The first carbene complex of a diorganoberyllium: Synthesis and structural characterization of Ph2Be(i-Pr-carbene) and Ph 2Be(n-Bu2O)

Article abstract of DOI:10.1021/om0603114

The reaction of base-free Ph₂Be with 1,3-di-isopropyl-4,5-dimethylimidazol-2-ylidene (i-Pr-carbene) in toluene gave the carbene adduct Ph₂Be(i-Pr-carbene) (1) as colorless crystal blocks. For comparison, the di-n-butyl ether adduct Ph₂-Be(n-Bu ₂O) (2) was prepared from BeCl₂ and PhLi in a mixture of Et₂O and n-Bu₂O. Single-crystal X-ray determinations reveal monomeric solid-state structures for both complexes.

Full text of DOI:10.1021/om0603114

3784
Organometallics 2006, 25, 3784-3786
Notes
The First Carbene Complex of a Diorganoberyllium: Synthesis and
Structural Characterization of Ph2Be(i-Pr-carbene) and
Ph2Be(n-Bu2O)
Jochen Gottfriedsen* and Steffen Blaurock
Chemisches Institut der Otto-Von-Guericke-UniVersita¨t Magdeburg, UniVersita¨tsplatz 2,
D-39106 Magdeburg, Germany
ReceiVed April 6, 2006
Summary: The reaction of base-free Ph2Be with 1,3-di-isopro-
pyl-4,5-dimethylimidazol-2-ylidene (i-Pr-carbene) in toluene
gaVe the carbene adduct Ph2Be(i-Pr-carbene) (1) as colorless
crystal blocks. For comparison, the di-n-butyl ether adduct Ph2-
Be(n-Bu2O) (2) was prepared from BeCl2 and PhLi in a mixture
of Et2O and n-Bu2O. Single-crystal X-ray determinations reVeal
monomeric solid-state structures for both complexes.
diphenylberyllium. A nucleophilic carbene complex of beryllium
is known only for the reaction of BeCl2 that forms the beryllium
carbene complex [(Me-carbene)3BeCl]Cl (Me-carbene ) 1,3-
dimethylimidazol-2-ylidene).11,12 Also, sophisticated theoretical
studies of a series of beryllium-carbene complexes were
performed.13 Herein we report the synthesis and structure
determination of novel diphenylberyllium complexes containing
1,3-di-isopropyl-4,5-dimethylimidazol-2-ylidene and di-n-butyl
ether as Lewis bases. The former represents the first well-defined
carbene complex of a diorganoberyllium.
Introduction
Beryllium chemistry has received the least attention among
the nonradioactive group 2 elements. The main reason for this
is the exceptionally high toxicity of beryllium and its com-
pounds.1,2 Nevertheless, the chemistry of beryllium was already
studied in the early years of organometallic chemistry. The
synthesis of diphenylberyllium was first reported in 1927 by
Gilman et al. starting from elemental Be and Hg(C6H5)2 in a
sealed tube at 225 °C.3 Various other ways to prepare diphen-
ylberyllium have been described using different methods such
as the Grignard, organolithium, or organomercury method.4
Several Lewis base adducts were studied, such as Ph2Be-
(Et2O)25-7, Ph2Be(TMEDA)2 (TMEDA ) tetramethylethylene-
diamine),7 and Ph2Be(DME)2 (1,2-dimethoxyethane).5,7 Fur-
thermore, reactivity studies of diphenylberyllium with ketones,
aldehydes, and azomethine compounds were performed.8 More
recently, the synthesis and structure of Mes2Be(Et2O) (Mes )
2,4,6-Me3C6H2)9 was reported as well as detailed studies of
heteroleptic ArBeX(Et2O) complexes (Ar ) 2,6-Mes2C6H3,
Results and Discussion
Diphenylberyllium reacts with the stable nucleophilic carbene
1,3-di-isopropyl-4,5-dimethylimidazol-2-ylidene in toluene at
room temperature to give the nucleophilic carbene complex Ph2-
Be(i-Pr-carbene) (1) in high yield in the form of colorless
crystals (eq 1).
9
In contrast to the starting material Ph2Be, which is only poorly
soluble in nonpolar organic solvents, the carbene adduct 1 is
highly soluble in toluene and pentane. The corresponding di-
n-butyl ether adduct Ph2Be(n-Bu2O) (2) was obtained from
BeCl2 dissolved in diethyl ether and PhLi dissolved in di-n-
butyl ether at room temperature (eq 2). This synthetic route
provides straightforward access to Lewis base adducts of
diphenylberyllium.
X ) Cl, Br) including Be NMR.10 No single-crystal X-ray
structures are known of Lewis base adducts of the simple
* To whom correspondence should be addressed. E-mail:
jochen.gottfriedsen@vst.uni-magdeburg.de.
(1) Skilleter, D. N. Chem. Br. 1990, 26, 26.
(2) Kumberger, O.; Schmidbaur, H. Chem. Uns. Zeit 1993, 27, 310.
(3) Gilman, H.; Schulze, F. J. Chem. Soc. 1927, 2663.
(4) (a) Schmidbaur, H. Gmelin, Handbook of Inorganic Chemistry; 1987;
Vol. Be-Org. 1, pp 69-76. (b) Bell, N. A. ComprehensiVe Organometallic
Chemistry I; Pergamon: New York, 1983; Vol. 1, Chapter 3. (c) Bell, N.
A. ComprehensiVe Organometallic Chemistry II; Pergamon: New York,
1995; Vol. 1, Chapter 2.
(5) Wittig, G.; Hornberger, P. Liebigs Ann. Chem. 1952, 577, 11.
(6) Ashby, E. C.; Arnott, R. C. J. Organomet. Chem. 1968, 14, 1.
(7) Coates, G. E.; Tranath, M. J. Chem. Soc. (A) 1967, 236.
(8) Andersen, R. A.; Coates, G. E. J. Chem. Soc., Dalton Trans. 1974,
1171.
(9) Ruhlandt-Senge, K.; Bartlett, R. A.; Olmstead, M. M.; Power, P. P.
Inorg. Chem. 1993, 32, 1724.
(11) Herrmann, W. A.; Runte, O.; Artus, G. J. Organomet. Chem. 1995,
501, C1.
(12) Herrmann, W. A.; Ko¨cher, C. Angew. Chem. 1997, 109, 2256.
(13) Fro¨hlich, N.; Pidun, U.; Stahl, M.; Frenking, G. Organometallics
1997, 16, 442.
(10) Niemeyer, M.; Power, P. P. Inorg. Chem. 1997, 36, 4688.
10.1021/om0603114 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/15/2006

Notes
Compound 2 is also freely soluble in nonpolar solvents as
Organometallics, Vol. 25, No. 15, 2006 3785
well as in Et2O and THF. Both compounds form colorless
1
crystals and exhibit high air- and moisture-sensitivity. The H
NMR data show the phenyl signals for both compounds in the
expected area, whereas the signal for the proton in ortho position
to beryllium in 1 is shifted downfield by 0.2 ppm in contrast to
2. The 13C NMR resonance shows the typical upfield shift of
the carbene carbon from 207.4 ppm in the “free” carbene to
173.6 ppm in 1 and is in good agreement with the value
determined for [(Me-carbene)3BeCl]Cl.11 The resonance of the
CH3 groups of the isopropyl groups is shifted to high field by
1
over 0.4 ppm in the H NMR and 2 ppm in the 13C NMR
compared to the corresponding free carbene. This might be due
to an interaction of the methyl groups with the metal, which
was also observed for a series of carbene complexes of the
heavier alkaline earth metals.14 The 9Be NMR resonances for 1
2+
and 2 relative to Be(H2O)4 as external standard were found
at 21.05 ppm (ω1/2 ) 464 Hz) and 17.4 ppm (ω1/2 ) 239 Hz),
respectively. Generally, an increasing coordination number of
beryllium results in a chemical shift at higher field, whereas
the chemical shifts of 9Be are in the range from δ ca. -25 to δ
+25 ppm.15,16 The results for 1 and 2 are in good agreement
with a coordination number of 3 (e.g., δ ) 20.8 ppm for Me2-
Figure 1. ORTEP plot of 1 with 50% probability thermal
ellipsoids. Selected bond lengths (Å) and angles (deg): Be-C(7)
) 1.745(4), Be-C(1) ) 1.757(4), Be-C(13) ) 1.807(4), N(1)-
C(13) ) 1.342(3), N(2)-C(13) ) 1.340(3), C(7)-Be-C(1) )
126.6(3), C(7)-Be-C(13) ) 115.9(2), C(1)-Be-C(13) ) 117.4-
(2), N(2)-C(13)-N(1) ) 105.6(2); Be′-C(7′) ) 1.749(4), Be′-
C(1′) ) 1.752(4), Be′-C(13′) ) 1.787(4), N(1′)-C(13′) )
1.350(3), N(2′)-C(13′) ) 1.353(3), C(7′)-Be′-C(1′) ) 125.7(2),
C(7′)-Be′-C(13′) ) 117.6(2), C(1′)-Be′-C(13′) ) 116.5(2),
N(1′)-C(13′)-N(2′) ) 104.7(2).
9
Be(Et2O)15 and are at lower field than the Be shifts for the
heteroleptic complexes ArBeX(Et2O) (Ar ) 2,6-Mes2C6H3,
X ) Cl, Br) (12.8 and 13.4 ppm, respectively), which also
possess a coordination number of 3 in solution.10
Single-crystal X-ray structure determinations of 1 and 2 reveal
monomeric molecular structures in the solid state (Figures 1
and 2). Compound 1 crystallizes in the space group P21 with
two different molecules in the asymmetric unit, whose distances
and angles are nearly identical. Refinement in the centrosym-
metric space group P21/n was not possible. Compound 2
crystallizes in the space group P21/c. The beryllium centers in
both complexes exhibit a distorted trigonal planar coordination
sphere with nearly equivalent angles around the metal center
(C(7)-Be-C(1) ) 126.6(3)°, C(7)-Be-C(13) ) 115.9(2)°,
C(1)-Be-C(13) ) 117.4(2)°/C(7′)-Be′-C(1′) ) 125.7(2)°,
C(7′)-Be′-C(13′) ) 117.6(2)°, C(1′)-Be′-C(13′) ) 116.5-
(2)° for 1 and O(1)-Be(1)-C(1) ) 116.80(12)°, O(1)-Be(1)-
C(7) ) 115.40(13)° for 2, respectively). The Be-C(aryl) bond
lengths in 1 (1.75-1.76 Å) and 2 (1.73-1.75 Å) are in the
typical range for beryllium aryl distances and are in good
agreement with the known values for Mes2Be(Et2O) (1.739(3)
Å)9 and ArBeX(Et2O) (1.74-1.78 Å).10 The Be-C(carbene)
bond in 1 is slightly longer (1.787(4) and 1.807(4) Å) and is
thus in good agreement with the distance found in the only other
known beryllium carbene complex, [(Me-carbene)3BeCl]Cl (Me-
carbene ) 1,3-dimethylimidazol-2-ylidene) (1.807(3) and 1.822-
(3) Å).11,12 Beryllium-oxygen distances normally vary from
1.60 to 1.69 Å. The value of the Be-O bond (1.647(2) Å) in 2
resulting from the coordination of the di-n-butyl ether to the
beryllium is within this range. The corresponding bond lengths
in Mes2Be(Et2O) (1.638(5) Å)9 and ArBeX(Et2O) (1.60-1.61
Å)10 are in the same range and match well with the Be-O
distance in 2.
Figure 2. ORTEP plot of 2 with 50% probability thermal
ellipsoids. Selected bond lengths (Å) and angles (deg): Be(1)-
O(1) ) 1.647(2), Be(1)-C(1) ) 1.734(2), Be(1)-C(7) ) 1.745-
(2), O(1)-Be(1)-C(1) ) 116.80(12), O(1)-Be(1)-C(7) ) 115.40-
(13), C(1)-Be(1)-C(7) ) 127.79(13).
phenyl groups, which are sterically less bulky than the mesityl
groups in Mes2Be(Et2O).9 The presented complexes with their
straightforward synthetic routes should facilitate further devel-
opment of this largely neglected class of compounds.
In summary we achieved the first structural characterization
of a diorganoberyllium carbene complex. In addition, we have
demonstrated that diphenylberyllium Lewis base adducts possess
a coordination number of 3 even when employing unsubstituted
Experimental Section
Cautionary note: Beryllium and its compounds are extremely
toxic. Any work with these materials should be conducted according
to the established safe-handling procedures.
General Procedures. The reactions were carried out in an inert
atmosphere of dry argon using standard drybox and Schlenk
(14) Schumann, H.; Gottfriedsen, J.; Glanz, M.; Dechert, S.; Demtschuk,
J. J. Organomet. Chem. 2001, 617-618, 588-600.
(15) Kovar, R. A.; Morgan, G. L. J. Am. Chem. Soc. 1970, 92, 5067.
(16) Gaines, D. F.; Coleson, K. M.; Hillenbrand, D. F. J. Magn. Reson.
1981, 44, 84.

3786 Organometallics, Vol. 25, No. 15, 2006
Notes
1
techniques. The melting points were determined in a sealed capillary
without correction. NMR spectra were recorded on a Bruker DPX
400 or AVANCE 600 NMR spectrometer. All chemical shifts are
reported in ppm. 1H and 13C chemical shifts are referenced to
tetramethylsilane as internal standard, and 9Be chemical shifts are
referenced to BeCl2, 0.1 mol/L in D2O. The mass spectra (EI, 70
eV) were obtained using a Finnigan SSQ 7000. Only characteristic
fragments containing the isotopes of the highest abundance are
listed. The elemental analysis was performed on a LECO CHNS932
apparatus. The starting materials beryllium powder, beryllium
chloride, and diphenylmercury were purchased from Aldrich
Chemical Co. and used as received. Solvent-free Ph2Be was
synthesized according to literature procedures17 without any activa-
tion of the beryllium powder, which was used as received. Beryllium
powder and diphenylmercury were mixed in a Schlenk flask in the
glovebox, and 200 mL of xylene was added. The reaction mixture
was heated at reflux conditions under argon for 3 days under
formation of metallic mercury.
Found: C 81.34, H 9.33. H NMR (400 MHz, C6D6, 25 °C): δ
7.98 (m, 4H, o-PhH), 7.47 (m, 4H, m-PhH), 7.38 (m, 2H, p-PhH),
3.65 (t, J(1H,1H) ) 7.3 Hz, 4H, OCH2), 1.24 (pent, J(1H,1H) )
3
3
7.3 Hz, 4H, OCH2CH2), 0.94 (d, J(1H,1H) ) 7.3 Hz, 4H, CH2-
3
CH3), 0.59 (d, 3J(1H,1H) ) 7.3 Hz, 6H CH2CH3). 13C NMR (100.6
MHz, C6D6, 25 °C): δ 154.8 (BeC(Ar)), 138.9 (2-C(Ar)), 127.4
(3-C(Ar)), 127.2 (4-C(Ar)), 73.4 (OCH2CH2), 30.2 (OCH2CH2),
9
18.6 (CH2CH3), 13.6 (CH2CH3). Be NMR (56.2 MHz, C6D6, 25
°C): δ 17.4 (ω1/2 ) 239 Hz). MS (EI, Be): m/z (%) 155 (100)
9
[C12H11]+•.
X-ray Crystal Structure Determination. X-ray crystal data for
1: C23H30BeN2, M ) 343.50, T (K), 200(2), λ ) 0.71073 Å,
monoclinic, P21, a ) 9.3630(3) Å, b ) 25.2755(8) Å, c ) 9.6082-
(3) Å, R ) 90°, â ) 112.7240(10)°, γ ) 90°, V ) 2097.32(11)
Å3, Z ) 4, density 1.088 mg/m3, abs coeff ) 0.062 mm-1
,
F(000) ) 744, θ range ) 2.30° to 28.67°, 16 367 reflections,
9130 unique, [R(int) ) 0.0301], completeness to θ ) 27.96° )
92.1%, absorption correction: SADABS, max./min. transmission
) 0.9755 and 0.9636, refinement method: full-matrix least-squares
on F2, 679 parameters, GOF ) 1.109, R1 [I > 2σ(I)] ) 0.0589,
wR2 ) 0.1563, R1 (all data) ) 0.0787, wR2 ) 0.1686.
X-ray crystal data for 2: C20H28BeO, M ) 293.43, T (K), 200(2),
λ ) 0.71073 Å, monoclinic, P21/c, a ) 9.4993(9) Å, b ) 10.5282-
(10) Å, c ) 18.7174(18) Å, R ) 90°, â ) 103.118(2)°, γ ) 90°,
V ) 1823.1(3) Å3, Z ) 4, density 1.069 mg/m3, abs coeff ) 0.062
mm-1, F(000) ) 640, θ range ) 3.31° to 28.29°, 12 185 reflections,
4258 unique, [R(int) ) 0.0409], completeness to θ ) 27.96° )
94.0%, absorption correction: SADABS, max./min. transmission
) 0.9877 and 0.9695, refinement method: full-matrix least-squares
on F2, 311 parameters, GOF ) 1.000, R1 [I > 2σ(I)] ) 0.0515,
wR2 ) 0.1284, R1 (all data) ) 0.0905, wR2 ) 0.1485. CCDC
603138 (1) and CCDC 603137 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, by
e-mailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, U.K.; fax: +49 1223 336033.
Ph2Be(i-Pr-carbene) (1). A 0.5 g (3.1 mmol) amount of Ph2Be
was suspended in 30 mL of toluene, and 0.56 g (3.1 mmol) of
1,3-di-isopropyl-4,5-dimethylimidazol-2-ylidene, dissolved in 20
mL of toluene, was added. The unsolvated Ph2Be dissolved
immediately under formation of a clear solution. After stirring for
another 12 h, the solvent was reduced in vacuo to 10 mL. The
product crystallized at -20 °C as colorless crystal blocks (0.91 g,
85%). Mp: 172 °C (dec). Anal. Calcd for [C23H30N2Be]: C 80.42,
1
H 8.80, N 8.16. Found: C 80.61, H 8.91, N 8.02. H NMR (400
MHz, C6D6, 25 °C): δ 8.21 (dd, 3J(1H,1H) ) 6.8 Hz, 5J(1H,1H) )
1.4 Hz, 4H, o-PhH), 7.53 (m, 4H, m-PhH), 7.41 (m, 2H, p-PhH),
3
3.89 (sept, J(1H,1H) ) 6.4 Hz, 2H, CH3CH), 1.49 (s, 6H, NC-
3
(CH3)), 1.06 (d, J(1H,1H) ) 6.4 Hz, 12H NCH(CH3)). 13C NMR
(100.6 MHz, C6D6, 25 °C): δ 173.6 (NCN), 160.2 (BeC(Ar)), 140.3
(2-C(Ar)), 126.8 (3-C(Ar)), 126.1 (4-C(Ar)), 123.8 (NCCH3), 50.9
(NCHCH3), 22.5 (NCHCH3), 8.7 (NCCH3). 9Be NMR (56.2 MHz,
9
C6D6, 25 °C): δ 21.05 (ω1/2 ) 464 Hz). MS (EI, Be): m/z (%)
344 (38) [M]+•, 329 (12) [M - CH3]+, 267 (100) [M - Ph]+.
Ph2Be(n-Bu2O) (2). A 0.5 g (6.3 mmol) portion of BeCl2 was
dissolved in 50 mL of diethyl ether, and 12.6 mmol of PhLi,
dissolved in di-n-butyl ether (5 mL, c ) 2.5 mol/L), was added
dropwise via a syringe at room temperature. After stirring the
solution for 12 h, the solvents were removed in vacuo and the
resulting white solid was dissolved in 10 mL of pentane. The
product crystallized at -20 °C as colorless crystals (1.4 g, 76%).
Mp: 45 °C. Anal. Calcd for [C20H28OBe]: C 81.86, H 9.62.
Acknowledgment. The authors thank the Otto-von-
Guericke-Universita¨t Magdeburg for financial support and Prof.
F. T. Edelmann for helpful discussions.
Supporting Information Available: Crystallographic informa-
tion files (CIFs). This material is available free of charge via the
Internet at http://pups.acs.org.
(17) Coates, G. E.; Tranath, M. J. Chem. Soc. (A) 1967, 236.
OM0603114