η3-, η4- and η6-Co-ordination complexes of the weakly co-ordinating anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate

Article abstract of DOI:10.1039/a706044k

Single-crystal X-ray diffraction has established η³-, η⁴- and η⁶-co-ordination of the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) in the complexes Ag(TFPB)(2,2′-bipy) (2,2′-bipy = 2,2′-bipyridine), Ag(TFPB)

Full text of DOI:10.1039/a706044k

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ç3-, ç4- and ç6-Co-ordination complexes of the weakly co-ordinating
anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
John Powell,* Alan Lough and Tahir Saeed
Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada
The rhodium complex Rh(TFPB)(cod) 3 (cod = cycloocta-
Single-crystal X-ray diffraction has established η3-, η4- and η6-
co-ordination of the anion tetrakis[3,5-
bis(trifluoromethyl)phenyl]borate (TFPB) in the complexes
Ag(TFPB)(2,2Ј-bipy) (2,2Ј-bipy = 2,2Ј-bipyridine),
Ag(TFPB)(1,2-C6H4I2) and Rh(TFPB)(cod) (cod = cycloocta-
1,5-diene) respectively.
1,5-diene) was similarly obtained from the reaction of [RhCl-
(cod)]2 with stoichiometric amounts of AgPF6 and Na[TFPB]
in CH2Cl2 solution. The molecular structures of complexes 1–3
as determined by single-crystal X-ray diffraction, together with
selected bond lengths are shown in Figs. 1–3. In the silver com-
plexes 1 and 2 the TFPB ligand adopts bidentate bonding
modes. In 1 two of the aryl rings are each η2-bonded to
silver via the ipso carbon and an adjacent ortho carbon in a
fairly symmetrical manner. The 1,2-diiodobenzene ligand also
functions as a reasonably symmetrical bidentate ligand in
contrast to the unsymmetrical bonding modes observed in
[Ag(1,2-C6H4I2)3]PF6 and [Ag(NO3)(1,2-C6H4I2)]n.7 In the 2,2Ј-
bipyridine complex 2 the TFPB ligand exhibits a less sym-
metrical η3-bonding mode comprized of an η2-interaction with
an ipso and ortho carbon atom at one aromatic ring together
with a weaker η1-interaction with the ipso carbon of a second
aromatic ring. The Ag᎐C bond distances for the η2-interaction
in 2 [2.424(3) and 2.493(3) Å] are significantly shorter than the
corresponding distances in 1 [2.507(3)–2.686(3) Å]. The ipso
carbon–silver distance of these η2-interactions is the shorter
distance in 2 but the longer one in 1. The change in co-
ordination geometry of the TFPB ligand on going from 1 to 2
may well be a consequence of the increased steric requirements
of the 2,2Ј-bipyridine ligand vis-à-vis the 1,2-diiodobenzene
ligand. In this regard it is noteworthy that the single-crystal
X-ray diffraction studies of the complex Ag(TFPB)(dppe) have
shown it to have the ionic structure [Ag2(dppe)2][TFPB]2.8
Presumably the steric size of the ligand now precludes co-
Very weakly nucleophilic anions are of interest for a variety of
applications which require the ‘stabilization’ of highly reactive
cationic species.1,2 Particularly useful in this regard is the anion
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB)3,4 and a
recent example of its use is the isolation and structural charac-
terization of trans-[PtH(η1-ClCH2Cl) (PPri3)][TFPB] contain-
ing the exceptionally weakly co-ordinating dichloromethane
ligand.5 We here report the synthesis and structural character-
ization by single-crystal X-ray diffraction of two silver and one
rhodium compound of the type M{B[3,5-C6H3(CF3)2]4}L2
which are the first examples of complexes in which the TFPB is
co-ordinated to the metal.†
The silver complexes Ag(TFPB)L2 [L2 = 1,2-C6H4I2 1, 2,2Ј-
bipyridine 2 (2,2Ј-bipy) and 1,2-bis(diphenylphosphino)ethane
(dppe)] were readily obtained as white crystalline products
according to equation (1).‡
CH2Cl2
AgPF6 ϩ L2 ϩ Na[TFPB]
Ag(TFPB)L2 ϩ NaPF6↓ (1)
† Crystal data for complex 1. C38H52AgBF24I2, M = 1300.99, mono-
clinic, a = 10.3372(11), b = 17.8488(12), c = 22.607(2) Å, β = 94.214(8)Њ,
U = 4159.8(6) Å3, T = 173(2) K, space group P21/c (no. 14), graphite-
monochromated Mo-Kα radiation, λ = 0.71071 Å, Z = 4, Dc = 2.077 g
cmϪ1, F(000) = 2472, colourless fragment with dimensions 0.46 ×
0.43 × 0.38, µ = 21.07 cmϪ1, no absorption correction; Siemens P4 dif-
fractometer using ω scan mode, 2θ = 52.00Њ, h Ϫ10 to 12, k Ϫ7 to 22,
l Ϫ27 to 27, no intensity decay from three standards measured every 97
reflections; 8577 measured, 8111 unique (Rint = 0.020). The structure
was solved and refined (on F2 using all data with negative intensities
included) using SHELXTL.6 All non-hydrogen atoms were refined anis-
tropically and hydrogen atoms were treated as riding atoms. The final
reflections) and wR2 (all data) = 0.1329 for 664 parameters, goodness
of fit = 1.042. Maximum and minimum peaks in final Fourier-
difference were 0.705 and Ϫ0.835 e ÅϪ3. The F atoms of two CF3
groups are disordered over two sites. The structure contains one dis-
ordered CH2Cl2 molecule.
Crystal data for complex 3. C40H24BF24Rhؒ0.87CH2Cl2, M = 1148.11,
monoclinic, a = 13.542(2), b = 24.403(4), c = 13.840(3) Å, β = 90.06(1)Њ,
U = 4573.9(13) Å3, T = 173(2) K, space group P21/n (no. 14), graphite-
monochromated Mo-Kα radiation, λ = 0.71071 Å, Z = 4, Dc = 1.667 g
cmϪ1, F(000) = 2266, colourless fragment with dimensions 0.23 ×
0.32 × 0.34, µ = 6.03 cmϪ1, absorption correction using ψ-scan data
(minimum and maximum transmission 0.6418 and 0.9562); Siemens
P4 diffractometer using ω-scan mode, 2θ = 50.00Њ, h 0 to 16, k 0 to 29,
l Ϫ16 to 16, no intensity decay from three standards measured every 97
reflections; 8264 measured, 7886 unique (Rint = 0.026). The structure
was solved and refined (on F2 using all data with negative intensities
included) using SHELXTL.6 All non-hydrogen atoms were refined anis-
tropically and hydrogen atoms were treated as riding atoms. The final
2
weighting scheme was w = 1/[σ2(Fo ) ϩ (0.0592P)2 ϩ 1.27P] where P =
(Fo2 ϩ 2Fc2)/3. The final R1[I > 2σ(I)] = 0.0343 (for 6686 reflections)
and wR2 (all data) = 0.0997 for 597 parameters, goodness of fit = 1.042.
Maximum and minimum peaks in final Fourier-difference were 0.704
and Ϫ0.822 e ÅϪ3
.
Crystal data for complex 2. C42H20AgBF24N2ؒCH2Cl2, M = 1212.21,
monoclinic, a = 12.3777(14), b = 17.334(2), c = 21.539(2) Å, β =
97.695(9)Њ, U = 4579.6(8) Å3, T = 173(2) K, space group P21/n (no. 14),
graphite-monochromated Mo-Kα radiation, λ = 0.71071 Å, Z = 4,
Dc = 1.758 g cmϪ1, F(000) = 2384, colourless fragment with dimensions
0.43 × 0.36 × 0.28, µ = 6.91 cmϪ1, absorption correction using ψ-scan
data (minimum and maximum transmission 0.2570 and 0.9495);
Siemens P4 diffractometer using ω-scan mode, 2θ = 50.00Њ, h 0 to 14, k 0
to 18, l Ϫ25 to 25, no intensity decay from three standards measured
every 97 reflections; 8264 measured, 7886 unique (Rint = 0.026). The
structure was solved and refined (on F2 using all data with negative
intensities included) using SHELXTL.6 All non-hydrogen atoms were
refined anistropically and hydrogen atoms were treated as riding atoms.
2
weighting scheme was w = 1/[σ2(Fo ) ϩ (0.0424P)2] where P = (Fo2 ϩ
2Fc2)/3. The final R1[I > 2σ(I)] = 0.0467 (for 5725 reflections) and wR2
(all data) = 0.1315 for 652 parameters, goodness of fit = 0.959. Max-
imum and minimum peaks in final Fourier-difference were 0.902 and
Ϫ0.868 e ÅϪ3. The F atoms of one of the CF3 groups are disordered
over two sites. The structure contains a partial occupancy, disordered
CH2Cl2 molecule. CCDC reference number 186/760.
‡ Satisfactory elemental analyses were obtained for complexes 1 and 2
(Found for 1: C, 34.85; H, 3.94; I, 19.84. Calc. for C38H52AgBF24I2: C,
35.08; H, 4.03; I, 19.51%. Found for 2: C, 42.30; H, 1.67; N, 2.05. Calc.
for C42H20AgBF24N2ؒCH2Cl2: C, 42.61; H, 1.83; N, 2.31%). Complex 3
was not very stable. Solutions of 3 in CH2Cl2 at 20 ЊC decomposed to
unidentified products in a matter of hours.
2
The final weighting scheme was w = 1/[σ2(Fo ) ϩ (0.0708P)2 ϩ 2.49P]
where P = (Fo2 ϩ 2Fc2)/3. The final R1[I > 2σ(I)] = 0.0469 (for 6028
J. Chem. Soc., Dalton Trans., 1997, Pages 4137–4138
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Fig. 1 Molecular structure of the complex Ag(η4-TFPB)(C6H4I2) 1.
Selected bond lengths (Å): Ag(1)᎐I(1) 2.7984(4), Ag(1)᎐I(2) 2.8080(5),
Ag(1)᎐C(11) 2.686(3), Ag(1)-C(12) 2.581(3), Ag(1)᎐C(21) 2.571(3),
Ag(1)᎐C(22) 2.507(3)
Fig. 3 Molecular structure of the complex Rh(η6-TFPB)(cod) 3.
Selected bond lengths (Å): Rh(1)᎐C(11) through to Rh(1)᎐C(16)
2.430(4), 2.251(4), 2.297(4), 2.324(4), 2.256(4), 2.253(4)
metal complexes with two available co-ordination sites and
complementary ligands with small steric profiles may result in
co-ordination of the TFPB anion.
Acknowledgements
We thank the Natural Science and Engineering Research
Council of Canada for financial support.
References
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8 J. Powell, A. Lough and T. Saeed, unpublished work.
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Fig. 2 Molecular structure of the complex Ag(η3-TFPB)(2,2Ј-bipy) 2.
Selected bond lengths (Å): Ag(1)᎐C(11) 2.640(3), Ag(1)᎐C(41) 2.424(3),
Ag(1)᎐C(42) 2.493(3), Ag(1)᎐N(1) 2.292(3), Ag(1)᎐N(2) 2.281(3)
ordination of the TFPB anion. In the rhodium complex 3 the
TFPB co-ordinates via an η6-interaction with one of the
aromatic rings in a manner that is similar to that observed in
several η6-BPh4 rhodium complexes.9
These studies indicate that the very poor co-ordinating prop-
erty of the TFPB anion is primarily steric in origin and that
Received 18th August 1997; Communication 7/06044K
4138
J. Chem. Soc., Dalton Trans., 1997, Pages 4137–4138