Structural isomers of aryl-substituted η3-propargyl complexes: η2-1-metalla(methylene)cyclopropene and η3-benzyl complexes

Article abstract of DOI:10.1021/ja020439m

Hydride abstraction from C₅Me₅(CO)₂Re (η²-PhC≡CCH₂Ph) (1) gave a 3:1 mixture of η³-propargyl complex C₅Me₅(CO)₂Re(η³- PhCH-C≡CPh)][BF₄

Full text of DOI:10.1021/ja020439m

Published on Web 10/10/2002
Structural Isomers of Aryl-Substituted η3-Propargyl
Complexes: η2-1-Metalla(methylene)cyclopropene and
η3-Benzyl Complexes
Charles P. Casey,* Timothy M. Boller, Stefan Kraft, and Ilia A. Guzei
Contribution from the Department of Chemistry, UniVersity of Wisconsin,
Madison, Wisconsin 53706
Received March 25, 2002. Revised Manuscript Received August 15, 2002
Abstract: Hydride abstraction from C5Me5(CO)2Re(η2-PhCtCCH2Ph) (1) gave a 3:1 mixture of η3-propargyl
complex [C5Me5(CO)2Re(η3-PhCHsCtCPh)][BF4] (5) and η2-1-metalla(methylene)cyclopropene complex
[C5Me5(CO)2Re(η2-PhCsCdCHPh)][BF4] (6). Observation of the η2-isomer requires 1,3-diaryl substitution
and is favored by electron-donating substituents on the C3-aryl ring. Interconversion of η3-propargyl and
1
η2-1-metalla(methylene)cyclopropene complexes is very rapid and results in coalescence of Cp* H NMR
resonances at about -50 °C. Protonation of the alkynyl carbene complex C5Me5(CO)2RedC(Ph)CtCPh
(22) gave a third isomer, the η3-benzyl complex {C5Me5(CO)2Re[η3(R,1,2)-endo,syn-C6H5CH(CtCC6H5)]}-
[BF4] (23) along with small amounts of the isomeric complexes 5 and 6. While 5 and 6 are in rapid equilibrium,
there is no equilibration of the η3-benzyl isomer 23 with 5 and 6.
Scheme 1
Introduction
η3-Propargyl complexes are the triple bond analogues of
synthetically important η3-allyl complexes. Werner prepared an
exo-alkylidene-η3-propargyl complex in 1985,1 and Krivykh
prepared the first unsubstituted η3-propargyl complex in 1991
(Scheme 1).2 The chemistry of η3-propargyl complexes has been
extended to many early3,4 and late5 transition metals, and the
use of these complexes in synthesis is expanding.6,7
We developed efficient syntheses of η3-propargyl rhenium
complexes, both by hydride abstraction from alkyne complexes8
and by protonation of propargyl alcohol complexes (a route
pioneered by Krivykh9) (Scheme 2). Related η3-allyl complexes
preferentially undergo nucleophilic addition at a terminal
carbon.10 In contrast, nucleophiles normally attack the central
Scheme 2
* Address correspondence to this author. E-mail: casey@chem.wisc.edu.
(1) Gotzig, J.; Otto, H.; Werner, H. J. Organomet. Chem. 1985, 287, 247.
(2) Krivykh, V. V.; Taits, E. S.; Petrovskii, P. V.; Struchkov, Y. T.; Yanovskii,
A. I. MendeleeV Commun. 1991, 103.
(3) (a) Blosser, P. W.; Gallucci, J. C.; Wojcicki, A. J. Organomet. Chem. 2000,
597, 125. (b) Ogoshi, S.; Stryker, J. M. J. Am. Chem. Soc. 1998, 120, 3514.
(c) Rodriguez, G.; Bazan, G. C. J. Am. Chem. Soc. 1997, 119, 343. (d)
Blosser, P. W.; Gallucci, J. C.; Wojcicki, A. J. Am. Chem. Soc. 1993, 115,
2994.
carbon of η3-propargyl complexes to give metallacyclobutenes.
However in some cases, nucleophiles attack at either the C1
terminus11 to give alkyne complexes or at the C3 terminus to
give allene complexes.12 The structures of η3-propargyl com-
plexes suggest that an allenyl formulation is an important reso-
nance contributor;6 the allenyl resonance contributor is useful
in explaining the nucleophilic attack to give η2-allene complexes.
(4) Ihara, E.; Tanaka, M.; Yasuda, H.; Kanehisa, N.; Maruo, T.; Kai, Y. J.
Organomet. Chem. 2000, 613, 26.
(5) (a) Blosser, P. W.; Calligaris, M.; Schimpff, D. G.; Wojcicki, A. Inorg.
Chim. Acta 2001, 320, 110. (b) Ogoshi, S.; Nishida, T.; Fukunishi, Y.;
Tsutsumi, K.; Kurosawa, H. J. Organomet. Chem. 2001, 620, 190. (c) Baize,
M. W.; Blosser, P. W.; Plantevin, V.; Schimpff, D. G.; Gallucci, J. C.;
Wojcicki, A. Organometallics 1996, 15, 164. (d) Blosser, P. W.; Schimpff,
D. G.; Gallucci, J. C.; Wojcicki, A. Organometallics 1993, 12, 1993. (e)
Huang, T.-M.; Chen, J.-T.; Lee, G. H.; Wang, Y. J. Am. Chem. Soc. 1993,
115, 1170. (f) Krivykh, V. V. Organomet. Chem. USSR 1992, 5, 113.
(6) (a) Wojcicki, A. Inorg. Chem. Commun. 2002, 5, 82. (b) Chen, J.-T. Coord.
Chem. ReV. 1999, 190, 1143. (c) Kurosawa, H,; Ogoshi, S. Bull. Chem.
Soc. Jpn. 1998, 71, 973. (d) Doherty, S.; Corrigan, J. F.; Carty, A. J.; Sappa,
E. AdV. Organomet. Chem. 1995, 37, 39. (e) Wojcicki, A. New J. Chem.
1994, 18, 61.
(9) Taits, E. S.; Petrovskii, P. V.; Krivykh, V. V. Russ. Chem. Bull. 1999, 48,
1774.
(10) (a) Trost, B. M.; Van Vranken, D. L. Chem. ReV. 1996, 96, 395. (b)
Consiglio, G.; Waymouth, R. M. Chem. ReV. 1989, 89, 257. (c) Tsuji, J.
Tetrahedron 1986, 42, 4361. (d) Trost, B. M.; Verhoeven, T. R. In
ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone, F. G.
A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 8, Chapter
57.
(7) Radinov, R.; Hutchings, S. D. Tetrahedron Lett. 1999, 40, 8955.
(8) Casey, C. P.; Selmeczy, A. D.; Nash, J. R.; Yi, C. S.; Powell, D. R.; Hayashi,
R. K. J. Am. Chem. Soc. 1996, 118, 6698.
(11) Here, we define the η3-propargyl-disubstituted carbon as C1 and the
monosubstituted carbon as C3.
9
10.1021/ja020439m CCC: $22.00 © 2002 American Chemical Society
J. AM. CHEM. SOC. 2002, 124, 13215-13221
13215

A R T I C L E S
Casey et al.
In attempting to extend the range of η3-propargyl rhenium
complexes, we initially experienced difficulty synthesizing aryl-
substituted η3-propargyl complexes because of their thermal
instability. Here, we report that 1,3-diaryl-substituted η3-
propargyl rhenium complexes can be synthesized at low
temperature, but surprisingly, they are in equilibrium with a
second isomer, an η2-1-metalla(methylene)cyclopropene com-
plex. The unprecedented equilibration of η3-propargyl and η2-
1-metalla(methylene)cyclopropene complexes is rapid and,
therefore, needs to be considered in explaining the regio-
selectivity of nucleophilic additions to η3-propargyl complexes.
A second potential route to diaryl-substituted η3-propargyl
rhenium complexes involves protonation of alkynyl carbene
complexes; however, this route led to the predominate formation
of a third isomer, an η3-benzyl complex.
Scheme 3
Results
Precursors of 1,3-Diaryl η3-Propargyl Complexes. When
we initiated this work, there was only one reported group 6 or
7 aryl-substituted η3-propargyl complex.13 The two best methods
for the synthesis of cationic η3-propargyl rhenium complexes
are abstraction of a propargylic hydrogen from alkyne complexes
and protonation of propargyl alcohol complexes. We have
applied both to the synthesis of 1,3-diaryl η3-propargyl com-
plexes. The precursor for hydride abstraction, C5Me5(CO)2Re-
(PhCtCCH2Ph) (1), was prepared by reaction of the corre-
sponding alkyne with C5Me5Re(CO)2(THF) (2). The propargyl
alcohol precursor, C5Me5(CO)2Re(PhCtCCH(OH)Ph) (3a and
b), was prepared as a 1.1:1 mixture of diastereomers by LiHBEt3
reduction of the corresponding ketone complex, C5Me5(CO)2-
Re[PhCtCC(O)Ph] (4), which in turn was prepared from the
alkynyl ketone and 2.14
Scheme 4
coupling constant 165 Hz in 5 is consistent with the sp2
hybridization of the C1 carbon in other η3-propargyl complexes8
and is inidicative of the strong contribution from an η3-allenyl
resonance form.6
Hydride Abstraction from C5Me5(CO)2Re(PhCtCCH2Ph)
(1) and Protonation of C5Me5(CO)2Re(PhCtCCHOHPh)
(3). Addition of Ph3C+BF4 to a yellow solution of 1,3-
-
diphenylpropyne complex 1 at 0 °C in CD2Cl2 led to the
The minor isomer displayed a high-frequency CH resonance
at δ 10.1 and 13C NMR resonances of the C1, C2, and C3 carbons
at δ 141.4, 108.7, and 239.7, which were consistent with the
η2-1-metalla(methylene)cyclopropene complex [C5Me5(CO)2-
Re(η2-PhCsCdCHPh)][BF4] (6). In particular, the δ 239.7 shift
of C3 provides evidence for a η2-1-metallacyclopropene; very
high-frequency chemical shifts are seen for the carbene-like
carbon of related 1-metallacyclopropenes. In the less resonance
stabilized 1-metallacylopropene [C5Me5(CO)2Re(η2-PhCCHPh)]-
[BF4] (7), the carbene carbon appears at δ 280.3;15 in the neutral
1-metalla(methylene)cyclopropene C5H5[P(OCH3)3]2Mo(E-η2-
PhCsCdCHPh) (8), the carbene carbon appears at δ 253.5.
η2-1-Metalla(methylene)cyclopropene complexes are isomers
of η3-propargyl compounds in which only two carbons are
bonded to the metal center. Several examples of group 6 η2-
1-metalla(methylene)cyclopropene transition metals are known.
Green reported16 that deprotonation of the cationic η2-alkyne
complex {C5H5[P(OCH3)3]2Mo(η2-PhCtCCH2Ph)][BF4] (9)
produced a 7:3 ratio of E:Z isomers of 8 (Scheme 5). The
product mixture displayed fluxional 31P NMR behavior (Tc )
-74 °C), involving rotation of the η2 fragment which rapidly
1
immediate formation of a deep green solution. The H NMR
spectrum at -78 °C revealed a 3:1 ratio of isomers with Cp*
resonances at δ 2.07 and 2.15. In a separate reaction, 85% HBF4‚
Et2O was added to a CD2Cl2 solution of 3a:3b at -78 °C. The
1H NMR spectrum of the resulting green solution taken at -78
°C showed a 3:1 ratio of the same two compounds.
The 1H and 13C NMR spectra of the major isomer are
consistent with its formulation as the η3-propargyl complex
[C5Me5(CO)2Re(η3-PhCHsCtCPh)][BF4] (5) (Scheme 3). A
singlet at δ 5.83 in the 1H NMR spectrum was assigned to the
proton on C1. The low temperature 13C NMR spectrum was
crucial in validating the η3-complexation, with the C1, C2, and
C3 resonances at δ 59.3, 67.5, and 85.2, respectively (Scheme
4). Related η3-propargyl rhenium complexes8 have similar
characteristic chemical shifts: [C5Me5(CO)2Re(η3-CH2-Ct
CH)][BF4] at δ 32.0, 64.2, 65.3; [C5Me5(CO)2Re(η3-CH2sCt
CC(CH3)3)][PF6] at δ 30.0, 60.5, 94.2; and [C5Me5(CO)2Re(η3-
1
CH3CHsCtCCH3][PF6] at δ 48.1, 59.8, 77.0. The JCH
(12) (a) Casey, C. P.; Nash, J. R.; Yi, C. S.; Selmeczy, A. D.; Chung, S.; Powell,
D. R.; Hayashi, R. K. J. Am. Chem. Soc. 1998, 120, 722. (b) Cheng, Y.-
C.; Chen, Y.-K.; Huang, T.-M.; Yu, C.-I.; Lee, G.-H.; Wang, Y.; Chen,
J.-T. Organometallics 1998, 17, 2953.
(13) Carfagna, C.; Deeth, R. J.; Green, M.; Mahon, M. F.; McInnes, J. M.;
Pellegrini, S.; Woolhouse, C. B. J. Chem. Soc., Dalton Trans. 1995, 3975.
(14) This two step procedure was required, since the reaction of 2 with the
propargyl alcohol gave intractable mixtures or very low yields.
(15) Casey, C. P.; Brady, J. T.; Boller, T. M.; Weinhold, F.; Hayashi, R. K. J.
Am. Chem. Soc. 1998, 120, 12500.
(16) Feher, F. J.; Green, M.; Rodrigues, R. A. J. Chem. Soc., Chem. Commun.
1987, 1206. Green refers to η2-1-metalla(methylene)cyclopropene as
η2(3e-)-allenyl complexes.
9
13216 J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002

Isomers of Aryl-Substituted η3-Propargyl Complexes
A R T I C L E S
Scheme 5
Table 1. Electronic Effects29 on η3-Propargyl/
η2-1-Metalla(methylene)cyclopropene Equilibrium Ratio, Measured
at -75 °C in CD2Cl2
η3/η2
C -ring
1
C -ring
3
η3
η2
5:6
H
H
p-CH3
p-CH3
m,m-CF3
H
75
98
9
50
50
25
2
91
50
50
12:13
15:16
18:19
20:21
p-CF3
p-CH3
H
H
interchanges the environments of the phosphite ligands in 8.
Templeton reported17 the deprotonation of a cationic η2-alkyne
tungsten complex to form the neutral η2-1-metalla(methylene)-
cyclopropene (dppe)(Me2NCS2)(CO)W[η2-(CH3O)CsCdCHPh]
(10), which equilibrated to a mixture of two isomers via rotation
of the η2-ligand.
Variable temperature 360 MHz 1H NMR spectroscopy of the
mixture of 5 and 6 in CD2Cl2 showed rapid equilibration of
these isomeric rhenium complexes. At 0 °C, a single sharp Cp*
resonance was seen at δ 2.12. This fluxionality requires a rapid
and reversible movement of C1 in and out of the coordination
sphere of the metal. At -100 °C,18 interconversion of 5 and 6
was slow enough that NOE transfer to the Cp* signal at δ 2.07
was observed upon selective irradiation of the methine proton
of 5 at δ 5.83; this established that the methine hydrogen was
in the endo position. At temperatures above -90 °C, inter-
conversion of 5 and 6 was fast enough that irradiation of the
methine resonance of 5 resulted in saturation transfer to the
vinylic CH of η2-isomer 6 at δ 10.1.
of 12 exhibited five inequivalent phenyl CH resonances at δ
122.87, 128.97, 129.19, 129.32, and 129.58.
Protonation of the 1:1 mixture of di-p-tolyl-substituted alcohol
complexes C5Me5(CO)2Re[(p-CH3C6H4)13Ct13C13CHOH(C6H4s
p-CH3)] (14a and b) with 85% HBF4‚Et2O in CD2Cl2 at -78
°C gave an ∼1:10 ratio of η3-propargyl complex (15): η2-1-
metalla(methylene)cyclopropene (16). The use of triple 13C-
labeled material firmly established the spectral assignments of
the η2-1-metalla(methylene)cyclopropene [C5Me5(CO)2Re[η2-
(p-CH3sC6H4)13Cs13Cd13CH(C6H4sp-CH3)][BF4] (16). At
-90 °C, the key features of the 1H and 13C NMR spectra of 16
are a predominant Cp* resonance at δ 2.09 and a high frequency
doublet for the CH at δ 9.99 (1JCH ) 159 Hz). The 13C labels
provide excellent evidence for the η2-1-metalla(methylene)-
cyclopropene bonding motif, with resonances for C1, C2, and
C3 at δ 141.8 (d, 1JCC ) 85 Hz), 107.1 (dd, 1JCC ) 85, 61 Hz),
1
and 233.8 (d, JCC ) 62 Hz).
Because of the use of triple 13C-labeled material, the
small amount of propargyl isomer [C5Me5(CO)2Re[η3-(p-
CH3sC6H4)13CHs13Ct13C(C6H4sp-CH3)][BF4] (15) was also
discernible in the 13C NMR spectrum; resonances for C1, C2,
The rapid interconversion of 5 and 6 makes it impossible to
determine the kinetic ratio of isomers formed either from hydride
abstraction or from protonation of the mixture of alcohol
diastereomers.
1
2
and C3 were observed at δ 59.8 (dd, JCC ) 65 Hz, JCC ) 8
Substituent Effects on the Equilibria between 1,3-Diaryl
η3-Propargyl Complexes and η2-1-Metalla(methylene)cyclo-
propenes. In an effort to obtain equilibrium mixtures that
favored either the η3-propargyl or η2-1-metalla(methylene)-
cyclopropene, we investigated the effect of substituents on each
of the aryl rings. Protonation of the 1:1 mixture of p-CF3-
C6H4-substituted alcohol complexes C5Me5(CO)2Re[(p-CF3s
C6H4)CtCCH(OH)Ph] (11a and b) with 85% HBF4‚Et2O in
CD2Cl2 at -78 °C gave an ∼50:1 ratio of η3-propargyl (12):
η2-1-metalla(methylene)cyclopropene (13) complexes. The key
1
1
Hz), 66.4 (dd, JCC ) 110, 65 Hz), and 85.4 (dd, JCC ) 110
2
Hz, JCC ) 8 Hz), respectively.
The equilibrium ratio of the η3 and η2 products was strongly
dependent on the nature of the electron-donating or -withdrawing
nature of substituents on the aromatic rings (Table 1).
Activation Barrier for Interconversion of η3-Propargyl
and η2-1-Metalla(methylene)cyclopropene Complexes. For
a quantitative 13C NMR investigation of the unique fluxional
process that interconverts η3-propargyl and η2-1-metalla(meth-
ylene)cyclopropene complexes, we chose to study a system with
a 1:1 ratio of isomers and we used 13C labeling at C1 to en-
hance sensitivity. Protonation of C5Me5(CO)2Re[η2-PhCt
C13CH(OH)(C6H4-p-CH3)] (17a and b) with HBF4‚Et2O at
-78 °C gave η3-propargyl complex {C5Me5(CO)2Re[η3-(p-
CH3sC6H4)13CHsCtCPh]}[BF4] (18) and η2-1-metalla-
(methylene)cyclopropene complex [C5Me5(CO)2Re(η2-PhCs
Cd13CH(C6H4sp-CH3)][BF4] (19). The temperature depend-
ence of the 13C label resonances was measured over the range
from -75 °C to -30 °C. Line broadening simulation of the
13C spectra allowed measurement of the rates of interconversion
of isomers. An Eyring plot gave activation parameters for the
isomerization process: ∆H‡ ) 10.8 kcal mol-1, ∆S‡ ) -0.5
eu, with ∆G‡ ) 10.3 kcal mol-1 at -45 °C.
1
features of the H and 13C NMR spectra of [C5Me5(CO)2Re-
(η3-PhCHsCtCC6H4-p-CF3)][BF4] (12) are the signature CH
signal at δ 5.98 and resonances for C1, C2, and C3 at δ 60.1
(1JCH ) 167 Hz), 70.2, and 83.6.
Evidence for steric crowding around the C1 center of
1
η3-propargyl complexes came from low temperature H NMR
1
studies of 12. The H NMR spectrum of 12 displayed five
different phenyl CH resonances at δ 6.59, 7.21, 7.29, 7.49, and
7.79, indicating asymmetry of the phenyl group due to restricted
rotation about the C1-Cipso bond. At -80 °C, selective irradia-
tion of the η3-CHPh resonance at δ 5.98 produced an NOE
enhancement at the Cp* signal at δ 2.08, indicating the endo-
orientation of the irradiated hydrogen. The 13C NMR spectrum
Protonation of Alkynyl Carbene Complexes as a Route
to η3-Propargyl Complexes. Recently, we reported the syn-
thesis of rhenium alkynyl carbene complexes and their [1,3]
metal shift and dimerization reactions.19 Protonation at either
the carbene carbon20 or the remote alkynyl carbon of these
(17) Gamble, A. S.; Birdwhistell, K. R.; Templeton, J. L. J. Am. Chem. Soc.
1990, 112, 1818.
(18) The addition of 20 vol % polar solvent mixture CDCl2F/CDClF2 (2:1)
[Siegel, J. S.; Anet, F. A. L. J. Org. Chem. 1988, 53, 2629] to a CD2Cl2
solution of 13/14 allowed NOESY1D gradient experiments at low tem-
perature. A negative NOE peak was observed in the Cp* resonance, -26%
in magnitude compared to the inverted CH signal.
9
J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002 13217

A R T I C L E S
Casey et al.
Scheme 6
complexes offered a potential route to diaryl-substituted η3-
propargyl complexes. Addition of HBF4‚Et2O to a black CD2Cl2
solution of alkynyl carbene complex C5Me5(CO)2RedC(Ph)Ct
Figure 1. X-ray crystal structure of η3-benzyl complex {C5Me5(CO)2Re-
[η3(R,1,2)-endo,syn-C6D5CH(CtCC6H5)]}[BF4] (23-d5B). The molecular
structure is drawn with 30% thermal probability ellipsoids, with hydrogens
omitted for clarity.
1
CPh (22) at -78 °C immediately produced a red solution. H
NMR spectroscopy at -78 °C showed the formation of a single
major product (different from either 5 or 6) containing a singlet
at δ 2.66, a doublet at δ 4.76, and an asymmetric aromatic
region. The 13C NMR spectrum revealed an intact acetylene
unit, signifying the absence of alkyne coordination to rhenium.
On the basis of these spectral features, this third isomer of η3-
propargyl was assigned as the η3-benzyl complex {C5Me5(CO)2-
Re[η3(R,1,2)-endo,syn-C6H5CH(CtCC6H5)]}[BF4] (23) (Scheme
6).
Scheme 7
To test our proposed η3-benzyl structure for 23, we prepared
a deuterium-labeled alkynyl carbene complex C5Me5(CO)2Red
C(Ph)CtCC6D5 (22-d5A), to allow unobscured viewing of the
NMR resonances of the η3-benzyl functionality in 23-d5A.
Addition of HBF4‚Et2O to a CD2Cl2 solution of 22-d5A at -78
°C and warming to 0 °C gave complex 23-d5A in 90% yield
1
by H NMR spectroscopy. The η3-benzyl unit gave rise to
for alkyl-substituted η3-propargyl complexes. This prompted us
to investigate the synthesis of both 1-phenyl- and 3-phenyl-
substituted η3-propargyl complexes. Interestingly, earlier at-
tempts to prepare such aryl-substituted complexes had been
unsuccessful. A wide variety of simple alkyl and aryl groups at
the C3 carbon of the η3-propargyl ligand are known for early
and late transition metals. However, examples of aromatic
substitution in group 6 and 7 metal complexes are limited.
Hydride abstraction from C5Me5(CO)2Re(η2-CH3CtCC6H5)
(24) with Ph3C+BAr′4- (BAr′4dB[C6H3(3,5-CF3)]4) in CD2Cl2
at 0 °C cleanly gave the desired 3-phenyl-substituted η3-
propargyl complex [C5Me5(CO)2Re(η3-CH2CtCC6H5)][BAr′4]
(25-BAr′4) (Scheme 7). Doublets were observed at δ 3.53 and
δ 4.65 in the 1H NMR spectrum with the characteristic geminal
coupling 10.4 Hz, a signature of the coordinated CH2 group.
The 3-phenyl η3-propargyl complex [C5Me5(CO)2Re(η3-CH2Ct
CC6H5)][BF4] (25-BF4) was also generated by protonation of
the η2-propargyl alcohol complex C5Me5(CO)2Re(η2-HOCH2Ct
CC6H5) (26) with 85% HBF4‚Et2O at -78 °C in CH2Cl2. 25-
BF4 was isolated in 53% yield but decomposed over hours in
CH2Cl2 at 0 °C and rapidly as a solid at room temperature. We
do not understand why phenyl-substituted η3-propargyl com-
plexes are less stable than their alkyl-substituted analogues.
aromatic resonances at δ 4.76, 7.33 (2H), 7.65, and 7.83. Upon
cooling 23-d5A to -75 °C, H NMR signals for 10% of a 3:1
1
mixture of 5-d5/6-d5 decoalesced and were readily detected.
While 5-d5 and 6-d5 are in rapid equilibrium, no equilibration
with η3-benzyl isomer 23-d5A was seen, even upon warming
to 25 °C. This labeling experiment also established that η3-
benzyl complex 23-d5A is predominantly formed by protonation
of the carbene carbon of 22-d5A and coordination of the C6H5
ring.
Single crystals of a different isotopomer 23-d5B were obtained
by slow diffusion of pentane into a CD2Cl2 solution of {C5Me5-
(CO)2Re[η3(R,1,2)-endo,syn-C6D5CH(CtCC6H5)]}[BF4] (23-
d5B), obtained from low temperature HBF4 addition to
C5Me5(CO)2RedC(C6D5)CtCC6H5 (22-d5B). While the struc-
ture was highly disordered, the trihapto coordination of the
benzyl of 23-d5B was confirmed with the three carbons within
bonding distance to rhenium (Figure 1).21
Monoaryl-Substituted η3-Propargyl Complexes. The ob-
servation of the equilibrium between diaryl-substituted η3-
propargyl complexes and the corresponding η2-1-metalla-
(methylene)cyclopropene is unusual and had not been observed
(19) (a) Casey, C. P.; Kraft, S.; Powell, D. R. J. Am. Chem. Soc. 2002, 124,
2584-2594. (b) Casey, C. P.; Kraft, S.; Powell, D. R. Organometallics
2001, 20, 2651. (c) Casey, C. P.; Kraft, S.; Powell, D. R. J. Am. Chem.
Soc. 2000, 122, 3771. (d) Casey, C. P.; Kraft, S.; Kavana, M. Organo-
metallics 2001, 20, 3795.
1
No evidence for the η2-isomer of 25 was observed: the H
NMR spectrum contained a single Cp* resonance and no
CH2dC resonances between δ 5.5-6.5,22 and the 13C NMR
spectrum exhibited no RedC resonance.
Next, we set out to prepare the first example of a C1-phenyl-
substituted η3-propargyl complex by hydride abstraction from
(20) For examples of metal carbene protonations, see: (a) Casey, C. P.;
Czerwinski, C. J.; Powell, D. R.; Hayashi, R. K. J. Am. Chem. Soc. 1997,
119, 5750. (b) Casey, C. P.; Vosejpka, P. C.; Askham, F. R. J. Am. Chem.
Soc. 1990, 112, 3713. (c) Klein, D. P.; Bergman, R. G. J. Am. Chem. Soc.
1989, 111, 3079. (d) Hill, A. F.; Roper, W. R.; Waters, J. M.; Wright, A.
H. J. Am. Chem. Soc. 1983, 105, 5939. (e) Clark, G. R.; Roper, W. R.;
Wright, A. H. J. Organomet. Chem. 1984, 273, C17.
(22) In a related allene complex, the terminal CH2d unit was observed at δ
5.48 and 6.52, with 2J ≈ 0 Hz: Casey, C. P.; Brady, J. T. Organometallics
1998, 17, 4620.
(21) Highly idealized phenyl and Cp* units were required for refinement. See
Supporting Information for bond distance tables.
9
13218 J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002

Isomers of Aryl-Substituted η3-Propargyl Complexes
A R T I C L E S
the 1-phenyl-2-butyne complex C5Me5(CO)2Re(η2-C6H5CH2Ct
CCH3) (27). While hydride abstraction from a rhenium 2-pen-
tyne complex showed only a 2.5:1 preference for abstraction
from the Et group over the Me group,8 we anticipated greater
selectivity favoring abstraction of a benzylic hydride from a
Scheme 8
1-phenyl-2-butyne rhenium complex. Addition of Ph3C+BF4
-
to a CD2Cl2 solution of 27 at -78 °C led to regioselective
abstraction of a secondary benzylic hydride and formation of a
single new species, the 1-phenyl-substituted η3-propargyl com-
plex [C5Me5(CO)2Re(η3-PhCHsCtCCH3)][BF4] (28) (Scheme
Scheme 9
1
7). The H NMR spectrum at -10 °C showed a doublet at δ
5
2.79 and a quartet at δ 5.38, with a long range J-coupling of
2.2 Hz, consistent with a 1-phenyl-substituted η3-propargyl
complex. The 13C NMR spectrum with resonances for C1, C2,
and C3 at δ 55.6, 57.6, and 79.5 provided further support for
the formulation of 28. Decomposition of 28 occurred above 0
°C. η3-Propargyl complexes bearing an aromatic group at C1
were unknown prior to the work reported here.
No abstraction of a methyl hydrogen from 27 to produce an
isomeric η3-propargyl complex was observed, consistent with
the expected higher reactivity of benzylic hydrogens. No
evidence for formation of the η2-isomer was observed by 1H or
13C NMR spectroscopy at -80 °C.
C3 site of the η2-isomer is the most electrophilic center in either
the η3- or the η2-isomer, and stabilization by electron donors is
crucial in perturbing the equilibrium. The second most electro-
philic carbon is C1 of the η2-isomer, which is in conjugation
with the carbene-like C3 position, with electron donors at C1
favoring the η2-isomer to a lesser extent than donors at the C3
site.
We have observed similar stabilization of the electron
deficient carbene center of rhenium diphenyl 1-metallacyclo-
propene complexes.15 Isomeric rhenium diaryl 1-metallacyclo-
propene complexes equilibrate rapidly by a [1,2]-hydrogen shift.
Protonation of the asymmetric η2-alkyne complex C5Me5(CO)2-
Re(η2-PhCtCTol) (29) with HBF4‚Et2O at -78 °C followed
by warming to -40 °C gave a kinetic 2.3:1 ratio of the two
isomeric 1-metallacyclopropene complexes [C5Me5(CO)2Re(η2-
PhCHCTol)][BF4] (30)/[C5Me5(CO)2Re(η2-PhCCHTol)][BF4]
(31). Upon warming to 25 °C, equilibration occurred to give a
4.5:1 mixture of 30/31. The favored isomer at equilibrium has
the more electron-donating tolyl group at the carbene center
(Scheme 8).
Discussion
Numerous η3-propargyl complexes have been reported, but
the isomeric η2-1-metalla(methylene)cyclopropene has never
been seen in equilibrium with an η3-propargyl complex. η2-1-
Metalla(methylene)cyclopropene complexes are limited to Mo
or W compounds derived from deprotonation of η2-alkyne
precursors,16,17,23,24 but the isomeric η3-propargyl complexes are
not seen in these systems.
In the course of investigating phenyl-substituted η3-propargyl
complexes, we discovered that 1,3-diaryl-substituted η3-pro-
pargyl complexes such as [C5Me5(CO)2Re(η3-PhCHsCt
CPh)][BF4] (5) were in equilibrium with the corresponding η2-
1-metalla(methylene)cyclopropene complex [C5Me5(CO)2Re-
(η2-PhCsCdCHPh)][BF4] (6). Aryl substitutions at both C1 and
C3 are apparently required for observation of an η2-1-metalla-
(methylene)cyclopropene, since phenyl substitution at only the
C1 or C3 position gave only the η3-propargyl isomer. What steric
or electronic factors might determine whether an η2-1-metalla-
(methylene)cyclopropene will be stable enough to be observed?
Electronic factors affect the equilibrium between η3- and η2-
isomers. Replacement of the phenyl group at C3 of 6 by an
electron-withdrawing p-CF3-C6H4 group in 13 led to a large
decrease in the percentage of η2-isomer from 25% for 6 to <2%
for 13. Replacement of the phenyl group at C1 of 6 by an
electron-donating tolyl group in 19 led to a moderate increase
in the percentage of η2-isomer from 25% for 6 to 50% for 19.
Addition of a second tolyl group to C3 in 19 led to a still larger
increase in the amount of η2-isomer from 50% for 19 to 90%
for 16. Thus, electron donors at C3 greatly favor the η2-isomer,
and electron donors at C1 favor the η2-isomer to a smaller extent.
We attribute this electronic preference for formation of the
η2-isomer to stabilization of the electrophilic carbene center at
C3 of the η2-isomer by an electron-donating aromatic ring. The
Steric effects at C1 also play a role in determining the
equilibrium between η3- and η2-isomers. Two major structural
changes occur in going from an η3- to an η2-isomer (Scheme
9). First, the sterically bulky C1HPh unit moves away from the
sterically large C5Me5(CO)2Re group in going to the η2-isomer.
Second, the C1HR plane in the η3-isomer, which is roughly
orthogonal to the Re-C1-C2-C3 plane (R1-C1-C2-C3 torsion
angle 90°-100°), must rotate about 90° to become nearly
coplanar in the η2-isomer. In the η3-isomer, C1 is bonded to Re
and there is an acute Re-C2-C1 angle (65-75° in X-ray
structures2,3a,8,16,25). But, in the η2-isomer, C1 is not bonded to
Re and there is an obtuse Re-C2-C1 angle (135-148° in
related η2-allene X-ray structures26).
Steric crowding at C1 of η3-propargyl complexes has been
shown to lead to kinetic (and probably thermodynamic)
destabilization.8 For example, protonation of C5Me5(CO)2Re-
(25) (a) Stang, P. J.; Crittel, C. M.; Arif, A. M. Organometallics 1993, 12, 4799.
(b) Wakatsuki, Y.; Yamazaki, Y.; Maruyama, H.; Shimizu, I. Chem.
Commun. 1991, 261.
(26) (a) Lentz, D.; Willemsen, S. Organometallics 1999, 18, 3962. (b) Werner,
H.; Lass, R. W.; Gevert, O.; Wolf, J. Organometallics 1997, 16, 4077. (c)
Esteruelas, M. A.; Lahoz, F. J.; Martin, M.; Onate, E.; Oro, L. A.
Organometallics 1997, 16, 4572. (d) Lee, L.; Wu, I.-Y.; Lin, Y.-C.; Lee,
G.-H.; Wang, Y. Organometallics 1994, 13, 2521. (e) Pu, J.; Peng, T.-S.;
Arif, A. M.; Gladysz, J. A. Organometallics 1992, 11, 3232. (f) Franck-
Neumann, M.; Neff, D.; Nouali, H.; Martina, D.; de Cian, A. Synlett 1994,
657. (g) Feher, F. J.; Gergens, D. D.; Ziller, J. W. Organometallics 1993,
12, 2810.
(23) Collins, M. A.; Feng, S. G.; White, P. A.; Templeton, J. L. J. Am. Chem.
Soc. 1992, 114, 3771.
(24) Frohnapfel, D. S.; Enriquez, A. E.; Templeton, J. L. Organometallics 2000,
19, 221.
9
J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002 13219

A R T I C L E S
Casey et al.
(η2-CH3CtCCH(CH3)OH) (32) at -78 °C produced a 4:1
mixture of the anti/syn η3-propargyl complexes [C5Me5(CO)2-
Re(η3-CH3CtCCHCH3)][BF4] (33-anti and 33-syn), which
differ in the orientation of the methyl group either away or
toward the Cp* ligand. Upon warming the solution above -20
°C, the less stable 33-syn isomer decomposed, while the more
stable 33-anti isomer remained and was isolated at room
temperature. Another case of steric destabilization was observed
for the bulky gem-dimethyl η3-propargyl complex [C5Me5(CO)2-
Re(η3-HCtCC(CH3)2][BF4] (34), which decomposed above
-20 °C, presumably because of the unfavorable steric interac-
tion of the endo-methyl group with the Cp* fragment.
Scheme 10
Evidence for steric crowding at the C1HAr site in the 1,3-
1
diaryl η3-propargyl complexes came from low temperature H
NMR spectroscopy of the p-CF3-C6H4-substituted η3-propargyl
complex 12, which showed five different CH phenyl resonances
for the phenyl group at C1. This asymmetry of the phenyl group
at C1 is due to restricted rotation about the C1-Cipso bond. We
do not fully understand the origin of the steric interactions
responsible for hindered phenyl rotation, but the hindered
rotation strongly suggests a sterically congested site.
In summary, the combination of steric destabilization of the
η3-isomer by the large C1HPh unit and electronic stabilization
of the η2-isomer by electron-donating aryl units at the C3
position (and also at the C1 position) is responsible for the
observation of η2-1-metalla(methylene)cyclopropenes only in
the presence of aryl substitution at both C1 and C3.
Not only is the observation of an equilibrium between η3-
propargyl and η2-1-metalla(methylene)cyclopropene isomers
unprecedented, the rapid nature of this fluxional process, which
involves simple, reversible π-bond complexation, is striking.
Other η2-η3 processes (such as allylic C-H activation of iron-
alkene complexes to give η3-allyl iron hydride intermediates
proposed for iron carbonyl catalyzed alkene isomerization27)
are known but involve more complicated mechanisms than the
simple, reversible π-bond complexation observed here. In the
deprotonation of a molybdenum bis(alkyne) complex, Green
proposed formation of an η2-1-metalla(methylene)cyclopropene
complex as an unobserved intermediate, which rearranges to
an η1-allenyl intermediate, followed by formation of a more
stable η3-propargyl complex.13 In light of the observations
reported here, a simple direct η2-η3 isomerization should be
considered as an alternative to Green’s proposed η2-η1-η3
process.
Attempted entry into mixtures of η2-η3 isomers via pro-
tonation of alkynyl carbene complex 22 instead produced
predominantly a third isomer, an η3-benzyl complex 23. The
η3-benzyl complex results from protonation at the carbene
carbon C1 and complexation of the aryl ring. A 16e intermediate
that partitions between aryl complexation to yield η3-benzyl
complex 23 and alkyne coordination to yield η3-propargyl
complex 5 can explain the formation of two types of products.
A possible variation on the mechanism involves initial proton-
ation at rhenium to give a metal hydride, followed by hydride
migration to the carbene carbon to give the 16e intermediate;
however, no rhenium hydride species was observed by low
temperature H NMR spectroscopy. The small percentage of
1
η2-η3 isomers in the mixture could be formed by a combination
of remote protonation at the C3 carbon to produce the η2-allenyl
isomer and C1 carbene protonation, followed by alkyne com-
plexation to yield the η3-propargyl complex, with immediate
equilibration for both pathways. The high selectivity of η3-
benzyl formation is attributed to a kinetic preference for
protonation at the carbene center and a kinetic preference for
complexation of the aryl ring versus complexation of the alkyne.
The rapid nature of the η3-η2 equilibration needs to be
considered in interpreting the regioselectivity of nucleophilic
additions to η3-propargyl systems (Scheme 10). Previously, we
had observed kinetic additions of phosphines and other nucleo-
philes to the center carbon of η3-propargyl rhenium complexes
to give metallacyclobutenes.12a At higher temperature, re-
arrangements to η2-allene or η2-alkyne products were observed.
These rearrangements are the result of reversible additions of
phosphines and amines to the central carbon, followed by
irreversible terminal addition to give η2-allene or η2-alkyne
products. The question now arises as to whether the η2-allene
or η2-alkyne products might arise from nucleophilic attack on
the η2-isomer rather than just the η3-isomer, as previously
assumed.
Experimental Section
C5Me5(CO)2Re(η2-PhCtCCH2Ph) (1). A solution of C5Me5(CO)2-
Re(THF) (2)8,28 (1.0 mmol) and 1,3-diphenylpropyne (1.0 g, 5.2 mmol)
in 5 mL of THF was stirred overnight. Volatile material was evaporated
under vacuum, and the solid residue was chromatographed (silica gel,
1
5:1 hexanes/Et2O) to give 1 as a yellow powder (236 mg, 42%). H
NMR (CDCl3, 300 MHz) δ 1.93 (s, C5Me5), 4.08 (d, J ) 17.2 Hz,
CHH), 4.33 (d, J ) 17.2 Hz, CHH), 7.1-7.4 (m, aromatic). 13C{1H}
NMR (CD2Cl2, 90 MHz) δ 10.75 (C5Me5), 35.48 (CH2), 80.43 (CtC),
89.83 (CtC), 100.24 (C5Me5), 126.49 (aromatic CHpara), 126.77
(aromatic CHpara), 128.21, 128.79, 131.56 (aromatic CHmeta/ortho), 129.97,
140.42 (aromatic Cipso), 208.82 (CO), 209.77 (CO). By 1H NMR
spectroscopy, the sample was >95% pure in the Cp* region δ 1.9-
2.2 and >98% pure in the aromatic region δ 7.0-7.5. IR (THF)
1950.22, 1868.04. MS (ESI) Calcd (obsd) for C27H27O2Re‚Na+
591.1439 (591.1420).
(27) (a) Long, G. T.; Weitz, E. J. Am. Chem. Soc. 2000, 122, 1431. (b) Galindo,
A.; Mealli, C.; Cuya´s, J.; Miguel, D.; Riera, V.; Pe´rez-Martinez, J. A.;
Bois, C.; Jeannin, Y. Organometallics 1996, 15, 2735. (c) Chang, S.; White,
P. S.; Brookhart, M. Organometallics 1993, 12, 3636. (d) Barnhart, T. M.;
Fenske, R. F.; McMahon, R. J. Inorg. Chem. 1992, 31, 2679. (e) Barnhart,
T. M.; McMahon, R. J. J. Am. Chem. Soc. 1992, 114, 5434. (f) Krivykh,
V. V.; Gusev, O. V.; Rybinskaya, M. I. J. Organomet. Chem. 1989, 362,
351. (g) Casey, C. P.; Cyr, C. R. J. Am. Chem. Soc. 1973, 95, 2248.
(28) Casey, C. P.; Sakaba, H.; Hazin, P. N.; Powell, D. R. J. Am. Chem. Soc.
1991, 113, 8165.
(29) (a) Carrol, F. A. PerspectiVes on Structure and Mechanism in Organic
Chemistry; Brooks/Cole Publishing Co.: Pacific Grove, CA, 1998; sec.
6.6. (b) Hansch, C.; Leo, A.; Taft, R. W. Chem. ReV. 1991, 91, 165. (c)
McDaniel, D. H.; Brown, H. C. J. Org. Chem. 1958, 23, 420.
9
13220 J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002

Isomers of Aryl-Substituted η3-Propargyl Complexes
A R T I C L E S
[C5Me5(CO)2Re(η3-PhCHCtCPh)][BF4] (5) and [C5Me5(CO)2Re-
(η2-PhCCdCHPh)][BF4] (6). Ph3CBF4 (21 mg, 0.064 mmol) was
added to a solution of 1 (33 mg, 0.058 mmol) in CD2Cl2 at 0 °C to
give a 3:1 mixture of 5/6, which was characterized spectroscopically.
For [C5Me5(CO)2Re(η3-PhCHsCtCPh)][BF4] (5): 1H NMR (CD2Cl2,
360 MHz, -75 °C) δ 2.07 (s, C5Me5), 5.83 (s, CHsCtC), 6.57-8.12
(m, aromatic, obscured by Ph3CH). 13C{1H} NMR (CD2Cl2, 90 MHz,
-75 °C) δ 10.13 (C5Me5), 59.28 (CHCtC), 67.46 (CHCtC), 85.24
(CHCtC), 105.79 (C5Me5), 118-132 (aromatic), 193.52 (CO), 199.36
(CO).
For [C5Me5(CO)2Re(η2-PhCCdCHPh)][BF4] (6): 1H NMR (CD2Cl2,
360 MHz, -75 °C) δ 2.15 (s, C5Me5), 6.56-8.21 (aromatic), 10.14 (s,
CHdCC). 13C{1H} NMR (CD2Cl2, 90 MHz, -75 °C) δ 10.29 (C5Me5),
104.38 (C5Me5), 108.68 (CHdCC), 118-132 (aromatic), 141.37
(CHdCC), 191.64 (CO), 195.96 (CO), 239.72 (RedC).
For [C5Me5(CO)2Re(η2-Tol13C13C)13CHTol)][BF4] (16): 1H NMR
(CD2Cl2, 500 MHz, -90 °C) δ 2.09 (s, C5Me5), 2.38 (s, CH3), 2.53 (s,
CH3), 7.38 (d, 3J ) 7.8 Hz, Hmeta), 7.62 (br s, Hmeta), 8.05 (br s, Hortho),
1
9.99 (d, JCH ) 159.4 Hz, 13CHdCC); 13C{1H} NMR (CD2Cl2, 125
1
MHz, -90 °C) δ 10.30 (C5Me5), 104.12 (C5Me5), 107.06 (dd, JCC
)
85.0, 61.0 Hz, 13CHd13C13C), 141.81 (d, JCC ) 85.0, 13CHd13C13C),
1
233.81 (d, JCC ) 61.9, 13CHd13C13C); H NMR (CD2Cl2, 360 MHz,
-75 °C) δ 2.08 (s, C5Me5), 2.36 (s, CH3), 2.51 (s, CH3), 7.36 (d, 3J )
8.0 Hz, Hmeta), 7.63 (br, Hmeta), 8.05 (br, Hortho), 10.01 (d, 1JCH ) 159.8
Hz, 13CHd13C13C); 13C{1H} NMR (CD2Cl2, 90 MHz, -75 °C) δ 10.19
(C5Me5), 21.95 (CH3), 22.89 (CH3), 103.90 (C5Me5), 106.81 (dd, 1JCC
1
1
) 84.20, 60.7 Hz, 13CHd13C13C), 141.72 (d, JCC ) 84.8 Hz, 13CHd
1
1
13C13C), 233.54 (d, JCC ) 61.8 Hz, 13CHd13C13C).
{C5Me5(CO)2Re[η3(r,1,2)-endo,syn-C6H5CH(CtCC6D5)]}[BF4]
(23-d5A). Addition of 8 µL of HBF4‚Et2O to a black solution of
C5Me5(CO)2RedC(Ph)CtCC6D5 (22-d5A)19c (23 mg, 0.04 mmol) in
CD2Cl2 at -78 °C gave a red solution, which changed to a green
solution upon warming to 0 °C. 23-d5A was characterized spectroscopi-
C5Me5(CO)2Re(η2-Tol13CH(OH)13Ct13CTol) (14). Addition of
LiHBEt3 (0.5 mL, 1.0 M in THF, 0.5 mmol) to a red solution of
C5Me5(CO)2Re(η2-Tol13C(O)13Ct13CTol) (37) (60 mg, 0.098 mmol)
in 10 mL of THF at 0 °C gave a yellow solution. After the solution
was stirred for 30 min at room temperature, 1.0 mL of EtOH/H2O (3:
1) was added and volatile material was evaporated under vacuum. The
residual solid was dissolved in diethyl ether and chromatographed (silica
gel, 4:1 hexanes/Et2O) to give a 1.1:1mixture of two diastereomers of
14 (48 mg, 80%) as a yellow oil. By 1H NMR, the sample was >98%
pure in the Cp* region δ 1.9-2.2.
1
cally. H NMR (CD2Cl2, 360 MHz, 0 °C) δ 2.22 (s, C5Me5), 2.66 (s,
CHsCtC), 4.76 (br d, 3JHH ) 5.8 Hz, H2), 7.33 (m, H3/H5), 7.65 (dt,
3JHH ) 7.6 Hz, 4JHH < 1.5 Hz, H4), 7.83 (br d, J ) 8.5 Hz, H6). 13C{1H}
NMR (CD2Cl2, 90 MHz, -75 °C) δ 10.48 (C5Me5), 35.06 (C7HsCtC),
76.30 (ortho, C2), 86.86 (CtCC6D5), 91.55 (CtCC6D5), 103.21 (ipso,
C1), 105.53 (C5Me5), 121.94 (ipso-C6D5), 128.38 (1:1:1 t, 1JCD ) 24.8
Hz, CorthosD), 129.84 (C3 or C5), 130.68 (C3 or C5), 131.61 (1:1:1 t,
1JCD ) 24.5 Hz, CmetasD), 133.76 (C4), 134.03 (C6), 134.73 (1:1:1 t,
1JCD ) 20.30 Hz, CparasD), 193.25 (CO), 193.47 (CO). Low temper-
Major diastereomer: 1H NMR (CD2Cl2, 300 MHz) δ 1.91 (s, C5Me5),
1
4
2
2.31 (s, CH3), 2.34 (s, CH3), 6.08 (dq, JCH ) 147.3 Hz, JHH ) JCH
) 4.7 Hz, CHOH), 6.9-7.4 (aromatic); 13C{1H} NMR (CD2Cl2, 90
1
2
MHz) δ 10.22 (C5Me5), 72.63 (dd, JCC ) 60.2 Hz, JCC ) 3.3 Hz,
13CH13Ct13CTol), 84.9 (dd, 1JCC ) 99.8 Hz, 2JCC ) 3.5 Hz, 13CH13Ct
13CTol), 93.3 (dd, 1JCC ) 100.6 Hz, 1JCC ) 60.1 Hz, 13CH13Ct13CTol).
Minor diastereomer: 1H NMR (CD2Cl2, 300 MHz) δ 1.98 (s, C5Me5),
1
ature H NMR (CD2Cl2, -75 °C) for 5: δ 2.06 (s, C5Me5), 5.81 (s,
CHsCtC), 6.57 (d, J ) 7.6 Hz, phenyl), 7.18 (t, J ) 7.1 Hz, phenyl),
7.46 (t, J ) 7.6 Hz, phenyl), 8.15 (d, J ) 6.4 Hz, phenyl). Low
temperature 1H NMR (CD2Cl2, -75 °C) for 6: δ 2.11 (s, C5Me5), 7.0-
7.9 (aromatic, obscured), 10.11 (s, CHdC).
1
4
2
2.34 (s, CH3), 2.39 (s, CH3), 5.80 (dm, JCH ) 147.3 Hz, JHH ) JCH
< 2 Hz, 13CHOH), 6.9-7.4 (aromatic); 13C{1H} NMR (CD2Cl2, 90
1
2
MHz) δ 10.41 (C5Me5), 71.94 (dd, JCC ) 59.7 Hz, JCC ) 2.3 Hz,
13CH13Ct13CTol), 84.1 (dd, 1JCC ) 98.3 Hz, 2JCC ) 2.5 Hz, 13CH13Ct
13CTol), 94.4 (dd, 1JCC ) 98.8 Hz, 1JCC ) 58.2 Hz, 13CH13Ct13CTol).
[C5Me5(CO)2Re(η3-Tol13CH13Ct13CTol)][BF4] (15) and [C5Me5-
(CO)2Re(η2-Tol13C13Cd13CHTol)][BF4] (16). Addition of 15 µL of
85% HBF4‚Et2O to a dark yellow solution of 14 (17 mg, 0.03 mmol)
in CD2Cl2 at -78 °C gave a deep green solution of a 1:10 mixture of
15/16. The mixture of isomers was characterized spectroscopically.
For [C5Me5(CO)2Re(η3-Tol13CH13Ct13CTol)][BF4] (15): 1H NMR
Acknowledgment. Financial support from the National Sci-
ence Foundation is gratefully acknowledged. Grants from NSF
(CHE-9629688) for the purchase of the NMR spectrometers and
a diffractometer (CHE-9709005) are acknowledged.
Supporting Information Available: General experimental
procedures, spectral characterizations, dynamic NMR, and X-ray
crystallographic information for 23-d5B (24 pages, PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
(CD2Cl2, 500 MHz, -90 °C) δ 2.02 (s, C5Me5), 5.71 (d, JCH ) 167
Hz, CH); 13C{1H} NMR (CD2Cl2, 125 MHz, -90 °C) δ 59.79 (dd,
1JCC ) 64.8 Hz, 2JCC ) 7.8 Hz, 13CH13Ct13C), 66.40 (dd, 1JCC ) 109.8,
1
2
64.8 Hz, 13CH13Ct13C), 85.42 (dd, JCC ) 109.8 Hz, JCC ) 7.8 Hz,
13CH13Ct13C).
JA020439M
9
J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002 13221