Reactive indolyl complexes of group 9 metals

Article abstract of DOI:10.1021/om060591n

A series of novel indolyl-imine ligand precursors have been synthesized. In particular, bidentate, tridentate, and potentially tetradentate ligands were prepared, each containing both indolyl sp²-N and imine sp ²-N donors. A series of neutral rhodium(I) and iridium(I) complexes of these ligands were synthesized, including monometallic and bimetallic complexes. The X-ray structures of three of the monometallic complexes with bidentate indolyl-imine ligands were determined. In each complex, the metal center was in a square planar conformation, as expected for Rh(I) and Ir(I) complexes. The five-and six-membered metallocycles formed on complexation of the metal with the ligands were all planar, and the aromaticity of the ligands was maintained. The Rh(I) complex with the tridentate indolyl ligand (L) reacted at room temperature with CH₂Cl₂ to form the Rh(III) chloromethyl complex [Rh(L)(CO)-(CH₂Cl)(Cl)] via oxidative addition of the C-Cl bond of CH₂Cl₂. The Rh/Ir(I) indolyl-imine complexes are efficient catalysts for the intramolecular cyclization of 4-pentynoic acid to form γ-methylene-γ-butyrolactone. A dinuclear Rh(I) complex was the most active catalyst, demonstrating a significant degree of bimetallic cooperativity.

Full text of DOI:10.1021/om060591n

5800
Organometallics 2006, 25, 5800-5810
Reactive Indolyl Complexes of Group 9 Metals
Joanne Hui Hui Ho,† David St Clair Black,† Barbara Ann Messerle,*,† Jack Kay Clegg,‡ and
Peter Turner‡
School of Chemistry, UniVersity of New South Wales, NSW 2052, Australia, and School of Chemistry,
The UniVersity of Sydney, NSW 2006, Australia
ReceiVed July 3, 2006
A series of novel indolyl-imine ligand precursors have been synthesized. In particular, bidentate,
tridentate, and potentially tetradentate ligands were prepared, each containing both indolyl sp2-N and
imine sp2-N donors. A series of neutral rhodium(I) and iridium(I) complexes of these ligands were
synthesized, including monometallic and bimetallic complexes. The X-ray structures of three of the
monometallic complexes with bidentate indolyl-imine ligands were determined. In each complex, the
metal center was in a square planar conformation, as expected for Rh(I) and Ir(I) complexes. The five-
and six-membered metallocycles formed on complexation of the metal with the ligands were all planar,
and the aromaticity of the ligands was maintained. The Rh(I) complex with the tridentate indolyl ligand
(L) reacted at room temperature with CH2Cl2 to form the Rh(III) chloromethyl complex [Rh(L)(CO)-
(CH2Cl)(Cl)] via oxidative addition of the C-Cl bond of CH2Cl2. The Rh/Ir(I) indolyl-imine complexes
are efficient catalysts for the intramolecular cyclization of 4-pentynoic acid to form γ-methylene-γ-
butyrolactone. A dinuclear Rh(I) complex was the most active catalyst, demonstrating a significant degree
of bimetallic cooperativity.
Introduction
Heterocyclic donors, in particular N-heterocyclic carbenes
(NHCs), have attracted significant attention as ligands in
homogeneous catalysis over the past decade. Metal complexes
with N-heterocyclic carbene ligands1 are, in many cases, more
robust than analogous complexes containing phosphine or
nitrogen donor ligands, because of their ability to form strong
σ-donor bonds. Other heterocyclic ligands containing nitrogen
donors such as pyrrole, carbazole, and indole rings display strong
σ-donor properties similar to those of carbenes. In particular,
indolyl ligands generate a very powerful anionic sp2-N σ-donor
group upon deprotonation and can bind strongly to positively
charged metal ions. Indolyl-based ligand systems have been
designed to include more labile donors such as imines as well
as take advantage of the strongly binding N-donor of the indolyl
system, and have been complexed with first-row transition
metals Co, Ni, Cu, Zn, and Mn (1-3).2 The complexes with
Mn (1) are active as catalysts for the epoxidation of alkenes.3
To date, mixed indolyl-imine complexes with group 9 metals
such Rh and Ir have not been studied.
phosphine ligands as well as metal complexes containing the
strongly binding NHC ligands are active catalysts for a large
number of organic transformations. Incorporating both the
stability of complexes with strongly bound ligands and the
reactivity of complexes with labile ligands, there are many
examples of metal complexes with mixed polydentate donor
ligands, in particular complexes with NHC-imine,4 NHC-
hydroxy/alkoxy/phenoxy,5 NHC-amine/amido,6 NHC-sulfide,7
NHC-phosphine,7,8 and NHC-pyrazolyl ligands.9 Mixed phos-
phine-N-donor ligands include ligands containing phosphine
and sp3 amino donors, and sp2 pyrazolyl10 or imidazolyl11
donors. Applications of these metal complexes with mixed
donors in catalysis have, however, been limited. Among the
P-N donor ligands, the phosphine-pyrazolyl and phosphine-
imidazolyl ligands have been used for the preparation of late
transition metal (Rh and Ir) complexes and act as efficient C-X
In the search for active catalysts, metal complexes containing
N-donor ligands as well as phosphine and N-heterocyclic
carbene donors have been investigated. Metal complexes with
* Corresponding author. E-mail: b.messerle@unsw.edu.au.
† University of New South Wales.
‡ The University of Sydney.
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10.1021/om060591n CCC: $33.50 © 2006 American Chemical Society
Publication on Web 10/18/2006

ReactiVe Indolyl Complexes of Group 9 Metals
Organometallics, Vol. 25, No. 24, 2006 5801
bond formation catalysts for allylic substitution,12 hydrogena-
tion,12 hydrothiolation,13 and asymmetric hydrogenation of
alkenes14 and imines.15 Metal complexes containing two or more
metal centers with multidentate ligands are also known to be
active catalysts for a variety of transformations, in particular
complexes (4-14) and the solid-state structures of 4, 6, 7, and
16. The catalytic activity of the monometallic and bimetallic
Rh/Ir(I) complexes for the intramolecular hydroalkoxylation of
pentynoic acid is also investigated. The effect of the presence
of two metals in a single catalyst on catalytic efficiency is
described using bimetallic complex 14.
16
17
hydroformylation catalyzed by Rh2 and Ru2 complexes;
alkene18 and alkyne19 hydrogenation catalyzed by Ir2 complexes;
20
21,22
and nitrile hydration catalyzed by Ni2 and Pd2
species.
Of particular interest are bimetallic complexes that display
cooperative effects between the metals, enhancing the rate of
catalysis.22
We report here the synthesis and structural characterization
of a new series of the novel bi-, tri-, and tetradentate indolyl-
imine ligand precursors as well as their Rh(I) and Ir(I)
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Results and Discussion
Synthesis and Characterization of Mixed Indolyl-Imine
Ligands. The synthesis of the indolyl-imine ligand precursors
(15-20) involves a three-step preparation following a modified
method of Black et al.2c,23,24, The first step is to obtain the
activated 4,6-dimethoxyindole, which involves the direct cy-
clization of an arylaminoketone with lithium bromide under
neutral conditions in a one-pot process.23 Subsequently, the
formylindoles were synthesized via the Vilsmeier reaction at
the 2- and/or 7-positions.24 The targeted ligand precursors (15-
20) were then obtained following Schiff base condensation of
the formylindoles with a series of alkyl and aryl amines.2c
(9) Vuong, K. Q. Ph.D. Thesis, University of New South Wales, 2005.
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1985, 24, 2334-2337.
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Dalton Trans. 2003, 4181-4191.
The monoanionic bidentate (15) and tridentate indolyl-imine
(16) ligand precursors were synthesized by refluxing the
appropriate formylindole with an excess amount of aniline in
toluene under nitrogen and in the presence of a catalytic amount
(14) Menges, F.; Neuburger, M.; Pfaltz, A. Org. Lett. 2002, 4, 4713-
4716.
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dron: Asymmetry 2004, 15, 3365-3373.
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S. A.; Stanley, G. G. Science 1993, 260, 1784-1788. (b) Matthews, R. C.;
Howell, D. K.; Peng, W.-J.; Train, S. G.; Treleaven, W. D.; Stanley, G. G.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2253-2256. (c) Kalck, P.
Polyhedron 1988, 7, 2441-2450. (d) Suess-Fink, G. Angew. Chem. 1994,
106, 71-73.
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Eur. J. 1999, 5, 1617-1630. (b) Meyer, F.; Hyla-Kryspin, I.; Kaifer, E.;
Kircher, P. Eur. J. Inorg. Chem. 2000, 771-781.
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476.

5802 Organometallics, Vol. 25, No. 24, 2006
Ho et al.
Figure 1. ORTEP representation of tridentate ligand precursor 16
shown with 50% probability ellipsoids.
water-stable solid. By reacting the dimeric [Rh(COD)OEt]2 with
2 equiv of bidentate indolyl-imine ligand 15 in a CH2Cl2
solution, complex [Rh(15′)(COD)] (5) was obtained as an orange
solid in moderate yield (68%) (Scheme 1).
The solid-state IR spectrum of 4 showed three intense peaks
including a broad shoulder at 2052 cm-1 and a symmetrical
doublet at 1997 and 1985 cm-1, which were attributed to the
carbonyl stretching frequencies. However, the liquid-state IR
(in CD2Cl2) showed only two bands at 2066 and 1998 cm-1, as
is commonly observed for Rh(I) dicarbonyl complexes.26 The
solid-state spectrum showed more absorption bands in this
region possibly due to the presence of two chemically different
molecules in the solid state (vide infra). The 13C{1H} NMR
spectrum of 4 displayed two doublet resonances at 187.93 and
187.01 ppm (1JRh-C ) 69 and 63 Hz) characteristic of two Rh-
bound carbonyl ligands.26,27 In the 1H NMR (CD2Cl2) spectrum
of 4 and 5, the indolyl NH resonance at 10.58 ppm disappeared
upon complexation with the metal precursors, confirming the
binding of the anionic ligand to the rhodium center. Additionally,
the high-field shift of the imine proton to 8.74 and 8.24 ppm,
in 4 and 5, respectively, and the doublet resonance observed
with coupling to 103Rh (3JRh-H ) 2.3 Hz) confirmed the imine
coordination to the Rh center.
Synthesis of 1,5-Cyclooctadiene and Dicarbonyl Ir(I)
Complexes with Bidentate Indolyl-Imine Ligands (6, 7).
Complex [Ir(15′)(COD)] (6) was synthesized using the same
method as was employed for the synthesis of complex 4
(Scheme 1). Deprotonation of the bidentate indolyl-imine
ligand precursor 15 with sodium acetate in dichloromethane
before addition to a solution of [Ir(µ-Cl)(COD)]2 in dichlo-
romethane led to the formation of 6 in good yield (94%). The
dicarbonyl indolyl-imine Ir(I) (7) complex was synthesized by
displacement of COD from 6 in either a suspension of a
methanol/hexane mixture or a dichloromethane solution under
an atmosphere of carbon monoxide (Scheme 1). The isolated
orange precipitate 7 was recrystallized from dichloromethane
as red crystals in moderately high yield (79%). The Ir analogues
6 and 7 show very similar IR and 1H NMR spectroscopic data
to those of 4 and 5.
of glacial acetic acid and 4 Å molecular sieves.25 The dianionic
tetradentate bis(indolyl-imine) ligand precursors 17-20 were
also prepared via condensation of 7-formylindole with the
corresponding alkyl and aryl diamine. In contrast to the bidentate
(15) and tridentate (16) indolyl-imine ligand precursors, the
tetradentate (17-20) ligand precursors have the flexibility to
support the formation of bimetallic complexes.
A broad resonance between 10.58 and 11.46 ppm due to the
1
indole N-H proton was observed in the H NMR spectra of
the indolyl-imine precursors 15-20 at ambient temperature,
and the downfield shift of this resonance is indicative of
hydrogen bonding to the imino nitrogens. This suggests that
only the E-configuration of the imino CdN double bond is
present in solution,25 which was confirmed by the solid-state
structure of the tridentate indolyl-imine precursor 16 as
determined by X-ray diffraction (Figure 1).
Crystals of 16 suitable for X-ray analysis were obtained by
slow evaporation of a saturated solution of CH2Cl2/toluene. The
molecular structure of this tridentate ligand precursor reveals a
planar geometry. The two imino CdN linkages [C(9)-N(2)
1.2851(18) Å and C(19)-N(3) 1.2836(18) Å] are similar to
those reported in the literature for similar tridentate imino
ligands.25
Synthesis and Characterization of Rh and Ir(I) Complexes
Containing Indolyl-Imine Ligands. Synthesis of Dicarbonyl
and 1,5-Cyclooctadiene Rh(I) Complexes with Bidentate
Indolyl-Imine Ligands (4, 5). The monoanionic bidentate
indolyl-imine ligand 15′ was generated and used in situ by
reacting the precursor ligand 15 with excess sodium acetate in
CH2Cl2 solution. Reaction of equimolar quantities of [Rh(µ-
Cl)(CO)2]2 and the deprotonated 15′ in CH2Cl2 at ambient
temperature gave the neutral dicarbonyl indolyl-imine Rh(I)
complex [Rh(15′)(CO)2] (4) in excellent yield (98%) (Scheme
1). The bright orange complex 4 was isolated as an air- and
Synthesis of a Carbonyl Rh(I) Complex with the Triden-
tate Indolyl-Imine Ligand (8). The deprotonated monoanionic
(26) Julius, G. R.; Cronje, S.; Neveling, A.; Esterhuysen, C.; Rauben-
heimer, H. G. HelV. Chim. Acta 2002, 85, 3737-3747.
(27) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics 2000,
19, 87-90.
(25) Gibson, V. C.; Spitzmesser, S. K.; White, A. J. P.; Williams, D. J.
Dalton Trans. 2003, 2718-2727.

ReactiVe Indolyl Complexes of Group 9 Metals
Organometallics, Vol. 25, No. 24, 2006 5803
Scheme 1
Scheme 2
tridentate ligand 16′ was prepared in situ by mixing the
corresponding tridentate ligand precursor 16 with a base in
dichloromethane. This mixture was added dropwise to a
dichloromethane solution of the dimeric [Rh(µ-Cl)(CO)2]2
(Scheme 2). The reaction proceeded cleanly to yield complex
8 as a dark maroon solid (71%) when sodium ethoxide was
used as the base. In contrast, using sodium acetate as the base
led to a mixture of products.
it a good candidate for oxidative addition reactions.31 The square
planar Rh(I) complex 8 in CD2Cl2, in an NMR tube sealed with
a concentric Teflon Young’s tap under an inert atmosphere,
underwent oxidative addition of CD2Cl2 to form the octahedral
Rh(III) derivative 21-d2 (Scheme 2). The transformation to 21-
d2 took 2 days for complete conversion. The IR spectrum of
21-d2 showed a carbonyl stretching frequency of complex 21
at 2085 cm-1, which is significantly shifted to higher wave-
number compared to that observed for complex 8, as expected
on oxidative addition of an alkyl halide to a square planar Rh-
(I) carbonyl complex. Similar oxidative addition reactions have
been reported for MeI addition to bis(imino)carbazolide,28
R-diimine,32 and pyridylbis(carbene)31 Rh(I) carbonyl com-
plexes.
For 8, one carbonyl stretching band was observed in each of
the solid- and liquid-state IR spectra at 1952 and 1962 cm-1
,
respectively, characteristic of Rh(I) carbonyl complexes with
monoanionic tridentate ligands.28,29
The 1H NMR ((CD3)2CO) spectrum of 8 showed two doublet
resonances due to coupling between the imine CH protons and
103Rh (3JRh-H ) 3.8 Hz). This coupling constant is within the
range typically observed (3.5-3.9 Hz) for similar square planar
Rh(I) complexes, confirming that both imino “arms” are bound
to the Rh center in 8.28,30
On reaction of 8 with protio-dichloromethane to form 21,
1H NMR resonances due to the activated chloromethyl moiety
were observed as two sets of doublets of doublets at 4.02 and
2
3.77 ppm, with a JRh-H coupling constant of 3.0 Hz.30,33
Resonances due to the Rh-bound carbonyl ligand at 184.54 ppm
(1JRh-C ) 58 Hz) in the 13C{1H} NMR spectrum and the
chloromethyl carbon atom at 37.84 ppm with a 1JRh-C coupling
constant of 27 Hz were observed at similar chemical shifts to
equivalent nuclei in similar Rh(III) complexes.33,34
Oxidative Addition of CH2Cl2 to the Carbonyl Rh(I)
Complex with a Tridentate Indolyl-Imine Ligand (8). The
relatively low ν(CO) frequency 1952 cm-1 observed for 8
indicates there is a high electron density at the Rh center, making
(28) Gaunt, J. A.; Gibson, V. C.; Haynes, A.; Spitzmesser, S. K.; White,
A. J. P.; Williams, D. J. Organometallics 2004, 23, 1015-1023.
(29) Wang, K.; Goldman, M. E.; Emge, T. J.; Goldman, A. S. J.
Organomet. Chem. 1996, 518, 55-68.
(30) Haarman, H. F.; Ernsting, J. M.; Kranenburg, M.; Kooijman, H.;
Veldman, N.; Spek, A. L.; van Leeuwen, P. W. N. M.; Vrieze, K.
Organometallics 1997, 16, 887-900.
(31) Wilson, J. M.; Sunley, G. J.; Adams, H.; Haynes, A. J. Organomet.
Chem. 2005, 690, 6089-6095.
(32) Gonsalvi, L.; Gaunt, J. A.; Adams, H.; Castro, A.; Sunley, G. J.;
Haynes, A. Organometallics 2003, 22, 1047-1054.
(33) Gash, R. C.; Cole-Hamilton, D. J.; Whyman, R.; Barnes, J. C.;
Simpson, M. C. J. Chem. Soc., Dalton Trans. 1994, 1963-1969.

5804 Organometallics, Vol. 25, No. 24, 2006
Ho et al.
Scheme 3
Synthesis of Ir/Rh(I) Complexes with Tetradentate Ligands
(9-14). The dianionic tetradentate bis(indolyl-imine) ligand
17′ was prepared by reaction of the tetradentate ligand precursor
17 with excess sodium acetate in dichloromethane solution.2c
The Ir/Rh(I) complexes 9 and 11 were synthesized by the
reaction of an equimolar amount of the deprotonated tetradentate
bis(indolyl-imine) ligand 17′ generated in situ with a dichlo-
romethane solution of the respective metal precursors, [Ir(µ-
Cl)(COD)]2 or [Rh(µ-Cl)(CO)2]2 (Scheme 3). An immediate
precipitation of the metal complex was observed in each case.
The complexes were isolated after washing with hexane and
methanol. The poor solubility of these complexes in common
organic solvents made complete characterization difficult.
Complexes 10 and 12, with methyl groups substituted at the
C2- and C3-positions of the indolyl donor, and complex 13 with
a bulky tert-butyl group at the C3-position of the indole ring
were prepared in an attempt to improve the solubility of the
metal complexes. Unfortunately, all of the isolated tetradentate
bis(indolyl-imine) Ir/Rh(I) complexes with an ethylene-bridged
backbone were insoluble in common organic solvents, which
precluded complete characterization. The IR spectra of these
complexes are discussed below.
The ligand precursor 20 contains a phenyl bridge between
the two bidentate indolyl-imine ligands in place of the ethylene
backbone of ligand precursors 17-19. The neutral tetracarbonyl
dirhodium(I) complex 14 was synthesized in excellent yield
(95%) using ligand precursor 20 and following the same
synthetic approach to that used for the synthesis of 11-13
(Scheme 3). This phenyl-bridged tetradentate bis(indolyl-imine)
Rh(I) complex (14) was soluble in chloroform and THF and
was fully characterized. A variable-temperature 1H NMR
experiment of 14 in CDCl3 showed that the unresolved broad
resonances observed at ambient temperature decoalesced at a
lower temperature (213 K), confirming the presence of two
indolyl-imine ligand units that are nonidentical at low tem-
perature and highly fluxional (with magnetically equivalent
protons) at room temperature (Figure 2).
Molecular Structures of Metal Complexes. Metal Com-
plexes with Bidentate Ligands 4, 6, and 7. Crystals of 4 and
6 suitable for X-ray analysis were obtained by slow diffusion
of pentane and hexane into concentrated CH2Cl2 solutions of 4
and 6, respectively. A crystal of 7 suitable for X-ray analysis
was obtained by slow evaporation of a saturated CH2Cl2 solution
of 7. The molecular structures of 4, 6, and 7 show that each
complex has a square planar geometry about the metal center
comprising one bidentate indolyl-imine ligand (15′), which
provides two nitrogen donor atoms, and either two carbonyl
donors (4, 7) or a 1,5-cyclooctadiene unit (6) as the co-ligands.
The X-ray data for 4 are presented in Table 1, and selected
bond lengths and angles in Table 2. For 4, the bidentate anionic
indolyl-imine ligand (15′) is essentially planar within the six-
membered metallocycle (Figure 3), with the exception of the
phenyl subsitituent on the imine-N. The bite angle N(1)-Rh-
(1)-N(2) of 89.07(7)° is close to the ideal 90° required for
square planar complexes. Complex 4 has a Rh(1)-N(1) (indolyl)
bond length of 2.0662(17) Å and a Rh(1)-N(2) (imino) bond
length of 2.0807(18) Å, which are comparable to the Rh-N
imino bond lengths in previously reported complexes with mixed
imino-phosphine32 and imino-pyridyl35 ligands. To date, there
have been no other reports of indolyl-imine Rh complex
structures.
The ORTEP illustration of the molecular structure of neutral
complex 6 is presented in Figure 4, crystal data and structure
refinement data are tabulated in Table 1, and selected bond
lengths and angles are given in Table 2. The bond lengths of
complex 6 for the Ir(1)-N(1) (indolyl) and Ir(1)-N(2) (imino)
bonds were 2.0905(19) and 2.110(2) Å, respectively. The Ir atom
is centered in an essentially square planar arrangement consisting
of two N atoms of the bidentate indolyl-imine ligand (15′) and
the centers of the CdC bonds of the COD ligand. The planar
six-membered metallocycle results in a N(1)-Ir(1)-N(2) bond
angle of 87.53(7)°, implying only a slight distortion from the
ideal 90° value. This indicates a very low level of ring strain
due to the binding of the indolyl-imine ligand.
IR Spectra of Bimetallic Complexes 11-14. The IR spectra
of the bimetallic tetradentate carbonyl complexes 11-14 each
contained two carbonyl stretching frequencies between 2058
and 1976 cm-1, indicating the presence of two different metal-
bound terminal CO groups. The ν(CO) stretching frequencies
were very similar for all four complexes. The presence of two
ν(CO) stretching frequencies in each case suggested these were
all symmetrical, bimetallic systems.
The ORTEP representation of the neutral complex 7 is
presented in Figure 5. Relevant molecular parameters are listed
in Table 2, while all other crystallographic data are presented
in Table 1. A geometry was displayed by complex 7 similar to
those of 4 and 6, with a four-coordinate square planar geometry
about the Ir center and the monoanionic bidentate indolyl-imine
ligand essentially planar within the six-membered iridacycle.
In comparison with complex 6, the substitution of the sterically
(34) Fennis, P. J.; Budzelaar, P. H. M.; Frijns, J. H. G.; Orpen, A. G. J.
Organomet. Chem. 1990, 393, 287-298.
(35) Pascu, S. I.; Coleman, K. S.; Cowley, A. R.; Green, M. L. H.; Rees,
N. H. J. Organomet. Chem. 2005, 690, 1645-1658.

ReactiVe Indolyl Complexes of Group 9 Metals
Organometallics, Vol. 25, No. 24, 2006 5805
1
Figure 2. Variable-temperature H NMR (500 MHz, CDCl3) spectra of complex 14: (a) 298 K, (b) 273 K, (c) 253 K, and (d) 213 K.
Table 1. Crystallographic Data for [Rh(15′)(CO)2] (4), [Ir(15′)(COD)] (6), [Ir(15′)(CO)2] (7), and Tridentate Ligand Precursor
(16)
[Rh(15′)(CO)2] (4)
[Ir(15′)(COD)] (6)
[Ir(15′)(CO)2] (7)
C21H19Ir1N2O4
16
C25H23N3O2
formula of refinement model
MW
C21H19N2O4Rh
466.29
C27H34IrN2O3.50
634.76
555.58
397.46
cryst syst
space group
a/Å
b/Å
c/Å
monoclinic
P21/n (#14)
11.1206(4)
27.5135(10)
13.4874(5)
triclinic
P1h (#2)
monoclinic
P21/n (#14)
11.099(2)
27.469(6)
13.464(3)
monoclinic
P21/c (#14)
12.8861(14)
8.4980(9)
19.738(2)
7.7020(14)
12.171(2)
14.506(3)
103.233(3)
101.973(3)
104.272(3)
1231.6(4)
1.712
R/deg
â/deg
111.600(2)
111.39(3)
107.691(2)
γ/deg
V/Å3
3836.9(2)
1.614
8
3822.4(13)
1.931
8
2059.2(4)
1.282
4
Dc/g cm-3
Z
2
cryst size/mm
cryst color
cryst habit
temp/K
0.253 × 0.065 × 0.030
0.35 × 0.30 × 0.20
0.31 × 0.038 × 0.018
0.49 × 0.39 × 0.30
red
red
red
red
needle
150(2)
prism
150(2)
needle
150(2)
prism
150(2)
λ(Mo KR)/Å
µ(Mo KR)/mm-1
T(empirical)min,max
2θmax/deg
hkl range
N
0.71073
0.920
0.890, 1.00
56.58
-14 14, -36 36, -17 17
92484
0.71073
5.454
0.228, 0.336
56.70
-10 10, -16 16, -18 18
12277
0.71073
7.016
0.626, 0.881
56.66
-14 14, -36 36, -17 17
72145
0.71073
0.083
0.856, 1.00
56.64
-16 16, -11 11, -25 26
20134
N
ind(Rmerge
)
9530(0.0341)
8062
513
0.0276, 0.0627
1.175
-0.456, 0.430
5759(0.0174)
5560
309
0.0173, 0.0459
1.047
-0.724, 1.309
9516(0.0423)
7682
513
0.0263, 0.0936
0.971
-0.585, 0.875
5003(0.0279)
3754
277
0.0480, 0.1376
1.047
-0.195, 0.373
Nobs - (I > 2σ(I))
Nvar
R1a (I > 2σ(I)), wR2a (all)
GoF
residual extrema/e- Å-3
a R1 ) ∑||Fo| - |Fc||/∑|Fo| for Fo > 2σ(Fo) and wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fc )2]}1/2 where w ) 1/[σ2(Fo ) + (AP)2 + BP], P ) (Fo + 2Fc )/3,
2
2
2
2
2
2
and A and B are listed in the crystal data information supplied.
demanding COD ligand with the smaller CO ligands in complex
7 results in a slightly larger bite angle of 88.57(13)° for the
N(1)-Ir-N(2) angle in the bidentate indolyl-imine ligand
iridacycle. The Ir(1)-N(1) (indolyl-N) bond length of 2.071-

5806 Organometallics, Vol. 25, No. 24, 2006
Ho et al.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)a for the Inner Coordination Spheres of [Rh(15′)(CO)2] (4),
[Ir(15′)(COD)] (6), and [Ir(15′)(CO)2] (7)
[Rh(15′)(CO)2] (4)
[Ir(15′)(COD)] (6)
[Ir(15′)(CO)2](7)
Rh(1)-C(20)
1.858(2)
1.865(3)
2.0662(17)
2.0807(18)
Ir(1)-C(20)
2.119(2)
2.125(2)
2.139(2)
2.154(2)
2.0905(19)
2.110(2)
Ir(1)-C(20)
Ir(1)-C(21)
Ir(1)-N(1)
Ir(1)-N(2)
1.855(5)
1.854(5)
2.071(3)
2.075(3)
Rh(1)-C(21)
Rh(1)-N(1)
Rh(1)-N(2)
Ir(1)-C(23)
Ir(1)-C(24)
Ir(1)-C(27)
Ir(1)-N(1)
Ir(1)-N(2)
C(20)-Rh(1)-C(21)
C(20)-Rh(1)-N(1)
C(21)-Rh(1)-N(1)
C(20)-Rh(1)-N(2)
C(21)-Rh(1)-N(2)
N(1)-Rh(1)-N(2)
82.32(10)
98.20(9)
177.96(10)
172.63(9)
90.46(9)
89.07(7)
C(21)-Ir(1)-C(20)
C(21)-Ir(1)-N(1)
C(20)-Ir(1)-N(1)
C(21)-Ir(1)-N(2)
C(20)-Ir(1)-N(2)
N(1)-Ir(1)-N(2)
82.8(2)
177.90(18)
98.55(18)
90.13(17)
172.65(18)
88.57(13)
N(1)-Ir(1)-N(2)
N(1)-Ir(1)-C(20)
N(2)-Ir(1)-C(20)
N(1)-Ir(1)-C(23)
N(2)-Ir(1)-C(23)
C(20)-Ir(1)-C(23)
N(1)-Ir(1)-C(24)
N(2)-Ir(1)-C(24)
C(20)-Ir(1)-C(24)
C(23)-Ir(1)-C(24)
N(1)-Ir(1)-C(27)
N(2)-Ir(1)-C(27)
C(20)-Ir(1)-C(27)
C(23)-Ir(1)-C(27)
C(24)-Ir(1)-C(27)
87.53(7)
90.12(8)
152.31(9)
156.12(9)
90.02(8)
81.14(9)
164.91(9)
92.46(8)
96.74(9)
38.92(9)
98.45(8)
168.10(8)
38.71(9)
88.58(9)
79.09(9)
Rh(2)-C(41)
Rh(2)-C(42)
Rh(2)-N(1)
Rh(2)-N(2)
1.860(2)
1.868(2)
2.0662(17)
2.0816(18)
Ir(2)-C(41)
Ir(2)-C(42)
Ir(2)-N(3)
Ir(2)-N(4)
1.849(5)
1.858(5)
2.066(3)
2.077(3)
C(41)-Rh(2)-C(42)
C(41)-Rh(2)-N(3)
C(42)-Rh(2)-N(3)
C(41)-Rh(2)-N(4)
C(42)-Rh(2)-N(4)
N(3)-Rh(2)-N(4)
82.51(10)
98.54(8)
178.10(9)
172.21(8)
89.75(8)
89.23(7)
C(41)-Ir(2)-C(42)
C(41)-Ir(2)-N(3)
C(42)-Ir(2)-N(3)
C(41)-Ir(2)-N(4)
C(42)-Ir(2)-N(4)
N(3)-Ir(2)-N(4)
83.08(19)
98.69(17)
177.54(17)
172.82(17)
89.75(17)
88.47(13)
a Estimated standard deviations in the least significant figure are given in parentheses.
Figure 3. ORTEP representation of [Rh(15′)(CO)2] (4) shown with
50% probability ellipsoids. Only one of the two independent
molecules in the asymmetric unit is shown.
Figure 5. ORTEP representation of [Ir(15′)(CO)2] (7) shown with
50% probability ellipsoids. Only one of the two independent
molecules in the asymmetric unit is shown.
center more electron deficient through π-back-bonding, causing
the indolyl-imine ligand to bind more strongly.
Catalyzed Intramolecular Hydroalkoxylation. Transition
metal catalyzed reactions such as the intramolecular cyclization
of acetylenic carboxylic acids offer a potentially efficient
approach to the synthesis of five- and six-membered ring
systems containing oxygen.36 Industrially, this catalytic process
is particularly useful for the preparation of pharmaceuticals,
flavors, and fragrances.36b The metal-catalyzed intramolecular
cyclization of 4-alkynyl carboxylic acids to form the five-
membered exocyclic enol lactones (22, Scheme 4) has been
performed previously using Rh,36a,37 Pd,36a and Hg36a,b com-
plexes. Rh(I) complexes with sp2-N donor ligands36b and cationic
(36) (a) Chan, D. M. T.; Marder, T. B.; Milstein, D.; Taylor, N. J. J.
Am. Chem. Soc. 1987, 109, 6385-6388. (b) Elgafi, S.; Field, L. D.;
Messerle, B. A. J. Organomet. Chem. 2000, 607, 97-104. (c) Jimenez-
Tenorio, M.; Carmen Puerta, M.; Valerga, P.; Javier Moreno-Dorado, F.;
Guerra, F. M.; Massanet, G. M. Chem. Commun. 2001, 2324-2325.
(37) (a) Marder, T. B.; Chan, D. M. T.; Fultz, W. C.; Milstein, D. J.
Chem. Soc., Chem. Commun. 1988, 996-998. (b) Marder, T. B.; Chan, D.
M. T.; Fultz, W. C.; Calabrese, J. C.; Milstein, D. J. Chem. Soc., Chem.
Commun. 1987, 1885-1887.
Figure 4. ORTEP representation of [Ir(15′)(COD)] (6) shown with
50% probability ellipsoids. Disordered solvent molecules have been
omitted for clarity.
(3) Å and the Ir(1)-N(2) (imino) bond length of 2.075(3) Å of
7 are each slightly longer than those of the Ir dicarbonyl
analogue, 6, possibly because the carbonyl ligands make the Ir

ReactiVe Indolyl Complexes of Group 9 Metals
Organometallics, Vol. 25, No. 24, 2006 5807
Scheme 4
The most efficient catalyst was the Rh(I) bimetallic complex
14, which promoted the quantitative conversion of starting
material after 3.5 h with a turnover number of 142 h-1 in CDCl3.
Comparing this with the equivalent Rh(I) monometallic species
(4) (which had a turnover number of 35 h-1 for the correspond-
ing transformation), a significant degree of cooperation between
the two metal centers of the bimetallic complex 14 during the
catalyzed reaction was indicated. Jones and James22 have
proposed an index of cooperativity to provide a numerical
estimate of the catalytic activity the complex appears to possess
beyond the expected value. The value of this index for complex
14 under investigation here, based on the turnover frequency
at 50% conversion, is 2.1, indicating that the reactivity of the
metal complex is enhanced by a cooperative mechanism
whereby the second metal center enhances the efficiency of the
first. In comparison, the cooperativity indices for the bimetallic
Rh(I) catalysts for hydroformylation reported previously22 are
as high as 422 or 34, suggesting a significantly greater degree
of cooperativity than observed here.
Table 3. Efficiency of Catalyzed Intramolecular Cyclization
of 4-Pentynoic Acid to Exocyclic
γ-Methylene-γ-butyrolactone (22) Using Rh(I) and Ir(I)
Complexes with Indoyl Ligands (65 °C, 2 mol % catalyst, N2
atmosphere, NMR scale)
deuterated 4-pentynoic acid reaction
%
Ntc
time (h) conversion (h-1
)
catalyst
solvents
amount (mg)
4a,b
4a,b
4a,b
4a,b
5
5
6
6
7
CDCl3
(CD3)2CO
CD3CN
26.9
26.9
26.9
26.9
17.3
17.3
26.9
26.9
26.4
26.4
27.9
17.2
3.4
3.0
4.6
3.9
2.8
2.8
6.2
2.5
9.9
>98
>95
>96
40
7
53
94
>98
73
31
35
5
CD3OD
(CD3)2CO
CD3OD
(CD3)2CO
CD3OD
CDCl3
(CD3)2CO
(CD3)2CO
CDCl3
17
26
52
5
7
8
14
90
20
3.5
60
61
>98
<5
<5
142
Conclusions
A series of novel indolyl-imine ligands with a variety of
binding modes have been synthesized. In particular, bidentate
and tridentate ligands were prepared and additionally a ligand
that can act as either a tetradentate ligand or a bis-bidentate
ligand. A series of neutral rhodium(I) and iridium(I) complexes
of these indolyl ligand derivatives have also been synthesized.
In each complex, the metal center was in a square planar
conformation, as expected for Rh(I) and Ir(I) complexes. The
five- and six-membered metallocycles formed on complexation
of the metal with the ligands were all planar, and the aromaticity
of the ligands was maintained. The Rh(I) complex with the
tridentate indolyl ligand (8) reacted at room temperature with
CH2Cl2 to form the Rh(III) chloromethyl complex [Rh(16′)-
(CO)(CH2Cl)(Cl)] (21) via oxidative addition of the C-Cl bond
of CH2Cl2.
The Rh/Ir(I) indolyl-imine complexes (4-6 and 14) are
efficient catalysts for the intramolecular cyclization of 4-pen-
tynoic acid to form γ-methylene-γ-butyrolactone (22). In this
work, the dinuclear complex [Rh2(20′)(CO)4] (14) was the most
active catalyst and produced exclusively the five-membered
exocyclic lactone γ-methylene-γ-butyrolactone (22), with a
turnover rate of 142 h-1 and quantitative conversion in 3.5 h.
The equivalent monometallic complex 4 gave a much lower
turnover rate of 35 h-1. Calculation of the cooperativity index
for 14 suggests that the catalyzed reaction follows a mechanism
that involves intramolecular intermetallic cooperativity. The next
most efficient catalyst was the monometallic [Ir(15′)(COD)] (6),
with a faster quantitative conversion time of 2.5 h and a slower
initial turnover rate of 52 h-1. These reaction rates are among
the best reported for the catalyzed hydroalkoxylation of 4-pen-
tynoic acid to 22.
a 2.3mol % catalyst. b 60 °C. c Nt (h-1) is the amount of product/mole
of catalyst/hour at the point of 50% conversion of substrate to product.
Rh/Ir(I) complexes of the tris-carbene (TIMEN) tris[2-(3-
isopropylimidazol-2-ylidenne)ethyl]amine ligand system38 are
efficient catalysts for the intramolecular cyclization of acetylenic
carboxylic acids.
Preliminary studies of the efficiency of the neutral Rh/Ir(I)
complexes with a bidentate indolyl-imine ligand system, [Rh-
(15′)(CO)2] (4), [Rh(15′)(COD)] (5), [Ir(15′)(COD)] (6), and
[Ir(15′)(CO)2] (7), the Rh(I) tridentate indolyl-imine complex
[Rh(16′)(CO)] (8), and the Rh(I) tetradentate bis(indolyl-imine)
complex [Rh2(20′)(CO)4] (14) as catalysts for the cyclization
of 4-pentynoic acid were carried out. The catalyzed reactions
of 4-pentynoic acid were performed on an NMR scale with 2
mol % catalyst loading at elevated temperature (∼60 °C), in a
variety of deuterated solvents. The reaction progress was
1
monitored at regular intervals using H NMR spectroscopy.
Percentage conversion was determined by integration of the
product resonances relative to the substrate resonances in the
1H NMR spectrum. The turnover rate (Nt) was calculated as
the amount of product/mole of catalyst/hour at the point of 50%
conversion of substrate to product, unless otherwise stated. The
results are presented in Table 3.
[Ir(15′)(COD)] (6) was the most efficient catalyst of the
monometallic complexes, with quantitative conversion to prod-
ucts in under 2.5 h and an efficiency of 52 h-1 turnovers at
50% conversion. The monometallic Rh(I) dicarbonyl system
[Rh(15′)(CO)2] (4) achieved quantitative conversion in 3 h, with
an efficiency of 35 h-1 turnovers. [Rh(15′)(COD)] (5) gave an
efficiency of 17 h-1, while [Ir(15′)(CO)2] (7) gave a low Nt of
5 h-1. The efficiency of the catalysts investigated was strongly
dependent on the solvent used (Table 3). Previous reports of
Rh-, Pd-, and Hg-based catalysts36a,37 with primarily phosphine
ligands achieved less than quantitative conversion in over 16
h. The most efficient catalyst reported to date by Mas-Marza´ et
al, a cationic Rh(I) complex of a tris-carbene ligand, achieves
quantitative conversion of the pentynoic acid substrate in under
3 h, which is comparable to the efficiency of the Rh/Ir(I) indolyl
complexes reported here.39
Experimental Section
General Procedures. All manipulations of metal complexes and
air-sensitive reagents were carried out using standard Schlenk
techniques or in a nitrogen-filled glovebox. Tetrahydrofuran,
hexane, toluene, and pentane were dried by distillation under argon
from benzophenone and sodium shavings. Methanol was predried
over activated 4 Å molecular sieves and distilled from magnesium
turnings. Dichloromethane was dried over and distilled from calcium
(38) Mas-Marza, E.; Peris, E.; Castro-Rodriguez, I.; Meyer, K. Orga-
nometallics 2005, 24, 3158-3162.
(39) Mas-Marza, E.; Sanau, M.; Peris, E. Inorg. Chem. 2005, 44, 9961-
9967.

5808 Organometallics, Vol. 25, No. 24, 2006
Ho et al.
1
hydride. The indolyl derivatives, the metal precursors [Rh(µ-Cl)-
(CO)2]2,40a [Rh(µ-Cl)(COD)]2,40b [Rh(µ-OEt)(COD)]2,40c and [Ir-
(µ-Cl)(COD)]2,40d and 4-pentynoic acid40e were prepared according
to published procedures. All other reagents were purchased from
Aldrich or Ajax Finechem and used as supplied. Nuclear magnetic
resonance spectra were recorded at ambient temperature unless
otherwise stated. Elemental analyses (C, H, N) were carried out at
the Campbell Microanalytical Laboratory, University of Otago, New
Zealand. Electrospray mass spectra were carried out at the Biologi-
cal Mass Spectrometry Facility, University of NSW. Single-crystal
X-ray structure analyses were obtained at the Crystal Structure
Analysis Facility, School of Chemistry, University of Sydney.
Synthesis of 7-(4,6-Dimethoxy-2,3-dimethylindol-2-yl)imi-
nobenzene (15). A mixture of 4,6-dimethoxy-2,3-dimethylindole-
7-carbaldehyde (1.00 g, 4.29 mmol), aniline (0.40 mL, 8.58 mmol),
and 4 Å molecular sieves (4.0 g) in toluene (150 mL) with glacial
acetic acid (5 drops) was refluxed for 1 day under a nitrogen
atmosphere. The solution was cooled to rt, the molecular sieves
were filtered off, and the solvent was evaporated under reduced
pressure to yield a pale yellow solid. The crude product (0.80 g,
2.61 mmol, 65%) was purified by washing from hot acetonitrile.
Mp: 168-170 °C. 1H NMR (300 MHz, CDCl3): δ 10.58 (bs, 1H,
NH), 9.02 (s, 1H, CHN), 7.41-7.37 (m, 2H, Ar-H), 7.27-7.16
(m, 3H, Ar-H), 6.17 (s, 1H, H5), 3.97, 3.94 (2s, 6H, OCH3) 2.36,
2.33 (2s, 6H, CH3). 13C{1H} NMR (75 MHz, CDCl3): δ 156.82
(CHN), 158.73, 158.42, 135.83, 128.92, 113.66, 106.90, 102.29
(Ar), 153.57, 129.22, 125.00, 121.37 (Ar′), 86.98 (C5), 57.04, 55.48
(OCH3), 11.46, 10.67 (CH3). IR (KBr): νNH 3390 (m), νCHdN 1623
(s) cm-1. ES-MS m/z (%): 309 ([LH]+, 100). Anal. Calcd for
(C19H20N2O + 0.6H2O): C, 71.09; H, 6.72; N, 8.73. Found: C,
71.17; H, 6.65; N, 8.58.
Synthesis of 4,6-Dimethoxy-3-methylindol-2,7-diylidenami-
nobenzene (16). A mixture of 4,6-dimethoxy-3-methylindole-2,7-
dicarbaldehyde (1.50 g, 6.06 mmol), aniline (2.20 mL, 24.2 mmol),
and 4 Å molecular sieves (4.0 g) in toluene (100 mL) with 5 drops
of glacial acetic acid was heated under reflux for 2 days under a
nitrogen atmosphere. The solution was cooled to rt, the molecular
sieves were filtered off, and the solvent was evaporated under
reduced pressure. The crude product was purified by washing from
hot acetonitrile to yield a brick red solid (1.87 g, 77%). Red single
crystals of 16 were obtained by slow evaporation of a saturated
solution of CH2Cl2/toluene. Mp: 190-192 °C. 1H NMR (300 MHz,
CDCl3): δ 11.46 (bs, 1H, NH), 9.05 (s, 1H, CH′N), 8.52 (s, 1H,
CHN), 7.42-7.17 (m, 10H, Ar-H), 6.16 (s, 1H, H5), 4.00, 3.97
(2s, 6H, OCH3), 2.64 (s, 3H, CH3). 13C{1H} NMR (75 MHz,
CDCl3): δ 161.07 (CH′N), 129.90 (CHN), 155.42, 152.84, 152.40,
147.74, 137.80, 130.91, 128.97, 128.93, 125.25, 124.98, 121.28,
121.00, 119.61, 113.92, 102.07 (Ar), 86.78 (C5), 56.42, 55.29
(-OCH3), 10.50 (CH3). IR (KBr) νNH 3380 (m), νCHdN 1610 (br,
m) cm-1. ES-MS m/z (%): 399 ([LH]+, 100). Anal. Calcd for
(C25H23N3O2 + 0.5H2O): C, 73.87; H, 5.95; N, 10.34. Found: C,
73.57; H, 5.89; N, 10.40.
55%). Mp: 260-262 °C. H NMR (300 MHz, CDCl3): δ 10.49
(bs, 1H, NH), 8.85 (s, 1H, CHN), 6.12 (s, 1H, H5), 3.95 (s, 2H,
CH2), 3.92, 3.84 (2s, 6H, OCH3) 2.30, 2.11 (2s, 6H, CH3). 13C-
{1H} NMR (75 MHz, CDCl3): δ 158.62 (CHN), 157.39 (Ar),
136.18, 129.14, 113.90, 106.60, 101.99 (Ar), 87.34 (C5), 63.43
(CH2), 57.40, 55.65 (-OCH3), 11.29, 10.86 (CH3). IR (KBr): νNH
3343 (m), VCHdN 1625 (s) cm-1. ES-MS m/z (%): 491 ([LH]+, 100).
Anal. Calcd for (C28H34N4O4 + 0.4H2O): C, 67.56; H, 7.05; N,
11.25. Found: C, 67.84; H, 6.83; N, 11.22.
Synthesis of 1,2-Di(4,6-dimethoxy-3-tertbutylindol-7-yliden-
amino)ethane (19). A mixture of 4,6-dimethoxy-3-tertbutylindole-
7-carbaldehyde (0.75 g, 2.87 mmol), 1,2-diaminoethane (0.38 mL,
5.75 mmol), and 4 Å molecular sieves (2.0 g) in toluene (100 mL)
was heated under reflux for 18 h under nitrogen. The solution was
allowed to cool, the molecular sieves were removed by filtration,
and the solvent of the filtrate was evaporated under reduced
pressure. The crude product was recrystallized from CH2Cl2/hexane
to yield the compound as a pale green solid (0.55 g, 1.01 mmol,
1
70%). Mp: 196-198 °C. H NMR (300 MHz, CDCl3): δ 11.04
(bs, 1H, NH), 8.84 (s, 1H, CHN), 6.71 (s, 1H, H2), 6.19 (s, 1H,
H5), 3.92 (s, 2H, CH2), 3.99, 3.86 (2s, 6H, OCH3), 1.40 (d, 9H,
C(CH3)3). 13C{1H} NMR (75 MHz, CDCl3): δ 158.23 (CHN),
157.71, 156.54, 138.70, 127.25, 118.48, 111.23, 101.59 (Ar), 87.12
(C5), 62.93 (CH2), 56.97, 55.00 (-OCH3), 31.46 (C(CH3)3), 31.32
(C(CH3)3). ES-MS m/z (%): 547 ([LH]+, 100).
Synthesis of 1,2-Di(4,6-dimethoxy-2,3-dimethylindol-7-yliden-
amino)benzene (20). A mixture of 4,6-dimethoxy-2,3-dimethylin-
dole-7-carbaldehyde (1.00 g, 4.29 mmol), 1,2-diaminobenzene (0.23
g, 2.10 mmol), and 4 Å molecular sieves (2.0 g) in toluene (80
mL) was heated under reflux for 18 h. The solution was cooled,
the molecular sieves were removed by filtration, and the solvent
was evaporated under reduced pressure. The product was recrystal-
lized from CHCl3/hexane to yield a yellow microcrystalline solid
(0.46 g, 0.855 mmol, 41%). Mp: 274-278 °C. 1H NMR (300 MHz,
CDCl3): δ 10.73 (bs, 1H, NH), 9.10 (s, 1H, CHN), 7.24 (m, 2H,
Ar-H), 6.14 (s, 1H, H5), 3.95, 3.87 (2s, 6H, OCH3) 2.27, 1.64 (2s,
6H, CH3). 13C{1H} NMR (75 MHz, CDCl3): δ 156.08(CHN),
158.08, 157.85, 135.53, 129.12, 113.31, 106.08, 102.43 (Ar),
146.25, 119.14, 113.31 (Ar′), 86.49 (C5), 56.66, 55.17 (OCH3),
10.33, 9.96 (CH3). IR (KBr): νNH 3299 (w); νCHdN 1621 (m) cm-1
.
ES-MS m/z (%): 539 ([LH]+, 100). Anal. Calcd for C32H34N4O4:
C, 71.35; H, 6.36; N, 10.40. Found: C, 71.10; H, 6.40; N, 10.40.
Synthesis of 4,6-Dimethoxy-2,3-dimethylindol-7-ylidenami-
nobenzyl Rhodium(I) Dicarbonyl, [Rh(15′)(CO)2] (4). A mixture
of imine 15 (0.11 g, 0.358 mmol) with NaOAc (0.08 g, 0.974 mmol)
in CH2Cl2 (10 mL) was stirred for 0.5 h under an inert atmosphere.
This mixture was added to a solution of [Rh(µ-Cl)(CO)2]2 (0.0695
g, 0.179 mmol) in CH2Cl2 (5 mL) and stirred for another 2 h before
the solvent was evaporated in vacuo and washed with diethyl ether
and methanol, yielding complex 4 as an orange solid (0.165 g, 0.35
mmol, 98%). Single crystals suitable for X-ray analysis were
obtained by slow diffusion of pentane into a concentrated CH2Cl2
Synthesis of 1,2-Di(4,6-dimethoxy-2,3-dimethylindol-7-yliden-
amino)ethane (18). A mixture of 4,6-dimethoxy-2,3-dimethylin-
dole-7-carbaldehyde (1.00 g, 4.29 mmol), 1,2-diaminoethane (0.4
mL, 4.39 mmol), and 4 Å molecular sieves (2.0 g) in toluene (100
mL) was heated under reflux for a day under nitrogen. The solution
was allowed to cool, the molecular sieves were removed by
filtration, and the solvent of the filtrate was evaporated under
reduced pressure. The crude product was washed with hexane,
diethyl ether, and ethyl acetate and the solvent evaporated in vacuo
to yield the compound as a pale yellow solid (0.65 g, 2.11 mmol,
1
solution of complex 5. H NMR (300 MHz, CD2Cl2): δ 8.74 (d,
3JRh-H ) 2.3 Hz, 1H, CHN), 7.47-7.39 (m, 4H, Ar-H), 7.33-
7.27 (m, 1H, Ar-H), 6.15 (s, 1H, H5), 4.00, 3.92 (2s, 6H, OCH3)
2.56, 2.42 (2s, 6H, CH3). 13C{1H} NMR (75 MHz, CD2Cl2): δ
187.47 (d, 1JRh-C ) 69 Hz, CO), 185.53 (d, 1JRh-C ) 63 Hz, CO),
160.53 (CHN), 162.02, 161.69, 114.27, 110.62, 102.93 (Ar), 156.49,
129.36, 126.84, 124.70 (Ar′), 86.13 (C5), 56.99, 56.01 (OCH3),
17.54 (C2), 12.10 (C3). IR (KBr): νCO 2052 (br), 1997, 1985 (s);
ν
N
CHdN 1610 (s) cm-1. IR (thin film): νCO 2066 (m), 1998 (m); νCHd
1610 (s) cm-1. ESMS m/z (%): 467 ([MH+], 100). Anal. Calcd
for C21H21N2O4Rh: C, 53.86; H, 4.52; N, 5.98. Found: C, 53.96;
H, 4.11; N, 5.79.
(40) (a) McCleverty, J. A.; Wilkinson, G. Inorg. Synth. 1990, 28, 84-
86. (b) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88-90. (c)
Burling, S.; Field, L. D.; Li, H. L.; Messerle, B. A.; Turner, P. Eur. J.
Inorg. Chem. 2003, 3179-3184. (d) Herde, J. L.; Lambert, J. C.; Senoff,
C. V. Inorg. Synth. 1974, 15, 18-20. (e) Holland, B. C.; Gilman, N. W.
Synth. Commun. 1974, 4, 203-210.
Synthesis of 4,6-Dimethoxy-2,3-dimethylindol-7-ylidenami-
nobenzyl Rhodium(I) Cyclooctadiene, [Rh(15′)(COD)] (5). Method
1. Complex 4 (0.1 g, 0.214 mmol) was heated under reflux with

ReactiVe Indolyl Complexes of Group 9 Metals
Organometallics, Vol. 25, No. 24, 2006 5809
excess 1,5-cyclooctadiene in methanol, under nitrogen for 1 day.
The brown precipitate obtained was filtered and washed with hexane
to yield the product as an orange solid (0.030 g, 0.058 mmol, 27%).
3 mL and the product precipitated by the addition of hexane. The
solid was isolated by filtration, washed with methanol and water,
and dried in vacuo, yielding complex 8 as a reddish-brown solid
1
(0.095 g, 0.180 mmol, 71%). H NMR (300 MHz, (CD3)2CO): δ
Synthesis of 4,6-Dimethoxy-2,3-dimethylindol-7-ylidenami-
nobenzyl Rhodium(I) Cyclooctadiene, [Rh(15′)(COD)] (5). Method
2. A mixture of imine 15 (0.10 g, 0.324 mmol) with [Rh(µ-OEt)-
(COD)]2 (0.0831 g, 0.162 mmol) was stirred in CH2Cl2 (10 mL)
for 2 h before the solvent was evaporated in vacuo and washed
with pentane and methanol, yielding complex 5 as an orange solid
(0.114 g, 0.22 mmol, 68%). Mp: 126-131 °C. 1H NMR (300 MHz,
3
3
8.34 (d, JRh-H ) 3.8 Hz, 1H, CHN), 8.11 (d, JRh-H ) 3.8 Hz,
1H, CHN), 7.36-7.25 (m, 6H, Ar-H), 7.23-7.13 (m, 4H, Ar-H),
6.14 (s, 1H, H5), 4.07, 3.99 (2s, 6H, OCH3), 2.65 (s, 3H, CH3).
13C{1H} NMR (75 MHz, (CD3)2CO): δ 193.60 (d, JRh-C ) 72
1
Hz, CO), (CHN), 166.43, 165.19, 161.95, 157.92, 154.34, 144.92,
138.53, 128.52, 128.13, 126.27, 125.26, 124.17, 122.99, 122.24,
113.12, 102.68 (Ar), 86.87 (C5), 55.93, 55.45 (OCH3), 11.25 (C3).
IR (KBr): νCO 1952 (s) cm-1. Anal. Calcd for (C26H23N3O3Rh +
1.5H2O): C, 56.23; H, 4.72; N, 7.57. Found: C, 56.57; H, 4.26;
N, 7.46.
General Procedure for the Synthesis of 1,2-Di(4,6-dimethoxy-
2,3-dimethylindol-7-ylidenamino)ethane Diiridium/Dirhodium-
(I) Tetracarbonyl/Dicyclooctadiene, [Ir2(17′-19′)(COD)2]/[Rh2-
(17′-19′)(CO)4] (9-13). A mixture of 1 equiv of the tetradentate
ligand precursors (17-19) and 3 equiv of NaOAc in CH2Cl2 (10
mL) was stirred for 0.5 h under an inert atmosphere. This mixture
was added to a solution of 1.2 equiv of [Ir(µ-Cl)(COD)]2/[Rh(µ-
Cl)(CO)2]2 in CH2Cl2 (5 mL) and stirred for a further 2 h before
the solvent was evaporated in vacuo. The residue was washed with
diethyl ether and methanol and dried under vacuum.
1,2-Di(4,6-dimethoxy-3-methylindol-7-ylidenamino)ethane Di-
iridium(I) Biscycloctadiene, [Ir2(17′)(COD)2] (9). Yield: 88%.
Mp < 287-290 °C (dec). ES-MS m/z (%): 1061([M]+, 30), 952
([M - COD]+, 25).
1,2-Di(4,6-dimethoxy-2,3-dimethylindol-7-ylidenamino)-
ethane Diiridium(I) Biscycloctadiene, [Ir2(17′)(COD)2] (10).
Yield: 91%. Anal. Calcd for C44H56Ir2N4O4 + 1.5CH2Cl2 + H2O:
C, 44.26; H, 4.98; N, 4.54. Found: C, 44.32; H, 4.74; N, 4.89.
1,2-Di(4,6-dimethoxy-2,3-dimethylindol-7-ylidenamino)-
ethane Dirhodium(I) Tetracarbonyl, [Rh2(17′)(CO)4] (11).
Yield: 92%. Mp < 245-250 °C (dec). IR (KBr): νCO 2055, 1976
(s) cm-1. Anal. Calcd for C30H28N4O8Rh2 + 0.7CH2Cl2: C, 44.01;
H, 3.54; N, 6.69. Found: C, 43.92; H, 3.53; N, 6.67.
1,2-Di(4,6-dimethoxy-2,3-dimethylindol-7-ylidenamino)-
ethane Dirhodium(I) Tetracarbonyl, [Rh2(17′)(CO)4] (12).
Yield: 90%. IR (KBr): νCO 2049, 1976 (s) cm-1. Anal. Calcd for
C32H32N4O8Rh2 + 0.6CH2Cl2: C, 45.67; H, 3.90; N, 6.53. Found:
C, 45.83; H, 3.94; N, 6.52.
3
CD2Cl2): δ 8.25 (d, JRh-H ) 2.3 Hz, 1H, CHN), 7.40-7.20 (m,
5H, Ar-H), 6.04 (s, 1H, H5), 4.60, 3.35, 2.24, 1.73-1.69, 1.63-
1.53 (COD), 3.98, 3.90 (2s, 6H, OCH3), 2.34, 2.22 (2s, 6H, CH3).
13C{1H} NMR (75 MHz, CD2Cl2): δ 156.98 (CHN), 159.87,
159.76, 142.69, 139.43, 1214.21, 110.17, 104.60 (Ar), 156.98,
1
128.33, 125.37, 124.09 (Ar), 84.25 (C5), 78.50 (d, JRh-C ) 13
Hz, COD), 76.69 (d, 1JRh-C ) 12 Hz, COD), 30.45, 29.72 (COD),
56.35, 55.06 (OCH3), 14.68, 11.15 (CH3). IR (KBr): νNH 3408 (br),
VCHdN 1608 (s) cm-1. ESMS m/z (%): 519 ([MH+], 49). Anal.
Calcd for (C27H31RhN2O2 + 0.5CH2Cl2): C, 58.88; H, 5.75; N,
4.99. Found: C, 58.58; H, 5.89; N, 4.94.
Synthesis of 4,6-Dimethoxy-2,3-dimethylindol-7-ylidenami-
nobenzyl Iridium(I) Cyclooctadiene, [Ir(15′)(COD)] (6). A
mixture of imine 15 (0.15 g, 0.487 mmol) with NaOAc (0.11 g,
1.34 mmol) in CH2Cl2 (10 mL) was stirred for 0.5 h under an inert
atmosphere. This mixture was added to a solution of [Ir(µ-Cl)-
(COD)]2 (0.180 g, 0.268 mmol) in CH2Cl2 (5 mL). The reacting
mixture was stirred for another 2 h before the solvent was
concentrated to dryness and washed with diethyl ether and methanol,
yielding complex 6 as a yellowish-brown solid (0.277 g, 0.455
mmol, 94%). Red single crystals suitable for X-ray analysis were
obtained by slow diffusion of pentane into a concentrated CH2Cl2
1
solution of complex 6. Mp < 100 °C (dec). H NMR (300 MHz,
CD2Cl2): δ 8.36 (s, 1H, CHN), 7.40-7.35 (m, 2H, Ar-H), 7.27-
7.21 (m, 3H, Ar-H), 6.05 (s, 1H, H5), 4.57, 3.07, 2.04, 1.50, 1.37
(COD), 3.97, 3.89 (2s, 6H, OCH3) 2.37, 2.27 (2s, 6H, CH3). 13C-
{1H} NMR (75 MHz, CD2Cl2): δ 156.03 (CHN), 161.10, 161.02,
154.40, 144.12, 139.29, 128.85, 126.57, 125.43, 113.85, 112.50,
104.56 (Ar), 85.69 (C5), 63.03, 59.27, 31.96, 30.78 (COD), 56.98,
55.90 (OCH3), 15.42, 11.85 (CH3). IR (KBr): νNH 3427 (br), νCHd
1608 (s) cm-1. ESMS m/z (%): 609 ([MH+], 100). Anal. Calcd
N
for C27H31IrN2O2: C, 53.36; H, 5.14; N, 4.61. Found: C, 53.8; H,
5.15; N, 4.52.
1,2-Di(3-tert-butyl-4,6-dimethoxyindol-7-ylidenamino)-
ethane Dirhodium(I) Tetracarbonyl, [Rh2(19′)(CO)4] (13).
Synthesis of 4,6-Dimethoxy-2,3-dimethylindol-7-ylidenami-
nobenzyl Ir(I) Dicarbonyl, [Ir(15′)(CO)2] (7). A brown solution
of complex 6 (0.100 g, 0.164 mmol) in CH2Cl2 (10 mL) was
exposed to 1 atm of CO at rt for 3 h. The solvent was removed in
vacuo and the crude product washed with hexane. The orange
product was isolated by column chromatography on silica (CH2-
Cl2 eluent) as an air-stable red crystalline solid (0.0723 g, 0.130
mmol, 79%). Mp: 228-230 °C. 1H NMR (300 MHz, CD2Cl2): δ
8.85 (s, 1H, CHN), 7.50-7.30 (m, 5H, Ar-H), 6.21 (s, 1H, H5),
4.04 3.95(2s, 6H, OCH3) 2.60 2.46(2s, 6H, CH3). 13C{1H} NMR
(75 MHz, CD2Cl2): δ 175.09, 174.55 (CO), 161.69 (CHN), 161.45,
159.35, 154.29, 143.65, 136.86, 128.48, 126.70, 124.60, 112.89,
111.23, 102.66 (Ar-C), 86.05 (C5), 56.25, 55.44 (OCH3), 16.70
(C2), 11.40 (C3). IR (KBr): νCO 2041 (br), 1982, 1968 (s), νCHdN
1607 (s) cm-1. IR (thin film): νCO 2053 (m), 1979 (m), νCHdN 1607
(s) cm-1. ESMS m/z (%): 557 ([M],75). Anal. Calcd for C21H21-
IrN2O4; C, 45.23; H, 3.80; N, 5.02. Found: C, 45.45; H, 3.71; N,
4.87.
Yield: 86%. IR (KBr): νCO 2058, 1984 (s); νCHdN 1592 (s) cm-1
ES-MS m/z (%): 806 ([M - 2CO]+, 80).
.
Synthesis of 1,2-(4,6-Dimethoxy-2,3-dimethylindol-7-yliden-
amino)benzene Rhodium(I) Dicarbonyl, [Rh2(20′)(CO)4] (14).
A mixture of the ligand precursor 20 (0.10 g, 0.186 mmol) and
NaOAc (0.10 g, 1.22 mmol) in CH2Cl2 (10 mL) was stirred for 0.5
h under an inert atmosphere. This mixture was added to a solution
of [Rh(µ-Cl)(CO)2]2 (0.0722 g, 0.186 mmol) in CH2Cl2 (5 mL).
This mixture was stirred for another 2 h before the solvent was
reduced to ∼3 mL and hexane added to precipitate the product.
The solid was washed with water and the solvent evaporated in
vacuo, yielding complex 14 as an orange solid (0.152 g, 0.177
mmol, 95%). Mp < 195-200 °C (dec). 1H NMR (500 MHz,
CDCl3, 213 K): δ 8.86, 8.04 (2s, 2H, CHN), 7.56-7.51 (m, 2H,
Ar-H), 7.44-7.26 (m, 2H, Ar-H), 6.05, 5.72 (2s, 2H, H5), 4.02,
3.95, 3.91, 3.48 (4s, 12H, OCH3), 2.35, 2.24, 2.00, 1.82 (4s, 12H,
CH3). 13C{1H} NMR (75 MHz, CDCl3, 298 K): δ 187.02, 186.10
(CO), 160.96, 161.12, 157.34, 152.72, 142.82, 137.91, 126.90,
123.57, 113.93, 109.36, 103.17 (Ar-C), 84.98 (C5), 56.20, 55.36
Synthesis of Rh(I) Tridentate Indolyl-imine Carbonyl, [Rh-
(16′)(CO)] (8). A mixture of 16 (0.10 g, 0.252 mmol) with NaOEt
(0.35 g, 1.22 mmol) in CH2Cl2 (10 mL) was stirred for 0.5 h under
an inert atmosphere. This mixture was added to a solution of [Rh-
(µ-Cl)(CO)2]2 (0.052 g, 0.13 mmol) in CH2Cl2 (5 mL). This mixture
was stirred for another 4 h before the solvent was concentrated to
(OCH3), 16.22, 11.66 (CH3). IR (KBr) νCO 2049, 1989 (s) cm-1
.
ES-MS m/z (%): 798 ([M - 2(CO)], 100). Anal. Calcd for
C36H36N4O8Rh2 + 2CH2Cl2 + H2O: C, 43.79; H, 3.67; N, 5.38.
Found: C, 43.9; H, 3.53; N, 5.42.

5810 Organometallics, Vol. 25, No. 24, 2006
Ho et al.
Synthesis of Rh(III) (Chloromethyl) Carbonyl Chloride, [Rh-
(16′)(CO)(CH2Cl)(Cl)] (21). On a NMR scale, complex 8 was
dissolved in CH2Cl2 and left to stand for 2 days. Pentane (2 equiv)
was added to precipitate the product as a brown solid. The solvent
tube in the former and a rotating anode in the latter (0.71073 Å).
Data integration and reduction were undertaken with SAINT and
XPREP,41a,b and subsequent computations were carried out using
the WinGX-32 graphical user interface.41c Multiscan empirical
absorption corrections were applied to the data using the program
SADABS.41d The structures were solved by direct methods using
SIR97,41e then refined and extended with SHELXL-97.41f Ordered
non-hydrogen atoms with occupancies greater than or equal to 0.5
were refined anisotropically. Carbon-bound hydrogen atoms were
included in idealized positions and refined using a riding model.
Nitrogen-bound hydrogen atoms were first located in the Fourier
difference map before refining with bond length restraints fixed at
0.88(2) Å.
1
was removed in vacuo to yield complex 21. H NMR (300 MHz,
3
3
CD2Cl2): δ 8.13 (d, JRh-H ) 3.0 Hz, 1H, H8), 7.84 (d, JRh-H
)
3.0 Hz, 1H, H9), 7.64-7.61 (m, 3H, Ar-H), 7.45-7.30 (m, 7H,
Ar-H), 5.99 (s, 1H, H5), 4.07 (s, 3H, H11), 3.97 (s, 3H, H12),
2
2
4.02, 4.00 (dd, JRh-H ) 3.0 Hz, 1H, H13), 3.78, 3.76 (dd, JRh-H
) 3.0 Hz, 1H, H14), 2.76 (s, 3H, H10). 13C{1H} NMR (75 MHz,
CD2Cl2): δ 184.54 (d, 1JRh-C ) 58 Hz, CO), 158.77 (C9), 156.83
(C8), 167.05, 166.96, 156.83, 152.38, 141.84, 137.09, 129.40,
129.12, 127.88, 127.40, 126.39, 123.4, 113.32, 101.20, 101.17 (Ar),
1
87.10 (C5), 56.81 (C12), 56.35 (C11), 37.84 (d, JRh-C ) 27 Hz,
Specific Details for 6. There is a region of disordered electron
density within this structure, which lies very close to and across a
crystallographic inversion site. Attempts were made to model this
electron density as disordered thf and cyclohexane molecules with
rigid body restraints; however, these attempts were unsuccessful.
This electron density was subsequently modeled as isotropic water
molecules, with a total occupancy of three water molecules per
unit cell. The oxygen-bound hydrogen atoms were not structurally
evident in the difference Fourier map and were not included in the
model.
1H, CH2Cl), 12.5 (C10). IR (KBr): νCO 2085 (s) cm-1. IR (thin
film): νCO ) 2091 (s) cm-1. ES-MS m/z (%): 576 ([(M - Cl),
52], 548 ([(M - Cl - CO), 100].
X-ray Structure Determination of Compounds 4, 6, 7, and
16. A single crystal of 16 was grown by slow evaporation of a
saturated solution of CH2Cl2/toluene, single crystals of 4 and 6 were
grown by slow diffusion of pentane into a concentrated solution of
CH2Cl2, and single crystals of 7 were grown by evaporation of a
saturated solution of CH2Cl2. Crystal data collection parameters
are summarized in Table 2. Data for complex 6 and ligand precursor
16 were collected with ω scans to approximately 56° 2θ using a
Bruker SMART 1000. For complex 4 and complex 7, data were
collected with æ and ω scans to approximately 56° 2θ using a
Bruker-Nonius APEX2-X8-FR591. Both diffractometers employed
graphite-monochromated Mo KR radiation generated from a sealed
General Method for the Catalytic Cyclization of 4-Pentynoic
Acid. In a NMR tube, 4-pentynoic acid (0.275 mol) and a catalytic
amount of the catalyst (2 mol %) were dissolved in deuterated
solvents (0.75 mL) under an atmosphere of argon. The mixture
was heated at 60 or 65 °C, and the reaction progress was monitored
by 1H NMR spectroscopy at regular intervals. The product spectra
were consistent with the data reported in the literature.
(41) (a) SMART, SAINT, and XPREP; Bruker Analytical X-ray Instru-
ments Inc.: Madison, WI, 1995. (b) APEX, SAINT, and XPREP, Area
detector control and data integration and reduction software; Bruker-Nonius
Analytical X-ray Instruments Inc.: Madison, WI, 2003. (c) WinGX-32,
System of programs for solving, refining and analysing single-crystal X-ray
diffraction data for small molecules. Farrugia, L. J. J. Appl. Crystallogr.
1999, 32, 837. (d) Sheldrick, G. M. SADABS: Empirical Absorption and
Correction Software; University of Go¨ttingen, Institu¨t fu¨r Anorganische
Chemie der Universita¨t: Tammanstrasse 4, D-3400 Go¨ttingen, Germany,
1999-2003. (e) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.
L.; Giocavazzo, C.; Guagliardi, A.; Moliterni, A. G. C.; Polidori, G.; Spagna,
S. J. Appl. Crystallogr. 1999, 32, 115. (f) Sheldrick, G. M. SHELX-97,
Programs for Crystal Structure Analysis; University of Go¨ttingen, Institu¨t
fu¨r Anorganische Chemie der Universita¨t: Tammanstrasse 4, D-3400
Go¨ttingen, Germany, 1997.
Acknowledgment. We gratefully acknowledge the Univer-
sity of New South Wales and the Australian Research Council
for financial support.
Supporting Information Available: Crystallographic data for
4, 6, 7, and 16 is available as CIF files free of charge via the Internet
at http://pubs.acs.org.
OM060591N