Skeletal rearrangement during rhodium-promoted ring opening of 1,2-diphenyl-3-vinyl-1-cyclopropene. Preparation and characterization of 1,2- and 2,3-diphenyl-3,4-pentadienediyl rhodium complexes and their ring closure to a 1,2-diphenylcyclopentadienyl complex

Article abstract of DOI:10.1021/om990159o

Under conditions of kinetic control, 1,2-diphenyl-3-vinyl-1-cyclopropene undergoes ring opening with the [Rh(Cl)(PMe₃)₂] fragment to give two isomeric η³:η¹-1,3-pentadienediyl compounds: the expected 1,2-diphenyl isomer, and the 2,3-diphenyl isomer resulting from an apparent skeletal rearrangement reaction. The latter complex has been characterized by X-ray crystallography. Both complexes underwent ring closure to give the same 1,2-diphenylcyclopentadienyl complex on treatment with silver ion. Addition of a third equivalent of trimethylphosphine to the 2,3-diphenyl isomer produced two meridional rhodacyclohexadienes, which exhibit facile solvent-dependent chloride dissociation. In contrast, phosphine added reversibly to the 1,2-diphenyl isomer to give only the chloride-dissociated compound, and the tris(phosphine) product could only be isolated after anion exchange with hexafluorophosphate. No deprotonation to give rhodabenzene complexes could be achieved. The mechanism of rearrangement is proposed to involve a carbocation rearrangement during the ring-opening reaction and is compared to other metal-promoted reactions of vinylcyclopropenes.

Full text of DOI:10.1021/om990159o

2766
Organometallics 1999, 18, 2766-2772
Sk eleta l Rea r r a n gem en t d u r in g Rh od iu m -P r om oted Rin g
Op en in g of 1,2-Dip h en yl-3-vin yl-1-cyclop r op en e.
P r ep a r a tion a n d Ch a r a cter iza tion of 1,2- a n d
2,3-Dip h en yl-3,4-p en ta d ien ed iyl Rh od iu m Com p lexes a n d
Th eir Rin g Closu r e to a 1,2-Dip h en ylcyclop en ta d ien yl
Com p lex
Russell P. Hughes,*,1a Hernando A. Trujillo,1a,b J ames W. Egan, J r.,1a and
Arnold L. Rheingold1c
Departments of Chemistry, Burke Laboratory, Dartmouth College,
Hanover, New Hampshire 03755, and University of Delaware, Newark, Delaware 19716
Received March 5, 1999
Under conditions of kinetic control, 1,2-diphenyl-3-vinyl-1-cyclopropene undergoes ring
opening with the [Rh(Cl)(PMe3)2] fragment to give two isomeric η3:η1-1,3-pentadienediyl
compounds: the expected 1,2-diphenyl isomer, and the 2,3-diphenyl isomer resulting from
an apparent skeletal rearrangement reaction. The latter complex has been characterized
by X-ray crystallography. Both complexes underwent ring closure to give the same
1,2-diphenylcyclopentadienyl complex on treatment with silver ion. Addition of a third
equivalent of trimethylphosphine to the 2,3-diphenyl isomer produced two meridional
rhodacyclohexadienes, which exhibit facile solvent-dependent chloride dissociation. In
contrast, phosphine added reversibly to the 1,2-diphenyl isomer to give only the chloride-
dissociated compound, and the tris(phosphine) product could only be isolated after anion
exchange with hexafluorophosphate. No deprotonation to give rhodabenzene complexes could
be achieved. The mechanism of rearrangement is proposed to involve a carbocation
rearrangement during the ring-opening reaction and is compared to other metal-promoted
reactions of vinylcyclopropenes.
Sch em e 1
In tr od u ction
3-Vinyl-1-cyclopropenes of general structure 1 (Scheme
1) undergo thermal and photochemical ring expansion
to cyclopentadienes and indenes.2-6 Transition metal
complexes also effect this ring expansion catalytically
and stoichiometrically, to give cyclopentadienes, η4-
cyclopentadiene complexes, and η5-cyclopentadienyl
complexes.7-11 On treatment with carbonyl-bearing
metal complexes, cyclohexadienones, η4-cyclohexadi-
enone complexes, and phenols have been prepared.7-14
(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) Breslow, R. In Molecular Rearrangements; de Mayo, P., Ed.;
Wiley: New York, 1963; Vol. 1, p 236.
(3) Padwa, A. Org. Photochem. 1979, 4, 261.
(4) Zimmerman, H. E.; Hovey, M. C. J . Org. Chem. 1979, 44, 2331.
(5) Zimmerman, H. E.; Kreil, K. J . J . Org. Chem. 1982, 47, 2060.
(6) Zimmerman, H. E.; Fleming, S. A. J . Org. Chem. 1985, 50, 2539.
(7) Hughes, R. P.; Trujillo, H. A.; Gauri, A. J . Organometallics 1995,
14, 4319-24.
In several of these closures, pentadienediyl intermedi-
ates 2 resulting from ring opening of the vinylcyclopro-
penes have been observed15,16 and have been shown to
be precursors to the ring-closed η4-cyclopentadiene
products 3.7-11,16-18 Use of selectively deuterated com-
(8) Grabowski, N. A.; Hughes, R. P.; J aynes, B. S.; Rheingold, A. L.
J . Chem. Soc., Chem. Commun. 1986, 1694-5.
(9) Egan, J . W., J r.; Hughes, R. P.; Rheingold, A. L. Organometallics
1987, 6, 1578-81.
(10) Hughes, R. P.; Robinson, D. J . Organometallics 1989, 8, 1015-
9.
(14) Padwa, A.; Kassir, J . M.; Xu, S. L. J . Org. Chem. 1991, 56,
6971-2.
(15) Donovan, B. T.; Egan, J . W., J r.; Hughes, R. P.; Spara, P. P.;
Trujillo, H. A.; Rheingold, A. L. Isr. J . Chem. 1990, 30, 351-60.
(16) Donovan, B. T.; Hughes, R. P.; Trujillo, H. A. J . Am. Chem.
Soc. 1990, 112, 7076-7.
(11) Donovan, B. T.; Hughes, R. P.; Kowalski, A. S.; Trujillo, H. A.;
Rheingold, A. L. Organometallics 1993, 12, 1038-43.
(12) Cho, S. H.; Liebeskind, L. S. J . Org. Chem. 1987, 52, 2631-4.
(13) Semmelhack, M. F.; Ho, S.; Steigerwald, M.; Lee, M. C. J . Am.
Chem. Soc. 1987, 109, 4397.
10.1021/om990159o CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/24/1999

Ring Opening of 1,2-Diphenyl-3-vinyl-1-cyclopropene
Organometallics, Vol. 18, No. 15, 1999 2767
Sch em e 2a
pounds has demonstrated the stereochemistry of both
the ring-opening and -closure reactions.15,16 While met-
allacyclohexadiene intermediates 4 may be energetically
accessible in the reaction,9,19 ring-closure reactions do
not require such intermediates and have been shown
to occur directly from nonplanar intermediates 2.7,15,16
The corresponding reactions of cyclopropenyl ketones
with Rh(I) and Rh(II) catalysts yield R-pyrones and
furans.12,14 One suggested pathway to pyrones is shown
in Scheme 2;12 the corresponding furans are the prod-
ucts if CO insertion is slow. A particularly interesting
feature of this reaction is the regiochemistry observed
in the cases of unsymmetrically substituted substrates.
A ring-opening mechanism involving initial binding of
rhodium to the ketone function, followed by interaction
of the metal with the cyclopropene double bond, was
suggested to give cationic intermediate 5; disrotatory
opening of 5 was proposed to afford 6, which is analo-
gous to one of the valence tautomers of the pentadiene-
diyl species 2 we have observed. To account for some
unexpected product regiochemistries, the metallacyclo-
butene portion of intermediate 6 was assumed to
rearrange via a cycloaddition cycloreversion pathway,
as shown in Scheme 2, thereby exchanging the positions
of the R and â carbons and their substituents.
R1 ) Me, R2 ) Ph, R3 ) OEt.
a
Here we report a different rearrangement encoun-
tered in the reaction of a symmetrically substituted
vinylcyclopropene with a Rh(I) precursor, which clearly
must proceed by a pathway quite different from that
proposed in Scheme 2.
Resu lts a n d Discu ssion
The previously observed ring opening of triphenyl-
vinylcyclopropene 7 on reaction with the [RhCl(PMe3)2]
fragment (obtained in situ by treatment of [Rh(C8H14)2-
Cl]2 with 2 equiv of PMe3 per Rh) cleanly affords the
pentadienediyl Rh(III) complex 8.9 However, examina-
F igu r e 1. ORTEP diagram and numbering scheme for
11a .
which the two compounds are formed occurs readily at
room temperature, the 1:3 product ratio clearly cannot
be due to an equilibration of the two compounds and is
the result of kinetic control. An X-ray diffraction study
of a single crystal of 11a confirmed its structure; the
ORTEP diagram shown in Figure 1 illustrates that the
phenyl rings are indeed in the 2 and 3 positions of the
pentadienediyl ligand. The crystallographic parameters,
atomic coordinates, and selected bond lengths and
angles for the structure are listed in Tables 1-3.
The location of the phenyl rings in the two isomers
was also clear from their low-temperature proton NMR
spectra. The connectivity of the four ring hydrogens in
the minor isomer, 10a , is demonstrable by COSY and
by the proton-proton coupling constants. The spectra
of the major isomer, 11a , show a set of three coupled
protons and an isolated proton coupled only to phos-
phorus and to rhodium. The lone ring hydrogen, H(1),
displays a surprisingly large coupling constant to one
of the phosphines. Since neither phosphine is trans to
C(1) in the structure, the 17 Hz coupling may arise from
the near coplanarity of the P(2)-Rh and C(1)-H(1)
bonds, which form a 14.2° dihedral angle. As in tri-
phenyl compound 8,9 broad room temperature NMR
resonances for the geminal hydrogens and for the
phosphines are consistent with an η3 f η1 f η3 allyl
tion of the corresponding reaction of diphenylvinyl-
cyclopropene 9a with the [RhCl(PMe3)2] fragment at
room temperature revealed a more complicated process.
While the expected 1,2-diphenyl compound 10a was
obtained, the major product was its 2,3-diphenyl isomer
11a ; the ratio of 10a to 11a was 1:3. The two isomers
could be separated, and on standing in solution for 2
weeks at 45 °C, a sample of pure 10a showed no
conversion to the major isomer 11a . As the reaction in
(17) Donovan, B. T.; Hughes, R. P.; Trujillo, H. A.; Rheingold, A. L.
Organometallics 1992, 11, 64-9.
(18) Donovan-Merkert, B. T.; Tjiong, H. I.; Rhinehart, L. M.; Russell,
R. A.; Malik, J . Organometallics 1997, 16, 819.
(19) Hughes, R. P.; Trujillo, H. A.; Rheingold, A. L. J . Am. Chem.
Soc. 1993, 115, 1583-5.

2768 Organometallics, Vol. 18, No. 15, 1999
Hughes et al.
Ta ble 3. Selected Bon d An gles for 11a
Ta ble 1. Cr ysta l, Da ta Collection , a n d Refin em en t
P a r a m eter s for 11a
P(1)-Rh-P(2)
P(1)-Rh-Cl
100.5(1)
86.5(1)
94.6(1)
94.0(2)
93.0(2)
172.1(2)
99.6(1)
148.8(1)
110.2(2)
62.0(3)
126.4(1)
133.1(1)
88.8(2)
84.6(3)
34.5(2)
164.1(2)
95.3(2)
94.0(2)
83.4(3)
65.3(2)
37.8(2)
117.6(2)
117.8(2)
102.8(4)
111.7(3)
103.2(4)
C(32)-P(1)-C(33)
Rh-P(2)-C(34)
Rh-P(2)-C(35)
C(34)-P(2)-C(35)
Rh-P(2)-C(36)
C(34)-P(2)-C(36)
C(35)-P(2)-C(36)
Rh-C(1)-C(2)
101.5(4)
114.8(3)
119.3(3)
102.2(4)
114.9(3)
101.5(4)
101.7(5)
106.5(5)
108.4(6)
128.0(6)
123.2(5)
83.1(3)
formula
C23H32ClP2Rh
P(2)-Rh-Cl
cryst syst
space group
a, Å
trigonal
R3h
20.165(7)
P(1)-Rh-C(1)
P(2)-Rh-C(1)
Cl-Rh-C(1)
b, Å
20.165(7)
P(1)-Rh-C(3)
P(2)-Rh-C(3)
Cl-Rh-C(3)
C(1)-Rh-C(3)
P(1)-Rh-C(4)
P(2)-Rh-C(4)
Cl-Rh-C(4)
c, Å
30.89(1)
10874(7)
V, Å3
C(1)-C(2)-C(3)
C(1)-C(2)-C(16)
C(3)-C(2)-C(16)
Rh-C(3)-C(2)
Z
18
1.46
7.8
23
D(calcd), g cm-3
µ(Mo KR), cm-1
temp, °C
cryst dimens, mm
radiation
Rh-C(3)-C(4)
65.2(3)
0.25 × 0.25 × 0.25
graphite-monochromated Mo
KR (λ ) 0.710 73 Å)
Nicolet R3m/µ
variable, 6-20
4 e 2θ e 48
Wykoff
+h,+k,(l
0.0010
3804 (4170 collected)
2541
3 stds/197 rflns
4.22
C(1)-Rh-C(4)
C(3)-Rh-C(4)
P(1)-Rh-C(5)
P(2)-Rh-C(5)
Cl-Rh-C(5)
C(1)-Rh-C(5)
C(3)-Rh-C(5)
C(4)-Rh-C(5)
Rh-P(1)-C(31)
Rh-P(1)-C(32)
C(31)-P(1)-C(32)
Rh-P(1)-C(33)
C(31)-P(1)-C(33)
C(2)-C(3)-C(4)
Rh-C(3)-C(26)
C(2)-C(3)-C(26)
C(4)-C(3)-C(26)
Rh-C(4)-C(3)
117.7(5)
125.5(3)
119.9(5)
122.3(6)
80.3(4)
68.0(4)
123.3(7)
74.1(3)
120.6(3)
119.3(3)
119.4(4)
120.5(4)
diffractometer
scan speed, deg min-1
scan limits, deg
scan technique
data collected
weighting factor, g
indep data
indep data with Fo g 5σ(Fo)
std rflns
R(F), %
Rh-C(4)-C(5)
C(3)-C(4)-C(5)
Rh-C(5)-C(4)
C(2)-C(16)-C(11)
C(2)-C(16)-C(15)
C(3)-C(26)-C(21)
C(3)-C(26)-C(25)
Rw(F), %
4.52
GOF
data/parameter
∆/σ
1.098
10.7
0.003
a
Sch em e 3
Ta ble 2. Selected Bon d Dista n ces for 11a
Rh-P(1)
2.325(2)
2.256(2)
2.486(3)
2.004(7)
2.416(6)
2.226(7)
2.146(6)
1.791(10)
1.815(7)
1.817(8)
1.819(7)
1.807(9)
1.811(14)
1.321(8)
1.518(10)
1.490(7)
1.387(10)
1.491(7)
1.420(9)
Rh-P(2)
Rh-Cl
Rh-C(1)
Rh-C(3)
Rh-C(4)
Rh-C(5)
P(1)-C(31)
P(1)-C(32)
P(1)-C(33)
P(2)-C(34)
P(2)-C(35)
P(2)-C(36)
C(1)-C(2)
C(2)-C(3)
C(2)-C(16)
C(3)-C(4)
C(3)-C(26)
C(4)-C(5)
rearrangement process via a metallacyclohexadiene
intermediate that exchanges both the syn and anti
proton environments with concomitant exchange of the
phosphine environments rapidly on the NMR time scale.
A mechanism consistent with the formation of 10a
and 11a is shown in Scheme 3. Initial coordination of
the metal followed by slippage would lead to structure
12, which is poised for ring expansion to 13. Breslow20
has shown the ease with which such cyclopropenylcar-
binyl expansions occur during solvolysis reactions, and
we have provided evidence that an analogous interme-
diate is important in the chloropalladation reactions of
other vinylcyclopropenes.21 The importance of initial
coordination to the vinyl group has been clearly dem-
onstrated for similar reactions, in which ring expansion
is significantly slowed by methylation of the vinyl
group.10,13,22 Attack of the metal at the less sterically
a
[Rh] ) Rh(Cl)(PMe3)2.
hindered site, a, of 13 would then lead to 2,3-diphenyl
structure 11. The formation of lesser amounts of 10 is
consistent with attack at b being disfavored by the
greater steric congestion at b than at a. When the
reaction was carried out using ring-deuterated 9b, the
deuterium was observed in the appropriate positions in
both compounds 10b and 11b, consistent with Scheme
3. Since these reactions are carried out in toluene, it is
doubtful whether the metal and carbon atoms in 12
carry substantial charges, but partial charge separa-
tion may be enough to trigger ring expansion, given the
ease with which analogous expansions are known to
occur.20
As earlier demonstrated for triphenyl compound 8 and
several related compounds, thermal phosphine loss
triggers ring closure followed by endo-H migration to
the metal, giving cyclopentadienyl compounds such as
(20) Breslow, R.; Lockhart, J .; Small, A. J . Am. Chem. Soc. 1962,
84, 2793-800.
(21) Donovan, B. T.; Hughes, R. P.; Spara, P. P.; Rheingold, A. L.
Organometallics 1995, 14, 489-94.
(22) Choi, H.; Pinhas, A. R. Organometallics 1992, 11, 1.

Ring Opening of 1,2-Diphenyl-3-vinyl-1-cyclopropene
Organometallics, Vol. 18, No. 15, 1999 2769
14.9,23 Similarly, on chloride abstraction from diphenyl
compound 10a or 11a by silver ion, the cyclopentadienyl
compound 15a was obtained. As expected, on treatment
with silver ion, the deuterated isotopomers 10b and 11b
both gave the same product 15b, having deuterium in
a position R to a phenyl group in the cyclopentadienyl
ring.
nance of the 2:1 17:18 ratio regardless of the fraction
of 19a present demonstrates that 17 and 18 are indeed
in equilibrium. Both the strong dependence of the
concentration of 19a on the solvent polarity and the
correspondence of the facial compound’s 31P NMR
spectrum in acetonitrile with that of the cation 16b
obtained from 17/18 by chloride abstraction lead to the
conclusion that the facial compound is actually a dis-
sociation isomer of 17 and 18. As such, 19a may provide
an interconversion path between 17 and 18. Similarly
to 1,2-diphenyl compound 16a , 19a may be trapped by
Both diphenyl complexes 10a and 11a readily coor-
dinate a third phosphine to afford metallacyclohexadi-
ene complexes. When 1,2-diphenyl complex 10a is
treated with a third equivalent of trimethylphosphine,
tris(phosphine) complex 16a is formed in solution,
although the third phosphine is lost on evaporation,
regenerating 10a . Similar behavior is also observed with
1,2,3-triphenyl compound 8. Tris(phosphine) cation 16b
may be trapped, however, through exchange of chloride
for an effectively noncoordinating anion, such as hexa-
fluorophosphate. The facile loss of phosphine from tris-
(phosphine) complexes 16 is most likely a result of steric
congestion due to the phenyl group on the carbon
adjacent to the metal.
-
anion exchange and isolated as its PF6 salt 19b.
The resemblance between cation 19 and the precursor
20 to Bleeke’s iridabenzene 2124-33 suggested that the
mixture of 17:18:19a might deprotonate to give an
analogous rhodabenzene. On treatment with several
strong bases (lithium diisopropylamide, lithium tetra-
methylpiperidide, potassium hydride) in various sol-
vents, 17:18:19a either decomposed or failed to react,
reminiscent of Bleeke’s observation that triethylphos-
phine complex 20 deprotonates readily, yet its trimeth-
ylphosphine analogue 22 is inert.25
On similar treatment with a third equivalent of
trimethylphosphine, the 2,3-diphenyl complex 11a be-
haves differently. Instead of reversibly losing chloride
to form an η3-allyl tris(phosphine) complex, a mixture
of two isomeric metallacyclohexadienes, 17 and 18, is
formed in a 2:1 ratio. Although the orientation of the
ligands in the two isomers was not pursued, the
observation of a Peq-H(4) NMR coupling in only the
minor isomer (J HP ) 14.0 Hz) suggests that the equato-
rial phosphine lies trans to the sp3 carbon in the minor
isomer; no Peq-H(4) coupling is observed in the major
compound. The same mixture of isomers could be
obtained in a one-pot reaction from 9a and “Rh(PMe3)2-
Cl” by adding an extra equivalent of PMe3 per Rh after
the ring-opening process.
On dissolution in chloroform, the 17:18 mixture
produced a third compound. The regeneration of the
original NMR spectrum, on evaporation of the chloro-
form sample and redissolution in benzene, suggested
that the third compound, 19a , was in equilibrium with
17 and 18 and was not the result of their decomposition
in the chlorinated solvent. In nonpolar solvents such as
benzene, ether, and dimethoxyethane, 17:18:19a ratios
of roughly 2.3:1:0 were observed by 31P NMR. In
deuteriochloroform, the ratio changed to 2.6:1:0.7, and
in deuterioacetonitrile, it was 2.2:1:8.9. The mainte-
Con clu sion
To summarize, diphenylvinylcyclopropene 9 under-
goes ring opening with the [Rh(Cl)(PMe3)2] fragment to
give 2,3- and 1,2-diphenyl isomers 10 and 11, presum-
ably by ring expansion via two different metallacyclo-
butenes. On treatment with silver ion, 10 and 11 both
undergo ring closure to give cyclopentadienyl compound
15a . In contrast, on treatment with a third equivalent
of phosphine, 10 reversibly exchanges phosphine for
chloride, to form a tris(phosphine) cation 16a , whereas
chloride dissociation from the tris(phosphine) complex
17:18 obtained from 11 is solvent dependent.
(24) Bleeke, J . R.; Rohde, A. M.; Boorsma, D. W. Organometallics
1993, 12, 970-4.
(25) Bleeke, J . R. Acc. Chem. Res. 1991, 24, 271-7.
(26) Bleeke, J . R.; Xie, Y. F.; Peng, W. J .; Chiang, M. J . Am. Chem.
Soc. 1989, 111, 4118-20.
(27) Bleeke, J . R.; Behm, R.; Xie, Y.-F.; Clayton, T. W., J r.; Robinson,
K. D. J . Am. Chem. Soc. 1994, 116, 4093-4.
(28) Bleeke, J . R.; Behm, R. J . Am. Chem. Soc. 1997, 119, 8503-
11.
(29) Bleeke, J . R.; Behm, R.; Beatty, A. M. Organometallics 1997,
16, 1103-5.
(30) Bleeke, J . R.; Behm, R.; Xie, Y.-F.; Chiang, M. Y.; Robinson, K.
D.; Beatty, A. M. Organometallics 1997, 16, 606-23.
(31) Bleeke, J . R.; Blanchard, J . M. B. J . Am. Chem. Soc. 1997, 119,
5443-4.
(32) Bleeke, J . R.; Xie, Y. F.; Bass, L.; Chiang, M. Y. J . Am. Chem.
Soc. 1991, 113, 4703-4.
(33) Bleeke, J . R.; Bass, L. A.; Xie, Y. F.; Chiang, M. Y. J . Am. Chem.
Soc. 1992, 114, 4213-9.
(23) Bleeke, J . R.; Peng, W. J .; Xie, Y. F.; Chiang, M. Y. Organo-
metallics 1990, 9, 1113-9.

2770 Organometallics, Vol. 18, No. 15, 1999
Hughes et al.
J HH ) 9.2, Hanti), 1.65, (s, 9H, PMe3), 1.22 (s, 9H, PMe3). 1H
NMR (-20 °C, toluene-d8): δ 6.71-7.18 (m, 10H, Ph), 5.50
(dt, 1H, J HH ) 10.4, 7.6, 7.6, Hcentral), 5.10 (ddd, 1H, J HH ) 7.4,
0.5, J HP ) 4.2, H3), 3.27 (ddd, 1H, J HH ) 7.4, J HP ) 2.5, 0.5,
Exp er im en ta l Section
Gen er a l P r oced u r es. 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. Petroleum ether
(35-65 °C), other hydrocarbon solvents, and ethers were
distilled under nitrogen from benzophenone ketyl; chlorinated
solvents, acetonitrile, and methanol, from CaH2. 1H (300 MHz),
2H{1H} (46.1 MHz), 13C{1H} (75 MHz) and 31P{1H} (121 MHz)
NMR spectra were recorded at 25 °C, unless otherwise noted.
Chemical shifts are reported as parts per million downfield of
H
H
syn), 2.56 (ddt, 1H, J HH ) 10.3, 0.8, J HP ) 8.0, J RhH ) 0.8,
anti), 1.34 (d, 9H, J HP ) 8.6, PMe3), 0.95 (d, 9H, J HP ) 9.7,
PMe3). 31P{1H} NMR (CDCl3): δ -0.4 (d, 1P, J PP ) 12, J RhP
)
170, PMe3), -11.2 (dd, 1P, J PP ) 12, J RhP ) 139, PMe3). IR
(KBr, cm-1): 943 vs, 848 m, 621 m.
Deuterated compounds 10b and 11b were prepared in the
same manner as their protic isotopomers, using ring-deuter-
ated vinylcyclopropene 9b. 11b 1H and 31P{1H} NMR spectra
(CDCl3) were identical to those of protic 11a , except for the
absence of the proton resonance at δ 6.80. 2H{1H} NMR
(CHCl3): δ 6.88 (br, D1). 10b 1H NMR (C6D6): 6.80-7.83 (m,
10H, Ph), 5.59 (t, 1H, J HH ) 8.6, Hcentral), 3.21 (br, 1H, Hsyn),
2.68 (br, 1H, Hanti), 1.80 (br, 9H, PMe3), 1.51 (br, 9H, PMe3).
2H{1H} NMR (C6H6): δ 5.12 (br, D3). The 31P{1H} NMR
spectrum (C6D6) was identical to that of protic 10a .
Attem p ted con ver sion of 10a to 11a . A yellow solution
of 10a (6.8 mg, 11.9 µmol) in C6D6 (0.25 mL) was freeze-
pump-thaw degassed and sealed under vacuum in an NMR
tube. No changes were observed visually or by 1H and 31P NMR
spectroscopy after 1 day at 45 °C. After 2 weeks at 45 °C, the
sample had darkened to a clear orange. 1H and 31P HMR
spectra showed no changes in the sample except the formation
of traces of trimethylphosphine oxide (δ 31P -33.3) and a
possible cyclopentadienyl compound (δ 31P -2.7, d, J RhP ) 213).
Rin g Closu r e Rea ction s To Give Com p ou n d s 15. P r o-
tic Com p ou n d s. A suspension of AgPF6 (0.06 g, 0.237 mmol,
1.0 equiv) and 11a (0.120 g, 0.237 mmol) in THF (25 mL) was
stirred overnight in the dark. Filtration of the yellow-brown
mixture gave a yellow solution. The filtrate was concentrated
in vacuo to approximately 1-2 mL, and 5 mL of ether was
added. A yellow precipitate formed and was recrystallized from
methanol/ether to give 15a as a yellow solid (0.080 g): 1H NMR
(THF-d8): δ -12.28 (td, J RhH ) 22.9, J HP ) 32.2, 1H, RhH),
2
either TMS (1H, H, and 13C NMR, referenced to the solvent)
or external 85% H3PO4 (31P NMR). Coupling constants are
reported in Hertz with estimated errors of (0.2 Hz. Reso-
nances are assigned using the numbering scheme of Figure 1.
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 an
Electrothermal device and are uncorrected. Elemental analy-
ses were performed by Spang (Eagle Harbor, MI).
Ammonium hexafluorophosphate, diisopropylamine, lithium
diisopropylamide, and potassium hydride were obtained from
Aldrich; silver hexafluorophosphate from Pennwalt; and so-
dium hydride from Alfa. 1,2-Diphenyl-3-vinylcyclopropene
(9a ),34 3-deuterio-1,2-diphenyl-3-vinylcyclopropene (9b),19 tri-
methylphosphine,35 and [Rh(C8H14)2Cl]2 (C8H14 ) cis-cyclo-
octene)36 were prepared by literature routes.
P r ep a r a tion of 10a a n d 11a a n d Th eir Deu ter a ted
Isotop om er s 10b a n d 11b. A benzene (250 mL) solution of
[Rh(C8H14)2Cl]2 (1.73 g, 4.83 mmol of Rh) was treated with
trimethylphosphine (0.98 mL, 9.6 mmol, 2.0 equiv) dissolved
in benzene (25 mL). After the orange solution had been stirred
for 5 min, a solution of 9a (1.10 g, 5.03 mmol, 1.02 equiv) in
benzene (25 mL) was added over 10 min, and the deep red
solution was stirred overnight. After concentration almost to
dryness and precipitation with petroleum ether (50 mL), 11a
was collected as an orange powder (2.20 g) containing traces
of 10a which could be removed by recrystallization from 1:1
CH2Cl2/petroleum ether. 11a mp: 135-136 °C dec. Calcd for
7.2-7.5 (Ph), 5.86 (d, J HH ) 3, 2H, lateral HCp), 5.32 (t, J HH
)
3, 1H, central HCp), 1.65 (filled doublet, 18H, PMe3). 31P{1H}
NMR (CDCl3): δ 9.2 (d, J RhP ) 127.8, PMe3), -143.8 (sept,
J PF ) 712.7, PF6).
C
23H32P2ClRh: 54.28, C; 6.35, H. Found: 54.18, C; 6.50, H.
1H NMR (-20 °C, CDCl3): δ 6.80* (exchange d(dd), 1H, J HP
)
Deu ter a ted Com p ou n d s. A suspension of 10b and 11b
(22 mg, 0.043 mmol, ∼1:2) and AgPF6 (9 mg, 0.04 mmol, 1
equiv) in DME (5 mL) was stirred overnight in the dark. The
resulting gray suspension was filtered through Celite and
evaporated. The red residue was extracted with methanol,
passed through Celite, concentrated, and precipitated with
ether. Filtration and drying of the solid gave 15b as a yellow-
orange solid (12 mg, 56%). 1H{31P} NMR (CD3CN): δ 6.90-
7.70 (m, 10H, Ph), 6.01 (d, 1H, J HH ) 2.1, lateral HCp), 5.15 (d,
1H, J HH ) 2.3, central HCp), 1.63 (filled d, 18 H, J HP ) 11.9,
PMe3), -11.9 (m, 1H, RhH). 2H{1H} NMR (CH3CN): δ 5.93
(br, lateral DCp). 31P{1H} NMR (CD3CN): δ 12.15 (d, 2P, J RhP
) 126, PMe3), -143 (sept, 1P, J PF ) 707, PF6).
Rh od a cycloh exa d ien e Com p lexes 17 a n d 18. (a ) F r om
[Rh (C8H14)2Cl]2. A solution of [Rh(C8H14)2Cl]2 (499 mg, 1.39
mmol Rh) in toluene (75 mL) was treated with trimethylphos-
phine (288 µL, 2.82 mmol, 2.0 equiv) dissolved in toluene (5
mL). After the orange solution had been stirred for 5 min, a
solution of 9a (314 mg, 1.43 mmol, 1.1 equiv) in toluene (5
mL) was added. The resulting red solution was stirred for 12
h and then treated with trimethylphosphine (150 µL, 1.47
mmol, 1.1 equiv) dissolved in toluene (5 mL). After being
stirred for 20 min, the solution was evaporated nearly to
dryness and precipitated with petroleum ether (50 mL) to give
a yellow powder, which was washed with petroleum ether (2
× 5 mL). Recrystallization from ether gave isomers 17 and 18
as orange crystals (427 mg, 71%). Mp: 148-160 °C dec. Calcd
for C26H41P3ClRh: 53.35, C; 7.06, H. Found: 53.45, C; 7.00,
H. IR (KBr, cm-1): 1383 m, 1282 m, 1020 s, 947 s. 17: 1H
NMR (C6D6) δ 8.31 (tdd, 1H, J HP(cis) ) 6.4, J HP(trans) ) 7.9, J RhH
17.6, J RhH ) 1.3, H1) 6.96-7.60 (m, 10H, Ph), 6.03 (ddd, 1H,
J HH ) 9.9, 7.6, J HP ) 1.5, Hcentral), 3.18 (ddd, 1H, J HH ) 7.6,
0.8, J HP ) 4.1, Hsyn), 2.28 (dddd, 1H, J HH ) 10.1, 1.0, J HP
)
9.9, J RhH ) 0.4, Hanti), 1.58 (d, 9H, J HP ) 10.0, PMe3), 0.97 (d,
9H, J HP ) 8.8, PMe3). The peak marked with an asterisk
decoalesced to a dd on further cooling to -40 °C. 13C{1H} NMR
(CDCl3, selected CH coupling constants and multiplicities in
square brackets): δ 139.56 (dd, J CP ) 24.3, J CRh ) 8.7, C1 [d,
J CH ) 161]), 137.98 (t, J CP ) 4.4, J CRh ) 4.4, C2), 137.56, 132.85,
128.27, 127.74, 126.24, 125.07, 122.86 (Ph), 111.5 (d, J CP
)
3.2, C4 [d, J CH ) 158]), 98.41 (d, J CP ) 28.6, C3), 45.90 (dd, J CP
) 48.7, J CRh ) 8.5, C5 [t, J CH ) 156]), 17.54 (d, J CP ) 29.4,
PMe3 [q, J CH ) 128]), 13.64 (d, J CP ) 24.4, PMe3 [q, J CH ) 131
Hz]). 31P{1H} NMR (CDCl3): δ 8.4 (dd, 1P, J PP ) 12.2, J RhP
)
169, PMe3), -14.4 (dd, 1P, J PP ) 14.4, J RhP ) 136, PMe3). IR
(KBr, cm-1): 1150 m, 1097 m, 1019 m, 963 s, 948 vs.
On cooling to -20 °C, the benzene/petroleum ether filtrate
precipitated 10a as a yellow powder, which was recrystallized
from ether for analysis: mp 142-145 °C, dec. Calcd for
C
23H32P2ClRh: 54.28, C; 6.35, H. Found: 54.29, C; 6.42, H.
1H{31P} NMR (-20 °C, CDCl3): δ 6.76-7.77 (m, 10H, Ph), 5.27
(m, 2H, H3, Hcentral), 3.24 (d, 1H, J HH ) 7.0, Hsyn), 2.55 (dd, 1H,
(34) Padwa, A.; Blacklock, T. J .; Getman, D.; Hatanaka, N.; Loza,
R. J . Org. Chem. 1978, 43, 1481.
(35) Gibson, V. C.; Grainman, C. E.; Hare, P. M.; Green, M. L. H.;
Brandy, J . A.; Grebenik, P. D.; Prout, K. J . Chem. Soc., Dalton Trans.
1985, 2025.
(36) van der Ent, A.; Onderdenlinden, A. L. Inorg. Synth. 1973, 14,
9.

Ring Opening of 1,2-Diphenyl-3-vinyl-1-cyclopropene
Organometallics, Vol. 18, No. 15, 1999 2771
) 3.3, H1), 6.8-7.7 (m, 10H, Ph), 5.63 (td, J HH ) 5.1, J RhH
)
acetonitrile (1 mL), allowed to stand overnight, and passed
through Celite to remove residual AgCl. Evaporation left an
oil, which solidified on the addition of methanol or petroleum
ether, to give 19b as a yellow-orange powder (43 mg, 95%).
2.3, H4), 2.26 (ddtd, 2H, J HH ) 5.2, J HP(eq) ) 10.1, J HP(ax) ) 8.0,
J RhH ) 3.6, H5), 1.16 (virtual t, 18H, J HP ) 3.1, axial PMe3),
0.92 (d, 9H, J HP ) 6.2, equatorial PMe3); 31P{1H} NMR (C6D6)
δ -7.0 (dd, 2P, J RhP ) 109, J PP ) 30, axial PMe3), -24.0 (dt,
1P, J RhP ) 81, J PP ) 30, equatorial PMe3). 18: 1H NMR (C6D6)
Mp: 168-170 °C. 1H NMR (CD3CN): δ 7.50 (dddd, 1H, J HP
)
18.2, 13.1, 1.7, J RhH ) 1.1, H1), 6.94-7.66 (m, 10H, Ph), 5.88
(ddddt, 1H, J HH ) 10.3, 7.0, J HP ) 2.6, 1.1, 0.7, J RhH ) 0.7,
central), 2.97 (dddddd, 1H, J HH ) 7.4, 1.6, J HP ) 5.6, 3.9, 1.0,
J RhH ) 0.7, Hsyn), 2.45 (ddddd, 1H, J HH ) 10.7, 1.3, J HP ) 8.5,
δ 6.83 (m, 1H, H1), 6.8-7.7 (m, 10H, Ph), 6.52 (dtd, 1H, J HH
)
5.8, J HP ) 14.0, J RhH ) 1.2, H4), 2.90 (tddd, 2H, J HH ) 5.7, J HP
) 10.1, 8.4, J RhH ) 3.7, H5), 1.14 (virtual t, 18H, J HP ) 3.2,
axial PMe3), 1.04 (d, 9H, J HP ) 6.3, equatorial PMe3); 31P{1H}
NMR (C6D6) δ -5.32 (dd, 2P, J RhP ) 100, J PP ) 31, axial PMe3),
-25.18 (dt, 1P, J RhP ) 79, J PP ) 31, equatorial PMe3).
On slow cooling to -78 °C, the toluene/petroleum ether
filtrate and washings precipitated 10a (93 mg, 18%). Similar
results were obtained when this preparation was performed
in benzene.
H
6.6, 3.6, J RhH ) 1.8, Hanti), 1.63 (dd, 9H, J HP ) 10.0, J RhH
1.3, PMe3), 1.23 (d, J HP ) 7.3, 9H, PMe3), 1.17 (d, 9H, J HP
8.3, PMe3). 31P {1H} NMR (CD3CN): δ 4.82, (ddd, 1P, J PP
23, 9, J RhP ) 155, PMe3), -17.73 (ddd, 1P, J PP ) 34, 9, J RhP
)
)
)
)
127, PMe3), -21.72 (ddd, 1P, J PP ) 34, 23, J RhP ) 79, PMe3),
-142.93 (sept, 1P, J PF ) 709, PF6). IR (KBr, cm-1): 1308 m,
964 s, 948 s, 870 s, 841 vs, 557 s. This abstraction may also be
performed in benzene or dimethoxyethane with similar results.
The deuterated isomers, 17-d and 18-d, were prepared in
the same manner, using ring-deuterated vinylcyclopropene 9b.
The deuterated isotopomer, 19b-d was prepared similarly.
1
The H and 31P{1H} NMR spectra (C6D6) of both isomers were
1H and 31P NMR spectra: identical to those of the protic
1
identical to those of their protic isotopomers, with the exception
of the missing resonances for H1 at δ 8.31 (17) and 6.83 (18).
17-d: 2H{1H} NMR (C6H6) δ 8.34 (br, D1). 18-d: 2H{1H} NMR
(C6H6) δ 6.81 (br, D1).
(b ) F r om Bis(p h osp h in e) Com p ou n d 11a . Trimethyl-
phosphine (100 µL, 0.98 mmol, 1.1 equiv) dissolved in benzene
(5 mL) was added to an orange solution of 11a (450 mg, 0.885
mmol) in benzene (50 mL). The resulting yellow solution was
stirred for 15 min and then evaporated. Recrystallization of
the resulting yellow residue from ether gave a yellow-orange
powder (674 mg, 79%) whose NMR spectra (C6D6) showed a
2:1 ratio of 17 to 18. 1H and 31P NMR: identical to the spectra
from the one-pot preparation above.
material except for the absence of the H1 signal at δ H 7.50.
2H{1H} NMR (MeCN): δ 7.55 (br s, D1).
(b) By Meta th esis of 17/18. A suspension of NH4PF6 (73
mg, 0.44 mmol, 5 equiv) in acetonitrile (3 mL) was added to a
solution of 17/18 (47 mg, 0.080 mmol) in acetonitrile (3 mL).
The resulting opaque orange suspension was passed through
Celite and evaporated to dryness. Extraction of the residue
with methylene chloride (5 × 1 mL), filtration through Celite,
concentration to near dryness, and precipitation with petro-
leum ether gave an orange powder (50.4 mg, 90%) identical to
that from the abstraction procedure above.
Attem p ted d ep r oton a tion of 19b. With LDA in THF .
Diisopropylamine (0.3 mL, 2 mmol) was treated with n-BuLi
(0.56 mL, 2.4 M in hexanes, 1.3 mmol) at -78 °C, warmed to
room temperature, and diluted to 10 mL. A portion of the
resulting LDA solution (1 mL, 0.13 mmol, 1.0 equiv) was added
to a solution of 19b (80 mg, 1.4 mmol) in THF (10 mL) at -78
°C. The mixture was stirred for 1 h at room temperature and
then evaporated to an oil, whose proton and phosphorus NMR
spectra showed only starting material.
Com p lexes 16. (a ) Ch lor id e Sa lt. Trimethylphosphine
(4.5 µL, 34 mmol, 2 equiv) was added to a yellow solution of
10a (8.8 mg, 17 µmol) in C6D6 (0.5 mL). No change was
observed initially either visually or by 31P NMR. After over-
night standing, the sample showed a 1:5 mixture of 10a and
16a by 31P NMR. On evaporation and redissolution in C6D6,
all of 16a reverted to 10a . 16a : 31P{1H} NMR (C6D6) δ -7.95
(ddd, J PP ) 29.2, 4.4, J RhP ) 146.5, PMe3), -13.90 (ddd, J PP
)
With LDA in Aceton itr ile. 19b (241 mg, 0.412 mmol) and
LDA (42 mg, 0.39 mmol. 0.965 equiv) were dissolved in
acetonitrile (10 1L) at -45 °C. The orange suspension dark-
ened slowly as it warmed to room temperature, although
periodic phosphorus NMR spectra showed no change over 3
h. Three additional equivalents of LDA was added over 48 h
without significant diminution of the starting material peaks,
after which time the mixture smelled strongly of acetamidine.
38.0, 4.5, J RhP ) 133.6, PMe3), -21.50 (ddd, J PP ) 37.9, 29.2,
J RhP ) 75.1, PMe3).
-
(b) P F 6 Sa lt. A solution of 10a (25 mg, 48 µmol) in
acetonitrile (4 mL) was treated with trimethylphosphine (25
µL, 0.24 mmol, 5 equiv), causing the yellow solution to pale
slightly. A solution of NH4PF6 (49 mg, 0.30 mmol, 6 equiv) in
acetonitrile (4 mL) was added and the resulting suspension
purged of NH4Cl by filtration through Celite. The filtrate was
evaporated, and the yellow residue was extracted with meth-
ylene chloride. The extracts were passed through Celite,
concentrated, precipitated with ether, and evaporated to give
16b as a yellow solid (34 mg, 100%). An analytical sample was
recrystallized from methanol. Mp: 115-120 °C, dec. Calcd for
With KH in Eth er . Three doses of potassium hydride (each
roughly 22 mg, 0.54 mmol, 6.4 equiv) were added to a
suspension of 19b (50 mg, 0.086 mmol) in ether (10 mL) over
4 h, followed by overnight stirring, without visible changes.
Sodium hydride (55 mg, 50% oil dispersion, 1.1 mmol, 13 equiv)
was washed with petroleum ether (2 × 1 mL), pumped dry,
and added to the reaction mixture. After being stirred for 4.5
h, the mixture was filtered and concentrated to 2 mL. The
31P{1H} NMR spectrum of the resulting yellow solution showed
primarily starting material and trimethylphosphine oxide.
C
26H41P4F6Rh: 44.97, C; 5.95, H. Found: 44.81, C; 5.96, H.
1H NMR (CD3CN): δ 6.8-7.3 (m, 10 H, Ph), 5.08 (dddd, 1H,
J HH ) 6.9, J HP ) 3.0, 0.9, 0.6, H3), 4.96 (dtdtd, 1H, J HH ) 10.8,
6.9, 6.9, J HP ) 3.9, 1.4, 1.4, J RhH ) 1.1, Hcent), 3.21 (ddddd, 1H,
J HH ) 6.8, 1.5, J HP ) 4.5, 1.8, 0.8, Hsyn), 2.83 (ddddd, 1H, J HH
) 10.7, 1.3, J HP ) 5.7, 5.3, 2.5, Hanti), 1.23 (dd, 9H, J HP ) 9.6,
J RhH ) 0.9, PMe3), 1.66 (dd, 9H, J HP ) 8.6, J RhH ) 0.6, PMe3),
1.30 (d, 9H, J HP ) 7.6, PMe3). 31P{1H} NMR (CD3CN): δ -6.73
(ddd, 1P, J PP ) 29, 4, J RhP ) 150, PMe3), -12.80 (ddd, 1 P, J PP
) 38, 4, J RhP ) 134, PMe3), -20.72, (ddd, 1P, J PP ) 38, 29,
J RhP ) 75, PMe3), -142.9 (sept, 1P, J PF ) 707, PF6). IR (KBr,
cm-1): 1437 s, 1428 s, 794 m, 774 m, 731 s.
Cr ysta l Str u ctu r e Deter m in a tion of 11a . The param-
eters used during the collection of diffraction data for 11a are
contained in Table 1. Orange crystals of 11a were attached to
a
fine glass fiber using epoxy cement. On the basis of
systematic absences in the intensity data, it was determined
that 11a crystallized in one of the rhombohedral space groups
R3, R3h, R32, R3m, or R3hm. R3h was initially chosen on the basis
of E-statistics and the supposed molecular structure and was
subsequently confirmed by the successful solution and well-
behaved refinement of the structure. Unit-cell parameters
were derived from the least-squares fit of the angular settings
of 25 reflections with 20° e 2θ e 26°. All intensity data were
corrected for absorption using an empirical procedure which
Com p lex 19b. (a ) By Ch lor id e Abstr a ction fr om 17/18.
AgPF6 (25 mg, 98 µmol, 1.5 equiv) and 17/18 (38 mg, 64 µmol)
were suspended in methylene chloride (10 mL) containing
trimethylphosphine (20 µL, 0.20 mmol, 3 equiv). The orange
suspension was stirred overnight in the dark, then filtered
through Celite, and evaporated. The residue was dissolved in

2772 Organometallics, Vol. 18, No. 15, 1999
Hughes et al.
uses six parameters to define a pseudoellipsoid. No significant
decay occurred in three standard reflections.
are in Tables 2 and 3. Additional crystallographic data is
available as Supporting Information.
The structure was solved using the direct methods program
SOLV, which located the Rh atom. Remaining non-hydrogen
atoms were located from subsequent difference Fourier syn-
theses and refined anisotropically. Idealized hydrogen atom
positions were calculated (dCH ) 0.96 Å, thermal parameters
equal to 1.2 times the isotropic equivalent for the attached
carbon). The phenyl rings were fixed to fit rigid hexagons.
Final difference Fourier syntheses showed only diffuse back-
grounds (maximum 0.57 e/Å3). All computer programs used
in the data collections and refinements are contained in the
Nicolet program packages p3 and SHELXTL (5.1), Nicolet
XRD, Madison, WI. Atomic coordinates for 11a are contained
in the Supporting Information, and bond lengths and angles
Ack n ow led gm en t. We are grateful to the National
Science Foundation for generous support of this re-
search. A generous loan of rhodium salts from J ohnson
Matthey Aesar/Alfa is also gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Atomic coordinates
and isotropic thermal parameters, bond distances, bond angles,
anisotropic thermal parameters, H-atom coordinates, and
isotropic thermal parameters for 11a . This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
OM990159O