A Methylene-Bridged Dialuminium Compound as a Chelating Lewis Acid: Complexation of Nitrite and Nitrate Anions by R2Al-CH2-AlR2 [R = CH(SiMe3)2]

Article abstract of DOI:10.1002/(SICI)1099-0682(199807)1998:7<921::AID-EJIC921>3.0.CO;2-5

Sodium nitrite (NaNO₂) dissolves readily in THF, when the methylene-bridged dialuminium compound R₂Al-CH₂-AlR₂ [R = CH(SiMe₃)₂] 1 with two coordinatively unsaturated aluminium atoms is adde

Full text of DOI:10.1002/(SICI)1099-0682(199807)1998:7<921::AID-EJIC921>3.0.CO;2-5

FULL PAPER
A Methylene-Bridged Dialuminium Compound as a Chelating Lewis Acid:
Complexation of Nitrite and Nitrate Anions by R2Al–CH2–AlR2
[R ؍ CH(SiMe3)2]Ƞ
Werner Uhl*a, Frank Hannemanna, Wolfgang Saaka, and Rudolf Wartchowb
Fachbereich Chemie der Universitäta,
Postfach 2503, D-26111 Oldenburg, Germany
Fax: (internat.) ϩ49(0)441/798-3352
Institut für Anorganische Chemie der Universitätb
Callinstraße 9, D-30167 Hannover, Germany
Fax: (internat.) ϩ49(0)511/762-3006
Received March 16, 1998
Keywords: Aluminium / Chelates / Lewis acids
Sodium nitrite (NaNO2) dissolves readily in THF, when the
methylene-bridged dialuminium compound R2Al–CH2–AlR2
[R = CH(SiMe3)2] 1 with two coordinatively unsaturated
aluminium atom to form a five-membered Al2CNO hetero-
cycle. The second oxygen atom of the nitrite anion is not
affected. Similarly, lithium nitrate (LiNO3) reacts with 1 to
aluminium atoms is added. Compound 1 reacts as a chelating yield a THF soluble product (6a). Single crystals were obtain-
Lewis acid, and, as shown by a crystal structure deter-
mination of the [Na([18]crown-6)(Et2O)]+ derivative 5c, a
compound (5) is formed, in which one oxygen atom and the
nitrogen atom of the nitrite ion are each coordinated by one
ed of the [Li(N,NЈ,NЈЈ-trimethyltriazinane)2]+ derivative 6c,
whose structure shows each aluminium atom to be
coordinated by one oxygen atom of the nitrate ion to give a
six-membered Al2CNO2 heterocycle.
Chelating Lewis bases for the effective coordination of thiomethanolate anion[13]. A remarkable five-membered
cations are extraordinarily important in all areas of chemis- ring (3) was obtained by the reaction of with
1
try as can be seen from thousands of known compounds. LiCH(PMe2)2, in which one Al atom is coordinated to the
In contrast, chelating Lewis acids as anion receptors for the central carbanion and the other one to a phosphorus
complexation and recognition of anions are investigated to atom[14]. A terminal coordination of a neopentyl group is
a much lower extent, and by far the most of these ligands observed by the reaction of 1 with neopentyllithium (4)[15]
.
were obtained by the protonation of amino groups of Much more interest deserve, however, the up to now un-
macrocyclic or polycyclic compounds[1]. Organoelement de- known complexes with multidentate inorganic anions like
rivatives of the elements of the third main-group have a nitrate, nitrite, azide, sulfate etc. in order to find specific
coordinatively unsaturated central atom and are therefore anion receptors or in order to use a Lewis-acid like 1 as a
suitable as Lewis acids, but only few examples exist, which phase transfer reagent to dissolve ionic compounds in or-
have more than one atom of those elements and could poss- ganic solvents and to study their changed, possibly en-
ibly be useful as a chelating ligand. Well documented and hanced reactivity. We started now with systematic investi-
characterized[2] compounds of this type are for instance gations into those reactions and wish to report here on the
1,8-naphthlenediylbis(dimethylborane)[3]
,
Cl2AlϪCH2Ϫ complexes of 1 with sodium nitrite and lithium nitrate. Car-
[4]
[5]
AlCl2
,
Cl2AlϪCH2CH2ϪAlCl2
,
R2AlϪCH2ϪAlR2 bon bridged dialuminium compounds have recently been
1 [R ϭ CH(SiMe3)2][6], R(Cl)AlϪCH2ϪAl(Cl)R [R ϭ used in organic syntheses to form for instance CϭC double
[8]
CH(SiMe3)2][7]
,
Me2(THF)AlOC6H4OAl(THF)Me2
,
bonds, but they usually were only used as reactive inter-
Cl2InϪCH2ϪInCl2 · 2 TMEDA[9]
,
and
Hg(C6H4Ϫ mediates, and they were not isolated or well charac-
InCl2 ·THF)2[10]. However, most of these compounds have terized[16]
up to now not been investigated concerning their ability to
.
Reactions of the Methylene-Bridged Dialuminium
Compound 1 with NaNO2 and LiNO3
act as a chelating Lewis acid. Exceptions are the diborane
compound with a single example of a hydrido bridge[3] and
the methylene bridged tetraalkyl dialuminium derivative 1, Both, sodium nitrite and lithium nitrate are insoluble even
which was recently synthesized by our group[6]. Few chelate in a large excess of THF. But upon addition of one equiva-
complexes of 1 have been isolated and characterized, in lent of the chelating Lewis-acid µ-methylene tetraalkyldialu-
which heterocycles are formed by the coordination of both minium R2AlϪCH2ϪAlR2 1 the complete dissolution of
aluminium atoms to one hydride (2)[11], hydroxide[12], or the crystalline salts occurred within several hours by stirring
Eur. J. Inorg. Chem. 1998, 921Ϫ926
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921

W. Uhl, F. Hannemann, W. Saak, R. Wartchow
FULL PAPER
crystals were obtained of compounds 5c {[Na([18]crown-
6)(Et2O)]ϩ} (Eq. 1) and 6c {[Li(triazinane)2]ϩ}; the last one
crystallized from a dilute solution of the mixed triazinane/
THF adduct 6b (Eq. 2) in diethyl ether in the presence of
triazinane.
at room temperature. Yellow solutions were formed, from
which the yellow addition products 5a and 6a were isolated
after concentration and cooling to Ϫ50°C in a high yield.
The crystals rapidly became amorphous upon drying in va-
cuo and had low melting points of 92°C and 135°C (5a
and 6a, respectively). The 1H- and 13C-NMR spectroscopic
characterization gave some important changes in compari-
son to the neutral starting compound 1, and all signals of
groups bound to aluminium showed a significant shift to
high field. In 1 the protons of the AlϪCH2ϪAl group res-
onated at δ ϭ Ϫ0.50, and we observed the methine protons
at δ ϭ Ϫ0.22 and the corresponding carbon atoms at δ ϭ
13.2; in 5a and 6a these resonances were shifted to δ(Al-
CH2Al) ϭ Ϫ1.24 and Ϫ1.27, δ(AlCHSi2) ϭ Ϫ1.06 and
Ϫ1.05, δ(AlCHSi2) ϭ 4.1 and 4.3, respectively. Such shifts
to a higher field are very indicative of the enhancement of
the coordination number at the aluminium atoms from
As shown in Eq. (1), the structure of the complex 5c com-
prises the nitrite anion coordinated by one oxygen atom
and the lone pair at the central nitrogen atom. This struc-
ture should result in two chemical different AlR2 moieties,
but at room temperature only one singlet was detected in
the 1H-NMR spectrum for both the methine and the SiMe3
protons. However, a splitting into two resonances was ob-
served upon cooling a sample of 5c dissolved in [D10]diethyl
ether to Ϫ70°C indicating a fast exchange process at elev-
ated temperatures.
three to four[11][12][13][14][15][17]
.
Both compounds were stable in THF solutions, but slow
decomposition by the precipitation of NaNO2 or LiNO3
and the formation of 1 was observed in more nonpolar sol-
vents like diethyl and diisopropyl ether or in mixtures of
ether with toluene or pentane. Single crystals of the nitrate
derivative 6a with the counterion [Li(THF)4]ϩ could not be
obtained, while single crystals of 5a showed a severe dis-
order of the Na(THF)3 cation, and the structure could not
be refined satisfactorily. Therefore, we synthesized several
Crystal Structures of 5c and 6c
derivatives of 5 and 6 by using different chelating Lewis- The molecular structures of the nitrito complex 5c and the
bases like the crown ether [18]crown-6, tetramethylethylen- nitrato complex 6c are depicted in Figures 1 and 2. To the
ediamine
(TMEDA),
tetramethylpropylenediamine best of our knowledge, it is the first time, that chelating
(TMPDA), pentamethyldiethylenetriamine (PMDETA), Lewis-acids like compound 1 with coordinatively unsatu-
and N,NЈ,NЈЈ-trimethyltriazinane. Some of the isolated rated atoms of the elements of group 13 are successfully
products are described in detail in the Experimental Sec- used for the coordination of at least bidentate anions and
tion, the spectroscopic properties of their anions as well as that the coordination mode could be determined by crystal
their solubility in polar or nonpolar solvents differ only structure determinations. Both anions are coordinated in a
slightly from those of the THF adducts. But owing to the chelating manner by both aluminium atoms of 1. As ex-
chelating coordination of the cations they show a signifi- pected, the nitrate anion in 6c is bound by two oxygen
cantly increased stability and can be stored in diethyl ether atoms to form a six-membered Al2CO2N heterocycle, while
solution at room temperature without decomposition and a five-membered Al2CNO heterocycle is observed in 5c with
precipitation of the corresponding salts. High quality single the nitrite anion coordinated via one oxygen and the central
922
Eur. J. Inorg. Chem. 1998, 921Ϫ926

Methylene-Bridged Dialuminium as Chelating Lewis Acids
FULL PAPER
nitrogen atom. One oxygen atom of each anion is in a ter- atoms[11][12][13][14][15][17], all distances are lengthened com-
minal position.
pared with the starting compound 1[6], which had the corre-
sponding values at 195.7 and 193.8 pm. The structure of 1
showed a strongly enlarged AlϪCϪAl angle (129.6°)
caused by steric and electrostatic repulsion between the
Figure 1. Molecular structure and numbering scheme of the anion
of 5c; the thermal ellipsoids are drawn at the 40% probability level;
methyl groups are omitted for clarity[a]
bulky substituents and the positively charged Al atoms[6]
.
Owing to the formation of five and six membered hetero-
cycles this angle is reduced in 5c and 6c to 111.3° and
116.2°, respectively.
The AlϪO distance in the nitrito compound 5c is slightly
lengthened to 196.0 pm compared with complexes of tri-
methylaluminium with sulfate or nitrate anions (ca. 191
pm)[18][19]. The AlϪN1 distance is long (212.3 pm) with re-
spect to some [bis(trimethylsilyl)methyl]aluminium com-
pounds recently obtained in our group[20], which may indi-
cate only a weak coordinative interaction to the Al atom
Al2. Unfortunately, the NϪO distances N1ϪO1 137.6 pm
and N1ϪO2 103.1 pm, which is in the range of the triple
bond in NOϩ, are incorrect due to a disorder of the atoms
N1 and O2. Both atoms could not be refined in split posi-
tions to give acceptable positions. The same disorder was
observed for the THF adduct, which could not be com-
pletely refined due to the severe disorder of the cation. The
distances should therefore not further be discussed in detail,
but it seems clear, that strong differing distances are present
with one value approaching a double bond and one ap-
proaching a single bond similar to the situation in nitrous
acid HONO (NϪO ϭ 142 and 118 pm)[21]. A similar coor-
dination mode with bridging µ-NO2-N,O groups has been
observed before in several coordination compounds of the
transition metals. As expected, the NϪO distances of the
bridging NO groups of these complexes are elongated com-
[a]
Selected bond lengths [pm] and angles [°]: Al1ϪO1 196.0(3),
Al2ϪN1 212.3(5), N1ϪO1 137.6(5), Al1ϪC 196.1(3), Al2ϪC
195.0(3), Al1ϪC1 202.7(3), Al1ϪC2 202.6(3), Al2ϪC3 199.9(3),
Al2ϪC4 201.3(3), CϪAl1ϪO1 96.8(1), Al1ϪO1ϪN1 114.4(2),
O1ϪN1ϪAl2 119.2(2), N1ϪAl2ϪC 89.5(2), Al1ϪCϪAl2 111.3(2).
Figure 2. Molecular structure and numbering scheme of the anion
of 6c; the thermal ellipsoids are drawn at the 40% probability level;
methyl groups are omitted for clarity[a]
pared to those of terminal NϭO groups by up to 17 pm[22]
.
The atoms of the nitrito group (N1, O1, O2) and the alu-
minium atom coordinated by nitrogen (Al2) lie almost ide-
ally within a plane (sum of the angles 359.8 pm). The most
acute angles in the five-membered central heterocycle are at
the Al atoms with 96.8° at Al1 and 89.5° at Al2, the last
one is coordinated by the nitrogen atom. The heterocycle
adopts an envelope conformation with the four atoms Al1,
Al2, O1, and N1 almost ideally within a plane and the
bridging carbon atom 58 pm above the plane. The angle
between the normals of the planes (Al1O1N1Al2 and Al1-
CAl2) is 31.7°.
In contrast to the strongly differing NϪO distances of
5c, a more delocalized electronic system is observed in the
nitrato compound 6c with three quite similar NϪO dis-
tances. The NϪO bond length to the terminal oxygen atom
is 121.4 pm, which is only 4.5 pm shorter than the distance
between nitrogen and the bridging oxygen atoms (125.7 pm
[a]
Selected bond lengths [pm] and angles [°]: Al1ϪO2 193.9(3),
Al2ϪO1 195.7(3), NϪO1 126.1(4), NϪO2 125.2(4), NϪO3
121.4(4), Al1ϪC 194.5(4), Al2ϪC 195.0(4), Al1ϪC1 201.4(3),
Al1ϪC2 202.7(4), Al2ϪC3 203.8(4), Al2ϪC4 200.8(4),
CϪAl2ϪO1 99.8(2), Al2ϪO1ϪN 136.0(3), O1ϪNϪO2 121.3(4),
NϪO2ϪAl1 135.9(3), O2ϪAl1ϪC 100.4(2), Al1ϪCϪAl2 116.2(2).
The methylene bridged tetraalkyldialuminium moieties of on average). The longer distances are similar to the NϪO
both compounds are quite similar. The AlϪC distances of bond lengths of the nitrate ions in many salt-like com-
the CH(SiMe3)2 substituents are 201.6 (5c) and 202.2 pm pounds, which are in the range of about 126 pm[23]. Two
(6c) on average, and the smallest distances are observed to metal atoms bridged by two different oxygen atoms of a
the aluminium atom bound to nitrogen. The bond lengths nitrato group as in 6c are for instance observed in some
to the carbon atom of the methylene bridge are 195.6 aquo Zn-, Cu-, or Ni nitrato complexes[24]. The AlϪO dis-
(5c) and 194.8 pm (6c). As expected from the enhance- tances of 6c are similar to 5c (194.8 pm on average). The
ment of the coordination number at the aluminium most acute angles of the six-membered heterocycle are
Eur. J. Inorg. Chem. 1998, 921Ϫ926
923

W. Uhl, F. Hannemann, W. Saak, R. Wartchow
FULL PAPER
yellow crystals, which become amorphous at room temperature.
Yield: 0.588 g (72%). Ϫ M. p. (argon, sealed capillary): 140°C. Ϫ
1H NMR ([D10]Et2O, 300 MHz): δ ϭ 2.48 and 2.38 (each: pseudo-
t, 8 H, NCH2 of PMDETA), 2.26 (s, 6 H, N-Me of PMDETA),
2.22 (s, 24 H, NMe2 of PMDETA), 0.10 (s, 72 H, SiMe3), Ϫ1.05
(s, 4 H, AlCHSi2), Ϫ1.23 (s, 2 H, AlCH2Al). Ϫ 13C NMR
([D10]Et2O, 75.5 MHz): δ ϭ 58.6 and 56.7 (NCH2 of PMDETA),
found at the aluminium atoms (100.1° on average), while
the angles AlϪOϪN are much enlarged to 136°. As ex-
pected, the nitrogen atom is planar surrounded by three
oxygen atoms (sum of the angles ϭ 360.0°). The heterocycle
has an envelope conformation similar to 5c with the bridg-
ing carbon atom 59.2 pm above the plane spanned by the
five atoms Al1, Al2, O1, O2, and N, which have a maximum
deviation from this plane of only 2.5 pm (angle between the
normals of the planes 34.9°).
46.4 (NMe2 of PMDETA), 43.7 (NMe of PMDETA), 6.0 (SiMe3),
˜
4.9 (br., AlCH2Al), 4.3 (AlCSi2). Ϫ IR (CsBr, paraffin): ν ϭ 1497
m cmϪ1 νNO; 1464 vs, 1377 s, 1366 s, 1355 m paraffin; 1341 vw,
No short bonding distances are observed between atoms 1308 s, 1291 s, 1252 vs, 1242 vs, 1225 vs δCH3; 1161 s, 1150 s, 1127
m, 1111 s, 1096 m, 1065 m, 1026 vs νCC, νCN; 1007 vs δCH; 930
vs, 901 vs, 843 vs, 777 vs, 750 vs, 727 s ρCH3(Si); 667 vs νasSiC;
629 m, 615 w νsSiC; 590 w, 559 s, 517 m, 503 m, 496 m, 465 w, 449
w, 424 vw νAlC, νAlO; 380 w, 353 vw δSiC. Ϫ UV/vis (diethyl
ether) (ε): 240 (2050), 270 nm (sh, br., 1230). C47H124Al2-
NaN7O2Si8 (1210.84): calcd. Al 4.8, Na 2.0; found Al 4.8, Na 2.0.
of the complex anions and the corresponding cations in
both compounds. The sodium atom in 5c is coordinated by
six oxygen atoms of the crown ether (NaϪO ϭ 248.7 to
271.8 pm) and one oxygen atom of an ether molecule
(NaϪO 247.0 pm) with a distorted coordination geometry.
In 6c, the Li atoms of the counterions [Li(triazinane)2]ϩ are
located on a crystallographic inversion center; the Li atoms
are coordinated by six nitrogen atoms with LiϪN distances
between 215.7 and 234.0 pm.
Synthesis of [(µ-NO2-N,O)R2AlCH2AlR2]Ϫ[Na([18]crown-
6)(Et2O)]ϩ (5c): An excess of solid NaNO2 (0.061 g, 0.884 mmol)
is treated with a solution of 0.507 g (0.719 mmol) of 1 and 0.252 g
(0.953 mmol) [18]crown-6 in 50 ml of diethyl ether. The mixture is
vigorously stirred for 18 h, and the solution adopts a pale yellow
color. After filtration the solution is concentrated in vacuo at room
temp. and cooled to Ϫ50°C. The product is isolated as yellow crys-
tals, which become amorphous upon thorough drying in vacuo and
include about 0.4 molecules of diethyl ether in each formula unit.
Yield: 0.455 g (59%). Ϫ M. p. (argon, sealed capillary): 163°C. Ϫ
1H NMR ([D10]Et2O, 300 MHz, 300 K): δ ϭ 3.69 (s, 24 H,
[18]crown-6), 3.39 (q, 1.6 H, OCH2 of Et2O), 1.12 (t, 2.4 H, CH3
of Et2O), 0.11 (s, 72 H, SiMe3), Ϫ1.04 (s, 4 H, AlCHSi2), Ϫ1.23 (s,
2 H, AlCH2Al). Ϫ 1H NMR ([D10]Et2O, 500 MHz, 203 K): δ ϭ
3.65 (s, 24 H, [18]crown-6), 3.38 (q, 1.6 H, OCH2 of Et2O), 1.15 (t,
2.4 H, CH3 of Et2O), 0.15 and 0.06 (each: s, 36 H, SiMe3), Ϫ1.0
and Ϫ1.1 (each: br., 2 H, AlCHSi2), AlCH2Al not detected. Ϫ13C
We are grateful to the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for generous financial support.
Experimental Section
General: All procedures were carried out under purified argon in
dried solvents (THF and diethyl ether over Na/benzophenone).
Compound 1 was synthesized as described in ref.[6], N,NЈ,NЈЈ-tri-
methyltriazinane and pentamethyldiethylenetriamine (PMDETA)
were distilled over Na (PMDETA under reduced pressure) and
stored over molecular sieve, commercially available crown ether 18-
crown-6 (Merck-Schuchardt), NaNO2 (Aldrich), and LiNO3
(Riedl-deHaen) were thoroughly evacuated at room temperature
and used without further purification.
NMR ([D10]Et2O, 75.5 MHz): δ ϭ 69.8 ([18]crown-6), 6.0 (SiMe3),
˜
Synthesis of [(µ-NO2-N,O)R2AlCH2AlR2]Ϫ[Na(THF)3]ϩ (5a):
A solution of 0.362 g (0.514 mmol) of 1 in 25 ml of THF is added
to an excess (0.057 g, 0.826 mmol) of solid NaNO2. The mixture
is vigorously stirred for 22 h, and the solution adopts a pale yellow
color. After filtration the solution is concentrated in vacuo at room
temp. and cooled to Ϫ50°C. The product is isolated as yellow crys-
tals, which rapidly become amorphous at room temperature and
normal pressure. Yield: 0.404 g (79%). Ϫ M. p. (argon, sealed capil-
5.0 (br., AlCH2Al), 4.2 (AlCSi2). Ϫ IR (CsBr, paraffin): ν ϭ 1501
m cmϪ1 νNO; 1462 vs, 1377 s, 1354 m paraffin; 1321 vw, 1296 m,
1244 vs δCH3; 1157 m, 1111 s, 1100 s, 1026 m νCC, νCO; 1005 s
δCH; 953 sh, 932 s, 899 s, 845 vs, 777 s, 750 s, 725 m ρCH3(Si);
669 s νasSiC; 629 w, 610 w νsSiC; 588 w, 561 m, 517 w, 505 w, 498
w, 463 vw, 449 vw νAlC, νAlO; 388 vw, 359 vw δSiC. Ϫ UV/vis
(diethyl ether) (ε): 230 (2530), 280 (sh, 870), 360 nm (90).
C41H102Al2NaNO8Si8 ·0.4 C4H10O (1068.55): calcd. Al 5.1, Na 2.2;
found Al 5.1, Na 2.0.
1
lary): 92°C. Ϫ H NMR ([D10]Et2O, 300 MHz): δ ϭ 3.66 (m, 12
H, OCH2 of THF), 1.82 (m, 12 H, CH2CH2 of THF), 0.09 (s, 72
H, SiMe3), Ϫ1.06 (s, 4 H, AlCHSi2), Ϫ1.24 (s, 2 H, AlCH2Al). Ϫ
13C NMR ([D10]Et2O, 75.5 MHz): δ ϭ 68.4 (OCH2 of THF), 26.2
Synthesis of [(µ-NO3-O,OЈ)R2AlCH2AlR2]Ϫ[Li(THF)4]ϩ (6a):
Solid LiNO3 (0.038 g, 0.554 mmol) is treated with a solution of an
equimolar amount of 0.391 g (0.554 mmol) of 1 in 50 ml of THF.
The mixture is vigorously stirred for 12 h. The yellow solution is
concentrated to about 1 ml, and the product crystallizes as yellow-
ish crystals upon cooling to Ϫ50°C. Yield: 0.490 g (83%). Ϫ M. p.
(argon, sealed capillary): 135°C. Ϫ 1H NMR ([D10]diethyl ether,
300 MHz): δ ϭ 3.64 (m, 16 H, OCH2 of THF), 1.79 (m, 16 H,
CH2CH2 of THF), 0.10 (s, 72 H, SiMe3), Ϫ1.05 (s, 4 H, AlCHSi2),
Ϫ1.27 (s, 2 H, AlCH2Al). Ϫ 13C NMR ([D10]diethyl ether, 75.5
MHz): δ ϭ 68.2 (OCH2 of THF), 26.3 (CH2CH2 of THF), 5.7
(CH2CH2 of THF), 5.9 (SiMe3), 5.0 (br., AlCH2Al), 4.1 (AlCSi2).
˜
Ϫ IR (CsBr, paraffin): ν ϭ 1497 m cmϪ1 νNO; 1462 vs, 1377 s
paraffin; 1339 w, 1316 w, 1244 vs δCH3; 1192 m, 1159 m, 1049 vs,
1028 s νCC, νCO; 1003 vs δCH; 934 vs, 918 vs, 899 vs, 843 vs, 777
vs, 750 vs, 725 s ρCH3(Si); 698 s, 669 vs νasSiC; 629 m, 613 w νsSiC;
588 w, 561 s, 521 m, 503 w, 496 m, 448 w νAlC, νAlO; 386 vw, 366
vw δSiC. Ϫ UV/vis (diethyl ether) (ε): 240 (1750), 290 (sh, 700),
370 nm (sh, 90). Ϫ C41H102Al2NNaO5Si8 (990.90): calcd. Al 5.4,
Na 2.3; found Al 5.4, Na 2.2.
(SiMe3), 5.0 (br., AlCH2Al), 4.3 (AlCSi2). Ϫ IR (CsBr, paraffin):
˜
Synthesis of [(µ-NO2-N,O)R2AlCH2AlR2]Ϫ[Na(PMDETA)2]ϩ ν ϭ 1501 s cmϪ1 νNO; 1462 vs, 1377 vs paraffin; 1344 m, 1281 vs,
(5b): An excess of solid NaNO2 (0.070 g, 1.01 mmol) is treated with
a solution of 0.513 g (0.727 mmol) of 1 in 50 ml of diethyl ether. 2 vs, 912 s, 845 vs, 777 vs, 750 s, 725 s ρCH3(Si); 667 s νasSiC; 629
ml of PMDETA is added to the suspension, and the mixture is m, 611 w νsSiC; 583 w, 556 s, 521 m, 505 m, 465 vw, 452 w, 421 w
vigorously stirred for 18 h. The solution adopts a pale yellow color. νAlC, νAlO, νLiO; 372 vw, 334 vw, 316 vw δSiC. Ϫ UV/vis (THF)
1248 vs δCH3; 1179 w, 1067 s, 1044 vs νCC, νCO; 1007 s δCH; 930
After filtration the solution is concentrated in vacuo at room temp.
(ε): 225 (2470), 260 nm (sh, br., 990). C45H110Al2LiNO7Si8
to about 4 ml and cooled to Ϫ50°C. The product is isolated as
(1062.96): calcd. Al 5.1, Li 0.6; found Al 5.1, Li 0.6.
924
Eur. J. Inorg. Chem. 1998, 921Ϫ926

Methylene-Bridged Dialuminium as Chelating Lewis Acids
FULL PAPER
Table 1. Crystal data, data collection parameters, and structure refinement for 5c and 6c[a] (crystal data of 5a and 5d [Na(TMPDA)2]
included)
5a
5c
5d
6c
Formula
Crystal system
Space group
Z
C41H102NO5NaAl2Si8
C45H112NO9NaAl2Si8
monoclinic
P2(1)/n; No. 14[25]
4
C43H114N5O2NaAl2Si8
C41H108LiN7O3Al2Si8
monoclinic
P2(1)/n; No. 14[25]
4
monoclinic
P2(1)/n; No. 14[25]
4
triclinic
¯
P1; No. 2[25]
2
293(2)
0.994
1404.5(2)
1437.6(2)
1935.3(2)
78.97(2)
85.54(2)
64.09(1)
3449.8(8)
0.215
Temperature [K]
dcalc. [g/cm3]
a [pm]
297(1)
0.842
1816.2(2)
1837.1(2)
2385.9(3)
90
100.98(2)
90
7815(1)
300(2)
297(1)
0.975
1989.6(3)
1507.0(3)
2393.1(5)
90
100.78(3)
90
7049(2)
1.041
1496.0(1)
2766.5(3)
1716.0(1)
90
b [pm]
c [pm]
α [°]
β [°]
90.594(7)
90
γ [°]
V [10Ϫ30 m3]
7102(1)
µ [mmϪ1
]
0.223
Crystal size [mm]
Diffractometer
Radiation
0.65 ϫ 0.65 ϫ 0.04
0.67 ϫ 0.70 ϫ 0.33
Stoe-IPDS
1.06 ϫ 0.72 ϫ 0.61
AED-2
0.65 ϫ 0.53 ϫ 0.53
AED-2
AED-2
Mo-Kα; graphite monochromator
2Θ range [°]
Index ranges
3.8 Յ 2Θ Յ 48.2
3.2 Յ 2Θ Յ 46
Ϫ15 Յ h Յ 15
Ϫ15 Յ k Յ 15
0 Յ l Յ 21
9621
Ϫ15 Յ h Յ 17
Ϫ31 Յ k Յ 31
Ϫ19 Յ l Յ 17
10572
Independent reflections
Reflections F > 4 σ(F)
Parameters
5380
5823
621
630
R ϭ ΣʈFo͉ Ϫ ͉Fcʈ/Σ͉Fo͉ [F >
4σ(F)]
0.0531
0.0873
wR2 ϭ {Σw(͉Fo͉2Ϫ͉Fc͉2)2/
Σw(Fo2)2}1/2 (all data)
Max./min. residual electron
density [1030 e/m3]
0.0795
0.1068
0.480/Ϫ0.280
0.295/Ϫ0.208
[a]
Programmes SHELXL-93; SHELXTL[26]; solutions by direct methods, full matrix refinement with all independent structure factors.
Synthesis of [(µ-NO3-O,OЈ)R2AlCH2AlR2]Ϫ[Li{(CH2NMe)3}-
solution in ether in the peresence of a small quantity of triazinane.
THF]ϩ (6b): Solid LiNO3 (0.048 g, 0.696 mmol) is treated with a Crystal data and structure refinement parameters are given in Table
solution of an equimolar amount of 0.490 g (0.694 mmol) of 1 and 1[27]. One of the [Li(triazinane)2]ϩ cations shows a disorder with a
2 ml of trimethyltriazinane in 45 ml THF. The mixture is vigorously
stirred for 24 h. The yellow solution is evaporated, the residue is
partial overlap of the atoms of the triazinane molecules. Crystal
data of 5a and of 5[Na(TMPDA)2] (5d) (TMPDA ϭ tetrameth-
treated with 5 ml of diethyl ether, and THF is added dropwise until ylpropylenediamine) are also given in Table 1; both structures could
a clear solution is obtained. Product 6b crystallizes as yellow crys- not be satisfactorily refined due to the severe disorder of the cat-
tals upon cooling to Ϫ50°C, which contain one molecule of THF ions. 5d was obtained on the same route as compound 5b, but was
and one molecule of trimethyltriazinane in each formula unit. The
product (6c) with two trimethyltriazinane molecules coordinated to
lithium, which was used for the crystal structure determination,
was obtained on slow cooling of a dilute solution of 6b in diethyl-
ether by the addition of a small amount of trimethyltriazinane.
Yield of 6b: 0.465 g (69%). Ϫ M. p. (argon, sealed capillary): 99°C.
not isolated in a high yield.
Ƞ
Dedicated to Prof. Dr. Heinrich Nöth on the occasion of his
70th birthday.
[1]
B. Dietrich, Pure Appl. Chem. 1993, 65, 1457Ϫ1464. M. M. G.
Antonisse, D. N. Reinhoudt, Chem. Commun. 1998, 443Ϫ448.
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Ϫ
1H NMR ([D8]THF, 300 MHz): δ ϭ 3.62 (m, 4 H, OCH2 of
THF), 3.10 (br., 6 H, NCH2 of triazinane), 2.20 (s, 9 H, Me of
triazinane), 1.78 (m, 4 H, CH2CH2 of THF), 0.10 (s, 72 H, SiMe3),
Ϫ1.06 (s, 4 H, AlCHSi2), Ϫ1.28 (s, 2 H, AlCH2Al). Ϫ 13C NMR
([D8]THF, 75.5 MHz): δ ϭ 78.3 (NCN of triazinane), 40.5 (Me of
[2]
Two compounds of the type R2AlϪCH2ϪAlR2 were described
in literature, which are, however, probably mixtures of dismu-
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˜
(CsBr, paraffin): ν ϭ 1503 m cmϪ1 νNO; 1466 vs, 1377 s paraffin;
H. E. Katz, J. Am. Chem. Soc. 1985, 107, 1420Ϫ1421.
[3]
[4]
M. R. Ort, E. H. Mottus, J. Organomet. Chem. 1973, 50,
1346 w, 1289 m, 1274 m, 1244 s δCH3; 1159 m, 1119 s, 1051 vs
νCC, νCO, νCN; 1015 s δCH; 916 s, 843 vs, 777 s, 737 m, 725 m
ρCH3(Si); 671 s νasSiC; 631 m, 611 w νsSiC; 579 m, 554 m, 519 s,
506 m, 465 m, 452 w, 419 w νAlC, νAlO; 395 w, 372 w, 339 w, 316
w δSiC. Ϫ UV/vis (THF) (ε): 240 (1710), 260 nm (sh, br., 1320).
Ϫ C39H101Al2LiN4O4Si8 (975.84): calcd. Al 5.5, Li 0.7; found Al
5.6, Li 0.7.
47Ϫ52.
[5]
H. Martin, H. Bretinger, Z. Naturforsch., B: Chem. Sci. 1991,
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M. Layh, W. Uhl, Polyhedron 1990, 9, 277Ϫ282. A methylene
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aluminium atoms {Li2[(Me3SiCH2)3AlCH2Al(CH2SiMe3)3} is
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124, 1511Ϫ1516.
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W. Uhl, M. Layh, J. Organomet. Chem. 1991, 415, 181Ϫ190.
Crystal Structure Determinations: Single crystals of compound
5c were obtained by recrystallization from diethyl ether, the crystals
of compound 6c were grown by recrystallization of 6b from a dilute
[8]
F. A. R. Kaul, M. Tschinkl, F. P. Gabbai, ibid. 1997, 539,
187Ϫ191. See also: T. Ooi, M. Takahashi, K. Maruoka, J. Am.
Chem. Soc. 1996, 118, 11307Ϫ11308.
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J. L. Atwood, K. D. Crissinger, R. D. Rogers, J. Organomet.
The crystallographic data of 5c and 6c (excluding structure fac-
tors) were deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-101256. Cop-
ies of the data can be obtained free of charge on application to
The Director, CCDC, 12 Union Road, GB-Cambridge CB2
1EZ, UK [fax: Int. Codeϩ44(0)1223/ 336-033; e-mail: deposit-
@chemcrys.cam.ac.uk].
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