [Δδ19Fm,p = 2.3 ppm] was
observed. The ethylene bridge connecting the boron Lewis acid
with the ferrocene core gave rise to an AA′XX′ pattern at δH
1.92 and 0.93 (δC: 28.8 and 22.5).
entry
substrate
product
conversion (%)
The X-ray crystal structure analysis confirmed the presence
of the −P(H)+Mes2 and −CH2CH2B(H)−(C6F5)2 substituents
at the ferrocene core, mutually rotated into an anti position
(derived from D5d ferrocene conformation;20 see Figure 5).
a
1
10a
10b
10c
12a
12b
14
11a
11b
10c
13a
13b
12b
11a
13b
>99
>99
>99
38
a
2
a
3
a
4
a
5
50
a
6
15
b
7
10a
12b
>99
b
c
8
>99 (84 )
a
Reagents and conditions: 0.3 mmol substrate, 10 mol % of catalyst 7,
C6D6 as solvent (1.5 mL), 50 bar of H2, 50 °C, 3 d reaction time.
b
Conversion was determined by 1H NMR spectroscopy. Reagents and
conditions were the same except that 10 mol % of catalyst 1/B(C6F5)3
c
was used. Isolated yield.
be hydrogenated into the respective conjugated eneone 12b
under these conditions,22 but a rather low conversion was
achieved in this case (see results in Table 1).
For a comparison, the catalytic hydrogenation tests were also
performed with the intermolecular 1/B(C6F5)3 FLP system.
Thus, quantitative hydrogenation of the CN double bond in
10a to give 11a was achieved with this catalyst under the same
reaction conditions (50 bar of H2, 50 °C, 3 d). Remarkably, the
1/B(C6F5)3 FLP system was able to hydrogenate the CC
double bonds of 12b to give 13b in a quantitative conversion.
As a representative sample, product 13b was purified and
isolated in a 84% yield by column chromatograph and fully
characterized by NMR spectroscopy (for details, see the
Supporting Information).
Figure 5. View of the molecular structure of the [P]H+/[B]H− system
8 (thermal ellipsoids are shown with 30% probability). Selected bond
lengths (Å) and angles (deg): C16−C1, 1.503(4); C1−C2, 1.535(4);
C2−B1, 1.630(4); C11−P1, 1.766(3); C16−C1−C2, 115.1(2); C1−
C2−B1, 109.8(2); ΣP1CCC = 339.9(1)°, ΣB1CCC = 333.7(2)°.
The −CH2CH2−[B] moiety adopts an antiperiplanar arrange-
ment with the bulky terminal −B(C6F5)2 group diverted away
from the ferrocene core (θ C16−C1−C2−B1 = −180.0(2)°).
The B−H vector lies practically in the plane of the bonding Cp
ring whereas the P−H bond in the P(H)+Mes2 moiety is
directed inside the ferrocene unit.
CONCLUSIONS
■
The bulky ferrocenyl-dimesitylphosphine 1 was shown to react
with in a remarkable way with Pier’s borane HB(C6F5)2. It
initially forms a Lewis adduct 1·HB(C6F5)2, which rapidly
undergoes disproportionation to a mixture of 1·H2B(C6F5) (4)
and B(C6F5)3. Compound 4 becomes the dominant product
when the amount of HB(C6F5)2 is increased to 2 equiv. The
role of the bulky phosphine moiety in this case consists in an
efficient trapping of the H2B(C6F5) component from the
mixture by adduct formation, thereby shifting the equilibrium
very effectively to the H2B(C6F5) side. This procedure of
generating the FcPMes2/H2B(C6F5) adduct may be viewed as a
complement to Lancaster’s Me2S/H2B(C6F5) reagent.23 We
will see which of the characteristic H2B(C6F5) reactions24 can
be performed using the new ferrocene-derived reagent 4.
The reaction between 1-(dimesitylphosphino)-1′-vinyl-
ferrocene (2) and HB(C6F5)2 takes a different course, as
expected. A clean hydroboration of the vinyl group conjugated
The ferrocene-based P/B FLP was found to be an active
hydrogenation catalyst, but it required relatively forcing
reaction conditions. We carried out the catalytic hydrogenation
reactions in benzene-d6 solution at 50 °C (3 d) with a
dihydrogen pressure of 50 bar using 10 mol % of 7 as a catalyst
1
(see Table 1). The conversion was then determined by H
NMR spectroscopy. Under these conditions, we obtained
quantitative hydrogenation of the CN double bond of the
bulky imine 10a to tertiary amine 11a (see Table 1) as well as
of the enamine CC double bonds of the piperidine-derived
enamines 10b,c (to afford the respective tertiary amines
11b,c).17,21 The P/B FLP catalyst 7 was also able to
hydrogenate the electron-deficient CC double bonds of the
α,β-unsaturated ketones 12a,b to give the respective saturated
ketones 13a,b under these conditions, albeit with markedly
lower overall conversions. Even the conjugated ynone 14 could
D
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CH3Mes), 20.4 (p-CH3Mes′). 11B NMR (160 MHz, 299 K, CD2Cl2): δ =
−24.2 (ν1/2 ∼ 300 Hz). 11B{1H} NMR (160 MHz, 299 K, CD2Cl2): δ
= −24.2 (ν1/2 ∼ 200 Hz). 19F NMR (470 MHz, 299 K, CD2Cl2): δ =
−127.2 (m, 2F, o-C6F6), −160.8 (m, 1F, p-C6F5), −166.4 (m, 2F, m-
C6F5). [Δδ19Fm,p = 5.6]. 31P{1H} NMR (202 MHz, 299 K, CD2Cl2): δ
= 5.7 (ν1/2 ∼ 120 Hz). Anal. Calc. for C34H33FePBF5: C, 64.39; H,
5.24. Found: C, 64.73; H, 4.92. Mp 173 °C.
Preparation of Compound 7. Compound 2 (96 mg, 0.2 mmol)
and HB(C6F6)2 (69 mg, 0.2 mmol) were mixed in pentane (3 mL) and
the resulting solution was stirred for 30 min. The reaction mixture was
filtered and the solvent was removed in vacuo to afford compound 7 as
an orange-red solid. Yield: 148 mg, 90%.
with the ferrocene core is observed as long as the reaction is
performed strictly under a 1:1 stoichiometry. The resulting
phosphine−borane product 7 can be isolated in pure form and
its spectroscopic data as well as the result of X-ray crystal
structure analysis indicate the presence of a non-interacting P/
B frustrated Lewis pair. Not unexpectedly, the ferrocene-
derived P/B FLP 7 is a dihydrogen activator, although the
dihydrogen cleavage reaction shows reversibility. Nevertheless,
the 7/H2 system can be used as a FLP catalyst for the
hydrogenation of a variety of organic π-systems, including a
bulky imine and a couple of bulky enamines. Remarkably, the
7/H2 system can also serve as a catalyst for the selective
hydrogenation of carbon−carbon multiple bonds in a small
series of conjugated enones and ynones, although these
reaction were markedly slower than the above-mentioned
imine or enamine reductions and resulted in only partial
conversions under our typical reaction conditions. The
ferrocene-based FLP 7/H2 catalyst system thus seems to be
suited to tackle both electron-rich as well as electron-poor
organic CN, CC, and CC π-systems under suitable
conditions as a functional main-group element hydrogenation
catalyst.
A comparison of the new ferrocene-based P/B FLP system 7
with our previously reported 1,2-P/B disubstituted FLP system
E (Chart 1)10a revealed the influence of the organometallic
scaffold on the properties of these isomeric compounds.
Whereas compound 7 possesses an open, nonbridged FLP
structure in both the solid state and in solution, its planar-chiral
isomer E shows an equilibrium of open and closed forms at
variable temperature, with the open form, however, strongly
favored at ambient temperature. We found that both the
systems 7 and E are active dihydrogen splitting reagents and
both can serve as hydrogenation catalysts, although the 1,2-
isomer E is more active. Compound 7 needs significantly
forcing conditions for the catalytic hydrogenations (50 bar, 50
°C, 3 d) to proceed satisfactorily, as compared to the previously
reported system E (1.5 bar, r.t., 1 d).
1H NMR (600 MHz, 299 K, Benzene-d6, 7.15 ppm): δ = 6.71 (d,
4JPH = 2.2 Hz, 4H, m-Mes), 4.30 (br s, 2H, Cp-Hβ), 4.17 (br s, 2H, Cp-
Hγ), 3.98 (br s, 2H, Cp-Hβ′), 3.91 (br s, 2H, Cp-Hγ′), 2.41 (s, 12H, o-
CH3Mes), 2.39 (t, 3JHH = 8.0 Hz, 2H, CH2), 2.15 (t, 3JHH = 8.0 Hz, 2H,
BCH2), 2.07 (s, 6H, p-CH3Mes). 13C{1H} NMR (151 MHz, 299 K,
Benzene-d6, 128.0 ppm): δ = 147.0 (dm, 1JFC ∼ 244 Hz, C6F5), 143.4
(dm, 1JFC ∼ 262 Hz, C6F5), 142.5 (d, 2JPC = 15.0 Hz, o-Mes), 137.7 (p-
1
1
Mes), 137.5 (dm, JFC ∼ 255 Hz, C6F5), 132.7 (d, JPC = 20.5 Hz, i-
3
Mes), 130.5 (d, JPC = 3.0 Hz, m-Mes), 114.3 (br m, i-C6F5), 90.8 (i-
Cpα′), 79.8 (d, JPC = 11.8 Hz, i-Cpα), 75.7 (d, JPC = 17.7 Hz, Cpβ),
1
2
71.5 (d, JPC = 4.0 Hz, Cpγ), 69.2 (Cpβ′), 69.0 (Cpγ′), 32.9 (br,
3
BCH2), 24.5 (CH2), 23.5 (d, JPC = 15.2 Hz, o-CH3Mes), 20.8 (p-
3
CH3Mes). 11B{1H} NMR (192 MHz, 299 K, Benzene-d6): δ = 72.9
(ν1/2 ∼ 1500 Hz). 19F NMR (564 MHz, 299 K, Benzene-d6): δ =
3
−130.3 (m, 2F, o-C6F6), −147.0 (t, JFF = 20.9 Hz, 1F, p-C6F5),
−160.9 (m, 2F, m-C6F5). [Δδ19Fm,p = 13.9]. 31P{1H} NMR (243
MHz, 299 K, Benzene-d6): δ = −34.8 (ν1/2 ∼ 2 Hz). Anal. Calc. for
C42H34FePBF10: C, 61.05; H, 4.15. Found: C, 61.14; H, 4.26. Mp 109
°C.
Preparation of Compound 8. (1) Preparation of 9: A freshly
prepared solution of compound 7 in pentane (2 mL), synthesized
from 2 (100 mg, 0.21 mmol) and HB(C6F5)2 (73 mg, 0.21 mmol; see
the procedure above), was added to a solution of triflic acid (30.5 mg,
0.20 mmol) in pentane (1 mL). Immediately, a viscous liquid phase
was formed. After stirring for 5 min at room temperature, the reaction
mixture was cooled down to −30 °C. Then, the viscous mass was
washed with pentane for several times (each 2 mL) until a yellow
powder was obtained. Yield of 9: 169 mg, 84%.
1H NMR (600 MHz, 299 K, CD2Cl2, 5.32 ppm): δ = 8.52 (d, 1JPH
=
4
495.0 Hz, 1H, PH), 7.07 (d, JPH = 3.6 Hz, 4H, m-Mes), 4.92 (s, 2H,
Cp-Hγ), 4.58 (s, 2H, Cp-Hβ), 4.27 (s, 2H, Cp-Hβ′), 4.07 (s, 2H, Cp-
Hγ′), 2.35 (s, 6H, p-CH3Mes), 2.34 (s, 12H, o-CH3Mes), 2.12 (m, 2H,
CH2), 1.54 (m, 2H, BCH2). 13C{1H} NMR (151 MHz, 299 K,
EXPERIMENTAL SECTION
■
For general information, preparative details (including the synthesis of
substrates 1 and 2), and complete spectroscopic and structural data of
all new compounds, see the Supporting Information.
1
CD2Cl2, 53.8 ppm): δ = 148.1 (dm, JFC ∼ 240 Hz, C6F5), 146.2 (d,
2
4JPC = 2.3 Hz, p-Mes), 143.3 (d, JPC = 10.6 Hz, o-Mes), 139.3 (dm,
Preparation of Compound 4. Compound 1 (91 mg, 0.2 mmol)
and HB(C6F6)2 (140 mg, 0.4 mmol) were mixed in toluene (3 mL)
and the mixture was stirred for 12 h. Pentane (3 mL) was layered onto
the resulting solution and the mixture was stored at −35 °C to provide
orange crystals and white floe. The obtained mixture was recrystallized
twice with toluene and pentane at −35 °C to yield pure adduct 4.
Yield: 99 mg, 78%.
1JFC ∼ 240 Hz, C6F5), 137.1 (dm, 1JFC ∼ 250 Hz, C6F5), 132.3 (d, 3JPC
1
= 11.3 Hz, m-Mes), 121.9 (br m, i-C6F5), 119.2 (q, JFC = 316.0 Hz,
1
3
CF3), 113.1 (d, JPC = 86.1 Hz, i-Mes), 98.9 (i-Cpα′), 76.2 (d, JPC
=
11.3 Hz, Cpγ), 74.4 (d, 2JPC = 15.0 Hz, Cpβ), 71.0 (Cpβ′), 69.4 (Cpγ′),
59.2 (d, JPC = 99.0 Hz, i-Cpα), 24.6 (br s, BCH2), 24.5 (CH2), 22.2
1
(d, JPC = 8.2 Hz, o-CH3Mes), 21.4 (d, JPC = 1.1 Hz, p-CH3Mes).
11B{1H} NMR (192 MHz, 299 K, CD2Cl2): δ = 6.3 (ν1/2 ∼ 650 Hz).
19F NMR (564 MHz, 299 K, CD2Cl2): δ = −79.2 (s, 3F, CF3), −134.5
3
5
1H NMR (500 MHz, 223 K, CD2Cl2, 5.32 ppm): δ = 7.01 (s, 1H,
m-Mes), 6.81 (s, 1H, m-Mes), 6.57 (s, 1H, m-Mes′), 6.55 (s, 1H, m-
Mes′), 5.28 (s, 1H, Cp-Hβ), 4.57 (s, 1H, Cp-Hγ), 4.49 (s, 1H, Cp-Hγ),
4.09 (s, 5H, C5H5), 4.03 (s, 1H, Cp-Hβ), 3.03 (s, 3H, o-CH3Mes), 2.95
(very br s, 2H, BH2), 2.27 (s, 3H, p-CH3Mes), 2.13 (s, 3H, p-CH3Mes′),
1.68 (s, 3H, o-CH3Mes), 1.58 (s, 3H, o-CH3Mes′), 1.48 (s, 3H, o-
CH3Mes′). 13C{1H} NMR (126 MHz, 223 K, CD2Cl2, 53.8 ppm): δ =
142.6 (d, 2JPC = 16.7 Hz, o-Mes), 141.4 (o-Mes), 140.5 (p-Mes), 140.1
(d, 2JPC = 13.4 Hz, o-Mes′), 139.5 (d, 2JPC = 4.1 Hz, o-Mes′), 139.2 (p-
3
(m, 4F, o-C6F6), −161.3 (t, JFF = 20.3 Hz, 2F, p-C6F5), −166.3 (m,
4F, m-C6F5). [Δδ19Fm,p = 5.0]. 31P{1H} NMR (243 MHz, 299 K,
CD2Cl2): δ = −13.7 (ν1/2 ∼ 11 Hz). 31P NMR (243 MHz, 299 K,
1
CD2Cl2): δ = −13.7 (d, JPH = 495.0 Hz). Anal. Calc. for
C43H35FeO3PSBF13: C, 52.89; H, 3.61. Found: C, 52.20; H, 3.49.
Mp 204 °C.
(2) Preparation of 8: (route a) Neat Et3SiH (60 mg, 5 equiv) was
added to a cooled CH2Cl2 (0.3 mL) solution of compound 9 (97.6
mg, 0.1 mmol) at −30 °C in a small sized vial (2 mL). This vial was
placed into a precooled (−30 °C) bigger vial (10 mL). Then, 2 mL of
precooled (−30 °C) pentane was then added to the bigger vial to
initiate crystallization. After several days, orange-red crystals were
grown from the CH2Cl2/pentane system, which were suitable for X-
ray diffraction analysis. The mixture was filtered to afford the orange-
3
3
Mes′), 131.0 (d, JPC = 7.0 Hz, m-Mes), 130.4 (d, JPC = 10.2 Hz, m-
3
3
Mes), 130.3 (d, JPC = 7.6 Hz, m-Mes′), 129.9 (d, JPC = 9.0 Hz, m-
1
1
Mes′), 125.8 (d, JPC = 56.2 Hz, i-Mes), 125.6 (d, JPC = 51.1 Hz, i-
Mes′), 76.8 (d, 2JPC = 14.2 Hz, Cpβ), 73.7 (d, 2JPC = 2.2 Hz, Cpβ), 72.4
(d, 1JPC = 65.3 Hz, i-Cpα), 72.0 (d, 3JPC = 7.1 Hz, Cpγ), 71.9 (d, 3JPC
=
8.0 Hz, Cpγ), 69.9 (C5H5), 24.7 (o-CH3Mes), 24.4 (d, 3JPC = 4.5 Hz, o-
CH3Mes), 24.0 (o-CH3Mes′), 22.9 (d, 3JPC = 7.2 Hz, o-CH3Mes′), 20.7 (p-
E
DOI: 10.1021/acs.organomet.7b00363
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
yellow solids, which were washed twice by cold pentane. Yield: 51 mg,
62%.
ACKNOWLEDGMENTS
■
The research reported in this paper received financial support
from the European Research Council (grant to G.E.) and the
Czech Science Foundation (P.S.; project no. 15-11571S).
(route b) Compound 7 (17.0 mg, 0.02 mmol) was dissolved in
CD2Cl2 (0.6 mL) and then transferred to a J. Young valve NMR tube.
The solution was degassed with freeze−pump−thaw cycles and then
exposed to dihydrogen atmosphere (1.5 bar). After storing the NMR
tube for 24 h at −5 °C, the reaction mixture was characterized by
NMR spectroscopy.
̌
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ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00363.
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lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
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Cambridge Crystallographic Data Centre, 12 Union Road,
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AUTHOR INFORMATION
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ORCID
(11) Ye, K.-Y.; Wang, X.; Daniliuc, C. G.; Kehr, G.; Erker, G. Eur. J.
Inorg. Chem. 2017, 2017, 368−371.
Gerald Kehr: 0000-0002-5196-2491
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Petr Stepnicka: 0000-0002-5966-0578
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