Clusters containing metal–metal bonds linking high- and low-valent metal centres: synthesis and structure of Ru 3 (CO) 12 {Mo(NAr) 2 } Shahbano Ali, a Arthur J. Carty,* b Antony J. Deeming, a Gary D. Enright b and Graeme Hogarth* ab a Chemistry Department, University College London, 20 Gordon Street, London, UK, WC1H 0AJ. E-mail: g.hogarth@ucl.ac.uk b The Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada, K1A 0R6. E-mail: Arthur.Carty@NRC.CA Received (in Basel, Switzerland) 8th November 1999, Accepted 7th December 1999 Room temperature reaction of K 2 [Ru 3 (CO) 11 ] with the molybdenum(VI) bis(imido) complexes Mo(NAr) 2 Cl 2 (dme) (Ar = C 6 H 3 X 2 -2,6; X = Me, Pr i , Cl; dme = 1,2-dimethoxy- ethane) affords new high-low valent clusters Ru 3 (CO) 12 {Mo- (NAr) 2 } which adopt a butterfly arrangement of metal centres with [Ru 3 (CO) 12 ] 22 acting as a ligand at a molybde- num(VI) centre. Molecular transition metal complexes can broadly be divided into those containing the metal centre in either a high and or low oxidation state. While in most respects the chemistry displayed in these two areas is quite different, metal–metal bonding is prevalent in both. Moreover, there is an increasing number of examples in which metal–metal bonds are formed between high- and low-valent metal centres. These include the classic W(V)–W(I) complex Cp * W(CO) 3 –WO 2 Cp * prepared by Alt et al., 1 while Sundermeyer has recently reported a range of related bi- and tri-nuclear imido-containing complexes. 2 In these, metal–metal bonds are found between the high- and low- valent centres but, even when more than one of the former is present, there are no metal–metal bonds between the low-valent centres. That is, clusters of this type are of the linear variety. Chi and coworkers 3,4 have synthesised a number of group 6/8 mixed-metal clusters containing imido ligands, however, here it is noted that the p-donor ligands are rarely bound in a monodentate fashion, 4 but rather bridge two or more metal centres. 3 As such, all metal centres in such clusters can be considered to be of similar valency. In contrast, Puddephatt and coworkers 5 have prepared the tetrahedral cluster cation [Pt 3 (ReO 3 )(m-dppm) 3 ] + where the formal metal oxidation states may be considered as Re(VII) and Pt(0), yet it is characterised by three strong Pt–Re interactions. Over the past thirty years, low-valent carbonyl clusters have been the focus of intensive research and a wide range of cluster geometries have been found. 6 Cluster frameworks are generally soft and deformable, with the geometries adopted dependent upon the number of electrons. Further, many are easily oxidised and/or reduced and as such have the ability to act as efficient electron sinks. Both of these properties, if controllable, would make the cluster useful as a ligand. Herein we describe the use of the low-valent cluster [Ru 3 (CO) 12 ] 22 as a ligand to a high- valent, bis(imido) stabilised molybdenum centre. Room temperature addition of thf solutions of K 2 [Ru 3 (CO) 11 ] 7 and Mo(NAr) 2 Cl 2 (dme) 8 resulted in the formation of very dark solutions which were left to stir overnight. Work-up in an aerobic atmosphere resulted after chromatography in the isolation of Ru 3 (CO) 12 and the new clusters Ru 3 (CO) 12 {Mo(NAr) 2 } 1a–c in yields of 20–30% Clusters 1a–c show good solubility in hexane and are air-stable in this solvent. Characterisation was made on the basis of IR, NMR and mass spectra.† Crystals of 1a suitable for X-ray analysis were easily grown upon cooling a saturated hexane solution to 220 °C, the results of which are summarised in Fig. 1.‡ The molecule consists of a butterfly arrangement of one molybdenum and three ruthenium atoms, with a fold angle of 25.4° about the hinge vector, Mo(1)–Ru(1). The molybdenum centre retains its two imido ligands while each ruthenium centre is ligated by four CO ligands. Of the three ruthenium– molybdenum interactions, two are extremely short [Mo(1)– Ru(2) 2.7165(5), Mo(1)–Ru(3) 2.7025(4) Å] while the third, the hinge vector, is much longer [Mo(1)–Ru(1) 3.1094(8) Å]. Indeed, as far as we are aware, these bonds within 1a span the range of all known molybdenum–ruthenium bonds in mixed- metal clusters. 9 The very short Mo–Ru interactions are probably a result of the smaller radii of high- vs. low-valent metal centres and high polarity of the heterometallic interaction M d+ –M d2 as noted previously by Sundermeyer et al. 2 The longer hinge vector is dative in origin, the electron-rich ruthenium tetra- carbonyl unit acting as a donor to the high-valent molybdenum centre. One way of looking at 1a is as a molybdenum(VI) bis(imido) centre bound to a chelating [Ru 3 (CO) 12 ] 22 ligand. In the free state this dianion would lose CO to afford Fig. 1 Molecular structure of 1a with selected bond lengths (Å) and angles (°): Mo(1)–Ru(1) 3.1094(8), Mo(1)–Ru(2) 2.7165(5), Mo(1)–Ru(3) 2.7025(4), Ru(1)–Ru(2) 2.9315(5), Ru(1)–Ru(3) 2.9556(5), Mo(1)–N(1) 1.766(2), Mo(1)–N(2) 1.761(2), Ru(2)–Mo(1)–Ru(3) 115.88(2), Mo(1)– Ru(3)–Ru(1) 66.50(2), Ru(3)–Ru(1)-Ru(2) 102.54(2), Ru(1)–Ru(2)–Mo(1) 66.68(2), N(1)–Mo(1)–N(2) 112.39(7), Mo(1)–N(1)–C(20) 163.60(13), Mo(1)–N(2)–C(30) 162.26(13). This journal is © The Royal Society of Chemistry 2000 Chem. Commun., 2000, 123–124 123