Activation of ethylene and ammonia at iridium: C-H versus N-H oxidative addition

Article abstract of DOI:10.1039/b906189d

The ammine complexes cis-trans-[Ir(4-C₅NF₄)(H) ₂(NH₃)(PiPr₃)₂] (3) and cis-[Ir(4-C₅NF₄)(H){(E)-(MeO₂C)CCH(CO ₂Me)}(NH₃)₂(Pi

Full text of DOI:10.1039/b906189d

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www.rsc.org/dalton | Dalton Transactions
Activation of ethylene and ammonia at iridium: C–H versus N–H
oxidative addition†
Marcel Ahijado Salomon, Ann-Katrin Jungton and Thomas Braun*
Received 30th March 2009, Accepted 12th June 2009
First published as an Advance Article on the web 27th July 2009
DOI: 10.1039/b906189d
The ammine complexes cis-trans-[Ir(4-C5NF4)(H)2(NH3)(PiPr3)2] (3) and cis-[Ir(4-C5NF4)(H){(E)-
=
(MeO2C)C CH(CO2Me)}(NH3)2(PiPr3)] (5) are generated on reaction of cis-trans-[Ir(4-C5NF4)(H)2-
=
(PiPr3)2] (1) or of the vinyl compound trans-[Ir(4-C5NF4)(H){(E)-(MeO2C)C CH(CO2Me)}-
2
(PiPr3)2] (4) with NH3, respectively. Photolysis of 5 gives complex [Ir(4-C5NF4)(H){k -(C,O)-(Z)-
=
(MeO2C)C CH(COOMe)}(NH3)(PiPr3)] (6). Treatment of the ethylene compound trans-[Ir(4-C5NF4)-
(C2H4)(PiPr3)2] (2) with ammonia yields C–H activation products such as the hydrido vinyl species
trans-[Ir(4-C5NF4)(H)(C2H3)(NH3)(PiPr3)2] (7) and the cyclometallation products [Ir(4-C5NF4)(H)-
2
(NH3){k -(P, C )-CH2CH(CH3)PiPr2}(PiPr3)] (8a, 8b). A subsequent reaction leads to the generation of
the binuclear oxidative addition product of ammonia [Ir(4-C5NF4)(H)(m-NH2)(NH3)(PiPr3)]2 (9).
We demonstrated recently that complex cis-trans-[Ir(4-
Introduction
C5NF4)(H)2(PiPr3)2] (1) reacts with ethylene to yield the tetraflu-
oropyridyl complex trans-[Ir(4-C5NF4)(C2H4)(PiPr3)2] (2).16 The
iridium–carbon bond in 1 is surprisingly stable and no reductive
elimination product has been observed.
An attractive route to use ammonia as a feedstock for the synthesis
of amines consists of its functionalization in homogeneous
catalytic reactions.1,2 Catalytic couplings of aryl halides with
ammonia in the presence of a base and a palladium or copper
catalyst have been realized.3 Homogeneous catalytic reductive
aminations of benzaldehydes with ammonia have also been
accomplished in the presence of hydrogen to give primary amines.4
A selective synthesis of primary amines directly from alcohols and
ammonia has been reported very recently by Gunanathan and
Milstein. The transformations are catalyzed by a ruthenium pincer
complex.5 They presumably proceed via an intermediate aldehyde
and imine and produce water as by-product. A recent report on
the hydroamination of alkynes and allenes with ammonia can be
considered as another breakthrough.6 The process is catalyzed by a
cationic gold carbene complex and yields imines, enamines or allyl
amines. Mechanistically, the insertion of the organic substrate into
the metal–nitrogen bond of an amido ligand has been proposed as
a possible key-step.6,7 A related suggestion involves coordination
of the amine to the gold centre prior to the C–N bond formation.8
The oxidative addition of ammonia can be regarded as a model
reaction for the development of new catalytic reaction cycles which
involve an N–H bond cleavage in NH3 by the insertion of a
transition metal as a key-step.2 Usually ammonia generates in the
coordination sphere of a transition metal simple “Werner-like”
Lewis acid–base adducts, although there is some precedent for the
activation of ammonia by transition-metal complexes via various
reaction pathways.9,10 So far, very little has been reported on an
oxidative addition reaction.11–15 A significant discovery involves
the oxidative addition of ammonia at an iridium(I) complex which
exhibits a tridentate pincer ligand.15
In this paper we report on the reactivity of ammonia towards
the iridium(I) and iridium(III) tetrafluoropyridyl complexes such
as 1 and 2. Complexes which bear a tetrafluoropyridyl ligand
often exhibit an unusual stability.17 This led us to investigate the
properties of iridium(I) and iridium(III) derivatives, towards C–H
and N–H activation reactions. We envisaged the generation of an
oxidative addition product of ammonia bearing a C4NF4 ligand at
iridium. In contrast to reactions at the {IrCl(PiPr3)2} moiety the
generation of cationic compounds is at {Ir(4-C5NF4)(PiPr3)2} not
feasible.2,12
Results
Formation of ammine complexes
A reaction of cis-trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (1) with ammo-
nia gave solely the “Werner-type” ammine complex cis-trans-[Ir(4-
1
C5NF4)(H)2(NH3)(PiPr3)2] (3) (Scheme 1). A singlet in the 31P{ H}
NMR spectrum of 3 at d 30.6 confirms the trans orientation of the
phosphine ligands. The 19F NMR spectrum shows four resonances
which suggests a restricted rotation about the tetrafluoropyridyl
ligand.16,17 The presence of the two hydrido ligands is revealed
in the 1H NMR spectrum by two signals at d -14.72 and
d -24.02. The coordinated ammine leads to a resonance at d(15N)
1
-88 in the H–15N NMR HBMC spectrum of the isotopomer
1
trans-[Ir(4-C5NF4)(H)2(15NH3)(PiPr3)2] (3¢). A H NMR EXSY
(400 MHz) spectrum of 3 exhibits cross-peaks with a positive
sign with respect to the diagonal peaks confirming exchange of
metal bound hydrogens. There is no indication for an exchange of
ammine protons and metal bound hydrogens.10 Moreover, we did
not find any reductive elimination of 2,3,5,6-tetrafluoropyridine.18
Humboldt-Universita¨t zu Berlin, Institut fu¨r Chemie, Brook-Taylor-Str., 2,
12489, Berlin, Germany. E-mail: thomas.braun@chemie.hu-berlin.de
† CCDC reference numbers 725696–725700. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b906189d
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˚
Table 1 Selected bond lengths (A) and angles ( ) in cis-trans-[Ir(4-
C5NF4)(H)2(PiPr3)2(NH3)] (3) with estimated standard deviations in
parentheses
Ir(1)–P(1)
Ir(1)–P(2)
Ir(1)–N(1)
Ir(1)–C(19)
Ir(1)–H(1A)
Ir(1)–H(1B)
N(2)–C(22)
N(2)–C(21)
P(1)–Ir(1)–P(2)
N(1)–Ir(1)–P(1)
N(1)–Ir(1)–P(2)
C(19)–Ir(1)–N(1)
C(19)–Ir(1)–P(1)
C(19)–Ir(1)–P(2)
Ir(1)–C(19)–C(23)
2.3098(8) C(19)–C(20)
2.3111(8) C(20)–C(21)
1.402(3)
1.374(4)
1.380(4)
1.396(3)
1.361(3)
1.349(3)
1.350(3)
1.355(3)
126.83(18)
109.1(2)
123.8(2)
124.9(2)
113.8(2)
124.8(2)
2.251(2)
2.144(2)
1.43(2)
C(22)–C(23)
C(19)–C(23)
C(20)–F(1)
C(21)–F(2)
1.38(2)
1.312(3)
1.310(3)
164.82(2)
90.38(6)
98.92(6)
96.44(9)
95.98(7)
94.87(7)
124.06(18)
C(22)–F(3)
C(23)–F(4)
Ir(1)–C(19)–C(20)
C(23)–C(19)–C(20)
C(21)–C(20)–C(19)
N(2)–C(21)–C(20)
C(21)–N(2)–C(22)
N(2)–C(22)–C(23)
˚
˚
H(1B) is 2.100 A. The iridium-carbon distance is 2.144(2) A. For
˚
comparison, the Ir–C separation of 2.144(4) A in the complex
cis-trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (1) is similar.16
Furthermore, we synthesised an iridium(III) hydrido vinyl com-
plex, which features in contrast to the dihydride 1 an additional
iridium-carbon bond. Treatment of complex 1 with acetylene di-
≡
carboxylate MeO2CC CCO2Me resulted in a colour change from
yellow to red within two hours to give trans-[Ir(4-C5NF4)(H){(E)-
=
(MeO2C)C CH(CO2Me)}(PiPr3)2] (4) (Scheme 1). It has been
=
reported that the chloro complex [Ir(Cl)(H){(E)-(MeO2C)C CH-
(CO2Me)}(PiPr3)2] can be prepared in a similar manner.19 Com-
pound 4 exhibits a singlet at d 17.4 in the 31P{ H} NMR spectrum
1
which can be assigned to the trans phosphines. The presence of
four signals in the 19F NMR spectrum again indicates a hindered
rotation of the tetrafluoropyridyl ligand about the Ir–C bond. The
IR spectrum of 4 exhibits an absorption band at 2338 cm-1 which
can be assigned to the IrH moiety.19
Scheme 1 Formation of vinyl ammine complexes.
The molecular structure of 3 was confirmed by X-ray diffraction
analysis at 100 K (Fig. 1). Selected bond lengths and angles
are summarised in Table 1. The structure reveals an octahedral
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. The separation between H(1A) and
The molecular structure of 4 was also confirmed by X-ray
diffraction analysis at 170 K (Fig. 2, Table 2). The structure
reveals a square pyramidal configuration with the expected trans
disposition of the phosphine ligands. There is a significant
Fig. 1 An ORTEP diagram of 3; Ellipsoids are drawn at the 50%
probability level; Hydrogen atoms have been omitted for clarity, except
for metal bound hydrogens.
Fig. 2 An ORTEP diagram of 4; Ellipsoids are drawn at the 50%
probability level; hydrogen atoms have been omitted for clarity, except
for metal bound hydrogen.
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Table 2 Selected bond lengths (A) and angles (◦) in trans-[Ir(4-
Table 3 Selected bond lengths (A) and angles ( ) in [Ir(4-C5NF4)(H){(E)-
˚
˚
=
=
C5NF4)(H){(E)-(MeO2C)C CH(CO2Me)}(PiPr3)2] (4) with estimated
(MeO2C)C CH(CO2Me)}(NH3)2(PiPr3)] (5) with estimated standard
standard deviations in parentheses
deviations in parentheses
Ir(1)–P(1)
Ir(1)–P(2)
Ir(1)–H(1a)
Ir(1)–C(19)
Ir(1)–C(25)
Ir(1)–O(1)
C(20)–O(1)
C(20)–O(2)
2.3651(9) C(22)–C(23)
2.3583(9) N(1)–C(27)
1.475(4)
1.316(4)
1.311(4)
1.412(5)
1.357(4)
1.360(4)
1.402(4)
1.369(4)
1.356(3)
1.357(3)
1.366(3)
Ir(1)–N(1)
Ir(1)–N(2)
Ir(1)–P(1)
Ir(1)–C(10)
Ir(1)–C(15)
C(16)–O(1)
C(16)–O(2)
C(19)–O(3)
2.172(5)
2.235(5)
2.2634(16) C(10)–C(11)
N(3)–C(12)
N(3)–C(13)
1.295(10)
1.318(9)
1.371(9)
1.403(9)
1.381(9)
1.373(9)
1.368(8)
1.348(8)
1.345(8)
1.371(8)
1.54(3)
N(1)–C(28)
C(25)–C(26)
C(26)–C(27)
C(28)–C(29)
C(25)–C(29)
C(26)–F(1)
C(27)–F(2)
C(28)–F(3)
C(29)–F(4)
2.084(3)
2.093(3)
2.446(2)
1.230(4)
1.325(4)
1.206(4)
1.351(4)
1.339(4)
2.085(6)
2.113(6)
1.204(8)
1.353(7)
1.219(9)
1.342(9)
1.341(9)
1.472(9)
172.07(16)
104.75(15)
83.1(2)
81.7(2)
84.4(2)
92.6(2)
90.1(2)
96.64(10)
96.59(17)
165.4(2)
122.8(5)
126.0(5)
C(10)–C(14)
C(11)–C(12)
C(13)–C(14)
C(11)–F(1)
C(12)–F(2)
C(13)–F(3)
C(14)–F(4)
C(23)–O(3)
C(23)–O(4)
C(19)–C(22)
C(19)–O(4)
C(15)–C(18)
C(18)–C(19)
C(19)–Ir(1)–C(25)
P(2)–Ir(1)–P(1)
P(2)–Ir(1)–O(1)
C(19)–Ir(1)–P(1)
C(19)–Ir(1)–P(2)
P(1)–Ir(1)–O(1)
C(19)–Ir(1)–O(1)
C(25)–Ir(1)–P(1)
C(25)–Ir(1)–P(2)
C(25)–Ir(1)–O(1)
Ir(1)–C(25)–C(29)
Ir(1)–C(25)–C(26)
C(28)–N(1)–C(27)
166.57(12) N(1)–C(27)–C(26)
125.3(3)
N(1)–Ir(1)–P(1)
N(2)–Ir(1)–P(1)
N(1)–Ir(1)–N(2)
C(10)–Ir(1)–N(1)
C(15)–Ir(1)–N(1)
C(10)–Ir(1)–N(2)
C(15)–Ir(1)–N(2)
C(10)–Ir(1)–P(1)
C(15)–Ir(1)–P(1)
C(10)–Ir(1)–C(15)
Ir(1)–C(10)–C(11)
Ir(1)–C(10)–C(14)
C(12)–N(3)–C(13)
N(3)–C(12)–C(11)
N(3)–C(13)–C(14)
C(10)–C(11)–C(12)
C(13)–C(14)–C(10)
Ir(1)–C(15)–C(18)
Ir(1)–C(15)–C(16)
C(15)–C(18)–C(19)
O(1)–C(16)–O(2)
O(1)–C(16)–C(15)
O(3)–C(19)–O(4)
O(3)–C(19)–C(18)
114.6(6)
166.55(3)
94.28(6)
89.71(8)
88.50(8)
96.51(6)
61.11(9)
92.50(9)
92.32(9)
N(1)–C(28)–C(29)
C(25)–C(26)–C(27)
C(25)–C(29)–C(28)
C(26)–C(25)–C(29)
Ir(1)–O(1)–C(20)
Ir(1)–C(19)–C(22)
C(19)–C(22)–C(23)
O(1)–C(20)–C(19)
125.5(3)
123.6(3)
123.7(3)
108.7(3)
86.07(18)
143.9(2)
127.2(3)
116.9(3)
122.8(3)
124.6(3)
123.4(4)
124.6(7)
124.0(7)
123.4(2)
122.8(7)
121.9(5)
120.5(4)
125.4(6)
123.0(6)
126.5(6)
123.4(7)
125.9(7)
105.47(11) O(1)–C(20)–O(2)
121.4(2)
129.8(3)
113.2(3)
O(3)–C(23)–C(22)
O(3)–C(23)–O(4)
additional contact of one of the ester groups to iridium with an
˚
O(1)-Ir(1) distance of 2.447(2) A, which completes an octahedral
coordination sphere at the metal centre. This is reflected in
˚
=
the C O separations which are 1.230(4) A for the ester group
˚
bound to iridium and 1.206(4) A for the distal ester group.
The cis arrangement of the ester moieties at the carbon-carbon
double bond results in the formation of a four-membered ring.
A comparable four-membered chelate has been found in trans-
=
[Ir(C3N2H4)(H)(MeO2CC CH2)(PPh3)2]BF4 with an iridium oxy-
gen distance of 2.28(1) A. The dihedral angle between the plane
20
˚
defined by the pyridyl ring and the coordination plane of the metal
defined by Ir1, C19, C25, P1 and P2 is 86.2◦. The iridium-carbon
˚
distance to the pyridyl ring is 2.095(3) A. For comparison, the Ir–C
separation of 2.144(4) in 1 is in a similar range.12 The metal-carbon
˚
bond length to the vinyl group is 2.084(3) A.
The hydride compound 4 reacted with NH3 to afford free
PiPr3 and the monophosphine complex cis-[Ir(4-C5NF4)(H){(E)-
Fig. 3 An ORTEP diagram of 5; ellipsoids are drawn at the 50%
probability level; hydrogen atoms and a benzene solvent molecule have
been omitted for clarity.
=
(MeO2C)C CH(CO2Me)}(NH3)2(PiPr3)] (5) (Scheme 1). The
1
31P{ H} NMR spectrum of 5 displays a singlet at d 13.9 for the
phosphine. The 31P NMR spectrum of the isotopomer cis-[Ir(4-
15
=
C5NF4)(H){(E)-(MeO2C)C CH(CO2Me)}( NH3)2(PiPr3)] (5¢)
=
exhibits one additional coupling to nitrogen of 46.7 Hz, pre-
sumably to the ammine ligand in the trans position to the
phosphorus. The 19F NMR spectrum of 5 depicts four resonances
for the tetrafluoropyridyl ligand. The signal for the hydrido ligand
appears at d -28.09 in the 1H NMR spectrum. The phosphorus–
hydrogen coupling of 13.8 Hz suggests a cis arrangement of metal
bound phosphorus and hydrogen. The molecular structure of the
octahedral complex 5 was also determined by X-ray diffraction at
100 K (Fig. 3, Table 3). Neither the iridium-carbon distance to the
led to a cis-trans isomerisation at the C C double bond with a
concomitant dissociation of one ammonia molecule and com-
2
=
plex [Ir(4-C5NF4)(H){k -(C,O)-(Z)-(MeO2C)C CH(COOMe)}-
(NH3)(PiPr3)] (6) was generated (Scheme 1). A comparable
cis-trans isomerisation has been observed at [Ir(Cl)(H){(E)-
2
=
(MeO2C)C CH(CO2Me)}(PiPr3)2] to yield [Ir(Cl)(H){k -(C,O)-
19
=
(Z)-(MeO2C)C CH(COOMe)}(PiPr3)2]. Complex 6 resembles
the structure of 4, but one phosphine has been replaced by an
ammine ligand. In addition, the ester groups are now orientated
in a trans position at the vinyl double bond, which leads to the
formation of a five-membered ring. The 1H NMR spectrum depicts
a signal at -28.36 with a doublet coupling to the phosphorus
nucleus of 21.9 Hz which is characteristic for a cis orientation of
the phosphine ligand and the hydride. The IR spectrum of 6 shows
˚
C5NF4 unit of 2.085(6) A nor the iridium-carbon distance to the
˚
vinyl group of 2.113(6) A show a significant difference to the Ir–C
distances found in 4.
Prolonged heating of a benzene of 5 solution at 50 ◦C did not
lead to any reduction elimination reaction. However photolysis
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2
˚
C–H via N–H bond activation
Table 4 Selected bond lengths (A) and angles ( ) in [Ir(4-C5NF4)(H){k -
=
(C,O)-(Z)-(MeO2C)C CH(COOMe)}(NH3)(PiPr3)] (6) with estimated
standard deviations in parentheses
In contrast to the reactions at Ir(III), in which only co-
ordination of ammonia has been achieved, the presence of
ammonia at Ir(I) leads either to C–H activation or to an
oxidative addition of a N–H bond. Thus, treatment of the
iridium(I) ethylene complex trans-[Ir(4-C5NF4)(C2H4)(PiPr3)2] (2)
with NH3 furnishes initially the C–H activation product trans-
[Ir(4-C5NF4)(H)(C2H3)(NH3)(PiPr3)2] (7) (Scheme 2). Complex
7 could not be isolated in the solid state, because it reacts
further to give the two isomeric cyclometallation products [Ir(4-
Ir(1)–N(1)
Ir(1)–O(1)
Ir(1)–P(1)
Ir(1)–H(1d)
Ir(1)–C(10)
Ir(1)–C(17)
C(15)–O(1)
C(15)–O(2)
C(19)–O(3)
C(19)–O(4)
C(15)–C(16)
C(16)–C(17)
N(1)–Ir(1)–P(1)
C(17)–Ir(1)–C(10)
P(1)–Ir(1)–O(1)
N(1)–Ir(1)–O(1)
C(17)–Ir(1)–P(1)
C(17)–Ir(1)–N(1)
C(17)–Ir(1)–O(1)
C(17)–Ir(1)–H(1d)
C(10)–Ir(1)–P(1)
C(10)–Ir(1)–N(1)
C(10)–Ir(1)–O(1)
Ir(1)–C(10)–C(11)
Ir(1)–C(10)–C(14)
2.1601(18) C(17)–C(19)
2.2700(16) C(10)–C(14)
1.480(3)
1.396(3)
1.386(3)
1.378(3)
1.373(3)
1.316(3)
1.307(3)
1.363(3)
1.350(3)
1.349(3)
1.351(3)
2.2608(6)
1.44(3)
C(10)–C(11)
C(13)–C(14)
C(11)–C(12)
N(2)–C(12)
N(2)–C(13)
C(11)–F(1)
C(12)–F(2)
C(13)–F(3)
C(14)–F(4)
2.102(2)
2.049(2)
1.237(3)
1.328(3)
1.211(3)
1.341(3)
1.452(3)
1.350(3)
2
C5NF4)(H)(NH3){k -(P, C )-CH2CH(CH3)PiPr2}(PiPr3)] (8a, 8b)
as well as free ethylene. The latter two were detected in the NMR
spectra.
178.20(5)
C(13)–N(2)–C(12)
C(12)–C(11)–C(10)
N(2)–C(12)–C(11)
N(2)–C(13)–C(14)
C(13)–C(14)–C(10)
Ir(1)–C(17)–C(16)
Ir(1)–C(17)–C(19)
Ir(1)–O(1)–C(15)
O(1)–C(15)–C(16)
O(1)–C(15)–O(2)
O(3)–C(19)–O(4)
C(15)–C(16)–C(17)
C(16)–C(17)–C(19)
114.2(2)
168.74(9)
100.16(4)
81.60(7)
95.07(6)
84.95(8)
76.45(8)
100.9(11)
95.90(6)
84.16(8)
99.08(7)
124.23(16)
124.22(16)
122.8(2)
124.8(2)
124.7(2)
122.6(2)
116.93(16)
124.00(17)
109.47(14)
122.4(2)
121.6(2)
122.1(2)
114.4(2)
117.6(2)
an absorption band at 2280 cm-1 which can be assigned to the IrH
moiety.16,19
The configuration of 6 at the metal centre was revealed by X-ray
diffraction analysis at 100 K (Fig. 4, Table 4). The iridium–carbon
˚
distances to the C5NF4 unit of 2.102(2) A and to the vinyl group
˚
of 2.049(2) A are comparable to the separations found in 4 and 5
and are in the expected range. The trans arrangement of the ester
moieties at the carbon-carbon double bond results, in contrast
to the situation in 4, in the formation of a five-membered ring.
˚
=
The C O separations are 1.237(3) A for the ester group bound to
˚
iridium and 1.211(3) A for the distal ester group. These values are
consistent with the literature data.21
Scheme 2 C–H activation at ammine complexes.
1
The 31P{ H} NMR spectrum of 7 displays a singlet at d 1.8
for the phosphines in the mutually trans position. The 19F NMR
spectrum depicts four resonances for the tetrafluoropyridyl ligand.
1
The H NMR spectrum shows a triplet of doublets at d -21.88
for the hydride at the iridium center. On 31P decoupling the signal
simplifies to a doublet with a hydrogen-fluorine coupling of 9.3 Hz.
Note that the latter is not indicative for a trans arrangement of
the hydride and fluoropyridyl moiety.16 The presence of the vinyl
ligand is revealed by resonances at d 8.36, d 6.03 and d 5.02. A
13
1H- C HMQC NMR spectrum exhibits resonances at d 143.6
and d 116.6 in the 13C domain for the a- and b- carbon atom in
the vinyl group, respectively. The presence of the ammine ligand is
15
revealed in the 1H- N NMR spectrum of the isotopologue trans-
Fig. 4 An ORTEP diagram of 6; ellipsoids are drawn at the 50%
probability level; hydrogen atoms and a benzene solvent molecule have
been omitted for clarity, except for metal bound hydrogen.
[Ir(4-C5NF4)(H)(C2H3)(15NH3)(PiPr3)2] (7¢). It shows a correlation
at d(15N) -72 with the signal for the metal hydride at d(1H) -21.88.22
7672 | Dalton Trans., 2009, 7669–7677
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◦
˚
There is no apparent nitrogen coupling on the signal for the metal
hydride in the 1H NMR spectrum. This suggests that the ammine
ligand and the hydrido ligand are not arranged in a trans position
Table 5 Selected bond lengths (A) and angles ( ) in [Ir(4-C5NF4)(H)(m-
NH2)(NH3)(PiPr3)]2 (9) with estimated standard deviations in parentheses
Ir(1)–C(10)
Ir(1)–N(1)
Ir(1)–N(1)#
Ir(1)–N(2)
Ir(1)–P(1)
N(3)–C(13)
N(3)–C(12)
2.036(2)
C(10)–C(11)
2.1261(18) C(11)–C(12)
2.1243(18) C(13)–C(14)
C(11)–F(1)
2.2735(6) C(12)–F(2)
1.408(3)
1.368(3)
1.369(3)
1.366(3)
1.354(3)
1.357(3)
1.366(3)
1
at the iridium center.23 However, the signal at d 8.36 in the H
NMR spectrum exhibits an additional coupling to the 15N nucleus
of 2.9 Hz. We propose a configuration with the ammine and vinyl
ligand in a mutual trans arrangement in 7, although we cannot
exclude entirely an isomer with the hydride an the vinyl group in
a mutual trans position.
2.239(2)
1.316(3)
1.317(3)
1.400(3)
89.40(8)
167.80(8)
94.29(8)
97.18(6)
94.97(5)
83.51(7)
126.56(17)
123.58(17)
78.40(8)
81.18(7)
C(13)–F(3)
C(14)–F(4)
C(10)–C(14)
C(10)–Ir(1)–N(1)#
C(10)–Ir(1)–N(1)
C(10)–Ir(1)–N(2)
C(10)–Ir(1)–P(1)
N(1)–Ir(1)–P(1)
N(1)–Ir(1)–N(2)
Ir(1)–C(10)–C(14)
Ir(1)–C(10)–C(11)
N(1)#–Ir(1)–N(1)
N(1)#–Ir(1)–N(2)
N(1)#–Ir(1)–P(1)
Ir(1)#–N(1)–Ir(1)
N(2)–Ir(1)–P(1)
C(12)–N(3)–C(13)
C(11)–C(10)–C(14)
C(10)–C(11)–C(12)
C(11)–C(12)–N(3)
N(3)–C(13)–C(14)
C(10)–C(14)–C(13)
170.20(5)
101.60(8)
105.44(5)
113.7(2)
109.4(2)
123.3(2)
125.0(2)
124.9(2)
123.7(2)
Compound 7 transformed completely into the isomers 8a and
8b within 8 hours. All NMR spectra reveal two sets of signals, but
we were not able to assign them to the according configurations in
8a or 8b. The inequivalent phosphorus atoms in both isomers are
revealed in the 31P NMR spectrum with phosphorus–phosphorus
coupling constants of 336 Hz. The size of the coupling constant is
typical for a trans arrangement of the two phosphorus containing
moieties.13 Selective decoupling experiments of the alkyl protons
give in the 31P NMR for all phosphorus nuclei in 8a and 8b a
hydrogen coupling of 14 Hz to the corresponding metal bound
1
proton. The H NMR spectrum shows signals at d -21.21 and
d -21.50 for the hydrido ligands at iridium. The spectrum of
2
the 15N labeled isotopologues [Ir(4-C5NF4)(H)(15NH3){k -(P, C )-
CH2CH(CH3)PiPr2}(PiPr3)] (8a¢ and 8b¢) exhibit no additional 15N
coupling which again suggests a cis arrangement for the hydride
and ammine ligands in both isomers.23 The presence of the ammine
ligands is confirmed by cross-peaks at d(15N) -75 and d(15N) -68
in the 1H–15N NMR correlation spectrum.22
Treatment of solution of 8a/8b in benzene with dihydrogen
gave the dihydrido complex 1 (Scheme 2). However, within
two days colourless crystals precipitated from a solution of
8a/8b in benzene. X-Ray crystallographic studies revealed that
the precipitate consisted of the N–H activation product [Ir(4-
C5NF4)(H)(m-NH2)(NH3)(PiPr3)]2 (9) (Scheme 3). The latter is
insoluble in all common organic solvents. Selected bond lengths
and angles of the structure of the binuclear complex 9 are depicted
in Fig. 5 and Table 5. The molecule is located on an inversion
centre. The bond distances from iridium to nitrogen compare well
with the separations found in [Ir(H)(m-NH2)(NH3)(PEt3)2]2(Cl)2.12
31P NMR spectra of the reaction solution showed the formation
Fig. 5 An ORTEP diagram of 9; ellipsoids are drawn at the 50%
probability level; hydrogen atoms and a benzene solvent molecule have
been omitted for clarity, except for metal bound hydrogen.
of free phosphine. Addition of phosphine to a solution of 8a and
8b does not inhibit the generation of 9.
Discussion
The syntheses of the iridium(III) ammine complexes cis-trans-
[Ir(4-C5NF4)(H)2(NH3)(PiPr3)2] (3), cis-[Ir(4-C5NF4)(H){(E)-
=
(MeO2C)C CH(CO2Me)}(NH3)2(PiPr3)] (5) and [Ir(4-C5NF4)-
2
=
(H){k -(C,O)-(Z)-(MeO2C)C CH(COOMe)}(NH3)(PiPr3)] (6)
are shown in Scheme 1. We did not observe any reactivity of the
hydrides or the ammine ligand at one of the metal centers neither
upon heating nor under photolytic conditions. Thus a reductive
elimination of dihydrogen or of a carbon–hydrogen to give an
iridium(I) complex which could be capable for an N–H oxidative
addition did not occur. We also have no indication for a C–N
coupling reaction at 5 or 6. Note that it has been reported before
≡
that a reaction of MeO2CC CCO2Me with ammonia leads to the
hydroamination product, even without the presence of a metal
centre.24
Scheme 3 Oxidative addition of ammonia.
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The ethylene complex trans-[Ir(4-C5NF4)(C2H4)(PiPr3)2] (2)
reacts with ammonia to give trans-[Ir(4-C5NF4)(H)(C2H3)(NH3)-
(PiPr3)2] (7), [Ir(4-C5NF4)(H)(NH3){k -(P, C )-CH2CH(CH3)-
ammonia coordination to give E. We also can’t exclude a direct
addition of ammonia at the iridium-carbon bond in 8a or 8b
or even at cyclometallated derivatives of B to give C, but the
insolubility of 9 does not permit any experiments with ND3 to
elucidate that issue. Phosphine loss at C or D or dimerisation of
E gives the binuclear compound 9, which is very stable because
of the bridging amido ligands. We were not able to detect any of
the suggested intermediates A–E; possibly because at 8a/8b the
C–H bond formation might be the rate determining step and also
because the generation of 9 is irreversible due to the insolubility
of 9. Free phosphine in the reaction solution does not inhibit the
generation of 9.
2
PiPr2}(PiPr3)] (8a/8b) and subsequently [Ir(4-C5NF4)(H)(m-
NH2)(NH3)(PiPr3)]2 (9). At first the oxidative addition of
ethylene has been observed to give 7, but after loss of the
olefin ligand cyclometallation of a phosphine ligand occurs.
The cyclometallation products 8a/8b finally transformed into
the dinuclear ammine compound 9. Initial intermediates for the
activation steps are presumably either an iridium(I) ammine
complex trans-[Ir(4-C5NF4)(NH3)(PiPr3)2] (A) or the 14-electron
species [Ir(4-C5NF4)(PiPr3)2] (B), one of which reacts in the
presence of NH3 further by oxidative addition of either a C–H
bond in the phosphine or a N–H bond in ammonia (Schemes 2–4).
The generation of C resembles the oxidative addition of
3
ammonia at [Ir{k -(C,P,P)-CH(CH2CH2PtBu2)2}(C2H4)] to yield
3
[Ir{k -(C,P,P)-CH(CH2CH2PtBu2)2})(H)(NH2)] which has been
reported by Zhao, Goldman and Hartwig.15 In this case the
ammonia activation occurs via a dissociative pathway by ethylene
dissociation to give an intermediate 14-electron species at which
the N–H oxidative addition takes place.
N–H oxidative addition can compete with C–H bond cleavage.
Schulz and Milstein showed that at trans-[Ir(Cl)(C2H4)(PEt3)2]
N–H activation of ammonia occurs to give the cationic
complex [Ir(H)(m-NH2)(NH3)(PEt3)2]2(Cl)2, whereas trans-
[Ir(Cl)(C2H4)(PiPr3)2] undergoes, even in the presence of
ammonia, C–H activation of ethylene to yield an hydrido vinyl
complex.13 At 353 K a cyclometallation has been observed to
2
give [Ir(Cl)(H){k -(P, C )-iPr2PCH(Me)CH2}(NH3)(PiPr3)]. We
demonstrated now that C–H activation products such as 7, 8a
or 8b can be formed at room temperature and that the C–H
activation is reversible to provide an iridium(I) compound as
precursor fo a N–H oxidative addition product.
Apparently at {Ir(Cl)(PEt3)2} a binuclear dicationic complex
is formed whereas at {Ir(4-C5NF4)(PiPr3)2} the neutral, but also
binuclear, species 9 is generated.2,12 The pincer ligand allows the
3
isolation of the mononuclear compound [Ir(H)(NH2){k -(C,P,P)-
3
CH(CH2CH2PtBu2)2}.15 It is interesting that at the [Ir{k -(C,P,P)-
C6H3(CH2CH2PtBu2)2} fragment, which exhibits an aromatic
pincer ligand, no oxidative addition of ammonia occurs.2,21 This
has been explained by the better s-donor capability of the
alkyl pincer ligand.15 However, it appears that the aromatic
tetrafluoropyridyl ligand and a chloro ligand also permit N–H
activation. Thus the electronic requirements to induce the N–H
activation step remain unclear.
Conclusions
We presented N–H and C–H activation reactions at {Ir(4-
C5NF4)(PiPr3)2} in the presence of ammonia. The C–H activa-
tion reactions are reversible and therefore provide access to an
N–H oxidative addition pathway of ammonia. The activation of
ammonia leads to a dinuclear iridium(III) amido complex 9.
Scheme 4 Proposed mechanism for the formation of 8a/8b and 9.
We propose that after C–H reductive elimination in 8a/8b
the ammonia activation occurs at trans-[Ir(4-C5NF4)(NH3)-
(PiPr3)2] (A) or [Ir(4-C5NF4)(PiPr3)2] (B) to yield trans-[Ir(H)(4-
C5NF4)(NH2)(PiPr3)2] (C), trans-[Ir(H)(4-C5NF4)(NH2)(NH3)-
(PiPr3)2] (D) or [Ir(H)(4-C5NF4)(NH2)(NH3)(PiPr3)] (E)
(Scheme 4) by oxidative addition. The reaction pathways
starting from A involve oxidative addition of the ammine ligand
to give C, ammonia coordination followed by N–H activation
to yield D, and phosphine loss followed by N–H cleavage and
Experimental
[D6]Benzene and [D8]THF were dried by stirring over Na/K and
then distilled. Complexes cis-trans-[Ir(4-C5NF4)(H)2(PiPr3)2] (1)
and trans-[Ir(4-C5NF4)(C2H4)(PiPr3)2] (2) were prepared accord-
ing to the literature.16
7674 | Dalton Trans., 2009, 7669–7677
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The NMR spectra were recorded on a Bruker DPX 300 or
Bruker AV 400 spectrometer at 300 K. The H NMR chemical
(s, br, for 5¢ dd, JHP = 3.6 Hz, JHN = 70.1 Hz, 3 H, NH3), 3.00 (s,
br, for 5¢ d, JHN = 68.1 Hz, 3 H, NH3), 2.13 (m, 3 H, CH(CH3)2),
1.36 (dd, JHP = 7.3 Hz, JHH = 6.3 Hz, 9 H, CH(CH3)2), 1.19
(dd, JHP = 7.2 Hz, JHH = 5.7 Hz, 9 H, CH(CH3)2), -22.08 (dd,
JHP = 23.5 Hz, JHF = 11.5 Hz, for 5¢ ddd, additional coupling
JHN = 5.6 Hz, 1 H, IrH); 19F NMR (282.4 MHz, [D8]THF):
d -101.4 (m, 1 F), -102.6 (m, 1 F), -113.4 (m, 1 F), -123.8 (m,
1
shifts were referenced to residual C6D5H at d = 7.15 or [D7]THF
at d = 1.8 ppm. The 19F NMR spectra were referenced to
1
external C6F6 at d = -162.9 ppm. The 31P{ H} NMR spectra were
referenced externally to H3PO4 at d 0.0 ppm. 15N NMR chemical
shifts were referenced externellay to 5 M 15NH4Cl in 2 M HCl.
Infrared spectra were recorded on a Bruker Vector 22 spectrometer
which was equipped with an ATR unit (ZnSe or diamond).
Irradiation experiments were carried out with a L.O.T. Xenon
lamp (150 W).
1
1
1 F); 31P{ H} NMR (121.5 MHz, [D8]THF): d 13.9 (s). 31P{ H}
NMR of 5¢ (121.5 MHz, [D8]THF): d 13.69 (dd, JPN = 46.7 Hz).
1H,15N HMBC NMR of 5¢ (40.5 MHz, [D8]THF): d(15N) -62; 13
NMR (100.6 MHz, C6D6): d 182.2 (s,C O), 165.8 (s, C O), 150.3
C
=
=
=
=
(s, IrC C), 125.9 (s, IrC C), 50.9 (s, OCH3), 50.7 (s, OCH3), 25.7
(t, JPC = 14 Hz, CHCH3), 19.6 (s, CHCH3), 19.4 (s, CHCH3), the
signals for the fluorinated pyridine ligand were not found.
Formation of cis-trans-[Ir(4-C5NF4)(H)2(NH3)(PiPr3)2] (3)
A slow stream of NH3 was passed for 1 min through an orange
solution of 1 (90 mg, 0.14 mmol) in 10 mL n-hexane. The solution
turned colourless. The volatiles were removed in vacuo to give a
colourless solid. Yield 71 mg (78%). Complex 3¢ was prepared in a
similar manner on using 15NH3. Analytical data for 3: (Found: C,
40.68; H, 6.95; N, 3.40. C23H47F4IrN2P2 requires C, 40.52; H, 6.95;
Formation of [Ir(4-C5NF4)(H){j2-(C,O)-
=
(Z)-(MeO2C)C CH(COOMe)}(NH3)(PiPr3)] (6)
A solution of 5 (33 mg, 0.05 mmol) in 0.5 mL C6H6 was transferred
into a quartz NMR tube. The reaction mixture was irradiated
for 14 h at room temperature. Yellow crystals formed at room
temperature which consisted of 6. Yield 31 mg (98%). Complex
6¢ was prepared in a similar manner on using 5¢ as starting
compound. Analytical data for 6: (Found: C, 39.44; H, 5.44; N,
1
N 4.11); v˜ (ATR, ZnSe)/cm-1 3407 (NH), 2243, 2037 (IrH); H
NMR (500 MHz, C6D6): d 1.98–1.71 (m, br, 9 H, CH(CH3)2,
NH3), 0.91 (s, br, 36 H, CH(CH3)2), -14.72 (s, br, 1H, IrH),
-24.02 (s, br, 1 H, IrH). 19F NMR (470.4 MHz, C6D6): d -98.6
1
(m, 1 F), -99.0 (m, 1 F), -104.7 (m, 1 F), -104.8 (m, 1 F). 31P{ H}
4.62. C20H32F4IrN2O4P · 1 C6H6 requires C, 39.31; H, 5.02; N 3.99);
2
NMR (202.4 MHz, C6D6): d 30.6 (s).1H,15N HMBC NMR of 3¢
(40.5 MHz, C6D6): d(15N) -88.
v˜ (ATR), diamond/cm-1 3340 (NH), 2280 (IrH), 1734 (C O), 1705
=
1
=
=
(C O); H NMR (300 MHz, [D8]THF): d 6.98 (s, 1 H, CH), 3.91
(s, 3 H, OMe), 3.66 (s, 3 H, OMe), 2.66 (s, d in the spectrum of
Formation of trans-[Ir(4-C5NF4)(H){(E)-
6¢, JHN ª 70 Hz, NH3), 2.16 (m, 3 H, CH(CH3)2), 1.18 (dd, JHP
=
=
(MeO2C)C CH(CO2Me)}(PiPr3)2] (4)
7.2 Hz, JHH = 6.3 Hz, 9 H, CH(CH3)2), 0.98 (dd, JHP = 7.3 Hz,
JHH = 5.9 Hz, 9 H, CH(CH3)2), -28.55 (dd, JHP = 21.9 Hz, JHF
=
≡
MeO2CC CCO2Me (33 mg, 0.24 mmol) was added to a solution
7.5 Hz); 19F NMR (282.4 MHz, C6D6): d -99.3 (m, 1 F), -100.2 (m,
of 1 (105 mg, 0.16 mmol) in 2 mL toluene. The solution turned
red within two hours. After 16 h the volatiles were removed
in vacuo to give an orange powder, which was extracted with 5 mL
n-hexane. The extract was stored at -30 ◦C to obtain 4 as orange
crystals. Yield 102 mg (78%). (Found: C, 43.00; H, 6.23; N, 1.55.
1 F), -115.6 (m, 1 F), -119.6 (m, 1 F); 31P{ H} NMR (121.5 MHz,
1
C6D6: d 17.3 (s). 1H,15N HMBC NMR of 6¢ (40.5 MHz, [D8]THF):
d(15N) -55.
C29H50F4IrNO4P2 requires C, 43.17; H, 6.25; N 1.74); v˜ (ATR,
Treatment of trans-[Ir(4-C5NF4)(C2H4)(PiPr3)2] (2) with ammonia
1
diamond)/cm-1 2338 (IrH), 1711 (C O); H NMR (300 MHz,
=
A slow stream of NH3 was passed for 30 s through a red solution of
2 (40 mg, 0.06 mmol) in 2 mL C6D6. The NMR spectroscopic data
of the solution reveal the initial formation of 7, 8a and 8b (ratio 2 :
7 : 8a : 8b after 3 h: 13 : 17 : 27 : 43). After 8 h only 8a and 8b could
be detected. The 1H NMR specrum showed the formation of free
ethylene. After 2d colourless crystals of 9 precipitated which were
identified by X-ray crystallography. The complexes 7¢, 8a¢ and 8b¢
=
C6D6): d 6.48 (s, 1 H, CH), 3.48 (s, 3 H, OMe), 3.47 (s, 3 H, OMe),
2.13 (m, 6 H, CH(CH3)2), 0.93 (m, 36 H, CH(CH3)2), -35.10 (td,
JHP = 13.8 Hz, JHF = 4.0 Hz, 1 H, IrH); 19F NMR (282.4 MHz,
C6D6): d–99.4 (m, 1 F), -101.6 (m, 1 F), -113.8 (m, 1 F), -117.2
(m, 1 F); 31P{ H} NMR (121.5 MHz, C6D6): d 17.4 (s); 13C NMR
1
=
=
(100.6 MHz, C6D6): d 179.5 (s,C O), 169.0 (s, C O), 150.6 (s,
=
=
IrC C), 133.8 (s, IrC C), 51.8 (s, OCH3), 51.6 (s, OCH3), 26.0
(t, JPC = 13 Hz, CHCH3), 19.4 (s, CHCH3), 18.8 (s, CHCH3), the
signals for the fluorinated pyridine ligand were not found.
were prepared in a similar manner on using 15NH3. Analytical
1
data for 7: H NMR (500 MHz, C6D6): d 8.36 (m, dd, JHH,trans
=
19.6 Hz, JHH,cis = 12.6 Hz, for 7¢ additional doublet coupling of
JHN = 2.9 Hz, 1 H, CH= CH2), 6.03 (d, JHH,cis = 12.5 Hz, 1 H,
CH= CHH), 5.02 (dd, JHH,trans = 20.0 Hz, JHH = 3.0 Hz, 1 H, CH=
CHH), 2.51 (s, br, NH3), 2.11 (m, JHH = 7.2 Hz, 6 H, CH(CH3)2),
0.87 (dvt, JHH = 7.2 Hz, N = 7.0 Hz, 36 H, CH(CH3)2), -21.88 (dt,
JHP = 17.4 Hz, JHF = 9.3 Hz, 1 H, IrH); the coupling constants
were confirmed by 19F and 31P decoupling; 19F NMR (282.4 MHz,
C6D6): d -101.1 (m, 1 F), -103.1 (m, 1 F), -109.8 (m, 1 F), -123.9
Formation of cis-[Ir(4-C5NF4)(H){(E)-
=
(MeO2C)C CH(CO2Me)}(NH3)2(PiPr3)] (5)
A slow stream of NH3 was passed for 1 min through a solution
of 4 (115 mg, 0.19 mmol) in 2 mL benzene. A yellow precipitate
formed which consisted of 5. Yield 94 mg (72%). Complex 5¢ was
prepared in a similar manner on using 15NH3. Analytical data for
5: (Found: C, 35.81; H, 5.08; N, 5.87. C20H35F4IrN3O4P requires C,
1
1
(m, 1 F); 31P{ H} NMR (202.4 MHz, C6D6): d = 1.8 (s). H,15N
35.29; H, 5.18; N 6.17); v˜ (ATR, diamond)/cm-1 3340 (NH), 2239
HMBC NMR of 7¢ (40.5 MHz, C6D6): d(15N) -72. Analytical data
1
1
=
=
(IrH), 1740 (C O), 1690 (C O); H NMR (300 MHz, C6D6): d
for 8a: H–NMR (500 MHz, C6D6): d 2.13 (s, d in the spectrum
1
31
=
6.27 (s, 1 H, CH), 3.81 (s, 3 H, OMe), 3.67 (s, 3 H, OMe), 3.05
of 8a¢, JHN ª 75 Hz, NH3), -21.21 (m, d in the H{ P} NMR,
This journal is The Royal Society of Chemistry 2009
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©

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Table 6 Crystallographic data
Compound
3
4a
5
6
9
Crystal dimensions/mm3
Empirical formula
Formula weight
Crystal system
0.20 ¥ 0.16 ¥ 0.08
C23H47F4IrN2P2
681.77
0.24 ¥ 0.12 ¥ 0.08
C29H50F4IrNO4P2
806.84
Orthorhombic
P212121
10.7834 (16)
14.3514 (16)
21.382(3)
—
—
—
3309.0(7)
4
1.620
0.20 ¥ 0.15 ¥ 0.12
C26H41F4IrN3O4P
758.79
Monoclinic
P21/n
10.7140(3)
13.1461(3)
21.3446(5)
—
93.574(2)
—
3000.48(13)
4
1.680
4.563
3.34 to 29.00
49585
0.36 ¥ 0.34 ¥ 0.28
C23H35F4IrN2O4P
702.70
Monoclinic
P21/n
14.7892(4)
10.4836(2)
17.1372(5)
—
98.780(7)
—
2625.89(12)
4
1.777
5.205
2.41 to 28.75
47604
0.23 ¥ 0.12 ¥ 0.08
C34H60F8Ir2N6P2
1151.22
Monoclinic
P21/c
13.6890 (2)
9.9290 (2)
15.0110 (2)
—
92.8640(10)
—
2037.72 (6)
2
1.876
6.672
2.91 to 27.50
47134
Triclinic
¯
Space group
P1
˚
a/A
8.7052(14)
10.2909(19)
16.232(3)
75.886(15)
86.624(14)
73.932(13)
1355.1(4)
2
1.671
5.086
2.59 to 27.50
22666
6215
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
V/A
Z
3
˚
Density (calcd.)/Mg m-3
m(Mo Ka)/mm-1
q range/◦
4.187
2.36 to 25.50
32822
6150
0.0385
Reflections collected
Independent reflections
Rint
7955
0.1414
0.836
0.1059, 0.0762
0.0436, 0.0653
4591
6817
0.0952
0.953
0.0255, 0.0415
0.0187, 0.0403
5946
4653
0.038
1.049
0.0186, 0.0340
0.0159, 0.0332
4306
0.0576
1.007
0.0222, 0.0511
0.0201, 0.0504
5845
Goodness-of-fit on F2
R1, wR2 on all data
R1, wR2 [Io > 2s(Io)]
Reflect. with Io > 2s(Io)]
0.915
0.0215, 0.0276
0.0158, 0.0272
5505
-3
˚
Max diff peak, hole/e A
2.545 and -1.920
0.599 and -0.472
2.812 and -2.805
1.545 and -0.954
0.956 and -0.575
a Flack parameter: -0.014(3).
19
JHF = 9.5 Hz, vt in the 1H{ F} NMR, JHP = 16.3 Hz, IrH). The
resonances for the iPr groups are obscured by signals of 8b. 19F
NMR (564.6 MHz, C6D6): d -100.9 (m, 1 F), -102.0 (m, 2 F),
fourier and refined isotropically. The hydrogen atom bound at Ir
in 5 was not located.
-103.5 (m, 1 F). 31P{ H-selective} NMR (162.0 MHz, C6D6):
1
Acknowledgements
d 13.0 (dd, JPP = 336 Hz, JPH = 16 Hz), -36.5 (dd, JPP = 336 Hz,
JPH = 14 Hz).1H,15N HMBC NMR of 8a¢ (40.5 MHz, C6D6):
We thank the “Fonds der Chemischen Industrie” for financial
support. The authors also acknowledge support from the Cluster
of Excellence “Unifying Concepts in Catalysis” funded by the
Deutsche Forschungsgemeinschaft. We are grateful to S. Hinze
for experimental assistance. We also thank P. Neubauer the X-ray
crystallography (3–6) as well as Dr B. Ziemer, and A. Penner for
helpful discussions concerning the crystal structure analyses.
d(15N) -75. Analytical data for 8b: H NMR (500 MHz, C6D6):
1
1
31
d -21.50 (m, d in the H{ P} NMR, JHF = 6.5 Hz, vt in the
1H{ F} NMR, JHP = 15.3 Hz, IrH). The resonances for the iPr
19
groups are obscured by signals of 8a. 19F NMR (564.6 MHz,
C6D6): d -100.9 (m, 1 F), -104.7 (m, 1 F), -124.8 (m, 1 F), -125.5
(m, 1 F). 31P{ H-selective} NMR (162.0 MHz, C6D6): d 10.9 (dd,
1
JPP = 336 Hz, JPH = 14 Hz), -28.1 (dd, JPP = 336 Hz, JPH
=
14 Hz). H,15N HMBC NMR of 8b¢ (40.5 MHz, C6D6): d(15N)
-68. Analytical data for 9: (Found: C, 36.02; H, 5.57; N, 7.33.
C28H54F8Ir2N6P2C6H6 requires C, 35.47; H, 5.25; N 7.30); v˜ (ATR,
diamond)/cm-1 3391, 3351 (NH), 2238 (IrH).
1
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