Syntheses and X-ray structures of some pyrrolylaldiminate metal complexes

Article abstract of DOI:10.1016/S0022-328X(03)00555-2

Several pyrrolylaldiminate complexes of Group 1, 4 and 13 metals are reported. The reaction of 5-tert-butyl-2-[(2,6-diisopropylphenyl) aldimino]pyrrole (HL) with NaH produced LNa(THF) (1). In situ lithiation of HL followed by addition of one equivalent of

Full text of DOI:10.1016/S0022-328X(03)00555-2

Journal of Organometallic Chemistry 679 (2003) 135Á142
/
www.elsevier.com/locate/jorganchem
Syntheses and X-ray structures of some pyrrolylaldiminate metal
complexes
Lan-Chang Liang a,*, Chih-Wei Yang a, Michael Y. Chiang a, Chen-Hsiung Hung b,
Pei-Ying Lee a
a Department of Chemistry, National Sun Yat-sen University, and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University,
Kaohsiung 80424, Taiwan, ROC
b Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan, ROC
Received 30 April 2003; received in revised form 3 June 2003; accepted 3 June 2003
Abstract
Several pyrrolylaldiminate complexes of Group 1, 4 and 13 metals are reported. The reaction of 5-tert-butyl-2-[(2,6-
diisopropylphenyl)aldimino]pyrrole (HL) with NaH produced LNa(THF) (1). In situ lithiation of HL followed by addition of
one equivalent of MClx (Mꢀ
MLCl2(m-Cl)2Li(OEt2)2 (MꢀZr, 3; Hf, 4) and AlLCl2 (5). Alkylation of 5 with MeMgBr generated AlLMe2 (6). In addition to the
spectroscopic data, complexes 3Á6 were characterized by X-ray crystallography.
/
Zr, xꢀ
/
4; Mꢀ
/
Hf, xꢀ
/
4, Mꢀ
/
Al, xꢀ/3) afforded the corresponding pyrrolylaldiminate complexes,
/
/
# 2003 Elsevier B.V. All rights reserved.
Keywords: Zirconium; Hafnium; Aluminum; Pyrrolylaldiminate
1. Introduction
[15,16]. Metal complexes of pyrrolylaldiminate, how-
ever, have received much less attention. Several reports
recently describe the formation of mono- and bis-chelate
complexes of Group 2, 4, 6, 8, 9, 10, 12 and 13 metals
Metal complexes containing chelating nitrogen li-
gands with bulky substituents continue to constitute
an active area of exploratory research [1]. Extensive
studies in this field have primarily focused on the
development of well-defined metal complexes as cata-
[17Á
titanium derivatives of the type [2-C4H3N(CHꢀ
NR)]2TiCl2 (RꢀC6H5, cyclo-C6H11), which lead to
/24]. Perhaps the most phenomenal examples are the
/
/
lysts for olefin polymerization [2Á5]. Monoanionic
/
cyclic olefin copolymerization in a living fashion [25].
We became interested in a more sterically demanding
ligand, 5-tert-butyl-2-[(2,6-diisopropylphenyl)-aldimi-
no]pyrrole (HL), for inorganic and organometallic
chemistry. The steric properties provided by the tert-
butyl and isopropyl groups are anticipated to preclude
possible side reactions on the pyrrole ring, to offer
partial protection to the metal center where possible,
and to discourage the formation of bis-chelate com-
plexes. Roesky and co-workers [17] recently described
the isolation of aluminum complexes containing Lꢁ
[26], but the solid-state structures have not been
reported. Herein we present the syntheses of some
mono-pyrrolylaldiminate derivatives of Group 1, 4 and
bidentate nitrogen ligands are of current interest,
particularly for the low-valent, low-coordinate metal
complexes of hard transition and main group elements,
from which intriguing structures and reactivity have
emerged significantly. Representative examples of such
ligands are depicted in Scheme 1 [6Á14].
/
The pyrrolylaldiminate ligands are closely related to
the salicylaldiminate ligands, which have evolved in
metal complexes that exhibit specific chemical transfor-
mations in both stoichiometric and catalytic manner
* Corresponding author. Fax: ꢂ886-7-5253-908.
E-mail address: lcliang@mail.nsysu.edu.tw (L.-C. Liang).
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00555-2

136
L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á142
/
Scheme 1. Representative examples of monoanionic bidentate N-ligands.
13 metals, along with the X-ray structures of Zr, Hf, and
Al complexes.
tion. The reaction mixture was stirred at room tempera-
ture overnight. The resulting red solution was passed
through a pad of Celite to remove the excess NaH. All
volatiles were removed. The reddish brown solid residue
was washed with pentane (5 ml) and dried in vacuo to
afford the title compound as an off-white solid; yield 625
mg (96%). Colorless crystals may be obtained by
recrystallization from diethyl ether. 1H-NMR (C6D6,
2. Experimental
2.1. General procedures
200 MHz) d 7.88 (s, 1H, CH Ä
7.04 (m, 1H), 6.60 (m, 1H), 3.42 (m, 4H, OCH2CH2),
3.18 (septet, Jꢀ8 Hz, 2H, CHMe2), 1.46 (s, 9H, CMe3),
1.34 (m, 4H, OCH2CH2), 1.17 (d, Jꢀ8 Hz, 12H,
CHMe2).
/
N), 7.11Á
/
7.24 (m, 3H),
Unless otherwise specified, all experiments were
performed under nitrogen using standard Schlenk or
glovebox techniques. All solvents were reagent grade or
better and purified by standard methods. Molecular
sieves and Celite were activated in vacuo (10ꢁ3 Torr) for
24 h at 175 and 125 8C, respectively. All NMR solvents
/
/
˚
were sparged with nitrogen and dried over activated 4 A
molecular sieves for days prior to use. All other
chemicals were used as received from commercial
vendors. The NMR spectra were recorded on Varian
instruments. Chemical shifts (d) are listed as parts per
million downfield from tetramethylsilane and coupling
2.3. Synthesis of ZrLCl2(m-Cl)2Li(OEt2)2 (3)
To a diethyl ether solution (5 ml) of HL (200 mg, 0.64
mmol) was added n-BuLi (0.40 ml, 1.6M solution in
hexanes, 0.64 mmol) at ꢁ
naturally warmed to room temperature and stirred for
2 h. The solution was cooled to ꢁ35 8C again and added
to a white suspension of ZrCl4 (150 mg, 0.64 mmol) in
diethyl ether (8 ml) at ꢁ35 8C with vigorous stirring.
/
35 8C. The solution was
1
constants (J) are given in hertz. H-NMR spectra are
referenced using the residual solvent peak at d 7.16 for
C6D6, and d 7.27 for CDCl3. 13C-NMR spectra are
referenced using the residual solvent peak at d 128.39
for C6D6, and d 77.23 for CDCl3. The assignment of the
carbon atoms for all new compounds is based on the
DEPT 13C-NMR spectroscopy. Routine coupling con-
stants are not listed. All NMR spectra were recorded at
room temperature in specified solvents. Elemental
/
/
The reaction mixture was stirred at room temperature
for 20 h and filtered through a pad of Celite, which was
further washed with diethyl ether until the washings
were colorless. The ether filtrate was concentrated in
vacuo and cooled to Á
solid; yield 160 mg (49%). 1H-NMR (C6D6, 200 MHz) d
7.58 (s, 1H, CH ÄN), 6.93Á6.99 (m, 3H), 6.70 (d, Jꢀ3.8
Hz, 1H, pyrrole CH), 6.25 (d, Jꢀ3.8 Hz, 1H, pyrrole
CH), 4.06 (septet, Jꢀ8 Hz, 2H, CHMe2), 3.35 (q, 8H,
O(CH2CH3)2), 1.61 (s, 9H, CMe3), 1.53 (d, Jꢀ8 Hz,
6H, CHMe2), 1.15 (d, Jꢀ8 Hz, 6H, CHMe2), 0.93 (t,
12H, O(CH2CH3)2); 13C{1H}-NMR (C6D6, 125 MHz) d
168.8, 162.0 (CHÄN), 144.8, 134.7, 128.6, 127.9 (CH),
/
35 8C to yield a yellow crystalline
analysis was performed on a Heraeus CHNÁ
/
O rapid
analyzer. Because complexes 1Á6 are all sensitive to air
/
/
/
/
and moisture, satisfactory analysis was hampered for
some compounds.
/
/
/
2.2. Synthesis of NaL(THF) (1)
/
Solid NaH (45 mg, 1.875 mmol, 1.16 equivalents) was
/
suspended in THF (5 ml) and cooled to ꢁ
solution of HL (500 mg, 1.610 mmol) in THF (8 ml) at
35 8C was added dropwise. Gas evolved upon addi-
/
35 8C. A
127.7 (CH), 124.3 (CH), 113.3 (CH), 66.7
(O(CH2CH3)2), 35.0 (CMe3), 32.6 (CH3), 28.6
(CHMe2), 25.8 (CH3), 24.4 (CH3), 14.7 (CH3). Anal.
ꢁ
/

L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á
/
142
137
Calc. for C29H49Cl4LiN2O2Zr: C, 46.95; H, 6.15; N,
4.38. Found: C, 47.02; H, 6.85; N, 4.29%.
2.6. Synthesis of AlLMe2 (6)
To a diethyl ether solution (6 ml) of AlLCl2 (200 mg,
0.49 mmol) was added MeMgBr (0.33 ml, 3 M solution
2.4. Synthesis of HfLCl2(m-Cl)2Li(OEt2)2 (4)
in Et2O, 0.99 mmol, 2 equivalents) at ꢁ35 8C. The
/
reaction mixture was naturally warmed to room tem-
perature and stirred for 24 h. Diethyl ether was removed
in vacuo. The solid residue was extracted with pentane
(7 ml). The pentane extract was filtered through a pad of
Celite. Pentane was removed in vacuo to yield a pale
yellow crystalline solid; yield 143 mg (80%). Recrystalli-
To a diethyl ether solution (5 ml) of HL (200 mg, 0.64
mmol) was added n-BuLi (0.40 ml, 1.6 M solution in
hexanes, 0.64 mmol) at ꢁ
naturally warmed to room temperature and stirred for
2 h. The solution was cooled to Á35 8C again and added
to a white suspension of HfCl4 (206 mg, 0.64 mmol) in
diethyl ether (8 ml) at ꢁ35 8C with vigorous stirring.
/
35 8C. The solution was
/
zation from a concentrated Et2O solution at ꢁ
gave X-ray quality crystals. 1H-NMR (C6D6, 500 MHz)
d 7.46 (s, 1H, CHꢀN), 7.12 (m, 1H), 7.07 (m, 2H), 6.80
(d, Jꢀ3.6 Hz, 1H, pyrrole CH), 6.36 (d, Jꢀ3.6 Hz, 1H,
pyrrole CH), 3.22 (septet, Jꢀ6.5 Hz, 2H, CHMe2), 1.37
(s, 9H, CMe3), 1.22 (d, Jꢀ6.5 Hz, 6H, CHMe2), 0.93 (d,
Jꢀ6.5 Hz, 6H, CHMe2), ꢁ0.22 (s, 6H, AlMe).
13C{1H}-NMR (C6D6, 125 MHz) d 164.1 (CAryl),
N), 144.2 (CAryl), 141.4 (CAryl), 135.2
/
35 8C
/
The reaction mixture was stirred at room temperature
for 20 h and filtered through a pad of Celite, which was
further washed with diethyl ether until the washings
were colorless. The ether filtrate was concentrated in
/
/
/
/
/
vacuo and cooled to ꢁ
solid; yield 403 mg (85%). 1H-NMR (C6D6, 500 MHz) d
7.72 (s, 1H, CH ÄN), 7.11Á7.17 (m, 3H), 6.67 (d, Jꢀ
Hz, 1H, pyrrole CH), 6.30 (d, Jꢀ4 Hz, 1H, pyrrole
CH), 4.10 (septet, Jꢀ7 Hz, 2H, CHMe2), 3.26 (br s,
8H, O(CH2CH3)2), 1.66 (s, 9H, CMe3), 1.49 (d, Jꢀ
Hz, 6H, CHMe2), 1.11 (d, Jꢀ7 Hz, 6H, CHMe2), 0.90
(t, 12H, O(CH2CH3)2); 13C{1H}-NMR (C6D6, 125
MHz) d 169.5, 162.0 (CHÄN), 144.3, 135.0, 128.7,
/
35 8C to yield a yellow crystalline
/
/
/
/
/
4
159.8 (CHÄ
/
/
(CAryl), 128.1 (CAryl), 124.6 (CAryl), 123.4 (CAryl), 113.2
(CAryl), 34.1 (CMe3), 31.4 (CMe3), 28.6 (CHMe2), 26.4
/
/
7
(CHMe2), 23.5 (CHMe2), ꢁ8.0 (br, AlMe).
/
/
2.7. X-ray crystallographic studies
/
127.9 (CH), 127.8 (CH), 124.4 (CH), 113.7 (CH), 66.4
(O(CH2CH3)2), 35.0 (CMe3), 32.6 (CH3), 28.6
(CHMe2), 26.0 (CH3), 24.5 (CH3), 14.9 (CH3).
Table 1 summarizes the crystallographic data for all
structurally characterized compounds. Data for com-
pounds 3 and 4 were collected on a Bruker SMART
1000 CCD diffractometer with graphite monochro-
˚
Ka radiation (lꢀ0.7107 A). Structures
2.5. Synthesis of AlLCl2 (5)
mated MoÁ
/
/
were solved by direct methods and refined by full matrix
least squares procedures against F2 using SHELXTL. All
non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were placed in calculated positions. Data
To a toluene solution (17 ml) of HL (2.0 g, 6.44
mmol) was added n-BuLi (4.03 ml, 1.6 M solution in
hexanes, 6.44 mmol) at ꢁ
naturally warmed to room temperature and stirred for
2 h. The solution was cooled to ꢁ35 8C again and added
to a white suspension of AlCl3 (0.859 g, 6.44 mmol) in
toluene (13 ml) at ꢁ35 8C. The reaction mixture was
/
35 8C. The solution was
for compounds 5 and 6 were collected using MoÁ
/
Ka
˚
0.71069 A) on a Rigaku AFC7S diffract-
/
radiation (lꢀ
/
ometer. Structures were solved by direct methods and
refined by full-matrix least-squares procedures against F
using TEXSAN. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were placed in calcu-
lated positions. In 5 the isopropylmethyl groups are
disordered in the ratio 50:25:25 over three conforma-
tions.
/
stirred at room temperature for 36 h and filtered
through a pad of Celite, which was further washed
with toluene until the washings were colorless. The
toluene filtrate was concentrated in vacuo and cooled to
ꢁ35 8C to yield a red crystalline solid; yield 2.31 g (3
/
1
crops, 88%). H-NMR (C6D6, 200 MHz) d 7.28 (s, 1H,
CHÄN), 7.03Á7.15 (m, 3H), 6.62 (d, Jꢀ4.4 Hz, 1H,
pyrrole CH), 6.21 (d, Jꢀ4.4 Hz, 1H, pyrrole CH), 3.43
(septet, Jꢀ8 Hz, 2H, CHMe2), 1.37 (s, 9H, CMe3), 1.30
(d, Jꢀ8 Hz, 6H, CHMe2), 0.91 (d, Jꢀ8 Hz, 6H,
CHMe2). 13C{1H}-NMR (C6D6, 75 MHz) d 167.5
(CAryl), 161.2 (CHꢀN), 144.8 (CAryl), 138.9 (CAryl),
/
/
/
/
3. Results and discussion
/
/
/
The ligand HL was readily prepared by a standard
condensation method from the reaction of 2,6-diisopro-
/
pylaniline
with
5-tert-butylpyrrole-2-carbaldehyde
134.1 (CAryl), 129.0 (CAryl), 126.9 (CAryl), 125.0 (CAryl),
115.4 (CAryl), 34.4 (CMe3), 31.3 (CMe3), 29.1 (CHMe2),
26.2 (CHMe2), 23.9 (CHMe2). Anal. Calc. for
C21H29AlCl2N2: C, 61.92; H, 7.18; N, 6.88. Found: C,
59.70; H, 7.97; N, 6.32%.
[20,27]. Deprotonation of HL proceeds cleanly with
alkali metal alkyl or hydride, affording the correspond-
ing metal derivatives. For instance, addition of a
solution of HL in THF to NaH suspended in THF at
ꢁ35 8C afforded LNa(THF) (1, Scheme 2) quantita-
/

138
L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á142
/
Table 1
Crystallographic data for compounds 3
/
6
Á
3
4
5
6
Formula
C
29H49Cl4LiN2O2Zr
697.66
0.52ꢃ
C29H49Cl4LiN2O2Hf
784.93
C21H29AlCl2N2
407.36
C23H35AlN2
366.52
M
Crystal size (mm3)
Crystal system
Space group
Unit cell dimensions
/
0.30ꢃ
/
0.08
0.38ꢃ/0.28ꢃ/0.14
0.4ꢃ/0.4ꢃ/0.8
0.4ꢃ
/
0.6ꢃ0.8
/
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/n
Orthorhombic
P21/n
˚
a (A)
10.874(2)
14.363(3)
23.036(5)
93.56(3)
3590.9(13)
4
10.8405(7)
14.3285(9)
23.0097(15)
93.4160(10)
3567.7(4)
4
10.218(2)
18.428(2)
13.044(2)
108.04(2)
2335.3(7)
4
16.166(2)
16.422(2)
8.760(2)
90.0
˚
b (A)
˚
c (A)
g (8)
3
V (A )
˚
2325.4(7)
4
1.047
Z
Dcalc (g cmꢁ3
2umax (8)
T (K)
)
1.159
55.04
1.461
55.04
1.159
52.0
52.0
298(2)
150(2)
Bruker SMART 1000 CCD Bruker SMART 1000 CCD Rigaku AFC7S
150(2)
298(2)
Diffractometer
Total reflections
Independent reflections
Tmax, Tmin
Rigaku AFC7S
2625
2625
22256
8177
0.9486, 0.6712
12665
7786
5015
4747
0.9486, 0.7683
3.249
1.0000, 0.9787
3.22
0.030
1.0000, 0.9784
0.95
Absorption coefficient/mmꢁ1 0.630
Rint
Goodness-of-fit
0.0596
0.815
0.0383
1.006
1.68
1.60
Final R indices [I ꢀ
R indices (all data)
/
2s(I)]
R1ꢀ
/
0.0408, wR2ꢀ
/
0.0581
R1ꢀ
/
0.0325, wR2ꢀ
/
0.0657
R1ꢀ
/
0.0506, wR2ꢀ
/
0.0749 R1ꢀ
/
0.0407, wR2ꢀ
/
0.0529
0.0688
R1ꢀ
/
0.0949, wR2ꢀ
/
0.0640
R1ꢀ
/
0.0639, wR2ꢀ
/
0.1047
R1ꢀ
/
0.1444, wR2ꢀ
/
0.0947 R1ꢀ
/
0.1390, wR2ꢀ
/
Scheme 2.

L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á
/
142
139
tively as colorless crystals. The reaction of HL with n-
BuLi gave what we formulated as LiL (2), which proved
to be a useful starting material for metathesis reactions
with metal chlorides.
Treatment of one equivalent of 2 to ZrCl4 suspended
in Et2O at ꢁ35 8C led to the formation of large yellow
/
crystals after standard work-up. An X-ray study of a
single crystal showed it to be an ‘ate’ complex ZrLCl2(m-
Cl)2Li(OEt2)2 (3). The hafnium analogue, HfLCl2(m-
Cl)2Li(OEt2)2 (4), was synthesized accordingly and
structurally characterized. Attempts to prepare the bis-
pyrrolylaldiminate complexes of Zr and Hf were not
successful, likely as a reflection of the steric size of the
ligand. This result is consistent with those reported by
Bochmann et al. that the less sterically demanding
pyrrolylaldiminate ligand [2-C4H3N(CHÄ
/
NC6Hi3Pr2)]ꢁ
forms bis-chelate complexes of Zr [20] and those
reported by Fujita et al. [18] that Ti complexes readily
Fig. 2. Molecular structure of HfLCl2(m-Cl)2Li(OEt2)2 (4).
adopt two [2-C4H3N(CHÄ
/
NC6H5)]ꢁ ligands that are
[20] and [2-C4H3N(CHÄ
/
NC6H5)]2TiCl2 (75.868 average)
Npyrrole are
shorter (by about 0.05 A in both 3 and 4) than those
of MÁNimine, consistent with the formally anionic
feature of the former donor. The bond distances of
MÁClbridging are slightly longer than those of MÁ
sterically much smaller. The reaction of 2 (one or two
equivalents) with TiCl4 under the condition similar to
those for 3 and 4 led to intractable materials that cannot
be identified so far.
[18]. As expected, the distances of MÁ
/
˚
/
The X-ray structures of 3 and 4 are shown in Figs. 1
and 2, respectively. Crystallographic details are sum-
marised in Table 1, and selected bond lengths and angles
for 3 and 4 are listed in Tables 2 and 3, respectively. The
two structures resemble each other closely; both are
found to have a six-coordinate metal center surrounded
by one bidentate pyrrolylaldiminate ligand and four
chlorine atoms in a distorted octahedral structure. The
pyrrolylaldiminate bite angles of 76.58(9)8 in 3 and
77.9(2)8 in 4 are far smaller than the ideal 908 for an
octahedral structure, but larger than those found in [2-
/
/
Clterminal. The five-membered metallacycles are virtually
planar. The diisopropylphenyl ring is nearly perpendi-
cular to the metallacycle plane. For both 3 and 4, the
coordination sphere is found to be more open on the
tert-butyl substituted pyrrole side than the arylated
imine part, as evidenced by, for example, the C(5)Á
N(1)ÁZr(1) angle being about 10.48 larger than C(10)Á
N(2)ÁZr(1). The lithium atom is separated from the
/
/
/
/
metal center at a distance that no chemical bonding is
possible. The lithium atoms in 3 and 4 are both distorted
from the ideal tetrahedral with angles ranging from ca.
C4H3N(CHÄ
NC6Hi3Pr2)]2Zr(NMe2)2 (70.168 average)
/
Table 2
˚
Selected bond lengths (A) and bond angles (8) for ZrLCl2(m-
Cl)2Li(OEt2)2 (3)
Bond lengths
Zr(1)Á
Zr(1)Á
Zr(1)Á
Zr(1)Á
/
N(1)
Cl(3)
Cl(4)
Li(1)
2.221(2)
Zr(1)Á
/
N(2)
Cl(1)
Cl(2)
2.273(2)
2.4313(10)
2.4819(10)
/
2.4104(10) Zr(1)Á
2.4784(9)
3.485(6)
/
/
Zr(1)Á
/
/
Bond angles
N(1)ÁZr(1)Á
N(2)ÁZr(1)Á
N(2)ÁZr(1)Á
N(1)ÁZr(1)Á
Cl(3)ÁZr(1)Á
N(1)ÁZr(1)ÁCl(2)
Cl(3)ÁZr(1)Á
Cl(4)ÁZr(1)Á
Li(1)ÁCl(2)Á
C(5)ÁN(1)ÁZr(1)
/
/
N(2)
Cl(3)
Cl(1)
Cl(4)
76.57(9)
92.46(6)
92.09(6)
159.69(7)
93.83(4)
113.05(7)
88.34(3)
87.23(3)
N(1)Á
N(1)Á
Cl(3)Á
N(2)ÁZr(1)Á
Cl(1)ÁZr(1)Á
N(2)ÁZr(1)ÁCl(2)
Cl(1)ÁZr(1)ÁCl(2)
Cl(4)ÁLi(1)Á
Cl(4)Á
C(10)ÁN(2)Á
/
Zr(1)Á
Zr(1)Á
Zr(1)Á
Cl(4)
Cl(4)
/
Cl(3)
87.97(7)
85.77(7)
/
/
/
/Cl(1)
/
/
/
/Cl(1)
171.21(3)
83.14(6)
/
/
/
/
/
/
Cl(4)
/
/
94.19(4)
/
/
/
/
170.37(6)
88.43(3)
/
/
Cl(2)
Cl(2)
/
/
/
/
/
/Cl(2)
89.47(18)
90.65(13)
132.66(18)
/
/
Zr(1)
90.17(13) Li(1)Á
143.0(2)
/
/Zr(1)
/
/
/
/Zr(1)
Fig. 1. Molecular structure of ZrLCl2(m-Cl)2Li(OEt2)2 (3).

140
L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á142
/
Table 3
considerable yield. The dichloride complex 5 does not
react with the dimethyl complex 6 under the condition
employed. Compound 6 is thermally stable; no decom-
position was observed when a C6D6 solution was heated
at 80 8C for 72 h.
The solid-state structures of 5 and 6 were also
determined by X-ray crystallographic studies. The
ORTEP diagrams are presented in Figs. 3 and 4, and
selected bond lengths and angles are listed in Tables 4
and 5. Crystals of 5 were grown from a concentrated
˚
Selected bond lengths (A) and bond angles (8) for HfLCl2(m-
Cl)2Li(OEt2)2 (4)
Bond lengths
Hf(1)Á
Hf(1)Á
Hf(1)Á
Hf(1)Á
/
N(1)
Cl(1)
Cl(2)
Li(1)
2.214(6)
2.403(2)
Hf(1)Á
/
N(2)
Cl(3)
Cl(4)
2.262(6)
2.4236(19)
2.4660(18)
/
Hf(1)Á
/
/
2.4662(19) Hf(1)Á
3.458(12)
/
/
Bond angles
N(1)ÁHf(1)Á
N(2)ÁHf(1)Á
N(2)ÁHf(1)Á
N(1)ÁHf(1)Á
Cl(1)ÁHf(1)Á
N(1)ÁHf(1)ÁCl(4)
Cl(1)ÁHf(1)Á
Cl(2)ÁHf(1)Á
Li(1)ÁCl(2)Á
C(5)ÁN(1)ÁHf(1)
/
/
N(2)
Cl(1)
Cl(3)
Cl(2)
77.9(2)
N(1)Á
/
Hf(1)Á
Hf(1)Á
92.26(15) Cl(1)ÁHf(1)Á
111.01(17) N(2)ÁHf(1)ÁCl(2)
88.21(8) Cl(3)ÁHf(1)ÁCl(2)
161.45(17) N(2)ÁHf(1)ÁCl(4)
Cl(3)ÁHf(1)ÁCl(4)
Cl(4)ÁLi(1)Á
Li(1)ÁCl(4)Á
C(10)ÁN(2)Á
/
Cl(1)
88.10(16)
85.95(15)
171.62(7)
171.10(15)
88.43(7)
83.59(15)
93.82(7)
89.6(4)
/
/
92.25(15) N(1)Á
/
/Cl(3)
toluene solution at ꢁ35 8C, while those of 6 from
/
/
/
/
/
Cl(3)
/
/
/
/
diethyl ether. As depicted in Figs. 3 and 4, both are
found to be monomeric, four-coordinate species with
the aluminum center in a distorted tetrahedral structure.
The pyrrolylaldiminate bite angles of 88.2(2)8 in 5 and
85.5(2)8 in 6 are far smaller than the ideal tetrahedral
angle (109.478), but notably larger than those found in
the tetrahedral bis-pyrrolylaldiminate complexes of Mg
(84.728 average) [17] and Fe (81.898 average) [20]. The
/
/Cl(2)
/
/
/
/
/
/
/
/Cl(4)
93.71(7)
87.51(6)
90.0(3)
/
/
/
/Cl(4)
/
/Cl(2)
/
/Hf(1)
/
/Hf(1)
90.1(3)
/
/
144.6(5)
/
/
Hf(1)
132.9(4)
898 to 1248, the most acute being associated with the two
bridging chlorine atoms.
Cl(1)Á
typical for a tetrahedral structure, whereas the C(1)Á
Al(1)ÁC(2) angle of 115.7(4)8 in 6 is wider. This result is
/
Al(1)ÁCl(2) angle of 110.85(9)8 in 5 is essentially
/
/
The metathesis reaction of 2 with AlCl3 in toluene
produced red crystalline AlLCl2 (5) in 88% yield. Again,
attempts to synthesize the bis-pyrrolylaldiminate deri-
vatives were not successful. Addition of two equivalents
of 2 to AlCl3 led to 5 as the only isolable product, which
/
consistent with the Bent’s rule [28] that the more
electronegative chlorine atoms in 5 prefer the hybrid
orbitals of Al having less s character, thereby resulting
in a smaller bond angle (electronegativity: Cl 3.16, C
˚
Cl distance of 2.11 A in 5 is
is in contrast to the formation of [2-C4H3N(CHÄ
/
2.55) [29]. The averaged AlÁ
/
NC6Hi3Pr2)]2AlCl [17] where less sterically demanding
pyrrolylaldiminate ligand is employed. No reaction was
observed between 5 and 2, even under forcing condi-
tions. Alkylation of 5 proceeds smoothly. Treatment of
two equivalents of MeMgBr or MeLi to 5 afforded
AlLMe2 (6) as pale yellow crystals in 80% yield.
Attempts to prepare AlLMeCl by reactions of 5 with
one equivalent of MeMgBr led to the isolation of 6 in
comparable to the averaged AlÁ
/
Clterminal distance of
˚
˚
Me distances in 6 (1.943 A
2.07 A in Al2Cl6 [30]. The AlÁ
/
average) also compare well with the AlÁMeterminal
/
˚
distances in Al2Me6 (1.97 A average) [30]. Remaining
parameters of 5 and 6 are unexceptional or similar to
those observed for 3 and 4.
The solution NMR data of 3-6 are all consistent with
the corresponding solid-state structures. The imine
Fig. 3. Molecular structure of AlLCl2 (5).

L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á
/
142
141
Fig. 4. Molecular structure of AlLMe2 (6).
proton of the pyrrolylaldiminate ligand is shifted upfield
as compared to that of HL, whereas the aromatic
hydrogen atoms on the pyrrole ring show downfield
shift. The isopropyl methyl groups are diastereotopic in
each compound, likely as a consequence of restricted
lylaldiminate ligand is demonstrated. As a result, the
Group 4 chemistry described here is in contrast to that
found in a closely related system reported by Bochmann
et al [20]. The X-ray structural analyses of the aluminum
derivatives 5 and 6 show them to be monomeric four-
coordinate species. Further studies directed to the
synthesis of other pyrrolylaldiminate derivatives and
the application of these compounds on catalysis are
currently underway.
rotation about the NÁCipso bond [31]. A variable-
/
temperature NMR study of 6 in C6D6 indicates that
the two doublet resonances for the diastereotopic
CHMe2 groups do not show the propensity to exchange
at temperatures below 80 8C. Room temperature NMR
spectra of 6 are consistent with a molecule having a Cs
symmetry as two chemically equivalent AlÁMe groups
/
are observed.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 205820 for 3, 205818 for 4,
205819 for 5 and 205817 for 6. Copies of this informa-
tion may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
4. Conclusion
We have prepared and structurally characterized a
variety of mono-pyrrolylaldiminate complexes. The
steric significance of the tert-butyl group in the pyrro-
Table 4
Table 5
˚
˚
Selected bond lengths (A) and bond angles (8) for AlLCl2 (5)
Selected bond lengths (A) and bond angles (8) for AlLMe2 (6)
Bond lengths
Bond lengths
Al(1)Á
Al(1)Á
N(1)Á
N(2)Á
C(1)Á
/
Cl(1)
N(1)
2.111(2)
1.911(4)
1.319(5)
1.392(6)
1.394(7)
Al(1)Á
Al(1)Á
N(1)Á
N(2)Á
/
Cl(2)
N(2)
2.102(2)
1.867(4)
1.439(6)
1.368(6)
Al(1)Á
Al(1)Á
N(1)Á
N(2)Á
C(3)Á
/
N(1)
1.976(4)
1.950(7)
1.303(7)
1.408(6)
1.390(7)
Al(1)Á
Al(1)Á
N(1)Á
N(2)Á
/
N(2)
1.923(4)
1.936(7)
1.446(7)
1.362(6)
/
/
/C(1)
/C(2)
/
C(1)
/
C(11)
/
C(3)
/
C(12)
/
C(2)
/
C(5)
/
C(4)
/
C(7)
/
C(2)
/
C(4)
Bond angles
Cl(1)ÁAl(1)Á
Cl(1)ÁAl(1)Á
Cl(2)ÁAl(1)Á
Al(1)ÁN(1)Á
Bond angles
N(1)ÁAl(1)Á
N(1)ÁAl(1)Á
N(2)ÁAl(1)Á
Al(1)ÁN(1)Á
/
/
Cl(2)
N(2)
N(2)
110.85(9)
117.5(1)
115.3(1)
131.4(3)
Cl(1)Á
Cl(2)Á
N(1)ÁAl(1)Á
Al(1)ÁN(2)Á
/
Al(1)Á
/
N(1)
108.8(2)
114.2(1)
88.2(2)
/
/
N(2)
C(2)
C(2)
C(12)
85.5(2)
112.6(2)
112.8(3)
131.1(3)
N(1)Á
N(2)Á
C(1)ÁAl(1)Á
Al(1)ÁN(2)Á
/
Al(1)Á
/
C(1)
C(1)
C(2)
109.8(3)
116.7(3)
115.7(4)
144.6(4)
/
/
/Al(1)Á
/
N(1)
/
/
/Al(1)Á
/
/
/
/
/
N(2)
C(5)
/
/
/
/
/
/
C(11)
/
/
145.1(3)
/
/
/
/
C(7)

142
L.-C. Liang et al. / Journal of Organometallic Chemistry 679 (2003) 135Á142
/
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Acknowledgements
We thank the National Science Council (NSC 91-
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