Stable exo-nido-metallacarboranes (M = OsIV) that incorporate meta-carborane-based dicarbollide ligands

Article abstract of DOI:10.1021/ja067838s

Reactions of the [K]⁺ salts of the [nido-7,9-C₂B ₉H₁₂]^- anion (2) and its C-phenylated derivative [7-Ph-nido-7,9-C₂B₉H₁₁]^- (4) with [OsCl₂(PPh₃)₃] (3) proceed in benzene at ambient temperature with the formation of 16-electron chlorohydrido-Os(IV) exo-nido complexes, [exo-nido-10,11-{(Ph₃P)₂OsHCl}-10,-11- (μ-H)₂-7-R-7,9-C₂B₉H₈] (5: R = H; 6: R = Ph), along with the small amounts of the charge-compensated nido-carboranes [nido-7,9-C₂B₉H₁₁ PPh ₃] (7) and [7-Ph-nido-7,9-C₂B₉H ₁₀PPh₃] (8) as byproducts. However, when carried out under mild heating in ethanol, the reaction of 2 with 3 selectively afforded a 16-electron dihydrido-Os(IV) exo-nido complex [exo-nido-10,11-{(Ph ₃P)₂OsH₂}-10,11-(μ-H)₂-7,9-C ₂B₉H₉] (9). Structures of both complexes 5 and 9 have been confirmed by single-crystal X-ray diffraction studies, which revealed that nido-carboranes in these species function as a bidentate dicarbollide ligands [7-R-nido-7,9-C₂B₉H ₁₀]^2- linked to the Os(IV) center via two B-H...Os bonds involving adjacent B-H vertices in the upper CBCBB belt of the carborane cage. Thus, compounds 5 and 9 represent the first structurally characterized exo-nido-metallacarboranes based on meta-dicarbollide-type ligands. Variable-temperature ¹H and ³¹P{¹H} NMR experiments indicate that complex 9 is fluxional in solution and shows an unusual exchange between terminal Os-(H)₂ and bridging {B-H} ₂...Os hydrogen atoms. Upon heating in d₈-THF at 65 °C, complex 9 converts irreversibly to its close isomer [2,2-(PPh ₃)₂-2,2-H₂-closo-2,1,7-OsC₂B ₉H₁₁] (13), which could thus be obtained as a pure crystalline solid. The structure of 13 has been established on the basis of analytical and multinuclear NMR data and a single-crystal X-ray diffraction study.

Full text of DOI:10.1021/ja067838s

Published on Web 03/07/2007
Stable exo-nido-Metallacarboranes (M ) OsIV) that Incorporate
meta-Carborane-Based Dicarbollide Ligands
Elena V. Balagurova, Dmitri N. Cheredilin, Galina D. Kolomnikova, Oleg L. Tok,
Fedor M. Dolgushin, Alexander I. Yanovsky, and Igor T. Chizhevsky*
Contribution from the A.N. NesmeyanoV Institute of Organoelement Compounds,
28 VaViloV Street, 119991 Moscow, Russia
Received November 2, 2006; E-mail: chizbor@ineos.ac.ru
Abstract: Reactions of the [K]+ salts of the [nido-7,9-C2B9H12]- anion (2) and its C-phenylated derivative
[7-Ph-nido-7,9-C2B9H11]- (4) with [OsCl2(PPh3)3] (3) proceed in benzene at ambient temperature with the
formation of 16-electron chlorohydrido-Os(IV) exo-nido complexes, [exo-nido-10,11-{(Ph3P)2OsHCl}-10,-
11-(µ-H)2-7-R-7,9-C2B9H8] (5: R ) H; 6: R ) Ph), along with the small amounts of the charge-compensated
nido-carboranes [nido-7,9-C2B9H11PPh3] (7) and [7-Ph-nido-7,9-C2B9H10PPh3] (8) as byproducts. However,
when carried out under mild heating in ethanol, the reaction of 2 with 3 selectively afforded a 16-electron
dihydrido-Os(IV) exo-nido complex [exo-nido-10,11-{(Ph3P)2OsH2}-10,11-(µ-H)2-7,9-C2B9H9] (9). Structures
of both complexes 5 and 9 have been confirmed by single-crystal X-ray diffraction studies, which revealed
that nido-carboranes in these species function as a bidentate dicarbollide ligands [7-R-nido-7,9-C2B9H10]2-
linked to the Os(IV) center via two B-H‚‚‚Os bonds involving adjacent B-H vertices in the upper CBCBB
belt of the carborane cage. Thus, compounds 5 and 9 represent the first structurally characterized exo-
nido-metallacarboranes based on meta-dicarbollide-type ligands. Variable-temperature 1H and 31P{1H} NMR
experiments indicate that complex 9 is fluxional in solution and shows an unusual exchange between terminal
Os-(H)2 and bridging {B-H}2‚‚‚Os hydrogen atoms. Upon heating in d8-THF at 65 °C, complex 9 converts
irreversibly to its closo isomer [2,2-(PPh3)2-2,2-H2-closo-2,1,7-OsC2B9H11] (13), which could thus be obtained
as a pure crystalline solid. The structure of 13 has been established on the basis of analytical and
multinuclear NMR data and a single-crystal X-ray diffraction study.
d metal and the number of heteroatom substituents.2 The exo-
nido-metallacarborane complexes of the d-block metals together
Introduction
Since the mid 1980s, much progress has been made in the
studies of a new class of complexes which became known as
exo-nido-metallacarboranes. The metal-containing moiety in
these complexes is attached to the {nido-C2B9} carborane cage
either through multiple 2e,3c {B-H}n‚‚‚M (n ) 2, 3) bonds1
or via one or two exo-polyhedral M-E bonds (E is a hetero-
atom-containing cage substituent), which may be supported by
one or two B-H‚‚‚M linkages, depending on the nature of the
with their closo isomers are known to play an important role in
the field, frequently representing efficient precatalysts for
organic reactions3 and, in some cases, useful building-block
reagents for the construction of novel mono- and binuclear
metallacarboranes of different types and structures.4 Although
exo-nido species are, at present, well documented and there are
about three dozen of the structurally studied exo-nido-metalla-
carboranes of p-, d-, and f-block elements,1,2,5 none of these
species found in the literature involved any carborane ligands
other than those derived from the [nido-7,8-C2B9H12]- anion,
(1) (a) Doi, J. A.; Teller, R. G.; Hawthorne, M. F. J. Chem. Soc., Chem.
Commun. 1980, 80. (b) Long, J. A.; Marder, T. B.; Behnken, P. E.;
Hawthorne, M. F. J. Am. Chem. Soc. 1984, 106, 2979. (c) Knobler, C. B.;
Marder, T. B.; Mizusawa, E. A.; Teller, R. G.; Long, J. A.; Behnken, P.
E.; Hawthorne, M. F. J. Am. Chem. Soc. 1984, 106, 2990. (d) Hewes, J.
D.; Kreimendahl, C. W.; Marder, T. B.; Hawthorne, M. F. J. Am. Chem.
Soc. 1984, 106, 5757. (e) Brew, S. A.; Jeffery, J. C.; Mortimer, M. D.;
Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1992, 1365. (f) Chizhevsky,
I. T.; Lobanova, I. A.; Bregadze, V. I.; Petrovskii, P. V.; Antonovich, V.
A.; Polyakov, A. V.; Yanovsky, A. I.; Struchkov, Yu. T. MendeleeV
Commun. 1991, 47. (g) Lobanova, I. A.; Bregadze, V. I.; Timofeev, S. V.;
Petrovskii, P. V.; Starikova, Z. A.; Dolgushin, F. M. J. Organomet. Chem.
2000, 597, 48. (h) Timofeev, S. V.; Lobanova, I. A.; Petrovskii, P. V.;
Starikova, Z. A.; Bregadze, V. I. Russ. Chem. Bull. 2001, 50, 2245. (i)
Kolomnikova, G. D.; Petrovskii, P. V.; Sorokin, P. V.; Dolgushin, F. M.;
Yanovsky, A. I.; Chizhevsky, I. T. Russ. Chem. Bull. 2001, 50, 706. (j)
Cheredilin, D. N.; Balagurova, E. V.; Godovikov, I. A.; Solodovnikov, S.
P.; Chizhevsky, I. T. Russ. Chem. Bull. 2005, 54, 2535. (k) Cheredilin, D.
N.; Dolgushin, F. M.; Korlyukov, A. A.; Godovikov, I. A.; Kadyrov, R.;
Balagurova, E. V.; Solodovnikov, S. P.; Chizhevsky, I. T. J. Organomet.
Chem. 2006, 691, 3989.
(2) (a) Teixidor, F.; Ayllo´n, J. A.; Vin˜as, C.; Kiveka¨s, R.; Sillanpa¨a¨, R.; Casabo,
J. J. Chem. Soc., Chem. Commun. 1992, 1281. (b) Teixidor, F.; Vin˜as, C.;
Casabo, J.; Romerosa, A. M.; Rius, J.; Miravitlles, C. Organometallics 1994,
13, 914. (c) Teixidor, F.; Ayllo´n, J. A.; Vin˜as, C.; Kiveka¨s, R.; Sillanpa¨a¨,
R.; Casabo, J. Organometallics 1994, 13, 2751. (d) Vin˜as, C.; Nun˜ez, R.;
Flores, M. A.; Teixidor, F.; Kiveka¨s, R.; Sillanpa¨a¨, R. Organometallics
1995, 14, 3952. (e) Vin˜as, C.; Nun˜ez, R.; Teixidor, F.; Kiveka¨s, R.;
Sillanpa¨a¨, R. Organometallics 1996, 15, 3850. (f) Teixidor, F.; Flores, M.
A.; Vin˜as, C.; Kiveka¨s, R.; Sillanpa¨a¨, R. Angew. Chem., Int. Ed. Engl.
1996, 35, 2251. (g) Vin˜as, C.; Flores, M. A.; Nun˜ez, R.; Teixidor, F.;
Kiveka¨s, R.; Sillanpa¨a¨, R. Organometallics 1998, 17, 2278. (h) Vin˜as, C.;
Nun˜ez, R.; Teixidor, F.; Kiveka¨s, R.; Sillanpa¨a¨, R. Organometallics 1998,
17, 2376. (i) Teixidor, F.; Benakki, R.; Vin˜as, C.; Kiveka¨s, R.; Sillanpa¨a¨,
R. Organometallics 1998, 17, 4630. (j) Teixidor, F.; Flores, M. A.; Vin˜as,
C.; Kiveka¨s, R.; Sillanpa¨a¨, R. Organometallics 1998, 17, 4675. (k) Barbera`,
G.; Vin˜as, C.; Teixidor, F.; Rosair, G. M.; Welch, A. J. J. Organomet.
Chem. 2002, 663, 221.
9
10.1021/ja067838s CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 3745-3753
3745

A R T I C L E S
Balagurova et al.
the most common representative among the 11-vertex nido-
carborane isomers.
In the present work, the synthesis of a short series of three
stable 16-electron exo-nido-osmacarborane complexes of the
general formula [exo-nido-{(Ph3P)2HXOs}-10,11-(µ-H)2-7-R-
7,9-C2B9H10] (5: R ) H, X ) Cl; 6: R ) Ph, X ) Cl; 9: R
) X ) H) is described. In each of these complexes, the dianionic
[nido-7-R-7,9-C2B9H10]2- cage ligand is bound to the Os(IV)-
containing moiety via the bidentate {B-H}2‚‚‚Os bonding
interaction, and an exo-nido structure of all species is retained
both in the solid state and in solution.
We are aware of several previous attempts to synthesize exo-
nido-metallacarborane complexes (M ) Rh) based on the related
{nido-7,9-C2B9} carborane derivatives and, in particular, via
the direct reaction of [RhCl(PPh3)3] with the [Me3NH]+ salt of
the [nido-7-Me-9-Ph-7,9-C2B9H10]- anion in hot ethanol.6
Although one would expect that the steric effects associated
with the bulky C,C′ cage substituents in the starting {nido-7,9-
C2B9} carborane salt should enhance the stability of the desired
Rh(I) exo-nido species, the isomeric Rh(III) closo complex
identified as [closo-2,2-(Ph3P)2-2-H-1-Me-7-Ph-2,1,7-RhC2B9H9]
(1) was, unexpectedly, isolated instead in moderate yield.6
Further attempts to stabilize exo-nido-rhodacarborane isomers
by the replacement of PPh3 ligands in 1 with phosphine groups
having larger cone angles, such as, P(m-tolyl)3, P(o-tolyl)3, and
PCy3, failed, although in the case of the substitution reaction
with PCy3, the formation of the species which presumably
retained an exo-nido structure in solution has been detected by
the 31P{1H} NMR spectroscopy.6 At last, when the carborane
ligand exchange reaction of the Cs+ salt of the [nido-7,9-
C2B9H12]- anion (2), employed as the nucleophilic reagent, with
the [exo-nido-4,9-{(PPh3)2Rh}-4,9-(µ-H)2-7-Me-8-Ph-7,8-C2B9H8]
was monitored by the 31P{1H} NMR spectroscopy, the kineti-
cally unstable unsubstituted exo-nido intermediate was initially
observed along with its conversion to the more stable closo
isomer [closo-2,2-(Ph3P)2-2-H-2,1,7-RhC2B9H11].4a
Results and Discussion
Synthesis of exo-nido-Osmacarborane Complexes 5, 6, and
9. As a part of our ongoing studies on the chemistry1f,i-k,4b,c,f,g
and catalytic activity3c,k of “three-bridge” exo-nido-metallacar-
boranes, we have previously developed a convenient synthetic
procedure allowing one to obtain a series of new 18-electron
exo-nido-metallacarboranes of the type [exo-nido-5,6,10-
{(Ph3P)2ClM}-5,6,10-(µ-H)3-10-H-7-R-8-R′-7,8-C2B9H6] (M )
Ru,1f Os;1i R, R′ ) H, Me, PhCH2) in modest to high yields.
This was based on the room-temperature reaction in benzene
between [RuCl2(PPh3)3] or [OsCl2(PPh3)3] (3) and the [K]+ salts
of the corresponding [nido-7-R-8-R′-7,8-C2B9H10]- anions.
Since all three-bridge exo-nido complexes thus prepared were
quite stable both in the solid state and in solution, we decided
to use this mild and efficient method to try to generate exo-
nido-osmacarborane complexes incorporating “carbons-apart”
{nido-7,9-C2B9} carborane ligands, which, as yet, have not been
known within this particular category of metallacarborane
complexes. Accordingly, similar reactions in benzene of osmium
reagent 3 with the [K]+ salts of the [nido-7,9-C2B9H12]- anion
2 or its C-phenylated derivative [nido-7-Ph-7,9-C2B9H11]- (4)
were carried out, and each has been found to afford “two-bridge”
16-electron exo-nido-osmacarboranes that were analyzed cor-
rectly for [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(µ-H)2-7-R-
7,9-C2B9H8] (5: R ) H; 6: R ) Ph), respectively.
These electron-deficient complexes 5 and 6 were isolated,
after silica gel column chromatography, in 56 and 62% yield,
respectively, along with small amounts of [nido-7-R-7,9-
C2B9H10PPh3] (7: R ) H; 8: R ) Ph) formed as byproducts
and a trace of an initially unidentified dark-green solid in the
case of the former reaction. Remarkably, when the reaction of
3 with a 10% molar excess of the [K]+ salt of an unsubstituted
anion 2 was carried out in hot ethanol (50 °C, ca. 2.5 h) instead
of benzene, the dark-green species was isolated in 68% yield,
and this, on the basis of analytical and multinuclear NMR data,
was formulated as a dihydrido-osmium complex [exo-nido-10,-
11-{(Ph3P)2OsH2}-10,11-(µ-H)2-7,9-C2B9H9] (9) (Scheme 1).
Complexes 5, 6, and 9 were all stable microcrystalline solids
soluble in CH2Cl2, THF, and moderately in C6H6 and could
thus be purified by recrystallization from CH2Cl2/n-hexane upon
cooling. Further support for the exo-nido structure of the
complexes so obtained and their precise connectivity pattern
was provided by X-ray diffraction studies of two selected
complexes 5 and 9. Zwitterionic triphenylphosphine-cage-
substituted nido-carboranes 7 and 8 were identified as such using
NMR spectroscopy by their characteristic 1H, 11B/11B{1H}, and
31P{1H} NMR spectra and by comparison of the data obtained
with those found in the literature for [nido-9-PPh3-7,8-
C2B9H11].7
(3) See, for instance: (a) Belmont, J. A.; Soto, J.; King, R. E., III; Donaldson,
A. J.; Hewes, J. D.; Hawthorne, M. F. J. Am. Chem. Soc. 1989, 111, 7475
and references therein. (b) Kang, H. C.; Hawthorne, M. F. Organometallics
1990, 9, 2327. (c) Demonceau, A.; Saive, E.; de Froidmont, Y.; Noels, A.
F.; Hubert, A. J.; Chizhevsky, I. T.; Lobanova, I. A.; Bregadze, V. I.
Tetrahedron Lett. 1992, 33, 2009. (d) Demonceau, A.; Simal, F.; Noels,
A. F.; Vin˜as, C.; Nun˜ez, R.; Teixidor, F. Tetrahedron Lett. 1997, 38, 4079.
(e) Demonceau, A.; Simal, F.; Noels, A. F.; Vin˜as, C.; Nun˜ez, R.; Teixidor,
F. Tetrahedron Lett. 1997, 38, 7879. (f) Simal, F.; Sebille, S.; Demonceau,
A.; Noels, A. F.; Nun˜ez, R.; Teixidor, F.; Vin˜as, C. Tetrahedron Lett. 2000,
41, 5347. (g) Teixidor, F.; Flores, M. A.; Vin˜as, C.; Sillanpa¨a¨, R.; Kiveka¨s,
R. J. Am. Chem. Soc. 2000, 122, 1963. (h) Brunner, H.; Apfelbacher, A.;
Zabel, M. Eur. J. Inorg. Chem. 2001, 917. (i) Tutusaus, O.; Delfosse, S.;
Demonceau, A.; Noels, A. F.; Vin˜as, C.; Teixidor, F. Tetrahedron Lett.
2003, 44, 8421. (j) Yinghuai, Z.; Carpenter, K.; Bun, C. C.; Bahnmueller,
S.; Ke, C. P.; Srid, V. S.; Kee, L. W.; Hawthorne, M. F. Angew. Chem.,
Int. Ed. 2003, 42, 3792. (k) Kolyakina, E. V.; Grishin, I. D.; Cheredilin,
D. N.; Dolgushin, F. M.; Chizhevsky, I. T.; Grishin, D. F. Russ. Chem.
Bull. 2006, 55, 89. (l) For the latest reviews, see: Teixidor, F.; Nun˜ez, R.;
Flores, M. A.; Demonceau, A.; Vin˜as, C. J. Organomet. Chem. 2000, 614-
615, 48; Grimes, R. Coord. Chem. ReV. 2000, 200-202, 773; Teixidor,
F.; Vin˜as, C.; Demonceau, A.; Nun˜ez, R. Pure Appl. Chem. 2003, 75, 1305.
(4) (a) Long, J. A.; Marder, T. B.; Hawthorne, M. F. J. Am. Chem. Soc. 1984,
106, 3004. (b) Lobanova, I. A.; Chizhevsky, I. T.; Petrovskii, P. V.;
Bregadze, V. I. Russ. Chem. Bull. 1996, 45, 241. (c) Chizhevsky, I. T.;
Lobanova, I. A.; Petrovskii, P. V.; Bregadze, V. I.; Dolgushin, F. M.;
Yanovsky, A. I.; Struchkov, Yu. T.; Chistyakov, A. L.; Stankevich, I. V.;
Knobler, C. B.; Hawthorne, M. F. Organometallics 1999, 18, 726. (d) Ellis,
D. D.; Couchman, S. M.; Jeffery, J. C.; Malget, J. M.; Stone, F. G. A.
Inorg. Chem. 1999, 38, 2981. (e) Lobanova, I. A.; Timofeev, S. V.;
Kudinov, A. R.; Meshcheryakov, V. I.; Petrovskii, P. V.; Starikova, Z. A.;
Bregadze, V. I. Russ. Chem. Bull. 2002, 51, 517. (f) Cheredilin, D. N.;
Kadyrov, F. M.; Dolgushin, F. M.; Balagurova, E. V.; Godovikov, I. A.;
Solodovnikov, S. P.; Chizhevsky, I. T. Inorg. Chem. Commun. 2005, 8,
614. (g) Chizhevsky, I. T.; Yanovsky, A. I.; Struchkov, Yu. T. J.
Organomet. Chem. 1997, 536-537, 51 (a review).
(5) In addition to refs 1 and 2, see: (a) Churchill, M. R.; Reis, A. N., Jr.;
Young, D. A. T.; Willey, G. R.; Hawthorne, M. F. J. Chem. Soc., Chem.
Commun. 1971, 298. (b) Young, D. A. T.; Wiersema, R. J.; Hawthorne,
M. F. J. Am. Chem. Soc. 1971, 93, 5687. (c) Schubert, D. M.; Bandman,
M. A.; Rees, W. S., Jr.; Knobler, C. B.; Lu, P.; Nam, W.; Hawthorne, M.
F. Organometallics 1990, 9, 2046. (d) Kim, J.; Kim, S.; Do, Y. J. Chem.
Soc., Chem. Commun. 1992, 938. (e) Park, Y.-W.; Kim, J.; Kim, S.; Do,
Y. Chem. Lett. 1993, 121. (f) Park, Y.-W.; Kim, J.; Do, Y. Inorg. Chem.
1994, 33, 1. (g) Crowther, D. J.; Swenson, D. C.; Jordan, R. F. J. Am.
Chem. Soc. 1995, 117, 10403. (h) Xie, Z.; Liu, Z.; Chiu, K.-y.; Xue, F.;
Mak, T. C. W. Organometallics 1997, 16, 2460. (i) Kwong, W.-C.; Chan,
H.-S.; Tang, Y.; Xie, Z. Organometallics 2004, 23, 4301.
(6) Hewes, J. D.; Thompson, M.; Hawthorne, M. F. Organometallics 1985, 4,
13.
9
3746 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Stable exo-nido-Metallacarboranes (M
)
OsIV
)
A R T I C L E S
Scheme 1
Single-Crystal X-ray Diffraction Studies of the “Two-
Bridge” exo-nido-Osmacarboranes 5 and 9. The molecular
structures of 5 and 9 are shown in Figures 1 and 2, respectively,
and selected geometrical parameters (bond distances and angles)
are listed in Table 1.
The crystallographic studies of 5 and 9 established these
species to be the first currently known exo-nido-metallacarbo-
ranes incorporating the carbons-apart [nido-7,9-C2B9H11]2-
ligand. The metal atom in 5 is bound to the two PPh3 groups
(2.355(2) and 2.343(2) Å), one terminal hydride ligand (1.64
Å), and a chlorine (2.442(2) Å). Complex 9 is similar in
composition to 5 except for the replacement of the Cl ligand
by the terminal H ligand. However, these small structural
changes cause a substantial difference in the architecture of the
exo polyhedrally bound osmium-containing moieties and the
metal-hydride orientation with respect to the open face of the
carborane cage ligand in these species (vide infra).
It has become apparent from the X-ray diffraction data that
the {nido-7,9-C2B9} carborane cage in both species 5 and 9
acts as a bidentate ligand forming two B-H‚‚‚M linkages; it is
particularly noteworthy that boron atoms, B(10) and B(11),
involved in the B-H‚‚‚Os bonding interaction with the metal
center are both from the upper CBCBB belt of the nido-
carborane cage. In both structures 5 and 9, there is a quite
noticeable folding of the {C2B3} open face about the C(7)‚‚‚
C(9) line of the cage ligand with the corresponding dihedral
angles between the B2C2 and C2B planes being equal to 26.4
and 27.0°, respectively. This, however, appears to be a typical
feature of the carbons-apart {nido-7,9-C2B9} cluster geometry.
For example, in the crystal structure of the protonated proton
sponge salt of an unsubstituted [nido-7,9-C2B9H12]- monoanion,
the boron atom between the two carbon atoms on the open
face is above the plane containing the other four atoms by
0.246 Å.8
(µ-H)2-7,8-C2B9H10] (11),5a,b and [exo-nido-9,10-{Cu(PPh3)2}-
9,10-(µ-H)2-7,8-C2B9H10] (12).5d In many other currently known
exo-nido-metallacarboranes of d-block metals, where the nido-
carborane ligand is connected with an exo-metal-containing unit
via the two B-H‚‚‚M linkages,1a-d those boron vertices involved
in such an interaction were from different belts of the cage
framework. It should also be noted that, among the crystallo-
graphically studied complexes 10-12, the position of the endo-
hydrogen atom postulated as a bridge between two adjacent
boron atoms on the pentagonal C2B3 open face was clearly
defined only for complex 10,1e whereas in the other two
complexes, the position of the H-bridging atom was determined
by NMR spectroscopy.5a,d Interestingly, in our case, the X-ray
diffraction experiments showed that there are no endo-hydrogen
atoms in complexes 5 and 9; all other hydrogen positions,
including those of the terminal osmium hydrides and the cluster
B-H units, have been objectively located in these structures.
Thus, the {nido-7,9-C2B9} carborane ligand in each structure 5
and 9 was defined as the dicarbollide dianion. As such, the exo-
nido-osmacarboranes obtained represent rare examples of 16-
electron complexes with the osmium atom in the 4+ oxidation
state. To the best of our knowledge, there are only a few
structurally studied examples of “two-bridge” and mixed “two/
three-bridge” exo-nido species that originated from dicarbollide
dianion derivatives,5f-h and among these, complexes 5 and 9
are the first having the carbons-apart dicarbollide system. The
facile formation and stability of such electron-deficient osmium
species, where the metal atom exists in the rather uncommon
oxidation state of 4, is surprising indeed since, within the family
of osmium complexes, the only precedent was reported to be
the sterically crowded osmium-phosphine complexes OsH3X-
9
10
(i-Pr3P)2 and OsH2X2(R3P)2 (where X ) halides; R ) i-Pr
or t-Bu2Me).
In relation to this, it is necessary to discuss a specific structural
detail of complex 5 regarding the orientation of the metal
hydride with respect to the pentagonal open face of the carborane
cage. It is seen from Figure 1 that the osmium hydride H(1M)
in 5, although located near the metal atom (Os‚‚‚H, 1.64 Å),
could, in principle, be involved in a weak four-center (OsHBB)
bonding interaction between the osmium center and the two
A similar 5 and 9 metal-to-carborane cage “two-bridge”
bonding pattern was previously observed for only a few exo-
nido-metallacarborane species, which are all, however, derived
from the “carbons-adjacent” [nido-7,8-C2B9H12]- anion and, in
particular, [exo-nido-9,10-{W(CO)2(η-C5Me5)}-9,10-(µ-H)2-7,8-
Me2-7,8-C2B9H8] (10),1e [exo-nido-9,10-{Al(CH3)2}-9,10-
(7) Kim, K. M.; Do, Y., Knobler, C.; Hawthorne, M. F. Bull. Korean Chem.
Soc. 1989, 10, 321.
(8) Fox, M. A.; Geoeta, A. E.; Hughes, A. K.; Johnson, A. L. J. Chem. Soc.,
Dalton Trans. 2002, 2132.
(9) Gusev, D. G.; Kuhlman, R.; Sini, G.; Eisenstein, O.; Caulton, K. G. J. Am.
Chem. Soc. 1994, 116, 2685.
(10) Aracama, M.; Esteruelas, M. A.; Lahoz, F. J.; Lopez, J. A.; Meyer, U.;
Oro, L. A.; Werner, H. Inorg. Chem. 1991, 30, 288.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3747

A R T I C L E S
Balagurova et al.
Figure 2. Perspective view of a single molecule of complex 9 with thermal
ellipsoids drawn at the 30% probability level (hydrogen atoms of the phenyl
substituents are omitted for clarity) (top) and schematic view of 9 with the
phenyl groups at the Os atom omitted for clarity (bottom).
Figure 1. Perspective view of a single molecule of complex 5 with thermal
ellipsoids drawn at the 30% probability level (hydrogen atoms of the phenyl
substituents are omitted for clarity) (top) and schematic view of 5 with the
phenyl groups at the Os atom omitted for clarity (bottom).
lying trans to the Cl ligand. Although the mode of the B(10)-
B(11)‚‚‚H‚‚‚M interaction postulated in 5 has not been exempli-
fied in the metallacarborane chemistry, at least several more or
less similar examples of smaller-cage metallacarborane clusters
published by Grimes and co-workers are known,11b where the
metal-bound hydrogen atom acts as a bridge between the metal
center and two neighboring cage boron atoms. It seemed
probable, therefore, that, to generate an electronically favored
Os(II) species in the case of complex 9, a similar bonding to 5
of the metal hydride to the C2B3 open face should take place.
In the solid-state structure of 9, metal-hydride ligands (Os-H,
1.52 and 1.40 Å), nevertheless, adopt a different orientation with
respect to the nido-carborane open face from that postulated.
One of the PPh3 groups (not the metal hydride) lies over the
cage boron atoms B(10) and B(11). If we then assume that such
a bridging B(10)‚‚‚H‚‚‚B(11) fragment, through the agostic-like
B2H‚‚‚Os interaction, contributes two electrons to the metal
center, complex 5 might formally be considered as a zwitterionic
Os(II) species with the metal atom having a saturated 18-electron
shell. If this were the case, the noticeable strengthening of the
bridging B(10)‚‚‚H‚‚‚B(11) bonds occurring in the structure of
5 (B(10)‚‚‚H(1M), 2.20; B(11)‚‚‚H(1M), 2.34 Å) could have
been explained by the four-center bridging nature of the
hydrogen H(1M) and, in addition, by its purely trans position
with respect to the chlorine ligand in the octahedral coordination
sphere of the Os(II) atom. Note, in all crystallographically
studied 18-electron Os(II) and Ru(II) exo-nido-{MCl(PPh3)2}-
metallacarboranes1f-j and the related exo-nido-{RuCl(PPh3)2}-
metallaheteroboranes2 as well, the longest of all of the B-H
bonds involved in the interaction with a metal center is that
(11) (a) Pipal, J. R.; Grimes, R. N. Inorg. Chem. 1979, 18, 252. (b) Stephan,
M.; Davis, J. H., Jr.; Meng, X.; Chase, K. J.; Hauss, J.; Zenneck, U.;
Pritzkow, H.; Siebert, W.; Grimes, R. N. J. Am. Chem. Soc. 1992, 114,
5214.
9
3748 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Stable exo-nido-Metallacarboranes (M
)
OsIV
)
A R T I C L E S
Table 1. Selected Bond Lengths (Å) and Angles (°) for Complexes 5 and 9
bond
5
9
angle
5
9
Os(1)-P(1)
Os(1)-P(2)
Os(1)-Cl(1)
Os(1)-H(1M)
Os(1)-H(2M)
Os(1)-H(10)
Os(1)-H(11)
Os(1)-B(10)
Os(1)-B(11)
B(10)-H(10)
B(11)-H(11)
C(7)-B(8)
2.355(2)
2.343(2)
2.442(2)
1.64
2.303(2)
2.367(2)
P(1)-Os(1)-P(2)
100.58(6)
93.03(6)
99.78(6)
172
167
173
150.34(5)
P(1)-Os(1)-Cl(1)
P(2)-Os(1)-Cl(1)
H(1M)-Os(1)-Cl(1)
H(10)-Os(1)-P(2)
H(11)-Os(1)-P(1)
H(10)-Os(1)-H(11)
H(1M)-Os(1)-H(2M)
H(1M)-Os(1)-H(10)
H(2M)-Os(1)-H(11)
B(11)-C(7)-B(8)
C(7)-B(8)-C(9)
1.40
1.52
1.75
1.69
2.227(6)
2.217(7)
1.45
1.85
1.74
2.194(6)
2.169(6)
1.29
81
118
110
169
179
97.7(5)
120.9(5)
96.6(5)
110.5(5)
108.4(5)
1.08
1.33
97.1(5)
119.5(5)
97.0(5)
110.7(5)
110.1(5)
1.651(10)
1.590(8)
1.650(10)
1.582(8)
1.747(9)
1.620(10)
1.587(9)
1.638(9)
1.569(8)
1.784(9)
C(7)-B(11)
B(8)-C(9)
B(10)-C(9)-B(8)
C(9)-B(10)-B(11)
C(7)-B(11)-B(10)
C(9)-B(10)
B(10)-B(11)
BBCBC open face, while both terminal hydrides are positioned
cisoid to one another (H(1M)‚‚‚H(2M), 2.39 Å), being, in fact,
far away from either of the boron atoms of the nido-carborane
ligand. At the same time, the crystal structure of 9 shows tight
interatomic distances between two pairs of osmium-bound and
boron-bound terminal hydrogen atoms, that is, between H(1M)
and H(11) (1.79 Å) and H(2M) and H(10) (1.70 Å), a feature
that will be discussed further in the following sections.
showing J(B,H) coupling of ca. 150-160 Hz. Due to the low
chemical shift and the observed line shape, the resonance at δ
+5.2 ppm was attributed to two equivalent B(10) and B(11)
atoms both involved in the relatively strong1i,12 B-H‚‚‚Os
bonding interaction in 5. Such an assignment correlates well
with the data obtained from the selective 1H{11B(10,11)} NMR
experiment discussed previously in this paper.
In accordance with the lack of the mirror plane symmetry in
the C-phenylated nido-carborane ligand in 6, the 1H NMR
spectrum of this species displays three separate resonances in a
high-field region, each of 1H relative intensity. Two of these
resonances centered at δ -4.83 and -7.37 ppm due to their
broad and unresolved character were readily assigned to
nonequivalent B-H‚‚‚Os bridging hydrogen atoms. The third
resonance appears as a sharp doublet of doublets at δ -14.24
ppm and was, therefore, attributed to the terminal osmium
hydride. The observed multiplicity of this resonance is due to
coupling of the osmium hydride to the two nonequivalent, in
this case, PPh3 groups (2J(H,P1) ) 30.0 Hz and 2J(H,P2) ) 31.0
Hz). Accordingly, the 31P{1H} NMR spectrum of 5 exhibits a
pair of equal-intensity doublets at δ 5.88 and 0.04 ppm with
2J(P,P) ) 12.0 Hz. The 11B/11B{1H} spectra of 6 proved to be
more complex than those of 5 displaying a set of seven partially
overlapping resonances of a 1:2:1:2:1:1:1 intensity ratio.
NMR Characterization of exo-nido-Osmacarboranes 5, 6,
and 9. Study of Dynamic Behavior of Complex 9 in Solution.
Parallel examination of the solution structures of complexes 5,
6, and 9 by a combination of multinuclear NMR spectroscopic
methods showed that 16-electron Os(IV) formulation has to be
1
made for all of these exo-nido clusters. Thus, in the H NMR
spectrum of 5, no high-field resonance in the range between δ
+0.5 and -2.5 ppm that might be attributed to the bridging
B‚‚‚H‚‚‚B hydrogen atom was observed. However, in the upper
field of this spectrum, there are two separate resonances at δ
-5.85 and -13.60 ppm in a 2:1 intensity ratio, respectively.
The 2H resonance at δ -5.85 ppm, due to its broad and
unresolved character, was assigned to the two equivalent
bridging hydrogen atoms arising from the B-H‚‚‚Os fragments,
and the 1H resonance at δ -13.60 ppm, seen as a sharp triplet
2
with J(H,P) ) 30.0 Hz, appears to be representative of the
terminal osmium hydride. The line width of the latter resonance
was indeed too narrow to consider the presence of even a weak
bonding interaction between this terminal hydride and the
adjacent boron atoms B(10) and B(11), and this fact allowed
us to rule out a hypothetical 18-electron structure for complex
5. This is also supported by the selective boron-decoupled
1H-{11B(10,11)} NMR spectrum of 5 where no additional
sharpening of this resonance had occurred. At the same time,
the broad 2H resonance at δ -5.85 ppm collapsed upon boron
decoupling to a significantly sharpened doublet with 2J(H,P) )
42.8 Hz due, apparently, to a long-range coupling of the two
equivalent B-H‚‚‚Os bridging hydrogens to the two equivalent
PPh3 groups positioned trans to them. Accordingly, the
31P{1H} NMR spectrum of 5 shows a single resonance at δ
2.36 ppm, supporting the equivalence of two PPh3 groups in
this molecule. The 11B{1H} NMR spectrum of 5 shows a set of
five resonances ranging from δ +5.0 to -21.0 ppm with the
relative intensities 2:1:3:1:2. Of these resonances, one at δ +5.2
ppm, integrating as a 2B peak, was seen in the 11B NMR
spectrum as a broadened singlet for which no J(B,H) coupling
was observed, while the other four resonances were doublets
An examination of complex 9 both by 1H and 31P{1H} NMR
spectroscopic methods provided evidence for the dynamic
process occurring in this species in solution. This is shown by
a series of temperature-dependent 1H and 31P{1H} NMR spectra
of 9 in the temperature range between -20 and +65 °C (Figure
3a,b), where the high-field region of the 1H NMR spectrum was
especially informative.
1
The room-temperature H NMR spectrum of 9 in d8-THF
exhibits two separate resonances of bridging (2H, δ -6.68 ppm)
and terminal (2H, δ -8.47 ppm) hydrides. Although the latter
resonance might be expected to have doublet of doublets
multiplicity, due to nonequivalency of the osmium-bound PPh3
ligands in the crystal structure of 9, at the observation temper-
ature (+20 °C), it displays as a broad triplet-like signal, which
only at -20 °C splits into the anticipated doublet of doublets
with 2J(H,P1) ) 30.7 Hz and 2J(H,P2) ) 22.0 Hz. As the
temperature is raised above room temperature, both bridging
and terminal hydride resonances become more broadened and,
(12) Fernandez, J. R.; Helm, G. F.; Haward, J. A. K.; Pilotti, M. U.; Stone, F.
J. A. J. Chem. Soc., Dalton Trans. 1990, 1747.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3749

A R T I C L E S
Balagurova et al.
Scheme 2. The Simplified Representation of the Reaction
Pathway (One Cycle) to Give B-Os-H Oxidative Addition
Products Affecting the H/H Exchange in Complex 9 in Solution
Although the two-electron, three-center B-H‚‚‚M bonds in
metallacarborane compounds may be highly fluxional,1b,4a,13 so
far, there are no reports on the direct spectroscopic evidence
for the exchange occurring between bridging B-H‚‚‚M and
terminal M-H hydrides in exo-nido-metallacarboranes having
hydrido ligands at the exo-positioned metal center.1a,2e Perhaps,
very close location of both terminal and bridging hydrogen
atoms H(1M) and H(11) as well as H(2M) and H(10), as it is
observed in the crystal structure of 9, may force such an unusual
H/H exchange in this complex in solution. The dynamic features
observed for 9 indicate that, at an earlier stage, there must be
an alternating intramolecular oxidative addition of the B(10)-
H‚‚‚Os and B(11)-H‚‚‚Os bonds, giving rise, through the
formation of a new B-Os-H fragment, to a third terminal
hydride at the Os center. The Os atom in such a transient
trihydrido complex (species A in Scheme 2) would be seven-
coordinate and adopt an entirely unfavorable high oxidation
state. However, both of these negative factors in A may be
relieved via coupling between two closely spaced terminal
hydrides at the Os center, either H(1M) and H(11) or H(2M)
and H(10), with subsequent formation of a coordinatively more
favorable dihydrogen 16-electron Os(IV) intermediate (species
B in Scheme 2), through which, by rapid spinning of the
dihydrogen ligand or via another viable mechanism,14 the mutual
H/H exchange in 9 could be operative.
Figure 3. A series of a variable-temperature 1H NMR (a) and 31P{1H}
NMR (b) spectra for 9 from -20 to +65 °C in a d8-THF solution (only the
1
hydride region of the H NMR spectrum is displayed).
at +65 °C (the highest temperature limit attained experimen-
tally), eventually coalesce into a very broad hump, indicating
that full exchange between these hydrogens does occur (Figure
3a). This hump at a higher temperature would presumably
transform into the 4H sharp resonance, but this, however, was
1
not achieved in the H NMR experiment due to the d8-THF
boiling point limitation.
The 31P{1H} NMR spectrum of 9, measured at room
temperature, exhibits a broad AB quadruplet with the doublet
components centered at δ ca. 20.0 and 14.0 ppm (Figure 3b).
Like the variable-temperature proton spectra, the 31P{1H} NMR
spectra of 9 in the temperature range from 0 to +65 °C exhibited
the dynamic behavior resulting from an intramolecular H/H
exchange process. Thus, increasing the temperature above +20
°C causes the AB pattern to broaden to give, primarily, a broad
doublet resonance, in which no discernible coupling constants
were observed; this doublet then merges into a broad singlet
resonance. Decoalescence of this resonance occurs at -20 °C
and results in the formation of a nicely resolved AB quadruplet
Synthesis of [closo-2,2-(PPh3)2-2,2-H2-2,1,7-OsC2B9H11]
(13) via Thermal exo-nido to closo Rearrangement of
Complex 9. Interestingly, when the high-temperature NMR
experiment on complex 9 in d8-THF was carried out, some
changes were observed both in the 1H and 31P{1H} NMR spectra
and, in particular, as can be seen from Figure 3a,b, one new
proton triplet at δ -9.33 ppm and a sharp phosphorus singlet
2
with 2J(P1,P2) coupling of 213.6 Hz. A high value of J(P1,P2)
is indicative of the PPh3 ligands lying trans to each other, in
accordance with the results of the X-ray diffraction data for 9.
We, therefore, concluded that the fluxional process occurring
(13) (a) Manning, M. J.; Knobler, C. B.; Khattar, R.; Hawthorne, M. F. Inorg.
Chem. 1991, 30, 2009. (b) Ellis, D. D.; Franken, A.; Jelliss, P. A.; Kautz,
J. A.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 2000, 2509. (c) Pisareva,
I. V.; Konoplev, V. E.; Petrovskii, P. V.; Vorontsov, E. V.; Dolgushin, F.
M.; Yanovsky, A. I.; Chizhevsky, I. T. Inorg. Chem. 2004, 43, 6228.
(14) Gusev, D. G.; Berke, H. Chem. Ber. 1996, 129, 1143.
1
in a solution of 9 is frozen out, and both the H and 31P{1H}
NMR spectra at the observation (-20 °C) temperature represent
the “static” structure of 9.
9
3750 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Stable exo-nido-Metallacarboranes (M
)
OsIV
)
A R T I C L E S
Scheme 3
resonance at δ 17.90 ppm appeared in these spectra, respectively.
Furthermore, once these new resonances had emerged, they
could not be reversed by recooling the solution down to room
1
temperature (Figure 3a, see the reversed H NMR spectrum).
These observations led us to believe that, during VT NMR
spectroscopic experiments, an irreversible thermal conversion
of 9 to produce a new PPh3-containing hydrido (or dihydrido)-
osmacarborane complex had occurred. Accordingly, we made
an attempt to obtain this new species in a quantitative manner
starting from complex 9. It has been found that mild heating of
9 in a THF solution at 65 °C for 3.5 h, followed by column
chromatography, yields white-grayish crystals in 62% yield, and
this compound, on the basis of analytical, IR, and NMR spectral
data, was formulated as closo-2,2-(PPh3)2-2,2-H2-2,1,7-OsC2B9H11
(13).The 1H and 31P{1H} NMR spectra of complex 13 in CD2-
Cl2 exhibited patterns similar to those seen in the spectra of 9
Figure 4. ORTEP representation of the molecular structure with the
numbering scheme for complex 13; ellipsoids are drawn at the 30%
probability level (hydrogen atoms of the phenyl substituents are omitted
for clarity). Selected bond lengths (Å): Os(2)-P(1) 2.316(2), Os(2)-P(2)
2.329(2), Os(2)-H(1M) 1.67, Os(2)-H(2M) 1.56, Os(2)-C(1) 2.248(7),
Os(2)-C(7) 2.318(7), Os(2)-B(3) 2.269(8), Os(2)-B(6) 2.222(8), Os(2)-
B(11) 2.283(9), C(1)-B(3) 1.714(11), C(1)-B(6) 1.725(11), B(3)-C(7)
1.690(11), C(7)-B(11) 1.690(12), B(6)-B(11) 1.831(13).
1
in d8-THF at a high temperature. In particular, the H NMR
spectrum showed a sharp triplet at δ -9.51 ppm with J(H,P) ∼
32 Hz, arising from two equivalent terminal metal hydrides,
and a somewhat broadened singlet resonance at δ 1.23 ppm,
assigned to the carborane cluster CH protons. The spectrum of
13 also contained aromatic resonances centered at δ 7.48, 7.27,
and 7.22 ppm with a total 15:1 intensity ratio relative to the
metal-hydride 2H resonance; these appeared as two triplet-like
and one quadruplet-like multiplets and correspond to phenyl
m-, p-, and o-protons of PPh3 ligands. The 31P{1H} NMR
spectrum of 13 in CD2Cl2 showed the only singlet at δ 17.65
ppm, which reflects the equivalence of the respective phosphine
groups in this molecule. The 11B{1H} NMR spectrum of 13
revealed the presence of five somewhat-broadened resonances
of relative areas 1:3:3:1:1 and was indicative of an overall Cs
symmetry of complex 13. Accordingly, the IR spectrum of 9
showed absorptions consistent with the presence of a carborane
unit (ν 2549 cm-1) and terminal metal hydrides (2166, 2096
cm-1) in the molecule.
(Os-H(1M) 1.67, Os-H(2M) 1.56 Å); the terminal hydride
atoms were located in 13 from difference Fourier maps, and
their position proved to be nearly symmetrical between two PPh3
groups. Thus, 13 can be regarded as a neutral seven-coordinated
Os(IV) complex in which the osmium atom has the stable 18-
electron configuration. At present, a few metallacarborane
complexes with seven-coordinate Os(IV)15 and Ru(IV),16 closely
related to 13, are known, and among these, one species, [closo-
2,2-(PPh3)2-2,2-H2-2,1,7-RuC2B9H11], studied long ago by Haw-
thorne and co-workers,16b happens to be the ruthenium congener
of 13.
A facile thermal exo-nido to closo conversion of 9 should be
associated directly with its fluxionality in solution. Clearly, the
isomerization reaction would proceed through intermediates
similar in nature to the 16-electron Os(IV) species A and/or A′
(Scheme 2), in which the osmium-containing moiety interacts
with the nido-carborane ligand via one labile B-H‚‚‚Os bond
and a σ-bond Os-B. Taking into account that these exo-nido
precursors do not have endo-hydrogen atoms on their CBCBB
open face, it is reasonable to assume that, upon warming, they
would easily undergo the η1 f η5 rearrangement with the shift
of the osmium-containing moiety from the exo to closo position
on the pentagonal face of the carborane cage, and simultaneous
transfer of the terminal osmium hydride in A/A′ to a cluster
BH hydrogen position would be the most probable last step,
completing the exo-nido to closo rearrangement of 9.
Since little attention has been given in the literature to closo-
hydrido-osmacarborane clusters15 and no examples with the
carbons-apart {nido-7,9-C2B9} ligands were reported, a single-
crystal X-ray diffraction study of 13 has been undertaken. This
study confirmed the closo structure of 13 and made clear some
details of its cluster geometry and the arrangement of ligands
at the metal vertex. Figure 4 depicts the molecular structure of
13 with selected bond lengths and angles. The dicarbollide [nido-
7,9-C2B9H11]2- ligand is bound to the metal atom in an η5-
fashion with osmium-to-boron/carbon (upper belt) distances
ranging from 2.222(8) to 2.318(7) Å. As expected, the Os
atom is additionally coordinated to two PPh3 ligands (Os-P(1)
2.316(2), Os-P(2) 2.329(2) Å) and two terminal hydrides
(16) (a) Wong, E. H. S.; Hawthorne, M. F. J. Chem. Soc., Chem. Commun.
1976, 257. (b) Wong, E. H. S.; Hawthorne, M. F. Inorg. Chem. 1978, 17,
2863. (c) Chizhevsky, I. T.; Lobanova, I. A.; Bregadze, V. I.; Petrovskii,
P. V.; Polyakov, A. V.; Yanovsky, A. I.; Struchkov, Yu. T. Organomet.
Chem. USSR (Engl. Transl.) 1991, 4, 469. (d) Cheredilin, D. N.; Dolgushin,
F. M.; Grishin, I. D.; Kolyakina, E. V.; Nikiforov, A. S.; Solodovnikov, S.
P.; Il’in, M. M.; Davankov, V. A.; Chizhevsky, I. T.; Grishin, D. F. Russ.
Chem. Bull. 2006, 55, 1163.
(15) Chizhevsky, I. T.; Petrovskii, P. V.; Sorokin, P. V.; Bregadze, V. I.;
Dolgushin, F. M.; Yanovsky, A. I.; Struchkov, Yu. T. Organometallics
1996, 15, 2619.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3751

A R T I C L E S
Balagurova et al.
Table 2. Crystal Data, Data Collection, and Structure Refinement
Parameters for 5, 9, and 13
Experimental Section
General Considerations. All reactions were carried out under an
argon atmosphere using standard vacuum line techniques. THF was
distilled from sodium/benzophenone under an argon atmosphere prior
to use. All other solvents, including those used for column chroma-
tography as eluents, were also distilled from appropriate drying agents
prior to use. Starting reagents 317 and both [K]+ salts of anions 218 and
418 were prepared according to the published methods. Short chroma-
tography columns packed with silica gel (Merck, 230-400 mesh) were
used for separation and purification of the reaction products, and these
were carried out under an argon atmosphere. The 1H, 1H{11B},
31P{1H}, and 11B/11B{1H} NMR as well as VT NMR measurements
were performed with a Bruker AMX-400 (1H at 400.13 MHz; 31P at
161.98 MHz; 11B at 128.33 MHz) instrument using either TMS as an
internal reference or 85% H3PO4 and BF3‚Et2O as external references,
respectively. IR spectra were obtained on a Carl-Zeiss M-82 spec-
trometer. Elemental analyses for all new compounds were performed
by the Analytical Laboratory of the Institute of Organoelement
Compounds of the Russian Academy of Sciences.
complex
5
9
13
formula
C38H42B9ClP2Os C38H43B9P2Os C38H43B9P2Os
molecular weight
crystal color, habit
temperature, K
crystal system
space group
a, Å
883.60
849.15
849.15
colorless plate
120(2)
triclinic
P1h
9.5182(9)
10.124(1)
19.786(2)
80.437(2)
78.666(2)
80.784(2)
1827.3(3)
2
purple prism
193(2)
green prism
295(2)
triclinic
P1h
12.819(3)
12.963(3)
13.787(3)
75.405(16)
62.997(15)
69.875(16)
1904.0(8)
2
triclinic
P1h
11.216(4)
12.711(6)
14.318(5)
95.62(3)
106.15(3)
91.10(3)
1948.8(13)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
d(calcd), g cm-3
diffractometer
scan mode
max, deg
µ(Mo KR,
1.506
1.481
1.543
Syntex P21
θ-2θ
Siemens P3/PC SMART 1000
θ-2θ
28.0
34.60
ω
28.0
36.06
θ
25.0
34.50
Preparation of [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(µ-H)2-7,9-
C2B9H9] (5). To a mixture of freshly prepared osmium reagent 3 (0.15
g, 0.143 mmol) and the [K]+ salt of anion 2 (0.035 g, 0.2 mmol) flushed
with argon was added 15 mL of the degassed C6H6, and the resulting
solution was stirred at room temperature for 1.5 h until the color of
solution became dark purple. The solvent was reduced under vacuum
to approximately one-third, and the residue was treated by column
chromatography on silica gel. The band that contained crude zwitterionic
nido-carborane 7 and traces of green complex 9 was eluted first with
C6H6. This material, after evaporation of solvent under vacuum and
crystallization of the residue from CH2Cl2/n-hexane, afforded 0.019 g
of NMR spectroscopically pure yellowish-white crystals of 7. 1H NMR
(CD2Cl2, 22 °C): δ 7.72-7.57 (m + m, 15H, Ph), 1.88 (s br, 1H,
CHcarb), 1.69 (s br, 1H, CHcarb), -1.1 (s v-br, 1H, B-H-B). 31P{1H}
λ)0.71073 Å),
cm-1
T
min/Tmax
0.791/1.303
0.580/0.745
9178 (0.0654) 8712 (0.0653)
0.362/0.869
no. unique reflections 6780 (0.0000)
(Rint
)
no. observed
reflections
(I > 2σ(I))
R1
5526
6695
6042
0.0391
0.0589
0.0585
(on F for
observed
reflections)a
wR2
0.0908
0.0865
1.065
0.1194
0.887
(on F2 for
all reflections)b
GOF
1
1.020
1.010/-1.313
NMR (CD2Cl2, 22 °C): δ +5.54 (q-like m, J(P,B) ) 130 Hz). The
largest diff peak
and hole, e/Å3
1.059/-0.654 2.821/-2.576
second purple band containing complex 5 was eluted next with a
mixture of C6H6/CH2Cl2 (4:1). Removal of solvent under vacuum
followed by crystallization from CH2Cl2/n-hexane yielded 0.07 g (56%
yield) of analytically pure complex 5 as a purple crystalline solid. IR
near Os(1)
near Os(1)
near Os(2)
a R1 ) ∑| |Fo| - |Fc| |/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc )2]/∑w(Fo )2}1/2
.
2
2
1
(KBr, cm-1): 2576 (νB-H). H NMR (CD2Cl2, 22 °C): δ 7.20-6.82
(m, 30H, PPh3), 3.03 (s br, 2H, CHcarb), -5.85 (s v-br, 2H, (BH)2‚‚‚
Os), -13.6 (t, 1H, 2J(H,P) ) 30 Hz, Os-H). 31P{1H} NMR (CD2Cl2,
Conclusion
1
22 °C): δ 2.36 (s, P(1,2)). H{31P} NMR (CD2Cl2, 22 °C, negative
zone): δ -5.85 (s v-br, 2H, (BH)2‚‚‚Os), -13.6 (s, 1H, Os-H). 11B
NMR (CD2Cl2, 22 °C, J ) J(B,H), Hz): δ 5.2 (s br, 2B, B(10,11)),
-0.4 (d, 1B, J ) 160 Hz), -7.4 (d, 3B, J ) 151 Hz), -16.4 (d, 1B,
In this paper, the syntheses of a short series of novel 16-
electron exo-nido-osmacarboranes of the general formula [exo-
nido-10,11-{(Ph3P)2OsIVHX}-10,11-(µ-H)2-7-R-7,9-C2B9H8]
(5: R ) H, X ) Cl; 6: R ) Ph, X ) Cl; 9: R ) X ) H) have
been described. Structural studies carried out for two of these
complexes, 5 and 9, revealed that the carbons-apart [nido-7,9-
C2B9H10]2- dianion behaves in these species as a bidentate
ligand and forms two 2e,3c B-H‚‚‚Os bonds, both involving
B-H vertices situated in the upper CBCBB belt of the cage
ligand. In solution, complex 9 proved to be fluxional, showing
H/H exchange between both terminal Os-H2 and bridging {B-
H}2‚‚‚Os hydrogen atoms, and this dynamic process can clearly
be monitored via VT 1H and 31P{1H} NMR spectroscopy. It is
important to note that this particular type of dynamic behavior
(bridging-to-terminal hydrogen exchange) has not previously
been observed within this category of exo-nido-metallacarborane
complexes. We have also demonstrated that the exo-nido
complex 9, upon warming, undergoes irreversible rearrangement
giving rise to the closo isomer [closo-2,2-(PPh3)2-2,2-H2-2,1,7-
OsC2B9H11], 13, whose structure was established by X-ray
crystallography.
1
J ) 148 Hz), -20.3 (d, 2B, J ) 157 Hz). Selective H{11B(10,11)}
2
NMR (CD2Cl2, 22 °C, negative zone): δ -5.85 (d, 2H, J(H,P) )
42.8 Hz, (BH)2‚‚‚Os), -13.6 (t, 1H, 2J(H,P) ) 30.0 Hz, Os-H). Anal.
Calcd for C38H42B9ClP2Os: C, 51.66; H, 4.76; B, 11.01; Cl, 3.70.
Found: C, 51.83; H, 4.75; B, 11.21; Cl, 3.82.
Preparation of [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(µ-H)2-7-
Ph-7,9-C2B9H8] (6). The complex was synthesized from 3 (0.15 g,
0.143 mmol) and the [K]+ salt of anion 4 (0.05 g, 0.2 mmol) in 15 mL
of C6H6 using similar reaction conditions and purification procedure
as those for 5; 0.085 g (62% yield) of complex 6 was thus obtained.
1
IR (KBr, cm-1): 2564 (νB-H). H NMR (CD2Cl2, 22 °C): δ 7.80-
6.60 (m, 35H, PPh3 + Ph), 2.26 (s br, 1H, CHcarb), -4.83 (s v-br, 1H,
2
BH‚‚‚Os), -7.37 (s v-br, 1H, BH‚‚‚Os), -14.24 (dd, 1H, J(H,P(1))
) 30.0 Hz, 2J(H,P(2)) ) 31.0 Hz, Os-H). 31P{1H} NMR (CD2Cl2, 22
2
2
°C): δ 5.88 (d, J(P,P) ) 12 Hz, P(1)), 0.04 (d, J(P,P) ) 12 Hz,
P(2)). 11B NMR (CD2Cl2, 22 °C, J ) J(B,H), Hz): δ 8.2 (s br, 1B),
1
(17) Oudeman, A.; Van Rantwijk, F.; Van Bekkum, H. J. Coord. Chem. 1974,
4, 1.
(18) Hawthorne, M. F.; Young, D. C.; Garrett, P. M.; Owen, D. A.; Schwerin,
S. G.; Tebbe, F. N.; Werner, P. A. J. Am. Chem. Soc. 1968, 90, 862.
9
3752 J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007

Stable exo-nido-Metallacarboranes (M
)
OsIV
)
A R T I C L E S
1.35 (d, 2B, J ) 128 Hz), -5.2 (s br, 1B), -7.3 (d, 2B, J ) 150 Hz),
-14.2 (d, 1B, J ) 165 Hz), -15.7 (d, 1B, J ) 165 Hz), -20.7 (d, 1B,
J ) 145 Hz). Anal. Calcd for C44H46B9ClP2Os: C, 55.07; H, 4.80; B,
10.14; P, 6.47; Os, 19.81. Found: C, 54.89; H, 4.87; B, 10.32; P, 6.54;
Os, 20.06. A small amount (0.016 g) of zwitterionic compound 8 was
also obtained; its structure is deduced from analysis of its 1H and
residue was purified by chromatography using a small silica gel column
(1,2 × 10 cm) and eluting a colorless fraction with benzene. Evaporation
of the solvent and crystallization of the residue from C6H6/n-hexane
(3:1) under conditions where slow evaporation of n-hexane at room
temperature occurs afforded 0.088 g (62%) of analytically pure grayish-
white crystals of 13. IR (KBr, cm-1): 2549 (νB-H), 2166, 2096 (νM-H).
1H NMR (d8-THF, 22 °C): δ 7.50 (t-like m, 12H, Ph-H(3,5)), (q-like
m, 18H, Ph-H(2,4,6)), 3.01 (s br, H2O (small solv. imp.)), 1.34 (s br,
2H, CHcarb), -9.33 (t, 2H, 2J(H,P) ) 32.0 Hz, Os-H2). 1H NMR (CD2-
Cl2, 22 °C): δ 7.48 (t-like, 12H, J(H,H) ) 8.5 Hz, Ph-H(3,5)), 7.27
1
31P{1H} spectra. H NMR (CD2Cl2, 22 °C): δ 7.72-7.58 (m + m,
15H, PPh3), 7.43 (m, 2H, Ph-H(2,6)), 7.15 (m, 2H, Ph-H(3,5)),
7.06 (m, 1H, Ph-H(4)), 1.84 (s br, 1H, CHcarb), -0.47 (s v-br, 1H,
1
B-H-B). 31P{1H} NMR (CD2Cl2, 22 °C): δ 5.69 (q-like m, J(P,B)
3
) 122 Hz).
(q, 6H, J(H,P) ) 14 Hz, J(H,H) ) 7 Hz, Ph-H(4)), 7.22 (q, 12H,
Preparation of [exo-nido-10,11-{(Ph3P)2OsH2}-10,11-(µ-H)2-7,9-
C2B9H9] (9). To a mixture of 3 (0.2 g, 0.19 mmol) and the [K]+ salt
of anion 2 (0.04 g, 0.23 mmol) flushed with argon was added 15 mL
of absolute ethanol, and the resulting suspension was heated under
stirring at 55-60 °C for 2.5 h and then for 15 min at 70 °C until the
suspension became dark green. After cooling, the ethanol was
evaporated under reduced pressure, and its traces were removed under
high vacuum. The resulting residue was dissolved in 1.5 mL of the
degassed CH2Cl2, and the solution was then treated by column
chromatography on silica gel. The grayish-green band eluted from the
column using benzene was found to contain crude 9. This solution was
repeatedly chromatographed on a smaller silica gel column using the
same solvent as the eluent to afford 9 as solid (0.11 g, 68% yield),
which after recrystallization from CH2Cl2/n-hexane at -5 °C, gave dark-
green microcrystals of analytically pure sample. IR (KBr, cm-1): 2565
(νB-H), 2066, 2037 (νM-H). 1H NMR (-20 °C): δ 7.61-7.45 (m, 30H,
PPh3), 3.64 (s br (partially overlapped), 2H, CHcarb), -6.68 (s br, 2H,
(BH)2‚‚‚Os), -8.47 (dd, 2H, 2J(H,P(1)) ) 30.7 Hz, 2J(H,P(2)) ) 22.0
3J(H,P) ) 13 Hz, J(H,H) ) 6.5 Hz, Ph-H(2,6)), 1.23 (s br, 2H, CHcarb),
-9.51 (t, 2H, 2J(H,P) ) 31.8 Hz, Os-H2). 31P{1H} NMR (d8-THF, 22
°C): δ 17.90 (s, P(1,2)). 31P{1H} NMR (CD2Cl2, 22 °C): δ 17.65 (s,
P(1,2)). 11B{1H} NMR (d8-THF, 22 °C): δ 3.5 (s v-br, 1B), -10.5 (s
v-br, 2B), -13.4 (s v-br, 2B), -14.4(s v-br, 2B), -17.7 (s v-br, 1B),
-18.7 (s v-br, 1B). Anal. Calcd for C38H43B9P2Os: C, 53.76; H, 5.07;
B, 11.01; P, 7.31. Found: C, 54.01; H, 4.97; B, 10.89; P, 7.28.
X-ray Structure Determination of Complexes 5, 9, and 13. Details
of the crystal data, data collection, and structure refinement parameters
for compounds 5, 9, and 13 are given in Table 2. The data were
corrected for Lorentz, polarization, and absorption effects. The structures
were solved by direct methods and refined by the full-matrix least-
squares technique against F2 with the anisotropic temperature factors
for all non-hydrogen atoms. All hydrogen atoms at the carborane cages,
including all hydride ligands, were located from the Fourier synthesis;
the remaining hydrogen atoms were placed geometrically. All hydrogen
atoms in 5, 9, and 13 were included in the structure factor calculations
in the riding motion approximation. SHELXTL-97 program packages19
were used throughout the calculations.
2
Hz, Os-H2). 31P{1H} NMR (d8-THF, J ) J(P,P), Hz, -20 °C): δ
20.0 (d, J ) 213.6 Hz, P(1)), 14.0 (d, J ) 213.6 Hz, P(2)). 11B{1H}
NMR (d8-THF, 22 °C) [1H{11B}]: δ 10.9 (2B) [-6.68, s br], -7.4
(4B) [+0.75, +2.1, +2.35 (2H)], -15.4 (1B) [+1.2], -19.6(2B) [1.4].
Anal. Calcd for C38H43B9P2Os: C, 53.78; H, 5.07; B, 11.46; P, 7.31;
Os, 22.30. Found: C, 53.92; H, 5.19; B, 11.58; P, 7.40; Os, 21.92.
Preparation of [closo-2,2-(PPh3)2-2,2-H2-2,1,7-OsC2B9H11] (13).
Complex 9 (0.12 g, 0.142 mmol) was dissolved in 10 mL of THF and
then heated in oil bath at 64-65 °C with stirring. For monitoring of
the occurring process by 1H and 31P{1H} NMR spectroscopy, a parallel
experiment with a sample of 9 in 0.7 mL of d8-THF in the sealed NMR
tube was carried out. The reaction was monitored by both 1H and
31P{1H} NMR spectroscopic methods every hour over the time of
heating. After ca. 3.5 h, an initially dark-green solution turned colorless,
and resonances of the starting compound 9 were no longer observed.
After this time, the reaction mixture was evacuated to dryness. The
Acknowledgment. This work has been supported by Grants
(Nos. 06-03-32172 and LS 1060.2003.3) from the Russian
Foundation for Basic Research. We are also grateful to Dr. I.
G. Barakovskaya for performing special research for obtaining
full analytical data for the osmium complexes 5 and 9. Thanks
are also due to Dr. E. G. Kononova for recording IR spectra.
Supporting Information Available: CIF files giving X-ray
crystallographic data for complexes 5, 6, and 13. This material
is available free of charge via the Internet at http://pubs.acs.org.
JA067838S
(19) Sheldrick, G. M. SHELXTL-97, version 5.10; Bruker AXS Inc.: Madison,
WI, 1997.
9
J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3753