Synthesis and characterization of the novel AlI compound Al(C5Me4Ph): Comparison of the coordination chemistry of Al(C5Me5) and Al(C5Me4Ph) at d 10 metal centers

Article abstract of DOI:10.1002/zaac.200500129

The synthesis of the novel Al^I compound AlCp*^Ph (Cp*^Ph = C₅Me₄Ph) is presented. This compound is characterized by ¹H, ¹³C, ²⁷Al NMR spectroscopy, elemental analysis as

Full text of DOI:10.1002/zaac.200500129

Synthesis and Characterization of the Novel AlI Compound Al(C5Me4Ph):
Comparison of the Coordination Chemistry of Al(C5Me5) and Al(C5Me4Ph)
at d10 Metal Centers1)
Beatrice Buchin, Tobias Steinke, Christian Gemel, Thomas Cadenbach, and Roland A. Fischer*
Bochum, Ruhr-Universität, Lehrstuhl für Anorganische Chemie II Ϫ Organometallics & Materials Chemistry
Received March 18th, 2005.
Dedicated to Professor Herbert W. Roesky on the Occasion of his 70th Birthday
Abstract. The synthesis of the novel AlI compound AlCp*Ph (Cp*
obtained by reaction of [(tmeda)PdCl2] with AlCp*, and
[Ni(AlCp*)4] is synthesized from [Ni(cod)2] and AlCp* via ligand
substitution. Both complexes are spectroscopically and crystallo-
graphically characterized. Finally, preliminary results on the coor-
dination of AlCp*Ph to Ni0 and Pd0 centers will be discussed.
Ph
ϭ C5Me4Ph) is presented. This compound is characterized by
1H, 13C, 27Al NMR spectroscopy, elemental analysis as well as its
reactivity towards the α,ω-diolefin dvds (dvds ϭ tetramethyl-divi-
nyl-disiloxane). Also the reactivity of AlCp* towards dvds is inves-
tigated and the product [(dvds)(µ2-AlCp*)2] characterized by NMR
spectroscopy, elemental analysis as well as X-ray crystallography.
Furthermore, two new coordination compounds of AlCp* to d10
metal centers are synthesized and characterized. [Pd(AlCp*)4] is
Keywords: Aluminum; Carbenoid ligands; Palladium; Nickel; Co-
ordination chemistry
Introduction
treated a metastable solution of AlCl with MgCp*2 [1]. The
major problem in this route is the preparation of the high
temperature species AlCl, which has to be done by high
temperature gas phase reaction of Al and HCl and rapid
condensation of the product in an excess of a solvent mix-
ture (e.g. toluene/THF). This is a rather sophisticated and
not generally available technique. The credit of having pro-
vided the inorganic chemistЈs community with a more easily
applicable laboratory protocol for the synthesis of AlCp*
goes to Roesky et al. who obtained AlCp* via reductive
dehalogenation of Cl2AlCp* with potassium in 1993 [2].
The rather low yield of this reaction could subsequently be
considerably increased by simply using Br2AlCp* instead of
the chloride derivative and using Na/K alloy as the reducing
agent [3a]. Thus, AlCp* can now be prepared in reproduc-
ible overall yields of 40-50 %, starting from AlBr3 and
Cp*SiMe3. We entered this scene in 1997 when we pub-
lished the synthesis of [(CO)4FeAlCp*] from K2[Fe(CO)4]
and Cl2AlCp* which at that time was the first example of
a AlCp* ligand in a terminal coordination mode at a tran-
sition metal fragment [16]. Since then a number of groups
were active to study the ligand properties of low valent
group-13 species. Our major research interest in the field
has been to obtain homoleptic, i.e. CO-free, metal rich clus-
ter compounds of the general type [Ma(ER)b] and elucidate
their chemistry including the potential of that chemistry for
advanced materials, e.g. nanoclusters of intermetallic com-
pounds MxEy [4]. We have reported on novel clusters of the
types M2(ECp*)5 or M3(ECp*)n (M ϭ Pd, Pt; n ϭ 6, 8),
their structures being without direct precedence in classical
CO or phosphine cluster chemistry [5Ϫ8]. In contrast to the
related Ga and In chemistry, the coordination of AlCp* to
a transition metal centers causes the Al centre to become
Low valent, carbenoid aluminum compounds of the general
type [AlR]n have attracted considerable interest not only be-
cause of fundamental issues in terms of structure and bond-
ing but even more attention is due their unique reactivity
including ligand properties in coordination chemistry. With
increasing atomic number within the group 13, the stability
of EI compounds increases and correspondingly their
chemical reactivity decreases. Thus, amongst all low valent
group 13 species, AlI compounds are unique. In particular,
they are significantly more reactive than GaI, InI or TlI
compounds, what is also reflected by their rich coordination
to transition metals. In general, AlI compounds are very
potent σ-donors and strongly increase the electron density
of transition metal centers on coordination, while the Al
atoms become very electrophilic. In contrast to the poten-
tially even more reactive organo BI compounds, if they were
accessible as monomers, the organo AlI congeners are stable
and isolable and can be used as novel starting compounds
for synthesis. This, of course, especially allows their use as
ligands in coordination chemistry. However, their prep-
aration is neither simple nor straightforward, what made
them chemically inaccessible until as late as the 1990’s. The
first synthesis of AlCp* was reported by Schnöckel, who
* Prof. Dr. R. A. Fischer
Anorganische Chemie II Ϫ Organometallics & Materials
Ruhr-Universität Bochum
D-44780 Bochum (Germany)
Fax (ϩ49)234 321 4174
e-mail: roland.fischer@ruhr-uni-bochum.de
1) Organo group 13 complexes of transition metals XXXVIII; com-
munication XXXVII see Ref. [10].
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Synthesis and Characterization of the Novel AlI Compound Al(C5Me4Ph)
1
very electrophilic and prone to subsequent reactions. Thus,
the reaction of [Ni(cod)2] with AlCp* in benzene does ne-
ither lead to homoleptic monomeric [Ni(AlCp*)4] nor clus-
ter structures [Nia(AlCp*)b], but instead yields a new com-
plex of the formula [Ni(AlCp*)3{AlCp*(Ph)}(H)] by C-H
activation of the solvent [9]. The product was shown to be
formed via the reactive intermediate [Ni(AlCp*)3]. Simi-
larly, the Fe0 source [Fe(η6-toluene)(η4-1,3-butadiene)] re-
acts with AlCp* under full ligand substitution giving un-
usual C-H activated isomers of [Fe(AlCp*)5]. [10] In order
to stabilize reactive intermediates [M(ER*)n] and to study
their chemistry in more detail, increasing the steric bulk of
the Cp*-type ligand appears to be a strategy. Maybe, that
the formation of the kinetically inert, inreactive monomer
[Ni(AlCp*)4] can be suppressed, which compound rep-
resents the thermodynamic sink in all substitution reactions
we have studied so far. In this paper we wish to report on
the synthesis and characterization of the new, bulky ligand
AlCp*Ph as well as the reactions of AlCp* and AlCp*Ph
with the di-olefin dvds (dvds ϭ tetramethyl-divinyl-disilox-
ane). In addition, the coordination chemistry of AlCp* and
AlCp*Ph to Ni0 and Pd0 will be compared looking into their
reactions with [(tmeda)PdCl2] and [Ni(cod)2].
The H NMR spectrum of 2 in C6D6 exhibits two singlets
at 1.92 and 1.77 ppm for the methyl groups and a multiplet
at 7.46-7.15 ppm for the phenyl group. The 13C NMR
shows four signals for the phenyl group (δ ϭ 136.8/131.0/
130.3/126.1) and two sets of signals for the Cp* methyl
groups (δ ϭ 121.8/116.1/ 115.1 and 12.1/11.1). The 27Al
NMR spectrum exhibits one signal at Ϫ102.5 ppm. This
signal is remarkably downfield-shifted with respect to the
27Al NMR signal of [AlCp*]4 (Ϫ81 ppm), but still signifi-
cantly lower than the signals for the monomers
Al[C5(CH2Ph)5] and Al[C5H2(SiMe3)3] (Ϫ155 and Ϫ165
ppm, respectively). [1b] Thus, also the 27Al-NMR does not
lead to definite conclusions concerning the degree of associ-
ation of 2 in solution, but the existence of aggregates other
than [AlCp*Ph]4 cannot be excluded on this basis.
Reaction of AlCp* and AlCp*Ph with dvds
Recently we reported on the synthesis of the novel trinu-
clear compound [Pd3(AlCp*)2(µ2-AlCp*)2(µ3-AlCp*)2],
which was obtained by reaction of [Pd2(dvds)3] with an ex-
cess of AlCp* in benzene at 60 °C [8]. The formation of
monomeric [Pd(AlCp*)4] or dimeric [Pd2(AlCp*)5] was not
observed. During this reaction the colorless product
[(dvds)(µ2-AlCp*)2] (3a) is formed as a by-product, thus ex-
cess AlCp* is consumed by dvds. The independent treat-
ment of free dvds with two equivalents of AlCp* in toluene
at 60 °C in absence of Pd0 complexes affords a colorless
solution. Crystallization at Ϫ30 °C affords 3a as colorless
crystals in a yield of 83 %. Analogously, reaction of dvds
with two equivalents of AlCp*Ph in toluene leads to the
adduct [(dvds)(µ2-AlCp*Ph)2] (3b) in a yield of 60 %. Both
complexes are air sensitive and readily dissolve in non polar
organic solvents such as benzene or toluene (Scheme 2).
Results and Discussion
Synthesis and Characterization of AlCp*Ph (2)
The preparation of AlCp*Ph (2) is carried out analogously
to the procedure published for AlCp*. Compound 2 is syn-
thesized from [Cp*PhAlBr(µ-Br)]2 (1), which is obtained
from Cp*PhSiMe3 and AlBr3 in hexane. Reduction of 2 with
a Na/K alloy in toluene gives a yellow solution and a light
gray precipitate. After filtration and removal of the solvent
in vacuo, the oily residue is recrystallized from diethylether
giving pure 2 as a yellow powder in reproducible yields of
70 % (Scheme 1). The main differences of this procedure to
the classical preparation described in literature for AlCp*
arises from the good solubility of 2 in toluene in contrast
to AlCp*. Compound 2 is also very well soluble in warm
n-hexane. Thus, all attemps to crystallize 2 failed, so far.
No definite conclusions concerning the structure of 2 in
solid state or in solution, i.e. the degree of association, can
be made at this point, but a tetrameric structure [AlCp*Ph
analogously to [AlCp*]4 is assumed.
]
4
Scheme 2 Synthesis of [(dvds)(µ2-AlR)2] (R ϭ Cp* 3a, Cp*Ph 3b)
The 1H NMR spectrum of 3a in C6D6 exhibits two
singlets at 1.96 and 1.95 ppm for the methyl groups of the
two AlCp* ligands. The dvds group shows four signals,
which can be assigned as follows: The four protons of the
two CH2 groups give rise to one broad multiplet due to
geminal and vicinal coupling in the range of 0.55-0.32 ppm.
A broad triplet at Ϫ0.26 ppm (J(H,H) ϭ 8.7 Hz) represents
the CH moieties, and the two singlets at 0.29 and 0.11 ppm
can be assigned to the SiMe2 groups. The 13C NMR spec-
trum reveals two sets of signals for the Cp* groups (δ ϭ
114.3/114.1 and 10.7/10.6). The CH und CH2 groups give
Scheme 1 Preparation of 2
However, the chemical nature of the obtained product 2
was confirmed by NMR spectroscopy, elemental analysis as
well as its chemical reactivity towards the α,ω-diolefin dvds.
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B. Buchin, T. Steinke, Ch. Gemel, Th. Cadenbach, R. A. Fischer
of two AlCp* units to the two CϭC double bonds of one
dvds ligand, resulting in a ninemembered bicyclic ring com-
parable to 9-BBN. Analogous olefin adducts of AlI were
recently synthesized and characterized in the literature [11,
12]. The central C, Si and Al atoms of the bicyclus show
only a small distortion, which is documented by the respect-
ive coordination sphere of these atoms. Thus, the angles C-
Al-C, Al-C-C, Al-C-Si and C-Si-C with values in the range
of 106.24(17)° (C(22)-Al(1)-C(24)) and 118.0(3)° Al(2)-
C(21)-C(22) only slightly deviate from an ideal tetrahedral
environment. As expected, the angle Si(1)-O(1)-Si(2)
(134.50(17)°) is significantly widened. The distances Al(1)-
C(22,24) and Al(2)-C(21,23) are found in the range of
˚
1.991(4)-2.002(4) A, corresponding to the bond lengths in
the Cp*AlIII compounds [{Cp*AlRCl}2] (R ϭ Me 1.931 A
˚
i
˚
[13], R ϭ Pr 1.951 A [14]). The Cp*centroid-Al distances in
3a (Cp*centroid-Al(1) 1.947, Cp*centroid-Al(2) 1.952) are simi-
Figure 1 Molecular structure of [(dvds)(µ2-AlCp*)2] (3a) (thermal
˚
˚
lar to those in [{Cp*AlRCl}2] (1.952 and 1.947 A), while
the Cp*centroid-Al distances in [{Cp*AlCl2}2] (1.871 A) or
ellipsoids set at 30 % probability). Selected bond lengths /A and
˚
angles /°:
Al(1)-C(22) 2.002(4), Al(1)-C(24) 1.991(4), Al(2)-C(21) 1.968(4), Al(2)-C(23)
1.993(4), Si(1)-O(1) 1.656(3), Si(1)-C(22) 1.908(4), Si(1)-C(25) 1.868(5),
C(21)-C(22) 1.551(6), Cp*centroid-Al(1) 1.947, Cp*centroid-Al(2) 1.952, C(22)-
Al(1)-C(24) 106.24(17), C(21)-Al(2)-C(23) 108.64(18), Al(1)-C(22)-C(21)
109.0(3), Al(2)-C(21)-C(22) 118.0(3), Al(1)-C(22)-Si(1) 109.5(2), C(22)-Si(1)-
O(1) 109.26(17), Si(1)-O(1)-Si(2) 134.50(17), C(25)-Si(1)-C(26) 108.6(2),
Al(1)-C(22)-C(21)-Al(2) 54.6(4), Al(1)-C(22)-Si(1)-O(1) 45.6(2).
in the mono substituted metal carbonyls [(CO)5Cr-AlCp*]
˚
˚
(1.819 A) [15] and [(CO)4Fe-AlCp*] (1.775 A) [16] are sig-
˚
nificantly shortened. The bonds C(21)-C(22) (1.551(6) A)
˚
and C(23)-C(24) (1.568(6) A) can be unequivocally ident-
ified as C-C-single bonds. In contrast, in the complex
[(dmi)Pd(dvds)] (dmi ϭ 1,3-dimesitylimidazoline-2-ylidene)
the ligand dvds is π-coordinated, giving C-C distances of
˚
˚
1.408(6) A and 1.388(6) A [17].
rise to two broad resonances at 13.8 and 10.1 ppm, respec-
tively. The two signals at 3.6 und Ϫ0.2 ppm can be assigned
to the SiMe2 moieties. Interestingly, no 27Al signal is visible.
Presumably, the two AlIII resonances are covered by the
broad peak of the probe head (δ ϭ 66.8).
Synthesis of M(AlCp*)4 (M ؍ Ni, Pd) and
Comparison of the Coordination Chemistry of AlCp*
and AlCp*Ph to Pd0 and Ni0
1
The NMR spectra of 3b are very similar to 3a. The H
NMR spectrum of 3b in C6D6 exhibits four singlets at 2.08,
2.03, 2.00 and 1.99 ppm for the Cp*Ph methyl groups and a
multiplet at 7.11-7.49 ppm for the phenyl group. For the
dvds part four signals are found: a broad multiplet at
0.59 ppm for the CH2 groups, two singlets at 0.25 and
0.13 ppm for the SiMe2 groups and a triplet at Ϫ0.13 ppm
for the CH groups. Also in the 13C NMR spectrum, two
sets of signals for the AlCp*Ph ligands are found, indicating
their slightly different chemical environment. Thus there are
eight signals for the phenyl groups (δ ϭ 136.2, 135.9, 131.0,
130.8, 128.9, 128.8, 128.5 and 126.5). The Cp* parts give
rise to overall nine signals (δ ϭ 121.6, 120.3, 117.5, 117.3,
114.7, 114.6 for the ring carbon atoms and 12.1 (2 C), 11.0,
10.9 ppm for the methyl groups). Two broad signals at 14.0
and 10.8 ppm can be assigned to CH and CH2 groups,
respectively. The SiMe2 groups result in two signals (δ ϭ
3.9 and Ϫ0.1). As in the spectrum of 3a there is no 27Al
signal visible.
While numerous M-E compounds with E ϭ Ga or In have
been synthesized in the past decade, only a small number
of examples of transition metal complexes bearing AlCp*
as a ligand are known [9, 16, 18]. In particular, the existing
class of homoleptic clusters [Ma(EIR)b] (M ϭ Ni, Pd, Pt;
E ϭ Al, Ga, In; R ϭ Cp*, C(SiMe3)3) is still focused on
gallium and indium containing ligands. As described above,
the reaction of [Pd2(dvds)3] with an excess of AlCp* leads
to the trimetallic compound [Pd3(AlCp*)6]. Also the di-
nuclear compound [Pd2(AlCp*)5] is accessible, but only “in-
directly” via ligand substitution of GaCp* versus AlCp* in
[Pd2(GaCp*)5] [8]. However, in these ligand substitution re-
actions the formation of the monomeric, saturated com-
pound [Pd(AlCp*)4] was never observed.
Analogously to the synthesis of [Pd(GaCp*)4] and
[Pd{InC(SiMe3)3}4] [6], treatment of [(tmeda)PdCl2] with
exactly five equivalents of AlCp* in hexane at 80 °C for 3 h
results in the formation of the monomeric complex
[Pd(AlCp*)4] (4a) via reductive coordination of AlCp* with
Cl2AlCp* being the by-product (Scheme 3). Crystallization
from hexane at Ϫ30 °C gives 4a as air-sensitive yellow crys-
tals in a good yield of 81 %.
Suitable crystals of 3a can be obtained by stepwise cool-
ing a concentrated solution in toluene to a final tempera-
ture of Ϫ30 °C. Important crystallographic data are sum-
marized in Table 1. The molecular structure of 3a is de-
picted in Figure 1.
As already described in a previous publication, the reac-
tion of [Ni(cod)2] with four equivalents of AlCp* in hexane
at 80 °C leads to a full substitution of the cod ligands, giv-
Compound 3a crystallizes in the orthorhombic space
group Pbca. The molecular structure represents an adduct
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Synthesis and Characterization of the Novel AlI Compound Al(C5Me4Ph)
Scheme 3 Synthesis of [M(AlCp*)4] (M ϭ Pd 4a, M ϭ Ni 4b)
ing the monomeric Ni0 complex [Ni(AlCp*)4] (4b) as yellow
crystals in a yield of 90 % [9]. However, this complex was
not fully discussed in the original communication, and is
therefore included herein and characterized in more detail.
Both complexes dissolve well in non polar organic sol-
vents such as hexane or toluene and decompose at 123 °C
(4a) and 94 °C (4b). The NMR spectra of 4a and 4b are
rather simple, as expected for highly symmetric homoleptic
mixtures of products. However, the fact that no monomers
of the type [M(AlCp*Ph)4] were isolated in the two cases
studied indicates well, that the formation of clusters with a
ratio of Al:M < 4 is favored over that of monomers just by
the small change of one methyl to phenyl in the Cp* ring
of AlCp*.It should be pointed out, that this change also
increases the solubility of [AlCp*Ph]4 very much over the
parent [AlCp*]4 which is likely to have a significant impact
on the kinetics of the reactions. The higher solubility is cer-
tainly a major advantage of AlCp*Ph with respect to the
unsubstituted AlCp*, as reactions can be carried out at
considerably lower temperatures and may be more easily
followed by in situ NMR studies.
1
compounds with η5-coordinated Cp* rings. The H-NMR
spectrum of 4a in C6D6 shows one singlet at 1.92 ppm (4b:
δ ϭ 1.92) and the 13C-NMR shows two resonances at 113.0
(C5Me5) and 10.8 (C5Me5) ppm (4b: δ ϭ 112.9/10.7),
respectively. The 27Al-NMR of 4a in C6D6 shows one broad
resonance at Ϫ67.2 ppm, which is shifted to higher field
compared to 4b (δ ϭ Ϫ37.3).
Structural Properties of 4a and 4b
Analogously to the reaction of [(tmeda)PdMe2] with
GaCp* or InC(SiMe3)3 [6], the reduction of PdII to Pd0 is
accompanied by a transfer of the chlorine atoms to AlCp*,
giving the AlIII side product [Cl2AlCp*], which could be
Suitable crystals of 4a and 4b could be obtained by stepwise
cooling a concentrated solution in hexane to a final tem-
perature of Ϫ30 °C. Important crystallographic data are
summarized in Table 1. The molecular structures of 4a and
4b are depicted in Figure 2 (as the structural differences of
4a and 4b are very small, both compounds are displayed in
one Figure). Both complexes crystallize in the tetragonal
1
characterized by means of H (δ ϭ 1.86) and 13C NMR
(δ ϭ 116.1/11.0) spectroscopy. The reaction of [(tmed-
a)PdMe2] with AlCp* affords several still unidentified prod-
ucts with only a small content of 4a, showing that methyl
transfer from Pd is less selective for Al in comparison with
Ga or In [6]. However, treatment of [(tmeda)PdCl2] with
GaCp* or InCp* leads to [Cl2ECp*] (E ϭ Ga, In), but these
reactions are again less selective with respect to the forma-
tion of [M(ECp*)4] and the yields are considerable lower [6,
7]. Preliminary investigations on the coordination chemistry
of AlCp*Ph show that it represents a very reactive ligand
which is thus quite difficult to handle.
¯
space group I 4 (Z ϭ 2) and are isostructural to all known
monomeric complexes of the type [M(ECp*)4] [6, 9, 21].
The transition metal atom is tetrahedrally surrounded by
four Al atoms with a Al-M-Al angle of 109.26(3)° (4a) and
˚
109.43(2)° (4b) and a M-Al distance of 2.2950(9) A (4a) and
˚
2.1727(8) A (4b). The Cp* units are nearly symmetrically
bonded to the Al atoms with a Al-Cp*centroid distance of
˚
˚
1.929 A (4a) and 1.933 A (4b), being close to the free ligand
In many examples we could show, that the formation of
cluster complexes [Ma(ECp*)b] is very sensitive to the reac-
tion conditions and often a mixture of inseparable products
is obtained. Only small “windows” of optimal reaction con-
ditions allow the isolation of defined clusters such as
[Pd3(GaCp*)8] or [Pd3(AlCp*)6]. This is obviously also the
case for the more bulky AlCp*Ph. Reaction of [(tmed-
a)PdCl2] with AlCp*Ph in C6D6 results in a dark red solu-
˚
of 2.015 A (gasphase, monomer) [22].
A small deviation from linearity is observed for the
Cp*centroid-Al(1)-Pd(1) angles (169.2°). This value is similar
to the arrangement in 4b (173.5°), while homoleptic GaCp*
substituted complexes such as [Pt(GaCp*)4] (160.7°) [6],
[Pd(GaCp*)4] (155.5°) [6] and [Ni(GaCp*)4] (164.7°) [21]
show a significant larger distortion from linearity.
1
tion. The H NMR spectrum of this reaction mixture indi-
cates free tmeda as well as several Pd-Al containing species,
which could neither be separated nor identified. These ob-
servations accentuate once more the delicate complexity of
the insertion reactions of EIR into M-X bonds, which we
have more extensively studied for the transition metals Rh
and Ru [19, 20]. Similar, the reaction of [Ni(cod)2] with
AlCp*Ph in either hexane or C6H6 leads to unidentifiable
Conclusions
In this paper we presented the isolation and characteriz-
ation of the new AlI compound AlCp*Ph. The reaction of
AlCp* with the diolefin dvds leads to an adduct of two
AlCp* units to the two CϭC double bonds of one dvds
ligand, resulting in a ninemembered bicyclic ring system.
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B. Buchin, T. Steinke, Ch. Gemel, Th. Cadenbach, R. A. Fischer
[Ni(cod)2] [23], [(tmeda)PdCl2] [24], Cp*H [25, 26], Cp*PhH [27],
and AlCp* [2, 3] were prepared according to recent literature meth-
ods. Elemental analyses were performed by the Microanalytical
Laboratory of the Ruhr-Universität Bochum. Melting or decompo-
sition points were determined thermogravimetrically on a Seiko
EXSTAR 6300S11 TG/DTA instrument. NMR spectra were re-
corded on
a
Bruker Avance DPX-250 spectrometer (1H,
250.1 MHz; 13C, 62.9 MHz) in C6D6 at 298 K unless otherwise
stated. Chemical shifts are given relative to TMS and were refer-
enced to the solvent resonances as internal standards.
The crystal structures of 3a, 4a and 4b were measured on an Oxford
˚
Excalibur 2 diffractometer using MoKα radiation (λ ϭ 0.71073 A).
The structures were solved by direct methods using SHELXS-97
and refined against F2 on all data by full-matrix least-squares with
SHELXL-97.
CCDC-265832 (3a), CCDC-265833 (4a) and CCDC-265834 (4b)
contain the supplementary crystallographic data for this paper.
These data can be obtain free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax:
(ϩ44)1223-336-033; or deposit@ccdc.cam.uk).
Figure 2 Molecular structure of [M(AlCp*)4] (M ϭ Pd 4a, M ϭ Ni
4b) (thermal ellipsoids set at 30 % probability). Selected bond
lengths /A and angles /° for
4a: Pd(1)-Al(1) 2.2950(9), Al(1)-C(1) 2.284(3), Al(1)-C(2) 2.284(3), Al(1)-
C(3) 2.267(3), Al(1)-C(4) 2.256(3), Al(1)-C(5) 2.265(3), Cp*centroid-Al(1)
1.929, Al(1)-Pd(1)-Al(2) 109.26(3), Cp*centroid-Al(1)-Pd(1) 169.2.
˚
[Cp*PhAlBr(µ2-Br)]2 (1)
A
suspension of K(C5Me4Ph) (14.0 g, 59.2 mmol) in THF
(150 mL) was treated dropwise with Me3SiCl (6.5 g, 59.8 mmol).
The mixture was allowed to stir for 2 h at room temperature. The
white precipitate was removed by filtration through Celite and
washed twice with THF (2 x 20 mL). The washings and filtrate
were combined and the solvent removed in vacuo to give
(C5Me5Ph)SiMe3 as yellow liquid (estimated yield: 11.7 g, 95 %).
Subsequently, a suspension of AlBr3 (11.0 g, 41.2 mmol) in hexane
(250 mL) was treated slowly (1h) with (C5Me5Ph)SiMe3 (12.9 g,
47.7 mmol) at room temperature according to literature. After re-
fluxing the mixture for 3 h, the solvent was removed by means of
cannulation. The residue was washed with hexane (2 x 20 mL).
Recrystallization in hexane gave the product as white solid. Yield:
9.56 g (60 %).
4b: Ni(1)-Al(1) 2.1727(8), Al(1)-C(1) 2.286(3), Al(1)-C(2) 2.285(3), Al(1)-
C(3) 2.273(3), Al(1)-C(4) 2.270(3), Al(1)-C(5) 2.273(3), Cp*centroid-Al(1)
1.933, Al(1)-Ni(1)-Al(2) 109.43(2), Cp*centroid-Al(1)-Ni(1) 173.5.
The same product is obtained by reaction of AlCp*Ph with
1
dvds, as indicated by H and 13C NMR spectroscopy, con-
firming the chemical nature of 2.
In contrast to AlCp*, the reaction of AlCp*Ph with [(tme-
da)PdCl2] as well as [Ni(cod)2] did not lead to monomers
of the type [M(AlCp*)4]. The steric bulk which is the result
of the substitution of one methyl group in AlCp* to one
phenyl group does not allow the coordination of four ligand
units to one metal center, thus suppressing the formation
of monomers and leading to the formation of clusters.
However, the general sensitivity of cluster formation did not
allow the isolation of defined cluster complexes. Investi-
gations on the reaction of AlCp*Ph towards more reactive
M0 sources such as [Ni(cdt)] (cdt ϭ t,t,t-cyclododecatriene)
or [Ni(C2H4)3], which are expected to allow very mild reac-
tion conditions, are subject of current research. It should
be pointed out finally, that the corresponding reactions of
GaCp*Ph with the above mentioned Ni0 and Pd0 sources
have been studied also and a number of well defined prod-
ucts, including for example [Pd2(GaCp*Ph)5] have been ob-
taind on which subject we will report elsewhere.
AlCp*Ph (2)
A Na/K alloy prepared from sodium (0.40 g, 17.4 mmol) and pot-
assium (1.26 g, 32.4 mmol) in toluene (10 mL) was treated with a
suspension of [Cp*PhAlBr(µ-Br)]2 (9.56 g, 24.9 mmol) in toluene
(30 mL) according to literature. The mixture was allowed to stir for
15 h at room temperature. The resulting gray solid was removed by
filtration, and washed with toluene (3 x 20 mL). The solvent was
removed in vacuo to give a yellow oil. The oil was dissolved in
hexane and the solvent again removed in vacuo. The residue was
recrystallized in diethylether to give a yellow solid. Yield: 4.1 g
(73 %). Elemental analysis calcd (%) for C15H17Al: C 80.33, H 7.64;
found: C 79.83, H 8.86.
1H NMR: (C6D6, 250 MHz, 25 °C): δ ϭ7.35 (m, 5 H), 1.92 (s, 6 H), 1.77 (s,
6 H). 13C NMR (C6D6, 62.9 MHz, 25 °C): δ ϭ 136.8 (C5Me4Ph, 1 C), 131.0
(C5Me4Ph, 2 C), 130.3 (C5Me4Ph, 1 C), 126.1 (C5Me4Ph, 2 C), 121.8
(C5Me4Ph, 1 C), 116.1 (C5Me4Ph, 2 C), 115.1 (C5Me4Ph, 2 C), 12.1
(C5Me4Ph, 2 C), 11.1 (C5Me4Ph, 2 C). 27Al NMR (C6D6, 65.2 MHz, 25 °C):
δ ϭ Ϫ102.5.
Experimental Section
All manipulations were carried out in an atmosphere of purified
argon using standard Schlenk and glove box techniques. Hexane,
toluene, THF and Et2O were dried using an mBraun Solvent Puri-
fication System, all other solvents were dried by distillation over
standard drying agents. The final H2O content in all solvents used
was checked by Karl-Fischer-Titration and did not exceed 5 ppm.
[(dvds)(µ2-AlCp*)2] (3a)
A mixture of dvds (0.144 g, 0.774 mmol) and [{AlCp*}4] (0.250 g,
0.387 mmol) in toluene (5 mL) was warmed to 60 °C for 1 h. The
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Synthesis and Characterization of the Novel AlI Compound Al(C5Me4Ph)
Table 1 Crystallographic data for [(dvds)(µ2-AlCp*)2] (3a) and [M(AlCp*)4] (M ϭ Pd 4a, M ϭ Ni 4b)
[(dvds)(µ2-AlCp*)2] (3a)
[Pd(AlCp*)4] (4a)
[Ni(AlCp*)4] (4b)
formula
C28H48Al2OSi2
510.80
103(2)
C50H75Al5Pd
755.20
213(2)
C40H60Al4Ni
707.51
213(2)
MT /g molϪ1
T /K
crystal system
space group
orthorhombic
Pbca
17.196(10)
15.346(8)
22.706(9)
90
90
90
5992(5)
8
tetragonal
I 4
12.178(2)
12.178(2)
15.015(5)
90
90
90
2226.6(9)
2
1.126
tetragonal
I 4
12.1322(19)
12.1322(19)
14.867(5)
90
90
90
2188.2(9)
2
1.074
¯
¯
˚
a /A
˚
b /A
˚
c /A
α /°
β /°
γ /°
3
˚
V /A
Z
ρcalc. /g cmϪ3
µ /mmϪ1
F (000)
2 θ /°
1.133
0.195
2224
0.519
796
0.547
760
3.20 Ϫ 25.10
Ϫ19ՅhՅ20,
Ϫ18ՅkՅ13,
Ϫ27ՅlՅ25
27732
5315 [Rint ϭ 0.0989]
0.958
R1 ϭ 0.0603,
wR2 ϭ 0.1245
R1 ϭ 0.1260,
wR2 ϭ 0.1493
2.15 Ϫ 25.00
Ϫ14ՅhՅ14,
Ϫ7ՅkՅ14,
Ϫ17ՅlՅ11
3002
1921 [Rint ϭ 0.0183]
1.057
R1 ϭ 0.0266,
wR2 ϭ 0.0645
R1 ϭ 0.0279,
wR2 ϭ 0.0651
2.74 Ϫ 24.99
Ϫ14ՅhՅ10,
Ϫ14ՅkՅ6,
Ϫ17ՅlՅ17
2809
1809 [Rint ϭ 0.0250]
1.044
R1 ϭ 0.0414,
wR2 ϭ 0.0983
R1 ϭ 0.0442,
wR2 ϭ 0.1015
index ranges
Reflection collected
Reflections unique
goodness-of-fit on F2
Final R indices
[I>2σ(I)]
R indices (all data)
resulting colorless solution was slowly cooled to Ϫ30 °C, where-
upon crystals are formed. The colorless crystals were isolated by
means of cannulation, washed twice with a small amount of cold
hexane and dried in vacuo. Yield: 0.326 g (83 %). m.p. 103 °C (de-
comp.). Elemental analysis calcd (%) for C28H48Al2Si2O: C 65.84,
H 9.47; found: C 65.57, H 9.32.
1H NMR (C6D6, 250 MHz, 25 °C): δ ϭ 1.96 (s, 15 H), 1.95 (s, 15 H), 0.55-
0.32 (m, 4 H), 0.29 (s, 6 H), 0.11 (s, 6 H), Ϫ0.26 (t, J(H-H) ϭ 8.7 Hz, 2 H).
13C NMR (C6D6, 62.9 MHz, 25 °C): δ ϭ 114.3 (C5Me5), 114.1 (C5Me5), 13.8
(CH), 10.7 (C5Me5), 10.6 (C5Me5), 10.1 (CH2), 3.6 (SiMe2), Ϫ0.2 (SiMe2).
resulting yellow precipitate was dissolved in hexane and the prod-
uct was crystallized by slow cooling to Ϫ30 °C. Yield: 0.312 g
(81 %). m.p. 123 °C (decomp.). Elemental analysis calcd (%) for
C40H60AlPd: C 63.62, H 8.01; found: C 64.01, H 8.32.
1H NMR (C6D6, 250 MHz, 25 °C): δ ϭ 1.92(s, 60 H). 13C NMR (C6D6,
62.9 MHz, 25 °C): δ ϭ 113.0 (C5Me5), 10.8(C5Me5). 27Al NMR (C6D6,
65.2 MHz, 25 °C): δ ϭ Ϫ67.2.
[Ni(AlCp*)4] (4b):
A suspension of [Ni(cod)2] (0.100 g, 0.364 mmol) and [{AlCp*}4]
(0.234 g, 0.364 mmol) in hexane (8 mL) was refluxed for 3 h, where-
upon an orange solution is formed. After filtration, the yellow solu-
tion was cooled to Ϫ30 °C, giving the product as a yellow crystal-
line solid. Yield: 0.312 g (81 %). m.p. 94 °C (decomp.). Elemental
analysis calcd (%) for C40H60AlNi: C 67.92, H 8.49; found: C 67.67,
H 8.54.
[(dvds)(µ2-AlCp*Ph)2] (3b)
A solution of Cp*PhAl (200 mg, 0,892 mmol) in toluene (5 mL) was
treated with dvds (84 mg, 0,450 mmol). After warming the yellow
solution for 1h a colorless solution was obtained. The solvent was
removed in vacuo. The residue was dissolved in hexane and the
solvent again removed in vacuo to give a white oil. Yield: 110 mg
(60 %).
1H NMR: (C6D6, 250 MHz, 25 °C): δ ϭ Ϫ0.13 (t, 2 H), 0.13 (s, 6 H), 0.25
(s, 6 H), 0.59 (d, 4 H), 1.99 (s, 6 H), 2.01 (s, 6 H), 2.03 (s, 6 H), 2.08 (s, 6 H),
7.35 (m, 10 H). 13C NMR (C6D6, 62.9 MHz, 25 °C): δ ϭ 136.2 (C5Me4Ph,
1 C), 135.9 (C5Me4Ph, 1 C), 131.0 (C5Me4Ph, 2 C), 130.8 (C5Me4Ph, 2 C),
128.9 (C5Me4Ph, 2 C), 128.8 (C5Me4Ph, 1 C), 128.5 (C5Me4Ph, 1 C), 126.5
(C5Me4Ph, 2 C), 121.6 (C5Me4Ph, 1 C), 120.3 (C5Me4Ph, 1 C), 117.5
(C5Me4Ph, 2 C), 117.3 (C5Me4Ph, 2 C), 114.7 (C5Me4Ph, 2 C), 114.6
(C5Me4Ph, 2 C), 15.0 (CH), 13.8 (CH), 12.8 (CH2), 12.1 (C5Me4Ph, 2 C),
11.0 (C5Me4Ph, 1 C), 10.9 (C5Me4Ph, 1 C), 10.8 (CH2), 3.9 (SiMe2), Ϫ0.1
(SiMe2).
1H NMR (C6D6, 250 MHz, 25 °C): δ ϭ 1.92(s, 60 H). 13C NMR (C6D6,
62.9 MHz, 25 °C): δ ϭ 112.9 (C5Me5), 10.7(C5Me5). 27Al NMR (C6D6,
65.2 MHz, 25 °C): δ ϭ Ϫ37.7.
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