The reaction of BeCl2 with carbodiphosphorane C(PPh 3)2; Experimental and theoretical studies

Article abstract of DOI:10.1002/zaac.201100328

The use of 2-Br-fluorobenzene as the solvent permitted the isolation of the addition compound [Cl₂Be(C{PPh₃}₂)] (5) from the reaction of the carbodiphosphorane 1 (carbon) with BeCl₂ featuring a three coordinate beryllium atom. In other solvents such as THF, DCM, etc. deprotonation occurs with formation of the cations (HC{PPh ₃}₂)⁺ or (H₂C{PPh₃} ₂)²⁺. Compound 5 was characterized by an X-ray diffraction analysis. The analysis of the bonding situation in Cl₂Be←1 reveals that the orbital donation comes mainly from the σ lone-pair orbital of 1, whereas the π donation is rather weak. However, the Cl ₂Be←1 π donation appears strong enough to make the donation of a second donor species 1 unfavorable. The calculation of 1→Cl ₂Be←1 shows that the latter complex is higher in energy than 1→Cl₂Be and free 1. The carbodiphosphorane may bind, albeit weakly, a second BeCl₂ species in the complex Cl₂Be← 1→BeCl₂. The bond dissociation energies for the first and second BeCl₂ fragments are D_e = 31.8 kcal·mol ^-1 and 7.0 kcal·mol^-1. The dimerization of Cl ₂Be←1 is energetically slightly endoenergetic. Copyright

Full text of DOI:10.1002/zaac.201100328

ARTICLE
DOI: 10.1002/zaac.201100328
The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)2; Experimental
and Theoretical Studies
Wolfgang Petz,*[a] the late Kurt Dehnicke, Nicole Holzmann,[a] Gernot Frenking,*[a] and
Bernhard Neumüller*[a]
In Memory of Professor Kurt Dehnicke
Keywords: Beryllium compounds; X-ray diffraction; Carbodiphosphorane adducts; Donor-acceptor complex; Bonding analysis
Abstract. The use of 2-Br-fluorobenzene as the solvent permitted the Cl2Beǟ1 π donation appears strong enough to make the donation of
isolation of the addition compound [Cl2Be(C{PPh3}2)] (5) from the a second donor species 1 unfavorable. The calculation of 1ǞCl2Beǟ1
reaction of the carbodiphosphorane 1 (carbon) with BeCl2 featuring a shows that the latter complex is higher in energy than 1ǞCl2Be and
three coordinate beryllium atom. In other solvents such as THF, DCM,
free 1. The carbodiphosphorane may bind, albeit weakly, a second
BeCl2 species in the complex Cl2Beǟ1ǞBeCl2. The bond dissoci-
etc. deprotonation occurs with formation of the cations (HC{PPh3}2)+
or (H2C{PPh3}2)2+. Compound 5 was characterized by an X-ray dif- ation energies for the first and second BeCl2 fragments are De
=
fraction analysis. The analysis of the bonding situation in Cl2Beǟ1 31.8 kcal·mol–1 and 7.0 kcal·mol–1. The dimerization of Cl2Beǟ1 is
reveals that the orbital donation comes mainly from the σ lone-pair energetically slightly endoenergetic.
orbital of 1, whereas the π donation is rather weak. However, the
known carbodicarbenes C(NHC)2 (4, NHC = N-heterocyclic
carbene), which feature unusual carbonǞcarbon donor-ac-
1. Introduction
ceptor bonds should be stable compounds.[3b] The prediction
was quickly verified by the synthesis and X-ray structure
analysis of the first carbodicarbenes by Bertrand[8] and by
Fürstner.[9] The experimentally observed bending angle of
134.8° for 4, which is similar to the value for 1 is in agreement
with the finding that the ligands NHC and PR3 bind in a similar
fashion to a Lewis acid.[10] The term carbone was suggested
for compounds CL2,[11] which due to the presence of two elec-
tron lone pairs have very large first and second proton affin-
ities,[12] and which exhibit a chemical behavior that is distinc-
tively different from carbenes CR2, which have only one lone
pair.[13]
Carbodiphosphoranes are versatile ligands, which are em-
ployed in a variety of adducts.[14] The presence of two electron
lone pairs makes 1 a powerful Lewis base, which forms
strongly bonded complexes with various main group Lewis
acids[15] particularly group 13 compounds[16] and with transi-
tion metal Lewis acids,[17] where one pair of electrons is em-
It has recently been shown that the bonding situation in
hexaphenylcarbodiphosphorane C(PPh3)2 (1),[1] which has a
bent equilibrium arrangement with a P–C–P angle of 131.7°,[2]
is best described in terms of donor-acceptor interactions be-
tween the phosphane ligands and a naked carbon(0) atom in
1
the D state (Scheme 1). The bonding interactions give rise to
two electron lone-pair orbitals at the divalent carbon(0)
atom.[3] The donor-acceptor model LǞCǟL for 1 (L = PPh3)
provides a straightforward explanation for the increase of the
bending angle in carbonylcarbophosphorane C(CO)(PPh3)2 (2,
bending angle 145.6°)[4] and carbon suboxide C3O2 (3, bend-
ing angle 156.5°)[5] because the phosphane ligands are substi-
tuted by the better π-acceptor ligand CO.[6] Carbon suboxide[7]
is usually written with double bonds O=C=C=C=O but should
better be considered as dicarbonyl complex of a naked carbon
atom in the excited 1D state OCǞCǟCO. The donor-acceptor
model LǞCǟL for 1 led to the prediction that hitherto un-
ployed in donor-acceptor bonding (compounds
A
in
* Prof. Dr. W. Petz
E-mail: petz@staff.uni-marburg.de
* Prof. Dr. G. Frenking
Scheme 1). Recently, compounds of the type 1ǞMǟ1 (M =
Cu+, Ag+, Hg2+) were also reported.[18] The presence of two
lone pairs in 1 was used for the isolation of complexes, where
both pairs of electrons coordinate to two gold[19] or two
boron[20] atoms as shown in B (Scheme 1). The extraordinary
donor strength of 1 has even been used for C–H activation in
the reaction with [(cod)PtX2].[21]
E-Mail: frenking@staff.uni-marburg.de
* Prof. Dr. B. Neumüller
Fax: +49-6421-2825653
E-Mail: neumuell@chemie.uni-marburg.de
[a] Fachbereich Chemie der Philipps-Universität
Hans-Meerwein-Strasse
35032 Marburg, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201100328 or from the au-
thor.
An intriguing question, which has so far not been studied
concerns the reaction of the double Lewis base 1 with a double
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The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)2
Scheme 1. Schematic representation of the bonding situation in the carbones 1–4 showing the experimental bending angles at the divalent
carbon(0) atom. Chemical bonding in complexes A and B, where the carbone binds to one Lewis acid (A) and to two Lewis acids (B).
Lewis acid such as BeCl2. The chemistry of beryllium com- an electron deficiency at the beryllium atom the compound is
pounds was not explored very much, mainly because beryllium monomeric containing a three coordinate beryllium atom. Such
and its compounds are regarded as highly toxic.[22] Recent compounds are rare and their existences are indebted to steri-
theoretical studies have shown that BeCl2 is a rather strong cally encumbered ligands and the small size of the beryllium
Lewis acid.[23] Although beryllium is less electronegative than atom preventing dimerization [Equation (1)]
boron, compound BeCl2 strongly attracts electron donors be-
cause it has two formally vacant valence orbitals, whereas
BCl3 has only one. Herein we report on the results of the reac-
tion of BeCl2 with 1 and on theoretical studies of various com-
plexes of 1 with BeCl2.
1 + BeCl2 Ǟ Cl2BeǟC(PPh3)2 (5)
(1)
The IR spectrum of 5 between 3000 and 400 cm–1 is mainly
governed by the frequencies of the carbodiphosphorane ligand;
however, there is a strong band at 890 cm–1, which has not
been found in the spectrum of the cation (HC{PPh3}2)+ or of
other addition compounds of 1 that can be assigned to the
2. Experimental Studies
One disadvantage of X3Eǟ1 complexes (X3E = group 13 ν(Be–C) vibration.[24]
compound) is the fact that they are insoluble in nonpolar sol-
The addition compound 5 crystallizes without incorporating
vents like toluene or benzene and they are unstable in haloge- solvent molecules and the molecular structure is shown in Fig-
nated hydrocarbons, THF, DME, or DMSO. In most cases pro- ure 1 and Figure 2. The sum of the angles at Be and at C(1)
ton abstraction from the solvents occurs to give the cations each amounts to 360°, which indicates perfect trigonal planar
(HC{PPh3}2)+ or (H2C{PPh3}2)2+. This feature complicates coordination at both atoms. The BeCl2 plane is rotated by 44°
spectroscopic characterization in solution or crystal growth for with respect to the CP2 plane. The average Be–Cl bond length
X-ray analyses. Thus, we were restricted to nonpolar solvents is somewhat longer (1.953 Å) than those observed in the Be–
such as toluene or benzene in spite of the fact that the beryl- N adduct [Cl2Be(N{SiMe3}PeEt3)] with 1.927 Å[25] and in the
lium salt is insoluble in these solvents. If solid BeCl2 was Be–Pt adduct [Cl2Be-Pt(PCy3)2] with 1.922 Å.[26] Both com-
added to a suspension of 1 in toluene (it totally dissolves only pounds are the only examples with a three coordinate BeCl2
in hot toluene) a colorless microcrystalline precipitate is base adduct so far. Similar compounds with a Cl2Be–C moiety
formed. From the IR spectrum of the solid limited structural as in 5 were not reported. If BeCl2 is embedded in a four-
information could be deduced but the formation of the cation membered ring, quite longer Be–Cl bond lengths of 2.018 Å
(HC{PPh3}2)+ could be excluded because of the lack of the were found.[27]
characteristic bands at 999 s, 1011 m, 1030 w cm–1.[21a] We
In order to grow also crystals from the toluene precipitate
suppose that the adduct (Cl2Beǟ1) has formed but also its to clear up its identity with 5 the suspension was filtered im-
dimeric nature cannot be excluded according to the electron mediately after adduct formation and the filtrate was allowed
demand of the beryllium atom. The difficulties to obtain crys- to stand for a couple of time. Some microcrystalline powder
tals prompted us to look for alternative solvents without any separated with time and after months some larger crystals have
donor properties or tendencies to transfer a proton to 1. Sur- formed but which turned out to be the salt (Ph3PMe)Cl
prisingly, we were successful when we switched to 2-Br-fluo- ·0.25toluene (6). The origin of 6 is unclear as yet; there was
robenzene as the solvent and [Cl2Be(C{PPh3}2)] (5) was ob- no sign for the presence of 6 as impurity in 1. For further
tained as colorless crystals in high yield. A 1:1 mixture of characterization the initial toluene precipitate was treated with
BeCl2 and 1 was heated for one minute in this solvent; layering several polar solvents. It dissolves readily in DMSO and the
of the resulting tan solution with n-pentane produced colorless 31P NMR spectrum exhibits only one singlet at 21.0 ppm,
crystals within one week, suitable for an X-ray analysis. Ap- which was assigned to the cation (HC{PPh3}2)+. Layering of
parently, the solvent used is polar enough to dissolve 5 and the DMSO solution with toluene gave some colorless crystals
puts up resistance to any abstraction of HX. 5 is the first ad- which turned out to be the salt [Be(DMSO)4]Cl2 (7) according
dition compound of 1 with a group 2 Lewis acid. In spite of to an X-ray analysis;[28] no further crystalline material was
Z. Anorg. Allg. Chem. 2011, 1702–1710
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W. Petz, G. Frenking, B. Neumüller, et al.
ARTICLE
Figure 1. Molecular structure of [Cl2Be(C{PPh3}2)] (5) showing the
atom numbering scheme. The ellipsoids are drawn at a 40% prob-
ability level. The hydrogen atoms at the phenyl rings are omitted for
clarity. Selected bond lengths /Å and angles /°: Be(1)–C(1) 1.742(9),
Be(1)–Cl(1) 1.944(7), Be(1)–Cl(2) 1.961(7), C(1)–P(2) 1.697(4),
C(1)–P(1) 1.711(5); C(1)–Be(1)–Cl(1) 124.8(4), C(1)–Be(1)–Cl(2)
120.3(4), Cl(1)–Be(1)–Cl(2) 114.9(4), P(2)–C(1)–P(1) 123.4(3), P(2)–
C(1)–Be(1) 115.2(4), P(1)–C(1)–Be(1) 121.2(3).
obtained. The formation of 7 reflects the high affinity of Be2+
to oxygen.
The precipitate does not dissolve in THF but contacts with
dry THF changed the IR spectrum and bands of the cation
(HC{PPh3}2)+ appeared. When dissolved in CH2Cl2 or DMF
a clear solution was obtained and only the cation (HC{PPh3}2)+
at 20.6 ppm was identified spectroscopically. Similar results
are obtained upon dissolving the precipitate in acetone or pyr-
idine. The precipitate was also dissolved in tetramethylguani-
dine [HN=C(NMe2)2]; the 31P NMR spectrum of the solution
shows two signals at 20.4 and 24.0 ppm in a 1:0.3 ratio,
respectively. The high field signal was again assigned to the
cation, whereas the nature of the other one remained unex-
plored so far. The results confirm our earlier findings that with
Mǟ1 (M = group 13 or group 12 Lewis acids) adducts in polar
and halogenated solvents extraction of a proton takes place.
The strong polarizing effect of the small Be2+ ion may enforce
this reaction pathway.
Addition of freshly dried DME (over potassium) to the pre-
cipitate gave a suspension, from which upon standing colorless
needle-like crystals separated, which were found to be the salt
(H2C{PPh3}2)Cl2·DME (8). The supernatant solution exhibits
a signal in the 31P NMR spectrum at δ = 20.8 ppm, which was
assigned to the cation (HC{PPh3}2)+, the same shift was found
upon dissolving the residue from the DME solution in DMSO
Figure 2. Unit cell of 5 viewed down [100] with several asymmetrical
units of 5.
(H2C{PPh3}2)Cl2 Ǟ (HC{PPh3}2)Cl + HCl
(2)
The experimental results prompted us to carry out theoreti-
cal studies on (Cl2Beǟ1) (5) and on the doubly coordinated
adducts (Cl2Beǟ1ǞBeCl2) and (1ǞBeCl2ǟ1). We also
studied the dimer 52, where two monomers 5 are bonded to
each other by beryllium–chlorine bridges.
3. Theoretical Studies
We optimized the arrangement of (Cl2Beǟ1) (5) at the
or CH2Cl2. We suppose that in solution dissociation occurs of BP86/SVP level (see method section for details). The calcu-
the dication to give the monocation according to Equation (2). lated structure is shown in Figure 3a. The most important bond
The IR spectrum of 8 from DME does not show the charac- lengths and angles are given in Table 1 together with the ex-
teristic set of bands (999 s, 1011 m, 1030 w cm–1) due to perimental values. The comparison between the theoretical and
the cation (HC{PPh3}2)+ but those of the coordinated solvent experimental data shows a very good agreement. The devia-
molecule. From a series of compounds with the dication tions between the two sets of data are within the error range
(H2C{PPh3}2)2+ [and the counterions Cl–, [BF4]–, [BeCl4]2–, of both methods but the differences will also be caused by
etc.] only one single medium to weak band is detected in this intermolecular forces in the solid state. The calculated
region at 997 cm–1.
(1.782 Å) and experimental (1.742(9) Å) Be–C bond length is
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The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)2
Figure 3. Optimized geometries (BP86/SVP) of the complexes (a) Cl2Beǟ1 (5), (b) Cl2Beǟ1ǞBeCl2, (c) (1ǞBeCl2ǟ1) and (d) (Cl2Beǟ1)2 (5)2.
The most important bond lengths and bond angles are given in Table 1.
in the range of Be–Ar single bonds (Ar = C6H3-2,6-Mes2), P–C–P and Cl–Be–Cl planes are coplanar. Table 2 gives the
which were recorded in various three coordinate ArBeX base numerical results of the EDA calculations. The total interaction
adducts.[29] Thus, the Be–C(1) bond in 5 suggests that a energy ΔEint between the donor and acceptor fragments with
double-bond character, which would come from significant the frozen arrangement of the complex amounts to
BeǟC π donation is not very large. This may be due to the –62.4 kcal·mol–1. The electrostatic term ΔEelstat contributes
unfavorable overlap of the p(π) orbitals of the beryllium and 55.7%, while the orbital interactions ΔEorb contributes 44.3%
carbon atoms in the twisted conformation about the C–Be to the total attraction. The latter term comes mainly from the
bond, which is caused by the steric interaction of the chlorine Cl2Beǟ1 σ donation, which provides 89% of the ΔEorb term
atoms with the phenyl groups. The calculated bond dissoci- (Table 2). This means that the donation of the π lone-pair
ation energy (BDE) of the Cl2Beǟ1 bond at BP86/TZVPP// HOMO of 1 in 5, which contributes only 11.0% to ΔEorb is
BP86/SVP is De = 42.9 kcal·mol–1. This is significantly higher not very strong. This is supported by the shape of the HOMO
than the calculated BDE of Cl2BeǟNH3 which is only of the complex Cl2Beǟ1. Figure 4e shows that the latter or-
27.4 kcal·mol–1.[23b] The theoretical BDE of Cl2Beǟ1 is also bital still has the character of a π lone-pair orbital, which is
much higher than the calculated value for the complex mainly located at the carbon donor atom of 1.
Cl2BeǟPPh2(CH2PPh2) (De = 24.3 kcal·mol–1),[23c] which in-
dicates the large donor strength of 1.
The analysis of the Cl2Beǟ1 donor-acceptor bond in 5
shows that the second electron lone pair of 1 is hardly involved
Figure 4 shows the two highest lying occupied orbitals of 1 in the binding interactions and may thus be available for bond-
and the two lowest lying vacant orbitals of BeCl2. It becomes ing to a second BeCl2 species. Figure 3b shows the optimized
obvious that the π lone-pair HOMO and the σ lone-pair arrangement of Cl2Beǟ1ǞBeCl2. The calculated bond
HOMO-1 of 1 are perfectly suited for electron donation in to lengths of the C–Be bonds in the latter compound (1.875 Å
the vacant π LUMO and the σ LUMO-1 of BeCl2. We ana- and 1.880 Å, Table 1) are significantly longer than in 5
lyzed the nature of the (Cl2Beǟ1) (5) donor-acceptor interac- (1.782 Å). The same holds for the C–P bonds, which are calcu-
tions with the EDA (Energy Decomposition Analysis) in order lated to be much longer in Cl2Beǟ1ǞBeCl2 (1.809 Å and
in quantitatively estimate the strength of the σ and π donation 1.811 Å) than in 5 (1.720 Å and 1.722 Å). The theoretically
from carbodiphosphorane to BeCl2. To this end we optimized predicted bond lengths suggest that the donor-acceptor bonds
the arrangement of 5 with enforced Cs symmetry, where the of the BeCl2 molecules in the former complex are much
Z. Anorg. Allg. Chem. 2011, 1702–1710
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W. Petz, G. Frenking, B. Neumüller, et al.
ARTICLE
Table 1. Calculated (BP86/SVP) bond lengths d(A–B) /Å bond angles α(A–B–C) /° and interplanar angles τ /° of the investigated complexes.
The values in parentheses refer to experimental data.
Cl2Beǟ1 (5)
Cl2Beǟ1ǞBeCl2
1ǞBeCl2ǟ1
(Cl2Beǟ1)2 (5)2
d(Be–Be)
d(Be–C)
d(Be–Cl)
d(Be–Clint
d(C–-P)
3.006
1.782 (1.742)
1.955–1.970 (1.944–1.961)
1.875–1.880
1.935–1.965
1.965–2.020
2.056–2.080
1.819–1.823
2.033–2.050
2.132–2.203
1.724–1.733
91.5–92.4
)
1.720–1.722 (1.697–1.711)
119.0 (114.9)
123.9 (123.4)
1.809–1.811
116.0–116.8
121.7
1.724–1.750
106.9
115.6–121.6
α(Cl–Be–Cl)
α(P–C–P)
120.8–121.5
τ(P–C–P plane / Cl–Be–Cl plane)
τ(C–Be–Cl plane / Clint–Be–Clint
plane)
58.2 (44)
89.0–89.6
Table 2. EDA results for Cl2Beǟ1 calculated with Cs symmetry. Ener-
gies in kcal·mol–1.
Fragments
BeCl2 + 1
ΔEint
–62.4
ΔEPauli
96.7
a)
ΔEelstat
–88.6 (55.7%)
–70.5 (44.3%)
–62.7 (89.0%)
–7.7 (11.0%)
a)
ΔEorb
b)
aЈ
b)
aЈЈ
a) The percentage values in parentheses give the contribution to the
total attractive interactions ΔEelstat + ΔEorb. b) The percentage values
in parentheses give the contribution to the total orbital interactions
ΔEorb
.
Two other donor-acceptor complexes of 1 and BeCl2 were
investigatedtheoretically.Oneistheadduct[BeCl2{C(PPh3)2}2],
where two carbodiphorphorane ligands bind to beryllium di-
chloride 1ǞBeCl2ǟ1. Complexes of BeCl2 with two ligands
BeCl2L2, where L is an oxygen or nitrogen donor ligand are
well known.[30]. It is thus possible that 1ǞBeCl2ǟ1 could be
formed when an excess of 1 is employed. Figure 3c shows the
optimized geometry of the latter complex. The tetracoordinate
beryllium atom of 1ǞBeCl2ǟ1 has much longer Be–C
(1.965 Å and 2.020 Å) and Be–Cl (2.056 Å and 2.080 Å)
bonds than in Cl2Beǟ1 (5) and Cl2Beǟ1ǞBeCl2 (Table 1).
The calculated energy for the dissociation reaction
1ǞBeCl2ǟ1 Ǟ Cl2Beǟ1 + 1 indicates that the complex
1ǞBeCl2ǟ1 is only a local energy minimum structure, which
is thermodynamically unstable toward loss of one ligand 1.
The fragments Cl2Beǟ1 + 1 are 40.9 kcal·mol–1 lower in en-
ergy than the complex 1ǞBeCl2ǟ1. This is a dramatic differ-
ence to many dicoordinated complexes LǞBeCl2ǟL such as
the adduct (CH2PPh2)Ph2PǞBeCl2ǟPPh2(CH2PPh2), which
could become isolated and characterized by X-ray structure
analysis.[23b] The latter complex has a calculated BDE for the
second PPh2(CH2PPh2) ligand of De = 16.8 kcal·mol–1 which
should be compared with a negative BDE for the second
C(PPh3)2 ligand of 1ǞBeCl2ǟ1 (De = –40.9 kcal·mol–1). The
latter value also underscores the difference between the donor
Figure 4. Shape of the frontier orbitals of 1, BeCl2, and 5.
weaker than in the latter. The calculated BDE for loss of the strength of carbenes and carbones. Theoretical studies have
second BeCl2 in the reaction Cl2Beǟ1ǞBeCl2 Ǟ Cl2Beǟ1 shown that BeCl2 may bind two nucleophilic carbenes such as
+ BeCl2 is only De = 7.0 kcal·mol–1 which is much less than CF2 in the complex Cl2Be(CF2)2 with nearly equal bond
the BDE of 5. Nevertheless, it seems possible that the “double- strength for the first (19.8 kcal·mol–1) and second CF2 donor
donor” complex Cl2Beǟ1ǞBeCl2 might be formed as weakly (18.6 kcal·mol–1).[23a] This underlines the particular donor abil-
bonded adduct with an excess of BeCl2.
ity of a single ligand 1.
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The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)2
Scheme 2. Schematic presentation of the relative energies /kcal·mol–1 at BP86/TZVPP//BP86/SVP of the complexes of BeCl2 and 1. The values
in parentheses give the BDEs at BP86/SVP. For (5)2 see also the tautomeric form of the Be2Cl2 ring. The double arrow in 5 represents the
double lone-pair donation of the carbone donor; for details see text.
Scheme 2 shows an overview of the relative energies for the nation of a second donor species 1 unfavorable. The calcula-
complexes of BeCl2 and 1. It shows also the energy for the tion of 1ǞCl2Beǟ1 shows that the latter complex is higher
formation of the chlorine bridged dimer (Cl2Beǟ1)2. The opti- in energy than 1ǞCl2Be and free 1. The carbodiphosphorane
mized geometry of the latter complex is shown in Figure 3d. may bind, albeit weakly, a second BeCl2 species in the com-
The Be–Cl bonds of the moieties 5 are much longer in the plex Cl2Beǟ1ǞBeCl2. The bond dissociation energies for the
dimer (2.033 Å and 2.050 Å) than in free 5, whereas the Be– first and second BeCl2 fragments are De = 31.8 kcal·mol–1 and
Cl bonds between the monomers (2.132 Å and 2.203 Å) are 7.0 kcal·mol–1. The dimerization of Cl2Beǟ1 is energetically
still longer. Scheme 2 shows that the formation of the dimer slightly endoenergetic.
(Cl2Beǟ1)2 is slightly endoenergetic with respect to two
monomers. It seems unlikely that (Cl2Beǟ1)2 is formed in the
reaction of BeCl2 with 1.
5. Experimental Section
All operations were carried out in an argon atmosphere in dried and
degassed solvents using Schlenk techniques. The solvents were thor-
4. Conclusion and Outlook
oughly dried and freshly distilled prior to use. The IR spectra were run
with a Nicolet 510 spectrometer in Nujol mull (the Nujol mull bands
The use of 2-Br-fluorobenzene as the solvent in reactions
with the carbodiphosphorane 1 instead of the usual solvents
like toluene, THF, CH2Cl2, DMSO, or DME opens new as-
pects to the access of addition compound of the type 1ǞM (M
= transition metal or main group Lewis acids). 2-Br-fluoroben-
zene is polar enough to dissolve such adducts. Proton abstrac-
tion to give the favored cation [1ǞH]+ is suppressed. The
analysis of the bonding situation in Cl2Beǟ1 reveals that the
orbital donation comes mainly from the σ lone-pair orbital of
1, whereas the π donation is rather weak. However, the
are omitted). For the 31P NMR spectra we used the instrument Bruker
AC 300. The carbodiphosphorane C(PPh3)2 (1) was prepared accord-
ing to a modified literature procedure;[31] BeCl2 was prepared from
the elements.[30a] The solvent 2-bromofluorobenzene was dried with
P2O5.
Preparation of [Cl2BeC{PPh3}2] (5): A mixture of 1 (0.18 g,
0.34 mmol) and BeCl2 (0.066 g, 0.55 mmol) in 2-Br-fluorobenzene
(2 mL) was treated in an ultrasonic bath for 5 min followed by heating
for 1 min. A tan colored solution with some insoluble material on top
of the solution was obtained. The mixture was filtered and the solution
Cl2Beǟ1 π donation appears strong enough to make the do- layered with n-pentane (0.5 mL). Colorless crystals of 5 formed after
Z. Anorg. Allg. Chem. 2011, 1702–1710
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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W. Petz, G. Frenking, B. Neumüller, et al.
Table 3. Crystallographic data of the compounds [Cl2Be(C{PPh3}2)] (5), (Ph3PMe)Cl·0.25toluene (6), and (H2C{PPh3}2)Cl2·DME (8).
ARTICLE
5
6
8
Formula
Mw /g·mol–1
a /Å
b /Å
c /Å
α /°
β /°
γ /°
C37H30BeCl2P2
616.46
C20.75H20ClP
335.79
12.236(1)
16.300(1)
18.563(1)
90
102.24(1)
90
0.23ϫ0.08ϫ0.06
3618.2(4)
8
C41H42Cl2O2P2
699.59
12.999(1)
19.720(1)
14.634(1)
90
106.09(1)
90
0.58ϫ0.08ϫ0.06
3604.3(4)
4
10.076(1)
10.883(1)
15.211(2)
79.22(1)
84.76(1)
69.90(1)
0.12ϫ0.11ϫ0.10
1538.1(3)
2
Crystal size /mm
Volume /Å3
Z
dcalc /g·cm–3
Crystal system
Space group
Diffractometer
Radiation
Temperature /K
μ /cm–1
1.331
1.233
1.289
triclinic
monoclinic
P21/c (Nr. 14)
IPDS II (Stoe)
Mo-Kα
100
2.96
monoclinic
P21/n (Nr. 14)
IPDS II (Stoe)
Mo-Kα
100
3.04
¯
P1 (Nr. 2)
IPDS II (Stoe)
Mo-Kα
100
3.14
2θmax
°
51.92
51.92
51.84
Index range
–12 Յ h Յ 12
–13 Յ k Յ 13
–17 Յ l Յ 18
11584
5888 (0.1168)
2479
–15 Յ h Յ 14
–20 Յ k Յ 20
–22 Յ l Յ 22
48136
7033 (0.2269)
2440
–14 Յ h Յ 15
–24 Յ k Յ 24
–17 Յ l Յ 17
25116
6981 (0.1053)
4641
Number of rflns collected
Number of indep. rflns (Rint
Number of observed rflns
with Fo Ͼ 4σ(Fo)
)
Parameters
380
427
508
Absorption correction
Structure solution
numerical
numerical
numerical
direct methods SIR-92[32]
direct methods SIR-92[32]
direct methods SIR-92[32]
Refinement against F2
Hydrogen atoms
SHELXL-97[33]
SHELXL-97[33]
SHELXL-97[33]
calculated positions with common calculated positions with common
displacement parameter
calculated positions with common
displacement parameter. H(1) and
H(2) were refined free
0.0492
0.1167
0.469
displacement parameter
R1
0.0567
0.1208
0.715
0.0409
0.0608
0.195
wR2 (all data)
max. electron density left /
e·Å–3
several days in high yields. 31P NMR (in 2-Br-fluorobenzene): BP86[35]/def2-SVP[36] level of theory. The resolution-of-identity
19.00 ppm. IR (Nujol mull): ν˜ = 1587 w, 1479 s, 1437 s, 1261 w, method was applied.[37] Stationary points were characterized as min-
1235 w, 1111 vs. 1050 m, 1027 m, 997 m, 890 vs, 821 m, 751 s, 688 s,
ima by calculating the Hessian matrix analytically at this level of
theory. Additional single-point energy calculations at BP86 using the
654 m 546 m, 530 s, 523 s, 515 s, 497 s, 450 w, 417 w cm–1. Although
the 31P NMR signals of 5 and of the cation (HC{PPh3}2)+ are close TZVPP basis set[36] were also performed.
together, a clear distinction by IR spectroscopy could be achieved.
For the bonding analysis of Cl2Beǟ1 we optimized the molecule with
Structure Determinations: Crystallographic data could be obtained
for the compounds 5, 6, and 8; crystals formed as described above.
The molecular structure of 5 is shown in Figure 1 and Figure 2; crys-
tallographic data are collected in Table 3. Compound 6 contains a mo-
lecule of toluene disordered around a center of symmetry. The DME
molecule in 8 is disordered in two positions with occupation param-
eters 0.6 and 0.4. For structural details of (Ph3PMe)Cl·0.25toluene (6),
and (H2C{PPh3}2)Cl2·DME (8) see Supporting Information.
the program package ADF2009.01.[38] BP86 was chosen applying un-
contracted Slater-type orbitals (STOs) as basis functions.[39] The latter
basis sets for all elements have triple-ζ quality augmented by two sets
of polarization functions (ADF-basis set TZ2P). This level of theory
is denoted BP86/TZ2P. An auxiliary set of s, p, d, f, and g STOs was
used to fit the molecular densities and to represent the Coulomb and
exchange potentials accurately in each SCF cycle.[40] Scalar relativistic
effects were incorporated by applying the zeroth-order regular approxi-
mation (ZORA) in all ADF calculations.[41]
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-833915 (5), CCDC-833914 (6), and CCDC-833913
(8) (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk,
http://www.ccdc.cam.ac.uk).
The interatomic interactions were investigated by means of an energy
decomposition analysis (EDA) developed independently by Morok-
uma[42] and by Ziegler and Rauk.[43] The bonding analysis focuses on
the instantaneous interaction energy ΔEint of a bond A–B between two
fragments A and B in the particular electronic reference state and in
the frozen geometry of AB. This interaction energy is divided into
Quantum Chemical Calculations: Geometry optimizations were car-
ried out using the TurboMole optimizer[34] and gradients at the three main components [Equation (3)].
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 1702–1710

The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)2
[7] O. Diels, B. Wolf, Ber. Dt. Chem. Ges. 1906, 39, 689–697.
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ΔEint = ΔEelstat + ΔEPauli + ΔEorb
(3)
The term ΔEelstat corresponds to the quasiclassical electrostatic interac-
tion between the unperturbed charge distributions of the prepared
atoms and is usually attractive. The Pauli repulsion ΔEPauli is the en-
ergy change associated with the transformation from the superposition
of the unperturbed electron densities ρA + ρB of the isolated fragments
to the wave function Ψ0 = NÂ[ΨAΨB], which properly obeys the Pauli
principle through explicit antisymmetrization (Â operator) and renor-
malization (N = constant) of the product wave function. ΔEPauli com-
prises the destabilizing interactions between electrons of the same spin
on either fragment. The orbital interaction ΔEorb accounts for charge
transfer and polarization effects. The ΔEorb term can be decomposed
into contributions from each irreducible representation of the point
group of the interacting system. Since the molecules in our study have
at least Cs symmetry, it is possible to estimate the intrinsic strength of
orbital interactions from orbitals having aЈ (σ) and aЈЈ (π) symmetry
quantitatively. This directly gives the contributions of the σ and π
orbital interactions to the ΔEorb term:
[12] R. Tonner, G. Heydenrych, G. Frenking, ChemPhysChem 2008,
9, 1474–1481.
[13] A striking example was recently reported by Alcarazo et al. who
+
showed that the carbone 1 stabilizes BH2 through σ and π do-
nation in the complex H2B+ǟ1 which could become isolated and
characterized through X-ray analysis. In contrast, the reaction
with NHC leads to the complex NHCǞ(B2H5+)ǟNHC: B. Inés,
M. Patil, J. Carreras, R. Goddard, W. Thiel, M. Alcarazo, Angew.
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[14] W. Petz, G. Frenking, Top. Organomet. Chem. 2010, 13, 49–92.
[15] a) H. Schmidbaur, C. E. Zybill, D. Neugebauer, Angew. Chem.
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Naturforsch. 1985, 40b, 1193–1300.
ΔEorb (Cs) = ΔEσ(aЈ) + ΔEπ(a")
(4)
[16] W. Petz, C. Kutschera, S. Tschan, F. Weller, B. Neumüller, Z.
Anorg. Allg. Chem. 2003, 629, 1135–1144.
Further details on the EDA method[38] and its application to the analy-
sis of the chemical bond[44] can be found in the literature.
[17] a) W. Petz, F. Weller, J. Uddin, G. Frenking, Organometallics
1999, 18, 619–626; b) H. Schmidbaur, C. E. Zybill, G. Müller, C.
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[19] J. Vicente, A. R. Singhal, P. G. Jones, Organometallics 2002, 21,
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[20] W. Petz, F. Öxler, B. Neumüller, R. Tonner, G. Frenking, Eur. J.
Inorg. Chem. 2009, 4507–4517.
Supporting Information: (see footnote on the first page of this arti-
cle). Additional structural views and information on compounds 6 and
8 are given. We also give tables with the total energies and the coordi-
nates of the calculated molecules.
Acknowledgement
We thank the Deutsche Forschungsgemeinschaft for financial support.
W.P. is also grateful to the Max-Planck-Society, Munich, Germany, for
supporting this research project.
[21] a) W. Petz, C. Kutschera, B. Neumüller, Organometallics 2005,
24, 5038–5043; b) W. Petz, B. Neumüller, Polyhedron 2011, 30,
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[22] a) B. Neumüller, K. Dehnicke, Z. Anorg. Allg. Chem. 2003, 629,
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Received: July 20, 2011
Published Online: September 27, 2011
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Z. Anorg. Allg. Chem. 2011, 1702–1710