Beryllium dichloride coordination by nitrogen donor molecules

Article abstract of DOI:10.1515/znb-2003-0127

The reaction of anhydrous beryllium chloride with nitrogen donors L in diethylether as a solvent under mild conditions affords 1:2 complexes of the type L₂BeCl₂ [L = benzonitrile (1), pyridine (2), 3,5-dimethylpyridine, pyrrolidine, piperidine (8), and diethylamine (10)]. Structural studies of compounds 1, 2, 8 (CHCl₃), and 10 have shown that the complexes have the beryllium centers N₂Cl₂-tetracoordinated with a distorted tetrahedral geometry of the core unit. In crystals of 8 and 10 these molecules are associated to form helical strings via distinct N-H-Cl hydrogen bonding. The reaction of the weak donor pyrazole (pyz) with (Et₂O)₂BeCl₂ at low temperature gives the mixed complex [(Et₂O)(pyz)BeCl₂] (4), in which one diethylether molecule is retained in the inner coordination sphere of the metal. In tetrahydrofuran (thf) solution, no reaction is observed with pyrazole, indicating that tetrahydrofuran is the stronger donor as compared to pyrazole, and the (thf)₂BeCl₂ solvate remains intact. By contrast, with the strong base pyrrolidine (pyrr) the same reaction leads to substitution of one chloride ligand to give the ionic product [(pyrr)₃BeCl]⁺Cl^-, (7). Both products (4, 7) have been structurally characterized. At room temperature the reactions with pyrazole or piperidine lead to ether cleavage as a side-reaction which may even become dominant at long reaction times and more forcing conditions. Dinuclear complexes of the type [LBeCl(μ₂-OR)]₂ are formed, the structures of which have also been determined. The results suggest that hydrogen bonding may assist in the ether cleavage process, since this reaction is not observed for ligands devoid of N-H functions.

Full text of DOI:10.1515/znb-2003-0127

Beryllium Dichloride Coordination by Nitrogen Donor Molecules
Martina P. Dressel, Stefan Nogai, Raphael J. F. Berger, and Hubert Schmidbaur
Anorganisch-chemisches Institut der Technischen Universita¨t
Mu¨nchen, Lichtenbergstraße 4, 85747 Garching, Germany
Reprint requests to Prof. Dr. H. Schmidbaur. E-mail: H.Schmidbaur@lrz.tum.de
Z. Naturforsch. 58b, 173 – 182 (2003); received December 20, 2002
The reaction of anhydrous beryllium chloride with nitrogen donors L in diethylether as a solvent
under mild conditions affords 1:2 complexes of the type L2BeCl2 [L = benzonitrile (1), pyridine (2),
3,5-dimethylpyridine, pyrrolidine, piperidine (8), and diethylamine (10)]. Structural studies of com-
pounds 1, 2, 8 (CHCl3), and 10 have shown that the complexes have the beryllium centers N2Cl2-
tetracoordinated with a distorted tetrahedral geometry of the core unit. In crystals of 8 and 10 these
molecules are associated to form helical strings via distinct N-H–Cl hydrogen bonding. The reaction
of the weak donor pyrazole (pyz) with (Et2O)2BeCl2 at low temperature gives the mixed complex
[(Et2O)(pyz)BeCl2] (4), in which one diethylether molecule is retained in the inner coordination
sphere of the metal. In tetrahydrofuran (thf) solution, no reaction is observed with pyrazole, indicat-
ing that tetrahydrofuran is the stronger donor as compared to pyrazole, and the (thf)2BeCl2 solvate
remains intact. By contrast, with the strong base pyrrolidine (pyrr) the same reaction leads to substi-
tution of one chloride ligand to give the ionic product [(pyrr)3BeCl]+Cl−, (7). Both products (4, 7)
have been structurally characterized. At room temperature the reactions with pyrazole or piperidine
lead to ether cleavage as a side-reaction which may even become dominant at long reaction times and
more forcing conditions. Dinuclear complexes of the type [LBeCl(µ2-OR)]2 are formed, the struc-
tures of which have also been determined. The results suggest that hydrogen bonding may assist in
the ether cleavage process, since this reaction is not observed for ligands devoid of N-H functions.
Key words: Beryllium Dichloride Coordination, Nitrogen Donor Molecules
Introduction
were all obtained from non-aqueous media [21– 24].
With very few entries in crystallographical data bases
[25], the knowledge of structural details has remained
very limited [26– 28]. In the present preparative and
structural study, a series of representative nitrogen-
functional molecules have been selected to probe the
donor-acceptor interactions with anhydrous beryllium
chloride in diethylether as a solvent (and a ligand).
Nitriles [29], pyridines [30, 31] and pyrazoles, and
secondary or tertiary amines [32, 33] are substrates
with uni-, di- and tri-coordinated nitrogen donor atoms
which become di-, tri- and tetracoordinated in the prod-
ucts, respectively.
Although diethylether was expected to be an
“innocent” oxygen-donor solvent as compared to wa-
ter, the investigations have shown that weakly basic
nitrogen-donors may not be able to fully displace the
ether ligands attached to the beryllium atoms. More-
over, donor-assisted ether cleavage may also occur
After a multi-decade slow-growth period there is
renewed interest in the chemistry of beryllium ow-
ing to an increase in applications of the element and
its compound in various technologies. Recent stud-
ies have focussed mainly on the solid state chem-
istry chemistry [1] and on the coordination chem-
istry in aqueous solutions [2 – 4]. From these stud-
ies it is obvious that the coordination chemistry of
the small and hard Be2+ cation by fluoride and by
oxygen donor components is by far the most impor-
tant area. The chemistry of beryllium with oxygen-
functional ligands is also of prime interest regard-
ing the toxicity of the metal [5 – 10]. It appears that
in complexes or solvation cages with multifunctional
O/S/N-ligands, like amino acids or peptides, beryl-
lium is coordinated solely to the oxygen donor centers
[11– 20].
The compounds with beryllium-nitrogen linkages even under mild conditions to give ethoxy-beryllium
described in the literature are very few in number and species.
c
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174
M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
Crystals of (PhCN)2BeCl2 are monoclinic, space
group P2/n with Z = 2 molecules in the unit cell.
The asymmetric unit contains one half of the molecule
with the other half generated by a twofold axis pass-
ing through the beryllium atom and bisecting the Cl-
Be-Cl’ angle (Fig. 1). The Be-N distance is 1.740(3),
˚
the Be-Cl distance 1.9685(19) A, and the angles N-
Be-N’ and Cl-Be-Cl’ are 102.1(2) and 117.68(17)◦, re-
spectively. The (N2Cl2)Be tetrahedron is therefore sig-
nificantly distorted with a smaller angle between the
nitrogen atoms and a much larger angle between the
chlorine atoms. The nitrile triple bond has a length of
˚
˚
1.145(2) A as compared to 1.138 A in the free PhCN
molecule [34]. These details corroborate the data doc-
umented for (MeCN)2BeCl2 and show that there is lit-
tle influence of the nitrile substituent (Me vs. Ph) on
the coordinative bonding in the (N2Cl2)Be core unit.
The packing of the molecules in the crystal shows no
anomalies.
Fig. 1: Molecular structure of (PhCN)2BeCl2 (1). The two
halves of the adduct are related by a twofold axis pass-
ing through the beryllium atom and bisecting the N-Be-
◦
˚
N’ angle. Selected bond lengths [A] and angles [ ]: Be-
Cl 1.9685(19), Be-N 1.740(3), C1-N 1.145(2); Cl-Be-Cl’
117.68(17), N-Be-N’ 102.1(2). Be-N-C1 178.78(17), N-
C1-C11 179.8(2).
Results and Discussion
Pyridine coordination
Nitrile coordination
From early work (1925, [29]) it is also known
that beryllium chloride can be dissolved in pyridine
(pyr) as an adduct the nature of which has not been
fully established. In later studies the structure of
(pyr)2Be(SCN)2 has been determined which was ob-
tained from (MeCN)2Be(SCN)2 and pyridine [27].
(pyr)2BeCl2, (2), has now been prepared from
the components in a pyridine/benzene or pyri-
dine/diethylether mixed solvent [2:3 or 1:1], from
which it was obtained as colourless, hygroscopic
crystals.
It has been reported as early as 1925 that anhydrous
BeCl2 can be dissolved in nitriles [29]. For acetonitrile
the existence of a 2:1 adduct has been confirmed by an-
alytical data and the structure of the complex has later
been determined [28]. In the present study therefore no
diethylether solvent was employed for the reaction of
BeCl2 with excess benzonitrile. The reaction was in-
vestigated in order to determine the extent of the chlo-
ride substitution with an excess of nitrile under forc-
◦
ing conditions (boiling point of PhCN: 190 C). Pale-
The same reaction was carried out with 3,5-
dimethylpyridine in diethylether and shown to give the
corresponding ◦2:1 adduct [(3,5-Me2C5H3N)2BeCl2
(3), m. p. 197 C, 79% yield]. The product was iden-
tified by analytical and spectroscopic data, but no sin-
gle crystals could be grown. With regard to the ob-
servations made with piperidine (below) it should be
noted that there was no evidence for cleavage of the
diethylether solvent molecules with excess pyridine or
3,5-dimethylpyridine.
yellow needles separated from the clear solutions upon
slow cooling to room temperature, which were identi-
fied as (PhCN)2BeCl2, (1), m. p. 214 C (86% yield).
The compound is hygroscopic, but stable in a dry at-
mosphere at room temperature and soluble in polar sol-
vents. The NMR spectra (in CDCl3 at 20 ◦C) show the
benzonitrile resonances (◦1H, 13C) and a broad 9Be sig-
nal at 2.01 ppm (at 50 C, rel. aqueous 1 M BeSO4
solution).
◦
(Et2O)2BeCl2 +2L → L2BeCl2
L = PhCN,1
(1)
Crystals of (pyr)2BeCl2 (2) are monoclinic, space
group P21 with Z = 8 formula units in the unit
cell. The asymmetric unit contains four independent
molecules which all have a very similar geometry.
One example is shown in Fig. 2. The Be-N and
Be-Cl distances are in the range 1.742(5)– 1.773(5)
L = pyridine,2
L = 3,5−Me2C5H3N,3
L = pyrrolidine,6
L = piperidine,8
L = Et2NH,10
˚
and 1.992(4)– 2.014(5) A, respectively. The N-Be-N
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M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
175
Fig. 3. Molecular structure of (pyz)(Et2O)BeCl2 (4). Se-
Fig. 2. Molecular structure of (pyr)2BeCl2 (2). Only one
of the four independent units present in the asymmet-
ric unit is shown. The adducts have no crystallographi-
cally imposed symmetry. Selected structural parameters:
Be1-Cl1 1.997(4), Be1-Cl2 2.011(5), Be1-N11 1.741(5),
lected structural parameters: Be1-Cl1 1.979(3), Be1-Cl2
˚
1.997(4), Be1-O21 1.677(4), Be1-N11 1.717(4) A. Cl1-
Be1-Cl2 115.30(18), O21-Be1-N11 108.2(2)◦.
˚
Be1-N21 1.758(5) A. Cl1-Be1-Cl2 114.7(2), N11-Be1-N12
105.2(3)◦.
angles [101.9(3)– 106.8(3)◦] are consistently smaller
than the Cl-Be-Cl angles [113.5(2)– 115.1(2)◦] and
this deviation represents the major distortion of the
tetrahedral arrangement of the complex.
Fig. 4. Association of the (pyz)(Et2O)BeCl2 molecules (4)
The packing of the molecules in the crystal leads to
a stacking of one of the two pyridine rings, but the dis-
into strings via hydrogen bonds: N12-H12 0.89(4), H12–
◦
˚
Cl2’ 2.43(3), N12–Cl2’ 3.219(2) A, N12-H12–Cl2’ 147 .
˚
tances of neighbouring rings are too large (ca. 3.90 A)
˚
tances of 1.979(3) and 1.997(4) A, a Be-N distance of
to suggest significant π-π interactions.
˚
˚
1.717(4) A and a Be-O distance of 1.677(4) A. The
angle Cl1-Be1-Cl2 of 115.30(18)◦ is the largest of the
six angles at the Be center, while all others are close
to the tetrahedral standard [107.9(2)– 108.7(2)◦]. The
pyrazole molecule is attached to the beryllium atom
through its non-protonated nitrogen atom N11 which
reaches a trigonal planar configuration in the product.
Through hydrogen bonding of the protonated nitrogen
atom N12 with a chlorine atom Cl2’ of a neighbour-
ing molecule the monomers are aggregated into helical
Pyrazole coordination
Treatment of a solution of BeCl2 in diethylether
◦
with pyrazole (pyz) at −78 C gives a colourless pre-
cipitate which has been identified as the 1:1 adduct
still containing one solvent molecule attached to the
beryllium atom: [(pyz)(Et2O)BeCl2] (4) (72% yield).
The product is sensitive to moisture and looses s◦ol-
vent upon heating. The residue finally melts at 264 C.
1
Solutions in CDCl3 show the H/13C resonances ex-
9
˚
strings [N12-H12 0.89(4), H12–Cl2’ 2.43(3) A, N12-
pected for the two ligands and a broad Be signal at
H12–Cl2’ 147(3)◦]. There may also be a very weak
hydrogen bonding between H12 and Cl1, but the ge-
ometrical data suggest that this contribution is small
(Fig. 4).
1.04 ppm. The parent ion (m/z 179.3) is observed in
the FAB mass spectrum, but the cation [(Et2O)BeCl2]+
is the most abundant species indicating that the pyra-
zole ligand is less tightly bound than the diethylether
molecule.
The reaction of a solution of BeCl2 in diethylether
with two equivalents of pyrazole at room temperature
leads to the formation of a colourless, crystalline pre-
cipitate which was identified as an ether cleavage prod-
(Et2O)2BeCl2 + C3H4N2 → (C3H4N2)(Et2O)BeCl2 (2)
(pyrazole)
4
Crystals of [(pyz)(Et2O)BeCl2] (4), are orthorhom- uct [(pyz)BeCl(OEt)]2 (5) (81% yield). The solid grad-
bic, space group P212121, with Z = 4 molecules in ually looses volatile compon◦ents upon heating and the
the unit cell. The structure of the individual monomer residue finally melts at 317 C. In air it is hydrolyzed
is shown in Fig. 3. The environment of the beryl- only very slowly. The NMR spectra (in CDCl3) show
lium atom is distorted tetrahedral with Be-Cl dis- the resonances expected for a pyrazole ligand and an
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176
M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
ethoxy group in the ratio 1:1 suggesting equivalent lig-
ands in the dimer. However, there are two 9Be reso-
◦
nances (5.57 and 5.97 ppm, at −50 C) of equal in-
tensity which indicate two beryllium atoms in a differ-
ent environment. In the FAB mass spectrum the parent
ion [(pyz)2(EtO)2Be2Cl]+ (7%) confirms the dimeric
nature of the compound. No single crystals could be
grown of compound 5 and therefore structure assign-
ments must remain tentative. The most plausible alter-
natives are formulae 5a and 5b.
(2Et2O)2BeCl2 +2L → [L(EtO)BeCl]2
(3)
L = pyrazole 5
Fig. 5. The ionic structure of [(pyrr)3BeCl]+Cl− (7). Se-
L = pyrimidine 9
lected bond lengths: Be1-Cl1 1.9981(18), Be1-N1 1.755(2),
˚
Be1-N2 1.746(2), Be1-N3 1.761(2) A.
Anhydrous BeCl2 is only sparingly soluble in pyrro-
lidine in the absence of an ether solvent even un-
der reflux conditions. After separation from the undis-
solved solid, colourless crystal separate on cooling
from the mother liquor, which have been shown to
be a 3:1 adduct of the ionic formula [(pyrr)3BeCl]+
Cl− (7) (m.p. 183 ◦C; for 500 mg of BeCl2 in
10 ml of pyrrolidine the yield was 28%). Solutions
Solutions of BeCl2 in tetrahydrofuran (thf) show
no reaction with pyrazole at room temperature. Upon
9
in CDCl3 show a Be resonance at 1.64 ppm, and the
◦
cooling of the reaction mixture to −20 C crystals of
FAB mass spectrum features predominantlythe cations
[(pyrr)2BeCl]+ and [(pyrr)4Be]2+, suggesting ligand
redistribution.
the adduct (C4H8O)2BeCl2 separate, but no pyrazole
adduct can be isolated. It therefore appears that pyra-
zole is not able to displace thf in the coordination
sphere of the beryllium atom. As observed for many
other hard Lewis acid centers, thf is a stronger base
than Et2O.
Crystals of compound7 are monoclinic, space group
P21/c, with Z = 4 formula units in the unit cell. The
structure is built of [(pyrr)3BeCl]+ cations and Cl−
anions (Fig. 5). The cation has no crystallographi-
cally imposed symmetry and the conformation and rel-
ative orientation of the pyrrolidine ligands does not
approach the maximum attainable symmetry of point
group C3v or C3. The orientation is probably deter-
mined or at least influenced by weak hydrogen bond-
ing of the N-H groups and the chloride anion (be-
low). The three Be-N bonds are of similar length
Pyrrolidine coordination
Treatment of a diethylether solution of BeCl2 with
two equivalents of pyrrolidine (pyrr) at room tempera-
ture leads to the precipitation of a 1:2 adduct (6) which
can be isolated in 78% yield. The colourless solid,
which is hygroscopic and rapidly decomposes in air
◦
(m.p. 181 C), was identified by elemental analysis.
˚
9
[1.755(2), 1.746(2) and 1.761(2) A for N1, N2 and
Solutions in CDCl3 show a very broad Be resonance
˚
N3, respectively], the Be-Cl distance is 1.9981(18) A.
at 1.70 ppm, and the molecular ion can be observed
in the FAB mass spectrum (m/z 221.4, 27%). How-
ever, both in the NMR and mass spectra small amounts
of an ether cleavage product could be detected for the
precipitate of the room temperature reaction. These by-
products were only absent if th◦e reaction was carried
out at temperatures below −30 C.
All six angles at the beryllium atom are very close to
the ideal angle of a regular tetrahedron [in the range
107.60(11)– 110.61(10)◦].
The three pyrrolidine rings have flat envelop con-
formations. Owing to their narrow C-N-C angles the
ligands can easily be accommodated at the small beryl-
lium atom without steric congestion. Even substitution
of the remaining chloride ligand would appear to be
sterically possible, but no such product was detected
BeCl2 + 3C4H8NH → [(C4H8NH)3BeCl]Cl
(4)
(pyrrolidine)
7
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M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
177
Fig. 7. Molecular structures of the two independent
molecules (pip)2BeCl2· (CHCl3) in the crystals of the chlo-
roform solvate 8a. Selected structural parameters: Be1-
Cl1 2.017(3), Be1-Cl2 2.014(3), Be1-N11 1.756(3), Be1-
Fig. 6. Hydrogen bonding between cation and anion in
[(pyrr)3BeCl]Cl, (7). N1-H1 0.88(2), H1–Cl2 2.63(2),
◦
˚
N1–Cl2 3.3691(12) A; N1-H1–Cl2 141.3(17) . N2-H2
˚
0.89(2), H1–Cl2 2.36(2), N2–Cl2 3.2025(12) A; N2-H2–
˚
N21 1.747(4) A; Cl1-Be1-Cl2 114.36(15), N11-Be1-N21
Cl2 156.4(18)◦. N3’-H3’ 0.89(2), H3’–Cl2 2.48(2), N3’–
110.60(19). Be2-Cl3 2.019(3), Be2-Cl4 2.014(3), Be2-N31
◦
˚
Cl2 3.3097(12) A; N3’-H3’–Cl2 155.5(17) .
˚
1.756(4), Be2-N41 1.745◦(3) A; Cl3-Be2-Cl4 114.25(15),
N31-Be2-N41 112.28(19) .
even though a large excess of pyrrolidine was ap-
plied under rather forcing conditions. This observation
suggests that no +2 charge can be built up at the beryl-
lium center without the proximity of at least one coun-
terion.
spectively. Solutions of 8 in CDCl3 show the expected
NMR spectra including a broad 9Be resonance at
−0.95 ppm. Only small amounts of a very pure sample
of compound 9 (single crystals of a chloroform solvate
9a [(pip)BeCl(µ2-OEt)]2· (CHCl3)) could be isolated
which were identified by the mass spectrum and an X-
ray diffraction study. Compound 8 also crystallized as
a chloroform solvate [(pip)2BeCl2]·(CHCl3), 8a.
Crystals of this solvate 8a are triclinic, space group
The independent chloride anion (Cl2) has close con-
tacts to three N-H groups suggesting weak hydrogen
bonding. Two of these contacts are to the same cation
(N1-H1, N2-H2) while the third one involves N3’-H3’
of a neighbouring unit (Fig. 6).
¯
P1, with Z = 2 formula units in the unit cell. There
are two independent complex molecules and two chlo-
roform molecules in the asymmetric unit, one of the
latter being highly disordered. The two adducts 8 have
a very similar geometry as shown in Fig. 7. The four
Be-N distances are in the narrow range 1.745(3)–
Piperidine coordination
The reaction of BeCl2 with two equivalents (or an
excess) of piperidine (pip) in diethylether at room tem-
perature gives a mixture of two products. Fractional
crystallization gave pure samples of the mononu-
clear 1:2 adduct (pip)2BeCl2 (8) and the dinuclear
[(pip)BeCl(µ2-OEt)]2 (9), the latter resulting from
cleavage of the diethylether solvent. The relative
amount of the ethoxy compound 9 could be reduced
˚
1.756(3) A, the Be-Cl distances between 2.014(3)
˚
and 2.019(3) A. The angles N-Be-N [110.60(19) and
112.28(19)◦] differ much less from the Cl-Be-Cl an-
gles [114.36(15) and 114.25(15)◦] than in the related
pyrrolidine or pyridine compounds (above). We ascribe
this difference to the increased steric bulk of piperi-
dine with its larger C-N-C angle. These differences
may also be responsible for the reluctance of complex
8 to accept another piperidine ligand the way it was
observed for the pyrrolidine ligand (above).
◦
by carrying out the reaction at −50 C, but the cleav-
age was not fully suppressed even under these much
milder conditions. The results suggest that piperidine
strongly promotes the ether cleavage by BeCl2 and is
more efficient in this respect than the more weakly
basic pyrrolidine, pyrazole, pyridine, or nitrile lig-
ands. The high basicity together with the ability to
form hydrogen bonds with the ether oxygen atom
may lead to a concerted process with lower activation
energy.
The piperidine ligands adopt the usual chair confor-
mation (Fig. 7). Their imino groups are engaged in hy-
drogen bonding with chlorine atoms of neighbouring
complexes to form chains with an alternating sequence
of non-equivalent molecules (Fig. 8). In these chains
Both products of the piperidine/diethylether/BeCl2 the beryllium atoms are spiro centers between puck-
reaction are hygroscopic and decompose in air. Grad- ered eight-membered rings. There are no sub-van-der
ual decomposition is observed on heating and the solid Waals contacts between the chains of complexes and
◦
◦
residues finally melt at 259 C (8) and 376 C (9), re- the chloroform molecules.
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178
M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
Fig. 8. Association of the molecular units shown in Fig. 7 via
Fig. 10. Association of the molecular units shown in
Fig. 9 via hydrogen bonds to give chains of alterat-
ing eight- and four-membered rings. N11-H11A 0.87(2),
H11–Cl1’ 2.53(2), N11–Cl1’ 3.3825(14); N11-H11A–Cl1’
165.4(19).
hydrogen bonds to give helical strings. N11-H11A 0.90(3),
˚
H11A–Cl1’ ◦2.56(3), N11–Cl1’ 3.461(2) A; N11-H11A–
Cl1’ 175(3) . N21-H21A 0.85(4), H21A–Cl4’ 2.54(4),
◦
˚
N21–Cl4’ 3.371(2) A; N21-H21A–Cl4’ 167(3) . N31-
˚
H31A 0.85(3), H31A-Cl2’ 2.65(3), N31–Cl2’ 3.468(2) A;
N31-H31A–Cl2’ 160(2)◦. N41-H41A 0.89(3), H41A–Cl3’
◦
˚
2.58(3), N41–Cl3’ 3.459(2) A; N41-H41A–Cl3’ 170(2) .
Fig. 11. Molecular structure of (Et2NH)2BeCl2 (10). The
adduct has no crystallographically imposed symmetry. Se-
lected structural parameters: Be1-Cl1 2.011(2), Be1-Cl2
˚
2.017(2), Be1-N1 1.763(3), Be1-N2 1.754(3) A; Cl1-Be1-
Cl2 114.94(11), N1-Be1-N2 112.33(13)◦.
dicate an almost perfect square for the core unit of the
dimer.
Fig. 9. Molecular structure of the dimer [(pip)BeCl(µ2-
OEt)]2 (9) in the trichlormethane solvate 9a. The two
monomers are related by a center of inversion. The ethyl
groups are disordered. Selected structural parameters: Be1-
Cl1 2.032(2), Be1-N11 1.755(2), Be1-O21 1.609(2), Be1-
The piperidine ligands are in a chair conformation
and their N-H groups are engaged in hydrogen bonding
with chlorine atoms of neighbouring dinuclear com-
plexes to form, together with the Be-O rings, chains
with an alternating sequence of eight- and four-mem-
bered rings in which the beryllium atoms are spiro cen-
ters between the two different types of rings (Fig. 10).
˚
O21’ 1.60◦4(2) A; O21-Be1-O21’ 89.◦91(11), Be1-O21-Be1’
90.09(11) , N1-Be1-Cl1 106.72(11) .
Crystals of [(pip)BeCl(µ2-OEt)]2 · (CHCl3)2, (9a),
are monoclinic, space group P21/c, with Z = 2 for-
mula units in the unit cell. The two monomers asso-
ciated in the dimer are related by a center of inversion
Diethylamine coordination
Beryllium dichloride forms a 1:2 addition com-
(Fig. 9). The methyl groups of the µ-ethoxy bridges are pound 10 with diethylamine which is readily isolated
disordered over two positions which are about equally in large colourless crystals and identified by its ana-
populated (57:43; only one orientation is shown in lytical and spectroscopic data. The crystals are mono-
the figure). The Be-N and Be-Cl distances [1.755(2) clinic, space group P21/c, with Z = 4 formula units in
˚
and 2.032(2) A] are only slightly longer than in the the unit cell. The mononuclear complex has no crystal-
piperidine reference compound 8. The Be-O distances lographically imposed symmetry, but its geometry ap-
are equal within the standard deviations of the data proaches quite closely a structure with point group C2
˚
[1.604(2) and 1.609(2) A] and together with angles O- symmetry (Fig. 11). The bond lengths and angles of the
Be-O’ and Be-O-Be’ at 89.91(11) and 90.09(11)◦ in- core unit are very similar to those of the bis(piperidine)
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M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
179
ing assists the formation of an energetically lower-
lying transition state of the ether cleavage.
Hydrogen bonding also plays a role in the
crystal structures of all complexes with secondary
amines (pyrrolidine, piperidine and diethylamine). The
monomeric units are tied together via N-H–Cl bridges
to form helical one-dimensional chains with the beryl-
lium atoms in the bridge-head positions.
Fig. 12: Association of molecule 10 into helical chains via
hydrogen bonds. N1-H1 0.87(2), H1–Cl1’ 2.64(2), N1–Cl1’
Experimental Section
◦
˚
3.5020(15) A; N1-H1–Cl1’ 169.3(16) . N2-H2 0.86(2),
All beryllium compounds should be considered extremely
toxic. The experiments should therefore be carried out with
greatest care to avoid any contamination. Most manipula-
tions were conducted in a dedicated glove-box in argon.
All wastes were disposed of following pertinent regulations.
Otherwise standard equipment was used throughout. Sol-
vents were dried and kept under nitrogen. Glassware was
oven-dried and filled with nitrogen. All chemicals were com-
mercially available.
˚
H2–Cl2” ◦2.61(2), N2–Cl2” 3.4688(15) A; N2-H2–Cl2”
173.8(19) .
˚
analogue 9 above: Be-N1/N2 1.760(3)/1.753(3) A; Be-
◦
˚
Cl1/Cl2 2.010(2)/2.015(2) A; N1-Be-N2 112.33(13) ,
Cl1-Be-Cl2 114.96(10)◦. This similarity is not unex-
pected considering the close analogy between piperi-
dine and diethylamine: The difference only arises be-
cause in the former the two ethyl groups are tied to-
gether by a bridging methylene unit.
Bis(benzonitrile)dichloroberyllium (1)
The molecular units are arranged in chains through
N-H–Cl hydrogen bonds to give an array closely anal-
ogous to the structure of the piperidine complex 8
(Fig. 12).
BeCl2 (500 mg, 6.30 mmol) was added to benzonitrile
(7.5 ml) and the mixture heated to reflux temperat◦ure un-
til all BeCl2 had dissolved. On slow cooling to 20 C pale
yellow, hygroscopic, needle-shaped crystals separated which
were filtered off and dried in a vacuum (1.55 g, 86% yield,
Conclusions
◦
◦
1
m.p. 214 C). NMR (CDCl3, 20 C), H: 7.36 – 7.71 ppm,
1
m, Ph. 13C{ H}: 129.10, 132.16, 132.73 for C2,C3,C4,
The reaction of anhydrous beryllium dichloride
BeCl2 with nitrogen donors L in diethylether was
shown to give – in the standard case – the expected
1:2 complexes L2BeCl2 with a tetrahedrally coordi-
nated beryllium atom. The geometry of the N2BeCl2
polyhedron is distorted depending on the steric re-
quirements of the donor molecules L. If on the one
hand the donor is a small and strongly basic amine,
like pyrrolidine, a third ligand may replace one of
the two chloride ligands to give a rare cationic com-
plex of the type [L3BeCl]+ Cl−. On the other hand,
with weak donors like pyrazole, a stepwise substitu-
tion of the ether molecules in the solvated precursor
(Et2O)2BeCl2 gives L(R2O)BeCl2. With the stronger
donor solvent tetrahydrofuran no reaction occurs be-
tween (thf)2BeCl2 and pyrazole.
resp.; C1 and CN were not observed. 9Be: 2.01, broad.
C14H10BeCl2N2 (286.17): calcd. Cl 24.80; found Cl 24.03.
Bis(pyridine)dichloroberyllium (2)
BeCl2 (1.5 g, 18.7 mmol) was dissolved in a mixture of
benzene (30 ml) and pyridine (20 ml) with gentle heating.
Colourless crystals separated on cooling (3.3 g, 74% yield).
For analytical data see ref. [29].
Bis(3,5-dimethylpyridine)dichloroberyllium (3)
BeCl2 (500 mg, 6.30 mmol) was reacted with 3,5-
Me2C5H3N (1.35 g, 12.6 mmol, 1.43 ml) in 50 ml of di-
ethylether at 20 ◦C. A small amount of undissolved material
was filtered off and the filtrate was cooled to 8 C. Colour-
less crystals formed which were separated and dried in a
◦
Secondary amines like pyrrolidine and piperidine
were found to promote the cleavage of diethylether by
BeCl2 to give dinuclear beryllium(alkoxide)chloride
compounds of the type [(L)BeCl(µ 2-OR)]2. This side-
reaction can be suppressed by carrying out the reaction
◦
vacuum (1.47 g, 79% yield, m. p. 197 C). NMR (CDCl3,
20 ◦C), 1H: 2.53 (s, 6H) Me; 7.99 (s, 1H) and 8.39 (s,
2H), C6H3. 13C: 29.37, s, Me; 137.60, 146.35, 155.00 (s,
C5H3N). 9Be: 1.73, s. MS (FAB) m/z 396.3 and 294.3
[L2BeCl2]+; 260.3 and 258.3 [L2BeCl]+. C14H18BeCl2N2
at low temperature. It is assumed that hydrogen bond- (294.23): calcd. Cl 24.10, found Cl 24.14.
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180
M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
Table 1. Crystal data,
data collection, and
structure refinement
of 1, 2, 4, 7.
1
2
5
7
Empirical formula
M
Crystal system
Space group
C14H10BeCl2N2
286.15
monoclinic
P2/n
7.4494(6)
6.4675(3)
14.9115(12)
90
91.484(4)
90
C10H10BeCl2N2
238.11
monoclinic
P21
12.1648(1)
12.7283(2)
15.2121(2)
90
89.9967(5)
90
C7H14BeCl2N2O
222.11
C12H27BeCl2N3
293.28
monoclinic
P21/c
11.7155(2)
11.2452(2)
11.9975(2)
90
94.6932(13)
90
orthorhombic
P212121
7.2396(2)
12.4141(4)
12.8139(4)
90
˚
a/[A]
˚
b/[A]
˚
c/[A]
α/[◦]
β/[◦]
γ/[◦]
90
90
3
˚
V/[A ]
ρ
Z
718.15(9)
1.323
2
2355.40(5)
1.343
8
1151.63(6)
1.281
4
1575.29(5)
1.237
4
calc/[g cm−3
]
F(000)
292
4.36
143
976
5.16
143
464
5.28
143
632
4.0
143
µ (Mo-Kα ) [cm−1
T/[K]
]
Refls. measured
Refls. unique
9511
1551
66578
5411
32224
1361
47072
3559
[Rint = 0.038]
107 / 0
0.0406
[Rint = 0.053]
542 / 1
0.0264
[Rint = 0.033]
124 / 0
0.0323
[Rint = 0.049]
271 / 0
0.0368
Refined parameters/restraints
R1[I ≥ 2σ(I)]
wR2[a]
0.1086
0.0625
0.0860
0.0991
Weighting scheme
a = 0.0487
b = 0.2910
0.308 / –0.369
a = 0.0290
b = 0.2163
0.155 / –0.170
a = 0.0428
b = 0.4770
0.283 / –0.230
a = 0.0553
b = 0.6143
0.302 / –0.298
−3
˚
σ
fin(max/min)/eA
[a]
wR2 = {Σ[w(Fo2 −Fc2)2]/Σ[w(Fo2)2]}1/2; w = 1/[σ2(Fo2)+(ap)2 +bp]; p = (F2 +2F2)/3.
o
c
Dichloro(diethylether)(pyrazole)beryllium (4)
C10H18Be2Cl2N4O2 (315.21): calcd. C 38.10, H 5.76,
N 17.77, Cl 22.49; found C 37.25, H 5.67, N 16.98, Cl 22.10.
BeCl2 (509 mg, 6.37 mmol) was dissolved in 50 ml of
Et2O, the solution cooled to −78 ◦C and treated with pyrazol
(430 mg, 6.37 mmol) dissolved in 10 ml of Et2O. The re-
action mixture was filtered to remove undissolved material,
Bis(pyrrolidine)dichloroberyllium (6)
BeCl2 (504.8 mg, 6.32 mmol) was reacted with pyrroli-
dine (900 mg, 13 mmol, 1.04 ml) in 50 ml of diethylether
at 20 ◦C. A colourless precipitate was collected, washed with
three 15 ml portions of hexane and dried in a vacuum (1.10 g,
78% yield, m.p. 181 ◦C). NMR (CDCl3, 20 ◦C), 1H: 2.01 (m,
◦
and the filtrate warmed to 20 C. Colourless crystals were
isolated and dried in a slow stream of nitrogen (1.02 g, 72%
yield, m.p. 264 ◦C). NMR (CDCl3, 20 ◦C), 1H: 1.19 (t, 6 H,
J = 8 Hz) Me, 3.45 (q, 2 H) CH2, 6.66 (m, 1 H) and 7.96
(m, 2 H) C3N2H3; NH not observed. 13C: 15.27, Me; 65.79,
CH2; 106.94 and 132.35, C3N2. 9Be: 1.04, broad. MS (FAB)
m/z 179.3 [M]+; 155.2 [(Et2O)BeCl2]+. C7H14BeCl2N2O
(222.11): calcd. C 37.85, H 6.35, N 12.61, Cl 31.92; found
C 37.05, H 6.67, N 12.15, Cl 30.91.
9
4 H) and 3.31 (m, 4 H) CH2; 9.71 (s, 1 H) NH. Be: 1.70,
very broad. MS (FAB) m/z 221.4 [M]+. C8H18BeCl2N2
(222.16): calcd. C 43.25, H 8.17, N 12.61, Cl 31.92; found
C 42.63, H 8.64, N 10.99, Cl 31.42.
Tris(pyrrolidine)chloroberyllium chloride (7)
Bis[chloro(ethoxy)(pyrazol)beryllium] (5)
BeCl2 (495.5 mg, 6.20 mmol) was reacted with pyra◦zol
A suspension of BeCl2 (500 mg, 6.26 mmol) in 10 ml of
(420 mg, 6.20 mmol) in a total of 55 ml of Et2O at 20 C. pyrrolidine was heated to reflux temperature for 2 h. Sub-
A precipitate formed which was filtered, washed three times sequently the reaction mixture was filtered and the filtrate
with 5 ml of Et2O and dried in a vacuum (0.79 g, 81% cooled to 8 ◦C. Colourless crystals precipitated which were
yield, m.p. 317 ◦C). NMR (CDCl3, 20 ◦C), 1H: 1.19 (t, 3 H) dried in a va◦cuum (514 mg, 28% yield, m.p. 183 ◦C). NMR
Me; 3.45 (q, 2 H) CH2; 6.65 and 7.96 (m, 2H/1H) C3H3N2; (CDCl3, 20 C), 1H: 2.00 (m, 4 H) and 3.29 (m, 4 H) CH2;
NH not observed. 13C: 15.21 and 65.77, Et; 107.04 (1 C) 9.68 (s, 1 H) NH. 13C: 24.35 and 45.92 (s) C4H4NH. Be:
9
and 132.20 (2 C), C3N2H4. 9Be: 5.57 (s, 1 Be) and 5.97 1.64, broad s. MS (FAB) m/z 181.3 and 179.3 [L2BeCl]+.
(s, 1 Be), broad. MS (FAB) m/z 279.4 [L2(EtO)2Be2Cl]+. C14H18BeCl2N2 (293.28): calcd. Cl 24.18, found Cl 23.14.
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M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
181
Table 2. Crystal data, data col-
lection, and structure refine-
ment of 8, 9a and 10.
8a
9a
10
[b]
Empirical formula
M
C21H45Be2Cl7N4
619.78[b]
C16H34Be2Cl8N2O2 C8H22BeCl2N4
588.07
452.37
Crystal system
Space group
triclinic
P1
monoclinic
P21/c
monoclinic
P21/c
¯
˚
a/[A]
11.2993(2)
12.4853(3)
14.3964(3)
76.5020(8)
82.8108(8)
65.2506(8)
1792.61(7)
1.148[b]
2
7.1927(1)
23.4250(4)
8.5790(2)
90
98.6625(8)
90
1428.98(5)
1.367
2
10.3616(3)
8.9624(3)
13.6822(5)
90
98.2645(15)
90
1257.40(7)
1.195
4
˚
b/[A]
˚
c/[A]
α/[◦]
β/[◦]
γ/[◦]
3
˚
V/[A ]
ρ
Z
calc/[g cm−3
]
F(000)
652[b]
608
8.04
143
488
4.79
143
µ (Mo-Kα ) [cm−1
T/[K]
]
5.69[b]
143
Refls. Measured
Refls. Unique
Refined parameters /restraints 487 / 0
52047
6135 [Rint = 0.035]
32999
3284 [Rint = 0.035]
203 / 1
35784
2254 [Rint = 0.051]
206 / 0
[b]
R1[I ≥ 2σ(I)]
0.0456
0.1267
0.0382
0.1044
0.0318
0.0759
wR2[a]
Weighting scheme
a = 0.0653
b = 1.4109
0.763 / - 0.436
a = 0.0515
a = 0.0318
0.428 / –0.540
b = 0.7556
b = 0.4874
0.222 / –0.217
−3
˚
σ
fin(max/min)/eA
[a]
[b]
wR2 = {Σ[w(Fo2 −Fc2)2]/Σ[w(Fo2)2]}1/2; w = 1/[σ2(Fo2)+(ap)2 +bp]; p = (F2 +2F2)/3;
o
c
without contributions of disordered solvent.
Bis(piperidine)dichloroberyllium (8), and Bis[chloro(µ2- in inert perfluoropolyalkylether and used for intensity data
ethoxy)(piperidine)beryllium] (9)
collection on a Nonius DIP2020 diffractometer, employing
graphite-monochromated Mo-Kα radiation. The structures
were solved by a combination of direct methods (SHELXS-
97) and difference-Fourier syntheses and refined by full ma-
trix least-squares calculations on F2 (SHELXL-97) [35].
The thermal motion was treated anisotropically for all non-
hydrogen atoms. The hydrogen atoms in all structures were
located and refined isotropically except those of the methyl
groups in 4, 9a and all hydrogen atoms in the structure of 2,
which were calculated in ideal positions and allowed to ride
on their parent atoms with fixed isotropic contributions. The
scattering contributions of a highly disordered chloroform
The reaction of BeCl2 (510 mg, 6.39 mmol) with piperi-
dine (1.09 g, 13 mmol, 1.26 ml) was carried out at 20 ◦C and
at −78 ◦C. In both cases mixtures of the two products 8 and
9 were obtained. Only small amounts of the pure compounds
could be obtained by fractional crystallization from chloro-
form/diethylether. Yields of the two compounds have there-
fore not been determined (8: m.p. 259 ◦C, 9: m.p. 376 ◦C).
The products decompose rapidly in air. NMR data were
only collected for compound 8: NMR (CDCl3, 20 C), H:
1.65 (q, 1 H, J = 5 Hz) H-C4, 187 and 3.12 (m, 2+2 H) H-
C3,5/H-C2,6; 2.17 (s, 1 H) NH. 13C: 22.43, 29.83 and 44.56
for C4, C3/5 and C2/6 resp. 9Be (−50 ◦C): −1.10.
◦
1
molecule in 8a were taken into account using the SQUEEZE
3
˚
method (total potential solvent accessible volume is 308.2A
containing 16 electrons/cell) [36]. The structure of 2 was re-
fined as a pseudo-merohedral twin in space group P21 with
a β-angle near 90◦ emulating orthorhombic symmetry. The
refined BASF parameter for the pseudo-merohedral twinning
is 0.4991(17). Further informations on crystal data, data col-
lection and structure refinement are summarized in Tables 1
and 2.
Displacement parameters and complete tables of inter-
atomic distances and angles for the structures 1, 2, 4, 7, 8a,
9a and 10 have been deposited with the Cambridge Crys-
Bis(diethylamine)dichloroberyllium (10)
Diethylamine (6.5 ml, 62 mmol, excess) was mixed with
100 ml of diethylether and treated with a solution of BeCl2
(1.0 g, 12.5 mmol) in 100 ml of diethylether. A two-phase
reaction mixture contained the product in both the upper and
lower layer. Colourless crystals (1.85 g, 66% yield). For an-
alytical data see ref. [32].
Crystal structure determinations
Specimens of suitable quality and size of 1, 2, 4, 7, tallographic Data Centre, CCDS 200898-200904. Copies
8a, 9a and 10 were mounted on the ends of quartz fibers of the data can be obtained free of charge on application
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182
M. P. Dressel et al. · Beryllium Dichloride Coordination by Nitrogen Donor Molecules
to The Director, CCDC, 12 Union Road, Cambridge CB2 Acknowledgements: This work was supported by Deutsche
1EZ, UK (Fax: int.code+(1223)336-033; e-mail for inquiry: Forschungsgemeinschaft and by Fonds der Chemischen In-
fileserv@ccdc.cam.ac.uk.
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