Double lithiation of 2,4,6-triphenylbromobenzene: Synthesis of bis-amidines and an aluminium bis-amidinate complex

Article abstract of DOI:10.1039/b205875h

The substituted m-terphenyl 2,4,6-triphenylbromobenzene (2Br) reacts cleanly with two equivalents of n-butyllithium in diethyl ether/hexane solution to produce the dilithiated species 2Li₂. Treatment of 2Li₂ with dialkylcarbodiimides (RN=C=NR, R = isopropyl or cyclohexyl) followed by aqueous work-up of the reaction mixture results in the formation of sterically hindered bifunctional amidines 5H₂ and 6H₂. Two bis-amidine derivatives were crystallographically characterised. Compound 5H₂ reacts readily with trimethylaluminium to form a novel dialkylaluminium bis-amidinate complex 5[AlMe₂]₂.

Full text of DOI:10.1039/b205875h

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Double lithiation of 2,4,6-triphenylbromobenzene: synthesis of
bis-amidines and an aluminium bis-amidinate complex
Hilary A. Jenkins,*a Deepa Abeysekera,b Diane A. Dickieb and Jason A. C. Clyburne*b
a Department of Chemistry, Saint Mary’s University, Halifax, Nova Scotia, B3H 3C3, Canada.
E-mail: hilary.jenkins@stmarys.ca
b Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, V5A 1S6,
Canada. E-mail: clyburne@sfu.ca
Received 18th June 2002, Accepted 5th August 2002
First published as an Advance Article on the web 23rd September 2002
The substituted m-terphenyl 2,4,6-triphenylbromobenzene (2Br) reacts cleanly with two equivalents of n-butyllithium
in diethyl ether/hexane solution to produce the dilithiated species 2Li2. Treatment of 2Li2 with dialkylcarbodiimides
(RN᎐C᎐NR, R = isopropyl or cyclohexyl) followed by aqueous work-up of the reaction mixture results in the
᎐ ᎐
formation of sterically hindered bifunctional amidines 5H2 and 6H2. Two bis-amidine derivatives were
crystallographically characterised. Compound 5H2 reacts readily with trimethylaluminium to form a novel
dialkylaluminium bis-amidinate complex 5[AlMe2]2.
Introduction
The 4-electron donor, monoanionic amidinate ligand 1 is an
important substituent in organometallic chemistry. This ligand
readily binds to numerous main group elements, transition
metals, lanthanides, and actinides to form stable amidinate
complexes.1 Research on alkyl aluminium amidinate complexes
has indicated that these complexes may serve as potential ethyl-
ene polymerisation catalysts.2–4 In addition, interest has also
been focused on the applicability of aluminium amidinate
complexes as potential single source precursors to materials
containing the nitride ion.5 Amidinate complexes such as these
are easily prepared by reacting AlX3 (X = halide or alkyl) with
the corresponding amidines 1H.6
The first use of an m-terphenyl substituted amidine was an
insightful study by Schmidt and Arnold7 in which they identi-
fied the first mono-amidinate complexes of yttrium. It was
found that the sterically demanding m-terphenyl group on the
central carbon atom provided steric protection in the plane of
the ligand as well as above and below that plane. This created a
2Br,11 is easily metallated on the central ring by treatment with
bowl-shaped environment for the amidinate ligand that could
stabilize unusual coordination patterns in main group and trans-
ition metals. Subsequently, we used the triphenylphenyl sub-
stituent 2 to prepare the amidines 3H and 4H in high yield.8,9
Treatment of 3H and 4H with AlMe3 produced robust
aluminium amidinate complexes 3[AlMe2] and 4[AlMe2].
During these studies we identified a novel reaction leading to
asymmetric bis-amidines.10 Herein we report a simple prepar-
ation of 2Li2 and the bulky bis-amidines 5H2 and 6H2. The
preparation (Scheme 1) and characterisation of the aluminium
bis-amidinate complex 5[AlMe2]2 are reported, as well as the
crystallographic characterisation of the mono-protonated
bis-amidine salt 6H3Cl.
one equivalent of 1.6 M n-BuLi in hexane and stirring for four
hours.12 Serendipitously, and under similar reaction conditions,
2Br reacts cleanly with two equivalents of 1.6 M n-BuLi at
room temperature to form the dilithium salt 2Li2.13,14 Attempts
to isolate a crystalline sample of 2Li2 failed, but evidence for its
intermediacy is supported by its treatment with carbodiimides
to produce bis-amidines 5H2 and 6H2.
Conversion of 2Li2 to a bis-amidine is achieved via treatment
of the reaction mixture with a carbodiimide R–N᎐C᎐N–R (R =
᎐ ᎐
isopropyl or cyclohexyl). This produces the lithium amidinate
intermediate, which upon aqueous work-up gives 5H2 and 6H2.
Purification of these compounds is achieved by extraction with
CH2Cl2 and recrystallisation from toluene to produce the highly
soluble bis-amidines 5H2 and 6H2 in 72% and 29% yield,
respectively.
Results and discussion
The N–H (5H2 ν = 3420, 3208 cmϪ1; 6H2 ν = 3402, 3205 cmϪ1),
C᎐N (5H ν = 1614 cmϪ1; 6H2 ν = 1623 cmϪ1), and C–N (5H2
Synthesis and characterisation of amidines
The substituted m-terphenyl, 2,4,6-triphenylbromobenzene
᎐
2
ν = 1298 cmϪ1; 6H2 ν = 1256 cmϪ1) stretching frequencies of
DOI: 10.1039/b205875h
J. Chem. Soc., Dalton Trans., 2002, 3919–3922
This journal is © The Royal Society of Chemistry 2002
3919

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treatment of 6H2 with a 4.0 M dioxane solution of HCl. The
resulting white solid was isolated and characterised as 6H3Cl.
The structure is shown in Fig. 2.
Scheme 1 Preparation of bis-amidines 5H2 and 6H2 and the bis-
aluminium amidinate 5[AlMe2]2.
5H2 and 6H2 are in agreement with IR spectral frequencies
previously reported for other amidines.15,16 NMR studies (1H
and 13C) in CD2Cl2 solution are consistent with the proposed
structures. Some of these resonances are broadened due to
interconversion between Z-syn and E-syn isomers that occurs
on the NMR timescale.17
X-Ray crystallographic studies were performed on 5H2 to
evaluate the steric demands of the m-terphenyl group with
respect to the two amidine fragments. The structure of 5H2 is
shown in Fig. 1 and full crystallographic details are given in
Fig. 2 Selected bond lengths (Å), angles (Њ) and torsion angles (Њ) for
6H3Cl (thermal ellipsoids are shown at 50% probability level): N1–C7
1.315(4), N1–C41 1.453(4), N2–C7 1.301(4), N2–C51 1.479(4), C7–C1
1.524(4), N3–C8 1.273(4), N3–C61 1.468(5), N4–C8 1.366(5), N4–C71
1.478(4), C8–C12 1.504(5), Cl1 ؒ ؒ ؒ N2 3.287(3) Cl1 ؒ ؒ ؒ H2A 2.4812,
N3 ؒ ؒ ؒ N1 2.812(4), N3 ؒ ؒ ؒ HIA 1.9467; C7–N1–C41 126.5(3), C7–
N2–C51 126.3(3), C8–N3–C61 121.1(3), C8–N4–C71 122.9(3), N1–C7–
C1 115.6(3), N2–C7–C1 120.8(3), N3–C8–C12 117.5(3), N4–C8–C12
115.8(3), Cl1 ؒ ؒ ؒ H2A–N2 154.43, N3 ؒ ؒ ؒ H1A–N1 172.45; N1–C7–
C1–C2 Ϫ60.6(4), N4–C8–C12–C13 Ϫ53.6(4), C12–C11–C2–C3
Ϫ83.5(4).
The molecule 6H3Cl crystallises in the space group Cc.
Location of the protonation was determined via measurements
of the hydrogen bond interactions between the cation and
anion, as well as by examination of the metrical parameters for
the amidine unit. For instance, as shown in Fig. 2, the chloride
anion engages in hydrogen bonding with the protonated
nitrogen (Cl1–N2 = 3.287(3), Cl1 ؒ ؒ ؒ H2A = 2.4812 Å) consist-
ent with other Cl ؒ ؒ ؒ H–N interactions.19 Also, the C–N bond
lengths within the central amidine fragment are 1.301(4) (C7–
N2) and 1.315(4) Å (C7–N1). Since they are close in length,
and both are intermediate in length between the C–N and
C᎐N lengths observed in the neutral 5H , this is the chemically
᎐
2
reasonable site of protonation. The flanking amidine fragment
possesses asymmetric C᎐N (C8–N3 = 1.273(4) Å) and C–N
(C8–N4 = 1.366(5) Å) bonds, consistent with the neutral
amidine moiety.
A notable structural feature (Fig. 2) of 6H3Cl is the
᎐
Fig. 1 Selected bond lengths (Å), angles (Њ) and torsion angles (Њ) for
5H2 (thermal ellipsoids are shown at 50% probability level): N1–C1
1.295(2), N1–C2 1.466(3), N2–C1 1.350(2), N2–C5 1.458(2), C1–C21
1.507(2), N3–C8 1.289(2), N3–C9 1.461(3), N4–C8 1.365(2), N4–C12
1.457(3), C8–C36 1.507(3), N1 ؒ ؒ ؒ N4 3.094(2), N1 ؒ ؒ ؒ H4A
2.240(19); C1–N1–C2 120.18(17), C1–N2–C5 128.12(18), C8–N3–C9
120.83(18), C8–N4–C12 123.01(19), N1–CI–C21 114.62(16), N2–C1–
C21 119.13(17), N3–C8–C36 127.54(17), N4–C8–C36 111.09(17),
NI ؒ ؒ ؒ H4A–N4 173.3(19); C35–C36–C8–N3 68.5(3), C36–C31–C22–
C23 64.2(2), C22–C21–C1–N1 61.1(2), C21–C26–C51–C56 45.8(3).
N–H ؒ ؒ ؒ N hydrogen bond (N1 ؒ ؒ ؒ N3
= 2.812(4) Å,
N3 ؒ ؒ ؒ H1A = 1.9467 Å, N3 ؒ ؒ ؒ H1A–N1 = 172.45Њ) that locks
the two amidine units. A bridging N–H ؒ ؒ ؒ N interaction
(Fig. 1) is also observed in 5H2 (N1 ؒ ؒ ؒ N4 = 3.094(2) Å,
N1 ؒ ؒ ؒ H4A = 2.240(19) Å, N1 ؒ ؒ ؒ H4A–N4 = 173.3(19)Њ).
This type of bridging hydrogen bond fits the definition of a
moderately strong hydrogen bond.20 The N–H ؒ ؒ ؒ N hydrogen
bond observed in 6H3Cl is shorter than that seen in 5H2 because
of charge assistance.
Table 1. The molecular structure indicates that 5H2 exists in the
solid state in the E-syn configuration. In general, the E conform-
ation is energetically more favoured than its Z counterpart.15
The structure of 6H2 was also confirmed by X-ray crystal-
lography. In one experiment, several crystals of 6H3Cl were
isolated in low yield from an attempted metallation reaction.18
This compound was subsequently prepared systematically by
Synthesis and characterisation of the aluminium complex
5[AlMe2]2
Drop-wise addition of a slight excess of AlMe3 to a toluene
3920
J. Chem. Soc., Dalton Trans., 2002, 3919–3922

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Table 1 Crystal data and structure refinement for 5H2 and 6H3Cl
Compound
5H2
6H3Cl
Empirical formula
M
C38H46N4
558.79
C50H63ClN4ؒ1.5CH2Cl2
882.88
T /K
Crystal system
Space group
223(2)
213(2)
Monoclinic
Cc
Triclinic
¯
P1
a/Å
b/Å
c/Å
9.0339(16)
10.1074(18)
18.511(3)
16.300(2)
15.3088(19)
20.157(3)
α/Њ
β/Њ
98.273(3)
90.256(4)
90
95.155(2)
γ/Њ
99.322(4)
1649.8(5)
90
V/Å3
5009.9(11)
Z
2
4
µ/mmϪ1
0.066
0.273
Reflections collected
Independent reflections
Final R indices [I>2σ(I)]
R indices (all data)
9644
14236
6389 [R(int) = 0.0232]
R1 = 0.0529, wR2 = 0.1016
R1 = 0.1045, wR2 = 0.1160
8381 [R(int) = 0.0171]
R1 = 0.0596, wR2 = 0.1693
R1 = 0.0693, wR2 = 0.1764
solution of 5H2 affords the bis-aluminium amidinate 5[AlMe2]2
Experimental
1
as a white solid. This compound was characterised by H and
13C NMR, as well as elemental analysis and infrared spec-
troscopy. Unfortunately, we were unable to crystallographically
characterise this material.
General
An MBraun UL-99-245 dry box and standard Schlenk tech-
niques on a double manifold vacuum line were used in the
manipulation of air and moisture sensitive compounds. NMR
spectra were recorded on a Bruker AMX 400 spectrometer in
The IR spectrum of the solid white reaction product
5[AlMe2]2, indicates that the N–H stretching frequency of the
1
amidine 5H2 (3420–3400 cmϪ1) is absent. Likewise, H NMR
five millimeter quartz tubes. H and 13C{1H} chemical shifts
1
studies show the disappearance of the signal attributed to the
N–H resonance. The elemental analysis is consistent with the
proposed formula, and the 1H NMR spectrum exhibits features
anticipated for this molecule. Most striking is the presence of
four unique 1H signals for the Al–CH3 fragments, which occur
at Ϫ0.66, Ϫ0.73, Ϫ0.94, and Ϫ1.19 ppm.
In an attempt to gain more insight into the structure of
5[AlMe2]2 semi-empirical calculations (PM3) were performed,
and the results are shown in Fig. 3. An important feature is the
are reported in parts per million (ppm) downfield from tetra-
methylsilane (TMS) and are calibrated to the residual signal
of the solvent. Infrared spectra were obtained using a Bomem
MB spectrometer with the % transmittance values reported
in cmϪ1. Melting points were measured using a Mel-Temp
apparatus and are uncorrected.
Syntheses
5H2. To a suspension of 15.0 g (38.9 mmol) 2,4,6-triphenyl-
bromobenzene in 60 cm3 anhydrous diethyl ether and 10 cm3
anhydrous hexane, 50.0 cm3 (80.0 mmol) of 1.6 M butyllithium
was added drop-wise and stirred for 4 h at room temperature.
To the resulting solution, 10.0 g (80 mmol) of N,NЈ-diiso-
propylcarbodiimide dissolved in ca. 30 cm3 THF was added
drop-wise and stirred overnight. After quenching with water,
the reaction mixture was extracted with CH2Cl2. The organic
layer was then washed with water and saturated NaCl and dried
over anhydrous MgSO4. After removal of solvent, the remain-
ing solid was dissolved in warm toluene and filtered to remove
insoluble LiBr. Upon cooling, the filtrate formed well-defined
crystals that were characterised as 5H2 (15.65 g, 28.0 mmol,
72%); mp 197–198 ЊC. 1H NMR (400 MHz, CDCl3) δ 0.18–1.43
(br, 24H, alkyl CH3), 3.25 (br, 2H, (CH3)2CH), 3.50 (br, 2H,
(CH3)2CH), 3.25–3.74 (br, 2H, NH), 7.16–8.02 (m, 16H, phenyl
CH). 13C NMR (100 MHz, CDCl3) δ 21.5, 23.0, 23.3, 24.3, 25.8,
26.1, 46.2, 53.3, 53.5, 53.8, 54.1, 54.3, 126.8, 127.4, 127.7, 127.9,
128.3, 128.6, 129.1, 129.7, 136.4, 140.7, 142.0, 142.2, 152.9
(quaternary carbons not observed). IR (Nujol) 3420 (br), 3208,
1614, 1546, 1493, 1298, 1173, 1120, 1030, 921, 886, 785, 767,
700. Anal. Calc. for C38H46N4: C, 81.68; H, 8.30; N, 10.03%.
Found: C, 81.48; H, 8.43; N, 9.82%.
Fig. 3 PM3 energy minimised structure of 5[AlMe2]2. Hydrogen
atoms have been removed for clarity.
6H2. Preparation same as for 5H2. Yield 8.14 g, 11.3 mmol,
29%; mp 202–205 ЊC. 1H NMR (400 MHz, CDCl3) δ 1.00–1.69
(m, 40H), 2.82 (br, 2H), 3.06 (br, 2H), 3.50 (br, 2H, NH), 7.13–
7.71 (m, 16H). 13C NMR (100 MHz, CDCl3) δ 24.8, 25.1, 25.2,
25.3, 25.4, 25.5, 26.0, 26.2, 31.9, 33.1, 34.3, 35.9, 36.1, 52.0,
126.6, 126.9, 127.4, 127.6, 128.2, 128.3, 129.0, 137.8, 140.0,
140.5, 141.5. IR (Nujol) 3402, 3205, 2727, 2668, 1947, 1623,
1548, 1343, 1302, 1256, 1150, 1105, 1074, 1030, 977, 886, 761.
proximity of one Al–CH3 fragment to an aryl ring. The high-
field resonance tentatively assigned to it appears at Ϫ1.19 ppm.
Note that the Al–CH3 groups are in different environments and
the 1H NMR data obtained for 5[AlMe2]2, namely four Al–CH3
as well as four CH(CH3)2 peaks, are consistent with the
proposed structure. The 27Al NMR signal was broad and
uninformative as expected for an asymmetric aluminium centre.
J. Chem. Soc., Dalton Trans., 2002, 3919–3922
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Anal. Calc. for C50H62N4: C, 83.52; H, 8.69; N, 7.79%. Found:
C, 83.69; H, 8.80; N, 7.52%.
asymmetric alternatives to binaphthyl and biphenyl ligands for
catalysts in organic reactions.25,26 This reaction may be applied
to the preparation of a wide variety of bifunctional poly-
aromatic compounds. Such systems will be of interest as
frameworks for supporting polyfunctional Lewis acids.27
6H3Cl. To a solution of 0.26 g (0.36 mmol) of 6H2 in ca.
25 cm3 of warm toluene, 0.09 mL of 4.0 M HCl in dioxane was
added. The solution was stirred for 1.5 h at room temperature
and then allowed to sit overnight. The resulting white solid
was isolated by filtration and characterised as 6H3Cl (0.22 g,
Acknowledgements
1
Financial support for this research was provided by Saint
Mary’s University, Simon Fraser University, and the Natural
Sciences and Engineering Research Council of Canada
(NSERC). The Atlantic Region Magnetic Resonance Centre at
Dalhousie University and Marcy Tracey (SFU) collected the
NMR data. We also thank Dr Noham Weinberg for advice
regarding molecular modeling.
0.29 mmol, 81%); mp 300 ЊC (decomp.). H NMR (400 MHz,
CD2Cl2) δ 0.82–1.93 (m, 40H), 2.85 (br, 2H), 3.17 (br, 2H), 3.74
(br, 3H, NH), 7.16–7.75 (m, 16H).13C NMR (100 MHz,
CD2Cl2) δ 22.9, 26.3, 26.6, 26.8, 27.0, 27.2, 27.3, 27.5, 33.0, 34.4,
35.6, 36.3, 37.1, 56.9, 127.1, 128.6, 129.8, 130.2, 130.6,
130.9, 131.7, 133.3, 140.9, 142.0, 143.0, 144.0, 157.2, 159.9. IR
(Nujol) 3668, 3410, 3129, 2728, 1941, 1594, 1492, 1347, 1307,
1261, 1152, 1074, 1029, 978, 890, 766. Anal. Calc for
C50H63N4Cl: C, 79.49; H, 8.40; N, 7.42%. Found: C, 79.59; H,
8.42; N, 7.11%.
References and notes
1 J. Barker and M. Kilner, Coord. Chem. Rev., 1994, 133, 219.
2 M. P. Coles and R. F. Jordan, J. Am. Chem. Soc., 1997, 119, 8125.
3 M. P. Coles, D. C. Swenson, R. F. Jordan and V. G. Young, Jr.,
Organometallics, 1997, 16, 5183.
4 S. Dagorne, I. A. Guzei, M. P. Coles and R. F. Jordan, J. Am. Chem.
Soc., 2000, 122, 274.
5 J. Barker, N. C. Blacker, P. R. Phillips, N. W. Alcock, W. Errington
and M. G. H. Wallbridge, J. Chem. Soc., Dalton Trans., 1996, 431.
6 S. Dagorne, R. F. Jordan and V. G. Young, Organometallics, 1999,
18, 4619.
7 J. A. R. Schmidt and J. Arnold, Chem. Commun., 1999, 2149.
8 D. Abeysekera, K. N. Robertson, T. S. Cameron and J. A. C.
Clyburne, Organometallics, 2001, 20, 5532.
9 Related derivatives as well as polymerisation studies have recently
been reported: J. A. R. Schmidt and J. Arnold, Organometallics,
2002, 21, 2306.
10 (a) Symmetrical polyamidines have been reported. See for example:
R. T. Boeré, R. T. Oakley and R. W. Reed, J. Organomet. Chem.,
1987, 331, 161–167; (b) A. W. Cordes, R. C. Haddon, R. G. Hicks,
R. T. Oakley, T. T. M. Palastra, L. F. Schneemeyer and
J. V. Waszczak, J. Am. Chem. Soc., 1992, 114, 5000.
11 The 2,4,6-triphenyl ligand may be considered to be a substituted
m-terphenyl ligand. For reviews see: (a) B. Twamley, S. T. Haubrich
and P. P. Power, Adv. Organomet. Chem., 1999, 44, 1; (b) J. A. C.
Clyburne and N. McMullen, Coord. Chem. Rev., 2000, 210, 73.
12 M. M. Olmstead and P. P. Power, J. Organomet. Chem., 1991, 408, 1.
13 (a) The addition of the second equivalent of lithium can be viewed
as a directed ortho-lithiation reaction. For reviews see: V. Snieckus,
Chem. Rev., 1990, 90, 879; (b) also related is 2,2Ј-dilithiobiphenyl.
See: T. Suzuki, J. Nishida and T. Tsuji, Chem. Commun., 1998, 2193;
(c) L. Engman, J. Heterocycl. Chem., 1984, 21, 413.
14 The m-terphenyl ligand 1-BrC6H(C6H3-2-Me-5-t-Bu)2 can also be
dilithiated – once on the central phenyl ring and once at an
ortho CH3 fragment. N. J. Hardman, B. Twamley, M. Stender,
R. Baldwin, S. Hino, B. Schiemenz, S. M. Kauzlarich and P. P.
Power, J. Organomet. Chem., 2002, 643–644, 461.
5[AlMe2]2. 5H2 (1.00 g, 2.31 mmol) was dissolved in ca.
20 cm3 of toluene. An aliquot (2.8 cm3, 4.62 mmol) of 2 M
AlMe3 in hexane was added drop-wise and stirred overnight.
The solvents were removed in vacuo. The resulting white solid
was washed with hexane, dried in vacuo, and characterised as
5[AlMe2]2. Yield, 0.89 g, 1.32 mmol, 73%; mp 192–197 ЊC
(decomp.). 1H NMR (400 MHz, CD2Cl2) δ Ϫ1.19 (s, 3H,
Al–CH3), Ϫ0.94 (s, 3H, Al–CH3), Ϫ0.73 (s, 3H, Al–CH3),
Ϫ0.66 (s, 3H, Al–CH3), 0.55 (d, JHH = 6 Hz, 6H), 0.72 (d, JHH
=
6 Hz, 6H), 0.74(d, J = 6 Hz, 6H), 0.96 (d, J = 6 Hz, 6H), 3.12 (m,
2H), 3.19 (m, 2H), 8.18–7.36 (m, 16H, aromatic CH). 13C NMR
(100 MHz, CDCl3) δ Ϫ10.5, Ϫ10.4, Ϫ9.7, 22.3, 22.6, 24.4, 25.2,
25.7, 26.3, 45.9, 46.0, 46.3, 49.5, 127.3, 127.7, 127.9, 128.0,
128.1, 128.2, 128.4, 129.0, 129.2, 129.3, 129.4, 129.6, 130.1,
130.5, 131.1, 136.9, 140.1, 140.5. IR (Nujol) 3442, 2725, 1598,
1499, 1347, 1311, 1268, 1182, 1157, 1120, 1023, 995, 967, 892,
786, 772, 744 Anal. Calc.: C, 75.19; H, 8.41; N, 8.35%. Found:
C, 74.90; H, 8.55; N, 8.12%.
X-Ray crystallography
A single crystal of 5H2 or 6H3Cl was mounted on a glass fibre
and centred on a Siemens 1K SMART/CCD diffractometer.
Data were collected at Ϫ50 ЊC using Mo(Kα) radiation.
Lorentz and polarisation corrections were applied and data
were also corrected for absorption using redundant data and
the SADABS program.21 Direct methods and Fourier tech-
niques were used to solve the crystal structures. Refinement was
conducted using full-matrix least-squares calculations and
SHELXTL-PC V 5.03.22 All non-hydrogen atoms were refined
with anisotropic displacement parameters. Full crystallo-
graphic details can be found in Table 1. Diagrams were drawn
using X-Seed.23
15 S. Patai and Z. Rappoport, The Chemistry of Amidines and Imidates,
John Wiley & Sons, New York, 1991.
16 W. Galezowski, A. Jarczewski, M. Stanczyk, B. Brzezinski, F. Bartl
and G. Zundel, J. Chem. Soc., Faraday Trans., 1997, 93, 2515.
17 R. T. Boeré, V. Klassen and G. Wolmershäuser, J. Chem. Soc.,
Dalton Trans., 1998, 4147.
18 One equivalent of 6H2 in THF solution was treated with two
equivalents of n-butyllithium followed by slow addition at Ϫ30 ЊC
of a solution of BCl3 in heptane. After filtration and removal of 90%
of the solvent, several small crystals were isolated and characterised
as 6H3Cl by X-ray crystallography.
CCDC reference numbers 180739 and 190139.
See http://www.rsc.org/suppdata/dt/b2/b205875h/ for crystal-
lographic data in CIF or other electronic format.
Conclusion
19 T. Steiner, Acta. Crystallogr., Sect. B, 1998, 54, 456.
20 T. Steiner, Angew. Chem., Int. Ed., 2002, 41, 48.
21 G. M. Sheldrick, SADABS, University of Göttingen, Germany, 1997.
22 SHELXTL-PC, Version 5.03, Siemens Industrial Automation, Inc.,
Madison, WI, 1994.
The preparation of 2Li2 provides an easy route to asymmetrical
bifunctional aryl compounds24 broadly based on the biphenyl
framework (Fig. 4). Such compounds are of great interest as
23 L. J. Barbour, X-Seed, Graphical interface to SHELX-97 and
POV-Ray, 1999 (http://www.x-seed.net).
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Fig. 4 Asymmetric bifunctional aryl compounds.
3922
J. Chem. Soc., Dalton Trans., 2002, 3919–3922