Iridium(III)-vinylidene chemistry: Conversion of an iridacyclopentadiene-chlorido complex and terminal alkynes to iridacyclopentadiene-vinyl complexes

Article abstract of DOI:10.1016/j.ica.2007.12.019

The reactions of [κ²(C¹,C⁴)-CR{double bond, long}CRCR{double bond, long}CR](PPh₃)₂Ir(Cl) (9, R = CO₂Me) with propargyl alcohol derivatives (2-propyn-1-ol, 2-methyl-3-butyn-2-ol, 1-ethynylcyclopentanol, and 1-ethynylcyclooctanol), in the presence of water leads to the formation of iridium(III)-vinyl complexes bearing the general structure [κ²(C¹,C⁴)-CR{double bond, long}CRCR{double bond, long}CR](PPh₃)₂Ir(CO)(κ¹-vinyl) where vinyl = -CH{double bond, long}CH₂, -(E)-CH{double bond, long}CHMe, -CH{double bond, long}C(CH₂)₄, or -CH{double bond, long}C(CH₂)₇. In these, the CO ligand was derived from the terminal carbon of the starting alkyne and the oxygen atom from water. Under anhydrous conditions, 9 undergoes reaction with 2-propyn-1-ol to give trimethyl 1,3-dihydro-3-oxo-4,5,6-isobenzofurantricarboxylate, the result of a cycloaromatization/transesterification involving the buta-1,3-dien-1,4-diyl ligand in 9 and 2-propyn-1-ol.

Full text of DOI:10.1016/j.ica.2007.12.019

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 3033–3041
www.elsevier.com/locate/ica
Iridium(III)–vinylidene chemistry: Conversion
of an iridacyclopentadiene-chlorido complex and terminal alkynes
to iridacyclopentadiene–vinyl complexes
a,
a,b,
a
*
Joseph M. O’Connor , Anna G. Wenzel *, Kristin Hiibner
a Department of Chemistry and Biochemistry (0358), University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0358, USA
b Joint Science Department, Claremont McKenna, Pitzer and Scripps Colleges, Claremont, CA 91711, USA
Received 31 October 2007; received in revised form 11 December 2007; accepted 15 December 2007
Available online 28 December 2007
This paper is dedicated to Professor Robert J. Angelici in recognition of his numerous important contributions to organometallic chemistry.
Abstract
The reactions of [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(Cl) (9, R = CO2Me) with propargyl alcohol derivatives (2-propyn-1-ol,
2-methyl-3-butyn-2-ol, 1-ethynylcyclopentanol, and 1-ethynylcyclooctanol), in the presence of water leads to the formation of irid-
ium(III)–vinyl complexes bearing the general structure [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(CO)(j1-vinyl) where vinyl = –CH@CH2, -
(E)-CH@CHMe, –CH@C(CH2)4, or –CH@C(CH2)7. In these, the CO ligand was derived from the terminal carbon of the starting
alkyne and the oxygen atom from water. Under anhydrous conditions, 9 undergoes reaction with 2-propyn-1-ol to give trimethyl
1,3-dihydro-3-oxo-4,5,6-isobenzofurantricarboxylate, the result of a cycloaromatization/transesterification involving the buta-1,3-dien-
1,4-diyl ligand in 9 and 2-propyn-1-ol.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Iridium(III)–vinylidene; Metallacyclopentadiene; Iridium–vinyl complexes; Iridacyclopentadiene; Iridium complexes; Propargyl alcohol; 2-
Propyn-1-ol; Oxygen-18 labeling; Cycloaromatization; Trimethyl 1,3-dihydro-3-oxo-4,5,6-isobenzofurantricarboxylate; Allenylidene ligand; Allenylidene
complex; Enolallenyl ligand; Allenol; Metallacycle
1. Introduction
ity patterns governing these increasingly important ligands
[1–4].
The transition metal-mediated conversion of terminal
alkynes to vinylidene (I) and allenylidene (II) ligands has
dramatically expanded the scope of alkyne chemistry in
recent years (Scheme 1) [1–4]. Interest in these readily avail-
able, strong pi-acceptor ligands stems in part from their
potential applications in synthesis, such as anti-Markovni-
kov addition reactions to alkynes [2]. To this effect, wide-
spread research efforts are currently being directed
toward the development and understanding of the reactiv-
Although vinylidene and allenylidene complexes have
been observed for many transition metals, most work in
this area has focused on the chemistry of the d6-metals
within the iron triad and the d8-metals of the cobalt triad
[3,4]. In this investigation, we selected to explore the higher
valent d6–iridium systems, as the vinylidene and allenylid-
ene ligands are anticipated to be more electrophilic than
d8 congeners and thereby potentially exhibit enhanced
reactivity patterns [5]. As early as 1973, indirect evidence
has existed to indicate that unobserved vinylidene interme-
diates may be generated from terminal alkynes at irid-
ium(III) metal centers. In that year, Clark and Manzer
demonstrated that the cationic iridium(III) solvate 1 could
undergo reaction with 3-butyn-1-ol to give carbene
*
Corresponding authors. Department of Chemistry and Biochemistry
(0358), University of California, San Diego, 9500 Gilman Drive, La Jolla,
CA 92093-0358, USA.
E-mail address: jmoconno@ucsd.edu (J.M. O’Connor).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.12.019

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J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
This paper reports the details of our work on the reac-
tions of the unsaturated iridium(III) metallacyclopentadi-
ene complex, [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(Cl)
(9, R = CO2Me) [9], with propargyl alcohols to afford
either [2 + 2 + 2]-cycloaromatization products or iridium–
carbon monoxide–vinyl complexes, depending upon the
reaction conditions.
Scheme 1.
complex 2 (Scheme 2) [6]. The authors proposed this trans-
formation to proceed via an iridium-stabilized carbonium
ion, the identity of which in today’s parlance would now
be described as the vinylidene complex 3. To our knowl-
edge, the only examples of stable, isolable iridium(III)–
vinylidene complexes are those reported by Paneque and
Carmona [4b]. In that work, hydridotris(3,5-dimethylpy-
razolyl)borate iridium (TpMe2Ir) vinylidene complexes,
such as 4, were generated from dinitrogen complex 5
and bis(trimethylsilyl)acetylene. The remarkable stability
observed for these complexes is presumably due to the elec-
tron–donor properties of both the TpMe2 ligand itself and
the trimethylsilyl (TMS) substituents on the vinylidene
ligand.
2. Results and discussion
The reactions of iridacyclopentadiene [j2(C1,C4)-CR@
CRCR@CR](PPh3)2Ir(Cl) (9, R = CO2Me) with alkynes
depends markedly on the nature of the alkyne substituents
(Scheme 3). For example, 9 undergoes reaction with the
internal alkyne dimethyl acetylenedicarboxylate to give
hexa(carbomethoxy)benzene 10, presumably via an g2-
alkyne intermediate such as 11 [9]. In contrast, the terminal
alkynes 3-butyn-1-ol and methyl propiolate undergo reac-
tion with 9 to give metallacycle–carbene complex 12 and
a-chlorovinyl complex 13, respectively [10,11]. A reason-
able mechanism for the formation of iridacycles 12 and
13 involves the formation of vinylidene intermediates 14
and 15, which are then trapped by nucleophilic attack at
the a-carbon of the vinylidene ligand.
Allenylidene complexes of iridium(I) are also relatively
well-established [7], but – once again – only two examples
of isolable iridium(III)–allenylidene complexes, (PiPr3)2-
t
(H)(Cl)2Ir[@C@C@C(Ph)(R)] (6, R = Ph, Bu), have been
reported to date. In these, complexes of general structure
6 were formed via the oxidative addition of HCl to the irid-
ium(I)–allenylidene complexes 7 (Scheme 2) [7b,8]. Nota-
bly, allenylidene 7 was prepared from the corresponding
propargyl alcohol derivatives and [(PiPr3)2IrCl(H)2] (8) in
the presence of light or catalytic amounts of acid.
An interesting aspect of the vinylidene reactions shown
in Scheme 3 is that halide migration to the vinylidene
ligand of 15 occurs readily; whereas, for intermediate 14
halide migration is not competitive with intramolecular
trapping of the vinylidene ligand by the pendant hydroxyl
Scheme 2.

J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
3035
Scheme 3.
group. Furthermore, the formation of the iridium(I)–
allenylidene complex 6 from propargyl alcohols and 8,
and the stability of the iridium(III) allenylidene complexes
6 and 7 with respect to halide migration suggested that irid-
ium(III)–allenylidene complexes generated directly from 9
and propargyl alcohols may lead to allenylidene ligand
insertion into the metallacycle ring [12,13]. We therefore
set out to investigate the reactivity of 9 toward propargyl
alcohols.
nances relative to those of an internal standard (p-bis(tri-
methylsilyl)benzene; Scheme 4). From this evidence, it
appears that, if vinylidene formation did occur, then it
was reversible – with the formation of 16 proceeding via
an g2-alkyne intermediate [14b]. By analogy to the reaction
of 9 with dimethyl acetylenedicarboxylate [9], the initial
product of cycloaromatization with 2-propyn-1-ol would
be 17, which then undergoes intramolecular transesterifica-
tion to 16.
The reaction of metallacycle 9 (25 mM) and 2-propyn-1-
ol (62 mM) in anhydrous methylene chloride-d2 was moni-
tored periodically by H NMR spectroscopy. After 48 h at
When the reaction of 9 with 2-propyn-1-ol was per-
formed under similar reaction conditions using wet methy-
lene chloride-d2, the unanticipated iridium–vinyl complex
[j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(CH@CH2)(CO) (18,
R = CO2Me) was produced, with no evidence for the
formation of 16 (Scheme 4). To investigate this further, a
small-scale reaction of 9 (32 mM) and 2-propyn-1-ol
1
room temperature, the quantitative formation of trimethyl
1,3-dihydro-3-oxo-4,5,6-isobenzofurantricarboxylate (16)
1
[14a] was observed by H NMR spectroscopic analysis of
the reaction mixture via integration of the product reso-
Scheme 4.

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J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
(164 mM) in CD2Cl2/H2O (3%) at room temperature was
monitored by H NMR spectroscopy. During the course
gen resonance was obscured by resonances in the phenyl
region of the spectrum between d7.27–7.65. The 13C{1H}
NMR spectrum (CD2Cl2) of 18 exhibited resonances
assigned to the four carbons bound directly to iridium at
175.8 (t, J = 8.4 Hz, IrCO), 162.1 (t, J = 6.87 Hz, IrC-
CO2Me), 152.5 (t, J = 11.83 Hz, IrCCO2Me), and 136.5
(t, J = 8.73 Hz, IrCH=) ppm, respectively. In addition,
the b-carbon of the vinyl ligand was tentatively assigned
to a broad singlet at 125.8 ppm. The assignments for the
ethenyl carbons were made on the basis of the coupling
constants and a comparison of the chemical shifts to those
for the ethenyl complex (g5-C5Me5)(PMe3)Ir(H)(CH@
CH2), which were observed at 142.5 (JPC = 17.5 Hz) and
118.7 ppm (JPC = 4.8 Hz) [15].
1
of reaction, an orange to pale-yellow color change was
observed and a new series of methyl-hydrogen resonances
at d 3.55, 3.43, 3.38, and 3.21 were observed to grow in
intensity with a concomitant decrease in the signals for 9.
After 48 h, 9 had quantitatively converted to 18, as deter-
mined by integration relative to an internal standard (1,4-
TMS2C6H4). When the reaction was performed on a larger
scale, complex 18 was isolated as a pale pink solid in 33%
yield. Table 1 lists the representative spectroscopic proper-
ties for 18 and its related vinyl complexes. In the 1H NMR
spectrum of 18 (CD2Cl2), the geminal vinyl-hydrogen reso-
nances were observed as doublets at d 5.84 (br d, J =
11.1 Hz) and 4.70 (br d, J = 19.1 Hz). Based on the magni-
tude of the coupling constants, the signal at d 4.70 was
assigned to the hydrogen cis to iridium. The a-vinyl-hydro-
The structure assigned to 18 is also consistent with the
observation that the protonation of 18 in methylene
chloride-d2 with dry HCl gas led to the known chlorido-
Table 1
Spectroscopic characterization of iridium-j1-vinyl complexes
j1-vinyl complex (R = CO2CH3)
1H NMRa, d
13C{1H} NMRb, ppm
(CD2C12)
175.8 (t, J = 8.4, Ir–CO)
162.1 (t, J = 6.8, Ir–C(R)@)
154.8 (t, J = 3.1, Ir–C(R)@)
136.5 (t, J = 87, Ir–CH@)
125.8 (br s, Ir–CH@CH2)
(CD2C12)
3.21 (s, 3H, CO2CH3)
3.38 (s, 3H, CO2CH3)
3.43 (s, 3H, CO2CH3)
PPh3
R
R
CO
H
I r
R
H
R
3.55 (s, 3H, CO2CH3)
H
PPh3
4.70 (br d, 1H, J = 19.1, @CH2)
5.84 (br d, lH, J = 11.1, @CH2)
7.51–7.27 (m, 30H, C6H5)
7.63 (q, 1H, J = 6.4, Ir–CH)
28
1.31 (d, 3H, J = 6, @CHCH3)
3.28 (s, 3H, CO2CH3)
3.37 (s, 3H, CO2CH3)
3.46 (s, 3H, CO2CH3)
3.57 (s, 3H, CO2CH3)
4.66 (dq, 1H, J = 17.1, 6, @CHMe)
6.43 (br d, 1H, J = 17.1, Ir–CH)
7.31 (m, 18H, C6H5)
175.4 (t, J = 6.9, Ir–CO)
161.3 (br s, Ir–C(R)@)
154.3 (t,J = 11.8, Ir–C(R)@)
132.7 (br s, Ir–CH@CH2)
125.8 (t, J = 8.4, Ir–CH@)
PPh3
I r
R
R
CO
H
R
Me
R
H
PPh3
31
7.48 (m, 12H, C6H5)
PPh3
1.10 (m, 2H, –CH2)
1.26 (m, 4H, –CH2)
2.01 (m, 2H, –CH2)
3.23 (s, 3H, CO2CH3)
3.31 (s, 3H, CO2CH3)
3.43 (s, 3H, CO2CH3)
3.48 (s, 3H, CO2CH3)
6.40 (m, 1H, Ir–CH)
7.25–7.80 (m,30H,C6H5)
176.4 (br s, Ir–CO)
159.0 (t, J = 6.5)c
157.7 (t, J = 11.8)c
152.8 (t, J = 3.1)c
151.6c
R
R
CO
I r
R
R
H
PPh3
149.9 (t, J = 3.5)c
33
PPh3
1.10 (m, 2H, –CH2)
1.26 (m, 4H, –CH2)
2.01 (m, 2H, –CH2)
3.23 (s, 3H, CO2CH3)
3.31 (s, 3H, CO2CH3)
3.43 (s, 3H, CO2CH3)
3.48 (s, 3H, CO2CH3)
6.40 (m, 1H, Ir–CH)
7.25–7.80 (m, 30H, C6H5)
176.7 (t, J = 8.0, Ir–CO)
160.2 (t, J = 7.0)c
155.8 (t, J = 12.0)c
146.2 (t, J = 2.9)c
120.7 (t, J = 9.1)c
R
R
CO
I r
R
R
H
PPh3
34
a
1H NMR spectra were recorded at 300 MHz in CDC13 and are referenced to the residual solvent resonance at d 7.26 ppm, unless otherwise noted. All
couplings are in Hertz.
b
13C{1H} NMR spectra were recorded at 126 MHz in CDC13 and were referenced to the solvent resonance at 77.0 ppm, unless otherwise noted.
Couplings are in Hertz.
c
a-C substituents on the metallacycle were not distinguished from the vinyl-carbons.

J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
3037
Scheme 5.
carbonyl complex [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir-
(CO)(Cl) (19, R = CO2Me) [9] and free ethylene, as
indicated by a resonance at d 5.4 in the proton spectrum
of the sample.
An isotope labeling experiment was employed to deter-
mine the source of the carbon monoxide oxygen in 18. This
was of particular interest as we had previously observed an
oxygen atom transfer from a methoxycarbonyl metallacy-
cle substituent to a vinylidene ligand in the reactions of
cationic iridacyclopentadiene complexes, such as that
observed in the conversion of cationic iridacycle 20 to 21
(Scheme 5) [16]. When 9 (20 mM) and 2-propyn-1-ol
(200 mM) were mixed in a two-phase solution of CD2Cl2
and 18OH2 (3% v/v), the 18O-enriched complex,
[j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(CH@CH2)(CO*)
(18-O, O* = 18O, R = CO2Me) was cleanly formed. The
position of the 18O-label was identified by the isotopic shift
of the terminal carbonyl-carbon resonance in the 13C{1H}
NMR spectrum (CD2Cl2, 126 MHz) of a ꢀ1:1 mixture of
18-O:18 (Fig. 1). The carbonyl-carbon resonances for 18-
O were observed 3.8 Hz upfield of the triplet corresponding
to the unlabeled complex at 175.8 ppm. The magnitude of
this isotopic shift in the 13C NMR spectrum upon substitu-
tion of oxygen-18 for oxygen-16 is consistent with litera-
ture precedent [17]. No additional isotopic shifts were
observed in the 13C{1H} NMR spectrum (CD2Cl2) for
the remaining carbon resonances of the 18/18-O sample.
A comparison of the high-resolution mass spectra for 18
and 18-O indicated >96% 18O-incorporation in 18-O. In
the IR spectrum (KBr), carbonyl stretches were observed
at 2028 and 1985 cmÀ1 for 18 and 18-O, respectively;
thereby confirming the 13C NMR chemical shift isotope
analysis.
Fig. 1. Lower trace: carbonyl ligand carbon resonance in the 13C{1H}
NMR spectrum of 18-O. The lines indicated by the stars are the triplet
observed for the carbon resonance of the C(18O) ligand. Upper trace: the
related spectrum for a ꢀ1:1 mixture of 18:18-O. The lines indicated by the
black dots are the triplet observed for the carbon resonance of the non-
enriched C(16O) ligand of 18. The lines indicated by the stars are the triplet
observed for the carbon resonance of the C(18O) ligand in 18-O.
and 1-ethynylcyclooctanol (Scheme 6, Table 1). The reac-
tion of 9 (0.04 M) with ( )-3-butyn-2-ol (0.4 M) in a
two-phase CD2Cl2/H2O solvent system followed a similar
course to that observed for 2-propyn-1-ol. After 21 h at
1
room temperature, H NMR spectroscopy revealed nearly
quantitative conversion to [j2(C1,C4)-CR@CRCR@CR]-
(PPh3)2Ir[(E)-CH@CHMe](CO) (22, R = CO2Me) relative
to p-bis(trimethylsilyl)benzene as an internal standard.
Vinyl complex 22 was isolated as an off-white solid in
95% yield from a preparative-scale reaction of 9 (250 mg,
0.03 M) and 3-butyn-2-ol (0.34 M) using a two-phase chlo-
The scope of this new propargyl alcohol reaction was
briefly explored by examining the reactions of 9 with 3-
butyn-2-ol, 2-methyl-3-butyn-2-ol, 1-ethynylcyclopentanol,
1
roform/water mixture (4% v/v). In the H NMR spectrum
of 22, four new carbomethoxy-protons at d 3.28, 3.37, 3.46,

3038
J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
Scheme 6.
and 3.57 were observed as singlets in addition to the allylic-
protons of the vinyl ligand and the vinyl-hydrogen reso-
nances at d 1.66 (d, 3H, J = 5.7 Hz), 4.66 (dq, 1H, J =
17.1, 5.7 Hz), and 6.43 (br d, 1H, J = 17.1 Hz), respec-
tively. The trans-alkene stereochemistry is consistent with
the 17-Hz coupling constant observed for the vicinal-
hydrogen atoms of the vinyl group. The resonance at d
4.66 was assigned to the proton on the b-carbon of the
ethenyl ligand based on its 5.7-Hz coupling constant to
the methyl protons. In the 13C{1H} NMR spectrum
(CD2Cl2), the Ir–CO carbon resonance was observed at
175.4 ppm as a triplet (J = 6.9 Hz). The two inequivalent
a-carbon substituents on the metallacycle were observed
as a broad singlet at 161.3 and as a triplet (J = 11.8 Hz)
at 154.3 ppm. The vinyl-carbons of the ethenyl ligand were
observed in the proton-decoupled carbon NMR spectrum
at 132.7 (br s) and 125.8 ppm (t, J = 8.4 Hz).
The reaction of 9 (0.01 M) and 1-ethynylcyclopentanol
(0.06 M) in a two-phase CDCl3/H2O solution at room tem-
1
perature was also monitored by H NMR spectroscopy.
After 96 hours, the solution was found to contain a 38%
yield of a new complex identified as [j2(C1,C4)-CR@
CRCR@CR](PPh3)2Ir[CH@C(CH2)4](CO) (24, R = CO2Me),
as well as a 52% yield of both 24 and methylenecyclopen-
tane. The methylene-protons of the ethenyl ligand in 24
were observed as multiplets from d 1.10–2.01 and the
vinyl-hydrogen was observed at 6.40 as a multiplet. The
methylenecyclopentane assignment was confirmed by
1
GC–MS analysis of the sample and comparison of the H
and 13C NMR spectral data with those of an authentic
sample. As we were unable to separate 24 from 19, charac-
1
terization of 24 by H and 13C NMR spectroscopy was
conducted by analysis of the crude reaction mixture.
A
similar small-scale reaction of 9 with 1-eth-
Unexpectedly, when a similar reaction was run with 9
(0.04 M) and 2-methyl-3-butyn-2-ol (0.42 M), the quantita-
tive formation of the iridium carbon monoxide complex 19
was observed after 48 h at room temperature, suggesting 2-
methylpropene loss from an initially-formed vinyl complex.
This speculation was supported by an NMR tube-scale
reaction in which 2-methyl-3-butyn-2-ol (0.22 M) was
added to a two-phase solution of metallacycle 9 (0.01 M)
in 2% aqueous CDCl3 (0.50 mL). The formation of a
new vinyl complex [j2(C1,C4)-CR@CRCR@CR](PPh3)2
Ir(CO)[CH@C(CH3)2] (23, R = CO2Me) was observed in
38% yield by 1H NMR spectroscopy. In addition to the for-
mation of 23, complex 19 was formed in 52% yield along
with 2-methylpropene. The vinyl hydrogen resonance for
23 was observed at d 6.28. The hydrogens for 2-methylpro-
pene were observed at d 4.57 and 1.60, respectively.
Attempts to isolate complex 23 were unsuccessful due to
conversion of the j1-vinyl complex to 19 and isobutylene
upon attempted purification.
ynylcyclooctanol in CDCl3/H2O led to the formation of
[j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir[CH@C(CH2)7](CO)
(25, R = CO2Me) in 98% yield, as determined by integra-
tion of the resonances for 25 relative to those of an internal
standard. The reaction between metallacycle 9 (100 mg,
0.10 mmol, 12.5 mM) and 1-ethynylcyclooctanol (150 mg,
0.97 mmol, 120 mM) in a CDCl3/H2O (3%) solution was
carried out on a preparative-scale, and the vinyl complex
25 was isolated as analytically pure crystals by slow evap-
oration of an ether solution. The spectroscopic properties
1
of 25 are displayed in Table 1. The H NMR spectrum of
25 in CDCl3 exhibits resonances at d 6.40 (s, 1H) and
7.25–7.80 (m, 30H), which were assigned to the vinyl-
hydrogen and the methylene-hydrogens of the vinyl ligand,
respectively. Four resonances between d 3.48–3.23 were
observed for the four unique carbomethoxy-protons. The
iridium carbonyl-carbon was observed in the 13C{1H}
NMR spectrum (CDCl3) at 176.7 ppm as a triplet
(J = 8.0 Hz). The two vinyl ligand carbons were in the

J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
3039
Scheme 7.
same range as the a-carbons of the metallacycle at 160.2–
120.7 ppm and could not be unambiguously assigned on
the basis of either chemical shift or coupling constants.
One reasonable mechanism for the formation of the
vinyl complexes 18 and 22–35 from 9 and propargyl alco-
hols involves the formation of unobserved vinylidene inter-
mediates, such as complex 26, which undergo rapid
dehydration to the corresponding allenylidene 27 (Scheme
7). Nucleophilic attack by water at the a-carbon of the
allenylidene, followed by loss of HCl, would then generate
the allenol complex 28. Subsequent tautomerization of 28
to the a,b-unsaturated acyl complex 29, followed by
decarbonylation, would then afford the vinyl-carbon mon-
oxide product 22 [18]. An organic analogue of the 28 to
a,b-unsaturated acyl 29 tautomerization is found in the
conversion of allenol ethers (30) to a,b-unsaturated silyl
ketones (31; Scheme 8) [19]. The high selectivity for the
E-isomer of 22 mirrors the selectivity observed in the for-
mation of 31.
A number of simple variations of the Scheme 6 mecha-
nism may also be valid, particularly with respect to the loss
of chloride from iridium, which could potentially occur at a
number of different intermediate stages. It should be noted
that there is a growing body of precedent for preferential
nucleophilic attack at the c-carbon of allenylidene ligands,
rather than at the a-carbon [1–4,7,8]. However, in the case
of 27, attack by water at the c-carbon of the allenylidene
ligand would simply lead back to vinylidene 26.
Scheme 9.
of 32 would then form hydroxyethyl complex 33, followed
by dehydration to afford complex 22. Bergman has pre-
pared iridium(III) hydroxyethyl complexes, Cp*Ir(Ph)(P-
Me3)CH2CH2OH, from the reaction of iridium hydroxide
precursors and ethene, but – as of yet – there is no evidence
that these undergo dehydration to iridium vinyl complexes;
rather, they are converted to formyl methyl complexes
(IrCH2CHO) [21].
3. Conclusions
A much different mechanistic possibility for the forma-
tion of iridium vinyl complexes from propargylic alcohols
involves trapping of vinylidene intermediate 26 by water
to give acyl complex 32 (Scheme 9) [20]. Decarbonylation
The reactions of neutral iridium(III) metallacyclopent-
adiene-halido complexes with terminal alkynes follow a
number of pathways depending on the reaction conditions
and the nature of the alkyne substituents. The primary
reaction pathway in the case of the propargyl alcohol sub-
strates depends on whether the reaction is carried out
under aqueous or anhydrous conditions. Both systems pre-
sumably involve the initial formation of an g2-alkyne com-
plex. Under anhydrous conditions, this intermediate inserts
into the metallacycle ring to give the [2 + 2 + 2]-cycloaro-
matization product 16. Under aqueous conditions the
Scheme 8.

3040
J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
g2-alkyne intermediate sequentially rearranges first to a
vinylidene and then to an allenylidene intermediate, which
is trapped by water to ultimately afford iridium(III)–vinyl
products. Studies are planned to further evaluate the scope
of these new routes to metal–vinyl complexes and to more
thoroughly establish the reactivity profile for the iridium–
vinyl complexes, with particular emphasis on the conver-
sion of these species into metallacyclopentadiene–alkyl-
idene complexes.
NMR (CDCl3, 300 MHz) d 8.00 (s, 1 H), 5.37 (s, 2H),
4.00 (s, 3H), 3.94 (s, 3H), 3.91 (s, 3H); 13C{1H} NMR
(CDCl3, 125.7 MHz) d 166.9, 166.0, 165.5, 164.8, 148.4,
136.0, 133.1, 132.3, 125.8, 124.8, 68.1, 53.4, 53.4, 53.3.
HRMS (EI, 50 eV), m/z calc. for C14H12O8: 308.0532,
obsd: 308.0528.
4.2. [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(CO)-
(CH@CH2) (18, R = CO2Me)
A 25-mL round-bottom flask equipped with a magnetic
stir bar was charged with 9 (0.30 g, 0.29 mmol, 19.3 mM),
chloroform (15 mL), and 2-propyn-1-ol (2.9 mmol,
0.19 M) under an atmosphere of N2. The solution was stir-
red at 23 °C for 24 h. The volatiles were evaporated; the
residue was taken up in chloroform (20 mL) and filtered
to give 18 as a pale pink powder. Recrystallization from
methylene chloride/diethyl ether afforded 18 in 33% yield:
m.p. 195–197 °C (sealed cap); IR (KBr) 2027 (vs), 1725
(br s), 1692 (s), 1680 (s), 1485 (s), 1435 (s), 1328 (s), 1219
4. Experimental
All reactions and reaction workups were performed in
air unless otherwise noted. Organic solvents were obtained
commercially and used without further purification unless
otherwise indicated. IR spectra were recorded on a Matt-
son 2020 FTIR spectrometer. H and 31P NMR spectra
1
were obtained on a GE QE 300 (1H 300 MHz, 31P
122 MHz) spectrometer. 1,4-(TMS)2C6H4 was used as the
internal standard in the integration of all small-scale reac-
tions monitored by 1H NMR spectroscopy. 13C NMR
spectra were obtained on a GE QE 300 (75.5 MHz) or a
Varian UNITY 500 (126 MHz) spectrometer. Chemical
shifts for protons are reported in parts per million from tet-
ramethylsilane and are referenced to residual protium in
the NMR solvent. Chemical shifts for carbon are reported
in parts per million from tetramethylsilane and are refer-
enced to the carbon resonances of the solvent. 31P NMR
chemical shifts are referenced to 85% H3PO4 (d = 0 ppm).
FAB mass spectra were obtained at the University of Cal-
ifornia, Riverside Mass Spectroscopy Facility. Elemental
analyses were performed by either Desert Analytics or Gal-
braith Laboratories, Inc. Methyl propiolate, ethyl propio-
late, dimethyl acetylene dicarboxylate, propiolic acid,
deuterated water, deuterated chloroform (the water con-
centration in the commercial chloroform-d was ca.
56 mM), and silver tetrafluoroborate were obtained from
Aldrich Chemical Company. Sodium bromide and potas-
sium iodide were obtained from Fisher Scientific. 18O-
labeled water (97 atom% 18O) was purchased from MSD
Isotopes.
1
(vs) cmÀ1; H NMR (CD2Cl2, 300 MHz) d7.63 (m, 1H),
7.51–7.27 (m, 30 H), 5.84 (br d, 1H, J = 11.1), 4.70 (br d,
1H, J = 19.1), 3.55 (s, 3H), 3.43 (s, 3H), 3.38 (s, 3H),
3.21 (s, 3H); 13C{1H} NMR (CD2Cl2, 125.7 MHz) d
176.5 (s), 173.5 (s), 175.8 (t, J = 8.4), 167.5 (s), 167.07 (s),
162.1 (t, J = 6.8), 154.8 (t, J = 3.1), 152.5 (t, J = 11.8),
150.9 (s), 136.5 (t, J = 8.7), 135.4 (t, J = 5.0), 130.4 (t,
J = 28.9), 130.5 (s), 127.6 (t, J = 5.4), 125.8 (br s), 51.2,
51.0, 50.9, 50.3; 31P{1H}NMR (CD2Cl2, 121.5 MHz) d
À6.60. HRMS(FAB), m/e calc. for C51H45O9P2IrH+-
(MH+): 1055.2223, obsd: 1055.2252.
4.3. [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(CO)[(E)-
CH@CHCH3] (22, R = CO2Me)
A 25-mL round-bottom flask equipped with a magnetic
stir bar was charged with 9 (250 mg, 0.24 mmol, 34.4 mM),
aqueous chloroform (7 mL, 4% v/v), and 2-methyl-3-
butyn-2-ol, (190 lL, 2.4 mmol). The solution was stirred
at 23 °C for 15 h in the air. The volatiles were evaporated,
and the residue was recrystallized from benzene/hexanes to
give 22 as an off-white powder in 95% yield (244 mg): m.p.
183–185 °C (sealed cap); IR(KBr) 2028 (s), 1720 (s), 1699
(s), 1988 (s), 1482 (s), 1433 (s), 1325 (s), 1209 (vs), 1091
4.1. Trimethyl 1,3-dihydro-3-oxo-4,5,6-isobenzofurantri-
carboxylate (16)
1
(s), 1067 (s), 1019 (vs), 748 (s), 696 (vs), 523 (s), cmÀ1; H
NMR (CDCl3, 300 MHz) d 7.48 (m, 12 H), 7.31 (m, 18
H), 6.43 (br d, 1H, J = 17.1 Hz), 1.66 (dq, 1H, J = 17.1,
5.7 Hz), 3.57 (s, 3H), 3.46 (s, 3H), 3.37 (s, 3H), 3.28 (s,
3H), 1.33 (d, 3H, J = 5.7 Hz); 13C{1H} NMR (CDCl3,
125.7 MHz) d176.47 (s), 175.41 (br s), 173.28 (s), 167.38
(s), 167.17 (s), 161.31 (s), 154.33 (t, J = 11.8 Hz), 153.77
(s), 150.73 (s), 134.99 (s), 132.67 (s), 130.09 (t, J =
28.2 Hz), 139.97 (s), 127.22 (br s), 125.24 (t, J = 8.4 Hz),
50.88 (s), 50.67 (s), 50.46 (s), 50.14 (s), 24.68 (s).
31P{1H}NMR (CDCl3, 121.5 MHz) d À 6.33 (s). HRMS
(FAB), m/z calc. for C52H47O9P2Ir: 1070.2325, obsd:
1070.2387.
A 50-mL round-bottom flask equipped with a magnetic
stir bar was charged with 9 (0.50 g, 0.48 mmol, 19.3 mM),
dry degassed chloroform (25 mL), and 2-propyn-1-ol
(1.21 mmol) under an atmosphere of N2. The solution
was then heated at 50 °C for 44 h. The volatiles were
removed in vacuo, and the residue was dried under vacuum
to give a viscous brown oil which was taken up in chloro-
form, filtered through a plug of silica gel, and chromato-
graphed on silica gel (5:1 CHCl3/ethyl acetate) to afford
16 as a solid in 57% yield: m.p. 151.8 °C; IR (KBr) 2962
1
(s), 1768 (br s), 1739 (br s), 1613 (s), 1435 (s) cmÀ1; H

J.M. O’Connor et al. / Inorganica Chimica Acta 361 (2008) 3033–3041
3041
4.4. [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir[CH@
C(CH2)4](CO) (24, R = CO2Me)
[2] (a) Y. Fukumoto, H. Asai, M. Shimizu, N. Chatani, J. Am. Chem.
Soc. 129 (2007) 13792;
(b) D.B. Grotjahn, D.A. Lev, J. Am. Chem. Soc. 126 (2004) 12232.
[3] For leading references to iron-triad vinylidenes: (a) A. Odedra, S.
Datta, R.-S. Liu, J. Org. Chem. 72 (2007) 3289;
A 50-mL round-bottom flask equipped with a magnetic
stir bar was charged with 9 (150 mg, 7 mM), chloroform
(20 mL), water (0.30 mL) and 1-ethynylcyclopentanol
(0.17 mL, 72 mM). The mixture was stirred at 23 °C for 5
d. The volatiles were removed under vacuum, and the res-
idue was recrystallized from methylene chloride/ethanol to
give 40 mg of a cream colored solid. 1H NMR spectroscopy
indicated a mixture of 19 and 24. For 24: 1H NMR
(CDCl3, 300 MHz) d 7.25–7.80 (m, 30H), 6.40 (br s, 1H),
3.48 (s, 3H), 3.43 (s, 3H), 3.31 (s, 3H), 3.23 (s, 3H), 2.02
(m, 2H), 1.10 (m, 2H), 1.26 (m, 4H); 13C{1H} NMR
(CDCl3, 125.7 MHz) d 176.4 (br s), 175.4, 173.0, 167.8,
166.7, 159.0 (t, J = 6.5 Hz), 157.7 (t, J = 11.8 Hz), 152.8
(t, J = 3.1 Hz), 151.6, 149.9 (t, J = 3.5 Hz), 135.0 (t,
J = 5.3 Hz), 130.3 (t, J = 28.7 Hz), 130.0 (br s), 127.2 (t,
J = 5.9 Hz), 114.4 (t, J = 9.9 Hz), 50.8, 50.6, 50.3, 50.2,
39.6, 33.2, 27.1, 26.7.
(b) M.I. Bruce, P.A. Humphrey, M. Jevric, G. Perkins, B.W. Skelton,
A.H. White, J. Organomet. Chem. 692 (2007) 1748;
(c) Y. Sun, H.-S. Chan, P.H. Dixneuf, Z. Xie, Organometallics 25
(2006) 2719.
[4] For leading references to cobalt-triad vinylidenes: (a) D.B. Grotjahn,
Z. Zeng, A.L. Cooksy, W.S. Kassel, A.G. DiPasquale, L.N. Zakha-
rov, A.L. Rheingold, Organometallics 26 (2007) 3385;
(b) K. Ilg, M. Paneque, M.L. Poveda, N. Rendon, L.L. Santos, E.
Carmona, K. Mereiter, Organometallics 25 (2006) 2230;
(c) X. Li, T. Vogel, C.D. Incarvito, R.H. Crabtree, Organometallics
24 (2005) 62;
(d) H. Werner, K. Ilg, B. Weberndo¨rfer, Organometallics 19 (2000) 3145.
[5] Portions of this work have been published in preliminary form: J.M.
O’Connor, K. Hiibner, J. Chem. Soc., Chem. Commun. (1995) 1209.
[6] H.C. Clark, L.E. Manzer, J. Organomet. Chem. 47 (1973) C17.
[7] (a) M.A. Esteruelas, L.A. Oro, J. Schrickel, Organometallics 16
(1997) 796;
(b) H. Werner, R.W. Lass, O. Gevert, J. Wolf, Organometallics 16
(1997) 4077;
(c) P. Steinert, H. Werner, Chem. Ber./Recueil 130 (1997) 1591;
(d) K. Ilg, H. Werner, Organometallics 18 (1999) 5426;
(e) K. Ilg, H. Werner, Organometallics 20 (2001) 3782.
[8] K. Ilg, H. Werner, Chem. Eur. J. 7 (2001) 4633.
[9] J.P. Collman, J.W. Kang, W.F. Little, M.F. Sullivan, Inorg. Chem. 7
(1968) 1298.
[10] (a) J.M. O’Connor, L. Pu, A.L. Rheingold, J. Am. Chem. Soc. 109
(1987) 7578;
(b) J.M. O’Connor, L. Pu, A.L. Rheingold, J. Am. Chem. Soc. 111
(1989) 4129.
[11] J.M. O’Connor, K. Hiibner, R. Merwin, L. Pu, J. Am. Chem. Soc.
117 (1995) 8861.
[12] The insertion of the carbene ligand of 12 into the metallacycle ring
occurs at elevated temperatures: (a) J.M. O’Connor, L. Pu, S.
Woolard, R.K. Chadha, J. Am. Chem. Soc. 112 (1990) 6731;
(b) E. Alvarez, M. Paneque, M.L. Poveda, N. Rendon, Angew.
Chem., Int. Ed. 45 (2006) 474;
4.5. [j2(C1,C4)-CR@CRCR@CR](PPh3)2Ir(CH@
C(CH2)7)(CO) (25, R = CO2Me)
A 50-mL round-bottom flask was charged with 9
(100 mg, 0.97 mmol, 0.12 M), chloroform (8 mL), distilled
water (0.20 mL), and 1-ethynylcyclooctanol (147 mg,
0.97 mmol). After 4 d at rt, the mixture was filtered, and
the mother liquor was evaporated to give a brown solid.
Recrystallization from diethyl ether afforded 25 as clear
amber slates (9.7 mg, 8.75%): IR(KBr) 3068 (w), 2924
(w), 2020 (s), 1718 (vs), 1436 (s), 1206 (vs), 1323 (w),
1089 (m), 1089 (m), 1014 (m), 753 (m), 701 (vs) cmÀ1; H
1
NMR (CDCl3, 300 MHz) d 7.52 (m, 30H), 6.75 (t, 1H,
J = 4.7 Hz), 3.45 (s, 3H), 3.39 (s, 3H), 3.27 (s, 3H), 3.23
(s, 3H), 1.208 (m, 14H); 13C{1H} NMR (CDCl3,
125.7 MHz) d 176.7 (t, J = 8.0 Hz), 175.1, 172.8, 167.4,
166.9, 160.2 (t, J = 7.0 Hz), 155.8 (t, J = 12.0 Hz), 153.5,
151.3, 146.2 (t, J = 2.9 Hz), 135.1 (t, J = 4.8 Hz), 130.3 (t,
J = 28.6 Hz), 120.7 (t, J = 9.1 Hz), 50.7, 50.7, 50.3, 50.1,
41.0, 36.3, 28.9, 28.1, 27.5, 26.1, 26.0. HRMS(FAB) m/e
calc. for C58H57O9P2Ir: 1152 (M+), obsd. 1152 – which
matched the calc. isotopic distribution pattern.
(c) J.M. O’Connor, L. Pu, R. Uhrhammer, J.A. Johnson, J. Am.
Chem. Soc. 111 (1989) 1889.
[13] For vinylidene ligand insertion into an iridacyclopentadiene ring see:
C.S. Chin, H. Lee, M.-S. Eum, Organometallics 24 (2005) 4849.
[14] (a) Dieck C. Munz, C. Muller, J. Organomet. Chem. 384 (1990) 243;
¨
(b) J.M. O’Connor, A. Closson, K. Hiibner, R. Merwin, P. Gantzel,
D.M. Roddick, Organometallics 20 (2001) 3710.
[15] P.O. Stoutland, R.G. Bergman, J. Am. Chem. Soc. 107 (1985) 4581.
[16] (a) J.M. O’Connor, L. Pu, J. Am. Chem. Soc. 112 (1990) 9013;
(b) J.M. O’Connor, L. Pu, A.L. Rheingold, J. Am. Chem. Soc. 112
(1990) 9663;
(c) J.M. O’Connor, L. Pu, R.K. Chadha, J. Am. Chem. Soc. 112
(1990) 9627.
[17] C.L. Perrin, J.D. Thoburn, J. Am. Chem. Soc. 111 (1989) 8010, and
references cited therein.
Acknowledgement
[18] Subsequent to our initial communication, the reaction of 8 with
HC„CCH(Ph)OH to give iridium(III)hydrido vinyl complexes was
reported (see Ref. [7b,7c]).
[19] H.J. Reich, M.J. Kelly, R.E. Olson, R.C. Holtan, Tetrahedron 39
(1983) 949.
The support of the National Science Foundation is
gratefully acknowledged (Grant CHE05-18707 and Instru-
mentation Grants CHE01-16662 and CHE97-09183).
[20] For attack of water on iridium vinylidene intermediates see: (a) U.
Belluco, R. Bertani, F. Meneghetti, R.A. Michelin, M. Mozzon, J.
Organomet. Chem. 583 (1999) 131;
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