The first 8-vertex monocarbon metallacarborane with an isolated boron-capped pentagonal bipyramidal cage. Synthesis and molecular structure of capped closo-2,2-(Ph3P)2-2-H-3,6,8-(MeO)3-RuCB 6H4

Article abstract of DOI:10.1021/ic010216h

The molecular structure of 8-vertex capped closo-[(Ph₃P)₂HRuCB₆H₄(OMe) ₃] has been elucidated by an X-ray diffraction study. The cluster features a unique RuCB₆ skeleton and cage geometry which is based on a boron-capped pentagonal bipyramid. This constitutes the first reported example of metallacarboranes with an isolated (nonfused) polyhedron exhibiting such geometry.

Full text of DOI:10.1021/ic010216h

5318
Inorg. Chem. 2001, 40, 5318-5319
The First 8-Vertex Monocarbon Metallacarborane with an “Isolated” Boron-Capped Pentagonal
Bipyramidal Cage. Synthesis and Molecular Structure of Capped
closo-2,2-(Ph3P)2-2-H-3,6,8-(MeO)3-RuCB6H4
Irina V. Pisareva, Fedor M. Dolgushin, Alexandr I. Yanovsky, Elena V. Balagurova, Pavel V. Petrovskii, and
Igor T. Chizhevsky*
A. N. Nesmeyanov Institute of Organoelement Compounds, 28 Vavilov Street, 119991 Moscow, Russian Federation
ReceiVed February 23, 2001
The electronic and cluster structures of electron-deficient closo-
metallacarboranes not conforming with Wade’s electron counting
rules have been of interest for a long time.1,2 Among the known
n-vertex metallacarboranes of this type, which formally possess
fewer than 2n + 2 electrons for skeletal bonding,3 species having
an 8-vertex cluster configuration with “isolated” (nonfused)
pentagonal bipyramidal polyhedra, to our best knowledge,
remained unknown. We now report the first such example of a
structurally characterized 8-vertex monocarbon metallacarborane
derived from the partially contracted monocarbon carborane [nido-
B10H12CH]-.
We recently reported the synthesis of the two novel hyper-
closo-type monocarbon RuCB8 clusters which were formed as
main products in the polyhedral contraction reaction of [nido-
B10H12CH]-Cs+ promoted by RuCl2(PPh3)3 in hot methanol.4
Among those species which were individually isolated from the
reaction mixture and identified as having low-coordinate boron
Figure 1. General view of molecule 1. Selected distances (Å) and bond
angles (deg): Ru(2)-P(1), 2.3630(15); Ru(2)-P(2), 2.3617(13); Ru(2)-
H(2), 1.40(4); Ru(2)-C(1), 2.301(5); Ru(2)-B(3-6), 2.258(5)-2.336(5);
Ru(2)-B(8), 1.961(5); B(8)‚‚‚H(2), 1.61(4); B(4)-B(8), 1.839(7); B(5)-
B(8), 1.838(8); C(1)-B(3), 1.530(7); C(1)-B(6), 1.538(7); P(1)Ru(2)P(2),
99.79(5); P(1)Ru(2)H(2), 85.1(2); P(2)Ru(2)H(2), 77.8(2); H(2)Ru(2)B(8),
54.0(2); H(2)B(8)Ru(2), 45.0(2); Ru(2)H(2)B(8), 81.0(2).
atoms, which are usually indicative of specific electronic cluster
structures, of particular interest is a pale yellow diamagnetic
crystalline solid with the formula (Ph3P)2HRuCB6H4(OMe)3 (1).4
1
Although the H and 11B/11B{1H} NMR spectra as well as the
FAB mass spectrum5 of this latter complex were consistent with
its 8-vertex geometry, these data alone were insufficient for
unambiguous assignment of the detailed cluster structure of this
species. An X-ray diffraction study6 of 1 was, therefore, under-
taken which proved this species to be a small monocarbon
ruthenacarborane capped closo-2,2-(Ph3P)2-2-H-3,6,8-(MeO)3-
RuCB6H4 with a number of interesting structural features (Fig-
ure 1).
The polyhedral cage geometry of 1 is based on a pentagonal
bipyramid with one additional boron vertex capping one of its
faces. Complex 1 may thus be regarded as the first boron-capped
pentagonal bipyramidal metallacarborane. The ruthenium center
in the cluster is bonded to one carbon and five boron atoms of
the monocarbon carborane cage, of which four are located in the
equatorial plane of the bipyramid and the fifth occupies the
capping position. The metal atom is additionally coordinated by
the two PPh3 groups and a terminal hydrogen ligand. In contrast
to the known bimetallacarboranes [Me4C4B8H8FeCo(η5-Cp)]7 and
[Me4C4B8H8FeCo(PEt3)2]8 consisting of two fused 7-vertex
pentagonal bipyramidal closo polyhedra with the unique boron
atom wedged between both cages, the capping B(8) atom in 1 is
(1) (a) Nishimura, E. K. J. Chem. Soc., Chem. Commun. 1978, 858. (b)
Crook, J. E.; Elrington, M.; Greenwood, N. N.; Kennedy, J. D.; Woollins,
J. D. Polyhedron 1984, 1, 901. (c) Baker, R. T. Inorg. Chem. 1986, 25,
109. (d) Kennedy, J. D. Inorg. Chem. 1986, 25, 111. (e) Johnston, R.
L.; Mingos, D. M. P. Inorg. Chem. 1986, 25, 3321. (f) Kennedy, J. D.
Prog. Inorg. Chem. 1986, 34, 211. (g) Johnston, R. L.; Mingos, D. M.
P.; Sherwood, P. New J. Chem. 1991, 15, 831.
(2) (a) Wade, K. J. Chem. Soc., Chem. Commun. 1971, 792. (b) Wade, K.
AdV. Inorg. Chem. Radiochem. 1976, 18, 1.
(3) (a) Gallahan, K. P.; Evans, W. J.; Lo, F. Y.; Strouse C. E.; Hawthorne
M. F. J. Am. Chem. Soc. 1975, 97, 296. (b) Salentine, C. G.; Hawthorne
M. F. Inorg. Chem. 1978, 17, 1498. (c) Jung, C. W.; Baker, R. T.;
Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc. 1980, 102, 5782.
(d) Jung, C. W.; Baker, R. T.; Hawthorne, M. F. J. Am. Chem. Soc.
1981, 103, 810. (e) Crook, J. E.; Greenwood, N. N.; Kennedy, J. D.;
McDonald, W. S. J. Chem. Soc., Chem. Commun. 1981, 933. (f) Bould,
J.; Greenwood, N. N.; Kennedy, J. D.; McDonald, W. S. J. Chem. Soc.,
Chem. Commun. 1982, 465. (g) Micciche, R. P.; Briguglio, J. J.; Sneddon,
L. G. Inorg. Chem. 1984, 23, 3992. (h) Crook, J. E.; Elrington, M.;
Greenwood, N. N.; Kennedy, J. D.; Thornton-Pett, M.; Woollins, J. D.
J. Chem. Soc., Dalton Trans. 1985, 2407.
(4) Pisareva, I. V.; Chizhevsky, I. T.; Petrovskii, P. V.; Bregadze, V. I.;
Dolgushin F. M.; Yanovsky, A. I. Organometallics, 1997, 16, 5598.
(5) Complex 1 was prepared in 8% yield as described elsewhere4 with some
modification of the purification procedure. Characterization data for 1:
1H NMR (400.13 MHz, C6D6, 22° C) δ 7.51, 6.97, (m + m, 12H +
18H, Ph), 4.17 (s, 3H, MeO), 3.05 (s, 6H, 2 × MeO), 2.99 (s, br, 1H,
CHCb), -9.02 (t, br, 1H, HRu, 2J(H,P) ) 20.7 Hz); 31P{1H} NMR (161.98
MHz, C6D6) 49.4 (s, PRu); 11B NMR (128.33 MHz, CD2Cl2, J(B,H) (Hz))
(6) Crystal data for 1: RuC40H44B6O3P2Ru‚n-C6H14, triclinic, space group
P1h, a ) 12.823(3) Å, b ) 13.125(3) Å, c ) 14.688(3) Å, R ) 86.34(3)°,
â ) 84.17(3)°, γ ) 68.22(3)°, V ) 2282.8(8) Å3 for Z ) 2, d(calc) )
1.290 g/cm3. Data collection was carried out on a Siemens P3/PC
diffractometer (λ(Mo KR) ) 0.71073 Å, T ) 293(2) K, θ/2θ scan, θ e
25°). The structure was solved by direct methods; 8110 independent
reflections (Rint ) 0.0603) were collected and used in the refinement;
R1 ) 0.0597 (on F for 5539 observed reflections with I > 2σ(I)), wR2
) 0.1047, and GOF ) 1.071 (on F2 for all data).
+68.9 (s, br, 1B, B(8)), +33.7 (s, 2B, B(3,6)), +12.8 (d, 1B, 140), -31.8
12
(d, 2B, 150); FAB MS (positive ion, m/e) calcd for
C
1H4411B616O3-
40
31P2101Ru 801.2, found 801.6 [M+], 724.4 [M - Ph]+, 647.3 [M - 2Ph]+,
570.2 [M - 3Ph], 539.4 [M - PPh3]+, 462.4 [M - PPh3 - Ph]+. Anal.
Calcd for C40H44B6O3P2Ru: C, 60.00; H, 5.54. Found: C, 59.46; H,
5.63.
(7) Maxwell, W. M.; Sinn, E.; Grimes, R. N. J. Am. Chem. Soc. 1976, 98,
3493.
(8) Barker, G. K.; Garcia, M. P.; Green, M.; Stone, F. G. A.; Welch, A. J.
J. Chem. Soc., Dalton Trans. 1982, 1679.
10.1021/ic010216h CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/06/2001

Communications
Inorganic Chemistry, Vol. 40, No. 21, 2001 5319
1
the cage boron atoms substituted by MeO groups. The H and
31P{1H} NMR spectra of 1, measured at room temperature, are
also consistent with its symmetrical structure. In particular, the
1
terminal hydride resonance appears in the H NMR spectra of 1
as a broadened triplet at δ(1H) -9.02 ppm (line width ca. 22 Hz)
exhibiting a coupling of hydrogen to two equivalent PPh3 groups
[2J(HRu,P) ) 20.7 Hz] and, apparently, a boron nucleus. Taking
into account the essentially short Ru-H‚‚‚B(8) distance found
in the solid-state structure of 1, the broadening of a high-field
triplet resonance is caused either by a unique spin-spin through-
space interaction of the metal hydride and the capping B(8) atom
or by the long-range coupling 2J(HRu,B8). Indeed, in the selective
boron-decoupling experiment, when the B(8) resonance at δ
+68.9 ppm was decoupled, the line width of the hydride triplet
at δ -9.02 ppm significantly decreased (from 22 to 12 Hz),
indicating the presence of this type of interaction in solution of
1. The 31P{1H} NMR spectrum of 1 showed one singlet at δ(31P)
49.4 ppm from the two equivalent PPh3 groups at the metal vertex.
Consequently, decoupling of 31P nuclei caused a collapse of the
hydride triplet at -9.02 ppm to a singlet with the same line width
Figure 2. Geometrical and structural relationship between the contracted
hyper-closo-RuCB8 (2) and hyper-closo-RuCB6 (1) clusters.
located roughly symmetrically over one of the faces of the
bipyramid (B(4)-B(5)-Ru) and has a formal cluster connectivity
of 3. The single cage carbon atom in the polyhedron framework
is in the trans position with respect to the capped BBRu face, so
that the complex can be considered as having overall Cs symmetry.
Two boron atoms B(3) and B(6) adjacent to the cage carbon as
well as the unique B(8) atom in 1 are substituted by methoxy
functions. This indicates that 1 is probably formed via methanolic
deboronation of hyper-closo-2,2-(PPh3)2-2-H-3,9-(MeO)2-2,1-
RuCB8H7 (2), one of the two RuCB8 clusters isolated as main
products from the polyhedral contraction reaction of [nido-
B10H12CH]-Cs+ with RuCl2(PPh3)3.4 It is apparent from the
comparison of the cluster geometry of 1 and 2 (Figure 2) that
formal removal of both low-connectivity boron atoms, B(6) and
B(9), from the RuCB8 skeleton of 2 would have produced a
metallacarborane framework identical to that of complex 1.9
The Ru(2)-B(8) bond 1.961(5) Å happens to be the shortest
Ru-B bond ever observed in ruthenium complexes of any boron
derivatives. It is about 0.25 Å shorter than the average bond length
calculated across all reported Ru-B distances (689 values
retrieved from 161 structures with Ru-B bonds of any type found
in the Cambridge Structural Database; Release April 2000) and
still noticeably shorter than the shortest Ru-B distance of 1.993
Å previously observed in the mixed-metal cluster Cy3PAuIr2Ru4B-
(CO)1610 featuring the interstitial boron atom in the center of the
Ir2Ru4 octahedron. Interestingly, the shortest ever recorded Fe-B
distance is the distance from a similar capping boron vertex to
the central iron atom in the electron-deficient complex [Me4C4B8H8-
FeCo(η5-Cp)]7 mentioned above. All these taken together indicate
that the capping boron atom has a rather peculiar electronic
environment which allows somewhat closer approach of such
boron vertexes to the metal centers as compared to boron atoms
within any other boron-containing units. The short Ru(2)-B(8)
distance in 1 results in the H(2) hydrogen being as close to the
B(8) atom as 1.61(4) Å. This close approach of the metal hydride
to the capping boron atom is reflected in the unique H(Ru)‚‚‚B(8)
spin-spin interaction observed in the 1H NMR spectra of 1 (vide
infra).
1
as the triplet had in the non-boron-decoupled H NMR spectra.
Following the skeletal electron-counting rules2 and considering
a (Ph3P)2HRu group as contributing three orbitals and one electron
(8 + 2 × 2 + 1 - 12 ) 1) to the monocarbon CB6 cage for
skeletal bonding, cluster 1 has only 16 skeletal electrons, i.e.,
two electrons fewer than required for a canonical 8-vertex closo
cluster. It may therefore be considered as a 2n skeletal electron
hyper-closo system. At the same time, there is an alternative way
for description of such complexes on the basis of the polyhedral
skeletal electron pair theory (PSEPT).11 Indeed, in accord with
the capping principle,12 which implies that both the capped and
parent uncapped closed polyhedra accommodate the same number
of skeletal electrons for cluster bonding, the 2n cluster electron
count for 1 predicts its capped-closo geometry. Thus, complex 1
may be regarded as a pileo cluster1f which clearly conforms to
PSEPT for 8-vertex clusters containing a total of 16 skeletal
electrons. Up to now, most of the known capped closo (or pileo)
clusters in the field are bimetalla- or trimetallaboranes based on
a capped octahedron which involves a BH or metal-containing
group capping one of the cluster faces.13 The structure of cluster
1 provides the first and a quite unique example of a capped closo-
metallacarborane based on pentagonal bipyramidal geometry.
Acknowledgment. The authors gratefully acknowledge the
financial support of the Russian Foundation for Basic Research
(Grants 00-03-32824 and 00-03-32807). We are indebted to Dr.
1
1
O. L. Tok for the recording of selective H{11B} and H{31P}
NMR spectra of 1.
In accord with the overall Cs symmetry, the 11B NMR spectra
of 1 revealed the presence of a set of four resonances of relative
areas 1:2:1:2 with one of the resonances shifted to extremely low
field. This unique signal at δ(11B) +68.9 ppm is highly indicative
of a low-coordinate boron atom and has been, therefore, tentatively
assigned to the capping B(8) atom. Two of the four resonances
mentioned above, namely, those at δ(11B) +68.9 (1B) and +33.7
(2B) ppm, on proton decoupling collapsed to somewhat broadened
and sharp singlets, respectively, supporting their assignment to
Supporting Information Available: Experimental details for the
preparation of 1. X-ray crystallographic file (CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
IC010216H
(11) (a) Williams, R. E. Inorg. Chem. 1971, 10, 210. (b) Mingos, D. M. P.
Acc. Chem. Res. 1984, 17, 311.
(12) (a) Mingos, D. M. P. Nature Phys. Sci. 1972, 236, 99. (b) Mingos, D.
M. P.; Forsyth, M. I. J. Chem. Soc., Dalton Trans. 1977, 610.
(13) See, for instance: (a) Pipal, J. R.; Grimes, R. N. Inorg. Chem. 1977, 12,
3255. (b) Venable, T. L.; Grimes, R. N. Inorg. Chem. 1982, 21, 887. (c)
Venable, T. L.; Sinn, E.; Grimes, R. N. Inorg. Chem., 1982, 21, 904.
(d) Bullick, H. J.; Grebenik, P. D.; Green, M. L. H.; Hughes, A. K.;
Leach, J. B.; Mountford, P. J. Chem. Soc., Dalton Trans. 1994, 3337.
(e) Bould, J.; Rath, N. P.; Barton, L. Organometallics 1995, 14, 2119.
(f) Bould, J.; Rath, N. P.; Barton, L. J. Chem. Soc., Chem. Commun.
1995, 1285. (g) Lei, X.; Shang, M.; Fehlner, T. P. J. Am. Chem. Soc.
1999, 121, 1275.
(9) A similar approach has been used for the explanation of an unusual cluster
geometry of isonido-[{IrC(OH)B8H6(OMe)}(C6H4PPh2)(PPh3)], which
is obtained via methanolic deboronation of closo-[B10H10]2- in the
presence of trans-Ir(CO)Cl(PPh3)2.3e The removal of a 4-connected rather
than the 6-connected vertex from closo-[B10H10]2- has been postulated
to occur in the reaction.
(10) Galsworthy, J. R.; Hattersley, A. D.; Housecroft, C. E.; Rheingold, A.;
Waller, L. A. J. Chem. Soc., Dalton Trans. 1995, 549.