New types of base-stabilized alkyl aluminum, gallium, and indium complexes

Article abstract of DOI:10.1021/om000285o

Novel dinuclear metal complexes with the general formula [(Me₂M){NC₅H₄C(R)NNC₆H₅}- (MMe₃)] (M = Al], R = CH₃ (1); M = Ga, R = CH₃ (2); M = Al, R = H (3); M = Ga, R = H (4)) result when 2-pyridinecarboxaldehyde phenyl hydrazone ligands are mixed with trimethyl-aluminum and -gallium. The decagallium complex (GaMe₂)₈(GaMe)₂(μ₄-O)₂(μ₃-O)₄ (C₁₂H₁₀N₃)₂ (5) was isolated during the synthesis of 4 as a minor orange product. Three dinuclear metal compounds of the general formula [(Me₂M)(SC₄H₃CHNNC₆H₅]₂ (M = Al (6); M = Ga (7); M = In (8)) were synthesized by the methane elimination reaction of thiophenecarboxaldehyde phenylhydrazone with trimethyl aluminum, -gallium, and -indium. The μ₄-oxo complex [(Me₂-In)₂(OC₄H₃CH NNC₆H₅)]₂O (9) was prepared via the reaction of furancarboxaldehyde phenylhydrazone with trimethylindium. The X-ray crystal structures of 1, 4, 5, 7, and 9 are described. The structural data revealed that 5 is a decanuclear gallium compound that contains an eight-membered Ga₄O₄ cyclic core and that 9 is a tetranuclear indium compound with a weak interaction between the pendant furan and the indium center.

Full text of DOI:10.1021/om000285o

4036
Organometallics 2000, 19, 4036-4042
New Typ es of Ba se-Sta bilized Alk yl Alu m in u m , Ga lliu m ,
a n d In d iu m Com p lexes
Sung-J oon Kim, Namkeun Yang, Dae-Hyun Kim, Sang Ook Kang,* and
J aejung Ko*
Department of Chemistry, Korea University,Chochiwon, Chungnam 339-700, Korea
Received April 3, 2000
Novel dinuclear metal complexes with the general formula [(Me2M){NC5H4 C(R)NNC6H5}-
(MMe3)] (M ) Al, R ) CH3 (1); M ) Ga, R ) CH3 (2); M ) Al, R ) H (3); M ) Ga, R ) H (4))
result when 2-pyridinecarboxaldehyde phenyl hydrazone ligands are mixed with trimethyl-
aluminum and -gallium. The decagallium complex (GaMe2)8(GaMe)2(µ4-O)2(µ3-O)4(C12H10N3)2
(5) was isolated during the synthesis of 4 as a minor orange product. Three dinuclear metal
compounds of the general formula [(Me2M)(SC4H3CHNNC6H5)]2 (M ) Al (6); M ) Ga (7); M
) In (8)) were synthesized by the methane elimination reaction of thiophenecarboxaldehyde
phenylhydrazone with trimethyl aluminum, -gallium, and -indium. The µ4-oxo complex [(Me2-
In)2(OC4H3CH NNC6H5)]2O (9) was prepared via the reaction of furancarboxaldehyde
phenylhydrazone with trimethylindium. The X-ray crystal structures of 1, 4, 5, 7, and 9 are
described. The structural data revealed that 5 is a decanuclear gallium compound that
contains an eight-membered Ga4O4 cyclic core and that 9 is a tetranuclear indium compound
with a weak interaction between the pendant furan and the indium center.
In tr od u ction
polynuclear complexes with an uncommon coordination
geometry. Motivated by an interest in the effects of
ligand geometry on the coordination environments of
the group 13 elements, we decided to investigate the
coordination ability of 2-pyridinecarboxaldehyde phenyl
hydrazone (L1), which contains an amine N-H bond and
two imine nitrogens. In addition, we were interested in
The chemistry of alkyl group 13 amido and imido
compounds has recently attracted much attention due
to the rich structural chemistry of this class of com-
plexes and because of their possible applications in the
preparation of ceramic materials.1-3 Because of the
efforts to investigate the assembly of the polynuclear
group 13 organometallic complexes using polydentate
amido and imido ligands, there has been a recent
resurgence of interest in the preparation of the alkyl
complexes of these elements. Polydentate amido and
imido ligands not only can offer additional coordination
sites but also may provide group 13 complexes with
unusual structural features and chemical reactivities.4
Recently, we prepared a series of di- and trinuclear
group 13 heterocyclic carboxaldehyde thiosemicarbazone
complexes5,6 and trinuclear group 13 complexes of bis-
(thiosemicarbazone).7,8 The coordination ability of the
thiosemicarbazone was useful for the construction of
conducting a systematic study of the use of possible
terdentate ligands obtained by replacing the pyridine
moiety with the thiophene (L2) and furan (L3) moieties.
Our interest in preparing intramolecularly base-coor-
dinated compounds of the group 13 elements focused
on their hydrolysis. We also were interested to what
extent alkyl species would coordinate additional ligands
if the donor sites were constrained to lie close to or
within the primary coordination sphere. As part of our
continuing studies on the synthetic utility and under-
standing of complexes of these ligands with group 13
elements, we attempted to synthesize a variety of such
complexes. We now report the synthesis and character-
ization of the group 13 complexes of 2-heterocyclic
(1) (a) Robinson, G. H.; Sangokoya, S. A. J . Am. Chem. Soc. 1987,
109, 6852. (b) Robinson, G. H.; Rae, A. D.; Campana, C. F.; Byram, S.
K. Organometallics 1987, 6, 1227. (c) Mole, T.; J effrey, E. A. Orga-
noaluminum Compounds; Elsevier: New York, 1972. (d) J anik, J . F.;
Duesler, E. N.; Paine, R. T. Inorg. Chem. 1988, 27, 4335. (e) J anik, J .
F.; Duesler, E. N.; Paine, R. T. Inorg. Chem. 1987, 26, 4341.
(2) (a) Ohmori, Y.; Uchida, M.; Muro, K.; Yoshino, K. J pn. J . Appl.
Phys. 1991, 30, L1941. (b) Edwards, A.; Blumstengel, S.; Sokolik, J .;
Dorsinville, R.; Yun, H.; Kwei, K.; Okamoto, Y. Appl. Phys. Lett. 1997,
70, 298. (c) Brouwer, H. J .; Krasnikov, V. V.; Hilberer, A.; Hadziioan-
nou, G. Adv. Mater. 1996, 8, 935.
(3) (a) Trepanier, S. J .; Wang, S. Organometallics 1996, 15, 760. (b)
Trepanier, S. J .; Wang, S. Can. J . Chem. 1996, 74, 2032. (c) Trepanier,
S. J .; Wang, S. J . Chem. Soc., Dalton Trans. 1995, 2425.
(4) (a) Trepanier, S. J .; Wang, S. Angew. Chem., Int. Ed. Engl. 1994,
33, 1265. (b) Liu, W.; Hassan, A.; Wang, S. Organometallics 1997, 16,
4257. (c) Trepanier, S. J .; Wang, S. Organometallics 1994, 13, 2213.
(5) Paek, C.; Kang, S. O.; Ko, J .; Carroll, P. J . Organometallics 1997,
16, 2110.
(7) Paek, C.; Kang, S. O.; Ko, J .; Carroll, P. J . Organometallics 1997,
16, 4755.
(6) Kang, Y.; Yang, N.; Kang, S. O.; Ko, J .; Lee, C. H.; Lee, Y. H.
Organometallics 1997, 16, 5522.
(8) Paek, C.: Kang, S. O.; Ko, J .; Carroll, P. J . Organometallics 1997,
16, 1503
10.1021/om000285o CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/25/2000

Base-Stabilized Alkyl Al, Ga, and In Complexes
Organometallics, Vol. 19, No. 20, 2000 4037
Ta ble 1. Cr ysta l Da ta of Com p ou n d s 1, 4, 5, 7, a n d 9
1
4
5
7
9
empirical formula
molecular wt
cryst syst
space group
a, Å
C
18H27N3Al2
C17H25N3Ga2
410.82
orthorhombic
Pnma
19.9100(8)
9.6473(15)
10.461(4)
C40H68N6O6Ga10
1426.25
monoclinic
P21/n
13.5489(14)
12.5542(13)
16.545(2)
C26H30N4S2Ga2
600.08
monoclinic
P21/n
15.996
17.768
C30H42N4O3In4
965.96
monoclinic
P21/n
15.670
11.927
339.39
triclinic
P1h
7.9844(4)
8.5123(6)
15.995(2)
86.262(9)
76.753(6)
81(47)
1043.97(16)
2
b, Å
c, Å
9.879
20.017
R, deg
â, deg
92.169(9)
100.07
103.66
γ, deg
V, Å
2009.4(7)
8
1.358
2811.3(5)
4
1.685
2764.5
4
1.442
3635.4
4
1.765
Z
d
calc, g cm-3
1.080
F(000)
364
0.142
0.71070
0.3 × 0.3 × 0.35
25.97
840
2.681
0.71070
0.4 × 0.4 × 0.5
25.97
1416
4.753
0.71070
0.6 × 0.5 × 0.5
25.97
1224
2.121
0.71070
0.3 × 0.4 × 0.4
25.21
1880
2.538
0.71070
0.5 × 0.5 × 0.4
25.97
abs coeff, mm-1
λ, Å3
cryst dimens, mm
θmax, deg
no. of reflns measd
4273
1947
5298
5186
7381
no. of obsd reflns
4040
1947
5102
4858
7136
no. vars
223
146
297
323
392
R
Rw
0.0513
0.1425
0.997
0.0452
0.0816
0.944
0.0398
0.0954
0.510
0.0535
0.1200
0.858
0.0436
0.1131
0.446
goodness of fit
carboxaldehyde phenylhydrazone and the single-crystal
X-ray structures of five of them.
0.56 and 0.01 ppm assigned to two kinds of methyl
groups in the aluminum moieties in a 9:6 ratio. The 13C
NMR spectrum shows two signals (9.25 and -0.03 ppm)
due to the Al(1)-CH3 and Al(2)-CH3 groups, respec-
tively. The carbon (C(6)) attached to the imine group
appears at 148.89 ppm in the 13C NMR spectrum. The
27Al NMR spectrum of 1 at room temperature shows two
broad resonances at 152 and 138 ppm. The resonance
at 138 ppm is assigned to the four-coordinate Al(1) in
an N2AlC2 coordination environment, which is charac-
teristic of a four-coordinate Al atom when compared to
the shift in complexes of type [R2AlR′2]2 (R ) Me, Et;
R′ ) NEt2, OMe, OEt).9 The 152 ppm resonance is
assigned to the four-coordinate Al(2). The structures of
Resu lts a n d Discu ssion
The reaction of 2-pyridinecarboxaldehyde phenylhy-
drazone with trimethyl aluminum or -gallium in toluene
at room temperature affords the corresponding di-
nuclear aluminum and gallium complexes, in which one
hydrogen atom has been lost from the aza hydrogen
atom via the methane elimination reaction (eq 1). The
1
2-4, as deduced from the H and 13C NMR data and
elemental analyses, are similar to that of 1. Although
all the spectra are consistent with the proposed formu-
lation, the bonding mode of C(6)-N(2)-N(3) in 1 still
was unclear because it could involve tautomerism, i.e.,
a 1,2-proton shift. Accordingly, the dinuclear nature and
the bonding mode of the aluminum and gallium centers
for both 1 and 4 have been confirmed through single-
crystal X-ray diffraction analyses.
Descr ip tion of th e Molecu la r Str u ctu r e of 1.
Compound 1 crystallizes in the space group P1h with two
molecules per unit cell. A summary of the data collection
and crystallographic parameters is given in Table 1. An
ORTEP diagram of the solid-state structure with se-
lected bond lengths and angles is shown in Figure 1.
No symmetric element can be present in this structure.
Compound 1 contains two types of methylaluminum
fragments. Two aluminum atoms, Al(1) and Al(2), have
the usual four-coordinate tetrahedral organoaluminum
coordination. The Al(1) atom is coordinated by two
chelated nitrogen atoms. The dinuclear aluminum
compound in 1, formed by removing one hydrogen atom
from the amine N-H, may be attributed to the strong
resulting red products 1-4 were isolated as air-sensi-
tive, crystalline solids in high yield. Compounds 1-4
are soluble in toluene, THF, and dichloromethane and
were characterized by 1H, 13C, and 27Al NMR, mass
spectroscopy, and elemental analysis. The structures of
1 and 4 were determined by single-crystal X-ray dif-
fraction. The initial indication of the dinuclear formula-
tion for 1 stemmed from the observation of a parent ion
in the mass spectrum at m/z 339, followed by a series
of fragmentations attributable to the loss of Me groups.
(9) (a) Francis, J . A.; Bott, S. G.; Barron, A. R. J . Chem. Soc., Dalton
Trans. 1998, 3305. (b) Benn, R.; Rufinska, A.; Lehmkuhl, H.; J annen,
E.; Kruger, C. Angew. Chem., Int. Ed. Engl. 1983, 10, 779. (c) J iang,
Z.; Interrante, L. V.; Kwon, D.; Tham, F. S.; Kulling, R. Inorg. Chem.
1991, 30, 995.
1
The H NMR spectrum of 1 contains two resonances at

4038 Organometallics, Vol. 19, No. 20, 2000
Kim et al.
intermediate between those of single and double bonds;
consistent with the delocalization of the C-N-N
π-bond. The change in bond distances for the hydrazone
group [C(6)N(2)N(3)] indicates that metalation shifts the
N(3)-N(2) toward its amine N(2)-H form, and bond
multiplicity shifts from C(6)-N(2) toward N(2)-N(3)
probably due to the displacement of the π-charge.
Compound 4 has a structure similar to that of 1. The
structures of 1 and 4 show no unusual behavior. They
contain two types of metal MMe2 group chelated by the
ligand and an MMe3 group coordinated to a nitrogen
atom in the ligand.
Syn th esis a n d Ch a r a cter iza tion of (Ga Me2)8-
(Ga Me)2(µ4-O)2(µ3-O)4(C12 H10N3)2 (5). Compound 5
was initially isolated in the synthesis of 4 as a minor
yellow product. Thus, the addition of 5 equiv of GaMe3
to a toluene solution of 2-pyridinecarboxaldehyde phen-
ylhydrazone at 25 °C resulted in formation of a mixture
of products from which compounds 4 and 5 could be
separated by fractional crystallizations as the major and
minor isolated products, respectively, in 19:1 ratio in
ca. 88% yield. Complex 5 is a yellow crystalline solid at
room temperature, soluble in benzene, toluene, and
THF.
F igu r e 1. X-ray crystal structure of 1 with 50% probability
thermal ellipsoids depicted. Selected bond lengths (Å) and
angles (deg): Al(1)-(1) 2.00(2). Al(1)-N(2) 1.97(5), Al(2)-
N(3) 1.97(15), C(6)-N(2) 1.30(4), N(2)-N(3) 1.40(4), N(3)-
C(13) 1.42(2), Al(1)-C(8) 1.93(8), Al(1)-N(9) 1.90(6), N(1)-
Al(1)-N(2) 81.09(10), C(6)-N(2)-N(3) 120.04(4), N(2)-
N(3)-C(13) 111.04(1).
tendency to form a stable four-coordinate configuration.
The pyridyl Al(1)-N(1) distance (2.00(2) Å) is slightly
longer than the amido Al(1)-N(2) distance (1.97(5) Å),
a feature consistent with the literature.10 The Al(2)-
N(3) bond distance (1.97(15) Å) is within the range
observed for amine adducts of AlMe3 (1.88-2.09 Å).11
Initially we expected the product to be an N,N-bridged
dimeric aluminum complex A. Shearer and co-work-
The decanuclear gallium compounds were fully char-
acterized by NMR spectroscopy, single-crystal X-ray
diffraction, and elemental analyses. Five singlets (0.30,
1
0.16, 0.03, -0.11, -0.44 ppm) in the H NMR spectrum
ers12reported that the reaction of the pyridine-2-carbal-
dehyde oxime, 2-C5H4NCHdNOH, with the trimethyls
MMe3 (M ) Al, Ga, In), formed the dinuclear complex
[MMe2 (ONdCHC5H4N)] similar to type A. The imine
C(6)-N(2) bond length (1.30(4) Å)13 and N(2)-N(3) bond
lengths (1.40(4) Å)14 within the hydrazone core are
and five singlets (0.46, -2.75, -3.24, -4.58, -4.93 ppm)
in the 13C NMR spectrum of 5 assigned to the methyl
group on the gallium atoms demonstrate that the five
methyl groups are not chemically equivalent. As the
structure of the product cannot be deduced on the basis
of the spectroscopic data, a single-crystal X-ray diffrac-
tion study was undertaken. The molecular structure is
shown in Figure 2. An alternative view of the basic
skeleton of the complex is shown in Figure 3. Crystal-
lographic data are given in Table 1, with selected bond
lengths and angles in Table 2. To our surprise, the X-ray
study of 5 showed it to be the decanuclear gallium
complex. The molecular structure of 5 has an inversion
center. The structure consists of an eight-membered
Ga4O4 cyclic core. The first such ring compound was
reported by Hoard et al.,15 and similar ring structures
(10) (a) Leman, J . T.; Roman, H. A.; Barron, A. R. Organometallics
1993, 12, 2986. (b) Tuck, D. G. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergaman
Press: Oxford, England, 1982; Vol. 1, Chapter 7. (c) Gardiner, M. G.;
Lawrence, S. M.; Raston, C. L. Inorg. Chem. 1996, 35, 1349. (d) Atwood,
J . L.; Lawrence, S. M.; Raston, C. L. J . Chem. Soc., Chem. Commun.
1994, 73.
(11) Robinson, G. H.; Zhang, H.; Atwood, J . L. J . Organomet. Chem.
1967. 89, 1530.
(12) Shearer, H. M. M.; Twiss, J .; Wade, K. J . Organomet. Chem.
1980, 184, 309.
(13) Koide, Y.; Francis, J . A.; Bott, S. G.; Barron, A. R. Polyhedron
1998, 17, 983.
(14) Peters, D. W.; Power, M. P.; Bourret, E. D.; Arnold, J . Chem.
Commun. 1998, 753.
(15) Smith, G. S.; Hoard, J . L. J . Am. Chem. Soc. 1959, 81, 3907.

Base-Stabilized Alkyl Al, Ga, and In Complexes
Organometallics, Vol. 19, No. 20, 2000 4039
bond lengths are in the normal range of the known
Ga-O bond lengths.21 The lengths and angles within
the ligand unit are indicative of delocalization through
the C(6)-N(2)-N(3) bonds.
The formation of compound 5 raises the following
question. What is the source of the oxygen atoms? A
possible solution is that traces of water in the solvent
entered the system, resulting in oxygen incorporation.
To generate the complex 5, in an independent experi-
ment, we carried out the controlled hydrolysis of a
mixture of 2-pyridinecarboxaldehyde phenylhydrazone,
GaMe3, and H2O in 1:5:3 ratio in toluene at -20 °C.
The 1H and 13C NMR analyses of the yellow powder that
was produced were identical to those of 5.
F igu r e 2. ORTEP drawing of 5. Thermal ellipsoids are
drawn at the 50% probability level.
A reasonable mechanism for the formation of 5
involves the initial hydrolysis of GaMe3 coordinated to
the nitrogen atom of 4, leading to intermediate B,
followed by the attack of GaMe3 and H2O.
F igu r e 3. Illustration of the central Ga4O4 cyclic core for
5.
Syn t h esis a n d Ch a r a ct er iza t ion of [(Me2M)-
(SC4H3 CHNNC6H5)]2 (M ) Al, Ga , In ). The orange
crystalline compounds 6-8 were prepared via the
methane elimination reaction of 2-thiophenecarboxal-
dehyde phenylhydrazone with trimethylaluminum, tri-
methylgallium, and trimethylindium in toluene, as
shown in eq 2. Compounds 6-8 are soluble in toluene
with sulfur have been described for several metal sulfur
derivatives.16 The eight-membered ring in 5 adopts a
chairlike conformation (Figure 3). Similar chairlike
conformations have been observed for the gallium
diphenyl phosphinate compounds [R2Ga(µ-O2PPh2)]2.17
The interesting feature of the molecular structure of 5
is the presence of two unusual five-coordinate gallium
centers,18 Ga(2) and Ga(2)*, and eight four-coordinate
gallium environments. The environment about the five-
coordinate Ga(2) and Ga(2)* may be described as a
distorted trigonal bipyramid in which N(1) and O(3)
occupy the axial positions, i.e., N(1)-Ga(2)-O(3) 157.l4-
(3)°. The eight gallium atoms have an approximate
tetrahedral configuration. The Ga-O distances are of
two types, those (1.850(6)-1.903 (5) Å) for the µ3-oxide
bridges and those (1.928(6)-2.094(6) Å) for the µ4-oxo
bridges. The µ3-oxo ligand bridges three aluminum
centers with an approximate pyramidal geometry. A
similar bonding mode of the µ3-oxo ligand has been
reported in the di-2-pyridylamido complex [Al4(CH3)6-
(µ3-O)2(dpa)2],4b the cube complex Ga8(pz)12O4Cl4‚2thf,19
and the galloxane complex [Ga12tBu12(µ3-O)8(µ-O)2(µ-
OH)4].20 The oxygen atoms O(3) and O(3)* have a
tetrahedral geometry and bridge four gallium atoms
with nearly equal Ga-O(3) bond lengths. The Ga-O
(16) Taghiof, M.; Heeg, M. J .; Bailey, M.; Dick, D. G.; Kumar, R.;
Hendershot, D. G.; Rahbarnoohi, H.; Oliver, J . P. Organometallics
1995, 14, 2903.
1
and THF and were characterized by H and 13C NMR
(17) (a) Hahn, F. E.; Schneider, B. Z. Naturforsch., Teil B 1990, 45,
134. (b) Landry, C. C.; Hynes, A.; Barron, A. R.; Haiduc, I.; Silvestu,
C. Polyhedron 1996, 15, 391.
(18) (a) Lee, B.; Pennington, W. T.; Robinson, G. H. Organometallics
1990, 9, 1709. (b) Rettig, S. J .; Storr, A.; Trotter, J . Can. J . Chem.
1975, 53, 753.
and mass spectroscopy and elemental analysis. Al-
though no parent ion was observed in the mass spec-
trum of 6 at m/e 517, the presence of fragmentation
(M+-CH3 ) 502 amu) confirmed the dimeric nature of
6. To determine the extent to which a sulfur atom in a
pendent arm is coordinated to the group 13 element
(19) Capparelli, M. V.; Hodge, P.; Piggott, B. Chem. Commun. 1997,
937.

4040 Organometallics, Vol. 19, No. 20, 2000
Ta ble 2. Selected Bon d Dista n ces [Å] a n d An gles [d eg] for 5 a n d 9
Kim et al.
5
N(2)-N(3)
O(3)-Ga(4)
Ga(5)-O(3)
Ga(2)-N(1)
1.336(9)
2.024(6)
1.996(6)
2.180(7)
N(3)-Ga(3)
Ga(4)-O(1)
Ga(5)-O(2)
1.983(7)
1.858(6)
1.940(6)
Ga(3)-O(3)
Ga(4)-O(2)
N(2)-C(6)
1.928(6)
1.852(5)
1.300(10)
O(2*)-Ga(1)-O(1)
Ga(2)-N(2)-N(3)
O(2)-Ga(4)-O(3)
Ga(4)-O(3)-Ga(5)
90.7(2)
O(1)-Ga(4)-O(2)
N(3)-Ga(3)-O(3)
Ga(2)-O(1)-Ga(4)
109.9(3)
91.5(3)
103.6(3)
O(1)-Ga(2)-N(2)
O(2)-Ga(5)-O(3))
Ga(2)-O(3)-Ga(4)
109.6(3)
85.6(2)
90.1(2)
119.1(5)
87.1(2)
89.9(2)
9
In(1)-N(1)
In(1)-O(1)
N(1)-N(2)
O(1)-In(1′)
In(2′)-O(1)
2.182(7)
2.318(8)
N(1)-C(5)
In(2)-O(1)
N(1′)-N(2′)
1.300(13)
2.229(6)
1.379(1)
1.349(11)
2.186(6)
2.189(6)
N(2)-In(2)
2.154(8)
2.300(8)
1.286(12)
In(1′)-N(1′)
N(1′)-C(5′)
O(1)-In(1)-N(1)
N(2)-In(2)-O(1)
O(1)-In(2′)-N(2′)
92.9(3)
88.4(3)
91.0(3)
In(1)-N(1)-N(2)
In(1)-O(1)-In(2)
In(2′)-N(2′)-N(1′)
111.0(6)
103.4(3)
116.1(6)
N(1)-N(2)-In(2)
In(1′)-O(1)-In(2′)
N(2′)-N(1′)-In(1′)
117.4(6)
105.0(3)
114.4(6)
F igu r e 5. ORTEP drawing of 9. Thermal ellipsoids are
drawn at the 30% probability level.
F igu r e 4. X-ray crystal structure of 1 with 50% probability
thermal ellipsoids depicted. Selected bond lengths (Å) and
angles (deg): N(1)-N(2) 1.422(9). N(1)-C(5) 1.296(11), Ga-
(1′)-N(2) 1.985(7), Ga(1)-N(1) 2.040(8), Ga(1)-N(1′) 2.023-
(7), N(1′)-N(2′) 1.422(9), Ga(1′)-N(2′) 1.991(7), N(1)-
Ga(1)-N(1′) 89.5(3), N(2)-Ga(1′)-N(2′) 94.7(3).
N(1)′ has a tilted butterfly shape around its Ga(1)-
Ga(1)′ hinge. The imine Ga(1)-N(1) distance (2.040 (8)
Å) is slightly longer than the amido Ga(1)-N(1)′ dis-
tance (2.023 (7) Å), a feature consistent with that
reported in the literature.6
centers, the 1H NMR spectra of 6 were measured in CD2-
Cl2 at temperatures ranging from room temperature to
-60 °C. In the 1H NMR spectrum of the aluminum
dimer 6 at room temperature two signals at 0.19 and
-0.08 ppm in the methyl region were observed; these
signals persisted down to -60 °C, and the chemical shift
values did not vary significantly. The equivalence of the
values suggests that the aluminum dimer 6 adopts the
same configuration in solution and in the solid. Confir-
mation of the dinuclear structure of 6 was provided by
X-ray crystallography.
The molecular sturcture of 7 is shown in Figure 5.
The solid-state structure of 7 comprises an individual
molecule, and there are no unusually short intermo-
lecular contacts between the monomeric units. The
molecule consists of a six-membered Ga2N4 cyclic core.
The coordination sphere of Ga(1) consists of a distorted
tetrahedral configuration. The six-membered skeleton
is very similar to that found in the related In(-N-
N-)2In core of the dimeric molecule.22 The six-mem-
bereddigalla cycle Ga(1)-N(1)-N(2)-Ga(1)′-N(2)′-
The next question arises as to which effect is the most
influential one in affording the different configuration
in the reaction of 2-pyridinecarboxaldehyde and thiophen-
ecarboxaldehyde phenylhydrazone with trimethylgal-
lium. Nitrogen is a stronger Lewis base toward gallium
than sulfur. Thus, the Ga-N bonding interaction would
be more extensive than the Ga-S interaction. Conse-
quently, the easy formation of the five-membered che-
late compound with an N,N-coordination mode may lead
to the stable dimeric structure of 2. On the other hand,
the reaction of 2-thiophenecarboxaldehyde phenylhy-
drazone with trimethylgallium afforded the cyclic, four-
coordinated compound by an intermolecular coordina-
tion of nitrogen because the Ga‚‚‚S contact between the
pendent thiophene appears to be absent. Therefore, any
association between the pendent donor atom and gal-
lium may be the most important factor in determing the
geometric configuration.
Syn th esis a n d Ch a r a cter iza tion of [(Me2In )2-
(OC4H3CHNNC6H5)]2(µ4-O) (9). The 2-furancarboxal-
dehyde phenylhydrazone complex of trimethylindium
was synthesized using the same procedure as described
for 1. Since there were no sources of oxygen available
in the original synthesis of 9, we postulated that the
(20) Storre, J .; Belgardt, T.; Stalke, D.; Roesky, H. W. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1244.
(21) (a) Schumann, H.; Frick, M.; Heymer, B.; Girgsdies, F. J .
Organomet. Chem. 1996, 512, 117. (b) Smith, G. S.; Hoard, J . L. J .
Am. Chem. Soc. 1959, 81, 3907.
(22) Hausen, H.-D.; Locke, K.; Weidlein, J . J . Organomet. Chem.
1992, 429, C27.

Base-Stabilized Alkyl Al, Ga, and In Complexes
Organometallics, Vol. 19, No. 20, 2000 4041
oxygen atom was produced by the reaction of the methyl
group of indium with a trace of H2O present in the
reaction medium. In fact, when the reaction was carried
out in the presence of 0.5 equiv of H2O in toluene at
-20 °C, it was converted into 9 in 30% yield after 12 h.
(8) Å), indicating that the negatively charged amido
nitrogen atom is a stronger donor to the indium center
than the neutral imine nitrogen atom. The In-N bond
distance compared well with those in diphenyltriazene
complex [InMe2(dpt)(3,5-Me2py)] (2.153(6)-2.430(4) Å)26
and indium benzylaminopyridine complex [In{2-[N-
(CH2C6H5) NC5H4}2 Me (2.146(2)-2.349(2) Å].27
Su m m a r y
The nine new compounds described here expand upon
the few examples of well-characterized aluminum, gal-
lium, and indium compounds of heterocyclic carboxal-
dehyde phenylhydrazones. A combination of X-ray
crystallographic and spectroscopic studies confirms the
nature of these compounds. The multidentate hetero-
cyclic carboxaldehyde phenylhydrazones are valuable
for the synthesis of new polynuclear alkylaluminum,
-gallium, and -indium compounds with different coor-
dination environments. The different bonding modes
may be attributable to the difference in the M-N, M-O,
and M-S contacts between the pendent moieties and
the metal. When the pendent nitrogen was strongly
coordinated to the aluminum and gallium, the dimeric
compounds such as 1-4 were formed. However, when
there is substantially no interaction between the pen-
dent thiophene and the group 13 compounds, the
tetrahedral configuration of the MN2C2 type by an
intermolecular coordination is more favored. On the
other hand, when the subsidiary M-O interaction is
included and the large metal such as indium is involved,
the most stable configuration at the indium is that of a
distorted trigonal bipyramid. These ligands also display
complicated bonding modes which require further in-
vestigation in order to be understood.
Complex 9 is an orange crystalline solid that is soluble
in benzene, toluene, and THF. Satisfactory elemental
data were obtained for the complex. The 1H and 13C
NMR spectra of 9 at 25 °C show two resonances for the
methyl groups, indicating that compound 9 is fluxional
in solution at that temperature. At lower temperature,
1
-35 °C, the H NMR spectrum in CD2Cl2 revealed two
resonances at 0.08 ppm (broad, two overlapping signals)
and -0.12 ppm (broad, two overlapping signals), dem-
onstrating the presence of the methyl groups in different
environments. Since these data were insufficient to
unambiguously determine the structure of the molecule,
an X-ray study was carried out. The molecular structure
of 9 is shown in Figure 5. Compound 9 crystallizes in
the space group P21/n with four molecules per unit cell.
Compound 9 contains four indium atoms. The ligand
binds to two indium centers through the imido and
amido sites. The oxo ligand, produced by the reaction
of one H2O with two methyl groups of the indium
complexes, bridges four indium centers with an ap-
proximate tetrahedral geometry. A similar bonding
mode for the µ4-oxo ligand has been reported in the
complex [InMe(OH)(O2PPh2)]4‚py4.23 The In-O bond
lengths (2.182(7)-2.229(6) Å) are in the normal range
of the known In-O bond lengths.24 In the previous
crystal structure of 7, any association in the solid via
Ga‚‚‚S interactions is likely to be weak. Oxygen is a
stronger Lewis base toward indium than sulfur. Thus,
the Ga-O bond interaction would be more extensive.
The In(1)‚‚‚O(2) contact (2.239 Å) appears to be strong,
having a bond length greater than that normally seen
for In-O dative bonds. The In‚‚‚O vector lies ap-
proximately trans to the In(1)-O(1) bond, with an O‚‚
‚In-O angle of 159.2(3)°. If this subsidiary In‚‚‚O
interaction is included, the overall geometry at indium
is that of a distorted trigonal bipyramid. Such interac-
tions have been observed in group 13 compounds.25 The
amido In(2)-N(2) bond distance (2.154 (8) Å) is slightly
shorter than the imine In(1)-N(1) bond distance (2.318
Exp er im en ta l Section
All experiments were performed in a dry nitrogen atmo-
sphere in a Vacuum Atmospheres drybox or by standard
Schlenk techniques. Toluene and hexane were distilled from
sodium benzophenone ketyl. All the 1H, 13C, and 27Al NMR
spectra were recorded on a Varian Gemini 200 spectrometer.
Chemical shifts were referenced relative to either TMS (1H)
or benzene-d6 (1H, δ 7.155; 13C{1H}, δ 128.00), while 27Al NMR
spectra were referenced relative to Al(H2O)63+. IR spectra were
recorded on a Biorad FTS-165 spectrophotometer. Mass spec-
tra were recorded on a high-resolution VG70-VSEG instru-
ment, and elemental analyses were performed with a Carlo
Erba Instruments CHNS-O EA 1108 analyzer. AlMe3, GaMe3,
and InMe3 were purchased from Strem Chemicals. Pyridin-
ecarboxaldehyde, thiophenecarboxaldehyde, furancarboxalde-
hyde, and phenylhydrazine were purchased from Aldrich
Chemical. The heterocyclic carboxaldehyde phenylhydrazones
were prepared from the condensation reaction of heterocyclic-
2-carboxaldehyde and phenylhydrazine according to published
procedures or slight adaptations thereof.28
Gen er a l Syn th esis of (Me2M)[NC5H4C(R)NNC6H5]-
(MMe3). In a typical synthesis, a solution of 2-acetylpyridine
phenylhydrazone (0.21 g, 1 mmol) in toluene (10 mL) was
treated with AlMe3 (0.48 mL, 5 mmol) in toluene (10 mL) at
room temperature. The color of the mixture immediately
changed from yellow to blackish red. The solution was stirred
(23) Arif, A. M.; Barron, A. R. Polyhendron 1988, 7, 2091.
(24) (a) Einstein, F. W. B.; Gilbert, M. M.; Tuck, D. G. J . Chem.
Soc., Dalton Trans. 1973, 248. (b) Uhl, W.; Pohlmann, M. Chem.
Commun. 1998, 451. (c) Cleaver, W.; Barron, A. R. J . Am. Chem. Soc.
1989, 111, 8966.
(25) Hendershot, D. G.; Barber, M.; Kumar, R.; Oliver, J . P.
Organometallics 1992, 10, 3302.
(26) Leman, J . T.; Roman, H. A.; Barron, A. R. Organometallics
1993, 12, 2986.
(27) Zhou, Y.; Richeson, D. S. Organometallics 1995, 14, 3558.
(28) Espinet, P.; Garc´ıa, G.; Herrero, F. J .; J eannin, Y.; Philoche-
Levisalles Inorg. Chem. 1989, 28, 4207.

4042 Organometallics, Vol. 19, No. 20, 2000
Kim et al.
for 12 h at that temperature and then decanted. The solution
was layered with hexane (5 mL) and stored at -15 °C for 2
days, whereupon red crystals formed in 80-86% yield.
(Me2Al)[NC5H4C(CH3)NNC6H5](AlMe3) (1). Mp: 101-104
(Th and Ph), -1.34 (AlCH3), -2.64 (AlCH3). 27Al NMR: δ 146.
MS (EI): m/z 502 (M+ - CH3). Anal. Calcd for C26H30N4S2Al2:
C, 60.45; H, 5.85. Found: C, 60.86; H, 5.98.
[(Me2Ga )(SC4H3CHNNC6H5)]2 (7). Yield: 54%. Mp: 138-
140 °C. 1H NMR (C6D6): δ 7.95-6.25 (m, 16H, Th and Ph),
3.20 (s, 2H, CH), 0.29 (s, 6H, GaCH3), 0.05 (s, 6H GaCH3),
13C{1H} NMR (C6D6): δ 145.27 (HCdN), 141.23, 132.22,
129.51, 128.33, 127.16, 126.13, 121.26, 120.35, 114.08, 113.10
(Th and Ph), -0.14 (GaCH3), -1.68 (GaCH3). MS (EI): m/z
602 (M+). Anal. Calcd for C26H30N4S2Ga2: C, 51.86; H, 5.02.
Found: C, 51.42; H, 4.94.
1
°C. H NMR (C6D6): δ 8.22-6.61 (m, 9H, Py and Ph), 2.03 (s,
3H, CCH3), 0.56 (s, 9H, AlCH3), 0.01 (s, 6H, AlCH3). 13C{1H}
NMR (C6D6): δ 148.89(C(CH3)N), 136.37, 129.50, 129.18,
128.53, 127.44, 127.40, 126.55, 123.18, 122.19, 121.37, 113.78
(Py and Ph), 25.48 (CCH3), 9.25 (AlCH3), -0.03(AlCH3). 27Al
NMR: δ 152, 138. MS(EI): m/z 339 (M+). Anal. Calcd for
C
18H27N3Al2: C, 63.70; H, 8.02. Found: C, 63.33; H, 7.84.
(Me2Ga )[NC5H4C(CH3)NNC6H5](Ga Me3) (2). Yield: 83%.
[(Me2In )(SC4H3CHNNC6H5)]2 (8). Yield: 34%. Mp: 152-
154 °C. 1H NMR (C6D6): δ 7.82-6.62 (m, 16H, Th and Ph),
3.06 (s, 2H, CH), 0.16 (s, 6H, InCH3), -0.98 (s, 6H InCH3).
13C{1H} NMR (C6D6): δ 145.92 (HC)N), 140.94. 137.24.
130.27. 128.23. 124.03. 122.13. 121.89. 116.39. 110.11. 109.13
(Th and Ph), -0.64 (InCH3), -2.82 (InCH3). MS (EI): m/z 692
(M+). Anal. Calcd for C26H30N4S2In2: C, 45.10; H, 4.37.
Found: C, 44.76; H, 4.18.
[(Me2In )(OC4H3CHNNC6H5)]2O (9). Compound 9 was
prepared using the same procedure as described for 1 from
2-furaldehyde phenylhydrazone (0.09 g, 0.5 mmol) and tri-
methylindium (0.24 g, 1.5 mmol) in 30% yield. Mp: 154-156
°C. 1H NMR (C6D6): δ 7.62-6.48 (m, 16H, Fu and Ph), 3.12
(s, 2H, CH), -0.06 (s, 12H, InCH3), -0.09 (s, 12H InCH3). 13C-
{1H} NMR (C6D6): δ 142.76 (HCdN), 129.63, 129.54, 128.55,
128.35, 127.78, 127.58, 120.41, 113.15, 111.87, 108.34 (Fu and
Ph), 3.44 (InCH3), -1.28 (InCH3). MS (EI): m/z 966 (M+). Anal.
Calcd for C30H42N4O3In4: C, 37.30; H, 4.38. Found: C, 37.68;
H, 4.52.
X-r a y Cr ysta llogr a p h y. Details of the crystal data and a
summary of the intensity data collection parameters for 1, 4,
5, 7, and 9 are given in Table 1. Crystals of 1, 4, 5, 7, and 9
suitable for X-ray diffraction were obtained from toluene/
hexane. For the room-temperature X-ray examination and data
collection, each crystal was coated with a light film of epoxy
resin and mounted on a glass fiber. Intensity data for 1, 4, 5,
7, and 9 were collected using graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å) on an Enraf-Nonious CAD-4 diffrac-
tometer. Each structure was solved by the application of direct
methods using the SHELXS-96 program29a and least-squares
refinement using SHELXL-97.29b All non-hydrogen atoms in
compounds 1, 4, 5, 7, and 9 were anisotropically refined. All
other hydrogen atoms were located from the difference Fourier
and then refined.
Mp: 108-112 °C. 1H NMR (C6D6): δ 8.08-6.64 (m, 9H, Py
and Ph), 2.02 (s, 3H, CCH3), 0.30 (s, 9H, GaCH3), 0.15 (s, 6H,
GaCH3). 13C{1H} NMR (C6D6): δ 144.63 (C(CH3)N), 141.33,
138.56, 0.131.64, 0.129.11, 125.60, 124.17, 123.71, 118.21,
116.83, 115.90, 109.81 (Py and Ph), 27.93 (CCH3), 5.26
(GaCH3), 0.14 (GaCH3). MS(EI): m/z 429 (M+). Anal. Calcd
for C18H27N3Ga2: C, 50.88; H, 6.41. Found: C, 50.41; H, 6.28.
(Me2Al)[NC5H4CHNNC6H5](AlMe3) (3). Yield: 82%. Mp:
101-102 °C. 1H NMR (C6D6): δ 8.18-6.58 (m, 9H, Py and Ph),
3.58 (s, 1H, CH), -0.09 (s, 9H, AlCH3), -0.79 (s, 6H, AlCH3).
13C{1H} NMR (C6D6): δ 149.22 (HC)N), 143.56, 141.42,
130.45, 129.37, 128.48, 128.28, 127.52, 126.90, 125.26, 120.79,
120.42 (Py and Ph), 3.11 (AlCH3), -8.76 (AlCH3). 27Al NMR:
δ 150, 136. MS(EI): m/z 325 (M+). Anal. Calcd for C17H25N3-
Al2: C, 62.76; H, 7.75. Found: C, 63.04; H, 7.96.
(Me2Ga )[NC5H 4CH NNC6H 5](Ga Me3) (4). Yield: 86%.
Mp: 105-108 °C. 1H NMR (C6D6): δ 8.08-6.62 (m, 9H, Py
and Ph), 3.49 (s, 1H, CH), 0.23 (s, 9H, GaCH3), -0.39 (s, 6H
GaCH3), 13C{1H} NMR (C6D6): δ 148.22 (HC)N), 143.29,
139.96, 129.40, 128.99, 128.47, 128.27, 127.50, 126.54, 126.27,
122.50, 120.43 (Py and Ph), 1.37 (GaCH3), -4.29 (GaCH3). MS
(EI): m/z 411 (M+). Anal. Calcd for C17H25N3Ga2: C, 49.70; H,
6.13. Found: C, 50.14; H, 6.32.
[(Me2Ga)3(NC5H4CHNNC6H5)(GaMe2)2]2(µ3-O)4(µ4-O)2 (5).
A solution of 2-pyridinecarboxaldeyhde phenylhydrazone (0.25
g, 0.61 mmol) in toluene (10 mL) was treated with GaMe3 (0.18
mL, 1.82 mmol) in toluene (5 mL) at room temperature. The
solution was cooled to -30 °C, whereupon degassed H2O (0.032
mL, 1.82 mmol) was slowly added. The reaction mixture was
stirred for 1 h at -30 °C and then warmed to room temper-
ature. The solution was layered with hexane (5 mL) and stored
at -15 °C for 2 days, whereupon a yellow powder formed in
42% yield. Mp: 148-152 °C. 1H NMR (C6D6): δ 7.92-6.58 (m,
18H, Py and Ph), 3.08 (s, 2H, CH), 0.30 (s, 12H, GaCH3), 0.16
(s, 12H GaCH3), 0.03 (s, 6H GaCH3), -0.11 (s, 12H GaCH3),
-0.44 (s, 6H GaCH3). 13C{1H} NMR (C6D6): δ 147.72 (HCd
N), 140.64, 137.83, 129.58, 128.50, 128.30, 127.53, 126.30,
125.63, 122.76, 121.05, 113.73 (Py and Ph), 0.46 (GaCH3),
-2.75 (GaCH3). -3.24 (GaCH3), -4.58(GaCH3), -4.93(GaCH3).
Anal. Calcd for C40H68N6O6Ga10: C, 33.69; H, 4.81. Found: C,
33.32; H, 4.58.
Ack n ow led gm en t. The authors wish to acknowl-
edge the financial support of the Korea Research
Foundation made in the program year of 1998 (1998-
001-D00410).
Su p p or tin g In for m a tion Ava ila ble: Tables listing crys-
tallographic information, atomic coordinates and Beq values,
anisotropic thermal parameters, and intramolecular bond
distances, angles, and torsion angles for 1, 4, 5, 7, and 9.
[(Me2Al)(SC4H3CHNNC6H5)]2 (6). Compound 6 was pre-
pared using the same procedure as described for 1 from
thiophenecarboxaldehyde phenlyhydrazone (0.20 g, 1 mmol)
and trimethylaluminum (0.48 mL, 5 mmol) in 63% yield. Mp:
132-136 °C. 1H NMR (C6D6): δ 7.94-6.55 (m, 16H, Th and
Ph), 3.14 (s, 2H, CH), 0.16 (s, 6H, AlCH3), -0.13 (s, 6H AlCH3),
13C{1H} NMR (C6D6): δ 144.89 (HC)N), 141.24, 132.16,
129.51, 128.32, 127.68, 127.12, 126.07, 125.88, 120.38, 113.10
OM000285O
(29) (a) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467. (b)
Sheldrick, G. M. SHELXL, Program for Crystal Structure Refinement;
University of Go¨ttingen, 1997.