C≡C triple bond activation by heterocyclic aluminum phosphinides

Article abstract of DOI:10.1021/om901051p

Treatment, of aryl-di(tert-butylethynyl)phosphines Aryl-P(C≡C- CMe₃)₂ [Aryl = C₆H₅ (4) 2,4,6-Me₃C₆H₂ (5)] with dialkylaluminum hydrides, R₂Al-H (R = CMe₃, CH₂CMe ₃), afforded heterocyclic, zwitterionic compounds 6-9 by hydroalumination and release of the corresponding dimeric tert-butylethynyl- dialkylaluminum derivatives, [R₂Al-C≡C-CMe₃] ₂ (10 and 11). The molecular structures of 6-8 reveal a P ₂C₂Al ring with a tetracoordinated aluminum atom, two exocyclic C=C double bonds, a tricoordinated phosphorus atom, and a phosphonium cation carrying an aryl and an alkynyl group. The C≡C triple bond of 7 was inserted into the Al-P bonds of the heterocycles upon warming to give the bicyclic compound 13. A similar compound (12) was directly formed when the bisalkyne 4 was treated with dineopentylaluminum hydride. Their molecular structures show the annulated four- (AlC₂P) and five-membered heterocycles (P₂C₃) to contain three different C=C double bonds. The sterically most shielded monocyclic compound (8; Aryl = 2,4,5-Me ₃C₆H₂; R = CMe₃) decomposed upon warming. DFT calculations were used to examine these reactions.

Full text of DOI:10.1021/om901051p

Organometallics 2010, 29, 1323–1330 1323
DOI: 10.1021/om901051p
CtC Triple Bond Activation by Heterocyclic Aluminum Phosphinides
†
‡
†
†
†
€
Hauke Westenberg, J. Chris Slootweg, Alexander Hepp, Jutta Kosters, Steffi Roters,
Andreas W. Ehlers,‡ Koop Lammertsma,‡ and Werner Uhl*,†
†
€
Institut fu€r Anorganische und Analytische Chemie der Universitat Munster, Corrensstrasse 30,
€
D-48149 Mu€nster, Germany, and ‡Department of Chemistry and Pharmaceutical Sciences, VU University
Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Received December 8, 2009
Treatment of aryl-di(tert-butylethynyl)phosphines Aryl-P(CtC-CMe3)2 [Aryl = C6H5 (4) 2,4,6-
Me3C6H2 (5)] with dialkylaluminum hydrides, R2Al-H (R = CMe3, CH2CMe3), afforded heterocyclic,
zwitterionic compounds 6-9 by hydroalumination and release of the corresponding dimeric tert-
butylethynyl-dialkylaluminum derivatives, [R2Al-CtC-CMe3]2 (10 and 11). The molecular structures
of 6-8 reveal a P2C2Al ring with a tetracoordinated aluminum atom, two exocyclic CdC double bonds, a
tricoordinated phosphorus atom, and a phosphonium cation carrying an aryl and an alkynyl group. The
CtC triple bond of 7 was inserted into the Al-P bonds of the heterocycles upon warming to give the
bicyclic compound 13. A similar compound (12) was directly formed when the bisalkyne 4 was treated
with dineopentylaluminum hydride. Their molecular structures show the annulated four- (AlC2P) and
five-membered heterocycles (P2C3) to contain three different CdC double bonds. The sterically most
shielded monocyclic compound (8; Aryl = 2,4,5-Me3C6H2; R = CMe3) decomposed upon warming.
DFT calculations were used to examine these reactions.
Introduction
hydrogallation of alkynes.2,7 Here we extend these studies by
addressing the influence of phosphine substituents on the
hydroalumination reaction. We anticipated that their presence
might lead to systems containing both donor (P) and acceptor
(Al) groups, which in the context of frustrated Lewis pairs are
of interest for the activation of small molecules.8
Hydroalumination is an effective method to reduce homo- or
heteronuclear double or triple bonds,1 but in most cases the
organoaluminum intermediates have not been isolated and
characterized. Recently, in examining the reactions with al-
kynes we found, besides the expected addition of R2Al-H to
the triple bond,2 unprecedented secondary processes leading to
aluminum/carbon clusters (carbaalanes 1, Scheme 1),3 cyclo-
phane-type cages with bridging Al-R groups (2),4 and carbo-
cations resulting from C-H bond activation (3).5 We have also
shown that dipolar-induced cis/trans isomerization of the
resulting olefins can occur depending on the nature of the
substituents.6 These reactions are mimicked by the selective
Results and Discussion
Phosphine-substituted alkynes are common building blocks
for the synthesis of molecular frames and cages, a topic that
has been reviewed recently,9 and are capable of undergoing
the so-called “click” reaction.10 Here we describe the uncon-
ventional hydroalumination of phosphines carrying two
*Corresponding author. Fax: þ49-251-8336660. E-mail: uhlw@
uni-muenster.de.
(7) (a) Uhl, W.; Claesener, M. Inorg. Chem. 2008, 47, 4463. (b) Uhl,
W.; Claesener, M. Inorg. Chem. 2008, 47, 729. (c) Uhl, W.; Claesener, M.;
Haddadpour, S.; Jasper, B.; Hepp, A. Dalton Trans. 2007, 417. (d) Uhl, W.;
Claesener, M.; Haddadpour, S.; Jasper, B.; Tiesmeyer, I.; Zemke, S. Z.
Anorg. Allg. Chem. 2008, 634, 2889.
(8) (a) Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124. (b) Welch, G. C.; Cabrera, L.; Chase, P. A.; Hollink,
E.; Masuda, J. D.; Wei, P.; Stephan, D. W. Dalton Trans. 2007, 3407. (c)
Chase, P. A.; Stephan, D. W. Angew. Chem. 2008, 120, 7543; Angew.
Chem., Int. Ed. 2008, 47, 7433. (d) Holschumacher, D.; Bannenberg, T.;
Hrib, C. G.; Jones, P. G.; Tamm, M. Angew. Chem. 2008, 120, 7538;
Angew. Chem., Int. Ed. 2008, 47, 7428. (e) Ullrich, M.; Lough, A. J.;
Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 52. (f) Sumerin, V.; Schulz, F.;
(1) (a) Zweifel, G.; Miller, J. A. Org. React. 1984, 32, 375. (b)
Winterfeldt, E. Synthesis 1975, 10, 617. (c) Marek, I.; Normant, J.-F. Chem.
Rev. 1996, 96, 3241. (d) Eisch, J. J. In Comprehensive Organic Synthesis;
Frost, B., Flemming, I., Eds.; Pergamon: Oxford, 1991; Vol. 8, p 733.
(2) Uhl, W. Coord. Chem. Rev. 2008, 252, 1540.
(3) (a) Uhl, W.; Breher, F. Angew. Chem. 1999, 111, 1578; Angew.
Chem., Int. Ed. 1999, 38, 1477. (b) Uhl, W.; Breher, F.; Lu€tzen, A.; Saak, W
Angew. Chem. 2000, 112, 414; Angew. Chem., Int. Ed. 2000, 39, 406. (c)
Uhl, W.; Breher, F.; Grunenberg, J.; L€utzen, A.; Saak, W Organometallics
2000, 19, 4536. (d) Uhl, W.; Breher, F.; Mbonimana, A.; Gauss, J.; Haase, D;
L€utzen, A.; Saak, W. Eur. J. Inorg. Chem. 2001, 3059.
€ €
Atsumi, M.; Wang, C.; Nieger, M.; Leskela, M.; Repo, T.; Pyykko, P.; Rieger,
(4) (a) Uhl, W.; Hepp, A.; Matar, M.; Vinogradov, A. Eur. J. Inorg.
Chem. 2007, 4133. (b) Uhl, W.; Claesener, M.; Hepp, A.; Jasper, B.;
€
B. J. Am. Chem. Soc. 2008, 130, 14117. (g) Momming, C. M.; Otten, E.;
€
€
Vinogradov, A.; van W€ullen, L.; Koster, T. K.-J. Dalton Trans. 2009, 10550.
Kehr, G.; Frohlich, R.; Grimme, S.; Stephan, D. W.; Erker, G. Angew. Chem.
(5) (a) Uhl, W.; Vinogradov, A.; Grimme, S. J. Am. Chem. Soc. 2007,
129, 11259. (b) Uhl, W.; Grunenberg, J.; Hepp, A.; Matar, M.; Vinogradov, A.
Angew. Chem. 2006, 118, 4465; Angew. Chem., Int. Ed. 2006, 45, 4358.
(6) (a) Uhl, W.; Bock, H. R.; Claesener, M.; Layh, M.; Tiesmeyer, I.;
2009, 121, 6770. Angew. Chem., Int. Ed. 2009, 48, 6643. (h) Spies, P.;
€
Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.; Erker, G. Angew.
Chem. 2008, 120, 7654; Angew. Chem., Int. Ed. 2008, 47, 7543.
(9) Low, P. J. J. Clust. Sci. 2008, 19, 5.
€
Wurthwein, E.-U. Chem.;Eur. J. 2008, 14, 11557. (b) Uhl, W.; Er, E.;
(10) van Assema, S. G. A.; Tazelaar, C. G. J.; de Jong, G. B.; van
Maarseveen, J. H.; Schakel, M.; Lutz, M.; Spek, A. L.; Slootweg, J. C.;
Lammertsma, K. Organometallics 2008, 27, 3210.
€
Hepp, A.; Kosters, J.; Layh, M.; Rohling, M.; Vinogradov, A.; W€urthwein,
E.-U.; Ghavtadze, N. Eur. J. Inorg. Chem. 2009, 3307.
r
2010 American Chemical Society
Published on Web 02/24/2010
pubs.acs.org/Organometallics

1324 Organometallics, Vol. 29, No. 6, 2010
Westenberg et al.
alkyne groups and examine the course of events by which the
novel heterocyclic products are formed.
Scheme 1
Hydroalumination of Dialkynylphosphines: Generating
AlP2C2 Heterocycles. Reaction of the readily available
aryl-di(tert-butylethynyl)phosphines, Aryl-P(CtC-CMe3)2
[Aryl = C6H5 (4),11 -2,4,6-Me3C6H2 (5)], in n-hexane at
room temperature with an equimolar amount of dineopen-
tyl- and di(tert-butyl)aluminum hydride gave upon isolation
red crystals of compounds 6-8 in 70-80% yield (eq 1). In
addition, upon concentration of the mother liquors, the
colorless dimeric dialkyl-ethynylaluminum compounds
(R2Al-CtC-CMe3)2 [R = CMe3 (10), CH2CMe3 (11)] could
be isolated, as for 10, on which one of us reported recently,12
or identified by its characteristic 1H NMR parameters, as for
11 [δ = 0.81 (Al-CH2), 1.05 (CtC-CMe3), and 1.36 (CMe3
of neopentyl) with a molar ratio of 2:1:2].
formation. The 13C NMR spectra reveal the presence of
one CtC bond (δ at about 73 and 123) and two different
CdC bonds (δ at about 133 and 165). Hindered rotation
causes two clearly resolved resonances for each set of ortho-
methyl groups of the mesityl substituents of compound 8.
These NMR data suggest an exceptional five-membered
AlC2P2 ring structure with two exocyclic double bonds as
depicted in eq 1. The molecular structure of these com-
pounds was established unequivocally by single-crystal
X-ray structure determinations (Figures 1-3), each reveal-
ing that the AlC2P2 heterocycle deviates only slightly, up
˚
to about 0.20 A, from planarity. The aluminum atom is
tetracoordinated, carrying two alkyl groups. One of the
phosphorus atoms is tricoordinated and has a trigonal-
pyramidal conformation (average sum of the angles 315°
for 6 and 7; 334° for the more congested 8), while the other
is best described as a phosphonium cation carrying an aryl
The complex NMR spectra of each of the three isolated
reaction products (6-8) reveal the unexpected presence of
five nonequivalent tert-butyl groups, making clear that the
reaction was not a simple hydroalumination. This is also
evident from the two observed 31P NMR resonances at δ =
-90 to -100 and -9 to -12 (2JPP = 4 to 30 Hz), indicating
that two phosphine molecules were used in the product
˚
and an ethynyl group (CtC 1.180 A on average). This
suggests zwitterionic character for these compounds, as
shown in eq 1. The two heterocyclic P-C bonds of the
phosphonium center differ in lengths by 0.06 to 0.09 A,
˚
˚
with the shortest being about 1.76 A long. Each of the ring
carbon atoms is part of an exocyclic CdC bond (CdC
˚
1.342 A on average). The cis Al,H arrangement of one
of these bonds suggests that cis-addition has occurred
to the CtC bonds of 4 and 5. The two bulky mesityl groups
in 7 and 8 are at opposite sides of the AlC2P2 ring, probably
due to steric crowding, as a cis-arrangement is found
(11) Skolimowski, J.; Skowronski, R.; Simalty, M. Phosphorus Sulfur
1984, 19, 159.
€
(12) Uhl, W.; Er, E.; Hubner, O.; Himmel, H.-J. Z. Anorg. Allg.
Chem. 2008, 634, 2133.

Article
Organometallics, Vol. 29, No. 6, 2010 1325
Figure 1. Molecular structure and numbering scheme of 6. Ther-
mal ellipsoids are drawn at the 40% probability level; hydrogen
atoms and methyl groups are omitted for clarity. Important bond
˚
lengths [A] and angles [deg] (values of the two other independent
molecules in square brackets): P(11)-C(141) 1.764(3) [1.753(3),
1.761(3)], P(11)-C(131) 1.831(2) [1.826(3), 1.817(3)], P(12)-C-
(131) 1.842(3) [1.854(3), 1.826(3)], Al(1)-P(12) 2.431(1) [2.414(1),
2.426(1)], Al(1)-C(141) 2.037(2) [2.039(2), 2.042(3)], C(131)-
C(132) 1.338(4) [1.335(4), 1.359(4)], C(141)-C(142) 1.345(4)
[1.352(3), 1.341(4)], C(151)-C(152) 1.180(4) [1.186(4), 1.171(4)],
P-C-Al 114.8 (av), P-C-P 119.3 (av), C-P-C 108.1 (av),
P-Al-C 96.1 (av), Al-P-C 95.8 (av).
Figure 2. Molecular structure and numbering scheme of 7. Ther-
mal ellipsoids are drawn at the 40% probability level; hydrogen
atoms and methyl groups of tert-butyl substituents are omitted
˚
for clarity. Important bond lengths [A] and angles [deg]: P(1)-C-
(31) 1.837(1), P(1)-C(41) 1.775(1), Al(1)-C(41) 2.045(1), Al-
(1)-P(2) 2.4138(7), P(2)-C(31) 1.832(1), C(31)-C(32) 1.349(2),
C(41)-C(42) 1.342(2), C(51)-C(52) 1.195(2), P(1)-C(41)-
Al(1) 115.60(7), P(1)-C(31)-P(2) 116.98(7), C(31)-P(1)-
C(41) 109.14(6), P(2)-Al(1)-C(41) 93.26(4), Al(1)-P(2)-C(31)
100.74(5).
for the two phenyl groups in 6. Nevertheless, steric crowd-
ing is a stabilizing factor, which is evident from the inabi-
lity to isolate the heterocyclic system from the reaction
of the sterically less demanding combination of 4 and
dineopentylaluminum hydride. Yet, monitoring this
reaction at room temperature by 31P NMR spectroscopy
did show the formation of the five-membered heterocycle 9
(δ = -7.8 and -99.1; 3JPP = 35.4 Hz), but after two hours
its concentration steadily diminished to give a different
product, which we discuss in the next section.
First, how are the novel AlC2P2 heterocyclic compounds
containing two phosphanyl fragments but only one di-
alkyaluminum group formed? Hydroalumination of one of
the CtC bonds of the starting dialkynylphosphines 4 and 5
is expected to give monoadduct A (eq 1) with an alkynyl
and an alkenyl group attached to the central phosphorus
atom. The exothermicity of this process is evident from the
-25.6 kcal/mol calculated for the reaction of 4 with one-
half of a di(tert-butyl)aluminum hydride dimer. The phos-
phorus-induced difference in charge separation between
the two alkyne carbon atoms (NBO charges R-C -0.40;
β-C þ0.03; P þ0.93) in 4 suggests a selective attack of the
aluminum atom at the R-carbon atom. The DFT calcula-
tions (B3LYP/6-31G(d)) reveal a weak electrostatic inter-
β-C (CdC) -0.18, P þ0.95. Similar interactions and Al-C
distances have been reported for several molecular struc-
tures of related silicon-centered compounds.13 This close
intramolecular Al,C-contact reflects the frustrated Lewis
pair nature of A and likely initiates the elimination of the
alkynyl-dialkylaluminum compounds C, which were de-
tected as dimeric byproduct 10 and 11, to afford the
phosphaallene B as reactive intermediate. Phosphaallenes
with their cumulated CdC and PdC bonds are well-known
in the literature14,15 and can be formed, for example,
from congested dialkynyl-tri(tert-butyl)phenylphosphines
by treatment with tert-butyllithium under expulsion of
an ethynyllithium derivative.15 The elimination of the
(13) (a) Uhl, W.; Heller, D. Z. Anorg. Allg. Chem., in press. Similar
products of hydroboration: (b) Wrackmeyer, B.; Khan, E.; Kempe, R. Appl.
Organomet. Chem. 2008, 22, 383. (c) Khan, E.; Kempe, R.; Wrackmeyer, B.
Appl. Organomet. Chem. 2009, 23, 124.
€
(14) (a) Markl, G.; Reitinger, S. Tetrahedron. Lett. 1988, 29, 463. (b)
€
€
Markl, G.; Herold, U. Tetrahedron Lett. 1988, 29, 2935. (c) Markl, G.;
€
Kreitmeier, P.; Noth, H.; Polborn, K. Angew. Chem. 1990, 102, 958. Angew.
Chem., Int. Ed. Engl. 1990, 29, 927. (d) Yoshifuji, M.; Toyota, K.;
Shibayama, K.; Inamoto, N. Tetrahedron Lett. 1984, 25, 1809. (e) Appel,
€
R.; Folling, P.; Josten, B.; Siray, M.; Winkhaus, V.; Knoch, F. Angew. Chem.
1984, 96, 621; Angew. Chem., Int. Ed. Engl. 1984, 23, 619. (f) Appel, R.;
Winkhaus, V.; Knoch, F. Chem. Ber. 1986, 119, 2466. (g) Guillemin, J.-C.;
Janati, T.; Denis, J.-M.; Guenot, P.; Savignac, P. Tetrahedron Lett. 1994, 35,
245.
(15) (a) Appel, R.; Knoll, F. Adv. Inorg. Chem. 1989, 33, 259. (b)
Niecke, E.; Ruban, A.; Raab, M. Science of Synthesis; Padwa, A., Ed.; Georg
Thieme Verlag: Stuttgart, 2004; Vol. 27, p 937.
˚
action (Al C 2.56 A; Wiberg bond index 0.1) between
3 3 3
the coordinatively unsaturated aluminum atom and the
R-carbon atom of the intact ethynyl group of A, based on
the NBO charges of the respective atoms, i.e., Al þ1.93,
R-C (CtC) -0.49, β-C (CtC) þ0.08, R-C (CdC) -0.99,

1326 Organometallics, Vol. 29, No. 6, 2010
Westenberg et al.
Figure 3. Molecular structure and numbering scheme of 8. Ther-
mal ellipsoids are drawn at the 40% probability level; hydrogen
atoms and methyl groups of tert-butyl substituents are omitted
˚
for clarity. Important bond lengths [A] and angles [deg] (values
of the second molecule in square brackets): P(11)-C(141) 1.848(3)
[1.825(3)], P(11)-C(131) 1.780(3) [1.778(3)], Al(11)-C(131)
2.053(3) [2.038(3)], Al(11)-P(12) 2.395(1) [2.399(2)], P(12)-C-
(141) 1.814(3) [1.804(3)], C(131)-C(132) 1.331(4) [1.341(4)], C-
(141)-C(142) 1.326(4) [1.339(4)], C(151)-C(152) 1.175(4)
[1.171(5)], P(11)-C(131)-Al(11) 116.1(2) [117.9(2)], P(11)-C-
(141)-P(12) 115.6(2) [115.6(2)], C(131)-P(11)-C(141) 108.2(1)
[108.4(2)], P(12)-Al(11)-C(131) 92.7(1) [91.2(1)], Al(11)-P-
(12)-C(141) 103.5(1) [104.7(1)].
Figure 4. Calculated reaction pathways for the cycloaddition of
the hydroalumintion product A with phosphallene B at the
B3LYP/6-31G(d) level of theory utilizing all-methyl-substituted
model systems.
mol (Figure 4). The calculated structure of 6 is -13.6 kcal/
mol more stable than A and B and shows a slightly longer
˚
˚
Al-P bond (2.468 A) than the experimental one (2.424 A,
Figure 1).
Bicyclic AlP2C3 Heterocycles: CtC Insertion into AlP2C2
Monocycles. We return to the room-temperature reaction of
phenyl-di(tert-butylethynyl)phosphine 4 with dineopentyl-
aluminum hydride. Whereas this reaction also afforded
the dialkyl-ethynylaluminum dimer 11, the AlC2P2 hetero-
cycle 9 that was observed only by 31P NMR spectroscopy
converted within 18 h fully into a single colorless product
12, isolated in 51% yield. Its 31P NMR spectrum showed
two resonances with chemical shifts at δ = þ56.0 and
þ11.5 that differ greatly from those of 6-9. The 13C NMR
spectrum showed the absence of ethynyl carbon resonances
and instead ones attributable to three different CdC
bonds, suggesting that an isomeric structure of the five-
membered AlC2P2 heterocycle was formed with the mono-
cyclic compound only as a reactive intermediate. This
hypothesis was supported by the formation of a similar
yellow compound (13) in 65% yield upon warming an n-
hexane solution of 7 to 60 °C for 14 h (eq 2). Instead, the
more congested monocyclic 8 (Aryl = 2,4,6-Me3C6H2;
R = CMe3) decomposed under these conditions, resulting
in di(tert-butyl)-tert-butylethynylaluminum 10 as the main
alkynylaluminum fragment C and the formation of the
unsaturated phosphorus intermediate B shows resem-
blance with this process. The likelihood of the fragmenta-
tion of A at room temperature is supported by the B3LYP-
calculated modest endothermicity of þ17.5 kcal/mol and is
further facilitated by the dimerization of C (-30.2 kcal/
mol). However, so far we have not been able to detect any in
situ formed phosphaallene. This could mean that the
phosphaallene B never reaches detectable concentrations
during the reaction, as it is consumed immediately. The
process by which this occurs is a 1,3-cycloaddition with the
initial hydroalumination product A to give the observed
heterocyclic compounds 6-9. The likely path by which this
happens is by coordinating first the aluminum atom of the
frustrated Lewis pair A to the phosphorus atom of phos-
phaallene B with subsequent ring closure on P-C bond
formation between the activated PdC bond and the tri-
coordinate phosphorus center (Figure 4). The cycloaddi-
tion is calculated to have a barrier of only 9.7 kcal/mol for
the all-methyl-substituted model system and is exothermic
by -17.6 kcal/mol. The alternative cycloaddition with the
CdC bond of the phosphaallene that would give an AlPC3
heterocycle with exocyclic CdC and CdP bonds instead is
both kinetically and thermodynamically disfavored with a
barrier of 18.7 kcal/mol and a reaction energy of -9.7 kcal/
1
component in the H NMR spectrum together with uni-
dentified products [δ(31P) 56.0 (s), -10.2 (s), -47.1 and
-69.8 (d; JPP = 126.2 Hz; -52.3 and -72.8 (d; JPP = 119.0
Hz), -95.5 (s)]. Also a mixture of two unidentified products

Article
Organometallics, Vol. 29, No. 6, 2010 1327
[δ(31P) 54.3 and 12.0, JPP = 15.1 Hz; δ = 44.5 and 14.7,
J
PP = 5.6 Hz] resulted upon heating of 6.
Figure 5. Molecular structure and numbering scheme of 12.
Thermal ellipsoids are drawn at the 40% probability level;
hydrogen atoms and methyl groups are omitted for clarity.
˚
Important bond lengths [A] and angles [deg]: P(1)-C(31)
1.790(3), P(1)-C(51) 1.797(3), P(1)-C(41) 1.808(3), P(2)-C-
(41) 1.865(3), P(2)-C(32) 1.873(3), Al(1)-C(51) 2.081(3), Al-
(1)-C(31) 2.069(3), C(31)-C(32) 1.339(4), C(41)-C(42)
1.326(4), C(51)-C(52) 1.336(4), Al(1)-C(31)-C(32) 146.7(2),
Al(1)-C(31)-P(1) 92.4(1), P(1)-C(31)-C(32) 113.4(2), C-
(31)-P(1)-C(41) 98.6(1), C(31)-P(1)-C(51) 95.6(1), C(41)-P-
(1)-C(51) 127.0(1).
Bicyclic compounds 12 and 13 represent isomeric forms of
monocyclic 6-9 and are formed by the formal insertion of
the ethynyl group into the Al-P bond. An unprecedented
cooperative activation of the triple bond appears to play an
essential role. Bending the alkynyl substituent out of its axial
position over the five-membered ring leads to overlap be-
tween the phosphorus lone pair and the ethynyl π* orbital at
the β-carbon to form a bicyclic intermediate (þ9.6 kcal/mol)
with an activation barrier of 16.3 kcal/mol (TS3, R, R0,
˚
Aryl = Me) and a weakened Al-P bond of 2.547 A. Break-
The constitution of 12 was revealed by crystal structure de-
ing this bond (TS4) requires only 7.7 kcal/mol to form the
more stable (-19.7 kcal/mol) bicyclic compound with the
aluminum atom favoring the R-carbon atom of the former
CtC bond (eq 2; the calculated energies are given for the all-
methyl-substituted model systems). The first step (7 or 9 to
TS3) resembles the nucleophilic activation of alkynes by
electron-rich phosphines,16 which in our case is followed
by an unusual migration of the AlR2 fragment from P to C.
termination (Figure 5) and showed it to be a bicyclic structure
in which a four- (AlC2P) and a five-membered heterocycle
(C3P2) are annulated across a central P-C bond. The structure
of the five-membered ring is essentially planar with a deviation
˚
of only up to 0.05 A. The angle between the planes of the two
rings amounts to 31.6°. The aluminum atoms have a coordina-
tion number of four. One phosphorus atom is attached to three
carbon atoms (trigonal pyramidal, sum of the angles 298.7°),
and the other is best described as a phosphonium atom bearing
a formal positive charge. Hence, also 12 is a zwitterionic
compound. The three different CdC double bonds have similar
(16) Reactions of tertiary phosphines with alkynes including second-
ary processes have been described: (a) Lu, X.; Zhang, C.; Xu, Z. Acc.
Chem. Res. 2001, 34, 535. (b) Methot, J. L.; Roush, W. R. Adv. Synth. Catal.
2004, 346, 1035. (c) Ramazani, A.; Kazemizadeh, A. R.; Ahmadi, E.;
Noshiranzadeh, N.; Souldozi, A. Curr. Org. Chem. 2008, 12, 59. Reports
on the reactions of lithium phosphides and phosphaallyl anions with alkynes:
(d) Niecke, E.; Nieger, M.; Wenderoth, P. Angew. Chem. 1994, 106, 362;
Angew. Chem., Int. Ed. Engl. 1994, 33, 353. (e) Niecke, E.; Nieger, M.;
Wenderoth, P. Angew. Chem. 1994, 106, 2045; Angew. Chem., Int. Ed.
˚
lengths [1.326(4) to 1.339(4) A] that are independent of their
endo- or exocyclic position. The phenyl groups attached to the
phosphorus atoms adopt a cis arrangement. In contrast, the
NMR spectroscopic data suggest that the mesityl groups of 13
are in trans positions. Hence, we observe different diastereo-
meric forms similar to the discussed monocyclic compounds
6-8. The mixture obtained upon heating of 6 may, in fact,
contain both forms, but we were unable to isolate them. The
steric congestion of the hypothetical bicyclic product is inter-
mediate between that of 12 and 13.
€
Engl. 1994, 33, 1954. (f) Issberner, K.; Niecke, E.; Wittchow, E.; Dotz, K. H.;
Nieger, M. Organometallics 1997, 16, 2370. Monocyclic structural motifs
similar to the five-membered ring of the bicyclic intermediate postulated in eq
2: (g) Bowmaker, G. A.; Herr, R.; Schmidbaur, H. Chem Ber. 1983, 116,
3567. (h) Biaso, F.; Cantat, T.; Mezailles, N.; Ricard, L.; Le Floch, P.;
Geoffroy, M. Angew. Chem. 2006, 118, 7194; Angew. Chem., Int. Ed.
2006, 45, 7036.

1328 Organometallics, Vol. 29, No. 6, 2010
Westenberg et al.
Recent investigations describe similar activations by so-
called frustrated Lewis-acid Lewis-base pairs in which the
interactions between the donor and acceptor atoms are
negligibly small.8 In the compounds presented here this
activation may be particularly favorable, as a phosphinide
anion is stabilized by adduct formation with a dialkylalumi-
num group. The negative charge localized at the phosphorus
atom of the activated species with a weakened Al-P bond is
balanced by the zwitterionic character.
bright red crystals of compound 6. Yield: 0.226 g (68%). Mp
(argon, closed capillary): 116 °C (dec). Anal. Calcd [C38H57-
AlP2] (602.8): C, 75.7; H, 9.5. Found: C, 75.3; H, 9.4. 1H NMR
(C6D6, 400 MHz): δ 0.98 (9 H, s, P-(Al)CdC(H)CMe3), 1.01 (9
H, s, P-CtC-CMe3), 1.32 (9 H, s, P2CdC(H)CMe3), 1.44 and
1.58 (each 9 H, s, Al-CMe3), 6.78 (1 H, m, p-H of Al-P-Ph), 6.87
(2 H, m, m-H of Al-P-Ph), 6.92 (2 H, m, m-H of CtC-P-Ph), 6.94
(1 H, m, p-H CtC-P-Ph), 7.24 (2 H, m, o-H of Al-P-Ph), 7.45 (1
H, dd, 3JHP = 31.4 and 16.9 Hz, P2CdC(H)CMe3), 7.59 (1 H, d,
3
3JHP= 74.9 Hz, P-(Al)CdC(H)CMe3), 7.79 (2 H, dd, JHH
=
7.5 Hz and 3JHP = 12.7 Hz, o-H of CtC-P-Ph). 13C NMR (C6D6,
100 MHz): δ 17.9 and 18.6 (each br, AlCMe3), 28.9 (d, 3JCP = 18.1
Hz, P-CtC-CMe3), 29.3 (P-CtC-CMe3), 29.9 (P-(Al)CdC(H)-
CMe3), 30.1 (P2CdC(H)CMe3), 32.2 and 32.9 (each AlCMe3),
37.7 (d, 3JCP = 20.1 Hz, P2CdC(H)CMe3), 40.9 (d, 3JCP = 12.0
Experimental Section
All procedures were carried out under an atmosphere of
purified argon in dried solvents (n-hexane and n-pentane over
LiAlH4; diethyl ether over Na/benzophenone). Di(tert-butyl-
ethynyl)phenylphosphine,9 dihalomesitylphosphine (MesPX2,
mixture with X = Cl, Br),17 and di(neopentyl)-18 and di(tert-
butyl)aluminum hydride19 were obtained according to literature
procedures. Commercially available tert-butylethyne (3,3-di-
methyl-1-butyne) was degassed, saturated with argon, and
stored over molecular sieves. The assignment of the NMR
spectra is based on HMBC, HSQC, ROESY, and DEPT135
data. Mass spectra were recorded with a Micromass Quattro
LC-Z; IR spectra, with a Shimadzu IR PRESTIGE 21.
Hz, P-(Al)CdC(H)CMe3), 69.9 (dd, 1JCP = 129.8 Hz and 3JCP
=
2
1.2 Hz, P-CtC), 123.7 (d, JCP = 14.4 Hz, P-CtC), 127.4 (d,
3JCP = 6.4 Hz, m-C of Al-P-Ph), 128.0 (p-C of Al-P-Ph), 128.7 (d,
1JCP = 10.7 Hz, P-(Al)CdC(H)CMe3), 129.1 (d, 3JCP = 12.0 Hz,
m-C of CtC-P-Ph), 130.3 (d, 2JCP = 19.0 Hz, o-C of Al-P-Ph),
131.1 (d, 1JCP = 79.4 Hz, ipso-C of CtC-P-Ph), 131.8 (d, 2JCP
=
10.5 Hz, o-C of CtC-P-Ph), 132.4 (d, 4JCP = 2.9 Hz, p-C of CtC-
P-Ph), 133.4 (dd, JCP = 67.8 and 62.8 Hz, P2CdC(H)CMe3),
=
1
144.0 (d, 1JCP = 32.3 Hz, ipso-C of Al-P-Ph), 173.5 (dd, 2JCP
2
15.0 and 12.4 Hz, P2CdC(H)CMe3), 174.4. (d, JCP = 6.4 Hz,
P-(Al)CdC(H)CMe3). 31P NMR (C6D6, 162 MHz): δ -100.4 (d,
Synthesis of 5. A solution of 3,3-dimethyl-1-butyne (1.84 mL,
15.0 mmol) in 50 mL of diethyl ether was treated dropwise with a
solution of n-butyllihium in n-hexane (1.6 M, 8.75 mL, 14 mmol)
at -78 °C. The reaction mixture was allowed to warm to room
temperature and further stirred for 1 h. After cooling to -78 °C
dihalomesitylphosphine (1.51 g, 5.80 mmol) dissolved in 25 mL
of diethyl ether was added dropwise. After 30 min at -78 °C the
solution was warmed to room temperature and stirred for 14 h.
Water was added. The organic layer was separated and washed
with 25 mL of water. The aqueous phase was extracted three
times with 25 mL of diethyl ether. The organic layers were dried
over MgSO4, and all volatiles were removed under vacuum. The
remaining solid was thoroughly evacuated and dissolved in a
mixture of 10 mL of diethyl ether and 10 mL of n-pentane.
Colorless crystals of 5 were obtained upon cooling of the
solution to -45 °C. Yield: 1.61 g (89%). Mp (argon, closed
capillary): 147 °C. Anal. Calcd [C21H29P] (312.4): C, 80.7; H,
9.4. Found: C, 80.5; H, 9.5. 1H NMR (C6D6, 400 MHz): δ 1.06
(18 H, s, CMe3), 2.02 (3 H, s, p-Me of phenyl), 2.91 (6 H, s, o-Me
2
2JPP = 29.8 Hz, P-Al), -8.5 (d, JPP = 29.8 Hz, P-CtC). IR
(paraffin, CsI plates, cm-1): 2210 s, 2166 s νCtC; 2062 m, 1985 w,
1964 w, 1935 w, 1910 w, 1890 w, 1861 w, 1838 w, 1589 s, 1568 s,
1551 vs, 1533 s aromatic ring, νCdC; 1452 (vs), 1375 vs (paraffin);
1308 m, 1252 s δCH3; 1202 s, 1103 m, 1067 w, 1026 m, 1001 m, 957
m, 935 m, 897 w, 880 w, 845 w, 812 m, 777 m νCC, δCH, δCC; 721 s
(paraffin); 692 m, 629 w, 588 m, 579 m, 534 w, 505 w, 461 vw νPC,
νAlC, δCC. MS(EI, 20eV, 90°C): m/z545(100%) (Mþ - CMe3),
489 (16%) (Mþ - CMe3 - butene).
Synthesis of 7. A solution of di(tert-butylethynyl)mesi-
tylphosphine 5 (0.102 g, 0.327 mmol) in 10 mL of n-hexane
was treated with a solution of dineopentylaluminum hydride
(0.056 g, 0.327 mmol) in 10 mL of n-hexane at room tempera-
ture. The reaction mixture became orange-red in a few minutes
and was stirred for 24 h. Orange crystals were obtained upon
concentration of the solution and cooling to 4 °C. Yield: 0.095
mg (81%). Mp (argon, closed capillary): 136 °C (dec). Anal.
Calcd [C46H73AlP2] (715.0): C, 77.3; H, 10.3. Found: C, 76.7; H,
10.1. 1H NMR (C6D6, 400 MHz): δ 0.65 and 0.69 (each 1 H, s,
CH2CMe3), 0.88 (9 H, s, P2CdC(H)CMe3), 0.95 (9 H, s,
P-(Al)CdC(H)CMe3), 0.97 and 1.07 (each 1 H, s, CH2CMe3),
1.15 (9 H, s, P-CtC-CMe3), 1.29 and 1.59 (9 H, s, CH2CMe3),
1.89 (3 H, s, p-Me of CtC-P-Mes), 2.15 (3 H, s, p-Me of Al-P-
Mes), 2.5-3.0 (12 H, br, m, o-Me), 6.15 (1 H, dd, 3JHP = 36.2
and 7.0 Hz, P2CdC(H)CMe3), 6.60 (2 H, br, m-H of CtC-P-
Mes), 6.93 (2 H, br., m-H of Al-P-Mes), 7.21 (1 H, d, 3JHP= 76.1
Hz, P-(Al)CdC(H)CMe3). 13C NMR (C6D6, 100 MHz): δ 20.8
(p-Me of CtC-P-Mes), 21.1 (p-Me of Al-P-Mes), 25.0 (br, o-Me
of CtC-P-Mes and of Al-P-Mes), 28.4 (dd, 4JCP = 4.6 and 1.3
Hz, P2CdC(H)CMe3), 29.0 (P-CtC-CMe3) 29.2 (d, 3JCP = 2.6
Hz, P-CtC-CMe3) 29.4 (P-(Al)CdC(H)CMe3), 32.3 and 32.9
(CH2CMe3), 33.9 and 34.4 (CH2CMe3), 35.6 and 35.9
4
of phenyl), 6.74 (2 H, d, JPH = 2.9 Hz, Aryl-H). 13C NMR
(C6D6, 100 MHz): δ 21.0 (p-Me), 23.1 (d, 3JCP = 19.7 Hz, o-Me),
28.9 (d, 3JCP = 1.1 Hz, CMe3), 30.5 (d, 4JCP = 1.2 Hz, CMe3),
73.8 (P-CtC; coupling to phosphorus not detectable), 115.0 (d,
2JCP = 8.2 Hz, P-CtC), 127.8 (ipso-C), 130.0 (d, 3JCP = 5.5 Hz,
2
m-C), 140.2 (p-C), 144.6 (d, JCP = 19.1 Hz, o-C). 31P NMR
(C6D6; 81 MHz): δ -83.4. IR (paraffin, CsI plates, cm-1): 2195
vs, 2149 vs νCtC, 2012 vw, 1946 vw, 1911 w, 1883 w, 1792 w,
1759 m, 1726 s, 1694 w, 1630 w, 1601 s, 1566 m, 1551 s, 1533 m
(aromatic ring); 1460 vs, 1356 vs (paraffin); 1290 m, 1238 vs
δCH3; 1200 vs, 1109 m, 1072 m, 1055 s, 1030 s, 937 vs, 849 vs, 768
vs νCC, δCH; 721 s (paraffin); 685 w, 640 vs, 613 vs, 571 vs, 530
vs, 509 s, 486 m, 436 s, 413 s νPC, δCC. MS (EI, 20 eV, 25 °C): m/
z 312 (40%) (Mþ), 297 (88%) (Mþ - Me), 255 (100%) (Mþ
CMe3).
-
3
(CH2CMe3), 36.7 (dd, JCP = 22.0 and 3.3 Hz, P2CdC-
(H)CMe3), 39.6 (dd, 3JCP = 12.7 and 5JCP = 1.7 Hz, P(Al)CdC-
(H)CMe3), 73.2 (d, 1JCP = 138.5 Hz and 3JCP = 3.2 Hz, P-CtC-
CMe3), 122.4 (d, 2JCP = 18.6 Hz, P-CtC-CMe3), 129.3 (br, m-C
of Al-P-Mes), 131.5 (br, m-C of CtC-P-Mes), 135.4 (p-C of Al-
Synthesis of 6. Di(tert-butylethynyl)phenylphosphine 4 (0.303
g, 1.12 mmol) was dissolved in 10 mL of n-hexane and treated
with a solution of di(tert-butyl)aluminum hydride (0.159 g, 1.12
mmol) in 10 mL of n-hexane at room temperature. The reaction
mixture adopted a bright red color. Stirring was continued for
24 h. The solution was concentrated and cooled to 4 °C to obtain
1
P-Mes), 135.6 (pseudo-t, JCP = 67.2 and 67.2 Hz, P2CdC-
(H)CMe3), 136.2 (d, br, JCP = 19 Hz, P-(Al)CdC(H)CMe3),
1
137.5 (dd, 1JCP = 30.5 Hz and 3JCP = 4.1 Hz, ipso-C of Al-P-
Mes), 138.5 (dd, 1JCP = 86.7 Hz and 3JCP = 3.0 Hz, ipso-C of
CtC-P-Mes), 142.1 (d, JCP = 2.9 Hz, p-C of CtC-P-Mes),
(17) Liddle, S. T.; Izod, K. Organometallics 2004, 23, 5550.
(18) Beachley, O. T., Jr.; Victoriano, L. Organometallics 1988, 7, 63.
(19) Uhl, W.; Cuypers, L.; Graupner, R.; Molter, J.; Vester, A.;
4
142.6 (br, o-C of CtC-P-Mes), 144.8 (br, o-C of Al-P-Mes),
160.5 (pseudo-t, JCP = 9.8 and 9.8 Hz, P2CdC(H)CMe3),
2
€
Neumuller, B. Z. Anorg. Allg. Chem. 2001, 627, 607.

Article
Organometallics, Vol. 29, No. 6, 2010 1329
168.1 (dd, JCP = 8.2 and 5.1 Hz, P-(Al)CdC(H)CMe3). 31P
(argon, closed capillary): 138 °C (dec); color change to yellow at
128 °C. Anal. Calcd [C40H61AlP2] (630.9): C, 76.2; H, 9.7.
Found: C, 75.9; H, 9.7. 1H NMR (C6D6, 400 MHz): δ 0.79
and 1.05 (each 1 H, s, CH2CMe3), 0.82 (9 H, s, P-(Al)CdC-
(H)CMe3), 0.96 and 1.04 (each 1 H, s, CH2CMe3), 1.32 (9 H, s,
P2CdC(H)CMe3), 1.34 (9 H, s, CH2CMe3), 1.39 (9 H, s,
Al-(P)CdC(P)CMe3), 1.53 (9 H, s, CH2CMe3), 6.70 (2 H, m,
m-H of (CdC)2P-Ph), 6.75 (2 H, m, m-H of (CdC)3P-Ph), 6.78
(1 H, m, p-H of (CdC)2P-Ph), 6.80 (1 H, m, p-H of (CdC)3P-
Ph), 7.13 (1 H, dd, 3JHP = 23.0 and 22.0 Hz, P2CdC(H)CMe3),
7.24 (1 H, d, 3JHP= 77.2 Hz, P-(Al)CdC(H)CMe3), 7.28 (2 H,
m, 3JHP = 6.9 Hz, o-H of (CdC)2P-Ph), 7.46 (2 H, pseudo-t, o-H
2
NMR (C6D6, 162 MHz): δ -89.4 (d, JPP = 8.9 Hz, P-Al),
2
-12.1 (d, JPP = 8.9 Hz, P-CtC). IR (paraffin, CsI plates,
cm-1): 2205 m, 2162 s νCtC; 2127 w, 1726 w, 1694 w, 1645 w,
1601 s, 1553 s, 1537 m aromatic ring, νCdC; 1460 vs (paraffin);
1406 w δCH3; 1375 vs (paraffin); 1306 w, 1288 m, 1246 s δCH3,
1221 s, 1196 s, 1119 m, 1099 m, 1055 m, 1028 s, 1013 s, 1001 sh,
949 m, 930 m, 910 w, 897 w, 880 m, 849 vs, 791 vs, 775 vs, 743 vs
νCC, δCH, δCC; 718 s (paraffin); 704 s, 677 vs, 648 s, 629 s, 608
m, 581 m, 550 w, 519 m, 501 m, 468 s, 457 s νPC, νAlC, δCC. MS
(EI, 20 eV, 100 °C): m/z 715 (0.5%) (Mþ þ H), 644 (100%) (Mþ
- CHCMe3).
of (CdC)3P-Ph). 13C NMR (C6D6, 100 MHz): δ 29.6 (d, 4JCP
=
Synthesis of 8. Di(tert-butylethynyl)mesitylphosphine
5
1.6 Hz, P-(Al)CdC(H)CMe3), 30.6 (d, 4JCP = 7.4 Hz, Al-(P)Cd
C(P)CMe3), 31.0 (d, JCP = 7.9 Hz, P2CdC(H)CMe3), 32.2
(CH2CMe3), 32.5 and 32.9 (CH2CMe3), 35.0 (br, CH2CMe3),
(0.131 g, 0.419 mmol) was dissolved in 10 mL of n-hexane and
treated with a solution of di(tert-butyl)aluminum hydride (0.059
g, 0.419 mmol) dissolved in 10 mL of n-hexane at room
temperature. The reaction mixture adopted immediately a red
color. After 24 h the solution was concentrated and cooled to
þ4 °C to afford red crystals of the heterocyclic product 8. Yield:
0.100 g (69%). Mp (argon, closed capillary): 114 °C (dec). Anal.
Calcd [C44H69AlP2] (687.0): C, 76.9; H, 10.1. Found: C, 76.6; H, 9.9.
1H NMR (C6D6, 400 MHz): δ 0.88 (9 H, s, P2CdC(H)CMe3), 0.95
(9 H, s, P-(Al)CdC(H)CMe3), 1.10 (9 H, s, P-CtC-CMe3), 1.32
and 1.66 (each 9 H, s, AlCMe3), 1.90 (3 H, s, p-Me of CtC-P-Mes),
2.16 (3 H, s, p-Me of Al-P-Mes), 2.47 (3 H, s, o-Me of CtC-P-Mes),
2.82 (3 H, s, o-Me of Al-P-Mes), 2.83 (3 H, s, o-Me of CtC-P-Mes),
2.99 (3 H, s, o-Me of Al-P-Mes), 6.09 (1 H, dd, 3JHP = 35.5 and 8.7
Hz, PCdC(H)CMe3), 6.56 and 6.65 (each 1 H, s, m-H of CtC-P-
Mes), 6.90 and 6.91 (each 1 H, s, m-H of Al-P-Mes), 7.14 (1 H, dd,
4
3
35.4 and 35.8 (CH2CMe3), 37.3 (d, JCP = 12.9 Hz, P2CdC-
(H)CMe3), 38.2 (d, 3JCP = 16.2 Hz, P-(Al)CdC(H)CMe3), 41.6
(dd, JCP = 29.6 and 26.7 Hz, Al-(P)CdC(P)CMe3), 127.9 (d,
3JCP = 6.0 Hz, m-C of (CdC)2P-Ph), 128.1 (d, 3JCP = 10.7 Hz,
m-C of (CdC)3P-Ph), 128.6 (p-C of (CdC)2P-Ph), 130.4 (d,
4JCP = 2.8 Hz, p-C of (CdC)3P-Ph), 131.7 (d, 2JCP = 9.0 Hz, o-
1
C (CdC)3P-Ph), 131.8 (d, JCP = 35 and 3 Hz, P2CdC-
(H)CMe3), 133.8 (d, JCP = 17.6 Hz, o-C of (CdC)2P-Ph),
4
1
133.9 (d, JCP = 53.8 Hz, ipso-C of (CdC)3P-Ph), 135.3 (d,
1JCP = 25.7 Hz, ipso-C of (CdC)2P-Ph), 139.2 (d, 1JCP = 24.7
Hz, P-(Al)CdC(H)CMe3), 164.3 (dd, 2JCP = 23.3 and 4.3 Hz,
P2CdC(H)CMe3), 168.7 (d, JCP = 13.7 Hz, P-(Al)CdC-
2
1
(H)CMe3), 170.5 (br, Al-(P)CdC(P)CMe3), 179.9 (d, JCP
=
25.8 Hz, Al-(P)CdC(P)CMe3). 31P NMR (162 MHz, C6D6): δ
56.0 (d, 2JPP = 13.7 Hz, (CdC)3P), 11.4 (d, 2JPP = 13.7 Hz, (Cd
C)2P). IR (paraffin, CsI plates, cm-1): 2073 w, 1967 w, 1950 w,
1898 w, 1883 w, 1823 w, 1809 m, 1780 vw, 1694 m, 1661 m, 1595
vs, 1568 s, 1551 m, 1508 vs aromatic ring, νCdC; 1466 vs, 1356 vs
(paraffin); 1306 m, 1244 s δCH3; 1221 s, 1202 s, 1157 w, 1109 s,
1069w, 1028 s, 1011s, 995s, 964 vs, 941vs, 932 s, 920 s, 905 vs, 878
vs, 860 vs, 847 vs, 775 s, 741 s νCC, δCH, δCC; 712 m (paraffin);
692 w, 677 w, 669 w, 638 w, 606 m, 559 s, 542 s, 530 s, 490 m, 465 s,
436 m νPC, νAlC, δCC. MS (EI, 20 eV, 90 °C): m/z 560 (100%)
(Mþ - CHCMe3), 502 (6%) (Mþ - CH2CMe3 - CMe3).
Synthesis of 13. A solution of the monocyclic aluminum
phosphinide 7 (0.048 g, 0.067 mmol) in 10 mL of n-hexane was
heated to 60 °C for 14 h. Concentration at room temperature
and cooling to þ4 °C gave yellow crystals of 13. Yield: 0.031 g
(65%). Mp (argon, closed capillary): 94 °C (dec). Anal. Calcd
[C46H73AlP2] (715.0): C, 77.3; H, 10.3. Found: C, 76.9; H, 10.1.
1H NMR (C6D6, 400 MHz): δ 0.72 (9 H, s, P2CdC(H)CMe3),
0.77 (2 H, s, CH2CMe3), 0.89 and 0.95 (each 1 H, s, CH2CMe3),
1.10 (9 H, s, CH2CMe3), 1.36 (9H, s, P-(Al)CdC(H)CMe3), 1.39 (9
H, s, Al-(P)CdC(P)CMe3), 1.49 (9 H, s, CH2CMe3), 1.93 (3 H, s, p-
Me of (CdC)2P-Mes), 2.01 (3 H, s, p-Me of (CdC)3P-Mes), 2.30 (3
H, s, o-Me of (CdC)3P-Mes), 2.73 (6 H, s, o-Me of (CdC)2P-Mes),
2.92 (3 H, s, o-Me of (CdC)3P-Mes), 6.59 (1H, s, m-H of (CdC)3P-
4
3JHP = 77.5 Hz and JHP = 1.1 Hz, P-(Al)CdC(H)CMe3). 13C
NMR (C6D6,100MHz):δ17.7(d, 2JCP =30Hz,AlCMe3),18.0(d,
2JCP = 40 Hz, AlCMe3), 20.8 (p-Me of CtC-P-Mes), 21.1 (p-Me of
Al-P-Mes),25.0(d,3JCP =31Hz,o-Me of Al-P-Mes),25.2(d,o-Me
of CtC-P-Mes), 26.1 (dd, JCP = 9.1 and 4.0 Hz, o-Me of CtC-P-
Mes), 27.5 (o-Me of Al-P-Mes), 28.4 (dd, 4JCP = 5.4 and 1.2 Hz,
P-(Al)CdC(H)CMe3), 28.9(d, 4JCP =1.9Hz, P-CtC-CMe3), 29.3
3
5
(dd, JCP = 21.6 Hz, JCP = 1.4 Hz, P-CtC-CMe3), 29.5
(P-(Al)CdC(H)CMe3), 32.9 (AlCMe3), 33.4 (d, JCP = 3.5 Hz,
3
AlCMe3), 37.0(dd, 3JCP =21.6and3.0Hz, P2CdC(H)CMe3),40.1
(dd, 3JCP = 12.7 and 1.7 Hz, P-(Al)CdC(H)CMe3), 73.1 (dd, 1JCP
=
= 139.8 Hz and 3JCP = 3.9 Hz, P-CtC-CMe3), 122.5 (d, 2JCP
17.9 Hz, P-CtC-CMe3), 127.1 (d, 1JCP = 71.4 Hz, ipso-C of CtC-
P-Mes), 129.5 (dd, 3JCP = 4.6 Hz and 4JCP = 5.0 Hz, m-C of Al-P-
Mes), 129.5 (d, 3JCP = 1.9 Hz, m-C of Al-P-Mes), 131.4 (d, 3JCP
=
3
5.2 Hz, m-C of CtC-P-Mes), 131.5 (d, JCP = 1.6 Hz, m-C of
1
CtC-P-Mes), 132.5 (d, JCP = 19 Hz, P-(Al)CdC(H)CMe3),
132.6 (dd, 1JCP = 65.9 and 61.3 Hz, P2CdC(H)CMe3), 134.9 (p-C
of Al-P-Mes), 137.2 (d, 1JCP = 24.5 Hz, ipso-C of Al-P-Mes), 141.2
(dd, 2JCP = 32.5 Hz and 4JCP = 3.4 Hz, o-C of Al-P-Mes), 141.4 (d,
2JCP = 6.9 Hz, o-C of Al-P-Mes), 141.8 (o-C of CtC-P-Mes), 142.3
(d, 4JCP = 2.9 Hz, p-C of CtC-P-Mes), 143.0 (d, 2JCP = 15.2 Hz,
o-C of CtC-P-Mes), 159.9 (t, 2JCP = 12.0 Hz, P2CdC(H)CMe3),
167.3 (d, 2JCP = 8.8 and 6.0 Hz, P-(Al)CdC(H)CMe3). 31P NMR
Mes), 6.65 (2 H, br, m-H of (CdC)2P-Mes), 6.74 (1 H, dd, 3JHP
=
21.6 and 17.2 Hz, P2CdCHCMe3), 6.79 (1 H, s, m-H of (CdC)3P-
2
(C6D6, 162 MHz): δ -95.6 (d, JPP = 4.4 Hz, Al-P), -10.2 (d,
2JPP = 4.4 Hz, P-CtC). IR (paraffin, CsI plates, cm-1): 2205 s,
2162 s νCtC; 2070 w, 1981 vw, 1886 w, 1746 w, 1728 w, 1697 w,
1649 vw, 1603 m, 1553 s, 1537 s, 1520 s aromatic ring, νCdC; 1454
vs, 1371 vs (paraffin); 1292 s, 1248 vs δCH3; 1198 s, 1175 m, 1053 m,
1030 s, 1007 s, 949 s, 935 s, 912 m, 893 m, 849 s, 810 m, 777 m, 741 m
νCC, δCH, δCC; 719 vs (paraffin); 673 m, 627 s, 583 s, 569 s, 554 s,
536 s, 519 m, 467 m, 419 m νPC, νAlC, δCC.MS(EI,20eV,100°C):
m/z 630 (19%) (Mþ - butene), 550 (100%) (Mþ - CtC-CMe3 -
butene þ H).
3
Mes), 7.04 (1 H, d, JHP = 48.0 Hz, P-(Al)CdC(H)CMe3). 13C
NMR (C6D6, 100 MHz): δ 20.7 (p-Me of (CdC)2P-Mes), 21.0 (p-
Me of (CdC)3P-Mes), 23.0 and 24.5 (o-Me of (CdC)3P-Mes), 23.3
and 27.2 (o-Me of (CdC)2P-Mes), 28.4 (dd, 4JCP = 4.6 and 1.5 Hz,
P2CdC(H)CMe3), 29.4 (d, 4JCP = 1.4 Hz, P-(Al)CdC(H)CMe3),
3
31.4 (d, JCP = 7.2 Hz, Al-(P)CdC(P)CMe3), 31.6 (CH2CMe3),
32.1 (CH2CMe3), 32.7 (CH2CMe3), 35.4 (CH2CMe3), 35.8
(CH2CMe3), 36.3 (dd, 3JCP = 11.8 and 2.0 Hz, P2CdC(H)CMe3),
37.6 (d, 3JHP = 30.0 Hz, P-(Al)CdC(H)CMe3), 37.7 (CH2CMe3),
41.5 (dd, JCP = 29.9 and 19.3 Hz, P-(Al)CdC(H)CMe3),126.7(dd,
1JCP3= 67.8 Hz and 3JCP = 3.7 Hz, ipso-C of (CdC)2P-Mes), 130.3
(d, JCP = 8.1 Hz, m-C of (CdC)3P-Mes), 130.5 (br, m-C of
(CdC)3P-Mes), 131.8 (d, 1JCP = 31.8 Hz, ipso-C of (CdC)3P-
Mes), 131.8 (br, m-C of (CdC)2P-Mes), 135.4 (dd, 1JCP = 38.9
and 10.0 Hz, P2CdC(H)CMe3), 140.6 (d, 4JCP = 1.3 Hz, p-C of
Synthesis of 12. A solution of di(tert-butylethynyl)phenylpho-
sphine 4 (0.200 g, 0.741 mmol) in 10 mL of n-hexane was treated
with a solution of dineopentylaluminium hydride (0.126 g, 0.741
mmol) in 10 mL of n-hexane at room temperature. The pale
yellow solution was stirred for 18 h, concentrated, and cooled to
-30 °C to yield a colorless powder of compound 12; repeated
crystallization gave colorless crystals. Yield: 0.118 g (51%). Mp

1330 Organometallics, Vol. 29, No. 6, 2010
Westenberg et al.
Table 1. Crystal Data, Data Collection Parameters, and Structure Refinement Details of Compounds 6, 7, 8, and 12
6
7
8
12
formula
C38H57AlP2
triclinic
P1
6
153(2)
1.013
10.9603(4)
23.8441(8)
24.3899(7)
74.501(3)
77.708(3)
78.105(3)
5.9256(3)
0.154 (Mo KR)
0.24 ꢀ 0.15 ꢀ 0.12
27.98
C46H73AlP2
monoclinic
P21/n
4
153(2)
1.032
12.956(3)
20.415(4)
17.439(4)
90
93.87(3)
90
C44H69AlP2
monoclinic
P21/c
8
153(2)
1.018
23.453(5)
18.823(4)
22.344(5)
90
114.66(3)
90
8.96(1)
C40H61AlP2
triclinic
P1
2
153(2)
1.068
10.4008(5)
10.9142(5)
18.2195(8)
76.269(3)
79.021(3)
81.930(3)
1.9625(2)
1.388 (Cu KR)
0.14 ꢀ 0.10 ꢀ 0.08
72.21
cryst syst
space group
Z
temp, K
Dcalcd, Mg m-3
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
V, nm3
4.602(2)
0.141 (Mo KR)
0.35 ꢀ 0.21 ꢀ 0.16
29.24
μ, mm-1
cryst dimens, mm
0.143 (Mo KR)
0.29 ꢀ 0.20 ꢀ 0.11
29.35
θ
max, deg
no. unique reflns
no. of params
26 250
1217
12 415
463
24 288
920
6654
403
R1 [reflns I > 2σ(I)]
wR2 (all data)
max./min. residual
electron density,
1030 e/m3
0.0566 (13 355)
0.1447
0.398/-0.389
0.0375 (7920)
0.0925
0.381/-0.342
0.0507 (5347)
0.0863
0.355/-0.277
0.0564 (5778)
0.1437
0.448/-0.255
(CdC)3P-Mes), 141.9 (d, 4JCP = 2.6 Hz, p-C of (CdC)2P-Mes),
142.9 (br, o-C of (CdC)2P-Mes), 144.2 (d, 2JCP = 3.4 Hz, o-C of
=
Quantum-Chemical Calculations. DFT calculations at the
B3LYP/6-31G(d) level21 were conducted by applying the Gauss-
ian03 program package.22 Second derivative calculations have
been performed to ensure that the transition states have only one
imaginary frequency. The calculations have been performed
utilizing all-methyl-substituted model systems in order to estab-
lish the principal mechanistic pathways. Therefore we have
chosen a standard DFT scheme being aware that substituent
effects have been neglected for which dispersion-corrected
density functional theory (DFT-D) would be a more appro-
priate approach.
(CdC)3P-Mes), 144.7 (br, o-C of (CdC)2P-Mes), 145.4 (d, 2JCP
1
5.4 Hz, o-C of (CdC)3P-Mes), 147.2 (d, JCP = 24.1 Hz,
P-(Al)CdC(H)CMe3), 159.3 (br, P-(Al)CdC(P)CMe3), 160.5 (d,
2
2JCP = 15.4 Hz, P2CdC(H)CMe3), 165.3 (d, JCP = 10.1 Hz,
P-(Al)CdC(H)CMe3), 175.4 (dd, 1JCP = 30.1 Hz and 2JCP = 2.2
Hz, Al-(P)CdC(P)CMe3). 31P NMR (C6D6; 162 MHz): δ 61.6 (d,
2JPP = 25.0 Hz, (CdC)3P), 13.7 (d, 2JPP = 26.0 Hz, (CdC)2P). IR
(paraffin, CsI plates, cm-1): 1726 w, 1713 w, 1694 w, 1661 w, 1645
w, 1605 m, 1578 m, 1557 w, 1520 w aromatic ring, νCdC; 1463 vs,
1378 vs (paraffin); 1304 (s), 1250 sh δCH3; 1225 s, 1206 m, 1167 s,
1155 s, 1118 m, 1101 w, 1080 m, 1057 w, 1032 m, 1011 w, 964 s, 935 s,
891 m, 849 s, 770 m νCC, δCH, δCC; 723 s (paraffin); 685 w, 652 m,
626 m, 563 m, 521 m, 461 m νPC, νAlC, δCC. MS (EI, 20 eV, 90
°C): m/z 644 (100%) (Mþ - CHCMe3).
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft (IRTG 1444) and The Nether-
lands Foundation for Chemical Sciences (CW) with
financial aid from The Netherlands Organization for
Scientific Research (NWO) for generous financial sup-
port.
Crystal Structure Determinations. Single crystals were ob-
tained directly after concentration of the reaction mixture and
cooling of the solutions as described with the synthetic procedures.
The crystallographic data were collected with Bruker SMART
APEX-II (Mo), STOE IPDS (Mo), and Bruker SMART 6000
(Cu) diffractometers. The crystals were coated with a perfluoropo-
lyether, picked up with a glass fiber, and immediately mounted in
the cooled nitrogen stream of the diffractometer. The crystallo-
graphic data and details of the final R values are provided in Table 1.
All structures were solved by direct methods using the program
system SHELXTL PLUS20 and refined with the SHELXL-9720
program via full-matrix least-squares calculations based on F2. All
non-hydrogen atoms were refined with anisotropic displacement
parameters; hydrogen atoms attached to carbon were calculated on
ideal positions and allowed to ride on the bonded atom with U =
1.2Ueq(C). Three tert-butyl groups of compound 6 were disordered;
their methyl groups were refined on split positions (C153: site
occupation factors 0.25:0.75; C343 0.34:0.66; C353 0.80:0.20).
Compound 8 showed a similar disorder of four tert-butyl groups
(C133 0.48:0.52; C153 0.41:0.59; C161 0.56:0.44; C253 0.33:0.67).
Compound 8 was obtained as only weakly scattering crystals.
Further details of the crystal structure determinations are also
available from the Cambridge Crystallographic Data Center on
quoting the depository numbers CCDC-755342 (6), -755343 (7),
-755344 (8), and -755345 (12).
Supporting Information Available: CIF files giving the crystal
data of compounds 6, 7, 8, and 12. Geometries of TS3 and TS4.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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M. Can. J. Phys. 1980, 58, 1200. (d) Stephens, P. J.; Devlin, F. J.;
Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623. (e)
Grimme, S.; Kruse, H.; Goerigk, L.; Erker, G. Angew. Chem., Int. Ed. 2010,
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Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
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