On the structural diversity of [K(18-crown-6)EPh3] complexes (E = C, Si, Ge, Sn, Pb): Synthesis, crystal structures and NOESY NMR study

Article abstract of DOI:10.1039/c3dt50523e

A series of homologous potassium triphenylelement complexes [K(18-crown-6)EPh₃] 6a-e of group 14 elements (E = C, Si, Ge, Sn, Pb) was synthesised by alkoxide induced heterolytic cleavage of boron-element compounds. The complexes 6a-e are isolated as storable solids possibly useful as sources of nucleophilic [EPh₃]^- moieties. The solid state structures of 6a-e were established by X-ray crystal structure determination. Whilst all structures can be described as polymeric chains consisting of alternating [K(18-crown-6)]⁺ and [EPh₃]^- units, the interaction within each chain varies systematically with the coordination properties of E. For Si and Ge, classical E-K coordination along with secondary phenyl-K interactions are characteristic, whilst for Sn and Pb, potassium coordination via the phenyl π-system is observed due to inefficient coordination by the free electron pair localised in an 'inert' s-orbital. The carbon derivative is exceptional as the central sp²-hybridised carbon atom gives rise to extensive charge delocalisation and coordination via these partially charged π-systems. A ¹H-¹H NOESY NMR spectroscopic study in THF-d₈ suggests appreciable anion/cation interactions for Si to Pb and hence the presence of contact ion pairs.

Full text of DOI:10.1039/c3dt50523e

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On the structural diversity of [K(18-crown-6)EPh3]
complexes (E = C, Si, Ge, Sn, Pb): synthesis, crystal
Cite this: Dalton Trans., 2013, 42, 8276
structures and NOESY NMR study†‡
Christian Kleeberg*
A series of homologous potassium triphenylelement complexes [K(18-crown-6)EPh3] 6a–e of group 14
elements (E = C, Si, Ge, Sn, Pb) was synthesised by alkoxide induced heterolytic cleavage of boron–
element compounds. The complexes 6a–e are isolated as storable solids possibly useful as sources of
nucleophilic [EPh3]− moieties. The solid state structures of 6a–e were established by X-ray crystal structure
determination. Whilst all structures can be described as polymeric chains consisting of alternating [K(18-
crown-6)]+ and [EPh3]− units, the interaction within each chain varies systematically with the coordination
properties of E. For Si and Ge, classical E–K coordination along with secondary phenyl–K interactions are
characteristic, whilst for Sn and Pb, potassium coordination via the phenyl π-system is observed due to
inefficient coordination by the free electron pair localised in an ‘inert’ s-orbital. The carbon derivative is
exceptional as the central sp2-hybridised carbon atom gives rise to extensive charge delocalisation and
coordination via these partially charged π-systems. A 1H-1H NOESY NMR spectroscopic study in THF-d8
suggests appreciable anion/cation interactions for Si to Pb and hence the presence of contact ion pairs.
Received 26th February 2013,
Accepted 8th April 2013
DOI: 10.1039/c3dt50523e
www.rsc.org/dalton
solution usually a certain degree of aggregation; hence, they
exist as contact ion pairs (CIP) in equilibrium with solvent-
Introduction
Anions of Group 14 elements of the type [ER3]− with alkali separated ion pairs (SSIP). This equilibrium depends strongly
metals (M) as counter ions ([MLn][ER3], L = additional ligand) on the counter ion (M), the polarity of the solvent, the concen-
have been the subject of various studies for some time. They tration and the temperature. However, the available structural
are typically prepared (for E ≠ C) by reduction of the corres- information in the solid state focuses on the lithium com-
ponding di-element compounds (E2R6) or element halides pounds [Li(Ln)–EPh3] (L = donor ligand) and/or the triphenyl-
(R3EX) with an alkali metal. This method is successful for a methyl derivatives (E = C).2–7 In particular, no systematic
variety of alkali metal/E2R6 combinations, but other methods studies on a homologous series of [M(Ln)–EPh3] compounds
have also been employed, e.g. the deprotonation of the respect- with one alkali metal cation ([M(Ln)]+) and all group 14
ive element hydrides, the nucleophilic cleavage of disilanes or elements (E) have been conducted.7b
the transmetallation of the corresponding mercury element
compounds.1
The use of boron–element (B–E) compounds with E = C is
widespread in synthetic chemistry, but also heavier homo-
The aggregation behaviour and the electronic structure of logues (especially E = Si) have been used e.g. as reagents in
triphenylelement alkali metal compounds (M–EPh3) in various transition metal catalysed reactions.10,11 In 2001 Kawachi et al.
solvents, as well as in the solid state, have been studied in suggested that the B–Si bond in certain silylboranes is hetero-
some detail.2–7 The different M–EPh3 compounds exhibit in lytically cleaved by alkali metal alkoxides and alkyls, respect-
ively, giving the silyl anions (Scheme 1).8a This route, the
Lewis base induced B–E cleavage, has recently been applied in
Institut für Anorganische und Analytischen Chemie der Technischen Universität
a series of transition metal free silyl transfer reactions with
Carolo-Wilhelmina zu Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
different Lewis bases.8b–d In the course of these studies the
E-mail: ch.kleeberg@tu-braunschweig.de; Fax: +49(0) 531 3915387;
Tel: +49(0) 531 3915312
reaction of certain silylboranes with alkoxides was investigated
†Dedicated to Prof. Dr Werner Uhl on the occasion of his 60th birthday.
in some detail.8b,e,9 The present work extends the scope of the
‡Electronic supplementary information (ESI) available: Additional analytical
alkoxide induced B–E bond activation in silylboranes to
boron–element compounds of all group 14 elements, as well
as to nitrogen substituted boron moieties.
data and the complete set of 1H-1H NOESY NMR spectra of 6a–e. CCDC
924392–924396 and 8937779 (6b, structure I). For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c3dt50523e
8276 | Dalton Trans., 2013, 42, 8276–8287
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Scheme 1 Selected examples of reactions involving the activation of silylbor-
anes by Lewis bases.8a–c,9
Results and discussion
A series of boron–element compounds was synthesised from
the dioxaborolane 1 or the diazaborolidine 2 and the corre-
sponding lithium triphenylelement species (Scheme 2).
Although boron–element compounds bearing dioxaborolane
or diazaborolidine moieties are relatively widespread, only 3b
had previously been synthesised and characterised in
detail.11–14 As the boron moiety the very common pinacol
derived dioxaborolane was chosen for E = C, Si, Ge (3a–c).8,11,12
However, for the tin and lead boron compounds (4b,c) a diaza-
borolidine moiety was used, as the respective dioxaborolane
derived compounds are suspected to be of low stability.14 The
silyl diazaborolidine derivative 4a was synthesised for compari-
son with the dioxaborolane 3b. The synthesis of 3a and 3c
from 1 follows a procedure reported for the silicon derivative
3b.12 The diazaborolidines 4a–4c were successfully synthesised
adopting established procedures for related compounds.15
Whilst the boron–element compounds 3a–c (E = C, Si, Ge)
and 4a–b (E = Si, Sn) are stable under exclusion of air, 4c (E =
Pb) decomposes readily in solution under inert conditions at
room temperature. During this process a black material, pre-
sumably elemental lead, is separated.16 Similar observations
have been reported for the related compound ((MeN)2C2H4)B–
Scheme 3 Synthesis of the [K(18-crown-6)EPh3] complexes 6a–e.
PbMe3 and the instability of those compounds may account
for the fact that only two related boron lead compounds have
been reported.15a,b
Adopting the recently established procedure for the syn-
thesis of 6b from 3b and [K(18-crown-6)OtBu] (5), the entire
series of homologous [K(18-crown-6)EPh3] complexes 6a–e
were isolated from 3a–c and 4a–c in good to excellent yields
(Scheme 3).9,17 This extends the scope of the B–E cleavage sig-
nificantly, on the one side to E ≠ Si and on the other side from
dioxaborolanes to diazaborolidines. The complexes 6a–e were
obtained as analytically pure, stable (micro-)crystalline solids.
No signs of decomposition were observed after storage under
inert conditions at −20 °C for several months or at ambient
temperature for several days. The complexes 6a–e were
thoroughly characterised by single crystal X-ray diffraction as
well as spectroscopically.
Solid-state structures
Single crystal structure determinations were successfully
carried out on all homologous complexes 6a–e. A crystal struc-
ture of 6b (structure I) has been reported earlier but will be dis-
cussed here in comparison with other complexes 6a, c, d and
an additional polymorph of 6b (structure II).9
The homologous complexes 6a–e crystallise in a series of
closely related structures (Table 1). This series is unique as for
the first time a complete set of structures with identical
ligands at the potassium atom is obtained. This enables a
detailed study of the influence of the nature of E1 on the struc-
tures of the complexes 6a–e.
For all structures 6a–e a similar general structural motive is
observed: the [K(18-C-6)EPh3] moieties form infinite chains,
consisting formally of alternating [K(18-C-6)]+ and [EPh3]− moi-
eties. However, the interactions and hence the detailed
Scheme 2 Synthesis of boron–element compounds.
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Table 1 Crystallographic data collection parameters for 6a–e
Compound
6aa
6b (structure I)9
6b (structure II)
6c
6d
6e
Chemical formula
Crystallisation conditions
C
31H39O6K
C30H39O6KSi
PhMe/C5H12, rt
C30H39O6KSi
C30H39O6KGe
C30H39O6KSn
C30H39O6KPb
THF/PhMe, rt
PhMe/C5H12
,
PhMe/C5H12
,
PhMe/C5H12
,
THF/C5H12
,
−20 °C
−20 °C
−20 °C
−20 °C
Formula mass (g mol−1
)
546.72
562.80
562.80
607.30
653.40
741.90
Crystal dimensions (mm3)
0.36 × 0.31 × 0.28 0.41 × 0.39 × 0.22 0.41 × 0.31 × 0.26 0.32 × 0.16 × 0.13 0.47 × 0.38 × 0.21 0.27 × 0.24 × 0.08
Crystal system
Space group (no.)
Z, Z′
Monoclinic
P21 (4)
8, 4
Monoclinic
P21/c (14)
4, 1
Orthorhombic
Pna21 (33)
4, 1
Monoclinic
P21/c (14)
4, 1
Orthorhombic
P212121 (19)
4, 1
Orthorhombic
P212121 (19)
4, 1
a (Å)
b (Å)
c (Å)
α (°)
9.8014(5)
28.769(1)
19.737(1)
90
10.0038(4)
17.7282(6)
17.1680(6)
90
18.3527(8)
15.2640(8)
10.4474(4)
90
9.8669(1)
17.2748(2)
17.9326(2)
90
9.6725(2)
12.6028(2)
24.4563(5)
90
9.6839(4)
12.5929(4)
24.5776(8)
90
β (°)
90.447(5)
90
5565.3(5)
1.305
93.224(4)
90
3039.9(2)
1.230
90
90
2926.7(2)
1.277
100(2)
99.857(1)
90
3011.47(6)
1.339
90
90
2981.2(1)
1.456
100(2)
90
90
2997.2(2)
1.644
100(2)
γ (°)
Volume (Å3)
Dcalcd (Mg m−3
T (K)
)
100(2)
100(2)
100(2)
Radiation, λ (Å)
MoKα, 0.71073
0.234
MoKα, 0.71073
0.253
MoKα, 0.71073
0.263
CuKα, 1.54184
2.940
MoKα, 0.71073
1.036
MoKα, 0.71073
5.507
μ (mm−1
)
Total reflections collected
Total unique reflections
No. of variables/restraints
θ range (°)
25 554
25 554
1396/1
66 552
8687
343/0
2.30 < θ < 29.99
1.022
0.0612
0.0419
0.0901
93 602
6396
343/1
2.22 < θ < 27.00
1.313
0.0827
0.0873
0.1150
77 176
6263
343/0
3.58 < θ < 75.91
1.036
0.0304
0.0236
0.0642
73 495
8585
343/0
2.26 < θ < 30.00
1.052
0.0365
0.0208
0.0403
52 235
7157
343/0
2.26 < θ < 28.00
1.016
0.0977
0.0380
0.0698
2.19 < θ < 26.00
0.869
GooF on F2
Rint
n/aa
R1 [I > 2σ(I)]b
0.0422
0.0781
wR2 (all data)c
Absolute structure parameter −0.05(3)
n/a
n/a
n/a
−0.021(9)
0.355/−0.311
924395
−0.031(7)
1.497/−0.788
924396
Largest diff. peak/hole (Å−3
)
0.291/−0.550
0.349/−0.273
893777
0.310/−0.306
924393
0.340/−0.342
924394
CCDC no.
924392
a The crystal is a non-merohedral twin; see crystallographic data for details. b R1 = ΣkFo│ − │Fck/Σ│Fo│. c wR2 = (Σ[w(Fo − Fc2)]/Σ[Fo4])1/2, where
2
w = 1/[σ2 (Fo2) + (0.0328P)2] (6a), w = 1/[σ2 (Fo2) + (0.0307P)2 + (0.9030P)] (6b) (structure I)), w = 1/[σ2 (Fo2) + (4.4268P)] (6b) (structure II)), w =
1/[σ2 (Fo2) + (0.0342P)2 + (1.2242P)] (6c), where P = (Fo + 2Fc2)/3, w = 1/[σ2 (Fo2) + (0.0144P)2 + (0.7527P)] (6d), where P = (Fo + 2Fc2)/3, w =
1/[σ2 (Fo2) + (0.0244P)2 ] (6e), where P = (Fo2 + 2Fc2)/3.
2
2
structural motives within these columns are different and columns exhibit a very similar structure; the one containing
depend strongly on the nature of E.
K1/C1 and K1A/C1A is discussed exemplarily. The O6 moiety is
The structures 6a–e may be categorised into three types: a: roughly planar as indicated by the small maximum deviation
6a (E = C); b: 6b (structure I) (E = Si) and 6c (E = Ge) and c: 6d of an individual oxygen atom from the mean plane of the
(E = Sn) and 6e (E = Pb). However, the second polymorph of 6b oxygen atoms (Δmax(O6), Table 2, Fig. 1). A comparably small
(structure II) is not fitting well into one of these categories deviation of the potassium atom from the oxygen atoms mean
(Tables 1 and 2). The three structure types differ in terms of plane (Δ(O6–K1), Table 2) indicates a rather symmetrical axial
cell metrics, space group type and other structural parameters. coordination of K1 by the two π-systems. However, the shorter
Especially instructive are the intracolumnar angle between the K–CPh distance is observed for the phenyl system with the
crown ether mean planes (φ(O6)), the minimum K1–E1 and the shorter C1–Cipso distance, and hence, for the π-system with
intracolumnar K1–K1′ distances (Table 2). Generally, the the higher negative charge and therefore better donor
angles (φ(O6)) included by the individually roughly planar properties.7b,18
crown ether moieties (Δmax(O6) ≤ 0.363(6) Å) and the K1–K1′
The environment of the central carbon atoms C1 and C1A,
distances are specific for a certain structure type (Table 2). respectively, is planar (angular sum ∼360°). The bond lengths
These geometrical data are directly correlated to three E1–Cipso are similar and indicative of bond orders between
different coordination modes of the [EPh3]− anion.
single and double bonds. These data support, together with a
Structure type a (6a, E = C). Complex 6a crystallises with bond length within the phenyl rings of 1.34–1.43 Å, an sp2
four independent [K(18-C-6)CPh3] moieties in the asymmetric hybridisation of the central carbon atoms and an appreciably
unit (Z = 8, Z′ = 4) in a non-centrosymmetric space group of delocalised negative charge. However, the individual phenyl
the type P21. The individual units of 6a are arranged in two groups are, due to steric reasons, not coplanar but in a propel-
crystallographically independent columns perpendicular to ler-like arrangement.7 Within a polymeric stack of [K(18-C-6)-
the screw axis and parallel to the c-axis, consisting of alternat- EPh3]n the [CPh3]− anions are bridging two potassium atoms
ing [K(18-C-6)]+ and [CPh3]− moieties (Fig. 1). The independent (K1, K1A) by coordination via the π-systems of two phenyl
columns consist of either the K1/C1 and K1A/C1A or the K1B/ rings. The differences in the K1/K1A–CPh distances for the
C1B and K1C/C1C containing moieties. Both independent individual atoms CPh indicate
a
very unsymmetrical
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Table 2 Selected bond lengths and angles for 6a–e
6aa
6b (structure I)9
6b (structure II)
Si1
6c
6d
6e
E1=
C1/C1A
Si1
Ge1
Sn1
Pb1
K1–E1a (Å)
4.875(4) (K1, C1)
5.790(4) (K1, C1A)
4.900(4) (K1A, C1A)
5.536(4) (K1A, C1)
3.087(4) (K1, C4)
3.293(4) (K1, C16A)
3.120(4) (K1A, C4A)
3.207(4) (K1A, C12)
1.435(5) (C2)
3.5404(5)
3.635(1)
3.4252(3)
5.9631(3)
6.4986(3)
6.031(1)
6.521(1)
K1–CPh b (Å)
E1–Cipso (Å)
3.645(2) (C27)
3.663(2) (C28)
3.472(4) (C21)
3.861(4) (C22)
3.290(1) (C16)
3.431(2) (C15)
3.212(2) (C4)
3.438(2) (C3)
3.208(2) (C16)
3.450(2) (C17)
2.227(2) (C13)
2.228(2) (C7)
2.245(2) (C1)
3.207(7) (C4)
3.436(6) (C3)
3.211(7) (C16)
3.485(6) (C17)
2.325(6) (C7)
2.344(6) (C1)
2.331(6) (C13)
1.929(1) (C13)
1.930(1) (C19)
1.929(1) (C25)
1.929(4) (C13)
1.934(4) (C19)
1.941(4) (C25)
2.026(1) (C1)
2.022(1) (C7)
2.026(1) (C13)
1.461(5) (C8)
1.465(5) (C14)
1.446(5) (C2A)
1.458(5) (C8A)
1.453(5) (C14A)
ipso–E1–Cipso (°) 120.4(3) (C2, C14)
C
98.85(6) (C13, C25) 101.7(2) (C13, C25) 100.23(5) (C7, C13) 95.14(6) (C7, C13) 93.3(2) (C7, C13)
99.30(6) (C13, C19) 102.4(2) (C13, C19) 101.04(5) (C13, C1) 96.29(6) (C7, C1) 96.9(2) (C1, C13)
98.85(6) (C19, C25) 102.7(2) (C19, C25) 97.51(5) (C1, C7) 97.46(5) (C1, C13) 94.6(2) (C7, C1)
122.1(3) (C2, C8)
117.5(3) (C8, C14)
122.7(3) (C2A, C14A)
119.6(3) (C2A, C8A)
117.7(3) (C8A, C14A)
K1–K1′c (Å)
9.980(1) (K1, K1A)
9.771(1) (K1A, K1)
24.12(4)
0.363(6)
0.2464(9)
9.107(5)
9.484(1)
9.1449(4)
12.2719(5)
12.334(2)
φ(O6)c (°)
81.75(1)
0.215(1)
0.5045(3)
15.60(5)
0.224(3)
0.4825(7)
81.81(1)
0.3018(9)
0.2286(3)
63.11(2)
0.239(1)
0.1372(3)
63.29(5)
0.204(4)
0.123(1)
Δmax(O6)d (Å)
Δ(O6–K1)d (Å)
a The geometrical data within one column are given; the data of the second are comparable (see the main text). b Only selected shortest distances
are given. c Angle and distance between two adjacent moieties within one column of [K(18-c-6)EPh3]n. d Maximum deviation of an oxygen
(Δmax(O6)) or potassium ((O6)–K1) from the O6 mean plane.
the respective distances found in a series of typical K–arene
solvates (3.29 Å).19 This coordination mode is not without pre-
cedence among triphenylmethyl potassium complexes. In the
monomeric complex ([K(thf)(PMDTA)CPh3]) a similar, though
more symmetric, coordination of the potassium atom is
observed. The similarity is illustrated by the comparable K–CPh
(3.14–3.25 Å) and C1–Cipso (1.435(5), 1.475(6), 1.460(6) Å) dis-
tances.7b On the other side the closely related complex
([K(PMDTA)CPh3]) exhibits a ‘benzylic’ coordination of the pot-
assium atom with rather short distances between the potass-
ium atom and the carbon atoms of the ‘benzylic’ system
(2.93–3.21 Å).7a However, secondary interactions to an adjacent
phenyl system with distances >4.06 Å are also observed. A
coordination mode similar to 6a is observed in the polymeric
complex ([K(diglyme)CPh3]). Here, alternating units of
[K(diglyme)]+ and [CPh3]− moieties form columns with short
K–CPh distances (3.15–3.25 Å).7a In contrast, the crown ether
complex [K(18-C-6)C(C6Cl5)3] exhibits a different structural
motive: the cation is coordinated by the chlorine atoms.7c
The preference of the potassium cation for the phenyl
π-system compared to the ‘benzylic’ system may be rationalised
Fig. 1 Detailed view of a column of 6a (left) and packing pattern of 6a (right)
in terms of hard/soft interactions.7b This affinity of the K+
with the atom labelling scheme.
cation to π-systems is well documented and may be competi-
tive with K+–dipol interactions.20 However, the energetic differ-
coordination by each phenyl π-system and in particular no ence between coordination to the π-system and the ‘benzylic’
coordination by the benzylic carbon atoms (C1/C1A).18 The system, respectively, is small. In conclusion, the motive
shortest K–CPh distances in 6a are significantly shorter than realised in a particular complex [K(L)CPh3] depends on subtle
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changes such as packing or steric effects and especially
additional potassium–donor-interactions within the crystal
structure (e.g. in [K(18-C-6)C(C6Cl5)3] or with additional solvent
molecules).7 In agreement with this the lighter and harder
alkali metals usually show a certain preference for coordi-
nation by the ‘benzylic’ system.7
Structure type b (6b, 6c, E = Si, Ge). The complexes 6b
(structure I) and 6c crystallise with one [K(18-C-6)EPh3] moiety
in the asymmetric unit (Z′ = 1) in a space group of the type
P21/c with similar cell axes and volumes, but different mono-
clinic angles. Whilst the structures are again best described as
[K(18-C-6)EPh3]n columns (parallel to the b-axis), the mutual
orientation of the [K(18-C-6)] moieties within each column is
significantly different from structure type a. In 6b (structure I)
and 6c nearly perpendicular crown ether oxygen mean planes
(φ(Ο6)) and slightly smaller intercolumnar K–K′ distances are
observed (Table 2, Fig. 2 and 3).
The difference to structure type a is caused by the funda-
mentally different coordination mode of the EPh3 anion in 6b
(E = Si) and 6c (E = Ge) compared to 6a (E = C). The atom E
may be best described as non- or sp3-hybridised with an
appreciable amount of distortion (sum of angles: 297.0° 6b
(structure I), 298.8° 6c and 306.8° 6b (structure II)). Thus, the
Fig. 3 Detailed view of a column of 6c (left) and packing pattern of 6c (right)
with the atom labelling scheme.
E(Cipso 3
)
moiety is no longer planar, but trigonal-pyramidal
The K atoms in 6b and 6c are unsymmetrically coordinated
with the negative charge essentially localised at E1.3 In agree- by two bridging bidentate [EPh3]− moieties. In these structures
ment with this are the E1–Cipso distances indicative of rather the coordination by the lone pair located at the atom E1 is – in
long single bonds (typical bond length: Ge–C(sp3) 1.98 Å, Si– contrast to 6a – evident. The distances K1–E1 (Table 2) are con-
C(sp2) 1.84 Å).21a These data resemble the values found in struc- siderably shorter than the sum of the van der Waals radii
turally characterised, virtually monomeric, lithium [EPh3]− (dvdW: 4.85 Å (K–Si); 4.75 Å (K–Ge)) but slightly longer than the
complexes (average Si–Cipso, sum of angles Cipso–Si–Cipso
:
sum of the covalence radii (dcov: 3.23 Å (K–Si); 3.20 Å (K–Ge)),
1.94 Å, 303.8° ([Li(thf)3SiPh3]); 2.01 Å, 294.9° ([Li- clearly indicating E–K interactions.21b
(Et2O)3GePh3]); 2.02 Å, 298.8° ([Li(tmeda)(thf)GePh3])).5,6
Short K–CPh distances on the other side indicate additional
interactions of K1 with the phenyl π-systems. The K1–CPh dis-
tances observed are again significantly shorter than the sum of
the van der Waals radii (dvdW: 4.45 Å (K–C)).21b However, in the
silyl complex 6b (both structures) they are significantly longer
than in the germyl complex 6c. In the latter one the K–CPh dis-
tances are only slightly longer than in 6a and in arene solvates
(vide supra).19 The unsymmetrical coordination of the potass-
ium atom is also reflected in the relative position of K1: in 6b
(both structures) the potassium atom is placed significantly
more out of the crown ether O6 mean plane towards E1 than in
6c (Table 2, Δ(O6–K1)). This may be rationalised by a weaker
K–Ge than K–Si interaction and hence a more competitive inter-
action of K1 with the π-system in 6c. This is also in agreement
with the expected more inert character of the free electron pair
in the germyl anion.
As mentioned above, a polymorph of 6b in an orthorhom-
bic space group Pna21 (Z = 4, Z′ = 1) was obtained by crystallisa-
tion at a lower temperature (structure II). Whilst the structural
parameters of the two structures of 6b are generally compar-
able the packing of the individual [K(18-C-6)SiPh3] entities
within a polymeric stack is significantly different. This is indi-
cated especially by the different angles between the O6 mean
planes (φ(O6)) of the crown ether moieties and intracolumnar
K1–K1′ distances (Table 2, Fig. 4). But most importantly the
Fig. 2 Detailed view of a column of 6b (structure I) (left) and packing pattern
of 6b (structure I) (right) with the atom labelling scheme.
8280 | Dalton Trans., 2013, 42, 8276–8287
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Fig. 4 Detailed view of a column of 6b (structure II) (left) and packing pattern
of 6b (structure II) (right) with the atom labelling scheme.
Fig. 6 Detailed view of a column of 6d (left) and packing pattern of 6d (right)
with the atom labelling scheme.
Fig. 5 Detail of Si1–K1 coordination in 6b structure I (left) and II (right).
Selected atoms are drawn as spheres with an arbitrary radius. Black: K–(Si1,C13,
C14)centroid distance.
interactions between the [K(18-C-6)]+ and the [SiPh3]− moieties
are different. In structure II as compared to structure I,
a longer Si1–K1 distance is observed. Moreover, in structure II
much shorter K–C13 and K–C14 distances within one [K(18-
C-6)EPh3] moiety are observed (Fig. 5). K1 is situated nearly
symmetrically above the Si1/C13/C14 moiety, suggesting
coordination by this ‘hetero-benzylic’ system rather than by
the Si1 atom alone (Fig. 5). However, the Si1–C13 distances in
both structures are identical and indicative of a C–Si single
bond (vide supra). This is also in agreement with spectroscopic
data for closely related systems indicating only minor charge
delocalisation between the silicon atom and the phenyl substi-
tuents.3 The different coordination may rather be explained by
the interaction of the potassium cation with both the electron
pair/electron density at the silicon atom and the π-system,
than with a classical ‘benzylic’ coordination to a delocalised
charged π-system. In addition, packing effects are certainly of
Fig. 7 Detailed view of a column of 6e (left) and packing pattern of 6e (right)
with the atom labelling scheme.
importance. However, the effects are obviously very small as unit in the asymmetric unit (Table 1). The individual columns
small differences in the crystallisation conditions result in the of [K(18-C-6)EPh3]n are situated on the screw axis parallel to the
formation of both polymorphs.
c-axis (Fig. 6 and 7).
Structure type c (6d, 6e, E = Sn, Pb). The third structure type
The crystal structure of 6e is only the second of an alkali
is realised in the compounds 6d (E = Sn) and 6e (E = Pb). These metal triphenylplumbyl complex and the first of a respective
compounds crystallise isomorphically in the orthorhombic potassium complex.4b The stannyl complex 6d was reported
system in the P212121 space group type with one [K(18-C-6)EPh3] earlier including a room temperature crystal structure.4a In this
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work 6d is fully characterised and its crystal structure was
redetermined at 100 K to ensure comparability with 6a–c,e.
The structure type c is again best described as columns of
alternating [K(18-C-6)]+ and [EPh3]− units. However, the K1–K1′
distance is significantly longer than in the previously
described compounds, whilst the angles between the 18-
C-6 moieties (φ(O6)) are in between the values found for types
a and b (Table 2). The deviation of K1 from the O6 mean plane
is the smallest found so far, indicating a symmetrical coordi-
nation of K1 by the two [EPh3]− moieties. The coordination
mode of the [EPh3]− entities is similar to 6a: K1 is coordinated
via the π-system of two phenyl rings (Fig. 6 and 7).18 This is indi-
cated by the short K1–CPh distances and the K1–E1 distances
(Table 2), significantly longer than the sum of the van der
Waals radii (dvdW: 4.92 Å (K–Sn), 4.77 Å (K–Pb)).21b However, in
contrast to 6a, no indication of charge delocalisation between
E1 and the aromatic system is apparent from the structural
parameters. The E1–Cipso distances are on the long side in the
range expected for single bonds (Sn–C(sp3) 2.14 Å, Pb–C(sp3)
2.29 Å)21a and the Cipso–E1–Cipso angles are indicative of an
essentially non-hybridised E1 atom. Hence, the negative
charge is localised at E1 and, in contrast to 6a, not delocalised
into the π-system.3 However, due to the inert character of the
Fig. 8 1H-1H-NOESY NMR spectrum of 6e in THF-d8 at rt. Inset: Trace of the
NOESY spectrum at the shift of the OCH2 signal. * THF signal.
free electron pair on E1 localised in an s-orbital, E–K coordi- with an AA′MM′Y spin system at −76 °C.7i,22,23 However, no
nation is not preferable compared to coordination via the comparable effect of the temperature on the line width of the
π-system. In contrast to 6a the π-systems of phenyl rings do not crown ether methylene singlet signal is observed. Hence, the
bear a negative (partial) charge and their coordination proper- dynamic process may be mainly associated with a dynamic
ties should be comparable to neutral π-systems. In fact the process within a separated [Ph3C]− anion.7i,22,23 The 13C NMR
K–CPh distances observed in 6d and 6e are typically longer than data show the expected signals for the crown ether methylene
in 6a but comparable to those found in selected arene solvates and the phenyl carbon atoms.9 The chemical shifts of the
(vide supra).19 In contrast to 6d/e the monomeric lithium com- phenyl carbon atoms resemble the data observed for the corres-
plexes [Li(PMDTA)SnPh3] and [Li(PMDTA)PbPh3] contain ponding crown ether free compounds.3c,d The observed shift
unambiguously Li–E bonds.4b,c In conclusion this shows again differences of 1–4 ppm, generally most pronounced at the ipso
that the strong K–π-system interactions are competitive with carbon atoms, may well be attributed to the influence of the
the classical cation–anion interaction.20
presence of the crown ether on the aggregation in solution.
Whilst the atom E1 is not coordinated to the cation in the
The chemical shift values for the different atoms E in the
complexes 6a,d, it is a nucleophilic site. The in situ prepared [EPH3]− anion in 6a,b,d may also be compared with the NMR
complexes 6a–d give smoothly the triphenylelement benzyl data reported for related compounds measured under similar
compounds Ph3E–CH2Ph (E = C, Si, Ge, Sn) upon reaction with conditions (solvent, temperature). For compound 6b (E = Si) a
benzyl bromide as an exemplary electrophile.9,22
29Si NMR shift of δ = −7.1 ppm is observed to be fitting well to a
value of δ = −7.5 ppm for the corresponding crown ether free
compound.3b,9 The differences in the respective chemical shifts
NMR spectroscopy
Numerous NMR spectroscopic investigations on the solution observed for 6a (E = C, δC = 90.9 ppm) and 6d (E = Sn, δSn
state structure of alkali metal triphenylelement compounds −103.2 ppm) compared to the crown ether free analogues (δC
=
=
have been reported. However, those studies are restricted to 88.5 ppm and δSn = −108.4 ppm) may again be explained by the
the analysis of resonances of the [EPh3]− anion and/or to influence of the crown ether on the aggregation in solution.3b,c,d
lithium or cesium derivatives due to the unfavourable NMR
Moreover, assuming that dissociation of the crown ether
properties of the other alkali metals.2,3,7b The compounds 6a–e ligand from the potassium ion is negligible the crown ether
were characterised by multinuclear NMR spectroscopy (1H, signal is well suited as an NMR probe for the cation. Thus, a
13C, 29Si, 119Sn). The 1H NMR spectra for 6b–e (E = Si to Pb) 1H-1H-NOESY NMR spectroscopic study was conducted in order
show a singlet for the crown ether methylene protons and to obtain a first insight into the aggregation/coordination beha-
three well resolved multiplets of the phenyl protons (Fig. 8).22 viour in THF-d8 solution. These experiments complement studies
In contrast, the 1H NMR spectra of 6a are indicative of the on the ion-pairing of KEPh3 derivatives performed with different
presence of dynamic processes in solution. At ambient temp- methods (1H/13C NMR, Mössbauer, and UV-Vis spectroscopy)
erature three broadened phenyl signals are observed which under different conditions.2,3,4a,7b However, this represents the
become three narrow well resolved multiplets in agreement first 1H-1H-NOESY NMR study on K(18-C-6)EPh3 compounds.4
8282 | Dalton Trans., 2013, 42, 8276–8287
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The 1H NMR spectra of 6b–e in THF-d8 are similar and C-6)]+ cation is coordinated by two phenyl rings of two
show well separated multiplets for the three groups of phenyl different [EPh3]− moieties. In the case of E = Si, Ge sp2-hybridi-
protons, whilst a singlet is observed for the crown ether signal sation is not realised, resulting in largely localised silyl/
(Fig. 8, exemplarily for 6e).22 1H-1H-NOESY NMR spectra (1.0 s germyl anions and E–K coordination. The solid state structure
mixing time, 40–46 μmol mL−1) are indicative of NOE between may best be described as molecular [K(18-C-6)EPh3] units con-
the crown ether signal and the phenyl protons. The strongest nected by additional secondary intermolecular π-system–K
NOE signal is observed for the ortho-proton, whilst smaller interactions to form polymeric columns. However, a poly-
NOE signals are observed for the meta- and para-protons.22 morph of [K(18-C-6)SiPh3] was obtained showing appreciable
These data suggest for 6b–e the presence of an appreciable intramolecular π-system–K interaction, and thus
a more
amount of contact ion pairs (CIP) in THF solution at ambient ‘benzylic’ coordination of the cation. On the other hand for
temperature. It has to be emphasised that the NOESY NMR E = Sn and Pb hybridisation is again not feasible, but due to the
data on 6b–e do not allow conclusions on the mode of coordi- inert character of the s-electron pair, E–K coordination by this
nation in solution. However, with all due care, in all solid state electron pair is also not efficient. This results in a coordination
structures of 6b–e, distances of the respective hydrogen atoms mode similar to the one observed for E = C, and hence, poly-
(OCH2 to the phenyl protons) are found below 4 Å and are in meric chains of alternating [K(18-C-6)]+ cations and [EPh3]−
agreement with the observation of an NOE.
anions with nearly symmetrical coordination of the potassium
These findings appear to be in agreement with the literature atom by two phenyl π-systems. In conclusion it may be stated
data: According to 13C NMR spectroscopic studies, KSiPh3 con- that the interplay of π-system potassium interactions and
sists in THF at 25 °C largely of contact ion pairs, although the anion (potassium) cation interactions governs the structural
addition of 18-crown-6 (in situ formation of 6b) leads to less aggre- chemistry of [K(18-C-6)EPh3] complexes.
gation.3d NMR spectroscopic studies on KEPh3 (E = Si to Pb) in
1H-1H-NOESY NMR spectroscopic studies on the [K(18-C-6)-
ethereal solvents generally suggest an equilibrium between solvent- EPh3] complexes revealed that for E = Si to Pb, contact ion
separated ion-pairs (SSIP) and contact ion-pairs (CIP).3b 119Sn pairs (CIP) are, at least partially, present, whilst for E = C no
Mössbauer studies on crystalline 6d and on KSnPh3 in frozen THF indications of their presence were found.
solution suggest that similar aggregates as in the crystalline
material are present to a certain extent in the frozen solution.4a
The 1H-1H-NOESY NMR of 6a in THF-d8 does not reveal any
NOE contacts of the crown ether signal to the phenyl proton
Experimental
General
signals even at −76 °C. Hence, the NOESY measurement does
not support the presence of contact ion pairs but it has to be pinB–OiPr24a (1), pinB–SiPh3 (3b), [K(18-crown-6)OtBu] (5),17
12
24b
24c
emphasised that this certainly does not exclude the presence [K(18-crown-6)SiPh3] (6b)9 (from 3b), Ph6Ge2
and Ph6Pb2
of anion–cation contacts not detectable within the limits of N,N′-iso-propylethylendiamine24d (((iPrN)2C2H4)H2) were syn-
the method. A UV-Vis spectrum of 6a in THF-d8 at ambient thesised as reported. ((iPrN)2(C2H4))B–Br (2) has been prepared
temperature exhibits strong absorption bands at 438 and adopting a reported procedure.15d All other reagents were pur-
505 nm. This is in agreement with the results from in situ pre- chased from commercial sources and used as received. All
pared 6a (λmax at 430 (sh) and 495 nm) which are reported to reactions were performed under an atmosphere of nitrogen
be indicative of the absences of CIP.2a,b
employing Schlenk or Glovebox techniques in dried
(MBraun solvent purification system) and degassed solvents.
NMR spectra were recorded on Bruker Avance II 300, Bruker
Avance 400 or Bruker DRX 400 spectrometers. The NMR sol-
Conclusions
1
vents were dried and degassed using standard techniques. H
The [K(18-crown-6)OtBu] (5) induced heterolytic B–E bond clea- and 13C chemical shifts (δ) are given in ppm relative to Me4Si,
vage of triphenylelement dioxoborlanes and diazaborolidines using the resonance of the (residual protio-) solvent as an
has proven to be a versatile route to isolable and stable potass- internal reference (C6D6: 1H NMR: 7.16 ppm, 13C NMR:
ium 18-crown-6 triphenylelement complexes (6a–e) of all group 128.06 ppm; THF-d8: 1H NMR: 1.72 ppm, 13C NMR:
14 elements. Whilst these compounds may be of interest as 25.31 ppm).24e 11B, 29Si and 119Sn chemical shifts are reported
storable, stoichiometric reagents they exhibit an unexpected relative to external BF3·Et2O, Me4Si and Me4Sn, respectively.
structural diversity in the solid state. The solid state structures 13C, 11B, 29Si and 119Sn NMR spectra were recorded employing
are best described as polymeric chains of alternating [K(18- (29Si, 119Sn: inverse-gated) composite pulse 1H decoupling.
C-6)]+ cations and [EPh3]− anions. However, the type of inter- 1H-1H-NOESY NMR measurements were performed at
a
action between both entities is different and depends strongly 400 MHz instrument employing standard techniques (mixing
on the nature of E. This may be rationalised by a simple time: 1 s).25 EI mass spectrometry was performed employing a
approach considering the increasing s–p-separation towards Finnigan MAT 95 XP spectrometer (70 eV). UV-Vis spectra were
the heavier group 14 elements. In the case of E = C, sp2-hybridi- recorded under inert conditions in a cuvette equipped with a
sation is energetically feasible and leads to delocalised J. Young valve on a Varian Cary 50 Scan spectrophotometer.
benzyl-anions. As a result the potassium atom in the [K(18- Melting points were determined using a Büchi 530 apparatus
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in flame sealed capillaries under nitrogen and are not cor- 0.65 g, 1.5 mmol, (30%). Mp 119–122 °C (from n-hexane).
rected. Elemental analyses were performed using an Elementar Found: C, 66.8; H, 6.4. Calc. for C24H27O2BGe: C, 66.9; H, 6.3.
vario MICRO cube instrument at the Institut für Anorganische δH(300 MHz; C6D6) 0.99 (12 H, s, (C(CH3)2)2), 7.10–7.24 (9 H,
und Analytische Chemie of the Technische Universität Carolo- m, CHAr), 7.83–7.78 (6 H, m, CHAr). δC(75 MHz; C6D6) 24.9 ((C-
Wilhelmina zu Braunschweig.
(CH3)2)2), 84.4 ((C(CH3)2)2), 128.5 (CHAr), 135.6 (CHAr), 136.0
1
((iPrN)2C2H4)B–Br (2). A solution of NEt3 (7.5 g, 74 mmol, (CHAr), 138.2 (ipso-C). δB(96 MHz; C6D6) 35.8 (1 B, s, Δw = 335
2
2 eq.) in dry n-hexane (160 mL) was cooled to 0 °C and BBr3 Hz). m/z (EI+) 448 ([M + O]+, 5), 433 ([M + H]+, 3), 432 (M+, 3),
(9.2 g, 37 mmol, 1 eq.) in n-hexane (25 mL) was added slowly. 305 ([GePh3]+, 10), 228 ([GePh2]+, 100).
After warming to rt, N,N′-iso-propylethylendiamine (5.4 g,
((iPrN)2C2H4)B–SiPh3 (4a). To granulated lithium (0.27 g,
37 mmol, 1 eq.) in n-hexane (25 mL) was added and the 39 mmol, 6 eq.) in dry THF (20 mL) a solution of Ph3SiCl
mixture was heated to 80 °C for 3 h. After cooling to rt the (2.20 g, 7.5 mmol, 1.2 eq.) in THF (30 mL) was added at 0 °C.
mixture was filtered and the volatiles were removed in vacuo. After stirring for 16 h at rt the solution was removed from
Crude 2 was obtained as a brown oil sufficiently pure for excess lithium and cooled to −78 °C. To this solution 2 (1.51 g,
further reactions. Analytically pure 2 was obtained by bulb-to- 6.5 mmol, 1.0 eq.) in n-pentane (30 mL) was added. After stir-
bulb distillation (0.01 mbar, 60–65 °C) as a colourless liquid. ring at −78 °C for 15 minutes and for 16 h at rt the volatiles
Yield: 5.1 g, 22 mmol, (59%). Found: C, 41.2; H, 7.8; N, 11.8. were removed in vacuo. The residue was extracted with dry
Calc. for C8H18N2BBr: C, 41.25; H, 7.8; N, 12.0%. δH(300 MHz; toluene (3 × 20 mL) and the extracts filtered over celite. After
3
C6D6) 0.95 (12 H, d, J = 6.7 Hz, CH(CH3)2), 2.92 (4 H, s, CH2), removal of the solvent the product was obtained as a brown
3
3.83 (2 H, sept., J = 6.7 Hz, CH(CH3)2). δC(75 MHz; C6D6) 21.3 solid. The product was further purified by fractional crystalliza-
(CH(CH3)2), 41.5 (CH2), 45.4 (CH(CH3)2). δB(96 MHz; C6D6) tion from hot n-hexane. Yield: 2.21 g, 5.4 mmol, (83%). Mp
+
+
1
25.7 (1 B, s, Δw = 100 Hz). m/z (EI ) 232 (M , 28), 217 ([M − 62–65 °C (from n-hexane). Found: C, 73.5; H, 7.95; N, 6.6. Calc.
2
CH3]+, 100).
for C26H33N2BSi: C, 75.7; H, 8.1; N, 6.8. δH(300 MHz; C6D6)
pinB–CPh3 (3a). In dry THF (50 mL) Ph3CH (2.0 g, 8 mmol, 0.84 (12 H, d, 3J = 6.7 Hz, CH(CH3)2), 3.12 (4 H, s, CH2), 3.56 (2
1 eq.) was cooled to 0 °C and nBuLi (5.2 mL (1.6 M in H, sept., 3J = 6.7 Hz, CH(CH3)2), 7.10–7.20 (9 H, m, CHAr),
n-pentane), 8 mmol, 1 eq.) was slowly added and the deep red 7.85–7.81 (6 H, m, CHAr). δC(75 MHz; C6D6) 21.0 (CH(CH3)2),
mixture was stirred for 2 h at rt. To this mixture neat 1 (2.6 g, 42.0 (CH2), 46.2 (CH(CH3)2), 128.2 (CHAr), 129.1 (CHAr), 136.7
1
14 mmol) was added and the reaction mixture was stirred for (CHAr), 137.9 (ipso-C). δB(96 MHz; C6D6) 31.9 (1 B, s, Δw = 390
2
40 h at rt. After removal of all volatiles in vacuo the residue was Hz). δSi(79.5 MHz; C6D6) −23.3 (1 Si, br. s). m/z (EI+) 412.25052
extracted with hot n-hexane (2 × 30 mL) and filtered. After (Calc. for C26H33N2BSi: 412.25061) (M+, 14), 397 ([M − CH3]+,
removal of the solvent in vacuo the residue was purified by 100), 335 ([M − C6H5]+, 4), 259 ([SiPh3]+, 54), 199 ([SiPh2]+, 15),
column chromatography (∅ 3 cm × 18 cm, Merck Silicagel 181 ([M − Ph3]+, 28).
60, n-pentane → n-pentane–Et2O 15 : 1; rf = 0.5 (n-hexane–Et2O
((iPrN)2C2H4)B–SnPh3 (4b). To granulated lithium (0.13 g,
5 : 1)). After solvent evaporation the raw product was recrystal- 17 mmol, 4 eq.) in dry THF (20 mL) a solution of Ph3SnCl
lised from hot n-hexane to give an off-white powder. Yield: (1.66 g, 4.3 mmol, 1.0 eq.) in THF (15 mL) was added at 0 °C
0.4 g, 1 mmol, (13%). Mp 148–150 °C (from n-hexane). Found: and the mixture was stirred for 16 h at rt. The solution was
C, 81.2; H, 7.4. Calc. for
C25H27O2B: C, 81.1; H, 7.4. removed from excess lithium and cooled to −78 °C. To this
δH(300 MHz; C6D6) 1.04 (12 H, s, (C(CH3)2)2), 7.09–7.15 (3 H, solution, 2 (1.00 g, 4.3 mmol, 1.0 eq.) in n-pentane (15 mL)
m, CHAr), 7.21–7.28 (6 H, m, CHAr), 7.53–7.58 (6 H, m, CHAr). was added. After stirring at −78 °C for 30 minutes and 16 h at
δC(75 MHz; C6D6) 24.4 ((C(CH3)2)2), 52.2 (CPh3), 84.0 ((C- rt the volatiles were removed in vacuo. The residue was
(CH3)2)2), 126.1 (CHAr), 128.2 (CHAr, overlapping with solvent extracted with dry toluene (3 × 20 mL) and the extracts were fil-
signal), 131.2 (CHAr), 146.5 (ipso-C). δB(96 MHz; C6D6) 33.8 (1 tered over celite. After concentration and addition of n-pentane
+
+
+
1
B, s, Δw = 375 Hz). m/z (EI ) 370 (M , 66), 355 ([M − CH3] , 5), the product was obtained as a colourless microcrystalline
2
293 ([M − C6H5]+, 6), 270 ([M − C6H12O]+, 100), 243 ([CPh3]+, powder. Yield: 1.42 g, 2.8 mmol, (66%). Mp 105–108 °C (from
34), 193 ([M − C6H5 − C6H12O]+, 22), 243 ([CPh2]+, 57).
toluene/n-pentane). Found: C, 61.7; H, 6.9; N, 5.9. Calc. for
pinB–GePh3 (3c). To granulated lithium (0.10 g, 14 mmol, C26H33N2BSn: C, 62.1; H, 6.6; N, 5.6. δH(300 MHz; C6D6) 0.90
2.9 eq.) in dry THF (10 mL), Ph6Ge2 (1.50 g, 2.46 mmol, 0.5 (12 H, d, 3J = 6.7 Hz, CH(CH3)2), 3.08 (4 H, s, CH2), 3.82 (2
eq.) was added and the mixture was stirred for 16 h at rt. The H, sept., 3J = 6.7 Hz, CH(CH3)2), 7.13–7.25 (9 H, m, CHAr),
brownish solution was removed from the excess lithium and 7.76–7.79 (6 H, m, 3J(SnH) = 49, 35 Hz (satellites), CHAr).
added to 1 (1.9 g, 10.2 mmol, 2.1 eq.) in n-hexane (30 mL). δC(75 MHz; C6D6) 22.2 (CH(CH3)2), 42.3 (CH2), 47.6 (CH
After 16 h at rt the solvent was removed, the residue extracted (CH3)2), 128.6 (CHAr), 128.8 (CHAr), 138.0 (2J(SnC) = 36 Hz
with hot n-hexane (3 × 20 mL) and the hot extracts were filtered (satellites), o-CHAr), 141.6 (1J(SnC)
= 389 Hz (satellites),
through a pad of celite. After concentration (∼15 mL) the ipso-CAr). δB(96 MHz; C6D6) 35.5 (1 B, s, 1J(SnB) = 943 Hz
1
product started to crystallise and the solution was cooled to (satellites), Δw = 290 Hz). δSn(149 MHz; C6D6) −168.5 (1 Sn,
2
−20 °C for 4 h. The supernatant solution was decanted, the br. q, 1J(SnB) = 943 Hz). m/z (EI+) 504 (M+, 29), 489
precipitate washed with cooled n-hexane (1 × 10 mL) and dried ([M − CH3]+, 68), 427 ([M − Ph]+, 100), 351 ([SnPh3]+, 3), 273
in vacuo to give the product as an off-white powder. Yield: ([SnPh2]+, 8).
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((iPrN)2C2H4)B–PbPh3 (4c). To Ph6Pb2 (1.00 g, 1.14 mmol, (6 H, m, m-CHAr), 7.38–7.42 (6 H, m, o-CHAr). δC(100 MHz;
1.0 eq.) in dry THF (20 mL), PhLi (0.63 mL (1.8 M in nBu2O), THF-d8) 71.1 (OCH2), 123.1 (p-CHAr), 126.3 (o/m-CHAr), 137.5
1.13 mmol) was added at 0 °C and stirred for 1 h at 0 °C. To (o/m-CHAr), 166.3 (ipso-CAr).
the resulting suspension, 2 (0.27 g, 1.2 mmol, 1.1 eq.) in
[K(18-C-6)SnPh3] (6d). As described for 6a: 5 (30 mg,
n-pentane (5 mL) was added at −70 °C. After stirring the colour- 80 μmol, 1.0 eq.), 4b (45 mg, 89 μmol, 1.1 eq.); yellow crystal-
less, heterogeneous mixture for 3 h at −70 to −10 °C the line powder. Single crystals suitable for an X-ray diffraction
solvent was removed in vacuo keeping the temperature below study were obtained by diffusion of n-pentane into the reaction
−10 °C. The residue was extracted with dry n-pentane (3 × mixture in PhMe at rt. Yield: 48 mg, 73 μmol, (91%). Mp
20 mL) at −20 °C, the extracts rapidly filtered over celite and 145–148 °C (from PhMe/n-pentane). Found: C, 55.3; H, 6.3.
the solvents removed in vacuo at −10 °C until the beginning of Calc. for C30H39O6KSn: C, 55.1; H, 6.0. δH(400 MHz; THF-d8)
crystallisation. After 2 h at −20 °C the solvent was decanted 3.50 (24 H, s, OCH2), 6.75–6.81 (3 H, m, p-CHAr), 6.90–6.84 (6
and the product dried in vacuo at −10 °C. The product was H, m, m-CHAr), 7.54–7.49 (6 H, m, o-CHAr). δC(100 MHz; THF-
obtained as a microcrystalline, off-white powder. The product d8) 71.1 (OCH2), 123.7 (p-CHAr), 126.5 (m-CHAr), 139.4 (2J(SnC)
decomposes at rt in C6D6 solution in 1 h significantly.22 Yield: = 54 Hz (satellites), o-CHAr), 168.3 (ipso-CAr). δSn(79.5 MHz;
0.17 g, 0.29 mmol, (25%). Mp 114–116 °C (from toluene/ THF-d8) −103.2 (1 Sn, s).
n-pentane) under decomposition.22 Found: C, 52.7; H, 5.8; N,
[K(18-C-6)PbPh3] (6e). In a nitrogen filled glovebox, 5
4.7. Calc. for C26H33N2BPb: C, 52.8; H, 5.6; N, 4.7. δH(300 MHz; (35 mg, 93 μmol, 1.0 eq.) and 4c (55 mg, 93 μmol, 1 eq.), each
3
C6D6) 0.90 (12 H, d, J = 6.6 Hz, CH(CH3)2), 3.05 (4 H, s, CH2), dissolved in dry, precooled THF (1 mL, −20 °C), were mixed.
3.84 (2 H, sept., 3J = 6.6 Hz, CH(CH3)2), 7.09–7.18 (3 H, m, After 5 min at −20 °C the mixture was layered with n-pentane
3
CHAr), 7.18–7.29 (6 H, m, CHAr), 7.71–7.96 (6 H, m, J(PbH) = (3 mL) and the product was crystallised at −20 °C (16 h) to give
61 Hz (satellites), CHAr). δC(75 MHz; C6D6) 22.1 (CH(CH3)2), the product as colourless plates suitable for X-ray crystallogra-
42.4 (CH2), 47.8 (2J(PbC) = 24 Hz (satellites), CH(CH3)2), 127.9 phy. The solution was decanted, the residue washed with dry
(CHAr, overlapping with solvent signal), 129.5 (3J(PbC) = 56 Hz n-pentane (3 × 3 mL) and dried in vacuo. Yield: 41 mg,
(satellites), CHAr), 138.6 (2J(PbC) = 61 Hz (satellites), o-CHAr), 55 μmol, (59%). Mp 152–156 °C (from THF/n-pentane). Found:
151.1 (ipso-CAr). δB(96 MHz; C6D6) 42.8 (1 B, s, 1J(PbB) = C, 48.4; H, 5.5. Calc. for C30H39O6KPb: C, 48.6; H, 5.3.
+
+
1
1379 Hz (satellites), Δw = 220 Hz)). m/z (EI ) 515 ([M − Ph] , 16), δH(400 MHz; THF-d8) 3.46 (24 H, s, OCH2), 6.72–6.81 (3 H, m,
2
439 ([PbPh3]+, 13), 285 ([PbPh]+, 65), 154 ([Ph2]+, 100). Attempts p-CHAr), 6.87–6.97 (6 H, m, m-CHAr), 7.71–7.81 (6 H, m,
to obtain a 207Pb NMR spectrum were unsuccessful due to the o-CHAr). δC(100 MHz; THF-d8) 71.1 (OCH2), 123.2 (p-CHAr), 127.7
instability of 4c at rt.15b,c
(3J(PbC) = 28 Hz (satellites), m-CHAr), 140.4 (2J(PbC) = 54 Hz
[K(18-C-6)CPh3] (6a). In a nitrogen filled glovebox, 5 (50 mg, (satellites), m-CHAr), 191.5 (ipso-CAr). Attempts to obtain a
135 μmol, 1 eq.) and 3a (50 mg, 135 μmol, 1 eq.), each dis- 207Pb NMR spectrum were unsuccessful.3b
solved in dry THF (2 mL), were mixed. After 10 minutes the
mixture was layered with PhMe (3–4 mL) and the product pre-
cipitated at −20 °C (16 h). The supernatant solution was de-
X-ray crystallography‡
canted, the residue washed with dry n-pentane (3 × 3 mL) and All crystals were mounted in inert perfluoroether oil on top of
dried in vacuo to give a deep red powder. Single crystals suit- a glass fiber using an XTEMP-2 apparatus at approx. −80 °C
able for the X-ray diffraction study were obtained by diffusion and rapidly transferred to the cold nitrogen gas stream of the
of PhMe into a solution in THF at rt. Yield: 61 mg, 112 μmol, diffractometer.26a–c The data were either collected on an
(84%). Mp >162 °C (from THF/toluene) under decomposition. Oxford Diffraction Xcalibur E instrument using monochro-
Found: C, 67.75; H, 7.1. Calc. for C31H39O6K: C, 68.1; H, 7.2. mated MoKα radiation at 100(2) K or on an Oxford Diffraction
δH(400 MHz; THF-d8; −70 °C) 3.51 (24 H, s, OCH2), 5.90 (3 H, Nova A instrument, using mirror-focused CuKα radiation at
vt, 3J = 7 Hz, p-CHAr), 6.46 (6 H, vdd, 3J = 8, 7 Hz, m-CHAr), 100(2) K. The data were integrated and an empirical absorp-
3
7.29 (6 H, vd, J = 8 Hz, o-CHAr). δC(100 MHz; THF-d8; −70 °C) tion correction was performed employing CrysAlisPro soft-
71.0 (OCH2), 90.9 (CPh3), 113.1 (p-CHAr), 123.9 (o-CHAr), 128.1 ware.26d All structures were solved by direct methods (6a, 6b
(m-CHAr), 149.8 (ipso-CAr). λmax/nm (THF) 438 (sh) and 505.
(both structures) and 6d: SIR-92;26e 6c and 6e: SHELXS-9726f
)
[K(18-C-6)SiPh3] (6b). For preparation from 3b and analyti- and refined anisotropically for all non-hydrogen atoms by full-
cal data, see ref. 9. 6b can also be obtained from 4a following matrix least squares on F2 using SHELXL-97.26f All hydrogen
the same procedure (yield: 58%).
atoms were refined employing a riding model. During refine-
[K(18-C-6)GePh3] (6c). As described for 6a: 5 (70 mg, ment and analysis of the crystallographic data the programs
186 μmol, 1 eq.), 3c (80 mg, 186 μmol, 1 eq.); yellow crystalline WinGX, PLATON, ORTEP-III and Diamond were used.26g–j
powder. Single crystals suitable for the X-ray diffraction study
The crystal of 6a is non-merohedrically twinned by a 180°
were obtained by diffusion of n-pentane into the reaction rotation about the b-axis. Both domains were indexed sepa-
mixture in PhMe at −20 °C. Yield: 71 mg, 117 μmol, (63%). Mp rately and the data were integrated into a dataset containing
171–174 °C (from PhMe/n-pentane). Found: C, 59.7; H, 6.4. intensities of both domains; this dataset was used in the
Calc. for C30H39O6KGe: C, 59.3; H, 6.5. δH(400 MHz; THF-d8) refinement (the twin factor refined to 0.3394(5)). The structure
3.51 (24 H, s, OCH2), 6.73–6.78 (3 H, m, p-CHAr), 6.84–6.89 was solved with intensity data of one domain only (Rint
=
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Dalton Transactions
0.1392, wR2 = 0.1479). Further crystallographic details are
given in the crystallographic data deposited.‡
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In ORTEP style plots the thermal ellipsoids are drawn at the
50% probability level. In packing diagrams the atoms are
drawn as spheres with arbitrary radii. Hydrogen atoms are
omitted for clarity. For clarity symmetry equivalent atoms are
not distinguished.
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Acknowledgements
Support for this research from a ‘Liebig-Stipendium’ of the
‘Fonds der Chemischen Industrie’ for CK is gratefully acknowl-
edged. The author thanks Cindy Döring, Matthias Reiners,
Óscar Árias and Kristof Jess for their help with the laboratory
work.
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3
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a
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Dalton Trans., 2013, 42, 8276–8287 | 8287