Iridium(III) hydrido amino acid compounds: Chiral complexes and a helical extended lattice

Article abstract of DOI:10.1016/j.jorganchem.2005.11.028

[Ir(COD)(PMe₃)₃]Cl, 1, reacts with amino acids in water to yield cationic hydride amino acid complexes, [Ir(aa)(H)(PMe₃)₃]Cl, 2. In general, complexes 2 display octahedral geometry with a meridional arrangement of the PMe₃ ligands, with the amino acid chelating through O and N and with hydride trans to N. Disubstituted amino acids on the other hand favor the formation of octahedral complexes with a facial arrangement of PMe₃ ligands. The crystal structure of the valine complex, 2c, was obtained and, in addition to confirming the structure of the complex, showed a helical extended lattice structure due to intermolecular N-H-O bonding.

Full text of DOI:10.1016/j.jorganchem.2005.11.028

Journal of Organometallic Chemistry 691 (2006) 2270–2276
www.elsevier.com/locate/jorganchem
Iridium(III) hydrido amino acid compounds: Chiral complexes
and a helical extended lattice
*
Christopher P. Roy, Lisa A. Huff, Nick A. Barker, Michael A.G. Berg, Joseph S. Merola
Department of Chemistry, Virginia Polytechnic Institute and State University, 107 Davidson Hall, Mail Stop 0212, Blacksburg,
VA 24061-0212, United States
Received 2 October 2005; received in revised form 14 November 2005; accepted 14 November 2005
Available online 22 December 2005
Abstract
[Ir(COD)(PMe3)3]Cl, 1, reacts with amino acids in water to yield cationic hydride amino acid complexes, [Ir(aa)(H)(PMe3)3]Cl, 2. In
general, complexes 2 display octahedral geometry with a meridional arrangement of the PMe3 ligands, with the amino acid chelating
through O and N and with hydride trans to N. Disubstituted amino acids on the other hand favor the formation of octahedral complexes
with a facial arrangement of PMe3 ligands. The crystal structure of the valine complex, 2c, was obtained and, in addition to confirming
the structure of the complex, showed a helical extended lattice structure due to intermolecular N–H–O bonding.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Iridium; Amino acid complex; Hydride; Helical lattice
1. Introduction
the type [RuCl(aa)(H)(PPh3)2] were prepared by Saito
et al. [12] and were studied for use as homogeneous cata-
lysts [13–15].
Metals play an important role in biological systems. It is
well known that the first row transition elements are
involved in a variety of biochemical reaction pathways,
but second and third row transition metals are rarely found
in bioinorganic systems in nature. In fact, the heavier
metallic elements are traditionally known for their toxic
effect on many organisms. Interest in the interaction of
platinum metals with biological molecules began with the
discovery that certain platinum complexes exhibit antican-
cer activity [1]. A wide variety of Pt-amino acid complexes
have been made as a result of this work [2–6]. Ruthenium
amino acid complexes have also been studied as potential
antitumor compounds [7]. Amino acid complexes of other
transition metals may be of interest for new therapies.
Research involving the interaction of amino acids and
transition metals has also found non-biological uses.
Ruthenium and osmium complexes have been studied as
catalysts in hydrolysis [8–11]. A series of complexes of
It is surprising that so many studies on platinum and
ruthenium with amino acids have been performed while
almost none exist with the remaining platinum metals.
Beck and co-workers have published a long series of papers
on ‘‘Metal Complexes with Biological Ligands’’ with many
of the later papers dealing with various modes of complex-
ation of amino acids to many different metals, including
iridium [16,17]. A DNA binding complex of amino acids
with pentamethylcyclopentadienyl fragments has also been
reported [18]. To our knowledge, the complexes character-
ized in this study are the first examples of iridium amino
acid hydride complexes.
Our interest in Ir(III) amino acid complexes was initially
based on their potential use as asymmetric catalysts. It was
our goal to develop water soluble catalysts that can be used
for hydrogenation as well as other organic transforma-
tions. We have previously demonstrated that [Ir(COD)(P-
Me3)3]Cl (1) will undergo oxidative addition reactions
with a number of bonds including H–H [19], B–H [20],
C–H [21,22], N–H [23], and O–H [24]. Preliminary studies
*
Corresponding author. Tel.: +1 540 231 4510; fax: +1 540 231 3255.
E-mail address: jmerola@vt.edu (J.S. Merola).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.11.028

C.P. Roy et al. / Journal of Organometallic Chemistry 691 (2006) 2270–2276
2271
of the oxidative addition of amino acids to the complex 1
have focused on the possible binding modes of the amino
acid to the iridium center.
P(CH3)3), 3.09 (m, 1H, CH), 3.26 (br s, 1H, NH), 6.69
(br s, 1H, NH); 13C NMR (CDCl3): d 17.25 (t,
J = 20 Hz), 21.5 (d, J = 40 Hz), 21.1, 52.3, 181.5; 31P
NMR (CDCl3): d À48.31 (t, J = 20 Hz), À34.52 (t,
J = 21 Hz). Elem. Anal. Calcd. for C12H34ClIrNO2P3: C,
26.45; H, 6.29. Found: C, 26.44; H, 6.44%.
2. Experimental
2.1. General methods
2.5. [Ir(L-valine)(H)(PMe3)3]Cl (2c)
All reactions were performed in an inert atmosphere of
purified nitrogen. Standard glassware and Schlenk line
techniques were used. All amino acids were used as
received without further purification. [Ir(COD)(PMe3)3]Cl
(1) was synthesized by a known procedure [25]. All other
chemicals were reagent grade and used without further
purification. The proton and carbon NMR spectra were
obtained on a Bruker WP270SY or WP200SY instrument.
The 31P NMR spectra were obtained on a Bruker
WP200SY instrument operating at 81 MHz and referenced
using an internal standard of 85% H3PO4. All elemental
analyses were performed by Atlantic Microlab Inc., Nor-
cross, GA. X-ray crystal structures were obtained using a
1
Yield: 71%. H NMR (CDCl3): d À19.10 (q, J = 17 Hz,
1H, IrH), 1.10 (dd, 6H, C(CH3)2), 1.57 (t, J = 5.6 Hz, 9H,
P(CH3)3), 1.65 (d, J = 5.8 Hz, 9H, P(CH3)3), 1.92 (d,
J = 10.4 Hz, 9H, P(CH3)3), 2.55 (m, 1H, CH(Me)2), 2.98
(m, 1H, CaH), 3.22 (br s, 1H, NH), 6.89 (br s, 1H, NH);
13C NMR (CDCl3): d 18.16 (t, J = 17 Hz), 21.17 (d,
J = 37 Hz), 19.43, 54.28, 109.31, 181.51; 31P NMR
(CDCl3): d À49.35 (t, J = 20 Hz), À35.02 (d, J = 20 Hz).
Elem. Anal. Calcd. for C14H38ClIrNO2P3: C, 29.34; H,
6.68. Found: C, 29.74; H, 6.58%.
2.6. [Ir(L-phenylalanine)(H)(PMe3)3]Cl (2d)
Siemens
R3m/v
diffractometer
and
Mo
Ka
1
˚
(k = 0.71071 A) radiation at 303 K.
Yield: 67%. H NMR (CDCl3): d À19.48 (q, J = 12 Hz,
1H, IrH), 0.96 (d, J = 6.4 Hz, 9H, P(CH3)3), 1.64 (d,
J = 6.2 Hz, 9H, P(CH3)3), 1.76 (d, J = 10.2 Hz, 9H,
P(CH3)3), 2.92 (br t, 1H, NH), 3.20 (dd, J = 6, 13.6 Hz,
1H, PhCHa), 3.41 (m, 1H, CaH), 3.62 (d, J = 13.6 Hz,
1H, PhCHb), 7.19 (t, 1H, ArH), 7.28 (t, 2H, ArH), 7.54
(d, 2H, ArH), 7.75 (br t, 1H, NH); 13C NMR (CDCl3): d
15.11 (d, J = 17 Hz), 18.80 (t, J = 17 Hz), 21.66 (d,
J = 42 Hz), 55.66, 58.94, 132.9, 134.66, 137.37, 142.05,
189.38; 31P NMR (CDCl3): d À48.6 (t, J = 21 Hz),
À34.51 (d, J = 19 Hz). Elem. Anal. Calcd. for C18H38ClI-
rNO2P3: C, 34.81; H, 6.17. Found: C, 34.26; H, 6.33%.
2.2. Synthesis of [Ir(aa)(H)(PMe3)3]Cl, general
procedure
A 100 mL reaction flask equipped with a stir bar and
septum, was charged with the amino acid (1.0 mmol) and
[Ir(COD)(PMe3)3]Cl (0.5 mmol) under inert atmosphere
in a drybox. The flask was connected to a double manifold
Schlenk line and distilled water (25 mL) was added via syr-
inge. The solution was heated with stirring. After 18 h at
reflux, the reaction was cooled and the solvent removed
in vacuo. The white solid residue was extracted with
CH2Cl2 (3 · 10 mL). The CH2Cl2 extracts were combined
and the solvent removed in vacuo. The solids were further
dried under reduced pressure to give the amino acid com-
plex. Yields and spectral data are given below.
2.7. [Ir(L-tryptophan)(H)(PMe3)3]Cl (2e)
1
Yield: 64%. H NMR (CDCl3): d À19.42 (q, J = 19 Hz,
IrH), 0.69 (d, J = 6.8 Hz, 9H, P(CH3)3), 1.59 (d,
J = 10.4 Hz, 9H, P(CH3)3), 1.64 (d, J = 6.05 Hz, 9 Hz,
P(CH3)3), 3.17 (br s, 1H, NH), 3.42 (m, 2H, CH2), 3.63
(m, 1H, CaH), 7.08 (m, 2H, ArH), 7.41 (m, 2H, ArH),
7.63 (br s, 1H, NH), 8.10 (m, 1H, ArH); 31P NMR
(CDCl3): d À48.39 (t, J = 20 Hz), À34.34 (t, J = 21 Hz).
Elem. Anal. Calcd. for C20H39ClIrN2O2P3: C, 36.39; H,
5.95. Found: C, 34.10; H, 5.82%.
2.3. [Ir(glycine)(H)(PMe3)3]Cl (2a)
Yield: 96%. 1H NMR (CDCl3):
d
À19.15 (q,
J = 18.7 Hz, 1H, IrH), 1.62 (t, J = 3.5 Hz, 18H,
P(CH3)3), 1.78 (d, J = 10.5 Hz, 9H, P(CH3)3), 3.39 (t, 2H,
CH2), 6.11 (br s, 2H, NH2); 13C NMR (CDCl3): d 18.71
(vt, J = 10 Hz, P(CH3)3), 20.63 (d, J = 39 Hz, P(CH3)3),
43.09, 185.43 ppm; 31P NMR (CDCl3): d À47.52 (t,
J = 20 Hz), À33.78 (d, J = 18 Hz). Elem. Anal. Calcd. for
C11H32ClIrNO2P3: C, 24.88%; H, 6.07%. Found: C,
24.70%; H, 6.18%.
2.8. [Ir(L-proline)(H)(PMe3)3]Cl (2f)
1
Yield: 61%. H NMR (CDCl3): d À20.32 (q, J = 20 Hz,
1H, IrH), 1.45 (d, J = 6.3 Hz, 9H, P(CH3)3), 1.58 (d,
J = 6.6 Hz, 9H, P(CH3)3), 1.76 (d, J = 10.2 Hz, 9H,
P(CH3)3), 2.11 (br m, 3H), 2.37 (m, 1H), 2.52 (m, 1H),
2.60 (m, 1H), 3.65 (q, 1H), 3.85 (br m, 1H), 7.70 (br m,
1H, NH); 13C NMR (CDCl3): d 18.06 (t, J = 17 Hz),
21.17 (d, J = 41 Hz), 26.81, 30.45, 53.20, 57.72, 18.89; 31P
NMR (CDCl3): d À48.59 (t, J = 20 Hz), À35.38 (d,
2.4. [Ir(L-alanine)(H)(PMe3)3]Cl (2b)
1
Yield: 79%. H NMR (CDCl3): d À19.36 (q, J = 17 Hz,
IrH), 1.65 (d, J = 10 Hz, 9H, P(CH3)3), 1.73 (d, J = 10 Hz,
9H, P(CH3)3), 1.80 (m, 3H, CH3), 1.92 (d, J = 6 Hz, 9H,

2272
C.P. Roy et al. / Journal of Organometallic Chemistry 691 (2006) 2270–2276
J = 22 Hz). Elem. Anal. Calcd. for C14H36ClIrNO2P3: C,
29.45; H, 6.35. Found: C, 29.17; H, 6.20%.
cipitate formed immediately. The precipitate was filtered
using cannula techniques to give crystals that were screened
for X-ray structural analysis.
2.9. [Ir(L-isoleucine)(H)(PMe3)3]Cl (2g)
2.14. X-ray crystallography
1
Yield: 47%. H NMR (CDCl3): d À19.77 (q, J = 19 Hz,
1H, IrH), 0.97 (t, J = 7.2 Hz, 3H, CH3), 1.17 (d,
J = 8.4 Hz, 3H, CH3), 1.60 (d, J = 6.8 Hz, 9H, P(CH3)3),
1.61 (d, J = 6.8 Hz, 9H, P(CH3)3), 1.73 (m, ꢀ3H, CH2,
NH), 1.93 (d, 9H, J = 10.4 Hz, P(CH3)3), 2.15 (m, 1H,
CH), 3.05 (m, 1H, CH), 6.90 (br d, 1H, NH); 13C NMR
(CDCl3): d 12.34, 13.15, 15.81 (m, J = 36 Hz), 21.08 (d,
J = 40 Hz), 24.3, 27.2, 55.6, 181.5; 31P NMR (CDCl3): d
À49.06 (t, J = 16 Hz), À33.69 (t, J = 22 Hz).
Clear rectangular prisms of [Ir(L-valine)(H)(PMe3)3]PF6
(0.2 · 0.2 · 0.4 mm3) were crystallized from CH2Cl2 by
slow diffusion into diethyl ether at room temperature.
The chosen crystal was mounted on a glass fiber using
epoxy cement and centered on the goniometer of a Siemens
R3m/V four-circle diffractometer equipped with a scintilla-
tion counter detector. The data collection routine, unit cell
refinement, and data processing were carried out with the
Siemens program package SHELXTL PLUS (VMS) [7]. The
Laue symmetry and systematic absences were consistent
with the tetragonal space group P43. The absolute configu-
ration was established from anomalous dispersion effects in
the structure. Structure solution and refinement were per-
formed with the graphical user interface WINGX [26]. The
structure was solved by direct methods and refined using
SHELX97 [27]. The asymmetric unit of the structure com-
prises one crystallographically independent molecule
(Flack parameter = À0.010(5)). The final refinement model
2.10. [Ir(L-tyrosine)(H)(PMe3)3]Cl (2h)
1
Yield: 43%. H NMR (CDCl3): d À19.52 (q, J = 18 Hz,
1H, IrH), 1.34 (d, J = 6.2 Hz, 9H), 1.90 (d, J = 6 Hz, 9H),
2.02 (d, J = 10 Hz, 9H), 2.31 (Br s, 1H, OH), 3.35 (m, 2H,
CH2), 3.63 (br m, 1H, NH), 3.78 (d, J = 14 Hz, 1H, CaH),
7.31 (d, J = 8.2 Hz, 2H, ArH), 7.58 (d, J = 8.2 Hz, 2H,
ArH), 7.62 (br s, 1H, NH); 31P NMR (CDCl3): d À48.99
(t, J = 20 Hz), À33.71 (t, J = 21 Hz).
2.11. [Ir(L-serine)(H)(PMe3)3]Cl (2i)
Table 1
1
Crystal data and structure refinement for [Ir(H)(L-Valine)(PMe3)3]PF6
Yield: 43%. H NMR (CDCl3): d À19.9 (q, J = 18 Hz,
1H, IrH), 1.88 (t, J = 6.8 Hz, 18H, P(CH3)3), 2.09 (d,
J = 10.4 Hz, 9H, P(CH3)3), 3.50 (m, 1H, CH), 4.26 (dq,
J = 3.6, 9.2 Hz, 2H, CH2), 5.21 (br t, 1H, NH), 6.20 (br
s, 1H, OH), 6.60 (br t, J = 9.6 Hz, 1H, NH); 31P NMR
(CDCl3): d À47.30 (t, J = 16 Hz), À33.72 (t, J = 22 Hz).
Identification code
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
2c
C14H38F6IrNO2P4
682.5
298
˚
0.71073
Tetragonal
P43
Unit cell dimensions
2.12. [Ir(diphenylglycine)(H)(PMe3)3]Cl (2j)
˚
a (A)
14.327(3)
14.397(4)
2955.3(16)
4
1.534
4.759
1344
0.2 · 0.2 · 0.4
3.5–45.0
0 < h < 15, 0 < k < 15,
À15 < l < 15
4250
3870 (0.0263)
3264 (F > 4.0r(F))
Semi-empirical
0.5122/1.0000
Full-matrix least-squares
Rx(Fo À Fc)2
254
˚
c (A)
Volume (A )
Using the general procedure above with the following
modifications: 1.34 mmol diphenylglycine (296.3 mg,
1.34 mmol), [Ir(COD)(PMe3)3]Cl (350 mg, 0.620 mmol).
3
˚
Z
Dcalc (Mg/m3)
Absorption coefficient (mmÀ1
F(000)
1
)
Yield: 47%. H NMR (CH2Cl2): d À8.40 (dt, J = 174.5,
19.9 Hz, 1H, IrH), 1.46 (d, J = 7.7 Hz, 9H, P(CH3)3),
1.66 (d, J = 10.7 Hz, 9H, P(CH3)3), 1.85 (d, J = 10.4 Hz,
9H, P(CH3)3), 4.76 (br s, 2H, NH2), 6.8–8.1 (br m, 10H,
ArH); 13C NMR (D2O): d 13.2 (d, J = 30.2 Hz), 17.8 (dd,
J = 42.2 Hz, J = 3 Hz), 18.96 (dd, J = 42.2 Hz, J = 3 Hz),
73.12, 126.94, 128.01, 128.79, 128.82, 128.90, 129.04,
138.28, 142.37, 183.04; 31P NMR (D2O): d À44.4 (dd),
À40.8 (dd), À38.0 (dd), IR: m 2040, 1648, 947 cmÀ1. Elem.
Anal. Calcd. for C23H40ClIrNO2P3: C, 40.44; H, 5.90.
Found: C, 40.50; H, 5.95%.
Crystal size (mm3)
Theta range (ꢁ)
Index range
Reflections collected
Independent reflections (Rint
Observed reflections
Absorption correction
Minimum/maximum transmission
Refinement method
Quantity minimized
Number of parameters refined
Goodness-of-fit
Final R indices (observed data)
R indices (all data)
)
1.26
2.13. [Ir(amino acid)(H)(PMe3)3][PF6], general
procedure
R1 = 0.0433, wR2 = 0.0506
R1 = 0.0560, wR2 = 0.0580
1.04(3)
0.071, 0.007
12.9:1
Absolute structure parameter
Largest and mean D/r
Data-to-parameter ratio
An excess of KPF6 was dissolved in distilled water, this
solution was added dropwise to solution of [Ir(amino
acid)(H)(PMe3)3]Cl in distilled water. A yellow-white pre-
À3
˚
Largest difference in peak and hole (e A
)
2.00 and À1.19

C.P. Roy et al. / Journal of Organometallic Chemistry 691 (2006) 2270–2276
2273
Table 2
involved anisotropic displacement parameters for non-
hydrogen atoms and a riding model for all hydrogen
atoms. The program package ORTEP-3 was used for molec-
ular graphics generation [28]. Crystallographic data for the
structural analysis has been deposited with the Cambridge
Crystallographic Data Centre, CCDC No. 285583 for com-
pound 2c. A summary of the experimental details and crys-
tallographic results can be found in Table 1.
Yields, chemical shift, d, of the hydride peak in the 1H NMR spectrum,
spin–spin coupling and coupling constants, J, for the complexes
[Ir(aa)(H)(PMe3)3]Cl. Spin–spin coupling q is a quartet, dt is a doublet
of triplets
Complex Amino acid
Yield d of Hydride Spin–spin
(%)
(ppm)
coupling, J (Hz)
2a
2b
2c
2d
2e
2f
Glycine
L-Alanine
L-Valine
L-Phenylalanine
L-Tryptophan
L-Proline
L-Isoleucine
L-Tyrosine
L-Serine
96
79
71
67
64
61
47
43
43
À19.15
À19.39
À19.10
À19.48
À19.42
À20.32
À19.77
À19.50
À19.90
À8.40
q, 19
q, 17
q, 17
q, 12
q, 19
q, 20
q, 19
q, 18
3. Results and discussion
Metal hydrides have assumed an important role in tran-
sition metal catalysis [29]. It is our desire to exploit the Ir–
H bonds in amino acid complexes of iridium in an attempt
to explore their catalytic activity. We initially prepared and
characterized a number of naturally and unnaturally occur-
ring amino acid complexes (Table 2). These complexes are
of interest because most of them possess excellent water
solubility which may lend themselves to use in ‘‘green’’ pro-
cesses. Additionally, a variety of binding modes of amino
acids to metals have been demonstrated [30]. Therefore,
we wished to fully understand the structure of amino acid
complexes of iridium and undertook a comprehensive
study of these complexes.
Since we knew that amino acids are not very soluble in
organic solvents and that C–H activation frequently occurs
with [Ir(cod)(PMe3)3]Cl upon heating [31], we chose to
react amino acids with [Ir(cod)(PMe3)3]Cl (1) in aqueous
solution. Water is an excellent solvent for complex 1 and
most amino acids. The reaction of a-amino acids with com-
plex 1 at 100 ꢁC in water leads to formation of hydridoiri-
dium amino acid complexes (2a–2j) in good to excellent
yields (Table 1). These complexes are the first examples
of amino acid iridium hydrido species.
2g
2h
2i
q, 18
dt, 174.5, 20
2j
Diphenylglycine 47
at 0.82 ppm correspond to the isopropyl methyl protons
of L-valine. The multiplet at 2.1 ppm is due to the isopropyl
methine proton and the doublet at 3.53 ppm corresponds
to the proton of the a carbon of valine. The resonance at
1.5 ppm corresponds to the methyl groups on the trimethyl
phosphines of complex 1, and at 2.0 and 3.3 ppm to the ali-
phatic and olefinic protons of the 1,5 COD ligand,
respectively.
1
From the H NMR spectrum (Fig. 2) of the mixture
after heating at 100 ꢁC for 18 h, it is clear that the L-valine
is attached to the metal center. The isopropyl methyl
groups of the bound valine are present as two distinct sets
of doublets, one set shifted upfield and the other shifted
downfield, bordering the resonances of the excess L-valine
still present in the solution. The resonance of the proton
on the a carbon remains a doublet shifted slightly upfield
from its free amino acid counterpart. Therefore, the amino
acid had formed a complex with the iridium.
O
H2N
+
PMe3
PMe3
PMe3
Cl-
OH
Ir
R
1
H
Ir
Me3P
PMe3
PMe3
Cl-
H2O, Δ
O
-COD
NH2
O
R
2
When L-valine was added to complex 1, a meridional
product, 2, was formed upon heating (Table 2). Initially,
L-valine was chosen as the amino acid ligand because the
isopropyl group gives a distinct NMR signal which can
1
be used in determining its binding to the metal. In the H
NMR spectrum of a simple mixture of L-valine and com-
plex 1, the resonances of the free amino acid and the irid-
ium complex are easily discerned (Fig. 1). The resonances
Fig. 1. 1H NMR spectrum of a 2:1 mixture of L-valine and [Ir(COD)-
(PMe3)3]Cl (1).

2274
C.P. Roy et al. / Journal of Organometallic Chemistry 691 (2006) 2270–2276
Fig. 3. ORTEP drawing of [Ir(L-valine)(H)(PMe3)3]PF4 derived from
compound 2c. The hydride ligand was not located in the mixture
determination and is not shown.
Fig. 2. 1H NMR spectrum of a 2:1 mixture of L-valine and [Ln(COD)(P-
Me3)3]Cl (1) heated at 100 ꢁC for 18 h.
locate additional electron density from possible disordered
solvent inclusion were unsuccessful. SQUEEZE did not
find sufficient electron density in the void to account for
The complex appears to be the meridional complex
(Scheme 1) from the coupling pattern of the hydride pro-
ton. The hydride resonance of the L-valine complex is a
quartet with a chemical shift of À19.1 ppm. The quartet
is due to P–H spin–spin coupling of three cis phosphorus
neighbors, indicative of a meridional arrangement of phos-
phines in the octahedral Ir(III) complex. The chemical shift
of the hydride is consistent with the hydride trans to either
N or O of the amino acid ligand [23].
The ORTEP plot from the single crystal diffraction
study of [Ir(L-valine)(H)(PMe3)3]PF6 clearly shows the
meridional arrangement with the hydride trans to the
amino acid nitrogen (Fig. 3). All of the other amino acid
complexes synthesized showed a peak at approximately
the same chemical shift and identical spin–spin coupling
pattern (Table 2) and, therefore, were assigned as meridio-
nal isomers.
solvent molecules. The highest electron density peak was
3
˚
˚
only 0.79 e/A and it was 1.03 A away from the iridium.
A reasonable hypothesis based on the size of the void space
is that the ions crystallized with one mole of diethyl ether
per cation/anion pair but the volatile solvent escaped from
the lattice before the diffraction experiment. This raises the
interesting question: if solvent was lost, why did the crystal
lattice remain intact and not collapse?
Examination of intermolecular contacts and the crystal
packing of 2c gives an answer to this question as well as
showing a fascinating extended-lattice. Complex 2c crystal-
lizes in the chiral tetragonal space group P43. The cation/
anion pairs lie around the 43 screw axis. The two hydrogen
atoms attached to the coordinated valine nitrogen atoms
are both hydrogen-bonded. One of the N hydrogen atoms
is bonded to a fluorine atom of the PF6 counter ion with a
Examination of the structural solution for 2c, it
appeared that the cation shown in Fig. 3 along with the
PF6 anion did not account for enough volume in the crystal
lattice. Attempts to locate additional electron density from
possible solvent inclusion were unsuccessful. The PLATON
program SQUEEZE [32] found a total void volume of
˚
NÁ Á ÁF distance of 3.227 A. The second N hydrogen atom is
bonded to the carbonyl oxygen of a second cation with a
˚
NÁ Á ÁO distance of 2.913 A. The N–H–O hydrogen bonding
leads to the 43 helix shown in Fig. 4.
2
˚
approximately 590 A which is a space that could accom-
modate quite a number of solvent molecules. Attempts to
H
H
R
H2N
PMe3
PMe3
Me3P
O
PMe3
PMe3
Cl-
Cl-
Ir
Ir
O
O
PMe3
NH2
O
R
facial
meridional
Fig. 4. Helical extended structure of 2c (PMe3 ligands removed for
Scheme 1. Meridional and facial isomers of [Ir(aa)(H)(PMe3)3].
clarity).

C.P. Roy et al. / Journal of Organometallic Chemistry 691 (2006) 2270–2276
2275
1
Table 4
Along with the hydride at À19.6 ppm, the H NMR
spectrum of 2j shows an additional multiplet at
À8.40 ppm. This hydride peak is consistent with the
hydride being trans to the less electronegative phosphorus
atom. Additionally, this proton is a doublet of triplets with
one coupling constant of 20 Hz which is consistent with P–
H coupling cis and a second coupling constant of 175 Hz,
consistent with P–H coupling trans. Additionally, we
observed small amounts of other hydride peaks: a doublet
of quartets at À11.4 and a triplet at À21.0 (t) ppm. We
have postulated that these peaks are due to other iridium
complexes which contain four PMe3 ligands and two
PMe3 ligands, respectively. We have as of yet been unable
to isolate and further analyze these compounds.
Further examination of the proton NMR spectra of sev-
eral of the amino acid complexes in the region of
À9.0 ppm, showed that trace amounts of the facial isomer,
by evidence of the same doublet of triplet patterns as with
the facial isomer of the diphenylglycine complex 2j, were
present. As can be seen from Table 3, all of the mono
substituted a-amino acid complexes give predominantly
the meridional isomer, while the a,a-disubstituted amino
acid gives significant amounts of the facial, meridional
and other complexes.
Distribution of mer, fac and other isomers of [Ir(diphenylgly-
cine)(H)(PMe3)3]Cl complexes as determined by the integration areas of
the corresponding hydride signals in the 1H NMR spectra compared to an
internal standard
Day
fac
isomer (%)
Other
isomer 1 (%)
mer
isomer (%)
Other
isomer 2 (%)
1
2
6
8
35
36
36
36
6
6
7
4
27
19
5
31
39
52
56
5
Our studies have indicated that these complexes are
not completely inert. The amino acid ligand can be
replaced with a less sterically hindered amino acid. For
example, when free glycine is added to an aqueous solu-
tion of the L-valine complex, 2c, at 100 ꢁC, the formation
of the glycine complex, 2a, and free valine is observed by
1H NMR spectroscopy. A series of reactions was per-
formed in which glycine replaced the alanine ligand
and alanine replaced the valine ligand. The bulk of the
side chain dictated which amino acid complex was
formed.
4. Conclusion
Interestingly, the ratio of hydrides for the diphenylgly-
cine complex changes with time when the compound is
kept in a CDCl3 solution. A solution of freshly prepared
2j in CDCl3 was prepared and the NMR spectrum was
obtained over time. The integration areas of the hydride
corresponding to the fac and mer isomers as well as the
hydride of the other isomers (isomer 1 and isomer 2) were
normalized compared to an internal standard. As can be
seen from Table 4, the mer isomer is not inert. However,
it does not appear that the mer isomerizes to the fac isomer.
Instead, the material that forms is one with a hydride
chemical shift of À21.0 ppm and is a triplet. Presumably,
the mer isomer has a PMe3 ligand exchanged with another
ligand, perhaps chloride.
We have found that hydrido amino acid complexes of
iridium can easily be formed in water and that their iso-
meric forms can be monitored by proton NMR spectros-
copy. Both meridional and facial isomers can form and
their ratios are dependent upon the degree of substitu-
tion of the amino acid; a-monosubstituted amino acids
give predominantly meridional isomers, while a,a-disub-
stituted amino acid give both meridional and facial
isomers.
We continue to explore the possibilities of using these
iridium amino acid complexes as possible catalysts. The
potential use of these complexes as catalysts is under inves-
tigation. The water solubility of these complexes as well as
the presence of the chiral amino acid ligands creates new
possibilities for catalytic systems.
The same experiment was performed on the D-phenyl-
glycine complex. Here, the ratio of facial, mer and other
complexes remained constant over time. We conclude that
monosubstituted amino acids, while giving predominately
meridional isomers, are also much more inert.
References
[1] B. Rosenberg, L. VanCamp, J.E. Trosko, V.H. Mansour, Nature 222
(1969) 385–386.
[2] N.C. Stephenson, J.F. McConnell, R.C. Warren, Inorg. Nucl. Chem.
Lett. (1967) 553–556.
[3] N.N. Chernova, I.G. Kurskii, V.V. Strukov, Z. Neorg. Khim. 23
(1978) 430–434.
[4] O. Vicol, N. Hurduc, I.A. Schneider, J. Inorg. Nucl. Chem. 41 (1979)
309–315.
Table 3
Distribution of mer and fac isomers and other complexes of the
[Ir(aminoacid)(H)(PMe3)3]Cl system as determined by the relative inte-
gration of the corresponding hydride signals in the 1H NMR spectra from
freshly prepared samples in CDCl3
Amino acid
fac (%)
mer (%)
Other (%)
[5] M. Chandrasekharan, M.R. Udupa, G. Aravamudan, Inorg. Chim.
Acta 7 (1973) 88–90.
[6] W. Levason, C.A. McAuliffe, D.M. Johns, Inorg. Nucl. Chem. Lett.
13 (1977) 123–127.
[7] W.S. Sheldrick, S. Heeb, Inorg. Chim. Acta 168 (1990) 93–100.
[8] R.W. Hay, P.J. Morris, Metal Ions Biol. Syst. 5 (1976) 173–243.
[9] D.P.N. Satchell, R.S. Satchell, Annu. Rep. Prog. Chem., Sect. A:
Inorg. Chem. 75 (1978) 25–48.
L-Leucine
6
8
6
3
5
91
86
84
85
84
27
3
6
9
12
12
37
L-Isoleucinea
L-tert-Leucine
L-Proline
D-Phenylglycine
Diphenylglycine
a
35
Spectrum obtained in D2O.

2276
C.P. Roy et al. / Journal of Organometallic Chemistry 691 (2006) 2270–2276
[10] H. Sigel, R.B. Martin, Chem. Rev. 82 (1982) 385–426.
[11] D.A. Buckingham, in: A.W. Addison, W.R. Cullen, D. Dolphin
[20] J.R. Knorr, J.S. Merola, Organometallics 9 (1990) 3008–3010.
[21] J.S. Merola, Organometallics 8 (1989) 2975–2977.
[22] J.S. Merola, A. Grieb, F.T. Ladipo, H.E. Selnau, Preprints – Am.
Chem. Soc., Div. Petrol. Chem. 38 (1993) 674–678.
(Eds.), Biological Aspects of Inorganic Chemistry, Wiley, New York,
1977, pp. 141–196.
[12] S. Shinoda, N. Inoue, K. Takita, Y. Saito, Inorg. Chim. Acta 65
[23] F.T. Ladipo, J.S. Merola, Inorg. Chem. 29 (1990) 4172–4173.
[24] F.T. Ladipo, M. Kooti, J.S. Merola, Inorg. Chem. 32 (1993) 1681–
1688.
(1982) L21–L23.
[13] S. Shinoda, Y. Yamaguchi, Y. Saito, Inorg. Chem. 18 (1979) 673–
678.
[25] J.F. Frazier, J.S. Merola, Polyhedron 11 (1992) 2917–2927.
[26] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837–838.
[27] G.M. Sheldrick, SHELX97 Programs for Crystal Structure Analysis,
University of Gottingen, Germany, 1997.
[14] S. Shinoda, Y. Sudo, Y. Yamaguchi, T. Iwayanagi, Y. Saito, J.
Organomet. Chem. 121 (1976) 93–112.
[15] T.F. Buckley, H. Rapoport, J. Am. Chem. Soc. 104 (1982) 4446–
4450.
[28] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[29] R.H. Crabtree, The Organometallic Chemistry of the Transition
Metals, second ed., Wiley, New York, 1994.
[16] B. Kayser, W. Beck, Z. Naturforsch. B: Chem. Sci. 59 (2004) 1423–
1428.
[17] D. Koch, K. Suenkel, W. Beck, Z. Anorg. Allg. Chem. 629 (2003)
[30] H. Kozlowski, L.D. Pettit, Stud. Inorg. Chem. 11 (1991) 530–545.
[31] H.E. Selnau Jr., C–H activation: oxidative addition to an iridium(I)
center and reactivity of the resulting iridium(III) species, 1992, p. 210.
[32] A.L. Speck, PLATON, A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht, The Netherlands, 2001. Available from: <http://
www.cryst.chem.uu.nl/platon/>.
1322–1328.
[18] D. Herebian, W.S. Sheldrick, J. Chem. Soc., Dalton Trans. (2002)
966–974.
[19] A.B. Akbarov, Y.Y. Kharitonov, M.N. Islamov, Z. Neorg. Khim. 38
(1993) 312–326.