Synthesis and structures of mono(1-aza-allyl) complexes of aluminum

Article abstract of DOI:10.1021/om981021t

The synthesis and structures of new aluminum complexes using the 1-aza-allyl ligand R (R = [N(SiMe₃)C(Ph)C(SiMe₃)₂]^-) are described. The reaction of RLi·THF with AlMe₂Cl, AlMeCl₂, AlCl

Full text of DOI:10.1021/om981021t

2256
Organometallics 1999, 18, 2256-2261
Syn th esis a n d Str u ctu r es of Mon o(1-a za -a llyl) Com p lexes
of Alu m in u m †
Chunming Cui,‡ Herbert W. Roesky,*,‡ Mathias Noltemeyer,‡
Michael F. Lappert,§ Hans-Georg Schmidt,‡ and Haijun Hao‡
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany, and University of Sussex, Brighton, BN1 9QJ , U.K.
Received December 15, 1998
The synthesis and structures of new aluminum complexes using the 1-aza-allyl ligand R
(R ) [N(SiMe3)C(Ph)C(SiMe3)2]-) are described. The reaction of RLi‚THF with AlMe2Cl,
AlMeCl2, AlCl3, and AlBr3 in diethyl ether or n-hexane, after workup, afforded RAlMe2 (1),
RAlMeCl (2), RAlCl2 (3), and RAlBr2 (4), respectively, while [RAlF(µ-F)]2 (5) or RAlI2 (6)
was prepared in high yield by the reaction of RAlMe2(1) with 2 equiv of Me3SnF or I2,
respectively, in toluene. The complex 2 or 3 reacts with an excess of THF to give the
corresponding THF adduct RAlClMe‚THF (7) or RAlCl2‚THF (8). Compounds 7 and 8 are
not stable; the coordinated THF can be easily removed in vacuo at ambient temperature.
The molecular structures of 3, 5, and 8 have been established by X-ray crystallography.
Compound 3 is a monomer with a chelating η3 1-aza-allyl ligand, while compound 8 forms
an open structure with an η1 pendant ligand. Compound 5 is the first example of a dimeric
aluminum difluoride, in which two bridging F atoms reside on the pseudo 2-fold axis of the
approximately C2 symmetric molecule. The two pentacoordinated aluminum atoms can be
described as having distorted trigonal-bipyramidal geometries, which have in common one
bridging F atom in an apical position and the other bridging F atom in an equatorial position.
In tr od u ction
generate three-coordinate cationic species.2,7 However,
base-free cationic sites have not been obtained using
these ligands.2,8 Interest in fundamental studies of the
relationships between ligand structure and metal coor-
dination geometry prompted us to extend the use of this
methodology to the synthesis of aluminum complexes
containing the bulky 1-aza-allyl ligand [N(SiMe3)C(Ph)C-
(SiMe3)2]-.9 The known 1-aza-allyl complexes are rare;
only a few main group (K, Li, Pb, Sn) and transition
metal (Cu, Hg, Zr, Sm, Yb, Th) complexes have been
reported.9-14 To the best of our knowledge, aluminum
complexes having 1-aza-allyl ligands are not known; the
only related compounds reported are bis[2-C(SiMe3)2-
Py]2AlCl and its corresponding cation.15 Herein, we
report the general preparative routes for the synthesis
of mono(1-aza-allyl) aluminum dialkyls and the related
dihalides using the bulky 1-aza-allyl [N(SiMe3)C(Ph)C-
(SiMe3)2]- ligand.
Major advances have been achieved in the polymer-
ization of olefins by single-site catalysts. The majority
of these catalysts are metallocene derivatives of group
4. However, Bochmann and Dawson1 and Coles and
J ordan2 recently reported the application of cationic
aluminum alkyl species for olefin polymerization reac-
tions to generate high molecular weight polyolefins. As
is the case of metallocenes of group 4, the stability of
cationic aluminum species will highly depend on the
ancillary ligand set and the choice of the counteranion.3-5
We have been interested in aluminum complexes used
in catalysis6 and are interested in developing the
chemistry of active aluminum species with monoanionic,
chelating spectator ligands. The modification of the
steric and electronic properties at the aluminum center
consequently will control the properties of the catalytic
site. Aluminum complexes containing bulky amidinates
have been extensively studied and have been used to
(8) Ihara, E.; Young, V. G.; J ordan, R. F. J . Am. Chem. Soc. 1998,
120, 8277.
(9) Hitchcock, P. B.; Lappert, M. F.; Layh, M. Inorg. Chim. Acta
1998, 269, 181.
(10) Hitchcock, P. B.; Lappert, M. F.; Layh, M. J . Chem. Soc., Dalton
Trans. 1998, 1619.
(11) Hitchcock, P. B.; Lappert, M. F.; Tian, S. J . Chem. Soc., Chem.
Commun. 1994, 2637.
(12) Hitchcock, P. B.; Hu, J .; Lappert, M. F.; Layh, M.; Severn, J .
J . Chem. Soc., Chem. Commun. 1997, 1189.
(13) Armstrong, D. R.; Clegg, W.; Dunbar, L.; Liddle, S. T.; Mac-
Grogor, M.; Mulvey, R. E.; Reed, D.; Quiss, S. A. J . Chem. Soc., Dalton
Trans. 1998, 3431.
† Dedicated to Professor Yu. A. Buslaev on the occasion of his 70th
birthday.
‡ Universita¨t Go¨ttingen.
§ University of Sussex.
(1) Bochmann, M.; Dawson, D. M. Angew. Chem. 1996, 108, 2371;
Angew. Chem., Int. Ed. Engl. 1996, 35, 2226.
(2) Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc. 1997, 119, 8125.
(3) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325.
(4) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc.
1989, 111, 2728.
(5) Chen, Y. H.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J . J .
Am. Chem. Soc. 1998, 120, 6287.
(6) Storre, J .; Schnitter, C.; Roesky, H. W.; Schmidt, H.-G.; Nolte-
meyer, M.; Fleischer, R.; Stalke, D. J . Am. Chem. Soc. 1997, 119, 7505.
(7) Coles, M. P.; Swenson, D. C.; J ordan, R. F.; Young, V. G.
Organometallics 1997, 16, 5183.
(14) Lappert, M. F.; Layh, M. Tetrahedron Lett. 1998, 39, 4745.
(15) Engelhardt, L. M.; Kynast, U.; Raston, C. L.; White, A. H.
Angew. Chem. 1987, 99, 702; Angew. Chem., Int. Ed. Engl. 1987, 26,
681.
10.1021/om981021t CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/07/1999

Mono(1-aza-allyl) Complexes of Aluminum
Organometallics, Vol. 18, No. 11, 1999 2257
RAlBr 2 (4). This compound was prepared using the same
procedure described for 3, RLi‚THF (0.62 g, 1.5 mmol) in
n-hexane (15 mL) and AlBr3 (0.40 g, 1.5 mmol) in n-hexane (5
mL). The crude product was crystallized from n-hexane to give
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
on a high-vacuum line or in a glovebox under a purified N2
atmosphere. Solvents were distilled from Na/benzophenone
ketyl prior to use, except for pentane, which was distilled from
potassium. Chemicals were purchased from Aldrich and used
as received, except for AlCl3 and AlBr3, which were sublimed
in vacuo prior to use. Trimethytin fluoride16 and [N(SiMe3)C-
(Ph)C(SiMe3)2]Li‚THF9,14 were prepared as described in the
literature.
Elemental analyses were performed by the Analytisches
Labor des Instituts fu¨r Anorganische Chemie der Universita¨t
Go¨ttingen. Bruker AM 200 and Bruker AM 250 spectrometers
were used to record 1H NMR (250.130 MHz), 13C NMR (100.600
MHz), 19F NMR (235.320 MHz), 27Al NMR (104.245 MHz), and
29Si NMR (79.460 MHz) spectra. The chemical shifts were
externally referenced to SiMe4 (1H, 13C, 29Si), CFCl3 (19F), and
AlCl3 (27Al), respectively. EI (70 eV) mass spectra were
measured on Finnigan MAT 8230 or Varian MAT CH5
instrument. Melting points were measured in sealed glass
tubes and were not corrected.
1
colorless crystals (0.48 g, 61%). Mp: 105 °C. H NMR (C6D6):
δ 0.02 (s, 9H, NSiMe3), 0.27 (s, 18H, SiMe3), 6.80-6.95 (m,
3H, Ph), 7.25 (d, 2H, Ph). 13C NMR (C6D6): δ 0.85 (s, NSiMe3),
3.54 (s, SiMe3), 41.0 (s, CSi2), 126.6, 128.6, 131.2 (s, Ph), 140.7
(s, ipso-C), 212.4 (s, CN). 29Si NMR (C6D6): δ -1.02 (s, SiMe3),
10.3 (s, NSiMe3). 27Al NMR (C6D6): δ 107.8 (ν1/2 ) 875 Hz).
MS: m/e (%): 521 (M+), 506 (M+ - Me), 422 (M+ - Br, 15).
Anal. Calcd for C17H32AlBr2NSi3 (521.48): C, 39.15; H, 6.18;
N, 2.68. Found: C, 39.22; H, 6.47; N, 2.99.
[RAlF (µ-F )]2 (5). Toluene (20 mL) was added to a mixture
of 1 (0.55 g, 1.4 mmol) and Me3SnF (0.48 g, 2.8 mmol) at room
temperature. The mixture was stirred for 15 h, resulting in a
clear solution. All volatiles were removed in vacuo to leave a
white solid, which was crystallized from toluene/n-hexane (1:
10) and stored at -20 °C for 2 days to afford colorless crystals
1
(0.35 g, 63%). Mp: 185 °C dec. H NMR (C6H6): δ 0.14 (s, 9H,
NSiMe3), 0.41 (br s, 18H, SiMe3), 6.87-7.00 (m, 3H, Ph), 7.32
(d, 2H, Ph). 1H NMR (toluene-d8, 303 K): δ 0.13 (s, 9H,
NSiMe3), 0.35 (s, 18H, SiMe3), 7.01-7.09 (m, 3H, Ph), 7.32 (d,
RAlMe2 (1). AlMe2Cl (10 mL, 1 M in n-hexane, 10 mmol)
was added to a stirred suspension of RLi‚THF (4.14 g, 10
mmol) in diethyl ether (30 mL) at -78 °C. The mixture was
allowed to warm to room temperature and stirred for an
additional 15 h. The volatiles were removed in vacuo, the crude
product was extracted with pentane (30 mL), and the extract
was concentrated to dryness in vacuo. Pure samples of 1 were
obtained by sublimation (65 °C, 0.005 mbar) (3.5 g, 85%). Mp:
1
2H, Ph). H NMR (toluene-d8, 213 K): δ 0.60 (s, SiMe3), 0.28
(s, SiMe3), 0.18 (s, NSiMe3), 0.14 (s, NSiMe3), Ph was not
recorded. 1H NMR(toluene-d8, 193 K): δ 0.15 (s, NSiMe3), 0.20
(s, NSiMe3), 0.31 (s, SiMe3), 0.62 (s, SiMe3), 6.81 (m,Ph), 6.93
(m,Ph), 7.27 (d, Ph), 7.34 (d,Ph). 13C NMR (C6H6): δ 0.63 (s,
NSiMe3), 2.98 (s, SiMe3), 40.9 (s, CSi2), 125.7, 128.4, 131.1 (s,
Ph), 147.2 (s, ipso-C), 212.8 (s, CN). 19F NMR (C6D6): δ -160.2
(br s, ν1/2 ) 400 Hz). 19F NMR (toluene-d8, 293 K): δ -160.6
(br s, ν1/2 ) 400 Hz). 19F NMR (toluene-d8, 258 K): δ -160.3
(s), -159.5 (s), -140.4 (br s, ν1/2 ) 180 Hz), -132.6 (br s, ν1/2
) 140 Hz), -120.5 (s br, ν1/2 ) 180 Hz). 19F NMR (toluene-d8,
213 K): δ -159.7 (t, 0.8F, J ) 15.0 Hz), -158.4 (t, 1.2F, J )
13.4 Hz), -141.1 (d, 0.4F, J ) 82.4 Hz), -133.3 (s, 1.2F),
-120.6 (d, 0.4F, J ) 81.9 Hz). Anal. Calcd for C34H64Al2F4N2-
Si6 (799.34): C, 51.09; H, 8.07; N, 3.50. Found: C, 50.67; H,
7.69; N, 3.22.
1
60-62 °C. H NMR (C6D6): δ -0.19 (s, 6H, AlMe2), -0.06 (s,
9H, NSiMe3), 0.20 (s, 18H, SiMe3), 6.90-7.00 (m, 3H, Ph), 7.25
(d, 2H, Ph). 13C NMR (C6D6): δ -5.50 (br s, AlMe2), 0.83 (s,
NSiMe3), 3.61(s, SiMe3), 49.5 (s, CSi2), 127.1, 128.1, 130.3 (s,
Ph), 143.1 (s, ipso-C), 208.5 (s, CN). 29Si NMR (C6D6): δ -4.11
(s, SiMe3), 15.7 (s, NSiMe3). 27Al NMR (C6D6): δ 161.2 (ν1/2
)
2920 Hz). MS: m/e (%): 391 (M+), 376 (M+ - Me). Anal. Calcd
for C19H38AlNSi3 (391.75): C, 58.25; H, 9.78; N, 3.57. Found:
C, 58.23; H, 9.41; N, 3.74.
RAlMeCl (2). AlMeCl2 (3 mL, 1 M in n-hexane, 3 mmol)
was added to a suspension of RLi‚THF (1.24 g, 3 mmol) in
n-hexane (20 mL) at -78 °C. The reaction mixture was allowed
to warm to room temperature and was stirred for 15 h. A
colorless precipitate was filtered, and volatiles were removed.
The crude product was sublimed (70 ˚C, 0.002 mbar) to give
analytically pure solid of 2 (0.96 g, 78%). Mp: 120-122 °C. 1H
NMR (C6D6): δ -0.03 (s, 9H, NSiMe3), -0.01 (s, 3H, AlCH3),
0.18 (d, 18H, SiMe3), 6.83-6.96 (m, 3H, Ph), 7.22 (d, 2H, Ph).
13C NMR (C6D6): δ -5.7 (br s, AlCH3), 0.60 (s, NSiMe3), 2.98,
3.41 (s, SiMe3), 53.5 (s, CSi2), 126.7, 128.0, 130.5 (s, Ph), 141.9
(s, ipso-C), 210.1 (s, CN). 27Al NMR (C6D6): δ 138.8 (ν1/2 ) 2120
Hz). MS: m/e (%) 411 (M+), 396 (M+ - Me), 376 (M+ - Cl, 4).
Anal. Calcd for C18H35AlClNSi3 (412.17): C, 52.23; H, 8.56; N,
3.34. Found: C, 51.63; H, 8.55; N, 2.94.
RAlCl2 (3). A solution of RLi‚THF (0.83 g, 2 mmol) in
n-hexane (20 mL) was added to a stirred suspension of AlCl3
in n-hexane (10 mL) at -78 °C. The mixture was allowed to
warm to room temperature and stirred for 15 h. After filtration
to remove LiCl, the solvent was removed in vacuo and the
residual was pumped in vacuo (0.01 mbar) for 4 h. The crude
product was crystallized from n-hexane (-8 °C) to give
colorless crystals (0.73 g, 84%). Mp: 170 °C dec. 1H NMR
(C6D6): δ 0.00 (s, 9H, NSiMe3), 0.24 (s, 18H, SiMe3), 6.85-
6.95 (m, 3H, Ph), 7.23 (d, 2H, Ph). 13C NMR (C6D6): δ 0.65 (s,
NSiMe3), 3.16 (s, SiMe3), 54.6 (s, CSi2), 126.6, 128.4, 131.1(s,
Ph), 140.7 (s, ipso-C), 212.8 (s,CN). 29Si NMR (C6D6): δ -1.14
(br s, SiMe3), 9.72 (s, NSiMe3). 27Al NMR (C6D6): δ 111.5 (ν1/2
) 772 Hz). MS: m/e (%) 431 (M+), 416 (M+ - Me). Anal. Calcd
for C17H32AlCl2NSi3 (432.56): C, 47.20; H, 7.45; N, 3.24.
Found: C, 47.46; H, 7.51; N, 3.17.
RAlI2 (6). A solution of 1 (4.02 g, 10.3 mmol) in toluene (20
mL) was added to a solution of I2 (5.25 g, 20.6 mmol) in toluene
(40 mL) at room temperature. The mixture was stirred for 18
h at room temperature, resulting in a slightly brown-yellow
solution. All volatiles were removed in vacuo, the residual was
extracted with n-hexane (2 × 60 mL), and the extract was
concentrated and stored at -20 °C overnight to give slightly
yellow crystals, which were collected by filtration and dried
(5.2 g, 92%). Mp: 84-85 °C. 1H NMR (C6D6): δ 0.06 (s, 9H,
NSiMe3), 0.30 (s, 18H, SiMe3), 6.85-6.94 (m, 3H, Ph), 7.21 (d,
2H, Ph). 13C NMR (C6D6): δ 1.25 (s, NSiMe3), 4.22 (s, SiMe3),
41.95 (s, CSi2), 126.1, 128.4 and 131.3 (s, Ph), 140.8 (s, ipso-
C), 211.7 (s, CN). 29Si NMR (C6D6): δ -0.96 (s, SiMe3), 11.1
(s, NSiMe3). 27Al NMR (C6D6): δ 80.1. MS: m/e (%) 615 (M+,
1.6), 600 (M+ - Me), 488 (M+ - I). Anal. Calcd for C17H32AlI2-
NSi3 (615.57): C, 33.14; H, 5.24; N, 2.27. Found: C, 32.72; H,
5.42; N, 2.04.
RAlMeCl‚THF (7). 2 (0.20 g, 0.48 mmol) was dissolved in
THF (5 mL). After 30 min of stirring at room temperature,
the excess THF was removed in vacuo. The crude product was
crystallized from pentane to give colorless crystals (0.20 g,
85%). Mp: 45-46 °C. 1H NMR (C6D6): δ -0.14 (s, 3H, AlCH3),
0.12 (s, 9H, NSiMe3), 0.23 (br s, 18H, SiMe3), 1.17 (m, 4H,
THF), 3.48 (m, 4H, THF), 6.88-6.98 (m, 3H, Ph), 7.28-7.35
(d, 2H, Ph). 13C NMR (C6D6): δ -6.0 (s, AlCH3), 0.81, 1.69 (s,
NSiMe3), 3.44 (s, SiMe3), 25.3 (s, THF), 41.2 (s, CSi2), 69.6 (s,
THF), 126.2, 128.8, 129.8 (s, Ph), 144.7 (s, ipso-C), 196.0 (s,
CN). 27Al NMR (C6D6): δ 130.2 (ν1/2 ) 980 Hz). Anal. Calcd
for C22H43AlClNOSi3 (484.17): C, 54.54; H, 8.88; N, 2.89.
Found: C, 54.17; H, 8.62; N, 3.13.
RAlCl2‚THF (8). This compound was prepared using 3 (0.43
g, 1 mmol) and THF (10 mL) as described for 7. After workup,
(16) Krause, E. Ber. Dtsch. Chem. Ges. 1918, 51, 1447.

2258 Organometallics, Vol. 18, No. 11, 1999
Ta ble 1. Su m m a r y of Cr ysta l Da ta for Com p lexes 3, 5, a n d 8
Cui et al.
3
5
8
formula
C
17H32AlCl2NSi3
C37H71Al2F4N2Si6
incl. 0.5 hexane
842.46
C21H40AlCl2NOSi3
fw
432.59
504.69
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
150(2)
orthorhombic
Pbca
16.895(2)
16.129(2)
17.769(2)
90
200(2)
triclinic
P1h
10.916(3)
13.712(6)
18.242(6)
79.13(3)
80.207(13)
69.784(15)
2499.9(15)
2
1.119
0.243
203(2)
monoclinic
P21/c
14.290(2)
11,217(2)
18.358(3)
90
98.268(11)
90
2912.1(9)
4
1.151
0.389
1080
90
90
4842.3(10)
8
1.187
0.454
840
Z
d(calcd) (Mg/m3)
abs coeff (mm-1
F(000)
)
906
cryst size (mm)
θ range (deg)
limiting indices
0.70 × 0.40 × 0.20
3.56-25.05
-18 e h e 20
-19 e k e 19
-21 e l e 19
10 178
4273 (Rint ) 0.0502)
4266/0/226
1.091
0.50 × 0.50 × 0.50
3.55-20.04
-10 e h e 10
-13 e k e 13
-17 e 1 e 17
8628
4653 (Rint ) 0.0498)
4634/319/493
1.040
0.60 × 0.60 × 0.50
3.63-21.95
-15 e h e 15
-8 e k e 11
-16 e l e 19
3809
3519 (Rint ) 0.1363)
3500/0/271
1.063
no. of reflns collected
no. of indep reflns
no. of data/restraints/params
GOF/F2
R indices [I > 2σ(I)]
R1 ) 0.0380
wR2 ) 0.0844
R1 ) 0.0590
wR2 ) 0.1007
0.361/-0.231
R1 ) 0.0493
wR2 ) 0.1130
R1 ) 0.0744
wR2 ) 0.1390
0.272/-0.323
R1 ) 0.0518
wR2 ) 0.1100
R1 ) 0.0518
wR2 ) 0.1384
0.266/-0.258
R indices (all data)
largest diff peak/hole (e Å-3
)
Sch em e 1
colorless crystals (0.45 g, 89%) were obtained from n-hexane
at -8 °C. Mp: 88-89 °C. 1H NMR (C6D6): δ 0.16 (s, 9H,
NSiMe3), 0.28 (s, 18H, SiMe3), 1.16 (m, 4H, THF), 3.55 (m,
4H, THF), 6.84-6.95 (m, 3H, Ph), 7.32 (d, 2H, Ph). 13C NMR
(C6D6): δ 1.00 (s, NSiMe3), 2.96 (s, SiMe3), 25.7 (s, THF), 40.9
(s, CSi2), 67.9 (s, THF), 126.2, 128.6, 129.9 (s, Ph), 147.3 (s,
ipso-C), 182.1 (s, CN). 29Si NMR (C6D6): δ -6.18 (s, SiMe3),
1.68 (s, NSiMe3). 27Al NMR (C6D6): δ62.66 (ν1/2 ) 5600 Hz).
Anal. Calcd for C21H40AlCl2NOSi3 (504.69): C, 49.98; H, 7.99;
N, 2.77. Found: C, 49.38; H, 8.06; N, 2.66.
X-r a y Str u ctu r e Deter m in a tion s a n d Refin em en ts.
Data for crystal structures of 3, 5, and 8 were collected on a
Stoe-Siemens four-circle diffractometer using Mo KR radiation
(λ ) 0.710 73 Å). All structures were solved by direct methods
(SHELXS-96)17 and refined against F2 using SHELXL-97.18 All
heavy atoms were refined anisotropically. Hydrogen atoms
were included using the riding model with Uiso tied to the Uiso
of the parent atom. Crystal data, data collection details, and
solution and refinement procedures are summarized in Table
1.
Sch em e 2
Resu lts a n d Discu ssion s
Syn th esis of Alu m in u m 1-Aza -a llyl Com p lexes.
The reaction of RLi‚THF with AlMe2Cl, AlMeCl2, AlCl3,
and AlBr3 in ether or n-hexane, after workup, afforded
RAlMe2 (1), RAlMeCl (2), RAlCl2 (3), RAlBr2 (4), re-
spectively, in high yield (Scheme 1). Initially these
products are in equilibrium with their corresponding
THF adducts, which was confirmed by the 1H NMR
analysis. However, solvent-free compounds can be easily
obtained by sublimation in high-vacuum or pumping the
crude products for a prolonged time in high vacuum at
ambient temperature. Finally, crystallization from n-
hexane yielded solvent-free products. On the other hand,
THF adducts can be easily prepared by dissolving
compounds 1-4 in an excess of THF. According to this
procedure, we prepared the adducts RAlMeCl‚THF (7)
and RAlCl2‚THF (8) (Scheme 2). Both compounds are
not stable; they are easily oxidized and hydrolyzed on
exposure to air, as indicated by an immediate color
change from colorless to red. The different stabilities of
compounds 1-4 and their corresponding THF adducts
can be explained by the different bonding modes of the
ligand, as demonstrated by the X-ray structure analyses
of compound 3 and 8. The solvents seem to be important
for the synthesis of compounds 1-4. Complex 1 can be
obtained in ether in high yield (85-98%), but for 2-4,
(17) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(18) Sheldrick, G. M. SHELXL, Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

Mono(1-aza-allyl) Complexes of Aluminum
Organometallics, Vol. 18, No. 11, 1999 2259
the synthesis in ether resulted in low yields (around
20%). The same reactions in n-hexane gave satisfactory
yields (61-84%) for all compounds.
The reaction of RAlMe2 (1) with 2 equiv of Me3SnF
in toluene yielded the dimeric difluoride [RAlF(µ-F)]2
(5, eq 1), while the reaction of 1 with 2 equiv of I2 in
toluene at room temperature generated the diiodide,
RAlI2 (6, eq 2).
2RAlMe2 + 4Me3SnF f [RAlF(µ-F)]2 + 4SnMe4 (1)
RAlMe2 + 2I2 f RAlI2 + 2MeI
(2)
Unlike trimeric aminoalane difluoride [(2,6-i-Pr2-
F igu r e 1. Molecular structure of 5 in the crystal. Hydro-
gen atoms and solvent molecules have been omitted for
clarity.
C6H3)N(SiMe3)AlF2]3 and [(Me3Si)3CAlF2]3,20 com-
19
pound 5 is a dimer in the solid state, as demonstrated
by X-ray crystallography. Compound 5 is the first
example of a dimeric aluminum difluoride.
1
Compounds 1-8 have been fully characterized by H
Dyn a m ic Beh a vior of 5. The 19F NMR spectra of 5
at room temperature in C6D6 and toluene-d8 both show
only one broad singlet, indicating rapid exchange of the
bridging and terminal fluorine atoms. This intramo-
lecular exchange was also observed for the previously
reported compounds [(2,6-i-Pr2C6H3)N(SiMe3)AlF2]3 and
[(Me3Si)3CAlF2]3. When a solution of 5 in toluene-d8 was
cooled below 213 K (to 193 K), there are five separated
signals in the 19F NMR spectrum (δ -159.69 ppm (t, J
) 15.0 Hz), -158.36 (t, J ) 13.4 Hz), -141.13 (d, J )
82.4 Hz), -133.29 (s), -120.61 (d, J ) 81.9 Hz)) in an
intensity ratio of 2:3:1:3:1. Herein, assignment of the
two signals (-159.69 and -158.36 ppm) to the bridging
F atoms and the others to the terminal F atoms seems
reasonable due to the large coupling constant difference
of the two groups of signals as well as their correct
integration (2:2). The ambient 1H NMR spectrum of 5
exhibits only one broad singlet for SiMe3 and one singlet
for NSiMe3 in toluene-d8. When the solution was cooled
to 273 K, the singlet for SiMe3 becomes broad and
separates into two singlets at 253 K. The singlet for
NSiMe3 and SiMe3, respectively, at ambient tempera-
ture gives two separated singlets for SiMe3 and two for
NMR and 13C NMR as well as elemental analyses (see
Experimental Section). It is interesting to note that the
13C chemical shifts of CN in compounds 2 and 3 are
significantly higher than those found in compounds 7
and 8, representing the most typical characteristics of
η3-chelating mode of the ligand in these compounds due
to the delocalization of the electrons in the backbone of
the ligand. 27Al NMR and MS spectra demonstrate that
compounds 1-4 and 6 are 4-fold coordinated at the
aluminum centers in solution and monomers in the gas
phase, respectively.
Molecu la r Str u ctu r e of [RAlF (µ-F )]2 (5). Molecu-
lar structure of 5 was determined by X-ray diffraction.
Single crystals suitable for analysis were obtained from
n-hexane/toluene at -20 °C. The structure of 5 with the
atom-labeling scheme is shown in Figure 1. Selected
bond distances and angles are listed in Table 3. Com-
pound 5 adopts a dimeric structure in which the two
bridging F atoms link two RAlF units in a planar four-
membered ring (Al(1)-F(2)-Al(2)-F(3), the mean de-
viation of the ring, ∆ ) 0.0002 Å) and has approximately
C2 symmetry, as the bridging F(2) and F(3) reside on a
2-fold axis. Thus, each Al center is bonded to an
η3-chelating R ligand, one terminal F atom, and two
bridging F atoms, resulting in three fused four-mem-
bered rings (Al(1)-C(2)-C(1)-N(1), ∆ ) 0.0052 Å;
Al(1)-F(2)-Al(2)-F(3), ∆ ) 0.0002 Å; Al(2)-C(4)-
C(3)-C(2), ∆ ) 0.0431 Å).
An important structural feature is the observation
that every Al atom is pentacoordinated and the geom-
etry of each aluminum coordination sphere can best be
described as a distorted trigonal-bipyramid (tbp). A
terminal F, a bridging F(3) atom, and a C(2) or C(4)
atom reside in the equatorial plane with bond distances
to Al on average of 1.668, 1.835, and 2.053 Å, respec-
tively. The Al atom lies almost exactly in this plane with
a negligible displacement. The sum of bond angles
involving Al in this plane is 359.33° for Al(1) or 359.66°
for Al(2), the angle F(1)-Al(1)-F(3) (102.23(15)°) or
F(3)-Al(2)-F(4) (102.56(15)°) is significantly smaller
than the angle F(3)-Al(1)-C(2) (142.2°) or F(3)-Al(2)-
C(4) (137.1°), resulting from crowded environments
around C(2) or C(4). The apical positions of this array
are occupied by the bridging F(2) atom for both tbp
geometries and the N(1) for Al(1) or N(2) for Al(2) with
a bond angle of N(1)-Al(1)-F(2) of 152.4(2)° or N(2)-
Al(2)-F(2) of 153.6(2)°. The deviation of the apical axis
1
NSiMe3 (213 K). On the basis of the H NMR data for
SiMe3 at 193 K (0.62 and 0.31 ppm, respectively), we
conclude that a change in the ligand backbone takes
place due to the quite different chemical shifts. Thus
rapid dissociation/association of the Al-C bonds was
also responsible for the fluxional process of 5 in solution.
This dynamic process achieves an equilibrium at 213
K, giving a mixture of five- and four-coordinated species,
while the [Al-(µ-F)]2 core is maintained at this tem-
perature. The broadening of the singlet at 0.31 ppm for
SiMe3 was probably due to the formation of four-
coordinated species containing the CdC bond. The
dissociation/association process is rapid at ambient
temperature; therefore only one singlet can be observed
for the SiMe3 group on the NMR time scale. This
assumption was further supported by the splitting of
the Ph group signals into two sets in the 1H NMR
spectrum at low temperature. This M-C cleavage
mechanism was also reported for compounds (ClMR)2
(M ) Sn, Pb; R ) [N(SiMe3)C(Ph)C(SiMe3)2]- ).9
(19) Waezsada, S. D.; Liu, F.-Q.; Murphy, E. F.; Roesky, H. W.;
Teichert, M.; Uson, I.; Schmidt, H.-G.; Albers, T.; Parisini, E.; Nolte-
meyer, M. Organometallics 1997, 16, 1260.
(20) Schnitter, C.; Klimek, K.; Roesky, H. W.; Albers, T.; Schmidt,
H.-G.; Ro¨pken, C.; Parisini, E. Organometallics 1998, 17, 2249.

2260 Organometallics, Vol. 18, No. 11, 1999
Cui et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for Com p lexes 3 a n d 8
RAlCl2 (3)
Al(1)-N(1)
1.918(2)
2.1321(10)
1.314(3)
1.903
73.68(10)
114.57(7)
132.1(2)
117.1(2)
113.9(2)
Al(1)-C(2)
Al(1)-Cl(2)
N(1)-Si(1)
C(1)-C(3)
N(1)-Al(1)-Cl(2)
C(2)-Al(1)-Cl(1)
Al(1)-N(1)-Si(1)
Al(1)-C(2)-Si(2)
N(1)-C(1)-C(3)
2.015(3)
2.1276
Al(1)-C(1)
C(1)-C(2)
C(2)-Si(2)
2.334(3)
1.498(3)
1.902(3)
Al(1)-Cl(1)
C(1)-N(1)
C(2)-Si(3)
N(1)-Al(1)- C(2)
N(1)-Al(1)-Cl(1)
C(1)-N(1)-Si(1)
C(1)-C(2)-Si(3)
N(1)-C(1)-C(2)
1.800(2)
1.484(4)
113.05(7)
120.70(8)
136.76
C(2)-Al(1)-Cl(2)
Cl(2)-Al(1)-Cl(1)
C(1)-C(2)-Si(2)
Al(1)-C(2)-Si(3)
C(2)-C(1)-C(3)
124.28(8)
106.53(4)
112.0(2)
108.84(12)
123.9(2)
118.75(13)
122.1(2)
RAlCl2(THF) (8)
Al(1)-N(1)
1.806(3)
2.134 (2)
1.888(4)
109.0(2)
114.00(12)
117.7(2)
122.3(4)
Al(1)-O(1)
1.872(3)
1.450(5)
1.891(5)
118.98(13)
102.64(11)
124.9(4)
Al(1)-Cl(1)
2.135(2)
1.356(6)
1.507
99.61(11)
110.34(8)
112.8(4)
120.8(3)
Al(1)-Cl(2)
N(1)-C(1)
C(1)-C(2)
C(2)-Si(1)
C(2)-Si(2)
C(1)-C(3)
N(1)-O(1)-Al(1)
N(1)-Al(1)-Cl(1)
Al(1)-N(1)-C(1)
C(2)-C(1)-C(3)
N(1)-Al(1)-Cl(2)
O(1)-Al(1)-Cl(1)
N(1)-C(1)-C(2)
C(1)-C(2)-Si(2)
O(1)-Al(1)-Cl(2)
Cl(2)-Al(1)-Cl(1)
N(1)-C(1)-C(3)
C(1)-C(2)-Si(1)
123.3(3)
Ta ble 3. Selected Bon d Len gth s a n d An gles for Com p lex [RAlF (µ-F )]2 (5)
Al(1)-F(1)
1.665(3)
1.977(4)
1.308(6)
1.829(3)
1.480(7)
1.504(7)
101.40(14)
105.6(2)
114.9(2)
71.3(2)
102.56(15)
106.6(2)
120.0(2)
114.2(4)
114.2(4)
71.4
Al(1)-F(2)
1.837(3)
2.051(5)
1.670(3)
1.964 (4)
1.312(6)
2.902(2)
102.23(15)
152.4(2)
102.5
103.81(14)
99.10(15)
92.6(2)
137.1(2)
91.1(3)
Al(1)-F(3)
C(1)-C(2)
Al(2)-F(2)
Al(2)-C(4)
C(1)-C(71)
1.841(3)
1.486(6)
1.850(3)
2.055(5)
1.508(6)
Al(1)-N(1)
Al(1)-C(2)
C(1)-N(1)
Al(2)-F(4)
Al(2)-F(3)
Al(2)-N(2)
C(4)-C(3)
C(3)-N(2)
C(3)-C(81)
Al(1)-Al(2)
F(1)-Al(1)-F(2)
F(1)-Al(1)-N(1)
F(1)-Al(1)-C(2)
N(1)-Al(1)-C(2)
F(4)-Al(2)-F(3)
F(4)-Al(2)-N(2)
F(4)-Al(2)-C(4)
N(1)-C(1)-C(2)
N(2)-C(3)-C(4)
N(2)-Al(2)-C(4)
F(1)-Al(1)-F(3)
F(2)-Al(1)-N(1)
F(2)-Al(1)-C(2)
Al(1)-F(2)-Al(2)
F(4)-Al(2)-F(2)
F(3)-Al(2)-N(2)
F(3)-Al(2)-C(4)
Al(1)-N(1)-C(1)
Al(2)-N(2)-C(3)
F(2)-Al(1)-F(3)
F(3)-Al(1)-N(1)
F(3)-Al(1)-C(2)
Al(1)-F(3)-Al(2)
F(3)-Al(2)-F(2)
F(2)-Al(2)-N(2)
F(2)-Al(2)-C(4)
Al(1)-C(2)-C(1)
Al(2)-C(4)-C(3)
75.86(13)
92.7(2)
142.2(2)
104.52(15)
75.81(12)
153.6(2)
100.9(2)
83.4(3)
90.8(3)
82.8(3)
(1.850(3) Å), leading to a longer Al(1)-N(1) distance
(1.977(4) Å) than Al(2)-N(2) (1.964(4) Å), and to the
slightly unequal environments about Al(1) and Al(2).
The N(1)-Al(1)-C(2) or N(2)-Al(2)-C(4) angle is very
acute (average 71.3°), which is slightly smaller than that
found in compound 3 (73.7°) because of the different
coordination number at Al atoms of the two compounds.
The acute angles of F(2)-Al(1)-F(3) and F(2)-Al(2)-
F(3) (75.86° and 75.81°) lead to a rather long Al-Al
distance (2.902 Å). Compared to compound 3, the Al-N
(1.971 Å) and Al-C (2.053 Å) bond lengths in the
chelating plane are longer than those observed in 3 (Al-
N, 1.918 Å; Al-C, 2.015 Å). The Al-F average distance
(bridging, 1.839 Å) is in line with those found in
compound [(Cp*AlF)2SiPh2]2 (average 1.846 Å)19 and
slightly longer than those found by electron diffraction
for (Me2AlF)4 (1.808 Å)21 or by X-ray diffraction for
[(Me3Si)3CAlF2]3 (1.785-1.815 Å)20 and for [(2,6-i-
Pr2C6H3)N(SiMe3)AlF2]3 (1.770-1.815 Å).19 The termi-
nal Al-F distances are 1.665 Å (Al(1)-F(1)) and 1.670
Å (Al(2)-F(4)) and are somewhat longer than those
observed in [(2,6-i-Pr2C6H3)N(SiMe3)AlF2]3 (1.634-1.642
Å) and AlF3 (1.63 Å)22 determined by electron diffraction
due to the higher coordination number of aluminum in
compound 5. No examples of five-coordinated aluminum
compounds containing either bridging or terminal F
atoms can be found in the literature for comparison.
F igu r e 2. Central core of 5 in the crystal. Carbon atoms
except for those in the ligand backbones have been omitted
for clarity.
N(1)-F(2) is 13.8°, arising from the constraints caused
by the specific angles in the chelating bidentate mono-
anionic ligand (average 71.4°) as well as in the acute
F(2)-Al-F(3) angles of average 75.84° in the (µ-F)2Al2
ring (Figure 2).
The most unique and interesting feature in this
structure is that the bridging F(2) and F(3) atoms
connect the two units in such a way that F(2) occupies
the same apical position and F(3) lies in the same
equatorial position in the two tbp coordination spheres,
resulting in a slightly longer Al-F(2) distance (average
1.844 Å) than Al-F(3) (average 1.836 Å). The distance
of Al(1)-F(2) (1.837(3) Å) is shorter than Al(2)-F(2)
(21) Gundersen, G.; Haugen, T.; Haaland, A. J . Chem. Soc., Chem.
Commun. 1972, 708.
(22) Shanmugasunderan, G.; Nagarajan, G. Z. Phys. Chem. 1969,
240, 363.
(23) Ergezinger, C.; Weller, F.; Dehnicke, K. Z. Naturforsch. 1988,
43b, 1621.

Mono(1-aza-allyl) Complexes of Aluminum
Organometallics, Vol. 18, No. 11, 1999 2261
F igu r e 4. Molecular structure of 8 in the crystal. Hydro-
gen atoms have been omitted for clarity.
N(1)-C(1)-C(2) unit. The Al-Cl distances are compa-
rable to those of compound 3, while the Cl-Al-Cl angle
(110.34(8)°) is slightly larger than that of compound 3
(106.53(4)°), reflecting the greater steric demand for η3-
chelating mode even though a THF molecule is coordi-
nated to Al in compound 8. The Al-O distance (1.872(3)
Å) is in agreement with that observed for the stable
compound (Me3Si)3CAlCl2(THF) (1.887 Å).20 Although
in the solid state the THF in compound 8 seems as
tightly coordinated to the aluminum center as that in
(Me3Si)3CAlCl2(THF) by the analysis of Al-O bond
lengths in the two compounds, the instability of this
compound is obviously due to easy removal of the THF
molecule in vacuo. Thus, the bonding fashion of the
ligand changes from η1 to η3 so as to stabilize the AlCl2
unit (Scheme 2). The distances between Al(1) and C(1)
as well as Al(1) and C(2) are 2.792 and 3.495 Å,
respectively, which are in the range of van der Waals
interaction, indicating that the C(1)dC(2) bond is not
free in the solid state. In line with this observation,
there is observed only one signal for the two SiMe3 on
F igu r e 3. Molecular structure of 3 in the crystal. Hydro-
gen atoms have been omitted for clarity.
X-r a y Cr ysta llogr a p h ic An a lyses of Com p ou n d s
3 a n d 8. Crystal data for compounds 3 and 8 are
summarized in Table 1, refinement details are discussed
in the Experimental Section, and selected bond dis-
tances and angles are collected in Table 2. Single
crystals of compounds 3 and 8 suitable for X-ray
diffraction analyses were obtained by recrystallization
from n-hexane at -8 °C. The molecular geometries and
atom-labeling schemes are shown in Figures 3 and 4.
Compound 3 adopts a distorted tetrahedral structure
(Figure 3). The core angle (N(1)-Al(1)-C(2)) is acute
(73.68°), which is compensated for by opening of the
N-Al-Cl and C-Al-Cl angles. The structure of 3 is
similar to that of the reported amidinate aluminum
dichloride Ph-C(NSiMe3)2AlCl2.23 Because the chelating
backbones in the two compounds are different, some
differences in the structures are obvious: (1) The core
angle N(1)-Al(1)-C(2) (73.68(10)°) is slightly larger
than N-Al-N (72.9°) in compound Ph-C(NSiMe3)2-
AlCl2; (2) the Al(2)-C(2)-Si(2,3) (118.75(13)° and
108.84(12)°) angles in 3 are significantly smaller than
the Al-N-Si angles in Ph-C(NSiMe3)2AlCl2 (average
139°), indicating that R is more shielding than the
amidinate.
The structure of compound 8 was also determined by
X-ray crystallography for comparison (Figure 4). Inter-
estingly, in the monomeric molecule of 8, the geometry
of the aluminum coordination sphere is also distorted
tetrahedral, while the aluminum atom is surrounded
by two chlorine atoms, one oxygen atom, and one
nitrogen atom. The ligand R in this compound is, in
contrast to 3, monohapto (η1) coordinated. The Al(1)-
N(1) distance (1.806 Å) in 8 is much shorter than that
in compound 3 (1.92 Å). The distinct bonding modes in
3 and 8 are also reflected in the different bond distances
in the backbone of the ligand (long C(1)-N(1) and short
C(1)dC(2) distances for 8 versus short C(1)-N(1) and
long C(1)-C(2) contacts for 3, Table 2). The long C(1)-
C(2) and short C(1)-N(1) distances in compound 3 are
indications of the delocalization of the electrons in the
1
C(2) in the H NMR spectrum of 8 in C6D6 at ambient
temperature, and the 13C NMR signal for C(2) is
significantly downfield compared with those for C in
compounds with normal CdC bonds. The 27Al NMR
spectrum showed a broad signal (62.66 ppm), which is
low field shifted compared to the compounds of coordi-
nation number four described herein, indicating more
electron density on the Al(1) and partial interactions
between Al(1) and the C(1)dC(2) bond in solution. This
may result from the Lewis acidic aluminum center
containing four electron-withdrawing groups, leading to
the flexibility of the C(1)dC(2) bond and the rotation of
the two SiMe3 groups around the C(1)dC(2) bond.
Ack n ow led gm en t. This work was supported by the
Deutsche Forschungsgemeinschaft.
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal
data, atom coordinates, and equivalent isotropic displacement
parameters for all non-hydrogen atoms, hydrogen positional
and thermal parameters, anisotropic displacement parameters,
and bond distances and angles for compounds 3, 5, and 8. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM981021T