Neutral and cationic aluminium complexes of a sterically demanding N-imidoylamidine ligand

Article abstract of DOI:10.1039/b513531a

The N-imidoylamidine ligand i-Pr₂C₆H ₃N(C(Me)NC₆H₃i-Pr₂)₂ 2 was prepared. Direct reactions with AlI₃ or AlMe₃ afforded [(i-Pr₂C₆H

Full text of DOI:10.1039/b513531a

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www.rsc.org/dalton | Dalton Transactions
Neutral and cationic aluminium complexes of a sterically demanding
N-imidoylamidine ligand†
Jason D. Masuda and Douglas W. Stephan*
Received 23rd September 2005, Accepted 24th January 2006
First published as an Advance Article on the web 3rd February 2006
DOI: 10.1039/b513531a
The N-imidoylamidine ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2 was prepared. Direct
reactions with AlI3 or AlMe3 afforded [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlI2][AlI4] 3 and
[i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4]·AlMe3 4, respectively. Thermolysis of 4 gave
=
(i-Pr2C6H3NC( CH2)(NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe2 6. Subsequent reaction with B(C6F5)3
=
gave the zwitterionic species [(i-Pr2C6H3)N(C( CH2)NC6H3i-Pr2)(C(Me)NC6H3i-
Pr2)AlMe(l-MeB(C6F5)3)] 7. In a related reactions of 2, [Ph3C][B(C6F5)4] and AlMe3, AlH3·NEtMe2 or
AlD3·NMe3, the complexes [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlR2][B(C6F5)4] (R = Me 5, H 8, D 9)
=
and [(i-Pr2C6H3)N(C( CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlH][B(C6F5)4] 10 are formed.
Single-crystal X-ray data for 2, 3, 5 and 10 are reported.
bulky ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 and its use in the
formation of Al-based alkyl and hydride cations.
Introduction
Sterically demanding chelating ligands continue to garner much
attention (Scheme 1). For example, neutral, diimine-based lig-
ands, have proven to be effective in the development of late
transition-metal olefin polymerization catalysts.1,2 Employing the
bulky ligand HC(C(Me)NC6H3i-Pr2)2, Roesky and co-workers
have recently isolated and characterized the first monomeric
Al(I) complex3 while Power and co-workers have prepared the
related Ga(I) system.4 Mindiola and co-workers have used this
ligand to isolate the first Ti–phosphinidene complex.5 Recent
efforts in our laboratory have focused on developing new bulky
ligand systems and exploiting their chemistries with both late
transition metals6–8 and main-group elements.9 For example,
we have recently reported the use of the bulky phosphin-
imineimine ligand (i-Pr2C6H3N)C(Me)CHPPh2(NC6H3i-Pr2) to
prepare neutral and cationic Al-complexes.9 Similar complexes
based on the ligand (i-Pr2C6H3N)C6H4PPh2(NC6H3i-Pr2) were
simultaneously developed by Welch et al.10 In keeping with
this theme, we have developed a route to a sterically demand-
ing N-arylimidoylamidine ligand. Although there are several
examples of metal complexes involving the N-imidoylamidine
systems (HN(C(R)NH)2)11–19 and the related 2,2ꢀ-dipyridylamino
ligand,20–30 a search of the literature shows only three previous
examples of N-arylimidoylamidine ligand complexes.31–33 Cotton
et al.31 isolated the cobalt complex [PhNCHN(Ph)CHNPh]CoCl2
via a serendipitous route while Uson et al.33 arylated the parent lig-
and to give [(4-MePh)NCHN(4-MePh)(4-MePh)NC]Pd(C6F5)2.
Finally, Wilkinson and co-workers32 isolated the iridium com-
plexes (C5Me5)Ir[N(2,6-MeC6H3)CHNRCNC6H3(Me)CH2] (R =
t-Bu, 2,6-i-PrC6H3) from the reaction of (C5Me5)IrNR with
2,6-MeC6H3NC. In this manuscript we report the synthesis of
Scheme 1 Bulky chelating ligand complexes.
Experimental
General data
All preparations were done under an atmosphere of dry, O2-
free N2 employing both Schlenk-line techniques and a Vacuum
Atmospheres inert atmosphere glove box. Solvents were purified
employing a Grubbs’ type solvent purification system manu-
factured by Innovative Technology. Deuterated solvents were
purified using the appropriate techniques. All organic reagents
1
1
were purified by conventional methods. 1H, 2D, 11B{ H}, 19F{ H},
1
1
27Al{ H} and 13C{ H} NMR spectra were recorded on Bruker
Avance-300 and 500 spectrometers. All spectra were recorded
in C6D6 at 25 ◦C unless otherwise noted. Trace amounts of
protonated solvents were used as references and chemical shifts are
1
1
1
reported relative to SiMe4. 11B{ H}, 19F{ H} and 27Al{ H} NMR
spectra were referenced to external BF3·Et2O, CFCl3 and AlCl3
in H2O, respectively. Combustion analyses were done in house
employing a Perkin Elmer CHN Analyzer. AlH3·NEtMe2, NEt3
and i-Pr2C6H3NH2 were purchased from the Aldrich Chemical
Co. AlD3·NMe3 was prepared by analogy to literature methods.34
Efforts to acquire 27Al NMR spectra for 4–10 were unsuccessful.
Department of Chemistry & Biochemistry, University of Windsor, Windsor,
Ontario, Canada N9B3P4. E-mail: stephan@uwindsor.ca
Synthesis of [Bu4N][AlMe4]. To a stirring solution of AlMe3
(0.100 g, 1.39 mmol) in 5 mL toluene cooled to −35 ◦C was added
an equivalent of MeLi (0.867 mL of a 1.6 M solution in Et2O).
† Electronic supplementary information (ESI) available: Fig. S1: 1H
=
NMR Spectrum of [(i-Pr2C6H3N(C( CH2)NC6H3i-Pr2)(C(Me)NC6H3i-
Pr2)AlH][B(C6F5)4]. See DOI: 10.1039/b513531a
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2089–2097 | 2089
©

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3
The mixture was allowed to warm to room temperature over 1 h.
Upon cooling again to −35 ◦C, a mixture of Bu4NCl (0.386 g,
1.39 mmol) in 5 mL toluene was added. The stirring mixture was
again allowed to warm to room temperature causing the formation
of a white oil. The toluene was decanted, the oil was then dissolved
in 10 mL of CH2Cl2 and filtered through Celite. The solvent was
then removed under vacuum leaving a colorless oil. Addition of
15 mL pentane and sonication of the mixture gave 0.391 g of a
white solid upon filtration. Yield: 85% 1H NMR (C6D5Br): d 2.80
(t, 8H, CH2, 3JH–H = 7 Hz), 1.34 (m, 8H, CH2), 1.22 (m, 8H, CH2),
d 7.23–7.41 (m, 9H, m, p-Ar), 2.85 (sept, 4H, JH–H = 7 Hz,
CH(CH3)2), 2.77 (sept, 2H, 3JH–H = 7 Hz, i-Pr), 1.70 (s, 6H, Me),
1.37 (d, 12H, 3JH–H = 7 Hz, i-Pr), 1.25 (d, 12H, 3JH–H = 7 Hz, i-Pr),
1.08 (d, 12H, 3JH–H = 7 Hz, i-Pr), −0.07 (br s, 21H, AlMe), −0.68
(s, 6H, AlMe2). 13C{ H} NMR (C6D5Br) (partial): d 171.5, 143.7,
1
141.4, 135.0, 133.2, 129.0–131.3 (m, obscured by C6D5Br), 127.0,
125.9–126.5 (m, obscured by C6D5Br), 28.7, 28.5, 24.6, 24.4, 24.1,
23.5, −4.0, −9.9. Anal. Calc. for C49H84N3Al3: C, 73.92; H, 10.63;
N, 5.28. Found: C, 74.07; H, 10.56; N, 5.33%.
=
Synthesis
of
(i-Pr2C6H3NC( CH2)(NC6H3i-Pr2)(C(Me)-
1
0.88 (t, 12H, CH3, 3JH–H = 7 Hz), 0.54 (br m, 12H, AlMe4). 13C{ H}
NC6H3i-Pr2)AlMe2 6. In 5 mL of toluene, 2 (0.300 g, 0.52 mmol)
and AlMe3 (0.037 g, 0.52 mmol) were combined. Upon refluxing
overnight the solution became dark yellow. Removal of volatiles
in vacuo gave a yellow solid that was dissolved in hot pentane.
Upon cooling to −35 ◦C overnight 0.264 g of yellow blocks of 6
were collected by filtration. Yield: 80% 1H NMR: d 7.03–7.37 (m,
9H, m, p-Ar), 3.97 (sept, 2H, CH, JH–H = 7 Hz), 3.60 (sept, 2H,
CH, JH–H = 7 Hz), 3.46 (sept, 2H, CH, JH–H = 7 Hz), 2.93 (d, 1H,
2JH–H = 2 Hz, CH2), 2.66 (d, 1H, 2JH–H = 2 Hz, CH2), 1.57 (d, 6H,
i-Pr, JH–H = 7 Hz), 1.47 (d, 12H, i-Pr, JH–H = 7 Hz), 1.46 (3H, Me),
1.37 (d, 6H, iPr, JH–H = 7 Hz), 1.23 (d, 6H, i-Pr, JH–H = 7 Hz), 1.14
NMR (C6D5Br): d 58.5, 23.6, 19.6, 13.6, −3.2 (1 : 1 : 1 : 1 : 1 : 1
1
sextet, AlMe4, 1JAl–C = 70 Hz). 27Al{ H} NMR (C6D5Br): d 153.8
(sharp singlet). Anal. Calc. for C20H48NAl: C, 72.88; H, 14.68; N,
4.25. Found: C, 73.04; H, 14.74; N, 4.29%.
Synthesis of i-Pr2C6H3NC(Me)Cl 1. This was prepared via
the literature method35 but was purified by distillation (80–85 ◦C,
1
0.5 mm) to give a yellow oil. H NMR: d 7.08–7.22 (m, 3H, m,
p-Ar), 2.97 (sept, 2H, CH, JH–H = 7 Hz), 2.17 (3H, Me), 1.18–1.28
(br m, 12H, i-Pr, JH–H = 7 Hz).
Synthesis of i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2. To a solution
of i-Pr2C6H3NH2 (2.30 g, 13.0 mmol) and 2.63 g of NEt3
(25.9 mmol) in 100 mL of toluene was added 6.17 g of 1
(25.9 mmol), whereupon a white precipitate formed. The mixture
was refluxed for 2.5 h and allowed to cool. The material was then
washed 5 × 100 mL H2O, the organic layer dried with MgSO4,
filtered and solvent removed under vacuum to give a white solid.
Recrystallization from ethanol gave 5.23 g of colorless crystals.
(d, 6H, i-Pr, JH–H = 7 Hz), −0.41 (6H, AlMe). 13C{ H} NMR
1
(partial): d 165.9, 156.1, 147.1, 145.9, 143.8, 142.0, 139.4, 138.6,
129.8, 127.7–129.1, 126.2, 125.1, 125.0, 124.6, 123.9, 75.2 (CH2),
28.4, 28.3, 26.5, 25.7, 25.6, 25.0, 24.9, 23.8, 23.7, −8.7 (AlMe).
Anal. Calc. for C42H62N3Al: C, 79.32; H, 9.83; N, 6.61. Found: C,
79.54; H, 10.16; N, 6.79%.
=
Synthesis of [(i-Pr2C6H3)N(C( CH2)NC6H3i-Pr2)(C(Me)-
1
Yield: 70% H NMR: d 7.18–7.29 (m, 9H, m, p-Ar), 3.60 (sept,
NC6H3i-Pr2)AlMe(l-MeB(C6F5)3)] 7. To
a solution of 6
2H, CH, JH–H = 7 Hz), 3.19 (sept, 4H, CH, JH–H = 7 Hz), 2.05
(0.100 g, 0.157 mmol) in 5 mL of toluene was added 0.080 g of
B(C6F5)3 (0.157 mmol) in 3 mL toluene. The solution was allowed
to stir overnight giving a light tan colored solution. The toluene
was removed in vacuo and 15 mL of pentane was added, followed
by sonication for 30 min. The resulting colorless powder was
then washed 3 × 5 mL pentane and dried under vacuum to give
0.086 mg of product. Yield: 48%. 1H NMR (C6D5Cl): d 7.03–7.27
(m, 9H, m, p-Ar), 3.17 (br sept, 2H, CH, JH–H = 7 Hz), 2.98
(6H, Me), 1.37 (d, 12H, i-Pr, JH–H = 7 Hz), 1.36 (d, 12H, i-Pr,
1
JH–H = 7 Hz), 1.21 (d, 12H, i-Pr, JH–H = 7 Hz). 13C{ H} NMR: d
158.3, 148.5, 145.6, 139.0, 137.8, 129.4, 124.8, 124.1, 123.8, 29.8,
28.7, 25.1, 24.4, 23.3, 19.9. Anal. Calc. for C40H57N3: C, 82.85; H,
9.91; N, 7.25. Found: C, 82.71; H, 9.65; N, 7.12%.
Synthesis of [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlI2][AlI4] 3.
To a solution of 2 (0.100 g, 0.172 mmol) in 10 ml toluene was
added AlI3 (0.142 g, 0.344 mmol). The AlI3 slowly dissolved and
a precipitate began to form. After 3 days of stirring, the solvent
was decanted off and the remaining solids washed with 3 × 5 mL
pentane. The colorless solid was dried in vacuo to give 0.175 g of
3. Yield: 73%, X-ray quality crystals were grown from a solution
in THF layered with toluene. 1H NMR (CD2Cl2): d 7.13–7.82 (m,
9H, m, p-Ar), 3.20 (sept, 4H, CH, JH–H = 7 Hz), 3.02 (sept, 2H,
CH, JH–H = 7 Hz), 2.19 (6H, Me), 1.48 (d, 12H, i-Pr, JH–H = 7 Hz),
1.37 (d, 12H, i-Pr, JH–H = 7 Hz), 1.22 (d, 12H, i-Pr, JH–H = 7 Hz).
2
2
(d, 1H, JH–H = 3 Hz, CH2), 2.81 (d, 1H, JH–H = 3 Hz, CH2),
2.77 (br sept, 4H, CH, JH–H = 7 Hz), 1.42 (3H, Me), 1.11–1.18
(m, 39H, i-Pr, Al–Me–B), −0.81 (br s, AlMe). 13C{ H} NMR
1
(partial, C6D5Cl): d 171.5, 152.9, 151.0, 147.7, 147.1, 144.5, 143.0,
139.2, 136.1, 134.6, 132.1, 131.0, 128.0–129.7 (m, obscured by
C6D5Cl), 125.7–126.2 (m, obscured by C6D5Cl), 125.2, 30.6, 29.4,
25.6, 25.5, 24.9, 24.5, 24.0, 23.6, 23.2. 11B{ H} NMR (C6D5Cl):
1
d −14.7. 19F{ H} NMR (C6D5Cl): d 138.6 (br s), −171.4 (br s),
1
−173.8 (br s). Anal. Calc. for C60H62N3AlBF15: C, 62.78; H, 5.44;
1
13C{ H} NMR (CD2Cl2): d 176.0, 144.4, 142.7, 134.8, 131.9, 129.6,
N, 3.66. Found: C, 62.75; H, 5.60; N, 3.78%.
1
128.7, 128.5, 127.5, 30.6, 29.8, 26.3, 26.2, 25.2, 25.0. 27Al{ H}
Synthesis of [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlR2][B(C6F5)4]
(R = Me 5, H 8, D 9). These compounds were prepared in
a similar fashion and thus only one preparation is detailed.
To a solution of 2 (0.100 g, 0.17 mmol) and AlMe3 (0.012 g,
0.17 mmol) in 4 mL toluene was slowly added [Ph3C][B(C6F5)4]
(0.159 g, 0.17 mmol). The resulting orange colored solution
became colorless after stirring overnight. Layering the solution
with pentane gave 0.203 g of colorless blocks which were isolated
by decantation. The crystals were washed 3 × 10 mL of pentane
and dried in vacuo. Yield: 89% 5: 1H NMR (C6D5Cl): d 7.00–7.31
NMR (CD2Cl2): d −27.3. Anal. Calc. for C40H60Al2I6N3·0.5THF:
C, 35.22; H, 4.36; N, 2.93. Found: C, 35.30; H, 4.42; N, 2.86%.
Synthesis of [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4]·
AlMe3 4. To a solution of 2 (0.200 g, 0.35 mmol) in 10 mL
of pentane was added AlMe3 (0.075 g, 1.03 mmol) in 15 mL
pentane. The mixture was allowed to stir overnight, resulting in the
formation of a white precipitate. The solution was decanted, the
solids washed with 2 × 5 mL pentane and dried under vacuum to
1
give 0.243 g of white powder. Yield: 88% H NMR (C6D5Br):
2090 | Dalton Trans., 2006, 2089–2097
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(m, 9H, m, p-Ar), 2.68 (sept, 4H, CH, JH–H = 7 Hz), 2.61 (sept,
C6D5Br) (partial): d 165.3, 154.8, 147.1, 145.3, 143.5, 139.7, 137.5,
137.3, 129.3–131.4 (m, obscured by C6D5Br), 126.1–126.6 (m,
obscured by C6D5Br), 126.0, 124.4, 74.3, 29.1, 28.4, 28.0, 25.9,
2H, CH, JH–H = 7 Hz), 1.76 (s, 6H, Me), 1.17 (d, 12H, i-Pr, JH–H
=
=
7 Hz), 1.04 (d, 12H, i-Pr, JH–H = 7 Hz), 0.90 (d, 12H, i-Pr, JH–H
1
1
7 Hz), −0.84 (s, 6H, AlMe). 13C{ H} NMR (partial, C6D5Cl):
d 171.8, 150.6 (br), 149.4, 147.4 (br), 144.3, 141.4, 135.5, 134.2,
133.2, 130.5, 128.0–129.7 (m, obscured by C6D5Cl), 127.0, 125.7–
126.2 (m, obscured by C6D5Cl), 30.6, 29.0, 28.8, 24.6, 24.4, 24.0,
25.6, 25.5, 25.2, 24.6, 23.9, 22.5. 11B{ H} NMR (C6D5Br): d
1
−16.6. 19F{ H} NMR (C6D5Br): d −132.2 (br s), −162.8 (d of d,
3JF–F = 23 Hz), −166.6 (br d of d, 3JF–F = 17 Hz).
23.5, −9.8 (AlMe2). 11B{ H} NMR (C6D5Cl): d −16.5. 19F{ H}
NMR (C6D5Cl): d −133.8 (br s), −164.7 (d of d, 3JF–F = 23 Hz),
−168.4 (d of d, 3JF–F = 17 Hz). Anal. Calc. for C66H63N3AlBF20:
C, 60.24; H, 4.82; N, 3.19. Found: C, 60.70; H, 4.96; N, 3.28%. 8:
1H NMR (C6D5Br): d 7.02–7.31 (m, 9H, m, p-Ar), 3.80 (br s, 2H,
Al–H, Dm1/2 = 50 Hz), 2.76 (sept, 4H, CH, JH–H = 7 Hz), 2.60 (sept,
1
1
Kinetic studies
In a typical kinetic experiment 4 or 5 was weighed in an inert
atmosphere dry-box into a re-sealable NMR tube equipped with
a Teflon screw cap. The appropriate amounts of C6D6, AlMe3
and/or [Bu4N][AlMe4] were then measured into the NMR tube
to give [4]0 of approximately 0.075 mol L−1. The NMR tube
was sealed and shaken to ensure proper mixing, and the kinetic
experiments were performed at temperatures between 313 and
353 K. Stochastic simulations were computed employing the
software Chemical Kinetics Simulator from IBM.36
2H, CH, JH–H = 7 Hz), 1.54 (6H, Me), 1.26 (d, 12H, i-Pr, JH–H
=
=
7 Hz), 1.13 (d, 12H, i-Pr, JH–H = 7 Hz), 1.05 (d, 12H, i-Pr, JH-–H
1
7 Hz). 13C{ H} NMR (partial, C6D5Br): d 171.2, 150.2 (br s), 147.0
(br s), 143.6, 141.2, 139.8 (br s), 138.1, 136.7 (br s), 134.9 (br s),
133.3, 133.1, 132.8, 121.10–131.4 (m, obscured by C6D5Br), 128.2,
125.9–126.6 (m, obscured by C6D5Br), 124.8, 29.1, 28.9, 24.4, 24.0,
1
1
22.4. 11B{ H} NMR (C6D5Cl): d −16.6. 19F{ H} NMR (C6D5Br):
X-Ray data collection and reduction
3
d 132.2 (br s), −162.5 (d of d, JF–F = 19 Hz), −166.4 (br s). IR
Crystals were manipulated and mounted in capillaries in a
glove-box, thus maintaining a dry, O2-free environment for each
crystal. Diffraction experiments were performed on a Siemens
SMART System CCD diffractometer. The data were collected in
a hemisphere of data in 1448 frames with 10 s exposure times.
The observed extinctions were consistent with the space groups in
each case. The data sets were collected (4.5 < 2h < 45–50.0◦). The
intensities of reflections within these frames showed no statistically
significant change over the duration of the data collections. The
data were processed using the SAINT and XPREP processing
packages. An empirical absorption correction based on redundant
data was applied to each data set. Subsequent solution and
refinement was performed using the SHELXTL solution package.
Crystallography parameters are reported in Table 1.
(KBr pellet, cm−1): 1910, 1881. Anal. Calc. for C64H59N3AlBF20:
C, 59.68; H, 4.62; N, 3.26. Found: C, 59.63; H, 4.72; N, 3.33%. 9:
2D NMR (C6H5Cl): d 3.51 (br s). IR (KBr pellet, cm−1): 1310.
=
Synthesis of [(i-Pr2C6H3)N(C( CH2)NC6H3i-Pr2)(C(Me)-
NC6H3i-Pr2)AlH][B(C6F5)4] 10. During the work-up of 8, a
few crystals were removed from the side of the flask. Single-
crystal X-ray diffraction proved this to be the three-coordinate
aluminium hydride cation 10. This species was prepared in high
yield following the procedure described for the synthesis of 8
1
with the use of two equivalents of alane. H NMR (C6D5Br): d
6.84–7.91 (m, 9H, m, p-Ar), 3.95 (br s, AlH), 3.62 (sept, 2H, i-Pr,
3JH–H = 7 Hz), 3.31 (sept, 2H, i-Pr, 3JH–H = 7 Hz), 3.11 (sept, 2H,
i-Pr, 3JH–H = 7 Hz), 2.55 (d, 1H, 2JH–H = 2 Hz, CH2), 2.30 (d, 1H,
3
2JH–H = 2 Hz, CH2), 1.31 (s, 3H, Me), 1.30 (d, 6H, i-Pr, JH–H
7 Hz), 1.27 (d, 6H, i-Pr, 3JH–H = 7 Hz), 1.21 (d, 6H, i-Pr, 3JH–H
7 Hz), 1.20 (d, 6H, i-Pr, 3JH–H = 7 Hz), 1.10 (d, 6H, i-Pr, 3JH–H
=
=
=
Structure solution and refinement
Non-hydrogen atomic scattering factors were taken from the
literature tabulations.37 The heavy atom positions were determined
7 Hz), 1.05 (d, 6H, i-Pr, JH–H = 7 Hz). 13C{ H} NMR (partial,
3
1
Table 1 Crystallography parameters
2
3·0.5THF
5
10
Formula
Mr
C40H57N3
579.89
Monoclinic
P21/n
12.553(7)
16.399(9)
19.072(11)
104.309(11)
3804(4)
4
C42H61Al2I6N3O0.50
1431.30
Orthorhombic
P212121
14.196(7)
35.926(17)
10.613(5)
C42H62AlN3
635.93
Monoclinic
P21/c
10.503(6)
21.773(13)
18.101(10)
105.680(10)
3985(4)
4
C64H57AlBF20N3
1285.92
Orthorhombic
P212121
16.0619(19)
18.950(2)
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
20.586(2)
b/◦
3
˚
V/A
5413(4)
4
1.756
3.505
21314
7706
6266.0(13)
4
1.363
0.134
60173
11040
818
0.0569
0.1372
1.065
Z
Dc/g cm−3
l/mm−1
1.013
0.058
16070
5424
1.060
0.081
16803
5698
Data collected
2
2
Data Fo > 3r(Fo
)
Variables
R
Rw
GOF
388
483
423
0.0472
0.1085
0.769
0.0980
0.2286
1.060
0.0388
0.0883
0.803
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2089–2097 | 2091
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using direct methods employing the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from
successive difference Fourier map calculations. The refinements
were carried out by using full-matrix least-squares techniques
on F, minimizing the function w(Fo − Fc)2 where the weight w
is defined as 4Fo2/2r(Fo2) and Fo and Fc are the observed and
calculated structure factor amplitudes. In the final cycles of each
refinement, all non-hydrogen atoms were assigned anisotropic
temperature factors in the absence of disorder or insufficient data.
In the latter cases atoms were treated isotropically. C–H atom
positions were calculated and allowed to ride on the carbon to
˚
which they are bonded assuming a C–H bond length of 0.95 A.
H-Atom temperature factors were fixed at 1.10 times the isotropic
temperature factor of the C-atom to which they are bonded.
The H-atom contributions were calculated, but not refined. The
locations of the largest peaks in the final difference Fourier map
calculation as well as the magnitude of the residual electron
densities in each case were of no chemical significance.
CCDC reference numbers 284668–284671.
Fig. 1 ORTEP drawing of 2; 30% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Distances (A) and angles
˚
(◦): N(1)–C(39) 1.272(3), N(2)–C(37) 1.269(3), N(3)–C(39) 1.395(3),
N(3)–C(37) 1.435(3), C(39)–C(40) 1.514(3), C(37)–C(38) 1.505(3);
C(39)–N(3)–C(37) 120.44(19), N(2)–C(37)–N(3) 115.6(2), N(1)–C(39)–
N(3) 118.9(2), N(1)–C(39)–C(40) 124.7(2), N(3)–C(39)–C(40) 116.4(2),
N(2)–C(37)–C(38) 126.2(2), N(3)–C(37)–C(38) 118.0(2).
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b513531a
Results and discussion
environment. Upon cooling a CD2Cl2 solution of 2, the imine-Me
signals become broad, coalescing at −72 ◦C, and splitting into two
The N-imidoylamidine ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2
was synthesized by reacting two equivalents of imidoyl chloride
1 with 2,6-diisopropylaniline in the presence of Et3N in refluxing
toluene (Scheme 2). The reaction proceeds via an amidine inter-
mediate, which has been extensively investigated by Boere´ et al.35,38
Ligand 2 is soluble in a range of solvents from pentane to CH3CN,
but is most easily recrystallized from hexane or ethanol solutions.
In the solid state, the ligand adopts a non-planar arrangement
(Fig. 1). The N(1)–C(39)–N(3) plane forms an angle of 50.6◦
with the plane through N(2)–C(37)–N(3). The imine N(1)–C(39)
◦
signals at 1.44 and 2.20 ppm at −90 C. Similarly the signal for
the isopropyl methine protons broadened and split giving signals
at 2.60 and 2.93 ppm at −90 ◦C. These observations are consistent
with slowing rotation about the imine–N single bonds, with the
ligand adopting a trans configuration at low temperature. The DG‡
for this process was estimated at ∼9 kcal mol−1.
Reacting 2 with two equivalents of AlI3 in toluene afforded
the precipitation of the new product 3. The 27Al NMR spectra
of 3 gave a sharp singlet at −27.3 ppm corresponding to the
symmetric [AlI4] anion although no signal was observed for the
corresponding cation. Single crystals of 3 were grown from a
THF solution layered with toluene and crystallographic analysis
confirmed the formulation of 3 as [(i-Pr2C6H3N(C(Me)NC6H3i-
Pr2)2)AlI2][AlI4] 3 (Fig. 2). The six-membered chelate ring
formed by the ligand bound to AlI2 adopts a boat confor-
mation with the aluminium atom displaced from the ligand
˚
and N(2)–C(37) bond lengths are 1.272(3) and 1.269(3) A, respec-
tively, while the amine N(3)–C(39) and N(3)–C(37) bond lengths
are 1.395(3) and 1.435(3) A, respectively. The difference in the
˚
amine bond lengths can be attributed to the conformation of
the imine fragment with respect to the lone pair on the central
amine. The nearly planar C(1)–N(1)–C(39)–N(3)–C(25) confor-
mation allows the lone pair on the amine N(3) atom to delocalize
into the N(1)–C(39) imine p*-antibonding orbital, giving the
N(3)–C(39) bond partial double bond character. However, in
relation to the other half of the molecule, the N(3) atom is twisted
out of the plane of the N(2)–C(37) imine fragment, preventing this
˚
plane (0.637 A). The Al–I bond lengths of the diimine chelate
˚
(2.463(5) and 2.483(5) A) are shorter than the correspond-
ing (HC(C(Me)CNC6H3i-Pr2)2)AlI2 compound (2.5010(12) and
3
˚
2.541(2) A), reflecting the cationic nature of the Al center. The
1
˚
delocalization from occurring. In solution, H NMR data reveal
Al–N bond lengths are 1.915(18) and 1.931(16) A, which are
the highly symmetrical features of the ligand, with the signals of
both imine-Ar substituents being equivalent. In addition, the iso-
propyl signals of the amine N–Ar group show a highly symmetrical
shorter on average than those previous reported for the phosphin-
imineimine ligand complex i-Pr2C6H3NC(Me)CHPPh2(NC6H3i-
˚
Pr2)AlMe2 (1.932(2) and 1.943(2) A), and those seen in the
analogous (HC(C(Me)CNC6H3i-Pr2)2)AlMe2 complex (1.920(2)
˚
and 1.942(2) A). The shorter Al–N distances reflect the positive
charge on Al in 3. The chelate bite angle in 3 is 92.4(6)◦,
which is significantly smaller than N–Al–N bite angle in (i-
Pr2C6H3N)C(Me)CHPPh2(NC6H3i-Pr2)AlMe2 (101.11(10)◦) and
(HC(C(Me)CNC6H3i-Pr2)2)AlMe2 (96.17(7)◦). The imine N–C
˚
bond lengths of 1.28(2) and 1.31(2) A are shorter than those seen
˚
in (i-Pr2C6H3N)C(Me)CHPPh2(NC6H3i-Pr2)AlMe2 (1.353(3) A)
˚
and (HC(C(Me)CNC6H3i-Pr2)2)AlMe2 (1.344(2) and 1.339(2) A)
Scheme 2 Synthesis of the sterically demanding diimine ligand 1.
2092 | Dalton Trans., 2006, 2089–2097
consistent with the charge on the cation of 3.
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protons of the anion and cation respectively. Similarly the 13C
NMR spectra showed resonances at 4.0 and −9.9 ppm attributable
to these respective Al-bound methyl groups. Attempts to observe
an 27Al NMR spectrum showed no resonance. Multiple attempts
to grow crystals of 4 resulted in either amorphous precipitate
or degradation of 4. Nonetheless, compound 4 was formulated
as [i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4]·AlMe3 based
on elemental analyses. While the observation of a 1H resonance at
−0.68 ppm is attributable to the methyl groups of the cation, the
broad resonance at −0.07 ppm attributed to the methyl groups of
the AlMe3 and [AlMe4]− and suggests methyl exchange between
them.
In a related reaction, 2 and AlMe3 were combined with
[Ph3C][B(C6F5)4]. The resulting salt 5 was isolated in 89% yield.
1H NMR data revealed the resonances attributable to the diimine
ligand as well as a singlet resonance at −0.84 ppm arising
from the two Al-bound methyl groups. These data together
1
1
with the 19F{ H} NMR data and the observation of 11B{ H}
resonance at −16.5 ppm support the formulation of 5 as [(i-
Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][B(C6F5)4].
Fig. 2 ORTEP drawing of the cation of 3, 30% thermal ellipsoids are
shown. Hydrogen atoms and the [AlI4] anion are omitted for clarity.
◦
˚
Distances (A) and angles ( ): I(1)–Al(2) 2.463(5), I(2)–Al(2) 2.483(5),
Al(2)–N(1) 1.915(18), Al(2)–N(3) 1.931(16), N(3)–C(3) 1.28(2), N(1)–C(1)
1.31(2), N(2)–C(3) 1.39(2), N(2)–C(1) 1.40(2), C(1)–C(2) 1.47(3),
C(3)–C(4) 1.48(3); N(1)–Al(2)–N(3) 92.4(6), N(1)–Al(2)–I(1) 116.4(5),
N(3)–Al(2)–I(1) 113.6(5), N(1)–Al(2)–I(2) 109.0(5), N(3)–Al(2)–I(2)
110.5(5), I(1)–Al(2)–I(2) 113.10(19), C(3)–N(3)–Al(2) 123.6(13),
C(1)–N(1)–Al(2) 122.6(13), C(3)–N(2)–C(1) 127.3(13), N(1)–C(1)–N(2)
121.4(17), N(1)–C(1)–C(2) 122.6(17), N(2)–C(1)–C(2) 116.0(16),
N(3)–C(3)–N(2) 122.0(16), N(3)–C(3)–C(4) 120.8(16), N(2)–C(3)–C(4)
117.1(14).
Compound 4 was observed to be unstable in solution affording a
faint yellow solution after standing for several weeks at room tem-
perature. In attempts to identify the degradation process, a solu-
tion of 4 was refluxed in toluene, and following a work-up, a yellow
solid 6 was isolated. 1H NMR data for 6 showed distinct doublets
=
at 2.93 and 2.66 ppm attributable to a C CH2 fragment and
resonance was observed at −0.41 ppm attributed to an AlMe2 unit.
These together with the remaining NMR data are consistent
=
with the formulation of 6 as (i-Pr2C6H3NC( CH2)(NC6H3i-
Pr2)(C(Me)NC6H3i-Pr2)AlMe2 (Scheme 3). In contrast with a
similar reaction, the pyridyl-diimine ligand reacts with AlMe3
to methylate an imine-carbon giving (2-(i-Pr2C6H3N)C(H)-6-(i-
Pr2C6H3N)CCH3(H)C5H3N) AlMe2.39 A crystallographic analysis
of 6 confirmed the presence of the methylene group in the ligand
backbone (Fig. 3). The methylene C(37)–C(38) bond length of
In a similar fashion, reaction of 2 with excess AlMe3 afforded
a white solid 4 in 88% yield (Scheme 3). H NMR data of 4 in
1
C6D5Br showed signals at −0.07 and −0.68 ppm integrating to
21 and 6 protons, and were attributed to the Al-bound methyl
˚
1.390(3) A is significantly shorter than the C(39)–C(40) bond
˚
length (1.475(3) A) of the methyl group. The N(2)–C(38) distance
˚
(1.369(3) A) is slightly longer than the N(1)–C(40) bond length
˚
(1.327(3) A) reflecting the amido and imine characters of these
differing N centers. This is also reflected in the marked difference
˚
in the Al–N bond distances of 1.8932(19) and 1.9343(19) A,
respectively. The latter Al–N bond length is similar to that
seen in (HC(C(Me)CNC6H3i-Pr2)2)AlMe2 (1.920(2) and 1.942(2)
40
˚
A) whereas the presence of the amido-N results in a N–Al–N
bite angle in 6 of 92.48(9)◦ that is markedly smaller than that
(96.17(7)◦) in (HC(C(Me)CNC6H3i-Pr2)2)AlMe2 but similar to
that seen in 3.
The transformation of 4 to 6 in C6D5Br was monitored by
NMR spectroscopy (Fig. 4) at 60 ◦C. A plot of 1/[4] vs. time
revealed a linear relationship consistent with an overall second-
order reaction (Fig. 5) and a second-order rate constant of 1.4(4) ×
10−2 M−1 s−1. Monitoring the reactions of 4 in the presence of
an excess (20 equivalents) of a 1 : 1 mixture of [Bu4N][AlMe4]
and AlMe3, revealed first-order dependency of the rate of the
reaction on the concentration of the cation of 4 (Fig. 6). However,
treatment of 5 with concentrations of [Bu4N][AlMe4] or AlMe3
did not show first-order dependence. In fact, while 5 fails to
react in the presence of excess AlMe3 alone, while the reaction
of 5 with excess [Bu4N][AlMe4] proceeds more slowly than the
Scheme 3 Synthesis of neutral and cationic complexes.
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Fig. 5 Representative data for the disappearance of 4; a plot of 1/[4]
vs. time (second-order kinetics). Reaction was performed at 333 K; [4]0 =
0.014 M (R2 = 0.99).
Fig. 3 ORTEP drawing of 6, 30% thermal ellipsoids are shown. Hydrogen
◦
˚
atoms are omitted for clarity. Distances (A) and angles ( ): Al(1)–N(2)
1.8939(19), Al(1)–N(1) 1.9348(18), Al(1)–C(41) 1.964(3), Al(1)–C(42)
1.993(3), N(1)–C(40) 1.332(3), N(2)–C(38) 1.370(3), N(3)–C(40) 1.4069(2),
N(3)–C(38) 1.440(3), C(37)–C(38) 1.3880(3), C(39)–C(40) 1.473(3);
N(2)–Al(1)–N(1) 92.47(8), N(2)–Al(1)–C(41) 112.54(10), N(1)–Al(1)–
C(41) 113.45(10), N(2)–Al(1)–C(42) 114.65(9), N(1)–Al(1)–C(42)
108.38(9), C(41)–Al(1)–C(42) 113.54(11), C(40)–N(1)–Al(1) 123.36(14),
C(38)–N(2)–Al(1) 122.67(14), C(40)–N(3)–C(38) 128.16(17), N(2)–C(38)–
C(37) 125.0(2), N(2)–C(38)–N(3) 117.67(19), C(37)–C(38)–N(3) 117.4(2),
N(1)–C(40)–N(3) 121.48(18), N(1)–C(40)–C(39) 122.1(2), N(3)–C(40)–
C(39) 116.37(19).
Fig. 6 Representative data for the disappearance of 4; A plot of ln[4] vs.
time (first-order kinetics). The reaction was performed at 333 K in the
presence of 20 equivalents of [Bu4N][AlMe4] and AlMe3; [4]0 = 0.006 M
(R2 = 0.98).
modeling of the decay of the concentration of 4 upon formation
of 6 using a stochastic approach does provide some evidence
of a complex anion. The model employed a reaction of 4 with
the anion formulated as [AlMe4]·AlMe3 which is formed in an
equilibrium involving [Bu4N][AlMe4] and AlMe3 (eqn (1) and (2)).
Iterative stochastic calculations36 afforded an approximation of the
equilibrium constant of Keq = 0.7 M−1 (Fig. 7, eqn (2)).
Fig. 4 Portions of 1H NMR spectra at 323 K, as a function of time.
This reveals the growth in the signals arising from CH4 and 6 and the
consumption of 4. Note the elevated temperature results in a change in the
chemical shift.
(1)
corresponding reaction of 4. These data imply that the formation
of 6 from 4 involves reaction of the cation with a species derived
from the equilibrium mixture of [Bu4N][AlMe4] and AlMe3.
Species involved in this equilibrium could not be resolved by
NMR spectroscopy on 4 at −30 ◦C in C6H5Br. Similarly a mixture
of [Bu4N][AlMe4] and AlMe3 in CH2Cl2 affords only broadening
resonances for the resonances attributable to the methyl protons
even on cooling to −85 ◦C. Thus the precise nature of the anionic
reactant could not unambiguously be determined. Nonetheless,
[AlMe4]− + AlMe3 ꢀ [AlMe4]−·AlMe3
(2)
The above kinetic data are consistent with a second-order rate
law and support the following speculation regarding the mecha-
nism. Methyl-transfer from a complex Al-anion to the cationic Al
center of 4 with concurrent chelate ring opening could provide
a complex geometry where the rate-determining methane elim-
ination takes place. Subsequently rapid complex rearrangement
gives 6 (Scheme 4). The proposition of chelate ring opening is also
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entropy is consistent with a bimolecular associative process, while
the entropy suggests substantial bond breakage in the transition
state. These parameters compare with those reported for the
methane elimination from (Me3SiO)2TiMe(NHSit-Bu3) (DH‡
=
∼ 85 kJ mol−1 and DS‡ = − 80 J mol−1 K−1).42 In contrast, C–
H activations of methyl–Ti–phosphinimide complexes by AlMe3
proceed with a significantly lower enthalpy of 63(2) kJ mol−1. The
present data support a proposed mechanism in which a Al–C bond
and a C–H bond adopt a six-membered ring transition state.41
Reaction of 6 with B(C6F5)3 in C6D5Cl gave the expected
=
cation [(i-Pr2C6H3)N(C( CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)-
AlMe(l-MeB(C6F5)3)] 7 (Scheme 3). The 1H NMR spectrum
shows the ligand signals broadened significantly with the Al–
Me signal at −0.81 ppm. Variable-temperature 1H NMR spectra
(−40 ◦C to 80 ◦C) shows a signal attributed to the bridging
methyl group at 1.39 ppm, −40 ◦C. This signal shifts to 1.23 ppm
at 0 ◦C and is obscured by the isopropyl group resonances
above 10 ◦C. The corresponding resonance attributed to the
terminal Al–Me group also broadens at 10 ◦C and is not observed
above 60 ◦C. These data suggest an exchange process for the
B(C6F5)3 group between the two Al-bound methyl groups. The
exchange rates were determined from the linewidth at half-
height in the slow exchange regime in the temperature range
between 283 and 333 K. These data afforded an Eyring plot
Fig. 7 Concentration/time plot for the conversion of 4 to 6 ([4]0 = 0.0063
M). Observed data are shown as squares, stochastic calculation data based
on mechanism shown as solid line.
and activation parameters DH‡ = 49(1) kJ mol−1 and DS‡
=
−54(6) J mol−1 K−1. By way of comparison, similar exchange
for zirconocene cation/methylborates were reported to have DG‡
values between 14.4 and 19.7 kcal mol−1.43 The relatively weak
Al–Me bond in comparison to Zr–Me is reflected in low energy
requirement for exchange in 7. While the entropy term suggests a
bimolecular process and thus favors the proposition of dissociative
exchange (Scheme 5), an intramolecular exchange process can not
be explicitly excluded.
Scheme 4 Proposed mechanism for formation of 6 from 4.
supported by the observation that dissolution of 4 in THF results
in degradation of 4 to (THF)AlMe3 and the free ligand 2. It is also
noteworthy that the present C–H activation is proposed to proceed
via a transient six-membered ring intermediate. A similar proposal
was described for C–H activations of alkyl–Ti–phosphinimide
complexes by AlMe3.41 Monitoring the reaction of 4 to 6 over
the albeit limited temperature range of 313–343 K provided an
Eyring plot (Fig. 8) and revealed the thermodynamic parameters,
DH‡ = 91(5) kJ mol−1 and DS‡ = −10(8) J mol−1 K−1. This negative
Scheme 5 Proposed dissociative exchange process for 7.
Attempts to prepare related Al–hydride complexes were
undertaken. Reaction of 2 in refluxing toluene with AlH3·NMe2Et
resulted only in complex mixture of products and the deposition of
Al metal. In a similar sense it was recently reported that reaction of
the diimine (i-Pr2C6H3N)C(Me)C(Me2)C(Me)(NC6H3i-Pr2) with
AlH3·OEt2 gave the corresponding diamine.44 However, treatment
of 2, with AlH3·NMe2Et with addition of [Ph3C][B(C6F5)4]
afforded the hydride salt [(i-Pr2C6H3N(C(Me)NC6H3i-
Pr2)2)AlH2][B(C6F5)4] 8 (Scheme 3). The 1H NMR data, in
particular the broad resonance at 3.80 ppm attributable to the
two Al-bound hydrides, were consistent with the formulation of
8. The analogous deuteride species [(i-Pr2C6H3N(C(Me)NC6H3i-
Pr2)2)AlD2][B(C6F5)4] 9 was also isolated using AlD3·NMe3.
Infrared spectroscopy of 8 shows the Al–H absorptions at 1881
and 1910 cm−1. These compare to the infrared absorptions at 1828
Fig. 8 Eyring plot for reaction of4 to 6; R2 = 0.99; DH‡ = − 91(5) kJ mol−1
and DS‡ = −10(8) J mol−1 K−1
.
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and 1770 cm−1 observed for i-Pr2C6H3NC(Me)CHPPh2(NC6H3i-
Pr2)AlH2 and 1324 and 1286 cm−1 for i-Pr2C6H3NC(Me)-
CHPPh2(NC6H3i-Pr2)AlD2.9 Compound 9 showed 2D NMR
resonance at 3.51 ppm which compare to 4.55 ppm observed for
i-Pr2C6H3N)C(Me)CHPPh2(NC6H3i-Pr2)AlD2.9 It is noteworthy
that attempts to react the cationic alkyl and hydrido-species 7, 8
with excess B(C6F5)3, [Ph3C][B(C6F5)4] or [H(OEt2)2][B(C6F5)4]
resulted in no reaction, consistent with the strong Lewis acidity
of the cationic Al-center in these species.
˚
3.56 A. The characterization of 10 is to our knowledge the first
three-coordinate Al-hydride complex, moreover it supports the
dissociative exchange intermediate proposed for 7.
The N-imidoylamidine ligand described herein readily affords
neutral and cationic Al–alkyl and –hydride complexes. Activation
oftheexocyclicmethylgroupaffords thedissymmetricamidoimine
ligand. The steric bulk and strong donor ability of this ligand
allowed the isolation of monometallic Al–alkyl and –hydrido
cations. Attempts to utilize this and related ligands for the
stabilization of transition-metal complexes are the subject of
current efforts.
In a similar reaction, 2, two equivalents of AlH3·NMe2Et
and [Ph3C][B(C6F5)4] were combined to give the complex
=
[(i-Pr2C6H3 )N(C( CH2 )NC6H3i-Pr2 )(C(Me)NC6H3i-Pr2 )AlH]-
[B(C6F5)4] 10. The observations of a doublet resonance at 2.50 ppm
Acknowledgements
1
in the H NMR spectrum is consistent with the alkene ligand
1
1
fragment while the 11B{ H} and 19F{ H} NMR spectra are
consistent with the presence of the borate anion. A single-crystal
X-ray diffraction study confirmed 10 is correctly formulated as
the borate salt of the three coordinate aluminium hydride cation
Financial support from NSERC of Canada and the ORDCF is
gratefully acknowledged. J. D. M. is grateful for the award of
an Ontario Graduate Scholarship and a Bayer Inc. Award from
the Macromolecular Science and Engineering Division of the
Canadian Institute for Chemistry. Jenny McCahill is thanked for
assistance with VT NMR spectra.
˚
(Fig. 9). The Al–N distances are 1.880(4) and 1.887(3) A while
the ligand bite-angle at 89.72(15)◦. There are slightly smaller
than those seen in 6, consistent with the cationic nature of
10. The presence of the exocyclic alkene fragment is confirmed
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19 M. N. Kopylovich, A. J. L. Pombeiro, A. Fischer, L. Kloo and V. Y.
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Fig. 9 ORTEP drawing of the cation of 10, 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Distances (A)
˚
and angles (◦): Al(1)–N(3) 1.881(4), Al(1)–N(1) 1.888(4), C(1)–C(2)
1.300(7), C(1)–N(1) 1.405(5), C(1)–N(2) 1.510(5), C(3)–N(3) 1.313(5),
C(3)–N(2) 1.360(5), C(3)–C(4) 1.485(6); N(3)–Al(1)–N(1) 89.68(15),
C(2)–C(1)–N(1) 126.4(4), C(2)–C(1)–N(2) 121.4(4), N(1)–C(1)–N(2)
110.7(4),
N(3)–C(3)–N(2)
120.9(3),
N(3)–C(3)–C(4)
120.4(4),
N(2)–C(3)–C(4) 118.7(4), C(1)–N(1)–C(5) 114.9(3), C(1)–N(1)–Al(1)
134.5(3), C(5)–N(1)–Al(1) 110.5(2), C(3)–N(2)–C(17) 117.3(3),
C(3)–N(2)–C(1) 129.9(3), C(17)–N(2)–C(1) 112.8(3), C(3)–N(3)–C(29)
118.4(3), C(3)–N(3)–Al(1) 131.0(3), C(29)–N(3)–Al(1) 110.5(2).
2096 | Dalton Trans., 2006, 2089–2097
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