Chiral Ir(I) and Ir(III) complexes [Ir{(R)-binap} (1, 2-diamine)]Cl and trans-[Ir(H)2{(R)-binap} (1, 2-diamine)]Cl: Synthesis and catalytic applications

Article abstract of DOI:10.1080/00958971003746108

The P2, N2-coordinated iridium(I) chelate complexes [Ir{(R)-binap}(1, 2-diamine)]Cl, where (R)-binap = (R)-2, 2'-bis(diphenylphosphino)-1, 1'-binaphthyl and 1, 2-diamine = H₂NCMe₂CMe ₂NH₂ (tmen) (1), (1R, 2R)-H<

Full text of DOI:10.1080/00958971003746108

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Chiral Ir(I) and Ir(III) complexes [Ir{(R)-
binap} (1,2-diamine)]Cl and trans-
[Ir(H)2{(R)-binap} (1,2-diamine)]Cl:
synthesis and catalytic applications
Lutz Dahlenburg a , Dagmar Kramer a & Frank W. Heinemann a
a Department Chemie und Pharmazie , Friedrich-Alexander-
Universität Erlangen-Nürnberg , Gerlandstraße 1, D-91058
Erlangen, Germany
Published online: 13 Apr 2010.
To cite this article: Lutz Dahlenburg , Dagmar Kramer & Frank W. Heinemann (2010) Chiral Ir(I)
and Ir(III) complexes [Ir{(R)-binap} (1,2-diamine)]Cl and trans-[Ir(H)2{(R)-binap} (1,2-diamine)]Cl:
synthesis and catalytic applications, Journal of Coordination Chemistry, 63:14-16, 2673-2684, DOI:
10.1080/00958971003746108
To link to this article: http://dx.doi.org/10.1080/00958971003746108
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Journal of Coordination Chemistry
Vol. 63, Nos. 14–16, 20 July–20 August 2010, 2673–2684
Chiral Ir(I) and Ir(III) complexes [Ir{(R)-binap}
(1,2-diamine)]Cl and trans-[Ir(H)2{(R)-binap}
(1,2-diamine)]Cl: synthesis and catalytic
applicationsy
LUTZ DAHLENBURG*, DAGMAR KRAMER
and FRANK W. HEINEMANN
Department Chemie und Pharmazie, Friedrich-Alexander-Universitat
Erlangen-Nurnberg, Gerlandstraße 1, D-91058 Erlangen, Germany
(Received 26 January 2010; in final form 23 February 2010)
The P2,N2-coordinated iridium(I) chelate complexes [Ir{(R)-binap}(1,2-diamine)]Cl, where (R)-
and
binap ¼ (R)-2,20-bis(diphenylphosphino)-1,10-binaphthyl
1,2-diamine ¼ H2NCMe2
CMe2NH2 (tmen) (1), (1R,2R)-H2NCH(Ph)CH(Ph)NH2 [(R,R)-dpen] (2), or cyclo-
(1R,2R)-1,2-(H2N)2C6H10 [(R,R)-dach] (3), were formed by treating [{(R)-binap}2Ir2(ꢀ-Cl)2]
with the respective N,N ligand in inert solvents at ambient conditions. They reacted with
methanol in benzene or toluene at reflux producing dihydridoiridium(III) complexes, trans-
[Ir(H)2{(R)-binap}(1,2-diamine)]Cl [1,2-diamine ¼ tmen (4), (R,R)-dpen (5), or (R,R)-dach (6)].
Compounds 4–6 are base-free (albeit rather slow) catalysts for both the transfer hydrogenation
of acetophenone and the hydrogenation of the ketone with molecular hydrogen, giving
(S)-1-phenylethanol with moderate enantioselectivities (eemax : 74%).
A cyclometallated
hydridoiridium(III) complex, characterized as (OC-6-54)-[Ir(H)(Cl){(R,R)-binap}{C6H4-2-
[(R,R)-CH(NH2)CH(Ph)N¼CMe2]-ꢁC1,ꢁNꢂ}] (7) by single-crystal X-ray diffraction, was
identified as one of the products formed from [{(R)-binap}2Ir2(ꢀ-Cl)2] and the (R,R)-dpen
ligand in acetone under hydrogen.
Keywords: Iridium; Nitrogen ligands; Phosphorus ligands; Asymmetric catalysis
1. Introduction
In previous work, we isolated the bis(ꢃ-aminophosphine)-chelated ionic IrIII complex
(OC-6-43)-[Ir(H)(Cl)(Ph2PCH2CH2NH2)2]Cl (scheme 1: I) by combining trans-
[Ir(Cl)(CO)(PPh3)2] with the P,N chelate ligand in refluxing xylenes and obtained the
trans-dihydride (OC-6-22)-[Ir(H)2(Ph2PCH2CH2NH2)2]Cl (II) upon treatment of I with
KOH in isopropanol [1]. Despite their structural resemblance to the isoelectronic P2,N2-
coordinated RuII compounds (OC-6-43)-[Ru(H)(Cl){bis(phosphine)}(1,2-diamine)] and
(OC-6-22)-[Ru(H)2{bis(phosphine)}(1,2-diamine)], which are powerful 4C¼O
*Corresponding author. Email: Lutz.Dahlenburg@chemie.uni-erlangen.de
yDedicated to Professor Rudi van Eldik on the occasion of his 65th birthday in recognition of his outstanding
contributions to the reactivity of inorganic and coordination compounds.
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958971003746108

2674
L. Dahlenburg et al.
Scheme 1. Complexes I–III.
hydrogenation (pre)catalysts [2, 3], the two IrIII-centered cations did not parallel their
neutral RuII equivalents in the ability to catalyze the reduction of ketones by molecular
hydrogen (referred to as ‘‘H2-hydrogenation’’ in the following) but only acted as
catalysts for transfer hydrogenations of the 4C¼O function with alcohols as proton/
hydride donors. Similar to the RuII-catalyzed H2- and transfer hydrogenations, the
presence of a strong base was mandatory for chloridohydrido complex I to be
catalytically active, whereas dihydrido complex II maintained catalysis even in the
absence of the added base and hence was attributed the role of the actual catalyst [1].
Theoretical calculations which used H2PCH2CH2NH2-coordinated molecules as
simplified models showed that both the RuII- and the IrIII-catalyzed hydrogenations
involve weakly solvated amidohydrides trans-[M(H)(solv)(H2P \ NH)(H2P \ NH2]0/þ
and aminodihydrides trans-[M(H)2(H2P \ NH2)2]0/þ as key intermediates. The failure of
the cationic IrIII system to support H2-hydrogenations was traced back to that step
of the catalytic cycle where the H2 molecule has to displace the coordinated solvent
from the amidohydrides to generate amido(dihydrogen) transients, trans-[M(H)(ꢄ2-
H2)(H2P \ NH)(H2P \ NH2]0/þ, which are needed to restore the aminodihydrides
trans-[M(H)2(H2P \ NH2)2]0/þ by proton transfer from the H2 ligand to the amide
function; because of the stronger coordination of the solvent molecule to the cationic
IrIII complex compared to the neutral RuII compound, this substitution reaction turned
out to be significantly endothermic for M ¼ IrIII, but close to thermoneutral for
M ¼ RuII [4].
Chelate ligands of spatial demand greater than that of Ph2PCH2CH2NH2 could
facilitate the decoordination of weakly bound molecules from the IrIII center through
‘‘steric pressure’’ [5] and thereby contribute to easier replacement of solvent by H2 in the
iridium-catalyzed H2-hydrogenations as well. In fact, the chloridohydrido complexes
(OC-6-43)-[Ir(H)(Cl){(R)-binap}(1,2-diamine)]BF4, where (R)-binap ¼ (R)-2,20-bis
(diphenylphosphino)-1,10-binaphthyl and 1,2-diamine ¼ H2NCMe2CMe2NH2 (tmen),
(1R,2R)-H2NCH(Ph)CH(Ph)NH2 [(R,R)-dpen], or cyclo-(1R,2R)-1,2-(H2N)2C6H10
[(R,R)-dach] (scheme 1: IIIaZIIIc), were shown to act as catalysts for the
H2-hydrogenation of acetophenone, if activated by a strong base [6]. This raised the
question as to whether IrIII-centered cationic dihydrido complexes trans-[Ir(H)2{(R)-
binap}(1,2-diamine)]þ would likewise support H2-hydrogenations of ketones, and
whether the close structural relationship of such cations to their catalytically active

Chiral Ir(I) and Ir(III) complexes
2675
neutral RuII equivalents trans-[Ru(H)2{(R)-binap}(1,2-diamine)] [2, 3] would be
favorable for their functioning as 4C¼O hydrogenation catalysts even in the absence
of a base.
In this article, we describe the somewhat elusive synthesis of three ionic trans-
dihydridoiridium(III) complexes [Ir(H)2{(R)-binap}(1,2-diamine)]BF4 and their IrI
precursors [Ir{(R)-binap}(1,2-diamine)]BF4 containing the diamine ligands tmen,
(R,R)-dpen, and (R,R)-dach, and also give a first account of the behavior of the
trans-dihydrides as base-free catalysts for the hydrogenation of acetophenone.
2. Experimental
2.1. General
All manipulations were performed under argon using standard Schlenk techniques.
Solvents were distilled from the appropriate drying agents prior to use. IR: Mattson
Infinity 60 AR. NMR: Bruker DPX 300 (300.1 MHz for 1H, 75.5 MHz for 13C,
and 121.5 MHz for 31P) with SiMe4 as internal or H3PO4 as external standards
(downfield positive) in CD2Cl2 at ambient temperature. Gas chromatography:
Shimadzu GC-17A (FID). Silver tetrafluoroborate and the bis(phosphine) and diamine
ligands (R)-binap, (R,R)-dpen, and (R,R)-dach were used as commercially supplied.
1,10,2,20-Tetramethylethylenediamine (tmen) [7] and [{(R)-binap}2Ir2(ꢀ-Cl)2] [8] were
prepared according to published procedures or slight modifications thereof.
2.2. Preparation and formation of IrI complexes [Ir{(R)-binap}(1,2-diamine)]Cl
2.2.1. Preparation of [Ir{(R)-binap}(tmen)]Cl (1). A solution of 80 mg (0.05 mmol) of
[{(R)-binap}2Ir2(ꢀ-Cl)2] and 44 mg (0.38 mmol) of tmen in 15 mL benzene was stirred at
ambient conditions. The mixture gradually changed from dark red to orange red, and
the product separated within 6 h as a bright red solid which was filtered off, washed
with diethyl ether, and dried under vacuum. Yield: 22 mg (24%). Anal. Calcd for
C50H48ClIrN2P2 (%): C, 62.13; H, 5.01; N, 2.70. Found: C, 62.09; H, 5.07; N, 2.77. 1H
2
NMR: ꢅ 1.17, 1.31 [both s, 6H each, C(CH3)2], 2.19, 4.67 (both br, d, JHꢀH ¼ 11.8 Hz
each, 2H each, NH2), 6.4ꢀ7.8 (m, 32H, aryl H) ppm. 31P{1H} NMR: ꢅ 16.99 (s) ppm.
2.2.2. Formation of [Ir{(R)-binap}{(R,R)-dpen}]Cl (2). Stirring the red suspension
of 237 mg (0.14 mmol) of [{(R)-binap}2Ir2(ꢀ-Cl)2] and 135 mg (0.64 mmol) of the diamine
in 30 mL of benzene for 30 min at room temperature gave a clear orange solution.
An orange solid began to precipitate after an additional 30 min and was collected by
filtration after stirring overnight. 1H and 31P{1H} NMR spectroscopy revealed
the presence of 2 along with trans-[Ir(H)(Cl){(R)-binap}{(R,R)-dpen}]Cl (2ꢁHCl)
in approximate 4 : 1 stoichiometry. 1H NMR: ꢅ ꢀ19.68 (dd, cis-2JP–H ¼ 15.6 and
18.4 Hz, IrH of 2ꢁHCl), 4.32, 4.42 (both br, 2H each, NH2 of 2), 4.77 (m, 2H, CH of 2),
6.4–8.2 (m, 42H, aryl H) ppm. 31P{1H} NMR: ꢅ ꢀ9.40, 0.05 (both d, cis-2JP–P ¼ 22.3 Hz,
2ꢁHCl), 18.00 (s, 2) ppm; relative 31P{1H} intensities 2 : 2ꢁHCl ffi 4 : 1. Comparative
data (CD2Cl2) for authentic trans-[Ir(H)(Cl){(R)-binap}{(R,R)-dpen}]þ (BF4ꢀ salt) [6]:

2676
L. Dahlenburg et al.
ꢅH ꢀ19.81 (dd, cis-2JP–H ¼ 15.9 and 18.0 Hz, IrH) ppm; ꢅP ꢀ9.99, 0.64 (both d,
cis-2JP–P ¼ 22.3 Hz) ppm.
2.2.3. Formation of [Ir{(R)-binap}{(R,R)-dach}]Cl (3). [{(R)-binap}2Ir2(ꢀ-Cl)2]
(431 mg, 0.25 mmol) and 69 mg (0.60 mmol) of (R,R)-dach were suspended in 25 mL
of toluene. Stirring for 30 min at ambient conditions caused the precipitation of a red
1
solid, the H and 31P{1H} NMR spectra of which showed the presence of 3, again
accompanied by trans-[Ir(H)(Cl){(R)-binap}{(R,R)-dach}]Cl (3ꢁHCl) as well as by an
unidentified additional by-product in 3 : 1 : 1 molar ratio. 1H NMR: ꢅ ꢀ20.17
(dd, cis-2JP–H ¼ 15.4 and 18.1 Hz, IrH of 3ꢁHCl), 1.2–1.7 (m, 8H, CH2), 2.81, 3.33
(both br, 2H each, NH2 of 3), 3.52 (m, 2H, CH of 3), 6.2–8.4 (m, 32H, aryl H) ppm.
31P{1H} NMR: ꢅ ꢀ32.16, ꢀ31.65 (both d, cis-2JP–P ¼ 20.0 Hz, unidentified), ꢀ10.36,
ꢀ1.06 (both d, cis-2JP–P ¼ 22.0 Hz, 3ꢁHCl), 16.99 (s, 3) ppm; relative 31P{1H} intensities
3 : 3ꢁHCl: ‘‘unidentified’’ ffi 3 : 1: 1. Comparative data (CD2Cl2) for authentic trans-
[Ir(H)(Cl){(R)-binap}{(R,R)-dach}]þ (BF4ꢀ salt) [6]: ꢅH ꢀ20.35 (dd, cis-2JP–H ¼ 15.5 and
18.2 Hz, IrH) ppm; ꢅP ꢀ10.69, ꢀ1.10 (both d, cis-2JP–P ¼ 22.3 Hz) ppm.
2.3. Preparation of trans-dihydridoiridium(III) complexes
[Ir(H)2{(R)-binap}(1,2-diamine)]Cl
2.3.1. Trans-[Ir(H)2{(R)-binap}(tmen)]Cl (4). A solution of 648 mg (0.38 mmol) of
[{(R)-binap}2Ir2(ꢀ-Cl)2] and 122 mg (1.05 mmol) of tmen in 45 mL benzene was stirred
at ambient temperature for 90 min to initiate the intermediate formation of [Ir{(R)-
binap}(tmen)]Cl, which was subsequently treated with 6 mL of methanol. The mixture
was refluxed for 40 h and then concentrated to a final volume of 10 mL. Dilution with
120 mL of diethyl ether resulted in the precipitation of the product as a yellow
solid which was filtered off, washed with diethyl ether, and dried under vacuum.
Yield: 522 mg (71%). Anal. Calcd for C50H50ClIrN2P2 (%): C, 62.00; H, 5.20; N, 2.89.
1
Found: C, 62.38; H, 5.33; N, 2.59. IR (KBr, cmꢀ1): 1735 (IrH2). H NMR: ꢅ ꢀ6.40
(t, cis-2JP–H ¼ 13.2 Hz, 2H, IrH2), 1.09, 1.29 [both s, 6H each, C(CH3)2], 1.76, 4.89
2
(both br, d, JH–H ¼ 10.7 Hz each, 2H each, NH2), 6.4–7.9 (m, 32H, aryl H) ppm.
31P{1H} NMR: ꢅ 17.63 (s) ppm.
2.3.2. Trans-[Ir(H)2{(R)-binap}{(R,R)-dpen}]Cl (5). [{(R)-binap}2Ir2(ꢀ-Cl)2] (298 mg,
0.17 mmol) and (R,R)-dpen (81 mg, 0.38 mmol) were suspended in 10 mL of toluene.
The mixture was stirred for 3 h at room temperature, then treated with 3 mL of
methanol, and heated at reflux for 20 h. Evaporation under vacuum to 2 mL followed
by the addition of 60 mL of diethyl ether caused 5 to separate from solution as an
off-white solid which was collected, washed with diethyl ether, and dried. Yield: 161 mg
(43%). Anal. Calcd for C58H50ClIrN2P2 (%): C, 65.43; H, 4.73; N, 2.63. Found:
C, 65.54; H, 4.81; N, 2.26. IR (KBr, cmꢀ1): 1719 (IrH2). 1H NMR: ꢅ ꢀ5.67
(t, cis-2JP–H ¼ 12.6 Hz, 2H, IrH2), 4.18 (br, 4H, NH2), 4.56 (m, 2H, CH), 6.4–8.0
(m, 42H, aryl H) ppm. 31P{1H} NMR: ꢅ 18.22 (s) ppm.

Chiral Ir(I) and Ir(III) complexes
2677
2.3.3. Trans-[Ir(H)2{(R)-binap}{(R,R)-dach}]Cl (6). The complex was prepared simi-
lar to the procedure outlined for 4 from 497 mg (0.29 mmol) of [{(R)-binap}2Ir2(ꢀ-Cl)2]
and 92 mg (0.81 mmol) of the diamine in 35 mL of benzene: Stirring at ambient
temperature for 2 h, followed by the addition of 5 mL of methanol and heating under
reflux for 40 h gave a dark red solution which was concentrated to 2 mL. The off-white
product was isolated by adding diethyl ether (150 mL), then washed with diethyl ether
and dried under vacuum. Yield: 273 mg (48%). Anal. Calcd for C50H48ClIrN2P2 (%):
C, 62.13; H, 5.01; N, 2.90. Found: C, 62.23; H, 5.43; N, 3.00. IR (KBr, cmꢀ1): 1722
(IrH2). 1H NMR: ꢅ ꢀ6.41 (t, cis-2JP–H ¼ 12.6 Hz, 2H, IrH2), 1.1–1.8 (m, 8H, CH2), 2.58,
3.09 (both br, 2H each, NH2), 3.68 (m, 2H, CH), 6.3–8.0 (m, 32H, aryl H) ppm. 31P{1H}
NMR: ꢅ 17.87 (s) ppm.
2.4. Isolation of (OC-6-54)-[Ir(H)(Cl){(R,R)-binap}{C6H4-2-[(R,R)-
CH(NH2)CH(Ph)N¼CMe2]-ꢁC1,ꢁNꢂ}] (7)
An acetone solution (15 mL) containing 548 mg (0.32 mmol) of [{(R)-binap}2Ir2(ꢀ-Cl)2]
and 144 mg (0.68 mmol) of the diamine was stirred for 20 h at ambient conditions,
cooled to ꢀ65ꢂC, and exposed to a stream of hydrogen. The mixture was then allowed
to warm to room temperature under hydrogen, treated with 2 mL of methanol, and
heated under reflux for 2 h. Dilution with 25 mL of diethyl ether resulted in deposition
of a pale yellow solid which was washed with diethyl ether and dried under vacuum.
31P{1H} spectroscopy showed predominantly the presence of a species displaying an
AB pattern at ꢅ 5.18 and 5.37 ppm (2JAB ¼ 11.1 Hz), accompanied by minor amounts of
trans-[Ir(H)(Cl){(R)-binap}{(R,R)-dpen}]Cl (ꢅ ꢀ9.41, 0.03; both d, cis-2JP–P ¼ 22.0 Hz;
see Section 2.2.2) and traces of additional unidentified side products. Recrystallization
from CH2Cl2/Et2O afforded the main product as single crystals, identified
by X-ray crystallography (see below) and 1H NMR spectroscopy as (OC-6-54)-
[Ir(H)(Cl){(R,R)-binap}{C6H4-2-[(R,R)-CH(NH2)CH(Ph)N¼CMe2]-ꢁC1,ꢁNꢂ}]
(7).
1H NMR: ꢅ ꢀ20.53 (dd, cis-2JP–H ¼ 11.6 and 19.2 Hz, 1H, IrH), 1.54, 1.86 (both s,
2
3H each, CH3), 3.78, 4.76 (both d, JH–H ¼ 9.3 Hz, 1H each, CH), 4.06 (br, 2H, NH2),
5.7–8.3 (m, 41H, aryl H) ppm.
2.5. General procedure for catalytic 4C¼O hydrogenation
A Schlenk tube equipped with a small magnetic stirring bar was charged with
0.01–0.02 mmol of the iridium catalysts 4–6, dissolved in 10–20 mL of benzene or in
MeOH, EtOH, and i-PrOH, respectively. The required amount of acetophenone
(table 1) was then added and the mixtures were stirred for 5 min at ambient conditions
under argon. In transfer hydrogenations catalyzed by 5 and 6, stirring was continued
for 24 or 36 h at 50ꢂC. In H2-hydrogenations catalyzed by 4–6, the tube was
subsequently inserted into an argon-filled stainless steel autoclave. The autoclave was
pressurized and vented several times with H2 (Messer-Griesheim; 99.999%), and finally
pressurized to 25 or 50 bar and kept at 50ꢂC for 24 h.
At the end of all catalytic runs, the residues remaining after evaporation of the
solvent were diluted with diethyl ether to precipitate the catalyst as a brownish black
solid. The ethereal solutions were decanted and chromatographed on a silica gel column
with diethyl ether as the eluent. Volatile material was distilled off and the mixtures of
the products were analyzed by 1H NMR spectroscopy. Conversions and product

2678
L. Dahlenburg et al.
Table 1. Enantioselective hydrogenation of acetophenone in the presence of 4–6 with s : c ¼ 1000 : 1
at T ¼ 50ꢂC for t ¼ 24 h, except otherwise noted.
Number
Catalyst
Solvent
p(H2) (bar)
% PhCH(OH)Me
TOF (hꢀ1
)
% ee (S)
1
2
3
4
5
6
7
8
9
4
5
5
5
6
6
6
6
5
MeOH
MeOH
CD3OD
i-PrOH
MeOH
EtOH
i-PrOH
C6H6
i-PrOH
MeOH
EtOH
25
25
25
50
50
50
50
14
18
22
12
35
33
58
7
7
8
9
46
44
38
43
50
74
58
38
34
53
25
50
5
15
14
24
3
2
8
25
– (Ar atm.)
– (Ar atm.)
– (Ar atm.)
– (Ar atm.)
5
10
11
12
6a
6b
6b,c
77
64
47
13
7
i-PrOH
as: c ¼ 250 : 1; bs: c ¼ 500 : 1; and ct ¼ 36 h. TOF, turnover frequency.
compositions were determined on the basis of the integrations of the PhC(O)CH3 and
PhCH(OH)CH3 signals. Enantiomeric excesses were measured by GC using a
Chrompack Chirasil Dex CB column.
2.6. X-ray structure determination
The crystal used for the structure analysis of 7 (size 0.28 Â 0.18 Â 0.08 mm3) was grown
from CH2Cl2/Et2O. Diffraction measurements were made at ꢀ123 Æ 2ꢂC on a
Bruker-Nonius Kappa CCD instrument using graphite-monochromated Mo-Kꢂ
˚
radiation (l ¼ 0.71073 A): orientation matrices and unit cell parameters from the
setting angles of 472 centered medium-angle reflections; diffraction data corrected for
absorption by empirical methods [9] (Tmin ¼ 0.501, Tmax ¼ 0.790). The structure
was solved by direct methods and subsequently refined by full-matrix least-squares
on F 2 with allowance for anisotropic thermal motion of all nonhydrogen atoms
employing both the SHELXTL NT [10] and the WinGX [11] package with some of the
relevant programs (SIR-97 [12], SHELXL-97 [13], Ortep-3 [14]) implemented therein.
C61H52ClIrN2P2 (1102.6); orthorhombic, P212121, a ¼ 12.4642(5), b ¼ 17.8904(14),
3
c ¼ 21.2814(9) A, V ¼ 4767.8(5) A , Z ¼ 4, dCalcd ¼ 1.536 g cmꢀ3
,
F(000) ¼ 2224,
˚
˚
ꢀ(Mo-Kꢂ) ¼ 2.967 mmꢀ1; 3.39ꢂ ꢃ ꢆ ꢃ 27.88ꢂ, 62617 reflections collected (ꢀ16 ꢃ h ꢃ
þ16, ꢀ22 ꢃ k ꢃ þ 23, ꢀ27 ꢃ l ꢃ þ 28), 11347 unique (Rint ¼ 0.049); wR2 ¼ 0.065 for
all data and 606 parameters, R1 ¼ 0.0294 for 10377 structure factors
Fo 4 4ꢇ(Fo); weighting scheme applied: w ¼ 1/[ꢇ2(Fo) þ (0.0107P)2 þ 8.656P], where
P ¼ ðFo2 þ 2Fc2Þ=3; absolute structure parameter x ¼ 0.05(5) [15]; largest difference peak
ꢀ3
˚
and hole: 2.668 and ꢀ1.121 e A
.
3. Results and discussion
3.1. Complexes
We recently described several (R)-binap-(1,2-diamine)-coordinated complexes of
rhodium(I), [Rh{(R)-binap}{(R,R)-dpen}]BF4 and the like, which were obtained

Chiral Ir(I) and Ir(III) complexes
2679
without difficulty by combining the cyclooctadiene precursor [(ꢄ4-1,5-C8H12)Rh{(R)-
binap}]BF4 with the required N,N-chelate ligand under an atmosphere of hydrogen [16].
In view of the pronounced tendency of iridium to form metal-hydride bonds, it was
expected that similar hydrogenation of [(ꢄ4-1,5-C8H12)Ir{(R)-binap}]BF4 in the
presence of a chelating 1,2-diamine would lead to dihydridoiridium(III) derivatives,
[Ir(H)2{(R)-binap}(1,2-diamine)]BF4, by oxidative addition of H2 to the initially formed
[Ir{(R)-binap}(1,2-diamine)]BF4 intermediates. However, only mixtures of the products
containing various unidentified hydrido species were obtained, from which no
well-defined compounds could be isolated [6].
Having shown that nucleophilic cleavage of the triply chlorido-bridged diiridium(III)
complex [{(R)-binap}2Ir2(H)2(ꢀ-Cl)3]BF4 by different 1,2-diamines presents a useful
method for the preparation of the mixed-ligand bis(chelates) trans-[Ir(H)(Cl){(R)-
binap}(1,2-diamine)]BF4 (scheme 1: IIIa–IIIc) [6], we examined the corresponding
reaction between the tmen ligand H2NCMe2CMe2NH2 and the doubly bridged
diiridium(I) compound [{(R)-binap}2Ir2(ꢀ-Cl)2] [8]. In benzene or toluene at room
temperature, opening of the chloride bridges by an excess of the diamine nucleophile
occurred smoothly to give [Ir{(R)-binap}(tmen)]Cl (1) which separated directly from
solution and was readily isolated in pure state (scheme 2). Because of the C2 symmetry
1
of the cation, the H NMR spectrum of 1 displays the resonances of the four methyl
groups as pairs of singlets with equal intensity (ꢅ 1.17 and 1.31 ppm), and the four NH2
protons likewise show up as two broad doublets centered at ꢅ 2.19 and 4.67 ppm
(2JH–H ¼ 11.8 Hz).
As expected, similar treatment of [{(R)-binap}2Ir2(ꢀ-Cl)2] with (1R,2R)-
1,2-diphenylethylenediamine and (1R,2R)-1,2-diaminocyclohexane resulted in the
formation of two related P2,N2-coordinated bis(chelates) of IrI, [Ir{(R)-binap}{(R,R)-
dpen}]Cl (2) and [Ir{(R)-binap}{(R,R)-dach}]Cl (3). Unlike 1, however, these complexes
could not be obtained as pure compounds but were invariably contaminated by
hydridic species, two of which could be identified as the chloridohydrido products
trans-[Ir(H)(Cl){(R)-binap}(1,2-diamine)]Cl [1,2-diamine ¼ (R,R)-dpen (2ꢁHCl) or
(R,R)-dach (3ꢁHCl)] by comparison of their 31P{1H} and IrH NMR data with
those of the authentic BFꢀ4 salts IIIb and IIIc [6] depicted in scheme 1. Competing
hydrogen abstraction from the solvent (or from the excess diamine), for which there
is ample precedence in literature, presents the most likely pathway to the
two hydridoiridium(III) complexes observed as unwanted by-products of these
chloride/amine exchange reactions.
Either of the two IrI compounds, [{(R)-binap}2Ir2(ꢀ-Cl)2] and [Ir{(R)-
binap}(tmen)]Cl (1), could be used as the starting material for the synthesis of the
trans-dihydrido complex [Ir(H)2{(R)-binap}(tmen)]Cl (4) which was obtained (1) upon
combination of the chlorido-bridged dimer with the tmen ligand in benzene (to generate
1 as an intermediate) followed by the addition of a few milliliters of methanol and
heating at reflux and (2) by direct methanolysis of preformed 1 in boiling benzene or
toluene solution. Similar treatment of [{(R)-binap}2Ir2(ꢀ-Cl)2], first with (R,R)-dpen or
(R,R)-dach and then with methanol, furnished the trans-dihydrides [Ir(H)2{(R)-
binap}{(R,R)-dpen}]Cl (5) and [Ir(H)2{(R)-binap}{(R,R)-dach}]Cl (6) as two additional
target complexes (scheme 2).
The presence, in molecules 4–6, of two metal-bonded hydrides in trans positions
follows from their spectral data. Thus, the low IR stretching frequencies of the Ir–H
bonds (ca 1720–1735 cmꢀ1) is highly characteristic of the trans-H–M–H fragment and is

2680
L. Dahlenburg et al.
Scheme 2. Preparation of complexes 1–6.
due to the strong mutual trans influence of the hydrido ligands [17]. Further
confirmation of the C2-symmetric coordination geometry sketched in scheme 2 arises
from 31P{1H} singlets (ꢅ ca 18 ppm) and, consistently, from the appearance of the IrH2
1H resonances as cis-P–H-coupled triplets centered around ꢅ ꢀ6 ppm (2JP–H ffi 13 Hz).
Whereas cis-dihydrido complexes are numerous, their trans counterparts are still
rather rare [1, 3h, 18], which is assumed to be a consequence of the high trans influence
of the hydride ligand rendering the trans-H–M–H arrangement less favorable than the
cis-MH2 configuration. We do not know the mechanism of formation of the trans-
dihydrides 4–6 from their in situ generated or isolated precursors 1–3 and methanol, but
note that a related trans-dihydridoiridium(III) compound, [Ir(H)2(C6H5)(PMe3)3], was
previously obtained from the action of the alcohol on [Ir(C6H5)(PMe3)3]. In that case,
oxidative addition of CH3OH to the iridium(I) complex was observed to produce the
trans-hydrido(methoxo) adduct [Ir(H)(OCH3)(C6H5)(PMe3)3] as the first-formed inter-
mediate, which cleanly decomposed to the trans-dihydrido compound and formalde-
hyde by an unusual ꢃ-hydride elimination process not requiring a vacant site cis to the
coordinated methoxide [18c].
Obvious attempts at the preparation of P2,N2-coordinated dihydridoiridium(III)
complexes by oxidative addition of dihydrogen to [{(R)-binap}2Ir2(ꢀ-Cl)2] in the
presence of a chelating diamine remained inconclusive in that mixtures of largely
ill-defined or unwanted products were obtained, some of which were already known.
Thus, the treatment of the bridged dimer in acetone with (R,R)-dpen, followed by
exposure of the solution to an atmosphere of hydrogen at low temperature, gave trans-
[Ir(H)(Cl){(R)-binap}{(R,R)-dpen}]Cl, in addition to traces of unidentified materials
1
and a predominantly formed compound displaying an IrH H doublet of doublets
centered at ꢅ ꢀ20.53 ppm (cis-2JP–H ¼ 11.6 and 19.2 Hz) together with two 31P{1H} AB
multiplets at ꢅ 5.18 and 5.37 ppm (2JAB ¼ 11.1 Hz). Repeated crystallization of the
mixture from dichloromethane/diethyl ether allowed the prevailing product to be
isolated as single crystals. Subsequent X-ray structure analysis revealed that
[Ir(H)(Cl){(R,R)-binap}{C6H4-2-[(R,R)-CH(NH2)CH(Ph)N¼CMe2]-ꢁC1,ꢁNꢂ}] (7) had
been formed by partial displacement of (1R,2R)-H2NCH(Ph)CH(Ph)NH2 through

Chiral Ir(I) and Ir(III) complexes
2681
chloride, orthometallation of one phenyl ring of the diamine backbone, and
condensation of the dangling amino group with Me2CO (scheme 3). As shown in
figure 1, 7 has (OC-6-54) stereochemistry with the metallated phenyl ring and the
hydride ligand cis and the chloride as the weakest trans-bond influencing ligand
Scheme 3. Formation of complex 7.
ꢂ
˚
Figure 1. Molecular structure of 7 in the crystal. Selected bond lengths (A) and angles ( ). Ir1–Cl1, 2.481(1);
Ir1–P1, 2.336(1); Ir1–P2, 2.241(1); Ir1–N1, 2.148(3); Ir1–C47, 2.099(4); Ir1–H1, 1.695 (unrefined). Cl1–Ir1–
P1, 87.40(4); Cl1–Ir1–P2, 101.28(4); Cl1–Ir1–N1, 83.9(1); Cl1–Ir1–C47, 86.7(1); Cl1–Ir1–H1, 176.8; P1–Ir1–
P2, 94.32(4); P1–Ir1–N1, 92.01(9); P1–Ir1–C47, 168.6(1); P1–Ir1–H1, 91.5; P2–Ir1–N1, 172.0(1); P2–Ir1–C47,
96.4(1); P2–Ir1–H1, 75.8; N1–Ir1–C47, 77.6(1); N1–Ir1–H1, 99.2; C47–Ir1–H1, 94.8; Ir1–N1–C45, 110.4(2);
Ir1–C47–C46, 114.9(3); N1–C45–C46, 105.6(3); C45–C46–C47, 115.6(4).

2682
L. Dahlenburg et al.
opposite to the Ir–H. The most prominent structural feature of 7 is the presence of a
five-membered Ir–C–C–C–N metalaheterocycle originating from the insertion of
iridium into one of the ortho-C–H bonds of the phenyl substituent adjacent to the
˚
coordinated NH2 function. The metal-to-carbon distance, 2.099(4) A, is slightly longer
˚
than, but still comparable to, the Ir–C bond length of 2.058(1) A, previously reported
for [(C5Me5)Ir{C6H4-2-[CH(NH2)CH(Ph)N(SO2C6H4Me-p)]-ꢁC1,ꢁNꢂ}] [19], which
represents the only other example of a structurally characterized iridium complex
bearing a cyclometallated dpen ligand [20]. The lengths of the two Irꢀbinap linkages
˚
differ significantly: while the Ir–P distance opposite to the Ir–N bond, 2.241(1) A,
˚
compares favorably with the corresponding values of 2.246–2.262 A measured for other
iridium complexes of binap [6, 8, 21], the Ir–P bond trans to the metallated carbon atom
˚
is long at 2.336(1) A, which thereby reflects the stronger trans influence of the aryl
ligand than that of the nitrogen donor.
3.2. Catalytic hydrogenation of acetophenone
With the standard test substrate acetophenone at an s : c ratio of 1000 : 1, the three
dihydrido complexes 4–6 were inspected for their ability to catalyze enantioselective
4C¼O hydrogenations. In fact, all of them act as catalysts for the asymmetric
hydrogenation of the ketone at 50ꢂC under 25 or 50 bar of H2, slowly producing
(S)-1-phenylethanol with moderate enantioselectivity (eemax : 74%; table 1). Formation
of the product alcohol was observed in the absence of any activating basic additive,
irrespective of whether the reactions were carried out in alcoholic solution (entries 1–7)
or in an aprotic solvent such as benzene (entry 8), which clearly demonstrates that the
three-dihydrido complexes operate as active catalysts.
The observation that hydrogenation of the substrate does proceed, albeit with low
activity, even in benzene, where no competing transfer of Hꢅþ and Hꢅꢀ equivalents
from the solvent to the 4C¼O dipole can occur, points to a reaction pathway involving
slow H2-hydrogenation rather than transfer hydrogenation of the ketone. On the other
hand, acetophenone was also slowly reduced to (S)-1-phenylethanol when the reactions
were carried out with catalysts 5 and 6 at s : c ratios of 250 : 1 or 500 : 1 in alcoholic
media in the absence of hydrogen, confirming that transfer hydrogenation is operative
under these conditions (table 1, entries 9ꢀ12). For an estimation of the extent to
which the two alternative pathways are competitive in alcoholic reaction media, a
solution of acetophenone in CD3OD was exposed to 25 bar of H2 employing 5 as
catalyst (entry 3). The product alcohol obtained from this experiment contained the two
isotopomers PhCH(OD)Me and PhCD(OD)Me in an almost 1 : 1 molar ratio as
1
demonstrated by H and 13C NMR. In principle, the formation of the ꢂ-deuterated
alcohol could be attributed to Dꢅꢀ/Dꢅþ transfer processes to the 4C¼O dipole
from HD or D2 gas, formed on the H2-hydrogenation route by accompanying
metal-assisted isotopic scrambling according to ‘‘H2 þ CD3OD ¼ CD3OH þ HD’’ and
‘‘HD þ CD3OD ¼ CD3OH þ D2’’, i.e., heterolytic activation of the H2 molecule [22].
Prior work [6] with the chloridohydrido precatalysts trans-[Ir(H)(Cl){(R)-binap}
(1,2-diamine)]BF4 (IIIaZIIIc), all of which must be activated by a strong base and
then will exclusively maintain the H2-hydrogenation of acetophenone, has established,
however, that such scrambling of isotopes into the cycle of H2-hydrogenation will
influence the isotopic distribution in the product alcohol only to a minor degree.

Chiral Ir(I) and Ir(III) complexes
2683
From the observed formation of PhCH(OD)Me and PhCD(OD)Me in approximate
1 : 1 stoichiometry it is, hence, inferred that dihydrido complex 5 supports the
H2-hydrogenation and the transfer hydrogenation of acetophenone, in methanol under
H2, at comparable rates.
4. Conclusions
This work has shown that cationic iridium(I) complexes [Ir{(R)-binap}(1,2-diamine)]Cl
bearing chelating N,N-donors tmen, (R,R)-dpen and (R,R)-dach together with the
(R)-binap ligand can be obtained by treatment of [{(R)-binap}2Ir2(ꢀ-Cl)2] with
the required 1,2-diamine in an inert solvent. They react with methanol in refluxing
benzene or toluene to afford trans-dihydridoiridium(III) complexes, [Ir(H)2{(R)-
binap}(1,2-diamine)]Cl, which work ꢀ with moderate enantioselectivity ꢀ as base-free,
albeit rather slow, catalysts for both the H2-hydrogenation and the transfer hydroge-
nation of acetophenone. That the dihydrides described are able to maintain the
H2-hydrogenation pathway in addition to the route of transfer hydrogenation comes up
to our expectation that the spatial demand of the coligands can lower the energy
required for displacing coordinated solvent by dihydrogen from feasible amidohydrido
intermediates, [Ir(H)(solv){(R)-binap}(HN\NH2)]þ [4], through steric pressure.
Supplementary material
Crystallographic data for the structure reported in this article have been deposited at
the Cambridge Crystallographic Data Centre and allocated the deposition number
CCDC 761553. Copies of this information can be had free of charge from The Director,
CCD, 12 Union Road, Cambridge, CB2 IEZ, UK (Fax: þ44-1223-336033; Email:
deposit@ccdc.com.ac.uk or www: http://www.ccdc.com.ac.uk).
Acknowledgments
Support of this work by the Deutsche Forschungsgemeinschaft (Bonn, SFB 583) is
gratefully acknowledged. We are also indebted to Ms S. Hoffmann and Mr
P. Bakatselos for their skillful assistance.
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