Synthesis, structural characterization and reactivity of the amino borane 1-(NPh2)-2-[B(C6F5) 2]C6H4

Article abstract of DOI:10.1016/S0022-328X(03)00384-X

The bright red title compound 1 was synthesized from (2-lithiophenyl) diphenylamine and bis(pentafluorophenyl)boron chloride. Its reactions with small acids like H₂O and HCl proceeded easily giving zwitterionic compounds. For 1 and its water adduct 2 the crystal structures were determined, the latter featuring an ammonium borate structure containing a short intramolecular hydrogen bond bridge. Treatment of 1 with Jutzi's acid, [H(OEt₂)₂] [B(C₆F₅)₄], did not result in protonation of the nitrogen, but reaction of 1 with LiH in the presence of 12-crown-4, led to the isolation of the aminoborate [1-(Ph₂N)-2-{B(H)(C₆F₅)₂} C₆H₄][Li(12-crown-4)] (3). Borohydride 3 reacted with Jutzi's acid to regenerate 1 and liberate hydrogen.

Full text of DOI:10.1016/S0022-328X(03)00384-X

Journal of Organometallic Chemistry 680 (2003) 218Á222
/
www.elsevier.com/locate/jorganchem
Synthesis, structural characterization and reactivity of the amino
borane 1-(NPh2)-2-[B(C6F5)2]C6H4
Roland Roesler *, Warren E. Piers *, Masood Parvez
Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Altberta, Canada T2N 1N4
Received 4 March 2003; received in revised form 4 May 2003; accepted 5 May 2003
Dedicated to Prof. M. Frederick Hawthorne on the occasion of his 75th birthday
Abstract
The bright red title compound 1 was synthesized from (2-lithiophenyl)diphenylamine and bis(pentafluorophenyl)boron chloride.
Its reactions with small acids like H2O and HCl proceeded easily giving zwitterionic compounds. For 1 and its water adduct 2 the
crystal structures were determined, the latter featuring an ammonium borate structure containing a short intramolecular hydrogen
bond bridge. Treatment of 1 with Jutzi’s acid, [H(OEt2)2][B(C6F5)4], did not result in protonation of the nitrogen, but reaction of 1
with LiH in the presence of 12-crown-4, led to the isolation of the aminoborate [1-(Ph2N)-2-{B(H)(C6F5)2}C6H4][Li(12-crown-4)]
(3). Borohydride 3 reacted with Jutzi’s acid to regenerate 1 and liberate hydrogen.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Boron; Lewis acid; Lewis base; X-ray diffraction; Hydrogen bonding
1. Introduction
Tris(pentafluorophenyl)borane is an efficient catalyst
for a variety of organic reactions and co-catalyst/
activator for olefin polymerization using d0 transition
metal catalysts [1Á3], due to its strong Lewis acid
/
character and stability. These applications have stimu-
lated research towards the development of other per-
fluoroaryl substituted boranes. Among these, the ortho-
This molecule is likely to react with Adꢁ Á
compounds containing polarized bonds forming stable
zwitterionic ammonium borates. For Aꢁ ꢀHꢁ and
ꢂ ꢀHꢂ, the zwitterion becomes a molecular dihydro-
/
Xdꢂ
/
phenylene bridged diboranes 1,2-[B(C6F5)2]2C6X4 (Xꢀ
/
X
/
H, F) are particularly interesting since the proximity of
the two boron centers allows for potential cooperation,
such as chelation of small Lewis bases [4,5]. These
diboranes inspired us to attempt the synthesis of a Lewis
amphoteric ortho-phenylene bridged aminoborane, 1-
(NPh2)-2-[B(C6F5)2]C6H4 (1).
gen storage device, able to release H2 upon heating or
during a chemical reaction, regenerating 1. Certain
resemblance with this hydride-proton containing mole-
cule have systems containing a transition metal hydride
in close proximity to an ammonium ion, which display
dihydrogen bonding and have been studied in this
respect [6]. The aminoborane 1 has also the potential
to act as a ‘‘trap’’ for reactive molecules or fragments
through the synergetic effects of the neighboring elec-
tron donor and electron acceptor sites. Similar ‘‘in series
coordination’’ has been observed before, without the
additional stabilization conferred by the chelate effect
[7].
* Corresponding authors. Tel.: ꢁ
9488.
E-mail address: roesler@ucalgary.ca (R. Roesler).
/
1-403-220-5366; fax: ꢁ1-403-289-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00384-X

R. Roesler et al. / Journal of Organometallic Chemistry 680 (2003) 218Á
/222
219
Although numerous amino boranes are known, most
of these are either coordinatively saturated through
intramolecular, dative boronÃnitrogen bond formation,
/
ð2Þ
or have the amino and borane moieties well separated
through a rigid carbon skeleton (i.e. para-phenylene). A
variety of analogs of 1 with alkyl and aryl substituted
nitrogen have recently been reported and studied with
respect to their good fluorescence properties [8]. All
these derivatives carry bulky, mesityl and duryl sub-
stituents on boron and are less suitable for coordination
studies because of their reduced Lewis acidity and high
1 reacts with HCl in the same way it reacts with water,
producing the ammonium borate 2-Ph2N(H)C6-
H4B(Cl)(C6F5)2 which displays very similar features to
2 in the NMR spectra.
The crystal structures of [1] and [2] were determined
by X-ray crystallography. Selected bond lenghts and
angles are given in Table 1. Both molecules are
monomeric in solid state. In the aminoborane 1, boron
and nitrogen have predictably planar environments,
with the sum of the bond angles being 359.8(2)8 around
the former and 358.2(2)8 around the latter. Steric
hindrance prevents, however, the planar arrangement
of the boron, nitrogen and phenylene planes required
for optimal electron delocalization over the entire
framework. The reference phenylene plane makes an
angle of 32.5(2)8 with the boron plane and 38.3(2)8 with
steric
encumbrance.
The
adducts
of
2-
(Me2NCH2)C6H4(BMe2) with MeLi have been synthe-
sized and extensively studied by NMR [9], without
preparation of the free ligand which is likely to
spontaneously undergo ring closure upon BÃ
/N bond
formation.
2. Results and discussion
2-Bromophenyl-diphenylamine [10] was prepared
through Ullmann condensation from diphenylamine
and 2-bromoiodobenzene, in analogy to a reported
procedure [11]. It was then easily lithiated with n-BuLi
and the lithiated derivative reacted smoothly with
the nitrogen plane. While the C(18)Ã
/
N(1) bond is
situated in the reference plane, forming with it an angle
of only 1.8(1)8, the deviation of the boron atom out of
this plane is significant, with the C(13)Ã
/
B(1) bond at an
(C6F5)2BCl at ꢂ20 8C forming 1 in good yield (Eq.
/
angle of 7.1(1)8 with respect to the same plane. As
expected, there is no evidence for any tendency towards
the closure of a very strained four membered CNBC
ring. In fact, the angles at C(13) and C(18) imply that
the repulsive steric forces prevail. The conformation of
the phenyl rings at both boron and nitrogen displays the
usual propeller-like arrangement.
(1)). The product was isolated upon recrystallization
1
from hexane in the form of bright red crystals. Its H-,
19F- and 11B-NMR spectra do not display any unex-
pected features.
While the CÃ
C(13) bond is slightly but meaningfully shorter than the
C bonds, indicating the contribution of the
/
N bonds are virtually equal, the B(1)Ã
/
other two BÃ
/
ð1Þ
The aminoborane 1 is soluble without decomposition
resonance structure to the overall structure of 1. The
in aprotic organic solvents, forming intensely red solu-
tions (lmax
Table 1
Bond lengths (pm) and angles (8) for compounds 1 and 2 in the crystal
ꢀ
/
517.3 nm in CH2Cl2), and is resistant
carbon
towards oxidation by air. Although the boronÃ
/
1
2
bond is not readily attacked by water, the aminoborane
is extremely sensitive to moisture. Reaction with traces
of water yields fast and quantitatively the colorless,
zwitterionic ammonium borate 2 (Eq. (2)). The reaction
was obvious in the 19F-NMR spectrum, where a
Bond lengths
N(1)Ã
B(1)Ã
B(1)Ã
B(1)Ã
O(1)ꢀ ꢀ ꢀN(1)
Bond angles
/
C
142.0(3)Á
/
142.8(3)
157.8(4), 159.0(4)
148.7(2)Á150.2(2)
/
/
C(1,7)
C(13)
O(1)
164.6(2), 165.7(1)
163.4(2)
152.1(2)
/
153.7(4)
/
characteristic shift to higher field (Ddꢀ/11.3 ppm) of
253.3(2)
the signal corresponding to the para-fluorine from the
borane 1 to the borate 2 is observed. In the 11B-NMR
spectrum, the very broad signal around 59 ppm due to
the tricoordinate borane is replaced by a much sharper
N(1)Ã
B(1)ÃC(13)Ã
O(1)Ã
O(1)Ã
CÃN(1)Ã
CÃB(1)Ã
N(1)ÃH(N)ꢀ ꢀ ꢀO(1)
/
C(18)Ã
/
C(13)
120.9(2)
126.2(2)
117.3(2)
121.5(2)
/
/
C(18)
/
B(1)Ã
/
C(13)
102.3(1)
107.3(1), 110.7(1)
/
B(1)Ã
/C(1,7)
signal at ꢂ2 ppm, characteristic of a tetracoordinate
/
/
/C
118.6(2)Á
/
120.7(2)
124.0(2)
112.4(1)Á
110.5(1)Á
152
/
115.6(1)
borate. No signals for either the ammonium or the
hydroxyl proton could be observed in the NMR at room
temperature.
/
/C
115.0(2)Á
/
/113.4(1)
/

220
R. Roesler et al. / Journal of Organometallic Chemistry 680 (2003) 218Á222
/
C(13)Ã
/
C(18) bond is with 141.6(3) pm somewhat longer
and HCl to form zwitterionic products containing an
intramolecular hydrogen bond bridge. However, it fails
to yield a ‘‘dihydrogen adduct’’ of type 2, as well as a
cationic ammonium ion. The latter finding confirms that
the basicity of the amino group is significantly reduced
by extended electron delocalization involving the aro-
matic rings and the borane moiety. The basicity of the
nitrogen center in an aminoborane of type 1 would have
to be significantly higher in order to thermodynamically
favor the formation of a dihydrogen adduct over the
elimination of hydrogen in the reaction of 3 with
[H(OEt2)2][B(C6F5)4].
than the average of the other CÃ
/C bonds in the ring
(138.8(4) pm), in agreement with a resonance structure
containing double bonded boron and nitrogen, although
such a small difference could also be a steric effect.
The most obvious difference between 1 and 2 is the
pyramidalization of boron and nitrogen in the later,
with the sum of the CÃ
of the CÃBÃC angles 336.1(1)8 (328.58 in a perfect
tetrahedron). This process is accompanied by an elonga-
tion of the NÃC and BÃC bonds with an average of 7
and 8 pm, respectively, with respect to 1. The water
molecule is split with an Oꢀ ꢀ ꢀH distance of 167 pm
(Oꢀ ꢀ ꢀN 253.3(2) pm), smaller than the hydrogen bond
distances in solid water (1.76 pm [12]). In order to
/
NÃ
/
C angles being 341.8(1)8 and
/
/
/
/
3. Experimental
facilitate the formation of the hydrogen bond, the OÃ
BÃC(13) angle is more acute (102.32(13)8) than the
other two OÃBÃC angles (average: 109.0(1)8) Table 1.
/
/
3.1. General remarks
/
/
The slow reaction of 1 with lithium hydride in
presence of a crown ether leads to the colorless borate
3, which crystallizes out of a benzene solution (Eq. (3)).
All experiments were performed under a purified
argon atmosphere, with complete exclusion of air and
moisture, using glovebox and Schlenk techniques. The
solvents were dried and deoxygenated prior to use [14].
NMR experiments were performed on a Bruker AMX-
300 instrument, using internal (C6D5H and CDHCl2 for
1H with dꢀ
(C6F6 for 19F, with dꢀ
11B, with dꢀ
0.0 ppm) reference. Elemental analyses
were performed by the Analytical Instrumentation
Centre at the University of Calgary. (C6F5)2BCl
[15,16] and [H(OEt2)2][B(C6F5)4] [13] were synthesized
according to published procedures, all other reagents are
commercial products.
/
7.15 and 5.32 ppm, respectively) or external
163.0 ppm and BF3×Et2O for
/
ꢂ
/
/
/
ð3Þ
The solubility of 3 in hydrocarbons is limited, but it
dissolves well in polar solvents like dichloromethane.
Although no signal corresponding to the boron hydride
could be observed in the NMR even at ꢂ
/
60 8C, the
peaks at ꢂ
/
2.4 ppm in the 11B-NMR spectrum and at ꢂ
/
165.5 ppm corresponding to the para-fluorine in the 19F-
NMR spectrum are characteristic for a borate ion.
Reaction of 3 with Jutzi’s acid, [H(OEt2)2][B(C6F5)4]
[13] failed to give a zwitterion of type 2 but instead
regenerated 1 with liberation of hydrogen and most
likely [Li(12-crown-4)][B(C6F5)4]. The reaction took
3.1.1. 1-Br-2(NPh2)C6H4
To a round bottom flask containing toluene (11 ml)
equipped with a DeanÁStark trap were added in the
/
following order with efficient stirring diphenylamine
(2.99 g, 17.67 mmol), 2-bromoiodobenzene (5 g, 17.67
mmol), 1,10-phenantroline (116 mg, 0.64 mmol), cop-
per(I) iodide (122 mg, 0.64 mmol), and finely divided
potassium hydroxide (7.75 g, 138 mmol). The mixture
was refluxed (125 8C) over night, while the color of the
solution changed from orange to brown, colorless and
finally green. After cooling to room temperature,
toluene (50 ml) and water (50 ml) were added, the green
organic phase was separated and the solvent removed on
a Rotavap, leaving behind a dark green oil. Chromato-
graphy on silica gel using hexane:ethyl acetate 99:1 gave
the product as a first fraction. Solvent removal and
vacuum distillation yielded the desired compound (2.15
only a few minutes to complete at ꢂ30 8C. In fact, an
/
ammonium cation could not be produced even by direct
combination of 1 with [H(OEt2)2][B(C6F5)4] (Eq. (4)).
No reaction was observed refluxing the reaction mixture
in dichloromethane for 2 days, while reflux in toluene
produced tris(pentafluorophenyl)borane as the only
identifiable product.
g, 37%) with satisfactory purity. B.p. 160Á
5ꢃ
10ꢂ3 Torr. 1H-NMR (282 MHz, 27 8C, C6D6) d
(ppm): 6.60 (m), 6.91 (m), 6.96 (m), 7.00 (s), 7.01Á7.07
(m), 7.12 (m), 7.19Á7.31(m), 7.39 (m), 8.07 (m). MS (EI,
70 eV, positive): [Mꢁ].
/
180 8C per
/
ð4Þ
The aminoborane 1 proves to be able to act as a Lewis
acid/Lewis base trap, reacting with small acids like H2O
/
/

R. Roesler et al. / Journal of Organometallic Chemistry 680 (2003) 218Á
/222
221
3.1.2. 1-(Ph2N)-2-[B(C6F5)2]C6H4 (1)
3.1.3. 1-(Ph2NH)-2-[B(OH)(C6F5)2]C6H4 (2)
1-Br-2(NPh2)C6H4 (2.153 g, 6.64 mmol) was lithiated
at 0 8C in diethyl ether (60 ml) using a 1.6 M solution of
n-BuLi in hexane (4.15 ml, 6.65 mmol). The solution
was allowed to warm up to room temperature and
stirred over night, the solvent was removed in vacuo and
the solid residue suspended in hexane. Filtration yielded
the lithium derivative as a fine white powder. Without
further purification, 1-Li-2-(NPh2)C6H4 (1 g, 3.98
mmol) was suspended in 60 ml toluene and added
A benzene solution of 1 was exposed to the air.
Within a few minutes, the color of the solution faded
and disappeared. Evaporation of the solvent left behind
the product quantitatively, as a colorless crystalline
solid. 1H-NMR (300 MHz, 27 8C, C6D6) d (ppm):
1
2
6.57 (dd, 1H, JHH
6.76 (m, 10 H), 6.89 (dt, 1H, JHH
ꢀ
/
8.0 Hz, JHH
1
ꢀ
/
0.6 Hz), 6.67Á
/
2
7.4 Hz, JHH
ꢀ
/
ꢀ
/
1
2
1.4 Hz), 7.03 (dt, 1H, JHH
ꢀ
/
7.4 Hz, JHH
7.5 Hz); 19F-NMR (282 MHz,
27 8C, C6D6) d (ppm): ꢂ164.4 (4F, m-C6F5), ꢂ158.6
(2F, p-C6F5), ꢂ
133.3 (4F, o-C6F5); 11B-NMR (96 MHz,
27 8C, C6D6) d (ppm): ꢂ0.8 (s) Fig. 2.
ꢀ1.0 Hz),
/
1
7.38 (d, 1H, JHH
ꢀ
/
/
/
slowly at ꢂ20 8C to a solution of (C6F5)2BCl (1.514 g,
/
/
3.98 mmol) in hexane (40 ml). Immediately, intense
bright red coloration indicated formation of the pro-
duct. The reaction mixture was stirred over night at
room temperature, the solvent was removed and the
residue extracted with hexane (50 ml). The hexane
/
3.1.4. 1-(Ph2NH)-2-[B(Cl)(C6F5)2]C6H4
To a dichloromethane solution of 1 was added the
stoichiometric amount of 1 M HCl in THF. The
solution discolored immediately. Evaporation of the
solvent left behind the product quantitatively, as a
extract was reduced to 10 ml and cooled to ꢂ50 8C.
/
After 2 days, the product deposited as a red crystalline
solid and the supernatant was decanted off. Yield: 1.70
g, 73%. Elemental analysis for C30H14BF10N: Anal.
Found (Calc.): C, 61.23 (61.15); H, 2.03 (2.39); N 2.39
1
colorless crystalline solid. H-NMR (300 MHz, 27 8C,
1
CD2Cl2) d (ppm): 7.05 (d, 1H, JHH
ꢀ
ꢀ
/
8.1 Hz), 7.19 (d,
6.9 Hz), 7.33Á
7.47 (m, 5H); 19F-NMR (282 MHz,
27 8C, CD2Cl2) d (ppm): ꢂ165.6 (4F, m-C6F5), ꢂ159.2
(2F, p-C6F5), ꢂ
129.5 (4F, o-C6F5); 11B-NMR (96 MHz,
27 8C, CD2Cl2) d (ppm): ꢂ2.2 (s).
1
1
1H, JHH
ꢀ
/
7.4 Hz), 7.29 (d, 1H, JHH
/
/
(2.38%); UVÁ
molꢂ1 cmꢂ1): 517.3 (3.28), 286.2 (4.12), 228.0 (4.14);
1H-NMR (300 MHz, 27 8C, C6D6) d (ppm): 6.69Á
6.81
(m, 7H), 6.87Á6.92 (m, 4H), 7.00Á7.08 (m, 1H), 7.13 (d,
2H); 19F-NMR (282 MHz, 27 8C, C6D6) d (ppm):
/
Vis: CH2Cl2, lmax (nm) (log(o), dm3
7.37 (m, 4H), 7.45Á
/
/
/
/
/
/
/
/
ꢂ
/
161.7 (4F, m-C6F5), ꢂ
/
147.3 (2F, p-C6F5), ꢂ128.1
/
3.1.5. [1-(Ph2N)-2-{B(H)(C6F5)2}C6H4][Li(12-
crown-4)] (3)
LiH (20 mg, 2.5 mmol) was added to a solution
containing 1 (150 mg, 0.25 mmol) and 12-crown-4 ether
(4F, o-C6F5); 11B-NMR (96 MHz, 27 8C, C6D6) d
(ppm): 58.8 (s, br) Fig. 1.
Fig. 1. Molecular structure of 1-(NPh2)-2-[B(C6F5)2]C6H4 (1) in the
crystal.
Fig. 2. Molecular structure of 1-[N(H)Ph2]-2-[B(OH)(C6F5)2]C6H4 (2)
in the crystal.

222
R. Roesler et al. / Journal of Organometallic Chemistry 680 (2003) 218Á222
/
Table 2
Crystallographic data for compounds 1 and 2
4. Supplementary material
Crystallographic data (excluding structure factors) for
the structures structural analysis have been deposited
with the Cambridge Crystallographic Data Centre,
CCDC Nos. 205366 and 205367 for compounds 1 and
2, respectively. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
1
2
Empirical formula
C
30H14BF10
589.23
0.15ꢃ
triclinic
N
C30H16BF10NO
607.25
Formula weight (g molꢂ1
)
Crystal size (mm3)
Crystal system
Space group
Z
/
0.12ꢃ
/
0.05 0.17ꢃ
/
0.10ꢃ0.08
/
triclinic
¯
P1
¯
P1
/
/
Union Road, Cambridge CB2 1EZ, UK (Fax: ꢁ33-
/
2
2
a (pm)
b (pm)
903.24(4)
1079.33(4)
1342.55(8)
96.761(2)
92.183(2)
102.979(3)
1.26372(10)
1.549
980.78(3)
1086.21(4)
1316.97(5)
105.1706(14)
104.4606(15)
101.0140(20)
1.26091(8)
1.599
1223-336033 or e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk).
c (pm)
a (8)
b (8)
Acknowledgements
g (8)
V (nm3)
Dcalc (mg mꢂ3
)
This work was supported by the Natural Sciences and
Engineering Research Council of Canada in the form of
a Postdoctoral Fellowship to R.R., a Discovery Grant
to W.E.P., and an E.W.R. Steacie Fellowship to W.E.P.
Absorption coefficient
(mmꢂ1
0.14
0.15
)
u Range (8)
Reflections collected/Rint
3.4Á
/
27.5
3.4Á30.0
/
10621/0.053
5689/379
1.00
12526/0.030
7075/392
1.02
Data/parameters
Goodness-of-fit on F2
(2001Á2003).
/
Final R indices [I ꢀ
/
2s(I)] R1ꢀ
0.120
R1ꢀ0.141, wR2ꢀ
0.148
Largest difference peak and 190 and ꢂ
hole (e nmꢂ3
/
0.056, wR2ꢀ
/
R1ꢀ
0.108
R1ꢀ0.095, wR2ꢀ
0.127
250 and ꢂ
/
0.052, wR2ꢀ
/
References
R indices (all data)
/
/
/
/
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[2] W.E. Piers, T. Chivers, Chem. Soc. Rev. (1997) 345.
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M.R.J. Elsegood, T.B. Marder, Angew. Chem. Int. Ed. Engl. 38
(1999) 3695.
/250
/260
)
(45 mg, 0.25 mmol) in 5 ml benzene. The flask was
capped and left standing for 2 weeks, while the solution
discolored and colorless crystals of product deposited on
the bottom and were separated. Yield: 126 mg, 64%.
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(2000) 2131.
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Chem. Soc. 116 (1994) 6474.
19F-NMR (282 MHz, 27 8C, CD2Cl2) d (ppm): ꢂ
(4F, m-C6F5), ꢂ164.9 (2F, p-C6F5), ꢂ129.1 (4F, o-
C6F5); 19F-NMR (282 MHz, 27 8C, CD2Cl2) d (ppm):
167.3 (4F, m-C6F5), ꢂ165.5 (2F, p-C6F5), ꢂ130.8
(4F, o-C6F5); 11B-NMR (96 MHz, 27 8C, CD2Cl2) d
(ppm): ꢂ2.4 (s).
/
166.8
/
/
[8] K. Albrecht, V. Kaiser, R. Boese, J. Adams, D.E. Kaufmann, J.
Chem. Soc. Perkin Trans. 2 (2000) 2153.
ꢂ
/
/
/
[9] E. Kalbarczyk-Bidelska, S. Pasynkiewicz, J. Organomet. Chem.
417 (1991) 1.
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/
[11] H.B. Goodbrand, N.-X. Hu, J. Org. Chem. 64 (1999) 670.
[12] N. Wiberg, Holleman-Wiberg, Lehrbuch der Anorganischen
Chemie, 101st ed., Walter de Gruyter, Berlin, 1995, p. 283.
3.2. X-ray crystallographic analyses
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¨
tallics 19 (2000) 1442.
[14] A.B. Pangborn, M.A. Giardello, R.H. Grubbs, R.K. Rosen, F.J.
Timmers, Organometallics 15 (1996) 1518.
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5492.
X-ray crystallographic analyses were performed on
suitable crystals coated in Paratone oil and mounted on
a Rigaku AFC6S diffractometer. Details of the crystal-
lographic data and data analysis are given in Table 2.