Reactivity of iridium(I) PNP amido complexes toward protonation and oxidation

Article abstract of DOI:10.1016/j.jorganchem.2013.04.022

Iridium PNP amido complex [Ir(PMe₃){N(CH₂CH ₂PiPr₂)₂}] (3^PMe3) was prepared in high yield starting from ethylene amine complex [Ir(C₂H ₄){HN(CH₂CH₂

Full text of DOI:10.1016/j.jorganchem.2013.04.022

Journal of Organometallic Chemistry 744 (2013) 35e40
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactivity of iridium(I) PNP amido complexes toward protonation and
oxidation
Bjorn Askevold b, Anja Friedrich b, Magnus R. Buchner b, Burhanshah Lewall c,
,
Alexander C. Filippou c, Eberhardt Herdtweck b, Sven Schneider a
*
a Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstr. 4, 37077 Göttingen, Germany
b Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany
c Institut für Anorganische Chemie, Universität Bonn, Gerhard-Domagk Str. 1, 53121 Bonn, Germany
a r t i c l e i n f o
a b s t r a c t
Iridium PNP amido complex [Ir(PMe3){N(CH2CH2PiPr2)2}] (3PMe3) was prepared in high yield starting
from ethylene amine complex [Ir(C2H4){HN(CH2CH2PiPr2)2}]PF6. The high nucleophilicity of the amido
nitrogen atom is demonstrated by facile N-methylation with MeOTf. The N-basicity within the series [IrL
{N(CH2CH2PiPr2)2}] (3L; L ¼ PMe3, cyclooctene, CO) is quantified by determination of the corresponding
amine complex pKa values. Examination of chemical and electrochemical oxidation of 3L point
toward decomposition of the primary oxidation product by ligand centered disproportionation. The
strong dependence of the basicity and oxidation potentials on the nature of L is rationalized on the basis
Article history:
Received 24 March 2013
Received in revised form
15 April 2013
Accepted 16 April 2013
Dedicated to Prof. Dr. Dr. h.c. mult. W. A.
Herrmann on the occasion of his 65th
birthday
of 3c-4e NeMeL
p-interactions.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Amido complex
Basicity
Oxidation
1. Introduction
coupling, bifunctional hydroelementation, or amine oxidation [7e
9]. While the general reactivity trends are well understood, a lack
of comprehensive studies, which allow for the estimation of
secondary ligand effects, is apparent.
Anionic pincer ligands, such as the archetypal aryl PCP pincer
{C6H3-2,6-(CH2PR2)2}e, have been popularized for catalysis owing
to the high thermal stability and versatile structural control by
steric adjustment of the substituents [10]. The variation of the
Covalently bound
p-donor (e.g. amido) ligands are frequently
used to stabilize complexes of early transition metals (TMs) in
high oxidation states [1]. In contrast, low-valent, late TM amido
complexes are much more rare [2]. Their distinct reactivity can be
attributed to MeNR2 bonding, particularly the lack of vacant
metal d-orbitals with suitable symmetry, which prevents charge
delocalization by N / M
p
-donation [3]. Hence, high N-centered
central functional group, e.g. by introduction of a p-donor group
basicity and nucleophilicity results, e.g. leading to the formation
of bridging amido complexes. Coordinatively unsaturated alkyla-
mides of these metals tend to decompose by b-H elimination [4].
as in disilylamido, diarylamido, or pyridine based PNP pincer li-
gands, allows for further control of the electronic structure
[2b,11]. Our and other groups recently set out to explore the
The strong contribution of the energetically high-lying nitrogen
lone pair to the HOMO also suggests amido ligand non-innocence
upon oxidation as demonstrated by the characterization of a few
molecular amides with predominant aminyl character [5,6]. These
(electronic) structure/reactivity-relationships have been exploited
in metal mediated or catalyzed processes, such as CeN cross
chemistry of complexes with highly p-basic alkyl- and vinyl-
amido ligands derived from the chelating amine ligand
HN(CH2CH2PR2)2 (HPNPR; R ¼ i-Pr, t-Bu) [12]. For example, we
reported the synthesis of some square-planar d8 amine com-
plexes, [ML(HPNPiPr)]þ (M ¼ Ir, L ¼ CO (1CO), cyclooctene (1COE),
C2H4 (1C2H4); M ¼ Pd, L ¼ Cl (2Cl), Me (2Me), Ph (2Ph)), and the
corresponding amido complexes [ML(PNPiPr)] (M ¼ Ir, L ¼ CO
(3CO), cyclooctene (3COE), C2H4 (3C2H4); M ¼ Pd, L ¼ Cl (4Cl), Me
(4Me), Ph (4Ph)) [13,14]. In the present paper, we present a study
which is aimed at assessing the reactivity trends with
* Corresponding author. Fax: þ49 551 3922582.
E-mail address: sven.schneider@chemie.uni-goettingen.de (S. Schneider).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.04.022

36
B. Askevold et al. / Journal of Organometallic Chemistry 744 (2013) 35e40
electrophiles and oxidizing agents as dependent on further sec-
ondary ligands.
2. Results and discussion
2.1. Syntheses and structural characterizations
[Ir(PMe3)(HPNPiPr)]PF6 (1PMe3) wassynthesized inhighyieldfrom
ethylene complex 1C2H4 and PMe3 (Scheme 1). The corresponding
dmso complex [Ir(OSMe2)(HPNPiPr)]BPh4 (1dmso) was prepared
directly from [IrCl(dmso)2]2, HPNPiPr, and NaBPh4. The NMR spec-
troscopic features of 1PMe3 and 1dmso strongly resemble those of the
related amine complexes 1CO and 1C2H4, indicating Cs symmetry on
the NMR timescale as a result of the pyramidally coordinated nitro-
gen atom. The 2JPP coupling constant of 1PMe3 (19 Hz) is in agreement
with a mutual cis configuration of the PMe3 ligand and the pincer
ligand phosphine atoms, respectively. Reaction of 1PMe3 with KOtBu
gives the corresponding amido complex [Ir(PMe3)(PNPiPr)] (3PMe3) in
high yield (Scheme 1). Deprotonation of the amine ligand effects C2v
symmetry on the NMR timescale, as expected for these square-
planar amido complexes with three-coordinate nitrogen. All at-
tempts to synthesize the corresponding amido complex from 1dmso
were unsuccessful and resulted in complex mixtures of products,
which were not further characterized.
The square-planar coordination geometry around the metal
centers of 1PMe3 and 3PMe3 was also confirmed by single crystal X-
ray diffraction (Fig. 1). Most structural parameters of 1PMe3 and
3PMe3 (Table 1) strongly resemble the respective ethylene and CO
complexes [13a]. As for these previously reported examples,
deprotonation of the nitrogen atom is accompanied by shortening
ꢀ
of the IreN bond by more than 0.1 A. The most apparent structural
Fig. 1. Molecular structures of complexes 1PMe3 (above, anion omitted) and 3PMe3
(below) with thermal ellipsoids drawn at the 50% probability level (hydrogen atoms,
except NeH) are omitted for clarity.
difference within the series of IrI amido complexes 3L (L ¼ PMe3,
C2H4, CO) in comparison with PdII complexes 4Cl, 4Me, and
[Pd(CNtBu){N(CH2CH2PiPr2)2}]PF6 (4CNtBu) is the more planar co-
ordination around the amido nitrogen for Ir than for Pd, as
expressed by the sum of bond angles around the nitrogen atoms (Ir:
355.7ꢀ (3CO), 356.6ꢀ (3C2H4), 353.0ꢀ (3PMe3); Pd: 337.4ꢀ (4Cl), 345.7ꢀ
(4Me), 343.2ꢀ (4CNtBu)) [13a,14]. Planarization of the nitrogen atom
coordination is a structural prerequisite for NeM
p-bonding,
indicating stronger
p
-interactions for 3L as compared with 4R in the
solid state. However, conformational changes regarding pyramid-
alization around the nitrogen atom within this flexible ligand
framework will exhibit a shallow potential energy surface.
2.2. Reaction of 3L with electrophiles
Complex 3PMe3 reacts with MeOTf to give [Ir(PMe3)
{MeN(CH2CH2PiPr2)2}]OTf (5), selectively (Scheme 1). Complex 5
Table 1
Selected bond lengths and angles of 1PMe3 and 3PMe3 in the crystal.
1PMe3
3PMe3
ꢀ
Bond lengths [A]
Ir1eN1
Ir1eP1
Ir1eP2
Ir1eP3
2.176(3)
2.3079(9)
2.3033(9)
2.2309(9)
2.069(2)
2.2892(7)
2.2764(7)
2.2225(7)
Bond angles [ꢀ]
P1eIr1eN1
P2eIr1eN1
P3eIr1eN1
P1eIr1eP2
82.04(8)
82.19(8)
178.07(8)
164.10(3)
81.29(6)
81.67(6)
178.48(7)
162.89(3)
Scheme 1. Synthesis and reactivity of amido complex 3PMe3
.

B. Askevold et al. / Journal of Organometallic Chemistry 744 (2013) 35e40
37
Table 2
pKa values of 1L in d6-dmso and oxidation potentials of 3L and of 1PMe3 (vs.
Fe(C5Me5)2/Fe(C5Me5)þ2 ) at room temperature; ratio anodic/cathodic currents
(Ipa/Ipc) in parantheses (electrolyte: THF, 0.1 M NBu4PF6; scan rate: 100 mV sꢁ1
E1/2 ¼ (Ea þ Ec)/2; n.m. ¼ not measured).
;
EI1/2 [V]b
E
[V]b
E
[V]b
a
II
III
L
pKa
1/2
1/2
PMe3
COE
CO
22.0(1)
16.0(4)
14.8(2)
ꢁ0.66 (3.3)
ꢁ0.06 (4.3)
þ0.04 (3.1)
ꢁ0.26 (1.0)
þ0.16 (1.0)
þ0.40 (2.0)
þ0.53 (1.9)c
þ0.80 (2.0)
þ0.78 (2.0)
a
Amine complexes [IrL{HN(CH2CH2PiPr2)2}]þ (1L).
b
c
Amido complexes [IrL{N(CH2CH2PiPr2)2}] (3L).
E
([IrL{HN(CH2CH2PiPr2)2}]PF6) ¼ þ0.52 V (2.0).
III
1/2
was characterized by multinuclear NMR spectroscopy and
elemental analysis. The singlet signals at 2.70 (1H NMR) and
44.9 ppm (13C NMR), respectively, can be assigned to the N-methyl
group. The same reactivity was found for 4Cl and other palladiu-
m(II) amido complexes [14,15]. In case of iridium(I), attack of C-
electrophiles at the metal center instead of the amido nitrogen
atom seems more likely as compared with PdII, considering the
thermodynamic and kinetic accessibility of Ir(III) by oxidative
addition to IrI. However, no indication for the formation of an iri-
dium(III) methyl complex was found in the present case.
Fig. 3. Cyclic voltammograms (CVs) of complexes 3PMe3 and of 1PMe3 (vs. Fe(C5Me5)2/
Fe(C5Me5)þ2 ) at room temperature (THF, 0.1 M NBu4PF6). Red: CVs of 3PMe3 at scan rate
100 mV sꢁ1. Green: CV of 3PMe3 at scan rate 800 mV sꢁ1. Blue: CV of 1PMe3 at scan rate
100 mV sꢁ1
.
with four electrons. The HOMO exhibits strong NeIr
character, resulting in the absence of a net NeIr
tantly, dxz *(CO) backbonding stabilizes the HOMO in terms of a
3c-4e NeIr-L pushepull
p
-antibonding
p
-bond. Impor-
/
p
The N-centered Brønstedt basicity of 3L (L ¼ PMe3, COE, CO) was
quantified from equilibrium constants with suitable acids by NMR
spectroscopy. As solvent, d6-dmso was chosen to prevent contact
ion formation and make use of the extensive reference pKa data
available for this solvent [16]. The corresponding amine (1L) pKa
values derived in this way are provided in Table 2. Despite the
relevance for catalysis, only few pKa values of amine complexes in
non-aqueous solvents were reported in the literature [17]. Within
this series, the ligand in trans-position to the PNP nitrogen atom
exhibits a strong influence on amine acidity, varying over a range of
more than seven orders of magnitude. The data follows the ex-
p
-interaction. Furthermore, the reactivity
of 3L as an N-nucleophile can be rationalized with the higher en-
ergy of this orbital, relative to the highest occupied, metal centered
orbital (dz2, HOMO-1).
2.3. Oxidation of 3L
We previously reported that chemical oxidation of palladium(II)
amide 4Ph with AgPF6 in THF gives amine complex 2Ph as major
product and minor quantities of imine [PdPh{N(CHCH2PiPr2)(CH2
CH2PiPr2)}] [14]. Deuterium labeling suggested the formation of
transient radical cation [PdPh(PNPiPr)]þ which decomposes by
hydrogen atom transfer from the solvent and disproportionation of
the chelate backbone to amine and imine complexes. Similarly, the
reaction of iridium(I) amide 3PMe3 with AgPF6, [FeCp2]PF6, or
CPh3PF6, respectively, in THF (Scheme 1) results in the formation of
1PMe3 as major product (85% by 31P NMR). As in case of Pd, the minor
product (15%) is assigned to imine complex [Ir(PMe3){N(CHCH2
PiPr2)(CH2CH2PiPr2)}][PF6] (6PMe3) on the basis of 31P and 1H NMR
spectroscopy. Unfortunately, 6PMe3 could not be isolated in pure
form, to date.
pected trend:
p
-acceptor ligands like cyclooctene (1COE/3COE) and
CO (1CO/3CO) stabilize the electron rich amido complexes resulting
in considerably lower pKa (see below). However, the large range of
the pKa values is remarkable in comparison with the ones derived
for Pd complexes. There, both 2Me (24.2(1)) and 2Ph (23.2(1))
exhibit almost identical pKa [14]. As indicated by the molecular
structures (see above), more pronounced
could be responsible.
p-bonding for iridium(I)
The electronic structure of 3CO was also examined by DFT
computations (B3LYP/6-311 þ G**) to evaluate the qualitative pic-
ture (Fig. 2). The p-interaction that mixes the nitrogen lone pair, the
The oxidation of the iridium(I) PNP amides 3L (L ¼ PMe3, COE, CO)
was further examined by cyclic voltammetry (CV) in a THF/
dxz orbital, and the respective in-plane
p*(CO)-orbital gives three
molecular orbitals (HOMO-3, HOMO, and LUMO) that are occupied
Fig. 2. Frontier KohneSham orbital scheme (left), graphical orbital representations (center) and three center
p .
-interaction (right) for 3CO

38
B. Askevold et al. / Journal of Organometallic Chemistry 744 (2013) 35e40
N(nBu)4PF6 electrolyte. The first oxidation (1eꢁ) is characterized by
an anodic wave at EI1/2 (Table 1 and Fig. 3), which is strongly
dependent on the ligand L. As expected, 3PMe3 is oxidized at
4.2. Analytical methods
Elemental analyses were obtained from the Microanalytical
Laboratory of Technische Universität München. The IR spectra
were recorded on a Jasco FT/IR-460 PLUS spectrometer as nujol
mulls between KBr plates. NMR spectra were recorded on Jeol
Lambda 400 spectrometers at room temperature and calibrated
to the residual proton resonance and the natural abundance 13C
resonance of the solvent (C6D6, dH ¼ 7.16 ppm, dC ¼ 128.1 ppm;
d6-dmso, dH ¼ 2.50 ppm, dC ¼ 39.5 ppm, d8-THF, dH ¼ 1.73
considerably more negative potential compared with 3COE and 3CO
,
which carry strong
p-acceptor ligands instead of PMe3. Irrevers-
ibility of this oxidation process at scan rates of 100 mV sꢁ1 is indi-
cated by the ratios of the anodic and cathodic currents, yet becoming
increasingly quasireversible at higher scan rates. A second oxidation
II
at higher potential (E ) was found to be quasi-reversible at scan
1/2
rates of 100 mV sꢁ1 for 3PMe3 and 3COE but irreversible for 3CO at all
experimental conditions (100e600 mV sꢁ1). Finally, all three com-
pounds exhibit an irreversible anodic wave at higher potentials (E1/
and 3.58 ppm, dC
¼
25.3 and 67.2 ppm, d6-acetone
dH ¼ 2.05 ppm, dC ¼ 29.8 ppm and 206.3). 31P NMR chemical
III). For 3PMe3, this last redox process was assigned to the oxidation
shifts are reported relative to external phosphoric acid
2
of the corresponding amine complex 1PMe3 by comparison with the
CV of an original sample. The results from electrochemical and
chemical oxidation are rationalized with an ECEE mechanism on the
electrochemical timescale [18]. The initial radical from one-electron
oxidation of 3L disproportionates by ligand backbone hydrogen
(
d
¼ 0.0 ppm). IR peak intensities are abbreviated as: m (me-
dium), s (strong). NMR Signal multiplicities are abbreviated as: s
(singlet), d (doublet), t (triplet), vt (virtual triplet), sp (septet), m
(multiplet), br (broad). Cyclic voltammograms were recorded
with a glassy carbon working electrode, a platinum wire counter
electrode, and a Fe(C5Me5)2/Fe(C5Me5)þ2 reference electrode. The
potential of the reference electrode vs. Fe(C5H5)2/Fe(C5H5)2þ
transfer. For 3PMe3, the resulting amine (1PMe3) and imine (6PMe3
)
complexes were detected by NMR spectroscopy after chemical
oxidation and 1PMe3 was unambiguously detected as product from
(
D
E
¼
þ466 mV) was derived by external standard
III
electrochemical oxidation (E ), as well. Hence, the redox process at
measurements.
1/2
potential E is tentatively assigned to the imine complexes 6L.
II
1/2
4.2.1. pKa determinations
The amido complexes 3L and an equimolar amount of a corre-
sponding acid with suitable pKa (3CO and 3COE: benzimidazole;
3PMe3: 2-pyrrolidinone) were dissolved in 0.6 mL of d6-dmso. Due
to fast proton exchange on the NMR time scale one peak resulted in
the 31P NMR with a chemical shift dmeas that was located between
those of pure 1L (d1L) and 3L (d3L) in d6-dmso. The equilibrium molar
fractions of 3L (x3L) and the corresponding 1L (x1L) conjugate acid
cation were derived using:
3. Conclusions
Electron rich metal amido complexes are particularly interesting
compounds owing to their distinct ligand centered basicity and
redox chemistry. In this context, a series of square planar iridium(I)
dialkylamido complexes 3L (L ¼ PMe3, COE, CO) was probed with
respect to the reactivity toward electrophiles and oxidation. 3L
readily reacts with C-electrophiles or Brønstedt acids upon N-
alkylation and eprotonation, respectively. In contrast to analogous
palladium complexes, the amine pKa values are strongly dependent
on the N-trans ligand allowing for facile tuning of this property.
Similarly, the oxidation of 3L exhibits a strong dependence on the
dmeas ¼ X1Ld1L þ X3Ld3L
X1L þ X3L ¼ 1
(1)
(2)
pKa values were calculated from the equilibrium constant (Keq
)
p-acceptor ability of L. Chemical and electrochemical oxidation
using the following equations (pKa(2-pyrrolidinone)
pKa(benzimidazole) ¼ 16.4) [20]:
¼
24.2;
studies indicate decomposition of the transient amido radical by
ligand-centered disproportionation. However, while ligand-
centered redox processes are prevalent, the electrochemical po-
tentials can be effectively tuned by choice of the appropriate Ir/
auxiliary ligand platform. This strong influence of the ligand in
trans-position is attributed to an NeMeL 3c-4e pushepull inter-
action, providing guidelines for the design of cooperative or redox-
catalysts.
Keq ¼ X23L=X21L
(3)
(4)
À
Á
À
Á
pKa 1L ¼ pKaðrefÞ ꢁ log Keq
4.3. Syntheses
4. Experimental section
4.3.1. [Ir(PMe3)(HPNPiPr)]PF6 (1PMe3
)
4.1. Materials and methods
[Ir(C2H4)(PNP)H][PF6] (1C2H4) (0.029 g; 0.043 mmol) is dis-
solved in THF (5 mL) and PMe3 (1.0 M in THF; 0.060 mL; 1.4 eq)
added via syringe. The yellow solution is stirred for 10 min,
filtered, and pentanes (20 mL) added to give a yellow precipitate.
The product is filtered off, washed with 10 mL pentanes and
dried i. vac. Yield: 0.030 g (0.042 mmol, 98%). Anal. Calcd. for
C19H46F6IrNP4 (718.68): C, 31.75; H, 6.45; N, 1.95. Found: C, 31.65;
All experiments were carried out under an atmosphere of argon
using Schlenk and glove-box techniques. The solvents were dried
over Na/benzophenone (THF) and distilled under argon or dried
and deoxygenated by passing through columns packed with acti-
vated alumina and Q5, respectively. C6D6 and d8-THF were dried by
distillation from Na/K alloy. d6-acetone and dmso were stirred over
H, 6.06; N, 1.88. IR (Nujol, cmꢁ1
)
n
¼ 3240 (m, NeH). NMR
4 A molecular sieve and distilled from B2O3 (d6-acetone) or CaH2
(C6D6/d8-THF, r.t., [ppm]) 1H NMR (399.8 MHz):
d
¼ 0.93 (m, 18H,
16.4 Hz,
ꢀ
(dmso), respectively. All deuterated solvents were deoxygenated by
three freezeepumpethaw cycles. KOtBu was purchased from VWR
and sublimed prior to use. AgPF6 (ABCR), [FeCp2]PF6 (Aldrich),
CPh3PF6 (VWR) and MeOTf (Aldrich) were used as purchased.
[IrCl(dmso)2]2 and 1C2H4 were prepared according to published
procedures [13a,19].
CH3), 1.09 (A3MXX0M0A3,
N
¼
j3JHP
þ
5JHP
j ¼
3JHH ¼ 7.2 Hz, 6H, CH3), 1.24 (d, 9H, JHP ¼ 8.0 Hz, P(CH3)3), 1.63
2
(m, 2H, PCH2), 1.72e1.98 (m, 8H, PCH2, CH(CH3)2, NCH2), 3.21 (m,
2H, NCH2), 4.50 (br, 1H, NH). 13C {1H} NMR (100.6 MHz):
d
¼ 17.6
(s, CH3), 18.4 (s, CH3), 20.1 (s, CH3), 20.4 (s, CH3), 23.2 (d,
JCP ¼36.0 Hz, P(CH3)3), 25.1 (AMXM0A0, N ¼ j1JCP þ 3JCPj ¼ 12.2 Hz,

B. Askevold et al. / Journal of Organometallic Chemistry 744 (2013) 35e40
39
3JCP ¼ 3.1 Hz, PCH2), 26.1 (AXX0A0, N ¼ j1JCP
þ
3JCPj ¼ 14.5 Hz,
CH(CH3)2), 44.9 (s, NCH3), 64.4 (s, NCH2). 31P {1H} NMR
2
CH(CH3)2), 27.7 (AXX0A0, N ¼ j1JCP
þ
3JCPj ¼ 13.8 Hz, CH(CH3)2),
(161.8 MHz):
d
¼ ꢁ47.6 (t, JPP ¼ 18.8 Hz, P(CH3)), 53.8 (d,
55.4 (s, NCH2). 31P {1H} NMR (161.8 MHz):
d
¼
56.5 (d,
2JPP ¼ 18.8 Hz, PiPr2), 19F NMR (376.2 MHz):
d
¼ ꢁ78.7 (s, SO3CF3).
2
2JPP ¼ 18.8 Hz, PiPr2), ꢁ45.5 (d, JPP ¼ 18.8 Hz, P(CH3)3), ꢁ143.0
1
(sp, JPF ¼ 712.0 Hz, PF6).
4.3.5. Chemical oxidation of 3PMe3 in THF
3PMe3 (5 mg, 8.7
mmol) is dissolved in THF (0.5 mL) in a J-Young
4.3.2. [Ir(SOMe2)(HPNPiPr)]BPh4 (1dmso
)
NMR tube and AgPF6 (2.2 mg, 8.7 mol) is added at room tem-
m
HN(CH2CH2PiPr2)2 (0.135 g; 0.443 mmol) in THF (5 mL) is added
to a mixture of [IrCl(dmso)2]2 (0.170 g; 0.221 mmol) and NaBPh4
(0.152 g; 0.443 mmol) in THF (5 mL). The solution is stirred for 1 h at
room temperature and filtered. The yellow, microcrystalline prod-
uct is precipitated by addition of diethylether (10 mL) and pentanes
(5 mL), filtered off, and dried i. vac. Yield: 0.318 g (0.355 mmol, 80%).
Anal. Calcd. for C42H63BIrNOP2S (895.00): C, 56.36; H, 7.10; N, 1.57.
perature. Immediately, the orange solution turns dark red and a
black precipitate forms (Ag). The starting material is quantitatively
converted to a mixture of 1PMe3 (85%) and another compound (15%)
that was assigned to [Ir(PMe3)(N(CHCH2PiPr2)(CH2CH2PiPr2))]
(7PMe3), based on NMR data: (d8-THF, r.t., [ppm]) 1H NMR
(399.8 MHz):
d
¼ 3.77 (m, 2H, NCHCH2), 8.71 (d, 3JHH ¼ 24.1 Hz, 1H,
2
NCHCH2). 31P{1H} NMR (161.8 MHz):
d
¼ ꢁ43.9 (t, JPP ¼ 19.8 Hz,
2
2
Found: C, 56.86; H, 6.99; N, 1.30. IR (Nujol, cmꢁ1
)
n
¼ 3181 (s, NeH).
P(CH3)), 59.0 (dd, JPP ¼ 19.8 Hz, JPP ¼ 288.3 Hz, PiPr2), 62.4 (dd,
NMR (d8-THF, r.t., [ppm]) 1H NMR (399.8 MHz):
d
¼
1.16
2JPP ¼ 18.8 Hz, JPP ¼ 295.2 Hz, PiPr2).
2
(A3MXX0M0A3 , N ¼ j JHP þ 5JHPj ¼ 14.0 Hz, 3JHH ¼ 7.2 Hz, 6H, CH3),
Upon using [FeCp2]PF6 (2.9 mg, 8.7 mmol) or CPh3PF6 (3.4 mg,
3
0
3
3
1.24 (A3MXX0M0A3 , N ¼ j JHP
þ
5JHPj ¼ 14.0 Hz, JHH ¼ 7.2 Hz, 6H,
8.7
mmol) as oxidants the same observations are made.
0
CH3), 1.31 (m, 12H, CH3), 1.46 (m, 2H, PCH2), 1.96 (m, 2H, PCH2), 2.15
(m, 2H, NCH2), 2.35 (m, 2H, CH(CH3)2), 2.45 (m, 2H, CH(CH3)2), 2.78
(m, 2H, NCH2), 3.36 (s, 6H, OS(CH3)2), 4.47 (br, 1H, NH), 6.72 (t,
4.4. Computational methods
3JHH ¼ 7.2 Hz, 4H, B(C6H5)4), 6.86 (t, JHH ¼ 7.2 Hz, 8H, B(C6H5)4),
DFT calculations on complex 3CO were performed with
GAUSSIAN03 RevC.02 using the B3LYP functional [21,22]. Geometry
optimizations were run without symmetry or internal coordinate
constraints using the Stuttgart-RSC-ECP and corresponding valence
3
7.28 (br, 8H, B(C6H5)4). 13C {1H} NMR (100.6 MHz):
d
¼ 17.1 (s, CH3),
17.9 (s, CH3), 19.3 (s, CH3), 19.6 (s, CH3), 23.6 (AXX0A0,
N ¼ j1JCP þ 3JCPj ¼ 13.0 Hz, PCH2), 24.4 (m, CH(CH3)2), 26.7 (AXX0A0,
N ¼ j1JCP
þ
3JCPj ¼ 14.5 Hz, CH(CH3)2), 53.3 (s, OS(CH3)2), 55.7 (br,
basis set for iridium and all-electron split valence triple-z basis set 6-
NCH2), 120.99 (s, B(C6H5)4), 124.8 (s, B(C6H5)4), 136.3 (s, B(C6H5)4),
311 þ G** for all other elements [23,24]. The optimized structure is in
good agreement with the experimental molecular structure from X-
ray diffraction and was verified as being a true minimum on the po-
tential surface by the absence of negative eigenvalues in the vibra-
tional frequency analysis. Orbitals were visualized with GaussView
via cube files generated from formatted checkpoint files [25].
164.3 (q, JCB ¼ 48.9 Hz, B(C6H5)4). 31P {1H} NMR (161.8 MHz):
1
d
¼ 58.13 (s, PiPr2). 11B {1H} NMR (128.3 MHz):
d
¼ ꢁ7.54 (s,
B(C6H5)4).
4.3.3. [Ir(PMe3)(PNPiPr)] (3PMe3
)
1PMe3 (0.200 g; 0.224 mmol) and KOtBu (0.025 g; 0.223 mmol)
were dissolved in THF (10 mL) and stirred for 10 min at room
temperature. The solvent is evaporated and the residue is extracted
with pentanes. After filtration, crystallization at ꢁ20 ꢀC gives 3PMe3
as orange crystals, which are filtered off and dried i. vac. Yield:
0.115 g (0.201 mmol, 90%). Anal. Calcd. for C19H45IrNP3 (572.71): C,
4.5. Single crystal X-ray structure determinations
Compound 1PMe3
: Crystal data: formula: C19H46F6IrNP4;
Mr ¼ 718.67; crystal color and shape: orange fragment, crystal di-
mensions: 0.46 ꢂ 0.51 ꢂ 0.51 mm; crystal system: monoclinic;
39.85; H, 7.92; N, 2.45. Found: C, 40.00; H, 8.46; N, 2.49. NMR (C06D6,
space group: C2/c (no. 15); a ¼ꢀ 14.7502(6), b ¼ 14.1777(4),
r.t., [ppm]) 1H NMR (399.8 MHz):
d
¼ 1.11 (A6M2XX0M2 A6 ,
c ¼ 27.5450(11) A,
b
¼ 99.002(3) ; V ¼ 5689.4(4) A ; Z ¼ 8;
3
0
ꢀ
ꢀ
3
N ¼ j3JHP
þ
5JHPj ¼ 12.8 Hz, JHH ¼ 6.8 Hz, 12H, CH(CH3)2), 1.20
m
(MoKa) ¼ 4.966 mmꢁ1
;
rcalcd ¼ 1.678 g cmꢁ3
;
q
-range ¼ 4.00e
3
3
(A6M2XX0M2 A6 , N ¼ j JHP
þ
5JHPj ¼ 15.2 Hz, JHH ¼ 7.6 Hz, 12H,
26.80ꢀ; data collected: 38361; independent data [Io>2
s(Io)/all data/
0
0
2
CH(CH3)2), 1.54 (d, JHP ¼ 6.8 Hz, 9H, P(CH3)3), 1.85 (m, 4H, PCH2),
Rint]: 5102/5995/0.056; data/restraints/parameter: 5995/0/295; R1
1.96 (m, 4H, CH(CH3)2), 3.43 (m, 4H, NCH2). 13C {1H} NMR
[Io>2s(Io)/all data]: 0.0259/0.0329; wR2 [Io>2s(Io)/all data]:
(100.6 MHz):
d
¼ 18.1 (s, CH3), 20.3 (s, CH3), 25.9 (d, 1JCP ¼ 29.2 Hz,
0.0619/0.0638; GOF ¼ 1.035; Drmax/min: 2.21/ꢁ1.18 eÅꢁ3. Com-
pound 3PMe3: Crystal data: formula: C19H45IrNP3; Mr ¼ 572.69;
crystal color and shape: orange fragment, crystal dimensions:
0.30 ꢂ 0.46 ꢂ 0.61 mm; crystal system: monoclinic; space group:
P(CH3)3), 26.6 (A2XX0A02, N ¼ j1JHP þ 3JHPj ¼ 13.1 Hz, CH(CH3)2), 28.6
(A2MXM0A02, N ¼ j1JHP þ 3JHPj ¼ 12.3 Hz, 3JCP ¼ 5.3 Hz PCH2), 62.6 (s
(br), NCH2). 31P {1H} NMR (161.8 MHz):
d
¼ 68.1 (d, 2JPP ¼ 18.3 Hz,
2
PiPr2), ꢁ55.2 (t, JPP ¼ 18.3 Hz, P(CH3)3).
P21/c (no. 14)ꢀ; a ¼ 10.1460(4), b ¼ 14.3405(5), c ¼ 16.9529(8) A,
ꢀ
3
ꢀ
b
¼ 97.606(4) ; V ¼ 2444.92(17) A ; Z ¼ 4;
m
(MoKa) ¼ 5.660 mmꢁ1
;
4.3.4. [Ir(PMe3)(MePNPiPr)]OTf (5)
rcalcd ¼ 1.556 g cmꢁ3
;
q
-range ¼ 4.05e26.81ꢀ; data collected:
MeOTf (4.7 mg, 3.2
mL, 28
m
mol) is added to a solution of [Ir(P-
35823; independent data [Io>2s(Io)/all data/Rint]: 5049/5169/
Me3)(PNPiPr)] (3PMe3) (15.3 mg, 28
mmol) in toluene (2 mL) and
0.058; data/restraints/parameter: 5169/0/229; R1 [Io>2
s
(Io)/all
stirred for 30 min until a yellow solid is formed. After removing of
all volatiles, the product is washed twice with diethylether and
dried i. vac. to give microcrystalline, yellow 5. Yield 19 mg
(0.026 mmol; 91%). Anal. Calcd. for C21H48F3IrNO3P3S (736.81): C,
34.23; H, 6.57; N, 1.90; S, 4.35. Found: C, 33.79; H, 6.20; N, 1.91; S,
data]: 0.0207/0.0217; wR2 [Io>2s(Io)/all data]: 0.0454/0.0458;
GOF ¼ 1.272; Drmax/min: 0.87/ꢁ0.74 eÅꢁ3
.
Acknowledgments
4.32. NMR (d6-acetone, r.t., [ppm]) 1H NMR (399.8 MHz):
d
¼ 1.24e
The authors thank the Deutsche Forschungsgemeinschaft (Emmy-
Noether Programm SCHN950/2-1) and the IDK NanoCat for funding.
2
1.43 (m, 24 H, CH3), 1.71 (d, JPH ¼ 8.8 Hz, 9H, P(CH3)3), 2.25e2.31
(m, 4H, PCH2), 2.25e2.31 (m, 4H, PCH2), 2.34e2.41 (m, 2H,
CH(CH3)2), 2.46e2.54 (m, 2H, CH(CH3)2), 2.70 (s, 3H, NCH3), 2.81e
2.91 (m, 2H, NCH2), 2.99e3.11 (m, 2H, NCH2). 13C {1H} NMR
Appendix A. Supplementary material
(100.6 MHz):
d
¼ 16.7 (s, CH3), 18.8 (s, CH3), 20.0 (s, CH3), 20.8 (m,
CCDC 929265 and 929266 contain the supplementary crystal-
lographic data for this paper. This data can be obtained free of
PCH2), 22.6 (d, PCH3, 1JCP ¼ 37.6 Hz), 23.1 (m, CH(CH3)2), 25.1 (m,

40
B. Askevold et al. / Journal of Organometallic Chemistry 744 (2013) 35e40
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