Macropolyhedral boron-containing cluster chemistry. Ligand-induced two-electron variations of intercluster bonding intimacy. Structures of nineteen-vertex [(η5-C5Me5)HIrB 18H19(PMe2PH)] and the related carbene complex [(η5-C5Me5)HIrB18H 19{C(NHMe)2}]

Article abstract of DOI:10.1039/b404322g

Addition of PMe₂Ph to fused-cluster syn-[(η⁵- C₅Me₅)-IrB₁₈H₂₀] 1 to give [(η⁵-C₅Me₅)HIrB₁₈H ₁₉(PMe₂Ph)] 3 entails a diminution in the degree of intimacy of the intercluster fusion, rather than retention of inter-subcluster binding intimacy and a nido → arachno conversion of the character of either of the subclusters. Reaction with MeNC gives [(η⁵-C ₅Me₅)HIrB₁₈H₁₉{C(NHMe)₂}] 4 which has a similar structure, but with the ligand now being the carbene {:C(NHMe)₂}, resulting from a reductive assembly reaction involving two MeNC residues and the loss of a carbon atom.

Full text of DOI:10.1039/b404322g

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Macropolyhedral boron-containing cluster chemistry. Ligand-
induced two-electron variations of intercluster bonding intimacy.
Structures of nineteen-vertex [(ꢀ5-C5Me5)HIrB18H19(PMe2Ph)] and
the related carbene complex [(ꢀ5-C5Me5)HIrB18H19{C(NHMe)2}]
b
a
Suzanne L. Shea,a Tomásˇ Jelínek,a,b Sarath D. Perera,a,c Bohumil Stíbr, Mark Thornton-Pett
ˇ
and John D. Kennedya
a The School of Chemistry of the University of Leeds, Leeds, UK LS2 9JT.
E-mail: johnk@chem.leeds.ac.uk; Fax: ϩ44 (0)113 343 6401
b Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic,
ˇ
25068 Rezˇ u Prahy, The Czech Republic
c The Department of Chemistry of the Open University, Nawala, Nugegoda, Sri Lanka
Received 22nd March 2004, Accepted 21st April 2004
First published as an Advance Article on the web 27th April 2004
Addition of PMe2Ph to fused-cluster syn-[(ꢀ5-C5Me5)-
IrB18H20] 1 to give [(ꢀ5-C5Me5)HIrB18H19(PMe2Ph)] 3 entails
a diminution in the degree of intimacy of the intercluster
fusion, rather than retention of inter-subcluster binding
elemental sulfur, the observed reductive opening to give the
[(η5-C5Me5)IrSB18H19]Ϫ anion 2 entails the addition of a sulfur
vertex to the non-metallated subcluster and the conversion of
this non-metal-containing subcluster from nido to arachno
(schematics II).4 The addition of a sulfur atom effectively adds
four reducing electrons to the double-cluster system, resulting
in a reductive two-electron opening of the non-metallated
subcluster from nido to arachno, and a reductive two-electron
diminution of intercluster bonding intimacy from three-atoms-
in-common to a two-atoms-in-common mode.
intimacy and a nido
arachno conversion of the character
of either of the subclusters. Reaction with MeNC gives
[(ꢀ5-C5Me5)HIrB18H19{C(NHMe)2}] 4 which has a similar
structure, but with the ligand now being the carbene
{:C(NHMe)2}, resulting from a reductive assembly reaction
involving two MeNC residues and the loss of a carbon
atom.
There is consequent interest in the effect of a single two-
electron reduction: will it result in an individual cluster-
opening, or in a decrease in intercluster bonding intimacy? In
this regard, we now report preliminary results on an interesting
complementary behaviour. Specifically, reaction of compound
1 with the two-electron ligand PMe2Ph results in addition of the
ligand to give a compound of formulation [(C5Me5)HIrB18-
H19(PHPh2)] 3† (eqn. (1) below). The ligand adds to a boron
atom on the cage, and there is a transfer of a boron-bound
hydrogen atom onto the iridium centre. The two-electron
reduction leaves the nido-decaboranyl ten-vertex cage intact,
with the reductive addition occurring now at the metal-contain-
ing subcluster, rather than at the metal-free subcluster. It is also
apparent that there is a decrease in the intimacy of intercluster
fusion, rather than an opening of either of the individual
subclusters from nido to arachno. This is manifested in the
conversion of the fusion mode from a three-atoms-in-common
triangle to a two-atoms-in-common edge, which thereby has
the effect of converting the iridium-containing subcluster
from twelve-vertex nido (schematics I) to eleven-vertex nido
(schematics III).
The addition of electrons to a single-cluster compound gener-
ally results in cluster opening; conversely, removal of electrons
results in cluster closure.1 In macropolyhedral boron-contain-
ing cluster compounds, in which single clusters are fused
together, the addition and removal of electrons can, altern-
atively, result in a respective decrease or increase in the degree
of intimacy of the intercluster fusion, rather than the opening
or closure of any of the subclusters.2–4 In the development of
macropolyhedral boron cluster chemistry, there is merit in
establishing systems in which such differential behaviour may
be observed, so that the controlling factors for this differential
behaviour may ultimately be defined.
The macropolyhedral metallaborane syn-[(η5-C5Me5)IrB18-
H20] 1 (Fig. 1) consists of nido twelve-vertex {IrB11} and nido
ten-vertex {B10} subclusters fused together, with three atoms
held in common between the two subclusters (schematic
skeletal structures I).3 In the reaction of compound 1 with
Thus, PMe2Ph (25 µl, 1.62 mmol) was added to an orange
solution of [(η5-C5Me5)Ir-syn-B18H20] 1 (44 mg, 810 µmol) in
CH2Cl2 (ca. 15 ml). After 24 h the solvent was removed from the
resulting yellow solution (rotary evaporator, water pump,
30 ЊC). TLC separation of the residue (silica gel G, CH2Cl2/
hexane 50/50 v/v) thence gave [BH3(PMe2Ph)] (RF 0.8, 3 mg,
200 µmol, 1%) and yellow [(η5-C5Me5)HIr-syn-B18H19(PMe2-
Ph)] 3 (RF 0.5, 49 mg, 720 µmol, 89%), the latter characterised
as such by single-crystal X-ray crystal diffraction analysis5 and
by NMR spectroscopy.6 The equation for its formation is
stoichiometric (eqn. (1)).
[(C5Me5)IrB18H20] 1 ϩ PMe2Ph
Fig. 1 ORTEP-type12 drawing of [(η5-C5Me5)IrB18H20] (compound
1).3 The hydride unit on Ir(9) bridges to B(12), and the distance Ir(9)–
B(12) is bonding at 2.387(11) Å; the three atoms B(7), B(8)and B(12)
are held in common between the two subclusters, and the angle
Ir(9)B(8)B(12), corresponding to Ir(9)B(8)B(2Ј) in compounds 3 and 4,
is acute at 75.0(6)Њ
[(C5Me5)HIrB18H19(PMe2Ph)] 3 (1)
The polyhedral cluster structure of 3 (Fig. 2 and schematics
III) is seen to consist of nido eleven-vertex {IrB10} and nido
ten-vertex {B10} subclusters conjoined with a common two-
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
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is interesting that the iridium centre does not switch to square-
planar {Ir(η4-C5HMe5)} iridium() for this purpose, in contrast
to the observation of a square-planar {Rh(η4-C5HMe5)} feature
in the single-borane-cluster rhodium species [(η4-C5HMe5)-
RhS2B9H9(SMe)].7 In this last regard, and in competitive
cluster-opening terms,7 it is pertinent to note that the
{M(η5-C5Me5)} units are six-vertex nido, whereas the {M(η4-
C5HMe5)} units, effectively containing two more electrons, are
six-vertex arachno.
We have also found that an additional interesting reductive
feature in this new type of system occurs when the two-electron
ligand used is MeNC. Thus, MeNC (23 µl, 4.0 mmol) was
added to a solution of [(η5-C5Me5)Ir-syn-B18H20] 1 (59 mg,
1.09 mmol) in CH2Cl2 (ca. 15 ml). The resulting orange solution
was heated at reflux for 3.5 h, allowed to cool, and stirred
overnight. Following removal of the solvent (rotary evaporator,
water pump, 30 ЊC), TLC separation of the product mixture
(silica gel G, CH2Cl2/hexane 60/40 v/v) thence gave yellow
[(η5-C5Me5)IrH-syn-B18H19(C(NHMe)2)] 4‡ (RF 0.2, 11 mg,
0.18 mmol, 16%) as a principal product, characterised as such
by single-crystal X-ray crystal diffraction analysis5 and by
NMR spectroscopy.6
Although the basic, more open, two-atoms in common,
metallaborane structural type of 3 above is again formed
(Fig. 3), compound 4 now exhibits an unusual reductive and
degradative combination of two MeNC moieties: it has the
carbene ligand, {:C(NHMe)2}, rather than a simple MeNC
moiety, in the 11-position. The carbene fragment is derived
from two MeNC residues with the loss of one carbon atom.
The nitrogen-bound hydrogen atoms in the carbene presumably
derive from the oxidation of other borane residues, the <50%
yield of 4 of being consistent with this. A related reductive/
degradative oligomerisation with loss of carbon has been
observed in the reaction of MeNC with the non-metallated
Fig. 2 ORTEP-type12 drawing of [(η5-C5Me5)HIrB18H19(PMe2Ph)]
(compound 3). There are two independent molecules in the unit cell,
differing principally in phosphine-ligand rotamer disposition. Cluster
dimensions for both are very similar. Dimensions here are for ‘molecule
1’. Selected interatomic distances (Å) are Ir(9)–B(4) 2.176(7), Ir(9)–B(5)
2.200(7), Ir(9)–B(8) 2.209(7), Ir(9)–B(10) 2.331(7), Ir(9)–H(9)
1.7155(3), Ir(9)–C(C5Me5) 2.215(6)–2.331(7), B(7)–B(8) 1.876(10),
B(7)–B(11) 1.892(8), B(7)–B(2Ј) 1.810(10), B(7)–B(10Ј) 2.063(10), B(8)–
B(2Ј) 1.804(9), B(8)–B(7Ј) 1.910(9), B(10)–B(11) 1.897(10), B(7Ј)–B(8Ј)
1.940(11), B(8Ј)–B(9Ј) 1.806(14), and B(9Ј)–B(10Ј) 1.768(12), with other
interboron distances between 1.754(10) and 1.892(8) Å for the {IrB10}
subcluster and between 1.721(11) and 1.824(12) Å for the {B10}
subcluster; B(11)–P(11) is 1.913(6) Å, and angles at P(11) are 105.6(3)–
113.2(3)Њ. In this less intimately conjoined double-cluster structure
(contrast with compound 1, Fig. 1), the hydride unit on Ir(9) is endo-
terminal, there is an exo-terminal hydrogen unit on B(2Ј), and Ir(9)–
B(2Ј) is non-bonding at 3.274(7) Å; only two atoms, B(7) and B(8), are
held in common between the two sub-clusters, and the angle
Ir(9)B(8)B(2Ј) is much more obtuse at 109.1(4)Њ than the otherwise
corresponding acute Ir(9)B(8)B912) angle in compound 1.
macropolyhedral B18H22: this last reaction results in
a
formation of a species [B18H20{:CN2Me2CHC(NHMe)}], which
contains an imidazole-like carbene ligand, now formed from
the assembly of three, rather than two, MeNC residues, but
Fig. 3 ORTEP-type12 drawing of [(η5-C5Me5)HIrB18H19{C(NHMe)2}]
(compound 4). Selected interatomic distances (Å) are Ir(9)–B(4)
2.170(4), Ir(9)–B(5) 2.178(5), Ir(9)–B(8) 2.203(4), Ir(9)–B(10) 2.234(4),
Ir(9)–H(9) 1.6097, Ir(9)–C(C5Me5) 2.214(4)–2.254(4), B(7)–B(8)
1.890(5), B(7)–B(11) 1.885(5), B(7)–B(2Ј) 1.823(5), B(7)–B(10Ј)
2.038(6), B(8)–B(2Ј) 1.776(5), B(8)–B(7Ј) 1.871(6), B(10)–B(11)
1.917(6), B(7Ј)–B(8Ј) 1.934(6), B(8Ј)–B(9Ј) 1.797(7), and B(9Ј)–B(10Ј)
1.787(6), with other interboron distances between 1.726(6) and 1.823(6)
Å for the {IrB10} subcluster and between 1.706(6) and 1.809(6) Å for
the {B10} subcluster. As with compound 3 (Fig. 2), the hydride unit on
Ir(9) is endo-terminal, B(2Ј)–H(2Ј) is exo-terminal, and Ir(9)–B(2Ј) is
non-bonding, now at 3.189(4) Å; again, only two atoms, B(7) and B(8),
are held in common between the two sub-clusters, and the angle
Ir(9)B(8)B(2Ј) is again obtuse, at 106.1(2)Њ. Within the carbene ligand,
B(11)–C(111) is 1.583(5), C(111)–N(111) is 1.326(4) and C(111)–N(112)
is 1.311(5), with N(111)–C(112) 1.455(5) and N(112)–C(113) 1.445(5)
Å, with angles B(11)C(111)N(111) 123.2(3), B(11)C(111)N(112)
118.5(3) and N(111)C(111)N(112) 118.3(3)Њ.
boron edge. Any Ir–H–B bonding to link between the sub-
clusters, as observed in 1 and 2 (Fig. 1 and schematics I A and
II A) is no longer present, and so the three-atom intercluster
intimacy observed for 1 (schematic I A) is thereby reduced to a
two-atom mode. The hydride unit that is effectively displaced
intramolecularly by the incoming ligand finds itself on the
metal atom (schematic III A), and the compound thence has
structural similarities to [(PMe2Ph)HPtB18H19(PMe2Ph)],4
which is based on nido-type eleven-vertex {PtB10} and nido
ten-vertex {B10} subclusters with two boron atoms held in
common. In 3, however, instead of a square-planar {PtH-
(PMe2Ph)} platinum() unit contributing two orbitals and one
electron to a simple cluster bonding scheme, this function is
fulfilled by the octahedral {IrH(η5-C5Me5)} iridium() unit. It
D a l t o n T r a n s . , 2 0 0 4 , 1 5 2 1 – 1 5 2 3
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again with the loss of one carbon atom.8 In this context also
the bis(carbene) species [B12H10{C(OH)2}2] may also be noted.9
Complexes of elements of Main-Group III (i.e. Group 13) with
carbenes are rare,10 as is loss of carbon from isocyanides upon
reaction with boron-containing clusters.11
C13H43B18IrN2: M = 614.27, monoclinic (yellow prism, 0.52 × 0.38 ×
0.22 mm, from CH2Cl2/C6H14), space group P21/n, a = 12.6547(2),
b = 11.4546(2), c = 21.2777(4) Å, β = 104.5570(11)Њ, U = 2985.29(9)
Å3, Dcalc = 1.367 Mg mϪ3, Z = 4, Mo-Kα, λ = 0.71073 Å, µ = 4.480
mm1, T = 160(2) K, R1{I > 2σ(I )} = 0.0390 and wR2 = 0.1132 for all
27971 collcted reflections. CCDC reference numbers 233343 (3) and
165856 (4). See http://www.rsc.org/suppdata/dt/b4/b404322g/ for
crystallographic data in CIF or other electronic format. For both 3
and 4, methods and programs were standard: G. M. Sheldrick,
SHELXS-97, Program for solution of crystal structures, University
of Göttingen, Germany, 1997; G. M. Sheldrick, SHELXL-97,
Program for refinement of crystal structures, University of
Göttingen, Germany, 1997.
Acknowledgements
ˇ
Contribution no. 92 from the Rez–Leeds Anglo–Czech
ˇ
Polyhedral Collaboration (ACPC). We thank the UK EPSRC
(grants nos. F/78323, J/56929, K/05818 and M/83360, and a
studentship to SLS), the Grant Agency of the Academy of
Sciences of the Czech Republic (Grant no. A 403 2701), the
Royal Society for help with reciprocal visits, Simon Barrett
for assistance with NMR spectroscopy, and Colin Kilner for
crystallographic help.
6 Criteria of bulk purity and identity were clean NMR spectra
consistent with the results of the X-ray diffraction analysis. In each
case positive-ion mass spectrometry (EI, 70 eV) gave highest
mass isotopomer envelopes corresponding to a mixture of Mϩ and
(M Ϫ 2H)ϩ, with principal fragmentations involving loss of PMe2Ph
(compound 3) and loss of {Me} and {C(NHMe)2} (compound 4).
NMR data at 297–300 K (CDCl3), ordered as δ(11B)/ppm [δ(1H)/
ppm of directly bound hydrogen atoms] (relative intensity): for
[(η5-C5Me5)HIrB18H19(PMe2Ph)] (compound 3) — ca. ϩ17.0 [ϩ3.86]
(1BH), ϩ16.5 [ϩ3.95] (1BH), ϩ5.0 [no exo H] (1B), ϩ2.9 [ϩ3.25]
(1BH), ca. ϩ1.5 [ϩ4.79] (1BH), ca. ϩ0.7 [ϩ3.01] (1BH), ca. Ϫ1.0
[ϩ2.30] (1BH), Ϫ2.0 [ϩ2.14] (1BH), Ϫ8.7 [ϩ1.98] (1BH), ca. Ϫ10.8
[no exo H] (1B), ca. Ϫ11.7 [ϩ1.97] (1BH), ca. Ϫ16.2 [ϩ2.03] (1BH),
ca. Ϫ16.8 [ϩ2.11] (1BH), ca. Ϫ20.4 [no exo H, unresolved coupling
1J(31P–11B) ca. 150 Hz] (1B), ca. Ϫ21.7 [ϩ0.15] (1BH), Ϫ25.3 [ϩ1.74]
(1BH), Ϫ29.4 [Ϫ1.24] (1BH), Ϫ40.0 [ϩ 0.07] (1BH); additionally
δ(1H) at ϩ1.12, Ϫ1.02, Ϫ2.63 [unresolved doublet splitting
2J(31P–1H) ] and Ϫ2.89 (4 × Hµ), at ϩ2.06 (15H, C5Me5), at ϩ1.98
(3H, PMe) and ϩ1.94 (3H, PMe), and at Ϫ14.89 (1H, IrH), with
δ(31P) Ϫ2.6 ppm [unresolved coupling 1J(31P–11B) ca. 150 Hz]; for
[(η5-C5Me5)HIrB18H19{C(NHMe)2}] (compound 4) — ca. ϩ6.0
[ϩ3.81] (1BH), ca. ϩ16.7 [ϩ3.98] (1BH), ϩ5.0 [no exo H] (1B), ϩ2.0
[ϩ3.22] (1BH), ca. ϩ0.5 [ϩ4.83] (1BH), ca. ϩ0.1 [ϩ3.01] (1BH),
Ϫ2.2 [ϩ2.31] (1BH), ca. Ϫ2.0 [ϩ1.95] (1BH), Ϫ10.9 [ϩ1.58] (1BH),
Ϫ10.2 [no exo H] (1B), ca. Ϫ9.1 [ϩ1.99] (1BH), ca. Ϫ17.5 [ϩ2.00]
(1BH), ca. Ϫ17.0 [ϩ2.38] (1BH), Ϫ16.4 [no exo H] (1B), ca. Ϫ22.1
[ϩ0.13] (1BH), Ϫ25.8 [ϩ1.70] (1BH), Ϫ28.9 [Ϫ1.17] (1BH), Ϫ40.3
[ϩ 0.08] (1BH); additionally δ(1H) at ϩ1.12, Ϫ1.04, Ϫ2.57 and
Ϫ2.84 (4 × Hµ), at ϩ2.07 (15H, C5Me5), at ϩ3.20 (3H, NMe) and
ϩ2.92 (3H, NMe), at ϩ0.96 (1NH) and ϩ0.88 (1NH) and at Ϫ14.93
(1H, IrH).
References
† A IUPAC nomenclature for compound 3 would be 11-(dimethyl-
phenylphosphine)-9-pentahapto-pentamethylcyclopentadienyl-9-
hydrido-nido-9-iridaundecaborano-〈7,8:5Ј,6Ј〉-nido-decaborane.
‡ A IUPAC nomenclature for compound 4 would be 11-{bis(methyl-
amino)carbene}-9-pentahapto-pentamethylcyclopentadienyl-9-
hydrido-nido-9-iridaundecaborano-〈7,8:5Ј,6Ј〉-nido-decaborane.
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2 J. D. Kennedy, in Advances in Boron Chemistry, ed. W. Siebert, Royal
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B. Stíbr, J. D. Kennedy and M. Thornton-Pett, in Advances in Boron
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5 Single-crystal X-ray data: compound 3, [(η5-C5Me5)HIrB18H19-
(PMe2Ph)], C18H46B18IrP: M = 680.30, triclinic (yellow block, 0.52 ×
¯
0.35 × 0.32 mm, from CH2Cl2/C6H14), space group P1, a =
10 See, for example, A. A. Arduengo, H. V. R. Dias, J. C. Calabrese and
F. Davidson, J. Am. Chem. Soc., 1992, 114, 9724.
11 E. J. Ditzel, X. L. R. Fontaine, N. N. Greenwood, J. D. Kennedy,
10.2788(9), b = 17.251(2), c = 18.126(2) Å, α = 99.201(8)Њ, β =
98.006(9)Њ, γ = 90.678(8)Њ, U = 3140.0(5) Å3, Dcalc = 1.439 Mg mϪ3
,
Z = 4, Mo-Kα, λ = 0.71073 Å, µ = 4.314 mm1, T = 160(2) K,
R1{I > 2σ(I )} = 0.0318 and wR2 = 0.0692 for all 10075 reflections
collected; compound 4, syn-[(η5-C5Me5)HIrB18H19{C(NHMe)2}],
Zhu Sisan, B. Stíbr and M. Thornton-Pett, J. Chem. Soc., Chem.
ˇ
Commun., 1990, 1741.
12 P. McArdle, ORTEX, version 5, J. Appl. Crystallogr., 1995, 28, 65.
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