Iridium-promoted reactions of carbon-carbon bonds. Skeletal rearrangement of a vinylcyclopropene during iridacyclohexadiene formation and subsequent isomerization of iridacyclohexadienes via α,α'-substituent migrations

Article abstract of DOI:10.1021/ja992407d

On treatment with [Ir(PMe₃)₂(acac)] at room temperature, 1,2,3- triphenyl-3-vinylcyclopropene undergoes ring opening accompanied by rearrangement to give, instead of the expected 1,2,3- triphenyliridacyclohexadiene complex, a crystallographically characterized 1,2,4-triphenyliridacyclohexadiene complex containing cis-phosphine ligands. Studies with ²H- and doubly ¹³C-labeled vinylcyclopropenes, the syntheses and characterization of which are also reported, show that this process involves a rearrangement of the carbon skeleton and not a substituent shift. The corresponding 1,2-diphenyl-3-vinylcyclopropene undergoes iridacyclohexadiene formation without any rearrangement. On heating at 90 °C, each iridacycle converts to its corresponding isomer containing trans- phosphine ligands without any skeletal or substituent rearrangement of the metallacycle, as evidenced by absence of change in the labeling pattern. At higher temperatures, further rearrangement occurs in the case of each metallacycle, which does not alter the metallacyclohexadiene backbone, but rather exchanges the substituents of the α and α' carbon atoms. This rearrangement is shown to occur even when there is no driving force due to relief of steric effects. Mechanisms for each rearrangement are proposed and discussed.

Full text of DOI:10.1021/ja992407d

J. Am. Chem. Soc. 2000, 122, 2261-2271
2261
Iridium-Promoted Reactions of Carbon-Carbon Bonds. Skeletal
Rearrangement of a Vinylcyclopropene during Iridacyclohexadiene
Formation and Subsequent Isomerization of Iridacyclohexadienes via
R,R′-Substituent Migrations
Russell P. Hughes,*,1a Hernando A. Trujillo,1a,b James W. Egan, Jr.,1a and
Arnold L. Rheingold1c
Contribution from the Departments of Chemistry, Burke Chemistry Laboratory, Dartmouth College,
HanoVer, New Hampshire 03755-3564, and UniVersity of Delaware, Newark, Delaware 19716
ReceiVed July 9, 1999
Abstract: On treatment with [Ir(PMe3)2(acac)] at room temperature, 1,2,3-triphenyl-3-vinylcyclopropene
undergoes ring opening accompanied by rearrangement to give, instead of the expected 1,2,3-triphenylirida-
cyclohexadiene complex, a crystallographically characterized 1,2,4-triphenyliridacyclohexadiene complex
containing cis-phosphine ligands. Studies with 2H- and doubly 13C-labeled vinylcyclopropenes, the syntheses
and characterization of which are also reported, show that this process involves a rearrangement of the carbon
skeleton and not a substituent shift. The corresponding 1,2-diphenyl-3-vinylcyclopropene undergoes iridacyclo-
hexadiene formation without any rearrangement. On heating at 90 °C, each iridacycle converts to its
corresponding isomer containing trans-phosphine ligands without any skeletal or substituent rearrangement of
the metallacycle, as evidenced by absence of change in the labeling pattern. At higher temperatures, further
rearrangement occurs in the case of each metallacycle, which does not alter the metallacyclohexadiene backbone,
but rather exchanges the substituents of the R and R′ carbon atoms. This rearrangement is shown to occur
even when there is no driving force due to relief of steric effects. Mechanisms for each rearrangement are
proposed and discussed.
Introduction
exist, and their reaction chemistry is poorly defined. They have
been invoked as key intermediates in the Do¨tz reaction,16 and
iridacyclohexadiene species, obtained by a different route,17 were
shown to undergo a facile deprotonation at the R-carbon to
afford the first examples of iridabenzene complexes, leading to
an extensive chemistry for these compounds.18-29 The first
isolable examples of metallacyclohexadiene complexes of
general structure 1 and their related η3-pentadienediyl relatives
2 were obtained from the ring-opening reactions of 3-vinyl-1-
The ring opening of vinylcyclopropenes by transition metal
complexes to give metallacyclohexadienes and related com-
pounds is now well-established.2-15 Metallacyclohexadienes are
compounds of considerable interest, yet few isolated examples
* Corresponding author. E-mail: RPH@dartmouth.edu. Fax: (603) 646-
3946.
(1) (a) Dartmouth College. (b) American Chemical Society, Division
of Organic Chemistry Fellow, 1990-1991 (Sponsored by the American
Cyanamid Company). (c) University of Delaware.
(2) Donovan, B. T.; Egan, J. W., Jr.; Hughes, R. P.; Spara, P. P.; Trujillo,
H. A.; Rheingold, A. L. Isr. J. Chem. 1990, 30, 351-360.
(3) Hughes, R. P.; Robinson, D. J. Organometallics 1989, 8, 1015-
1019.
(16) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587-608. For
more recent discussion see: Bos, M. E.; Wulff, W. D.; Miller, R. A.;
Chamberlin, S.; Brandvold, T. A. J. Am. Chem. Soc. 1991, 113, 9293-
9319.
(4) Semmelhack, M. F.; Ho, S.; Steigerwald, M.; Lee, M. C. J. Am. Chem.
Soc. 1987, 109, 4397-4399.
(17) Bleeke, J. R.; Peng, W. J. Organometallics 1987, 6, 1576-1578.
(18) Bleeke, J. R.; Peng, W. J.; Xie, Y. F.; Chiang, M. Y. Organome-
tallics 1990, 9, 1113-19.
(5) Egan, J. W.; Hughes, R. P.; Rheingold, A. L. Organometallics 1987,
6, 1578-1581.
(19) Bleeke, J. R.; Rohde, A. M.; Boorsma, D. W. Organometallics 1993,
12, 970-4.
(6) Grabowski, N. A.; Hughes, R. P.; Jaynes, B. S.; Rheingold, A. L. J.
Chem. Soc., Chem. Commun. 1986, 1694-1695.
(7) Hughes, R. P.; Trujillo, H. A.; Gauri, A. J. Organometallics 1995,
14, 4319-24.
(8) Donovan, B. T.; Hughes, R. P.; Kowalski, A. S.; Trujillo, H. A.;
Rheingold, A. L. Organometallics 1993, 12, 1038-43.
(9) Hughes, R. P.; Trujillo, H. A.; Egan, J. W.; Rheingold, A. L.
Organometallics 1999, 18, 2766.
(10) Cho, S. H.; Liebeskind, L. S. J. Org. Chem. 1987, 52, 2631-4.
(11) Padwa, A.; Kassir, J. M.; Xu, S. L. J. Org. Chem. 1991, 56, 6971-
2.
(12) Donovan, B. T.; Hughes, R. P.; Trujillo, H. A. J. Am. Chem. Soc.
1990, 112, 7076-7.
(13) Donovan, B. T.; Hughes, R. P.; Trujillo, H. A.; Rheingold, A. L.
Organometallics 1992, 11, 64-9.
(20) Bleeke, J. R. Acc. Chem. Res. 1991, 24, 271-7.
(21) Bleeke, J. R.; Xie, Y. F.; Peng, W. J.; Chiang, M. J. Am. Chem.
Soc. 1989, 111, 4118-20.
(22) Bleeke, J. R.; Behm, R.; Xie, Y.-F.; Clayton, T. W., Jr.; Robinson,
K. D. J. Am. Chem. Soc. 1994, 116, 4093-4.
(23) Bleeke, J. R.; Behm, R. J. Am. Chem. Soc. 1997, 119, 8503-11.
(24) Bleeke, J. R.; Behm, R.; Beatty, A. M. Organometallics 1997, 16,
1103-5.
(25) Bleeke, J. R.; Behm, R.; Xie, Y.-F.; Chiang, M. Y.; Robinson, K.
D.; Beatty, A. M. Organometallics 1997, 16, 606-23.
(26) Bleeke, J. R.; Blanchard, J. M. B. J. Am. Chem. Soc. 1997, 119,
5443-4.
(27) Bleeke, J. R.; Xie, Y. F.; Bass, L.; Chiang, M. Y. J. Am. Chem.
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(14) Donovan-Merkert, B. T.; Tjiong, H. I.; Rhinehart, L. M.; Russell,
R. A.; Malik, J. Organometallics 1997, 16, 819.
(15) Hughes, R. P.; Trujillo, H. A.; Rheingold, A. L. J. Am. Chem. Soc.
1993, 115, 1583-5.
(28) Bleeke, J. R.; Bass, L. A.; Xie, Y. F.; Chiang, M. Y. J. Am. Chem.
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(29) Gilbertson, R. D.; Weakley, T. J. R.; Haley, M. M. J. Am. Chem.
Soc. 1999, 121, 2597-98.
10.1021/ja992407d CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/18/2000

2262 J. Am. Chem. Soc., Vol. 122, No. 10, 2000
Hughes et al.
Scheme 1
cyclopropenes with low valent transition metal complexes, as
shown in Scheme 1.6 The reaction can be thought of as occurring
via initial coordination of the alkene, followed by insertion of
the metal into one of the flanking C-C σ-bonds of the
cyclopropene ring. Canonical form 3 is a valid resonance
structure of 2, and much of the known chemistry of these
compounds can be rationalized in terms of reductive elimination/
oxidative addition of C-C bonds using 3 as shown in Scheme
1. For example, reductive elimination of bonds cd affords the
vinylcyclopropene complex, elimination of bonds bc yields a
metallacyclohexadiene, and coupling of bonds ad generates a
coordinated cyclopentadiene; examples of all these reactions
have been observed previously.2-15 We believe this model is
useful for understanding the chemistry described in this paper,
in which we describe other skeletal contortions and substituent
gymnastics observed in these systems.
Skeletal rearrangements have been observed previously during
the reactions of vinylcyclopropenes with transition metal
complexes. Various vinylcyclopropenes and cyclopropenyl
ketones have been observed to undergo skeletal rearrangements
in the presence of Rh(I) and Rh(II) en route to furans,
cyclopentadienes, and carbonylation products.10,11 In the transi-
tion-metal-catalyzed ring opening and carbonylation of cyclo-
propenyl ketones, both Liebeskind10 and Padwa11 have observed
a skeletal rearrangement in which the carbons presumed adjacent
to the metal exchange positions. This exchange was ascribed
to fragmentation of the ligand into an acetylene and a ketocar-
bene over the course of the ring closure; rotation of the η2-
alkyne in an intermediate like 4 (Scheme 1) affords the observed
rearrangement. Liebeskind has observed that the substituents
on the organic substrate greatly affect whether the rearrangement
is observed,10 while Padwa has noted that the nature of the
metal-ligand combination also exerts a strong influence.11
We have recently reported that the ring opening of 1,2-
diphenyl-3-vinyl-1-cyclopropene 5 (Chart 1) with the rhodium
fragment [RhCl(PMe3)2] unexpectedly proceeds via a skeletal
rearrangement during the kinetically controlled ring-opening
process, to give a mixture of 6 and 7.9 Here we report that an
iridium(I)-promoted reaction of 5 to give an iridacyclohexadiene
does not proceed with any skeletal rearrangement but that 1,2,3-
triphenylvinylcyclopropene 8 undergoes a previously unobserved
skeletal rearrangement during ring opening at room temperature.
However, both the kinetically formed iridacyclohexadienes
undergo ring substituent migrations on subsequent heating. Part
of this work has been communicated previously.15
[Ir(acac)(PMe3)2] (acac ) acetylacetonate) with 5 affords the
iridacyclohexadiene complex 9 as a single stereoisomer. This
and isotopic labeling results described below clearly show that
there is no skeletal rearrangement of the type previously
observed in Rh(I) chemistry. In contrast, the corresponding
triphenylvinylcyclopropene 8 reacts at room temperature with
[Ir(acac)(PMe3)2] to form a single product whose phenyl groups
are clearly no longer on contiguous carbon atoms. This reaction
works equally well when the [Ir(acac)(PMe3)2] is prepared and
isolated ahead of time, or when it is prepared in situ from PMe3
and [Ir(acac)(C2H4)2]. NMR spectra of the product suggested
structure 10, which was confirmed by a single crystal X-ray
diffraction study. An ORTEP diagram is presented in Figure 1;
crystal data collection and refinement parameters for the
structure are presented in Table 1, and selected bond distances
and angles, in Table 2. The octahedral geometry around the
iridium is relatively unremarkable, with the exception of the
difference in the Ir-PMe3 bond lengths. At 2.409(2) Å, the bond
to the equatorial phosphine P(1) is slightly longer than a typical
Ir(III)-PMe3 bond (2.30-2.38 Å),30 while the bond to the axial
phosphine P(2) is significantly shorter (2.219(2) Å). Although
Ir(III)-PMe3 bonds are known to be strongly subject to the
influence of the ligand trans to it,30 to our knowledge, only [Ir-
(C5H5)(Cl)(Me)(PMe3)] has a comparably short Ir(III)-PMe3
bond distance (2.228 Å).30a The near perpendicularity of the
bond angles around the iridium also suggests that this difference
arises from the trans influence of the other ligands in the
coordination sphere, rather than from steric factors.
The NMR spectra of 10 jibe with the crystal structure. A
1
small H NMR coupling (3 Hz) between the methine proton
(H9 on C9) and one of the methylene protons (H11a on C11) is
consistent with a W-interaction, although no coupling between
H9 and the other methylene proton (H11b) is observed. In the
13C{1H} spectrum, the large coupling between C11 and the
equatorial phosphine P1 is consistent with their trans-orienta-
tion;17,18,31 this coupling is also observed in diphenyl compound
(30) (a) For the structure of [Ir(C5H5)(Cl)(Me)(PMe3)], see: Foo, T.;
Bergman, R. G. Organometallics 1992, 11, 1801-1810. (b) Examples of
other compounds can be found in: Deeming, A. J.; Doherty, S.; Marshall,
J. E. Polyhedron 1991, 10, 1857-1864. Einstein, F. W. B.; Yan, X.; Sutton,
D. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1991, C47, 1957-
1976. (d) Knorr, J. R.; Merola J. S. Organometallics 1990, 9, 3008-3010.
Stevens, R. C.; Bau, R.; Milstein, D.; Blum, O. J. Chem. Soc., Dalton Trans.
1990, 1429-1432. Behr, A.; Hertweck, E.; Herrmann, W. A.; Keim, W.;
Kipshagen, W. J. Chem. Soc. 1986, 1262-1263. Milstein, D.; Calabrese,
J. C.; Williams, I. D. J. Am. Chem. Soc. 1986, 108, 6387-6389. Kaner, R.
B.; Kouvetakis, J.; Mayorga, S. G. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1986, C42, 500-501. Calabrese, J. C.; Roe, D. C.; Thorn, D. L.;
Tulip, T. H. Organometallics 1984, 3, 1223-1230. Kalck, P.; Bonnet, J.
J.; Poilblanc, R. J. Am. Chem. Soc. 1982, 104, 3069-3077. Nolte, M. J.;
Singleton, E.; Van der Stok, E. J. Chem. Soc., Chem. Commun 1978, 973-
974. Tuggle, R. M.; Weaver, D. L. Inorg. Chem. 1972, 11, 2237-2242.
Results and Discussion
Observation of the Low Temperature Rearrangement.
Room-temperature reaction of the 16-electron Ir(I) complex

Iridium-Promoted Reactions of C-C Bonds
J. Am. Chem. Soc., Vol. 122, No. 10, 2000 2263
Chart 1
Figure 1. Molecular structure of 10 with thermal ellipsoids at 50%
probability level.
Preparation of Isotopically Labeled Vinylcyclopropenes.
To aid in elucidating the mechanism for this (and subsequent)
rearrangement(s), a number of 2H- and doubly 13C-labeled
vinylcyclopropenes were prepared. trans-Deuterated vinylcyclo-
propenes 11 and 12 were prepared by coupling the appropriate
cyclopropenyl cations with trans-deuterated vinyllithium and
magnesium bromide, as shown in Scheme 2. The starting bis-
(tributylstannyl)ethylene 13 has been prepared by two routes
in the literature. Corey’s preparation,32 in which (tributylstan-
nyl)chloroacetylene, prepared from dichloroethylene, is hydro-
stannylated and reduced, is convenient on the small scale
reported, but the low yield (typically 30-40% overall) and the
need for 3 equiv of tin reagent make this procedure less desirable
on a larger scale. Bottaro’s preparation,33 which quenches
acetylide anion with tributyl tin chloride and then hydrostan-
nylates the resulting stannylacetylene, on the other hand, requires
only 2 equiv of tin and is more convenient on a large scale.
Sequential exchanges of lithium for tin on 13 provide trans-
deuterated vinyllithium 14. Minimal yields of the vinylcyclo-
propenes are obtained when the lithiate is used to couple with
cyclopropenyl cations. The lithiate can be converted to a
Grignard reagent 15, however, by the addition of magnesium
bromide-ether complex,34 which allows the preparation of the
phenyl-substituted vinylcyclopropenes 11 and 12 in reasonable
yields. Presumably, the more strongly reducing lithiate causes
the cyclopropenyl cation to be reduced to a greater extent than
does the more covalent magnesium bromide.
The ring-deuterated vinylcyclopropene, 16, was prepared by
coupling of vinyl Grignard reagent with deuteriodiphenylcyclo-
propenyl fluoroborate, which was prepared identically to its
protic analogue35,36 by the addition of phenylchlorocarbene to
1-deuteriophenylacetylene,37 as shown in Scheme 3.
Doubly 13C-labeled di- and triphenylvinylcyclopropenes 17
and 18 were likewise prepared from labeled vinylmagnesium
bromide, which had in turn been prepared from a labeled vinyltin
precursor, as shown in Scheme 3. Smolin has prepared tributyl-
(31) Bleeke, J. R.; Boorsma, D.; Chiang, M. Y.; Clayton, T. W., Jr.;
Halle, T.; Beatty, A. M.; Xie, Y.-F. Organometallics 1991, 10, 2391-2398.
(32) Corey, E. J.; Wollenberg, R. H. J. Org. Chem. 1975, 40, 3788-
3791.
(33) Bottaro, J. C.; Hanson, R. N.; Seitz, D. E. J. Org. Chem. 1981, 46,
5221-5222.
(34) Sibi, M. P.; Miah, M. A. J.; Snieckus, V. J. Org. Chem., 1984, 49,
737-742.
(35) Padwa, A.; Blacklock, T. J.; Getman, D.; Hatanaka, N.; Lorza, R.
J. Org. Chem. 1978, 43, 1481-1492.
(36) Hughes, R. P.; Lambert, J. M. J.; Whitman, D. W.; Hubbard, J.
W.; Henry, W. P.; Rheingold, A. L. Organometallics 1986, 5, 789-797.
(37) Wood, J. T.; Arney, J. S.; Corte`s, D.; Berson, J. A. J. Am. Chem.
Soc. 1978, 100, 3855-3860.
9. Clearly, to establish whether the molecular gymnastics
involved in the formation of 10 occurred by a skeletal
reorganization or a substituent shift, a number of isotopically
labeled vinylcyclopropenes were required.

2264 J. Am. Chem. Soc., Vol. 122, No. 10, 2000
Hughes et al.
Table 1. Crystal Data Collection and Refinement Parameters for 10
(a) Crystal Parameters
formula
cryst system
space group
a, Å
b, Å
c, Å
C34H42O2P2Ir
monoclinic
P21/c
15.532(3)
12.425(3)
17.547(7)
104.77(3)
V, Å3
3274(2)
4
1.49
44 5
Z
d
calc, 9 cm-1
µ, cm-l
cryst size, mm
cryst color
0.34 × 0.34 × 0.34
yellow
â, deg
(b) Data Collection
diffractometer
radiation
monochromator
scan technique
28 scan range, deg
data collected
Nicolet R3M/µ
scan speed (deg min-1
)
variable, 5-20
6985
6442
4478
3 stds/197 rflns
< 1%
Mo KR (λ ) 0.71073 Å)
rflns collected
indpdnt data
indpdnt data g 5σ(Fo)
std rflns
graphite
Wyckoff
4-52
(h, +k, +l
decay
(c) Refinement
R(F), X
3.55
3.71
1.22 (near Ir)
GOF
data/parameter
(∆/σ), final
0.973
13.5
0.007
wR(F), %
∆(F), e Å-3
Table 2. Selected Bond Distances and Angles for 10
Scheme 3
(a) Bond Distances (Å)
Ir-P(1)
2.409(2)
2.219(2)
2.125(4)
2.161(4)
2.023(5)
2.111(7)
1.824(8)
1.806(8)
1.276(8)
O(2)-C(14)
1.256(9)
1.364(8)
1.466(9)
1.329(8)
1.496(8)
1.385(9)
1.506(11)
1.406(11)
1.526(10)
Ir-P(2)
C(7)-C(8)
Ir-O(1)
C(8)-C(9)
Ir-O(2)
C(9)-C(10)
C(10-C(11)
C(12)-C(13)
C(12)-C(15)
C(13)-C(14)
C(14)-C(16)
Ir-C(7)
Ir-C(11)
P(1)-C aVg
P(2)-C aVg
O(1)-C(12)
(b) Bond Angles (deg)
P(1)-Ir-P(2)
P(1)-Ir-O(l)
P(2)-Ir-O(1)
P(1)-Ir-O(2)
P(2)-Ir-O(2)
O(1)-Ir-O(2)
P(1)-Ir-C(7)
P(2)-Ir-C(7)
O(1)-Ir-C(7)
O(2)-Ir-C(7)
P(1)-Ir-C(11)
P(2)-Ir-C(11)
O(1)-Ir-C(11)
O(2)-Ir-C(11)
96.2(1)
88.4(1)
175.5(1)
84.7(1)
92.0(1)
88.5(2)
100.5(2)
90.9(2)
88.2(2)
173.7(2)
166.3(2)
89.9(2)
85.6(2)
82.8(2)
C(7)-Ir-C(10)
91.7(2)
126.8(3)
114.2(3)
119.5(3)
117.5(3)
112.8(3)
124.8(4)
124.3(4)
125.7(5)
125.6(5)
128.6(5)
122.4(6)
122.5(5)
Ir-P(1)-C(l)
Ir-P(1)-C(2)
Table 3. Calculated Chemical Shifts (ppm) and Coupling
Constants (Hz) for Diphenyl[13C2]vinylcyclopropene 17
Ir-P(2)-C(4)
Ir-P(2)-C(5)
Ir-P(2)-C(6)
Ir-O(1)-C(l2)
Ir-O(2)-C(14)
Ir-C(7)-C(8)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
C(9)-C(10)-C(11)
Ir-C(11)-C(10)
Scheme 2
which would be desirable for safety, led to a drastic reduction
in product formation. An unexpected side product formed in
these lower pressure reactions was trans-bis(tributylstannyl)-
ethylene. The subsequent formation of the 13C-labeled Grignard
reagents from the labeled vinyltin and the coupling to di- and
triphenylcyclopropenyl cations proceeded uneventfully. The
1
products were fully characterized by H and 13C NMR spec-
troscopy, and spectral simulations39 generated the couplings
presented in Table 3. In its 1H and 13C NMR spectra, the
diphenyl vinylcyclopropene 17 shows slight second-order effects
for its six coupled nuclei.
vinyltin by hydrostannylation of unlabeled acetylene,38 but the
expense of [13C2]acetylene renders the 2-fold excess of acetylene
necessitated by this procedure undesirable for the labeled
reaction. Using a stoichiometric amount of acetylene and a lower
pressure (5 vs 10 atm), a reasonable yield (70%) of the labeled
vinyltin was obtained. The use of still lower pressures (2 atm),
Ring-Opening Reactions with Labeled Vinylcyclopro-
penes. Using doubly 13C-labeled diphenylvinylcyclopropene 17
1
as the substrate, H NMR spectra of the product 19 showed
(39) Simulated NMR spectra were generated using LAOCOON III:
(38) Smolin, E. M. Tetrahedron Lett. 1961, 4, 143-145.
Castellano, S.; Bothner-By, A. A. J. Chem. Phys. 1964, 41, 4863-4869.

Iridium-Promoted Reactions of C-C Bonds
J. Am. Chem. Soc., Vol. 122, No. 10, 2000 2265
Table 4. Geminal Proton/Phosphine Couplings and NOE Results
for 10a
Scheme 4
NOE to
δb
(PMe3)ax
(PMe3)eq
JHP(ax)
JHP(eq)
c
c
H5a
H5b
4.42d
2.81
n.o.
+
n.o.
n.o.
9.4
7.6
3.0
5.6
a ax, axial; eq, equatorial; n.o., not observed. b In ppm relative to
TMS (C6D6). c In Hz. d Resonance which disappears in deuterated
compound 23.
that the labeled carbons remained in the methylene and methine
groups and that the labeled carbons were adjacent, with a large
1JCC ) 41 Hz. Typical one-bond carbon-carbon couplings fall
in the ranges 35-40 Hz (sp3-sp3), 40-55 Hz (sp3-sp2), 55-
70 Hz (sp2-sp2), and 155-170 Hz (sp-sp); two- and three-
bond couplings are generally <10 Hz.40 In contrast, reaction of
the doubly labeled triphenyl compound 18 afforded the rear-
ranged product 20, in which the labeled carbons remained in
the methylene and methine groups, but were no longer adjacent
2
as indicated by a much smaller JCC ) 3.0 Hz.40 This result
conclusively demonstrates that the rearrangement in the forma-
tion of 20 (and 10) is indeed skeletal and is not due to substituent
migrations on a fixed carbon framework. That no rearrangement
of any type occurs in the diphenyl system is confirmed by
reaction using ring-deuterated vinylcyclopropene 16, which
afforded a single isotopomer 21 with the deuterium label in the
position shown adjacent to the phenyl groups.
Repetition of these reactions using trans-deuterated vinylcy-
clopropenes 11 and 12 gave in each case clean conversion to
single isotopomers of the resultant metallacyclohexadienes 21
and 23, respectively. No intermediates could be observed during
NMR monitoring of the evolving reaction systems. Thus,
stereochemical information is retained at both the metal and at
the methylene carbon over the course of the reaction, whether
skeletal rearrangement occurs or not! The position of the
deuterium on the metallacycle face opposite (anti to) the axial
phosphine was established by NOE experiments on the protic
material. For example, NOE difference spectra (Table 4) of 10
showed that the position which remains undeuterated in 23 is
syn to the axial phosphine P1. Although too small to be
conclusive in themselves, the different couplings of the two
geminal protons to the axial phosphine accord with this
assignment: a larger coupling constant is observed to the proton
assigned anti to the axial phosphine than to the corresponding
syn proton.
We have been able to devise two mechanisms by which the
observed skeletal rearrangement can be accomplished. Other
rearrangements of the type observed previously for Rh-promoted
rearrangements of vinylcyclopropenes9 can be excluded, since
they cannot give rise to the observed carbon reorganization. Each
path invokes an initial intermediate 24, analogous to structure
3 (Scheme 1) discussed previously, with subsequent chemistry
evolving from it. It is clear that in order to accommodate
intermediate 24, only three other ligands can be bound to
iridium. We propose that the acac ligand becomes monodentate
at this stage, as phosphine dissociation must give the metalla-
cyclohexadiene isomers with PMe3 ligands mutually trans, as
shown later. In the first mechanism, illustrated in Scheme 4,
the exchange of carbons and their appended groups occurs by
rotation of a cyclopropene bearing both. Initial reaction of the
vinylcyclopropene to give intermediate 24 followed by elimina-
tion of bonds bc affords unrearranged metallacyclohexadiene
25. However, if formation of 24 is followed by reductive
elimination of bonds ac with retention of configuration at each
carbon to give 26, reversible retrocyclization of 26 affords the
alkyne-cyclopropene species 27. Rotation of the cyclopropene
as shown, followed by reconnection of the carbon-carbon bonds
and subsequent ring opening (the microscopic reverse of the
original ac coupling with retention of configuration at each
carbon atom), affords the correct carbon disposition in the
resultant metallacyclohexadiene 28. When X ) Ph, a driving
force exists to alleviate steric strain between phenyl groups;
when X ) H (or D), no rearrangement occurs. It is noteworthy
that reaction of diazoalkanes with metallacyclopentadiene
complexes is known to afford cyclopentadienes;41 cyclopropa-
nation of one of the metallacyclopentadiene double bonds would
afford an analogue of 26, and the eventual cyclopentadiene may
arise from collapse of this compound to the analogue of 24,
followed by ad coupling to give the cyclopentadiene, a reaction
which we have demonstrated previously.12 The coupling of
alkynes with three carbon fragments to afford metallacyclo-
hexadiene intermediates has also been noted in the literature.42
Appealing as this pathway might be, it suffers from a
potentially fatal flaw. If we assume that intermediate 24 is
formed regardless of whether X is Ph or H and that the
vinylcyclopropene approaches iridium to give 24 in the same
stereochemical sense in either case, Scheme 4 predicts that the
labeled atom Y (deuterium) should appear on opposite faces of
the metallacyclohexadiene product 25 or 28, depending on
(41) O’Connor, J. M.; Pu, L.; Rheingold, A. L.; Uhrhammer, R.; Johnson,
J. A. J. Am. Chem. Soc. 1989, 111, 1889-91.
(42) Albright, T. A.; Clemens, P. R.; Hughes, R. P.; Hunton, D. E.;
Margerum, L. D. J. Am. Chem. Soc. 1982, 104, 5369-79.
(40) Breitmaier, E.; Voelter, W. Carbon-13 NMR Spectroscopy, 3rd ed.;
VCH: New York, 1987; pp 147-155.

2266 J. Am. Chem. Soc., Vol. 122, No. 10, 2000
Hughes et al.
Scheme 5
90° rotation (and formal bond isomerization) of the cyclobuta-
diene in 30, as shown in path ii. Similar reinsertion and ring
opening leads to the appropriately rearranged product 28. The
retrocyclization/cyclization sequence to give a cyclobutadiene
and a carbene and their recombination is reminiscent of the
accepted mechanism for olefin metathesis.44 Provided that no
rotation occurs about the iridium-carbon double bond during
the rearrangement, this mechanism allows for the label Y to
maintain its spatial location relative to other ligands on the metal,
while accommodating the presence or absence of skeletal
rearrangement in the remainder of the carbon framework. The
driving force for this mechanism is less easy to appreciate,
however, since relief of steric interactions does not come into
play until the very end of the sequence. This mechanism also
requires that in path ii the cyclobutadiene ligand in 30 rotates
only by 90°, and not by 180°, to obtain the single observed
product.
However, while the required conspiracy of circumstances in
Scheme 5 seems improbable, we have been unable to devise
an alternative reaction pathway that accommodates both the
observed carbon and deuterium labeling patterns.
Substituent Shifts in Metallacyclohexadienes. On heating
at 90 °C in benzene solution, each of the metallacyclohexadiene
complexes with PMe3 ligands originally cis rearranged smoothly
to the corresponding trans-isomers 33-39. No scrambling of
isotopic labels was observed in any system under these
conditions; for example, rearrangement of 19 afforded 36, in
which the 13C-labels in the product remained adjacent (1JCC
)
40 Hz) and the corresponding 1H resonances showed one-bond
1
couplings to the labeled carbons (CH, JCH ) 148 Hz; CH2,
1JCH ) 123, 124 Hz). Similar to Bleeke’s observations,17,18,31
the 13C NMR resonance for the sp3 ring carbons of trans-
phosphine compounds all appear far upfield (ca. -10 ppm),
whereas those of the corresponding cis compounds appear at
ca. 20 ppm. We assume that dissociation of PMe3 followed by
recombination is responsible for this change in stereochemistry
at the metal, but we have done no experiments to verify this.
The most important conclusion is that stereochemical change
at the metal by ligand loss of some type does not result in any
rearrangement of the skeleton or the substituent pattern of the
metallacyclohexadienes.
whether the cyclopropene rearrangement occurs or not, i.e., if
the labeled carbons maintain their contiguity, Y must point up
in 25, in the sense shown; if the labeled carbons become
disconnected by the mechanism shown in Scheme 4, label Y
must point down in 28. The NOE results indicate that the
deuterium label in the CHD group is on the same side of the
metallacycle, regardless of whether skeletal reorganization has
occurred. So, either the mechanism in Scheme 4 is flawed, or
the vinylcyclopropene adopts two different approaches to iridium
in the initial binding and ring opening. We note that the
stereochemistry of cyclopropane ring formation and opening
has been assumed here to occur with retention of configuration
at carbon, effectively corresponding to a disrotatory opening
and closure of the type demonstrated previously for other
palladium-promoted methylenecyclopropane ring openings.42
Whatever the stereochemistry might be, in fact, as long as
closure and opening of the ring are the microscopic reverse of
each other, substituent Y must switch ring faces as a result.
To accommodate this awkward fact, we are obliged to
propose the more complicated mechanism outlined in Scheme
5, in which retrocyclization to give an alkylidene-cyclobuta-
diene intermediate is required. A similar initial ring opening of
the vinylcyclopropene gives intermediate 24. Coupling of bonds
bd as shown would give the “Dewar cyclohexadiene” 29.
Retrocyclization of 29 into cyclobutadiene and carbene frag-
ments would give 30. Two paths may then exchange the
hydrogen and phenyl substituents: following path i, the metal
would slide across the face of the cyclobutadiene to coordinate
the other double bond, giving 31. Reinsertion of the carbene
group leads to 32, and ring-opening produces rearranged product
28. Alternatively, the skeletal rearrangement may occur by a
However, further heating of the iridacyclohexadienes to 130
°C revealed yet another rearrangement process. Under these
conditions, complex 33 yields a new isomer 40, in which the
two phenyl groups occupy positions 1 and 4 on the iridacyclo-
hexadiene ring. The molecular structure of 40 has been
confirmed in a previously reported single-crystal X-ray diffrac-
tion study.15 The nature of this novel rearrangement can be
clearly defined using the available series of isotopically labeled
analogues. Transformation of the doubly 13C-labeled iridacycle
36 yields 40, in which the labeled carbons are still adjacent,
but in which the CH2 carbon atom is unlabeled; one labeled
carbon has a single H atom directly bound, and the other bears
2
3
no hydrogens. The absence of a triplet JCH or JCH also
demonstrates that neither labeled carbon is R or â to the CH2.
Given the known substitution pattern from the X-ray structure
of 40,15 these observations are consistent only with the presence
of 13C labels in 41 at positions 1 (CPh) and 2 (CH) in the
(43) Feher, F. J.; Green, M.; Orpen, A. G. J. Chem. Soc. Chem. Commun.
1986, 291-293.
(44) For examples, see: Grubbs, R. H.; Miller, S. J.; Fu, G. C. Acc.
Chem. Res. 1995, 28, 446-52. Calderon, N.; Lawrence, J. P.; Ofstead, E.
A. AdV. Organomet. Chem. 1979, 17, 449-492. Casey, C. P.; Burkhardt,
T. J. J. Am. Chem. Soc. 1974, 96, 7808-7809. Schrock, R. R. Science 1983,
219, 13-18.

Iridium-Promoted Reactions of C-C Bonds
J. Am. Chem. Soc., Vol. 122, No. 10, 2000 2267
Scheme 6
Figure 2. 1H NMR resonances for the CH2 group of 39 and 44: (a)
before heating, the sample is all isotopomer 39; (b) after 30 h at 120
°C it is a 1:1 mixture of 39:44.
also been reported.47 These results demonstrate that analogous
migrations from ligated carbon atoms may also be feasible, but
we must note that our data do not exclude the possibility that
the subsistent migrations occur by [1,5] sigmatropic shifts of
the hydrogen and the phenyl substituents instead of by their
traversal across the metal. Although phenyl migrations are less
common than hydrogen migrations, examples of overall [1,2],
[1,3], [1,5], and [1,7] phenyl migrations have been reported.48
While some driving force for the rearrangement of the
diphenylmetallacyclohexadiene ligands can arise from relief of
steric repulsions between the initially adjacent phenyl groups,
the same argument is clearly not valid for the triphenyl
analogues. Barring any isotope effects, the corresponding
substituent rearrangement of 37 is a degenerate automerization
whose availability is revealed using the doubly labeled com-
pound 39, which on heating does indeed undergo the same
metallacyclic ring. Rearrangement of monodeuteriomethylene
complex 35 to 42 occurs with preservation of the CHD group,
implying that the rearrangement is intramolecular, and the
corresponding conversion of 34 to 43 confirms that the
deuterium at position 3 is not involved in any migrations.
1
substituent migration process. Figure 2 shows the H NMR
These labeling experiments clearly demonstrate that this
rearrangement is not a skeletal transformation of the metallacycle
but must involve an interchange of substituents between the
two carbon atoms directly bonded to iridium, perhaps driven
by relief of steric repulsion between adjacent phenyl groups.
An attractive mechanism involves a sequence of R-elimination/
addition reactions, via iridabenzene intermediates, to accomplish
the observed transformation, as shown in Scheme 6. Reversible
migrations of H from R-carbon positions to metals are well-
known,45 as are iridabenzene species,20,29 but the unprecedented
step required by this mechanism is transfer of a phenyl
substituent from one R-carbon to the other. While we have no
direct evidence that this process occurs via an iridium-phenyl
intermediate, we note the well-precedented migrations of phenyl,
and other carbon substituents, from coordinated tertiary phos-
phorus centers to transition metals.46 Such an intermediate
presumably requires dissociation of a phosphine, or one arm of
the acac ligand, to free up the required coordination sites. An
example of a phenyl migration from silicon to platinum has
spectrum of the CH2 protons of doubly 13C labeled 39; the entire
population of geminal protons showed the expected one-bond
13C-H coupling of 124 Hz. As the sample was held at 120 °C,
the fraction of protons with this coupling dropped steadily, until
a 1:1 mixture of 39 and 44 was obtained after 30 h. This
rearrangement presumably occurs by the same mechanism
proposed for the diphenyl compounds (Scheme 6) and demon-
strates that relief of steric strain between adjacent substituents
is not required for such rearrangements to occur, since ∆G for
the triphenyl case must be zero.
Conclusions
In summary, the ring opening of triphenylvinylcyclopropenes
by [Ir(PMe3)2(acac)] has been shown to involve a skeletal
rearrangement possibly through a cyclobutadiene-carbene
(47) Chang, L. S.; Johnson, M. P.; Fink, M. J. Organometallics 1991,
10, 1219-1221.
(48) (a) [1,5] migrations: Cowley, A. H.; Hall, S. W.; Jones, R. A.;
Nunn, C. M. J. Chem. Soc., Chem. Commun. 1988, 867-868. Oldaker, G.
B., III; Perfetti, T. A.; Ogliaruso, M. A. J. Org. Chem. 1980, 45, 3910-
3912. Bramley, R. K.; Grigg, R.; Guilford, G.; Milner, P. Tetrahedron 1973,
29, 4159-4167. (b) Migrations from PPh3: ref 46, and: Beck, W.; Keubler,
M.; Leidl, E.; Nagel, U.; Schall, M.; Cenni, S.; Del Buttero, P.; Licandro,
E.; Maiorana, S.; Chiesi Villa, A. J. Chem. Soc., Chem. Commun. 1981,
446-448. Vierling, P.; Riess, J. G.; Grand, A. J. Am. Chem. Soc. 1981,
103, 2466-2467. (c) Reductive eliminations: Bassetti, M.; Sunley, G. J.;
Maitlis, P. M. J. Chem. Soc., Chem. Commun. 1988, 1012-1013. Fanchetti,
G.; Floriani, C. J. Chem. Soc., Chem. Commun. 1974, 516-517. Burt, J.
C.; Knox, S. A. R.; McKinney, R. J.; Gordon, A. J. Chem. Soc., Dalton
Trans. 1977, 1-4. (d) [1,3] migration: Eaborn, C.; Lickiss, P. D.; Najim,
S. T.; Stanczyk, W. Z. J. Chem. Soc., Chem. Commun. 1987, 1461-1462.
(e) [1,7] migration: Shen, K, McEwen, W. E.; Wolf, A. P. Tetrahedron
Lett. 1969, 827-831.
(45) For examples involving iridium, see ref 20, and: Burk, M. J.;
McGrath, M. P.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 620. Fryzuk,
M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc. 1985, 107, 6708-
6710. Crocker, C.; Empsall, H. D.; Errington, R. J.; Hyde, E. M.; McDonald,
W. S.; Markham, R.; Norton, M. C.; Shaw, B. L.; Weeks, B. J. Chem.
Soc., Dalton Trans. 1982, 1217-1224.
(46) Morita, D. K.; Stille, J. K.; Norton, J. R. J. Am. Chem. Soc. 1995,
117, 8576-81. Garrou, P. E. Chem. ReV. 1985, 85, 171-185. Dubois, R.
A.; Garrou, P. E.; Lavin, K. D.; Allcock, H. R. Organometallics 1984, 3,
649-650; 1986, 5, 460-466. Dubois, R. A.; Garrou, P. E. Organometallics
1986, 5, 466-473. Jung, C. W.; Fellmann, J. D.; Garrou, P. E. Organo-
metallics 1983, 2, 1042-1044. A theoretical treatment appears: Ortiz, J.
V.; Havlas, Z.; Hoffmann, R. HelV. Chim. Acta 1984, 67, 1-17.

2268 J. Am. Chem. Soc., Vol. 122, No. 10, 2000
Hughes et al.
22.3 mmol, 1 equiv) was condensed into the tube. The tube was sealed
(Youngs O-ring valve), and its contents were allowed to thaw
(CAUTION: PRESSURE BUILD-UP!) and then heated to 80 °C while
being agitated on a Parr hydrogenator for 30 min. Hydroquinone (10
mg) was added to the cooled mixture, and the product was distilled to
1
give 4.96 g (70%) labeled vinyltin (bp: 50-52 °C, 0.04 mmHg). H
NMR (CDCl3): δ 6.43 (dddd, 1H, JHH ) 20.3, 13.6, JCH ) 144.0, 4.3,
HR), 6.14 (dddd, 1H, JHH ) 14.1, 3.7, JCH ) 153.8, 5.2, Htrans), 5.63
(dddd, 1H, JHH ) 20.6, 3.8, JCH ) 155, 1.4, Hcis), 0.75-1.60 (m, 27H,
Bu). 13C NMR (CDCl3): δ 139.31 (ddd, JCC ) 59.1, JCH ) 144.5, 5.0,
JSnC ) 355.8/372.1 CR), 133.62 (dddd, JCC ) 59.0, JCH ) 154.4, 152.4,
4.8, Câ). 119Sn{1H} NMR (CDCl3): δ -119.6 (d, JSnC ) 371.9).
trans-3-(â-Deuteriovinyl)-1,2-diphenyl-1-cyclopropene, 11. n-Bu-
tyllithium (3.6 mL, 2.3 M in hexanes, 8.3 mmol, 1.0 equiv) was added
to a -78 °C solution of bis(tributylstannyl)ethylene (4.4 mL, 8.2 mmol,
1.0 equiv) in THF (60 mL). After stirring for 1.5 h at -78 °C, the
yellow solution was quenched with DOAc (0.48 mL, 8.2 mmol, 1.0
equiv), and a second equivalent of BuLi (3.6 mL) was added. The
yellow solution was stirred 1.5 h at -78 °C, then treated with MgBr2/
ether complex (3.8 mL, 10.0 mmol, 1.2 equiv) and allowed to warm
to room temperature with stirring. The straw-colored solution was
cooled back to -78 °C and added to a -78 °C slurry of 1,2-diphenyl-
1-cyclopropenyl fluoroborate (1.49 g, 5.36 mmol, 0.65 equiv) in THF
(60 mL). The mixture was stirred for 8 h at room temperature, to give
an orange solution, and quenched with aqueous ammonium chloride
(90 mL, 20%), and the layers were separated. The aqueous layer was
extracted with ether (3 × 30 mL); the combined organic layers were
washed with water (3 × 50 mL) and brine (1 × 10 mL). Drying over
MgSO4 and evaporation gave an orange oil which was passed through
a flash chromatography column55 (5 × 30 cm SiO2) with hexanes (2
L). Bu4Sn eluted first, followed by the vinylcyclopropene. Evaporation
1
Figure 3. Numbering scheme used for the H and 13C NMR data of
metallacyclohexadienes.
complex en route to iridacyclohexadienes. In contrast, this
rearrangement is not observed with the analogous diphenyl
compounds. On heating, iridacyclohexadienes with cis-phos-
phines convert to their trans-phosphine isomers, which on
further heating undergo a different rearrangement, in which the
geminal R-hydrogens and R′-phenyl group exchange on an
unaltered cyclic framework.
Experimental Section
General Procedures. All reactions were performed in oven-dried
glassware, using standard Schlenk techniques, under an atmosphere of
nitrogen which had been deoxygenated over BASF catalyst and dried
over Aquasorb. Hydrocarbon reaction solvents and ethers were distilled
under nitrogen from benzophenone ketyl, and halogenated solvents and
methanol, from CaH2, 4 Å molecular sieves, or 10% Na/Pb alloy.
Aromatic and unsaturated components of 35-65 °C petroleum ether
were removed before distillation by prolonged standing over H2SO4
(concentrated), followed by washing with Na2CO3 (10% aqueous). 1H
and H{31P} (300 MHz), H{1H} (46.1 MHz), 13C and 13C{1H} (75.4
MHz), 119Sn{1H} (112 MHz), and 31P {1H} (121 MHz) NMR spectra
were recorded on a Varian XL-300 spectrometer at 25 °C. Chemical
1
2
1
gave 11 (570 mg, 48%) as a cloudy white oil. H NMR (CDCl3): δ
7.23-7.80 (m, 10H, Ph), 5.64 (dd, 1H, J ) 17.0, 7.8, HR), 5.33 (d,
1H, J ) 17.4, Hcis), 2.78 (d, 1H, J ) 7.8, Hring). 2H{1H} NMR
(CHCl3): δ 5.07 (Dtrans).
shifts are reported as ppm downfield of either TMS (1H, H, and 13C
2
NMR, referenced to the solvent), neat Me4Sn (119Sn, referenced to
external neat Bu4Sn: -12.0 ppm), or external 85% H3PO4 (31P NMR).
Metallacyclohexadiene resonances are assigned using the numbering
scheme of Figure 3; H5a and H5b are respectively on the opposite and
the same face of the ring as the axial phosphine. Coupling constants
3-Deutero-1,2-diphenyl-3-vinyl-1-cyclopropene, 16. â-Deuterio-
phenylacetylene was converted to deuteriodiphenylcyclopropenyl fluo-
roborate, which was alkylated to give diphenylvinylcyclopropene 16,
in a manner analogous to the preparation of the protic vinylcyclopropene
5.35,49 16: white crystals from ether, mp: 32-32.5 °C. 1H NMR
(CDCl3): δ 7.19-7.71 (m, 10H, Ph), 5.64 (dd, 1H, JHH ) 17.2, 10.1,
HR), 5.34 (dd, 1H, JHH ) 17.0, 1.7, Htrans), 4.96 (dd, 1H, JHH ) 10.2,
are reported in hertz; tin satellites are reported using the notation “J117Sn
119Sn”. IR spectra were recorded on a Bio-Rad Digilab FTS-40 Fourier
transform infrared spectrophotometer. Melting points of samples in
capillaries sealed under vacuum were obtained using a Thomas-Hoover
device, and are uncorrected. Elemental analyses were performed by
Spang (Eagle Harbor, MI).
/
J
2
1.8, Hcis). H{1H} NMR (CHCl3): δ 2.76 (s, Dring).
1,2,3-Triphenyl-3-[13C2]vinyl-1-cyclopropene, 18. n-Butyllithium
(2.3 mL, 2.4 M (hexanes), 5.6 mmol, 1 equiv) was added to a -78 °C
solution of tributyl[13C2]vinyltin (1.80 g, 5.64 mmol, 1 equiv) in THF
(50 mL). After standing for 1 h at -78 °C, the yellow solution was
treated with magnesium bromide/ether complex (2.6 mL, 7.0 mmol,
1.2 equiv) and allowed to warm to room temperature. After stirring
for 15 min at room temperature, the colorless solution was cooled to
-78 °C and added to a -78 °C suspension of 1,2,3-triphenylcyclo-
propenyl bromide (0.991 g, 2.87 mmol, 0.5 equiv) in THF (50 mL).
The mixture was allowed to warm to room temperature and was stirred
for 6 h, giving a pale yellow solution. The reaction mixture was
quenched with aqueous ammonium chloride (40 mL, 20%), and the
layers were separated. The aqueous layer was extracted with ether (3
× 25 mL), and the combined organic layers were washed with water
(3 × 25 mL) and brine (2 × 10 mL) and then dried over MgSO4.
Flash chromatography55 (3 × 27 cm SiO2, 2 L hexanes) of the orange
oil obtained on solvent removal gave Bu4Sn followed by the vinyl-
cyclopropene. Evaporation of the fractions containing the vinylcyclo-
propene afforded 18 as soapy white crystals (326 mg, 38%). 1H NMR
(C6D6): δ 6.95-7.75 (m, 15 H, Ph), 6.70 (ddd, 1H, JHH ) 17.2, 10.4,
JCH ) 151.9, HR), 5.33 (dddd, 1H, JHH ) 17.2, 1.6, JCH ) 153.9, 3.3,
Hcis), 5.12 (ddd, 1H, JHH ) 10.3, 1.5, JCH ) 158.6, Htrans). 13C NMR
(C6D6): δ 142.37 (ddd, JCC ) 70.5, JCH ) 152.1, 2.4, CR), 114.60 (ddd,
JCC ) 70.4, JCH ) 158.4, 154.2, Câ).
n-Butyllithium (2.5 M in hexanes), vinylmagnesium bromide (1 M
in THF), deuterioacetic acid, and tributyltin hydride were purchased
from Aldrich; azobis(isobutyronitrile) (AIBN) was from Alfa, acetylene-
13C2 was from Cambridge Isotope Laboratories, and trimethylphosphine
was from Strem. 1,2-Diphenyl-3-vinylcyclopropene35 (5), 1,2,3-triphen-
yl-3-vinylcyclopropene49 (8), trans-Bis(tributylstannyl)ethylene32,33 (13),
triphenylcyclopropenyl bromide,50 diphenylcyclopropenyl fluorobor-
ate,36,51 â-deuteriophenylacetylene,37 MgBr2/ether complex,52 [Ir(C8H14)2-
Cl]2 (C8H14 ) cis-cyclooctene),53 and [Ir(C2H4)2(acac)]54 were prepared
by literature routes. Tl(acac) (acac ) acetylacetonate) was sublimed
before use.
Tributyl[13C2]vinyltin. The labeled vinyltin was prepared by a
modification of Smolin’s procedure.38 A solution of AIBN (26.6 mg)
in benzene (10 mL) was frozen in a 100 mL heavy-walled reaction
tube. Tributyltin hydride (6.0 mL, 22 mmol, 1 equiv) was introduced,
then the system was evacuated and acetylene-13C2 (500 mL at STP,
(49) Zimmerman, H. E.; Aasen, S. M. J. Org. Chem. 1978, 43, 1493-
1506.
(50) Breslow, R.; Chan, H. W. J. Am. Chem. Soc. 1961, 83, 2367-2375.
(51) Padwa, A.; Pulwer, M. J.; Blacklock, T. J. Org. Synth. 1981, 60,
53-57.
(52) Maercker, A.; Roberts, J. D. J. Am. Chem. Soc. 1966, 88, 1742-
1759.
trans-3-(â-Deuteriovinyl)-1,2,3-triphenyl-1-cyclopropene, 12. n-
Butyllithium (4.6 mL, 2.81 M (hexanes), 13 mmol, 1 equiv) was added
(53) Herede, J. L.; Lambert, J. C.; Senoff, C. V. Inorg. Synth. 1974, 15,
18-20.
(54) Van Gaal, H. L. M.; Van der Ent, A. Inorg. Chim. Acta 1973, 7,
653-659.
(55) Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923-
2925.

Iridium-Promoted Reactions of C-C Bonds
J. Am. Chem. Soc., Vol. 122, No. 10, 2000 2269
to a -78 °C solution of trans-bis(tributylstannyl)ethylene (7.0 mL, 13
mmol, 1.0 equiv) in THF (90 mL). The resulting pale yellow solution
was stirred for 1 h at -78 °C and then quenched with DOAc (0.75
mL, 13 mmol, 1 equiv) and warmed to room temperature. The colorless
mixture was cooled back to -78 °C and treated with a second equivalent
of BuLi (4.6 mL, 13 mmol). After stirring for 1 h at -78 °C, the yellow
mixture was treated with MgBr2/ether complex (6.0 mL, 16 mmol, 1.2
equiv) and allowed to warm to room temperature, giving a clear yellow
solution. The solution was added to a -78 °C slurry of 1,2,3-
triphenylcyclopropenyl bromide (2.26 g, 6.56 mmol, 0.5 equiv) in THF
(90 mL), warmed to room temperature, and stirred 8 h to give a pale
yellow solution. The reaction was quenched with aqueous ammonium
chloride (100 mL, 20%), and the layers were separated. The aqueous
layer was extracted with ether (3 × 50 mL); the combined organic
layers were washed with water (3 × 50 mL) and brine (2 × 10 mL).
Drying over MgSO4 and evaporation left a yellow oil, which was
purified by flash chromatography55 (SiO2, 5 × 16 cm). Elution with
hexanes (2.5 L) gave Bu4Sn, followed by the desired vinylcyclopropene
(1.00 g, 50% soapy white crystals after evaporation). 1H NMR (C6D6):
δ 6.98-7.68 (m, 15 H, Ph), 6.70 (d, 1H, J ) 17.2, HR), 5.32 (d, 1H,
and 33, and trans-acetylacetonato(1,5-η-1,4-diphenyl-1,3-pentadi-
enediyl)bis(trimethylphosphine)iridium(III), 40. (a) General Pro-
cedure. An orange solution of [Ir(PMe3)2(acac)] (29 mg, 66 µmol) and
diphenylvinylcyclopropene 5 (15 mg, 69 µmol, 1.0 equiv) in C6D6 (0.6
mL) was freeze-pump-thaw degassed and sealed in an NMR tube
under vacuum. After standing for 3 d at room temperature, the sample
had converted entirely to 9. The sample was then heated at 95 °C for
33 h, giving a red solution containing 33. Further heating at 120 °C
for 45 h gave 40.
9: 1H NMR (C6D6 ): δ 6.52-7.89 (m, 10 H, Ph), 6.41 (dd, 1H,
JHH ) 10.0, 3.0, H3), 6.03 (dddd, 1H, JHH ) 9.3, 6.3, 3.2, JHP ) 16.3,
H4), 5.06 (s, 1H, acac CH), 3.97 (dddt, 1H, JHH ) 16.7, 3.2, 3.2, JHP
) 9.2, 3.8, H5a), 2.46 (dq, 1H, JHH ) 16.1, 6.3, JHP ) 6.3, 6.3, H5b),
1.76 (s, 3H, acac Me), 1.67 (s, 3H, acac Me), 1.32 (d, 9H, JHP ) 10.6,
axial PMe3), 0.59 (d, 9H, JHP ) 7.4, equatorial PMe3). 31P{1H} NMR
(C6D6 ): δ -37.2 (d, JPP ) 7.0, equatorial PMe3), -42.9 (d, JPP ) 6.8,
axial PMe3). IR (KBr, cm-1): 2914 m, 1584 s, 1515 s, 960 s, 947 s.
33: 1H NMR (C6D6 ): δ 6.63-7.95 (m, 10H, Ph), 6.41 (dt, 1H, JHH
1
) 10.4, 1.9, H3), 5.42 (dt, H, JHH ) 10.4, 4.6, H4), 4.90 (s, 1H, acac
CH), 3.37 (ddt, 2H, JHH ) 4.2, 2.0, JHP ) 13.5, H5), 1.59 (s, 3H, acac
Me), 1.43 (s, 3H, acac Me) 1.06 (virtual t, 18 H, JHPobs ) 3.5). 31P{1H}
NMR (C6D6 ): -25.76 (s, PMe3).
2
J ) 17.3, Hcis). H{1H} NMR (C6H6): δ 5.14 (br, Dtrans).
1,2-Diphenyl-3-[13C2]vinyl-1-cyclopropene, 17. A -78 °C solution
of [13C2]vinyltributyltin (2.01 g, 6.30 mmol) in THF (50 mL) was treated
with n-butyllithium (2.6 mL, 2.43 M in hexanes, 6.3 mmol, 1.0 equiv).
After stirring for 1.5 h at -78 °C, the yellow mixture was treated with
MgBr2/Et2O complex (2.9 mL, 8.1 mmol, 1.3 equiv) and warmed to
room temperature, giving a colorless solution. The mixture was cooled
to -78 °C and added dropwise to a -78 °C suspension of diphenyl-
cyclopropenyl fluoroborate (1.14 g, 4.09 mmol, 0.65 equiv) in THF
(50 mL) The cloudy mixture was warmed to room temperature, stirred
for 9 h to give a yellow solution, and then quenched with aqueous
NH4Cl (20 mL, 20%). The aqueous layer was extracted with ether (3
× 25 mL), and the combined organic layers were washed with water
(3 × 25 mL) and brine (2 × 10 mL). The extracts were dried over
MgSO4 and evaporated, giving an orange oil, which was purified by
flash chromatography55 (3 × 33 cm silica, 400 mL petroleum ether).
Removal of the solvent under vacuum yielded 17 (707 mg, 78%) as a
40: 1H NMR (C6D6): δ 6.85-7.84 (m, 10H, Ph), 6.70 (dt, 1H, JHH
) 6.5, 1.4, H3), 6.59 (dt, 1H, JHH ) 6.9, JHP ) 2.3, H2), 4.96 (s, 1H,
acac CH), 3.69 (td, 2H, JHH ) 1.4, JHP ) 13.1, H5), 1.61 (s, 1H, acac
Me), 1.56 (s, 1H, acac Me), 0.97 (virtual t, 18 H, JHPobs ) 3.4, PMe3).
13C NMR (C6D6 ): δ 185.32 (s, acac CO), 184.88 (s, acac CO), 154.84
(s, C4 or Cipso), 145.62 (s, C4 or Cipso), JCH ) 144, JCP ) 2, C3), 140.51
(tdd, JCH ) 8, 2, JCP ) 10, C1), 134.87 (s, C4 or Cipso), 130.13 (dt, JCH
) 148, JCP ) 4, C2), 129.28 (dt, JCH ) 144, JCP ) 2, C3), 128.75 (dt,
JCH ) 153, 7, Cmeta), 128.23 (dd, JHH ) 142, 9, Cortho), 126.62 (dd, JCH
) 154, 9, Cortho), 125.58 (dt, JCH ) 156, 8, Cmeta), 125.26 (dt, JCH
)
152, 7, Cpara), 124.26 (dt, JCH ) 151, 8, Cpara), 100.69 (d JCH ) 155,
acac CH), 28.15 (q, JCH ) 127, acac Me), 27.85 (q, JCH ) 126.6, acac
Me), 10.78 (qt, JCH ) 130, JCP ) 16, PMe3), -10.27 (tt, JCH ) 128,
JCP ) 6, C5). 31P{1H} NMR (C6D6): δ -29.46 (s, PMe3).
(b) Isolation of 33. [Ir(PMe3)2(acac)] (0.169 g, 0.381 mmol) and 5
(0.083 g, 0.381 mmol) were placed in a nitrogen-purged 50 mL Schlenk
flask which was then equipped with a reflux condenser. The reaction
vessel was purged again and C6H6 (30 mL) was added. The resultant
bright yellow solution was refluxed overnight with little color change.
Removal of solvent in vacuo gave a yellow-brown oil. The oil was
extracted with 3 mL of diethyl ether/petroleum ether (2/1) and the
extract brought to dryness. The dried extract was dissolved in 5 mL of
refluxing petroleum ether, filtered, and concentrated to 2 mL. Cooling
to -20 °C gave 30 mg of 33 as dark yellow crystals. A second crop of
crystals (30 mg) was isolated from the mother liquor in a similar manner
(yield, 24%). 1H, 31P NMR identical to those reported above. 13C{1H}
NMR (CDCl3, selected JCH values and multiplicities included in square
1
pale yellow oil. H NMR (CDCl3): δ 7.32-7.76 (m, 10H, Ph), 5.67
(dddd, 1H, JHH ) 17.2, 10.1, 7.8, JCH ) 152.2, HR), 5.38 (dddd, 1H,
JHH ) 17.1, 1.9, JCH ) 153.8, 3.3, Hcis), 5.00 (ddd, 1H, JHH ) 10.2,
1.8, JCH ) 158.4, Htrans), 2.80 (ddd, 1H, JHH ) 7.8, JCH ) 8.7, 3.2,
H
ring). 13C NMR (CDCl3): δ 143.77 (dddd, JCC ) 69.0, JCH ) 152.2,
8.8, 3.3, CR), 112.26 (dddd, JCC ) 68.3, JCH ) 153.6, 158.2, 3.2, Câ).
Note that both the H and 13C NMR spectra for this compound show
1
slight second-order effects; the coupling constants reported are averages
of the values observed, and accord well with the absolute value of those
obtained by simulation.39
[Ir(PMe3)2(acac)]. [IrCl(C8H14)2]2 (537 mg, 1.20 mmol Ir) was stirred
for 2 h with Tl(acac) (361 mg, 1.19 mmol, 1.0 equiv) in methylene
chloride (10 mL) at room temperature. The resultant mustard yellow
suspension was evaporated to dryness and extracted with petroleum
ether until no more yellow color was discharged (6 × 10 mL). The
extracts were filtered through Celite and diluted to 90 mL. A solution
of PMe3 (0.25 mL, 2.5 mmol, 2.0 equiv) in petroleum ether (30 mL)
was added dropwise to the diluted extracts over 20 min with vigorous
stirring, causing the mixture to darken slightly and to grow turbid. After
stirring overnight, the orange mixture was passed through Celite,
concentrated to 3 mL, and cooled slowly to -78 °C. The solid which
precipitated was isolated, rinsed with petroleum ether (1 mL), and dried
under vacuum, to give [Ir(PMe3)2(acac)] as dark orange crystals (388
mg, 78%). This solid decomposes rapidly in air. Calculated for
2
brackets): δ 185.67 (s, acac CO), [quint, JCH ) 5]); 184.24 (s, acac
CO, [quint, 2JCH ) 5]), 135.04 (s, C3, [d, JCH ) 147]), 133.83 (virtual
t, JCP ) 9.8, C1), 134.18 (virtual t, JCP ) 3.8, C4), 128.75 (br s, C4, [d,
JCH ) 147]), 151.16, 148.71, 129.81, 126.64, 125.10, 123.22, 122.33,
1
(s, phenyl C’s), 100.43 (s, acac CH, [d, JCH ) 154]), 27.95 (s, acac
CH3 [qd, 1JCH ) 126, 3JCH ) 2]), 27.74 (s, acac CH3 [qd, 1JCH ) 126,
3JCH ) 2]), 10.93 (virtual t, JCP ) 16.4, PMe3, [q, JCH ) 129 Hz]),
-10.20 (virtual t, JPC ) 6.2, C5, [t, JCH ) 127 Hz]). Calculated for
C28H39O2P2Ir: 50.81% C, 5.95% H. Found: 50.80% C, 6.06% H.
(c) Isolation of 40. An orange solution of [Ir(PMe3)2(acac)] (38 mg,
86 µmol) and diphenylvinylcyclopropene 5 (19 µL, 19 mg, 86 mmol,
1.0 equiv) in C6D6 (0.3 mL) was heated at 125 °C for 28 h, by which
time conversion to 40 was complete. The sample was evaporated, and
crystals suitable for diffraction were grown by slow evaporation of an
ether solution. Mp: 138-140 °C. 1H NMR data were identical to those
reported above.
1
C11H25O2P2Ir: 29.79% C, 5.69% H. Found: 29.36% C, 5.88% H. H
NMR (C6D6): δ 5.39 (s, 1H, CH), 1.64 (s, 6H, acac Me), 1.38 (filled
d, 18 H, Jobs ) 9.4, PMe3). 13C NMR (C6D6): δ 181.01 (quint, JCH
5.0, CO), 102.04 (d(sept), JCH ) 155.9, 2.4, CH), 27.81 (qdt, JCH
)
)
126.1, 3.8, JCP ) 3.1, acac Me), 18.83 (br q, JCH ) 127.1, PMe3). In
Geminally Deuterated cis- and trans-Acetylacetonato(1,5-η-5-
deutero-1,2-diphenyl-1,3-pentadienediyl)bis(trimethylphosphine)-
iridium(III), 22 and 35, and trans-Acetylacetonato(1,5-η-5-
deutero-1,4-diphenyl-1,3-pentadienediyl)bis(trimethylphosphine)-
iridium(III), 42. A solution of [Ir(PMe3)2(acac)] (18 mg, 20 µmol/
sample) and trans-deuterated diphenylvinylcyclopropene 11 (9.4 mg,
the 13C{1H} NMR spectrum, the PMe3 peak appears as a five-line AA′X
pattern, which may be simulated with JCP ) 45, JCP′ ) 0, and JPP′
)
17.39 IR (KBr, cm-1): 1576 s, 1515 s, 1397 s, 973 s, 947 s.
Protic Compounds cis- and trans-Acetylacetonato(1,5-η-1,2-
diphenyl-1,3-pentadienediyl)bis(trimethylphosphine)iridium(III), 9

2270 J. Am. Chem. Soc., Vol. 122, No. 10, 2000
Hughes et al.
21 µmol/sample, 1.0 equiv) in benzene (1.4 mL) was loaded equally
into two NMR tubes. The contents of one tube was freeze-dried and
dissolved in C6D6 (0.7 mL), then both tubes were freeze-pump-thaw
degassed and sealed under vacuum. The tubes were heated as described
for the protic compounds above (procedure a), with similar observations.
22: 1H NMR (C6D6): δ 6.74-7.86 (m, 10H, Ph), 6.44 (d, 1H, JHH
) 10.0, H3), 6.04 (ddd, 1H, JHH ) 10.1, 6.3, JHP ) 16.0, H4), 5.06 (s,
1H, acac CH), 2.45 (br d, 1H, JHH ) 6.6, H5b), 1.72 (s, 3H, acac Me),
2.63 (s, 3H, acac Me), 1.28 (d, 9H, JHP ) 10.7, axial PMe3), 0.56 (d,
124, H5b), 1.76 (s, 3H, acac Me), 1.66 (s, 3H, acac Me), 1.32 (d, 9H,
JHP ) 10.6, axial PMe3), 0.59 (d, 9H, JHP ) 7.2, equatorial PMe3). 13
C
NMR (C6D6): δ 131.50 (ddtdd, JCC ) 40.8, JCP ) 3.2, 1.4, JCH
)
146.9, 8.8, C4), 18.93 (tdddd, JCC ) 40.8, JCP ) 90.5, 7.2, JCH ) 123.1,
9.2, C5). 31P{1H} NMR (C6D6): δ -36.81 (dd, JPP ) 7.0, JCP ) 90.5,
3.1, equatorial PMe3), -42.56 (t, JPP ) JCP ) 7.2, axial PMe3).
36: 1H NMR (C6D6): δ 6.75-7.89 (m, 10H, Ph), 6.45 (tt, 1H, JHH
) 10.8, 2.2, JCH ) 10.8, H3), 5.46 (dm, 1H, JCH ) 142, H4), 4.93 (s,
1H, acac CH), 3.41 (dm, 2H, JCH ) 122, H5), 1.63 (s, 3H, acac Me),
1.47 (s, 3H, acac Me), 1.10 (virtual t, 18H, JHPobs ) 3.4, PMe3). 13C
NMR (C6D6): 129.52 (br ddt, JCH ) 146.5, JCC ) 40.4, JCP ) 2.4,
C4), -9.69 (tdt, JCH ) 123.6, 6.7, JCC ) 40.3, JCP ) 6.1, C5). 31P{1H}
NMR (C6D6): δ -25.57 (dd, JCP ) 6.1, 2.4, PMe3).
2
9H, JHP ) 7.2, equatorial PMe3). H{1H} NMR (C6H6): δ 3.92 (br,
1
D5a). 35: H NMR (C6D6): δ 6.72-7.74 (m, 10H, Ph), 6.42 (dd, 1H,
JHH ) 10.4, 2.2 H3), 5.41 (ddd, 1H, JHH ) 10.5, 4.4, JHP ) 0.8, H4),
4.90 (s, 1H, acac CH), 3.34 (m, 1H, H5), 1.60 (s, 3H, acac Me), 1.42
2
(s, 3H, acac Me), 1.06 (m, 18H, PMe3). H{1H} NMR (C6H6): 3.32
1
41: H NMR (C6D6): δ 6.79-7.89 (m, 10H, Ph), 6.75 (br t, 1H,
(br, D5). 31P{1H} NMR (C6D6): δ -25.54 (s, PMe3), -25.87 (s, PMe3).
JHH ) JCH ) 7.9, H3), 6.63 (ddq, 1H, JHH ) 6.9, JCH ) 146.7, 2.3, JHP
) 2.3, H2), 4.99 (s, 1H, acac CH), 3.72 (tq, 2H, JHH ) JCH ) 2.1, JHP
) 13.2, H5), 1.65 (s, 3H, acac Me), 1.60 (s, 3H, acac Me), 1.00 (virtual
42: 1H NMR (C6D6): 6.82-7.88 (m, 10H, Ph), 6.71 (dd, 1H, JHH
)
6.9, 1.5, H3), 6.61 (dd, 1H, JHH ) 6.9, JHP ) 2.4, H2), 4.95 (s, 1H, acac
CH), 3.67 (apparent tdd, 1H, JHH ) 1.5, JHPobs ) 12.4, 5.3, H5), 1.62
(s, 3H, acac Me), 1.56 (s, 3H, acac Me), 0.97 (m, 18H, PMe3). 2H{1H}
NMR (C6H6): δ 3.62 (br, D5). 31P{1H} NMR (C6D6): δ -26.47 (br s,
PMe3).
t, 18H, JHPobs ) 3.6, PMe3). 13C NMR (C6D6): δ 140.51 (dtdd, JCC
63.1, JCH ) 8.4, 1.9, JCP ) 9.9, C1), 130.20 (ddt, JCC ) 63.0, JCH
)
)
146.9, JCP ) 3.6, C2). 31P{1H} NMR (C6D6): δ -24.85 (dd, JCP ) 9.9,
3.6, PMe3).
Ring-Deuterated Isomers cis- and trans-Acetylacetonato(1,5-η-
3-deutero-1,2-diphenyl-1,3-pentadienediyl)bis(trimethylphosphine)-
iridium(III), 21 and 34. A solution of [Ir(PMe3)2(acac)] (6.4 mg, 14
µmol) and 16 (3.8 mg, 17 µmol, 1.2 equiv) in C6D6 (1 mL) was sealed
in an NMR tube under vacuum. The yellow solution darkened slightly
Protic Compounds cis- and trans-(Acetylacetonato)bis(trimeth-
ylphosphine)(1,5-η-1,2,4-triphenyl-1,3-pentadienediyl)-
iridium(III), 10 and 37. (a) General Procedure. An orange solution
of [Ir(PMe3)2(acac)] (24 mg, 54 µmol) and triphenylvinylcyclopropene
8 (17 mg, 57 µmol, 1.1 equiv) in C6D6 (0.5 mL) was loaded into an
NMR tube, freeze-pump-thaw degassed, and sealed under vacuum.
After 2 d at room temperature, conversion to 10 was complete. The
sample was then heated for 35 h at 100 °C, during which time 37 was
formed.
1
as 21 formed over 3 d at room temperature. After H and 31P NMR
spectra were obtained, the sample was evaporated and redissolved in
C6H6 for 2H NMR. 1H NMR (C6D6): δ 6.55-7.87 (m, 10 H, Ph), 6.08
(ddd, 1H, JHH ) 6.2, 3.1, JHP ) 16.2, H4), 5.10 (s, 1H, acac CH), 4.02
10: 1H NMR (C6D6): δ 6.59-7.86 (m, 15H, Ph), 6.83 (dd, 1H, JHH
) 3.0, 1.2, H3), 5.15 (s, 1H, acac CH), 4.42 (ddt, 1H, JHH ) 15.9, 3.0,
JHP ) 9.4, 3.0, H5a), 2.81 (ddd, 1H, JHH ) 16.1, JHP ) 7.6, 5.6, H5b),
1.78 (s, 3H, acac Me), 1.68 (s, 3H, acac Me), 1.27 (d, 9H, JHP ) 10.1,
axial PMe3), 0.59 (d, 9H, JHP ) 7.4, equatorial PMe3). 31P{1H} NMR
(C6D6): δ -35.88 (d, JPP ) 8.2, axial PMe3), -42.76 (d, JPP ) 8.1,
equatorial PMe3).
(ddt, 1H, JHH ) 16.6, 2.9, JHP ) 9.0, 2.9, H5a), 2.52 (ddt, 1H, JHH
)
16.7, 6.2, JHP ) 7.4, 6.2, H5b), 1.75 (s, 3H, acac Me), 1.67 (s, 3H, acac
Me), 1.32 (d, 9H, JHP ) 10.4, axial PMe3), 0.59 (d, 9H, JHP ) 7.4,
equatorial PMe3). 2H{1H} NMR (C6H6): δ 6.42 (br, D3). 31P{1H} NMR
(C6D6): δ -36.60 (d, 1P, JPP ) 6.8, equatorial PMe3), -42.38 (d, 1P,
JPP ) 7.0, axial PMe3).
The NMR sample of 21 was evaporated, redissolved in C6D6 (0.5
mL), and sealed under vacuum. After 16 h at 80 °C, 1H and 31P NMR
showed the sample to be completely converted to 34. The sample was
evaporated and redissolved in C6H6 for 2H NMR. 1H NMR (C6D6): δ
6.73-7.76 (m, 10 H, Ph), 5.49 (m, 1H, H4), 4.92 (s, 1H, acac CH),
3.43 (td, 2H, JHH ) 4.4, JHP ) 13.5, H5), 1.63 (s, 3H, acac Me), 1.47
1
37: H NMR (C6D6): δ 6.85-7.81 (m, 15H, Ph), 6.79 (t, 1H, JHH
) 1.4, H3), 4.92 (s, 1H, acac CH), 3.71 (dt, 2H, JHH ) 1.4, JHP ) 12.3,
H5), 1.61 (s, 3H, acac Me), 1.47 (s, 3H, acac Me), 1.02 (virtual t, 18H,
JHPobs ) 3.5, PMe3). 13C NMR (CDCl3): δ 185.70 (s, acac CO), 184.91
(s, acac CO), 138.12 (t, JCP ) 11.3, C1), 135.20 (d, JCH ) 149.8, C3),
100.70 (d, JCH ) 154.3, acac CH), 27.86 (q, JCH ) 130.3, acac Me),
27.73 (q, JCH ) 130.3, acac Me), 10.79 (qt, JCH ) 128.4, JCP ) 16.3,
PMe3), -8.81 (tt, JCH ) 110.8, JCP ) 6.3, C5). Other resonances could
not be assigned unambiguously. 31P{1H} NMR (C6D6): δ -25.91 (s,
PMe3).
2
(s, 3H, acac Me), 1.10 (virtual t, 18H, JHPobs ) 3.3, PMe3). H{1H}
NMR (C6H6): δ 6.39 (br, D3). 31P{1H} NMR (C6D6): δ -25.42 (s,
PMe3).
The NMR sample of 34 was evaporated, redissolved in C6D6 (0.5
mL), and sealed under vacuum. After 12 d at 80 °C, no evidence of
1
deuterium scrambling was observed by H or (after evaporation and
(b) Preparation of 10 from [Ir(C2H4)2(acac)]. Solid triphenylvi-
nylcyclopropene 8 (0.148 g, 0.504 mmol) was added to a solution of
[Ir(C2H4)2(acac)] (0.175 g, 0.504 mmol) in THF (20 mL) at -70 °C,
followed by the addition of PMe3 (0.103 mL, 1.01 mmol). The orange
color was partially bleached, and the mixture was allowed to come to
room temperature. Removal of solvent in vacuo from the resultant
orange solution yielded an orange-red oil. The oil was washed with
hexanes (2 × 5 mL) and recrystallized at -78 °C from THF/hexanes
(1/20), yielding a yellow solid. 1H and 31P NMR spectra were identical
to those reported above. 13C{1H}NMR (CDCl3, selected CH multiplici-
ties and coupling constants in square brackets): δ 183.42 (s, acac CO),
182.51 (d, JCP ) 1.8, acac CO), 100.00 (s, [d, 155.4], acac CH), 28.53
(d, JCP ) 6.3, [q, 127.0], acac CH3), 28.42 (s, [q, 126.5], acac CH3),
19.43 (dd, JHP ) 91.9, JHP ) 7.4,[t, ∼124], C5), 15.51(dd, JHP ) 39.4,
JHP ) 3.4, [q, 128.6], PMe3), 14.73 (d, JCP ) 20.9, [q, 128.7], PMe3);
other resonances due to phenyl and ring carbons were not unambigu-
ously assigned.
(c) Preparation of 10 from [Ir(PMe3)2(acac)]. The reaction of [Ir-
(PMe3)2(acac)] (0.058 g, 0.131 mmol) with triphenylvinylcyclopropene
(0.040 g, 0.136 mmol) in benzene (10 mL) yielded an identical product
after stirring overnight and recrystallization from petroleum ether/ether
(0.033 g, 43% yield). Single crystals were obtained from this sample.
Crystal Structure Determination of 10. A crystal of 10 was
attached to a fine glass fiber with epoxy cement. On the basis of
2
dissolution in C6H6) H NMR.
Ring-Deuterated Isomer trans-Acetylacetonato(1,5-η-3-deutero-
1,4-diphenyl-1,3-pentadienediyl)bis(trimethylphosphine)iridium-
(III), 43. An NMR sample was prepared as described for the protic
compound 40 above (procedure b), with the substitution of ring-
deuterated 34 for the protic ligand. After heating, the sample was
1
1
opened, evaporated, and redissolved in C6H6 for H NMR. H NMR
(C6D6): δ 6.80-7.88 (m, 10 H, Ph), 6.63 (t, 1H, JHP ) 2.3, H2), 5.01
(s, 1H, acac CH), 3.71 (t, 2H, JHP ) 13.1, H5), 1.65 (s, 3H, acac Me),
2
1.60 (s, 3H, acac Me), 1.00 (virtual t, 18H, JHPobs ) 3.6, PMe3). H-
{1H} NMR (C6H6): δ 6.73 (br, D3). 31P NMR identical to that of the
unlabeled complex.
13C-Labeled Isomers cis- and trans-Acetylacetonato(1,5-η-1,2-
diphenyl-1,3-[4,5-13C2]pentadienediyl)bis(trimethylphosphine)iridium-
(III), 19 and 36, and trans-Acetylacetonato(1,5-η-1,4-diphenyl-1,3-
[1,2-13C2]pentadienediyl)bis(trimethylphosphine)iridium(III), 41. An
NMR sample was prepared from [Ir(PMe3)2(acac)] and 13C-labeled 17
as described for the unlabeled compounds (procedure a). On standing
at room temperature and on subsequent heating, the sample underwent
the changes noted for the unlabeled compounds.
1
19: H NMR (C6D6): δ 6.54-7.89(m, 10H, Ph), 6.46 (td, 1H, JCH
) 10.1, JHH ) 2.7, 10.1, H3), 6.08 (dm, 1H, JCH ) 148, H4), 5.10 (s,
1H, acac CH), 4.01 (dm, 1H, JCH ) 123, H5a), 2.50 (dm, 1H, JCH
)

Iridium-Promoted Reactions of C-C Bonds
J. Am. Chem. Soc., Vol. 122, No. 10, 2000 2271
systematic absences, 10 was determined to crystallize in monoclinic
P21/c. Unit-cell dimensions were derived from the least-squares fit of
the angular settings of 25 reflections with 20° e 2θ e 26°. An empirical
absorption correction was applied where six parameters are employed
to define a pseudoellipsoid. The structure was solved via heavy-atom
methods which located Ir. Remaining non-hydrogen atoms were located
from subsequent difference Fourier synthesis and were refined aniso-
tropically. Phenyl carbon atoms were fixed to fit rigid hexagons.
Hydrogen atom positions were calculated (dCH ) 0.96 Å, U ) 1.2 times
the isotropic equivalent for the carbon to which it was attached). All
computer programs used in the crystal data collection and refinement
are contained in Shelxtl (version 5.1) (G. Sheldrick, Nicolet XRD,
Madison, WI). Crystal data collection parameters and selected bond
distances and angles are provided in Tables 1 and 2; additional
crystallographic data is available as Supporting Information.
propene 18, as described for the unlabeled compound above. Over the
course of 30 h at 100 °C, 39 was formed with no scrambling of the
13C labels. The sample was then heated at 125 °C for 40 h, during
which time the labels scrambled to give a 1:1 mixture of 39 and 44.
The NMR sample was opened, evaporated, and redissolved in a
minimum of toluene. Passage through a Florisil column (1 × 23 cm,
-60 °C under N2, 1:6 ether/toluene) gave a yellow eluate. Evaporation
of the eluate and recrystallization from petroleum ether gave clean
product as a 1:1 mixture of isotopomers 39 and 44.
1
20: H NMR (C6D6): δ 6.58-7.81 (m, 15H, Ph), 6.81 (d, 1H, JCH
) 148, H3), 5.15 (s, 1H, acac CH), 4.41 (dm, 1H, JCH ) 126, H5a),
2.80 (dm, 1H, JCH ) 124, J5b), 1.78 (s, 3H, acac Me), 1.68 (s, 3H, acac
Me), 1.27 (d, 9H, JHP ) 10.4, axial PMe3), 0.89 (d, 9H, JHP ) 7.3,
equatorial PMe3). 13C NMR (C6D6): δ 133.10 (dt, JCC ) 2.9, JCH
)
148.4, JCP ) 2.9, C3), 20.77 (tddd JCC ) 3.2, JCH ) 124.1, JCP ) 92.1,
7.3, C5). 31P{1H} NMR (C6D6): δ -36.71 (ddd JPP ) 7.7, JCP ) 92.0,
2.7, equatorial PMe3), -43.67 (t, JPP ) JCP ) 7.5, axial PMe3).
Geminally Deuterated Isomers cis- and trans-Acetylacetonato-
(1,5-η-5-deutero-1,2,4-triphenyl-1,3-pentadienediyl)bis(trimeth-
ylphosphine)iridium(III), 23 and 38. A solution of [Ir(PMe3)2(acac)]
(20.5 mg, 23 µmol/sample) and 12 (13.7 mg, 23 µmol/sample, 1.0
equiv) in benzene (1.4 mL) was loaded equally into two NMR tubes.
One sample was freeze-dried and redissolved in C6D6 (0.7 mL). The
samples were then freeze-pump-thaw degassed and sealed under
vacuum. Treatment as described for the protic compounds above
(procedure a) gave 23 followed by 38. The C6D6 sample was then heated
at 120, 140, and 150 °C with only slight decomposition, but decomposed
extensively after 24 h at 165 °C.
1
39: H NMR (C6D6): δ 6.95-7.79 (m, 15H, Ph), 6.83 (br dd, 1H,
JCH ) 145.1, 8.5, H3), 5.26 (s, 1H, acac CH), 3.73 (dtdd, 2H, JHH
)
0.6, JCH ) 123.7, 6.6, JHP ) 12.4, H5), 1.64 (s, 3H, acac Me), 1.50 (s,
3H, acac Me), 1.05 (virtual t, 18H, JHPobs ) 3.4, PMe3). 13C NMR
(C6D6): δ 135.24 (ddt, JCC ) 3.1, JCH ) 145.2, JCP ) 1.6, C3), -8.82
(tdtd, JCC ) 2.9, JCH ) 123.7, 8.9, JHP ) 6.1, C5). 31P{1H} NMR
(C6D6): δ -26.08 (dd, JCP ) 5.7, 1.9, PMe3).
1
44: H NMR and 31P NMR: identical to the spectra of 39 except
for the absence of the 124 Hz carbon coupling to the geminal hydrogens.
1
23: H NMR (C6D6): δ 6.70-7.84 (m, 15H, Ph), 6.80 (d, 1H, JHH
13C{1H} NMR (C6D6): δ 138.02 (t, JCP ) 10.0, C1), 135.24 (m, C3).
) 1.4, H3), 5.11 (s, 1H, acac CH), 2.76 (dd, 1H, JHP ) 7.7, 5.5, H5b),
1.75 (s, 3H, acac Me), 1.64 (s, 3H, acac Me), 1.23 (d, 9H, JHP ) 10.3,
Acknowledgment. We are grateful to the National Science
Foundation and to the donors of the Petroleum Research Fund,
administered by the American Chemical Society, for generous
support of our research. A generous loan of iridium salts from
Johnson Matthey Aesar/Alfa is also gratefully acknowledged.
2
axial PMe3), 0.56 (d, 9H, JHP ) 7.2, equatorial PMe3). H{1H} NMR
(C6H6): δ 4.34 (br, D5a).
38: 1H NMR (C6D6): δ 6.65-7.77 (m, 15 H, Ph), 6.80 (d, 1H, JHH
) 1.4, H3), 4.92 (s, 3H, acac CH), 3.70 (br t, 1H, JHP ) 12.3, H5), 1.60
2
(s, 3H, acac Me), 1.47 (s, 3H, acac CH), 1.02 (m, 18H, PMe3). H-
{1H} NMR (C6H6): δ 3.66 (br, D5). 31P{1H} NMR (C6D6): δ -26.05
(s, PMe3), -26.08 (s, PMe3).
Supporting Information Available: Atomic coordinates and
isotropic thermal parameters, bond distances, bond angles,
anisotropic thermal parameters, H-atom coordinates and iso-
tropic thermal parameters for 10 (PDF). This material is
available free of charge via the Internet at http://www.pubs.acs.org.
13C-Labeled Compounds cis- and trans-Acetylacetonato(1,5-η-
1,2,4-triphenyl-1,3-[3,5-13C2]pentadienediyl)bis(trimethylphosphine)-
iridium(III), 20 and 39, and Automerization of 39 to trans-
Acetylacetonato(1,5-η-1,2,4-triphenyl-1,3-[1,3-13C2]pentadienediyl)-
bis(trimethylphosphine)iridium(III), 44. An NMR sample of 20 was
prepared from [Ir(PMe3)2(acac)] and 13C-labeled triphenylvinylcyclo-
JA992407D