Osmabenzenes from the reactions of a dicationic osmabenzyne complex

Article abstract of DOI:10.1021/ja064570w

Treatment of the osmabenzyne Os(≡CC(SiMe₃)=C(Me) C(SiMe₃)=CH)Cl₂(PPh₃)₂ (1) with 2,2′-bipyridine (bipy) and thallium triflate (TIOTf) produces the thermally stable dicationic osmabenzyne [Os(≡CC(SiMe₃)=C(Me) C(SiMe₃)=CH)(bipy)(PPh₃)₂](OTf)₂ (2). The dicationic osmabenzyne 2 reacts with ROH (R = H, Me) to give osmabenzene complexes [Os(=C(OR)CH=C(Me)C(SiMe₃)=CH)(bipy)(PPh ₃)₂]OTf, in which the metallabenzene ring deviates significantly from planarity. In contrast, reaction of the dicationic complex 2 with NaBH₄ produces a cyclopentadienyl complex, presumably through the osmabenzene intermediate [Os(=CHC(SiMe₃)=C(Me)C(SiMe ₃)=CH)(bipy)(PPh₃)₂]OTf. The higher thermal stability of [Os(=C(OR)CH=C(Me)C(SiMe₃)=CH)(bipy)(PPh ₃)₂]OTf relative to [Os(=CHC(SiMe₃)=C(Me) C(SiMe₃)=CH)(bipy)(PPh₃)₂]OTf can be related to the stabilization effect of the OR groups on the metallacycle. A theoretical study shows that conversion of the dicationic osmabenzyne complex [Os(≡CC(SiMe₃)=C(Me)C(SiMe₃)= CH)(bipy)(PPh ₃)₂](OTf)₂ to a carbene complex by reductive elimination is thermodynamically unfavorable. The theoretical study also suggests that the nonplanarity of the osmabenzenes [Os(=C(OR)CH=C(Me)C(SiMe ₃)=CH)(bipy)(PPh₃)₂]OTf is mainly due to electronic reasons.

Full text of DOI:10.1021/ja064570w

Published on Web 10/04/2006
Osmabenzenes from the Reactions of a Dicationic
Osmabenzyne Complex
Wai Yiu Hung, Jun Zhu, Ting Bin Wen, Ka Po Yu, Herman H. Y. Sung,
Ian D. Williams, Zhenyang Lin,* and Guochen Jia*
Contribution from the Department of Chemistry, The Hong Kong UniVersity of Science and
Technology, Clear Water Bay, Kowloon, Hong Kong
Received June 28, 2006; E-mail: chzlin@ust.hk; chjiag@ust.hk
Abstract: Treatment of the osmabenzyne Os(tCC(SiMe3)dC(Me)C(SiMe3)dCH)Cl2(PPh3)2 (1) with 2,2′-
bipyridine (bipy) and thallium triflate (TlOTf) produces the thermally stable dicationic osmabenzyne [Os-
(tCC(SiMe3)dC(Me)C(SiMe3)dCH)(bipy)(PPh3)2](OTf)2 (2). The dicationic osmabenzyne 2 reacts with ROH
(R ) H, Me) to give osmabenzene complexes [Os(dC(OR)CHdC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf, in
which the metallabenzene ring deviates significantly from planarity. In contrast, reaction of the dicationic
complex 2 with NaBH4 produces a cyclopentadienyl complex, presumably through the osmabenzene
intermediate [Os(dCHC(SiMe3)dC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf. The higher thermal stability of [Os-
(dC(OR)CHdC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf relative to [Os(dCHC(SiMe3)dC(Me)C(SiMe3)dCH)-
(bipy)(PPh3)2]OTf can be related to the stabilization effect of the OR groups on the metallacycle. A theoretical
study shows that conversion of the dicationic osmabenzyne complex [Os(tCC(SiMe3)dC(Me)C(SiMe3)d
CH)(bipy)(PPh3)2](OTf)2 to a carbene complex by reductive elimination is thermodynamically unfavorable.
The theoretical study also suggests that the nonplanarity of the osmabenzenes [Os(dC(OR)CHdC(Me)C-
(SiMe3)dCH)(bipy)(PPh3)2]OTf is mainly due to electronic reasons.
ruthenium.4c Very rich chemical properties of metallabenzenes
have also been demonstrated. For example, metallabenzenes
Introduction
Transition metal-containing metallabenzenes1 are an interest-
ing class of compounds, because they can display properties of
both organic and organometallic compounds. These species were
first predicted theoretically in 1979.2 The first stable transition
metal-containing metallabenzenes were reported in 1982 by
Roper et al.3 Since then, the chemistry of transition metal-
containing metallabenzenes has attracted considerable attention
both experimentally4 and theoretically,5 especially in recent
years. Previous study has led to the isolation and characterization
of an impressive number of stable metallabenzenes, especially
those of osmium,3,4a,6-8 iridium,4b,d-f,9-14 platinum,15 and
were found to undergo electrophilic substitution6 and [4+2]
cycloaddition13,16 reactions and to form coordination complexes
with transition metals.13,17
Compounds closely related to metallabenzenes are metalla-
benzynes.18,19 At first sight, one may expect that metallaben-
zynes may, like benzynes,20 be thermally unstable due to the
presence of ring strain. However, several stable metallabenzynes
have been successfully isolated.21-24 Metallabenzynes are also
interesting because they may show properties similar to those
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Roper, W. R.; Wright, L. J. Organometallics 2006, 25, 1771. (b) Alvarez,
E.; Paneque, M.; Poveda, M. L.; Rendon, N. Angew. Chem., Int. Ed. 2006,
45, 474. (c) Zhang, H.; Xia, H.; He, G.; Wen, T. B.; Gong, L.; Jia, G.
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M. A.; Lucassen, A. C. B.; Cohen, H.; van der Boom, M. E.; Martin, J. M.
L. J. Am. Chem. Soc. 2004, 126, 11699. (c) Iron, M. A.; Martin, J. M. L.;
van der Boom, M. E. Chem. Commun. 2003, 132. (d) Iron, M. A.; Martin,
J. M. L.; van der Boom, M. E. J. Am. Chem. Soc. 2003, 125, 13020. (e)
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On˜ate, E.; Mereiter, K. J. Am. Chem. Soc. 2003, 125, 9898.
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9
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J. AM. CHEM. SOC. 2006, 128, 13742-13752
10.1021/ja064570w CCC: $33.50 © 2006 American Chemical Society

Osmabenzenes Formed from a Dicationic Osmabenzyne
A R T I C L E S
of metallabenzenes, benzenes, and benzynes. Indeed, electro-
philic substitution reactions of metallabenzynes have been
recently reported.22
ized metallabenzenes.25 The thermodynamics and the kinetic
of the transformation are critically dependent on the metal
fragment and the substituents on the metallacycle. In principle,
metallabenzynes could also undergo similar transformations to
give carbene complexes. In this regard, generation of metalla-
benzynes and metallabenzenes with the same metal fragment
is interesting, because it provides the opportunity to compare
the relative thermal stability of metallabenzenes and metalla-
benzynes without complication from the effect of the metal
fragment.
In this work, we have prepared a thermally stable dicationic
osmabenzyne complex and investigated its conversion to
osmabenzenes by nucleophilic addition to the carbyne carbon.
We indeed found that the nucleophilic addition reactions lead
to the formation of metallabenzene species, which may be
thermally stable at ambient temperature or rearrange to a
cyclopentadienyl complex, depending on the nucleophiles. To
better understand the chemistry, a computational study was
carried out to compare the thermodynamics and kinetics of the
conversion of osmabenzynes to carbene complexes and the
conversion of osmabenzenes to cyclopentadienyl complexes.
While stable metallabenzenes and metallabenzynes are known,
and benzene and benzyne derivatives can be transformed into
each other chemically, similar transformations have not been
demonstrated with metallabenzenes and metallabenzynes. In-
terconversion of metallabenzenes and metallabenzynes can
provide a route to generate metallabenzynes from metallaben-
zenes, or metallabenzenes from metallabenzynes. An attractive
feature of the transformation is that it could give metallaben-
zynes and metallabenzenes with the same metal fragment, which
are virtually unknown at present.
It is now well established that metallabenzenes can thermally
rearrange to cyclopentadienyl (Cp) complexes.4d,10b,25,26 The
rearrangements have been elegantly demonstrated with isolated
metallabenzene complexes4d,10b and spectroscopically character-
(17) Additional examples of coordinated metallabenzenes. Coordinated irida-
benzenes: (a) Bleeke, J. R.; Bass, L. A.; Xie, Y. F.; Chiang, M. Y. J. Am.
Chem. Soc. 1992, 114, 4213. Coordinated molybdabenzenes: (b) Kralik,
M. S.; Rheingold, A. L.; Ernst, R. D. Organometallics 1987, 6, 2612. (c)
Kralick, M. S.; Rheingold, A. L.; Hutchinson, J. P.; Freeman, J. W.; Ernst,
R. D. Organometallics 1996, 15, 551. Ferrabenzene: (d) Hein, J.; Jeffery,
J. C.; Sherwood, P.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1987,
2211. Coordinated nickelabenzenes: (e) Bertling, U.; Englert, U.; Salzer,
A. Angew. Chem., Int. Ed. Engl. 1994, 33, 1003. Coordinated ruthenaben-
zenes: (f) Bosch, H. W.; Hund, H. U.; Nietlispach, D.; Salzer, A.
Organometallics 1992, 11, 2087. (g) Lin, W.; Wilson, S. R.; Girolami, G.
S. J. Chem. Soc., Chem. Commun. 1993, 284. (h) Lin, W.; Wilson, S. R.;
Girolami, G. S. Organometallics 1997, 16, 2356. (i) Englert, U.; Podewils,
F.; Schiffers, I.; Salzer, A. Angew. Chem., Int. Ed. 1998, 37, 2134. (j) Ohki,
Y.; Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 3463. (k) Liu, S. H.; Ng,
W. S.; Chu, H. S.; Wen, T. B.; Xia, H.; Zhou, Z. Y.; Lau, C. P.; Jia, G.
Angew. Chem., Int. Ed. 2002, 41, 1589. (l) Bruce, M. I.; Zaitseva, N. N.;
Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 2002, 1678.
(m) Effertz, U.; Englert, U.; Podewils, F.; Salzer, A.; Wagner, T.; Kaupp,
M. Organometallics 2003, 22, 264.
Results and Discussions
Preparation of a Dicationic Osmabenzyne. We have
previously shown that the osmabenzyne Os(tCC(SiMe3)d
C(Me)C(SiMe3)dCH)Cl2(PPh3)2 (1),21 like organic aromatic
compounds and metallabenzenes, can undergo electrophilic
substitution reactions at the 3,5-positions of the metallacycle.22,23
A theoretical study indicates that the regiochemistry is controlled
by the highest occupied molecular orbital (HOMO).22,27 The
study also suggests that the lowest unoccupied molecular ortibal
(LUMO) of the metallacycle is mainly made of a d orbital of
the metal and p orbitals of the carbyne carbon and carbons at
the 4,6-positions of the metallacycle.27 Thus, it is expected that
nucleophiles will attack the carbyne carbon and carbons at the
4,6-positions of the metallacycle. Since attack on the carbyne
carbon can relieve the ring strain, we expect that reactions of
osmabenzynes with nucleophiles are more likely to give
osmabenzenes by nucleophilic attack on the carbyne carbon of
osmabenzynes.
To test this possibility, we initially studied the reactivity of
1 with NaBH4. However, complex 1 is not electrophilic enough
to react with NaBH4 in tetrahydrofuran (THF) at room temper-
ature. To increase the electrophilicity of the metallacycle, we
have prepared the dicationic osmabenzyne 2 by replacement of
the chloride ligands in 1 with 2,2′-bipyridine (bipy). The
transformation is accomplished by treatment of 1 with bipy in
the presence of thallium triflate (TlOTf; eq 1).
(18) Roper, W. R. Angew. Chem., Int. Ed. 2001, 40, 2440.
(19) Other complexes closely related to metallabenzenes. Isometallabenzenes:
(a) Barrio, P.; Esteruelas, M. A.; Onate, E. J. Am. Chem. Soc. 2004, 126,
1946. Metallabenzavalenes: (b) Wu, H. P.; Weakley, T. J. R.; Haley, M.
M. Organometallics 2002, 21, 4320. Metallathiabenzenes: (c) Bleeke, J.
R.; Hinkle, P. V.; Shokeen, M.; Rath, N. P. Organometallics 2004, 23,
4139. (d) Bleeke, J. R.; Hinkle, P. V.; Rath, N. P. Organometallics 2001,
20, 1939. (e) Bleeke, J. R.; Hinkle, P. V.; Rath, N. P. J. Am. Chem. Soc.
1999, 121, 595. (f) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Moneti,
S.; Herrera, V.; Sanchez-Delgado, R. A. J. Am. Chem. Soc. 1994, 116,
4370. (g) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Frediani, P.;
Herrera, V.; Sanchez-Delgado, R. A. J. Am. Chem. Soc. 1993, 115, 2731.
(h) Jones, W. D.; Chin, R. M. J. Am. Chem. Soc. 1992, 114, 9851. (i)
Chin, R. M.; Jones, W. D. Angew. Chem., Int. Ed. Engl. 1992, 31, 357. (j)
Chen, J.; Daniels, L. M.; Angelici, R. J. J. Am. Chem. Soc. 1990, 112,
199. Metallapyridines: (k) Weller, K. J.; Filippov, I.; Briggs, P. M.; Wigley,
D. E. Organometallics 1998, 17, 322. Metallapyryliums: (l) Bleek, J. R.;
Blanchard, J. M. B.; Donnay, E. Organometallics 2001, 20, 324. (m) Bleke,
J. R.; Blanchard, J. M. B. J. Am. Chem. Soc. 1997, 119, 5443. Dimetalla-
benzenes: (n) Profilet, R. D.; Fanwick, P. E.; Rothwell, I. P. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 1261. (o) Riley, P. N.; Profilet, R. D.; Salberg, M.
M.; Fanwick, P. E.; Rothwell, I. P. Polyhedron 1998, 17, 773.
(20) Jiao, H.; Schleyer, P. v. R.; Beno, B. R.; Houk, K. N.; Warmuth, R. Angew.
Chem., Int. Ed. 1997, 36, 2761.
(21) Wen, T. B.; Zhou, Z. Y.; Jia, G. Angew. Chem., Int. Ed. 2001, 40, 1951.
(22) Wen, T. B.; Ng, S. M.; Hung, W. Y.; Zhou, Z. Y.; Lo, M. F.; Shek, L. Y.;
Williams, I. D.; Lin, Z.; Jia, G. J. Am. Chem. Soc. 2003, 125, 884.
(23) Jia, G. Acc. Chem. Res. 2004, 37, 479.
(24) Wen, T. B.; Hung, W. Y.; Sung, H. H. Y.; Williams, I. D.; Jia, G. J. Am.
Chem. Soc. 2005, 127, 2856.
(25) Conversion of transient metallabenzenes to cyclopentadienyl complexes:
Yang, J.; Jones, W. M.; Dixon, J. K.; Allison, N. T. J. Am. Chem. Soc.
1995, 117, 9776.
(26) Metallabenzenes have been suggested as the intermediates in the formation
of cyclopentadienyl complexes. For example, chromo- and tungstaben-
zenes: (a) Sivavec, T. M.; Katz, T. J. Tetrahedron Lett. 1985, 26, 2159.
(b) Schrock, R. R.; Pedersen, S. F.; Churchill, M. R.; Ziller, J. W.
Organometallics 1984, 3, 1574. Rhenabenzenes: (c) Ferede, R.; Hinton,
J. F.; Korfmacher, W. A.; Freeman, J. P.; Allison, N. T. Organometallics
1985, 4, 614. (d) Mike, C. A.; Ferede, R.; Allison, N. T. Organometallics
1988, 7, 1457. (e) Plantevin, V.; Wojcicki, A. J. Organomet. Chem. 2004,
689, 2013. Ferrabenzenes: (f) Ferede, R.; Allison, N. T. Organometallics
1983, 2, 463. Ruthenabenzenes: (g) Yang, J.; Yin, J.; Abboud, K. A.; Jones
W. M. Organometallics 1994, 13, 971. Platinabenzenes: (h) Jacob, V.;
Weakley, T. J. R.; Haley, M. M. Organometallics 2002, 21, 5394.
Complex 2 was isolated as a purple solid. Its structure has
been confirmed by X-ray diffraction. The molecular structure
is shown in Figure 1, and selected bond distances and angles
(27) (a) Ng, S. M.; Huang, X.; Wen, T. B.; Jia, G.; Lin, Z. Organometallics
2003, 22, 3898. (b) Yang, S. Y.; Li, X. Y.; Huang, Y. Z. J. Organomet.
Chem. 2002, 658, 9.
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J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006 13743

A R T I C L E S
Hung et al.
in osmium vinylidene complexes (1.786-1.892 Å).28,30 The
Os-C5 bond length of 2.015(3) Å is within the range of Os-
C(vinyl) bonds (1.897-2.195 Å)28,31 and is at the high end of
those reported for Os-CH(carbene) bonds (1.831-2.050 Å).28,32
Overall, the structural feature associated with the metallacycle
of 2 is very similar to that of 1,21 although the Os-C1 bond
(1.780(3) Å) is slightly shorter and the Os-C5 bond (2.015(3)
Å) is slightly longer than the corresponding bonds (1.815(4)
and 1.939(5) Å, respectively) in 1. The structural data indicate
that the metallacycle of 2 has a delocalized structure with
contributions from the resonance structures 2 and 2A, with 2
being more important.
Figure 1. X-ray structure of complex 2. Counteranion and some of the
hydrogen atoms are omitted for clarity.
Table 1. Selected Bond Distances (Å) and Angles (deg) for
Osmabenzyne 2 and Osmabenzenes 3 and 5
compound
2
3
5
The solid-state structure of 2 is fully supported by NMR
spectroscopy. In particular, the H NMR (in CDCl3) spectrum
showed the OsCH signal at 13.45 ppm, and the 13C{1H} NMR
spectrum showed the five ring carbon signals at 316.4 (OsC),
216.3 (OsCH), 118.7 (OstCCSiMe3), 145.6 (CSiMe3), and
198.4 (CMe) ppm.
1
Os1-C1
C1-C2
C2-C3
C3-C4
C4-C5
Os1-C5
Os1-P1
Os1-P2
Os1-N1
Os1-N2
1.780(3)
1.370(5)
1.419(5)
1.436(5)
1.379(5)
2.015(3)
2.4156(9)
2.4403(9)
2.173(3)
2.208(3)
1.921(4)
1.464(4)
1.362(6)
1.472(6)
1.383(5)
2.010(4)
2.3704(9)
2.3988(9)
2.142(3)
2.190(3)
1.958(5)
1.436(7)
1.390(7)
1.461(7)
1.343(7)
2.008(5)
2.3795(15)
2.4056(14)
2.177(4)
2.181(4)
Reactions of Complex 2 with H2O. Solid sample of complex
2 can be stored in an inert atmosphere for at least one week
without appreciable decomposition, indicating that it is thermally
stable at ambient temperature. However, it is very electrophilic
and readily reacts with nucleophiles. Even water can function
as a nucleophile to react with 2. The products of the reaction
of 2 with H2O depend on the reaction conditions, especially
the amount of water present and the reaction time. When a
solution of 2 in THF/water (4:3, v/v) was stirred at room
temperature for 2 h, the osmabenzene complex 3 was formed
and precipitated out from the reaction mixture as a brownish-
red solid (Scheme 1). The poor solubility of 3 in the solvent
mixture helps the isolation of 3. When a solution of 2 in a mixed
solvent of THF/water (15:1, v/v) was stirred at room temper-
ature, the reaction initially produced complex 3 along with
unreacted 2 and a small amount of the vinyl complex 4, and
eventually all complexes 2 and 3 were completely consumed
to produce a mixture of species with complex 4 as the dominant
Os1-C1-C2
C1-C2-C3
C2-C3-C4
C3-C4-C5
C4-C5-Os1
C1-Os1-C5
C1-Os1-P1
C1-Os1-P2
C1-Os1-N1
C1-Os1-N2
C5-Os1-P1
C5-Os1-P2
C5-Os1-N1
C5-Os1-N2
P1-Os1-P2
P1-Os1-N1
P1-Os1-N2
P2-Os1-N1
P2-Os1-N2
N1-Os1-N2
153.8(3)
111.1(3)
122.2(3)
120.0(3)
123.0(3)
124.9(4)
122.9(4)
117.2(4)
123.7(4)
124.1(5)
123.6(5)
117.4(5)
134.3(4)
85.0(2)
134.7(3)
132.5(3)
76.32(14)
87.98(11)
97.57(11)
120.29(13)
163.56(13)
96.46(10)
89.26(10)
163.01(12)
89.12(12)
172.85(3)
88.19(7)
85.53(15)
91.42(11)
89.57(11)
105.13(14)
177.26(12)
89.08(10)
95.04(10)
168.95(13)
94.18(13)
175.83(3)
87.76(8)
91.44(17)
88.30(17)
106.09(19)
175.6(2)
87.31(16)
96.93(16)
168.2(2)
94.12(19)
175.72(5)
88.28(12)
92.80(12)
87.69(12)
87.55(12)
75.15(16)
86.10(7)
85.12(7)
89.71(7)
74.86(11)
91.30(7)
88.07(8)
87.74(7)
75.32(11)
(28) Based on a search of the Cambridge Structural Database, CSD version
5.26 (November 2004).
(29) More recent examples. (a) Os(tCC6H4CHMe2)H2(N(SiMe2CH2PtBu2)
(1.746(3) Å): Lee, J. H.; Pink, M.; Caulton, K. G. Organometallics 2006,
25, 802. (b) [OsH(tCCHdCPh2)(H2O)2(PiPr3)2][BF4]2 (1.733(6) Å):
Bolano, T.; Castarlenas, R.; Esteruelas, M. A.; Modrego, F. J.; Onate, E.
J. Am. Chem. Soc. 2005, 127, 11184. (c) Os(tCCH3)Cl3(PPh3)2 (1.724(5)
Å): Wen, T. B.; Hung, W. Y.; Zhou, Z. Y.; Lo, M. F.; Williams, I. D.;
Jia, G. Eur. J. Inorg. Chem. 2004, 2837.
(30) A recent example, CpOsCl(dCdCHPh)(PiPr2(C(CH3)dCH2)) (1.817(5)
Å): Baya, M.; Buil, M. L.; Esteruelas, M. A.; Onate, E. Organometallics
2005, 24, 2030.
(31) Recent examples. (a) [Os(OTf)(NC5H4CHdCH)(NC5H4CHdCH2)(PiPr3)]-
OTf (1.995(2) Å): Esteruelas, M. A.; Fernandez-Alvarez, F. J.; Olivan,
M.; Onate, E. J. Am. Chem. Soc. 2006, 128, 4596. (b) CpOs(CHd
CHCOMe)(PiPr3) (1.989(4) Å): Esteruelas, M. A.; Hernandez, Y. A.;
Lopez, A. M.; Olivan, M.; Onate, E. Organometallics 2005, 24, 5989. (c)
Os(SnPh2Cl)(NC5H4CHdCH)(H2)(PiPr3)2 (2.068(4) Å): Eguillor, B.; Es-
teruelas, M. A.; Olivan, M.; Onate, E. Organometallics 2005, 24, 1428.
(d) OsCl(CHdCH(p-tolyl)(CO)(PPh3)3 (2.105(7) Å): Xia, H.; Wen, T. B.;
Hu, Q. Y.; Wang, X.; Chen, X.; Shek, L. Y.; Williams, I. D.; Wong, K. S.;
Wong, G. K. L.; Jia, G. Organometallics 2005, 24. 562.
are given in Table 1. As shown in Figure 1, the complex contains
an essentially coplanar six-membered metallacycle. The maxi-
mum deviation from the least-squares plane through Os1 and
C1-C5 is 0.086 Å for C3, and the sum of angles in the six-
membered ring is 718.1°, which is very close to the ideal value
of 720°. The Os-C1-C2 angle of 153.8(3)° is significantly
smaller than that expected for either a carbyne or a vinylidene
complex, owing to the constraint of the six-membered ring. The
metallacycle has a delocalized structure, as reflected by the
observation that the C1-C2 distance (1.370(5) Å) is comparable
to that of C4-C5 (1.379(5) Å) and that the C2-C3 distance
(1.419(5) Å) is similar to that of C3-C4 (1.436(5) Å). The Os-
C1 bond length of 1.780(3) Å is at the high end of those
observed for typical OstC bond distances (1.694-1.792 Å)28,29
and is slightly shorter than those found for typical OsdC bonds
(32) A recent example, CpOsCl(dCHPh)(PiPr2(C(CH3)dCH2)) (1.895(5) Å):
Esteruelas, M. A.; Gonzalez, A. I.; Lopez, A. M.; Onate, E. Organometallics
2004, 23, 4858.
9
13744 J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006

Osmabenzenes Formed from a Dicationic Osmabenzyne
A R T I C L E S
Scheme 1
Figure 2. X-ray structure of complex 3. Counteranion and some of the
hydrogen atoms are omitted for clarity.
product (Scheme 1). Complex 4 could be isolated as a yellow
solid in 41% yield after a solution of complex 2 in THF/water
(15:1, v/v) was stirred at room temperature for 2 days. In the
mixed solvent of CH2Cl2/H2O, complex 2 is also reactive toward
water to give 3 and 4, although the reaction is slow and usually
produced a mixture of species.
some of the transition states calculated for the conversion of
metallabenzenes to cyclopentadienyl complexes.5b
The electron delocalization in the metallacycle of 3 is poor,
as reflected by the marked short-long C-C distance alterna-
tions. The C1-C2 (1.464(5) Å) and C3-C4 (1.472 (6) Å) bonds
are appreciably longer than the C2-C3 (1.362 (6) Å) and C4-
C5 (1.383(5) Å) bonds. The Os-C1 bond (1.921(4) Å) is also
shorter than the Os-C5 bond (2.010(4) Å). The shorter Os-
C(OH) bond compared with Os-CH is probably not surprising,
as a similar trend has been observed in Bleeke’s iridaphenol
[Ir(dC(OH)C(Me)dCHC(Me)dCH)(OTf)(PMe3)3]OTf (1.916-
(16) and 2.031(16) Å, respectively).12 In osmabenzenes Os(d
C(SMe)CHdCHCX)CH)I(CO)(PPh3)2 (X ) NO2, Br), in
which I is trans to CH and CO is trans to C(SMe), the Os-
C(SMe) bond is also slightly shorter than Os-CH.6
Complex 3 can be stored in the solid form under an inert
atmosphere for at least one week without appreciable decom-
position. The structure of 3 can be readily deduced on the basis
of the NMR spectroscopy. The 31P{1H} NMR (in CD2Cl2)
spectrum showed a singlet at 2.5 ppm. The 1H NMR spectrum
showed the OsCH signal at 13.80 ppm, the CH signal at 5.41
ppm, and the OH signal at 9.15 ppm. The 13C NMR spectrum
showed the five carbon signals of the metallacycle at 252.3
(OsC(OH)), 223.6 (OsCH), 164.1 (CCH3), 141.5 (CSiMe3), and
119.7 (OsC(OH)CH) ppm. Complex 3 is structurally related to
Roper’s osmabenzene complex [Os(dC(SH)CHdCHCHdCH)-
(CO)2(PPh3)2]+.3 Complex 3 can be regarded as a metallaphenol.
The iridaphenols [Ir(dC(OH)C(Me)dCHC(Me)dCH)(X)-
(PMe3)3]OTf (X ) OTf, CF3CO2) reported by Bleeke et al. are
the rare stable metallaphenols reported previously.12 We noted
that metallaphenoxides of Ru, Fe, and Re and metallaphenan-
threne oxides of Ru and Re have been proposed or detected
spectroscopically at low temperature.25,26c,f,g
The structure of 4 can be readily assigned on the basis of the
1
spectroscopic and analytical data. In particular, the H NMR
(in CD2Cl2) spectrum showed the 1H signals of OsCHd
C(SiMe3)CMedCH2 at ca. 8.43 (OsCH), -0.03 (SiMe3), 1.68
(Me), 4.36, and 4.44 (dCH2) ppm. The 13C{1H} NMR spectrum
showed the carbon signals of the vinyl ligand OsCHdC(SiMe3)-
CMe)CH2 at 146.9 (Os(CH), 154.9 (C(Me)), 151.8 (C(SiMe3),
112.2 (CH2), 25.0 (CH3), and 0.3 (SiMe3) ppm and the CO
signal at 188.6 ppm. The 31P{1H} NMR spectrum showed a
singlet at -1.7 ppm. The structure has been confirmed by an
X-ray diffraction study. A view of the complex cation is shown
in Figure 3.
The structure of 3 has been confirmed by X-ray diffraction.
The molecular structure is shown in Figure 2, and selected bond
distances and angles are given in Table 1. The X-ray diffraction
study confirms that the complex contains a six-membered
metallacycle with an OH group attached to one of the R-carbons.
Several osmabenzenes have been previously characterized
structurally.3,4a,6-8 In these reported examples, the osmabenzene
ring usually has a planar or nearly planar structure. However,
the metallacycle of complex 3 deviates significantly from
planarity, as reflected by the sum of angles in the six-membered
ring of 706.03°, which is significant smaller than the ideal value
of 720°. The mean deviation from the least-squares plane
through the C1-C5 chain is 0.0771 Å. The Os is out of the
plane of the metallacyclic carbon atoms by 0.68 Å. The OH at
C1 and H at C5 are also out of the plane. Although not common,
a few nonplanar metallabenzenes are known. For example, in
iridabenzenes supported by a Tp ligand, the iridium metal is
bent by 0.50-0.76 Å out of the plane of the metallacyclic carbon
atoms;4b,f,11 in the ruthenabenzene [Ru(dCHC(PPh3)dCHC-
(PPh3)dCH)(bipy)Cl(PPh3)]Cl2, the ruthenium center lies
-0.6722(56) Å out of the plane of the ring carbon atoms.4c The
conformation of the metallacycle of 3 is somewhat similar to
In the reaction of 2 with water, complex 3 can be formed
either by first nucleophilic attack of water on the carbyne carbon
of 2, followed by desilylation, or by first desilylation of 2,
followed by nucleophilic attack of water on the carbyne carbon
of a desilylated osmabenzyne intermediate. We have no
experimental evidence to differentiate the two possibilities.
Desilylation of 2 by water is not unusual, as there are many
reports on the cleavage of the Si-C bond by water to give C-H
bonds, especially in the reactions of LnM with HCtCSiMe3 to
give vinylidene complexes LnM(dCdCH2).33 As will be
discussed below, the fact that only the SiMe3 adjacent to the
carbyne carbon is preferentially desilylated can be related to
the higher nucleophilicity of the Si-bound carbon.
(33) See, for example: (a) Espuelas, J.; Esteruelas, M. A.; Lahoz, F. J.; Oro, L.
A.; Ruiz, N. J. Am. Chem. Soc. 1993, 115, 4683. (b) Bianchini, C.; Marchi,
A.; Marvelli, L.; Peruzzini, M.; Romerosa, A.; Rossi, R. Organometallics
1996, 15, 3804. (c) Kawata, Y.; Sato, M. Organometallics 1997, 16, 1093.
(d) Werner, H.; Lass, R. W.; Gevert, L. O.; Wolf, J. Organometallics 1997,
16, 4077. (e) Werner, H.; Jung, S.; Weberndo¨rfer, B.; Wolf, J. Eur. J.
Inorg.Chem. 1999, 951.
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J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006 13745

A R T I C L E S
Hung et al.
Scheme 2
Figure 3. X-ray structure of complex 4. Counteranion and some of the
hydrogen atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Os(1)-C(1) 1.851(6), Os(1)-C(2) 2.093(5), Os(1)-P(1)
2.3804(14), Os(1)-P(2) 2.4112(14), Os(1)-N(1) 2.149(5), Os(1)-N(2)
2.170(4), C(1)-O(1) 1.152(7), C(2)-C(3) 1.353(8), C(3)-C(4) 1.491(10),
C(4)-C(5) 1.308(5), C(4)-C(6) 1.478(13), O(1)-C(1)-Os(1) 176.3(5),
Os(1)-C(2)-C(3) 140.6(5), C(2)-C(3)-C(4) 124.2(6), C(3)-C(4)-C(5)
121.1(9), C(3)-C(4)-C(6) 121.8(8), C(5)-C(4)-C(6) 116.8(9).
As mentioned previously, nucleophilic attack at the carbyne
carbon of osmabenzynes is expected if we assume that the
reaction is frontier orbital (LUMO here) controlled. The
reactivity is similar to that of Fischer carbynes, which can be
nucleophilically attacked at the carbyne carbon to give carbene
complexes.34 For osmium carbyne complexes, nucleophilic
addition reactions with methanol and water have been reported,
for example, in the reactions of CpOs(CPh)(L) (L ) P(iPr)3,
P(iPr2)CHdCH2) with MeOH to give CpOsH(C(OMe)Ph)(L),35
the reaction of [Os(CPh)(NH3)5]3+ with MeOH to give [Os-
isomerization of 3 to the ketone form B can be related to the
interconversion of enols and ketones, which is well known in
organic chemistry and can be catalyzed by both acids and
bases.39 A six-electron retro-electrocyclization reaction of B
would give complex 4. Six-electron electrocyclization of
hexatrienes and retro-electrocyclization of cyclohexadienes are
well-known reactions.40 We noted that 16e acyl complexes Ln-
MCOR usually undergo de-insertion reactions to give 18e
complexes LnMR(CO).41 In our case, complex 4, formed via
retro-electrocyclization from B, is an 18e complex, while a
normal CO de-insertion of B would give a 20e metallacycle,
and therefore is very unlikely.
(C(OMe)Ph)(NH3)5]2+ 36
, and the reaction of [Os(CPh)ICl(CO)-
(PPh3)2)]+ with H2O to give OsPhCl(CO)2(PPh3)2.37 Reactions
of vinylidene complexes LnMdCdCHR with methanol usually
give carbene complexes LnMdC(OMe)CH2R.38 In this sense,
in the reaction of 2 with H2O, complex 2 shows more carbyne
than vinylidene character.
Reaction of Complex 2 with Methanol. Complex 2 is also
reactive toward methanol. In the presence of K2CO3, complex
2 in dichloromethane readily reacted with MeOH (Scheme 1)
to give the osmabenzene 5. In the absence of K2CO3, formation
of complex 5 also occurred, although the reaction is much slower
and also produced other uncharacterized products. Like the
reaction with water, one of the SiMe3 groups in 2 is also changed
to H in the reaction with MeOH. Complex 5 can be formed
either by first nucleophilic addition of OMe- to the carbyne
carbon of 2, followed by desilylation, or by first desilylation of
2, followed by nucleophilic addition of OMe- to the carbyne
carbon of a desilylated osmabenzyne intermediate.
Complex 5 is isolated as a brownish-red solid. The structure
of 5 has been confirmed by X-ray diffraction (Figure 4). The
structural features of the metallacycle of 5 are similar to those
of osmabenzene 3 in that the metallacycle ring also deviates
significantly from planarity. The sum of angles in the six-
membered ring of 5 is 708.1°. The mean deviation from the
least-squares plane through the C1-C5 chain is 0.0669 Å. The
Os is out of the plane of the metallacyclic carbon atoms by
The formation of 4 from the reaction of 2 with water
presumably proceeds through complex 3. In fact, it can be
demonstrated that the isolated complex 3 can also be converted
to complex 4. Conversion of complex 3 to 4 seems to be
promoted by acid/H2O. Transformation of the isolated complex
3 to 4 is very slow in drying solvents. In a mixed solvent of
THF/H2O, the conversion of 3 to 4 was observed, but the
reaction was not completed even after 5 days. When a solution
of the isolated complex 3 in CD2Cl2 was treated with water in
the presence of purposely added HBF4, the reaction was
completed after 12 h to give 4 as the dominant product. Indeed,
in the reaction of 2 with water, HOTf can be generated in situ
during the formation of 3, which may catalyze the transformation
of 3 to 4. On the basis of the above observations, a plausible
mechanism for the formation of 4 from 3 is proposed in Scheme
2. Protonation of 3 at C2 may give intermediate A, which can
be deprotonated with H2O to give the ketone form B. The
(34) Engel, P. F.; Pfeffer, M. Chem. ReV. 1995, 95, 2281.
(35) (a) Esteruelas, M. A.; Gonzalez, A. I.; Lopez, A. M.; Onate, E. Organo-
metallics 2003, 22, 414. (b) Reference 32.
(36) Hodges, L. M.; Sabat, M.; Harman, W. D. Inorg. Chem. 1993, 32, 371.
(37) Gallop, M. A.; Roper, W. R. AdV. Organomet. Chem. 1986, 25, 121.
(38) For reviews on vinylidene complexes, see, for example: (a) Bruce, M. I.
Chem. ReV. 1991, 91, 197. (b) Bruce, M. I.; Swincer, A. G. AdV. Organomet.
Chem. 1983, 22, 59. (c) Puerta, M. C.; Valerga, P. Coord. Chem. ReV.
1999, 193-195, 977. (d) Bruneau, C.; Dixneuf, P. H. Angew. Chem., Int.
Ed. 2006, 45, 2176.
(39) Loudon, G. M. Organic Chemistry, 2nd ed.; Benjamin/Cummings Publish-
ing Co. Inc.: 1984; Chapter 22, p 919.
(40) Ansari, F. L.; Oureshi, R.; Qureshi, M. L. Electrocyclic Reactions, From
Fundamental to Research; Wiley-VCH: Weinheim, 1999.
(41) Crabtree, R. H. Organometallic Chemistry of the Transition Metals, 4th
ed.; Wiley-VCH: Weinheim, 2005.
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13746 J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006

Osmabenzenes Formed from a Dicationic Osmabenzyne
A R T I C L E S
Figure 4. X-ray structure of complex 5. Counteranion and some of the
hydrogen atoms are omitted for clarity.
Figure 5. X-ray structure of the complex 6. Counteranion and hydrogen
atoms are omitted for clarity. Selected bond distances (Å) and angles
(deg): Os(1)-P(1) 2.3218(12), Os(1)-N(1) 2.078(3), Os(1)-N(2) 2.088-
(3), Os(1)-C(1) 2.181(4), Os(1)-C(2) 2.261(3), Os(1)-C(3) 2.235(4), Os-
(1)-C(4) 2.236(4), Os(1)-C(5) 2.152(4), C(1)-C(2) 1.460(5), C(2)-C(3)
1.445(6), C(3)-C(4) 1.438(5), C(4)-C(5) 1.426(5), C(1)-C(5) 1.405(6),
C(3)-C(6) 1.500(5), N(1)-Os(1)-P(1) 88.91(8), N(2)-Os(1)-P(1) 94.61-
(9), N(1)-Os(1)-N(2) 75.74(11).
Scheme 3
reaction to give the η1-cyclopentadienyl complex D, which then
rearranges to give 6. Formation of Cp complexes via metalla-
benzenes has been previously proposed26 and confirmed by
reactions of isolated metallabenzene complexes4d,10b and spec-
troscopically characterized metallabenzenes.25 The easy forma-
tion of the Cp complex 6 from intermediate C is somewhat
unexpected, because the related complexes 3 and 5 can be
isolated and were found to be thermally stable at ambient
temperature.
Ready conversion of metallabenzene C to Cp complex 6 is
interesting, especially in view of the fact that osmabenzyne 2,
although it has ring strain, does not undergo reductive elimina-
tion to give a carbene complex under similar conditions.
Intuitively, the difference can be related to the fact that C can
evolve to the 18e Cp complex 6, but a similar reductive
elimination reaction of 2 would lead to a 16e osmium carbene
complex. A better understanding of the interesting observation
comes from a computational study (see below).
0.64 Å. The OMe at C1 and H at C5 are also out of the plane.
Consistent with the solid-state structure, the 1H NMR (in CDCl3)
spectrum showed the OsCH signal at 14.20 ppm, the CH signal
at 5.25 ppm, and the OMe signal at 3.47 ppm. The 13C{1H}
NMR spectrum showed the five carbon signals of the metalla-
cycle at 251.8 (OsC(OMe)), 227.5 (OsCH), 121.8 (OsC(OMe)-
CH), 165.0 (CCH3), and 141.0 (CSiMe3) ppm. Roper and Wright
et al. have previously isolated the related osmabenzene com-
plexes [Os(dC(SMe)CHdCHCHdCH)(CO)2(PPh3)2]+ and Os-
(dC(SMe)CHdCHCXdCH)I(CO)(PPh3)2 (X ) NO2, Br).3,6
Another related complex, Ru(dC(OEt)CPhdCHCHdCPh)(Cp)-
(CO), has been detected spectroscopically at low temperature
by Jones et al.25 Unlike complex 5, complexes Os(dC(SMe)-
CHdCHCXdCH)I(CO)(PPh3)2 (X ) NO2, Br) have a planar
metallacycle.6
Density Functional Theory (DFT) Calculations. Several
questions arise from the experimental data. (i) It is noted that
metallabenzene C readily rearranges to Cp complex 6, but
osmabenzenes 3 and 5, and even osmabenzyne 2, which has
ring strain, are stable at ambient temperature. It is not obvious
whether the difference is kinetic or thermodynamic in origin.
(ii) The metallacycles of osmabenzenes 3 and 5 deviate
significantly from planarity. However, the closely related
osmabenzenes Os(dC(SMe)CHdCHC(X)dCH)I(CO)(PPh3)2
(X ) NO2, Br) adopt a nearly planar structure.6 One may ask
what causes the nonplanarity in our complexes. (iii) In the
reactions of 2 with H2O and MeOH, one of the SiMe3 groups
in 2 is selectively removed. It is not clear why the SiMe3
adjacent to the carbyne carbon is preferentially desilylated. To
address these problems, DFT calculations were carried out. In
consideration of the computational cost, unless otherwise stated,
PH3 and SiH3 were used to model PPh3 and SiMe3, respectively,
in our calculations.
Reaction of Complex 2 with NaBH4. Treatment of 2 with
NaBH4 in THF produced the cyclopentadienyl complex 6
(Scheme 3), rather than the expected metallabenzene. The
structure of 6 has also been confirmed by X-ray diffraction.
The X-ray structure (Figure 5) clearly shows that the complex
is a cyclopentadienyl complex with one bipy and one PPh3
ligand. The solution NMR spectroscopic data are consistent with
1
the solid-state structure. In particular, the H NMR spectrum
showed a characteristic Cp proton signal at 4.47 ppm, and the
13C{1H} NMR spectrum showed the three Cp carbon signals at
109.8 (C(Me)), 80.9 (CH), and 76.0 (CSiMe3) ppm.
Mechanistically, complex 6 can be formed by initial attack
of the carbyne carbon of the osmabenzyne 2 by H- to give
intermediate C, although we have failed to observe the
intermediate. Intermediate C can undergo a reductive elimination
The osmabenzyne [Os(tCC(SiMe3)dC(Me)C(SiMe3)dCH)-
(bipy)(PPh3)2](OTf)2 (2) is structurally closely related to the
osmabenzene intermediate [Os(dCHC(SiMe3)dC(Me)C(SiMe3)d
CH)(bipy)(PPh3)2](OTf)2 (C). C is thermally unstable and
9
J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006 13747

A R T I C L E S
Scheme 4
Hung et al.
rearranges to cyclopentadienyl complex 6 through a formal
reductive elimination reaction. In principle, metallabenzyne 2
could also undergo a similar transformation to give a carbene
complex containing a five-membered ring. However, such
transformation was not observed for 2. To gain insight into why
the reaction did not proceed, we have studied, by DFT
calculations, the reductive elimination reaction of 2-benzyne,
a model complex of 2. The reductive elimination product,
2-carbene, is an 18e complex with a C-H agostic interaction
(Scheme 4). In the model complexes, we replace only one SiMe3
with SiH3 and retain one SiMe3 group in order to avoid the
unexpected interaction between an H-Si bond and the metal
center in 2-carbene. ∆G°, the relative Gibbs free energy at T
) 298 K, and ∆E, the relative electronic energy of the reaction,
given in Scheme 4, show that 2-benzyne is thermodynamically
much more stable than 2-carbene, consistent with the experi-
mental observation that metallabenzyne 2 does not undergo
reductive elimination to give a carbene complex. The higher
stability of metallabenzyne 2-benzyne versus carbene 2-carbene
is likely a result of the former having a high degree of
conjugation,27 while the latter has very limited conjugation.
Figure 6. Energy profiles for the conversion of metallabenzenes to Cp
complexes. The calculated relative free energies and electronic energies
(in parentheses) are given in kcal/mol.
5-benzene, a model complex of 5, to a Cp complex 5-Cp. We
did not calculate the energetics for the conversion of 3 because
we expect that the results should be similar to those calculated
for 5. Interestingly, the results of calculations show that both
of the conversions are one-step processes and do not occur via
an η1-Cp intermediate species such as D shown in Scheme 3.
Consistent with the experimental observations, the conversion
of C-benzene to 6-Cp is exothermic and has a relatively small
barrier, while the conversion of 5-benzene to 5-Cp is slightly
endogonic and has a significantly high barrier. The finding that
the conversion of the metallabenzene complex C-benzene to
6-Cp is thermodynamically favorable is not unusual, as it has
been found that 18e Cp complexes generally have higher
thermodynamic stability when compared with the corresponding
metallabenzene complexes.5b
The finding that the conversion of 5-benzene to 5-Cp is
slightly endogonic is unexpected. This unexpected result has
the following important implication: one might be able to
synthesize metallabenzenes from Cp complexes if the substit-
uents on the Cp ring and metal fragments were finely tuned. A
plausible explanation is given below to explain the unexpected
result. The OMe substituent is highly electron-donating and is
able to stabilize the metallabenzene structure C-benzene because
C-benzene is expected to have Fischer carbene character and
can be stabilized significantly by an electron-donating substituent
at the carbene carbon. In addition, the electron-donating OMe
substitutent on the Cp ligand may also destabilize the Cp
complex 5-Cp because Cp is not a large ring and strong electron-
donating substituents, such as OMe or OH, could make the ring
too electron-rich to be very stable. To support the plausible
explanation, we replaced the OMe substituent in 5-benzene with
H to give the model complex 5-benzene-H and calculated the
reaction energy for the corresponding benzene-to-Cp conversion
for 5-benzene-H. The energetics is similar to that we found
for the conversion of C-benzene to 6-Cp shown in Figure 6.
The nonplanarity of the metallabenzene complexes 3 and 5
was reasonably reproduced by our calculations on the model
Reactions of osmium carbyne complexes LnOs(tCR)(R′)
with a two-electron donor ligand L′ are known to give carbene
complexes LnL′Os(dCRR′).29a,b,42 Thus, one may think that an
additional ligand is able to stabilize the reductive elimination
product. Therefore, we also calculated the energetics associated
with the reaction of 2-benzyne + PH3 f 2-carbene-A (Scheme
4). Indeed, the additional ligand stabilizes the carbene complex
significantly. The reaction (electronic) energy becomes -12.8
kcal/mol. However, when the entropy effect is considered, the
reaction has a reaction free energy of 4.2 kcal/mol, indicating
that the reaction is still thermodynamically unfavorable. We
expect that when more realistic phosphine ligands (PPh3) were
employed in the calculations, the reaction (electronic) energy
should be much less negative and, therefore, the reaction free
energy much more positive. These theoretical calculations
indicate that conversion of metallabenzynes to carbene com-
plexes is, in general, thermodynamically unfavorable.
As discussed above, the metallabenzene intermediate C easily
rearranges to the Cp complex 6, while the metallabenzene
complexes 3 and 5 do not. Figure 6 shows the energetics
calculated for the conversion of C-benzene, a model complex
of C, to 6-Cp, a model complex of 6, and the conversion of
(42) See, for example: Spaivak, C. J.; Caulton, K. G. Organometallics 1998,
17, 5260.
9
13748 J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006

Osmabenzenes Formed from a Dicationic Osmabenzyne
A R T I C L E S
Scheme 5
Figure 7. Schematic illustration of the four occupied π-molecular orbitals
for osmabenzenes.
found in benzene. A planar geometry should maximize the
metal-carbon π-bonding interaction derived from the three
bonding orbitals as well as the metal-carbon π-antibonding
interaction derived from the HOMO. The π-interactions are
reduced in a nonplanar geometry. In theory, the three versus
one pattern in the occupied π molecular orbitals should ensure
planarity. However, the occupied π orbital that has an anti-
bonding interaction between the metal center and the metal-
bonded ring carbon atoms is the HOMO and is expected to have
a greater impact than other π orbitals on the structure. Therefore,
in certain cases that have a proper combination of ligands and
a metal center, such as the osmabenzenes we studied here, the
antibonding effect of the HOMO can lead to a nonplanar
geometry. The calculation results suggest that strong π-acceptor
ligands are able to alleviate the antibonding interaction in the
HOMO, giving a planar geometry. Ligands with weak π-ac-
ceptor, π-neutral, or π-donor ligands are not able to alleviate
the antibonding interaction in the HOMO. Therefore, a non-
planar geometry minimizes the antibonding π-interaction. We
are now expanding our calculations in order to better understand
how the two opposite forces (three versus one) balance each
other and affect the nonplanarity in other related systems.
In the reactions of 2 with H2O or MeOH, the SiMe3 group at
the carbon next to the carbyne carbon in 2 is removed. As
mentioned above, there are two possible pathways, i.e., either
first nucleophilc attack on the carbyne carbon of 2, followed
by desilylation, or first desilylation of 2, followed by nucleo-
philic attack on the carbyne carbon of a desilylated osmabenzyne
intermediate. Experimentally, it is hard to differentiate the two
pathways. Desilylation could be initiated by electrophilic attack
on the metallacycle by H+ or by nucleophilic attack on the
silicon centers by water or MeOH. The former process is related
to the π electron densities on the carbon centers of the
metallacycle, while the latter process is related to the partial
atomic charges of the silicon centers in the silyl substituents
on the metallacycle. We therefore calculated the partial atomic
charges on the Si centers and the π electron densities on the
carbon centers of the metallacycles in 2-benzyne′, a model
complex 5-benzene (see the dihedral angles given in Scheme
5). We also calculated the structure of 7-benzene, a model of
Roper’s Br-containing osmabenzene 7. The calculated geometry
of 7-benzene also reproduces well the planarity found in Roper’s
osmabenzene (see also Scheme 5). Initially, we thought that
the OMe or silyl substituent might play a role in the nonpla-
narity. However, the relevant dihedral angles calculated for
5-benzene-H and 5-benzene-all-H (Scheme 5) do not differ
much from those calculated for 5-benzene, suggesting that the
OMe and silyl substituents do not play a major role. We also
suspected that the repulsive interactions derived from the close
contact of C1-OMe and C5-H with their respective nearest
C-H bonds in the bipyridine ligand were responsible for the
nonplanarity. The nonplanarity remains in the model complex
5-benzene-bpdz, indicating that the suspicion is not well
founded.
Further calculations on 5-benzene-2NH3, 5-benzene-2Cl, and
5-benzene-2CO (Scheme 5) allow us to see that strong
π-acceptor ligands (CO) promote planarity while weak π-ac-
ceptor (bipy), π-neutral (NH3), or π-donor (Cl-) ligands give a
nonplanar geometry. The results can be explained by considering
the four occupied π molecular orbitals, shown in Figure 7, that
are characteristics for any given planar osmabenzene. Among
the four occupied π orbitals, three have bonding interactions
between the metal center and the metal-bonded ring carbon
atoms and one, which is the HOMO, has an antibonding
interaction between the metal center and the metal-bonded ring
carbon atoms. In the π-conjugation system of metallabenzene
complexes, two metal d orbitals (dxz and dyz; see Figure 7 for
the Cartesian coordinates), instead of one, participate in the
π-bonding interactions, making the HOMO different from that
9
J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006 13749

A R T I C L E S
Scheme 6
Hung et al.
The higher thermal stability of [Os(dC(OR)CHdC(Me)C-
(SiMe3)dCH)(bipy)(PPh3)2]OTf relative to [Os(dCHC(SiMe3)d
C(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf can be related to the
stabilization effect of the OR groups on the metallacycle. Unlike
reported osmabenzenes, the new osmabenzene complexes devi-
ate significantly from planarity. A theoretical study suggests
that the nonplanarity of the osmabenzenes [Os(dC(OR)CHd
C(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf is mainly of electronic
origin. Deviation from a planar structure can help to reduce the
antibonding π interaction between the metal center and the
metal-bonded ring carbon atoms in the HOMO of the metalla-
cycle.
complex of 2, and 5-benzene′, a model complex of an
intermediate formed by nucleophilic attack of 2 (Scheme 6).
The process involving first desilylation of 2, followed by
nucleophilic attack of water on the carbyne carbon of a
desilylated osmabenzyne intermediate, is not supported by
calculations. The regiochemistry observed for desilylation cannot
be explained by the charge distribution on the two silicon centers
of 2-benzyne′ (Scheme 6). The partial atomic charges, which
were calculated on the basis of the natural bond orbital analysis,
associated with the two silicon centers in 2-benzyne′ are almost
indistinguishable. The partial atomic charge on the Si center of
the silyl substituent at C2 is +0.999, while the partial atomic
charge on the Si center of the silyl substituent at C4 is +0.994.
When the three occupied π molecular orbitals, which represent
the π system of the ring (π stands for π orbitals perpendicular
to the six-memberred ring of each complex), were considered,
we found that the C2 and C4 centers of 2-benzyne′ have 0.55
and 0.60 π electrons, respectively. Electrophilic desilylation
based on the π electron density distribution of 2-benzyne′ would
give a regiochemistry opposite to what we observed.
Experimental Section
All manipulations were carried out at room temperature under a
nitrogen atmosphere using standard Schlenk techniques, unless other-
wise stated. Solvents were distilled under nitrogen from sodium-
benzophenone (hexane, diethyl ether, THF, benzene) or calcium hydride
(dichloromethane, CHCl3). The starting material Os(tCC(SiMe3)d
C(Me)C(SiMe3)dCH)Cl2(PPh3)2 (1)21 was prepared following the
procedure described in the literature. Microanalyses were performed
at M-H-W Laboratories (Phoenix, AZ). 1H, 13C{1H}, and 31P{1H} NMR
spectra were collected on a Bruker ARX-300 spectrometer (300 MHz).
1H and 13C NMR chemical shifts are relative to tetramethylsilane, and
31P NMR chemical shifts are relative to 85% H3PO4.
[Os(tCC(SiMe3)dC(Me)C(SiMe3)dCH)(bipy)(PPh3)2](OTf)2 (2).
A mixture of 1 (0.32 g, 0.32 mmol), 2,2′-bipyridine (0.10 g, 0.63 mmol),
and thallium triflate (0.34 g, 0.96 mmol) in CH2Cl2 (30 mL) was stirred
at room temperature for 18 h to give a brownish-purple solution along
with a white precipitate. The volume of the reaction mixture was
reduced to ca. 5 mL. The mixture was filtered through Celite to remove
the insoluble white solid (TlCl and excess TlOTf). The filtrate was
concentrated to ca. 2 mL, and diethyl ether (30 mL) was added slowly
with stirring to give a brownish-purple precipitate, which was collected
by filtration, washed with diethyl ether (10 mL), and dried under
vacuum. THF (5 mL) was added to the crude product to give a
suspension, which was stirred for 5 min. The mixture was then allowed
to stand for ca. 2 min to afford a purple solid and a brown solution,
which were separated by filtration. The solid was collected, washed
with diethyl ether (5 mL), and dried under vacuum (0.33 g). The filtrate
was also collected and concentrated to ca. 1 mL to produce additional
purple solid, which was collected by filtration, washed with diethyl
ether (2 mL), and dried under vacuum (0.06 g). Total yield: 0.39 g,
88%. 31P{1H} NMR (121.5 MHz, CDCl3): δ 8.4 (s). 1H NMR (300.13
MHz, CDCl3): δ 0.20 (s, 9 H, Si(CH3)3), 0.61 (s, 9 H, Si(CH3)3), 2.37
(s, 3 H, CH3), 6.88-6.95 (m, 12 H, o-PPh3), 7.27-7.32 (t, J(HH) )
7.5 Hz, 12 H, m-PPh3), 7.41 (t, J(HH) ) 7.3 Hz, 6 H, p-PPh3), 7.75 (t,
J(HH) ) 6.6 Hz, 1 H, bipy), 7.85 (d, J(HH) ) 7.9 Hz, 1 H, bipy),
7.98-8.09 (m, 3 H, bipy), 8.17 (d, J(HH) ) 8.0 Hz, 1 H, bipy), 9.21
(d, J(HH) ) 5.7 Hz, 1 H, bipy), 9.23 (d, J(HH) ) 5.7 Hz, 1 H, bipy),
13.45 (s, 1 H, OsCH). 13C{1H} NMR (75.5 MHz, CDCl3): δ 316.4 (t,
J(PC) ) 8.7 Hz, OstC), 216.3 (t (unresolved), J(PC) ≈ 4.9 Hz,
OsCHd), 198.4 (s, C-CH3), 156.4 (s, CH of bipy), 156.1 (s, quaternary
C of bipy), 155.3 (s, quaternary C of bipy), 148.9 (s, CH of bipy),
145.6 (s, OsCHdC(SiMe3)), 142.8 (s, CH of bipy), 142.3 (s, CH of
bipy), 133.6 (t, J(PC) ) 4.7 Hz, o-PPh3), 132.8 (s, p-PPh3), 130.4 (s,
CH of bipy), 129.9 (t, J(PC) ) 4.7 Hz, m-PPh3), 127.9 (s, CH of bipy),
127.0 (s, CH of bipy), 126.7 (s, CH of bipy), 126.1 (t, J(PC) ) 27.6
Hz, ipso-PPh3), 118.7 (s, OstCC(SiMe3)), 28.9 (s, CH3), 1.8 (s, SiMe3),
1.5 (s, SiMe3). (13C{1H} assignment has been confirmed by DEPT-
The process involving nucleophilic attack on the carbyne
carbon of 2, followed by desilylation, gains support from our
calculations. While the partial atomic charges on the Si centers
of the silyl substituents at C2 and C4 (+0.960 versus +0.992)
in 5-benzene′ are not correlated with the observed regiochem-
istry of desilylation, we found that the C2 and C4 centers of
5-benzene′ have 0.66 and 0.54 π electrons, respectively. These
results show that, after the nucleophilic addition of OMe- to
the carbyne carbon of 2-benzyne′, the π electron density on
C2 becomes higher than that on C4. The π electron density
distributions of 5-benzene′ correlate well with the regiochem-
istry when we assume that desilylation is an electrophilic
substitution process.
Conclusion. The thermally stable dicationic osmabenzyne
[Os(tCC(SiMe3)dC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]-
(OTf)2 (2) was obtained by treatment of Os(tCC(SiMe3)d
C(Me)C(SiMe3)dCH)Cl2(PPh3)2 (1) with 2,2′-bipyridine and
TlOTf. The osmabenzyne complex 2 can be converted to
osmabenzenes by nucleophilic addition at its carbyne carbon.
The thermal stability of the osmabenzenes generated from the
reactions is dependent on the nucleophiles. Thus, 2 reacts with
water or methanol to give osmabenzene complexes [Os(d
C(OR)CHdC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf (R ) H,
Me), but it reacts with NaBH4 to produce a cyclopentadienyl
complex, presumably through the osmabenzene intermediate
[Os(dCHC(SiMe3)dC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]-
OTf. Ready conversion of the intermediate to a Cp complex is
interesting, especially in view of the fact that osmabenzyne 2,
although it has ring strain, does not undergo reductive elimina-
tion to give a carbene complex under similar conditions. A
computational study shows that the higher thermal stability of
the dicationic osmabenzyne is mainly of thermodynamic origin.
135, H-13C COSY, and H-13C COLOC experiments.) Anal. Calcd
for C60H60N2F6O6OsP2S2Si2: C, 51.79; H, 4.35; N, 2.01. Found: C,
51.59; H, 4.55; N, 1.93.
[Os(dC(OH)CHdC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf (3).
To a suspension of 2 (0.10 g, 0.072 mmol) in water (4 mL) was added
1
1
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13750 J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006

Osmabenzenes Formed from a Dicationic Osmabenzyne
A R T I C L E S
THF (3 mL) with stirring. The reactant was dissolved immediately to
give a clear, brownish-purple solution. The reaction mixture was stirred
for 2 h to give a brownish-red precipitate. The solid was collected by
filtration, washed with diethyl ether (2 × 5 mL), and dried under
vacuum. Yield: 78 mg (91%). 31P{1H} NMR (121.5 MHz, CD2Cl2):
δ 2.5 (s). 1H NMR (300.13 MHz, CD2Cl2): δ 0.16 (s, 9 H, Si(CH3)3),
1.58 (s, 3 H, CH3), 5.41 (s, 1 H, OsC(OH)CH), 6.69-6.75 (m, 12 H,
o-PPh3), 7.04 (t, J(HH) ) 7.6 Hz, 12 H, m-PPh3), 7.21 (t, J(HH) ) 7.3
Hz, 6 H, p-PPh3), 7.23-7.30 (m, 2 H, bipy), 7.49-7.56 (m, 2 H, bipy),
7.76 (d, J(HH) ) 8.0 Hz, 1 H, bipy), 7.84 (t, J(HH) ) 7.7 Hz, 1 H,
bipy), 8.71 (d, J(HH) ) 5.3 Hz, 1 H, bipy), 9.15 (s, 1 H, OsC(OH)),
9.81 (d, J(HH) ) 5.3 Hz, 1 H, bipy), 13.80 (t (unresolved), J(PH) ≈
3.9 Hz, 1 H, OsCH). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 252.3 (t,
J(PC) ) 11.0 Hz, OsdC(OH)), 223.6 (t, J(PC) ) 9.4 Hz, OsCH), 164.1
(s, C-CH3), 158.5 (s, quaternary C of bipy), 156.5 (s, CH of bipy),
156.4 (s, quaternary C of bipy), 149.3 (s, CH of bipy), 141.5 (s, OsCHd
C(SiMe3)), 138.5 (s, CH of bipy), 137.0 (s, CH of bipy), 134.1 (t, J(PC)
) 4.9 Hz, o-PPh3), 131.6 (t, J(PC) ) 23.2 Hz, ipso-PPh3), 130.1 (s,
p-PPh3), 128.3 (t, J(PC) ) 4.4 Hz, m-PPh3), 127.3 (s, CH of bipy),
127.2 (s, CH of bipy), 124.2 (s, CH of bipy), 123.6 (s, CH of bipy),
119.7 (s, OsC(OH)CH), 27.2 (s, CH3), 2.1 (s, SiMe3). Anal. Calcd for
C56H53N2F3O4OsP2SSi: C, 56.65; H, 4.50; N, 2.36. Found: C, 56.13;
H, 4.63; N, 2.38.
was stirred at room temperature for 24 h and then filtered through Celite
to give a brownish-red filtrate. The solvent was evaporated to dryness
under vacuum, and the residue was extracted with CH2Cl2 (4 mL). The
mixture was filtered through Celite to remove the insoluble solid (K2-
CO3). The extractant was concentrated to ca. 0.5 mL, and diethyl ether
(10 mL) was added slowly with stirring to afford a brownish-red solid,
which was collected by filtration, washed with diethyl ether (2 × 5
mL), and dried under vacuum. Yield: 65 mg, 63%. 31P{1H} NMR
1
(121.5 MHz, CDCl3): δ 1.7 (s). H NMR (300.13 MHz, CDCl3): δ
0.16 (s, 9 H, Si(CH3)3), 1.55 (s, 3 H, C-CH3), 3.47 (s, 3 H, OCH3),
5.25 (s, 1 H, OsdC(OMe)CH), 6.57-6.63 (m, 12 H, o-PPh3), 7.01 (t,
J(HH) ) 7.4 Hz, 12 H, m-PPh3), 7.19 (t, J(HH) ) 7.2 Hz, 6 H, p-PPh3),
7.22-7.35 (m, 2 H, bipy), 7.63 (t, J(HH) ) 7.8 Hz, 1 H, bipy), 7.90
(d, J(HH) ) 7.8 Hz, 1 H, bipy), 8.05 (t, J(HH) ) 7.8 Hz, 1 H, bipy),
8.27 (d, J(HH) ) 8.1 Hz, 1 H, bipy), 8.70 (d, J(HH) ) 5.1 Hz, 1 H,
bipy), 9.43 (d, J(HH) ) 5.4 Hz, 1 H, bipy), 14.20 (t, J(PH) ) 3.6 Hz,
1 H, OsCH). 13C{1H} NMR (75.5 MHz, CDCl3): δ 251.8 (t, J(PC) )
9.2 Hz, OsdC(OMe)), 227.5 (t, J(PC) ) 8.1 Hz, OsCH), 165.0 (s,
C-CH3), 158.3 (s, quaternary C of bipy), 156.4 (s, quaternary C of
bipy), 155.2 (s, CH of bipy), 148.7 (s, CH of bipy), 141.0 (s, OsCHd
C(SiMe3)), 139.2 (s, CH of bipy), 137.7 (s, CH of bipy), 133.7 (t, J(PC)
) 4.9 Hz, o-PPh3), 131.6 (t, J(PC) ) 23.0 Hz, ipso-PPh3), 130.1 (s,
p-PPh3), 128.2 (t, J(PC) ) 4.5 Hz, m-PPh3), 127.1 (s, CH of bipy),
126.9 (s, CH of bipy), 125.6 (s, CH of bipy), 124.8 (s, CH of bipy),
121.8 (s, OsdC(OMe)CH), 58.6 (s, OCH3) 27.9 (s, C-CH3), 2.2 (s,
SiMe3). Anal. Calcd for C57H55N2F3O4OsP2SSi: C, 56.99; H, 4.61; N,
2.33. Found: C, 56.68; H, 4.48; N, 2.31.
[Os(η5-C5H2Me(SiMe3)2)(bipy)(PPh3)]OTf (6). A mixture of 2
(0.32 g, 0.23 mmol) and sodium borohydride (0.33 g, 8.6 mmol) in
THF (10 mL) was stirred for 4 h to give a brown solution with some
white precipitate. The mixture was filtered to remove the white
precipitate. The filtrate was evaporated to dryness under vacuum, and
the resulting residue was redissolved in CH2Cl2 (2 mL). Addition of
diethyl ether (30 mL) to the solution gave a reddish brown precipitate,
which was collected by filtration, washed with hexane (2 × 2 mL),
and dried under vacuum. Yield: 0.18 g, 57%. 31P{1H} NMR (121.5
MHz, CDCl3): δ 13.8 (s). 1H NMR (300.13 MHz, CDCl3): δ 0.11 (s,
18 H, Si(CH3)3), 1.77 (s, 3 H, CH3), 4.63 (s, 2 H, CH), 7.13 (t, J(HH)
) 8.1 Hz, 6 H, o-PPh3), 7.30 (t, J(HH) ) 6.6 Hz, 2 H, bipy), 7.43 (t,
J(HH) ) 8.4 Hz, 6 H, m-PPh3), 7.51 (t, J(HH) ) 7.2 Hz, 3 H, p-PPh3),
7.93 (t, J(HH) ) 7.5 Hz, 2 H, bipy), 8.40 (d, J(HH) ) 8.1 Hz, 2 H,
bipy), 9.35 (d, J(HH) ) 5.7 Hz, 2 H, bipy). 13C{1H} NMR (75.5 MHz,
CDCl3): δ 158.7 (s, quaternary C of bipy), 156.6 (s, CH of bipy), 136.6
(s, CH of bipy), 133.7 (d, J(PC) ) 10.6 Hz, o-PPh3),131.0 (d, J(PC) )
50.2 Hz, ipso-PPh3), 131.0 (s, p-PPh3), 129.0 (d, J(PC) ) 10.1 Hz,
m-PPh3), 127.0 (s, CH of bipy), 124.7 (s, CH of bipy), 109.8 (d, J(PC)
) 5.0 Hz, C(CH3)), 80.9 (s, CH), 76.0 (d, J(PC) ) 3.8 Hz, C(SiMe3),
14.0 (s, C(CH3)), 0.4 (s, SiMe3). Anal. Calcd for C41F3H46O3N2PSSi2-
Os: C, 50.18; H, 4.73, N, 2.85. Found: C, 50.01; H, 4.65, N, 2.75.
[Os(CHdC(SiMe3)C(Me)dCH2)(CO)(bipy)(PPh3)2]OTf (4). To a
suspension of 2 (0.16 g, 1.15 mmol) in THF (15 mL) was added H2O
(1 mL) with stirring. The reactant was dissolved immediately to give
a clear, brownish-purple solution. The reaction mixture was stirred at
room temperature for 2 days to give a reddish-brown solution. The
solvent was reduced to one-third under reduced pressure. CH2Cl2 (15
mL) and degassed water (5 mL) were added to the solution. The mixture
was stirred for 1 min and then allowed to stand for 5 min. The aqueous
layer (top layer), of which the pH value was found to be 1-2, was
removed via cannulation. The organic layer was again washed with
water (5 mL) and collected by cannulation. The solvent was evaporated
to dryness under vacuum. The residue was dissolved in THF (10 mL),
and the solution was concentrated to ca. 1 mL. Addition of benzene
(10 mL) with stirring produced an orange solid, which was collected
by filtration, washed with diethyl ether (5 mL), and dried under vacuum.
The solid was then redissolved in CH2Cl2 (5 mL). The resulting solution
was concentrated to ca. 0.5 mL. Diethyl ether (15 mL) was added to
the residue to give a yellow solid, which was collected by filtration,
washed with diethyl ether (2 × 5 mL), and dried under vacuum.
Yield: 56 mg, 41%. 31P{1H} NMR (121.5 MHz, CD2Cl2): δ -1.7 (s).
1H NMR (300.13 MHz, CD2Cl2): δ -0.03 (s, 9 H, Si(CH3)3), 1.68 (s,
3 H, CH3), 4.36 (d (unresolved), J(HH) ≈ 2.0 Hz, 1 H, C(CH3)dCH2),
4.44 (d (unresolved), J(HH) ≈ 2.0 Hz, 1 H, C(CH3)dCH2), 6.96 (t,
J(HH) ) 6.7 Hz, 1 H, bipy), 7.01-7.16 (m, 12 H, o-PPh3), 7.13 (t,
J(HH) ) 7.7 Hz, 12 H, m-PPh3), 7.25-7.32 (m, 7 H, p-PPh3 and 1
1
CH of bipyridine (confirmed by a H-1H COSY experiment)), 7.49
(t, J(HH) ) 7.5 Hz, 1 H, bipy), 7.66 (d, J(HH) ) 8.1 Hz, 1 H, bipy),
8.04-8.11 (m, 2 H, bipy), 8.42-8.45 (m, 2 H, OsCHdC(SiMe3) and
Crystallographic Analysis. Crystals suitable for X-ray diffraction
were grown from CH2Cl2 solutions layered with hexane for 2, 3, 5,
and 6 and from CH2Cl2 solution layered with benzene and hexane for
4. Selected crystals of 2-6 were mounted on top of a glass fiber and
transferred into a cold stream of nitrogen. Data collections were
performed on a Bruker Apex CCD area detector using graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). Multiscan
absorption corrections (SADABS) were applied. All structures were
solved by direct methods, expanded by difference Fourier syntheses,
and refined by full-matrix least-squares on F 2 using the Bruker
SHELXTL (Version 6.10) program package. Non-H atoms were refined
anisotropically unless otherwise stated. Hydrogen atoms were introduced
at their geometric positions and refined as riding atoms. The OH group
at the C1 of the metallabenzene 3 was hydrogen-bonded to the solvent
water molecule, and the solvent water molecule was hydrogen-bonded
to one of the O atoms of the OTf anion. The OTf counteranion in 3
was disordered over two sites, which were refined with common
1
1 CH of bipyridine, confirmed by H-13C COSY), 8.62 (d, J(HH) )
5.3 Hz, 1 H, bipy). 13C{1H} NMR (100.40 MHz, CD2Cl2): δ 188.6 (t,
J(PC) ) 9.1 Hz, Os(CO)), 158.9 (s, quaternary C of bipy), 157.8 (s,
quaternary C of bipy), 154.9 (s, sC(CH3)dCH2), 153.4 (s, CH of bipy),
151.8 (s, OsCHdC(SiMe3)), 149.4 (s, CH of bipy), 146.9 (t, J(PC) )
9.0 Hz, OsCHdC(SiMe3)), 140.9 (s, CH of bipy), 137.9 (s, CH of bipy),
134.4 (t, J(PC) ) 5.0 Hz, o-PPh3), 131.2 (s, p-PPh3), 130.0 (t, J(PC)
) 24.3 Hz, ipso-PPh3), 128.9 (t, J(PC) ) 4.8 Hz, m-PPh3), 128.2 (s,
CH of bipy), 127.6 (s, CH of bipy), 126.0 (s, CH of bipy), 125.2 (s,
CH of bipy), 112.2 (s, sC(CH3)dCH2), 25.0 (s, CH3), 0.3 (s, SiMe3).
Anal. Calcd for C56H53N2F3O4OsP2SSi: C, 56.65; H, 4.50; N, 2.36.
Found: C, 56.98; H, 4.09; N, 2.11.
[Os(dC(OMe)CHdC(Me)C(SiMe3)dCH)(bipy)(PPh3)2]OTf (5).
To a mixture of 2 (0.12 g, 0.086 mmol) and K2CO3 (0.12 g, 0.87 mmol)
were added CH2Cl2 (8 mL) and MeOH (2 mL). The reaction mixture
9
J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006 13751

A R T I C L E S
Hung et al.
Table 2. Crystal Data and Structure Refinement for 2-6
compound
2
3
4
5
6
empirical formula
C60H60F6N2O6Os-
P2S2Si2
C56H55F3 N2 O5 Os-
P2SSi
C62H61F3N2O5Os-
P2SSi
C57H55F3N2O4Os-
P2SSi
C42H48Cl2F3N2O3Os-
PSSi2
formula weight
1391.54
1205.31
1283.42
1201.32
1066.13
temperature, K
100(2)
173(2)
173(2)
100(2)
298(2)
radiation (Mo KR), Å
0.71073
monoclinic
P21/c
21.5222(11)
22.0572(11)
12.4107(6)
90
98.1510(10)
90
5832.1(5)
4
1.585
2.426
2808
0.71073
monoclinic
P21/n
13.857(3)
19.181(4)
19.294(4)
90
97.087(3)
90
5089.1(17)
4
1.573
2.696
2432
0.71073
monoclinic
P21/n
16.294(3)
20.435(4)
18.652(4)
90
109.188(4)
90
5866(2)
4
1.453
2.344
0.71073
monoclinic
P21/n
13.7519(7)
19.6084(11)
19.1742(11)
90
97.3640(10)
90
5127.7(5)
4
1.556
2.674
2424
0.71073
triclinic
P1h
crystal system
space group
a, Å
b, Å
10.7215(11)
11.4672(11)
20.273(2)
104.072(2)
101.455(2)
95.036(2)
2345.1(4)
2
c, Å
R, °
â, °
γ, °
V, Å3
Z
d
calcd, g cm-3
1.510
3.012
1068
abs coeff, mm-1
F(000)
2600
crystal size, mm
θ range, °
reflns collected
indep reflns
obsd reflns (I > 2σ(I))
data/restraints/params
goodness-of-fit on F 2
final R (I > 2σ(I))
0.20 × 0.20 × 0.12
1.90-27.50
35 203
13 278 (Rint ) 0.0468)
10 960
0.14 × 0.10 × 0.06
1.71-25.50
30 361
9455 (Rint ) 0.1063)
5971
0.24 × 0.16 × 0.10
1.44-25.00
30 563
10 302 (Rint ) 0.0349)
8406
0.15 × 0.12 × 0.10
1.49-25.50
26 797
9521 (Rint ) 0.0675)
6997
0.18 × 0.15 × 0.13
2.00-25.00
15 084
8025 (Rint ) 0.0555)
5734
13 278/0/730
1.005
9455/41/629
0.993
10 302/31/652
1.072
9521/0/640
0.949
8025/0/514
0.993
R1 ) 0.0378,
wR2 ) 0.0751
R1 ) 0.0514,
wR2 ) 0.0787
1.366 and -0.600
R1 ) 0.0564,
wR2 ) 0.1218
R1 ) 0.1082,
wR2 ) 0.1322
2.469 and -2.351
R1 ) 0.0415,
wR2 ) 0.1179
R1 ) 0.0534,
wR2 ) 0.1231
1.528 and -0.706
R1 ) 0.0427,
wR2 ) 0.0786
R1 ) 0.0695,
wR2 ) 0.0845
1.313 and -0.649
R1 ) 0.0448,
wR2 ) 0.0678
R1 ) 0.0756,
wR2 ) 0.0726
1.371 and -0.799
R indices (all data)
peak and hole, e Å-3
variable isotropic thermal parameters using suitable restraints. The
benzene solvent molecule in 4 was disordered over two sites; each site
was treated as a rigid body and refined with common variable isotropic
thermal parameters. The solvent water molecule in 4 was also disordered
over two sites, which were refined isotropically without addition of
hydrogen atoms. Further details on crystal data, data collection, and
refinements are summarized in Table 2.
Computational Study. All structures were optimized at the mPW1K
level of density functional theory.43 Frequency calculations were also
performed to confirm the characteristics of the calculated structures as
minima or transition states. In the DFT calculations, the effective core
potentials (ECPs) of Stuttgart/Dresden (SDD)44 were used to describe
Os, I, Cl, Br, S, Si, and P atoms, while the standard 6-31g basis set
was used for C, O, N, and H. Polarization functions were added for Os
(úf ) 0.707), I (úd ) 0.266), Cl (úd ) 0.514), P (úd ) 0.340), and Si
(úd ) 0.262).5b,45 Calculations of intrinsic reaction coordinates46 were
also performed on transition states to confirm that such structures are
indeed connecting two minima. All the calculations were performed
with the Gaussian 03 software package.47
Acknowledgment. This work was supported by the Hong
Kong Research Grant Council (Project Nos. 602304, 601804),
National Natural Science Foundation of China, through the
Outstanding Young Investigator Award Fund (Project No.
20429201).
Supporting Information Available: Complete ref 47; tables
giving Cartesian coordinates and electronic energies for all the
calculated structures (PDF). X-ray crystallographic files (CIF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA064570W
(43) (a) Lynch, B. J.; Fast, P. L.; Harris, M.; Truhlar, D. G. J. Phys. Chem. A
2000, 104, 4811. (b) This DFT method has also been used to calculate
other metallabenzene complexes (see ref 5b).
(44) (a) Haeusermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Mol. Phys. 1993, 78,
1211. (b) Kuechle, W.; Dolg, M.; Stoll, H.; Preuss, H. J. Chem. Phys. 1994,
100, 7535. (c) Leininger, T.; Nicklass, A.; Stoll, H.; Dolg, M.; Schwerdt-
feger, P. J. Chem. Phys. 1996, 105, 1052.
(45) Huzinaga, S. Gaussian Basis Sets for Molecular Calculations; Elsevier
Science Pub. Co.: Amsterdam, 1984.
(46) (a) Fukui, K. J. Phys. Chem. 1970, 74, 4161. (b) Fukui, K. Acc. Chem.
Res. 1981, 14, 363.
(47) Frisch, M. J.; et al. Gaussian 03, revision B05; Gaussian, Inc.: Pittsburgh,
PA, 2003.
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13752 J. AM. CHEM. SOC. VOL. 128, NO. 42, 2006