Ring strain perturbation of the equilibria between hydroxycarbene complexes and metal acyl hydride complexes

Article abstract of DOI:10.1021/ja9637311

The acyl anion complex [(CO)₂ReC(=O)CH₂CH₂(η⁵-C₅H₄)]^-Li⁺ (7) in which a two-carbon tether links the cyclopentadienyl ring to the acyl carbon was synthesized by attachment of a 2-lithioethyl side chain to the cyclopentadiene ring of CpRe(CO)₃ followed by intramolecular attack of the lithium reagent on a carbonyl group. Alkylation of 7 with (CH₃)₃O⁺BF₄^- occurred at oxygen to give the methoxycarbene complex (CO)₂Re=C(OCH₃)CH_2- CH₂(η⁵-C₅H₄) (9), which was shown by X-ray crystallography to have significant strain associated with the tethered ring. Protonation of 7 gave a mixture of hydroxycarbene complex (CO)₂Re=C(OH)CH₂CH₂(η⁵-C₅H₄) (2) and the metal acyl hydride complex trans-(CO)₂HReC(=O)CH₂CH₂(η⁵-C₅H₄) (3). The unusual observation of the metal acyl hydride is attributed to the two- carbon tether introducing strain into the three-legged piano stool geometry of 2 but leaving the four-legged piano stool geometry of 3 relatively unstrained. In agreement with this hypothesis, no strain was apparent in the X-ray structure of the three-carbon-tethered methoxycarbene complex (CO)₂Re=C(OCH₃)CH₂CH₂CH₂(η⁵-C₅H₄) (17) and only the hydroxycarbene tautomer (CO)₂Re=C(OH)CH₂CH₂CH₂(η⁵-C₅H₄) (18) was observed at equilibrium. A two-carbon tether did not introduce sufficient strain into the aminocarbene complex (CO)₂Re=C[NH(CH₃)]CH₂CH₂(η⁵-C₅H₄) (19) to allow observation of its iminoacyl hydride tautomer.

Full text of DOI:10.1021/ja9637311

J. Am. Chem. Soc. 1997, 119, 3971-3978
3971
Ring Strain Perturbation of the Equilibria between
Hydroxycarbene Complexes and Metal Acyl Hydride
Complexes
Charles P. Casey,* Curtis J. Czerwinski, Kerry A. Fusie, and Randy K. Hayashi
Contribution from the Department of Chemistry, UniVersity of Wisconsin,
Madison, Wisconsin 53706
ReceiVed October 28, 1996X
Abstract: The acyl anion complex [(CO)2ReC(dO)CH2CH2(η5-C5H4)]-Li+ (7) in which a two-carbon tether links
the cyclopentadienyl ring to the acyl carbon was synthesized by attachment of a 2-lithioethyl side chain to the
cyclopentadiene ring of CpRe(CO)3 followed by intramolecular attack of the lithium reagent on a carbonyl group.
Alkylation of 7 with (CH3)3O+BF4- occurred at oxygen to give the methoxycarbene complex (CO)2RedC(OCH3)CH2-
CH2(η5-C5H4) (9), which was shown by X-ray crystallography to have significant strain associated with the tethered
ring. Protonation of 7 gave a mixture of hydroxycarbene complex (CO)2RedC(OH)CH2CH2(η5-C5H4) (2) and the
metal acyl hydride complex trans-(CO)2HReC(dO)CH2CH2(η5-C5H4) (3). The unusual observation of the metal
acyl hydride is attributed to the two-carbon tether introducing strain into the three-legged piano stool geometry of
2 but leaving the four-legged piano stool geometry of 3 relatively unstrained. In agreement with this hypothesis, no
strain was apparent in the X-ray structure of the three-carbon-tethered methoxycarbene complex (CO)2RedC-
(OCH3)CH2CH2CH2(η5-C5H4) (17) and only the hydroxycarbene tautomer (CO)2RedC(OH)CH2CH2CH2(η5-C5H4)
(18) was observed at equilibrium. A two-carbon tether did not introduce sufficient strain into the aminocarbene
complex (CO)2RedC[NH(CH3)]CH2CH2(η5-C5H4) (19) to allow observation of its iminoacyl hydride tautomer.
Introduction
equilibrium between the two isomers. For example, Fischer
saw no metal acyl hydride in equilibrium with 1.
Metal acyl hydride complexes are important in organometallic
chemistry as key proposed intermediates in hydroformylation
and aldehyde decarbonylation.1 A number of stable acyl hydride
complexes have been isolated.2 Hydroxycarbene complexes are
important as proposed intermediates in CO reduction processes,
including the Fischer-Tropsch process.3 In 1968, Fischer
isolated the first transition metal hydroxycarbene complex, (η5-
C5H5)(CO)2RedC(OH)CH3 (1), by protonation of a rhenium
acyl anion.4 Since Fischer’s report, other hydroxycarbene
complexes have been synthesized by protonation of acyl anions,
by addition of HX to metal alkyl complexes, and by other
methods.5 Although metal acyl hydrides and hydroxycarbene
complexes are tautomers, no one has previously reported an
We have found that introduction of a two-carbon tether
between the carbene carbon and the cyclopentadienyl ring of
Fischer’s compound perturbs the equilibrium between hydroxy-
carbene complexes and metal acyl hydrides to such a large
extent that both isomers are readily observed in equilibrium.
We have hypothesized that the tether introduces ring strain into
the three-legged piano stool geometry of the hydroxycarbene
complex (CO)2RedC(OH)CH2CH2(η5-C5H4) (2) but leaves the
four-legged piano stool geometry of the metal acyl hydride
complex trans-(CO)2HReC(dO)CH2CH2(η5-C5H4) (3) relatively
X Abstract published in AdVance ACS Abstracts, March 15, 1997.
(1) (a) Ohno, K.; Tsuji, J. J. Am. Chem. Soc. 1968, 90, 99. (b) Lochow,
C. F.; Miller, R. G. J. Am. Chem. Soc. 1976, 98, 1281. (c) Milstein, D.
Acc. Chem. Res. 1988, 21, 428.
(2) (a) Landvatter, E. F.; Rauchfuss, T. B. Organometallics 1982, 1, 506.
(b) Dahlenburg, L.; Mirzaei, F. J. Organomet. Chem. 1983, 251, 103. (c)
Bleeke, J. R.; Haile, T.; Chiang, M. Y. Organometallics 1991, 10, 19. (d)
Moore, E. J.; Santarsiero, B. D. Acta Crystallogr. 1989, C45, 579. (e) von
Deuten, K.; Dahlenburg, L. Transition Met. Chem. (London) 1980, 5, 222.
(f) Wong, W.-K.; Chiu, K. W.; Wilkinson, G.; Galas, A. M. R.; Thornton-
Pett, M.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1983, 1557. (g)
Wong, W.-K.; Wilkinson, G.; Galas, A. M. R.; Thornton-Pett, M. A.;
Hursthouse, M. B. Polyhedron 1982, 1, 842. (h) Arpac, E.; Dahlenburg, L.
Chem. Ber. 1985, 118, 3188. (i) Milstein, D. J. Am. Chem. Soc. 1982, 104,
5227. (j) Milstein, D. Organometallics 1982, 1, 1549. (k) Bianchini, C.;
Meli, A.; Peruzzini, M.; Ramirez, J. A.; Vacca, A.; Vizza, F.; Zanobini, F.
Organometallics 1989, 8, 337. (l) Bianchini, C.; Meli, A.; Peruzzini, M.;
Vizza, F.; Bachechi, F. Organometallics 1991, 10, 820. (m) Koh, J. J.; Lee,
W.-H.; Williard, P. G.; Risen, W. M. Jr. J. Organomet. Chem. 1985, 284,
409. (n) Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini, A. J. Chem.
Soc., Dalton Trans. 1988, 1833. (o) Milstein, D.; Fultz, W. C.; Calabrese,
J. C. J. Am. Chem. Soc. 1986, 108, 1336. (p) Suggs, J. W. J. Am. Chem.
Soc. 1978, 100, 640.
unstrained.6 Here we report the full details of this first
observation of an equilibrium between a hydroxycarbene
(5) For other examples of hydroxycarbene complexes see: (a) Green,
M. L. H.; Mitchard, L. C.; Swanwick, M. G. J. Chem. Soc. A 1971, 794.
(b) Fischer, E. O.; Kreis, G.; Kreissl, F. R. J. Organomet. Chem. 1973, 56,
C37. (c) Webb, M. J.; Stewart, R. P. Jr.; Graham, W. A. G. J. Organomet.
Chem. 1973, 59, C21. (d) Wong, W.-K.; Tam, W.; Gladysz, J. A. J. Am.
Chem. Soc. 1979, 101, 5440. (e) Darst, K. P.; Lenhert, P. G.; Lukehart, C.
M.; Warfield, L. T. J. Organomet. Chem. 1980, 195, 317. (f) Buhro, W.
E.; Wong, A.; Merrifield, J. H.; Lin, G.-Y.; Constable, A. C.; Gladysz, J.
A. Organometallics 1983, 2, 1852. (g) Powell, J.; Farrar, D. H.; Smith, S.
J. Inorg. Chim. Acta 1984, 85, L23. (h) Gibson, D. H.; Mandal, S. K.;
Owens K.; Richardson, J. F. Organometallics 1990, 9, 1936 and references
therein. (i) Casey, C. P.; Sakaba, H.; Underiner, T. L. J. Am. Chem. Soc.
1991, 113, 6673 and references therein. (j) Asdar, A., Lapinte, C. J.
Organomet. Chem. 1987, 327, C33.
(3) For reviews of CO hydrogenation and the Fischer-Tropsch process,
see: (a) Muetterties, E. L.; Stein, J. Chem. ReV. 1979, 79, 479. (b) Masters,
C. AdV. Organomet. Chem. 1979, 17, 61. (c) Herrmann, W. A. Angew.
Chem., Int. Ed. Engl. 1982, 21, 117.
(6) Casey, C. P.; Czerwinski, C. J.; Hayashi, R. K. J. Am. Chem. Soc.
1995, 117, 4189.
(4) Fischer, E. O.; Riedel, A. Chem. Ber. 1968, 101, 156.
S0002-7863(96)03731-6 CCC: $14.00 © 1997 American Chemical Society

3972 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Casey et al.
Scheme 1
complex and its isomeric metal acyl hydride. Support for the
ring strain hypothesis was obtained from the observation that
an unstrained longer chain tethered compound behaves like
Fischer’s hydroxycarbene complex 1 in that only the carbene
tautomer is observed.
Figure 1. X-ray crystal structure of (CO)3Re(η5-C5H4CH2CH2OTs)
(5).
angle). These angles in the unstrained complex 5 are important
for comparison with strain in the tethered hydroxycarbene
complex 2 as detailed later.
Results and Discussion
The rhenium carbene complex Cp(CO)2RedCHCH2CH2-
CMe3 (4) displays highly unusual amphiphilic behavior: both
nucleophiles and electrophiles added to the carbene carbon of
4.7 While the addition of nucleophiles such as PMe3 to the
carbene carbon of 4 to give Cp(CO)2ReCH(PMe3)CH2CH2CMe3
is the expected reactivity of a d6 carbene complex such as 4,
the addition of the electrophile H+ to the carbene carbon of 4
in its reaction with HCl is very unusual and was investigated
in detail. The addition of HCl to the deuterium-labeled carbene
complex Cp(CO)2RedCDCH2CH2CMe3 (4-d) occurred ste-
reospecifically to give a single diastereomer of cis-Cp-
(CO)2ClReCHDCH2CH2CMe3.7 However, the absolute stere-
ochemistry of this process could not be determined because of
the expected rapid rotation about the RedC bond which
interconverts syn and anti rotamers about the RedC bond.8 To
determine the absolute stereochemistry of the addition of HCl
across the RedC bond, we set out to construct complexes in
which rotation about the RedC bond was prevented by the
incorporation of a two-carbon tether between the cyclopenta-
dienyl ring and the carbene carbon atom.9
Reaction of 5 with LiI gave the iodide (η5-C5H4CH2CH2I)-
Re(CO)3 (6) in 85% isolated yield.11 When a solution of iodide
6 in Et2O at -78 °C was treated with 2 equiv of t-BuLi and
then warmed to room temperature, lithium-halogen exchange
followed by intramolecular attack on a carbonyl ligand gave
the desired acyl anion complex [(CO)2ReC(dO)CH2CH2(η5-
C5H4)]-Li+ (7) which was isolated as an air sensitive yellow
1
powder in 59% yield.12 The H NMR spectrum of 7 in THF-
d8 exhibited two AA′BB′ pseudotriplets at δ 5.20 and 5.11
assigned to the two sets of cyclopentadienyl protons and two
triplets at δ 2.83 and 1.98 assigned to the two methylene groups
of the alkyl side chain. The observation of two bands of equal
intensity at 1898 and 1819 cm-1 in the IR spectrum (THF) is
consistent with the formulation of 7 as an anionic dicarbonyl
complex.
Alkylation of Rhenium Acyl Anion 7 at Oxygen and at
Re. By changing reagents, we were able to regioselectively
methylate 7 at either rhenium or oxygen. Reaction of 7 with
1
CH3I gave exclusive Re methylation on the basis of H NMR
Synthesis of an Acyl Rhenium Anion with a Two-Carbon
Tether. Our synthetic approach to a rotationally restricted
rhenium carbene complex involved initial attachment of a
2-lithioethyl side chain to the cyclopentadiene ring of CpRe-
(CO)3 followed by intramolecular attack of the lithium reagent
on a carbonyl group (Scheme 1). Reaction of CpRe(CO)3 with
n-BuLi in THF at -78 °C generated the known ring-metalated
spectroscopy of the crude reaction mixtures. Reaction of 7 with
CH3I in THF gave the methyl acyl complex (CO)2-
(CH3)ReC(dO)CH2CH2(η5-C5H4) (8) as a yellow oil in 45%
yield. Regioselective methylation of 7 at oxygen to give 9 was
10
complex (η5-C5H4Li)Re(CO)3 which reacted with ethylene
oxide and then tosyl chloride to give the tosylate (η5-C5H4CH2-
CH2OTs)Re(CO)3 (5) as a white solid in 89% isolated yield.
Tosylate 5 was characterized spectroscopically and by X-ray
crystallography (Figure 1). As expected for an unstrained
CpML3 three-legged piano stool complex, the angles between
the carbonyl ligands are near 90° (87.5, 88.7, and 92.0) and the
Cp centroid-Re-CO angles are 126°. The alkyl side chain is
bent slightly away from Re (182.7° Cp centroid-C(8)-C(9)
best accomplished using (CH3)3O+BF4- in acetone.13 1H NMR
spectroscopy of the reaction mixture showed exclusive formation
of methoxycarbene complex (CO)2RedC(OCH3)CH2CH2(η5-
C5H4) (9), which was isolated as a yellow crystalline solid in
-
75% yield. Similarly, reaction of 7 with (CH3CH2)3O+BF4
gave the ethoxycarbene complex (CO)2RedC(OCH2CH3)CH2-
(11) The bromide (η5-C5H4CH2CH2Br)Re(CO)3 was made similarly. See
the Supporting Information for full experimental details and characterization.
(12) Reaction of the bromide (η5-C5H4CH2CH2Br)Re(CO)3 with n-BuLi
gave the elimination product (η5-C5H4CHdCH2)Re(CO)3. Reaction of the
bromide with t-BuLi gave a 67:33 mixture of elimination and metal-halogen
exchange products. Reaction of the iodide with n-BuLi gave a 38:62 mixture
of elimination and metal-halogen exchange products. See the Supporting
Information for full experimental details and characterization.
(7) Casey, C. P.; Vosejpka, P. C.; Askham, F. R. J. Am. Chem. Soc.
1990, 112, 3713.
(8) (a) Kiel, W. A.; Lin, G.-Y.; Bodner, G. S.; Gladysz, J. A. J. Am.
Chem. Soc. 1983, 105, 4958. (b) Kiel, W. A.; Lin, G.-Y.; Constable, A.
G.; McCormick, F. B.; Strouse, C. E.; Eisenstein, O.; Gladysz, J. A. J. Am.
Chem. Soc. 1982, 104, 4865. (c) Brookhart, M.; Tucker, J. R.; Husk, G. R.
J. Am. Chem. Soc. 1981, 103, 979. (d) Nakatsuji, H.; Ushio, J.; Han, S.;
Yonezawa, T. J. Am. Chem. Soc. 1983, 105, 426.
(9) This approach has allowed us to determine the absolute stereochem-
istry of HCl addition to an amphiphilic carbene complex. Casey, C. P.;
Czerwinski, C. J.; Hayashi, R. K. Manuscript in preparation.
(10) (a) Nesmeyanov, A. N.; Anisimov, K. N.; Kolobova, N. E.; Makarov,
Yu. V. Dokl. Akad. Nauk SSSR 1968, 178, 111. (b) Nesmeyanov, A. N.;
Anisimov, K. N.; Kolobova, N. E.; Makarov, Yu. V. IzV. Akad. Nauk SSSR,
Ser. Khim. 1968, 686.
(13) Methylations of 7 with (CH3)3O+BF4-, CH3I, and CF3SO3CH3 in
1
acetone, THF, and CH2Cl2 were analyzed by H NMR spectroscopy. For
(CH3)3O+BF4-, in acetone, 8:9 ) 0:100 (72% yield), in THF, 8:9 ) 33:67
(88% yield), and in CH2Cl2, 8:9 ) 33:67 (55% yield). For CH3I, in acetone,
8:9 ) 100:0 (75% yield), in THF, 8:9 ) 100:0 (43% yield), and in CH2-
Cl2, 8:9 ) 100:0 (55% yield). For CF3SO3CH3, in acetone, 8:9 ) 20:80
(39% yield), in THF, 8:9 ) 25:75 (20% yield), and in CH2Cl2, 8:9 ) 20:
80 (48% yield).

Ring Strain Perturbation of Equilibria
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3973
acyl carbon of 3. In the coupled 13C NMR spectrum, the
resonance at δ 292.5 appears as a singlet, excluding the
possibility that the minor species is the aldehyde formed from
reductive elimination from 3. An aldehyde carbon would appear
near δ 200 as a doublet with JCH ) 100-150 Hz.
The IR spectrum of the 25:75 mixture of 2/3 in CH2Cl2 has
carbonyl stretching bands at 1954 and 1870 cm-1 assigned to 2
and more intense bands at 2023 and 1925 cm-1 assigned to 3.
In addition, a weaker band at 1615 cm-1 is assigned to the acyl
group of 3.
The ratio of hydroxycarbene complex 2 to metal acyl hydride
3 showed a strong solvent dependence. In CD3OD and THF-
d8, hydroxycarbene complex 2 was the only species observed
1
by H NMR, in acetone-d6, a 91:9 mixture of 2/3 was seen,
1
and in C6D6, a 50:50 mixture of 2/3 was seen. The H NMR
spectra of mixtures of 2 and 3 in 10:1, 5:1, 2:1, and 1:1 mixtures
of CD2Cl2-acetone-d6 showed a smooth change in the 2:3 ratio
from 25:75 in pure CD2Cl2 to the 91:9 ratio observed in acetone-
d6.16 While there is no correlation of the equilibrium constant
with solvent polarity, more of the hydroxycarbene is seen in
the better hydrogen-bonding solvents methanol, THF, and
acetone.
The equilibrium between 2 and 3 is temperature dependent,
and shifts toward the hydroxycarbene isomer at low temperature.
1
Equilibrium constants (Keq ) [3]/[2]) measured by H NMR
Figure 2. Top: X-ray structure of (CO)2RedC(OCH3)CH2CH2(η5-
C5H4) (9). Bottom: X-ray structure of (CO)2RedC(OCH3)CH2CH2CH2-
(η5-C5H4) (17).
spectroscopy in a 9:1 mixture of CD2Cl2-acetone-d6 changed
from 0.46 at -60 °C to 0.77 at 24 °C (Table 1 and Figure 1 in
the Supporting Information). The derived thermodynamic
parameters were ∆G ) 0.14 ( 0.06 kcal mol-1, ∆H ) 0.82 (
0.03 kcal mol-1, and ∆S ) 2.3 ( 0.1 cal K-1 mol-1 at 297 K.
The interconversion of 2 and 3 is rapid at low temperature.
When acetone-d6 was condensed into a CD2Cl2 solution of 2
and 3 at -78 °C, the conversion from a 25:75 ratio of 2/3 to an
CH2(η5-C5H4). Bergman and Goldberg observed similar de-
pendence of regioselectivity on the nature of the alkylating agent
in studies of the acyl anion [(η5-C5H5)Re(CO)2COCH3]-Li+.14
The X-ray crystal structure of tethered methoxycarbene
complex 9 (Figure 2, top) shows that ring closure produces a
moderately strained CpReL3 system in comparison with un-
tethered carbene complexes such as (C5H5)(CO)2RedC(OH)-
CH3 (1). The alkyl tether of the cyclopentadienyl ring of 9 is
bent down 9° toward Re [Cp(cent)-C(5)-C(6) ) 171°], while
in untethered systems the alkyl groups bend up away from the
metal center.15 Ring strain also narrows the angle between the
Cp centroid, rhenium, and the carbene carbon atom to 112° from
the 126° ideal angle for a three-legged piano stool CpReL3
system. The C(6)-C(5)-C(4)-C(3) torsion angle of only 30°
is indicative of substantial torsional strain in the tether.
Equilibrium between Hydroxycarbene Complex 2 and
Metal Acyl Hydride Complex 3. Protonation of an aqueous
solution of acyl rhenium anion 7 with HCl followed by
extraction into CH2Cl2 led to the isolation of a mixture of the
expected hydroxycarbene complex (CO)2RedC(OH)CH2CH2-
(η5-C5H4) (2) and the unanticipated metal acyl hydride complex
trans-(CO)2HReC(dO)CH2CH2(η5-C5H4) (3) as a yellow oil in
50% isolated yield. Treatment of this mixture with n-BuLi in
Et2O at -78 °C regenerated acyl anion 7.
1
80:20 equilibrium mixture was monitored by H NMR spec-
troscopy at -50 °C. Within 6 min, half of excess 3 was
converted to 2 (62:38 ratio of 2/3). After 45 min, an 80:20
equilibrium ratio of 2:3 was observed.
Aldehyde Formation in the Decomposition of 2 and 3. The
mixture of hydroxycarbene complex 2 and metal acyl hydride
3 decomposed to a number of unidentifiable products when it
was heated above 40 °C in C6D6. When the thermolysis of the
mixture of 2 and 3 was carried out in the presence of excess
PPh3 in benzene at 80 °C, clean formation of a single new
compound, the untethered aldehyde (η5-C5H4CH2CH2CHO)Re-
(CO)2PPh3 (10), occurred in 80% isolated yield. A singlet (ω1/2
) 2 Hz) at δ 9.7 in the 1H NMR spectrum of 10 in CD2Cl2 was
assigned to the aldehyde proton. In the 13C{1H} NMR spectrum,
the aldehyde carbonyl resonance appeared at δ 200.7. The IR
spectrum in CH2Cl2 exhibited two strong bands of equal
intensity at 1920 and 1856 cm-1, consistent with a CpM(CO)2L
unit, and a less intense band at 1703 cm-1 assigned to the
aldehyde carbonyl.
We suggest that aldehyde formation results from reductive
elimination from an unseen cis metal acyl hydride isomer that
generates reactive intermediate A in which a tethered aldehyde
is connected to a coordinatively unsaturated rhenium dicarbonyl
fragment (Scheme 2). Decomposition of A in the absence of
added ligand produces a mixture of unidentified products, but
A is efficiently trapped by PPh3 to give 10. Fischer reported
that thermal decomposition of the untethered hydroxycarbene
complex (C5H5)(CO)2RedC(OH)CH3 (1) gave CpRe(CO)3 and
acetaldehyde.3 Fischer proposed that cleavage of the RedC
bond produced free methylhydroxycarbene that rearranged to
The 1H NMR spectrum in CD2Cl2 indicated the presence of
a 25:75 mixture of 2/3. Each tautomer had its own well-
separated AA′BB′ patterns for cyclopentadienyl protons and two
triplets for the two-carbon tether. The minor species 2 had a
resonance at δ 11.00 assigned to a hydroxycarbene proton, while
the major species 3 had a resonance at δ -8.69 characteristic
of a metal hydride. Upon treatment with D2O, both the hydroxyl
and hydride resonances of 2 and 3 disappeared immediately.
In the 13C NMR spectrum of the 25:75 mixture of 2/3 in CD2-
Cl2, a resonance at δ 292.5 is assigned to the carbene carbon
of 2 and a more intense resonance at δ 234.3 is assigned to the
(14) Goldberg, K. I.; Bergman, R. G. J. Am. Chem. Soc. 1989, 111, 1285.
(15) For example, in (C5H4COCH3)Re(CO)3, the acyl carbon is bent 1.7°
away from Re. Khotsyanova, T. L.; Kuznetsov, S. I.; Bryukhova, E. V.;
Makarov, Yu. V. J. Organomet. Chem. 1975, 88, 351.
(16) In 10:1 CD2Cl2-acetone-d6, 2:3 ) 53:47. In 5:1 CD2Cl2-acetone-
d6, 2:3 ) 66:33. In 2:1 CD2Cl2-acetone-d6, 2:3 ) 77:23. In 1:1 CD2Cl2-
acetone-d6, 2:3 ) 83:17.

3974 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Casey et al.
Scheme 2
Scheme 3
acetaldehyde. We suggest that decomposition of 1 may also
occur via reductive elimination from an unseen metal acyl
hydride intermediate in equilibrium with 1.
a rationale for the observation of acyl metal hydrides only in
the tethered system.
Reexamination of Fischer’s Acyclic Hydroxycarbene Com-
plex 1. Our observation of an acyl hydride complex in
equilibrium with a hydroxycarbene complex contrasts with
Fischer’s report that only a hydroxycarbene isomer was observed
for (C5H5)(CO)2RedC(OH)CH3 (1). We have repeated Fis-
cher’s synthesis of 1 and looked for spectroscopic evidence for
an acyl hydride species in solvents that favor this isomer. Close
examination of the hydride region of the 1H NMR spectra of 1
in either C6D6 (25 °C) or CD2Cl2 (-80 °C) showed no signals
(3% would have been readily detected) attributable to an acyl
hydride. Similarly, the 13C NMR spectrum in C6D6 showed a
resonance at δ 286.7 for the carbene carbon of 1 and no evidence
for an acyl hydride isomer. This implies that, in an untethered
system such as 1, the hydroxycarbene form is >2 kcal mol-1
more stable than the acyl hydride.
Ring Strain Hypothesis for Selective Destabilization of
Tethered Hydroxycarbene Complex 2. The observation that
no metal acyl hydride can be detected in equilibrium with 1
demonstrates that the Cp(CO)2Re system has a strong preference
for the hydroxycarbene tautomer. The observation that the
tethered metal acyl hydride 3 is of comparable stability to its
tethered hydroxycarbene tautomer 2 requires a significant
perturbation of the normal equilibrium by the tether. The
possibility that the hydroxycarbene complex is destabilized
by having an enforced arrangement of the hydroxycarbene
ligand in a plane perpendicular to the Cp ring and with the
oxygen anti to the ring can be excluded by the observation
that this geometry is seen in the X-ray crystal structures
of (η5-C5H5)(CO)2RedC(OCH2C(CH3)2CH2Cl)C6H4CH3,17 (η5-
C5H5)(CO)2RedC(OCH2CH3)C6H5,18 and η5-C5H5(CO)2RedC-
(OCH3)[η5-C5H4Re(CO)3].19
A Longer Chain Tether To Test the Ring Strain Hypoth-
esis. To test the role of strain on the equilibrium between 2
and 3, we prepared an unstrained hydroxycarbene with a three-
carbon tether connecting the cyclopentadienyl ligand and the
carbene carbon. Our strain hypothesis predicted that only the
hydroxycarbene tautomer should be seen for the unstrained
three-carbon tether system.
Our synthetic approach involved attaching an allyl substituent
to the cyclopentadienyl ligand and converting it to a primary
iodide. A lithium-halogen exchange reaction would gener-
ate the three-carbon-chain alkyllithium species that would react
to form the intramolecular three-carbon-tethered acyl anion
(Scheme 3).
Treatment of CpRe(CO)3 with n-BuLi in THF at -78 °C gave
the ring-metalated anion which reacted with allyl bromide to
give the allyl-substituted (η5-C5H4CH2CHdCH2)Re(CO)3 (11)
in 85% yield. Hydroboration-oxidation gave a mixture of the
desired primary alcohol (η5-C5H4CH2CH2CH2OH)Re(CO)3 (12)
and the secondary alcohol [η5-C5H4CH2CH(OH)CH3]Re(CO)3
(13) in a 4:1 ratio. The alcohols could not be separated, but
when the mixture was treated with tosyl chloride in pyridine,
only the primary alcohol 12 reacted to give the tosylate (η5-
C5H4CH2CH2CH2OTs)Re(CO)3 (14), which was isolated by
thin-layer chromatography. Reaction of 14 with LiI gave the
iodide (η5-C5H4CH2CH2CH2I)Re(CO)3 (15) in 90% yield.
Treatment of 15 with 2 equiv of t-BuLi gave the three-carbon-
tethered acyl anion [(CO)2ReC(dO)CH2CH2CH2(η5-C5H4)]-Li+
(16) as an air sensitive yellow powder in 48% yield. Methy-
-
lation of 16 with (CH3)3O+BF4 in acetone gave methoxycar-
bene complex (CO)2RedC(OCH3)CH2CH2CH2(η5-C5H4) (17)
as a yellow solid in 95% isolated yield.
We suggest that the tether introduces significant strain that
destabilizes hydroxycarbene tautomer 2, but leaves the tethered
metal acyl hydride tautomer 3 unstrained. The X-ray crystal
structure of the tethered methoxycarbene complex 9 showed
strain in the distortion of the expected three-legged piano stool
geometry: the alkyl substituent on the Cp ring was pulled down
9° toward rhenium and the Cpcentroid-Re-carbene carbon angle
was contracted from the normal 126° to the observed 112° angle.
The two-carbon tether does not significantly strain the four-
legged piano stool geometry of the rhenium acyl hydride
tautomer 3. In general, four-legged piano stool complexes
CpML4 have substantially wider L-M-L angles and narrower
Cp(centroid)-M-L angles than related three-legged piano stool
compounds. For example, trans-Cp(CO)2Re(COCH3)CH314 has
a 112° Cp(centroid)-Re-acyl carbon angle, which is similar
to the angle in the tethered carbene complex 9. Overall,
tethering the side chain destabilizes 2 relative to 3 and provides
X-ray crystallography of 17 (Table 1 and Figure 2, bottom)
revealed little strain in this three-legged piano stool complex
compared with the two-carbon-tethered carbene complex 9. Its
structure is similar to that of unstrained CpReL3 complexes.
The first carbon of the tether of 17 is nearly in the plane of the
cyclopentadienyl ring [Cp(cent)-C(6)-C(5) ) 179.2°], as ex-
pected for an unstrained complex. The Cp(cent)-Re-C(3) angle
of 123.1° is close to the ideal 126° angle of unstrained three-
legged piano stool complexes. The nearly staggered torsion
angles of the tether [C(4)-C(45)-C(5)-C(6), -65°; C(3)-
C(4)-C(45)-C(5), 72°] are indicative of a relaxed geometry.
Reaction of an aqueous suspension of acyl anion 16 with
aqueous HCl followed by extraction into CH2Cl2 led to the
isolation of the three-carbon-tethered hydroxycarbene complex
(CO)2RedC(OH)CH2CH2CH2(η5-C5H4) (18) in 57% isolated
(17) Mercando, L. A.; Handwerker, B. M.; MacMillan, H. J., Geoffroy,
G. L.; Rheingold, A. L.; Owens-Waltermire, B. E. Organometallics 1993,
12, 1559.
(18) Chen, J.; Yu, Y.; Liu, K.; Wu, G.; Zheng, P. Organometallics 1993,
12, 1213.
yield. Only the hydroxycarbene species was seen by NMR and
IR spectroscopy; no evidence for an acyl metal hydride in
(19) Casey, C. P.; Czerwinski, C. J.; Hayashi, R. K. Organometallics,
in press.

Ring Strain Perturbation of Equilibria
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3975
Table 1. Selected Bond Lengths (Å) and Angles (deg) for (CO)2RedC(OCH3)CH2CH2(η5-C5H4) (9) and
(CO)2RedC(OCH3)CH2CH2CH2(η5-C5H4) (17)
9
17
9
17
Re1-C1
1.894(14)
1.882(14)
1.982(10)
87.2(5)
97.7(4)
96.5(4)
1.884(10)
1.908(12)
1.989(10)
87.2(4)
94.8(4)
92.3(4)
126.0
126.0
123.1
136.2(7)
120.8(7)
C3-O3
1.329(12)
1.483(12)
118.6(7)
105.1(8)
111.8(9)
1.342(11)
1.436(11)
124.8(6)
101.5(7)
Re1-C2
O3-C11
Re1-C3
Re-C3-C4
O3-C3-C4
C3-C4-C5
C3-C4-C45
C4-C45-C5
C4-C5-C6
C45-C5-C6
Cp(cent 1)-C6-C5
C1-Re1-C2
C1-Re1-C3
C2-Re1-C3
Cp(cent 1)-Re-C1
Cp(cent 1)-Re-C2
Cp(cent 1)-Re-C3
Re-C3-O3
C3-O3-C11
115.8(7)
114.3(8)
126.8
129.3(9)
111.8(9)
136.2(7)
119.4(8)
111.5(8)
170.7
114.5(8)
179.2
equilibrium with 18 was found. Even in CH2Cl2, the solvent
which favored the acyl hydride species in the mixture of 2 and
3, only hydroxycarbene 18 was observed. The 1H NMR
spectrum of 18 in CD2Cl2 exhibited a sharp singlet at δ 9.15
assigned to the hydroxyl proton, and only one set of AA′BB′
pseudotriplets in the Cp region, at δ 5.35 and 5.25. Close
examination of the hydride region of the spectrum revealed no
metal hydride resonances between δ 0 and δ -20. 13C NMR
spectroscopy of 18 also provided evidence for only one isomer.
The carbene carbon resonance appeared at characteristically high
frequency (δ 296.0), and no acyl carbon resonances were seen
between δ 260 and δ 210. The IR spectrum of 18 in CH2Cl2
had only two carbonyl bands of equal intensity at 1945 and
1864 cm-1, as expected for a Cp(CO)2ReX complex.
complexes, none have been reported. We investigated the
possibility that a two-carbon tether between a cyclopentadienyl
ring and an aminocarbene carbon might introduce sufficient
strain to allow observation of an iminoacyl hydride complex.
Reaction of the two-carbon-tethered methoxycarbene complex
9 with a 10-fold excess of methylamine in THF produced the
(methylamino)carbene complex (CO)2RedC[NH(CH3)]CH2-
CH2(η5-C5H4) (19) in quantitative yield. No evidence for a
metal iminoacyl hydride was obtained even in CD2Cl2, which
favored the metal acyl hydride in the mixture of 2 and 3. A
5:1 ratio of two isomers about the N-carbene carbon partial
1
double bond of 19 was observed. The H NMR spectrum of
The observation that only the hydroxycarbene tautomer is
seen for the unconstrained hydroxycarbene complex (η5-
C5H5)(CO)2RedC(OH)CH3 (1) and for the unstrained three-
carbon-tethered hydroxycarbene complex 18 supports our ring
strain hypothesis. Only the two-carbon-tethered hydroxycarbene
complex 2 is so destabilized by ring strain that its energy is
increased to that of the unstrained four-legged piano stool metal
acyl hydride tautomer 3.
The effect of ring strain on equilibria has been observed
previously. For example, variation in ring size affects the
equilibria between cyclic hemiacetals and acyclic hydroxy
aldehydes20 and the equilibria between ω-hydroxy acids and
lactones.21 In organometallic chemistry, the diphosphine chelate
ring size often influences equilibria. For example, the equilibria
between tetrahedral and square planar forms of Br2Ni[Ph2P(CH2)n-
PPh2)2 depends strongly on the chelate ring size.22 Recently,
Angelici reported that the equilibrium constants for protonation
at the metal atom of iron-diphosphine complexes are affected
by the chelate ring size.23 Heinekey reported that the equilib-
rium between Ru(η2-H2)(diphosphine) and Ru(H)2(diphosphine)
complexes depends upon the ring size of chelating diphos-
phine.24
19 in CD2Cl2 shows a resonance for the amine proton of the
major isomer as a broad singlet at δ 9.00, and for the minor
isomer at δ 9.15. A doublet at δ 3.20 is assigned to the amine
methyl group of the major isomer, and a doublet at δ 3.17 is
assigned to the amine methyl group of the minor isomer. The
13C NMR shows a resonance for the carbene carbon of the major
isomer of 19 at δ 247.5 and for the minor isomer at δ 247.0.
No resonances attributable to a metal iminoacyl hydride complex
were observed.25
Experimental Section
(η5-C5H4CH2CH2OTs)Re(CO)3 (5). n-BuLi (4.0 mL, 1.5 M pen-
tane solution, 6.0 mmol) was added to a solution of CpRe(CO)3 (2.00
g, 5.97 mmol) in THF (50 mL) at -78 °C. After the solution was
stirred for 3 h at -78 °C, ethylene oxide26 (12.29 mmol) was condensed
into it under vacuum. After 2 h the bright yellow solution was warmed
to 0 °C, and tosyl chloride (1.15 g, 6.00 mmol) in THF (5 mL) was
added. After 30 min at 25 °C, THF was evaporated under vacuum,
and the resulting brown paste was extracted with CH2Cl2 (2 × 20 mL).
The CH2Cl2 solution was filtered through Celite to remove LiCl, and
solvent was evaporated. The resulting brown oil was purified by
column chromatography (silica gel, CH2Cl2) to give 5 as an orange oil
(2.83 g, 89%). Crystalline 5 was obtained by slow cooling of a CH2-
Cl2-hexane solution, mp 82-83 °C. 1H NMR (acetone-d6, 200
MHz): δ 7.75 (d, J ) 8 Hz, 2H, aryl), 7.45 (d, J ) 8 Hz, 2H, aryl),
Relative Stability of Tethered Aminocarbene Complexes
and Metal Iminoacyl Hydride Complexes. Although imi-
noacyl hydride complexes are tautomers of aminocarbene
(25) Similarly, no evidence for a metal iminoacyl hydride species in
equilibrium with the analogous three-carbon aminocarbene complex
(CO)2RedC[NH(CH3)]CH2CH2CH2(η5-C5H4) or with the acyclic aminocar-
bene complex (η5-C5H4)(CO)2RedC[NH(CH3)]CH3 was observed. See the
Supporting Information for details.
(20) Hurd, C. D.; Saunders, W. H., Jr. J. Am. Chem. Soc. 1952, 74, 5324.
(21) Carter, S. R.; Haworth, W. N.; Robinson, R. A. J. Chem. Soc. 1930,
(26) Ethylene oxide as obtained from MG Industries was contaminated
with approximately 10% CO2 (gas phase IR spectroscopy). Use of the
contaminated ethylene oxide followed by protonation gave the known acid
(η5-C5H4CO2H)Re(CO)310a rather than the expected alcohol (η5-C5H4CH2-
CH2OH)Re(CO)3. Ethylene oxide from a lecture bottle was purified by
condensation into a flask at -23 °C and 400 mmHg. Carbon dioxide did
not condense under these conditions. Pure ethylene oxide was distilled from
the collection flask as needed.
2125.
(22) Van Hecke, G. R.; Horrocks, W. DeW., Jr. Inorg. Chem. 1966, 5,
1968.
(23) Sowa, J. R., Jr.; Zanotti, V.; Facchin, G.; Angelici, R. J. J. Am.
Chem. Soc. 1992, 114, 160.
(24) Conroy-Lewis, F. M.; Simpson, S. J. J. Chem. Soc., Chem. Commun.
1987, 1675.

3976 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Casey et al.
5.47 (m, C5H4), 4.18 (t, J ) 7.4 Hz, CH2O), 2.80 (t, J ) 7.4 Hz, CH2-
CH2O), 2.45 (s, CH3). 13C{1H} NMR (CD2Cl2, 125 MHz): δ 194.5
(CO); 145.6 (CSO2); 132.9 (CCH3); 130.3, 128.1 (aryl CH); 104.6 (Cp
CCH2); 85.1, 84.5 (Cp CH); 71.1 (CH2O); 28.2 (CH2CH2O); 21.7 (CH3).
IR (THF): 2020 (s), 1928 (vs) cm-1. HRMS: m/z calcd for C17H15-
ReO6S 534.0148, found 534.0147. Anal. Calcd for C17H15ReO6S: C,
38.27; H, 2.83. Found: C, 38.60; H, 2.82.
13C{1H} NMR (THF-d8, 125 MHz) (only 2 observed): δ 292.5
(RedC); 204.0 (CO); 84.7 (Cp CCH2); 84.3, 79.7 (Cp CH); 30.1 (C5H4-
CH2CH2); 29.5 (C5H4CH2). 13C{1H} NMR (CD2Cl2, 125 MHz) (2:3
) 25:75): (for 2) δ 292.4 (RedC); 204.0 (CO); 84.3 (Cp CCH2); 84.1,
79.2 (Cp CH); 27.9 (C5H4CH2CH2); 26.5 (C5H4CH2); (for 3) δ 234.3
(ReCdO); 203.5 (CO); 85.0 (Cp CCH2); 82.3, 76.1 (Cp CH); 30.6
(C5H4CH2CH2); 29.9 (C5H4CH2).
(η5-C5H4CH2CH2I)Re(CO)3 (6). A solution of 5 (1.79 g, 3.36
mmol) and LiI (0.500 g, 3.73 mmol) in acetone (40 mL) was refluxed
overnight. Solvent was evaporated, and the brown residue was
extracted with CH2Cl2, filtered through Celite to remove lithium
tosylate, and purified by column chromatography (silica gel, CH2Cl2)
to give 6 as a yellow oil (1.40 g, 85%). 1H NMR (acetone-d6, 200
MHz): δ 5.70 (three-line pattern, AA′BB′, 4.2 Hz separation of outer
lines, 2H, C5H4), 5.53 (three-line pattern, AA′BB′, 4.2 Hz separation
of outer lines, 2H, C5H4), 3.37 (t, J ) 7.4 Hz, CH2I), 3.00 (t, J ) 7.4
Hz, CH2CH2I). 13C{1H} NMR (CD2Cl2, 125 MHz): δ 194.6 (CO);
104.5 (Cp CCH2); 85.0, 84.3 (Cp CH); 32.7 (CH2CH2I); 5.3 (CH2I).
IR (THF): 2019 (m), 1923 (s) cm-1. HRMS: m/z calcd for C10H8-
ReO3I 489.9073, found 489.9046.
The ratio of 2 to 3 was also estimated by IR spectroscopy. 2 has
νsym at 1945 cm-1 and νasym at 1870 cm-1 of approximately equal
intensity; 3 has νsym at 2020 cm-1 and νasym at 1925 cm-1 overlapping
with the 1945 cm-1 band of 2. Comparison of the relative integrated
intensities of νasym of 2 at 1870 cm-1 and νsym of 3 at 2020 cm-1 (after
making corrections for relative absorbances as outlined below) were
used to approximate the ratio of 2 to 3. A 1:1 ratio of (CO)2RedC-
(OCH3)CH2CH2(η5-C5H4) (9)/(CO)2(CH3)ReC(dO)CH2CH2(η5-C5H4)
1
(8) (as determined by H NMR spectroscopy) had relative integrated
absorbances for νasym for 9 at 1864 cm-1 and νsym for 8 at 2019 cm-1
of 1.2:1. Similar intensity differences were assumed for 2 and 3, and
an appropriate correction was applied.
IR ν (relative integrated absorbance, assignment): (solid (Nujol
mull)) 2026 (0.07, νsym(3)), 1954 (0.42, νsym(2)), 1935 (0.09, νasym(3)),
Li+[(CO)2ReC(dO)CH2CH2(η5-C5H4)]- (7). t-BuLi (0.75 mL, 1.7
M pentane solution, 1.3 mmol) was added to a solution of 6 (0.310 g,
0.634 mmol) in Et2O at -78 °C. Upon warming to room temperature,
a fine yellow precipitate formed and was collected on a frit, washed
with cold pentane, and dried under vacuum to give 7 (0.146 g, 0.377
mmol, 59%), which was shown to contain ∼0.25 mol of Et2O/mol of
7 by 1H NMR. 1H NMR (THF-d8, 200 MHz): δ 5.20 (three-line
pattern, AA′BB′, 4.2 Hz separation of outer lines, 2H, C5H4), 5.11
(three-line pattern, AA′BB′, 4.2 Hz separation of outer lines, 2H, C5H4),
2.83 (t, J ) 7.7 Hz, C5H4CH2), 1.98 (t, J ) 7.7 Hz, C5H4CH2CH2). IR
1882 (0.42, νasym(2)) cm-1; (2:3 ) 6:1) (in CH2Cl2) 2023 (0.10, νsym
-
(3)), 1954 and 1925 (0.18, νsym(2) and νasym(3)), 1870 (0.04, νasym(2)),
1615 (0.04, 3) cm-1; (2:3 ) 1:3) (in acetone) (2) 1946 (0.17), 1869
(0.14); (3) 2019 (0.10), 1924 (0.17) cm-1; (C6H6) (2) 1949 (0.12), 1872
(0.08); (3) 2021 (0.13), 1927 (0.22) cm-1; (THF) (2) 1944 (0.19), 1869
(0.17); (3) 2019 (0.10), 1924 (0.21) cm-1
.
Thermolysis of 2 and 3 in the Presence of PPh3. Formation of
(η5-C5H4CH2CH2CHO)Re(CO)2PPh3 (10). A solution of 2 and 3 (30
mg, 0.08 mmol) in C6H6 was combined with PPh3 (50 mg, 0.19 mmol)
and heated for 12 h at 80 °C in a sealed tube. Solvent was evaporated,
and thin layer chromatography gave 10 as a white solid (30 mg, 60%).
1H NMR (acetone-d6, 300 MHz): δ 9.74 (s, ω1/2 ) 2.0 Hz, CHO),
7.70-7.40 (m, PPh3), 5.05 (three-line pattern, AA′BB′, 4.0 Hz
separation of outer lines, 2H, C5H4), 4.78 (three-line pattern, AA′BB′,
5.5 Hz separation of outer lines, 2H, C5H4), 2.65 (m, C5H4CH2CH2).
13C{1H} NMR (CD2Cl2, 125 MHz): δ 202.8 (ReCdO); 200.7 (CHO),
137.8 (d, JPC ) 50 Hz, ipso phenyl), 133.0 (d, JPC ) 10.9 Hz, ortho
phenyl), 129.6 (s, para phenyl), 128.0 (d, JPC ) 10.9, meta phenyl),
105.3 (Cp CCH2), 84.4 (Cp CH), 82.3 (Cp CH), 45.4 (C5H4CH2CH2),
29.6 (C5H4CH2). 31P NMR (CD2Cl2, 121 MHz): δ 38.6. IR (CH2-
(THF): 1898 (s), 1819 (s), 1515 (w) cm-1
.
(CO)2RedC(OH)CH2CH2(η5-C5H4) (2) and (CO)2(H)ReC(dO)-
CH2CH2(η5-C5H4) (3). Aqueous HCl (0.5 M, 4 mL) was added via
syringe to a mixture of 10 mL of CH2Cl2 and 10 mL of a yellow
aqueous solution of 7 (0.600 g, 1.55 mmol). After 15 min of vigorous
stirring, the CH2Cl2 layer was decanted, washed with H2O, dried
(MgSO4), and concentrated to give a mixture of 2 and 3 as a dark
yellow oil (0.284 g, 0.78 mmol, 50%). HRMS: m/z calcd for C10H9-
ReO3 364.0111, found 364.0119.
1H NMR (THF-d8, 200 MHz) (only 2 observed): δ 13.17 (br s, OH),
5.59 (three-line pattern, AA′BB′, 4.2 Hz separation of outer lines, 2H,
C5H4), 5.45 (three-line pattern, AA′BB′, 4.2 Hz separation of outer
lines, 2H, C5H4), 3.02 (t, J ) 7.7 Hz, C5H4CH2CH2), 2.33 (t, J ) 7.7
Hz, C5H4CH2). 1H NMR (acetone-d6, 200 MHz) (2:3 ) 91:9): (for 2)
δ 13.11 (br s, OH), 5.67 (three-line pattern, AA′BB′, 4.2 Hz separation
of outer lines, 2H, C5H4), 5.47 (three-line pattern, AA′BB′, 4.2 Hz
separation of outer lines, 2H,C5H4), 3.07 (t, J ) 7.7 Hz, C5H4CH2CH2),
2.39 (t, J ) 7.7 Hz, C5H4CH2); (for 3) δ 5.79 (three-line pattern,
AA′BB′, 4.2 Hz separation of outer lines, 2H, C5H4), 5.31 (three-line
pattern, AA′BB′, 4.2 Hz separation of outer lines, 2H, C5H4), 3.36 (t,
J ) 7.7 Hz, C5H4CH2CH2), 2.28 (t, J ) 7.7 Hz, C5H4CH2), -8.91 (s,
ReH). 1H NMR (CD2Cl2, 200 MHz) (2:3 ) 25:75): (for 2) δ 11.0 (br
s, OH), 5.60 (three-line pattern, AA′BB′, 4.2 Hz separation of outer
lines, 2H, C5H4), 5.48 (three-line pattern, AA′BB′, 4.2 Hz separation
of outer lines, 2H, C5H4), 3.05 (t, J ) 7.7 Hz, C5H4CH2CH2), 2.41 (t,
J ) 7.7 Hz, C5H4CH2); (for 3) δ 5.76 (three-line pattern, AA′BB′, 4.2
Hz separation of outer lines, 2H, C5H4), 5.16 (three-line pattern,
AA′BB′, 4.2 Hz separation of outer lines, 2H, C5H4), 3.38 (t, J ) 7.7
Hz, C5H4CH2CH2), 2.34 (t, J ) 7.7 Hz, C5H4CH2), -8.69 (s, ReH).
1H NMR (C6D6, 200 MHz) (2:3 ) 50:50): (for 2) δ 10.75 (br s, OH),
4.90 (s, 4H, C5H4), 3.08 (t, J ) 7.7 Hz, C5H4CH2CH2), 1.30 (t, J ) 7.7
Hz, C5H4CH2); (for 3) δ 4.68 (three-line pattern, AA′BB′, 4.2 Hz
separation of outer lines, 2H, C5H4), 4.17 (three-line pattern, AA′BB′,
4.2 Hz separation of outer lines, 2H, C5H4), 2.59 (t, J ) 7.7 Hz, C5H4-
CH2CH2), 1.58 (t, J ) 7.7 Hz, C5H4CH2), -8.65 (s, ReH).
Cl2): 1920 (s), 1856 (s), 1703 (m) cm-1
C28H24O3PRe 626.1021, found 626.1017.
. HRMS: m/z calcd for
(C5H5)(CO)2RedC(OH)CH3 (1) was prepared as described by
Fischer9 and more fully characterized spectroscopically. MeLi (1.4 mL,
1.4 M Et2O solution, 2.0 mmol) was added to a solution of CpRe-
(CO)3 (620 mg, 1.85 mmol) in Et2O (50 mL) at -78 °C. The solution
was warmed to 25 °C, and a yellow precipitate formed which was
collected on a frit and washed with Et2O to give Li+[(C5H5)-
(CO)2RedC(O)CH3]- as a yellow powder (270 mg, 79%). Aqueous
H2SO4 (1 mL, 2 N) was added to a suspension of the acyl anion in
Et2O at -78 °C. Upon being warmed to 25 °C, the solution turned
clear orange. The solution was dried (MgSO4), filtered, and concen-
trated to leave an orange residue. Preparative thin layer chromatography
(silica gel, 1:1 hexane-toluene) gave a yellow band (Rf ) 0.1) from
which 1 was obtained as a yellow solid. 1H NMR: (C6D6, 300 MHz)
δ 4.71 (s, C5H5), 4.34 (s, OH), 1.85 (s, CH3); (CD2Cl2, 500 MHz, 25
°C) δ 5.54 (s, C5H5), 9.32 (s, OH), 2.31 (s, CH3); (CD2Cl2, 500 MHz,
-80 °C) δ 5.54 (s, C5H5), 9.92 (s, OH), 2.23 (s, CH3). 13C{1H} NMR
(C6D6, 125 MHz): δ 286.7 (RedC), 205.0 (CO), 90.0 (C5H5), 30.6
(CH3). IR (KBr): 1944 (s), 1845 (s) cm-1. HRMS: m/z calcd for
C9H9ReO3 352.0111, found 352.0129.
(CO)2(CH3)ReC(dO)CH2CH2(η5-C5H4) (8). A solution of 7 (100
mg, 0.26 mmol) and CH3I (0.31 mmol) in THF was stirred at room
temperature for 1 h. THF was evaporated under vacuum. The yellow
residue was extracted with CH2Cl2 and filtered through Celite.
Preparative TLC (silica gel, 1:1 hexane-Et2O) gave a pale yellow band
(Rf ) 0.30) from which 8 was isolated as a yellow oil (43.8 mg, 0.116
mmol, 45%). 1H NMR (THF-d8, 300 MHz): δ 5.96 (three-line pattern,
AA′BB′, 7.1 Hz separation of outer lines, 2H, C5H4), 4.94 (three-line
pattern, AA′BB′, 6.7 Hz separation of outer lines, 2H, C5H4), 3.23 (t,
J ) 7.4 Hz, C5H4CH2CH2), 2.23 (t, J ) 7.4 Hz, C5H4CH2), 0.65 (s,
ReCH3). 13C{1H} NMR (C6D6, 125 MHz): δ 230.9 (ReCdO); 195.7
The ratio of 2:3 in CD2Cl2-acetone-d6 solvent mixtures was
measured by 1H NMR spectroscopy. Complete equilibration occurred
prior to the first measurement. The equilibrium constant varied
as a function of the molar ratio of solvents: In 10:1 CD2Cl2-acetone-
d6, 2:3 ) 47:53. In 5:1 CD2Cl2-acetone-d6, 2:3 ) 66:33. In 2:1
CD2Cl2-acetone-d6, 2:3 ) 77:23. In 1:1 CD2Cl2-acetone-d6, 2:3 )
83:17.

Ring Strain Perturbation of Equilibria
J. Am. Chem. Soc., Vol. 119, No. 17, 1997 3977
(CO); 90.4 (Cp CCH2); 86.9, 86.1 (Cp CH); 28.7 (C5H4CH2CH2); 14.6
(C5H4CH2); -37.3 (CH3). IR (CH2Cl2): 2020 (s), 1948 (vs), 1616 (w)
cm-1. HRMS: m/z calcd for C11H11ReO3 378.0267, found 378.0232.
cm-1. HRMS (for mixture of 12 and 13): m/z calcd for C11H11ReO4
394.0217, found 394.0181. The spectroscopic data for 13 are the
following. 1H NMR (CD2Cl2, 300 MHz): δ 5.39 (three-line pattern,
AA′BB′, 4.3 Hz separation of outer lines, 2H, C5H4), 5.34 (three-line
pattern, AA′BB′, 4.1 Hz separation of outer lines, 2H, C5H4), 3.60 (d,
J ) 7.7 Hz, C5H4CH2), 2.45 (m, CHOH), 2.05 (br s, OH), 1.18 (d, J
) 7.7 Hz, CH3). 1H NMR (acetone-d6, 300 MHz): δ 5.55 (m, C5H4),
3.82 (d, J ) 7.7 Hz, C5H4CH2), 2.50 (m, CH2OH), 1.15 (d, J ) 7.7
Hz, CH3). 13C{1H} NMR (C6D6, 125 MHz): δ 194.3 (CO), 107.3 (Cp
CCH2), 84.6, (Cp CH), 83.3 (Cp CH), 65.8 (COH), 37.7 (C5H4CH2),
29.9 (CH3).
(η5-C5H4CH2CH2CH2OTs)Re(CO)3 (14). A solution of 12 and 13
(1.06 g, 2.7 mmol) was combined with tosyl chloride in pyridine at
-78 °C. After 24 h at -20 °C, the solution was poured into aqueous
HCl at 0 °C. The aqueous solution was extracted with CH2Cl2 (3 ×
50 mL), and the combined organic extracts were dried (MgSO4), filtered,
and concentrated. Excess tosyl chloride and residual CpRe(CO)3 were
removed by sublimation at 50 °C, and the remaining material was
chromatographed (SiO2, 1:1 hexane-Et2O) to give 14 as a white solid
(0.737 g, 50%). 1H NMR (acetone-d6, 300 MHz): δ 7.81 (d, J ) 8
Hz, 2H, aryl), 7.49 (d, J ) 8 Hz, 2H, aryl), 5.50 (three-line pattern,
AA′BB′, 4.3 Hz separation of outer lines, 2H, C5H4), 5.47 (three-line
pattern, AA′BB′, 4.1 Hz separation of outer lines, 2H, C5H4), 4.10 (t,
J ) 6.2 Hz, C5H4CH2), 2.48 (dd, J ) 7.5, 6.0 Hz, CH2O), 2.45 (s,
CH3), 1.86 (ddt, J ) 7.5, 6.2, 6.0 Hz, CH2CH2O). 13C{1H} NMR (CD2-
Cl2, 125 MHz): δ 194.3 (CO); 144.9 (CSO2); 132.7 (CCH3); 129.8,
127.6 (aryl CH); 109.1 (Cp CCH2); 83.8, 83.3 (Cp CH); 69.2 (CH2O);
30.7 (C5H4CH2); 23.9 (CH2CH2O); 21.3 (CH3). IR (CH2Cl2): 2021
(s), 1924 (vs) cm-1. HRMS: m/z calcd for C18H17ReO6S 548.0305,
found 548.0311. Anal. Calcd for C18H17ReO6S: C, 39.48; H, 3.13.
Found: C, 39.28; H, 2.82.
(η5-C5H4CH2CH2CH2I)Re(CO)3 (15). A solution of 14 (0.700 g,
1.4 mmol) and LiI (0.380 g, 2.8 mmol) in acetone (40 mL) was refluxed
overnight. Solvent was evaporated, and the brown residue was
extracted with CH2Cl2, filtered through Celite to remove lithium
tosylate, and purified by column chromatography (silica gel, CH2Cl2)
to give 15 as a yellow oil (0.634 g, 90%). 1H NMR (acetone-d6, 200
MHz): δ 5.22 (m, 4H, C5H4), 3.13 (t, J ) 6.7 Hz, C5H4CH2), 2.45
(dd, J ) 7.7, 7.5 Hz, CH2I), 1.91 (ddt, J ) 7.7, 7.5, 6.7 Hz, CH2CH2I).
13C{1H} NMR (CD2Cl2, 125 MHz): δ 194.4 (CO); 109.2 (Cp CCH2);
84.0, 83.5 (Cp CH); 31.5 (C5H4CH2); 20.2 (CH2CH2I); 5.3 (CH2I). IR
(THF): 2022 (m), 1926 (s) cm-1. HRMS: m/z calcd for C10H10ReO2I
(M - CO+) 475.9280, found 475.9307 (molecular ion C11H10ReO3I,
503.9230, overlapped with an instrument reference peak).
(CO)2RedC(OCH3)CH2CH2(η5-C5H4) (9). A solution of 7 (222
-
mg, 0.57 mmol) and (CH3)3O+BF4 (90 mg, 0.61 mmol) in acetone
was stirred for 24 h at 25 °C. Solvent was evaporated under vacuum,
and the resulting yellow residue was extracted with CH2Cl2 and filtered
through Celite. Preparative TLC (silica gel, 1:1 hexane-Et2O) gave a
bright yellow band (Rf ) 0.70) from which 9 was isolated as a yellow
solid. Recrystallization by slow cooling of a CH2Cl2-hexane solution
gave pure 9 (162 mg, 0.429 mmol, 75%). 1H NMR (CD2Cl2, 200
MHz): δ 5.56 (three-line pattern, AA′BB′, 4.2 Hz separation of outer
lines, 2H, C5H4), 5.45 (three-line pattern, AA′BB′, 4.0 Hz separation
of outer lines, 2H, C5H4), 4.16 (s, OCH3), 3.12 (t, J ) 7.4 Hz, C5H4-
CH2CH2), 2.33 (t, J ) 7.4 Hz, C5H4CH2). 13C{1H} NMR (CD2Cl2,
125 MHz): δ 296.2 (RedC); 201.2 (CO); 99.6 (Cp CCH2); 86.1, 85.1
(Cp CH); 67.1 (OCH3); 29.6 (C5H4CH2CH2); 29.2 (C5H4CH2). IR
(CH2Cl2): 1945 (s), 1865 (s) cm-1. HRMS: m/z calcd for C11H11O3-
Re 378.0267, found 378.0269. Anal. Calcd for C11H11O3Re: C, 35.01;
H, 2.94. Found: C, 34.77; H, 2.78.
(CO)2RedC(OCH2CH3)CH2CH2(η5-C5H4). A solution of 7 (3.1
-
g, 8.0 mmol) and (CH3CH2)3O+ BF4 (2.3 g, 12.0 mmol) in acetone
was stirred for 24 h at 25 °C. Solvent was evaporated, and the resulting
yellow residue was extracted with CH2Cl2 and filtered through Celite.
Column chromatography (silica gel, 1:1 hexane-Et2O) gave a bright
yellow band (Rf ) 0.80) from which (CO)2RedC(OCH2CH3)CH2CH2-
(η5-C5H4) was isolated as a yellow solid, mp 103-106 °C (2.2 g, 5.6
mmol, 70%). 1H NMR (acetone-d6, 300 MHz): δ 5.71 (three-line
pattern, AA′BB′, 4.1 Hz separation of outer lines, C5H4), 5.52 (three-
line pattern, AA′BB′, 4.4 Hz separation of outer lines, C5H4), 4.44 (q,
J ) 7.4 Hz, OCH2), 3.15 (t, J ) 7.4 Hz, CH3), 2.35 (t, J ) 7.4 Hz,
C5H4CH2CH2), 1.44 (t, J ) 7.4 Hz, C5H4CH2). 13C{1H} NMR (C6D6,
125 MHz): δ 292.5 (RedC), 205.0 (CO), 124.1 (Cp CCH2), 85.9 (Cp
CH), 85.2 (Cp CH), 84.8 (OCH2), 77.3 (CH3), 25.0 (C5H4CH2), 14.8
(C5H4CH2CH2). IR (hexane): 1959 (s), 1887 (s) cm-1. HRMS: m/z
calcd for C12H13O3Re 392.0424, found 392.0427. Anal. Calcd for
C12H13O3Re: C, 36.82; H, 3.35. Found: C, 36.92; H, 3.37.
(η5-C5H4CH2CHdCH2)Re(CO)3 (11). n-BuLi (4.0 mL, 1.5 M
pentane solution, 6.0 mmol) was added to a solution of CpRe(CO)3
(2.00 g, 5.97 mmol) in THF (50 mL) at -78 °C. After the solution
was stirred for 3 h at -78 °C, allyl bromide (13.2 mmol) was condensed
into it under vacuum. After 2 h the bright yellow solution was warmed
to room temperature. THF was evaporated under vacuum, and the
resulting yellow oil was purified by column chromatography (silica
gel, CH2Cl2) to give 11 as a yellow oil (1.90 g, 85%). 1H NMR
(acetone-d6, 300 MHz) δ 5.84 (ddt, J ) 17, 10, 6.9 Hz, 1H, CH)CH2),
5.50 (s, 4H, C5H4), 5.14 (ddt, J ) 17, 2.0, 1.7 Hz, 1 H, CHdCHH),
5.08 (ddt, J ) 10, 2.0, 1.0 Hz, CHdCHH), 3.23 (ddd, J ) 6.9, 1.7, 1.0
Hz, C5H4CH2). 13C{1H} NMR (CD2Cl2, 125 MHz): δ 194.9 (CO);
136.0 (CHdCH2); 117.7 (CHdCH2); 109.5 (Cp CCH2); 84.2, 83.9 (Cp
Li+[(CO)2ReC(dO)CH2CH2CH2(η5-C5H4)]- (16). t-BuLi (1.5 mL,
1.7 M pentane solution, 2.55 mmol) was added to a solution of 15
(0.600 g, 1.19 mmol) in Et2O at -78 °C. Upon warming to room
temperature, a fine yellow precipitate formed and was collected on a
frit, washed with cold Et2O, and dried under vacuum to give 16 (0.268
g, 0.64 mmol, 48%), which was shown to contain ∼0.5 mol of Et2O/
mol of 16 by 1H NMR. 1H NMR (THF-d8, 200 MHz): δ 5.51 (three-
line pattern, AA′BB′, 4.3 Hz separation of outer lines, 2H, C5H4); 5.43
(three-line pattern, AA′BB′, 4.3 Hz separation of outer lines, 2H, C5H4);
3.26 (t, J ) 6.9 Hz, C5H4CH2), 2.55 (m, C5H4CH2CH2CH2), 2.02 (m,
CH); 32.5 (C5H4CH2). IR (CH2Cl2): 2020 (s), 1925 (vs) cm-1
HRMS: m/z calcd for C11H9ReO3 376.0082, found 376.0098.
.
(η5-C5H4CH2CH2CH2OH)Re(CO)3 (12) and (η5-C5H4CH2CH-
(OH)CH3)Re(CO)3 (13). A THF solution of BH3‚THF (4.4 mL, 1.0
M) was added to a solution of 11 (1.64 g, 4.4 mmol) in THF at -78
°C. After 2 h at room temperature, H2O (5 mL), NaOH (5 mL, 15%
aqueous solution), and H2O2 (5 mL, 30% aqueous solution) were added.
After 1 h, solid K2CO3 (2 g, 14.5 mmol) was added. The organic layer
was removed, and the aqueous layer was extracted with CH2Cl2 (3 ×
30 mL). The combined organic extracts were dried (MgSO4), filtered,
and chromatographed to give a 4:1 mixture of 12/13 (1.06 g, 61%) as
a clear oil used without further purification. The spectroscopic data
for 12 are the following. 1H NMR (CD2Cl2, 300 MHz): δ 5.29 (m,
C5H4), 3.62 (t, J ) 6.3 Hz, C5H4CH2), 2.49 (dd, J ) 8.1, 7.7 Hz, CH2-
OH), 1.96 (br s, OH) 1.71 (ddt, J ) 8.1, 7.7, 6.3 Hz, C5H4CH2CH2).
1H NMR (acetone-d6, 300 MHz): δ 5.50 (three-line pattern, AA′BB′,
4.1 Hz separation of outer lines, 2H, C5H4), 5.45 (three-line pattern,
AA′BB′, 4.0 Hz separation of outer lines, 2H, C5H4), 3.60 (m,
C5H4CH2), 2.51 (m, CH2OH), 1.74 (m, C5H4CH2CH2). 13C{1H} NMR
(C6D6, 125 MHz): δ 195.0 (CO), 111.1 (Cp CCH2), 84.6, (Cp CH),
83.8 (Cp CH), 61.5 (COH), 34.6 (C5H4CH2), 24.5 (CH2CH2CH2). IR
(for mixture of 12 and 13) (CH2Cl2): 3416 (w, br), 2020 (s), 1925 (vs)
C5H4CH2CH2). IR (THF): 1902 (s), 1822 (s), 1505 (w) cm-1
.
(CO)2RedC(OCH3)CH2CH2CH2(η5-C5H4) (17). A solution of 16
(0.300 g, 0.72 mmol) and (CH3)3O+BF4- (0.120 g, 0.8 mmol) in acetone
was stirred for 24 h at 25 °C. Solvent was evaporated, and the resulting
yellow residue was extracted with CH2Cl2 and filtered through Celite.
Preparative TLC (silica gel, 1:1 hexane-Et2O) gave a yellow band (Rf
) 0.80) from which 17 was isolated as a yellow solid (0.270 g, 0.69
mmol, 95%). 1H NMR (acetone-d6, 200 MHz) δ 5.46 (three-line
pattern, AA′BB′, 4.0 Hz separation of outer lines, C5H4), 5.38 (three-
line pattern, AA′BB′, 4.0 Hz separation of outer lines, C5H4), 4.20 (s,
OCH3), 2.44 (m, C5H4CH2), 1.88 (m, C5H4CH2CH2CH2), 1.68 (m, C5H4-
CH2CH2). 1H NMR (CD2Cl2, 200 MHz): δ 5.31 (s, C5H4), 4.21 (s,
OCH3), 2.40 (m, C5H4CH2), 1.88 (m, C5H4CH2CH2CH2), 1.67 (m, C5H4-
CH2CH2). 13C{1H} NMR (CD2Cl2, 125 MHz): δ 297.7 (RedC); 204.6
(CO); 110.3 (Cp CCH2); 86.6 (Cp CH); 84.3 (Cp CH); 64.4 (OCH3),
51.2 (C5H4CH2); 29.8 (C5H4CH2CH2); 25.6 (C5H4CH2CH2CH2). IR
(hexane): 1958 (vs), 1886 (vs) cm-1. HRMS: m/z calcd for C12H13O3-
Re 392.0424, found 392.0423. Anal. Calcd for C12H13O3Re: C, 36.82;
H, 3.35. Found: C, 37.12; H, 3.46.

3978 J. Am. Chem. Soc., Vol. 119, No. 17, 1997
Casey et al.
Table 2. Crystal Structure Data for (η5-C5H4CH2CH2OTs)Re(CO)3 (5), (CO)2RedC(OCH3)CH2CH2(η5-C5H4) (9),
(CO)2RedC(OCH3)CH2CH2CH2(η5-C5H4) (17)
compound
empirical formula
color; habit
crystal size, mm
crystal system
space group
unit cell dimens
a, Å
5
9
17
C17H15ReO6S
white; block
0.5 × 0.2 × 0.2
monoclinic
P21/n
C11H11ReO3
yellow; needle
0.5 × 0.1 × 0.1
triclinic
C12H13ReO3
yellow; prism
0.5 × 0.4 × 0.3
monoclinic
P21/c
P1h
10.969(3)
8.128(2)
20.227(3)
90
104.152(9)
90
1748.5(7)
48
1.94-22.49
116(2)
4
7.965(2)
8.624(2)
9.224(2)
116.48(2)
90.53(2)
109.43(2)
525.4(2)
51
8.3767(5)
8.0042(4)
17.1995
90
95.170(2)
90
1148.51(11)
5120
3-25.5
133(2)
4
b, Å
c, Å
R, deg
â, deg
γ, deg
vol, Å3
no. of peaks to determine cell
θ range of cell peaks
temperature, K
Z
1.50-22.50
113(2)
2
formula wt
density (calcd), Mg m-3
abs coeff, mm-1
F(000)
533.55
2.027
7.099
1024
3.60
377.40
2.386
11.546
352
391.42
2.264
10.568
736
R1, %
4.06
3.46
wR2, %
S, gof
8.36
1.038
10.66
1.101
9.70
1.121
(CO)2RedC(OH)CH2CH2CH2(η5-C5H4) (18). Aqueous HCl (0.5
M, 4 mL) was added to a mixture of 10 mL of CH2Cl2 and 10 mL of
a yellow aqueous solution of 16 (0.268 g, 0.64 mmol). After 15 min
of vigorous stirring, the CH2Cl2 layer was decanted, washed with H2O,
dried (MgSO4), and concentrated to give 18 (0.137 g, 0.36 mmol, 57%)
as a dark yellow oil. 1H NMR (acetone-d6, 200 MHz): δ 12.30 (s,
OH), 5.35 (s, C5H4), 2.40 (m, C5H4CH2), 1.75 (m, RedCCH2), 1.70
(m, C5H4CH2CH2). 1H NMR (CD2Cl2, 200 MHz): δ 9.15 (s, OH),
5.35 (three-line pattern, AA′BB′, 4.4 Hz separation of outer lines, C5H4),
5.25 (three-line pattern, AA′BB′, 4.0 Hz separation of outer lines, C5H4),
2.38 (m, C5H4CH2), 1.77 (m, RedCCH2), 1.68 (m, C5H4CH2CH2). 1H
NMR (C6D6, 200 MHz): δ 8.70 (s, OH), 4.75 (three-line pattern,
AA′BB′, 4.4 Hz separation of outer lines, C5H4), 4.50 (three-line pattern,
AA′BB′, 4.0 Hz separation of outer lines, C5H4), 1.60 (m, C5H4CH2),
1.20 (m, RedCCH2), 1.05 (m, C5H4CH2CH2). 13C{1H} NMR (C6D6,
125 MHz): δ 296.0 (RedC); 205.0 (CO); 110.1 (Cp CCH2); 86.0 (Cp
CH); 85.1 (Cp CH); 50.6 (C5H4CH2); 30.1 (C5H4CH2CH2); 25.0 (C5H4-
CH2CH2CH2). IR (THF): 1945 (s), 1864 (s) cm-1. HRMS: m/z calcd
for C11H11ReO3 378.0267, found 378.0282.
(CH2Cl2): 1916 (s), 1837 (s) cm-1. HRMS: m/z calcd for C11H12-
NO2Re 377.0428, found 377.0431.
X-ray Crystallographic Determination and Refinement. Slow
cooling of a saturated CH2Cl2-hexane solution of 5 gave white crystals
suitable for X-ray analysis. Slow cooling of a saturated CH2Cl2-hexane
solution of 9 gave yellow crystals suitable for X-ray analysis. Slow
diffusion of hexane into a saturated solution of 17 in Et2O in an inert
atmosphere glovebox gave yellow crystals suitable for X-ray analysis.
Intensity data were obtained with graphite-monochromated Mo KR
radiation on a Siemens P4 diffractometer at -125 °C. Crystallographic
computations were carried out with SHELXTL and SHELXL-93.27
A semi-empirical absorption correction was applied. The initial
positions of the Re atoms were obtained by automatic Patterson
interpretation. Other non-hydrogen atoms were obtained from succes-
sive Fourier difference maps coupled with isotropic least-squares
refinement. All non-hydrogen atoms were refined anisotropically.
Idealized positions were used for the hydrogen atoms. Crystallographic
data are presented in Table 2. Atomic coordinates and equivalent
isotropic displacement parameters and a complete list of bond lengths
and angles are presented in the Supporting Information.
(CO)2RedC(HNCH3)CH2CH2(η5-C5H4) (19). Methylamine (9
mmol) was condensed into a solution of 9 (400 mg, 1.06 mmol) in
THF (10 mL). After 12 h solvent was evaporated to give 19 as a yellow
solid (366 mg, 92%). 1H NMR (CD2Cl2, 200 MHz) (two isomers, 5:1
major/minor): (major isomer) δ 9.00 (br s, NH), 5.40 (three-line pattern,
AA′BB′, 4.1 Hz separation of outer lines, C5H4), 5.27 (three-line pattern,
AA′BB′, 4.1 Hz separation of outer lines, C5H4), 3.36 (t, J ) 7.3 Hz,
C5H4CH2), 3.20 (d, J ) 4.7 Hz, CH3), 2.26 (t, J ) 7.3 Hz,
C5H4CH2CH2); (minor isomer) δ 9.15 (br s, NH), 5.70 (three-line
pattern, AA′BB′, 4.1 Hz separation of outer lines, C5H4), 5.55 (three-
line pattern, AA′BB′, 4.1 Hz separation of outer lines, C5H4), 3.71 (t,
J ) 7.3 Hz, C5H4CH2), 3.17 (d, J ) 4.7 Hz, CH3), 2.85 (t, J ) 7.3 Hz,
C5H4CH2CH2). 13C{1H} NMR (C6D6, 125 MHz): (major isomer) δ
247.5 (RedC); 206.1 (CO); 120.0 (Cp CCH2); 83.2 (Cp CH); 82.5
(Cp CH); 69.9 (CH3); 41.2 (C5H4CH2); 23.3 (C5H4CH2CH2); (minor
isomer) δ 247.0 (RedC); 205.0 (CO); 117.9 (Cp CCH2); 80.1 (Cp CH);
79.8 (Cp CH); 65.0 (CH3); 41.5 (C5H4CH2); 23.6 (C5H4CH2CH2). IR
Acknowledgment. Financial support from the National
Science Foundation is gratefully acknowledged.
Supporting Information Available: Tables listing X-ray
crystallographic data for 5, 9, and 17 and bond angles and
distances and text describing general experimental methods and
experimental details and charcterization for (η5-C5H4CH2CH2-
Br)Re(CO)3, (η5-C5H4CHdCH2)Re(CO)3, (CO)2RedC[NH-
(CH3)]CH2CH2CH2(η5-C5H4), and (η5-C5H4)(CO)2RedC[NH-
(CH3)]CH3 (28 pages). See any current masthead page for
ordering and Internet access instructions.
JA9637311
(27) Sheldrick, G. M. SHELXTL Version 5 Reference Manual; Siemens
Analytical X-ray Instruments, Inc., 1994.