The synthesis, molecular structure and supramolecular architecture of complexes between the ammonia adduct of tris(pentafluorophenyl)boron and a series of mono and polydentate hydrogen-bond acceptors

Article abstract of DOI:10.1039/b808208a

The ammonia adduct of tris(pentafluorophenyl)boron, (C₆F ₅)₃B·NH₃, is a potentially tri-functional hydrogen-bond donor. Co-crystallisation with the bases acetonitrile, pyridine, tetrahydrofuran, tetramethylethyl

Full text of DOI:10.1039/b808208a

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The synthesis, molecular structure and supramolecular architecture of
complexes between the ammonia adduct of tris(pentafluorophenyl)boron and a
series of mono and polydentate hydrogen-bond acceptors†
Anna-Marie Fuller,a Andrew J. Mountford,a Simon J. Coles,b Peter N. Horton,b David L. Hughes,a
Michael B. Hursthouse,b Louise Maleb and Simon J. Lancaster*a
Received 15th May 2008, Accepted 15th August 2008
First published as an Advance Article on the web 30th September 2008
DOI: 10.1039/b808208a
The ammonia adduct of tris(pentafluorophenyl)boron, (C6F5)3B·NH3, is a potentially tri-functional
hydrogen-bond donor. Co-crystallisation with the bases acetonitrile, pyridine, tetrahydrofuran,
tetramethylethylenediamine, 15-crown-5, 1,4-diazabicyclo[2.2.2]octane (DABCO), pyrazine and
4,4¢-bipyridine results, not in donor exchange, but in the formation of supermolecules assembled
through hydrogen bonding to second coordination sphere acceptors. The complexes have been
characterised by elemental analysis, multinuclear NMR and single-crystal diffraction methods. The
solid-state architectures range in complexity, from the hydrogen bonded pairing of (C6F5)3B·NH3, with
a single monodentate acceptor molecule (e.g. MeCN to form (C6F5)3B·NH3·NCMe), through
complexation with all three N–H groups to the macrocycle 15-crown-5, to the formation of infinite
one-dimensional chains with pyrazine and DABCO, and to two-dimensional networks with the
divergent acceptor 4,4¢-bipyridine.
hydrogen bonds to other oxygen containing species such as MeOH,
Introduction
15
tBuOH,9 (CH3)2SO2 and 1,4-dioxane.16 The divergent nature of
Whilst tris(pentafluorophenyl)boron was first reported in 1963,1–3
the 1,4-dioxane acceptor leads to the formation of an infinite
one-dimensional chain.16 If a stronger base, such as an amine is
employed a formal proton transfer occurs resulting in a hydrogen
bonded ion pair of the form [HNRR¢R¢¢]+[(C6F5)3BOH]-.7,9,17–21
Recently, we reported that (C6F5)3B forms the supermolecule
(C6F5)3B·NH3·NH3 when treated with an excess of ammonia.11
This suggested that (C6F5)3B·NH3 (1) might also exhibit a rich
supramolecular chemistry as a potent hydrogen-bond donor
in combination with suitable basic acceptors. The ammonia
adduct, with significantly less Brønsted acidity, has three potential
hydrogen-bond donors leading to the possibility of two- and even
three-dimensional infinite structures.
There is increasing interest in the assembly of inorganic
networks without recourse to dative bonding. Very recently, the
closely related cationic hydrogen-bond donor, [Ph3CNH3]+ was
shown to form supramolecular cubane and ladder fragments
analogous to alkali metal phosphinimides.22 Earlier examples
of intermolecular hydrogen bonding for the construction of
supermolecules and infinite supramolecular architectures include
the interactions between crown ethers and transition metal coor-
dinated ammonia ligands.23–26 (C6F5)3B·NH3 (1) is differentiated
from these examples by its combination of simplicity, neutrality
and the absence of a good integral hydrogen-bond acceptor. Here,
we will demonstrate that by choice of complementary hydrogen-
bond acceptors, infinite structures can be assembled that show
parallels to metal coordination polymers.
it has only risen to prominence since its introduction as a compo-
nent of highly productive alkene polymerisation systems. In poly-
merisation catalysis, it is used either for alkyl abstraction (catalyst
activation) or in the preparation of poorly coordinating anions.4
Recent studies have exploited the Lewis acidity of (C6F5)3B to
catalyse organic transformations, including the allylstannation of
aldehydes,5,6 ring-opening reactions of non-activated aziridines7,8
and the hydrosilation of unsaturated enones.5
The Lewis acidity of tris(pentafluorophenyl)boron is compara-
ble to that of BF3,9 and it forms robust adducts with a range of
nitrogen containing Lewis bases.10 Arguably, the simplest example
is the ammonia complex, which was amongst the first adducts
prepared,2 but until our recent investigations,11 had received little
attention, in sharp contrast to the aqua complex.12–16
In addition to the utilisation as a precursor to complexes of
the [(C6F5)3BOH]- and [(C6F5)3BO]2- ligands, (C6F5)3B·OH2 has
been shown to form hydrogen bonded supramolecular complexes
with suitable acceptors. The hydrogen atoms of the coordinated
water are activated towards hydrogen bonding and readily form
second coordination sphere supramolecular complexes with one13
or two14 further water molecules in a stepwise process that has been
monitored by NMR spectroscopy.13 (C6F5)3B·OH2 will also form
aWolfson Materials and Catalysis Centre, School of Chemical Sciences
and Pharmacy, University of East Anglia, Norwich, UK NR4 7TJ.
E-mail: S.Lancaster@uea.ac.uk; Fax: +44 1603 592003; Tel: +44 1603
592009
bSchool of Chemistry, University of Southampton, Highfield, Southampton,
UK SO17 1BJ
Results and discussion
We have previously shown that the reaction between a donor-
free light petroleum solution of (C6F5)3B and ammonia gas yields
† CCDC reference numbers 688045–688055. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b808208a
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) with standard deviations in parentheses
B–N
B–C(11)
B–C(21)
B–C(31)
N–B–C(11)
N–B–C(21)
N–B–C(31)
1a11
1.623(2)
1.624(2)
1.617(2)
1.622(2)
1.608(6)
1.599(2)
1.601(9)
1.599(2)
1.594(7)
1.608(6)
1.602(3) 1.614(4)
1.606(3)
1.600(4)
1.627(2)
1.635(2)
1.643(2)
1.640(2)
1.644(3)
1.652 (2)
1.664(10)
1.643(2)
1.653(8)
1.645(6)
1.641(4) 1.636(4)
1.635(3)
1.633(4)
1.643(2)
1.633(2)
1.639(2)
1.638(2)
1.644(3)
1.638(2)
1.629(10)
1.637(2)
1.650(8)
1.640(6)
1.651(3) 1.659(3)
1.636(3)
1.631(4)
1.636(2)
1.639(2)
1.642(2)
1.637(2)
1.644(3)
1.647(2)
1.637(10)
1.652(2)
1.640(8)
1.637(6)
1.639(4) 1.643(4)
1.633(2)
1.648(4)
108.96(12)
109.28(12)
107.85(9)
105.95(12)
106. 5(2)
103.26(9)
104.9(5)
111.89(13)
103.7(4)
105.8(4)
106.17(12)
103.40(12)
102.66(9)
105.35(12)
106.5(2)
110.28(10)
106.5(5)
103.47(12)
108.8(4)
109.2(4)
103.85(12)
106.30(12)
109.38(9)
106.40(12)
106.5(2)
108.22(9)
108.8(5)
107.88(13)
111.9(4)
105.3(4)
2
3
4
5
6
7
8a
8b
9b
10a
10b
110.0(2) 105.8(2)
104.0(2)
106.6(2)
105.4(2) 105.4(2)
106.31(14)
107.0(2)
105.9(2) 110.2(2)
110.4(2)
105.5(2)
a There are two independent molecules of 1 in the asymmetric unit, the atomic numbering of ref. 11 has been changed to maintain consistency with that
employed herein. b There are two independent molecules of 9 in the asymmetric unit.
the hydrogen bonded supermolecule (C6F5)3B·NH3·NH3 and that
(C6F5)3B·NH3 (1) can be obtained by dissolution in toluene and
removal of the volatiles.11 More conveniently, the same second
coordination sphere ammonia adduct (C6F5)3B·NH3·NH3 is also
produced if the ether adduct (C6F5)3B·OEt2 is employed as the
(C6F5)3B source.
In principle, (C6F5)3B·NH3 is a potentially tri-functional
hydrogen-bond donor. The stoichiometry of the supramolecular
complex formation was initially explored by the treatment of
(C6F5)3B·NH3 with either a single equivalent of a hydrogen-
bond acceptor or by crystallisation from a solution containing
an excess of the monodentate bases acetonitrile, pyridine and
tetrahydrofuran (Scheme 1).
by X-ray crystallography (Fig. 1, selected geometric parameters
are given in Table 1). One N–H is engaged in hydrogen bonding to
an acetonitrile molecule (Fig. 1, Table 2). Both of the remaining
hydrogen atoms show contacts to ortho-fluorines (Table 2). Where
we observe contacts within the sum of the van der Waals
radii, they are given in Table 2, however those interactions with
˚
distances approaching 2.40 A and acute angles do not meet our
interpretation of the Dunitz criteria for classification as hydrogen
bonds.11 The contribution of individual X–H ◊ ◊ ◊ F–C interactions
to the lattice energy will be very small but collectively their
influence may be significant.11 Of the two hydrogen atoms in 2
interacting with fluorine rather than nitrogen, one is engaged in a
bifurcated intramolecular hydrogen bond. The other participates
in a bifurcated inter/intramolecular hydrogen bond, linking two
second coordination sphere adducts together in a supramolecular
pair. These pairs are linked further through intermolecular offset
face-to-face or edge-to-face pentafluorophenyl-pentafluorophenyl
interactions to form an infinite 3D network.27 Attempts to
The treatment of 1 with a modest excess of acetonitrile, followed
by crystallisation from a mixed dichloromethane–light petroleum
solution, yielded a sample for which the 1H NMR and elemental
analysis indicated the composition (C6F5)3B·NH3·NCCH3 (2). The
stoichiometry and supramolecular character of 2 was confirmed
Scheme 1
6382 | Dalton Trans., 2008, 6381–6392
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Table 2 Hydrogen bond distances (A) and angles ( )
Symmetry operation for
intermolecular interaction
∠(DHA)/◦
˚
˚
˚
D–H ◊ ◊ ◊ A
d(D–H)/A
d(H ◊ ◊ ◊ A)/A
d(D ◊ ◊ ◊ A)/A
1a11
N(1)–H(1A) ◊ ◊ ◊ F(12)
N(1)–H(1A) ◊ ◊ ◊ F(22)
N(1)–H(1B) ◊ ◊ ◊ F(32)
N(1)–H(1B) ◊ ◊ ◊ F(64(1)
N(1)–H(1C) ◊ ◊ ◊ F(12)
N(1)–H(1C) ◊ ◊ ◊ F(52)
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.88(2)
0.88(2)
0.91(2)
0.90(2)
0.90(2)
0.93(2)
0.93(2)
0.93(2)
0.90(2)
0.88(2)
0.91(2)
0.91(2)
0.91 (2)
0.93(2)
0.88(2)
0.89
2.44
2.18
2.27
2.34
2.28
2.39
2.38
2.43
2.24
2.39
2.38
2.13
2.31
2.32
2.22(2)
2.28(2)
2.11(2)
2.34(2)
2.38(2)
2.08(2)
2.41(2)
2.00(2)
2.40(2)
1.99(3)
2.11(2)
2.33(2)
2.25(2)
2.05(2)
2.33(2)
2.09
2.630(2)
2.747(2)
2.870(2)
3.117(2)
2.630(2)
3.270(2)
2.954(2)
3.011(2)
2.865(2)
2.636(2)
3.201(2)
2.742(2)
3.160(2)
2.636(2)
2.7660(14)
2.6464(13)
2.981(2)
3.2196(12)
2.9434(13)
2.994(2)
2.782(2)
2.926(2)
2.780(2)
2.868(3)
2.906(2)
2.6714(13)
2.7663(14)
2.893(2)
3.195(2)
2.744(6)
2.623(6)
3.256(5)
2.794(7)
3.295(5)
2.988(2)
2.969(2)
2.709(2)
2.818(2)
3.102(2)
3.023(2)
3.035(7)
2.811(6)
2.691(6)
3.048(6)
3.093(7)
2.947(6)
3.092(6)
2.658(5)
2.728(5)
2.918(5)
2.936(3)
2.890(3)
2.672(3)
2.743(3)
2.928(3)
2.936(3)
2.737(3)
2.689(3)
2.874(2)
3.159(2)
2.830(2)
2.642(2)
2.872(3)
2.941(4)
3.001(4)
2.770(3)
2.942(4)
92
120
123
143
103
163
121
122
125
95
151
124
154
100
120.5(12)
105.1(11)
158.1(13)
165.6(13)
120.9(12)
169(2)
103.7(13)
171(2)
105(2)
169(3)
145.6(14)
102.4(11)
116.1(12)
151.2(13)
168(2)
130
114
139
129
138
169(2)
144(2)
102(2)
121(2)
128(2)
147(2)
152(6)
123(5)
96(4)
154(6)
171(5)
151(4)
168(4)
107(4)
108(4)
133(4)
164(2)
176(2)
105(2)
112(2)
164(2)
176(3)
107(2)
117(2)
114(2)
147(2)
119(2)
101(2)
170(2)
142(3)
161(3)
106(2)
163(3)
)
x, y - 1, z
N(2)–H(2A) ◊ ◊ ◊ F(23(2)
N(2)–H(2A) ◊ ◊ ◊ F(35(3)
N(2)–H(2A) ◊ ◊ ◊ F(56)
N(2)–H(2B) ◊ ◊ ◊ F(42)
)
)
x - 1, 1 + y, z
x - 1, y, z
N(2)–H(2B) ◊ ◊ ◊ F(43(4)
N(2)–H(2B) ◊ ◊ ◊ F(66)
N(2)–H(2C) ◊ ◊ ◊ F(36(5)
N(2)–H(2C) ◊ ◊ ◊ F(42)
N(1)–H(1A) ◊ ◊ ◊ F(12)
N(1)–H(1A) ◊ ◊ ◊ F(36)
N(1)–H(1B) ◊ ◊ ◊ N(4)
N(1)–H(1C) ◊ ◊ ◊ F(22¢)
N(1)–H(1C) ◊ ◊ ◊ F(22)
N(1)–H(1A) ◊ ◊ ◊ N(51)
N(1)–H(1A) ◊ ◊ ◊ F(32)
N(1)–H(1B) ◊ ◊ ◊ N(41)
N(1)–H(1C) ◊ ◊ ◊ F(22)
N(1)–H(1) ◊ ◊ ◊ O(21)
N(1)–H(1A) ◊ ◊ ◊ N(46)
N(1)–H(1A) ◊ ◊ ◊ F(26)
N(1)–H(1A) ◊ ◊ ◊ F(36)
N(1)–H(1B) ◊ ◊ ◊ N(43)
N(1)–H(1C) ◊ ◊ ◊ F(14¢)
N(1)-H(1A) ◊ ◊ ◊ F(12)
N(1)-H(1B) ◊ ◊ ◊ F(32)
N(1)-H(1B) ◊ ◊ ◊ Cl(1)
N(1)-H(1C) ◊ ◊ ◊ F(22)
N(1)-H(1C) ◊ ◊ ◊ Cl(1¢)
N(1)–H(1A) ◊ ◊ ◊ O(47)
N(1)–H(1B) ◊ ◊ ◊ O(41)
N(1)–H(1B) ◊ ◊ ◊ F(16)
N(1)–H(1B) ◊ ◊ ◊ F(36)
N(1)–H(1C) ◊ ◊ ◊ O(50)
N(1)–H(1C) ◊ ◊ ◊ O(53)
N(1)–H(1A) ◊ ◊ ◊ N(51)
N(1)–H(1B) ◊ ◊ ◊ F(22)
N(1)–H(1B) ◊ ◊ ◊ F(32)
N(1)–H(1B) ◊ ◊ ◊ F(25¢)
N(1)–H(1C) ◊ ◊ ◊ N(41)
N(1)–H(1A) ◊ ◊ ◊ N(41)
N(1)–H(1B) ◊ ◊ ◊ N(44¢)
N(1)–H(1C) ◊ ◊ ◊ F(26)
N(1)–H(1C) ◊ ◊ ◊ F(32)
N(1)–H(1C) ◊ ◊ ◊ F(35¢¢)
N(1)–H(1A) ◊ ◊ ◊ N(78)
N(1)–H(1B) ◊ ◊ ◊ N(81)
N(1)–H(1C) ◊ ◊ ◊ F(16)
N(1)–H(1C) ◊ ◊ ◊ F(22)
N(2)–H(2A) ◊ ◊ ◊ N(71)
N(2)–H(2B) ◊ ◊ ◊ N(88¢)
N(2)–H(2C) ◊ ◊ ◊ F(56)
N(2)–H(2C) ◊ ◊ ◊ F(66)
N(1)–H(1A) ◊ ◊ ◊ F(26)
N(1)–H(1B) ◊ ◊ ◊ F(15¢)
N(1)–H(1B) ◊ ◊ ◊ F(16)
N(1)–H(1A) ◊ ◊ ◊ F(36)
N(1)–H(1C) ◊ ◊ ◊ N(41)
N(1)–H(1A) ◊ ◊ ◊ N(61)
N(1)–H(1B) ◊ ◊ ◊ N(41)
N(1)–H(1B) ◊ ◊ ◊ F(32)
N(1)–H(1C) ◊ ◊ ◊ N(50¢)
)
-x, 1 - y, 1 - z
x - 1, y, z
)
2
3
1 - x, 2 - y, -z
4
5
1 - x, 2 - y, -z
6
7
0.89
0.89
0.89
0.89
2.14
2.53
2.15
2.58
1 - x, 1 - y, 1 - z
0.89(2)
0.90(2)
0.90(2)
0.90(2)
0.87(2)
0.87(2)
0.96(7)
1.02(7)
1.02(7)
1.02(7)
0.92(6)
0.89(5)
0.82(5)
0.90(5)
0.90(5)
0.90(5)
0.93(3)
0.93(3)
0.88(3)
0.88(3)
0.92(3)
0.90(3)
0.89(3)
0.89(3)
0.93(2)
0.90(2)
0.90(2)
0.93(2)
0.93(2)
0.90(3)
0.93(4)
0.93(4)
0.89(3)
2.11(2)
2.19(2)
2.37(2)
2.25(2)
2.49(2)
2.26(2)
2.15(7)
2.12(7)
2.39(7)
2.10(7)
2.18(6)
2.14(5)
2.28(5)
2.25(5)
2.31(5)
2.23(5)
2.03(3)
1.96(3)
2.30(3)
2.29(3)
2.03(3)
2.04(3)
2.34(3)
2.16(3)
2.36(2)
2.37(2)
2.29(2)
2.30(2)
1.95(2)
2.18(3)
2.11(4)
2.36(3)
2.08(3)
8a
8b
9
1 + x, y, z
x, 1/2 - y, z - 1/2
x - 1, y, z
1/2 + x, 1/2 - y, 1/2 + z
1 - x, 1 - y, 2 - z
10a
10b
1/2 - x, y - 1/2, 1/2 - z
a See footnote a in Table 1.
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hydrogen bonds with pyridine acceptors, the third hydrogen atom
is involved in an intramolecular interaction with an ortho-fluorine
(o-F) atom. We note that one of the hydrogen atoms interacting
with pyridine should strictly be regarded as bifurcated, with weak
interactions to the o-F atom (Table 2).
The highly crystalline supermolecule 4 was obtained through
crystallising 1 from a tetrahydrofuran and light petroleum sol-
vent mixture. Compound 4 proved to have the composition
(C6F5)3B·NH3·(THF)3, suggesting that all three N–H groups
might be participating in hydrogen bonding, a hypothesis subse-
quently confirmed by diffraction methods (Fig. 3). In the solid
state, 4 has perfect three-fold symmetry, crystallising in space
28
¯
group R3 with the three-fold axis running along the B–N bond.
The three symmetry-related hydrogen bonds show a H ◊ ◊ ◊ O
◦
˚
separation of 1.99(3) A with a N–H ◊ ◊ ◊ O angle of 169(3) . Since
each of the N–H groups is exclusively engaged in intermolecular
hydrogen bonding, this is a rare example of an amine adduct
of (C6F5)3B that is not supported by intramolecular N–H ◊ ◊ ◊ F–
C hydrogen bonds.11 The absence of an intramolecular hydrogen
bond does not have a significant influence on the B–N bond length
in 4, which is similar to the other structures reported herein. The
second coordination sphere complexes of 4 pack together to form
a two-dimensional net through offset face-to-face C6F5 ◊ ◊ ◊ C6F5
interactions leaving hexagonal voids in which highly disordered
Fig. 1 ORTEP representation of 2 with displacement ellipsoids at 50%,
hydrogen atoms not involved in hydrogen bonding have been omitted for
clarity.
crystallise 1 from neat acetonitrile or acetonitrile–light petroleum
mixtures, in order to obtain a sample with more than one
associated acetonitrile molecule, were unsuccessful.
Compound 1 proved to be highly soluble in pyridine. Evapora-
tion of excess pyridine under reduced pressure followed by crys-
tallisation from a dichloromethane and light petroleum solvent
mixture yielded 3. Compound 3 was found by X-ray crystallogra-
phy to be the second coordination sphere complex between 1 and
two pyridine molecules, (Fig. 2), and this composition was later
confirmed for the bulk sample by elemental analysis and 1H NMR
spectroscopy. Attempts to prepare samples with one equivalent
of pyridine, through the addition of a stoichiometric amount, or
three equivalents, through crystallisation from neat pyridine, either
failed to yield crystalline solids or led to the preferential formation
of 3. Whilst two of the hydrogen atoms of (C6F5)3B·NH3 form
¯
solvent molecules are situated. The R3 space group is found
for a number of structures with an EPh3 fragment indicating
similar features in the supramolecular lattices.29 It is possible
that the observed preference for the crystallisation of a species
with three hydrogen bonded THF molecules is directed by the
favourable nature of the resulting crystal lattice, which optimises
the C6F5 ◊ ◊ ◊ C6F5 interactions.
Fig. 3 ORTEP representation of 4 with displacement ellipsoids at the
40% probability level and viewed almost along the three-fold rotation axis.
The THF molecules show disorder, with alternative sites for the methylene
group of C(24); atom numbers with suffixes ¢ and ¢¢ are related by the
symmetry operations 1 - y, x - y, z and 1 - x + y, 1 - x, z, respectively.
Fig. 2 ORTEP representation of 3, displacement ellipsoids are drawn
at the 40% probability level, hydrogen atoms not engaged in hydrogen
bonding or interactions with fluorine atoms have been omitted for clarity.
The current study is predominantly concerned with the nature
of the crystalline supermolecules resulting from the interaction of
6384 | Dalton Trans., 2008, 6381–6392
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Table 3 1H and 19F NMR data recorded in CDCl3 (unless otherwise
stated) for the NH3 group and the fluorine atoms
ortho-F/ppm meta-F/ppm para-F/ppm 1H NH3/ppm
1 (C6D6)11 -135.3
-162.9
-161.9
-162.8
-163.4
-162.9
-163.0
-163.0
-164.7
-162.3
-162.5
-162.7
-155.5
-154.6
-155.8
-156.5
-155.6
-156.2
-156.4
-158.5
-155.1
-155.3
-155.8
2.67
4.75
4.81
4.93
3.14
5.48
5.46
5.39
4.80
5.03
5.45
1
-135.0
-135.4
-134.9
-135.2
-135.3
-134.4
-134.1
-135.4
-135.4
-135.3
2
Scheme 2
3 (C6D6)
4 (C6D6)
5
6
the crude product subsequently recrystallised from toluene,
yielding X-ray quality crystals. Confounding expectations,
the structural solution revealed, not 5, but (C6F5)3B·NH3,
[(CH3)2NCH2CH2N(CH3)2CH2Cl]+ and Cl- entities, comprising
compound 6. It appears that (C6F5)3B·NH3 serves to promote
nucleophilic attack of the amine upon the dichloromethane
solvent, giving rise to the observed cation, since the reaction
does not otherwise take place under ambient conditions. Similar
reactivity has been observed in the presence of electrophilic metal
centres.30–32 We have subsequently found that NEt3 will also react
with CH2Cl2 in the presence of 1.33 The solution-phase stability
of (C6F5)3B·NH3 and the instability of tertiary amine adducts11
suggest that it is indeed 1, and not (C6F5)3B, that is the electrophile
responsible but this mechanism awaits further investigation.
The solid state structure of 6 consists of the ion pair
[(CH3)2NCH2CH2N(CH3)2(CH2Cl)][Cl] co-crystallised with com-
pound 1. The cation is unremarkable and resembles previously
characterised [NR3(CH2Cl)]+ salts.34 Within the context of this
study, two molecules of 1 and two Cl- ions (Fig. 4) can be regarded
as forming a hydrogen bonded supramolecular complex. The N–H
bonds involved in hydrogen bonding to the Cl- ion are both strictly
bifurcated since each also interacts with an o-F. The remaining N–
H group participates in a single short hydrogen bond to a third
o-F. Cation–anion interactions are restricted to a close contact
between a hydrogen atom from a methyl group of the quaternary
ammonium and the chloride ion.
7 (C6D6)
8b
9
10b
1 with basic hydrogen-bond acceptors. Amongst the monodentate
bases, only in the THF example did we find interactions with more
than two hydrogen bonded acceptor molecules in the solid state.
However, we cannot rule out the possibility that tris complexes are
formed in solution in the presence of excess base. Indeed one might
expect tris complexation to be favoured for the more basic nitrogen
donors, despite the fact that we did not obtain any crystalline
examples.
During the course of the routine spectroscopic characterisation,
it was readily apparent that determining the nature of any second
coordination sphere interactions maintained in solution would
present a significant challenge (selected spectroscopic data are
provided in Table 3). The hydrogen bonds are obviously highly
labile and the spectra are therefore averaged. Evidently, the 19F
NMR data, which are diagnostic for the formation of (C6F5)3B
adducts, show little value for identifying the second sphere
coordination.
The 1H chemical shift of the NH3 group is unsurprisingly more
sensitive to the hydrogen bonding environment. In comparing the
data in Table 3, it is worth noting that reference compound 1
itself is not hydrogen bond free and that it exhibits relatively weak
intramolecular N–H ◊ ◊ ◊ F interactions, (Table 2). Furthermore,
1
there is a significant H NMR chemical shift difference between
1 in d6-benzene and d1-chloroform solutions, which we attribute
to the mode of solvation. While it is apparent that second sphere
coordination complexes are present in solution, we can say little
about their precise composition. However, the distinctly high-
field value for compound 4 does appear significant. Despite the
fact that the solid-state structure has three hydrogen bonds, the
solution-phase NMR data are much closer to those of 1 than the
supermolecule formed with 15-crown-5, (7), which is discussed
below. It therefore seems probable that the second coordination
sphere complex, with the weak monodentate tetrahydrofuran
acceptors, is largely dissociated in the benzene solution.
The isolation of 3 and 4 demonstrated that supermolecule
formation through hydrogen bonding to two or three N–H groups
was possible. We therefore reasoned that second coordination
sphere complexes formed through multiple hydrogen bonds to
‘chelating’ bases would be both accessible and, where sterically
compatible, exhibit increased stability.
The treatment of 1 with one equivalent of tetramethylethylene-
diamine (TMEDA) was expected to yield a compound with
the composition (C6F5)3B·NH3·(TMEDA) (5) (Scheme 2). The
reaction was conducted in dichloromethane solution and
Fig. 4 ORTEP representation of 6 indicating the hydrogen bonding
interaction of (C6F5)3B·NH3 and Cl- anion pairs and the relative positions
of the associated counter cations. Displacement ellipsoids are drawn at
the 50% probability level and hydrogen atoms not engaged in hydrogen
bonding have been omitted for clarity.
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In light of the reactivity towards dichloromethane, X-ray quality
crystals of 5 were grown from a toluene solution. TMEDA chelates
to two of the ammonium hydrogen atoms of (C6F5)3B·NH3. One
of these H-atoms is also engaged in a trifurcated arrangement
with two o-F atoms. The third hydrogen is hydrogen bonded
to the para-fluorine (p-F) of a symmetry-related (C6F5)3B·NH3
molecule so that the solid-state architecture is composed of
supramolecular dimers (Fig. 5). These dimers are linked further
through aryl–perfluoraryl interactions with a toluene solvent
molecule disordered about a centre of symmetry to generate
infinite 1D chains.
NMR spectra and elemental analysis were consistent with the 1 : 1
second coordination sphere adduct formulation (C6F5)3B·NH3·15-
crown-5 and this was confirmed by diffraction methods.
As is the case for F3B·NH3·18-crown-6,35 all three of the
ammonia hydrogen atoms on 1 are hydrogen bonded to 15-
crown-5 (Fig. 6 and Table 2). However, while the macrocycle of
F3B·NH3·18-crown-6 retained pseudo D3d symmetry and a near-
symmetrical triangle of hydrogen bonds, with a short average
35
˚
H ◊ ◊ ◊ O distance very similar to that in 4 at 1.99 A, the
arrangement in 7 is somewhat more complex and the hydrogen
bonds somewhat longer. The first of the hydrogen atoms is involved
in a single hydrogen bond to an oxygen atom H(1A) ◊ ◊ ◊ O(47)
˚
2.11(2) A. The second is engaged in a trifurcated hydrogen bond
to one of the 15-crown-5 oxygen atoms H(1B) ◊ ◊ ◊ O(41) 2.19(2)
˚
A and to two o-F atoms of the C6F5 rings. The third hydrogen
atom participates in a bifurcated hydrogen bonding to two oxygen
atoms of the 15-crown-5, while one of the hydrogen bonds is of
˚
˚
medium length (2.26(2) A) the other is long (2.49(2) A). The
molecules pack together through offset face-to-face and edge-
to-face C6F5 ◊ ◊ ◊ C6F5 interactions. In 7, accommodating all three
N–H in hydrogen bonds to the 15-crown-5 macrocycle requires
considerable distortion from the near ideal geometries observed
for F3B·NH3·18-crown-6 and 4, and the poor crystallinity of the
18-crown-6 analogue is difficult to rationalise.
Fig. 5 ORTEP representation of 5 illustrating the formation of pairs
of (C6F5)3B·NH3 molecules through hydrogen bonding, the disordered
toluene solvent molecule and the hydrogen atoms on the TMEDA have
been omitted for clarity and displacement ellipsoids are at the 40%
probability level.
Since TMEDA forms a 1 : 1 supramolecular complex with 1, and
compound 4 demonstrates the ability to hydrogen bond through
all three N–H donors, we reasoned that a suitable macrocyclic
acceptor might engage all the protic hydrogens. A literature survey
revealed an extensive chemistry of second coordination sphere
complexes between crown ethers and ammonia adducts of both
transition metals and main group Lewis acids.22–25 The success
of the Stoddart and Colquhoun group in crystallographically
characterising 1 : 1 complexes between F3B·NH3 and H3B·NH3
with 18-crown-6 is of obvious relevance.35 Attempts to prepare
a supermolecule suitable for crystallographic investigation by
treating 1 with 18-crown-6, dibenzo-18-crown-6 and 12-crown-
4 were unsuccessful. However, 1 and 15-crown-5 co-crystallised
from dichloromethane solution to give 7 (Scheme 3). Multinuclear
Fig. 6 ORTEP representation of 7 illustrating the hydrogen bonding of
(C6F5)3B·NH3 to 15-crown-5, displacement ellipsoids are drawn at the
40% probability level with the hydrogen atoms not engaged in hydrogen
bonding and the solvent molecule have been omitted for clarity.
The successful structural characterisation of discrete super-
molecules, assembled through hydrogen bonding to convergent
acceptors, suggested that choice of a divergent acceptor would
lead to the generation of infinite supramolecular assemblies related
to those formed between di- or tri-functional Lewis acids and
divergent bases.
The treatment of 1 with an excess of pyrazine in dichloro-
methane solution and subsequent crystallisation yielded a sample
Scheme 3
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Scheme 4
with the gross composition 1·NC4H4N by elemental analysis and
1H NMR (Scheme 4). However, X-ray diffraction revealed that al-
though the sample appeared homogeneous there were two crystal
forms present. The first crystal characterised proved to be a minor
component with the composition {(C6F5)3B·NH3}2{pyrazine}3,
(8a, Fig. 7). Each molecule of (C6F5)3B·NH3 is hydrogen bonded
to two pyrazine acceptors. One pyrazine bridges two symmetry-
related molecules of (C6F5)3B·NH3 with a crystallographic in-
version centre at the centroid of the pyrazine ring. The second
pyrazine is terminal: N(44) does not accept a hydrogen bond. The
remaining N–H group is engaged in an intramolecular hydrogen
bonding interaction to two o-F atoms in a very similar fashion to
that present in 3. There is a further N–H ◊ ◊ ◊ F contact to a meta-
fluorine (m-F) of a neighbouring molecule. One of the two pyrazine
molecules is involved in a somewhat displaced aryl–perfluoroaryl
interaction.
The second crystal selected reflected the elemental analysis
result and thus the bulk composition (C6F5)3B·NH3·pyrazine,
8b, and was therefore assumed to be the major component
(Fig. 8). The supramolecular structure consists of infinite 1D
‘zig-zag’ chains constructed from hydrogen bonds between two
ammonia hydrogen atoms, each to a pyrazine acceptor (Fig. 9).
The third N–H participates in a trifurcated hydrogen bond
Fig. 8 Molecular ORTEP representation of 8b illustrating the hydrogen
bonding within the asymmetric unit, displacement ellipsoids are drawn
at the 50% probability level. Hydrogen atoms not engaged in hydrogen
bonding and the dichloromethane solvent molecule have been omitted for
clarity.
Fig. 7 ORTEP representation of the structure of 8a with displacement
ellipsoids at 50% and hydrogen atoms on the pyrazine molecules being
omitted for clarity.
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Fig. 9 An illustration of the infinite chains of 8b, solvent molecules and
intramolecular hydrogen bonds have been omitted for clarity.
Fig. 11 Illustrating the one-dimensional chains of 9, only the major
components of the disordered DABCO molecules are shown here and
the dichloromethane solvent molecules have been omitted for clarity.
to two intramolecular o-F atoms and one intermolecular m-F
atom, linking the chains together to form a 2D sheet. These
sheets are linked further through offset face-to-face C6F5 ◊ ◊ ◊ C6F5
interactions, extending the network into a third dimension.
The reaction between 1,4-diazabicyclo[2.2.2]octane (DABCO)
and 1 proceeds similarly to that with pyrazine, giving crystals with
The nature of the supramolecular complex formed between 1
and 4,4¢-bipyridine (bipy) proved to be dependent upon, but not
to directly follow, the molar ratio employed. The treatment of 1
with one equivalent of bipy yielded a crystalline material (10a). X-
Ray analysis showed that the 4,4¢-bipyridine molecule is hydrogen
bonded to two (C6F5)3B·NH3 (Fig. 12). There is an inversion centre
on the C(44)–C(44¢) bond at the centre of the bipy ligand, hence the
asymmetric unit contains one (C6F5)3B·NH3 molecule and half a
bipy molecule. Since only one N–H is engaged in an intermolecular
hydrogen bond, the structure can therefore be regarded as related
to 2. As was found for 2, one of the remaining hydrogen atoms
participates in a bifurcated intramolecular hydrogen bond to two
ortho-fluorine atoms, whilst the other is involved in a bifurcated
hydrogen bond to one intra and one intermolecular fluorine atom
(Table 2). However, unlike 2, the intermolecular hydrogen bonds
are divergent and generate one-dimensional chains through the
N–H ◊ ◊ ◊ F contacts.
1
a 1 : 1 composition confirmed by H NMR, elemental analysis
and X-ray crystallography (9, Fig. 10). Two of the ammonia
hydrogen atoms in each molecule are involved in intermolecular
hydrogen bonding to the DABCO molecules, thus forming a 1D
chain. The third is engaged in a bifurcated hydrogen bond to two
ortho-fluorine atoms. In contrast to 8b however, rather than ‘zig-
zagging’ the chain follows more of a wave-like pattern, with half the
DABCO molecules lying disordered over two positions between
two rows of (C6F5)3B·NH3 in the crystal structure (Fig. 11). The
other DABCO molecules lie along two parallel lines defining the
peaks and troughs of the wave-like chain. The infinite hydrogen
bonded chains observed for 8b and 9 resemble 1D coordination
polymers in which pyrazine,36–39 DABCO40–42 or 4,4¢-bipyridine43–45
bridge transition metals through dative interactions. As was the
case for 8b, the infinite chains of 9 pack together through offset
face-to-face C6F5 interactions.
Fig. 12 ORTEP representation of 10a showing
a molecule of
(C6F5)3B·NH3 hydrogen bonded to each end of the 4,4¢-bipyridine
molecule. Displacement ellipsoids are drawn at the 50% probability level.
Spectroscopic characterisation of the material obtained at a
1 : 1 molar ratio of 1 and bipy, in contrast to the structurally
characterised crystals of 10a, indicated that 1 and bipy were
present in a 2 : 3 molar ratio (10b). However, X-ray quality crystals
with this composition were only obtained from solutions in which
bipy was in excess. The solid-state structure of 10b was determined
Fig. 10 ORTEP representation of 9 illustrating the asymmetric unit,
the hydrogen bonding within the structure and the disorder of one of
the DABCO molecules, displacement ellipsoids are drawn at the 50%
probability level. Hydrogen atoms not involved in hydrogen bonding and
the dichloromethane solvent molecules have been omitted for clarity.
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by X-ray crystallography (Fig. 13). Each ammonia hydrogen is
involved in hydrogen bonding to a bipy molecule, which links
in turn to another (C6F5)3B·NH3 molecule. This connectivity
extends infinitely, generating a two-dimensional hydrogen bonded
grid (Fig. 14). The grids are linked together through displaced
aryl–perfluoroaryl interactions between one C6F5 ring and half
of a bipyridine and through face-to-face and vertex-to-face
C6F5 ◊ ◊ ◊ C6F5 interactions. Diagonal threads can be traced through
the grid shown in Fig. 14, which closely resemble the ‘zig-zag’
chains present in 8b.
Conclusion
The ammonia adduct of tris(pentafluorophenyl)borane forms
discrete second coordination sphere complexes with monodentate
and convergent polydentate hydrogen-bond acceptors in solution
and in the solid-state. The solution structures are labile and the
resulting crystals do not always reflect the composition of the
solution medium from which they are grown. Indeed, even in the
presence of a large excess of base, discrete complexes in which all
three N–H groups participate in intermolecular hydrogen bonding
were only obtained in the cases of 4 and 7. Where the N–H
groups are not engaged in intermolecular hydrogen bonding, they
participate in intramolecular interactions with ortho-fluorines very
similar to those we observed for amine adducts of (C6F5)3B,
such that the intramolecular hydrogen bonding in 2 resembles
(C6F5)3B·N(R)H2 and 3 resembles that in (C6F5)3B·N(R)2H.11
Interactions between pentafluorophenyl groups play a significant
role in directing the supramolecular architectures of these lattices.
¯
Particularly noteworthy is the R3 space group found for 4, which
suggests that its favourable supramolecular architecture can play
a part in dictating the composition of the crystalline second
coordination sphere adduct.
The careful control of stoichiometry and the addition of
divergent acceptors results in the transition from supermolecules
incorporating a single molecule of 1 to more complex structures,
such as 8a and 10a and on to infinite one-dimensional chains 8b
and 9 and the infinite two-dimensional grid 10b. In this respect,
it is possible to draw close structural analogies to the field of
supramolecular coordination chemistry despite the much weaker
character of these hydrogen bonding interactions.
Fig. 13 ORTEP representation of 10b showing
a molecule of
(C6F5)3B·NH3 forming hydrogen bonds to three 4,4¢-bipyridine molecules.
Hydrogen atoms not involved in hydrogen bonding and the disordered
dichloromethane molecule have been omitted for clarity. Displacement
ellipsoids are drawn at the 50% probability level.
Experimental
All reactions were carried out under a dry nitrogen atmo-
sphere using standard Schlenk techniques in pre-dried glass-
ware. Solvents were dried using an appropriate drying agent
and distilled under nitrogen prior to use, dichloromethane
(CaH2), light petroleum (Na–K alloy), tetrahydrofuran (sodium–
benzophenone) and toluene (sodium). Samples for NMR analysis
were prepared using degassed deuterated solvents dried over
˚
activated 4 A molecular sieves. NMR spectra were obtained using
a Bruker Avance DPX300 spectrometer at 23 ◦C, J values are
given in Hz. Elemental analyses were carried out at the London
Metropolitan University. Pyridine and acetonitrile were dried over
˚
activated 4 A molecular sieves and all other reagents were used as
supplied from commercial sources.
(C6F5)3B·NH3 (1)
Fig. 14 The extended ring system generated in 10b, the solvent and the
C6F5 rings have been omitted for clarity.
Following
a
modification of the literature procedure,11
(C6F5)3B·NH3 was prepared directly from the ether adduct of
tris(pentafluorophenyl)boron. Gaseous ammonia was passed over
a solution of B(C6F5)3·OEt2 (5.94 g, 10.1 mmol) in light petroleum
(ca. 350 cm3) for 5 min, during which time a white precipitate
of (C6F5)3B·NH3·NH3 formed. The precipitate was filtered, dried
under vacuum and the resulting solid was dissolved in toluene
(40 cm3). The second equivalent of ammonia was removed
with the toluene under vacuum, yielding crude 1. Colourless
crystals of (C6F5)3B·NH3 were obtained through crystallisation
The ‘chicken-wire’ grid pattern of 10b (Fig. 14), is a familiar
motif in hydrogen bonded organic networks,46–47 while two-
dimensional coordination polymers are often found in a square-
grid arrangement.48–50 To the best of our knowledge, this example
is unique amongst the metal-free networks, in that the grid is not
interpenetrated. The absence of interpenetration is a consequence
of the steric bulk of the (C6F5)3B group and small size of the NH3
node.
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from a dichloromethane and light petroleum solvent mixture at
-25 ◦C. The NMR data were in agreement with the literature
data.11
(C6F5)3B·NH3·[(CH3)2NCH2CH2N(CH3)2CH2Cl]Cl (6)
Tetramethylelthylenediamine (TMEDA) (0.2 cm3, 1.3 mmol) was
added to a solution of (C6F5)3B·NH3 (0.529 g, 1 mmol) in CH2Cl2
(4 cm3). The solution was layered with light petroleum and
cooled slowly to -25 ◦C to afford colourless crystals, which were
unsuitable for X-ray crystallography. The crystals were separated
by filtration and recrystallised from toluene–light petroleum to
afford colourless X-ray quality crystals. dH/ppm (300.1 MHz,
CDCl3) 5.66 (2H, s, CH2Cl), 5.46 (3H, br, NH3), 3.81 (2H, t, 3JHH
6.0, CH2), 3.42 (6H, s, CH3), 2.72 (2H, t, 3JHH 6.0, CH2), 2.26 (6H, s,
(C6F5)3B·NH3·CH3CN (2)
Acetonitrile (0.3 cm3, 5.7 mmol) was added to a solution of
(C6F5)3B·NH3 (0.529 g, 1 mmol) in dichloromethane (5 cm3) at
room temperature. X-Ray quality colourless crystals were grown
upon the addition of light petroleum (5 cm3) and cooling the
solution to -25 ◦C. Elemental analysis found: C 41.6, H 0.8, N
4.8. Calculated for C20H6BF15N2: C 42.1, H 1.0, N 4.9. dH/ppm
(300.1 MHz, CDCl3) 4.81 (3H, s, NH3), 1.97 (3H, s, CH3). dC/ppm
1
CH3). dC/ppm (75.5 MHz, { H}, CDCl3) 69.65 (CH2Cl), 58.86
(CH2) 54.13 (CH2), 49.74 (CH3), 45.11 (CH3). dB/ppm (96.3 MHz,
CDCl3) -10.10. dF/ppm (282.4 MHz, CDCl3) -134.4 (6F, m, o-F),
-156.4 (3F, t, 3JFF 20, p-F) -163.0 (6F, m, m-F).
1
(75.5 MHz, { H}, CDCl3) 116.90 (CN), 2.15 (CH3). dB/ppm
(96.3 MHz, CDCl3) -9.38. dF/ppm (282.4 MHz, CDCl3) -135.4
(6F, m, o-F), -155.8 (3F, t, 3JFF 20, p-F), -162.8 (6F, m, m-F).
(C6F5)3B·NH3·(C10H20O5) (7)
A solution of (C6F5)3B·NH3 (0.45 g, 0.9 mmol) in toluene (5 cm3)
was treated with 15-crown-5 (0.17 cm3, 0.9 mmol) at ambient
temperature affording a colourless emulsion. The solvent was
removed under reduced pressure giving a solid, which when
washed with light petroleum gave an elemental analysis consistent
with the composition (C6F5)3B·NH3·15-crown-5 (0.60 g, 0.8 mmol,
93%). Recrystallisation from dichloromethane–light petroleum
yielded X-ray quality crystals of 7. Elemental analysis found: C
44.8, H 3.1, N 1.8. Calculated for C28H23BF15NO5: C 44.9, H 3.1,
N 1.9. dH/ppm (300.1 MHz, CDCl3) 5.39 (3H, br, NH3), 3.46
(20H, s, 15-crown-5). dB/ppm (96.3 MHz, CDCl3) -10.7. dF/ppm
(C6F5)3B·NH3·(C5H5N)2 (3)
(C6F5)3B·NH3 (0.64 g, 1.2 mmol) was dissolved in pyridine (1 cm3)
at room temperature giving a colourless solution. The removal of
the solvent under vacuum afforded a fine powdery material with
the composition (C6F5)3B·NH3·(C5H5N)2 (0.72 g, 1.2 mmol, 99%).
X-Ray quality crystals were obtained by recrystallisation from
a dichloromethane–light petroleum solution. Elemental analysis
found: C 48.8, H 1.9, N 6.15. Calculated for C28H13BF15N3: C 48.9,
H 1.9, N 6.1. dH/ppm (300.1 MHz, C6D6) 8.24 (6H, m, C5H5N),
6.91 (2H, m, C5H5N), 6.58 (6H, m, C5H5N), 4.93 (3H, br, NH3).
dB/ppm (96.3 MHz, C6D6) -10.2. dF/ppm (282.4 MHz, C6D6)
3
(282.4 MHz, CDCl3) -134.1 (6F, d, JFF 20, o-F), -158.5 (3F, t,
3JFF 20, p-F), -164.7 (6F, t, 3JFF 20, m-F).
3
-134.9 (6F, m, o-F), -156.5 (3F, t, JFF 20, p-F) -163.4 (6F, m,
m-F).
{(C6F5)3B·NH3}2{l-C4H4N2}3 (8a) and
[{(C6F5)3B·NH3}{l-C4H4N2}]n (8b)
(C6F5)3B·NH3·(C4H8O)3 (4)
A solution of (C6F5)3B·NH3 (0.529 g, 1 mmol) in dichloromethane
(3 cm3) at room temperature was treated with a dichloromethane
solution (3 cm3) of pyrazine (0.080 g, 1 mmol). The reaction
mixture was then cooled to -25 ◦C overnight to yield two visually
indistinguishable sets of X-ray quality crystals 8a (towards the top
of the Schlenk tube) and the major constituent, 8b. The solvent of
crystallisation was removed under reduced pressure. Elemental
analysis (for 8b) found: C 43.3, H 1.0, N 6.8. Calculated for
C22H7BF15N3: C 43.4, H 1.2, N 6.9. dH/ppm (300.1 MHz, CDCl3)
(C6F5)3B·NH3 (0.44 g, 0.83 mmol) was dissolved in THF (3 cm3).
The solution was cooled slowly to -25 ◦C to afford colourless
crystals. The solvent of crystallisation was removed under re-
duced pressure. Elemental analysis found: C 48.3, H 3.5, N 2.0.
Calculated for C30H27BF15NO3: C 48.35, H 3.65, N 1.9. dH/ppm
(300.1 MHz, C6D6) 3.52 (6H, m, C4H8O), 3.14 (3H, br, NH3),
1
1.45 (6H, m, C4H8O). dC/ppm (75.5 MHz, { H}, C6D6) 67.86
(CH2), 25.84 (CH2). dB/ppm (96.3 MHz, C6D6), -9.98. dF/ppm
3
(282.4 MHz, C6D6), -135.2 (6F, m, o-F), -155.6 (3F, t, JFF 21,
1
4.80 (3H, s, NH3), 8.57 (4H, s, CH). dC/ppm (75.5 MHz, { H},
p-F), -162.9 (6F, m, m-F).
CDCl3) 145.56 (CH). dB/ppm (96.3 MHz, CDCl3) -9.08. dF/ppm
(282.4 MHz, CDCl3) -135.4 (6F, m, o-F), -155.1 (3F, m, p-F),
-162.3 (6F, m, m-F).
(C6F5)3B·NH3·(CH3)2NCH2CH2N(CH3)2·C7H8 (5)
Tetramethylethylenediamine (0.2 cm3, 1.3 mmol) was added to a
solution of (C6F5)3B·NH3 (0.529 g, 1 mmol) in toluene (5 cm3) and
the resulting reaction mixture was then cooled to -25 ◦C affording
colourless X-ray quality crystals. The solvent of crystallisation
was removed under reduced pressure. Elemental analysis found: C
44.6, H 2.8, N 6.2. Calculated for C24H19BF15N3: C 44.9, H 3.0, N
6.5. dH/ppm (300.1 MHz, CDCl3) 5.48 (3H, s, NH3), 2.29 (4H, s,
[{(C6F5)3B·NH3}{l-N(CH2CH2)3N}]n (9)
The addition of 1,4-diazabicyclo-[2.2.2]-octane (DABCO)
(0.168 g, 1.5 mmol) in CH2Cl2 (5 cm3) to a solution of (C6F5)3B·
NH3 (0.529 g, 1 mmol) in CH2Cl2 (5 cm3) resulted in the immediate
precipitation of a fine white precipitate. X-Ray quality crystals
weregrownbylayeringdilutesolutionsof(C6F5)3B·NH3 inCH2Cl2
and DABCO in light petroleum and cooling to -25 ◦C. Elemental
analysis found: C 45.1, H 2.0, N 6.4. Calculated for C24H15BF15N3:
C 45.0, H 2.4, N 6.55. dH/ppm (300.1 MHz, CDCl3) 5.03 (3H, s,
1
CH2), 2.10 (12H, s, CH3). dC/ppm (75.5 MHz, { H}, CDCl3) 57.57
(CH2), 45.74 (CH3). dB/ppm (96.3 MHz, CDCl3) -9.97. dF/ppm
3
(282.4 MHz, CDCl3) -135.3 (6F, m, o-F), -156.2 (3F, t, JFF 21,
1
p-F), -163.0 (6F, m, m-F).
NH3), 2.76 (12H, s, CH2). dC/ppm (75.5 MHz, { H}, CDCl3) 47.20
6390 | Dalton Trans., 2008, 6381–6392
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(CH2). dB/ppm (96.3 MHz, CDCl3) -9.35. dF/ppm (282.4 MHz,
CDCl3) -135.4 (6F, m, o-F) -155.3 (3F, m, p-F) -162.5 (6F,
m, m-F).
{(C6F5)3B·NH3}2{l-C10H8N2} (10a) and
[{(C6F5)3B·NH3}2{l-C10H8N2}3]n (10b)
A solution of 4,4¢-bipyridine (0.156 g, 1 mmol) in CH2Cl2 (4 cm3)
was added to a solution of (C6F5)3B·NH3 (0.529 g, 1 mmol) in
CH2Cl2 (4 cm3). The solution was cooled slowly to -25 ◦C to
yield X-ray quality crystals of 10a and a crystalline solid (10b).
Spectroscopic data for 10b: dH/ppm (300.1 MHz, CDCl3) 8.61
(6H, dd, J 4.6 and 1.5, CH), 7.51 (6H, dd, J 4.5 and 1.6, CH),
1
5.45 (3H, br, NH3). dC/ppm (75.5 MHz, { H}, CDCl3) 150.7 (CH),
146.1 (C), 122.0 (CH). dB/ppm (96.3 MHz, CDCl3) -9.43. dF/ppm
3
(282.4 MHz, CDCl3) -135.3 (6F, m, o-F) -155.8 (3F, t, JFF 20,
p-F), -162.7 (6F, m, m-F). Due to the presence of a mixture of 10a
and 10b, satisfactory elemental analysis could not be obtained.
Preparation of X-ray quality crystals of
{(C6F5)3B·NH3}2{l-C10H8N2}3 (10b)
A solution of (C6F5)3B·NH3 (0.529 g, 1 mmol), in CH2Cl2 (4 cm3)
was added to a solution of 4,4¢-bipyridine (0.468 g, 3 mmol)
in CH2Cl2. The solution was then cooled to -25 ◦C to afford
colourless crystals of 10b.
X-Ray crystallography
Diffraction data for 3, 7 and 9 were collected by the EPSRC
Crystallography Service at the University of Southampton on
a Bruker-Nonius KappaCCD diffractometer and the data were
processed using the DENZO/SCALEPACK programs.51 All other
data were collected at UEA on an Oxford Diffraction Xcalibur-
3 CCD diffractometer, and processed using the CrysAlis-CCD
and RED programs. In each case, the structure was determined
by direct method routines in the SHELXS program and refined
by full-matrix least-squares methods on F2 in SHELXL52 within
the WinGX program suite.53 The results are collated in Table 4.
Scattering factors for neutral atoms were taken from literature
values.54
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©