Oxidative-addition of organic monochloro derivatives to dinuclear iridium complexes: the detection of tautomeric equilibria and their implications on the reactivity

Article abstract of DOI:10.1021/om000314v

Reactions of MeCOCH₂Cl, MeCO₂CH₂Cl, and (-)-methyl(S)-2-chloropropionate with [{Ir(μ-Pz)(CNBu^t)₂}₂] (Pz = pyrazolate, 1) gave the metal-metal bonded diiridium(II) complexes [(CNBu^t)₂(Cl)Ir(μ-Pz)₂Ir(η¹-CH₂R) (CNBu^t)₂] (R = COMe (2), CO₂Me (3)) and the two enantiomers of [(CNBu^t)₂(Cl)Ir(μ-Pz)₂Ir(η¹-CH(Me)CO₂Me) (CNBu^t)₂] (4). Similar reactions of 1 with equimolar amounts of benzyl chloride and allyl chloride rendered [(CNBu^t)₂(Cl)Ir(μ-Pz)₂Ir(η¹-CH₂R) (CNBu^t)₂] ((R = Ph (5), CHqqCH₂ (7)), which were found to be the metal-metal bonded complexes in the solid state, but in equilibrium with the mixed-valence Ir(I)-Ir(III) complexes [(CNBu^t)₂Ir(μ-Pz)₂Ir(Cl)(η¹-CH₂R) (CNBu^t)₂] in solution. Replacement of chloride by iodide in 5 affords only the diiridium(II) complex [(CNBu^t)₂(I)Ir(μ-Pz)₂Ir(η¹-CH₂Ph) (CNBu^t)₂] (6). Complexes 5 and 7 reacted further with a second molar equivalent of chloro derivative to render dialkyldiiridium(III) complexes [{Ir(μ-Pz)(η¹-CH₂R)(CNBu^t)₂}₂ (μ-Cl)]Cl, ((R = Ph (8), CHqqCH₂ (10a)), while those showing a single static species in solution (2-4 and 6) were inactive. The reaction of 7 with allyl chloride gave also the isomer [(CNBu^t)₂(Cl)Ir(η¹,η²-CH₂CHqqCH₂) (μ-Pz)₂Ir(η¹-allyl)(CNBu^t)₂]Cl (10b), in which one allyl group bridges the two iridium atoms in an unsymmetrical fashion. This complex isomerizes into the thermodynamic products [{Ir(μ-Pz)(η¹-allyl)(CNBu^t)₂}₂ (μ-Cl)]Cl, an stereoisomer of 10a. The structures of 10b and 5 were solved by single-crystal X-ray diffraction methods.

Full text of DOI:10.1021/om000314v

Organometallics 2000, 19, 4977-4984
4977
Oxid a tive-Ad d ition of Or ga n ic Mon och lor o Der iva tives
to Din u clea r Ir id iu m Com p lexes: Th e Detection of
Ta u tom er ic Equ ilibr ia a n d Th eir Im p lica tion s on th e
Rea ctivity
Cristina Tejel, Miguel A. Ciriano,* J ose´ A. Lo´pez, Fernando J . Lahoz, and
Luis A. Oro*
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
Received April 13, 2000
Reactions of MeCOCH2Cl, MeCO2CH2Cl, and (-)-methyl(S)-2-chloropropionate with [{Ir-
(µ-Pz)(CNBut)2}2] (Pz ) pyrazolate, 1) gave the metal-metal bonded diiridium(II) complexes
[(CNBut)2(Cl)Ir(µ-Pz)2Ir(η1-CH2R)(CNBut)2] (R ) COMe (2), CO2Me (3)) and the two
enantiomers of [(CNBut)2(Cl)Ir(µ-Pz)2Ir(η1-CH(Me)CO2Me)(CNBut)2] (4). Similar reactions
of 1 with equimolar amounts of benzyl chloride and allyl chloride rendered [(CNBut)2(Cl)-
Ir(µ-Pz)2Ir(η1-CH2R)(CNBut)2] ((R ) Ph (5), CHdCH2 (7)), which were found to be the metal-
metal bonded complexes in the solid state, but in equilibrium with the mixed-valence Ir(I)-
Ir(III) complexes [(CNBut)2Ir(µ-Pz)2Ir(Cl)(η1-CH2R)(CNBut)2] in solution. Replacement of
chloride by iodide in 5 affords only the diiridium(II) complex [(CNBut)2(I)Ir(µ-Pz)2Ir(η1-CH2-
Ph)(CNBut)2] (6). Complexes 5 and 7 reacted further with a second molar equivalent of chloro
derivative to render dialkyldiiridium(III) complexes [{Ir(µ-Pz)(η1-CH2R)(CNBut)2}2(µ-Cl)]Cl,
((R ) Ph (8), CHdCH2 (10a )), while those showing a single static species in solution (2-4
and 6) were inactive. The reaction of 7 with allyl chloride gave also the isomer [(CNBut)2-
(Cl)Ir(η1,η2-CH2CHdCH2)(µ-Pz)2Ir(η1-allyl)(CNBut)2]Cl (10b), in which one allyl group bridges
the two iridium atoms in an unsymmetrical fashion. This complex isomerizes into the
thermodynamic product [{Ir(µ-Pz)(η1-allyl)(CNBut)2}2(µ-Cl)]Cl, an stereoisomer of 10a . The
structures of 10b and 5 were solved by single-crystal X-ray diffraction methods.
In tr od u ction
dium-iridium bond, has not been described. In this way,
access to alkyl diiridium(III) dinuclear complexes through
oxidative-addition reactions is restricted either by the
stability of the Ir-Ir bond or by the lack of an easy
reaction pathway for a further reaction. However, few
methylene-bridged diiridium(III) complexes become ac-
cessible either directly by reaction9 with CH2I2 or
through a thermal oxidative-isomerization reaction3,6,10
of iodomethyldiiridium(II) complexes. These observa-
tions show a relative inertness of dinuclear d7-d7
iridium systems with diolefin, carbonyl, and phosphine
ligands to react with haloalkanes. Exceptions to this
general behavior were exemplified by the compounds
[(L)2(Me)Ir(µ-Pz)2(µ-I)Ir(Me)(CNBut)2]I (L ) CNBut, 1/2
cod), coming unexpectedly from the double oxidative-
addition of CH3I to the complexes [(L)2Ir(µ-Pz)2Ir-
(CNBut)2].11
Oxidative-addition reactions of haloalkanes to bi-
nuclear iridium(I) complexes follow a common pattern
yielding diiridium(II) metal-metal bonded compounds.
The two fragments R and X become systematically
located trans to the Ir-Ir bond in the reactions with
the most usual haloalkanes, namely, MeI and CH2I2,
with independence of the type of bridging ligands in the
starting complexes: pyrazolate,1 tert-butylthiolate,2 di-
amidonaphthalene,3 pyridine-2-thiolate,4 7-azaindolate,5
or mixed ligands Pz, SBut.6 The few exceptions to this
pattern are the addition of MeI to [{Ir(µ-NHPhMe)-
(CO)2}2]7 and [Ir2(CO)2(µ-PPh2)(µ-PNNP)],8 resulting in
mixed-valence Ir(I)-Ir(III) compounds.
A further oxidative-addition of haloalkane to these
diiridium(II) complexes, which would cleavage the iri-
Very few reactions of diiridium(I) compounds with
(1) (a) Oro, L. A.; Sola, E.; Lo´pez, J . A.; Torres, F.; Elduque, A.;
Lahoz, F. J . Inorg. Chem. Commun. 1998, 1, 64. (b) Bushnell, G. W.;
Fjeldsted, D. O. K.; Stobart, S. R.; Wang, J . Organometallics 1996,
15, 3785, and references therein.
(2) El Amane, M.; Maisonnat, A.; Dahan, F.; Poilblanc, R. New. J .
Chem. 1988, 12, 661.
(3) Ferna´ndez, M. J .; Modrego, J .; Lahoz, F. J .; Lo´pez, J . A.; Oro, L.
A. J . Chem. Soc., Dalton Trans. 1990, 2587.
(4) Ciriano, M. A.; Viguri, F.; Oro, L. A.; Tiripicchio, A.; Tiripicchio-
Camellini, M. Angew. Chem., Int. Ed. Engl. 1987, 26, 444.
(5) Ciriano, M. A.; Pe´rez-Torrente, J . J .; Oro, L. A. J . Organomet.
Chem. 1993, 445, 273.
chloroalkanes have been reported so far.5,12 They re-
(7) Kolel-Veetil, M. K.; Rheingold, A. L.; Ahmed, K. J . Organome-
tallics 1993, 12, 3439.
(8) Schenck, T. G.; Milne, C. R. C.; Sawyer, J . F.; Bosnich, B. Inorg.
Chem. 1985, 24, 2338.
(9) El Amane, M.; Maisonnat, A.; Dahan, F.; Pince, R.; Poilblanc,
R. Organometallics 1985, 4, 773.
(10) Brost, R. D.; Stobart, S. R. J . Chem. Soc., Chem. Commun. 1989,
498.
(11) Tejel, C.; Ciriano, M. A.; Edwards, A. J .; Lahoz, F. J .; Oro, L.
A. Organometallics 1997, 16, 45.
(12) Caspar, J . V.; Gray, H. B. J . Am. Chem. Soc. 1984, 106, 3029.
(6) Pinillos, M. T.; Elduque, A.; Lo´pez, J . A.; Lahoz, F. J .; Oro, L. A.
J . Chem. Soc., Dalton Trans. 1991, 1391.
10.1021/om000314v CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/28/2000

4978 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
Ch a r t 1
quired visible or UV light irradiation to produce the
oxidative-addition of the chloroalkane leading to metal-
metal bonded complexes containing “Cl-Ir(II)-Ir(II)-
X” (X ) R, Cl) frameworks.
In this paper we describe the reactivity of the complex
[{Ir(µ-Pz)(CNBut)2}2] with several chloroalkanes to give
either metal-metal bonded diiridium(II) compounds or
bis(alkyl)diiridium(III) complexes. In addition, we dis-
cuss the reasons for this differential behavior based on
the intermediacy of unusual active mixed-valence Ir-
(I)-Ir(III) species in solution. Part of this work has been
previously communicated.13
membered ring “Ir(N-N)2Ir” in the species B. Indeed,
related Rh complexes of this type were found to exist
as two interconverting conformers,15 for which the major
species were the endo conformer, a stereochemistry and
equilibria not found for complexes 2 and 3.
Resu lts
Meta l-Meta l Bon d ed Din u clea r Ir id iu m P yr a -
zola te Com p lexes. The dinuclear complex [{Ir(µ-Pz)-
(CNBut)2}2] (Pz ) pyrazolate, 1) reacted with MeCOCH2-
Cl and MeCO2CH2Cl in benzene and in the dark to give
[{Ir(µ-Pz)(CNBut)2}2(Cl)(η1-CH2R)] (R ) COMe, 2;
CO2Me, 3) (Scheme 1). Both complexes were found to
be single and static in solution by 1H NMR, with
equivalent pyrazolate groups. The bonding of the RCH2-
group to the iridium through the CH2 carbon was
evidenced by a high-field resonance in the 13C{1H} NMR
spectra. Further information about their structures was
given by NOE difference spectra (Figure 1), which
revealed the close proximity of the RCH2- group and
the H3 protons of the pyrazolate rings. These data agree
with the two structures shown in Chart 1: the diirid-
ium(II) species (A) containing the chloride and CH2R
groups trans to the metal-metal bond and the mixed-
valence Ir(I)-Ir(III) complex (B) containing these frag-
ments in a trans disposition on one iridium center, with
the RCH2- ligand at the exo position. However, com-
plexes 2 and 3 must be formulated as the metal-metal
bonded species, A, since their variable (low and high)
temperature 1H NMR spectra in several solvents did not
reveal the presence of any fluxional process, which
should be expected for the facile inversion14 of the six-
The reaction of 1 with the simplest chiral chloro
derivative (-)-methyl(S)-2-chloropropionate, MeCO2CH-
(Me)Cl, provided some information on the mechanism
involved, at least, for this reaction. The product,
[(CNBut)2(Cl)Ir(µ-Pz)2Ir{CH(Me)CO2Me}(CNBut)2] (4),
was found to be a single and nonfluxional species in
C6D6. Spectroscopic NMR data indicated the bonding
of the CH(Me)CO2Me group through the secondary
carbon to iridium. In addition, preliminary X-ray dif-
fraction16 studies on a single crystal of 4 confirmed the
location of the Cl and CH(Me)CO2Me groups at different
iridium centers, both trans to the iridium-iridium bond.
Measurements of the rotatory specific power of the crude
of the reaction and of the isolated solid 4 showed a value
close to zero, evidencing the presence of a racemic
mixture. Accordingly, the two enantiomers were ob-
served by 1H NMR upon addition of Eu(hfc)3 {hfc )
3-(heptafluoropropylhydroxymethylene)-(+)-camphora-
to}. As only the SN2 profile produces inversion of the
configuration of the asymmetric carbon (Walden inver-
sion), either a radical or an SN1 mechanism (unlikely
in benzene) operates for the addition of the chiral
chloroderivative to 1.
Equ ilibr ia betw een Din u clea r Ir id iu m P yr a -
zola te Com p lexes. Complex 1 easily reacted with 1
molar equiv of PhCH2Cl in benzene to give 5, which was
isolated as long orange needles. A recently reported
X-ray diffraction study13 showed that 5 is the diiridium-
(II) complex [(CNBut)2(Cl)Ir(µ-Pz)2Ir(η1-CH2Ph)(CNBut)2]
(5a ), with an Ir-Ir bond in the solid state (Figure 2).
However, solutions of monocrystals of 5 showed the
presence of two species in the 1H NMR spectrum (Figure
3a). Both species have identical formulation [{Ir(µ-Pz)-
(CNBut)2}2(Cl)(η1-CH2Ph)] and symmetry (Cs); the major
species (82%) contains the PhCH2 group close to the H3
protons of the pyrazolate rings, as shown by positive
cross-peaks between these resonances in the phase-
sensitive NOESY spectrum at room temperature (Fig-
ure 4a), while these protons are far away in the minor
species. Accordingly, the major species could be 5a or
5c (Scheme 2), while the minor one is the Ir(III)-Ir-
(I)complex [(CNBut)2Ir(µ-Pz)2Ir(Cl)(η1-CH2Ph)(CNBut)2],
F igu r e 1. NOE difference spectra of [{Ir(µ-Pz)(CNBut)2}2-
(Cl)(η1-CH2COMe)] (2) in acetone-d6 upon irradiation at the
CH2 protons: (a) normal spectrum, (b) difference spectrum.
Sch em e 1
(13) Tejel, C.; Ciriano, M. A.; Lo´pez, J . A.; Lahoz, F. J .; Oro, L. A.
Organometallics 1998, 17, 1449.
(14) Tejel, C.; Villoro, J . M.; Ciriano, M. A.; Lo´pez, J . A.; Eguiza´bal,
E.; Lahoz, F. J .; Bakhmutov, V. I.; Oro, L. A. Organometallics 1996,
15, 2967.
(15) Tejel, C.; Ciriano, M. A.; Edwards, A. J .; Lahoz, F. J .; Oro, L.
A. Organometallics 2000, 19, 4968.
(16) Edwards, A. J .; Clegg, W. Private communication.

Addition of Monochloro Derivatives to Ir Complexes
Organometallics, Vol. 19, No. 24, 2000 4979
phase-sensitive ROESY spectrum carried out at 313 K
1
(Figure 4b). Variable-temperature H NMR spectra of
solutions of the orange needles in toluene-d8 indicated
that this interconversion is a high-energy process, since
only line-broadening effects were detected at 378 K.
As a conformational equilibrium between 5b and 5c is
expected to be a low-energy process,15 the main spe-
cies in the equilibrium needs to be 5a , the species
characterized in the solid state. Replacement of chloride
by iodide on reacting 5 with potassium iodide in acetone
gave [(CNBut)2(I)Ir(µ-Pz)2Ir(η1-CH2Ph)(CNBut)2] (6),
which was found to be the diiridium(II) complex with a
metal-metal bond as the single species in solution
(Figure 3b). Therefore, the replacement of the chloride
by iodide in 5 shifts the equilibrium to the diiridium-
(II) species.
Figu r e 2. Structure of the diiridium(II) complex [(CNBut)2-
(Cl)Ir(µ-Pz)2Ir(η1-CH2Ph)(CNBut)2] (5a ).
A second example of such equilibria in dinuclear
complexes was found for [{Ir(µ-Pz)(CNBut)2}2(Cl)(η1-
CH2CHdCH2)] (7), obtained from the reaction of 1 with
1 molar equiv of allyl chloride in benzene. In this case,
the two species were in a 1:10 ratio, the main species
being the metal-metal bonded complex [(CNBut)2(Cl)-
Ir(µ-Pz)2Ir(η1-CH2CHdCH2)(CNBut)2] (7a ), while the
minor one was [(CNBut)2Ir(µ-Pz)2Ir(Cl)(η1-CH2CHd
CH2)(CNBut)2] (7b), analogous to 5b. These species are
in chemical equilibrium, evidenced by magnetization
transfer techniques.
Compounds 2-7 could be classified into two types,
namely, those compounds that exist in solution as a
single static species with an iridium-iridium bond
(complexes 2-4 and 6) and those for which the metal-
metal bonded species is in equilibrium with the mixed-
valence Ir(I)-Ir(III) complexes (5 and 7). While com-
plexes 2-4 and 6 were found to be unable to react
further, even in an excess of substrate, complexes 5 and
7 reacted with a second molar equivalent of RCH2Cl.
Thus, the diiridium(III) complexes [(CNBut)2(η1-CH2Ph)-
Ir(µ-Pz)2(µ-Cl)Ir(η1-CH2R)(CNBut)2]Cl (R ) CH2Ph, 8;
CO2Me, 9) were obtained by reacting 5 with PhCH2Cl
and MeCO2CH2Cl, respectively, in the dark. The oxida-
tion of both iridium centers can be followed by the shift
to higher frequencies of ν(CN) in their IR spectra, as a
consequence of the different σ-donation of the isocyanide
ligands. The experimental data support folded struc-
tures, containing two pyrazolate and a chloride as
bridging ligands. The two organic fragments were trans
to the chloride bridging ligand and cis to both pyrazolate
rings, which was definitively confirmed by NOE experi-
ments. However, it is noteworthy that complex 5 does
not react with the secondary alkyl chloride MeCO2CH-
(Me)Cl under identical conditions.
F igu r e 3. 1H NMR spectra of 5 showing the two species
5a and 5b (a) and of 6 (b) in C6D6. The astrerisk denotes
the signal of the nondeuterated solvent.
Sch em e 2
with the PhCH2 group in the pocket of the complex (5b,
Scheme 2).
Complex 7 reacted with 1 molar equiv of CH2dCHCH2-
Cl, yielding two diiridium(III) complexes of formula [{Ir-
(µ-Pz)(CNBut)2}2(Cl)(CH2CHdCH2)2]Cl (10). The minor
product (15%), characterized by multinuclear NMR
spectroscopy, corresponds to the static bridging chloride
complex [{Ir(µ-Pz)(η1-CH2CHdCH2)(CNBut)2}2(µ-Cl)]Cl
(10a , Scheme 3), while the major one (85%) (10b) was
found to be the asymmetric isomer depicted in Scheme
3 and was fully characterized by X-ray methods (vide
infra). The 1H NMR of 10b showed broad signals at
room temperature, while a well-defined spectrum was
obtained on cooling. A complete spectroscopic NMR
study including H,H-COSY, 1H,13C-HETCOR, and
A relevant spectroscopic difference between 5a /c and
5b is the chemical shift for the benzyl protons, which
are separated 1.3 ppm in the 1H NMR spectrum.
According to previous observations,15 the low-field shifted
resonance corresponds to the compound with the RCH2-
group situated in the pocket of the complex, which
indeed agrees with the lack of NOE between the CH2
and pyrazolate protons for the minor species 5b. The
most remarkable feature of complex 5 is that the two
species observed in solution are in chemical equilibrium,
detected by the presence of negative cross-peaks be-
tween all pairs of resonances of both complexes in the

4980 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
F igu r e 4. Phase-sensitive (a) NOESY and (b) ROESY spectra of [{Ir(µ-Pz)(CNBut)2}2(Cl)(η1-CH2Ph)] (5a and 5b), showing
the cross-peaks due to proximity effects (positive peaks), and the exchange of the pyrazolate and CH2R groups of both
species (negative peaks), respectively.
Sch em e 3
Sch em e 4
is more simple than at low temperature, as if the
averaged species possesses a plane of symmetry bisect-
ing the dihedral angle between the two pyrazolate rings.
Complexes 10a and 10b do not interconvert. More-
over, while 10a remained unchanged, complex 10b
evolved into 10c on heating above room temperature.
The chemical transformation, quantitative by NMR,
corresponded to an isomerization of 10b into the non-
symmetric stereoisomer of 10a containing a chloride-
bridging ligand (Scheme 4).
Complex 10c was found to be a 1:1 electrolyte in
acetone. The lack of symmetry of the cation was evident
from the observation of distinct signals for all protons
and carbons in the 1H and 13C{1H} NMR spectra. In
addition, the two inequivalent η1-CH2CHdCH2 groups
were terminal and σ-bonded to the iridium atoms, as
deduced from the similarity of the chemical shifts in the
13C{1H} NMR spectrum to those of 10a . Moreover, these
allyl groups are in a relative transoid disposition, which
was corroborated by the NOESY spectrum, since only
ROESY experiments, allowed us to conclude that in 10b
one allyl group was η1-bonded to one iridium atom and
the other allyl group was bridging, η1-bonded to the
second iridium and coordinated through the double Cd
C bond to the first one, as found in the solid state. The
unsymmetric coordination of the allyl group as a σ,π-
bonded propenyl bridge, evidenced for the frozen struc-
ture, is quite uncommon. Indeed, only two crystal
structures of platinum complexes with σ,π-bonded pro-
penyl bridges have been reported,17 while symmetrical
π-allyl bridging groups are well documented.18 Most
probably, the fluxionality observed for 10b is related
with the change of coordination of the two faces of the
CdC bond to the second iridium atom (Scheme 4).
Indeed, the room-temperature 1H NMR spectrum of 10b
(17) Raper, G.; McDonald, W. S. J . Chem. Soc., Dalton Trans. 1972,
265.
(18) (a) Kurosawa, H.; Hirako, K.; Natsume, S.; Ogoshi, S.; Kane-
hisa, N.; Kai, Y.; Sakaki, S.; Takeuchi, K. Organometallics 1996, 15,
2089. (b) Werner, H. Adv. Organomet. Chem. 1981, 19, 155.

Addition of Monochloro Derivatives to Ir Complexes
Organometallics, Vol. 19, No. 24, 2000 4981
and η2 to Ir(1). The long Ir-Cl bond distance, 2.480(5)
Å, is in agreement wit the high structural trans influ-
ence of the σ-bonded carbon C(9), and the similar Ir-
(1)-C bond distances to C(8) and C(9), 2.47 and 2.51(2)
Å, corroborate the σ,π-coordination of the bridging allyl
ligand. Unfortunately, the geometric restraints needed
to deal with the crystallographic disorder, applied to the
C-C bond distances and angles, hinder any comparison
within the C(7)-C(9) propenyl ligand.
Discu ssion
In this paper we show rare nonphotochemical reac-
tions of dinuclear iridium complexes with activated alkyl
chlorides leading to a variety of functionalized orga-
noalkyldiiridium compounds. These dinuclear oxidative-
addition reactions produce an already known type of
metal-metal bonded diiridium(II) complexes in a first
step and bis(alkyl)diiridium(III) complexes by further
reaction of some of them with alkyl chlorides. Interest-
ingly, some diiridum(II) complexes are in chemical equi-
librium with the corresponding valence isomer Ir(I)-
Ir(III) complexes in solution. The state of the equilib-
rium is determined by the nature of the halide ligand
and the organic group on the iridium atoms. The
influence of the halide on the equilibrium is exemplified
by complexes 5 and 6, which differ on the halide ligand.
The Ir(II)-Ir(II) metal-metal bonded species and the
Ir(I)-Ir(III) mixed-valence complex are found to be in
equilibrium for the chloride complex 5. However, addi-
tion of iodide shifts the equilibrium to the diiridium(II)
complex 6. A similar trend was also observed for the
heterodinuclear complexes [{(η6-p-cymene)Ru(µ-Pz)2Ir-
(CO)2}X] (X ) Cl, Br, I).19 Regarding the influence of
the organic group of the type -CH2R on the equilibrium,
the III/I isomer is more favored for R ) CHdCH2, Ph
than for R ) COMe, CO2Me. The incorporation of a
methyl group at the R-carbon (R ) CH(Me)CO2Me) does
not produce any appreciable effect. The main difference
between these two groups is the stronger electron-
withdrawing character of the carbonyl versus the CdC
groups. A plausible interpretation for the influences of
the halide and organic groups in the X-Ir-Ir-R moiety
on the stabilization of the Ir(I)-Ir(III) isomer involves
a polarization of the Ir-Ir bond determined by the
nature of the X and R groups bonded in trans position.
The more electronegative the halogenide, the more
polarized the metal-metal bond, favoring the mixed-
valence species. However, the result of this inductive
effect can be blocked by electron-withdrawing organic
groups on the second iridium atom, which in turn favors
the diiridium(II) isomer.
F igu r e 5. ORTEP molecular drawing (40% probability
ellipsoids) of the cation of complex 10b showing the
distribution of ligands and the labeling scheme used. Only
one set of the disordered ligands is shown. The molecule
exhibits a crystallographic imposed symmetry plane through
the iridium and Cl(1) atoms; primed atoms are related to
the unprimed ones by the symmetry transformation x, -y
- 1/ 2, z.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [(CNBu t)2(η1-CH2CHdCH2)Ir (µ-P z)2(η1,η2-µ-
CH2CHdCH2)Ir (Cl)(CNBu t)2]Cl (10b)a
Ir(2)-Cl(1)
Ir(2)-N(2)
Ir(2)-C(9)
2.480(5)
2.075(11)
2.132(18)
Ir(1)-N(1)
Ir(1)-C(4)
Ir(1)-C(7)
Ir(1)-C(8)
Ir(1)-C(10)
2.060(10)
2.169(15)
2.47(2)
2.51(2)
1.925(15)
Ir(2)-C(15)
1.949(19)
N(1)-Ir(1)-N(1′)
N(1)-Ir(1)-C(4)
N(1)-Ir(1)-CGb
N(1)-Ir(1)-C(10)
N(1)-Ir(1)-C(10′)
N(1′)-Ir(1)-C(4)
N(1′)-Ir(1)-CGb
C(4)-Ir(1)-CGb
C(4)-Ir(1)-C(10)
C(4)-Ir(1)-C(10′)
CGb-Ir(1)-C(10)
CGb-Ir(1)-C(10′)
C(10)-Ir(1)-C(10′)
92.0(6) Cl(1)-Ir(2)-N(2)
81.0(6) Cl(1)-Ir(2)-C(9)
93.7(6) Cl(1)-Ir(2)-C(15)
89.5(5) N(2)-Ir(2)-N(2′)
175.2(5) N(2)-Ir(2)-C(9)
91.7(6) N(2)-Ir(2)-C(15)
94.2(6) N(2)-Ir(2)-C(15′)
172.9(6) N(2′)-Ir(2)-C(9)
84.0(6) C(9)-Ir(2)-C(15)
94.4(6) C(9)-Ir(2)-C(15′)
90.3(6) C(15)-Ir(2)-C(15′)
90.8(6)
89.4(3)
172.2(8)
91.8(4)
91.4(6)
86.0(7)
91.3(6)
177.0(6)
97.0(7)
82.1(7)
92.5(8)
85.9(10)
88.7(8)
a
Primed atoms are related to the unprimed ones by a symmetry
b
plane (symm transf: x, -y - 1/2, z). CG represents the centroid
of the C(7)-C(8) double bond.
three positive cross-peaks between the H3,5 protons of
the pyrazolate rings and the CH2 protons of the allyl
ligands were observed. Therefore, one allyl ligand is cis
to both pyrazolate and trans to the chloride bridging
ligand, while the other allyl moiety is cis to one
pyrazolate but trans to the other.
The X-ray crystal structure analysis of 10b (Figure
5) confirms the presence of the bridging σ,π-bonded
propenyl ligand, for which there is not a fully character-
ized precedent in iridium and rhodium chemistry.
Selected bond distances are collected in Table 1. The
molecular structure shows two iridium atoms bridged
by two exobidentate pyrazolate groups and by one allyl
ligand, σ-bonded to Ir(2) and π-bonded to Ir(1) through
the CdC bond. Both metals exhibit slightly distorted
octahedral geometries, with an intermetallic separation
of 3.8397(9) Å. Although the bridging and terminal
propenyl ligands are involved in a situation of static
disorder (see Experimental Section), the molecular
structural determination clearly confirms the asym-
metric coordination of the bridging ligand, η1 to Ir(2)
The access to bis(alkyl)diiridium(III) complexes by
reaction of diiridium(II) compounds with chloroalkanes
is only possible for those that are able to isomerize to a
detectable mixed-valence Ir(I)-Ir(III) complex. This
suggests that the reactions of 5 and 7 reported herein
occur with the species possessing an Ir(I) center that
can undergo oxidative-addition of a second molecule of
RCH2Cl. Therefore, the diiridium(II) compounds and the
mixed-valence Ir(I)-Ir(III) complex species not only are
valence isomers but fall into the category of tautomers,
(19) Carmona, D.; Ferrer, J .; Mendoza, A.; Lahoz, F. J .; Reyes, J .;
Oro, L. A. Angew. Chem., Int. Ed. Engl. 1991, 30, 1171.

4982 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
mixing times were optimized in the range of 0.4-1 s on the
Bruker spectrometer.
and therefore, the process could be called a “dinuclear
valence-tautomerism”. However, the term valence-tau-
tomerism has been used to describe internal metal-
ligand electron transfer (valence tautomers) in mono-
nuclear complexes.20 As the mixed-valence tautomer
reacts, the equilibrium regenerates this active species,
and the reactions eventually go to completion.
P r epar ation of th e Com plexes. [(CNBu t)2(Cl)Ir (µ-P z)2Ir -
(η1-CH2COMe)(CNBu t)2] (2). Chloroacetone (20 µL, 0.25
mmol) was added to a solution of [{Ir(µ-Pz)(CNBut)2}2] (1) (200
mg, 0.23 mmol) in benzene (5 mL). After 30 min, the resulting
pale yellow solution was carefully layered with hexane (20 mL)
and allowed to stand 2 days in the darkness. The resulting
pale yellow microcrystals were separated by decantation,
washed with cold hexane (2 × 5 mL), and vacuum-dried.
Yield: 200 mg (90%). Anal. Calcd for C29H47N8ClOIr2: C, 36.91;
H, 5.02; N, 11.87. Found: C, 36.72; H, 5.29; N, 11.54. IR
Regarding the species in the tautomeric equilibria,
we have been able to detect only a single conformer of
the mixed-valence Ir(I)-Ir(III) species, namely, that
possessing the organic fragment in the pocket of the
complex (for example 5b in Scheme 2). Most probably,
the unobserved conformer (5c, Scheme 2) exists also in
solution but in a percentage under the limit of detection
of the NMR and could be the responsible for further
reactions of 5 with a second molecule of chloro derivative
to account for the structure of the products (8 and 9).
Interestingly, the reaction of the allyl complex 7 with
allyl chloride provides a unique case in which the two
isomers coming from both conformers are observed
(Scheme 3). Most probably, the isomer 10b comes from
the tautomer (7b) observed in the NMR spectrum, while
10a comes from the 7c conformer. Assuming an anchi-
meric effect and SN2 mechanism for the second oxida-
tive-addition reaction, both the chloride and allyl ligands
could donate electronic density to the iridium undergo-
ing the reaction, and therefore the speed of these
reactions would become alike, producing both isomers
in a ratio similar to those found in other conformational
equilibria.15
The isomer 10b with the bridging allyl ligand is a rare
binuclear compound with an asymmetric allyl bridging
ligand in which the CdC bond is localized. Moreover,
this is a kinetic product for the addition of allyl chloride
to 7, since an isomerization takes place on heating to
render the thermodyamic product 10c, which contains
the bridging chloride. A simple mechanism for this
isomerization involves the rupture of the π-Ir-CdC
bond, followed by the inversion of the six-membered
metallacycle. This facilitates the access of the chloride
to both iridium atoms becoming a bridging ligand, which
produces the migration of one isocyanide from an
equatorial to the axial position.
1
(toluene, cm-1): ν(CN) 2179 (s), 2137 (s); ν(CO) 1641 (m). H
NMR (rt, acetone-d6): δ 7.54 (d, 2.1 Hz, 2H, H3Pz), 7.49 (d,
2.1 Hz, 2H, H5Pz), 5.92 (t, 2H, H4Pz), 3.46 (s, 2H, CH2COMe),
2.32 (s, 3H, CH2COMe), 1.51 and 1.50 (s, 2 × 18H, CNBut).
13C{1H} NMR (rt, acetone-d6): δ 208.3 (CO), 135.4 (C3Pz), 132.1
(br) and 122.7 (br) (CN), 133.6 (C5Pz), 104.0 (C4Pz), 58.4 and
57.9 (C-(CH3)3), 31.5 and 31.0 (C-(CH3)3), 14.1 (CH2COMe),
-5.4 (CH2COMe). MS (FAB+, acetone, m/z): 943, 7% (M + H+);
907, 70% (M - Cl+).
[(CNBu t)2(Cl)Ir (µ-P z)2Ir (η1-CH2CO2Me)(CNBu t)2] (3) was
prepared as yellow microcrystals as described for 2 starting
from [{Ir(µ-Pz)(CNBut)2}2] (1) (129 mg, 0.15 mmol) and
methylchloroacetate (14 µL, 0.15 mmol). Yield: 115 mg (80%).
Anal. Calcd for C29H47N8ClO2Ir2: C, 36.30; H, 4.94; N, 11.68.
Found: C, 36.09; H, 4.54; N, 11.50. IR (toluene, cm-1): ν(CN)
1
2187 (s), 2144 (s); ν(CO) 1679 (m). H NMR (rt, C6D6): δ 8.20
(d, 2.0 Hz, 2H, H3Pz), 7.63 (d, 2.0 Hz, 2H, H5Pz), 5.94 (t, 2H,
H4Pz), 3.71 (s, 3H, CH2CO2Me), 3.53 (s, 2H, CH2CO2Me), 1.84
and 1.22 (s, 2 × 18H, CNBut). 13C{1H} NMR (rt, C6D6) δ: 181.2
(CO), 136.3 (C3Pz), 135.4 (br) and 125.2 (br) (CN), 136.3
(C5Pz), 104.6 (C4Pz), 57.8 and 57.2 (C-(CH3)3), 49.7 (CH2-
CO2Me), 31.6 and 31.2 (C-(CH3)3), -2.8 (CH2CO2Me). MS
(FAB+, acetone, m/z): 959, 55% (M+); 907, 10% (M - Cl+); 941,
100% (M - Cl + H2O+).
(()-[(C N B u t )2 (C l)I r (µ-P z )2 I r {η1 -C H (M e )C O 2 M e }-
(CNBu t)2] (4) was prepared as yellow needles as described
for 2 starting from [{Ir(µ-Pz)(CNBut)2}2] (1) (200 mg, 0.23
mmol) and (-)-methyl(S)-2-chloropropionate (26 µL, 0.23
mmol). Yield: 149 mg (65%). Anal. Calcd for C30H49N8O2-
ClIr2: C, 37.01; H, 5.07; N, 11.51. Found: C, 37.31; H, 4.95;
N, 11.61. IR (diethyl ether, cm-1): ν(CN) 2181 (s), 2139 (s),
2080 (sh), 2052 (m). 1H NMR (rt, C6D6): δ 8.22 (d, 2.0 Hz, 1H),
8.20 (d, 2.0 Hz, 1H), 8.08 (d, 1.7 Hz, 1H) and 7.69 (d, 1.8 Hz,
1H) H3,3′,5,5′Pz, 6.00 (t, 1H) and 5.95 (t, 1H) H4,4′Pz, 4.05 (q, 6.8
Hz, 1H, CH(Me)CO2Me), 3.69 (s, 3H, CH(Me)CO2Me), 2.07 (d,
6.8 Hz, 3H, CH(Me)CO2Me), 1.24, 1.24, 1.13, and 1.04 (s, 4 ×
9H, CNBut). 13C{1H} NMR (rt, C6D6): δ 182.9 (CO), 136.6,
136.4, 134.3 and 134.1 (C3,3′,5,5′Pz), 138.7, 138.5, 123.6 (br) and
123.3 (br) (CN), 104.6 and 104.4 (C4,4′Pz), 58.2 and 57.0 (C-
(CH3)3), 49.6 (CH(Me)CO2Me), 31.8, 31.0 and 30.8 (C-(CH3)3),
22.9 (CH(Me)CO2Me), 7.0 (CH(Me)CO2Me). MS (FAB+, ac-
etone, m/z): 973, 35% (M+); 937, 100% (M - Cl+). ΛM (5.02
Exp er im en ta l Section
Sta r tin g Ma ter ia ls a n d P h ysica l Meth od s. All reactions
were carried out under argon using standard Schlenk tech-
niques. [{Ir(µ-Pz)(CNBut)2}2] (1) was prepared according to
literature methods.11 The organochlorinated compounds were
distilled under argon prior to use. Solvents were dried and
distilled under argon by standard methods. Pure complex 1
gives yellow-orange solutions in dried and deoxygenated
solvents; otherwise purple or blue solutions were obtained. The
new complexes described herein are light-sensitive and should
be stored in the dark. The formulas of the hydrates, complexes
8-10, are indicated with the analytical data, and the water
of crystallization was observed at 1.56 ppm in CDCl3 and at
2.81 and 2.84 ppm in acetone-d6 in their 1H NMR spectra.
Physical measurements were carried out on the apparatus
described in the preceding paper. NOE experiments were
carried out using the standard CYCLENOE pulse sequence
on the Varian spectrometer. The phase-sensitive NOESY and
ROESY experiments were carried out with 512 FIDs, and the
10-4 M in acetone): 2 S cm2 mol-1
.
[{Ir (µ-P z)(CNBu t)2}2(Cl)(η1-CH2P h )] (5). To a solution of
[{Ir(µ-Pz)(CNBut)2}2] (1) (200 mg, 0.23 mmol) in benzene (5
mL) was added benzyl chloride (27 µL, 0.23 mmol) in the
darkness. After 30 min, the reaction mixture was carefully
layered with pentane (20 mL) and then left in the refrigerator
overnight. The resulting orange crystals were separated by
decantation, washed with pentane, and dried under vacuum.
Yield: 230 mg (82%). Anal. Calcd for C33H49N8ClIr2‚0.5 C6H6:
C, 42.57; H, 5.15; N, 11.02. Found: C, 42.23; H, 5.11; N, 11.13.
IR (diethyl ether, cm-1): ν(CN) 2177 (s), 2133 (s), 2091 (sh),
2039 (m). 1H NMR (rt, C6D6) (major isomer): δ 8.27 (d, 2.0
Hz, 2H, H3Pz), 7.54 (d, 2.0 Hz, 2H, H5Pz), 7.58 (d, 7.6 Hz, 2H,
HoPh), 7.29 (t, 7.6 Hz, 2H, HmPh), 7.05 (t, 1H, HpPh), 5.99 (t,
2H, H4Pz), 4.15 (s, 2H, CH2), 1.24 and 0.94 (s, 2 × 18H,
CNBut); (minor isomer, data obtained from the COSY spec-
trum): δ 8.48 (d, 2.2 Hz, 2H, H3Pz), 8.19 (d, 2.2 Hz, 2H,
(20) (a) Roux, C.; Adams, D. M.; Itie´, J . P.; Polian, A.; Hendrickson,
D. N.; Verdaguer, M. Inorg. Chem. 1996, 35, 2846.

Addition of Monochloro Derivatives to Ir Complexes
Organometallics, Vol. 19, No. 24, 2000 4983
H5Pz), 7.21 (2H, HoPh), 7.05 (2H, HmPh), 6.99 (1H, HpPh), 6.33
(t, 2H, H4Pz), 5.44 (s, 2H, CH2), 1.04 and 0.88 (s, 2 × 18H,
CNBut). MS (FAB+, acetone, m/z): 977, 100% (M+). ΛM (4.99
Ch a r t 2
10-4 M in acetone): 12 S cm2 mol-1
.
[(CNBu t)2(I)Ir (µ-P z)2Ir (η1-CH2P h )(CNBu t)2] (6). To an
orange solution of [{Ir(µ-Pz)(CNBut)2}2(Cl)(η1-CH2Ph)] (5) (90
mg, 0.09 mmol) in acetone (4 mL) was added solid KI (30 mg,
0.18 mmol). After stirring for 2 h the resulting suspension was
evaporated to dryness and extracted with dichloromethane to
remove the KCl formed. Concentration of the orange solution
and crystallization with hexane gives orange microcrystals of
7, which were separated by decantation and vacuum-dried.
Yield: 75 mg (76%). Anal. Calcd for C33H49N8IIr2: C, 37.07;
H, 4.62; N, 10.48. Found: C, 37.27 H, 4.56; N, 10.34. IR (CH2-
Ch a r t 3
1
Cl2, cm-1): ν(CN) 2214 (s), 2183 (s); ν(Ph) 1634 (m). H NMR
(rt, acetone-d6): δ 7.62 (d, 2.4 Hz, 2H, H3Pz), 7.42 (d, 2.0 Hz,
2H, H5Pz), 7.34 (d, 7.3 Hz, 2H, HoPh), 7.16 (t, 7.3 Hz, 2H,
HmPh), 6.91 (t, 1H, HpPh), 5.91 (t, 2H, H4Pz), 3.75 (s, 2H, CH2),
1.46 and 1.37 (s, 2 × 18H, CNBut). 13C{1H} NMR (rt, acetone-
d6): δ 140.2 (C3Pz), 133.1 (C5Pz), 154.8, 128.2, 127.2 and 121.5
(Ph), 104.1 (C4Pz), 58.0 and 59.1 (C-(CH3)3), 31.4 and 30.7
(C-(CH3)3), 2.8 (CH2Ph).
and 139.7 (C3,5Pz), 149.8, 128.7, 128.4, and 125.3 (Ph), 106.9
(C4Pz), 59.2 and 59.0 (C-(CH3)3), 50.9 (CO2CH3), 30.4 and 30.1
(C-(CH3)3), 8.8 (CH2Ph), 1.6 (CH2CO2CH3). MS (FAB+, CH2-
Cl2, m/z): 1050, 100% (M+). ΛM (4.99 10-4 M in acetone): 89
S cm2 mol-1
.
[{Ir (µ-P z)(CNBu t)2}2(Cl)(η1-CH2CHdCH2)] (7) was pre-
pared as orange crystals as described for 5 starting from [{Ir-
(µ-Pz)(CNBut)2}2] (1) (129 mg, 0.15 mmol) and allyl chloride
(12 µL, 0.15 mmol). Yield: 112 mg (80%). Anal. Calcd for
[{Ir (µ-P z)(CNBu t)2}2(Cl)(η1-CH2CHdCH2)2]Cl (10a , 10b)
were prepared as described for 8 starting from [{Ir(µ-Pz)-
(CNBut)2}2(Cl)(η1-CH2CHdCH2)] (6) (102 mg, 0.11 mmol) and
allyl chloride (10 µL, 0.12 mmol) to give white microcrystals
of a mixture of 10a /10b in 15:85 molar ratio (Chart 2). Yield:
88 mg (80%). Anal. Calcd for C32H52N8Cl2Ir2‚2H2O: C, 36.95;
H, 5.43; N, 10.77. Found: C, 37.04; H, 5.30; N, 10.92. IR (CH2-
Cl2, cm-1): ν(CN) 2218 (s), 2187 (s); ν(CdC) 1612 (m). MS
(FAB+, CH2Cl2, m/z): 969, 100% (M+). Pure 10b as monocrys-
tals was obtained by recrystallization of the above mixture
from dichloromethane/diethyl ether. Spectroscopic data were
assigned from H,H-COSY, H,H-NOESY, and H,C-HETCOR.
C
29H47N8ClIr2: C, 37.55; H, 5.11; N, 12.08. Found: C, 37.52;
H, 5.04; N, 12.13. IR (toluene, cm-1): ν(CN) 2179 (s), 2137 (s),
2075 (sh), 2044 (sh); ν(CdC) 1610 (m). 1H NMR (233 K,
toluene-d8) major isomer: δ 8.20 (d, 1.8 Hz, 2H, H3Pz), 7.49
(d, 1.8 Hz, 2H, H3Pz), 6.82 (m, 1H, η1-CH2CHdCH2), 5.93 (t,
2H, H4Pz), 5.30 (dd, 16.5 and 2.7 Hz, 1H) and 4.97 (dd, 9.6
and 2.7 Hz, 1H) (η1-CH2CHdCH2), 3.63 (d, 8.7 Hz, 2H, η1-CH2-
CHdCH2), 1.15 and 0.98 (s, 2 × 9H, CNBut); minor isomer: δ
8.46 (d, 2.4 Hz, 2H, H3Pz), 8.10 (d, 2.4 Hz, 2H, H5Pz), 6.46 (m,
1H, η1-CH2CHdCH2), 6.32 (t, 2H, H4Pz), 5.08 (dd, 16.5 and
2.7 Hz, 1H) and 4.89 (dd, 9.9 and 3.0 Hz, 1H) (η1-CH2CHd
CH2), 4.66 (d, 8.4 Hz, 2H, η1-CH2CHdCH2), 1.03 and 0.95 (s,
2 × 9H, CNBut). 13C{1H} NMR (233K, toluene-d8) mayor
isomer: δ 136.7 (C3Pz), 132.4 (C5Pz), 104.6 (C4Pz); 57.6 and
56.8 (C-(CH3)3), 31.6 and 30.9 (C-(CH3)3); 151.6 (η1-CH2CHd
CH2), 102.2 (η1-CH2CHdCH2), 2.9 (η1-CH2CHdCH2). MS (FAB+,
acetone, m/z): 927, 100% (M + H+).
(10a ) 1H NMR (233 K, acetone-d6): δ 7.88 (d, 2.1 Hz, 4H, H3,5
-
Pz), 6.39 (t, 2H, H4Pz), 6.41 (m, 2H, η1-CH2CHdCH2), 5.31 (dd,
16.8 and 1.8 Hz, 2H) and 5.03 (dd, 9.9 and 2.1 Hz, 2H) (η1-
CH2CHdCH2), 2.97 (d, 8.4 Hz, 4H, η1-CH2CHdCH2), 1.61 (s,
36H, CNBut). 13C{1H} NMR (233 K, acetone-d6): δ 140.3 (C3,5
-
Pz), 107.6 (C4Pz); 59.6 (C-(CH3)3), 30.1 (C-(CH3)3); 147.3 (η1-
CH2CHdCH2), 110.7 (η1-CH2CHdCH2), 9.17 (η1-CH2CHdCH2).
1
(10b) H NMR (233 K, acetone-d6): δ 7.87 (d, 2.1 Hz, 1H) and
7.73 (d, 2.1 Hz, 1H) (H3,3′Pz), 7.64 (d, 2.1 Hz, 1H) and 7.47 (d,
2.1 Hz, 1H) (H5,5′Pz), 6.27 (t, 1H) and 6.24 (t, 1H) (H4,4′Pz);
6.38 (m, 1H, η1-CH2CHdCH2), 5.13 (dd, 16.8 and 1.8 Hz, 1H)
and 4.97 (dd, 9.6 and 2.1 Hz, 1H) (η1-CH2CHdCH2), 2.77 (t,
9.0 Hz, 1H) and 2.41 (t, 9.0 Hz, 1H) (η1-CH2CHdCH2); 5.55
(m, 1H, µ-CH2CH)CH2), 5.52 (m, 1H) and 4.92 (m, 1H) (µ-
CH2CHdCH2), 3.82 (dd 16.5 and 2.0 Hz, 1H) and 1.79 (d, 16.5
Hz, 1H) (µ-CH2CHdCH2); 1.77, 1.67, 1.61, and 1.55 (s, 4 ×
9H, CNBut). 13C{1H} NMR (233 K, acetone-d6): δ 144.9 and
[{Ir (µ-P z)(η1-CH2P h )(CNBu t)2}2(µ-Cl)]Cl (8). Benzyl chlo-
ride (12 µL, 0.10 mmol) was added to a solution of [{Ir(µ-Pz)-
(CNBut)2}2(Cl)(η1-CH2Ph)] (5) (97 mg, 0.10 mmol) in benzene
(3 mL) and carefully layered with pentane (15 mL) overnight
in the darkness. The resulting white crystals were separated
by decantation, washed with diethyl ether, and dried under
vacuum. Yield: 116 mg (92%). Anal. Calcd for C40H56N8Cl2-
Ir2‚2H2O: C, 42.13; H, 5.21; N, 9.98. Found: C, 42.57; H, 5.13;
1
N, 9.87. IR (CH2Cl2, cm-1): ν(CN) 2220 (s), 2187 (s). H NMR
144.1 (C3,3′Pz), 142.9 and 141.9 (C5,5′Pz), 107.3 and 107.1 (C4,4′
-
(rt, CDCl3): δ 7.64 (d, 2.3 Hz, 4H, H3,5Pz), 7.23 (d, 7.2 Hz, 4H,
HoPh), 7.14 (t, 7.2 Hz, 4H, HmPh), 7.04 (t, 2H, HpPh), 6.31 (t,
2H, H4Pz), 3.46 (s, 4H, CH2), 1.08 (s, 36H, CNBut). 13C{1H}
NMR (rt, CDCl3): δ 139.7 (C3,5Pz), 149.8, 128.5, 128.4 and
125.0 (Ph), 106.8 (C4Pz), 58.7 (C-(CH3)3), 29.9 (C-(CH3)3), 8.8
(CH2Ph). MS (FAB+, CH2Cl2, m/z): 1069, 100% (M+). ΛM (4.99
Pz); 60.4, 60.2, 59.2 and 59.1 (C-(CH3)3), 146.1 (η1-CH2CHd
CH2), 111.3 (η1-CH2CHdCH2), 21.1 (η1-CH2CHdCH2); 129.7
(µ-CH2CHdCH2), 86.2 (µ-CH2CHdCH2), -4.1 (µ-CH2CHd
CH2).
[{Ir (µ-P z)(η1-CH 2CH dCH 2)(CNBu t )2}2(µ-Cl)]Cl (10c).
Heating a pure sample of 10b in acetone-d6 or in CDCl3 at 60
°C in the NMR cavity for 2 h produces the complete transfor-
mation into 10c (Chart 3). Complex 10c was isolated as a white
solid by crystallization, layering the acetone solution (0.5 mL)
with diethyl ether (5 mL). Anal. Calcd for C32H52N8Cl2Ir2‚
2H2O: C, 36.95; H, 5.43; N, 10.77. Found: C, 37.04; H, 5.30;
N, 10.92. IR (CH2Cl2, cm-1): ν(CN) 2218 (s), 2187 (s); ν(CdC)
1606 (m). 1H NMR (rt, CDCl3): δ 7.55 (d, 1.8 Hz, 1H) and 7.53
(d, 2.4 Hz, 1H) (H5,5′ Pz), 7.49 (d, 1.9 Hz, 1H) and 7.43 (d, 2.1
Hz, 1H) (H3′,3 Pz), 6.28 (t, 2.4 Hz, 1H) and 6.26 (t, 2.1 Hz, 1H)
(H4′,4 Pz); 6.71 (m, 2H, CH2CHdCH2 a and b), 5.19 (dm, 16.8
Hz, 1H) and 4.97 (dd, 9.9 and 2.1 Hz, 1H) (η1-CH2CHdCH2
a), 3.01 (t, 9.6 Hz, 1H) and 2.93 (t, 9.9 Hz, 1H) (CH2CHdCH2
10-4 M in acetone): 89 S cm2 mol-1
.
[(CNBu t)2(η1-CH2P h )Ir (µ-P z)2(µ-Cl)Ir (η1-CH2CO2CH3)-
(CNBu t)2]Cl (9) was prepared as described for 8 starting from
[{Ir(µ-Pz)(CNBut)2}2(Cl)(η1-CH2Ph)] (5) (68 mg, 0.07 mmol) and
methylchloroacetate (6.5 µL, 0.07 mmol) to give white micro-
crystals. Yield: 70 mg (92%). Anal. Calcd for C36H54N8O2Cl2-
Ir2‚2H2O: C, 38.53; H, 5.20; N, 9.98. Found: C, 38.00; H, 5.30;
N, 9.75. IR (CH2Cl2, cm-1): ν(CN) 2224 (s), 2193 (s); ν(CO)
1
1713 (m). H NMR (rt, CDCl3): δ 7.69 (d, 2.2 Hz, 2H, H3Pz),
7.62 (d, 2.2 Hz, 2H, H5Pz), 7.19 (m, 4H, Ho,mPh), 7.09 (t, 6.8
Hz, 1H, HpPh), 6.26 (t, 2H, H4Pz), 3.64 (s, 3H, CO2CH3), 3.45
(s, 2H, CH2Ph), 2.75 (s, 2H, CH2CO2CH3), 1.44 and 1.28 (s, 2
× 18H, CNBut). 13C{1H} NMR (rt, CDCl3): δ 180.4 (CO), 140.1

4984 Organometallics, Vol. 19, No. 24, 2000
Tejel et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta for
[(CNBu t)2(η1-CH2CHdCH2)Ir (µ-P z)2(η1,η2-µ-
CH2CHdCH2)Ir (Cl)(CNBu t)2]Cl (10b)
symmetry plane. The two allyl ligands (C(4)-C(6) terminal
and C(7)-C(9) bridging) are not congruent with this plane,
and they have been refined as two moieties disordered in the
crystal (0.50 fixed occupancy). To prevent the atoms of these
two disordered ligands from collapsing during refinement into
the symmetry plane, geometric restraints were placed on the
C-C bond distances (C-C 1.51(2), CdC 1.46(2), C‚‚‚C 2.60(2)
Å for the terminal allyl23 and C-C 1.46(2), CdC 1.40(2), C‚‚
‚C 2.50(2) Å for the bridging allyl).17 As the presence of this
disorder involving the allylic ligands could be interpreted in
terms of an erroneous selection of the spatial group, an
alternative refinement with a symmetry reduction to the P21
space group was carried out; under this symmetry no conver-
gence was obtained,24 and the huge anisotropic displacement
parameters obtained for the carbon atoms of the allylic ligands
confirmed the existence of static disorder.
The tert-butyl group of one tert-butylisocyanide ligand was
also found to be disordered: two moieties with equal occupancy
were introduced in the refinement (C(16a)-C(19a) and C(16b)-
C(19b); 0.50(4) refined occupancy). The bond distances and
angles within both disordered moieties were restrained to
common values, and a 3-fold symmetry was maintained within
each set of atoms. A dichloromethane solvent molecule was
also observed highly disordered; it was refined as three
different models (and two more symmetry-generated) in the
same spatial zone. Bond distances and angles were also
restrained to the usual values for this molecule.23 The sum of
the refined occupancy factors was restrained to one, and two
common isotropic displacement parameters were used: one
for carbon atoms and a second one for chlorides.
chem formula
fw
C32H52Cl2Ir2N8‚CH2Cl2
1089.04
temp, K
cryst syst
space group
a, Å
b, Å
c, Å
293
monoclinic
P21/m (no. 11)
13.0890(6)
11.4237(7)
15.3290(6)
101.290(4)
2247.7(2)
2
1.609
6.182
1.9-25.0
5153
â, deg
V, Å3
Z
F
(calcd), g cm-3
µ, mm-1
θ range data collec, deg
no. of reflns collected
no. of unique reflns
no. of data/restraints/params
R(F) [F2 > 2σ(F2)]a
wR(F2) [all data]b
4169 (Rint ) 0.0503)
4169/47/227
0.0614
0.1422
a
R(F) ) ∑||Fo| - |Fc||/∑|Fo|, for 2434 observed reflections.
wR(F2) ) (∑[w(Fo - Fc2)2]/∑[w(Fo2)2])1/2
.
b
2
a); 4.95 (dm, 16.8 Hz, 1H), 4.71 (dd, 9.9, 2.4 Hz, 1H) (CH2-
CHdCH2 b), 2.90 (t, 9.3 Hz, 1H) and 2.53 (t, 9.3 Hz, 1H) (CH2-
CHdCH2 b); 1.60, 1.57, 1.56 and 1.52 (s, 4 × 9H, CNBut).
13C{1H} NMR (rt, CDCl3): δ 140.4, 139.3, 138.4, 138.2 (C3,3′,5,5′
-
Pz); 106.8, 106.7 (C4,4′Pz); 59.5, 59.1, 59.1, 58.9 (C-(CH3)3);
30.7, 30.7, 30.6, 30.6 (C-(CH3)3); 147.6, 146.3 (CH2CHdCH2);
110.9, 108.3 (CH2CHdCH2); 8.9, 3.2 (CH2CHdCH2).
Anisotropic displacement parameters were used in the last
cycles of refinement for all nondisordered atoms, while iso-
tropic ones were included for disordered groups. No attempt
was made to include hydrogen atoms in the refinement. Atomic
scattering factors, corrected for anomalous dispersion, were
used as implemented in the refinement program. The calcu-
lated weighting scheme was 1/[σ2(Fo2) + (xP)2 + yP], where x
Cr ysta l Str u ctu r e Deter m in a tion of Com p lex 10b. A
summary of crystal data, intensity collection, and refinement
parameters is reported in Table 2. A colorless irregular crystal
was glued to a glass fiber and mounted on a Siemens-Stoe
AED2 diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Cell constants were obtained from
the least-squares fit on the setting angles of 100 reflections in
the range 25° e 2θ e 35°. Data were collected at room
temperature using the ω/2θ scan method (4° e 2θ e 50°; -15
e h e 2, 0 e k e 13, -18 e l e 18). Three standard reflections
were monitored every 55 min throughout the data collection;
a decay of 11.4% was observed and consequently corrected
according standard intensities. All data were corrected for
Lorentz and polarization effects and for absorption using the
ψ-scan method (min. and max. transm factors 0.1009 and
0.1273).21
) 0.0591, y ) 4.7225, and P ) (Fo2 + 2Fc2)/3. Final agreements
2
factors were R(F) ) 0.0614 (2434 observed reflections, Fo
<
2σ(Fo2)) and wR(F2) ) 0.1422. Largest peak and hole in the
difference map were 1.451 (close to one iridium atom) and
-0.972 e Å-3
.
Ack n ow led gm en t. The generous financial support
from Direccio´n General de Ensen˜anaza Superior e
Investigacio´n (DGES) is gratefully acknowledged (Pro-
jects PB98-641 and PB94-1186).
The structures were solved by Patterson methods (SHELXS-
97)22 and Fourier techniques and refined by full-matrix least-
squares on F2 (SHELXL-97).22 The dinuclear complex sits at
both sides of a crystallographic mirror plane with the Ir(1),
Ir(2), and Cl(1) atoms occupying special positions on the
Su p p or tin g In for m a tion Ava ila ble: Full listings of
crystallographic data, complete atomic coordinates, isotropic
and anisotropic displacement parameters, and complete bond
distances and angles for complex 10b. This material is
available free of charge via the Internet at http://pubs.acs.org.
(21) (a) XPREP Program, Rel. 5.03; Siemens Analytical X-ray
Instruments, Inc.: Madison, WI, 1994. (b) North, A. C. T.; Phillips, D.
C.; Mathews, F. S. Acta Crystallogr., Sect. A 1968, 24, 351.
(22) Sheldrick, G. M. SHELX-97; University of Go¨ttingen: Germany,
1997.
OM000314V
(23) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993,
8, 31.
(24) Watkin, D. Acta Crystallogr., Sect. A 1994, 50, 411.