Oxidation of Tricarbonylmolybdacarborane. 1. First Examples of Oxomolybda(VI)carboranes

Full text of DOI:10.1021/ic960223j

5112
Inorg. Chem. 1996, 35, 5112-5113
Oxidation of Tricarbonylmolybdacarborane. 1. First Examples of Oxomolybda(VI)carboranes
Jae-Hak Kim, Eunkee Hong, Jinkwon Kim,† and Youngkyu Do*
Department of Chemistry and Center for Molecular Science, Korea Advanced Institute of Science and Technology,
Taejon 305-701, Korea, and Department of Chemistry, Kongju National University, Kongju 314-701, Korea
ReceiVed February 29, 1996
The chemistry of transition metal oxo complexes has drawn
considerable interest due to its relevance to metal-centered
oxygen-transfer reactions in biological systems,1 metal-catalyzed
oxidation processes for industrial catalysts,2 and the synthesis
of high oxidation state organometallics.3 Synthesis of oxometals
has been achieved by various means,4 including oxidative
decarbonylation,3d,5 and hydrolysis followed by air oxidation.3b,3c,6
In particular, cyclopentadienyl ligands, among others, have been
used very often as ancillary ligands because of their ability to
stabilize both low and high formal oxidation states.5a On the
other hand, the dicarbollide anion [nido-7,8-C2B9H11]2-, which
is isolobal with the η5-cyclopentadienyl ligands, has not been
employed in synthesizing metal oxo complexes in spite of its
Figure 1. Molecular structure of [(η5-C2B9H11)Mo(CO)2(SPh)2]2- (2)
known ability to stabilize higher formal oxidation states in
showing the atom-labeling scheme.
metallacarborane complexes.7 Consequently, a synthetic search
for oxometallacarboranes was undertaken. The work reported
legged piano-stool” coordination geometry about the molybde-
herein includes stepwise oxidation of [(η5-C2B9H11)Mo(CO)3]2-
num atom with two thiolates and two carbonyl groups consisting
(1)8 to [(η1-C2B9H11)MoO3]2- (3) and [(η5-C2B9H11)O2Mo(µ-
of a cis square base. The symmetry of anion 2 approaches Cs
O)MoO2(η5-C2B9H11)]2- (4) via [(η5-C2B9H11)Mo(CO)2(SPh)2]2-
with a plane containing Mo3, B6, B8, and B10 atoms as well
(2) as well as the molecular structures of three oxidized products.
as bisecting the C1-C2 bond. While the Mo-S bond distances
To a yellow solution of 1(NMe4)2 (460 mg, 1.0 mmol) in
in 2 are similar to those found in the analogous cyclopentadienyl
CH3CN was added 1 equiv of solid phenyl disulfide, resulting
in a prompt color change from yellow to dark red. The reaction
mixture was stirred for 12 h and filtered. The filtrate was treated
complex [TlMo(SC6F5)2(CO)2(Cp)], the C-O distances (1.166-
(11), 1.235(10) Å) in 2 are slightly longer than those (1.116-
(21), 1.121(22) Å) of the latter.11 This is in good agreement
with the lower carbonyl stretching frequencies observed for 2
compared to the Cp analog. In contrast to the anion 1 with
zero formal oxidation state, the oxidized species 2, where Mo
with an excess amount of THF, affording analytically pure dark
red microcrystalline 2(NMe4)2 in 48% yield.9a The molecular
structure of the anion 2,10a shown in Figure 1, reveals a “four-
is in the formal oxidation state of +2, undergoes a well-behaved
* To whom all correspondence should be addressed at the Korea
oxidative decarbonylation reaction.
Advanced Institute of Science and Technology.
† Kongju National University.
A dark red solution of 2(NMe4)2 (650 mg, 1.0 mmol) in CH3-
(1) (a) Enemark, J. H.; Young, C. G. AdV. Inorg. Chem. 1993, 40, 1. (b)
Holm, R. H.; Berg, J. M. Acc. Chem. Res. 1986, 19, 363.
(2) (a) Holm, R. H. Chem. ReV. 1987, 87, 1401. (b) Basset, J.; Gates, B.
C.; Candy, J.; Choplin, A.; Leconte, M.; Quignard, F.; Santin, C.
Surface Organometallic Chemistry: Molecular Approaches to Surface
Catalysis; Kluwer Academic Publishers: Dordrecht, The Netherlands,
Boston, MA, and London, 1988.
(3) (a) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1988, 27, 1297.
(b) Rau, M. S.; Kretz, C. M.; Mercando, L. A.; Geoffroy, G. L. J.
Am. Chem. Soc. 1991, 113, 7420. (c) Rau, M. S.; Kretz, C. M.;
Geoffroy, G. L.; Rheingold, A. L. Organometallics 1993, 12, 3447.
(d)Wolowiec, S.; Kochi, J. K. Inorg. Chem. 1991, 30, 1215.
(4) (a) Bottomley, F. Polyhedron 1992, 11, 1707. (b) Bottomley, F.; Sutin,
L. AdV. Organomet. Chem. 1988, 28, 339.
(5) (a) Klahn-Oliva, A. H.; Sutton, D. Organometallics 1984, 3, 1313.
(b) Herrmann, W. A.; Serrano, R.; Bock, H. Angew. Chem., Int. Ed.
Engl. 1984, 23, 383. (c) Wieghardt, K.; Pomp, C.; Nuber, B.; Weiss,
J. Inorg. Chem. 1986, 25, 1659. (d) Faller, J. W.; Ma, Y. J.
Organomet. Chem. 1988, 340, 59. (e) Leoni, P.; Pasquali, M.; Salsini,
L.; di Bugno, C.; Braga, D.; Sabatino, P. J. Chem. Soc. Dalton Trans.
1989, 155. (f) Harper, J. R.; Rheingold, L. J. Am. Chem. Soc. 1990,
112, 4037.
(6) Bottomley, F.; Boyle, P. D.; Karslioglu, S.; Thompson, R. C.
Organometallics 1993, 12, 4090.
(7) (a) Wilson, R. J.; Warren, L. F., Jr.; Hawthorne, M. F. J. Am. Chem.
Soc. 1969, 91, 758. (b) Wing, R. M. J. Am. Chem. Soc. 1968, 90,
4828. (c) Clair, D. St.; Zalkin, A.; Templeton, D. H. J. Am. Chem.
Soc. 1970, 92, 1173.
(8) (a) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Howe, D. V.;
Pilling, R. L.; Pitts, A. D.; Reintjes, M.; Warren, L. F., Jr.; Wegner,
P. A. J. Am. Chem. Soc. 1968, 90, 879. (b) The structure of compound
1 was determined crystallographically in our group and will be reported
in due course.
CN was treated with a 4-fold molar amount of iodosylbenzene.
(9) (a) Data for 2(NMe4)2: Anal. Calcd for C24H45N2B9O2S2Mo: C,
44.28; H, 6.97; N, 4.30. Found. C, 44.02; H, 7.32; N, 4.01. IR (KBr,
cm-1): νBH ) 2582, 2542, 2523, 2489, 2447; νCO ) 1896, 1793. 1H
NMR (ppm, CD3CN): 3.10 (s, 24H, NMe4), 3.18 (br, 2H, carbonyl
CH), 7.4-6.7 (m, 10H, phenyl). 11B{1H} NMR (ppm, CD3CN): 1.33,
-5.96, -11.23, -13.52, -16.89, -19.92 (1:2:1:2:2:1). (b) Data for
3(NMe4)2: Anal. Calcd for C10H35N2B9O3Mo: C, 28.29; H, 8.31;
N, 6.60. Found. C, 27.72; H, 8.26; N, 6.51. IR (KBr, cm-1): νBH
) 2570, 2536, 2516, 2497, 2472, 2460; νModO ) 897, 855. 1H NMR
(ppm, DMSO-d6): 1.54 (br, 2H, carboranyl CH), 3.10 (s, 24H, NMe4).
11B{1H} NMR (ppm, DMSO-d6): -12.98, -17.66, -18.82, -20.46,
-37.92 (2:3:1:2:1). (c) Data for 4(Ph3P-p-xylyl-PPh3): Anal. Calcd
for C48H60B18O5P2Mo2: C, 49.47; H, 5.19. Found. C, 48.95; H, 5.03.
IR (KBr, cm-1): νBH ) 2560, 2535, 2528, 2520; νModO ) 927, 878;
νMosOsMo ) 776. 1H NMR (ppm, DMSO-d6): 2.87 (br, 4H,
carboranyl CH), 5.07 (d, 4H, CH2), 6.75 (s, 4H, C6H4), 7.9-7.5 (m,
30H, phenyl). 11B{1H} NMR (ppm, DMSO-d6): -2.22, -5.50,
-9.91, -13.73, -20.89 (1:2:2:3:1).
(10) (a) Crystallographic data for 2(NMe4)2‚THF: monoclinic, P1121/b, a
) 10.307(1) Å, b ) 19.069(4) Å, c ) 19.608(2) Å, γ ) 95.67(1)°, V
) 3835.0(10) Å3, Z ) 4, R ) 0.0714. (b) Crystallographic data for
3(NMe4)2: orthorhombic, Pna21, a ) 20.104(2) Å, b ) 7.0278(5) Å,
c ) 30.648(3) Å, V ) 4330.1(7) Å3, Z ) 4, R ) 0.0881. (c)
Crystallographic data for 4‚(Ph3P-p-xylyl-PPh3): triclinic, P1h, a )
10.059(2) Å, b ) 10.701(2) Å, c ) 13.3998(14) Å, R ) 103.880(10),
â ) 96.61(2), γ ) 100.84(2)°, V ) 1355.8(3) Å3, Z ) 1, R ) 0.0285.
(11) (a) Bakar, W. A. W. A.; Davidson, J. L.; Lindsell, W. E.; MaCullough,
K. J.; Muir, K. W. J. Organomet. Chem. 1987, 322, C1. (b) Bakar,
W. A. W. A.; Davidson, J. L.; Lindsell, W. E.; MaCullough, K. J.;
Muir, K. W. J. Chem. Soc., Dalton Trans. 1989, 991.
S0020-1669(96)00223-6 CCC: $12.00 © 1996 American Chemical Society

Communications
Inorganic Chemistry, Vol. 35, No. 18, 1996 5113
tetrahedral with the large O1-Mo-B10 angle of 122.7(6)°. The
distorted molybdenum center is slipped by an average 1.544 Å
toward the unique boron atom B10 of the dicarbollide cage.
One oxo group which forms a longer Mo-O bond (average
1.769 Å) compared with other two oxo groups (average 1.706
Å) in the MoO3 moiety is situated on top of the C2B3 plane as
shown in Figure 2b. The variance of ModO distances in 3
reflects different extent of π-donor ability of three oxo groups
and two oxo groups associated with the shorter Mo-O bonds
may act as formal 4e- donors, leading to η1 behavior of the
dicarbollide anion.
In contrast to 3, the structure10c of 4 reveals η5 bonding of
the dicarbollide anion as illustrated in Figure 3. The closo-
MoC2B9 cages in the dinuclear anion 4 are related by a
crystallographic inversion center lying at the bridging oxygen
atom. The ModO and Mosµ-O bond distances are comparable
with those in analogous complexes [{Cp*Mo(O)2}2(µ-O)]5d,5e
and [{(Me39N3)Mo(O)2}2(µ-O)]2+ 16 where the multiple bond
character in the interaction between molybdenum and oxygen
atoms exists. The linear nature of oxo bridge in the anion 4
should provide efficient dπ-pπ orbital overlap between the Mo
atoms and the bridging oxygen.
Figure 2. (a) Molecular structure of [(η1-C2B9H11)MoO3]2- (3) showing
the atom-labeling scheme. (b) Projection of the MoO3 fragment of 3
onto the open C2B3 pentagonal plane.
The in situ 11B- and 13C-NMR experiments indicate simul-
taneous conversion of complex 2 to 3 and 4 with the formation
of phenyl disulfide. While the role of 2 in the convenient
stepwise oxidation of 1 to 3 and 4 remains as speculation, it is
interesting to note that direct treatment of 1 with iodosylbenzene
also provides 3 in low yield along with other new products.
The nature of these and the reactivity studies of 3 and 4 are
currently under investigation and will be the subject of future
reports.
Figure 3. Molecular structure of [(η5-C2B9H11)O2Mo(µ-O)MoO2(η5-
C2B9H11)]2- (4) showing the atom-labeling scheme.
Acknowledgment. Support of this work by the Korea
Science and Engineering Foundation (Y.D.) and the Nondirected
Research Fund, Korea Research Foundation, 1994 (J.K.) is
gratefully acknowledged.
The reaction mixture was stirred for 12 h, causing gradual
formation of a white precipitate, which was collected and
washed with cold CH3CN. The white solid was recrystallized
from DMF/CH3NO2/Et2O, giving colorless crystals of 3(NMe4)2
in 45% yield.9b The use of the dicationic Ph3P-p-xylyl-PPh3
salt of 2 in the above reaction system gave a yellow solid which
was collected and recrystallized from DMF/CH2Cl2, affording
yellow crystals of 4(Ph3P-p-xylyl-PPh3) in 13% yield.9c
Shown in Figure 2a is the anionic molecular structure of one
of the two independent 3(NMe4)2 molecules in the asymmetric
unit.10b In the anion 3, an endo-(MoO3) moiety interacts with
the unique boron atom of the nido-C2B9 cage vai a σ-Mo-
B(10) bond, providing in 3 the first example of an oxometal-
lacarborane as well as a σ-bonded dicarborane complex of the
early transition metal series. Previous examples of σ-bonded
Supporting Information Available: Tables giving details of the
crystallographic data, positional and thermal parameters, and bond
distances and angles for three reported compounds (24 pages). Ordering
information is given on any current masthead page.
IC960223J
(12) Schubert, D. M.; Bandman, M. C.; Rees, W. S., Jr.; Knobler, C. B.;
Lu, P.; Nam, W.; Hawthorne, M. F. Organometallics 1990, 9, 2046.
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Organometallics 1990, 9, 2938.
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899.
2-
heterocarboranes are limited to C2B9H11 complexes of Al-
(III),12 M(IV) (M ) Si,13 Ge, and Sn14), and Ag(I).15 The
geometry about the molybdenum atom is slightly distorted