DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 1939–1940 1939 Coupling reaction of alkyl cyanide (RCN, R 5 Me or Et) with 7-azaindole on a hexaosmium carbonyl cluster core; molecular structure of [Os6(CO)14(Ï-CO)(Ï-H)(Ï-Á1 :Á2-C9H8N3)] Kelvin Sze-Yin Leung and Wing-Tak Wong *,† Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China Treatment of [Os6(CO)16(NCR)2] (R = Me or Et) with 7-azaindole resulted in the formation of [Os6(CO)14(m-CO)- (m-H)(m-h1 :h2-C8H5N3)(R)] involving coupling of the alkyl cyanide and 7-azaindole.The interaction of two organic fragments bound to the metal cluster core to give a larger and more complex molecular fragment is of basic scientific interest and has potential industrial applications.1 We are currently interested in the study of transition-metal cluster assisted coupling of organic molecules and have recently observed some ruthenium clusters with a coordinated phenoxazinone-like ligand that arose from a ‘quinone–imine or –nitrene’ intermediate via the reductive deoxygenation of the quinone–oxime by the transition-metal carbonyl cluster.2 As part of our continuing investigations, we have studied the interaction of 7-azaindole with the hexaosmium cluster [Os6(CO)16(NCMe)2] and observed that a novel coupling between the co-ordinated acetonitrile ligand and 7-azaindole gave a metallaheterocycle involving osmium metal.Reaction of 1 equivalent of 7-azaindole with the preformed labile bis(acetonitrile)hexaosmium carbonyl cluster [Os6(CO)16- (NCMe)2],3 in CH2Cl2, gave [Os6(CO)14(m-CO)(m-H)(m-h1 :h2- C9H8N3)] 1.‡ The stoichiometry of 1 was initially established by FAB-MS and 1H NMR spectroscopic techniques.§ Single crystals of 1 suitable for X-ray analysis ¶ were obtained from slow evaporation of a toluene–CHCl3 solution at room temperature for 2 d.A perspective drawing of cluster 1 together with some selected bond parameters is shown in Fig. 1. This analysis revealed that complex 1 contains a bicapped-tetrahedron metal core identical to the parent compound Os6(CO)18.5 However, the co-ordinated 7-azaindole ligand was found to couple with a co-ordinated acetonitrile to form three fused rings involving osmium metal [Os(6)]. Such a ring system is nearly planar with a maximum deviation of 0.30 Å. The 7-azaindole also underwent orthometallation and co-ordinated to Os(5), which is a very common observation for pyridine-containing osmium † E-Mail: wtwong@hkucc.hku.hk ‡ Treatment of 7-azaindole (7.1 mg) with [Os6(CO)16(NCMe)2] (100 mg, 0.06 mmol) in CH2Cl2 (25 cm3) under ambient conditions over a period of 24 h aVorded a deep brown reaction mixture.Purification by TLC on silica Merck Kieselgel 60 GF254 (hexane–CH2Cl2, 1 : 3) gave the brown air-stable cluster 1 (35%) together with two uncharacterized products in low yields. Deprotonation of 1 (10 mg) with a slight excess of dbu was carried out in CH2Cl2 (10 cm3) at room temperature.Proton NMR monitoring indicated that the deprotonation to give 2 was complete within 10 min. The subsequent reprotonation of 2 to give 1 was achieved by the addition of excess trifluoroacetic acid (0.2 cm3). Carbonylation of 1 (20 mg) was carried out in CH2Cl2 (30 cm3) at room temperature for 4 h to give the light brown cluster 3. Due to the instability of 3 in solution no accurate yield could be determined. A similar synthetic methodology to 1 was used for the preparation of 4 with EtCN instead of MeCN (yield 30%).clusters. Recently we also reported the reaction of 7-azaindole with [Os3(CO)10(NCMe)2] to give a major product [Os3(m-H)- (CO)9(m-C7H5N2)] containing an orthometallated ligand.6 All the carbonyl ligands were terminally bonded except a bridging CO across the Os(3)]Os(6) edge. This Os]Os edge is found to be significantly shorter than other Os]Os bonds in 1 which might probably be due to the ‘clamping’ eVect of the bridging CO.The hydride and the imine hydrogen, as evident from 1H NMR, could not be located directly by X-ray analysis. However, potential-energy calculations 7 suggested that the hydride bridges Os(4)]Os(5). This is also consistent with the observed long Os(4)]Os(5) distance compared with other Os]Os distances in the structure.8 The imino hydrogen was found to undergo dissociation in the presence of a strong base such as 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu) so that a cluster anion [Os6(CO)14(m-CO)(m-H)(m-h1 :h2-C9H7N3)]2 2 resulted.However, the hydride ligand does not undergo dissociation in § Spectroscopic data: complex 1. IR (CH2Cl2, cm21) 2086m, 2055s, 2022s, 2012vs, 1956w [n(CO)]. Positive-ion FAB mass spectrum: m/z 1720 (Calc. 1720). 1H NMR (CD2Cl2): d 214.33 (s, 1 H, metal hydride), 1.26 (s, 3 H, methyl), 6.75 [dd, 1 H, H1, J(H1,2) 7.8, J(H1,3) 2.0], 7.26 [dd, 1 H, H4, J(H4,3) 7.7, J(H4,2) 1.6], 7.46 [ddd, 1 H, H2, J(H2,1) 7.8, J(H2,3) 4.3, J(H2,4) 1.6], 7.82 [ddd, 1 H, H3, J(H3,4) 7.7, J(H3,2) 4.3, J(H3,1) 2.0 Hz], 8.69 (s br, 1 H, NH) (Found: C, 18.93; H, 0.54; N, 2.44.Calc. for C24H9N3O15Os6?0.5C7H8: C, 18.68; H, 0.74; N, 2.38%). Complex 2. 1H NMR (CD2Cl2): d 214.58 (s, 1 H, metal hydride), 1.26 (s, 3 H, methyl), 6.75 [dd, 1 H, H1, J(H1,2) 7.7, J(H1,3) 2.0], 7.30 [dd, 1 H, H4, J(H4,3) 7.5, J(H4.2) 1.8], 7.52 [ddd, 1 H, H2, J(H2,1) 7.7, J(H2,3) 4.3, J(H2,4) 1.8], 7.82 [ddd, 1 H, H3, J(H3,4) 7.5, J(H3,2) 4.3, J(H3,1) 2.0 Hz].Complex 3. IR (CH2Cl2, cm21) 2019s, 1992vs, 1967s [n(CO)]. Positive-ion FAB mass spectrum: m/z 1749 (Calc. 1748). 1H NMR (CD2Cl2): d 214.46 (s, 1 H, metal hydride), 1.25 (s, 3 H, methyl), 6.50 [dd, 1 H, H1, J(H1,2) 7.8, J(H1,3) 1.9], 7.22 (dd, 1 H, H4, J(H4,3) 7.5, J(H4,2) 1.7], 7.46 [ddd, 1 H, H2, J(H2,1) 7.8, J(H2,3) 4.2, J(H2,4) 1.7], 7.95 [ddd, 1 H, H3, J(H3,4) 7.5, J(H3,2) 4.2, J(H3,1) 1.9 Hz], 11.27 (s br, 1 H, NH).Complex 4. IR (CH2Cl2, cm21) 2085m, 2053s, 2022s, 2012vs, 1950w [n(CO)]. Positive-ion FAB mass spectrum: m/z 1734 (Calc. 1733). 1H NMR (CD2Cl2): d 215.13 (s, 1 H, metal hydride), 1.15 (t, 3 H, J 7.3, methyl), 1.41 (q, 2 H, J 7.3, methylene), 7.32 [dd, 1 H, H1, J(H1,2) 7.9, J(H1,3) 1.9], 7.48 [dd, 1 H, H4, J(H4,3) 7.7, J(H4,2) 1.8], 7.82 [ddd, 1 H, H2, J(H2,1) 7.9, J(H2,3) 4.4, J(H2,4) 1.8], 8.23 [ddd, 1 H, H3, J(H3,4) 7.7, J(H3,2) 4.4, J(H3,1) 1.9 Hz], 8.67 (s, br, 1 H, NH) (Found: C, 18.73; H, 0.79; N, 2.42.Calc. for C25H11N3O15Os6: C, 18.89; H, 0.83; N, 2.32%). ¶ Crystal data: C24H9N3O15Os6?0.5C7H8 1, M = 1766.62, primitive monoclinic, space group P21/n (no. 14, non-standard setting of P21/c), a = 10.223(1), b = 28.137(2), c = 12.357(1) Å, b = 97.70(1)8, U = 3522.4(5) Å3, Z = 4, Dc = 3.331 g cm23, T = 298 K, F(000) = 3100, Mo-Ka radiation (l = 0.710 73 Å), m(Mo-Ka) = 216.17 cm21, dimensions 0.12 × 0.12 × 0.18 mm, 4002 observed diVractometer data [I > 1.0s(I )].The structure was solved by direct methods (SIR 88) 4 and Fourier-diVerence techniques, refined by full-matrix least-squares analysis on F to R = 0.074, R9 = 0.073, w = 1/s2(Fo). A disordered toluene solvate was found and located on a centre of inversion. Therefore, the methyl group [C(28)] on the toluene molecule was assigned an occupancy factor of 0.5. Refinement with this model led to reasonable thermal parameters for this molecule. CCDC reference number 186/997.1940 J. Chem.Soc., Dalton Trans., 1998, Pages 1939–1940 the presence of excess dbu. The reaction was reversible as 2 converted to 1 quantitatively with addition of CF3CO2H, see Scheme 1. Cluster 1 also reacted with CO at room temperature to give an unstable compound with a molecular formula of [Os6(CO)16H(C9H8N3)] 3. However, attempts to obtain single crystals for X-ray analysis have met with little success. Cluster 3 was unstable in solution and reverted back to 2 even when being kept in the CO atmosphere.The coupling reaction of 7-azaindole with the co-ordinated cyanides is also applicable for ethyl cyanide. The analogous compound [Os6(CO)14(m-CO)(m-H)(C10H10N3)] 4 was isolated as the major product (30%) and characterized by solution spectroscopic methods § and is believed to have a similar structure to 1. However, extension of this work to phenyl cyanide is hampered by the poor stability of the precursor complex [Os6(CO)16(NCPh)2]. Interaction of co-ordinated cyanide ligands with other organic ligands on the co-ordination sphere of the cluster core is rather rare.Previously it was believed that the cyanide ligands, in particular MeCN, were good leaving groups and serve as labile substituents for substitution chemistry of transition-metal clusters. Although recent work indicates that the co-ordinated acetonitrile is not necessarily displaceable in the higher nuclearity systems such as [Os6(CO)15H- (MeCN)(C5H5N)(C5H4N)],9 [Os6(CO)20(m4-S)(MeCN)] 10 and [Os6Pt(CO)17H(m3-NCMe)(C8H12)].11 Acknowledgements We gratefully acknowledge financial support from the Hong Kong Research Grants Council and the University of Hong Kong.K. S.-Y. L. acknowledges the receipt of a postgraduate Fig. 1 Molecular structure of [Os6(CO)14(m-CO)(m-H)(C9H8N3)] 1 showing the atomic numbering scheme. Selected bond lengths (Å) and angles (8): Os(1)]Os(2) 2.764(2), Os(1)]Os(3) 2.732(2), Os(1)]Os(5) 2.877(2), Os(2)]Os(3) 2.717(1), Os(2)]Os(5) 2.889(2), Os(3)]Os(5) 2.793(2), Os(2)]Os(4) 2.824(2), Os(3)]Os(4) 2.827(2), Os(4)]Os(5) 2.903(1), Os(3)]Os(6) 2.598(2), Os(4)]Os(6) 2.927(2), Os(5)]Os(6) 2.820(1), Os(5)]C(16) 2.11(3), Os(6)]N(1) 2.08(2), Os(6)]N(3) 2.11(2), N(3)]C(23) 1.32(3), N(2)]C(23) 1.35(3), N(2)]C(20) 1.39(4), N(1)] C(20) 1.36(3); Os(6)]N(3)]C(23) 129(1), N(3)]C(23)]N(2) 124(2), C(23)]N(2)]C(20) 124(2), N(2)]C(20)]N(1) 127(2), C(20)]N(1)]Os(6) 124(1), N(1)]Os(6)]N(3) 85.4(8) studentship and a scholarship, administered by the University of Hong Kong and the Epson Foundation respectively.References 1 D. F. Shriver, H. D. Kaesz and R. D. Adams, The Chemistry of Metal Cluster Complexes, VCH, New York, 1992. 2 K. K.-H. Lee and W.-T. Wong, J. Chem. Soc., Dalton Trans., 1997, 2987. 3 B. F. G. Johnson, R. A. Kamarudin, F. J. Lahoz, J. Lewis and P. R. Raithby, J. Chem. Soc., Dalton Trans., 1988, 1205. 4 M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, G. Polidori, R. Spagna and D. Viterbo, J. Appl. Crystallogr., 1989, 22, 389. 5 C. R. Eady, B. F. G. Johnson and J. Lewis, J. Chem. Soc., Dalton Trans., 1975, 2606; A. J. Blake, B. F. G. Johnson and J. G. M. Nairn, Acta Crystallogr., Sect. C, 1994, 50, 1052. 6 F.-S. Kong and W.-T. Wong, J. Chem. Soc., Dalton Trans., 1997, 1237. 7 A. G. Orpen, J. Chem. Soc., Dalton Trans., 1980, 2509. 8 A. P. Humphries and H. D. Kaesz, Prog. Inorg. Chem., 1979, 2, 145. 9 K. S.-Y. Leung and W.-T. Wong, J. Chem. Soc., Dalton Trans., 1997, 4357. 10 S.-M. Lee, K.-K. Cheung and W.-T. Wong, J. Organomet. Chem., 1995, 503, C19. 11 C. Couture and D. H. Farrar, J. Chem. Soc., Dalton Trans., 1987, 2245. Received 20th February 1998; Communication 8/02325E Scheme 1 Os Os Os Os CO H Os N N N Os 4 3 2 1 2 Os Os Os Os CO H Os N N N Os 4 3 2 1 1 H – CF3CO2H dbu +CO –CO [Os6(CO)16H(C9H8N3)] 3