Functional group chemistry at intramolecular frustrated Lewis pairs: Substituent exchange at the Lewis acid site with 9-BBN

Article abstract of DOI:10.1039/c2dt31737k

The vicinal frustrated P/B Lewis pair (FLP) Mes₂PCH ₂CH₂B(C₆F₅)₂ reacts with 9-borabicyclo[3.3.1]nonane (9-BBN) by C₆F₅vs. H exchange at boron to give the new [B]-H functionalized FLP Mes₂PCH ₂CH₂B(H)(C₆F₅) (4) and 9-C ₆F₅-BBN. The latter was characterized as an isonitrile adduct by X-ray diffraction. The new FLP 4 forms an adduct with pyridine and it undergoes clean hydroboration reactions with 1-pentyne or added styrene or dimesitylvinylphosphane. The products formed stable adducts with pyridine; two such examples were also characterized by X-ray crystal structure analysis. A similar alkyl vs. hydrogen exchange was observed upon treatment of an Al/N based Lewis pair, iBu₂Al-(Me₃Si)C=C(H)-N(CH₂CH ₂)₂NMe (14), with 9-BBN.

Full text of DOI:10.1039/c2dt31737k

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Functional group chemistry at intramolecular frustrated
Lewis pairs: substituent exchange at the Lewis acid site
with 9-BBN†
Cite this: Dalton Trans., 2013, 42, 709
Markus Erdmann,a Christian Rösener,b Thorsten Holtrichter-Rößmann,a
Constantin G. Daniliuc,a‡ Roland Fröhlich,a‡ Werner Uhl,*b Ernst-Ulrich Würthwein,*a
Gerald Kehra and Gerhard Erker*a
The vicinal frustrated P/B Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 reacts with 9-borabicyclo[3.3.1]nonane
(9-BBN) by C6F5 vs. H exchange at boron to give the new [B]–H functionalized FLP Mes2PCH2CH2B(H)-
(C6F5) (4) and 9-C6F5–BBN. The latter was characterized as an isonitrile adduct by X-ray diffraction.
The new FLP 4 forms an adduct with pyridine and it undergoes clean hydroboration reactions with
1-pentyne or added styrene or dimesitylvinylphosphane. The products formed stable adducts with
pyridine; two such examples were also characterized by X-ray crystal structure analysis. A similar alkyl vs.
hydrogen exchange was observed upon treatment of an Al/N based Lewis pair, iBu2Al–(Me3Si)CvC(H)–N-
(CH2CH2)2NMe (14), with 9-BBN.
Received 31st July 2012,
Accepted 6th September 2012
DOI: 10.1039/c2dt31737k
www.rsc.org/dalton
Introduction
Frustrated Lewis pairs (FLPs) have shown remarkable potential
in small molecule binding and/or activation in the recent
years.1,2 Many intra- as well as intermolecular FLPs were
shown to activate dihydrogen3 and often serve as active metal-
free catalysts for the hydrogenation of a variety of organic sub-
strates.4 FLPs were shown to bind to alkenes and alkynes,5 to
various carbonyl compounds6 including carbon dioxide.7 FLP
examples bind nitrogen oxides8,9 and an example was even
shown to selectively react with thionylchloride.10 Alkalimetal
hydride coordination and phase transfer catalysis are further
aspects of the broad applicability of FLPs.11
Chart 1
route, here by treatment of dimesitylvinylphosphane (1)
with Piers’ borane [HB(C6F5)2].13 Although this synthetic
approach to vicinal FLPs is very convenient and, consequently,
has been used extensively for the preparation of many related
vicinal P/B or N/B frustrated Lewis pairs,14 it is somewhat
limited with regard to variation of the substituents at the
Lewis acid site. We have now found a way to post-synthetically
change substituents at the boron Lewis-acid site to generate a
new synthetic way into variations of vicinal FLPs. This was
achieved by treatment of the FLP 2 with the 9-borabicyclo
[3.3.1]nonane (9-BBN) reagent. First representative examples of
this interesting synthetic development are described in this
account. We have then consequently extended this new
method in FLP backbone chemistry even to related N/Al Lewis
pairs. These compounds were obtained by hydroalumination
of trimethylsilyl-substituted ynamines and have the vicinal
arrangement of nitrogen and aluminium atoms similar to
Compound 2 is a typical example of a vicinal intramolecular
FLP. It is a very active H2 activating system (see Chart 1)12
and has served as an active hydrogenation catalyst.4 Like
many of its congeners it has been prepared by a hydroboration
aOrganisch-Chemisches Institut, Universität Münster, Corrensstraße 40, 48149
Münster, Germany. E-mail: erker@uni-muenster.de, wurthwe@uni-muenster.de;
Fax: +49 251 83-36503+49 251 83-39772
bInstitut für Anorganische und Analytische Chemie, Corrensstrasse 30, 48149
Münster, Germany. E-mail: uhlw@uni-muensdter.de; Fax: +49 251 83-36660;
Tel: +49 251 83-36610
†Electronic supplementary information (ESI) available: Experimental details of
the preparation and characterization of the compounds 4–13. CCDC 894610 to
894613. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c2dt31737k
2
with
a
relatively weak intramolecular Al–N bonding
interaction.15
‡X-ray crystal structure analyses.
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Fig. 2 1H NMR spectrum of the FLP 4 ([d6] benzene (*), 299 K).
Fig. 1 Molecular structure of the 9-C6F5–9-BBN isonitrile adduct 6 (thermal
ellipsoids are shown with 50% probability).
Results and discussion
Reactions at vicinal P/B frustrated Lewis pair systems
For our synthesis we generated the ethylene-bridged vicinal
P/B FLP 2 in situ by treatment of dimesitylvinylphosphane (1)
with a stoichiometric amount of HB(C6F5)2 in pentane at
ambient temperature (15 min). 9-Borabicyclo[3.3.1]nonane
(1 molar equiv.) was added to the yellow solution and the
mixture stirred overnight at ambient temperature. Workup
then gave the new FLP 4 in close to 80% yield as a white solid.
In a separate experiment we treated the pentane solution that
remained after precipitation of 4 with tert-butylisocyanide and
isolated the 9-C6F5–9-borabicyclo[3.3.1]nonane product (5),
resulting from H vs. C6F5 exchange, as its isonitrile adduct 6.
The tert-butylisocyanide adduct 6 was characterized by X-ray
diffraction. Single crystals were obtained from pentane at
−40 °C. The structure (see Fig. 1) features the typical 9-borabi-
cyclo[3.3.1]nonane framework. A pentafluorophenyl substitu-
ent is bonded to boron (B1–C21 1.655(2) Å) and the boron
atom has the linear isonitrile donor ligand attached to
it (B1–C9 1.613(2) Å, N1–C9 1.145(2) Å, angles B1–C9–N1
176.1(1)°, C9–N1–C10 175.9(2)°). The boron atom features
Scheme 1
we have observed a total of six mesityl-CH3 1H-NMR signals
and four mesityl-m(CH) resonances. The hydrogen atoms of
the –CH2–CH2– bridge of compound 4 are pairwise diastereo-
topic (see Fig. 2).
We performed a series of chemical reactions with the newly
synthesized FLP 4. First we reacted it with pyridine. This gave
the respective borane–pyridine adduct 7 as expected (see
Scheme 1). The tricoordinated phosphorus atom in 7 gives rise
to a 31P NMR resonance at δ −16.2 and the boron chemical
shift of 7 is at δ −3.1. The corresponding 1H NMR [B]–H signal
of 7 is found at 3.98. The mesityl substituents of the –PMes2
unit of the (chiral) adduct 7 are diastereotopic (for details see
the ESI†).
We then carried out a series of hydroboration reactions.
Although the new vicinal FLP 4 features some P–B-interaction,
the system serves as an active hydroboration reagent toward a
variety of olefins or acetylenes. We first reacted the P/BH FLP 4
with 1-pentyne. The reaction was initially carried out in
[d6]-benzene and the product 8 characterized spectroscopically.
It features the newly formed alkenyl substituent at boron
a
pseudotetrahedral coordination geometry (C9–B1–C21
103.9(1)°, C1–B1–C5 104.8(1)°).
In solution compound 6 shows a 11B NMR resonance at
δ −16.6. The 19F NMR resonances of the –C6F5 substituent
at boron show a small Δδ19Fpm = 5.0 difference of the p- and
m-resonances indicating tetracoordinate boron. The 13C NMR
resonance of the coordinated tBu–NuC ligand occurs at
δ 132.9.
The new FLP product 4 shows a 31P NMR resonance at
δ 12.6 [in [d6]-benzene]. It features a typical tetra-coordinate
1
boron resonance at δ −15.8 and a H NMR [B]–H resonance at
δ 3.62. Due to the internal P–B coordination and the substitu-
ent pattern at boron compound 4 is chiral. In addition, the
rotations around both P–C(aryl) and the B–C(aryl) vectors are
“frozen” on the NMR time scale at 299 K. Consequently
1
showing a characteristic set of olefin H NMR features [δ 6.43
(vCH[B]), δ 6.52 (RCHv), 3JHH = 17.4 Hz]. It shows a 31P NMR
signal at δ −11.4 and a 11B NMR resonance at δ = 63.6.
710 | Dalton Trans., 2013, 42, 709–718
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Scheme 2
Fig. 3 A view of the molecular structure of compound 9 (thermal ellipsoids are
shown with 50% probability).
The 19F NMR signals of the single –C6F5 substituent at boron
occur at δ −131.8 (o), −154.0 (p), and −162.4 (m, Δδ19Fpm
=
8.4).
This hydroboration reaction was also carried out on a pre-
parative scale. In this case we decided to prepare the corres-
ponding adduct by pyridine addition before workup. The
pyridine adduct 9 of the alkyne hydroboration product 8 was
isolated in 81% yield. It shows a 31P NMR signal at δ −15.9
and a 11B NMR resonance at δ 0.5. The mesityl substituents at
phosphorus are again diastereotopic and the 19F NMR
spectrum shows a small chemical shift difference of the
m- and the p-fluorine resonances of the single –C6F5 substitu-
ent at boron (Δδ19Fpm = 4.4) that is typical for the presence of a
tetracoordinated boron center (Scheme 2).
In the crystal compound 9 features a typical non-planar
coordination geometry at phosphorus (sum of C–P–C bond
angles 314.1°) and tetracoordinate boron. The boron atom
in compound 9 is a chiral center. It features four different sub-
stituents bonded to it. The trans-alkenyl substituent (B1–C3
1.601(4) Å, C3–C4 1.331(3) Å, dihedral angle B1–C3–C4–C5
168.4(3)°) was formed in the hydroboration reaction. The
boron atom has also bonded to it the single –C6F5 substituent
(B1–C31 1.656(4) Å), the pyridine donor ligand (B1–N41
1.635(3) Å) and carbon atom C2 of the ethylene bridge to
phosphorus (B1–C2 1.615(4) Å). The bulky [–PMes2] and
[–B(pyridine)(C6F5)(alkenyl)] groups were found in an anti-
periplanar arrangement at the connecting –CH2–CH2– unit
(dihedral angle P1–C1–C2–B1– 173.1(2)°) (Fig. 3).
Scheme 3
δ −5.5 and a 11B NMR signal at δ 40.5. We generated the hydro-
boration product 12 from 4 and Mes2P–CHvCH2 in CD2Cl2
and monitored its NMR spectra at low temperature. The
31P NMR resonance of 12 gets very broad at 183 K, which prob-
ably indicates an unsymmetrical global minimum structure
of 12.
Styrene is also readily hydroborated by the P/[B]H FLP 4. We
again added pyridine after the hydroboration was complete in
order to facilitate the workup. The pyridine adduct 11 of the
phenylethyl substituted P/B FLP system 10 was isolated in 56%
We treated the P/[B]H FLP 4 with Mes2P–CHvCH2 (2)
in toluene for 6 days at ambient temperature and then added
pyridine and eventually isolated the respective pyridine adduct
13 of the hydroboration product 12 in 38% yield. Compound
13 was characterized by X-ray diffraction. Suitable single
crystals were obtained from dichloromethane/heptane at
−40 °C by the diffusion method. In the crystal compound 13
features two –CH2–CH2–PMes2 substituents at boron, one orig-
inating from the reagent 4 the other having been formed by
the subsequent hydroboration reaction. The two –CH2–CH2–
PMes2 substituents are crystallographically independent in the
crystal although they are probably chemically equivalent in
solution. The central boron atom is tetracoordinated featuring
1
yield (see Scheme 3). It features the typical H NMR signals of
the 2-phenylethyl substituent at boron and the heteroatom
NMR resonances at δ −15.9 (31P) and δ 1.6 (11B), respectively
(for details see the ESI†).
Eventually, we reacted the new P/[B]–H FLP 4 with dimesi-
tylvinylphosphane. The reaction is slow but we obtained the
hydroboration product 12 admixed with some starting material
after 5 days in [d6] benzene. At 299 K product 12 shows a
symmetrical set of NMR features with a 31P NMR resonance at
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Fig. 4 Molecular structure of compound 13 (thermal ellipsoids are shown with
50% probability).
Scheme 4
the pair of –CH2CH2–PMes2 substituents (B1–C2 1.621(5) Å,
B1–C3 1.614(5) Å), the –C6F5 group (B1–C51 1.656(5) Å) and
the pyridine donor ligand bonded to it (B1–N1 1.634(5) Å,
angles C2–B1–C3 111.3(3)°, C51–B1–N1 105.4(2)°) (Fig. 4).
In solution compound 13 shows
a
single 31P NMR
resonance at δ −15.8 and a 11B NMR signal at δ 1.5. The
19F NMR signals of the single C6F5 substituent at boron were
found at δ −132.7 (o), δ −159.5 (p) and δ −164.0 (m-C6F5),
respectively (for further details see the ESI†).
Reactions at vicinal N/Al systems
Hydroalumination of the ynamine Me3Si–CuC–N(CH2CH2)2-
NMe afforded the aluminium–nitrogen compound 14 in
almost quantitative yield.15 A relatively long Al–N distance (207
pm) and an acute angle Al–CvC of almost 90° indicated con-
siderable ring strain which enabled the application of 14 for
the activation of phenylethyne by C–H bond cleavage and
opening of the Al–N bond.15 Hydridoboranes were expected
to react similarly with the formation of cyclic compounds
with the negatively charged hydrogen atom coordinated to
aluminium and the Lewis-acidic boron atom attached to
nitrogen. However, addition of solid 9-BBN to a solution of 14
in cyclopentane at room temperature in a 1 : 1 ratio gave a
mixture of compounds with residual quantities of the starting
aluminium compound. Complete consumption of 14 was only
achieved with two equivalents of 9-BBN (Scheme 4). Two broad
resonances in the 11B NMR spectrum of the reaction mixture
(δ 88.9 and −7.7) verified the formation of two boron com-
pounds. One (δ(11B) 88.9) was identified as iBu–BBN (15) with
the B–H hydrogen atom of 9-BBN replaced by an isobutyl
group.16 Recrystallization of the crude product from n-hexane
yielded colorless crystals of 16 with an impurity of 5% of 15.
Only repeated recrystallization afforded pure samples of 16
with a relatively low yield of 31%. X-ray crystal structure deter-
mination (Fig. 5) revealed the formation of an adduct in
which an isobutyl group of 14 is replaced by a hydrogen atom.
The aluminium atom is coordinated by an [H2–BBN]− ligand
via two 3c–2e B–H–Al bonds. The bridging hydrogen atoms
Fig. 5 Molecular structure of compound 16 (thermal ellipsoids are shown with
50% probability).
of B–H–Al bridges. The methyl groups and the CH2 hydrogen
atoms of the isobutyl substituents are diastereotopic. The
methylene hydrogen atoms give two doublets of doublets
(δ 0.16 and 0.61) by geminal coupling and coupling to the
β-hydrogen atom.
In the solid state the aluminium atom of 16 is in a spiro-
position and bridges two almost ideally planar AlH2B and
AlNC2 heterocycles. With a terminal isobutyl group it has
a coordination number of five which is quite common for
aluminium hydrido species.17 The AlC2N heterocycle includes
an endocyclic CvC (C11–C12 1.330(2) Å) and a relatively long
Al1–N1 bond (2.089(1) Å) which despite the larger coordination
number of the metal atom is only slightly lengthened com-
pared to 14 (2.073(1) Å). An unusually small angle Al–CvC of
91.2 (1)° (14: 90.3(1)°) may indicate considerable ring strain
and may facilitate secondary reactions. Few compounds having
aluminium and boron atoms bridged by hydrogen atoms are
known in the literature.18 The relatively short Al⋯B distance of
2.255(2) Å corresponds to published data and is in accordance
with a closed 3c–2e bonding interaction.
1
exhibit a singlet in the H NMR spectrum at δ 1.61, and in the
IR spectrum a broad absorption at 2025 cm−1 is characteristic
712 | Dalton Trans., 2013, 42, 709–718
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Quantum chemical calculations at the B97-D/def2-TZVP- instrument. NMR: Bruker Avance 400 (1H, 400 MHz;
level of theory19 based on all reaction partners indicate a 11B: 128 MHz; 13C, 100 MHz; 29Si: 79 MHz), Varian Inova 500
strongly exothermic reaction (−34.4 kcal mol−1 incl. zero point (1H, 500 MHz; 13C, 126 MHz, 31P, 202 MHz, 11B, 160 MHz,
energy). Calculated bond lengths of 16 are in reasonable agree- 19F, 470 MHz), Varian UnityPlus 600 (1H, 600 MHz;
ment with the experimental data (Al–H: 1.7594 and 1.8321 Å, 13C, 151 MHz, 31P, 242 MHz, 11B, 192 MHz, 19F, 564 MHz).
B–H: 1.2804 and 1.2692 Å, Al–B: 2.2280 Å, Al–N: 2.1359 Å). The Assignments of the resonances were supported by 2D experi-
discussed bonding parameters of 16 are nicely supported by ments. X-ray diffraction: data sets were collected with a Nonius
Wiberg bond indices: Al–C(vCH): 0.482, Al–N: 0.189, Al–H: KappaCCD or a BRUKER APEX II diffractometer. Programs
0.154 and 0.129, B–H: 0.784 and 0.811, Al–B: 0.226.
used: data collection, COLLECT;25 data reduction Denzo-
SMN;26 absorption correction, Denzo;27 structure solution
SHELXS-97;28 structure refinement SHELXL-9729 and graphics,
XP (BrukerAXS, 2000). Thermal ellipsoids are shown with 50%
probability, R-values are given for observed reflections, and
Conclusions
Intramolecular frustrated Lewis pairs have been prepared in a wR2 values are given for all reflections.
great variety. Often, hydroboration or hydroalumination reac-
Preparation of compound 4. Dimesitylvinylphosphane
tions have been used as simple and reliable tools for their syn- (364.4 mg, 1.23 mmol, 1.00 equiv.) and bispentafluorophenyl-
thesis. Since a sufficiently Lewis acidic site is needed for many borane (425.3 mg, 1.23 mmol, 1.00 equiv.) were dissolved
FLP applications the hydroboration reagent of choice was in pentane (30 mL). After this solution was stirred for 15 min,
Piers’ borane [HB(C6F5)2]. This practical issue has limited the 9-borabicyclononane (150.0 mg, 1.23 mmol, 1.00 equiv.) was
variability of formation of the vicinal FLPs by and large to the added to the solution and the solution was stirred overnight at
Lewis base component. One might, of course, have used the room temperature. The formed white precipitate was isolated
[H2B(C6F5)(SMe2)] reagent, that has very recently become avail- and washed with pentane (30 mL). The remaining white solid
able,20 for the hydroboration reaction, but this would also have was dissolved in dichloromethane (30 mL) and afterwards
encountered chemo-selectivity problems in some cases. There- dried in vacuo (yield 462.5 mg, 79%). Decomp.: 187 °C (DSC).
fore, we regard our new synthetic way to the [B]–H functiona- Anal. calc. for C26H27BF5P (476.27 g mol−1): C 65.57, H 5.71;
1
lized FLPs that is described in this article as first examples as found: C 65.07, H 5.76. IR (KBr): ˜ν = 2429 (m, B–H). H NMR
a well suited way of achieving functionalization at the Lewis (600 MHz, [d6]-benzene, 299 K): δ = 7.34 (s, 1H, m-Mesa), 6.44
acid site of boron containing reactive FLPs. The value of this (s, 1H, m′-Mesa), 6.43 (s, 1H, m-Mesb), 5.97 (s, 1H, m′-Mesb),
a
method is further supported by its extensions to aluminum- 3.62 (br, 1H, BH), 3.35 (s, 3H, o-CH3 ), 3.16/2.56 (each m, each
a
containing vicinal FLPs as was demonstrated here with a 1H, CH2P), 2.37 (s, 3H, p-CH3 ), 2.12 (s, 3H, o-CH3b), 1.92/1.36
representative example. Interestingly, the higher Lewis acidity (each m, each 1H, CH2B), 1.89 (s, 3H, o′-CH3b), 1.80 (s, 3H,
a
and the larger radius of aluminium caused the formation of a p-CH3b), 1.27 (s, 3H, o′-CH3 ). 13C{1H} NMR (151 MHz, [d6]-
persistent adduct with a second equivalent of the hydride benzene, 299 K): δ = 144.8 (br, o-Mesa), 141.5 (o′-Mesa), 141.4
transfer reagent via 3c–2e Al–H–B bonding interactions. (br, o-Mesb), 141.1 (p-Mesa), 139.6 (o′-Mesb), 139.5 (p-Mesb),
Functionalization of the Lewis acid site by this and related 132.0 (br, m′-Mesa), 131.9 (br, m-Mesb), 131.0 (br, m-Mesa),
1
methods might potentially become an important tool in 130.6 (br, m′-Mesb), 126.9 (br d, JPC ∼ 50 Hz, i-Mesb), 126.6
a
synthetic FLP chemistry.
(br d, 1JPC ∼ 54 Hz, i-Mesa), 30.9 (br, CH2P), 24.3 (o-CH3 ), 24.1
a
a
(o′-CH3b), 23.8 (o-CH3b), 21.4 (o′-CH3 ), 20.9 (p-CH3 ), 20.3
(p-CH3b), 12.7 (br, CH2B) [C6F5 not listed]. 31P{1H} NMR
(243 MHz, [d6]-benzene, 299 K): δ = 12.6 (ν1/2 ∼ 30 Hz). 11B{1H}
NMR (192 MHz, [d6]-benzene, 299 K): δ = −15.8 (ν1/2 ∼ 620 Hz).
19F NMR (564 MHz, [d6]-benzene, 299 K): δ = −124.0 (m, 1F,
Experimental section
Experimental work carried out by the Erker group
General information. All reactions were carried out under o-C6F5), −128.2 (m, 1F, o-C6F5), −160.1 (m, 1F, p-C6F5), −164.3
an argon atmosphere with Schlenk-type glassware. Solvents (m, 1F, m-C6F5), −164.9 (m, 1F, m-C6F5), [Δδ19Fpm = 4.2, 4.8].
were dried using a Grubbs-type system,21 which uses activated
In situ reaction of 4 with 9-BBN (generation of compounds 4
basic alumina and/or molecular sieves as drying agents and 5). Dimesitylvinylphosphane (24.3 mg, 0.08 mmol,
in combination with copper metal as an oxygen scavenger. 1.00 equiv.) and bispentafluorophenylborane (28.4 mg,
Pentane, toluene and dichloromethane were dried in this 0.08 mmol, 1.00 equiv.) were dissolved in [d6]-benzene
manner. Cyclopentane and n-hexane were dried over LiAlH4. (0.8 mL). After 15 min 9-borabicyclononane (10 mg,
Dimesitylvinylphosphane (1),22 bis(pentafluorophenyl)borane23 0.08 mmol, 1.00 equiv.) was added to the solution and the
and {2-[bis(pentafluorophenyl)boryl]ethyl}dimesitylphosphane solution was stored overnight. The mixture of compounds 4
(2)24 were prepared according to modified literature pro- and 5 (ratio 1 : 1 from 19F NMR) could be obtained as a colour-
cedures. Caution: many isonitriles are toxic and must be handled less solution.
5
(in the mixture): 1H NMR (500 MHz,
with due care. The following instruments were used for phys- [d6]-benzene, 299 K): δ = 2.04 (m, 2H, CHB), 1.87/1.84 (each m,
ical characterization of the compounds. Elemental analyses: each 4H, CH2), 1.86/1.22 (each m, each 2H, CH2). 13C{1H}
Foss-Heraeus CHN–O-Rapid and Vario EL III CHNS NMR (126 MHz, [d6]-benzene, 299 K): δ = 33.8 (CH2), 32.7 (br,
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BCH), 23.2 (CH2) [C6F5 not listed]. 11B{1H} NMR (160 MHz, 299 K): δ = 7.90 (m, 2H, o-Py), 6.70 (m, 2H, m-Mesa), 6.68 (m,
[d6]-benzene, 299 K): δ = 85.1 (ν1/2 ∼ 300 Hz). 19F NMR 2H, m-Mesb), 6.55 (m, 1H, p-Py), 6.18 (m, 2H, m-Py), 3.98 (br,
(470 MHz, [d6]-benzene, 299 K): δ = −131.2 (m, 2F, o-C6F5), 1H, BH), 2.75/2.49 (each m, each 1H, CH2P), 2.46 (s, 6H,
a
−150.8 (m, 1F, p-C6F5), −162.4 (m, 2F, m-C6F5), [Δδ19Fpm
11.6].
=
o-CH3 ), 2.43 (s, 6H, o-CH3b), 2.08 (s, 6H, p-CH3a/b), 1.39/1.26
(each m, each 1H, CH2B). 13C{1H} NMR (151 MHz, [d6]-
2
Preparation of compound 6. Dimesitylvinylphosphane benzene, 299 K): δ = 146.3 (o-Py), 142.4 (d, JPC = 12.7 Hz,
(341.7 mg, 1.15 mmol, 1.00 equiv.) and bispentafluorophenyl- o-Mesb), 142.1 (d, JPC = 12.8 Hz, o-Mesa), 139.5 (p-Py), 137.02,
2
borane (398.8 mg, 1.15 mmol, 1.00 equiv.) were dissolved in 137.00 (p-Mesa/b), 135.5 (d, JPC = 24.6 Hz, i-Mesb), 135.1 (d,
1
pentane (30 mL). After this solution was stirred for 15 min, 1JPC = 25.1 Hz, i-Mesa), 130.3 (d, JPC = 2.5 Hz, m-Mesa), 130.2
3
9-borabicyclononane (140.7 mg, 1.15 mmol, 1.00 equiv.) was (d, 3JPC = 2.6 Hz, m-Mesb), 125.0 (m-Py), 26.7 (d, JPC = 16.3 Hz,
1
3
a
3
added to the solution and the solution was stirred overnight at CH2P), 23.49 (d, JPC = 12.7 Hz, o-CH3 ), 23.47 (d, JPC
=
room temperature. The solution above the white precipitate 12.9 Hz, o-CH3b), 20.82, 20.80 (p-CH3a,b), 19.1 (br, CH2B), [C6F5
was separated and tert-butylisocyanide (132 μL, 1.15 mmol, not listed]. 31P{1H} NMR (243 MHz, [d6]-benzene, 299 K): δ =
1.00 equiv.) was added. The mixture was stirred for 2 h at −16.2 (ν1/2 ∼ 7 Hz). 11B{1H} NMR (192 MHz, [d6]-benzene,
room temperature and then stored at −40 °C to start the crys- 299 K): δ = −3.1 (ν1/2 ∼ 300 Hz). 19F NMR (564 MHz, [d6]-
tallization. The product was isolated as colourless crystals and benzene, 299 K): δ = −133.6 (m, 2F, o-C6F5), −159.4 (m, 1F,
was dried in vacuo (yield 223.3 mg, 52%). Crystals of 6 suitable p-C6F5), −164.2 (m, 2F, m-C6F5), [Δδ19Fpm = 4.8].
for X-ray crystal structure analysis were obtained by crystal
Generation of compound 8. Compound 4 (62.8 mg,
growth in pentane at −40 °C. M.p.: 126 °C (DSC). Anal. calc. 0.13 mmol, 1.00 equiv.) and 1-pentyne (13 μL, 0.13 mmol, 1.00
for C19H23BF5N (371.20 g mol−1): C 61.48, H 6.25, N 3.77; equiv.) were dissolved in 0.8 mL [d6]-benzene. After one day
1
found: C 61.36, H 6.17, N 3.76. 1H NMR (500 MHz, [d6]- the desired product was formed as a yellow solution. H NMR
benzene, 299 K): δ = 2.27/1.77 (each m, each 1H, CH2),1 2.09/ (600 MHz, [d6]-benzene, 299 K): δ = 6.64 (m, 4H, m-Mes), 6.52
3
3
3
1.69 (each m, each 1H, CH2),1 2.15/1.96 (each m, each 2H, (dt, JHH = 17.4 Hz, JHH = 6.2 Hz, 1H, vCH), 6.43 (d, JHH
=
CH2),1 2.05/2.00 (each m, each 2H, CH2),1 1.97 (m, 2H, CHB),1 17.4 Hz, 1H, vCHB), 2.71 (m, 2H, CH2P), 2.33 (s, 12H, o-CH3),
0.69 (s, 9H, CH3), [1 from the GHSQC experiment]. 13C{1H} 2.04 (s, 6H, p-CH3), 1.97 (m, 2H, vCH2), 1.81 (m, 2H, CH2B),
NMR (126 MHz, [d6]-benzene, 299 K): δ = 132.9 (br, CuN), 1.25 (sex, JHH = 7.5 Hz, 2H, CH2), 0.76 (t, JHH = 7.5 Hz, 3H,
120.2 (br, i-C6F5), 58.6 (CCH3), 34.5 (CH2), 30.8 (CH2), 28.6 CH3). 13C{1H} NMR (151 MHz, [d6]-benzene, 299 K): δ = 161.9
3
3
2
(CH3), 24.65 (CH2), 24.62 (CH2), 22.1 (br, CHB) [C6F5 not (vCH), 142.2 (d, JPC = 12.7 Hz, o-Mes), 138.0 (p-Mes), 135.2
listed]. 11B{1H} NMR (160 MHz, [d6]-benzene, 299 K): δ = −16.6 (br, vCHB), 132.9 (d, JPC = 19.2 Hz, i-Mes), 130.4 (d, JPC
=
1
3
(ν1/2 ∼ 140 Hz). 19F NMR (470 MHz, [d6]-benzene, 299 K): δ = 3.3 Hz, m-Mes), 38.5 (vCH2), 23.9 (br d, 2JPC = 15.6 Hz, CH2B),
1
3
−132.5 (m, 2F, o-C6F5), −159.3 (m, 1F, p-C6F5), −164.3 (m, 2F, 23.7 (d, JPC = 11.9 Hz, CH2P), 23.3 (d, JPC = 12.7 Hz, o-CH3),
m-C6F5), [Δδ19Fpm = 5.0]. 21.5 (CH2), 20.8 (p-CH3), 13.8 (CH3) [C6F5 not listed]. 31P{1H}
X-ray crystal structure analysis of 6. Formula C19H23BF5N, NMR (243 MHz, [d6]-benzene, 295 K): δ = −11.4 (ν1/2 ∼ 10 Hz).
M = 371.19, colourless crystal, 0.42 × 0.35 × 0.18 mm, a = 11B{1H} NMR (192 MHz, [d6]-benzene, 299 K): δ = 63.6
27.7049(7), b = 9.8068(2), c = 13.6633(5) Å, β = 93.373(2)°, V = (ν1/2 ∼ 1000 Hz). 19F NMR (564 MHz, [d6]-benzene, 299 K): δ =
3705.84(18) Å3, ρcalc = 1.331 g cm−3, μ = 0.956 mm−1, empirical −131.8 (m, 2F, o-C6F5), −154.0 (m, 1F, p-C6F5), −162.4 (m, 2F,
absorption correction (0.689 ≤ T ≤ 0.846), Z = 8, monoclinic, m-C6F5), [Δδ19Fpm = 8.4].
space group C2/c (No. 15), λ = 1.54178 Å, T = 223(2) K, ω and φ
Preparation of compound 9. Compound 4 (100.0 mg,
scans, 11 474 reflections collected ( h, k, l), [(sin θ)/λ] = 0.21 mmol, 1.00 equiv.) and 1-pentyne (20.8 μL, 0.21 mmol,
0.60 Å−1, 3167 independent (Rint = 0.030) and 3026 observed 1.00 equiv.) were dissolved in toluene (20 mL) and stirred over-
reflections [I > 2σ(I)], 238 refined parameters, R = 0.038, wR2 = night. Pyridine (17 μL, 0.21 mmol, 1.00 equiv.) was added and
0.101, max. (min.) residual electron density 0.22 (−0.15) e Å−3
,
the reaction mixture was again stirred overnight. The solvent
hydrogen atoms calculated and refined as riding atoms.
was removed in vacuo and to the remaining crude product
Preparation of compound 7. Compound
4 (200.0 mg, pentane (10 mL) was added. The solution was stored at −40 °C
0.42 mmol, 1.00 equiv.) and pyridine (17 μL, 0.42 mmol, overnight, and the formed white crystals were separated by
1.00 equiv.) were dissolved in toluene (20 mL). After stirring removal of the pentane through cannula. The product was
for one day the solvent was removed in vacuo and the remain- dried in vacuo (105.9 mg, 81%). Crystals suitable for X-ray
ing crude product was dissolved in pentane (20 mL). The solu- crystal structure analysis were obtained by crystal growth in
tion was stored overnight at −40 °C. The pentane was removed pentane at −40 °C. M.p.: 131 °C (DSC). Anal. calc. for
via cannula and the remaining white precipitate was dried C36H40BF5NP (544.39 g mol−1): C 69.35, H 6.47, N 2.25; found:
in vacuo. The remaining solid was dissolved in dichloro- C 68.32, H 6.40, N 2.01. 1H NMR (600 MHz, [d6]-benzene,
methane (20 mL) and afterwards dried in vacuo. The product 299 K): δ = 7.94 (m, 2H, o-Py), 6.71 (m, 1H, p-Py), 6.70 (m, 2H,
could be obtained as a white solid (168.8 mg, 72%). M.p.: m-Mesa), 6.67 (m, 2H, m-Mesb), 6.35 (m, 2H, m-Py), 6.21 (d,
3
3
146 °C (DSC). Anal. calc. for C31H32BF5NP (476.27 g mol−1): 3JHH = 17.3 Hz, 1H, vCHB), 5.46 (dt, JHH = 17.3 Hz, JHH
=
C 67.04, H 5.81, N 2.52; found: C 66.14, H 5.74, N 2.32. IR 6.5 Hz, 1H, vCH), 2.48/1.80 (each m, each 1H, CH2P), 2.43
(KBr): ˜ν = 2373 (m, B-H). 1H NMR (600 MHz, [d6]-benzene, (s, 6H, o-CH3 ), 2.34 (s, 6H, o-CH3b), 2.18 (m, 2H, vCH2), 2.08
a
714 | Dalton Trans., 2013, 42, 709–718
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(s, 3H, p-CH3 ), 2.07 (s, 3H, p-CH3b), 1.54/1.22 (each m, each (77.0 mg, 56%). M.p.: 58 °C (DSC). 1H NMR (500 MHz,
a
3
3
1H, CH2B), 1.44 (sex, JHH = 7.4 Hz, 2H, CH2), 0.93 (t, JHH
=
[d6]-benzene, 299 K): δ = 7.74 (m, 2H, o-Py), 7.18 (m, 2H,
7.4 Hz, 3H, CH3). 13C{1H} NMR (151 MHz, [d6]-benzene, m-Ph), 7.14 (m, 2H, o-Ph), 7.06 (m, 1H, p-Ph), 6.72 (m, 2H,
299 K): δ = 145.2 (o-Py), 142.20 (d, JPC = 12.5 Hz, o-Mesa), m-Mesa), 6.671 (m, 1H, p-Py), 6.668 (m, 2H, m-Mesb), 6.30 (m,
2
2
a
142.16 (d, JPC = 12.8 Hz, o-Mesb), 139.4 (p-Py), 138.9 (br, 2H, m-Py), 2.45 (s, 6H, o-CH3 ), 2.41/1.90 (each m, each 1H,
vCHB), 137.8 (vCH), 137.1 (p-Mesa), 137.0 (p-Mesb), 135.3 (d, CH2P), 2.35 (s, 6H, o-CH3b), 2.26/2.13 (each m, each 1H,
1JPC = 25.3 Hz, i-Mesb), 135.0 (d, JPC = 25.0 Hz, i-Mesa), 130.3 CH2Ph), 2.09 (s, 3H, p-CH3 ), 2.07 (s, 3H, p-CH3b), 1.46/1.26
1
a
(d, JPC = 2.5 Hz, m-Mesa), 130.2 (d, JPC = 2.5 Hz, m-Mesb), (each m, each 1H, PhCH2B), 1.43/1.15 (each m, each 1H,
3
3
124.8 (m-Py), 38.9 (vCH2), 24.6 (d, 1JPC = 16.0 Hz, CH2P), 23.43 PCH2B). 13C{1H} NMR (126 MHz, [d6]-benzene, 299 K): δ =
(d, JPC = 13.0 Hz, o-CH3 ), 23.41 (d, JPC = 13.0 Hz, o-CH3b), 146.9 (i-Ph), 144.9 (o-Py), 142.2 (d, JPC = 12.7 Hz, o-Mesa),
3
a
3
2
23.1 (CH2), 21.6 (br, CH2B), 20.8 (p-CH3a,b), 14.1 (CH3) [C6F5 142.1 (d, JPC = 12.7 Hz, o-Mesb), 139.3 (p-Py), 137.3 (p-Mesa),
2
not listed]. 31P{1H} NMR (243 MHz, [d6]-benzene, 299 K): δ = 136.9 (p-Mesb), 135.3 (d, JPC = 25.5 Hz, i-Mesb), 135.0 (d, JPC
1
1
−15.9 (ν1/2 ∼ 4 Hz). 11B{1H} NMR (192 MHz, [d6]-benzene, = 24.5 Hz, i-Mesa), 130.29 (d, JPC = 2.7 Hz, m-Mesa), 130.26 (d,
3
299 K): δ = 0.5 (ν1/2 ∼ 500 Hz). 19F NMR (564 MHz, 3JPC = 2.6 Hz, m-Mesb), 128.44 (m-Ph), 128.36 (o-Ph), 125.4
[d6]-benzene, 299 K): δ = −132.3 (m, 2F, o-C6F5), −159.8 (m, 1F, (p-Ph), 124.8 (m-Py), 32.8 (CH2Ph), 26.6 (br, PhCH2B), 24.1 (d,
p-C6F5), −164.2 (m, 2F, m-C6F5), [Δδ19Fpm = 4.4].
1JPC = 15.9 Hz, CH2P), 23.08 (d, JPC = 12.9 Hz, o-CH3b), 23.06
3
3
a
X-ray crystal structure analysis of 9. Formula C36H40BF5NP, (d, JPC = 13.1 Hz, o-CH3 ), 20.813, 20.810 (p-CH3a,b), 20.5 (br,
M = 623.47, colourless crystal, 0.23 × 0.15 × 0.05 mm, a = PCH2B) [C6F5 not listed]. 31P{1H} NMR (202 MHz, [d6]-benzene,
7.5810(2), b = 16.8998(4), c = 31.7784(8) Å, β = 98.408(1)°, V = 299 K): δ = −15.9 (ν1/2 ∼ 3 Hz). 11B{1H} NMR (160 MHz, [d6]-
3315.73(13) Å3, ρcalc = 1.249 g cm−3, μ = 1.188 mm−1, empirical benzene, 299 K): δ = 1.6 (ν1/2 ∼ 470 Hz). 19F NMR (470 MHz,
absorption correction (0.771 ≤ T ≤ 0.943), Z = 4, monoclinic, [d6]-benzene, 299 K): δ = −132.6 (m, 2F, o-C6F5), −159.2 (m, 1F,
space group P21/c (No. 14), λ = 1.54178 Å, T = 223(2) K, ω and φ p-C6F5), −164.0 (m, 2F, m-C6F5) [Δδ19Fpm = 4.8].
scans, 28 006 reflections collected ( h, k, l), [(sin θ)/λ] =
Generation of compound 12. Compound 4 (16.1 mg,
0.60 Å−1, 5714 independent (Rint = 0.064) and 4354 observed 0.03 mmol, 1.00 equiv.) and dimesitylvinylphosphane
reflections [I > 2σ(I)], 404 refined parameters, R = 0.053, wR2 = (10.0 mg, 0.03 mmol, 1.00 equiv.) were dissolved in 0.8 mL
0.141, max. (min.) residual electron density 0.15 (−0.27) e Å−3
,
[d6]-benzene. After five days the desired product was formed
hydrogen atoms calculated and refined as riding atoms.
(ratio of 12 and the remaining dimesitylvinylphosphane from
1
Generation of compound 10. Compound
4
(54.1 mg, 1H-NMR = 2 : 1). H NMR (600 MHz, [d6]-benzene, 299 K): δ =
0.11 mmol, 1.00 equiv.) and styrene (13 μL, 0.11 mmol, 6.60 (br, 4H, m-Mes), 2.56 (br m, 2H, CH2P), 2.26 (br, 12H,
3
1.00 equiv.) were dissolved in 0.8 mL [d6]-benzene. After one o-CH3), 2.03 (s, 6H, p-CH3), 1.67 (br dm, JPH = 24.8 Hz, 2H,
day the desired product was formed as a clear solution (ratio CH2B). 13C{1H} NMR (151 MHz, [d6]-benzene, 299 K): δ = 142.1
1
1
2
1
of 10 and remaining styrene from H-NMR = 1 : 0.2). H NMR (br d, JPC ∼ 12 Hz, o-Mes), 138.3 (br, p-Mes), 131.9 (br d, JPC
(600 MHz, [d6]-benzene, 299 K): δ = 7.12 (m, 2H, m-Ph), 7.03 ∼ 12 Hz, i-Mes), 130.5 (br, m-Mes), 25.0 (br, CH2P), 23.1 (br d,
(m, 2H, o-Ph), 7.02 (m, 1H, p-Ph), 6.58 (m, 4H, m-Mes), 2.62 3JPC = 12.4 Hz, o-CH3), 22.4 (br, CH2B), 20.7 (p-CH3). 31P{1H}
(m, 2H, CH2P), 2.59 (m, 2H, CH2Ph), 2.26 (s, 12H, o-CH3), 2.00 NMR (243 MHz, [d6]-benzene, 299 K): δ = −5.5 (m). 11B{1H}
3
(s, 6H, p-CH3), 1.81 (dm, JPH = 28.5 Hz, 2H, PCH2B), 1.80 NMR (192 MHz, [d6]-benzene, 299 K): δ = 40.5 (ν1/2 ∼ 620 Hz).
(m, 2H, PhCH2B). 13C{1H} NMR (151 MHz, [d6]-benzene, 19F NMR (564 MHz, [d6]-benzene, 299 K): δ = −131.5 (br m, 2F,
2
299 K): δ = 144.4 (i-Ph), 142.1 (d, JPC = 11.5 Hz, o-Mes), 138.7 o-C6F5), −155.8 (br, 1F, p-C6F5), −163.3 (br m, 2F, m-C6F5),
(p-Mes), 131.1 (d, 1JPC = 10.7 Hz, i-Mes), 130.5 (d, 3JPC = 4.3 Hz, [Δδ19Fpm = 7.5].
m-Mes), 128.6 (m-Ph), 128.1 (o-Ph), 125.9 (s, p-Ph), 31.6 (d, J =
Preparation of compound 13. Compound 4 (100.0 mg,
7.3 Hz, CH2Ph), 29.9 (br, PhCH2B), 24.6 (CH2P). 24.2 (br d, JPC 0.21 mmol, 1.00 equiv.) and dimesitylvinylphosphane
= 17.0 Hz, PCH2B), 23.0 (d, 3JPC = 11.0 Hz, o-CH3), 20.7 (p-CH3), (62.2 mg, 0.21 mmol, 1.00 equiv.) were dissolved in toluene
[C6F5 not listed]. 31P{1H} NMR (243 MHz, [d6]-benzene, 299 K): (10 mL) and stirred for six days. Then pyridine (17 μL,
δ = −3.4 (ν1/2 ∼ 10 Hz). 11B{1H} NMR (192 MHz, [d6]-benzene, 0.21 mmol, 1.00 equiv.) was added and the solution was
299 K): δ = 58.8 (ν1/2 ∼ 950 Hz). 19F NMR (564 MHz, stirred overnight. The solvent was removed in vacuo and the
[d6]-benzene, 299 K): δ = −132.0 (m, 2F, o-C6F5), −154.6 (m, 1F, remaining crude product was dissolved in dichloromethane
2
p-C6F5), −162.7 (m, 2F, m-C6F5), [Δδ19Fpm = 8.1].
(10 mL). After removing the dichloromethane the crude
Preparation of compound 11. Compound 4 (100.0 mg, product was dissolved in pentane (10 mL) and stored at −40 °C
0.21 mmol, 1.00 equiv.) and styrene (24.0 μL, 0.21 mmol, for one day. Since there was no crystallisation observed half of
1.00 equiv.) were dissolved in toluene (20 mL) and stirred over- the pentane was removed and the solution was again stored at
night. Pyridine (17 μL, 0.21 mmol, 1.00 equiv.) was added and −40 °C. After removing the pentane through cannula filtration
the reaction mixture was again stirred overnight. The solvent the desired product could be obtained as a white solid
was removed in vacuo and to the remaining crude product (68.7 mg, 38%). Crystals suitable for X-ray crystal structure
pentane (10 mL) was added. The solution was stored at −40 °C analysis were obtained by the diffusion method of a dichloro-
overnight, and the resulting colourless solid was separated by methane–heptane solution at −40 °C. M.p.: not observed
removal of the pentane through cannula and dried in vacuo between 40 and 350 °C (DSC). Anal. calc. for C51H57BF5NP2
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(851.76 g mol−1): C 71.92; H 6.75; N 1.64; found: C 70.46; 299 K) δ 6.04 (1H, s, N-CHvC), 2.42 (4H, m, CvCH–N–CH2),
H 6.53; N 1.34. 1H NMR (500 MHz, [d6]-benzene, 299 K): δ = 2.23 and 1.85 (each 2H, m, BCH–CH2–CH2), 2.13 (5H, m,
7.67 (m, 2H, o-Py), 6.69 (m, 4H, m-Mesa), 6.67 (m, 4H, Al–CH2–CH and H3C–N–CH2), 2.06 and 1.94 (each 4H, m,
m-Mesb), 6.62 (m, 1H, p-Py), 6.24 (m, 2H, m-Py), 2.38 (s, 12H, BCH–CH2), 1.86 (3H, s, N–CH3), 1.61 br. (2H s, AlH2B), 1.45
a
3
o-CH3 ), 2.34 (s, 12H, o-CH3b), 2.23/1.87 (each m, each 2H, (2H, m, BCH), 1.19 and 1.18 (each 3H, d, JH–H = 6.4 Hz,
CH2P), 2.09 (s, 6H, p-CH3 ), 2.06 (s, 6H, p-CH3b), 1.29/1.01 Al–CH2–CHMe2), 0.61 (1H, dd, JH–H = 6.2 Hz, JH–H = 14.1 Hz,
a
3
2
(each m, each 2H, CH2B). 13C{1H} NMR (126 MHz, [d6]- Al–CH2), 0.16 (1H, dd, 3JH–H = 7.4 Hz, 2JH–H = 14.1 Hz, Al–CH2),
benzene, 299 K): δ = 144.8 (o-Py), 142.2 (d, JPC = 12.8 Hz, 0.21 (9H, s, SiMe3); 11B{1H} NMR (128 MHz, [d6]-benzene,
2
o-Mesb), 142.1 (d, JPC = 12.7 Hz, o-Mesa), 139.2 (p-Py), 137.1 299 K) −7.7. 13C{1H} NMR (100 MHz, [d6]-benzene, 299 K)
2
(p-Mesa), 137.0 (p-Mesb), 135.17 (d, JPC = 25.1 Hz, i-Mesb), δ 156.5 (Al–CvC), 150.8 (Al–CvC), 53.3 (N–CH2–CH2–N–CH3),
1
135.04 (d, JPC = 25.1 Hz, i-Mesa), 130.23 (d, JPC = 2.4 Hz, 52.5 (N–CH2–CH2–N–CH3), 45.6 (N–CH3), 34.8 and 34.7
1
3
m-Mesa), 130.21 (d, JPC = 2.5 Hz, m-Mesb), 124.8 (m-Py), 23.8 (B–CH–CH2), 28.6 and 28.0 (Al–CH2–CHMe2), 26.7 (Al–CH2–
3
(d, JPC = 15.9 Hz, CH2P), 23.5, 23.4 (o-CH3a,b), 20.8 (p-CH3a,b), CH), 25.5 (B–CH–CH2–CH2), 20.3 (Al–CH2), 19.2 (BCH), −0.5
1
20.1 (br, CH2B) [C6F5 not listed]. 31P{1H} NMR (202 MHz, [d6]- (SiMe3); 29Si{dept} NMR (79 MHz, [d6]-benzene, 299 K) δ −10.2.
benzene, 299 K): δ = −15.8 (ν1/2 ∼ 3 Hz). 11B{1H} NMR MS (EI, 20 eV, 80 °C): 347 (4) [M − i-Bu]+, 248 (3) [M − i-Bu −
(160 MHz, [d6]-benzene, 299 K): δ = 1.5 (ν1/2 ∼ 660 Hz). N(CH2CH2)2NMe]+, 220 (69) [M − H − C8H14 − SiMe3]+, 114 (9),
19F NMR (470 MHz, [d6]-benzene, 299 K): δ = −132.7 (m, 2F, 113 (100) [c-octane + H]+. Anal. calcd for C22H46AlBN2Si
o-C6F5), −159.5 (m, 1F, p-C6F5), −164.0 (m, 2F, m-C6F5), (404.5): C, 65.3; H, 11.5; N, 6.9. Found: C, 65.3; H, 11.5; N, 6.8.
[Δδ19Fpm = 4.5].
X-ray crystal
X-ray crystal structure analysis of 16. Formula C22H46AlBN2-
13. Formula Si, M = 404.49, colourless crystal, 0.27 × 0.19 × 0.09 mm, a =
structure
analysis
of
C51H57BF5NP2, M = 851.73, colourless crystal, 0.10 × 0.08 × 10.2424(5), b = 10.8886(6), c = 13.5329(6) Å, α = 70.176(4), β =
0.05 mm, a = 10.8480(20), b = 13.0140(30), c = 19.4660(40) Å, 88.676(4), γ = 68.055(4)°, V = 1307.62(11) Å3, ρcalc = 1.027 g
α = 95.900(30), β = 92.540(30), γ = 110.500(30)°, V = 2550.9(9) Å3, cm−3, μ = 0.133 mm−1, empirical absorption correction
ρcalc = 1.109 g cm−3, μ = 1.183 mm−1, empirical absorption (0.965 ≤ T ≤ 0.988), Z = 2, triclinic, space group P1 (No. 2), λ =
ˉ
ˉ
correction (0.890 ≤ T ≤ 0.943), Z = 2, triclinic, space group P1 0.71073 Å, T = 153(2) K, ω and φ scans, 10 412 reflections
(No. 2), λ = 1.54178 Å, T = 223(2) K, ω and φ scans, 29 514 collected ( h, k, l), 6227 independent (Rint = 0.031) and 4403
reflections collected ( h, k, l), [(sin θ)/λ] = 0.60 Å−1, 8352 observed reflections [I > 2σ(I)], 258 refined parameters, R =
independent (Rint = 0.114) and 4806 observed reflections 0.038, wR2 = 0.089, max. (min.) residual electron density 0.41
[I > 2σ(I)], 553 refined parameters, R = 0.066, wR2 = 0.176, max. (−0.26) e Å−3, H1 and H2 atoms were refined freely, other
(min.) residual electron density 0.27 (−0.23) e Å−3, hydrogen hydrogen atoms were calculated and refined as riding atoms.
atoms calculated and refined as riding atoms.
Work carried out by the Uhl and Würthwein groups
Acknowledgements
Generation of compound 16. The Al–N compound 14
(1.265 g, 3.74 mmol) was dissolved in 50 mL of cyclopentane Financial support from the Deutsche Forschungsgemeinschaft
and treated with neat 9-BBN (0.912 g, 7.47 mmol, 2 equiv.) at is gratefully acknowledged.
room temperature. The mixture was stirred for 20 h at room
temperature. Small quantities of unknown and insoluble
impurities were filtered off. The solvent of the filtrate was
removed in vacuo, and the residue was dissolved in n-hexane.
Notes and references
Colourless crystals of the mixed aluminium/boron compound
16 precipitated on cooling the solution to −28 °C. They con-
tained approximately 5% of an impurity of the by-product
1 D. W. Stephan and G. Erker, Angew. Chem., 2010, 122, 50,
(Angew. Chem. Int. Ed., 2010, 49, 46).
2 (a) G. Erker, Dalton Trans., 2011, 40, 7475; (b) G. Erker,
Organometallics, 2011, 30, 358; (c) D. W. Stephan, Dalton
Trans., 2009, 3129; (d) D. W. Stephan, Org. Biomol. Chem.,
2008, 6, 1535.
1
9-isobutyl–9-BBN [15; H NMR (400 MHz, [d6]-benzene) δ 2.02
(1H, m, B-CH2-CH), 1.78–1.85 (6H, m), 1.60–1.76 (6H, m), 1.37
(2H, d, 3JH–H = 7.9 Hz, BCH2), 1.23 (2H, m), 0.98 (6H, d, 3JH–H
=
6.6 Hz, CH3)16] which could be removed by a second recrystalli-
zation step. The yield is based on the purified product
(0.474 g, 31%); mp 106 °C (dec.). IR (CsI, paraffin) 2054 s, 2025
s, br., 1975 s, 1962 s ν(Al–H–B), 1557 s ν(CvC), 1462 vs
(paraffin), 1400 w δ(CH3), 1375 vs (paraffin), 1346 m, 1315 m,
1288 vs, 1246 vs δ(CH3), 1205 w, 1177 m, 1157 vs, 1126 m,
1111 s, 1076 m, 1049 vs, 1013 s ν(CC), ν(BC), ν(CN), 984 s,
932 m, 914 m, 845 vs, 775 w, 748 s ρ(CH3Si), 721 w (paraffin),
691 m, 660 s νas(SiC), 631 m, 610 w νs(SiC), 528 vs, 517 vs, 471
s, 440 vs ν(AlC), ν(AlN) cm−1. 1H NMR (400 MHz, [d6]-benzene,
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