Synthesis and reactivity of half-sandwich (η5-C 5Me5)Ir(iii) complexes of a cyclometallated aryl phosphine ligand

Article abstract of DOI:10.1039/c1nj20244h

Reaction of the Ir(iii) dimer [(η⁵-C₅Me ₅)IrCl₂]₂ with PMeXyl₂ (Xyl = 2,6-C₆H₃Me₂), in the presence of the poorly coordinating base 2,2,6,6-tetramethyl piperidine, gives a chloride complex 1-Cl, resulting from hydrogen chloride elimination involving one of the phosphine benzylic hydrogen atoms and concomitant cyclometallation. Related compounds containing other halide or pseudohalide ligands, 1-Br, 1-Cl, 1-SCN, can be made, the latter featuring S-coordination of the ambidentate thiocyanate to the soft Ir(iii) Lewis acid centre, as suggested by IR data and demonstrated by X-ray crystallography. Hydride 2-H, and alkyl derivatives 3 (Me) and 4 (CH ₂SiMe₃) can also be prepared from 1-Cl and appropriate hydride and alkylating reagents. An interesting H/D exchange chemistry that occurs in the presence of CD₃OD has been disclosed for 1-Cl, 1-Br and 2-H. For the halide derivatives, deuterium incorporation takes place into the methylene and methyl sites of their cyclometallated ligand, whereas for 2-H only the hydride and methylene (Ir-CH₂) protons participate in the exchange, which is strikingly accelerated by catalytic amounts of acids.

Full text of DOI:10.1039/c1nj20244h

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PAPER
Synthesis and reactivity of half-sandwich (g5-C5Me5)Ir(III) complexes of
a cyclometallated aryl phosphine ligandwz
Jesu
´
´
s Campos, Eleuterio Alvarez and Ernesto Carmona*
Received (in Victoria, Australia) 15th March 2011, Accepted 5th May 2011
DOI: 10.1039/c1nj20244h
Reaction of the Ir(III) dimer [(Z5-C5Me5)IrCl2]2 with PMeXyl2 (Xyl = 2,6-C6H3Me2), in the presence
of the poorly coordinating base 2,2,6,6-tetramethyl piperidine, gives a chloride complex 1-Cl, resulting
from hydrogen chloride elimination involving one of the phosphine benzylic hydrogen atoms and
concomitant cyclometallation. Related compounds containing other halide or pseudohalide ligands,
1-Br, 1-Cl, 1-SCN, can be made, the latter featuring S-coordination of the ambidentate thiocyanate to
the soft Ir(III) Lewis acid centre, as suggested by IR data and demonstrated by X-ray crystallography.
Hydride 2-H, and alkyl derivatives 3 (Me) and 4 (CH2SiMe3) can also be prepared from 1-Cl and
appropriate hydride and alkylating reagents. An interesting H/D exchange chemistry that occurs in
the presence of CD3OD has been disclosed for 1-Cl, 1-Br and 2-H. For the halide derivatives,
deuterium incorporation takes place into the methylene and methyl sites of their cyclometallated
ligand, whereas for 2-H only the hydride and methylene (Ir–CH2) protons participate in the exchange,
which is strikingly accelerated by catalytic amounts of acids.
Introduction
Cyclometallated iridium complexes are attractive synthetic
targets due to their remarkable chemical reactivity, their use
in catalysis and their applications in a wide range of areas of
materials science.1,2 An important group of complexes of this
kind consists of half-sandwich (Z5-C5Me5)Ir units bound to a
cyclometallated ligand. Often the latter consists of a donor
heteroatom (for instance, O, N or P; see structure A in
Scheme 1) and a carbon atom that forms a sigma Ir–C bond
Scheme 1
as a consequence of a metal-mediated intramolecular C–H
activation reaction (for example an ortho-metallation). Neutral
compounds of this type or their cationic derivatives (structure B)
are expected to exhibit unusual reactivity in processes that
imply the activation of H–H, H–C and other H–element bonds
(e.g. B, N, Si, etc.).
phosphine and alkyl functionalities are the constituents of a
cyclometallated ligand.4 To avoid side reactions like b-H
elimination, while at the same time achieving formation of a
five-membered metallacycle, aryl phosphines metallated at a
benzylic position (structure C in Scheme 1) have been chosen.
Herein we report the synthesis and characterization of
compounds of type C (Scheme 1) derived from the phosphine
PMeXyl2 (Xyl = 2,6-Me2C6H3), in which iridium is also bonded
to a halide or pseudohalide unit. Corresponding alkyl and
hydride derivatives are also reported. A preliminary commun-
ication describing part of this work has already appeared.5
With the precedent of the remarkable reactivity toward
C–H activation discovered by the group of Bergman3 for the
Ir(III) cation ꢀ[(Z5-C5Me5)Ir(Me)(PMe3)(ClCH2Cl)]+ (isolated
as the BArF salt; BArF = B(3,5-C6H3(CF3)2)4), we have
recently started to develop related complexes in which the
´
Departamento de Quımica Inorganica-Instituto de Investigaciones
Quımicas, Universidad de Sevilla-Consejo Superior de Investigaciones
´
´
´
´
Cientıficas, Avda. Americo Vespucio 49, Isla de la Cartuja,
Results and discussion
41092 Sevilla, Spain. E-mail: guzman@us.es; Fax: +34 954460565
w This paper is dedicated with much appreciation to Professor Didier
Astruc, on the occasion of his 65th birthday, in recognition of his
fundamental contributions to Inorganic and Organometallic Chemistry.
z CIF files for compounds 1-Cl, 1-SCN, 2-H and 3. CCDC reference
numbers 817784–817787. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1nj20244h
Halide and pseudohalide complexes
As already reported,5 reaction of the Ir(III) dimer [{(Z5-C5Me5)-
IrCl2}2] with one equivalent of PMe(Xyl)2 in the presence of
the weakly coordinating base 2,2,6,6-tetramethylpiperidine
c
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(TMPP in Scheme 2a) yields the cyclometallated compound
1-Cl, in the form of two diastereomers in a ca. 7 : 3 ratio.
Metathesis reactions of 1-Cl with LiBr, MgI2 or NH4SCN
afford corresponding complexes 1-X, as shown in Scheme 2b.
Under the stated experimental conditions, 1-Br and 1-I are
produced as single stereomers, whereas 1-SCN forms two
isomers in an approximately 6 : 1 mixture. In each case, the
major (or exclusive) reaction product is proposed to be the
sterically more favourable isomer, namely that minimizing
steric interactions by the adoption of a syn distribution of
the X and methyl phosphine groups. This has been demon-
strated by X-ray studies carried out for complexes 1-Cl and
1-SCN, and by NOE experiments performed with the related
methyl complex 3 (vide infra). While for 1-Cl mild heating
of the stereomers mixture (CH2Cl2/MeOH, 40 1C) causes
conversion into its major component, interconversion between
the two isomers of 1-SCN is less facile. As discussed below,
complex 1-Cl undergoes facile chloride dissociation under
these conditions (see structure D in Scheme 4) facilitating this
exchange.
to 31P. The 31P{1H} resonances of complexes 1 cluster in a
narrow chemical shift range (7–11 ppm).
The thiocyanate compound 1-SCN has been prepared with
the aim of ascertaining whether iridium coordination of the
ligand occurs through the nitrogen or the sulfur atom. N- or
S- bonding of the thiocyanate anion can be rationalized in
terms of the hardness or softness of the metal Lewis acid
centre.6 Since the iridium Lewis acid present in these complexes
may be viewed as soft,7 S-coordination would be electronically
favoured.8 However, N-coordination might be preferred on
steric grounds in view of the bulkiness of the C5Me5 and
cyclometallated PMeXyl2 ligands.7 Infrared spectroscopy has
often been used as diagnostic for S- or N-thiocyanate binding.
Even if the following criteria do not have general application,
the CN stretching frequency (around 2100 cmꢀ1) occurs at
higher wavenumbers for S-thiocyanates than for N-bonded
complexes,9 whereas for the C–S stretching frequency
(ca. 800 cmꢀ1) the opposite is observed.9 For 1-SCN these
bands are registered at 2100 cmꢀ1 and 795 cmꢀ1, suggesting
coordination through the sulfur atom. This has been demon-
strated by X-ray crystallography.
Compounds 1 are orange or yellow crystalline solids that
exhibit good solubility properties in common organic solvents.
Although they have been prepared and manipulated under an
inert atmosphere, they display moderate stability toward
oxygen and moisture, particularly in the form of crystalline
samples. NMR data are in accord with the proposed formulation.
For all compounds the Z5-C5Me5 ligand yields a doublet in the
1H NMR spectrum due to weak coupling between the C5Me5
Fig. 1 collects ORTEP diagrams for complexes 1-Cl and
1-SCN. Crystallographic data for these and other complexes
described in this work are provided in the Experimental
section. The molecular structure of the complexes confirms
that cyclometallation of the xylyl-substituted phosphine has
occurred at one of the benzylic carbon atoms, giving rise
to a five-membered iridacycle. This unit is characterized by
Ir–C and Ir–P bonds with lengths of ca. 2.12 and 2.25 A,
respectively. Bond angles between the P, C and X (Cl or S)
atoms that complete the three-legged piano stool structure are
close to 901, in particular the P1–Ir1–X angles (ca. 89.61). The
X-ray analysis confirms also the proposed syn arrangement of
the X ligand and the phosphine methyl group that leaves the
larger, non-metallated phosphine xylyl substituent on the
opposite region of space.
4
protons and the phosphorus nucleus (d 1.3–1.6 ppm, JHP of
ca. 2 Hz). Resonances due to the diastereotopic Ir–CH2
protons are characteristic and can be considered as diagnostic
of the metallation reaction. They appear as two multiplets that
can be readily identified as the AB portions of an ABX spin
system (X = 31P), where only one of the two 1H nuclei features
observable coupling to 31P. Data for each of these complexes
can be found in the Experimental section that includes also
NMR features for the minor stereomers of 1-Cl and 1-SCN.
These proton signals are associated with a 13C{1H} resonance
in the range of 17–20 ppm, which exhibits negligible coupling
Cyclometallated iridium complexes with hydride and alkyl
ligands
Compound 1-Cl is also a good starting material for the
synthesis of complexes that contain Ir–H and Ir–C s bonds.
Iridium hydride 2-H is best prepared (Scheme 3) by reaction of
tetrahydrofuran (THF) solutions of 1-Cl and LiAlH4, at 45 1C
for 2 h. In an alternative and also high-yield procedure, THF
solutions of 1-Cl can be treated with cold pentane solutions
(ꢀ40 1C) of LiBut and stirred at room temperature for a
Scheme 2 Synthesis of halide and thiocyanate complexes 1-X.
Fig. 1 ORTEP diagrams for complexes 1-Cl and 1-SCN.
c
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Scheme 3 Synthesis of hydride and alkyl complexes 2–4.
period of 4 h. The crude hydride forms as a pale yellow powder
that converts into a colourless crystalline material after
crystallization from pentane. For the deuterated isotopologue,
2-D, LiAlD4 or NaOCD3 may be utilized as a deuteride
source. The hydride forms in an approximate 20 : 1 mixture
of diasteromers.
0.30–0.19 ppm. As expected, the 13C{1H} resonances found
for these Ir–C units are strongly shielded and appear at
ꢀ22.9 (complex 3) and ꢀ29.6 (4) ppm.
The molecular structures of 2-H and 3 have been confirmed
by X-ray studies (Fig. 2). The Ir1–C17 bonds in the two
complexes are identical within experimental error (ca. 2.11 A)
and are also identical to corresponding bonds in 1-Cl and
1-SCN. For the methyl complex 3, the two Ir–C bonds, i.e.
Ir1–C17 and Ir1–C28, have practically the same length. For
the latter compound, the solid-state structure corroborates the
syn distribution of the Ir–Me and P–Me groups deduced in
solution from NOE studies.
A medium-to-weak intensity infrared absorption at 2090 cmꢀ1
that shifts to 1470 cmꢀ1 in 2-D is indicative of the presence of an
Ir–H (and Ir–D) functionality. This is further demonstrated by
the observation for 2-H of a characteristic 1H NMR signal with
d ꢀ17.24 (2JHP = 35.2 Hz) that is absent in the spectrum of 2-D.
EXSY NMR studies performed at 0 1C give no indication for
exchange between the Ir–H and Ir–CH2 sites of 2-H. However,
H/D exchange takes place when solutions of 2-D, or of [D11]-2-H
(the latter deuterated at the methylene and methyl sites of the two
xylyl groups), are heated at 90 1C in C6D6. This may occur by a
series of C–H reductive couplings of the Ir–CH2 and Ir–H
moieties of 2-H, and oxidative additions of the C–H bonds of
the xylyl methyl substituents in a putative Ir(I) intermediate,
[(Z5-C5Me5)Ir(PMeXyl2)]. Since heating a solution of 2-H in
C6D6 at 200 1C in a pressure vessel for 48 h results in no
deuteration of the metallated ligand, intermolecular benzene
C–D activation must be either unproductive or much slower
than intramolecular oxidative C–H cleavage.
Hydrogen/deuterium exchange reactions
As already indicated, the cyclometallated complexes described
in this work have been prepared with the aim of ascertaining
their role in the activation of E–H bonds (E stands for H, C or
other main-group element like N or Si) and their utility as
precursors for the synthesis of related, neutral or cationic,
iridium complexes, which may be useful for the same purpose.
Compounds labelled with the hydrogen isotopes are widely
employed as internal standards for mass spectrometric studies,
as well as in the investigation of the interaction of small
molecules with receptors, enzymes and other biomolecules.10
The importance of deuterium labelling of organic molecules11
has prompted a number of studies in this field by different
research groups.12–15 Heating compounds 1 in a 1 : 1 mixture
of CH2Cl2 : CD3OD at 45 1C in a closed reaction vessel for
As summarized in Scheme 3, the methyl derivative 3 is best
prepared by reaction of 1-Cl with ZnMe2 or Mg(Me)Br.
The stronger methylating reagent, LiMe, also yields 3 but
accompanied by a product with three Ir–C s bonds, as a
consequence of metallation of the P-bound methyl group.5
The latter compound will be described elsewhere. Alkylation
of 1-Cl can be readily extended to other alkyl groups that lack
b-H atoms. This is shown in Scheme 3 for the synthesis of the
Ir–CH2SiMe3 complex 4.
The NMR data recorded for the C5Me5 and cyclometallated
phosphine ligands of 3 and 4 are similar to those already
discussed for 1 and 2. They are collected in the Experimental
section and need no further explanation. The alkyl groups of 3
1
and 4 produce high-field H NMR signals that are observed
3
for the former compound at 0.35 ppm (d, JHP = 5.2 Hz).
In the latter, the Ir–CH2SiMe3 protons are diastereotopic
and appear as multiplets in the chemical shift range of
Fig. 2 ORTEP diagrams of complexes 2-H and 3 (50% probability
thermal ellipsoids; H atoms have been omitted for clarity).
c
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ca. 24 h results in clean incorporation of deuterium into all
sp3-hybridized C–H bonds of the phosphine xylyl substituents
only for 1-Cl and 1-Br. In contrast to a somewhat related
derivative containing a cyclometallated N-heterocyclic carbene
ligand reported by Peris and co-workers,13b the iodide complex
1-I does not undergo H/D exchange under similar conditions.
The thiocyanate complex 1-SCN also fails to promote H/D
scrambling, which might be due to the less polar and more
covalent character of the Ir–I and Ir–S bonds in the two
complexes. For 1-Cl and 1-Br the deuteration is facile and
occurs with a half-live, t1/2 = 490 min at 45 1C for 1-Cl, using
the above 1 : 1 mixture of solvents.
unaltered after being heated in CH2Cl2 : CD3OD (1 : 1) at
60 1C for 24 h. It thus seems likely that methanol is unable
to protonate 3 and generate the cationic Ir(V) methyl hydride
intermediate that could promote H/D scrambling in this
complex.
At variance with the lack of reactivity of 3, hydride 2-H
experiences facile D incorporation, albeit exclusively in the
Ir–H and Ir–CH2 bonds. A CD3OD concentration of only
10% in the CH2Cl2 : CD3OD solvent mixture utilized suffices
to promote the scrambling at 20 1C, with t1/2 = 130 min.
1H NMR monitoring of the exchange reveals no detectable
differences in the rates of deuteration of the chemically distinct
hydride and alkyl functionalities. Addition of 5% of p-toluene-
sulfonic acid uncovers a remarkable catalytic effect, as
deuteration occurs with t1/2 r 3 min. Larger acid amounts
(Z20%) produce fully deuterated [D11]-2-D, as a consequence
of additional incorporation of deuterium in the benzylic
positions of the phosphine ligand. Most likely, this results
from cleavage by the acid of the Ir–CH2 bond, to give an
agostic species similar to E in Scheme 4. Addition of a base
(NaOCD3 or NaOD) completely inhibits the H/D scrambling.
In fact this observation explains that generation of 2-D from
1-Cl and LiAlD4 (Scheme 3) occurs selectively with more than
95% deuterium incorporation at the hydride position (and not
into the methylene sites, despite addition of H2O to quench the
excess of the deuteride reagent). In much the same manner, the
alternative synthesis of 2-D in Scheme 3 uses NaOCD3 to
selectively label with deuterium the hydride position.
In parallel experiments, the deuteration of 1-Cl has been
observed to slow down by a factor of ten when the CH2Cl2/
CD3OD solvent mixture is saturated with LiCl.12a,14b
Moreover, the H/D exchange is significantly accelerated when
the concentration of CD3OD in the solvent mixture is increased
(see Experimental section). Accordingly, participation of a
cationic species resulting from momentary dissociation of
chloride (structure D in Scheme 4) in the H/D exchange
appears to be a reasonable proposal. Subsequent incorporation
of deuterium onto all benzylic positions of 1-Cl (or 1-Br)
requires, in all probability, cleavage of the Ir–CH2 bond to the
cyclometallated carbon. Hence, D may undergo deuteration of
this bond giving an agostic structure such as E in Scheme 4,
which would afterwards experience C–H (or C–D) activation
at all benzylic sites. Whether this C–H activation occurs by an
internal electrophilic substitution or a related mechanism14,16
is unclear at this stage. Evidence for a similar H/D exchange
involving D2 as the deuterium source has been obtained
recently for a closely related rhodium compound.15b
The remarkable selectivity of the acid-catalysed H/D
scrambling in 2-H suggests the participation as a key inter-
mediate of a cationic iridium alkylidene, resulting from an a-H
elimination, or a H-abstraction reaction. Despite our efforts, a
clear mechanistic picture has not yet evolved. However,
work in progress with complexes of related PR2Xyl ligands
may shine light on this intriguing rearrangement. This advises
deferring a definitive mechanistic proposal until sufficient
information is gathered.
Recent work from Goldberg, Brookhart and their
co-workers17 has revealed that an Ir(I)–CH3 complex stabilized
by the pincer ligand PONOP17 experiences facile deuterium
incorporation in the methyl group in the presence of the acidic
deuterated solvents CD3OD and D2O. For this proton-
assisted C–D/H activation a mechanism implying generation
of an Ir(III) methyl hydride (or deuteride) intermediate that
features reductive coupling and oxidative cleavage reactivity
was proposed, with participation of an Ir(I) s–methane
complex intermediate.17 In contrast with these observations
the Ir(III) compound 3 does not participate in H/D exchange
under the conditions given above for 1-X, and is recovered
Conclusions
In summary, readily prepared cyclometallated complex 1-Cl
has proved to be an excellent synthetic precursor for the
synthesis of related halide (or pseudohalide), hydride and
alkyl derivatives. Compounds 1-Cl and 1-Br feature H/D
scrambling in the presence of CD3OD affecting all benzylic
sites whereas for the hydride 2-H an unusual acid-catalysed
reaction permits D incorporation exclusively into the Ir–H and
Ir–CH2 units.
Experimental section
General
All operations were performed under an argon atmosphere
using Standard Schlenk techniques, employing dry solvents
and glassware. Microanalyses were performed by the Micro-
analytical Service of the Instituto de Investigaciones Quımicas
´
(Sevilla, Spain). Infrared spectra were recorded on a Bruker
Vector 22 spectrometer. The NMR instruments were Bruker
Scheme 4 Deuteration of 1-Cl and 1-Br with CD3OD.
c
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DRX-500, DRX-400 and DRX-300 spectrometers. Spectra
were referenced to external SiMe4 (d 0 ppm) using the
residual proton solvent peaks as internal standards (1H NMR
experiments), or the characteristic resonances of the solvent
nuclei (13C NMR experiments), while 31P was referenced to
external H3PO4. Spectral assignments were made by routine
one- and two-dimensional NMR experiments where appropriate.
The crystal structures were determined in a Bruker-Nonius,
X8Kappa diffractometer. Dimer [(Z5-C5Me5)IrCl2]2 was prepared
as described in the literature.18 In the 1H NMR spectra all
aromatic couplings are of ca. 7.5 Hz. 1H NMR simulations
were performed employing the P.H.M. Budzelaar gNMR
V4.01 package, Cherwell Scientific Publishing, Oxford, U.K.
in THF (10 mL) under argon, and heated at 60–70 1C for 12 h
(for 1-Br the reaction mixture was refluxed for three days). The
solvent was then evaporated under reduced pressure and the
resulting residue extracted with CH2Cl2 (1-Br) or with toluene
(3 ꢁ 10 mL for 1-I and 1-SCN). Filtration of the solution and
removal of the solvent under vacuum yielded the desired
complexes in the form of orange (1-Br: 98 mg, 0.15 mmol,
92% yield) or yellow powders (1-I: 91 mg, 0.13 mmol, 80%;
1-SCN: 85 mg, 0.13 mmol, 83%). Crystalline, analytically pure
samples of the compounds were obtained by crystallization
from CH2Cl2/pentane solvent mixtures. The thiocyanate
complex forms as a ca. 85 : 15 mixture of stereomers. Analytical
and spectroscopic data for these compounds are given below.
|
|
[(g5-C5Me5)I r(Cl){PMe(2,6-CH2(Me)C6H3)(2,6-Me2C6H3)}]
(1-Cl)
1-Br
1H NMR (400 MHz, CDCl3, 25 1C) d: 7.32 (d, 1 H, Ha), 7.12,
6.86 (m, 2 H and 1 H, Hd, He, Hf), 7.04 (td, 1 H, JHP =
5
[(Z5-C5Me5)IrCl2]2 (1.53 g, ca. 1.92 mmol) was dissolved in dry
CH2Cl2 (40 mL) in a Schlenk flask with a stir bar. The dark
solution was cooled to 0 1C and PXyl2Me (1.00 g, 3.89 mmol)
dissolved in CH2Cl2 (10 mL) was added, followed by the
addition of 2,2,6,6-tetramethyl piperidine (660 mL, 3.89 mmol).
The reaction mixture was allowed to warm to room temperature
and additionally stirred for 2 h. The solvent was removed
in vacuo and the product extracted with toluene in air. The
solution was evaporated to dryness providing a bright yellow
powder, which was washed with pentane to yield compound
1-Cl as a mixture of two isomers (ca. 7 : 3 ratio; 2.16 g,
3.50 mmol, 90%). Heating this mixture to 40 1C in CH2Cl2/
MeOH (1 : 1) for 2 h provides exclusively the major stereomer
for which characterization data are given below. Crystallization
from CH2Cl2/pentane provides analytically pure samples of
the desired product. Fig. 3 includes labelling for the assignment
of NMR data. 1H NMR (500 MHz, C6D6, 25 1C) d: 7.54
(d, 1 H, Ha), 7.04 (td, 1 H, 5JHP = 1.6 Hz, Hb), 6.89 (td, 1 H,
1.8 Hz, Hb), 6.75 (dd, 1 H, 4JHP = 3.0 Hz, Hc), 3.82 (dd, 1 H,
3
2JHH = 14.9 Hz, JHP = 3.9 Hz, IrCHH), 3.74 (d, 1 H,
2JHH = 14.9 Hz, IrCHH), 2.61, 1.45 (s, 3 H each, Meb, Meg),
2
2.42 (d, 3 H, JHP = 10.2 Hz, PMe), 1.96 (s, 3 H, Mea), 1.49
4
(d, 15 H, JHP = 1.7 Hz, C5Me5). 13C{1H} NMR (100 MHz,
2
CDCl3, 25 1C) d: 157.9 (d, JCP = 31 Hz, C1), 141.4, 139.9
(d, 2JCP = 8 Hz, C4, C6), 140.1 (d, 1JCP = 62 Hz, C2), 139.3 (C3),
131.4 (d, 1JCP = 45 Hz, C5), 129.9, 129.5 (d, J = 8 Hz, CHd,
CHf), 129.6 (CHb), 129.1 (CHe), 127.4 (d, 3JCP = 14 Hz, CHa),
3
2
127.1 (d, JCP = 7 Hz, CHc), 92.1 (d, JCP = 3 Hz, C5Me5),
3
1
25.5, 22.7 (d, JCP = 5 Hz, 7 Hz, Meb, Meg), 21.3 (d, JCP
=
41 Hz, PMe), 20.5 (Mea), 18.6 (IrCH2), 8.2 (C5Me5). 31P{1H}
NMR (160 MHz, CDCl3, 25 1C) d: 7.9. Anal. calcd. for
C27H35BrIrP: C, 48.94; H, 5.32. Found: C, 48.7; H, 5.3%.
1-I
1H NMR (400 MHz, CD2Cl2, 25 1C) d: 7.30 (d, 1 H, Ha), 7.18,
6.91 (m, 2 H and 1 H, Hd, He, Hf), 7.10 (td, 1 H, JHP =
4
3JHP = 1.0 Hz, He), 6.84, 6.62 (dd, 1 H each, JHP = 2.3 Hz,
5
4
Hd, Hf), 6.69 (dd, 1 H, JHP = 2.7 Hz, Hc), 4.15 (dd, 1 H,
1.8 Hz, Hb), 6.83 (dd, 1 H, 4JHP = 2.9 Hz, Hc), 4.04 (dd, 1 H,
3
2
2JHH = 14.5, JHP = 3.8 Hz, IrCHH), 3.87 (d, 1 H, JHH
=
3
2JHH = 14.8 Hz, JHP = 4.7 Hz, IrCHH), 3.76 (d, 1 H,
2JHH = 14.8 Hz, IrCHH), 2.70 (d, 3 H, 2JHP = 10.0 Hz, PMe),
14.5 Hz, IrCHH), 2.35, 1.47 (s, 3 H each, Meb, Meg), 2.28 (d, 3 H,
2JHP = 10.4 Hz, PMe), 1.78 (s, 3 H, Mea), 1.32 (d, 15 H,
4JHP = 1.9 Hz, C5Me5). 13C{1H} NMR (125 MHz, C6D6,
2.60, 1.44 (s, 3 H each, Meb, Meg), 1.98 (s, 3 H, Mea), 1.60
4
(d, 15 H, JHP = 1.7 Hz, C5Me5). 13C{1H} NMR (100 MHz,
2
1
2
25 1C) d: 158.3 (d, JCP = 32 Hz, C1), 140.8 (d, JCP = 61 Hz,
C2), 141.5, 139.9 (d, JCP = 8 Hz, C4, C6), 139.2 (C3), 131.7
CD2Cl2, 25 1C) d: 159.1 (d, JCP = 30 Hz, C1), 141.6, 140.5
2
(C4, C6), 141.3 (1JCP = 60 Hz, C2), 140.2 (C3), 132.1
(d, 1JCP = 44 Hz, C5), 129.4, 129.3 (CHd, CHf), 129.8 (CHb),
1
3
(d, JCP = 44 Hz, C5), 130.4, 129.9 (d, JCP = 8 Hz, CHd,
CHf), 129.8 (CHe), 129.5 (CHb), 127.70 (d, 4JCP = 7 Hz, CHc),
3
128.9 (CHe), 128.0 (CHa), 127.1 (d, JCP = 6 Hz, CHc), 91.7
2
(d, JCP = 2 Hz, C5Me5), 25.0, 22.7 (d, JCP = 4 Hz, 8 Hz,
3
4
1
127.3 (d, JCP = 14 Hz, CHa), 93.0 (C5Me5), 28.2 (d, JCP
=
1
43 Hz, PMe), 26.1, 22.9 (d, 3JCP = 5, 7 Hz, Meb, Meg), 20.8 (Mea),
14.8 (IrCH2), 8.9 (C5Me5). 31P{1H} NMR (160 MHz, CD2Cl2,
25 1C) d: 3.2. Anal. calcd. for C27H35IIrP: C, 45.70; H, 4.97.
Found: C, 45.5; H, 4.6%.
Meb, Meg), 20.8 (Mea), 20.3 (IrCH2), 18.0 (d, JCP = 40 Hz,
PMe), 7.8 (C5Me5). 31P{1H} NMR (200 MHz, C6D6, 25 1C)
d: 11.3. Anal. calcd. for C27H35ClIrP: C, 52.46; H, 5.71.
Found: C, 52.0; H, 6.1%.
The minor diastereomer of compound 1-Cl is characterized
1
by H NMR multiplets with d 4.70 and 3.59 ppm, due to the
1-SCN
IrCH2 protons and by a doublet at 1.47 ppm associated with
the C5Me5 ligand. In the 31P{1H} NMR spectrum a singlet is
recorded with d 7.8 ppm.
IR (Nujol): major diastereomer: n(CN) 2100, n(CS) 795 cmꢀ1
;
minor diastereomer: n(CS) 2123 cmꢀ1. H NMR (400 MHz,
CD2Cl2, 25 1C) d: 7.35 (d, 1 H, Ha), 7.20 (m, 2 H, Hd/f, He),
7.13 (t, 1 H, Hb), 6.93 (m, 1 H, Hd/f), 6.86 (dd, 1 H, 4JCP = 7.2,
2.9 Hz, Hc), 3.55 (d, 1 H, 2JHH = 15.2 Hz, IrCHH), 2.87 (dd,
1
Synthesis of complexes 1-Br, 1-I and 1-SCN
2
3
A mixture of 1-Cl (100 mg, 0.16 mmol), with a ca. ten- or
1 H, JHH = 15.2 Hz, JHP = 4.1 Hz, IrCHH), 2.59, 1.47
1
(s, 3 H each, Meb, Meg), 2.30 (d, 3 H, JCP = 9.8 Hz, PMe),
twenty-fold excess of LiBr, MgI2 or NH4SCN, was suspended
c
2126 New J. Chem., 2011, 35, 2122–2129
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2
(s, 3 H each, Meb, Meg), 2.21 (d, 3 H, JHP = 10.8 Hz,
4
PMe), 1.92 (s, 3 H, Mea), 1.69 (d, 15 H, JHP = 1.5 Hz,
2
C5Me5), ꢀ17.24 (d, 1 H, JHP = 35.2 Hz, Ir-H). 13C{1H}
NMR (100 MHz, C6D6, 25 1C) d: 160.1 (d, 2JCP = 31 Hz, C1),
143.9 (d, JCP = 60 Hz, C2), 141.8, 139.1 (d, JCP = 8 Hz,
1
2
1
C4, C6), 139.3 (C3), 133.0 (d, JCP = 40 Hz, C5), 129.9, 129.7
(d, 3JCP = 7 Hz, CHd, CHf), 129.5 (CHb), 128.6 (CHe), 127.6
3
(d, JCP = 14 Hz, CHa), 127.1 (d, JCP = 6 Hz, CHc), 91.9
3
1
(d, 2JCP = 3 Hz, C5Me5), 31.0 (d, JCP = 44 Hz, PMe), 25.1,
20.9 (d, 3JCP = 4 Hz, Meb, Meg), 21.9 (d, 3JCP = 9 Hz, Mea),
8.7 (C5Me5), 4.3 (IrCH2). 31P{1H} NMR (160 MHz, C6D6,
25 1C) d: 8.3. Anal. calcd. for C27H36IrP: C, 55.55; H, 6.22.
Found: C, 56.0; H, 6.7%.
Fig. 3 Compound 1-Cl labelled for the assignment of 1H and 13C-NMR
signals. The same labelling criteria are used for all complexes.
Only very small amounts of a minor isomer are present in
solutions of compound 2-H. This is characterized by a hydride
4
2.01 (s, 3 H, Mea), 1.52 (d, 15 H, JHP = 1.7 Hz, C5Me5).
13C{1H} NMR (100 MHz, CD2Cl2, 25 1C) d: 157.3 (d, 2JCP
=
=
1
signal with d ꢀ17.57 ppm in the H NMR spectrum and by a
30 Hz, C1), 141.8, 140.8 (d, 2JCP = 8 Hz, C4, C6), 140.2 (d, 2JCP
31P{1H} resonance at 7.70 ppm.
2 Hz, C3), 140.1 (d, 1JCP = 60 Hz, C2), 130.6 (d, 1JCP = 46 Hz,
|
|
3
C5), 130.4, 130.0 (d, JCP = 8 Hz, CHd, CHf), 130.3, 129.9
[(g5-C5Me5)I r(Me){PMe(2,6-CH2(Me)C6H3)(2,6-Me2C6H3)}] (3)
4
(d, JCP = 2 Hz, CHb, CHe), 128.1 (d, JCP = 7 Hz, CHc),
3
A solution of 1-Cl (100 mg, 0.16 mmol) in CH2Cl2 (4 mL) was
cooled to 0 1C and a solution of ZnMe2 in toluene (2 M,
120 mL) was added dropwise. The yellow solution rapidly
cleared up to become nearly colourless. The mixture was
stirred at 20 1C for 1 h, quenched with H2O (10 mL) and the
solvent removed in vacuo to provide crude compound 3 as a
pale yellow solid. The product was extracted with pentane,
concentrated and cooled to ꢀ25 1C. Yellow crystals of
complex 3 were isolated in 63% yield (62 mg, 0.10 mmol).
1H NMR (400 MHz, C6D6, 25 1C) d: 7.56 (d, 1 H, Ha), 7.04
(td, 1 H, 5JHP = 1.8 Hz, Hb), 6.91, 6.70 (m, 2 H each, Hc, Hd
He, Hf), 3.50 (d, 1 H, 2JHH = 15.0 Hz, IrCHH), 2.89 (dd, 1 H,
2JHH = 15.0, 3JHP = 3.2 Hz, IrCHH), 2.32, 1.58 (s, 3 H each,
3
127.5 (d, JCP = 14 Hz, CHa), 121.2 (d, JCP = 4 Hz, SCN),
3
2
94.4 (d, JCP = 3 Hz, C5Me5), 25.5, 22.9 (d, JCP = 6 Hz,
3
1
8 Hz, Meb, Meg), 20.7 (Mea), 18.5 (d, JCP = 41 Hz, PMe),
17.0 (IrCH2), 7.8 (C5Me5). 31P{1H} NMR (160 MHz, CD2Cl2,
25 1C) d: 7.70. Anal. calcd. for C28H35IrNPS: C, 52.48; H,
5.50; N, 2.19; S, 5.00. Found: C, 52.5; H, 5.6; N, 2.2; S, 4.8%.
The minor isomer of compound 1-SCN is characterized by
1H NMR multiplets with d 3.49 and 3.36 ppm, due to the
IrCH2 protons and by a doublet at 2.20 ppm associated with
the PMe methyl group. The signal corresponding to the C5Me5
ligand overlaps with that of the major diastereomer. In the
31P{1H} NMR spectrum a singlet is recorded with d 12.7 ppm.
|
|
2
[(g5-C5Me5)I r(H){PMe(2,6-CH2(Me)C6H3)(2,6-Me2C6H3)}]
(2-H)
Meb, Meg), 1.91 (s, 3 H, Mea), 1.83 (d, 3 H, JHP = 9.4 Hz,
4
PMe), 1.43 (d, 15 H, JHP = 1.5 Hz, C5Me5), 0.35 (d, 3 H,
3JHP = 5.2 Hz, Ir-Me). 13C{1H} NMR (100 MHz, C6D6,
25 1C) d: 159.2 (d, 2JCP = 31 Hz, C1), 142.4 (d, 1JCP = 57 Hz,
C2), 141.8, 139.2 (d, JCP = 8 Hz, C4, C6), 139.6 (C3), 133.6
Compound 1-Cl (100 mg, 0.16 mmol) was dissolved in THF
(5 mL) under an argon atmosphere. A solution of LiAlH4 in
THF (1 M, 0.49 mL) was added via a syringe. The reaction was
heated at 45 1C for 2 h and then quenched with H2O (20 mL).
The solvent was removed under vacuum and the residue
extracted with pentane, then evaporated to dryness to provide
the product as a pale yellow powder (88 mg, 0.151 mmol,
93%). For further purification, recrystallization from pentane
yielded colourless crystals (69 mg, 0.12 mmol) in 73% yield.
The same procedure was followed using LiAlD4 (1 M) in THF
for the preparation of the deuterated material 2-D with a
similar yield. A second procedure for the preparation of
compound 2-H was developed. A solution of 1-Cl (40 mg,
0.065 mmol) in THF (2 mL) was cooled to ꢀ40 1C and a
solution of LitBu in pentane (1.7 M, 50 mL) was added
dropwise. The reaction mixture was allowed to warm gradually
to room temperature and stirred for 4 h. The solvent was
removed in vacuo and the product extracted with pentane, then
evaporated to dryness to provide the hydride as a yellow
powder in 85% crude yield (32 mg, 0.06 mmol). IR (Nujol):
n(Ir–H) 2090 cmꢀ1. 1H NMR (400 MHz, C6D6, 25 1C) d: 7.54
(d, 1 H, Ha), 7.04 (dt, 1 H, 5JHP = 1.6 Hz, Hb), 6.91, 6.70 (m,
2
(d, 1JCP = 42 Hz, C5), 129.9, 129.8 (d, 3JCP = 7 Hz, CHd, CHf),
129.5 (CHb), 128.6 (CHe), 128.5 (d, 3JCP = 6 Hz, CHa), 127.3
3
2
(d, JCP = 6 Hz, CHc), 91.7 (d, JCP = 4 Hz, C5Me5), 25.3,
22.3 (d, 3JCP = 7 Hz, Meb, Meg), 21.0 (d, 3JCP = 9 Hz, Mea),
16.9 (IrCH2), 16.4 (d, 1JCP = 38 Hz, PMe), 8.2 (C5Me5), ꢀ22.9
2
(d, JCP = 8 Hz, Ir-Me). 31P{1H} NMR (160 MHz, C6D6,
25 1C) d: 8.4. Anal. calcd. for C28H38IrP: C, 56.26; H, 6.41.
Found: C, 56.2; H, 6.6%.
|
|
[(g5-C5Me5)I r(CH2SiM3){PMe(2,6-CH2(Me)C6H3)-
(2,6-Me2C6H3)}] (4)
Compound 1-Cl (100 mg, 0.16 mmol) was placed in a Schlenk
flask and dissolved in THF (10 mL) under argon. A solution of
LiCH2SiMe3 (1.78 mL, 0.1 M in pentane) was added at 0 1C
and the mixture was allowed to warm slowly to room
temperature, and then stirred for two hours. The solvent was
evaporated under vacuum and the residue extracted with
pentane and filtered under argon through a pad of silica.
The bright yellow filtrate was evaporated to dryness to yield
the product as a fine yellow powder (69 mg, 0.10 mmol, 64%).
1H NMR (400 MHz, C6D6, 25 1C) d: 7.50 (d, 1 H, Ha), 7.00
2
2 H each, Hc, Hd He, Hf), 3.98 (d, 1 H, JHH = 14.9 Hz,
2
IrCHH), 3.20 (d, 1 H, JHH = 14.9, IrCHH), 2.41, 1.60
c
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5
(td, 1 H, JHP = 1.7 Hz, Hb), 6.90 (m, 2 H, Hd/f, He), 6.66
X-Ray crystallography
(m, 2 H, Hc, Hd/f), 3.47 (m, 2 H, IrCH2), 2.34, 1.47 (s, 3 H
2
Data collections for compounds 1-Cl, 1-SCN, 2-H and 3 were
performed on a Bruker-Nonius X8Apex II CCD diffracto-
meter equipped with graphite-monochromated Mo-Ka
radiation (l = 0.71073 A). Intensity data were collected at
173 K. Empirical absorption corrections were applied using
the SADABS program.19 All structures were solved by direct
methods and refined by full-matrix least squares fitting on F2
by SHELXS-97.20 All non-hydrogen atoms were refined
anisotropically. The Ir-bound hydrogen atom H1Ir, in compound
2-H, was located on a difference Fourier map and refined
without restraints. All hydrogen atoms were placed in
geometrically idealized positions and constrained to ride on
their parent atoms. Crystal data for 1-Cl: C27H35ClIrP,
M = 618.17, monoclinic, a = 8.2431(7) A, b = 8.5307(7) A,
c = 17.2481(14) A, a = 90.001, b = 91.802(2)1, g = 90.001,
V = 1212.28(17) A3, T = 173(2) K, space group P21, Z = 2,
m = 5.695 mmꢀ1, 22 032 reflections measured, 5845 independent
reflections (Rint = 0.0555). The final R1 values were 0.0435
(I 4 2s(I)). The final wR(F2) values were 0.0934 (I 4 2s(I)).
The final R1 values were 0.0586 (all data). The final wR(F2)
values were 0.0988 (all data). The goodness of fit on F2 was
1.051. The Flack parameter was 0.065(12). Crystal data for
each, Meb, Meg), 1.95 (d, 3 H, JHP = 9.4 Hz, PMe), 1.91
(s, 3 H, Mea), 1.37 (d, 15 H, 4JHP = 1.7 Hz, C5Me5), 0.30–0.19
(m, 2 H, IrCH2Si, AB part of ABX system (X = 31P), 0.18
(s, 9 H, SiMe3). The multiplet signal at 0.30–0.19 ppm, which
may be described as the AB part of an ABX system (X = 31P),
has been simulated using gnmr software. The peak distribution
within this region is in agreement with dA = 0.28 and
2
dB = 0.23 ppm, and coupling constants JAB = 13.0,
3
3JAX = 8.9 and JBX = 3.5 Hz. 13C NMR (100 MHz,
2
C6D6, 25 1C) d: 159.7 (d, JCP = 32 Hz, C1), 143.1
(d, JCP = 59 Hz, C2), 141.5, 140.0 (d, JCP = 8 Hz, C4,
1
2
1
C6), 139.4 (C3), 134.0 (d, JCP = 44 Hz, C5), 129.9, 129.6
3
(d, JCP = 8 Hz, CHd, CHf), 129.5, 128.7 (CHb, CHe), 128.1
3
(CHa, overlapped with C6D6), 127.4 (d, JCP = 6 Hz, CHc),
92.6 (d, 2JCP = 4 Hz, C5Me5), 26.1, 23.0 (d, 3JCP = 7 Hz, Meb,
Meg), 21.1 (Mea), 17.9 (d, 1JCP = 39 Hz, PMe), 12.2 (IrCH2),
2
8.4 (C5Me5), 4.2 (SiMe3), ꢀ29.6 (d, JCP = 7 Hz, IrCH2Si).
31P{1H} NMR (160 MHz, C6D6, 25 1C) d: 6.41. Anal. calcd.
for C31H46IrPSi: C, 55.57; H, 6.92. Found: C, 55.6; H, 6.7%.
Hydrogen/deuterium exchange reactions
H/D exchange of complexes 1. Following by 1H NMR
spectroscopy the reaction of compounds 1 with a 1 : 1 mixture
of CD2Cl2 and CD3OD, under argon, a progressive decline in
the intensity of the resonances due to the methylene and
methyl protons of the metallated ligand, and a concomitant
increase of the CD3OH signal was apparent. In a typical
experiment, a solution of 1 (0.01 mmol) in 0.5 mL of a 1 : 1
mixture of CD2Cl2 : CD3OD was heated in an oil bath at 45 1C
(bath temperature). From these experiments a t1/2 value of
490 min was determined for 1-Cl. After ca. 24 h the deuteration
was essentially complete. The velocity of deuteration was
proved to be dependent upon the concentration of CD3OD,
as shown in Table 1.
1-SCN: C28H35IrNPS,
M = 640.80, monoclinic, a =
18.1597(9) A, b = 8.2917(4) A, c = 16.8404(7) A, a =
90.001, b = 95.1430(10)1, g = 90.001, V = 2525.5(2) A3,
T = 173(2) K, space group P21/c, Z = 4, m = 5.449 mmꢀ1
,
53 297 reflections measured, 7644 independent reflections
(Rint = 0.0277). The final R1 values were 0.0372 (I 4 2s(I)).
The final wR(F2) values were 0.0988 (I 4 2s(I)). The final R1
values were 0.0397 (all data). The final wR(F2) values were
0.1001 (all data). The goodness of fit on F2 was 1.093. Crystal
data for 2-H: C27H36IrP, M = 583.73, monoclinic, a =
17.9598(5) A, b = 8.2824(2) A, c = 17.0958(5) A, a =
90.001, b = 111.7080(10)1, g = 90.001, V = 2362.66(11) A3,
T = 173(2) K, space group P21/c, Z = 4, m = 5.730 mmꢀ1
,
The rate of deuteration of 1-Br under the same conditions
is similar to that observed for 1-Cl, whereas no exchange
was observed either for 1-I or for 1-SCN, even by heating at
80 1C.
38 266 reflections measured, 7141 independent reflections
(Rint = 0.0369). The final R1 values were 0.0231 (I 4 2s(I)).
The final wR(F2) values were 0.0519 (I 4 2s(I)). The final R1
values were 0.0326 (all data). The final wR(F2) values were
0.0547 (all data). The goodness of fit on F2 was 1.046. Crystal
data for 3: C28H38IrP, M = 597.75, monoclinic, a = 8.459(4) A,
b = 8.524(4) A, c = 17.285(8) A, a = 90.001, b = 93.025(18)1,
g = 90.001, V = 1244.5(10) A3, T = 173(2) K, space group
P21, Z = 2, m = 5.441 mmꢀ1, 25 407 reflections measured,
7543 independent reflections (Rint = 0.0690). The final R1 values
were 0.0333 (I 4 2s(I)). The final wR(F2) values were 0.0498
(I 4 2s(I)). The final R1 values were 0.0585 (all data). The final
wR(F2) values were 0.0542 (all data). The goodness of fit on F2
was 0.870. Because of an intermediate value of the Flack
parameter compound 3 was refined as a racemic twin using the
TWIN and BASF instructions; the final value of the BASF
parameter was 0.130(7).
H/D exchange of complex 2-H. Deuteration experiments
with 2-H were performed as described above for 1 although in
this case a ca. 10 : 1 mixture of CD2Cl2 : CD3OD was utilized.
Deuteration occurred at room temperature with a half-live of
t1/2 = 130 min. For comparative purposes t1/2 for the H/D
exchange in 1-Cl measured also at 25 1C is ca. 10 days.
Table 1 Dependence of the rate of deuteration of 1-Cl with CD3OD
concentrationa
CD3OD (%)
t1/2/min
25
40
50
60
75
900
560
490
240
180
Acknowledgements
a
Deuteration reactions carried out in an NMR tube at 45 1C with
0.5 mL of a deuterated solvent at variable ratios of CD2Cl2 : CD3OD.
Financial support (FEDER support) from the Spanish Ministerio
de Ciencia e Innovacion (Project No. CTQ2010-17476) and
´
c
2128 New J. Chem., 2011, 35, 2122–2129
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Consolider-Ingenio2010 (No. CSD2007-0000), and the Junta
de Andalucia (Projects Nos FQM-119 and P09-FQM-4832)
is gratefully acknowledged. J.C. thanks the Ministerio de
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