Iridium complexes with chiral and achiral β-aminophosphane ligands: Catalysts for >C=O hydrogenation and H/D exchange involving both homo-and heterolytic H2 activation

FULL PAPER

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands:

Catalysts for ϾC

؍

O Hydrogenation and H/D Exchange Involving both Homo-

and Heterolytic H₂Activation^[‡]

Lutz Dahlenburg*^[a]and Rainer Götz^[a]

Dedicated to the memory of Professor Dieter Sellmann, who has shed much light!

Keywords: Chirality / Hydrogenations / Isotopic exchange / Iridium

Chiral and achiral P,N-chelated Ir^Icomplexes of the general

type [(COD)Ir(PʝNR¹R²)]BF₄, where COD = η⁴-1,5-C₈H₁₂

systems

[(COD)Ir(PʝNHR)]BF₄−KOH

(PʝNHR

=

Ph₂PCH₂CMe₂NH₂, 2-Ph₂PC₆H₄NHMe). The ability of both

the cationic β-amino- and the neutral β-amidophosphane Ir^I

complexes to undergo oxidative H₂addition and the observa-

tion of H₂/D⁺as well as H₂/D₂exchange processes during

and PʝNR¹R²

=

(1R,2R)-, (1S,2S)-, or (1R,2S)-

Ph₂PC¹H(Ph)C²H(Me)NR¹R²(NR¹R²

NH₂, NHMe,

NHCH₂Ph, NHCHMe₂, NMe₂), Ph₂PCH₂CR₂NH₂(R = H,

=

Me), or 2-Ph₂PC₆H₄NHMe, have been prepared by treating catalysis provided evidence for a mechanism involving re-

[Ir(COD)₂]BF₄with the required β-aminophosphane in THF.

The monolithiated ligands Ph₂PCH₂CMe₂N(Li)H and 2-

Ph₂PC₆H₄N(Li)Me interacted with [{(COD)Ir(µ-Cl)}₂] to give

the neutral alkyl- and arylamido compounds [(COD)-

Ir(Ph₂PCH₂CMe₂NH)] and [(COD)Ir(2-Ph₂PC₆H₄NMe)]. All

Ir^Icomplexes [(COD)Ir(PʝNR¹R²)]BF₄acted as catalysts for

versible ‘‘[Ir^III(H)₂−PʝNHR]⁺[(η²-H₂)−Ir^III(H)−PʝNR]⁺’’

o

proton-to-hydride transfer and heterolytic H₂cleavage on

amino−dihydride and amido−dihydrogen−monohydride tau-

tomers. The crystal structures of [(COD)Ir{(1S,2S)-

Ph₂PCH(Ph)CH(Me)NHCH₂Ph}]BF₄·2THF, [(COD)Ir{1R,2S-

Ph₂PCH(Ph)CH(Me)NHMe}]BF₄·THF, and the orthometal-

the direct hydrogenation of alkyl aryl ketones to the corres- ated 18e Ir^Icomplex [(COD)Ir{(1R,2S)-Ph₂PCH(C₆H₄-o)-

ponding 1-phenylalkanols, if combined with an alkaline or

amine base in methanol under H₂(10−50 bar) between 25

and 50 °C. The reaction occurred with modest to moderate

CH(Me)NHCHMe₂}], which resulted from treatment of

[(COD)Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)NHCHMe₂}]BF₄with

excess KOH, have been determined by single crystal X-ray

enantioselectivity (ca. 20−75% ee) if chelate complexes bear- diffraction studies.

ing the various optically active β-aminophosphanes were

used as catalysts. The base-free amido complexes [(COD)-

( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,

Ir(PʝNR)] displayed similar catalytic activity to the combined

Germany, 2004)

Introduction

been shown to be a key step involved in the catalytic cycle.

From the latter, H^δϪ/H^δϩequivalents are transferred simul-

taneously to the ketonic substrate once the carbonyl group

has come into close contact with the second coordination

sphere of the catalyst through an unconventional

RuϪH^δϪ···ϾC^δϩϭO^δϪ···H^δϩϪN ‘‘metalϪligand bifunc-

tional’’ interaction.^[2,3,4]

Metal complexes containing both P and N donor ligands

have been dominating the field of homogeneous catalytic

hydrogenation of organic carbonyl compounds for several

years. In particular, Noyori’s ruthenium complexes

[RuCl₂{bis(phosphane)}(1,2-diamine)] have been found to

be excellent catalysts for the enantioselective reduction, by

H₂, of simple ketones if activated by an excess of strong

base.^[1]Intramolecular heterolytic H₂splitting across the

polar metalϪamide bond of initially formed amine-amido

hydrido complexes, [RuH(PʝP)(HNʝNH₂)], to reversibly

give diamine dihydrides, [RuH₂(PʝP)(H₂NʝNH₂)], has

A different type of a highly enantioselective ϾCϭO

hydrogenation catalyst is exemplified by Zhang’s

RhϪPennPhos system, made up from in situ generated

[(COD)Rh{(R,S,R,S)-Me-PennPhos}]Cl and a weakly co-

ordinating base of moderate strength, such as 2,6-lutidine

[‘‘(R,S,R,S)-Me-PennPhos’’ denotes P,PЈ-1,2-phenylene-

bis{(1R,2S,4R,5S)-2,5-dimethyl-7-phosphabicyclo[2.2.1]-

heptane}].^[5]Zhang’s catalyst is believed to support the

homogeneous hydrogenation of ketones following the

classic SchrockϪOsborn pathway,^[6]i.e., homolytic scission

of the H₂molecule by oxidative addition with subsequent

[‡]

Functional Phosphanes, XIII. Part XII: Ref.^[7b]

.

[a]

Institut für Anorganische Chemie der Universität Erlangen-

Nürnberg,

Egerlandstrasse 1, 91058 Erlangen, Germany

Fax: (internat.) ϩ49-9313-85-27387

E-mail: dahlenburg@chemie.uni-erlangen.de

888

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI: 10.1002/ejic.200300503

Eur. J. Inorg. Chem. 2004, 888Ϫ905

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

ϾCϭO/RhϪH insertion to produce an alkoxo hydrido rho- Beck and Nagel^[13][Scheme 1, reaction (1)]. (Ϫ)-(2S,3R)-cis-

dium() complex, in which the remaining hydride is trans 1-benzyl-2-methyl-3-phenylaziridine analogously afforded

to the alkoxo ligand so that reductive elimination of the (ϩ)-(1S,2S)-Ph₂PCH(Ph)CH(Me)NHCH₂Ph [(S,S)-3]. The

product alcohol cannot easily occur. The authors specu- required N-benzylaziridine had earlier been synthesized

lated that the key function of the basic additive is to depro- from (Ϫ)-norephedrine by consecutive reactions with PCl₅,

tonate the RhϪH bond forming baseH^ϩas the conjugate benzaldehyde, and sodium borohydride^[14]but was also re-

acid, which in turn cleaves the RhϪalkoxo function by pro- adily accessible by alkylating the corresponding N-unsubsti-

tonation.^[5]

tuted aziridine with nBuLi/benzyl chloride [Scheme 1, reac-

Based on this background, our recent activities have fo- tion (2)]. The (Ϫ)-(2S,3R)-cis- and (ϩ)-(2S,3S)-trans-1-iso-

cussed on the catalytic potential in asymmetric ϾCϭO propyl-2-methyl-3-phenylaziridine isomers were obtained

hydrogenation of a class of optically active β-aminophos- from (Ϫ)-N-isopropylnorephedrine^[15]by the Gabriel

phane complexes of Ir^Iand Rh^I, [(COD)M{Ph₂PCH- method^[9]or by reaction with the Horner reagent PPh₃/

[11a]

(Ph)CH(Me)NHR}]BF₄(COD ϭ η⁴-1,5-C₈H₁₂; R ϭ H, Br₂

and nucleophilically opened with Ph₂PH/F₃B·OEt₂

alkyl), having a chelated d⁸metal center (as found in to furnish (ϩ)-(1S,2S)-Ph₂PCH(Ph)CH(Me)NHCHMe₂

Zhang’s catalyst) embedded in a P,N-dominated coordi- [(S,S)-4] and the corresponding (Ϫ)-(1R,2S) diastereomer

nation environment (which is an important characteristic of (R,S)-4 [Scheme 1, reaction (3)]. Conversion of (Ϫ)-N-

the Noyori systems).^[7a,7b]An important further aspect of methylephedrine with methanesulfonyl chloride to the N,N-

our work with these complexes arose from our interest in dimethylaziridinium salt,^[16]followed by treatment of the

establishing whether the dihydrogen molecule is activated latter with Ph₂PH/NEt₃, cleanly afforded the N,N-dialkyl-

during catalysis by homolytic or heterolytic HϪH bond ated P,N ligand (Ϫ)-(1R,2S)-Ph₂PCH(Ph)CH(Me)NMe₂

breaking.^[7b]Since it is well known that MϪH derivatives [(R,S)-5 Scheme 1, reaction (4)]. Additional β-aminophos-

of iridium, especially of Ir^III, are generally more stable and, phanes used in this study included the known achiral com-

hence, more readily accessible than those of rhodium, it has pounds Ph₂PCH₂CH₂NH₂(6),^[17]and 2-Ph₂PC₆H₄NHMe

primarily been the family of iridium complexes that has (7)^[18]and, as a new member of this family of ligands,

been studied in detail up to now, notwithstanding a single Ph₂PCH₂CMe₂NH₂(8) which resulted in the usual fashion

observation that the Rh-based catalysts could be somewhat from ring-opening of 2,2-dimethylaziridine, itself made

more selective than their iridium homologues (see below). from

Additional justification for the choice of aminophosphane- method^[10,19][Scheme 1, reaction (5)].

coordinated iridium complexes as potential ϾCϭO hydro- Similar to the procedures previously employed for

2-amino-2-methylpropanol

by

the

Wenker

genation catalysts arises from the observation that in situ the preparation of (Ϫ)-[(COD)Ir{(1S,2S)-Ph₂PCH(Ph)-

systems composed of [{(COD)Ir(µ-Cl)}₂] or [Ir(COD)₂]BF₄CH(Me)NH₂}]BF₄[Ir^ϩ-(S,S)-1] and [(COD)M{(1R,2R)-

and 1,2-diphenylethylene-based chiral diamines can indeed Ph₂PCH(Ph)CH(Me)NHMe}]BF₄[M ϭ Rh: Rh^ϩ-(R,R)-2;

catalyze the asymmetric reduction of ketones and α-keto M ϭ Ir: Ir^ϩ-(R,R)-2],^[7a]the new optically active chelate

esters with reasonable enantioselectivities.^[8]

complexes

[(COD)Ir{(1S,2S)-Ph₂PCH(Ph)CH(Me)-

NHR}]BF₄[R ϭ CH₂Ph: Ir^ϩ-(S,S)-3; R ϭ CHMe₂: Ir^ϩ-

(S,S)-4] and [(COD)Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)-

NR¹R²}]BF₄[R¹ϭ H, R²ϭ Me: Ir^ϩ-(R,S)-2; R¹ϭ H,

R²ϭ CHMe₂: Ir^ϩ-(R,S)-4; R¹ϭ R²ϭ Me: Ir^ϩ-(R,S)-5] as

Results

Synthesis and Characterization of Ligands and Complexes

well

as

their

achiral

analogues

[(COD)Ir-

In earlier work^[7a]we have worked out several useful pro- (Ph₂PCH₂CR₂NH₂)]BF₄(R ϭ H: Ir^ϩ-6, R ϭ Me: Ir^ϩ-8)

cedures for the preparation of various optically active bi- and [(COD)Ir(2-Ph₂PC₆H₄NHMe)]BF₄(Ir^ϩ-7) were iso-

dentate β-aminophosphanes, starting from commercially lated in high yield (Ͼ80%) from ligand exchange reactions

available (nor)ephedrine and pseudoephedrine dia- between [Ir(COD)₂]BF₄and equimolar quantities of the

stereomers. In the first step of the syntheses, the different corresponding β-aminophosphane in THF (Scheme 2).

β-amino alcohols were stereospecifically converted into cis

The monolithiated ligands 2-Ph₂PC₆H₄N(Li)Me and

or trans aziridines using established synthetic organic Ph₂PCH₂CMe₂N(Li)H interacted with [{(COD)Ir(µ-Cl)}₂]

methods.^[9,10,11,12]Transformation of the aziridines into the in hydrocarbon solution to give the neutral aryl- and alkyl-

desired P,N ligands was subsequently accomplished amido complexes [(COD)Ir(2-Ph₂PC₆H₄NMe)] [Ir-7a] and

by regio- and stereospecific ring-opening with Ph₂PH in the [(COD)Ir(Ph₂PCH₂CMe₂NH)] [Ir-8a] as conjugate bases of

presence of BF₃as an activating additive. Enantiopure their parent Ir^ϩ-7 and Ir^ϩ-8 cations (Scheme 3).

P,N ligands thus prepared included (ϩ)-(1S,2S)-

Crystallization of Ir^ϩ-(S,S)-3 and Ir^ϩ-(R,S)-2 from THF/

Ph₂PCH(Ph)CH(Me)NH₂[(S,S)-1] hereafter, (Ϫ)-(1R,2S)- pentane solvent mixtures afforded the two complexes as sin-

Ph₂PCH(Ph)CH(Me)NH₂[(R,S)-1], and (Ϫ)-(1R,2R)- gle-crystalline addition compounds, [(COD)Ir{(1S,2S)-

Ph₂PCH(Ph)CH(Me)NHMe [(R,R)-2].^[7a]

Ph₂PCH(Ph)CH(Me)NHCH₂Ph}]BF₄·2THF and [(COD)-

In a similar manner, (ϩ)-(2S,3S)-trans-1,2-dimethyl-3- Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)NHMe}]BF₄·THF, respec-

phenylaziridine^[12]was used as a source of (Ϫ)-(1R,2S)- tively. The X-ray structural analyses of the two adduct com-

Ph₂PCH(Ph)CH(Me)NHMe [(R,S)-2] for which a less di- plexes showed the presence of discrete ion pairs with the

rect four-step sequence had previously been described by tetrafluoroborate anion hydrogen-bonded to the coordi-

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889

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FULL PAPER

Scheme 1. Syntheses of new chiral and achiral β-aminophosphane ligands used in this work; step (a): 1. F₃B·OEt₂, 2. Ph₂PH

nated amino functions (Figures 1 and 2). The IrϪP bond also into account, crystals of Ir^ϩ-(S,S)-3·2THF are seen to

˚

lengths of 2.279(7) and 2.298(4) A, measured for the two contain the chelate complex as a δ(S_C-1,S_C-2,S_N) dia-

compounds respectively, differ only slightly, if at all, and stereomer, the λ(R_C-1,S_C-2,R_N) form being present in the

the same applies to the IrϪN distances which are 2.14 A in solid state of Ir^ϩ-(R,S)-2·THF.

˚

both complexes. The chelate bite angles PϪIrϪN are

For Rh^ϩ-(R,R)-2, single crystals of which have been

83.0(6) and 83.7(3)° and thus compare well with the value shown to be composed of the λ(R_C-1,R_C-2,S_N) stereoiso-

of 82.3(2)° previously measured for the related rhodium cat- mer,^[7a]and for its iridium homologue Ir^ϩ-(R,R)-2 as well,

ion Rh^ϩ-(R,R)-2.^[7a]A common structural feature of the ³¹P NMR spectroscopic data indicated the presence in solu-

three complexes in the solid state is the equatorial align- tion of three diastereomers in a roughly 10:3:1 distribution.

ment of the phenyl ring bonded to C-1 with respect to the Assuming that steric hindrance between the substituents

five-membered chelate ring, causing the puckered metalla- attached to the chelate ring increases in the series

cycle to adopt the δ conformation if the configuration at C- λ(R_C-1,R_C-2,S_N) (C-Ph, C-Me, and N-Me groups all-trans-

1 is S and, vice versa, to exist as a λ conformer if C-1 is in eq aligned) Ͻ δ(R_C-1,R_C-2,S_N) (all-trans-ax conformer) ഠ

the R configuration. As a further consequence, the adjacent λ(R_C-1,R_C-2,R_N) (C-Ph/C-Me trans-eq oriented, C-Me/

methyl group attached to C-2 is oriented equatorially if the N-Me cis-eq-ax positioned) Ͻ δ(R_C-1,R_C-2,R_N) (C-Ph/C-Me

two carbon atoms have like configuration (Figure 3; see also in trans-ax, C-Me/N-Me in cis-ax-eq orientation), the ob-

Figure 4 of ref.^[7a]) but points to an axial direction if the served isomers were previously assigned as sterically locked

configuration at C-2 is opposite to that at C-1 (Figure 4). conformers λ(R_C-1,R_C-2,S_N) (major), δ(R_C-1,R_C-2,S_N) (inter-

Taking the surrounding of the coordinated nitrogen atom mediate), and λ(R_C-1,R_C-2,R_N) (minor).^[7a]We have now ob-

890

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Eur. J. Inorg. Chem. 2004, 888Ϫ905

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

Figure 1. Perspective view of the [(COD)Ir{(1S,2S)-

Scheme 2. Collection of cationic β-aminophosphane Ir^Icomplexes

Ph₂PCH(Ph)CH(Me)NHCH₂Ph}]BF₄ion pair; selected bond

˚

Ϫ

lengths [A] and angles [°]: Ir1ϪP1, 2.279(7); Ir1ϪN1, 2.14(2);

(all BF₄salts) and abbreviations

Ir1ϪC29, 2.18(2); Ir1ϪC30, 2.13(2); Ir1ϪC33, 2.24(2); Ir1ϪC34,

2.24(2); N1ϪH···F1, 2.88(3). P1ϪIr1ϪN1, 83.0(6); N1ϪH···F1,

166.7

Scheme 3. Synthesis of β-amidophosphane Ir^Icomplexes

served that acetone solutions of the N-benzyl complex Ir^ϩ-

(S,S)-3 exhibit NMR spectra (¹H, ¹³C, ³¹P) consistent with

the existence of the cation in the dissolved state existing as

only two ring conformers in an approximately 2:3 molar

ratio (from ³¹P{¹H} NMR; cf. Table 1). Assuming that the

crystallographically established δ(S_C-1,S_C-2,S_N) form con-

tributes significantly to the isomeric distribution formed in

solution, we can assign the NMR spectra displaying 40%

relative intensity to that (C-Ph/C-Me)-trans-eq/(C-Me/

N-Me)-cis-eq-ax conformer and ascribe the resonances

showing up with 60% relative intensity to the sterically

more favorable all-trans-eq δ(S_C-1,S_C-2,R_N) isomeric cation.

By implication, it becomes necessary to re-assign the con-

formers previously observed for the two Rh and Ir

complexes M^ϩϪ(R,R)-2 at intermediate concentration

Figure 2. Perspective view of the [(COD)Ir{(1R,2S)-

Ph₂PCH(Ph)CH(Me)NHMe}]BF₄ion pair; selected bond lengths

[A] and angles [°]: Ir1ϪP1, 2.298(4); Ir1ϪN1, 2.137(11); Ir1ϪC23,

2.224(14); Ir1ϪC24, 2.181(16); Ir1ϪC27, 2.165(16); Ir1ϪC28,

˚

2.126(13); N1ϪH···F2,

N1ϪH···F2, 170.7

2.925(16).

P1ϪIr1ϪN1,

83.7(3);

Solution ³¹P NMR spectra of Ir^ϩ-(R,S)-2 and Ir^ϩ-(R,S)-

(vide supra)^[7a]as λ(R_C-1,R_C-2,R_N), i.e. enantiomeric to 4 indicate the presence of one exclusive [Ir^ϩ-(R,S)-4] or at

δ(S_C-1,S_C-2,S_N), rather than δ(R_C-1,R_C-2,S_N), which accord- least one predominant [Ir^ϩ-(R,S)-2] conformer. These can

ingly can be attributed to the conformational isomers be assigned as λ(R_C-1,S_C-2,R_N), i.e. identical with the iso-

formed at minor concentration (Table 1 and Scheme 4). By meric form observed for Ir^ϩ-(R,S)-2 in the solid state. The

similar reasoning the conformers of Ir^ϩ-(S,S)-4 in a 1:3 dis- favorable δ(S_C-1,S_C-2) or λ(R_C-1,S_C-2) foldings of the chelate

tribution in solution can be formulated as δ(S_C-1,S_C-2,S_N) rings with like or unlike configurations of the two bridging

and δ(S_C-1,S_C-2,R_N), respectively.

carbon atoms can also be ascribed to the single conformers

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FULL PAPER

Table 1. ³¹P NMR spectroscopic data of complex conformers ob-

served in [D₆]acetone solution

Conformer^[a]

δ(³¹P)

Rel. conc. [%]

δ(S_C-1,S_C-2,R_N)-Ir^ϩ-(S,S)-3

δ(S_C-1,S_C-2,S_N)-Ir^ϩ-(S,S)-3

46.65

39.97

60

40

δ(S_C-1,S_C-2,R_N)-Ir^ϩ-(S,S)-4

δ(S_C-1,S_C-2,S_N)-Ir^ϩ-(S,S)-4

45.44

40.79

75

25

λ(R_C-1,R_C-2,S_N)-Ir^ϩ-(R,R)-2

λ(R_C-1,R_C-2,R_N)-Ir^ϩ-(R,R)-2

δ(R_C-1,R_C-2,S_N)-Ir^ϩ-(R,R)-2

45.70^[7a]

41.99^[7a]

38.07^[7a]

76

17

7

λ(R_C-1,S_C-2,R_N)-Ir^ϩ-(R,S)-2^[b]

λ(R_C-1,S_C-2,R_N)-Ir^ϩ-(R,S)-4

38.10

37.54

94

100

δ(S_C-1,S_C-2)-Ir^ϩ-(S,S)-1

λ(R_C-1,S_C-2)-Ir^ϩ-(R,S)-5

46.44^[7a]

35.70

100

Figure 3. Schematic front view of the cation Ir^ϩ-(S,S)-3 emphasiz-

ing the δ(S_C-1,S_C-2,S_N) conformation of the chelate ring

[a]

[b]

For stereochemical assignments, see text. Low intensity sing-

lets at δ ϭ 38.01 and 41.27 are stereochemically unassigned.

Scheme 4. Drawings of preferred (less preferred) conformers ob-

served in solution (cf. Table 1)

Figure 4. Schematic front view of the cation Ir^ϩ-(R,S)-2 emphasiz-

ing the λ(R_C-1,S_C-2,R_N) conformation of the chelate ring

produced upon dissolution of the two complexes Ir^ϩ-(S,S)-

1 and Ir^ϩ-(R,S)-5 possessing achiral amine functions

(Table 1).

Catalytic ϾC

؍

O Hydrogenation

If combined with an alkaline or amine base (1Ϫ5 equiv.)

in methanol under H₂(10Ϫ50 bar) between 25 and 50 °C,

all the complexes shown in Scheme 2 act as catalysts for the

hydrogenation of alkyl aryl ketones to the corresponding

1-phenylalkanols (Tables 2Ϫ4). The homogeneous ϾCϭO

reduction occurs enantioselectively if chelate complexes

bearing the various (pseudo)ephedrine-based β-aminophos-

phanes are used as catalysts (Scheme 5).

Scheme 5. Enantioselective hydrogenation of prochiral ketones

using the Ir^ϩ-(R,R)-2 precatalyst in the presence of different bases

ϾCϭO reduction occurred in methanol in the absence of

The success of the hydrogenation reaction depends on the an amine or an alkali metal hydroxide and, vice versa, in

presence of an extra base in the catalytic system and the aprotic solvents, e.g. benzene, dichloromethane, or THF,

use of a protic reaction medium. Thus, virtually no catalytic containing such a basic additive. The likelihood of the ke-

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Eur. J. Inorg. Chem. 2004, 888Ϫ905

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

Table 2. Enantioselective hydrogenation of acetophenone using the Ir^ϩ-(R,R)-2 catalyst modified by different bases

FULL PAPER

Auxiliary base (equiv. rel. to c_Ir)^[a]

p(H₂) [bar]

T [°C]

t [h]

yield [%]

ee [%] (polar.)

ee [%] (HPLC)

iPr₂NH (5.0)

NEt₃(5.0)

(Ϫ)-sparteine (5.0)

(ϩ)-Tröger’s base (5.0)

(Ϫ)-Tröger’s base (5.0)

pyridine (5.0)

25

50

40

16

40

100

Ϫ

46 (S)

39 (S)

53 (S)

41 (S)

30 (S)

47 (S)

(S)-PhCH₂CH(NH₂)CH₂OH (5.0)

(R)-PhCH₂CH(NH₂)CH₂OH (5.0)

(1R,2R)-Ph₂PCH(Ph)CH(Me)NHMe (5.0)

25

50

80

55

56

69

53 (S)

60 (S)

48 (S)

54 (S)

41 (S)

LiOH (1.1)

K₂CO₃(1.1)

KOH (1.1)

10

25

22

16

7

100

58 (S)

43 (S)

62 (S)

52 (S)

40 (S)

55 (S)

[a]

0.02 mmol of metal complex plus added base together with 2.0 mmol of acetophenone in 3 mL of methanol.

Table 3. Homogeneous hydrogenation of acetophenone using different KOH- and (Ϫ)-sparteine-activated [(COD)M(PʝNR¹R²)]^ϩcatalyst

complexes; M ϭ Ir (Rh)

Complex

Ir^ϩ-(S,S)-1

Ir^؉-(S,S)-3

Ir^؉-(S,S)-4

Rh^ϩ-(R,R)-2

Ir^ϩ-(R,R)-2

Ir^ϩ-(R,S)-2

Ir^؉-(R,S)-4

Ir^ϩ-(R,S)-5

Ir^ϩ-6

Base^[a]

t [h]

yield [%]

ee [%] (polar.)

ee [%] (HPLC)

KOH^[b]

7

100

51

42 (R)

19 (R)

27 (R)

33 (R)

51 (R)

44 (R)

77 (S)

39 (S)

62 (S)

53 (S)

45 (S)

5 (S)

38 (R)

15 (R)

26 (R)

31 (R)

51 (R)

44 (R)

71 (S)

34 (S)

55 (S)

47 (S)

38 (S)

4 (S)

(Ϫ)-sparteine^[c]

KOH

16

32

70

12

16

6

(Ϫ)-sparteine

KOH

(Ϫ)-sparteine

KOH

(Ϫ)-sparteine

KOH

(Ϫ)-sparteine

KOH

(Ϫ)-sparteine

KOH

(Ϫ)-sparteine

KOH

(Ϫ)-sparteine

KOH

100

25

100

92

100

82

100

92

28

7

16

32

43

50

55

58

70

4

40

65

3

21 (S)

9 (S)

36 (S)

10 (S)

19 (S)

7 (S)

36 (S)

9 (S)

(Ϫ)-sparteine

Ir^ϩ-7

KOH^[d]

(Ϫ)-sparteine^[d]

KOH

Ir^ϩ-8

(Ϫ)-sparteine

35

[a]

0.02 mmol of [(COD)M(PʝNR¹R²)]^ϩϪKOH or [(COD)M(PʝNR¹R²)]^ϩϪ(Ϫ)sparteine (M/KOH ϭ 1:1.1; M/(Ϫ)-sparteine ϭ 1:5.0),

[b]

[c]

and 2.0 mmol of acetophenone in 3 mL of methanol.

modified complexes: p(H₂) ϭ 25 bar, T ϭ 50 °C. p(H₂) ϭ 50 bar, T ϭ 50 °C.

KOH-activated precatalysts: p(H₂) ϭ 10 bar, T ϭ 25 °C.

(Ϫ)-Sparteine-

[d]

tone reduction proceeding by metal-assisted direct transfer 40 h in Me₃COH which, as a tertiary alcohol, cannot serve

of H^δϪ/H^δϩequivalents from the H₂molecule to the car- as a proton/hydride source.

bonyl function was substantiated by ruling out the alterna-

The influence on the catalytic activity of the different

tive pathway involving H^δϪ/H^δϩtransfer from the primary oxygen and nitrogen bases depicted in Scheme 5 was quali-

alcohol. No transformation of acetophenone to 1-phenyle- tatively studied for a standard system composed of the ace-

thanol was observed when the ketone and a catalytic system tophenone substrate and the Ir^ϩ-(R,R)-2Ϫbase catalyst in

composed of Ir^ϩ-(R,R)-2 and (Ϫ)-sparteine in a 1:5 molar question (Table 2). While pyridine and the two enantiomers

ratio (vide infra) were kept in a catalyst-to-substrate ratio of Tröger’s base did not support the hydrogenation reac-

of 1:100 in methanol at 50 °C for 40 h in the absence of tion, tertiary and secondary alkylamines such as NEt₃, (Ϫ)-

hydrogen gas, although quantitative ϾCϭO hydrogenation sparteine, and iPr₂NH performed reasonably if added in

did occur if the same catalyst was combined with the ketone fivefold excess relative to the Ir^ϩ-(R,R)-2 concentration. Re-

in a 1:100 stoichiometry under 25 bar of H₂at 50 °C for action times required for complete transformation of the

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L. Dahlenburg, R. Götz

FULL PAPER

ketone at 50 °C under a pressure of 25 bar of H₂were ഠ Similar stereoselection has previously been documented for

40 h with triethyl and isopropylamine and only ca. 16 h Ru^II-catalyzed ϾCϭO hydrogenations.^[3c][3d]The somewhat

with (Ϫ)-sparteine as auxiliary bases. It can therefore be disappointing result that the product alcohols are generally

concluded that the strength of the base which, compared formed, at best, in moderate optical yields either indicates

with alkylamines, is low for heteroaromatic and arylam- an inherently low enantioselectivity of the systems or points

ines,^[20]exerts the important influence. In full agreement to side reactions overriding the true selectivity of the com-

with this reasoning, strong oxygen bases such as LiOH, plexes; e.g. the mixture of diastereomeric ring conformers

K₂CO₃, and particularly KOH were found to further de- detected in solution (Table 1) might act as interfering cata-

crease the times needed for quantitative hydrogenation, lysts involved in competitive hydrogenation reactions.

even if employed in a near equimolar Ir^ϩ-(R,R)-2/base ratio

Prochiral alkyl aryl ketones other than acetophenone

at reduced temperature (25 °C) and H₂pressure (10 bar). which could be enantioselectively hydrogenated included

The addition of optically active chelating β-amino alcohols propio- and isobutyrophenone, 3-chlorobutyrophenone, as

or -phosphanes had no significant influence on the selec- well as 1-indanone (Table 4). Using the Ir^ϩ-(R,R)-2-(Ϫ)-

tivity of the catalysts but exerted a detrimental effect on sparteine catalytic system, the product alcohols were

their activity in that only reduced yields of the alcohol formed as (S) enantiomers with optical yields between 29

products were obtained after prolonged periods of time. and 68%, in full agreement with the empirical λ/δ rule for-

Hence, for the catalytic runs described in the next section, mulated before. Attempts at the metal-assisted hydrogen-

potassium hydroxide or (Ϫ)-sparteine were employed as the ation of dialkyl ketones such as 2-butanone, isopropyl

‘‘optimized’’ alkaline and amine bases.

methyl ketone, or pinacolone failed. Due to the basic con-

The enantiomeric excesses of (R)- or (S)-PhCH(OH)Me ditions, these substrates underwent aldol reactions rather

that could be achieved in the hydrogenation of the standard than reduction to give solids that were also isolated if the

acetophenone substrate in the presence of KOH-activated ketones were allowed to react in the presence of base but

complexes ranged from 19Ϫ21% (S) for the iridium (pre)- the absence of any added metal complex.

catalyst Ir^ϩ-(R,S)-4 to 71Ϫ77% (S) for the rhodium system

Rh^ϩ-(R,R)-2 (Table 3). Although the iridium homologue of

Table 4. Enantioselective hydrogenation of alkyl aryl ketones using

the Ir^ϩ-(R,R)-2Ϫ(Ϫ)-sparteine catalytic system^[a]

the latter, Ir^ϩ-(R,R)-2, was comparable in activity (ഠ 7

vs. ഠ 6 h for quantitative ϾCϭO reduction) it afforded a

decidedly lower ee of only 55Ϫ62%. In the series of iridium

complexes bearing chiral β-aminophosphanes with like con-

figuration of their chelate backbone carbon atoms, viz. Ir^ϩ-

(R,R)-2 and Ir^ϩ-(S,S)-1,-3,-4, the eeЈs were observed to in-

crease in the order of their nitrogen substituents i.e. R ϭ

CH₂Ph Ͻ H Ͻ CHMe₂Ͻ Me, suggesting that substitution

by a medium sized methyl group is sufficient to afford the

maximum enantioselectivity that can be achieved with these

systems. Catalyst complexes bearing chiral P,N ligands with

unlike stereochemistry of their backbone carbon atoms, i.e.

Ir^ϩ-(R,S)-2, Ir^ϩ-(R,S)-4, and Ir^ϩ-(R,S)-5, required much

longer times for complete ϾCϭO hydrogenation and also

showed lower selectivities than their diastereomers with like

carbon configurations in the C₂linkages, viz. Ir^ϩ-(R,R)-2

and Ir^ϩ-(S,S)-4. Furthermore, catalytically sluggish as N,N-

dialkylated Ir^ϩ-(R,S)-5 proved to be, its mere ability to act

as a catalyst gives unequivocal evidence that the presence

of at least one NH function (which is met in all other

[a]

0.02 mmol of Ir^ϩ-(R,R)-2, 0.1 mmol of (Ϫ)-sparteine, and

complexes) is not a prerequisite for the particular com-

pound to exhibit catalytic behavior. Nevertheless there exist 2.0 mmol of the ketonic substrate in 3 mL of methanol; p(H₂) ϭ

25 bar, T ϭ 50 °C. ^[b]As a result of base-induced HCl elimination,

major differences between the two classes of complexes with

the formation of 2-phenyltetrahydrofuran in low yield (ഠ4%) was

respect to their reactivity towards the dihydrogen molecule

also observed.

as will be shown below. Finally, the preferential formation

of the product alcohol in the (R) configuration induced by

complexes with δ(S_C-1) stereochemistry of their chelate

The mandatory presence of base in the catalytic systems

rings and, correspondingly, the predominance of the (S) en- suggests the intermediacy of in situ generated species that

antiomer in the isomeric mixtures resulting from reactions have lost H^ϩ. For all catalysts derived from precursor com-

promoted by all λ(R_C-1) conformers shows that the hydro- plexes possessing P,N ligands with primary or secondary

genation catalysts described herein follow a λ/δ rule which amine functions these could conceivably be amidoiridium()

predicts that λ chelates will give the (S) enantiomeric al- or -rhodium() complexes. In fact, the amides Ir-7a and Ir-

cohol while δ chelates will produce the (R) enantiomer. 8a (which were intentionally prepared for this specific pur-

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Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

pose) did catalyze the hydrogenation of acetophenone to 1-

phenylethanol without the addition of base, quantitatively

transforming the ketone to the alcohol under the usual con-

ditions in approximately the same periods of time as the

combined catalytic systems Ir^ϩ-7ϪKOH and Ir^ϩ-8ϪKOH,

respectively. Thus, with 1 mol % of Ir-7a and Ir^ϩ-7ϪKOH

as catalysts, the reactions were complete after 2 and 3 h

under 10 bar of H₂at 25 °C, while 60Ϫ65 h at 50 °C under

50 bar of H₂were needed for the quantitative formation of

the alcohol in the presence of 1 mol % of Ir-8a or Ir^ϩ-

8ϪKOH. The ability of the two base-free β-amidophos-

phane iridium() complexes to catalyze the homogeneous

ϾCϭO reduction by molecular hydrogen likewise depends

on the use of alcohols (MeOH, tBuOH) as reaction media,

wherein the iridiumϪamide bond remains unprotonated.

The obviously low amide basicity can be attributed to the

involvement of the nitrogen lone-pair in π bonding to the

central metal^[21]with resultant sp³Ǟ sp²rehybridization,

similar to the situation that has previously been encoun-

tered for the closely related anilide [Ir(CO)(PPh₃)(2-

Ph₂PC₆H₄NMe)], where the nitrogen atom features a trig-

onal-planar rather than a pyramidal surrounding and can

be protonated only by very strong acids such as hydro-

chloric^[22a]or tetrafluoroboric.^[22b]

Figure 5. Perspective view of one of the two crystallographically

independent molecules of orthometalated [(COD)Ir{(1R,2S)-

Ph₂PCH(C₆H₄-o)CH(Me)NHCHMe₂] (‘‘molecule 1’’); selected

˚

bond lengths [A] and angles [°]: Ir1ϪP1, 2.2917(18); Ir1ϪN1,

2.514(6); Ir1ϪC1, 2.099(7); Ir1ϪC2, 2.137(7); Ir1ϪC5, 2.183(7);

Ir1ϪC6, 2.216(7); Ir1ϪC9, 2.104(7). P1ϪIr1ϪN1, 78.86(14);

P1ϪIr1ϪC9, 77.13(19); N1ϪIr1ϪC9, 75.3(2). Corresponding

structural parameters for ‘‘molecule 2’’: Ir2ϪP2, 2.2942(18);

Ir2ϪN2, 2.448(6); Ir2ϪC33, 2.213(7); Ir2ϪC34, 2.200(7);

Ir2ϪC37, 2.119(7); Ir2ϪC38, 2.090(7); Ir2ϪC41, 2.119(7).

P2ϪIr2ϪN2, 80.50(14); P2ϪIr2ϪC41, 77.11(19); N2ϪIr2ϪC41,

75.3(2)

In view of the catalytic efficacy of Ir-7a and Ir-8a, numer-

ous attempts were made to obtain similar amides also by

deprotonation of the chiral [(COD)Ir(PʝNHR]^ϩprecata-

lysts but they remained unsuccessful. Either the amine func-

tion stayed unattacked, e.g. by amines or dilute KOH/meth-

anol, or complex reaction mixtures containing ketonic and/

˜

or imine-type components [IR (KBr): ν ϭ 1685 and 1715

cm^Ϫ1] were produced, if the cationic aminophosphane com-

plexes were treated with very strong bases such as excess

alkoxide or nBuLi. Obviously, those amine complexes

which are different from Ir^ϩ-7 and Ir^ϩ-8 and possess CH

units adjacent to the amino group tend to undergo degra-

dation of their P,N ligands in the presence of strong base

Ϫ most probably by ϾCϭNR elimination from initially

formed β-H containing amides which decompose easily due

to their coordinative unsaturation.

Only in a single and probably serendipitous case we were

able to isolate a well-defined product from such reactions.

Combination of Ir^ϩ-(R,S)-4 with concentrated methanolic

KOH and subsequent crystallization of the crude product

from hot acetone gave cyclometalated [(COD)Ir{(1R,2S)-

Scheme 6. KOH-assisted orthometalation

of enantioselective ϾCϭO reduction but should rather be

looked upon as a by-product resulting from a base-induced

side reaction.

H/D Exchange Processes and H₂Activation

When aceto- or benzophenone, dissolved in CH₃OD,

Ph₂PCH(C₆H₄-o)CH(Me)NHCHMe₂}] [Ir-(R,S)-4a] (Fig- were hydrogenated with H₂employing either the base-free

ure 5); i.e. deprotonation had occurred at one of the ortho amide Ir-8a or the combined system Ir^ϩ-(R,R)-2-(Ϫ)-spar-

CϪH bonds of the phenyl ring attached to chelate back- teine as catalysts, the product alcohols were invariably

2

bone rather than at the amino function; Scheme 6. Presum- characterized by NMR spectroscopy (¹H, H, ¹³C{¹H}; see

ably because of the hemilabile nature of the extraordinarily Exp. Sect.) as mixtures containing the two isotopomers

long IrϪN bond, measured as 2.448(6) and 2.514(6) A for R¹R²CHOD and R¹R²CDOD in an almost 1:1 molar ratio.

˚

the two crystallographically independent molecules, this co- The evolution of HD gas was observed to be concomitant

ordinatively saturated complex does exhibit some catalytic with the incorporation of solvent deuterons as D^δϪequiva-

activity, slowly transforming acetophenone in methanol un- lents into the product carbinols [Scheme 7, reation (1)], as

der 10 bar of H₂to racemic 1-phenylethanol. The formation was the increasing formation of non-deuterated MeOH. No

of the product alcohol without any notable stereodiscrimin- such uptake of D^ϩas D^Ϫby the ketonic substrate was

ation strongly suggests that the orthometalated complex is noted if the hydrogenation was catalyzed by complex Ir^ϩ-

not an actual intermediate maintaining the catalytic cycle (R,S)-5 possessing a tertiary amino donor group. Iridium-

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catalyzed H₂/D^ϩexchange with concomitant formation of alyzed by the two amido complexes Ir-7a and Ir-8a

HD was similarly observed when MeOD solutions of all [Scheme 7, reations (2) and (3)]. Furthermore, the initial

base-free aminophosphane complexes containing at least product of the reaction between dihydrogen (5 bar) and Ir-

one NϪH bond were pressurized in the absence of any ke- 8a in CD₃CN solution was unequivocally identified (see

tonic substrate in an NMR tube to 5Ϫ10 bar of H₂Exp. Sect.) as an amido dihydride, cis-[(CO-

[Scheme 7, reation (2)], but again did not take place on at- D)IrH₂(Ph₂PCH₂CMe₂NH)] (Ir-9a), originating from

tempted catalysis by the N,N-dialkylated cation Ir^ϩ-(R,S)- homolytic oxidative H₂addition to the central metal

5. Hence, the exchange of isotopes between the protic sol- (Scheme 8), rather than an amino monohydride, [(CO-

vent and the hydrogen atmosphere, which is typical of het- D)IrH(Ph₂PCH₂CMe₂NH₂)] which would result from het-

erolytic HϪH cleavage during reaction,^[3,23Ϫ30]neither de- erolytic H₂addition to the NϪH bond. The preference of

pends on the presence of base nor is contingent on simul- Ir-8a to add the dihydrogen molecule by homolytic bond

taneous ϾCϭO hydrogenation but requires at least one cleavage clearly contrasts with the heterolytic HϪH fission

acidic NϪH bond in the coordination sphere of the cata- concluded from the foregoing exchange experiments, not-

lyst complex.

withstanding that it corresponds to the low basicity of its

amide function and also parallels the behavior of the related

anilide [Ir(CO)(PPh₃)(2-Ph₂PC₆H₄NMe)] described in pre-

vious work.^[22a]As a further seemingly paradoxical result,

the cationic aminophosphane complexes Ir^ϩ-8 and Ir^ϩ-

(S,S)-1 were likewise seen to interact with molecular hydro-

gen by conventional oxidative addition, giving cis-[(CO-

D)IrH₂(Ph₂PCH₂CMe₂NH₂)]BF₄

(Ir^ϩ-9)

and

cis-

[(COD)IrH₂{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂]BF₄(Ir^ϩ-

10) as the first formed products (Scheme 8). Prolonged

exposure of the iridium() precursors to H₂at elevated

pressures (Ͼ 10 bar) resulted in hydrogenic loss of the

cyclooctadiene ligand with formation of solvate-stabilized

adducts

with

cis,cis-[(MeCN)₂IrH₂{(1R,2S)-Ph₂PCH-

(Ph)CH(Me)NHMe}]BF₄(Ir^ϩ-11) being a representative

example.

Scheme 7. Catalytic H₂/D^ϩisotope exchange and H₂/D₂scram-

bling in the presence [reation (1)] and absence of ketonic substrates

[reations (2) and (3)]

Catalytic scrambling of isotopes with formation of HD

was also detected when acetonitrile solutions of all NH-

containing [(COD)Ir(PʝNHR)]^ϩcomplexes were exposed

to 10 bar of an equimolar H₂/D₂mixture [Scheme 7, reation

(3)] but once more did not occur in the presence of the N,N-

dialkylated derivative Ir^ϩ-(R,S)-5. Control experiments in

CD₃CN making use of a D₂-free hydrogen atmosphere

ruled out the possibility that the observed HD did actually

result from H₂/D^ϩexchange between the H₂component

Scheme 8. Products of oxidative H₂addition to β-amino- and β-

Ϫ

amidophosphane iridium() precursors (cationic complexes: BF₄

salts)

It was two important properties of the neutral amido and

and the moderately acidic CϪD bonds of the solvent mol- the cationic amino iridium() dihydrides that served to un-

ecules. The observed exchange of isotopes between the two ravel the perplexing inconsistencies emerging, on the one

gases implies the intermediate coordination of H₂or D₂to hand, from the experimentally established homolytic H₂ad-

iridium, although the formation of any sufficiently long- dition by both the [(COD)Ir(PʝNHR)]^ϩand [(CO-

lived IrϪH₂adduct could not be traced by NMR spec- D)Ir(PʝNR)] complexes and, on the other hand, from the

troscopy down to Ϫ60 °C. Similar to the H₂/D^ϩexchange ability of the very same compounds to catalyze H₂/D₂and

described above, the observed H₂/D₂scrambling process H₂/D^ϩscrambling processes.

should involve heterolytic fission of the HϪH and DϪD

Firstly, while the aminophosphane iridium() complex

bonds, respectively, since any isotope exchange brought Ir^ϩ-8 and its (formally) conjugate amide Ir-8a do not co-

about by homolytic cleavage of the two molecules would exist in alcoholic media in an acidϪbase equilibrium, the

require simultaneous coordination of H₂and D₂to the products of oxidative H₂addition to these two d⁸sub-

same central metal, which is regarded as highly un- strates, Ir^ϩ-9 and Ir-9a, do so (Scheme 9). Pressurizing a

likely.^[23c,23i,30]

solution of Ir-8a in methanol to 5 bar of H₂which, as men-

Despite all failures to transform the iridium() amine tioned above, does not lead to any detectable Ir^ϩ-8, not

complexes into their conjugate amides (vide supra), both only gave the amido dihydride Ir-9a but also produced the

the H₂/D₂and the H₂/D^ϩexchange processes were also cat- conjugate amino dihydro complex Ir^ϩ-9 at spectroscopically

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Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

detectable concentrations. The same result was obtained if ence of the ³¹P singlet (δ ϭ 31.4 for the deuterated com-

2

a droplet of water was added to a solution of preformed Ir- pound) and (iii) the appearance of two high-field H peaks

9a in carefully dried CD₃CN. Vice versa, the latter amido at δ ϭ Ϫ15.7 and Ϫ12.7, indicating an IrD₂substructure

dihydride was detected in addition to the predominantly with non-equivalent IrϪD bonds. As a particularly illumi-

formed amino dihydride Ir^ϩ-9, if a solution of Ir^ϩ-8 in nating feature, the ²H NMR spectrum furthermore dis-

methanol containing dilute aqueous KOH at low concen- played an HD doublet at δ ϭ 4.37 (¹J_H,Dϭ 42.6 Hz) in

tration was pressurized with H₂(Scheme 9). The basic addition to the D₂singlet at δ ϭ 4.33, demonstrating that

properties of the amido function of the 18e complex Ir-9a catalytic H₂/D₂scrambling goes together with IrH₂Ǟ IrD₂

can safely be attributed to its coordinative saturation which exchange (Scheme 10). A comparatively broad resonance

prevents the nitrogen lone-pair from engaging in π-bonding centered at δ ϭ 2.3 and partly overlapping the CDH₂CN

to the central metal. The reversible protonation of amido triplet at δ ϭ 1.98, could not be assigned with certainty It

donor groups attached to an Ir^IIIcenter has some precedent may originate from deuterated amino functions which

in the literature: the amido-/aminophosphane complexes would then be consistent with the presence in solution of

[Ir(H)(Cl)(2-Ph₂PC₆H₄NR)(2-Ph₂PC₆H₄NHR)] (R ϭ Et, [(COD)IrD₂(Ph₂PCH₂CMe₂NHD)]^ϩand [(COD)IrD₂-

CH₂Ph) react with protic acids HX (X ϭ Cl, OH, O₂CMe) (Ph₂PCH₂CMe₂ND₂)]^ϩisotopomers as required by the

to yield cationic bis(aminophosphane) products, equilibria shown in Scheme 10. However, the assignment to

[Ir(H)(Cl)(2-Ph₂PC₆H₄NHR)₂]^ϩ, from which the amido-/ CϪD bonds resulting from deuteration and de-coordi-

aminophosphane precursors can be restored by the ad- nation of the cyclooctadiene ligand, could not be excluded.

dition of strong bases such as .^[31]

Scheme 10. Intermolecular D₂/IrϪH exchange and intramolecular

IrϪD/NϪH scrambling involving reversible ‘‘[Ir^III(H)₂ϪPʝNH₂]^ϩ’’ o

‘‘[(η²-H₂)-Ir^III(H)ϪPʝNH]^ϩ’’ tautomerization

Scheme 9. Reversible (de)protonation of coordinatively saturated

amino and amido dihydro Ir^IIIcomplexes

In an independent concluding experiment aiming at the

Secondly, cationic amino dihydrido complexes of the type unequivocal demonstration of the [(COD)Ir(PʝNHR)]^ϩ-

[(COD)IrH₂(PʝNHR)]^ϩwill undergo substitution of their catalyzed exchange of protons between the amino group

hydride ligands by deuteride forming [(COD)IrD₂- and

the

gas,

N-deuterated

[(COD)Ir{(1R,2S)-

(PʝNHR)]^ϩ(and presumably [(COD)IrD₂(PʝNDR)]^ϩas Ph₂PCH(Ph)CH(Me)NDCHMe₂}]^ϩ[IR (KBr): ν˜ ϭ 2398

well) if treated with D₂. This behavior has been verified for (ND) cm^Ϫ1] was first prepared from Ir^ϩ-(R,S)-4 [IR (KBr):

Ir^ϩ-9, which was generated in situ by exposing an aceto- ν ϭ 3209 (NH) cm^Ϫ1] and [D₁]methanol and then allowed

˜

nitrile solution of Ir^ϩ-8 at Ϫ60 °C in a high-pressure NMR to interact with H₂under pressure in dry [D₈]THF. The

tube to 5 bar of H₂. The diagnostic NMR signals of the H₂solid that was recovered after removal of all volatile mate-

adduct [δ(IrH) ϭ Ϫ15.78 (d, cis-²J_P,Hϭ 10.95 Hz), Ϫ12.60 rial displayed the characteristic NϪH stretching vibration

(d, cis-²J_P,Hϭ 15.91 Hz); δ(³¹P) ϭ 31.87] persisted when of the starting Ir^ϩ-(R,S)-4^ϩcomplex, showing that an H₂/

the excess pressure was released from the tube showing that ϪNDR Ǟ HD/ϪNHR re-exchange of isotopes had oc-

Ir^ϩ-9, which at ambient conditions under an inert atmos- curred.

phere reductively eliminates dihydrogen, remains stable if

The formation of HD as a product obligatorily ac-

kept under 1 bar of hydrogen at low temperature. With con- companying the hydride/deuteride exchange at the Ir^III

stant cooling to Ϫ60 °C, the H₂atmosphere was then re- center and the observation that both the catalyzed H₂/D₂

placed by D₂under normal pressure, which was sub- scrambling and the exchange of isotopes between dihydro-

sequently raised again to 5 bar. As a result, the original gen molecules and solvent protons is only supported by

dihydride [(COD)IrH₂(Ph₂PCH₂CMe₂NH₂)]^ϩwas con- complexes containing at least one NϪH bond [Scheme 7,

verted into the dideuteride [(COD)IrD₂(Ph₂PCH₂- reactions (2) and (3)] are strongly suggestive of an

CMe₂NH₂)]^ϩmanifesting itself by (i) the disappearance of equilibrium

between

two

aminoϪdihydrido

and

the IrH doublets in the H NMR spectrum, (ii) the persist- amidoϪdihydrogenϪmonohydrido tautomers, ‘‘[Ir^III(H)₂Ϫ

1

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L. Dahlenburg, R. Götz

FULL PAPER

PʝNH₂]^ϩ’’ and ‘‘[(η²-H₂)-Ir^III(H)ϪPʝNH]^ϩ’’, even if

the η²-H₂isomeric form, which maintains the exchange

of isotopes by intramolecular H/D scrambling

(cf. Scheme 10),^{[23c,23e,23i,25]}remained undetected by NMR

spectroscopy down to Ϫ60 °C. Related equilibria that have

previously been established, generally in an indirect fashion

by the observation of H₂/D^ϩexchange processes and/or iso-

topic scrambling between metalϪhydride and protonated li-

gand sites, include the pairs of tautomers ‘‘HϪM^IIϪS(H)R

o (η²-H₂)ϪM^IIϪSR’’ (M ϭ Ru,^{[23h,27c,27d]}Os,^[28b,28c]

,

Ni^[27e,27f]) and ‘‘HϪM^IIIϪLH o (η²-H₂)ϪM^IIIϪL’’ (M ϭ

Rh: LH ϭ RSH;^[27a,27b]M ϭ Ir: LH ϭ NH₃,^[26]

OH₂,^[25a,25b]RSH^[28a]) as well as a family of Ir^IIIcomplexes

containing a pendant basic aniline (acidic anilinium) func-

tion in addition to an acidic η²-bound H₂ligand (basic hy-

dride).^[25c,25d]Only in favorable cases where the pK_aof the

coordinated dihydrogen molecule and the protonated ancil-

lary ligand were similar^[23i]was it possible to directly ob-

serve the equilibrium between the two tautomers.^[28c]For

the most part however, either the η²-H₂com-

plex^{[25c,25d,26,27b,28]}or the metal hydride containing the pro-

tonated N,^[25c,25d]O,^[25a]or S^[27c]ligand remained unde-

tected transients in the isotopic scrambling, depending on

whether the coordinated H₂molecule or the ligand bearing

the proton was the stronger Brønsted acid or, vice versa,

whether the ancillary deprotonated ligand or the

metalϪhydride bond^[32]was the stronger Brønsted

base.^[25c,25d]With regard to the ‘‘[IrH₂(Ph₂PCH₂-

CMe₂NH₂)]^ϩ’’

o

‘‘[(η²-H₂)(H)(Ph₂PCH₂CMe₂NH)]^ϩ’’

tautomerization, we conclude that the amidoϪ

dihydrogenϪmonohydrido complex cannot be seen but re-

sembles the undetected dihydrogen amide forms ‘‘[Ir^III(η²-

H₂)NH₂]^nϩ’’ of the long known hydrido ammine complexes

[Ir^III(H)(NH₃)₂(PEt₃)₂L]^nϩ(n ϭ 1; L ϭ Cl; n ϭ 2: L ϭ

NH₃, PEt₃)^[26]in being a transient species immediately

yielding the other tautomer because the basicity of the co-

ordinated amide by far exceeds that of the metalϪhydride

bond in the adjacent cis position.

Scheme 11. Proposed catalytic cycle for ϾCϭO hydrogenation and

concomitant H₂/D^ϩand H₂/D₂exchange reactions (unlabeled co-

ordination sites occupied by weakly bonded solvent molecules)

account for the observed H/D exchange processes since cat-

ionic Ir^III(µ-H₂)(H) complexes combine the possibility of

facile intermolecular exchange between the bound H₂li-

gand and free D₂molecules (or molecules containing ex-

changeable protons) with low barriers to intramolecular ex-

Concluding Discussion

Putting all evidence together, we propose that H₂acti- change with the hydride ligand.^[23c,23i]

vation as well as H₂/D^ϩand H₂/D₂exchange follow the

The transient formation of tautomers F also explains the

cycle outlined in Scheme 11, which rests on the formation incorporation of solvent deuterons as D^δϪequivalents into

of either COD-coordinated or solvated amino and amido the product alcohols that were obtained if the

dihydro iridium() complexes, A and B, as the first key [(COD)Ir(PʝNHR)]^ϩϪbase-assisted hydrogenation of ke-

intermediates. Because of their coordinative saturation, am- tones was conducted in MeOD [Scheme 7, reaction (1)]. We

ides B can act as bases toward the protic solvent to generate propose that the catalysts described herein follow the classic

the conjugate amino complexes A at equilibrium concen- SchrockϪOsborn pathway^[6]of ϾCϭO/IrϪH insertion

trations (step a) and, equally important, are inert towards rather than the alternative NoyoriϪMorris mechanism of

elimination of imine fragments from P,N ligands possessing ‘‘metalϪligand bifunctional’’ interaction with the sub-

β-hydrogen atoms. The readily occurring H₂/D₂exchange strate,^[2,3,4]mainly because the latter^[5,6]does not depend on

processes, which require the presence of at least one acidic the use of protic reaction media but also occurs with com-

NϪH function, points to a tautomeric equilibrium between parable results in aprotic solvents such as benzene.^[3]In the

A and the dihydrogenϪhydridoϪamido form F. Even if the associated catalytic cycle the first formed amido dihydrides

tautomerization step f yields F only at spectroscopically un- B are converted via ketone adducts C into alkoxo hydrides

detectable transitory concentrations, these are sufficient to D, where the trans bond weakening H^Ϫligand is expected

898

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Eur. J. Inorg. Chem. 2004, 888Ϫ905

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

(estimated accuracy: Ϯ3%), c in g 100 mL^Ϫ1. HPLC: Thermoquest

P 4000 (UV detector).

to be bonded opposite to the alkoxide so that release of the

alcohol by reductive elimination is impeded (steps b and

c).^[5]Protonation of the alkoxide ligand by the solvent with

subsequent release of the product from the metal (step d) is

a more feasible option which would also explain why the

use of protic reaction media is essential for the catalysis.

Addition of H₂to the vacant (or weakly solvated) coordi-

nation site of the remaining cationic Ir^IIIspecies E (step e)

(2-Aminoethyl)diphenylphosphane as well as the β-amino alcohols

(Ϫ)-norephedrine, (Ϫ)-ephedrine, (Ϫ)-N-methylephedrine, (ϩ)-

pseudoephedrine, (Ϫ)-pseudoephedrine, and 2-amino-2-methylpro-

panol were used as obtained commercially (Fluka, Aldrich). Other

starting materials, including (Ϫ)-N-isopropylnorephedrine,^[15]di-

phenylphosphane,^[34]the aziridines 2,2-dimethyl-,^[19](Ϫ)-(2S,3R)-

cis-2-methyl-3-phenyl-,^[7a][9b](Ϫ)-(2S,3S)-trans-2-methyl-3-phenyl-

^[7a][12c](ϩ)-(2R,3S)-cis-1,2-dimethyl-3-phenyl-,^[7a]and (ϩ)-(2S,3S)-

trans-1,2-dimethyl-3-phenylaziridine,^[12b][12c]the P,N ligands (2-di-

leads back to F as the key transient that is able to connect

,

the cycle of catalytic ϾCϭO hydrogenation with the path-

way of H₂/D^ϩscrambling. Intramolecular deprotonation of

phenylphosphanyl)-N-methylaniline,^[18]

(ϩ)-(1S,2S)-(2-amino-1-

phenylpropyl)-, (Ϫ)-(1R,2S)-(2-amino-1-phenylpropyl)-, and (Ϫ)-

(1R,2R)-(2-methylamino-1-phenylpropyl)diphenylphosphane^[7a]as

well as the iridium and rhodium complexes trans-

[IrCl(CO)PPh₃)₂],^[35][{(COD)Ir(µ-Cl)}₂],^[36][Ir(COD)₂]BF₄,^[37]

the acidic H₂ligand by the amide site (step f) will restore

the amino dihydrido species A, which in turn can be con-

verted into the conjugate amides B by the added base.

Alternatively, intermolecular deprotonation (g) by the me-

thoxide released during product formation (or even by the

solvent itself) will directly regenerate the starting amido di-

hydrides B and, hence, can likewise serve to close the two

(Ϫ)-[(COD)Ir{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂}]BF₄,

and

[(COD)M{(1R,2R)-Ph₂PCH(Ph)CH(Me)NHMe}]BF₄(M ϭ Rh,

Ir)^[7a]were prepared as described previously.

interlinked cycles. An additional function of the mandatory (؊)-(2S,3R)-cis-1-Benzyl-2-methyl-3-phenylaziridine: A solution of

(Ϫ)-(2S,3R)-cis-2-methyl-3-phenylaziridine (480 mg, 3.60 mmol) in

THF (40 mL) was treated with n-butyllithium (2.25 mL of a 1.6 

solution in hexane) at 0 °C. After the addition of benzyl chloride

(0.44 mL, 3.80 mmol) and stirring overnight, 2% aqueous citric

acid (40 mL) and dichloromethane (50 mL) were added. The aque-

ous layer was saturated with NaCl and repeatedly extracted with

CH₂Cl₂. The combined organic phases were thoroughly washed

with NaHCO₃and the solvents evaporated to dryness. The remain-

ing colorless oil was purified by chromatography on a silica gel

column with diethyl ether/n-pentane (1:8) as the eluent. Evapor-

base may be to deprotonate the alkoxo hydride D at the

IrϪH bond forming G as a transient anionic Ir^IIIspecies

which then is re-protonated by the conjugate acid baseH^ϩ

at the alkoxo site^[5,6]to release the product and regenerate

the starting Ir^Iamido complex (steps h and i). In this con-

text, we briefly note that the proposed ϾCϭO/IrϪH path-

way can also explain the finding that N,N-dialkylated

[(COD)Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)NMe₂}]^ϩ

[Ir^ϩ-

(R,S)-5] in the presence of base does exhibit some catalytic

activity for homogeneous ketone hydrogenation but does ation of the solvent from the eluate left the product as a colorless

oil; yield 460 mg (57%). ¹H NMR (CDCl₃, ppm): δ ϭ 0.87 (d,

not act as a catalyst for either the H₂/D₂or H₂/D^ϩexchange

processes. Oxidative addition of H₂, followed by coordi-

nation and insertion of the ketone, will give a cationic al-

koxo hydrido intermediate in place of the neutral species D

proposed in Scheme 11. Removal of the alcohol from the

coordination sphere on the MeO^Ϫ/MeOH-driven pathway

³J_H,Hϭ 5.49 Hz, 3 H, CH₃), 1.82 [‘‘qui’’, 1 H, C(2)-H)], 2.57 [d,

2

³J_H,Hϭ 6.57 Hz, 1 H, C(3)-H], 3.49, 3.66 (AB-dd, J_H,H

ϭ

13.91 Hz, 2 H, CH₂), 7.1Ϫ7.5 (m, 10 H, C₆H₅). ¹³C{¹H} NMR

(CDCl₃, ppm): δ ϭ 12.79 (CH₃), 41.72 (C-2), 46.18 (C-3), 64.42

(CH₂), 126.4Ϫ139.4 (C₆H₅). The NMR spectroscopic data corre-

sponded to those reported in the literature in every respect.^[14]

[α]₅₈₉ϭ Ϫ112.4 (c ϭ 1.3, CH₂Cl₂).

h

Ǟ

i

therefore leads back to [L₂Ir{(1R,2S)-

Ph₂PCH(Ph)CH(Me)NMe₂}]^ϩas a solvated analogue of

the starting compound Ir^ϩ-(R,S)-5, thus maintaining the

cycle of ϾCϭO hydrogenation but barring the way to con-

comitant isotopic scrambling.

(؊)-(2S,3R)-cis-1-Isopropyl-2-methyl-3-phenylaziridine: (Ϫ)-

(1R,2S)-N-Isopropylnorephedrine (830 mg, 3.97 mmol) was com-

bined in chloroform (30 mL) at 0 °C with PCl₅(1.10 g, 5.30 mmol).

The mixture was heated to reflux for 1 h, then cooled in an ice bath

and worked up by the cautions addition of methanol (15 mL). The

residue remaining after evaporation to dryness, addition of ethanol

(20 mL), and renewed removal of all volatile material was triturated

with diethyl ether, separated by filtration and re-dissolved in chilled

5  sodium hydroxide solution (40 mL). The resultant mixture was

heated at 90 °C for 2 h, cooled to room temperature and extracted

with diethyl ether. The combined organic layers were dried with

Na₂SO₄, evaporated, and then distilled at 70 °C in the vacuum of

an oil pump to give the product as a colorless liquid which solidi-

fied overnight forming tiny needle-shaped crystals; yield 375 mg

In summary, evidence has been presented for a mecha-

nism of ϾCϭO hydrogenation and H/D exchange catalyzed

by iridium β-aminophosphane complexes which involves

both homo- and heterolytic H₂activation at the same me-

tal center.^[33]

Experimental Section

General Remarks: All manipulations were performed under nitro-

gen using standard Schlenk techniques. Solvents were distilled from

the appropriate drying agents prior to use. IR: Mattson Polaris.

NMR: Bruker DPX 300 (300.1 MHz for ¹H, 75.5 MHz for ¹³C,

121.5 MHz for ³¹P, and 46.1 MHz for ²H) at 20Ϯ2 °C (if not stated

otherwise) using SiMe₄(or the solvent) or H₃PO₄as internal or

external standards, respectively (downfield positive; ‘‘m’’: decep-

tively simple multiplets); high-pressure experiments in Wilmad 528-

1

3

(54%). H NMR (CDCl₃, ppm): δ ϭ 0.74 (d, J_H,Hϭ 5.67 Hz, 3

3

H, CH₃), 1.00, 1.02 [both d, J_H,Hϭ 5.85 Hz each, both 3 H,

CH(CH₃)₂], 1.53 [sept, CH(CH₃)₂], 1.58 [‘‘qui’’, 1 H, C(2)-H], 2.33

3

[d, J_H,Hϭ 6.75 Hz, 1 H, C(3)-H], 7.0Ϫ7.2 (m, 5 H, C₆H₅).

¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ 13.70 (CH₃), 21.88, 22.08 [both

CH(CH₃)₂], 40.51 (C-2), 45.87 (C-3), 61.34 [NCH(CH₃)₂],

125.4Ϫ138.0 (C₆H₅). [α]₅₈₉ϭ Ϫ106.1 (c ϭ 6.1, CH₂Cl₂).

PV-1 tubes (inner diameter: 2.2 mm). Polarimetry: PerkinϪElmer (؉)-(2S,3S)-trans-1-Isopropyl-2-methyl-3-phenylaziridine:

A solu-

PE 241 (1 dm cells at room temperature). [α]_λin 10 deg·cm²·g^Ϫ1tion of bromine (255 µL, 4.95 mmol) in acetonitrile (5 mL) was

Eur. J. Inorg. Chem. 2004, 888Ϫ905

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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

899

L. Dahlenburg, R. Götz

FULL PAPER

added dropwise at 0 °C to triphenylphosphane (1.30 g, 4.95 mmol)

dissolved in MeCN (15 mL). The resultant mixture was stirred for

2 h at room temperature, cooled in an ice bath, and then treated

with an acetonitrile solution (5 mL) containing (Ϫ)-(1R,2S)-N-iso-

propylnorephedrine (1.035 g, 4.95 mmol) together with triethyl-

CH(CH₃)₂], 2.74 [m, 1 H, C(2)-H], 2.91 [sept, 1 H, CH(CH₃)₂],

3.81 [dd, ²J_P,H/³J_H,Hϭ 3.84/6.60 Hz, 1 H, C(1)-H], 6.9Ϫ7.7 (m, 15

H, C₆H₅); NH not observed. ¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ

3

18.20 (d, J_P,Cϭ 8.72 Hz, CCH₃), 22.24, 23.04 [both s, both

CH(CH₃)₂], 43.94 [s, NCH(CH₃)₂], 47.70, 50.00 (both d, J_P,C

ϭ

amine (1.38 mL, 9.89 mmol). Stirring overnight caused a precipi- 14.53, 16.71 Hz, C-1/C-2), 126.4Ϫ137.7 (C₆H₅). ³¹P{¹H} NMR

tate of triethylammonium bromide to separate from the solution,

which was filtered off. The filtrate was thoroughly extracted with

n-pentane and the combined extracts were concentrated to a small

residual volume to deposit a white precipitate of triphenylphos-

phane oxide which was removed by filtration. The filtrate was eva-

porated in vacuo and then distilled with an oil pump generated

(CDCl₃, ppm): δ ϭ Ϫ9.04. [α]₅₈₉ϭ ϩ37.1 (c ϭ 2.4, CH₂Cl₂).

C₂₄H₂₈NP (361.5): calcd. C 79.75, H 7.81, N 3.87; found C 79.63,

H 7.99, N 3.79.

(؊)-(1R,2S)-(2-Isopropylamino-1-phenylpropyl)diphenylphosphane

[(R,S)-4]: The compound was prepared in a similar way to its

(1S,2S) diastereomer above using BF₃-activated (ϩ)-(2S,3S)-trans-

1-isopropyl-2-methyl-3-phenylaziridine (371 mg, 2.12 mmol) to-

gether with an equimolar quantity of diphenylphosphane

(0.37 mL) in CHCl₃; yield 669 mg (87%) of a colorless sticky solid.

vacuum at 70 °C to give 317 mg (43%) of the aziridine as a colorless

3

liquid. ¹H NMR (CDCl₃, ppm): δ ϭ 1.07, 1.10 [both d, J_H,H

ϭ

3

6.21 Hz each, both 3 H, CH(CH₃)₂], 1.33 (d, J_H,Hϭ 5.85 Hz, 3

H, CH₃), 2.06 [d, J_H,Hϭ 2.91 Hz, 1 H, C(3)-H], 2.11 [m, 1 H,

3

¹H NMR (CDCl₃, ppm): δ ϭ 0.64 (d, J_H,Hϭ 6.24 Hz, 3 H,

C(2)ϪH], 2.36 [sept, 1 H, CH(CH₃)₂], 7.0Ϫ7.3 (m, 5 H, C₆H₅).

¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ 11.14 (CH₃), 22.87, 22.94 [both

CH(CH₃)₂], 42.45 (C-2), 46.94 (C-3), 51.70 [NCH(CH₃)₂],

126.1Ϫ141.1 (C₆H₅). [α]₅₈₉ϭ ϩ64.8 (c ϭ 4.7, CH₂Cl₂).

3

CCH₃), 0.86, 0.88 (both d, J_H,Hϭ 6.39 Hz each, both 3 H,

CH(CH₃)₂], 2.70 [sept, 1 H, CH(CH₃)₂], 2.99 [m, 1 H, C(2)-H],

3.52 [dd, ²J_P,H/³J_H,Hϭ 4.84/6.60 Hz, 1 H, C(1)-H], 6.9Ϫ7.6 (m, 15

H, C₆H₅); NH not observed. ¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ

(؊)-(1R,2S)-(2-Methylamino-1-phenylpropyl)diphenylphosphane

3

20.32 (d, J_P,Cϭ 5.08 Hz, CCH₃), 22.01, 24.22 [both s, both

[(R,S)-2]:

Boron

trifluorideϪdiethyl

etherate

(2.32 mL,

CH(CH₃)₂], 45.34 [s, NCH(CH₃)₂], 51.41, 51.90 (both d, J_P,C

ϭ

18.50 mmol) was added dropwise to a CHCl₃solution of (ϩ)-

(2S,3S)-trans-1,2-dimethyl-3-phenylaziridine (2.717 g, 18.45 mmol)

and diphenylphosphane (3.20 mL, 18.50 mmol). The mixture was

heated to reflux overnight, then hydrolyzed and adjusted to pH 8

by addition of NaHCO₃. The organic phase was separated, washed

with 5% aqueous sodium hydrogencarbonate, dried over Na₂SO₄,

and the solvents evaporated to leave a yellowish oily residue. The

oil was re-dissolved in diethyl ether, filtered, evaporated again, and

heated at 100 °C under a dynamic vacuum in order to remove any

15.26, 12.35 Hz, C-1/C-2), 126.4Ϫ130.5 (C₆H₅). ³¹P{¹H} NMR

(CDCl₃, ppm): δ ϭ Ϫ7.68. [α]₅₈₉ϭ Ϫ205 (c ϭ 1.1, CH₂Cl₂).

C₂₄H₂₈NP (361.5): calcd. C 79.75, H 7.81, N 3.87; found C 79.52,

H 8.02, N 3.73.

(؊)-(1R,2S)-(2-Dimethylamino-1-phenylpropyl)diphenylphosphane

[(R,S)-5]: Methanesulfonyl chloride (1.27 mL, 16.35 mmol) and tri-

ethylamine (3.50 mL, 24.52 mmol) were sequentially added to a

chilled THF solution (40 mL) of (Ϫ)-N-methylephedrine (1.465 g,

8.17 mmol). The aziridinium methanesulfonate which was formed

after stirring the mixture for 1 h at room temperature was further

reacted by heating to reflux a toluene solution (50 mL) containing

diphenylphosphane (1.42 mL, 8.17 mmol) and an additional

amount of NEt₃(2.30 mL, 16.35 mmol). After hydrolysis the prod-

uct was isolated following the workup procedure described above

for (R,S)-2; yield 1.11 g (39%) of the aminophosphane as a color-

remaining diphenylphosphane; yield 289 mg (47%) of (R,S)-2 as a

3

colorless wax. ¹H NMR (CDCl₃, ppm): δ ϭ 0.98 (d, J_H,H

ϭ

6.39 Hz, 3 H, CCH₃), 1.83 [s (br), 1 H, NH], 2.30 (s, 3 H, NCH₃),

2.80 [m, 1 H, C(2)-H], 3.62 [‘‘t’’, Σ|²J_P,Hϩ³J_H,H| ϭ 11.70 Hz, 1 H,

C(1)-H], 7.0Ϫ7.7 (m, 15 H, C₆H₅). ¹³C{¹H} NMR (CDCl₃, ppm):

3

δ ϭ 18.60 (d, J_P,Cϭ 4.36 Hz, CCH₃), 34.11 (s, NCH₃), 51.89,

56.52 (both d, J_P,Cϭ 13.08, 16.72 Hz, C-1/C-2), 126.5Ϫ138.6

(C₆H₅). ³¹P{¹H} NMR (CDCl₃, ppm): δ ϭ Ϫ7.00. [α]₅₈₉ϭ Ϫ218

(c ϭ 0.9, THF). C₂₂H₂₄NP (333.4): calcd. C 79.25, H 7.26, N 4.20;

found C 79.47, H 7.43, N 4.11.

1

3

less wax. H NMR (CDCl₃, ppm): δ ϭ 0.87 (d, J_H,Hϭ 6.75 Hz,

3 H, CCH₃), 1.96 [s, 6 H, N(CH₃)₂], 3.04 [m, 1 H, C(2)-H], 3.55

2

[dd, J_P,H/³J_H,Hϭ 6.03/7.68 Hz, 1 H, C(1)-H], 6.9Ϫ7.7 (m, 15 H,

3

C₆H₅). ¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ 18.60 (d, J_P,C

ϭ

(؉)-(1S,2S)-(2-Benzylamino-1-phenylpropyl)diphenylphosphane

[(S,S)-3]: The preparation was carried out as described for (R,S)-2

by reacting BF₃-activated (Ϫ)-(2S,3R)-cis-1-benzyl-2-methyl-3-phe-

nylaziridine (367 mg, 1.65 mmol) with diphenylphosphane

(0.29 mL, 1.65 mmol); yield 325 mg (48%) of (S,S)-3 as a white

4.36 Hz, CCH₃), 34.11 [s, N(CH₃)₂], 51.89, 56.52 (both d, J_P,C

ϭ

13.08, 16.72 Hz, C-1/C-2), 126.5Ϫ138.6 (C₆H₅). ³¹P{¹H} NMR

(CDCl₃, ppm): δ ϭ Ϫ4.24. [α]₅₈₉ϭ Ϫ318 (c ϭ 3.1, THF).

C₂₃H₂₆NP (347.4): calcd. C 79.51, H 7.54, N 4.03; found C 79.84,

H 7.88, N 3.92.

1

3

powder. H NMR (CDCl₃, ppm): δ ϭ 1.04 (d, J_H,Hϭ 6.57 Hz, 3

H, CCH₃), 1.41 [s (br), 1 H, NH], 2.81 [m, 1 H, C(2)-H], 3.64, 3.66

(AB-dd, ²J_H,Hϭ 13.45 Hz, 2 H, CH₂), 3.83 [dd, ²J_P,H/³J_H,Hϭ 5.49/

5.67 Hz, 1 H, C(1)-H], 6.9Ϫ7.5 (m, 20 H, C₆H₅). ¹³C{¹H} NMR

(2-Amino-2-methylpropyl)diphenylphosphane (8): A mixture com-

posed of 9.96 mmol in each case of 2,2-dimethylaziridine (708 mg),

boron trifluoride diethyl etherate (1.26 mL), and diphenylphos-

phane (1.73 mL) in CHCl₃(50 mL) was heated to reflux for 3 h.

An oily precipitate resulting from polymerization of the aziridine

was removed by decanting the supernatant liquid, which was

worked up by hydrolysis as outlined before for (R,S)-2 to give

3

(CDCl₃, ppm): δ ϭ 17.90 (d, J_P,Cϭ 9.45 Hz, CCH₃), 50.63 (s,

NCH₂), 48.98, 53.54 (both d, J_P,Cϭ 14.53, 17.43 Hz, C-1/C-2),

119.5Ϫ140.2 (C₆H₅). ³¹P{¹H} NMR (CDCl₃, ppm): δ ϭ Ϫ8.05.

[α]₅₈₉ϭ ϩ64.5 (c ϭ 6.7, CH₂Cl₂). C₂₈H₂₈NP (409.5): calcd. C

82.12, H 6.89, N 3.42; found C 81.95, H 7.01, N 3.31.

1

870 mg (34%) of the P,N ligand as a clear colorless oil. H NMR

(؉)-(1S,2S)-(2-Isopropylamino-1-phenylpropyl)diphenylphosphane

[(S,S)-4]: This material was obtained as outlined before by treating

(Ϫ)-(2S,3R)-cis-1-isopropyl-2-methyl-3-phenylaziridine (263 mg,

1.50 mmol) in the presence of F₃B·OEt₂with diphenylphosphane

(0.26 mL, 1.50 mmol); yield 421 mg (78%) of a colorless waxy solid.

(CDCl₃, ppm): δ ϭ 1.21 (s, 6 H, CH₃), 1.36 [s (br), 2 H, NH₂], 2.36

2

(d, J_P,Hϭ 3.66 Hz, CH₂), 7.2Ϫ7.6 (m, 10 H, C₆H₅). ¹³C{¹H}

3

NMR (CDCl₃, ppm): δ ϭ 32.01 (d, J_P,Cϭ 7.99 Hz, CH₃), 45.83,

50.00 (both d, J_P,Cϭ 15.25, 15.26 Hz, C-1/C-2), 128.3Ϫ139.5

(C₆H₅). ³¹P{¹H} NMR (CDCl₃, ppm): δ ϭ Ϫ23.09. C₁₆H₂₀NP

(257.3): calcd. C 74.69, H 7.83, N 5.44; found C 74.79, H 7.98,

3

¹H NMR (CDCl₃, ppm): δ ϭ 0.63 (d, J_H,Hϭ 6.03 Hz, 3 H,

3

CCH₃), 0.83, 1.00 [both d, J_H,Hϭ 6.21, 6.60 Hz, both 3 H, N 5.21.

900

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org

Eur. J. Inorg. Chem. 2004, 888Ϫ905

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

[(COD)Ir(Ph₂PCH₂CH₂NH₂)]BF₄[Ir^؉-6]: To [Ir(COD)₂]BF₄

6.75/4.41 Hz, 1 H, PhC(1)-H], 4.71, 4.75 (AB-dd, J_H,Hϭ 6.48 Hz,

2

(472 mg, 0.95 mmol) suspended in THF (10 mL) was added drop-

2 H, CH₂), 5.51 (m, 2 H, diene CH), 5.9 [s (br), 1 H, NH],

wise a solution of 6 (220 mg, 0.96 mmol) in THF (15 mL). The 6.8Ϫ8.1 (m, 20 H, C₆H₅). ¹³C{¹H} NMR ([D₆]acetone, ppm:

3

dark red solution which formed on stirring overnight was reduced

in vacuo to a small residual volume. Dilution with diethyl ether

and n-pentane (20 mL each) caused the product to separate from

solution as an orange microcrystalline precipitate which was col-

δ[δ(S_C-1,S_C-2,S_N)] ϭ 17.37 (d, J_P,Cϭ 13.80 Hz, CCH₃), 26.1Ϫ37.6

1

(diene CH₂; partially obscured by solvent), 47.09 (d, J_P,C

ϭ

2

24.71 Hz, PCH), 51.23 (s, CH₂), 64.40 (d, J_P,Cϭ 9.45 Hz, NCH),

64.52, 69.12 (both s, CHϭCH trans N), 82.35, 94.20 (both d,

²J_P,Cϭ 16.72, 7.99 Hz, CHϭCH trans P), 125.0Ϫ138.5 (C₆H₅);

lected by filtration, thoroughly washed with diethyl ether, and dried

1

under a dynamic vacuum; yield 540 mg (91%). H NMR (CDCl₃, δ[δ(S_C-1,S_C-2,R_N)] ϭ 16.50 (d, ³J_P,Cϭ 13.80 Hz, CCH₃), 26.1Ϫ37.6

ppm): δ ϭ 1.7Ϫ2.3 (m, 8 H, diene CH₂), 2.85, 2.95 (both m, 2 H (diene CH₂; partially obscured by solvent), 53.45 (s, CH₂), 54.18 (d,

2

each, PCH₂/NCH₂), 3.36 [s (br), 2 H, NH₂], 4.7, 5.1 (both m, 2 H

¹J_P,Cϭ 25.43 Hz, PCH), 60.02 (d, J_P,Cϭ 9.45 Hz, NCH), 60.79,

each, both diene CH), 7.1Ϫ7.7 (m, 10 H, C₆H₅). ¹³C{¹H} NMR 65.65 (both s, CHϭCH trans N), 92.89, 98.31 (both d, ²J_P,Cϭ 14.54,

1

(CDCl₃, ppm): δ ϭ 29.30 (s, 2 diene CH₂), 31.56 (d, J_P,C

ϭ

8.72 Hz, CHϭCH trans P), 125.0Ϫ138.5 (C₆H₅). ³¹P{¹H} NMR

32.69 Hz, PCH₂), 32.41 (s, 2 diene CH₂), 44.69 (d, ²J_P,Cϭ 5.09 Hz, ([D₆]acetone, ppm): δ ϭ 39.97 [δ(S_C-1,S_C-2,S_N) conformer], 46.65

2

NCH₂), 61.64 (s, CHϭCH trans N), 93.33 (d, J_P,Cϭ 11.62 Hz, [δ(S_C-1,S_C-2,R_N) conformer]. C₃₆H₄₀BF₄IrNP (796.8): calcd. C

31

CHϭCH trans P), 128.8Ϫ133.2 (C₆H₅).

P{¹H} NMR (CDCl₃,

54.27, H 5.06, N 1.76; found C 54.52, H 5.21, N, 1.62.

ppm): δ ϭ 38.61. C₂₂H₂₈BF₄IrNP (616.5): calcd. C 42.86, H 4.58,

N 2.27; found C 43.02, H 4.67, N 2.09.

[(COD)Ir{(1S,2S)-Ph₂PCH(Ph)CH(Me)NHCHMe₂}]BF₄

[Ir^؉-

(S,S)-4]: Yield, from [Ir(COD)₂]BF₄(347 mg, 0.70 mmol) and

(S,S)-4 (300 mg, 0.76 mmol), 456 mg (87%) of the product as an

orange solid composed of the two ring conformers δ(S_C-1,S_C-2,S_N), ഠ

25%, and δ(S_C-1,S_C-2,R_N), ഠ 75% (isomeric distribution estimated

from the relative intensities of the ³¹P resonances). ¹H NMR

(CDCl₃, ppm): δ[δ(S_C-1,S_C-2,R_N)] ϭ 1.37 [‘‘t’’, Σ|³J_H,Hϩ⁵J_H,H| ϭ

The following complexes were prepared by a procedure analogous

to that detailed before.

[(COD)Ir(2-Ph₂PC₆H₄NHMe)]BF₄[Ir^؉-7]: Yield, from [Ir-

(COD)₂]BF₄(574 mg, 1.16 mmol) and the chelate ligand (338 mg,

1.16 mmol), 630 mg (80%) of Ir^ϩ-7 as a reddish brown solid. ¹H

NMR (CDCl₃, ppm): δ ϭ 1.6Ϫ2.5 (m, 8 H, diene CH₂), 2.85 (d,

³J_H,Hϭ 6.03 Hz, 3 H, CH₃), 3.1, 4.0, 5.2, 5.75 (all m, 1 H each, all

diene CH), 7.2Ϫ8.0 (m, 14 H, C₆H₅and C₆H₄); NH not observed.

¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ 28.94, 31.13, 31.48, 34.77 (all

s, all diene CH₂), 48.28 (s, CH₃), 61.92, 65.92 (both s, CHϭCH

3

13.14 Hz, 6 H, CH(CH₃)₂], 1.50 (d, J_H,Hϭ 6.78 Hz, 3 H, CCH₃),

1.5Ϫ2.4 (m, 8 H, diene CH₂), 3.22 [m, 1 H, MeC(2)-H], 3.34 [s

3

(br), 1 H, NH], 3.63 (sept, J_H,Hϭ 6.57 Hz, 1 H, CH(CH₃)₂], 4.29

2

3

[dd, J_P,Hϭ 12.17, J_H,Hϭ 7.04 Hz, 1 H, PhC(1)-H], 4.87, 5.15,

5.37, 5.75 (all m, 1 H each, all diene CH), 6.8Ϫ7.6 (m, 15 H, C₆H₅).

¹³C{¹H} NMR (CDCl₃, ppm): δ[δ(S_C-1,S_C-2,R_N)]

ϭ 19.83

2

3

trans N), 94.81, 98.99 (both d, J_P,Cϭ 13.08, 10.17 Hz, CHϭCH

(d, J_P,Cϭ 13.08 Hz, CCH₃), 21.98, 24.23 [both s, CH(CH₃)₂],

2

1

trans P), 123.3Ϫ135.5 (C₆H₅and C₆H₄), 157.83 (d, J_P,C

ϭ

26.10, 27.18, 31.81, 36.78 (all s, all diene CH₂), 54.71 (d, J_P,C

ϭ

18.17 Hz, phenylene C-1). ³¹P{¹H} NMR (CDCl₃, ppm): δ ϭ

30.39. C₂₇H₃₀BF₄IrNP (678.6): calcd. C 47.79, H 4.46, N 2.06;

found C 47.62, H 4.67, N 1.94.

25.43 Hz, PCH), 55.03 [s, CH(CH₃)₂], 56.31, 62.88 (both s, CHϭ

2

CH trans N), 60.75 (d, J_P,Cϭ 7.99 Hz, NCH), 93.90, 97.87 (both

2

d, J_P,Cϭ 13.80, 9.44 Hz, CHϭCH trans P), 124.5Ϫ136.9 (C₆H₅);

¹H and ¹³C{¹H} spectra of the minor δ[δ(S_C-1,S_C-2,S_N)] conformer

not assigned. ³¹P{¹H} NMR ([D₆]acetone, ppm): δ ϭ 40.79

[δ(S_C-1,S_C-2,S_N) conformer], 45.44 [δ(S_C-1,S_C-2,R_N) conformer].

C₃₂H₄₀BF₄IrNP (748.7): calcd. C 51.34, H 5.39, N 1.87; found C

51.83, H 5.77, N 1.73.

[(COD)Ir(Ph₂PCH₂CMe₂NH₂)]BF₄[Ir^؉-8]: Yield, from [Ir-

(COD)₂]BF₄(131 mg, 0.26 mmol) and the β-aminophosphane

(68 mg, 0.26 mmol), 151 mg (88%) of Ir^ϩ-8 as a dark reddish brown

solid. ¹H NMR (CDCl₃, ppm): δ ϭ 1.40 (s, 6 H, CH₃), 1.7Ϫ2.4

(m, 8 H, diene CH₂), 2.51 (d, ²J_P,Hϭ 9.51 Hz, 2 H, PCH₂), 3.41 [s

(br), 2 H, NH₂], 4.8, 5.3 (both m, 2 H each, both diene CH),

7.3Ϫ7.8 (m, 10 H, C₆H₅). ¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ 28.88,

[(COD)Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)NHMe}]BF₄[Ir^؉-(R,S)-2]:

Yield, from [Ir(COD)₂]BF₄(206 mg, 0.42 mmol) and the P,N li-

gand (153 mg, 0.46 mmol), 243 mg (81%) of Ir^ϩ-(R,S)-2 as a dark

red precipitate containing the λ(R_C-1,S_C-2,R_N) conformer (94%) in

addition to two further sterically locked isomers of unassigned

stereochemistry. ¹H NMR ([D₆]acetone, ppm): δ[λ(R_C-1,S_C-

3

28.98, 29.28, 31.72 (all s, all diene CH₂), 32.31 (d, J_P,Cϭ 2.91 Hz,

CH₃), 43.61 (d, ¹J_P,Cϭ 30.52 Hz, PCH₂), 61.77 (d, ²J_P,Cϭ 5.09 Hz,

2

NCH₂), 61.86 (s, CHϭCH trans N), 93.73 (d, J_P,Cϭ 12.35 Hz,

CHϭCH trans P), 129.0Ϫ133.4 (C₆H₅). ³¹P{¹H} NMR (CDCl₃,

ppm): δ ϭ 29.14. C₂₄H₃₂BF₄IrNP (644.6): calcd. C 44.73, H 5.00,

N 2.17; found C 44.42, H 5.09, N 2.09.

3

₂,R_N)] ϭ 1.14 (d, J_H,Hϭ 6.54 Hz, 3 H, CCH₃), 1.4Ϫ2.6 (m, 8 H,

3

diene CH₂), 2.67 (d, J_H,Hϭ 5.85 Hz, 3 H, NCH₃), 2.88 [m, 1 H,

MeC(2)-H], 3.11 (m, 1 H, diene CH), 3.22 [s (br), 1 H, NH], 3.71

[(COD)Ir{(1S,2S)-Ph₂PCH(Ph)CH(Me)NHCH₂Ph}]BF₄

[Ir^؉-

2

3

(m, 1 H, diene CH), 4.31 [dd, J_P,Hϭ 14.26, J_H,Hϭ 4.20 Hz, 1

H, PhC(1)-H], 5.27, 5.61 (both m, 1 H each, both diene CH),

6.7Ϫ8.2 (m, 15 H, C₆H₅). ¹³C{¹H} NMR ([D₆]acetone, ppm):

δ[λ(R_C-1,S_C-2,R_N)] ϭ 15.17 (d, ³J_P,Cϭ 11.62 Hz, CCH₃), 27.4Ϫ36.6

(diene CH₂; partially obscured by solvent), 40.13 (s, NCH₃), 56.76

(S,S)-3]: Yield, from [Ir(COD)₂]BF₄(235 mg, 0.48 mmol) and

(S,S)-3 (195 mg, 0.48 mmol), 314 mg (82%) of the complex as an

orange solid containing the δ(S_C-1,S_C-2,S_N) conformer (ഠ 40%) to-

gether with the δ(S_C-1,S_C-2,R_N) form (ഠ 60%) as sterically locked

ring conformers (isomeric distribution estimated from ¹H and

³¹P{¹H} NMR). ¹H NMR ([D₆]acetone, ppm): δ[δ(S_C-1,S_C-2,S_N)] ϭ

1

(d, J_P,Cϭ 29.79 Hz, PCH), 60.07, 62.61 (both s, CHϭCH trans

2

N), 66.49 (d, ²J_P,Cϭ 9.45 Hz, NCH), 93.59, 96.20 (both d, J_P,C

ϭ

3

1.32 (d, J_H,Hϭ 6.39 Hz, 3 H, CCH₃), 1.4Ϫ2.5 (m, 8 H, diene

10.17, 13.08 Hz, CHϭCH trans P), 126.0Ϫ136.4 (C₆H₅). ³¹P{¹H}

NMR ([D₆]acetone, ppm): δ ϭ 38.10 [94%; λ(R_C-1,S_C-2,R_N)], 38.01

(ഠ 4%), 41.27 (ഠ 2%); both unassigned. C₃₀H₃₆BF₄IrNP (760.6):

calcd. C 50.00, H 5.04, N 1.94; found C 50.24, H 5.32, N 2.01.

CH₂), 2.92 [m, 1 H, MeC(2)-H], 3.20, 3.39 (both m, 1 H each, both

2

diene CH), 4.20, 4.22 (AB-dd, J_H,Hϭ 6.93 Hz, 2 H, CH₂), 4.58

2

[dd, J_P,H/³J_H,Hϭ 6.39/3.63 Hz, 1 H, PhC(1)-H], 5.63 (m, 2 H,

diene CH), 6.3 [s (br), 1 H, NH], 6.8Ϫ8.1 (m, 20 H, C₆H₅);

3

δ[δ(S_C-1,S_C-2,R_N)] ϭ 1.19 (d, J_H,Hϭ 6.03 Hz, 3 H, CCH₃), (؊)-[(COD)Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)NHCHMe₂}]BF₄

1.4Ϫ2.5 (m, 8 H, diene CH₂), 2.65 [m, 1 H, MeC(2)-H], 3.61,

[Ir^؉-(R,S)-4]: Yield, from [Ir(COD)₂]BF₄(863 mg, 1.74 mmol) and

the β-aminophosphane (634 mg, 1.75 mmol), 1.070 g (82%) of the

2

3.67 (both m, 1 H each, both diene CH), 4.57 [dd, J_P,H/³J_H,H

ϭ

Eur. J. Inorg. Chem. 2004, 888Ϫ905

www.eurjic.org

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

901

L. Dahlenburg, R. Götz

FULL PAPER

complex as an orange solid. ¹H NMR ([D₆]acetone, ppm): δ ϭ CH₂), 2.28 (d, J_P,Cϭ 10.23 Hz, 2 H, PCH₂), 2.40, 2.59 (both m,

2

3

1.24, 1.32 [both d, J_H,Hϭ 6.78 Hz each, both 3 H, CH(CH₃)₂],

2 H each, both diene CH₂), 2.99 (m, 2 H, diene CH), 4.5 [s (br), 1

3

1.39 (d, J_H,Hϭ 6.57 Hz, 3 H, CCH₃), 1.7 (m, 1 H, diene CH₂), H, NH], 4.90 (m, 2 H, diene CH), 7.15 (m, 6 H, C₆H₅), 7.74 (m, 4

1.9Ϫ2.3 (m, 5 H, diene CH₂), 2.3Ϫ2.6 (m, 2 H, diene CH₂), 3.12 H, C₆H₅). ¹³C{¹H} NMR (C₆D₆, ppm): δ ϭ 31.14, 35.60 (both s,

[m, 1 H, MeC(2)-H], 3.4Ϫ3.6 (m, 2 H, diene CH), 3.65 [s (br), 1 both diene CH₂), 36.09 (d, ³J_P,Cϭ 7.99 Hz, CH₃), 46.89 (d, ¹J_P,Cϭ

2

H, NH], 4.51 [dd, ²J_P,Hϭ 12.99, ³J_H,Hϭ 4.95 Hz, 1 H, PhC(1)-H],

31.24 Hz, PCH₂), 47.62 (s, CHϭCH trans N), 67.30 (d, J_P,C

ϭ

2

4.80 (sept, 1 H, CH(CH₃)₂], 5.41, 5.87 (both m, 1 H each, both 9.45 Hz, NCH₂), 84.33 (d, J_P,Cϭ 14.54 Hz, CHϭCH trans P),

diene CH), 6.8Ϫ7.9 (m, 15 H, C₆H₅). ¹³C{¹H} NMR ([D₆]acetone, 128.7Ϫ134.1 (C₆H₅). ³¹P{¹H} NMR (C₆D₆, ppm): δ ϭ 49.85.

3

ppm): δ ϭ 18.47 (d, J_P,Cϭ 7.99 Hz, CCH₃), 22.46, 23.71 [both s,

CH(CH₃)₂], 26.37Ϫ35.90 (diene CH₂; partially obscured by sol-

C₂₄H₃₁IrNP (556.7): calcd. C 51.78, H 5.61, N 2.52; found C 52.55,

H 5.97, N 2.12.

1

vent), 53.98 (d, J_P,Cϭ 27.61 Hz, PCH), 55.80 [s, CH(CH₃)₂],

[(COD)Ir{(1R,2S)-Ph₂PCH(C₆H₄-o)CH(Me)NHCHMe₂]

[Ir-

2

61.67, 62.10 (both s, CHϭCH trans N), 62.37 (d, J_P,Cϭ 7.99 Hz,

(R,S)-4a]: A solution of potassium hydroxide (400 mg, 7.13 mmol)

in methanol (10 mL) was combined with Ir^ϩ-(R,S)-4 (103 mg,

0.14 mmol) dissolved in MeOH (10 mL) to give an orange precipi-

tate which was collected by filtration and washed with a few millili-

ters of methanol. Re-dissolution of the solid in hot acetone, fol-

lowed by cooling to room temperature afforded the orthometalated

complex as orange crystals which tenaciously retained some re-

sidual acetone solvent. ¹H NMR ([D₆]acetone, ppm): δ ϭ 0.95, 1.08

[both d, ³J_H,Hϭ 6.24 each, both 3 H, CH(CH₃)₂], 1.20 (d, ³J_H,Hϭ

6.42 Hz, 3 H, CCH₃), 1.4Ϫ2.6 (m, 8 H, diene CH₂), 2.65 [m, 2 H,

MeC(2)-H and CH(CH₃)₂], 3.95 [s (br), 1 H, NH], 4.05, 4.22 (both

m, 1 H each, both diene CH), 4.39 [m, 1 H, PhC(1)-H], 5.21, 5.47

(both m, 1 H each, both diene CH), 6.81 (m, 2 H, C₆H₄), 7.08 (m,

1 H, C₆H₄), 7.26 (m, 3 H, C₆H₅), 7.29 (m, 1 H, C₆H₄), 7.44, 7.67

(both m, 7 H each, C₆H₅). ³¹P{¹H} NMR ([D₆]acetone, ppm): δ ϭ

44.99. C₃₂H₃₉IrNP (660.9): calcd. C 58.16, H 5.95, N 2.12.

C₃₂H₃₉IrNP·C₃H₆O (718.9) calcd. C 58.47, H 6.31, N 1.95; found

C 58.67, H 6.33, N 1.91.

NCH), 90.25, 93.91 (both d, ²J_P,Cϭ 14.54, 8.72 Hz, CHϭCH trans

P), 128.4Ϫ135.3 (C₆H₅). ³¹P{¹H} NMR ([D₆]acetone, ppm): δ ϭ

37.54. [α]₅₈₉ϭ Ϫ295 (c ϭ 0.7, MeOH). C₃₂H₄₀BF₄IrNP (748.7):

calcd. C 51.34, H 5.39, N 1.87; found C 51.65, H 5.30, N 2.00.

(؊)-[(COD)Ir{(1R,2S)-Ph₂PCH(Ph)CH(Me)NMe₂}]BF₄

[Ir^؉-

(R,S)-5]: Yield, from [Ir(COD)₂]BF₄(104 mg, 0.21 mmol) and the

P,N ligand (80 mg, 0.23 mmol), 140 mg (83%) of Ir^ϩ-(R,S)-5 as an

3

orange solid. ¹H NMR (CDCl₃, ppm): δ ϭ 1.40 (d, J_H,H

ϭ

6.60 Hz, 3 H, CCH₃), 1.5Ϫ2.4 (m, 8 H, diene CH₂), 2.90, 3.13

(both s, both NCH₃), 3.15 [m, 1 H, MeC(2)-H], 3.27, 3.37 (both

2

3

m, 1 H each, both diene CH), 4.53 [dd, J_P,Hϭ 9.78, J_H,H

ϭ

4.65 Hz, 1 H, PhC(1)-H], 4.71, 5.26 (both m, 1 H each, both diene

CH), 6.8Ϫ7.6 (m, 15 H, C₆H₅). ¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ

3

15.97 (d, J_P,Cϭ 6.54 Hz, CCH₃), 29.36, 29.69, 30.74, 32.63 (all s,

1

all diene CH₂), 47.41 (d, J_P,Cϭ 23.25 Hz, PCH), 48.75, 50.15

(both s, both NCH₃), 59.00, 65.56 (both s, CHϭCH trans N), 76.07

2

(d, J_P,Cϭ 7.26 Hz, NCH), 93.34, 97.34 (both d, J_P,Cϭ 12.35,

10.90 Hz, CHϭCH trans P), 127.1Ϫ137.5 (C₆H₅). ³¹P{¹H} NMR

(CDCl₃, ppm): δ ϭ 35.70. [α]₅₈₉ϭ Ϫ95.4, [α]₅₇₈ϭ Ϫ112 (both c ϭ

0.3, MeOH). C₃₁H₃₈BF₄IrNP (734.7): calcd. C 50.68, H 5.21, N

1.91; found C 50.65, H 5.30, N 2.00.

cis-[(COD)IrH₂(Ph₂PCH₂CMe₂NH₂)]BF₄, (Ir^؉-9): A sample of

Ir^ϩ-8 (20 mg) was dissolved in CD₃CN (2 mL), transferred into a

1

high-pressure NMR tube and treated with 5 bar of H₂. H NMR

(CD₃CN, ppm): δ ϭ Ϫ15.78 (d, cis-²J_P,Hϭ 10.95 Hz, 1 H, IrH

trans N), Ϫ12.60 (d, cis-²J_P,Hϭ 15.91 Hz, 1 H, IrH trans ϾCϭ

CϽ), 1.17 (s, 6 H, CH₃), 1.6Ϫ2.9 (m, 8 H, diene CH₂), 3.00 (d,

²J_P,Hϭ 9.33 Hz, 2 H, PCH₂), 3.89, 4.67 (both m, 1 H each, both

diene CH), 4.93 [s (br), 2 H, NH₂], 5.58, 5.71 (both m, 1 H each,

both diene CH), 7.1Ϫ8.2 (m, 10 H, C₆H₅). ³¹P{¹H} NMR

(CD₃CN, ppm): δ ϭ 31.87.

[(COD)Ir(2-Ph₂PC₆H₄NMe)] (Ir-7a): A solution of 7 (318 mg,

1.09 mmol) in n-pentane (10 mL) was cooled to Ϫ70 °C and treated

with n-butyllithium (0.44 mL, 1.10 mmol of a 2.5  hexane solu-

tion). The resultant suspension of the monolithiated P,N ligand

was allowed to warm to ambient temperature and then added to a

stirred suspension of [{(COD)Ir(µ-Cl)}₂] (366 mg, 0.54 mmol) in

benzene. Stirring for 3 h at ambient conditions caused the precipi-

tation of lithium chloride which was separated by filtration. The

filtrate was reduced in volume in vacuo to give 558 mg (87%) of a

bright red solid retaining some residual solvent even after pro-

cis-[(COD)IrH₂(Ph₂PCH₂CMe₂NH)] (Ir-9a): A CD₃CN solution

of Ir-8a was pressurized, in an NMR tube, to 5 bar of H₂. ¹H

NMR (CD₃CN, ppm): δ ϭ Ϫ18.13 (d, cis-²J_P,Hϭ 8.79 Hz, 1 H,

IrH trans N), Ϫ7.09 (d, cis-²J_P,Hϭ 13.18 Hz, 1 H, IrH trans ϾCϭ

CϽ), 1.13 (s, 6 H, CH₃), 1.5Ϫ2.7 (m, 10 H, diene CH₂overlapping

with PCH₂), 3.17 (m, 2 H, diene CH), 3.85 [s (br), 1 H, NH], 4.17

(m, 2 H, diene CH), 7.1Ϫ8.0 (m, 10 H, C₆H₅). ³¹P{¹H} NMR

(CD₃CN, ppm): δ ϭ 17.68.

1

longed drying under a dynamic vacuum. H NMR (CDCl₃, ppm):

δ ϭ 1.82, 2.18 (both m, 4 H each, both diene CH₂), 2.81 (m, 2 H,

diene CH), 3.05 (s, 3 H, CH₃), 4.96 (m, 2 H, diene CH), 6.26, 6.53,

6.96, 7.08 (all m, 1 H each, all C₆H₄), 7.2Ϫ7.7 (m, 10 H, C₆H₅).

¹³C{¹H} NMR (CDCl₃, ppm): δ ϭ 30.47, 32.77 (both s, both diene

CH₂), 39.24 (s, CH₃), 52.98 (s, CHϭCH trans N), 91.62 (d, ²J_P,Cϭ

13.08 Hz, CHϭCH trans P), 110.70, 114.29, (both d, J_P,Cϭ 12.82,

cis-[(COD)IrH₂{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂]BF₄(Ir^؉-10): A

sample of Ir^ϩ-(S,S)-1 (ഠ 20 mg) in [D₈]THF (2 mL) was exposed

to 1 bar of H₂and immediately characterized by NMR spec-

6.79 Hz, both phenylene C), 118.66 (d, ¹J_P,Cϭ 54.34 Hz, phenylene

2

troscopy. ¹H NMR ([D₈]THF, ppm): δ ϭ Ϫ16.31 (d, cis-²J_P,H

ϭ

C-2), 128.2Ϫ133.2 (C₆H₅and 2 phenylene C), 171.84 (d, J_P,C

ϭ

24.71 Hz, phenylene C-1). ³¹P{¹H} NMR (C₆D₆, ppm): δ ϭ 42.61.

C₂₇H₂₉IrNP (590.7): calcd. C 54.90, H 4.95, N 2.73. C₂₇H₃₀IrNP·

1/2C₆H₆(629.8): calcd. C 57.21, H 5.12, N 2.22; found C 57.98, H

5.17, N 2.22.

11.52 Hz, 1 H, IrH trans N), Ϫ12.44 (d, cis-²J_P,Hϭ 14.82 Hz, 1 H,

IrH trans ϾCϭCϽ), 0.89 (d, ³J_H,Hϭ 6.03 Hz, 3 H, CH₃), 1.5Ϫ2.9

2

(m, 8 H, diene CH₂), 2.74 [m, 1 H, MeC(2)-H], 4.01 [dd, J_P,H

ϭ

12.63, ³J_H,Hϭ 4.95 Hz, 1 H, PhC(1)-H], 4.16, 4.56, 4.77, 4.96, 5.27,

5.45 (all m, 1 H each, diene CH overlapping with NH₂), 6.9Ϫ7.7

(m, 15 H, C₆H₅). ³¹P{¹H} NMR ([D₈]THF, ppm): δ ϭ 46.03.

[(COD)Ir(Ph₂PCH₂CMe₂NH)] (Ir-8a): The complex was prepared

by analogy to the procedure outlined before employing ligand 8

(218 mg, 0.85 mmol), an equimolar portion of nBuLi in hexane,

and [{(COD)Ir(µ-Cl)}₂](284 mg, 0.42 mmol); yield 385 mg (82%) of

cis,cis-[(MeCN)₂IrH₂{(1R,2S)-Ph₂PCH(Ph)CH(Me)NHMe]BF₄

(Ir^؉-11): A solution of Ir^ϩ-(R,S)-2 (90 mg, 0.12 mmol) in aceto-

the amido complex as a dark red solid. ¹H NMR (C₆D₆, ppm): nitrile (2 mL) was stirred under 25 bar of H₂for 2 h in an autoclave.

δ ϭ 1.36 (s, 6 H, CH₃), 2.03, 2.24 (both m, 2 H each, both diene

The solid residue remaining after removal of all volatiles in vacuo

www.eurjic.org

902

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Eur. J. Inorg. Chem. 2004, 888Ϫ905

Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

was re-dissolved in CD₂Cl₂and immediately characterized by

cally 0.02 mmol in 3.0 mL). The required equivalent of activating

NMR spectroscopy. ¹H NMR (CD₂Cl₂, ppm): δ ϭ Ϫ21.20, Ϫ21.14 nitrogen or alkaline base (cf. Tables 2Ϫ4) and 2.0 mmol of aceto-

(ABX m, cis-²J_P,Hϭ 17.22, 22.11, cis-²J_H,Hϭ 7.13 Hz, 1 H each, phenone were added, the mixture was stirred for 10 min at ambient

3

IrH₂), 1.09 (d, J_H,Hϭ 6.06 Hz, 3 H, CHCH₃), 1.73, 2.37 (both s, conditions, and the tube was inserted into an argon-filled stainless

3

3 H each, both CH₃CN), 2.87 (d, J_H,Hϭ 6.06 Hz, 3 H, NCH₃),

steel autoclave. The autoclave was sealed, pressurized and vented

2

3.19 [m, 1 H, MeC(2)-H], 3.42 [s (br), 1 H, NH)], 4.01 [dd, J_P,Hϭ several times with H₂(Messer-Griesheim; 99.999%), and sub-

13.71, ³J_H,Hϭ 4.38 Hz, 1 H, PhC(1)-H], 6.9Ϫ7.7 (m, 15 H, C₆H₅).

sequently pressurized (usually to 10Ϫ25 bar) and maintained with

¹³C{¹H} NMR (CD₂Cl₂, ppm): δ ϭ 1.70, 2.97 (both s, CH₃CN), stirring at 25 or 50 °C. At the end of the reaction, the pressure was

3

15.27 (d, J_P,Cϭ 10.90 Hz, CHCH₃), 37.04 (s, NCH₃), 51.62, (d,

released, the solvent removed in vacuo, and the residue diluted with

n-pentane to precipitate the catalyst as a red oil. The pentane solu-

2

¹J_P,Cϭ 34.15 Hz, PCH), 64.40 (d, J_P,Cϭ 5.81 Hz, NCH), 115.99

[s (br), CH₃CN trans H], 119.63 (d, ³J_P,Cϭ 18.90 Hz, CH₃CN trans tion was decanted and chromatographed on a silica gel column

P), 123.0Ϫ134.4 (C₆H₅). ³¹P{¹H} NMR (CD₂Cl₂, ppm): δ ϭ 32.27. using diethyl ether/n-pentane (1:1) as the eluent. Volatiles were dis-

tilled off and the mixture of products was analyzed by ¹H NMR

X-ray Structure Determinations: Single crystals of Ir^ϩ-(S,S)-

spectroscopy. Conversions and product compositions were deter-

mined on the basis of the integrations of the PhC(O)CH₃and

3·2THF (size 0.33 ϫ 0.10 ϫ 0.08 mm), Ir^ϩ-(R,S)-2·THF (size 0.38

ϫ 0.33 ϫ 0.28 mm), and Ir-(R,S)-4a (size 0.50 ϫ 0.45 ϫ 0.23 mm)

were grown from THF/n-pentane [Ir^ϩ-(S,S)-3·2THF and Ir^ϩ-(R,S)-

2·THF] or acetone [Ir-(R,S)-4a]. Diffraction measurements were

made at Ϫ90Ϯ2 °C [Ir^ϩ-(R,S)-2·THF] and at Ϫ80Ϯ2 °C [Ir^ϩ-(S,S)-

3·2THF and Ir-(R,S)-4a] on an EnrafϪNonius CAD-4 MACH 3

diffractometer using graphite-monochromated Mo-K_αradiation

PhCH(OH)CH₃signals. Enantiomeric excesses were measured

either by HPLC using a Daicel Chiralcel OD column or by polari-

metry as detailed elsewhere.^[7a]Optical rotations were referenced to

the following [α]_Dvalues of the pure enantiomers taken from the

literature: (R)-1-phenylethanol, ϩ48.6 (c ϭ 1, CH₂Cl₂);^[44a](S)-1-

phenylpropanol, Ϫ47.7 (c ϭ 6.8, Et₂O);^[44b](S)-2-methyl-1-phenyl-

propanol, ϩ5.3 (c ϭ 1.1, EtOH);^[44c](S)-1-indanol, ϩ31.7 (c ϭ 1,

CHCl₃);^[44d](S)-4-chloro-1-phenylbutanol, Ϫ33 (c ϭ 1, CHCl₃).^[44e]

˚

(λ ϭ 0.71073 A); orientation matrices and unit cell parameters

from the setting angles of 25 centered medium-angle reflections;

collection of the diffraction intensities by ω scans (data corrected

for absorption either empirically by ψ scans^[38][Ir^ϩ-(S,S)-3·2THF:

T_minϭ 0.406, T_maxϭ 0.777; Ir^ϩ-(R,S)-2·THF: T_minϭ 0.217,

T_maxϭ 0.316] or by refined absorption methods^[39][Ir-(R,S)-4a:

T_minϭ 0.087, T_maxϭ 0.318]. The structures were solved by direct

methods and subsequently refined by full-matrix least-squares pro-

cedures on F²allowing for anisotropic thermal motion of all non-

hydrogen atoms employing the WinGX package^[40a]with the rel-

evant programs (SIR-97,^[41]SHELXL-97,^[42]ORTEP-3^[40b]) im-

plemented therein. Ir^ϩ-(S,S)-3·2THF: C₃₆H₄₀IrNP, BF₄, 2(C₄H₈O)

Representative Catalytic ϾC

؍

O Hydrogenations and H₂/D^؉Ex-

change Experiments in CH₃OD: (a) A solution of of Ir^؉-(R,R)-2

(9.5 mg, 0.013 mmol), (Ϫ)-sparteine (14 µL, 0.065 mmol) and

benzophenone (150 mg, 1.25 mmol) in CH₃OD (3 mL) was kept,

in an autoclave, under 10 bar of H₂at 50 °C for 10 h. The residue

remaining after removal of the solvent was analyzed by NMR spec-

1

troscopy. H NMR (CD₂Cl₂, ppm): δ ϭ 5.76 (s with half intensity

2

relative to 10 phenyl H, Ph₂CHOD), 7.2Ϫ7.5 (m, 10 H, C₆H₅). H

NMR (CH₂Cl₂, ppm): δ ϭ 2.42 (br., OD), 5.78 (s, Ph₂CDOD).

1

¹³C{¹H} NMR (CD₂Cl₂, ppm): δ ϭ 76.52 (1:1:1 t, J_C,D

ϭ

(940.9); monoclinic, P2₁, a ϭ 14.8593(15), b ϭ 9.215(2), c ϭ

3

˚

22.16 Hz, Ph₂CDOD), 76.93 (s, Ph₂CHOD). (b) The solution of

catalyst complex, auxiliary base, and ketone in [D₁]methanol was

prepared as before, transferred into a high-pressure NMR tube,

exposed to 10 bar of H₂at ambient conditions overnight, and then

examined by ¹H NMR (ppm): δ ϭ 4.37 (1:1:1 t, ¹J_H,Dϭ 42.63 Hz,

HD), 4.42 (s, H₂), 4.46 (s, OH), 5.92 (s, ഠ 0.6 H relative to 10

phenyl H, CH), 7.2Ϫ7.5 (m, 10 H, C₆H₅). (c) Experiment (b) was

15.108(2) A, β ϭ 93.506(9)°, V ϭ 2064.8(5) A , Z ϭ 2, d_calcd.

ϭ

1.513 g·cm^Ϫ3, µ(Mo-K_α) ϭ 3.327 mm^Ϫ1; 2.59° Յ Θ Յ 22.48°, 6018

reflections collected (Ϫ15 Յ h Յ ϩ15, Ϫ9 Յ k Յ ϩ9, Ϫ16 Յ l Յ

ϩ16, including Friedel pairs), 5363 unique; wR ϭ 0.1824 for all

data and 488 parameters, R ϭ 0.0835 for 3495 structure factors F_o

Ͼ 4σ(F_o), absolute structure parameter^[43]x ϭ 0.00(3). Ir^ϩ-(R,S)-

2·THF: C₃₀H₃₆IrNP, BF₄, C₄H₈O (792.7); orthorhombic, P2₁2₁2₁,

1

3

˚

repeated in the absence of the base and the ketone. H NMR: δ ϭ

a ϭ 9.268(2), b ϭ 12.889(1), c ϭ 27.147(6) A, V ϭ 3243(1) A ,

Z ϭ 4, d_calcd.ϭ 1.642 g·cm^Ϫ3, µ(Mo-K_α) ϭ 4.218 mm^Ϫ1; 2.18° Յ

Θ Յ 25.17°, 6122 reflections collected (Ϫ11 Յ h Յ ϩ11, Ϫ15 Յ k

Յ ϩ15, Ϫ25 Յ l Յ ϩ25, including Friedel pairs), 5418 unique;

wR ϭ 0.1328 for all data and 390 parameters, R ϭ 0.0633 for 3963

structure factors F_oϾ 4σ(F_o), x ϭ 0.02(2). Ir-(R,S)-4a: C₃₂H₃₉IrNP

1

4.39 (1:1:1 t, J_H,Dϭ 42.63 Hz, HD), 4.42 (s, H₂), 4.46 (s with

increasing intensity, OH).

General Procedure for H₂/D₂Exchange Experiments: A high press-

ure NMR tube was charged with a solution of ഠ0.01 mmol of any

[(COD)Ir(PʝNHR]BF₄complex in CD₃CN or CH₃CN. The solu-

tion was exposed to 10 bar of a 1:1 H₂/D₂mixture and immediately

analyzed by NMR spectroscopy. ¹H NMR (CD₃CN, ppm): δ ϭ

(660.8); monoclinic, P2₁, a ϭ 9.097(2), b ϭ 19.312(4), c ϭ 15.709(6)

3

A, β ϭ 98.99(2)°, V ϭ 2726(1) A , Z ϭ 4, d_calcd.ϭ 1.610 g·cm^Ϫ3

,

˚

µ(Mo-K_α) ϭ 4.978 mm^Ϫ1; 2.11^°Յ Θ Յ 26.56°, 12154 reflections

collected (Ϫ11 Յ h Յ ϩ11, Ϫ24 Յ k Յ ϩ24, Ϫ19 Յ l Յ ϩ19,

including Friedel pairs), 11382 unique; wR ϭ 0.0734 for all data

and 637 parameters, R ϭ 0.0321 for 10345 structure factors F_oϾ

4σ(F_o), x ϭ Ϫ0.012(6). CCDC-215609 [Ir^ϩ-(S,S)-3·2THF], CCDC-

215607 [Ir^ϩ-(R,S)-2·THF], and CCDC-215608 [Ir-(R,S)-4a] con-

tain the supplementary crystallographic data for this paper. These

data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/

retrieving.html [or from the Cambridge Crystallographic Data

Center, 12, Union Road, Cambridge CB2 1EZ, UK; Fax: (in-

ternat.) ϩ44Ϫ1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].

1

4.37 (1:1:1 t, J_H,Dϭ 42.63 Hz, HD), 4.41 (s, H₂). ²H NMR

1

(CH₃CN, ppm): δ ϭ 4.33 (s, D₂), 4.37 (d, J_H,Dϭ 42.5 Hz, HD).

Acknowledgments

We thankfully remember many fruitful and inspiring discussions

with Professor Dieter Sellmann, initiator and first speaker of the

Sonderforschungsbereich 583: Redox-Active Metal Complexes Ϫ

Control of Reactivity via Molecular Architecture. Support of this

work by the Deutsche Forschungsgemeinschaft (Bonn, SFB 583)

General Procedure for Catalytic ϾC

؍

O Hydrogenation: A 10 mL and the Fonds der Chemischen Industrie (Frankfurt/Main) is grate-

capacity Schlenk tube equipped with a small magnetic stirring bar

was charged with the catalyst complex dissolved in methanol (typi-

fully acknowledged. We are also indebted to Mrs. S. Kammerer for

her skilful assistance.

Eur. J. Inorg. Chem. 2004, 888Ϫ905

www.eurjic.org

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

903

L. Dahlenburg, R. Götz

FULL PAPER

[1]

complexes, see, for example: L. Dahlenburg, N. Höck, H.

Berke, Chem. Ber. 1988, 121, 2083Ϫ2093.

For leading overviews on enantioselective reduction of organic

[1a]

carbonyl compounds, see:

R. Noyori, T. Ohkuma, Angew.

[22] [22a]

L. Dahlenburg, K. Herbst, Chem. Ber./Recueil 1997,

Chem. 2001, 113, 40Ϫ75; Angew. Chem. Int. Ed. 2001, 40,

[22b]

[1b]

1693Ϫ1698.

K. Herbst, Dissertation, Universität Er-

40Ϫ74.

R. Noyori, Angew. Chem. 2002, 114, 2108Ϫ2123;

langen-Nürnberg, 1998.

For pertinent reviews on heterolytic H₂activation, see:

Angew. Chem. Int. Ed. 2002, 41, 2008Ϫ2022 (2001 Nobel Lec-

ture in Chemistry).

[23]

[23a]

P.

G. J.

[23b]

[2] [2a]

J. Bothers, Progr. Inorg. Chem. 1981, 28, 1Ϫ61.

M. Yamakawa, H. Ito, R. Noyori, J. Am. Chem. Soc. 2000,

122, 1466Ϫ1478. ^[2b]R. Noyori, M. Yamakawa, S. Hashiguchi,

J. Org. Chem. 2001, 66, 7931Ϫ7944.

[23c]

Kubas, Acc. Chem. Res. 1988, 21, 120Ϫ128.

P. G. Jessop,

[23d]

R. H. Morris, Coord. Chem. Rev. 1992, 121, 121Ϫ284.

D.

[3] [3a]

M. Heinekey, W. J. Oldham Jr., Chem. Rev. 1993, 93, 913Ϫ926.

K. Abdur-Rashid, A. J. Lough, R. H. Morris, Organomet-

^[23e]R. H. Crabtree, Angew. Chem. 1993, 105, 828Ϫ845; Angew.

allics 2000, 19, 2655Ϫ2657. ^[3b]K. Abdur-Rashid, A. J. Lough,

Chem. Int. Ed. Engl. 1993, 32, 789Ϫ805. ^[23f]M. A. Esteruelas,

[3c]

Organometallics 2001, 20, 1047Ϫ1049.

K. Abdur-Rashid,

[23g]

L. A. Oro, Chem. Rev. 1998, 98, 577Ϫ588.

G. Jia, C.-P.

M. Faatz, A. J. Lough, R. H. Morris, J. Am. Chem. Soc. 2001,

[23h]

[3d]

Lau, Coord. Chem. Rev. 1999, 190Ϫ192, 83Ϫ108.

D.

123, 7473Ϫ7474.

K. Abdur-Rashid, S. E. Clapham, A.

Sellmann, A. Fürsattel, J. Sutter, Coord. Chem. Rev. 2000,

Hadzovic, J. N. Harvey, A. J. Lough, R. H. Morris, J. Am.

Chem. Soc. 2002, 124, 15104Ϫ15118.

R. Hartmann, P. Chen, Angew. Chem. 2001, 113, 3693Ϫ3697;

Angew. Chem. Int. Ed. 2001, 40, 3581Ϫ3585.

Q. Jiang, Y. Jiang, A. Xiao, P. Cao, X. Zhang, Angew. Chem.

1998, 110, 1203Ϫ1207; Angew. Chem. Int. Ed. 1998, 37,

1100Ϫ1103.

[23i]

200Ϫ202, 545Ϫ561.

G. J. Kubas, Metal Dihydrogen and σ-

[4]

[5]

Bond Complexes, Kluver Academic/Plenum Publishers, New

York, 2001, chapters 9 and 10.

[24] [24a]

M. D. Fryzuk, P. A. MacNeil, Organometallics 1983, 2,

[24b]

682Ϫ684.

Organometallics 1991, 10, 467Ϫ472.

M. D. Fryzuk, C. D. Montgomery, S. J. Rettig,

[24c]

M. D. Fryzuk, M. J.

[6]

Petrella, R. C. Coffin, B. O. Patrick, Compt. Rend. Chimie

2002, 5, 451Ϫ460.

R. R. Schrock, J. A. Osborn, J. Chem. Soc., Sect. D: Chem.

Commun. 1970, 567Ϫ658.

^{[25] [25a]}R. H. Crabtree, M. Lavin, L. Bonneviot, J. Am. Chem. Soc.

1986, 108, 4032Ϫ4037. ^[25b]A. C. Albeniz, D. M. Heinekey, R.

H. Crabtree, Inorg. Chem. 1991, 30, 3632Ϫ3635. ^[25c]D.-H. Lee,

[7] [7a]

L. Dahlenburg, R. Götz, J. Organomet. Chem. 2001, 619,

[7b]

88Ϫ98.

Preliminary communication: L. Dahlenburg, R.

Götz, Inorg. Chem. Commun. 2003, 6, 443Ϫ446 (Paper pre-

sented at the XXXVth Int. Conf. Coord. Chem.; Heidelberg,

July 21Ϫ26, 2002).

B. P. Patel, E. Clot, O. Eisenstein, R. H. Crabtree, Chem. Com-

[25d]

mun. 1999, 297Ϫ298.

K. Gruet, E. Clot, O. Eisenstein, D.

[8] [8a]

H. Lee, B. Patel, A. Macchioni, R. H. Crabtree, New. J. Chem.

M. L. Tommasino, C. Thomazeau, F. Touchard, M. Le-

[8b]

2003, 27, 80Ϫ87.

maire, Tetrahedron Asymm. 1999, 10, 1813Ϫ1819.

C. Mail-

[26]

R. Koelliker, D. Milstein, J. Am. Chem. Soc. 1991, 113,

8524Ϫ8525.

let, T. Praveen, P. Janvier, S. Minguet, M. Evain, C. Saluzzo, M.

L. Tommasino, B. Bujoli, J. Org. Chem. 2002, 67, 8191Ϫ8196.

^{[27] [27a]}D. Sellmann, J. Käppler, M. Moll, J. Am. Chem. Soc. 1993,

[9] [9a]

[9b]

S. Gabriel, Ber. Dtsch. Chem. Ges. 1888, 21, 1049.

A.

[27b]

115, 1830Ϫ1836.

D. Sellmann, G. H. Rackelmann, F. W.

´

Galindo, L. Orea F., D. Gnecco, R. G. Enrıquez, R. Toscano,

W. F. Reynolds, Tetrahedron Asymm. 1997, 8, 2877Ϫ2879.

[27c]

Heinemann, Chem. Eur. J. 1997, 3, 2071Ϫ2080.

Sellmann, T. Gottschalk-Gauding, F. W. Heinemann, Inorg.

D.

[10] [10a]

[10b]

H. Wenker, J. Am. Chem. Soc. 1935, 57, 2328.

Brois, J. Org. Chem. 1962, 27, 3532Ϫ3534.

S. J.

[27d]

Chem. 1998, 37, 3982Ϫ3988.

D. Sellmann, A. Fürsattel,

[11] [11a]

Angew. Chem. 1999, 111, 2142Ϫ2145; Angew. Chem. Int. Ed.

L. Horner, H. Oediger, H. Hoffmann, Justus Liebigs Ann.

[27e]

Chem. 1959, 626, 26Ϫ34. ^[11b]I. Okada, K. Ichimura, R. Sudo,

Bull. Chem. Soc. Jpn. 1970, 43, 1185Ϫ1189. ^[11c]W. Danzer, R.

Höfer, H. Menzel, B. Olgemöller, W. Beck, Z. Naturforsch. Teil

B: Anorg. Chem. Org. Chem. 1984, 39, 167Ϫ179.

1999, 38, 2023Ϫ2026.

D. Sellmann, F. Geipel, M. Moll,

Angew. Chem. 2000, 112, 570Ϫ572; Angew. Chem. Int. Ed.

[27f]

2000, 39, 561Ϫ563.

D. Sellmann, J. Sutter, Z. Anorg. Allg.

Chem. 2003, 629, 893Ϫ910.

[28] [28a]

^{[12] [12a]}O. Mitsunobu, Synthesis 1981, 1Ϫ28. ^[12b]J. R. Pfister, Syn-

P. G. Jessop, R. H. Morris, Inorg. Chem. 1993, 32,

[28b]

[12c]

2236Ϫ2237.

M. Schlaf, A. J. Lough, R. H. Morris, Or-

thesis 1984, 969Ϫ970.

M. A. Poelert, R. P. Hof, N. C. M.

[28c]

ganometallics 1993, 12, 3808Ϫ3809.

M. Schlaf, A. J.

Lough, R. H. Morris, Organometallics 1996, 15, 4423Ϫ4436.

J. Huhmann-Vincent, B. L. Scott, G. F. Kubas, Inorg. Chim.

Acta 1999, 294, 240Ϫ254.

W. Peper, R. M. Kellog, Heterocycles 1994, 37, 461Ϫ475.

[13] [13a]

W. Beck, U. Nagel, Z. Anorg. Allg. Chem. 1979, 258,

22Ϫ28. ^[13b]U. Nagel, H. Menzel, W. Beck, A. Guyot, M. Bar-

tholin, Z. Naturforsch. Teil B: Anorg. Chem. Org. Chem. 1981,

36, 578Ϫ584.

T. N. Van, N. De Kimpe, Tetrahedron 2000, 56, 7299Ϫ7304.

J. E. Saavedra, J. Org. Chem. 1985, 50, 2271Ϫ2273.

R. K. Dieter, N. Deo, B. Lagu, J. W. Dieter, J. Org. Chem. 1992,

57, 1663Ϫ1671.

K. Issleib, A. Tzschach, Chem. Ber. 1959, 92, 1118Ϫ1126.

K. Issleib, D. Haferburg, Z. Naturforsch. Teil B: Anorg.

Chem. Org. Chem. 1965, 20, 916Ϫ918.

A. B. van Oort, P. H. M. Budzelaar, J. H. G. Frijns, A. G.

Orpen, J. Organomet. Chem. 1990, 396, 33Ϫ47. ^[18b]M. K. Co-

oper, J. M. Downes, P. A. Duckworth, E. R. T. Tiekink, Aust.

J. Chem. 1992, 45, 595Ϫ609.

T. L. Cairns, J. Am. Chem. Soc. 1941, 63, 871Ϫ872.

pK_A(BH^ϩ) values: 3.2 (Tröger’s base),^[20a]5.4 (pyridine),^[20b]

10.6 (NEt₃),^[20c]11.0 (iP₂NH),^[20c]and 11.3 (sparteine);^[20d]with

[29]

[30]

A. Llamazares, H. W. Schmalle, H. Berke, Organometallics

[14]

[15]

[16]

2001, 20, 5277Ϫ5288.

[31] [31a]

S. Park, D. Hedden, D. M. Roundhill, Organometallics

[31b]

1985, 5, 2151Ϫ2152.

Roundhill, Organometallics 1989, 8, 1700Ϫ1707.

S. Park, M. P. Johnson, D. M.

[17] [17a]

[17b]

[32]

[33]

R. Kuhlman, Coord. Chem. Rev. 1997, 167, 205Ϫ232.

In the reviewing process, an alternate mechanism based on the

intermediacy of [Ir(PʝNR)] and [IrH(PʝNHR)] as spectro-

scopically undetected but kinetically relevant transients was

proposed for isotopic scrambling and ϾCϭO reduction:

[Ir(PʝNR)] ϩ H₂ϭ [IrH(PʝNHR)]; [IrH(PʝNHR] ϩ H₂ϭ

[18] [18a]

[IrH₃(PʝNHR)];

[IrH₃(PʝNDR)]

[IrH₃(PʝNHR)]

MeOH;

ϩ

MeOD

ϭ

[19]

[20]

ϩ

[IrH₃(PʝNDR)]

[IrH(PʝNDR)] ϩ H₂; [IrH(PʝNDR)] ϭ [Ir(PʝNR)] ϩ HD

etc.; [IrH₃(PʝNHR)] ϩ R₂CO ϭ [IrH₂(PʝNR)] ϩ R₂CHOH.

This sequence does not, however, fit the experimental evidence

in that it involves IrH₃intermediates which should be quite

stable and inert but were never met in the chemistry described

in this communication. Furthermore, in order to make the sug-

gested ϾCϭO reduction step catalytic, the resulting amido di-

hydrides [IrH₂(PʝNR)] must regenerate the postulated

[IrH₃(PʝNHR)] amino trihydrides either by hydrogen transfer

the exception of Tröger’s base (50% aqueous alcohol) all in

[20a]

water.

B. M. Wepster, Recl. Trav. Chim. Pays-Bas Belg.

1953, 72, 661Ϫ672. ^[20b]Th. J. Lane, M. G. Kappil, A. J. Kand-

[20c]

athil, J. Chem. Eng. Data 1963, 8, 569Ϫ571.

Jr., J. Am. Chem. Soc. 1957, 79, 5441Ϫ5444.

Aust. J. Chem. 1959, 12, 474Ϫ482.

H. K. Hall

W. D. C row,

[20d]

[21]

For ligand-to-metal pǞp_zπ interactions in square-planar d⁸

904

 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Iridium Complexes with Chiral and Achiral β-Aminophosphane Ligands

FULL PAPER

from the solvent or by H₂addition across the IrϪN bond.

Again, no such chemistry was observed for amido dihydro

^{[40] [40a]}L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837Ϫ838. ^[40b]

L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.

A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.

Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.

Spagna, J. Appl. Crystallogr. 1999, 32, 115Ϫ119.

[42]

[41]

complex Ir-9a reacting with MeOH under H₂to reversibly pro-

duce [IrH₂(PʝNHR)]^ϩ(Ir^ϩ-9; Scheme 9) rather than H₂CO

and/or [IrH₃(PʝNHR)].

[34]

[35]

V. D. Bianco, S. Doronzo, Inorg. Synth. 1976, 16, 161Ϫ163.

J. P. Collman, C. T. Sears Jr., M. Kubota, Inorg. Synth. 1990,

28, 92Ϫ94.

G. M. Sheldrick, SHELXL-97 (Release 97Ϫ2), University of

Göttingen, 1998.

H. D. Flack, Acta Crystallogr., Sect. A 1983, 39, 876Ϫ881.

[43]

[36]

J. L. Herde, J. C. Lambert, C. V. Senoff, Inorg. Synth. 1974,

^{[44] [44a]}T. Hayashi, Y. Matsumoto, Y. Ito, J. Am. Chem. Soc. 1989,

[44b]

15, 18Ϫ20.

111, 3426Ϫ3428.

T. Sato, Y. Goto, T. Fujisawa, Tetra-

[37] [37a]

[44c]

J. A. Osborn, R. R. Schrock, J. Am. Chem. Soc. 1971, 93,

hedron Lett. 1982, 23, 4111Ϫ4112.

S. Masamune, B. M.

3089Ϫ3091. ^[37b]T. G. Schenck, J. M. Downes, C. R. C. Milne,

Kim, J. S. Petersen, T. Sato, S. J. Veenstra, T. Imai, J. Am.

[44d]

P. B. Mackenzie, T. G. Boucher, B. Bosnich, Inorg. Chem. 1985,

Chem. Soc. 1985, 107, 4549Ϫ4551.

S. Top, G. Jaouen, J.

[37c]

24, 2334Ϫ2337.

M. J. Burk, J. E. Feaster, W. A. Nugent,

Organomet. Chem. 1980, 197, 199Ϫ215. ^[44e]T. H. Chan, P. Pel-

lon, J. Am. Chem. Soc. 1989, 111, 8737Ϫ8738.

Received July 24, 2003

R. L. Harlow, J. Am. Chem. Soc. 1993, 115, 10125Ϫ10138.

A. C. T. North, D. C. Phillips, F. S. Mathews, Acta Crystallogr.,

Sect. A 1968, 24, 351Ϫ359.

N. Walker, D. Stuart, Acta Crystallogr., Sect. A 1983, 39,

159Ϫ166.

[38]

[39]

Early View Article

Published Online January 19, 2004

Eur. J. Inorg. Chem. 2004, 888Ϫ905

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Article Doi

Iridium complexes with chiral and achiral β-aminophosphane ligands: Catalysts for >C=O hydrogenation and H/D exchange involving both homo-and heterolytic H2 activation

DOI: 10.1002/ejic.200300503

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