DOI: 10.1002/zaac.200800043

Synthesis and Characterization of an Enantiomerically Pure Lutetium BenzylComplex

Nils Meyer and Peter W. Roesky*

Karlsruhe, Institut für Anorganische Chemie der Universität (TH)

Received February 8th, 2008.

Dedicated to Professor Bernt Krebs on the Occasion of his 70th Birthday

Abstract. The synthesis and the single-crystal X-ray structure of theenantiopure ligand (S,S)-H2{(iPrATI)2diph} 1) are reported. Reac-tion of (S,S)-H2{(iPrATI)2diph} with the lutetium benzyl complex[Lu(CH2Ph)3(THF)3] resulted in the mono benzyl complex

IntroductionRecently many enantiomerically pure lanthanide complexeshave been prepared and characterized. Many of these com-pounds have applications such as chiral shift reagents forresolving NMR spectra of chiral Lewis bases and more re-cently as highly enantioselective catalysts and reagents [1].The vast majority of these compounds have either enanti-omerically pure O-donor ligands or cyclopentadienyl li-gands in the coordination sphere. N-donors have little beenused in lanthanide chemistry, but there is a growing interestin amides as analogues for the well established cyclo-pentadienyl ligand in d- and f-transition metal chemistry. Inthis context we and others recently reported on the use ofchiral aminotroponiminates as cyclopentadienyl alterna-tives for group 3 (A) [2], 4 (B) [3] and lanthanide elements(C) [4] (Scheme 1).

Some of these compounds were further reacted to givecatalysts for the enantioselective hydroamination [5].Herein, we now report on a new synthetic pathway to intro-duce the (S,S)-H2{(iPrATI)2diph} (D) [4] ligand into thecoordination sphere of lutetium using the recently reportedlutetium benzyl complex, [Lu(CH2Ph)3(THF)3] [6], asalternative starting material to the well established amidoand alkyl reagents [LnR3(THF)n] (R � CH2SiMe3,CH(SiMe3)2, N(SiMe3)2, N(SiMe2H)2, n � 0, 2, 3) [7, 8, 9,10, 11].

Results and DiscussionThe enantiomerically pure bridged aminotroponimine,(S,S)-H2{(iPrATI)2diph}, in which two aminoisopropyl-

* Prof. Dr. Peter W. RoeskyInstitut für Anorganische Chemie der UniversitätEngesserstraße Geb. 30.45D-76128 Karlsruhee-mail: roesky@chemie.uni-karsruhe.de

Z. Anorg. Allg. Chem. 2008, 634, 2171�2174 © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2171

[(S,S)-{(iPrATI)2diph}Lu(CH2Ph)(THF)] 2), which is the firstchiral benzyl compound of the lanthanides.Keywords: Chirality; Coordination Chemistry; Lutetium; N Li-gands; Rare-earth compounds

Scheme 1

troponimine moieties are linked by 1,2-(S,S)-diamino-1,2-diphenylethane [12], was obtained in a straightforwardsynthesis. 2-(Tosyloxo)tropone was reacted with iso-propylamine first to form 2-(N-isopropylamino)tropone inalmost quantitative yield. Further treatment of 2-(N-isopro-pylamino)tropone with [Me3O] · [BF4], triethylamine, and1,2-(S,S)-diamino-1,2-diphenylethane led to the desiredproduct as an analytically pure yellow solid in 60 % yield(Scheme 2) [4]. The molecular structure of (S,S)-H2{(iPrATI)2diph} was established by single crystal X-raydiffraction in the solid-state (Fig. 1). X-ray quality crystalswere grown at �22 °C from a toluene/pentane solution. Thecompound crystallizes in the chiral orthorhombic space

1) N,N�-bis[7-[(1-methylethyl)imino]-1,3,5-cycloheptatrien-1-yl]-1,2-diphenyl-(1S,2S)-1,2-ethanediamine

2) [(1S,2S)-N,N�-bis[7-[(1-methylethyl)imino]-1,3,5-cycloheptatrien-1-yl]-1,2-diphenyl-1,2-ethanediaminato](benzyl)tetrahydrofuran]-lutetium

N. Meyer, P. W. Roesky

group P212121 with two independent molecules in the asym-metric unit and eight molecules in the unit cell. All bondlengths and angles are in the expected range. The absolutestereochemistry was concluded from the starting materialand later on from the lutetium complex, because the abso-lute structure parameter of (S,S)-H2{(iPrATI)2diph} doesnot allow any conclusions of the absolute stereochemistry.

Scheme 2

Fig. 1 Solid-state structure of one independent (S,S)-H2{(iPrATI)2diph} molecule in the solid state, showing the disorde-ring around the N4 atom (C-H hydrogen atoms are omitted forclarity).

Selected distances/A and angles/°: N1-C1 1.317(5), N2-C7 1.319(4), N2-C81.446(4), N3-C9 1.442(4), N3-C10 1.326(4), N4a-C16 1.36(2); N1-C1-C7112.9(3), C7-N2-C8 123.2(3), C9-N3-C10 124.1(3), C10-C16-N4a 109.0(8).

Reaction of (S,S)-H2{(iPrATI)2diph} with one equiva-lent of [Lu(CH2Ph)3(THF)3] in toluene at room tempera-ture resulted via toluene elimination in the formation of[(S,S)-{(iPrATI)2diph}Lu(CH2Ph)(THF)] (1) (Scheme 2),which is a very air and moisture sensitive crystalline orangesolid. Compound 1 has been characterized by 1H and 13CNMR spectroscopy as well as elemental analysis. As a resultof the coordination of the ligand to the metal atom thesymmetry of the ligand is broken. This results in two setsof signals for the isopropyl groups in the NMR spectra.Thus, two isopropyl CH signals, which are well resolvedinto two septets at 3.53 and 4.12 ppm are observed in the1H NMR spectrum (13C NMR: 48.5, 49.3 ppm). Due thechirality of the ligand system each set of signals of the iso-propyl CH3 groups also shows a diastereotopic splitting inthe 1H NMR spectrum of 1, resulting in four resonances at1.04, 1.37, 1.41, and 1.63 ppm. Furthermore the expectedtwo signals for the methylene protons of the CH2Ph group

www.zaac.wiley-vch.de © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2008, 2171�21742172

at 1.25 and 1.27 ppm are doublets. The doublets are a resultof a diastereotopic splitting concomitant with a geminalcoupling of the protons.

Scheme 3

Fig. 2 Solid-state structure of 1 in the solid state (hydrogen atomsare omitted for clarity).

Selected distances/A and angles/°: Lu-N1 2.360(7), Lu-N2 2.285(6), Lu-N32.269(7), Lu-N4 2.381(7), Lu-O1 2.351(6), Lu-C39 2.465(6); N1-Lu-N266.8(3), N1-Lu-N3 138.5(3), N1-Lu-N4 151.3(3), N1-Lu-O1 82.8(2), N1-Lu-C39 90.0(2), N2-Lu-N3 72.1(2), N2-Lu-N4 141.3(3), N2-Lu-O1 98.9(2), N2-Lu-C39 101.6(2), N3-Lu-N4 69.3(3), N3-Lu-O1 98.8(2), N3-Lu-C39103.5(2), N4-Lu-O1 85.9(2), N4-Lu-C39 88.5(2).

The solid-state structure of the new complex was estab-lished by single crystal X-ray diffraction (Fig. 2). Singlecrystals of 1 were grown from a saturated toluene solution.1 crystallizes in the chiral orthorhombic space groupP212121 with four molecules of the complex in the unit cell.As a result of the chirality of the ligand the complex isenantiomerically pure. The solid state structure of 1 is con-sistent with the NMR spectra in solution. The lutetiumatom is coordinated in a distorted octahedral fashion bythe four nitrogen atoms of the chiral (S,S)-{(iPrATI)2diph}ligand, one molecule of THF and the benzyl ligand. Asimilar coordination polyhedron is observed in thepreviously reported complexes of the composition[(S,S)-{(iPrATI)2diph}LnCl(THF)] (Ln � Lu, Yb, Er, Ho)[4, 13]. The Lu-N bond lengths are in the expected rangeof 2.269(7) A to 2.381(7) A [10], similar to the Lu-N dis-tances in C (2.264(3) A to 2.339(3) A). As observed in[Lu(CH2Ph)3(THF)3] [6] the benzyl group is η1 coordinated

Enantiomerically Pure Lutetium Benzyl Complex

to the metal atom. This is in contrast to benzyl complexesof the larger rare-earth elements such as[La(CH2Ph)3(THF)3], in which a η2 coordination of the li-gand onto the metal atom is observed [14]. The Lu-C bondlength in compound 1 is 2.465(6) A, which is in the rangeof the starting material [Lu(CH2Ph)3(THF)3] (Lu-C:2.408(4) A, 2.408(4) A, and 2.413(5) A) [6].

Summary

The structure of the enantiopure ligand (S,S)-H2{(iPrATI)2diph} in the solid state was established by X-ray crystallographic studies. Furthermore, we reported thefirst derivative of the previously described lutetium benzylcomplex [Lu(CH2Ph)3(THF)3] by reaction of the chiral li-gand (S,S)-H2{(iPrATI)2diph} with this compound. Theresulting product [(S,S)-{(iPrATI)2diph}Lu(CH2Ph)(THF)](1) was characterized by standard analytical methods andthe solid state structure was established by a single crystalX-ray structure. 1 represents to the best of our knowledgethe first chiral benzyl compound of the lanthanides.

Experimental Section

General Considerations. All manipulations of air sensitive materialswere performed with the rigorous exclusion of oxygen and moisturein flame-dried Schlenk-type glassware either on a dual-manifoldSchlenk line, interfaced to a high-vacuum (10�4 Torr) line, or in anargon-filled MBraun glovebox. Tetrahydrofuran was predried overNa wire and distilled under nitrogen from Na/K benzophenoneprior to use. Hydrocarbon solvents were distilled under nitrogenfrom LiAlH4. All solvents for vacuum line manipulations werestored in vacuo over LiAlH4 in resealable flasks. Deuterated sol-vents were obtained from Chemotrade ChemiehandelsgesellschaftmbH (all > 99 atom % D) and were dried, degassed, and storedin vacuo over Na/K alloy in resealable flasks. NMR spectra wererecorded on a JNM-LA 400 FT-NMR spectrometer. Chemicalshifts are referenced to internal solvent resonances and are reportedrelative to tetramethylsilane respectively. Elemental analysis wereperformed with an Elementar vario EL. (S,S)-H2{(iPrATI)2diph}[4] and [Lu(CH2Ph)3(THF)3] [6] were prepared according to litera-ture procedures.

Synthesis of [(S,S)-{(iPrATI)2diph}Lu(CH2Ph)(THF)]

At �73 °C toluene (10 ml) was condensed onto a mixture of[Lu(CH2Ph)3(THF)3] (360 mg, 0.54 mmol) and (S,S)-H2[(iPrATI)-2diph] (270 mg, 0.54 mmol). The orange suspension was stirred for16 h at room temperature and an orange microcrystalline solid wasformed. The mixture was carefully warmed to obtain a clear darkorange solution. The solution was filtered off and was allowed tostand at ambient temperature. After 1 h yellow crystalline needleswere formed. The needles were collected and washed with pentaneto obtain the analytically pure product. X-ray quality crystals wereobtained from an oversaturated toluene solution. Yield: 220 mg(0.26 mmol, 48 %). Anal. Calcd. for C45H51N4Olu (838.88): C,64.43, H, 6.13, N 6.68 found: C, 64.22, H, 6.27, N 6.16 %.1H NMR (THF-d8, 400 MHz, 25 °C): δ � 1.04 (d, 3 H, CH3, JH,H � 6.4 Hz),1.25 (d, 1 H, CH2Ph, JH,H � 5.9 Hz), 1.27 (d, 1 H, CH2Ph, JH,H � 5.9 Hz),

Z. Anorg. Allg. Chem. 2008, 2171�2174 © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 2173

1.37 (d, 3 H, CH3, JH,H � 6.4 Hz), 1.41 (d, 3 H, CH3, JH,H � 6.4 Hz), 1.63(d, 3 H, CH3, JH,H � 6.4 Hz), 3.53 (sept., 1 H, CH2(CH3)2, JH,H � 6.4 Hz),4.12 (sept, 1 H, CH2(CH3)2, JH,H � 6.4 Hz), 5.44 (s, 1 H, CH), 5.47 (s, 1 H,CH), 5.99 � 6.13 (m, 4 H, CHring), 6.20 � 6.28 (m, 4 H, CHring), 6.59 �6.67 (m, 5 H, CHring � Ph), 6.81 � 6.91 (m, 2 H, CHring � Ph), 7.03 � 7.09(m, 2 H, CHring � Ph), 7.13 � 7.19 (m, 4 H, Ph), 7.25 (d, 2 H, Ph, JH,H �7.6 Hz), 7.37 (d, 2 H, Ph, JH,H � 7.8 Hz). � 13C{1H} NMR (THF-d8,100.4 MHz, 25 °C): δ � 20.3, 20.5, 21.3, 22.5, 23.0, 48.5, 49.3, 66.9, 72.1,112.9, 114.7, 115.3, 115.4, 116.1, 116.3, 116.9, 123.3, 125.1, 126.3, 126.4,126.7, 126.8, 127.5, 127.9, 128.0, 128.1, 128.8, 133.0, 133.6, 134.1, 164.2,164.3, 164.6, 164.8, 165.4.

X-ray Crystallographic Studies of (S,S)-H2{(iPrATI)2diph} and 1

A suitable crystal was covered in mineral oil (Aldrich) and mountedonto a glass fiber. The crystal was transferred directly to the�73 °C cold N2 stream of a Stoe IPDS 2T diffractometer. Sub-sequent computations were carried out on an Intel Core2Duo PC.

Data collection and refinement: SHELXS-97 [15], SHELXL-97[16]: (S,S)-H2{(iPrATI)2diph}: orthorhombic space group P212121

(No. 19); lattice constants: a � 18.007(4), b � 18.106(4), c �

18.347(4) A; V � 5981.347(4) A3; Z � 8; μ(Mo-Kα) � 0.710 mm�1;2θmax � 29.24°; 39580 (Rint � 0.0880) independent reflectionsmeasured, of which 5260 were considered to be observed with I >2σ(I); max. residual electron density 0.318 and �0.247 e/A�3; 739parameters (the position of the H atoms were calculated for ideal-ized positions); R1 � 0.0664; wR2 � 0.1505.

1: orthorhombic space group P212121 (No. 19); lattice constants:a � 9.1929(4), b � 18.7428(13), c � 28.2502(14) A; V �

4867.53(50) A3; Z � 4; μ(Mo-Kα) � 0.71073 mm�1; 2θmax �

27.50°; 20798 (Rint � 0.0806) independent reflections measured, ofwhich 11112 were considered to be observed with I > 2σ(I); max.residual electron density 2.680 and �2.586 e/A�3; 486 parameters(all non hydrogen atoms except the solvent molecules were calcu-lated anisotropic, the position of the H atoms were calculated foridealized positions); absolute structure parameter �0.02(2); R1 �

0.0627; wR2 � 0.1519. Crystallographic data (excluding structurefactors) for the structures reported in this paper have been de-posited with the Cambridge Crystallographic Data Centre as a sup-plementary publication no. CCDC-676669-676670. Copies of thedata can be obtained free of charge on application to CCDC, 12Union Road, Cambridge CB21EZ, UK (fax: (�(44)1223-336-033;email: deposit@ccdc.cam.ac.uk).

Acknowledgement. This work was supported by the Deutsche For-schungsgemeinschaft (DFG Schwerpunktprogramm (SPP 1166):Lanthanoidspezifische Funktionalitäten in Molekül und Material)and the Fonds der Chemischen Industrie.

References

[1] Review about chiral lanthanide complexes: H. C. Aspinall,Chem. Rev. 2002, 102, 1807.

[2] P. W. Roesky, J. Organomet. Chem. 2001, 621, 277.[3] D. P. Steinhuebel, S. J. Lippard, Organometallics 1999, 18,

3959.[4] N. Meyer, A. Zulys, P. W. Roesky, Organometallics 2006, 25,

4179.[5] Review about hydroamination: T. E. Müller, M. Beller, Chem.

Rev. 1998, 98, 675.

N. Meyer, P. W. Roesky

[6] N. Meyer, P. W. Roesky, S. Bambirra, A. Meetsma, B. Hessen,K. Saliu, J. Takats, Organometallics 2008, 27, 1501.

[7] R � Alkyl: Reviews: (a) F. T. Edelmann, Angew. Chem. 1995,107, 2647; Angew. Chem., Int. Ed. 1995, 34, 2466; (b) F. T.Edelmann, D. M. M. Freckmann, H. Schumann, Chem. Rev.

2002, 102, 1851.[8] R � CH2SiMe3: (a) M. F. Lappert, R. Pearce, J. Chem. Soc.,

Chem. Commun. 1973, 126; (b) H. Schumann, J. Müller, J.

Organomet. Chem. 1978, 146, C5; (c) H. Schumann, J. Müller,J. Organomet. Chem. 1979, 169, C1; (d) J. L. Atwood, W. E.Hunter, R. D. Rogers, J. Holton, J. McMeeking, R. Pearce, M.F. Lappert, J. Chem. Soc., Chem. Commun. 1978, 140; (e) M.Niemeyer, Acta Crystallogr. 2001, E57, m553; (f) W. J. Evans,J. C. Brady, J. W. Ziller, J. Am. Chem. Soc. 2001, 123, 7711;(g) S. Arndt, T. P. Spaniol, J. Okuda, Chem. Commun. 2002,896; (h) H. Schumann, D. M. M. Freckmann, S. Dechert, Z.

Anorg. Allg. Chem. 2002, 628, 2422; (i) S. Arndt, T. P. Spaniol,J. Okuda, Angew. Chem. 2003, 115, 5229; Angew. Chem., Int.

Ed. 2003, 42, 5075; (j) S. Bambirra, A. Meetsma, B. Hessen,A. P. Bruins, Organometallics 2006, 25, 3486; (k) S. Bambirra,H. Tsurugi, D. van Leusen, B. Hessen, Dalton Trans. 2006,1157; (l) C. G. J. Tazelaar, S. Bambirra, D. Van Leusen, A.

www.zaac.wiley-vch.de © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2008, 2171�21742174

Meetsma, B. Hessen, J. H. Teuben, Organometallics 2004, 23,936; (m) S. Bambirra, M. W. Bouwkamp, A. Meetsma, B.Hessen, J. Am. Chem. Soc. 2004, 126, 9183.

[9] R � CH(SiMe3)2: (a) P. B. Hitchcock, M. F. Lappert, R. G.Smith, R. A. Bartlett, P. P. Power, J. Chem. Soc. Chem. Com-

mun. 1988, 1007; (b) C. J. Schaverien, A. G. Orpen, Inorg.

Chem. 1991, 30, 4968.[10] R � N(SiMe3)2, N(SiMe2H)2: Review: R. Anwander, Top.

Curr. Chem. 1996, 179, 33.[11] R � N(SiMe3)2, N(SiMe2H)2: (a) R. Anwander, O. Runte, J.

Eppinger, G. Gerstberger, E. Herdtweck, M. Spiegler, J. Chem.

Soc., Dalton Trans. 1998, 847; (b) J. Eppinger, M. Spiegler, W.Hieringer, W. A. Herrmann, R. Anwander, J. Am. Chem. Soc.

2000, 122, 3080.[12] S. Pikul, E. J. Corey, Org. Synth. 1993, 71, 22.[13] N. Meyer, P. W. Roesky, Dalton Trans. 2007, 25, 2652.[14] S. Bambirra, A. Meetsma, B. Hessen, Organometallics 2006,

25, 3454.[15] G. M. Sheldrick, SHELXS-97, Program of Crystal Structure

Solution, University of Göttingen, Germany, 1997.[16] G. M. Sheldrick, SHELXL-97, Program of Crystal Structure

Solution, University of Göttingen, Germany, 1997.