~~~~~~~Use of [Ru(q5-C,H,)(MeCN),]’ as a capping reagent in cluster build-up:synthesis and structural characterisation of [ Os,Ru,(C0),,(q5-C5H,),]Jack Lewis,* Catherine A. Morewood, Paul R. Raithby and M. Carmen Ramirez de ArellanoDepartment of Chemistry, Lensjield Road, Cambridge CB2 I E IT? UKIonic coupling of the mononuclear cation [Ru(qS-C,H,)-(MeCN),]’ with the cluster dianion [Os,(CO),,]’- afforded theneutral heptanuclear cluster [Os,Ru2(CO),,(qS-C,H,),1 whichhas been shown by X-ray diffraction studies to contain atricapped tetrahedral metal core.There is considerable current interest in the chemistry of transi-tion-metal clusters which contain cyclic, unsaturated organicligands such as arenes and dienes.’ This interest has been stimu-lated by the appealing analogy between the co-ordination of anorganic group to a cluster and to a metal surface, and the rele-vance of the latter to heterogeneous catalytic processes.’ Thecomplexes obtained can be prepared by one of two syntheticroutes, (i) where the co-ordination mode and level ofunsaturation of the organic ligand is modified once it has beenco-ordinated to the cluster’ and (ii) where a cationic organo-metallic fragment containing the organic group is coupled to acarbonyl cluster anion.4 For this second method of the syn-thesis the dicationic species ‘M(q6-C6H6-nRn)”’ (M = Ru or 0s;R = H or and ‘Rh(q5-C,Me,)2” have been used exten-~ively,~ however, reactions with monocationic species such as‘Ru(q5-C,H,)+’ have not been attempted, and the only clustersystems containing ‘Ru(qs-C,H,)’ units have been prepared bythe reaction of ruthenium-containing clusters with C,H,.’There are some advantages in using a monocationic cappingreagent in reactions with cluster dianions compared to using adicationic species such as [RU(q6-C6H6)(MeCN),]”. With amonocation it is, in principle, possible to add one or two unitsto a dianionic cluster thereby increasing the nuclearity by twometal atoms.Also, because [Ru(q5-C,H,)(MeCN),]’ is lessredox active than [RU(q6-c6H6)(MeCN),]’’ less redox chemistryshould occur, and higher yields of the reaction products shouldbe obtained.In this communication we report the first use of ‘[Ru(qs-C,H,)]”, generated from [Ru(q5-CsHs)(MeCN),]’, as a cap-ping reagent in the synthesis of higher-nuclearity clusters andthe formation of the new mixed-metal heptanuclear cluster[ossR~2(co) I s(q5’csHs)21 1 -In an ionic coupling reaction 2 molar equivalents of themonocation [Ru(q5-C,H,)(MeCN),]’, as its [PI?,]- salt (59 mg,0.134 mmol),’ were added to a dichloromethane solution (25cm’) of the osmium cluster dianion [Os,(CO),,]’-, as its[N(PPh,)J’ salt (150 mg, 0.061 mmol),” and the mixture stirredat room temperature for ca.15 min. During this time the solu-tion turned green, and after removal of the solvent, the solidresidue was purified by TLC, using CH,Cl,-hexane (80 : 20) aseluent. The cluster [Os,Ru2(CO),,(qs-C,Hs)J 1 was isolated asthe sole product in 87% yield (90 mg, 0.053 mmol) andrecrystallised from CH,Cl,-hexane. The complex was initiallycharacterised from spectroscopic data.? The FAB mass spec-t IR (CH2CI,): v(C0) 2074w, 2055% 2024~s 2007% 1987s and 1933 (br) m cm-’;‘H NMR (CDCI,): 6 5.19 (s, 10 H).Positive-ion FAB mass spectrum: ml: 1703(calc. 1702 based on I9OOs and ‘“Ru) (Found: C, 17.65; H, 0.55. Calc. forCUHlOO,,O~,R~,: C, 17.65; H, 0.6%).trum exhibits a molecular ion peak at m/z 1703, and also showsfragments corresponding to the sequential loss of 15 carbonylgroups. The ‘H NMR spectrum, at room temperature, exhibitsa singlet at 6 5.19 which is indicative of the protons on twoequivalent qS-CSH, rings. This chemical shift is comparablewith that observed for the protons on the q5-C5H, ligandsin the mixed-metal cluster [RU~R~C(~~-C,M~,)(T~~-C~(6 5.14).8In order to establish the molecular structure of cluster 1 andestablish the geometry of the metal core and the positions ofthe ‘Ru(qS-C,H,)’ units a crystal structure determination wasundertaken. The molecular structure $ is shown in Fig. 1 whichincludes some selected bond parameters. The metal frameworkmay be described as a bicapped trigonal bipyramid, with thetwo ‘Ru(qs-C,H,)’ units at the two apical sites of the trigonalbipyramid, or as four Os,Ru tetrahedra sharing four commonfaces. In the latter case the metal core can be viewed as beingrelated to that observed in [ O S ~ ( C O ) ~ ~ ( ~ ~ - C ~ H , ) ] , ~ which itself isderived from that of the bicapped tetrahedral core found in theparent binary carbonyl [os~(Co)~~].” In terms of the eighteen-electron rule, as with the two osmium cluster examples, it is notpossible formally to assign each metal atom 18 electronsalthough the total electron count of 96e- for the cluster is con-sistent with the Mingos condensed polyhedral count for thestr~cture.’~ If the two q5-C,H, rings each donate five electronsand the two bridging carbonyl ligands, C( 12)0( 12) andC(13)0(13), donate one to each of the bridged metalatoms, then Os(2) and Os(4) are each associated with 17e-,Os(l), Ru(1) and Ru(2) with 18e-, and Os(3) and Os(5) with19e-.The two ‘Ru(qS-C,H,)’ units have not simply clipped onas caps to the Os, trigonal-bipyramidal core, occupying 17e-sites, as might be expected, but the formation of 1 has involveda metal-core rearrangement in which the two ‘RU(T~~-C,H,)’units occupy two of the three 18e- sites. This is consistent withthe fact that the q5-C,H, groups are much better donors andpoorer n acceptors than carbonyl groups, and so the ‘Ru(qs-CSHS)’ units are better suited to sites of higher formal electrondensity.The two bridging carbonyl ligands, which are betteracceptors than terminal carbonyl ligands, are associated withthe two ruthenium centres and the formally 18e- 0 s atom,Os(1); in this way the higher electron density provided by the‘Ru(qs-C,H,)’ units can be balanced. Similar effects have been1 Crystal data: C,,H,,O,,Os,Ru,, M = 1703.47, green plate, crystal dimensions0.12 x 0.31 x 0.33 mm, monoclinic, space group P2 /n (alternative setting P2,lc,no.14), a = 11.692(4), h = 17.699(6), c = 14.984(6) 1, J3 = 92.88(4)”, U = 3097(2)A’, 0, = 3.654 Mg m-’, Z = 4, F(000) = 2992, Mo-Ka radiation, h = 0.710 73 A.p(Mo-Ku) = 21.45 mm-I, T = 293(2) K. Siemens RSm Vfour-circle diffractometer,4425 reflections collected in the range 2.54 22.54”, 4053 unique absorption-corrected data (R,,, = 0.039). Structure solved by direct methods ( 0 s and Ruatoms) (SHELXTL PLUS”) and refined with Os, Ru and 0 atoms anisotropic byfull-matrix least squares based on F2 (SHELXL 93 I*); H atoms were not includedin the refinement. Refinement converged at R1 = 0.0686, wR2 = 0.1268 for 2336unique data with F =- 4a(F), and R1 = 0. I505 and 1vR2 = 0.1645 (all data), good-ness of fit = 1.089.weightingscheme NJ = I/[d(F:) + (0.0514P)* + 146.12PJ whereP = (F: + 2F,’)/3. Atomic coordinates, thermal parameters. and bond lengthsand angles have been deposited at the Cambridge Crystallographic Data Centre(CCDC). See Instructions for Authors,J Chem. Soc., Dalton Trtlris., 1996, Issue 1.Any request to the CCDC for this material should quote the full literature citationand the reference number I86/3 15.0.l Chem. Soc., Dalton Trans., 1996, Pages 4509-4510 450Fig. 1 Molecular structure of [O~,RU,(CO),,(T~-C~H,),~ 1 showing the atom numbering scheme. Selected bond lengths (A) and angles (O):OS( I)-Ru( I ) 2.604(4), OS( I)-Ru(2) 2.610(4), OS( 1)-0~(2) 2.692(3), OS( 1)-0~(3) 2.757(2), OS( I)-0~(4) 2.686(3), OS( 1)-0~(5) 2.759(2), Os(2)-Ru(2)2.735(4), Os(2)-0s(3) 2.884(2), Os(3)-Ru( 1) 2.857(4), Os(3)-Ru(2) 2.844(4), Os(3)-0s(5) 2.770(3), Os(4)-Ru( 1) 2.736(4), Os(4)-0s(5) 2.880(3),0~(5)-Ru(l) 2.815(4), 0~(5)-Ru(2) 2.837(4), Ru(l)-C(101) 2.22(4), Ru(l)-C(102) 2.22(4), R~(l)-C(103) 2.19(4), Ru(l)-C(104) 2.17(5), Ru(l)-C(lO5)2.19(5), Ru(2)-€(201) 2.18(4), Ru(2)-C(202) 2.23(4), Ru(2)-C(203) 2.31(4), Ru(2)-C(204) 2.30(4), Ru(2)-C(205) 2.22(4), OS( l)-C(12) 2.02(3),Os( I)<( 13) 2.02(3), Ru( 1 )-C( 12) 1.99(3), Ru(2)-C( 13) 2.08(4), Ru( I)-Cp( l)(centroid) 1.887 and Ru(2)-Cp(2)(centroid) 1.91 3; Os( I)<( 12)-Ru( 1)8 1 .O( 13) and Os( 1 )-C( 1 3 jRu(2) 79.0( 12)observed in the osmium arene clusters [OS~(CO),S(~~-C~H~)]and [Os,(CO),,(r16-C,H,)],6 but in the case of 1 any possibilityof arene migration over the cluster surface can be eliminatedbecause of the positions of the rutheniums in the mixed-metalcluster.The fact that the ‘Ru(qS-CSHs)’ units do not occupy the19e- sites may have a steric origin. In the related cluster [Ru,(q2-CL4-CO),(CO),,(r16-C6H,Me3-l,3,5)] l5 the Ru(q6-C6H3Me,) unit,which is a good donor group, does occupy one of the 19e-centres in the formally bicapped tetrahedral core, but the coreopens out to generate a structure in which two edges of thecentral tetrahedron are bridged by Ru atoms and two of thecarbonyls co-ordinate in the novel q2-p4 mode. A similarstructural rearrangement might be required if ‘Ru(qS-CsHs)’units were to occupy 19e- sites in 1.The crystal structure of cluster 1 shows that the moleculesare separated by normal van der Waals distances, with thecyclopentadienyl rings packing facing carbonyl groups, so thatthere is no cyclopentadienyl-cyclopentadienyl stacking.It is Literesting to note that the reaction of 1 equivalent of[Ru(q5-CSHs)(MeCN),]’ with the hydrido monoanionic clus-ter [Os,H(CO),,]- does not yield the expected product[OssRuH(CO),s(qs-C,H5)], and the only product is the green,neutral species [Os,Ru2(C0),s(qs-C,Hs)2] 1 in 43% yield.Thissuggests that the introduction of one ‘Ru(qS-C,H,)’ unit, underthe reaction conditions, leads to ready deprotonation of theproduct, although the anion [OssRu(CO)lS(qS-CsHS)]- has notbeen isolated and a further coupling reaction to afford 1 takesplace.AcknowledgementsWe gratefully acknowledge the financial support of the Cam-bridge Overseas Trust, the Overseas Research Scheme, and ICIplc (to C.A. M.), and the European Union for a Human Cap-ital and Mobility grant (to M. C. R. de A.). We thank JohnsonMatthey plc for a generous loan of osmium and rutheniumsalts.References1 B. F. G. Johnson, J. Lewis, M. A. Gallop and M. Martinelli,Faraday Discuss., R. SOC. Cliem., 1991, 92, 241; H. Wadepohl,Angew. Chem., Int. Ed. Engl., 1992, 31, 247; D. Braga, P. J. Dyson,F. Grepioni and B. F. G. Johnson, Cliem. Rev., 1994,94, 1585.2 G. A. Somorjai, J Pliys. Chem., 1990, 94, 1013; H. P. Steinruck,W. Huber, T. Pache and D. Menzel, Surf: Sci., 1989, 218; H. P.Steinruck, P. Heinmann, W. Huber, P. Jokob, T. Pache and D.Menzel, A Electron Spectrosc.Relat. Phenom., 1990,52, 5 1 .3 M. P. Gomez-Sal, B. F. G. Johnson, J. Lewis, P. R. Raithby andA. H. Wright, J. Cliem. SOC., Cliem. Commun., 1985, 1682; A. J.Blake, P. J. Dyson, B. F. G. Johnson, C. M. Martin, J. G. M. Nairn,E. Parisini and J. Lewis, J Chem. SOC., Dalton Trans., 1993, 981;A. J. Edwards, M. A. Gallop, B. F. G. Johnson, J. U. Kohler, J. 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