Synthetic, spectral and structural studies of mononuclear tris(κ2-amidate) aluminium complexes supported by tripodal ligands

Article abstract of DOI:10.1016/j.poly.2009.06.013

The synthesis and characterization of mononuclear tris(κ²-amidate) aluminium complexes supported by the tripodal ligands, [N(o-PhNC(O)R)₃]^3- (R = ⁱPr and ^tBu), are described. The molecular structures

Full text of DOI:10.1016/j.poly.2009.06.013

Polyhedron 29 (2010) 116–119
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthetic, spectral and structural studies of mononuclear tris(
aluminium complexes supported by tripodal ligands
j
2-amidate)
*
Matthew B. Jones, Kenneth I. Hardcastle, Cora E. MacBeth
Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, GA 30322, USA
a r t i c l e i n f o
a b s t r a c t
The synthesis and characterization of mononuclear tris(j
2-amidate) aluminium complexes supported by
Article history:
Available online 11 June 2009
the tripodal ligands, [N(o-PhNC(O)R)3]3ꢀ (R = iPr and tBu), are described. The molecular structures of
[Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-PhNC(O)tBu)3)] have been determined by X-ray diffraction studies.
Both neutral six-coordinate aluminium complexes display coordination geometries that are intermediate
between octahedral and trigonal prismatic. Solution-state NMR studies (1H, 13C and 27Al) indicate that
these structures are non-fluxional in solution. Detailed analysis of the solid-state structures shows that
slight changes in the relative size of the amidate acyl substituents do not significantly impact the
solid-state structures. However, large substituents may be required to prevent the formation of multinu-
clear species.
Keywords:
Amidate ligands
j
2-Amidate coordination
Aluminium
Tripodal ligands
27Al NMR
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
These spectroscopic studies and the dearth of structurally char-
acterized tris(j
2-amidate) metal complexes [2,16–18] prompted
Deprotonated organic amides (amidates) have recently been
recognized as potent ligand scaffolds for metal-ion mediated cata-
lytic and stoichiometric transformations [1,2]. Amidate ligands can
interact with metal centres through a variety of coordination
modes, including: (1) monodentate (where the amidate coordi-
nates through either the N- or O-amidato donor), (2) bridging
(where the N- and O-donors coordinate to two separate metal-
ions), and (3) chelating (where the N- and O-donors coordinate
to the same metal-ion). The possible coordination modes for ami-
date ligands interacting with a single metal centre are shown in
Fig. 1. Studies involving deprotonated amides and aluminium cen-
tres have largely focused on the synthesis and characterization of
organoaluminium amidates. The majority of these organoalumin-
ium amidate complexes are multinuclear or oligomeric species in
which the amidate donors bridge more than one aluminium centre
[3–10]. However, two separate studies have identified monomeric
organoaluminium complexes stabilized by O-amidate ligands
[11,12].
us to explore the coordination chemistry of Al(III) with the tripo-
dal, tris(amidate) ligand systems, [N(o-PhNC(O)R)3]3ꢀ (R = alkyl)
recently developed in our laboratories as a means of stabilizing
these species [19]. Specifically, we sought to use tris(amidate) li-
gand systems with bulky, acyl substituents to favour monomeric
aluminium amidates. Herein, we report the synthesis and charac-
terization of two Al(III) tris(
these ligands.
j
2-amidate) complexes stabilized by
2. Results and discussion
2.1. Syntheses
The aluminium complex [Al(N(o-PhNC(O)iPr)3)] is readily ob-
tained by reacting the ligand, N(o-PhNHC(O)iPr)3 with three equiv-
alents of potassium hydride followed by in situ transmetallation
with AlCl3 (Scheme 1a). The resulting complex is soluble in a vari-
ety of organic solvents including benzene, toluene and chloroform,
making removal and quantification of the potassium chloride by
Recently, Stahl and co-workers have demonstrated that the di-
meric, homoleptic amidoaluminium species (Al2(NMe2)6) can be
used to efficiently catalyze the transamidation of carboxamides
[13]. In subsequent mechanistic studies [14,15], they were able
to use NMR spectroscopy to characterize the resting state of the
t
product simple. In contrast, the aluminium complex of the Bu li-
gand derivative, [Al(N(o-PhNC(O)tBu)3)], is prepared by reacting
the ligand directly with one equivalent of AlMe3 in toluene
(Scheme 1b). Attempts to synthesize [Al(N(o-PhNC(O)iPr)3)] di-
rectly from the reaction of the protio ligand with AlMe3 were
unsuccessful and lead to a complex reaction mixture, presumably
due to the insolubility of the ligand in toluene. Attempts were
made to synthesize and isolate the aluminium complex of the
methyl ligand congener, [Al(N(o-PhNC(O)Me)3)], using analogous
catalyst, an Al(III) tris(j
2-amidate) species.
* Corresponding author. Tel.: +1 404 727 7033.
E-mail address: cora.macbeth@emory.edu (C.E. MacBeth).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.06.013

M.B. Jones et al. / Polyhedron 29 (2010) 116–119
117
R'
respectively. These data are consistent with non-fluxional, octahe-
dral Al(III) centres with mixed donor ligands [20,21].
O
R'
NR
M
R
R
O
N
N
R'
Infrared spectroscopy can also be used to determine the coordi-
nation mode of the amidate ligands. Specifically, the absence of
O
M
M
amide m
(N–H) bands at ca. 3260 cmꢀ1 and the appearance of new
Monodentate
O-amidate
Monodentate
N-amidate
Chelating
-amidate
medium to strong intensity m(Al–O) and m(Al–N) bands between
ꢁ620–740 cmꢀ1 are indicative of
j
2-coordination. The diagnostic
m
(CO) bands of the free ligands (ꢁ1650 cmꢀ1) are also shifted to
Fig. 1. Coordination modes possible for an amidate ligand ([RNC(O)R0]) interacting
significantly lower energies (ꢁ1580 cmꢀ1) upon coordination to
with a single metal centre.
the aluminium centres. The m(CO) band observed for the j
2-ami-
date coordination mode is also significantly lower in energy than
the m(CO) frequency observed in four-coordinate transition metal
O
complexes of the same ligands (i.e., [Co(N(o-PhNC(O)iPr)3)],
1610 cmꢀ1) in which the ligand coordinates through three mono-
dentate, N-amidate donors and the tertiary amine of the ligand
backbone [19].
O
iPr
O
iPr
Al
N
1. 3.1 KH, DMF
2. AlCl3
iPr
N
N
N(o-PhNHC(O)iPr)3
(a)
- 3 KCl
N
2.3. X-ray crystallography
37 %
[Al(N(o-PhNC(O)iPr)3)]
The molecular structures of [Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-
PhNC(O)tBu)3)] were determined by X-ray diffraction studies and
are shown in Fig. 2A and B, respectively. These studies confirm
O
O
tBu
tBu
the chelating tris(j
2-amidate) coordination mode of each ligand
O
tBu
Al
N
in the solid-state. Selected bond lengths and angles for both com-
plexes are listed in Table 1.
N
AlMe3, toluene
-CH4
N
N(o-PhNHC(O)tBu)3
(b)
The coordination geometries about the aluminium centres are
intermediate between octahedral and trigonal prismatic. The de-
gree of distortion between these two idealized geometries can be
N
59%
[Al(N(o-PhNC(O)tBu)3)]
Table 1
Scheme 1. Synthesis of (a) [Al(N(o-PhNC(O)iPr)3)] and (b) [Al(N(o-PhNC(O)tBu)3)].
Selected average bond lengths (Å), angles (°), and metrical parameters for
[Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-PhNC(O)tBu)3)].
[Al(N(o-PhNC(O)iPr)3)]
[Al(N(o-PhNC(O)tBu)3)]
synthetic strategies. These reactions, however, yielded complicated
product mixtures that contained a number of inseparable alumin-
ium species.
Al–O(av)
Al–N(av)
C–O(av)
C–N(av)
O–Al–N(av)
1.927(1)
1.967(1)
1.300(2)
1.306(2)
67.07
3.14
2.15
35.7
1.10
1.895(3)
1.980(4)
1.301(5)
1.302(5)
67.10
3.15
2.15
36.3
1.10
2.2. Spectroscopy
a
Alꢂ ꢂ ꢂNtert
b
Nꢂ ꢂ ꢂO(av)
The 1H and 13C spectra of [Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-
PhNC(O)tBu)3)] in deuterated chloroform are indicative of pseudo
C3-symmetric species in solution. The 13C NMR spectra of both
complexes exhibit single carbonyl resonances at approximately
185 ppm consistent with chelating amidate donors [2,15]. Both
[Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-PhNC(O)tBu)3)] exhibit single
peaks in their 27Al NMR spectra (CDCl3, 25 °C) at 26 and 27 ppm,
/(O/N)c
d
b(av)
a
Through space distance between Al(III) centre and non-coordinated, tertiary
amine of the ligand.
b
Bite distance between the chelating O- and N-donors.
c
Ligand twist angle.
d
Normalized bite of the ligand.
Fig. 2. Thermal ellipsoid diagrams of (A) [Al(N(o-PhNC(O)iPr)3)] and (B) [Al(N(o-PhNC(O)tBu)3)] (one of two independent molecules in the asymmetric unit) drawn at 35%
probability. Hydrogen atoms have been omitted for clarity. (C) Illustration of the dihedral angle (trigonal twist angle /) between the trigonal faces formed by the O-amidate
(red) and N-amidate (blue) donors.

118
M.B. Jones et al. / Polyhedron 29 (2010) 116–119
quantified by measuring the dihedral or twist angle (/) between
the two trigonal coordination planes [22–25]. A twist angle of
60° is indicative of ideal octahedral coordination, whereas a twist
angle of 0° indicates an ideal trigonal prismatic geometry. The
average trigonal twist angles for [Al(N(o-PhNC(O)iPr)3)] and
[Al(N(o-PhNC(O)tBu)3)] are 35.7° and 36.3°, respectively, indicating
a significant degree of distortion away from octahedral geometry.
This distortion can be explained by considering the relatively small
chelate bite angles (O–Al–N) and bite distances (non-bonded,
aluminium centre consists of three chelating, j
2-amidate ligands.
The small bite angle and bite distance afforded by the amidate li-
gands give rise to overall coordination geometries that are best de-
scribed as intermediate between octahedral and trigonal prismatic.
Spectroscopic studies indicate that the six-coordinate geometry is
maintained in solution.
4. Experimental
Nꢂ ꢂ ꢂO distance) afforded by the chelating
These parameters can be described by the normalized bite, b, of
the bidentate, chelating ligands (b = 2 sin ( /2), where = the O–
j
2-amidate ligands.
4.1. General considerations
a
a
Al–N bond angle) [26]. Both [Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-
PhNC(O)tBu)3)] give rise to normalized bite values of 1.10. This va-
lue is similar to normalized bite values (1.12–1.23) observed for
tris(N,N-disubsubstitued-dithiocarbamato) metal complexes with
similar, four-membered chelate rings [27]. Complexes exhibiting
b values of this magnitude are expected to significantly distort
away from an idealized octahedral geometry in order to reduce
electrostatic repulsion between the donor atoms [26,27].
All manipulations were conducted in an MBraun Labmaster
130 drybox under a nitrogen atmosphere. All reagents used were
purchased from commercial vendors and used as received unless
otherwise noted. Anhydrous solvents were purchased from Sig-
ma–Aldrich and further purified by sparging with Ar gas followed
by passage through activated alumina columns. Deuterated chlo-
roform (CDCl3-d1) was purchased from Aldrich and degassed and
dried according to standard procedures prior to use. Elemental
analyses were performed by Atlantic Microlabs, Norcross, GA. 1H
and 13C NMR spectra were recorded on a Varian Unity Plus
600 MHz spectrometer at ambient temperature. Chemical shifts
were referenced to residual solvent peaks. The 27Al NMR spectrum
was recorded in CDCl3-d1 on a Varian Unity Plus 600 MHz spec-
trometer (156.2 MHz) and referenced to an external standard
(0.2 M Al(NO3)3 in D2O). The 27Al background signal [30] was
determined using a CDCl3 blank. The background signal appeared
as a very broad singlet centred at 57 ppm. Infrared spectra were
recorded as KBr pellets on a Varian Scimitar 800 Series FT-IR spec-
trophotometer. X-ray diffraction studies were carried out in the X-
ray Crystallography Centre at Emory University on a Bruker Smart
1000 CCD diffractometer. The Mass Spectrometry Centre at Emory
University recorded Mass spectra on a JEOL JMS-SX102/SX102A
mass spectrometer. The synthesis and characterization of the li-
gand, [N(o-PhNHC(O)iPr)3)], [19] and the ligand precursor, N(o-
PhNH2)3, have been previously reported [19,31].
The primary coordination spheres of [Al(N(o-PhNC(O)tBu)3)]
and [Al(N(o-PhNC(O)iPr)3)] are very similar (Table 1). The
Al–O(amidate) bond lengths of [Al(N(o-PhNC(O)iPr)3)] and
[Al(N(o-PhNC(O)tBu)3)] (1.927 and 1.895 Å, respectively) are
significantly longer than the Al–O(amidate) bond length (1.77 Å)
observed in the previously reported mononuclear aluminium com-
plex [Me2Al-(PhNC(O)PH)(ONMe3)] that contains an O-amidate
donor and has been characterized by X-ray diffraction [11]. The
delocalization of anionic charge within the chelating
j
2-amidate
OCN group is apparent from the similarities in C–O and C–N bond
lengths (Table 1).
In the structure of [Al(N(o-PhNC(O)iPr)3)], each amidate acyl
substituent is oriented so that either a methyl group or a methine
proton of the isopropyl group is positioned between adjacent phe-
nyl rings of the ligand backbone (Fig. 2A). Replacing the isopropyl
substituents with larger tert-butyl substituents does not result in a
significant change in solid-state structure, suggesting that subtle
changes in the amidate substituents do not significantly alter the
coordination geometries of these species. However, attempts to
synthesize the analogous [Al(N(o-PhNC(O)Me)3)] complex using
similar synthetic strategies were unsuccessful and gave rise only
to complex reaction mixtures by spectroscopic analysis. These re-
sults indicate that the bulky acyl substituents may be required to
prevent the formation of multinuclear aluminium species. Similar
observations have been reported for tris(amido) aluminium com-
plexes in which small amido substituents give rise to dimeric alu-
minium species in solution [28,29].
4.2. Synthesis of 2,20200-tris(pivalamidotriphenyl)amine
A suspension of N(o-PhNH2)3 (1.79 g, 6.2 mmol) in dichloro-
methane (CH2Cl2, 80 mL) was cooled to 0 °C under an atmosphere
of N2. Distilled triethylamine (3.20 mL, 23.0 mmol) was then
added, followed by pivaloyl chloride (2.71 mL, 22.0 mmol). The
mixture stirred for 20 h as it slowly warmed to room temperature.
The crude reaction mixture was washed with aqueous HCl (0.1 M,
3 ꢃ 50 mL), dried over magnesium sulfate, and concentrated in va-
cuo. The resulting solid was washed with diethyl ether (ꢁ10 mL)
and ethyl acetate (ꢁ10 mL), and the white solid was collected by
filtration (69%, 2.29 g). 1H NMR (d, CDCl3, 300 MHz): 7.95 (s, 3H,
NH), 7.79 (dd, 3H, J = 1.2, 7.8 Hz, ArH), 7.11 (td, 3H, J = 1.2,
7.5 Hz, ArH), 7.02 (td, 3H, J = 1.2 Hz, J = 7.5 Hz, ArH), 6.84 (dd, 3H,
J = 1.2, 7.8 Hz, ArH), 0.95 (s, 27H, C(CH3)3). 13C NMR (d, CDCl3,
300 MHz): 176.64, 137.94, 131.56, 126.01, 125.67, 124.78,
124.42, 39.44, 27.22. HRESI-MS: C33H43O3N4 m/z Calc. 543.33297;
The six coordinate geometries observed for [Al(N(o-
PhNC(O)iPr)3)] and [Al(N(o-PhNC(O)tBu)3)] were not unexpected,
as hard metal-ions tend to favour either the
j
2-amidate binding
mode or a binding mode in which the O-amidate donor spans
two different metal centres [1]. However, given the large number
of well-characterized four-coordinate azaalumatranes supported
by tripodal tetradentate, tris(amido) [28] ligand systems that con-
tain bulky amide substituents i.e., [Al(N(CH2CH2NSiMe3)3], four-
coordinate geometries and/or fluxional solution-state behaviour
in these systems could not be ruled out.
found: 543.33352 [M + 1]+. FT-IR (KBr, cmꢀ1):
m(NH) 3258, m(CO)
1653, 3387, 3309, 2959, 2909, 2871, 1680, 1653, 1594, 1516,
1479, 1439, 1303, 1265, 1160, 928, 756, 734, 625, 480.
3. Conclusions
4.3. Synthesis of [Al(N(o-PhNC(O)iPr)3)]
In conclusion, the aluminium complexes [Al(N(o-PhNC(O)iPr)3)]
and [Al(N(o-PhNC(O)tBu)3)] have been prepared and completely
characterized. The structures of both complexes have been deter-
mined by X-ray diffraction and are very similar. Each complex is
six-coordinate and the primary coordination sphere about each
To a stirred solution of N(o-PhNHC(O)iPr)3 (98 mg, 0.20 mmol)
in DMF (2 mL) was added KH (26 mg, 0.65 mmol) as a solid. When
H2 evolution ceased, AlCl3 (26 mg, 0.20 mmol) was added as a so-
lid. Upon complete dissolution of the metal salt, solvent was re-
moved in vacuo. The colorless solid was extracted into toluene

M.B. Jones et al. / Polyhedron 29 (2010) 116–119
119
Table 2
were refined anisotropically. Structure solution, refinement, graph-
ics and generation of publication materials were performed by
using SHELXTL, V6.12 software. Additional details of data collection
and structure refinement are given in Table 2.
Crystal and refinement data for complexes [Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-
PhNC(O)tBu)3)]a.
[Al(N(o-PhNC(O)iPr)3)]
[Al(N(o-PhNC(O)tBu)3)]
Formula
C30H33AlN4O3
524.58
C33H39AlN4O3
566.66
trigonal, P31c
11.2793(8)
11.2793(8)
28.563(4)
90
Formula weight
Lattice, space group
a (Å)
b (Å)
c (Å)
Supplementary data
orthorhombic, Pbca
15.9429(3)
9.8814(2)
34.5625(7)
90
CCDC 703388 and 729894 contains the supplementary crystal-
lographic data for [Al(N(o-PhNC(O)iPr)3)] and [Al(N(o-PhNC
(O)tBu)3)]. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
a
(°)
b (°)
90
90
8
90
120
4
3147.0(6)
173(2)
0.71073
38246
c
(°)
Z
V (Å3)
5444.91(19)
173(2)
0.71073
36660
Temperature (K)
Radiation (k, Å)
Reflections measured
Unique reflections [Rint
Acknowledgments
]
5585
3881
Financial support from the donors of the American Chemical
Society Petroleum Research Fund (PRF-DNI) and the Emory Univer-
sity Research Committee (URC) is gratefully acknowledged. The
authors wish to thank Dr. S. Wu and Dr. B. Wang (Emory Univer-
sity’s NMR Research Centre) for assistance and Professor K.S. Hagen
for helpful discussions. Leslie A. Alexander is acknowledged for the
original synthesis of the N(o-PhNHC(O)tBu)3 ligand.
R1 (I > 2
wR2, all data
r
(l))
0.0499
0.1375
0.0713
0.1777
and filtered to remove KCl (3 equiv.). X-ray quality crystals were
obtained by vapour diffusion of hexanes into a concentrated tolu-
ene solution. (38 mg, 37%). 1H NMR (d), CDCl3, 600 MHz: 7.45 (dd,
3H, J = 7.8, 1.2 Hz, ArH), 7.09 (dt, 3H, J = 7.8, 1.2 Hz, ArH), 7.04 (dt,
3H, J = 7.8, 1.8 Hz, ArH), 6.95 (dd, 3H, J = 7.8, 1.8 Hz, ArH), 2.94 (7,
3H, J = 7.2 Hz, CH), 1.28 (d, 9H, J = 7.2 Hz, CH3), 0.55 (d, 9H,
J = 6.6 Hz, CH3). 13C NMR (d (ppm), CDCl3, 600 MHz): 184.84,
141.22, 140.48, 130.67, 126.29, 124.25, 122.25, 28.32, 19.14,
17.97. 27Al NMR (d, CDCl3, 600 MHz): 26 ppm (W1/2 = 3000 Hz).
References
[1] A.V. Lee, L.L. Schafer, Eur. J. Inorg. Chem. (2007) 2243.
[2] L.J.E. Stanlake, J.D. Beard, L.L. Schafer, Inorg. Chem. 47 (2008) 8062.
[3] J. Fawcett, G.A. Solan, Acta Crystallogr., Sect. E: Struct. Rep. Online E 61 (2005)
m1210.
[4] B.-H. Huang, T.-L. Yu, Y.-L. Huang, B.-T. Ko, C.-C. Lin, Inorg. Chem. 41 (2002)
2987.
[5] Y.-L. Huang, B.-H. Huang, B.-T. Ko, C.-C. Lin, J. Chem. Soc., Dalton Trans. (2001)
1359.
[6] R.P. Davies, D.J. Linton, R. Snaith, A.E.H. Wheatley, Chem. Commun.
(Cambridge) (2000) 193.
FT-IR (KBr, cmꢀ1):
m(CO) 1580, 1474, 1435, 1373, 1295, 1271,
1079, 976, 751, 507. Anal. Calc. for [AlIII(N(o-PhNC(O)iPr)3)]: C,
68.69; H, 6.34; N, 10.68. Found: C, 68.35; H, 6.41; N, 10.57%.
4.4. Synthesis of [Al(N(o-PhNC(O)tBu)3)]
To
a
stirred suspension of N(o-PhNHC(O)tBu)3 (250 mg,
[7] A. Klemp, I. Uson, J.-T. Ahlemann, T. Belgardt, J. Storre, H.W. Roesky, Main
Group Chem. 1 (1995) 127.
0.46 mmol) in toluene (4 mL) was added AlMe3 via syringe
(2.0 M in toluene, 0.23 mL, 0.46 mmol). After 20 min of stirring,
the reaction mixture became homogeneous and solvent was re-
moved in vacuo; leaving a colorless solid. X-ray quality crystals
were obtained by vapour diffusion of petroleum ether into a con-
centrated toluene solution of the complex (154 mg, 59%). 1H
NMR (d), CDCl3, 600 MHz: 7.24 (dd, 3H, J = 7.8, 1.2 Hz, ArH), 7.01
(m, 9H, ArH), 0.917 (s, 27H, CH3C). 13C NMR (d), CDCl3, 600 MHz:
184.706, 141.409, 140.62, 129.45, 125.17, 125.00, 124.21, 38.51,
28.15. 27Al NMR (d (ppm), CDCl3, 600 MHz): 27 (W1/2 = 3000 Hz).
[8] P. Fischer, R. Graef, J.J. Stezowski, J. Weidlein, J. Am. Chem. Soc. 99 (1977) 6131.
[9] J.R. Jennings, K. Wade, B.K. Wyatt, J. Chem. Soc., A (1968) 2535.
[10] J.R. Horder, M.F. Lappert, J. Chem. Soc., A (1968) 2004.
[11] Y. Kai, N. Yasuoka, N. Kasai, M. Kakudo, Bull. Chem. Soc. Jpn. 45 (1972) 3388.
[12] M.B. Power, S.G. Bott, D.L. Clark, J.L. Atwood, A.R. Barron, Organometallics 9
(1990) 3086.
[13] S.E. Eldred, D.A. Stone, S.H. Gellman, S.S. Stahl, J. Am. Chem. Soc. 125 (2003)
3422.
[14] J.M. Hoerter, K.M. Otte, S.H. Gellman, Q. Cui, S.S. Stahl, J. Am. Chem. Soc. 130
(2008) 647.
[15] J.M. Hoerter, K.M. Otte, S.H. Gellman, S.S. Stahl, J. Am. Chem. Soc. 128 (2006)
5177.
[16] J. Ruiz, M. Vivanco, C. Floriani, A. Chiesi-Villa, C. Guastini, J. Chem. Soc., Chem.
Commun. (1991) 762.
[17] M. Vivanco, J. Ruiz, C. Floriani, A. Chiesi-Villa, C. Rizzoli, Organometallics 12
(1993) 1802.
[18] M. Vivanco, J. Ruiz, C. Floriani, A. Chiesi-Villa, C. Rizzoli, Organometallics 12
(1993) 1794.
FT-IR (KBr, cmꢀ1):
m(CO) 1562, 1480, 1363, 1302, 1190, 968, 760,
749, 623, 529. Anal. Calc. for [AlN(o-PhNC(O)tBu)3]: C, 69.94; H,
6.94; N, 9.89. Found: C, 69.97; H, 6.84; N, 9.80%.
[19] M.B. Jones, C.E. MacBeth, InorgChem 46 (2007) 8117.
[20] J.W. Akitt, Prog. NMR Spectrosc. 21 (1989) 1.
[21] G.H. Robinson (Ed.), Coordination Chemistry of Aluminium, VCH Publishers,
INC., New York, 1993.
[22] P.B. Donaldson, P.A. Tasker, N.W. Alcock, J. Chem. Soc., Dalton Trans. (1977)
1160.
[23] E.B. Fleischer, A.E. Gebala, D.R. Swift, P.A. Tasker, Inorg. Chem. 11 (1972) 2775.
[24] E. Larsen, G.N. LaMar, B.E. Wagner, J.E. Parks, R.H. Holm, Inorg. Chem. 11
(1972) 2652.
[25] E.I. Stiefel, G.F. Brown, Inorg. Chem. 11 (1972) 434.
[26] D.L. Kepert, Inorg. Chem. 11 (1972) 1561.
[27] H. Abrahamson, J.R. Heiman, L.H. Pignolet, Inorg. Chem. 14 (1975) 2070.
[28] J.G. Verkade, Coord. Chem. Rev. 137 (1994) 233.
[29] J. Pinkas, B. Gaul, J.G. Verkade, J. Am. Chem. Soc. 115 (1993) 3925.
[30] R. Benn, A. Rufinska, E. Janssen, H. Lehmkuhl, Organometallics 5 (1986) 825.
[31] R. Celenligil-Cetin, P. Paraskevopoulou, R. Dinda, R.J. Staples, E. Sinn, N.P. Rath,
P. Stavropoulos, Inorg. Chem. 47 (2008) 1165.
4.5. X-ray structure determinations
Suitable
crystals
of
[Al(N(o-PhNC(O)tBu)3)]and[Al(N(o-
PhNC(O)iPr)3)] were coated with Paratone N oil, suspended in
small fiber loops and placed in a cooled nitrogen gas stream at
173 K on a Bruker D8 APEX II CCD sealed tube diffractometer with
graphite monochromated Mo Ka (0.71073 Å) radiation. Data were
measured using a series of combinations of phi and omega scans
with 10 s frame exposures and 0.5° frame widths.
The structures were solved using Direct methods and difference
Fourier techniques (SHELXTL, V6.12) [32]. Hydrogen atoms were
placed their expected chemical positions using the HFIX command
and were included in the final cycles of least squares with isotropic
Uij’s related to the atom’s ridden upon. All non-hydrogen atoms
[32] G.M. Sheldrick, Acta Crystallogr., Sect. A: Foundations A64 (2008) 112.