Bis(tetramethylpiperidino)aluminum Halide Adducts tmp2AlX·Do and Tetrahaloaluminates of Tricoordinated Aluminum Cations [tmp2Al(Do)]AlX4

Article abstract of DOI:10.1002/(sici)1099-0682(199807)1998:7<927::aid-ejic927>3.0.co;2-i

Upon treatment with Lewis bases Do (Do = pyridine bases or THF), the Lewis acids tmp₂AlX (X = Cl, Br, I) are converted exclusively to the monoadducts tmp₂AlX·Do (2-4). The AlX bonds of these addition compounds are considerably elongated, indicating a tendency towards the formation of ionic species [tmp₂Al(Do)]X. Due to the steric requirements of the bulky tmp ligands, addition of an excess of the Lewis base does not force these compounds to form tetracoordinated aluminum cations [tmp₂Al(Do)₂]⁺ or pentacoordinated adducts tmp₂AlX·Do₂. Attempts to prepare ionic representatives by reaction of tmp₂AlX·Do with "ate" complexes of comparatively low nucleophilicity [MY = NaBPh₄, AgBPh₄, LiB(C₆F₅)₄, AgBF₄, AgOtos] result in phenylation products [e.g. tmp₂AlPh (5a) and BPh₃·py (5b)] or tetracoordinated addition compounds tmp₂AlY·Do (Y = anion). However, addition of one equivalent of AlX₃ (X = Br, I) initiates halide abstraction with formation of the ionic [tmp₂Al(Do)]AlX₄ species 6a-f, as indicated by ²⁷Al-NMR data and conductivity measurements. Solid [tmp₂Al(Py)]AlI₄ (6b) decomposes readily into tmpAlI₂ and tmpAlI₂·py (7c) Addition of non-polar aliphatic solvents to solutions of [tmp₂Al(Do)]AlX₄ (6) leads to slow decomposition into tmp₂AlX and AlX₃·Do (7a-b, d). This also occurs in polar donor solvents, where compounds AlX₃·Do are favoured due to the formation of penta- or hexacoordinated species AlX₃·Do·Solv_n (n = 1, 2). Semiempirical AM1 calculations reveal the gas-phase stability of the tricoordinated bis(tmp)aluminum cation in the salt [tmP₂AlPy]AlCl₄ as the only representative in a series of calculated aluminum cations [(R₂N)₂AlPy]AlCl₄ (R₂N = Me₂N, Et₂N, iPr₂N, tmp). According to these calculations, the stability of a given cation increases when tetrachloroalummate is replaced by tetraiodoaluminate. Ab initio calculations have been performed on two cations [(H₂N)₂Al(Do)]⁺ (Do = NH₃, py) and indicate very short Al-N bond lengths owing to ionic bonding contributions.

Full text of DOI:10.1002/(sici)1099-0682(199807)1998:7<927::aid-ejic927>3.0.co;2-i

FULL PAPER
Bis(tetramethylpiperidino)aluminum Halide Adducts tmp2AlX·Do and
Tetrahaloaluminates of Tricoordinated Aluminum Cations [tmp2Al(Do)]AlX4
Ingo Krossing[1], Heinrich Nöth*, and Holger Schwenk-Kircher[2]
Institute of Inorganic Chemistry, University of Munich,
Meiserstraße 1, D-80333 Munich, Germany
Received December 3, 1997
Keywords: Bis(tetramethylpiperidino)aluminum halide complexes / Tricoordinated aluminum cations / 27Al-NMR
spectroscopy / X-ray crystal structure analysis / Ab initio calculations
Upon treatment with Lewis bases Do (Do = pyridine bases or data and conductivity measurements. Solid [tmp2Al(py)]AlI4
THF), the Lewis acids tmp2AlX (X = Cl, Br, I) are converted
(6b) decomposes readily into tmpAlI2 and tmpAlI2 ·py (7c).
exclusively to the monoadducts tmp2AlX·Do (2–4). The Al–
Addition of non-polar aliphatic solvents to solutions of
X bonds of these addition compounds are considerably [tmp2Al(Do)]AlX4 (6) leads to slow decomposition into
elongated, indicating a tendency towards the formation of tmp2AlX and AlX3 ·Do (7a–b, d). This also occurs in polar
ionic species [tmp2Al(Do)]X. Due to the steric requirements donor solvents, where compounds AlX3 ·Do are favoured due
of the bulky tmp ligands, addition of an excess of the Lewis to the formation of penta- or hexacoordinated species
base does not force these compounds to form AlX3 ·Do·Solvn (n = 1, 2). Semiempirical AM1 calculations
tetracoordinated aluminum cations [tmp2Al(Do)2]+ or
pentacoordinated adducts tmp2AlX·Do2. Attempts to
prepare ionic representatives by reaction of tmp2AlX·Do
reveal the gas-phase stability of the tricoordinated
bis(tmp)aluminum cation in the salt [tmp2AlPy]AlCl4 as the
only representative in a series of calculated aluminum
with “ate” complexes of comparatively low nucleophilicity cations [(R2N)2AlPy]AlCl4 (R2N = Me2N, Et2N, iPr2N, tmp).
[MY = NaBPh4, AgBPh4, LiB(C6F5)4, AgBF4, AgOtos] result According to these calculations, the stability of a given cation
in phenylation products [e.g. tmp2AlPh (5a) and BPh3 ·py increases when tetrachloroaluminate is replaced by
(5b)] or tetracoordinated addition compounds tmp2AlY·Do tetraiodoaluminate. Ab initio calculations have been
(Y = anion). However, addition of one equivalent of AlX3 (X = performed on two cations [(H2N)2Al(Do)]+ (Do = NH3, py) and
Br, I) initiates halide abstraction with formation of the ionic
[tmp2Al(Do)]AlX4 species 6a–f, as indicated by 27Al-NMR
indicate very short Al–N bond lengths owing to ionic
bonding contributions.
As aluminum compounds exhibit the highest Lewis acid- ies of this type have been reported, namely
ity amongst main group III species[3][4], tetra-, penta- and [tBu2Al(tmeda)]ϩ by Uhl[11] and A by Raston[12]
hexacoordinated Lewis acidϪbase complexes with many
different neutral donor molecules have been described in
the literature[5]. Due to their importance in industrial pro-
cesses[6], complexes involving AlCl3 and trimethylaluminum
as Lewis acids [e.g. AlCl3 ·NMe3, AlCl3 ·(NMe3)2,
AlBr3 ·diglyme (diglyme ϭ diethylene glycol dimethyl
ether), AlMe3 ·OMe3, etc.][4][7][8] have been particularly well
studied. These addition compounds can exist as covalent
.
molecules or as ion pairs, as shown by X-ray crystal struc-
To the best of our knowledge, tricoordinated aluminum
ture determinations {e.g. [AlCl2(py)4]AlCl4}[3] 27Al-NMR cations [R2Al(Do)]ϩ (Do ϭ monofunctional ligand) have
,
and conductivity measurements, e.g. of solutions of AlCl3 yet to be observed and characterized.
or AlBr3 in THF, diglyme, DME etc.[8][9]. A fine example
In contrast to the aminoboron halides, aminoaluminum
of this feature has recently been published by Atwood et halides can be expected to be sufficiently acidic to form
al.[10]. They investigated reactions of Me2AlX (X ϭ Cl, Br, addition compounds [see (Me3Si)2NAl(H)(Cl)·NMe3][13]
.
I) with tBuNH2 as a donor molecule. Whereas the chloride Even aminoorganylalanes form Lewis acidϪbase adducts,
gave the molecular adduct Me2AlCl·NH2tBu, the bromide as exemplified by Ph2NAlMe2 ·NMe3 and Ph2NAl-
and iodide were forced to dissociate upon addition of excess Me2 ·OEt2[14]. Thus, the question arose as to whether the
tBuNH2, forming the salts [Me2Al(NH2tBu)2]X (X ϭ Br, recently synthesized series of monomeric bis(amino)alumi-
I). The chemistry of tetracoordinated aluminum cations has num halides, tmp2AlX (tmp ϭ 2,2,6,6-tetramethylpiperid-
so far been explored only fleetingly, and apart from the lat- ino, X ϭ Cl 1a, Br 1b, I 1c)[15] and some products of nucleo-
ter compounds, as far as we are aware, only two other spec- philic substitution derived from these[16][17] would still show
Eur. J. Inorg. Chem. 1998, 927Ϫ939
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
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I. Krossing, H. Nöth, H. Schwenk-Kircher
FULL PAPER
Lewis acidity. This was indeed found to be the case for pair [tmp2Al(py)]BF4. This dissociation is accompanied by
1a؊c. Here, we report on the addition compounds dramatic shifts of the 11B- and 19F-NMR resonances.
tmp2AlX·Do (X ϭ Cl, Br, I) as well as the salts [tmp2Al(-
Do)]Y (Y ϭ AlI4).
Synthesis and Reactions
Addition of one equivalent of a donor molecule Do to
n-hexane solutions of tmp2AlX, 1a؊c, leads to immediate
precipitation of the adducts tmp2AlX·Do 2a, b, 3a؊c, and
4a؊c in almost quantitative yield, according to Eq. 1.
The adducts 2؊4 are stable in vacuo and do not lose
their donor molecules, even when subjected to high vacuum
conditions at 50°C. On the other hand, Et2O, tBuPH2,
NEt3, and acridine do not give stable addition compounds
(with respect to the application of vacuum). Moreover,
tmp2AlI (1c), the most Lewis acidic compound in the series
of the halides 1a؊c, crystallizes from Et2O as its tricoordi-
nated monomer, as proven by NMR and by examination
of its unit cell parameters[15]. Compounds 2؊4 are readily
soluble in aromatic hydrocarbons, CH2Cl2, CH2Br2, THF,
and Et2O. Addition of a large excess of donor (up to ten-
As all the tested tetraphenylborates and tetrafluorobo-
fold, or, in the case of THF, using the donor as solvent)
rates turned out to be either unstable (due to dephenylation)
does not force coordination of a further donor molecule
or too basic (formation of adducts) to give ionic componds
(i.e. bring about pentacoordination at the aluminum atom),
of the type [tmp2Al(Do)]Y, a different approach was evalu-
ated, in which strong halide acceptors were employed in
order to induce a reaction according to Eq. 3a.
nor does it induce dissociation into ionic [tmp2Al(Do)2]X
species. The addition compounds 2؊4 can be crystallized
from THF and no replacement of Do by the solvent is ob-
served.
Attempts to prepare low coordinated ionic species of the
type [tmp2Al(py)]Y (Y ϭ anion) by addition of NaBPh4,
AgBPh4, or LiB(C6F5)4 to solutions of tmp2AlI·py in vari-
ous solvents at ambient temperature, did not lead to substi-
tution of the iodine atom by the weakly coordinating ions
BR4Ϫ, even after a reaction time of several weeks. In the
case of the reaction with AgBPh4, the only species detec-
table after heating were tmp2AlPh (5a) and BPh3 ·py (5b).
This implies that [tmp2Al(py)]BPh4 is formed initially,
which then decomposes to give 5a and 5b. The aluminum
compound 5a has been synthesized independently from
Addition of one equivalent of AlX3 (X ϭ Br, I) to solu-
tions of tmp2AlX·Do (X ϭ Br, I) in CH2Br2 (for 6a) or in
PhLi and tmp2AlCl[17]
.
Upon reaction with AgOtos (Otos ϭ tosylate), 4a gives aromatic solvents such as toluene leads smoothly to the
only the tetracoordinated, covalent product of nucleophilic ionic compounds [tmp2Al(iq)]AlBr4 (6a), [tmp2Al(py)]AlI4
substitution, tmp2AlOtos·py (5c). Likewise, a mixture of (6b), [tmp2Al(4-Me-py)]AlI4 (6c), [tmp2Al(4-tBu-py)]AlI4
AgBF4, 2,6-lutidine (ϭ lut) and 1b yields the adduct (6d), [tmp2Al(iq)]AlI4 (6e), and [tmp2Al(acr)]AlI4 (6f), (iq ϭ
tmp2Al(BF4)·lut (5d). Replacing the sterically hindered, isoquinoline, acr ϭ acridine). If a solution of tmp2AlCl·thf
less powerful donor 2,6-lutidine by pyridine leads to (2a) in THF is treated with AlCl3, only the adduct
tmp2Al(BF4)·py (5e). The latter compound, molecular in AlCl3 ·(thf)2 is formed, according to the 27Al-NMR spec-
n-pentane solution, dissociates in CH2Cl2 to give an ion trum. In contrast to the iodide [tmp2Al(acr)]AlI4 (6f), ad-
928
Eur. J. Inorg. Chem. 1998, 927Ϫ939

Bis(tetramethylpiperidino)aluminum Halide Adducts
FULL PAPER
dition of AlBr3 to a 1:1 mixture of tmp2AlBr (1b) and acri- at δ ϭ 1.29; for tmp2AlBr·iq (3c) at δ ϭ 1.37, and for
dine leads to exclusive formation of AlBr3 ·acr (7d), leaving tmp2AlI·iq (4b) at δ ϭ 1.41. Similarily, the methyl protons
1b uncoordinated. The tetraiodoaluminates were found to resonate at δ ϭ 1.58 in tmp2AlBr·py (3b) and at δ ϭ 1.62
be the most stable of all the tetrahaloaluminates. Never- in tmp2AlI·py (4a). These changes point to a predis-
theless, NMR spectroscopic evidence was found even for sociation of the weakest AlϪX bond (AlϪI). The aluminum
the formation of ionic tetrachloroaluminates. Solutions of centre thus becomes more positively charged (see B), and
6b؊f in aromatic hydrocarbons or CH2Cl2 are stable for the resonances appear at lower field.
weeks at ambient temperature, but addition of n-pentane
1
Table 1. 27Al chemical shifts and line-widths, and selected H- and
(in an attempt to induce crystallization) results in slow de-
composition to give tmp2AlI (1c) and AlI3 ·Do. This was
proven by the isolation and full characterization of AlI3 ·iq
(7a) and AlI3 ·(4-tBu-py) (7b), as well as by NMR spectro-
scopic characterization of tmp2AlI (1c) (see Eq. 4a and
4b)[15]. The preparation of 6b also proceeds smoothly in
Et2O, but storing the concentrated solution at Ϫ78°C in
the hope of obtaining crystals leads to decomposition into
soluble AlI3 ·py·(OEt2)n and insoluble tmp2AlI (1c), ac-
cording to Eq. 4c[15]. Upon standing for one week at 35°C,
solid 6b disproportionates into tmpAlI2 and tmpAlI2 ·py
(7c).
13C-NMR data of compounds 2b, 3a؊c, and 4a؊c
Com-
pound
(solv.)
2b
3b
3c
3a
4a
4b
4c
[CDCl3] [C6D6] [CDCl3] [C6D6] [C6D6] [CDCl3] [C6D6]
δ27Al[a] 102
96
4.360
109
7.500
125
8.000
92
4.900
108
8.900
76
5.900
s9.27 s
[b]
∆
8.300
1/2
δ1H[a]
10.07
s9.25 s 10.17
9.18 d[c]
155.7
s3.76 t 9.06 s 10.21
9.21 d[d]
155.3
9.11 d[e]
155.1
δ13C[a]
150.4
68.3
148.0
150.2
[a]
[b]
In ppm. Ϫ
In Hz. Ϫ [c] 3J(H,H) ϭ 7.4 Hz. Ϫ [d] 3J(H,H) ϭ
6.4 Hz. Ϫ [e] 3J(H,H) ϭ 6.6 Hz.
The chemical shifts of hydrogen and carbon atoms adjac-
ent to the heteroatoms of the donor molecules proved to be
valuable indicators in ascertaining whether or not a com-
pound tmp2Al(Do)Y (Y ϭ anion or ligand) is dissociated
into an ion pair (see Table 2). In comparison with the free
pyridine bases, the resonances for these bases in the adducts
2؊4 are shifted downfield by 0.6 to 1 ppm (1H-NMR) and
by 0.6 to 3.5 ppm (13C-NMR), respectively.
The decomposition products of the tetraphenylborate, as
1
described by Eq. 2b, were identified by their H-, 13C-, and
27Al-NMR shifts, as reported in the literature (tmp2AlPh,
5a)[17], or by the known 11B-NMR shift of δ ϭ 5.0[20]
.
1
Further evidence was provided by the H-NMR spectrum,
elemental analysis, and X-ray crystal structure determi-
nation of BPh3 ·py (5b)[21]
.
Characterization
Compared to the shifts and half-widths of the 27Al-NMR
Since tmp2AlOtos·py (5c) exhibits a 27Al-NMR signal in
signals of the tricoordinated alanes tmp2AlX 1a؊c the same range as the adducts 2؊4 (δ27Al ϭ 97, ∆1/2
ϭ
(δ27Al ϭ 130Ϫ131, ∆1/2 ϭ 9100Ϫ13700 Hz)[15], the signals 5500 Hz), as well as a similar shift of the ortho-protons on
of the adducts 2؊4 are shifted by 30Ϫ60 ppm to higher the pyridine ring (δ1H ϭ 9.29, cf. the data in Table 1), it
field due to the higher electron-density at the aluminum appears that this species is not ionic. A very similar situ-
center and are narrower. As compounds 2؊4 have tetraco- ation is found for tmp2Al(lut)BF4 (5d). In its 27Al-NMR
ordinated aluminum atoms, and thus the local symmetry at spectrum, a line at δ ϭ 1 (∆1/2 ϭ 3400 Hz) is found, too
the aluminum nuclei is increased (as compared to 1a؊c), narrow to be attributable to a tricoordinated aluminum cen-
the average half-widths of the 27Al-NMR signals are re- tre. Moreover, the 11B-NMR spectrum consists of a single,
duced to approximately 6800 Hz (see Table 1)[18][19]. Single broadened line at δ11B ϭ 17.9. Due to the coordination at
1
sets of lines are observed in the H- and 13C-NMR spectra the aluminum centre, the resonance is deshielded by 18 ppm
of the tmp ligands, indicating free rotation about the AlϪN compared to the free, ionic tetrafluoroborate[20]. Similarly,
bond as well as rapid inversion of the piperidinyl ring. a solution of tmp2Al(py)BF4 (5e) in pentane exhibits a sig-
Compared to the halides 1a؊c, the signals are shifted nal at δ11B ϭ 19.3. If the spectrum is recorded in CDCl3 or
downfield [by about 0.3 ppm (1H NMR) and 2.7 ppm (13C CH2Cl2, a line at δ11B ϭ 0.9 is observed, indicating the
NMR)]. Moreover, the chemical shifts show a strong sol- presence of uncoordinated, free BF4Ϫ[20]. This is ac-
vent dependence. In CDCl3, the signals are found at higher companied by correspondingly dramatic differences in the
field than in C6D6. The decrease in Lewis acidity in the 19F-NMR signals. Whereas in pentane a broadened reson-
series AlϪI > AlϪBr > AlϪCl[3][4] and the bond enthalpy ance at δ19F ϭ Ϫ111 (analogous to 5d: δ19F ϭ Ϫ104.5 and
order AlϪX (AlϪI < AlϪBr < AlϪCl)[6] are mirrored by Ϫ111.0) is found, in CDCl3 a 1:1:1:1 quartet at δ19F ϭ
the chemical shifts of the tmp methyl groups. For Ϫ151 with 1J(B,F) ϭ 12 Hz supports the salt formation [cf.
1
tmp2AlCl·iq (2b), the methyl protons give rise to a signal F3BOH, J(B,F) ϭ 16.4 Hz; F3B·N(H)xMe3Ϫx, x ϭ 0Ϫ3,
Eur. J. Inorg. Chem. 1998, 927Ϫ939
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I. Krossing, H. Nöth, H. Schwenk-Kircher
FULL PAPER
1J(B,F) ϭ 15.1 to 16.4 Hz][20]. The 27Al-NMR signal of 5e As the calculated AlϪN bond lengths and NϪAlϪN bond
˚
in CH2Cl2 is additional evidence for the ionic behavior in angles are very similar (to within ±0.01 A and ±1°), similar
polar solvents: a very broad signal is observed, covering the NMR spectroscopic data can be expected.
1
full spread of the spectrum. The H-NMR signals of the
Addition of n-pentane to a solution of 6b or 6d in aro-
ortho-protons on the pyridine ring also reflect this change: matic hydrocarbons leads to disproportionation according
the shift for 5e (δ ϭ 8.71) is consistent with an ionic struc- to Eq. 4c. In solution, the characteristic chemical shifts of
ture {cf. [tmp2Al(py)]AlI4, (6b), δ1H ϭ 8.59}, but not with tmp2AlI (1c) could be detected (1H-, 13C-, 27Al-NMR)[15]
.
the adduct tmp2AlI·py (4a), where the corresponding sig- Crystals of AlI3 ·4-tBu-py (7b), which separated on cooling
nal appears at δ ϭ 9.06. to 5°C, were characterized spectroscopically and analyti-
Compared to the adducts 2؊4, the formation of the ionic cally, as was a sample of AlBr3 ·acr (7d), obtained according
species 6a؊f is accompanied by dramatic changes in the to Eq. 3b. Due to the highly symmetrical coordination at
line-widths of the 27Al-NMR signals. Whereas 2؊4 exhibit the aluminum nuclei, these compounds give sharp lines at
average line widths of 6800 Hz, a single sharp line attribu- δ27Al ϭ 51 (∆1/2 ϭ 46 Hz) (7b) and δ ϭ 83 (∆1/2 ϭ 34 Hz)
table to the AlX4Ϫ fragment (∆1/2 ϭ 17 to 134 Hz) is found (7d). Since only one distinct line was observed in each 27Al-
for compounds 6a؊f. The second aluminum nucleus, as- NMR spectrum, dissociation into ionic species as found for
sumed to be tricoordinated, should contribute to the spec- AlCl3 ·py2 can be ruled out[5]. Moreover, AlI3 ·iq (7a) pre-
tra with a very broad line. Due to the presence of highly cipitated under these conditions as a molecular adduct. It
symmetrical, NMR-sensitive and unsymmetrical, tricoordi- was only characterized by its X-ray crystal structure.
nated aluminum centres, this line is not usually detected
In the solid state, 6b decomposes into tmpAlI2 and
{e.g. in the ambient temperature 27Al-NMR spectrum of tmpAlI2 ·py (7c) (Eq. 4c). This is demonstrated by its 27Al-
[Al(OiPr)3]4 one sharp line, assigned to the central, hexaco- NMR spectrum: one signal at δ27Al ϭ 69 (∆1/2 ϭ 2640 Hz)
ordinated aluminum atom is readily detected (δ27Al ϭ is observed for 7c, the half-width of which resembles that
Ϫ2.62, ∆1/2 ϭ 102 Hz), while signals due to the tetracoordi- of signals of other tmpAlX2иDo compounds[15][19]. The 1H-
nated aluminum atoms are not seen[19]}. As the chemical and 13C-NMR shifts of 7c are very similar to those ob-
shifts of the tetrahaloaluminates (6a: δ27Al ϭ 104; 6b؊e: served for tmp2AlI·py (4a), differing by only about 0.01
δ27Al ϭ 50Ϫ55; 6f: δ27Al ϭ Ϫ22) are, with the exception ppm (δ1H) and 0.1 ppm (δ13C). Thus, it is most likely that
of 6f, found at lower field than those reported in the litera- 7c is present in solution as a tetracoordinated adduct.
ture [AlBr4Ϫ: δ27Al ϭ 80Ϫ83, AlI4Ϫ: δ27Al ϭ Ϫ27
Conductivity Measurements
(CH2Cl2)][19], a weak coordination of the anions to the cat-
ionic aluminum center is indicated. Considering the narrow
line-width for 6a؊f (∆1/2 ϭ 17Ϫ134 Hz), this interaction
cannot be very strong, since the aluminum nucleus is very
sensitive to a disturbance of symmetry. Due to the positive
To prove the formation of ions, conductivity measure-
ments were carried out on well-defined CH2Cl2 solutions of
5d, 6a؊b, e and the dissociation patterns were deduced
from the calculated gradients of the resulting Fuoss-Kraus
plots[22]. These salts are stable in CH2Cl2 solution and do
not undergo halogen-exchange with the solvent, as is ob-
served for AlX3 solutions (X ϭ Br, I). The gradient of these
plots gives an indication of the ion pair formation from the
undissociated parent species. An equilibrium as described
by Eq. 5a corresponds to a gradient of Ϫ0.5, that according
to Eq. 5b exhibits a gradient of 0, while a dissociation pat-
tern described by Eq. 5c is represented by a value of 0.5.
1
charge of 6a؊f, the H- and 13C-NMR signals of the pro-
tons and the carbon atoms adjacent to the heteroatoms of
the donor molecules are shifted by about 0.4 ppm (1H
NMR) and 1Ϫ3 ppm (13C NMR), respectively, to higher
field, compared to the corresponding signals in compounds
2؊4. This is a characteristic feature for these ionic com-
Table 2. Selected NMR data of compounds 6
Compound
δ27Al [ppm] ∆1/2 [Hz]
δ1H [ppm]
δ13C [ppm]
6a [CDCl3] 104
66
134
35
75
17
70
9.89 s[a], 8.94 d[b]
8.59 s[a]
152.5
147.0
146.9
146.6
152.4
6b [C6D6]
6c [C6D6]
6d [C6D6]
50
51
51
8.47 s[a]
8.54 s[a]
6e [CDCl3] 55
6f [CDCl3] Ϫ22.0
9.70 s[a], 8.75 d[b]
8.80 s[a][c], 8.21 d[d] 148.7
[a]
[b]
[c]
Broad. Ϫ
[d] 3J(H,H) ϭ 8.1 Hz.
3J(H,H) ϭ 6.4 Hz. Ϫ
At C7, trans to N1. Ϫ
pounds (see Table 2 and compare with the data in Table 1).
A solution of 5d in CH2Cl2 shows no electrical conduc-
Single sets of lines are observed for the tmp ligand in 6, tivity and thus this compound remains as a molecular ad-
indicating free rotation about the AlϪN bond and rapid duct, as already shown by its NMR data. Solutions of 6a,
inversion of the piperidinyl ring. Compared to the adducts b, e exhibit electrical conductivity, indicating ion pair for-
2؊4, the signals appear at higher field and resemble those mation. The gradient of the plot for 6b reaches a value of
found for the halides 1b؊c. This is in line with calculated approximately Ϫ0.6, indicating a reaction according to Eq.
AM1 data[29] for 1b, c and [tmp2Al(py)]AlX4 (X ϭ Br, I). 5a. However, the gradients for 6a, e are Ϫ0.1 and Ϫ0.2,
930
Eur. J. Inorg. Chem. 1998, 927Ϫ939

Bis(tetramethylpiperidino)aluminum Halide Adducts
FULL PAPER
respectively. This corresponds with ion formation according Figure 1. Molecular structure of 2a in the solid state. Thermal el-
lipsoids are shown at a 25% probability level
to Eq. 5a and Eq. 5b, with a greater percentage of the dis-
sociation behavior conforming to Eq. 5b. 8a and 8b re-
present two possible structures of the ionic products formed
according to Eq. 5b.
Crystal Structures
The adducts of tmp2AlCl (2a, b) and tmp2AlBr (3a) crys-
tallize in the monoclinic space group P21/n with four mol-
ecules in the unit cell, while tmp2AlBr·py (3b) and
tmp2AlI·py (4a) are isotypical having the monoclinic space
group C2/c (Z ϭ 8). Structural parameters of these com-
Figure 2. Molecular structure of 2b in the solid state. Thermal el-
lipsoids are shown at a 25% probability level
pounds are given in Table 3, crystallographic details in
Table 6.
Table 3. Selected bonding parameters of compounds 2a, b, 3a, b,
and 4a
Compound
2a
2b
3a
3b
4a
˚
Bond lengths [A]
d(AlϪX)
d(AlϪN1)
2.227(3)
1.836(5)
1.843(6)
2.041(7)
2.220(1)
1.844(2)
1.851(3)
1.913(2)
2.408(2)
1.836(4)
1.844(4)
1.928(4)
2.429(2)
1.838(4)
1.844(4)
2.030(4)
2.704(1)
1.849(3)
1.854(4)
2.022(3)
d(AlϪN2)
d(AlϪN3/O1)
Bond angles [°]
N1ϪAlϪN2
N1ϪAlϪX
N2ϪAlϪX
N3/O1ϪAlϪX
N3/O1ϪAlϪN1 111.6(3)
N3/O1ϪAlϪN2 99.1(3)
AlϪN1ϪC1
AlϪN1ϪC5
AlϪN2ϪC10
AlϪN2ϪC14
126.0(3)
106.3(2)
113.8(2)
95.7(2)
126.6(1)
104.22(8) 104.9(2)
115.40(8) 115.2(2)
126.7(2)
125.7(2)
105.2(1)
115.5(1)
93.6(1)
111.7(2)
100.4(2)
127.5(3)
114.9(4)
125.8(3)
120.8(3)
358.8
126.1(2)
104.4(1)
116.0(1)
92.7(1)
111.9(2)
100.7(2)
127.4(3)
116.8(3)
124.9(2)
121.0(2)
359.4
95.13(7)
111.8(1)
99.2(1)
127.4(2)
117.0(2)
123.9(2)
121.5(2)
358.9
94.3(2)
111.9(2)
98.9(2)
125.9(4)
116.7(3)
124.8(3)
121.2(4)
358.8
127.4(4)
116.8(4)
124.7(4)
121.9(4)
Figure 3. Molecular structure of 3a in the solid state. Thermal el-
lipsoids are shown at a 25% probability level
Sum of bond an-Σ(N1)
gles [°]
Σ(N2)
Σ(N3/O1)
359.5
360.0
359.8
360.0
359.7
359.6
359.6
359.9
359.6
360.0
Torsion angles [°]
C1ϪN1ϪAlϪX 69.81
C5ϪN1ϪAlϪX 57.20
C10ϪN2ϪAlϪX 29.23
C14ϪN2ϪAlϪX 19.68
75.95
60.41
35.06
19.39
75.06
60.49
22.49
16.27
72.36
59.88
26.69
18.36
Ϫ
Ϫ
Ϫ
Ϫ
Each of the aluminum centres in the five compounds is
coordinated in a distorted tetrahedral fashion by one tmp
ligand in the chair conformation, one tmp ligand in the
twist conformation, the N or O atom of the donor mol-
ecule, and the halogen atom. The N and O atoms of the
ligands are tricoordinated and exhibit bond angle sums
close to 360° (358.8Ϫ360.0°). The most interesting feature
of these adducts are the long AlϪX bond lengths: 2.220(1)
˚
˚
to 2.227(3) A for X ϭ Cl; 2.408(2) to 2.429(2) A for X ϭ
Eur. J. Inorg. Chem. 1998, 927Ϫ939
931

I. Krossing, H. Nöth, H. Schwenk-Kircher
FULL PAPER
Figure 4. Molecular structure of 3b in the solid state. Thermal el- bond lengths d(AlϪCl) in 2a, b and the AlϪCl distance
lipsoids are shown at a 25% probability level
found in the molecular adduct Me2AlCl·NH2tBu [2.204(2)
˚
A][10] reveal that the adducts 2a, b are in a state of predis-
sociation {cf. the related salts [Me2Al(NH2tBu)2]X, X ϭ Br,
I}[10]. Thus, AlϪCl bond lengths shorter than those in the
adducts 2a, b have been observed even for usually longer
bridging AlϪClϪAl distances, e.g. in the centrosymmetric
organoaluminum
dichloride
Ar(Cl)Al(µ-Cl)2Al(Cl)Ar
(Ar ϭ 2,6-Mes2C6H3), where the AlϪCl bond lengths
˚
˚
amount to 2.195(2) A, terminal: 2.125(2) A][24]. This is also
true for 3؊4, which exhibit long AlϪX distances in the
range typical of bridging AlϪXϪAl units, e.g. of the same
˚
order as those in (tBu2Alµ-X)2 [X ϭ Br 2.463(3) A, X ϭ I
˚
2.708 A][25] or in (trip2Alµ-Br)2 [d(AlϪBr) ϭ 2.475(4) and
˚
2.500(3) A; trip ϭ 2,4,6-iPr3C6H2][26]. This elongation can
be viewed as the initial stage of dissociation. For the AlϪI
bond in particular, a strongly polar AlδϩϪIδϪ bonding situ-
˚
ation follows [cf. Me2AlI·NMe3; d(AlϪI) ϭ 2.58 A][28]
,
which also explains the poor solubility of these compounds
in non-polar solvents.
Crystals of the adduct AlI3 ·iq (7a) are monoclinic, space
group C2/c (Z ϭ 8, Figure 7). For compound tmpAlI2 ·py
(7c), the monoclinic space group P21/n with four molecules
in the unit cell has been determined (Figure 8). The alumi-
num atoms in these adducts are tetracoordinated by the
pyridine base, the iodine atoms, and the tmp ligand. The
latter substituent adopts the chair conformation and pos-
sesses a planarized nitrogen centre (sum of bond angles
356.2°). The AlϪN distance to the donor molecule de-
Figure 5. Molecular structure of 4a in the solid state. Thermal el-
lipsoids are shown at a 25% probability level
˚
˚
creases from 1.978(5) A (7c) to 1.947(9) A (7a) (cf. the ad-
ducts 2؊4 in Table 2) as the number of iodine atoms in-
creases. This gives an indication that AlI3 is a stronger
Lewis acid than tmpAlI2. For AlCl3 ·NMe3, d(AlϪN)
˚
amounts to 1.96 A[4], while for cyclo-Me2NCH2CH2(Et)-
˚
NAlCl2, this distance is 1.963(2) A[27]. However, in 7c, the
˚
AlϪN bond to the tmp ligand is short [1.809(5) A] and
resembles that in [tmp(Br)Alµ-OEt]2, [d(AlϪN) ϭ 1.810(3)
˚
A][15]. Thus, the difference between the coordinative AlϪN
˚
linkage and the covalent AlϪN bond is about 0.17 A.
Given these bonding parameters for 7a, c, it is not surpris-
ing that the AlϪI bond lengths in 7a are Ϫ on average Ϫ
˚
Br, and 2.704(1) A for X ϭ I. The AlϪN bond lengths fall
6.5 pm shorter than those in 7c [7a: 2.500(4) to 2.510(4),
˚
in a narrow range, varying only from 1.836(5) to 1.854(4)
A. There are no differences in the bond distances between
the tmp ligand present in the chair conformation and that
in the twist conformation. AlϪDo distances range from
1.913(2) to 1.928(4) A (THF) and from 2.022(3) to 2.041(7)
A (pyridine bases). As the tmp ligands are quite bulky, the
NϪAlϪN bond angle [125.7(2) to 126.7(2)°] shows a con-
siderable deviation from the tetrahedral bond angle of
109.5°.
˚
7c: 2.572(2) and 2.573(2) A]. This is in accord with a de-
crease of the Lewis acidity of the aluminum centre in 7c
˚
and compares well with the d(AlϪI) of 2.58 A observed
[28]
˚
in Me2AlI·NMe3
.
˚
Semiempirical and Ab Initio Calculations
Semiempirical AM1[29] calculations have been performed
in order to investigate the extent of steric shielding and the
Compared to the sums of their covalent radii (AlϪCl bond strength factors that are necessary to favor ionization.
˚
2.10, AlϪBr 2.28, AlϪI 2.48 A, corrected for ionic contri- Thus, the structures of the cations [(R2N)2Al(py)]ϩ and the
butions by the Schomaker-Stevenson method[23]), which salts [(R2N)2Al(py)ϩ]AlCl4Ϫ, as well as of the halide-
normally correspond well with the experimental AlϪX bridged adduct compounds (R2N)2(py)AlϪClϪAlCl3 were
atom distances (X ϭ Cl, Br, I), the bond lengths found for computed (R ϭ Me, Et, iPr, and R2N ϭ tmp). The heats
tmp2AlX·Do (2؊4) are unusually long. They exceed the of formation of the respective minimum geometries and the
sums of their covalent radii by 12 (Cl) to 23 pm (I). The shortest AlϪClAlCl3 distances are presented in Table 4.
932
Eur. J. Inorg. Chem. 1998, 927Ϫ939

Bis(tetramethylpiperidino)aluminum Halide Adducts
FULL PAPER
Figure 6. Molecular structure of 7b in the solid state. Thermal el-
The free cations exhibit positive heats of formation (in
the range ϩ82.5 to ϩ113.1 kcal/mol), whereas the tetra-
chloroaluminum compounds are exergonic by Ϫ231.1 to
Ϫ254.3 kcal/mol. Shielding of the aluminum center by the
amido ligands R2N (R ϭ Me, Et, iPr) is insufficient to pre-
vent coordination of one chlorine atom [d(AlϪCl) of the
lipsoids are shown at a 25% probability level[a]
tetrachloroaluminate to the aluminum center of the cation:
˚
2.41Ϫ2.42 A]. It is only the sterically most demanding am-
ido ligand, tmp, that allows the induction of ionization, as
˚
demonstrated by the shortest AlϪCl distance of 4.45 A. In
another series of calculations, the enthalpies for the forma-
tion of [tmp2Al(py)]AlX4 (X ϭ Cl, Br, I), as well as for the
observed decomposition reactions of the salts into tmp2AlX
and AlX3 ·py, were calculated from the computed heats of
formation of every compound involved (see Scheme 1)
using HessЈ rule.
Scheme 1. AM1 computed heats of formation and enthalpies of
reaction for the formation and decomposition of
[tmp2Al(py)]AlX4 (X ϭ Cl, Br, I)
˚
[a]
Selected atom distances [A] and bond angles [°]: Al1ϪI1
2.500(4), Al1ϪI2 2.508(4), Al1ϪI3 2.510(4), Al1ϪN1 1.947(9);
N1ϪAl1ϪI1 104.8(3), N1ϪAl1ϪI2 106.7(3), N1ϪAl1ϪI3
106.8(3), I1ϪAlϪI2 112.2(1), I1ϪAlϪI3 112.2(2), I2ϪAl1ϪI3
113.5(1).
Figure 7. Molecular structure of 7c in the solid state. Thermal el-
lipsoids are shown at a 25% probability level[a]
˚
[a]
Selected atom distances [A] and bond angles [°]: Al1ϪI1
2.573(2), Al1ϪI2 2.572(2), Al1ϪN1 1.809(5), Al1ϪN2 1.978(5);
N1ϪAl1ϪI1 122.3(2), N1ϪAl1ϪI2 123.5(2), N1ϪAl1ϪN2
106.3(2), I1ϪAlϪN2 103.4(2), I2ϪAlϪN2 101.2(2), I1ϪAl1ϪI2
96.89(6), C1ϪN1ϪAl1 120.1(4), C5ϪN1ϪAl1 118.7(4),
C1ϪN1ϪC5 117.4(5).
Two opposing trends are observed: whereas the heat of
formation for the salt [tmp2Al(py)]AlX4 decreases on going
from the chloride to the iodide (but still remains exergonic),
the enthalpies for the formation of the salts increase in this
direction. In fact, in the case of the iodide, the salt is stable
with respect to decomposition into tmp2AlI and AlI3 ·py.
This is partly due to the thermodynamically less favored
AlϪI bond [E(AlϪCl) ϭ 494 kJ/mol; E(AlϪI) ϭ 364 kJ/
mol][6], but is mainly attributable to the contribution of
electrostatic stabilization of the tetraiodoaluminate, since
the decomposition products, which also contain AlϪX
bonds, are less favored on going from the chloride to the
iodide.
Table 4. AM1 calculated heats of formation of various model com-
pounds
R2N
Heat of formation Heat of formation
Al...ClAlCl3
˚
[(R2N)2Al(py)]ϩ
(R2N)2(py)Al...Cl d(AlϪCl) [A]
ϪAlCl3
Me2N
Et2N
iPr2N
tmp
ϩ113.1 kcal/mol
ϩ93.3 kcal/mol
ϩ82.5 kcal/mol
ϩ90.1 kcal/mol
Ϫ231.1 kcal/mol
2.42
2.41
2.42
4.45
Ϫ251.7 kcal/mol
Ϫ254.3 kcal/mol
Ϫ235.0 kcal/mol
Eur. J. Inorg. Chem. 1998, 927Ϫ939
933

I. Krossing, H. Nöth, H. Schwenk-Kircher
FULL PAPER
As no X-ray crystal structures of the ionic species could AlϪN bond is responsible for the short AlϪN distances in
be determined, an ab initio study (MP2/6-31ϩG*)[30] of 8a, b.
two model compounds [(H2N)2Al(Do)]ϩ (Do ϭ NH3 8a,
Discussion
py 8b) was performed, in order to assess the structural par-
The aim of this study was the synthesis and characteriz-
ameters of these cations. The minimum structures of the
ation of low coordinated, cationic aluminum compounds.
cations 8a, b are depicted in Figure 9, and their structural
parameters are given in Table 5.
In contrast to the R2AlX/tBuNH2 system described by At-
wood et al.[10], the compounds tmp2AlX (X ϭ Cl, Br, I)
Figure 8. Computed structures of [(H2N)2Al(NH3)]ϩ (8a) and
could not be forced to ionize by the addition of an excess
of a donor molecule. The steric demand of the tmp and
[(H2N)2Al(py)]ϩ (8b)
donor ligands prevents the formation of cations of the type
ϩ
tmp2Al(Do)2 and of adducts of the type tmp2AlX·Do2.
However, comparison of the AlϪX bond lengths deter-
mined for 2؊4, having conventional terminal and bridging
AlϪX bonds, reveals that tmp2AlX·Do shows the early
stages of dissociation into [tmp2Al(Do)ϩ]XϪ. Dissociation
of compounds of the type tmp2AlX·Do should be facili-
tated by weakly coordinating anions XϪ. However, such a
Ϫ
strategy did not succeed with X ϭ BPh4Ϫ, B(C6F5)4
,
BF4Ϫ, or tosylate. Instead, decomposition reactions or co-
ordination of the various anions occurred. Nevertheless, the
Table 5. Selected ab initio calculated bonding parameters for the two model cations, 8a,b
Compound[a]
Sym.
d(AlϪN) d(AlϪL)
NϪAlϪN q(Al)
q(N)
[e]
q(L)
[e]
B.O.
AlϪN
LP*[b]
(Al)
˚
˚
[A]
[A]
[°]
[e]
[(H2N)2Al(NH3)]ϩ 8a
[(H2N)2Al(py)]ϩ 8b
Cs
C1
1.758
1.764
1.996
1.947
139.34
136.86
2.12
2.14
Ϫ1.54
Ϫ1.54
Ϫ1.26
Ϫ0.78
0.62
0.60
0.19
0.13
[a]
[b]
All calculations MP2/6-31ϩG*. Ϫ Number of electrons in 3pz orbital of Al.
The tricoordinated aluminum cations 8a, b represent tetrabromo- and tetraiodoaluminates turned out to be suf-
highly charged species [q(Al) ϭ ϩ2.12e and ϩ2.14e, q(N) ϭ ficiently non-basic (and suitably large) to stabilize the salts
Ϫ1.54e and Ϫ1.54e, q(Do-N) ϭ Ϫ1.26e and Ϫ0.78e], with [tmp2Al(Do)]AlX4 (6a؊f) in solution. The formation of the
˚
˚
Ϫ
short AlϪN bond lengths of 1.758 A (8a) and 1.764 A (8b) AlX4 units (X ϭ Br, I) is favoured due to the decreasing
as well as wide NϪAlϪN bond angles of 139.3° and 136.8°, strength of the AlϪX bonds in tmp2AlX·Do on proceeding
respectively. The AlϪN distances to the nitrogen atoms of from chlorine to iodine, so that the additional stabilization
the donor molecules reflect their degree of hybridization. energy provided by ion pair formation governs the overall
As expected, for the sp3-hybridized donor NH3, a longer enthalpy for the decomposition of [tmp2Al(py)]AlI4 (as pre-
˚
AlϪN bond length (1.996 A) was calculated, compared to dicted by AM1 calculation). Since decomposition products
˚
that for the aromatic pyridine donor [d(AlϪN) ϭ 1.947 A]. of even tetraiodoaluminates have been found [e.g. AlI3 ·iq
According to NBO analysis, the 3pz(Al) orbital is populated (7a), AlI3 ·4-tBu-py (7b)], this seems to be contradictory.
with 0.19 (8a) and 0.13 (8b) electrons, indicating the pres- However, the calculations can only simulate gaseous species
ence of only weak pp(π) AlϪN bonding. This compares in vacuo. As the variations in the reaction enthalpies are
well with the calculated minimum structures of (H2N)2AlY small, solvent effects must play a role in the behavior of the
[Y ϭ Cl, OH, SH, NH2, PH2, CH3, SiH3, Al(NH2)2][17]
.
tetrahaloaluminate salts. Nevertheless, both the experimen-
For these compounds, it was shown that the AlϪN bond is tal and theoretical approaches indicate that the iodo com-
highly polar and that the shorter the AlϪN distance, the pounds represent the most stable species. Non-polar sol-
wider the NϪAlϪN bond angle[17]. Since the AlϪN bond vents disfavour the formation of ionic species of type
lengths in 8a, b are 2 pm shorter than in (H2N)2AlCl (9) [tmp2Al(Do)]AlX4 (6a؊f), whereas polar donor solvents
[the compound with the shortest AlϪN bond in the stabilize the ions, but may also abstract AlX3 as
˚
(H2N)2AlY series, d(AlϪN) ϭ 1.782 A], the NϪAlϪN AlX3 ·Do·(Solv.)n (n ϭ 1, 2), providing an alternative de-
bond angles in 8a, b of 139.3° and 136.8° are widened by composition pathway for the system.
about 16° compared to that in the chloride 9 (123.2°). The
Conclusion
short AlϪN bonds are mirrored by an increased positive
charge of 0.16e and 0.18e residing on the aluminum centres
The aluminum atoms in the tricoodinated bis(tetrame-
of 8a, b, compared to that calculated for the chloride 9. thylpiperidino)aluminum halides 1a؊c are Lewis acidic and
Since the charge on the nitrogen atoms in 8a, b, and 9 re- form monoadducts of the type tmp2AlX·Do (2؊4) with
mains almost constant (Ϫ1.53 to Ϫ1.55e), a strongly polar THF and pyridine bases. Since the AlϪX (X ϭ Cl, Br, I)
934
Eur. J. Inorg. Chem. 1998, 927Ϫ939

Bis(tetramethylpiperidino)aluminum Halide Adducts
FULL PAPER
tration of the filtrate to one-third of its original volume, storage at
Ϫ20°C overnight led to the deposition of well-shaped crystals of
2؊4. Precipitates were washed twice with pentane and dried in va-
cuo. Yields varied between 80 and 95%. Where suitable crystals for
X-ray diffraction studies were required, aromatic solvents or
n-hexane/THF mixtures proved to be appropriate media for recrys-
tallization.
bonds in 2؊4 are considerably longer than those in 1a؊c,
a tendency towards dissociation into tmp2(Do)Alϩ and XϪ
is indicated. Attempts to prepare salts of the type [tmp2Al-
(Do)]YϪ [Y ϭ BPh4, B(C6F5)4, Otos] led either to de-
composition or to the formation of molecular adducts. The
solution behavior of tmp2Al(py)BF4 (5e) shows a solvent
dependence: in pentane, a tetracoordinated molecular prod-
uct is observed, while in CH2Cl2 or CDCl3 solution, it dis-
sociates into an ion pair. However, halide abstraction from
tmp2AlX·Do can be achieved by the addition of AlX3 to
generate salts of the type [tmp2Al(Do)]AlX4, as demon-
strated by electrical conductivity in CH2Cl2 solution. These
experimental results are supported by semiempirical AM1
calculations on the [(R2N)2Al(py)]AlX4 species. The results
show that the steric demand of the tmp ligand is essential
for ion pair formation. The formation of tetraiodoalumin-
ate compounds is favored over that of the corresponding
tetrabromo- or tetrachloroaluminates. Further ab initio
studies of some model systems explain the presence of short
AlϪN distances in terms of ionic contributions to the
AlϪN bond. Whether the Lewis acidic aluminum centre in
these cations can act as catalyst, e.g. in olefin polymeriz-
ation, needs to be evaluated experimentally. Since these salts
are highly Lewis acidic, are soluble in aromatic hydro-
carbons, and are sterically encumbered so as to possibly
induce regioselectivity, these aspects will be investigated and
communicated in forthcoming reports.
tmp2AlCl·iq (2a): tmp2AlCl (43.2 ml, 0.11 , 4.8 mmol); isoquin-
oline (0.99 g, 4.8 mmol), yield of 2a: 1.95 g (86%), m.p.
148Ϫ151°C. Ϫ 1H NMR (CDCl3) (400 MHz): δ ϭ 1.37 (t, 8 H,
tmp-β-CH2), 1.29 [s, 24 H, tmp-C(CH3)2], 1.62 (m, 4 H, tmp-γ-
CH2), 7.80 (t, 1 H, iq-CH), 7.93 (m, 3 H, iq-CH), 8.15 (d, 1 H, iq-
CH), 9.14 [d, 1 H, 3J(H,H) ϭ 6.5 Hz, iq-CH], 10.10 (s, 1 H, iq-
CH). Ϫ 13C NMR (CDCl3) (100 MHz): δ ϭ 18.1 (tmp-C4), 34.0
(tmp-C7-10), 41.5 (tmp-C3/5), 52.7 (tmp-C2/6), 122.0 (iq-C), 126.8
(iq-C), 127.7 (iq-C), 129.2 (iq-C), 129.5 (iq-C), 134.3 (iq-C), 137.3
(iq-C), 141.1 (iq-C), 155.1 (iq-C). Ϫ 27Al NMR (CDCl3) (70 MHz):
δ ϭ 102 (∆1/2 ϭ 8300 Hz). Ϫ C27H43AlClN3 (473.10): calcd. C
68.69, H 9.18, N 8.90; found C 67.67, H 8.62, N 8.68.
tmp2AlBr·iq (3c): tmp2AlBr (40.7 ml, 0.27 , 11.0 mmol); isoqui-
noline (2.28 g, 11.0 mmol), yield of 3c: 5.06 g (89%), m.p.
155Ϫ160°C. Ϫ 1H NMR (CDCl3) (400 MHz): δ ϭ 1.41 (t, 8 H,
tmp-β-CH2), 1.37 [s, 24 H, tmp-C(CH3)2], 1.66 (m, 4 H, tmp-γ-
CH2), 7.78 (t, 1 H, iq-CH), 7.94 (m, 3 H, iq-CH), 8.13 (d, 1 H, iq-
CH), 9.18 [d, 1 H, 3J(H,H) ϭ 7.4 Hz, iq-CH], 10.17 (s, 1 H, iq-
CH). Ϫ 13C NMR (CDCl3) (100 MHz): δ ϭ 17.9 (tmp-C4), 34.1
(tmp-C7-10), 41.5 (tmp-C3/5), 52.9 (tmp-C2/6), 121.8 (iq-C), 126.8
(iq-C), 127.7 (iq-C), 129.4 (iq-C), 129.5 (iq-C), 134.2 (iq-C), 137.5
(iq-C), 141.6 (iq-C), 155.7 (iq-C). Ϫ 27Al NMR (CDCl3) (70 MHz):
˜
δ ϭ 109 (∆1/2 ϭ 7500 Hz). Ϫ IR (Nujol) [ν(AlϪBr)]: ν ϭ 332 cmϪ1
Once again, the tmp ligand is found to produce a remark-
able stabilizing effect and allows the generation of unusual
bonding situations, such as the tricoordinated aluminum
cations. As yet, the most weakly coordinating anions
CB11H11XϪ (X ϭ H, Cl) have not been tested[31], but they
are certainly good candidates for achieving the formation
of tmp2Al(Do)ϩ cations, or the even more demanding goal
of generating the dicoordinated cation tmp2Alϩ.
vs. Ϫ C27H43AlBrN3 (516.54): calcd. C 62.78, H 8.39, N 8.13, Br
15.5; found C 58.75, H 8.13, N 7.42, Br 15.9.
tmp2AlI·iq (4b): tmp2AlI (84.9 ml, 0.10 , 8.5 mmol); isoquino-
line (1.76 g, 8.5 mmol), yield of 4b: 3.93 g (82%), 152°C (decomp.
to a black material), m.p. 168°C. Ϫ 1H NMR (CDCl3) (400 MHz):
δ ϭ 1.41 (t, 8 H, tmp-β-CH2), 1.44 [s, 24 H, tmp-C(CH3)2], 1.65
(m, 4 H, tmp-γ-CH2), 7.76 (t, 1 H, iq-CH), 7.93 (m, 3 H, iq-CH),
8.15 (d, 1 H, iq-CH), 9.21 [d, 1 H, 3J(H,H) ϭ 6.4 Hz, iq-CH], 10.21
(s, 1 H, iq-CH). Ϫ 13C NMR (CDCl3) (100 MHz): δ ϭ 17.7 (tmp-
C4), 34.1 (tmp-C7-10), 41.3 (tmp-C3/5), 53.1 (tmp-C2/6), 121.7 (iq-
C), 126.8 (iq-C), 127.5 (iq-C), 129.4 (iq-C), 129.5 (iq-C), 134.0 (iq-
We are grateful to the Fonds der Chemischen Industrie and
Chemetall mbH for supporting our studies. We also thank Mrs. G.
Käser and Mrs. C. Ullmann for performing the elemental analyses,
Mr. P. Mayr, Dr. R. Waldhör and Dr. C. Miller for recording many
NMR spectra, Mrs. D. Ewald for mass spectra and Mrs. E. Kiese-
wetter for IR spectra. Access to the calculation facilities of Leibniz
Rechenzentrum is also acknowledged.
C), 137.2 (iq-C), 141.8 (iq-C), 155.3 (iq-C). Ϫ 27Al NMR (CDCl3)
˜
(70 MHz): δ ϭ 108 (∆1/2 ϭ 8900 Hz). Ϫ IR (Nujol) [ν(AlϪI)]: ν ϭ
341 cmϪ1 vs. Ϫ C27H43AlIN3 (563.54): calcd. C 57.55, H 7.91, N
7.10, I 22.4; found C 56.55, H 7.69, N 7.46, I 22.5.
tmp2AlBr·thf (3a): tmp2AlBr (35.1 ml, 0.27 , 9.5 mmol); THF
(5 ml, excess), yield of 3a: 3.97 g (91%), m.p. 50Ϫ53°C. Ϫ 1H NMR
(C6D6) (270 MHz): δ ϭ 1.45 (s, 24 H, tmp-CH3), 1.31 (t, 8 H, tmp-
β-CH2), 1.58 (m, 4 H, tmp-γ-CH2), 3.76 (br s, 4 H, thf-α-CH2),
1.84 (br s, 4 H, thf-β-CH2). Ϫ 13C NMR (C6D6) (100 MHz): δ ϭ
18.2 (tmp-C4), 34.3 (tmp-C7-10), 40.0 (tmp-C3/5), 52.5 (tmp-C2/
Experimental Section
All manipulations were performed using Schlenk techniques un-
der a dinitrogen or argon atmosphere. All solvents were rigorously
dried prior to use and stored under N2 or argon. Discrepancies in
the elemental analyses of a number of compounds can be attributed
to insufficient protection against oxidation and hydrolysis of the
air- and moisture-sensitive compounds during the weighing pro-
cedures. Ϫ NMR: Bruker ACP 200, Jeol GSX400 and Jeol
GSX270. Ϫ IR: Nicolet FT-IR spectrometer model 6000, CsI
plates, Nujol. Ϫ MS: Varian Atlas CH7 spectrometer.
6), 25.6 (thf-β-CH2), 68.3 (thf-α-CH2). Ϫ 27Al NMR (C6D6) (70
˜
MHz): δ ϭ 125 (∆1/2 ϭ 8080 Hz). Ϫ IR (Nujol) [ν(AlϪBr)]: ν ϭ
342 cmϪ1 vs. Ϫ C22H44AlBrN2O (459.49): calcd. C 57.51, H 9.65,
N 6.10, Al 5.9, Br 17.4; found C 56.01, H 9.65, N 5.81, Al 5.4,
Br 17.1.
General Procedure for the Synthesis of the Adducts tmp2AlX·Do
tmp2AlBr·py (3b): tmp2AlBr (50.0 ml, 0.27 , 13.5 mmol); pyri-
2؊4: The concentrations of stock solutions of tmp2AlX (X ϭ Cl, dine (1.00 g, 13.5 mmol), yield of 3b: 5.98 g (95%), m.p.
Br, I), 1a؊c, in n-hexane were determined by titration of aluminum
121Ϫ125°C. Ϫ 1H NMR (C6D6) (400 MHz): δ ϭ 1.51 (t, 8 H,
and halide. At ambient temperature, the stoichiometric amount of tmp-β-CH2), 1.58 [s, 24 H, tmp-C(CH3)2], 1.74 (m, 4 H, tmp-γ-
the appropriate donor was added as a hexane solution. Most of
the adducts precipitated immediately. After filtration and concen-
CH2), 6.43 (t, 2 H, py-CH), 6.75 (t, 1 H, py-CH), 9.25 (br. s, 2 H,
py-CH). Ϫ 13C NMR (C6D6) (100 MHz): δ ϭ 18.6 (tmp-C4), 34.5
Eur. J. Inorg. Chem. 1998, 927Ϫ939
935

I. Krossing, H. Nöth, H. Schwenk-Kircher
FULL PAPER
(tmp-C7-10), 42.2 (tmp-C3/5), 53.4 (tmp-C2/6), 124.1 (py-C), 140.4 the mixture was cooled to Ϫ78°C. A solution of tmp2AlBr (22.9
(py-C), 150.4 (py-C). Ϫ 27Al NMR (C6D6) (70 MHz): δ ϭ 96 (∆1/
ml, 0.35 , 8.0 mmol) in n-hexane was then added slowly and the
˜
ϭ 4360 Hz). Ϫ IR (Nujol) [ν(AlϪBr)]: ν ϭ 347 cmϪ1 vs. Ϫ mixture was allowed to attain ambient temperature. After stirring
2
C23H41AlBrN3 (466.48): calcd. C 59.22, H 8.86, N 9.01, Al 5.7, Br
17.2; found C 57.59, H 8.74, N 8.49, Al 5.8, Br 16.5.
overnight, the brownish insoluble material was filtered off (2.32 g,
calcd. AgBr 1.61 g) and the resulting yellow filtrate was stored for
several days at Ϫ78°C. Colorless crystals of tmp2Al(lut)(BF4) 5d
separated. Yield: 2.47 g (62%); m.p. > 328°C (decomp.). Ϫ 1H
NMR (C6D6) (400 MHz): δ ϭ 1.23 (t, 8 H, tmp-β-CH2), 1.06 [s,
24 H, tmp-C(CH3)2], 1.53 (m, 4 H, tmp-γ-CH2), 2.41 (s, 6 H, lut-
CH3), 6.57 (d, 2 H, lut-H), 7.00 (t, 1 H, lut-H). Ϫ 13C NMR (C6D6)
(100 MHz): δ ϭ 18.8 (tmp-C4), 32.0 (tmp-C7-10), 38.6 (tmp-C3/
5), 49.6 (tmp-C2/6), 52.4 (lut-CH3), 119.8 (lut-C), 136.9 (lut-C). Ϫ
27Al NMR (C6D6) (70 MHz): δ ϭ 1 (∆1/2 ϭ 3900 Hz). Ϫ 11B NMR
tmp2AlI·py (4a): tmp2AlI (64.5 ml, 0.10 , 6.5 mmol); pyridine
(0.48 g, 6.5 mmol), yield of 4a: 3.17 g (95%), m.p. 134Ϫ137°C. Ϫ
1H NMR (C6D6) (400 MHz): δ ϭ 1.48 (t, 8 H, tmp-β-CH2), 1.62
[s, 24 H, tmp-C(CH3)2], 1.76 (m, 4 H, tmp-γ-CH2), 6.30 (t, 2 H,
py-CH), 6.62 (t, 1 H, py-CH), 9.06 (br s, 2 H, py-CH). Ϫ 13C NMR
(C6D6) (100 MHz): δ ϭ 17.8 (tmp-C4), 34.8 (tmp-C7-10), 42.7
(tmp-C3/5), 53.3 (tmp-C2/6), 125.0 (py-C), 141.9 (py-C), 148.0 (py-
C). Ϫ 27Al NMR (C6D6) (70 MHz): δ ϭ 92 (∆1/2 ϭ 4900 Hz). Ϫ
C23H41AlIN3 (513.48): calcd. C 53.80, H 8.05, N 8.18, Al 5.3, I
24.7; found C 50.73, H 7.46, N 7.60, Al 5.7, I 25.0.
(C6D6) (64 MHz): δ ϭ 17.9. Ϫ 19F NMR (C6D6) (85 MHz): δ ϭ
˜
Ϫ104.5 (s), Ϫ111.0 (s). Ϫ IR (Nujol): ν ϭ 421 w, 452 m, 468 s, 507
vs, 527 vs, 551 vs, 568 s, 596 s, 745 w, 762 w, 851 w, 870 w, 900 m,
918 s, 936 vs, 957 vs, 982 vs, 997 vs, 1064 s, 1082 w, 1130 vs, 1180
s, 1202 m, 1236 vs, 1294 w, 1346 m, 1364 s, 1375 s, 1384 s, 1435 m,
1470 s, 1594 w, 1645 w, 1732 w, 2458 w, 2672 w, 2766 w, 2873Ϫ3007
vs. Ϫ C25H45AlBF4N3 (501.44): calcd. C 59.88, H 9.05, N 8.38, Al
5.4; found C 60.06, H 10.07, N 7.47, Al 6.0.
tmp2AlI·pic (4c): tmp2AlI (32.8 ml, 0.10 , 3.3 mmol); γ-picoline
(0.29 g, 3.3 mmol), yield of 2a: 1.70 g (80%), m.p. 136Ϫ139°C. Ϫ
1H NMR (C6D6) (400 MHz): δ ϭ 1.52 (t, 8 H, tmp-β-CH2), 1.66
[s, 24 H, tmp-C(CH3)2], 1.73 (m, 4 H, tmp-γ-CH2), 1.54 (s, 3 H, γ-
pic-CH3), 6.32 (br s, 2 H, β-pic-CH), 9.27 (br s, 2 H, α-pic-CH). Ϫ
13C NMR (C6D6) (100 MHz): δ ϭ 18.3 (tmp-C4), 34.4 (tmp-C7-
10), 42.2 (tmp-C3/5), 53.5 (tmp-C2/6), 125.0 (β-pic-C), 150.2 (α-
tmp2Al(py)BF4 (5e): To a solution of AgBF4 (1.06 g, 4.96 mmol)
pic-C). Ϫ 27Al NMR (C6D6) (70 MHz): δ ϭ 77 (∆1/2 ϭ 5900 Hz). in 35 ml of CH2Cl2, a solution of tmp2AlI·py (37.0 ml, 0.134 ,
˜
Ϫ IR (Nujol) [ν(AlϪI)]: ν ϭ 318 cmϪ1 s. Ϫ C24H43AlIN3 (527.51): 4.96 mmol) in toluene was added at ambient temperature. Immedi-
calcd. C 54.65, H 8.22, N 7.39; found C 50.98, H 8.13, N 6.75.
ately, a dark precipitate formed. After stirring the mixture over-
night, the insoluble material was filtered off and the filtrate was
concentrated in vacuo. The resulting yellow oil (1.89 g, 80%) was
found to be soluble in aliphatic as well as in aromatic or chlori-
Reaction of tmp2AlI·py 4a with AgBPh4 To Give BPh3 ·py (5b)
and tmp2AlPh (5a): AgBPh4 (0.58 g, 1.36 mmol) was suspended in
10 ml of benzene. A solution of tmp2AlI·py (18.1 ml, 0.075 , 1.36
mmol) in benzene was added at ambient temperature. The mixture
was heated to reflux for 3 days and the insoluble material was fil-
tered off (0.46 g, calcd. AgI: 0.32 g). From the resulting filtrate, all
volatiles were removed in vacuo. The residue was extracted with 20
ml of toluene and this solution was stored overnight at Ϫ78°C. A
microcrystalline precipitate of BPh3·py (5b), (0.17 g, 39%) sepa-
rated; tmp2AlPh (5a) was characterized in solution by its NMR
1
nated solvents. Crystallization could not be achieved. Ϫ H NMR
(CDCl3) (270 MHz): δ ϭ 0.83 (t, 8 H, tmp-β-CH2), 1.23 [s, 24 H,
tmp-C(CH3)2], 1.60 (m, 4 H, tmp-γ-CH2), 7.75 (t, 2 H, py-H), 8.22
(t, 1 H, py-H), 8.71 (br s, 2 H, py-H). Ϫ 27Al NMR (CDCl3) (70
MHz): Only an extremely broad, poorly-defined signal was ob-
served. Ϫ 11B NMR (CDCl3) (64 MHz): δ ϭ 0.9; (pentane): δ ϭ
19.3 (no BF coupling observed). Ϫ 19F NMR (CDCl3) (85 MHz):
1
δ ϭ Ϫ151.0 [q, J(B,F) ϭ 12 Hz]; (pentane): δ ϭ Ϫ111.0 (br s).
data[15]
5b: 1H NMR (C6D6) (270 MHz): δ ϭ 7.25 (t, 3 H, p-Ph-H), 7.32
.
[tmp2Al(iq)]AlBr4 (6a): To a solution of tmp2AlBr·iq in
(t, 6 H, m-Ph-H), 7.51 (d, 6 H, o-Ph-H), 6.15 (br s, 2 H, m-py-H), CH2Br2 (33.1 ml, 0.178 , 5.89 mmol), AlBr3 (1.57 g, 5.89 mmol)
6.57 (br. s, 1 H, p-py-H), 8.15 (br s, 2 H, o-py-H). Ϫ 11B NMR in 10 ml of CH2Br2 was added dropwise at 0°C. After 30 min., the
(C6D6) (64 MHz): δ ϭ 5.1 (br). Ϫ C23H20BN (321.23): calcd. C
86.00, H 6.28, N 4.36; found C 84.20, H 6.61, N 4.28.
clear red solution was reduced to half of its original volume and
stored overnight at Ϫ20°C. 6a separated as an orange microcrystal-
line powder. Yield: 4.43 g (96%), m.p. > 302°C (decomp.). Ϫ 1H
NMR (CDCl3) (270 MHz): δ ϭ 1.34 (t, 8 H, tmp-β-CH2), 1.47 [s,
24 H, tmp-C(CH3)2], 1.62 (m, 4 H, tmp-γ-CH2), 7.94 (t, 1 H, iq-
CH), 8.10 (m, 2 H, iq-CH), 8.28 (d, 1 H, iq-CH), 8.30 (d, 1 H, iq-
CH), 8.94 [d, 1 H, 3J(H,H) ϭ 6.4 Hz, iq-CH], 9.89 (s, 1 H, iq-CH).
tmp2AlOtos·py (5c): To a suspension of AgOtos (1.00 g, 3.6
mmol) and pyridine (0.29 ml, 3.6 mmol) in 30 ml of toluene, a
solution of tmp2AlBr (13.3 ml, 0.27 , 3.6 mmol) in n-hexane was
added at ambient temperature. Immediately, a yellow precipitate of
tmp2AlBr·py separated. The mixture was allowed to stir overnight,
and then the insoluble material, which had become somewhat
brown, was filtered off and weighed (2.41 g, calcd. AgBr 0.67 g).
Extraction with 50 ml of benzene resulted in a yellow solution,
which was concentrated in vacuo to a volume of 10 ml. Storage of
this solution overnight at 8°C afforded tmp2AlOtos·py as a color-
Ϫ
13C NMR (CDCl3) (100 MHz): δ ϭ 17.5 (tmp-C4), 34.2 (tmp-
C7-10), 39.9 (tmp-C3/5), 52.5 (tmp-C2/6), 124.2 (iq-C), 127.0 (iq-
C), 127.5 (iq-C), 130.1 (iq-C), 130.1 (iq-C), 136.4 (iq-C), 137.1 (iq-
C), 137.7 (iq-C), 152.5 (iq-C). Ϫ 27Al NMR (CDCl3) (70 MHz):
δ ϭ 102 (∆1/2 ϭ 66 Hz); (CH2Br2): δ ϭ 104 (∆1/2 ϭ 53 Hz). Ϫ IR
˜
(Nujol) [ν(AlϪBr)]: ν ϭ 429 cmϪ1 vs. Ϫ C27H43Al2Br4N3 (783.24):
1
less precipitate. Yield of 5c: 0.54 g (28%), decomp. > 311°C. Ϫ H
calcd. C 41.40, H 5.53, N 5.36, Al 6.9, Br 40.8; found C 36.01,
H 5.12, N 4.43, Al 7.2, Br 40.7 (C, H, N ratio: calcd. 9:14.33:1;
found 9.48:16.06:1).
NMR (CDCl3) (270 MHz): δ ϭ 1.27 (t, 8 H, tmp-β-CH2), 1.09 [br
s, 24 H, tmp-C(CH3)2], 1.54 (m, 4 H, tmp-γ-CH2) 2.24 (s, 3 H, tos-
CH3), 7.55 (t, 2 H, m-py-H), 7.96 (t, 1 H, p-py-H), 9.29 (br s, 2 H,
o-py-H). Ϫ 13C NMR (CDCl3) (100 MHz): δ ϭ 18.1 (tmp-C4),
33.9 (tmp-C7-10), 40.9 (tmp-C3/5), 52.2 (tmp-C2/6), 21.4 (tos-
CH3), 125.0 (py-C), 141.8 (py-C), 149.8 (py-C), 127.0 (tos-C), 128.3
(tos-C), 128.8 (tos-C), 139.1 (tos-C). Ϫ 27Al NMR (C6D6) (70
MHz): δ ϭ 97 (∆1/2 ϭ 5500 Hz).
[tmp2Al(py)]AlI4 (6b): To AlI3 (0.62 g, 1.5 mmol) dissolved in
5 ml of benzene, a solution of tmp2AlI·py (20.0 ml, 0.075 , 1.5
mmol) in benzene was added at ambient temperature. The mixture
was stirred overnight. Subsequent addition of 5 ml of pentane led
to the precipitation of yellowish 6b. Yield: 1.10 g (79%), decomp.
1
tmp2Al(lut)(BF4) (5d): AgBF4 (1.65 g, 8.5 mmol) and 2,6-luti-
at T > 166 C (blackens). Ϫ H NMR (C6D6) (270 MHz): δ ϭ 1.31
dine (0.86 g, 8.5 mmol) were suspended in 50 ml of n-hexane and (t, 8 H, tmp-β-CH2), 1.48 [s, 24 H, tmp-C(CH3)2], 1.55 (m, 4 H,
936 Eur. J. Inorg. Chem. 1998, 927Ϫ939

Bis(tetramethylpiperidino)aluminum Halide Adducts
FULL PAPER
˜
tmp-γ-CH2), 6.21 (t, 2 H, py-CH), 6.57 (t, 1 H, py-CH), 8.59 (br Hz). Ϫ IR (Nujol) [ν(AlϪI)]: ν ϭ 362 cmϪ1 vs. Ϫ C27H43Al2I4N3
s, 2 H, py-CH). Ϫ 13C NMR (C6D6) (100 MHz): δ ϭ 18.1 (tmp- (783.24): calcd. C 33.39, H 4.46, N 4.33, Al 5.6, I 52.3; found C
C4), 34.5 (tmp-C7-10), 40.2 (tmp-C3/5), 52.9 (tmp-C2/6), 125.5 (py-
35.54, H 4.97, N 3.98, Al 5.2, I 52.8 (C,H ratio: calcd. 1:1.59;
C), 142.2 (py-C), 147.0 (py-C). Ϫ 27Al NMR (C6D6) (70 MHz): found 1:1.65).
˜
δ ϭ 50 (∆1/2 ϭ 134 Hz). Ϫ IR (Nujol) [ν(AlϪI)]: ν ϭ 338 cmϪ1 vs.
[tmp2Al(acr)]AlI4 (6f): To a solution of tmp2AlI (0.81 g, 1.84
Ϫ C23H41Al2I4N3 (921.18): calcd. C 29.99, H 4.49, N 4.56, Al 5.9,
I 55.1; found C 29.55, H 4.62, N 3.67, Al 5.8, I 55.6.
mmol) in 50 ml of CH2Cl2, a solution of acridine (8.80 ml, 0.209
, 1.84 mmol) in CH2Cl2 was added at Ϫ78°C. The mixture was
kept at this temperature for 1 h and then 0.75 g (1.84 mmol) of
[tmp2Al(4-Me-py)]AlI4 (6c): To a solution of tmp2AlI (50 ml,
0.10 , 5.0 mmol) in n-hexane, γ-picoline (0.50 ml, 5.0 mmol) was AlI3 was added in one portion. The suspension was slowly allowed
added at ambient temperature. From the resulting suspension, all
volatiles were removed in vacuo. The residue was redissolved in 50
to warm to ambient temperature and then filtered. From the or-
ange-red filtrate, all volatiles were removed in vacuo. The residue
ml of diethyl ether and the solution was cooled to Ϫ78°C. After was characterized as 6f (1.86 g, 99%). Attempts to crystallize the
the addition of AlI3 powder (2.04 g, 5.0 mmol), the mixture was
product from various solvents were not successful. Ϫ 1H NMR
allowed to warm to ambient temperature (1.5 h). The cloudy solu- (CDCl3) (270 MHz): δ ϭ 1.34 (t, 8 H, tmp-β-CH2), 1.47 [s, 24 H,
tion was filtered and the filtrate was concentrated to a volume of
25 ml. At this stage, the NMR spectra of 6c were recorded by
removal of all volatiles from a portion of the solution in vacuo and
tmp-C(CH3)2], 1.65 (m, 4 H, tmp-γ-CH2), 7.53 (t, 2 H, acr-CH),
7.78 (t, 2 H, acr-CH), 8.01 (d, 2 H, acr-CH), 8.21 (d, 2 H, acr-CH),
8.80 (s, 1 H, acr-CH). Ϫ 13C NMR (CDCl3) (100 MHz): δ ϭ 17.7
redissolving the residue in C6D6. Storage of the filtrate for several (tmp-C4), 34.3 (tmp-C7-10), 39.8 (tmp-C3/5), 52.6 (tmp-C2/6),
weeks at Ϫ78°C afforded colorless crystals of tmp2AlI 1c (2.07 g, 125.8 (acr-C), 126.6 (acr-C), 128.3 (acr-C), 128.8 (acr-C), 136.6
95%) (characterized by its NMR spectra and check of the unit
(acr-C), 148.7 (acr-C). Ϫ 27Al NMR (CDCl3) (70 MHz): δ ϭ Ϫ22
(∆1/2 ϭ 70 Hz); (CH2Cl2): δ ϭ Ϫ27 (∆1/2 ϭ 65 Hz). Ϫ
cell parameters)[15]
.
C31H45Al2I4N3 (1021.28): calcd. Al 5.3, I 49.7; found Al 5.1, I 50.0.
1
6c: H NMR (C6D6) (270 MHz): δ ϭ 1.29 (t, 8 H, tmp-β-CH2),
1.46 [s, 24 H, tmp-C(CH3)2], 1.56 (m, 4 H, tmp-γ-CH2), 1.49 (s, 3
AlBr3 ·acr (7a): To a solution of tmp2AlBr (50 ml, 0.12 , 6.0
H, γ-pic-CH3), 6.12 (d, 2 H, γ-pic-CH), 8.47 (br. s, 2 H, γ-pic-CH). mmol) in n-hexane, a solution of acridine (4.88 ml, 1.23 , 6.0
Ϫ
13C NMR (C6D6) (100 MHz): δ ϭ 18.1 (tmp-C4), 34.5 (tmp- mmol) in toluene was added at ambient temperature. After the ad-
C7-10), 40.0 (tmp-C3/5), 52.8 (tmp-C2/6), 21.3 (γ-pic-CH3) 126.5 dition of AlBr3 (1.60 g, 6.0 mmol), a greenish-yellow precipitate of
(γ-pic-C), 145.9 (γ-pic-C), 156.9 (γ-pic-C). Ϫ 27Al NMR (C6D6) AlBr3 ·acr formed immediately. The insoluble material was filtered
(70 MHz): δ ϭ 51 (∆1/2 ϭ 35 Hz).
off and washed twice with pentane. Yield: 2.40 g (90%); decomp.
at T > 186°C. Ϫ The 27Al-NMR spectrum of the filtrate exhibited
the chemical shift of tmp2AlBr (1b) (d27Al ϭ 130; ∆1/2 ϭ 10200
Hz)[15]. Ϫ 1H NMR (CDCl3) (270 MHz): δ ϭ 7.68 (t, 2 H, acr-H),
7.96 (t, 2 H, acr-H), 8.16 (d, 2 H, acr-H), 8.45 (br d, 2 H, acr-H),
[tmp2Al(4-tBu-py)]AlI4 (6d): To a solution of tmp2AlI (25 ml,
0.10 , 2.5 mmol) in n-hexane, 4-tBu-py (0.36 ml, 2.5 mmol) was
added at ambient temperature. From the resulting suspension of
tmp2AlI·4-tBu-py, all volatiles were removed in vacuo and the yel-
low residue was redissolved in 35 ml of toluene. AlI3 powder (1.01
g, 2.5 mmol) was then added in one portion. The mixture was
stirred for 1 h, then the cloudy solution was filtered. After concen-
tration of the filtrate to one-third of its original volume, the solu-
tion was cooled to Ϫ78°C. NMR spectra of 6d were obtained from
this solution. Even after weeks at various temperatures and at dif-
9.14 (s, 1 H, acr-H). Ϫ 27Al NMR (CDCl3) (70 MHz): δ ϭ 83
˜
(∆1/2 ϭ 38 Hz). Ϫ IR (Nujol) [ν(AlϪBr)]: ν ϭ 404 cmϪ1 vs, 460 vs.
Ϫ C13H9AlBr3N (379.68): calcd. C 35.02, H 2.03, N 3.14; found C
35.59, H 3.18, N 3.28.
AlI3 ·4-tBu-py (7b): A solution of tmp2AlI (51.5 ml, 0.10 , 5.15
mmol) in n-hexane was diluted with a further 150 ml of the solvent.
Then, 4-tBu-py (0.75 ml, 5.15 mmol) was added. To this clear solu-
ferent concentrations, no crystals suitable for X-ray structure deter-
1
mination were formed. Ϫ H NMR (C6D6) (270 MHz): δ ϭ 1.28 tion, powdered AlI3 (2.10 g, 5.15 mmol) was added at ambient tem-
(t, 8 H, tmp-β-CH2), 1.45 [s, 24 H, tmp-C(CH3)2], 1.56 (m, 4 H, perature. On leaving the mixture to stand overnight, a copius
tmp-γ-CH2), 0.69 (s, 9 H, tBu-CH3), 6.35 (d, 2 H, 4-tBu-py-CH), amount of a colorless precipitate was deposited, which was re-
8.54 (br s, 2 H, 4-tBu-py-CH). Ϫ 13C NMR (C6D6) (100 MHz): moved by filtration. Washing the solid with pentane afforded (2.70
δ ϭ 18.1 (tmp-C4), 34.4 (tmp-C7-10), 40.0 (tmp-C3/5), 52.8 (tmp-
g, 96%) of 7b, m.p. 154Ϫ158°C (becomes red). NMR analysis of
1
C2/6), 29.5 (4-tBu-CH3) 127.8 (4-tBu-py-C), 146.6 (4-tBu-py-C), the filtrate showed only the signals of 1c. Ϫ H NMR (C6D6) (400
156.9 (4-tBu-py-C). Ϫ 27Al NMR (C6D6) (70 MHz): δ ϭ 51 MHz): δ ϭ 0.65 [s, 9 H, tBu-C(CH3)3], 6.42 (t, 2 H, py-CH), 8.63
(∆1/2 ϭ 74 Hz).
(d, 2 H, py-CH). Ϫ 13C NMR (C6D6) (100 MHz): δ ϭ 29.3 [tBu-
C(CH3)3], 35.1 [tBu-C(CH3)3], 122.9 (py-C), 146.6 (py-C). Ϫ 27Al
[tmp2Al(iq)]AlI4 (6e): To tmp2AlI·iq (1.71 g, 3.03 mmol) dis-
solved in 15 ml of toluene, a solution of AlI3 (1.24 g, 3.03 mmol)
in 10 ml of toluene was added at a temperature of 5Ϫ10°C. After
stirring for 1.5 h, the mixture was filtered and the clear filtrate
was concentrated to dryness in vacuo. A reddish-brown residue of
NMR (C6D6) (70 MHz): δ ϭ 51 (∆1/2 ϭ 46 Hz). Ϫ IR (Nujol)
˜
[ν(AlϪI)]: ν ϭ 371 cmϪ1 vs, 385 vs. Ϫ C9H13AlI3N (542.89): calcd.
C 19.91, H 2.41, N 2.58; found C 21.08, H 2.88, N 2.63.
tmpAlI2 ·py (7c): To a solution of tmp2AlI·py (28.7 ml, 0.134 ,
[tmp2Al(iq)]AlI4 was obtained. Yield: 2.91 g (99%); m.p. > 330°C 3.85 mmol) in toluene, AlI3 (1.57 g, 3.85 mmol) was added at 0°C
(decomp.). Ϫ 1H NMR (CDCl3) (270 MHz): δ ϭ 1.32 (t, 8 H, tmp- and the mixture was kept stirring overnight. The turbid solution
β-CH2), 1.41 [s, 24 H, tmp-C(CH3)2], 1.61 (m, 4 H, tmp-γ-CH2), was then filtered and the filtrate was concentrated to dryness in
7.91 (t, 1 H, iq-CH), 8.08 (m, 2 H, iq-CH), 8.14 (d, 1 H, iq-CH),
vacuo. The resulting brownish oil was stored for some days at tem-
8.26 (d, 1 H, iq-CH), 8.75 [d, 1 H, 3J(H,H) ϭ 8.4 Hz, iq-CH], 9.70 peratures up to 35°C. After one week, colorless crystals of 7c
(s, 1 H, iq-CH). Ϫ 13C NMR (CDCl3) (100 MHz): δ ϭ 17.6 (tmp- formed. These were isolated from the oil (1.70 g, 88%) and washed
C4), 34.0 (tmp-C7-10), 39.5 (tmp-C3/5), 52.0 (tmp-C2/6), 124.4 (iq-
1
twice with pentane; m.p. > 202°C (decomp.). Ϫ H NMR (C6D6)
C), 127.1 (iq-C), 127.7 (iq-C), 130.1 (iq-C), 130.8 (iq-C), 136.4 (iq- (400 MHz): δ ϭ 1.39 (t, 4 H, tmp-β-CH2), 1.63 [s, 12 H, tmp-
C), 137.0 (iq-C), 137.9 (iq-C), 152.4 (iq-C). Ϫ 27Al NMR (CDCl3) C(CH3)2], 1.60 (m, 2 H, tmp-γ-CH2), 6.26 (t, 2 H, py-CH), 6.59 (t,
(70 MHz): δ ϭ 55 (∆1/2 ϭ 17 Hz); (CH2Cl2): δ ϭ 54 (∆1/2 ϭ 43 1 H, py-CH), 9.05 (br s, 2 H, py-CH). Ϫ 13C NMR (C6D6) (100
Eur. J. Inorg. Chem. 1998, 927Ϫ939
937

I. Krossing, H. Nöth, H. Schwenk-Kircher
FULL PAPER
Table 6. Crystallographic data and details relating to the data collection and structure solution of the compounds examined by X-ray
diffraction analysis
Compound
tmp2AlCl·iq
2a
tmp2AlCl·thf
2b
tmp2AlBr·thf
3a
tmp2AlBr·py
3b
tmp2AlI·py4a AlI3 ·iq
tmpAlI2 ·py
7c
4a
7b
Chem. formula
Form wght.
Cryst. size [mm]
Cryst. system
C27H43AlClN3
472.07
0.4 ϫ 0.5 ϫ 0.5
monoclinic
P21/n
10.685(3)
16.945(1)
14.745(5)
90
100.83(2)
90
C22H44AlClN2O
415.02
0.2 ϫ 0.3 ϫ 0.3
monoclinic
P21/n
7.715(3)
18.396(6)
17.139(6)
90
94.444(5)
90
C22H44AlBrN2O C23H41AlBrN3
C23H40AlIN3
512.46
0.2 ϫ 0.2 ϫ 0.3
monoclinic
C2/c
32.21(1)
11.063(6)
14.886(8)
90
110.394(1)
90
C9H7AlI3N
536.84
0.1 ϫ 0.1 ϫ 0.3
monoclinic
C2/c
20.01(3)
10.23(1)
14.12(2)
90
107.27(5)
90
C14H23AlI2N2
500.12
0.7 ϫ 0.5 ϫ 0.4
monoclinic
P21/n
9.861(3)
18.133(1)
10.113(4)
90
99.41(3)
90
459.48
0.4 ϫ 0.3 ϫ 0.3
monoclinic
P21/n
8.104(3)
16.986(6)
17.576(9)
90
466.48
0.6 ϫ 0.4 ϫ 0.4
monoclinic
C2/c
31.700(1)
11.086(5)
14.671(6)
90
Space group
˚
a [A]
˚
b [A]
˚
c [A]
α [°]
β [°]
98.62(4)
90
2392.1(2)
4
108.64(3)
90
4885.3(3)
8
γ [°]
˚
V [A3]
2622.0(2)
4
1.196
2425.0(2)
4
1.137
4971.2(4)
8
1.369
2759(7)
8
2.585
1784.0(1)
4
1.862
Z
ρcalcd [Mg/m3]
1.276
1.769
1.268
1.732
µ [mmϪ1
]
0.199
0.208
1.337
6.828
3.566
absol.
min./max. transm.
F(000)
Ϫ
Ϫ
1024
Ϫ
Ϫ
912
Ϫ
Ϫ
984
Ϫ
Ϫ
1984
semiempirical
0.621 and 0.851
2120
semiempirical
0.144 and 1.000
1920
semiempirical
0.055, 0.107
960
Index range
0 Յ h Յ 12
0 Յ k Յ 19
Ϫ16 Յ l Յ 16
48.00
Ϫ9 Յ h Յ 9
Ϫ23 Յ k Յ 21
Ϫ21 Յ l Յ 22
58.14
5 Յ h Յ 0
0 Յ k Յ 19
Ϫ19 Յ l Յ 19
47.10
Ϫ35 Յ h Յ 0
0 Յ k Յ 12
Ϫ15 Յ l Յ 16
47.12
Ϫ35 Յ h Յ 35
Ϫ13 Յ k Յ 13
Ϫ18 Յ l Յ 18
54.76
Ϫ24 Յ h Յ 24
Ϫ12 Յ k Յ 12
Ϫ17 Յ l Յ 17
54.78
Ϫ11 Յ h Յ 11
Ϫ3 Յ k Յ 21
Ϫ4 Յ l Յ 12
50.06
2 θ [°]
Temp. [K]
Refl. collected
Refl. unique
233
4267
4030
173
13580
4752
4159
223
2899
2618
2042
213(2)
3709
3636
2581
213
13202
3735
3291
213
7175
2684
1561
223
3081
2948
2667
Refl. observed (4σ) 2191
Rint
No. variables
0.0826
297
0.0416
252
0.0383
252
0.0614
261
0.0725
261
0.0832
127
0.0868
176
Weighting scheme 0.0841/12.9220
0.0225/3.8906
0.1000/0.0000
0.0539/9.6308
0.0622/13.5922
0.1334/18.0998
0.0783/ 5.0904
x/y[a]
GooF
Final R (4σ)
Final wR2
1.025
1.214
1.169
1.034
1.144
1.152
1.088
0.0915
0.2043
0.894
0.0669
0.1332
0.577
0.0479
0.1467
0.658
0.0495
0.1050
0.768
0.0474
0.1116
0.885
0.0669
0.1756
2.760
0.0457
0.1241
1.785
Larg. res. peak
˚
[e/A3]
[a]
wϪ1 ϭ σ2Fo ϩ (xP)2 ϩ yP; P ϭ (Fo ϩ 2Fc )/3.
2
2
2
MHz): δ ϭ 17.6 (tmp-C4), 34.8 (tmp-C7-10), 42.7 (tmp-C3/5), 53.3 be requested by quoting the depository number CSD-101038, the
(tmp-C2/6), 124.9 (py-C), 141.7 (py-C), 148.0 (py-C). Ϫ 27Al NMR
names of the authors, and the full journal citation.
(C6D6) (70 MHz): δ ϭ 69 (∆1/2 ϭ 2640 Hz). Ϫ IR (Nujol)
˜
[ν(AlϪI)]: ν ϭ 315 cmϪ1 vs, 335 vs, 355 vs. Ϫ C14H23AlI2N2
(500.14): calcd. C 33.62, H 4.64, N 4.80; found C 33.40, H 4.80,
N 5.13.
[1]
I. Krossing, Dissertation, University of Munich, 1997.
[2]
Responsible for some X-ray crystal structure determinations.
[3]
J. D. Smith, I. J. Worrall, A. McKillop, Dictionary of Organome-
X-ray Crystal Structure Determinations: Data collection for X-
ray structure determinations was performed on a Syntex P4 or a
tallic Compounds, Chapman and Hall, London 1984؊1989,
Aluminum pp. 9Ϫ120, Gallium pp. 940Ϫ962, Indium pp.
1138Ϫ1151.
Syntex R3 four-circle diffractometer using graphite-monochrom-
˚
[4]
A. Haaland, Angew. Chem. 1989, 101, 1017Ϫ1032; Angew.
ated Mo-Kα (λ ϭ 0.71073 A) radiation. Single crystals were
mounted in Lindemann capillaries and sealed under argon atmos-
phere. Other data collection for X-ray structure determinations was
performed on a Siemens P4 four-circle diffractometer equipped
with a CCD area detector[32]. Single crystals were mounted in poly-
fluoroether oil and fixed on top of a glass fibre. Data was collected
at Ϫ80 to Ϫ100°C. All calculations were performed on PCЈs and
workstations using the Siemens SHELXTL-Plus[33] or SHELX-
93[34] software packages. The structures were solved by direct or
heavy atom methods and successive interpretation of the difference
Fourier maps, followed by least-squares refinement. All non-hydro-
gen atoms were refined anisotropically. The hydrogen atoms were
included in the refinement in calculated positions by a riding model
using fixed isotropic thermal parameters. Data relevant to the crys-
tallography, data collection and refinement are compiled in Table
6. Further details of the crystal structure determinations are de-
posited at the Cambridge Crystallographic Data Centre and may
Chem. Int. Ed. Engl. 1989, 28, 992.
[5] [5a]
P. Pullmann, K. Hensen, J. W. Bats, Z. Naturforsch. Part B
[5b]
1982, 37, 1312Ϫ1316. Ϫ
D. M. Brown, D. T. Stewart, D.
[5c]
E. H. Jones, Spectrochim. Acta 1973, 29a, 213Ϫ217. Ϫ
Dalibart, J. Derouault, M. T. Forel, J. Mol. Struct. 1981, 70,
M.
I. R. Beattie, P. J. Jones, J. A. K. Howard, L.
[5d]
119Ϫ123. Ϫ
E. Smart, C. J. Gilmore, J. W. Akitt, J. Chem. Soc., Dalton
[5e]
Trans. 1979, 528Ϫ541. Ϫ
J. Meunier, M. T. Forel, Can. J.
Chem. 1972, 50, 1157Ϫ1161.
[6]
[6a] A. J. Downs (Ed.), Chemistry of Aluminium, Gallium, Indium
and Thallium, Blackie Academic and Professional, London,
1993. Ϫ [6b] N. N. Greenwood, K. Wade, Friedel-Crafts and Re-
lated Reactions (Ed.: G. Olah), Interscience, New York, 1963.
P. J. Olgren, J. P. Cannon, C. F. Smith Jr., J. Phys. Chem. 1971,
75, 282Ϫ289.
[7]
[8]
L. Jakobsmeier, I. Krossing, H. Nöth, M. J. H. Schmidt, Z.
Naturforsch. Part B 1996, 51, 1117Ϫ1126.
[9]
H. Nöth, R. Rurländer, P. Wolfgardt, Z. Naturforsch. Part B
1982, 37, 29Ϫ35.
[10]
D. A. Atwood, J. Jegler, Inorg. Chem. 1996, 35, 4277Ϫ4282.
938
Eur. J. Inorg. Chem. 1998, 927Ϫ939

Bis(tetramethylpiperidino)aluminum Halide Adducts
FULL PAPER
R. M. Fuoss, C. A. Kraus, J. Am. Chem. Soc. 1933, 55,
2387Ϫ2399.
V. Shomaker, D. P. Stevenson, J. Am. Chem. Soc. 1941, 63,
37Ϫ40.
R. J. Wehmschulte, W. J. Grigsby, B. Schiemenz, R. A. Bartlett,
P. P. Powe r, Inorg. Chem. 1996, 35, 6694Ϫ6702.
I. Krossing, Dissertation, University of Munich, 1997.
M. A. Petrie, P. P. Power, H. V. Rasika Dias, K. Ruhlandt-
Senge, K. M. Waggoner, R. J. Wehmschulte, Organometallics
1993, 12, 1086Ϫ1093.
M. J. Zaworotko, J. L. Atwood, Inorg. Chem. 1980, 19,
268Ϫ271.
J. L. Atwood, P. A. Milton, J. Organomet. Chem. 1973, 52,
275Ϫ279.
Performed with the program Hyperchem, V3.0, Autodesk, 1993.
Performed with the program Gaussian 94, Revision B.2, M. J.
Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. John-
son, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson,
J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G.
Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala,
W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gom-
perts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J.
Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, and J. A.
Pople, Gaussian, Inc., Pittsburgh PA, 1995.
S. H. Strauss, Chem. Rev. 1993, 93, 927Ϫ942.
Siemens Industrial Automation, 1995.
[11]
[22]
[23]
[24]
W. Uhl, J. Wagner, D. Fenske, G. Baum, Z. anorg. allg. Chem.
1992, 612, 25Ϫ33.
[12]
U. Kynast, B. W. Skelton, A. H. White, M. J. Henderson, C. L.
Raston, J. Organomet. Chem. 1990, 384, C1.
[13]
K. Ruhlandt-Senge, P. P. Power, Inorg. Chem. 1991, 30,
2633Ϫ2639.
[25]
[26]
[14]
M. G. Gardiner, M. G. Koutsantonis, S. M. Lawrence, F.-C.
Lee, C. L. Raston, Chem. Ber. 1996, 129, 545Ϫ549.
[15]
I. Krossing, H. Nöth, C. Tacke, M. Schmidt, H. Schwenk,
Chem. Ber. 1997, 130, 1047Ϫ1052.
[27]
[28]
[16]
I. Krossing, H. Nöth, B. N. Anand, Inorg.Chem. 1997, 36,
1979Ϫ1981.
[17]
K. Knabel, I. Krossing, H. Nöth, H. Schwenk-Kircher, M. J.
H. Schmidt-Amelunxen, T. Seifert, unpublished results.
[29]
[30]
[18]
Low local symmetry leads to broad signals and vice versa. See
refs.[19a] and[19b]
.
[19] [19a] J. Mason, Multinuclear NMR, Plenum Press, New York and
[19b]
London, 1987, 259Ϫ278. Ϫ
Chem. 1991, 411, 37Ϫ55.
H. Lehmkuhl, J. Organomet.
[20]
[21]
H. Nöth, B. Wrackmeyer, NMR Spectroscopy of Boron Com-
pounds, Vol. 14 (Eds.: P. Diehl, E. Fluck, R. Korfeld), Springer
Verlag, Berlin, Heidelberg, New York, 1978.
¯
BPh3 ·py (5b) precipitates in triclinic crystals of space group P1
(Z ϭ 2) from benzene/pentane solutions. As the BϪN and CϪC
bonds are isoelectronic, the pyridine and phenyl ligands are site
disordered, so that every phenyl position is occupied to 1/4 by
the pyridine molecule. Therefore, bond lengths cannot be dis-
cussed, but the structure is an additional proof for the reaction
described by Eq. 2b.
[31]
[32]
[33]
PC SHELXTL Rel. 5.03, Siemens Analytical Instruments, Ver-
sion 4.1, 1994.
G. M. Sheldrick, University of Göttingen, 1993.
[97292]
[34]
Eur. J. Inorg. Chem. 1998, 927Ϫ939
939