Synthetic, structural and computational studies on adducts of the 4,1,2-SnC2B10 supraicosahedral stannacarborane

Article abstract of DOI:10.1039/b922644c

The stannacarborane 1,2-μ-(CH₂)₃-4,1,2-closo- SnC₂B₁₀H₁₀ (1) and its adducts with 2,2′-bipyridine (bipy), 1,10-phenanthroline (o-phen) and 4,4′-diphenyl-2,2′-bipyridine (Ph₂bipy), 1,2-μ-(CH₂)₃-4-(bipy)-4,1,2-closo-SnC₂B ₁₀H₁₀ (2), 1,2-μ-(CH₂)₃-4-(o- phen)-4,1,2-closo-SnC₂B₁₀H₁₀ (3) and 1,2-μ-(CH₂)₃-4-(Ph₂bipy)-4,1,2-closo- SnC₂B₁₀H₁₀ (4), respectively, together with the analogous compound 1,2-μ-{C₆H₄(CH₂) ₂}-4-(bipy)-4,1,2-closo-SnC₂B₁₀H₁₀ (5) have been prepared and characterised. In solution at ambient temperature, compounds 1-5 all display NMR spectra which are interpreted in terms of (time-averaged) C_s molecular symmetry, but whilst (effectively) C_s symmetry is retained in the structures of 2-5 in the crystal (i.e. henicosahedral cage structures are observed), 1 has a (C₁-symmetric) docosahedral structure. A method for quantifying the percentage docosahedral character of 13-vertex 1,2-C₂ heteroboranes is described, based on the angles around the C1C2B9B5 quadrilateral. The structures of carbons adjacent 1-5 all reveal less slipping of the Sn atom (or {SnL₂} fragment) across the C₂B₄ carborane face than has previously been observed in analogous carbons apart 4,1,6-closo-SnC₂B₁₀ species, a surprising result in the context of previous studies of slipping in icosahedral platinacarboranes. A computational study of carbons adjacent and carbons apart icosahedral and supraicosahedral platinacarboranes has revealed that the origin of this observation is steric control of the slipping distortion in both carbons apart species and in the carbons adjacent 13-vertex species, with orbital interactions proving dominant only in the case of the carbons adjacent icosahedral compound. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b922644c

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Synthetic, structural and computational studies on adducts of the
4,1,2-SnC2B10 supraicosahedral stannacarborane†
Peter D. Abram, David McKay, David Ellis, Stuart A. Macgregor,* Georgina M. Rosair and Alan J. Welch*
Received 29th October 2009, Accepted 2nd December 2009
First published as an Advance Article on the web 27th January 2010
DOI: 10.1039/b922644c
The stannacarborane 1,2-m-(CH2)3-4,1,2-closo-SnC2B10H10 (1) and its adducts with 2,2¢-bipyridine
(bipy), 1,10-phenanthroline (o-phen) and 4,4¢-diphenyl-2,2¢-bipyridine (Ph2bipy),
1,2-m-(CH2)3-4-(bipy)-4,1,2-closo-SnC2B10H10 (2), 1,2-m-(CH2)3-4-(o-phen)-4,1,2-closo-SnC2B10H10 (3)
and 1,2-m-(CH2)3-4-(Ph2bipy)-4,1,2-closo-SnC2B10H10 (4), respectively, together with the analogous
compound 1,2-m-{C6H4(CH2)2}-4-(bipy)-4,1,2-closo-SnC2B10H10 (5) have been prepared and
characterised. In solution at ambient temperature, compounds 1–5 all display NMR spectra which are
interpreted in terms of (time-averaged) Cs molecular symmetry, but whilst (effectively) Cs symmetry is
retained in the structures of 2–5 in the crystal (i.e. henicosahedral cage structures are observed), 1 has a
(C1-symmetric) docosahedral structure. A method for quantifying the “percentage docosahedral
character” of 13-vertex 1,2-C2 heteroboranes is described, based on the angles around the C1C2B9B5
quadrilateral. The structures of “carbons adjacent” 1–5 all reveal less slipping of the Sn atom (or
{SnL2} fragment) across the C2B4 carborane face than has previously been observed in analogous
“carbons apart” 4,1,6-closo-SnC2B10 species, a surprising result in the context of previous studies of
slipping in icosahedral platinacarboranes. A computational study of “carbons adjacent” and “carbons
apart” icosahedral and supraicosahedral platinacarboranes has revealed that the origin of this
observation is steric control of the slipping distortion in both “carbons apart” species and in the
“carbons adjacent” 13-vertex species, with orbital interactions proving dominant only in the case of the
“carbons adjacent” icosahedral compound.
greater in 3,1,2-MC2B9 species (cage C atoms adjacent)5 than in
Introduction
2,1,7-MC2B9 species (cage C atoms separated),6 a result that was
In 2002 we reported the first supraicosahedral p-block met-
rationalised by the results of molecular orbital (MO) calculations
allacarboranes 4,1,6-closo-SnC2B10H12 and 1,6-Me2-4,1,6-closo-
SnC2B10H10, arising from reduction of 1,2-closo-C2B10H12 or its
C,C¢-dimethyl analogue, followed by treatment with SnCl2.1 Very
recently we described a number of adducts of the dimethyl
species with chelating Lewis bases L2.2 The structures of these
adducts, studied both crystallographically and computationally,
confirmed that the supraicosahedral stannacarboranes resemble
their icosahedral3 and sub-icosahedral4 analogues in their Lewis
acid behaviour, giving rise to adducts in which (i) there is an
enhanced slip of the Sn atom relative to the uncomplexed precursor
and (ii) the stereochemical influence of the Sn lone pair of electrons
is clearly evident.
at the extended Hu¨ckel level.
In 4,1,6-MC2B10 supraicosahedral compounds the cage C atoms
are separated by a single B atom, as they are in 2,1,7-MC2B9
icosahedral species. A known 13-vertex C-adjacent isomer is
4,1,2-MC2B10, but to prepare this it is usually necessary to first
tether the cage C atoms of 1,2-closo-C2B10 icosahedra with a
short exopolyhedral tether, to prevent their separation in the
initial reduction step, the same strategy used to prepare the
first supraicosahedral carborane.7 Following our report of 4,1,6-
SnC2B10 species, Xie prepared such a 4,1,2-SnC2B10 compound
and determined the structures of its adducts with MeCN, THF
and dme (dme = dimethoxyethane).8
The slip of metal atoms across a carborane ligand face was
thoroughly studied with respect to icosahedral {L2M}C2B9 species
more than 30 years ago (M = Pt or Pd, L = typically phosphine).5
A key finding of this work was that the slip distortion, D, was
In view of the superficial similarity in the relationship be-
tween 4,1,6-SnC2B10 and 4,1,2-SnC2B10 and that between 2,1,7-
MC2B9 and 3,1,2-MC2B9, we wondered if adducts of 4,1,2-
SnC2B10 compounds would also show increased slip distor-
tions relative to their 4,1,6-SnC2B10 cousins. Hence we report
here the results of synthetic and structural studies on a num-
ber of adducts of 4,1,2-SnC2B10 stannacarboranes using ex-
clusively bidentate L2 bases similar to those we used in our
earlier work. Surprisingly, the 4,1,2-SnC2B10 species are less
slipped than their 4,1,6-SnC2B10 analogues. We trace the origin
of this unexpected result by computational studies of model
compounds.
Department of Chemistry, School of Engineering & Physical Sciences,
Heriot-Watt University, Edinburgh, UK EH14 4AS. E-mail: a.j.welch@
hw.ac.uk, s.a.macgregor@hw.ac.uk; Fax: +44 (0)131 451 3180; Tel: +44
(0)131 451 3217 +44 (0)131 451 8031
† Electronic supplementary information (ESI) available: Computational
models and additional plots referred to in the text. CCDC reference
numbers 751644–751648 (compounds 1–5 respectively). For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/b922644c
2412 | Dalton Trans., 2010, 39, 2412–2422
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Results and discussion
Synthesis and spectroscopy
Reduction of 1,2-m-(CH2)3-1,2-closo-C2B10H10 by sodium in THF
in the presence of naphthalene, followed by treatment with SnCl2,
affords a modest yield of the pale yellow stannacarborane 1,2-
m-(CH2)3-4,1,2-closo-SnC2B10H10 (1) after work-up. Compound
1 was initially characterised by mass spectrometry and NMR
spectroscopy. The highest mass signal in the mass spectrum
appears as a characteristic heteroborane envelope from 298 to
1
308 with the most intense peak at m/z 302. In the H NMR
spectrum are multiplets of equal intensity between d 3.20 and
1
1.90 due to the tether protons, whilst the 11B{ H} spectrum
consists of five signals between d +8.0 and -0.5, of relative
ratio 2 : 4 : 1 : 1 : 2 from high frequency to low frequency, all
of which become doublets on retention of proton coupling.
The molecular structure of 1, subsequently determined crystal-
lographically (vide infra), is that of an asymmetric docosahe-
dral cage, and the presence of a mirror plane implied by the
Fig. 1 The docosahedron (left) and henicosahedron (right) and number-
ing schemes.
imply a Cs-symmetric molecule, at least in solution at room
temperature.
1
11B{ H} spectrum is readily rationalised by a diamond-trapezium-
diamond fluctional process in solution, similar to that pro-
posed for the transition-metal metallacarboranes 1,2-m-(CH2)3-
4,4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10 and 1,2-m-(CH2)3-4-dppe-
4,1,2-closo-NiC2B10H10 (dppe = Ph2PCH2CH2PPh2),9 which is
rapid on the NMR timescale.
Molecular structures
The molecular structures of compounds 1–5 have all been
determined by single-crystal diffraction studies.
We have previously shown9 that 4,1,2-MC2B10 compounds can
exist in the solid-state with either docosahedral or henicosahedral
structures, the topological difference between which is the formal
absence of a C2–B5 connectivity in the latter. Thus, in the do-
cosahedron the C1C2B9B5 unit is a diamond, with a measureable
difference in C1–C2–B9 and C2–C1–B5 angles and a measureable
difference in C2–B9–B5 and B9–B5–C1 angles, whereas in the
henicosahedron the C1C2B9B5 unit is trapezoidal and the C1–
C2–B9 and C2–C1–B5 angles are equal, as are the C2–B9–B5 and
B9–B5–C1 angles (Fig. 1). For the series of metallacarboranes
1,2-m-(CH2)3-4-L-4,1,2-closo-MC2B10H10 we found a continuum
of structure type from henicosahedral (ML = CoCp, Ru{p-
cym} {p-cym = C6H4MeiPr-1,4}), through intermediate (ML =
Pt{PMe2Ph}2) to essentially docosahedral (ML = Ni{dppe},
although both the platinum and nickel species were clearly
fluctional in solution via a henicosahedral intermediate as noted
above.
Room temperature reaction of a toluene solution of 1 and
toluene solutions of 2,2¢-bipyridine (bipy), 1,10-phenanthroline
(o-phen) and 4,4¢-diphenyl-2,2¢-bipyridine (Ph2bipy) result in
immediate precipitation of the yellow adducts 1,2-m-(CH2)3-4-
(bipy)-4,1,2-closo-SnC2B10H10 (2), 1,2-m-(CH2)3-4-(o-phen)-4,1,2-
closo-SnC2B10H10 (3) and 1,2-m-(CH2)3-4-(Ph2bipy)-4,1,2-closo-
SnC2B10H10 (4), respectively, in good yields. The 1H NMR spectra
of 2–4 all show, in addition to resonances due to the bipy, o-phen
or Ph2bipy ligands, four multiplets in the ratio 2 : 2 : 1 : 1 at d 3.15–
2.95, 2.85–2.65, 2.05–1.90 and 1.80–1.65, respectively, assigned
1
to the protons of the (CH2)3 tether. Peaks in the 11B{ H} NMR
spectra of 2–4 are shifted to low frequency compared to those in 1,
appearing as a 3 : 2 : 2 : 2 : 1 pattern for 2 and 3 and a 3 : 2 : 4 : 1 for
4, between d +4.0 and -11.0. The 1H and 11B spectra imply (at least
time-averaged) Cs molecular symmetry in solution (assuming, in
the latter, that the integral-3 resonances are 2+1 co-incidences
and the integral-4 resonance is a 2+2 co-incidence). As will be
discussed subsequently, the structures of 2–4 in the solid state are
effectively henicosahedral (Fig. 1, right) and Cs-symmetric for a
4,1,2-SnC2B10 heteroatom pattern.
In the present study it is immediately apparent that the cage
of the ligand-free stannacarborane 1 (Fig. 2) appears to be best
described as docosahedral, whilst those of the adducts 2–5 (Fig. 3–
6) are best described as henicosahedral. To place these and other
1,2-C2 carboranes and heterocarboranes quantitatively on the
continuum of structure type from docosahedral to henicosahedral
we define the angle f as the average of the differences between
angles C1–C2–B9 and C2–C1–B5 and angles C2–B9–B5 and B9–
B5–C1, i.e.
To provide a link between these adducts of the (CH2)3-tethered
stannacarborane 1 and the MeCN, THF and dme adducts of
1,2-m-{C6H4(CH2)2}-4,1,2-closo-SnC2B10H10 previously reported
by Xie,8 we have further treated a toluene solution of 1,2-
m-{C6H4(CH2)2}-4,1,2-closo-SnC2B10H10 with bipy to afford the
bright yellow bipyridyl adduct 1,2-m-{C6H4(CH2)2}-4-(bipy)-
f = (|C1–C2–B9 - C2–C1–B5| + |C2–B9–B5 - B9–B5–C1|)/2
1
4,1,2-closo-SnC2B10H10 (5). In compound 5 the H NMR spec-
trum is unremarkable, with appropriate resonances in terms
of multiplicity, integral and chemical shift, for the protons
of the bipy ligand and a,a-o-xylylene tether. Peaks in the
For a Cs-symmetric henicosahedron f = 0, and f increases
as the C2–B5 distance shortens and the structure becomes do-
cosahedral. Table 1 lists f values for all structurally characterised
13-vertex 1,2-C2 carboranes and heterocarboranes of which we
are aware. The “most docosahedral” species, 1,2-m-(CH2)3-4-
dppe-4,1,2-closo-NiC2B10H10, has f = 41.55◦. We now define x,
1
11B{ H} NMR spectrum are considerably broader than those
of 2–4, but nevertheless a clear 2 : 2 : 2 : 1 : 1 : 2 pattern, from
d +7.5 to -10.5, is evident. Again, the NMR spectra of 5
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Fig. 2 Perspective view of compound 1. Thermal ellipsoids are drawn at
the 50% probability level except for H atoms.
Fig. 5 Perspective view of compound 4 (molecule b). Thermal ellipsoids
as for Fig. 2.
Fig. 3 Perspective view of compound 2 (molecule a). Thermal ellipsoids
are drawn at the 40% probability level except for H atoms.
Fig. 6 Perspective view of compound 5. Thermal ellipsoids as for Fig. 2.
The ligand-free stannacarborane 1 has x = 80.3% and is confirmed
as essentially docosahedral, whilst the adducts 2–5, with x between
0.0 and 21.6, are essentially henicosahedral.
This report constitutes the first time a ligand-free 4,1,2-SnC2B10
species has been structurally characterised. Table 2 hosts selected
molecular parameters for compounds 1–5 studied, where D is the
slip distortion of the Sn atom measured relative to the centroid of
the B5B9B12B13B8 least-squares plane, DD is the additional slip
accompanying adduct formation, z is the perpendicular distance of
the Sn atom from that least-squares plane and q is the inclination
of the L2 ligand, the dihedral angle between B5B9B12B13B8 and
Sn4N41CCN42 planes. In 1 the Sn-cage atom distances vary
somewhat from the corresponding distances in 1,6-Me2-4,1,6-
closo-SnC2B10,1 connectivities to vertex atoms 1, 2, 3 and 7 being
Fig. 4 Perspective view of compound 3. Thermal ellipsoids as for Fig. 2.
˚
longer (by 0.04–0.13 A) whilst those to 6 and 10 are shorter (by
the “percentage docosahedral character”, as x = (f/41.55) ¥
100%.‡ For a perfect henicosahedron x = 0% and for the
docosahedral nickelacarborane x = 100%. By this approach
the percentage docosahedral character of all 13-vertex 1,2-C2
carboranes and heterocarboranes can be assessed on a common
scale. The 1,2-C2B11 carboranes are all essentially henicosahedral.
The 4,1,2-MC2B10 metallacarboranes appear to be predominantly
henicosahedral,§ but are somewhat more spread, displaying heni-
cosahedral, docosahedral and effectively intermediate, e.g. 1,2-
m-(CH2)3-4,4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10 (III), structures.
˚
0.09 and 0.05 A respectively). Moreover, there is greater internal
˚
˚
variation in these distances, 0.35 A in 1 compared to 0.26 A in
the 4,1,6-SnC2B10 species, in spite of which the Sn atom in 1 is
˚
less slipped (D = 0.14 A) than that in the 4,1,6-isomer (D =
2
˚
0.27 A). As noted in the introduction, in studies of isomeric
icosahedral platinacarboranes in which the two cage C atoms were
both adjacent5 and non-adjacent,6 it was found that the greater
slip distortion occurred in the former case. Thus the measurement
of a smaller slip in 1 (C atoms adjacent) compared to that in 1,6-
Me2-4,1,6-closo-SnC2B10 (C atoms non-adjacent) is significant. We
return to this point later.
The molecular structures of the bipy, o-phen and Ph2bipy
adducts of 1, compounds 2–4, respectively, are shown in Fig. 3–5
(compounds 2 and 4 crystallise with two independent molecules
in the asymmetric fraction of the unit cell; only molecule A is
‡ Since our docosahedral model compound is chosen arbitrarily it may be
that future species will be “more docosahedral” and have x values >100%.
§ However this has not always been recognised, e.g. in ref. 8 the
line diagrams of the adducts are drawn as docosahedral whilst the
crystallographically-determined structures are clearly henicosahedral.
2414 | Dalton Trans., 2010, 39, 2412–2422
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Table 1 Structural analysis of the cages of 13-vertex 1,2-C2 heteroboranesa
Compound
Type
CCDC refcode
Reference
f/◦
x
I
4,1,2-CoC2B10
4,1,2-RuC2B10
4,1,2-PtC2B10
4,1,2-NiC2B10
4,1,2-CoC2B10
4,1,2-SnC2B10
4,1,2-SnC2B10
4,1,2-SnC2B10
4,1,2-CoC2B10
4,1,2-NaC2B10
4,1,2-ZrC2B10
4,1,2-ZrC2B10
1,2-C2B11
1,2-C2B11
1,2-C2B11
1,2-C2B11
4,1,2-SnC2B10
4,1,2-SnC2B10
4,1,2-SnC2B10
4,1,2-SnC2B10
4,1,2-SnC2B10
GAQHIQ
GAQHOW
GAQHUC
GAQJAK
BOKZAC
GUZSOJ
GUZSUP
GUZTAW
POYHEQ
BIYVOU
IYUVED
IYUVIH
9
9
9
9
10
8
8
8
11
12
13
13
7
14
0.20
0.33
28.44
41.55
32.53, 41.32b
0.93
4.23
4.98
6.17
3.32
0.5
0.8
68.4
100
78.3, 99.4
2.2
10.2
12.0
14.8
8.0
22.6
1.6
27.9
0
16.1
7.2, 14.7
80.3
18.0, 0.02
11.3
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
XIII
XIV
XV
XVI
1
9.41
0.66
TUSGAP
JEWZER
JEWZAN
NEGSUO
11.61
0.00c
14
6.70
15d
2.99, 6.09e
33.37
7.46, 0.97e
4.68
this work
this work
this work
this work
this work
2
3
4
6.76, 8.98c
5.80
16.3, 21.6
14.0
5
I, 1,2-m-(CH2)3-4-Cp-4,1,2-closo-CoC2B10H10; II, 1,2-m-(CH2)3-4-(p-cym)-4,1,2-closo-RuC2B10H10; III, 1,2-m-(CH2)3-4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10;
IV, 1,2-m-(CH2)3-4-dppe-4,1,2-closo-NiC2B10H10; V, 1-Me-4-(PEt3)-4,6/7-m-{Co(PEt3)2-m-(H)2}-4,1,2-closo-CoC2B10H10; VI, 1,2-m-{C6H4(CH2)2}-4-
MeCN-4,1,2-closo-SnC2B10H10; VII, 1,2-m-{C6H4(CH2)2}-4-thf-4,1,2-closo-SnC2B10H10; VIII, 1,2-m-{C6H4(CH2)2}-4-dme-4,1,2-closo-SnC2B10H10; IX,
1-CN-4-Cp-4,1,2-closo-CoC2B10H11; X, [[1,2-m-{C6H4(CH2)2}-4-thf-4,1,2-closo-NaC2B10H10.Na(thf)2]2]n; XI, [4,4¢-(Cl)2-4,4¢-Zr-(1,2-m-{C6H4(CH2)2}-
1,2-closo-C2B10H10)2]2- (monoclinic); XII, [4,4¢-(Cl)2-4,4¢-Zr-(1,2-m-{C6H4(CH2)2}-1,2-closo-C2B10H10)2]2- (triclinic); XIII, 1,2-m-{C6H4(CH2)2}-
3-Ph-1,2-closo-C2B11H10; XIV, 1,2-Me2-1,2-closo-C2B11H11; XV, 1,2-m-{Me2Si(CH2)2}-1,2-closo-C2B11H11; XVI, 1,2-m-{C6H4(CH2)2}-1,2-closo-
C2B11H11.a ConQuest (version 1.11) search of the Cambridge Structural Database (September 2009 update) at the Daresbury Laboratory. b C2 disordered
over vertices 2 and 3. c Crystallographically-imposed Cs symmetry. d This paper reports four further, similar, species, two of which have multiple
˚
crystallographically-independent molecules, but all are essentially docosahedral, with C1–B9 and C2–B5 distances ranging from 2.139(3) to 2.629(3) A.
e Two crystallographically-independent molecules.
◦
Table 2 Selected molecular parameters (A, ) in experimental compounds 1–5 and model compounds A and Ba
˚
1
A
2a
2b
B
3
4a
4b
5
Sn4–C1
Sn4–C2
Sn4–B6
Sn4–B10
Sn4–B7
Sn4–B3
C1–C2
C2–B5b
Sn4–N41
Sn4–N42
Dc
2.545(2)
2.727(3)
2.582(3)
2.375(3)
2.492(3)
2.692(3)
1.445(3)
2.056(4)
2.549
2.762
2.560
2.365
2.514
2.675
1.463
1.954
2.813(17)
2.92(2)
2.95(2)
2.50(2)
2.46(2)
2.786(19)
1.40(3)
2.33(3)
2.419(16)
2.396(15)
0.392
2.879(18)
2.824(17)
2.82(2)
2.43(2)
2.47(2)
2.897(19)
1.44(3)
2.45(3)
2.399(15)
2.396(14)
0.410
2.832
2.787
2.742
2.458
2.535
2.903
1.437
2.434
2.623
2.608
0.330
0.212
3.612
31.23
3.3
2.803(2)
2.820(2)
2.899(3)
2.521(2)
2.448(2)
2.755(2)
1.433(3)
2.410(3)
2.4481(17)
2.4460(18)
0.341
2.821(4)
2.797(4)
2.732(5)
2.469(5)
2.585(5)
2.949(5)
1.431(6)
2.359(7)
2.433(4)
2.419(4)
0.331
2.782(4)
2.864(5)
2.988(6)
2.604(6)
2.441(5)
2.671(5)
1.420(6)
2.378(7)
2.462(4)
2.415(4)
0.400
2.849(4)
2.852(4)
2.872(4)
2.550(5)
2.485(5)
2.775(5)
1.430(5)
2.399(6)
2.382(3)
2.418(3)
0.320
0.144
3.455
0.117
3.432
d
DD
0.248
3.644
24.26
7.46
0.266
3.644
25.68
0.97
0.197
3.631
30.16
4.68
0.187
3.648
27.13
8.98
0.256
3.635
16.04
6.76
0.176
3.661
29.51
5.80
ze
f
q
g
f
33.37
80.3
28.8
69.2
xh
18.0
0.02
7.8
11.3
21.6
16.3
14.0
a A is the optimised model of compound 1 and B the optimised model of compound 2. In both model compounds the exopolyhedral –(CH2)3– tethers
were replaced by two H substituents. Optimisation was performed using Gaussian 03. Optimised parameters shown italicised for emphasis. b For the
henicosahedral species 2–5 the smaller of the C2–B5 and C1–B9 distances is quoted, since these molecules could be numbered in one of two enantiomorphic
ways. c D is the slipping parameter of the Sn4 atom, defined as its displacement, parallel to the best (least-squares) plane through B5B9B12B13B8, from the
point directly above the centroid of that plane. d DD is the increase in slipping for compounds 2–5 relative to 1. e z is the perpendicular displacement of the
Sn4 atom from the B5B9B12B13B8 plane. f q is the inclination of the bipyridyl ligand, the dihedral angle between Sn4N41CCN42 and B5B9B12B13B8
planes. g f is defined in the text as (|C1–C2–B9 - C2–C1–B5| + |C2–B9–B5 - B9–B5–C1|)/2. h x is the “percentage docosahedral character”, defined
as (f/41.55) ¥ 100%.
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shown in Fig. 3 and only B is shown in Fig. 5). Structurally,
adduct formation is accompanied by (i) a change in cage structure
from essentially docosahedral (x = 80.3% in 1) to essentially
henicosahedral (x = 0–21.6% in 2–4), (ii) increased slipping of
which may be related to the smaller slipping distortions in the
present compounds.
We determined the structure of 5 (Fig. 6) for comparison
with that of 2, to see if the two different tethers, m-(CH2)3-
and m-{C6H4(CH2)2}-, had any effect on structure. Although the
comparison is somewhat compromised by the relatively poor
precision of the structural determination of 2 (a consequence
of poor crystal size and quality) it is evident from the data in
Table 2 that any differences are minor. One interesting feature
of the structure of 5 is that the C6 ring of the tether and the
Sn4N41CCN42 sequence are nearly co-planar (dihedral angle
8.14◦). In the crystal both the a,a-o-xylylene tether and the
bipy ligand are involved in quasi-graphitic interactions with
equivalent units across inversion centres.
The overall similarity between the molecular structures of 2
and 5 provides a link between the structures of our supraicosa-
hedral 4,1,2-SnC2B10 adducts and those of Xie, who used the m-
{C6H4(CH2)2}-tethered carborane and MeCN, THF and dme as
external ligands (compounds VI, VII and VIII, respectively, of
Table 1). Even though he used a mixture of mono- and bidentate
Lewis bases in his study Xie concluded “a stronger base leads to an
increased slip distortion of the tin from the centre of the C2B4 bonding
face”.8 However, Xie based this conclusion on measured Sn–cage
atom distances, and did not actually calculate the slip distortions.
In view of our interest in this general family of compounds we
˚
˚
the Sn atom, from D = 0.14 A to D = 0.33–0.41 A and (iii)
˚
a slight reduction (ca. 0.01–0.04 A) in the length of the C1–
C2 connectivity. The slipping is predominantly away from cage
C atoms, as evidenced by significantly increased Sn–C1/C2 and
˚
˚
Sn–B3/B6 distances (averages¶ of 2.64 A in 1 to 2.81–2.86 A
˚
˚
in 2–4 for Sn–C1/C2, and 2.64 A in 1 to 2.83–2.86 A in 2–4
for Sn–B3/B6) although the fact that Sn–B7/B10 also increases
˚
˚
(average 2.43 A in 1 to 2.47–2.52 A in 2–4) means that the overall
structural change is more complicated and, indeed, we note that
the Sn atom in 2–4 is displaced further from the B5 reference
˚
˚
plane (3.63–3.65 A) than it is in 1 (3.45 A). A similar phenomenon
accompanied adduct formation of 1,6-Me2-4,1,6-closo-SnC2B10.2
The increase in slipping that accompanies adduct formation, DD, is
˚
0.19–0.27 A in 2–4, less than in the isomeric 4,1,6-SnC2B10 species
2
˚
(0.28–0.39 A). Since they both start from a smaller base and
change by less, overall, therefore, the slipping parameters in the
˚
˚
carbons adjacent compounds 2–4, 0.33–0.41 A, are ca. 0.2–0.25 A
smaller than in the 4,1,6 species. The origins of this unexpected
result are discussed subsequently. The slight shortening of C1–C2
as a consequence of increasing slip is reminiscent of the situation in
slipped icosahedral 3,1,2-MC2B9 species in which case the origin
has been traced to reduced depopulation of a carborane ligand
orbital which is C/C bonding in nature.
˚
have calculated D for Xie’s compounds (0.205, 0.253 and 0.223 A,
respectively, measuring slip with respect to the lower B5 pentagon,
˚
The bipy, o-phen and Ph2bipy ligands in 2–4 are oriented such
that their N atoms are opposite the cage C atoms. This reflects
the greater trans influence of the facial boron atoms, B3, B7, B10
and B6, over the (facial) carbon atoms, C1 and C2. Thus Sn–C
bonding is somewhat weaker than Sn–B bonding (further evidence
for this is the direction of slip of the Sn atom) and, to compensate,
the bipy, o-phen and Ph2bipy ligands position themselves trans
to cage C with the Sn lone pair of electrons trans to B. In the
related 4,1,6-SnC2B10 adducts a broadly similar orientation of the
exopolyhedral ligands was observed, with one N atom trans to the
degree-5 C atom C6 and the other trans to the connectivity between
the degree-4 C atom C1 and the degree-5 B atom B2.2 In bipyridyl
adducts of 4,1,10-SnC2B10 the exopolyhedral ligand lies trans to the
degree-5 C atom C10, whilst in 4,1,12-SnC2B10 it lies trans to the
degree-4 C atom C1,16 these results affording the ranking of trans
influence as Bdegree-5 > Cdegree-4 > Cdegree-5. The origin of the general
result that the carbon atoms in heterocarboranes have a relatively
weak trans influence lies in the fact that the frontier molecular
orbitals of carborane ligands are predominantly localised on the
facial boron atoms.5
or 0.320, 0.377 and 0.365 A, respectively, measuring slip with
respect to the centroid of the upper C2B4 ring) and find no such
correlation.
Computational studies
A significant conclusion from the structural studies above is that
the slipping distortion in the “carbons adjacent” 4,1,2-SnC2B10
stannacarborane 1 is less than in its “carbons apart” 4,1,6- ana-
logue 1,6-Me2-4,1,6-closo-SnC2B10H10,1 and that this difference
is maintained in the adducts of 1 reported here compared to
adducts of 1,6-Me2-4,1,6-closo-SnC2B10H10.2 This is in contrast
to established work on the slipping distortions in icosahedral
platina- or palladacarboranes5,6 where the reverse is true. To check
whether this difference is due to the change from icosahedral to
supraicosahedral or from group 10 element to Sn, we have calcu-
lated D for the supraicosahedral platinacarboranes 1,2-m-(CH2)3-
9
4,4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10 and 4,4-(PMe2Ph)2-4,1,6-
closo-PtC2B10H12.17 These are 0.08 and 0.52 A, respectively, clearly
˚
revealing a fundamental difference between icosahedral and
supraicosahedral metallacarboranes in terms of the magnitude
of metal slipping as a function of C atom position.
The stereochemical influence of the Sn lone pair of electrons
is reflected not only in the orientation of the bipy, o-phen and
Ph2bipy ligands in 2–4 but also in their inclination, at an angle q of
ca. 30◦ to the B5B9B12B13B8 reference plane. A slight difference
in inclination angle (q = 16◦) exists for 4B although we note that in
4 there is clear evidence of intermolecular p–p interactions in the
To probe the origins of this difference, we have extended our pre-
vious density functional theory (DFT) calculations18 on 13-vertex
stannacarboranes2 to include the “carbons-adjacent” species 1
and 2 reported here. In addition, we have revisited the structural
trends in icosahedral and supraicosahedral platinacarboranes
noted above.5,17 Calculations on 1 and 2 employed the model
systems A and B respectively, where the exopolyhedral–(CH2)3–
tethers were replaced by two H substituents. Table 2 shows that
key computed and derived distances in A and B compare well with
those determined experimentally for 1 and 2 although, as noted
˚
crystal. Sn–N distances in 2–4 are 2.42–2.46 A, somewhat longer
than those (2.35–2.43 A) in the related 4,1,6-SnC2B10 adducts,2
˚
¶ Since compounds 2–4 are essentially henicosahedral with local mirror
symmetry passing through the cage it is necessary to average Sn–C1 and
Sn–C2, Sn–B3 and Sn–B6, and Sn–B7 and Sn–B10.
2416 | Dalton Trans., 2010, 39, 2412–2422
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in our previous studies,2 there is a tendency to overestimate the
Sn–cage interactions in the bipy adduct B.
Table 3 Comparison of experimentally- (X-ray diffraction) and
˚
computationally- (DFT) determined connectivities and slip distances (A)
and conformations (c, ◦) in platinacarboranes
In order to assess the factors controlling the degree of slip-
ping in 12- and 13-vertex metallacarboranes we turned to the
family of platinacarboranes, specifically icosahedral 3,3-(PEt3)2-
3,1,2-closo-PtC2B9H11 (XVII)5 and 1,7-Me2-2,2-(PMe2Ph)2-2,1,7-
closo-PtC2B9H9 (XVIII)6 and supraicosahedral 1,2-m-(CH2)3-4,4-
(PMe2Ph)2-4,1,2-closo-PtC2B10H10 (III)9 and 4,4-(PMe2Ph)2-4,1,6-
closo-PtC2B10H12 (XIX).17 Focussing on these platinum systems
has the benefit of benchmarking the approach adopted here
against earlier studies of slipping in the icosahedral species.5 In the
calculations, species XVII, XVIII, III and XIX were represented
by simplified models C, D, E and F respectively, in which all
phosphine ligands were replaced by PH3 and all exopolyhedral
C-substituents were replaced by H (see Fig. 7 for line diagrams
of all the model compounds A–F). As found previously17 the
calculations reproduce the experimental structures well, both in
terms of the orientations of the {Pt(PH3)2} fragments relative to
the open face of the carborane cage and the slipping parameters
(see Table 3 for the latter; full computed geometries are supplied
in the ESI†).
(i) 12-vertex compounds
XVII5
Ca
XVIII6
Da
CCDC
Pt3–C1
Pt3–C2
Pt3–B4
Pt3–B7
Pt3–B8
Pt3–P1
Pt3–P2
D
EPTBOR10
2.530(7)
2.613(7)
2.283(8)
2.277(8)
2.264(8)
2.2759(18)
2.2843(18)
0.411
CCDC
Pt2–C1c
Pt2–C7
Pt2–B6
Pt2–B11
Pt2–B3
Pt2–P1d
Pt2–P2
D
CMPBPT10
2.442(7)
2.452(8)
2.261(8)
2.255(9)
2.270(9)
2.303(2)
2.249(2)
0.141
2.794
2.465
b
b
2.240
2.283
b
b
2.212
2.253
2.381
2.342
0.081
0
2.379
b
0.699
90
e
e
c
75.9
c
10.1
(ii) 13-vertex compounds
III9
Ef
XIX17
Ff
CCDC
Pt4–C1
Pt4–C2
Pt4–B3
Pt4–B6
Pt4–B7
Pt4–B10
Pt4–P1g
Pt4–P2
D
GAQHUC
2.381(8)
2.626(8)
2.322(8)
2.301(7)
2.305(7)
2.265(7)
2.3046(18)
2.3001(17)
0.080
CCDC
Pt2–C1
Pt2–B2
Pt2–B3
Pt2–C6
Pt2–B7
Pt4–B10
Pt2–P1h
Pt2–P2
D
HEYZOB
2.1652(12)
2.4438(15)
2.3961(14)
2.8131(13)
2.2631(14)
2.3692(14)
2.2710(3)
2.3129(4)
0.518
2.396
2.855
2.299
2.292
2.279
2.236
2.383
2.398
0.195
68.2
2.153
2.439
2.442
2.894
2.230
2.412
2.346
2.420
0.583
141.3
i
i
c
61.1
c
148.7
a Structure optimised in Cs symmetry. b Equivalent to previous distance by
symmetry. c Molecule renumbered relative to that in reference 6. d P1 lies
over B3. e Conformation defined as dihedral angle between PtP2 and PtB3
planes, where the three B atoms in the latter are those that lie in the cage
mirror plane. f Structure optimised in C1 symmetry. g P1 lies over B6. h P1
lies over B7–B10. i Conformation defined as dihedral angle between PtP2
and C1B10B11 planes, where 0 < c < 90 represents, in projection, one
phosphine ligand lying in the B3 quadrant and 90 < c < 180 represents
one phosphine ligand lying in the B7 quadrant.
the analysis and so for this reason the geometries of C and D (and
E, see below) were recomputed in Cs symmetry with the ADF code.
Importantly, this did not significantly affect the extent of slipping
compared to the data in Table 3 where no symmetry constraint
was applied.
Fig. 7 Line diagrams and numbering of computational models A–F.
The origins of the slipping distortions in C–F were investigated
In the following we will consider how the steric and orbital
2+
interaction energy terms vary as the {Pt(PH3)2} fragment is
2-
moved across the open face of the {C2Bn} fragment. The
2+
by considering the interaction of the {Pt(PH3)2} fragment with
approach adopted is shown in Fig. 8 for the “carbons adjacent”
2-
the appropriate nido-{C2Bn} cage (n = 9, 10). In the analysis
2+
icosahedral model C. Initially, the Pt atom of the {Pt(PH3)2}
we have made use of the energy decomposition scheme available
within the Amsterdam Density Functional (ADF) code.19 In
this approach the interaction between two fragments can be
broken up into “steric” and “orbital interaction” energy terms.
The steric interaction is overall destabilising and is composed
of the electrostatic interaction derived from the different charge
distributions associated with each fragment, as well as a Pauli
repulsion term due to interaction of occupied orbitals in each
fragment. The orbital interaction arises from the overlap of
occupied orbitals on one fragment with unoccupied orbitals of
the other and is therefore stabilising. Where appropriate, this
term can be further factored into contributions arising within
different orbital symmetries. Symmetry therefore greatly facilitates
fragment is placed directly above the centroid of the lower {B5}
belt (D = 0) and then displaced, either toward (-D) or away
Fig. 8 Definition of slipping in the model compound C.
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Fig. 9 Frontier orbital interactions in C and D.
(+D) from the carbon atoms, along the vector perpendicular to
˚
interactions [plot (b), in green] which minimise at D ca. +0.2 A.
Plot (c) shows that the stabilising a¢¢ orbital interaction (in blue) is
the more significant orbital interaction, it being more stabilising at
higher D; the a¢ interaction (in red) does, however, also contribute
to the positive slip. Thus, although the a¢¢ orbital interaction is
the most important single contribution to the positive slipping
(as revealed by the earlier EHMO analysis5) the present approach
highlights the role played by other factors, especially the steric
interaction, in controlling the detailed extent of slipping.
this Pt-centroid axis which passes through the position of the
2+
metal atom in the {Pt(PH3)2} fragment in the fully-optimised
geometry. In all cases except F (see below) this analysis could be
performed such that Cs symmetry was maintained throughout. At
each point thus generated the steric and orbital interaction terms
2+
were calculated without any relaxation of either the {Pt(PH3)2}
or {C2Bn}2- fragments. Although this approach will tend therefore
to exaggerate the various contributions to the interaction energy,
the trends within these terms should be secure.
For model species D the total energy is dominated by the
steric interaction term with the relevant two plots being nearly
superimposable. In contrast, the orbital interaction is only weakly
dependent on D and this arises from counteracting trends in the
a¢ and a¢¢ contributions. This weak dependence of the orbital
interaction on D is again consistent with the EHMO study.5 What
emerges in the present study is the far greater importance of the
steric interaction term in determining the extent of slipping in
the “carbons apart” 12-vertex system, a feature that will also be
prominent in rationalising the structures of the 13-vertex systems.
Results of the energy decomposition analysis for the 13-vertex
model systems E and F are shown in Fig. 11 and some further
comment is required on the models used in these cases. Both E
and F exhibit C1 structures in their fully optimised forms. For E,
in order to facilitate the analysis, a henicosahedral Cs structure was
adopted which corresponds to a transition state that interconverts
two equivalent docosahedral minima. This Cs structure is only
7.3 kcal mol-1 above the C1 minimum and allows Cs symmetry
2+
Previously, the orientation and slipping of the {Pt(PR3)2}
fragment in XVII/C have been rationalised in terms of preferential
frontier molecular orbital interactions (see Fig. 9ꢀ). Thus strong
2+
overlap of the {Pt(PR3)2} a¢¢ LUMO with the HOMO of
2-
the C2B9H11 cage dictates a perpendicular orientation of the
2+
{Pt(PR3)2} moiety with respect to the mirror plane of the cage.
Positive slipping towards a position above B8 arises via maximising
2+
bonding overlap between the {Pt(PR3)2} LUMO+1 and the a¢
HOMO-1 of the {C2B9H11}2- fragment which is strongly localised
on the B atoms of the open face (especially B8). For the carbons
apart isomer, XVIII/D, the a¢¢ HOMO–LUMO interaction again
2+
controls {Pt(PH3)2} fragment orientation which in this case lies
2-
in the cage mirror plane. The a¢ HOMO-1 of the {C2B9H11}
fragment now displays little localisation and this, coupled to the
relatively even distribution of the {C2B9H11}2- HOMO means that
only a minor slipping is seen.
The results of the energy decomposition analyses for these 12-
vertex systems are shown in Fig. 10, with C on the left hand side
and D on the right. For C the total interaction energy shown in
2+
to be maintained upon displacement of {Pt(PH3)2} to D. Test
calculations on the C1 form indicate that the outcomes of the
analysis are not significantly affected by this simplification (see
ESI†). For F no convenient close-lying Cs structure exists and so
the analysis was performed on the fully optimised C1 form.
As shown in Fig. 11, for E (left hand side) the destabilising
steric interaction is minimised around D = 0.0 while the orbital
interaction terms are actually least stabilising at that point. Dis-
placement in either direction therefore enhances the overall orbital
˚
plot (a) finds a minimum value at D ª +0.7 A and appears to
be a compromise between the orbital interaction term [plot (b),
˚
in purple] which is most stabilising at D ca. +1.0 A and steric
2-
ꢀ The fragmentation of C employed here, into doubly charged {C2B9H11}
and {Pt(PH3)2} fragments, differs from that used previously,5 where
2+
neutral {C2B9H11} and {Pt(PH3)2} fragments were used.
2418 | Dalton Trans., 2010, 39, 2412–2422
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Fig. 10 Energy decomposition analyses for C (left) and D (right). Plots are (a) total interaction energy, (b) steric (green) and orbital (purple) interaction
energy terms and (c) a¢ (red) and a¢¢ (blue) orbital interaction terms vs. D.
interaction, however, this does not outweigh the destabilisation
species 1,2-m-{C6H4(CH2)2}-4,1,2-closo-SnC2B10H10. In the solid
arising from the steric interaction. The net result is that only a
small negative slipping occurs. Orbital interactions are therefore
less important in determining D in this case and for this reason
the contributions from a¢ and a¢¢ symmetry are relegated to the
ESI.† For F the somewhat larger positive slipping is again seen
to result primarily from the steric interaction term that minimises
state compound 1 has a docosahedral structure, whilst 2–5
are essentially henicosahedral. A method of quantifying the
“percentage docosahedral character” of a closo-13-vertex cluster
is described. The “carbons adjacent” compounds 1–5 are all
significantly less slipped than analogous “carbons apart” 4,1,6-
SnC2B10 species, an apparently surprising result in the context
of earlier work on “carbons adjacent” and “carbons apart”
icosahedral platinacarboranes. However, a computational study
of “carbons adjacent” and “carbons apart” 12- and 13-vertex
platinacarboranes reveals that only in one case, that of the
“carbons adjacent” 12-vertex metallacarborane, is the degree of
slipping determined by orbital effects. For all the other systems
studied (12-vertex “carbons apart” and both “carbons apart”
and “carbons adjacent” 13-vertex species) orbital effects are less
˚
around D ca. +0.5 A. This is only slightly perturbed by the orbital
˚
interaction term, resulting in an overall slip of D ca. +0.6 A.
Conclusions
The ligand-free 4,1,2-SnC2B10 compound 1 and its bipy, o-
phen and Ph2bipy adducts 2–4 have been prepared and fully
characterised, together with the bipy adduct 5 of the known
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Fig. 11 Energy decomposition analyses for E (left) and F (right). Plots are (a) total interaction energy, (b) steric (green) and orbital (purple) interaction
energy terms vs. D.
significant and the degree of slipping reflects the dominant role
played by steric interactions.
variations thereof. All other reagents and solvents were supplied
commercially.
1,2-l-(CH2)3-4,1,2-closo-SnC2B10H10 (1). A solution of 1,2-m-
(CH2)3-1,2-closo-C2B10H10 (150 mg, 0.81 mmol) in dry, degassed,
THF (20 mL) was stirred with sodium pieces (130 mg, 5.7 mmol)
and naphthalene (ca. 10 mg) at room temperature for 48 h. The
resulting dark-green solution was transferred via cannula to a dry,
degassed, frozen (-196 ◦C) solution of SnCl2 (153 mg, 0.81 mmol)
in◦THF (10 mL), and the reagents then allowed to warm to
0 C with stirring. The crude, dark brown reaction mixture was
evaporated to dryness and then suspended in CH2Cl2 (40 mL).
The mixture was filtered and all volatiles were removed in vacuo,
yielding a white solid (60 mg, 25%). C5H16B10Sn requires C 19.8, H
Experimental
Synthesis
Experiments were performed under dry, oxygen-free N2, using
standard Schlenk techniques, although subsequent manipulations
were sometimes performed in the open laboratory. All solvents
were freshly distilled from the appropriate drying agents under
nitrogen immediately before use [CH2Cl2; CaH2: THF, toluene
˚
and 40–60 petroleum ether; sodium wire] or were stored over 4 A
molecular sieves and were degassed (3 ¥ freeze–pump–thaw cycles)
before use. IR spectra were recorded from CH2Cl2 solutions on a
Perkin-Elmer Spectrum RX FT spectrophotometer. NMR spectra
at 400.1 MHz (1H) or 128.4 MHz (11B) were recorded on a Bruker
DPX-400 spectrometer from CD2Cl2 solutions at room tempera-
ture. EI mass spectrometry was carried out using a Kratos Concept
mass spectrometer. Elemental analyses were determined by the
departmental service (compound 1 only; for 2–5 only sufficient
material was obtained for NMR and crystallographic studies).
1,2-m-(CH2)3-1,2-closo-C2B10H1020 and 1,2-m-{C6H4(CH2)2}-4,1,2-
1
5.82. Found C 19.9, H 5.44%. IR, nmax 2547 cm-1 (B–H). 11B{ H}
NMR, d 7.73 (2B), 6.45 (4B), 4.12 (1B), 1.06 (1B), -0.27 (2B). 1H
NMR, d 3.20–3.10 (m, 2H, (CH2)3), 2.85-2.75 (m, 2H, (CH2)3),
2.05–1.90 (m, 2H, (CH2)3). MS: m/z 302 (M+), 119 (M-C5H16B10).
Recrystallisation by diffusion of a CH2Cl2 solution and 40–60
petroleum ether at -30 ◦C afforded pale-yellow diffraction-quality
block crystals of 1.
1,2-l-(CH2)3-4-(bipy)-4,1,2-closo-SnC2B10H10 (2). A solution
of 1 (10 mg, 0.03 mmol) in dry, degassed toluene (5 mL) was added
8
closo-SnC2B10H10 were prepared by literature methods or slight
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to a dry, degassed toluene solution (3 mL) of 2,2¢-bipyridine (6 mg,
0.04 mmol), and the resulting yellow suspension stirred for 24 h.
On settling, the toluene was removed using a gas-tight syringe,
leaving a yellow solid which was washed with petroleum ether (2 ¥
10 mL) and dried in vacuo to afford 2 as a yellow solid (10 mg,
1,2-l-{C6H4(CH2)2}-4-(bipy)-4,1,2-closo-SnC2B10H10 (5).
A
solution of 1,2-m-{C6H4(CH2)2}-4,1,2-closo-SnC2B10H10 (70 mg,
0.192 mmol) in dry, degassed toluene (10 mL) was added to a
dry, degassed toluene solution (10 mL) of 2,2¢-bipyridine (90 mg,
0.575 mmol), and the resulting yellow suspension stirred for 24 h.
After settling, the toluene was removed using a gas-tight syringe,
leaving a yellow solid, subsequently washed with petroleum ether
(2 ¥ 10 mL) and dried in vacuo to afford 5 as a yellow solid
1
73%). IR, nmax 2518 cm-1 (B–H). 11B{ H} NMR, d 3.55 (3B), 2.30
(2B), -4.05 (2B), -5.16 (2B), -10.78 (1B). 1H NMR, d 8.99 (d, 2H,
bipy), 8.22 (d, 2H, bipy), 8.13 (d of d, 2H, bipy), 7.69 (d of d, 2H,
bipy), 3.05–2.95 (m, 2H, (CH2)3), 2.77–2.68 (m, 2H, (CH2)3), 1.99–
1.90 (m, 1H, (CH2)3), 1.78–1.66 (m, 1H, (CH2)3). Small crystals
were grown by vapour diffusion of 40–60 petroleum ether and a
CH2Cl2 solution of 2 at 5 ◦C.
1
(61 mg, 61%). IR, CH2Cl2, nmax 2521 cm-1 (B–H). 11B{ H} NMR,
d 7.19 (br, 2B), 4,16 (br, 2B), 2.92 (br, 2B), -3.65 (br, 1B), -5.62
1
(br, 1B), -10.48 (br, 2B). H NMR, d 8.87 (d, 2H, bipy), 8.24
(d, 2H, bipy), 8.04 (d of d, 2H, bipy), 7.60 (d of d, 2H, bipy),
7.27–7.10 (m, 4H, C6H4(CH2)2), 3.98 (d, 2H, C6H4(CH2)2), 3.82
(d, 2H, C6H4(CH2)2). Diffraction-quality crystals were grown by
slow evaporation of a CH2Cl2 solution of 5 at room temperature.
1,2-l-(CH2)3-4-(o-phen)-4,1,2-closo-SnC2B10H10 (3). Likewise,
a solution of 1 (30 mg, 0.10 mmol) in dry, degassed toluene (10 mL)
was stirred with a dry, degassed toluene solution (10 mL) of 1,10-
Crystallography
phenanthroline (20 mg, 0.11 mmol) to afford 31 mg (64%) of 3. IR,
1
n
max 2540 cm-1 (B–H). 11B{ H} NMR, d 3.73 (3B), 2.36 (2B), -4.25
Intensity data from 1 and 3–5 were collected from single crystals
on a Bruker X8 APEX2 diffractometer using Mo-Ka X-radiation,
with crystals mounted in inert oil on a cryoloop and cooled
to 100 K by an Oxford Cryosystems Cryostream. Data from
compound 2, which affords only very small crystals were collected
by the EPSRC National Crystallographic Service at Southampton
using a Bruker-Nonius APEX II diffractometer equipped with
a Bruker-Nonius FR591 rotating anode and confocal mirror
monochromator with Mo-Ka X-radiation at 120 K. The struc-
tures were solved by direct methods and refined by full-matrix
least-squares. All non-H atoms were refined with anisotropic
displacement parameters, although it was necessary to restrain
the anisotropy, in 2, of four B atoms and four C atoms (two
methylene, one solvent and one bipy) and, in 4, of three B atoms,
one cage C and one bipy C atom, using the ISOR command.21
(2B), -5.07 (2B), -10.69 (1B). 1H NMR, d 9.34 (d, 2H, phen), 8.59
(d, 2H, phen), 8.05 (s, 2H, phen), 8.00 (d of d, 2H, phen), 3.15–
3.05 (m, 2H, (CH2)3), 2.82–2.72 (m, 2H, (CH2)3), 2.05–1.95 (m, 1H,
(CH2)3), 1.80–1.70 (m, 1H, (CH2)3). Crystals by solvent diffusion
of 40–60 petroleum ether and a CH2Cl2 solution of 3 at 5 ◦C.
1,2-l-(CH2)3-4-(Ph2bipy)-4,1,2-closo-SnC2B10H10 (4). In the
same way, a solution of 1 (10 mg, 0.03 mmol) in dry, degassed
toluene (10 mL) was allowed to react with a dry, degassed
toluene solution (10 mL) of 4,4¢-diphenyl-2,2¢-bipyridine (12 mg,
0.04 mmol), yielding 15 mg (82%) of 4. IR, nmax 2522 cm-1 (B–H).
1
11B{ H} NMR, d 3.70 (3B), 2.41 (2B), -4.13 (4B), -10.79 (1B). 1H
NMR, d 9.03 (d, 2H, Ph2bipy), 8.45 (2, 2H, Ph2bipy), 7.91 (d, 2H,
Ph2bipy), 7.82–7.73 (m, 4H, Ph2bipy), 7.64–7.55 (m, 6H, Ph2bipy),
3.05–2.99 (m, 2H, (CH2)3), 2.80–2.70 (m, 2H, (CH2)3), 2.01–1.920
(m, 1H, (CH2)3), 1.78–1.69 (m, 1H, (CH2)3). The product was
crystallised by solvent diffusion of 40–60 petroleum ether and a
CH2Cl2 solution of 4 at 5 ◦C.
1
In compound 2 there is molecule of CH2Cl2 per molecule of
stannacarborane, and in 54the solvent was modelled as molecule
1
3
of hexane per molecule of stannacarborane. The crystal of 1 was
treated as a two-component twin, indexed using CELL_NOW,22
Table 4 Crystallographic data for compounds 1–5
1
2
3
4
5
1
4
1
3
Formula
M
C5H16B10Sn
302.97
C15H24B10N2Sn· CH2Cl2
C17H24B10N2Sn
483.17
C27H32B10N2Sn
611.34
C20H26B10N2Sn· C6H14
480.38
549.94
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/n
Monoclinic
P21/c
Monoclinic
P21/n
˚
a/A
11.520(3)
7.4934(17)
14.040(3)
92.078(10)
1211.2(5)
4
584
1.661
2.062
27.53
10.1522(8)
18.4533(17)
22.9010(19)
93.834(5)
4280.7(6)
8
1908
1.491
1.261
27.59
8.2556(14)
23.479(4)
10.8500(15)
98.566(9)
2079.6(6)
4
960
1.543
1.236
34.33
7.58370(10)
37.9500(8)
19.5831(4)
96.6860(10)
5597.71(18)
8
2464
1.451
0.935
23.61
11.8737(7)
14.0561(8)
15.2938
109.310(3)
2408.9(2)
4
1107
1.516
1.077
28.62
˚
b/A
˚
c/A
b (◦)
U/A
Z
3
˚
F(000)/e
Dc/Mg m-3
m(Mo-Ka)/mm-1
qmax (◦)
Data measured
Unique data, n
Rint
31929
3577
0.0643
26476
9313
0.1057
67393
8582
0.1006
77776
8186
0.0712
54270
6141
0.0690
R, wR2 (obs. data)
S
0.0251, 0.0792
1.150
164
0.1885, 0.3476
2.375
533
0.0392, 0.0788
0.967
301
0.0376, 0.0695
1.076
721
0.0396, 0.0889
0.932
346
Variables
-3
˚
E
max, Emin/e A
0.733, -0.637
1.931, -1.824
1.307, -1.411
0.986, -0.771
1.175, -1.100
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 2412–2422 | 2421
©

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scaled and absorption corrected using TWINABS23 and refined
using HKLF5 which includes both components. Data from 2 were
also treated as a two-component twin but refined using the twin
law -1 0 0 0 -1.0 0 1.65 0 1 and HKLF4 data. This proved to be
the best model and data set for these crystals arising from many
attempts including the use of synchrotron data. Data from 3–5 was
corrected for absorption using SADABS.24 For 3, 5 and some H
atoms in 1, cage-bound H atoms were located in difference Fourier
maps and freely refined. Cage H atoms of 4 and the remaining cage
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and F. G. A. Stone, J. Am. Chem. Soc., 2007, 129, 3302.
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˚
H atoms in 1 were constrained to B–H 1.10 A. In all cases, H atom
thermal parameters were set to 1.2 ¥ Ueq of the attached B or C
atom. Table 4 contains further experimental details.
Calculations
All geometries were optimised without constraints using Gaussian
03, Revision C.0218 employing the BP86 functional.25 6-31G**
basis sets were used for B, C, H and N atoms26 whilst for P, Pt and
Sn the Stuttgart relativistic ECP27 was employed with additional
d-polarization functions for P and Sn. Local minima were con-
firmed as such through analytical frequency calculations. Energy
decomposition analyses were performed with ADF2009.01,19
applying symmetry constraints, if appropriate, as described in the
text. The BP86 function was employed and ZORA/TZ2P basis
sets were used for all atoms. Geometry measurements were made
using Mercury.28
Acknowledgements
We thank the EPSRC for funding (PDA supported by DTA stu-
dentship; DE and DMcK supported by project EP/E02971X/1)
and the EPSRC National Crystallographic Service at the Univer-
sity of Southampton for data from compound 2.
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2422 | Dalton Trans., 2010, 39, 2412–2422
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The Royal Society of Chemistry 2010
©