Intramolecular CH insertion reactions of (pentamethylcyclopentadienyl)rhenium alkynylcarbene complexes

Article abstract of DOI:10.1021/om010276v

Thermolysis of the alkynylcarbene complex Cp*(CO)₂Re=C(Ph)¹³C≡¹³CTol (5) at 120°C resulted in rapid equilibration (t_1/2 = 33 min) to a 1:1 mixture of 5 and Cp*(CO)₂Re=¹³C(Tol)¹³C??CPh (7) via a [1,3]-rhenium shift. Extended thermolysis of this mixture provided the CH insertion products {η⁵:η²-[C₅ (CH₃)₄CH₂¹³ CH(Tol)¹³C≡CPh]}Re(CO)₂ (8) and {η⁵:η²-[C₅ (CH₃)₄CH₂CH(Ph)¹³ C≡¹³CTol]}Re(CO)₂ (9). Thermolysis of the symmetrically substituted alkynylcarbene complex Cp*(CO)₂Re=C(Ph)C≡CPh (6) produced the CH insertion product {η⁵:η²-[C₅ (CH₃)₄CH₂CH(Ph)C≡CPh]} Re(CO)₂ (10). The CH insertion of Cp*(CO)₂Re=C(Ph)-C≡CC₆D₅ (6-HD) was monitored at low conversion before complete equilibration with Cp*(CO)₂Re=C(C₆D₅)C≡CPh (6-DH) occurred. An excess of {η⁵:η²-[C₅ (CH₃)₄CH₂CH(C₆D₅) C≡CPh]}Re(CO)₂ (13-HD) over {η⁵:η²-[C₅ (CH₃)₄CH₂CH(Ph) C≡CC₆D₅]}Re(CO)₂ (13-DH) provides evidence for site-selective CH insertion of the remote alkyne carbon into the CH bond of a Cp* methyl group.

Full text of DOI:10.1021/om010276v

Organometallics 2001, 20, 3795-3799
3795
In tr a m olecu la r CH In ser tion Rea ction s of
(P en ta m eth ylcyclop en ta d ien yl)Rh en iu m Alk yn ylca r ben e
Com p lexes
Charles P. Casey,* Stefan Kraft, and Michael Kavana
Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706
Received April 3, 2001
Thermolysis of the alkynylcarbene complex Cp*(CO)2RedC(Ph)13Ct13CTol (5) at 120 °C
resulted in rapid equilibration (t1/2 ) 33 min) to a 1:1 mixture of 5 and Cp*(CO)2Red13C-
(Tol)13CtCPh (7) via a [1,3]-rhenium shift. Extended thermolysis of this mixture provided
the CH insertion products {η5:η2-[C5(CH3)4CH213CH(Tol)13CtCPh]}Re(CO)2 (8) and {η5:η2-
[C5(CH3)4CH2CH(Ph)13Ct13CTol]}Re(CO)2 (9). Thermolysis of the symmetrically substituted
alkynylcarbene complex Cp*(CO)2RedC(Ph)CtCPh (6) produced the CH insertion product
{η5:η2-[C5(CH3)4CH2CH(Ph)CtCPh]}Re(CO)2 (10). The CH insertion of Cp*(CO)2RedC(Ph)-
CtCC6D5 (6-H D) was monitored at low conversion before complete equilibration with
Cp*(CO)2RedC(C6D5)CtCPh (6-DH) occurred. An excess of {η5:η2-[C5(CH3)4CH2CH(C6D5)-
CtCPh]}Re(CO)2 (13-HD) over {η5:η2-[C5(CH3)4CH2CH(Ph)CtCC6D5]}Re(CO)2 (13-DH)
provides evidence for site-selective CH insertion of the remote alkyne carbon into the CH
bond of a Cp* methyl group.
Heteroatom-substituted alkynylcarbene complexes
such as (OC)5MdC(OR)CtCR′ have become the focus
of extensive research in the past 15 years. Their rich
chemistry combines easy accessibility, high reactivity,
and large variations in the products formed. In particu-
lar, nucleophilic additions to either the carbene carbon
or the remote alkyne carbon (conjugate addition) and
cycloadditions to the triple bond have been exploited
synthetically.1 Despite the large number of donor-
substituted alkynylcarbene complexes, [1,3]-metal mi-
grations such as (OC)5MdC(OR)CtCR′ S (OC)5Md
C(R′)CtCOR have never been observed due to either a
high kinetic barrier or an unfavorable equilibrium.2,3
Recently, we began a search for [1,3]-metal shifts in non-
donor-substituted rhenium alkynylcarbene complexes
such as Cp(CO)2RedC(Tol)CtCPh (1) and found small
amounts of the [1,3]-shifted isomer Cp(CO)2RedC(Ph)Ct
CTol (2).4 Surprisingly, the major product was the
dimeric enediyne complex 3 formed by coupling two
molecules of 1 at their remote alkyne carbon.5,6 Mecha-
nistic studies of the dimerization led to the hypothesis
of a carbene intermediate A formed by a [1,1.5]-rhenium
shift reacting with the triple bond of a second alkynyl-
carbene complex to give cyclopropene intermediate B,
which then underwent ring opening to form the ene-
diyne complex 3 (Scheme 1).
In an effort to accelerate the [1,3]-shift relative to
dimerization, we studied the effect of para substituents
on the rate of [1,3]-shifts in a series of rhenium alky-
nylcarbene complexes Cp(CO)2RedC(Tol)CtCC6H4X (X
) N(CH3)2, H, CF3, SO2CF3) and found that the 1,3-
shifted isomer Cp(CO)2RedC(C6H4X)CtCTol formed 88
times faster with X ) SO2CF3 than with X ) H. An even
more dramatic rate acceleration, 550-fold, was observed
for the indenyl complex 4 compared to the cyclopenta-
dienyl complex 1. We proposed a mechanism for the
[1,3]-rhenium shift that involves coordination of the
alkyne triple bond to Re concerted with an η5- to η3-Cp
ring slip to give the 18-electron dehydrometallacyclob-
utadiene intermediate C (Scheme 2). Ring slippage
avoids a 20-electron intermediate. The acceleration of
[1,3]-rhenium shifts by electron-withdrawing substitu-
(1) For reviews of heteroatom-substituted alkynylcarbene complexes,
see: (a) Aumann, R.; Nienaber, H. Adv. Organomet. Chem. 1997, 41,
163. (b) Wulff, W. D. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, U.K., 1995; Vol. 12, Chapter 5.3. (c) Herndon, J . W. Coord.
Chem. Rev. 1999, 181, 177. (d) de Meijere, A.; Schirmer, H.; Duetsch,
M. Angew. Chem., Int. Ed. 2000, 39, 3964.
(2) A [1,3]-shift was postulated in a rhodium alkynylcarbene pre-
sumably formed in a catalytic cycle: Padwa, A.; Austin, D. J .; Gareau,
Y.; Kassir, J . M.; Xu, S. L. J . Am. Chem. Soc. 1993, 115, 2637.
(3) [1,3]-Transition-metal shifts are common in σ-propargyl to
σ-allenyl rearrangements: (a) Keng, R.-S.; Lin, Y.-C. Organometallics
1990, 9, 289. (b) Hajela, S.; Schaefer, W. P.; Bercaw, J . E. J . Organomet.
Chem. 1997, 532, 45. (c) Barluenga, J .; Trabanco, A. A.; Flo´rez, J .;
Garc´ıa-Granda, S.; Llorca, M.-A. J . Am. Chem. Soc. 1998, 120, 12129.
(d) Blosser, P. W.; Schimpff, D. G.; Gallucci, J . C.; Wojcicki, A.
Organometallics 1993, 12, 1993. (e) Liang, K.-W.; Lee, G.-H.; Peng,
S.-M.; Liu, R.-S. Organometallics 1995, 14, 2353. (f) Pu, J .; Peng, T.-
S.; Arif, A. M.; Gladysz, J . A. Organometallics 1992, 11, 3232. (g) Caro,
B.; Le Poul, P.; Robin-Le Guen, F.; Se´ne´chal-Tocquer, M.-C.; Saillard,
J .-Y.; Kahlal, S.; Ouahab, L.; Golhen, S. Eur. J . Org. Chem. 2000, 577.
(4) Casey, C. P.; Kraft, S.; Powell, D. R. J . Am. Chem. Soc. 2000,
122, 3771.
(5) It was surprising to find that dimerization of 1a occurred by
coupling at the remote carbon atoms rather than the carbene carbons,
since formation of symmetric alkenes by coupling of the carbene
carbons of two non-heteroatom-substituted metal carbene complexes
is well-known: (a) Casey, C. P.; Anderson, R. L. J . Chem. Soc., Chem.
Commun. 1975, 895. (b) Casey, C. P.; Burkhardt, T. J .; Bunnell, C.
A.; Calabrese, J . C. J . Am. Chem. Soc. 1977, 99, 2127. (c) Casey, C. P.;
Polichnowski, S. W. J . Am. Chem. Soc. 1977, 99, 6097. (d) Fischer, H.;
Schmid, J . J . Mol. Catal. 1988, 46, 277. (e) Fischer, H.; Zeuner, S.;
Ackermann, K.; Schmid, J . Chem. Ber. 1986, 119, 1546. (f) Fischer,
H.; Zeuner, S.; Ackermann, K. Chem. Commun. 1984, 684. (g) Hohm-
ann, F.; Siemoneit, S.; Nieger, M.; Kotila, S.; Do¨tz, K. H. Chem. Eur.
J . 1997, 3, 853.
(6) In contrast, the Pd-catalyzed dimerization of (CO)5Crd(OEt)Ct
CPh gave an E/ Z mixture of the enediyne PhCtCC(OEt)dC(OEt)Ct
CPh: Sierra, M. A.; del Amo, J . C.; Manchen˜o, M. J .; Go˜mez-Gallego,
M. J . Am. Chem. Soc. 2001, 123, 851.
10.1021/om010276v CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/27/2001

3796 Organometallics, Vol. 20, No. 17, 2001
Casey et al.
Sch em e 1
Sch em e 2
Figu r e 1. X-ray crystal structure of Cp*(CO)2RedC(Ph)Ct
CAr (6).
Sch em e 3
ents was explained by invoking enhanced d-π* back-
bonding to the alkyne-like dehydrometallacyclobutadi-
ene ligand in the transition state leading to C.
Since electron-withdrawing substituents on the alky-
nylcarbene ligand accelerated the [1,3]-shift relative to
dimerization, we sought to determine how the more
electron-donating pentamethylcyclopentadienyl (Cp*)
ligand would affect the rates of [1,3]-metal shift and
dimerization. Here we report that the Cp* ligand
accelerates the [1,3]-shift and, more interestingly, that
a CH insertion product is formed upon thermolysis. The
observation of CH insertion provides support for the
formation of an intermediate with carbene like reactiv-
ity in the thermolysis of alkynylcarbene complexes.
d8 at 120 °C, a 1:1 equilibrium mixture of 5 and
Cp*(CO)2Red13C(Tol)13CtCPh (7) was formed within 1
h (Scheme 3). 13C NMR spectroscopy provided a conve-
nient way of monitoring the reaction. In the 13C{1H}
NMR spectrum of 5, intense resonances were observed
at δ 110.98 (d, 1J
C ) 172 Hz, 13Ct13CAr) and 119.37
13C13
(d, 1J
C ) 172 Hz, 13Ct13CAr). Upon thermolysis, new
13C13
1
13C13
C
resonances were observed at δ 111.1 (d, J
) 64.4
Hz) and 249.5 (d, 1J
) 64.4 Hz) and were assigned
13C13
C
to the labeled alkyne and carbene carbons of 7. Equili-
bration of the Cp* complexes (5 S 7, kobs ) (3.6 ( 0.2)
× 10-4 s-1) was 84 times faster than that of the
analogous Cp complexes (1 S 2, kobs ) (4.3 ( 0.1) ×
10-6 s-1).
Resu lts a n d Discu ssion
Cp* rhenium alkynylcarbene complexes Cp*(CO)2Red
C(Ph)13Ct13CTol (5) and Cp*(CO)2RedC(Ph)CtCAr (Ar
) Ph (6), C6D5 (6-HD)) were synthesized in moderate
yield by addition of BrZn13Ct13CTol or BrZnCtCAr to
[Cp*(CO)2RetCPh]BCl4.7,8 The X-ray crystal structure
of 6 (Figure 1) is similar to that of Cp analogues.4,9
[1,3]-R h en iu m Sh ift . When a solution of Cp*-
(CO)2RedC(Ph)13Ct13CTol (5) was heated in toluene-
We propose that the [1,3]-rhenium shift that equili-
brates 5 S 7 proceeds via a ring-slipped dehydromet-
allacyclobutadiene complex analogous to C in Scheme
1. Interestingly, the faster rates seen for our Cp*
complexes (5 S 7) compared with Cp complexes (1 S 2)
contrasts with Basolo’s observation that η5 to η3 ring
slippage is 2 orders of magnitude slower for Cp* than
for the Cp complexes in the phosphine substitution
reactions of (η5-Cp)Rh(CO)2 (reaction 1).10 These seem-
(7) For the synthesis of [Cp*(CO)2RetCPh]BCl4, see: Fischer, E.
O.; Apostolidis, C.; Dornberger, E.; Filippou, A. C.; Kanellakopulos,
B.; Lungwitz, B.; Mu¨ller, J .; Powietzka, B.; Rebizant, J .; Roth, W. Z.
Naturforsch., B 1995, 50, 1382.
(8) We were able to obtain an X-ray crystal structure of [Cp*-
(CO)2RetCPh]BCl4 (see the Supporting Information).
(9) Casey, C. P.; Kraft, S.; Powell, D. R. Submitted for publication
in J . Am. Chem. Soc.
(10) Rerek, M. E.; Basolo, F. J . Am. Chem. Soc. 1984, 106, 5908.

C5Me5 Rhenium Alkynyl Carbene Complexes
Organometallics, Vol. 20, No. 17, 2001 3797
Ta ble 1. Tim e Cou r se of Con cen tr a tion s [6-HD], [6-DH], [13-HD], a n d [13-DH]
[6-HD],
[6-DH],
10-1
[13-HD],
[13-DH],
[6-HD]/{[6-HD] +
[6-DH]}
[13-HD]/{[13-HD] +
[13-DH]}
conversn
[6] f[13], %
t, min
10-1
M
M
10-3
M
10-3
M
0
2
5
10
20
30
40
1.09
1.04
0.0116
0.0539
0.116
0.202
0.325
0.383
0.419
0
0.53
0
0.99
0.95
0.89
0.81
0.70
0.63
0.58
0
0.016
0.15
0.43
1.2
1.9
2.6
0.97
0.89
0.84
0.78
0.75
0.73
0.5
1.3
2.4
4.9
7.4
9.5
0.958
0.883
0.748
0.639
0.582
1.3
2.2
4.1
5.7
6.9
(η5-Cp)Rh(CO)2 + PR3 f (η3-Cp)Rh(CO)2PR3 f
(η5-Cp)Rh(CO)PR3 + CO (1)
effect for the vicinal meta hydrogen (δ 7.08, 1.8%) but
no enhancement >0.2% to other hydrogens in the
molecule.
We suggest that the tethered alkyne complexes 8-10
are formed by insertion of the remote alkyne carbon into
a Cp* methyl group induced by a [1,1.5]-rhenium shift
to give the intermediate D with “free carbene” character
(path A, Scheme 4).12 Previously, we provided evidence
for carbene-like reactivity at the remote alkyne carbon
in 11, which formed cyclopropyl derivative 12 upon
heating at 120 °C (Scheme 5).13
The possibility that CH insertion products might
result from a net insertion of the metal-bound carbene
carbon into a methyl CH bond was also considered. Such
an insertion might result from an initial 1,2-addition
of a CH bond across the RedC bond to form the tuck-in
complex E, followed by a reductive C-C elimination and
alkyne complexation (path B, Scheme 4). Bercaw dem-
onstrated the viability of an intramolecular CH addition
of a Cp* methyl group across a HfdC bond to form a
tuck-in complex.14,15 Moreover, intra- and intermolecu-
lar CH insertions have been reported for Fischer car-
bene complexes.16,17
ingly conflicting observations can be reconciled by
assuming that addition of a phosphine to (η5-Cp)Rh-
(CO)2 increases the electron density around the metal
during the formation of (η3-Cp)Rh(CO)2PR3; the intro-
duction of an electron-donating Cp* ligand provides an
electronically unfavorable interaction. In contrast, the
π coordination of a triple bond to rhenium in C is
stabilized by enhanced d-π* interactions (back-bond-
ing), effectively “diffusing” charge density from the
electron-rich metal center onto the ligand. A faster [1,3]-
shift in the Cp* complex 5 compared with its Cp
analogue 1 is a direct consequence of an increased
π-basicity at the metal center in C.
CH In ser tion P r od u cts. Extended thermolysis of
the equilibrium 5 S 7 at 120 °C for 14 h did not produce
the expected dimeric enediyne complexes similar to the
Cp analogue 3. Instead, a 1:1 mixture of {η5:η2-[C5(CH3)4-
CH213CH(Tol)13CtCPh]}Re(CO)2 (8) and {η5:η2-[C5(CH3)4-
CH2CH(Ph)13Ct13CTol]}Re(CO)2 (9) was formed by a
net insertion of an alkynylcarbene carbon into a CH
bond of a methyl group on the Cp* ligand (Scheme 3).
In the 13C{1H} NMR spectrum, enhanced signals at δ
In principle, it should be possible to identify the
terminus of the alkynylcarbene that inserts into the
methyl group by monitoring the conversion of the
67.2 and 89.2 (1J
) 54 Hz) were assigned to the
13C13
C
labeled methine and alkyne carbons of 8. An additional
(12) A similar [1,1.5]-shift has been postulated in the rearrangement
of chromium alkynylcarbene complexes [(CO)5CrdC(O)(CtCOEt)]- to
a cyclopropenylidene complex: J uneau, K. N.; Hegedus, L. S.; Roepke,
F. W. J . Am. Chem. Soc. 1989, 111, 4762.
(13) It should be admitted that we have no direct evidence for the
intermediacy of the “free carbene” shown as an intermediate in the
cyclopropanation; [1,1.5]-rhenium shifts and CH insertion might
proceed in a concerted fashion.
splitting (1J
) 133.9 Hz) was observed for the
13CH
methine carbon in the H-coupled 13C NMR spectrum.
1
The labeled alkyne carbons in isomer 9 (δ 76.7, 86.8)
1
showed a one-bond coupling of J
) 111 Hz.11
13C13
C
Thermolysis of the symmetrically substituted diphe-
nyl alkynylcarbene complex 6 cleanly formed CH inser-
tion product 10 in 85% yield (Scheme 4). Four different
(14) (a) McDade, C.; Green, J . C.; Bercaw, J . E. Organometallics
1982, 1, 1629. (b) Bulls, A. R.; Schaefer, W. P.; Serfas, M.; Bercaw, J .
E. Organometallics 1987, 6, 1219.
1
methyl resonances in the H NMR spectrum at δ 1.39,
(15) For inter- and intramolecular CH insertions of early-transition-
metal alkylidene complexes, see: (a) Adams, C. S.; Legzdins, P.; Tran,
E. J . Am. Chem. Soc. 2001, 123, 612. (b) Duncalf, D. J .; Harrison, R.
J .; McCamley, A.; Royan, B. W. J . Chem. Soc., Chem. Commun. 1995,
2421. (c) van der Heijden, H.; Hessen, B. J . Chem. Soc., Chem.
Commun. 1995, 145. (d) Vilardo, J . S.; Lockwood, M. A.; Hanson, L.
G.; Clark, J . R.; Parkin, B. C.; Fanwick, P. E.; Rothwell, I. P. J . Chem.
Soc., Dalton Trans. 1997, 3353. (e) Chamberlain, L. R.; Rothwell, I.
P.; Huffman, J . C. J . Am. Chem. Soc. 1986, 108, 1502. (f) Schrock, R.
R.; DePue, R. T.; Feldman, J .; Yap, K. B.; Yang, D. C.; Davis, W. M.;
Park, L.; DiMare, M.; Schofield, M.; Anhaus, J .; Walborsky, E.; Evitt,
E.; Kru¨ger, C.; Betz, P. Organometallics 1990, 9, 2262. (g) van Doorn,
J . A.; van der Heijden, H.; Orpen, A. G. Organometallics 1994, 13, 4271.
(16) (a) Fischer, H.; Schmid, J .; Ma¨rkl, R. J . Chem. Soc., Chem.
Commun. 1985, 572. (b) Wang, S. L. B.; Su, J .; Wulff, W. D.; Hoogsteen,
K. J . Am. Chem. Soc. 1992, 114, 10665. (c) Barluenga, J .; Rodr´ıguez,
F.; Vadecard, J .; Bendix, M.; Fan˜ana´s, F. J .; Lo´pez-Ortiz, F. J . Am.
Chem. Soc. 1996, 118, 6090. (d) Barluenga, J .; Rodr´ıguez, F.; Vadecard,
J .; Bendix, M.; Fan˜ana´s, F. J .; Lo´pez-Ortiz, F.; Rodr´ıguez, M. A. J .
Am. Chem. Soc. 1999, 121, 8776. (e) Barluenga, J .; Aznar, F.;
Ferna´ndez, M. Chem. Eur. J . 1997, 3, 1629. (f) Wienand, A.; Reissig,
H.-U. Angew. Chem., Int. Ed. Engl. 1990, 29, 1129. (g) Takeda, K.;
Okamoto, Y.; Nakajima, A.; Yoshii, E.; Koizumi, T. Synlett 1997, 1181.
(17) Werner documented an intramolecular insertion of a carbene
ligand into a CH bond of an η5-indenyl ligand accompanied by a
complete detachment from the metal (Bleuel, E.; Laubender, M.;
Weberndo¨rfer, B.; Werner, H. Angew. Chem., Int. Ed. 1999, 38, 156).
1.95, 2.05, and 2.27 are in accordance with a C1-
symmetric molecule. The methine resonance (δ 5.13) is
a triplet (3J ) 9.7 Hz) coupled to the neighboring
2
diastereotopic methylene hydrogens at δ 2.08 (dd, J )
3
2
13.5 Hz, J ) 9.6 Hz, Hanti) and δ 2.57 (dd, J ) 13.6
3
Hz, J ) 9.6 Hz, Hsyn), which have a strong geminal
coupling. NOE studies were undertaken to ascertain the
spatial proximity of methylene and methine hydrogens
to the adjacent methyl groups of the ring. Irradiation
of the methine signal resulted in NOE signal enhance-
ments for Hsyn (2.6%), Hanti (0.6%), an adjacent ring CH3
group (δ 2.26, 2.1%), and the ortho hydrogen Ho(1) (δ
7.21, 1.7%). Irradiation of Hanti gave NOE enhancements
for Hsyn (6.7%), a ring-CH3 group (δ 1.39, 1.1%), the
methine hydrogen (0.6%), and Ho(1) (0.6%). Irradiation
of Ho(2) on the lower phenyl group showed only an NOE
(11) Typical one-bond CC coupling constants (1J CC) in alkynes range
between 170 and 180 Hz. We attribute the significantly lower coupling
constant in 9 to metal complexation.

3798 Organometallics, Vol. 20, No. 17, 2001
Casey et al.
Sch em e 4
Sch em e 5
ring methyl group (δ 2.27) common to both isomers. The
comparison of the ratios [6-HD]/{[6-HD] + [6-DH]} and
[13-HD]/{[13-HD] + [13-DH]} at any given point of the
reaction indicated a high selectivity for the conversion
of 6-HD to 13-HD (Table 1).
In summary, we found that replacement of a Cp
ligand with the more electron rich Cp* ligand speeds
up [1,3]-metal shifts in rhenium alkynylcarbene com-
plexes by almost 2 orders of magnitude. Over several
hours, new CH insertion products were identified. Site-
selective CH insertion implies carbenoid reactivity at
the remote alkyne carbon and supports the hypothesis
of carbene intermediates such as A in dimerization
reactions shown in Scheme 1.
Exp er im en ta l Section
Cp *(CO)2RedC(P h )13Ct13CTol (5). Addition of BrZn13Ct
13CPh (from Li13Ct13CPh (11 mg, 0.089 mmol) and ZnBr2 (20
mg, 0.089 mmol) in 1 mL of THF) to an orange solution of [Cp*-
(CO)2RetCPh]BCl4 (110 mg, 0.179 mmol) in 25 mL of CH2Cl2
at -35 °C produced a black solution. The cold reaction mixture
was poured onto a silica gel column (30 × 2 cm), and a black
fraction was eluted with a 4/1 hexane/diethyl ether mixture.
Evaporation of solvent under reduced pressure gave a solid
which was redissolved in 2 mL of 4/1 hexane/CH2Cl2. Slow
evaporation gave black crystals of 5 (14 mg, 0.024 mmol, 28%).
1H NMR (CD2Cl2, 500 MHz): δ 2.16 [s, C5(CH3)5], 2.30 (s,
Sch em e 6
3
3
ArCH3), 7.19 (d, J ) 7.9 Hz, aromatic CH), 7.29 (t, J ) 7.4
Hz, aromatic CH), 7.40 (t, 3J ) 7.3 Hz, aromatic CH), 7.53
3
3
3
13
(dd, J ) 8.1 Hz, J
) 5.1 Hz, aromatic CH), 7.97 (d, J )
CH
7.3 Hz, aromatic CH). 1H NMR (toluene-d8, 500 MHz): δ 1.91
[s, (C5(CH3)5], 1.97 (s, Ar-CH3), 6.85 (d, 3J ) 6.9 Hz, aromatic
CH), 7.15-7.18 (m, aromatic CH), 7.49-7.53 (m, aromatic CH),
8.33-8.42 (m, aromatic CH). 13C{1H} NMR (CD2Cl2, 125
1
13 13
MHz): δ 110.98 (d, J
) 172 Hz, 13Ct13CAr), 119.37 (d,
C
C
1
J
) 172 Hz, 13Ct13CAr). IR (CH2Cl2): 1954, 1878 cm-1
.
13 13
deuterium-labeled alkynylcarbene complex 6-HD into
either 13-HD or 13-DH (Scheme 6). Since the [1,3]-
rhenium shift 6-HD S 6-DH (kobs ) 7.5 × 10-4 s-1) is
14 times faster than the CH insertion step (kobs ) 5.3
× 10-5 s-1), it was crucial to determine the ratio of 13-
HD to 13-DH at less than 10% conversion to 13 to avoid
complications from equilibration of 6-HD and 6-DH.
The concentrations [6-HD], [6-DH], and [13-HD] were
C
C
HRMS (EI): m/z calcd for C2613C2H27O2Re (M+) 584.1697, found
584.1636.
Kin etic Mea su r em en t of th e Con ver sion of 5 to 7 a t
120 °C. A C6D5CD3 solution of 5 (5.0 mg, 0.0084 mmol, 0.42
mL total volume and 0.020 M at 120 °C) containing 1,4-bis-
(trimethylsilyl)benzene (1.0 mg, internal NMR standard) was
heated at 120 ( 0.3 °C. 1H NMR spectra were acquired at room
temperature after 0, 1, 15, 40, 122, and 260 min at 120 °C (5,
δ(tolyl CH3) 1.97; 7, δ(tolyl CH3) ) 1.86). The decrease in the
ratio 5:(5 + 7) was followed (kobs ) (3.6 ( 0.2) × 10-4 s-1, Keq
) 1.0 ( 0.1, k1 ) (1.8 ( 0.1) × 10-4 s-1, k-1 ) (1.8 ( 0.1) ×
10-4 s-1).
1
directly determined by H NMR spectroscopy (Table 1)
via their ortho hydrogens (6-HD, δ 8.35; 6-DH, δ 7.55;
13-HD, δ 7.43); [13-DH] was inferred from the sum of
[13-HD] and [13-DH] determined by integration of a

C5Me5 Rhenium Alkynyl Carbene Complexes
Organometallics, Vol. 20, No. 17, 2001 3799
Spectroscopic characterization of 7 was undertaken without
isolation. 1H NMR (toluene-d8, 500 MHz): δ 1.86 (s, C6H4CH3),
1.90 [s, (C5(CH3)5], 6.90-7.11 (m, aromatic CH), 8.40-8.45 (m,
aromatic CH, partially obscured by signals from 5). 13C{1H}
preparative thin-layer chromatography (silica, 10/1 hexane/
diethyl ether, Rf ) 0.5, yellow band). A yellow solid was
obtained, which was dissolved in 1.5 mL of 1/1 CH2Cl2/hexane.
Slow evaporation gave 10 as orange-yellow needles (28.1 mg,
0.049.5 µmol, 85%). 1H NMR (toluene-d8, 500 MHz): δ 1.39
(s, CH3), 1.95 (s, CH3), 2.05 (s, CH3), 2.08 (dd, 2J ) 13.5 Hz, 3J
1
13 13
NMR (toluene-d8, 125 MHz): δ 111.1 (d,
J
) 64.4 Hz,
C
C
13
1
13 13
CtC), 249.5 (d, J
) 64.4 Hz, Red13C).
C
C
2
) 9.6 Hz, CHHCHPh), 2.27 (s, CH3), 2.57 (dd, J ) 13.6 Hz,
Exten d ed Th er m olysis of 5 a n d 7. Thermolysis of 5 and
3
3J ) 9.6 Hz, CHHCHPh), 5.13 (t, J ) 9.5 Hz, CHPh), 6.97 (t,
7 for 14 h at 120 °C afforded a 5:1 mixture of (8 + 9) and (5 +
7). 1H NMR (8 + 9, toluene-d8, 500 MHz): δ 1.40 (s, CH3),
1.41 (s, CH3), 1.95 (s, CH3), 1.96 (s, CH3), 2.058 (s, CH3), 2.061
(s, tolyl CH3), 2.13 (s, tolyl CH3), 2.26 (s, CH3), 2.27 (s, CH3),
3J ) 7.3 Hz, aromatic CH), 7.08 (t, 3J ) 7.8 Hz, aromatic CH),
7.14 (t, 3J ) 7.2 Hz, aromatic CH), 7.21 (d, 3J ) 7.7 Hz,
aromatic CH), 7.43 (d, 3J ) 7.5 Hz, aromatic CH). 1H NMR
(CD2Cl2, 500 MHz): δ 1.66 (s, CH3), 2.29 (s, CH3), 2.34 (s, CH3),
2.38 (dd, 2J ) 13.4 Hz, 3J ) 9.7 Hz, CHHCHPh), 2.56 (s, CH3),
2
2.50 (m, CHHCHPh and CHH13CHTol), 5.12 (dtd, J
) 11.5
13
CH
1
3
3
13
13
Hz, J ) 9.5 Hz, J
) 5.3 Hz, CHPh, 9), 5.14 (ddt, J
)
CH
CH
2
3
3
2
3
136.2 Hz, J
) 11.5 Hz, J ) 9.5 Hz, 13CHTol, 8), 6.97 (t,
13
3.05 (dd, J ) 13.5 Hz, J ) 9.4 Hz, CHHCHPh), 5.30 (t, J )
9.6 Hz, CHPh), 7.19-7.24 (m, aromatic CH), 7.25-7.34 (m,
CH
3J ) 7.3 Hz, aromatic CH), 7.08 (t, 3J ) 7.8 Hz, aromatic CH),
3
3
6.75-7.20 (m, aromatic CH), 7.24 (d, 3J ) 7.4 Hz, aromatic
aromatic CH), 7.36 (t, J ) 7.3 Hz, aromatic CH), 7.43 (d, J
) 7.4 Hz, aromatic CH). 13C NMR (CD2Cl2, 125 MHz): δ 9.23
3
3
13
CH), 7.38 (dd, J ) 8.0 Hz, J
) 5.6 Hz, aromatic CH). The
CH
1
1
(q, J CH ) 127.9 Hz, CH3), 11.25 (q, J CH ) 127.9 Hz, CH3),
signals for the CHHCHPh hydrogens of both isomers are
1
1
obscured by the solvent pentet at δ 2.09. 13C NMR (8 + 9,
11.61 (q, J CH ) 127.9 Hz, CH3), 12.24 (q, J CH ) 127.3 Hz,
1
2
1
1
CH3), 30.34 (td, J CH ) 132.8, J CH ) 5.9 Hz, CH2), 67.40 (d,
toluene-d8, 125 MHz): 8, δ 67.27 (dd, J CC ) 55.5 Hz, J CH
)
)
1J CH ) 137.6 Hz, CHPh), 76.21 (q, J CH ) J CH(Ph) ) 5.4 Hz,
3
3
133.9 Hz, 13CHTol), 89.21 (dt, J CC ) 55.5 Hz, J CH
1
2
2
3
3J CH(one of diastereotopic CH ) ) 11.0 Hz, 13CtCPh); 9, δ 76.7 (dq, 1J CC
CtCPh), 89.71 (t, J CH ) J CH(one
CtCPh), 91.14 (m, CCH3), 99.08 (m, CCH3), 100.60 (m, CCH3),
) 11.6 Hz,
of diastereotopic CH
)
2
2
) 111.7 Hz, J CH ) J CH(Tol) ) 4.8 Hz, 13Ct13CTol), 87.41 (dt,
3
3
1
2
1J CC ) 111.6 Hz, J CH
)
3J CH(one
) 11.3 Hz,
103.88 (m, CCH3), 115.13 (m, CCH3), 127.19 (dt, J CH ) 160.2
of diastereotopic CH
)
2
Hz, 3J CH ) 7.1 Hz, aromatic), 127.49 (dt, 1J CH ) 157.9 Hz, 3J CH
13Ct13CTol).
1
3
) 5.4 Hz, aromatic), 127.73 (dt, J CH ) 160.2 Hz, J CH ) 7.7
Cp *(CO)2Red(P h )CtCP h (6). Addition of BrZnCtCPh
(from LiCtCPh (71 mg, 0.66 mmol) and ZnBr2 (148 mg, 0.658
mmol) in 1 mL of THF) to an orange solution of [Cp*(CO)2Ret
CPh]BCl4 (401 mg, 0.648 mmol) in 5 mL of THF at -35 °C
slowly produced a black solution. After 10 min, the cold
reaction mixture was poured onto a silica gel column (30 × 2
cm) and a black fraction was eluted with 5/1 hexane/diethyl
ether. Evaporation of solvent under reduced pressure gave a
solid which was redissolved in 2 mL of 3/1 hexane/CH2Cl2. Slow
evaporation gave 6 as black plates (88 mg, 0.155 mmol, 24%)18
suitable for X-ray crystal structure analysis. 1H NMR (CD2-
Cl2, 500 MHz): δ 2.17 [s, C5(CH3)5], 7.30 (t, 3J ) 7.3 Hz,
aromatic CH), 7.39 (m, aromatic CH), 7.47 (d, 3J ) 7.5 Hz,
1
3
Hz, aromatic), 128.77 (dd, J CH ) 160.2 Hz, J CH ) 7.9 Hz,
3
aromatic), 130.02 (t, J CH ) 7.0 Hz, aromatic), 130.90 (ddd,
1J CH ) 160.8 Hz, J CH ) 6.8 Hz, J CH ) 5.4 Hz, aromatic),
143.44 (m, aromatic), 209.65 (CO), 210.16 (CO). IR (CH2Cl2)
1955, 1855 cm-1. HRMS (EI): m/z calcd for C27H25O2187Re (M+)
568.1412, found 568.1408.
3
3
Kin etic Mea su r em en t of th e Con ver sion of 6-HD to
6-DH a n d of (6-HD + 6-DH) to (13-HD + 13-DH) a t 120
°C. A C6D5CD3 solution of 6-HD (30.2 mg, 0.0527 mmol, 0.48
mL total volume and 0.11 M at 120 °C) containing 1,4-bis-
(trimethylsilyl)benzene (1.0 mg, internal NMR standard) was
heated at 120 ( 0.3 °C. 1H NMR spectra were acquired at room
temperature after 0, 2, 5, 40, 10, 20, 30, 40, 111, 216, and 375
min at 120 °C (6-HD, δ(CHortho) 8.36; 6-DH, δ(CHortho) 7.55;
13-HD, δ(CHortho) 7.44; 13-DH, δ(CHortho) 7.21). The rate of
approach to equilibrium (6-HD S 6-DH) (kobs ) (7.5 ( 0.2) ×
10-4 s-1, Keq ) 1.0 ( 0.1, k1 ) (3.8 ( 0.1) × 10-4 s-1, k-1 ) (3.8
( 0.1) × 10-4 s-1) and the rate of disappearance of combined
alkynylcarbene complex concentration ((6-HD + 6-DH, δ(Cp*)
1.91) f (13-HD + 13-DH)] (kobs ) (5.3 ( 0.2) × 10-5 s-1) were
determined. Ratios of [6-HD] to ([6-HD] + [6-DH ]) and
[13-HD] to ([13-HD] + [13-DH]) are shown in Table 1.
3
3
aromatic CH), 7.63 (d, J ) 8.0 Hz, aromatic CH), 7.99 (d, J
) 7.5 Hz, aromatic CH). 1H NMR (toluene-d8, 500 MHz): δ
1.89 [s, C5(CH3)5], 7.00-7.20 (m, aromatic CH), 7.55 (d, J )
3
7.3 Hz, aromatic CH), 8.35 (d, 3J ) 7.3 Hz, aromatic CH). 13C-
{1H} NMR (CD2Cl2, 125 MHz): δ 10.48 [C5(CH3)5], 104.83 [C5-
(CH3)5], 110.95 (CtCPh), 118.60 (CtCPh), 125.75 (aromatic),
126.43 (aromatic), 128.34 (aromatic), 128.63 (aromatic), 128.70
(aromatic), 129.26 (aromatic), 129.46 (aromatic), 161.90 (aro-
matic), 208.34 (CO), 249.18 (RedC). IR (CH2Cl2): 1956, 1880
cm-1. HRMS (EI): m/z calcd for C27H25O2Re (M+) 566.1384,
found 566.1395.
{η5:η2-[C5(CH3)4CH2CH(P h )CtCP h ]}Re(CO)2 (10). A so-
lution of Cp*(CO)2RedC(Ph)CtCPh (6; 33.1 mg, 58.3 µmol)
in toluene-d8 (0.49 mL, 0.12 M) containing 1,4-bis(trimethyl-
silyl)benzene (5.4 mg) as an internal NMR standard was
heated at 120 °C for 14 h. 1H NMR showed that more than
95% of 6 had been consumed. After the solvent was evaporated
under reduced pressure, the crude product was purified by
Ack n ow led gm en t. Financial support from the Na-
tional Science Foundation is gratefully acknowledged.
Grants from the NSF (Grant No. CHE-9629688) for the
purchase of the NMR spectrometers and a diffractome-
ter (Grant No. CHE-9709005) are acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Preparation of com-
pounds, spectral data, description of kinetics, and X-ray crystal
structures. This material is available free of charge via the
Internet at http://pubs.acs.org.
(18) Later we found that the yields of Cp*(CO)2Re-alkynylcarbene
complexes can be increased significantly, if the initial crude product
solution is warmed from -35 °C to room temperature for 10 min (see
preparation of 6-DH in supporting information).
OM010276V