1528 Organometallics, Vol. 28, No. 5, 2009
Lin et al.
Scheme 3. Proposed Mechanism for Formation of 2 and 4
of alkynes addition to osmafuran, the osmium in the nine-
membered intermediate C is apparently saturated by intramo-
lecular coordination of the vinyl group. Thus, a third or more
alkynes addition process is disfavored. Nevertheless, these
complexes might serve as intermediates trapped after two
turnovers of alkynes polymerization by internal coordinated
olefin to the metal center. It should also be mentioned that it is
a head-to-tail double insertion of PhCt CH molecular into the
osmafuran. A head-to-head double insertion of PhCt CH into
a Rh-O bond have been reported.22g
Furthermore, metallacycles are attracting increasing attention
in chemical research, as they are seem to be promising reagents
and catalysts in organic and organometallic chemistry as well
as intermediates in sorts of reactions.20,21 The insertion of
unsaturated molecular into organometallic compounds can not
only construct various of metallacycles but also undergo ring
expansion.22 In particular, the alkynes insertion into various of
transition-metal-containing metallacycles with ring expansion
23-27
have been reported.
The ongoing work provides an
efficient method to realize the ring expansion from five- to nine-
membered by alkynes insertion.
The proton signal on C6 is observed at 5.8 ppm, which is typical
for the olefinic compound.16 In the 13C{1H} NMR spectrum,
the carbon signals of the metallacycle appear at 243.4 (C1),
88.0 (C2), 184.5 (C3), 63.3 (C4), 13.6 (C5), 137.6 (C6), 179.8
(C7), 66.3 (C8), and 62.1 (C9) ppm, respectively. The 31P{1H}
NMR spectrum shows two singlets at 6.0 (CPPh3) and -2.5
(OsPPh3) ppm, respectively.
(20) For recent reviews, see: (a) Dupont, J.; Consorti, C. S.; Spencer, J.
Chem. ReV. 2005, 105, 2527. (b) Rubin, M.; Rubina, M.; Gevorgyan, V.
Chem. ReV. 2007, 107, 3117. (c) Bleeke, J. R. Acc. Chem. Res. 2007, 40,
1035. (d) Chopade, P. R.; Louie, J. AdV. Synth. Catal. 2006, 348, 2307. (e)
Xi, Z.; Li, Z. Top. Organomet. Chem. 2004, 8, 27.
(21) For examples, see: (a) Wheaton, C. A.; Jennings, M. C.; Puddephatt,
R. J. J. Am. Chem. Soc. 2006, 128, 15370. (b) Liu, J.; Zhang, W.-X.; Guo,
X.; Hou, Z.; Xi, Z. Organometallics 2007, 26, 6812. (c) Takahashi, T.;
Kuzuba, Y.; Kong, F.; Nakajima, K.; Xi, Z. J. Am. Chem. Soc. 2005, 127,
Possible mechanisms for the formation of 2 and 3 are shown
in Scheme 3. Replacement of the PPh3 ligand by the alkyne in
1 gives π-alkyne intermediate A, which undergoes the first
alkyne insertion into the osmium-carbon double bond followed
by cycloreversion of the metallacyclobutene to form a seven-
membered osmacycle B. Then, [2 + 2] cycloaddition of the
second molecule of alkyne with the OsdC in B gives a nine-
membered intermediate C. Coordination of the internal double
bond to the metal center affords the 18-e products 2a and 2b.
We note that the related process on the formation of osmium-
η3-allenylcarbene,14b,e,17 ruthenium-η3-vinylcarbene,18a ruthe-
nium-η3-allenylcarbene,18b,c and tungsten-η3-vinylcarbene19 have
been reported. Isomerization of 2a and 2b to 4 is presumably
driven by the dissociation of PPh3, coordination of another olefin
double bond, electronic tautomerization, and subsequent R-H
elimination to give hydride-osmabenzene E. Finally, reductive
elimination of the vinyl and the hydride from E as well as the
recoordination of PPh3 ligand produces complex 4. It is worth
noting that the mechanism for the isomerization of 2 to 4
involves an intramolecular hydrogen shift process.
´
17188. (d) Cadierno, V.; D´ıez, J.; Garc´ıa-Alvarez, J.; Gimeno, J. Organo-
´
metallics 2004, 23, 2421. (e) Cadierno, V.; D´ıez, J.; Garc´ıa-Alvarez, J.;
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´
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In the metal carbene catalyzed polymerization of alkynes, a
metallacyclobutene is produced by the reaction of an alkylidene
and an alkyne, which is followed by rearrangement to give a
new alkylidene. If the process continues, a growing polymer
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(16) Dean, J. A. Lange’s Handbook of Chemistry; McGraw-Hill: New
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