Investigation of the C-H activation potential of [hydrotris(1H-pyrazolato-κN1)borato(1-)]iridium (IrTpx) fragments featuring aromatic substituents x at the 3-position of the pyrazole rings

Article abstract of DOI:10.1002/1522-2675(20011017)84:10<2868::AID-HLCA2868>3.0.CO;2-P

A series of pyrazole-substituted [hydrotris(1H-pyrazolato-κN¹)borato(1-)]iridium complexes of the general composition [Ir(Tp^x)(olefin)₂] (Tp^x = Tp^Ph and Tp^Th) and their capability to activate C-H bonds is presented. As a test reaction, the double C-H activation of cyclic-ether substrates leading to the corresponding Fischer carbene complexes was chosen. Under the reaction conditions employed, the parent compound [Ir(Tp^Ph)(ethene)₂] was not isolable; instead, (OC-6-25)-[Ir(Tp^PhκC^Ph,κ³N, N′,N″)(ethyl)(η²-ethene)] (1) was formed diastereoselectively. Upon further heating, 1 could be converted exclusively to (OC-6-24)-[Ir(Tp^Phκ²C^Ph,C ^Ph,κ³N,N′,N″)(η²- ethene)] (2). Complex 1, but not 2, reacted with THF to give (OC-6-35)-[Ir(Tp^Phκ³N,N′,N″)H (dihydrofuran-2(3H)-ylidene)] (3), a cyclic Fischer carbene formed by double C-H activation of THF. Accordingly, complexes of the general formula [Ir(Tp^x)(butadiene)] (see 4-6; butadiene = buta-1,3-diene, 2-methylbuta-1,3-diene (isoprene), 2,3-dimethylbuta-1,3-diene) reacted with THF to yield 3 or the related derivative 9. The reaction rate was strongly dependent on the steric demand of the butadiene ligand and the nature of the substituent at the 3-position of the pyrazole rings.

Full text of DOI:10.1002/1522-2675(20011017)84:10<2868::AID-HLCA2868>3.0.CO;2-P

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Helvetica Chimica Acta ± Vol. 84 (2001)
Investigation of the C H Activation Potential of [Hydrotris(1H-pyrazolato-
kN1)borato(1 )]iridium (IrTpx) Fragments Featuring Aromatic Substituents
x at the 3-Position of the Pyrazole Rings
Part 1
The Choice of the Precursor
by Christian Slugovc*a), Kurt Mereiterb), Swiatoslaw Trofimenkoc), and Ernesto Carmona*d)
a) Institute of Inorganic Chemistry, Vienna University of Technology, Getreidemarkt 9/153, A-1060 Vienna
(fax: (‡43)-1-5880115399; e-mail: slugi@mail.zserv.tuwien.ac.at)
b) Institute of Mineralogy, Crystallography and Structural Chemistry, Vienna University of Technology,
Getreidemarkt 9/171, A-1060 Vienna
c) Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716-2522, USA
d
Â
) Instituto de Investigaciones Químicas, Departamento de Química Inorganica Universidad de Sevilla,
Â
Consejo Superior de Investigaciones Científicas, Avda. Americo Vespucio s/n, E-41092 Sevilla
(fax: (‡ 34)-954460565; e-mail: guzman@cica.es)
In memory of Professor Luigi M. Venanzi
A series of pyrazole-substituted [hydrotris(1H-pyrazolato-kN1)borato(1 )]iridium complexes of the
general composition [Ir(Tpx)(olefin)2] (Tpx ˆ TpPh and TpTh) and their capability to activate C H bonds is
presented. As a test reaction, the double C H activation of cyclic-ether substrates leading to the corresponding
Fischer carbene complexes was chosen. Under the reaction conditions employed, the parent compound
[Ir(TpPh)(ethene)2] was not isolable; instead, (OC-6-25)-[Ir(TpPhkCPh,k3N,N',N'')(ethyl)(h2-ethene)] (1) was
formed diastereoselectively. Upon further heating,
[Ir(TpPhk2CPh,CPh,k3N,N',N'')(h2-ethene)] (2). Complex 1, but not 2, reacted with THF to give (OC-6-35)-
[Ir(TpPhk3N,N',N'')H(dihydrofuran-2(3H)-ylidene)] (3), a cyclic Fischer carbene formed by double C
1 could be converted exclusively to (OC-6-24)-
H
activation of THF. Accordingly, complexes of the general formula [Ir(Tpx)(butadiene)] (see 4 ± 6; butadiene ˆ
buta-1,3-diene, 2-methylbuta-1,3-diene (isoprene), 2,3-dimethylbuta-1,3-diene) reacted with THF to yield 3 or
the related derivative 9. The reaction rate was strongly dependent on the steric demand of the butadiene ligand
and the nature of the substituent at the 3-position of the pyrazole rings.
Introduction. ± The selective activation of the C H bonds of organic substrates by
transition-metal complexes and the utilization of this reaction for the functionalization
of unreactive compounds constitute an important and active area of research [1]. We
have recently developed an efficient, straightforward synthetic route to Fischer-type
carbene iridium complexes by double C H activation of cyclic-ether substrates
(Scheme 1). IrIII Species like [Ir(TpMe )(H)(CHˆCH2)(H2CˆCH2)] or [Ir-
2
1
(TpMe )(Ph)2(m-N2)] (TpMe ˆ [tris(3,5-dimethyl-1H-pyrazolato-kN )hydroborato(1 )-
k3N2,N2',N2'']), are able to induce this reaction in five- or six-membered cyclic ethers [2].
The utilization of TpPh (TpPh ˆ [hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(1 )])
as the coligand has brought about a substantial improvement of this synthetic
methodology. [Ir(TpPh)(isoprene)] is able to activate a variety of ethers and amines to
give Fischer-type carbenes by means of double C H bond cleavage reactions [3].
2
2

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Scheme 1
In complexes of RhI and IrI, with Tpx ligands, different coordination modes have
been demonstrated [4]. [M(Tpx)(L)2] Derivatives of d8-metals adopt either a square-
planar geometry with bidentate Tpx-k2, or the trigonal-bipyramidal structure that
results from Tpx-k3 coordination. These structures often interconvert. The dynamics of
the intramolecular exchange have been extensively studied by Venanzi and co-workers
[5]. The adoption of one or another structure, or, in other words, the denticity of the
Tpx ligand, depends largely upon the size of the substituent at the 3-position of the
pyrazole rings. The Tpx-k3 coordination becomes comparatively disfavored for bulky
substituents. Less attention has been paid to the role of the neutral ligands L, but recent
studies by Akita, Moro-oka, and co-workers on compounds of the composition
[Rh(TpiPr )(Ph2P(CH2)nPPh2)] have demonstrated an important effect of the chelate
2
size [6] and of the conformation (flat or folded) of the RhP2(CH2)n ring [7] on the TpiPr
2
coordination.
In this line of work, we undertook the preparation and characterization of a series
of [Ir(Tpx)(olefin)] compounds, with Tpx ˆ TpPh and TpTh (TpTh ˆ [hydrotris(3-thienyl-
1H-pyrazolato-kN1)borato(1 )]; olefin ˆ ethene, buta-1,3-diene, 2-methylbuta-1,3-
diene (isoprene), and 2,3-dimethylbuta-1,3-diene) and tested their capacity to achieve
the double C H bond activation of THF, to produce the corresponding Fischer carbenes.
Results and Discussion. ± The ꢀBis(ethene)ꢁ Compound. The bis(ethene) complex
2
Me2
1
[Ir(TpMe )(h -ethene)2] (Tp ˆ[hydrotris(3,5-dimethyl-1H-pyrazolato-kN )borato(1 )]),
2
readily prepared from [IrCl(coe)2]2 (coeˆcyclooctene) with ethene and [K(TpMe )] at
2
low temperatures [8], constitutes a versatile entry to various C H activation reactions.
If [Tl(TpPh)] is used instead of [K(TpMe )], under otherwise similar conditions, a complex
2
with the analytical composition expected for [Ir(TpPh)(C2H4)2], but of a very different
nature, namely the cyclometalated IrIII compound (OC-6-25)-[Ir(TpPh-kCPh,k3N,N',N'')-
(ethyl)(h2-ethene)] (1) is obtained in 86% isolated yield (see Scheme 2). Compound 1
is further characterized in the solid-state by X-ray studies (Fig. 1). As can be seen, the
Ir-center is in a distorted, nonsymmetrical environment that consists of the three N-
atoms of the TpPh ligand, the C2H4 and C2H5 groups, and a C-metallated phenylpyrazole
unit. At variance with structurally characterized [M(Tpx-k3)] moieties, which exhibit
similar N
M N angles close to 908, the three N Ir N bite angles of 1 amount to
83.3(1), 92.8(2), and 76.1(1)8. The difference between the latter two, 16.78, is larger
than usual differences (<108) (for a closer discussion of the structure, see [9]).

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Scheme 2
Fig. 1. ORTEP Plot of 1. H-Atoms are omitted for clarity; thermal ellipsoids are at the 20% probability level.
1
Crude mixtures of 1 contain a by-product (<4% as established by H-NMR
spectroscopy; de of 1 > 92%), which cannot be isolated, but, arguably, is the other
isomer (OC-6-35)-[Ir(TpPh-kCPh,k3N,N',N'')(ethyl)(h2-ethene)]. Both its h2-bonded
ethene and ethyl ligands are obvious in the 1H-NMR spectrum of the by-product, with
the chemical shifts distinctly different from those in 1.

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Heating of 1 in benzene gives the bis-cyclometalated product (OC-6-24)-[Ir(TpPh-
k2CPh,CPh,k3N,N',N'')(h2-ethene)] (2) as the only isolable product (Scheme 2). Accord-
ingly, the second metallation process proceeds diastereoselectively to yield 2, regardless
of whether crude 1 (containing the minor isomer) or pure 1 is used. Nevertheless, some
decomposition occurs (92 Æ 2% isolated yield of 2), so that it is not clear whether or
not the minor isomer contributes to the formation of 2. The identity of 2 is apparent
from three nonequivalent pyrazole rings in the NMR spectra. Note that the other
isomer of 2 should have C2v symmetry.
The thermal conversion of 1 into 2 can be monitored by NMR spectroscopy in
different solvents. No other species is detected in C6F6, CDCl3, or (D12)cyclohexane,
but, in C6D6, an intermediate is observed (vide infra), whereas (D8)THF gives a
different reaction product. Generation of the latter on a preparative scale by heating 1
in THF (808, 16 h) allows its formulation as (OC-6-35)-[Ir(TpPh-kCPh,k3N,N',N'')-
H(dihydrofuran-2(3H)-ylidene)] (3; see below, Fig. 4), a cyclic Fischer carbene
formed by double C H activation of THF (isolated yield 91%). Again, the
transformation is diastereoselective, a by-product present in the raw mixture (< 5%;
de of 3 > 90%) is assumed to be the other diastereoisomer based on the NMR-
spectroscopic properties. A 2D-NOE experiment with 3 suggests a configuration
similar to that of 1, with the neutral (p-accepting) ligand trans to the iridium-bonded N-
atom of the C-metalated phenylpyrazole unit. A cross-peak of the hydrido ligand with
the ortho-protons of a nonmetallated phenyl ring is observed.
Proposed Mechanism for the Formation of 1 ± 3. Previous work has shown that the
increase of the steric bulk of the Tpx ligand that accompanies the change from Tp to
TpMe facilitates the activation of a coordinated molecule of ethene of [Ir(Tpx)(C2H4)2]
2
compounds [8]. The resulting [Ir(Tpx)(H)(ethenyl)(h2-ethene)] species (see, e.g., B in
Scheme 3) react readily with 2-electron donors (e.g., MeCN, PMe3) to generate
[IrIII(ethyl)(ethenyl)] adducts in which the molecule of the Lewis base takes up the
vacant coordination site of C [10]. For the system under investigation, which is based on
the bulkier TpPh ligand, a combination of steric hindrance and of the close proximity of
the Ph rings of the TpPh group explains the facile formation of 1 as the direct product of
the reaction of [IrCl(coe)2]2 with C2H4 and [Tl(TpPh)]. Clearly, in this case, one of the
Ph substituents at the pyrazole moieties promotes the B ! C transformation via the
formal oxidative addition of an aromatic C H bond and subsequent hydrido-vinyl
reductive coupling, giving rise to 1. Since intermediates of kind B have been shown to
add two molecules of C6H6 to produce, e.g., [Ir(TpMe )(C6H5)2(N2)] [2] through a
2
species like C, the mechanism of the formation of 1 may be viewed as readily
established. Heating of solutions of 1 allows its conversion into 2. The reaction may
proceed intramolecularly (C6F6 as the reaction solvent) or by intervention of a
molecule of C6H6 when this substance is used as the solvent. In the latter case, an
intermediate D would be formed, and, while this could not be isolated, it can be
assumed to be [Ir(TpPh-kCPh,k3N,N',N'')(Ph)(h2-ethene)] on the basis of its character-
istic NMR signals (1H-NMR: 3.60 (m, 2 H, H2CˆCH2); 3.17 (m, 2 H, H2CˆCH2);
13C{1H}-NMR: 64.9 (2 C, H2CˆCH2)).
A
related intermediate, [Ir(TpPh-
kCPh,k3N,N',N'')(tetrahydrofuran-2-yl-kC2)(h2-ethene)], is proposed for the formation
of 3 (for a study of the THFactivation see [3]). Finally, evolution of ethane (monitored
by NMR spectroscopy) is confirmed.

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Scheme 3. Proposed Mechanism for the Formation of 1 and 2
The clean activation of THF by 1 to give 3 encouraged us to employ 1 as a precursor
for similar activation reactions of ethers, bearing a CH2 group in a-position.
Disappointingly, 1 reacts in neat tetrahydropyran, giving 2 as the major product
(82%) and only 18% of the expected (OC-6-35)-[Ir(TpPh-kCPh,k3N,N',N'')H(tetrahy-
dro-2H-pyran-2-ylidene)] (8 ˆ 6-membered cyclic ether analogue of 3). Moreover, the
use of 2 equiv. of THF in different solvents (toluene, benzene, cyclohexane) leads to
mixtures of 2 and 3. Finally 2 does not convert to 3 upon heating in neat THF (24 h at
808). This observation may be seen in connection with the inertness of d6-transition
x
1
metal complexes with Tp ), but is nevertheless somewhat surprising because of the
1
2
pronounced lability of the ethene ligand in [Ir(TpMe )(phenyl-kC )2(h -ethene)]. This
particular compound could not be isolated, instead the related compound [Ir(Tpx)(-
phenyl-kC1)2(N2)] has been formed with the N2 ligand stemming from the inert gas
used [2]. These results clearly show that intramolecular metalation of a phenyl
substituent competes favorably with the formation of the Fischer carbenes, perhaps as a
reflection of the strength of the Ir Ph bond [12]. On the other hand, 3 does not give 2
upon prolonged heating (72 h toluene, 1208).
2
To overcome this problem, we changed our strategy and prepared compounds in
which the incoming substrate (e.g., the ether to be activated) can interact with the metal
at an early stage of the reaction pathway. Since complexes of the type [Ir(Tpx)(bu-
tadiene)] (Tpx ˆ Tp, TpMe ) are reluctant to form allyl-hydride compounds upon
2
thermal activation [13], but are instead prone to bind an additional ligand, rearranging
into the corresponding ꢀiridacyclobutenediylꢁ complexes [Ir(Tpx)(but-2-en-1,4-diyl-
k2C1,C4)(L)] (L ˆ aldehydes, CO, phosphines, pyridine) [14], we considered these IrI
diene derivatives suitable for the above purposes.
The Butadiene Compounds. Reacting [IrCl(coe)2]2 with butadienes (buta-1,3-diene,
2-methylbuta-1,3-diene (ˆ isoprene), and 2,3-dimethylbuta-1,3-diene) and subsequent-
ly with [Tl(TpPh)] or [Tl(TpTh)] in CH2Cl2 at room temperature results in the formation
‡
1
)
For instance, the self-exchange reaction of MeCN in [RuTp(MeCN)3] has been found to be more than
‡
eight orders of magnitude slower than in the corresponding complex [Ru(Cp)(MeCN)3] [11].

Helvetica Chimica Acta ± Vol. 84 (2001)
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of compounds of the general formula [Ir(Tpx)(butadiene)]. A subsequent activation
reaction of either the butadiene or the Tpx ligand is not observed under these
conditions, consequently, the iridium core stays formally at oxidation state ‡ 1.
[Ir(TpPh)(buta-1,3-diene)] (4a), [Ir(TpTh)(buta-1,3-diene)] (4b), [Ir(TpPh)(2-methyl-
buta-1,3-diene)] (5a), and [Ir(TpTh)(2-methylbuta-1,3-diene)] (5b) are fluxional in
solution (see Scheme 4), as deduced from the observation of only one set of signals for
the Tpx ligand in the 1H- and 13C-NMR spectra. It is worth noting that the fluxionality of
the C4H6 compounds 4a,b is less pronounced than that of the analogous isoprene
1
derivatives 5a,b. For example, the H-NMR spectrum of 4a,b becomes sharp at 408,
while the spectrum of 5a,b is already nicely resolved at 208. From the coalescence
temperatures measured (1H-NMR at 300 MHz) for 4a,b and 5a,b of 18 Æ 18 and 24 Æ
1
18, respectively, activation energies DG=ˆ 59 Æ 3 and DG=ˆ 50 Æ 3 kJ ´ mol can be
computed for the dynamics of the exchange in the compounds.
Scheme 4. Dynamic Behavior of the [Ir(Tpx)butadiene)] Complexes 4a, 4b, 5a, and 5b
The use of the sterically more demanding 2,3-dimethylbuta-1,3-diene introduces
unexpected complexity, at least six products (according to TLC and NMR) are formed
when TpPh is employed as the coligand. The two major products are isolated by column
chromatography and identified as four-coordinated [Ir(TpPh-k2N,N')(h4-2,3-dimethyl-
buta-1,3-diene)] (6a; Scheme 5), and (OC-6-43)-[Ir(TpPh-k2CPh,k3N,N',N'')(5-phenyl-
1H-pyrazole-kN2)] (7; see below, Fig. 3), respectively. The reaction giving [Ir(TpTh-
k2N,N')(h4-2,3-dimethylbuta-1,3-diene)] (6b) proceeds in a cleaner way, and only small
amounts of unidentified by-products are formed. The identity of 6a and 6b as square-
planar 16-electron compounds in solution is established by a combination of NMR and
IR spectroscopy (cf. Table). Using as first criterion Venanziꢁs evaluation of 13C-NMR
data of olefins and following the suggestion that there is a more pronounced high-field
shift for coordinated olefinic C-atoms in a k3-compound than in the analogous k2-
compound due to higher p-back-bonding in the 18-electron system [5], we find that 6a
and 6b, indeed, fulfill this rule, despite that only the terminal butadiene C-atoms are
affected. Further comparison with [Ir(Tp-k3)(2,3-dimethylbuta-1,3-diene)] and
3
x
3
[Ir(TpMe -k )(2,3-dimethylbuta-1,3-diene)], which exhibit Tp -k coordination [13],
2

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Helvetica Chimica Acta ± Vol. 84 (2001)
provides additional support. Comparison of the 1J(C,H) coupling constants of C(1) and
C(4) also points in the same direction. Moro-okaꢁs IR criterion [15] confirms the k2-
formulation of 6a and 6b, since both display a distinctly low B H stretching frequency
(55 to 75 cm 1 lower than for 4a,b and 5a,b). However, Jonesꢁ 11B-NMR criterion [16]
delivers ambiguous results for our TpPh and TpTh compounds. In our view, the data in
the Table clearly show that compounds 4a,b and 5a,b are best described as trigonal
bipyramidal 18-electron complexes featuring a Tpx-k3 ligand, whereas 6a,b should be
considered as square-planar 16-electron compounds with Tpx-k2 coordination. Some
brief additional comments should be given for the 1H- and 13C-NMR spectra of 6a and
6b. Both compounds exist as a mixture of two diastereoisomers, as deduced from the
observation of two different but closely related sets of resonances in a 5 :2 ratio. In
accord with literature precedents, these two sets of signals can be attributed to the
isomers that differ in the axial or equatorial arrangement of the third Ir-uncoordinated
pyrazole group [5][17][18] (Scheme 5). Due to the absence of NOE-cross peaks, we
have been unable to assign the resonances corresponding to each of the isomers.
Scheme 5. Dynamic Behavior of the [Ir(Tpx)(2,3-dimethylbuta-1,3-diene)] Complexes 6a and 6b
Table. IR and NMR Data of 4 ± 6 and of [Ir(Tp)(C6H10)] and [Ir(TpMe )(C6H10)]
2
IR (nÄBH [cm 1])
11B-NMR [ppm]
13C-NMR [ppm] a)
1J(C,H) [Hz] b)
4a
b
5a
b
6a
b
2476, 2456
2461
2473, 2457
2482, 2462
2406
3.4
3.4
3.3
3.3
2.7
3.0
8.5
9.4
152
150
11.1, 7.8
11.9, 9.5
35.4, 35.0
36.0, 35.5
14.6
151, 148
152, 150
158, 160
160, 162
151
2405
[IrTp(C6H10)]c)
[IrTpMe (C6H10)]c)
5.3
150
2
a
b
)
13C-NMR Shifts for C(1) and C(4) of the butadiene ligand. ) 1J(C,H) coupling constant of C(1) and C(4)
with their attached H-atoms. c) C6H10 ˆ 2,3-dimethylbuta-1,3-diene, IR and 11B-NMR data not comparable.
The solid-state structure of 6b is established by X-ray diffraction and corresponds
to a distorted square-planar geometry, as shown by the angles given in Fig. 2. The
dangling pyrazole arm is in an equatorial position, the six-membered IR(
N N )2B
ring adopts a boat conformation, as is usual for [Ir(Tpx-k2] or [Rh(Tpx-k2] compounds

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[4]. The 2,3-dimethylbuta-1,3-diene ligand is bonded in such a way that the two Me
groups (C(26) and C(27)) point away from the thienyl substituents at the coordinated
pyrazole rings. The diene part shows the expected short (C(24) C(22)) ± long
(C(22) C(23)) ± short (C(23) C(25)) binding pattern for the olefinic C-atoms. There
is no interaction of the B-bonded hydride with the Ir-atom. Even though the solid-state
structure does not often correspond with the solution structure, we believe that both 6a
and 6b exhibit the same kind of coordination with Tpx-k2 in solution and in the solid
state, i.e., they are four-coordinate, distorted square-planar complexes. A similar
conclusion was reached by Cano and co-workers [17a] for the analogous
[Rh(TpPh)(cod)] compound.
Fig. 2. ORTEP Plot of 6b. H-Atoms are omitted for clarity; thermal ellipsoids are at the 20% probability level.
Selected bond lengths [Š] and angles [8]: Ir N(1) 2.079(8), Ir N(3) 2.055(7), Ir C(24) 2.132(10), Ir C(22)
2.080(9), Ir C(23) 2.096(10), Ir C(25) 2.127 (10), C(22) C(24) 1.399(13), C(22) C(23) 1.450(14),
C(23) C(25) 1.413(15); N(3) Ir N(1) 85.6(3), N(1) Ir C(22) 109.6(3), N(3) Ir C(23) 113.2(4),
C(22) Ir C(23) 40.6(4), C(25) Ir C(24) 79.2(4), N(3) Ir C(25) 97.8(4), N(1) Ir C(24) 96.3(3).
The second main product from the reaction of [Ir(2,3-dimethylbuta-1,3-diene)Cl]2
with [Tl(TpPh)] is the doubly cyclometallated complex (OC-6-43)-[Ir(TpPh-
k2CPh,CPh,k3,N,N',N'')(5-phenyl-1H-pyrazole-kN2)] (7), as characterized by NMR and
IR spectroscopy as well as by a X-ray structure determination (Fig. 3). This study
confirms the structure proposed for 2 on the basis of spectroscopic data. As already
discussed, this includes a k5-coordination of the TpPh ligand, as a result of the
cyclometallation by two phenyl substituents located at the pyrazole rings. Compounds 2
and 7 differ only in the nature of the sixth neutral ligand, a molecule of C2H4 in 2 and 5-
phenyl-1H-pyrazole in the case of 7, the latter stemming from partial decomposition of

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the TpPh ligand [5][18][19]. The most salient structural feature of 7 is doubtless the
considerable distortion of the pentadentate TpPh group, manifested, e.g., in the values of
the cisoid and transoid angles around the Ir-atom of 77.7 ± 103.6(1)8 and 154.4 ±
172.7(1)8, respectively [7][9].
Fig. 3. ORTEP Plot of 7. H-Atoms are omitted for clarity; thermal ellipsoids are at the 20% probability level.
To ascertain the usefulness of the diene complexes 4 ± 6 in C H bond-activation
reactions, we tested their capacity to give Fischer carbenes derived from tetrahydro-
furan by cleavage of two of its a-CH bonds [2]. Compounds 4 ± 6 all react with THF to
generate complex
3
or the analogous TpTh derivative (OC-6-35)-[Ir(TpTh-
kCTh,k3N,N',N'')H(dihydrofuran-2(3H)-ylidene)] (9). Exclusive formation of the cyclic
carbene 3 or 9 is observed, even when only 1 equiv. of THF is added to a solution of the
appropriate complex in toluene. In a series of experiments, whose results are
summarized in Fig. 4, the diene complexes are allowed to react in neat THF at 708
(bath temperature) to study the dependency of the reaction rate with the nature of
both, the diene and Tpx ligands. Compound 6a (TpPh and 2,3-dimethylbuta-1,3-diene:
complete conversion within ca. 3 h) and 4b (TpTh and buta-1,3-diene: ca. 17%
conversion within 48 h) are found to exhibit the fastest and the slowest reaction rate,
respectively.
As the data in Fig. 4 show, the TpPh derivatives 4a, 5a, and 6a react faster than their
TpTh counterparts 4b, 5b, and 6b (see, e.g., 6a and 6b). Since [Ir(TpMe )(2,3-
2

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Fig. 4. Reaction of 1 (*), 4a (*), 5a (&), 6a (~), 4b (*), 5b (&), or 6b (~) with THF to give 3 or 9,
respectively. Conditions: 20 mg of the corresponding compound in 2 ml of neat THF at 708 bath temp.
dimethylbuta-1,3-diene)] does not react with THF after heating at 708 for 5 days, the
conclusion can be reached that a very bulky Tpx ligand is needed for the
[Ir(Tpx)(diene)] complexes to be able to activate THF at a reasonable reaction rate.
Additionally, and in line with previous observations [20], the coordination behavior of
TpTh appears to resemble the less bulky Tpx ligands, rather than TpPh. As for the
influence of the diene moiety, the experimental reactivity order, namely buta-1,3-
diene < isoprene < 2,3-dimethylbuta-1,3-diene, points, once more, to the importance of
steric factors and to the facility with which the 16-electron, four-coordinate [Ir(Tpx-
k2)(diene)] structure can be accessed.
Note, however, that as the DG= values for the k3 ! k2 isomerism within 4a and 4b or
5a and 5b are the same within experimental error, the generation of the square-planar
intermediate is not rate-determining in this reaction sequence. Finally, the high
reactivity of 5a and 6a (TpPh; 2-methyl- and 2,3-dimethylbuta-1,3-diene, resp.) in the
double C H bond activation of cyclic ethers can be exploited to improve the
preparation of the tetrahydro-2H-pyran-2-ylidene derivative 8 (vide supra). This
compound can be obtained in ca. 75% yield by reacting 5a with tetrahydro-2H-pyran
(see Exper. Part), whereas the analogous reaction of 1 and the cyclic ether produces
yields of 8 lower than 20%.
Experimental Part
General. All preparations and manipulations were carried out under O2-free N2 or Ar following
conventional Schlenk techniques. Solvents were dried rigorously and degassed before use. Light petroleum ether
(p.e.), b.p. 40 ± 608, was used. The complexes [IrCl(coe)2]2 [21], [Tl(TpPh)] [22], and [Tl(TpTh)] [20] were
prepared according to the literature. The given temp. for heating experiments is always that of the oil bath
employed. CC ˆ Column chromatography. IR Spectra: Bruker Vector-22 spectrometer; in cm 1. NMR Spectra:

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Helvetica Chimica Acta ± Vol. 84 (2001)
Bruker AMX-300, AMX-400, and AMX-500 spectrometers; d(H) and d(C) with respect to the solvent as
internal standards, but reported with respect to SiMe4, d(B) referenced to BF3 ´ Et2O; most assignments by
extensive 1H,1H decoupling experiments, NOE-DIFF measurements, and homo- and heteronuclear two-
q
m
dimensional spectra; denotes a quaternary C-atom, a metallated C-atom or H-atom of the metallated Ph
substituent, and v a virtual multiplicity. Microanalyses were performed by the Microanalytical Service of the
Instituto de Investigaciones Químicas (Sevilla).
(OC-6-25)-(h2-Ethene)(ethyl)[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(2 )-kC2,kN2,kN2',kN2'']iri-
dium (1). Through a suspension of [(IrCl(coe)2)2] (433 mg, 0.483 mmol) in CH2Cl2 (15 ml), ethene was bubbled
at 358 for 5 min to give a colorless soln., whereupon a soln. of [Tl(TpPh)] (624 mg, 0.966 mmol) in CH2Cl2
(15 ml) was added. Stirring the mixture for 4 h and then allowing a gradual warming from 358 to r.t. resulted in
the precipitation of TlCl (starting at 208). The mixture was transferred via a cannula to separate part of the
precipitate and was then centrifuged. The clear soln. was again evaporated and the residue treated with p.e.
(7 ml). Upon cooling at 208, a pale yellow precipitate was formed, which was collected on a glass frit and
washed with p.e. (2 Â 2 ml). Drying the residue in vacuo gave anal. pure 1 (570 mg, 86%). IR (Nujol): 2473m
(BH). 1H-NMR (300 MHz, (D6)benzene, 208): 7.62 (d, 3J ˆ 2.3, H C(5)(pz)); 7.51 (d, 3J ˆ 2.5, H C(5)(pz));
7.43 (m, 1 H, Phm); 7.35 (d, 3J ˆ 2.3, H C(5)(pz)); 7.15 ± 6.90 (m, 12 H, Ph); 6.34 (m, 1 H, Phm); 6.14 (d, 3J ˆ 2.5,
H
C(4)(pz)); 5.94 (d, 3J ˆ 2.3, H C(4)(pz)); 5.92 (d, 3J ˆ 2.3, H C(4)(pz)); 3.40 (m, 2 H, H2CˆCH2); 2.80
(m, 2 H, H2CˆCH2); 2.05 (br. q, 3J ˆ 7.4, MeCH2); 0.25 (t, 3J ˆ 7.4, MeCH2). 13C{1H}-NMR (75.5 MHz,
(D6)benzene, 208): 161.6, 156.6, 156.3 (3 C(3)(pz)); 141.6, 140.3 (2 C, Phq); 136.8, 136.2, 135.9 (3 C(5)(pz));
134.1, 134.0 (2 C, Phq,m); 130.4 (1 C, Phm); 129.8, 129.3, 128.4, 127.9, 127.8, 127.5, 126.2 (11 C, Ph); 122.2, 121.9
(2 C, Phm); 108.4, 106.3, 102.1 (3 C(4)(pz)); 60.2 (H2CˆCH2); 15.9 (MeCH2); 4.7 (MeCH2). 11B{1H}-NMR
(96.3 MHz, CDCl3, 208): 2.6. Anal. calc. for C31H30BIrN6 (689.84): C 54.0, H 4.4, N 12.2; found: C 54.0, H 4.5,
N 12.3.
A by-product (<4%) was also formed, as seen by integration of the 1H-NMR of the crude mixture. It was
not isolated but assumed to be the second diastereoisomer (OC-6-35). Observable 1H-NMR data (CDCl3, 208):
3.50 (m, 2 H, H2CˆCH2); 2.38 (m, 2 H, H2CˆCH2); 0.05 (t, 3J ˆ 7.3, MeCH2).
(OC-6-24)-(h2-Ethene)[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(3 )-kC2,kC2',kN2',kN2'']iridium
(2). A soln. of 1 (60 mg, 0.087 mmol) in benzene (4 ml) was heated at 808 for 17 h, or in toluene (4 ml) at
1158 for 4 h 30 min. The solvent was evaporated and the crude mixture purified by CC (Al2O3, p.e./Et2O 1 :1).
The yellow band yielded, after evaporation and drying in vacuo, 2 (53 mg, 92%). IR (Nujol): 2482m (BH).
1H-NMR (300 MHz, CDCl3, 208): 8.15 (d, 3J ˆ 2.5, H C(5)(pz)); 7.90 (d, 3J ˆ 7.8, 1 H, Ph); 7.79 (d, 3J ˆ 2.3,
H
C(5)(pz)); 7.61 (d, 3J ˆ 2.6, H C(5)(pz)); 7.55 (dd, 3J ˆ 7.3, 4J ˆ 1.5, 1 H, Ph); 7.47 ± 7.37 (m, 3 H, Ph); 7.31 ±
4
7.23 (m, 3 H, Ph); 6.89 (br. d, 3J ˆ 7.2, 2 H, Ph); 6.83 (d, 3J ˆ 7.1, 2 H, Ph); 6.75 (dd, 3J ˆ 7.3, J ˆ 1.5, 1 H, Ph);
6.70 (d, 3J ˆ 2.5,
H
C(4)(pz)); 6.42 (d, 3J ˆ 2.6,
H
C(4)(pz)); 6.17 (d, 3J ˆ 2.3,
H C(4)(pz)); 3.15
(m, 2 H, H2CˆCH2); 2.74 (m, 2 H, H2CˆCH2). 13C{1H}-NMR (75.5 MHz, CDCl3, 208): 164.0, 161.3, 154.8
(3 C(3)(pz)); 144.5 (1 C, Phq); 140.5 (C(5)(pz)); 140.1, 139.6 (2 C, Phq); 137.8 (1 C, Ph); 136.9, 135.8
(2 C(5)(pz)); 135.4, 132.3 (2 C, Phq,m); 129.7, 128.74, 128.70, 128.68, 128.65, 128.59, 128.3, 127.0 (8 C, Ph);
123.2, 122.9, 122.7, 122.5 (4 C, Phm); 106.3, 105.1, 103.2 (3 C(4)(pz)); 60.6 (H2CˆCH2). 11B{1H}-NMR
(96.3 MHz, CDCl3, 208): 2.4. Anal. calc. for C29H24BIrN6 (659.59): C 52.8, H 3.7, N 12.7; found: C 52.4, H 3.8,
N 12.4.
(OC-6-35)-(Dihydrofuran-2(3H)-ylidene)hydro[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(2 )-kC2,
kN2,kN2',kN2'']iridium (3). A soln. of 1 (92 mg, 0.133 mmol) in THF (4 ml) was heated at 808 for 16 h. The soln.
was evaporated, the resulting yellow oil precipitated upon treatment with p.e. (2 ml), and the precipitate
collected on a glass frit and dried in vacuo: 85 mg (91%) of 3. Additional purification might be done
by CC (neutral aluminium oxide 90 active, Et2O/p.e. 1:1), sampling the yellow band. IR (Nujol): 2475m
(BH), 2230m (IrH). 1H-NMR (500 MHz, CDCl3, 208): 7.89 (d, 3J ˆ 2.3, H C(5)(pz)); 7.82 (d, 3J ˆ 2.3,
H
C(5)(pz)); 7.69 (d, 3J ˆ 7.6, 1 H, Phm); 7.61 (d, 3J ˆ 2.3, H C(5)(pz)); 7.58 (m, 2 H, Ph); 7.54 (d, 3J ˆ 7.4,
1 H, Phm); 7.28 ± 7.10 (m, 9 H, Ph); 7.01 (vt, 3J ˆ 7.2, 1 H, Phm); 6.51 (d, 3J ˆ 2.3, H C(4)(pz)); 6.28 (d, 3J ˆ 2.3,
H
C(4)(pz)); 6.15 (d, 3J ˆ 2.3, H C(4)(pz)); 3.92 (m, H C(5)); 3.61 (m, H C(5)); 1.84 (m, H C(3));
1.36 (m, H C(3)); 0.60 ± 0.51 (m, 2 H C(4)); 20.78 (s, H Ir). 13C{1H}-NMR (75.5 MHz, CDCl3, 208):
267.7 (CˆIr); 163.2, 154.6, 153.7 (3 C(3)(pz)); 142.2, 141.4 (2 C, Phq); 138.0 (1 C, Phm); 137.8, 137.1,
136.1 (3 C(5)(pz)); 134.3, 134.26 (2 C, Phq); 129.8, 129.3, 128.02, 128.00, 127.8, 127.7, 126.7 (11 C, Ph); 122.7,
121.5 (2 C, Phm); 106.9, 104.8, 103.0 (3 C(4)(pz)); 81.0 (C(5)); 56.4 (C(3)); 21.2 (C(4)). 11B{1H}-NMR
(96.3 MHz, CDCl3, 208): 3.3. Anal. calc. for C31H28BIrN6O (703.64): C 52.9, H 4.0, N 11.9; found: C 52.7,
H 3.9, N 12.2.

Helvetica Chimica Acta ± Vol. 84 (2001)
2879
A by-product (< 5%) was also formed, as seen by integration of the 1H-NMR of the crude mixture. It was
not isolated but assumed to be the other diastereoisomer (OC-6-52)-3). Observable 1H-NMR data (500 MHz,
208): 4.37 (m, H C(5)); 4.15 (m, H C(5)); 18.86 (s, H Ir).
(h4-Buta-1,3-diene)[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(1 )-kN2,kN2',kN2'']iridium (4a).
Through a suspension of [(IrCl(coe)2)2] (175 mg, 0.196 mmol) in CH2Cl2 (6 ml), buta-1,3-diene was bubbled
at r.t. to give a colorless soln., whereupon a soln. of [TlTpPh] (253 mg, 0.392 mmol) in CH2Cl2 (6 ml) was added.
Stirring the mixture for 4 h at r.t. resulted in the precipitation of TlCl. The mixture was transferred via a cannula
to separate from TlCl and was then centrifuged. The clear soln. was evaporated, the residue treated with p.e.
(9 ml), and the white precipitate formed collected on a glass frit and washed with p.e. (2 Â 2 ml). Drying
the residue in vacuo gave anal. pure 4a (180 mg, 67%). IR (Nujol): 2476m, 2456m (BH). 1H-NMR
(300 MHz, CDCl3, 208): 7.75 (br. s, 3 H C(5)(pz)); 7.28 (br. s, 15 H, Ph); 6.12 (br. s, 3 H C(4)(pz));
3.42 (m, H C(2),
H
C(3)); 1.43 (m, Htrans C(1), Htrans C(4));
1.56 (m, Hcis C(1), Hcis C(4)).
1H-NMR (CDCl3, 678): 7.78 (d, 3J ˆ 2.1, 3 H C(5)(pz)); 7.29 (br. s, 15 H, Ph); 6.14 (d, 3J ˆ 2.1, 3 H C(4)(pz));
3.45 (m, H C(2),
H
C(3)); 1.48 (m, Htrans C(1), Htrans C(4));
1.50 (m, Hcis C(1), Hcis C(4)).
1H-NMR ((D6)acetone, 138): 8.05 (d, 3J ˆ 2.1, H C(5)(pz)); 7.83 (d, 3J ˆ 2.2, 2 H C(5)(pz)); 7.40 ± 7.14
(m, 15 H, Ph); 6.26 (d, 3J ˆ 2.1,
H
C(4)(pz)); 6.07 (d, 3J ˆ 2.2, 2 H C(4)(pz)); 3.40 (m, H C(2),
H
C(3)); 1.34 (m, Htrans C(1), Htrans C(4)); 1.64 (m, Hcis C(1), Hcis C(4)). 1H-NMR (CDCl3, 678): 7.78
(d, 3J ˆ 2.1, 3 H C(5)(pz)); 7.29 (br. s, 15 H, Ph); 6.14 (d, 3J ˆ 2.1, 3 H C(4)(pz)); 3.45 (m, H C(2),
H
C(3)); 1.48 (m, Htrans C(1), Htrans C(4)); 1.50 (m, Hcis C(1), Hcis C(4)). 13C{1H}-NMR (CDCl3, 208):
156.5 (3 C(3)(pz)); 135.4 (br. s, 3 C(5)(pz)); 135.0 (br. s, 3 Cipso); 130.4 (s, 6 Cm); 128.4 (br. s, 3 Cp); 127.6 (br. s,
6 Co); 107.7 (3 C(4)(pz)); 72.1 (1J(C,H) ˆ 173, C(2), C(3)); 8.5 (1J(C,H) ˆ 152, C(1), C(4)). 11B{1H}-NMR
(96.3 MHz, CDCl3, 208): 3.4. Anal. calc. for C31H28BIrN6 (687.64): C 54.2, H 4.1, N 12.2; found: C 54.1, H 4.2,
N 12.5.
(h4-Buta-1,3-diene){hydrotris[3-(2-thienyl)-1H-pyrazolato-kN1]borato(1 )-kN2,kN2',kN2''}iridium (4b).
As described for 4a, from [(IrCl(coe)2)2] (177 mg, 0.198 mmol) and [TlTpTh] (262 mg, 0.262 mmol): 165 mg
(89%) of 4b. IR (Nujol): 2461m (BH). 1H-NMR (300 MHz, CDCl3, 208): 7.75 (br. s, 3 H C(5)(pz)); 7.33 (br. s,
3 H, Th); 7.02 (br. s, 6 H, Th); 6.23 (br. s, 3 H C(4)(pz)); 3.65 (m, H C(2), H C(3)); 1.78 (m, Htrans C(1),
Htrans C(4)); 1.12 (m, Hcis C(1), Hcis C(4)). 1H-NMR (300 MHz, (D6)acetone, 138): 8.20 (d, 3J ˆ 2.1,
H
H
C(5)(pz)); 7.95 (d, 3J ˆ 2.1, 2 H C(5)(pz)); 7.63 (dd, 3J ˆ 5.4, 4J ˆ 1.1, 2 H C(5)(Th)); 7.44 (br. vt, 3J ˆ 3.2,
C(3)(Th)); 7.11 ± 7.05 (m, 4 H, Th); 6.92 (br. d, 3J ˆ 3.2, 2 H C(3)(Th)); 6.45 (d, 3J ˆ 2.1, H C(4)(pz));
6.25 (d, 3J ˆ 2.1, 2 H C(4)(pz)); 3.62 (m, H C(2),
H C(3)); 1.75 (m, Htrans C(1), Htrans C(4));
1.17 (m, Hcis C(1), Hcis C(4)). 1H-NMR (300 MHz, CDCl3, 678): 7.77 (d, 3J ˆ 2.0, 3 H C(5)(pz));
7.32 ( br. d, 3J ˆ 5.4, 3 H C(5)); 6.99 ± 6.94 (m, 6 H,
H C(3), H C(4)(Th)); 3.70 (m, H C(2),
H
C(3)); 1.82 (m, Htrans C(1), Htrans C(4)); 1.01 (m, Hcis C(1), Hcis C(4)). 13C{1H}-NMR (75.5 MHz,
CDCl3, 208): 148.0 (3 C(3)(pz)); 134.8 (3 C(2)(Th), 3 C(5)(pz)); 129.0 (6 C, Th); 126.2 (3 C, Th); 109.6
(3 C(4)(pz)); 72.4 (1J(C,H) ˆ 172, C(2), C(3)); 9.4 (1J(C,H) ˆ 150, C(1), C(4)). 11B{1H}-NMR (96.3 MHz,
CDCl3, 208): 3.4. Anal. calc. for C25H22BIrN6S3 (705.71): C 42.6, H 3.1, N 11.9; found: C 42.7, H 3.2,
N 12.1.
[Hydrotris(3-phenyl-1H)-pyrazolato-kN1)borato(1 )-kN2,kN2',kN2''](h4-2-methylbuta-1,3-diene)iridium
(5a). As described for 4a, with [(IrCl(coe)2)2] (177 mg, 0.198 mmol), CH2Cl2 (6 ml), 2-methylbuta-1,3-diene
(0.3 ml, excess), and [TlTpPh] (255 mg, 0.395 mmol). Removing the solvent and drying in vacuo gave pure 5a
(198 mg, 71%). Additionally, the product (orange powder) can be purified by CC (neutral aluminium oxide 90
active, p.e./Et2O 15 :1 (pale violet band), then 4 :1 (yellow band). IR (Nujol): 2473m, 2457m (BH). 1H-NMR
(300 MHz, CDCl3, 208): 7.80 (d, 3J ˆ 2.1, 3 H C(5)(pz)); 7.31 (m, 15 H, Ph); 6.14 (d, 3J ˆ 2.1, 3 H C(4)(pz));
2.91 (vt, 3J ˆ 6.3, H C(3)); 2.21 (d, 2J ˆ 3.5, Htrans C(1)); 1.31 (dd, 3J ˆ 6.0, 2J ˆ 3.3, Htrans C(4)); 0.67 (s, Me);
1.34 (d, 2J ˆ 3.5, Hcis C(1)); 1.36 (dd, 3J ˆ 6.6, 2J ˆ 3.4, Hcis C(4)). 1H-NMR (300 MHz, (D6)acetone,
538): 8.15 (d, 3J ˆ 2.1, H C(5)(pz)); 7.95 (d, 3J ˆ 2.2, 3 H C(5)(pz)); 7.92 (d, 3J ˆ 2.2, H C(5)(pz)); 7.38 ±
7.10 ( m, 15 H, Ph); 6.31 (d, 3J ˆ 2.1,
H
C(4)(pz)); 6.10 (d, 3J ˆ 2.2,
H
C(4)(pz)); 6.02 (d, 3J ˆ 2.2,
H
C(4)(pz)); 2.77 (vt, 3J ˆ 6.2,
H
C(3)); 2.32 (d, 2J ˆ 3.3, Htrans C(1)); 1.11 (dd, 3J ˆ 6.0, 2J ˆ 3.3,
Htrans C(4)); 0.53 (s, Me); 1.36 (d, 2J ˆ 3.2, Hcis C(1)); 1.55 (dd, 3J ˆ 6.3, 2J ˆ 3.1, Hcis C(4)). 13C{1H}-
NMR (75.5 MHz, CDCl3, 208): 156.5 (3 C(3)(pz)); 135.5 (3 Cipso); 135.1 (3 C(5)(pz)); 130.7 (6 Co); 128.3
(3 Cp); 127.6 (6 Cm); 108.1 (3 C(4)(pz)); 85.4 (C(2)); 75.3 (1J(C,H) ˆ 168, C(3)); 18.3 (Me); 11.1 (1J(C,H) ˆ 151,
C(1)); 7.8 (1J(C,H) ˆ 148, C(4)). 11B{1H}-NMR (96.3 MHz, CDCl3, 208): 3.3. Anal. calc. for C32H30BIrN6
(701.67): C 54.8, H 4.3, N 12.0; found: C 54.4, H 4.1, N 12.2.
{Hydrotris[3-(2-thienyl)-1H-pyrazolato-kN1]borato(1 )-kN2,kN2',kN2''}(h4-2-methylbuta-1,3-diene)iridium
(5b). As described for 5a, with [(IrCl(coe)2)2] (100 mg, 0.112 mmol), CH2Cl2 (6 ml), 2-methylbuta-1,3-diene

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Helvetica Chimica Acta ± Vol. 84 (2001)
(0.3 ml, excess), and [TlTpTh] (149 mg, 0.223 mmol): 136 mg (85%) of 5b. IR (Nujol): 2482m, 2462m (BH).
1H-NMR (300 MHz, CDCl3, 208): 7.76 (d, 3J ˆ 2.3, 3 H C(5)(pz)); 7.30 (dd, 3J ˆ 5.1, 4J ˆ 1.3, 3 H C(5)(Th));
7.02 (dd, 3J ˆ 3.5, 4J ˆ 1.3, 3 H C(3)(Th)); 6.96 (dd, 3J ˆ 5.1, 3J ˆ 3.5, 3 H C(4)(Th)); 6.22 (d, 3J ˆ 2.3,
3
2
3 H C(4)(pz)); 3.11 (dd, 3J ˆ 6.7, J ˆ 6.0, H C(3)); 2.53 (d, 2J ˆ 3.6, Htrans C(1)); 1.63 (dd, 3J ˆ 6.0, J ˆ 2.8,
Htrans C(4)); 0.95 (s, Me); 0.93 (d, 2J ˆ 3.6, Hcis C(1)); 0.99 (dd, 3J ˆ 6.7, 2J ˆ 2.8, Hcis C(4)). 1H-NMR
(300 MHz, (D6)acetone, 538): 8.18 (d, 3J ˆ 1.7, H C(5)(pz)); 7.96 (d, 3J ˆ 2.2, H C(5)(pz)); 7.94 (d, 3J ˆ 2.2,
H
H
H
C(5)(pz)); 7.60 (br. d, 3J ˆ 4.9,
H
C(5)); 7.56 (br. d, 3J ˆ 4.6,
H
C(5)(Th)); 7.48 (br. d, 3J ˆ 4.9,
C(5)(Th)); 7.17 ± 6.96 (m, 6 H, H C(3), H C(4)(Th)); 6.45 (d, 3J ˆ 2.3, H C(4)(pz)); 6.24 (d, 3J ˆ 2.2,
C(4)(pz)); 6.13 (d, 3J ˆ 2.0, H C(4)(pz)); 2.63 (vt, 3J ˆ 6.4, H C(3)); Htrans C(1) overlapped by acetone;
1.51 (dd, 3J ˆ 6.3, J ˆ 2.1, Htrans C(4)); 0.84 (s, 3 Me); 0.95 (d, 2J ˆ 3.0, Hcis C(1)); 1.16 (dd, 3J ˆ 6.5, J ˆ
2.3, Hcis C(4)). 13C{1H}-NMR (75.5 MHz, CDCl3, 208): 149.5 (3 C(3)(pz)); 135.6 (3 C(2)(Th), 3 C(5)(pz));
130.0 (3 C, C(4)(Th)); 126.5 (3 C(3), 3 C(5)(Th)); 110.6 (3 C(4)(pz)); 86.5 (C(2)); 75.3 (1J(C,H) ˆ 170, C(3));
18.7 (1 Me); 11.9 (1J(C,H) ˆ 152, C(1)); 9.5 (1J(C,H) ˆ 150, C(4)). 11B{1H}-NMR (96.3 MHz, CDCl3, 208): 3.3.
Anal. calc. for C26H24BIrN6S3 (719.73): C 43.4, H 3.4, N 11.7; found: C 43.6, H 3.7, N 11.6.
2
2
(h4-2,3-Dimethylbuta-1,3-diene)[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(1 )-kN2,kN2']iridium
(6a). As described for 5a, with [(IrCl(coe)2)2] (180 mg, 0.201 mmol), CH2Cl2 (6 ml), 2,3-dimethylbuta-1,3-diene
(0.3 ml, excess), and [TlTpPh] (260 mg, 0.403 mmol). The crude product (red oil) was purified by CC (silica gel,
p.e./Et2O 1:1), then 4 :1 (red band; Rf (p.e./Et2O 4 :1) 0.48). Evaporation and drying in vacuo yielded 90 mg
(24%) of 6a as a diastereoisomer mixture 5 :2 as seen by integration of appropriate 1H-NMR signals2). IR
(Nujol): 2406w (BH). 11B{1H}-NMR (96.3 MHz, CDCl3, 208): 2.7. Anal. calc. for C33H32BIrN6 (715.69):
C 55.4, H 4.5, N 11.7; found: C 55.5, H 4.7, N 11.4.
First (Major) Isomer: 1H-NMR (300 MHz, CDCl3, 208): [8.07 ± 8.06 (m, 4 H, Ph); 7.98 ± 7.93 (m, 5 H, Ph);
7.60 (br. s, H C(5)(pz)); 7.49 ± 7.25 (m, 17 H, Ph, H C(5)(pz))]2); 6.71 (d, 3J ˆ 2.3, H C(4)(pz)); 6.45
(m, 2 H C(4)(pz)); 1.80 (s, 6 H, Me); 1.70 (br. s, Htrans C(1), Htrans C(4));
0.21 (br. s, Hcis C(1),
Hcis C(4)). 13C{1H}-NMR (75.5 MHz, CDCl3, 208): 156.2 (2 C(3)(pz)); 154.6 (C(3)(pz)); 139.4 (C(5)(pz));
[135.6 (2 C(5)(pz)); 135.2, 134.8, 134.7 (3 C, Phq); 129.7, 128.8, 128.7, 128.5, 128.3, 128.2, 127.6, 126.2 (15 C,
Ph)]2); 105.4 (2 C(4)(pz)); 102.7 (C(4)(pz)); 85.3 (C(2), C(3)); 35.0 (1J(C,H) ˆ 160, C(1), C(4)); 19.3
(2 Me).
Second (Minor) Isomer: 1H-NMR (300 MHz, CDCl3, 208): [8.07 ± 8.06 (m, 4 H, Ph); 7.98 ± 7.93 (m, 5 H,
Ph); 7.60 (br. s, H C(5)(pz)); 7.49 ± 7.25 (m, 17 H, Ph, H C(5)(pz)]2); 6.56 (m, 3 H C(4)(pz)); 1.58 (br. s,
Htrans C(1), Htrans C(4)); 1.19 (s, 2 Me); 0.43 (br. s, Hcis C(1), Hcis C(4)). 13C{1H}-NMR (75.5 MHz,
CDCl3, 208): 156.2 (2 C(3)(pz)); 155.8 (C(3)(pz)); 137.4 (C(5)(pz)); [135.6 (2 C(5)(pz)); 135.2, 134.8, 134.7
(3 C, Phq); 129.7, 128.8, 128.7, 128.5, 128.3, 128.2, 127.6, 126.2 (15 C, Ph)]2); 105.1 (2 C(4)(pz)); 102.7 (C(4)(pz));
85.5 (C(2), C(3)); 35.4 (1J(C,H) ˆ 158, C(1), C(4)); 18.4 (2 Me).
On further separation by CC (p.e./Et2O 4 :1; Rf (p.e./Et2O 4 :1) 0.20), evaporation, and drying in vacuo,
55 mg (19%) of (OC-6-43)[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(3 )-kC2,kC2',kN2,kN2',kN2''](5-phen-
yl-1H-pyrazole-kN2)iridium (7) was obtained. IR (Nujol): 3361m (NH), 2474m (BH). 1H-NMR (300 MHz,
CDCl3, 208): 9.72 (br. s, NH); 8.02 (d, 3J ˆ 2.5, H C(5)(pz)); 7.81 (d, 3J ˆ 2.3, H C(5)(pz)); 7.63 (d, 3J ˆ 7.4,
1 H, Ph); 7.52 ± 7.31 (m, 7 H, H C(5)(pz), Ph); 7.17 ± 6.99 (m, 9 H, Ph); 6.90 (vt, 3J ˆ 2.3, H C(3)(neutral pz));
6.86 ± 6.70 (m, 2 H, Ph); 6.59 (d, 3J ˆ 2.5 Hz, H C(4)(pz)); 6.31 (d, 3J ˆ 2.5, H C(4)(pz)); 6.23 (d, 3J ˆ 2.3,
H
C(4)(pz)); 5.93 (vt, 3J ˆ 2.3, H C(4)(neutral pz)). 13C{1H}-NMR (75.5 MHz, CDCl3, 208): 166.0, 163.2,
154.7, 151.3 (4 C(3)(pz)); 143.6 (1 C, Phq); 143.5 (C(5)(pz)); 142.8 (1 C, Phq); 141.5 (1 C, Phq); 140.8 (1 C, Phq);
140.4 (C(3)(neutral pz)); 137.1, 137.0, 136.7, 136.3 (6 C, Ph, C(5)(pz)); 133.2 (1 C, Phq,m); 129.5, 129.40, 129.38
(3 C, Ph); 129.32 (1 C, Phq,m); 128.34, 128.26, 127.5, 127.4, 125.7 (6 C, Ph); 122.9, 122.5, 122.4, 121.5 (4 C, Phm);
106.1, 105.9, 103.6 (3 C(4)(pz)); 103.0 (C(4)(neutral pz)). 11B{1H}-NMR (96.3 MHz, CDCl3, 208): 2.5. Anal.
calc. for C36H28BIrN8 (775.71): C 55.7, H 3.6, N 14.5; found: C 55.8, H 3.8, N 14.6.
(h4-2,3-Dimethylbuta-1,3-diene){hydrotris[3-(2-thienyl)-1H-pyrazolato-kN1]borato(1 )-kN2,kN2'}iridium
(6b). As described for 5a, with [(IrCl(coe)2)2] (167 mg, 0.186 mmol), CH2Cl2 (6 ml), 2,3-dimethylbuta-1,3-diene
(0.75 ml, excess), and [TlTpTh] (248 mg, 0.373 mmol): 210 mg (77%) of 6b as diastereoisomer mixture 5 :2 as
seen by integration of appropriate 1H-NMR signals. Red powder. IR (Nujol): 2405m (BH). 11B{1H}-NMR
(96.3 MHz, CDCl3, 208): 3.0. Anal. calc. for C27H26BIrN6S3 (733.76): C 44.2, H 3.6, N 11.5; found: C 44.4,
H 3.9, N 11.6.
2
)
The Ph signals are given in the spectra for both isomers as found; assignment to neither the H- nor to the C-
atoms, nor according to isomer was possible.

Helvetica Chimica Acta ± Vol. 84 (2001)
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1
First (Major) Isomer: H-NMR (400 MHz, CDCl3, 208): 7.84 (d, 3J ˆ 2.3, H C(5)(pz)); 7.60 (dd, 3J ˆ 3.5,
4
4
4J ˆ 1.1, 2 H C(3)(Th)); 7.46 (dd, 3J ˆ 5.1, J ˆ 1.1, 2 H C(5)(Th)); 7.40 (dd, 3J ˆ 3.6, J ˆ 1.1, H C(3)(Th));
7.20 (d, 3J ˆ 2.5, 2 H C(5)(pz)); 7.18 (dd, 3J ˆ 5.1, 4J ˆ 1.2,
H
C(5)(Th)); 7.14 (dd, 3J ˆ 5.1, 3J ˆ 3.6,
2 H C(4)(Th)); 7.04 (dd, 3J ˆ 5.1, 3J ˆ 3.6, H C(4)(Th)); 6.50 (d, 3J ˆ 2.3, H C(4)(pz)); 6.22 (d, 3J ˆ 2.5,
2 H C(4)(pz)); 2.00 (d, 2J ˆ 2.4, Htrans C(1), Htrans C(4)); 1.85 (s, 2 Me); 0.07 (d, 2J ˆ 2.4, Hcis C(1),
Hcis C(4)). 13C{1H}-NMR (75.5 MHz, CDCl3, 208): 150.4 (2 C(3)(pz)); 150.2 (C(3)(pz)); 138.7, 137.8
(3 C(2)(Th)); 136.2 (C(5)(pz)); 136.1 (2 C(5)(pz)); 127.9 ± 127.7 (3 C(3), 3 C(4)(Th)); 124.5 (C(4)(Th));
123.9 (2 C(4)(Th)); 106.2 (2 C(4)(pz)); 103.2 (C(4)(pz)); 86.3 (C(2), C(3)); 35.5 (1J(C,H) ˆ 162, C(1), C(4));
19.8 (2 Me).
Second (Minor) Isomer: 1H-NMR (400 MHz, CDCl3, 208): 7.84 (overlapped by H C(5)(pz) of the major
isomer, H C(5)(pz)); 7.55 (br. s, 2 H C(5)(pz)); 7.50 (dd, 3J ˆ 3.4, 4J ˆ 1.1, 2 H C(3)(Th)); 7.35 (dd, 3J ˆ 5.1,
4J ˆ 1.1, 2 H C(5)(Th)); 7.31 (dd, 3J ˆ 3.6, 4J ˆ 1.2, H C(3)(Th)); 7.17 (dd, 3J ˆ 5.1, 4J ˆ 1.2, H C(5)(Th));
7.08 (dd, 3J ˆ 5.1, 3J ˆ 3.6, 2 H C(4)(Th)); 7.00 (dd, 3J ˆ 5.1, 3J ˆ 3.6,
H
C(4)(Th)); 6.59 (d, 3J ˆ 2.2,
2 H C(4)(pz)); 6.52 (d, 3J ˆ 2.5, H C(4)(pz)); 1.88 (d, 2J ˆ 2.4, Htrans C(1), Htrans C(4)); 1.28 (s, 2 Me);
0.13 (d, 2J ˆ 2.4, Hcis C(1), Htrans C(4)). 13C{1H}-NMR (75.5 MHz, CDCl3, 208): the TpTh signals are apart
from small deviations, the same as those of the major isomer; 86.6 (C(2), C(3)); 36.0 (1J(C,H) ˆ 160, C(1),
C(4)); 18.8 (2 Me).
(OC-6-35)-Hydro[hydrotris(3-phenyl-1H-pyrazolato-kN1)borato(2 )-kC2,kN2,kN2',kN2''](tetrahydro-2H-
pyran-2-ylidene)iridium (8). A soln. of 5a (67 mg, 0.096 mmol) and tetrahydro-2H-pyran (100 ml, excess) in
toluene (3 ml) was heated at 808 for 5 h. The soln. was evaporated and the crude product (yellow green oil)
purified by CC (neutral aluminium oxide 90 active, Et2O/p.e. 1:1 (yellow band)). Evaporation and drying in
1
vacuo yielded 52 mg (76%) of 8. IR (Nujol): 2474m (BH), 2219m (IrH). H-NMR (300 MHz, (D6)benzene,
208): 7.94 (d, 3J ˆ 7.4, 1 H, Ph); 7.69 ± 7.63 (m, 2 H, Ph, H C(5)(pz)); 7.56 ± 7.52 (m, 4 H, Ph, H C(5)(pz)); 7.46
(d, 3J ˆ 2.3, H C(5)(pz)); 7.41 (vt, 3J ˆ 7.4, 1 H, Phm); 7.21 (vt, 3J ˆ 7.4, 1 H, Phm); 7.11 ± 6.91 (m, 6 H, Ph); 6.31
(d, 3J ˆ 2.4, H C(4)(pz)); 6.10 (d, 3J ˆ 2.3, H C(4)(pz)); 6.02 (d, 3J ˆ 2.3, H C(4)(pz)); 3.30 (m, H C(6));
3.16 (m, H C(6)); 1.18 (m, H C(3)); 0.93 (m, H C(3)); 0.64 (m, H C(5)); 0.45 (m, 2 H C(4)); 0.16 (m,
H
C(5)); 20.84 (s, H Ir). 13C{1H}-NMR (75.5 MHz, (D6)benzene, 208): 271.7 (CˆIr); 163.2, 154.6, 153.6
(3 C(3)(pz)); 143.6, 141.8 (2 C, Phq); 138.3 (1 C, Phm); 137.1, 136.3, 135.5 (3 C(5)(pz)); 134.7, 134.6 (2 C, Phq);
129.8, 129.3, 128.02, 128.00, 127.8, 127.7, 126.7 (11 C, Ph); 122.9, 121.3 (2 C, Phm); 106.8, 104.9, 102.9
(3 C(4)(pz)); 70.7 (C(6)); 49.7 (C(3)); 20.7 (C(5)); 14.8 (C(4)). 11B{1H}-NMR (96.3 MHz, (D6)benzene, 208):
2.0. Anal. calc. for C32H30BIrN6O (717.67): C 53.6, H 4.2, N 11.7; found: C 53.9, H 4.5, N 11.6.
(OC-6-35)-(Dihydrofuran-2(3H)-ylidene)hydro{hydrotris[3-(2-thienyl)-1H-pyrazolato-kN1]borato(2 )-
kC2,kN2,kN2,kN2',kN2''}iridium (9). A soln. of 5b (50 mg, 0.063 mmol) and THF (2 ml) was heated at 808 for
1
8 h. Workup as described for 8 yielded 30 mg (66%) of 9. IR (Nujol): 2488m (BH), 2193m (IrH). H-NMR
(400 MHz, CDCl3, 208): 7.87 (d, 3J ˆ 2.4, H C(5)(pz)); 7.76 (d, 3J ˆ 2.6, H C(5)(pz)); 7.55 (d, 3J ˆ 2.4,
H
H
C(5)(pz)); 7.46 (d, 3J ˆ 4.8, H C(5)(Th)); 7.45 (dd, 3J ˆ 3.5, 4J ˆ 1.3, H C(3)Th)); 7.41 (d, 3J ˆ 4.8,
C(4)(Thm)); 7.19 (dd, 3J ˆ 5.1, 4J ˆ 1.1, H C(5)(Th)); 7.10 (dd, 3J ˆ 5.0, 4J ˆ 1.2, H C(5)(Th)); 6.90
(m, H C(3), H C(4)(Th)); 6.83 (dd, 3J ˆ 5.0, 3J ˆ 3.5, H C(4)(Th)); 6.35 (d, 3J ˆ 2.6, H C(4)(pz)); 6.33
(d, 3J ˆ 2.5, H C(4)(pz)); 6.11 (d, 3J ˆ 2.4, H C(4)(pz)); 4.17 (m, H C(5)); 3.97 (m, H C(5)); 1.76 (m,
H
C(3)); 1.53 (m, H C(3)); 1.05 (m, H C(4)); 0.86 (m, H C(4)); 20.5 (s, H Ir). 13C{1H}-NMR
(75.5 MHz, CDCl3, 208): 267.8 (CˆIr); 159.8, 149.0, 147.1 (3 C(3)(pz)); 141.3 (C(2)(Th)); 139.2, 137.6, 136.5
(3 C(4)(pz)); 136.1 (C(2)(Th)); 136.0 (C(5)(Thm)); 135.6 (C(2)(Th)); 129.7 (1 C, Thq,m); 128.7 (C(3)(Th));
127.9, 127.7, 127.5 (C(3), 2 C(4)(Th)); 126.6 (C(5)(Th)); 125.9 (C(5)(Th)); 124.6 (C(5)(Thm)); 108.2, 106.3,
102.7 (3 C(4)(pz)); 81.8 (C(5)); 57.1 (C(3)); 22.1 (C(4)). 11B{1H}-NMR (96.3 MHz, CDCl3, 208): 2.3. Anal.
calc. for C25H22BIrN6OS3 (721.70): C 41.6, H 3.1, N 11.6; found: C 41.8, H 3.2, N 11.5.
X-Ray Structure Determination for 6b. X-Ray crystal data for C27H26BlrN6S3: monoclinic, space group
P2(1)/n (No. 14), 1calc 1.714 g cm 3, Z ˆ 4, a ˆ 12.906(4) Š, b ˆ 13.436(4) Š, c ˆ 16.423(4) Š, b ˆ 93.390(10)8,
Vˆ 2842.8(14) Š3; MoKa radiation, l 0.71073 Š, qmax ˆ 278, completeness to q ˆ 99.5%, index ranges 16 ꢀ
h ꢀ 16, 17 ꢀ k ꢀ 17, 20 ꢀ l ꢀ 20, 6169 unique reflections, T 297(2) K. Crystals of 6b were obtained by slow
evaporation of a p.e.-layered CH2Cl2 soln. of 6b. X-Ray data were collected with a Siemens Smart-CCD area
detector diffractometer (graphite-monochromated MoKa radiation, l 0.71073 Š, nominal crystal-to-detector
distance 4.45 cm, 0.38 w-scan frames). Corrections for Lorentz and polarization effects, for crystal decay, and for
absorption were applied (multiscan method, program SADABS [23]). The structure was solved by direct
methods with SHELXS97 [24]. Structure refinement on F2 was carried out with SHELXL97 [25]. Final
R(F) ˆ 0.0320, wR/(F2) ˆ 0.0693 for 364 parameters and 4112 reflections with I > 2s(I). All non-H-atoms were
refined anisotropically. H-Atoms were inserted in idealized positions and were refined riding with the atoms to

2882
Helvetica Chimica Acta ± Vol. 84 (2001)
which they were bonded. Crystallographic data for compound 6b have been deposited with the Cambridge
Crystallographic Data Centre as deposition No. CCDC 157587. Copies of the data can be obtained, free of
charge, from: The Director, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ,
UK (e-mail: deposit@ccdc.cam.ac.uk).
This work was supported by the Fonds zur Förderung der wissenschaftlichen Forschung with a Schrödinger
Stipendium for C. S. (J1756-CHE), the Spanish Ministry of Education (DGES, Project PB97-0733), and the
Junta de Andalucía.
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Received March 16, 2001