Syntheses of metallabenzynes from an allenylcarbene complex

Article abstract of DOI:10.1021/ja0429061

Treatment of the allenylcarbene complex OsCl₂(=CPh-CH=C=CHPh)(PPh₃)₂ with (PPh₃)AuC_≡CR in the presence of HNEt₃Cl in CH₂Cl₂ produces osmabenzynes Os(_≡CC(R)=

Full text of DOI:10.1021/ja0429061

Published on Web 02/10/2005
Syntheses of Metallabenzynes from an Allenylcarbene Complex
Ting Bin Wen, Wai Yiu Hung, Herman H. Y. Sung, Ian D. Williams, and Guochen Jia*
Department of Chemistry, The Hong Kong UniVersity of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong
Received November 24, 2004; E-mail: chjiag@ust.hk
The chemistry of transition metal-containing metallabenzenes1
has attracted considerable attention both experimentally2 and theo-
retically.3 In contrast, the chemistry of the related compounds, met-
allabenzynes, is much less developed,4 partially due to the lack of
convenient synthetic routes to construct metallabenzyne rings. The
only reported route to construct a metallabenzyne ring is the reaction
of OsCl2(PPh3)3 with HCtCSiMe3 in wet benzene.4a However,
extension of the chemistry involving OsCl2(PPh3)3 as the starting
material to prepare metallabenzynes apparently failed when other
alkynes such as HCtCCMe3 and HCtCCH(OH)Ph2 were used.5
To develop the chemistry of metallabenzynes, it is obviously highly
desirable to find alternative and more general routes to prepare met-
allabenzynes. In this Communication, we disclose a more efficient
route to prepare osmabenzynes starting from an allenylcarbene
complex.
Figure 1. Structure of 2. Selected bond distances (Å) and angles (°):
Os(1)-C(2), 2.067(11); Os(1)-C(3), 2.167(11); Os(1)-C(4), 1.894(9);
C(1)-C(2), 1.316(16); C(2)-C(3), 1.441(15); C(3)-C(4), 1.437(15); C(2)-
C(3)-C(4), 115.9(10); C(2)-Os(1)-C(4), 75.9(4); C(1)-C(2)-C(3),
139.5(11).
A metallacyclobutene complex formed from cycloaddition of
HCtCSiMe3 with OsCl2(dCdCH2)(PPh3)2 was proposed as one
of the key intermediates in the formation of the osmabenzyne
complex Os(tCC(SiMe3)dC(CH3)C(SiMe3)dCH)Cl2(PPh3)2.4a How-
ever, the intermediate could not be isolated. We have now isolated
the related cycloaddition product from the reaction of the vinylidene
complex OsCl2(dCdCHPh)(PPh3)26 with HCtCPh. The X-ray as
well as the NMR data suggest that the compound can be best
described as an η3-allenylcarbene complex.
ported for typical Os-C single bonds10 and are similar to the Os-
C(allene) bond distances in OsCl(C(MedCHPh)(η2-CH2dCd
CHPh)(PPh3)2.11 The C-C bond distances within the metallacycle
(C(2)-C(3) ) 1.441(15) Å, C(3)-C(4) ) 1.437(15) Å) are com-
parable, indicating the presence of substantial π-electron delocal-
ization. On the basis of the structural data, this complex can be
described as an η3-allenylcarbene complex with contributions from
limiting structures such as 2, 2A (which most closely resembles
the actual structure), and 2B. The structural features associated with
Os, C(2), C(3), and C(4), are similar to those of RuCl2(η3-
PhCdCPhCHPh)(H2IMes), where the C-C bond distances within
the metallacycle are observed at 1.437(6) and 1.409(6) Å.7
The allenylcarbene complex OsCl2(dCPh-η2-CHdCdCHPh)-
(PPh3)2 (2) was obtained as a green precipitate by treatment of the
vinylidene complex OsCl2(dCdCHPh)(PPh3)26 with HCtCPh in
benzene (eq 1). The complex could also be prepared from the one-
pot reaction of OsCl2(PPh3)3 with HCtCPh in benzene, where 2
is presumably formed from the cycloaddition reaction of HCtCPh
with OsCl2(dCdCHPh)(PPh3)2 generated in situ. Grubbs et al. have
recently reported the related ruthenium η3-vinylcarbene complex
RuCl2(η3-PhCdCPhCHPh)(H2IMes) from the reaction of PhCt
CPh with RuCl2(dCHPh)(PCy3)(H2IMes) [H2IMes ) 1,3-dimesityl-
4,5-dihydroimidazol-2-ylidene].7
Complex 2 has been characterized by elemental analysis, MS,
and NMR spectroscopy.8 The structure of 2 has also been confirmed
by an X-ray diffraction study (Figure 1). The most interesting struc-
tural feature of 2 is that it contains a bent four-membered metal-
lacycle. The Os-C(4) bond distance of 1.894(9) Å is characteristic
of an osmium-carbon double bond and is almost identical to the
values found in the osmium carbene complexes such as OsCl2-
(dCHCH2Ph)(CO)(PiPr3)2 (1.887(9) Å)9a and OsCl2(dCHPh)(CO)-
(PiPr3)2 (1.89(2) Å.9b The bond distances of Os-C(2) (2.067(11)
Å) and Os-C(3) (2.167(11) Å) are comparable to the values re-
The solid-state structure is fully supported by the solution NMR
1
(31P, H, and 13C) spectroscopic data. In particular, the 31P{1H}
NMR spectrum (in CD2Cl2) at 210 K showed two doublets at -8.3
and -32.3 ppm with a 2J(PP) of 329.1 Hz, and the 13C{1H} NMR
spectrum (in CD2Cl2) showed the three Os-bound carbon signals
at 249.8 (CPh), 136.6 (C), and 36.1 (CH) ppm. At room temper-
ature, the complex is fluxional, and the 31P{1H} NMR spectrum
showed two broad singlets at -8.4 and -28.1 ppm.
Formation of allenylcarbene 2 from the reaction of 1 with HCt
CPh is interesting, as allenylcarbene complexes have often been
proposed as the key intermediates in metal-catalyzed polymerization
of terminal alkynes.12 However, very few such complexes have been
13
previously isolated.
The reactions of 2 with alkynes were carried out to see if
osmabenzynes can be obtained. When 2 was treated with HCt
CPh in CH2Cl2, most of the HCtCPh was polymerized, and a
9
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J. AM. CHEM. SOC. 2005, 127, 2856-2857
10.1021/ja0429061 CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
Scheme 1
give osmabenzynes. Apparently, the γ-carbon of the allenylcarbene
ligand attacked at the â-carbon atom of the acetylide ligands in
the cyclization reaction. At this stage, we are not sure whether the
intramolecular cyclization reactions proceed before or after the
protonation of the terminal CHPh group. Alkynyl transfer from gold
to rhenium has been reported recently.15 Intramolecular coupling
of alkenylcarbene and acetylide ligands has been proposed for the
formation of a novel osmium isometallabenzene.2b
In summary, we have developed a more efficient synthetic route
to prepare osmabenzynes starting from an allenylcarbene complex.
The new method allows us to obtain metallabenzynes with various
substituents in short reaction time under mild reaction conditions.
Extension of the chemistry to prepare metallabenzynes with other
metals and substituents is in progress.
Acknowledgment. This work was supported by the Hong Kong
Research Grant Council.
mixture of phosphorus-containing species was produced. The
expected osmabenzyne was produced in only trace amount, if any.
Interestingly, when the reaction was performed in the presence of
NEt3, osmabenzyne 3 was produced as the major species detectable
by 31P NMR (eq 2), although the reaction is slow and takes a day
to go to completion. The reaction also produced oligomers of HCt
Supporting Information Available: Experimental procedures and
characterization data (PDF); X-ray crystallographic files (CIF). This
material is available free of charge via the Internet at http://pubs.acs.org.
References
(1) Bleeke, J. R. Chem. ReV. 2001, 101, 1205.
(2) Examples of recent experimental work: (a) Landorf, C. W.; Jacob, V.;
Weakley, T. J. R.; Haley, M. M. Organometallics 2004, 23, 1174. (b)
Barrio, P.; Esteruelas, M. A.; Onate, E. J. Am. Chem. Soc. 2004, 126,
1946. (c) Xia, H. P.; He, G. M.; Zhang, H.; Wen, T. B.; Sung, H. H. Y.;
Williams. I. D.; Jia, G. J. Am. Chem. Soc. 2004, 126, 6682. (d) Gilbertson,
R. D.; Lau, T. L. S.; Lanza, S.; Wu, H. P.; Weakley, T. J. R.; Haley, M.
M. Organometallics 2003, 22, 3279. (e) Paneque, M.; Posadas, C. M.;
Poveda, M. L.; Rendo´n, N.; Salazar, V.; On˜ate, E.; Mereiter, K. J. Am.
Chem. Soc. 2003, 125, 9898. (f) Effertz, U.; Englert, U.; Podewils, F.;
Salzer, A.; Wagner, T.; Kaupp, M. Organometallics 2003, 22, 264. (g)
Jacob, V.; Weakley, T. J. R.; Haley, M. M. Angew. Chem., Int. Ed. 2002,
41, 3470. (h) Wu, H. P.; Lanza, S.; Weakley, T. J.; Haley, M. M.
Organometallics 2002, 21, 2824. (i) Bleeke, J. R.; Hinkle, P. V.; Rath,
N. P. Organometallics 2001, 20, 1939. (j) Bleeke, J. R.; Blanchard, J. M.
B.; Donnay, E. Organometallics 2001, 20, 324. (k) Rickard, C. E. F.;
Roper, W. R.; Woodgate, S. D.; Wright, L. J. Angew. Chem., Int. Ed.
2000, 39, 750.
CPh and other unidentified phosphorus-containing species, which
can cause difficulty in the isolation of pure samples of 3 from the
reaction mixture. Our attempts to obtain osmabenzynes from the
reactions of 2 with other alkynes such as HCtCSiMe3 or aliphatic
terminal alkynes under similar conditions were unsuccessful.
The promoting effect of NEt3 in the production of osmabenzyne
3 from the reaction of 2 with HtCPh led us to speculate that 3
may be formed from an acetylide intermediate. To test this
hypothesis, we have treated 2 with (PPh3)AuCtCPh14 in the
presence of HNEt3Cl. We were pleased to learn that the reaction
quickly produced the expected 3 (Scheme 1). In the absence of
HNEt3Cl, the reaction also produced 3, but the rate was slow and
other unidentified species were also formed, as one might expect.
The chemistry can be extended to prepare new osmabenzynes
using other gold(I) acetylide derivatives. Thus, treatment of 2 with
(PPh3)AuCtC-tolyl produced the tolyl-containing osmabenzyne 4,
treatment with (PPh3)AuCtC-n-Bu produced the n-Bu-containing
osmabenzyne 5, and treatment with (PPh3)AuCtCSiMe3 produced
the SiMe3-containing osmabenzyne 6. Most of the reactions are
completed in less than 3 h. It is noted that the reported preparation
of the osmabenzyne complex Os(tCC(SiMe3)dC(CH3)C(SiMe3)d
CH)Cl2(PPh3)2 from the reaction of OsCl2(PPh3)3 with HCtCSiMe3
takes 5 days.
All the new osmabenzynes have been characterized by elemental
analysis, MS, and NMR spectroscopy.8 The structures of 3-5 have
been confirmed by X-ray diffraction.8 The structural features of
the metallacycles are very similar to those of reported ones.4 The
NMR (31P, 1H, and 13C) spectroscopic data are fully consistent with
the solid-state structures.
The detailed mechanism for the formation of 3-6 in the reactions
of 2 with (PPh3)AuCtCR in the presence of HNEt3Cl is not very
clear yet. It is possible that reactions of 2 with (PPh3)AuCtCR
may initially produce the acetylide complexes OsCl(CtCR)(dCPh-
η2-CHdCdCHPh)(PPh3)2 or allenylcarbene osmium complexes
with a coordinated gold acetylide, which react with HNEt3Cl to
(3) Examples of recent theoretical work: (a) Iron, M. A.; Martin, J. M. L.;
van der Boom, M. E. Chem. Commun. 2003, 132. (b) Iron, M. A.; Martin,
J. M. L.; van der Boom, M. E. J. Am. Chem. Soc. 2003, 125, 13020. (c)
Iron, M. A.; Martin, J. M. L.; van der Boom, M. E. J. Am. Chem. Soc.
2003, 125, 11702. (d) Iron, M. A.; Lucassen, A. C. B.; Cohen, H.; van
der Boom, M. E.; Martin, J. M. L. J. Am. Chem. Soc. 2004, 126, 11699.
(4) (a) Wen, T. B.; Zhou, Z. Y.; Jia, G. Angew. Chem., Int. Ed. 2001, 40,
1951. (b) Jia, G. Acc. Chem. Res. 2004, 37, 479.
(5) (a) Wen, T. B.; Yang, S. Y.; Zhou, Z. Y.; Lin, Z.; Lau, C. P.; Jia, G.
Organometallics 2000, 19, 3757. (b) Wen, T. B.; Zhou, Z. Y.; Lo, M. F.;
Williams, I. D.; Jia, G. Organometallics 2003, 22, 5217.
(6) Wen, T. B.; Hung, W. Y.; Zhou, Z. Y.; Lo, M. F.; Williams, I. D.; Jia, G.
Eur. J. Inorg. Chem. 2004, 2837.
(7) Trnka, T. M.; Day, M. W.; Grubbs, R. H. Organometallics 2001, 20, 3845.
(8) See Supporting Information for details.
(9) (a) Esteruelas, M. A.; Lahoz, F. J.; On˜ate, E.; Oro, L. A.; Valero, C.;
Zeier, B. J. Am. Chem. Soc. 1995, 117, 7935. (b)Werner, H.; Stu¨er, W.;
Laubender, M.; Lehmann, C.; Herbst-Irmer, R. Organometallics 1997,
16, 2236.
(10) (a) Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. Organometallics 2001,
20, 2294. (b) Liu, S. H.; Lo, S. T.; Wen, T. B.; Zhou, Z. Y.; Lau, C. P.;
Jia, G. Organometallics 2001, 20, 667. (c) Bohanna, C.; Buil, M. L.;
Esteruelas, M. A.; On˜ate, E.; Valero, C. Organometallics 1999, 18, 5176.
(11) Wen, T. B.; Zhou, Z. Y.; Lau, C. P.; Jia, G. Organometallics 2000, 19,
3466.
(12) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.
(13) (a) Ruba, E.; Mereiter, K.; Schmid, R.; Sapunov, V. N.; Kirchner, K.;
Schottenberger, H.; Calhorda, M. J.; Veiros, L. F. Chem. Eur. J. 2002, 8,
3948. (b) Beckhaus, R.; Sang, J.; Englert, U.; Bo¨hme, U. Organometallics
1996, 15, 4731.
(14) Coates, G. E.; Parkin, C. J. Chem. Soc. 1962, 3220.
(15) Ferrer, M.; Rodr´ıguez, L.; Rossell, O.; Lima, J. C.; Go´mez-Sal, P.; Mart´ın,
A. Organometallics 2004, 23, 5096.
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