(Η2-Thioaldehyde)Zirconocene Cation Complex

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Synthesis of a Dinuclear µ-(η2-Thioaldehyde)zirconocene Cation Complex Silke Courtenayb, Sarah Smithb, Emily Hollinkb, Ulrich Blaschkea, Gerald Kehra, Roland Fröhlicha#, Gerhard Erkera, and Douglas W. Stephanb a Organisch-Chemisches Institut der Universität Münster, Corrensstr. 40, D-48149 Münster, Germany b School of Physical Sciences, Chemistry and Biochemistry, University of Windsor, Windsor, ON Canada N9B 3P4 Reprint requests to Prof. Dr. G. Erker. E-mail: [email protected] Z. Naturforsch. 57b, 1184Ð1188 (2002); received July 11, 2002 X-Ray Data, (Butadiene)zirconocene, Metallocene Cation Treatment of (butadiene)zirconocene with two molar equivalents of benzylmercaptane results in the formation of Cp2Zr(SCH2Ph)2 (11). Subsequent reaction of 11 with + Ð [Cp2ZrCH3 ][CH3B(C6F5)3 ](12) leads to rapid elimination of methane to yield the di- µ η2 µ + nuclear [ -( -thiobenzaldehyde)( -SCH2Ph)(ZrCp2)2 ] cation complex 14. A similar reaction is observed upon treatment of Cp2Zr(SC2H5)2 (15) with 12 to yield the thioacetaldehyde- µ η2 µ bridged dinuclear metallocene cation complex Cp2Zr- -( -MeCHS)- -(SEt)ZrCp2 (16).

Introduction In contrast to the typically di- and trinuclear (η2- η2 (η2-Ketone)-, (η2-aldehyde)-, and (η2-imine) aldehyde)zirconocene chemistry, the ( -thioalde- complexes of the group 4 metallocenes exhibit a hyde)MCp2 systems described so far are mostly mo- variety of interesting structural and chemical fea- nonuclear. We have now found an easy synthetic µ η2 tures. The latter have served as organometallic entry to sulfur-bridged dinuclear -( -thioalde- reagents in organic synthesis [1]. The former have hyde)zirconocene complexes that may eventually served as molecular model systems for Fischer- open pathways to similar dimetallic chemistry. Re- η2 η2 Tropsch-type reduction of carbon monoxide and lated examples of the ( -ketone)- and ( -aldehy- carbon-carbon coupling of CO-derived building de)zirconocene complexes have been previously re- blocks [2]. Especially the (η2-aldehyde)zircono- ported [3]. Typical examples are described in this cene complexes, including the parent compound paper. Scheme 2 shows the conversion 7 5 8 5 9 (η2-formaldehyde)zirconocene, show a high ten- with PMe3 as the auxiliary ligand. dency to form homo-dimetallic systems in which the aldehyde oxygen atom serves as a bridging atom. A variety of reactions has been shown to proceed readily with a number of organometallic reagents which were attached to the (η2-aldehyde)zirconocene template (for selected examples see Scheme 1) [3]. (η2-Thioaldehyde) group 4 metallocene complexes are also readily available, e. g. by methane elimination from (alkylthio)methylzirconocenes 7 (Scheme 2). The intramolecular abstraction of the hydrogen atom in the α-position to the sulfur atom in such systems probably proceeds concertedly; the CH4 elimination has a typical activation bar- rier of ∆G Ϸ 25 kcal molÐ1 at 80 ∞C [4].

# X-ray crystal structure analysis. Scheme 1.

0932Ð0776/2002/1000Ð1184 $06.00 ” 2002 Verlag der Zeitschrift für Naturforschung, Tübingen · www.znaturforsch.com D S. Courtenay et al. · Synthesis of a Dinuclear µ-(η2-Thioaldehyde)zirconocene Cation Complex 1185

Scheme 2.

Results and Discussion

We used Cp2Zr(SCH2Ph)2 (11) as the starting material for our synthesis (Scheme 3). Related bis(arylmethylthio)zirconocene complexes had been described previously [5]: They were prepared in a conventional salt metathesis by treatment of

Cp2ZrCl2 with two molar equivalents of Fig. 1. Molecular structure of complex 11 in the crystal. LiSCH2Ar. We have synthesized 11 by a different Selected bond lengths (A˚ ) and angles (∞): Zr-S1 2.511(1), route. (Butadiene)zirconocene (10) [6] was treated Zr-S2 2.496(1), Zr-C30 2.495(2), Zr-C31 2.489(2), Zr-C32 with two molar equivalents of benzylthiol in 2.480(2), Zr-C33 2.519(2), Zr-C34 2.517(2), Zr-C35 pentane at reflux temperature. This gave cleanly 2.496(2), Zr-C36 2.507(2), Zr-C37 2.536(2), Zr-C38 2.535(2), Zr-C39 2.523(2), S1-C1 1.838(2), S2-C2 the product Cp2Zr(SCH2Ph)2 (11) in 85% yield. 1.829(2), C1-C11 1.491(3), C2-C21 1.506(3); S1-Zr-S2 Complex 11 shows a singlet of the SCH2-protons 99.52(2), Zr-S1-C1 110.36(8), Zr-S2-C2 112.56(8), S1-C1- in the 1H NMR spectrum at δ 4.20 (in C D , corre- C11 109.4(2), S2-C2-C21 109.8(1). For additional values 6 6 see the text. sponding 13C NMR signal at δ 43.0) and a 1H NMR Cp singlet at δ 5.79 (13C NMR: δ 110.6). Recrystallization from hot toluene gave single the arene solvent the reaction between 11 and the crystals of 11 that were suited for an X-ray crystal reagent 12 took place instantaneously at room structure analysis. Complex 11 exhibits a pseudo- temperature. Methane evolution occurred, and the tetrahedral coordination geometry around zirco- precipitation of the product 14 as a dark red oil nium. The two Cp-rings are η5-coordinated with was observed. After the usual workup, complex 14 Zr-C(Cp) bond lengths ranging from 2.480(2) to was isolated as a bright red amorphous solid in 2.536(2) A˚ . The Cp(centroid)-Zr-Cp(centroid) an- > 80% yield. gle amounts to 131.8 ∞. The benzylthio ligands are The organometallic salt 14 shows very charac- both σ-bonded to zirconium (Zr-S1: 2.511(1) A˚ , teristic NMR spectra. These revealed that selec- Zr-S2: 2.496(1) A˚ ) [7]. The S1-Zr-S2 angle was tive deprotonation at the α-position to one of the found at 99.52(2) ∞.Theσ-ligands are both mark- sulfur atoms had occurred with formation of a bi- edly bent at the sulfur atoms [8] with bond angles nuclear ligand-bridged bis(zirconocene) cation Zr-S1-C1 = 110.36(8) ∞ and Zr-S2-C2 = 112.56(8) ∞. complex. In the 1H NMR spectrum of 14 a typical The S1-C1 and S2-C2 vectors are pointing to dif- set of four Cp resonances is observed at δ 5.80, ferent sectors at the front side of the bent metallocene wedge (dihedral angles S2-Zr-S1-C1: Ð 58.9(1) ∞, S1-Zr-S2-C2: Ð64.4(1) ∞), which leads to a conformation of the pair of -SCH2-Ph ligands at the Cp2Zr framework, approaching C2 symme- try.

The complex Cp2Zr(SCH2Ph)2 (11) was treated with one molar equivalent of the methylzircono- + Ð cene cation complex [Cp2ZrCH3 ][CH3B(C6F5)3 ] (12) [9], which was generated in situ by treatment of dimethylzirconocene with the strong organometallic Lewis acid B(C6F5)3 [10] in toluene. In Scheme 3. 1186 S. Courtenay et al. · Synthesis of a Dinuclear µ-(η2-Thioaldehyde)zirconocene Cation Complex

complete within 5 min at ambient temperature and the binuclear µ-(η2-thioacetaldehyde)bis(zirconocene) cation complex 16 was isolated in close to 80% yield (for details see the Experimental Section).

Experimental Section Scheme 4. All reactions were carried out in an inert atmo- sphere (argon) using Schlenk-type glassware or in 5.71, 5.58 and 5.16, each representing five hy- a glove box. Solvents (including deuterated drogen atoms (corresponding 13C NMR signals at solvents used for NMR spectroscopy) were dried δ and distilled under argon prior to use or purified 113.3, 110.8, 109.2, and 108.6 in d5-bromobenzene). This indicates the presence of a center of by a column system [14]. The substrates and rea- chirality. The CH unit of the (η2-thiobenzalde- gents Cp2Zr(butadiene) [6], Cp2Zr(SC2H5)2 [13], and [Cp ZrCH +][CH B(C F ) Ð] [9] were pre- hyde) group gives rise to a 1H NMR singlet at δ 2 3 3 6 5 3 pared according to literature procedures. For addi- 13 δ 4.82 (1H) and a typical C NMR resonance at tional general information, including a list of in- 83.7. The two phenyl substituents give rise to two struments used for physical characterization of the separate sets of 13C NMR signals (ipso-resonances compounds, see ref. 3. Most NMR assignments at δ 148.1 and δ 138.4, o, m, p-CH signals at δ were confirmed by 2D NMR experiments [14]. 129.1, 128.7, 128.6, 128.3, 125.3, and 123.2). As ex- pected, the methylene group of the remaining in- Synthesis of Cp2Zr(SCH2Ph)2 (11) 13 δ tact -SCH2Ph ligand ( C NMR of -SCH2: 41.7) Benzylthiol (1.70 ml, 14.4 mmol) was added to a shows a strongly split AB 1H NMR pattern (δ 3.96 suspension of (butadiene)zirconocene (2.00 g, 2 and 3.55) with a typical JHH = 12.7 Hz coupling 7.26 mmol) in 70 ml of pentane. The mixture was Ð constant. The NMR signals of the [CH3B(C6F5)3 ] refluxed for 3 h and then stirred for 12 h at ambi- anion were observed in the typical range [1H ent temperature. Volatiles were removed in vacuo δ 11 1 δ and the residue stirred with 100 ml of pentane. The NMR: = 1.30 (CH3); B{ H} NMR: = Ð14.7; 19F NMR: δ = Ð131.8, Ð163.9, Ð166.3 (o, m, p- resulting yellow solid was collected by filtration of C F )]. and dried in vacuo. Single crystals suitable for 6 5 the X-ray crystal structure analysis were ob- These results indicate that the strongly electro- + tained by recrystallization from hot toluene. philic cation [Cp2ZrCH3 ] rapidly reacts with the Yield: 2.8 g (85%). Ð M.p. 164 ∞C (DSC). Ð 1H neutral substrate Cp Zr(SCH Ph) , probably in- δ 2 2 2 NMR (400.1 MHz, d6-benzene): = 7.44 (psd, 4 duced by the donor properties of the Zr-thiolate H), 7.19 (pst, 4 H), 7.07 (pst, 2 H, o-, m-, p-Ph), 13 1 sulfur atoms [11,12]. Although a complete mecha- 5.79 (s, 10 H, Cp), 4.20 (s, 4 H, SCH2). Ð C{ H} δ nistic description must await further detailed ex- NMR (100.6 MHz, d6-benzene): = 143.8, 128.9, perimental studies, we assume that CH4 elimina- 128.6, 126.6 (ipso-, o-, m-, p-Ph), 110.6 (Cp), 43.0 tion probably takes place at the stage of some (SCH2). Ð C24H24S2Zr (467.8): calcd. C 61.62, bimetallic intermediate (such as e. g. 13, see H 5.17; found C 62.26, H 5.65. Scheme 3), since in the present system the methane elimination reaction takes place much faster X-ray crystal structure analysis of 11: than in the mononuclear reference system (7 5 9, Formula C24H24S2Zr, M = 467.77, yellow crystal, see Scheme 2) previously described in the litera- 0.60 ¥ 0.50 ¥ 0.50 mm, monoclinic, space group ture. P21/n (No. 14), a = 13.091(1), b = 9.906(1), c = ˚ ˚ 3 This reaction type is not limited to the specific 16.760(1) A, = 90.81(1)∞, V = 2173.2(3) A , ρ = 1.430 g cm-3, Z =4,µ = 7.04 cm-1, λ = case of the benzylthio substrate described above, calc 0.71073 A˚ , T = 293 K, ω and scans, empirical but seems to be quite general. We have also absorption correction by SORTAV (transmission treated bis(ethylthio)zirconocene (15, prepared factor 0.677 Յ T Յ 0.720), 10273 reflections col- conventionally by the salt metathesis route) [13] lected (ðh, ðk, ðl), [(sin θ)/λ] = 0.67 A˚ Ð1, 5256 + Ð with [Cp2ZrCH3 ][CH3B(C6F5)3 ](12) in dichlo- independent (Rint = 0.030) and 3591 observed re- romethane. The methane elimination reaction was flections [I Ն 2 σ(I)], 244 refined parameters, R = S. Courtenay et al. · Synthesis of a Dinuclear µ-(η2-Thioaldehyde)zirconocene Cation Complex 1187

0.033, wR2 = 0.065, max. (min.) residual electron 10 H, Ph), 5.80, 5.71, 5.58, 5.16 (s, each 5 H, Cp), density 0.22 (Ð0.48) e A˚ Ð3, hydrogens in calcu- 4.82 (s, 1 H, SCH), 3.96 and 3.55 (AB, each 1 H, 2 lated positions and refined as riding atoms. JHH = 12.7 Hz, SCH2), 1.30 (br., 3H, CH3-[B]). Ð 13 1 δ The data set was collected with a Nonius Kap- C{ H} NMR (100.6 MHz, d5-bromobenzene): = paCCD diffractometer, equipped with a rotating 148.1 (ipso-C of SCHPh), 138.4 (ipso-C of 1 anode generator Nonius FR591. Programs used: SCH2Ph), 148.5, 137.7, 136.8 (each d, JCF = data collection COLLECT (Nonius B. V., 1998), 240 Hz, o, p, m-C6F5), 129.1, 128.7, 128.6, 128.3, data reduction Denzo-SMN (Z. Otwinowski, W. 125.3, 123.2 (o-, p-, m-Ph), 113.3, 110.8, 109.2, Minor, Methods in Enzymology 276, 307 (1997), 108.6 (Cp), 83.7 (SCH), 41.7 (SCH2), ipso-C of 11 1 absorption correction SORTAV (R. H. Blessing, C6F5 and CH3[B] not observed. Ð B{ H} NMR δ 19 Acta Crystallogr. A51, 33 (1995); R. H. Blessing, (64.2 MHz, d5-bromobenzene): = Ð14.7. Ð F δ J. Appl. Crystallogr. 30, 421 (1997), structure NMR (282.4 MHz, d5-bromobenzene): = solution SHELXS-97 (G. M. Sheldrick, Acta Ð131.8, Ð163.9, Ð166.3 (o-, p-, m-C6F5). Crystallogr. A46, 467 (1990), structure refine- Ð C53H36BF15S2Zr2 (1215.2): calcd. C 52.38, ment SHELXL-97 (G. M. Sheldrick, Universität H 2.99; found C 52.35, H 3.17. Göttingen, 1997), graphics SCHAKAL (E. Keller, Universität Freiburg, 1997). Reaction of Cp2Zr(SC2H5)2 (15) with + Ð Crystallographic data (excluding structure [Cp2ZrCH3 ][CH3B(C6F5)3 ] (12); preparation of factors) for the structure reported in this paper 16: have been deposited with the Cambridge Crystal- The reagent 12 was generated by treatment lographic Data Centre as supplementary publica- of Cp2Zr(CH3)2 (37 mg, 0.147 mmol) in 2 ml tion no. CCDC-186417. Copies of the data can be of dichloromethane with B(C6F5)3 (75 mg, obtained free of charge on application to The Di- 0.146 mmol). After stirring the solution for 5 min a rector, CCDC, 12 Union Road, Cambridge CB2 solution of 51 mg (0.148 mmol) of Cp2Zr(SC2H5)2 1EZ, UK [Fax: int. code +44(1223)336-033, E- (15) in 2 ml of CH2Cl2 was added with stirring, mail: [email protected]]. effecting a colour change from yellow to bright orange. Evaporation of the solvent in vacuo af- forded the product as an orange powder. Yield Reaction of Cp Zr(SCH Ph) (11) with 2 2 2 124 mg (77%). Ð 1 [Cp ZrCH +][CH B(C F ) Ð] (12); synthesis of 14: H NMR (500 MHz, CD2Cl2): 2 3 3 6 5 3 δ = 6.53, 5.97, 5.94, 5.64 (s, each 5 H, Cp), 3.72 (q, 3 The reagent 12 was generated by adding 5 ml of JHH = 6.4 Hz, 1 H, CHMe), 3.03 and 2.83 (m, each 3 toluene to a solid mixture of tris(pentafluorophe- 1H,CH2Me), 2.28 (d, JHH = 6.4 Hz, 3 H, 3 nylborane) (200 mg, 390 µmol) and 98.2 mg CHCH3), 1.50 (t, JHH = 7.3 Hz, 3 H, CH2CH3), 13 1 (390 µmol) of dimethylzirconocene. The substrate 0.57 (br., 3 H, CH3[B]). Ð C{ H} NMR δ 11 (182.7 mg, 390 µmol) was added slowly with (125 MHz, CD2Cl2): = 152.2, 142.0, 140.0 (o-, p-, stirring to the solution. A gas evolution took place m-C6F5), 117.1, 114.8, 112.1 (double intensity), instantaneously and a dark red oil precipitated. (Cp), 90.2 (SCHMe), 37.7 (SCH2Me), 33.6 The mixture was stirred for 10 min and the oil al- (SCHCH3), 23.4 (SCH2CH3), 12.3 (br., CH3[B]), 11 1 lowed to settle. The supernatant liquid was dec- ipso-C of C6F5 not observed. Ð B{ H} NMR δ anted off. The oil was washed with toluene (2 ml) (CD2Cl2): Ð14.6 Ð C43H32BF15S2Zr2 (1091.1): and pentane (2 ¥ 3 ml). The dinuclear complex 14 calcd. C 47.34, H 2.96; found C 47.03, H 2.99. was obtained as a bright red powder after drying in vacuo. Yield: 390 mg (82%). Ð M. p. 143 ∞C (de- Acknowledgements comp.). Ð IR (KBr): ν˜ = 3114, 3089, 2963, 2919, Financial support from the Fonds der Chemi- 2848, 1641, 1511, 1458, 1265, 1087, 1016, 995, 977, schen Industrie, the Deutsche Forschungsgemein- 951, 934, 810, 761, 734, 699, 670 cmÐ1. Ð 1H NMR schaft, and NSERC of Canada is gratefully ac- δ (400.1 MHz, d5-bromobenzene): = 7.25Ð6.85 (m, knowledged. 1188 S. Courtenay et al. · Synthesis of a Dinuclear µ-(η2-Thioaldehyde)zirconocene Cation Complex

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