Alkyl dehydrogenation in iridium tri-cyclopentyl phosphines

Article abstract of DOI:10.1016/j.ica.2009.03.004

The iridium cyclooctadiene complex incorporating a tricyclopentyl phosphine ligand (PCyp₃), Ir(η²:η²-C₈H₁₂)(PCyp₃)Cl, has been prepared. Removal of the chloride from this complex using Na [BAr^F₄] [Ar^F = C₆ H₃ (CF₃)₂] in CH₂Cl₂/arene solvent results in dehydrogenation (C-H activation followed by β-H transfer) of one of the alkyl phosphine rings and formation of the complexes [Ir (η⁶ - C₆ H₅ X) {PCyp₂ (η² - C₅ H₇)}] [BAr^F₄] (X = H, F) which contain a hybrid phosphine-alkene ligand. These complexes are formed alongside another product (5-20% yield) that has been identified as [Ir (η² : η² - C₈ H₁₂) {PCyp₂ (η² - C₅ H₇)}] [BAr^F₄], which can be prepared in high yield by an alternative, and slightly modified, route. This complex is with a minor isomer that has been tentatively identified as [Ir (η² : η³ - C₈ H₁₁) (H) {PCyp₂ (η² - C₅ H₇)}] [BAr^F₄], which results from allylic C-H activation of cyclooctadiene. Addition of H₂ to [Ir (η² : η² - C₈ H₁₂) {PCyp₂ (η² - C₅ H₇)}] [BAr^F₄] and its isomer in arene solvent (C₆H₅X, X = F, H) forms the dihydrido η⁶-arene Ir(III) complexes [Ir (H)₂ (η⁶ - C₆ H₅ X) (PCyp₃)] [BAr^F₄]. In contrast, hydrogenation in CH₂Cl₂ alone results in the formation of Ir (H)₂ (PCyp₃) {η⁶ - (C₆ H₃ (CF₃)₂) BAr^F₃} in which the [BAr^F₄]^- anion is now acting as a ligand through one of its aryl rings. The fluorobenzene complex [Ir (H)₂ (η⁶ - C₆ H₅ F) (PCyp₃)] [BAr^F₄] can be cleanly converted to [Ir (η⁶ - C₆ H₅ F) {PCyp₂ (η² - C₅ H₇)}] [BAr^F₄] by addition of the hydrogen acceptor tert-butylethene (tbe).

Full text of DOI:10.1016/j.ica.2009.03.004

Inorganica Chimica Acta 363 (2010) 574–580
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Alkyl dehydrogenation in iridium tri-cyclopentyl phosphines
Séverine Moret 1, Romaeo Dallanegra, Adrian B. Chaplin, Thomas M. Douglas, Rachel M. Hiney,
*
Andrew S. Weller
Department of Inorganic Chemistry, University of Oxford, Oxford OX1 3QR, United Kingdom
a r t i c l e i n f o
a b s t r a c t
The iridium cyclooctadiene complex incorporating a tricyclopentyl phosphine ligand (PCyp3), Ir(g2 g2
: -
Article history:
Received 14 December 2008
Received in revised form 25 February 2009
Accepted 1 March 2009
C8H12)(PCyp3)Cl, has been prepared. Removal of the chloride from this complex using
Na½BArF4ꢀ½ArF ¼ C6H3ðCF3Þ ꢀ in CH2Cl2/arene solvent results in dehydrogenation (C–H activation followed
2
by b-H transfer) of one of the alkyl phosphine rings and formation of the complexes
Available online 13 March 2009
½Irð
g
6-C6H5XÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ (X = H, F) which contain a hybrid phosphine–alkene ligand. These
complexes are formed alongside another product (5–20% yield) that has been identified as
Dedicated to Paul Pregosin.
½Irðg2
:
g
2-C8H12ÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ, which can be prepared in high yield by an alternative, and
slightly modified, route. This complex is with a minor isomer that has been tentatively identified as
Keywords:
Phosphine
Alkene
Iridium
Dehydrogenation
Anion
½Irðg2
:
g
3-C8H11ÞðHÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ, which results from allylic C–H activation of cyclooctadi-
ene. Addition of H2 to ½Irðg2
:
g
2-C8H12ÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ and its isomer in arene solvent
(C6H5X, X = F, H) forms the dihydrido
g
6-arene Ir(III) complexes ½IrðHÞ2ð
g
6-C6H5XÞðPCyp3Þꢀ½BArF4ꢀ. In con-
trast, hydrogenation in CH2Cl2 alone results in the formation of IrðHÞ2ðPCyp3Þf
g
6-ðC6H3ðCF3Þ2ÞBArF3g in
which the ½BArF4ꢀꢁ anion is now acting as a ligand through one of its aryl rings. The fluorobenzene com-
plex ½IrðHÞ2ð
g
6-C6H5FÞðPCyp3Þꢀ½BArF4ꢀ can be cleanly converted to ½Irð
g
6-C6H5FÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ
by addition of the hydrogen acceptor tert-butylethene (tbe).
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
phosphine, PCyp3 [17,18], that can undergo dehydrogenation when
complexed with a metal, to form phosphine–alkene ligands pre-
organised on Ru [19,20] or Rh [6,21–23] centres (e.g. Scheme 1).
In some cases the dehydrogenation is fully reversible, in that addi-
tion of H2 hydrogenates the double bond to form a phosphine with
a saturated backbone, which can then itself undergo dehydrogena-
tion to re-establish the phosphine–alkene ligand coordinated to
the metal centre [20–22]. Grützmacher and co-workers have also
reported reversible dehydrogenation in cyclic phosphine systems
complexed with iridium (Scheme 1) [24].
We report here an extension to our recent studies using rho-
dium-PCyp3 materials to encompass iridium complexes. Low va-
lent iridium complexes are known to be active alkane
dehydrogenation catalysts [25] and we anticipated that dehydro-
genation of the cyclic alkyl group in PCyp3 would occur readily,
leading to Ir(I) complexes containing a hybrid phosphine–alkene
ligand.
Hybrid phosphine–alkene ligands are receiving increased atten-
tion due to the role that they play in homogeneous catalysis, given
the enhanced selectivity and reactivity that they promote when
complexed with a metal centre [1]. Examples include: dehydroge-
native silylation [2], functionalisation of nitrogen heterocycles via
C–H activation [3], hydrogenation of imines [4], 1,4-addition reac-
tions [5,6], Suzuki–Miyaura reactions [7] and allylic substitutions
[8]. Such ligands can be prepared via standard chemical routes,
but an attractive alternate methodology is to prepare the ligands
in situ by a dehydrogenation procedure, which also furnishes an ac-
tive metal complex with the ligand of interest. Indeed it has re-
cently been demonstrated by Ellman, Bergman and co-workers
that in situ dehydrogenation of cyclic phosphines can lead to a sig-
nificantly more active and stable catalysts for C–H activation reac-
tions [3]. Dehydrogenation of coordinated ligands is well
established, and examples involving Ru [9], Rh [3,10–12], Re [13],
Os [14], Ir [11,12,15] and Pt [16] have been reported. We, concur-
rently but independent to Sabo-Etienne and co-workers, have re-
ported upon the late transition-metal chemistry of tricyclopentyl
2. Results and discussion
We have previously reported that removal of the chloride ligand
in Rh(nbd)Cl(PCyp3) using Na½BArF4ꢀ {nbd = norbornadiene,
ArF = C6H3(CF3)2} results in dehydrogenation of one of the PCyp3
alkyl groups, with norbornadiene acting as a sacrificial hydrogen
acceptor. If this reaction is performed in an arene solvent, such
* Corresponding author.
E-mail address: andrew.weller@chem.ox.ac.uk (A.S. Weller).
Visiting undergraduate student from EPFL, Switzerland.
1
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.03.004

S. Moret et al. / Inorganica Chimica Acta 363 (2010) 574–580
575
Scheme 1. Selected examples of alkyl dehydrogenation in PCyp3 and related complexes of Rh [31], Ru [29] and Ir [24].
as C6H5F, an arene adduct is formed, e.g. ½Rhð
g
6-C6H5FÞ
a single crystal X-ray diffraction study confirms that dehydrogena-
tion of one of the PCyp3 alkyl rings has occurred, as well as coordi-
nation of the benzene solvent to give a formally Ir(I), 18-electron,
metal centre. The bond lengths and angles around the metal centre
are unremarkable, and not dissimilar to those reported for
fPCyp2ð
g
2-C5H7Þgꢀ½BArF ꢀ, (Scheme 1). By contrast, in CH2Cl2,
4
where there is little stabilisation available from the solvent, a rare
example of a complex with a coordinated ½BArF4ꢀꢁ anion is formed,
RhfPCyp2ð
g
2-C5H7Þgf
g
6-ðC6H3ðCF3Þ2ÞBArF3g, in which the metal’s
coordination sphere is completed by an g6
-p
-interaction from
½Rhð
g
6-C6H5XÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ (X = H, F) [22]. Dissolution
the anion [23]. Following the same protocol, addition of Na½BArF4ꢀ
of the bulk crystalline sample showed that it was also contami-
nated with 4a/4b which clearly co-crystallises with 2. This was also
confirmed by an ESI-MS of the crystalline material dissolved in
CH2Cl2. Similarly, complex 3 could not be produced free of 4a/4b
by this method (80:20 relative ratio), but an alternative synthetic
route produces 3 pure (vide infra) which allows for complete char-
acterisation. The 1H NMR spectrum for 3 is broadly similar to 2 and
shows a coordinated fluorobenzene ligand [d 6.47 (4H), 5.90 (1H)].
In the 13C{1H} NMR spectrum the coordinated fluorobenzene is
indicated by resonances observed at d 141.7, 94.7, 88.7 and 82.9.
Three resonances appear as doublets of doublets [19F and 31P cou-
pling] while the one at d 88.7 is simply a doublet and can also be
correlated to the integral 1-H resonance in the 1H NMR spectrum
at d 5.90. It is thus assigned to the para-{CH} group on the arene.
The coordinated, dehydrogenated, cyclopentene ring is observed
in the 1H NMR spectrum at d 3.81 (2-H) and in the 13C{1H} NMR
spectrum as a singlet at d 45.8, with no 31P–13C coupling being ob-
served. Finally, the 31P{1H} NMR spectrum displays a single envi-
ronment, at d 69.2, that shows coupling to 19F [J(FP) 2.2 Hz], a
to the new, but straightforwardly synthesised, complex Ir(g2 g2
: -
C8H12)Cl(PCyp3) (1) resulted in the formation of three new com-
pounds in a variable ratio that depended on the solvent used. These
compounds have been identified by NMR spectroscopy and X-ray
crystallography as ½Irð
g
6-C6H5XÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ (X = H,
2, or F, 3) and the isomeric pair ½Irðg2
:
g
2-C8H12ÞfPCyp2ðg2
-
C5H7Þgꢀ½BArF4ꢀ (4a) and ½IrHðg2
:
g
3-C8H11ÞfPCyp2ð
g
2-C5H7Þgꢀ
½BArF4ꢀ (4b) (Scheme 2).
In benzene/CH2Cl2 solvent complex 2 is formed in 95% relative
yield compared to 4a/b, but could not be isolated in bulk form
away from traces of 4a/b by recrystallisation. The 1H NMR spec-
trum of 2 shows a coordinated benzene ligand, d 6.31, and an al-
kene that comes from dehydrogenation of the cyclopentyl ligand,
d 3.76, in a 6:2 relative integral ratio. The 31P{1H} NMR spectrum
shows a single environment, at d 68.4, while the 13C{1H} NMR
spectrum is in full accord with the 1H NMR spectrum, showing sig-
nals due to coordinated arene, free anion, and the phosphine–al-
kene ligand. A solid-state structure of 2 (Fig. 1) as determined by
Scheme 2. Synthesis of 2, 3 and 4a/4b.

576
S. Moret et al. / Inorganica Chimica Acta 363 (2010) 574–580
Fig. 1. Solid-state structure of the cationic portion of complexes ½Irð
g
6-C6H5XÞðPCyp2ð
g
2-C5H7Þꢀ½BArF4ꢀ (X = H 2 or F 3). Thermal ellipsoids are shown at the 30% probability
level, and the minor disordered components are omitted for clarity. Selected bond lengths and angles: Complex 2 Ir–P1 2.244(2) Å, C9–C10 1.396(11) Å; Ir–C9 2.120(6) Å, Ir–
C10 2.132(6) Å, Ir–P–C7 98.8(2)°. Complex 3 Ir–P1 2.235(3) Å, C9–C10 1.333(2) Å; Ir–C9 2.075(14) Å, Ir–C10 2.142(15) Å, Ir–P–C7 98.2(5)°.
shift of 56 ppm to lower field compared with Ir(COD)Cl(PCyp3)
reflecting the ring-strain associated with the chelating ligand and
the overall cationic charge on the complex [26]. The 19F NMR spec-
trum of 3 shows, as well as a signal due to free anion d ꢁ62.9, a res-
onance due to coordinated fluorobenzene, d ꢁ123.7. Single crystal
X-ray diffraction experiments on a sample of 3 produced by the
alternative method (vide infra) afforded a data set that was gener-
ally rather poor (R = 8.7%) but the solution gave the structure of the
complex as shown in Fig. 1. Bond lengths and angles are best not
discussed in detail, but clearly complex 3 is very similar to 2 in
its main structural features.
The isomeric pair 4a/4b were formed in a variable proportion
compared with the arene products 2 or 3 depending on the solvent
used. In strongly coordinating benzene the ratio of 2: 4a/4b is 95:5,
while in more weakly ligating fluorobenzene this ratio is 80:20 for
3: 4a/4b. The relative ratio of 4a/4b is approximately 4:1 under
these conditions. In CH2Cl2 solvent no arene complex is formed,
but reaction results in a variety of products, and 4a/4b are only
formed in approximately 35% conversion. The other products were
not identified. Addition of excess COD to the reaction in CH2Cl2 in-
creases the conversion for 4a/4b to be essentially quantitative by
NMR spectroscopy, which allows for full characterisation. Analysis
of a single crystal obtained from the CH2Cl2/COD reaction by X-ray
diffraction (Fig. 2) shows a pseudo square planar Ir(I) coordination
environment formed from
a dehydrogenated PCyp3 ligand
and COD. This structure is related to that observed for
½RhðnbdÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ [22]. The 1H NMR spectrum of
these crystals when dissolved in CH2Cl2 also shows the presence
of the isomeric pair 4a/4b. Cooling a CH2Cl2 solution to 250 K did
not change the relative ratio of these two components (by 1H
NMR spectroscopy) suggesting that these complexes are not in
equilibrium with one another, implying they are formed via paral-
lel routes in the reaction. We were not able to obtain a structure of
the minor component 4b, despite repeated attempts.
The 1H, 1H–1H COSY, 13C{1H} and 1H–13C HSQC NMR spectra of
the major component, 4a, identify it as ½Irðg2
:g
2-C8H12
Þ
fPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ. Signals assigned to two COD alkene
groups and a single dehydrogenated Cyp environment are ob-
served in the 1H NMR spectrum at d 5.13 (2H), 4.97 (2H) and
4.58 (2H), respectively, which show strong correlations to 13C envi-
ronments at d 105.2, 83.1 and 82.9, respectively. Only one of these
13C resonances shows coupling to 31P, d 105.2 [J(PC) 10 Hz], and
this is thus assigned to the alkene ligand trans to the phosphine
(C5–C6 in Fig. 2). The 31P{1H} NMR spectrum displays the major
peak at d 59.2, similar to 2 and 3.
The minor component of the mixture is identified as the hydri-
do complex ½IrHðg2
:g
3-C8H11ÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ (4b). Due
to the low relative abundance of this species characterisation
was principally by 1H, 1H–1H COSY and 31P{1H} NMR spectrosco-
pies. The 1H NMR spectrum of 4b shows a hydride signal at d
ꢁ13.44 [J(PH) 17 Hz]. 8 resonances are observed between d 4.87
and 2.48 in the ratio 1:2:1:1:1:1:1:3 with the highest-field reso-
nance showing a 1H–1H correlation in the 1H–1H COSY spectrum
to a signal in the aliphatic region at d 1.30. The 31P{1H} NMR spec-
trum shows a signal due to 4b at d 45.8. The 13C{1H} NMR spectrum
of 4b is more difficult to interpret due to the relative intensity of
the signals, but resonances at d 98.0 [d J(PC) 3 Hz], 95.1, 64.2,
58.8, 56.3, 55.5 and 50.6 can be assigned to alkene and allyl reso-
nances. Complex 4b would formally arise from a C–H activation
of an allylic methylene group on a coordinated COD ligand, and
although the characterisation of 4b remains tentative, examples
of C–H activation of COD to form
cyclooctadienyl ligands [28] have been previously reported and
the 1H NMR data for 4b are broadly similar to those of [Ir(g2
C8H11)(C(Ph)@CHPh) (NCMe)(PMe3)][BF4] [28]. An electrospray
ionisation-mass spectrum (ESI-MS) of the 4a/4b mixture shows
only one species at m/z = 537.2267 which corresponds to the
molecular formula for the isomeric cations 4a/4b [IrC33H37P m/z
r
-vinyl hydrides [27] or g2
:
g3
Fig. 2. Solid-state structure of the cationic portion of ½Irðg2
:
g2
-
g3
-
C8H12ÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ (4a). Thermal ellipsoids are shown at the 30%
:
probability level, and the minor disordered components are omitted for clarity.
Selected bond length and angles: Ir1–P1 2.884(9) Å; C11–C12 1.398(6) Å; Ir1–C11
2.180(3) Å; Ir1–C12 2.213(3), C1–C2 1.427(6); C5–C6 1.373(6); Ir1–C1
2.165(3) Å; Ir1–C2 2.168(3) Å; Ir1–C5 2.293(3) Å; Ir1–C6 2.250(4) Å; Ir–P1–C9
97.16(11)°.

S. Moret et al. / Inorganica Chimica Acta 363 (2010) 574–580
577
calc. 537.2257]. Addition of COD (1.2 equiv.) to a CH2Cl2 solution of
3 did not result in displacement of the arene ligand.
Addition of H2 to 4a/4b in C6H5F solution results in the hydro-
genation of the phosphine/alkene ligand, as well as the coordinated
COD, and the formation of
a
single Ir(III) complex
½IrðHÞ2ð
g
6-C6H5FÞðPCyp3Þꢀ½BArF4ꢀ (5). Similarly addition of hydro-
gen to 4a/4b in CH2Cl2/C6H6 solvent mixture leads to the formation
of ½IrðHÞ2ð
g
6-C6H6ÞðPCyp3Þꢀ½BArF4ꢀ (6) (Scheme 3). Both complexes
are isolated as analytically pure solids upon recrystallisation. The
presence of the hydrides in both complexes is revealed by a rela-
tive integral 2-H signal at d ꢁ16.23 [dd J(PH) 27, J(FH) 2 Hz] for
5, and a simple doublet, d ꢁ16.34 [d J(PH) 27 Hz], in 6. The coordi-
nated arene ligands are observed in the 1H NMR spectra as for 2
and 3, and the other NMR data are fully consistent with its formu-
lation. Complexes 5 and 6 form on hydrogenation of the COD and
phosphine–alkene ligand to leave a coordinative and electronically
unsaturated metal centre which is stabilised by coordination with
arene solvent, and are closely related to dihydrido arene triisopro-
pylphosphine iridium complexes previously reported by Oro and
co-workers [29]. In contrast, hydrogenation of 4a/4b in CH2Cl2 in
the absence of arene leads to a complex spectroscopically charac-
Scheme 4. Equilibrium between 5 and 7 established in CH2Cl2.
Scheme 5. Dehydrogenation of PCyp3 in 5.
terised as the zwitterionic
g
6-anion complex IrðHÞ2ðPCyp3Þ
for the coordinated arene. These observations might suggest the
formation of a Ir(I) species with a coordinated [C6H4(CF3)2] ligand
via B–C bond cleavage, a reaction that has been shown to occur
with electrophilic late transition-metals and the ½BArF4ꢀꢁ anion
[31]; but in the absence of further data this is rather a speculative
characterisation.
fg
6-ðC6H3ðCF3Þ2ÞBArF3g (7). Complex 7 is readily characterised by
a characteristic loss of symmetry for the ½BArF4ꢀꢁ anion, which
shows signals due to free and metal-coordinated arene rings in
the 1H NMR spectrum in a ratio of 1:3, while two signals in the
19F NMR spectrum at d ꢁ62.0 and d ꢁ63.1 in the ratio 1:3 are ob-
served. For comparison, the 19F NMR spectrum of 3 shows a single
resonance at d ꢁ62.9 for the free anion. The spectroscopic data for
A suggested mechanism for the formation of the products dis-
cussed herein, that takes into account their relative distributions,
is shown in Scheme 6. Removal of halide from IrCl(COD)(PCyp3)
generates a reactive, 14-electron, intermediate A, which undergoes
C–H activation to give B. This complex can then proceed along two
reaction pathways. Reversible b-Hydrogen transfer followed by
hydrogenation of the COD ligand gives C, with a coordinated cyclo-
octene ligand. This is displaced by arene to give the final product 2
or 3. The liberated cyclooctene from this process can itself coordi-
nate with B to afford D. Cyclooctene would be expected to be a sig-
nificantly better sacrificial hydrogen acceptor than coordinated
COD, which undergoes hydrogenation on the Ir-centre relatively
slowly [32], and thus aids in dehydrogenation of the PCyp3 ligand
liberating cyclooctane and affording 4a. Cyclooctane is observed by
1H NMR spectroscopy in the reaction mixture (d 1.53). This mech-
anism accounts for dependence on solvent. In benzene the reaction
between C and arene is fast, however, in weakly coordinating fluo-
robenzene C is not trapped as quickly and the liberated cyclooctene
present in the reaction mixture can react with B. The presence of
the minor isomer 4b can be accounted for by allylic C–H activation
in B or D, or allylic C–H activation in A in preference to cyclopentyl
C–H activation, albeit all invoking a perfectly reasonable Ir(V) oxi-
dation state along the pathway. The low yield of 4a/4b in CH2Cl2
solvent (35%) presumably arises from the inability to trap out C
in this solvent, and decomposition becomes competitive with the
pathway to form 4a/4b. Addition of excess COD to the reaction
brings about the sole formation of 4a/4b and is consistent with
the trapping of C with COD.
the coordinated anion in
7
follow those reported for
RhfPCyp2ð
g
2-C5H7Þgf
g
6-ðC6H3ðCF3Þ2ÞBArF3g [23] and the tetra-
phenyl borate complex Ir(H)2(PiPr3){ 6-(C6H5)B(C6H5)3} [29].
g
Complex 7 could not be isolated as a solid in analytically pure form
in our hands.
Dissolution of 5 in CH2Cl2 solution results in a slow-to-establish
(hours) equilibrium between 5 and 7 + free C6H5F, that leads to an
equilibrium ratio of 1:0.6 [
D
G(298) ꢂ 2.5 kJ molꢁ1 in favour of 5],
showing that fluorobenzene and ½BArF4ꢀꢁ bind almost isoenergeti-
cally in this system (Scheme 4). This underscores that when con-
sidering the mode of coordination of anions in solvents which
are weakly binding, competition between anion and solvent be-
comes important, as has been noted previously [30].
Addition of hydrogen acceptor tert-butylethene (tbe) to 5 re-
sults (1 day, 40 °C) in the clean formation of the dehydrogenated
complex 3 in quantitative yield (Scheme 5). Indeed, this method
proves to be the best way of preparing 3 free of 4a/4b. Addition
of tbe to 6 resulted in no reaction, demonstrating the stronger
binding of benzene over fluorobenzene in these complexes, as
these formally 18-electron arene complexes would require ligand
dissociation, or a hapacity change, prior to coordination of the
hydrogen acceptor. Addition of a large excess of tbe to 7 resulted
in no immediate change, and slow decomposition to a mixture of
products over time was observed. One of these showed a 31P{1H}
resonance at d 68.0, and resonances between d 7.2 and 6.6 in the
1H NMR spectrum, which are similar to that observed in that of 3
Scheme 3. Reaction of 4a/4b with H2 in various solvents.

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S. Moret et al. / Inorganica Chimica Acta 363 (2010) 574–580
Scheme 6. Suggested routes to the formation 2, 3 and 4a.
significantly disordered phosphine ligands – this disorder was
3. Conclusions
treated by modelling the appropriate phosphine substituents
over two sites and restraining their geometry. The fluorobenzene
ligand in 3 is also disordered – this was treated by modelling the
position of the fluorine atom over two sites and restraining its
1,2 and 1,3 bond distances; a rigid body restraint was applied
to the arene moiety. Large Fourier peaks surrounding Ir1 in 2
and 3 are attributed to truncation errors. Rotational disorder in
the CF3 groups of the anions in all structures was treated by
modelling the fluorine atoms over two sites and restraining their
geometry. Restraints to the thermal parameters were applied
where necessary in order to maintain sensible values. Residual
solvent disorder in the structure of 4a was treated using the
SQUEEZE algorithm [40]. Graphical representations of the structures
were made using ORETP3 [41].
Tricyclopentyl phopshine undergoes alkyl dehydrogenation on
iridium(I) centres, similar to that previously observed for rho-
dium(I) and ruthenium(o), leading to hybrid phosphine–alkene li-
gands complexed with a potentially catalytically active metal
centre. Future studies will explore the use of these new com-
plexes in catalysis, that may mirror the capabilities of the Rh
congeners that have proved to be useful in 1,4-addition reactions
[6].
4. Experimental
All the experiments were carried out under an atmosphere of
argon, using Schlenk line and glove-box techniques. CH2Cl2, pen-
tane and benzene were dried using a Grubbs’ type purification sys-
tem (MBraun SPS-800) and degassed by freeze/pump/thaw cycles.
CD2Cl2 and fluorobenzene were distilled under vacuum from CaH2
and stored over 3 Å molecular sieves. Glassware was pre-dried at
130 °C and flamed under vacuum before use. PCyp3 [17], [Ir(-
COD)Cl]2 [33] and Na½BArF4ꢀ [34] were prepared following the liter-
ature methods. NMR data were obtained at room temperature on
300 MHz (1H, 31P, 19F) and 500 MHz (1H, 31P, 13C) Varian Inova
and Bruker Avance spectrometers. Residual protio solvent was
used as reference for 1H NMR spectra (CD2Cl2: d = 5.33). 31P{1H}
spectra were referenced against 85% H3PO4 (external) and 19F spec-
tra against CFCl3. Chemical shift values are quoted in ppm and cou-
pling constants in Hz. High resolution ESI-MS data were recorded
on a Bruker MicroOTOF-Q instrument in positive ion mode. Micro-
analysis was performed by Elemental Microanalysis Limited, De-
von, UK.
4.1.1. Ir(PCyp3)Cl(1,5-C8H12) (1)
A pentane solution of PCyp3 (1.011 M, 2.5 eq, 1 mmol, 244 mg,
1 cm3) was added to
a solution of [Ir(COD)Cl]2 (0.5 mmol,
336 mg) in CH2Cl2 (10 cm3). The resulting orange solution was stir-
red overnight, evaporated to dryness (in vacuo), and the resulting
orange residue washed with cold pentane (2 ꢃ 2 cm3, ꢁ78 °C) to
give 1 as an orange powder (406 mg, 86%).
1H NMR (CD2Cl2): d 4.67 m, 2H, COD), 3.49 (m, 2H, COD), 2.48
(m, 3H, P-CH), 2.26–1.47 (m, 32H, CH2).
31P{1H} NMR (CD2Cl2): d 13.27 (s).
13C{1H} NMR (CD2Cl2): d 90.09 [d, J(PC), 14, HC@CH], 51.11 [d,
J(PC), 1.2, HC@CH], 35.71 [d, J(PC), 27, P-CH], 34.57 [d, J(PC), 3,
CH2], 30.57 [d, J(PC), 1, CH2], 29.30 [d, J(PC), 2, CH2], 26.52 [d,
J(PC), 9, CH2].
Microanalysis: Anal. Calc. for IrPC23H39Cl: C, 48.11; H, 6.85.
Found: C, 48.15; H, 6.97%.
4.1. Crystallography
4.1.2. ½Irð
g
6-C6H6ÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ ð2Þ
F
Relevant details about the structure refinements are given in
Table 1. Data for compounds 2, 3 and 4a were collected on an
Enraf Nonius Kappa CCD diffractometer using graphite mono-
Na½BAr4
ꢀ
(0.046 mmol, 42 mg), [Ir(COD)Cl(PCyp3)] (1)
(0.046 mmol, 26.3 mg) were dissolved in a solution of CH2Cl2/
C6H6 (9 cm3/1 cm3). The resulting dark orange solution was stirred
during 3 h, filtered, evaporated to dryness (in vacuo) and the result-
ing dark orange oil washed with pentane (2 ꢃ 2 cm3) to give 2 as
an orange powder. Diffusion of pentane into a solution of the res-
idue in CH2Cl2 gave 2 as orange crystals (26.4 mg, 41%). Complex 2
was contaminated with 4a/4b (ꢂ5%) which could not be removed
by recrystallisation.
chromated Mo Ka radiation (k = 0.71073 Å) and a low-tempera-
ture device (150 K) [35]; reduction and cell refinement was
performed using DENZO/SCALEPACK [36]. Structures were solved
by Patterson methods using SHELXS-86 (3) [37] or by direct meth-
ods using SIR92 (4a) [38] and SIR2004 (2) [39] and refined full-ma-
trix least squares on F2 using SHELXL-97 [37]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed
in calculated positions using the riding model with the exception
of the alkene hydrogens, which were located on the Fourier dif-
ference map, restrained and their displacement parameters fixed
to ride on the parent atoms. The structures of 2, 3 and 4a exhibit
1H NMR (CD2Cl2): d 7.72 (s, 8H, BArF4), 7.56 (s, 4H, BArF4), 6.31
(s, 6H, ArH), 3.76 (s, 2H, HC@CH), 2.11 (m, 3H, PCH), 1.95–1.37 (m,
22H, CH2).
31P{1H} NMR (CD2Cl2): d 68.35 (s).
19F NMR (CD2Cl2): d ꢁ62.87 (s).

S. Moret et al. / Inorganica Chimica Acta 363 (2010) 574–580
579
Table 1
Crystallographic data for 2, 3, and 4a.
2
3
4a
Formula
M
C53H43BF24IrP
1369.85
C53H42BF25IrP
1387.85
C55H49BF24IrP
1399.92
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
19.5691(1)
16.4516(1)
34.3154(3)
monoclinic
C2/c
19.7679(3)
16.3754(3)
34.3949(6)
triclinic
P1
ꢀ
12.8580(1)
12.9878(1)
18.7740(2)
74.6476(4)
71.5774(4)
78.0639(5)
2842.28(4)
2
a
(°)
b (°)
106.5774(3)
106.2336(7)
c
(°)
V (Å3)
10588.41(13)
8
1.719
10690.0(3)
8
1.725
Z
Density (g cmꢁ3
)
1.636
2.492
l
(mmꢁ1
)
2.674
2.652
h range (°)
Reflections collected
[R(int)
No. of data/parameter/restraints
5.10 6 h 6 26.37
35192
0.0359
5.10 6 h 6 25.03
13656
0.0292
5.10 6 h 6 26.37
19240
0.0200
11519/444/916
0.0283, 0.0729
1.046
0.806, ꢁ1.396
]
10718/423/925
0.0449, 0.1012
1.030
9151/435/847
0.0899, 0.1763
1.125
R1, wR2 [I > 2r(I)]
GOF
Largest difference peak and hole (e Åꢁ3
)
5.846,b ꢁ2.132
5.428,a ꢁ3.163
a
Excluding large Fourier peak near Ir1: 1.78.
Excluding large Fourier peak near Ir1: 0.95.
b
4.1.3. ½Irð
g
6-C6H5FÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF ꢀ ð3Þ
[d, J(PC) 30, P-CH], 29.70 [d, J(PC) 1.9, CH2], 26.82 [d, J(PC) 7.6,
CH2], 26.42 [d, J(PC) 9.5, CH2].
An orange solution of ½IrðCODÞfPCyp2ð4
g
2-C5H7Þgꢀ½BArF4ꢀ 4a/4b
(0.0216 mmol, 30.3 mg) was hydrogenated (4 atm) in a solution
of C6H5F (2 cm3) to give 3. The resulting pale yellow solution was
degassed, an excess of tbe added and then left to react for 24 h
at 40 °C. Diffusion of pentane into this pale yellow solution gave
3 as yellow crystals (18 mg, 60%).
Complex 4b: Selected 1H NMR (CD2Cl2): 4.87 (d, 1H, CH), 4.74
(m, 2H, CH), 4.22 (t, 1H, CH), 3.79 (m, 1H, CH), 3.28 (dt, 1H, CH),
3.14 (m, 1H, CH), 2.62 (m, 1H, CH), 2.48 (m, 3H), -13.44 [d, J(PH)
17, 1H, IrH].
31P{1H} NMR (CD2Cl2): d 45.75 (s).
1H NMR (CD2Cl2): d 7.72 s, 8H, BArF4), 7.56 (s, 4H, BArF4), 6.47
(m, 4H, ArH), 5.90 (m, 1H, ArH), 3.81 (s, 2H, HC@CH), 2.15 (m,
3H, PCH), 2.02 - 1.44 (m, 22H, CH2).
ESI-MS (CH2Cl2): m/z: calcd for [IrC23H37P]+: 537.2257; found:
537.2267.
Microanalysis: Anal. Calc. for IrC55H49PBF24: C, 47.19; H, 3.53.
Found: C, 47.27; H, 3.72%.
31P{1H} NMR (CD2Cl2): d 69.20 [d, J(FP), 2.2].
19F NMR (CD2Cl2): d ꢁ62.87 s, 24F, BArF4), ꢁ123.68 (s, 1F,
C6H5F).
4.1.5. ½Irð
g
6-C6H5FÞðPCyp3ÞðHÞ ꢀ½BArF4ꢀ ð5Þ
13C{1H} NMR (CD2Cl2): d 162.30 [q, J(BC) 50, BArF4], 141.69 [dd,
J(FC) 280, J(PC) 2.86, CF], 135.13 s, BArF4), 129.30 [qq, J(FC) 31, J(PC)
2.86, BArF4], 125.15 [q, J(FC) 273, BArF4], 118.03 [m, J(FC) 3.81,
BArF4], 94.69 [dd, J 6.67, J 1.91, ArH], 88.86 [d, J(PC) 2.86, ArH],
82.92 [dd, J(FC) 20.03, J(PC) 2.86 ArH], 45.82 s, HC@CH), 36.53 [d,
J(PC) 3.81, CH2], 34.67 [d, J(PC) 33, P-CH], 32.83 (s, CH2), 30.21 (s,
CH2), 29.98 [d, J(PC) 34, P-CH], 27.35 [d, J(PC) 8.58, CH2], 26.46
[d, J(PC) 9.54, CH2].
2
An orange solution of 4a/4b (0.015 mmol, 21.2 mg) in C6H5F
was hydrogenated (4 atm). Diffusion of pentane into the resulting
pale yellow solution gave 5 as colourless crystals (14 mg, 66%).
1H NMR (CD2Cl2): d 7.72 s, 8H, BArF4), 7.56 (s, 4H, BArF4), 6.68
(m, 4H, ArH), 6.22 (m, 1H, ArH), 2.17 (m, 3H, P-CH), 1.87–1.30
(m, 24H, CH2), ꢁ16.23 [dd, J(PH) 27, J(FH) 2.18, 2H, IrH].
31P{1H} NMR (CD2Cl2): d 42.40 (s).
19F NMR (CD2Cl2): d ꢁ62.87 s, 24F, BArF4), ꢁ113.89 (s, 1F,
C6H5F).
4.1.4. ½Irðg2
:g
2-C8H12ÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ ð4aÞ and
Microanalysis: Anal. Calc. for IrC53H46PBF25 ꢄ 1/4 C6H5F: C,
46.23; H, 3.36. Found: C, 46.15; H, 3.29%.
½Irðg2
:
g
3-C8H11ÞðHÞfPCyp2ð
g
2-C5H7Þgꢀ½BArF4ꢀ ð4bÞ
F
Na½BAr4
ꢀ
(0.1 mmol, 88.3 mg), [Ir(COD)Cl(PCyp3)] (1)
(0.1 mmol, 56.5 mg) and an excess of COD (10 eq, 1 mmol,
l), were dissolved in CH2Cl2 (15 cm3). The resulting dark or-
4.1.6. ½Irð
g
6-C6H6ÞðPCyp3ÞðHÞ ꢀ½BArF4ꢀ ð6Þ
122
l
2
An orange solution of 4a/4b (0.029 mmol, 40.6 mg) was hydro-
genated (4 atm, 298 K/77 K) in a solution of CH2Cl2/C6H6 (1.8 cm3/
0.2 cm3). Diffusion of pentane into the resulting pale yellow solu-
tion gave 7 as colourless crystals (31.1 mg, 77%).
ange solution was stirred for 3 h, filtered, evaporated to dryness
(in vacuo) and the resulting dark orange oil washed with pentane
(2 ꢃ 2 cm3) to give an orange powder. Diffusion of pentane into a
CH2Cl2 solution gave 4a/4b as inseparable red crystals (100.2 mg,
71.8%).
1H NMR (CD2Cl2): d 7.72 s, 8H, BArF4), 7.56 (s, 4H, BArF4), 6.55 (s,
6H, ArH), 2.13 (m, 3H, P-CH), 1.86–1.25 (m, 24H, CH2), ꢁ16.34 [d,
J(PH), 27, 2H, IrH].
Complex 4a: 1H NMR (CD2Cl2): d 7.71 (s, 8H, BArF4), 7.55 (s, 4H,
BArF4), 5.13 (m, 2H, COD), 4.97 (m, 2H, COD), 4.58 (s, 2H, HC@CH),
2.45–1.25 (m, 33H, CH/CH2).
31P{1H} NMR (CD2Cl2): d 42.53s.
13C{1H} NMR (CD2Cl2): d 162.3: [q, J(BC) 50, BArF4], 135.35 s,
BArF4), 129.4 [qq, J(FC) 31, J(BC) 2.9, BArF4], 125,2 [q, J(FC) 273,
BArF4], 118.03s, BArF4), 97.77 [d, J(PC), 1.9, ArH], 39.72 [d, J(PC),
39, P-CH], 30.90 [s, CH2], 26.34 [d, J(PC), 10, CH2].
31P{1H} NMR (CD2Cl2): d 59.23 (s).
13C{1H} NMR (CD2Cl2): d 162.15 [q, J(BC) 50, BArF4], 135.19 s,
BArF4), 129.42 [q, J(FC) 31, BArF4], 125 [q, J(FC) 273, BArF4],
118.02 s, BArF4), 105.25 [d, J(PC) 10, HC@CH], 83.1 [s, HC@CH],
82.9 [s, HC@CH], 38.64 [d, J(PC) 3.8, CH2], 33.44 [d, J(PC) 2.9,
CH2], 32.3 [d, J(PC), 29, P-CH], 30.73 s, CH2), 30.32 (s, CH2), 29.94
Microanalysis: Anal. Calc. for IrC53H47PBF24.2/3C6H6: C, 47.41;
H, 3.49. Found: C, 47.42; H, 3.40%.

580
S. Moret et al. / Inorganica Chimica Acta 363 (2010) 574–580
6-ðC6H3ðCF3Þ2ÞBArF3g ð7Þ
[15] (a) W.H. Bernskoetter, E. Lobkovsky, P.J. Chirik, Organometallics 24 (2005)
4.1.7. IrðHÞ2ðPCyp3Þf
g
6250;
An orange solution of 4a/4b (0.015 mmol, 21.4 mg) was hydro-
genated (4 atm, 298 K/77 K) in CH2Cl2 (2 cm3). 7 was characterised
in situ by 1H, 19F and 31P{1H} NMR spectroscopy.
1H NMR (CD2Cl2): d 7.77 s, 6H, BArF4), 7.69 (s, 3H, BArF4), 7.06 (s,
1H, Ir-BArF4), 6.84 (s, 2H, Ir-BArF4), 2.02 (m, 3H, PCH), 1.75–1.09
(m, 24H, CH2), ꢁ16.61 [d, J(PH), 28, 2H, IrH].
(b) M. Prinz, M. Grosche, E. Herdtweck, W.A. Herrmann, Organometallics 19
(2000) 1692.
[16] (a) N.M. West, P.S. White, J.L. Templeton, J. Am. Chem. Soc. 129 (2007) 12372;
(b) S.M. Kloek, K.I. Goldberg, J. Am. Chem. Soc. 129 (2007) 3460;
(c) A. Baber, C. Fan, D.W. Norman, A.G. Orpen, P.G. Pringle, R.L. Wingad,
Organometallics 27 (2008) 5906.
[17] T.M. Miller, G.M. Whitesides, Organometallics 5 (1986) 1473.
[18] M. Grellier, L. Vendier, B. Chaudret, A. Albinati, S. Rizzato, S. Mason, S. Sabo-
Etienne, J. Am. Chem. Soc. 127 (2005) 17592.
[19] P.D. Bolton, M. Grellier, N. Vautravers, L. Vendier, S. Sabo-Etienne,
Organometallics 27 (2008) 5088.
[20] M. Grellier, L. Vendier, S. Sabo-Etienne, Angew. Chem., Int. Ed. 46 (2007)
2613.
31P{1H} NMR (CD2Cl2): d 38.47 (s).
19F NMR (CD2Cl2): d ꢁ62.01 s, 6F, Ir-BArF4), ꢁ63.11 (s, 18F,
BArF4).
References
[21] T.M. Douglas, A.S. Weller, New J. Chem. 32 (2008) 966.
[22] T.M. Douglas, S.K. Brayshaw, R. Dallanegra, G. Kociok-Kohn, S.A. Macregor, G.L.
Moxham, A.S. Weller, T. Wondimagegn, F. Vadivelu, Chem. Eur. J. 14 (2008)
1004.
[23] T.M. Douglas, E. Molinos, S.K. Brayshaw, A.S. Weller, Organometallics 26
(2007) 463.
[24] E. Piras, F. Läng, H. Rüegger, D. Stein, M. Wörle, H. Grützmacher, Chem. Eur. J.
12 (2006) 5849.
[25] (a) A.S. Goldman, A.H. Roy, Z. Huang, R. Ahuja, W. Schinski, M. Brookhart,
Science 312 (2006) 257;
[1] (a) C. Defieber, H. Grützmacher, E.M. Carreira, Angew. Chem., Int. Ed. 47 (2008)
4482;
(b) P.S. Pregosin, Chem. Commun. (2008) 4875;
(c) J.B. Johnson, T. Rovis, Angew. Chem., Int. Ed. 47 (2008) 840.
[2] M.L. Christ, S. Sabo-Etienne, B. Chaudret, Organometallics 14 (1995) 1082.
[3] (a) J.C. Lewis, A.M. Berman, R.G. Bergman, J.A. Ellman, J. Am. Chem. Soc. 130
(2008) 2493;
(b) J.C. Lewis, R.G. Bergman, J.A. Ellman, Acc. Chem. Res. 41 (2008) 1013.
[4] P. Maire, S. Deblon, F. Breher, J. Geier, C. Böhler, H. Rüegger, H. Schönberg, H.
Grützmacher, Chem. Eur. J. 10 (2004) 4198.
(b) C.M. Jensen, Chem. Commun. (1999) 2443;
(c) M.J. Burk, R.H. Crabtree, J. Am. Chem. Soc. 109 (1987) 8025.
[26] P.S. Pregosin, R.W. Kunz, 31P and13C NMR of Transition Metal Phosphine
Complexes, Springer, Berlin, 1979.
[27] D. Hermann, M. Gandelman, H. Rozenberg, L.J.W. Shimon, D. Milstein,
Organometallics 21 (2002) 812.
[28] M. Martin, E. Sola, O. Torres, P. Plou, L.A. Oro, Organometallics 22 (2003) 5406.
and references therin.
[29] F. Torres, E. Sola, M. Martin, C. Ochs, G. Picazo, J.A. Lopez, F.J. Lahoz, L.A. Oro,
Organometallics 20 (2001) 2716.
[5] (a) W.L. Duan, H. Iwamura, R. Shintani, T. Hayashi, J. Am. Chem. Soc. 129 (2007)
2130;
(b) R. Shintani, W.-L. Duan, T. Nagano, A. Okada, T. Hayashi, Angew. Chem., Int.
Ed. 44 (2005) 4611;
(c) P. Kasak, V.B. Arion, M. Widhalm, Tetrahedron-Asymmetr. 17 (2006) 3084.
[6] T.M. Douglas, J.L. Notre, S.K. Brayshaw, C.G. Frost, A.S. Weller, Chem. Commun.
(2006) 3408.
[7] C. Thoumazet, L. Ricard, H. Grützmacher Grützmacher, P. Le Floch, Chem.
Commun. (2005) 1592.
[8] C. Defieber, M.A. Ariger, P. Moriel, E.M. Carreira, Angew. Chem., Int. Ed. 46
(2007) 3139.
[9] (a) S. Sabo-Etienne, B. Chaudret, Coord. Chem. Rev. 180 (1998) 381;
(b) A.F. Borowski, S. Sabo-Etienne, M.L. Christ, B. Donnadieu, B. Chaudret,
Organometallics 15 (1996) 1427.
[10] (a) K. Mauthner, K.M. Soldouzi, K. Mereiter, R. Schmid, K. Kirchner,
Organometallics 18 (1999) 4681;
[30] (a) S.H. Strauss, Chem. Rev. 93 (1993) 927;
(b) A. Macchioni, Chem. Rev. 105 (2005) 2039;
(c) I. Krossing, I. Raabe, Angew. Chem., Int. Ed. 43 (2004) 2066.
[31] (a) W.V. Konze, B.L. Scott, G.J. Kubas, Chem. Commun. (1999) 1807;
(b) H. Salem, L.J.W. Shimon, G. Leitus, L. Weiner, D. Milstein, Organometallics
27 (2008) 2293.
[32] R.H. Crabtree, P.C. Demou, D. Eden, J.M. Mihelcic, C.A. Parnell, J.M. Quirk, G.E.
Morris, J. Am. Chem. Soc. 104 (1982) 6994.
[33] J.L. Herde, J.C. Lambert, C.V. Senoff, Inorg. Synth. 15 (1974) 18.
[34] W.E. Buschmann, J.S. Miller, Inorg. Synth. 33 (2002) 85.
[35] J. Cosier, A.M. Glazer, J. Appl. Crystallogr. 19 (1986) 105.
[36] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307.
[37] G.M. Sheldrick, Acta. Crystallogr. A A64 (2008) 112.
[38] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori,
M. Camalli, J. Appl. Crystallogr. 27 (1994) 435.
[39] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro, C.
Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 38 (2005) 381.
[40] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
(b) A.B. Chaplin, A.I. Poblador-Bahamonde, H.A. Sparkes, J.A.K. Howard, S.A.
Macgregor, A.S. Weller, Chem. Commun. (2009) 244.
[11] Y.O. Ma, R.G. Bergman, Organometallics 13 (1994) 2548.
[12] S. Deblon, L. Liesum, J. Harmer, H. Schönberg, A. Schweiger, H. Grützmacher,
Chem. Eur. J. 8 (2002) 601.
[13] O.V. Ozerov, L.A. Watson, M. Pink, K.G. Caulton, J. Am. Chem. Soc. 129 (2007)
6003.
[14] (a) A.J. Edwards, M.A. Esteruelas, F.J. Lahoz, A.M. Lopez, E. Onate, L.A. Oro, J.I.
Tolosa, Organometallics 16 (1997) 1316;
(b) P.B. Glaser, T.D. Tilley, Organometallics 23 (2004) 5799;
(c) M. Baya, M.L. Buil, M.A. Esteruelas, E. Onate, Organometallics 23 (2004) 1416.
[41] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.