Chiral proline-based P,O and P,N ligands for iridium-catalyzed asymmetric hydrogenation

Article abstract of DOI:10.1002/hlca.201200437

Two new classes of proline-based P,O and P,N ligands were prepared and applied in the iridium-catalyzed asymmetric hydrogenation of alkenes. Both types of ligands induced high enantioselectivities in the hydrogenation of trisubstituted C=C bonds. Iridium complexes derived from P,O ligands bearing sterically demanding amide or urea groups at the pyrrolidine N-atom proved to be especially efficient catalysts for the conjugate reduction of α,β-unsaturated esters and ketones, whereas analogous P,N ligands led to better results with dialkyl-phenyl-substituted alkenes and an allylic alcohol as substrates.

Full text of DOI:10.1002/hlca.201200437

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Chiral Proline-Based P,O and P,N Ligands for Iridium-Catalyzed Asymmetric
Hydrogenation
by Denise Rageot and Andreas Pfaltz*
Department of Chemistry, University of Basel, St. Johanns-Ring 19, CH-4056 Basel
Dedicated to Professor Dieter Seebach on the occasion of his 75th birthday
Two new classes of proline-based P,O and P,N ligands were prepared and applied in the iridium-
catalyzed asymmetric hydrogenation of alkenes. Both types of ligands induced high enantioselectivities
in the hydrogenation of trisubstituted C¼C bonds. Iridium complexes derived from P,O ligands bearing
sterically demanding amide or urea groups at the pyrrolidine N-atom proved to be especially efficient
catalysts for the conjugate reduction of a,b-unsaturated esters and ketones, whereas analogous P,N
ligands led to better results with dialkyl-phenyl-substituted alkenes and an allylic alcohol as substrates.
Introduction. – Homogeneous chiral iridium catalysts have considerably enhanced
the scope of the asymmetric hydrogenation of alkenes, because, unlike Rh- or Ru-
diphosphine complexes, they do not require the presence of a coordinating substituent
near the C¼C bond. Inspired by the seminal work of Crabtree et al. [1] that had
uncovered the unusually high reactivity of cationic Ir(monophosphine)(pyridine)
catalysts in the hydrogenation of tri- and even tetraalkyl-substituted C¼C bonds, initial
studies focused on Ir complexes with chiral P,N ligands. The first highly enantioselective
Ir-catalyzed hydrogenations were achieved with phosphino-oxazoline (PHOX) ligands,
which had originally been developed for enantioselective allylic substitutions [2].
Subsequently, we and other groups developed various other oxazoline-based P,N
ligands that were derived from enantiomerically pure a-amino acids (Scheme 1) [3]. In
addition, Burgess and co-workers showed that the chiral C,N ligand L2 (R1 ¼ ada-
mantyl, R2 ¼ 2,5-iPr2ꢀPh) containing an N-heterocyclic carbene and an oxazoline as
coordinating units also forms efficient enantioselective Ir catalysts [4].
Although high enantioselectivities can be obtained for a wide range of alkenes
using oxazoline-based ligands of this type, none of the chiral Ir complexes developed so
far is a universally applicable catalyst. Depending on the structure of the alkene,
different catalysts perform best. For instance, SimplePHOX and NeoPHOX complexes
provide high enantioselectivities in the hydrogenation of various trisubstituted alkenes
[5][6]. In contrast, the structurally related phosphino-oxazolines L1 give poor results
with substrates of this type, but form very reactive, highly enantioselective catalysts for
the hydrogenation of tetrasubstituted C¼C bonds [7]. For a long time, no suitable
catalysts were available for the asymmetric hydrogenation of purely alkyl-substituted
C¼C bonds, until a new class of pyridine-derived P,N ligands led to a breakthrough for
this substrate class [8]. P,N Ligands based on other aromatic backbones such as furan or
thiophene were also developed and successfully applied to new substrate classes.
ꢀ 2012 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Scheme 1. Chiral Ligands Derived from a-Amino Acids
Nevertheless, there are still challenging substrates left that give unsatisfactory results
with the available catalysts. Therefore, the search for new efficient ligands to close such
methodical gaps continues.
Ideally, a new ligand should be readily accessible from enantiomerically pure
precursors through a synthetic route that allows variation of the individual structural
elements. Good examples of such ligands are ThrePHOX and SerPHOX which are
derived from serine or threonine, respectively, and can be structurally modified at the
R1, R2, R3, and R4 substituents [9][10]. In this way, the catalyst structure can be
sterically and electronically tuned for a specific application. Here, we discuss two new
classes of modular proline-derived ligands for Ir-catalyzed hydrogenation that fulfill
these criteria in an ideal way.
Proline-derived monophosphines LO (Scheme 2) were originally developed by
Tomioka and co-workers for enantioselective conjugate additions of organocuprates
Scheme 2. Proline-Based P,O and P,N Ligands

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[11]. Later on, they were also successfully applied in the Rh-catalyzed 1,4-addition of
arylboronic acids to a,b-unsaturated carbonyl compounds. In a broad automated
screening of various metalꢀligand combinations in collaboration with Solvias AG in
Basel, we found that Tomiokaꢂs ligand LO (R1 ¼ Ph, R2 ¼ tBu) induced up to 68% ee in
the Ir-catalyzed hydrogenation of (E)-1,2-diphenylprop-1-ene. We were surprised that
this ligand performed so well in view of the hemilabile nature of the IrꢀO bond [11f].
Encouraged by this initial result, we optimized the ligand structure for Ir-catalyzed
asymmetric hydrogenation by systematic modification of the substituents at the P- and
N-atom [12]. Furthermore, we also investigated analogous proline-based P,N ligands
LN (Scheme 2), which would be a useful addition to the known P,N ligands, because the
structure of the corresponding Ir complexes differs substantially from the structures of
Ir catalysts developed so far.
Ligand Synthesis. – Proline-based P,O ligands were readily prepared from
commercially available N-Boc-l-proline. The desired carbamate precursors (S)-1 –
(S)-4 were obtained in moderate-to-excellent yields (54 – 97%) according to reported
procedures [12]1). After removal of the Boc protecting group and reaction of the
resulting pyrrolidinium salt with various acid chlorides, isocyanates, or carbamoyl
chlorides, a series of amides and ureas was obtained. Dialkyl-substituted phosphines
(S)-3 and (S)-4 were used as their borane adducts in order to avoid oxidation of the P-
atom. In these cases, an additional deprotection step was required to obtain the free
ligands (Scheme 3). Various derivatives (S)-LO, bearing different R2 substitutents, were
prepared in good yields in this manner (56 – 96%; Scheme 3) [12].
Scheme 3. Synthesis of Proline-Based P,O Ligands
1
)
For the synthesis of N-[(tert-butoxy)carbonyl]-l-prolinol and (S)-tert-butyl 2-[(tosyloxy)methyl]-
pyrrolidine-1-carboxylate, see [13].

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All these ligands could be readily converted to the corresponding [Ir(cod)(L)]BArF
salts (cod ¼ cycloocta-1,5-diene; BArF ¼ tetrakis[3,5-bis(trifluoromethyl)phenyl]bo-
rate). From two complexes, crystals suitable for X-ray analysis could be obtained
[12a]. The crystal-structure data and NMR analyses clearly confirmed that the ligands
were coordinated to the Ir-center in a bidentate fashion through the P- and the C¼O O-
atom. Although P,O complexes could be isolated in analytically pure form, they proved
to be less stable than P,N complexes and could not be stored for longer times. In
contrast to P,N complexes, they did not survive purification by chromatography on
silica gel. Therefore, they were usually prepared in situ when they were applied as
cataysts for hydrogenation.
In a similar way, proline-based P,N ligands (S)-LN1 and (S)-LN2 were synthesized
(Scheme 4). After removal of the Boc protecting group, the resulting ammonium salt
was deprotonated and then reacted with 2-chlorobenzoxazole or 2-chlorobenzothia-
zole, respectively. Both ligands were obtained in good yields. They were then converted
to the corresponding Ir complexes using standard complexation methods for P,N
ligands [14].
Scheme 4. Synthesis of Proline-Based P,N Ligands (S)-LN1 and (S)-LN2
The synthetic route depicted above did not afford the desired dialkylphosphine
derivatives (S)-LN5 to (S)-LN8; no conversion of the deprotonated amine was
observed. Therefore, a second synthetic route was investigated (Scheme 5). Starting
from tBuMe2Si (TBDMS)-protected (S)-prolinol 5, the intermediates (S)-6 and (S)-7
were obtained after deprotonation of the pyrrolidine N-atom, followed by reaction with
2-chlorobenzoxazole or 2-chlorobenzothiazole, respectively, and subsequent removal
of the TBDMS protecting group2). The alcohols (S)-8 and (S)-9, were then converted
to the bromides (S)-8 and (S)-9, respectively, through an Appel reaction. Subsequent
nucleophilic substitution with phosphides generated in situ from 10, 11, and 12 led to
the desired P,N ligands (S)-LN3 to (S)-LN8 in good yields (59 – 89%). The di(tert-butyl)
and dicyclohexylphosphine derivatives (S)-LN5 – (S)-LN8 were obtained after an
additional synthetic step required for the deprotection of the phosphine moiety.
Proline-based ligands (S)-LN3 – (S)-LN8 were finally converted to the correspond-
ing Ir complexes by reaction with [Ir(cod)2]BArF according to the procedure for
proline-based P,O ligand/Ir complexes [12a].
2
)
For the synthesis of (S)-2-({[(tert-butyl)dimethylsilyl]oxy}methyl)pyrrolidine ((S)-5), see [15].

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Scheme 5. Synthesis of Proline-Based P,N Ligands (S)-LN3 – (S)-LN8
Iridium-Catalyzed Asymmetric Hydrogenation. – To evaluate the potential of these
new proline-based ligands in the Ir-catalyzed asymmetric hydrogenation, we inves-
tigated their efficiency in the reduction of several trisubstituted functionalized and
unfunctionalized alkenes. In general, conversion of the starting material was complete
within 2 h, using 1 mol-% of catalyst and 50 bar H2 pressure for both ligand classes. As
mentioned above, the P,O-ligand complexes were generated in situ with [Ir(cod)2]BArF
prior to the hydrogenation reaction, whereas the more stable P,N ligand complexes
were isolated and purified prior to their use.
In the hydrogenation of ethyl (E)-3-phenylbut-2-enoate (S1), proline-based P,O
ligand complexes afforded excellent enantioselectivities of up to 99% ee. The best
results are compiled in Scheme 6. Dialkylphosphines (S)-LO5 and (S)-LO6 generally
gave higher enantioselectivities for this transformation than the corresponding diaryl-
substituted phosphine derivatives. Also, ligands with more sterically demanding C¼O
moieties, such as the trityl-substituted derivatives (S)-LO2, (S)-LO4, and (S)-LO6
provided higher ee values than less hindered amide and urea derivatives. The analogous
P,N ligands induced lower enantioselectivities, with the exception of (S)-LN5 and (S)-
LN6 that led to the saturated ester (R)-P1 with 98 and 96% ee, respectively. In general,

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Scheme 6. Ir-Catalyzed Asymmetric Hydrogenation of Ethyl (E)-3-Phenylbut-2-enoate
benzoxazoles (S)-LN3, (S)-LN5, and (S)-LN7 gave slightly higher enantioselectivities
than benzothiazoles (S)-LN4, (S)-LN6, and (S)-LN8.
Excellent enantioselectivities were obtained as well in the Ir-catalyzed asymmetric
hydrogenation of the unfunctionalized diaryl alkene S2. P,O Ligand complexes (S)-
LO4, (S)-LO6, and (S)-LO10 afforded the product (R)-P2 with 99% ee and full
conversion (Scheme 7). Also for this substrate, dialkylphosphine-based catalysts gave
in general better enantioselectivities than the diarylphosphine analogs. Nevertheless,
the sterically demanding ligand (S)-LO4 bearing a Ph2P moiety also induced 99% ee.
Overall, the P,N ligand complexes proved to be less selective catalysts. However, three
catalysts, (S)-LN3, (S)-LN5, and (S)-LN7, rivaled the P,O ligand complexes with
enantioselectivities of 97 and 99% ee. In this reaction too, benzoxazole ligands were
superior to the corresponding benzothiazole derivatives. Furthermore, di(ortho-
tolyl)phosphines gave higher enantioselectivities than diphenylphosphines, in contrast
to the P,O-ligand complexes that displayed the opposite trend.
We subsequently compared the performance of P,O and P,N ligands in the Ir-
catalyzed asymmetric hydrogenation of the a,b-unsaturated ketone S5 and three other
trisubstituted alkenes including an allylic alcohol (Scheme 8).
Proline-based P,O ligands provided only moderate ee values of up to 83% in the
hydrogenation of allylic alcohol S3. In this case, diarylphosphines generally induced
higher enantioselectivities than dialkylphosphines. The best results are compiled in
Scheme 8, with the highest ee achieved by the di(ortho-tolyl)-substituted phosphine
(S)-LO9. For this substrate, the corresponding P,N ligands proved to be superior with
enantioselectivities of up to 89% ee with (S)-LN4).

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Scheme 7. Iridium-Catalyzed Asymmetric Hydrogenation of (E)-1,2-Diphenylprop-1-ene
Scheme 8. Iridium-Catalyzed Asymmetric Hydrogenation of Other Trisubstituted Alkenes

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In the hydrogenation of the alkenes (E)-S4 and (Z)-S4 as well, P,N ligand
complexes outperformed the P,O ligand complexes. While the best P,O ligands afforded
up to 55% ee and 53% ee in the reduction of the (Z)- and the (E)-isomer, respectively,
the best P,N ligands induced up to 76% ee and 86% ee. However, these values are
distinctly lower than the highest enantioselectivities reported for the hydrogenation of
these substrates with other classes of Ir catalysts [8b][9][16].
Proline-based P,N ligands gave lower enantioselectivities than P,O ligands in the
reduction of the C¼C bond of substrate S5. The di(tert-butyl)-substituted phosphine
(S)-LN5 provided the best result with 90% ee. Conversion of substrate S5 was always
complete using proline-based P,N ligands (S)-LN4 – 5 and (S)-LN7 – 8. However, it was
often accompanied by overreduction to the saturated alcohol in variable amounts. For
the P,O ligand complexes, this problem, which had been observed before [17], could be
solved by using isolated complexes rather than in situ generated catalysts. However, for
the analogous P,N complexes overreduction could not be suppressed.
The enantioselectivities induced by the proline-based P,O and P,N ligands are
consistent with Anderssonꢂs transition-state model for the enantioselective step
[3b][18]. According to computational studies, the substrate is coordinated trans to
the P-atom with the olefin axis arranged orthogonally to coordination plane, as shown
in the Figure. In the preferred coordination mode, which leads to the major enantiomer,
the H-atom points toward the most sterically crowded region of the coordination
sphere, minimizing the steric interaction between the substrate and the ligand. In the Ir-
PHOX catalyst the interaction with the substituent at the stereogenic center is the
enantioselectivity-determining factor. Based on crystal-structure data [12a], we assume
that the proline-based P,O ligands adopt a conformation, which results in a sterically
similar situation near the substrate (structure A in the Fig.). An analogous chiral
environment is also expected for the related proline-based P,N ligands (structure B). In
accordance with these qualitative models, the three catalyst types shown in the Figure
furnish the same product enantiomer in the hydrogenations discussed above.
Figure. Qualitative models to rationalize the enantioselectivity
Conclusions. – We have developed efficient practical syntheses of two new classes
of chiral P,O and P,N ligands for Ir-catalyzed asymmetric hydrogenation starting from
commercially available proline derivatives. Both types of ligands form seven-
membered chelate rings. The structures of the N- or O-donor, and the phosphine
moiety can be easily modified, allowing the electronic and steric properties to be tuned

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for a specific application. Both proline-derived P,O and P,N ligands gave high
enantioselectivities in the hydrogenation of trisubstituted olefins. Iridium complexes
derived from P,O ligands bearing sterically demanding amide or urea groups at the
pyrrolidine N-atom proved to be especially efficient catalysts for the conjugate
reduction of a,b-unsaturated esters and ketones, where they afforded similar or even
better enantioselectivities than the state-of-the-art catalysts. Some of the proline-based
P,N ligands also performed very well, indicating a promising potential of this ligand
class. In view of these results, it would seem worthwhile to explore further applications
of proline-derived ligands of this type.
We thank the Swiss National Science Foundation for financial support of this work.
Experimental Part
General. Commercially available reagents were purchased from Acros, Aldrich, or Fluka, and used as
received. Et2NH was distilled from CaH2. The solvents were collected from a purification column system
(PureSolv, Innovative Technology Inc.), or purchased from Aldrich or Fluka in sure/sealedTM bottles over
molecular sieves. All prep. reactions with air- or moisture-sensitive compounds were carried out in flame-
dried glassware under inert atmosphere using Schlenk techniques. Column chromatography (CC): Fluka
silica gel 60 (Buchs, particle size 40 – 63 nm), distilled eluents. TLC: Macherey-Nagel (Polygram SIL/
UV254, 0.2 mm silica with fluorescence indicator); UV light (254 nm) or basic permanganate soln. for
visualization. HPLC: Shimadzu systems, SLC-10A system controller, CTO-10AC column oven, LC10-
AD pump system, DGU-14A degasser, and SPD-M10A diode-array or UV/VIS detector, chiral columns
Chiracel OD-H or OJ (4.6 ꢁ 250 mm). GC: Carlo Erba HRGC Mega2 Series 800 (HRGS Mega2)
instruments, Restek Rtx-1701 (30 m ꢁ 0.25 mm ꢁ 0.25 mmol) for achiral phases, Chiraldex g-cyclodextrin
TFA G-TA (30 m ꢁ 0.25 mm ꢁ 0.12 mm) column for enantiomer separation. M.p.: Bꢀchi 535 apparatus;
not corrected. Optical rotations ([a]2D0 ): Perkin Elmer Polarimeter 341, Na lamp, 1-dm cuvette, c in g/
100 ml. IR Spectra: Shimadzu FTIR-8400S spectrometer, ˜n in cmꢀ1; s (strong), m (medium), w (weak).
NMR Spectra: Bruker Avance 400 (400 MHz) or Bruker Avance 500 (500 MHz) spectrometer, d in ppm,
J in Hz. MS: VG70-250 spectrometer (EI) or MAR 312 spectrometer (FAB), or Finnigan MAT LCQ
(ESI-MS); m/z in rel. %. HR-MS: Thermo Fisher Scientific LTQ Orbitrap XL (ESI-MS) spectrometer.
Elemental analyses: Leco CHN-900 (C, H, and N). For the syntheses and anal. data of P,O ligands (S)-
LO, see [12a].
2-{(2S)-2-[(Diphenylphosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzoxazole ((S)-LN1). HCl (4.0m in
1,4-dioxane; 2.00 ml) was added dropwise at 08 to a soln. of (S)-1 (300 mg, 812 mmol, 1.0 equiv.) in 1,4-
dioxane (1 ml). The mixture was stirred at r.t. for 1.5 – 2 h and then reduced to dryness. The crude product
was treated three times with benzene (2 ꢁ 2 ml), and the solvent was evaporated each time. Drying under
high vacuum afforded a colorless foam that was dissolved in THF (8 ml). A 1.6m soln. of BuLi (800 ml,
1.28 mmol, 1.6 equiv.) in hexanes was slowly added at ꢀ 788 in a acetone/dry ice bath, and the resulting
soln. was stirred for 30 min at ꢀ 788 and for 1 h at r.t., accompanied by a color change to yellow. After
cooling the soln. again to ꢀ 788, 2-chlorobenzoxazole (187 mg, 1.22 mmol, 1.5 equiv.) was added, and the
mixture was allowed to warm to r.t. overnight. At 08 in an ice bath, aq. sat. NaHCO3 (5 ml) was added
dropwise. AcOEt (10 ml) was added, and the layers were separated. The aq. layer was extracted with
AcOEt (2 ꢁ 10 ml). The combined org. layers were washed with brine (20 ml) and dried (MgSO4). The
solvent was evaporated under reduced pressure, and the crude product was purified by CC (SiO2;
cyclohexane/AcOEt 4 :1) to give (S)-LN1 (257 mg, 665 mmol, 82%). Colorless solid. Rf (SiO2;
cyclohexane/AcOEt 4 :1) 0.26. M.p. 87 – 898. [a]2D0 ¼ ꢀ85.2 (c ¼ 0.520, CHCl3). IR (neat): 3054w,
2951w, 2875w, 1636s, 1576s, 1458m, 1383m, 1355m, 1243m, 1149w, 1002w, 912m, 794w, 736s, 695s.
1H-NMR (400 MHz, CDCl3): 7.68 – 7.59 (m, 2 arom. H); 7.45 – 7.33 (m, HꢀC(7), 5 arom. H); 7.26 – 7.20
(m, 3 arom. H); 7.20 – 7.10 (m, HꢀC(4), HꢀC(5)); 6.99 (t, J ¼ 7.7, HꢀC(6)); 4.31 – 4.16 (m, HꢀC(2’));
3.72 – 3.56 (m, CH2(5’)); 2.86 (dt, J ¼ 14, 3.0, 1 H of CH2P); 2.33 (t, J ¼ 12, 1 H of CH2P); 2.23 – 2.05 (m,

Helvetica Chimica Acta – Vol. 95 (2012)
2185
CH2(3’), 1 H of CH2(4’)); 2.05 – 1.91 (m, 1 H of CH2(4’)). 13C-NMR (101 MHz, CDCl3): 160.5 (s, C(2));
1
1
148.9 (s, C(7a)); 143.4 (br. s, C(3a)); 138.6 (d, J(C,P) ¼ 12, C(1) of Ph); 137.7 (d, J(C,P) ¼ 12, C(1) of
Ph’); 133.1 (d, 2J(C,P) ¼ 19, C(2), C(6) of Ph); 132.7 (d, 2J(C,P) ¼ 19, C(2), C(6) of Ph’); 129.0 (s, C(4) of
Ph); 128.7 (d, 3J(C,P) ¼ 7.0, C(3), C(5) of Ph); 128.6 (s, C(4) of Ph’); 128.5 (d, 3J(C,P) ¼ 7.0, C(3), C(5) of
Ph’); 123.9 (s, C(5)); 120.2 (s, C(6)); 116.2 (s, C(4)); 108.6 (s, C(7)); 57.5 (d, 2J(C,P) ¼ 21, C(2’)); 48.4 (s,
C(5’)); 33.7 (d, 1J(C,P) ¼ 15, CH2P); 31.7 (d, 3J(C,P) ¼ 7.6, C(3’)); 24.1 (br. s, C(4’)). 31P-NMR (162 MHz,
CDCl3): ꢀ 22.8 (s). EI-MS (70 eV): 386 (4, Mþ), 310 (20), 309 (100), 187 (27).
2-{(2S)-2-[(Diphenylphosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzothiazole ((S)-LN2). Compound
(S)-LN2 (75%) was prepared as described for (S)-LN1, using 2-chlorobenzothiazole instead of 2-
chlorobenzoxazole. Rf (SiO2; cyclohexane/AcOEt 4 :1) 0.23. M.p.: 101 – 1058. [a]2D0 ¼ ꢀ61.6 (c ¼ 0.530,
CHCl3). IR (neat): 3066w, 2964w, 2918w, 2867w, 1595m, 1564m, 1533s, 1481m, 1452m, 1441s, 1431m,
1363m, 1313m, 1269m, 1254w, 1186w, 1124m, 1066m, 1018m, 914m, 852m, 734s. 1H-NMR (500 MHz,
CDCl3): 7.70 (m, 2 arom. o-H); 7.57 (d, J ¼ 8.0, HꢀC(4)); 7.54 (d, J ¼ 7.8, HꢀC(7)); 7.45 – 7.34 (m, 5 arom.
H); 7.31 – 7.25 (m, HꢀC(5)); 7.26 – 7.22 (m, 3 arom. H); 7.05 – 7.02 (m, HꢀC(6)); 4.02 – 4.08 (m, HꢀC(2’));
2
3.62 – 3.44 (m, CH2(5’)); 2.99 (br. d, J(H,P) ¼ 14, 1 H of CH2P); 2.24 – 2.09 (m, 1 H of CH2P, CH2(3’),
1 H of CH2(4’)); 2.05 – 1.99 (m, 1 H of CH2(4’)). 13C-NMR (126 MHz, CDCl3): 164.6 (s, C(2)); 153.1 (s,
1
1
2
C(3a)); 138.6 (d, J(C,P) ¼ 12, C(1) of Ph); 137.4 (d, J(C,P) ¼ 12, C(1) of Ph’); 133.4 (d, J(C,P) ¼ 19,
2
C(2), C(6) of Ph); 132.7 (d, J(C,P) ¼ 19, C(2), C(6) of Ph’); 130.7 (s, C(7a)); 128.9 – 128.5 (m, arom.
CH); 125.8 (s, C(5)); 120.8 (d, C(6)); 120.7 (C(7)); 118.8 (s, C(4)); 59.3 (d, 2J(C,P) ¼ 21, C(2’)); 50.2 (s,
1
3
C(5’)); 32.3 (d, J(C,P) ¼ 15, CH2P); 31.4 (d, J(C,P) ¼ 7.5, C(3’)); 23.9 (s, C(4’)). 31P-NMR (202 MHz,
CDCl3): ꢀ 21.6 (s). ESI-MS: 403 (100, [M þ H]þ). Partial oxidation was observed during recording.
[(2S)-1-(1,3-Benzoxazol-2-yl)pyrrolidin-2-yl]methanol ((S)-6). (2S)-2-({[(tert-Butyl)(dimethyl)si-
lyl]oxy}methyl)pyrrolidine [15] ((S)-5; 1.00 g, 4.64 mmol, 1.0 equiv.) was dissolved in THF (15 ml), and a
1.6m soln. of BuLi (3.30 ml, 5.28 mmol, 1.1 equiv.) in hexanes was slowly added at ꢀ 788 in an acetone/
dry ice bath. The resulting soln. was then stirred for 30 min at ꢀ 788 and for 1 h at r.t. After cooling the
soln. again to ꢀ 788, 2-chlorobenzoxazole (700 ml, 6.13 mmol, 1.3 equiv.) was added, and the mixture was
allowed to warm to r.t. over 14 h. At 08 in an ice bath, aq. sat. NaHCO3 (10 ml) was added dropwise.
AcOEt (30 ml) was added, and the layers were separated. The aq. layer was extracted with AcOEt (2 ꢁ
30 ml). The combined org. layers were washed with brine (40 ml) and dried (MgSO4). The solvents were
evaporated under reduced pressure and the crude product, 2-[(2S)-2-({[(tert-butyl)(dimethyl)silyl]oxy}-
methyl)pyrrolidin-1-yl)-1,3-benzoxazole, was dried in vacuo. The residue was then dissolved in THF
(10 ml) and tBu4NF (TBAF) · 3 H2O (2.93 g, 9.29 mmol, 2.0 equiv.) was added portionwise, at 08 in an ice
bath. The resulting mixture was allowed to stir at r.t. for 3 h. AcOEt (30 ml) and H2O (50 ml) were
added. The resulting layers were separated, and the aq. layer was extracted with AcOEt (3 ꢁ 50 ml). The
org. extracts were combined, washed with brine (70 ml), and dried (MgSO4). The solvents were removed
under reduced pressure, and the residue was filtered through a plug of SiO2 (5 ꢁ 5 cm), eluting with
AcOEt. After evaporation of the solvent, the product was purified by CC (SiO2 (5 ꢁ 15 cm);
cyclohexane/AcOEt 1:1 ! 3 :7) to give (S)-6 (576 mg, 2.64 mmol, 57%). Yellowish semisolid. Rf (SiO2;
cyclohexane/AcOEt 7:3) 0.11. [a]2D0 ¼ ꢀ70.6 (c ¼ 0.720, CHCl3). IR (neat): 3270w, 2929w, 2873m, 1631s,
1573s, 1458s, 1386m, 1354m, 1242s, 1168w, 1151w, 1052m, 1003m, 962w, 912m, 793w, 753m, 737s. 1H-NMR
(400 MHz, CDCl3): 7.31 (d, J ¼ 7.8, HꢀC(7)); 7.24 (d, J ¼ 8.0, HꢀC(4)); 7.15 (t, J ¼ 7.8, HꢀC(6)); 7.00 (t,
J ¼ 7.8, HꢀC(5)); 5.99 – 5.76 (br. s, OH); 4.19 – 4.08 (m, HꢀC(2’)); 3.86 – 3.71 (m, CH2O, 1 H of CH2(5’));
3.70 – 3.59 (m, 1 H of CH2(5’)); 2.24 – 2.14 (m, 1 H of Pyr); 2.09 – 1.99 (m, 1 H of Pyr); 1.99 – 1.89 (m, 1 H
of Pyr); 1.82 – 1.68 (m, 1 H of Pyr). 13C-NMR (101 MHz, CDCl3): 162.0 (s, C(2)); 148.9 (s, C(7a)); 142.4
(s, C(3a)); 124.2 (s, C(5)); 120.7 (s, C(6)); 116.1 (s, C(4)); 108.9 (s, C(7)); 66.6 (s, C(2’)); 63.1 (s, CH2O);
48.8 (s, C(5’)); 29.6 (s, C(4’)), 24.4 (s, C(3’)). EI-MS (70 eV): 218 (20, Mþ), 188 (20), 187 (100).
[(2S)-1-(1,3-Benzothiazol-2-yl)pyrrolidin-2-yl]methanol ((S)-7). (2S)-2-({[(tert-Butyl)(dimethyl)si-
lyl]oxy}methyl)pyrrolidine [15] (750 mg, 3.48 mmol, 1.0 equiv.) was dissolved in THF (5 ml), and a 1.6m
soln. of BuLi (2.50 ml, 4.00 mmol, 1.2 equiv.) in hexanes was slowly added at ꢀ 788 in a acetone/dry ice
bath. The resulting soln. was then stirred for 30 min at ꢀ 788 and for 1 h at r.t. After cooling the soln.
again to ꢀ 788, 2-chlorobenzothiazole (540 ml, 4.15 mmol, 1.2 equiv.) was added, and the mixture was
allowed to warm to r.t. over 14 h. At 08 in an ice bath, aq. sat. NaHCO3 (10 ml) was added dropwise.
AcOEt (20 ml) was added, and the layers were separated. The aq. layer was extracted with AcOEt (2 ꢁ

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20 ml). The combined org. extracts were washed with brine (30 ml) and dried (MgSO4). The solvents
were evaporated under reduced pressure, and the crude product was purified by CC (SiO2 (4 ꢁ 15 cm);
cyclohexane/AcOEt 19 :1). The isolated hydroxy-protected compound 2-[(2S)-({[(tert-butyl)(dime-
thyl)silyl]oxy}methyl)pyrrolidin-1-yl)-1,3-benzothiazole (331 mg, 949 mmol, 1.0 equiv.) was then dis-
solved in THF (7 ml) and tBu4NF · 3 H2O (599 mg, 1.90 mmol, 2.0 equiv.) was added at 08 in an ice bath.
The resulting mixture was stirred at r.t. for 3 h. AcOEt (10 ml) and H2O (20 ml) were added. The layers
were separated, and the aq. layer was extracted with AcOEt (3 ꢁ 10 ml). The org. layers were combined,
washed with brine (15 ml) and dried (MgSO4), and the solvent was removed under reduced pressure. The
product was purified by CC (SiO2 (4 ꢁ 10 cm); cyclohexane/AcOEt 1:1) to afford (S)-7 (199 mg,
849 mmol, 57% over two steps). Yellowish semisolid. Rf (SiO2; cyclohexane/AcOEt 1:1) 0.24. [a]D20
¼
ꢀ104 (c ¼ 0.989, CHCl3). IR (neat): 3265m, 2906m, 2869m, 1594m, 1564m, 1528s, 1473w, 1442s, 1359s,
1314m, 1274m, 1253m, 1238m, 1185w, 1153w, 1124w, 1067w, 1047m, 1016m, 925w, 902w, 848w, 749s, 724s,
1
684w. H-NMR (400 MHz, CDCl3): 7.60 (d, J ¼ 7.9, HꢀC(4)); 7.54 (d, J ¼ 8.1, HꢀC(7)); 7.31 (t, J ¼ 7.7,
HꢀC(5)); 7.09 (t, J ¼ 7.7, HꢀC(6)); 6.65 – 6.45 (br. s, OH); 4.30 – 4.20 (m, HꢀC(2’)); 3.86 – 3.71 (m,
CH2O); 3.60 – 3.51 (m, 1 H of CH2(5’)); 3.50 – 3.40 (m, 1 H of CH2(5’)); 2.27 – 2.16 (m, 1 H of Pyr); 2.13 –
2.193 (m, 2 H of Pyr); 1.83 – 1.70 (m, 1 H of Pyr). 13C-NMR (101 MHz, CDCl3): 167.2 (s, C(2)); 151.7 (s,
C(3a)); 130.2 (s, C(7a)); 130.2 (C(5)); 126.1 (s, C(6)); 120.7 (s, C(7)); 118.6 (s, C(4)); 66.8 (s, C(2’)); 64.8
(s, CH2O); 51.8 (s, C(5)); 29.8 (s, C(4’)), 21.0 (s, C(3’)). EI-MS (70 eV): 234 (20, Mþ), 204 (21), 203 (100).
2-[(2S)-2-(Bromomethyl)pyrrolidin-1-yl]-1,3-benzoxazole ((S)-8). Compound (S)-6 (336 mg,
1.54 mmol, 1.0 equiv.), Br4C (765 mg, 2.31 mmol, 1.5 equiv.), and Ph3P (605 mg, 2.31 mmol, 1.5 equiv.)
were dissolved in CH2Cl2 (10 ml) at 08 in an ice bath. The resulting mixture was allowed to warm to r.t.
overnight. The solvent was evaporated, and the crude was purified by CC (SiO2 (4 ꢁ 17 cm);
cyclohexane/AcOEt 4 :1) to furnish (S)-8 (417 mg, 1.48 mmol, 96%). Colorless solid. M.p. 51 – 548. Rf
(SiO2; cyclohexane/AcOEt 4 :1) 0.25. [a]2D0 ¼ ꢀ59.1 (c ¼ 0.981, CHCl3). IR (neat): 2956w, 2875w, 1630s,
1569s, 1456s, 1435m, 1381m, 1345m, 1328m, 1281m, 1244s, 1224m, 1203m, 1189m, 1137m, 1085w, 1004m,
1
902m, 824m, 795m, 739s, 644s. H-NMR (400 MHz, CDCl3): 7.38 (d, J ¼ 8.3, HꢀC(4)); 7.28 (d, J ¼ 7.9,
HꢀC(7)); 7.17 (td, J ¼ 7.7, 1.0, HꢀC(5)); 7.02 (td, J ¼ 7.8, 1.1, HꢀC(6)); 4.39 – 4.31 (m, HꢀC(2’)); 3.79 – 3.67
(m, CH2(5’), 1 H of CH2Br); 3.61 (dd, J ¼ 9.9, 8.3, 1 H of CH2Br); 2.24 – 1.95 (m, 4 H of Pyr). 13C-NMR
(101 MHz, CDCl3): 160.5 (s, C(2)); 149.0 (s, C(7a)); 143.3 (s, C(3a)); 124.1 (s, C(5)); 120.8 (s, C(6)); 116.5
(s, C(4)); 109.9 (s, C(7)); 59.6 (s, C(2’)); 49.0 (s, C(5’)); 34.4 (s, CH2Br), 30.2 (s, C(4’)), 23.8 (s, C(3’)). EI-
MS (70 eV): 282 (17), 280 (17, Mþ), 201 (20), 188 (13), 187 (100).
2-[(2S)-2-(Bromomethyl)pyrrolidin-1-yl]-1,3-benzothiazole ((S)-9). Compound (S)-7 (321 mg,
1.37 mmol, 1.0 equiv.), Br4C (683 mg, 2.06 mmol, 1.5 equiv.), and Ph3P (539 mg, 2.05 mmol, 1.5 equiv.)
were dissolved in CH2Cl2 (8 ml) at 08 in an ice bath. The resulting mixture was allowed to warm to r.t.
overnight. The solvent was evaporated, and the crude product purified by CC (SiO2 (4 ꢁ 17 cm);
cyclohexane/AcOEt 4 :1) to provide (S)-9 (180 mg, 606 mmol, 44%). Colorless solid. M.p. 130 – 1338. Rf
(SiO2; cyclohexane/AcOEt 4 :1) 0.47. [a]2D0 ¼ ꢀ113 (c ¼ 0.123, CHCl3). IR (neat): 3439w, 2959w, 2872w,
1594m, 1558m, 1530s, 1473m, 1442m, 1418m, 1358m, 1325m, 1269m, 1246m, 1120m, 1065w, 1017w, 912w,
880w, 751s, 727s, 684m. 1H-NMR (400 MHz, CDCl3): 7.53 (t, J ¼ 7.4, 2 H of BzTh); 7.27 – 7.16 (m, 1 H of
BzTh); 7.00 (t, J ¼ 7.4, 1 H of BzTh); 4.38 – 4.25 (m, HꢀC(2’)); 5.76 (d, J ¼ 9.8, 1 H of CH2Br); 3.62 – 3.52
(m, 1 H of CH2Br, 1 H of CH2(5’)); 3.47 – 3.38 (m, 1 H of CH2(5’)); 2.20 – 1.98 (m, 4 H of Pyr). 13C-NMR
(101 MHz, CDCl3): 164.9 (s, C(2)); 153.0 (s, C(3a)); 130.8 (s, C(7a)); 126.1 (s, C(5)); 121.3 (s, C(6)); 120.8
(s, C(7)); 119.2 (s, C(4)); 61.3 (s, C(2’)); 51.2 (s, C(5’)); 34.0 (s, CH2Br), 30.1 (s, C(3’)); 23.8 (s, C(4’)). EI-
MS (70 eV): 298 (17), 296 (17, Mþ), 217 (30), 216 (18), 204 (13), 203 (100).
2-[(2S)-2-{[Bis(2-methylphenyl)phosphanyl]methyl}pyrrolidin-1-yl]-1,3-benzoxazole ((S)-LN3).
Bis(2-methylphenyl)phosphine (10; 91.4 mg, 427 mmol, 1.2 equiv.) was dissolved in THF (5 ml), and a
1.6m soln. of BuLi (270 ml, 432 mmol, 1.2 equiv.) in hexanes was slowly added at ꢀ 788 in an acetone/dry
ice bath. The resulting soln. was stirred for 20 min at ꢀ 788 and then for 2 h at r.t. A soln. of (S)-8
(100 mg, 356 mmol, 1.0 equiv.) in THF (3 ml) was added, after cooling the soln. again to ꢀ 788. The
mixture was allowed to warm to r.t. overnight. At 08 in an ice bath, aq. sat. NaHCO3 was added dropwise
to quench the reaction. AcOEt was then added, and the layers were separated. The aq. layer was
extracted with AcOEt (3ꢁ). The combined org. layers were washed with brine, dried (MgSO4), and then

Helvetica Chimica Acta – Vol. 95 (2012)
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reduced to dryness under reduced pressure. CC (SiO2 (5 ꢁ 17 cm); cyclohexane/AcOEt 4 :1) afforded
(S)-LN3 (122 mg, 294 mmol, 83%). Colorless solid. Rf (SiO2; cyclohexane/AcOEt 4 :1) 0.35. [a]2D0 ¼ ꢀ87.1
(c ¼ 0.421, CHCl3). IR (neat): 3054w, 2969w, 2875w, 1636s, 1576s, 1457s, 1381m, 1355m, 1283w, 1243m,
1148w, 1031w, 1003w, 917m, 739s. 1H-NMR (500 MHz, CDCl3): 7.78 – 7.73 (m, 1 H of oTol); 7.38 – 7.28 (m,
HꢀC(7), 2 H of oTol/oTol’); 7.22 – 7.10 (m, HꢀC(4), HꢀC(5), 4 H of oTol/oTol’); 7.08 – 6.97 (m, HꢀC(6),
1 H of oTol/oTol’); 4.28 – 4.16 (m, HꢀC(2’)); 3.77 – 3.69 (m, 1 H of CH2(5’)); 3.68 – 3.61 (m, 1 H of
CH2(5’)); 2.87 – 2.80 (m, 1 H of CH2P); 2.49 (s, Me of oTol); 2.44 (s, Me of oTol’); 2.39 – 1.96 (m, 1 H of
CH2P, 4 H of Pyr). 13C-NMR (101 MHz, CDCl3): 160.6 (s, C(2)); 148.9 (s, C(7a)); 143.4 (s, C(3a)); 142.6
(d, 2J(C,P) ¼ 26, C(2) of oTol); 141.8 (d, 2J(C,P) ¼ 26, C(2) of oTol’); 136.6 (d, 1J(C,P) ¼ 12, C(1) of oTol) ;
135.6 (d, 1J(C,P) ¼ 13, C(1) of oTol’); 131.8 (s, C(6) of oTol); 131.6 (s, C(6) of oTol’); 130.2 (d, 3J(C,P) ¼
4.8, C(3) of oTol); 130.1 (d, 3J(C,P) ¼ 5.0, C(3) of oTol’); 128.8 (s, C(4) of oTol); 128.6 (s, C(2) of oTol’);
126.3 (s, C(5) of oTol); 126.1 (s, C(5) of oTol’); 123.9 (s, C(5)); 120.2 (s, C(6)); 116.2 (s, C(4)); 108.6 (s,
C(7)); 57.4 (d, 2J(C,P) ¼ 23, 1 H, C(2’)); 48.2 (s, C(5’)); 32.7 (d, 1J(C,P) ¼ 15, CH2P); 31.6 (d, 3J(C,P) ¼ 7.7,
3
C(3’)); 24.0 (s, C(4’)); 21.4 (d, J(C,P) ¼ 5.9, Me of oTol) , 21.2 (s, Me of oTol’). 31P-NMR (162 MHz,
CDCl3): ꢀ 43.2 (s). EI-MS (70 eV): 414 (5, Mþ), 324 (21), 323 (100), 187 (27).
2-[(2S)-2-{[Bis(2-methylphenyl)phosphanyl]methyl}pyrrolidin-1-yl]-1,3-benzothiazole ((S)-LN4).
Compound (S)-LN4 (59%) was prepared as described for (S)-LN3 from (S)-9 and 10. M.p. 114 – 1188.
Rf (SiO2; cyclohexane/AcOEt 4 :1) 0.47. [a]D20 ¼ ꢀ80.7 (c ¼ 0.851, CHCl3). IR (neat): 3055w, 2966w,
2930w, 2874w, 1593m, 1560m, 1531s, 1444s, 1359m, 1318m, 1272m, 1254m, 1184w, 1141w, 1065w, 1016m,
925m, 909m, 847m, 754s, 748s, 725m, 680m. 1H-NMR (500 MHz, CDCl3): 7.99 – 7.91 (m, HꢀC(6) of oTol) ;
7.62 (d, J ¼ 8.1, HꢀC(7)); 7.57 (d, J ¼ 7.8, HꢀC(4)); 7.40 (t, J ¼ 7.2, HꢀC(5) of oTol); 7.36 – 7.29 (m, HꢀC(4)
of oTol, HꢀC(6)); 7.24 – 7.20 (m, HꢀC(3) of oTol); 7.20 – 7.14 (m, HꢀC(3), HꢀC(4), HꢀC(6) of oTol’
each); 7.10 – 7.07 (m, HꢀC(5) of oTol’); 7.07 – 7.03 (m, HꢀC(5)); 4.23 – 4.09 (m, HꢀC(2’)); 3.67 – 3.60 (m,
1 H of CH2(5’)); 3.56 – 3.47 (m, 1 H of CH2(5’)); 3.04 – 2.95 (m, 1 H of CH2P); 2.49 (s, Me of oTol); 2.46 (s,
Me of oTol’); 2.31 – 2.24 (m, 1 H of CH2(3’)); 2.22 – 2.13 (m, 1 H of CH2(3’), 1 H of CH2(4’)); 2.10 – 2.01
(m, 1 H of CH2(4’)); 1.99 – 1.91 (m, 1 H of CH2P). 13C-NMR (101 MHz, CDCl3): 164.7 (s, C(2)); 153.3 (s,
C(7a)); 142.2 (d, 2J(C,P) ¼ 26, C(2) of oTol); 141.7 (d, 2J(C,P) ¼ 26, C(2) of oTol’); 137.0 (d, 1J(C,P) ¼ 12,
C(1) of oTol); 135.6 (d, 1J(C,P) ¼ 13, C(1) of oTol’); 132.5 (s, C(6) of oTol); 131.6 (s, C(6) of oTol’); 131.0
(s, C(3a)); 130.2 – 130.1 (m, C(3) of oTol, C(3) of oTol’); 128.8 (s, C(4) of oTol); 128.6 (s, C(4) of oTol’);
126.4 (s, C(5) of oTol); 126.2 (s, C(5) of oTol’); 125.9 (s, C(6)); 120.8 (s, C(5)); 120.7 (s, C(4)); 118.9 (s,
2
3
1
C(7)); 59.4 (d, J(C,P) ¼ 23, C(2’)); 50.1 (s, C(5’)); 31.4 (d, J(C,P) ¼ 7.9, C(3’)); 31.2 (d, J(C,P) ¼ 15,
CH2P), 24.0 (s, C(4’)), 21.4 (d, J(C,P) ¼ 12, Me of oTol) ; 21.3 (d, J(C,P) ¼ 12, Me of oTol’). 31P-NMR
(162 MHz, CDCl3): ꢀ 42.5 (s). EI-MS (70 eV): 430 (6, Mþ), 340 (22), 339 (100), 267 (13), 217 (13), 215
(11), 203 (61).
3
3
2-((2S)-2-{[Di(tert-butyl)phosphanyl]methyl}pyrrolidin-1-yl)-1,3-benzoxazole Borane ((S)-LN5 ·
BH3). Compound (S)-LN5 · BH3 (89%) was prepared as described for (S)-LN3 from (S)-8 and di(tert-
butyl)phosphine borane adduct (11). M.p. 52 – 568. Rf (SiO2; cyclohexane/AcOEt 4 :1) 0.36. [a]2D0 ¼ ꢀ68.4
(c ¼ 0.252, CHCl3). IR (neat): 2953m, 2874m, 1637s, 1578s, 1458m, 1382m, 1373m, 1284w, 1244m, 1147w,
1072m, 1023w, 919w, 813m, 740s. 1H-NMR (400 MHz, CDCl3): 7.33 (d, J ¼ 7.7, HꢀC(7)); 7.20 (d, J ¼ 7.8,
HꢀC(4)); 7.17 – 7.10 (m, HꢀC(5)); 7.03 – 6.94 (m, HꢀC(6)); 4.44 – 4.32 (m, HꢀC(2’)); 3.77 – 3.67 (m, 1 H
of CH2(5’)); 3.67 – 3.56 (m, 1 H of CH2(5’)); 2.64 (t, J ¼ 14, 1 H of CH2P); 2.37 – 2.26 (m, 1 H of CH2(3’));
2.26 – 2.24 (m, 1 H of CH2(3’)); 2.06 – 1.94 (m, CH2(4’)); 1.63 – 1.51 (m, 1 H of CH2P); 1.45 (d, 3J(H,P) ¼
t
3
t
13, Bu); 1.25 (d, J(H,P) ¼ 13, Bu); 0.93 – 0.08 (br. m, BH3). 13C-NMR (101 MHz, CDCl3): 160.5 (s,
C(2)); 148.9 (s, C(7a)); 143.6 (s, C(3a)); 124.0 (s, C(5)); 120.4 (s, C(6)); 116.3 (s, C(4)); 108.5 (s, C(7));
57.3 (d, 2J(C,P) ¼ 6.2, C(2’)); 48.1 (s, C(5’)); 33.4 (d, 1J(C,P) ¼ 29, Me3C); 32.8 (s, C(3’)); 32.1 (d,
1J(C,P) ¼ 27, Me3C); 28.2 (br. s, Me of tBu); 27.9 (br. s, Me of tBu’); 23.6 (s, C(4’)), 21.9 (d, 1J(C,P) ¼ 23,
CH2P). 31P-NMR (162 MHz, CDCl3): 39.8 (br. d, 1J(P,B) ¼ 68). EI-MS (70 eV): 360 (14), 359 (22, [M ꢀ
H]þ), 343 (32), 303 (33), 290 (17), 289 (100), 247 (27), 245 (17), 233 (26), 232 (15), 213 (14), 201 (22),
187 (21), 178 (10), 57 (28). Anal calc. for C20H34BN2OP (360.2502): C 66.67, H 9.51, N 7.78; found: C
66.39, H 9.52, N 7.30.
2-((2S)-2-{[Di(tert-butyl)phosphanyl]methyl}pyrrolidin-1-yl)-1,3-benzoxazole ((S)-LN5). Com-
pound (S)-LN5 · BH3 (34.6 mg, 100 mmol) was dissolved in HNEt2 (3.0 ml) under Ar and stirred at r.t.
for 5 – 10 d. The conversion was monitored by 31P-NMR analysis. After completion of the reaction, all

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Helvetica Chimica Acta – Vol. 95 (2012)
volatiles were removed under high vacuum at 608, and (S)-LN5 was isolated as a colorless semisolid in
quant. yield. 31P-NMR (162 MHz, CD2Cl2): 21.2 (s).
2-{(2S)-2-[(Di-(tert-butyl)phosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzothiazole Borane ((S)-LN6 ·
BH3). Compound (S)-LN6 · BH3 (81%) was prepared as described for (S)-LN3 from (S)-9 and 11. M.p.
171 – 1768. Rf (SiO2; cyclohexane/AcOEt 4 :1) 0.54. [a]2D0 ¼ ꢀ120 (c ¼ 0.210, CHCl3). IR (neat): 2948m,
2906m, 2871m, 1597m, 1538s, 1444s, 1393w, 1354m, 1316w, 1274m, 1184m, 1147m, 1123m, 1070s, 1019m,
921m, 815m, 753s, 678m. 1H-NMR (400 MHz, CDCl3): 7.61 (d, J ¼ 7.7, HꢀC(7)); 7.48 (d, J ¼ 7.8, HꢀC(4));
7.31 – 7.22 (m, HꢀC(6)); 7.05 (t, J ¼ 7.4, HꢀC(5)); 4.52 – 4.39 (m, HꢀC(2’)); 3.60 – 3.47 (m, 1 H of CH2(5’));
3.46 – 3.33 (m, 1 H of CH2(5’)); 3.06 – 2.91 (m, 1 H of CH2P); 2.41 – 2.19 (m, 2 H of Pyr); 2.13 – 1.97 (m,
2 H of Pyr); 1.62 – 1.37 (m, 1 H of CH2P); 1.52 (d, 3J(H,P) ¼ 13, tBu); 1.25 (d, 3J(H,P) ¼ 12, tBu); 0.93 –
0.12 (br. q, BH3). 13C-NMR (101 MHz, CDCl3): 164.5 (s, C(2)); 153.4 (s, C(3a)); 131.0 (s, C(7a)); 126.0 (s,
C(6)); 120.9 (s, C(5)); 120.9 (s, C(7)); 118.8 (s, C(4)); 59.3 (d, 2J(C,P) ¼ 5.7, C(2’)); 50.5 (s, C(5’)); 33.7 (d,
1J(C,P) ¼ 27, Me3C); 32.7 (s, C(3’)); 32.2 (d, 1J(C,P) ¼ 27, Me3C); 28.4 (br. s, Me of tBu); 28.0 (br. s, Me of
1
tBu’); 23.9 (s, C(4’)); 20.7 (d, J(C,P) ¼ 23, CH2P). 31P-NMR (162 MHz, CDCl3): 39.7 (br. d). EI-MS
(70 eV): 376 (24), 375 (63, [M ꢀ H]þ), 374 (14), 343 (12), 320 (12), 319 (60), 318 (14), 306 (18), 305
(100), 263 (21), 261 (13), 249 (30), 248 (15), 231 (15), 229 (17), 217 (20), 215 (13), 203 (33), 57 (24).
2-((2S)-2-{[Di(tert-butyl)phosphanyl]methyl}pyrrolidin-1-yl)-1,3-benzothiazole ((S)-LN6). Product
(S)-LN6 was prepared as described for (S)-LN5 from (S)-LN6 · BH3. 31P-NMR (162 MHz, CDCl3): 20.8
(s).
2-{(2S)-2-[(Dicyclohexylphosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzoxazole Borane ((S)-LN7 ·
BH3). Compound (S)-LN7 · BH3 (78%) was prepared as described for (S)-LN3 from (S)-8 and
dicyclohexylphosphine borane adduct (12). M.p. 159 – 1628. Rf (SiO2; cyclohexane/AcOEt 9 :1) 0.16.
[a]2D0 ¼ ꢀ60.7 (c ¼ 0.560, CHCl3). IR (neat): 3288m, 2926m, 2849m, 1635s, 1627s, 1593m, 1523s, 1516s,
1493m, 1381m, 1355m, 1346m, 1331w, 1240m, 1217w, 1192w, 1174m, 1068w, 951w, 916w, 882w, 737s, 692s.
1H-NMR (400 MHz, CDCl3): 7.33 (d, J ¼ 7.7, HꢀC(7)); 7.21 (d, J ¼ 7.9, HꢀC(4)); 7.15 (td, J ¼ 7.7, 1.0,
HꢀC(5)); 7.00 (td, J ¼ 7.7, 1.1, HꢀC(6)); 4.37 – 4.25 (m, HꢀC(2’)); 3.75 – 3.69 (m, 1 H of CH2(5’)); 3.63 –
3.56 (m, 1 H of CH2(5’)); 2.41 (t, J ¼ 15, 1 H of CH2P); 2.32 – 1.17 (m, 1 H of CH2P, CH2(3’), CH2(4’),
CH2(5’), 20 H of Cy and Cy’); 0.82 – 0.05 (br. q, BH3). 13C-NMR (101 MHz, CDCl3): 160.4 (s, C(2)); 149.0
(s, C(7a)); 143.5 (s, C(3a)); 124.1 (s, C(5)); 120.4 (s, C(6)); 116.3 (s, C(4)); 108.6 (s, C(7)); 56.4 (d,
2J(C,P) ¼ 6.3, C(2’)); 48.1 (s, C(5’)); 33.1 (d, 1J(C,P) ¼ 33, C(1) of Cy); 32.8 (s, C(3’)); 31.9 (d, 1J(C,P) ¼
34, C(1) of Cy’); 27.3 – 26.0 (m, Cy/Cy’), 23.9 (d, 1J(C,P) ¼ 26, CH2P), 23.7 (s, C(4’)). 31P-NMR (162 MHz,
CDCl3): 21.0 (br. d). EI-MS (70 eV): 412 (17, Mþ), 411 (29, [M ꢀ H]þ), 396 (13), 395 (50), 394 (12), 329
(11), 316 (20), 315 (100), 313 (25), 292 (10), 247 (11), 233 (13), 215 (17), 213 (17), 201 (12), 187 (13).
2-{(2S)-2-[(Dicyclohexylphosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzoxazole ((S)-LN7). Product
(S)-LN7 was prepared as described for (S)-LN5 from (S)-LN7 · BH3. 31P-NMR (162 MHz, CDCl3):
ꢀ 11.2 (s).
2-{(2S)-2-[(Dicyclohexylphosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzothiazole Borane ((S)-LN8 ·
BH3). Compound (S)-LN8 · BH3 (66%) was prepared as described for (S)-LN3 from (S)-9 and 12. M.p.
120 – 1238. Rf (SiO2; cyclohexane/AcOEt 9 :1) 0.40. [a]2D0 ¼ ꢀ53.8 (c ¼ 0.131, CHCl3). IR (neat): 2922m,
2915m, 2849m, 2369m, 1595m, 1560w, 1536s, 1442s, 1361m, 1318m, 1272m, 1252m, 1180w, 1125m, 1067m,
1016m, 1006m, 931m, 858m, 801m, 754s, 726s, 679m. 1H-NMR (400 MHz, CDCl3): 7.61 (d, J ¼ 7.7,
HꢀC(7)); 7.50 (d, J ¼ 7.3, HꢀC(4)); 7.29 (t, J ¼ 7.8, HꢀC(6)); 7.06 (t, J ¼ 7.5, HꢀC(5)); 4.46 – 4.33 (m,
HꢀC(2’)); 3.61 – 3.48 (m, 1 H of CH2(5’)); 3.48 – 3.34 (m, 1 H of CH2(5’)); 2.72 – 2.58 (m, 1 H of CH2P);
2.33 – 1.11 (m, 1 H of CH2P, C H2(3’), CH2(4’), CH2(5’), 20 H of Cy and Cy’); 0.79 – 0.10 (br. q, BH3).
13C-NMR (101 MHz, CDCl3): 164.5 (s, C(2)); 153.4 (s, C(3a)); 131.0 (s, C(7a)); 126.1 (s, C(6)); 121.0 (s,
C(5)); 120.9 (s, C(7)); 118.8 (s, C(4)); 58.1 (br. s, C(2’)); 50.4 (s, C(5’)); 33.2 (d, 1J(C,P) ¼ 32, C(1) of Cy);
32.6 (s, C(3’)); 32.0 (d, 1J(C,P) ¼ 33, C(1) of Cy’); 27.4 – 25.9 (m, Cy/Cy’); 23.8 (s, C(4’)); 22.8 (d, 1J(C,P) ¼
27, CH2P). 31P-NMR (162 MHz, CDCl3): 21.5 (br.). EI-MS (70 eV): 428 (26), 427 (85, [M ꢀ H]þ), 426
(19), 395 (17), 345 (14), 332 (21), 331 (100), 292 (12), 249 (11), 231 (20), 217 (13), 203 (18).
2-{(2S)-2-[(Dicyclohexylphosphanyl)methyl]pyrrolidin-1-yl}-1,3-benzothiazole ((S)-LN8). Product
(S)-LN8 was prepared as described for (S)-LN5 from (S)-LN8 · BH3. 31P-NMR (162 MHz, CDCl3): ꢀ 10.9
(s).

Helvetica Chimica Acta – Vol. 95 (2012)
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Synthesis of Ir Complexes: General Procedure 1 (GP 1). Ligand (200 – 300 mmol, 1.0 equiv.) and
bis(cycloocta-1,5-diene)diiridium(I) dichloride (0.50 equiv.) were dissolved in CH2Cl2 (5 ml). The
resulting soln. was heated at reflux for 2 h, before it was allowed to cool to r.t. At r.t., NaBArF (1.3 equiv.)
was added, and the resulting mixture was allowed to stir for 5 min. H2O (5 ml) was then added, and the
resulting biphasic mixture was vigorously stirred for 30 min. The layers were separated, and the aq. layer
was extracted with CH2Cl2 (3 ꢁ 10 ml). The combined org. extracts were dried (MgSO4), and the solvent
was evaporated under reduced pressure. The product was purified by CC (SiO2: elution of the side
products with cyclohexane/CH2Cl2 100 :0 ! 1:1, and then of the product 1:1 ! 0 :100 to afford the
desired complex.
General Procedure 2 (GP 2). Ligand (10.0 – 20.0 mg, 1.0 equiv.) and [Ir(cod)2]BArF (1.0 equiv.) were
mixed in abs. CH2Cl2 (1 – 2 ml) and stirred for 1 h at r.t. The solvent was evaporated, and the residue was
purified by CC (SiO2; elution of the side products with cyclohexane/CH2Cl2 100 :0 ! 1:1, and then of the
product 1:1 ! 0 :100 to furnish the desired complex.
[(h4-Cycloocta-1,5-diene)((S)-2-{2-[(diphenylphosphino)methyl]pyrrolidin-1-yl}benzo[d]oxazo-
le)iridium(I)] Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN1). Complex (S)-CN1 (89%) was
prepared according to GP 1 from (S)-LN1 and [Ir(cod)Cl]2. M.p. 131 – 1338. [a]2D0 ¼ ꢀ36.3 (c ¼ 0.860,
CHCl3). IR (neat): 2928w, 2848w, 1643m, 1618m, 1589m, 1467m, 1436w, 1402w, 1353s, 1271s, 1251m,
1113s, 999w, 885m, 838m, 742m, 711m, 680s, 667s. 1H-NMR (500 MHz, CD2Cl2): 7.76 (br. s, HꢀC(4), 8 o-
H of ArF); 7.58 (br. s, 4 p-H of ArF); 7.50 – 7.44 (m, 2 arom. o-H); 7.44 – 7.38 (m, HꢀC(5), 3 arom. H);
7.32 – 7.27 (m, 1 p-H of Ph/Ph’); 7.23 – 7.11 (m, HꢀC(6), HꢀC(7), 4 arom. H); 5.87 – 5.77 (m, HꢀC(2’));
5.13 – 5.06 (m, 1 H of cod); 4.97 – 4.88 (m, 1 H of cod); 3.96 – 3.88 (m, 1 H of cod); 3.74 – 3.65 (m, 1 H of
CH2(5’)); 3.65 – 3.56 (m, 1 H of CH2(5’)); 3.31 (ddd, J ¼ 15, 10, 2.2, 1 H of CH2P); 3.10 – 2.98 (m, 1 H of
CH2P, 1 H of cod); 2.71 – 2.56 (m, 1 H of CH2(3’), 1 H of cod); 2.44 – 2.36 (m, 1 H of cod); 2.33 – 2.08 (m,
CH2(4’), 1 H of CH2(3’), 4 H of cod); 1.75 – 1.65 (m, 1 H of cod); 1.65 – 1.56 (m, 1 H of cod). 13C-NMR
1
(101 MHz, CD2Cl2): 161.9 (q, J(C,B) ¼ 50, ipso-C of ArF), 158.9 (s, C(2)); 147.6 (s, C(7a)); 138.7 (s,
2
4
C(3a)); 134.9 (s, o-C of ArF); 133.6 (d, J(C,P) ¼ 13, C(2), C(6) of Ph); 131.9 (d, J(C,P) ¼ 2.3, C(4) of
Ph); 131.2 (d, 4J(C,P) ¼ 2.5, C(4) of Ph’); 130.9 (d, 3J(C,P) ¼ 9.4, C(3), C(5) of Ph); 130.4 (d, 1J(C,P) ¼ 51,
C(1) of Ph); 129.5 – 128.5 (m, CH of Ph’, m-C of ArF); 127.4 (d, 1J(C,P) ¼ 50, C(1) of Ph’); 125.4 (s, C(5));
124.7 (q, 1J(C,F) ¼ 272, CF3); 123.7 (s, C(6)); 117.7 – 117.4 (m, p-C of ArF); 117.4 (s, C(4)); 110.3 (s, C(7));
97.7 (d, 2J(C,P) ¼ 9.6, CH of cod), 88.1 (d, 2J(C,P) ¼ 15, CH of cod); 66.1 (s, CH of cod); 61.1 (s, CH of
cod); 60.5 (d, 2J(C,P) ¼ 5.8, C(2’)); 49.9 (s, C(5’)); 41.1 (d, 1J(C,P) ¼ 29, CH2P); 36.1 (d,3J(C,P) ¼ 4.3, CH2
3
3
of cod); 34.8 (d, J(C,P) ¼ 13, C(3’)); 33.5 (s, CH2 of cod); 29.2 (d, J(C,P) ¼ 1.6, CH2 of cod); 26.2 (d,
3J(C,P) ¼ 2.6, CH2 of cod); 23.5 (s, C(4’)). 31P-NMR (162 MHz, CD2Cl2): 15.6 (s). 19F-NMR (377 MHz,
CD2Cl2): ꢀ 62.8 (s). FAB-MS (NBA): 688 (34), 687 (100, Mþ), 686 (27), 685 (67), 577 (23), 575 (23), 573
(10). Anal calc. for C64H47BF24IrN2OP (1550.03): C 49.59, H 3.06, N 1.81; found: C 49.40, H 3.39, N 1.81.
[(h4-Cycloocta-1,5-diene)((S)-2-{2-[(diphenylphosphino)methyl]pyrrolidin-1-yl}benzo[d]thiazo-
le)iridium(I)] Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN2). Complex (S)-CN2 (81%) was
prepared according to GP 1 from (S)-LN2 and [Ir(cod)Cl]2. M.p. 69 – 718. [a]2D0 ¼ þ17.9 (c ¼ 1.08,
CHCl3). IR (neat): 2889w, 1610w, 1534m, 1452m, 1352s, 1272s, 1113s, 1024w, 999w, 937w, 885m, 838m,
744m, 711m, 686m, 669m. 1H-NMR (500 MHz, CDCl3): 8.34 (d, 2J ¼ 8.2, HꢀC(4)); 7.77 (s, 8 m-H of ArF);
7.56 (s, 4 p-H of ArF); 7.55 – 7.51 (m, HꢀC(5)); 7.49 (d, J ¼ 7.9, HꢀC(7)); 7.47 – 7.37 (m, 5 H of Ph/Ph’);
7.32 – 7.28 (m, 1 H of Ph/Ph’); 7.28 – 7.22 (m, HꢀC(6)); 7.20 – 7.10 (m, 4 H of Ph/Ph’); 6.35 – 6.22 (m,
HꢀC(2’)); 4.85 – 4.77 (m, 1 H of cod); 4.51 – 4.42 (m, 1 H of cod); 4.12 – 4.06 (m, 1 H of cod); 3.52 – 3.34
(m, CH2(5’), 1 H of CH2P); 3.02 – 2.87 (m, 1 H of CH2P, 1 H of cod); 2.78 – 2.63 (m, 1 H of CH2(3’), 1 H
of cod); 2.36 – 2.10 (m, 1 H of CH2(3’), CH2(4’), 4 H of cod); 2.10 – 1.97 (m, 1 H of cod); 1.63 – 1.45 (m,
2 H of cod). 13C-NMR (101 MHz, CDCl3): 165.8 (s, C(2)); 162.0 (q, 1J(C,B) ¼ 50, ipso-C of ArF); 148.6 (s,
C(3a)); 135.0 (s, o-C of ArF); 133.2 (d, 2J(C,P) ¼ 13, C(2), C(6) of Ph); 132.1 (s, C(4) of Ph); 131.5 (s, C(4)
of Ph’); 130.7 (d, 3J(C,P) ¼ 9.4, C(3), C(5) of Ph); 130.1 (d, 1J(C,P) ¼ 51, C(1) of Ph); 129.5 – 128.6 (m, o-
C of Ph’, m-C of Ph’, m-C of ArF); 128.0 (d, 1J(C,P) ¼ 50, C(1) of Ph’); 127.1 (s, C(5)); 126.8 (s, C(7a));
128.4 (q, 1J(C,F) ¼ 272, CF3); 124.2 (s, C(6)); 122.1 (s, C(4)); 121.9 (s, C(7)); 117.1 (s, p-C of ArF); 97.3 (d,
2J(C,P) ¼ 9.4, CH of cod); 89.6 (d, 2J(C,P) ¼ 15, CH of cod); 65.3 (s, CH of cod); 61.9 (s, CH of cod); 61.9
(d, 2J(C,P) ¼ 6.7, C(2’)); 53.5 (s, C(5’)); 40.8 (d, 1J(C,P) ¼ 31, CH2P), 36.7 (d, 3J(C,P) ¼ 3.6, CH2 of cod);
35.8 (d, 3J(C,P) ¼ 13, C(3’)); 33.6 (s, CH2 of cod); 28.7 (s, CH2 of cod); 25.9 (s, CH2 of cod); 23.8 (s, C(4’)).

2190
Helvetica Chimica Acta – Vol. 95 (2012)
31P-NMR (162 MHz, CD2Cl2): 15.6 (s). 19F-NMR (377 MHz, CD2Cl2): ꢀ 62.8 (s). FAB-MS (NBA): 705
(11), 704 (37), 703 (100), 702 (27), 701 (60), 595 (12), 594 (16), 593 (30), 592 (10), 591 (18). Anal calc.
for C64H47BF24IrN2PS (1566.25): C 49.08, H 3.02, N 1.79; found: C 49.06, H 2.94, N 2.02.
{(h4-Cycloocta-1,5-diene)[(S)-2-(2-{[bis(2-methylphenyl)phosphino]methyl}pyrrolidin-1-yl)benzo-
[d]oxazole]iridium(I)} Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN3). Complex (S)-CN3
(55%) was prepared according to GP 2 from (S)-LN3 and [Ir(cod)2]BArF. M.p. 72 – 778. [a]2D0 ¼ ꢀ37
(c ¼ 0.140, CHCl3). IR (neat): 2965w, 2888w, 1647m, 1620m, 1468m, 1404w, 1355m, 1274s, 1117s, 1003w,
887m, 840m, 745m, 713m, 680m. 1H-NMR (400 MHz, CD2Cl2): 8.32 – 8.19 (br. m, HꢀC(6) of oTol); 7.81
(d, J ¼ 7.8, HꢀC(4)); 7.73 (br. s, 8 o-H of ArF); 7.56 (s, 4 p-H of ArF); 7.48 – 6.80 (m, 10 H of oTol/oTol’ and
BzOx); 5.96 – 5.85 (m, HꢀC(2’)); 4.98 – 4.89 (m, 1 H of cod); 4.68 – 4.53 (m, 1 H of cod); 3.98 – 3.89 (m,
1 H of cod); 3.89 – 3.74 (m, 2 H of cod); 3.61 – 3.52 (m, 1 H of CH2P); 2.77 – 2.58 (m, 1 H of CH2P, 1 H of
CH2(5’), 1 H of CH2(3’)); 2.58 – 1.98 (m, 8 H of cod and Pyr, Me of oTol); 1.93 (s, Me of oTol’); 1.67 – 1.43
1
(m, 1 H of CH2(4’), 2 H of cod). 13C-NMR (101 MHz, CD2Cl2): 161.8 (q, J(C,B) ¼ 50, ipso-C of ArF);
158.0 (s, C(2)); 147.7 (s, C(7a)); 141.7 (br., C(2) of oTol); 141.2 (br, C(2) of oTol’); 140.3 (br. d, C(6) of
oTol); 138.8 (s, C(3a)); 134.9 (s, o-C of ArF); 132.8 – 132.3 (m, C(4) of oTol, C(3) of oTol, C(3) of oTol’);
131.6 (br. s, C(6) of oTol’); 130.0 (br., C(1) of oTol); 129.3 – 128.4 (m, m-C of ArF); 128.4 (q, 1J(C,F) ¼
272, CF3); 127.9 – 125.0 (m, C(1) of oTol’, C(4) of oTol’, C(5) of oTol, C(5) of oTol, C(5)); 123.7 (s, C(6));
117.8 – 117.4 (m, p-C of ArF, C(4’)); 110.4 (s, C(7)); 96.9 (br. d, CH of cod); 87.2 (d, 2J(C,P) ¼ 15, CH of
cod); 66.7 (s, CH of cod); 62.6 (s, CH of cod); 59.6 (br. d, 2J(C,P) ¼ 4.0, C(2’)); 50.0 (s, CH2 of cod); 43.9
(d, 1J(C,P) ¼ 26, CH2P); 36.8 (br. s, C(5’)); 36.0 (d, 3J(C,P) ¼ 11, C(3’)); 33.9 (s, CH2 of cod); 28.4 (s, CH2
of cod); 25.6 (s, C(4’)); 24.0 (br. s, Me of oTol); 23.1 (s, CH2 of cod); 21.8 (br. s, Me of oTol) . 31P-NMR
(162 MHz, CD2Cl2): 26.1/10.2 (2 br. s). These signals indicate the presence of a mixture of rotamers in a
ratio of 25 :1. 19F-NMR (377 MHz, CD2Cl2): ꢀ 62.8 (s). ESI-MS: 715 (100, Mþ). Anal calc. for
C66H51BF24IrN2OP (1578.09): C 50.23, H 3.26, N 1.78; found: C 50.69, H 3.94, N 1.93.
{(h4-Cycloocta-1,5-diene)-[(S)-2-(2-{[bis(2-methylphenyl)phosphino]methyl}pyrrolidin-1-yl)ben-
zo[d]thiazole]iridium(I)} Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN4). Complex (S)-CN4
(97%) was prepared according to GP 2 from (S)-LN4 and [Ir(cod)2]BArF. M.p. 118 – 1218. [a]2D0 ¼ ꢀ1.0
(c ¼ 0.271, CHCl3). IR (neat): 3064w, 2964w, 2889w, 1787w, 1545m, 1453m, 1355m, 1275s, 1116s, 888m,
839m, 744m, 714m, 681m. 1H-NMR (400 MHz, CD2Cl2): 8.52 (d, J ¼ 8.3, HꢀC(4)); 8.18 – 8.08 (m, HꢀC(6)
of oTol); 7.75 (s, 8 o-H of ArF); 7.69 – 7.60 (m, HꢀC(5), HꢀC(7)); 7.57 (s, 4 p-H of ArF); 7.44 – 7.22 (m,
HꢀC(6), HꢀC(6) of oTol’, HꢀC(5) of oTol, HꢀC(4) of oTol, HꢀC(3) of oTol); 7.18 – 7.10 (m, HꢀC(3) of
oTol’); 7.08 – 6.95 (m, HꢀC(4) of oTol’); 6.94 – 6.85 (m, HꢀC(5) of oTol’); 6.54 – 6.41 (m, HꢀC(2’)); 4.82 –
4.72 (m, 1 H of cod); 4.31 – 4.20 (m, 1 H of cod); 4.14 – 4.05 (m, 1 H of cod); 3.77 – 3.64 (m, 1 H of CH2P);
3.63 – 3.52 (m, 2 H of cod); 2.85 – 2.65 (m, CH2(5’), 1 H of CH2P); 2.65 – 2.55 (m, 1 H of cod); 2.46 – 2.15
(m, CH2(3’), CH2(4’), Me of oTol, 2 H of cod); 2.15 – 1.95 (m, 3 H of cod); 1.90 (s, Me of oTol’); 1.57 – 1.44
1
(m, 1 H of cod). 13C-NMR (101 MHz, CD2Cl2): 165.2 (s, C(2)); 161.8 (q, J(C,B) ¼ 50, ipso-C of ArF);
2
148.8 (s, C(3a)); 141.5 (br. s, C(2) of oTol); 140.6 (br. d, C(2) of oTol’); 139.4 (d, J(C,P) ¼ 30, C(6) of
oTol); 134.9 (s, o-C of ArF); 132.7 – 132.3 (m, C(4) of oTol, C(3) of oTol, C(3) of oTol’); 131.5 (br. s, C(6)
of oTol’); 131.0 (br. s, C(4) of oTol); 130.3 (br. d, C(1) of oTol); 129.5 – 128.4 (m, m -C of ArF); 127.2 (s,
C(7a)); 127.0 (s, C(5)); 126.7 (d, 3J(C,P) ¼ 9.6, C(5) of oTol); 125.6 (d, 3J(C,P) ¼ 9.6, C(5) of oTol’); 125.0
(q, 1J(C,F) ¼ 272, CF3); 125.2 (br. d, C(1) of oTol’); 124.0 (s, C(6)); 120.6 (s, C(7)); 121.8 (s, C(4)); 117.7 –
117.4 (m, p-C of ArF); 96.2 (d, 2J(C,P) ¼ 8.1, CH of cod); 87.9 (d, 2J(C,P) ¼ 16, CH of cod); 66.3 (s, CH of
cod); 63.1 (s, CH of cod); 62.2 (d, 2J(C,P) ¼ 9.0, C(2’)); 53.9 (s, CH2 of cod); 43.7 (d, 1J(C,P) ¼ 29, CH2P),
37.2 (br. s, C(5’)); 36.7 (d, 3J(C,P) ¼ 13, C(3’)); 34.0 (s, CH2 of cod); 28.3 (s, CH2 of cod); 25.5 (s, CH2 of
3
cod); 24.3 (s, C(4’)); 23.0 (d, J(C,P) ¼ 5.6, Me of oTol); 21.6 (br. s, Me of oTol’). 31P-NMR (162 MHz,
CD2Cl2): 22.4/3.32 (br. s). These signals indicate the presence of a mixture of rotamers in a ratio of 17:1.
19F-NMR (377 MHz, CD2Cl2): ꢀ 62.8 (s). FAB-MS (NBA): 733 (12), 732 (38), 731 (100, Mþ), 730 (24),
729 (59), 623 (11), 622 (11), 621 (21), 620 (11), 619 (19), 617 (13).
{(h4-Cycloocta-1,5-diene)-[(S)-2-(2-{[di(tert-butyl)phosphino]methyl}pyrrolidin-1-yl)benzo[d]oxa-
zole]iridium(I)} Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN5). Complex (S)-CN5 (95%) was
prepared according to GP 2 from (S)-LN5 and [Ir(cod)2]BArF. M.p. 210 – 2138. [a]2D0 ¼ þ7.1 (c ¼ 0.220,
CHCl3). IR (neat): 2968w, 2892w, 1650m, 1622m, 1469m, 1406w, 1354m, 1272s, 1162s, 1121s, 1005w, 887m,
840m, 714m. 1H-NMR (400 MHz, CD2Cl2): 7.73 (br. s, 8 o-H of ArF); 7.59 – 7.52 (m, 4 p-H of ArF,

Helvetica Chimica Acta – Vol. 95 (2012)
2191
HꢀC(4)); 7.40 – 7.33 (m, HꢀC(5), HꢀC(7)); 7.23 (td, J ¼ 7.8, 1.1, HꢀC(6)); 5.32 – 5.20 (m, 2 H of cod);
4.45 – 4.37 (m, 1 H of cod); 4.13 – 4.05 (m, HꢀC(2’)); 3.97 – 3.76 (m, CH2(5’), CH of cod); 2.82 (ddd,
2J(H,P) ¼ 16, 2J ¼ 12, J ¼ 1.8, 1 H of CH2P); 2.70 – 2.57 (m, 2 H of cod); 2.42 – 2.34 (m, 1 H of cod); 2.34 –
2.22 (m, 1 H of CH2(3’)); 2.20 – 1.95 (m, 1 H of CH2(3’), CH2(4’), 2 H of cod); 1.95 – 1.77 (m, 1 H of CH2P,
1 H of cod); 1.46 – 1.22 (m, Me3C, 2 H of cod); 1.17 (d, 3J(H,P) ¼ 14, Me3C). 13C-NMR (101 MHz,
CD2Cl2): 161.8 (q, 1J(C,B) ¼ 50, ipso-C of ArF); 157.5 (s, C(2)); 148.0 (s, C(7a)); 138.9 (s, C(3a)); 134.9 (s,
o-C of ArF); 129.5 – 128.4 (m, m-C of ArF); 125.2 (s, C(5)); 124.7 (q, 1J(C,F) ¼ 272, CF3); 123.8 (s, C(6));
2
118.8 (s, C(4)); 117.5 (br. s, p-C of ArF); 110.4 (s, C(7)); 92.0 (d, J(C,P) ¼ 8.5, CH of cod); 82.9 (d,
2J(C,P) ¼ 15, CH of cod); 65.7 (s, CH of cod); 58.5 (s, CH of cod); 57.9 (d, 2J(C,P) ¼ 7.4, C(2’)); 49.7 (s,
3
1
3
C(5’)); 38.5 (d, J(C,P) ¼ 4.2, CH2 of cod); 38.3 (d, J(C,P) ¼ 17, Me3C); 36.5 (d, J(C,P) ¼ 8.1, CH2 of
cod); 36.0 (d, 1J(C,P) ¼ 18, Me3C); 34.3 (d, 1J(C,P) ¼ 21, CH2P); 33.7 (s, C(3’)); 30.7 (d, 2J(C,P) ¼ 4.5, Me
of tBu); 30.0 – 29.2 (br. m, Me of tBu’); 28.8 (s, CH2 of cod); 24.6 (s, C(4’)); 24.1 (s, CH2 of cod). 31P-NMR
(162 MHz, CD2Cl2): 46.8 (s). 19F-NMR (377 MHz, CD2Cl2): ꢀ 62.9 (s). FAB-MS (NBA): 648 (32), 647
(100, Mþ), 646 (21), 645 (61), 537 (12), 423 (12).
{(h4-Cycloocta-1,5-diene)-[(S)-2-(2-{[di(tert-butyl)phosphino]methyl}pyrrolidin-1-yl)benzo[d]thia-
zole]-iridium(I)} Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN6). Complex (S)-CN6 (94%)
was prepared according to GP 2 from (S)-LN6 and [Ir(cod)2]BArF. M.p. 228 – 2318. [a]2D0 ¼ þ140 (c ¼
1.30, CHCl3). IR (neat): 2962w, 2888w, 1611w, 1546m, 1455w, 1353m, 1272s, 1163s, 1122s, 1021w, 887m,
1
839w, 747w, 714m, 681m. H-NMR (400 MHz, CD2Cl2): 8.35 (d, J ¼ 8.2, HꢀC(4)); 7.73 (br. s, 8 o-H of
ArF); 7.65 (d, J ¼ 7.9, HꢀC(7)); 7.59 – 7.51 (m, HꢀC(5), 4 p-H of ArF); 7.30 (t, J ¼ 7.7, HꢀC(6)); 5.76 – 5.65
(m, HꢀC(2’)); 5.37 – 5.29 (m, 1 H of cod); 4.43 – 4.34 (m, 1 H of cod); 4.07 – 3.97 (m, 1 H of cod); 3.78 –
2
2
3.58 (m, CH2(5’)); 3.37 – 3.26 (m, 1 H of cod); 2.86 (ddd, J(H,P) ¼ 16, J ¼ 11, J ¼ 1.9, 1 H of CH2P);
2.75 – 2.62 (m, 2 H of cod); 2.33 – 2.16 (m, 1 H of CH2(3’), 1 H of CH2(4’), 1 H of cod); 2.16 – 1.91 (m, 1 H
of CH2P, 1 H of CH2(3’), 1 H of CH2(4’), 2 H of cod); 1.82 – 1.71 (m, 1 H of cod); 1.50 – 1.17 (m, tBu, 2 H
of cod); 1.11 (d, 3J(H,P) ¼ 14, tBu’). 13C-NMR (101 MHz, CD2Cl2): 164.6 (s, C(2)); 161.8 (q, 1J(C,B) ¼ 50,
ipso-C of ArF); 149.2 (s, C(3a)); 134.9 (s, o-C of ArF); 129.5 – 128.2 (m, m-C of ArF); 127.2 (s, C(7a));
126.8 (s, C(5)); 124.7 (q, 1J(C,F) ¼ 272, CF3); 124.0 (s, C(6)); 123.5 (s, C(4)); 121.7 (s, C(7)); 117.5 (br. s, p-
C of ArF); 91.2 (d, 2J(C,P) ¼ 7.6, CH of cod); 83.8 (d, 2J(C,P) ¼ 16, CH of cod); 67.3 (s, CH of cod); 59.6
2
3
(d, J(C,P) ¼ 7.7, C(2’)); 57.5 (s, CH of cod); 53.4 (s, C(5’)); 38.7 (d, J(C,P) ¼ 4.4, CH2 of cod); 37.6 (d,
1J(C,P) ¼ 16, Me3C); 37.3 (d, 3J(C,P) ¼ 8.1, CH2 of cod); 35.7 (d, 1J(C,P) ¼ 18, Me3C); 34.2 (s, C(3’)); 34.0
(d, 1J(C,P) ¼ 21, CH2P), 30.4 (d, 2J(C,P) ¼ 4.6, Me of tBu); 28.3 (br. s, Me of tBu’); 27.0 (s, CH2 of cod);
24.8 (s, C(4’)); 24.0 (d, 3J(C,P) ¼ 2.9, CH2 of cod). 31P-NMR (162 MHz, CD2Cl2): 46.7 (s). 19F-NMR
(377 MHz, CD2Cl2): ꢀ 62.7 (s). FAB-MS (NBA): 664 (31), 663 (100, Mþ), 662 (21), 661 (59), 555 (11),
553 (15), 497 (12), 441 (11), 439 (14). Anal calc. for C60H55BF24IrN2PS (1526.12): C 47.22, H 3.63, N 1.84;
found: C 46.78, H 3.92, N 1.91.
[(h4-Cyclooctadiene)-((S)-2-{2-[(dicyclohexylphosphino)methyl]pyrrolidin-1-yl}benzo[d]oxazo-
le)iridium(I)] Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN7). Complex (S)-CN7 (84%) was
prepared according to GP 2 from (S)-LN7 and [Ir(cod)2]BArF. M.p.: 142 – 1468. [a]2D0 ¼ þ60.9 (c ¼ 0.330,
CHCl3). IR (neat): 2937w, 2860w, 1648m, 1620w, 1596w, 1467w, 1402w, 1354m, 1273s, 1119s, 1005w, 887m,
840w, 745m, 713m, 681m. 1H-NMR (400 MHz, CD2Cl2): 7.74 (s, 8 m-H of ArF); 7.61 (d, 2J ¼ 8.0, HꢀC(4));
7.57 (s, 4 p-H of ArF); 7.40 – 7.34 (m, HꢀC(5), HꢀC(7)); 7.24 (td, 2J ¼ 7.9, J ¼ 1.1, HꢀC(6)); 5.21 – 5.08 (m,
HꢀC(2’)); 4.77 – 4.70 (m, 1 H of cod); 4.70 – 4.62 (m, 1 H of cod); 4.20 – 4.10 (m, 1 H of cod); 3.93 – 3.77
(m, CH2(5’)); 3.54 – 3.44 (m, 1 H of cod); 2.66 – 2.54 (m, 1 H of CH2P, 2 H of cod); 2.40 – 2.24 (m, 1 H of
CH2(3’), 1 H of cod); 2.21 – 1.84 (m, 1 H of CH2P, 10 H of Pyr, cod, Cy/Cy’); 1.84 – 1.67 (m, 5 H of Cy/
Cy’); 1.64 – 1.01 (m, 14 H of cod, Cy/Cy’); 0.95 – 0.82 (m, 1 H of cod). 13C-NMR (101 MHz, CD2Cl2): 161.8
(q, 1J(C,B) ¼ 50, ipso-C of ArF); 158.0 (s, C(2)); 147.8 (s, C(7a)); 138.8 (s, C(3a)); 134.9 (s, o-C of ArF);
1
129.6 – 128.4 (m, m-C of ArF); 125.4 (s, C(5)); 124.6 (q, J(C,F) ¼ 272, CF3); 123.9 (s, C(6)); 118.0 (s,
C(4)); 117.6 (br. s, p-C of ArF); 110.4 (s, C(7)); 95.3 (d, 2J(C,P) ¼ 9.5, CH of cod); 86.8 (d, 2J(C,P) ¼ 15,
CH of cod); 65.8 (s, CH of cod); 58.8 (s, CH of cod); 58.8 (d, 2J(C,P) ¼ 6.1, C(2’)); 49.9 (s, C(5’)); 37.5 (d,
3J(C,P) ¼ 3.9, CH2 of cod); 37.0 (d, 1J(C,B) ¼ 26, C(1) of Cy); 35.9 (d, 3J(C,P) ¼ 10, CH2 of cod); 33.4 (s,
C(3’)); 33.0 (d, 1J(C,P) ¼ 26, CH2P), 31.6 (d, 1J(C,B) ¼ 26, C(1) of Cy’); 30.1 (s, CH2 of Cy/Cy’); 29.8 (s,
CH2 of Cy/Cy’); 29.5 (s, CH2 of Cy/Cy’); 29.0 (s, CH2 of Cy/Cy’); 26.9 – 26.7 (m, CH2 of cod, CH2 of Cy/
Cy’); 26.1 (s, CH2 of Cy/Cy’); 25.9 (s, CH2 of Cy/Cy’); 24.8 (d, 3J(C,P) ¼ 2.5, CH2 of cod); 24.3 (s, C(4’)).

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Helvetica Chimica Acta – Vol. 95 (2012)
31P-NMR (162 MHz, CD2Cl2): 24.9 (s). 19F-NMR (377 MHz, CD2Cl2): ꢀ 62.7 (s). FAB-MS (NBA): 700
(34), 699 (100, Mþ), 698 (25), 697 (62), 587 (18), 585 (1).
[(h4-1,5-Cyclooctadiene)-((S)-2-{2-[(dicyclohexylphosphino)methyl]pyrrolidin-1-yl}benzo[d]thia-
zole)-iridium(I)]-tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ((S)-CN8). Complex (S)-CN8 (98%)
was prepared according to GP 2 from (S)-LN8 and [Ir(cod)2]BArF. M.p. 120 – 1248. [a]2D0 ¼ þ123 (c ¼
0.450, CHCl3). IR (neat): 2936m, 2859m, 1611w, 1544m, 1453m, 1354s, 1273s, 1115s, 1003w, 887m,
839m, 747m, 713m, 680m. 1H-NMR (400 MHz, CD2Cl2): 8.29 (d, 2J ¼ 8.1, HꢀC(4)); 7.74 (br. s, 8 o-H of
ArF); 7.66 (d, 2J ¼ 7.9, HꢀC(7)); 7.62 – 7.50 (m, HꢀC(5), 4 p-H of ArF), 7.31 (t, 2J ¼ 8.1, HꢀC(6)); 5.63 –
5.51 (m, HꢀC(2’)); 4.89 – 4.80 (m, 1 H of cod); 4.58 – 4.50 (m, 1 H of cod); 3.71 – 3.52 (m, CH2(5’), 2 H of
cod); 2.74 – 2.54 (m, 1 H of CH2P, 2 H of cod); 2.38 – 2.22 (m, 1 H of CH2(3’), 1 H of cod); 2.22 – 1.82 (m,
1 H of CH2P, 1 H of CH2(3’), CH2(4’), 7 H of cod, Cy/Cy’); 1.82 – 1.55 (m, 7 H of Cy/Cy’); 1.55 – 1.45 (m,
1 H of cod, 1 H of Cy/Cy’); 1.45 – 1.20 (m, 8 H of cod, Cy/Cy’); 1.20 – 1.02 (m, 2 H of Cy/Cy’); 0.97 – 0.81
1
(m, 1 H of cod). 13C-NMR (101 MHz, CD2Cl2): 165.2 (s, C(2)); 161.8 (q, J(C,B) ¼ 50, ipso-C of ArF);
148.8 (s, C(3a)); 134.9 (s, m-C of ArF); 129.6 – 128.3 (m, m-C of ArF); 127.0 (s, C(5)); 127.0 (s, C(7a));
124.7 (q, 1J(C,F) ¼ 272, CF3); 124.1 (s, C(6)); 122.2 (s, C(4)); 121.7 (s, C(7)); 117.6 (s, p-C of ArF); 94.4 (d,
2J(C,P) ¼ 9.2, CH of cod); 92.9 (d, 2J(C,P) ¼ 14, CH of cod); 65.7 (s, CH of cod); 60.9 (d, 2J(C,P) ¼ 6.4,
C(2’)); 58.1 (s, CH of cod); 53.6 (s, C(5’)); 37.7 (d, 3J(C,P) ¼ 3.8, CH2 of cod); 37.2 (d, 1J(C,P) ¼ 25, C(1) of
Cy); 36.7 (d, 3J(C,P) ¼ 10, CH2 of cod); 33.6 (s, C(3’)); 32.9 (d, 1J(C,P) ¼ 27, CH2P), 32.2 (d, 1J(C,P) ¼ 25,
C(1) of Cy’); 29.5 – 29.2 (m, CH2 of Cy/Cy’); 28.8 (s, CH2 of Cy/Cy’); 27.2 – 26.6 (m, CH2 of cod, CH2 of
Cy/Cy’); 26.1 (s, CH2 of Cy/Cy’); 25.8 (s, CH2 of Cy/Cy’); 24.8 (br. d, 3J(C,P) ¼ 2.4, CH2 of cod); 24.6 (s,
C(4’)). 31P-NMR (162 MHz, CD2Cl2): 22.9 (s). 19F-NMR (377 MHz, CD2Cl2): ꢀ 62.8 (s). FAB-MS
(NBA): 716 (36), 715 (100, Mþ), 714 (23), 713 (59), 605 (13), 604 (14), 603 (27), 601 (16). Anal calc. for
C64H59BF24IrN2PS (1578.20): C 48.71, H 3.77, N 1.78; found: C 48.78, H 4.06, N 1.91.
Catalytic Hydrogenation at Elevated Pressure: General Procedure for Proline-Based P,N Catalysts. A
stock soln. of the precatalyst was prepared in CH2Cl2 (5 mm in precatalyst). The substrate (250 mmol) was
weighed into a separate vial, and 0.5 ml of the stock soln. (1 mol-% of precatalyst) were added. A stir bar
was added, and four vials (1.5 ml) were placed into a 60-ml autoclave (Premex AG, CH-Lengnau). The
autoclave was purged, pressurized with H2 gas (Carbagas, Switzerland; 99.995%), and placed on a stirring
plate. The mixtures were stirred at r.t. for 2 h. After pressure release, the soln. was concentrated in a
stream of N2 and taken up in heptane (3 ml), and filtered through a short plug of SiO2 (0.5 ꢁ 6 cm),
eluting with heptane/iPrOH 7:3. The filtrates were analyzed by GC and HPLC [12a][6a].
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Received August 9, 2012