Stepwise reactions of acetylenes with iridium thiocarbonyl complexes to produce isolable iridacyclobutadienes and conversion of these to either cyclopentadienyliridium or tethered iridabenzene complexes

Article abstract of DOI:10.1021/om061066r

Treatment of IrCl(CS)(PPh₃)₂ with an excess of KI gives orange IrI(CS)(PPh₃)₂ (1). IrI(CS)(PPh ₃)₂ (1) reacts reversibly with dioxygen to form the brown dioxygen complex Ir(O₂)I(CS)(PPh₃)₂ (2). Reaction between IrI(CS)(PPh₃)₂ (1) and 2 equiv of ethyne produces the green-brown tethered iridacyclobutadiene complex Ir[C ₃H₂(CH=CHS-1)]I(PPh₃)₂ (3), one ethyne combining in a cycloaddition reaction with the IrC multiple bond to the CS ligand to form the four-membered IrC₃ ring and the second ethyne alkylating the sulfur atom to give the vinylthio substituent at the 1-position of the metallacyclic ring, which is tethered to the indium through an Ir - C bond. In reactions related to those with ethyne, phenylacetylene reacts with IrCl(CS)(PPh₃)₂ to give as the major product the tethered iridacyclobutadiene Ir[C₃H(CH= C{Ph}S-1)(Ph-3)]Cl(PPh ₃)₂ (4), with the phenyl substituent adjacent to the iridium, and as the minor product the isomeric tethered iridacyclobutadiene Ir[C₃H(CH=C{Ph}S-1)(Ph-2)]Cl(PPh₃)₂ (5). A thermal reaction of Ir[C₃H(CH=C{Ph}S-1)(Ph-3)]Cl(PPh ₃)₂ (4) with further phenylacetylene produces the tethered, substituted cyclopentadienyliridium complex Ir[η⁵- C₅H₂(SCPh=CH-1)(Ph-3)(Ph-5)]Cl(PPh₃) (6), which retains the iridium-carbon bond to the vinylthio substituent. Methyl propiolate reacts with Irl(CS)-(PPh₃)₂ (1) to form exclusively the tethered iridacyclobutadiene Ir[C₃H(CH=C{CO₂Me}S-1) (CO₂Me-2)]I(PPh₃)₂ (7). Treatment of this iridacyclobutadiene, 7, with silver triflate allows introduction of a third methyl propiolate, which brings about ring expansion of the iridacyclobutadiene to form the stable tethered iridabenzene Ir[C₅H₂(CH= C{CO₂Me}S-1)(CO₂Me-2)(CO₂Me-4)]Cl(PPh ₃)₂ (8). Complex 8 retains the same vinylthio tethering group as found in 7. The structures of 2-8 have been confirmed by X-ray crystal structure determinations. Both NMR spectroscopic and structural data for 8 support the formulation of this compound as a tethered metallaaromatic molecule.

Full text of DOI:10.1021/om061066r

Organometallics 2007, 26, 2167-2177
2167
Stepwise Reactions of Acetylenes with Iridium Thiocarbonyl
Complexes To Produce Isolable Iridacyclobutadienes and
Conversion of These to either Cyclopentadienyliridium or Tethered
Iridabenzene Complexes
George R. Clark, Guo-Liang Lu, Warren R. Roper,* and L. James Wright*
Department of Chemistry, The UniVersity of Auckland, PriVate Bag 92019, Auckland, New Zealand
ReceiVed NoVember 20, 2006
Treatment of IrCl(CS)(PPh3)2 with an excess of KI gives orange IrI(CS)(PPh3)2 (1). IrI(CS)(PPh3)2 (1)
reacts reversibly with dioxygen to form the brown dioxygen complex Ir(O2)I(CS)(PPh3)2 (2). Reaction
between IrI(CS)(PPh3)2 (1) and 2 equiv of ethyne produces the green-brown tethered iridacyclobutadiene
complex Ir[C3H2(CHdCHS-1)]I(PPh3)2 (3), one ethyne combining in a cycloaddition reaction with the
IrC multiple bond to the CS ligand to form the four-membered IrC3 ring and the second ethyne alkylating
the sulfur atom to give the vinylthio substituent at the 1-position of the metallacyclic ring, which is
tethered to the iridium through an Ir-C bond. In reactions related to those with ethyne, phenylacetylene
reacts with IrCl(CS)(PPh3)2 to give as the major product the tethered iridacyclobutadiene Ir[C3H(CHd
C{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4), with the phenyl substituent adjacent to the iridium, and as the minor
product the isomeric tethered iridacyclobutadiene Ir[C3H(CHdC{Ph}S-1)(Ph-2)]Cl(PPh3)2 (5). A thermal
reaction of Ir[C3H(CHdC{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4) with further phenylacetylene produces the tethered,
substituted cyclopentadienyliridium complex Ir[η5-C5H2(SCPhdCH-1)(Ph-3)(Ph-5)]Cl(PPh3) (6), which
retains the iridium-carbon bond to the vinylthio substituent. Methyl propiolate reacts with IrI(CS)-
(PPh3)2 (1) to form exclusively the tethered iridacyclobutadiene Ir[C3H(CHdC{CO2Me}S-1)(CO2Me-
2)]I(PPh3)2 (7). Treatment of this iridacyclobutadiene, 7, with silver triflate allows introduction of a third
methyl propiolate, which brings about ring expansion of the iridacyclobutadiene to form the stable tethered
iridabenzene Ir[C5H2(CHdC{CO2Me}S-1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8). Complex 8 retains the
same vinylthio tethering group as found in 7. The structures of 2-8 have been confirmed by X-ray
crystal structure determinations. Both NMR spectroscopic and structural data for 8 support the formulation
of this compound as a tethered metallaaromatic molecule.
Scheme 1
Introduction
In the first metallabenzene synthesis, the OsC5 ring of the
osmabenzene was assembled from two ethyne molecules and
the single carbon atom from a thiocarbonyl ligand already
resident on the osmium in the starting material, Os(CS)(CO)-
(PPh3)3.1 An intriguing possibility is that other low-oxidation-
state transition-metal thiocarbonyl complexes might also provide
a simple route into metallabenzene systems, through reactions
with acetylenes; however, this has not yet been adequately
explored. We address this question in this paper by examining
reactions between neutral iridium thiocarbonyl complexes and
several acetylenes.
A computational study of the formation of the original
osmabenzene, Os[C5H4(S-1)](CO)(PPh3)2,2 considered two dis-
tinct pathways. The first step in both pathways involves
coordination of one ethyne to the metal, producing intermediate
A in Scheme 1. According to the computational results,2 the
next step in the more favorable pathway is formation of an
osmacyclobutenethione ring (intermediate B) from combination
of CS with the ethyne molecule, followed by ring expansion
through reaction with a second ethyne to give an osmacyclo-
hexadienethione (intermediate C) and finally aromatization of
this osmacyclohexadienethione through coordination of sulfur
to osmium to give osmabenzene D. In practice, osmabenzene
D proved to alkylate readily at sulfur to give osmabenzene E.1
There are experimental precedents for intermediate A (Os(CS)-
(PhC2Ph)(PPh3)2),3 intermediate B (Os[C3(S-1)(Ph-2)(Ph-3)]-
(CO)2(PPh3)2),3 and intermediate C (Os[C5H4(S-1)](CO)2-
(PPh3)2).1 The less favorable pathway, according to the
computational results, involves initial formation of an osma-
cyclopentadiene (intermediate G) from combination of one
further ethyne molecule with intermediate A, followed ultimately
(1) Elliott, G. P.; Roper, W. R.; Waters, J. M. J. Chem. Soc., Chem.
Commun. 1982, 811.
(2) Iron, M. A.; Lucassen, A. C. B.; Cohen, H.; van der Boom, M. E.;
Martin, J. M. L. J. Am. Chem. Soc. 2004, 126, 11699.
(3) (a) Elliott, G. P.; Roper, W. R. J. Organomet. Chem. 1983, 250, C5.
(b) Burrell, A. K.; Elliott, G. P.; Rickard, C. E. F.; Roper, W. R. Appl.
Organomet. Chem. 1990, 4, 535.
10.1021/om061066r CCC: $37.00 © 2007 American Chemical Society
Publication on Web 03/27/2007

2168 Organometallics, Vol. 26, No. 9, 2007
Clark et al.
Scheme 2
Scheme 3
by ring expansion through insertion of the thiocarbonyl ligand
into this five-membered ring to give C. Either pathway depends
for its success on the readiness with which the thiocarbonyl
ligand undergoes insertion reactions. In related work we have
demonstrated that the thiocarbonyl ligand will insert into Os-
H,4 Os-C,5 Os-Si,6 and Os-B7 bonds. With the exception of
the Os-C bond, insertion of the related carbonyl ligand into
these bonds has not been observed.
A variant of the favored route, A to B to C to D, involves an
electrophile intercepting B and effecting S-alkylation to give
the metallacyclobutadiene complex F. Metallacyclobutadiene
complexes are well-characterized species and have been pro-
posed as key intermediates in metal-catalyzed alkyne metathesis
reactions.8 Some metallacyclobutadiene complexes react with
acetylenes to form metal cyclopentadienyl complexes. This
reaction has been proposed to proceed through metallabenzene
intermediates9 and has also been suggested as a route for catalyst
deactivation in metal-catalyzed alkyne metathesis.8 Computa-
tional studies have shown that many metallabenzene complexes
can readily rearrange to cyclopentadienyl complexes (see
Scheme 2).10 As far as we are aware, no direct conversion of a
stable metallacyclobutadiene complex to a stable metallabenzene
complex through ring expansion with an acetylene, i.e., conver-
sion of F to E in Scheme 1, has been reported.
Results and Discussion
Preparation of IrI(CS)(PPh3)2 (1), the Reversible Reaction
of This Compound with Dioxygen To Form Ir(O2)I(CS)-
(PPh3)2 (2), and the Crystal Structure of 2. For the carbonyl
complexes IrX(CO)(PPh3)2 it is well-established that the reactiv-
ity of individual compounds toward oxidative addition reactions
is dependent upon the nature of the anionic ligand X: e.g., for
IrCl(CO)(PPh3)2 dioxygen uptake is reversible, whereas for IrI-
(CO)(PPh3)2 dioxygen uptake is irreversible.11 The thiocarbonyl
complex IrCl(CS)(PPh3)2 is not particularly soluble in chlori-
nated solvents, and anticipating both greater solubility and
enhanced reactivity of the iodo analogue IrI(CS)(PPh3)2, we
chose to examine the reactivity of both compounds toward
acetylenes.
In this paper we report (i) the formation of the thiocarbonyl
complex IrI(CS)(PPh3)2 (1) and the structural characterization
of the dioxygen adduct Ir(O2)I(CS)(PPh3)2 (2), (ii) the reaction
of IrI(CS)(PPh3)2 (1) with ethyne to form the tethered iridacy-
clobutadiene complex Ir[C3H2(CHdCHS-1)]I(PPh3)2 (3), (iii)
the reaction of IrCl(CS)(PPh3)2 with phenylacetylene to form
the isomeric tethered iridacyclobutadienes Ir[C3H(CHdC{Ph}S-
1)(Ph-3)]Cl(PPh3)2 (4) and Ir[C3H(CHdC{Ph}S-1)(Ph-2)]Cl-
(PPh3)2, (iv) the thermal reaction of Ir[C3H(CHdC{Ph}S-1)(Ph-
3)]Cl(PPh3)2 (4) with further phenylacetylene to produce the
tethered, substituted cyclopentadienyliridium complex Ir[η5-
C5H2(SCPhdCH-1)(Ph-3)(Ph-5)]Cl(PPh3) (6), (v) the reaction
of IrI(CS)(PPh3)2 (1) with methyl propiolate to give the tethered
iridayclobutadiene Ir[C3H(CHdC{CO2Me}S-1)(CO2Me-2)]I-
(PPh3)2 (7), (vi) the reaction of Ir[C3H(CHdC{CO2Me}S-1)-
(CO2Me-2)]I(PPh3)2 (7) with silver triflate followed by methyl
propiolate to bring about ring expansion of the iridacyclobuta-
diene to form the tethered iridabenzene Ir[C5H2(CHdC{CO2-
Me}S-1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8), and (vii) the
crystal structures of 2-8.
As illustrated in Scheme 3 (carbon atoms are numbered for
NMR discussion), treatment of IrCl(CS)(PPh3)2 with an excess
of potassium iodide effectively produces orange IrI(CS)(PPh3)2
(1) in high yield. In the IR spectrum of 1 ν(CS) appears as a
strong band at 1322 cm-1, and in the 31P NMR spectrum there
is a singlet resonance at 24.36 ppm arising from the two
equivalent, mutually trans PPh3 ligands. Orange solutions of 1
become brown on exposure to air, with formation of the brown
dioxygen adduct Ir(O2)I(CS)(PPh3)2 (2). This dioxygen uptake
could be reversed on heating solutions of 2 under vacuum. In
the IR spectrum of 2 ν(Ir-O2) is observed as a band of medium
intensity at 858 cm-1. This can be compared with the reported
values of 858 cm-1 for Ir(O2)Cl(CO)(PPh3)2 and 862 cm-1 for
Ir(O2)I(CO)(PPh3)2.11 Although the ν(CS) band for 2 at 1321
cm-1 is not changed significantly from that of the parent
compound (ν(CS) values typically are less responsive to any
molecular change than is ν(CO) and occur in a narrower range),
in the 31P NMR spectrum the two equivalent, mutually trans
PPh3 ligands appear as a singlet resonance at the considerably
upfield position of 5.19 ppm. Both 1 and 2 have good solubility
in benzene and chlorinated solvents. Furthermore, the reversible
dioxygen uptake allowed samples of IrI(CS)(PPh3)2 (1) contain-
ing variable quantities of Ir(O2)I(CS)(PPh3)2 (2) to be used in
reactions with acetylenes without adversely affecting the overall
yield.
(4) (a) Collins, T. J.; Roper, W. R. J. Chem. Soc., Chem. Commun. 1976,
1044. (b) Roper, W. R.; Town, K. G. J. Chem. Soc., Chem. Commun. 1977,
781.
(5) Clark, G. R.; Collins, T. J.; Marsden, K.; Roper, W. R. J. Organomet.
Chem. 1978, 157, C23.
(6) Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright, L. J.
Organometallics 1992, 11, 3931.
(7) Irvine, G. J.; Lesley, M. J. G.; Marder, T. B.; Norman, N. C.; Rice,
C. R.; Robins, E. G.; Roper, W. R.; Whittell, G. R.; Wright, L. J. Chem.
ReV. 1998, 98, 2685.
(8) (a) Schrock, R. R.; Pedersen, S. F.; Churchill, M. R.; Ziller, J. W.
Organometallics 1984, 3, 1574. (b) Zhu, J.; Jia, G.; Lin, Z. Organometallics
2006, 25, 1812.
(9) (a) Plantevin, V.; Wojcicki, A. J. Organomet. Chem. 2004, 689, 2013.
(b) Wu, H.-P.; Weakley, T. J. R.; Haley, M. M. Chem. Eur. J. 2005, 11,
1191.
The crystal structure of Ir(O2)I(CS)(PPh3)2 (2) was deter-
mined, and the molecular structure is shown in Figure 1. The
crystal data and refinement details for 2 and for the other crystal
structures reported in this paper are collected in Table 1. Selected
bond lengths and angles for 2 are presented in Table 2. The
geometry of 2 is closely similar to that of the carbonyl analogue
Ir(O2)I(CO)(PPh3)2. However, the measured O-O distance at
(10) Iron, M. A.; Martin, J. M. L.; van der Boom, M. E. J. Am. Chem.
Soc. 2003, 125, 13020.
(11) McGinnety, J. A.; Doedens, R. J.; Ibers, J. A. Inorg. Chem. 1967,
6, 2243.

Iridacyclobutadienes
Organometallics, Vol. 26, No. 9, 2007 2169
Scheme 4
Reaction of IrI(CS)(PPh3)2 (1) with Ethyne To Form the
Tethered Iridacyclobutadiene Ir[C3H2(CHdCHS-1)]I(PPh3)2
(3) and the Crystal Structure of 3. Reaction between IrI(CS)-
(PPh3)2 (1) and ethyne in benzene at 75 °C leads to the formation
of the tethered iridacyclobutadiene Ir[C3H2(CHdCHS-1)]I-
(PPh3)2 (3) as green-brown crystals in reasonable yield (see
Scheme 3). Two molecules of ethyne have been incorporated
into this product, the first (C2 and C3, see numbering in Scheme
3) combining with the thiocarbonyl ligand to generate a four-
membered IrC3 ring and the second molecule (C4 and C5)
effectively alkylating the sulfur atom and in so doing forming
a five-membered ring back to the iridium atom. Although excess
ethyne was available as a reactant in the preparation of 3, there
was no evidence for any further insertion of ethyne into either
the four-membered or five-membered iridacyclic rings. Unam-
biguous characterization of this substituent-free iridabicyclic
complex follows from 1H and 13C NMR spectra. In the 1H NMR
spectrum the most downfield signal at 12.06 ppm is assigned
to H3 and appears as a doublet (3JHH ) 5.1 Hz) coupling to
H2, which is assigned to the multiplet signal at 8.35 ppm. The
other Ir-CH, which is H4, appears as a doublet (3JHH ) 7.9
Hz) at 9.83 ppm, and H5 appears at 6.88 ppm as a doublet of
Figure 1. Molecular geometry of Ir(O2)I(CS)(PPh3)2 (2), showing
the atom labeling and atoms as 50% probability displacement
ellipsoids.
4
triplets (3JHH ) 7.9 Hz, JPH ) 1.5 Hz). In the 13C NMR
spectrum the most downfield CH signal is again associated with
C3 in the iridacyclobutadiene ring, which appears as a triplet
signal at 177.6 ppm (2JPC ) 9.3 Hz), while C4 appears as a
triplet signal at 157.1 ppm (2JPC ) 9.1 Hz). C2 and C5 appear
at 147.7 and 139.2 ppm, respectively, also as triplet signals.
The remaining iridium-bound iridacyclobutadiene carbon, C1,
appears as a triplet at 211.8 ppm (2JPC ) 5.1 Hz), the very
downfield position reflecting the multiple-bond character in this
Ir-C bond. In the 31P NMR spectrum the two equivalent
phosphorus atoms appear as a singlet at -10.13 ppm. To
confirm the structure of 3 and to gain further information relating
to the iridacyclobutadiene ring, an X-ray crystal structure
determination of 3 was undertaken.
The molecular structure of 3 is shown in Figure 2, and
selected bond distances and angles are collected in Table 3.
The geometry about iridium is close to octahedral, with the two
triphenylphosphine ligands arranged trans to one another, and
the bicyclic ring system is essentially planar. The Ir-C(1) bond
is easily the shortest of the three Ir-C bonds at 1.940(8) Å,
suggesting a bond order approaching 2. The bond distances Ir-
C(3) and Ir-C(4), on the other hand, are appropriate for single
bonds at 2.125(8) and 2.070(10) Å, respectively. In keeping
with these observed Ir-C single bonds, the measured distances
for C(2)-C(3) and C(4)-C(5) are 1.337(14) and 1.331(13) Å,
Figure 2. Molecular geometry of Ir[C3H2(CHdCHS-1)]I(PPh3)2
(3), showing the atom labeling and atoms as 50% probability
displacement ellipsoids.
1.454(8) Å in 2 is shorter than the observed value of 1.509(26)
Å in Ir(O2)I(CO)(PPh3)2.11 This would be expected, in view of
the reversibility of the dioxygen addition, and could possibly
be attributed to the greater π-accepting abilities of the CS ligand.
The attachment of the dioxygen is quite symmetrical, with the
two Ir-O distances being Ir-O(1) ) 2.049(5) Å and Ir-O(2)
) 2.035(5) Å. The Ir-I distance is 2.6850(6) Å, which is short
compared with the reported values for Ir(O2)I(CO)(PPh3)2
(2.767(5) and 2.738(5) Å)11 and is also shorter than the average
for 123 recorded observations for Ir-I bonds in six-coordinate
iridium (2.7564 with a SD of 0.060 Å; Cambridge Crystal-
lographic Data Base).

2170 Organometallics, Vol. 26, No. 9, 2007
Table 1. Data Collection and Processing Parameters for Compounds 2-8
Clark et al.
2‚CH2Cl2
3‚CH2Cl2
4‚2CH2Cl2
5‚CH2Cl2‚3C2H6O
6‚CH2Cl2
7‚3CDCl3
8‚1.75C6H6
formula
C37H30IIrO2-
P2S‚CH2Cl2
1004.64
monoclinic
P21/n
10.6388(2)
22.4279(5)
14.9570(3)
90.0
92.459(1)
90.0
3565.54(13)
85(2)
C41H34IIr-
P2S‚CH2Cl2
1024.71
monoclinic
P21
12.0872(3)
14.3121(3)
12.0945(3)
90.0
114.590(1)
90.0
1902.52(8)
85(2)
C53H42ClIr-
P2S‚2CH2Cl2
1170.40
monoclinic
P21
11.9631(2)
11.567292)
17.7181(1)
90.0
95.758(1)
90.0
2439.45(6)
83(2)
C53H42ClIrP2S‚
CH2Cl2‚3C2H6O
1223.65
triclinic
C43H33ClIr-
PS‚CH2Cl2
1850.60
triclinic
P1h
9.9230(1)
14.4690(1)
14.5649(1)
91.269(1)
108.801(1)
106.762(1)
1880.14(2)
83(2)
C45H38IIrO4-
P2S‚3CDCl3
1417.00
triclinic
P1h
11.8918(1)
13.5695(1)
18.9304(2)
70.741(1)
85.553(1)
65.585(1)
2619.74(4)
84(2)
C49H42ClIrO6-
P2S‚1.75C6H6
1185.17
monoclinic
P21/c
12.0065(4)
19.2784(6)
22.4702(8)
90.0
100.255(1)
90.0
5118.0(3)
83(2)
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
P1h
10.6941(1)
12.0101(1)
19.9108(1)
85.507(1)
83.165(1)
80.417(1)
2499.20(3)
83(2)
R, deg
â, deg
γ, deg
V, Å3
T, K
Z
4
2
2
2
2
2
4
d(calcd), g cm-3
F(000)
µ, mm-1
cryst size, mm
1.872
1944
4.943
1.789
996
4.630
1.593
1168
3.157
1.626
1240
2.986
0.40 × 0.20 ×
1.634
916
3.894
1.796
1380
3.740
1.538
2390
2.817
0.34 × 0.20 ×
0.20 × 0.20 × 0.42 × 0.34 × 0.26 × 0.20 ×
0.38 × 0.22 × 0.30 × 0.16 ×
0.06
0.30
3.70, 54.30
12 203
0.08
3.94, 52.70
14 814
0.20
0.12
3.92, 54.22
19 213
0.10
0.20
2θ (min, max), deg
no. of rflns collected 21 250
4.24, 52.82
4.12, 50.04
24 876
1.74, 25.70
24 044
1.72, 25.68
29 039
no. of indep rflns
7286
7714
9194
8816
8156
9896 (Rint
0.0395)
0.4000,
0.7061
1.035
)
29 039 (Rint
0.0216)
0.4476,
0.6027
)
T (min, max)
0.5171,
0.7719
0.2466,
0.3372
0.986
0.71877,
0.84328
1.018
0.461 99,
0.660 35
1.128
0.3193,
0.6523
1.041
goodness of fit on F2 1.027
1.086
R1, wR2 (obsd
data)a
R1, wR2 (all data)
0.0451,
0.1162
0.0556,
0.1233
0.0412,
0.1079
0.0419,
0.1091
0.0313,
0.0762
0.0324,
0.0771
0.0772,
0.1894
0.0831,
0.1930
0.0208,
0.0501
0.0231,
0.0514
0.0285,
0.0644
0.0348,
0.0666
0.0246,
0.0534
0.0306,
0.0567
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2
(see above). This reflects the different trans influencr of a
“carbene” carbon atom relative to that of a “peroxide” oxygen
atom.
Bond Lengths
Ir-C(1)
Ir-O(2)
Ir-O(1)
Ir-P(2)
1.833(9)
2.035(5)
2.049(5)
2.3695(17)
Ir-P(1)
2.3782(17)
2.6850(6)
1.454(8)
Ir-I
Reaction of IrCl(CS)(PPh3)2 with Phenylacetylene To
Form the Isomeric Tethered Iridacyclobutadienes Ir[C3H-
(CHdC{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4) and Ir[C3H(CHdC-
{Ph}S-1)(Ph-2)]Cl(PPh3)2 (5) and the Crystal Structures of
4 and 5. To explore the direction of addition of a substituted
alkyne, reaction between IrCl(CS)(PPh3)2 and phenylacetylene
was investigated. As shown in Scheme 4, two green-brown
isomers of a product analogous to complex 3 were detected,
arising from the direction of addition of the phenylacetylene
in the formation of the iridacyclobutadiene ring. Both com-
pounds have the same arrangement of the phenylacetylene in
the five-membered ring. The major isomer, Ir[C3H(CHd
C{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4), has the phenyl substituent in
the iridacyclobutadiene ring on the R-carbon atom: i.e., C(3).
The minor isomer, Ir[C3H(CHdC{Ph}S-1)(Ph-2)]Cl(PPh3)2
(5), has the phenyl substituent in the iridacyclobutadiene
ring on the â-carbon atom: i.e., C(2). Complex 5 was formed
in an impure state and in a yield of less than 5%. It was therefore
not possible to collect comprehensive experimental data for
this compound; however, a single crystal suitable for X-ray
analysis was obtained and the characterization of 5 rests mainly
O(1)-O(2)
Bond Angles
C(1)-Ir-O(2)
O(2)-Ir-O(1)
P(2)-Ir-P(1)
117.5(3)
41.7(2)
171.73(6)
C(1)-Ir-I
O(1)-Ir-I
105.2(3)
95.54(16)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 3
Bond Lengths
Ir-C(1)
Ir-C(4)
Ir-C(3)
Ir-P(1)
Ir-P(2)
Ir-I
1.940(8)
2.070(10)
2.125(8)
2.3487(15)
2.3513(15)
2.7810(5)
S-C(1)
1.661(9)
S-C(5)
1.739(11)
1.337(14)
1.491(14)
1.331(13)
C(3)-C(2)
C(2)-C(1)
C(4)-C(5)
Bond Angles
C(1)-Ir-C(4)
C(3)-Ir-C(1)
C(4)-Ir-C(3)
C(1)-Ir-I
84.3(4)
63.4(4)
C(2)-C(3)-Ir
C(3)-C(2)-C(1)
C(2)-C(1)-S
C(2)-C(1)-Ir
S-C(1)-Ir
C(4)-C(5)-S
C(5)-C(4)-Ir
97.7(6)
98.3(8)
147.7(3)
172.6(3)
102.7(3)
109.7(3)
96.7(4)
137.2(7)
100.7(6)
122.0(5)
122.2(8)
114.7(7)
C(4)-Ir-I
C(3)-Ir-I
C(1)-S-C(5)
1
on the structure determination (see below). In the H NMR
respectively, values which are indicative of double bonds
between these carbon atoms. Furthermore, the measured C(1)-
C(2) distance is 1.491(14) Å, indicative of a single bond.
Therefore, the valence bond structure used to depict complex 3
in Scheme 3 is quite appropriate: i.e., there is no evidence for
any significant bond delocalization in either the iridacyclob-
utadiene ring or the fused iridathiophene ring. The Ir-I distance
is 2.7810(5) Å, longer than the same distance in the dioxygen
adduct, complex 2, which is 2.6850(6) Å, and longer than the
average value in the Cambridge Crystallographic Data Base
spectrum of 4 the two ring protons H2 and H4 appear at
9.61 and 8.57 ppm, respectively, with H4 showing weak
phosphorus coupling (3JPH ) 3.0 Hz). In the 13C NMR spectrum
the most downfield carbon signal is again associated with
C1 in the iridacyclobutadiene ring, which appears as a triplet
signal at 206.3 ppm (2JPC ) 5.4 Hz), while C2 appears as a
triplet signal at 141.2 ppm (3JPC ) 4.6 Hz) and C3 as a triplet
signal at 195.3 ppm (2JPC ) 8.4 Hz). In the five-membered
ring C4 is observed as a triplet signal at 151.8 ppm (2JPC
10.7 Hz) and C5 as a singlet at 139.1 ppm. In the 31P
)

Iridacyclobutadienes
Organometallics, Vol. 26, No. 9, 2007 2171
Figure 5. Molecular geometry of Ir[C3H(CHdC{Ph}S-1)(Ph-2)]-
Cl(PPh3)2 (5), showing the atom labeling and atoms as 50%
probability displacement ellipsoids. Only the major component of
the disorder model (see Figure 4) is shown.
Figure 3. Molecular geometry of Ir[C3H(CHdC{Ph}S-1)(Ph-3)]-
Cl(PPh3)2 (4), showing the atom labeling and atoms as 50%
probability displacement ellipsoids.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for 5
Bond Lengths
Ir-C(1B)
Ir-C(1A)
Ir-C(4)
1.915(19)
1.953(15)
2.054(14)
2.107(12)
2.331(2)
2.332(2)
2.481(3)
1.60(2)
SB-C(1B)
1.67(2)
1.947(16)
1.44(2)
SB-C(2)
C(1A)-C(2)
C(1B)-C(5)
C(2)-C(3)
C(2)-C(6)
C(4)-C(5)
C(5)-C(12)
Ir-C(3)
1.40(2)
Ir-P(2)
Ir-P(1)
Ir-Cl(1)
SA-C(1A)
SA-C(5)
1.374(18)
1.454(17)
1.36(2)
Figure 4. Diagram illustrating the disorder of C1 and S atoms in
the crystal structure of complex 5.
1.461(16)
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 4
1.915(15)
Bond Lengths
Bond Angles
Ir-C(1)
Ir-C(4)
Ir-C(3)
Ir-P(1)
Ir-P(2)
Ir-Cl(1)
S-C(1)
1.940(5)
2.097(6)
S-C(5)
1.798(7)
1.420(9)
1.389(9)
1.473(8)
1.338(9)
1.496(8)
C(1A)-Ir-C(4)
C(1B)-Ir-C(3)
P(2)-Ir-P(1)
C(1A)-SA-C(5)
C(1B)-SB-C(2)
C(2)-C(1A)-SA
C(2)-C(1A)-Ir
89.0(7)
95.2(7)
SA-C(1A)-Ir
SB-C(1B)-Ir
124.0(10)
120.6(12)
92.3(11)
101.5(10)
109.4(11)
81.5(12)
C(1)-C(2)
C(2)-C(3)
C(3)-C(6)
C(4)-C(5)
C(5)-C(12)
2.125(6)
177.74(9)
93.1(7)
92.4(8)
129.6(12)
106.4(12)
C(3)-C(2)-C(1A)
C(2)-C(3)-Ir
2.3541(10)
2.3615(13)
2.4953(12)
1.685(6)
C(5)-C(4)-Ir
C(4)-C(5)-C(1B)
Bond Angles
single bonds. The observed distances for C(2)-C(3) and C(4)-
C(5) are 1.389(9) and 1.338(9) Å, respectively, values which
are appropriate for a somewhat delocalized bond between C(2)-
C(3) and for a double bond between C(4)-C(5). The C(1)-
C(2) distance is 1.420(9) Å. The Ir-Cl distance is 2.4953(12)
Å, which is long when compared with the average for 572
recorded observations for Ir-Cl bonds in six-coordinate iridium
(2.4046 Å with a SD of 0.066 Å; Cambridge Crystallographic
Data Base). This reflects the strong trans influence of the
“carbene” carbon atom (C1) in the iridacyclobutadiene ring. The
elongating effect of a genuine carbene ligand on the Ir-Cl bond
is well-illustrated in the structure of IrCl3(dCCl2)(PPh3)2, where
Ir-Cl (trans to CCl2) is 2.407(2) Å, whereas Ir-Cl (trans to
Cl) is 2.359(1) Å.12
P(1)-Ir-P(2)
C(4)-Ir-Cl(1)
C(3)-Ir-Cl(1)
C(1)-S-C(5)
C(2)-C(1)-Ir
176.10(11)
105.39(18)
106.40(18)
97.1(3)
S-C(1)-Ir
122.4(3)
100.4(5)
94.2(4)
116.7(5)
119.5(5)
C(3)-C(2)-C(1)
C(2)-C(3)-Ir
C(5)-C(4)-Ir
C(4)-C(5)-S
101.5(4)
NMR spectrum the two equivalent phosphorus atoms
appear as a singlet at -12.48 ppm. The 1H NMR spectroscopic
data collected for 5 are restricted to a signal at 12.78 ppm
for H3 and a signal at 10.03 ppm for H4. In the 31P NMR
spectrum of 5 the two equivalent phosphorus atoms appear
as a singlet at -4.38 ppm. To confirm the structures of 4
and 5, X-ray crystal structure determinations were under-
taken.
The molecular structure of 4 is shown in Figure 3, and
selected bond distances and angles are collected in Table 4.
The geometry about iridium is closely related to that observed
for complex 3 described above. The Ir-C(1) bond distance of
1.940(5) Å is identical with that found for 3 and again is much
shorter than the other two Ir-C bonds. The bond distances Ir-
C(3) ) 2.125(6) Å and Ir-C(4) ) 2.097(6) Å are very close to
those for complex 3 and are again indicative of these being
The crystal structure of 5 is disordered, and a diagram
illustrating the disorder of C1 and S atoms in the crystal structure
is shown in Figure 4. The molecular geometry of the major
component of the disorder model is shown in Figure 5. Selected
bond distances and angles are collected in Table 5. The Ir-
(12) Clark, G. R.; Roper, W. R.; Wright, A. H. J. Organomet. Chem.
1982, 236, C7.

2172 Organometallics, Vol. 26, No. 9, 2007
Clark et al.
Scheme 5
Figure 6. Molecular geometry of Ir[η5-C5H2(SCPhdCH-1)(Ph-
3)(Ph-5)]Cl(PPh3) (6), showing the atom labeling and atoms as 50%
probability displacement ellipsoids.
(PPh3) (6) is formed in high yield. The same compound is
formed when IrCl(CS)(PPh3)2 is heated with excess pheny-
lacetylene in toluene at reflux, but the yield is lower. A
feature unique to complex 4, which may contribute to this
particular reactivity, is the presence of a substituent (phenyl)
on the R-carbon atom of the iridacyclobutadiene ring. It is
probable that this reaction proceeds through an intermediate
tethered iridabenzene complex (formed through insertion of
the acetylene into the iridacyclobutadiene ring) and
subsequent elimination of the C5 fragment as a cyclopentadienyl
ligand (see Introduction, Scheme 2).10 In the 1H NMR spectrum
of 6 the two Cp ring protons H2 and H4 appear as doublets at
5.11 (4JHH ) 2.0 Hz) and 6.93 (4JHH ) 2.0 Hz) ppm. The
iridium-bound CH of the tethering arm (H6) appears as a
doublet at 8.09 ppm (3JPH ) 7.5 Hz). In the 13C NMR spectrum
the most downfield carbon signal is C7, which appears as a
doublet at 163.3 ppm (3JPC ) 4.0 Hz), while C6 appears at 130.4
ppm. The cyclopentadienyl ring carbons are observed at 82.5
(C2 or C4), 85.8 (C1), 93.2 (C3 or C5), 100.6 (C3 or C5), and
102.1 (C2 or C4) ppm. C1 alone shows phosphorus coupling
(2JPC ) 15.1 Hz), and the structural data to be discussed
below show that Ir-C(1) is considerably shorter than the
other Ir-C(2-5) distances: i.e., the tethered Cp ring is
displaced away from a symmetrical bonding position. In the
31P NMR spectrum the single phosphorus atom appears at
1.63 ppm.
The molecular structure of 6 is shown in Figure 6, and
selected bond distances and angles are collected in Table 6. As
is the case for other CpML3 complexes, the geometry about
iridium in 6 is that of a piano stool, with the presence of the
tether causing a displacement of the Cp ligand. This is clearly
revealed by the Ir-C distances, which are as follows (Å): Ir-
C(1) ) 2.122(2), Ir-C(2) ) 2.175(2), Ir-C(3) ) 2.370(2), Ir-
C(4) ) 2.320(2), Ir-C(5) ) 2.245(2) Å. The Ir-C(6) distance
is 2.029(2) Å, and the C(6)-C(7) distance is 1.354(3) Å. The
Ir-Cl distance is 2.3818(6) Å, which in this very different
geometrical environment is much shorter than the values found
in complexes 4 and 5 but is comparable to the values found
(2.408(3) and 2.406(3) Å) in the structurally related cyclopen-
tadienyl complex Cp*IrCl2(PPh3).13
Table 6. Selected Bond Lengths (Å) and Angles (deg) for 6
Bond Lengths
Ir-C(6)
Ir-C(1)
Ir-C(2)
Ir-C(5)
Ir-P(1)
Ir-C(4)
Ir-C(3)
Ir-Cl(1)
S(1)-C(1)
S(1)-C(7)
2.029(2)
2.122(2)
2.175(2)
2.245(2)
2.2858(6)
2.320(2)
2.370(2)
2.3818(6)
1.773(3)
1.798(2)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(3)-C(4)
C(3)-C(14)
C(4)-C(5)
C(5)-C(8)
C(6)-C(7)
C(7)-C(20)
1.443(3)
1.467(3)
1.449(3)
1.418(4)
1.478(4)
1.451(4)
1.479(3)
1.354(3)
1.481(3)
Bond Angles
P(1)-Ir-Cl(1)
89.93(2)
97.55(11)
108.3(2)
122.48(18)
128.98(19)
108.6(2)
C(4)-C(3)-C(2)
C(3)-C(4)-C(5)
C(4)-C(5)-C(1)
C(7)-C(6)-Ir
106.5(2)
111.2(2)
105.1(2)
121.46(18)
118.51(19)
C(1)-S(1)-C(7)
C(2)-C(1)-C(5)
C(2)-C(1)-S(1)
C(5)-C(1)-S(1)
C(1)-C(2)-C(3)
C(6)-C(7)-S(1)
C(1A) bond distance is 1.953(15) Å, similar to that found for
4. The bond distances Ir-C(3) ) 2.107(12) Å and Ir-C(4) )
2.054(14) Å are close to those for complex 4 and are again
indicative of these being single bonds. The observed distances
for C(2)-C(3) and C(4)-C(5) are 1.374(18) and 1.36(2) Å,
respectively, values which are appropriate for a somewhat
delocalized bond between C(2) and C(3) and for a double bond
between C(4) and C(5). The C(1A)-C(2) distance is 1.44(2)
Å. The Ir-Cl distance is 2.481(3) Å, which is longer than
the average for 572 recorded observations for Ir-Cl bonds in
six-coordinate iridium (2.4046 Å with a SD of 0.066 Å;
Cambridge Crystallographic Data Base), clearly reflecting the
marked trans influence of C(1), which is effectively a carbene
carbon. Similar observations have already been made for
complex 4.
Thermal Reaction of Ir[C3H(CHdC{Ph}S-1)(Ph-3)]Cl-
(PPh3)2 (4) with Phenylacetylene To Form the Tethered
Cyclopentadienyl Complex Ir[η5-C5H2(SCPhdCH-1)(Ph-3)-
(Ph-5)]Cl(PPh3) (6) and the Crystal Structure of 6. Of the
three tethered iridacyclobutadiene complexes described in this
paper, 3, 4, and 7 (see below), only complex 4 reacted with an
excess of the added acetylene at an elevated temperature to give
as the ultimate product a tethered cyclopentadienyl complex.
As shown in Scheme 4, when complex 4 is heated with excess
phenylacetylene at toluene reflux, the red, tethered cyclopen-
tadienyl complex Ir[η5-C5H2(SCPhdCH-1)(Ph-3)(Ph-5)]Cl-
Reaction of IrI(CS)(PPh3)2 (1) with Methyl Propiolate To
Form the Tethered Iridacyclobutadiene Ir[C3H(CHdC-
{CO2Me}S-1)(CO2Me-2)]I(PPh3)2 (7) and the Crystal Struc-
ture of 7. As shown in Scheme 5, when IrI(CS)(PPh3)2 (1) is
(13) Le Bras, J.; Amouri, H.; Vaissermann, J. J. Organomet. Chem. 1997,
548, 305.

Iridacyclobutadienes
Organometallics, Vol. 26, No. 9, 2007 2173
Table 7. Selected Bond Lengths (Å) and Angles (deg) for 7
Bond Lengths
Ir-C(1)
Ir-C(4)
Ir-C(3)
Ir-P(1)
Ir-P(2)
Ir-I
1.941(4)
2.042(3)
2.137(4)
2.3594(9)
2.3696(9)
2.7763(3)
1.670(4)
S-C(5)
1.806(4)
1.440(5)
1.373(6)
1.471(5)
1.342(5)
1.476(5)
C(1)-C(2)
C(2)-C(3)
C(2)-C(6)
C(4)-C(5)
C(5)-C(7)
S-C(1)
Bond Angles
C(1)-Ir-C(4)
C(1)-Ir-C(3)
C(4)-Ir-C(3)
C(1)-Ir-P(1)
C(4)-Ir-P(1)
C(3)-Ir-P(1)
C(1)-Ir-P(2)
C(4)-Ir-P(2)
C(3)-Ir-P(2)
P(1)-Ir-P(2)
C(1)-Ir-I
84.66(15)
63.46(15)
148.10(15)
92.77(11)
91.71(10)
89.15(10)
92.84(11)
93.31(10)
89.31(10)
172.79(3)
172.80(10)
102.54(11)
109.35(10)
86.83(2)
P(2)-Ir-I
87.04(2)
95.23(18)
135.0(3)
101.7(2)
123.2(2)
99.7(3)
129.8(3)
130.4(3)
95.1(2)
116.6(3)
129.5(4)
120.3(3)
110.2(3)
C(1)-S-C(5)
C(2)-C(1)-S
C(2)-C(1)-Ir
S-C(1)-Ir
C(3)-C(2)-C(1)
C(3)-C(2)-C(6)
C(1)-C(2)-C(6)
C(2)-C(3)-Ir
C(5)-C(4)-Ir
C(4)-C(5)-C(7)
C(4)-C(5)-S
C(7)-C(5)-S
C(4)-Ir-I
C(3)-Ir-I
P(1)-Ir-I
recorded observations for Ir-I bonds in six-coordinate iridium
(2.7564 Å with a SD of 0.060 Å; Cambridge Crystallographic
Data Base).
Figure 7. Molecular geometry of Ir[C3H(CHdC{CO2Me}S-1)-
(CO2Me-2)]I(PPh3)2 (7), showing the atom labeling and atoms as
50% probability displacement ellipsoids.
Ring Expansion of the Tethered Iridacyclobutadiene Ir-
[C3H(CHdC{CO2Me}S-1)(CO2Me-2)]I(PPh3)2 (7) through
Sequential Treatment First with AgO3SCF3, Followed by
Methyl Propiolate and LiCl, To Form the Tethered Irida-
benzene Ir[C5H2(CHdC{CO2Me}S-1)(CO2Me-2)(CO2Me-
4)]Cl(PPh3)2 (8) and the Crystal Structure of 8. Under the
conditions used for the preparation of complex 7, there was no
indication of further reaction with the excess methyl propiolate
present. This could be attributed to the inertness of the octahedral
iridium(III) complex toward ligand dissociation, which in turn
prevents further methyl propiolate coordinating to iridium as a
prelude to expansion of the four-membered ring. We therefore
explored the use of silver triflate as a reagent to remove the
iodide ligand as silver iodide from complex 7, thus facilitating
coordination of methyl propiolate, which was added in a
subsequent step. As depicted in Scheme 5, this strategy is
successful and addition of lithium chloride to the blue-green
solution resulting from sequential addition of silver triflate and
methyl propiolate to 7 at room temperature allowed isolation
of the blue tethered iridabenzene Ir[C5H2(CHdC{CO2Me}S-
1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8) in high yield. It can be
noted here that similar ring-expansion reactions, using silver
triflate followed by methyl propiolate, were attempted with both
complexes 3 and 4 but led only to intractable mixtures. This
successful synthesis of 8 represents a verification of the often
postulated ring-expansion step converting a metallacyclobuta-
diene to a metallabenzene through reaction with an acetylene.8,9
A possibly related observation is the ultimate formation of a
cyclopentadienyl complex (from two acetylene moieties and a
CS ligand) via a postulated metallabenzene intermediate, which
in turn may arise from a related ring-expansion reaction.14
heated at benzene reflux with an excess of methyl propiolate,
the dark green tethered iridacyclobutadiene Ir[C3H(CHdC{CO2-
Me}S-1)(CO2Me-2)]I(PPh3)2 (7) is formed. It can be noted that
this compound has the same positioning of substituents on the
four- and five-membered rings as was found in complex 5. No
evidence was found for the formation of any other isomers, as
was the case in the reactions with phenylacetylene (see above).
Treatment of 1 with excess methyl propiolate at elevated
temperatures gave no indication of the formation of a tethered
Cp complex analogous to complex 6. In the 1H NMR spectrum
of 7 the two ring protons H3 and H4 appear at 13.23 and 11.45
ppm, respectively, both signals appearing as singlets. In the 13
C
NMR spectrum the most downfield carbon signal is again
associated with C1 in the iridacyclobutadiene ring, which
appears as a triplet signal at 214.2 ppm (2JPC ) 4.4 Hz), while
C2 appears as a triplet signal at 153.5 ppm (3JPC ) 4.5 Hz) and
C3 as a triplet signal at 198.9 ppm (2JPC ) 10.6 Hz). These
values are all close to those discussed above for complexes 3
and 4. In the five-membered ring C4 is observed as a triplet
signal at 177.9 ppm (2JPC ) 8.5 Hz) and C5 as a singlet at
148.8 ppm. In the 31P NMR spectrum the two equivalent
phosphorus atoms appear as a singlet at -8.75 ppm.
A crystal structure determination of complex 7 revealed the
same basic geometry for the tethered iridacyclobutadiene
skeleton that had been found in complexes 3-5. The molecular
geometry of 7 is shown in Figure 7. Selected bond distances
and angles are collected in Table 7. The Ir-C(1) bond distance
of 1.941(4) Å is similar to those found for 3-5. The bond
distances Ir-C(3) ) 2.137(4) Å and Ir-C(4) ) 2.042(3) Å are
close to those for complexes 3-5 and are again indicative of
these being single bonds. The observed distances for C(2)-
C(3) and C(4)-C(5) are 1.373(6) and 1.342(5) Å, respectively,
values which are appropriate for a somewhat delocalized bond
between C(2) and C(3) and for a double bond between C(4)
and C(5). The C(1)-C(2) distance is 1.440(5) Å. The Ir-I
distance of 2.7763(3) Å is very close to that found in complex
3 (2.7810(5) Å) and is long compared with the average for 123
1
In the H NMR spectrum of 8 the two protons in the six-
membered iridabenzene ring, H3 and H5, appear as doublets at
7.63 (4JHH ) 2.4 Hz) and 13.25 (4JHH ) 2.4 Hz) ppm,
respectively. These chemical shifts are entirely consistent with
those of other reported iridabenzenes.12 H6, in the five-
membered tethering ring, appears as a singlet at 10.70 ppm. In
(14) Hill, A. F.; Schultz, M.; Willis, A. C. Organometallics 2005, 24,
2027.

2174 Organometallics, Vol. 26, No. 9, 2007
Clark et al.
Table 8. Selected Bond Lengths (Å) and Angles (deg) for 8
Bond Lengths
Ir-C(1)
Ir-C(5)
Ir-C(6)
Ir-P(1)
Ir-P(2)
Ir-Cl
1.973(3)
2.042(3)
2.106(3)
2.3622(7)
2.3667(8)
2.4685(7)
1.722(3)
1.765(3)
C(1)-C(2)
C(2)-C(3)
C(2)-C(8)
C(3)-C(4)
C(4)-C(5)
C(4)-C(9)
C(6)-C(7)
C(7)-C(10)
1.449(4)
1.361(4)
1.515(4)
1.434(4)
1.360(4)
1.480(4)
1.341(4)
1.477(4)
S-C(1)
S-C(7)
Bond Angles
C(1)-Ir-C(5)
C(1)-Ir-C(6)
C(5)-Ir-C(6)
C(1)-Ir-P(1)
C(5)-Ir-P(1)
C(6)-Ir-P(1)
C(1)-Ir-P(2)
C(5)-Ir-P(2)
C(6)-Ir-P(2)
P(1)-Ir-P(2)
C(1)-Ir-Cl
91.39(12)
84.17(12)
175.49(11)
91.11(8)
93.10(8)
86.17(8)
94.93(8)
89.53(8)
91.67(8)
173.35(3)
176.46(9)
85.07(9)
99.36(8)
88.86(2)
85.28(2)
98.80(14)
C(2)-C(1)-S
114.6(2)
C(2)-C(1)-Ir
S-C(1)-Ir
125.5(2)
119.84(16)
124.5(3)
116.0(3)
119.5(3)
128.2(3)
121.8(3)
122.6(3)
115.6(3)
128.3(2)
117.8(2)
124.2(3)
119.1(2)
116.2(2)
C(3)-C(2)-C(1)
C(3)-C(2)-C(8)
C(1)-C(2)-C(8)
C(2)-C(3)-C(4)
C(5)-C(4)-C(3)
C(5)-C(4)-C(9)
C(3)-C(4)-C(9)
C(4)-C(5)-Ir
C(7)-C(6)-Ir
C(6)-C(7)-C(10)
C(6)-C(7)-S
C(5)-Ir-Cl
C(6)-Ir-Cl
P(1)-Ir-Cl
P(2)-Ir-Cl
C(10)-C(7)-S
C(1)-S-C(7)
Figure 8. Molecular geometry of Ir[C5H2(CHdC{CO2Me}S-1)-
(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8), showing the atom labeling and
atoms as 50% probability displacement ellipsoids.
double bonds. The carbon-carbon distances within this six-
membered ring are as follows (Å): C(1)-C(2) ) 1.449(4),
C(2)-C(3) ) 1.361(4), C(3)-C(4) ) 1.434(4), C(4)-C(5) )
1.360(4) Å. These values lie between single- and double-bond
distances and are similar to measured carbon-carbon distances
in other iridabenzenes,15 but the delocalization is clearly not
perfect and the values suggest that valence bond structure A in
Figure 9 is more important than B. In fact, a very similar set of
carbon-carbon distances has been reported for a related
“iridaphenol” complex,16 which is represented in Figure 9 by
valence bond structures C and D. The six-membered iridaben-
zene ring exhibits a high degree of planarity, the deviations from
the mean plane through Ir, C(1), C(2), C(3), C(4), and C(5)
being Ir (0.042 Å), C(1) (0.025 Å), C(2) (0.017 Å), C(3) (0.041
Å), C(4) (0.001 Å), and C(5) (0.042 Å). In the five-membered
ring the Ir-C(6) distance is 2.106(3) Å, indicative of a single
bond, and the C(6)-C(7) distance is 1.341(4) Å, entirely
appropriate for a double bond. Clearly there is no structural
support for any significant delocalization within the five-
membered ring. The Ir-Cl distance of 2.4685(7) Å is shorter
than that found in either complex 4 (2.4953(12) Å) or complex
5 (2.481(3) Å) but is still long compared with the average for
572 recorded observations for Ir-Cl bonds in six-coordinate
iridium (2.4046 Å with a SD of 0.066 Å; Cambridge Crystal-
lographic Data Base).
Despite the fact that complex 4 reacts with further pheny-
lacetylene under forcing conditions to give as the ultimate
product the tethered Cp complex 6 (presumably through the
intermediate iridabenzene Ir[C5H2(CHdCPhS-1)(Ph-3)(Ph-5)]-
Cl(PPh3)2), the ester-substituted iridabenzene Ir[C5H2(CHdC{CO2-
Me}S-1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 is recovered un-
changed after heating under reflux in toluene for 1 h. This
increased thermal stability, and resistance to elimination of the
C5 fragment as a cyclopentadienyl ligand, may be due to the
fact that C(5) is unsubstituted, as well as to the electron-
withdrawing nature of the ester substituents and the ring
positions of these substituents.
Figure 9. Contributing valence bond structures for complex 8 and
for the related iridaphenol.
the 13C NMR spectrum the iridium-bound carbon atoms C1 and
C5 appear as triplets at characteristic downfield positions of
252.7 (2JPC ) 2.8 Hz) and 247.5 (2JPC ) 7.8 Hz) ppm. These
positions are conspicuously further downfield than the positions
observed in any of the tethered iridacyclobutadiene complexes
3, 4, and 7 and are consistent with significant multiple bonding
in both the Ir-C(1) and Ir-C(5) bonds. The remaining three
iridabenzene ring carbon atoms all appear as singlets at 124.0
(C2), 162.0 (C3), and 126.8 (C4) ppm. In the five-membered
ring C6 is observed as a triplet signal at 198.2 ppm (2JPC
)
11.0 Hz) and C7 also as a triplet at 143.7 ppm (3JPC ) 2.5 Hz).
In the 31P NMR spectrum the two equivalent phosphorus atoms
appear as a singlet at -0.34 ppm.
A crystal structure determination of complex 8 confirmed the
presence of the tethered iridabenzene and provided structural
evidence for delocalization of bonds within the six-membered
ring. The molecular geometry of 8 is shown in Figure 8. Selected
bond distances and angles are collected in Table 8. In
comparison with all of the tethered iridacyclobutadiene com-
plexes, the two Ir-C bonds in the six-membered ring tend
toward equalization, with Ir-C(1) being 1.973(3) Å and Ir-
C(5) being 2.042(3) Å, values intermediate between single and
(15) (a) Bleeke, J. R. Chem. ReV. 2001, 101, 1205. (b) Landorf, C. W.;
Haley, M. M. Angew. Chem., Int. Ed. 2006, 45, 3914.
(16) Bleeke, J. R.; Behm, R. J. Am. Chem. Soc. 1997, 119, 8503.

Iridacyclobutadienes
Organometallics, Vol. 26, No. 9, 2007 2175
Preparation of IrI(CS)(PPh3) (1). Potassium iodide (0.622 g,
3.75 mmol) dissolved in a mixture of ethanol (10 mL) and water
(1 mL) was added to a solution of IrCl(CS)(PPh3)2 (0.600 g, 0.75
mmol) in chloroform (60 mL) under nitrogen. The resulting solution
was stirred under nitrogen at room temperature for 18 h, during
which time the color became a darker orange. Removal of all the
volatiles under vacuum produced a solid which was washed with
water, ethanol, and finally hexane. This solid was recrystallized
with exclusion of air from dichloromethane/ethanol to give pure 1
as orange needles (0.635 g, 92%). Anal. Calcd for C37H30IIrP2S:
C, 50.05; H, 3.40; P, 6.97. Found: C, 49.86; H, 3.58; P, 7.13. IR
(cm-1): 1322 s ν(CS). 1H NMR (CDCl3, δ): 7.37-7.80 (m, 30H,
PPh3). 13C NMR (CDCl3, δ): 127.8 (broad, P coupling not resolved,
o-PPh3), 130.1 (s, p-PPh3), 135.3 (broad, P coupling not resolved,
m-PPh3), 240.8 (broad, P coupling not resolved, CS). 31P NMR
(CDCl3, δ): 24.36 (s).
A final observation regarding the tethering arm in complex
8, and also in the tethered iridabutadiene complexes 3-5
and 7, may be appropriate. Because the tethering arm in
complex 8 is unsaturated, an alternative way of viewing this
molecule would be as a complex which arises from a fusion
of an iridabenzene and an iridathiophene: i.e., as an
iridabenzothiophene. Likewise the complexes 3-5 and 7 could
be viewed as arising from a fusion of iridabutadienes and
iridathiophenes. We have chosen not to emphasize this
point of view mainly because, as discussed above, there is
very little evidence for delocalization within the five-membered
rings.
Conclusions
The first step in the often postulated ring-expansion reaction
of a metallacyclobutadiene with an acetylene, to give first an
unstable intermediate metallabenzene and subsequently a stable
cyclopentadienyl complex, has been verified by converting a
structurally characterized iridacyclobutadiene, Ir[C3H(CHdC{CO2-
Me}S-1)(CO2Me-2)]I(PPh3)2 (7), through reaction with methyl
propiolate, to a stable iridabenzene, Ir[C5H2(CHdC{CO2Me}S-
1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8). This iridabenzene proves
to be resistant to conversion to a cyclopentadienyl complex,
even under very forcing conditions. However, treatment of
another iridacyclobutadiene, Ir[C3H(CHdC{Ph}S-1)(Ph-3)]Cl-
(PPh3)2 (4), involving different ring substituents, with pheny-
lacetylene does not give an isolable iridabenzene but instead
forms the tethered cyclopentadienyl complex Ir[η5-C5H2(SCPhd
CH-1)(Ph-3)(Ph-5)]Cl(PPh3) (6) directly. The formation of the
iridabenzene 8 demonstrates that thiocarbonyl ligands are useful
for preparing metallabenzene complexes not only on osmium
but also on iridium.
Preparation of Ir(O2)I(CS)(PPh3) (2). A solution of IrI(CS)-
(PPh3) (1; 0.600 g) in CH2Cl2 (60 mL) was stirred in air for 1 h,
during which time the color changed from orange to a dark red-
brown. Addition of ethanol (10 mL) and removal of the CH2Cl2
using a rotary evaporator produced pure 2 as a brown microcrys-
talline solid in quantitative yield. Brown crystals suitable for X-ray
study were grown by slow evaporation from a solution in CH2Cl2/
heptane at room temperature over several days. A crystal structure
determination confirmed the presence of one molecule of CH2Cl2
of solvation. Anal. Calcd for C37H30IIrO2P2S‚CH2Cl2: C, 45.43;
H, 3.21. Found: C, 44.80; H, 3.30. IR (cm-1): 1321 s ν(CS); 858
m ν(Ir-O2). 1H NMR (CDCl3, δ): 7.35-7.62 (m, 30H, PPh3). 13
C
NMR (CDCl3, δ): 127.6 (t′,17 1,3JPC ) 58.4 Hz, i-PPh3), 128.0 (t′,
2,4
3,5
J
) 10.0 Hz, o-PPh3), 130.9 (s, p-PPh3), 135.1 (t′,
J
)
PC
PC
10.0 Hz, m-PPh3), 259.6 (t, 2JPC ) 9.1 Hz, CS). 31P NMR (CDCl3,
δ): 5.19 (s).
Preparation of Ir[C3H2(CHdCHS-1)I(PPh3)2 (3). This syn-
thesis may be carried out using either IrI(CS)(PPh3)2 or IrI(O2)-
(CS)(PPh3)2 as the starting material. A solution of IrI(O2)(CS)-
(PPh3)2 (0.310 g, 0.34 mmol) in benzene (30 mL) was placed in a
Fisher-Porter bottle and subjected to ethyne under a pressure of
20 psi (Caution! A safety shield is neededspotential explosion risk.)
with heating at a temperature of 75 °C for 21 h to give a green-
brown solution. After the mixture was cooled and the bottle vented,
the solvent was removed under reduced pressure to give a brown
solid, which was recrystallized from CH2Cl2 and EtOH to give pure
3 as a green-brown crystalline solid (0.184 g, 56%). Crystal structure
determination confirmed the presence of one molecule of CH2Cl2
of solvation. Anal. Calcd for C41H34IIrP2S‚CH2Cl2: C, 49.23; H,
3.54. Found: C, 49.05; H, 3.65%. 1H NMR (CDCl3, δ): 6.88 (dt,
Spectroscopic data are supportive of extensively delocalized
bonding in the stable iridabenzene Ir[C5H2(CHdC{CO2Me}S-
1)(CO2Me-2)(CO2Me-4)]Cl(PPh3)2 (8), but the structural data,
while confirming the aromatic nature of the IrC5 ring, indicates
that there is perhaps some localization of the bonds in a pattern
which is very similar to that of a previously reported iridaphenol.
Experimental Section
General Procedures and Instruments. Standard laboratory
procedures were followed as have been described previously.17 The
18,19
compound IrCl(CS)(PPh3)2
literature methods.
was prepared according to the
3
4
1H, JHH ) 7.9 Hz, JPH ) 1.5 Hz, H5 (see atom numbering in
Scheme 1)), 7.27-7.61 (m, 30H, PPh3), 8.35 (m, 1H, H2), 9.83
Infrared spectra (4000-400 cm-1) were recorded as Nujol mulls
between KBr plates on a Perkin-Elmer Paragon 1000 spectrometer.
NMR spectra were obtained on either a Bruker DRX 400 or a
Bruker Avance 300 instrument at 25 °C. For the Bruker DRX 400,
1H, 13C, and 31P NMR spectra were obtained operating at 400.1
(1H), 100.6 (13C), and 162.0 (31P) MHz, respectively. For the Bruker
Avance 300, 1H, 13C, and 31P NMR spectra were obtained operating
at 300.13 (1H), 75.48 (13C), and 121.50 (31P) MHz, respectively.
Resonances are quoted in ppm and 1H NMR spectra referenced to
either tetramethylsilane (0.00 ppm) or the protio impurity in the
solvent (7.25 ppm for CHCl3). 13C NMR spectra were referenced
to CDCl3 (77.00 ppm) and 31P NMR spectra to 85% orthophos-
phoric acid (0.00 ppm) as an external standard. Elemental analyses
were obtained from the Microanalytical Laboratory, University of
Otago.
(d, 1H, 3JHH ) 7.9 Hz, H4), 12.06 (d, 1H, 3JHH ) 5.1 Hz, H3). 13
C
NMR (CDCl3, δ): 127.1-135.4 (m, PPh3 carbon resonances
3
not individually assigned), 139.2 (t, JPC ) 3.1 Hz, C5), 147.7 (t,
3JPC ) 4.7 Hz, C2), 157.1 (t, 2JPC ) 9.1 Hz, C4), 177.6 (t, 2JPC
)
2
9.3 Hz, C3), 211.8 (t, JPC ) 5.1 Hz, C1). 31P NMR (CDCl3, δ):
-10.13 (s).
Preparation of Ir[C3H(CHdC{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4).
A suspension of IrCl(CS)(PPh3)2 (0.500 g, 0.63 mmol) together
with phenylacetylene (1 mL) in benzene (50 mL) was heated under
reflux for 6 h to give a dark brown solution. All volatiles were
removed under reduced pressure, and the residue was recrystallized
from CH2Cl2 and heptane to give a brown solid, which was further
recrystallized from CH2Cl2 and EtOH (twice) to give pure 4 as a
green-brown, crystalline solid (0.250 g, 36%). The filtrates from
these recrystallizations were combined and used for the isolation
of the other isomer, compound 5 (see below). Anal. Calcd for
C53H42ClIrP2S‚CH2Cl2: C, 59.75; H, 4.09. Found: C, 59.73; H,
(17) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J.
Organometallics 1996, 15, 1793.
(18) Lu, G.-L.; Roper, W. R.; Wright, L. J.; Clark, G. R. J. Organomet.
Chem. 2005, 690, 972.
1
4.10. H NMR (CDCl3, δ): 6.84-7.68 (m, 40H, Ph and PPh3),
(19) Hill, A. F.; Wilton-Ely, J. D. E. T. Inorg. Synth. 2002, 33, 244.
8.57 (t, 3JPH ) 3.0 Hz, 1H, H4), 9.61 (s, 1H, H2). 13C NMR (CDCl3,

2176 Organometallics, Vol. 26, No. 9, 2007
Clark et al.
δ): 126.1-135.0 (m, PPh3 and Ph carbon resonances not individu-
) 57.0 Hz, i-PPh3), 130.4 (s, p-PPh3), 134.9 (broad, P coupling
not resolved, m-PPh3), 148.8 (s, C5), 153.5 (t, 3JPC ) 4.5 Hz, C2),
159.1 (s, C6), 161.8 (s, C7), 177.9 (t, 2JPC ) 8.5 Hz, C4), 198.9 (t,
2JPC ) 10.6 Hz, C3), 214.2 (t, 2JPC ) 4.4 Hz, C1). 31P NMR (CDCl3,
δ): -8.75 (s).
3
ally assigned), 139.1 (s, C5), 141.2 (t, JPC ) 4.6 Hz, C2), 146.6
(s, Ph on C5), 151.8 (t, 2JPC ) 10.7 Hz, C4), 157.1 (s, Ph on C3),
2
2
195.3 (t, JPC ) 8.4 Hz, C3), 206.3 (t, JPC ) 5.4 Hz, C1). 31P
NMR (CDCl3, δ): -12.48 (s).
Preparation of Ir[C5H2(CHdC{CO2Me}S-1)(CO2Me-2)-
(CO2Me-4)]Cl(PPh3)2 (8). A green solution of compound 7 (0.150
g, 0.14 mmol) in THF (15 mL) was treated with AgO3SCF3 (0.039
g, 0.15 mmol) in THF (1.5 mL) to give a brown solution together
with a pale yellow precipitate of AgI. After 1 h, methyl propiolate
(0.028 mL, 0.30 mmol) was added and the resulting mixture was
stirred for another 1 h to give a green solution. LiCl (0.032 g, 0.75
mmol) was added and the reaction mixture stirred for another 1 h.
All volatiles were then removed under vacuum. The resulting solid
was extracted with benzene and the extract filtered through Celite.
The filtrate was then concentrated, and hexane was added to produce
a brownish green precipitate. This was recrystallized from CH2-
Cl2/EtOH/benzene to give pure 3 as a blue-green solid (0.120 g,
82%). The elemental analysis of this sample corresponded to 1
benzene of solvation per molecule of 3. However, the blue single
crystal chosen for X-ray structure determination that was grown
over several days from CH2Cl2/EtOH/benzene proved to contain
1.75 benzenes of solvation per molecule of 3. Anal. Calcd for
C49H42ClIrO6P2S‚C6H6: C, 58.63; H, 4.29. Found: C, 58.84; H,
Preparation of Ir[C3H(CHdC{Ph}S-1)(Ph-2)]Cl(PPh3)2 (5).
The solid isolated from the combined filtrates obtained during the
isolation of compound 4 (see above) was subjected to column
chromatography on silica gel using CH2Cl2 as eluent. Three bands
were observed, the first of which proved to contain complex 6 (in
5% yield, see below), the second of which was not identified, and
the third brown band yielded impure 5 in very low yield (less than
5%). Because of the low yield and impure nature of this material
only limited spectroscopic data were collected for this compound,
but fortuitously a single crystal of compound 5, suitable for X-ray
study, was grown from CH2Cl2/heptane and characterization of this
1
compound rests principally on the crystal structure obtained. H
NMR (CDCl3, δ): 10.03 (s, H4), 12.78 (s, H3). 31P NMR (CDCl3,
δ): -4.38 (s).
Preparation of Ir[η5-C5H2(SCPhdCH-1)(Ph-3)(Ph-5)]Cl-
(PPh3) (6). Ir[C3H(CHdC{Ph}S-1)(Ph-3)]Cl(PPh3)2 (4; 0.100 g,
0.10 mmol) and phenylacetylene (0.110 mL, 1.00 mmol) in toluene
(20 mL) were heated under reflux for 1 h to give a dark red solution.
All volatiles were removed under reduced pressure, and the resulting
residue was washed with hexane. The resulting solid was recrystal-
lized from CH2Cl2/EtOH to give pure 6 as red crystals (0.080 g,
93%). Compound 6 could also be made directly from IrCl(CS)-
(PPh3)2 and excess phenylacetylene by heating in toluene under
reflux for 1 h and using an isolation procedure similar to that
described above but with an additional step involving chromatog-
raphy on silica gel with a mixture of CH2Cl2 and hexane (1:1) as
eluent. The yield by this route is approximately 50%. Crystals
suitable for X-ray study were grown from CH2Cl2/EtOH over
several days and proved to be a 1:1 CH2Cl2 solvate. Anal. Calcd
for C43H33ClIrPS‚CH2Cl2: C, 57.11; H, 3.81. Found: C, 57.41; H,
1
4.34. IR (cm-1): 1703, 1698, 1694 (CO2Me). H NMR (CDCl3,
δ): 3.54 (s, 3H, CO2CH3 on C7), 3.56 (s, 3H, CO2CH3 on C4),
3.60 (s, 3H, CO2CH3 on C2), 7.23-7.62 (m, 30H, PPh3), 7.63 (d,
4
4JHH ) 2.4 Hz, 1H, H3), 10.70 (s, 1H, H6), 13.25 (d, JHH ) 2.4
Hz, 1H, H5). 13C NMR (CDCl3, δ): 51.4 (broad, CO2CH3 on C2,
C4, C7 not resolved), 124.0 (s, C2), 126.8 (s, C4), 127.6 (t′, 2,4JPC
) 10.0 Hz, o-PPh3), 129.9 (t′, 1,3JPC ) 58.4 Hz, i-PPh3), 130.3 (s,
p-PPh3), 134.4 (t′, 3,5JPC ) 10.0 Hz, m-PPh3), 143.7 (t, 3JPC ) 2.5
Hz, C7), 161.0 (s, C10), 162.0 (s, C3), 165.3 (s, C9), 166.6 (s,
2
2
C8), 198.2 (t, JPC ) 11.0 Hz, C6), 247.5 (t, JPC ) 7.8 Hz, C5),
252.7 (t, JPC ) 2.8 Hz, C1). 31P NMR (CDCl3, δ): -0.34 (s).
2
1
4
X-ray Crystal Structure Determinations for Complexes 2-8.
X-ray intensities were recorded on a Siemens SMART diffracto-
meter with a CCD area detector using graphite-monochromated Mo
KR radiation (λ ) 0.710 73 Å) between 83 and 85 K. Data were
integrated and corrected for Lorentz and polarization effects using
SAINT.20 Semiempirical absorption corrections were applied on
the basis of equivalent reflections using SADABS.21 The structures
were solved by direct or Patterson methods and refined by full-
matrix least squares on F2 using the programs SHELXS9722 and
SHELXL97.23 All hydrogen atoms which have been included were
located geometrically and refined using a riding model. In the
structure of 2 there is a small elongation of the thermal ellipsoid
of the sulfur atom and the presence nearby of peaks in the final
difference map. This suggests that there may be a minor partial
positional disorder between the I and CS ligands; however, no
attempt was made to model this. Diagrams were produced using
ORTEP3.24
3.97. H NMR (CDCl3, δ): 5.11 (d, JHH ) 2.0 Hz, 1H, H2 or
H4), 6.75-6.80 (m, 3H, Ph substituents), 6.99-7.43 (m, 27H, PPh3
and Ph substituents), 6.93 (d, 4JHH ) 2.0 Hz, 1H, H2 or H4), 8.09
(d, JPH ) 7.5 Hz, 1H, H6). 13C NMR (CDCl3, δ): 82.5 (s, CH,
3
C2 or C4), 85.8 (d, 2JPC ) 15.1 Hz, C1), 93.2 (s, C3 or C5), 100.6
(s, C3 or C5), 102.1 (s, CH, C2 or C4), 128.0 (d, 2JPC ) 11.1 Hz,
o-PPh3), 130.5 (s, p-PPh3), 131.3 (d, 1JPC ) 57.3 Hz, i-PPh3), 134.3
3
(d, JPC ) 10.1 Hz, m-PPh3), 124.8, 125.9, 126.1, 127.2, 127.6,
127.7, 128.2, 128.7, 128.8, 130.9, 132.2, 139.8 (s, carbon atoms of
Ph substituents), 130.4 (s (P coupling not resolved), CH, C6), 163.3
3
(d, JPC ) 4.0 Hz, C7). 31P NMR (CDCl3, δ): 1.63 (s).
Preparation of Ir[C3H(CHdC{CO2Me}S-1)(CO2Me-2)]I-
(PPh3)2 (7). IrI(CS)(PPh3)2 (0.400 g, 0.45 mmol) and methyl
propiolate (0.400 mL, 4.5 mmol) were added to benzene (40 mL),
and the resulting suspension was stirred for 1 h at room temperature.
The suspension was then heated under reflux for 5 min to give a
dark brown solution. After the mixture was cooled, its volume was
reduced to ca. 2 mL, and hexane (10 mL) was added to precipitate
a solid. This crude product was dissolved in CH2Cl2 and purified
by chromatography on a silica gel column (3 cm) using CH2Cl2 as
eluent. A green band was collected and solvent removed to give a
brownish green solid. This was recrystallized first from CH2Cl2/
heptane and then from CH2Cl2/EtOH to give pure 2 as a dark green
crystalline solid (0.258 g, 54%). The single crystal chosen for X-ray
structure determination was grown from CDCl3/MeOH over several
days and proved to have three CDCl3 molecules of solvation. Anal.
Calcd for C45H38IIrO4P2S: C, 51.19; H, 3.63. Found: C, 51.39; H,
All the crystal structures contain solvent molecules of crystal-
lization. For complex 5, Squeeze indicates that the crystals may
also contain three disordered molecules of ethanol of solvation.
Crystal data and refinement details for all structures are presented
in Table 1.
(20) SAINT: Area Detector Integration Software; Siemens Analytical
Instruments Inc., Madison, WI, 1995.
(21) Sheldrick, G. M. SADABS: Program for Semi-empirical Absorption
Correction; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(22) Sheldrick, G. M. SHELXS97: Program for Crystal Structure
Determination; University of Go¨ttingen, Go¨ttingen, Germany, 1977.
(23) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(24) Burnett, M. N.; Johnson, C. K. ORTEP-III: Oak Ridge Thermal
Ellipsoid Plot Program for Crystal Structure Illustrations; Report ORNL-
6895; Oak Ridge National Laboratory, Oak Ridge, TN, 1996.
1
3.68%. IR (cm-1): 1704, 1694 (CO2Me). H NMR (CDCl3, δ):
3.53 (s, 3H, CO2CH3 on C2), 3.77 (s, 3H, CO2CH3 on C5), 7.28-
7.47 (m, 30H, PPh3), 11.45 (s, 1H, H4), 13.23 (s, 1H, H3). 13C
NMR (CDCl3, δ): 50.6 (s, CO2CH3 on C2), 52.1 (s, CO2CH3 on
C5), 127.6 (broad, P coupling not resolved, o-PPh3), 129.6 (t′, 1,3JPC

Iridacyclobutadienes
Organometallics, Vol. 26, No. 9, 2007 2177
is available free of charge via the Internet at http://pubs.acs.org.
Crystal data are also available from the Cambridge Crystallographic
DataCentre(fax,+44-1223-336-033;e-mail,deposit@ccdc.cam.ac.uk;
web, www: http://www.ccdc.cam.ac.uk) as Supplementary Publica-
tion Nos. CCDC 627308-627314 for 2-8, respectively.
Acknowledgment. We thank the Marsden Fund, adminis-
tered by the Royal Society of New Zealand, for granting a
Postdoctoral Fellowship to G.-L.L. We also thank The Univer-
sity of Auckland Research Committee for partial support of this
work through grants-in-aid.
Supporting Information Available: CIF files containing
X-ray crystallographic data for complexes 2-8. This material
OM061066R