Platination of [3-X-7,8-Ph2-7,8-nido-C2 B9H8]2- (X=Et, F)Synthesis and characterisation of slipped and 1,2→1,7 isomerised products

Article abstract of DOI:10.1016/S0022-328X(03)00406-6

The reaction of the labelled carborane ligand [3-Et-7, 8-Ph₂-7,8- nido -C₂B₉H₈] ^2- with a source of {Pt(PMe₂Ph)₂} ²⁺ affords non-isomerised 1,2-Ph₂-3, 3-(PMe₂Ph) ₂-6-Et-3,1,2-closo-PtC₂ B₉H₈ (1). The analogous reaction between [3-F-7, 8-Ph₂-7,8- nido -C₂B₉H₈] ^2- and {Pt(PMe₂Ph)₂}²⁺ yields 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-F-2,1, 8- closo -PtC₂B₉H₈ (3). Compound 1 has a heavily slipped structure (Δ 0.72 A?), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the reaction is evident from the fact that it reverts to isomerised 1,8-Ph₂-2,2-(PMe₂Ph) ₂-4-Et-2,1,8-closo-PtC₂B₉H₈ (2) slowly at room temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2 and 3 may be explained most simply by the rotation of a CB₂ face of an intermediate based on the structure of 1. Compounds 1-3 were characterised by a combination of spectroscopic and crystallographic techniques.

Full text of DOI:10.1016/S0022-328X(03)00406-6

Journal of Organometallic Chemistry 680 (2003) 286Á293
/
www.elsevier.com/locate/jorganchem
Platination of [3-X-7,8-Ph2-7,8-nido-C2B9H8]2ꢀ (Xꢁ
Synthesis and characterisation of slipped and 1,201,7 isomerised
productsꢀ
/
Et, F)
/
Susan Robertson, David Ellis, Georgina M. Rosair, Alan J. Welch *
Department of Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, UK
Received 25 February 2003; received in revised form 17 April 2003; accepted 17 April 2003
Dedicated to Professor M. Frederick Hawthorne on the occasion of his 75th birthday in recognition of his outstanding achievements in carborane
and metallacarborane chemistry
Abstract
The reaction of the labelled carborane ligand [3-Et-7,8-Ph2-7,8-nido-C2B9H8]2ꢀ with a source of {Pt(PMe2Ph)2}2ꢂ affords non-
isomerised 1,2-Ph2-3,3-(PMe2Ph)2-6-Et-3,1,2-closo-PtC2B9H8 (1). The analogous reaction between [3-F-7,8-Ph2-7,8-nido-
C2B9H8]2ꢀ and {Pt(PMe2Ph)2}2ꢂ yields 1,8-Ph2-2,2-(PMe2Ph)2-4-F-2,1,8-closo-PtC2B9H8 (3). Compound 1 has a heavily slipped
˚
structure (D 0.72 A), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the
reaction is evident from the fact that it reverts to isomerised 1,8-Ph2-2,2-(PMe2Ph)2-4-Et-2,1,8-closo-PtC2B9H8 (2) slowly at room
temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2
and 3 may be explained most simply by the rotation of a CB2 face of an intermediate based on the structure of 1. Compounds 1Á3
/
were characterised by a combination of spectroscopic and crystallographic techniques.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Carborane; Metallacarborane; Isomerisation; Synthesis; Spectroscopy; Crystallographic study; Vertex labelling
1. Introduction
models for carboranes but which offer considerably
more scope for electronic and steric modification. We
have shown [5] that preparing a metallacarborane that is
deliberately overcrowded can result in C-atom isomer-
We are engaged in a programme of low-temperature
isomerisations of metallacarboranes as models for the
isomerisation of carboranes. Carborane isomerisation
has been known for 40 years [1]. The mechanism of
carborane isomerisation, however, remains poorly de-
fined experimentally. In large measure, this is because
such isomerisations only occur at high temperatures,
meaning that vertex-labelling studies are unreliable [2].
However, Hawthorne’s discovery of metallacarboranes
[3], in which the {BH} fragment of a carborane is
replaced by a metal fragment with which it is isolobal
[4], afforded a new class of compounds that are good
isation which mimics the 1,20
/
1,7 isomerisation of
C2B10H12, either spontaneously or on mild heating.
This, then, reawakens interest in vertex-labelling studies
as mechanistic probes [6], and offers the opportunity to
establish an experimental mapping of (hetero)carborane
isomerisation to complement the numerous theoretical
ideas advanced [7].
Following the synthesis of [3-Et-7,8-Ph2-7,8-nido-
C2B9H8]2ꢀ [8], we showed [9] that its reaction with
Ni(dppe)Cl2 afforded not only the expected 1,20
atom isomerised product, but also an unexpected 1,20
1,7 C-atom isomerised species, the latter having a
bearing on the 1,201,7 isomerisation of C2B10H12.
/1,2 C-
/
/
ꢀ Steric effects in heteroboranes. Part 29. For part 28 see Ref. [9].
Using the labelled B vertex as a tag, we noted that the
architecture of the 1,7 isomerised product most simply
fitted with an isomerisation mechanism in which a CB2
* Corresponding author. Tel.: ꢂ
451-3180.
E-mail address: a.j.welch@hw.ac.uk (A.J. Welch).
/
44-131-451-3217; fax: ꢂ44-131-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00406-6

S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á
/293
287
face of the presumed intermediate underwent a triangle
face rotation (tfr). Since net 1,201,7 C-atom isomerisa-
CH2CH3), 0.58 (app t, 2H, CH2CH3). 11BÁ
d (ppm): 21.44 (1B), 4.64 (2B), ꢀ
15.95 (2B). 31PÁ{1H}-NMR d (ppm): ꢀ
1JPtꢀP
3064 Hz).
/
{1H}-NMR
/
/
2.78 (2B), ꢀ
/
4.07 (2B),
tion in metallacarboranes tends to follow from platina-
tion [5] of a crowded nido carborane rather than
nickelation [10], we were naturally interested in the
reaction of [3-Et-7,8-Ph2-7,8-nido-C2B9H8]2ꢀ or its
analogues with a source of {Pt(PR3)2}2ꢂ. This paper
reports the results of such reactions.
ꢀ
/
/
/
8.28 (br s, 2P,
ꢁ
/
2.1.2. Synthesis of 1,8-Ph2-2,2-(PMe2Ph)2-4-Et-2,1,8-
closo-PtC2B9H8 (2)
Compound 1 slowly converts to a new species (2) on
standing in solution at room temperature (close inspec-
tion of relatively uncluttered NMR spectra, e.g. 31P,
shows traces of 2 after several hours). Sufficient
amounts of 2 for characterisation were afforded by
heating 1 to reflux in THF. Although this conversion
was never complete, and orange 1 and yellow 2 could
not be separated by chromatography, 1 crystallises first
and so could be removed.
2. Experimental
2.1. Synthetic and spectroscopic studies
Experiments were performed under dry, oxygen-free,
N2 using standard Schlenk techniques, with some
subsequent manipulation in the open laboratory. Sol-
vents were freshly distilled over CaH2 (CH2Cl2) or Na
Compound 2: Anal. Found: C, 48.8; H, 5.80. Calc. for
C32H45B9P2Pt: C, 49.0; H 5.79%. IR n (cmꢀ1): 2556
1
wire (THF, Et2O, 40Á
/
60 petroleum ether) or stored over
(br). H-NMR d (ppm): 7.4Á
/
6.7 (m, 20H, C6H5), 1.7Á
0.4 (br unresolved m, 5H,
{1H}-NMR d (ppm): ꢀ
0.95 (2B),
10.19 (1B), ꢀ13.06 (1B), ꢀ15.95 (1B),
22.41 (1B). 31PÁ{1H}-NMR d (ppm): ꢀ
14.69 (br
14.15 (br un-
3290 Hz), from highest fre-
21 Hz.
/
˚
4 A molecular sieves (CDCl3). NMR spectra at 200.13
(1H), 128.38 (11B), 161.98 MHz (31P) or 376.50 MHz
(19F) were recorded on Bruker AC 200 or DPX 400
spectrometers from CDCl3 solutions at ambient tem-
perature, chemical shifts being recorded relative to
1.3 (m, 12H, PCH3), 0.5Á
CH2CH3). 11BÁ
5.53 (3B), ꢀ
/
/
/
ꢀ
/
/
/
/
ꢀ
/
/
/
1
unresolved d, 1P, JPtꢀP
ꢁ
/
3319 Hz), ꢀ
/
SiMe4 (1H), BF3×
(19F). IR spectra were recorded from CH2Cl2 solutions
on a PerkinÁElmer Spectrum RX FTIR spectrophot-
/
OEt2 (11B), H3PO4 (31P) or CFCl3
resolved d, 1P, JPtꢀP
ꢁ
/
1
2
quency satellite JPꢀP
:
/
/
ometer. Elemental analyses were determined by the
departmental service. The starting [HNMe3][3-Et-7,8-
Ph2-7,8-nido-C2B9H9] [8], [HNMe3][3-F-7,8-Ph2-7,8-
nido-C2B9H9] [8] and cis-Pt(PMe2Ph)2Cl2 [11] were
prepared by literature methods or slight variants
thereof. All other reagents were used as supplied.
2.1.3. Synthesis of 1,8-Ph2-2,2-(PMe2Ph)2-4-F-2,1,8-
closo-PtC2B9H8 (3)
In a procedure similar to that described in Section
2.1.1, [HNMe3][3-F-7,8-Ph2-7,8-nido-C2B9H9] (0.106 g,
0.29 mmol) was converted to its Liꢂ salt and treated
with cis-Pt(PMe2Ph)2Cl2 (0.158 g, 0.29 mmol). Prepara-
tive TLC (CH2Cl2/40Á60 pet. ether, 1:1) afforded a
/
2.1.1. Synthesis of 1,2-Ph2-3,3-(PMe2Ph)2-6-Et-3,1,2-
closo-PtC2B9H8 (1)
[HNMe3][3-Et-7,8-Ph2-7,8-nido-C2B9H9] (0.098 g,
single mobile band, compound 3, recovered as a yellow
solid.
Compound 3: Yield 0.035 g, 16%. Anal. Found: C,
0.26 mmol) in Et2O (20 ml) was cooled to 0 8C and n-
44.5; H, 5.11. Calc. for C30H38B9FP2Pt×
44.7; H 4.80%. IR n (cmꢀ1): 2562 (br). 1H-NMR d
(ppm): 7.5Á7.0 (m, 20H, C6H5), 1.7Á1.45 (m, 12H,
PCH3). 11BÁ{1H}-NMR d (ppm): ꢀ
0.42 (unresolved d,
45 Hz, B4), ꢀ2.49 (2B), ꢀ6.87 (1B),
/
0.6CH2Cl2: C,
BuLi in hexanes (0.23 ml of 2.5 M solutionꢀ0.58
/
mmol) added. The solution was allowed to warm to
room temperature, and then heated to reflux for 1 h,
affording the salt Li2[3-Et-7,8-Ph2-7,8-nido-C2B9H8].
Solvent was removed from this product, which was
/
/
/
/
1
1B, JFꢀB
:
/
/
/
ꢀ
/
14.35 (4B), ꢀ
/
23.71 (1B). 31PÁ{1H}-NMR d (ppm):
/
1
then redissolved in THF (20 ml) and frozen to ꢀ
/
196 8C.
ꢀ
/
15.06 (s, 2P, JPtꢀP
ꢁ
/
3259 Hz). 19F-NMR d (ppm):
1
Solid cis-Pt(PMe2Ph)2Cl2 (0.143 g, 0.26 mmol) was
added, and the mixture allowed to warm to room
temperature under constant stirring, affording a yellow
solution. The solvent was exchanged for CH2Cl2 and the
product filtered through Celite†. Preparative TLC on
ꢀ
/
209.5 (partially resolved q, JFꢀB
:39 Hz).
/
2.2. Crystallographic studies
Single, diffraction-quality, crystals were grown by
diffusion of a CH2Cl2 solution of compounds 1, 2 and 3,
silica using CH2Cl2/40Á/60 pet. ether as eluent (60:40)
afforded one mobile band, recovered as an oily yellow/
orange solid.
Compound 1: Yield 0.040 g, 20%. Anal. Found: C,
and a 5-fold excess of 40Á60 petroleum ether at room
/
temperature. Diffraction data were measured at 160(2)
K on a Bruker AXS P4 diffractometer equipped with an
Oxford Cryosystems Cryostream cooler. One asym-
metric fraction of intensity data was collected [12] to
48.0; H, 5.73. Calc. for C32H45B9P2Pt: C, 49.0; H 5.79%.
IR n (cmꢀ1): 2554 (br). H-NMR d (ppm): 7.6Á
1
/7.0 (m,
20H, C6H5), 1.5Á/1.1 (m, 12H, PCH3), 0.70 (t, 3H,
umax
ꢁ
/
258 with graphite-monochromated MoÁKa ra-
/

288
S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á293
/
˚
0.71069 A) using v-scans. Standard reflec-
diation (lꢁ
/
Et group, the last a consequence of the adjacent
carborane cage [8,9].
tions were re-measured every 100 data and any crystal
decay corrected. Data were corrected for absorption by
c-scans. All structures were solved [13] by direct and
difference Fourier methods and refined by full-matrix
least-squares against F2, with non-hydrogen atoms
assigned anisotropic displacement parameters. Crystals
of 3 become opaque after several minutes in air by loss
of solvate. Freshly grown crystals contain 134 molecules
The nature of compound 1 was unambiguously
established by a single-crystal diffraction study. Fig. 1
hosts a perspective view of a single molecule and Table 2
lists selected molecular parameters. Compound 1 is a
non-isomerised 6-Et-3,1,2-PtC2B9 platinacarborane in
which the {Pt(PMe2Ph)2} fragment has nonetheless
undergone a significant slippage distortion to relieve
otherwise untenable steric crowding with the cage Ph
groups. The structural confirmation of 1 is important, in
that we have previously assumed [6,14] that the initial
product of platination of a 7,8-Ph2-7.8-nido-C2B9 ligand
was indeed a 3,1,2-PtC2B9 species which then underwent
isomerisation, but this is the first time such an initial
product has been isolated. The {PtP2} unit is slipped [15]
of CH2Cl2 of solvation per molecule of 3, comprising
one ordered molecule and two fractionally (/12 and )
1
4
ordered molecules. For the last two Cꢀ
/
Cl was restrained
1
˚
to 1.70(5) A in the refinement, and for the molecule
4
refinement was isotropic only. H atom positions were
H
calculated and allowed to ride during refinement (Cꢀ
/
˚
˚
˚
distances 0.95 A [phenyl], 0.99 A [methylene] and 0.98 A
˚
ca. 0.72 A away from C1C2, considerably more than the
˚
corresponding distortion, ca. 0.42 A, in 3,3-(PEt3)2-
˚
H distances 1.12 A) with displacement
[methyl], Bꢀ
/
parameters calculated as 1.2, 1.2, 1.5 and 1.2 times the
bound atom Ueq, respectively. The only exception to this
was 2, where H atoms bound to B were allowed to refine
3,1,2-closo-PtC2B9H11 [15], further illustrating that
crowded diphenyl metallacarboranes exhibit enhanced
structural distortions relative to analogues with no Ph
groups attached to the cage C atoms [16]. As a
consequence of this slipping, the Ptꢀ ꢀ ꢀC distances are
positionally although restrained to a Bꢀ/H distance of
˚
1.12(2) A with free thermal refinement. Table 1 lists
details of unit cell data, intensity data collection and
structure refinement.
˚
˚
very extended, 2.857(10) A to C1 and 2.805(10) A to C2,
and are not included in Fig. 1.
The distortion in compound 1 is not restricted to
slipping of the {PtP2} unit. The Ph rings on the cage C
atoms are both twisted from their conformations in [3-
Et-7,8-Ph2-7,8-nido-C2B9H9]ꢀ [8] to accommodate the
steric demands both of the phosphine ligands on Pt and
the Et label on B6. As we have noted, the orientations of
Ph groups on C-adjacent diphenylcarboranes are con-
veniently described by the angle uPh, defined [17] as the
3. Results and discussion
3.1. Synthesis and spectroscopy
The
reaction
between
[3-Et-7,8-Ph2-7,8-nido-
C2B9H8]2ꢀ and cis-Pt(PMe2Ph)2Cl2 in THF affords
the orange compound 1,2-Ph2-3,3-(PMe2Ph)2-6-Et-
3,1,2-closo-PtC2B9H8 (1) in moderate yield (not opti-
mised) following work-up involving preparative TLC.
Compound 1 was initially characterised by microana-
lysis, and IR and multinuclear NMR spectroscopy.
modulus of the average Ccage
ꢀ
/
Ccage
ꢀ
/
CPh CPh torsion
ꢀ
/
angle. In [3-Et-7,8-Ph2-7,8-nido-C2B9H9]ꢀ [8], the Ph
rings are disrotated to uPh values of 12.98 and 24.18 to
accommodate the Et substituent on B6. In 1, the Ph
rings are conrotated to subtend uPh values of 43.68 (ring
on C2) and 64.28 (ring on C1), the latter reflecting the
fact that the Et substituent is angled to lie underneath
C1. These are some of the highest uPh values recorded.
In non-slipped 3,1,2-MC2B9 diphenylmetallacarboranes,
high uPh values frequently result in partially opened,
pseudo-closo structures [18] characterised by C1ꢀ ꢀ ꢀC2
The 11BÁ
broad peaks, 1:2:2:2:2 from high to low frequency. The
chemical shift range, ꢂ22 to ꢀ16 ppm, is consistent
/
{1H}-NMR spectrum of 1 reveals five fairly
/
/
with a formally closo although slipped platinacarborane
[5], and the pattern of integrals suggests that the Cs
symmetry of the ligand precursor has been maintained.
However, the relative broadness of the resonances
meant it was not possible to identify which arose from
the Et-substituted B atom in the 11B-NMR spectrum.
˚
distances in excess of 2.4 A. In 2, however, a pseudo-
closo distortion is obviated by the slipping away of the
The 31PÁ
/
{1H}-NMR spectrum contains only a singlet
3064 Hz), meaning
{PtP2} fragment, and the C1ꢀ
/
C2 distance is short,
1.530(13) A, reminiscent of the CꢀC distance in 7,8-
nido-C2B9 carboranes. In fact, the CꢀC distance in 1 is
actually shorter than that in [3-Et-7,8-Ph2-7,8-nido-
with platinum satellites (1JPtꢀP
ꢁ
/
˚
/
/
either that the P atoms are symmetrically disposed or
that the {PtP2} unit undergoes rotation about the Pt-
cage axis which is rapid on the NMR timescale. In the
1H-NMR spectrum are the expected resonances for
C2B9H9]ꢀ [8] [1.602(3) A, average uPh
ꢁ18.58] and in
/
˚
[7,8-Ph2-7,8-nido-C2B9H10]ꢀ [19] [1.590(5) A, average
˚
˚
uPh
ꢁ
/
7.88 in [HNEt3]ꢂ salt; 1.602(3) A, average uPh
ꢁ
/
C6H5 protons, a multiplet around 1Á1.5 ppm due to
/
19.08 in [C6H5CH2NMe3]ꢂ salt], providing support for
the suggestion [20] that the CꢀC bond strength increases
pairs of prochiral Me groups and 2JPꢀH coupling, and at
lower frequency a triplet and apparent triplet due to the
/

S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á
/293
289
Table 1
Crystallographic data for compounds 1, 2 and 3× CH2Cl2
143
/
/
1
2
3×
/
143
/
CH2Cl2
Formula
Mr
C32H45B9P2Pt
784.00
C32H45B9P2Pt
784.00
C30H40B9FP2Pt× CH2Cl2
/
143
/
922.56
yellow
plate
Colour
Habit
orange
block
yellow
block
Crystal system
Space group
Unit cell dimensions
monoclinic
P21/c
monoclinic
P21/n
monoclinic
P21/n
˚
a (A)
21.060(7)
9.474(3)
17.546(9)
90
9.2589(16)
28.113(9)
13.729(3)
90
12.547(2)
10.7074(19)
30.850(4)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
101.93(4)
90
104.267(12)
90
95.379(14)
90
3
˚
U (A )
3425(2)
4
3463.3(14)
4
1.504
4126.3(11)
4
1.485
Z
Dcalc (Mg mꢀ3
)
1.520
0.421
1560
m(MoÁ
F(0 0 0)
/
Ka) (mmꢀ1
)
0.417
1560
0.373
1822
Crystal size (mm3)
Trans. factors
Data collected
Ind. data, n
Rint
0.72ꢃ
/
0.48ꢃ
0.781
/
0.24
0.58ꢃ
/
0.38ꢃ
0.943
/
0.28
0.42ꢃ
/
0.30ꢃ
0.729
/
0.14
0.215Á
/
0.506Á
/
0.479Á
/
6602
5346
0.0624
397
7549
6069
0.0338
429
9216
7207
0.0429
469
No. variables, p
R, wR2 (all data)
S (all data)
a, b
0.0787, 0.1695
1.040
0.09, 55.35
0.0327, 0.0746
1.049
0.03, 7.06
0.0607, 0.0990
1.037
0.04, 7.33
ꢀ3
˚
Emax, Emin (e A
)
2.804, ꢀ
/
3.081
0.796, ꢀ
/0.883
1.527, ꢀ
/
0.736
Rꢁ
/
SjjFojꢀ
/
jFcjj/SjFoj, wR2ꢁ
/
[S[w(Fo2ꢀFc2)2]/Sw(Fo2)2]1/2, where wꢀ1ꢁ
/
/
[s2(Fo)2ꢂ
/
(aP)2ꢂ
/
bP] and Pꢁ
/
[0.333(Fo)2ꢂ
/
0.667(Fc)2], Sꢁ
/
[S[w(Fo2ꢀ
/
Fc2)2]/(nꢀ
/
p)]1/2, where n is the number of data and p the number of parameters.
2
as uPh, at least until intolerably large uPh values are
reached.
vironments with JPꢀP measured on the highest fre-
quency Pt satellite at ca. 21 Hz. It was not possible to
1
resolve the CH2 and CH3 ethyl resonances in the H-
The fact that compound 1 has accommodated its
significant overcrowding by severe slipping rather than
isomerisation is somewhat surprising [6]. However, in
solution at room temperature, 1 clearly converts to a
new, yellow, species, 2, with very different spectral
characteristics. Sufficient amounts of 2 for complete
characterisation are afforded by heating 1 to reflux in
NMR spectrum measured at 200 MHz, these appearing
as an ill-defined multiplet of overall integral 5 centred
around 0.45 ppm.
A crystallographic study of 2 (Fig. 2 and Table 3)
a
revealed
1,8-Ph2-2,2-(PMe2Ph)2-4-Et-2,1,8-closo-
PtC2B9H8 architecture. The cage has undergone isomer-
isation such that its C atoms are no longer adjacent, but
THF. Although by this method the conversion of 10
/
2
is never quantitative, and 1 and 2 proved impossible to
separate chromatographically, pure 2 could easily be
obtained by fractional crystallisation which removed 1
first.
Compound 2 proved to be the anticipated 1,7 C-atom
isomerised platinacarborane. The 11B-NMR spectrum
shows evidence of asymmetry with resonances in the
ratio 2:3:1:1:1:1 from high to low frequency, the integral
3 resonance including a low-frequency shoulder due to
1B. Again, it was not possible to assign the resonance
due to the Et-bound B atom, except to note that it is
separated by the B3ꢀ
/
B4 connectivity, B4 carrying the Et
label. The Pt atom is bound to a B4C face, but is slipped
˚
by ca. 0.41 A away from C1, affording Ptꢀ
/B distances
˚
between 2.2 and 2.3 A and a Ptꢀ
/
C1 distance of 2.628(4)
˚
A. Thus compound 2 is analogous to the previously
characterised species 1,8-Ph2-2,2-(PMe2Ph)2-2,1,8-closo-
PtC2B9H9 [5,21] which has the same structure save for
the Et label and very similar molecular dimensions [D
˚
˚
0.36 A, Ptꢀ
nickelacarborane
NiC2B9H8 [9] formed as a minor product in the
nickelation of [3-Et-7,8-Ph2-7,8-nido-C2B9H8]2ꢀ
/
C1 2.610(5) A]. It is also related to the
1,8-Ph2-2-dppe-4-Et-2,1,8-closo-
clearly not the lowest frequency one (ꢀ
/
22.4 ppm). The
31PÁ{1H}-NMR spectrum indicates inequivalent P en-
.
/

290
S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á293
/
Table 2
˚
Selected interatomic distances (A) and interbond angles (8) for 1
Bond lengths
Pt(3)ꢀ ꢀ ꢀC(1)
Pt(3)ꢀ ꢀ ꢀC(2)
2.857(10) B(7)ꢀ
2.805(10) B(7)ꢀ
2.269(11) B(8)ꢀ
2.164(12) B(8)ꢀ
2.294(11) B(9)ꢀ
1.530(13) B(9)ꢀ
1.803(15) B(10)ꢀ
1.652(15) B(10)ꢀ
1.730(15) B(11)ꢀ
1.739(14) B(6)ꢀ
1.682(15) C(61)ꢀ
/
B(12)
1.850(17)
1.834(16)
1.765(16)
1.792(18)
1.778(16)
1.773(18)
1.778(16)
1.760(17)
1.771(17)
1.583(16)
1.529(15)
2.281(3)
/
B(8)
Pt(3)ꢀ
/
B(7)
B(8)
B(4)
/
B(9)
Pt(3)ꢀ
Pt(3)ꢀ
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
C(2)ꢀ
C(2)ꢀ
C(2)ꢀ
B(4)ꢀ
B(4)ꢀ
B(4)ꢀ
B(5)ꢀ
B(5)ꢀ
B(5)ꢀ
B(6)ꢀ
B(6)ꢀ
B(7)ꢀ
/
/
B(12)
B(10)
B(12)
/
/
/
C(2)
B(4)
B(5)
B(6)
B(6)
B(11)
B(7)
/
/
/
B(11)
B(12)
B(12)
/
/
/
/
/
/
C(61)
C(62)
/
/
/
1.807(16) Pt(3)ꢀ
1.800(17) Pt(3)ꢀ
1.804(16) P(1)ꢀ
1.771(17) P(1)ꢀ
1.793(17) P(1)ꢀ
1.795(17) P(2)ꢀ
1.780(17) P(2)ꢀ
1.777(17) P(2)ꢀ
1.778(17) C(1)ꢀ
1.811(15) C(2)ꢀ
/P(1)
/B(5)
/
P(2)
2.292(3)
/B(9)
/
C(101)
C(111)
C(112)
C(201)
C(211)
C(212)
1.811(11)
1.823(12)
1.814(10)
1.808(11)
1.806(11)
1.817(11)
1.514(15)
1.511(14)
/B(8)
/
/B(6)
/
/B(10)
/
/B(9)
/
/
B(10)
B(11)
B(11)
/
/
/
C(11)
C(21)
/
/
Bond angles
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(21)ꢀC(2)ꢀ
C(21)ꢀC(2)ꢀ
C(21)ꢀC(2)ꢀ
C(21)ꢀC(2)ꢀ
C(61)ꢀB(6)ꢀ
C(61)ꢀB(6)ꢀ
C(61)ꢀB(6)ꢀ
C(61)ꢀB(6)ꢀ
C(61)ꢀB(6)ꢀ
B(6)ꢀC(61)ꢀ
/
/
C(2)
B(6)
B(5)
B(4)
C(1)
B(6)
B(11)
B(7)
124.2(9)
117.2(9)
115.6(8)
117.5(9)
123.5(9)
123.4(8)
119.6(8)
111.5(7)
P(1)ꢀ
Pt(3)ꢀ
Pt(3)ꢀ
Pt(3)ꢀ
C(101)ꢀ
C(101)ꢀ
C(111)ꢀ
Pt(3)ꢀP(2)ꢀ
P(2)ꢀ
P(2)ꢀ
C(201)ꢀ
C(201)ꢀ
C(211)ꢀ
/
Pt(3)ꢀ
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
/
P(2)
93.48(9)
116.2(3)
115.1(4)
114.5(4)
106.1(5)
100.9(5)
102.2(6)
109.5(3)
118.6(4)
118.7(3)
101.7(5)
106.2(5)
100.2(5)
/
/
/
/
C(101)
C(111)
C(112)
/
/
/
/
/
/
/
/
Fig. 1. Perspective view of compound 1. Thermal ellipsoids are drawn
at the 50% probability level, except for H atoms.
/
/
/
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
/
C(111)
C(112)
C(112)
/
/
/
/
/
/
/
/
Seeking further information on the nature of the
products of platination of 3-labelled-7,8-nido-diphenyl-
carborane, the fluoro-substituted anion [3-F-7,8-Ph2-
/
/
/
/
C(201)
C(211)
C(212)
/
/C(1)
126.7(10) Pt(3)ꢀ
/
/
/
/C(2)
124.3(9)
123.2(9)
124.9(9)
128.4(9)
113.9(9)
Pt(3)ꢀ
/
/
/
/
B(11)
B(10)
B(5)
/
P(2)ꢀ
P(2)ꢀ
P(2)ꢀ
/
C(211)
C(212)
C(212)
7,8-nido-C2B9H8]2ꢀ
was
treated
with
cis-
/
/
/
/
/
/
/
/
/
/C(62)
Pt(PMe2Ph)2Cl2 in THF. Work-up involving TLC
afforded one mobile product, the yellow species 3, in
modest yield.
In the 11BÁ{1H}-NMR spectrum of 3 are five
/
resonances, 1:2:1:4:1, high frequency to low frequency.
The highest frequency resonance appears as an unre-
solved doublet (1JFꢀB of ca. 45 Hz) which is unchanged
in the proton-coupled spectrum, and therefore arises
from the labelled B atom. The integral-4 resonance
includes an integral-1 shoulder to the high-frequency
side. In the 19F-NMR spectrum is a partially resolved
quartet, from which 1JFꢀB of ca. 39 Hz is measured. The
FB coupling constant in 3 compares with those in the
closo and nido precursors 1,2-Ph2-3-F-1,2-closo-
C2B10H9 and [3-F-7,8-Ph2-7,8-nido-C2B9H9]ꢀ of ca. 49
and 55 Hz, respectively [8]. The 31PÁ
/
{1H}-NMR
spectrum is a sharp singlet with Pt satellites (1JPtꢀP
3259 Hz). Given that 3 is subsequently shown (vide
infra) to be isostructural with 2 this implies that the
ꢁ
/
Fig. 2. Perspective view of compound 2. Thermal ellipsoids are drawn
at the 50% probability level, except for H atoms.

S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á
/293
291
Table 3
P distances and Pꢀ
/
Ptꢀ
/
P angles in the two compounds
˚
Selected interatomic distances (A) and interbond angles (8) for 2
are practically identical.
Bond lengths
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
B(3)ꢀ
B(3)ꢀ
B(3)ꢀ
B(4)ꢀ
B(4)ꢀ
B(4)ꢀ
B(5)ꢀ
B(5)ꢀ
B(5)ꢀ
B(6)ꢀ
B(6)ꢀ
B(7)ꢀ
/
C(1)
B(3)
B(7)
B(11)
B(6)
2.628(4) B(7)ꢀ
2.240(5) B(7)ꢀ
2.201(4) C(8)ꢀ
2.229(5) C(8)ꢀ
2.292(5) B(9)ꢀ
1.678(6) B(9)ꢀ
1.685(6) B(10)ꢀ
1.669(6) B(10)ꢀ
1.735(6) B(11)ꢀ
1.873(6) B(4)ꢀ
1.754(6) C(41)ꢀ
/
B(12)
1.776(6)
1.826(6)
1.749(6)
1.728(6)
1.785(7)
1.768(6)
1.763(7)
1.772(7)
1.766(7)
1.576(7)
1.451(9)
2.3028(11)
2.2925(11)
1.828(4)
1.821(4)
1.819(4)
1.820(4)
1.828(4)
1.811(4)
1.503(6)
1.511(6)
3.2. Mechanistic implications
/
/B(11)
/
/
B(9)
/
/
B(12)
B(10)
B(12)
We undertook this study as an extension of recent
work [9] on the metallation of [3-Et-7,8-Ph2-7,8-nido-
C2B9H8]2ꢀ with a {Ni(dppe)}2ꢂ fragment. The nick-
/
/
/
B(3)
B(4)
B(5)
B(6)
/
/
/
B(11)
B(12)
B(12)
elation produced not only the expected 1,20
isomerised metallacarborane, but also an (unexpected)
1,201,7 C atom isomerised species. The position of the
/
1,2 C atom
/
/
/
/
/
B(7)
C(8)
B(4)
C(8)
B(9)
B(5)
B(9)
B(10)
B(6)
B(10)
B(11)
C(8)
/C(41)
/
/
/C(42)
Et label in the latter compound did not accord with that
anticipated if the (presumed transient) compound 1,2-
Ph2-3-dppe-6-Et-3,1,2-closo-NiC2B9H8, which would be
/
1.855(6) Pt(2)ꢀ
1.750(6) Pt(2)ꢀ
1.767(7) P(1)ꢀ
1.759(7) P(1)ꢀ
1.736(8) P(1)ꢀ
1.779(7) P(2)ꢀ
1.835(7) P(2)ꢀ
1.815(7) P(2)ꢀ
1.855(7) C(1)ꢀ
1.721(6) C(8)ꢀ
/P(1)
/
/
P(2)
/
/
C(101)
C(111)
C(112)
C(201)
C(211)
C(212)
/
/
expected to form first, underwent the same 1,20
/1,7 C
/
/
atom isomerisation process predicted for 1,2-closo-
C2B10H12 [7g]. Instead, the simplest explanation of the
observed product, which has a 4-Et-2,1,8-closo-NiC2B9
architecture, is that it is formed from the transient initial
species by rotation of a CB2 triangular face [9].
/
/
/
/
/
/
/
/
C(11)
C(81)
/
/
In the present case, similar 4-X-2,1,8-closo-PtC2B9
Bond angles
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(41)ꢀB(4)ꢀ
C(41)ꢀB(4)ꢀ
C(41)ꢀB(4)ꢀ
C(41)ꢀB(4)ꢀ
C(41)ꢀB(4)ꢀ
/
/
Pt(2)
B(3)
B(4)
B(5)
B(6)
B(3)
B(7)
B(12)
B(9)
B(4)
112.0(3) B(4)ꢀ
122.9(3) P(1)ꢀ
119.2(3) Pt(2)ꢀ
118.1(3) Pt(2)ꢀ
119.0(3) Pt(2)ꢀ
122.6(3) C(101)ꢀ
115.7(3) C(101)ꢀ
117.6(3) C(111)ꢀ
117.7(3) Pt(2)ꢀP(2)ꢀ
116.4(3) Pt(2)ꢀP(2)ꢀ
122.4(4) Pt(2)ꢀP(2)ꢀ
119.7(4) C(201)ꢀ
122.8(4) C(201)ꢀ
126.7(4) C(211)ꢀ
128.7(4)
/
C(41)ꢀ
/
C(42)
119.7(5)
96.16(4)
geometries are displayed by compounds 2 (Xꢁ
/Et) and
/
/
/
Pt(2)ꢀ
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
/
P(2)
3 (XꢁF), which can therefore be rationalised by the
/
/
/
/
/
C(101)
C(111)
C(112)
114.45(14)
113.64(15)
118.30(15)
104.6(2)
same CB2 triangle face mechanism, shown in Scheme 1.
To try to gain further insight into the precise isomerisa-
tion mechanism operating, experiments are currently in
hand in which B atoms in this CB2 face are additionally
/
/
/
/
/
/
/
/
/
/
/
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
/
C(111)
C(112)
C(112)
/
/
/
/
102.0(2)
/
/
/
/
102.0(2)
/
/
/
/
C(201)
C(211)
C(212)
113.31(13)
116.26(15)
117.71(17)
101.2(2)
/
/
/
/
/
/
C(1)
B(3)
C(8)
B(9)
B(5)
/
/
/
/
/
P(2)ꢀ
P(2)ꢀ
P(2)ꢀ
/
C(211)
C(212)
C(212)
/
/
/
/
105.2(2)
/
/
/
/
101.1(2)
/
/
{PtP2} unit in 3 is rapidly spinning about the metal-cage
axis on the NMR timescale.
Compound 3 crystallises from CH2Cl2 in the presence
of 40Á
/
60 petroleum ether as the solvate 3×
/
143
CH2Cl2, but
/
this loses solvent on standing in air (microanalytical
results fit best with 0.6 mol of solvate per platinacarbor-
ane). A freshly crystallised sample was subject to
crystallographic study. A perspective view of a single
molecule of the platinacarborane is shown in Fig. 3, and
in Table 4 are selected molecular parameters. The
compound is confirmed as 1,8-Ph2-2,2-(PMe2Ph)2-4-F-
2,1,8-closo-PtC2B9H8, isostructural with 2. Thus the Pt
˚
atom is slipped, by ca. 0.37 A, away from C1, rendering
˚
C1 the longest metal-cage atom distance, 2.625(6) A
Ptꢀ
/
˚
(cf. Ptꢀ
/
B distances of 2.20Á2.29 A). There is a high
/
degree of congruence between the orientations of the
cage-Ph groups in 2 and 3, and, although this does not
Fig. 3. Perspective view of compound 3. Thermal ellipsoids are drawn
at the 50% probability level, except for H atoms.
extend to the orientations of the phosphine ligands, Ptꢀ
/

292
S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á293
/
Table 4
nickelation reactions. We believe this may be linked to
the greater electronic preference of {PtP2} fragments to
undergo slipping distortions in 3,1,2-closo-MC2B9 spe-
cies [15] relative to similar nickel fragments [10]. By
slipping away from C1 and C2, the {Pt(PMe2Ph)2}
fragment avoids to some degree unfavourable steric
crowding, and hence the need to isomerise, in a way that
a {Ni(dppe)} fragment cannot. The fact that 1 trans-
forms into 2 on gentle heating confirms that the former
is only kinetically preferred. The subtle interplay be-
tween electronic and steric preferences in these metalla-
carboranes affords them a considerably greater degree
of complexity and interest than their much more simple
carborane cousins, and is appropriate testimony to the
pioneering work of Hawthorne et al. [3] nearly 40 years
ago.
143
/
˚
Selected interatomic distances (A) and interbond angles (8) for 3×
/
CH2Cl2
Bond lengths
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
B(3)ꢀ
B(3)ꢀ
B(3)ꢀ
B(4)ꢀ
B(4)ꢀ
B(4)ꢀ
B(5)ꢀ
B(5)ꢀ
B(5)ꢀ
B(6)ꢀ
B(6)ꢀ
B(7)ꢀ
/
C(1)
B(3)
B(7)
B(11)
B(6)
2.625(6)
2.216(6)
2.206(7)
2.222(7)
2.281(7)
1.669(8)
1.624(9)
1.682(9)
1.747(8)
B(7)ꢀ
B(7)ꢀ
C(8)ꢀ
C(8)ꢀ
B(9)ꢀ
B(9)ꢀ
B(10)ꢀ
B(10)ꢀ
B(11)ꢀ
/
B(12)
1.778(10)
1.797(10)
1.770(9)
/
/B(11)
/
/
B(9)
/
/
B(12)
B(10)
B(12)
1.731(9)
/
/
1.787(10)
1.751(10)
1.777(11)
1.787(10)
1.770(10)
1.351(8)
/
B(3)
B(4)
B(5)
B(6)
/
/
/
B(11)
B(12)
B(12)
/
/
/
/
/
B(7)
C(8)
B(4)
C(8)
B(9)
B(5)
B(9)
B(10)
B(6)
B(10)
B(11)
C(8)
1.854(10) B(4)ꢀF(4)
/
/
1.742(9)
1.841(9)
1.733(9)
Pt(2)ꢀ
Pt(2)ꢀ
P(1)ꢀ
/
P(1)
2.2982(17)
2.2893(16)
1.829(7)
1.808(8)
1.813(7)
1.824(7)
1.815(7)
1.835(7)
1.498(8)
1.513(8)
/
/P(2)
/
/
C(101)
C(111)
C(112)
C(201)
C(211)
C(212)
/
1.773(10) P(1)ꢀ
1.749(10) P(1)ꢀ
1.751(10) P(2)ꢀ
1.784(10) P(2)ꢀ
1.827(10) P(2)ꢀ
1.800(10) C(1)ꢀ
/
/
/
/
/
/
/
/
/
/
/C(11)
4. Supplementary material
/
1.857(10) C(8)ꢀ
/C(81)
/
1.700(9)
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 204400 (1), 204401 (2) and
Bond angles
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(11)ꢀC(1)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
C(81)ꢀC(8)ꢀ
F(4)ꢀB(4)ꢀ
F(4)ꢀB(4)ꢀ
F(4)ꢀB(4)ꢀ
F(4)ꢀB(4)ꢀ
/
/
Pt(2)
B(3)
B(4)
B(5)
B(6)
B(3)
B(7)
B(12)
B(9)
B(4)
112.3(4)
121.2(5)
118.4(5)
118.4(5)
121.4(5)
121.3(5)
119.6(5)
120.4(5)
116.0(5)
113.3(5)
123.2(5)
119.6(5)
119.9(5)
123.8(6)
F(4)ꢀ
P(1)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
Pt(2)ꢀ
C(101)ꢀ
C(101)ꢀ
C(111)ꢀ
Pt(2)ꢀP(2)ꢀ
Pt(2)ꢀP(2)ꢀ
Pt(2)ꢀP(2)ꢀ
C(201)ꢀ
C(201)ꢀ
C(211)ꢀ
/
B(4)ꢀ
Pt(2)ꢀ
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
/
B(5)
128.1(5)
96.87(6)
119.4(2)
113.0(3)
103.4(3)
102.6(4)
103.4(3)
103.3(4)
116.8(2)
113.4(3)
115.4(2)
105.2(3)
102.7(3)
101.6(4)
/
/
/
/P(2)
204402 (3×
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: ꢂ44-
/
143
/
CH2Cl2). Copies of this information may be
/
/
/
/
C(101)
C(111)
C(112)
/
/
/
/
/
/
/
/
/
/
/
/
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
/
C(111)
C(112)
C(112)
1233-336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
/
/
/
/
/
/
/
/
/
/
/
/
C(201)
C(211)
C(212)
/
/
/
/
/
/
C(1)
B(3)
C(8)
B(9)
/
/
/
/
/
P(2)ꢀ
P(2)ꢀ
P(2)ꢀ
/
C(211)
C(212)
C(212)
Acknowledgements
/
/
/
/
/
/
/
/
We thank the Leverhulme Trust (DE) and Heriot-
Watt University (SR) for support, Mr G. Evans and
Mrs. C. Graham for microanalysis and Dr A.S.F. Boyd
for NMR spectra. A.J.W. acknowledges the receipt of a
Royal Society Leverhulme Trust Senior Research Fel-
labelled, and the results of these studies will be published
separately [22].
Finally, we comment on the isolation of the non-
isomerised species 1, which has no precedent in the
lowship, 2002Á2003.
/
Scheme 1. Metallation of [3-X-7,8-Ph2-7,8-nido-C2B9H8]2ꢀ with a {Pt(PMe2Ph)2}2ꢂ fragment (abbreviated to {PtP2}2ꢂ for clarity) generating a 4-
X-labelled C-atom isomerised 2,1,8-PtC2B9 species via rotation of the (bold) CB2 face of a notional 6-X-3,1,2-PtC2B9 intermediate. Compound 1
corresponds to the intermediate and compounds 2 and 3 to the final product.

S. Robertson et al. / Journal of Organometallic Chemistry 680 (2003) 286Á
/293
293
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