Macropolyhedral boron-containing cluster chemistry. Synchrotron X-ray structural analysis of [(PMe2Ph)2Pd2B 16H20(PMe2Ph)2] and [(PMe 2Ph)3Pt2B<s

Article abstract of DOI:10.1039/b419242g

Thermolyses of [(PMe₂Ph)₂PdB₈H ₁₂] and [(PMe₂Ph)₂PtB₈H ₁₂] respectively yield eighteen-vertex [(PMe₂Ph) ₂Pd₂B₁₆H₂₀

Full text of DOI:10.1039/b419242g

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Macropolyhedral boron-containing cluster chemistry. Synchrotron
X-ray structural analysis of [(PMe2Ph)2Pd2B16H20(PMe2Ph)2] and
[(PMe2Ph)3Pt2B16H18(PMe2Ph)]: models of intermediates to more
condensed metallaboranes from the [(PMe2Ph)2PtB8H12] thermolysis
system
Michael G. S. Londesborough,a Elizabeth J. MacLean,b Simon J. Teat,b Mark Thornton-Petta and
John D. Kennedya
Received (in Cambridge, UK) 23rd December 2004, Accepted 7th February 2005
First published as an Advance Article on the web 17th February 2005
DOI: 10.1039/b419242g
compounds upon simple thermolysis.7 Identified products include
Thermolyses of [(PMe2Ph)2PdB8H12] and [(PMe2Ph)2PtB8H12]
[(PMe2Ph)2Pt2B12H18], [(PMe2Ph)PB16H18(PMe2Ph)], [(PMe2Ph)2-
Pt2B16H15(C6H4Me)(PMe2Ph)] and [(PMe2Ph)4Pt3B14H16], of
schematic cluster structures II, III, IV and V respectively,
The combined yield of these products is non-trivial,7 indicating
that their skeletal configurations constitute thermodynamic or
kinetic sinks among the complex of multi-step reaction co-
ordinates. However, the initial cluster geometry I is not traceable
in any of these products, and the constitutions of III and V
additionally indicate that intermolecular transfers of platinum and/
or boron atoms occur. Similar considerations apply to the related
[(PPh3)2PdB8H12] system, which, for example, gives
[(PPh3)4Pd4ClB16H17(PPh3)] of schematic structure VI.8 The
mechanisms associated with these systems are therefore of interest,
and further information is valuable: firstly, such information may
give clues to the mechanisms within this particular system, and,
secondly, it may then give clues for the ultimate design and
establishment of general transferable generic routes for intercluster
fusion.
respectively yield eighteen-vertex [(PMe2Ph)2Pd2B16H20(PMe2-
Ph)2] and [(PMe2Ph)3Pt2B16H18(PMe2Ph)], which exhibit struc-
ture models for probable successive precursive intermediates
for the more condensed macropolyhedral metallaboranes
[(PMe2Ph)4Pt3B14H16], [(PMe2Ph)2Pt2B12H16] and [(PMe2Ph)2-
Pt2B16H15(C6H4Me)(PMe2Ph)] that have previously been
reported as products from [(PMe2Ph)2PdB8H12] thermolyses.
The rich and fertile chemistry of the polyhedral boranes is at
present most strongly manifested in the study and manipulation of
single-cluster species. The investigation of the manner in which
such single-cluster species may interact, either (a) covalently to
form intimately condensed ‘big-borane’ assemblies, often dubbed
‘macropolyhedral’ molecules,1 or (b) by weaker inter-molecular
binding modes to form supramolecular aggregations,2 constitute
two ways in which this single-cluster chemistry can be extended
beyond the experimental and sometimes intellectual hiatus
represented by the stable twelve-vertex single-cluster icosahedron.
An additional extension is (c) by the expansion of the twelve-
vertex icosahedron itself to give single clusters with more than
twelve vertices.3 Of these three areas, the generation of macro-
polyhedral boron-containing cluster species requires the intimate
covalent fusion of single clusters, but at present this has no
generally applicable generic synthetic route. Empirically, however,
it is found that several arachno nine-vertex species are prone to
homofusion to generate macropolyhedral molecules on mild
thermolysis.4–6 In this context, the arachno {B8Pt} system, as
represented by [(PMe2Ph)2PtB8H12] (schematic skeletal structure
I), is known to give a variety of interesting macropolyhedral
In this context we report the isolation9 and characterisation10,11
of two new species. These are of formulation
[(PMe2Ph)2Pd2B16H20(PMe2Ph)2] [compound 1, Fig. 1 (upper),
schematic cluster structure VII A] from [(PMe2Ph)2PdB8H12]
thermal autofusion, and [(PMe2Ph)3Pt2B16H18(PMe2Ph)] [com-
pound 2, Fig. 1 (lower), schematic cluster structure VIII A] from
[(PMe2Ph)2PtB8H12] thermal autofusion. Obtainable crystals of 1
and 2 were small and required synchrotron X-radiation12
for sufficient diffraction intensity for molecular structure
determination.{
Their skeletal configurations are represented in schematic cluster
structures VII A and VIII A respectively. In each of these, the
skeletal pattern I of the {B8M} starting substrate is now readily
traced. The simple reaction stoichiometries of eqn. (1) and (2)
thence suggest that the structures may represent initial steps in the
1584 | Chem. Commun., 2005, 1584–1586
This journal is ß The Royal Society of Chemistry 2005

View Article Online
structure VII A is related to that invoked in the initial stages of
autofusion of the arachno nine-vertex thiaborane [SB8H12] to give
[S2B16H16] isomers.13 There is also a parallel with a similar spiro-
type connection established for neutral [S2B18H20].14
The more condensed platinum compound [(PMe2Ph)3-
Pt2B16H18(PMe2Ph)] (schematic VIII A) hence could represent a
second step. Cluster fusion and subsequent condensation to
increase the intimacy of the fusion are oxidative processes. This is
implicit in eqn. (1) and (2), which show the loss of two and three
dihydrogen molecules respectively. Mechanistically, the basic
skeletal type VIII A derives from a simple skeletal closure from
a spiro-type structure VIII B related to that exhibited by the
{Pd2B16H20} species (schematic VII A). There are again some
parallels with thiaborane chemistry, in that the two-electron
oxidative closure from VIII B to VIII A together with the
concomitant subcluster swing resemble the characteristics of the
two-electron oxidative closure of the [S2B17H18]2 anion to form
neutral S2B17H17.15
Fig. 1 ORTEP-316 diagrams of the crystallographically determined10
cluster structures of (upper diagram) [(PMe2Ph)2Pd2B16H20(PMe2Ph)2]
(compound 1) (schematics VII) and (lower diagram) [(PMe2Ph)3-
Pt2B16H18(PMe2Ph)] (compound 2) (schematics VIII), with P-organyl
group atoms omitted for clarity; ellipsoid probability 70%. For 1,
unbridged palladium–boron distances are in the range 2.205(3)–
In conclusion, it seems reasonable to postulate that condens-
ations such as VII B A VII A and VIII B A VIII A will typify
successive initial steps in at least one of the pathways that
ultimately lead to more severely modified species represented by
configurations II, III, IV, V and VI. The link between these two
initially formed {B16M2} frameworks and the more condensed and
rearranged skeletons is, however, not yet made. It is to be hoped
that the continued isolation of species from these and related
reaction systems will continue to give clues for the further
understanding of the overall mechanism. Any understanding here
will aid the development of generic cluster fusion routes.
˚
2.298(3) A, and hydrogen-bridged Pd(6)–B(99) is 2.365(3) A; the
˚
˚
palladium–phosphorus distances are 2.3364(7) and 2.3329(7) A; B(5)–
˚
˚
P(5) is 1.919(3) A , B(89)–P(89) is 1.916(3) A, and interboron distances are
˚
in the range 1.730(4)–1.882(5) A; diagram and data are for one of four
similar but crystallographically independent molecules. For 2, platinum–
˚
boron distances are in the range 2.204(4)–2.340(5) A; Pt (9)–P(9a) is
˚
2.319(1) A, Pt (9)–P(9b) is 2.297(1) A and Pt(6)–P(6) is 2.284(1), A;
˚
˚
˚
B(29)–P(29) is 1.918(4) A and interboron distances are in the range
˚
1.705(7)–1.883(7) A.
complex fusion-condensation processes that ultimately engender
We thank the UK EPSRC for support (grants nos. J/56929,
L/49505 and M/83360, and a studentship to MGSL), and Dr
Jonathan Bould for useful advice and discussions.
skeletons such as II, III, IV, V and VI.
2 [(PMe2Ph)2PdB8H12] A
(1)
Michael G. S. Londesborough,a Elizabeth J. MacLean,b Simon J. Teat,b
Mark Thornton-Petta and John D. Kennedya
aSchool of Chemistry, University of Leeds, Leeds, UK LS2 9JT.
E-mail: johnk@chem.leeds.ac.uk
bCLRC Daresbury Laboratory, Daresbury, Warrington, Cheshire,
UK WA4 4AD
[(PMe2Ph)2Pd2B16H20(PMe2Ph)2] 1 + 2 H2
2 [(PMe2Ph)2PtB8H12] A
[(PMe2Ph)3Pt2B16H18(PMe2Ph)] 2 + 3 H2
(2)
Mechanistically, the formation of [(PMe2Ph)2Pd2B16H20-
(PMe2Ph)2] (schematic VII A) can be envisaged as the simple
confluence of two starting-material arachno {B8M} geometries
(schematic VII B below). As such it can be in turn envisaged as an
initial step of cluster fusion. This initially formed spiro-type
Notes and references
{ CCDC 198684 and 198685. See http://www.rsc.org/suppdata/cc/b4/
b419242g/ for crystallographic data in .cif or other electronic format.
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 1584–1586 | 1585

View Article Online
1 J. Bould, W. Clegg, S. J. Teat, L. Barton, N. P. Rath, M. Thornton-Pett
and J. D. Kennedy, Inorg. Chim. Acta, 1999, 289, 95; J. Bould,
D. L. Ormsby, H.-J. Yao, C.-H. Hu, J. Sun, R.-S. Jin, S. L. Shea,
W. Clegg, T. Jel´ınek, N. P. Rath, M. Thornton-Pett, R. Greatrex,
C32H62B16P4Pt2: M 5 1133.84, monoclinic (red plate 0.40 6 0.10 6
0.02 mm3, from C6H12/C6H6/CDCl3), space group P21/c,
˚
a 5 25.3975(11), b 5 10.2760(5), c 5 18.4033(8) A, b 5 106.0630(10)u,
V 5 4615.5(4) A , Z 5 4, m 5 6.218 mm21, T 5 150(2) K, R1 5 0.0348
3
˚
ˇ
P.-J. Zheng, L. Barton, B. St´ıbr and J. D. Kennedy, in Contemporary
for 10418 reflections with I . 2s(I) and wR2 5 0.0768 for all 29614
unique reflections, CCDC reference number 198685.
Boron Chemistry, Eds. M. Davidson, A. K. Hughes, T. B. Marder and
K. Wade, Royal Society of Chemistry, Cambridge, England, 2000, 171.
2 C. O’Dowd, J. D. Kennedy and M. Thornton-Pett, J. Organomet.
Chem., 2002, 657, 20; A. Franken, C. A. Kilner, M. Thornton-Pett and
J. D. Kennedy, Chem. Commun., 2002, 2048.
3 R. N. Grimes, Angew. Chem. Int. Ed., 2003, 42, 1198; A. Burke, D. Ellis,
B. T. Giles, B. E. Hodson, S. A. Macgregor, G. M. Rosair and
A. J. Welch, Angew. Chem. Int. Ed., 2003, 42, 225.
11 Selected NMR data for [(PMe2Ph)3Pt2B16H18(PMe2Ph)] 2 are as
follows: d(11B)/ppm [with d(1H)/ppm for directly bound H(exo) atoms
in square brackets] (CD2Cl2 solution) +31.0 [+4.96], +30.3 [+5.10], +7.5
[+2.70], +6.1 [no exo-H, probably B(5) on the basis that 11B coupling to
the 1H bridging resonance at 22.39 was removed upon selective
irradiation of this 11B resonance in 1H-{11B} experiments], ca. +2.0
[+3.98], ca. +1.2 [+2.32], ca. +0.5 [+4.17], ca. 25.5 [+1.61], ca. 25.5
[+1.38], 27.0 [+2.78], ca. 213.5 [no exo-H, probably B(29) on the basis
that no 11B coupling to any 1H resonances in the BHB-bridging region
was definitively removed upon selective irradiation of this 11B resonance
in 1H-{11B} experiments], ca. 214.0 [+1.19], ca. 214.3 [+1.96], 215.8
[+3.19], 223.0 [+1.49] and 234.5 [+0.80], with d(1H)(mH) at 21.41,
22.39, 22.50 and 23.82 ppm, and with d(31P)/ppm (CDCl3 solution) at
ca. 225 with 1J(31P–11B) ca. 135 Hz, at 24.3 with 1J(195Pt–31P) 3325 Hz,
at 25.7 with 1J(195Pt–31P) 2945 Hz, and at 29.9 with 1J(195Pt–31P)
2675 Hz; 31P couplings are given ¡10 Hz. Because of overlapping
resonances, cluster d(11B) and d(1H) data for [(PMe2Ph)2-
Pd2B16H20(PMe2Ph) 2] 1 were less well defined. Tentative 11B resonance
positions are: +28.0. +24.7, +20.2, +8.0, +3.1, ca. +1.0, ca. 212.4, ca.
213.5, 218.1, 220.0, 227.0 233.0 and 245.8 ppm, plus two other
resonances in the region +10 to 25 ppm; tentative 1H resonance
positions are +5.83, +5.59, +5.20, +4.83, +4.33, +4.10, + 3.63, +3.40,
+2.76, +2.75, +2.68, +2.60, +2.17, +1.77, +1.04, +0.10, 20.38, 22.07,
22.17 and 25.17 ppm; with 31P resonances (CDCl3 solution) at d(31P)
210.9 and 28.5 [both sharper, two doublets, 2J(31P–31P) ca. 50 Hz], and
21.6 (broader) and 25.2 ppm (broader).
ˇ
ˇ
4 J. Pleˇsek, S. Herma´nek, B. St´ıbr and F. Hanousek, Collect. Czech.
Chem. Commun., 1967, 32, 1095; J. Plesˇek, S. Herma´nek and
ˇ
F. Hanousek, Collect. Czech. Chem. Commun., 1968, 33, 699;
J. Dobson, P. C. Keller and R. Schaeffer, Inorg. Chem., 1968, 7, 399;
G. B. Jacobsen, D. G. Meina, J. H. Morris, C. Thompson,
S. J. Andrews, D. Reed, A. J. Welch and D. F. Gaines, J. Chem.
Soc., Dalton Trans., 1985, 1645; D. F. Gaines, C. K. Nelson and
G. A. Steehler, J. Am. Chem. Soc., 1984, 106, 7266.
ˇ
5 T. Jel´ınek, J. D. Kennedy and B. St´ıbr, J. Chem. Soc., Chem. Commun.,
ˇ
1994, 1415; P. Kaur, J. Holub, N. P. Rath, J. Bould, L. Barton, B. St´ıbr
and J. D. Kennedy, J. Chem. Soc., Chem. Commun., 1996, 273.
6 L. Barton, J. Bould, J. D. Kennedy and N. P. Rath, J. Chem. Soc.,
Dalton Trans., 1996, 3145.
7 M. A. Beckett, J. E. Crook, N. N. Greenwood and J. D. Kennedy,
J. Chem. Soc., Dalton Trans., 1986, 1879; M. A. Beckett,
N. N. Greenwood, J. D. Kennedy, P. A. Salter and M. Thornton-
Pett, J. Chem. Soc., Chem. Commun., 1986, 556.
8 M. G. S. Londesborough, C. A. Kilner, M. Thornton-Pett and
J. D. Kennedy, J. Organomet. Chem., 2002, 657, 262.
9 [(PMe2Ph)2PdB8H12] (197 mg, 410 mmol) was heated for 60 min in
refluxing toluene (20 ml), the toluene evaporated, and preparative TLC
(silica G, CH2Cl2/n-C6H12 80:20) thence gave a number of coloured
bands, including a red component (RF 0.2) which was further purified
by HPLC [silica (Lichrosorb Si60, 7 mm), 25 6 2.1 cm; CH2Cl2/n-C6H12
40:60 at 20 ml min21] to give pure red 1 (RT 18 min; 1.5 mg, 3.5 mmol,
ca. 1%). An exactly analogous procedure starting with
[(PMe2Ph)2PtB8H12] (194 mg, 340 mmol) gave pure red 2 (TLC RF
0.2; HPLC RT 12 min; 2 mg, 3.5 mmol, ca. 1%).
12 R. J. Cern´ık, W. Clegg, C. R. A. Catlow, G. Bushnell-Wye,
J. V. Flaherty, G. N. Greaves, I. Burrows, D. J. Taylor, S. J. Teat
and M. Maichi, J. Synchrotron Rad., 1997, 4, 279; J. Bould, W. Clegg,
J. D. Kennedy, S. J. Teat and M. Thornton-Pett, J. Chem. Soc., Dalton
Trans., 1997, 2005; W. Clegg, M. R. J. Elsegood, S. J. Teat, C. Redshaw
and V. C. Gibson, J. Chem. Soc., Dalton Trans., 1998, 3037.
13 P. K. Dosangh, J. Bould, M. G. S. Londesborough, T. Jel´ınek,
ˇ
M. Thornton-Pett, B. St´ıbr and J. D. Kennedy, J. Organomet. Chem.,
2003, 680, 312.
14 D. L. Ormsby, T. Jel´ınek, S. L. Shea, R. Greatrex, B. St´ıbr and
ˇ
10 Crystal and X-ray data (synchrotron X-radiation, Station 9.8,
Daresbury, UK,12 l 5 0.6942 A, SHELX solution and refinement
˚
J. D. Kennedy, Abstracts Tenth International Meeting on Boron
Chemistry (IMEBORON X), Durham, England, July 11–15 1999,
Abstract no. PA-38, p.14; and work in preparation for submission to
Dalton Trans.
methods)17: compound 1, C32H64B16P4Pd2: M 5 958.47, triclinic
(orange needle, 0.60 6 0.06 6 0.03 mm3, from dichloromethane/
¯
hexane), space group P1,
a 5 9.5388(4), b 5 30.0590(14),
˚
ˇ
c 5 33.0514(15) A, a 5 84.051(2)u, b 5 83.8669(2)u, c 5 81.165(2)u,
15 T. Jel´ınek, J. D. Kennedy, B. St´ıbr and M. Thornton-Pett, Inorg. Chem.
Commun., 1998, 1, 179.
3
V 5 9270.8(7) A , Z 5 8, m 5 0.938 mm21, T 5 150(2) K, R1 5 0.0389
˚
for 36747 reflections with I . 2s(I) and wR2 5 0.0864 for all 92143
unique reflections, CCDC reference number 198684: compound 2,
16 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
17 SHELXTL software, Bruker AXS Inc., Madison, WI, USA, 1997.
1586 | Chem. Commun., 2005, 1584–1586
This journal is ß The Royal Society of Chemistry 2005