Synthesis, structure, and reactivity of β-diketiminato aluminum complexes

Article abstract of DOI:10.1021/om970886o

The preparation and reaction chemistry of β-diketiminato aluminum complexes are described. (TTP)AlCl₂ (1) (TTPH = 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene) is formed by the treatment of AlCl₃ with LiTTP. Sequential alkylation of 1 with CH₃Li results in the formation of the mono- and dimethyl aluminum complexes (TTP)AlMeCl (2) and (TTP)-AlMe₂ (3), respectively. Only monoalkyl complexes are produced when more hindered alkyllithium reagents are used. Compounds 2 and 3 are more conveniently prepared by treating Al(CH₃)₃ with TTPH·HCl and TTPH, respectively. The more sterically hindered β-diketimine ligand 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene (DDPH) also reacts smoothly with Al(CH₃)₃ to yield (DDP)Al(CH₃)₂ (4). Compound 3 undergoes methyl abstraction reactions upon addition of B(C₆F₅)₃ or AgOTf. Cationic species formed from 3 and B(C₆F₅)₃ are unstable and decompose to (TTP)Al(CH₃)(C₆F₅) and MeB-(C₆F₅)₂. In contrast, (TTP)Al(CH₃)(OTf) (6) is thermally stable, but the triflate group is surprisingly inert toward displacement by Lewis bases. Compounds 1, 3, 4, and 6 were crystallographically characterized. The structures all indicate that the β-diketiminato backbone is essentially planar. The pseudotetrahedral aluminum center is displaced from the plane formed by the ligand backbone in 4 by 0.72 A?.

Full text of DOI:10.1021/om970886o

3070
Organometallics 1998, 17, 3070-3076
Syn th esis, Str u ctu r e, a n d Rea ctivity of â-Dik etim in a to
Alu m in u m Com p lexes
Baixin Qian, Donald L. Ward, and Milton R. Smith, III*
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824
Received October 14, 1997
The preparation and reaction chemistry of â-diketiminato aluminum complexes are
described. (TTP)AlCl2 (1) (TTPH ) 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene) is formed
by the treatment of AlCl3 with LiTTP. Sequential alkylation of 1 with CH3Li results in the
formation of the mono- and dimethyl aluminum complexes (TTP)AlMeCl (2) and (TTP)-
AlMe2 (3), respectively. Only monoalkyl complexes are produced when more hindered
alkyllithium reagents are used. Compounds 2 and 3 are more conveniently prepared by
treating Al(CH3)3 with TTPH‚HCl and TTPH, respectively. The more sterically hindered
â-diketimine ligand 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pen-
tene (DDPH) also reacts smoothly with Al(CH3)3 to yield (DDP)Al(CH3)2 (4). Compound 3
undergoes methyl abstraction reactions upon addition of B(C6F5)3 or AgOTf. Cationic species
formed from 3 and B(C6F5)3 are unstable and decompose to (TTP)Al(CH3)(C6F5) and MeB-
(C6F5)2. In contrast, (TTP)Al(CH3)(OTf) (6) is thermally stable, but the triflate group is
surprisingly inert toward displacement by Lewis bases. Compounds 1, 3, 4, and 6 were
crystallographically characterized. The structures all indicate that the â-diketiminato
backbone is essentially planar. The pseudotetrahedral aluminum center is displaced from
the plane formed by the ligand backbone in 4 by 0.72 Å.
In tr od u ction
As is the case in transition-metal chemistry, the stabil-
ity of group 13 alkyl cations will depend on the ancillary
ligand set and the choice of counteranion.10-12
Reactivity of transition-metal and main-group alkyl
complexes holds considerable scientific and economic
importance. In polymerization catalysis, main-group
compounds play important roles as activators in the
generation of cationic transition-metal alkyl species that
polymerize R-olefins. Aluminum alkyl complexes have
long been known to catalyze olefin oligomerizations;1
however, the rates have been generally inferior to those
attainable using transition-metal catalysts for preparing
high molecular weight polymers. From the extensive
body of work in group 4 metallocene polymerization
catalysis, cationic alkyl species of the formula Cp2MR+
are catalytically active while the neutral Cp2MR2 com-
plexes are not.2,3 The importance of cationic species has
emerged as a common theme demonstrated by recent
reports on group 44-7 and late-metal systems.8 This was
recently shown to be the case in main-group systems
as Coles and J ordan’s recent report of ethylene polym-
erization by cationic aluminum species demonstrates.9
We have begun to explore reaction chemistry of main-
group and transition-metal alkyl complexes supported
by mono- and diketiminato ligands. Synthesis of this
class of compounds by condensation reactions between
primary amines and 2,4-pentanedione has been known
for many years.13 The chemistry of mono- and di-
ketiminato ligand complexes has been explored;14-17
however, complexes with these ligands have received
less attention than those with tetraazamacrocylic ligands
derived from 2,4-pentanedione and diamines.18,19 Ket-
iminato ligands share some similarities with their
acetylacetonato counterparts but offer potential advan-
tages of modulating steric and electronic properties by
varying the amine used in the ligand synthesis. In
(10) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc.
1989, 111, 2728-2729.
(11) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325-387.
(12) J ia, L.; Yang, X.; Stern, C. L.; Marks, T. J . Organometallics
1997, 16, 842-857.
(13) Schiebe, G. Chem. Ber. 1923, 56, 137-148.
(1) Ziegler, K.; Krupp, F.; Zosel, K. Angew. Chem. 1955, 67, 425.
(2) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew, Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(3) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255-270.
(4) Schollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996, 118,
10008-10009.
(14) Parks, J . E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408-1416.
(15) McGeachin, S. G. Can. J . Chem. 1968, 46, 1903-1912.
(16) Feldman, J .; McLain, S. J .; Parthasarathy, A.; Marshall, W.
J .; Calabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514-
1516.
(17) The chemistry of diketiminato Ti, V, and Cr compounds was
recently presented: Kim, W.-K.; MacAdams, L.; Fevola, M.; Liable-
Sands, L.; Rheingold, A. L. Theopold, K. H. Abstracts of Papers, 215th
National Meeting of the American Chemical Society, Dallas, TX, March
29-April 2, 1998; American Chemical Society: Washington, DC, 1998;
No. INOR 279.
(18) Weiss, M. C.; Bursten, B.; Peng, S.-M.; Goedken, V. L. J . Am.
Chem. Soc. 1976, 98, 8021-8031.
(19) For an excellent review on the chemistry of tetraazamacrocyclic
complexes see: Cotton, F. A.; Czuchajowska, J . Polyhedron 1990, 9,
2553-2566.
(5) Schollard, J . D.; McConville, D. H.; Rettig, S. J . Organometallics
1997, 16, 1810-1812.
(6) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg, H.
Organometallics 1996, 15, 2672-2674.
(7) Baumann, R.; Davis, W. M.; Schrock, R. R. J . Am. Chem. Soc.
1997, 119, 3830-3831.
(8) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 11664-11665.
(9) Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc. 1997, 119, 8125-
8126.
S0276-7333(97)00886-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/16/1998

â-Diketiminato Aluminum Complexes
Organometallics, Vol. 17, No. 14, 1998 3071
Sch em e 1
For example, the reaction of LiTTP with AlCl3 affords
the dichloride (TTP)AlCl2 (1) in reasonable yield (71%)
(Scheme 2). Compound 1 is sparingly soluble in ali-
phatic hydrocarbon solvents and is conveniently crystal-
lized as pale yellow crystals from toluene. Compound
1 is moisture sensitive and gives TTPH as the primary
organic hydrolysis product. Attempts to prepare
(TTP)2AlCl by halide metathesis of compound 1 with
LiTTP were not successful.
Compound 1 reacts with alkyllithium reagents to
produce mono- and dialkyl aluminum complexes. Reac-
tion of 1 with 1 equiv of CH3Li gives (TTP)Al(CH3)Cl
(2); however, the isolation of a pure compound is
hampered by contamination by significant quantities of
1 and the dimethyl complex (TTP)Al(CH3)2 (3, eq 1).
(TPP)AlMe
1 + MeLi f 1 + (TPP)AlMeCl +
(1)
2
2
3
With more hindered lithium reagents, only monoalkyl-
ation is observed as demonstrated by the reaction of
compound 1 with Li[CH(TMS)2], which cleanly affords
(TTP)Al[CH(TMS)2]Cl (5) in 43% yield (eq 2). Reaction
addition, ketimines can be prepared in good yields and
on large scale from inexpensive starting materials
(Scheme 1). In this paper, we describe initial efforts in
preparing aluminum alkyl complexes supported by
â-diketiminato ligands derived from 2,4-pentanedione
and arylamines (Scheme 2).
(TPP)AlCl2 + Li[CH(TMS)2] f
(TTP)Al[CH(TMS)2]Cl
(2)
5
of 1 with 2 equiv of CH3Li gives compound 3, which can
be isolated in 64% yield upon crystallization from
pentane. Compound 3 can be handled in air without
decomposition. The kinetic stability of 3 toward hy-
drolysis is considerable and markedly contrasts that of
(TP)Al(CH3)2, the compound derived from 4-toluidino-
pent-3-en-2-one or CH3C(O)CHdC(NH-p-Tol)(Me) (TPH)
Resu lts a n d Discu ssion
The reaction of nBuLi with 2-(p-tolylamino)-4-(p-
tolylimino)-2-pentene (TTPH) gives the yellow LiTTP
in good yield. This toluene-soluble lithium compound
is a useful reagent for effecting metathesis reactions
with various main-group and transition-metal halides.
Sch em e 2

3072 Organometallics, Vol. 17, No. 14, 1998
Qian et al.
F igu r e 1. ORTEP diagram of 1 (ellipsoids drawn at 50%
probability level).
F igu r e 3. ORTEP diagram of 4 (ellipsoids drawn at 50%
probability level).
satisfactorily refine its structure due to disorder of C
and Cl that were linked to aluminum.
F igu r e 2. ORTEP diagram of 3 (ellipsoids drawn at 50%
Compounds 3 and 4 are related to N-isopropyl-2-
(isopropylamino)troponimine ([(i-Pr)2ATI]) and amidi-
nate dimethylaluminum complexes. The Al-CH3 dis-
tances in 3 (1.955(4) and 1.961(3) Å) and 4 (1.958(3) and
1.970(3) Å) are comparable to the Al-CH3 distance in
[(i-Pr)2ATI]Al(CH3)2 (A) (1.969(1) Å).21 The Al-N dis-
probability level).
and Al(CH3)3.20 Under forcing conditions, compound 3
hydrolyzes slowly to give TTPH and uncharacterized
aluminum species. Compound 3 does not react with
additional TTPH to give (TTP)2AlCH3. Compounds 2
and 3 are more conveniently prepared by reacting
trimethylaluminum with TTPH‚HCl and TTPH, respec-
tively. In the reaction between Al(CH3)3 and TTPH‚
HCl, compounds 2 and 3 are present in the crude
reaction mixture, with 2 being the major product (2:3
) 15:1). Recrystallization from hot heptane gives pure
2 in 84% yield. The reaction between Al(CH3)3 and
TTPH gives compound 3 in high yield (90% isolated) on
a large scale (10 g). 1H NMR (tol-d8, -50 to +85 °C)
data indicate that mirror symmetry of the TTP ligand
is maintained in these compounds, and characteristic
high-field resonances for the aluminum methyl groups
are observed for compounds 2 (δ -0.98, s) and 3 (δ
-1.05, s). Although 27Al resonances can be detected for
compounds 1-3, with the exception of those for 1, the
peaks are broad (ν1/2 = 4000 Hz); thus application of
27Al NMR for characterization is limited.
To test the accessibility of compounds with more
sterically demanding ligands, 2-((2,6-diisopropylphenyl)-
a m in o)-4-((2,6-diisopr opylph en yl)im in o)-2-pen t en e
(DDPH) was synthesized in a similar fashion from 2,6-
diisopropylaniline and 2,4-pentanedione.16 Despite the
increased steric bulk of the ligand, DDPH and Al(CH 3)3
react smoothly to afford (DDP)Al(CH3)2 (4) in 75% yield.
Compound 4 is considerably more soluble than com-
pound 3 and can be crystallized from concentrated
pentane solutions at low temperature. 1H NMR spectra
exhibit the expected set of ligand proton signals and a
high-field singlet for the Al methyl groups (δ -1.00, s).
To glean more detailed information with respect to
the coordination environment about aluminum, the
molecular structures of compounds 1, 3, and 4 were
determined. ORTEP diagrams of the compounds are
shown in Figures 1-3, data collection parameters and
refinement statistics are listed in Table 1, and selected
bond distances and angles are given in Table 2. Al-
though we were able to obtain what appeared to be
single crystals of compound 2, we were not able to
tances in 3 and 4 are also similar to those in A for
AlIII-N bonds, while the slightly shorter Al-N distances
in 1 are likely due to the difference in inductive effects
for Cl and CH3 ligands. The N-Al-N angles in
compounds 1, 3, and 4 are more obtuse than the
corresponding angle in A.
The ArNdC(CH3)-C(H)dC(CH3)-NAr backbone of
the â-diketiminato ligand in compounds 1, 3, and 4 is
essentially planar. While compound 1 has rigorous C2
symmetry as C(3) and Al(1) lie on a crystallographic
2-fold axis, the Al center in compounds 3 and 4 is
displaced from the â-diketiminato plane. This pucker-
ing is most pronounced in compound 4 where Al(1) lies
0.72 Å above the least-squares plane defined by N(1),
N(2), C(4), C(5), and C(6). Displacement of the Al center
in compound 3 is significant (0.33 Å from the ligand
plane) but less severe than that observed in 4. In the
solid state, the methyl group environments are distinct,
with C(1) lying in the least-squares plan of the ligand
while C(2) is displaced 2.32 Å from the ligand plane. A
single methyl environment is observed in low-temper-
1
ature H NMR spectra for compounds 3 and 4. Hence,
if the solid-state structures are maintained in solution,
methyl site exchange is rapid on the NMR time scale.
We have examined methyl abstraction by B(C6F5)3 for
1
compound 3. The complex H NMR spectra that result
when 3 and B(C6F5)3 dissolved at low temperature
(CD2Cl2) are not readily interpreted in terms of a simple
cationic species or rotamers of [{(TTP)AlMe}2(µ-Me)]-
(21) Dias, H. V. R.; J in, W.; Ratcliff, R. E. Inorg. Chem. 1995, 34,
6100-6105.
(20) Qian, B.. Unpublished results.

â-Diketiminato Aluminum Complexes
Organometallics, Vol. 17, No. 14, 1998 3073
Ta ble 1. Da ta Collection P a r a m eter s for Com p ou n d s 1, 3, 4, a n d 6
1
3
4
6
empirical formula
fw
C
19H21AlCl2N2
C21H27AlN2
334.43
C31H47AlN2
474.69
C21H24AlF3N2O3S
468.46
375.26
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
142(2)
0.710 73
monoclinic
C2/c
15.014(3)
7.782(2)
17.037(3)
102.97(3)
1940.0(7)
4
1.285
0.383
142(2)
0.710 73
monoclinic
P21/c
8.737(2)
14.114(3)
17.021(3)
93.82(3)
2094.4(7)
4
142(2)
0.710 73
monoclinic
P21/n
12.6955(7)
19.4992(11)
13.4623(8)
116.8980(10)
2972.1(3)
173(1)
0.710 73
orthorhombic
P212121
7.562(2)
12.049(2)
25.411(5)
90
2315.4(8)
4
1.344
0.226
b (Å)
c (Å)
â (deg)
V (Å3)
Z
4
d(calc) (Mg/m3)
1.061
0.101
720
1.061
0.088
1040
abs coeff (mm-1
F(000)
)
784
976
cryst size (mm)
2θ range (deg)
index ranges
0.15 × 0.12 × 0.12
4.90-56.58
-15 e h e 20
-9 e k e 10
-21 e l e 22
5875
2291 [R(int) ) 0.0354]
2291/0/110
1.249
0.18 × 0.16 × 0.15
3.76-46.50
-9 e h e 9
-10 e k e 15
-18 e l e 17
8078
2965 [R(int) ) 0.0995]
2965/0/218
0.946
0.18 × 0.15 × 0.14
3.66-56.58
-16 e h e 14
-25 e k e 25
-17 e l e 16
17 525
6926 [R(int) ) 0.0703]
6926/0/307
1.017
0.25 × 0.12 × 0.05
3.2-56.36
-10 e h e 10
-15 e k e 15
-32 e l e 32
25 453
5471 [R(int) ) 0.1255]
5471/0/280
1.102
no. of reflns collected
no. of indep reflns
data/restraints/params
GOF/F2
R indices [I > 2σ(I)]
R1 ) 0.0385,
wR2 ) 0.0912
R1 ) 0.0556,
wR2 ) 0.0970
+0.492 to -0.511
R1 ) 0.0460,
wR2 ) 0.0894
R1 ) 0.1184,
wR2 ) 0.1057
+0.137 to -0.148
R1 ) 0.0723,
wR2 ) 0.1670
R1 ) 0.1432,
wR2 ) 0.1950
+0.410 to -0.385
R1 ) 0.1022,
wR2 ) 0.1868
R1 ) 0.1770,
wR2 ) 0.2183
+0.301 to -0.307
R indices (all data)
largest diff peak (e Å-3
)
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d s 1, 3, 4, a n d 6
1
3
4
6
Al-N1
Al-N2
Al-C1
Al-C2
1.850(2) 1.905(3) 1.922(2)
1.907(3) 1.935(2)
1.875(4)
1.873(4)
1.928(6)
1.955(4) 1.958(3)
1.961(3) 1.970(3)
N(1)-Al(1)-N(1)#1
N(1)-Al(1)-Cl(1)#1
99.41(12)
113.56(6)
N(1)#1-Al(1)-Cl(1)#1 110.04(6)
N(1)-Al(1)-Cl(1)
N(1)#1-Al(1)-Cl(1)
Cl(1)#1-Al(1)-Cl(1)
N(2)-Al(1)-N(1)
N(2)-Al(1)-C(2)
N(1)-Al(1)-C(2)
N(2)-Al(1)-C(1)
N(1)-Al(1)-C(1)
C(2)-Al(1)-C(1)
110.04(6)
113.56(6)
109.95(6)
94.72(14) 96.18(9)
111.2(2) 107.15(11)
109.6(2) 108.67(11)
111.4(2) 114.49(11) 117.9(2)
112.7(2) 110.79(11) 117.5(2)
115.4(2) 117.40(13)
99.1(2)
F igu r e 4. ORTEP diagram of 6 (ellipsoids drawn at 50%
probability level).
[MeB(C6F5)3]; however, a single resonance in 11B NMR
- 9
between those of BMe3 (δ 86.0) and BPh3 (δ 60.0). These
data have not been confirmed by independent synthe-
sis.22
(δ -14) is consistent with the formation of MeB(C6F5)3
.
Attempts to isolate putative cationic species were not
successful because degradation occurred (as judged by
19F and 11B data). We propose that the degradation
products are (TTP)Al(CH3)(C6F5) and MeB(C6F5)2.
The reaction between compound 3 and AgOTf (OTf
) OSO2CF3) deposits silver metal and affords modest
yields of (TTP)Al(CH3)(OTf) (6). This reaction is similar
to reaction between Ag salts and d0 Zr alkyl com-
pounds.23 The X-ray structure indicates η1 coordination
for the triflate ligand (Figure 4). Compound 6 is
surprisingly inert for a triflate complex. For example,
the triflate ion does not undergo metathesis with
Na[B(3,5(CF3)2-C6H3)4],24,25 nor is it displaced by pyri-
Formation of (TTP)Al(CH3)(C6F5) is supported by (i)
5
1
a high-field triplet (δ -0.18, | J H-F| ) 1.6 Hz) in the H
NMR spectrum and (ii) the fact that reaction of (TTP)-
Al(CH3)(OTf) and LiC6F5 affords an oil that is spectro-
scopically identical to (TTP)Al(CH3)(C6F5) generated
from 3 and B(C6F5)3. We have not been able to obtain
an analytically pure compound because all attempts to
crystallize (TTP)Al(CH3)(C6F5) have been unsuccessful.
(22) A comprehensive literature search for Me(C6F5)2 retrieved one
citatation: Biagini, P.; Lugli, G.; Garbassi, F. Andreussi, P. Eur. Pat.
Appl. EP 667,357, 1995; Chem. Abstr. 1995, 123, 341326t.
(23) J ordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.;
Willett, R. J . Am. Chem. Soc. 1987, 109, 4111-4113.
(24) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970-1973.
(25) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
For MeB(C6F5)2 the following evidence is offered: (i)
5
a quintet at 1.33 ppm (| J H-F| ) 1.8 Hz) is assigned to
CH3B(C6F5)2 where the H-F coupling arises from four
chemically equivalent ortho fluorines and (ii) a reso-
nance in the 11B spectrum (δ 72) that is intermediate

3074 Organometallics, Vol. 17, No. 14, 1998
Qian et al.
B(C6F5)3 was prepared from BCl3 and C6F5Li.29 MeLi was
prepared from lithium metal and ClCH3 and stored as a 1.4
M solution in ether. LiCH(SiMe3)2 was prepared from lithia-
tion of ClCH(SiMe3)2.30
dine. Compounds 2 and 6 will undergo metathesis
reactions with alkyllithium reagents. Thus, 3 can be
generated upon reaction of 2 or 6 with CH3Li, and
mixed-alkyl complexes of the formula (TTP)Al(CH3)(R)
from 2 and RLi (R * CH3).
LiTTP . nBuLi (45 mL, 1.6 M in hexanes, 72 mmol) was
added dropwise via syringe over 10 min to a stirred solution
of TTPH (20 g, 72 mmol) in 350 mL of pentane at -78 °C. The
mixture was stirred at -78 °C for an additional 10 min and
allowed to warm to room temperature, and reduced in volume
to approximately 150 mL after 2 h at room temperature.
Yellow solid LiTTP was isolated by filtration, washed with 3
× 20 mL of pentane, and dried in vacuo (18 g, 88% yield): mp
185-187 °C dec; 1H NMR (C6D6) δ 1.79 (s, 6 H), 2.15 (s, 6 H),
Su m m a r y
Our initial results suggest that â-diketiminato ligands
are well-suited for preparing various alkyl aluminum
products. In particular, it should be possible to modu-
late reactivity at the aluminum center by designing
ligands with different steric and electronic properties.
Significantly, we have seen no evidence for ligand
methylation reactions that have been observed for
related reactions between Al(CH3)3 and 1,4-diazabuta-
diene systems.26,27 The ability to prepare mixed-alkyl
complexes (TTP)Al(CH3)(R), R * CH3, in addition to the
flexible ligand syntheses, may prove to be useful in the
preparation of unassociated, three-coordinate aluminum
cations with the proper match of ligand, alkyl group,
and counterion. Efforts along these lines and extension
syntheses to other group 13 complexes will be the
subject of future reports.28
3
3
4.67 (s, 1 H), 6.61 (d, J H-H ) 8.1 Hz, 4 H), 6.91 (d, J H-H
)
8.1 Hz, 4 H); 13C{1H} NMR (C6D6) δ 20.87, 23.08, 95.49, 124.3,
129.6, 131.2, 151.4, 165.6. Anal. Calcd for C19H21LiN2: C,
80.26; H, 7.44; N, 9.85. Found: C, 80.18; H, 7.15; N, 9.50.
(TTP )AlCl2 (1). Freshly sublimed AlCl3 (1.07 g, 8.0 mmol)
in 10 mL of ether was added to an orange solution of LiTTP
(2.3 g, 8.0 mmol) in 20 mL of toluene at 0 °C. The cloudy
solution was allowed to warm to room temperature and stirred
for 12 h. The mixture was filtered, and the filtrate was
reduced in volume to approximately 5 mL. Yellow 1 deposited
overnight at -78 °C. The solid was isolated by filtration,
washed with copious amounts of pentane, and dried in vacuo
(2.1 g, 71% yield): mp 199-201 °C dec; 1H NMR (CDCl3) δ
3
1.88 (s, 6 H), 2.33 (s, 6 H), 5.16 (s, 1 H), 7.05 (d, J H-H ) 8.4
3
Hz, 4 H), 7.18 (d, J H-H ) 8.4 Hz, 4 H); 13C{1H} NMR (CDCl3)
δ 21.02, 23.26, 98.29, 126.5, 130.0, 136.8, 139.7, 171.0; 27Al
NMR (CDCl3) δ 98.6 (ν1/2 ) 189 Hz). LRMS 374 (M+, 1); HRMS
calcd for C19H21AlCl2N2 376.0868, found 376.0862. Anal.
Calcd for C19H21AlCl2N2: C, 60.81; H, 5.64; N, 7.46. Found:
C, 60.87; H, 5.47; N, 7.35.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out using standard Schlenk techniques. Solvents were freshly
distilled over sodium/benzophenone ketyl and were saturated
with N2 before use. Elemental analyses (C, H, N) were
performed by Desert Analytics, Tucson, AZ, and Atlantic
Microlabs, Inc. A Nicolet IR/42 spectrometer was used to
record IR spectra. Varian Gemini-300 andVXR-300 NMR
spectrometers were used to record 1H (300 MHz), 11B (96 MHz),
13C (75 MHz), 19F (282 MHz), and 27Al (78 MHz) NMR spectra.
1H and 13C chemical shifts were referenced to the residual
solvent peaks. 11B chemical shifts were referenced to a neat
BF3‚OEt2 (0 ppm) external standard. 27Al NMR spectra were
referenced to an [Al(H2O)6]3+ (0 ppm) external standard. 19F
NMR spectra were referenced to a neat CFCl3 (0 ppm) external
standard. CDCl3 was dried over activated 4 Å molecule sieves
and vacuum-transferred to an air-free flask. C6D6 was dried
over activated 4 Å molecule sieves and vacuum-transferred to
a sodium-mirrored air-free flask. Uncorrected melting points
of crystalline samples in sealed capillaries (under an argon
atmosphere) were reported as ranges. Low-resolution mass
spectra were obtained on a portable Trio-1 VG Masslab Ltd.
mass spectrometer and were reported in the form (M, %I),
where M is the highest mass observed for a molecular ion or
fragment peak and %I is the intensity of the peak relative to
the most intense peak in the spectrum. High-resolution mass
spectra were obtained at the MSU Mass Spectrum Facility.
(TTP )AlClMe (2). Meth od a . MeLi (2 mL, 1.4 M in ether,
2.8 mmol) was added to a stirred suspension of (TTP)AlCl2
(1.07 g, 2.8 mmol) in 15 mL of ether at 0 °C. The mixture
was allowed to warm to room temperature, stirred for 14 h,
and was filtered, and the filtrate was reduced in volume to
approximately 3 mL. 2 can be obtained by repeated crystal-
lization from toluene at -78 °C (0.15 g, 15% yield).
Meth od b. AlMe3 (7.2 mL, 2 M, 14.4 mmol) was added over
a 5 min period to a stirred suspension of throughly dried
TTPH‚HCl (4.55 g, 14.5 mmol) in 100 mL of toluene at 0 °C.
Following the addition, the mixture was stirred at room
temperature for 4 h, during which a clear yellow solution was
formed. The solution was reduced in volume to approximately
20 mL and layered with 30 mL of pentane. Cooling at -78 °C
overnight deposited 2 as a pale yellow solid which was isolated
by filtration, washed with pentane, and dried in vacuo (4.3 g,
84%): mp 129-133 °C dec; 1H NMR (CDCl3) δ -0.98 (s, 3 H),
3
1.86 (s, 5 H), 2.33 (s, 6 H), 5.07 (s, 1 H), 7.01 (d, J H-H ) 8.4
3
Hz, 4 H), 7.15 (d, J H-H ) 8.4 Hz, 4 H); 13C{1H} NMR (CDCl3)
δ -10.9 (br, ν1/2 ) 30 Hz), 20.98, 23.13, 97.81, 126.2, 129.8,
136.0, 141.3, 169.1; 27Al NMR (CDCl3) δ 126 (ν1/2 ) 3920 Hz);
LRMS 354 (M+, 5), 339 (M+ - CH3, 100). Anal. Calcd for
C
20H24AlClN2: C, 67.70; H, 6.82; N, 7.89. Found: C, 67.82;
nBuLi, AlMe3, and AgOTf were purchased from Aldrich and
used as received. AlCl3 was purchased from Aldrich and
sublimed prior to use. 2-(p-Tolylamino)-4-(p-tolylimino)-2-
pentene (TTPH) and 2-((2,6-diisopropylphenyl)amino)-4-((2,6-
diisopropylphenyl)imino)-2-pentene (DDPH) were prepared by
straightforward modification of the literature methods.13,16
H, 6.84; N, 7.91.
(TTP )AlMe2 (3). Meth od a . AlMe3 (3.6 mL, 2 M in
hexanes, 7.2 mmol) was added to a solution of TTPH (2.0 g,
7.2 mmol) in 20 mL of pentane at 0 °C with stirring. The
mixture was stirred at 0 °C for 5 min, allowed to warm to room
temperature, stirred for an additional hour, and filtered, and
the filtrate was reduced in volume to approximately 3 mL. Pale
yellow 3 deposited overnight at -78 °C. The solid was
collected by filtration, washed with cold pentane, and dried
in vacuo (2.2 g, 90% yield).
(26) Geoffrey, F.; Cloke, F.; Dalby, C. I.; Henderson, M. J .; Hitchcock,
P. B.; Kennard, C. H. L.; Lamb, R. N.; Raston, C. L. J . Chem. Soc.,
Chem. Commun. 1990, 1394-1396.
(27) Wissing, E.; J astrzebski, J . T. B. H.; Boersma, J .; van Koten,
G. J . Organomet. Chem. 1993, 459, 11-16.
(28) Preliminary results have been recently presented: Qian, B.;
Smith, M. R., III. Abstracts of Papers, 215th National Meeting of the
American Chemical Society, Dallas, TX, March 29-April 2, 1998;
American Chemical Society: Washington, DC, 1998; No. INOR 290.
(29) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245-
250.
(30) Davidson, P. J .; Harris, D. H.; Lappert, M. F. J . Chem. Soc.,
Dalton Trans. 1976, 2268.

â-Diketiminato Aluminum Complexes
Organometallics, Vol. 17, No. 14, 1998 3075
Met h od b. MeLi (2 mL, 1.4 M in ether, 2.8 mmol) was
added to a stirred suspension of 1 (0.50 g, 1.3 mmol) in 15 mL
of ether at 0 °C. The mixture was allowed to warm to room
temperature and stirred for 14 h. The solvent was removed
in vacuo, and the residue was extracted with pentane. The
pentane extracts were reduced in volume, and 3 deposited at
-78 °C (0.28 g, 64% yield).
for 24 h, and filtered, and the filtrate was placed under
vacuum. The resulting yellow oil (0.90 g) contained both
(TTP)AlMe(C6F5) and MeB(C6F5)2. The oil was placed under
high vacuum at 45 °C overnight to remove the relatively
volatile MeB(C6F5)2. The gel residue was redissolved in
pentane, the solution was concentrated, and the concentrate
was cooled to -78 °C. A colorless oil deposited overnight and
was isolated by decantation and dried in vacuo (0.37 g, 65%
yield). Attempts to crystallize this oil have been unsuccessful.
The identity of (TTP)AlMe(C6F5) was confirmed by an inde-
pendent synthesis. Compound 6 (1.31 g, 2.8 mmol) was
suspended in 20 mL of ether, and the solution was treated
with an ether solution of C6F5Li, which was generated by
treating freshly distilled C6F5Br (0.69 g, 2.8 mmol) with nBuLi
(2.5 M, 1.1 mL, 2.8 mmol) at -78 °C. The mixture was
warmed to room temperature and was stirred at room tem-
perature for 2 h. After filtration and solvent removal, an oil
remained. All attempts to crystallize the product were unsuc-
cessful, and chromatography on silica gel gave decomposition.
Nonetheless, chemical shifts of the major component in 1H
NMR spectra of the crude reaction mixture corresponded to
those assigned to (TTP)AlMe(C6F5) generated in the reaction
between (TTP)AlMe2 and B(C6F5)3. In (TTP)AlMe(C6F5), the
two carbon atoms directly attached to aluminum were not
observed in 13C NMR spectra. Spectroscopic data for
Meth od c. MeLi (1 mL, 1.4 M in ether, 1.4 mmol) was
added to 2 (0.38 g, 1.1 mmol) suspended in 20 mL of ether at
0 °C. The mixture was allowed to warm to room temperature
and stirred for 5 h. The solvent was removed in vacuo, and
the residue was extracted with pentane. The pentane extracts
were reduced in volume, and 3 deposited at -78 °C (0.30 g,
84%): mp 110-113 °C dec; 1H NMR (CDCl3) δ -1.05 (s, 6 H),
3
1.78 (s, 5 H), 2.32 (s, 6 H), 4.83 (s, 1 H), 6.88 (d, J H-H ) 8.1
3
Hz, 4 H), 7.12 (d, J H-H ) 8.1 Hz, 4 H); 13C{1H} NMR (CDCl3)
δ -9.67 (br, ν1/2 ) 16 Hz), 20.96, 22.90, 96.02, 126.0, 129.6,
135.1, 142.8, 167.9; 27Al NMR (CDCl3) δ 143 (ν1/2 ) 3900 Hz);
LRMS 319 (M+ - CH3, 100). Anal. Calcd for C21H27AlN2: C,
75.42; H, 8.14; N, 8.37. Found: C, 75.07; H, 7.97; N, 8.18.
(DDP )AlMe2 (4). This was prepared by the same procedure
described for 3 (method a) using AlMe3 and DDPH in 75%
yield: mp 163-164 °C dec; 1H NMR (CDCl3) δ -1.00 (s, 6 H),
3
3
1.14 (d, J H-H ) 6.9 Hz, 12 H), 1.23 (d, J H-H ) 6.9 Hz, 12 H),
3
3.22 (sept, d, J H-H ) 6.9 Hz, 4 H), 5.12 (s, 1 H), 7.14-7.25
5
(TTP)AlMe(C6F5): 1H NMR (C6D6) δ -0.18 (t, J HF ) 1.6 Hz,
(m, 6 H); 13C{1H} NMR (CDCl3) δ -10.78 (br, ν1/2 ) 17 Hz),
23.58, 24.61, 25.15, 28.02, 97.02, 124.0, 126.5, 140.7, 144.22,
169.56; 27Al NMR (CDCl3) δ 160 (ν1/2 ) 4060 Hz); LRMS 459
(M+ - CH3, 100). Anal. Calcd for C31H47AlN2: C, 78.44; H,
9.98; N, 5.90. Found: C, 77.73; H, 10.00; N, 5.79.
3 H), 1.60 (s, 6 H), 1.93 (s, 6 H), 4.88 (s, 1 H), 6.80 (m, 8 H);
13C{1H} NMR (C6D6) δ 20.74, 22.86, 98.25, 125.9, 130.3, 136.1,
137.4 (d, |J CF| ) 260 Hz), 142.1, 147.5 (d, |J CF| ) 240 Hz), 151.1
(d, |J CF| ) 238 Hz), 169.6; 19F NMR (C6D6) δ -162.4 (m),
-154.9 (t, J ) 19.2 Hz), -121.7 (dd, J ) 12.8, 27.8 Hz); LRMS
486 (M+, 1), 471 (M+ - CH3, 12); HRMS calcd for C26H24AlF5N2,
486.1675, found 486.1701. MeB(C6F5)2 has only been spec-
trosopically identified in the reaction mixture. Since pure
material was not obtained, collection of 13C data was not
(TTP )Al[CH(TMS)2]Cl (5). LiCH(TMS)2 (0.42 g, 2.5 mmol)
in 10 mL of ether was added to 1 (0.94 g, 2.5 mmol) in 15 mL
of toluene at 0 °C. The mixture was allowed to warm to room
temperature, stirred for 10 min, and then filtered. The ether
was removed in vacuo, and the residue was extracted with 3
× 10 mL of pentane. The combined pentane extracts were
reduced in volume to approximately 5 mL. Pale yellow 5
deposited overnight at -78 °C and was collected by filtration
(0.54 g, 43%): mp 159-162 °C. 1H NMR (CDCl3) δ -1.65 (s,
1 H), -0.23(s, 1 H), 1.84 (s, 6 H), 2.34 (s, 6 H), 5.08 (s, 1 H),
7.06-7.18 (m, 8 H); 13C{1H} NMR (CDCl3) δ -1.88 (br), 3.26,
21.00, 23.69, 98.05, 126.7, 129.7, 136.2, 141.5, 169.3; 27Al NMR
(CDCl3) δ 135 (ν1/2 ) 4600 Hz); LRMS 483 (M+ - CH3, 6);
HRMS calcd for C26H40AlClN2Si2 498.2234, found 498.2241.
Anal. Calcd for C26H40AlClN2Si2: C, 62.55; H, 8.08; N, 5.36.
Found: C, 61.90; H, 7.81; N, 5.67.
1
possible for MeB(C6F5)2, but we were able to assign the H and
19F NMR data by comparing the spectrum of the reaction
mixture with that of 7. Spectroscopic data for MeB(C6F5)2: 1H
5
NMR (C6D6) δ 1.33 (quintet, J H-F ) 2.0 Hz); 11B NMR (C6D6)
δ 72 (br, ν1/2 ∼252 Hz); 19F NMR (C6D6) δ -161.3 (m), -147.0
(m), -130.0 (m); LRMS 360 (M+, 15).
Cr ysta l Str u ctu r e Deter m in a tion a n d Refin em en t.
Crystals of 1, 3, 4, and 6 were coated with Paratone-N oil, and
a suitable single crystal was selected and mounted on a glass
fiber. The crystals were then transferred to the goniometer
of a Siemens CCD diffractometer using Mo KR radiation (λ )
0.710 73 Å). Data were collected as 30 s frames at 142 or 173
K. An initial cell was calculated by Smart from three sets of
15 frames. All data sets were collected over a hemisphere of
reciprocal space. SAINT was used to integrate 1025 frames
and to generate the raw file. Final unit cell parameters were
obtained by least-squares refinement of strong reflections
obtained. Absorption and time decay were applied to the data
by SADABS. In all structures, the non-hydrogen atoms were
found using SHELXS-86. Atomic coordinates and thermal
parameters were refined using the full-matrix least-squares
program SHELXL-97, and calculations were based on F2 data.
All non-hydrogen atoms were refined using anisotropic thermal
parameters. All hydrogen atoms were placed in calculated
positions using HFIX. All crystallographic computations were
performed on Silicon Graphics Indigo computers.
(TTP )AlMe(OTf) (6). A 20 mL portion of toluene was
added to a Schlenk flask containing 3 (0.75 g, 2.24 mmol) and
AgOTf (1.15 g, 4.47 mmol) at -78 °C. The reaction mixture
immediately turned black and was slowly warmed to room
temperature. After 12 h, during which
a silver mirror
developed inside the Schlenk flask, the mixture was filtered.
The filtrate was concentrated, the concentrate was layered
with pentane, and the mixture was cooled to -78 °C. Yellow
6 deposited overnight and was collected by filtration, washed
with pentane, and dried in vacuo (0.34 g, 32% yield). Using
of 1 equiv of AgOTf led to the same compound 6, but in lower
yield. We were not able to observe 27Al NMR signals for 6.
Analytical data: mp 140 °C (dec); IR (Nujol) 1537, 1383, 1302,
1244, 1203, 1109, 1031, 1020, 943; 1H NMR (C6D6) δ -0.62 (s,
3
3 H), 1.54 (s, 6 H), 1.99 (s, 6 H), 4.85 (s, 1 H), 6.87 (d, J H-H
)
8.1 Hz, 4 H), 7.00 (m, J H-H ) 8.1 Hz, 4 H); 13C{1H} NMR
(C6D6) δ -14.1 (br, s, ν1/2 ) 75 Hz), 20.78, 22.88, 99.28, 120.0
(q, 1J C-F ) 316 Hz), 126.1, 130.46, 136.8, 141.0, 171.0; 19F NMR
(C6D6) δ -77.9 (s, ν1/2 ) 8.9 Hz); LRMS 453 (M+ - CH3, 5).
Anal. Calcd for C21H24AlF3N2O3S: C, 53.84; H, 5.16; N, 5.98.
Found: C, 53.44; H, 4.98; N, 5.92.
3
Crystals of 1 (fw 375.26) were grown via pentane diffusion
into a concentrated toluene solution at room temperature.
Compound 1 crystallized in a monoclinic crystal system. The
space group C2/c was chosen over Cc on the basis of intensity
statistics and the successful refinement of the structure. Al
and C(5) were located on a 2-fold rotation axis; therefore Z )
4. Relevant details and data statistics are summarized in
Table 1.
(TTP )AlMe2 + B(C6F 5)3. A solution of B(C6F5)3 (0.60 g, 1.2
mmol) in 20 mL of pentane was added to a stirred suspension
of 3 (0.39 g, 1.2 mmol) in 5 mL of pentane at -78 °C. The
mixture was allowed to warm to room temperature, stirred
Crystals of 3 (fw 334.43) were grown from a concentrated
pentane solution cooled to -78 °C. Compound 3 crystallized

3076 Organometallics, Vol. 17, No. 14, 1998
Qian et al.
in a monoclinic crystal system with systematic absences
indicating the space group P21/c. Relevant details and data
statistics are summarized in Table 1.
Crystals of 4 (fw 474.69) were grown from a concentrated
pentane solution cooled to -78 °C. Compound 4 crystallized
in a monoclinic crystal system with systematic absences
indicating the space group P21/n. Relevant details and data
statistics are summarized in Table 1.
MSU. We also thank Mr. Sung W. Baek, who aided in
ligand synthesis. The single-crystal X-ray equipment at
MSU was supported by the National Science Foundation
(Grant CHE-8403823), and the NMR equipment was
provided by the National Science Foundation (Grant
CHE-8800770) and the National Institutes of Health
(Grant 1-S10-RR04750-01).
Crystals of 6 (fw 468.46) were grown by diffusing pentane
into a toluene solution of 6 at -30 °C. Compound 6 crystal-
lized in an orthorhombic crystal system with systematic
absences indicating the space group P212121. Relevant details
and data statistics are summarized in Table 1.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and bond distances and
angles for 1, 3, 4, and 6 (19 pages). Ordering information is
given on any current masthead page.
Ack n ow led gm en t. We are grateful for support from
the Center for the Fundamental Material Research at
OM970886O