Unprecedented reactivity of Iridium(I) secondary phosphine oxide complexes: Formation of P-coordinated phosphinate complexes by P-aryl bond cleavage

Article abstract of DOI:10.1021/om1007874

Aryl-iridium(III) hydride complexes with a P-coordinated phosphinate were formed from [Ir(cod)Cl]₂ and secondary phosphine oxide-oxazoline ligands under basic conditions. The structure of these complexes, whose formation involved C-P cleavage, was assigned by X-ray analysis and NMR spectroscopy.

Full text of DOI:10.1021/om1007874

Organometallics 2010, 29, 5953–5958 5953
DOI: 10.1021/om1007874
Unprecedented Reactivity of Iridium(I) Secondary Phosphine
Oxide Complexes: Formation of P-Coordinated Phosphinate
Complexes by P-Aryl Bond Cleavage
†
†
‡
‡
€
Marc Liniger, Bjorn Gschwend, Markus Neuburger, Silvia Schaffner, and
Andreas Pfaltz*,†
†Department of Chemistry, University of Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland, and
‡Laboratory for Chemical Crystallography, Spitalstrasse 51, CH-4056 Basel, Switzerland
Received August 12, 2010
Aryl-iridium(III) hydride complexes with a P-coordinated phosphinate were formed from
[Ir(cod)Cl]2 and secondary phosphine oxide-oxazoline ligands under basic conditions. The structure
of these complexes, whose formation involved C-P cleavage, was assigned by X-ray analysis and
NMR spectroscopy.
Introduction
Examples are Rh- and Co-catalyzed hydroformylations,7,8 Pd-
catalyzed Heck reactions,9 Ni- and Pd-catalyzed allylic sub-
stitutions,10 and Ir-catalyzed dehydrogenation reactions of
cycloalkanes.11
Here we report an unusual P-aryl bond cleavage reaction
in iridium complexes with a secondary phosphine oxide
ligand, leading to iridium hydride complexes with a P-
coordinated phenylphosphinate unit.
The activation of C-H or C-heteroatom bonds by
transition-metal complexes is a well-known process that forms
the basis for numerous important synthetic methods.1 While
insertions of metal centers into C-H and C-halogen bonds
have been studied extensively,2,3 analogous oxidative addi-
tion reactions involving other C-heteroatom bonds4 or C-
C bonds5 are far less documented. The literature on inser-
tions into C-P bonds is especially scarce,6 although the
cleavage of P-aryl bonds has been identified as a deactivation
mode of transition-metal catalysts with arylphosphine ligands.
Results and Discussion
In the course of our work on Ir-catalyzed asymmetric
hydrogenation,12 we became interested in P,N ligands con-
taining a secondary phosphine oxide (SPO).13 The ligands
4 and 5 were easily prepared from the corresponding oxazolines
1 and 2 by lithiation and reaction with phenyl(diethyl-
amino)chlorophosphine14 (3) followed by hydrolysis (Scheme 1).
*To whom correspondence should be addressed. E-mail:
andreas.pfaltz@unibas.ch. Tel: þ41 (0)61 2671108. Fax: þ41 (0)61
2671103.
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2010 American Chemical Society
Published on Web 10/20/2010
pubs.acs.org/Organometallics

5954 Organometallics, Vol. 29, No. 22, 2010
Liniger et al.
After column chromatography the air-stable ligands were
obtained in yields of 74% (4) and 80% (5). The diastereo-
isomers (S,SP)-5 and (S,RP)-5 were separated by semipre-
parative HPLC. The configuration of these compounds was
assigned by X-ray analysis.15
to substantial amounts of a side product in addition to the
expected complex (S,RP)-7 or (S,SP)-7, respectively.
Reaction of ligand (S,SP)-5 (1.0 equiv), [Ir(cod)Cl]2 (0.5
equiv), and NaOH (2.5 equiv) in deuterated methanol for
15 min gave two complexes, the expected SPO complex
(S,RP)-7 and an unknown product, as indicated by 31P{1H}
NMR (Scheme 3). After concentration of the reaction mix-
ture, yellow air-stable crystals were formed in the NMR tube,
which according to NMR analysis corresponded to the
unknown product. The structure of this complex was elucid-
ated by single-crystal X-ray diffraction (structure 8, Figure 1).
The iridium atom in this complex is surrounded by a C,N-
coordinated phenyloxazoline ligand and a P-coordinated
deprotonated phosphinic acid monoester. The remaining
three coordination sites in the distorted-octahedral complex
are occupied by the P,N-bound SPO ligand (S,SP)-5 and a
deuteride. This unusual structure results from cleavage of the
P-aryl bond and formation of a C,N-coordinated Ir(I)-
phenyloxazoline complex. The Ir-bound phosphorus moiety
is transformed to a phosphinic acid methyl ester by addition
of methoxide with concomitant protonation of the Ir(I) atom
leading to an Ir(III)-hydride complex (Scheme 4). During
this transformation the cod ligand is replaced by a second
molecule of the SPO ligand. The deuteride ligand was located
Iridium complexes of such ligands ([Ir(cod)(SPO∧N]-
BArF; BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)
proved to be active catalysts in the asymmetric hydrogena-
tion of imines, comparable to analogous [Ir(cod)(PHOX)]BArF
complexes.15
We undertook the preparation of zwitterionic iridium
complexes by deprotonation of the corresponding [Ir(cod)-
(SPO∧N]þ complexes to evaluate their application as hydro-
genation catalysts. Although the reaction of the SPO∧N
ligands and [Ir(cod)Cl]2 in basic methanol gave the desired
complexes 6 and 7 (Scheme 2), attempts to isolate these
zwitterionic iridium(I) complexes failed. However rac-6,
(S,RP)-7, and (S,SP)-7 could be characterized in solution
by 1H, 13C, and 31P NMR spectroscopy.
Unfortunately, the zwitterionic complexes were very sensi-
tive and, moreover, their performance in asymmetric hydro-
genation was disappointing. However, in our complexation
studies we observed the formation of unexpected side prod-
ucts that had undergone drastic changes in the ligand
structure. The product composition strongly depended on
the conditions and the ligand used for complexation. Where-
as ligand 4 was cleanly converted to the corresponding Ir
complex 6, complexation with ligand (S,SP)-5 or (S,RP)-5 led
2
in the difference Fourier map. The resonances in the H
NMR spectrum confirmed the existence of this deuteride
(-21.3 ppm) and a phosphinic acid trideuteromethyl ester
(2.76 ppm). Furthermore, two doublets consistent with two P
ligands in a cis arrangement were observed in the 31P{1H}
2
NMR spectrum (53.5 and 49.9 ppm, JP,P =18 Hz) and a
Scheme 1. Ligand Synthesis
Scheme 2. Observed Zwitterionic Iridium(I) Complexes in So-
lution
Figure 1. Crystal structure of complex (4S,40S,1RP,10SP)-8
(ellipsoids at the 50% probability level). Solvent molecules
and hydrogen atoms are omitted for clarity.
Scheme 3. Complexation of (S,SP)-5 in MeOH-d4

Article
Organometallics, Vol. 29, No. 22, 2010 5955
Scheme 4. Proposed Mechanism for the P-Ar Bond Cleavage
Scheme 5. Complexation of rac-4 under Basic Conditions
in CH2Cl2
Figure 2. Crystal structure of complex 9 (ellipsoids at the 50%
probability level). Hydrogen atoms are omitted for clarity.
characteristic peak for the Ir-D stretching (2069 cm-1) in
the IR spectrum. In the solid state, the Ir complex 8 forms a
dimeric structure, in which the two sodium ions are con-
nected by two bridging methanol molecules (see the Support-
ing Information).
An analogous reaction was observed when [Ir(cod)Cl]2
and 4 were reacted in a biphasic mixture of aqueous NaOH
and CH2Cl2 (Scheme 5). The red reaction solution contained
several unidentified species, as indicated by 31P NMR spec-
troscopy; thereafter complex 9 was isolated as red highly air-
sensitive crystals and analyzed by X-ray diffraction. The
solid-state structure of this iridium(III)-hydride complex is
shown in Figure 2.
Instead of a deprotonated secondary phosphine oxide and
a monomethyl phosphinate anion as in structure 8 (Figure 1),
cyclooctadiene and P-phenylphosphinate are bound at the
˚
metal center of complex 9. The short O-O distance of 2.53 A
between the two symmetry-related phosphinate groups is an
indication of hydrogen bridges in the solid state, resulting in
a dimeric structure. Evidence for the prescence of a hydride,
which could not be localized by X-ray diffraction, was
provided by 1H NMR spectroscopy (-16.43 ppm).
Motivated by these unexpected results, we decided to
search for conditions that allowed the synthesis of phos-
phinate complexes on a preparative scale.
Figure 3. Crystal structure of complex (4S,40S,1SP,10RP)-11
(ellipsoids at the 50% probability level). Hydrogen atoms are
omitted for clarity.
Scheme 6. Optimized Synthesis of Complexes
(4S,40S,1RP,10SP)-10 and (4S,40S,1SP,10RP)-11
Reaction of 2 equiv of the secondary phosphine oxide (S,
SP)-5 or (S,RP)-5, [Ir(cod)Cl]2, and NaOH in methanol for
2 h at room temperature provided, after column chromatog-
raphy and recrystallization from CH2Cl2/hexane, the corre-
sponding iridium hydride complexes in moderate yields of
25% (10) and 58% (11) (Scheme 6). Characteristic bands
for Ir-H streching (2233 cm-1 (10), 2177 cm-1 (11)) were
observed in the IR spectra. Crystals of complex 11 suitable
for X-ray analysis were obtained using a vapor diffusion
˚
method (Figure 3). The O-O distance of 2.43 A is consistent
with an intramolecular hydrogen bridge between the phos-
phinate and the SPO units in the solid state. The prescence of
an Ir-bound hydride, which could not be localized by X-ray
diffraction, was confirmed by 1H NMR spectroscopy
(-21.71 ppm).
chromatography the iridium(III) hydride complex 12 in 85%
yield as a mixture of four diastereoisomers (49:35:12:4). The
four diastereoisomers (each a pair of enantiomers) result from
the combination of the stereogenic centers at the two phosphorus
atoms and the stereogenic center at the iridium atom. The
diastereoisomeric ratio implies a moderately diastereoselective
The analogous reaction of the racemic ligand 4,
[Ir(cod)Cl]2, and NaOH (Scheme 7) gave after column
(15) Ribourdouille, Y.; Pfaltz, A. Unpublished results.

5956 Organometallics, Vol. 29, No. 22, 2010
Liniger et al.
formation of the complexes rather than a statistical combina-
tion of the chiral units. By two-dimensional hetereonuclear
correlation experiments the 1H, 13C, and 31P resonances of the
phosphorus atoms, the hydrides, and methyl ester groups were
assigned to the corresponding diastereoisomer (Table 1). A
more detailed interpretation of the complex NMR data was not
possible. ESI-MS data (m/z 823 [M þ H]þ) and elemental
analysis were consistent with structure 12.
Experimental Section
General Comments. All manipulations were conducted un-
der nitrogen or argon atmosphere, using standard Schlenk
or glovebox techniques (MBraun Labmaster 130) except for
the synthesis of complex 10-12. Absolute solvents were
purchased from Fluka (absolute over molecular sieves), de-
gassed using three freeze-pump-thaw cycles, and stored
under argon. Commercial chemicals were used without fur-
ther purification. Freshly crushed NaOH pellets were weighted
in and used immediately for the corresponding reaction.
Chloro(diethylamino)phenylphosphine (3)14 and phenyloxa-
zolines 116 and 217 were prepared according to literature
procedures.
Conclusion
We have shown that zwitterionic iridium(I) complexes
with secondary phosphine oxide ligands undergo an un-
precedented rearrangement under basic conditions, yield-
ing hydrido-iridium(III) complexes with a P-coordinated
phosphinate unit. These complexes are remarkably stable
and survive purification by chromatography on silica gel.
This unexpected P-aryl bond cleavage reaction, which
leads to a hitherto unknown class of Ir-phosphinate
complexes, represents a new reactivity pattern of Ir-SPO
complexes.
NMR spectra were recorded on Bruker Avance 400 and
500 MHz NMR spectrometers. NMR spectra are referenced
to the residual hydrogen signal of the deuterated solvent (1H), to
the signals of the deuterated solvent (13C), and to the residual
deuterium signal of the non-deuterated solvent (2H). 1H and 13
C
signals were assigned using DEPT135 experiments and two-
dimensional correlation experiments (COSY, HMQC, HMBC,
NOESY). pro-S/pro-R are abbreviated by HS/HR for stereo-
heterotopic CH2 groups. IR spectra were measured as KBr
pellets on a Perkin-Elmer 1600 FTIR spectrometer or as the
pure substance using the ATR technique on a Shimadzu FTIR-
8400S instrument. EI-MS spectra were measured on a Finnigan
MAT 95Q instrument and ESI-MS on a Varian 1200 L quad-
rupole MS/MS spectrometer. Microanalytical data were ob-
tained using Leco CHN-900 analyzers. X-ray structural data
were collected on a Nonius KappaCCD diffractometer.
Scheme 7. Synthesis of Complex 12 (Mixture of Four
Diastereoisomers)
Synthesis of Complex (4S,40S,1RP,10SP)-8. The secondary
phosphine oxide (S,SP)-5 (29.5 mg, 90.1 μmol), 30.3 mg
[Ir(cod)Cl]2 (45.1 μmol), and 9.01 mg of NaOH (225 μmol) were
dissolved in 2 mL of MeOH-d4, and the mixture was stirred for
15 min at room temperature. The red solution was reduced to 0.4
mL under reduced pressure and analyzed by NMR. Yellow
crystals suitable for X-ray analysis formed in the NMR tube
after standing for 1 h at room temperature. The red mother
liquor was removed, and the residue was dried under high
vacuum to give 8 as a yellow solid (4.7 mg, 6%). 1H NMR
Table 1. Assigned NMR Data for the Diastereoisomers of Complex 12 (A-D, 49:35:12:4) in CD2Cl2 (δ/ppm)a
diastereoisomer A
diastereoisomer B
1H
IrH
OMe
-20.19 (t, 2JH,P = 17.8 Hz, 2JH,P = 17.8 Hz)
3.26 (d, 3JH,P = 7.9 Hz)
-20.54 (dd, 2JH,P = 24.9 Hz, 2JH,P = 18.7 Hz)
3.08 (d, 3JH,P = 10.8 Hz)
13C{1H}
OMe
51.0 (d, 2JC,P = 7 Hz)
49.6 (d, 2JC,P = 10 Hz)
31P{1H}
POMe
POx
66.0 (dd, 2JP,P = 23 Hz, 2JH,P = 17 Hz)
55.9 (dd, 2JP,P = 23 Hz, 2JH,P = 18 Hz)
56.1 (t, 2JP,P = 23 Hz, 2JH,P = 23 Hz)
57.6 (dd, 2JP,P = 22 Hz, 2JH,P = 18 Hz)
diastereoisomer C
diastereoisomer D
1H
IrH
OMe
-20.06 (dd, 2JH,P = 18.0 Hz, 2JH,P = 14.9 Hz)
3.10 (d, 3JH,P = 12.1 Hz)
-20.46 (dd, 2JH,P = 23.6 Hz, 2JH,P = 18.8 Hz)
3.15 (d, 3JH,P = 10.6 Hz)
13C{1H}
OMe
50.3 (d, 2JC,P = 8 Hz)
49.5 (d, 2JC,P = 10 Hz)
31P{1H}
POMe
POx
62.9 (dd, 2JP,P = 19 Hz, 2JH,P = 14 Hz)
43.6 (t, 2JP,P = 18 Hz, 2JH,P = 18 Hz)
55.2 (t, 2JP,P = 20 Hz, 2JH,P = 20 Hz)
44.8 (t, 2JP,P = 20 Hz, 2JH,P = 20 Hz)
a 1H at 500.1 MHz, 13C{1H} at 125.8 MHz, and 31P{1H} at 202.4 MHz at 295 K.

Article
Organometallics, Vol. 29, No. 22, 2010 5957
(400.1 MHz, CD2Cl2, 300 K, δ/ppm): 0.15 (s, 9 H, -C(CH3)3),
0.77 (s, 9 H, -C(CH3)3), 1.86 (dd, 3JH,H = 9.4 Hz, 3JH,H = 3.1
Hz, 1 H, Ox 4-H), 2.21 (d, 3JH,H = 9.0 Hz, 1 H, Ox 4-H), 3.26 (t,
2JH,H = 8.9 Hz, 3JH,H = 2.2 Hz, 1 H, Ox 5-H), 7.01 (mc, 2 H, Ar
40-H and Ar 50-H), 7.22 (t, 3JH,H = 6.2 Hz, 4JH,P = 6.2 Hz, 1 H,
Ar 30-H), 7.27 (mc, 3 H, PPh m-H and PPh p-H), 7.38-7.43 (m, 6
H, Ar 60-H, PPh m-H, PPh o-H, and PPh p-H), 7.49 (mc, 2 H,
2JH,H = 8.9 Hz, 3JH,H = 8.9 Hz, 1 H, Ox 5-HS), 3.80 (t, 2JH,H
=
9.2 Hz, 3JH,H = 9.2 Hz, 1 H, Ox 5-HS), 3.99 (dd, 2JH,H = 9.1 Hz,
PPh o-H), 7.58 (t, JH,H = 7.7 Hz, 1 H, Ar 500-H), 7.86 (t,
3
3JH,H = 1.8 Hz, 1 H, Ox 5-HR), 4.38 (dd, JH,H = 8.9 Hz,
3JH,H = 7.4 Hz, 1 H, Ar 400-H), 8.08 (dd, JH,H = 7.4 Hz,
2
3
3JH,H = 3.0 Hz, 1 H, Ox 5-HR), 6.74 (mc, 2 H, Ar H), 6.84 (t,
4JH,P = 3.7 Hz, 1 H, Ar 600-H), 8.28 (t, 3JH,P = 3JH,H = 7.9 Hz, 1
H, Ar 300-H). 13C{1H} NMR (125.8 MHz, CD2Cl2, 295 K, δ/
ppm): 24.7 (s, -C(CH3)3), 24.8 (s, -C(CH3)03), 34.4 (s, -C-
JH,H = 7.8 Hz, 1 H, Ar H), 7.14 (mc, 1 H, Ar H), 7.20 (t, JH,H =
7.1 Hz, 2 H, Ar H), 7.27 (t, JH,H = 6.8 Hz, 2 H, Ar H), 7.33 (mc,
2 H, Ar H), 7.44 (mc, 3 H, Ar H), 7.51 (t, JH,H = 8.1 Hz, 2 H, Ar
H), 7.74 (dt, JH,H = 7.5 Hz, JH,H = 0.9 Hz, 1 H, Ar H), 7.92 (dd,
2
(CH3)3), 34.7 (s, -C(CH3)03), 49.1 (d, JC,P = 9 Hz, POCH3),
70.0 (s, Ox 50-CH2), 71.1 (s, Ox 5-CH2), 71.5 (s, Ox 4-CH), 74.7
JH,H = 7.7 Hz, JH,P = 2.1 Hz, 1 H, Ar H), 8.38 (dt, JH,P = 7.3
(s, Ox 40-CH), 121.5 (s, Ar 50-CH), 126.5 (d, 3JC,P = 4 Hz, Ar 60-
Hz, JH,H = 7.3 Hz, JH,H = 0.8 Hz, 1 H, Ar H). 2H NMR (76.8
MHz, CH2Cl2, 295 K, δ/ppm): -21.3 (br s, 1 H, IrD), 2.76 (br s,
3 H, POCD3). 31P{1H} NMR (162.0 MHz, CD2Cl2, 300 K, δ/
ppm): 53.5 (d, 2JP,P = 19 Hz), 49.9 (d, 2JP,P = 18 Hz). IR (neat,
ν~/cm-1): 3057 w, 2951 w, 2890 w, 2068 w, 1602 s, 1480 m, 1449
m, 1432 m, 1385 w, 1360 m, 1315 w, 1238 m, 1210 w, 1103 m,
1021 s, 955 m, 781 m, 733 s, 690 s.
CH), 126.9 (d, JC,P = 11 Hz, PPh m-CH), 127.0 (d, JC,P =
3
2
17 Hz, Ar 100-C), 127.3 (d, 3JC,P = 10 Hz, PPh m-CH), 128.5 (s,
PPh p-CH), 129.1 (s, PPh p-CH), 129.8-130.0 (m, 2 C, Ar 40-CH
and Ar 500-CH), 130.1-130.4 (m, 3 C, Ar 600-CH, PPh o-CH, and
PPh o-CH), 130.8 (s, Ar 300-CH), 132.8 (d, 3JC,P = 6 Hz, Ar 400-
CH), 134.3 (s, Ar 10-C), 140.9 (d, 2JC,P = 37 Hz, Ar 200-C), 143.1
(s, Ar 30-CH), 143.8 (d, 1JC,P = 114 Hz, PPh i-C), 143.9 (d, 1JC,P
= 35 Hz, PPh i-C), 165.6 (mc, Ox 20-C), 170.5-172.6 (m, Ox
Synthesis of Complex rac-9. To a solution of the secondary
phosphine oxide rac-4 (74.4 mg, 248 μmol) and [Ir(cod)Cl]2 (83.5
mg, 124 μmol) in 3.5 mL CH2Cl2 was added 3.5 mL of aqueous 1
M NaOH. The biphasic reaction mixture was vigorously stirred
for 1 h at room temperature. Then the red organic layer was
transferred by a syringe into a 25 mL Schlenk tube. The aqueous
phase was extracted once with 5 mL of CH2Cl2. The combined
organic layers were concentrated under reduced pressure and
overlaid with pentane. After 3 days at room temperature, the
red-green mother liquor was removed through a cannula and the
red crystals were washed once with pentane. Crystals suitable
for X-ray analysis were embedded into perfluorinated polyether
in the glovebox and measured. The residual crystals were dried
under high vacuum to afford 9 as a highly air-sensitive, red solid
2-C), 179.1 (d, 2JC,P = 7 Hz, Ar 20-C). 31P{1H} NMR (202.4
trans
MHz, CD2Cl2, 295 K, δ/ppm): 66.5 (dd, 2JP,P = 22 Hz, 2JP,H
=
16 Hz), 62.0 (dd, 2JP,P = 29 Hz, 2JP,H = 20 Hz). IR (KBr, ν~/
cm-1): 3050 w, 2955 s, 2233 w, 1614 s, 1561 w, 1544 w, 1481 m,
1435 m, 1386 m, 1364 m, 1319 w, 1240 m, 1211 w, 1112 s, 1023 s,
957 m, 813 w, 783 w, 737 s, 704 s, 603 w, 492 w. MS (ESIþ,
CH2Cl2/MeOH, 10:1): m/z 879 ([MþH]þ). [R]D20 = þ350° (c =
0.205, CH2Cl2). Anal. Calcd (found): C, 53.35 (53.67); H, 5.40
(5.35); N, 3.19 (2.91).
Complex (4S,40S,1SP,10RP)-11. This complex was prepared
according to the general procedure from 25.8 mg of the second-
ary phosphine oxide (S,RP)-5 (78.8 μmol), 13.2 mg of [Ir(cod)-
Cl]2 (19.7 μmol), and 3.9 mg of NaOH (97.5 μmol). After
chromatography (2 ꢀ 10 cm column), 11 was obtained as an
air-stable, yellow solid (20.0 mg, 58%). Single crystals suitable
for X-ray analysis were grown by slow diffusion of hexane into a
saturated solution of complex 11 in CH2Cl2. Rf = 0.18 (SiO2,
CH2Cl2). 1H NMR (500.1 MHz, CD2Cl2, 295 K, δ/ppm):
-21.71 (dd, 2JH,P = 25.6 Hz, 2JH,P = 19.1 Hz, 1 H, IrH), 0.24
1
(2 mg, 1%). H NMR (500.1 MHz, CD2Cl2, 295 K, δ/ppm):
-16.43 (d, 2JH,P = 16.2 Hz, 1 H, IrH), 0.08 (s, 6 H, -C(CH3)2),
2.06 (mc, 1 H, cod CHH), 2.26 (mc, 2 H, cod CH2), 2.41 (mc, 4 H,
cod CH2), 2.68 (mc, 1 H, cod CHH), 3.38 (br s, 1 H, Ox 5-H),
3.95 (mc, 1 H, cod CH), 4.14 (d, 2JH,H = 6.0 Hz, 1 H, Ox 5-H),
4.56 (mc, 1 H, cod CH), 4.77 (mc, 1 H, cod CH), 5.14 (mc, 1 H,
cod CH), 6.91 (mc, 2 H, Ar H), 7.00 (mc, 3 H, Ar H), 7.08-7.18
(m, 3 H, Ar H), 7.31 (d, 3JH,H = 7.0 Hz, 1 H, Ar H). 31P{1H}
NMR (162.0 MHz, CD2Cl2, 300 K, δ/ppm): 40.5 (s).
(s, 9 H, -C(CH3)03), 0.59 (s, 9 H, -C(CH3)3), 3.22 (d, 3JH,H
=
6.8 Hz, 1 H, Ox 40-H), 3.25 (d, 3JH,P = 10.7 Hz, 3 H, POCH3),
3.71 (d, 3JH,H = 8.1 Hz, 1 H, Ox 4-H), 4.19 (t, 2JH,H = 8.1 Hz,
3JH,H = 8.1 Hz, 1 H, Ox 50-H), 4.31 (t, 2JH,H = 8.9 Hz, 3JH,H
=
General Procedure for the Preparation of Iridium(III) Hydride
Monomethyl Phosphinate Complexes 10-12. The secondary
phosphine oxide (2.0 equiv), [Ir(cod)Cl]2 (0.5 equiv), and NaOH
(2.5 equiv) were dissolved in MeOH (0.8 M), and the mixture
was stirred at room temperature for 1.5 h under argon and
30 min under air. The solvent was removed under reduced pres-
sure. The residue was purified by column chromatography
(SiO2; CH2Cl2 f CH2Cl2/MeOH (50:1)) and recrystallized from
CH2Cl2/hexane.
8.9 Hz, 1 H, Ox 5-H), 4.74 (d, 2JH,H = 9.2 Hz, 2 H, Ox 5-H and
Ox 50-H), 6.31 (t, 3JH,H = 6.5 Hz, 4JH,P = 6.5 Hz, 1 H, Ar 30-H),
6.55 (t, 3JH,H = 7.4 Hz, 1 H, Ar 40-H), 6.91 (t, 3JH,H = 7.4 Hz, 1
H, Ar 50-H), 7.06 (dd, 3JH,P = 10.5 Hz, 3JH,H = 7.9 Hz, 2 H, PPh
o-H), 7.20 (t, 3JH,H = 6.6 Hz, 2 H, PPh m-H), 7.24-7.32 (m, 2 H,
2 PPh p-H), 7.35 (mc, 3 H, Ar 500-H and PPh m-H), 7.43 (d,
3JH,H = 7.6 Hz, 1 H, Ar 60-H), 7.57 (mc, 4 H, Ar 400-H, Ar 600-H
and PPh o-H), 8.02 (t, 3JH,P = 3JH,H = 7.9 Hz, 1 H, Ar 300-H).
13C{1H} NMR (125.8 MHz, CD2Cl2, 295 K, δ/ppm): 24.9
(s, -C(CH3)3), 26.1 (s, -C(CH3)03), 35.7 (s, -C(CH3)03), 35.8
(s, -C(CH3)3), 50.2 (d, 2JC,P = 10 Hz, POCH3), 71.4 (s, Ox 40-
CH), 71.6 (s, Ox 4-CH), 71.8 (s, Ox 50-CH2), 72.4 (s, Ox 5-CH2),
122.0 (s, Ar 50-CH), 126.2 (d, 3JC,P = 4 Hz, Ar 60-CH), 126.8 (s,
Ar 300-CH), 126.9 (d, 3JC,P = 11 Hz, PPh m-CH), 128.0 (d, 2JC,P
= 19 Hz, Ar 100-C), 128.3 (d, 3JC,P = 8 Hz, Ar 600-CH), 128.6 (d,
3JC,P = 9 Hz, PPh m-CH), 128.9 (d, 4JC,P = 2 Hz, PPh p-CH),
129.1 (d, 2JC,P = 12 Hz, PPh o-CH), 129.2 (d, 4JC,P = 1 Hz, Ar
500-CH), 129.4 (d, 4JC,P = 2 Hz, PPh p-CH), 130.5 (d, 4JC,P = 4
Complex (4S,40S,1RP,10SP)-10. This complex was prepared
according to the general procedure from 77.6 mg of the second-
ary phosphine oxide (S,SP)-5 (237 μmol), 39.8 mg of [Ir(cod)Cl]2
(59.3 μmol), and 11.9 mg of NaOH (296 μmol). After chroma-
tography (2 ꢀ 10 cm column), 10 was obtained as an air-stable,
yellow solid (26.3 mg, 25%). Rf = 0.19 (SiO2, CH2Cl2). 1H
NMR (500.1 MHz, CD2Cl2, 295 K, δ/ppm): -21.26 (dd, 2JH,P
= 28.9 Hz, 2JH,P = 17.6 Hz, 1 H, IrH), 0.25 (s, 9 H, -C(CH3)03),
0.82 (s, 9 H, -C(CH3)3), 2.08 (dd, 3JH,H = 8.9 Hz, 3JH,H = 1.9
Hz, 1 H, Ox 4-H), 2.45 (d, 3JH,H = 8.3 Hz, 1 H, Ox 40-H), 3.14 (d,
3JH,P = 10.9 Hz, 3 H, POCH3), 3.52 (t, 2JH,H = 8.9 Hz, 3JH,H
=
2
Hz, Ar 40-CH), 131.3 (d, JC,P = 10 Hz, PPh o-CH), 131.9 (d,
8.9 Hz, 1 H, Ox 50-H), 3.90 (t, 2JH,H = 9.1 Hz, 3JH,H = 9.1 Hz,
1 H, Ox 5-H), 4.19 (d, 2JH,H = 9.6 Hz, 1 H, Ox 50-H), 4.49 (dd,
3JC,P = 6 Hz, Ar 400-CH), 134.1 (s, Ar 10-C), 143.0 (d, 1JC,P = 97
Hz, PPh i-C), 145.1 (d, 1JC,P = 38 Hz, PPh i-C), 146.2 (s, Ar 30-
2
CH), 147.0 (d, JC,P = 41 Hz, Ar 200-C), 167.6-168.5 (m, Ox
2
2-C), 169.3 (mc, Ox 20-C), 181.1 (d, JC,P = 7 Hz, Ar 20-C).
trans
31P{1H} NMR (202.4 MHz, CD22Cl2, 295 K, δ/ppm): 58.6 (t,
(16) (a) Schwekendiek, K.; Glorius, F. Synthesis 2006, 2996–3002.
(b) Katritzky, A. R.; Cai, C.; Suzuki, K.; Singh, S. K. J. Org. Chem. 2004, 69,
811–814.
2
2
2JP,P = JP,H = 22 Hz), 51.5 (t, JP,P = JP,H = 18 Hz). IR
(neat, ν~/cm-1): 3048 w, 2953 m, 2919 m, 2177 w, 1613 s, 1476 m,
1435 m, 1387 m, 1363 m, 1319 w, 1248 m, 1233 m, 1213 m, 1111s,
€
(17) Bernardinelli, G.; Gillet, S.; Kundig, E. P.; Liu, R.; Ripa, A.;
Saudan, L. Synthesis 2001, 2040–2054.

5958 Organometallics, Vol. 29, No. 22, 2010
Liniger et al.
1091 m, 1014 s, 945 s, 731 s, 692 s. MS (ESIþ, CH2Cl2/MeOH
(10:1)): m/z 879 ([M þ H]þ). [R]D20=þ444° (c = 0.209, CH2Cl2).
Anal. Calcd (found): C, 53.35 (53.41); H, 5.40 (5.25); N, 3.19
(2.87).
Complex 12. This complex was prepared according to the
general procedure from 47.2 mg of the secondary phosphine
oxide rac-4 (157 μmol), 26.5 mg of [Ir(cod)Cl]2 (39.4 μmol), and
7.88 mg of NaOH (197 μmol). After chromatography (2 ꢀ 16 cm
column), 12 was obtained as an air-stable, yellow solid (55.0 mg,
85%). Rf = 0.20 (SiO2, CH2Cl2). MS (ESIþ, CH2Cl2/MeOH,
10:1): m/z 823 ([M þ H]þ). Anal. Calcd (found): C, 51.15 (50.86);
H, 4.78 (4.80); N, 3.41 (3.15).
Acknowledgment. We thank Christian Ebner for re-
cording the ESI-MS spectra and York Schramm for
performing heteronuclear 1H-31P NMR correlation ex-
periments. Support of this work by the Swiss National
Science Foundation is gratefully acknowledged.
Supporting Information Available: Text and figures giving
procedures and analytical data for all ligands and complexes
and a table, figure, and CIF files giving X-ray crystallographic
data for complexes (4S,40S,1RP,10SP)-8, rac-9, and (4S,40S,1SP,-
10RP)-11. This material is available free of charge via the Internet at
http://pubs.acs.org.