Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine

Article abstract of DOI:10.1016/j.jorganchem.2004.03.024

Further investigations into the chemistry of the rhenacyclobutadiene complexes (CO)₄Re(η²-C(R)C(CO₂Me) C(X)) (1: R=Me, X=OEt (1a), O(CH₂)₃C=CH (1b), NEt₂ (1c); R=CHEt₂, X=OEt (1d); R=Ph, X=OEt (1e)) are reported. Reactions of 1 with alkynes at reflux temperature of toluene and at ambient temperature either under photochemical conditions or in the presence of PdO yield ring-substituted η⁵-cyclopentadienylrhenium tricarbonyl complexes, 2. The symmetrical alkynes R′C=CR′ (R′=Ph, Me, CO₂Me) afford the pentasubstituted complexes (η⁵-C₅(Me)(CO₂Me) (OEt)(Ph)(Ph))Re(CO)₃ (2d), (η⁵- C₅(Me)(CO₂Me)(OEt)(Me)(Me)) Re(CO)₃ (2e), (η⁵-C₅(Me) (CO₂Me)(OEt) (CO₂Me)(CO₂Me)) Re(CO)₃ (2f), and (η⁵-C₅ (Me)(CO₂Me) (NEt₂)(CO₂Me) (CO₂Me)) Re(CO)₃ (2i) on reaction with the appropriate 1, whereas the unsymmetrical alkynes R′C=CR″ (R′=Ph; R″=H, Me) give either only one, (η⁵- C₅(Me)(CO₂Me)(OEt) (Ph)H)Re(CO)₃ (2a)), or both, (η⁵-C₅(Me)(CO₂Me) (OEt)(Ph)(Me))Re(CO)₃ (2b) and (η⁵- C₅(Me)(CO₂Me)(OEt)(Me)(Ph)) Re(CO)₃ (2c), (η⁵-C₅(Ph) (CO₂Me)(OEt) (Ph)H)Re(CO)₃ (2g) and (η⁵-C₅ (Ph)(CO₂Me)(OEt)(H)(Ph)) Re(CO)₃ (2h), of the possible products of [3 + 2] cycloaddition of alkyne to η²-C(R)C(CO₂Me) C(X). Thermolysis of (CO)₄Re(η²-C(Me) C(CO₂Me) C(O(CH₂)₃C=CH)) (1b) containing a pendant alkynyl group proceeds to (η⁵-C₅(Me) (CO₂Me)(O(CH₂) ₃)H)Re(CO)₃ (2j), a η⁵-cyclopentadienyl-dihydropyran fused-ring product. Competition experiments showed that each of PhC=CH and MeO₂CC=CCO₂Me reacts faster than PhC=CPh with 1a. The results with unsymmetrical alkynes are rationalized by steric properties of substituents at the C=C and Re=C bonds and by a preference of Re=C(Me) over Re=C(OEt) to undergo alkyne insertion. A mechanism is proposed that involves substitution of a trans CO by alkyne in 1, insertion of alkyne into Re=C bond to give a rhenabenzene intermediate, and collapse of the latter to 2. Complexes 1a and 1d undergo rearrangement in MeCN at reflux temperature to give rhenafuran-like products, (CO)₄Re(κ²- OC(OMe)C(CH=CR₂)C(OEt)) (R=H (3a) or Et (3b)). The reaction of 1d also proceeds in EtCN, PhCN, and t-BuCN at comparable temperature, but is slower (especially in t-BuCN) than in MeCN. In pyridine at reflux temperature, 1a undergoes a similar rearrangement, with CO substitution, to give (CO)₃(py)Re(κ²-OC(OMe) C(CH=CEt₂)C(OEt)) (4). A mechanism is proposed for these reactions. The sulfonium ylides Me₂S=CHC(O)Ph and Me₂S=C(CN)₂ (Me₂S=CRR′) react with 1a in acetonitrile at reflux temperature by nucleophilic addition of the ylide to the Re=C(Me) carbon, loss of Me₂S, and rearrangement to a rhenafuran-type structure to yield (CO)₄Re(κ²-OC(OMe)C(C(Me)=CRR′)C(OEt)) (R=H, R′=C(O)Ph (5a); R=R′=CN (5b)). All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.

Full text of DOI:10.1016/j.jorganchem.2004.03.024

Journal of Organometallic Chemistry 689 (2004) 2013–2024
www.elsevier.com/locate/jorganchem
Chemistry of Fischer-type rhenacyclobutadiene complexes. II.
Reactions with alkynes and sulfonium ylides, and rearrangements
induced by nitriles and pyridine
1
Veronique Plantevin , Andrew Wojcicki
*
ꢀ
Department of Chemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, OH 43210-1185, USA
Received 29 December 2003; accepted 8 March 2004
Abstract
Further investigations into the chemistry of the rhenacyclobutadiene complexes (CO)4Re(g2-C(R)C(CO2Me)C(X)) (1: R ¼ Me,
X ¼ OEt (1a), O(CH2)3CBCH (1b), NEt2 (1c); R ¼ CHEt2, X ¼ OEt (1d); R ¼ Ph, X ¼ OEt (1e)) are reported. Reactions of 1 with
alkynes at reflux temperature of toluene and at ambient temperature either under photochemical conditions or in the presence of
PdO yield ring-substituted g5-cyclopentadienylrhenium tricarbonyl complexes, 2. The symmetrical alkynes R0CBCR0 (R0 ¼ Ph, Me,
CO2Me) afford the pentasubstituted complexes (g5-C5(Me)(CO2Me)(OEt)(Ph)(Ph))Re(CO)3 (2d), (g5-C5(Me)(CO2Me)(OEt)(Me)
(Me))Re(CO)3 (2e), (g5-C5(Me)(CO2Me)(OEt)(CO2Me)(CO2Me))Re(CO)3 (2f), and (g5-C5(Me)(CO2Me)(NEt2)(CO2Me)
(CO2Me))Re(CO)3 (2i) on reaction with the appropriate 1, whereas the unsymmetrical alkynes R0CBCR00 (R0 ¼ Ph; R00 ¼ H, Me)
give either only one, (g5-C5(Me)(CO2Me)(OEt)(Ph)H)Re(CO)3 (2a)), or both, (g5-C5(Me)(CO2Me) (OEt)(Ph)(Me))Re(CO)3 (2b)
and (g5-C5(Me)(CO2Me)(OEt)(Me)(Ph))Re(CO)3 (2c), (g5-C5(Ph)(CO2Me)(OEt)(Ph)H)Re(CO)3 (2g) and (g5-C5(Ph)(CO2Me)
(OEt)(H)(Ph))Re(CO)3 (2h), of the possible products of [3 + 2] cycloaddition of alkyne to g2-C(R)C(CO2Me)C(X). Thermolysis of
(CO)4Re(g2-C(Me)C(CO2Me)C(O(CH2)3CBCH)) (1b) containing a pendant alkynyl group proceeds to (g5-C5(Me)(CO2Me)
(O(CH2)3)H)Re(CO)3 (2j), a g5-cyclopentadienyl-dihydropyran fused-ring product. Competition experiments showed that each of
PhCBCH and MeO2CCBCCO2Me reacts faster than PhCBCPh with 1a. The results with unsymmetrical alkynes are rationalized
by steric properties of substituents at the CBC and Re@C bonds and by a preference of Re@C(Me) over Re@C(OEt) to undergo
alkyne insertion. A mechanism is proposed that involves substitution of a trans CO by alkyne in 1, insertion of alkyne into Re@C
bond to give a rhenabenzene intermediate, and collapse of the latter to 2. Complexes 1a and 1d undergo rearrangement in MeCN at
reflux temperature to give rhenafuran-like products, (CO)4Re(j2-OC(OMe)C(CH@CR2)C(OEt)) (R ¼ H (3a) or Et (3b)). The re-
action of 1d also proceeds in EtCN, PhCN, and t-BuCN at comparable temperature, but is slower (especially in t-BuCN) than in
MeCN. In pyridine at reflux temperature, 1a undergoes a similar rearrangement, with CO substitution, to give (CO)3(py)Re(j2-
OC(OMe)C(CH@CEt2)C(OEt)) (4). A mechanism is proposed for these reactions. The sulfonium ylides Me2S@CHC(O)Ph and
Me2S@C(CN)2 (Me2S@CRR0) react with 1a in acetonitrile at reflux temperature by nucleophilic addition of the ylide to the Re-
@C(Me) carbon, loss of Me2S, and rearrangement to
a
rhenafuran-type structure to yield (CO)4Re(j2-OC(O-
Me)C(C(Me)@CRR0)C(OEt)) (R ¼ H, R0 ¼ C(O)Ph (5a); R ¼ R0@CN (5b)). All new compounds were characterized by a
combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Rhenium complexes; Metallacyclobutadiene complexes; Fischer carbene complexes; Cyclopentadienyl complexes; Rearrangement
reactions; Nucleophilic addition
1. Introduction
* Corresponding author. Tel.: +1-614-292-4750; fax: +1-614-292-
In the accompanying paper we reported a general
synthetic method for Fischer rhenacyclobutadiene
1685.
E-mail address: wojcicki@chemistry.ohio-state.edu (A. Wojcicki).
Celgene, Signal Research Division, 4550 Towne Centre Court, San
Diego, CA 92121, USA.
complexes of the type (CO)4Re(g2-C(R)C(CO2Me)C
1
(OR0)) (1). Also presented were a number of reactions of
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.03.024

2014
V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
1, viz., deprotonation followed by alkylation at R
(R ¼ alkyl), aminolysis at C(OR0), nucleophilic addition
(at C(R)) and substitution (at Re) by tertiary phosphine,
and insertion of oxygen atom and the isoelectronic NH
fragment into the Re@C bonds [1]. This paper focuses
on additional chemistry of 1 and derivatives, including
reactions with alkynes to yield tetra- and pentasubsti-
tuted g5-cyclopentadienylrhenium complexes (CpzRe
(CO)3 (2)) and with sulfonium ylides to give nucleophilic
addition at C(R) followed by rearrangement, as well as
rearrangements induced by nitriles and pyridine.
alumina using first hexane and then hexane/CH2Cl2 as
the eluent. Yields of (g5-C5(Me)(CO2Me)(OEt)(Ph)H)
Re(CO)3 (2a) were typically higher than 0.26 g (ca.
90%). IR (hexane): m(CO) 2025 (m), 1945 (s), 1729 (w)
cmꢀ1. 1H NMR (CDCl3): d 7.7–7.1 (m, 5H, Ph), 5.29 (s,
1H, CH), 3.87 (s, 3H, CO2Me), 3.80 (m, 2H, CH2Me),
3
2.49 (s, 3H, CMe), 1.25 (t, J ¼ 7:0 Hz, 3H, OCH2Me).
13C NMR (CDCl3): d 192.5 (s, CO), 165.3 (s, CO2Me),
137.5 (s, COEt), 130.8 (s, C of Cp), 128.9, 128.6, 128.4,
127.8 (s, 3d, C of Ph), 101.6, 95.3, 79.2 (2s, d, C of Cp),
74.9 (t, OCH2Me), 51.9 (q, CO2Me), 15.3 (q, CMe), 14.8
(q, OCH2Me). MS (FAB): m=z 528 (Mþ). Anal. Found:
C, 43.42; H, 3.12%. Calc. for C19H17O6Re: C, 43.26; H,
3.25%.
2. Experimental
Alternatively, 2a was prepared from 1a (0.300 g,
0.662 mmol) and PhCBCH (0.075 ml, 0.068 g) in 1.5 ml
of toluene in a sealed tube heated at 120 °C overnight.
Workup was similar to that detailed above. Yield: 0.315
g (90%).
Complex 2a was also synthesized at ambient tem-
perature from 1a (0.162 g, 0.357 mmol) and PhCBCH
(0.040 ml, 0.037 mmol, 1 equivalent) in MeCN (7 ml) in
the presence of PdO (0.044 g). The resulting yellow so-
lution with suspended black particles of PdO turned
green within 1 h of stirring. Completion of the reaction
required 2 days. The solvent was then evaporated and
the residue was extracted with 20 ml of hexane. The rest
of the workup paralleled that for the thermal reaction.
Product 2a was isolated as an oil that did not readily
crystallize. Typical yields were ca. 90%.
2.1. General procedures and measurements
All general procedures were the same as those de-
scribed in the immediately preceding paper [1]. IR and
NMR spectra were obtained as reported earlier [2,3].
Mass spectra were recorded on a Kratos VG70-250S
spectrometer by using either electron impact (EI) or fast
atom bombardment (FAB) techniques. All listed mass
peaks are those of ions containing 187Re. Photochemical
experiments were conducted on ca. 10ꢀ4 M solutions
with 300-nm lamps in a Rayonet reactor.
2.2. Materials
Reagents were obtained from various commercial
sources and used as received except as indicated below.
The sulfonium ylides Me2S@CHC(O)Ph and Me2S@C
(CN)2 were prepared by reported procedures [4,5].
The rhenacyclobutadienes (CO)4Re(g2-C(R)C(CO2Me)
C(X)) (R ¼ Me, X ¼ OEt (1a), O(CH2)3CBCH (1b),
NEt2 (1c); R ¼ CHEt2, X ¼ OEt (1d); R ¼ Ph, X ¼ OEt
(1e)) were synthesized as described in the accompanying
paper [1].
2.3.2. Synthesis of (g5-C5(Me)(CO2Me)(OEt)(Ph)-
(Me))Re(CO)3 (2b) and (g5-C5(Me)(CO2Me)(OEt)-
(Me)(Ph))Re(CO)3 (2c) from (CO)4Re(g2-C(Me)C-
(CO2Me)C(OEt)) (1a) and PhCBCMe
A solution of 1a (0.060 g, 0.13 mmol) in 5 ml of
toluene was treated with 1 equivalent of PhCBCMe
(0.017 ml, 0.015 g), and the mixture was heated at reflux
temperature for 5 h. The workup was similar to that
described in Section 2.3.1. Chromatography on a grade
III alumina column using CH2Cl2 as the eluent afforded
after solvent removal a 3:1 mixture of g5-C5(Me)
(CO2Me)(OEt)(Ph)(Me))Re(CO)3 (2b) and (g5-C5(Me)
(CO2Me)(OEt)(Me)(Ph))Re(CO)3 (2c) as a yellow oil.
2.3. Reactions of (CO)4Re(g2-C(R)C(CO2Me)C(X))
(1) with alkynes
2.3.1. Synthesis of (g5-C5(Me)(CO2Me)(OEt)(Ph)H)-
Re(CO)3 (2a) from (CO)4Re(g2-C(Me)C(CO2Me)C-
(OEt)) (1a) and PhCBCH
1
Yield: 0.044 g (62%). H NMR (CDCl3): d 7.7–7.1 (m,
To a solution of 1a (0.244 g, 0.538 mmol) in 20 ml of
toluene was added ca. 1 equivalent of PhCBCH (0.059
ml, 0.055 g), and the mixture was heated at reflux tem-
perature. After 4 h the solvent was removed under re-
duced pressure, and the brown residue was extracted
with 10-ml portions of hexane. The extracts were fil-
tered, and the filtrate was concentrated to a brown oil
under reduced pressure. The oil partially solidified upon
storage at room temperature overnight. Further
purification was achieved by dissolution in hexane
and filtration through a plug of grade III deactivated
5H, Ph), 3.97 (minor), 3.88 (2m, 2H, OCH2Me), 3.82
(minor), 3.80 (2s, 3H, CO2Me), 2.40, 2.16 (minor), 1.97
(minor), 1.95 (4s, 6H, CMe), 1.30 (minor), 1.00 (2t,
3J ¼ 7:0 Hz, 3H, OCH2Me).
2.3.3. Synthesis of (g5-C5(Me)(CO2Me)(OEt)(Ph)-
(Ph))Re(CO)3 (2d) from (CO)4Re(g2-C(Me)C(CO2-
Me)C(OEt)) (1a) and PhCBCPh
A solution of 1a (0.100 g, 0.221 mmol) in 10 ml
of toluene was treated with 1 equivalent of PhCB
CPh (0.040 g), and the mixutre was heated at reflux

V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
2015
temperature for 3 h. The workup procedure followed
that given in Section 2.3.1. After chromatography on
grade III alumina with CH2Cl2/hexane as the eluent,
0.107 g (80%) of (g5-C5(Me)(CO2Me)(OEt)(Ph)(Ph))-
Re(CO)3 (2d) was obtained. IR (hexane): m(CO) 2016
3H, CMe), 1.31 (t, 3J ¼ 7:0 Hz, 3H, OCH2Me. 13C
NMR (CDCl3): d 192.1 (s, CO), 163.8, 163.7, 163.5 (3s,
CO2Me), 140.0 (s, COEt), 105.6 (s, CMe), 84.2, 84.1,
79.4 (3s, CCO2Me), 73.7 (t, OCH2Me), 53.1, 51.8, 51.2
(3q, CO2Me), 15.0 (q, CMe), 12.7 (q, OCH2Me). MS
(FAB): m=z 568 (Mþ).
1
(m), 1971 (s), 1720 (w) cmꢀ1. H NMR (CDCl3): d 7.5–
7.0 (m, 10H, Ph), 3.90 (s, 3H, CO2Me), 3.70 (m, 2H,
OCH2Me), 2.43 (s, 3H, CMe), 1.17 (t, 3J ¼ 7:0 Hz,
OCH2Me). 13C NMR (CDCl3): d 194.0 (s, CO), 165.6
(s, CO2Me), 123.3 (s, COEt), 103.7, 100.1, 97.2 (3s,
CPh), 89.3 (s, CCO2Me), 75.0 (t, OCH2Me), 52.0 (q,
CO2Me), 15.1 (q, CMe), 12.8 (q, OCH2Me).
2.3.6. Synthesis of (g5-C5(Ph)(CO2Me)(OEt)(Ph)H)-
Re(CO)3 (2g) and (g5-C5(Ph)(CO2Me)(OEt)(H)-
(Ph))Re(CO)3 (2h) from (CO)4Re(g2-C(Ph)C(CO2-
Me)C(OEt)) (1e) and PhCBCH
The reaction in a sealed tube and workup were con-
ducted as in Section 2.3.1 by using 1e (0.100 g, 0.194
mmol) and PhCBCH (0.021 ml, 0.020 g, 1 equivalent) in
toluene (2 ml). The resulting orange oil was identified by
1H NMR spectroscopy as a 2:1 mixture of isomers (g5-
C5(Ph)(CO2Me)(OEt)(Ph)H)Re(CO)3 (2g) and (g5-
C5(Ph)(CO2Me)(OEt)(H)(Ph))Re(CO)3 (2h). Yield:
Complex 2d was also prepared by irradiating a so-
lution of 1a and PhCBCPh (1 equivalent) in hexane.
After ca. 12 h, a mixture of 60% 2d and 40% unreacted
1
1a was observed by H NMR spectroscopy.
2.3.4. Synthesis of (g5-C5(Me)(CO2Me)(OEt)(Me)-
(Me))Re(CO)3 (2e) from (CO)4Re(g2-C(Me)C(CO2-
Me)C(OEt)) (1a) and MeCBCMe
1
0.075 g (65%). H NMR (CDCl3): d 7.6–6.9 (m, 10H,
Ph), 5.62, 5.32 (minor) (2s, 2H, CH), 4.2–3.9 (m, 2H,
A solution of 1a (0.100 g, 0.221 mmol) and
MeCBCMe (0.090 ml, 0.060 g, 5 equivalents) in 2 ml of
toluene in a sealed tube was heated at 110 °C overnight.
The contents were cooled to room temperature, evapo-
rated to dryness, and extracted with two 10-ml portions
of hexane. The extracts were filtered, and hexane was
removed from the filtrate to yield a yellow oil. Further
purification was effected by chromatography on alumina
with CH2Cl2 as the eluent. The pale yellow oil solidified
under vacuum overnight to furnish 0.060 g (57% yield)
of pure (g5-C5(Me)(CO2Me)(OEt)(Me)(Me))Re(CO)3
(2e). IR (hexane): m(CO) 2098 (m), 1977 (s), 1729 (w)
OCH2Me), 3.74, 3.62 (minor) (2s, 3H, CO2Me), 1.48
3
(minor), 1.32 (2t, J ¼ 7:1 Hz, OCH2Me).
2.3.7. Synthesis of (g5-C5(Me)(CO2Me)(NEt2)-
(CO2Me)(CO2Me))Re(CO)3 (2i) from (CO)4Re(g2-
C(Me)C(CO2Me)C(NEt2)) (1c) and MeO2CCBC-
CO2Me
To a solution of 1c (0.125 g, 0.260 mmol) in 10 ml of
toluene was added MeO2CCBCCO2Me (0.048 ml, 0.055
g, 1.5 equivalents), and the mixture was heated at reflux
temperature for 2 h. Workup was similar to that in
Section 2.3.1. The yield of (g5-C5(Me)(CO2Me)
(NEt2)(CO2Me)(CO2Me))Re(CO)3 (2i), a green solid,
was 0.102 g (66%). IR (toluene): m(CO) 2025 (m), 1978
(s), 1730 (w) cmꢀ1. 1H NMR (CDCl3): d 3.84, 3.83, 3.81
(3s, 9H, CO2Me), 3.05 (m, 4H, NCH2Me), 2.62 (s, 3H,
cmꢀ1
.
1H NMR (CDCl3): d 3.97, 3.88 (2m, 2H,
OCH2Me), 3.80 (s, 3H, CO2Me), 2.41, 2.16, 2.15 (3s,
9H, CMe), 1.33 (t, 3J ¼ 7:0 Hz, OCH2Me).
13C{1H}NMR (CDCl3): d 194.8 (s, CO), 165.6 (s,
CO2Me), 137.6 (s, COEt), 98.3, 95.3, 92.3 (3s, CMe),
75.3 (s, OCH2Me), 75.2 (s, CCO2Me), 51.7 (s, CO2Me),
15.4 (s, OCH2Me), 11.8, 10.5, 9.4 (3s, CMe). MS (EI):
m=z 480 (Mþ).
3
CMe), 1.06 (t, J ¼ 7:2 Hz, 6H, NCH2Me). 13C NMR
(CDCl3): d 192.4 (s, CO), 165.2, 165.1, 164.6 (3s,
CO2Me), 134.5 (s, CNEt2), 106.2 (s, CMe), 83.0, 82.7,
82.6 (3s, CCO2Me), 53.6, 53.4, 52.4 (3q, CO2Me), 46.2
(t, NCH2Me), 12.8 (q, CMe), 12.2 (q, NCH2Me). MS
(FAB): m=z 595 (Mþ). Anal. Found: C, 38.51; H, 3.91%.
Calc. for C19H22NO9Re: C, 38.38; H, 3.73%.
2.3.5. Synthesis of (g5-C5(Me)(CO2Me)(OEt)(CO2-
Me)(CO2Me))Re(CO)3 (2f) from (CO)4Re(g2-
C(Me)C(CO2Me)C(OEt)) (1a) and MeO2CCBC-
CO2Me
2.3.8. Synthesis of (g5-C5(Me)(CO2Me)(O(CH2)3)H)-
Re(CO)3 (2j) by thermolysis of (CO)4Re(g2-C(Me)C-
(CO2Me)C(O(CH2)3CBCH)) (1b)
A
solution of 1a (0.060 g, 0.13 mmol) and
MeO2CCBCCO2Me (0.016 ml, 0.019 g, 1 equivalent) in
2 ml of toluene in a sealed tube was heated at 120 °C for
4 h. Cooling to room temperature, evaporation to dry-
ness, and extraction of the residue with 10-ml portions
of hexane afforded 0.049 g (65% yield) of (g5-
C5(Me)(CO2Me)(OEt)(CO2Me)(CO2Me))Re(CO)3 (2f)
as a yellowish green oil upon removal of the solvent. IR
(toluene): m(CO) 2031 (m), 1952 (s), 1743 (w), 1732 (w)
A solution of 1b (0.312 g, 0.640 mmol) in 20 ml of
toluene was heated at reflux temperature for 4 h. After
evaporation of the solvent, the crude product was dis-
solved in a minimum volume of hexane, and the solution
was filtered and cooled to )78 °C. Yellowish green
crystals of (g5-C5(Me)(CO2Me)(O(CH2)3)H)Re(CO)3
(2j) were isolated by filtration in 56% yield (0.166 g). IR
(toluene): m(CO) 2065 (m), 2006 (s), 1972 (m), 1935 (m),
.
cmꢀ1 1H NMR (CDCl3): d 4.07, 3.92 (2m, 2H,
OCH2Me), 3.83, 3.82, 3.80 (3s, 9H, CO2Me), 2.68 (s,
1
1720 (w) cmꢀ1. H NMR (CDCl3): d 5.01 (s, 1H, CH),

2016
V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
3
4.3, 4.1 (2m, 2H, OCH2(CH2)2), 3.84 (s, 3 H, CO2Me),
2.65 (m, 2H, O(CH2)2CH2), 2.47 (s, 3H, CMe), 1.95 (m,
2H, OCH2CH2CH2). 13C NMR (CDCl3): d 194.0 (s,
CO), 190.9 (br s, CO), 165.6 (s, CO2Me), 139.3 (s,
COCH2), 100.2 (s, CMe), 82.5 (s, C of Cp), 78.0 (d, CH),
71.9 (s, C of Cp), 68.6 (t, OCH2(CH2)2), 51.8 (q, CO2
Me), 21.6 (t, O(CH2)2CH2), 19.9 (t, OCH2CH2CH2),
14.6 (q, CMe). MS (FAB): m=z 464 (Mþ).
2J ¼ 2:67 Hz, Jcis ¼ 12:1 Hz, 1H, CH@CH2), 4.38 (q,
3J ¼ 7:1 Hz, 2H, OCH2Me), 3.89 (s, 3H, CO2Me), 1.50
(t, 3J ¼ 7:1 Hz, 3H, OCH2Me). 13C{1H}NMR (CDCl3):
d 234.3 (s, ReCOEt), 191.5, 190.5, 186.37 (3s, CO),
186.36 (s, COMe), 126.4 (s, CCH@CH2), 114.9 (s,
CH@CH2), 110.8 (s, CH@CH2), 75.4 (s, OCH2Me),
53.4 (s, COMe), 15.3 (s, OCH2Me).
2.4.2.
Synthesis
of
(CO)4Re(j2-OC(OMe)C-
2.3.9. Competition reaction of (CO)4Re(g2-C(Me)-
C(CO2Me)C(OEt)) (1a) with 1:1 PhCBCH and
PhCBCPh
(CH@CEt2)C(OEt)) (3b) from (CO)4Re(g2-C(CH-
Et2)C(CO2Me)C(OEt)) (1d) in CD3CN
A solution of 1d (0.051 g, 0.10 mmol) in 0.5 ml of
A solution of 1a (0.050 g, 0.11 mmol) in 10 ml of
toluene at room temperature was treated with both
PhCBCH (0.014 ml, 0.013 g, 1 equivalent) and
PhCBCPh (0.020 g, 1 equivalent). The mixture was then
heated at reflux temperature for 4 h. Solvent was re-
moved under reduced pressure, and the residue was
extracted with 10-ml portions of hexane. Examination
CD3CN in a pressure NMR tube was heated at 78–80 °C,
with the reaction being monitored by H NMR spec-
1
troscopy. After 5 days, the reaction was essentially
complete. The solvent was evaporated from the reaction
mixture, the residue was extracted with 0.5 ml of
CH2Cl2, and the extract was layered with hexane.
Evaporation of hexane afforded a yellow oil. The oil
crystallized on dissolution in hexane and cooling at 0 °C
for a few hours. The isolated yield of (CO)4Re(j2-
OC(OMe)C(CH@CEt2)C(OEt)) (3b) was 0.028 g (55%).
IR (hexane): m(CO) 2018 (m), 1938 (s), 1899 (s) cmꢀ1. 1H
NMR (CD3CN): d 5.34 (br s, 1H, @CH), 4.35 (q,
3J ¼ 7:1 Hz, 2H, OCH2Me), 3.78 (s, 3H, OMe), 2.08 (qd,
3J ¼ 7:5 Hz, 4J ¼ 1:34 Hz, 2H, @CCH2Me), 1.92 (q,
1
of the extracts by H NMR spectroscopy showed the
exclusive formation of the phenylacetylene-derived
product,
(2a).
(g5-C5(Me)(CO2Me)(OEt)(Ph)H)Re(CO)3
2.3.10. Competition reaction of (CO)4Re(g2-C(Me)-
C(CO2Me)C(OEt)) (1a) with 1:1 PhCBCPh and
MeO2CCBCCO2Me
This reaction was conducted similarly to that in
Section 2.3.9 and utilized 1a (0.050 g, 0.11 mmol),
PhCBCPh (0.020 g, 1 equivalent), and MeO2CCBC-
CO2Me (0.014 ml, 0.016 g, 1 equivalent) in 10 ml of
3
3J ¼ 7:6 Hz, 2H, @CCH2Me), 1.32 (t, J ¼ 7:1 Hz, 3H,
OCH2Me), 1.02 (t, 3J ¼ 7:5 Hz, 3H, @CCH2Me), 0.92 (t,
3J ¼ 7:5 Hz, 3H, @CCH2Me). 13C NMR (CD3CN): d
242.2 (s, ReCOEt), 199.4, 197.4, 194.7 (3 s, CO), 188.3 (s,
COMe), 146.0 (s, CCH@CEt2), 116.1 (d, CH@CEt2),
114.5 (s, @CEt2), 74.4 (t, OCH2Me), 53.7 (q, OMe), 29.0,
25.4 (2t, @CCH2Me), 16.3 (q, OCH2Me), 13.2, 12.5 (2q,
@CCH2Me). MS (EI): m=z 510 (Mþ), 482 (Mþ–CO).
Anal. Found: C, 37.63; H, 3.80%. Calc. for C16H19O7Re:
C, 37.72; H, 3.76%.
toluene.
Only
(g5-C5(Me)(CO2Me)(OEt)(CO2Me)
(CO2Me))Re(CO)3 (2f) was observed by 1H NMR
spectroscopy.
2.4. Rearrangement reactions of (CO)4Re(g2-
C(R)C(CO2Me)C(OEt)) (R ¼ Me (1a), CHEt2 (1d))
in nitriles and pyridine
2.4.3. Synthesis of (CO)4Re(j2-OC(OMe)C(CH@
CEt2)C(OEt)) (3b) from (CO)4Re(g2-C(CHEt2)C-
(CO2Me)C(OEt)) (1d) in other nitriles
2.4.1.
Synthesis
of
(CO)4Re(j2-OC(OMe)C-
(CH@CH2)C(OEt)) (3a) from (CO)4Re(g2-C(Me)C-
(CO2Me)C(OEt)) (1a) in MeCN
Solutions of 1d (0.020 g, 0.039 mmol) in 0.5 ml of
EtCN, PhCN, or t-BuCN in a pressure NMR tube were
heated at 78–80 °C for 5 days. In each case, the mixture
was evaporated to dryness, and the residue was extracted
with hexane. The extract was filtered and freed of the
solvent under reduced pressure. 1H NMR spectra of the
residue showed presence of (CO)4Re(j2-OC(O-
Me)C(CH@CEt2)C(OEt)) (3b) and some nitrile for the
reactions of 1d in EtCN and PhCN. For the reaction in t-
BuCN, more than 60% unreacted 1d was observed as well.
A solution of 1a (0.105 g, 0.232 mmol) in 10 ml of
MeCN was heated at reflux temperature for 2 h, with the
reaction being monitored by 1H NMR spectroscopy.
The solvent was removed under reduced pressure, and
the residue was extracted with 10-ml portions of hexane.
A green oil was isolated upon removal of hexane from
the extracts. Yield: 0.074 g (70%). The proposed struc-
ture of (CO)4Re(j2-OC(OMe)C(CH@CH2)C(OEt)) (3a)
1
is based on H and 13C{1H} NMR spectroscopy. The
product was insufficiently stable for chemical analysis.
IR (hexane): m(CO) 2092 (w), 1998 (s), 1947 (s), 1726 (w)
2.4.4. Synthesis of (CO)3(py)Re(j2-OC(OMe)C-
(CH@CEt2)C(OEt)) (4) from (CO)4Re(g2-C(CH-
Et2)C(CO2Me)C(OEt)) (1d) and pyridine
A solution of 1d (0.020 g, 0.039 mmol) in 0.5 ml (ca. 6
mmol) of pyridine in a pressure NMR tube was heated
1
3
cmꢀ1. H NMR (CDCl3): d 6.43 (dd, Jcis ¼ 12:1 Hz,
3Jtrans ¼ 18:0 Hz, 1H, CH@CH2), 5.58 (dd, 2J ¼ 2:67
3
Hz, Jtrans ¼ 18:0 Hz, 1H, CH@CH2), 4.95 (dd,

V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
2017
at 78–80 °C for 2 days. The mixture was concentrated to
an oil and extracted by slow diffusion into 5 ml of
hexane. The yellowish green hexane solution was fil-
tered, the solvent was removed under reduced pressure,
and the residue was dried under vacuum to afford
(CO)3(py)Re(j2-OC(OMe)C(CH@CEt2)C(OEt)) (4) as
a green solid in 69% yield (0.015 g). IR (hexane): m(CO)
2014 (m), 1928 (s), 1898 (m) cmꢀ1. 1H NMR (CDCl3): d
8.7–7.3 (m, 5H, py), 5.37 (br s, 1 H, @CH), 4.54 (m, 2H,
2.5.2. Synthesis of (CO)4Re(j2-OC(OMe)C(C-
(Me)@C(CN)2)C(OEt)) (5b) from (CO)4Re(g2-
C(Me)C(CO2Me)C(OEt)) (1a) and Me2S@C(CN)2
A solution of 1a (0.231 g, 0.510 mmol) and 1 equiv-
alent of Me2S@C(CN)2 (0.063 g) in 10 ml of MeCN was
1
treated for 6 h as described in Section 2.5.1. The H
NMR spectrum of the oil residue from evaporation of
the initial hexane extracts indicated a mixture of three
products. The major one was obtained by further ex-
traction of this mixture using 2 ml of THF and a layer of
hexane. The product (CO)4Re(j2-OC(OMe)C(C
(Me)@C(CN)2)C(OEt)) (5b) was isolated from the hex-
ane layer by evaporation of the solvent. The yield was
0.063 g (24%). IR (CH2Cl2): m(CO) 2102 (w), 2067 (s),
3
OCH2Me), 3.80 (s, 3H, OMe), 2.07 (qd, J ¼ 7:5 Hz,
3
2H, @CCH2Me), 1.68 (q, J ¼ 7:6 Hz, 2H, @CCH2Me,
3
3
1.43 (t, J ¼ 7:1 Hz, 3H, OCH2Me), 1.02 (t, J ¼ 7:5
Hz, 3H, @CCH2Me), 0.80 (t, 3J ¼ 7:5 Hz, 3H,
@CCH2Me). 13C NMR (CDCl3): d 247.4 (s, ReCOEt),
200.9, 198.6, 194.7 (3s, CO), 187.4 (s, COMe), 153.7 (d,
py), 145.8 (s, CCH@CEt2), 144.3 (d, CH@CEt2), 137.7,
125.4 (2d, py), 114.0 (s, @CEt2), 73.8 (t, OCH2Me), 53.2
(q, OMe), 28.3, 24.7 (2t, @CCH2Me), 15.8 (q,
OCH2Me), 12.8, 12.1 (2q, @CCH2Me). MS (EI): m=z
561 (Mþ), 533 (Mþ–CO), 504 (Mþ–CO–Et), 476 (Mþ–
2CO–Et). Anal. Found: C, 42.87; H, 4.15%. Calc. for
C20H24NO6Re: C, 42.85; H, 4.31%.
1
2004 (s), 1972 (m), 1943 (m), 1723 (w) cmꢀ1. H NMR
(CDCl3): d 4.46 (q, 3J ¼ 7:1 Hz, 2H, OCH2Me), 3.91 (s,
3H, CO2Me), 2.32 (s, 3 H, @CMe), 1.48 (t, 3J ¼ 7:1 Hz,
3H, OCH2Me). 13C NMR (CDCl3): d 239.8 (s, Re-
COEt), 194.1, 190.3, 189.7 (3s, CO), 185.5 (s, COMe),
114.3 (s, @C(CN)2), 113.3, 112.3 (2 s, CN), 87.0 (s,
C(Me)@C), 76.8 (t, OCH2Me), 54.1 (q, COMe), 23.2 (q,
@CMe), 15.2 (q, OCH2Me). MS (EI): m=z 518 (Mþ),
490 (Mþ–CO), 462 (Mþ–2CO), 434 (Mþ–3CO), 406
(Mþ–4CO).
2.5. Reactions of (CO)4Re(g2-C(Me)C(CO2Me)C-
(OEt)) (1a) with sulfonium ylides
2.5.1. Synthesis of (CO)4Re(j2-OC(OMe)C(C-
(Me)@CHC(O)Ph)C(OEt)) (5a) from (CO)4Re(g2-
C(Me)C(CO2Me)C(OEt)) (1a) and Me2S@CH-
C(O)Ph
3. Results and discussion
3.1. Formation of substituted g5-cyclopentadienylrhenium
tricarbonyl complexes from (CO)4Re(g2-C(R)C-
(CO2Me)C(X)) (1) and alkynes
A solution of 1a (0.123 g, 0.270 mmol) and 1 equiv-
alent of Me2S@CHC(O)Ph (0.049 g, 0.27 mmol) in
12 ml of MeCN was heated at reflux temperature.
Within 15 min, the color of the solution turned orange,
and after 30 min complete conversion to the product
was observed by IR spectroscopy. Acetonitrile was
removed under reduced pressure, and the residue was
extracted with 10-ml portions of hexane. The extracts
were filtered, and the filtrate was evaporated to leave
Reactions of 1 with 1 equivalent of alkyne in toluene
at reflux temperature for 2–5 h were found to proceed as
illustrated in Scheme 1. The alkynes employed include
both electron-rich (e.g., MeCBCMe) and electron-defi-
cient (e.g., MeO2CCBCCO2Me), symmetrical (e.g.,
PhCBCPh) and unsymmetrical (e.g., PhCBCH,
PhCBCMe), as well as a pendant alkynyl group on the
rhenacyclobutadiene ring (O(CH2)3CBCH). After
workup, tetra- and pentasubstituted g5-cyclopentadie-
nylrhenium complexes 2 were obtained as yellow or
green oils or solids in 56–90% isolated yields. Most
losses were sustained on purification by extraction and
chromatography. Thermal reactions were also con-
ducted, with similar results, in a sealed tube at 110–
120 °C; this procedure is particularly applicable to the
more volatile alkynes such as MeCBCMe. Synthesis of 2
from 1 and alkyne was also effected at ambient tem-
perature under photochemical conditions or by use of
PdO for abstraction of CO from 1 [6]. Irradiation of 1a
and MeO2CCBCCO2Me in hexane for 1 h afforded a
large amount of decomposition material as well as some
(g5-C5(Me)(CO2Me)(OEt)(CO2Me)(CO2Me))Re(CO)3
(2f); however, the method has no synthetic advantage
over the thermal one. Corresponding reaction of 1a with
a
yellow oil of (CO)4Re(j2-OC(OMe)C(C(Me)@
CHC(O)Ph) C(OEt)) (5a) in 49% yield (0.075 g). The
product undergoes slow decomposition even on stor-
age under argon. IR (hexane): m(CO) 2096 (w), 2001 (s),
1
1996 (s), 1941 (m), 1665 (w) cmꢀ1. H NMR (CDCl3):
4
d 7.8–7.4 (m, 5H, Ph), 6.59 (q, J ꢁ 1 Hz, 1H, @CH),
4.20 (q, 3J ¼ 7:1 Hz, 2H, OCH2Me), 3.72 (s, 3 H,
COMe), 2.05 (d, 4J ꢁ 1 Hz, 3H, @CMe), 1.29 (t,
3J ¼ 7:1 Hz, 3H, OCH2Me). (nOe: irradiation of the
signal at d 2.05 resulted in a 4% enhancement of the
signal at d 6.59). 13C NMR (CDCl3): d 214.7 (s, Re-
COEt), 191.9, 191.7, 190.7 (3s, CO), 186.5, 185.1 (2s,
C(O)Ph, COMe), 147.4 (s, CC(Me)@CH), 138.9 (s, ipso
C of Ph), 132.1, 128.25, 128.17 (3d, other C of Ph), 124.3
(d, C(Me)@CH), 117.4 (s, C(Me)@CH), 74.7 (t,
OCH2Me), 53.4 (q, COMe), 25.0 (q, @CMe), 15.4 (q,
OCH2Me).

2018
V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
spectroscopic data. Two regioisomers are expected from
[3 + 2] cycloaddition of an unsymmetrical alkyne to the
g2-C(R)C(CO2Me)C(OEt) ligand of 1.
Complexes 2a–2j were characterized by a combina-
tion of IR and NMR spectroscopy, mass spectrometry,
and elemental analysis. The IR spectra feature two
metal carbonyl m(CO) bands, generally at 2031–2016 (m)
and 1978–1945 (s) cmꢀ1, as reported for other ring-
substituted derivatives of CpRe(CO)3 [7,8]. In addition,
a weaker m(CO) band is observed at 1745–1720 cmꢀ1
,
and is attributed to the CO2Me substituent(s) on the
ring. For complex 2j, four metal carbonyl m(CO) ab-
sorptions are noted, probably owing to the presence of
two conformers. Conformational isomerism has been
implicated by IR spectra for other g5-cyclopentadie-
nylmetal carbonyl complexes [9].
1
The H NMR spectra are in accord with the struc-
tures assigned to 2. Thus, the g5-cyclopentadienyl CH of
2a, 2g, 2h, and 2j resonates at d 5.62–5.01, in agreement
with the literature reports on related compounds
[7,8,10]. In the complexes containing more than one Me
group as CMe or CO2Me, each Me group gives rise to a
separate resonance, as expected for these structures. All
of the 13C NMR spectra show five resonances for their
five inequivalent g5-cyclopentadienyl carbon atoms;
they occur in the range d 140–75, depending on the
substituent. Accordingly, the COR or CNEt2 carbon
resonates at the lowest field (d 140–123), followed by the
CPh, CCO2Me, CMe (d 106–75), and CH (d 79–78),
again in agreement with the literature [8–10]. However,
in some cases, unambiguous assignment is not possible
owing to overlap of the chemical shift ranges. For the
CH ring carbon, 13C DEPT NMR experiments provide
a definitive signal attribution. Like the ring carbons, all
of the CMe, CO2Me, and CO2Me carbons display sep-
arate resonances for every appropriate complex. With
the exception of 2j, all complexes 2 show one 13C NMR
signal of CO at d 194.9–192.1 to indicate that ring ro-
tation is rapid on the NMR time scale. For 2j, two
singlet CO resonances are observed, again suggesting
presence of rotational isomers.
A limited study was carried out on relative reactivity
of 1a toward alkynes by competition reactions with
mixtures of two acetylenes as described in Sections 2.3.9
and 2.3.10 (Scheme 2). These experiments showed that
when PhCBCH and PhCBCPh were used together, only
2a was observed by 1H NMR spectroscopy. With
MeO2CCBCCO2Me and PhCBCPh, 2f was the sole
detected product. Thus, each of PhCBCH and
MeO2CCBCCO2Me reacts faster than PhCBCPh. Ste-
ric considerations seem to be important assuming that
insertion of alkyne into Re@C bond represents the dis-
criminating step in the reaction. The electrophilic nature
of MeO2CCBCCO2Me also appears to play a role, al-
though steric factors control the reactivity order
PhCBCH > PhCBCPh.
Scheme 1.
PhCBCPh proceeded cleanly but slowly, and after 12 h
only 60% of 1a was converted to (g5-C5(Me)(CO2Me)
(OEt)(Ph)(Ph))Re(CO)3 (2d).
Complexes 1 and each of the symmetrical alkynes
PhCBCPh, MeCBCMe, and MeO2CCBCCO2Me af-
forded only one product 2, as expected in such [3 + 2]
cycloadditions without rearrangement of the ring car-
bon atoms. H and 13C NMR spectra showed that 1a
1
and the unsymmetrical alkyne PhCBCH also gave only
one product 2 (cf. Section 2.3.1), which was assigned the
isomeric structure (g5-C5(Me)(CO2Me)(OEt)(Ph)H)Re
1
(CO)3 (2a) from a H NMR nOe experiment. Irradia-
tion of the CH signal at d 5.29 enhanced the intensity of
the CMe signal at d 2.49 to show proximity of H and Me
on the ring. Similarly to the reaction of 1a with
PhCBCH, thermolysis of 1b, containing pendant alky-
nyl group O(CH2)3CBCH, afforded also a single
product, a g5-cyclopentadienyl-dihydropyran fused-
ring complex, (g5-C5(Me)(CO2Me)(O(CH2)3)H)Re(CO)3
(2j). In contrast, reactions of 1a with PhCBCMe and of
1e with PhCBCH gave mixtures of two products each –
(g5-C5(Me)(CO2Me)(OEt)(Ph)(Me))Re(CO)3 (2b)/(g5-C5
(Me)(CO2Me)(OEt)(Me)(Ph))Re(CO)3 (2c) and (g5-
C5(Ph)(CO2Me)(OEt)(Ph)H)Re(CO)3 (2g)/(g5-C5(Ph)
(CO2Me)(OEt)(H)(Ph))Re(CO)3 (2h) – in 3:1 and 2:1
respective ratios based on the intensities of the 1H NMR
signals in their spectra. However, it was not possible to
assign structure to the major and minor isomers from

V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
2019
(i) replacement of CO with alkyne in 1 to generate in-
termediate I,
(ii) insertion of coordinated alkyne into Re@C bond to
give a rhenabenzene complex, intermediate II, and
(iii) extrusion of Re from the rhenabenzene ring of II
and coordination to resultant cyclopentadienyl li-
gand to afford 2.
Step 1 requires that the reactions be conducted at
elevated temperatures such as reflux temperature of
toluene for 2–5 h to reach completion. Less stringent
conditions are not effective; for example, use of THF at
reflux (66 °C) afforded no reaction of 1a with
MeO2CCBCCO2Me, and use of boiling hexane (69 °C)
with the same reactants gave only partial conversion to
2f in 4 h. Reversible loss of CO followed by coordina-
tion of alkyne is also the rate determining step in an-
nulation reactions of (CO)5Cr(carbene) complexes with
alkynes [13]. Under the high-temperature conditions
employed, no reaction intermediate could be observed
with 1a and alkynes. To possibly detect such species,
reactions were carried out at ambient temperature in the
presence of PdO, an effective reagent for abstraction of
CO from metal carbonyls [6]. When a suspension of
PdO in a MeCN solution of 1a and PhCBCH was
stirred for 2 days, complete conversion to 2a was
achieved. However, no reaction intermediates were de-
tected. Significantly, as in the thermal reaction, only one
regioisomer, 2a, was obtained. Use of 1e with PhCBCH
and PdO under similar conditions resulted in the for-
mation of a mixture of 2g and 2h, again as in the reac-
tion at elevated temperature. These results support the
proposal that loss of CO from 1 is the initial step in the
conversion of 1 to 2 by alkynes.
Scheme 2.
We now turn to mechanistic considerations of the
reactions presented in Scheme 1. A pathway consistent
with the formation of complexes 2 and with related
chemistry, including reactions of other metallacyclo-
butadienes with alkynes [10b,11,12], is set out in Scheme
3. It represents an adaptation of the mechanism pro-
posed in similar studies and consists of 3 steps:
Coordination of alkyne to Re leads to its insertion
into one of the Re@C bonds to give a rhenabenzene
intermediate II (step 2). Since the report of an osma-
benzene complex by Roper and co-workers in 1982 [14],
a number of stable metallabenzenes have been prepared
and characterized [15]. Rhenabenzene carbonyl com-
plexes have been proposed as intermediates in several
investigations [8,16], including those concerned with
synthesis of g5-CpzRe(CO)3 (Cpz ¼ multisubstituted
Cp) from (CO)4Re(g2-C(Ph)C(Ph)C(Ph)) and alkynes
[10] and from Re(CO)4(PPh3)Br and 1,4-dilithio-1,4-di-
phenyl-1,3-butadiene [8], but were not isolated, pre-
sumably owing to their relative instability. Schrock-type
metal alkylidynes and metallacyclobutadienes react with
alkynes also to yield g5-cyclopentadienylmetal com-
plexes [11,12,17], and intermediacy of metallabenzenes
has been proposed in some cases. However, other in-
termediates are possible as well [11,18].
There is an additional point that we want to address.
It concerns structure of intermediate I and regiochem-
istry of its conversion to II. Since mutually trans CO’s
are substitutionally more labile than those trans to
g2-C(R)C(CO2Me)C(X) [19], we propose that the
Scheme 3.

2020
V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
entering alkyne is positioned cis to the bidentate ligand in
I (overall fac-tricarbonyl geometry). When coordinated in
this position, its C–CBC–C backbone can assume an
orientation that either eclipses one of the OC–Re–C(R
or X) vectors (as drawn in Scheme 3) or staggers them.
Although for a d4 (or d<4) octahedral complex, eclipsed
species may promote this conversion. Scrambling of the
ring carbon atoms in going from metallacyclobutadiene
to g5-cyclopentadienyl product, reported for reactions of
Schrock-type complexes of tungsten [11], in all proba-
bility does not occur here. This is because the number of
1
products 2 observed by H and 13C NMR spectroscopy
alkyne orientation is favored because a vacant t2g
d
for each reaction never exceeds that predicted for rear-
rangement-free [3 + 2] cycloaddition of alkyne to the g2-
C(R)C(CO2Me)C(X) ligand of 1.
orbital on metal participates in bonding [20], in inter-
mediate I of d6 configuration no such bonding interac-
tion occurs, and electronic stabilization of any possible
alkyne orientation appears to be insignificant. Never-
theless, alkyne orientation for further reaction is im-
portant to the understanding of observed regiochemistry
in the formation of 2 (and presumably II) from I. An-
swers to the questions of which carbon atom of
R0CBCR00 is directed toward g2-C(R)C(CO2Me)C(X)
during the insertion and which Re@C bond interacts
with the alkyne may provide clues as to why certain
regioisomers arise from I and an unsymmetrical alkyne.
Of the reactions examined here, three are relevant in this
context, viz., 1a with PhCBCMe to afford 2a, 1a with
PhCBCMe to give 2b and 2c, and 1e with PhCBCH to
yield 2g and 2h. The conversion of 1b to 2j is a special
case, since ring constraints associated with the forma-
tion of a bicyclic system dictate regiochemical course of
the reaction.
The foregoing results may be rationalized by one or
both of the following factors: increased steric crowding
on going from PhCBCH to PhCBCMe and to
PhCBCPh, and a preference for insertion into Re@C(R)
rather than Re@C(OEt). The exclusive formation of 2a
from 1a suggests that the unsubstituted end of PhCBCH
interacts with the organic ligand of I for steric reasons
and that it forms a CH–C(Me) bond during insertion
into Re@C(Me). The observation that PhCBCH reacts
faster than PhCBCPh supports the importance of steric
factors. The formation of both 2b and 2c from 1a and
PhCBCMe may be attributed to a greater steric repul-
sion of PhCBCMe than of PhCB CH with Re@C(Me).
This could lead to insertion of PhCBCMe into Re-
@C(OEt) as well as into Re@C(Me). A similar ratio-
nalization may apply to the formation of both 2g and 2h
from 1e and PhCBCH. It is relevant that annulation
reactions of (CO)5Cr(carbene) complexes with unsym-
metrical alkynes proceed by ineraction of the smaller
BCR fragment of the latter with the carbene carbon
[13]. Also, insertion of oxygen atom or the NH group
into Re@C bond of 1 involves either Re@C(Me) or
Re@C(OEt) depending on the nature of reactant and/or
reaction conditions; however, insertion into Re@C(Me)
is more common [1,19,21].
The reactions of 1 with alkynes reported herein, to-
gether with the preparation of 1 described elsewhere
[1,19], represent a new synthetic approach to a variety of
ring-substituted g5-cyclopentadienylrhenium carbonyl
complexes, 2. Substituted g5-cyclopentadienylmetal
complexes have been the subject of considerable interest
[22], especially in connection with their application in
alkene polymerization reactions. The scope of the
chemistry described in our studies, including extensions
to other transition metals, still needs to be elaborated.
3.2. Rearrangement reactions of (CO)4Re(g2-C(R)C-
(CO2Me)C(OEt)) (1) in nitriles and pyridine
Fischer carbene complexes are known to undergo
insertion of RCBN into the M@C bond [23]. Since
complexes 1 react with alkynes to afford CpzRe(CO)3
(2), similar reactions with nitriles would be expected
to result in substituted heterocyclic compounds of
rhenium.
We find that acetonitrile solutions of 1a maintain
their integrity on storage at ambient temperature.
However, heating at reflux temperature for 2 h affords
(CO)4Re(j2-OC(OMe)C(CH@CH2)C(OEt)) (3a) as a
moderately stable oil in 70% yield (Scheme 4). Use of
deuteriated acetonitrile leads to 3a that shows no in-
2
corporation of deuterium by H NMR spectroscopy.
Little can be said about step 3 in Scheme 3. Very likely
conversion of II to 2 occurs rapidly, since no rhenaben-
zene complex was detected when reaction of 1a or 1b
with PhCBCH was conducted at room temperature in
the presence of PdO. The fact that II is a 16-electron
Scheme 4.

V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
2021
Complex 3a was characterized by H and 13C NMR
spectroscopy to possess a rhenafuran ring structure. It
may be considered as derived from 1a by cleavage of the
Re@C(Me) bond with transfer of one Me hydrogen to
the Re@C carbon followed by formation of a 5-mem-
bered ring via coordination of the terminal C(O)OMe
oxygen to rhenium. The IR spectrum of 3a shows three
metal carbonyl m(CO) bands at 2092 (w), 1998 (s), and
1947 (s) cmꢀ1; these bands are very similar in position
and relative intensity to those observed for III and IV,
derived from oxygen atom insertion into Re@C bond of
1a [19]. The absence of the methyl group as Re@C(Me)
and the presence of a vinyl group CH@CH2 in its place
are demonstrated by the 1H NMR spectrum (cf. Section
2.4.1). In support of the assigned rhenafuran structure,
the ester carbonyl CO2Me 13C resonance occurs at d
186.36 and replaces the corresponding signal of 1a at d
159.4 [19]. The new position is identical with that of the
O-coordinated CO2Et in IV. Furthermore, the signal at
d 234.3, assigned to Re@C(OEt), comes close to that at d
243.7 for the corresponding carbon nucleus of 1a.
the spectroscopic data (cf. Section 2.4.2) is also in good
agreement with the proposed structure.
1
Behavior of 1d toward pyridine was investigated,
since the latter is known to displace carbene ligand from
its complexes [24,25]; for example, reaction between
(CO)5Cr@C(OMe)(CHRR0) and pyridine produces
(CO)5Cr(py) and (MeO)CH@CRR0, where shift of hy-
drogen occurred to the adjacent carbon atom [24].
Heating a solution of 1d in pyridine at 78–80 °C for
2 days afforded after workup a green solid, (CO)3-
(py)Re(j2-OC(OMe)C(CH@CEt2)C(OEt)) (4), in 69%
yield (cf. Scheme 4). The IR spectrum of 4 in the metal
carbonyl m(CO) region features three medium- or strong-
intensity bands between 2014 and 1898 cmꢀ1, consistent
with such a six-coordinate fac-tricarbonyl structure [26].
Its 1H and 13C NMR spectra, presented in Section 2.4.4,
are very similar to those of 3b, except for the presence of
additional signals assigned to coordinated pyridine. The
structure receives further support from the observed
parent molecular ion and the fragmentation pattern in
the mass spectrum.
A proposed mechanism of formation of 4 from 1d
and pyridine is set out in Scheme 5. The initial role of
pyridine is to abstract the methine hydrogen of Re-
@C(CHEt2) as Hþ to form pyHþ and the conjugate base
of 1d, V. The latter then undergoes protonation by
pyHþ at rhenium to afford a metal hydrido intermediate,
Since 3a decomposes on storage, we turned to the
corresponding reaction of 1d to seek a more stable
product. A similar rearrangement of 1d would lead to
the trisubstituted double bond CCH@CEt2 instead of
CCH@CH2 in 3a, and therefore confer additional sta-
bility on the resulting rhenafuran complex. The reaction
of 1d in MeCN solution is cleaner but slower than that
of 1a. When carried out in CD3CN at 78–80 °C, it was
essentially complete in 5 days (Scheme 4). Again, the
product
(CO)4Re(j2-OC(OMe)C(CH@CEt2)C(OEt))
(3b) contained no deuterium from the nitrile. Use of
EtCN or PhCN in place of MeCN at the same tem-
perature resulted in a greater than 90% yield of 3b in 5
days. In t-BuCN under similar conditions, 40% 3b and
60% unreacted 1d were observed by 1H NMR spec-
troscopy. No reaction occurs of 1d in benzene in the
absence of RCN at comparable temperature.
1
The assigned structure of 3b is based on IR and H
and 13C NMR spectroscopic evidence, and its chemical
composition is supported by mass spectrometric and
elemental analysis. The structure is strictly analogous to
that of 3a, with the vinyl substituent on the rhenafuran
ring being, as expected, CH@CEt2. Two separate 1H
and 13C NMR signals are observed for the CH2 and Me
parts of each Et group. In the 13C NMR spectrum, the
signals of CO2Me at d 188.3 and of Re@C(OEt) at d
242.2 compare well with those noted for 3a. The rest of
Scheme 5.

2022
V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
VI. Reductive elimination of H and the C(@CEt2)-
C(CO2Me)C(OEt) end of the chelate converts VI to VII,
which, after rotation about the (EtO)C–C bond, gener-
ates a rhenafuran ring of 3b by coordination of the
OC(OMe) oxygen to rhenium. Substitution of a carbonyl
ligand by pyridine yields 4. Precedence exists in the lit-
erature for pyridine-promoted deprotonation of a car-
bene ligand and reprotonation at adjacent carbon atom
[24,25], presumably by intermediacy of a metal hydrido
complex. The step in Scheme 5 involving rotation about
the C–C bond is driven by the formation of a stable 5-
membered rhenafuran ring, a process proposed for a
similar ruthenium system [27].
The nitrile-promoted rearrangement of 1a and 1d to
3a and 3b, respectively, probably proceeds by a mech-
anism similar to that depicted in Scheme 5, but does not
involve replacement of CO with nitrile. A troublesome
step in such a pathway, however, is deprotonation of 1
with RCN, a very weak base compared to pyridine (pKa
of MeCNHþ ¼ )10.1 vs. pKa of pyHþ ¼ 5.2 [28]). Nev-
ertheless, involvement of RCN in the reaction must
occur, since 1d in benzene alone does not undergo re-
arrangement, and the reaction shows dependence on
steric bulk of RCN, with the rate increasing as a func-
Scheme 6.
more slowly than that with Me2S@CHC(O)Ph and re-
quired 6 h to reach completion under similar conditions.
Three products were detected by 1H NMR spectros-
copy, but only the major one, (CO)4Re(j2-OC(O-
Me)C(C(Me)@C(CN)2)C(OEt)) (5b), could be isolated
(24% yield) after extensive extraction of the crude re-
action mixture.
Complexes 5a and 5b were characterized by a com-
bination of IR and 1H and 13C NMR spectroscopic and
mass spectrometric techniques. Their H and 13C NMR
spectra show striking similarities to those of 3a, 3b, and
4 to implicate a rhenafuran structure in each case. For
example, 13C resonances of 5a and 5b occur at d 214.7
and 239.8 and at d 185.1 and 185.5 for Re@C(OEt) and
COMe, respectively, as expected [19]. Only one double
2
tion of R in the order t-Bu < Ph, Et < Me.
1
3.3. Reactions of (CO)4Re(g2-C(Me)C(CO2Me)C-
(OEt)) (1a) with sulfonium ylides
The acidity of the Me substituent on the rhenacy-
clobutadiene ring in 1a precludes addition of organoli-
thium or similar basic reagents [1]. Wittig reagents
probably would also be too basic to undergo addition
[29]; however, sulfur-stabilized carbanions (sulfonium
ylides), which possess lower basicity, present themselves
as suitable candidates for such a reaction. Cleavage of
the organic ligand by sulfonium ylides with no depro-
tonation has been reported to proceed under thermal or
photochemical conditions for chromium Fischer car-
bene complexes [30]. Accordingly, we extended our
studies on the chemistry of 1a to reactions with
Me2S@CHC(O)Ph [4] and Me2S@C(CN)2 [5].
Reaction of 1a with Me2S@CHC(O)Ph in acetonitrile
at reflux temperature was complete in 30 min, and after
workup resulted in the isolation of (CO)4Re(j2-OC(O-
Me)C(C(Me)@CHC(O)Ph)C(OEt)) (5a) as a yellow oil
in 49% yield (Scheme 6). The product undergoes slow
decomposition even if kept under argon. The corre-
sponding reaction of 1a with Me2S@C(CN)2 proceeded
2
As an alternative mechanism, it was suggested by a reviewer that
the CHEt2 proton could possibly be transferred to the adjacent carbon
via an agostic interaction with Re. The resulting alkene group would
most likely be g2 bound to the Re center, but would be easily displaced
by either pyridine or nitrile. The rest of the mechanism is similar to
that in Scheme 5.
Scheme 7.

V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
2023
bond geometry was observed for C(Me)@CHC(O)Ph in
5a, and the assigned cis disposition of Me and H is
supported by a H NMR nOe experiment (cf. Section
2.5.1).
latter reactions 1a and Me2S@CR0R00 furnish analogous
(CO)4Re(j2-OC(OMe)C(C(Me)@CR0R00)C(OEt)) (5).
1
A proposed mechanism for the reactions of 1a with
Me2S@CHC(O)Ph and Me2S@C(CN)2 (Me2S@CRR0)
is presented in Scheme 7. It consists of nucleophilic
addition of Me2S@CRR0 to the Re@C(Me) carbon,
formation of intermediate VIII by dissociation of the
Re–C bond and release of Me2S, and ring closure to give
the rhenafuran structure in 5. Intermediate VIII is
strictly analogous to VII in Scheme 5. Likewise, the ring
closure step occurs as depicted in Scheme 5. An alter-
native to this pathway involves cyclopropanation reac-
tion between the ReC(Me)@C(CO2Me) double bond of
1a and Me2S@CRR0. Sulfur-stabilized carbanions are
known to undergo addition to a,b-unsaturated carbonyl
compounds to afford cyclopropane products [31]. If one
considers 1a as an a,b-unsaturated ester equivalent, then
addition of Me2S@CRR0 might yield a highly strained
cyclopropane, IX, which is likely to rearrange to a rhe-
nafuran product.
Acknowledgements
This research was supported in part by the National
Science Foundation and The Ohio State University.
References
[1] V. Plantevin, A. Wojcicki, J. Organomet. Chem., Xref
doi:10.1016/j.jorganchem.2004.03.026.
:
[2] R.R. Willis, M. Calligaris, P. Faleschini, J.C. Gallucci, A.
Wojcicki, J. Organomet. Chem. 193–194 (2000) 465.
[3] R.T. Dunsizer, V.M. Marsico, V. Plantevin, A. Wojcicki, Inorg.
Chim. Acta 342 (2003) 279.
[4] K.W. Ratts, A.N. Yao, J. Org. Chem. 31 (1966) 1689.
[5] W.J. Middleton, E.L. Buhle, J.G. McNally Jr., M. Zanger, J. Org.
Chem. 30 (1965) 2384.
[6] M.O. Albers, N.J. Coville, Coord. Chem. Rev. 53 (1984) 227.
[7] (a) S.S. Jones, M.D. Rausch, T.E. Bitterwolf, J. Organomet.
Chem 396 (1990) 279;
(b) P. Singh, M.D. Rausch, T.E. Bitterwolf, J. Organomet. Chem.
352 (1988) 273;
(c) R.B. King, M.B. Bisnette, J. Organomet. Chem. 8 (1967) 287.
[8] R. Ferede, J.F. Hinton, W.A. Korfmacher, J.P. Freeman, N.T.
Allison, Organometallics 4 (1985) 614.
[9] (a) F.A. Cotton, T.J. Marks, J. Am. Chem. Soc. 91 (1969) 7523;
(b) A. Davison, W.C. Rode, Inorg. Chem. 6 (1967) 2124.
€
[10] (a) C. Lowe, V. Shklover, H. Berke, Organometallics 10 (1991)
3396;
(b) C. Lowe, V. Shklover, H.W. Bosch, H. Berke, Chem. Ber. 126
€
(1993) 1769.
[11] R.R. Schrock, S.F. Pedersen, M.R. Churchill, J.W. Ziller,
Organometallics 3 (1984) 1574.
[12] H. van der Heijden, A.W. Gal, P. Pasman, A.G. Orpen,
Organometallics 4 (1985) 1847.
4. Summary
€
[13] K.H. Dotz, P. Tomuschat, Chem. Soc. Rev. 28 (1999) 187.
In this paper we have reported additional chemical
transformations of Fischer rhenacyclobutadiene com-
plexes of the type (CO)4Re(g2-C(R)C(CO2Me)C(X))
(1). The new reactions, in a broad sense, fall into two
classes. The first class is comprised of reactions with
alkynes which lead to the formation of ring-substituted
[14] G.P. Elliott, W.R. Roper, J.M. Waters, J. Chem. Soc., Chem.
Commun. (1982) 811.
[15] J.R. Bleeke, Chem. Rev. 101 (2001) 1205.
[16] (a) J. Yang, W.M. Jones, J.K. Dixon, N.T. Allison, J. Am. Chem.
Soc. 117 (1995) 9776;
(b) C.A. Mike, R. Ferede, N.T. Allison, Organometallics 7 (1988)
1457;
g5-cyclopentadienylrhenium
tricarbonyl
products,
(c) R. Ferede, N.T. Allison, Organometallics 2 (1983) 463.
[17] S.F. Pedersen, R.R. Schrock, M.R. Churchill, H.J. Wasserman, J.
Am. Chem. Soc. 104 (1982) 6808.
CpzRe(CO)3 (2). A number of tetra- and pentasubsti-
tuted complexes were synthesized by this methodology
through use of various symmetrical and unsymmetrical
alkynes as well as a pendant alkynyl group on 1. A
second group of reactions features rearrangement with
expansion of the 4-membered rhenacyclobutadiene ring
of 1 to a 5-membered rhenafuran ring in product com-
plexes. This transformation is made possible by the
presence of a CO2Me group on C(2) of 1, and can be
effected by nitriles and pyridine on heating, or by use of
sulfonium ylides. In the former reactions, (CO)4Re(g2-
C(CHR2)C(CO2Me)C(OEt)) (R2@H2 (1a), Et2 (1d))
undergo conversion to (CO)3(L)Re(j2-OC(OMe)C
(CH@CR2)C(OEt)) (L ¼ CO (3), py (4)), whereas in the
[18] B.T. Donovan, R.P. Hughes, H.A. Trujillo, J. Am. Chem. Soc.
120 (1990) 7076.
[19] L.L. Padolik, J.C. Gallucci, A. Wojcicki, J. Am. Chem. Soc. 115
(1993) 9986.
[20] L. Ricard, R. Weiss, W.E. Newton, G.J.-J. Chen, J.W. McDon-
ald, J. Am. Chem. Soc. 100 (1978) 1318, and references therein..
[21] V. Plantevin, J.C. Gallucci, A. Wojcicki, Inorg. Chim. Acta 222
(1994) 199.
€
[22] (a) H.G. Alt, A. Koppl, Chem. Rev. 100 (2000) 1205;
(b) G.W. Coates, Chem. Rev. 100 (2000) 1223;
(c) L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 100
(2000) 1253;
€
(d) H. Butenschon, Chem. Rev. 100 (2000) 1527;
(e) M.L. Hays, T.P. Hanusa, Adv. Organomet. Chem. 40 (1996)
117;

2024
V. Plantevin, A. Wojcicki / Journal of Organometallic Chemistry 689 (2004) 2013–2024
[26] P.S. Braterman, Metal Carbonyl Spectra, Academic Press, New
York, 1975.
(f) C. Janiak, H. Schumann, Adv. Organomet. Chem. 33 (1991)
291;
(g) M.I. Bruce, A.H. White, Aust. J. Chem. 43 (1990) 949;
(h) D.W. Macomber, W.P. Hart, M.D. Rausch, Adv. Organomet.
Chem. 21 (1982) 1.
[27] M.I. Bruce, A. Catlow, M.G. Humphrey, G.A. Koutsantonis,
M.R. Snow, E.R.T. Tiekink, J. Organomet. Chem. 338 (1988) 59.
[28] A. Streitwieser, C.H. Heathcock, E.M. Kosower, Introduction to
Organic Chemistry, fourth ed., Macmillan, New York, 1992, pp.
314, 1108.
[23] (a) D.C. Yang, V. Dragisich, W.D. Wulff, J.C. Huffman, J. Am.
Chem. Soc. 110 (1988) 307;
(b) H. Fischer, S. Zeuner, J. Organomet. Chem. 327 (1987) 63;
[29] (a) C.P. Casey, T.J. Burkhardt, J. Am. Chem. Soc. 94 (1972) 6543;
(b) C.P. Casey, S.H. Bertz, T.J. Burkhardt, Tetrahedron Lett.
(1973) 1421.
€
(c) H. Fischer, R. Markl, Chem. Ber. 118 (1985) 3683;
(d) H. Fischer, J. Organomet. Chem. 197 (1980) 303.
[24] (a) E.O. Fischer, D. Plabst, Chem. Ber. 107 (1974) 3326;
[30] (a) B. Alcaide, G. Dominguez, J. Rodriguez-Lopez, M.A. Sierra,
Organometallics 11 (1992) 1979;
€
(b) E.O. Fischer, A. Maasbol, J. Organomet. Chem. 12 (1968)
P15.
(b) B. Alcaide, L. Casarrubios, G. Dominguez, M.A. Sierra, J.
Jimenez-Barbero, Organometallics 13 (1994) 2934.
[31] F.H. Greenberg, E.M. Schulman, J. Org. Chem. 58 (1993)
5853.
[25] (a) C.P. Casey, W.R. Brunsvold, Inorg. Chem. 16 (1977) 391;
(b) C.P. Casey, R.L. Anderson, J. Chem. Soc., Chem. Commun.
(1975) 895.