An optically pure P-alkene-ligated IrI complex

Article abstract of DOI:10.1107/S0108270110036413

The asymmetric unit of (P)-chloridobis[(S)-(+)-5-(3,5-dioxa-4-phosphacyclo- hepta-[2,1-a:3,4-a′]dinaphthalen-4-yl)dibenz[b,f]azepine]iridium(I) -benzene-pentane (1/1/1), [IrCl(C₃₄H₂₂NO ₂P)₂]·C₆H₆·C ₅H₁₂, contains two formula units. The two symmetry-independent mol-ecules of the Ir complex have similar conformations and approximate C 2 symmetry, with small deviations arising from slightly different puckering of the seven-membered di-oxa-phospha-cyclo-hepta-di-ene rings. The Ir atoms have trigonal-bipyramidal coordination geometry, with the P atoms in axial positions. The steric strain of the bidentate coordination of the P-alkene ligand through its P and alkene C atoms causes the N atom to have pyramidal geometry, compared with the trigonal-planar geometry observed in the free ligand. The coordination also results in an anti conformation of the binaphthyl and alkene groups within the P-alkene ligand.

Full text of DOI:10.1107/S0108270110036413

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
a competent catalyst for the stereospecific substitution of
chiral allylic alcohols with sulfamic acid to afford optically
active allylic amines with enantiospecificities >98%. Breher et
al. (2004) described a crystal structure of a related achiral
[IrCl(P–alkene)2] complex also displaying trans or axial
positioning of the P atoms in the trigonal–bipyramidal coor-
dination environment. We note that the aforementioned
pentacoordinate Ir complexes are per se chiral, possessing
stereogenic Ir centres, but obviously without the use of
enantiodiscriminating auxiliaries they are obtained as race-
mates. Here, we disclose the crystal structure of such a
complex that is optically pure. The enantiomerically pure
ligand (S)-(1) was used to synthesize the title complex, (3),
and to our surprise its formation was perfectly diastereo-
specific based on NMR spectroscopy [possible diastereomers
are (M,S,S) and (P,S,S); see also the pair of enantiomers of (3)
depicted in the scheme]. Single-crystal X-ray analysis then
allowed us to determine the absolute configuration at Ir,
which is (P).
ISSN 0108-2701
An optically pure P–alkene-ligated IrI
complex
Anthony Lindena* and Romano Dortab*
aInstitute of Organic Chemistry, University of Zurich, Winterthurerstrasse 190,
¨
b
´
´
CH-8057 Zurich, Switzerland, and Departamento de Quımica, Universidad Simon
¨
´
Bolıvar, Caracas 1080A, Venezuela
Correspondence e-mail: alinden@oci.uzh.ch, rdorta@usb.ve
Received 8 September 2010
Accepted 11 September 2010
Online 17 September 2010
The asymmetric unit of (P)-chloridobis[(S)-(+)-5-(3,5-dioxa-4-
phosphacyclohepta[2,1-a:3,4-a0]dinaphthalen-4-yl)dibenz[b,f]-
azepine]iridium(I)–benzene–pentane (1/1/1), [IrCl(C34H22N-
O2P)2]ꢀC6H6ꢀC5H12, contains two formula units. The two
symmetry-independent molecules of the Ir complex have
similar conformations and approximate C2 symmetry, with
small deviations arising from slightly different puckering of
the seven-membered dioxaphosphacycloheptadiene rings.
The Ir atoms have trigonal–bipyramidal coordination
geometry, with the P atoms in axial positions. The steric
strain of the bidentate coordination of the P–alkene ligand
through its P and alkene C atoms causes the N atom to have
pyramidal geometry, compared with the trigonal–planar
geometry observed in the free ligand. The coordination also
results in an anti conformation of the binaphthyl and alkene
groups within the P–alkene ligand.
Comment
Chiral P–alkene ligands are attracting growing interest in the
field of enantioselective catalysis (Defieber et al., 2008). For
example, the alkene-phosphoramidite (S)-(+)-N-(3,5-dioxa-4-
phosphacyclohepta[2,1-a:3,4-a0]dinaphthalen-4-yl)dibenz[b,f]-
azepine, (1) (Bricen˜o & Dorta, 2007; Mariz et al., 2008), was
used as a ligand in the Ir-catalyzed enantioselective formation
of allylic amines from allylic alcohols (70% ee) (Defieber et
al., 2007) and for the Rh-catalyzed conjugate addition (CA) of
arylboronic acids to enones with up to 99% ee (Drinkel et al.,
2010). In the latter case, the fully characterized monomeric Rh
precatalysts, (2), of composition [RhCl(ꢀ1-P–alkene)(ꢀ2-P–
alkene)] bearing two equivalents of P–alkene ligand (1),
displayed exclusive cis coordination of the P atoms and a
square-planar coordination environment. Roggen & Carreira
(2010) recently described the crystal structure of a similar
monomeric Ir–iodide complex of composition [IrI(P–
alkene)2] bearing, in a trans arrangement, the achiral variant
of P–alkene ligand (1), i.e. featuring the 2,20-biphenol motif
instead of the chiral auxiliary (S)-binaphthol. This complex is
The asymmetric unit of (3) contains two molecules of the Ir
complex, two of benzene and two of pentane. The two inde-
pendent molecules of the Ir complex have largely similar
conformations (Fig. 1), with the largest differences being in
the orientations of the binaphthyl rings as a result of different
puckering of the seven-membered dioxaphosphacyclohepta-
diene rings. The Cremer & Pople (1975) puckering parameters
for the seven-membered rings are listed in Table 2 and show
that the total puckering amplitude, Q, is somewhat different
for the two seven-membered rings in each independent Ir
complex molecule, but that the pattern is similar across the
two molecules. An overlay of the two molecules is shown in
Fig. 2, which demonstrates that small variations in the ring
puckering have a significant effect on the positions of the
atoms at the remote ends of the naphthyl rings. The molecules
are approximately C2 symmetric about the Ir—Cl axis,
although the different ring puckering in the two seven-
membered rings diminishes the exactness of the fit to C2
symmetry. In contrast, the corresponding Ir complex with
m290 # 2010 International Union of Crystallography
doi:10.1107/S0108270110036413
Acta Cryst. (2010). C66, m290–m293

metal-organic compounds
Figure 1
View of (a) molecule A and (b) molecule B of the Ir complex of (3), showing the atom-labelling schemes. Displacement ellipsoids are drawn at the 50%
probability level and H atoms have been omitted for clarity.
˚
biphenyl groups in the P–alkene ligands has crystallographic
C2 symmetry (Roggen & Carreira, 2010).
The alkene C—C bond lengths [1.447 (6)–1.453 (6) A]
compare well with those in the complexes reported by Breher
et al. (2004) and Roggen & Carreira (2010), and are signifi-
cantly longer than those of the coordinated alkene in Rh
The coordination environment in the Ir complex of (3) can
be considered as trigonal bipyramidal, with the P atoms in
axial positions, and the equatorial positions occupied by the Cl
atom and the two alkene functions, each of which may be
regarded as occupying a single site in the formal equatorial
trigonal plane. This arrangement parallels the architecture
reported by Roggen & Carreira (2010). In each of the inde-
pendent molecules, the Ir atom lies well within the plane
defined by the Cl atom and the four alkene C atoms. The
maximum deviations of these six atoms from the mean plane
˚
complex (2) [1.405 (9) A; Drinkel et al., 2010] and the alkene
˚
˚
are 0.028 (4) A for atom C48 in molecule A and 0.081 (5) A
for atom C118 in molecule B. The P—Ir—X bond angles,
where X is any equatorial atom, lie in the narrow range
85.66 (12)–94.16 (12)ꢁ. Taking the bisector, Y, of each alkene
C—Ir—C angle as the effective ‘bond’ position of the alkene
group gives Cl—Ir—Y angles in the range 109.85 (12)–
112.70 (13)ꢁ and Y—Ir—Y angles of 139.31 (17) and
136.10 (17)ꢁ. These angles are closer to those required for a
trigonal–bipyramidal coordination geometry than those ex-
pected for a square-planar arrangement with the Cl atom at
the apex, thus indicating that the former is a more suitable
description of the coordination geometry of the Ir atoms in (3).
Figure 2
Overlay of the two independent complex molecules of (3), generated by
matching the positions of the Ir, P, Cl and N atoms. H atoms have been
omitted for clarity. Molecule B is shown in black.
ꢂ
Acta Cryst. (2010). C66, m290–m293
Linden and Dorta
[IrCl(C34H22NO2P)2]ꢀC6H6ꢀC5H12 m291

metal-organic compounds
˚
0.652 mmol) in benzene (3.6 g). The resulting deep-red solution was
stirred for 2 d at 353 K and gradually turned a brighter red.
Evaporation of the volatiles followed by washing with pentane and
drying in vacuo afforded a beige powder (yield 1.350 g, 74%).
Diffraction quality colourless monocrystals were obtained by layering
a solution of (3) (50 mg, containing ca 2 equivalents of cocrystallized
benzene) in CDCl3 (0.6 ml) in an NMR tube with pentane (1.2 ml).
function in the free ligand, (1) [1.34 (2) A; Mariz et al., 2008],
which suggests a relatively high ꢁ-basicity of IrI (Dewar, 1951;
˚
Chatt & Duncanson, 1953). The Ir—P [mean 2.274 (2) A] and
˚
Ir—Cl [mean 2.4453 (15) A] distances (Table 1), are consistent
with those reported by Roggen & Carreira (2010) and collated
by Orpen et al. (2006). The dihedral angles between the planes
of the naphthalene systems within the binaphthyl units, which
are in the range 56.24 (17)–64.62 (13)ꢁ across the four inde-
pendent binaphthyl groups, are similar to those found in the
free ligand (53.2ꢁ; Mariz et al., 2008) and in (2) (ca 52ꢁ; Drinkel
et al., 2010).
Crystal data
3
˚
[IrCl(C34H22NO2P)2]ꢀC6H6ꢀC5H12
V = 6298.19 (8) A
Z = 4
Mr = 1392.97
Monoclinic, P21
a = 22.2716 (1) A
Mo Kꢃ radiation
ꢄ = 2.27 mmꢃ1
T = 160 K
˚
˚
The four independent N atoms in the P–alkene ligands of
(3) have distinctly pyramidal geometry, with the sum of the
bond angles about the N atoms in the range 335.6 (5)–
337.0 (5)ꢁ. In contrast, the corresponding N atom in the free
ligand, (1), has a trigonal–planar geometry, subtending a
bond-angle sum of 360 (1)ꢁ (Mariz et al., 2008). The pyrami-
dalization of the ligand N atom in (3) is similar to that
observed in the bidentate ligand of the Rh complex, (2)
(Drinkel et al., 2010), and may be a consequence of steric
strain introduced by the bidentate coordination to the Ir atom
through the P and alkene C atoms, which effectively creates
six-membered boat-shaped chelate rings. The bite angles of
the four independent ligands in the structure, P—Ir—Y, where
Y is the bisector of each allyl C—Ir—C angle, are in the range
86.51 (13)–87.90 (13)ꢁ. When viewed along the P—Ir bond,
the P—N bond closely eclipses the Ir—Y vector. Drinkel et al.
(2010) discussed the torsion angle Yꢀ ꢀ ꢀN—Pꢀ ꢀ ꢀZ, where Z is
the mid-point of the bond joining the two naphthyl units in the
binaphthyl group. This torsion angle for the bidentate
P–alkene ligand of (2) is approximately 180ꢁ, which indicates
an anti conformation of the binaphthyl and alkene groups,
whereas syn conformations are found in the free ligand and in
the monodentate ligand of (2). The absolute values of the
corresponding torsion angles for (3) are in the range 170.8 (2)–
179.1 (2)ꢁ and also indicate an anti conformation for the
bidentate ligands, which is consistent with the previous
observations.
b = 12.6944 (1) A
˚
c = 23.6689 (2) A
0.28 ꢄ 0.12 ꢄ 0.10 mm
ꢂ = 109.7487 (4)ꢁ
Data collection
Nonius KappaCCD area-detector
diffractometer
Absorption correction: multi-scan
(SORTAV; Blessing, 1995)
Tmin = 0.536, Tmax = 0.649
99162 measured reflections
21763 independent reflections
20907 reflections with I > 2ꢅ(I)
Rint = 0.049
Refinement
ꢃ3
R[F2 > 2ꢅ(F2)] = 0.028
wR(F2) = 0.068
S = 1.05
21762 reflections
1610 parameters
90 restraints
Áꢆmax = 1.36 e A
˚
ꢃ3
˚
Áꢆmin = ꢃ1.06 e A
Absolute structure: Flack &
Bernardinelli (1999, 2000), with
10122 Friedel pairs
Flack parameter: ꢃ0.018 (3)
H-atom parameters constrained
Table 1
Selected geometric parameters (A, ).
ꢁ
˚
Ir1—P1
Ir1—P2
2.2756 (12)
2.2676 (11)
2.4512 (11)
2.184 (4)
2.189 (4)
2.189 (5)
2.185 (4)
1.452 (6)
1.447 (6)
Ir2—P3
Ir2—P4
Ir2—Cl2
Ir2—C117
Ir2—C118
Ir2—C131
Ir2—C132
C117—C118
C131—C132
2.2790 (11)
2.2717 (11)
2.4394 (11)
2.187 (4)
2.192 (4)
2.185 (4)
2.187 (4)
1.453 (6)
1.449 (6)
Ir1—Cl1
Ir1—C47
Ir1—C48
Ir1—C61
Ir1—C62
C47—C48
C61—C62
The packing of the molecules is fairly unremarkable, with
one of each of the independent benzene and pentane solvent
molecules lying in narrow channels running parallel to the
[010] direction. The remaining solvent molecules occupy
interstices between the complex molecules. There are no ꢁ–ꢁ
interactions, with the shortest distance between the centres of
P1—Ir1—P2
P1—Ir1—Cl1
P2—Ir1—Cl1
C47—Ir1—P1
C48—Ir1—P1
C61—Ir1—P1
C62—Ir1—P1
C47—Ir1—P2
C48—Ir1—P2
C61—Ir1—P2
C62—Ir1—P2
175.06 (4)
91.85 (4)
93.08 (4)
P3—Ir2—P4
179.35 (4)
89.45 (4)
89.91 (4)
P3—Ir2—Cl2
P4—Ir2—Cl2
C117—Ir2—P3
C118—Ir2—P3
C131—Ir2—P3
C132—Ir2—P3
C117—Ir2—P4
C118—Ir2—P4
C131—Ir2—P4
C132—Ir2—P4
87.93 (12)
85.86 (12)
90.91 (12)
91.81 (12)
92.35 (12)
91.26 (12)
85.66 (12)
87.74 (12)
86.33 (12)
89.74 (12)
91.57 (12)
92.96 (12)
94.16 (12)
90.38 (12)
88.37 (12)
87.40 (12)
˚
gravity of any aromatic rings being approximately 4.0 A. The
shortest contacts of C—Hꢀ ꢀ ꢀꢁ and C—Hꢀ ꢀ ꢀO types are also
considered to be too long to be indicative of significant
attractive interactions.
The use of complex (3) as an enantioselective catalyst for
organic transformations is currently being investigated, and
results will be published in due course.
The asymmetric unit of (3) contains two molecules of the Ir
complex, two of benzene and two of pentane. The atomic coordinates
were tested carefully for a relationship from a higher-symmetry space
group using the program PLATON (Spek, 2009), but none could be
found. The solvent molecules may be slightly disordered. A disor-
dered model was not developed, but the bond lengths and angles in
the two benzene solvent molecules were restrained to be similar and
Experimental
The title iridium complex, (3), was prepared by adding dropwise a
solution of (S)-(1) (1.325 g, 2.610 mmol) in benzene (10.3 g) to a
vigorously stirred slurry of [IrCl(coe)2]2 (coe is cyclooctene; 0.585 g,
˚
the C—C distances were restrained to a target value of 1.395 (5) A.
ꢂ
m292 Linden and Dorta [IrCl(C34H22NO2P)2]ꢀC6H6ꢀC5H12
Acta Cryst. (2010). C66, m290–m293

metal-organic compounds
Table 2
Puckering parameters (Cremer & Pople, 1975) for the seven-membered
dioxaphosphacycloheptadiene rings of (3).
Similarly, the bond lengths and angles in the two pentane solvent
molecules were restrained to be similar and the C—C distances were
˚
restrained to a target value of 1.520 (4) A. Neighbouring atoms
within one benzene and one pentane molecule were restrained to
have similar atomic displacement parameters. All H atoms were
placed in geometrically idealized positions and constrained to ride on
˚
their parent atoms, with C—H = 0.95 A for the aromatic H atoms and
˚
1.00 A for the alkene H atoms, and with Uiso(H) = 1.2Ueq(C). The
Ring
Total puckering
˚
amplitude, Q (A)
’2 (ꢁ)
’3 (ꢁ)
Molecule A
P1/O1/O2/C11/C12/C2/C1
P2/O3/O4/C21/C22/C32/C31
1.008 (4)
1.459 (3)
126.6 (3)
296.1 (3)
16.4 (4)
234.59 (18)
determined absolute configuration established by the structure
determination agreed with that expected from the synthesis [(S)-
binaphthyl groups].
Molecule B
P3/O5/O6/C81/C82/C72/C71
P4/O7/O8/C91/C92/C102/C101
0.998 (4)
1.418 (3)
135.5 (3)
298.3 (3)
21.2 (5)
234.01 (17)
Data collection: COLLECT (Nonius, 2000); cell refinement:
DENZO-SMN (Otwinowski
& Minor, 1997); data reduction:
DENZO-SMN and SCALEPACK (Otwinowski & Minor, 1997);
program(s) used to solve structure: DIRDIF94 (Beurskens et al.,
1994); program(s) used to refine structure: SHELXL97 (Sheldrick,
2008); molecular graphics: ORTEPII (Johnson, 1976); software used
to prepare material for publication: SHELXL97 and PLATON
(Spek, 2009).
Bricen˜o, A. & Dorta, R. (2007). Acta Cryst. E63, m1718–m1719.
Chatt, J. & Duncanson, L. A. (1953). J. Chem. Soc. pp. 2939–2947.
Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354–1358.
Defieber, C., Ariger, M. A., Moriel, P. & Carreira, E. M. (2007). Angew. Chem.
Int. Ed. 46, 3139–3143.
¨
Defieber, C., Grutzmacher, H. & Carreira, E. M. (2008). Angew. Chem. Int.
Ed. 47, 4482–4502.
Dewar, M. J. S. (1951). Bull. Soc. Chim. Fr. 18, C71–C79.
Drinkel, E., Bricen˜o, A., Dorta, R. & Dorta, R. (2010). Organometallics, 29,
2503–2514.
RD thanks FONACIT for financial support (grant No. S1-
2001000851).
Flack, H. D. & Bernardinelli, G. (1999). Acta Cryst. A55, 908–915.
Flack, H. D. & Bernardinelli, G. (2000). J. Appl. Cryst. 33, 1143–1148.
Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National
Laboratory, Tennessee, USA.
Mariz, R., Bricen˜o, A., Dorta, R. & Dorta, R. (2008). Organometallics, 27,
6605–6613.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FG3194). Services for accessing these data are
described at the back of the journal.
Nonius (2000). COLLECT. Nonius BV, Delft, The Netherlands.
Orpen, A. G., Brammer, L., Allen, F. H., Watson, D. G. & Taylor, R. (2006).
International Tables for Crystallography, Vol. C, edited by E. Prince, pp.
812–896. Chester: International Union of Crystallography.
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M.
Sweet, pp. 307–326. New York: Academic Press.
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Acta Cryst. (2010). C66, m290–m293
Linden and Dorta
[IrCl(C34H22NO2P)2]ꢀC6H6ꢀC5H12 m293