Extending the range of pentasubstituted cyclopentadienyl compounds: The synthesis of a series of tetramethyl(alkyl or aryl)cyclopentadienes (Cp?R), their iridium complexes and their catalytic activity for asymmetric transfer hydrogen

Article abstract of DOI:10.1016/j.poly.2014.06.053

Tetramethyl(alky or aryl)cyclopentadienes were synthesized and the organometallic half-sandwich iridium complexes of the form [(η⁵-Cp^?R)Ir(aa)Cl], Cp^?R = tetramethyl(phenyl)cyclopentadienyl (Cp^?<

Full text of DOI:10.1016/j.poly.2014.06.053

Polyhedron 84 (2014) 120–135
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Extending the range of pentasubstituted cyclopentadienyl compounds:
The synthesis of a series of tetramethyl(alkyl or aryl)cyclopentadienes
(Cp⁄R), their iridium complexes and their catalytic activity for asymmetric
transfer hydrogenation
⇑
David M. Morris, Michael McGeagh, David De Peña, Joseph S. Merola
Department of Chemistry, Virginia Tech, 306 Hahn Hall North, Blacksburg, VA 24061, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Tetramethyl(alky or aryl)cyclopentadienes were synthesized and the organometallic half-sandwich
iridium complexes of the form [(g
5-Cp⁄R)Ir(aa)Cl], Cp⁄R = tetramethyl(phenyl)cyclopentadienyl (Cp⁄Ph),
Received 10 April 2014
Accepted 26 June 2014
Available online 8 July 2014
tetramethyl(benzyl)cyclopentadienyl (Cp⁄Bn), tetramethyl(2-propyl)cyclopentadienyl (Cp⁄iPr), or tetra-
methyl(cyclohexyl)cyclopentadienyl (Cp⁄Cy) were prepared and characterized. The complexes adopt a
piano stool configuration, forming diastereomers, with ratios similar to reported [(g
5-Cp⁄)Ir(aa)Cl] com-
This paper is dedicated to Professor John
Bercaw on the occasion of his 70th birthday.
Your friendship and advice over the years
has always been good and always valuable.
plexes. The complexes display an intermolecular hydrogen bonding network in the solid state. These
complexes were tested for the asymmetric transfer hydrogenation of several ketones, showing that the
R of the Cp⁄R drastically impacts both selectivity and rate of reaction. Additionally, severe solvent effects
are displayed when the reaction media is changed from aqueous to organic solvent.
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Iridium
Cyclopentadiene
Amino acid
Half-sandwich compounds
ATH
1. Introduction
substitution blocks some direct reactions of the metal with the
ligand due to the absence of cyclopentadienyl C–H bonds. One of
The discovery of ferrocene [1] in 1951 is arguably the starting
point for the modern era of organometallic chemistry. The history
of that discovery and the early years of ferrocene chemistry are
nicely related by Kauffman [2], by Werner [3], and by Wilkinson
[4] in a personal recounting. Fischer and Wilkinson were awarded
the Nobel Prize in Chemistry in 1973 for their investigations into
the syntheses and chemistry of a wide variety of metallocene com-
pounds. One of the more intriguing aspects of ferrocene is the
enhanced reactivity of the cyclopentadienyl ring toward a number
of reactions, especially electrophilic aromatic substitution [5].
The enhanced reactivity of the unsubstituted cyclopentadienyl
rings attached to metals made the cyclopentadienyl ligand less
than desirable for examining some chemistry at the metal since
the Cp ring often became involved in reactions at the metal center
[6]. 1,2,3,4,5-pentamethylcyclopenta-1,3-dienyl, (Cp⁄), is one of the
most common ancillary ligands in organometallic chemistry due to
its steric bulk, good electron density and the full methyl
the first Cp⁄ metal complexes was made by reaction between IrCl3-
Á3H2O and hexamethyldewarbenzene [7]. A complete review of Cp⁄
complexes would be massive, but recent publications show that
Cp⁄ may be used in complexes for transfer hydrogenation [8–11],
water oxidation [12–14], anti-cancer activity [15,16], and anti-
microbial activity [17]. The development of much early metal
chemistry was made possible in large part to the use of pentameth-
ylcyclopentadiene. The contributions of Bercaw and a host of
co-workers for the development of an efficient synthesis of
pentamethylcyclopentadiene [18] and the use of pentamethylcy-
clopentadienyl complexes of metal compounds across the periodic
table have been critical in the development of modern organome-
tallic chemistry [19,20].
Further modification of the penta-alky substituted cyclopenta-
dienyl ligands could have potential utility, especially in the realm
of catalytic chemistry. Asymmetrically penta-substituted cyclo-
pentadienyl ligands, specifically C5Me4R variants, would provide
the opportunity to probe the effect of changing a single substitu-
tion and note any changes in catalytic activity and/or selectivity.
One of the most successful and intriguing of catalytic systems is
⇑
Corresponding author.
E-mail address: jmerola@vt.edu (J.S. Merola).
http://dx.doi.org/10.1016/j.poly.2014.06.053
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
121
asymmetric transfer hydrogenation (ATH), for which a share of the
Nobel Prize was awarded to Ryoji Noyori in 2001 [21]. Noyori and
co-workers have shown that half-sandwich compounds of ruthe-
nium are excellent catalysts for ATH [22–24]. It has been postu-
lated that interaction of ATH substrates with the methyl groups
of C6Me6 ruthenium compounds plays an important role in the
enantioselectivity of the products [25]. This led us to test C5Me4R
systems for ATH catalysis and determine if varying the R group
would have an effect on the activity or selectivity of Cp⁄Ir(aa)Cl
complexes, where aa = aminoacidato ligands.
1H and 13C NMR spectra were collected on a Varian MR-400
NMR spectrometer. For many of the 1H spectra reported below, a
number of factors made assignment of coupling constants difficult:
overlap of major/minor isomer peaks, non-first order behavior and
some very complex multiplets. In some cases while coupling con-
stants could be read for one of the protons, the coupling proton
was often obscured. Thus there are some listings with J values
for one proton without the same corresponding J value for the cou-
pled proton for the reasons just described. Also, in a number of
cases, the non-first order systems could not be modeled adequately
and so are described as multiplets(m). GC chromatograms were
collected on a Hewlett Packard 5890 equipped with a CP-Chiral-
Sil–Dex CB 25 Â 0.25 column. HRMS were collected on an Agilent
6220 Accurate Mass TOF LC-MS. X-ray crystallographic data were
collected at 100 K on an Oxford Diffraction Gemini diffractometer
Although some substitutionally-modified Cp⁄ type ligands have
been reported, an extended series of these ligands is not readily
available. Because of this there has been limited reporting on func-
tionalized Cp⁄ complexes for both catalysis and biological activity
studies.[26–29] Bercaw and Threlkel reported on the specific vari-
ants C5Me4R with R = ethyl, propyl, butyl and phenyl [18]. Modifi-
cation to the Cp portion of the molecule allows tailoring of the
hydrophobicity and sterics of the organometallic complex. Sadler
has shown previously that modification to the Cp⁄ moiety effects
cytotoxicity, hydrolysis and pKa of Ir organometallic complexes
[16]. Mintz and co-workers have shown that addition of vinyl Grig-
nard to 2,3,4,5-tetramethylcyclopent-2-enone provides good yields
of pentamethylfulvene that, in turn, can provide a route to C5Me4R
complexes [30]. We decided upon an approach utilizing 2,3,4,5-
tetramethycyclopent-2-enone with Grignard reagents followed
by dehydration because of the wide availability of commercial
Grignard reagents and the ease of synthesis of many others. As
we were developing this chemistry, as mentioned above, Sadler
and co-workers reported on the syntheses of C5Me4R compounds
with R = phenyl and naphthyl using the same general methodology
[31]. Wills and co-workers have also used this tetramethylcycl-
opentenone route to make amino aryl pentamethylcyclopentadie-
nyl complexes with a diamine tethered to the ring thus tethering
the asymmetric diamine ligand to the tetramethylcyclopentadi-
enyl ligand [32]. The work reported herein is the first on
tetramethylcyclopentadienyl ligands with benzyl, isopropyl and
cyclohexyl groups and their iridium complexes as well as the
examination of the iridium complexes for ATH catalysis.
with an EOS CCD detector and Mo K
a radiation. Crystals were
coated in ParatoneÒ oil and mounted on a fiber under nitrogen at
100 K. Data collection and data reduction were performed using
Agilent’s CrysAlisPro soft-ware [33], Structure solution and refine-
ment were performed with SHELXS and SHELXL [34], and Olex2 was
used for graphical representation of the data [35].
2.2. Cyclopentadiene ligand syntheses
2.2.1. Synthesis of (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-
yl)benzene (D1)
To a stirred solution of 2,3,4,5-tetramethyl-2-cyclopentenone
(2.00 g, 15.2 mmol) in anhydrous THF (20 mL) was added a solu-
tion of phenylmagnesium bromide (6.4 mL of a 3.0 M solution
19.1 mmol) in THF. The mixture was refluxed for 3 h, then cooled
to 0 °C and quenched with HCl (20 mL of a 1.0 M solution,
20 mmol). This solution was warmed to room temperature and
stirred for 1 h. The products were washed with water
(30 mL Â 3), and the organic layer was dried over MgSO4. The
products were concentrated under reduced pressure, and purified
by column chromatography (silica gel, hexanes) to afford 2.064 g
(68.5%) of the products as an orange liquid.
2. Experimental
2.1. Materials and methods
Unless otherwise stated, synthetic work was carried out in air
with untreated solvents. Commercially available reagents were
obtained from the following sources: IrCl3xH2O from Pressure
Chemical, Pittsburgh, PA 15201. Sodium formate, pinacolone,
L-alanine, L-proline, benzylmagnesium chloride, and 2,3,4,5-
tetramethylcyclopent-2-en-1-one were purchased from Alfa
Aesar, Ward Hill, MA 01835. Reagent grade solvents and
L-phenylglycine, L-piperidine-2-carboxylic acid, L-phenylalanine,
cyclohexylmagnesium bromine, phenylmagnesium chloride, 2-
propylmagnesium bromide, 2,2-dimethyl-1-phenylpropan-1-one,
and acetophenone were purchased from Sigma–Aldrich, St. Louis,
MO 63103. Glycine was purchased from Qiagen Sciences, Ger-
mantown, MD 20874. N,N-dimethylglycine was purchased from
Spectrum Chemical, Gardena, CA 90248. Deuterated solvents for
NMR spectroscopy were obtained from Cambridge Isotope Labo-
ratories, Tewksbury, MA 01876. L-azetidine-2-carboxylic acid
was purchased from Indofine Chemical, Hillsborough, NJ 08844.
Elemental analyses were performed by Atlantic Microlabs, Nor-
cross, GA. All compounds were dried in vacuo at 100 °C for at least
12 h before submitting for elemental analysis. In some complexes,
the elemental analysis indicated solvent retention, especially H2O,
even after this treatment.
.
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.38–7.28 (m, 2H),
7.25–7.14 (m, 3H), 3.19 (dddt, J = 9.3, 7.6, 5.8, 1.7 Hz, 1H), 2.02
(d, J = 1.8 Hz, 3H), 1.93 (d, J = 1.0 Hz, 3H), 1.86 (dt, J = 2.4, 1.1 Hz,
3H), 0.95 (d, J = 7.7 Hz, 3H) ppm. 13C NMR (101 MHz, CDCl3) d
142.70, 140.68, 137.14, 134.97, 128.42, 128.05, 125.35, 50.08,
14.72, 12.65, 11.90, 11.07 ppm.
HRMS/ESI+ (m/z): Calc. for C15H19 199.1481. Found: 199.1475.
2.2.2. Synthesis of ((2,3,4,5-tetramethylcyclopenta-2,4-dien-1-
yl)methyl)benzene (D2)
To a stirred solution of 2,3,4,5-tetramethyl-2-cyclopentenone
(5.00 g, 36.2 mmol) in anhydrous THF (20 mL) was added a solu-
tion of benzylmagnesium bromide (45.3 mL of a 1.0 M solution
45.3 mmol) in THF. The mixture was refluxed for 4 h, then cooled
to 0 °C and quenched with HCl (15 mL of a 1.0 M solution,
15 mmol). This solution was warmed to room temperature and
stirred for 1 h. The products were washed with water

122
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
(30 mL Â 3), and the organic layer was dried over MgSO4. The
products were concentrated under reduced pressure, and purified
by column chromatography (silica gel, hexanes) to afford 7.124 g
(92.7%) of the product as a yellow liquid.
1H unassignable due to signal overlap between isomers. 13C
NMR (101 MHz, CDCl3) d 147.11, 135.65, 134.92, 133.88, 62.55,
49.68, 39.23, 38.49, 32.88, 32.29, 30.14, 29.64, 27.25, 26.85,
26.38, 14.97, 14.07, 13.38, 11.39, 11.00 ppm.
Isomer 1: 1H NMR (400 MHz, CDCl3) d 7.43–7.04 (m, 5H), 6.10 (s,
1H), 2.52 (q, J = 7.7 Hz, 2H), 1.90 (s, 3H), 1.61 (s, 3H), 1.06 (d,
J = 2.3 Hz, 3H), 1.04 (d, J = 2.2 Hz, 3H) ppm.
HRMS/ESI+ (m/z): Calc. for C17H31 204.1878. Found: 204.1891.
2.3. Synthesis of Cp⁄R chloro-bridged dimers
Isomer 2: 1H NMR (400 MHz, CDCl3) d 7.43–7.04 (m, 5H), 3.68–
3.53 (m, 2H), 2.60 (q, J = 7.4 Hz, 1H), 1.80 (s, 6H), 1.79 (s, 3H), 1.75
(s, 3H) ppm.
2.3.1. Synthesis of [(
0.200 g (0.569 mmol) of IrCl3 Â 3H2O was combined with
(2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)benzene (0.135 g
g
5-C5Me4C6H5)IrCl2]2 (1)
Isomer 3: 1H NMR (400 MHz, CDCl3) d 7.46–7.03 (m, 5H), 3.76 (d,
J = 15.3 Hz, 1H), 3.44 (d, J = 15.2 Hz, 1H), 2.98–2.88 (m, 1H), 1.89–
1.86 (m, 3H), 1.79 (d, J = 1.6 Hz, 3H), 1.76–1.74 (m, 3H), 0.98 (d,
J = 7.6 Hz, 3H) ppm.
0.683 mmol) in methanol (1 mL) in a microwave pressure tube.
The reaction mixture was heated to 115 °C at 150 watts and 88
psi and held there for 30 min. Upon cooling, an orange powder
formed and was collected by filtration. This orange powder was
washed with cold methanol and hexanes to yield 0.1187 g
(45.3%) of 1.
HRMS/ESI+ (m/z): Calc. for C16H21 213.1638. Found: 213.1635.
2.2.3. Synthesis of 5-isopropyl-1,2,3,4-tetramethylcyclopenta-1,3-
diene (D3)
1H NMR (400 MHz, CDCl3) d 7.62–7.53 (m, 4H, ArH), 7.4.–7.32
(m, 6H, ArH), 1.72 (s, 12H, 4 CpMe), 1.63 (s, 12H, 4 CpMe) ppm.
13C NMR (101 MHz, CDCl3) d 130.18 (ArC), 129.79 (ArC), 128.62
(ArC), 128.42 (ArC), 93.43 (CpC), 85.48 (CpC), 10.33 (CpMe), 9.60
(CpMe) ppm.
To a stirred solution of 2,3,4,5-tetramethyl-2-cyclopentenone
(2.50 g, 18.09 mmol) in anhydrous THF (30 mL) was added a solu-
tion of 2-propylmagnesium bromide (7.34 mL of a 2.9 M solution,
22.60 mmol) in THF. The mixture was refluxed for 24 h, then
cooled to 0 °C and quenched with HCl (30 mL of a 1.0 M solution,
30 mmol). This solution was then stirred for 1.5 h. The organic
phase was washed with water (30 mL Â 3), and the organic layer
was dried over MgSO4. The products were concentrated under
reduced pressure and purified by column chromatography (silica
gel, hexanes) to afford 1.102 g (37.1%) of the product as a yellow
liquid.
HRMS/ESI+ (m/z): Calc. for C30 H34
885.1018.
Anal. Calc. for C30H34Cl4Ir2; C, 39.130; H, 3.720. Found: C, 38.11;
H, 3.61%.
[
193Ir]2 Cl3 885.0979. Found:
2.3.2. Synthesis of [(g
5-C5Me4CH2C6H5)IrCl2]2 (2)
1.000 g (2.84 mmol) of IrCl3 Â 3H2O was combined with
(2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)methylbenzene
0.9033 g (4.25 mmol) in methanol (30 mL) in a 100 mL Schlenk flask.
The reaction was refluxed for 48 h. Upon cooling, an orange powder
formed and was collected by filtration. This orange powder was
washed with cold methanol and hexanes to yield 0.3543 g of a first
crop. Solvent was reduced to half volume and the flask was stored
overnight with refrigeration and a second crop of crystals were col-
lected (0.1878 g) for a combined yield of 0.542 g (42.3%) of 2.
1H NMR (400 MHz, CDCl3) d 7.29–7.24 (m, 4H, ArH), 7.22–7.16
(m, 2H, ArH), 7.12–7.05 (m, 4H, ArH), 3.55 (s, 4H, 2CH2), 1.63 (s,
12H, 4CpMe), 1.61 (s, 12H, 4CpMe) ppm. 13C NMR (101 MHz,
CDCl3) d 136.79 (ArC), 128.70 (ArC), 128.21 (ArC), 126.73 (ArC),
87.52 (CpC), 86.76 (CpC), 85.80 (CpC), 30.41 (CH2), 9.78 (CpMe),
9.35 (CpMe) ppm.
Major isomer: 13C NMR (101 MHz, CDCl3) d 135.83 (CpC), 134.84
(CpC), 62.71 (CpCH), 28.07 (Me2CH), 18.91 (CH3), 13.22 (CpMe),
10.96 (CpMe).
HRMS/ESI+ (m/z): Calc. for C12H21 165.1638. Found: 165.1627.
HRMS/ESI+ (m/z): Calc. for C32H38Cl3Ir2 913.1298. Found:
913.1347.
Anal. Calc. for C32H38Cl4Ir2; C, 40.50; H, 4.04. Found: C, 40.40; H,
3.98%.
2.2.4. (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)cyclohexane (D4)
To a stirred solution of 2,3,4,5-tetramethyl-2-cyclopentenone
(4.00 g, 28.9 mmol) in anhydrous THF (20 mL) was added a solu-
tion of cyclohexylmagnesium chloride (18.1 mL of a 2.0 M solution,
36.2 mmol) in THF. The mixture was refluxed for 2 h. The mixture
was cooled to 0 °C and quenched with HCl (40 mL of a 1.0 M solu-
tion, 40 mmol). This solution was then stirred for 1 h. The organic
phase was washed with water (30 mL Â 3), and the organic layer
was dried over MgSO4. The products were concentrated under
reduced pressure and purified by column chromatography (silica
gel, hexanes) to afford 4.825 g (71.4%) of the product as a yellow
liquid.
2.3.3. Synthesis of [(g
5-C5Me4iPr)IrCl2]2 (3)
1.000 g (2.84 mmol) of IrCl3 Â 3H2O was combined with
5-isopropyl-1,2,3,4-tetramethylcyclopenta-1,3-diene (0.699 g
4.25 mmol) in methanol (30 mL) with stirring. The mixture was
refluxed for 48 h. Solvent was reduced to half volume and the
reaction was cooled to 0 °C produce an orange solid. The product
was isolated by filtration and washed with cold methanol to yield
1.37 g (56.7%) of 3.

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
123
1H NMR (400 MHz, CDCl3) d 2.47 (sept, J = 7.1 Hz, 2H, 2 (Me2-
CH), 1.67 (s, 12H, 4CpMe), 1.59 (s, 12H, 4CpMe), 1.28 (d,
J = 7.1 Hz, 12H, 2CHMe2) ppm. 13C NMR (101 MHz, CDCl3) d 25.24
(Me2CH), 20.58 (Me2CH), 10.21 (CpMe), 9.51 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C24H38Cl4[193Ir]2 Na; 875.0878.
Found: 875.0898.
(CpC), 81.50 (CpC), 81.31 (CpC), 51.50 (CH), 19.86 (CH3), 9.97
(CpMe), 9.94 (CpMe), 9.35 (CpMe), 9.15 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C18H23 193Ir]NO2; 478.1358. Found:
[
478.1391.
Anal. Calc. for C18H23ClIrNO2ÁH2O, C, 40.71; H, 4.74. Found: C,
40.62; H, 4.47%.
Anal. Calc. for C24H36Cl4Ir2; C, 33.80; H, 4.49. Found: C, 33.98; H,
4.62%.
2.4.3. Synthesis of [(g
5-C5Me4C6H5)Ir(L-phenylglycinate)Cl] complex
(6)
2.3.4. Synthesis of [(
2.00 g (5.67 mmol) of IrCl3 Â 3H2O was combined with 1.74 g
(8.51 mmol) of (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-
g
5-C5Me4C6H10)IrCl2]2 (4)
Following the general procedure: 0.1000 g (0.109 mmol) of
[(g
5-C5Me4C6H5)IrCl2]2 was combined with 0.0345 (0.228 mmol)
of L-phenylglycine and 0.0192 g (0.228 mmol) of sodium hydrogen
carbonate in methanol (30 mL) to give 6, 0.1176 g (94.2% yield). 6
was identified based on the following information:
yl)cyclohexane in 50 mL of methanol with stirring. The mixture
was refluxed for 48 h. After 48 h the reaction mixture was cooled
in an ice bath to produce an orange powder. The powder was iso-
lated on a frit and washed with cold methanol and ether (1.23 g).
Removal of solvent and overnight storage at 4 °C produced a sec-
ond crop of crystals what were isolated as stated previously,
(0.05 g). Combined yield was 1.28 g (48.5%) of 4.
Major isomer: 1H NMR (400 MHz, Acetone-d6) d 7.69–7.61 (m,
2H, ArH), 7.43–7.36 (m, 3H, ArH), 7.36–7.22 (m, 5H, ArH), 6.98–
6.84 (m, 1H, NH), 4.42–4.29 (m, 1H, aCH), 4.16–4.03 (m, 1H, NH),
1.89 (s, 3H, CpMe), 1.78 (s, 3H, CpMe), 1.73 (s, 3H, CpMe), 1.69 (s,
3H, CpMe) ppm. 13C NMR (101 MHz, DMSO-d6) d 181.61 (COO),
140.56 (ArC), 131.66 (ArC), 131.02 (ArC), 129.44 (ArC), 128.73
(ArC), 128.54 (ArC), 128.38 (ArC), 127.94 (ArC), 92.14 (CpMe),
90.72 (CpMe), 83.07 (CpMe), 81.29 (CpMe), 81.06 (CpMe), 59.40
(CH), 9.14 (CpMe), 9.05 (CpMe), 8.94 (CpMe) ppm.
1H NMR (400 MHz, CDCl3) d 2.03 (tt, J = 12.1, 3.2 Hz, 2H, CH2),
1.96–1.85 (m, 4H, 2CH2), 1.80–1.70 (m, 4H, 2CH2), 1.66 (s, 12H,
2CpMe), 1.62–1.59 (m, 2H, CH2), 1.58 (s, 12H, 2CpMe), 1.43–1.19
(m, 8H, 4CH2), 1.13 (tt, J = 12.6, 3.5 Hz, 2H, CH2) ppm. 13C NMR
(101 MHz, CDCl3) d 90.57 (CpC), 85.85 (CpC), 84.73 (CpC), 35.60
(Cp-CH), 30.72 (CH2), 26.93 (CH2), 26.03 (CH2), 10.51 (CpMe),
9.56 (CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, Acetone-d6) d 7.71–7.61 (m,
2H, ArH), 7.43–7.36 (m, 3H, ArH), 7.36–7.22 (m, 5H, ArH), 5.54–
5.42 (m, 1H, NH), 5.32–5.18 (m, 1H, NH), 4.60–4.53 (m, 1H, aCH),
HRMS/ESI+ (m/z): Calc. for C30H50Cl4[193Ir]2N 950.1950. Found:
950.1946.
Anal. Calc. for C30H46Cl4Ir2 C, 38.62; H, 4.970. Found: C, 38.77; H,
4.92%.
1.74 (s, 3H, CpMe), 1.72 (s, 3H, CpMe), 1.66 (s, 3H, CpMe), 1.65 (s,
3H, CpMe) ppm. 13C NMR (101 MHz, DMSO-d6) d 181.61 (COO),
141.54 (ArC), 131.64 (ArC), 131.05 (ArC), 129.14 (ArC), 128.84
(ArC), 128.66 (ArC), 128.45 (ArC), 92.08 (CpC), 90.28 (CpC), 82.52
(CpC), 81.65 (CpC), 80.72 (CpC), 60.68 (CH), 10.11 (CpMe), 9.88
(CpMe), 9.79 (CpMe), 9.73 (CpMe) ppm.
2.4. Synthesis of amino acid complexes
HRMS/ESI+ (m/z): Calc. for C23H25Cl[193Ir]Cl; 575.1198. Found:
575.1238.
2.4.1. General procedure for synthesis of [(g
5-Cp⁄R)Ir(aa)Cl] complexes
Anal. Calc. for C23H25ClIrNO2ÁH2O, C, 46.57; H, 4.59. Found: C,
A round bottom flask was charged with appropriate amounts of
the respective [Cp⁄R IrCl2]2, amino acid, sodium hydrogen carbon-
ate, and methanol with magnetic stirring. The initially orange solu-
tion changed to yellow over the course of approximately 30 min.
The solvent was then removed under reduced pressure. The prod-
uct was extracted away from unreacted amino acid and sodium
hydrogen carbonate with dichloromethane (3 Â 10 mL) and fil-
tered. The complexes were recrystallized from dichloromethane
and ether or hexanes and collected on a frit as yellow crystalline
powders.
46.91; H, 4.41%.
2.4.4. Synthesis of [(g
5-C5Me4C6H5)Ir(L-phenylalaninate)Cl] complex
(7)
Following the general procedure: 0.1000 g (0.109 mmol) of
[(g
5-C5Me4C6H5)IrCl2]2 was combined with 0.0377 (0.228 mmol)
of L-phenylalanine and 0.0192 g (0.228 mmol) of sodium hydrogen
carbonate in methanol (30 mL) to give 7, 0.055 g (43.0% yield). 7
was identified based on the following information:
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.46–7.19 (m, 8H,
ArH), 7.18–7.10 (m, 2H, ArH), 4.12 (br s, 1H, NH), 3.98–3.84 (m,
2.4.2. Synthesis of [(g
5-C5Me4C6H5)Ir(L-alaninate)Cl] complex (5)
Following the general procedure: 0.1000 g (0.109 mmol) of
1H, aCH), 3.76 (br s, 1H, NH), 3.24 (dd, J = 14.4, 6.6 Hz, 1H, CHH),
[(
g
5-C5Me4C6H5)IrCl2]2 was combined with 0.0203 (0.228 mmol)
3.06 (dd, J = 14.4, 5.2 Hz, 1H, CHH), 1.63 (s, 3H, CpMe), 1.62 (s,
3H, CpMe), 1.58 (s, 3H, CpMe), 1.49 (s, 3H, CpMe) ppm. 13C NMR
(101 MHz, CDCl3) d 182.42 (COO), 135.87 (ArC), 130.08 (ArC),
129.70 (ArC), 129.34 (ArC), 129.22 (ArC), 128.92 (ArC), 128.47
(ArC), 127.49 (ArC), 90.57 (CpC), 89.89 (CpC), 84.30 (CpC), 81.92
of L-alanine and 0.0192 g (0.228 mmol) of sodium hydrogen car-
bonate in methanol (30 mL) to give 5, 0.0578 g (51.9% yield). 5
was identified based on the following information:
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.51–7.43 (m, 2H,
ArH), 7.39–7.30 (m, 3H, ArH), 6.23 (br s, 1H, NH), 3.54 (br s, 1H,
NH), 3.47–3.33 (m, 1H, CH), 1.69 (s, 6H, 2CpMe, 1.67 (s, 3H, CpMe),
1.65 (s, 3H, CpMe), 1.43 (d, J = 6.9 Hz, 3H, CH3) ppm. 13C NMR
(101 MHz, CDCl3) d 182.70 (COO), 130.43 (ArC), 130.29 (ArC),
128.84 (ArC), 128.75 (ArC), 91.97 (CpC), 91.45 (CpC), 82.92 (CpC),
82.83 (CpC), 81.94 (CpC), 53.04, (CH), 21.61, CH3, 10.04 (CpMe),
9.89 (CpMe), 9.35 (CpMe), 9.26 (CpMe) ppm.
(CpC), 81.42 (CpC), 55.03 aC, 38.47, CH2, 9.66 (CpMe), 9.58 (CpMe),
8.81 (CpMe), 8.79 (CpMe) ppm.
Note⁄ significant overlap is observed between benzyl protons in
the spectra.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.44–7.19 (m, 8H,
ArH), 7.18–7.12 (m, 2H, ArH), 4.43–4.24 (m, 1H, NH), 3.71–3.61
(m, 1H, NH), 3.57–3.48 (m, 1H,
aCH), 3.00 (d, J = 9.9 Hz, 1H,
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.52–7.43 (m, 2H,
ArH), 7.40–7.30 (m, 3H, ArH), 4.48 (d, J = 6.3 Hz, 2H, NH2), 3.45–
3.35 (m, 1H, aCH), 1.82 (s, 3H, CpMe), 1.80 (s, 3H, CpMe), 1.77 (s,
3H, CpMe), 1.77 (s, 3H, CpMe), 1.34 (d, J = 7.2 Hz, 3H, CH3) ppm.
13C NMR (101 MHz, CDCl3) d 184.44 (COO), 130.72 (ArC), 130.54
(ArC), 128.48 (ArC), 128.34 (ArC), 92.53 (CpC), 91.70 (CpC), 82.33
CHH), 1.77 (s, 3H, CpMe), 1.75 (s, 3H, CpMe), 1.67 (s, 3H, CpMe),
1.63 (s, 3H, CpMe) ppm. 13C NMR (101 MHz, CDCl3) d 180.32
(COO), 136.88 (ArC), 130.27 (ArC), 130.06 (ArC), 129.40 (ArC),
129.17 (ArC), 129.10 (ArC), 128.58 (ArC), 91.10 (CpC), 90.59
(CpC), 83.80 (CpC), 82.32 (CpC), 58.44 (
aC), 40.73 (CH2), 9.95
(CpMe), 9.80 (CpMe), 9.17 (CpMe), 9.09 (CpMe) ppm.

124
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
HRMS/ESI+ (m/z): Calc. for C24 H27 N O2 [193Ir] 554.1666. Found:
2.4.7. Synthesis of [(g
5-C5Me4CH2C6H5)Ir(L-phenylalaninate)Cl]
554.1632.
complex (10)
Anal. Calc. for C24H27ClIrNO2; C, 48.93; H, 4.62. Found: C, 49.10;
H, 4.76%.
Following the general procedure: 0.1000 g (0.105 mmol) of
[(g combined with 0.0360 g
5-C5Me4CH2C6H5)IrCl2]2 was
(0.221 mmol) of L-phenylalanine and 0.0186 g (0.221 mmol) of
sodium hydrogen carbonate in methanol (30 mL) to give 10,
0.1187 g (93.4% yield). 10 was identified based on the following
information:
2.4.5. Synthesis of [(g
5-C5Me4C6H5)Ir(L-prolinate)Cl] complex (8)
Following the general procedure: 0.1000 g (0.109 mmol) of
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.40–7.25 (m, 6H,
ArH), 7.05–7.01 (m, 2H, ArH), 4.30 (br s, 1H, NH), 4.01 (br s, 1H,
[(g
5-C5Me4C6H5)IrCl2]2 was combined with 0.0281 (0.244 mmol)
of L-proline and 0.0205 g (0.244 mmol) of sodium hydrogen car-
bonate in methanol (30 mL) to give 8, 0.1102 g (94.1% yield). 8
was identified based on the following information:
NH), 3.94–3.83 (m, 1H,
aCH), 3.40 (dd, J = 14.2, 6.1 Hz, 1H, CHH),
3.33–3.21 (m, 2H, CH2), 3.10 (dd, J = 14.2, 5.2 Hz, 1H, CHH), 1.57
(s, 3H, CpMe), 1.55 (s, 3H, CpMe), 1.54 (s, 3H, CpMe), 1.53 (s, 3H,
CpMe) ppm. 13C NMR (101 MHz, CDCl3) d 182.76 (COO), 137.16
(ArC), 136.20 (ArC), 129.90 (ArC), 129.28 (ArC), 128.72 (ArC),
128.09 (ArC), 126.77 (ArC), 86.17 (CpC), 85.68 (CpC), 84.39 (CpC),
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.47–7.41 (m, 2H,
ArH), 7.40–7.33 (m, 3H, ArH), 4.79–4.65 (m, 1H, NH), 4.11–3.98
(m, 1H,
aCH), 3.31–3.20 (m, 1H, N-CH), 2.68 2.75–2.62 (m, 1H,
N-CH), 2.25–2.14 (m, 1H, CHH), 2.04–1.92 (m, 1H, CHH), 1.77
(s, 3H, CpMe), 1.75 (s, 3H, CpMe), 1.74 (s, 3H, CpMe), 1.66 (s,
3H, CpMe), 1.65–1.54 (m, 2H, CH2) ppm. 13C NMR (101 MHz,
83.81 (CpC), 83.17 (CpC), 55.06 (aC), 38.47 (Cp-CH2-Ar), 29.71
(CH2), 9.16 (CpMe), 8.82 (CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.42–7.25 (m, 6H,
ArH), 7.24–7.13 (m, 2H, ArH), 7.10–7.06 (m, 2H, ArH), 5.11 (br s,
CDCl3)
(ArC), 128.51 (ArC), 91.44 (CpC), 91.12 (CpC), 85.38 (CpC),
80.90 (CpC), 80.68 (CpC), 62.54 ( C), 54.53 (N–C), 29.09 (CH2),
d 184.45 (COO), 130.52 (ArC), 130.10 (ArC), 128.88
1H, NH), 3.71–3.58 (m, 1H, NH), 3.62–3.51 (m, 1H,
aCH), 3.46 (s,
a
2H, CH2), 1.71 (s, 3H, CpMe), 1.69 (s, 3H, CpMe), 1.68 (s, 3H, CpMe),
1.67 (s, 3H, CpMe) ppm. 13C NMR (101 MHz, CDCl3) d 136.77 (ArC),
137.13 (ArC), 129.58 (ArC), 129.10 (ArC), 128.70 (ArC), 128.19
(ArC), 127.53 (ArC), 85.63 (CpC), 84.66 (CpC), 84.16 (CpC), 58.49
26.94 (CH2), 10.52 (CpMe), 9.68 (CpMe), 9.16 (CpMe), 9.09
(CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 1.79 (s, 3H, CpMe),
1.68 (s, 3H, CpMe), 1.67 (s, 3H, CpMe) ppm. (Significant overlap
with major isomer obscures other peaks).
HRMS/ESI+ (m/z): Calc. for C20H26NO2 [193Ir]Cl 540.1276. Found:
540.1231.
(a
C), 40.45 (CH2), 30.03 (Cp-CH2-Ar), 9.49 (CpMe), 9.12 (CpMe)
ppm.
HRMS/ESI+ (m/z): Calc. for C25H29ClIrNO2; 603.1511. Found:
603.1597.
Anal. Calc. for C25H29ClIrNO2; C, 49.78; H, 4.85. Found: C, 50.01;
Anal. Calc. for C20H25ClIrNO2ÁH2O; C, 43.12; H, 4.88. Found: C,
43.52; H, 4.88%.
H, 5.04%.
2.4.8. Synthesis of [(g
5-C5Me4CH2C6H5)Ir(L-prolinate)Cl] complex (11)
2.4.6. Synthesis of [(
g
5-C5Me4C6H5)Ir(L-piperidine-2-carboxylate)Cl]
Following the general procedure: 0.1000 g (0.105 mmol) of [(g5
-
complex (9)
C5Me4CH2C6H5)IrCl2]2 was combined with 0.0255 (0.221 mmol) of
L-proline and 0.0186 g (0.221 mmol) of sodium hydrogen carbonate
in methanol (20 mL) to give 11, 0.1032 g (88.5% yield). 11 was iden-
tified based on the following information:
Following the general procedure: 0.1000 g (0.109 mmol) of
[(g
5-C5Me4C6H5)IrCl2]2 was combined with 0.0295 (0.228 mmol)
of L-piperidine-2-carboxylic acid and 0.0192 g (0.228 mmol) of
sodium hydrogen carbonate in methanol (30 mL) to give 9,
0.1133 g (94.3% yield). 9 was identified based on the following
information:
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.30–7.25 (m, 2H,
ArH), 7.23–7.16 (m, 1H, ArH), 7.13–7.05 (m, 2H, ArH), 4.92 (br s,
1H, NH), 4.10–3.98 (m, 1H, N-CH), 3.63–3.56 (m, 1H, N-CH), 3.49
(s, 2H, CH2), 2.93 (qd, J = 11.0, 5.8 Hz, 1H, CHH), 2.32–2.18 (m,
2H, CH2), 2.17–1.81 (m, 2H, CH2), 1.70 (s, 3H CpMe), 1.69 (s, 3H
CpMe), 1.67 (s, 3H CpMe), 1.67 (s, 3H, CpMe) ppm. 13C NMR
(101 MHz, CDCl3) d 184.55 (COO), 137.02 (ArC), 128.75 (ArC),
128.10 (ArC), 126.79 (ArC), 86.25 (CpC), 85.71 (CpC), 84.41 (CpC),
1H NMR (400 MHz, CDCl3) d 7.54–7.47 (m, 2H, ArH), 7.41–7.32
(m, 3H, ArH), 4.00 (br s, 1H, NH), 3.46–3.33 (m, 1H, N-CH), 3.09
(td, J = 11.8, 3.1 Hz, 1H,
aCH), 2.82 (qd, J = 12.4, 3.1 Hz, 1H, N-
CH), 2.28–2.13 (m, 1H, CHH), 2.08–1.83 (m, 1H, CHH), 1.77 (s,
3H, CpMe), 1.73 (s, 3H, CpMe), 1.68 (s, 3H, CpMe), 1.65 (s, 3H,
CpMe), 1.58–1.38 (m, 4H, CH2–CH2) ppm. 13C NMR (101 MHz,
CDCl3) d 177.93 (COO), 130.34 (ArC), 130.28 (ArC), 128.79 (ArC),
128.46 (ArC), 94.89 (CpC), 93.02 (CpC), 82.46 (CpC), 81.44 (CpC),
84.36 (CpC), 83.73 (CpC), 62.53 (N-C), 54.98 (aC), 30.14 (Cp-CH2-
Ar), 28.79 (CH2), 27.12 (CH2), 9.64 (CpMe), 9.55 (CpMe), 9.29
(CpMe), 9.23 (CpMe) ppm.
79.33 (CpC), 66.15 (
23.57 (CH2), 10.56 (CpMe), 10.05 (CpMe), 9.38 (CpMe), 9.13 (CpMe)
a
C), 53.27 (N–C), 30.83 (CH2), 27.71 (CH2),
Minor isomer: 1H NMR (400 MHz, CDCl3) d 1.73 (s, 1H, CpMe),
1.72 (s, 1H, CpMe), 1.71 (s, 1H, CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C21H28Cl[193Ir]NO2; 554.1432. Found:
554.1431.
ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.56–7.47 (m, 2H,
ArH), 7.40–7.31 (m, 3H, ArH), 4.36 (br s, 1H, NH), 3.90–3.76 (m,
Anal. Calc. for C21H27ClIrNO2ÁCH2Cl2; C, 41.41; H, 4.58. Found: C,
1H, N-CH), 3.30–3.16 (m, 1H, N-CH), 3.04–2.94 (m, 1H,
aCH),
41.27; H, 4.74%.
2.28–2.13 (m, 1H, CHH), 2.00–1.92 (m, 1H, CHH), 1.75 (s, 3H,
CpMe), 1.70 (s, 3H, CpMe), 1.69 (s, 3H, CpMe), 1.64 (s, 3H, CpMe),
1.57–1.38 (m, 4H, CH2–CH2) ppm. 13C NMR (101 MHz, CDCl3) d
180.92 (COO), 130.73 (ArC), 130.14 (ArC), 128.46 (ArC), 128.32
2.4.9. Synthesis of [(g
5-C5Me4CH2C6H5)Ir(L-azetidine 2-
carboxylate)Cl] complex (12)
Following the general procedure: 0.1000 g (0.105 mmol) of
(ArC), 91.96 (CpC), 83.64 (CpC), 81.42 (CpC), 62.48 (
a
C), 52.24
[(g
5-C5Me4CH2C6H5)IrCl2]2
was
combined
with
0.0255
(N–C), 31.53 (CH2), 29.00 (CH2), 23.70 (CH2), 9.70 (CpMe), 9.55
(CpMe), 8.90 (CpMe), 8.74 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C21H27O2[193Ir] 518.1666. Found:
518.1677.
(0.221 mmol) of L-azetidine-2-carboxylic acid and 0.0186 g
(0.221 mmol) of sodium hydrogen carbonate in methanol (30 mL)
with slight heating to give 12, 0.0936 g (82.4% yield). 12 was iden-
tified based on the following information:
Anal. Calc. for C21H27ClIrNO2ÁCH2Cl2; C, 41.48; H, 4.58. Found: C,
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.30–7.25 (m, 2H,
ArH), 7.23–7.16 (m, 1H, ArH), 7.13–7.06 (m, 2H, ArH), 5.55 (br s,
40.63; H, 4.50%.

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
125
1H, NH), 4.62–4.43 (m, 1H,
aCH), 4.35–4.24 (m, 1H, N-CH), 3.95–
2.4.12. Synthesis of [(g
5-C5Me4iPr)Ir(N,N-dimethyl-glycinate)Cl]
3.83 (m, 1H, N-CH), 3.52 (s, 2H, CH2), 3.04–2.90 (m, 1H, CHH),
2.50–2.36 (m, 1H, CHH), 1.73 (s, 3H, CpMe), 1.71 (s, 3H, CpMe),
1.71 (s, 3H, CpMe), 1.70 (s, 3H, CpMe) ppm. 13C NMR (101 MHz,
CDCl3) d 137.09 (ArC), 128.74 (ArC), 128.10 (ArC), 126.78 (ArC),
86.06 (CpC), 85.40 (CpC), 84.28 (CpC), 84.23 (CpC), 83.72 (CpC),
complex (15)
Following the general procedure: 0.1000 g (0.173 mmol) of
[(g
5-C5Me4iPr)IrCl2]2 was combined with 0.0254 (0.246 mmol) of
N,N-dimethyl-glycine and 0.0207 g (0.246 mmol) of sodium hydro-
gen carbonate in methanol (30 mL) to give 15, 0.0859 g (74.4%
yield). 14 was identified based on the following information:
1H NMR (400 MHz, CDCl3) d 4.06 (d, J = 14.6, 1H, CHH), 3.07 (s,
3H, N-CH3), 2.95 (d, J = 14.6 Hz, 1H, CHH), 2.92 (s, 3H, N-CH3), 2.58
(sept, J = 7.4 Hz, 1H, Me2CH), 1.68 (s, 3H, CpMe), 1.65 (s, 3H, CpMe),
1.57 (s, 3H, CpMe), 1.56 (s, 3H, CpMe), 1.29 (overlapping doublets,
J = 7.4 Hz, 6H, CHMe2) ppm. 13C NMR (101 MHz, CDCl3) d 180.40
(COO), 87.73 (CpC), 87.47 (CpC), 86.77 (CpC), 85.10 (CpC), 81.88
60.76 (N-C), 51.29 (aC), 30.03 (Cp-CH2-Ar), 26.26 (CH2), 9.43
(CpMe), 9.38 (CpMe), 9.08 (CpMe), 9.06 (CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 4.96–4.80 (m, 1H, N-
CH), 4.16–3.99 (m, 1H, NH), 2.77–2.64 (m, 1H, CHH), 2.64–2.55 (m,
1H, CHH), 1.68 (s, 3H, CpMe), 1.67 (s, 3H, CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C20H26Cl[193Ir]NO2; 540.1276. Found:
540.1258.
Anal. Calc. for C20H25ClIrNO2; C, 44.56; H, 4.67. Found: C, 44.41;
H, 4.76%.
(CpC), 66.32 (aC), 56.26 (N-CH3), 50.65 (N-CH3), 25.16 (Me2CH),
20.58 (CH3), 20.35 (CH3), 9.91 (CpMe), 9.42 (CpMe), 9.23 (CpMe),
9.02 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C16H28Cl[193Ir]NO2; 494.1432. Found:
494.1455.
2.4.10. Synthesis of [(g
5-C5Me4CH2C6H5)Ir(L-piperidine-2-
carboxylate)Cl] complex (13)
Anal. Calc. for C16H27ClIrNO2; C, 38.98; H, 5.52. Found: C, 39.01;
H, 5.43%.
Following the general procedure: 0.1000 g (0.105 mmol) of
[(
g
5-C5Me4CH2C6H5)IrCl2]2
was
combined
with
0.0224
2.4.13. Synthesis of [(g
5-C5Me4iPr)Ir(L-alaninate)Cl] complex (16)
(0.221 mmol) of L-piperidine-2-carboxylic acid and 0.0186 g
(0.221 mmol) of sodium hydrogen carbonate in methanol (20 mL)
with slight heating to give 13, 0.1102 g (92.2% yield). 13 was iden-
tified based on the following information:
Following the general procedure: 0.1000 g (0.173 mmol) of
[(g
5-C5Me4iPr)IrCl2]2 was combined with 0.0220 (0.246 mmol) of
L-alanine and 0.0207 g (0.246 mmol) of sodium hydrogen carbon-
ate in methanol (30 mL) to give 16, 0.0762 g (68.2% yield). 16
was identified based on the following information: Significant sig-
nal overlap is observed for this complex for the 2-propyl portion of
the Cp ring.
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.31–7.25 (m, 2H,
ArH), 7.24–7.17 (m, 1H, ArH), 7.10–7.04 (m, 2H, ArH), 3.92 (br s,
1H, NH), 3.61–3.50 (m, 1H, N-CH), 3.48 (s, 2H, CH2), 3.18–3.10
(m, 1H,
aCH), 2.30–2.20 (m, 1H, N-CH), 2.03–1.91 (m, 1H, CHH),
Major isomer: 1H NMR (400 MHz, CDCl3) d 6.65 (br s, 1H, NH),
1.88–1.75 (m, 2H, CH2), 1.69 (s, 3H, CpMe), 1.69 (s, 3H CpMe),
1.68 (s, 3H CpMe), 1.67 (s, 3H, CpMe), 1.59–1.37 (m, 4H, CH2–
CH2) ppm. 13C NMR (101 MHz, CDCl3) d 177.76 (COO), 136.72
(ArC), 128.82 (ArC), 127.99 (ArC), 126.91 (ArC), 86.35 (CpC),
86.20 (CpC), 84.76 (CpC), 84.25 (CpC), 83.96 (CpC), 66.39 (N-C),
3.50–3.40 (m, NH), 3.41–3.33 (m, 1H,
aCH), 2.63 (sept, J = 7.3,
1H, (Me2CH), 1.71–1.64 (m, 12H, 4CpMe), 1.44 (d, J = 6.7 Hz, 3H,
CH2), 1.28 (overlapping doublets, J = 7.3 Hz, 6H, CHMe2) ppm. 13C
NMR (101 MHz, CDCl3) d 183.21 (COO), 89.01 (CpC), 88.77 (CpC,
85.77 (CpC), 83.18 (CpC), 82.40 (CpC), 52.97 (aC), 25.07 (Me2CH),
21.71 (CH3), 21.32 (CH3), 10.03 (CpMe), 9.87 (CpMe), 9.26 (CpMe),
53.85 (aC), 30.79 (CH2), 30.29 (Cp-CH2-Ar), 27.82 (CH2), 23.62
(CH2), 9.73 (CpMe), 9.65 (CpMe), 9.36 (CpMe) ppm.
9.19 (CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.32–7.25 (m, 2H,
ArH), 7.24–7.17 (m, 1H, ArH), 7.15–7.11 (m, 2H, ArH), 3.82–3.71
Minor isomer: 1H NMR (400 MHz, CDCl3) d 4.94 (br s, 1H, NH),
4.45–4.23 (m, 1H, NH), 3.70–3.56 (m, 1H,
aCH), 2.63 (h, J = 7.1,
(m, 1H, N-CH), 3.45–3.37 (m, 1H,
aCH), 3.10–2.97 (m, 1H, N-CH),
1H, (Me2CH), 1.78–1.71 (m, 12H, 4CpMe), 1.40 (d, J = 7.2 Hz, 3H,
CH3), 1.28 (overlapping doublets, J = 7.1 Hz, 6H, CHMe2) ppm. 13C
NMR (101 MHz, CDCl3) d 184.72 (COO), 88.97 (CpC), 88.71 (CpC),
85.58 (CpC), 83.06 (CpC), 82.55 (CpC), 51.60 (aC), 21.35 (CH3),
21.26 (CH3), 19.63 (CH3), 10.08 (CpMe), 9.85 (CpMe), 9.30 (CpMe),
9.13 (CpMe) ppm.
Anal. Calc. for C15H25ClIrNO2; C, 3.61; H, 5.26. Found: C, 37.37;
H, 5.36%.
2.13–2.05 (m, 1H, CHH), 1.72 (s, 3H, CpMe), 1.67 (s, 3H, CpMe),
1.64 (s, 3H, CpMe), 1.59–1.38 (m, 4H, CH2-CH2) ppm. 13C NMR
(101 MHz, CDCl3) d 128.90 (ArC), 128.48 (ArC), 9.25 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C22H29 193Ir]NO2; 532.1822. Found:
[
532.1830.
Anal. Calc. for C22H29IrNO2ÁH2O; C, 45.16; H, 5.34. Found: C,
45.78; H, 5.43%.
2.4.14. Synthesis of [(g
5-C5Me4iPr)Ir(L-phenylalaninate)Cl] complex
(17)
2.4.11. Synthesis of [(
g
5-C5Me4iPr)Ir(glycinate)Cl] complex (14)
Following the general procedure: 0.1000 g (0.173 mmol) of
Following the general procedure: 0.1000 g (0.173 mmol) of
[(
g
5-C5Me4iPr)IrCl2]2 was combined with 0.0198 (0.246 mmol) of
[(g
5-C5Me4iPr)IrCl2]2 was combined with 0.0410 (0.246 mmol) of
glycine and 0.0207 g (0.246 mmol) of sodium hydrogen carbonate
in methanol to give 14, 0.0963 g (88.3% yield). 14 was identified
based on the following information:
L-phenylalanine and 0.0207 g (0.246 mmol) of sodium hydrogen
carbonate in methanol (30 mL) to produce 17, 0.1071 g (82.3%
yield). 17 was identified based on the following information:
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.37–7.25 (m, 5H,
ArH), 4.20 (br s, 1H, NH), 3.97–3.91 (m, 1H, NH), 3.87 (tt, J = 7.6,
1H NMR (400 MHz, Methanol-d4) d 3.49–3.27 (m, 2H, CH2), 2.63
(sept, J = 7.1 Hz, 1H, (Me2CH), 1.75 (s, 3H, CpMe), 1.73 (s, 3H,
CpMe), 1.66 (br s, 6H, 2CpMe), 1.31 (overlapping doublets,
J1 ꢀ J2 = 7.0, 6H, CHMe2) ppm. 13C NMR (101 MHz, Methanol-d4) d
185.47 (COO), 88.37 (CpC), 88.27 (CpC), 85.99 (CpC), 83.65 (CpC),
5.2 Hz, 1H,
aCH), 3.39 (dd, J = 14.3, 5.4 Hz, 1H, CH), 3.06 (dd,
J = 14.3, 5.0 Hz, 1H, CH), 2.43 (sept, J = 7.1 Hz, 1H, Me2CH), 1.59
(s, 3H, CpMe), 1.55 (s, 3H, CpMe), 1.49 (s, 3H, CpMe), 1.48 (s, 3H,
CpMe), 1.16 (overlapping doublets J = 7.1 Hz, 6H, CHMe2) ppm.
13C NMR (101 MHz, CDCl3) d 182.34 (COO), 136.12 (ArC), 129.90
(ArC), 129.25 (ArC), 127.49 (ArC), 88.40 (CpC), 87.79 (CpC), 85.88
82.59 (CpC), 44.19 (aC), 24.93 (Me2CH), 20.09 (CH3), 19.84 (CH3),
8.51 (CpMe), 8.25 (CpMe), 7.53 (CpMe), 7.43 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C15H25IrNO2; 444.1515. Found:
444.1492.
(CpC), 83.44 (CpC), 82.38 (CpC), 54.88 (aC), 38.40 (CH2), 25.05
Anal. Calc. for C14H23ClIrNO2; C, 36.16; H, 4.99. Found: C, 35.98;
H, 4.94%.
(Me2CH), 21.14 (CH3), 21.04 (CH3), 9.58 (CpMe), 9.54 (CpMe),
8.79 (CpMe), 8.76 (CpMe) ppm.

126
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.36–7.25 (m, 5H,
ArH), 4.88–4.75 (m, 1H, NH), 3.66–3.51 (m, 2H, NH, CH), 3.45
Major isomer: 1H NMR (400 MHz, CDCl3) d 6.15 (br s, 1H, NH),
3.52–3.34 (m, 2H, NH, CH), 2.17 (ddt, J = 15.6, 12.4, 3.1 Hz, 1H,
a
a
(dd, J = 14.7, 3.1 Hz, 1H, CH), 3.04 (dd, J = 14.7, 3.1 Hz, 1H, CH),
2.56 (sept, J = 7.1 Hz, 1H, Me2CH), 1.71 (s, 3H, CpMe), 1.68 (s, 3H
CpMe), 1.64 (s, 3H CpMe), 1.63 (s, 3H CpMe), 1.26 (overlapping
doublets, J = 7.1 Hz, 6H, CHMe2) ppm. 13C NMR (101 MHz, CDCl3)
d 180.52 (COO), 136.99 (ArC), 129.47 (ArC), 129.10 (ArC), 127.09
(ArC), 88.67 (CpC), 88.46 (CpC), 86.17 (CpC), 83.16 (CpC), 82.68
Cp-CH), 1.88–1.77 (m, 4H, 2CH2), 1.77–1.71 (m, 12H, 4CpMe),
1.47 (d, J = 6.7 Hz, 3H, CH3), 1.45–1.41 (m, 1H, CHH), 1.36–1.22
(m, 4H, 2CH2), 1.15 (ddd, J = 16.3, 8.3, 3.6 Hz, 1H, CHH) ppm. 13C
NMR (101 MHz, CDCl3) d 183.20 (COO), 89.77 (CpC), 89.28 (CpC),
83.97 (CpC), 82.86 (CpC), 82.22 (CpC), 52.97 (aC), 35.42 (Cp-CH),
31.56 (CH2), 27.00 (CH2), 25.99 (CH2), 21.70 (CH3), 10.34 (CpMe),
10.15 (CpMe), 9.27 (CpMe), 9.22 (CpMe) ppm.
(CpC), 58.50 (aC), 40.67 (CH2), 25.12 (Me2CH), 21.29 (CH3), 21.26
(CH3), 9.84 (CpMe), 9.81 (CpMe), 9.15 (CpMe), 9.11 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C21H28Cl[193Ir]NNaO2; 577.133.
Found:, 577.1385.
Anal. Calc. for C21H29ClIrNO2; C, 45.44; H, 5.27. Found: C, 45.67;
H, 5.25%.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 4.59–4.48 (m, 1H,
NH), 4.46–4.32 (m, 1H, NH), 3.75–3.62 (m, 1H,
aCH), 2.17 (tt,
J = 12.4, 3.2 Hz, 1H, Cp-CH), 1.88–1.77 (m, 4H, 2CH2), 1.71–1.64
(m, 12H, 4CpMe), 1.45–1.41 (m, 2H, CH2), 1.40 (d, J = 7.2 Hz, 3H,
CH3), 1.30 (ddt, J = 17.2, 13.9, 6.9 Hz, 2H, CH2), 1.16 (tt, J = 12.8,
3.2 Hz, 2H, CH2) ppm. 13C NMR (101 MHz, CDCl3) d 184.73 (COO),
89.68 (CpC), 89.32 (CpC), 83.72 (CpC), 82.79, 82.35 (CpC), 51.60
2.4.15. Synthesis of [(g
5-C5Me4iPr)Ir(L-prolinate)Cl] complex (18)
Following the general procedure: 0.1000 g (0.173 mmol) of
(aC), 35.48 (Cp-CH), 31.51 (CH2), 27.00 (CH2), 25.99 (CH2), 19.65
[(g
5-C5Me4iPr)IrCl2]2 was combined with 0.0339 (0.293 mmol) of
(CH3), 10.38 (CpMe), 10.12 (CpMe), 9.32 (CpMe), 9.15 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C18H30Cl[193Ir]NO2 520.1589. Found:
520.1603.
L-proline and 0.0246 g (0.293 mmol) of sodium hydrogen carbon-
ate in methanol (20) to produce 18, 0.0839 g (70.8% yield). 18
was identified based on the following information:
Anal. Calc. for C18H29ClIrNO2ÁH2O: C, 40.25; H, 5.82. Found: C,
Major isomer: 1H NMR (400 MHz, CDCl3) d 4.68 (br s, 1H, NH),
41.00; H, 5.78%.
4.08–3.98 (m, 1H,
aCH), 3.64–3.52 (m, 1H, N-CH), 3.00–2.86 (m,
1H, N-CH), 2.57 (sept, J = 7.1 Hz, 1H, (Me2CH), 2.30–2.17 (m, 1H,
CHH), 2.06–1.86 (m, 3H, CH2-CHH), 1.71 (s, 3H, CpMe), 1.70 (s,
3H, CpMe), 1.65 (s, 3H, CpMe), 1.62 (s, 3H, CpMe), 1.29 (overlap-
ping doublets, J = 7.1 Hz, 6H, CHMe2) ppm. 13C NMR (101 MHz,
CDCl3) d 184.41 (COO), 89.20 (CpC), 87.81 (CpC), 86.16 (CpC),
2.4.18. Synthesis of [(g
5-C5Me4C6H10)Ir(L-phenylglycinate)Cl] complex
(21)
Following the general procedure: 0.1000 g (0.107 mmol) of
[(g
5-C5Me4C6H10)IrCl2]2 was combined with 0.0342 (0.225 mmol)
of L-phenylglycine and 0.019 g (0.225 mmol) of sodium hydrogen
carbonate in methanol (30 mL) to give 21, 0.1072 g (86.2% yield).
21 was identified based on the following information:
84.18 (CpC), 82.24 (CpC), 62.46 (aC), 54.92 (NC), 28.83 (CH2),
27.19 (CH2), 25.07 (Me2CH), 21.03 (CH3), 20.92 (CH3), 9.96 (CpMe),
9.83 (CpMe), 9.26 (CpMe), 9.20 (CpMe) ppm.
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.38–7.31 (m, 2H,
ArH), 7.24–7.16 (m, 4H, ArH), 6.39 (br s, 1H, NH), 4.20 (dd,
Minor isomer: 1H NMR (400 MHz, CDCl3) d 4.42–4.25 (m, 1H,
NH), 3.82–3.62 (m, 1H,
aCH), 3.82–3.65 (m, 1H, N-CH), 2.79–2.62
J = 10.0, 7.6 Hz, 1H, aCH), 3.65 (br s, 1H, NH), 2.18 (tt, J = 12.2,
(m, 1H, CHH), 1.75 (s, 3H, CpMe), 1.73 (d, 3H, CpMe), 1.68 (s, 3H,
3.1 Hz, 1H, Cp-CH), 1.89–1.75 (m, 4H, 2CH2), 1.73 (s, 3H, CpMe),
1.71 (s, 3H, CpMe), 1.68 (s, 3H, CpMe), 1.65 (s, 3H, CpMe), 1.32–
1.22 (m, 4H, 2CH2), 1.20–1.06 (m, 2H, CH2) ppm. 13C NMR
(101 MHz, CDCl3) d 181.24 (COO), 140.63 (ArC), 129.28 (ArC),
128.90 (ArC), 128.86 (ArC), 128.06 (ArC), 89.74 (CpC), 89.37
CpMe), 1.66 (s, 3H, CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C17H28Cl[193Ir]Cl; 506.1432. Found:
506.1432.
Anal. Calc. for C17H27ClIrNO2; C, 40.43; H, 5.39. Found: C, 40.82;
H, 5.56%.
(CpC), 84.20 (CpC), 83.60 (CpC), 82.55 (CpC), 58.76 (aC), 35.50
(Cp-CH), 31.60 (CH2), 27.01 (CH2), 25.86 (CH2), 10.33 (CpMe),
2.4.16. Synthesis of [(g
5-C5Me4C6H10)Ir(glycinate)Cl] complex (19)
10.19 (CpMe), 10.17 (CpMe), 10.11 (CpMe) ppm.
Following the general procedure: 0.1000 g (0.107 mmol) of
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.35–7.32 (m, 1.9 Hz,
2H, ArH), 7.24–7.16 (m, 4H, ArH), 4.73 (br s, 1H, NH), 4.53 (dd,
[(g
5-C5Me4C6H10)IrCl2]2 was combined with 0.0170 (0.225 mmol)
of glycine and 0.019 g (0.225 mmol) of sodium hydrogen carbonate
in methanol (30 mL) to give 19, 0.0634 g (57.5% yield). 19 was
identified based on the following information:
J = 7.9, 4.9 Hz, 1H, aCH), 4.11 (br s, 1H, NH), 2.09 (tt, J = 12.4,
3.2 Hz, 1H, Cp-CH), 1.89–1.76 (m, 4H, 2CH2), 1.64 (s, 3H, CpMe),
1.60 (s, 3H, CpMe), 1.55 (s, 3H, CpMe), 1.52 (s, 3H, CpMe), 1.48–
1.32 (m, 4H, 2CH2), 1.18–1.06 (m, 2H, CH2) ppm. 13C NMR
(101 MHz, CDCl3) d 180.70 (COO), 138.90 (ArC), 129.28 (ArC),
128.86 (ArC), 128.77 (ArC), 128.06 (ArC), 89.70 (CpC), 89.64
1H NMR (400 MHz, Methanol-d4) d 5.82 (br s, 1H, NH), 4.92 (br
s, 1H, NH), 3.51–3.39 (m, 1H, CHH), 3.39–3.31 (m, 1H, CHH), 2.21
(tt, J = 12.4, 3.2 Hz, 1H, Cp-CH), 1.92–1.83 (m, 2H, CH2), 1.83–1.77
(m, 2H, CH2), 1.75 (s, 3H, CpMe), 1.73 (s, 3H, CpMe), 1.67–1.62
(m, 6H, 2CpMe), 1.58–1.43 (m, 2H, CH2), 1.42–1.15 (m, 4H, 2CH2)
ppm. 13C NMR (101 MHz, Methanol-d4) d 185.46 (COO), 88.62
(CpC), 83.60 (CpC), 82.96 (CpC), 82.69 (CpC), 61.08 (aC), 35.39
(Cp-CH), 31.57 (CH2), 26.93 (CH2), 26.01 (CH2), 10.17 (CpMe),
10.11 (CpMe), 9.27 (CpMe), 9.00 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C23H32Cl[193Ir]O2 582.1745. Found:
582.1726.
(CpC), 84.28 (CpC), 83.61 (CpC), 44.31 (aC), 35.46 (Cp-CH), 31.08
(CH2), 30.94 (CH2), 26.70 (CH2), 25.71 (CH2), 8.80 (CpMe), 8.50
(CpMe), 7.47 (CpMe) ppm.
Anal. Calc. for C23H31ClIrNO2ÁH2O: C, 46.10; H, 5.55. Found: C,
HRMS/ESI+ (m/z): Calc. for C18H29 193Ir]NO2 484.1828. Found:
[
46.39: H, 5.50%.
484.1832.
Anal. Calc. for C17H27ClIrNO2ÁH2O: C, 39.03; H, 5.59. Found: C,
2.4.19. Synthesis of [(
(22)
g
5-C5Me4C6H10)Ir(L-phenylalaninate)Cl] complex
39.05; H, 5.54%.
0.1000 g (0.107 mmol) of [(
g
5-C5Me4C6H10)IrCl2]2 was com-
2.4.17. Synthesis of [(
g
5-C5Me4C6H10)Ir(L-alaninate)Cl] complex (20)
bined with 0.0373 (0.225 mmol) of L-phenylalanine and 0.019 g
(0.225 mmol) of sodium hydrogen carbonate in a round bottom
flask. Upon addition of 30 mL methanol and a magnetic stir bar
the mixture slowly turned yellow over the course of 30 min.
Solvent was removed and the product extracted using dichloro-
methane (3 Â 10 mL). This solution was filtered to remove any
Following the general procedure: 0.1000 g (0.107 mmol) of
[(g
5-C5Me4C6H10)IrCl2]2was combined with 0.0210 (0.225 mmol)
of L-alanine and 0.019 g (0.225 mmol) of sodium hydrogen carbon-
ate in methanol (30 mL) to give 20, 0.0089 g (80.0% yield). 20 was
identified based on the following information:

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
127
excess amino acid or sodium hydrogen carbonate. The product was
recrystallized from dichloromethane and ether, and isolated on a
frit as a yellow solid, 0.1081 g (84.9% yield) of 22. 22 was identified
based on the following information.
with stirring for 30 min. Sodium formate, (0.2 mmol) and 3,3-dim-
ethylbutan-2-one, (0.04 mmol) were added. The reaction was
maintained at set temperature until the total reduction of the
ketone was achieved or conversion of the ketone ceased (moni-
tored by GC). The product was extracted with diethyl ether
(3 Â 2 mL), the extracts were dried over MgSO4, and evaporated
under reduced pressure. The product was purified by TLC with hex-
anes/ethyl acetate mixture. Enantiomeric excess was determined
by chiral GC.
Major isomer: 1H NMR (400 MHz, CDCl3) d 7.42–7.25 (m, 5H,
ArH), 4.25–4.07 (m, 1H, NH), 3.97–3.76 (m, 2H, NH,
aCH), 3.38
(dd, J = 14.3, 4.9 Hz, 1H, CHH), 3.06 (dd, J = 14.3, 4.6 Hz, 1H, CHH),
2.02 (tt, J = 12.2, 3.1 Hz, 1H, Cp-CH), 1.84–1.71 (m, 4H, 2CH2),
1.60 (s, 3H, CpMe), 1.55 (s, 3H, CpMe), 1.49 (s, 3H, CpMe), 1.48
(s, 3H, CpMe), 1.44–1.03 (m, 6H, 3CH2) ppm. 13C NMR (101 MHz,
CDCl3) d 182.22 (COO), 136.07 (ArC), 129.87 (ArC), 129.23 (ArC),
127.51 (ArC), 88.91 (CpC), 88.16 (CpC), 84.16 (CpC), 83.34 (CpC),
(S)-3,3-dimethylbutan-2-ol: 1H NMR (400 MHz, CDCl3) d 3.45
(q, J = 6.4 Hz, 1H), 1.44 (s, 1H), 1.10 (d, J = 6.4 Hz, 3H), 0.87 (s,
9H) ppm. T = 75 °C, P = 15 psi, retention times: tR = 7.163 min,
tS = 7.384 min.
82.27 (CpC), 54.85 (aC), 38.43 (CH2), 35.47 (Cp-CH), 31.46 (CH2),
31.29 (CH2), 26.96 (CH2), 25.89 (CH2), 9.89 (CpMe), 9.87 (CpMe),
(R)-2,2-dimethyl-1-phenylpropan-1-ol: 1H NMR (400 MHz,
CDCl3) d 7.30–7.28 (m, 5H), 4.38 (s, 1H), 0.91 (s, 12H) ppm.
T = 120 °C, P = 15 psi, tR = 9.633 min, tS = 10.016 min.
(R)-1-phenylethan-1-ol: 1H NMR (400 MHz, CDCl3) d 7.33–7.25
(m, 3H), 7.23–7.18 (m, 2H), 4.83 (q, J = 6.5 Hz, 1H), 1.43 (d,
J = 6.5 Hz, 3H) ppm. T = 140 °C, P = 15 psi retention times:
tR = 8.471 min, tS = 9.137 min.
8.81 (CpMe), 8.77 (CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 7.43–7.25 (m, 5H,
ArH), 3.64–3.56 (m, 1H, NH), 3.55–3.42 (m, 2H, NH,
aCH), 3.03–
2.98 (m, 1H, CHH), 2.11 (tt, J = 12.4, 3.2 Hz, 1H, Cp-CH), 1.83–1.71
(m, 4H, 2CH2), 1.70 (s, 3H, CpMe), 1.67 (s, 3H, CpMe), 1.65 (s, 3H,
CpMe), 1.63 (s, 3H, CpMe), 1.45–1.01 (m, 6H, 3CH2) ppm. 13C
NMR (101 MHz, CDCl3) d 180.23 (COO), 137.08 (ArC), 129.38
(ArC), 129.14 (ArC), 127.12 (ArC), 89.29 (CpC), 84.54 (CpC), 82.75
3. Results and discussion
(CpC), 58.70 (aC), 40.79 (CH2), 35.58 (Cp-CH), 31.56 (CH2), 27.01
(CH2), 26.95 (CH2), 10.13 (CpMe), 9.18 (CpMe), 9.12 (CpMe) ppm.
HRMS/ESI+ (m/z): Calc. for C24H33Cl[193Ir]NO2 595.1824. Found:
595.1871.
Anal. Calc. for C24H33ClIrNO2: C, 48.43; H, 5.59. Found: C, 48.38;
H, 5.77%.
3.1. General comments and naming scheme
Chart 1 lists the abbreviations and numbering scheme used for
the various ligands and complexes discussed in this paper.
2.4.20. Synthesis of [(
g
5-C5Me4C6H10)Ir(L-prolinate)Cl] complex (23)
5-C5Me4C6H10)IrCl2]2 was com-
3.2. Cyclopentadienyl ligand synthesis
0.1000 g (0.107 mmol) of [(
g
The Cp⁄R variants were synthesized via reaction of 1.25–1.50
molar equivalents of a Grignard reagent and 2,3,4,5-tetramethylc-
ylopent-2-enone in anhydrous THF (Scheme 1). This reaction
results in an alcohol product which is then dehydrated to its
respective diene using HCl. Purification of the final Cp⁄R variant is
carried out with column chromatography on silica gel using hex-
anes as the eluent. Yields ranged from fair to excellent, with the
product being a combination of several isomers. The 1H NMR spec-
tra of the pentasubstituted dienes are fairly complex due to signal
overlap of the multiple isomers that are produced (for an example
of isomers, see Scheme 2). Yields are summarized in Table 1.
bined with 0.0259 g (0.225 mmol) of L-proline and 0.019 g
(0.225 mmol) of sodium hydrogen carbonate in a round bottom
flask. Upon addition of 30 mL methanol and a magnetic stir bar
the mixture slowly turned yellow over the course of 30 min. Sol-
vent was removed and the product extracted away using dichloro-
methane (3 Â 10 mL). This solution was filtered to remove any
excess amino acid or sodium hydrogen carbonate. The product
was recrystallized from dichloromethane and ether, and isolated
on a frit as a yellow solid to yield 0.0810 g (67.8%) of 23 identified
on the basis of the following information:
Major isomer: 1H NMR (400 MHz, CDCl3) d 4.56 (br s, 1H, NH),
4.10–3.97 (m, 1H,
aCH), 3.60–3.51 (m, 1H, N-CH), 2.98–2.85 (m,
1H, N-CH), 2.29–2.17 (m, 1H, CHH), 2.12 (tt, J = 12.4, 3.0 Hz, 1H,
Cp-CH), 2.06–1.89 (m, 2H, CH2), 1.89–1.75 (m, 4H, 2CH2), 1.71 (s,
3H, CpMe), 1.70 (s, 3H, CpMe), 1.69–1.65 (m, 2H, CH2), 1.64 (s, 3H,
CpMe), 1.62 (s, 3H, CpMe), 1.51–1.35 (m, 2H, CH2), 1.36–1.21 (m,
2H, CH2), 1.21–1.09 (m, 1H, CHH) ppm. 13C NMR (101 MHz, CDCl3)
d 184.16 (COO), 90.11 (CpC), 88.29 (CpC), 84.15 (CpC), 83.98 (CpC),
3.3. Synthesis of chloro-bridged iridium complexes
With the HCp⁄R variants in hand, a standard reaction of the
dienes with IrCl3 Â 3H2O was performed in refluxing methanol to
obtain the respective chloro-bridged iridium dimer complexes.
Upon complexation, the NMR pattern observed for the diene is
simplified with each Cp⁄R isomer becoming aromatic and planar
81.92 (CpC), 62.44 (aC), 54.83 (CH2), 35.73 (Cp-CH), 31.35 (CH2),
31.30 (CH2), 28.79 (CH2), 27.22 (CH2), 27.06 (CH2), 26.03 (CH2),
10.31 (CpMe), 10.09 (CpMe), 9.32 (CpMe), 9.22 (CpMe) ppm.
Minor isomer: 1H NMR (400 MHz, CDCl3) d 6.53 (br s, 1H, NH),
on the metal. As an example, the 1H spectra of complex 3(Cp⁄iPr
)
is shown in Fig. 1. Yields of the chloride complexes range from fair
to good and are summarized in Table 2. All iridium dimer com-
plexes were isolated as orange powders with overall appearances
and behaviors the same as the standard [IrCp⁄Cl2]2 dimer. The var-
ious dimer complexes were characterized by NMR spectroscopy,
HRMS, CH analysis, and X-ray crystallography when able. Complex
1(Cp⁄Ph) was previously reported by Sadler et al. [16], but we found
that the yield of this compound could be improved by carrying out
the synthesis in a microwave reactor, 60% yield with microwave
compared with 39% under methanol reflux conditions.
3.81–3.72 (m, 1H,
aCH), 3.24–3.11 (m, N-CH, 1H), 1.73 (s, 3H,
CpMe), 1.72 (s, 3H, CpMe), 1.66 (s, 3H, CpMe) ppm. Other signals
not detectable due to signal overlap.
HRMS/ESI+ (m/z): Calc. for C20H31Cl[193Ir]NO2 545.1673. Found:
545.1684.
Anal. Calc. for C20H31ClIrNO2: C, 44.06; H, 5.73. Found: C, 44.72;
H, 6.01%.
2.5. Asymmetric transfer hydrogenation
The dimers 2–4 exhibit similar structures, each with bridging
chlorides and with an inversion center that relates the unique por-
tion of the dimer to the other half. The bond lengths of these chlo-
rides are 2.4549(7), 2.4444(13), and 2.4393(11), for 2(Cp⁄Bn),
2.5.1. General procedure for catalytic reduction of ketones
In a 2 dram vial, 4 Â 10À4 mmol of catalyst was dissolved in
water (2 mL), and allowed to equilibrate to reaction temperature
3(Cp⁄iPr), and 4(Cp⁄Cy), respectively. There is no
p–p interaction

128
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
Cp*H
Cp*ph D1
Cp*bn D2
Cp*iPr D3
O
CHC
H2N OH
Cp*cyc D4
O
H O
CHC
O
3-1=n
aa
CHC
CH C
O
R2N
OH
H2N
OH
CHC
N
H
OH
H2N
OH
R = H Gly
R = Me NN-d-Me-Gly
Cpx
Ala
Phengly
Phe
n = 1 Aze
n = 2 Pro
n = 3 Pip
Cp*R Dimer
Cp*ph
1
Ir
Cl
Cl
Cl
Cp*bn
Cp*iPr
Cp*cyc
2
3
4
Cl
Ir
Cpx
Complex
aa
Cp*R
5
6
7
8
9
Ala
Phengly
Phe
Cp*ph
Cp*ph
Cp*ph
Cp*ph
Cp*ph
Cp*bn
Cp*bn
Cp*bn
Cp*bn
Pro
Pip
Phe
10
11
12
13
Pro
Aze
Pip
14
15
16
17
18
19
20
21
22
Gly
NN-di-Me-Gly
Ala
Phe
Pro
Gly
Ala
Phengly
Phe
Pro
Cp*iPr
Cp*iPr
Cp*iPr
Cp*iPr
Cp*iPr
Cp*cyc
Cp*cyc
Cp*cyc
Cp*cyc
23
Cp*cyc
Chart 1. Iridium tetramethyl(R)cyclopentadienyl amino acid complexes.
O
OH
R
R
+
XMg
R
THF
Reflux
2-6 hrs
HCl
48 hr
Reflux
Methanol
IrCl3 x H2O
D1
D2
D3
D4
Scheme 1. Synthesis of tetramethyl(R)cyclopentadienes.
observed for complex 2(Cp⁄Bn), unlike what was seen in earlier
work with complex 1(Cp⁄Ph), which has a weak interaction with
the symmetry related phenyl group in a neighboring molecule.
Most interesting is that in the case of 4(Cp⁄Cy), two different chair
configurations of the cyclohexane ring are observed in the struc-
ture when the disorder is appropriately modeled. The crystal struc-
tures for the dimers characterized crystallographically are
displayed in Fig. 2.
Ir
Cl
Cl
Cl
Cl
Ir
Scheme 2. Synthesis of complex 3(Cp⁄iPr).

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
129
Table 1
Table 2
Percent yields of tetramethyl(R)cyclopentadienyl ligands.
Percent yields of iridium dimer complexes.
R group
% Yield
Complex
1 (Cp⁄Ph
2 (Cp⁄Bn
3 (Cp⁄iPr
4 (Cp⁄Cy
Yield%
Phenyl D1
Benzyl D2
Isopropyl D3
Cyclohexyl D4
69
94
37
41
)
)
)
)
60
40
57
49
3.4. Synthesis of amino acid complexes
for complex 22(Cp⁄Cy) results in the enhancement of the phenyl
protons of the phenylalaninate portion of the complex. Irradiation
of the minor component Cp⁄R methyls results in no such enhance-
ment (Fig. 3). Complexes 7(Cp⁄Ph), 10(Cp⁄Bn), and 17(Cp⁄iPr) exhibit
similar results, indicating that the major component for each
L-phenylalaninate complex is SCSIr. The 1H NMR spectrum of
17(Cp⁄iPr) displays markedly different splitting patterns and chem-
ical shifts for the diastereotopic 2-propyl methyl groups between
the two diastereomers, with the major component having greater
steric clash due to placement of the phenyl ring up and near the
Cp⁄ portion of the molecule (Fig. 4). For the CpiPr complexes, the
diastereotopic methyl groups display as a pair of overlapping dou-
blets. In some cases, the overlap of the major and minor isomer
peaks for these resonances lead to a complex signal from which
it is difficult to extract coupling information.
Complexes 5–23 were synthesized in a fashion similar to other
piano stool amino acid complexes reported previously.[22,23,36–
40] All complexes adopt the three-legged piano-stool (half-sand-
wich) configuration, as expected. As is the case with Cp⁄Ir amino
acid complexes previously reported, the iridium atom becomes a
pseudo-tetrahedral chiral center upon coordination of the amino
acid, resulting in diastereomers that differ at configuration of the
metal when using an enantiomerically pure amino acid. Since
homo chiral amino acids were used, these complexes will only dif-
fer in configuration at the metal center. In the case of glycine, two
enantiomers form. The diastereomers formed from enantiomeri-
cally pure amino acids are distinguishable by both 1H and 13C
NMR spectroscopies. Yields and isolated diastereomer ratios are
shown in Table 3.
In the case of alkylated amino acids with only one hydrogen on
the nitrogen, such as L-proline, the nitrogen becomes a chiral site
upon chelation as well, leading to the possibility of SIrSCSN, RIrSCSN,
RIrSCRN, and SIrSCRN configurations. It was found that, in the smaller
ring systems of 8(Cp⁄Ph), 11(Cp⁄Bn), 12(Cp⁄Bn), 18(Cp⁄iPr), and
23(Cp⁄Cy), the chirality of the nitrogen is the same as the chirality
of the carbon center, leading to the formation of RIrSCSN and SIrSCSN
configurations for the complexes. The major components in each
case are SIrSCSN, which is determined by measuring the NOE inter-
action between the N-CH2 groups and the Cp⁄R methyls. The minor
component, though difficult to observe, displays an interaction
between the Cp⁄ methyls and the amine proton, Fig. 5. These con-
The diastereomer ratios obtained for these modified complexes
are similar to what has been reported for the Cp⁄ variants. Diaste-
reomer selectivity is dependent for the most part on the amino acid
ligand used, with ring-based systems such as L-proline and L-azeti-
dine-2-carboxylic acid having the highest selectivity, whereas the
less bulky L-alanine produces the least selectivity. The Cp⁄R variant
seems to have very little effect on the diastereomer ratio compared
with (g
5-Me5C5)Ir(aa)Cl complexes presumably because a large R
group such as benzyl or cyclohexyl on the ring may rotate away
from the bulkiest portion of the amino acid ligand (see crystal
structure discussion below.) These ratios remained unchanged
over time in solution, as observed by NMR spectroscopy.
The major configurations of these complexes, (SC, SIr) or (SC, RIr)
are the same as those reported for unmodified (
figurations are again what has been shown for (
complexes.
g
5-Me5C5)Ir(aa)Cl
g
5-Me5C5)Ir(aa)-Cl
The larger ring system of L-piperidine-2-carboxylate displays
the opposite chirality on the nitrogen, with configurations of SIrSC-
RN and RIrSCRN. NOE experiments showed that the major
complexes, and was determined through NOE experiments. For
example, irradiation of the Cp⁄R methyls of the major component
Fig. 1. 1H NMR spectrum of 3(Cp⁄iPr).

130
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
Fig. 2. Thermal ellipsoid plots of the asymmetric units of complexes 2(Cp⁄Bn), 3(Cp⁄iPr), and 4(Cp⁄Cy). Hydrogens omitted for clarity. Ellipsoids shown at 50%.
Table 3
Irraditated
Yields and diastereomeric ratios of isolated complexes.
AA(Compound #)
Yield% Ratio AA(Compound #) Yield% Ratio
Cp⁄Ph
Cp⁄Bn
*
Ir
Ala (5)
Phengly (6)
Phe (7)
Pro (8)
Pip (9)
52
43
94
94
94
54
68
55
89
69
Phe (10)
Pro (11)
Aze (12)
Pip (13)
93
77
98
83
69
85
69
88
Cl
NH2
O
*
Enhanced
H
Cp⁄iPr
Gly (14)
N,N-dimeth-Gly (15) 74
Ala (16)
Phe (17)
Pro (18)
Cp⁄Cy
O
88
na
na
50
71
83
Gly (19)
Ala (20)
Phe (21)
Phengly (22)
Pro (23)
59
80
85
80
69
na
56
68
58
88
68
82
71
Irraditated
Ir
H2N
*
Cl
O
component has an interaction between the amine proton and the
Cp⁄R methyls, precisely the opposite from the smaller ring systems.
The minor component displays interactions between the alpha car-
bon proton and the Cp⁄R methyls. NOE interactions are displayed in
Fig. 6.
O
*
H
No enhancement
3.5. Crystal structures
Fig. 3. NOE effects for complex 22(Cp⁄Cy), displaying interaction of Cp⁄Cy methyls
and the phenyl portion of phenylalaninate.
None of the NOE experiments show an interaction between the
R group on the Cp⁄R ligand and the amino acid ligand. This leads to
the conclusion that the R group’s steric bulk forces it away from the
sterically demanding amino acid and chloride ligands. This is seen
not only in a lack of NOE interactions, but in the solid state as well.
In the case of complexes formed from 1(Cp⁄Ph), 3(Cp⁄iPr), and 4(Cp⁄-
Cy) the R group of the Cp⁄R moiety is forced in-between the chlorine
and nitrogen to relieve the steric interaction. Complexes formed
from 2 with the Cp⁄Bn ligand adopt a configuration similar to Cp⁄
complexes, with the benzyl portion having freedom of rotation

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
131
Fig. 4. Splitting pattern differences between the 2-propyl groups of the isomers of complex 17(Cp⁄iPr).
the NMR section. The chloro-bridged dimer complex 3 with the
same Cp⁄iPr ligand lacks this spectral feature, indicating that inter-
actions with the amino acid ligand are what is inducing this hin-
dered rotation.
Enhanced
Irraditated
Comparison of the bond lengths and angles of the L-prolinate
based complexes shows a significant lengthening of the Ir–Cl bond
in the case of 8(Cp⁄Ph) compared to 11(Cp⁄Bn) and 18(Cp⁄iPr). Dis-
tances from the centroid to the iridium are nearly identical, with
complex 8(Cp⁄Ph) being shorter by 0.01 angstroms. Complexes
11(Cp⁄Bn) and 18(Cp⁄iPr) are nearly identical to the unmodified
complex, which has a distance of 1.766 Å. Ir-N bonds are also
nearly identical between 8(Cp⁄Ph), 11(Cp⁄Bn), and 18(Cp⁄iPr), but
shorter than the unmodified complex (2.140 Å). Ir–O bond lengths
are similar between the phenyl and benzyl complexes of 8 and 11,
but the 2-propyl based 18 has a lengthening of more than 0.3 Å. All
Ir–O bonds in these complexes are significantly longer than the Cp⁄
complex (2.086 Å). Bond lengths and angles are summarized in
Table 4.
Enhanced
H
*
Ir
H
H
*
Ir
Irraditated
*
Cl
H
Cl
N
N
*
O
O
*
H
*
H
O
O
Fig. 5. Observed NOE enhancement of irradiated protons, showing absolute
configuration of complex 8(Cp⁄Ph).
Unlike the crystal structures obtained of the (g
5-Me5C5)Ir(Pro)Cl
complex by Beck and co-workers [41] only one diastereomer is
present in the lattice in the cases of 8(Cp⁄Ph), 11(Cp⁄Bn), and 18(Cp⁄-
iPr) (see Fig. 7). The water molecule found in the Beck structure that
hydrogen bonds between the two diastereomers is not present in
any of these structures. However, a hydrogen-bonding network
still persists, being formed through the amine proton and the car-
bonyl oxygen of a symmetry related complex in the lattice (see
Fig. 8) such as that found in complex 18. The network is also seen
in complexes 12(Cp⁄Bn) and 13(Cp⁄Bn), which also show one diaste-
reomer in the crystal lattice. The hydrogen bond lengths vary
slightly between the 5 complexes, with the L-prolinate based com-
plexes have the shortest lengths of 2.050, 2.027, and 1.935 Å for
8(Cp⁄Ph), 11(Cp⁄Bn), and 18(Cp⁄iPr), respectively. Complexes 12(Cp⁄-
Ph) and 13(Cp⁄Ph) have slightly longer bonds of 2.166 and 2.139 Å,
respectively.
Enhanced
Enhanced
*
Irradiated
Ir
H
Cl
H
Ir *
Cl
N
O
H
O
N
*
Irradiated
*
O
*
H
O
Fig. 6. NOE of complex 9(Cp⁄Ph), showing enhancement of Cp⁄Ph methyls with the
amine proton or H is irradiated.
a
Because only a single diastereomer is present in the crystal
structure for complexes 8(Cp⁄Ph), 11(Cp⁄Bn), 12(Cp⁄Bn), 13(Cp⁄Bn),
and 18(Cp⁄iPr), yet there is an observed second diastereomer
observed in the NMR spectra. Finding a single diastereomer in a
solid state structure is not uncommon and may simply reflects that
the compounds pack more efficiently as a single diastereomer. No
placing the phenyl group in a position anti with respect to the
metal. Complex 14 with the Cp⁄iPr ligand displays hindered rota-
tion in the proton NMR spectra yielding peaks as described in

132
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
Table 4
Table 6
Selected bond lengths and angles of complexes 8(Cp⁄Ph), 11(Cp⁄Bn), and 18(Cp⁄iPr).
Asymmetric transfer hydrogenationa of acetophenone.
8(Cp⁄Ph
)
11(Cp⁄Bn
)
18(Cp⁄iPr
)
Entry
Complex
Ketone
T (h)
Conv%c
ee%d
Conf.e
Ir–Cl
Ir–O
Ir–N
Ir–W
C5–C10
Cl–Ir–O
Cl–Ir–N
O–Ir–N
Cl–Ir–W⁄
O–Ir–W
N–Ir–W
2.434(4)
2.12(1)
2.12(1)
1.755
1.50(2)
86.9(3)
83.4(3)
78.4(4)
125.03
129.91
135.72
2.3999(7)
2.111(2)
2.127(2)
1.767
1.490(5)
86.92(7)
84.35(7)
77.44(9)
127.08
2.416(1)
2.155(3)
2.129(3)
1.76
1.513(6)
86.14(8)
86.34(9)
76.5(1)
125.75
129.58
134.95
9
10
11
12
13
14
15
16
17
18
19
20
8a
8b
21
25
21
25
21
24.5
21
25
48
50
13
81
14
99
11
75
26
85
38
84
5
0
5
6
10
4
70
20
4
17
46
75
0
Na
R
R
R
R
R
R
R
S
11a
11b
18a
O
b
18
23a
23b
12b
9b
126.91
136.38
25.5
45
48
S
S
Na
13b
15a
W = Centroid of pentamethylcyclopentadienyl ligand.
a
Performed in water at 40 °C, substrate/catalyst/formate ratios were 1/.1/5 with
2 mL of water and no inert protection.
b
Performed in 2-propanol at 40 °C, substrate/catalyst/base ratio of 1/.1/.2.
Determined by GC.
Determined by chiral GC.
Comparison against literature values.
great pains were taken to screen other crystals for ones that would
contain the other diastereomer. Fully alkylated amino acids such as
N-methyl-L-proline produce exclusively one diastereomer in solu-
tion, as reported by Carmona et al. [36].
c
d
e
The complexes are soluble in water, though to less of a degree
as the hydrophobicity of the Cp⁄R group is increased, with Cp⁄iPr
>
Cp⁄Ph > Cp⁄Bn > Cp⁄Cy being the trend. Potential chloride disassocia-
tion and subsequent formation of a mono-aqua cation as well as
the hydrogen bonding interactions between the NH and CO groups
assists in this solubility. Mono-aqua cation formation is commonly
seen in similar piano stool complexes [9,12,42,43].
rate of reduction. Of the complexes 8(Cp⁄Ph), 11(Cp⁄Bn), 18(Cp⁄iPr),
and 23(Cp⁄Cy), 11(Cp⁄Bn) had the highest selectivity, though at a
reduced rate of reaction. The cyclohexyl and isopropyl based sys-
tems had the same selectivity, though complex 23(Cp⁄Cy) reached
only 36% conversion at 44 h. The phenyl based system reduces
both rate of reduction and selectivity. The reduction in rate is most
likely brought about through the steric hindrance of the Cp⁄R
group. The mechanism implied by Noyori goes through a six mem-
bered transition state formed through the metal hydride, amine
proton, and the C@O of the substrate.[25] The positioning of the
R groups on the Cp⁄ ring conflicts with this, with the phenyl system
being the most rigid, leading to reduced conversion. The loss in
selectivity can be justified through a similar process. The smaller
ring system of complex 12(Cp⁄Bn) produces an ee% of 92 with a
conversion of 40% at 44 h. Most interesting to note is that when
the reaction is performed with complex 18(Cp⁄iPr) in 2-propanol
only one percent conversion is witnessed after 27 h, even under
inert conditions. The selectivity is also decreased by 10%. A sum-
mary of the reduction of pinacolone is presented in Table 5.
Acetophenone reduction also gains a rate enhancement when
performed in water, as seen prior by Xiao [46]. The differences in
percent conversion at similar times of 21 and 25 h is staggering,
for example complex 18(Cp⁄iPr) reaches full conversion is 21 h in
water, with the 2-propanol-based reaction only reaching 11 per-
cent in 24.5 h. In the case of the L-prolinate based variants the
trend observed with the pinacolone reduction is retained, with
the sterically hindered variants of 8(Cp⁄Ph) and 23(Cp⁄Cy) having
the lowest conversion. Selectivity in these L-prolinate complexes
is low, generally below 20 percent. Interestingly, while performing
the reaction in 2-propanol reduced selectivity in the case of pina-
colone, the trend is reversed for the aromatic acetophenone. Com-
plex 18(Cp⁄iPr) goes from a near racemic mixture in water to an ee%
of 70 percent in 2-propanol. Of the other variants tested, the com-
plex 13(Cp⁄Bn), had the highest selectivity of 75, in 2-propanol.
Complex 15(Cp⁄iPr), containing a fully methylated amine, reached
5 percent conversion at 48 h. This is interesting since the rate
determining step in the classic mechanism is the concerted trans-
fer of the hydride and hydrogen to the ketone. Since conversion
still takes place with a methylated ligand, the hydrogen source
must be solvent itself, not an amine proton. A step-wise mecha-
nism, which has been presented by several groups prior to this
study, accounts for the reduction when no amine protons are pres-
ent [9,47,48]. A summary of the reduction of acetophenone is dis-
played in Table 6.
3.6. Asymmetric transfer hydrogenation using amino acid catalysts
Asymmetric transfer hydrogenation (ATH) of both aliphatic and
aromatic ketones was performed using complexes 8(Cp⁄Ph), 9(Cp⁄-
Ph), 11(Cp⁄Bn), 12(Cp⁄Bn), 13(Cp⁄Bn), 15(Cp⁄iPr), 18(Cp⁄iPr), 23(Cp⁄Cy).
Prior work has shown that the ring based systems are the most
selective, at least in the case of aromatic substrates [22,23,44,45].
This is due to only one active hydride complex being formed under
ATH conditions. The second diastereomer places the proton and
hydride at too great of a distance to reduce the ketone substrate.
The L-prolinate, L-piperidine-2-carboxylate, and L-azetidine-2-
carboxylate variants were tested for the catalytic reduction of
pinacolone and acetophenone to 3,3-dimethylbutan-2-ol and 1-
phenylethan-1-ol, respectively. The reactions were carried out in
both water with sodium formate and 2-propanol with sodium
hydroxide as base. In the case of water-based reactions the sub-
strate/catalyst/formate ratios were 1/.1/5 with 2 mL of water and
no inert protection. The 2-propanol based reactions have a sub-
strate/catalyst/base ratio of 1/.1/.2 and must be conducted under
inert atmosphere conditions.
The aliphatic substrate pinacolone reduction proceeds best in
aqueous media, in regards to both enantiomeric selectivity and
Table 5
Asymmetric transfer hydrogenationa of pinacolone.
Entry
Complex
Ketone
T (h)
Conv%c
ee%d
Conf.e
1
2
8
44
44
44
27
44
44
50
9
32
60
1
36
40
58
63
80
74
65
74
92
43
S
S
S
S
S
S
R
11
18
18
23
12
13
3
4b
5
O
6
7
a
Performed in water at 40 °C, substrate/catalyst/formate ratios were 1/.1/5 with
2 mL of water and no inert protection.
b
Performed in 2-propanol at 40 °C, substrate/catalyst/base ratio of 1/.1/.2.
Determined by GC.
Determined by chiral GC.
Comparison against literature values.
c
d
e

D.M. Morris et al. / Polyhedron 84 (2014) 120–135
133
Table 7
the L-prolinate based variants, though conversion was very low,
and seemingly ceased at 13 h. The L-piperidine-2-carboxylate
based 13(Cp⁄Bn) achieved a conversion and selectivity of 52 and
69, respectively on a similar time frame. 12(Cp⁄Bn), while having
the highest selectivity in the reduction of pinacolone, was the least
selective and the least active, with an ee and conversion of 7 and
43, respectively. This is likely due to the steric constraints from
both the small ring system and the benzyl group conflict with
the highly hindered nature of the 2,2-dimethyl-1-phenylpropan-
1-one (see Table 7).
The chirality of the product is determined primarily by the chi-
rality of the nitrogen. For example, in the case of pinacolone, the L-
prolinate and L-azetidine-2-carboxylate based systems possess SN,
leading to an R product. The larger L-piperidine-2-carboxylate sys-
tems possess an RN, which leads to an S product. This implies a
transition state where the sterically bulky t-butyl portion of pina-
colone is directed away from the bulky Cp⁄ portion of the com-
plexes. In the reduction of acetophenone, selectivity again
corresponds to the chirality of the nitrogen, however, the bulky
portion of acetophenone is directed up toward the Cp⁄ portion of
Asymmetric transfer hydrogenationa of 2,2-dimethyl-1-phenylpropan-1-one.
Entry
Complex
Ketone
T (h)
Conv%c
ee%d
Conf.e
20
21
22
23
24
25
26
27
28
8
13
13
13
43
13
13
13
43
48
4
13
18
2
51
61
70
18
57
67
69
37
43
R
R
R
R
R
S
S
S
R
11
18
18b
23
9
13
13b
12
9
O
17
52
40
7
a
Performed in water at 40 °C, substrate/catalyst/formate ratios were 1/.1/5 with
2 mL of water and no inert protection.
b
Performed in 2-propanol at 40 °C, substrate/catalyst/base ratio of 1/.1/.2.
Determined by GC.
Determined by chiral GC.
Comparison against literature values.
c
d
e
The reduction of 2,2-dimethyl-1-phenylpropan-1-one achieved
the best selectivity when performed in water, similar to pinaco-
lone. Again, complex 18(Cp⁄iPr) had the best selectivity between
the molecule, which coincides with the CH–p interaction described
Fig. 7. Crystal structures of 18, 8 and 11. All hydrogens except the amine hydrogen are omitted. Ellipsoids shown at 50% probability.
Fig. 8. Extended lattice showing the intermolecular hydrogen-bonding network of complex 18.

134
D.M. Morris et al. / Polyhedron 84 (2014) 120–135
by Noyori and co-workers [25] The loss of selectivity with com-
plexes 8(Cp⁄Ph), 11(Cp⁄Bn), and 23(Cp⁄Cy) can be explained by a dis-
ruption of this effect, as compared to complex 18(Cp⁄iPr).
Interestingly, in the reduction of 2,2-dimethyl-1-phenylpropan-1-
MOL files and InChiKeys of the most important compounds
described in this article.
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Ir(L-azetidine-2-carboxylate)Cl], [(
dine-2-carboxylate)Cl], and [(
5-C5Me4iPr)Ir(L-prolinate)Cl] are
the first structures of iridium complexes containing Cp⁄Bn and Cp⁄iPr
g
5-C5Me4CH2C6H5)Ir(L-prolinate)Cl], [(
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assistance with resolving several crystal structures. We thank the
National Science Foundation for funds (CHE-01311288) for the
purchase of the Oxford Diffraction XCalibur2 single-crystal diffrac-
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funds for supplies and the Hamilton Company for a generous grant
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Appendix A. Supplementary data
CCDC 996090–996097 contain the supplementary crystallo-
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can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
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