Synthesis and molecular structure studies of [Me2AlN(i-Pr)CH2PH]2 and the related orthometalated dimers [RAlN(i-Pr)-μ-(CH2C6H4)]2, where R = Me, n-Pr, n-Bu, i-Bu

Article abstract of DOI:10.1021/om020768n

The synthesis and molecular structure studies of [Me₂AlN(i-Pr)CH₂Ph]₂ and the related orthometalated dimers [RAIN(i-Pr)-μ-(CH₂C₆H₄)]₂, where R = Me, n-Pr, n-Bu, i-Bu were conduct

Full text of DOI:10.1021/om020768n

Organometallics 2002, 21, 5987-5990
5987
Notes
Syn th esis a n d Molecu la r Str u ctu r e Stu d ies of
[Me2AlN(i-P r )CH2P h ]2 a n d th e Rela ted Or th om eta la ted
Dim er s [RAlN(i-P r )-µ-(CH2C6H4)]2, w h er e R ) Me, n -P r ,
n -Bu , i-Bu
Omar M. Kekia, Larry K. Krannich,* and Charles L. Watkins*
Department of Chemistry, University of Alabama at Birmingham,
Birmingham, Alabama 35294
Christopher D. Incarvito and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received September 16, 2002
Summary: [Me2AlN(i-Pr)CH2Ph]2 (1) and the related
dimer series [RAlN(i-Pr)-µ-(CH2C6H4)]2, R ) Me (2), n-Pr
(3), n-Bu (4), and i-Bu (5), were synthesized by ther-
molysis of 1:1 mixtures of R3Al and HN(i-Pr)CH2Ph. The
reaction times and temperatures required and the mo-
lecular structure and NMR data for 1-5 are compared
with reported data for [Me2AlN(CH2Ph)2]2 and the series
orthometalated dimers [RAlN(t-Bu)-µ-(CH2C6H4)]2 are
obtained at lower temperatures, with much shorter
reaction times, and in higher yields. In fact, the ortho-
metalation reactions are so facile that they proceed
before the initial reactants are consumed and dimer
formation, [R2AlN(t-Bu)CH2Ph]2, is complete; as a con-
sequence, no dimers were isolated for the tert-butylben-
zylamine reaction system. To our knowledge, the syn-
thesis and characterization of only two similar alumi-
num-nitrogen orthometalated dimers have been re-
ported.7,8 Therefore, to understand more fully the
requirements for orthometalation in these systems, we
have chosen the amine HN(i-Pr)CH2Ph, with the less
bulky isopropyl group, for reaction with R3Al in an
attempt to optimize both dimer and orthometalated
dimer formation and to investigate in more detail the
influence of the groups attached to the aluminum and
nitrogen atoms. In this paper, we report the study of
the thermolysis reactions of HN(i-Pr)CH2Ph with
R3Al. The ease of synthesis and spectral and molecular
structure properties of the three orthometalated dimer
series [RAlN(R′)-µ-(CH2C6H4)]2 (R′ ) benzyl, i-Pr, t-Bu)
are compared in terms of R and R′.
[RAlN(CH2Ph)-µ-(CH2C6H4)]2 and
(CH2C6H4)]2.
[RAlN(t-Bu)-µ-
In tr od u ction
Recently, there have been several reports discussing
the influence that bulky substituents have on the
formation of orthometalated palladium complexes.1 Also,
we have reported the synthesis and characterization of
two series of orthometalated aluminum-nitrogen dimers
from the thermolysis of R3Al (R ) Me, Et, n-Pr, n-Bu,
i-Bu) with dibenzylamine and with tert-butylbenz-
ylamine.1-3 Therein, the effects of the steric bulk of the
organic substituents on the nitrogen and aluminum
atoms were investigated in terms of the ease of the
formation of the orthometalated dimers and their
spectral and structural properties. The reactions of R3-
Al and HN(CH2Ph)2 lead to the formation of [R2AlN-
(CH2Ph)2]2 at 120 °C,3-6 but the orthometalated dimers
are obtained only after heating at 150 °C for three
weeks. The thermolysis reactions of mixtures of R3Al
and HN(t-Bu)CH2Ph proceed more readily,1 and the
Resu lts a n d Discu ssion
Syn t h esis. Equimolar mixtures of R3Al and HN-
(i-Pr)CH2Ph in toluene (R ) Me, Et, n-Pr, n-Bu, i-Bu)
1
were heated from 80 to 120 °C and monitored by H
NMR to establish experimental conditions for dimer
formation. The aminoalane dimers, [R2AlN(i-Pr)CH2-
Ph]2 (R ) Me, Et, n-Pr, n-Bu), were formed under
moderate conditions (80-100 °C, 12-36 h) and isolated
in almost quantitative yields (90-98%),9 but crystals
suitable for X-ray diffraction studies were obtained only
* Corresponding authors. (L.K.K.) E-mail: krannich@uab.edu. Tel:
(205) 934-8017. Fax: (205) 934-2543. (C.L.W.) E-mail: watkins@uab.edu.
(1) Kekia, O. M.; Watkins, C. L.; Krannich, L. K.; Rheingold, A. L.;
Liable-Sands, L. M. Organometallics 2001, 20, 582.
(2) Styron, E. K.; Lake, C. H.; Watkins, C. L.; Krannich, L. K.;
Incarvito, C. D.; Rheingold, A. L. Organometallics 2000, 19, 3253.
(3) Styron, E. K.; Lake, C. H.; Watkins, C. L.; Krannich, L. K.
Organometallics 1998, 17, 4319.
(4) Thomas, C. J .; Krannich, L. K.; Watkins, C. L. Polyhedron 1993,
12, 389.
(5) Styron, E. K.; Lake, C. H.; Schauer, S. J .; Watkins, C. L.;
Krannich, L. K. Polyhedron 1999, 18, 1595.
(7) Waggoner, K. M.; Olmstead, M. M.; Power, P. P. Polyhedron
1990, 9, 257.
(8) Lee, B.; Pennington, W. T.; Robinson, G. H. Inorg. Chim. Acta
1991, 190, 173.
(6) Styron, E. K.; Lake, C. H.; Powell, D. H.; Watkins, C. L.;
Krannich, L. K. Polyhedron 2002, 21, 1747.
(9) The synthesis and characterization of [R2AlN(i-Pr)CH2Ph]2,
where R ) Et, n-Pr, n-Bu, is given in the Supporting Information.
10.1021/om020768n CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/23/2002

5988 Organometallics, Vol. 21, No. 26, 2002
Notes
from the methyl derivative, 1. Reaction of (i-Bu)3Al with
HN(i-Pr)CH2Ph leads initially to dimer formation,
[(i-Bu)2AlN(i-Pr)CH2Ph]2, but its decomposition occurs
before the reactants are consumed. The reaction condi-
tions for formation of [R2AlN(i-Pr)CH2Ph]2 are similar
to those for the series [R2AlN(CH2Ph)2]2, but for the
latter all five dimers were isolated and characterized.3-6
However, the thermolysis reactions of 1:1 mixtures of
R3Al with HN(t-Bu)CH2Ph at 100 °C are similar to the
reaction of (i-Bu)3Al with HN(i-Pr)CH2Ph in that the
reactions are facile and the dimers formed are subject
to further alkane elimination.1 The role of R and R′ in
influencing the reaction sequence 2R3Al + HNR′2 f 2R3-
Al‚HNR′2 f [R2AlNR′2]2 + 2RH has been discussed in
terms of the steric and electronic effects of the R and R′
groups.10 Our results are in agreement with those of
Bradley10 in that the influence of R′ is more important
than that of R and that the effect is primarily steric in
nature. Mass spectral studies on the related series [Me2-
InNR′2]211 and on [Me2AlN(CH2Ph)2]2 and [Me2AlN(H)-
CH2Ph]212,13 suggest that the dimers become less stable
in the vapor phase with increasing steric bulk of the R′
group.
Thermolysis of the R3Al/HN(i-Pr)CH2Ph mixtures at
higher temperatures results in additional alkane elimi-
nation. Orthometalated dimer formation is complete for
2 after heating for 6 days at 150 °C followed by 4 days
at 175 °C, whereas compounds 3-5 require less heating
(6 days at 155 °C).14 The synthesis of [RAlN(CH2Ph)-
µ-(CH2C6H4)]2 requires heating of the R3Al/HN(CH2Ph)2
mixtures at 150-155 °C for three weeks, independent
of R; however, the reaction conditions for the formation
of [RAlN(t-Bu)-µ-(CH2C6H4)]2 from thermolysis of R3Al/
HN(t-Bu)CH2Ph are more moderate (120 °C, 1-4 days,
with R ) Me requiring heating for the longest time).1
Substitution of an isopropyl or tert-butyl group for a
benzyl group in the secondary amine facilitates the
orthometalation reaction, and as the steric bulk of the
R′ group increases, the reaction conditions depend more
on the nature of the R alkyl group. Also, [R2AlN(Me)-
CH2Ph]2 is readily formed from the thermolysis of R3-
Al/HN(Me)CH2Ph mixtures, but the corresponding orth-
ometalated dimers are obtained from these reaction
mixtures only at high temperatures and very long
heating times.15 The thermolysis reaction of Me3Al with
the primary amine H2NCH2Ph, where R′ ) H instead
of benzyl, at 135 °C results in the formation of the
hexameric cage compound [MeAlNCH2Ph]6,12 rather
than the orthometalated dimer.
F igu r e 1. ORTEP diagram of [Me2AlN(i-Pr)CH2Ph]2 (1a ).
Hydrogen atoms omitted for clarity and thermal ellipsoids
at 30% probability.
metalated dimers [RAlN(R′)-µ-(CH2C6H4)]2 have estab-
lished that aluminum-nitrogen dimer stability and the
subsequent ease of orthometalation depend to a signifi-
cant degree on the steric nature of the group on the
nitrogen atom of the amine, R′, and are affected only
slightly by the alkyl group R. These findings are in
agreement with reactivity studies involving the forma-
tion of orthometalated palladium complexes from di-
benzylamine or similar aromatic amines.1
1H a n d 13C NMR Da ta . The 1H and 13C NMR
chemical shift assignments for 1-5 were made using a
combination of 1D and 2D NMR techniques and the
procedures established for the NMR chemical shift
assignments of [Me2AlN(H)CH2Ph]2,12 [R2AlN(CH2-
Ph)2]2,3,6 [RAlN(CH2Ph)-µ-(CH2C6H4)]2,2 and [RAlN-
1
(t-Bu)-µ-(CH2C6H4)]2.1 The H and 13C NMR spectra of
[Me2AlN(i-Pr)CH2Ph]2 (1) indicate the presence of both
cis (1a ) and trans (1b) isomers with respect to the Al2N2
ring in benzene-d6 solution at RT in a 60:40 cis/trans
1
isomer ratio. The H NMR chemical shift assignments
for the individual isomers were made from the 1D and
1
the 2D H{1H} COSY and NOESY NMR spectra. The
two 1H NMR cis isomer methyl chemical shifts H(1) and
H(2) (Figure 1), were assigned from the NOESY NMR
spectra. Substitution of the more sterically demanding
isopropyl group for a benzyl group in [Me2AlN(CH2-
3
Ph)2]2 causes significant downfield NMR chemical
shifts for the ortho protons (H(12), H(16); ∆δH ) 0.41
ppm) and the ipso (C(11); ∆δC ) 3.4 ppm), ortho (C(12),
C(16); ∆δC ) 0.94), and methyl (C(1), ∆δC ) 1.2; C(2),
∆δC ) 3.1; trans-CH3, ∆δC ) 2.6 ppm) carbons. 13C NMR
chemical shifts are known to be sensitive to steric effects
in related aluminum-nitrogen4-6,10,16 and aluminum-
phosphorus17 systems.
Restricted conformational averaging is observed in
portions of the 1H NMR spectra for compounds 2-5
(Figure 2). There is chemical shift nonequivalence for
the C(1) methylene group protons in 3-5, the C(10)
methylene group protons, the C(21) and C(22) methyl
group protons in the isopropyl group, and the methyl
group protons for the isobutyl group in 5. The C(21) and
C(22) methyl group protons were assigned from the 2D
NOESY spectra, where the C(22) methyl group protons
correlate with one of the C(10) methylene protons and
the C(21) methyl group protons correlate with the C(13)
aromatic ring proton. Interestingly, the C(22) methyl
group protons are, on average, 0.30 ppm to higher field
and the C(21) methyl group protons are 0.14 ppm to
Therefore, our systematic study of the formation of
the aluminum-nitrogen dimers [R2AlN(R′)CH2Ph]2
(where R′ ) Me; benzyl, isopropyl, tert-butyl) and the
requirements for formation of their respective ortho-
(10) Bradley, D. C.; Harding, I. S.; Maia, I. A.; Motevalli, M. J . Chem.
Soc., Dalton Trans. 1997, 2969.
(11) Aitchison, K. A.; Backer-Dirks, J . D. J .; Bradley, D. C.; Faktor,
M. M.; Frigo, D. M.; Hursthouse, M. B.; Hussain, B.; Short, R. L. J .
Organomet. Chem. 1989, 366, 11.
(12) Styron, E. K.; Lake, C. H.; Powell, D. H.; Krannich, L. K.;
Watkins, C. L. J . Organomet. Chem. 2002, 649, 78.
(13) Beachley, O. T., J r. Inorg. Chem. 1981, 20, 2825.
(14) The synthesis and characterization of [EtAlN(i-Pr)-µ-(CH2C6H4)]2
is given in the Supporting Information. No crystals suitable for X-ray
analysis could be obtained.
(15) Kekia, O. M.; Lake, C. H.; Krannich, L. K.; Watkins, C. L.
Presented at the 216th National Meeting of the American Chemical
Society, Boston, MA, August 1998, INORG 255.
(16) Schauer, S. J .; Watkins, C. L.; Krannich, L. K.; Gala, R. B.;
Gundy, E. M.; Lagrone, C. B. Polyhedron 1995, 14, 3505.
(17) Barron, A. R. J . Chem. Soc., Dalton Trans. 1988, 3047.

Notes
Organometallics, Vol. 21, No. 26, 2002 5989
Ta ble 2. Selected Bon d Len gth s (Å) for 2-5
bond
2
3
4
5
Al(1)-N(1)
1.968 (3)
1.977 (3)
1.978 (2)
1.978 (2)
1.977 (3)
1.972 (3)
1.978 (3)
1.505 (3)
1.514 (4)
1.9629 (15) 1.9705 (17)
1.9707 (16) 1.9793 (16)
1.9707 (16) 1.9793 (16)
1.9629 (15) 1.9705 (17)
1.9645 (18) 1.970 (2)
Al(1)-N(1A) 1.984 (3)
Al(1A)-N(1) 1.989 (3)
Al(1A)-N(1A) 1.973 (3)
Al(1)-C(1)
Al(1)-C(12)
N(1)-C(10)
N(1)-C(20)
1.972 (4)
1.974 (4)
1.511 (5)
1.525 (5)
1.962 (2)
1.499 (2)
1.507 (2)
1.970 (2)
1.501 (2)
1.502 (3)
Al(1)‚‚‚Al(1A) 2.7782 (17) 2.7711 (15) 2.7605 (10) 2.7712 (11)
C(10)-C(11) 1.531 (6)
C(11)-C(12) 1.419 (6)
1.521 (4)
1.397 (5)
1.514 (3)
1.411 (2)
1.511 (3)
1.405 (3)
Ta ble 3. Selected Bon d An gles (d eg) for 2-5
angle
2
3
4
5
Figu r e 2. ORTEP diagram of [n-BuAlN(i-Pr)-µ-(CH2C6H4)]2
(4). Hydrogen atoms omitted for clarity and thermal
ellipsoids at 30% probability.
N(1)-Al(1)-C(1)
N(1)-Al(1)-C(12)
C(1)-Al(1)-C(12) 125.43 (19) 123.65 (13) 123.00 (8) 129.40 (9)
C(1)-Al(1)-N(1A) 113.68 (17) 112.90 (12) 113.55 (8) 109.18 (8)
N(1)-Al(1)-N(1A)
Al(1)-N(1)-C(20) 119.5 (2)
C(12)-Al(1)-N(1A) 109.09 (15) 109.53 (11) 109.38 (7) 107.40 (8)
Al(1)-N(1)-Al(1A) 89.21 (13) 88.97 (10) 89.14 (6) 89.11 (6)
Al(1)-N(1)-C(10) 108.7 (2)
C(20)-N(1)-Al(1A) 110.5 (2)
C(10)-N(1)-C(20) 111.9 (3)
C(10)-C(11)-C(12) 119.2 (3)
C(10)-N(1)-Al(1A) 115.5 (2)
N(1)-C(10)-C(11) 112.4 (3)
Al(1)-C(12)-C(13) 135.2 (3)
Al(1)-C(12)-C(11) 108.3 (3)
120.04 (18) 123.60 (14) 123.74 (8) 122.87 (9)
90.75 (16) 90.13 (12) 90.36 (7) 89.86 (8)
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1a
90.94 (14) 91.03 (10) 90.86 (6)
90.89 (6)
120.04 (18) 119.78 (11) 119.69 (13)
Al(1)-N(1A)
Al(1)-C(1)
Al(1)‚‚‚‚Al(1A)
N(1)-C(20)
1.977 (2)
1.990 (3)
2.7948 (15)
1.524 (3)
Al(1)-N(1)
Al(1)-C(2)
N(1)-C(10)
N(1)-Al(1A)
2.031(2)
1.979 (3)
1.515 (3)
1.977 (2)
108.20 (17) 108.66 (11) 108.43 (12)
111.05 (17) 110.76 (12) 111.81 (12)
111.7 (2)
119.4 (2)
111.54 (14) 111.29 (14)
119.14 (16) 119.01 (19)
N(1A)-Al(1)-C(2) 120.10 (11) N(1A)-Al(1)-C(1) 110.64 (11)
115.35 (18) 115.45 (12) 115.02 (13)
C(2)-Al(1)-C(1)
C(2)-Al(1)-N(1)
112.40 (13) N(1A)-Al(1)-N(1)
112.05 (11) C(1)-Al(1)-N(1)
88.42 (9)
110.84 (12)
C(10)-N(1)-Al(1A) 119.02 (15)
112.8 (2)
134.4 (2)
108.8 (2)
112.51 (14) 112.20 (16)
134.43 (14) 134.38 (17)
108.57 (14) 108.75 (14)
C(10)-N(1)-C(20) 113.9 (2)
C(20)-N(1)-Al(1A) 114.27 (16) C(10)-N(1)-Al(1) 107.30 (15)
C(20)-N(1)-Al(1) 110.43 (16) Al(1A)-N(1)-Al(1) 88.40 (9)
N(1)-C(10)-C(11) 119.4 (2)
structure data for 1a are in agreement with published
data and correlations of the steric properties of func-
tional groups attached to the amine nitrogen with the
corresponding dimer geometries.3,6,10-12,18-22
N(1)-C(20)-C(21) 113.2 (2)
lower field in 2-5, compared to 1a and 1b. In contrast,
the 1H NMR spectra show that the C(21) and C(22)
methyl group protons are chemically equivalent in 1a
and in 1b, as are the C(10) methylene group protons;
also, the tert-butyl methyl group protons are equivalent
in [RAlN(t-Bu)-µ-(CH2C6H4)]2.1 The NOESY data sug-
gest a trans conformation for 2-5 in solution with
respect to the Al2N2 ring, consistent with the X-ray data,
and the 1H NMR solution and X-ray data for [RAlN-
(t-Bu)-µ-(CH2C6H4)]2.1 Substitution of a tert-butyl for a
benzyl group in the othometalated dimer series [RAlN-
(CH2Ph)-µ-(CH2C6H4)]22 results in significant 13C NMR
chemical shift changes at the C(1) (∆δC(av) ) 5.9 ppm),
C(10) (-4.8 ppm), and C(12) (4.8 ppm) carbons. Substi-
tution of an isopropyl group for a benzyl group leads to
a large 13C chemical shift change only at the C(10)
carbon (∆δC(av) ) -9.1 ppm). This 13C NMR chemical
shift change, larger than any observed for the substitu-
tion of a tert-butyl group for a benzyl group, may arise
due to a significant interaction with the C(22) methyl
group, as evidenced by the restricted rotation of iso-
propyl group in 2-5.
X-r a y Cr ysta llogr a p h y Da ta . The ORTEP drawing
of the molecular structure and the atom labeling scheme
for cis-[Me2AlN(i-Pr)CH2Ph]2 (1a ) are shown in Figure
1, with selected bond lengths (Å) and angles (deg)
summarized in Table 1. The molecular structure of 1a
has a nonplanar Al2N2 core with a fold angle about the
Al‚‚‚Al axis of 26.9°. These data are consistent with
those reported for cis-[Me2AlN(H)i-Pr]2,18 cis-[Me2AlN-
(Me)CH2Ph]2,15 and [Me2AlN(C6H11)2]2,19 with fold angles
of 15.5°, 20.4°, and 27.4°, respectively. The molecular
The ORTEP drawing of the molecular structure of the
orthometalated dimer [n-BuAlN(i-Pr)-µ-(CH2C6H4)]2 (5)
is shown in Figure 2, and representative bond lengths
and bond angles for 2-5 are listed in Tables 2 and 3.
The molecular structures of [RAlN(i-Pr)-µ-(CH2C6H4)]2
each exhibit a planar Al2N2 core that possesses inversion
symmetry. The Al2N2 ring is flanked on both sides by
bridging CH2C6H4 groups in a trans orientation relative
to the core ring. The Al2N2 ring geometry is almost
square planar; the N-Al-N angle varies from
90.80(14)° to 91.03(10)° and the Al-N-Al angle from
88.97(10)° to 89.20(13)° with R. The two Al-N distances
are very similar, with the Al-N bond included in the
five-membered orthometalated ring being slightly shorter
(1.9629(15)-1.977(3) Å) than the other Al-N bond
(1.9707(16)-1.986(3) Å). There are only minor varia-
tions in the Al2N2 ring geometry with R.
The Al2N2 ring geometries for the [RAlN(i-Pr)-µ-
(CH2C6H4)]2 and [RAlN(CH2Ph)-µ-(CH2C6H4)]2 dimers
are very similar. Substitution of the isopropyl for a
benzyl group results in small increases in the nonortho-
metalated Al-N bond distances (average, 0.027 Å) and
slight changes in the N-Al-N and Al-N-Al bond
angles, with the Al2N2 rings becoming more square.
Modest changes occur in certain angles external to the
ring, with the greatest change being 6.8° for the C(1)-
(19) Belgardt, T.; Storre, J .; Klemp. A.; Gornitzka, H.; Ha¨ming, L.;
Schmidt, H.-G.; Roesky, H. W. J . Chem. Soc., Dalton Trans. 1995, 3747.
(20) Schauer, S. J .; Robinson, G. H. J . Coord. Chem. 1993, 30, 197.
(21) Lagrone, C. B.; Schauer, S. J .; Thomas, C. J .; Gray, G. M.;
Watkins, C. L.; Krannich, L. K. Organometallics 1996, 15, 2458.
(22) Du¨michen, U.; Gelbrich, T.; Sieler, J . Z. Anorg. Allg. Chem.
1999, 625, 262.
(18) Amirkhalili, S.; Hitchcock, P. B.; J enkins, A. D.; Nyathi, J . Z.;
Smith, J . D. J . Chem. Soc., Dalton Trans. 1981, 377.

5990 Organometallics, Vol. 21, No. 26, 2002
Notes
126.37 (C14), 128.68 (C15), 136.11 (C13), 145.2 (C12), 150.86
(C11). Anal. Calcd (found) for C22H32Al2N2: C, 69.82 (69.77);
H, 8.52 (8.49); N, 7.40 (7.38).
Al(1)-N(1) angle. Substitution of the more sterically
demanding tert-butyl group for a benzyl group causes a
reversal in the relative magnitudes of the N-Al-N and
Al-N-Al angles1 with elongation of the Al2N2 ring now
along the Al‚‚‚Al line. For the dibenzylamine and
isopropylbenzylamine orthometalated dimers, the
N‚‚‚N distances are longer. Also, four angles external
to the Al2N2 ring change more than 10° upon t-Bu group
substitution.
Ch a r a cter iza tion of [n -P r AlN(i-P r )-µ-(CH2C6H4)]2 (3).
1
Mp: 156-160 °C. Yield: 1.20 g, 55%. H NMR: δH 0.14, 0.29
(m, 4H, H1), 0.63 (d, 6H, H22), 1.07 (d, 6H, H21), 1.15 (t, 6H,
H3), 1.64 (m, 4H, H2), 3.07 (m, 2H, H20), 3.96, 4.16 (dd, 4H,
H10), 7.15 (2H, H16), 7.27 (2H, H14), 7.29 (2H, H15), 7.84 (2H,
H13). 13C NMR: δC 10.9 (C1), 19.39 (C2), 20.91 (C3), 20.11
(C22), 22.94 (C21), 48.86 (C20), 49.75 (C10), 123.83 (C16),
126.35 (C14), 128.64 (C15), 136.38 (C13), 145.1 (C12), 150.98
(C11). Anal. Calcd (found) for C26H40Al2N2: C, 71.86 (70.96);
H, 9.28 (9.27); N, 6.45 (6.79).
Exp er im en ta l Section
Standard inert atmosphere and vacuum line techniques
were employed for the synthesis and purification of the
compounds. All solvents were dried by refluxing over sodium
and were distilled under nitrogen. The trialkylaluminum
compounds (Texas Alkyls) were used as received. Isopropyl-
benzylamine (Aldrich) was stored over molecular sieves. 1H
and 13C NMR spectra were obtained on a Bruker DRX-400 FT-
NMR spectrometer, operating at 400.132 and 100.625 MHz,
respectively. Solutions for NMR analysis were prepared using
benzene-d6 with (CH3)4Si as internal reference. Complete 1H
and 13C NMR chemical shift assignments were made on the
basis of both coupled and decoupled 1D NMR, 13DEPT, and
1H{1H} COSY, 13C{1H} HETCOR, and 1H{1H} NOESY 2D
NMR experiments. The FT-IR spectra were obtained using
split mull samples in Nujol and Kel-F (halocarbon emulsions)
on KBr disks. Elemental analyses were carried out by E & R
Microanalytical Laboratory, Inc. Parsippany, NJ . All melting
points reported are uncorrected and were obtained in sealed
capillaries under nitrogen.
Gen er al Syn th esis of [Me2AlN(i-P r )CH2P h ]2 an d [RAlN-
(i-P r )-µ-(CH2C6H4)]2. [Me2AlN(i-Pr)CH2Ph]2 (1) and [RAlN-
(i-Pr)-µ-(CH2C6H4)]2, R ) Me (2), n-Pr (3), n-Bu (4), i-Bu (5),
were synthesized by mixing in the drybox at room temperature
in a high-pressure thick-walled glass tube R3Al (10 mmol)
diluted in 5 mL of dry toluene with HN(i-Pr)CH2Ph (1.486 g,
10 mmol) also diluted in 5 mL of dry toluene. The total volume
of the solution was then brought up to 15 mL with toluene.
Each tube was then heated in an oil bath to the desired
temperature. The progress of each reaction was monitored by
1H NMR After the reaction was complete, the toluene was
removed under reduced pressure, and the products were
isolated as white solids. The products were purified by crystal-
lization from pentane. X-ray grade crystals were obtained
Ch a r a cter iza tion of [n -Bu AlN(i-P r )-µ-(CH2C6H4)]2 (4).
Mp: 153-155 °C. Yield: 1.15. g, 50%. 1H NMR: δH 0.14, 0.30
(m, 4H, H1), 0.66 (d, 6H, H22), 1.08 (d, 6H, H21), 0.99 (t, 6H,
H4), 1.49 (m, 4H, H3), 1.60 (m, 4H, H2), 3.09 (m, 2H, H20),
3.98, 4.18 (dd, 4H, H10), 7.16 (2H, H16), 7.26 (2H, H14), 7.28
(2H, H15), 7.85 (2H, H13). 13C NMR: δC 7.6 (C1), 14.08 (C4),
28.18 (C2), 29.21 (C3), 20.14 (C22), 22.96 (C21), 48.86 (C20),
49.75 (C10), 123.84 (C16), 126.36 (C14), 128.65 (C15), 136.36
(C13), 145.1 (C12), 151.00 (C11). Anal. Calcd (found) for C28H44
Al2N2: C, 72.69 (72.19); H, 9.59 (9.74); N, 6.06 (6.16).
-
Ch a r a cter iza tion of [i-Bu AlN(i-P r )-µ-(CH2C6H4)]2 (5).
1
Mp: 159-162 °C. Yield: 1.37 g, 59%. H NMR: δH 0.12, 0.27
(m, 4H, H1), 0.66 (d, 6H, H22), 1.10 (d, 6H, H21), 1.13 (d, 6H,
H3 or H4), 1.16 (d, 6H, H3 or H4), 2.01 (m, 2H, H2), 3.07 (m,
2H, H20), 3.98, 4.16 (dd, 4H, H10), 7.14 (2H, H16), 7.26 (2H,
H14), 7.27 (2H, H15), 7.89 (2H, H13). 13C NMR: δC 20.1 (C1),
26.40 (C2), 28.43 (C3 or C4), 28.55 (C3 or C4), 20.18 (C22),
22.91 (C21), 48.85 (C20), 49.85 (C10), 123.83 (C16), 126.39
(C14), 128.62 (C15), 136.50 (C13), 145.3 (C12), 150.99 (C11).
Anal. Calcd (found) for C28H44Al2N2: C, 72.69 (72.64); H, 9.59
(9.56); N, 6.06 (5.99).
X-r a y Cr ysta llogr a p h y. Crystals suitable for single-crystal
X-ray diffraction were selected and mounted in nitrogen-
flushed capillaries. The data were collected on a Siemens P4
diffractometer equipped with a SMART/CCD detector. The
systematic absences and diffraction symmetry are consistent
for the space groups C2/c and Cc for 1a and P1 and P1h for 2
and 4 and were uniquely consistent with the assigned space
group options for 3 and 5. The E-statistics suggested the
centrosymmetric options for 1a , 2, and 4, which yielded
chemically reasonable and computationally stable results of
refinement. Compound 1a exists as 0.5 molecule per asym-
metric unit lying on a 2-fold rotation axis, while compound 2
has 1.5 molecules per asymmetric unit with one molecule lying
on a general position and 0.5 molecule lying on an inversion
center. Compounds 3, 4, and 5 exist as 0.5 molecule per
asymmetric unit lying on an inversion center. The structures
were solved by direct methods, completed by subsequent
difference Fourier syntheses, and refined by full-matrix, least-
squares procedures. All non-hydrogen atoms were refined with
anisotropic displacement coefficients, and all hydrogen atoms
were treated as idealized contributions. All software and
sources of the scattering factors are contained in the SHELXTL
(5.10) program library (G. Sheldrick, Siemens XRD, Madison,
WI). X-ray crystal data collection and refinement parameters
and structural data for 1a -5 are included in the Supporting
Information. Selected bond distances and angles are given in
Tables 1-3.
either by slowly cooling the toluene solution or from
a
saturated pentane solution of the isolated product. The reac-
tion times for the completion of each reaction were as follows:
1, 36 h at 80 °C; 2, 6 days at 150 °C followed by 4 days at 175
°C; 3, 4, and 5, 6 days at 155 °C.
Ch ar acter ization of [Me2AlN(i-P r )CH2P h ]2 (1). Mp: 141-
145 °C. Yield: 1.84 g, 90%. 1 exists as a cis-trans (1a , 1b)
mixture in solution in a 60:40 ratio. 1a : 1H NMR: δH -0.19
(s, 6H, H1), -0.11 (s, 6H, H2), 0.91 (d, 12H, H21, H22), 3.57
(m, 2H, H20), 4.03 (s, 4H, H10), 7.05 (2H, H14), 7.10 (4H, H13,
H15), 7.39 (4H, H12, H16). 13C NMR: δC -6.41 (C1), -4.49
(C2), 23.01 (C21, C22), 50.01 (C20), 52.48 (C10), 127.58 (C14),
128.30 (C13, C15), 130.43 (C12, C16), 140.12 (C11). 1b: 1H
NMR: δH -0.13 (s, 12H, H1, H2), 0.94 (d, 12H, H21, H22),
3.46 (m, 2H, H20), 4.16 (s, 4H, H10), 7.06 (2H, H14), 7.10 (4H,
H13, H15), 7.39 (4H, H12, H16). 13C NMR: δC -5.0 (C1, C2),
23.15 (C21, C22), 48.39 (C20), 51.85 (C10), 127.33 (C14), 128.45
(C13, C15), 130.08 (C12, C16), 139.98 (C11). Anal. Calcd
(found) for C24H40Al2N2: C, 70.21(70.17); H, 9.82 (9.75); N, 6.82
(6.76).
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
crystallographic data, crystal data and structure refinement,
atomic coordinates, interatomic distances and angles, and
hydrogen atom coordinates for compounds 1a -5. Synthesis
and characterization data for [R2AlN(i-Pr)CH2Ph]2, where R
) Et (6), n-Pr (7), n-Bu (8), and [EtAlN(i-Pr)-µ-CH2C6H4]2 (9).
IR data for compounds 1-9. This material is available free of
charge via the Internet at http://pubs.acs.org.
Ch a r a cter iza tion of [MeAlN(i-P r )-µ-(CH2C6H4)]2 (2).
1
Mp: 186-190 °C. Yield: 1.02 g, 54%. H NMR: δH -0.41 (s,
6H, H1), 0.59 (d, 6H, H22), 1.03 (d, 6H, H21), 3.10 (m, 2H,
H20), 3.95, 4.13 (dd, 4H, H10), 7.14 (2H, H16), 7.26 (2H, H14),
7.28 (2H, H15), 7.80 (2H, H13). 13C NMR: δC -12.1 (C1), 19.88
(C22), 22.57 (C21), 48.85 (C20), 49.59 (C10), 123.86 (C16),
OM020768N