The cluster dication½ðg6-C6H6Þ2ðg6-C6Me6Þ4Ru8ðl2-HÞ2ðl3-OÞ2ðl2-ClÞ2�

2þ:

a chloro-bridged framework containing two metal tetrahedra

Matthieu Faure, Helen Stœckli-Evans, Georg S€uuss-Fink *

Institut de Chimie, Universit�ee de Neuchaatel, Case postale 2, Avenue de Bellevaux 51, CH-2007 Neuchaatel, Switzerland

Received 12 September 2001; accepted 2 October 2001

Abstract

The title complex was obtained by reacting ½ðg6-C6H6Þðg6-C6Me6Þ2Ru3ðl2-HÞ3ðl3-OÞ�þ with RuCl3 � nH2O in aqueous solution;

it crystallises as the tetrafluoroborate salt. The cationic cluster is formed of two tetrahedral Ru4 substructures which are held to-

gether by two chloro bridges. � 2002 Elsevier Science B.V. All rights reserved.

Keywords: Cluster; Octanuclear; Terahedral; Ruthenium; Arene ligand; Oxo cap

Ligand-stabilised transition metal clusters are fasci-nating molecules due to their diverse structural featuresand to their – sometimes unique – catalytic properties[1,2]. In recent years we have shown that the water-stable arene–ruthenium unity can be used to assemblewater-soluble tri- and tetranuclear clusters [3–7]. Inparticular, the reaction of the dinuclear cation½ðg6-C6Me6Þ2Ru2ðl2-HÞ3�

þ with the mononuclear com-plex ½ðg6-C6H6ÞRuðH2OÞ3�

2þ was found to give thetrinuclear cluster cation ½ðg6-C6H6Þðg6-C6Me6Þ2Ru3ðl2-HÞ3ðl3-OÞ�þ ð1Þ, which can be isolated as the tetra-fluoroborate salt [8] and which turned out to be anoutstanding catalyst for the hydrogenation of benzeneto cyclohexane under biphasic conditions [8,9]. In thispaper, we report the reaction of 1 with ruthenium(III)chloride which, in aqueous solution, gives rise to anunprecedented octanuclear cluster cation in which twoRu4 subclusters are held together by two chloro bridges.

The trinuclear cluster ½ðg6-C6H6Þðg6-C6Me6Þ2Ru3ðl2-HÞ3ðl3-OÞ�þ ð1Þ reacts in aqueous solution withRuCl3 � nH2O to give the octanuclear cluster

½ðg6-C6H6Þ2ðg6-C6Me6Þ4 Ru8ðl2-HÞ2ðl 3-OÞðl2-ClÞ2�2þ

ð2Þ, which can be isolated as a tetrafluoroborate salt: 1

2½ðg6-C6H6Þðg6-C6Me6Þ2Ru3ðl2-HÞ3ðl3-OÞ�þþ2RuCl3

!½ðg6-C6H6Þ2ðg6-C6Me6Þ4Ru8ðl2-HÞ2ðl3-OÞðl2-ClÞ2�2þþ4Cl�þ4Hþ

The spectroscopic and analytical data 2 of 2 (tetra-fluoroborate salt) are consistent with the formula½ðg6-C6H6Þ2ðg6-C6Me6Þ4Ru8ðl2-HÞ2ðl3-OÞðl2-ClÞ2�

2þ:The infrared spectrum exhibits two bands in the region2900–3100 cm�1, assigned to the C–H (aromatic andaliphatic) stretching vibrations of the arene ligands; abroad band between 3300 and 3500 cm�1 is due tocrystal water. In the 1H NMR spectrum (acetone-d6), 2

Inorganic Chemistry Communications 5 (2002) 9–11

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*Corresponding author. Tel.: +41-32-7182405; fax +41-32-7182511.

E-mail address: georg.suess-fink@ich.unine.ch (G. S€uuss-Fink).

1 An aqueous solution (30 ml) of 1½BF4� (60 mg, 0.074 mmol) and

RuCl3 � nH2O (20 mg, 0.076 mmol) was heated under nitrogen

atmosphere to 50 �C for 2 h. Then the solution was cooled to room

temperature and stirred for 3 days. After filtration of the solution,

a solution of NaBF4 (81 mg, 0.74 mmol) in 5 ml H2O was added,

which caused the precipitation of the pure product ½ðg6-C6H6Þ2ðg6-C6Me6Þ4Ru8ðl2-HÞ2ðl3-OÞðl2-ClÞ2�½BF4�2. Yield 30 mg (0.016

mmol, 43%). It can be recrystallised from a solution of benzene and

acetone to give orange-red crystals.2 Spectroscopic data for 2½BF4�2: IR (KBr, cm�1): 3445 (w), 3282 (w),

m(O–H); 3077 (w), mðC–HarÞ; 2922 (s), m(C–H); 1439 (m), 1390 (m),

mðC@CÞ; 1083 (br, vs), mðBF4Þ; 1H NMR (200 MHz, aceton-d6, 294 K):

d 6.25 ppm (C6H6), d 2.29 ppm ðC6Me6Þ; d � 13:65 ppm (hydrido

ligands); Anal. found: C 38.63%, H 5.02%. Calc. for

C60H86O2Ru8Cl2B2F8: C 38.08%, H 4.58%.

1387-7003/02/$ - see front matter � 2002 Elsevier Science B.V. All rights reserved.

PII: S1387-7003 (01 )00329-X

gives rise to a singlet for the two equivalent benzene li-gands and a singlet for the four equivalent hexamethyl-benzene ligands; the two equivalent hydrido ligandsappear as a singlet in the high-field region. In the elec-trospray mass spectrum, a molecular peak is observed atm=z 860 (calculated for 102Ru: 860) displaying the ex-pected Ru8 isotope pattern (see Fig. 1).

The molecular structure of 2 was confirmed by asingle-crystal X-ray structure analysis. 3 Cluster 2 has anoctanuclear metal framework in which two Ru4 sub-clusters are held together by two chloro bridges. In theRu4 subclusters the four ruthenium atoms form a closedtetrahedron, one triangular face of which is capped by al3-oxo ligand. The ruthenium atom opposite to the oxocap is coordinated to the two chloro bridges, whereas

the other three ruthenium atoms in the triangular planeperpendicular to the symmetry plane are coordinated toarene ligands. Due to the different arene ligands, theseRu3 planes are isoceles triangles. The distances betweenthe two ruthenium atoms coordinated to hexamethyl-benzene [Ru(2)–Ru(2c), Ru(2a)–Ru(2b): 2.8365(14) �AA]are slightly longer than those between the rutheniumatoms coordinated to two different arene ligands[Ru(1)–Ru(2), Ru(1)–Ru(2c), Ru(1a)–Ru(2a), Ru(1a)–Ru(2b): 2.7723(12) �AA]. Consequently, the bond anglesRu(2)–Ru(1)–Ru(2c) and Ru(2a)–Ru(1a)-Ru(2b)[61.54(4)�] are wider than those centred at the otherruthenium atoms [59.230(19)�] in the triangular planes.The two oxo ligands are symmetrically coordinated overthe two Ru3 triangles, the six ruthenium–oxygen dis-tances being almost equal [Ru(1)–O(1), Ru(1a)–O(1a):2.015(8) �AA, Ru(2)–O(1), Ru(2c)–O(1), Ru(2a)–O(1a),Ru(2b)–O(1a): 2.013(6) �AA]. The ruthenium–rutheniumbonds Ru(1)–Ru(4) and Ru(1a)–Ru(4a) are longer[3.0372(6)�AA] than the other ruthenium–ruthenium bondsof the tetrahedra [Ru(2)–Ru(4), Ru(2c)–Ru(4), Ru(2a)–Ru(4a), Ru(2b)–Ru(4a): 2.9527(12) �AA], being indicativeof the l2-hydrido ligands bridging the Ru(1)–Ru(4) andRu(1a)–Ru(4a) edges, but the two hydrido ligands couldnot be localised and fully refined. The distance Ru(4)–Ru(4a) is too long [3.39 �AA] for a metal–metal bond. Twowater molecules are hydrogen-bonded to the two l3-oxo3 See footnote 3 on next page.

Fig. 1.

Fig. 2. ORTEP view of ½ðg6-C6H6Þ2ðg6-C6Me6Þ4Ru8ðl2-HÞ2ðl3-OÞðl2-ClÞ2�2þ ð2Þ, showing the atom-labelling scheme. Selected bond lengths (�AA)

and angles (�): Ru(1)–Ru(2) 2.7723(15), Ru(1)–Ru(2c) 2.7723(12), Ru(1)–Ru(4) 3.0372(16), Ru(2)–Ru(2c) 2.8365(14), Ru(2)–Ru(4) 2.9527(12),Ru(1)–O(1) 2.015(8), Ru(2)–O(1) 2.013(6), Ru(2c)–O(1) 2.013(6), Ru(4)–Cl(1) 2.548(4), Ru(4)–Cl(1a) 2.556(5), O(1)–Ru(1)–Ru(2) 46.47(18), O(1)–

Ru(2)–Ru(1) 46.5(2), O(1)–Ru(2)–Ru(2c) 45.20(17), O(1)–Ru(1)–Ru(4) 92.2(3), Ru(1)–Ru(2)–Ru(2c) 59.230(19), Ru(2)–Ru(1)–Ru(2c) 61.54(4),

Ru(2)–Ru(1)–Ru(4) 60.89(3), Ru(2c)–Ru(4)–Ru(1) 55.12(3), Ru(2)–O(1)–Ru(1) 87.0(3), Ru(2)–O(1)-Ru(2c) 89.6(3), Ru(4)–Cl(1)–Ru(4a) 83.59(14),

Cl(1)–Ru(4)–Cl(1a) 96.41(14).

10 M. Faure et al. / Inorganic Chemistry Communications 5 (2002) 9–11

caps [Oð1Þ � � �O (water), Oð1aÞ � � �O (water) distances2.6467�AA] and cannot be removed in vacuo. The molecule2 possesses amirror plane, in which lie atomsO(1), Ru(1),Ru(4), Cl(1), Cl(1a), Ru(4a), Ru(1a), O(1a) and an in-version centre at the intersection of theRu(4)–Ru(4a) andCl(1)–Cl(1a) vectors (see Fig. 2).

1. Supplementary data

Full tables of atomic parameters, bond lengths andangles are deposited at the Cambridge CrystallographicData Centre, 12 Union Road, Cambridge CB2 1EZ,UK. Deposition Number: 2 CCDC 169833.

Acknowledgements

We thank the Swiss National Science Foundation forthe financial support of this work and the JohnsonMatthey Research Centre for a generous loan of Ru-thenium(III) chloride hydrate.

References

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Catalysis by Di- and Polynuclear Metal Cluster Complexes,

Wiley-VCH, New York, 1998, p. 167.

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G. Wilkinson (Eds.), Comprehensive Organometallic Chemistry 2,

vol. 10, Elsevier, Oxford, 1995, p. 351.

[3] G. Meister, G. Rheinwald, H. Stoeckli-Evans, G. S€uuss-Fink, J.

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[4] B. Cornils, Angew. Chem., Int. Ed. Engl. 34 (1995) 1575.

[5] W.A. Hermann, B. Cornils (Eds.), Aqueous-Phase Organometallic

catalysis, Wiley-VCH, New York, 1998.

[6] F. Ch�eerioux, A. Maisse-Franc�ois, A. Neels, H. Stoeckli-Evans, G.S€uuss-Fink, J. Chem. Soc., Dalton Trans. (2001) 2184.

[7] G. S€uuss-Fink, L. Plasseraud, A. Maisse-Franc�ois, H. Stoeckli-Evans, H. Berke, T. Fox, R. Gauthier, J.Y. Saillard, J. Organo-

met. Chem. 609 (2001) 196.

[8] M. Faure, M. Jahncke, A. Neels, H. Stoeckli-Evans, G. S€uuss-

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Organomet. Chem. 621 (2001) 103.

[10] G.M. Sheldrick, SHELXS-97 program for crystal structure

determination, Acta Crystallogr. A 46 (1990) 467.

[11] G.M. Sheldrick, SHELXL-97, Universit€aat G€oottingen, G€oottingen,Germany, 1997.

3 Crystallographic data for 2½BF4�2: C30H50B1Cl1F4O5Ru4 (including

four molecules of water), monoclinic, space group, C 2/m,

a ¼ 17:5513ð13Þ, b ¼ 18:7755ð14Þ, c ¼ 10:7074ð8Þ �AA, a ¼ 90�;b ¼94:404ð9Þ�; c ¼ 90�, U ¼ 3518:0ð5Þ �AA

3, Z ¼ 4; Dc ¼ 1:917 g=cm3,

T ¼ 153(2) K, lðMo-KaÞ ¼ 1:818 mm�1. The data were measured

using a Stoe Image Plate Diffraction System equipped with a / circle,

using Mo-Ka graphite monochromated radiation (k ¼ 0:71073 �AA) with

/ range 0–200�, increment 1, 2h range 3.27–52.1�, Dmax–Dmin ¼12:45–0:81 �AA, 2563 observed reflections ½I > 2rðIÞ� used in the

refinement, R1 ¼ 0:0779, wR2 ¼ 0:1973 (R1 ¼ 0:0973, wR2 ¼ 0:2081

for all data). The structure was solved by direct methods using the

programme SHELXS-97 [10]. The refinement and all further calcula-

tions were carried out using SHELXL-97 [11]. The water H-atoms

were located from Fourier difference maps and refined isotropically or

held fixed. The remainder of the H-atoms were included in calculated

positions and treated as riding atoms using the SHELXL default

parameters. The non-H atoms were refined anisotropically, using

weighted full-matrix least-squares on F 2. It was not possible to locate

the hydride H-atoms.

M. Faure et al. / Inorganic Chemistry Communications 5 (2002) 9–11 11