Synthesis of 1-stannacyclopent-3-enes and their pyrolysis to stannylenes

Article abstract of DOI:10.1021/om800541f

1,1-Diorgano-1-stannacyclopent-3-enes have been synthesized by condensation in THF of magnesium complexes of 1,3-dienes and dichlorodiorganostannanes. 1,1-Dimethyl-, 1,1-di-n-butyl-, 1,1-di-tert-butyl-, and 1,1-diphenyl-1- stannacyclopent-3-enes and 1,1,3

Full text of DOI:10.1021/om800541f

Organometallics 2009, 28, 2595–2608
2595
Synthesis of 1-Stannacyclopent-3-enes and Their Pyrolysis to
Stannylenes
Dong Zhou,†,# Clemens Reiche,† Mrinmoy Nag,† John A. Soderquist,‡ and
Peter P. Gaspar*,†
Department of Chemistry, Washington UniVersity, St. Louis, Missouri 63130-4899, and Department of
Chemistry, UniVersity of Puerto Rico-Rio Piedras, Box 23346, UPR Station, San Juan,
Puerto Rico 00931-3346
ReceiVed June 10, 2008
1,1-Diorgano-1-stannacyclopent-3-enes have been synthesized by condensation in THF of magnesium
complexes of 1,3-dienes and dichlorodiorganostannanes. 1,1-Dimethyl-, 1,1-di-n-butyl-, 1,1-di-tert-butyl-,
and 1,1-diphenyl-1-stannacyclopent-3-enes and 1,1,3,4-tetramethyl-, 1,1-di-tert-butyl-3,4-dimethyl-, and
3,4-dimethyl-1,1-diphenyl-1-stannacyclopent-3-enes were prepared. Kinetic studies of the pyrolysis at
temperatures as low as 75 °C of several of these stannacyclopent-3-enes resulted in their first-order
disappearance, consistent with a unimolecular dissociation to the corresponding stannylene and diene.
Activation parameters are reported. Trapping of dimethylstannylene by dienes was overwhelmed by
oligomerization of Me2Sn:, but for t-Bu2Sn: a high yield of diene adduct was obtained. The
dimethylstannylene oligomer(s) functioned as stannylenoids and were responsible for several reactions
previously attributed to free Me2Sn:. cyclo-(t-Bu2Sn)4 may also function as a stannylenoid.
The low thermal stability of this stannanorbornene makes it
an inconvenient stannylene precursor, and variation of its
substituents on tin is not straightforward.
The finding that 1,1-dimethyl-1-stannacyclopent-3-ene (4) can
be handled at room temperature was encouraging for the
prospects of using simple stannacyclopentenes as stannylene
precursors. Soderquist and Leon synthesized a 1:1 mixture of
4 and 1,1-dimethyl-1-stannacyclopent-2-ene (5) by the route in
Scheme 3.1e
The promise held by 1-stannacyclopent-3-enes as precursors
for the generation of stannylenes R2Sn:, molecules containing
divalent and dicoordinate tin atoms, and the absence from the
literature of general methods for the preparation of such
stannacyclopentenes led to this study of their synthesis and
pyrolysis.
Introduction
The number of stannacyclopent-3-enes reported in the
literature is surprisingly small,1 and this has delayed their
adoption as precursors for the generation of stannylenes, R2Sn:.
In previous work the extrusion of dimethylsilylene Me2Si: and
dimethylgermylene Me2Ge: from the corresponding heterocy-
clopent-3-enes 1 under pyrolysis conditions2 led to the expecta-
tion that stannacyclopent-3-enes would be useful stannylene
precursors (Scheme 1).
Indeed the 7-stannanorbornene 2 prepared by Neumann, the
only previously well-established precursor to dimethylstannylene
Me2Sn: (3), is a substituted stannacyclopent-3-ene that undergoes
unimolecular thermal dissociation (Scheme 2).3
* Corresponding author. Phone: (314) 935 6568. Fax: (314) 935 4481.
E-mail: gaspar@wustl.edu.
Previous Pyrolysis Studies of Molecules Proposed As
Stannylene Precursors. Previous studies of precursor pyrolysis
and trapping experiments have provided limited support for the
thermal generation of free stannylenes. Stannanorbornene 2
prepared from the Diels-Alder reaction of 1,1-dimethyl-2,3,4,5-
tetraphenylstannole and tetracyanoethylene (Scheme 2) decom-
posed above -20 °C with a half-life of 17 min at -10 °C in a
first-order process giving a quantitative yield of 1,1,2,2-
tetracyano-3,4,5,6-tetraphenylcyclohexa-3,5-diene.3 Formation
of free Me2Sn: (3) in a concerted extrusion was suggested, since
the alternative stepwise decomposition via a diradical intermedi-
ate was expected to give rise to CIDNP signals, which were
not observed; nor could an intermediate be trapped.3 Oligomers
of Me2Sn: (3) were obtained, but an adduct of unknown structure
was found when stannanorbornene 2 was allowed to decompose
in the presence of dimethylacetylenedicarboxylate. Attempts to
trap Me2Sn: (3) from this precursor by means of 1,3-dienes
failed.4
† Washington University.
‡ University of Puerto Rico-Rio Piedras.
# Current affiliation: Mallinckrodt Institute of Radiology, Washington
University School of Medicine, St. Louis, MO 63110.
(1) A search of Chemical Abstracts files located only 17 distinct
structures, of which all but three (1d, 1e, and 1j) resulted from stannylene
addition to dienes:(a) Iwamoto, T.; Masuda, H.; Ishida, S.; Kabuto, C.; Kira,
M. J. Organomet. Chem. 2004, 689, 1337. (b) Neale, N. R.; Tilley, T. D.
J. Am. Chem. Soc. 2002, 124, 3802. (c) Setaka, W.; Sakamoto, K.; Kira,
M.; Power, P. P. Organometallics 2001, 20, 4460. (d) Fan˜ana´s, F. J.;
Granados, A.; Sanz, R.; Ignacio, J. M.; Barluenga, J. Chem.-Eur. J. 2001,
7, 2896. (e) Soderquist, J. A.; Leon, G. Tetrahedron Lett. 1998, 39, 2511.
(f) Saito, M.; Tokitoh, N.; Okazaki, R. Organometallics 1996, 15, 4531.
(g) Saito, M.; Tokitoh, N.; Okazaki, R. Chem. Lett. 1996, 265; (h)
Weidenbruch, M.; Stilter, A.; Schlaefke, J.; Peters, K.; von Schnering, H. G.
J. Organomet. Chem. 1995, 501, 67. (i) Saito, M.; Tokitoh, N.; Okazaki,
R. Organometallics 1995, 14, 3620. (j) Wrackmeyer, B.; Klaus, U.; Millius,
W. Chem. Ber. 1995, 128, 679. (k) Tokitoh, N.; Saito, M.; Okazaki, R.
J. Am. Chem. Soc. 1993, 115, 2065. (l) Gruetzmacher, H.; Freitag, S.;
Herbst-Irmer, R.; Sheldrick, G. M. Angew. Chem., Int. Ed. Engl. 1992, 31,
437. (m) Weidenbruch, M.; Schaefer, A.; Kilian, H.; Pohl, S.; Saak, W.;
Marsmann, H. Chem. Ber. 1992, 125, 563–566. (n) Marx, R.; Neumann,
W. P.; Hillner, K. Tetrahedron Lett. 1984, 25, 625.
(2) (a) Dimethylsilylene: Lei, D.; Gaspar, P. P. Organometallics 1985,
4, 1471. (b) Dimethylgermylene: Lei, D.; Gaspar, P. P. Polyhedron 1991,
10, 1221.
(3) Grugel, C.; Neumann, W. P.; Schriewer, M. Angew. Chem., Int. Ed.
Engl. 1979, 18, 543.
(4) Neumann, W. P. Chem. ReV. 1991, 91, 311.
10.1021/om800541f CCC: $40.75
2009 American Chemical Society
Publication on Web 03/31/2009

2596 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
yielding the corresponding 1-stannacyclopent-3-ene.8 It had
earlier been proposed by Masamune and Sita that this stannylene
mediates the equilibrium between its cyclotristannane “trimer”
and its distannene “dimer”.9 Weidenbruch obtained the 1-stan-
nacylopent-3-ene by heating the cyclotristannane in the presence
of diene and assumed that addition occurred by free stannylene
from dissociation of the cyclotristannane. NMR evidence for
the presence of free stannylene was presented, but the possibility
that the stannacyclopentene resulted from direct reaction of the
cyclotristannane or the distannene with 2,3-dimethylbutadiene
was not considered.
The first dialkylstannylene monomeric in the solid state was
synthesized by Kira in 1991.10 It is 2,2,5,5-tetrakis(trimethyl-
silyl)-1-stannacyclopentane-1-diyl (14), whose addition to 2,3-
dimethylbutadiene in hexane solution at room temperature
yielded the corresponding 1-stannacyclopent-3-ene quantitatively
(Scheme 8, A).11 A related but more crowded persistent
stannylene, 15, prepared by Eaborn12 failed to react with several
substituted butadienes (Scheme 8, B).13 Two other persistent
stannylenes, 16 (Scheme 8, C)14 and 17 (Scheme 8, D),15 have
been found to add smoothly to 2,3-dimethylbutadiene at room
temperature.
Scheme 1
The extrusion of dialkylstannylenes by R-elimination from
1,2-dihalotetraalkyldistannanes, a process whose silicon ana-
logue is well known in silylene chemistry,5 was first proposed
in 1974 for the pyrolysis of 1,2-dichlorotetrabutyldistannane (6)
in the range 120-130 °C (Scheme 4).6
The formation of products expected from the insertion of
stannylene 7 into C-X bonds of benzyl, allyl, propargyl, and
allenyl halides and the Sn-Sn bond of hexamethyldistannane
and a lack of acceleration of the reactions in the presence of
trapping agents were taken as evidence for the formation of the
free stannylene (but see below). The products of formal insertion
were formed in yields of 15% to 25%, together with one or
more oligomers of the stannylene [(n-Bu)2Sn]n. The oligomeric
material was found to be stable under the reaction conditions,
so its decomposition was believed not to contribute to the
formation of the products attributed to the free stannylene.
Adducts of (n-Bu)2Sn: (7) to substituted 1,3-dienes (1,4-
diphenyl-, 2,3-dimethyl-, and 1,2,3,4-tetraphenyl-) were not
found; polystannanes were the only products obtained. Results
presented below suggest that 1,1-dialkyl-1-stannacyclopent-3-
enes are unstable at the temperatures employed for 1,2-
dichlorotetrabutyldistannane pyrolysis, so their absence as
products is understandable and leaves open the question whether
they were formed.
Results and Discussion
Synthesis. Separation of the stannacyclopentene isomers
synthesized by the method of Soderquist and Leon1e was not
successful, so a new route to stannacyclopent-3-enes was
developed employing magnesium-butadiene complexes. Richter
reported high yields of 1,1-diorgano-1-silacyclopent-3-enes, with
no indication of the formation of the silacyclopent-2-ene
isomers, from the condensation of magnesium-butadiene16 with
organodichlorosilanes.17 Richter employed toluene solvent, but
we had employed ethereal solvents for this reaction,18 and THF
proved useful in the preparation of stannacyclopent-3-enes
(Scheme 9).
Addition of Persistent Stannylenes to Butadienes. Lappert
reported the formation of a 1-stannacyclopent-3-ene from the
addition of bis(bisyl)stannylene 8 [where bisyl ) bis(trimeth-
ylsiyl)methyl, (Me3Si)2CH] to 2,3-dimethylbutadiene in 1976
(Scheme 5).7 In an important series of experiments reported in
1984, Neumann examined effects of substituents on, and the
stereochemistry of addition of several stannylenes to, substituted
1,3-dienes. Addition of the stannylenes studied to the meso-
and dl-isomers 9 and 10, respectively, of a diallene 2,7-
diphenylocta-2,3,5,6-tetraene gave products 11a and 11b, and
12, respectively, compatible with an exclusively disrotatory
linear chelotropic process (Scheme 6).1n With trans,trans-1,4-
disubstituted-1,3-dienes 13 the Lappert bis(bisyl)stannylene (8)
underwent addition only with strongly electron-withdrawing
substituents CO2Me or CN; no adduct was obtained with
substituents Ph, Me, NHCO2Et, or OMe (Scheme 7). This result
was interpreted as indicating that the dominant frontier orbital
interaction was stannylene HOMO-diene LUMO, the stan-
nylene thus acting as a nucleophile. For substituents in the 2-
and 3-positons of the diene, sterics apparently plays a dominant
role, with 2,3-diphenylbutadiene undergoing addition by 8 more
slowly than 2,3-dimethylbutadiene. The order of reactivity
toward 8 was 2,3-dimethyl g trans,trans-1,4-carbomethoxy >
2,3-diphenyl > trans,trans-dicyano > meso-2,7-diphenylocta-
2,3,5,6-tetraene.
Yields as low as 10% provided useful quantities of stanna-
cyclopent-3-enes, because they were the only monomeric
products and could be isolated in high purity. This was not the
case with 3-phenylstannacylopent-3-enes, whose yields were
<10% and could not be separated from side products.
While elemental analysis and mass spectrometric precise mass
determination was not possible for all the stannacyclopent-3-
1
enes formed, the combination of H, 13C{1H}, and 119Sn{1H}
NMR spectra led to unambiguous structure determinations.
Vinyl 1H signals at 6.1 to 6.7 ppm with JH-Sn in the range 117
to 131 Hz, SnCH3 1H signals at 0.1 ppm with JH-Sn in the range
54 to 57 Hz, and ring SnCH signals at 1.4 to 1.8 ppm with
JH-Sn in the range 35 to 42 Hz were characteristic, as were 119Sn
signals in the range -2 to 77 ppm. Vinylic 13C signals for alkyl-
(8) Weidenbruch, M.; Scha¨fer, A.; Kilian, H.; Pohl, S.; Saak, W.;
Marsmann, H. Chem. Ber. 1991, 125, 563.
(9) Masamune, S.; Sita, L. R. J. Am. Chem. Soc. 1985, 107, 6390.
(10) Kira, M.; Yauchibara, R.; Hirano, R.; Kabuto, C.; Sakurai, H. J. Am.
Chem. Soc. 1991, 113, 7785.
(11) Kira, M.; Ishida, S.; Iwamoto, T. Chem. Rec. 2004, 4, 243.
(12) Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Patel, D.; Smith, J. D.;
Zhang, S. Organometallics 2000, 19, 49.
(13) Asadi, A.; Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Meehan, M. M.;
Smith, J. D. Organometallics 2002, 21, 2430.
Weidenbruch reported in 1991 that bis(2,4,6-triisopropylphe-
nyl)stannylene undergoes addition to 2,3-dimethylbutadiene,
(14) Saito, M.; Tokitoh, N.; Okazaki, R. Organometallics 1996, 15, 4531.
(15) Setaka, W.; Sakamoto, K.; Kira, M.; Power, P. P. Organometallics
2001, 20, 4460.
(16) Fujita, K.; Ohnuma, Y.; Yasuda, H. J. Organomet. Chem. 1976,
113, 201.
(5) (a) Atwell, W. H.; Weyenberg, D. R. J. Organomet. Chem. 1966, 5,
594. (b) J. Am. Chem. Soc. 1968, 90, 3438.
(6) Schro¨er, U.; Neumann, W. P. Angew. Chem., Int. Ed. Engl. 1975,
14, 246.
(7) Cotton, J. D.; Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Dalton
Trans. 1976, 2275.
(17) Richter, W. J. Synthesis 1982, 12, 1102.
(18) Jiang, P.; Gaspar, P. P. J. Am. Chem. Soc. 2001, 123, 8622.

Synthesis of 1-Stannacyclopent-3-enes
Organometallics, Vol. 28, No. 8, 2009 2597
Scheme 2
Scheme 3
Pyrolysis of 1,1,3,4-tetramethyl-1-stannacyclopent-3-ene (18)
displays a similar picture. First-order kinetics is observed over
three half-lives in cyclohexane-d12 and benzene-d6, but in 2,3-
dimethylbutadiene there is an indication of a slight rate decrease
after two half-lives (Figure 2). This, and a smaller rate
acceleration (10%) upon pyrolyses of 18 in 2,3-dimethylbuta-
diene compared with cyclohexane-d12 than that (20%) observed
for the pyrolysis of 1,1-dimethyl-1-stannacyclopent-3-ene (4)
(cf. Table 1), can be explained by competition, at lower
stannylene concentrations later in the reaction, between read-
dition of dimethylstannylene (3) to the diene and second-order
dimerization of the stannylene. At higher stannylene concentra-
tions the dimerization of Me2Sn: (3) to Me2SndSnMe2 has been
found to be very rapid in a time-resolved laser-flash spectro-
scopic experiment.19
Scheme 4
Scheme 5
When 1,1-dimethyl- and 1,1,3,4-tetramethyl-1-stannacyclo-
pent-3-ene (4 and 18) were pyrolyzed in benzene-d6 or cyclo-
hexane-d12, the only products detectable by NMR were the
corresponding butadiene and dimethylstannylene oligomers,
formed in yields in the range 70% to 100%. Formation of
substituted stannacyclopent-3-enes fell in the narrow range of
131 to 133 ppm. In the case of 1,1-dimethyl-1-stannacyclopent-
3-ene (4), agreement was found with the spectroscopic data of
Soderquist and Leon.1e
No stannacyclopent-3-ene was detected when the magnesium
complex of trans,trans-1,4-diphenylbutadiene was reacted with
dichlorodimethylstannane. As was the case with the reactions
from which low but useful yields of stannacyclopent-3-enes were
obtained, as given above, the major product was believed to be
one or more oligomers of the stannylene. In some cases, e.g.,
cyclo-(Ph2Sn)6, unambiguous characterization of the oligomer
resulted from comparison of its 119Sn NMR spectrum with that
of an authentic sample. A characteristic of all the diorganotin
oligomers was their rapid air-oxidation to insoluble organotin
oxides.
1
dimethylstannylene oligomers was indicated by both H and
119Sn NMR spectroscopy. At the beginning of the pyrolysis a
single broad peak was observed at 0.6 ppm (1H) assigned to
cyclo-(Me2Sn)6.20 In the course of the pyrolysis several single
sharp peaks were observed near 0.5 ppm whose formation
occurred at the expense of the 0.6 ppm peak. These were
attributed to cyclo-(Me2Sn)n (n ) 5, 7, 8).21 Neumann reported
the transformation of the cyclic hexamer to a mixture containing
the pentamer, heptamer, and octamer in benzene solution even
at 20 °C.20
When a larger scale pyrolysis of 1,1-dimethyl-1-stannacy-
clopent-3-ene (4) was carried out in toluene, peaks at ppm 0.61
(broad) and 0.51 (sharp) were attributed to cyclo-(Me2Sn)n, n
) 6 and n ) 5, respectively (lit.20 ppm 0.63 and 0.53,
respectively). In the 119Sn NMR spectrum, several peaks were
observed in the -230 to -250 ppm range in addition to the
peak at 56.37 ppm due to the stannacyclopentene. A single broad
peak at -231.13 ppm was attributed to cyclo-(Me2Sn)6 (lit.20
ppm 231.04 [broad]). A large sharp peak at -241.51 ppm with
satellites (J ) 85.5, 750.7, 1175.1) was assigned to cyclo-
(Me2Sn)5 (lit.21 ppm -241.40, J ) 83, 755, 1176), while the
peaks at -243.47 and -245.11 could be attributed to cyclo-
(Me2Sn)7 and cyclo-(Me2Sn)8, respectively (lit.21 ppm -243.40
and -244.99, respectively. A peak at -233.37 ppm was also
observed by Neumann20 as an unidentified peak (-233.22 ppm)
in a mixture of equilibrating cyclostannanes.
Kinetic Studies of the Pyrolysis of 1-Stannacyclopent-3-
enes. As a first step in determining whether pyrolysis of simple
1-stannacyclopent-3-enes would be a useful route to the
generation of sterically unencumbered stannylenes, the kinetics
of the thermal decomposition of several stannacyclopent-3-enes
was examined.
Pyrolysis of 1,1-dimethyl-1-stannacyclopent-3-ene (4) in
benzene and in cyclohexane was cleanly first-order. Figure 1 is
a representative first-order kinetic plot for the disappearance of
the stannacyclopentene over three half-lives in benzene-d6 at
373.1 K. Plotting these data as a second-order process led to
distinct curvature (plot not shown). The products were butadiene
and oligomers of dimethylstannylene (Me2Sn)n formed in yields
above 70% and often approaching 100%, as determined by
NMR analysis. Table 1 indicates that the first-order rate constant
for pyrolysis of 4 varies with solvent, increasing by a half from
cyclohexane-d12 to benzene-d6, both considered to be inert
solvents in this reaction. 2,3-Dimethylbutadiene is not inert
toward dimethylstannylene, suggested to be an intermediate in
the pyrolysis (Vide infra), but the 30% rate enhancement in neat
2,3-dimethylbutadiene compared with cyclohexane-d12 is likely
to be due to a solvent effect, rather than a sign of a direct
reaction between the diene and stannacyclopentene 4. Induced
decomposition of 4 by reaction with Me2Sn: (3) would have
led to a decrease in the pyrolysis rate when cyclohexane was
replaced by a solvent, 2,3-dimethylbutadiene, capable of reacting
with 3. Again, first-order kinetics was observed, but the reaction
was followed for only two half-lives.
An authentic mixture of dimethylstannylene oligomers was
prepared according to Neumann’s procedure20 and displayed
the same NMR spectra. A similar mixture of dimethylstannylene
oligomers was obtained in 92% (1H NMR) yield when 1,1,3,4-
tetramethyl-1-stannacyclopent-3-ene (18) was subjected to py-
rolysis in benzene-d6 at 373 K for 4 h. The conversion was
(19) Becerra, R.; Gaspar, P. P.; Harrington, C. R.; Leigh, W. J.; Vargas-
Baca, I.; Walsh, R.; Zhou, D. J. Am. Chem. Soc. 2005, 127, 17469.
(20) Watta, B.; Neumann, W. P.; Sauer, J. Organometallics 1985, 4,
1954.
(21) Dra¨ger, M.; Mathiasch, B.; Ross, L.; Ross, M. Z. Anorg. Allg. Chem.
1983, 506, 99.

2598 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
Scheme 6
Scheme 7
The Ea and log A activation parameters were obtained from
the slope and intercept, respectively, of Arrhenius plots of the
observed rate constants vs 1/T. The ∆H‡ and ∆S‡ activation
parameters were computed from the slope and intercept,
respectively, of Eyring plots of ln(kobs/T) vs 1/T. Representative
Arrhenius and Eyring plots are shown in Figures 3 and 4,
respectively, and the others are included in the Supporting
Information.
41%, and a 90% yield of 2,3-dimethylbutadiene was observed
by H NMR.
1
The first-order loss of 1,1-disubstituted-1-stannacyclopent-
3-enes observed upon their heating in an inert solvent, together
with a high yield of butadiene product, is compatible with a
stannylene extrusion mechanism. The small effect observed of
BHT radical scavenger and 2,3-dimethylbutadiene on the
diphenyl and di-tert-butyl systems suggests a limited role for
carbon-centered free-radical intermediates. In the diphenyl and
di-tert-butyl cases, for which the diene can compete for the
stannylene with oligomerization (Vide infra), the modest reduc-
tion in the pyrolysis rate in the presence of 2,3-dimethylbuta-
diene may be due to induced decomposition, but the small effect
of BHT and 2,3-dimethylbutadiene on the activation parameters
suggests that unimolecular decomposition is the major pathway
for the loss of the 1-stannacyclopent-3-enes studied upon
heating. The rate reduction in the presence of 2,3-butadiene may
also be a sign of readdition to butadiene in the absence of a
trapping agent for t-Bu2Sn:.
When reaction mixtures containing mixtures of dimethyl-
stannylene oligomers were exposed to air, white solids precipi-
tated that were no longer soluble in common organic solvents.
These were presumed to be oligomers of dimethylstannylene
oxide (Me2SnO)n, observed as oxidation products of dimethyl-
stannylene oligomers by Neumann.3
Pyrolysis of 1,1-diphenyl-1-stannacyclopent-3-ene in benzene-
d6 in the range 355.5 to 403.2 K also led to first-order
disappearance of the stannacyclopentene. Doubling its concen-
tration did not alter the first-order rate constant. 1H NMR yields
of butadiene declined from 100% at the beginning of the
pyrolysis to ca. 80% at the end (3 half-lives). The insolubility
of the bulk of the oligomers of diphenylstannylene led to the
observation of only a trace of (Ph2Sn)6 by 119Sn NMR
spectroscopy as a peak at -216 ppm (lit. [CDCl3]21 -208 ppm).
1,1-Di-tert-butyl-1-stannacyclopent-3-ene possesses much
higher thermal stability than the corresponding methyl and
phenyl compounds; no thermal decomposition was noted after
24 h at 100 °C (373.1 K) in toluene solution. First-order
disappearance was observed in the range 414.5 to 448.6 K. No
cyclo-(t-Bu2Sn)4, the only known cyclic oligomer of t-Bu2-
Sn:22 was detected by 119Sn NMR in the reaction mixtures, but
it was found that cyclo-(t-Bu2Sn)4 was unstable under these
reaction conditions. Heating a suspension of authentic cyclic
tetramer in toluene (insoluble at room temperature) at 414.5 K
for 65 min led to marked decomposition: the reaction mixture
turned black, and insoluble products were formed. The reaction
mixtures containing the di-tert-butylstannacyclopentene also
turned black and deposited precipitates as well as a tin mirror.
Butadiene yields were ca. 70% at the beginning of the pyrolysis,
but fell to 15-20% at the end, due to self-condensation of the
butadiene. Addition of a scavenger for carbon-centered radicals,
2,6-di-tert-butyl-4-hydroxytoluene (BHT), did not alter the rate
of pyrolysis or of the loss of butadiene.
Product Studies of the Pyrolyses of 1-Stannacyclopent-3-
enes in the Presence of Dienes. 1,1-Dimethyl-1-stannacyclopent-
3-ene (4). 1,1-Dimethyl-1-stannacyclopent-3-ene (4) was sub-
jected to pyrolysis at 100 °C in neat 2,3-dimethylbutadiene, and
1
the reaction was monitored by H NMR spectroscopy. After
4 h, conversion was 32%, and the products observed were
butadiene, (Me2Sn)6, and stannylene adduct 1,1,3,4-tetramethyl-
1-stannacyclopent-3-ene (18) in absolute yields of 70%, 50%,
and 12%, respectively. After 9 h the conversion was 62% and
the product yields were 92%, 42%, and 9%, respectively.
Exposure of the reaction mixture to air resulted in the formation
of white solids from oxidation of the tin oligomer (see Scheme
10).
When 1,1-dimethyl-1-stannacyclopent-3-ene (4) was sub-
jected to pyrolysis under similar conditions for 4 h at 100 °C
in C6D6 (0.082 M in 4 containing a lower concentration, 0.11
M, of 2,3-dimethylbutadiene), the conversion was 43%, and a
51% yield of dimethylstannylene oligomers was observed in
the 1H NMR spectrum as broad peaks at 0.4-0.8 ppm. Spectral
interference from the 2,3-dimethylbutadiene prevented the
determination of the butadiene yield. None of the stannylene
adduct, 1,1,3,4-tetramethyl-1-stannacylopent-3-ene (18), was
Activation parameters for the pyrolysis of several of the
1-stannacyclopent-3-enes were determined in a series of experi-
ments in which the temperature dependence of the first-order
rate constants, presented in Tables 2, 3, and 4, was measured.
1
observed by H NMR, but GC/MS analysis of the reaction
(22) Neumann, W. P.; Pedain, J.; Sommer, R. Ann. Chem. 1966, 694,
9.
mixture revealed its formation in <1% yield. The stannylene

Synthesis of 1-Stannacyclopent-3-enes
Organometallics, Vol. 28, No. 8, 2009 2599
Scheme 8
Scheme 9
Radical intermediates scavengeable by MeI do not seem to play
a significant role in this chemistry.
Authentic cyclo-(Me2Sn)620 was employed to examine the role
of dimethylstannylene oligomers in the pyrolysis of 1,1-
dimethyl-1-stannacyclopent-3-enes (see Supporting Informa-
tion). When 1,1-dimethyl-1-stannacyclopent-3-ene (4) was
subjected to pyrolysis in neat 2,3-dimethylbutadiene for 8 h or
less, greater than 80% of the 1,1,3,4-tetramethyl-1-stannacy-
clopent-3-ene (18) product arises from addition of free Me2Sn:
(3). The presence of dimethylstannylene oligomers does not
affect the rate of decomposition of 4 but does reduce the rate
of formation of the Me2Sn: (3) adduct 1,1,3,4-tetramethyl-1-
stannacyclopent-3-ene (18) by competition between the dim-
ethylstannylene oligomer and 2,3-dimethylbutadiene for free
stannylene 3. The oligomer is ca. 130 times as reactive as 2,3-
dimethylbutadiene toward stannylene 3.
oligomers precipitated as white solids when the reaction mixture
was dissolved in dry hexane and exposed to air.
Pyrolysis of 1,1-Dimethyl-1-stannacylopent-3-ene (4) in
the Presence of Other Potential Stannylene Trapping
Agents. As previously mentioned, the formation of products
expected from the insertion of n-Bu2Sn: into carbon-halogen
bonds of several alkyl halides was taken as support for the
intermediacy of the free stannylene in the pyrolysis of Cl(n-
Bu2Sn)2Cl in 1:6 mixtures with the alkyl halide at 120-130
°C.6 The rate of loss of the Cl(n-Bu2Sn)2Cl was unaffected by
the presence of alkyl halide. The stability under the reaction
conditions of the dibutyltin oligomers that were also formed
was believed to preclude their participation in product forma-
tion.6 Similar evidence was cited for the formation of Et2Sn:
and Me2Sn: (3) in the pyrolysis of Et3SnSnEt2Br (100 °C),
Me3SnSnMe2Br (20 °C), and ClMe2SnSnMe2Cl (50 °C), re-
spectively.23 All these halodistannane decompositions were
reported as being accelerated by light.
Upon pyrolysis of 1,1,3,4-tetramethyl-1-stannacyclopent-3-
ene (18) in neat 1,3-butadiene at 100 °C for 4 h, 1H NMR assay
of the residue after evaporation of butadiene indicated a 5%
yield of 1,1-dimethyl-1-stannacyclopent-3-ene (4) and a 31%
yield of cyclo-(SnMe2)6, some of which was lost by oxidation
during the workup.
Control Experiments for 1,1-Dimethyl-1-stannacyclopent-
3-ene (4). In a control experiment (see Supporting Information)
the presence of MeI led at most to a small depression of the
conversion of 4 upon pyrolysis, the yield of stannylene
oligomers, the rate of Me2Sn: (3) extrusion, and the yield of
the formal adduct of Me2Sn: (3) to 2,3-dimethylbutadiene.
With the thermal extrusion of free dimethylstannylene (3)
from 1,1-dimethyl-1-stannacyclopent-3-enes 4 and 18 having
been placed on a firm footing by the kinetic studies reported
here, it was decided to examine the reactions of free Me2Sn:
(3) with several haloalkanes.
CDCl3. 4 was heated in neat CDCl3 for 6 h at 100 °C, and
1
the reaction was monitored by H NMR; 42% conversion led
to a 75% yield of butadiene and a 76% yield of dimethylstan-
nylene oligomers. No NMR peaks attributable to the C-Cl
insertion product from Me2Sn: (3), (CH3)2Sn(CDCl2)Cl, were
observed. Authentic (CH3)2Sn(CHCl2)Cl was synthesized and
Figure 1. First-order kinetic plot for the pyrolysis of 1,1-dimethyl-
1-stannacyclopent-3-ene (4) in benzene-d6 at 373.1 K.
(23) Grugel, C.; Neumann, W. P.; Seifert, P. Tetrahedron Lett. 1977,
18, 2205.

2600 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
Table 1. First-Order Rate Constants for Pyrolysis of 1-Stannacyclopent-3-enes at 373.1 K
rate constant (s-1) at 373.1 K
substrate
cyclohexane-d12
2,3-dimethylbutadiene
benzene-d6
1,1-dimethyl-1-stannacyclopent-3-ene (4)
1,1,3,4-tetramethyl-1-stannacyclopent-3-ene (18)
2.01 ( 0.02 × 10-5
2.60 ( 0.02 × 10-5
2.75 ( 0.02 × 10-5
3.12 ( 0.02 × 10-5
2.52 ( 0.03 × 10-5
3.79 ( 0.04 × 10-5
Table 2. Temperature Dependence of First-Order Rate Constants
Table 4. Temperature Dependence of First-Order Rate Constants
(units: 10-5 s-1) and Activation Parameters (units: kcal · mol-1
cal · mol-1 · K-1, s-1) for the Pyrolysis of
,
(units: 10-5 s-1) and Activation Parameters (units: kcal · mol-1
cal · mol-1 · K-1, s-1) for the Pyrolysis of
,
1,1-Dimethyl-1-stannacyclopent-3-ene (4) in Benzene-d6 and
Cyclohexane-d12
1,1-Di-tert-butyl-1-stannacyclopent-3-ene in Toluene-d8
rate constants (× 10-5 s-1
)
rate constants ( × 10-5 s-1
)
a
b
T, °C
in C7D8
in C7D8
in C7D8
T, °C
in C6D6
in C6D12
141.4
155.6
163.1
175.5
Ea
log A
∆H‡
∆S‡
2.35 ( 0.09
10.23 ( 0.24
22.34 ( 0.33
73.70 ( 3.31
37.5 ( 0.6
2.15 ( 0.04
9.27 ( 0.10
20.02 ( 0.75
61.51 ( 2.40
36.4 ( 0.4
14.5 ( 0.5
35.6 ( 0.4
5.3 ( 0.9
1.89 ( 0.06
10.19 ( 0.33
18.81 ( 0.37
64.03 ( 1.50
37.7 ( 0.4
87.4
88.0
100.0
110.6
126.0
Ea
log A
∆H‡
∆S‡
0.73 ( 0.02
0.46 ( 0.01
2.01 ( 0.02
5.52 ( 0.20
27.3 ( 0.9
30.2 ( 0.3
13.0 ( 0.8
29.4 ( 0.3
-1.6 ( 0.8
3.12 ( 0.02
9.29 ( 0.08
43.8 ( 1.3
30.1 ( 0.2
13.2 ( 0.3
29.4 ( 0.2
0.9 ( 0.5
15.1 ( 0.6
15.2 ( 0.5
36.6 ( 0.6
8.0 ( 0.6
36.9 ( 0.4
8.7 ( 1.0
a Solution contains BHT. b Solution contains BHT and 2,3-dimeth-
ylbutadiene.
Table 3. Temperature Dependence of First-Order Rate Constants
(units: 10-5 s-1) and Activation Parameters (units: kcal · mol-1
cal · mol-1 · K-1, s-1) for the Pyrolysis of
,
1,1-Diphenyl-1-stannacyclopent-3-ene in Benzene-d6
rate constants ( × 10-5 s-1
)
a
b
T, °C
in C6D6
in C6D6
in C6D6
82.2
82.4
82.6
100.0
110.4
110.6
130.1
130.4
Ea
2.74 ( 0.07
2.26 ( 0.05
2.59 ( 0.31
13.80 ( 1.07
75.08 ( 10.26
20.03 ( 0.70
57.17 ( 2.34
16.35 ( 0.32
51.27 ( 1.55
189.21 ( 1.37
194.09 ( 10.13
335.88 ( 1.40
28.3 ( 0.1
12.8 ( 0.2
27.5 ( 0.1
-2.2 ( 0.2
25.6 ( 0.1
11.2 ( 0.2
28.2 ( 0.3
-0.8 ( 0.8
25.8 ( 0.7
11.3 ( 0.9
25.0 ( 0.7
-9.4 ( 1.7
log A
∆H‡
∆S‡
Figure 2. First-order kinetic plot for the pyrolysis of 1,1,3,4-
tetramethyl-1-stannacyclopent-3-ene (18) in 2,3-dimethylbutadiene
at 373.1 K.
a Solution contains BHT. b Solution contains BHT and 2,3-dimethyl-
butadiene.
shown to be stable at 100 °C for 4 h in C6D6. A mixture of the
stannacyclopentene 4 and (CH3)2Sn(CHCl2)Cl heated at 100 °C
for 4 h in C6D6 led to a 10% loss of the latter compound and
42% decomposition of stannacyclopentene 4 with a 100% yield
of butadiene and a 64% yield of dimethylstannylene oligomers.
These control experiments suggested that thermally generated
Me2Sn: was not trapped by CDCl3 under the conditions
employed.
Control experiments (see Supporting Information) indicated
that at longer times (100 °C, 14 h) dimethylstannylene oligomers
react with EtBr to give the product of formal stannylene insertion
into the C-Br bond of EtBr, EtMe2SnBr. When the reaction
mixture is exposed to light, the reaction of oligomer with EtBr
is rapid even at room temperature.
CH2Cl2. 4 was similarly heated in neat CH2Cl2 at 100 °C for
6 h and monitored by H NMR; 45% conversion led to yields
MeI. When solutions 0.25 M in 4 and 2.1 M in MeI,
degassed, sealed, and protected from light were heated at 100
°C for 5 h in C6D6 or cyclohexane-d12, conversions of 48% and
33% respectively led to 84% and 100% yields of butadiene,
respectively, and 73% and 79% yields of dimethylstannylene
oligomers, as determined by 1H NMR. No Sn-I insertion
product Me3SnI was detected, although it is stable under these
conditions. When a 0.25 M solution of 4 in neat MeI was
subjected to the same reaction conditions, 55% conversion led
to the observation of butadiene and Me3SnI in 90% and 31%
yields, respectively, but no dimethylstannylene oligomer was
observed. It appeared that direct reaction of dimethylstannylene
oligomers with MeI contributed to the formation of Me3SnI in
the latter experiment.
1
of butadiene and dimethylstannylene oligomers of 100% and
77%, respectively. Absence of other 1H NMR signals suggested
that thermally generated Me2Sn: (3) was not trapped by CH2Cl2,
but stability studies were not carried out on the known authentic
insertion product (CH3)2Sn(CH2Cl)Cl.
EtBr. 4 was similarly heated in neat EtBr at 100 °C for 4 h
1
and monitored by H NMR; 42% conversion led to yields of
butadiene and dimethylstannylene oligomers of 84% and 65%,
respectively. No other products were observed by 1H NMR, and
neither EtMe2SnBr nor any other products containing Br were
observed by GC/MS analysis. Me2Sn: (3) does not appear to
be trapped by EtBr under the conditions employed. Since the
reaction mixture was shielded from light, it was also found that
dimethylstannylene oligomers do not react with EtBr in the
absence of light under these conditions.
Control experiments (see Supporting Information) with
authentic dimethylstannylene oligomers indicated that the oli-
gomers react with MeI forming the product of formal C-I bond

Synthesis of 1-Stannacyclopent-3-enes
Organometallics, Vol. 28, No. 8, 2009 2601
subjected to pyrolysis at 100 °C for periods of 4 and 8 h. The
formation of butadiene and dimethylstannylene oligomers in
high yield was revealed by 1H NMR, but neither NMR nor GC/
MS analysis of the reaction mixture gave any indication of the
formation of the expected stannylene-alkyne adduct 2,3,5,6-
tetraethyl-1,1,4,4-tetramethyl-1,4-distannacyclohexa-2,5-di-
ene. A pair of similar pyrolysis experiments with 4 in neat
3-hexyne gave similar results.
Trimethyltin Hydride, Me3SnH. Having found that Me2Sn:
(3) photochemically generated from 4 was trapped by insertion
into the H-Sn bond of Me3SnH,19 it was expected that thermally
generated 3 would also undergo this trapping reaction. The
results, however, were ambiguous. When a 0.29 M solution of
4 in Me3SnH was heated at 89.0 °C, 29% conversion after 14 h
and 50% after 26 h were found. No butadiene coproduct nor
dimethylstannylene oligomers were detected. The reaction
mixture had not been shielded from ambient light. Analysis of
the volatiles by GC/MS led to the detection of Me3SnSnHMe2,
Me3SnSnMe3, and Me3SnSnMe2SnMe3 in a ratio of 1.3:1:1.6.
These products in ratio 1:4.5:2.8 were also formed when a 0.67
M solution of dimethylstannylene oligomers in Me3SnH was
prepared. The oligomers were largely insoluble until the
suspension was exposed to daylight. Then they dissolved within
2 h, and within 5 h the yellow color associated with the
oligomers in solution disappeared. The volatiles were analyzed
by GC/MS. Under these conditions oligomerization of any free
Me2Sn: (3) formed from 4 and reaction of the oligomers with
Me3SnH is indicated as the major source of the volatile tin
products. The absence of the butadiene coproduct of stannylene
extrusion may be due to its consumption by radical chain
processes involving the tin hydrides.
Figure 3. Arrhenius plot for the pyrolysis of 1,1-dimethyl-1-
stannacyclopent-3-ene (4) in benzene-d6 solution in the temperature
range 87.4 to 126.0 °C.
Pyrolysis of 1,1-Diphenyl-1-stannacyclopent-3-ene and 1,1-
Di-tert-butyl-1-stannacyclopent-3-ene in the Presence of Trap-
ping Agents. Diphenyldisulfide, Ph2S2. Neumann reported that
Me2Sn: (3) from the pyrolysis of ClMe2SnSnMe2Cl at 37 °C in
a benzene solution of Ph2S2 gave a quantitative yield of the
S-S insertion product Me2Sn(SPh)2.23 With t-Bu2S2, only
dimethylstannylene oligomers were obtained.33 We decided to
determine whether Ph2Sn: upon thermal extrusion from a
stannacyclopent-3-ene would undergo reaction with Ph2S2. A
C6D6 solution containing 0.031 M 1,1-diphenyl-1-stannacyclo-
pent-3-ene and 0.5 M Ph2S2 was heated at 100 °C and monitored
by NMR spectroscopy. The loss of the stannacyclopent-3-ene
followed a first-order rate law with a rate constant 15% greater
than in the absence of Ph2S2. After 45 min conversion was 48%
and the butadiene yield was ca. 60%. Ph2Sn(SPh)2 was found
Figure 4. Eyring plot for the pyrolysis of 1,1-di-tert-butyl-1-
stannacyclopent-3-ene in benzene-d6 solution containing 3,5-di-tert-
butyl-4-hydroxytoluene (BHT) radical scavenger and 2,3-dimeth-
ylbutadiene stannylene trapping agent in the temperature range
141.4 to 175.5 °C.
Scheme 10
1
in >90% yield, as gauged by H NMR, but no diphenylstan-
nylene oligomer was found.
When a similar pyrolysis experiment was carried out with
1,1-di-tert-butyl-1-stannacyclopent-3-ene at 140 °C, 53% con-
version was observed at the end of 1.6 h, and the formal S-S
insertion product t-Bu2Sn(SPh)2 was formed in >95% yield as
determined by 1H NMR, with a butadiene yield of ca. 60%, but
the first-order rate constant was significantly enhanced (by a
factor of 5) above that observed in the absence of Ph2S2. No
(t-Bu2Sn)4, the only known oligomer of t-Bu2Sn:, was observed.
It appears that at 140 °C, direct reaction of the trapping agent
with the 1,1-di-tert-butyl-1-stannacyclopent-3-ene takes place.
2,3-Dimethylbutadiene. In the kinetic studies of the pyrolysis
of 1,1-diphenyl- and 1,1-di-tert-butyl-1-stannacyclopent-3-ene,
those carried out in the presence of 2,3-dimethylbutadiene led
to the formation of the corresponding 3,4-dimethyl-1-stanna-
insertion by stannylene 3, Me3SnI, in quantitative yield under
both thermal (100 °C, 14 h) and daylight-induced (rt, 5 min)
conditions. In the absence of light the reaction of the oligomer
with MeI was slow at room temperature.
3-Hexyne. Trapping reactions of Me2Ge: with alkynes are
known to produce adducts containing two units of the ger-
mylene, 1,1,4,4-tetramethyl-1,4-digermacyclohexa-2,5-dienes.24
Seeking an analogous reaction of dimethylstannylene 3, 0.25
M solutions of 4 in C6D6 containing 1.7 M 3-hexyne were
(24) (a) Billeb, G.; Neumann, W. P.; Steinhoff, G. Tetrahedron Lett.
1988, 29, 5245. (b) Johnson, F.; Gohlke, R. S.; Nasulavicus, W. A. J.
Organomet. Chem. 1965, 3, 233. (c) Vol’pin, M. E.; Struchkov, Yu.T.;
Vilkov, L. V.; Mastryukov, V. S.; Dulova, V. G.; Kusanov, D. N. IzV. Akad.
Nauk. SSSR, Ser. Khim. 1963, 2067. (d) Johnson, F.; Gohlke, R. S.
Tetrahedron Lett. 1962, 1291.
(25) Dewar, M. J. S.; Friedheim, J. E.; Grady, G. L. Organometallics
1985, 4, 1784.

2602 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
cyclopent-3-ene, characterized by comparison with the authentic
compounds. Solutions of 0.031 M of the diphenylstannacyclo-
pentene in C6D6 containing 5% (0.44 M) 2,3-dimethylbutadiene
were heated at 82.6, 100.0, 110.6, and 126.0 °C, and the kinetic
measurements are reported in Table 3. Yields determined by
1H NMR were butadiene, 60% to 90%, and 3,4-dimethyl-1,2-
diphenyl-1-stannacyclopent-3-ene adduct, characterized by com-
parison with authentic material, ca. 30%. Oligomer (Ph2Sn)6
was formed, but its yield could not be determined.
Solutions of 0.035 M of 1,1-di-tert-butyl-1-stannacyclopent-
3-ene in toluene-d8 containing 5% (0.44M) 2,3-dimethylbuta-
diene were heated at 141.4, 155.6, 163.1, and 175.5 °C, and
the kinetic measurements are reported in Table 4. Yields
determined by 1H NMR were butadiene, decreasing from 85%
at the beginning of the reaction to ca. 30%, and 1,1-di-tert-
butyl-3,4-dimethyl-1-stannacyclopent-3-ene adduct, character-
ized by comparison with authentic material, 75% to 83%. The
presence of the dimethylbutadiene led to <10% change in
the measured first-order rate constants, as shown in Table 4.
The cyclic tetramer cyclo-(Sn-t-Bu2)4, the only known oligomer
of di-tert-butylstannylene, is unstable under the conditions that
1,1-di-tert-butyl-1-stannacyclopent-3-ene underwent pyrolysis.
When a solution (initially a suspension) of cyclo-(Sn-t-Bu2)4 in
toluene-d8 containing 5% (0.44 M) 2,3-dimethylbutadiene was
heated at 140 °C, decomposition was noted within 4 h as
indicated by the formation of insoluble material and the
darkening of the reaction mixture. At 4.38 h, a 43% yield of
the stannylene-diene adduct was recorded by 1H NMR, and this
rose to 56% after 19.5 h. Thus it is possible that oligomer did
form during the stannacyclopentene pyrolysis and its decom-
position under the reaction conditions contributed to the high
yield of stannylene-diene adduct observed upon stannacyclo-
pentene pyrolysis.
Figure 5. Transition structure from ref 26 for the extrusion of
Me2Sn: (3) from 1,1-dimethyl-1-stannacyclopent-3-ene (4) calcu-
lated at B3LYP/6-31G(d,p)/LANL2DZ (for Sn).
Figure 6. Predicted B3LYP energy profile from ref 26 for addition
of Me2Sn: (3) to 1,3-butadiene and the retro-addition, extrusion of
Me2Sn: (3) from 1,1-dimethyl-1-stannacyclopent-3-ene (4).
The increasing yield of formal 1,4-adducts with increasing
steric congestion at the tin atom, Me < Ph < t-Bu, is understand-
able in light of the finding19 that oligomerization of Me2Sn: is
initiated by a second-order dimerization. Reduction of the
dimerization rate, second-order in stannylene concentration, is
expected to be greater than the reduction in the rate of reaction
with 2,3-dimethylbutadiene, which is first-order in stannylene
concentration. Thus addition competes with oligomerization
more effectively, the larger the substituent. Tetramethyldistan-
nene, Me2SndSnMe2, has been found not to dissociate to
Me2Sn: (3) at room temperature,19 so it is unlikely that the steric
effect is exerted on distannene dissociation.
Our recent computational studies26 point to asynchronous
concerted 1,4-addition and retroaddition as the exclusive
pathways connecting Me2Sn: (3) and butadiene with 1,1-
dimethylstannacyclopent-3-ene (4). The transition structure for
the extrusion of Me2Sn: (3) from stannacyclopent-3-ene 4
calculated at B3LYP/6-31G(d,P) for C and H, LANL2DZ for
Sn is shown in Figure 5. An energy profile is shown in Figure
6, and B3LYP predictions of the energies26 are included in the
Supporting Information. The ball-and-stick models shown with
the structures of the stationary states along the reaction
coordinate are representations of the theoretical predictions. The
favored concerted pathway is comprised of Sn1 ) 4; Sn2, the
transition structure for extrusion of 3 from 4; Sn3, an association
complex between 3 and butadiene leading to 1,4-addition; and
Sn4 ) 3 plus butadiene. The disfavored stepwise pathway is
comprised of Sn1 ) 4; Sn5, the transition structure for the
rearrangement connecting 4 and vinylstannirane Sn6; Sn7, the
transition structure for 1,2-addition and retroaddition of 3 and
butadiene; Sn8, an association complex of 3 and butadiene
leading to 1,2-addition, differing in structure from but isoen-
ergetic with Sn3; and Sn4 ) free 3 plus butadiene.
Mechanism of Stannylene Extrusion from 1-Stannacyclo-
pent-3-enes and the Reverse Process, Addition of Stannylenes
to Butadiene. Neither the mechanism of stannylene extrusion
from 1,1-stannacyclopent-3-enes nor the reverse process, the
addition of stannylenes to 1,3-dienes, has received much
attention. Neumann reported in 1984 that reaction of five
stannylenes in solution with a pair of diasteromeric bis(allenes),
shown in Scheme 6, was compatible with a stereospecific
chelotropic process, concerted 1,4-addition.1n Shortly thereafter
Dewar reported that MNDO semiempirical calculations on the
1,4-addition of SnBr2 to butadiene predicted a synchronous
process via a symmetrical transition state.25 An activation barrier
of 19.5 kcal/mol was predicted.
According to our calculations,26 1,1-dimethyl-2-vinylstan-
nirane is a local minimum on the potential surface, but it is
highly unstable, protected from dissociation to the corresponding
stannylene and butadiene by a barrier of less than 1 kcal/mol.
Its barrier for rearrangement to the stannacyclopentene is ca.
(26) Nag, M.; Gaspar, P. P. A computational study of the mechanism
of addition of singlet carbene analogs to 1,3-butadiene to form 1,1-dimethyl-
1-metallacylopent-3-enes [cyclo-Me2MCH2CHdCHCH2, M ) Si, Ge, Sn]
and its reverse retro-addition reaction. Organometallics, in preparation.
(27) Gross, L. W.; Moser, R.; Neumann, W. P.; Scherping, K. H.
Tetrahedron Lett. 1975, 23, 635.

Synthesis of 1-Stannacyclopent-3-enes
Organometallics, Vol. 28, No. 8, 2009 2603
or a Varian Unity-600 (600 MHz) NMR spectrometer. Unless 500
or 600 MHz is specified, the spectrum was recorded at 300 MHz.
Benzene-d6 or chloroform-d was used as the solvent. The small
amount of protiated benzene impurity in benzene-d6 was used as
an internal standard (δ 7.15 ppm). In the case of chloroform-d, the
peak from CHCl3 at δ 7.25 ppm was used as an internal standard.
All coupling constants (J) are given in hertz (Hz). Splitting patterns
are typically described as follows: s, singlet; d, doublet; t, triplet;
m, multiplet. 13C NMR spectra were recorded on a Varian Unity-
300 (75.4 MHz), a Varian Unity-500 (125 MHz), or a Varian Unity-
600 (150 MHz) NMR spectrometer. Unless otherwise indicated,
they are proton decoupled. Unless 125 or 150 MHz is specified,
the spectrum was recorded at 75.4 MHz. Benzene-d6 or chloro-
form-d was used as solvent. The peaks from benzene-d6 at δ 128.0
ppm or the peak from chloroform-d at δ 77.0 ppm was used as the
22 kcal/mol. The intrinsic reaction coordinate (irc) calculated
for the extrusion of Me2Sn: (3) from stannacyclopent-3-ene (4)
does not traverse a vinylstannirane structure.
The pathway favored by these calculations is a concerted but
asynchronous 1,4-addition and retroaddition with barriers of 2
and 31.8 kcal/mol, respectively. The computationally predicted
gas phase enthalpy barrier (see Supporting Information) of 31.75
kcal/mol calculated at 106 °C (average temperature used in
pyrolyses experiments) is in reasonable agreement with the
experimental values of 29.4 ( 0.2 (C6D6) and 29.2 ( 0.3 (C6D12)
reported here.
Summary
Condensation of magnesium-1,3-diene complexes and dichlo-
rodiorganostannanes in THF produces stannacyclopent-3-enes
that can, in favorable cases, be separated in high purity from
their polystannane coproducts, thus rendering their modest yields
preparatively useful. The pyrolyses of 1,1-dimethyl, 1,1-
diphenyl, 1,1-di-tert-buyl, and 1,1,3,4-tetramethyl-1-stannacy-
clopent-3-enes were all first-order processes whose rates were
independent of stannacyclopentene concentration, compatible
with unimolecular thermal extrusion of the corresponding
diorganostannylene. A small effect of carbon-centered radical
scavenger and diene trapping agent on the reaction rate suggests
no more than a minor role for radical intermediates. In the case
of the smallest substituent, addition of Me2Sn: (3) to butadiene
and 1,3-dimethylbutadiene to form stannacyclopent-3-enes 4 and
18 was much slower than oligomerization, with addition yields
of ca. 5% compared with >40% yields of dimethylstannylene
oligomers. The oligomerization had been found in kinetic
spectroscopy experiments to be initiated by dimerization at
nearly the diffusion-controlled rate.19
The oligomers are themselves stannylenoids, but, when
protected from light, they make at most minor contributions to
the formation of stannylene-diene adducts. The dimethylstan-
nylene oligomers compete with dienes for free Me2Sn: (3) but
do not induce decomposition of stannacylopent-3-enes. In the
absence of light, substrates previously believed to trap diorga-
nostannylenes, e.g., chloroform, methylene chloride, ethyl
bromide, and methyl iodide, were found not to undergo reaction
with thermally generated Me2Sn: (3), but dimethylstannylene
oligomers were found to react with EtBr and MeI. Me3SnH was
found previously to undergo H-Sn insertion by photochemically
generated Me2Sn: (3), but under thermal reaction conditions
reaction of dimethylstannylene oligomers with Me3SnH was the
major source of the volatile tin-containing products, including
Me3SnSnHMe2, Me3SnSnMe3, and Me3SnSnMe2SnMe3. Inser-
tion of Ph2Sn: into the S-S bond of Ph2S2 previously suggested
by Neumann27 was confirmed.
1
internal standard in that solvent. All H and 13C chemical shifts
were reported as parts per million (ppm) downfield from tetram-
ethylsilane (TMS). 119Sn NMR spectra were recorded on a Varian
Unity-300 (111.9 MHz) NMR spectrometer employing Me4Sn as
the external standard. All spectra were recorded with proton
decoupling, and all chemical shifts were reported as ppm downfield
from Me4Sn. All NMR spectra were recorded at room temperature.
High-resolution mass spectra data were recorded on a VG ZAB-
SE mass spectrometer in the Washington University MS Facility;
GC/MS data were recorded on an HP 5890A instrument coupled
with a HP integrator or on a Thermo Finnigan QIT GC/MS. The
GC/MS data are all 70 eV EI spectra. Ultraviolet spectral data were
recorded on a Varian Cary 219 spectrometer with baseline correc-
tion. Uncorrected melting points were measured on a Thomas-
Hoover capillary melting point apparatus. The preparative GC was
constructed in this laboratory with dual rhenium tungsten filaments
as the thermal conductivity detector.
Materials. Unless otherwise indicated, all chemicals used for
the reactions were reagent grade quality. Liquid compounds were
distilled before use, and solids were used as supplied or dried as
appropriate. Diethyl ether, benzene, and tetrahydrofuran were
distilled from a blue solution of the benzophenone sodium ketyl
under nitrogen and used immediately. Pentane and hexane were
distilled from calcium hydride under nitrogen. Methylene chloride
was distilled from phosphorus pentoxide under nitrogen. Preparative
reactions were carried out under dry N2.
2,3-Dimethylbutadiene (99%), 3-hexyne (99%), n-Bu2O (anhy-
drous, 99.3%), LiAlH4 (95%), MgCl2 (99.9%, anhydrous), Li
powder (99%, Na 0.5%), MeI (99.5%), Na (99%), 1,3-butadiene
(99+%), Mg turnings (98%), Me4Sn (95%), Ph2SnCl2 (96%), 1,4-
diphenyl-1,3-butadiene (98%), 9-borabicyclo[3.3.1]nonane (98%),
CH2dCHBr (98%), (Me3Si)2CHCl (97%), Me2NH (99.5%), and
n-BuLi (1.6 M, hexanes) were obtained from Aldrich Chemicals,
Me2SnCl2 (98+%) was obtained from TCI America, n-Bu2SnCl2
and Me3SnCl were obtained from Gelest, and SnCl2 (98%) was
obtained from Fisher Scientific.
Me3SnH, Me2SnH2 were synthesized by the method of Finholt
Concerted 1,4-addition of several stannylenes to 1,3-dienes
had been suggested on the basis of the stereospecificity
experimentally observed and theoretically predicted by semiem-
pirical molecular orbital calculations. The mechanism of Me2Sn:
(3) addition to 1,3-butadiene has been probed by hybrid density
functional calculations that supported a concerted asynchronous
1,4-addition mechanism with vinylstannirane intermediates
playing a negligible role due to their low thermal stability.
et al.28
Me2Sn(NEt2)2 was synthesized by the method of Jones and
Lappert.30
Dimethylstannylene oligomers (Me2Sn)n were synthesized by
the method of Watta, Neumann, and Sauer.20
Detailed experimental procedures for the preparation of the above
compounds can be found in the Supporting Information.
Magnesium-butadiene complex from magnesium turnings
(MgBD) was synthesized by the method of Fujita et al.33 To a 250
mL heavy duty Schlenk flask with a magnetic stirring bar was added
20 g (0.83 mol) of magnesium turnings, which were flame dried in
the flask under vacuum. Then 125 mL of freshly dried and distilled
Experimental Section
1
General Instrumentation. H NMR spectra were recorded on
a Varian Unity-300 (300 MHz), a Varian Unity-500 (500 MHz),
(28) Finholt, A. E.; Bond, A. C.; Wilzbach, K. E.; Schlesinger, H. J. Am.
Chem. Soc. 1947, 69, 2692.
(29) Birchall, T.; Pereira, A. R. J. Chem. Soc., Dalton Trans. 1975, 1087.
(30) Jones, J.; Lappert, M. F. J. Chem. Soc. 1965, 1944.

2604 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
THF was transferred to the Schlenk flask via a cannula, and 0.3
mL of 1,2-dibromoethane was added by syringe. The flask was
cooled in a dry ice-acetone bath so that butadiene (12 g, 0.22 mol),
condensed and weighed in a 50 mL Schlenk flask containing ca.
4 g of P2O5 as drying agent, could be transferred and condensed
under vacuum. The flask was closed and heated in a 37 °C water
bath while the mixture was being stirred rapidly. The reaction
mixture became cloudy within hours, and a quantity of slightly
yellow solids was formed overnight. After 3 days, so much solid
had formed that the reaction mixture was difficult to stir, and the
reaction was stopped.
The suspension of magnesium-butadiene complex in THF was
transferred to a 250 mL Schlenk flask via a cannula. The solids
settled, and the top layer was removed via a cannula. Two potions
of 50 mL of THF were used to wash the solids. The washed yellow
solids were stored in THF as a dispersion before use.
(SnCH2), 132.7 (HCdCH)). 119Sn NMR (C6D6, 111.9 MHz): δ
57.43. MS (EI) m/e (relative intensity): 204(6), 202(6), 200(5) (M+•),
189(11), 187(8), 185(6) (M+ - 15), 165(16), 163(11), 161(9),
150(82), 148(53), 146(35), 135(100), 133(71), 131(41), 120(8),
118(7), 116(5), 54(13), 53(19). HRMS: calcd for C6H12Sn 203.9961;
found 203.9956.
1,1-Diphenyl-1-stannacyclopent-3-ene was synthesized by a
similar procedure: 10 g (29.1 mmol) of Ph2SnCl2 in 300 mL of
THF, 6.47 g (29.1 mmol) of MgBD in 150 mL of THF, and an
addition time of 4 h were employed. When the reaction was
complete, THF was removed under low pressure. The residue was
shaken with 200 mL of dry hexane, and solids were removed by
filtration. A clear hexane solution resulted, and crude product was
obtained after hexane was removed under low pressure. The product
was purified by silica gel chromatography (5 cm × 4 cm, hexane,
Rf ) 0.2), and 1.2 g (13% yield) was obtained as a white crystalline
solid: 1H NMR (C6D6, 300 MHz): δ 1.76 (s, 4H, JH-Sn ) 36.9 Hz,
SnCH2), 6.31 (s, 2H, JH-Sn ) 124.2 Hz, HCdCH), 7.14 (m, 6H,
Ph), 7.44 (m, 4H, Ph). 13C NMR (CDCl3, 75.4 MHz): δ 13.39
(SnCH2), 128.50, 128.93, 132.50, 136.78,138.56 (HCdCH, Ph).
119Sn{1H} NMR (C6D6, 111.9 MHz): δ -1.95. Anal. (C,H): Calcd:
C (58.77%), H (4.93%). Found: C (58.94%), H (4.99%).
The yield of magnesium-butadiene complex was estimated to
be almost 100% based on the magnesium consumed and the
butadiene added. The complex was tested by reaction with Ph2SiCl2
in THF to form 1,1-diphenyl-1-silacyclopent-3-ene as the only
product observed by GC/MS.17
Caution. Magnesium-butadiene complex is EXTREMELY
FLAMMABLE; it must be kept in THF with the exclusion of
air. Dry magnesium-butadiene complex may burn in air.
Magnesium-2,3-dimethylbutadiene complex (Mg*DMB) from
activated Mg was synthesized by the method of Rieke.34 Activated
magnesium (Mg*) from 0.29 g (42 mmol) of lithium wire, 5.9 g
(46 mmol) of naphthalene, and 2.0 g (21 mmol) of anhydrous MgCl2
were added to 40 mL of freshly distilled THF. Then 1.64 g (20
mmol) of 2,3-dimethylbutadiene was dried in a Schlenk flask
containing 5 g of P2O5 as drying agent; DMB was transferred to
the flask containing Mg* and THF by using a cannula. The reaction
mixture was stirred at ambient temperature, and the black Mg*
became gray within 30 min. Stirring was continued for 4 to 8 h.
The complex was tested by reacting with Ph2SiCl2 in THF to form
1,1-diphenyl-2,3-dimethyl-1-silacyclopent-3-ene as the only product
observed by GC/MS.17
1,1-Dimethyl-1-stannacyclopent-3-ene (4). In a 1000 mL flame-
dried three-neck flask, equipped with a mechanical stirrer, a nitrogen
inlet/outlet, and a septum, were added 7 g (31.9 mmol) of Me2SnCl2
and 700 mL of freshly distilled THF. MgBD dispersion, ca. 10 g
(44 mmol) in 150 mL of THF in another flask, while being stirred,
was added dropwise via a cannula over 4 to 8 h, while the Me2SnCl2
solution was being stirred rapidly at ambient temperature. Once
the MgBD was added to the solution of Me2SnCl2, the solid
complex disappeared immediately. The reaction mixture was
checked by moistened pH paper when the reaction was close to
completion. When the reaction mixture was neutral, addition of
the MgBD was stopped, and stirring was continued for 15 min.
While stirring continued, saturated NH4Cl solution was added
by syringe, the reaction mixture became cloudy, and white solids
formed. More NH4Cl solution was added until the supernatant
became clear while further white solids formed. MgSO4 drying
agent was added. Solids were removed by filtration, and a clear
solution was obtained. The volume was reduced to ca. 25 mL; then
50 mL of hexane was added and more white solids formed.
Separation (15% yield) was achieved by passing the mixture through
a silica gel column (3 × 5 cm), and the silica gel was washed with
hexane to collect any product left on it. 1H NMR (C6D6, 300 MHz):
δ 0.10 (s, 6H, JH-Sn ) 54.6 Hz, SnCH3), 1.47 (s, 4H, JH-Sn ) 35.1
Hz, SnCH2), 6.27 (s, 2H, JH-Sn ) 113.1 Hz, HCdCH) (lit:35
(CDCl3): δ 0.36 (s, 6H, JH-Sn ) 54.4 Hz), 1.56 (s, 4H), 6.2 (s,
2H)). 13C NMR (C6D6, 75.4 MHz): δ-10.3 (SnCH3), 13.56
(SnCH2), 133.03 (CHdCH) (lit:35 (CDCl3): δ -10.6 (SnCH3), 13.3
1,1-Di-n-butyl-1-stannacyclopent-3-ene was synthesized by a
similar procedure: 8.7 g (28.6 mmol) of n-Bu2SnCl2 in 300 mL of
THF, 6.4 g (28.7 mmol) of MgBD in 150 mL of THF, and an
addition time of 4 h were employed. When the reaction was
complete, and THF was removed under low pressure, the residue
was shaken with 200 mL of dry hexane, and solids were removed
by filtration. A clear hexane solution resulted, and crude product
was obtained after hexane was removed under low pressure.
Purification by silica gel chromatography (5 cm × 4 cm, hexane,
Rf ) 0.5) gave 1.2 g (15% yield) of product as a colorless liquid:
1H NMR (CDCl3, 300 MHz): δ 0.88 (t, 6H, J ) 7.2 Hz, CH3),
1.04 (t, 4H, J ) 8.1 Hz, Sn-CH2), 1.30 (m, 4H, CH2), 1.44 (s, 4H,
CdC-CH2-Sn) 1.52 (m, 4H, CH2), 6.12 (s, 2H, HCdCH, JH-Sn
) 131.7 Hz). 13C NMR (CDCl3, 75.4 MHz): δ 10.09, 11.82, 13.69,
27.00, 29.29 (SnCH2, SnCH2CH2CH2-CH3), 132.97 (CdC). 119Sn
NMR (CDCl3, 111.9 MHz): δ 58.62. MS (EI) m/e (relative
intensity): 234 (15), 231(10), 229(6) (M+ - 54), 177(64), 175(51),
173(39), 147(14), 121(100), 120(91), 119(96), 53(4).
1,1-Di-tert-butyl-1-stannacyclopent-3-ene was synthesized from
MgBD made from magnesium turnings. To a solution of 7 g (23
mmol) of t-Bu2SnCl2 dissolved in 700 mL of THF was added an
excess of a suspension of MgBD in THF via a cannula over 4 h at
ambient temperature until the pH of the reaction mixture reached
7. The mixture was heated at reflux for 1 h, and its volume was
reduced to 50 mL by removing THF under vacuum. Hexane (250
mL) was added and solids were removed by filtration. Hexane was
removed in Vacuo, and the crude product was purified by flash
column chromatography (silica gel, hexane eluent, Rf ) 0.88),
giving 1.7 g (25% yield) of product as a colorless liquid: 1H NMR
(C6D6, 300 MHz): δ 1.18 (s, 18H, SnCMe3), 1.46 (s, 2H, CH2),
1.47 (s, 2H, CH2), 6.32 (s, 2H, CH). 13C NMR (C6D6): δ 10.80 (s,
CH2), 26.98 (s, CMe3), 31.37 (s, CMe3), 133.11 (s, CH). 119Sn NMR
(C6D6): δ 78.00 (s). MS (EI): m/z (relative intensity) 288 (2) (M+),
234 (45) (M+ - C4H6), 177 (100) (M+ - C4H6, - CMe3), 135(46),
121(46). HRMS: calcd for C12H24Sn 288.0900; found 288.0903; d
) 1.215 g/mL.
1,1,3,4-Tetramethyl-1-stannacyclopent-3-ene (18) was syn-
thesized by reacting Mg*DMB with Me2SnCl2. In a 250 mL
Schlenk flask was placed 100 mL of freshly dried and distilled THF
and 1.2 g (5.46 mmol) of Me2SnCl2; then this solution was cooled
to -78 °C. While it was being stirred rapidly by a magnetic stir
bar, Mg*DMB complex was added via a cannula dropwise for 4 h
until the pH value was close to 7. Saturated NH4Cl solution was
added until the reaction mixture became clear. MgSO4 was added
to dry the solution, and solids were removed by filtration through
(31) Kofron, W.; Baclawski, L. M. J. Org. Chem. 1976, 41, 1879.
(32) van den Berghe, E. V.; van der Kelen, G. P. J. Organomet. Chem.
1973, 61, 197.

Synthesis of 1-Stannacyclopent-3-enes
Organometallics, Vol. 28, No. 8, 2009 2605
a 5 cm silica gel column. After further purification by silica gel
by a magnetic stirring bar, MgPhBD (7.52 mmol) in 40 mL of
THF was added dropwise via a cannula. Addition was stopped when
the pH of the reaction mixture neared 7. After warming slowly to
ambient temperature, THF was removed under vacuum, and the
white residue was extracted with 250 mL of dry Et2O. A clear
solution was obtained after filtration, Et2O was removed under
vacuum, and white solids again were formed. Crude product was
chromatography with pentane eluent (Rf ) 0.8), 0.32 g of product
1
(25% yield) was obtained as a colorless liquid: H NMR (C6D6,
300 MHz): δ 0.13 (s, 6H, JH-Sn ) 57 Hz, CH3), 1.59 (s, 4H, JH-Sn
) 42 Hz, SnCH2), 1.81 (s, 6H, CdC-CH3). 13C NMR (C6D6, 75.4
MHz): δ -11.56 (SnCH3), 20.87 (SnCH2), 130.91 (CdCCH3). 119Sn
NMR (C6D6, 111.9 MHz): δ 21.65. MS (EI) m/e (relative intensity):
232(8), 230(7), 228(3) (M+•), 217(47), 215(40), 213(19) (M+
-
analyzed by NMR and a <10% yield estimated: H NMR (C6D6,
1
15), 165(27), 163(16), 161(12), 150(19), 148(18), 146(10), 135(100),
133(71), 131(46), 120(11), 82(15), 67(62), 65(29). HRMS: calcd
for C8H16Sn 232.0259; found 232.0269.
300 MHz): δ 0.86 (t, 6H, CH3), 0.96 (t, 4H, SnCH2), 1.26 (m, 4H,
CH2), 1.47 (m, 4H, CH2), 1.75 (m, 2H, SnCH2), 1.86 (m, 2H,
SnCH2), 6.75 (m, 1H, JH-Sn ) 117 Hz, CdCH), 7.24 (m, Ph), 7.56
(m, Ph). 13C NMR (C6D6, 300 MHz): δ 10.42, 13.79, 27.27, 29.45
(CH2CH2CH2CH3), 126-130, 143.57, 144.45 (Ph, CdCH). 119Sn
NMR (C6D6, 111.9 MHz): δ 77.26.
3,4-Dimethyl-1,1-diphenyl-1-stannacyclopent-3-enene was syn-
thesized by condensing 6.9 g (20 mmol) of Ph2SnCl2 with
Mg*DMB using the same procedure described for the preparation
of 18. Pure product (1.5 g, 21% yield) was obtained after silica gel
Synthesis of Me2SnCl(CHCl2). To a 250 mL Schlenk flask with
a magnetic stirring bar were added 40 mL of freshly dried and
distilled THF and 2 mL (32 mmol) of dichloromethane; then the
flask was cooled in a liquid nitrogen ethanol slush bath at -100
°C. n-Butyllithium solution (13.3 mL, 1.50 M, 20 mmol) was added
via syringe carefully along the cold flask wall during 20 min.
Stirring was continued for 15 min at -100 °C. CHCl2Li was formed
as a white precipitate. Then this solution at -100 °C was transferred
quickly to a -100 °C stirred THF solution of 6.6 g (30 mmol) of
Me2SnCl2 via cannula. The reaction mixture turned clear quickly,
and stirring was continued at -100 °C for 1 h; then the reaction
mixture was allowed to warm to room temperature overnight. The
reaction flask was placed in a 30 °C bath, and solvents were
removed from the mixture under 0.1-0.2 Torr and trapped in liquid
nitrogen. White crystals were obtained on the upper wall of the
flask, which were stable at room temperature, as Me2SnCl(CHCl2)
1
chromatography (hexane, Rf ) 0.56) as a white solid: H NMR
(C6D6, 300 MHz): δ 1.80 (s, 6H, CCH3), 1.896 (s, 2H, CH2), 1.899
(s, 2H, CH2), 7.1-7.3 (m, 6H, Pho, p), 7.4-7.6 (m, 4H, Phm). 13C
NMR (C6D6, 75.4 MHz): δ 21.46 (s, CCH3), 21.65 (s, CH2), 108.42
(s, Ph), 128.69 (s, Ph), 128.99 (s, Ph), 137.10 (s, Ph), 138.69 (s,
Ph). 119Sn NMR (C6D6, 111.9 MHz): δ -31.80 (s). MS (EI) m/z
(relative intensity): 356 (11, M+), 274 (53, M+ - C6H10), 226 (100),
197 (43), 183 (38), 144 (37), 120 (54).
1,1-Di-tert-butyl-3,4-dimethyl-1-stannacyclopent-3-ene was
synthesized by condensing 6.1 g (20 mmol) of t-Bu2SnCl2 with
Mg*DMB using the same procedure described above. A 16% yield
(1.0 g) of pure product was obtained after silica gel chromatography
1
(hexane, Rf ) 0.92) as a white solid: H NMR (toluene-d8, 300
MHz): δ 1.31 (s, 18H, C(CH3)3), 1.65 (s, 2H, CH2), 1.66 (s, 2H,
CH2), 1.92 (s, 6H, CCH3). 13C NMR (toluene-d8, 75.4 MHz): δ
18.95 (s, CMe), 22.14 (s, CH2), 26.61 (s, CMe3), 31.49 (s, CMe3),
131.95 (s, CMe). 119Sn NMR (C6D6, 111.9 MHz): δ 43.16 (s). MS
(EI) m/z (relative intensity): 316 (4, M+), 259 (87), 234 (48, M+ -
C6H10), 203 (73), 177 (100), 135 (49). HRMS: calcd for C14H28Sn
316.1213; found 316.1214.
1
(10% yield) containing a small amount of Me2SnCl2. H NMR: δ
1
1.2. H NMR (C6D6, 300 MHz): δ 0.90 (s, 6H, JH-Sn ) 59.4 Hz;
JH-Sn ) 62.4 Hz, SnCH3), 5.70 (s, 1H, JH-Sn ) 13.5 Hz, SnCHCl2).
MS 70 eV m/e (relative intensity): 252(1), 230(1), 204(18),
185(100), 155(74), 135(24), 120(25), 83(9), 63(6), 48(6).
2-Phenyl-1,3-butadiene magnesium complex (Mg*PhBD) was
synthesized by the method of Jiang36 from 1.0 g (7.7 mmol) of
2-phenyl-1,3-butadiene37 and activated Mg*, from 0.18 g (25.94
mmol) of Li wire, 3.54 g (27.6 mmol) of naphthalene, and 1.24 g
(13.0 mmol) of anhydrous MgCl2. The reaction, usually complete
within 3 h, was monitored by GC/MS on an aliquot of reaction
mixture hydrolyzed with D2O. Unreacted Mg* was removed by
standing or filtration.
Diphenyldiphenylthiostannane, Ph2Sn(SPh)2, was synthesized
by the method of Schmidt, Dersin, and Schumann,38 from 10.3 g
(30 mmol) of Ph2SnCl2 and 6.6 g (60 mmol) of thiophenol. A 60%
yield (8.0 g) was obtained: 1H NMR (C6D6, 300 MHz): δ 6.84 (m,
Ph), 7.04 (m, Ph). 119Sn NMR (C6D6, 111.9 MHz): δ -3.90.
Octa-tert-butylcyclotetrastannane, cycylo-[(t-Bu2)Sn]4, was syn-
thesized by the method of Farrar and Skinner.39 1H NMR (300
MHz) in (toluene-d8): δ 1.71; in (C6D6): δ 1.60; in (CDCl3): δ 1.51
[lit:40 (C6D6): δ 1.61].
Kinetic Studies. Samples for NMR studies of rates of pyrolysis
of 1-stannacyclopent-3-enes were prepared in small, sealed Pyrex
tubes inserted into standard 5 mm NMR tubes for analysis or
directly in sealed NMR tubes. The reaction mixtures were ther-
mostatted by immersion in the vapors of boiling liquids of
appropriate boiling points. Temperatures were periodically moni-
tored using thermocouples mounted near the reaction mixtures. Two
typical procedures are described:
1,1-Dimethyl-3-phenyl-1-stannacyclopent-3-ene was obtained
in low yield. Into a 500 mL Schlenk flask were combined 250 mL
of freshly dried and distilled THF and 1.68 g (7.67 mmol) of
Me2SnCl2, and the resulting solution was cooled to -78 °C while
stirred rapidly by a magnetic stirring bar. MgPhBD (7.68 mmol)
was added via a cannula dropwise during 1 h, and the red color
associated with MgPhBD disappeared upon addition to the reaction
mixture. After warming slowly to ambient temperature overnight,
THF was removed under low pressure, and the white residue was
shaken with 250 mL of dry hexane, giving a clear solution after
filtration. Hexane was then removed under low pressure, and white
solids again appeared. Recrystallization from hexane at -30 °C
failed. A yield of <10% was estimated from the NMR spectroscopic
1. A mixture of 10 mg of 1-stannacyclopent-3-ene and ca. 2 mg
of tetramethylsilane internal standard in 1 mL of C6D6 was
freeze-pump-thaw degassed and sealed in a 5 mm NMR tube
o
that was suspended in the vapors of boiling tert-butanol (82.4
1
characterization: H NMR (C6D6, 300 MHz): δ 0.09 (s, 6H, JH-Sn
C), water (100 °C), toluene (110.4 °C), or 3-methyl-1-butanol (130.1
°C), respectively. For kinetic studies at higher temperatures 5 µL
of toluene internal standard and toluene-d8 solvent were employed,
and the vapor baths were di-n-butyl ether (141.4 °C), n-hexanol
(155.6 °C), mesitylene (163.1 °C), or p-cymene (175.5 °C),
) 54.0 Hz, SnCH3), 1.6 (m, 2H, SnCH2), 1.8 (m, 2H, SnCH2), 6.7
(m, 1H, CdC-H), 7.20 (m, Ph), 7.60 (m, Ph). 119Sn NMR (C6D6,
111.9 MHz): δ 76.17.
1,1-Di-n-butyl-3-phenyl-1-stannacyclopent-3-ene was obtained
in low yield. Into a 500 mL Schlenk flask were added 200 mL of
freshly distilled THF and 1.75 g (5.76 mmol) of n-Bu2SnCl2, and
the resulting solution was cooled to -78 °C. With rapid stirring
(35) Unpublished data of J. A. Soderquist.
(36) Jiang, P. Doctoral Dissertation, Washington University, St. Louis,
2002.
(33) Fujita, K.; Ohnuma, Y.; Yasuda, H.; Tani, H. J. Organomet. Chem.
1976, 113, 201.
(34) Rieke, R. D.; Xiong, H. J. Org. Chem. 1991, 56, 3109.
(37) Marvel, C. S.; Woolford, R. G. J. Org. Chem. 1958, 23, 1658.
(38) Schmidt, M.; Dersin, H. J.; Schumann, H. Chem. Ber. 1962, 95,
1428.

2606 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
respectively. Temperatures were periodically checked with a
thermocouple inserted near the reaction tube. The vapor bath
apparatus, consisting of a boiling flask, a tube in which the reaction
tube was suspended in such a way that refluxing liquid did not
contact it, and a reflux condenser, was protected from the
atmosphere by a slow stream of dry N2 passing through a T-joint
at the top of the condenser. The apparatus was wrapped in aluminum
foil to protect it from light. The reaction tubes were periodically
removed and immediately quenched for NMR analysis.
wrapped in aluminum foil and heated behind a shield at 100 °C
for 4 h and then cooled to 0 °C and opened. Most of the butadiene
was evaporated slowly at 0 °C with slight reduction of pressure;
white solids were observed during removal of butadiene. The
residue was dissolved in C6D6, and more white solids were
observed. According to 1H NMR, little toluene remained after
removal of butadiene, so the extent of decomposition of the 1,1,3,4-
tetramethyl-1-stannacyclopent-3-ene (18) was assumed to be 41%
during 4 h in benzene at 100 °C. From the SnCH3 1H NMR peak
of 4 a 5% yield was estimated; the single broad peak for (Me2Sn)6
observed at 0.6 ppm corresponds to a 31% yield. 119Sn NMR
confirmed the identity of the products, and GC/MS analysis also
indicated that 4 was the major volatile product.
2. 16.0 µL (0.10 mmol) of 4 and 25.6 µL (0.24 mmol) of toluene
as internal standard were dissolved in 1.2 mL of C6D6, and 150 µL
of the solution was injected into a small tube (3 mm o.d.). After
the solution was freeze-pump-thaw degassed to 10-4 Torr, the
tube was sealed and heated at 85 °C. The reaction was monitored
by 1H NMR. The reaction tube was immersed in C6D6 in a normal
NMR tube during an NMR experiment. The concentrations were
Pyrolysis of 4 in the Presence of Other Potential Stannylene
Trapping Agents. CDCl3. Yields are based on integral ratios in 1H
NMR analyses.
1
calculated from the integral ratios of H NMR peaks from 4, the
To a small tube (3 mm o.d.) were added 10.0 µL (0.064 mmol)
of 4, 10.0 µL (0.095 mmol) of toluene as internal standard (δ 2.4
ppm in CDCl3), and 150 µL (1.78 mmol) of CDCl3. The tube was
heated at 100 °C for 6 h and then immersed in CDCl3 in a normal
NMR tube during 1H NMR analysis. Conversion of 42% was found,
and butadiene, observed at δ 5.12-5.27 and 6.37-6.48 ppm, was
formed in 75% yield. Dimethylstannylene oligomers were observed
in 76% yield at δ 0.36-0.56 ppm with a single broad peak with
broad satellites at 0.41 ppm (JH-Sn ) 20.7 Hz). No other new peaks
products, and the toluene internal standard. In 1H NMR, peaks from
butadiene were observed at 4.90-5.10 and 6.10-6.20 ppm, and
dimethylstannylene oligomers at 0.5-0.7 ppm as broad multiple
peaks that formed gradually during pyrolysis. After 14 h at 85 °C,
28% 4 was depleted, with formation of butadiene in 78% yield
and dimethylstannylene oligomers in 75% yield. When the tube
was opened in the air, white solids precipitated gradually from the
solution from oxidation of the oligomers.
Product Studies. Pyrolysis of 1-Stannacyclopent-3-enes in the
Presence of Dienes. Pyrolysis of 4 in Neat 2,3-Dimethylbutadiene
(DMB). All reaction mixtures were freeze-pump-thaw degassed
to 10-4 Torr and sealed prior to pyrolysis.
1
1
were observed in the H NMR. 4 in neat CDCl3: H NMR (300
MHz, CDCl3/CDCl3): δ 0.34 (s, 6H, JH-Sn ) 55.8, 53.4 Hz, SnCH3),
1.54 (d, 4H, J ) 1.2 Hz, JH-Sn ) 35.4 Hz), 6.19 (s, 2H, JH-Sn
113.4 Hz).
)
To a 3 mm o.d. Pyrex tube was added 3.0 µL (0.019 mmol) of
4, 5.0 µL (0.047 mmol) of toluene internal standard (δ CH3 2.90
in neat DMB), and 150 µL (1.33 mmol) of DMB. The reaction
tube was heated at 100 °C for 4 h and then immersed in C6D6 in
CH2Cl2. To a small tube (3 mm o.d.) were added 10.0 µL (0.064
mmol) of 4, 10.0 µL (0.0946 mmol) of toluene as internal standard
(δ 2.3 ppm in CH2Cl2), and 150 µL (2.34 mmol) of CH2Cl2. The
tube was heated at 100 °C for 6 h and then immersed in CDCl3 in
1
an NMR tube for H NMR analysis. Conversion of 4 was 32%.
1
an NMR tube during the H NMR analysis. Conversion of 45%
Butadiene was obtained in 70% yield. Oligomeric dimethylstan-
nylene was observed in 50% yield as a single broad peak at 1.16
ppm. 1,1,3,4-Tetramethyl-1-stannacyclopent-3-ene (18) was formed
in 12% yield. After 9 h of pyrolysis at 100 °C, 62% of 4 was
consumed with the formation of butadiene in 92% yield, dimeth-
ylstannylene oligomers in 42% yield, and tetramethylstannacyclo-
pentene 18 in 9% yield. When the reaction mixture was dissolved
in dry hexane, white solids formed gradually and were removed
before GC/MS analysis, which revealed a dimer of dimethylbuta-
diene as an additional product. 1,1,3,4-Tetramethyl-1-stannacyclo-
pent-3-ene (18) was observed as the major product peak upon GC/
MS analysis.
was found, butadiene was observed at 6.28-6.37 ppm in ca. 100%
yield, and dimethylstannylene oligomers were observed in 77%
yield at 0.36-0.48 ppm as a single broad peak with broad satellites
at 0.40 ppm (J ) 20.7 Hz). No other new peaks were observed in
1
1
the H NMR. 4 in neat CH2Cl2: H NMR (300 MHz, CH2Cl2/
CDCl3): δ 0.24 (s, 6H, JH-Sn ) 56.1, 54.0 Hz, SnCH3), 1.44 (s,
4H, JH-Sn ) 35.4 Hz, CH2), 6.09 (s, 2H, CH).
EtBr. To a small tube (3 mm o.d.) were added 6.0 µL (0.038
mmol) of 4, 6.0 µL (0.068 mmol) of toluene as internal standard
(Ph-CH3: δ 2.31 ppm), and 150 µL (2.01 mmol) of EtBr. The tube
was heated at 100 °C for 4 h and then immersed in C6D6 in an
NMR tube during 1H NMR analysis. Conversion of 42% was found,
butadiene was observed at 5.1-5.3 and 6.3-6.4 ppm in 84% yield,
and broad peaks, observed at 0.48 ppm, were assigned to dimeth-
ylstannylene oligomers formed in 65% yield. No other products
were observed by 1H NMR spectroscopy. White solids were formed
when the reaction mixture was dissolved in dry hexane. No
Me2EtSnBr or other compounds containing bromine were observed
1,1,3,4-Tetramethyl-1-stannacyclopent-3-ene (18) in neat DMB:
1H NMR (300 MHz, DMB/C6D6): δ 0.88 (s, 6H, JH-Sn ) 55.8,
52.8 Hz, SnCH3), 1.70 (s, 4H), CdC-CH3 overlapping with CH3
of DMB.
Pyrolysis of 4 in a Mixture of DMB and MeI. To an NMR
tube were added 0.042 g (0.21 mmol) of 4, 10.0 µL (0.094 mmol)
of toluene as internal standard (CH3 δ 2.10 ppm), 370 µL (2.9
mmol) of 2,3-dimethyl-1,3-butadiene, and 200 µL (2.9 mmol) of
MeI. A C6D6 capillary was placed in the NMR tube as locking
agent. The tube was heated at 100 °C for 8 h. By 1H NMR analysis,
ca. 61% 4 was converted. 1,1,3,4-Tetramethyl-1-stannacyclopent-
3-ene (18) (confirmed by GC/MS analysis), butadiene, and (Me2Sn)n
were observed in yields of 4%, 48%, and 93%, respectively. When
the reaction mixture was dissolved in dry hexane, white solids
formed gradually, which were removed before GC/MS analysis,
and a dimer of butadiene was observed in GC/MS.
Pyrolysis of 18 in Neat Butadiene. Into a thick-walled glass
tube (7 mm o.d., 2.5 mm I.D.) were loaded, by bulb-to-bulb
distillation on a vacuum line, 25.0 µL (0.14 mmol) of 18 and 25
µL (0.24 mmol) of toluene as internal standard. Then ca. 300 µL
of butadiene was condensed in the tube. The sealed tube was
1
by GC/MS analysis. 4 in neat EtBr: H NMR (300 MHz, EtBr/
C6D6): δ 0.27 (s, 6H, JH-Sn ) 56.1, 53.1 Hz, SnCH3), 1.45 (s, 4H,
CH2), 6.07 (s, 2H, CH).
MeI. To a small tube (3 mm o.d.) were added 6.0 µL (0.038
mmol) of 4, 6.0 µL (0.068 mmol) of toluene as internal standard,
20.0 µL (0.32 mmol) of MeI, and 150 µL of C6D6. After the
solution was freeze-pump-thaw degassed to 10-4 Torr, the tube
was sealed and wrapped in aluminum foil and then heated at
100 °C for 5 h. The reaction tube was immersed in C6D6 (7.15
1
ppm) solvent in a normal NMR tube during H NMR analysis.
A 48% conversion was found, butadiene (84% yield) was
observed at 4.9 and 6.2 ppm, and dimethylstannylene oligomers
(73% yield) were observed at 0.4 to 0.6 ppm. No sharp signal
was observed at 0.44 ppm corresponding to Me3SnI superim-

Synthesis of 1-Stannacyclopent-3-enes
Organometallics, Vol. 28, No. 8, 2009 2607
posed on the broad peaks from dimethylstannylene oligomers
found in that region.
of Me3SnH transferred to the tube under vacuum. After warming
from -178 °C, dimethylstannylene oligomers began to dissolve
and the solution turned yellow. Ultrasound was used to help the
dissolution of the oligomers. After 2 h, all dimethylstannylene
oligomers were dissolved, and the color became slightly yellow.
After 5 h, the yellow color was gone, and then Me3SnH was
removed from the reaction mixture at ambient temperature at
15 Torr. The residue was analyzed by 1H and 119Sn NMR
The same procedure was employed with cyclohexane solvent:
6.0 µL (0.038 mmol) of 4, 6.0 µL (0.068 mmol) of toluene as
internal standard, 20.0 µL (0.321 mmol) of MeI, and 150 µL of
C6D12. 4 was observed at 0.50, 1.72, and 6.31 ppm with a
conversion of 33%, butadiene (100% yield) was observed at
6.48-6.58 and 5.23-5.41 ppm, and dimethylstannylene oligo-
mers (79% yield) were observed at 0.64 to 0.78 ppm. No peak
from Me3SnI was observed.
1
spectroscopy and GC/MS. H NMR (300 MHz, C6D6): δ 0.035
(d, Me3SnH) 0.2 to 0.6 (broad), 0.2 to 0.4 (several sharp peaks).
4.74 (m, Me3SnH), 4.45 (septet, J ) 3.1 Hz, Me2SnH). 119Sn
NMR (111.9 MHz, C6D6): δ -95.65, -96.53, -98.24, -101.2
(Me3SnH), -103.14, -107.92, -234.29, -249.3, -261.62 (lit.42
119Sn (33.55 MHz, CDCl3): Me3Sn-SnMe3: δ -108.7; Me3Sn-
SnMe2SnMe3: δ -99.5, -261.7). Volatiles were removed from
the mixture and trapped in liquid nitrogen under high vacuum.
The residue comprised ca. half the reaction mixture and was
identified by 1H NMR as oligomers with only broad peaks
observed at 0.2 to 0.8 ppm. In the analysis of the volatiles by
GC/MS, Me3SnSnMe2H, Me3SnSnMe3, and Me3SnSn-
Me2SnMe3 were observed in the ratio 1:4.5:2.8 as 95% of the
compounds containing tin and 90% of all compounds observed.
Pyrolysis of 1,1-Diphenyl-1-stannacyclopent-3-ene and 1,1-Di-
tert-butyl-1-stannacyclopent-3-ene in the Presence of Ph2S2. A
degassed mixture of 10 mg (0.048 mmol) of 1,1-diphenyl-1-
stannacyclopent-3-ene, a 16-fold excess of diphenyldisulfide (150
mg, 0.77 mmol), and ca. 2 mg of Me4Si internal standard in 1
mL of C6D6 was sealed in an NMR tube and pyrolyzed at 100
°C in a boiling water vapor bath. The mixture was monitored
by NMR spectroscopy. After 45 min the conversion was 48%,
butadiene was formed in 60% yield, and a 90% yield of
The same procedure was used with neat MeI as reactant and
solvent: 6.0 µL (0.038 mmol) of 4, 6.0 µL (0.068 mmol) of
toluene as internal standard, and 150 µL of MeI. Conversion of
55% was found, butadiene (90% yield) and Me3SnI (31% yield)
were observed by 1H NMR analysis, but no peaks from
1
dimethylstannylene oligomers were found. 4 in neat MeI: H
NMR (300 MHz, MeI/C6D6): δ -0.40 (s), 0.76 (s), 5.37 (s);
1
Me3SnI in neat MeI: H NMR (300 MHz, MeI/C6D6): δ 0.20;
butadiene in neat MeI: 1H NMR (300 MHz, MeI/C6D6): δ
4.35-4.53 (m), 5.57-5.67 (m).
3-Hexyne. In Neat 3-Hexyne. To a small tube (3 mm o.d.)
were added 6.0 µL (0.038 mmol) of 4, 2.0 µL of cyclohexane
as internal standard (δ 2.01 ppm in 3-hexyne), and 150 µL (132
mmol) of EtCt CEt. The tube was heated at 100 °C for 4 h and
1
then immersed in C6D6 in a normal NMR tube during H NMR
analysis. A ca. 31% conversion was found, butadiene was
observed at 5.57-5.82 and 6.83-6.93 ppm in 100% yield, and
dimethylstannylene oligomers were observed in 76% yield as a
single peak at 0.096 ppm. After 8 h of pyrolysis at 100 °C, 46%
conversion was found, with the formation of butadiene in 86%
yield and dimethylstannylene oligomers in 92% yield. When the
reaction mixture was dissolved in dry hexane, white solids were
formed gradually, which were removed before GC/MS analysis.
None of the very small (relative to 4) peaks observed cor-
responded to 2,3,5,6-tetraethyl-1,4-distannacyclohexa-2,5-diene.
4 in neat diethylacetylene: 1H NMR (300 MHz, 3-hexyne/C6D6):
δ 0.84 (s, 6H, JH-Sn ) 55.5, 53.1 Hz, SnCH3), 2.04 (s, 4H, CH2),
6.64 (s, 2H, CH).
3-Hexyne in C6D6. A similar procedure was used with 6.0 µL
(0.038 mmol) of 4, 2.0 µL of cyclohexane as internal standard,
30.0 µL (0.26 mmol) of 3-hexyne, and 150 µL of C6D6. The
solution was heated for 4 h at 100 °C, and 37% conversion was
observed, with formation of butadiene in 85% yield and
dimethylstannylene oligomers in 62% yield. After 8 h at 100
°C, the corresponding quantities were 58%, 86%, and 75%,
respectively.
1
Ph2Sn(SPh)2 was observed. H NMR (300 MHz, C6D6): δ 1.76
(s, SnCH2), 5.0-5.15 (m, C4H6), 6.1-6.2 (m, C4H6), 6.30 (s,
HCdCH of 1,1-diphenyl-1-stannacyclopent-3-ene) 6.78-6.91
(m, SPh of Ph2S2 and Ph2Sn(SPh)2), 7.11-7.14 (m, SnPh of 1,1-
diphenyl-1-stannacyclopent-3-ene), 7.34-7.41 (SnPh of 1,1-
diphenyl-1-stannacyclopent-3-ene and Ph2Sn(SPh)2) [authentic
compounds Vide supra Ph2S2: δ 6.78-6.85, 7.13, 7.36-7.40;
1,1-diphenyl-1-stannacyclopent-3-ene: δ 1.76 (s, SnCH2), 6.31
(s, HCdCH), 7.14 (m, Ph), 7.44 (m, Ph); Ph2Sn(SPh)2: δ
6.82-6.92 (m, Ph), 7.35-7.39 (m, Ph)]. 119Sn NMR (111.9 MHz,
C6D6): δ -2.10 (1,1-diphenyl-1-stannacyclopent-3-ene), -3.92
(Ph2Sn(SPh2) [authentic compounds, Vide supra 1,1-diphenyl-
1-stannacyclopent-3-ene: -1.95; Ph2Sn(SPh)2: -3.90]. The first-
order rate constant for loss of 1,1-diphenyl-1-stannacyclopent-
3-ene in C6D6 at 100 °C in the presence of Ph2S2 was 22.7 ×
10-5 s-1 compared with 19.80 ( 0.81 × 10-5 s-1 in the absence
of Ph2S2. No diphenyltin oligomer (119Sn NMR at δ -216) was
observed.
Trimethyltin Hydride, Me3SnH. To a small tube (3 mm o.d.)
were added 7.0 µL (0.044 mmol) of 4, 6.0 µL (0.068 mmol) of
toluene as internal standard, and 150 µL (1.17 mmol) of Me3SnH
transferred to the tube under vacuum. The sealed tube was
wrapped in aluminum foil and heated at 89.0 °C and then
A similar reaction mixture of 10 mg (0.030 mmol) of 1,1-
di-tert-butyl-1-stannacyclopent-3-ene, 150 mg (0.77 mmol) of
Ph2S2, and 5 µL of toluene-H8 internal standard in 1 mL of
toluene-d8 was similarly heated in a standard NMR tube at 140
°C. After 1.6 h, 53% conversion was found by 1H NMR analysis,
butadiene was formed in ca. 60% yield, and a product believed
to be t-Bu2Sn(SPh)2 was formed in >95% yield. A first-order
rate constant of 0.47 h-1 was found (cf. 0.084 h-1 in the absence
1
immersed in C6D6 (7.15 ppm) in an NMR tube during H NMR
analysis. Conversion of 29% was found after 14 h and 50% after
26 h at 89.0 °C. No peaks for butadiene were observed at 5 to
6 ppm, and no broad peaks for dimethylstannylene oligomers at
0.6 ppm. Volatile compounds were removed from the reaction
mixture under vacuum, and the resulting solution was subject
to GC/MS analysis. Me3SnSnMe2H (<10%), Me3SnSnMe3, and
Me3SnSnMe2SnMe3 were observed in the ratio 1.3:1:1.6, but
these products comprised less than 40% of the compounds
observed in GC/MS. The residue was dissolved in C6D6, and in
the 119Sn NMR spectrum peaks were observed at δ 57.37 (4),
2.469, -0.068, -3.029, -101.185, -103.191, -107.979, -234.32,
-258.67, and -261.71.
1
of Ph2S2). H NMR (300 MHz, toluene-d8): δ 1.20 (s, t-Bu of
t-Bu2Sn(SPh)2 1.27 (s, t-Bu of stannacyclopentene), 2.20 (s,
SnCH2 of stannacyclopentene), 6.39 (s, HCdCH of stannacy-
clopentene), 5.0-5.15 (m, C4H6), 6.2-6.33 (m, C4H6), 6.39 (s,
HCdCH of stannacyclopentene), 6.90-7.02 (m, Ph), 7.41-7.45
(m, Ph of stannacyclopentene and t-Bu2Sn(SPh)2). 119Sn (111.9
(39) Farrar, W. V.; Skinner, H. A. J. Organomet. Chem. 1964, 1, 434.
(40) Adams, S.; Dra¨ger, M. J. Organomet. Chem. 1985, 288, 295.
(41) van den Berghe, E. V.; van der Kelen, G. P. J. Organomet. Chem.
1973, 59, 175.
Control Experiment: Dimethylstannylene Oligomers in Me3-
SnH with Daylight. In an O-ring tube was added 30 mg (0.20
mmol) of dimethylstannylene oligomers and 0.3 mL (2.3 mmol)

2608 Organometallics, Vol. 28, No. 8, 2009
Zhou et al.
1
MHz, toluene-d8): δ 57.75 (t-Bu2Sn(SPh)2), 78.16 (stannacy-
clopentene [authentic Vide supra 78.00]; no cyclo-(t-Bu2Sn)4 was
observed [authentic40 1H (C6D6) δ 1.61, 119Sn (C6D6) δ 87.4]).
Supporting Information Available: Control experiments, H
NMR spectra of stannacyclopent-3-enes, Arrhenius and Eyring
plots for all kinetic studies of stannacyclopent-3-ene pyrolysis,
and energies of stationary points predicted by electronic structure
calculations for the addition of Me2Sn: (3) to 1,3-butadiene are
available free of charge via the Internet at http://pubs.acs.
org.
Acknowledgment. We are grateful for financial support
from the National Science Foundation under grants CHE-
9981759 and 0316124. This research was supported in
part by the NSF through TeraGrid resources provided by
NCSA under grant TG-CHE070050N. This work made
use of the Washington University Computational Chem-
istry Facility, supported by NSF grant CHE-0443501.
OM800541F
(42) Mitchell, T. N.; Walter, G. J. Chem. Soc., Perkin Trans. 2 1977,
1842.