Iridium derivatives of fluorinated aromatics by C-H activation: Isolation of classical and non-classical hydrides

Article abstract of DOI:10.1039/b807077f

A reaction of trans-[Ir(H)₅(PiPr₃)₂] (1) with 2,3,5,6-tetrafluoropyridine, pentafluorobenzene or 1,3-difluorobenzene in the presence of neohexene affords the square-pyramidal C-H activation products cis-trans-[Ir(4-C₅NF₄)(H)₂(PiPr ₃)₂] (2), cis-trans-[Ir(C₆F₅)(H) ₂(PiPr₃)₂] (4) and cis-trans-[Ir(2-C ₆H₃F₂)(H)₂(PiPr₃) ₂] (6). Irradiation of complex 1 with 2,3,5,6-tetrafluoropyridine or pentafluorobenzene gave the hydrides cis-trans-[Ir(4-C₅NF ₄)(H)₂(H₂)(PiPr₃)₂] (3) or cis-trans-[Ir(C₆F₅)(H)₂(H ₂)(PiPr₃)₂] (5). The presence of non-classical bound H₂ moieties has been demonstrated by the measurement of T ₁ times at different temperatures. For 3 the H-H distance in the H₂ ligand can be estimated to be 0.82 A. The dihydride compounds 2, 4 and 6 react with CO to yield the complexes cis-trans-[Ir(Ar)(H) ₂(CO)(PiPr₃)₂] (7: Ar = 4-C₅NF ₄, 8: Ar = C₆F₅, 9: Ar = 2-C₆H ₃F₂). A reaction of 2 or 3 with an excess of ethylene leads to the formation of ethane and the Ir(i) ethylene complex trans-[Ir(4-C₅NF₄)(η²-C₂H ₄)(PiPr₃)₂] (10). Treatment of 10 with CO furnishes the Ir(i) complex trans-[Ir(4-C₅NF₄)(CO) (PiPr₃)₂] (11). The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b807077f

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www.rsc.org/dalton | Dalton Transactions
Iridium derivatives of fluorinated aromatics by C–H activation: isolation of
classical and non-classical hydrides†‡
Marcel Ahijado Salomon,a Thomas Braun*a and Ingo Krossingb
Received 28th April 2008, Accepted 19th June 2008
First published as an Advance Article on the web 11th August 2008
DOI: 10.1039/b807077f
A reaction of trans-[Ir(H)5(PiPr3)2] (1) with 2,3,5,6-tetrafluoropyridine, pentafluorobenzene or
1,3-difluorobenzene in the presence of neohexene affords the square-pyramidal C–H activation
products cis–trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (2), cis–trans-[Ir(C6F5)(H)2(PiPr3)2] (4) and
cis–trans-[Ir(2-C6H3F2)(H)2(PiPr3)2] (6). Irradiation of complex 1 with 2,3,5,6-tetrafluoropyridine or
pentafluorobenzene gave the hydrides cis–trans-[Ir(4-C5NF4)(H)2(H2)(PiPr3)2] (3) or
cis–trans-[Ir(C6F5)(H)2(H2)(PiPr3)2] (5). The presence of non-classical bound H2 moieties has been
demonstrated by the measurement of T1 times at different temperatures. For 3 the H–H distance in the
˚
H2 ligand can be estimated to be 0.82 A. The dihydride compounds 2, 4 and 6 react with CO to yield
the complexes cis–trans-[Ir(Ar)(H)2(CO)(PiPr3)2] (7: Ar = 4-C5NF4, 8: Ar = C6F5, 9: Ar = 2-C6H3F2).
A reaction of 2 or 3 with an excess of ethylene leads to the formation of ethane and the Ir(I) ethylene
2
complex trans-[Ir(4-C5NF4)(h -C2H4)(PiPr3)2] (10). Treatment of 10 with CO furnishes the Ir(I) complex
trans-[Ir(4-C5NF4)(CO)(PiPr3)2] (11).
Oxidative addition reactions of fluorinated pyridines and pyrim-
Introduction
idines at nickel exhibit a strong preference for C–F activation.9
Subsequent derivatization reactions at the metal center can
provide new routes to fluorinated building blocks and fluori-
nated organics.9,10 On the other hand, the intrinsic strength and
kinetic inertness of the metal–carbon bond to a fluorinated
anionic ligand can be employed to stabilize organometallic
compounds, and sometimes allows the identification and isolation
of otherwise unstable complexes.11 We were able to show that
2,3,5,6-tetrafluoropyridine can be activated at [RhH(PEt3)3] to
give the Rh(I) pyridyl complex [Rh(4-C5NF4)(PEt3)3].12 Further
investigations on its reactivity revealed that the rhodium tetraflu-
oropyridyl ligand can be applied as building block for C–C
coupling reactions in the coordination sphere of the metal.12
However, the tetrafluoropyridyl moiety also has a stabilizing
influence on reaction intermediates. This led to the isolation of
The C–F activation of fluoroaromatic compounds has proven to be
a useful tool to access their metal derivatives.1 One critical issue of
these reactions is their chemoselectivity. Very often the activation
of a C–H bond is preferred to C–F bond activation.1–3 Theoretical
investigations on the oxidative addition of 1,2-difluorobenzene at
a cyclopentadienyl rhodium system suggest that the activation of
a C–F bond is energetically favourable, but a high kinetic barrier
5
leads to a preference for C–H activation.4 In contrast [Rh(h -
C5Me5)(H)2(PMe3)] reacts with C6F6, C6F5H, in pyridine–benzene
to give the C–F cleavage products.5 Kinetic studies reveal that
the reactions have autocatalytic character, and fluoride anions
are responsible for the catalysis. They act by deprotonating the
rhodium dihydride, allowing nucleophilic attack of an anionic
rhodium complex at the fluorinated substrate. The iridium or
rhodium catalyzed borylation of pentafluorobenzene gave also
products of C–H activation, whereas a borylation of tetrafluo-
ropyridines at rhodium resulted in derivatives produced by C–
H or C–F activation.6 Ozerov et al. reported that at iridium
complexes bearing anionic pincer ligands, C–Hal (Hal = Cl,
Br) oxidative addition of PhHal is thermodynamically preferred,
but the C–H activation products are kinetically accessible.7 No
products arising from the oxidative addition of the carbon–
fluorine bond in fluorobenzene were observed. C–H activation
reactions of fluorobenzene and difluorobenzenes at {IrCl(PiPr3)2}
are in accordance with that observation.8
1
1
surprisingly stable rhodium(III) h -hydroperoxo and h -silylperoxo
compounds, which are intermediates in the formation of hydrogen
2
peroxide or silyl peroxides from an h -peroxo complex and the
corresponding electrophilic sources.13
In this paper we report on the synthesis of iridium tetrafluo-
ropyridyl and fluoroaryl complexes by thermal or photochemical
C–H activation of 2,3,5,6-tetrafluoropyridine, pentafluorobenzene
or 1,3-difluorobenzene at trans-[Ir(H)5(PiPr3)2] (1). The investiga-
tions led to the isolation of classical and fairly stable non-classical
hydrogen complexes. The isolation of a stable Ir(I) ethylene
complex bearing a tetrafluoropyridyl ligand is also reported.
aHumboldt-Universita¨t zu Berlin, Institut fu¨r Chemie, Brook-Taylor-Str. 2,
12489, Berlin, Germany
Results
bInstitut fu¨r Anorganische und Analytische Chemie, Albert-Ludwigs-
Universita¨t Freiburg, Albertstr. 21, D-79104, Freiburg i. Br., Germany
† Dedicated to Professor Peter Jutzi on the occasion of his 70th birthday.
C–H activation of fluorinated aromatics
‡ Electronic supplementary information (ESI) available: Computational
details of 2, 3 and trans-[Ir(Cl)(H)2(PiPr3)2]. CCDC reference numbers
686375–686378. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b807077f
A reaction of trans-[Ir(H)5(PiPr3)2] (1) with 2,3,5,6-tetrafluoro-
pyridine at reflux conditions (n-hexane) affords the C–H ac-
tivation products cis–trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (2) and
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cis–trans-[Ir(4-C5NF4)(H)2(H2)(PiPr3)2] (3) in a ratio of approx-
imately 3 : 1 after 6 h. Prolonged heating of a hexane solution of
2 and 3 for further 12 h leads to the formation of a pure sample
of 2. Complex 2 can also be produced by a reaction of 1 with
the fluorinated pyridine in the presence of neohexene (Scheme 1).
However, irradiation of complex 1 with 2,3,5,6-tetrafluoropyridine
in benzene or hexane generates the tetrahydride 3 (Scheme 1).
Compound 3 is fairly stable in solution under argon. It can be
converted into 2 by repeatedly bringing solutions of 3 to dryness.
On treatment of 2 with dihydrogen the reverse reaction takes place.
31
Fig. 1 Part of the 1H NMR spectrum (top, 600.1 MHz), 1H{ P} NMR
19
spectrum (middle) and 1H{ F} NMR spectrum (bottom) of 2.
solution is consistent with the molecular structure in the solid
state, the IR spectra and the DFT calculations (vide infra).The
hydrides are characterized by a very rapid exchange on the NMR
time scale. The IR spectrum of 2 exhibits an absorption band at
1935 cm-1 in solution and in the solid state which can be assigned
to a pure Ir–H vibration involving the hydride in the trans position
to the pyridyl ligand. DFT calculations reveal two well separated
absorption bands for Ir–H stretchings at 1939 cm-1 and 2410 cm-1
(very weak). Note that the trigonal-bipyramidal complex trans-
[Ir(Cl)(H)2(PiPr3)2] exhibits an M–H stretch at 2249 cm-1.15 Our
calculations of trans-[Ir(Cl)(H)2(PiPr3)2] reveal bands at 2247 cm-1
and 2285 cm-1, which correspond to an asymmetric and symmetric
vibration of the IrH2 unit.
The molecular structure of 2 was also confirmed by X-ray
diffraction analysis at 100 K (Fig. 2). Suitable crystals have been
obtained from a hexane solution at 243 K. Selected bond lengths
and angles are summarised in Table 1. The molecular structure
reveals a square pyramidal configuration with the expected trans
disposition of the phosphine ligands. The hydrides at iridium have
been located and found to be in a cis position, one of them at the
apical vertex of the square pyramid. The separation between H(19)
Scheme 1 C–H activation reactions of fluorinated arenes at 1.
In a comparable manner as described above the com-
plexes cis–trans-[Ir(C6F5)(H)2(PiPr3)2] (4) and cis–trans-[Ir(C6F5)-
(H)2(H2)(PiPr3)2] (5) are accessible (Scheme 1). Compound 5 is less
stable than 3 and can be detected in solution, only. Evaporation
of a hexane solution of 5 leads to the formation of 4. Treatment of
4 with H2 gives pentafluorobenzene, 1 and 5. A reaction of 1 with
1,3-difluorobenzene furnishes selectively the dihydride complex
cis–trans-[Ir(2-C6H3F2)(H)2(PiPr3)2] (6) and no generation of a
tetrahydride has been observed. As a matter of fact, 6 reacts
with H2 to yield 1 and 1,3-difluorobenzene. Note that the C–H
activation reaction occurs at the 2-position of the aromatic ring,
whereas {IrCl(PiPr3)2} leads to activation products with the metal
at the 4-position.8 Photochemical activation of 1,3-difluorbenzene
with [CpRh(PPh3)(C2H4)] gives the C–H activation product with
the metal at the 2-position.3
1
The 31P{ H} NMR spectrum of 2 displays a singlet at d 52.0
for the phosphines in the mutually trans position. The 19F NMR
spectrum depicts two resonances for the tetrafluoropyridyl ligand.
The integration of the signals for the isopropyl groups and a
1
resonance at d -28.09 in the H NMR spectrum suggests the
presence of two hydrido ligands, compatible with either equivalent
hydrides or a fluxional structure. The fluorine decoupled spectrum
of 2 reveals a proton–phosphorus coupling of 15 Hz (Fig. 1). Low
temperature 1H NMR spectra did not lead to decoalescence. The
longitudinal T1 spin lattice relaxation times for the hydrides in 2
1
were determined by H NMR spectroscopy between 193 K and
263 K. All data indicate the presence of classical hydrido ligands.14
The T1 at 233 K is 300 ms at 600 MHz. Comparable data have been
obtained for the dihydrides 4 and 6. At 223 K values of 420 ms
and 440 ms have been found, respectively. For 2, 4 and 6 we favor
a square-pyramidal geometry with a cis-hydrido configuration.
This assumption is reasonable, because such a configuration in
Fig. 2 An ORTEP diagram of 2. Ellipsoids are drawn at the 50%
probability level.
5198 | Dalton Trans., 2008, 5197–5206
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) in cis–trans-[Ir(4-
C5NF4)(H)2(PiPr3)2] (2) with estimated standard deviations in parentheses
Ir(1)–C(19)
Ir(1)–H(19)
Ir(1)–H(20)
Ir(1)–P(1)
2.144(4)
1.55(2)
1.56(2)
2.3209(9)
2.3303(9)
1.327(5)
1.316(5)
1.396(5)
C(19)–C(20)
C(20)–C(21)
C(22)–C(23)
F(1)–C(20)
F(2)–C(21)
F(3)–C(22)
F(4)–C(23)
1.404(5)
1.382(5)
1.390(5)
1.374(4)
1.352(4)
1.357(4)
1.378(4)
Ir(1)–P(2)
N(1)–C(21)
N(1)–C(22)
C(19)–C(23)
P(1)–Ir(1)–P(2)
167.37(4)
96.21(9)
96.41(9)
87(2)
85(1)
93(1)
176(2)
85(2)
97(2)
P(2)–Ir(1)–H(20)
C(22)–N(1)–C(21)
N(1)–C(21)–C(20)
N(1)–C(22)–C(21)
C(23)–C(19)–C(20)
C(23)–C(19)–Ir(1)
C(20)–C(19)–Ir(1)
C(21)–C(20)–C(19)
C(22)–C(23)–C(19)
83(2)
C(19)–Ir(1)–P(1)
C(19)–Ir(1)–P(2)
H(19)–Ir(1)–H(20)
P(1)–Ir(1)–H(19)
P(2)–Ir(1)–H(19)
C(19)–Ir(1)–H(20)
P(1)–Ir(1)–H(20)
C(19)–Ir(1)–H(19)
115.1(3)
124.0(4)
124.0(4)
110.7(3)
122.4(3)
126.8(3)
123.0(4)
123.2(4)
Fig. 3 Plot of lnT1 vs. 1/H for complex 3.
3 on partial deuteration of the hydride sites (d -9.23, -8.96 and
-8.81). This could be explained by a non-statistical site-preference
of the deuterium consistent with a perturbation of the equilibrium
between the different hydride sites rather than a simple isotope
effect.17 Solid state ATR IR spectra of 3 exhibit absorption bands
at 2046 and 2192 cm-1, which we assign to vibration modes of the
iridium hydrides, which are bound in a classical mode. For the
isotopologue cis–trans-[Ir(4-C5NF4)(D)2(D2)(PiPr3)2] (3b) these
bands disappear. DFT calculations of 3 give bands at 1990 cm-1
and 2275 cm-1 which can be assigned to pure Ir–H stretchings.
They correspond to the Ir–H bonds in the trans position to
˚
and H(20) is 2.144 A. The dihedral angle between the plane defined
by the pyridyl ring and the coordination plane of the metal defined
by Ir1, C19, P1 and P2 is 73.8◦. The iridium–carbon distance is
˚
˚
2.144(4) A. For comparison, the Ir–C separation of 2.010(5) A
in the complex trans-[Ir(Cl)(H)(Ph)(PiPr3)2], which exhibits a
distorted trigonal-bipyramidal structure, is in a similar range.16
Complex 3 was characterized by its spectroscopic data. The 1H
NMR spectrum displays a broad signal at d -9.36, which can be
assigned to the metal bound hydrogen nuclei. The signal stays
broad even at 193 K (600 MHz) indicating a very low barrier
for hydrogen exchange. Comparable observations have been made
for the hydrides cis–trans-[Ir(X)(H)2(H2)(PiPr3)2] (X = Cl, Br, I).15
Measurement of the T1 times for 3 at different temperatures H
reveal a minimum at 233 K with a T1 = 39 ms (600 MHz). This
demonstrates the presence of dihydrogen bound in a non-classical
mode.14 However, the plot ln T1 vs. 1/H does not follow the typical
V-shaped curve as a result of exchange between classical and
non-classical hydride sites (Fig. 3).14 Comparable data have been
obtained for the tetrahydride 5 (T1 = 20 ms at 233K (600 MHz)).
Another indication for the presence of classical and non-classical
moieties in 3 is given by the downfield isotope shifts of the signals
2
the pyridyl unit and in the trans position to the h -H2 ligand,
respectively.
The geometries of 2 and 3 were further examined by density
functional theory {RI-DFT, BP86, SV(P)}. The optimized struc-
tures are shown in Fig. 4. The calculations reproduce correctly
the geometries and bonding modes which have been proposed
for 2 and 3 on the basis of the analytical data. The calculated
bond lengths and angles of 2 compare reasonable well with
those determined by the X-Ray diffraction analysis. A trigonal-
bipyramidal geometry for 2 seems not to be a minimum structure.
In contrast, the optimized structure of the chloro complex
trans-[Ir(Cl)(H)2(PiPr3)2] reveals a trigonal-bipyramidal geometry
1
in the H NMR spectrum of the d1, d2 and d3 isotopologues of
Fig. 4 BP86/SV(P) optimized structure of cis–trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (2) and cis–trans-[Ir(4-C5NF4)(H)2(H2)(PiPr3)2] (3).
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(Fig. 5). This result is in good agreement to the calculations
of trans-[Ir(Cl)(H)2(PH3)2] and trans-[Ir(Cl)(H)2(PMe3)2] as well
as to results from neutron diffraction experiments for trans-
[Ir(Cl)(H)2(PtBu2Ph)2], which also reveal trigonal-bipyramidal
structures.18
IR spectrum of 7 exhibits two absorption bands at 2161 and
2079 cm-1 for the hydride vibrations, as well as an absorption
band at 1979 cm-1 which can be assigned to the CO–ligand.8,19 We
note that Werner et al. reported similar IR data for the complex
cis–trans-[Ir(Cl)(H)2(CO)(PiPr3)2] (2205, 2100, 1965 cm-1).8 The
spectroscopic data for 8 and 9 are comparable to these found
for 7.
The structures of the octahedral complexes 7 and 9 were
determined by X-ray diffraction at 100 K (Fig. 6 and 7). Selected
bond lengths and angles are summarised in Table 2 (7) and Table 3
(9). The structure found for 9 confirms the configuration which
has been suggested for 9 as well as for 6, with the iridium in the
ortho position to the fluorines at the arene ligand. Neither the
˚
iridium–carbon distance in 7 to the C5NF4 unit of 2.143(5) A nor
˚
the iridium–carbon distance to the arene in 9 of 2.161(2) A show
˚
a significant difference to the Ir–C distance in 2 (2.137(3) A).
A reaction of 2 with an excess of ethylene leads within hours
to the formation of ethane and the Ir(I) ethylene complex trans-
2
[Ir(4-C5NF4)(h -C2H4)(PiPr3)2] (10) (Scheme 2). The 19F NMR
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) in cis–trans-[Ir(4-
C5NF4)(H)2(CO)(PiPr3)2] (7) with estimated standard deviations in
parentheses
Fig. 5 BP86/SV(P) optimized structure of cis–trans-[Ir(Cl)(H)2(PiPr3)2].
Ir–C(19)
Ir–C(20)
Ir–P(1)
Ir–P(2)
C(20)–C(24)
C(20)–C(21)
C(21)–C(22)
C(23)–C(24)
1.923(5)
2.143(5)
2.338(1)
2.345(1)
1.381(8)
1.404(8)
1.356(8)
1.371(8)
N(1)–C(23)
N(1)–C(22)
C(19)-O(1)
F(1)–C(21)
F(2)–C(22)
F(3)–C(23)
F(4)–C(24)
1.306(8)
1.309(8)
1.146(6)
1.367(7)
1.368(6)
1.357(6)
1.368(6)
Reactivity of the dihydride complexes 2, 4 and 6
The dihydride compounds 2, 4 and 6 react with CO to afford the
complexes cis–trans-[Ir(Ar)(H)2(CO)(PiPr3)2] (7: Ar = 4-C5NF4,
8: Ar = C6F5, 9: Ar = 2-C6H3F2) within seconds (Scheme 2). The
C(19)–Ir(1)–C(20)
C(19)–Ir(1)–P(1)
C(19)–Ir(1)–P(2)
C(20)–Ir(1)–P(1)
C(20)–Ir(1)–P(2)
P(1)–Ir(1)–P(2)
98.4(2)
95.3(2)
95.6(2)
95.2(1)
94.9(1)
163.89(5)
123.5(5)
113.7(5)
C(24)–C(20)–C(21)
C(24)–C(20)–Ir(1)
C(21)–C(20)–Ir(1)
C(22)–C(21)–C(20)
N(1)–C(22)–C(21)
N(1)–C(23)–C(24)
O(1)–C(19)–Ir(1)
109.9(5)
125.6(4)
124.5(4)
122.8(5)
125.4(5)
124.7(5)
174.3(4)
1
31P{ H} NMR spectrum of 7 reveals a singlet at d 30.6, which
can be assigned to the trans phosphines. The presence of four
signals in the 19F NMR spectrum indicates a hindered rotation
1
of the tetrafluoropyridyl ligand about the Ir–C bond.13 The H
NMR spectrum shows two signals for the hydrides at the iridium
center, confirming a cis configuration of the hydride nuclei. The
C(23)–C(24)–C(20)
C(23)–N(1)–C(22)
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) in cis–trans-[Ir(2-
C6H3F2)(H)2(CO)(PiPr3)2] (9) with estimated standard deviations in
parentheses
Ir(1)–C(25)
Ir(1)–C(19)
Ir(1)–P(1)
1.912(2)
2.161(2)
2.3337(5)
2.3339(5)
1.50(3)
1.58(3)
1.146(2)
1.397(3)
C(19)–C(20)
C(20)–C(21)
C(21)–C(22)
C(22)–C(23)
C(23)–C(24)
F(1)–C(20)
F(2)–C(24)
1.397(3)
1.384(3)
1.383(3)
1.381(4)
1.389(3)
1.380(2)
1.374(3)
Ir(1)–P(2)
Ir(1)–H(1A)
Ir(1)–H(1B)
O(1)–C(25)
C(19)–C(24)
H(1A)–Ir(1)–H(1B)
C(25)–Ir(1)–H(1A)
C(25)–Ir(1)–H(1B)
C(25)–Ir(1)–C(19)
C(25)–Ir(1)–P(1)
C(25)–Ir(1)–P(2)
C(19)–Ir(1)–H(1A)
C(19)–Ir(1)–H(1B)
C(19)–Ir(1)–P(1)
C(19)–Ir(1)–P(2)
P(1)–Ir(1)–H(1A)
P(1)–Ir(1)–H(1B)
81(1)
172(1)
91(1)
98.54(8)
95.67(7)
95.62(7)
90(1)
170(1)
94.93(5)
95.29(5)
82(1)
P(1)–Ir(1)–P(2)
163.47(2)
86(1)
83(1)
P(2)–Ir(1)–H(1A)
P(2)–Ir(1)–H(1B)
C(24)–C(19)–Ir(1)
C(20)–C(19)–Ir(1)
C(24)–C(19)–C(20)
C(21)–C(20)–C(19)
C(22)–C(21)–C(20)
C(23)–C(22)–C(21)
C(22)–C(23)–C(24)
C(23)–C(24)–C(19)
O(1)–C(25)–Ir(1)
125.7(2)
124.6(2)
109.7(2)
127.5(2)
118.1(2)
119.1(2)
118.7(2)
126.8(2)
174.0(2)
Scheme 2 Reactivity of dihydride complexes 2, 4 and 6 towards ethylene
and CO.
85(1)
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Table 4 Selected bond lengths (A) and angles (◦) in trans-[Ir(4-
˚
2
C5NF4)(h -C2H4)(PiPr3)2] (10) with estimated standard deviations in
parentheses
Ir(1)–C(21)
Ir(1)–C(19)
Ir(1)–C(20)
Ir(1)–P(2)
2.083(2)
2.149(2)
2.181(2)
2.3679(5)
2.3684(5)
1.304(4)
1.309(4)
1.390(3)
C(21)–C(25)
C(21)–C(22)
C(22)–C(23)
C(24)–C(25)
F(1)–C(22)
F(2)–C(23)
F(3)–C(24)
F(4)–C(25)
1.392(3)
1.394(3)
1.375(3)
1.386(3)
1.367(3)
1.350(3)
1.348(3)
1.351(3)
Ir(1)–P(1)
N(1)–C(24)
N(1)–C(23)
C(19)–C(20)
C(19)–Ir(1)–P(1)
C(19)–Ir(1)–P(2)
C(19)–Ir(1)–C(20)
C(20)–Ir(1)–P(2)
C(20)–Ir(1)–P(1)
C(21)–Ir(1)–C(19)
C(21)–Ir(1)–C(20)
C(21)–Ir(1)–P(2)
90.18(5)
90.22(5)
37.45(8)
90.92(5)
89.71(5)
155.38(8)
167.08(8)
90.49(5)
C(21)–Ir(1)–P(1)
P(2)–Ir(1)–P(1)
88.93(5)
179.35(2)
124.7(3)
124.9(3)
122.8(2)
122.3(2)
114.4(2)
110.8(2)
N(1)–C(23)–C(22)
N(1)–C(24)–C(25)
C(23)–C(22)–C(21)
C(24)–C(25)–C(21)
C(24)–N(1)–C(23)
C(25)–C(21)–C(22)
Fig. 6 An ORTEP diagram of 7. Ellipsoids are drawn at the 50%
probability level.
Fig. 8 An ORTEP diagram of 10. Ellipsoids are drawn at the 50%
probability level.
Fig. 7 An ORTEP diagram of 9. Ellipsoids are drawn at the 50%
probability level.
(Scheme 2). The 19F NMR spectrum of 11 shows two multiplets
in a ratio of 1 : 1 at d -98.8 and -113.3 for the four fluorine
atoms of the pyridyl ligand. The IR spectrum of 11 exhibits an
absorption band at 1949 cm-1 for the CO–ligand, consistent with
the presence of an Ir(I) compound. Note, that this IR-band appears
at higher energy in comparison to the corresponding bands in
trans-[Ir(X)(CO)(PiPr3)2] (X = Cl, Br, I: 1935, 1935, 1938 cm-1,
respectively).21 This suggests less electron density at the iridium
center for the tetrafluoropyridyl complex 11.
spectrum exhibits two multiplets in a ratio of 1 : 1 at d -100.5 and
-114.4 for the four fluorine atoms of the pyridyl ligand. The H
1
NMR spectrum shows a triplet at d 2.34 for the C2H4 ligand, with a
H,P coupling constant of 4.2 Hz. The proposed structure of 10 was
also confirmed by X-ray crystallography (Fig. 8). Suitable crystals
were grown at 243 K from a hexane solution. Selected bond lengths
and angles are summarised in Table 4. The molecular structure
reveals a slightly distorted trigonal-bipyramidal geometry with
the expected trans disposition of the phosphine ligands. The
plane which is defined by the Ir and the ethylene ligand is
almost perpendicular to the P–Ir–P axis. Thus, the carbon–
iridium–phosphorus angles are 88.93(5)◦ and 90.49(5)◦, indicating
a nearly perfectly arranged plane of the three carbon atoms C19–
C21 between the phosphorus atoms. The C–C separation in the
Discussion
The syntheses of the complexes cis–trans-[Ir(Ar)(H)2(PiPr3)2] (2:
Ar = 4-C5NF4, 4: Ar = C6F5, 6: Ar = 2-C6H3F2) by C–H
activation of the fluorinated arenes ArH at trans-[Ir(H)5(PiPr3)2]
(1) are shown in Scheme 1. In accordance to studies on the C–H
activation of difluorobenzenes at {IrCl(PiPr3)2}, we did not
observe any C–F activation of the fluorinated substrates.8 As
suggested by Goldman and Halpern, we assume that the formation
˚
ethylene ligand is with 1.390(3) A identical with the analogous
2
20
˚
distance in trans-[Ir(Cl)(h -C2H4)(PPh3)2] (1.375(10) A).
Treatment of 10 with CO furnishes the Ir(I) complex trans-[Ir(4-
C5NF4)(CO)(PiPr3)2] (11) by replacement of the ethylene ligand
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of trans-[Ir(H)3(PiPr3)2] is the initial step for the C–H activa-
tion reactions.22 Nevertheless, a competition experiment with 1,
neohexene and equimolar amounts of 2,3,5,6-tetrafluoropyridine,
pentafluorobenzene and 1,3-difluorobenzene reveals a preference
for the formation of 2 over 4 (ratio 4 : 1), whereas no formation of
6 was observed, indicating that the loss of dihydrogen is not the
rate-determining step in the formation of the iridium dihydrides.
A few examples of C–H activation reactions at 1 are known,
among them is the C–H activation of indene yielding cis–cis-
NMR spectra at room temperature. A 1H NMR EXSY spectrum
(400 MHz) of a mixture of 2 and 3 shows cross-peaks for the
hydrides confirming exchange of hydrogen between these two
compounds.
NMR-relaxation experiments show a very short T1-relaxation
time for 3 and 5 (Fig. 3). The data represent population-weighted
average values for all four hydrogens, but nevertheless indicate
the presence of a non-classical bound hydrogen molecule. The
T1,non-classic time at 233 K for the non-classical hydrides in 3 can be
calculated by eqn (1)14
[Ir(h -C9H7)(H)2(PiPr3)2] and [Ir(h -C9H7)(H)2(PiPr3)].23 The C–
H activation of alkynes and olefins at 1 has also been observed.23,24
No C–H activation of fluorinated arenes have been known at
1, but Smith III et al. succeeded in derivatizing C–H bonds of
pentafluoro- and 1,3,5-trifluorobenzene with 4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (pinacolborane = HBpin) to give C6F5(Bpin)
and C6F3H(Bpin) (pin = O2C2Me4) using [Cp*Ir(PMe3)(H)2] as a
catalyst.6
3
5
-1
-1
-1
(a + b)(T1,min
)
= a(T1,classic
)
+ b(T1,non-classic
)
(1)
where a is the number of classical bound H-atoms and b is the
number of non-classical bound H-atoms.
As an estimation of T1,classic of complex 3 we used the T1 of the
hydrides in cis–trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (2) at 233 K, which
is 300 ms at 600 MHz. This assumption leads with T1,min = 39 ms
to a longitudinal relaxation time T1,nonclassic of 20 ms (600 MHz)
for the non-classical hydrogens in 3. If dipole–dipole interactions
are the main contributors for the hydride relaxation, the H–H
A photochemical approach allows the selective synthesis of
the tetrahydrides cis–trans-[Ir(4-C5NF4)(H)2(H2)(PiPr3)2] (3) and
cis–trans-[Ir(4-C6F5)(H)2(H2)(PiPr3)2] (5). Whereas the complexes
3 and 5 are also accessible by reactions of cis–trans-[Ir(4-
C5NF4)(H)2(PiPr3)2] (2) or cis–trans-[Ir(C6F5)(H)2(PiPr3)2] (4)
withdihydrogen, treatment of cis–trans-[Ir(2-C6H3F2)(H)2(PiPr3)2]
(6) with dihydrogen leads to the generation of 1 and 1,3-
difluorobenzene, only. A tetrahydride with the C6H3F2 ligand
could not be detected. The tetrahydrides 3 and 5 are stable at room
temperature, and 3 is in contrast to trans-[IrX(H)2(H2)(PiPr3)2]
(X = Cl, Br, I) even stable without a hydrogen atmosphere.15 The
higher stability of 3 in comparison to trans-[IrX(H)2(H2)(PiPr3)2]
can be attributed to the stabilizing properties of the C5NF4
ligand.11–13 The p-acceptor properties of C5NF4, which would be
conceivable for 2 and 3, are not supported by the shapes of the
HOMO or HOMO-1 in 2 or 3. Although the C5NF4 ligand seems
not to be a p-acceptor at iridium(III), it is also not a p-donor such
as halogen ligands. Note that in contrast to the square-pyramidal
geometry found for 2, the complexes cis–trans-[Ir(X)(H)2(PiPr3)2]
exhibit a trigonal-bipyramidal structure, which is favoured for
X = p-donor ligands.18 We believe that the stabilizing influence
of the fluorinated ligands at our Ir(III) compounds are due
to s- rather than p-interactions.11 Pyridyl ligands as well as a
fluorinated organyl group are electron withdrawing and have
higher group electronegativities which results in a stronger metal–
carbon bond.11
˚
distance in the metal bound H2 can be estimated to be 0.82 A for
2
˚
the case of a rapid rotation of h -H2 at the metal centre (1.04 A
for a slow rotation).14,27 This value is nearly identical with the
˚
H–H distance in trans-[Ir(I)(H)2(H2)(PiPr3)2] of 0.856(9) A which
has been determined by neutron diffraction analysis.28 The DFT
˚
calculations for 3 reveal a H–H separation of 0.88 A.
The hydride ligands in 2 or 3 can be removed on treatment
2
with ethylene yielding trans-[Ir(4-C5NF4)(h -C2H4)(PiPr3)2] (10)
(Scheme 2). A reaction of 10 with H2 refurnishes a mixture
of 2 and 3. Note that Werner et al. reported the synthesis of
2
the iridium(I) ethylene complex trans-[Ir(Me)(h -C2H4)(PiPr3)2],
which also features an anionic carbon ligand.29 The dihydride
complexes 2, 4 and 6 react readily with CO, yielding the octahedral
complexes cis–trans-[Ir(Ar)(H)2(CO)(PiPr3)2] (7: Ar = 4-C5NF4, 8:
Ar = C6F5, 9: Ar = 2-C6H3F2). The compounds are fairly stable
and do not lose hydrogen to give iridium(I) carbonyls. However,
11 can be synthesized on treatment of the ethylene complex 10
with CO.
Conclusions
The 1H NMR spectra of 3 and 5 at 193 K at 600 MHz
show only one signal for the four hydrides. This reflects a very
low kinetic barrier for hydrogen exchange at the metal center.
In conclusion, we presented new carbon–hydrogen activation
reactions of fluorinated compounds at Ir. In contrast to the
trigonal-bipyramidal complexes trans-[Ir(X)(H)2(PR3)2] (X = Cl,
Br, I), the dihydride species feature a square-pyramidal geometry.
This has been predicted for a {Ir(H)2(PR3)2} fragment with an
additional anionic ligand which is not a p-donor, but has never
been observed before.18 In addition, the fluorinated ligands have a
stabilizing influence. This allows the preparation of non-classical
hydrido complexes which also feature two hydrides bound in a
classical fashion. The compounds are highly dynamic involving
exchange of all four hydrogen nuclei. For future investigations,
2
Decoalescence into separate resonances for the h -H2 and the
classical hydrides could not be achieved at low temperature. The
exchange process might involve an oxidative addition/reductive
elimination pathway via an Ir(V) compound.25 However, direct
hydrogen-transfer steps from a non-classical bound H2 to a metal
hydride are also conceivable. This resembles a mechanism which
has recently been discussed as s-CAM (s-CAM = s-complex-
assisted-metathesis).26 The reversible loss of H2 from 3 or 5 to
give the dihydrides 2 or 4, respectively, suggests an additional
exchange process with free hydrogen. However, in contrast to
trans-[Ir(Cl)(H)2(H2)(PiPr3)2] this process is slow on the NMR
time scale, because separate resonances for the tetrahydride 3 and
the dihydride 2 as well as for 5 and 4 can be observed in the
2
the ethylene complex trans-[Ir(4-C5NF4)(h -C2H4)(PiPr3)2] (10)
might be a valuable starting compound for various trans-
formations such as C–H activation and C–C coupling reac-
tions.29,30
5202 | Dalton Trans., 2008, 5197–5206
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(IrH2); 1H NMR (500 MHz, C6D6): d 2.04 (m, 6 H, CH), 0.92 (m,
36 H, CH3), -28.09 (tt, JHP = 15.3 Hz, JHF = 7.5 Hz, 2 H, IrH);
19F NMR (470.4 MHz, C6D6): d -138.6 (m, 2 F), -153.6 (m, 1 F),
Experimental
[D6]Benzene and [D8]toluene were dried by stirring over potassium
and then distilled under vacuum. 2,3,5,6-Tetrafluoropyridine,
pentafluorobenzene and 1,3-difluorobenzene were obtained from
Aldrich and distilled before use; trans-[Ir(H)5(PiPr3)2] (1) was
prepared according to the literature.31
1
-161.8 (m, 2 F); 31P{ H} NMR (202.4 MHz, C6D6): d 51.8 (s).
Formation of cis–trans-[Ir(C6F5)(H)2(H2)(PiPr3)2] (5)
The NMR spectra were recorded on a Bruker DRX 500 or
Bruker Avance 600 spectrometer at 300 K. The 1H NMR chemical
shifts were referenced to residual C6D5H at d = 7.15 or [D7]toluene
at d = 2.09 ppm. The 13C NMR chemical shifts were referenced to
C6D6 at d = 128.0 ppm. The 19F NMR spectra were referenced to
A solution of 1 (50 mg, 0.1 mmol), pentafluorobenzene (0.03 mL,
0.2 mmol) in 0.5 mL [D8]toluene was transferred into a quartz-
NMR-tube. The reaction mixture was irradiated for 4 h at room
temperature. According to the NMR data, the solution contained
-1
1
˜
5 and 1 in a ratio of 90 : 10. n(ATR)/cm 2176, 2104 (IrH2); H
NMR (500 MHz, [D8]toluene): d 1.65 (m, 6 H, CH), 1.09 (m, 36 H,
CH), -9.46 (s, br, 4 H, IrH); 19F NMR (470.4 MHz, [D8]toluene):
1
external C6F6 at d = -162.9 ppm. The 31P{ H} NMR spectra were
referenced externally to H3PO4 at d 0.0 ppm. Infrared spectra
were recorded on a Bruker Vector 22 spectrometer. Preparative
irradiation experiments were carried out with a Hanau TQ 150
immersion mercury lamp with 25 W.
1
d -98.5 (m, 2 F), -163.4 (m, 1 F), -163.9 (m, 2 F); 31P{ H} NMR
(202.4 MHz, [D8]toluene): d 33.0 (s).
Synthesis of cis–trans-[Ir(H)2(2-C6H3F2)(PiPr3)2] (6)
Synthesis of cis–trans-[Ir(H)2(4-C5NF4)(PiPr3)2] (2)
A solution of 1 (200 mg, 0.4 mmol) and neohexene (0.12 ml,
1.0 mmol) in 1,3-difluorobenzene (10 mL, 100 mmol) was heated
to reflux for 10 h. The solution turned orange within the first hour.
The volatiles were removed in vacuo. The residue was then
extracted with n-hexane (10 mL) and the extract was brought to
dryness to give an orange oil. Yield 150 mg (59%). A comparable
preparation without neohexene leads to a mixture of 6 and 1 in a
ratio of 4 : 1 according to the NMR data of the reaction solution.
A solution of 1 (520 mg, 1.0 mmol), neohexene (0.25 ml, 2.1 mmol)
and 2,3,5,6-tetrafluoropyridine (0.2 mL, 2.0 mmol) in 20 mL n-
hexane was heated to reflux for 6 h. The solution turned orange
within one hour. The volatiles were removed in vacuo to give
an orange powder, which was dissolved in 5 mL n-hexane. The
solution was stored at -30 ◦C to obtain 2 as orange crystals. Yield
558 mg (84%). A comparable transformation without neohexene
leads to a mixture of 2 and 3 in a ratio of 3 : 1 according to the
NMR data of the reaction solution. Analytical data for 2. Found:
C, 41.31; H, 6.69; N, 2.11. C23H44F4IrNP2 requires C, 41.49; H,
-1
1
˜
n(ATR)/cm 1945 (IrH2); H NMR (500 MHz, C6D6): d 6.91–
6.87 (m, 3 H, C6H3F2), 2.14 (m, 6 H, CH), 1.02 (m, 36 H, CH3),
-28.62 (tt, JHP = 16.3 Hz, JHF = 7.9 Hz, 2 H, IrH); 19F NMR
6.67; N 2.10); n(ATR)/cm 1935 (IrH2); H NMR (500 MHz,
(470.4 MHz, C6D6): d -85.1 (m); 31P{ H} NMR (202.4 MHz,
-1
1
1
˜
C6D6): d 1.96 (m, 6 H, CH), 0.86 (m, 36 H, CH3), -28.09 (tt, JHP
=
C6D6): d 51.9 (s).
15.3 Hz, JHF = 7.5 Hz, 2 H, IrH); 19F NMR (470.4 MHz, C6D6):
1
d -100.0 (m, 2 F), -119.3 (m, 2 F); 31P{ H} NMR (202.4 MHz,
Competition experiment of the reaction of 1 with 2,3,5,6-
tetrafluoropyridine, pentafluorobenzene and 1,3-difluorobenzene
C6D6): d 52.0 (s).
A mixture of 1 (150 mg, 0.3 mmol), neohexene (0.2 ml, 1.7 mmol),
2,3,5,6-tetrafluoropyridine (0.10 mL, 1.0 mmol), pentafluoroben-
zene (0.12 mL, 1.0 mmol) and 1,3-difluorobenzene (0.10 mL,
1.0 mmol) in 10 mL n-hexane was heated to reflux for 6 h.
The solution turned orange within one hour. The volatiles were
removed in vacuo to give an orange powder which consists of 2
and 4 in a ratio of approximately 4 : 1 according to the NMR data.
There is no indication for the formation of 6.
Formation of cis–trans-[Ir(4-C5NF4)(H)2(H2)(PiPr3)2] (3)
Complex 1 (50 mg, 0.1 mmol), 2,3,5,6-tetrafluoropyridine
(0.03 mL, 0.3 mmol) and 0.5 mL [D6]benzene were transferred into
a quartz-NMR-tube. The reaction mixture was irradiated for 4 h
at room temperature. According to the NMR data, the solution
-1
˜
contained 3 and 1 in a ratio of 95 : 5. n(ATR)/cm 2192, 2046
(IrH2); 1H NMR (500 MHz, C6D6): d 1.60 (m, 6 H, CH), 0.87 (m,
36 H, CH3), -9.36 (s, br, 4 H, IrH); 19F NMR (470.4 MHz, C6D6):
d -98.7 (m, 2 F), -104.4 (m, 2 F); 31P{ H} NMR (202.4 MHz,
1
Synthesis of cis–trans-[Ir(H)2(4-C5NF4)(CO)(PiPr3)2] (7)
C6D6): d 33.7 (s).
CO gas was bubbled for a few seconds into an orange solution of
2 (90 mg, 0.14 mmol) in 10 mL n-hexane until the solution turned
colourless. After removing the volatiles in vacuo, the colourless
residue was d◦issolved in 5 mL n-hexane and the solution was
stored at -30 C to obtain colourless crystals of 7. Yield: 90 mg
Synthesis of cis–trans-[Ir(H)2(C6F5)(PiPr3)2] (4)
A solution of 1 (260 mg, 0.5 mmol), neohexene (0.12 ml, 1.0 mmol)
and pentafluorobenzene (0.2 mL, 1.8 mmol) in 20 mL n-hexane
was heated to reflux for 6 h. The solution turned orange within
one hour. The volatiles were removed in vacuo to give an orange
solid, which was dissolved in 5 mL n-hexane. The solution was
stored at -30 ◦C and orange crystals were obtained. Yield 267 mg
(78%). A comparable transformation without neohexene leads to
a mixture of 4 and 5 in a ratio of 2.8 : 1 according to the NMR data
(95%). Found: C, 41.44; H, 6.16; N, 1.71. C24H44F4IrNOP2 requires
-1
˜
C, 41.61; H, 6.40; N, 2.02; n(ATR)/cm 2161, 2079 (IrH2), 1979
(CO); 1H NMR (500 MHz, C6D6): d 1.76 (m, 6 H, CH), 0.88 (m,
two d at 0.89 and 0.88 in the 1H{ P} NMR due to the prochirality,
31
JHH = 7.0 Hz, 36 H, CH3), -10.72 (m, 1 H, IrH), -14.55 (m, 1 H,
IrH); 19F NMR (470.4 MHz, C6D6): d -98.6 (m, 1 F), -99.0 (m,
1
of the reaction solution. Analytical data for 4. Found: C, 42.28; H,
1 F), -104.7 (m, 1 F) -104.8 (m, 1 F); 31P{ H} NMR (202.4 MHz,
-1
˜
6.62. C24H44F5IrP2 requires C, 42.21; H, 6.50; n(ATR)/cm 1937
C6D6): d 30.6 (s).
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Synthesis of cis–trans-[Ir(H)2(C6F5)(CO)(PiPr3)2] (8)
to deep-red (approx. 1 h). The reaction mixture was then stirred
under an atmosphere of ethylene for 16 h. After removing the
volatiles in vacuo the residue was dissolved in 5 mL n-hexane and
the solution was stored at -30 ◦C to obtain deep-red crystals. Yield:
130 mg (67%). Found: C, 43.13, H, 6.56; N, 2.22 C25H46F4IrNP2
A slow stream of CO was passed for 1 min through an orange
solution of 4 (40 mg, 0.06 mmol) in 5 mL n-hexane. The solution
turned immediately colourless. The volatiles were removed in
vacuo to give a colourless solid, which was dissolved in 2 mL
n-hexane and the solution was stored at -30 ◦C. A colourless
powder was obtained. Yield: 37 mg (86%). Analytical data for 8.
Found: C, 42.13; H, 6.32. C25H44F5IrOP2 requires C, 42.24; H, 6.24;
1
requires C, 43.47; H, 6.71; N, 2.03; H NMR (500 MHz, C6D6):
d 2.34 (t, JHP = 4.2 Hz, 4 H, C2H4), 1.89 (m, 6 H, CH), 0.99 (m,
1
36 H, CH3); 13C{ H} NMR (125.8 MHz, C6D6): d 23.4 (t, JCP
=
13 Hz, C2H4); 19F NMR (470.4 MHz, C6D6): d -100.5 (m, 2 F),
n(ATR)/cm-1 2139, 2077 (IrH2), 1977 (CO); 1H NMR (500 MHz,
˜
-114.4 (m, 2 F); 31P{ H} NMR (202.4 MHz, C6D6): d 14.6 (s).
1
C6D6): d 1.81 (m, 6 H, CH), 0.94 (m, two d at 0.93 and 0.94 in the
31
1H{ P} NMR due to the prochirality, JHH = 7.1 Hz, 36 H, CH3),
Synthesis of trans-[Ir(4-C5NF4)(CO)(PiPr3)2] (11)
-10.72 (m, 1 H, IrH), -14.69 (m, 1 H, IrH); 19F NMR (470.4 MHz,
C6D6): d -96.1 (m, 1 F), -96.3 (m, 1 F), -162.5 (m, 1 F), -162.8
A slow stream of CO was passed through a red solution of 10
(65 mg, 0.09 mmol) in 10 mL n-hexane. Within seconds the colour
of the solution turned yellow. The volatiles were removed in vacuo.
The residue was then extracted with n-hexane (10 mL) and the
extract was brought to dryness to give 11 as a yellow powder. Yield:
1
(m, 1 F), -162.9 (m, 1 F); 31P{ H} NMR (202.4 MHz, C6D6): d
29.8 (s).
Synthesis of cis–trans-[Ir(H)2(2-C6H3F2)(CO)(PiPr3)2] (9)
60 mg (92%). Found: C, 42.02; H, 6.32; N, 1.88. C22H42F4IrNOP2
-1
requires C, 41.73; H, 6.13; N, 2.03; n(ATR)/cm 1949 (CO); 1H
CO was bubbled into an orange solution of 6 (60 mg, 0.1 mmol) in
5 mL n-hexane until the colour of the solution disappeared (within
seconds). After removing the volatiles in vacuo the colourless
residue was dissolved in 5 mL n-hexane and stored at -30 ◦C
˜
NMR (500 MHz, C6D6): d 2.02 (m, 6 H, CH), 1.04 (m, 36 H,
CH3); 19F NMR (470.4 MHz, C6D6): d -98.78 (m, 2 F), -113.3
1
(m, 2 F); 31P{ H} NMR (202.4 MHz, C6D6): d 35.8 (s).
to obtain colourless crystals. Yield: 60 mg (88%). Found: C, 45.98;
-1
˜
H, 7.12. C25H47F2IrOP2 requires C, 45.79; H, 7.22; n(ATR)/cm
Structure determinations for the complexes 2, 7, 9 and 10‡
2165, 2059 (IrH2), 1973 (CO); 1H NMR (500 MHz, C6D6): d 6.89–
Yellow crystals of 2, colourless crystals of 7 and 9 and red
crystals of 10 were obtained from a solution in hexane at
243 K. All diffraction data were collected on a Nonius Kappa CCD
diffractometer at 100 K. Crystallographic data are depicted in
Table 5. The structures were solved by direct methods (SHELXTL
PLUS or SIR 97) and refined with the full matrix least square
methods on F2 (SHELX-97).32–34
6.77 (m, 3 H, C6H3F2), 1.95 (m, 6 H, CH), 1.04 (m, two doublets
31
at 1.04 and 1.03 in 1H{ P} due to the prochirality JHH = 7.0 Hz,
36 H, CH3), -10.58 (m, 1 H, IrH), -14.30 (m, 1 H, IrH); 19F NMR
1
(470.4 MHz, C6D6): d -66.9 (m, 1 F), -67.2 (m, 1 F); 31P{ H}
NMR (202.4 MHz, C6D6): d 30.5 (s).
Synthesis of trans-[Ir(4-C5NF4)(g2-C2H4)(PiPr3)2] (10)
Hydrogen atoms were placed at calculated positions and refined
using a riding model. For complex 2 H19 and H20 were located in
Ethylene was bubbled into an orange solution of 2 (180 mg,
0.28 mmol) in n-hexane until the colour of the solution turned
˚
the difference Fourier with a distance to Ir1 of 1.4 A. They were
Table 5 Crystallographic data
Compound
2
7
9
10
Crystal dimensions/mm3
Empirical formula
Formula weight
Crystal system
0.14 ¥ 0.13 ¥ 0.08
C23H44F4IrNP2
664.73
Monoclinic
P21/c
12.1550(12)
16.7400(11)
13.5350(13)
99.313(8)
2717.7(4)
4
1.625
5.069
3.21 to 27.5
43911
6233
0.16 ¥ 0.06 ¥ 0.06
C24H42F4IrNOP2
690.73
Orthorhombic
P212121
12.4740(3)
13.0700(2)
0.32 ¥ 0.25 ¥ 0.16
C25H47F2IrOP2
655.77
Monoclinic
P21/c
13.0680(6)
12.7220(9)
16.8010(13)
92.181(6)
2791.2(3)
4
1.561
4.926
3.20 to 30.00
54355
8070
0.50 ¥ 0.38 ¥ 0.24
C25H46F4IrNP2
690.77
Monoclinic
P21/n
9.1850(1)
23.4600(2)
12.7920(1)
90.437(4)
2756.34(4)
4
1.665
5.001
3.05 to 27.5
101272
6287
Space group
˚
a/A
˚
b/A
˚
c/A
17.2910(4)
b/◦
V/A
Z
3
˚
2819.04(10)
4
1.627
4.892
3.26 to 27.49
33849
6464
0.083
1.035
0.0404, 0.0618
0.0318, 0.0591
5858
2.105 and -0.785
686376
Density (calcd.)/Mg m-3
m(Mo-Ka)/mm-1
q Range/◦
Reflections collected
Independent reflections
Rint
0.0693
1.032
0.0316
1.097
0.047
1.060
Goodness-of-fit on F2
R1, wR2 on all data
R1, wR2 [Io > 2s(Io)]
Reflect. with Io > 2s(Io)
0.0510, 0.0474
0.0275, 0.0420
4780
0.945 and -0.665
686375
0.0311, 0.0358
0.0181, 0.0316
6748
1.927 and -0.933
686377
0.0167, 0.0349
0.0151, 0.0345
5986
0.827 and -0.609
686378
-3
˚
Max diff peak, hole/e A
CCDC
5204 | Dalton Trans., 2008, 5197–5206
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then refined isotropically using a dfix “anti-bumping” restraint
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of -1.6 with an estimated standard deviation of 0.02 leading
˚
to the distances Ir(1)–H(19)= 1.548(18) A and Ir(1)–H(20) =
˚
1.558(19) A. The hydrogen atoms bound at Ir in 7 were not
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located. However the largest diff. peaks are found near iridium.
For compound 9 the hydrogens at iridium have been located
and refined isotropically. The largest diff. peak is located near
7742.
6 J.-Y. Cho, C. N. Iverson and M. R. Smith III, J. Am. Chem. Soc., 2000,
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˚
Ir (0.76 A).
Computational details
The complexes were investigated with the BP8635,36 DFT method
without introducing symmetry. (Analytical) vibrational frequen-
cies were calculated at the BP86/SV(P)-level to verify the nature of
the obtained minima and to determine the zero point vibrational
energy.37 All reported compounds are true minima with no
imaginary frequencies. DFT calculations were performed with
the TURBOMOLE program package (Version 5.7).38,39 The DFT
calculations with the BP86 functional have been carried out with
the resolution of identity (RI) approximation.40 The def-SV(P)41
basis set was used for all atoms; for Ir the scalar relativistic effective
core potential def-ECP was used together with def-SV(P) valence
basis set.42 XYZ coordinates of the optimized compounds as well
as the calculated frequencies and total energies are deposited.
The assignment of the calculated vibrational frequencies and the
calculated molecular orbitals was done by visualization of the
modes/orbitals with the help of the program Molden.
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Acknowledgements
We acknowledge the “Fonds der Chemischen Industrie” for
financial support. The authors also acknowledge support from
the Cluster of Excellence “Unifying Concepts in Catalysis”
coordinated by the Technische Universita¨t Berlin and funded by
the Deutsche Forschungsgemeinschaft. We are grateful to S. Hinze
(Berlin) for experimental assistance.
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5206 | Dalton Trans., 2008, 5197–5206
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©