Reactions of group 13 metal trialkyls with oxamides

Article abstract of DOI:10.1016/j.jorganchem.2010.11.005

Alkyl aluminum-, gallium-, and indium oxamidates Me₄Al ₂(dpoa) (1), Me₄Al₂(dboa) (2), Me ₄Ga₂(dpoa) (3), Me₄Ga₂(dboa) (4), ^tBu₄Ga₂(dpo

Full text of DOI:10.1016/j.jorganchem.2010.11.005

Journal of Organometallic Chemistry 696 (2011) 2079e2085
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactions of group 13 metal trialkyls with oxamides
,
a
a
b
Wanda Ziemkowska a , Eliza Jaskowska , Ewa Zygad1o-Monikowska , Micha1 K. Cyranski
*
ꢀ
ꢀ
a Warsaw University of Technology, Faculty of Chemistry, Koszykowa 75, 00-662 Warsaw, Poland
b Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Alkyl aluminum-, gallium-, and indium oxamidates Me4Al2(dpoa) (1), Me4Al2(dboa) (2), Me4Ga2(dpoa)
(3), Me4Ga2(dboa) (4), tBu4Ga2(dpoa) (5) and Me4In2(dboa) (6) (dpoa-H2 ¼ N,N0-diphenyloxamide,
dboa-H2 ¼ N,N0-di-tert-butyloxamide) have been prepared and characterized. Compounds 1e3, 5 and 6
exist in the form of isomers a only, with a skeleton framework of the molecules consisting of two almost
flat, coplanar and fused MNOC2 (M ¼ Al, Ga, In) heterocyclic rings. Depending on the reaction conditions,
the compound 4 was obtained as the isomer 4a or as the mixture of two isomers 4a and 4b. Molecular
structures of the compounds 1ae6a have been determined by X-ray crystallography. A structure of the
isomer 4b was proposed on the basis of NMR spectroscopy. A skeleton framework of the 4b molecule
consists of two fused different cycles, GaO2C2 and GaN2C2.
Received 8 October 2010
Received in revised form
2 November 2010
Accepted 8 November 2010
Keywords:
Aluminum
Gallium
Indium
Amides
Ó 2010 Elsevier B.V. All rights reserved.
Oxamidates
1. Introduction
a particular attention in the supramolecular chemistry [10], group
13 oxamidates are rather poorly described. It was demonstrated in
Studies involving deprotonated amides and group 13 metal
centers have largely focused on the synthesis and characterization
of alkylaluminum amidates. First results on reactions between
organoaluminum compounds and N-substituted acid amides
were reported in 1966 by Tani et al. [1]. In 1968, Wade et al. [2],
Lappert et al. [3] and Tani et al. [4] published [Me2Al(RNC(O)R0)]2
compounds as the dimeric molecules composed of a centro-
symmetrical eight-membered ring with aluminum atoms bridged
by OCN groups. The alkylaluminum amidates have been of
considerable interest for their activity in acetaldehyde polymeri-
zation [4] and transamidation of secondary carboxamides [5].
Despite intensive studies on a synthesis, structure and catalytic
activity of alkylaluminum amidates [1e6], only Lin and coworkers
[7,8] reported a discussion the factors affecting coordination mode
of aluminum atoms in these compounds.
Contrary to the organoaluminum acid amidates, organogallium
and indium amidates are highly unexplored. Similarly, literature
data concerning reactions of alkyl compounds of group 13
metals with acid multi-amides are poor. Recently, mononuclear
aluminum complexes supported by the tripodal tris(amidate)
ligands and a reaction product of Me3Al with 1,2-C6H4[NHC(tBu)O]2
have been described [9]. Although oxamidate ligands deserve
1975, that trialkyl derivatives of gallium and indium reacted with
N,N0-dimethyloxamide to yield products of the general formula
(R2M)2(CONMe)2 [11]. On the basis of the NMR spectroscopy and
X-ray diffraction studies, Fischer and Stezowski [12] found that the
gallium compounds can exist in the form of two configurational
isomers, A and B (Scheme 1). Recently, we have reinvestigated
the reactions of alkyl aluminum compounds with N,N0-dimethy-
loxamide obtaining four complexes (R2Al)2(CONMe)2 (R ¼ Me, Et,
t
iBu, Bu), each in the form of the isomer A [13]. An occurrence of
the unusual configurational isomerism for the gallium oxamidates
described by Fischer and Stezowski [12] prompted us to study the
structure of group 13 N,N0-substituted oxamidates depending on
the reaction conditions and N-substituents in oxamidate moieties.
We report herein the study of the reaction products from the
treatment of N,N0-substituted oxamidate ligand precursors with
trialkyl aluminum, -gallium and -indium compounds. The main aim
of the investigation is the synthesis and structural characterization
of group 13 metal oxamidates.
2. Results and discussion
N,N0-Diphenyloxamide (dpoa-H2) and N,N0-di-tert-butylox-
amide (dboa-H2) reacted with R3M in a 1:2 M ratio to produce
quantitatively the oxamidates of group 13 metals, Me4Al2(dpoa)
t
(1), Me4Al2(dboa) (2), Me4Ga2(dpoa) (3), Me4Ga2(dboa) (4), Bu4
Ga2(dpoa) (5) and Me4In2(dboa) (6) (Scheme 2).
-
* Corresponding author. Tel.: þ48 22 2347316; fax: þ48 22 6605462.
E-mail address: ziemk@ch.pw.edu.pl (W. Ziemkowska).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.11.005

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W. Ziemkowska et al. / Journal of Organometallic Chemistry 696 (2011) 2079e2085
Scheme 1.
In the syntheses, R3M compounds were used in an excess. The
excess of R3M was easily removable from the post-reaction
mixtures with other volatiles in vacuo. Although the resulting
compounds are soluble in a variety of organic solvents including
methylene dichloride, chloroform, toluene, diethyl ether, THF and
toluene, they precipitate easily as crystals from the solutions at
lower temperature (10 ꢀC). All compounds were characterized by
NMR and IR spectroscopies, elemental analyses and melting point
measurements. The molecular structures were determined on the
basis of an X-ray diffraction study and are shown in Figs. 1e6. Data
collection and structure analyses are listed in Tables 1 and 2.
The reaction of Me3Ga with N,N0-di-tert-butyloxamide, carried
out in CH2Cl2, is the only reaction leading to a mixture of the
isomers 4a and 4b. On the other hand, the same reaction in
a refluxed THF yielded 4a only. The products 1e3, 5 and 6 were
formed as the isomers a exclusively. Attempts to isolate the
compound 4b from the post-reaction mixture were unsuccessful,
therefore the structure was proposed on the basis of spectroscopic
measurements.
Fig. 1. (top) Molecular structure of Me4Al2(dpoa) (1a). Displacement ellipsoids are
drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected
interatomic distances (Å) and angles (ꢀ): Al(1)eO(1) 1.865(2), Al(1)eN(1) 1.968(2), N
(1)eC(1) 1.301(3), C(1)eO(1) 1.280(3), C(1)eC(1) 1.516(4), N(1)eC(2) 1.446(3), O(1)eAl
(1)eN(1) 85.54(8), C(1)eN(1)eAl(1) 111.3(2), O(1)eC(1)eN(1) 130.1(2), O(1)eC(1)eC
(1) 116.8(3), C(1)eO(1)eAl(1) 113.3(1). (Bottom) View of the molecule showing that
two fused C2NOAl cycles are coplanar.
The 13C NMR spectra of the compounds 1ae6a exhibited single
carbonyl resonances at approximately 162e165 ppm consistent
with oxamidate donors. In the 1H NMR spectra, signals of protons of
methyl groups bonded to the metal atoms of each compound
(1ae4a, 6a) appeared as one singlet. The spectrum of the tert-butyl
derivative 5a revealed one singlet at 1.08 ppm of tert-butyl protons.
These data indicated the equivalence of alkyl groups bonded to the
metal atoms which is in agreement with the structures of 1ae6a.
The structure of the compound 4b was proposed on the basis of
spectroscopic measurements of the 4a and 4b mixture and litera-
ture data. The 1H NMR spectrum revealed one signal at ꢁ0.24 ppm
of GaCH3 protons of 4a and two singlets (at ꢁ0.22 and ꢁ0.23 ppm)
assigned to the GaCH3 protons of 4b. In contrast to the four
equivalent GaMe groups in 4a, the compound 4b consisted of two
kinds of GaMe groups. On the basis of the integration ratio of GaCH3
protons, we found that the ratio of the isomers is the same during
30 days. The signals of (CH3)3CN group protons of 4a and 4b
isomers appeared as two singlets at 1.37 and 1.36 ppm respectively,
which indicated the equivalence of tBu groups in the both isomers.
The 13C NMR spectrum exhibited one signal (at 162.14 ppm) of C]O
carbons of 4b, which was the evidence of an equivalence of CO
groups in this compound. In the IR spectrum, besides nC
]O band of
4a isomer (1616 cmꢁ1), the nC band (1608 cmꢁ1) of 4b was
]
O
present. Regarding the results of spectroscopic measurements, we
consider that the structure of 4b is similar to this of gallium
N,N0-dimethyloxamidate B published by Fischer and Stezowski [12]
(Scheme 1). The molecule of 4b consists of two fused rings, GaO2C2
and GaN2C2, in which two gallium atoms with different environ-
ment are present.
The molecular studies of the compounds 1ae6a showed that
a skeleton framework of the molecules consists of two almost flat,
coplanar and fused MNOC2 (M ¼ Al, Ga, In) heterocyclic rings. (As an
example of two fused MNOC2 cycles see the compound 1a, Fig. 1
bottom). All molecules are centrosymmetric. They are composed
of an oxamidate unit bonded to two four-coordinated metal atoms.
R'
R'
N
R'
HN
O
O
O
O
N
R
R
R
R
R
R
R
R
2 R M
M
M
M
+
+
M
3
- 2 RH
O
NH
R'
O
N
N
R'
R'
(a)
(b)
M = Al
M = Al
R = Me
R = Me
R' = Ph
R' = tBu
R' = Ph
R' = tBu
R' = Ph
R' = tBu
1a
2a
3a
M = Ga R = Me
M = Ga R = Me
M = Ga R = tBu
4a + 4b
5a
6a
M = In
R = Me
Scheme 2.

W. Ziemkowska et al. / Journal of Organometallic Chemistry 696 (2011) 2079e2085
2081
Fig. 2. Molecular structure of Me4Al2(dboa) (2a). Displacement ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å) and angles (ꢀ): Al(1)eO(1) 1.850(2), Al(1)eN(1) 1.962(2), O(1)eC(3) 1.296
(3), C(3)eN(1) 1.297(3), C(3)eC(3) 1.498(5), N(1)eC(4) 1.490(3), O(1)eAl(1)eN(1)
86.39(8), C(3)eO(1)eAl(1) 113.1(2), O(1)eC(3)eC(3) 115.6(2), N(1)eC(3)eC(3) 115.2(2),
C(3)eN(1)eAl(1) 109.7(2), O(1)eC(3)eN(1) 129.2(2).
Fig. 4. Molecular structure of Me4Ga2(dboa) (4a). Displacement ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å) and angles (ꢀ): Ga(1)eO(1) 1.9621(9), Ga(1)eN(1) 2.005(1), C(3)eN(1)
1.297(2), O(1)eC(3) 1.279(2), C(3)eC(3) 1.524(3), N(1)eC(4) 1.492(2), O(1)eGa(1)eN
(1) 83.62(4), C(3)eN(1)eGa(1) 112.04(9), C(3)eO(1)eGa(1) 112.70(8), O(1)eC(3)eC(3)
117.0(1), N(1)eC(3)eC(3) 114.6(1), O(1)eC(3)eN(1) 128.4(1).
Each of the metal atoms is bonded to two alkyl groups and oxygen
and nitrogen atoms originating from two different amidate groups
which are a part of the same amidate unit. The geometry around the
metal atoms is a distorted tetrahedron. The torsion angles Al(1)N(1)
C(2)C(7) 43.5(2)ꢀ, Ga(1)N(1)C(2)C(3) 41.0(5)ꢀ, Ga(1)N(1)C(4)C(41)
30.9(1)ꢀ for 1a, 3a and 5a, respectively, indicate, that in the
compounds with phenyl groups bonded to the nitrogen atoms,
aromatic ringsare at an anglewith reference tothe planeof (MNOC)2
skeleton.
The structure of the compounds 1a and 2a is the same as this of
previously reported methyl- and tert-butyl aluminum N,N0-dime-
thyloxamidates [13]. The lengths of AleO bonds of 1a and 2a are
equal 1.865(2) and 1.850(2) Å, respectively. The lengths of AleO
bonds of methyl- and tert-butyl aluminum N,N0-dimethylox-
amidates are situated in the same region as those of 1a and 2a
[1.859(1) and 1.862(1) Å for methyl- and tert-butyl aluminum
derivatives, respectively]. The AleN bond lengths are almost the
same in all aluminum oxamidates [1.968(2) and 1.962(2) Å for 1a
and 2a, 1.958(2) and 1.957 (1) Å for methyl- and tert-butyl
aluminum N,N0-dimethyloxamidates, respectively]. Values of the
OeAleN angles are practically the same in all compounds (about
86ꢀ). The structural data show, that the oxamidate skeleton is the
same in all compounds independently on substituents bonded to
aluminum and nitrogen atoms.
The similar bond lengths for CeN and CeO in each compound
1ae6a are indicative of delocalized structure within the OCCN
groups. A degree of the double bond delocalization, however,
depends on the kind of compounds. The CeN and CeO bond
lengths in 2a are almost the same [C(3)eN(1) 1.297(3), C(3)eO(1)
1.296(3) Å], indicating a significant degree of delocalization,
whereas in the compound 5a, the C(3)eN(1) [1.305(2) Å] bond is
of 0.032 Å longer than C(3)eO(1) [1.273(2) Å] bond showing more
double character of the CeO bond than that of 2a. The difference of
CeN and CeO bond lengths in other compounds is situated in
the region of 0.016e0.026 Å. The delocalization structure within
Fig. 3. Molecular structure of Me4Ga2(dpoa) (3a). Displacement ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å) and angles (): Ga(1)eO(1) 1.956(3), Ga(1)eN(1) 2.014(3), O(1)eC(1) 1.273
(4), N(1)eC(1) 1.289(5), C(1)eC(1) 1.513(7), N(1)eC(2) 1.421(5), O(1)eGa(1)eN(1) 82.7
(1), C(1)eN(1)eGa(1) 112.9(2), C(1)eO(1)eGa(1) 112.9(2), O(1)eC(1)eC(1) 117.9(4), N
(1)eC(1)eC(1) 113.5(4), O(1)eC(1)eN(1) 128.6(3).
Fig. 5. Molecular structure of tBu4Ga2(dpoa) (5a). Displacement ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å) and angles (ꢀ):Ga(1)eO(1) 1.9782(9), Ga(1)eN(1) 2.027(1), N(1)eC(3)
1.305(2), O(1)eC(3) 1.273(2), C(3)eC(3) 1.519(2), N(1)eC(4) 1.431(2), O(1)eGa(1)eN(1)
82.48(4), C(3)eN(1)eGa(1) 112.85(8), C(3)eO(1)eGa(1) 113.02(8), N(1)eC(3)eC(3)
113.5(1), O(1)eC(3)eC(3) 118.1(1), O(1)eC(3)eN(1) 128.4(1).

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W. Ziemkowska et al. / Journal of Organometallic Chemistry 696 (2011) 2079e2085
coordination of the indium centre in the compound 6a. In the light
of almost the same C]O bond lengths in all compounds [from 1.273
(4) Å for 3 and 5 to 1.296(3) Å for 2] and less NeCeO delocalization
in the indium compound 6, the C]O stretching frequencies are
surprising. However, the C]O bonds should be regarded as a part
of rigid conjugated oxamidate units, not as independent separable
bonds. In our opinion, an influence of oxamidate units on C]O
bond stretching is the most reasonable explanation of the lack of a
correlation between C]O stretching frequencies and structural
data.
In conclusion, N,N0-disubstituted oxamides react with group 13
metal trialkyls to form mainly the isomers a with oxamidate ligands
in the trans configuration. Some reactions of trialkylgallium com-
pounds lead to the production of isomers b with cis oxamidate
ligands. The conformational isomerism was not observed for any
aluminum oxamidates published until now (1a, 2a and five
aluminum compounds described elsewhere [12,13]). Three of five
gallium oxamidates (3ae5a and two compounds reported by
Fischer and Stezowski [12]) were mixtures of isomers. On the other
hand, it is difficult to discuss the isomerism of indium oxamidates
on the basis of one compound 6a only. Very probably the formation
of aluminum oxamidates as one trans isomer and gallium oxami-
dates as the mixture of isomers is in accordance with the hard and
soft acids and bases principle (HSAB). The harder metal aluminum
prefers the oxygen atom as the harder coordination site. The softer
metal gallium is eager to coordinate also the nitrogen atoms as
the softer ligands.
Fig. 6. Molecular structure of Me4In2(dboa) (6a). Displacement ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å) and angles (ꢀ): In(1)eO(1) 2.1660(9), In(1)eN(1) 2.206(1), N(1)eC(3)
1.303(2), O(1)eC(3) 1.277(2), C(3)eC(3) 1.540(2), N(1)eC(4) 1.488(2), O(1)eIn(1)eN(1)
76.44(3), C(3)eN(1)eIn(1) 114.53(8), C(3)eO(1)eIn(1) 115.25(7), O(1)eC(3)eC(3) 118.3
(1), N(1)eC(3)eC(3) 115.4(1), O(1)eC(3)eN(1) 126.3(1).
the OCCN groups was also observed in the previously reported
methyl- and tert-butyl aluminum N,N0-dimethyloxamidates [CeN
1.289(2) Å, CeO 1.287(2) Å and CeN 1.294(1) Å, CeO 1.280(1) Å,
respectively] [13].
The bond lengths for MeN of all compounds were found to be
longer than those for MeO. The differences between AleN
and AleO bond length of the aluminum derivatives are 0.103 Å and
0.112 Å for 1a and 2a, respectively, whereas those of gallium and
indium oxamidates are situated in the region of 0.040e0.058 Å.
According to our investigations and literature data [12], isomers
b are only present in inseparable mixtures of the isomers a and
b. Conditions of the isomers b formation are still difficult for
determination. It seems that the presence of alkyl group bonded to
the nitrogen atom of the oxamidate moiety promotes the formation
The nC
] bands in the IR spectra observed for the compounds
O
were rather independent on N-substituents and depended on
metal atoms. The nC
] bands of aluminum oxamidates were the
O
highest in energy (1628 and 1630 cmꢁ1 for 1a and 2a, 1662 and
of the isomer b, because the reactions of N,N
0-dimethyloxamide and
1649 cmꢁ1 for methyl- and tert-butyl aluminum N,N0-dimethylox-
N,N0-di-tert-butyloxamide with gallium trialkyls produce the
mixtures of isomers. The formation of isomers b was not observed
amidates [13], respectively). On the other hand, the nC
] band
O
t
was shifted to a significantly lower energy (1580 cmꢁ1) upon
in the reactions of N,N0-diphenyloxamide with Me3Ga and Bu3Ga
Table 1
Crystal data and data collection parameters for 1ae3a.
1a
2a
3a
Empirical formula
Formula weight
Temperature (K)
Wavelength Å
Crystal system
Space group
a(Å)
C18H22Al2N2O2
352.34
100(2)
0.71073
Monoclinic
P2(1)/c
6.1120(5)
C14H30Al2N2O2
312.36
100(2)
0.71073
Monoclinic
P2(1)/n
11.494(1)
C18H22Ga2N2O2
437.82
100(2)
0.71073
Monoclinic
P2(1)/c
6.1290(9)
b(Å)
14.872(2)
6.2605(5)
14.736(3)
c(Å)
11.337(1)
90
117.659(9)
90
13.102(1)
90
100.440(9)
90
11.158(2)
90
117.22(2)
90
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
V(Å3)
913.1(2)
927.2(1)
826.2(3)
Z
2
2
2
Dcalc(g cmꢁ3
)
1.282
0.171
372
1.119
0.160
340
1.623
3.018
444
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm)
Q
0.2 ꢂ 0.20 ꢂ 0.10
0.25 ꢂ 0.20 ꢂ 0.20
0.25 ꢂ 0.15 ꢂ 0.15
range for data collection (ꢀ)
3.41 to 28.72
3.16 to 25.50
3.44 to 28.34
Index ranges
ꢁ6 ꢃ h ꢃ 8,ꢁ19 ꢃ k ꢃ 19,ꢁ14 ꢃ l ꢃ 14
8180
2190 [Rint ¼ 0.0605]
Full-matrix least-squares on F2
2190/0/111
ꢁ13 ꢃ h ꢃ 13,ꢁ15 ꢃ k ꢃ 14,ꢁ7 ꢃ l ꢃ 7
6925
1722 [Rint ¼ 0.0540]
Full-matrix least-squares on F2
1722/0/96
ꢁ6 ꢃ h ꢃ 8,ꢁ19 ꢃ k ꢃ 19,ꢁ14 ꢃ l ꢃ 14
7876
2087 [Rint ¼ 0.0508]
Full-matrix least-squares on F2
2087/0/111
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
0.892
0.983
0.902
Final R indices [I > 2
R indices (all data)
Max/min of residual electron density
s
(I)]
R1 ¼ 0.0494, wR2 ¼ 0.1027
R1 ¼ 0.0989, wR2 ¼ 0.1149
0.519 and ꢁ0.357
R1 ¼ 0.0552, wR2 ¼ 0.1404
R1 ¼ 0.0687, wR2 ¼ 0.1461
0.591 and ꢁ0.462
R1 ¼ 0.0423 wR2 ¼ 0.0923
R1 ¼ 0.0712, wR2 ¼ 0.0983
1.408 and ꢁ0.871

W. Ziemkowska et al. / Journal of Organometallic Chemistry 696 (2011) 2079e2085
2083
Table 2
Crystal data and data collection parameters for 4ae6a.
4a
5a
6a
Empirical formula
Formula weight
Temperature (K)
Wavelength Å
Crystal system
Space group
a(Å)
C14H30Ga2N2O2
397.84
100(2)
0.71073
Monoclinic
P2(1)/c
11.3962(6)
6.2484(3)
15.7621(9)
90
124.924(5)
90
920.3(1)
2
1.436
2.930
C30H46Ga2N2O2
606.13
100(2)
0.71073
Monoclinic
P2(1)/c
8.5863(3)
16.2347(4)
12.5304(4)
90
118.204(3)
90
1539.30(8)
2
1.308
1.777
C14H30In2N2O2
488.04
100(2)
0.71073
Monoclinic
P2(1)/c
11.3514(3)
6.4105(2)
15.8032(5)
90
123.236(3)
90
961.86(5)
2
1.685
2.400
b(Å)
c(Å)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
V(Å3)
Z
D
calc(g cmꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
)
412
636
484
Crystal size (mm)
Q
0.3 ꢂ 0.3 ꢂ 0.2
0.20 ꢂ 0.20 ꢂ 0.15
0.3 ꢂ 0.3 ꢂ 0.25
range for data collection (ꢀ)
3.15 to 27.93
2.97 to 28.09
3.0760 to 29.6712
Index ranges
ꢁ14 ꢃ h ꢃ 14,ꢁ7 ꢃ k ꢃ 7,ꢁ19 ꢃ l ꢃ 20 ꢁ11 ꢃ h ꢃ 11,ꢁ21 ꢃ k ꢃ 21,ꢁ16 ꢃ l ꢃ 11 ꢁ15 ꢃ h ꢃ 14,ꢁ8 ꢃ k ꢃ 8,ꢁ21 ꢃ l ꢃ 21
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
6080
10888
8099
2035 [Rint ¼ 0.0112]
Full-matrix least-squares on F2
2035/0/96
3497 [Rint ¼ 0.0156]
Full-matrix least-squares on F2
3497/0/169
2564 [Rint ¼ 0.0089]
Full-matrix least-squares on F2
2564/0/97
1.057
0.930
1.093
Final R indices [I > 2
R indices (all data)
Max/min of residual electron density 0.515 and ꢁ0.344
s
(I)]
R1 ¼ 0.0164, wR2 ¼ 0.0468
R1 ¼ 0.0186, wR2 ¼ 0.0437
R1 ¼ 0.0263, wR2 ¼ 0.0444
0.378 and ꢁ0.199
R1 ¼ 0.0132, wR2 ¼ 0.0315
R1 ¼ 0.0143, wR2 ¼ 0.0319
0.417 and ꢁ0.343
R1 ¼ 0.0181, wR2 ¼ 0.0473
probably due to decreasing of a softness of the nitrogen coordina-
tion centers connected with aromatic rings.
was allowed to warm to room temperature. A solution of the post-
reaction mixture was obtained. The solvent and the excess of R3M
were removed in vacuo from the post-reaction mixture.
3. Experimental
3.3.2. Characterization of Me4Al2(dpoa) (1)
3.1. Materials and instrumentation
According to the general procedure, Me3Al (0.4 cm3) reacted
with 0.480 g of N,N0-diphenyloxamide to yield a compound 1a as
the only product. The compound 1a was obtained quantitatively as
a white solid (yield 0.70 g). Elemental anal.: Al, 15.70; hydrolysable
methyl groups, 16.81; Calc. for Me4Al2(C14H12N2O2): Al, 15.33;
All manipulations were carried out using standard Schlenk
techniques under an inert gas atmosphere. The solvents were
distilled over
a blue benzophenoneeK complex. Me3Al was
purchased from Aldrich. tBu3Al and Me3In were synthesized as
described in the literature [14,15]. Prof. K. B. Starowieyski (Warsaw
University of Technology) kindly supported us with Me3Ga. 1H and
13C NMR spectra were obtained on a Mercury-400BB spectrometer.
1H NMR spectra were recorded at 400.09 MHz. Chemical shifts
were referenced to the residual proton signals of CDCl3 (7.26 ppm).
13C NMR spectra were acquired at 100.60 MHz (standard: chloro-
form 13CDCl3, 77.20 ppm). IR spectra were obtained using a Nicolet
6700 FTIR (ATR) infrared spectrometer. Hydrolysable alkyl groups
and a content of aluminum for compounds 1a and 2a were deter-
mined according to the literature [16]. Elemental analyses of 3ae6a
were obtained on a PerkineElmer 2400 analyzer.
Me, 17.03 wt.%. 1H NMR (CDCl3):
d 7.62(m, 4H, Haromat), 7.47 (m, 4H,
Haromat), 7.34 (m, 2H, Haromat), ꢁ0.56 (s, 12H, CH3Al) ppm. 13C NMR
(CDCl3):
d 162.07 (C]O), 138.59, 129.49, 127.59, 123.65 (Caromat),
ꢁ10.56 (CH3Al) ppm. FTIR (nujol):
n
]
¼
3056(w);
CH (arom)
nC]
¼ 1628(s); nC
]
C (arom)
¼ 1591, 1489, 1454(m); nCeN ¼ 1346
O
(m);
g
]
CH (arom)
¼ 760, 679(m) cmꢁ1
.
Crystals proper for X-ray diffraction study were obtained from
a CH2Cl2 solution at 10 ꢀC as colorless crystals. Mp.: 200 ꢀC.
3.3.3. Characterization of Me4Al2(dboa) (2)
According to the general procedure, Me3Al (0.4 cm3) reacted
with 0.400 g of N,N0-di-tert-butyloxamide to yield a compound 2a
as the only product. The compound 2a was obtained quantitatively
as a white solid (yield 0.62 g). Elemental anal.: Al, 17.55; hydro-
lysable methyl groups, 18.89; Calc. for Me4Al2(C14H12N2O2): Al,
3.2. Synthesis of ligand precursors
The oxamides used as ligand precursors were prepared as white
solids by reaction of the appropriate amine with oxalyl chloride
according to the literature [17]. N,N0-Diphenyloxamide: yield 80%,
Mp.: 252e253 ꢀC. N,N0-di-tert-butyloxamide: yield 77%, Mp.:
175 ꢀC.
17.29; Me, 19.21 wt.%. 1H NMR (CDCl3):
d
1.42 (s, 18H, (CH3)3CN),
163.44 (C]O), 54.77
ꢁ0.71 (s, 12H, CH3Al) ppm. 13C NMR (CDCl3):
d
[(CH3)3CN], 28.34 [(CH3)3CN] ppm. FTIR (nujol) nCH3(as) ¼ 2970(w);
nCH3(sym) ¼ 2870(w); nC
]
¼ 1630(s); d(CH3)3C(as) ¼ 1456(m); d(CH3)
O
¼ 1365(m); nCeN ¼ 1319(m) cmꢁ1
.
3C(sym)
Crystals proper for X-ray diffraction study were obtained from
a CH2Cl2en-C6H14 solution at 10 ꢀC as colorless crystals. Mp.:
194e197 ꢀC.
3.3. Compound syntheses
3.3.1. General procedure of 1e6 compounds synthesis
R3M (4.5 mmol) was injected to a stirred suspension of 2 mmol
of N,N0-diphenyloxamide (or a solution of 2 mmol of N,N0-di-tert-
butyloxamide) in CH2Cl2 (20 cm3) at ꢁ76 ꢀC. The reaction mixture
3.3.4. Characterization of Me4Ga2(dpoa) (3)
According to the general procedure, Me3Ga (0.5 cm3) reacted
with 0.480 g of N,N0-diphenyloxamide. A white solid of the pure

2084
W. Ziemkowska et al. / Journal of Organometallic Chemistry 696 (2011) 2079e2085
compound 3a precipitated from the post-reaction mixture (yield
0.630 g, 72%). In the post-reaction solution, the compound 3a was
found as the only product after removal volatiles. Elemental anal.:
Calcd for C18H22Ga2N2O2: C, 49.34; H, 5.03. Found: C, 49.64; H,
(s); d(CH3)3C(as) ¼ 1452(m); d(CH3)3C(sym) ¼ 1358(m); nCeN ¼ 1319
(m) cmꢁ1
Colorless crystals of 6a for X-ray diffraction studies were
obtained from a THF solution at 10 ꢀC. Mp.: 177e181 ꢀC. Elemental
anal.: Calcd for C14H30In2N2O2: C, 34.43.; H, 6.15. Found: C, 34.21; H,
6.32 wt.%.
.
5.22 wt.%. 1H NMR (CDCl3):
d 7.52(m, 4H, Haromat), 7.43 (m, 4H,
Haromat), 7.27 (m, 2H, Haromat), ꢁ0.06 (s, 12H, CH3Ga) ppm. 13C NMR
(CDCl3):
d 161.84 (C]O), 140.13, 128.98, 126.15, 123.26 (Caromat),
ꢁ6.19 (CH3Ga). FTIR (nujol):
n
]
¼ 3041(w); nC
]
¼ 1614
3.2.6. X-ray crystal structure determinations
CH (arom)
O
(s); nC
]
¼ 1579, 1492, 1452(m); nCeN ¼ 1351(m);
g
]
CH
Determination of the crystal structures was performed on
C
(arom)
¼ 754, 689(m) cmꢁ1
.
a KUMA CCD
k-axis diffractometer with graphite-monochromated
(arom)
Colorless crystals for X-ray diffraction studies were obtained
Mo-K radiation. A crystal of 1 was positioned at 62.25 mm from
a
from a CH2Cl2 solution at 10 ꢀC. Mp.: 202e205 ꢀC.
the KM4CCD camera and 1000 frames were measured at 0.6ꢀ
intervals with a counting time of 35 s. A crystal of 2 was positioned
at 62.25 mm from the KM4CCD camera and 856 frames were
measured at 0.7ꢀ intervals with a counting time of 35 s. A crystal of
3 was positioned at 62.25 mm from the KM4CCD camera and 1000
frames were measured at 0.6ꢀ intervals with a counting time of
30 s. A crystal of 4 was positioned at 61.2 mm from the KM4CCD
camera and 603 frames were measured at 0.8ꢀ intervals with
a counting time of 5 s. A crystal of 5 was positioned at 61.2 mm from
the KM4CCD camera and 675 frames were measured at 0.7ꢀ
intervals with a counting time of 8 s. A crystal of 6 was positioned at
61.2 mm from the KM4CCD camera and 1068 frames were
measured at 0.5ꢀ intervals with a counting time of 5 s. Data
reduction and analysis were carried out with the Kuma Diffraction
programs. The data were corrected for Lorentz and polarization
effects and multi-scan absorption correction was applied [18]. The
structures were solved by direct methods [19] and refined using
SHELXL [20]. The non-hydrogen atoms were refined anisotropically.
The hydrogen atoms were located from a difference map and
refined isotropically. The atomic scattering factors were taken
from the International Tables [21].
3.3.5. Synthesis and characterization of Me4Ga2(dboa) (4)
Method 1: Me3Ga (0.5 cm3) was injected to a stirred solution of
N,N0-di-tert-butyloxamide (0.400 g) in THF (20 cm3) at room
temperature. The reaction mixture was refluxed during 1 h. Vola-
tiles were removed in vacuo yielding a white solid of 4a as the only
product (yield 0.790 g, 100%). 1H NMR (CDCl3):
d
1.37(s, 18H,
163.12
[(CH3)3CN]), ꢁ0.24(s, 12H, GaCH3) ppm. 13C NMR (CDCl3):
d
(C]O), 54.46 [(CH3)3CN], 28.54 [(CH3)3CN], ꢁ5.19 (CH3Ga) ppm.
FTIR (nujol): nCH3(as) ¼ 2967(w); nCH3(sym) ¼ 2869(w); nC
(s); d(CH3)3C(as) ¼ 1461(m); d(CH3)3C(sym) ¼ 1361(m); nCeN ¼ 1315
(m) cmꢁ1
]
¼ 1616
O
.
After few days, colorless crystals of 4a precipitated from the
post-reaction mixture at room temperature. Mp.: 185e187 ꢀC.
Elemental anal.: Calcd for C14H30Ga2N2O2: C, 42.23; H, 7.54. Found:
C, 41.93; H, 7.71 wt.%.
Method 2: According to the general procedure, Me3Ga (0.5 cm3)
reacted with 0.400 g of N,N0-di-tert-butyloxamide. A mixture of
two isomers 4a and 4b was obtained as the product (yield 100%). 1H
NMR (CDCl3) of the mixture of two isomers:
d 4a 1.37{s, 18H,
[(CH3)3CN]}, ꢁ0.24(s, 12H, GaCH3); 4b 1.36(s, 18H, [(CH3)3CN],
The X-ray structures were measured in the Crystallography Unit
of the Physical Chemistry Laboratory at the Chemistry Department
of the University of Warsaw.
ꢁ0.22(s, 6H, GaCH3), ꢁ0.23(s, 6H, GaCH3) ppm. 13C NMR (CDCl3):
d
4a 163.12 (C]O), 54.46 [(CH3)3CN], 28.54 [(CH3)3CN], ꢁ5.18,
(CH3Ga); 4b 162.14 (C]O), 54.77 [(CH3)3CN], 28.57 [(CH3)3CN],
ꢁ3.94, ꢁ6.34 (CH3Ga) ppm. FTIR (nujol) of the mixture of two
Acknowledgements
isomers: 4a nC
]
O
¼ 1616(s); 4b nC
]
¼ 1608(s) cmꢁ1
O
On the basis of proton signals integration [e0.24 ppm (4a): ꢁ0.22
and ꢁ0.23 ppm (4b)], the ratio of isomers was equal 4a:4b ¼ 0.9:1.
Crystals of 4a for X-ray diffraction studies were obtained from
a CH2Cl2 solution at 10 ꢀC.
We thank Warsaw University of Technology for financial
support. We gratefully acknowledge Dr Romana Anulewicz-
Ostrowska for her kind assistance.
Appendix A. Supplementary data
t
3.3.6. Characterization of Bu4Ga2(dpoa) (5)
According to the general procedure, Bu3Ga (1.0 cm3) reacted
t
CCDC 795312e795317 contain the supplementary crystallo-
graphic data for 1ae6a. These data can be obtained free of charge
from The Cambridge Crystallographic Data Center via www.ccdc.
cam.ac.uk/data_request/cif.
with 0.480 g of N,N0-di-phenyloxamide. An isomer 5a was obtained
as the product (yield 100%). 1H NMR (CDCl3):
d
7.57 (m, 4H, Haromat),
7.44 (m, 4H, Haromat), 7.27 (m, 2H, Haromat), 1.08 [s, 36H, Ga(CH3)3].
13C NMR (CDCl3):
163.02 (C]O), 141.26, 129.23, 126.30, 123.71
(Caromat), 29.76 [GaC(CH3)3], 23.98 [GaC(CH3)3] ppm. FTIR (pure
compound as powder): ¼ 1608(s);
¼ 3041(w); nC
nC
d
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