Reaction of Cp*(CO)2Re=Re(CO)2Cp* with alkynes produces dimetallacyclopentenones Cp*(CO)2Re(μ-η1,η 3-CR=CR′CO)Re(CO)Cp* which react with acid to form cationic bridging vinyl complexes

Article abstract of DOI:10.1021/om960658e

Cp*(CO)₂Re=Re(CO)₂Cp* (1) reacted with terminal alkynes HC≡CR (R = H, CH₃, C₆H₅, C(CH₃)=CH₂, OCH₂CH₃) to produce dimetallacyclopentenones Cp*(CO)₂Re(μ-η¹,η ³-CH=CRCO)-Re(CO)Cp* (4-8). The reaction of 1 with alkynes having one ester substituent also gave dimetallacyclopentenones. Reaction of 1 with HC≡CCO₂Me gave Cp*(CO)₂Re[μη¹,η³-CH=C(CO ₂CH₃)CO]Re(CO)Cp* (9) and with CH₃C≡CCO₂Me gave Cp*(CO)₂Re[μ-η¹,η³-(CO ₂-CH₃)C=C(CH₃)CO]Re(CO)Cp* (10). At low temperature, the η²-propyne complex Cp*(CO)₂-Re(μ-CO)Re(CO)(HC≡CCH₃)Cp* (12) and Cp*(CO)₂Re[μ-η¹,η³-C(CH ₃)=CHCO]Re(CO)Cp* (11) were observed as intermediates in the formation of Cp*(CO)₂Re[μ-η¹,η ³-CH=C(CH₃)-CO]Re(CO)Cp* (5). Protonation of dimetallacyclopentenone 2 with CF₃CO₂H produced [Cp*(CO)₂Re(μ-η¹,η²-CH=CH ₂)Re(CO)₂Cp*]⁺CF₃CO ₂^- (14), a species with a bridging vinyl group. Protonation of the thermodynamically favored regioisomeric dimetallacyclopentenone 5 gave [Cp*(CO)₂Re(μ-η¹,η ²-(E)-CH=CHCH₃)Re(CO)₂Cp*] ⁺CF₃CO₂^- (15). Protonation of kinetically formed regioisomeric dimetallacyclopentenone 11 at low temperature gave [Cp*-(CO)₂Re(μ-η¹,η²-CCH ₃=CH₂)Re(CO)₂Cp*]⁺CF ₃CO₂^- (16).

Full text of DOI:10.1021/om960658e

Organometallics 1997, 16, 419-426
419
Rea ction of Cp *(CO)2RedRe(CO)2Cp * w ith Alk yn es
P r od u ces Dim eta lla cyclop en ten on es
Cp *(CO)2Re(µ-η1,η3-CRdCR′CO)Re(CO)Cp * Wh ich Rea ct
w ith Acid To F or m Ca tion ic Br id gin g Vin yl Com p lexes
Charles P. Casey,* Ronald S. Carin˜o, and Hiroyuki Sakaba
Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706
Received August 6, 1996X
Cp*(CO)2RedRe(CO)2Cp* (1) reacted with terminal alkynes HCtCR (R ) H, CH3, C6H5,
C(CH3)dCH2, OCH2CH3) to produce dimetallacyclopentenones Cp*(CO)2Re(µ-η1,η3-CHdCRCO)-
Re(CO)Cp* (4-8). The reaction of 1 with alkynes having one ester substituent also gave
dimetallacyclopentenones. Reaction of 1 with HCtCCO2Me gave Cp*(CO)2Re[µ-η1,η3-
CHdC(CO2CH3)CO]Re(CO)Cp* (9) and with CH3CtCCO2Me gave Cp*(CO)2Re[µ-η1,η3-(CO2-
CH3)CdC(CH3)CO]Re(CO)Cp* (10). At low temperature, the η2-propyne complex Cp*(CO)2-
Re(µ-CO)Re(CO)(HCtCCH3)Cp* (12) and Cp*(CO)2Re[µ-η1,η3-C(CH3)dCHCO]Re(CO)Cp*
(11) were observed as intermediates in the formation of Cp*(CO)2Re[µ-η1,η3-CHdC(CH3)-
CO]Re(CO)Cp* (5). Protonation of dimetallacyclopentenone 2 with CF3CO2H produced
[Cp*(CO)2Re(µ-η1,η2-CHdCH2)Re(CO)2Cp*]+CF3CO2 (14), a species with a bridging vinyl
-
group. Protonation of the thermodynamically favored regioisomeric dimetallacyclopentenone
5 gave [Cp*(CO)2Re(µ-η1,η2-(E)-CHdCHCH3)Re(CO)2Cp*]+CF3CO2 (15). Protonation of
-
kinetically formed regioisomeric dimetallacyclopentenone 11 at low temperature gave [Cp*-
(CO)2Re(µ-η1,η2-CCH3dCH2)Re(CO)2Cp*]+CF3CO2 (16).
-
Sch em e 1
In tr od u ction
Cp*(CO)2RedRe(CO)2Cp* (1) is a rare example of a
dimer of a d6, 16 electron fragment.1 1 is thermally
stable but is extremely reactive toward H2 and nucleo-
philes. 1 forms the bridging dihydride Cp*(CO)2Re(µ-
H)2Re(CO)2Cp* upon exposure to H2 at -78 °C and adds
ligands such as CO, PMe3, CH2dCH2, and CH3CN to
form the binuclear adducts Cp*(CO)2Re(µ-CO)Re(CO)-
(L)Cp*.2 The reactions of 1 with alkynes are particu-
larly intriguing because of the wide variety of products
observed (Scheme 1). Acetylene2 and HCtCC-
3
(CH3)dCH2 react with 1 to form dimetallacyclopenten-
ones which are stable at room temperature but rear-
range to bridging vinylidene complexes upon heating.
2-Butyne reacts with 1 to form the observable 1:1 adduct
Cp*(CO)2Re(µ-CO)Re(CO)(η2-CH3CtCCH3)Cp* (2) which
rearranges to a dimetallacyclopentenone at -40 °C,
which in turn fragments at room temperature to give
Cp*Re(CO)3 and the 4-electron donor alkyne complex
Cp*Re(CO)(CH3CtCCH3).2 Dimethyl acetylenedicar-
boxylate (DMAD), an alkyne with strong electron-
withdrawing substituents, reacts with 1 to give the
effort to probe the steric and electronic effects of
substituents on the stability of the dirhenium products.
We also report that protonation of dimetallacyclopen-
tenones leads to bridging vinyl dirhenium cations.
dimetallacyclobutene
Cp*(CO)2Re(µ-η1,η1-CH3O2-
CCdCCO2CH3)Re(CO)2Cp* (3), which upon photolysis
rearranges to the dimetallabicylobutane complex Cp*-
(CO)2Re(µ-η2,η2-CH3O2CCtCCO2CH3)Re(CO)2Cp*.4
Here we report the reactions of 1 with terminal and
internal alkynes bearing a variety of substituents in an
Resu lts
Dim et a lla cyclop en t en on es
fr om
Ter m in a l
Alk yn es. Reaction of a dark green C6D6 solution of
Cp*(CO)2RedRe(CO)2Cp* (1) with a variety of terminal
alkynes gave the dimetallacyclopentenone complexes
Cp*(CO)2Re(µ-η1,η3-CHdCRCO)Re(CO)Cp* [alkyne )
HCtCH (4),2 HCtCCH3 (5), HCtCC6H5 (6), HCtCC-
(CH3)dCH2 (7),3 and HCtCOCH2CH3 (8)]. All reactions
took place very rapidly at room temperature as indi-
cated by an immediate color change from green to
orange (4-7) or red (8). In each reaction, only a single
regioisomer with hydrogen â to the ketone carbonyl was
X Abstract published in Advance ACS Abstracts, J anuary 1, 1997.
(1) Casey, C. P.; Sakaba, H.; Hazin, P. N.; Powell, D. R. J . Am. Chem.
Soc. 1991, 113, 8165.
(2) Casey, C. P.; Carin˜o, R. S.; Sakaba, H.; Hayashi, R. K. Organo-
metallics 1996, 15, 2640.
(3) Casey, C. P.; Ha, Y.; Powell, D. R. J . Am. Chem. Soc. 1994, 116,
3424.
(4) Casey, C. P.; Carin˜o, R. S.; Hayashi, R. K.; Schladetzky, K. D.
J . Am. Chem. Soc. 1996, 118, 1617.
S0276-7333(96)00658-9 CCC: $14.00 © 1997 American Chemical Society

420 Organometallics, Vol. 16, No. 3, 1997
Casey et al.
observed. The dimetallacyclopentenones were formed
in >95% NMR yield (except for 6 which was formed in
70% NMR yield) and were isolated in moderate to good
yields (48-73%) as colored powders. The solid dimet-
allacyclopentenones are slightly air sensitive but were
stable in solution in sealed tubes.
Dim eta lla cyclop en ten on es fr om Alk yn es w ith
On e Ester Su bstitu en t. In contrast to the formation
of dimetallacyclopentenones from the reactions of 1 with
terminal alkynes, the reaction of 1 with dimethyl
acetylenedicarboxylate produced the 3,4-dimetalla-
cyclobutene 3. The formation of dimetallacyclobutenes
from reactions of alkynes bearing two electron-with-
drawing groups such as CO2R or CF3 with bimetallic
compounds is common.8 Calculations performed by
Hoffmann8a showed that electron-withdrawing substit-
uents stabilize the dimetallacyclobutene. The reactions
of 1 with alkynes bearing a single ester substituent were
studied to see whether a dimetallacyclopentenone or a
dimetallacyclobutene would be formed. Dimetallacy-
clobutenes with a single electron withdrawing substitu-
ent are rare.9
1
In the H NMR spectra of dimetallacyclopentenones
4-8, the inequivalent Cp* ligands gave rise to two
intense singlets between δ 1.6 and 1.9. A characteristic
high-frequency resonance (δ 7.99-9.29 in C6D6) was
observed for the proton â to the ketone carbonyl and
bound to the carbon bridging the rhenium centers. This
assignment was based on a comparison to the chemical
shift of the corresponding proton in Cp*(CO)2Re{µ-η1,η3-
CHdC[C(CH3)dCH2]CO}Re(CO)Cp* (7) (δ 8.27), a com-
pound for which an X-ray crystal structure has been
reported.3 In the acetylene adduct 4, the resonance for
the proton on the carbon R to the ketone appeared at δ
3.57.2
In the 1H NMR spectrum at 100 °C, the Cp* reso-
nances of the dimetallacyclopentenone 5 derived from
propyne remained sharp. The significance of this
important observation in relation to the mechanism of
interconversion of dimetallacyclopentenones and dimet-
allabicyclobutenes will be dealt with in the Discussion
section.
The 13C NMR spectra for 4-8 showed two sets of
resonances for the Cp* ring and methyl carbons. Each
compound exhibited four resonances between δ 214 and
206 which were assigned to the terminal CO and ketone
carbonyls. The resonance for the CH carbon â to the
ketone appeared between δ 112 and 136, which is in
the region expected for a methine carbon bridging two
metal centers.5 The resonances assigned to the carbon
R to the ketone appeared between δ 21 and 53, except
in the case of the ethyl ethynyl ether adduct 8 which
was observed at δ 91.5.
The reaction of methyl propynoate with a green
solution of 1 gave a red-orange solution from which Cp*-
(CO)2Re[µ-η1,η3-CHdC(CO2CH3)CO]Re(CO)Cp* (9) was
isolated as an orange powder in 70% yield. Spectral
data established the dimetallacyclopentenone structure
of 9. The infrared spectrum of 9 had terminal CO
absorbances at 1953 (s), 1906 (vs), and 1869 (s) cm-1
with an intensity pattern similar to that of dimetalla-
cyclopentenones 4-8 and lower energy bands at 1729
(m) and 1704 (m) cm-1 assigned to the ester and ketone
1
carbonyls. In the H NMR spectrum of 9 in CD2Cl2 at
-10 °C, resonances were observed at δ 1.88 and 1.84
for inequivalent Cp* ligands and at δ 8.9210 for the CH
â to the ketone carbonyl and bound to the carbon
bridging the rhenium centers. In the 13C NMR spec-
trum of 9, characteristic resonances at δ 34.7 and 124.8
were assigned to the R- and â-carbons of the dimetalla-
cyclopentenone unit.
The carbonyl region of the infrared spectra of dimet-
allacyclopentenones 4-8 displayed three bands for
terminal CO’s (1951-1848 cm-1) and one lower energy
band (1712-1676 cm-1) for the ketone carbonyl. The
stretching frequencies of the ketones were in the range
for µ-η1,η3-dimetallacyclopentenones in which the alkene
was coordinated to the metal bearing the acyl group.6,7
All spectral data for dimetallacyclopentenones 4-8
were similar to those of related Fe2 and Ru2 and mixed
Fe-Pt, Os-Rh, and Os-Co dimetallacyclopentenones
such as the following structures:6,7
Reaction of a green solution of 1 with methyl 2-bu-
tynoate gave an instantaneous color change to a purple
solution from which the dimetallacyclopentenone Cp*-
(CO)2Re[µ-η1,η3-(CO2CH3)CdC(CH3)CO]Re(CO)Cp* (10)
was isolated as a purple solid in 62% yield. The IR
spectrum of 10 displayed the “fingerprint” for a dimet-
allacyclopentenone with absorbances for the terminal
CO ligands at 1944 (s), 1909 (vs), and 1867 (s) cm-1 and
lower energy bands at 1712 (m), 1702 (m), and 1689 (m)
(5) Casey, C. P.; Audett, J . Chem. Rev. 1986, 86, 339.
(6) (a) Dyke, A. F.; Knox, S. A. R.; Naish, P. J .; Taylor, G. E. J . Chem.
Soc., Dalton Trans. 1982, 1297. (b) Muller, F.; Han, I. M.; van Koten,
G.; Vrieze, K.; Heijdenrijk, D.; van Mechelen, J .; Stam, C. H. Inorg.
Chim. Acta 1989, 158, 99. (c) Fontaine, X. L. R.; J acobsen, G. B.; Shaw,
B. L.; Thornton-Pett, M. J . Chem. Soc., Dalton Trans. 1988, 741. (d)
Burn, M. J .; Kiel, G.-Y.; Seils, F.; Takats, J .; Washington, J . J . Am.
Chem. Soc. 1989, 111, 6850. (e) Washington, J . S. Ph.D. Thesis, Univ.
of Alberta, 1994. (f) Dyke, A. F.; Knox, S. A. R.; Morris, M. J .; Naish,
P. J . J . Chem. Soc., Dalton Trans. 1983, 1417.
(8) (a) Hoffman, D. M.; Hoffmann, R.; Fisel, C. R. J . Am. Chem. Soc.
1982, 104, 3858 and references therein. (b) Holton, J .; Lappert, M. F.;
Pearce, R.; Yarrow, P. I. W. Chem. Rev. 1983, 83, 135.
(9) (a) Mague, J . T.; Klein, C. L.; Majeste, R. J .; Stevens, E. D.
Organometallics 1984, 3, 1860. (b) Bushnell, G. W.; Decker, M. J .;
Eadie, D. T.; Stobart, S. R.; Vefghi, R.; Atwood, J . L.; Zaworotko, M. J .
Organometallics 1985, 4, 2106. (c) Muller, F.; van Koten, G.; Polm, L.
H.; Vrieze, K.; Zoutberg, M. C.; Heijdenrijk, D.; Kragten, E.; Stam, C.
H. Organometallics 1989, 8, 1340.
(7) The absorbance for the ketone in the µ-η1,η1-dimetallacyclopen-
tenone (CO)2Ru(µ-η1,η1-CHdCHCO)(µ-DPPM)2Ru(CO)2 appears at
1534 cm-1: Mirza, H. A.; Vittal, J . J .; Puddephatt, R. J . Organometallics
1994, 13, 3063. See also: J ohnson, K. A.; Gladfelter, W. L. Organo-
metallics 1992, 11, 2534.
(10) The resonance at δ 8.92 was sharp at -10 °C (ω1/2 ) 0.63 Hz)
but selectively broadened at higher temperature (ω1/2 ) 7.4 Hz, 25 °C).
We do not understand this broadening.

Dimetallacyclopentenones
Organometallics, Vol. 16, No. 3, 1997 421
cm-1 assigned to the ester and ketone carbonyls. In the
13C NMR spectrum of 10, resonances at δ 41.4 and 135.9
were assigned to the R- and â-carbons of the dimetal-
lacyclopentenone.
δ ∼7 for (η2-HCtCC6H5)2Mo(Ph2PCH2CH2PPh2)2,13 and
δ 7.68 for Cp2Mo(η2-HCtCH)14 ]. However, this low-
frequency chemical shift is also consistent with formula-
tion of the first intermediate as the dimetallatricyclo-
pentanone Cp*(CO)Re(µ-CO)[µ-η2,η2-C(CH3)CHCO]-
Re(CO)Cp* (A). The only reported dimetallatricyclo-
pentanone with a hydrogen substituent is Chetcuti’s
CpNi[µ-η2,η2-C(Ph)CHCO]Mo(CO)2Cp, which has a 1H
NMR chemical shift of δ 7.45 for the key hydrogen.15
When the temperature of the reaction mixture of 1
and propyne was raised to -70 °C, the amount of 12
decreased and the amount of the minor component 11
increased. After 14 min at -70 °C, the ratio of 12:11
was 67:33. When the temperature was raised to -60
°C, a third compound 5 slowly began to appear. After
13 min at -60 °C, the ratio of 12:11:5 was 16:69:15.
After 23 min at -60 °C, 12 had completely disappeared
and 11 and 5 were observed in a ratio of 58:42. After
63 min at -60 °C, the dimetallacyclopentenone Cp*-
(CO)2Re[µ-η1,η3-CHdC(CH3)CO]Re(CO)Cp* (5) (the iso-
lated product of the room-temperature reaction) was the
major product and only a trace of 11 remained (11:5 )
5:95).
Without a proton substituent on the dimetallacyclo-
pentenone, the regiochemistry of 10 was more difficult
to assign. The regiochemistry of 10 was assigned on
the basis of the comparison of the chemical shift of the
methyl group in 10 (δ 1.93) to the chemical shifts of the
methyl groups in the two regioisomeric propyne adducts
Cp*(CO)2Re[µ-η1,η3-CHdC(CH3)CO]Re(CO)Cp* (5, δ 1.83)
and Cp*(CO)2Re[µ-η1,η3-(CH3)CdCHCO]Re(CO)Cp* (11,
δ 2.95, see below). From this we conclude that the ester
substituent is bound to the bridging carbon and the
methyl group is bound to the carbon R to the ketone.
Sch em e 2
The spectra of the second intermediate 11 are con-
sistent with its formulation as the regioisomeric dimet-
allacyclopentenone Cp*(CO)2Re[µ-η1,η3-C(CH3)dCHCO]-
Re(CO)Cp* (11) in which the methyl-substituted carbon
1
bridges the two Re centers. In the H NMR spectrum
Low -Tem p er a tu r e Obser va tion of Tw o In ter m e-
d ia tes in th e Rea ction of P r op yn e w ith 1. To probe
the mechanism of alkyne addition to 1, the reactions
of 11, inequivalent Cp* resonances were observed at δ
1.75 and 1.52. The chemical shift of the methine proton
of 11 at δ 3.06 (br s) was quite similar to that of the
proton R to the ketone in the dimetallacyclopentenone
4 formed from acetylene (δ 3.57) and greatly different
from that of the proton â to the ketone in 4 (δ 8.14).
The chemical shift of the methyl resonance of 11 at δ
2.95 (br s) appeared near that of one of the two methyl
resonances (δ 2.92, 1.68) of the dimetallacyclopentenone
13 formed from 2-butyne.2
µ-Vin yl Com p lexes fr om P r oton a tion of Dim et-
a lla cyclop en ten on es. Knox6f has shown that diferra-
and diruthenacyclopentenones undergo selective proto-
nolysis of the CRsCdO bond to give cationic bridging
vinyl complexes. We began a study of the protonation
of dirhenacyclopentenones in an effort to provide more
evidence concerning the regiochemistry of 11, the kinetic
regioisomer obtained in the reaction of 1 with propyne.
1
were monitored at low temperature by H NMR spec-
troscopy. The reaction of 1 with acetylene was too fast
to observe an intermediate even at -78 °C.2 However,
when the course of the reaction of propyne with 1 was
1
followed by H NMR spectroscopy at low temperature,
two intermediates were observed prior to the formation
1
of dimetallacyclopentenone 5 (Scheme 2). A H NMR
spectrum taken after 21 min at -80 °C revealed an 80:
1
20 mixture of two compounds. The H NMR spectrum
of the major component is consistent with formulation
as the η2-alkyne complex Cp*(CO)2Re(µ-CO)Re(CO)(η2-
HCtCCH3)Cp* (12). Resonances for inequivalent Cp*
ligands were observed at δ 1.73 and 1.51. The reso-
nance for the alkyne proton appeared at δ 6.84 (q, J )
2.2 Hz) and a methyl resonance appeared at δ 2.30 (d,
J ) 2.2 Hz). Due to the short lifetime of 12, 13C NMR
and IR spectra were not obtained.
The reaction of dimetallacyclopentenone 4 (from
HCtCH and 1) with CF3CO2H in toluene led to cleavage
of the CRsCdO bond and formation of the yellow µ-vinyl
complex [Cp*(CO)2Re(µ-η1,η2-CHdCH2)Re(CO)2Cp*]+CF3-
The structure of 12 is similar to that previously
assigned to the 1:1 adduct Cp*(CO)2Re(µ-CO)Re(CO)-
(η2-CH3CtCCH3)Cp* (2) which was formed in the
reaction of 1 with 2-butyne at -60 °C and which
rearranged to the dimetallacyclopentenone Cp*(CO)2Re-
[µ-η1,η3-C(CH3)dC(CH3)CO]Re(CO)Cp* (13) at -40 °C.
The structure of 2 was supported by low-temperature
-
CO2 (14) in 52% isolated yield. In the 1H NMR
spectrum (CD2Cl2), inequivalent Cp* resonances were
seen at δ 2.06 and 2.05. The vinyl hydrogen on the
1
(11) Bullock, R. M. J . Chem. Soc., Chem. Commun. 1989, 165.
(12) Casey, C. P.; Yi, C. S.; Gavney, J . A., J r. J . Organomet. Chem.
1993, 443, 111.
(13) Hills, A.; Hughes, D. L.; Kashef, N.; Lemos, M. A. N. D. A.;
Pombeiro, A. J . L.; Richards, R. L. J . Chem. Soc., Dalton Trans. 1992,
1775.
IR and H NMR spectroscopy. The infrared spectrum
of 2 at -78 °C showed bands for three terminal
carbonyls (1925, 1892, 1855 cm-1) and a bridging
1
carbonyl (1662 cm-1). The H NMR spectrum of 2 at
-60 °C showed inequivalent Cp*’s (δ 1.73, 1.56) and a
single broad resonance for the methyl groups (δ 2.41,
ω1/2 ) 8 Hz).
The δ 6.84 chemical shift for the CH resonance
assigned to 12 falls in the range previously reported for
η2-terminal alkyne complexes [δ 4.02 for CpRu(PMe3)2-
(η2-HCtCCH3),11 δ 4.8 for Cp*Re(CO)2(η2-HCtCCH3),12
(14) Wong, K. L. T.; Thomas, J . L.; Brintzinger, H. H. J . Am. Chem.
Soc. 1974, 96, 3694.
(15) Chetcuti, M. J .; Eigenbrot, C.; Green, K. A. Organometallics
1987, 6, 2298. For other reports of dimetallatricyclopentanones, see:
Dickson, R. S.; Evans, G. S.; Fallon, G. D. Aust. J . Chem. 1985, 38,
273. Finnimore, S. R.; Knox, S. A. R.; Taylor, G. E. J . Chem. Soc.,
Dalton Trans. 1982, 1783. Boag, N. M.; Goodfellow, R. J .; Green, M.;
Hessner, B.; Howard, J . A. K.; Stone, F. G. A. J . Chem. Soc., Dalton
Trans. 1983, 2585.

422 Organometallics, Vol. 16, No. 3, 1997
Casey et al.
regiospecific. Treatment of 10 with CF3CO2H in toluene
gave a 60:40 mixture of the two regioisomeric µ-vinyl
cation complexes {Cp*(CO)2Re[µ-η1,η2-(E)-CC(CO2-
CH3)dCH(CH3)]Re(CO)2Cp*}+CF3CO2- (20) and {Cp*-
(CO)2Re[µ-η1,η2-(E)-C(CH3)dCH(CO2CH3)]Re(CO)2-
-
Cp*}+CF3CO2 (21).
Treatment of dimetallacyclobutene 316 with CF3CO2H
produced the µ-vinyl complex {Cp*(CO)2Re[µ-η1,η2-(E)-
(CH3CO2)CdCH(CO2CH3)]Re(CO)2Cp*}+CF3CO2- (22).
carbon bridging the rheniums appeared at δ 7.92 (dd,
J trans ) 12 Hz, J cis ) 9 Hz) and the dCH2 protons were
observed at δ 4.07 (dd, J cis ) 9 Hz, J gem ) 1.4 Hz) and
2.63 (dd, J trans ) 12 Hz, J gem )1.4 Hz). The reaction of
4 with CF3CO2D was stereospecific. The δ 2.63 reso-
nance due to the vinyl hydrogen cis to Re was absent
in deuterated vinyl complex [Cp*(CO)2Re(µ-η1,η2-(Z)-
-
CHdCHD)Re(CO)2Cp*]+CF3CO2 (14-d).
Reaction of the thermodynamic regioisomer 5 (from
1 and propyne) with CF3CO2H gave a single µ-vinyl
complex, [Cp*(CO)2Re(µ-η1,η2-(E)-CHdCHCH3)Re(CO)2-
The 1H NMR spectrum of 22 had resonances for in-
equivalent Cp* ligands (δ 2.13, 2.06), inequivalent
methoxy groups (δ 3.78, 3.75), and a vinyl proton (δ
2.37). Previously, Stone reported that protonation of
the diplatinacyclobutene (cod)Pt(µ-η1,η1-CF3C)CCF3)-
Pt(cod) (cod ) cyclooctadiene) with HBF4‚Et2O gave the
-
Cp*]+CF3CO2 (15), in 62% isolated yield (Scheme 2).
The 1H NMR spectrum of 15 consisted of resonances
for inequivalent Cp* ligands at δ 2.11 and 2.05, a methyl
doublet at δ 1.90 (d, J ) 6.2 Hz), and vinyl resonances
at δ 7.50 (d, J trans ) 11.4 Hz) and 3.06 (dq, J trans ) 11.6,
J ) 6.2 Hz). The magnitude of the coupling between
the vinyl protons is consistent with an E configuration
of the vinyl group.
µ-vinyl cation [(cod)Pt(µ-η1,η2-CF3CdCHCF3)Pt(cod)]+-
-
BF4
and that protonation of (cod)Pt(µ-η1,η1-p-
MeOC6F4CdCC6F4-p-OMe)Pt(cod) gave the bridging
hydride [(cod)Pt(µ-H)(µ-η1,η1-p-MeOC6F4CdCC6F4-p-
The protonation of the kinetic regioisomer 11 formed
in the reaction of 1 with propyne at -60 °C gave a
different µ-vinyl complex. In an NMR tube reaction of
1 with propyne at -60 °C, a color change to orange over
5 min indicated the formation of the initial dimetalla-
cyclopentenone 11 (Scheme 2). Treatment of this solu-
tion of 11 with excess CF3CO2H at -60 °C gave a fast
- 17
OMe)Pt(cod)]+BF4
.
Discu ssion
Mech a n ism of In ter con ver sion of Regioisom er ic
Dim eta lla cyclop en ten on es. The dimetallacyclopen-
tenones Cp*(CO)2Re(µ-η1,η3-HCdCHCO)Re(CO)Cp* (4)
and Cp*(CO)2Re(µ-η1,η3-C(CH3)dC(CH3)CO)Re(CO)Cp*
(13) are both fluxional molecules. Variable-temperature
1H NMR spectroscopy of 4 showed coalescence of the
Cp* resonances at 70 °C (∆Gq ) 16.8 kcal mol-1).
Magnetization transfer experiments on 4 showed that
the methine protons exchanged environments with an
activation barrier (∆Gq ) 16.9 kcal mol-1) similar to that
for the Cp* exchange. Substantially lower barriers were
seen for coalescence of the Cp* resonances (∆Gq ) 13.6
( 0.3 kcal mol-1) and the methyl resonances (∆Gq )
14.6 ( 1.0 kcal mol-1) of 13. While an η2-alkyne
complex such as 2 could account for interchange of
methyl environments, a symmetric intermediate such
as dimetallacyclobutene B or dimetallabicyclobutane C
are required to explain the simultaneous interchange
of both the Cp* and dimetallacyclopentenone substitu-
ent environments (Scheme 3).
1
color change to yellow. The H NMR spectrum of the
yellow solution indicated the clean formation of the
cationic bridging vinyl complex [Cp*(CO)2Re(µ-η1,η2-
CCH3dCH2)Re(CO)2Cp*]+CF3CO2- (16); no resonances
for the µ-vinyl complex 15 derived from the thermo-
dynamic regioisomer 5 were observed. Evaporation of
solvent and crystallization from Et2O gave pure 16 in
52% isolated yield.
The 1H NMR spectrum of 16 (CD2Cl2) showed in-
equivalent Cp* resonances (δ 2.07, 2.03), a broad methyl
resonance at δ 3.13, and vinyl resonances at δ 4.09 (d,
J ) 0.8 Hz) and 1.95 (d, J ) 0.8 Hz). The absence of a
far downfield resonance for a proton on a bridging
carbon confirmed that the methyl occupied the R posi-
tion. The chemical shifts and the small geminal cou-
pling constant for the vinyl protons were similar to those
seen for the dCH2 group of the unsubstituted bridging
vinyl complex 14.
When CF3CO2H was added to the solution of 1 and
propyne after 15 min reaction time at -60 °C, a 1:1
mixture of µ-vinyl complexes 15 and 16 was observed.
Dimetallacyclopentenones 6, 8, and 9 also reacted with
CF3CO2H in toluene to produce cationic bridging vinyl
complexes 17, 18, and 19 which were isolated as yellow-
orange powders in low to moderate yields (37-65%).
Sch em e 3
(16) Protonation of the dimetallabicyclobutane complex Cp*(CO)2Re-
(µ-η2,η2-CH3O2CCtCCO2CH3)Re(CO)2Cp* with CF3CO2H also pro-
duced µ-vinyl complex 22.
(17) Boag, N. M.; Green, M.; Stone, F. G. A. J . Chem. Soc., Chem.
Commun. 1980, 1281.
Surprisingly, protonation of the dimetallacyclopen-
tenone 10 derived from methyl 2-butynoate was not

Dimetallacyclopentenones
Organometallics, Vol. 16, No. 3, 1997 423
1
Variable-temperature H NMR spectroscopy experi-
ments on Cp*(CO)2Re(µ-η1,η3-CHdCCH3CO)Re(CO)Cp*
(5) allowed us to rule out dimetallabicyclobutanes as
intermediates in the isomerization of regioisomeric
dimetallacyclopentenones and the fluxional process that
interchanges the environments of Cp* ligands in 4 and
13. No excess line broadening (ω1/2 ) 1.0 Hz) in the
Cp* resonances of 5 was observed at 100 °C. Assuming
a maximum excess line broadening of 0.2 Hz at 100 °C
allowed calculation of a maximum rate of exchange of
3 s-1 and a minimum barrier of ∆Gq ) 23 kcal mol-1
for the interchange of Cp* environments. If propyne-
derived dimetallacyclopentenone 5 interconverts with
its regioisomer 11 via a dimetallabicyclobutane, then
the barrier for Cp* interchange would be expected to
be intermediate between that of the HCtCH derived
dimetallacyclopentenone 4 (∆Gq ) 16.8 kcal mol-1) and
that of the CH3CtCCH3 derived dimetallacyclopenten-
one 13 (∆Gq ) 13.6 kcal mol-1). Since the barrier for
Cp* interchange must be higher than 23 kcal mol-1, a
dimetallabicyclobutane can be excluded as an interme-
diate.
symmetry-forbidden 2 + 2 cycloaddition; we suggested
that 3 is formed in a stepwise manner by initial
formation of an unstable η2-alkyne dirhenium complex
followed by rearrangement.
The fluxional behavior of dirhenacyclopentenones 4
and 13 taken together with the rearrangement of 11 to
its regioisomer 5 provides compelling evidence for an
equilibrium between dirhenacyclopentenones and dirhen-
acyclobutenes and for the greater stability of dirhena-
cyclopentenones derived from most alkynes. Two ester
substituents are apparently required to invert the
normally greater stability of the dimetallacyclopenten-
ones as seen in the formation of dimetallacyclobutene
3 from reaction of DMAD with 1. Even alkynes with a
single ester substituent such as HCtCCO2Me and
MeCtCCO2Me form only dimetallacyclopentenones 9
and 10. Apparently, the strongly electron-withdrawing
ester substituents selectively stabilize dirhenacyclo-
butenes relative to dirhenacyclopentenones. The sta-
bilizing effect of electron-withdrawing substituents on
a dirhenacyclobutene are readily explained; a µ-DMAD
unit is electronically similar to a µ-CO group and can
effectively remove electron density from the electron rich
rhenium centers. There are numerous examples of
dimetallacyclobutenes with electron-withdrawing CF3
or CO2R substituents.8 Electron-withdrawing substit-
uents apparently have less influence on the stability of
dirhenacyclopentenones.
Crude estimates of the half-life for the conversion of
Cp*(CO)2Re(µ-η1,η3-CCH3dCHCO)Re(CO)Cp* (11) to its
regioisomer 518 allowed us to calculate ∆Gq ) 15 kcal
mol-1 for the process. This barrier is intermediate
between the barriers measured for the Cp* coalescence
of 4 (16.8 kcal mol-1) and 13 (13.6 kcal mol-1). We
suggest that conversion of 11 to its regioisomer 5
proceeds via the same process which equilibrates the
Cp* signals in 4 and 13 and that these processes all
involve dimetallacyclobutene intermediates.
Rela tive Sta bility of (η2-Alk yn e)d ir h en iu m Com -
p lexes, Dir h en a cyclobu ten es, a n d Dir h en a cyclo-
p en ten on es. Cp*(CO)2RedRe(CO)2Cp* (1) reacts with
various alkynes to give a fascinating array of products
including (η2-alkyne)dirhenium complexes, dimetalla-
cyclopentenones, dimetallacyclobutenes, and dimetall-
abicyclobutanes (Scheme 1). The dimetallacyclopen-
tenone 4 derived from acetylene was stable at 105 °C
for over 10 min, but the dimetallacyclopentenone 13
derived from 2-butyne fragmented to Cp*Re(CO)3 and
the 4-electron donor alkyne complex Cp*Re(CO)(CH3-
CtCCH3) at room temperature. These results prompted
us to further investigate the factors which determine
the chemoselectivity of the reaction of 1 with alkynes
and the factors which control the stability of dimetal-
lacyclopentenones.
Electronic effects are apparently unimportant in
controlling the stability of dimetallacyclopentenones
with respect to fragmentation to 4-electron donor alkyne
complexes Cp*Re(CO)(alkyne). Dimetallacyclopenten-
ones with a single electron-withdrawing ester substitu-
ent (9 and 10) or an electron donor alkoxy substituent
(8) are thermally stable. The fact that dirhenacyclo-
pentenone 13 derived from 2-butyne fragmented at room
temperature while adducts of terminal alkynes were
stable suggested that steric factors may determine the
stability of the dirhenacyclopentenones. Examination
of molecular models revealed that a substituent on the
carbon R to the ketone was in a relatively uncrowded
environment while a substituent on the â carbon bridg-
ing the two rhenium was in close proximity to the Cp*
ligands on both metals. In dimetallacyclopentenones
derived from terminal alkynes a proton occupies the
more crowded â site, but this option does not exist for
dimetallacyclopentenone 13 derived from 2-butyne.
It is curious that the internal alkyne methyl 2-bu-
tynoate forms the stable dimetallacyclopentenone 10.
One could argue that the ester group is small enough
to occupy the crowded â site without significant interac-
tion with the Cp* ligands. It is also possible that the
electron-withdrawing group stabilizes the product with
respect to fragmentation. One possible reason that the
2-butyne adduct fragments is that the product Cp*Re-
(CO)(CH3CtCCH3) contains an alkyne acting as a four-
electron donor. A less electron-releasing alkyne such
as methyl 2-butynoate may not be able to stabilize a
similar product.
Overall, our observations on the reactions of 1 with
alkynes suggest that (η2-alkyne)dirhenium complexes,
dirhenacyclobutenes, and dirhenacyclopentenones are
all readily interconverted. The least stable of these
species are the η2-alkyne dirhenium complexes such as
propyne complex 12 and 2-butyne complex 2; these
kinetically formed products rearranged to dimetallacy-
clopentenones well below room temperature. Earlier we
suggested the possibility that the decomposition of the
dimetallacyclopentenone 13 occurred by initial reversal
to the less stable η2-alkyne complex 2 followed by
fragmentation to Cp*Re(CO)3 and Cp*Re(CO)-
(CH3CtCCH3). The reaction of DMAD with 1 produced
the dirhenacyclobutene 3, the formal product of a
Regioselectivity of th e Rea ction of 1 w ith P r o-
p yn e. Any explanation of the regioselectivity of the
addition of propyne to 1 is necessarily complicated by
the low barrier to interconversion of dirhenacyclopen-
tenones and dirhenacyclobutenes, either of which might
be the kinetic product of rearrangement of the initially
(18) Assuming a first-order rate constant for the conversion of 11
to 5 allowed estimation of a rate constant k ) 9.6 × 10-4 s-1 and an
activation barrier of ∆Gq ) 15 kcal mol-1
.

424 Organometallics, Vol. 16, No. 3, 1997
Casey et al.
Sch em e 4
ment of the dimetallacyclopentenone to a dimetallacy-
clobutene prior to protonation can be excluded since it
is inconsistent with the regioselective cleavage of the
regioisomeric dimetallacyclopentenones 5 and 11. The
observation that the dimetallacyclobutene 3 derived
from DMAD is cleaved by acid to give a (µ-vinyl)-
dirhenium cation is consistent with the latter mecha-
nism.
Knox found that diruthenacyclopentenone 23 is cleaved
by acid to give a µ-vinyl cation 24.6f The reaction
proceeds via the isolable intermediate 25. It is not clear
whether 25 is converted directly to the µ-vinyl cation
24 or whether it first reverts to the starting dimetalla-
cyclopentenone 23.
observed η2-propyne complex 12. The most straight-
forward explanation for the course of the reaction of 1
with propyne involves initial formation of η2-propyne
complex 12, followed by conversion to the more crowded
kinetic regioisomeric dimetallacyclopentenone 11, and
finally isomerization to the less crowded thermodynami-
cally favored dimetallacyclopentenone 5 via dimetalla-
cyclobutene intermediate D (Scheme 4). A possible
rationale for the selective formation of kinetic regioiso-
mer 11 is that carbon-carbon bond formation between
CO and the less crowded terminal alkyne carbon is
preferred even though it leads to the less stable regio-
isomer.
Another route to the kinetic regioisomer 11 that
cannot be excluded involves initial conversion of η2-
propyne complex 12 to dimetallacyclobutene intermedi-
ate D which then undergoes highly selective rearrange-
ment to 11 in preference to 5. Eventually, 11 could be
converted to 5 via D.
Mech a n ism of (µ-Vin yl)d ir h en iu m Com p lex F or -
m a tion . Any mechanism for the conversion of dimet-
allacyclopentenones to µ-vinyl cations must account for
the regiospecific protonation of the regioisomeric dimet-
allacyclopentenones 5 and 11 derived from propyne and
for the stereospecific deuteration of the dimetallacyclo-
pentenone 4 derived from acetylene. The interconver-
sion of dimetallacyclopentenones and dimetallacy-
clobutenes also complicates the determination of the
mechanism of these protonations. The net transforma-
tion involving cleavage of a carbon-carbon bond R to a
ketone by H+ is unusual.
Protonation of the dimetallacyclopentenone 10 de-
rived from methyl 2-butynoate was nonregiospecific and
gave a mixture of the regioisomeric (µ-vinyl)dirhenium
cations 20 and 21. In this case, it is possible that the
reaction proceeds by prior rearrangement to dimetal-
lacyclobutene H, followed by protonation at either
rhenium and elimination to give µ-vinyl cations 20 and
21 (Scheme 6). The ability of ester substituents to
stabilize dimetallacyclobutenes makes this mechanism
plausible for protonation of 10 than for dimetallacyclo-
pentenones without ester substituents.
Sch em e 6
Exp er im en ta l Section
Sch em e 5
Gen er a l Meth od s. 1H NMR spectra were obtained on a
Bruker WP200, AC300, or AM500 spectrometer. 13C{1H}
spectra were obtained on a Bruker AM500 spectrometer (126
MHz). Infrared spectra were measured on a Mattson Polaris
(FT) or a Mattson Genesis (FT) spectrometer. High resolution
mass spectra were obtained on a Kratos MS-80. LSIMS was
performed on a VG Autospec M using a 3-nitrobenzyl alcohol
matrix.
Toluene-d8, THF-d8, THF, C6D6, ether, and pentane were
distilled from purple solutions of sodium benzophenone ketyl
immediately prior to use. CH2Cl2 was distilled from CaH2.
CD2Cl2 was dried over P2O5 and distilled from CaH2. Air-
sensitive materials were manipulated by standard Schlenk
techniques or in an inert-atmosphere glovebox. Propyne was
purified by fractional distillation under vacuum at -78 °C to
remove acetylene. Phenylacetylene, methyl propynoate, ethyl
ethynyl ether, and methyl 2-butynoate were purchased from
Aldrich and freeze-pump-thaw degassed.
One possible mechanism involves stereospecific pro-
tonation of the carbon alpha to the ketone from the side
opposite Re to give E, followed by ring opening (Scheme
5). Such a protonation for an organic ketone is unprec-
edented. A second possible mechanism involves proto-
nation at rhenium bound to the ketone carbonyl to give
F , followed by ring contraction of the dimetallacyclo-
pentenone to give a protonated dimetallacyclobutene G
and reductive elimination of the vinyl unit. Rearrange-
Cp *(CO)2Re[µ-η1,η3-CHdC(CH3)CO]Re(CO)Cp * (5). Ex-
cess propyne (0.12 mmol) was condensed onto a solution of 1
(30 mg, 40 µmol) in THF (10 mL) at -196 °C. The mixture

Dimetallacyclopentenones
Organometallics, Vol. 16, No. 3, 1997 425
was warmed to room temperature, and the resulting red
solution was concentrated under vacuum. Hexane was added,
and the solution was cooled to -78 °C to give 5 (23 mg, 29
µmol, 73%) as an orange solid. 1H NMR (300 MHz, C6D6): δ
8.04 (s, ReCH), 1.83 (s , CH3), 1.80 (s, Cp*), 1.69 (s, Cp*). 13C-
{1H} NMR (126 MHz, C6D6): δ 211.1, 210.4, 208.8, 208.0
(CO’s); 124.4 (CH); 98.6, 98.1 (s, C5Me5); 46.7 (s, CCH3); 21.6
(CCH3); 10.8, 10.0 (Cp*CH3). IR (toluene): 1944 (s), 1899 (vs),
orange solutions containing some toluene-insoluble material.
Volitile materials were evaporated to give oily residues. Et2O
(4 mL) was added by vacuum-transfer and stirring gave yellow
orange to orange precipitates which were filtered out, washed
with Et2O (2 × 4 mL), and dried. Alternatively, isolated
dimetallacyclopentenones 4-6, and 8-10 were used as start-
ing materials. The yields from the two methods were compa-
rable.
1849 (s), 1700 (m) cm-1
O4187Re2: m/ z 796.157 (796.159).
. HRMS calcd (found) for C26H34-
-
[Cp *(CO)2R e(µ-η1,η2-CH dCH 2)R e(CO)2Cp *]+CF 3CO2
(14). Addition of CF3CO2H to isolated and purified 4 (48 mg,
61 µmol) gave 14 (30 mg, 55%) as a yellow-orange solid. 1H
NMR (300 MHz, CD2Cl2): δ 7.92 (dd, J ) 11.8, 9.2 Hz, CH),
4.07 (dd, J ) 9.3, 1.4 Hz, dCHH), 2.63 (dd, J ) 12.0, 1.4 Hz,
dCHH), 2.06 (s, Cp*), 2.05 (s, Cp*). 13C {1H} NMR (126 MHz,
CD2Cl2): δ 201.8, 198.8, 198.3, 198.2 (CO); 132.5 (ReCd);
104.2, 103.7 (C5Me5); 53.0 (CH2); 10.8, 9.8 (Cp*CH3). IR (CH2-
Gen er a l P r oced u r e for P r ep a r a tion of Dim eta lla cy-
clop en ten on es 6 a n d 8-10. At room temperature, a green
solution of 1 (25-50 mg, 33-66 µmol) in C6H6 (1 mL) was
titrated with a colorless solution containing one drop of alkyne
(∼10 mg, ∼100 µmol) in C6H6 (2 mL) until the color changed
(about 30-60% of benzene solution) from green to orange (6),
red (8, 9), or purple (10). Volatiles were evaporated under
vacuum and the solid residue was suspended in 6 mL of
pentane with minimal THF added to nearly dissolve the
remaining solids. The suspensions were filtered, cooled to -40
°C overnight, and filtered cold to give the dimetallacyclopen-
tenones as powders which were washed twice with 2 mL of
pentane and dried.
Cp *(CO)2R e[µ-η1,η3-CH dC(C6H 5)CO]R e(CO)Cp * (6).
Phenylacetylene and 1 (20 mg, 27 µmol) gave 6 (11 mg, 48%)
as an orange solid. 1H NMR (300 MHz, THF-d8): δ 8.70 (s,
ReCH), 7.71 (dd, J ) 7.8, 1.0 Hz, Ho), 7.35 (td, J ) 7.2, 1.0 Hz,
Hm), 7.22 (tt, J ) 7.5, 1.2 Hz, Hp), 1.88 (s, Cp*), 1.71 (s, Cp*).
13C{1H} NMR (126 MHz, C6D6): δ 211.0, 209.6, 208.4, 208.2
(CO's); 138.2 (Cipso); 130.2, 129.0 (Cm, Co); 127.9 (Cp); 114.6
(ReCH); 99.3, 98.8 (C5Me5); 52.2 [C(C6H5)]; 10.9, 9.8 (Cp*CH3).
IR (KBr): 1951 (s), 1902 (vs), 1851 (s), 1699 (m) cm-1. HRMS
calcd (found) for C32H36O4187Re2: m/ z 858.173 (858.176). Anal.
Calcd for C32H36O4Re2: C, 44.85; H, 4.23. Found: C, 44.68;
H, 4.16.
Cl2): 2011 (m), 1981 (vs), 1939 (s), 1910 (m) cm-1
.
[ C p *( C O ) 2 R e ( µ-η1 ,η2 -( E ) -C H dC H C H 3 ) R e ( C O ) 2 -
-
Cp *]+CF 3CO2 (15). Addition of CF3CO2H to isolated and
purified 5 (10 mg, 13 µmol) in C6H6 (300 µL) gave 15 (7 mg,
62%) as a brown oil . 1H NMR (300 MHz, CD2Cl2): δ 7.50 (d,
J ) 11.4 Hz, ReCH), 3.06 (dq, 11.6, 6.2 Hz, 1 H, dCHCH3),
2.11 (s, Cp*), 2.05 (s, Cp*), 1.90 (d, J ) 6.2 Hz, dCHCH3).
13C{1H} NMR (126 MHz, CD2Cl2): δ 202.2, 201.3, 200.7, 199.4
(CO); 129.8 (ReCd); 104.2, 103.7 (C5Me5); 76.8 (CHCH3); 25.4
(CHCH3); 10.6,10.5 (Cp*CH3). IR (CH2Cl2): 2002 (m), 1978
(vs), 1924 (s), 1879 (m) cm-1
[C p *(C O ) 2 R e (µ-η1 ,η2 C C H 3 dC H 2 )R e (C O ) 2 C p *] +
.
-
CF 3CO2- (16). In a reversible frit apparatus, a green solution
of 1 (38 mg, 50 µmol) in toluene (5 mL) was treated with excess
propyne at -60 °C for 5 min to give an orange solution. CF3-
CO2H (excess) was condensed into the solution. Solvent and
excess propyne were evaporated under vacuum to give a brown
oil. CH2Cl2 (1 mL) and pentane (5 mL) were condensed into
the flask to give an orange precipitate. The solution was
filtered cold and washed once with cold pentane to give 16 (24
mg, 52%) as a yellow-orange powder that was >95% pure by
1H NMR spectroscopy. 1H NMR (300 MHz, CD2Cl2): δ 4.09
(d, J ) 0.8 Hz, dCHH), 3.13 (br s, CH3), 2.07 (s, Cp*), 2.03 (s,
Cp*), 1.95 (d, 0.8 Hz, dCHH). 13C{1H} NMR (126 MHz, CD2-
Cl2): δ 204.0, 200.6, 200.2, 199.8 (CO); 145.6 (ReCd); 105.8,
103.9 (C5Me5); 53.5 (CH2); 42.6 (CH3); 10.0, 9.7 (Cp*CH3). IR
(CH2Cl2): 2006 (s), 1976 (vs), 1935 (vs), 1903 (m) cm-1. LSIMS
calcd (found) for C27H33O4187Re2: m/z 797.2 (797.1).
Cp*(CO)2Re[µ-η1,η3-CHdC(OCH2CH3)CO]Re(CO)Cp* (8).
Ethyl ethynyl ether and 1 (50 mg, 66 µmol) gave 8 (37 mg,
68%) as a red solid. 1H NMR (300 MHz, C6D6): δ 7.98 (s, CH);
4.25 and 4.10 (two dq, J ) 10.2, 7.2 Hz, diastereotopic CH2);
1.81 (s, Cp*); 1.79 (s, Cp*); 1.20 (t, J ) 7.2 Hz, CH3). 13C {1H}
NMR (126 MHz, C6D6): δ 213.6, 210.8 208.6, 206.2 (CO); 112.3
(ReCH); 99.2, 98.1 (C5Me5); 91.5 [C(OEt)]; 63.2 (CH2); 15.8
(CH2CH3); 10.9, 9.7 (Cp*CH3). IR (THF): 1943 (s), 1899 (vs),
1848 (s), 1676 (m) cm-1
. HRMS calcd (found) for C28H36-
O5187Re2: m/ z 826.163 (826.163). Anal. Calcd for C28H36O5-
Re2: C, 40.77; H, 4.40. Found: C, 40.69; H, 4.28.
{C p *(C O )2 R e [µ-η1 ,η2 -(E )-C H dC H (C 6 H 5 )]R e (C O )2 -
Cp *}+CF 3CO2- (17). Orange 6 was prepared from 1 (54 mg,
71 µmol) and excess phenylacetylene in toluene (3 mL). Crude
6 was washed with ether to remove black ether-soluble
impurities and was dissolved in toluene. Addition of CF3CO2H
gave 17 as an orange powder (22 mg, 37%). 1H NMR (300
MHz, CD2Cl2): δ 8.37 (d, J ) 12.5 Hz, ReCH), 7.51 (d, J ) 7.0
Hz, Ho), 7.43 (t, J ) 7.0 Hz, Hm), 7.39 (d, J ) 7.0 Hz, Hp), 4.42
(d, J ) 12.2 Hz, dCHC6H5), 2.09 (s, Cp*), 1.86 (s, Cp*).
13C{1H} NMR (126 MHz, CD2Cl2): δ 202.0, 201.5, 199.0, 198.0
(CO); 138.5 (Cipso); 130.3 (Cp); 129.3 and 127.3 (Co and Cm);
122.7 (ReCHd); 104.4, 104.0 (C5Me5); 79.4 (dCHC6H5); 10.7,
10.0 (Cp*CH3). IR (CH2Cl2): 2004 (s), 1988 (vs), 1932 (vs),
1894 (m) cm-1. LSIMS calcd (found) for C32H37O4187Re2: m/ z
859.18 (859.2) M+.
Cp *(CO)2Re[µ-η1,η3-CHdC(CO2CH3)CO]Re(CO)Cp * (9).
Methyl propynoate and 1 (40 mg, 48 µmol) gave 9 (30 mg, 70%)
as a red-orange solid. 1H NMR (500 MHz, CD2Cl2, -10 °C):
δ 8.92 (s, CH), 3.77 (s, OCH3), 1.88 (s, Cp*), 1.84 (s, Cp*).
13C{1H} NMR (126 MHz, CD2Cl2, -30 °C): δ 208.1, 207.1,
206.8, 205.7 (CO); 173.4 (CO2); 124.8 (CH); 99.1, 98.2 (C5Me5);
52.1 (OCH3); 34.7 (CCO2); 10.6, 9.5 (Cp*CH3). IR (THF): 1953
(s), 1906 (vs), 1869 (s), 1704 (m) cm-1. HRMS calcd (found)
for C28H34O6187Re2: m/ z 840.147 (840.153).
Cp *(CO)2R e [µ-η1,η3-(CO2CH 3)CdC(CH 3)CO]R e (CO)-
Cp * (10). Methyl 2-butynoate and 1 (50 mg, 66 µmol) gave
10 (35 mg, 62%) as a purple solid. 1H NMR (300 MHz, C6D6):
δ 3.64 (s, OCH3), 1.93 (s, CH3), 1.79 (s, Cp*), 1.77 (s, Cp*). 13
C
{1H} NMR (126 MHz, C6D6): δ 211.3, 207.3, 206.0, 205.8 (CO);
176.4 (CO2); 135.9 (ReCCO2); 101.0, 99.2 (C5Me5); 50.7 (OCH3);
41.4 (CCH3); 17.2 (CCH3); 10.4, 10.2 (Cp*CH3). IR (THF):
{Cp *(CO)2R e[µ-η1,η2-(E)-CH dCH (OCH 2CH 3)]R e(CO)2-
-
Cp *}+CF 3CO2 (18). Purple 8 was prepared from 1 (64 mg,
85 µmol) and excess ethyl ethynyl ether in toluene (3 mL).
Addition of CF3CO2H gave 18 as an orange powder (40 mg,
50%). 1H NMR (300 MHz, CD2Cl2): δ 7.17 (d, J ) 9.6 Hz,
ReCHd), 5.32 (d, J ) 9.0 Hz, dCHO), 4.04 (qd, J ) 7.0, 1.5
Hz, OCH2), 2.08 (s, 2 Cp*), 1.33 (t, J ) 6.9 Hz, CH2CH3). 13C
{1H} NMR (126 MHz, CD2Cl2): δ 203.4, 202.0, 198.9, 197.8
(CO); 119.4 (ReCHd); 106.2 (dCHO); 104.2, 103.4 (C5Me5);
70.0 (OCH2); 15.1 (CH2CH3); 10.9, 10.2 (Cp*CH3). IR (CH2-
Cl2): 1956 (m), 1924 (vs), 1887 (s), 1863 (m) cm-1. LSIMS calcd
(found) for C28H36O5187Re2: m/ z 827.176 (827.2).
1944 (s), 1909 (vs), 1867 (s), 1701 (m) cm-1
.
Gen er a l P r oced u r e for P r ep a r a tion of Br id gin g Vin yl
Com p lexes (14-20). Dimetallacyclopentenones were pre-
pared from a solution of Cp*(CO)2RedRe(CO)2Cp* (1) in
toluene (3 mL) and the appropriate alkyne. The resulting
solutions were evaporated to remove excess alkyne. A flask
containing the dimetallacyclopentenone was attached to a
reversible frit apparatus, and toluene (3 mL) was added.
Addition of excess CF3CO2H by vacuum-transfer at -78 °C
and warming to room temperature gave yellow-orange to dark
{Cp *(CO)2R e [µ-η1,η2-(E )-CH dCH (CO2CH 3)]R e (CO)2-

426 Organometallics, Vol. 16, No. 3, 1997
Casey et al.
-
Cp *}+CF 3CO2 (19). Red-orange 9 was prepared from 1 (60
Spectrum assigned to 20, δ 136.2 (ReCCO2CH3), 106.2, 103.7
(C5Me5), 66.9 (OCH3), 52.6 (CCH3), 24.0 (CCH3), 9.8, 9.5
(Cp*CH3); spectrum assigned to 21, δ 136.2 (ReCCH3), 105.7,
103.2 (C5Me5), 61.3 (OCH3), 52.4 (CCO2CH3), 35.7 (CCH3), 9.6,
9.2 (Cp*CH3). Unassignable: 201.2, 200.1, 199.6, 197.4, 197.1
(2), 196.3 (2) (CO’s). Ester carbonyl carbons were not observed.
IR (CH2Cl2) of mixture: 1956 (m), 1924 (vs), 1887 (s), 1863
(m) cm-1. LSIMS calcd (found) for C28H36O5187Re2 (cation): m/z
827.176 (827.2) M+.
mg, 79 µmol) and excess methyl propynoate in toluene (3 mL).
Addition of CF3CO2H gave 19 (44 mg, 65%) as an orange
powder. 1H NMR (300 MHz, CD2Cl2): δ 8.24 (d, J ) 11.2 Hz,
ReCH), 3.79 (s, OCH3), 2.95 (d, J ) 11.0 Hz, dCHCO2CH3),
2.10 (s, Cp*), 2.06 (s, Cp*). 13C{1H} NMR (126 MHz, CD2Cl2):
δ 200.8, 198.6, 196.80, 196.76 (CO); 171.9 (CO2); 128.5 (ReCHd);
105.3, 104.3 (C5Me5); 59.5 (OCH3); 53.0 (dCHCO2CH3); 10.6,
10.0 (Cp*CH3). IR (CH2Cl2): 2013 (m), 1991 (vs), 1937 (s),
1898 (m), 1726 (m) cm-1
. LSIMS calcd (found) for C28H35-
1
2
2
{Cp *(CO) Re[µ-η ,η -(E)-(CH3CO2)CdCH(CO2CH3)]Re-
O6187Re2: m/ z 841.16 (841.2).
-
(CO)2Cp *}+ CF 3CO2 (22). Addition of excess CF3CO2H to
{C p *(C O )2R e [µ-η1,η2-(E )-C (C O 2C H 3)dC H (C H 3)]R e -
an orange solution of 3 (32 mg, 42 µmol) in toluene (3 mL)
gave an immediate color change to yellow. Evaporation of
solvent followed by washing with ether gave 22 (20 mg, 43%)
as an orange solid. 1H NMR (300 MHz, CD2Cl2): δ 3.79 (s,
OCH3), 3.75 (s, OCH3), 2.37 (s, CdCH), 2.14 (s, Cp*), 2.06 (s,
Cp*). LSIMS calcd (found) for C30H37O8187Re2 (cation): m/ z
899.2 (899.2).
-
(CO)2Cp *}+CF 3CO2 (20) a n d {Cp *(CO)2Re[µ-η1,η2-(E)-
C(CH3)dCH(CO2CH3)]Re(CO)2Cp *}+CF 3CO2- (21). 10 was
prepared from 1 (54 mg, 71 µmol) and excess methyl 2-bu-
tynoate in 3 mL of toluene. The purple solution of 10 was
evaporated to remove excess alkyne. Toluene (3 mL) and
excess CF3CO2H were added to give a 60:40 mixture of 20:21,
which was isolated as an orange powder (29 mg, 48%) and
characterized as a mixture.
1H NMR (300 MHz, CD2Cl2): Spectrum assigned to 20, δ
3.86 (s, OCH3), 2.47 (q, J ) 6.3 Hz, dCHCH3), 2.12 (s, Cp*),
2.04 (s, Cp*), 1.82 (d, J ) 6 Hz, dCHCH3); spectrum assigned
to 21, δ 3.76 (s, OCH3), 3.34 (s, CH3), 2.57 (s, dCHCO2Me),
2.10 (s, Cp*), 2.05 (s, Cp*). 13C{1H} NMR (126 MHz, CD2Cl2):
Ack n ow led gm en t. Financial support from the De-
partment of Energy, Office of Basic Energy Sciences, is
gratefully acknowledged.
OM960658E