Dimeric aluminum-phosphorus compounds as masked frustrated Lewis pairs for small molecule activation

Article abstract of DOI:10.1039/c2dt30080j

Hydroalumination of aryldialkynylphosphines RP(CC-^tBu) ₂ (R = Ph, Mes) with equimolar quantities of diethylaluminum hydride afforded mixed alkenyl-alkynyl cyclic dimers in which the dative aluminum-phosphorus bonds are geminal to the exocyclic alkenyl groups. Addition of triethylaluminum to isolated 1 (R = Ph) or to the in situ generated species (R = Mes) caused diethylaluminum ethynide elimination to yield the arylethylphosphorus dimers 2 and 3. These possess a chair-like Al ₂C₂P₂ heterocycle with intermolecular Al-P interactions. The boat conformation (4) was obtained by the reaction of ^tBu-P(CC-^tBu)₂ with di(tert-butyl)aluminum hydride. Despite being dimeric, 2 behaves as a frustrated Lewis pair and activates small molecules. The reaction with carbon dioxide gave cis/trans isomeric AlPC₂O heterocycles that differ only by the configuration of the exocyclic alkenyl unit. Four isomers resulted from the reaction with phenyl isocyanate. This is caused by cis/trans isomerization of the initial CO adduct and subsequent rearrangement to the AlPC₂N heterocycle, being the CN adduct.

Full text of DOI:10.1039/c2dt30080j

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Frustrated Lewis Pairs
Guest Editor: Douglas Stephan
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Communication
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Konstantin Chernichenko, Martin Nieger, Markku Leskelä and Timo Repo
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derivatives
Philipp Feldhaus, Birgitta Schirmer, Birgit Wibbeling, Constantin G. Daniliuc, Roland Fröhlich,
Stefan Grimme, Gerald Kehr and Gerhard Erker
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Fixation of carbon dioxide and related small molecules by a bifunctional frustrated pyrazolylborane
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Eileen Theuergarten, Janin Schlösser, Danny Schlüns, Matthias Freytag, Constantin G. Daniliuc,
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PAPER
Dimeric aluminum–phosphorus compounds as masked frustrated Lewis pairs
for small molecule activation†
Steffi Roters,a Christian Appelt,a Hauke Westenberg,a Alexander Hepp,a J. Chris Slootweg,b
Koop Lammertsma*b and Werner Uhl*a
Received 12th January 2012, Accepted 13th February 2012
DOI: 10.1039/c2dt30080j
Hydroalumination of aryldialkynylphosphines RP(CuC–tBu)2 (R = Ph, Mes) with equimolar quantities
of diethylaluminum hydride afforded mixed alkenyl–alkynyl cyclic dimers in which the dative
aluminum–phosphorus bonds are geminal to the exocyclic alkenyl groups. Addition of triethylaluminum
to isolated 1 (R = Ph) or to the in situ generated species (R = Mes) caused diethylaluminum ethynide
elimination to yield the arylethylphosphorus dimers 2 and 3. These possess a chair-like Al2C2P2
heterocycle with intermolecular Al–P interactions. The boat conformation (4) was obtained by the
reaction of tBu–P(CuC–tBu)2 with di(tert-butyl)aluminum hydride. Despite being dimeric, 2 behaves as
a frustrated Lewis pair and activates small molecules. The reaction with carbon dioxide gave cis/trans
isomeric AlPC2O heterocycles that differ only by the configuration of the exocyclic alkenyl unit. Four
isomers resulted from the reaction with phenyl isocyanate. This is caused by cis/trans isomerization of the
initial CvO adduct and subsequent rearrangement to the AlPC2N heterocycle, being the CvN adduct.
substituents FLP dimers result by intermolecular P–Al Lewis
pair formation, but they remain capable of activating carbon
dioxide and phenyl isocyanate.
Introduction
Frustrated Lewis pairs (FLPs)1–7 are of enormous interest
because of their dipolar activation of small molecules such as
dihydrogen, carbon dioxide, and nitrogen oxide. Applications
Results and discussion
are also directed toward their catalytic activity in hydrogen trans-
fer reactions and the activation of organic substrates. The unpre-
cedented reactivity of FLPs is based on the presence of Lewis
acidic and basic centers that interact simultaneously with the
substrate. Typically, boron-based Lewis acids, activated by
fluorinated aryl groups, are used together with bulky phosphines,
being the Lewis base. Other basic centers such as nitrogen or
carbene carbon atoms have been applied to a much smaller
extent.3 Metal atoms are also becoming popular as Lewis acidic
sites.7–10 They allow efficient tuning of the FLP’s reactivity and
limit the need for fluorinated substituents because of the metal’s
inherently high acidity. In a recent study we reported on the syn-
thesis of an Al–P-based FLP that was generated by hydroalumi-
nating11 an alkynylphosphine with di(tert-butyl)aluminum
hydride.9 This sterically protected FLP proved to be very effec-
tive for the reversible dipolar coordination of carbon dioxide and
for the activation of the C–H and CuC bonds of terminal
alkynes (A to C; Scheme 1).9 Herein we report that with smaller
Formation of dimeric Al–P Lewis pairs
The starting point of this study are the diethynylarylphosphines
(aryl = phenyl, mesityl). Recently, we found their hydroalumina-
tion with sterically encumbered HAlR2 (R = tert-butyl or neo-
pentyl) to cause elimination of dialkylaluminum ethynides with
concomitant formation of five-membered AlC2P2 heterocycles,10
which contrasts with the reactions with mono-alkynylpho-
sphines9 and silicon- and germanium-centered diethynes.12 We
now examine the hydroalumination with a sterically non-con-
gested reagent. Surprisingly, reaction of phenyldi(tert-butylethy-
nyl)phosphine with diethylaluminum hydride at ambient
temperature results in the six-membered Al2C2P2 heterocycle 1,
which is the dimer of the mixed alkenyl–alkynyl product that is
expected from hydroaluminating one CuC bond, eqn (1). The
complex 31P{1H} NMR spectrum of 1 showed four major reson-
ances with different intensities at δ = −8, −28, −34 and −48. 1H
and 13C NMR spectra were very complicated with a multitude of
partially overlapping resonances and do not allow an unambigu-
ous assignment. The shape of the spectra changed only little at
lower temperature and did not depend on concentration or the
solvent toluene or benzene. Decomposition occurred at elevated
temperatures. We reasoned that the complex spectrum might be
due to a change of ring size and conformation, exchange
between axial and equatorial groups, partial monomerization,
aInstitut für Anorganische und Analytische Chemie, Universität Münster,
D-48149 Münster, Germany. E-mail: uhlw@uni-muenster.de
bDepartment of Chemistry and Pharmaceutical Sciences, VU University
Amsterdam, De Boelelaan 1083, 1081 HVAmsterdam, The Netherlands.
E-mail: k.lammertsma@vu.nl
†CCDC 861398–861405. For crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt30080j
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9033

alkynyl groups with a less reactive substituent by treating 1 with
a slight excess of AlEt3 in toluene for eleven days, eqn (1). The
resulting product 2 was isolated as colorless crystals in 68%
yield after concentration and cooling of the reaction mixture to
−30 °C. Shorter reaction times could not be achieved by heating
of the solutions because 1 decomposes at elevated temperature.
The expected byproduct Et2Al–CuC–tBu, which probably
forms dimers,16 was characterized in solution. In contrast to the
ethynyl compound 1, solutions of 2 in benzene or toluene
showed simple NMR spectra with the expected resonances at
room temperature. A singlet at δ = −14.5 was observed in the
31P{1H} NMR spectrum. The vinylic hydrogen atoms gave a
3
doublet with the coupling constant JPH = 48.0 Hz which is
Scheme 1
and/or the cis- or trans-arrangement of the terminal alkynyl
groups. To confirm the purity of the product we added some
THF to form the monomeric adduct in which the THF molecules
should be coordinated to the aluminum centers, Et2Al(THF)–C
(vCH–tBu)–P(Ph)–CuC–tBu. Indeed, the spectra simplified
with a single 31P{1H} NMR singlet at δ = −44.2 and 13C NMR
resonances at δ = 79.4 and 115.4 for the ethynyl carbons and δ =
Fig. 1 Molecular structure of 1. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms are omitted. Important bond
lengths (pm) and angles (deg): P(1)–C(2) 176.6(3), C(2)–C(21) 119.2
(4), P(1)–C(3) 180.2(2), C(3)–C(31) 133.9(3), Al(1)–C(3)′ 203.1(2), Al
(1)–P(1) 250.04(9), P(1)–Al(1)–C(3)′ 101.55(7), Al(1)′–C(3)–P(1) 114.8
(1), Al(1)–P(1)–C(3) 114.73(8), P(1)–C(2)–C(21) 172.2(2), C(2)–C
(21)–C(22) 178.5(3); Al(1)′ and C(3)′ generated by −x + 1, −y + 2, −z.
3
145.1 and 167.4 for those of the ethenyl group. The JPH coup-
ling constant of 47.2 Hz between the phosphorus and vinylic
hydrogen atoms verifies their trans arrangement and thereby the
cis-addition of Et2Al–H to the alkynyl group.13 Whereas these
observations suggest the formation of a pure product, the spectra
obtained in non-coordinating solvents are indicative of the pres-
ence of equilibria. We were fortunate that crystalline material
was generated from solution that was suitable for a crystal struc-
ture determination. The molecular structure (Fig. 1) confirmed
the dimeric nature and revealed a chair conformation for the
Al2C2P2 heterocycle of 1, having tetracoordinate aluminum and
phosphorus atoms and a trans arrangement of the phosphorus
and vinylic hydrogens, in accord with the NMR data. The Al–P
[250.04(9) pm]14 and Al–C distances [203.1(2) pm] in the rings
are in the normal range and so are the exocyclic CvC [133.9(3)
pm] and equatorial CuC bonds [119.2(4) pm];15 the P–CuC–C
group approaches linearity [angles P–CuC 172.2(2)° and
CuC–C 178.5(3)°]. The molecular structure of 1 resembles the
Al2C2P2 heterocycles reported in the literature.14
Fig. 2 Molecular structure of 2. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms omitted. Important bond
lengths (pm) and angles (deg): P(1)–C(2) 181.7(2), C(2)–C(21) 134.9
(2), Al(1)–C(2) 203.7(2), Al(1)′–P(1) 252.30(5), P(1)′–Al(1)–C(2) 92.55
(4), Al(1)–C(2)–P(1) 118.57(8), Al(1)′–P(1)–C(2) 114.29(5); Al(1)′ and
P(1)′ generated by −x + 1, −y, −z.
In solution, 1 decomposed slowly (>one week), presumably
by activation of the CuC bonds and formation of heterocycles
similar to those described for sterically shielded dialkylalumi-
num hydrides.10 To prevent this occurring, we replaced the
9034 | Dalton Trans., 2012, 41, 9033–9045
This journal is © The Royal Society of Chemistry 2012

characteristic of a trans-arrangement of P and H across the CvC
double bond. Two different sets of signals resulted for the ethyl
groups and two resonances for the vinylic carbon atoms [δ =
133.6 and 166.3]. No significant change of the spectra was
detected on cooling of a solution of 1 in toluene to 200 K. The
data for the THF adduct are given for comparison in the Exper-
imental section. The molecular structure obtained by a crystal
structure determination confirmed that 2, like 1, had a chair con-
formation for the Al2C2P2 heterocycle (Fig. 2).
cooling of the reaction mixture. Because 4 is only sparingly
soluble in non-coordinating solvents, the NMR spectra were
recorded in THF-d8, which should give monomeric units with
THF molecules coordinated to the aluminum atoms. Only one
resonance was observed in the 31P{1H} (δ = −22.7) and 1H
NMR spectra (δ = 4.04, 1JPH = 208.3 Hz) for the P–H group and
1
three H NMR resonances (2 : 1 : 1 ratio) for the four tert-butyl
groups. The molecular structure of solvent-free 4 in the solid
state (Fig. 4) confirmed its dimeric nature and showed bonding
characteristics similar to 2 and 3, but in contrast the molecule is
not centrosymmetric and has instead a boat conformation for the
Al2C2P2 heterocycle. The most remarkable feature is the arrange-
ment of the two P–H groups, one adopting an endo- and the
Fig. 3 Molecular structure of 3. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms are omitted. Important bond
lengths (pm) and angles (deg): P(1)–C(2) 181.5(2), C(2)–C(21) 135.1
(3), Al(1)′–C(2) 204.8(2), Al(1)–P(1) 255.05(7), P(1)–Al(1)–C(2)′ 92.42
(6), Al(1)′–C(2)–P(1) 121.6(1), Al(1)–P(1)–C(2) 101.83(6); Al(1)′ and
C(2)′ generated by −x + 1, −y, −z + 1.
ð1Þ
Hydroalumination with the more shielded mesityl (instead of
phenyl) substituted diethynylphosphine Mes–P(CuC–tBu)2
behaved differently. The reaction with H–AlEt2 gave a similar
complex product mixture as that on stirring 1 for over a week;
Et2Al–CuC–tBu was identified by NMR as one of the pro-
ducts.16 Evidently, the initial product decomposes faster than
forming a stabilizing dimer akin to 1. To circumvent this, we
used an excess of the hydride to accelerate the formation of the
addition product and added an equimolar quantity of AlEt3 after
only 10 min to replace the alkynyl for an ethyl substituent, eqn
(1). After 18 h colorless crystals of 3 were isolated in 34% yield;
Et2Al–CuC–tBu was detected as byproduct. The NMR data of
3 are similar to those of 2 (see experimental part). The molecular
structure of 3 is also analogous to that of 2, showing a chair con-
formation for the Al2C2P2 ring (Fig. 3), while the rather long
Al–C bond [204.8(2) pm] may indicate strain in the heterocycle.
Hydroalumination of the tert-butyl derivative tBu–P
(CuC–tBu)2 with the more bulky H–AltBu2 reagent (instead of
H–AlEt2) in n-hexane gave full conversion of the phosphine
only in a 1 : 2 ratio of the starting compounds, eqn (2). Colorless
crystals of 4 precipitated in 62% yield after concentration and
Fig. 4 Molecular structure of 4. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms with the exception of P–H
are omitted. Important bond lengths (pm) and angles (deg): P(1)–C(71)
185.6(3), C(71)–C(72) 134.9(3), Al(1)–C(81) 203.1(3), Al(1)–P(1)
255.9(2), P(2)–C(81) 179.0(2), C(81)–C(82) 134.2(3), Al(2)–C(71)
203.2(3), Al(2)–P(2) 257.7(1), P(1)–Al(1)–C(81) 103.21(8), Al(1)–C
(81)–P(2) 112.7(2), Al(1)–P(1)–C(71) 113.4(1), P(2)–Al(2)–C(71) 94.8
(1), Al(2)–C(71)–P(1) 129.3(1), Al(2)–P(2)–C(81) 113.33(9).
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9035

Reaction of dimeric Al–P-based Lewis pair 2 with carbon
dioxide
other an exo-position, causing the phosphorus atoms to be
chemically different and making the eight tert-butyl groups
diastereotopic.
To explore the six-membered Al2C2P2 structures as potential
FLPs, we concentrated on the reactivity of 2 toward CO2,
because 1 is less stable and 4 is difficult to solubilize. As noted,
complexation of CO2 by Al–P-based FLPs are rare.6,9 Earlier we
showed that the monomeric FLP Mes2P–C[vC(H)–Ph]–AltBu2
complexes CO2 reversibly. A reduced reactivity might be
expected for dimeric 2. While we were conducting the present
study, Fontaine and coworkers7 reported the surprising obser-
vation that the dimers (R2PCH2AlMe2)2 (R = Me, Ph) react
readily with CO2 to monomeric adducts (D) that rearrange above
−35 °C to yield dimeric aluminum carboxylates (E, Scheme 2).
This stimulating finding suggests that also 2 might act as a
masked FLP. Indeed, treating a suspension of 2 in n-hexane with
CO2 resulted within seconds in a clear solution of a single
adduct (cis-5) that rearranged to trans-5 within 22 h, eqn (3); cis
and trans refer to the olefinic positions of the Al and H atoms.
Cis-5 could not be isolated due to its limited thermal stability,
but was characterized by NMR spectroscopy. Trans-5 was iso-
lated in 43% yield by concentrating the reaction mixture under a
CO2 flow with subsequent cooling to −20 °C. After recrystalliza-
tion, trans-5 could be handled at room temperature in different
solvents and in high vacuum without decomposition or
rearrangement. The NMR spectra of cis- and trans-5 are similar,
respectively showing 31P{1H} NMR singlets at δ = −4.6 and
2.3, characteristic 13C NMR doublets for the carbonyl carbons at
δ = 168.0 and 165.3,5,7,9 large JPC couplings of 120.0 and 109.4
Hz for these carbon atoms that indicate P–C bonding, and two
1
sets of H NMR resonances for the diastereotopic ethyl groups
3
for each isomer. Most distinguishing is the JPH coupling
between the phosphorus and vinylic hydrogen atoms with the
larger value of 69.9 Hz assigned to cis-5 and the smaller of 38.3
Hz to trans-5. Cis-5 is the expected kinetic product that sub-
sequently isomerizes. The mechanism for the cis/trans isomeri-
zation in hydroalumination and hydrogallation has been
discussed recently.11,13 The molecular structure obtained from an
X-ray structure determination confirmed trans-5 (Fig. 5) to be a
CO2 adduct of a monomeric fragment of 2. The P(1)–C(14)
bond of 187.4(1) pm between the phosphorus and carbonyl
ð2Þ
The mechanism for the formation of 4 may be similar to that
elucidated for the reported H–AltBu2 hydroalumination of aryl
substituted diethynylphosphines Ar–P(CuC–tBu)2 (Ar = Ph,
Mes), which rendered five-membered Al2C2P heterocycles.10
Thus, following hydroalumination of one CuC bond of the
starting material with H–AltBu2, the coordinatively unsaturated
aluminum atom of the resulting intermediate may interact with
the α-carbon of the remaining CuC bond to form a phosphaal-
lene,17 tBu–PvCvC(H)–tBu, by eliminating [tBu2Al–
CuC–tBu]2, eqn (2). But instead of undergoing a cycloaddition
with the intermediate to give a five-membered heterocycle, the
transient phosphaallene undergoes hydroalumination with H–
AltBu2 to form the Al–P-based FLP that subsequently dimerizes
to 4. DFT calculations on phosphaallenes revealed a partial nega-
tive charge for the α-carbon atom and a small positive charge for
the phosphorus atom,18 in accord with the regioselectivity of the
observed hydroalumination. Evidently, the phosphorus substitu-
ent of the starting alkyne determines the course of events with
the phenyl and mesityl derivatives giving the five-membered
AlP2C2 and with tert-butyl derivative an Al2C2P2 heterocycle.
Scheme 2
9036 | Dalton Trans., 2012, 41, 9033–9045
This journal is © The Royal Society of Chemistry 2012

evidence for aluminum carboxylates. Clearly, trans-5 has a con-
siderably increased stability as compared to D (Scheme 2).
Fig. 5 Molecular structure of trans-5. The thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted. Important
bond lengths (pm) and angles (deg): P(1)–C(12) 176.9(1), C(12)–C
(121) 134.5(2), P(1)–C(14) 187.4(1), C(14)–O(11) 128.6(2), C(14)–O
(12) 121.0(2), Al(1)–C(12) 204.2(1), Al(1)–O(11) 186.9(1), Al(1)–C
(12)–P(1) 106.49(6), C(12)–Al(1)–O(11) 92.61(5), Al(1)–O(11)–C(14)
123.26(8), O(11)–C(14)–P(1) 112.17(9), C(12)–P(1)–C(14) 102.45(6),
O(11)–C(14)–O(12) 127.9(1).
carbon atoms is relatively long as is the Al(1)–O(11) bond of
186.9(1) pm.19 The C–O bond lengths of 121.0(2) (CvO) and
128.6(2) pm indicate π-delocalization, whereas the exocyclic
CvC bond of 134.5(2) pm is nearly the same as that in 2.
ð4Þ
Reaction of dimeric Al–P-based Lewis-pair 2 with phenyl
isocyanate
Encouraged by the formation of a stable monomeric CO2 adduct
we then decided to explore whether the masked FLP 2 would
react likewise with the CvO or CvN bond of phenyl isocya-
nate. First, we treated a suspension of 2 in n-hexane with one
equivalent of the isocyanate at room temperature. Concentrating
and cooling of the instantly formed clear solution to −20 °C
afforded adduct cis-6 in 60% yield as colorless needles, eqn (4),
of which, unfortunately, none was suited for a crystal structure
determination, but the NMR data unambiguously revealed the
addition of the isocyanate’s CvO bond to a monomeric unit of
ð3Þ
Heating trans-5 in solution at 80 °C for 38 h or at 67 °C as a
solid resulted in decomposition to unknown products without
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9037

1
2. Characteristic are the two sets of H NMR resonances for the
diastereotopic ethyl groups attached to aluminum, the doublet at
3
δ = 7.38 for the vinylic hydrogen, the JPH coupling of 67.8 Hz
supporting a trans alkenyl arrangement of the P and H atoms (as
1
in 2), and the JPC coupling of 147.3 Hz for the doublet of the
former carbonyl carbon (δ = 159.4) that indicates bonding to the
phosphorus atom.
Cis-6 has limited stability and rearranges even at room temp-
erature slowly to a mixture of isomers, eqn (4). Heating a
toluene solution for 17 h at 85 °C gave a 68 : 28 : 3 ratio of
trans-6, cis-7, and trans-7 and on prolonged heating (7 days at
95 °C) a 37 : 63 ratio of trans-6 and trans-7 from which only
crystals of the trans-isomer of 7 could be isolated in 53% yield.
Trans-6, identified in an isomeric mixture, results on CvC bond
isomerization of cis-6 and has expectedly nearly identical NMR
3
characteristics, except for the smaller JPH coupling constant
(37.5 Hz) for the vinylic hydrogen atom (δ(1H) = 6.96).
Most interesting are the isomerizations to cis- and trans-7 in
which the CvN, instead of the CvO bond of the isocyanate, is
connected to the dipolar monomeric FLP unit of 2. Cis-7 is the
first rearrangement product of cis-6, as monitored by NMR spec-
troscopy, in competition with the formation of trans-6. Whereas
cis/trans isomerization of the CvC bond is well documented for
aluminum or gallium derivatives,13 this is not the case for the
intramolecular rearrangement of the isocyanate group (6 → 7),
which is currently topic of further investigation.4e
Fig. 6 Molecular structure of cis-7. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms are omitted. Important bond
lengths (pm) and angles (deg): P(1)–C(12) 176.4(1), C(12)–C(121)
134.4(2), P(1)–C(14) 187.1(1), C(14)–O(1) 123.0(1), C(14)–N(1) 133.4
(2), Al(1)–C(12) 202.6(1), Al(1)–N(1) 192.8(1), Al(1)–C(12)–P(1)
107.97(6), C(12)–Al(1)–N(1) 92.71(4), Al(1)–N(1)–C(14) 121.10(8), N
(1)–C(14)–P(1) 113.10(8), C(12)–P(1)–C(14) 103.96(5), N(1)–C(14)–O
(1) 130.2(1), C(14)–N(1)–C(17) 117.39(9).
The structural assignments of both isomers of 7 are supported
by the NMR spectroscopic data, which differ only slightly from
those of 6. The 1H NMR spectrum showed a 3JPH coupling con-
stant of 42.0 Hz for the vinylic hydrogen (δ = 6.96) of trans-7,
indicating a trans arrangement with the dialkylaluminum group;
3JPH is 69.0 Hz for the vinylic H of cis-7 (δ = 7.37). The promi-
nent differences between 6 and 7 are the 13C NMR chemical
1
shifts of the imine versus carbonyl carbon and the JPC coup-
For this purpose we chose to react phenyl isocyanate with the
heavily congested, monomeric FLP Mes2P–C[vC(H)–Ph]–
AltBu2, having trans alkenyl H and Al substituents, to obtain
trans-8 in 99% yield, eqn (5); no rearrangement was observed.
A crystal structure determination (Fig. 8) indeed revealed an
AlPC2O heterocycle with an exocyclic imine bond [127.4(3)
pm], a single C–O bond [131.2(3) pm] and an Al–O bond
[185.7(2) pm] like those found for CO2 adduct trans-5. The
NMR characteristics of trans-8 resemble those of trans-6, par-
lings that are respectively δ = 159.4/156.1 and 147.3/137.5 Hz
for cis/trans-6 and δ = 167.7/165.7 and 125.3/114.1 Hz for cis/
trans-7. As expected, also the 13C NMR chemical shifts and
3JPC couplings differ correspondingly for the ipso-carbon of the
phenyl group attached to the nitrogen with respective values of δ
= 147.8/147.4 and 22.9/21.5 Hz for cis/trans-6 and δ = 144.4/
3
144.2 and 12.3/14.1 Hz for cis/trans-7 with the JPC coupling
constants being most indicative for the respective structure. The
usual mixtures of cis-6 and cis-7 could not be separated by
recrystallization. Only once, upon cooling a solution in n-
hexane, could solid material be obtained that contained the
needles characteristic of cis-6 beside colorless blocks of pure
cis-7, allowing its characterization. The crystal structure determi-
nations confirmed the molecular structures of the AlPC2N het-
erocycles cis-7 (Fig. 6) and trans-7 (Fig. 7), corroborating an
exocyclic keto group and Al–N [192.8(1) and 196.5(2) pm] and
P–C(O) bonds [176.4(1) and 177.3(2) pm] between the isocya-
nate and the FLP unit; the longer Al–N bond for trans-7 may be
due to steric interaction between the substituents. The average
ring C–N and exocyclic CvO bond lengths of 133.5 and 123.1
pm, respectively, for the two isomers indicate some
π-delocalization.15
3
ticularly the JPH of 38.4 Hz for the vinylic hydrogen (δ =
7.77 ppm) and the 3JPC of 23.8 Hz for the ipso-carbon (δ = 147.5)
of the phenyl group attached to nitrogen, albeit that the vinyl
hydrogen is more deshielded. With these results we feel that the
structural motifs of cis-6 and trans-6 have been confirmed.
ð5Þ
Because we were unable to obtain crystals for cis-6 and trans-
6 to ascertain their molecular structure unequivocally, we
decided to use an independent route to eliminate any ambiguity.
In conclusion, we have shown that the dimeric aluminum–
phosphorus compound 2 acts as a masked frustrated Lewis pair.
9038 | Dalton Trans., 2012, 41, 9033–9045
This journal is © The Royal Society of Chemistry 2012

Fig. 8 Molecular structure of 8. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms are omitted. Important bond
lengths (pm) and angles (deg): P(1)–C(1) 179.6(2), C(1)–C(2) 134.1(3),
P(1)–C(6) 184.2(2), C(6)–O(1) 131.2(3), C(6)–N(1) 127.4(3), Al(1)–C
(1) 206.8(2), Al(1)–O(1) 185.7(2), Al(1)–C(1)–P(1) 105.2(1), C(1)–Al
(1)–O(1) 91.13(8), Al(1)–O(1)–C(6) 121.7(1), O(1)–C(6)–P(1) 111.9(2),
C(1)–P(1)–C(6) 98.7(1), N(1)–C(6)–O(1) 131.5(2), C(6)–N(1)–C(71)
121.8(2).
Fig. 7 Molecular structure of trans-7. The thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted. Important
bond lengths (pm) and angles (deg): P(1)–C(12) 177.3(2), C(12)–C
(121) 135.0(3), P(1)–C(14) 185.3(2), C(14)–O(2) 123.3(2), C(14)–N(1)
133.6(2), Al(2)–C(12) 202.8(2), Al(2)–N(1) 196.5(2), Al(2)–C(12)–P(1)
107.25(9), C(12)–Al(2)–N(1) 91.80(7), Al(2)–N(1)–C(14) 122.3(1), N
(1)–C(14)–P(1) 110.5(1), C(12)–P(1)–C(14) 105.58(8), N(1)–C(14)–O
(2) 130.8(2), C(14)–N(1)–C(17) 118.6(1).
addition to the monomeric FLP. With longer reaction time and
prolonged heating it rearranges to the corresponding trans-
isomer and to the cis/trans isomeric AlPC2N heterocycles (cis/
trans-7), representing the CvN adducts. Trans-7 is finally (7 d,
95 °C) enriched in the reaction mixture and was isolated in a
pure form after recrystallization. It may represent the most ther-
modynamically favoured isomer. The structural assignments of
the products are in part supported by X-ray crystallographic data
and the synthesis and characterization of a related adduct.
It effectively captures CO2 and isocyanate just like its stable
monomeric counterparts that have coordinatively unsaturated
aluminum and phosphorus atoms. Because these dimeric Al–P
compounds are readily accessible and require less bulky substitu-
ents, masked FLPs may lead to broad applicability in activating
small molecules.
Isomeric CO2 and phenyl isocyanate adducts were formed by
cis/trans isomerization of the exocyclic olefinic group with the
cis Al–H-vinyl form as the kinetically controlled product. The
cis-forms originate directly from the starting compounds 1 to 4
and are in accordance with the concerted hydroalumination
mechanism.20 Formation of dimeric formula units and coordina-
tive saturation of the aluminum atoms in 1 to 4 may hinder cis/
trans isomerisation in these cases.9,13 The reaction with phenyl
isocyanate gives two additional isomers, and all four possible
isomers have been assigned unambiguously by NMR spec-
troscopy in a complicated equilibrium which is not fully under-
stood yet and may include the reversible formation and
consumption of intermediates. The first occurrence of the pro-
ducts in the NMR spectra in dependency of reaction time
follows the order cis-6, cis-7, trans-6 and trans-7, however, this
sequence must not really be representative of the thermodynami-
cally controlled reaction pathway. The initial cis AlPC2O hetero-
cycle (cis-6) was isolated in a pure form and results from CvO
Experimental section
General considerations
All procedures were carried out under purified argon by use of
standard Schlenk methods or within an mBraun Glovebox.
Cyclopentane and n-hexane were dried over LiAlH4, toluene
over Na–benzophenone and 1,2-difluorobenzene over molecular
sieves. Diethylaluminum hydride,21 di(tert-butyl)aluminum
hydride,22 (E)–Mes2P–[CvC(H)–Ph]–AltBu2 (Mes = 2,4,6-
Me3H2C6),9 Ph–P(CuC–tBu)2,23 tBu–P(CuC–tBu)2,24 and
Mes–P(CuC–tBu)2 were synthesized according to literature
10
procedures. Triethylaluminum was used as purchased. Commer-
cially available phenyl isocyanate was distilled and stored over
1
molecular sieves (4 Å). H, 13C{1H} and 31P{1H} NMR spectra
were recorded on Bruker Avance I and III spectrometers. The
chemical shifts (δ) were referenced to the residual solvent signals
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9039

of C6D6 or d8-THF. The assignment of the NMR spectra is
based on HMBC, HSQC, ROESY, and DEPT135 data. Mass
spectra were recorded using a Varian MAT 212 Micromass
Quattro LC-Z spectrometer. IR spectra were recorded on a Shi-
madzu IR Prestige 21 spectrometer. CHN analyses were detected
on a Vario EL III CHNS instrument.
cooled to −30 °C to obtain colorless crystals of 2 (1.84 g,
1
3.02 mmol, 68%). H NMR (400 MHz, C6D6): δ = 7.66 (ddd,
3
4
3JPH = 9.6 Hz, JHH = 7.5 Hz, JHH = 2.1 Hz, 2H, o-HPh), 7.10
3
(d, JPH = 48.0 Hz, 1H, P–CvC–H), 7.05 (m, 2H, m-HPh), 7.04
(m, 1H, p-HPh), 2.32 (dq, JHH = 14.7 Hz, JHH = 7.4 Hz, 1H,
P–CH2CH3), 2.04 (dq, JHH = 14.8 Hz, JHH = 7.5 Hz, 1H, P–
2
3
2
3
3
CH2CH3), 1.64 (t, JHH = 6.9 Hz, 3H, Al–CH2CH3), 1.61 (t,
3JHH = 6.9 Hz, 3H, Al–CH2CH3), 0.89 (s, 9H, P–CvCH–
3
3
Synthesis of compound 1
CMe3), 0.75 (dt, JHH = 7.5 Hz, JPH = 15.8 Hz, 3H, P–
CH2CH3), 0.66 (m, 2H, Al–CH2CH3), 0.62 (m, 2H, Al–
CH2CH3); 13C{1H} NMR (101 MHz, C6D6): δ = 166.3 (dd,
2JCP = 2.6 Hz, 3JCP = 1.2 Hz, P–CvC–H), 135.5 (d, 1JCP = 21.1
Hz, ipso-CPh), 134.0 (t, JCP = 5.5 Hz, o-CPh), 133.6 (m, P–
CvC–H), 130.0 (s, p-CPh), 128.8 (t, JCP = 4.4 Hz, m-CPh),
Diethylaluminum hydride, Et2AlH, (0.54 g, 6.28 mmol) was
added to a solution of phenyldi(tert-butylethynyl)phosphine,
Ph–P(CuC–tBu)2, (1.64 g, 6.09 mmol) in n-hexane (15 mL).
The mixture was stirred for 2 h at ambient temperature and the
dimeric hydroalumination product 1 precipitated as a colorless
solid. The suspension was filtered, and the crude product 1 was
washed two times with n-hexane (10 mL) and thoroughly evacu-
ated. The filtrate was concentrated and a second fraction of 1
crystallized upon cooling to −30 °C (1.22 g, 1.71 mmol, 56%).
Compound 1 is only sparingly soluble in non-coordinating sol-
vents, therefore its THF adduct was characterized by NMR spec-
2
3
3
38.5 (t, JCP = 4.9 Hz, P–CvCH–CMe3), 30.3 (s, P–CvCH–
1
4
CMe3), 23.3 (dd, JCP = 36.2 Hz, JCP = 3.0 Hz, P–CH2CH3),
11.1 (s, Al–CH2CH3), 10.5 (s, Al–CH2CH3), 8.9 (s, P–
CH2CH3), 5.1 (br., Al–CH2CH3), 3.4 (br., Al–CH2CH3); 31P
{1H} NMR (162 MHz, C6D6): δ = −14.5; MS (EI, 20 eV,
413 K) m/z (%) = 465 (2) [M+ − 2tBu–Et], 304 (8) [1/2 M+],
275 (100) [1/2 M+ − Et], 247 (54) [1/2 M+ − Et–ethene]; IR
(cm−1, paraffin, CsI plates): 1973 vw, 1953 w, 1901 vw, 1884 w,
1832 vw, 1813 w, 1762 w, 1658 vw, 1606 m, 1587 w, 1571 w,
1535 s (νCvC, phenyl); 1465 vs, 1454 vs (paraffin); 1436 vs,
1413 m (δCH3); 1377 vs (paraffin); 1357 vs, 1325 w, 1305 m,
1273w, 1251 m (δCH3); 1240 m, 1190 m, 1159 w, 1101 s,
1070 m, 1028 s, 1001 m, 979 m, 947 m, 921 w, 896 w, 869 m,
844 w, 802 m, 759 w, 740 m (νCC); 719 m (paraffin); 694 m
(δphenyl); 646 w, 623 m, 611 m, 576 w, 536 m, 491 m, 455 m,
432 w (δCC, νAlC, νPC); Anal. Calcd for C36H60Al2P2: C,
71.0; H, 9.9. Found: C, 71.0; H, 9.8; MP (sealed capillary,
argon): 165 °C.
1
troscopy. H NMR (400 MHz, d8-THF): δ = 7.47 (m, 2H, o-
2
HPh), 7.23 (m, 2H, m-HPh), 7.11 (t, JHH = 7.3 Hz, 1H, p-HPh),
3
6.78 (d, JPH = 47.2 Hz, 1H, P–CvC–H), 1.30 (s, 9H, P–
3
CvCH–CMe3), 1.28 (s, 9H, P–CuC–CMe3), 0.85 (t, JHH
=
8.1 Hz, 6H, Al–CH2CH3), −0.29 (m, 4H, Al–CH2CH3); 13C
{1H} NMR (126 MHz, d8-THF): δ = 167.4 (d, JCP = 24.8 Hz,
2
1
P–CvC–H), 145.1 (br., P–CvC–H), 142.4 (d, JCP = 9.4 Hz,
2
3
ipso-CPh), 131.1 (d, JCP = 16.5 Hz, m-CPh), 128.4 (d, JCP
=
4.3 Hz, o-CPh), 126.9 (s, p-CPh), 115.4 (s, P–CuC–C), 79.4 (d,
1JCP = 13.2 Hz, P–CuC–C), 38.0 (d, 3JCP = 5.7 Hz, P–CvCH–
4
CMe3), 32.6 (d, JCP = 10.9 Hz, P–CvCH–CMe3), 31.3 (s, P–
CuC–CMe3), 29.9 (s, P–CuC–CMe3), 10.0 (s, Al–CH2CH3),
1.1 (s, Al–CH2CH3); 31P{1H} NMR (162 MHz, d8-THF): δ =
−44.2; MS (EI, 20 eV, 333 K) m/z (%) = 569 (5) [M+ − Et–
2tBu], 517 (100) [M+ − Et–AlEt2–CuC–tBu], 327 (8) [1/2 M+
− Et]; IR (cm−1, paraffin, CsI plates): 2200 m, 2156 s (νCuC);
1978 vw, 1957 w, 1907 w, 1888 w, 1811 w, 1699 s, 1666 w,
1573 s br., 1548 s br., 1475 vs (νCvC), phenyl; 1462 vs, 1446
vs (paraffin); 1431 s, 1408 w (δCH3); 1377 s (paraffin); 1361 m,
1311 w, 1253 m br. (δCH3); 1234 w, 1199 w, 1184 w, 1157 m,
1101 m, 1070 w, 1028 s, 979 s, 952 s, 929 s, 916 s, 850 vs, 796
s, 771 s, 744 s (νCC); 719 m (paraffin); 692 m (δphenyl); 659
w, 621 vw, 588 w, 559 vw, 524 m, 486 s, 462 m, 435 m (δCC,
νAlC, νPC); Anal. Calcd for C44H68Al2P2: C, 74.1; H, 9.6.
Found: C, 74.4; H, 9.6; MP (sealed capillary, argon): 94 °C
(decomposition).
Characterization of the THF-adduct of 2
1
Compound 2 (10 mg) was dissolved in d8-THF (1.5 mL). H
NMR (500 MHz, d8-THF): δ = 7.31 (m, 2H, o-HPh), 7.19 (dd,
2
2
2JHH = 7.3 Hz, JHH = 6.5 Hz, 2H, m-HPh), 7.08 (t, JHH = 7.3
3
Hz, 1H, p-HPh), 6.86 (d, JPH = 47.2 Hz, 1H, P–CvC–H), 1.95
(m, 1H, P–CH2CH3), 1.72 (m, 1H, P–CH2CH3), 1.31 (s, 9H, P–
3
CvCH–CMe3), 1.13 (m, 3H, P–CH2CH3), 0.86 (t, JHH = 8.2
Hz, 6H, Al–CH2CH3), −0.33 (m, 4H, Al–CH2CH3); 13C{1H}
2
NMR (126 MHz, d8-THF): δ = 168.5 (d, JCP = 20.8 Hz, P–
1
CvC–H), 150.2 (br., P–CvC–H), 145.8 (d, JCP = 18.2 Hz,
2
3
ipso-CPh), 131.3 (d, JCP = 14.2 Hz, m-CPh), 128.4 (d, JCP
=
3
3.8 Hz, o-CPh), 126.6 (s, p-CPh), 37.8 (d, JCP = 4.9 Hz, P–
4
CvCH–CMe3), 32.9 (d, JCP = 10.8 Hz, P–CvCH–CMe3),
1
2
21.0 (d, JCP = 10.6 Hz, P–CH2CH3), 11.7 (d, JCP = 21.1 Hz,
P–CH2CH3), 9.9 (s, Al–CH2CH3), 1.8 (s, Al–CH2CH3); 31P
{1H} NMR (162 MHz, d8-THF): δ = −22.9.
Synthesis of compound 2
Triethylaluminum, Et3Al, (1.11 g, 9.74 mmol) was added at room
temperature to a solution of compound 1, [(Ph)(tBu–CuC)-
P–C{vC(H)–tBu}–AlEt2]2, (3.16 g, 4.43 mmol) in toluene
(150 mL). The mixture was stirred for 11 days at room tempera-
ture. The alkynyl compound Et2Al–CuC–tBu was identified as
a byproduct by its characteristic NMR data (1H: δ = 0.45 (q,
AlCH2), 1.01 (s, CMe3), 1.42 (t, CH2CH3); 13C: δ = 3.5
(AlCH2), 9.7 (CH2CH3), 29.5 (CMe3), 29.8 (CMe3), 81.6 (Al–
CuC), 149.5 (Al–CuC)). The solution was concentrated and
Synthesis of compound 3
Diethylaluminum hydride, Et2AlH, (0.36 g, 4.19 mmol) was
added at room temperature to a solution of mesityldi(tert-butyl-
ethynyl)phosphine, Mes–P(CuCtBu)2, (0.66 g, 2.12 mmol) in
toluene (25 mL). After stirring for 10 min at room temperature
triethylaluminum, AlEt3, (0.24 g, 2.11 mmol) was added. The
9040 | Dalton Trans., 2012, 41, 9033–9045
This journal is © The Royal Society of Chemistry 2012

2
mixture was stirred for 18 h at room temperature. The solution
was concentrated and cooled to −30 °C to obtain colorless crys-
tals of 3 (0.25 g, 0.36 mmol, 34%). 1H NMR (400 MHz, C6D6):
298 K, d8-THF): δ = 161.9 (d, JCP = 3.0 Hz, CvC–CMe3),
1
3
141.7 (d, JCP = 53 Hz, CvC–CMe3), 38.3 (d, JCP = 4.5 Hz,
CvC–CMe3), 32.7 (Al(CMe3)2), 32.2 (d, JCP = 12.0 Hz, P–
2
3
4
1
δ = 6.92 (d, JPH = 52.6 Hz, 1H, P–CvC–H), 6.71 (s, 1H, m-
CMe3), 31.9 (d, JCP = 3.4 Hz, CvC–CMe3), 30.3 (d, JCP =
4
H
Mes), 6.68 (d, JPH = 3.6 Hz, 1H, m-HMes), 2.71 (m, 1H, P–
11.5 Hz, P–CMe3), 17.2 (Al(CMe3)2); 31P{1H} NMR
(162 MHz, 298 K, d8-THF): δ = −22.7; MS (EI, 20 eV, 433 K)
CH2CH3), 2.67 (s, 3H, o-CH3), 2.53 (s, 3H, o-CH3), 2.24 (m,
2JHH = 15.2 Hz, 3JHH = 7.6 Hz, 1H, P–CH2CH3), 2.01 (s, 3H, p-
m/z (%) = 624 (0.1) [M+ − Bu], 255 (100) [1/2 M+ − Bu], 199
t
t
3
3
t
CH3), 1.62 (t, JHH = 8.1 Hz, 3H, Al–CH2CH3), 1.57 (dd, JHH
(15) [1/2 M+ − Bu–butene]; IR (cm−1, paraffin, CsI plates):
3
= 17.4 Hz, JHH = 9.5 Hz, 3H, Al–CH2CH3), 0.98 (s, 9H, P–
1568 m, 1553 m, 1533 s (νCvC, phenyl); 1452 vs, 1375 vs
(paraffin); 1306 w, 1242 m (δCH3); 1190 s, 1175 s, 1067 vw,
1028 m, 999 s, 930 s, 893 m, 874 m, 841 m, 804 vs, 781 vs
(νCC); 723 m (paraffin); 689 s (phenyl); 650 m, 637 m, 598 w,
561 s, 534 s, 465 s (δCC, νAlC, νPC); Anal. Calcd for
C36H76Al2P2: C, 69.2; H, 12.3. Found: C, 69.5; H, 12.1; MP
(sealed capillary, argon): 118 °C.
CvCH–CMe3), 0.80 (m, 1H, Al–CH2CH3), 0.78 (m, 3JHH = 7.5
3
Hz, JPH = 15.4 Hz, 3H, P–CH2CH3), 0.70 (m, 1H, Al–
CH2CH3), 0.65 (m, 1H, Al–CH2CH3), 0.62 (m, 1H, Al–
CH2CH3); 13C{1H} NMR (101 MHz, C6D6): δ = 164.0 (coup-
2
ling constants not resolved, P–CvC–H), 142.7 (d, JCP = 5.6
Hz, o-CMes), 142.6 (d, 2JCP = 14.8 Hz, o-CMes), 139.9 (d, 4JCP
=
1
1.8 Hz, p-CMes), 134.8 (br., P–CvC–H), 131.4 (d, JCP = 19.4
Hz, ipso-CMes), 131.2 (d, 3JCP = 4.9 Hz, m-CMes), 129.4 (d, 3JCP
3
Synthesis of compound cis-5
= 8.0 Hz, m-CMes), 38.5 (d, JCP = 8.1 Hz, P–CvCH–CMe3),
3
29.6 (s, P–CvCH–CMe3), 26.0 (d, JCP = 14.7 Hz, o-CH3),
CO2 was bubbled through a solution of compound 2 (ca. 20 mg)
in deuterated benzene (4 mL). The suspension adopted immedi-
ately a yellow color which disappeared within seconds by the
formation of a clear solution. The integration of the resonances
in the NMR showed 99% conversion. Although cis-5 was
formed almost quantitatively, its relative instability did not allow
its purification by recrystallization. H NMR (400 MHz, C6D6):
δ = 7.43 (dd, JHH = 7.3 Hz, JHP = 11.7 Hz, 2H, o-HPh), 7.29
(d, JHP = 69.9 Hz, 1H, P–CvC–H), 6.90 (m, 1H, p-HPh), 6.87
(m, 2H, m-HPh), 2.58 (m, 1H, P–CH2CH3), 1.55 (m, 1H, P–
3
1
24.1 (d, JCP = 2.9 Hz, o-CH3), 20.9 (s, p-CH3), 19.9 (d, JCP
=
32.5 Hz, P–CH2CH3), 11.2 (s, Al–CH2CH3), 10.2 (s, Al–
2
CH2CH3), 9.2 (d, JCP = 4.4 Hz, P–CH2CH3), 6.7 (br., Al–
CH2CH3), 3.9 (br., Al–CH2CH3); 31P{1H} NMR (162 MHz,
C6D6): δ = −25.5; MS (EI, 20 eV, 333 K) m/z (%) = 346 (7) [1/2
M+], 317 (100) [1/2 M+ − Et], 289 (33) [1/2 M+ − Et–ethene];
IR (cm−1, paraffin, CsI plates): 1768 vw, 1697 vw, 1653 w, 1633
vw, 1604 m, 1558 w, 1504 w (νCvC, phenyl); 1469 vs, 1454
vs (paraffin); 1448 vs (δCH3); 1375 s (paraffin); 1290 w,
1247 m (δCH3); 1188 w br., 1103 vw, 1060 w, 1029 w, 964 w,
954 w, 920 w, 896 vw, 848 m, 754 vw (νCC); 721 m (paraffin);
657 vw, 630 w (δphenyl); 553 vw, 534 w, 514 w, 457 w, 437 w,
414 w (δCC, νAlC, νPC); Anal. Calcd for C42H72Al2P2: C,
72.8; H, 10.5. Found: C, 72.7; H, 10.3; MP (sealed capillary,
argon): 107 °C (decomposition).
1
3
3
3
2
3
CH2CH3), 1.48 (dt, JHH = 15.9 Hz, JHH = 8.1 Hz, 6H, Al–
3
3
CH2CH3), 0.89 (dt, JHH = 7.6 Hz, JHP = 20.7 Hz, 3H, P–
CH2CH3), 0.65 (s, 9H, P–CvCH–CMe3), 0.50 (m, 2H, Al–
CH2CH3), 0.45 (m, 2H, Al–CH2CH3); 13C{1H} NMR
2
(126 MHz, C6D6): δ = 176.2 (d, JCP = 11.7 Hz, P–CvC–H),
1
4
168.0 (d, JCP = 120.0 Hz, P–CO2), 133.0 (d, JCP = 3.1 Hz, p-
CPh), 131.5 (d, JCP = 8.9 Hz, o-CPh), 129.4 (d, JCP = 11.4 Hz,
m-CPh), 124.2 (d, JCP = 64.3 Hz, ipso-CPh), 120.38 (br., P–
CvC–H), 39.7 (d, JPC = 12.5 Hz, P–CvCH–CMe3), 28.6 (s,
2
3
1
3
Synthesis of compound 4
1
P–CvCH–CMe3), 18.6 (d, JCP = 37.7 Hz, P–CH2CH3), 10.3
t
A solution of tert-butyldi(tert-butylethynyl)phosphine, Bu–P-
(s, Al–CH2CH3), 6.7 (s, P–CH2CH3), 0.7 (br., Al–CH2CH3), 0.4
(CuC–tBu)2, (0.30 g, 1.18 mmol) in 10 mL of n-hexane was
cooled to −78 °C and treated with a solution of di(tert-butyl)-
(br., Al–CH2CH3); 31P{1H} NMR (162 MHz, C6D6): δ = −4.6.
t
aluminum hydride, Bu2AlH, (0.34 g, 2.37 mmol) in 10 mL of
n-hexane. The mixture was allowed to warm to room temperature
Synthesis of compound trans-5
t
and stirred for 22 h. The alkynyl compound Bu2Al–CuC–tBu
was identified as a byproduct by its characteristic NMR data16
(1H: δ = 1.05 (s, CuC–CMe3), 1.34 (s, AlCMe3); 13C: δ = 17.4
(AlCMe3), 29.6 (CuC–CMe3), 30.1 (CuC–CMe3), 31.9
(AlCMe3), 79.6 (Al–CuC), 152.0 (Al–CuC)). The pale orange
solution was concentrated until product 4 started to precipitate
and subsequently cooled to −45 °C. The solvent was removed,
the remaining solid dried in vacuum and recrystallized from
toluene (0.23 g, 0.37 mmol, 62%). Once crystallized 4 is almost
insoluble in non-coordinating solvents, d8-THF was used as a
solvent for the NMR spectroscopic characterization. Hence, the
NMR data refers probably to the THF adduct of the monomer.
CO2 was bubbled through a suspension of compound 2 (0.71 g,
1.16 mmol) in n-hexane (45 mL). The suspension adopted a
yellow color which disappeared within seconds to give a clear
colorless solution. It was concentrated by removal of the solvent
under normal pressure in the heat and a constant CO2 stream.
The hot solution was filtered and the crude product precipitated
at −20 °C. Recrystallization from 1.2 mL of 1,2-diflourobenzene
at −45 °C gave colorless crystals of trans-5 (0.35 g, 1.00 mmol,
1
3
43%). H NMR (400 MHz, C6D6): δ = 7.48 (ddd, JHH = 7.1
3
3
Hz, JHP = 11.3 Hz, JHP = 1.3 Hz, 2H, o-HPh), 6.93 (m, 1H, p-
3
HPh), 6.89 (m, 2H, m-HPh), 6.85 (d, JHP = 38.3 Hz, 1H, P–
3
3
1H NMR (200 MHz, 298 K, d8-THF): δ = 6.49 (d, JHP = 32.7
CvC–H), 1.85 (m, 1H, P–CH2CH3), 1.49 (t, JHH = 8.1 Hz,
Hz, 1 H, P–CvC–H), 4.04 (d, 1JHP = 208.3 Hz, 1 H, P–H), 1.20
3H, Al–CH2CH3), 1.42 (m, 1H, P–CH2CH3), 1.30 (t, 3JHH = 8.1
Hz, 3H, Al–CH2CH3), 1.08 (s, 9H, P–CvCH–CMe3), 0.76 (dt,
3
(s, 9 H, P–CvCH–CMe3), 1.20 (d, JHP = 11.2 Hz, 9 H, P–
CMe3), 0.97 (s, 18 H, AltBu2); 13C{1H} NMR (101 MHz,
3H, JHH = 7.9 Hz, JHP = 15.1 Hz, P–CH2CH3), 0.59 (m, 1H,
3
3
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9041

Al–CH2CH3), 0.45 (m, 2H, Al–CH2CH3), 0.33 (m, 1H, Al–
νCN); 723 vs (paraffin); 706 vw, 691 s (δphenyl); 664 vw,
667 m, 637 m, 596 w, 548 vw, 529 w, 509 vw, 486 vw, 459 vw,
428 vw, 418 vw, 401 vw (δCC, νAlC, νAlO, νPC); Anal. Calcd
for C25H35AlNOP: C, 70.9; H, 8.3; N, 3.3. Found: C, 71.5; H,
8.0; N, 3.3; MP (sealed capillary, argon): 98.5 °C.
2
CH2CH3); 13C{1H} NMR (126 MHz, C6D6): δ = 176.9 (d, JCP
1
= 8.2 Hz, P–CvC–H), 165.3 (d, JCP = 109.4 Hz, P–CO2),
133.1 (d, 4JCP = 3.1 Hz, p-CPh), 132.1 (d, 2JCP = 8.3 Hz, o-CPh),
129.5 (d, 3JCP = 11.1 Hz, m-CPh), 126.0 (br., P–CvC–H), 121.9
1
3
(d, JCP = 63.9 Hz, ipso-CPh), 39.1 (d, JCP = 26.4 Hz, P–
1
CvCH–CMe3), 28.5 (s, P–CvCH–CMe3), 16.8 (d, JCP = 38.7
Synthesis of compound cis–7
Hz, P–CH2CH3), 10.33 (s, Al–CH2CH3), 10.27 (s, Al–
2
CH2CH3), 6.4 (d, JCP = 3.2 Hz, P–CH2CH3), 2.4 (br., Al–
Cis-7 was generally obtained as a mixture with cis-6 and trans-6
when solutions of cis-6 were stirred at room temperature for
several days. In only a single case colorless crystals of cis-7 were
obtained in an irreproducible procedure by repeated recrystalliza-
tion from n-hexane and 1,2-difluorobenzene over several weeks.
CH2CH3), 1.7 (br., Al–CH2CH3); 31P{1H} NMR (162 MHz,
C6D6): δ = 2.3; MS (EI, 20 eV, 333 K): m/z (%) = 319 (6) [M+
− Et], 304 (2) [M+ − CO2], 275 (39) [M+ − Et–CO2], 247 (23)
[M+ − Et–CO2–ethene], 220 (78) [M+ − AlEt2–CO2 + H], 205
(100) [(Et)(Ph)P–C(H)vC(H)tBu+–Me]; IR (cm−1, paraffin, CsI
plates): 1815 vw; 1695 vs, 1604 vw, 1568 vs, 1535 s (νCvC,
νCvO, phenyl); 1460 vs (paraffin); 1404 w (δCH3); 1377 vs
(paraffin); 1332 w, 1305 vw, 1255 s (δCH3); 1199 vw, 1184 vw,
1159 w, 1103 m, 981 m, 943 w, 914 w, 850 m, 817 w, 763 m,
736 vs (νCC, νCO); 723 vs (paraffin); 694 vs (δphenyl); 634 w,
596 m, 542 m, 489 w, 460 w, 447 w, 418 vw (δCC, νAlC, νAlO,
νPC); Anal. Calcd for C19H30AlO2P: C, 65.5; H, 8.7. Found: C,
65.3; H, 8.6; MP (sealed capillary, argon): 67 °C.
3
1H NMR (400 MHz, C6D6): δ = 7.77 (m, JHH = 7.8 Hz, 2H, o-
3
H
PhIso), 7.63 (m, 2H, o-HPh), 7.37 (d, JHP = 69.0 Hz, 1H, P–
CvC–H), 7.18 (m, 2H, m-HPhIso), 6.96 (m, 1H, p-HPhIso), 6.95
2
(m, 2H, m-HPh), 6.95 (m, 1H, p-HPh), 2.87 (m, JHH = 14.5 Hz,
3JHH = 7.5 Hz, 1H, P–CH2CH3), 1.62 (m, 1H, P–CH2CH3),
1. 45 (dt, 3JHH = 8.0 Hz, 3H, Al–CH2CH3), 1.04 (dt, 3H, 3JHH
=
3
7.6 Hz, JHP = 20.4 Hz, P–CH2CH3), 0.74 (s, 9H, P–CvCH–
CMe3), 0.46–0.53 (m, 4H, Al–CH2CH3); 13C{1H} NMR
2
(101 MHz, C6D6): δ = 175.2 (d, JCP = 12.9 Hz, P–CvC–H),
1
3
167.7 (d, JCP = 125.3 Hz, P–CN), 144.4 (d, JCP = 12.3 Hz,
4
2
ipso-CPhIso), 132.9 (d, JCP = 3.1 Hz, p-CPh), 131.8 (d, JCP
8.8 Hz, o-CPh), 129.3 (d, JCP = 11.6 Hz, m-CPh), 129.0 (m-
CPhIso), 125.5 (d, JCP = 66.6 Hz, ipso-CPh), 125.1 (p-CPhIso),
125.1 (o-CPhIso), 118.5 (br., P–CvC–H), 39.6 (d, JCP = 12.8
Hz, P–CvCH–CMe3), 28.8 (d, JCP = 1.3 Hz, P–CvCH–
CMe3), 18.4 (d, JCP = 41.7 Hz, P–CH2CH3), 10.7 (s, Al–
=
3
Synthesis of compound cis-6
1
Phenyl isocyanate (0.08 mL, 0.088 g, 0.739 mmol) was added to
a suspension of compound 2 (0.225 g, 0.370 mmol) in n-hexane
(20 mL). The color of the suspension changed to colorless
within seconds. A clear solution resulted, which was concen-
trated and stored at −20 °C. Compound cis-6 crystallized as col-
orless needles (0.189 g, 0.446 mmol, 60%). 1H NMR
3
4
1
CH2CH3), 10.6 (s, Al–CH2CH3), 6.8 (s, P–CH2CH3), 1.8 (br.,
Al–CH2CH3), 1.6 (br., Al–CH2CH3); 31P{1H} NMR (162 MHz,
C6D6): δ = −0.7; MS (EI, 20 eV, 333 K) m/z (%) = 422 (1) [M+
− H], 394 (100) [M+ − Et], 275 (12) [M+ − Et–ethene–NPh]; IR
(cm−1, paraffin, CsI plates): 1977 vw, 1958 vw, 1938 vw, 1896
w, 1870 vw, 1849 w, 1820 vw, 1790 vw, 1769 vw, 1724 vw,
1689 vw, 1630 vs, 1576 vs (νCvO, νCvC, phenyl); 1450 vs
(paraffin); 1406 s (δCH3); 1375 s (paraffin); 1360 s, 1331 w,
1298 s, 1254 w (δCH3); 1234 vw, 1223 vw, 1184 s, 1155 m,
1107 s, 1070 m, 1026 s, 980 s, 941 s, 924 w, 895 s, 847 vw,
822 m, 795 s, 766 w, 750 vs (νCC, νCN); 723 s (paraffin); 691
s, 675 w, 646 s, 633 s, 596 s, 581 s, 550 m, 536 m, 507 s, 494 s,
459 s, 432 s (δCC, νAlC, νAlN, νPC); Anal. Calcd for
C25H35AlNOP: C, 70.9; H, 8.3; N, 3.3. Found: C, 70.6; H, 7.9;
N, 3.2; MP (sealed capillary, argon): 108 °C.
3
(400 MHz, C6D6): δ = 7.75 (d, JHH = 7.27 Hz, 2H, o-HPhIso),
3
7.62 (m, 2H, o-HPh), 7.38 (d, JHP = 67.8 Hz, 1H, P–CvC–H),
7.19 (t, 3JHH = 7.8 Hz, 2H, m-HPhIso), 6.95 (m, 2H, p-HPh), 6.93
2
(m, 1H, p-HPhIso), 6.93 (m, 2H, m-HPh), 3.00 (m, JHH = 14.9
3
2
Hz, JHH = 7.5 Hz, 1H, P–CH2CH3), 1.80 (m, JHH = 14.9 Hz,
3JHH = 7.5 Hz, 1H, P–CH2CH3), 1.48 (t, 3JHH = 8.1 Hz, 6H, Al–
CH2CH3), 1.04 (dt, JHH = 7.5 Hz, JHP = 20.3 Hz, 3H, P–
CH2CH3), 0.74 (s, 9H, P–CvCH–CMe3), 0.46 (m, 2H, Al–
CH2CH3), 0.46 (m, 2H, Al–CH2CH3); 13C{1H} NMR
(101 MHz, C6D6): δ = 175.0 (d, JCP = 8.8 Hz, P–CvC–H),
159.4 (d, JCP = 147.3 Hz, P–CON), 147.8 (d, JCP = 22.9 Hz,
ipso-CPhIso), 132.7 (d, JCP = 3.0 Hz, p-CPh), 131.6 (d, JCP
9.1 Hz, o-CPh), 129.2 (d, JCP = 11.4 Hz, m-CPh), 128.8 (m-
PhIso), 126.5 (d, JCP = 68.7 Hz, ipso-CPh), 125.1 (o-CPhIso),
3
3
2
1
3
2
4
=
3
1
C
1
124.8 (p-CPhIso), 121.0 (br., d, JCP = 7.8 Hz, P–CvC–H), 38.8
Synthesis of compound trans-6
3
4
(d, JCP = 11.7 Hz, P–CvCH–CMe3), 28.8 (d, JCP = 1.4 Hz,
1
P–CvCH–CMe3), 20.2 (d, JCP = 41.6 Hz, P–CH2CH3), 10.48
(s, Al–CH2CH3), 10.46 (s, Al–CH2CH3), 6.6 (d, JCP = 1.5 Hz,
Phenyl isocyanate (0.04 mL, 0.043 g, 0.361 mmol) was added to
a suspension of compound 2 (0.109 g, 0.179 mmol) in toluene
(10 mL) and stirred for 5 min at ambient temperature. A clear
solution was formed. Heating for 17 h at 85 °C gave a mixture
of 68% of trans-6, 28% of compound cis-7 and 3% of trans-7,
which was used for the NMR spectroscopic characterization of
trans-6. Attempts for further purification by recrystallization
2
P–CH2CH3), 1.2 (br., Al–CH2CH3), 0.9 (br., Al–CH2CH3); 31P
{1H} NMR (162 MHz, C6D6): δ = 1.4; MS (EI, 20 eV, 298 K)
m/z (%) = 394 (100) [M+ − Et], 275 (44) [M+ − Et–ethene–
NPh]; IR (cm−1, paraffin, CsI plates): 1683 vw, 1653 w, 1628 vs,
1589 s, 1576 s, 1570 s, 1558 s, 1539 vw, 1506 vw (νCvC,
νCvN, phenyl); 1458 vs (paraffin); 1406 vw (δCH3); 1375 vs
(paraffin); 1298 m, 1259 m (δCH3); 1182 w, 1153 w, 1107 m,
1072 w, 1034 w, 1026 w, 1009 w, 998 w, 941 w, 918 vw, 891 w,
853 w, 822 w, 802 w, 795 m, 773 w, 766 m, 745 m, 731 s (νCC,
1
remained unsuccessful. H NMR (400 MHz, C6D6): δ = 7.94
3
5
(dd, JHH = 7.6 Hz, JHP = 0.8 Hz, 2H, o-HPhIso), 7.68 (m, 2H,
3
o-HPh), 7.25 (t, JHH = 7.8 Hz, 2H, m-HPhIso), 6.95 (m, 1H, p-
HPh), 6.95 (m, 2H, m-HPh), 6.95 (m, 1H, p-HPhIso), 6.95 (d, 3JHP
9042 | Dalton Trans., 2012, 41, 9033–9045
This journal is © The Royal Society of Chemistry 2012

= 37.5 Hz, 1H, P–CvC–H), 2.17 (m, 1H, P–CH2CH3), 1.62 (m,
1H, P–CH2CH3), 1.51 (t, 3JHH = 8.1 Hz, 3H, Al–CH2CH3), 1.33
for C25H35AlNOP: C, 70.9; H, 8.3; N, 3.3. Found: C, 70.8; H,
8.3; N, 3.2; MP (sealed capillary, argon): 126 °C.
3
(t, JHH = 8.1 Hz, 3H, Al–CH2CH3), 1.15 (s, 9H, P–CvCH–
3
3
CMe3), 0.91 (dt, 3H, JHH = 7.5 Hz, JHP = 18.5 Hz, P–
CH2CH3), 0.58 (m, 1H, Al–CH2CH3), 0.38 (m, 1H, Al–
Synthesis of compound 8
2
CH2CH3); 13C{1H} NMR (101 MHz, C6D6): δ = 175.7 (d, JCP
Phenyl isocyanate (0.10 mL, 0.114 g, 0.96 mmol) was added to
1
= 6.1 Hz, P–CvC–H), 156.1 (d, JCP = 137.5 Hz, P–CNO),
a
solution of (E)–Mes2P–[CvC(H)–Ph]–AltBu2 (0.49 g,
3
4
147.4 (d, JCP = 21.5 Hz, ipso-CPhIso), 132.9 (d, JCP = 3.1 Hz,
0.96 mmol) in toluene (15 mL). The mixture was stirred for 3 h
at room temperature. All volatiles were removed in vacuum.
Crystallization from cyclopentane afforded the pure product 8 as
2
3
p-CPh), 132.2 (d, JCP = 8.4 Hz, o-CPh), 129.3 (d, JCP = 11.1
Hz, m-CPh), 128.9 (m-CPhIso), 126.5 (br., P–CvC–H), 125.6 (o-
1
C
PhIso), 125.1 (p-CPhIso), 123.9 (d, JCP = 68.0 Hz, ipso-CPh),
1
yellow crystals (0.60 g, 0.95 mmol, 99%). H NMR (200 MHz,
3
4
39.1 (d, JCP = 25.9 Hz, P–CvCH–CMe3), 28.7 (d, JCP = 1.4
Hz, P–CvCH–CMe3), 17.9 (d, JCP = 43.0 Hz, P–CH2CH3),
10.54 (s, Al–CH2CH3), 10.48 (s, Al–CH2CH3), 6.4 (d, JCP
3
3
C6D6): δ = 7.90 (d, JHH = 8.1 Hz, 2 H, o-HPhIso), 7.77 (d, JHP
1
3
= 38.4 Hz, 1 H, P–CvC–H), 7.49 (d, JHH = 7.5 Hz, 2 H, o-
HPh), 7.24 (t, JHH = 7.8 Hz, 2 H, m-HPhIso), 7.18 (t, JHH = 7.5
2
=
3
3
3.5 Hz, P–CH2CH3), 2.9 (br., Al–CH2CH3), 2.0 (br., Al–
3
Hz, 2 H, m-HPh), 7.06 (t, JHH = 7.4 Hz, 1 H, p-HPh), 6.96 (t,
CH2CH3); 31P{1H} NMR (162 MHz, C6D6): δ = 10.4.
3JHH = 7.4 Hz, 1 H, p-HPhIso), 6.62 (d, JHP = 3.8 Hz, 4 H, m-
4
H
Mes), 2.38 (s, 12 H, o-CH3), 1.95 (s, 6 H, p-CH3), 1.16 (s, 18
H, AlCMe3); 13C{1H} NMR (101 MHz, C6D6): δ = 158.3 (d,
2JCP = 4.5 Hz, P–CvC–H), 158.0 (d, JCP = 141.0 Hz, P–CN),
147.5 (d, JCP = 23.8 Hz, ipso-CPhIso), 144.8 (d, JCP = 9.2 Hz,
1
3
2
Synthesis of compound trans-7
4
3
o-CMes), 143.2 (d, JCP = 3.0 Hz, p-CMes), 140.6 (d, JCP = 32.1
Phenyl isocyanate (0.09 mL, 0.102 g, 0.857 mmol) was added to
a suspension of compound 2 (0.26 g, 0.427 mmol) in toluene
(10 mL). A clear solution was obtained after stirring at ambient
temperature for 5 min. Heating to 95 °C for 7 d gave a mixture
of trans-6 (37%) and trans-7 (63%). The solvent was removed in
vacuum, and the residue was dissolved in 6 mL of n-hexane.
trans-7 crystallized as a colorless solid upon cooling to −30 °C
1
Hz, ipso-CPh), 139.4 (d, JCP = 5,0 Hz, P–CvC–H), 132.4 (d,
3JCP = 10.7 Hz, m-CMes), 129.9 (p-CPh), 129.3 (m-CPh), 128.9
(m-CPhIso), 128.2 (o-CPh), 125.7 (o-CPhIso), 125.4 (p-CPhIso),
119.4 (d, 1JCP = 67.8 Hz, ipso-CMes), 32.0 (Al(CMe3)2), 25.0 (d,
3JCP = 4.5 Hz, o-CH3), 20.8 (d, JCP = 1.0 Hz, p-CH3), 16.7 br.
5
(Al(CMe3)2); 31P{1H} NMR (162 MHz, C6D6): δ = 15.2; MS
(EI, 20 eV, 403 K): m/z = 574 (7) [M+ − Bu], 512 (10) [M+ −
t
1
(0.191 g, 0.45 mmol, 53%). H NMR (400 MHz, C6D6): δ =
Ph–NCO], 455 (52) [M+ − Ph–NCO–tBu], 399 (18) [M+ − tBu–
butane–Ph–NCO], 372 (71) [M+ − Ph–NCO–Al(CMe3)2 + H];
IR (cm−1, paraffin, CsI plates): 1931 vw, 1888 vw, 1865 vw,
1775 vw, 1736 vw, 1628 m, 1582 w, 1553 w, 1503 vw (νCvC,
νCvO, phenyl); 1449 s, 1375 m (paraffin); 1294 w, 1271 w,
1248 w (δCH3); 1153 w, 1101 vw, 1067 vw, 1028 vw, 1003 vw,
934 vw, 885 vw, 853 w, 806 w, 783 w, 746 m (νCC, νCN); 723
s (paraffin); 689 w, 673 vw (δphenyl); 638 w, 625 w, 548 w, 503
vw, 471 vw, 453 vw, 438 vw, 403 vw, 365 vw, 341 vw (δCC,
νAlC, νAlO, νPC); Anal. Calc. for C41H51PAlNO: C, 77.9; H,
8.1; N, 2.2. Found: C, 77.0; H, 7.7; N, 1.9; MP (sealed capillary,
argon): 154 °C (decomposition).
7.71 (m, 3JHH = 5.7 Hz, 2H, o-HPh), 7.62 (d, 3JHH = 8.2 Hz, 2H,
o-HPhIso), 7.20 (t, 3JHH = 7.8 Hz, 2H, m-HPhIso), 7.00 (m, 2H, p-
HPh), 6.98 (m, 2H, m-HPh), 6.96 (m, 1H, p-HPhIso), 6.96 (d, 3JHP
= 42.0 Hz, 1H, P–CvC–H), 2.19 (m, 1H, P–CH2CH3), 1.57 (m,
1H, P–CH2CH3), 1.35 (t, 3JHH = 8.1 Hz, 3H, Al–CH2CH3), 1.26
3
(t, JHH = 8.1 Hz, 3H, Al–CH2CH3), 1.17 (s, 9H, P–CvCH–
3
3
CMe3), 0.96 (dt, JHH = 7.5 Hz, JHP = 18.4 Hz, 3H, P–
CH2CH3), 0.40 (m, 4H, Al–CH2CH3); 13C{1H} NMR
2
(101 MHz, C6D6): δ = 176.8 (d, JCP = 9.4 Hz, P–CvC–H),
165.7 (d, JCP = 114.1 Hz, P–CN), 144.2 (d, JCP = 14.1 Hz,
ipso-CPhIso), 133.2 (d, JCP = 8.0 Hz, o-CPh), 133.0 (d, JCP
3.1 Hz, p-CPh), 129.3 (d, JCP = 11.1 Hz, m-CPh), 128.9 (m-
PhIso), 126.0 (o-CPhIso), 125.4 (p-CPhIso), 123.4 (d, JCP = 67.1
Hz, ipso-CPh), 123.3 (br., P–CvC–H), 39.1 (d, JCP = 26.4 Hz,
P–CvCH–CMe3, 28.7 (d, JCP = 1.17 Hz, P–CvCH–CMe3),
16.7 (d, JCP = 43.2 Hz, P–CH2CH3), 10.5 (s, Al–CH2CH3),
1
3
2
1
=
3
1
C
3
Crystal structure determinations
4
1
Single crystals were obtained as described above with the syn-
thetic procedures. The crystallographic data were collected with
Bruker SMART 6000 (Cu) and STOE IPDS II (Mo) diffract-
ometers. The crystals were coated with a perfluoropolyether,
picked up with a glass fiber and immediately mounted in the
cooled nitrogen stream of the diffractometer. The structures were
solved by direct methods and refined with the program
SHELXL-9725 by a full-matrix least-squares method based on
F2. Crystal data, data collection parameters and structure refine-
ment details are given in Table 1. The molecules of 1, 2 and 3
are located on crystallographic inversion centers. Compound 4
crystallizes as twinned crystals with three independent domains.
Reflections were separated by applying the diffractometer soft-
ware, those of the main domain were used for structure solution
and refinement. The P–H groups of 4 are disordered. Their
2
10.26 (s, Al–CH2CH3), 6.6 (d, JCP = 2.8 Hz, P–CH2CH3), 2.6
(br., Al–CH2CH3); 31P{1H} NMR (162 MHz, C6D6): δ = 6.1;
MS (EI, 20 eV, 333 K) m/z (%) = 422 (0.1) [M+ − H], 394 (100)
[M+ − Et], 275 (38) [M+ − Et–ethene–NPh]; IR (cm−1, paraffin,
CsI plates): 1953 w, 1938 w, 1901 vw, 1875 vw, 1852 w, 1825
vw, 1802 w, 1788 w, 1755 vw, 1715 m, 1678 vw, 1659 w,
1641 m, 1622 s, 1575 m, 1564 m, 1555 m, 1500 m, 1485 s
(νCvC, νCvO, phenyl); 1454 vs (paraffin); 1410 w (δCH3);
1375 m (paraffin); 1348 w, 1302 s, 1261 w (δCH3); 1240 vw,
1225 vw, 1184 m, 1134 vw, 1109 s, 1098 m, 1070 s, 1030 s,
1013 m, 999 w, 984 w, 966 m, 941 w, 910 m, 893 w, 860 s,
821 m, 812 s, 766 vs, 754 vs (νCC, νCN); 731 vs (paraffin);
692 s (δphenyl); 623 vs, 596 vs, 581 vs, 538 m, 513 m, 492 m,
463 m, 430 m, 409 vw (δCC, νAlC, νAlN, νPC); Anal. Calcd
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9043

Table 1 Crystal data, data collection parameters, and structure refinement details for 1 to 4, trans-5, cis- and trans-7, and 8
1
2
3
4
trans-5
cis-7
trans-7
8·0.5C6F2H4
Formula
Fw
Crystal
system
C44H68Al2P2
712.9
Monoclinic
C36H60Al2P2
608.7
Monoclinic
C42H72Al2P2
692.9
Monoclinic
C36H76Al2P2 C19H30AlO2P C25H35AlNOP C25H35AlNOP C44H52.5AlFNOP
624.9
Triclinic
348.4
Triclinic
423.5
Triclinic
423.5
Monoclinic
688.3
Monoclinic
ˉ
ˉ
ˉ
Space group P21/c (no. 14) P21/c (no. 14) P21/n (no. 14) P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
P21/n (no. 14) C2/c (no. 15)
Z
2
2
2
2
2
2
4
8
a (pm)
b (pm)
c (pm)
α (°)
1083.70 (2)
1252.41 (2)
1722.99 (3)
90
108.281 (1)
90
2.22048 (7)
153 (2)
1.459 (Cu
Kα)
1022.66 (1)
1949.00 (2)
966.15 (1)
90
109.275 (1)
90
1.81775 (3)
153 (2)
1.703 (Cu
Kα)
1044.90 (1)
1539.75 (2)
1366.43 (2)
90
106.326 (1)
90
2.10978 (5)
153 (2)
1.519 (Cu
Kα)
992.85 (3)
1077.38 (4)
2136.57 (7)
79.662 (2)
84.097 (2)
66.108 (1)
2.0545 (1)
153 (2)
777.90 (3)
912.98 (3)
1595.43 (5)
91.206 (3)
91.247 (3)
114.460 (3)
1.03058 (6)
153 (2)
835.16 (5)
897.67 (5)
1734.93 (9)
81.019 (4)
76.329 (4)
80.138 (4)
1.2360 (1)
153 (2)
1285.46 (5)
1239.67 (9)
1644.03 (7)
90
110.714 (3)
90
2.4505 (2)
153 (2)
0.163 (Mo
Kα)
3821.57 (4)
1410.78 (1)
1565.68 (2)
90
112.305 (1)
90
7.8096 (1)
153 (2)
1.133 (Cu Kα)
β (°)
γ (°)
V (nm3)
T (K)
μ (mm−1
)
1.508 (Cu
Kα)
0.183 (Mo
Kα)
0.162 (Mo
Kα)
Unique rflns 3839
3315
3099 (0.1896) 5997
(0.0183)
0.0527 (2673) 0.0488
(5474)
4907
(0.0394)
0.0353
(3990)
0.0932
5896 (0.0230) 5885 (0.0893) 6803 (0.0383)
(Rint
)
(0.0931)
0.0549
(3000)
0.1542
(0.0423)
0.0376
(2966)
R1 (reflns I
> 2σ(I))
wR2 (all
data)
0.0314 (4711) 0.0513 (4263) 0.0544 (5961)
0.1080
0.1335
0.1208
0.0814
861403
0.1459
861404
0.1610
861405
CCDC
861398
861399
861400
861401
861402
R. Fröhlich and G. Erker, Organometallics, 2010, 29, 1067;
(o) A. J. P. Cardenas, B. J. Culotta, T. H. Warren, S. Grimme, A. Stute,
G. Kehr and G. Erker, Angew. Chem., 2011, 123, 7709, (Angew. Chem.,
Int. Ed., 2011, 50, 7567).
phosphorus atoms were refined on split positions (0.70 : 0.30);
the hydrogen atoms are on fixed positions with artificial displa-
cement parameters. 8 crystallizes with half a molecule of difluor-
obenzene per formula unit. The solvent molecule is disordered
across a twofold rotational axis. In addition a fluorine atom
occupies two positions. Only three hydrogen atoms of the
difluorobenzene molecule were considered.
3 (a) D. Holschumacher, T. Bannenberg, C. G. Hrib, P. G. Jones and
M. Tamm, Angew. Chem., 2008, 120, 7538, (Angew. Chem., Int. Ed.,
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Angew. Chem., 2008, 120, 6090, (Angew. Chem., Int. Ed., 2008, 47,
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M. Leskelä, T. Repo, P. Pyykkö and B. Rieger, J. Am. Chem. Soc., 2008,
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2008, 120, 7543, (Angew. Chem., Int. Ed., 2008, 47, 7433);
( j) M. Alcarazo, C. Gomez, S. Holle and R. Goddard, Angew. Chem.,
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Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft and
The Netherlands Foundation for Chemical Sciences (CW) with
financial aid from The Netherlands Organization for Scientific
Research (NWO) for generous financial support.
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This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9033–9045 | 9045