Synthesis, NMR characterization, and molecular structural studies of a series of ortho-metalated aluminum-nitrogen dimers

Article abstract of DOI:10.1021/om000072z

The thermolysis of 1:1 mole ratio reaction mixtures of R₃Al/HN(CH₂Ph)₂, where R = Me, Et, Prⁿ, Buⁿ, Buⁱ and of a 1:2 reaction mixture of Me₃Al with HN(CH₂Ph)₂ yield ortho-metalated aminoalane dimers as products. These dimers were characterized by elemental analysis, ¹³C and ¹H NMR, FT-IR, and single-crystal X-ray determination. The results obtained are discussed in terms of the influence of R on the ease of ortho metalation, structural parameters of the Al₂N₂ ring, and the nature of the alkyl chain conformations in solution and the solid state.

Full text of DOI:10.1021/om000072z

Organometallics 2000, 19, 3253-3256
3253
Syn th esis, NMR Ch a r a cter iza tion , a n d Molecu la r
Str u ctu r a l Stu d ies of a Ser ies of Or th o-Meta la ted
Alu m in u m -Nitr ogen Dim er s
Eric K. Styron, Charles H. Lake,† Charles L. Watkins,* and Larry K. Krannich*
Department of Chemistry, University of Alabama at Birmingham,
Birmingham, Alabama 35294-1240
Christopher D. Incarvito and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received J anuary 27, 2000
Summary: The thermolysis of 1:1 mole ratio reaction
mixtures of R3Al/ HN(CH2Ph)2, where R ) Me, Et, Prn,
Bun, Bui and of a 1:2 reaction mixture of Me3Al with
HN(CH2Ph)2 yield ortho-metalated aminoalane dimers
as products. These dimers were characterized by elemen-
support a stepwise elimination of 2 equiv of methane
from [Me2GaN(CH2Ph)2]2, which results in the ortho-
metalation of one benzyl moiety on each nitrogen.
Subsequently, thermolysis of the Me3Al/HN(CH2Ph)2
reaction mixture at 155 °C led to the formation of the
analogous AlN-ortho-metalated dimer and [MeAlN(CH2-
Ph)-µ-(CH2C6H4)]2 (1) was isolated and characterized.7
To our knowledge, only two other molecular structures
of ortho-metalated aminoalane dimers have been re-
ported.10,11 Thus, we investigated the thermolysis of R3-
Al/HN(CH2Ph)2 reaction systems to study the require-
ments for orthometalation as a function of the steric
bulk of the R group and to establish the generality of
this reaction.
1
tal analysis, 13C and H NMR, FT-IR, and single-crystal
X-ray determination. The results obtained are discussed
in terms of the influence of R on the ease of ortho
metalation, structural parameters of the Al2N2 ring, and
the nature of the alkyl chain conformations in solution
and the solid state.
In tr od u ction
Our research group has investigated the synthesis,
characterization, spectral properties, and molecular
structures of several series of group 13/15 Lewis acid-
base complexes and their correspondence to thermolysis
products.1-9 We recently reported1 that the thermolysis
of 1:1 mole ratio reaction mixtures of Me3Al with HN-
(CH2Ph)2 at 120 °C led to the formation of the expected
aminoalane dimer [Me2AlN(CH2Ph)2]2 . However, ther-
molysis of the analogous Me3Ga/HN(CH2Ph)2 reaction
mixture at 120 °C led initially to the formation of the
aminogallane dimer, [Me2GaN(CH2Ph)2]2,6 but before
there was total conversion to the dimer, additional
alkane elimination occurred. Careful monitoring of the
Exp er im en ta l Section
Gen er a l P r oced u r es. Standard inert-atmosphere tech-
niques were employed for the synthesis and manipulation of
all compounds. Hexane and toluene were distilled under
nitrogen over calcium hydride. Dibenzylamine, toluene-d8, and
benzene-d6 (Aldrich) were stored over molecular sieves. Tri-
alkylaluminum reagents (Texas Alkyls) were used as obtained.
1H and 13C NMR spectra were obtained on a Bruker DRX-400
NMR spectrometer operating at 400.132 and 100.625 MHz,
respectively. All 1H and 13C NMR chemical shifts were
referenced to the solvent at 300 K. IR spectra were obtained
using split mull samples in Nujol and Kel-F (halocarbon) on
KBr plates. EI-MS data were obtained with an electron energy
of 70 eV. The samples were introduced using a direct-insertion
probe under inert-atmosphere conditions. Elemental analyses
were performed by E&R Microanalytical Laboratory, Inc.,
Parsippany, NJ . Melting points were obtained using sealed
capillaries under nitrogen and are uncorrected.
Gen er a l Syn t h esis of Or t h o-Met a la t ed Com p ou n d s,
[RAlN(CH2P h )-µ-(CH2C6H4)]2. Dibenzylamine (1.00 g, 5.07
mmol) and the respective trialkylaluminum, R3Al (R ) Et, Prn,
Bun, Bui) were mixed in a 1:1 mole ratio in 15 mL of toluene
at room temperature. A high-pressure reaction tube containing
each mixture was placed in an oil bath at 155 ( 5 °C. The
progress of each reaction was monitored by 1H NMR. [(PhCH2)2-
NAlN(CH2Ph)-µ-(CH2C6H4)]2 was synthesized by mixing 2.00
g of dibenzylamine (10.14 mmol) with 0.365 g (5.06 mmol) of
Me3Al in 15 mL of toluene and heating at 155 °C. The time
required for conversion to the ortho-metalated product was
approximately the same for all five compounds and varied
between 21 and 25 days. The solvent was removed in vacuo
1
reaction as a function of temperature and time by H
NMR spectroscopy established reaction conditions at
155 °C for obtaining the unique GaN-ortho-metalated
species [MeGaN(CH2Ph)-µ-(CH2C6H4)]2.5 The NMR data
* To whom correspondence should be addressed. E-mail: krannich@
uab.edu. Tel: (205) 934-8017. Fax: (205) 934-2543.
† Present address: Department of Chemistry, Indiana University
of Pennsylvania, Indiana, PA 15705-1087.
(1) Thomas, C. J .; Krannich, L. K.; Watkins, C. L. Polyhedron 1993,
12, 389.
(2) Thomas, C. J .; Krannich, L. K.; Watkins, C. L. Polyhedron 1993,
12, 89.
(3) Schauer, S. J .; Watkins, C. L.; Krannich, L. K.; Gala, R. B.;
Gundy, E. M.; Lagrone, C. B. Polyhedron 1995, 14, 3505.
(4) Lagrone, C. B.; Schauer, S. J .; Thomas, C. J .; Gray, G. M.;
Watkins, C. L.; Krannich, L. K. Organometallics 1996, 15, 2458.
(5) Schauer, S. J .; Lake, C. H.; Watkins, C. L.; Krannich, L. K.
Organometallics 1996, 15, 5641.
(6) Schauer, S. J .; Lake, C. H.; Watkins, C. L.; Krannich, L. K.;
Powell, D. H. J . Organomet. Chem. 1997, 549, 31.
(7) Styron, E. K.; Lake, C. H.; Watkins, C. L.; Krannich, L. K.
Organometallics 1998, 17, 4319.
(8) Lake, C. H.; Schauer, S. J .; Krannich, L. K.; Watkins, C. L.
Polyhedron 1999, 18, 879.
(9) Styron, E. K.; Lake, C. H.; Schauer, S. J .; Watkins, C. L.;
Krannich, L. K. Polyhedron 1999, 18, 1599.
(10) Waggoner, K. M.; Olmstead, M. M.; Power, P. P. Polyhedron
1990, 9, 257.
(11) Lee, B.; Pennington, W. T.; Robinson, G. H. Inorg. Chim. Acta
1991, 190, 173.
10.1021/om000072z CCC: $19.00 © 2000 American Chemical Society
Publication on Web 06/23/2000

3254 Organometallics, Vol. 19, No. 16, 2000
Notes
to obtain a yellow solid, which was washed with hexane to
leave a white solid. Recrystallization from toluene at -15 °C
gave X-ray-quality crystals of each compound. All compound
yields are reported in terms of recrystallized product. IR and
elemental analysis data are given in the Supporting Informa-
tion.
Syn th esis of [AlN-µ-(CH2C6H4)2]x. Dibenzylamine (1.00
g, 5.07 mmol) and Me3Al (0.372 g, 5.16 mmol) were mixed neat
in a high-pressure reaction tube and placed in a sand bath at
270 °C. The reaction appeared to be complete after heating
for 36 h. The light green product was washed with hexanes
and dried under vacuum. The product was only sparingly
soluble in common organic solvents. X-ray-quality crystals
could not be obtained.
Da ta Collection , Solu tion , a n d Refin em en t of X-r a y
Cr ysta llogr a p h ic Stu d ies. For each of the structural studies,
an X-ray-quality crystal was sealed into a thin-walled glass
capillary under anaerobic conditions. The crystals of com-
pounds 2-5 were mounted and aligned upon an Enraf-Nonius
CAD4 single-crystal diffractometer. Intensity data (Mo KR, λ
) 0.710 73 Å) were collected at room temperature using graph-
ite-monochromated radiation. All data were corrected for Lor-
entz and polarization effects as well as for absorption. The cry-
stallographic calculations for 2-5 were carried out on an IBM-
PC using the Siemens SHELXTL-PC program package.12 The
analytical scattering factors for neutral atoms were corrected
for both ∆f ′ and i∆f ′′ components of anomalous dispersion.13
Each structure was solved by the use of direct methods. Pos-
itional and anisotropic thermal parameters of all non-hydrogen
atoms were refined. Hydrogen atoms were not located directly
but were input in calculated positions with d(C-H) ) 0.96 Å
and with the appropriate staggered-tetrahedral geometry.14
The isotropic thermal parameter of each hydrogen atom was
defined as equal to the Ueq value of that carbon atom to which
it was bonded. Refinement continued until convergence was
reached with ∆/σ < 0.001; the structural solution was then
verified by means of a final difference Fourier synthesis in
which no chemically meaningful residuals were found.
The crystal structure data for 6 (Mo KR, λ ) 0.710 73 Å)
were collected using a Siemens P4 diffractometer equipped
with a SMART/CCD detector at 203(2) K. The structure was
solved by direct methods, completed by subsequent difference
Fourier synthesis and refined by full-matrix, least-squares pro-
cedures. All non-hydrogen atoms were refined with anisotropic
displacement parameters and hydrogens were treated as ideal-
ized contributions. There are two independent, but chemically
equivalent, half-molecules in the asymmetric unit, both of
which lie on crystallographic inversion centers. Because the
structural data for the two molecules are very similar (within
3σ), data are reported in Table 3 for molecule 1 and in the
Supporting Information for molecule 2. All software and
sources of the scattering factors are contained in the SHELTXL
(5.10) program library (G. Sheldrick, Siemens XRD, Madison,
WI).
Ch a r a cter iza tion of [EtAlN(CH2P h )-µ-(CH2C6H4)]2 (2).
Yield: 45%. Mp: 193-197 °C. 1H NMR (C6D6): δH 0.39 (qd,
2H, H1B); 0.25 (qd, 2H, H1A); 1.30 (t, 6H, H2); 3.76 (d, 2H,
H10A); 4.44 (d, 2H, H10B); 7.65 (d, 2H, H13); 7.08 (dd, 2H,
H14); 7.16 (dd, 2H, H15); 6.90 (d, 2H, H16); 3.49 (d, 2H, H20A);
4.11 (d, 2H, H20B); 7.26 (m, 4H, H22, H26); 7.25 (m, 4H, H23,
H25); 7.13 (m, 2H, H24). 13C NMR (C6D6): δC -1.8 (C1); 9.44
(C2); 58.72 (C10); 149.98 (C11); 143.5 (C12); 136.81 (C13);
126.49 (C14); 128.92 (C15); 123.98 (C16); 56.10 (C20); 139.53
(C21); 127.76 (C22, C26); 128.97 (C23, C25); 127.56 (C24).
Ch a r a cter iza tion of [P r n AlN(CH2P h )-µ-(CH2C6H4)]2 (3).
1
Yield: 46%. Mp: 161-165 °C. H NMR (C6D6): δH 0.29 (ddd,
2H, H1A); 0.42 (ddd, 2H, H1B); 1.70 (m, 4H, H2); 1.12 (t, 6H,
H3); 3.78 (d, 2H, H10A); 4.45 (d, 2H, H10B); 7.66 (d, 2H, H13);
7.08 (dd, 2H, H14); 7.14 (dd, 2H, H15); 6.90 (d, 2H, H16); 3.50
(d, 2H, H20A); 4.13 (d, 2H, H20B); 7.26 (m 4H, H22, H26);
7.25 (m, 4H, H23, H25); 7.13 (m, 2H, H24). 13C NMR (C6D6):
δC 10.15 (C1); 19.49 (C2); 20.59 (C3); 58.77 (C10); 149.90 (C11);
143.92 (C12); 136.76 (C13); 126.54 (C14); 128.91 (C15); 123.94
(C16); 56.32 (C20); 139.52 (C21); 127.87 (C22, C26); 128.95
(C23, C25); 127.57 (C24).
Ch ar acter ization of [Bu n AlN(CH2P h )-µ-(CH2C6H4)]2 (4).
1
Yield: 31%. Mp: 138-141 °C. H NMR (C6D6): δH 0.29 (ddd,
2H, H1A); 0.42 (ddd, 2H, H1B); 1.66 (m, 4H, H2); 1.46 (h, 4H,
H3); 0.97 (t, 6H, H4); 3.80 (d, 2H, H10A); 4.46 (d, 2H, H10B);
7.68 (d, 2H, H13); 7.09 (dd, 2H, H14); 7.16 (dd, 2H, H15); 6.92
(d, 2H, H16); 3.53 (d, 2H, H20A); 4.14 (d, 2H, H20B); 7.28 (m,
4H, H22, H26); 7.26 (m, 4H, H23, H25); 7.13 (m, 2H, H24).
13C NMR (C6D6): δC 7.06 (C1); 28.35 (C2); 28.01 (C3); 14.17
(C4); 58.75 (C10); 149.93 (C11); 143.97 (C12); 136.76 (C13);
126.55 (C14); 128.92 (C15); 123.97 (C16); 56.28 (C20); 139.51
(C21); 127.92 (C22, C26); 128.94 (C23, C25); 127.60 (C24).
Ch a r a cter iza tion of [Bu iAlN(CH2P h )-µ-(CH2C6H4)]2 (5).
Selected bond distances and angles for structures 1-5 are
listed in Tables 1 and 2 and for 6 in Table 3.
Resu lts a n d Discu ssion
Thermolysis of 1:1 mole ratio mixtures of R3Al with
HN(CH2Ph)2 at 100-120 °C led to the formation of the
expected aluminum-nitrogen dimer, [R2AlN(CH2Ph)2]2,
where R ) Me,1 Et,9 Prn,15 Bun,15 and Bui.15 Additional
heating of these mixtures at 155 °C in toluene solution
over a period of 3 weeks resulted in the formation of
[RAlN(CH2Ph)-µ-(CH2C6H4)]2, as reported for the R )
1
Yield: 35%. Mp: 178-181 °C. H NMR (C6D6): δH 0.27 (dd,
2H, H1A); 0.46 (dd, 2H, H1B); 2.11 (n, 2H, H2); 1.09 (d, 6H,
H3); 1.13 (d, 6H, H4); 3.81 (d, 2H, H10A); 4.43 (d, 2H, H10B);
7.69 (d, 2H, H13); 7.08 (dd, 2H, H14); 7.15 (dd, 2H, H15); 6.91
(d, 2H, H16); 3.55 (d, 2H, H20A); 4.14 (d, 2H, H20B); 7.31 (m,
4H, H22, H26); 7.27 (m, 4H, H23, H25); 7.15 (m, 2H, H24).
13C NMR (C6D6): δC 19.22 (C1); 26.51 (C2); 28.26 (C3); 28.03
(C4); 58.82 (C10); 149.69 (C11); 144.40 (C12); 136.78 (C13);
126.63 (C14); 128.85 (C15); 123.93 (C16); 56.74 (C20); 139.48
(C21); 128.07 (C22, C26); 128.89 (C23, C25); 127.61 (C24).
Ch a r a ct er iza t ion of [(P h CH2)2NAlN(CH2P h )-µ-(CH2-
C6H4)]2 (6). Yield: 25.1%. Mp: 285 °C dec. 1H NMR (C6D6):
δH 3.85 (d, 2H, H10); 4.59 (d, 2H, H10); 7.73 (d, 2H, H13); 6.99
(m, 2H, H14); 6.99 (m, 2H, H15); 6.56 (d, 2H, H16); 3.49 (d,
2H, H20); 4.30 (d, 2H, H20); 7.64 (d, 4H, H22, H26); 7.37 (dd,
4H, H23, H25); 7.24 (m, 2H, H24); 3.94, 4.11 (dd, 8H, H30,
H37); 7.17 (m, 8H, H32, H36, H39, H43); 7.08-7.10 (m, 8H,
H33, H35, H40, H42); 7.08-7.10 (m, 4H, H34, H41).
1
Me derivative.7 Monitoring each of the reactions by H
NMR, as a function of time, suggests that the reactions
for R ) Et, Prn, Bun, and Bui follow generally the same
pathway as that of the R ) Me reaction.7 While the time
required for reaction completion does not depend on the
nature of the R group on aluminum, the percent yield
of recovered product, which ranges from 57% for R )
Me7 (1) to 31% for R ) Bun (4), decreases with increasing
steric bulk of R.
Because thermolysis of 1:1 mixtures of R3Al and
dibenzylamine led to elimination of one R group at 120
°C and to two R groups at 155 °C from the Al atom,
Ch a r a cter iza tion of [AlN-µ-(CH2C6H4)2]x (7). Yield: 26%.
Mp: >300 °C dec. H NMR (C6D6): δH 3.59 (d, 2H, H10); 4.02
(d, 2H, H10); 7.42 (d, 2H, H13); 7.07 (dd, 2H, H14); 7.09 (dd,
2H, H15); 6.62 (d, 2H, H16). 13C NMR (C6D6): δC 60.54 (C10);
149.2 (C11); 142.0 (C12); 137.2 (C13); 126.6 (C14); 128.9 (C15);
124.2 (C16).
(12) Siemens SHELXTL-PC Manual, Release 4.1; Siemens Analyti-
cal Instruments, Madison, WI, 1990.
(13) . International Tables for X-ray Crystallography; Kynoch
Press: Birmingham, England, 1974; Vol. 4, pp 99-101, 149-150.
(14) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.
(15) Styron, E. K. Ph.D. Dissertation, University of Alabama at
Birmingham, March 1999.
1

Notes
Organometallics, Vol. 19, No. 16, 2000 3255
experimental conditions were sought which would lead
to the removal of all three R groups. Two approaches
were taken. First, thermolysis of 1:1 mixtures of Me3Al
and dibenzylamine was attempted at higher tempera-
tures. Heating the reactants neat in a high-pressure
tube inserted into a 270 °C sand bath led to the
formation of a light green solid. Elemental analysis and
1H and 13C NMR data indicate that all three methyl
groups were eliminated from the Al moiety upon heating
at 270 °C and that the resulting Al-N compound is fully
ortho-metalated, [AlN-µ-(CH2C6H4)2]x. Unfortunately,
all attempts at growing X-ray-quality crystals failed.
The presence of a parent ion peak with m/z 572.18 in
the EI mass spectrum suggests the existence of a trimer,
C35H29Al3N3, in the gas phase. This ion could arise from
the loss of a benzyl group (m/z 91) from the trimer,
C42H36Al3N3. The ion peaks at m/z 91 and 572 are the
most prominent peaks in the mass spectrum and are of
almost equal intensity. Typically, EI mass spectra of
aminoalanes exhibit [M -R]+ as the molecular ion.1,2,4,16,17
The formation of a trimer in the gas phase is not
unexpected, as Waggoner and Power18 have shown that
the reactions of trimethylaluminum with bulky primary
amines upon heating lead to compounds of the type
[MeAlNR]x, where x depends on the steric nature of R.
F igu r e 1. ORTEP diagram of [PrnAlN(CH2Ph)-µ-(CH2-
C6H4)]2 (3). Thermal ellipsoids at 20% probability.
NMR chemical shift difference, ∆δH (ppm), ranges from
0.14 to 0.19 ppm. Assignments for the chemically
nonequivalent C(1) methylene protons in 2-5 and for
the two methyl groups in 5 were made by comparison
1
of the H 2-D NMR NOESY data with calculated H-H
3
distances from the X-ray data. Analysis of the J (H,H)
The second approach involved performing a thermoly-
sis reaction between Me3Al and dibenzylamine in a 1:2
mole ratio at 155 °C. This reaction led to an ortho-
metalated species, 6, wherein a dibenzylamino moiety
has replaced the methyl group on the Al. An indepen-
dent reaction of a 1:1 mole reaction mixture of 1 and
dibenzylamine at 155 °C also led to the formation of 6.
coupling data suggests that the Prn group is in a trans
conformation in solution with regard to the C(1)-C(2)
bond, similar to that demonstrated in the solid-state
1
molecular structure (Figure 1). The H NMR spectrum
for the n-butyl group in 4 is similar to that of 3 for the
C(1) and C(2) methylene protons; however, the C(3) CH2
protons demonstrate rapid conformational averaging in
solution. Variable-temperature 1H NMR studies of
compounds 2-5 conducted in toluene-d8 solution from
30 to 90 °C detected no additional conformational
averaging with increased temperature. The 13C NMR
chemical shifts for the alkyl groups in 1-5 were
determined by comparison of the 13C 2-D NMR hetero-
nuclear-correlated spectra with the known 1H NMR
chemical shifts. The δC data for 1-5 are comparable to
those reported for [R2AlN(CH2Ph)2]2,1,9,15 except that the
C(1) δC signal is to higher field by about 4 ppm in the
ortho-metalated dimers.
13C a n d 1H NMR Stu d ies. The 1H and 13C NMR
chemical shift assignment procedure for the benzyl
groups in compounds 2-5 was similar to that for 1.7
(See Figure 1 for atom numbering.) The 1H NMR as-
signments were determined from 1H NMR 2-D COSY
1
spectra and by comparing the results of the H NMR
2-D NOESY spectra with calculated H-H distances
from the X-ray data for the compounds.5,7 The 13C NMR
chemical shift assignments were obtained by a combi-
nation of 13C decoupled and 13C DEPT-45 NMR spectra,
1
2-D 13C{1H} heteronuclear J (C,H) correlations (HET-
1
3
COR), and 2-D H{13C} heteronuclear J (C,H) correla-
Almost complete 1H NMR chemical shift assignments
were made for [(PhCH2)2NAlN(CH2Ph)-µ-(CH2C6H4)]2
tions (HMBC).5,7 The H and 13C NMR chemical shifts
1
for the ortho-metalated and normal benzyl groups in
compounds 1-5 are similar to each other and show no
significant variation with the nature of the attached
alkyl group.
1
(6). The H NMR chemical shift assignments for that
portion of 6 common with 1-5 are consistent with, but
slightly different from, those of compounds 1-5. The
1H and 13C NMR spectra of 7 showed only one set of
resonances each for all of the ortho-metalated benzyl
groups in the molecule, suggesting an oligomeric form
where all the benzyl groups are chemically equivalent.
1
The H NMR chemical shifts for the alkyl groups in
compounds 2-5 were determined from the 1-D 1H NMR
and 2-D 1H COSY NMR spectra. These spectra are
interesting in that restricted conformational averaging
is observed on the NMR time scale, leading to chemical
shift nonequivalence for most of the methylene protons,
as well as for the methyl protons in the Bui group of 5.
The C(1) CH2 protons are nonequivalent and appear as
AB quartets with further 3J (H,H) coupling; their 1H
1
The H and 13C NMR chemical shift assignments and
values for 7 are similar to those of the orthometalated
benzyl groups in 1-5.
X-r a y Cr ysta llogr a p h ic Da ta . X-ray structures of
the five ortho-metalated aminoalane dimers were de-
termined in order to identify any structural differences
in the compounds due to the nature of the alkyl group
bound to the aluminum atoms and for comparison with
the structure of 1,7 where R ) Me. The ORTEP drawing
of the molecular structure of compound 3 is given in
Figure 1. Selected structural data for 1-6 are given in
Tables 1-3.All the ortho-metalated dimers crystallized
(16) Cesari, M.; Cucinella, S. In The Chemistry of Inorganic Homo-
and Heterocycles; Haiduc, I., Sowerby, D. B., Eds.; Academic: London,
1987; Vol. 1, Chapter 6.
(17) Bradley, D. C.; Harding, I. S.; Maia, I. A.; Motevalli, M. J . Chem.
Soc., Dalton Trans. 1997, 2969.
(18) Waggoner, K. M.; Power, P. P. J . Am. Chem. Soc. 1991, 113,
3385.

3256 Organometallics, Vol. 19, No. 16, 2000
Notes
Ta ble 1. Selected Bon d Len gth s (Å)
Al2N2 ring is a slightly distorted square plane where
the internal angles are very similar, ranging from
90.60(17)° for 6 to 91.4(1)° for 2 for the N-Al-N and
from 88.5(1)° for 3 to 89.40(17)° for 6 for the Al-N-Al
angles. The two Al-N bond distances associated with
each four-membered core are slightly asymmetric. The
Al-N distances (1.971(4) Å for 6 to 1.984(4) Å for 1)
included in the five-membered ortho-metalated ring are
slightly longer than the Al-N distances (1.944(4) Å for
6 to 1.960(3) Å for 5) in the four-membered core. Varying
the steric bulk of the R group bound to the group 13
metal atom had only a minor impact on the Al-N
bond distances. These geometries are representative of
those found in dimeric aminoalanes of the type [R2-
AlNR′2]2.4,16,17,19 The Al-N distance associated with the
(PhCH2)2N ligand in 6 (Al(1A)-N(2A) bond distance is
1.776(4) Å) is significantly different. This distance is
similar to that reported in systems containing a four-
coordinate aluminum atom bonded to a three-coordinate
nitrogen atom.18,20,21 Haaland has suggested that when
the aluminum and nitrogen are three-coordinate Al-N
bonds contain a greater percentage of covalent character
and therefore should be shorter than the four-coordinate
case.22 The angles about the aluminum atoms in all the
compounds are highly distorted, as previously observed
in the structure of 1, due to the incorporation of the
aluminum atom in the five-membered ring formed upon
orthometalation. The internal angles and Al-N dis-
tances for the Al2N2 ring in 1-6 are comparable with
those reported for the [BuiAl-iminodibenzyl] orthometa-
lated dimer.11 The n-propyl (3) and n-butyl (4) alkyl
chains are in an extended trans conformation in the
solid state. The H(1A)-C(1)-C(2)-H(2A) and H(1B)-
C(1)-C(2)-H(2B) angles are 179.5 and 178.8°, respec-
tively, in compound 3 (see Figure 1) with similar values
for the dihedral angles about the C(1)-C(2) (174.7,
173.2°) and C(2)-C(3) (175.9, 175.9°) bonds in 4, sug-
gesting that the alkyl chain conformations are similar
in solution and the solid state.
bond
1a
2
3
4
5
Al(1)-N(1)
Al(1)-C(1)
1.984(4) 1.977(2) 1.982(2) 1.979(3) 1.978(2)
1.911(5) 1.951(2) 1.949(3) 1.962(4) 1.969(3)
Al(1)-C(12) 1.965(5) 1.970(3) 1.959(3) 1.957(4) 1.966(3)
Al(1)-N(1A) 1.945(3) 1.947(2) 1.947(2) 1.955(3) 1.960(3)
N(1)-C(10)
N(1)-C(20)
1.497(5) 1.496(3) 1.493(3) 1.504(5) 1.491(3)
1.496(6) 1.498(3) 1.501(4) 1.477(5) 1.497(3)
C(10)-C(11) 1.516(8) 1.516(5) 1.514(4) 1.522(5) 1.514(3)
C(11)-C(12) 1.400(6) 1.393(3) 1.400(4) 1.391(5) 1.402(3)
C(11)-C(16) 1.394(6) 1.392(3) 1.385(4) 1.389(5) 1.387(3)
C(12)-C(13) 1.405(8) 1.407(5) 1.396(4) 1.399(5) 1.401(4)
a
Data taken from ref 7.
Ta ble 2. Selected Bon d An gles (d eg)
angle
1a
2
3
4
5
N(1)-Al(1)-C(1)
N(1)-Al(1)-C(12)
C(1)-Al(1)-C(12)
116.0(2) 115.7(1) 115.6(1) 115.0(1) 116.6(1)
89.9(2) 89.8(1) 89.9(1) 89.9(1) 89.5(1)
126.2(2) 129.3(1) 129.2(1) 124.7(2) 131.1(1)
C(1)-Al(1)-N(1A) 116.3(2) 114.0(1) 113.7(1) 117.0(1) 113.6(1)
N(1)-Al(1)-N(1A) 91.2(1) 91.4(1) 91.5(1) 90.7(1) 91.3(1)
Al(1)-N(1)-C(20) 114.8(3) 115.8(1) 114.5(2) 113.9(2) 117.2(1)
C(12)-Al(1)-N(1A) 107.7(2) 107.9(1) 108.3(1) 110.7(1) 105.7(1)
Al(1)-N(1)-Al(1A)
88.8(1) 88.6(1) 88.5(1) 89.3(1) 88.7(1)
Al(1)-N(1)-C(10) 107.6(3) 108.0(2) 107.8(2) 108.2(2) 107.5(1)
C(20)-N(1)-Al(1A) 115.5(3) 116.0(2) 116.6(2) 113.7(2) 115.2(2)
C(10)-N(1)-C(20) 109.3(3) 109.6(2) 110.1(2) 111.2(3) 108.5(2)
C(10)-C(11)-C(12) 119.3(4) 119.2(2) 119.0(2) 119.5(3) 118.3(2)
C(10)-N(1)-Al(1A) 119.2(3) 117.3(1) 117.3(2) 118.5(2) 118.7(2)
C(12)-C(11)-C(16) 121.7(5) 122.2(3) 121.4(3) 121.5(4) 121.9(2)
N(1)-C(10)-C(11) 112.7(3) 112.1(2) 112.2(2) 112.1(3) 111.9(2)
Al(1)-C(12)-C(13) 134.3(3) 134.9(2) 134.0(2) 133.1(3) 134.9(2)
Al(1)-C(12)-C(11) 108.7(4) 108.7(2) 108.8(2) 109.3(2) 108.8(2)
C(11)-C(12)-C(13) 117.0(4) 116.2(2) 117.0(3) 117.5(3) 116.1(2)
a
Data taken from ref 7.
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 6 (Molecu le 1)
Al(1A)-N(1A)
Al(1A)-N(2A)
Al(1A)-C(12A)
Al(1A)-N(1AA)
N(1A)-C(10A)
N(1A)-C(20A)
1.971(4)
1.776(4)
1.938(5)
1.944(4)
1.494(6)
1.481(6)
C(10A)-C(11A)
C(11A)-C(12A)
C(11A)-C(16A)
C(12A)-C(13A)
N(2A)-C(30A)
N(2A)-C(37A)
1.514(7)
1.395(6)
1.407(6)
1.387(7)
1.444(6)
1.480(6)
N(1A)-Al(1A)-N(2A)
N(1A)-Al(1A)-C(12A)
N(2A)-Al(1A)-C(12A)
N(2A)-Al(1A)-N(1AA)
N(1A)-Al(1A)-N(1AA)
Al(1A)-N(1A)-C(20A)
C(12A)-Al(1A)-N(1AA)
Al(1A)-N(1A)-Al(1C)
Al(1A)-N(1A)-C(10A)
C(20A)-N(1A)-Al(1C)
C(10A)-N(1A)-C(20A)
C(10A)-C(11A)-C(12A)
C(10A)-N(1A)-Al(1C)
C(12A)-C(11A)-C(16A)
N(1A)-C(10A)-C(11A)
Al(1A)-C(12A)-C(13A)
Al(1A)-C(12A)-C(11A)
C(11A)-C(12A)-C(13A)
118.60(19)
90.70(18)
121.9(2)
115.97(17)
90.60(17)
113.7(3)
112.5(2)
89.40(17)
107.7(3)
113.3(3)
110.3(4)
119.8(4)
120.6(3)
121.1(5)
111.8(4)
134.6(4)
108.4(4)
116.9(5)
Ack n ow led gm en t. This work was supported in part
by a U.S. Department of Education GAANN Fellowship
to E.K.S. We thank Dr. David Powell, Department of
Chemistry, University of Florida, Gainesville, FL, for
obtaining the mass spectrum of 7.
Su p p or tin g In for m a tion Ava ila ble: Tables of summary
of crystallographic data, X-ray crystal data, structure solution
and refinement, atomic coordinates, interatomic distances and
angles, and hydrogen atom coordinates for compounds 2-6,
1
IR data and elemental analyses, H NMR spectra of the alkyl
regions of 2-5, and COSY spectra of 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM000072Z
(19) Schauer, S. J .; Robinson, G. H. J . Coord. Chem. 1993, 30, 197.
(20) Sheldrick, G. M.; Sheldrick, W. S. J . Chem. Soc. A 1969, 2279.
(21) Waggoner, K. M.; Power, P. P. Angew. Chem., Int. Ed. Engl.
1988, 27, 1699.
(22) Haaland, A. In Coordination Chemistry of Aluminum; Robinson,
G. H., Ed.; VCH: New York, 1993; Chapter 1.
with a planar Al2N2 core that possesses inversion
symmetry. The asymmetric unit of 2-5 consists of half
of the appropriate dimeric molecule, while that of 6
consists of two half-molecules. The structure of the