Al/P-based frustrated lewis pairs: Limitations of their synthesis by hydroalumination and formation of dialkylaluminum hydride adducts

Article abstract of DOI:10.1021/om4012246

Aluminum-phosphorus-based frustrated Lewis pairs (Al/P FLPs) are valuable reagents for the dipolar activation or coordination of small molecules or ionic compounds. They are accessible by hydroalumination of alkynylphosphines. However, as reported in this article, the application of this simple method for the synthesis of a broad variety of different compounds is limited to sterically shielded systems. Hydroalumination of Mes₂PC≡CPh with small dialkyl- or diarylaluminum hydrides HAlR₂ (R = Me, iBu, Ph) afforded unique adducts in which an HAlR₂ molecule was coordinated by the Al/P FLP Mes₂PC(=CHPh)AlR₂ via an Al-P and an Al-H-Al 3c bond. A new Al/P FLP was obtained with equimolar quantities of dineopentylaluminum hydride. The less shielded alkynylphosphine Ph₂PC≡CPh yielded a hydride adduct with HAlNp₂ and an alkyne adduct with HAltBu ₂. The latter compound resulted from triple-bond activation and had a five-membered AlPC₃ heterocycle in which a C=C bond was bonded to the P and Al atoms of an Al/P FLP. Both compounds were isolated in high yields by application of the appropriate stoichiometric ratios of the starting materials.

Full text of DOI:10.1021/om4012246

Article
pubs.acs.org/Organometallics
Al/P-Based Frustrated Lewis Pairs: Limitations of Their Synthesis by
Hydroalumination and Formation of Dialkylaluminum Hydride
Adducts
Werner Uhl,* Christian Appelt, Jana Backs, Hauke Westenberg, Agnes Wollschlager, and Jens Tannert
̈
Institut fur Anorganische und Analytische Chemie der Universitat Munster, Corrensstraße 30, D-48149 Munster, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Aluminum−phosphorus-based frustrated Lewis
pairs (Al/P FLPs) are valuable reagents for the dipolar
activation or coordination of small molecules or ionic
compounds. They are accessible by hydroalumination of
alkynylphosphines. However, as reported in this article, the
application of this simple method for the synthesis of a broad
variety of different compounds is limited to sterically shielded
systems. Hydroalumination of Mes2PCCPh with small
dialkyl- or diarylaluminum hydrides HAlR2 (R = Me, iBu, Ph) afforded unique adducts in which an HAlR2 molecule was
coordinated by the Al/P FLP Mes2PC(CHPh)AlR2 via an Al−P and an Al−H−Al 3c bond. A new Al/P FLP was obtained
with equimolar quantities of dineopentylaluminum hydride. The less shielded alkynylphosphine Ph2PCCPh yielded a hydride
adduct with HAlNp2 and an alkyne adduct with HAltBu2. The latter compound resulted from triple-bond activation and had a
five-membered AlPC3 heterocycle in which a CC bond was bonded to the P and Al atoms of an Al/P FLP. Both compounds
were isolated in high yields by application of the appropriate stoichiometric ratios of the starting materials.
butyl groups prevents direct Al−P interactions by adduct
formation, and the conflicting Lewis acidic and basic
functionalities are preserved. The simple method for the
generation of these compounds by hydroalumination of easily
accessible alkynylphosphines with versatile dialkylaluminum
hydrides should allow the facile synthesis of a broad variety of
different Al/P FLPs and an optimization of their properties
with respect to steric shielding and inductive or mesomeric
effects. Systematic investigations into the course of such
reactions are reported in this article. The unique geminal
arrangement of donor and acceptor atoms in compounds 1 and
2 favors their specific and in part unprecedented reactivity; a
similar structure has in the meantime been reported also for a
B/P system.11
INTRODUCTION
■
Aluminum−phosphorus-based frustrated Lewis pairs (Al/P
FLPs) have attracted considerable interest in current research
as powerful alternatives to the well-established class of
corresponding boron−phosphorus compounds.1 These Al/P
FLPs effectively coordinate and activate small molecules such as
carbon dioxide,2−4 terminal alkynes,2,5 alkenes,6 hydrogen,7
carbonyl compounds,8 and isocyanates.4 They have been
successfully applied as ion-pair receptors for the coordination
of strongly polar alkali-metal hydrides and in hydride transfer
reactions by phase transfer catalysis,9 and they proved to be
efficient catalysts for the dehydrogenation of amine−boranes.10
Unimolecular Al/P FLPs were conveniently obtained in high
yield by hydroalumination of ethynyldimesitylphosphines with
dineopentyl- or di-tert-butylaluminum hydride.2 The polarity of
the phosphorus−alkynyl bonds with a partial negative charge at
the α-carbon atoms causes the selective arrangement of the Al
and P atoms in geminal positions (1 and 2; Scheme 1). The
high steric shielding by two mesityl and two neopentyl or tert-
RESULTS AND DISCUSSION
■
Reactions of Dimesityl(phenylethynyl)phosphine
with Dialkyl- and Diarylaluminum Hydrides. Reactions
of Mes2PCCPh with equimolar quantities of R2AlH bearing
relatively small alkyl or aryl groups (R = Me, iBu, Ph) resulted
in the formation of new Al/P compounds, but 50% of the
starting phosphine remained unchanged. Its complete con-
sumption was only observed with an excess of the hydride of at
least 100% (eq 1). The solid products 3−5 were isolated in
high yields of 66−95%. Crystal structure determinations
(Figures 1 and 2) verified the formation of adducts of an Al/
Scheme 1. Al/P FLPs Obtained by Hydroalumination of
Alkynyldimesitylphosphines
a
a
Received: December 23, 2013
Published: February 18, 2014
Abbreviations: Np, neopentyl; Mes, mesityl; Ph, phenyl.
© 2014 American Chemical Society
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Article
differ, the smaller values were found to the Al atoms bonded to
P (1.63 vs 1.78 Å on average; Al···Al 3.17 Å). Al and H atoms at
the CC double bonds adopt trans positions in all cases
(similar to the case for 2; Scheme 1). Other structural
parameters are unexceptional (P−C in the heterocycle 1.811 Å
(on average); Al−C in the heterocycle 2.018 Å; CC 1.345 Å;
Al−C−P 115.1°). The NMR spectra were in accordance with
these molecular structures and exhibited the resonances of the
bridging H atoms between both Al atoms (δ 3.96 (3), 3.84 (4),
and 5.11 (5)) and of two different AlR2 groups. The Al−H
resonances were split into doublets caused by coupling to the P
atoms (2JPH = 36.0, 36.7, and 43.0 Hz). The unusual low-field
shift of the bridging H atom in the spectrum of 5 was similarly
observed for the starting compound diphenylaluminum hydride
(δ 4.63).13 The vinylic H atoms resonated at δ 7.57 (3), 7.58
3
(4), and 7.87 (5) with JPH coupling constants of 37.2, 37.8,
and 37.0 Hz. These values are characteristic of a cis-
arrangement of H and four-coordinate P atoms across CC
double bonds and were observed in the same range for cyclic
adducts of FLP 2 and related compounds.3,6 The 31P NMR
shifts (δ −10.4 to −11.8) were in the expected range of Al/P-
based FLP adducts.3,8−10 The Al−H−Al bridges gave broad
absorptions in the IR spectra at about 1700 cm−1. Only the
mass spectrum of the dimethylaluminum compound 3 is
indicative of the formation of the adduct (M+ − CH3), while in
all other cases only fragments of the aluminum-free vinyl-
phosphine backbone were detected. In attempts to generate the
free FLPs, we heated reaction mixtures containing equimolar
quantities of the alkynylphosphine and the corresponding
dialkylaluminum hydride adducts 3−5 in toluene for several
days (50−75 °C). In no case did we observe any alteration of
the NMR intensities, and there was no indication for the
formation of an FLP similar to 1 or 2.
Figure 1. Molecular structure and atomic numbering scheme of
compound 3. A similar structure was observed for compound 4.
Displacement ellipsoids are drawn at the 40% level. Hydrogen atoms
(except H(1) and the vinylic H atom, arbitrary radius) are omitted for
clarity. Important bond lengths (Å) and angles (deg): compound 3,
Al(1)−C(1) 2.013(3), Al(1)−H(1) 1.81(3), P(1)−C(1) 1.812(3),
C(1)−C(11) 1.344(4), P(1)−Al(2) 2.505(1), Al(2)−H(1) 1.64(3),
P(1)−C(1)−Al(1) 114.5(3), C(1)−P(1)−Al(2) 98.05(9); compound
4, Al(1)−C(1) 2.027(2), Al(1)−H(1) 1.78(2), P(1)−C(1) 1.812(2),
C(1)−C(2) 1.344(2), P(1)−Al(2) 2.5214(7), Al(2)−H(1) 1.61(2),
P(1)−C(1)−Al(1) 114.85(8), C(1)−P(1)−Al(2) 99.96(5).
The steric demand of neopentyl groups is intermediate
between those of tert-butyl and isobutyl groups, which causes a
unique behavior of dineopentylaluminum hydride. Treatment
of Mes2PCCPh with equimolar quantities of the hydride
afforded a mixture of three compounds which were identified
1
by their characteristic H and 31P NMR resonances as the
starting alkynylphosphine, the noncoordinated FLP 6, and the
hydride adduct 7. Only in this case warming of the mixture in
toluene to 75 °C for 31 h gave further reaction with the
complete consumption of the starting phosphine and the
quantitative formation of the Al/P FLP 6 (eq 2). 6 was isolated
Figure 2. Molecular structure and atomic numbering scheme of
compound 5. Displacement ellipsoids are drawn at the 40% level.
Hydrogen atoms (except H(1), arbitrary radius) are omitted for
clarity. Important bond lengths (Å) and angles (deg): Al(1)−C(1)
2.014(2), Al(1)−H(1) 1.74(2), P(1)−C(1) 1.809(2), C(1)−C(2)
1.348(2), P(1)−Al(2) 2.5318(7), Al(2)−H(1) 1.63(2), P(1)−C(1)−
Al(1) 115.87(9), C(1)−P(1)−Al(2) 98.79(6).
P FLP with a molecule of HAlR2. Five-membered Al2HPC
heterocycles resulted which have an almost planar arrangement
of the five ring atoms (maximum deviation from the average
plane: 0.11 Å (4) or 0.09 Å (5); C(1)) or an envelope
conformation (3; Al(2) 0.80 Å above the plane of the four
remaining atoms). The Al atoms of the bridging R2AlH
moieties are coordinated by the P atoms and are further
involved in 3c-2e Al−H−Al bonds to the metal atoms of the
FLP backbone. The Al−P bond lengths (2.505(1) (3),
2.5214(7) (4), and 2.5318(7) Å (5)) are in a narrow range
and correspond to standard values.12 The Al−H distances
as a yellow oil and could not be purified by crystallization from
several noncoordinating solvents. Its purity was sufficient for an
unambiguous spectroscopic characterization and may allow its
application in secondary reactions. Treatment of the
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alkynylphosphine with 2 equiv of the hydride afforded a similar
mixture of all three components, but prolonged heating to 75
°C did not result in the quantitative formation of adduct 7.
Instead, unreacted hydride was detected in the NMR spectra.
Almost complete consumption of the alkyne and the FLP 6 was
only observed with a large excess of the hydride (molar ratio
1:3; concentration of residual 6 ∼4%). We suppose that in
solution an equilibrium exists in which the adduct 7 dissociates
partially into the FLP 6 and dineopentylaluminum hydride. A
large excess of the hydride shifted it toward adduct 7. In
addition, compound 7 could not be obtained in a pure,
crystalline form. The 1H NMR spectrum of Al/P FLP 6 showed
the expected integration ratio of two neopentyl to two mesityl
groups. The vinylic H atom gave a doublet at δ 7.33 with a 3JPH
coupling constant of 20.6 Hz, which is similar to that of the
analogous compound 2 (17.7 Hz, cis arrangement of P and H;
see for comparison 1 with 37.9 Hz).3 The P atom resonated at
δ −21.0 in the 31P{1H} NMR spectrum. Adduct 7 showed
NMR parameters closely related to those of compounds 3−5
with two sets of resonances of different neopentyl groups. The
Figure 3. Molecular structure and atomic numbering scheme of
compound 8. Displacement ellipsoids are drawn at the 40% level.
Hydrogen atoms are omitted for clarity. Important bond lengths (Å)
and angles (deg): Al(1)−C(11) 2.039(3), Al(1)−C(61) 2.080(3),
P(1)−C(11) 1.768(3), C(11)−C(12) 1.359(5), C(61)−C(62)
1.356(5), P(1)−C(62) 1.816(3), C(61)−P(2) 1.805(3), P(1)−
C(11)−Al(1) 109.3(2), C(11)−P(1)−C(62) 104.4(2), P(1)−
C(62)−C(61) 118.6(3), C(62)−C(61)−Al(1) 113.5(2), C(61)−
Al(1)−C(11) 92.0(1), Al(1)−C(61)−P(2) 118.5(2).
1
31P NMR signal was shifted to δ −6.9. In the H NMR
spectrum the vinylic H atom gave a doublet at δ 7.66 with a
3JPH coupling constant of 37.5 Hz (37−38 Hz in 3−5; cis
arrangement of P and H), which indicates retention of the
configuration at the CC double bond upon complex
formation. The bridging H atom of the Al−H−Al group was
detected as a doublet at δ 4.03 (2JPH = 38.3 Hz) in the expected
range. The mass spectrum of FLP 6 gave the molecular ion
peak, while only an unspecific fragmentation pattern was
observed for the relatively impure (excess hydride) adduct 7.
Reactions of Diphenyl(phenylethynyl)phosphine.
Steric shielding of the Al/P FLPs may be influenced not only
by the size of the alkyl or aryl groups attached to Al but also by
the substituents at the P atom. We therefore replaced the
mesityl with phenyl groups and applied the alkynylphosphine
Ph2PCCPh in further reactions. Di-tert-butylaluminum
hydride and equimolar quantities of Mes2PCCPh afforded
the Al/P FLP 2 in a selective reaction in more than 80% yield
(Scheme 1).2 It has been applied in many secondary
transformations.2,8−10 The similar reaction of sterically less
shielded Ph2PCCPh (eq 3) gave surprisingly a mixture of a
coordinated by a P and an Al atom. Similar compounds were
obtained by treatment of FLP 2 with terminal alkynes.2 The Al
atom binds to that C atom of the alkyne which is attached to
the phosphine substituent. A relatively high partial negative
charge2 strongly favors the attack of the Al atom at this
position. The P−C and Al−C bonds to the endocyclic ethenyl
moiety are longer than those to the sp2-C atom of the exocyclic
double bond (1.816(3) vs 1.768(3) Å and 2.080(3) vs 2.039(3)
Å; C(61)−P(2) (exocyclic) 1.805(3) Å). The CC bond
lengths (C(11)−C(12) 1.359(5); C(61)−C(62) 1.356(5)) are
closely related to the standard value. The ring deviates slightly
from planarity with the atoms of the endocyclic CC bond
0.10 and 0.09 Å above the average plane. The alkenyl group has
1
a Z configuration, which is also evident from the H NMR
3
parameters of the vinylic hydrogen atom (δ 8.71; JPH = 67.7
Hz). The 31P NMR resonances of the three- and four-
coordinate phosphorus atoms differ only slightly with values of
δ 9.8 and 8.9 (3JPP = 30.4 Hz).
Less shielded dineopentylaluminum hydride gave another
reaction under similar conditions. Complete consumption of
Ph2PCCPh was only observed with 2 equiv of the hydride.
An adduct (9) analogous to those described above (eq 1; 3−5,
7) was isolated in 81% yield after concentration and cooling of
the reaction mixture to −30 °C. A crystal structure
determination (Figure 4) revealed the expected parameters
(Al−P 2.476; Al−H 1.75 and 1.67 Å; Al···Al 3.19 Å; average
values). In contrast to compounds 3−5 and 7 with the
relatively bulky mesityl groups attached to P the diphenyl
compound 9 has the Z configuration at its CC double bond
1
with Al and H atoms on the same side. In the H NMR
spectrum the vinylic H atom gave a doublet at δ 8.26 with a
relatively large 3JPH coupling constant of 53.9 Hz, which verifies
the Z configuration (37−38 Hz in 3−5 and 7). The H atom of
the Al−H−Al bridge resonated at δ 3.74 (2JPH = 28.3 Hz). We
did not find any evidence for the intermediate formation of a
simple FLP corresponding to compounds 1, 2, and 6.
new compound (8) with excess HAltBu2. 8 was isolated in 83%
yield by treatment of HAltBu2 with 2 equiv of Ph2PCCPh
(eq 3). The formation of 8 may be described by the
coordination of an alkyne molecule to an intermediately
formed FLP (Ph2PC(C(H)Ph)AlNp2). A crystal structure
determination (Figure 3) revealed a central unsaturated five-
membered AlPC3 heterocycle with a CC double bond
CONCLUSION
Al/P FLPs contain coordinatively unsaturated Al and P atoms
and are highly reactive amphiphilic compounds which are
■
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with liquid nitrogen. The assignment of the NMR spectra is based on
HMBC, HSQC, ROESY, and DEPT135 data.
Synthesis of the Dimethylaluminum Hydride Adduct 3. A
solution of Mes2PCCPh (0.362 g, 0.98 mmol) in 10 mL of toluene
was added to a solution of excess dimethylaluminum hydride (0.170 g,
2.93 mmol) in 5 mL of toluene at room temperature. The mixture was
stirred for 14 h at 75 °C. All volatiles (excess hydride, solvent) were
removed in vacuo. The residue was dissolved in cyclopentane.
Colorless crystals of 3 precipitated slowly at room temperature. Yield:
0.316 g (66%; based on alkyne). Mp (argon, sealed capillary): 161 °C
dec. Anal. Calcd for C30H41Al2P (486.58): C, 74.1; H, 8.5. Found: C,
74.2; H, 8.7. 31P{1H} NMR (C6D6, 162 MHz, 300 K): δ −11.8 (s, br).
1H NMR (C6D6, 400 MHz, 300 K): δ −0.34 (6 H, d, br, 3JPH = 2.9 Hz,
PAlMe2), −0.19 (6 H, s, CAlMe2), 2.00 (6 H, s, p-CH3), 2.67 (12 H, s,
o-CH3), 3.96 (1 H, d, br, 2JPH = 36.0 Hz, Al−H−Al), 6.62 (4 H, d, 4JPH
3
Figure 4. Molecular structure and atomic numbering scheme of
compound 9. Displacement ellipsoids are drawn at the 40% level.
Hydrogen atoms (except H(1), arbitrary radius) are omitted for
clarity; only one of the two independent molecules is considered.
Important bond lengths (Å) and angles (deg): Al(11)−C(111)
2.009(2), Al(11)−H(1) 1.76(2), P(1)−C(111) 1.804(2), C(111)−
C(112) 1.343(3), P(1)−Al(12) 2.4759(9), Al(12)−H(1) 1.66(2),
P(1)−C(111)−Al(11) 111.5(1), C(111)−P(1)−Al(12) 100.14(8).
= 2.6 Hz, m-HMes), 7.02 (1 H, m, p-HvinylPh), 7.08 (2 H, t, JHH = 7.4
3
Hz, m-HvinylPh), 7.35 (2 H, d, JHH = 7.3 Hz, o-HvinylPh), 7.57 (1 H, d,
3JPH = 37.2 Hz, PCCH). 13C{1H} NMR (C6D6, 101 MHz, 300K): δ
−7.5 (s, br, AlMe2, both resonances coincide), 20.8 (s, p-CH3), 24.1
3
1
(d, JPC = 7.9 Hz, o-CH3), 125.4 (d, JPC = 31.2 Hz, i-CMes), 128.1 (s,
covered, o-CvinylPh), 128.88 (s, m-CvinylPh), 128.91 (s, p-CvinylPh), 131.1
(d, 3JPC = 7.5 Hz, m-CMes), 140.4 (d, 4JPC = 1.9 Hz, p-CMes), 141.6 (d,
3JPC = 24.7 Hz, i-CvinylPh), 142.6 (d, 2JPC = 9.1 Hz, o-CMes), 146.0 (d, br,
2
1JPC = 29.0 Hz, PCCH), 156.0 (d, JPC = 9.6 Hz, PCCH). IR
(paraffin, CsI, cm−1): 1890 w, br ν(AlH); 1688 vw, 1580 vs, 1558 vs
ν(CC), phenyl; 1470 vs (paraffin); 1402 (vs) δ(CH3); 1377 vs
(paraffin); 1339 m, 1321 w, 1306 m δ(CH3); 1152 vs, br ν(AlHAl);
970 vw, 930 vw, 889 vw, 849 vw, 814 w, 785 vw, 762 vw δ(aromatic),
ν(CC); 721 vs (paraffin); 592 w, 559 m, 511 w, 482 m, 447 m δ(CC),
ν(AlC), ν(PC). MS (EI, 30 eV, 373 K): m/z (%) 471 (1), 472 (0.3)
[M+ − CH3], 428 (6), 429 (2) [M+ − HAlMe2], 413 (7), 414 (3) [M+
− HAlMe2 − CH3], 372 (36), 373 (10) [Mes2PC(H)C(H)Ph+],
357 (22), 358 (6) [Mes2PC(H)C(H)Ph+ − CH3], 280 (100), 281
(21) [Mes2PC(H)C(H)Ph+ − CH3 − Ph], 119 (25) [Mes+], 57 (7)
[Me2Al+].
applicable in many stoichiometric or catalytic secondary
reactions. Monomolecular derivatives such as 1,2 2,2 and 6
are easily accessible by hydroalumination of alkynylphosphines.
They have bulky mesityl groups attached to P and tert-butyl or
neopentyl groups bonded to Al. However, there are important
steric limitations for their syntheses. Small groups at Al gave
persistent adducts of the Al/P FLP with the corresponding
dialkylaluminum hydrides, even in those cases where
stoichiometric 1:1 ratios of the starting compounds were
applied. This observation demonstrates impressively the
capability of these FLPs to act as bifunctional ligands for the
effective coordination of polar or ionic compounds. Only
neopentyl groups with a size between those of tert-butyl and
isobutyl groups allowed the generation of both the uncoordi-
nated FLP and the hydride adduct and their mutual
transformation. The hydride adduct 7 seems to be relatively
unstable and dissociated partially in solution to give an
equilibrium mixture with the free FLP and HAlNp2.
Interestingly, the expected formation of dimeric compounds
via intermolecular Al−P interactions was not observed. We
isolated such dimeric Al/P FLPs from the reaction of sterically
less shielded dialkynylphosphines with dialkylaluminum
hydrides,4 which alternatively gave heterocyclic compounds
by condensation.14 These dimeric compounds are still active
Lewis pairs and are capable of coordinating CO2 or PhNC
O after dissociation.4 The compounds described in this paper
will stimulate further investigations. Compound 6 is important
for systematic investigations into the influence of steric
shielding on the reactivity of Al/P FLPs, and the unique
hydride adducts may be applicable to the deprotonation of
acidic compounds and the chelating coordination of the
resulting anions or to hydroalumination reactions.
Synthesis of the Diisobutylaluminum Hydride Adduct 4. A
solution of Mes2PCCPh (0.500 g, 1.35 mmol) in 20 mL of toluene
was treated with diisobutylaluminum hydride (0.384 g, 2.70 mmol) at
room temperature. The mixture was stirred at 65 °C for 17 h. All
volatiles were removed in vacuo. The residue was dissolved in 1,2-
difluorobenzene and cooled to −20 °C to afford colorless crystals of 4.
Yield: 0.842 g (95%). Mp (argon, sealed capillary): 125 °C dec. Anal.
Calcd for C42H65Al2P (654.90): C, 77.0; H, 10.0. Found: C, 77.2; H,
1
10.1. 31P{1H} NMR (C6D6, 162 MHz, 300 K): δ −11.3. H NMR
(C6D6, 400 MHz, 300 K): δ 0.30 and 0.44 (each 2 H, m, CH2 of
PAliBu2), 0.51 (4 H, m, CH2 of CAliBu2), 1.12 (6 H, d, 3JHH = 6.5 Hz,
3
CH3 of PAliBu2), 1.16 (6 H, d, JHH = 6.5 Hz, CH3 of PAliBu2), 1.19
(6 H, d, 3JHH = 6.5 Hz, CH3 of CAliBu2), 1.25 (6 H, d, 3JHH = 6.4 Hz,
CH3 of CAliBu2), 2.02 (2 H, m, CH of PAliBu2), 2.02 (6 H, s, p-CH3),
2.12 (2 H, m, CH of CAliBu2), 2.25 (12 H, s, br, o-CH3), 3.84 (1 H, d,
2
4
br, JPH = 36.7 Hz, Al−H−Al), 6.63 (4 H, d, JPH = 2.8 Hz, m-HMes),
7.03 (1 H, m, p-HvinylPh), 7.11 (2 H, m, m-HvinylPh), 7.33 (2 H, m, o-
HvinylPh), 7.58 (1 H, d, JPH = 37.8 Hz, PCCH). 13C{1H} NMR
3
(C6D6, 101 MHz, 300 K): δ 20.8 (s, p-CH3), 23.7 (d, 2JPC = 12.4 Hz,
CH2 of PAliBu2), 24.4 (s, CH2 of CAliBu2), 24.5 (s, br, o-CH3), 26.8
(d, 3JPC = 2.9 Hz, CH2 of PAliBu2), 27.4 (s, CH of CAliBu2), 28.2 and
28.4 (s, CH3 of PAliBu2), 28.6 and 28.7 (s, CH3 of CAliBu2), 126.4 (d,
1JPC = 29.3 Hz, i-CMes), 128.2 (d, 4JPC = 1.5 Hz, o-CvinylPh), 128.9 (s, m-
3
CvinylPh), 129.0 (s, p-CvinylPh), 131.0 (d, JPC = 7.4 Hz, m-CMes), 140.3
4
3
(d, JPC = 1.9 Hz, p-CMes), 141.6 (d, JPC = 24.6 Hz, i-CvinylPh), 142.3
(d, 2JPC = 9.0 Hz, o-CMes), 146.1 (d, 1JPC = 33.9 Hz, PCCH), 157.6
2
(d, JPC = 10.5 Hz, PCCH). IR (paraffin, CsI, cm−1): 1724 m, br
EXPERIMENTAL SECTION
■
ν(Al−H); 1601 s, 1580 m, 1533 s ν(CC), phenyl; 1462 vs
(paraffin); 1402 s δ(CH3); 1377 vs (paraffin); 1317 s, 1292 m, 1244 w
δ(CH3); 1200 m, 1173 m, 1157 m, 1063 s, 1013 s, 943 s, 924 s, 886 w,
864 m, 847 s, 812 m, 789 m, 746 s δ(aromatic), ν(CC); 721 vs
(paraffin); 702 s, 662 s, 627 s, 611 sh, 592 m, 559 m, 538 sh, 488 m,
451 w, 411 w δ(CC), ν(AlC), ν(PC). MS (EI, 30 eV, 298−573 K): m/
All procedures were carried out under an atmosphere of purified argon
in dried solvents (toluene with Na/benzophenone, n-hexane with
LiAlH4, 1,2-difluorobenzene with molecular sieves). Mes2PCCPh,2
Ph2PCCPh,15 HAlMe2,16 HAltBu2,17 HAlNp2,18 and HAlPh213 were
obtained according to literature procedures. Commercially available
HAliBu2 was distilled under vacuum at room temperature and trapped
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z (%) 373 (100), 374 (27) [Mes2PC(H)C(H)Ph+ + H], 297 (85),
298 (18) [Mes2PC(H)C(H)Ph+ − Ph + 2 H], 119 (5) [Mes+].
Synthesis of the Diphenylaluminum Hydride Adduct 5. A
solution of Mes2PCCPh (0.255 g, 0.69 mmol) in 20 mL of toluene
was treated with a solution of excess diphenylaluminum hydride
(0.326 g, 1.79 mmol) in 20 mL of toluene at room temperature. The
mixture was stirred at room temperature for 24 h. All volatiles were
removed in vacuo. The residue was treated with 20 mL of n-pentane
and filtered to separate the excess diphenylaluminium hydride. The
solvent was removed in vacuo to afford a colorless solid of 5 in high
purity. Yield: 0.470 g (93%, based on alkyne). Mp (argon, sealed
capillary): 104 °C dec. Anal. Calcd for C50H49Al2P (734.86): C, 81.7;
H, 6.7. Found: C, 80.9; H, 6.7. 31P{1H} NMR (C6D6, 162 MHz, 300
noncoordinating solvents. It consisted of the hydride adduct 7, the
excess dineopentylaluminum hydride (dimeric and trimeric formula
units:12 δ 0.65 (CH2), 1.15 (CMe3), 3.34 (AlH) and 0.75, 1.17 and
3.15), and residual solvent. 31P{1H} NMR (C6D6, 162 MHz, 300 K): δ
1
−6.9 (s). H NMR (C6D6, 400 MHz, 300 K): δ 0.60 and 0.74 (4 H,
2
AB spin system, JHH = 15.2 Hz, PAlCH2), 0.89 (4 H, s, CAlCH2),
1.23 (18 H, s, PAl(CH2CMe3)2), 1.30 (18 H, s, CAl(CH2CMe3)2),
2
2.02 (6 H, s, p-CH3), 2.27 (12 H, s, o-CH3), 4.03 (1 H, d, br, JPH
=
38.3 Hz, Al−H−Al), 6.63 (4 H, d, 4JPH = 2.3 Hz, m-HMes), 7.03 (1 H, t,
3JHH = 7.1 Hz, p-HvinylPh), 7.13 (2 H, pseudo-t, m-HvinylPh), 7.39 (2 H,
3
3
d, JHH = 7.5 Hz, o-HvinylPh), 7.66 (1 H, d, JPH = 37.5 Hz, PCCH).
13C{1H} NMR (C6D6, 101 MHz, 300 K): δ 20.7 (s, p-CH3), 25.3 (d,
3JPC = 8.9 Hz, o-CH3), 31.4 (s br, PAlCH2), 31.9 (d, JPC = 2.9 Hz,
3
1
K): δ −10.4. H NMR (C6D6, 400 MHz, 300 K): δ 1.93 (6 H, s, p-
PAl(CH2CMe3)2), 32.1 (s, CAl(CH2CMe3)2), 33.0 (s br, CAlCH2),
35.2 (s, PAl(CH2CMe3)2), 35.3 (s, CAl(CH2CMe3)2), 127.3 (s, ipso-
CMes), 128.6 (s, m-CvinylPh), 128.9 (s, o-CvinylPh), 129.1 (s, p-CvinylPh),
CH3), 2.21 (12 H, s, o-CH3), 5.11 (1 H, d, br, 2JPH = 43.0 Hz, Al−H−
4
Al), 6.44 (4 H, d, JPH = 3.0 Hz, m-HMes), 6.86 (1 H, m, p-HvinylPh),
3
4
6.97 (2 H, m, m-HvinylPh), 7.07 (4 H, m, m-H of PAlPh2), 7.13 (2 H, m,
p-H of PAlPh2), 7.27 (2 H, m, p-H of CAlPh2), 7.29 (4 H, m, m-H of
CAlPh2), 7.53 (4 H, m, o-H of PAlPh2), 7.57 (2 H, m, o-HvinylPh), 7.87
131.0 (d, JPC = 7.1 Hz, m-CMes), 140.1 (d, JPC = 1.9 Hz, p-CMes),
141.6 (d, 3JPC = 25.0 Hz, ipso-CvinylPh), 142.2 (d, 2JPC = 8.9 Hz, o-CMes),
159.3 (d, 2JPC = 10.7 Hz, PCCH); PCCH not observed. MS (EI,
20 eV, 402 K): m/z (%) 539 (0.2) [M+ − 3 CMe3], 457 (1), 458 (0.5)
[M+ − 2 Mes − Me], 372 (31), 373 (11) [Mes2PC(H)C(H)Ph+].
Synthesis of the Diphenyl(phenylethynyl)phosphine Ad-
duct 8. Ph2PCCPh (0.328 g, 1.15 mmol) was dissolved in 10 mL of
n-hexane and treated with a solution of di-tert-butylaluminum hydride
(0.081 g, 0.57 mmol) in 10 mL of n-hexane at room temperature. The
solution was stirred for 10 days. The color changed to yellow, and the
product started to precipitate. The yellow solid was isolated by
filtration. The filtrate was concentrated and cooled to 4 °C to isolate a
second fraction of the solid material. Yield: 0.338 g (83%). Mp (argon,
sealed capillary): 203 °C dec. Anal. Calcd for C48H49AlP2 (714.8): C,
80.7; H, 6.9. Found: C, 80.3, H, 6.9. 31P{1H} NMR (C6D6, 162 MHz,
3
(1 H, d, JPH = 37.0 Hz, PCCH), 7.91 (4 H, m, o-H of CAlPh2).
13C{1H} NMR (C6D6, 101 MHz, 300 K): δ 20.7 (d, 5JPC = 7.8 Hz, p-
3
1
CH3), 25.0 (d, JPC = 8.0 Hz, o-CH3), 124.2 (d, JPC = 33.6 Hz, i-
CMes), 127.4 (s, m-C of PAlPh2), 127.7 (s, m-C of CAlPh2), 128.2 (s,
overlap, o-CvinylPh), 128.3 (s, overlap, o-C of PAlPh2), 128.3 (s, overlap,
o-C of CAlPh2), 129.3 (s, m-CvinylPh), 129.7 (s, p-CvinylPh), 131.3 (d,
3JPC = 7.8 Hz, m-CMes), 138.5 (s, o-C of PAlPh2), 138.9 (s, o-C of
CAlPh2), 141.0 (d, 4JPC = 1.8 Hz, p-CMes), 141.1 (d, 3JPC = 24.5 Hz, i-
CvinylPh), 142.9 (d, 3JPC = 9.3 Hz, o-CMes), 144.0 (s, br, i-C of PAlPh2),
145.9 (s, br, i-C of CAlPh2), 159.0 (d, 2JPC = 9.5 Hz, PCCH); PC
CH not detected. IR (paraffin, CsI, cm−1): 1697 m, br ν(AlH); 1603
m, 1580 w, 1557 w, 1535 m ν(CC), phenyl; 1458 vs (paraffin);
1420 s δ(CH3); 1375 vs (paraffin), 1292 m, 1246 m δ(CH3); 1192 w,
1153 w, 1086 s, 1047 vw, 1026 w, 995 w, 945 m, 931 m, 893 vw, 870
w, 849 m, 795 w, 770 vw, 748 m δ(aromatic), ν(CC); 727 s (paraffin);
700 vs, 665 m, 652 m phenyl; 629 m, 611 vw, 592 w, 579 m, 554 vw,
498 w, 465 m, 453 sh, 419 w δ(CC), ν(AlC), ν(PC). MS (EI, 20 eV,
483 K): m/z (%) 372 (26), 373 (22) [Mes2PC(H)C(H)Ph+], 357
(16), 358 (4) [Mes2PC(H)C(H)Ph+ − CH3], 119 (7) [Mes+].
Synthesis of (E)-Mes2P[CC(H)Ph]AlNp2 (6). A solution of
dineopentylaluminum hydride (0.071 g, 0.42 mmol) in 6 mL of
toluene was treated with a solution of Mes2PCCPh (0.154 g, 0.42
mmol) in 6 mL of toluene at room temperature. The mixture was
stirred for 31 h at 75 °C. The 31P{1H} NMR spectrum showed 10% of
unreacted Mes2PCCPh. To achieve full conversion, a solution of
dineopentylaluminum hydride (0.007 g, 0.04 mmol) in 2 mL of
toluene was added at room temperature. The mixture was stirred for
29 h at 75 °C. All volatiles were removed in vacuo. Compound 6 could
not be purified by crystallization from different noncoordinating
solvents and remained as a yellow waxy material. 31P{1H} NMR
(C6D6, 162 MHz, 300 K): δ −21.0 (s, br). 1H NMR (C6D6, 400 MHz,
300 K): δ 0.41 (4 H, s, CH2CMe3), 1.08 (18 H, s, CMe3), 2.10 (6 H, s,
3
3
300 K): δ 8.9 (d, JPP = 30.4 Hz, endocyclic), 9.8 (d, JPP = 30.4 Hz,
exocyclic). 1H NMR (C6D6, 400 MHz, 300 K): δ 1.54 (18 H, s,
3
CMe3), 6.35 (2 H, d, JHH = 7.8 Hz, o-CH, CC(P)Ph), 6.45 (2 H,
pseudo-t, m-CH, CC(P)Ph), 6.59 (3 H, m, m-CH, CCHPh and
p-CH, CC(P)Ph), 6.69 (1 H, pseudo-t, p-CH, CCHPh), 6.79 (2
3
H, d, JHH = 7.3 Hz, o-CH, CCHPh), 6.85 (4 H, m, m-CH, (C
C)2PPh2), 6.92 (2 H, m, p-CH, (CC)2PPh2), 6.96 (2 H, m, p-CH,
(CC)PPh2), 6.99 (4 H, m-CH, (CC)PPh2), 7.46 (4 H, m, o-CH,
(CC)2PPh2), 7.66 (4 H, m, o-CH, (CC)PPh2), 8.71 (1 H, d, 3JPH
= 67.7 Hz, CCH). 13C{1H} NMR (C6D6, 100 MHz, 300 K): δ 17.3
1
4
(CMe3), 33.1 (CMe3), 124.9 (dd, JPC = 68.3 Hz, JPC = 4.3 Hz, i-C,
(CC)2PPh2), 126.9 (p-C, CC(P)Ph), 127.6 (m-C, CC(P)Ph),
127.6 (m-C and p-C, CCHPh), 127.8 (m-C, (CC)PPh2), 128.4
(p-C, (CC)PPh2), 128.5 (m-C, (CC)2PPh2), 128.7 (d, 4JPC = 1.4
Hz, o-C, CCHPh), 131.2 (d, 3JPC = 2.1 Hz, o-C, CC(P)Ph), 132.1
4
2
(d, JPC = 2.7 Hz, p-C, (CC)2PPh2), 133.5 (d, JPC = 8.8 Hz, o-C,
2
(CC)2PPh2), 136.1 (d, JPC = 21.4 Hz, o-C, (CC)PPh2), 138.5
3
2
(dd, JPC = 19.6 Hz, JPC = 11.9 Hz, i-C, CC(P)Ph), 138.7 (br.,
P(Al)CCH), 139.6 (d, 1JPC = 11.7 Hz, i-C, (CC)PPh2), 139.8 (d,
3JPC = 16.0 Hz, i-C, CCHPh), 140.9 (dd, 1JPC = 96.1 Hz, 2JPC = 8.9
4
Hz, P(Ph)CC)), 160.9 (d, 2JPC = 8.2 Hz, CCH), 199.8 (dd, 1JPC
=
p-CH3), 2.54 (12 H, s, o-CH3), 6.77 (4 H, d, JPH = 2.4 Hz, m-HMes),
6.95 (1 H, t, 3JHH = 7.6 Hz, p-HvinylPh), 7.07 (2 H, pseudo-t, m-HvinylPh),
65.0 Hz, 2JPC = 34.0 Hz, P(Al)CCP). IR (paraffin, CsI, cm−1): 1985
w, 1964 m, 1944 m, 1892 vw, 1861 vw, 1822 w, 1805 w, 1765 vw, 1687
w, 1678 w, 1663 w, 1645 w, 1585 m, 1553 s, 1537 m, 1514 m ν(C
C), phenyl; 1466 vs, 1371 vs (paraffin); 1300 m, 1271 m δ(CH3);
1190 m, 1173 s, 1157 sh, 1101 s, 1069 s, 1022 s, 997 s, 966 m, 932 s,
891 m, 849 s, 806 s, 777 s, 743 s δ(aromatic), ν(CC); 721 s (paraffin);
689 m, 665 m, 635 w phenyl; 615 m, 561 vs, 546 s, 511 m, 490 m, 446
m, 417 m δ(CC), ν(AlC), ν(PC). MS (EI, 20 eV, 393 K): m/z (%)
657 (100), 658 (48) [M+ − CMe3], 601 (11), 602 (4) [M+ − CMe3 −
butene], 371 (13), 372 (3) [M+ − Ph2PC2Ph − CMe3].
3
3
7.12 (2 H, d, JHH = 9.0 Hz, o-HvinylPh), 7.33 (1 H, d, JPH = 20.6 Hz,
PCCH). 13C{1H} NMR (C6D6, 101 MHz, 300 K): δ 20.9 (s, p-
3
CH3), 23.9 (d, JPC = 14.1 Hz, o-CH3), 31.7 (s, CMe3), 33.8 (s,
4
AlCH2), 34.9 (s, CMe3), 125.2 (d, JPC = 1.7 Hz, o-CvinylPh), 127.8 (s,
p-CvinylPh), 130.41 (s, m-CMes), 130.44 (s, m-CvinylPh), 131.1 (d, JPC
1
=
22.4 Hz, ipso-CMes), 138.6 (s, p-CMes), 143.7 (two resonances coincide,
d, 2JPC = 14.5 Hz, o-CMes and PCCH), 145.3 (d, 3JPC = 13.7 Hz, ipso-
CvinylPh), 157.6 (d, 1JPC = 55.2 Hz, PCCH). MS (EI, 20 eV, 393 K):
m/z (%) 540 (2), 541 (0.5) [M+], 469 (6), 470 (2) [M+
−
CH2CMe3], 372 (33), 373 (10) [Mes2PC(H)C(H)-+], 357 (15),
Synthesis of the Dineopentylaluminum Hydride Adduct 9. A
solution of Ph2PCCPh (0.380 g, 1.33 mmol) in 10 mL of n-hexane
was treated with a solution of dineopentylaluminum hydride (0.451 g,
2.65 mmol) in 20 mL of n-hexane at room temperature. The mixture
adopted a pale yellow color. It was stirred for 19 h at room
temperature, concentrated, and cooled to −30 °C. Compound 8
precipitated as a colorless powder. Yield: 0.678 g (81%). Mp (argon,
sealed capillary): 123 °C dec. Anal. Calcd for C40H61Al2P (626.9): C,
358 (4) [Mes2PC(H)C(H)Ph+ − CH3].
Synthesis of the Dineopentylaluminum Hydride Adduct 7. A
solution of excess dineopentylaluminum hydride (0.146 g, 0.86 mmol)
in 15 mL of toluene was treated with a solution of Mes2PCCPh
(0.103 g, 0.28 mmol) in 6 mL of toluene at room temperature. The
mixture was stirred for 16 h at 75 °C. All volatiles were removed in
vacuo. An oily residue remained which could not be crystallized from
1216
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Organometallics
Article
76.6; H, 9.8. Found: C, 77.1; H, 9.9. 31P{1H} NMR (C6D6, 162 MHz,
300 K): δ −17.9. 1H NMR (C6D6, 400 MHz, 300 K): δ 0.72 (4 H, d,
3JPH = 3.4 Hz, PAl(CH2CMe3)2), 0.76 and 0.86 (each 2 H, AB spin
(2) Appelt, C.; Westenberg, H.; Bertini, F.; Ehlers, A. W.; Slootweg, J.
C.; Lammertsma, K.; Uhl, W. Angew. Chem. 2011, 123, 4011−4014;
Angew. Chem., Int. Ed. 2011, 50, 3925−3928.
2
(3) (a) Men
́
ard, G.; Stephan, D. W. J. Am. Chem. Soc. 2010, 132,
ard, G.; Stephan, D. W. Angew. Chem. 2011, 123,
system, JHH = 13.9 Hz, CAl(CH2CMe3)2), 1.09 (18 H, s,
1796−1797. (b) Men
́
PAl(CH2CMe3)2), 1.39 (18 H, s, CAl(CH2CMe3)2), 3.74 (1 H, d,
2JHP = 28.3 Hz, Al−H−Al), 6.55 (2 H, pseudo-t, m-CH, CCPh),
6.66 (1 H, m, p-CH, CCPh), 6.85 (2 H, m, o-CH, CCPh), 6.92
(6 H, m, p-CH and m-CH, PPh2), 7.45 (4 H, m, o-CH, PPh2), 8.26 (1
H, d, 3JPH = 53.9 Hz, CCH). 13C{1H} NMR (C6D6, 100 MHz, 300
8546−8549; Angew. Chem., Int. Ed. 2010, 50, 8396−8399.
(4) (a) Roters, S.; Appelt, C.; Westenberg, H.; Hepp, A.; Slootweg, J.
C.; Lammertsma, K.; Uhl, W. Dalton Trans. 2012, 41, 9033−9045. See
also: (b) Boudreau, J.; Courtemanche, M. A.; Fontaine, F. G. Chem.
Commun. 2011, 11131−11133.
2
K): δ 28.7 (d, JPC = 15.7 Hz, PAl(CH2CMe3)2), 31.5 (CAl-
3
(5) (a) Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131,
8396−8397. (b) Dureen, M. A.; Brown, C. C.; Stephan, D. W.
Organometallics 2010, 29, 6594−6607.
(CH2CMe3)2), 31.6 (d, JCP = 2.3 Hz, PAl(CH2CMe3)2), 35.0
1
(PAl(CH2CMe3)2), 35.7 (CAl(CH2CMe3)2), 126.9 (d, JPC = 28.9
Hz, i-CH, PPh2), 127.4 (m-CH, CCPh), 127.9 (p-CH, CCPh),
3
(6) Men
4488; Angew. Chem., Int. Ed. 2012, 51, 4409−4412.
(7) Menard, G.; Stephan, D. W. Angew. Chem. 2012, 124, 8397−
́
ard, G.; Stephan, D. W. Angew. Chem. 2012, 124, 4485−
128.8 (o-CH, CCPh), 128.8 (d, JPC = 9.2 Hz, m-CH, PPh2), 130.6
(d, 4JPC = 2.3 Hz, p-CH, PPh2), 133.4 (d, 2JPC = 10.6 Hz, o-CH, PPh2),
3
1
́
137.9 (d, JPC = 16.3 Hz, i-CH, CCPh), 139.4 (d, JPC = 36.4 Hz,
CCH), 158.9 (d, 2JPC = 16.9 Hz, CCH). IR (paraffin, CsI, cm−1):
1950 m, 1894 m, 1803 m phenyl; 1670 m, br ν(AlH); 1582 s, 1551 s
ν(CC), phenyl; 1464 vs, 1377 vs, 1360 vs (paraffin); 1308 s, 1271 m
δ(CH3); 1225 vs 1155 w, 1123 s, 1098 s, 1072 m, 1011 s, 997 vs, 968
vs, 930 s, 885 w, 851 s, 741 vs ν(CC), δ(CH), paraffin; 692 vs, 654 s
phenyl; 534 s, 509 m, 459 s, 426 w δ(CC), ν(AlC), ν(PC). MS (EI, 20
eV, 373 K): m/z (%): 441 (2) [M+ − HAl(CH2CMe3)2 − CH3], 287
8400; Angew. Chem., Int. Ed. 2012, 51, 8272−8275.
(8) Uhl, W.; Appelt, C. Organometallics 2013, 32, 5008−5014.
(9) Appelt, C.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Angew.
Chem. 2012, 124, 6013−6016; Angew. Chem., Int. Ed. 2012, 51, 5911−
5914.
(10) Appelt, C.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Angew.
Chem. 2013, 125, 4350−4353; Angew. Chem., Int. Ed. 2013, 52, 4256−
4259.
+
(100) [PhPC(CCMe3)AlCH2CMe3 ].
Crystal Structure Determinations. Single crystals were obtained
by recrystallization from cyclopentane (3, dissolved at room
temperature, concentrated and stored at room temperature), 1,2-
difluorobenzene (4, −20 °C; 8 and 9, +4 °C), and n-hexane (5,
dissolved at 50 °C, slowly cooled to room temperature). The
crystallographic data were collected with Bruker Venture (Mo Kα; 3−
5) and SMART diffractometers (Cu Kα; 8 and 9). The structures were
solved by direct methods and refined with the program SHELXL-9719
by a full-matrix least-squares method based on F2. Hydrogen atoms,
with the exception of the hydridic atoms attached to aluminum, were
positioned geometrically and allowed to ride on their respective parent
atoms. Compounds 4 and 8 crystallized with a molecule of 1,2-
difluorobenzene per formula unit. The solvent molecule of 4 was
disordered and refined on split positions (0.73:0.27). Both isobutyl
groups of 4 at Al2 were disordered (C81, 0.63:0.37; C91, 0.49:0.52).
Compound 9 crystallized with two independent molecules; all
neopentyl groups of one molecule were disordered and refined on
split positions. Further details of the crystal structure determinations
are available from the Cambridge Crystallographic Data Center on
quoting the depository numbers CCDC-977811 (3), −-977810 (4),
-977809 (5), -977813 (8), and -977812 (9).
(11) Rosorius, C.; Daniliuc, C. G.; Frohlich, R.; Kehr, G.; Erker, G. J.
̈
Organomet. Chem. 2013, 744, 149−155.
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A.; Barron, A. R. Polyhedron 1989, 8, 831−834. (c) McMahon, C. N.;
Barron, A. R. J. Cryst. Chem. 1997, 27, 195−197. (d) Kuczkowski, A.;
Schulz, S.; Nieger, M.; Schreiner, P. R. Organometallics 2002, 21,
1408−1419. (e) Karsch, H. H.; Appelt, A.; Kohler, F. H.; Muller, G.
̈
̈
Organometallics 1985, 4, 231−238. (f) Karsch, H. H.; Zellner, K.;
Lachmann, J.; Muller, G. J. Organomet. Chem. 1991, 409, 109−118.
̈
(13) Uhl, W.; Appelt, C.; Backs, J.; Klocker, H.; Vinogradov, A.;
̈
Westenberg, H. Z. Anorg. Allg. Chem. 2014, 640, 106−109.
(14) (a) Roters, S.; Hepp, A.; Slootweg, J. C.; Lammertsma, K.; Uhl,
W. Chem. Commun. 2012, 48, 9616−9618. (b) Westenberg, H.;
Slootweg, J. C.; Hepp, A.; Kosters, J.; Roters, S.; Ehlers, A. W.;
̈
Lammertsma, K.; Uhl, W. Organometallics 2010, 29, 1323−1330.
(15) Miller, A. D.; Johnson, S. A.; Tupper, K. A.; McBee, J. L.; Don
Tilley, T. Organometallics 2009, 28, 1252−1262.
(16) Downs, A. J.; Greene, T. M.; Collin, S. E.; Whitehurst, L. A.
Organometallics 2000, 19, 527−538.
(17) Uhl, W.; Cuypers, L.; Graupner, R.; Molter, J.; Vester, A.;
Neumuller, B. Z. Anorg. Allg. Chem. 2001, 627, 607−614.
̈
ASSOCIATED CONTENT
* Supporting Information
CIF files giving the crystal data for compounds 3−5, 8, and 9
and figures giving the NMR spectra of compounds 5−7. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(18) Beachley, O. T., Jr.; Victoriano, L. Organometallics 1988, 7, 63−
67.
■
S
(19) (a) SHELXTL-Plus, REL. 4.1; Siemens Analytical X-Ray
Instruments Inc., Madison, WI, 1990. (b) Sheldrick, G. M. SHELXL-
97, Program for the Refinement of Structures; Universitat Gottingen,
̈
̈
Gottingen, Germany, 1997.
̈
AUTHOR INFORMATION
Corresponding Author
*W.U.: fax, +49-251-8336660; e-mail, uhlw@uni-muenster.de.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the Deutsche Forschungsgemeinschaft for
generous financial support.
REFERENCES
■
(1) Frustrated Lewis Pairs; Erker, G., Stephan, D. W., Eds.; Springer:
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