Monomeric organoaluminium complexes RAl(OR*)2 and R2AlOR* with an optically active amino alkoxide ligand

Article abstract of DOI:10.1016/S0022-328X(99)00516-1

The reactions of trialkylaluminium, R₃Al, with (S)-(-)α,α-diphenyl-2-pyrrolidinyl-methanol have been investigated, in which unusual bis-complexes RAl(OR*)₂ were obtained [OR=(S)-α,α-diphenyl-2-pyrrolidinyl-methoxide (Dpm), R=Me (1), Et (2), 1-Nor (3)]. A similar reaction carried out with R=t-Bu yields, by contrast, the expected mono-alkoxide R₂AlOR* (4). All compounds were characterised by X-ray crystallography and NMR spectroscopy. The molecular structures are monomeric. In 1-3, the aluminium centres bonded to the nitrogen atoms of two chelating ligands are five-coordinate, while the metal atom contained in 4 is tetrahedrally surrounded. The absolute structures of all complexes were determined from X-ray diffraction data. The formation of the dative Al-N bonds is stereospecific in all cases.

Full text of DOI:10.1016/S0022-328X(99)00516-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 595 (2000) 21–30
Monomeric organoaluminium complexes RAl(OR*)2 and
R2AlOR* with an optically active amino alkoxide ligand
T. Gelbrich a,1, E. Hecht b, K.-H. Thiele b, J. Sieler a,*
a Institut fu¨r Anorganische Chemie der Uni6ersita¨t Leipzig, Linne´strasse 3, D-04103 Leipzig, Germany
b Institut fu¨r Anorganische Chemie der Martin-Luther-Uni6ersita¨t Halle-Wittenberg, Geusaer Strasse, D-06217 Merseburg, Germany
Received 2 June 1999; accepted 4 August 1999
Dedicated to Professor Dr Dirk Walther on the occasion of his 60th birthday.
Abstract
The reactions of trialkylaluminium, R3Al, with (S)-(−)a,a-diphenyl-2-pyrrolidinyl-methanol have been investigated, in which
unusual bis-complexes RAl(OR*)2 were obtained [OR*=(S)-a,a-diphenyl-2-pyrrolidinyl-methoxide (Dpm), R=Me (1), Et (2),
1-Nor (3)]. A similar reaction carried out with R=t-Bu yields, by contrast, the expected mono-alkoxide R2AlOR* (4). All
compounds were characterised by X-ray crystallography and NMR spectroscopy. The molecular structures are monomeric. In
1–3, the aluminium centres bonded to the nitrogen atoms of two chelating ligands are five-coordinate, while the metal atom
contained in 4 is tetrahedrally surrounded. The absolute structures of all complexes were determined from X-ray diffraction data.
The formation of the dative AlꢀN bonds is stereospecific in all cases. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Aluminium; Alkoxides; Amines; X-ray diffraction; Chirality
1. Introduction
R3Al with the respective optically active amino alcohol
HOR* [3–12]. Structurally characterised compounds
During the past several years the chemistry of
show the metal centre coordinated by the nitrogen
organoaluminium complexes has attracted considerable
atom of the amino alkoxide ligand. Additionally, OR*
attention due to possible applications of those com-
may act as a bridging ligand. Therefore, complexes are
pounds in both material science and organic synthesis.
usually dimeric (x=2) with two chelating rings linked
For the latter, chiral complexes with the ability to
by a planar Al2O2 unit, and a pentagonal polyhedron is
support stereospecific transformations are of special
observed around the metal atom. Only one monomeric
interest. Several chiral alkylaluminium alkoxides have
been described as intermediates in stereospecific organic
reactions [1]. Moreover, organoaluminium compounds
containing a bifunctional amino alkoxide group have
been considered as potential catalysts in polymerisation
reactions of lactone rings yielding polyesters [2].
species
(OR*=(2S,3R)-(+)-4-(dimethylamino)-1,2-
diphenyl-3-methyl-2-butoxide) has been published up to
now and little is known about those parameters which
determine the degree of association [6]. Previous investi-
gations showed that the optical activity of the amino
alcohol is transferred to the resulting alkoxide in each
case.
In general, complexes with composition [R2AlOR*]x
can be obtained by reaction of the aluminiumorganyl
This study is part of our systematic investigations of
the chemistry of organometal complexes of Group 13
elements with various types of optically active
aminoalkoxides [10–12]. We report the preparation
and structures of organoaluminium derivatives, which
contain the (S)-a,a-diphenyl-2-pyrrolidinyl-methoxide
(Dpm) ligand bearing two sterically demanding phenyl
groups substituted to the a-carbon atom.
* Corresponding author. Tel.: +49-341-9736-218; fax: +49-341-
9736-249.
E-mail address: sieler@server1.rz.uni-leipzig.de (J. Sieler)
1 Present address: Department of Chemistry, EPSRC National
Crystallography Service, University of Southampton, Highfield,
Southampton, SO17 1BJ, UK.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00516-1

22
T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
2. Results and discussion
Compounds 1, 2 and 4 are highly sensitive to both
moisture and oxygen, while 3 decomposes in air after 5
min, and its reaction with water proceeds rather
smoothly due to the bulkiness of the alkyl group at-
tached to the metal atom.
Compounds 1–3 are very soluble in aromatic sol-
vents and ethers but less soluble in aliphatic hydrocar-
bons, whereas 4 was found to be very soluble in both
aromatic hydrocarbons and ethers. Crystals of 1–4 are
colourless and transparent.
In a second reaction, compound 1 was obtained by
addition of dimethylaluminium-1-diphenylamide 5 to
the amino alcohol at r.t. The amide ligand and one
methyl group of 5 are replaced by two Dpm moieties
even if the starting materials are used in stochiometric
quantities (Eq. (4c)). Compound 5 was produced as
pale yellow powder by reaction of lithium-1-dipheny-
lamide with dimethylaluminium chloride (Eqs. (4a) and
(4b)). This compound is very soluble in aromatic and
less soluble aliphatic hydrocarbons.
2.1. Preparation
The addition in molar ratio of 1:1 R3Al (R=Me,
1-Nor) to a slurry of the (S)-a,a-diphenyl-2-pyrro-
lidinyl-methanol in n-pentane results in the formation
of bis-aminoalkoxides [MeAl(Dpm)2] (1) and [(1-
Nor)Al(Dpm)2] (3), respectively, rather than the ex-
pected mono-complexes [R2Al(Dpm)]x. Thus, two alkyl
groups in R3Al are substituted for two alkoxide ligands
(Eq. (1)). 3 can be prepared in higher yields using a 1:2
molar ratio of the starting materials. The products
could be isolated in good yields. Previously, the prepa-
ration and NMR spectroscopic characterisation of a
structurally related complex MeAl{OC6H4(CH2NMe)-
2}2 obtained by 1:2 reaction of AlMe3 with the respec-
tive mono-ortho-chelating phenolate ligand has been
reported [13].
(4a)
(4b)
(1)
A reaction similar to Eq. (1) carried out with R=t-
Bu led, by contrast, to the mono-complex [(t-
Bu)2Al(Dpm)] (4). This result is consistent with the
reaction pathway described in earlier studies (Eq. (2))
[3–10].
(4c)
Alternatively, high yields of 1 can be obtained by
reaction of dimethylaluminium-(R)-2-aminobutoxide
[11] with (S)-a,a-diphenyl-2-pyrrolidinyl-methanol
leading to substitution of one methyl group and the
(R)-2-aminobutoxide moiety by two Dpm ligands (Eq.
(5)). Dimethylaluminium-(R)-2-aminobutoxide and
(R)-2-aminobutanol were found in the reaction mixture
(2)
1
using H-NMR spectroscopy.
The ethyl compound, being analogous with 1 and 2,
was obtained by reaction of diethyl-t-butylcyclopenta-
dienyl-aluminium with (S)-a,a-diphenyl-2-pyrrolidinyl-
methanol in n-pentane at room temperature (r.t.). One
ethyl group and the cyclopentadienyl moiety are substi-
tuted for two aminoalkoxide ligands, e.g. the starting
materials are converted in ratio 1:2 (Eq. (3)). The
postulated by-products could not be detected.
(5)
2.2. X-ray structures
The bis-aminoalkoxides 1, 2 and 3 crystallise in space
groups without inversion centres and mirror planes —
P21, P212121 and P212121, respectively — with one
molecule of the alkoxide in each asymmetric unit. To
(3)

T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
23
Fig. 1. Molecular structure of [MeAl(Dpm)2] (1). Thermal ellipsoids at 40% level. Hydrogen atoms other than those attached to asymmetric
coordinated atoms were omitted for clarity.
the author’s knowledge, no structure of any other
metalorganic bis-complex [RAl(OR%)2] has been pub-
lished (OR% can mean either chiral or achiral
aminoalkoxide ligand). Compound 3, the first struc-
turally characterised norbonyl derivative of aluminium,
co-crystallises with diethylether as a 1:1 adduct.
Within the series 1–3, similar molecular structures
are formed (Figs. 1–3). They show the central five-co-
ordinate aluminium atom surrounded by the alkyl moi-
ety and both oxygen and nitrogen atoms of two Dpm
ligands. Analysing the metal coordination throughout
the series, the transition from trigonal bipyramidal
Fig. 2. Molecular structure of [EtAl(Dpm)2] (2). Thermal ellipsoids at 40% level. Hydrogen atoms other than those attached to asymmetric
coordinated atoms were omitted for clarity.

24
T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
Fig. 3. Molecular structure of [1-NorAl(Dpm)2] (3). Thermal ellipsoids at 40% level. Hydrogen atoms other than those attached to asymmetric
coordinated atoms and minor disorder of the 1-Nor moiety were omitted for clarity.
Furthermore, the angle formed by AlꢀO ring bonds is
opened by 9.4°. The distortion of the TBP geometry
(28%), caused by the bulky exocyclic substituent at-
tached to aluminium, is remarkably higher than in
1–3 (Table 1).
(TBP) to square pyramidal (SP) geometry along the
Berry coordinate was found to consistantly deviate by
10% (the departure from a geometry representing a
true Berry pseudo rotation was calculated to be ap-
proximately 4°) [14,15]. Thus, the respective polyhe-
dron around aluminium is close to a perfect TBP
with apical nitrogen atoms. In 1 the axial–axial angle
N1ꢀAl1ꢀN2 is 172.1° and the equatorial plane (Al1,
O1, O2, C1) adopts an almost ideal geometry. The
greatest distortion from idealised TBP geometry is
shown in the OꢀAl1ꢀN intra-ring angles of 84.0 and
84.2°. Appropriate angles in analogous dimeric struc-
tures [R2AlOR%]2 are effected by the strained Al2O2
unit and lie around 75° [7,10,11]. The angle between
least-square planes defined by the atoms of the two
chelating rings is 52.7 (1), 55.9 (2) and 60.1° (3). Its
variation reflects the sterical demands of the respec-
tive alkyl substituents attached to aluminium.
N1ꢀAl1ꢀN2 is simultaneously reduced from 171.2° in
1 to 167.9° in 3. In 1, both the AlꢀO and the AlꢀN
bond lengths are nearly equalised with mean values
Table 1
,
Bond lengths (A), bond angles (°) and distortion of the geometry
around Al for compounds 1, 2 and 3·Et2O
1
2
3
Bond lengths
Al1ꢀO1
Al1ꢀO2
Al1ꢀC1
Al1ꢀN1
Al1ꢀN2
1.788(1)
1.784(1)
1.978(2)
2.124(2)
2.117(1)
1.784(1)
1.779(1)
2.037(2)
2.115(2)
2.138(2)
1.781(3)
1.786(3)
2.022(4)
2.141(4)
2.145(4)
Bond angles
O2ꢀAl1ꢀO1
O1ꢀAl1ꢀN2
O2ꢀAl1ꢀN2
O2ꢀAl1ꢀN1
O1ꢀAl1ꢀN1
N2ꢀAl1ꢀN1
O2ꢀAl1ꢀC1
O1ꢀAl1ꢀC1
C101ꢀO1ꢀAl1
C201ꢀO2ꢀAl1
C1ꢀAl1ꢀN1
C1ꢀAl1ꢀN2
120.1(1)
92.1(1)
84.0(1)
91.7(1)
84.2(1)
172.1(1)
118.5(1)
121.4(1)
118.3(1)
119.2(1)
93.1(1)
94.8(1)
119.2(1)
92.3(1)
84.0(1)
90.7(1)
84.2(1)
171.2(1)
119.5(1)
121.2(1)
119.3(1)
119.0(1)
96.6(1)
92.2(1)
117.0(1)
90.2(1)
83.2(1)
90.1(2)
83.9(1)
167.9(2)
122.8(2)
120.2(2)
119.2(3)
120.6(3)
97.7(2)
94.4(2)
,
of 1.786 and 2.120 A, respectively, both being of the
expected magnitudes. By comparison, the AlꢀO intra-
ring and the AlꢀN distances are slightly shorter in
Al{OC6H4(CH2NMe)-2,6-Me-4}3 and average 1.759(3)
,
and 2.078(3) A [13]. The larger (six-membered) and
less strained chelating rings causes a widening of en-
TBP“SP (%)
10.4
9.8
10.4
docyclic OꢀAlꢀN angles by 5.5° in the same complex.

T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
25
the metalꢀnitrogen bond has been confirmed for two
mono-derivatives of Group 13 elements with Dpm,
Me2Ga(Dpm) and [Me2In(Dpm)]2 [12,16].
According to the characteristics of the amino alcohol
used for the preparation of 1–3, the chiral centres C102
and C202 are S. The nitrogen atoms become four-coor-
dinate — they are additional asymmeterically substi-
tuted atoms. The configuration of the N1 and N2
centres is S in each case. Thus, the forming of the
dative AlꢀN bond proceeds stereospecifically. This is a
feature observed in some related chiral mono-alkoxides
of aluminium [6,9,11]. Only one exception has been
found up until now, the epimeric dimethylaluminium-
cis-(1R,2S)-2-N-benzylamino-1-cyclohexyl-methoxide
complex. Its nitrogen centres contained in two crystal-
lographically independent six-membered chelating rings
are R and S [11]. Moreover, stereospecific formation of
Compound 4 is the first monomeric aminoalkoxide
of aluminium [R2AlOR%]x (x=1) with a five-membered
chelating ring. Until now, only a six-membered species
has been shown to be monomeric and the possible
correlation between ring size and degree of association
has been discussed in this connection [6]. Comparison
of all reported structures [R2AlOR%]x however shows
that the degree of association is more likely controlled
by the bulkiness of the exo-cyclic substituents at the
a-carbon atom rather than by the chain length of OR%
(Table 2). Interestingly, even those complexes with only
one sterically demanding substituent at a-C or N and
those with two SiMe3 groups bonded to Al are dimeric.
The gallium and indium derivatives [Me2Ga(Dpm)] and
[Me2In(Dpm)]2, are monomeric and dimeric, respec-
tively [12,16]. Structural differences occuring between
mono-complexes of Group 13 elements with Dpm are
due to the fact that the size of the atom increases but
the Lewis acidity decreases with higher atomic num-
bers, and both effects influence the degree of associa-
tion in opposite directions.
Table 2
Degree of association x in dialkyl aluminium complexes [R2AlOR%]x
containing chelating rings of different sizes
OR%
x
Ref.
Fi6e-membered
Me
Me
Me
Me
Et, SiMe3
Me
t-Bu
OCH2CHEtNH2
OCHMeCH2NMe2
OCH2CH2NH2
OCH2CH(C4H8)NH
OCH2CH(CH2Ph)NH2
OCHPhCMeHNHMe
OCPh2CH(C3H6)NH
2
2
2
2
2
2
1
[11]
[10]
[10]
[11]
[9]
The aluminium centre in 4 is coordinated in a dis-
torted tetrahedral fashion by two t-Bu groups and both
the oxygen and the nitrogen atom of the Dpm moiety
(Fig. 4). The intra-ring angle Al1ꢀO1ꢀN1 of 86.1° is
remarkably reduced in comparison with the idealised
tetrahedral angle, but it is by 8° greater than in dimeric
[3]
4
Six-membered
Me
Me
Me
OCH2CH2CH2NMe2
OCH2CH(C5H9)NH(CH2Ph)
OCPh(CH2Ph)CHMeCH2NMe2
2
2
1
[16]
[11]
[6]
,
complexes [9–11]. At 1.769 A, Al1ꢀO1 is longer than
Fig. 4. Molecular structure of [t-Bu2Al(Dpm)] (4). Thermal ellipsoids at 40% level. Hydrogen atoms other than those attached to asymmetric
coordinated atoms were omitted for clarity.

26
T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
Table 3
Complex multiplets at l= −0.21–0.89 ppm in the
1H-NMR spectrum of 3 are observed for the norbornyl
moiety, followed by signals associated with the hydrogen
atoms of the ligand. In the 13C-NMR spectrum chemical
shifts at 31.43–43.62 ppm are due to the carbon atoms
in the norbornyl residue.
,
Selected bond lengths (A) and angles (°) for compound 4
Bond lengths
Al1ꢀO1
Al1ꢀN1
Al1ꢀC18
Al1ꢀC19
O1ꢀC1
Bond angles
O1ꢀAl1ꢀC18
O1ꢀAl1ꢀC19
C18ꢀAl1ꢀC19
O1ꢀAl1ꢀN1
C18ꢀAl1ꢀN1
C19ꢀAl1ꢀN1
1.769(2)
2.035(3)
2.016(3)
2.031(3)
1.407(4)
1.501(4)
1.499(5)
118.3(1)
108.7(1)
116.2(1)
86.9(1)
105.9(2)
117.8(2)
In contrast to what would be expected for a dimeric
1
complex [R2AlOR%]2, the H-NMR resonances for t-Bu
N1ꢀC2
N1ꢀC5
bonded to aluminium in 4 are nonequivalent (0.78 and
1.35 ppm). Chemical shifts at 31.11 and 31.74 ppm in the
13C-NMR spectrum are due to the methyl groups of the
t-Bu moiety. No signal could be assigned to the tertiary
carbon atom.
[4]
,
expected for idealised normal Al ꢀO bonds (1.69 A),
,
whereas Al1ꢀN1=2.035 A is significantly shortened
Broad signals in the 27Al-NMR spectra of 1–3 at
l=124–128 ppm indicate a five-coordinate aluminium
atom. In the spectrum of 4, by contrast, a signal
associated with the four-coordinate metal centre appears
at 158 ppm. These values are comparable with those of
similar five- and four-coordinate aluminium compounds
[10,18].
compared with the reference value for dative Al[4]ꢀN
,
distances, 2.08 A [17]. This indicates a significant delocal-
isation between both bond types. In accordance with the
structures of [Me2Ga(Dpm)], [Me2In(Dpm)]2 and 1–3,
the configuration of the N1 centre is S.
In each chelating ring of 1 the two carbon atoms are
displaced by almost equal amounts but in opposite
directions from a plane defined by N, Al and O (C101,
,
,
,
0.34 A, and C102, −0.29 A; C201, 0.32 A, and C202,
3. Experimental
,
−0.29 A) corresponding with C–C twist conformation.
Comparison with appropriate parameters calculated for
other structures in this study shows that this particular
ring pucker is remarkably stable. The same holds true for
the pyrrolidinyl moieties adopting conformations close
to the C103 and C203 envelope (C3 envelope in the case
of 4). We consider the constant ring conformations
observed in 1–4 to be a direct consequence of the
identical configuration of chiral centres within the Dpm
moieties (Table 3).
3.1. General remarks
All manipulations were performed under an atmo-
sphere of argon using normal Schlenk techniques. Com-
mercially available trimethylaluminium and amino
alcohols were used for the preparations. Amino alco-
hols were freshly distilled prior use. t-Bu3Al was pre-
pared according to the literature method [19,20].
Solvents were dried over LiAlH4, purified and saturated
with argon prior use.
2.3. NMR studies
3.2. X-ray crystallographic study
1
The major features of the H, 13C and 27Al spectra of
1–4 are listed in Table 4. They are generally consistent
with the solid-state structures discussed above. In the
1H-NMR spectrum of 1, the aluminium-bonded methyl
group gives rise to a sharp singlet at −1.42 ppm. In
comparison with dimeric complexes [R2AlOR%]2, the
coordination of aluminium by nitrogen atoms of two
Dpm ligands causes an upfield shift by about 1 ppm
[6,10]. This signal is followed by multiplets for the
pyrrolidinyl rings. Four signals at l=7−7.62 ppm are
associated with phenyl groups. In the 13C-NMR spec-
trum a resonance of very low intensity for the aluminium-
bonded methyl group is detected at l= −15.05 ppm,
followed by the expected signals for the ligands.
Details of the crystal data and a summary of collec-
tion and refinement parameters for 1–4 are given in
Table 5. Selected bond lengths and angles are listed in
Tables 1 and 3. Single crystals of compounds were
obtained by crystallisation from Et2O (at 5°C for 1, 2,
3·Et2O and −12°C for 4). Data were collected on a
SMART CCD (Siemens) using graphite monochromated
,
Mo–Ka radiation (u=0.71073 A; ꢀ scans) at −60°C.
An empirical absorption correction was performed with
SADABS [21]. All structures were solved by direct meth-
ods (SHELXS [22]) and refined against F2 using SHELXL
-
97 [23]. All heavy atoms were refined anisotropically,
hydrogen atoms were refined either independently or
the riding model was used. The intermolecular atomic
distances in 1, 2, 3·Et2O and 4 indicate Van der Waals
type interactions. The absolute structures for 1–4 were
confirmed by refinement of the Flack parameter [24].
In structure 3 the 1-norbornyl ligand is disordered. It
was refined with distance restraints for chemically
equivalent bonds. Both components are related by a
In the 1H-NMR spectrum of 2, two complex multiplets
are observed which are associated with the CH2 moiety
of EtAl, and the methyl group causes a triplet at 0.47
ppm. The chemical shifts for the ligands are observed in
the expected ranges. Two signals of low intensity (−4.25
and 11.19 ppm) in the 13C-NMR spectrum can by
attributed to the aluminium-bonded ethyl group.

T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
27
Table 4
1H-, 13C- and 27Al-NMR data for compounds 1–4 (C6D6, 22°C [ppm])
Compound
IH
13C
27Al
(w1/2 [Hz])
−1.42 (s, 3H)
1.27 (m, 4H)
1.52 (m, 4H)
2.05 (m, 2H)
2.26 (m, 2H)
2.39 (m, 2H)
3.87 (m, 2H)
7.04 (m, 8H)
7.17 (m, 4H)
7.58 (m, 4H)
7.62 (m, 4H)
CH3Alꢀ
ꢀCH2ꢀ
ꢀCHCH2ꢀ
ꢀNHCH2ꢀ
−15.05 (br)
23.90
26.71
44.72
67.47
CH3Alꢀ
ꢀCH2ꢀ
ꢀCHCH2ꢀ
ꢀNHCH2ꢀ
ꢀCHNHꢀ
ꢀOCꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ
126
(1980)
ꢀCHNHꢀ
ꢀCHNHꢀ
Phꢀ
Phꢀ
Phꢀ
77.13
125.09
126.40
150.45
150.80
Phꢀ
−0.94 (m, 1H)
−0.77 (m, 1H)
0.47 (t, 3H)
CH3CH2Alꢀ
−4.25 (br)
11.19
24.03
26.80
44.87
67.20
77.06
125.91
126.45
150.93
150.98
CH3CH2Alꢀ
CH3CH2Alꢀ
ꢀCH2CH2CH2ꢀ
ꢀCHCH2CH2ꢀ
ꢀNHCH2ꢀ
ꢀCHNHꢀ
ꢀOCꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ
128
(2230)
CH3CH2Alꢀ
ꢀCH2ꢀ
ꢀCH2ꢀ
1.26 (m, 4H)
1.51 (m, 4H)
2.10 (m, 2H)
2.27 (m, 2H)
2.48 (m, 2H)
3.89 (m, 2H)
7.04 (m, 8H)
7.19 (m, 4H)
7.58 (m, 4H)
7.63 (m, 4H)
ꢀNHCH2ꢀ
ꢀCHNHꢀ
ꢀCHNHꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ
0.21 (m, 1H)
0.41 (m, 4H)
0.71 (m, 4H)
0.89 (m, 2H)
1.23 (m, 4H)
1.97 (m, 4H)
2.14 (m, 2H)
2.35 (m, 2H)
3.26 (m, 2H)
4.13 (m, 2H)
7.01 (m, 8H)
7.06 (m, 4H)
7.44 (m, 4H)
7.60 (m, 4H)
Nor
Nor
Nor
Nor
ꢀCH2ꢀ
ꢀCH2ꢀ
ꢀCH2ꢀ
24.67
28.32
31.34
31.63
35.14
35.47
37.84
43.62
45.71
66.42
77.78
125.75
126.50
151.64
151.94
ꢀCH2CH2CH2ꢀ
ꢀCHCH2CH2ꢀ
C3
C5
C2
C6
C4
124
(2320)
C7
ꢀCHNHꢀ
ꢀCHNHꢀ
Phꢀ
Phꢀ
Phꢀ
ꢀNHCH2CH2ꢀ
ꢀCHNHꢀ
ꢀOCꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ
0.78 (s, 9H)
1.35 (s, 9H)
1.27 (m, 2H)
1.59 (m, 2H)
2.20 (m, 1H)
2.69 (m, 1H)
2.86 (m, 1H)
3.91 (m, 1H)
7.00 (m, 4H)
7.13 (m, 2H)
7.46 (m, 2H)
7.58 (m, 2H)
(CH3)3C
(CH3)3Cꢀ
ꢀCH2ꢀ
ꢀNHCH2ꢀ
ꢀCHCH2ꢀ
23.69
27.08
31.11
31.74
44.91
67.32
78.36
125.73
125.87
149.65
150.19
ꢀCH2CH2CH2ꢀ
ꢀCHCH2CH2ꢀ
(CH3)3Cꢀ
(CH3)3Cꢀ
ꢀNHCH2ꢀ
ꢀCHNHꢀ
ꢀOCꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ
158
(1720)
ꢀCHNHꢀ
ꢀCHNHꢀ
Phꢀ
Phꢀ
Phꢀ
Phꢀ

28
T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
Table 5
Crystallographic data for compounds 1, 2, 3·Et2O and 4
Compound
1
2
3·Et2O
4
Formula
C35H39AlN2O2
546.66
C36H41AlN2O2
560.69
C45H57AlN2O3
700.90
Platelet
Colourless
0.40×0.35×0.20
Orthorhombic
P212121
C25H36AlNO
393.53
Platelet
Colourless
0.40×0.45×0.45
Monoclinic
P21
Formula weight (g mol−1
Crystal
)
Pyramidal faces
Colourless
0.25×0.50×0.70
Monoclinic
P21
Rectangular blocks
Colourless
0.45×0.45×0.40
Orthorhombic
P212121
Colour
Crystal size (mm)
Crystal system
Space group
Z
2
4
4
2
,
a (A)
9.493(2)
12.0762(8)
14.058(1)
18.394(1)
90
3122.7(3)
1.193
0.099
1.8–26.2
23083/0.044
5717/529
1.106
12.278(1)
17.605(1)
18.219(1)
90
3938.1(5)
1.182
9.875(2)
13.461(3)
10.230(2)
118.55(3)
1194.5(4)
1.094
,
b (A)
13.565(3)
12.011(2)
106.40(3)
1483.8(5)
1.224
0.102
1.8–26.4
11471/0.017
5336/508
1.063
,
c (A)
i (°)
3
,
V (A )
Dcalc. (Mg m−3
)
Absorption coefficient (mm−1
q range (°)
)
0.093
0.099
1.6–24.0
25442/0.079
6052/643
1.012
2.3–24.8
7772/0.047
3530/376
0.997
Reflections/Rint
Data/parameters
GOF on F2
R1/wR2 [I\2|(I)]
R1/wR2 (all data)
Largest difference peak (e A
Absolute structure parameter
0.028/0.066
0.030/0.067
−0.11/0.12
−0.1(1)
0.039/0.083
0.052/0.090
−0.17/0.21
0.02(5)
0.071/0.125
0.088/0.136
−0.52/0.31
−0.02(3)
0.048/0.124
0.053/0.132
−0.15/0.18
−0.1(2)
−3
,
)
rotation of 116° about Al1ꢀC1 (site occupation 3:2).
The t-butyl group in structure 4 is disordered. It was
refined with distance restraints for chemically equiva-
lent bonds. The disordered moieties are related by a
rotation of 40° about Al1ꢀC19 (site occupation 3:2).
had evolved from the reaction mixture, the solution was
filtered and dried in vacuum yielding lithium-1-phenyl-
ethylamide as a pale yellow, highly air- and moisture-
sensitive powder. Yield: 5.6 g (89%). H-NMR (THF-
d8): l= −0.25 (br. s, NH, 1H); 1.26 (d, CH3; 3H); 4.18
(m, CH, 1H); 6.99–7.32 (3m, Ph, 5H).
1
3.3. [MeAl(Dpm)2] (1)
3.3.2. Dimethylaluminium-1-phenylethylamide (5)
To a stirred solution of 2.8 g (0.03 mol) dimethylalu-
miniumchloride in n-pentane lithium-1-phenylethyl-
amide (3.81 g, 0.03 mol) was added. The reaction
mixture was stirred for 2 h, then LiCl was filtered off.
A pale yellow precipitate was allowed to separate from
the clear solution at −50°C. The solid was dried in
To a stirred solution of 1.8 g (0.025 mol) trimethyl-
aluminium in n-pentane (50 ml) S-(−)-a,a-diphenyl-2-
pyrrolidinyl-methanol (6.3 g, 0.025 mol) was added at
r.t. After stirring the reaction mixture for 12 h the
colourless precipitate was filtered off. Recrystallisation
from diethyl ether yielded MeAl(Dpm)2 (1). Yield: 6.2 g
(46% with respect to DpmH). Anal. Found for
C35H39O2N2Al; (546 g mol−1): C, 76.22; H, 6.98; N,
5.98; Al, 4.53. Calc.: C, 76.92; H, 7.14; N, 5.13; Al,
4.94%.
To a solution of 1.6 g (0.01 mol) of 5 in 30 ml
n-pentane S-(−)-a,a-diphenyl-2-pyrrolidinyl-methanol
(2.5 g, 0.01 mol) was added at r.t. After stirring the
reaction mixture for 2 h the colourless precipitate was
filtered off and extracted with diethyl ether. The solu-
tion was cooled to −50°C yielding colourless crystals
of 1. Yield: 3.5 g (64% with respect to DpmH).
vacuum. Yield: 4.2
g (86%). Anal. Found for
C10H16NAl; (163 g mol−1): C, 73.41; H, 9.01; N, 8.96;
Al, 16.32. Calc.: C, 73.62; H, 9.81; N, 8.59; Al, 16.56%.
1H-NMR, (C6D6): l= −0.55 (q, (CH3)2, 6H); 1.04 (d,
NH, 1H); 1.14 (d, CH3, 3H); 3.88 (m, CH, 1H); 6.88–
7.18 (3m, Phꢀ, 5H). 13C-NMR (C6D6): l= −5.32
((CH3)2ꢀ); 23.17 (CH3); 48.71 (CH); 120.33–141.59
(Ph). 27Al-NMR (C6D6): l=162.
To a solution of 1.5 g (0.01 mol) of dimethylalu-
minium-(R)-2-aminobutoxide [11] in 50 ml diethyl ether
S-(−)-a,a-diphenyl-2-pyrrolidinyl-methanol (2.5 g,
0.01 mol) was added at r.t. After the reaction mixture
had been stirred for 24 h the colourless precipitate was
filtered off and extracted with diethyl ether. The solu-
tion was cooled to −50°C yielding colourless crystals
of 1. Yield: 4.1 g (75% with respect to DpmH).
3.3.1. Lithium-1-phenyl-ethylamide
To a solution of 6.1 g (0.05 mol) 1-phenyl-ethylamine
in n-pentane (100 ml) a solution of n-butyllithium in
n-hexane (55.5 ml, 0.9 molar) was added. After the gas

T. Gelbrich et al. / Journal of Organometallic Chemistry 595 (2000) 21–30
29
3.4. [EtAl(Dpm)2] (2)
3.6. [t-Bu2Al(Dpm)] (4)
To a solution of 5.2 g (0.025 mol) diethyl-t-butyl-
cyclopentadienyl-aluminium in 50 ml n-pentane S-
(−)-a,a-diphenyl-2-pyrrolidinyl-methanol (6.3 g, 0.025
mol) was added at r.t. The reaction mixture was
stirred for 24 h then the colourless precipitate was
filtered off and extracted with diethyl ether. Cooling
the solution to −50°C yielded colourless crystals of
3. Yield: 5.01 g (36% with respect to DpmH). Anal.
Found for C36H41O2N2Al (560 g mol−1): C, 77.01; H,
6.89; N, 5.23; Al, 4.57. Calc.: C, 77.14; H, 7.32; N,
5.00; Al, 4.82%.
To a solution of 1.8 g (0.009 mol) tri-t-butyl-alu-
minium in 50 ml n-pentane S-(−)-a,a-diphenyl-2-
pyrrolidinyl-methanol (2.3 g, 0.009 mol) was added at
r.t., spontaneous gas evolution (iso-butane) was ob-
served. The reaction mixture was allowed to stir for
24 h. Then the solvent was removed under vacuum
and the residue was extracted with diethyl ether.
Cooling the solution to −50°C yielded crystals of 4.
Yield: 2.1 g (58%). Anal. Found for C25H36ONAl;
(393 g mol−1): C, 76.21; H, 10.03; N, 3.8; Al, 6.35.
Calc. C, 76.33; H, 9.16; N, 3.56; Al, 6.87%.
3.4.1. Diethyl-t-butylcyclopentadienyl-aluminium
To a solution of 13.4 g (14.6 ml, 0.12 mol) diethyl-
aluminiumchloride in 150 ml n-pentane 15.1 g (0.12
mol) t-butyl-cyclopentadienyllithium was added at r.t.
The reaction was stirred for 24 h, then LiCl was
filtered off. The solvent was removed and the residue
distilled under vacuum. B.p.: 105°C/3 Torr. Yield:
16.2 g (65%). 1H-NMR (C6D6): l=0.08 (m, CH2,
4H); 0.71 (t, CH3, 6H); 1.24 (s, (CH3)3, 9H); 3.39 (m,
Cp; 2H); 5.92 (m, Cp, 1H); 6.13 (m, Cp, 1H).
4. Supplementary material
Crystallographic data (excluding structure factors)
for the structures in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
supplementary publication nos. CCDC 119269 (1),
119270 (2), 119271 (3), 119272 (4). Copies of the data
can be obtained, free of charge, on application to
The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44-1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk).
3.5. [1-NorAl(Dpm)2] (3)
To a stirred solution of 4.0 g (0.013 mol) tris-(1-
norbornyl)-aluminium in 50 ml n-pentane S-(−)-a,a-
diphenyl-2-pyrrolidinyl-methanol (6.4 g, 0.026 mol)
was added at r.t. After the reaction mixture was
stirred for 2 h the colourless precipitate was filtered
off and extracted with diethyl ether. Cooling the solu-
tion to −50°C yielded colourless crystals of 3. Yield:
4.5 g (58%). (If the starting materials are reacted in
a molar ratio of 1:1 the yield of 3 decreases to
35% with respect to DpmH.) Anal. Found for
C41H47O2N2Al; (626 g mol−1): C, 78.52; H, 7.87; N,
4.10; Al, 4.12. Calc.: C, 78.59; H, 7.53; N, 4.49; Al,
4.31%.
Acknowledgements
We are grateful to the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie for
financial support.
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