DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 515–516 515 Saturated and unsaturated triruthenium clusters containing three sterically demanding phosphine ligands: synthesis and structure of [Ru3(CO)9(PCy3)3] and [Ru3H2(CO)6(PCy3)3] Georg Süss-Fink,* Isabelle Godefroy, Vincent Ferrand, Antonia Neels and Helen Stoeckli-Evans Institut de Chimie, Université de Neuchâtel, Avenue de Bellevaux 51, CH-2000 Neuchâtel, Switzerland The reaction of Na[Ru3H(CO)11] with an excess of tricyclohexylphosphine in methanol afforded, depending on the reaction conditions, the tri-substituted clusters [Ru3(CO)9- (PCy3)3] (48e) and [Ru3H2(CO)6(PCy3)3] (44e), inaccessible hitherto.Ligand substitution reactions of dodecacarbonyltriruthenium with tertiary phosphines have been studied in great detail.1 The thermal reaction of Ru3(CO)12 with PR3 (R = Ph, Et, Bun, OPh) in general leads to the mono-, di- and tri-substituted derivatives [Ru3(CO)11(PR3)], [Ru3(CO)10(PR3)2] and [Ru3(CO)9(PR3)3].2 For the directed synthesis of these substitution products, the trimethylamine oxide-induced carbonyl substitution,3 the radical ion-initiated ligand substitution,4 and the bis(triphenylphosphine) iminium salt-catalysed carbonyl substitution 5 have been developed.However, with sterically demanding phosphine ligands, the synthesis of the tri-substituted derivatives failed. Even a six-fold excess of tricyclohexylphosphine with [Ru3(CO)12] in the presence of Na[Ph2CO] gave only the mono- and the di-substituted complexes, but no [Ru3(CO)9(PCy3)3].4b On the other hand, bulky phosphines containing cyclohexyl or tert-butyl substituents are known to allow unusual structures and unsaturated configurations for steric reasons.6 Thus the electron-deficient triruthenium cluster [Ru3H2(CO)5(PBut 2)2- (Ph2PCH2PPh2)] with an electron count of 46 was synthesized by Böttcher et al. in 1996.6b Apart from this complex and its adamantyl derivative,6b the only electron-deficient Ru3 clusters reported so far are [Ru3H(CO)9(NSOMePh)],7 and (very recently) [Ru3H2(CO)10] as well as its phosphine derivative [Ru3H2(CO)9(PPh3)];8 all of which have an electron count of 46.Interestingly, no unsaturated triruthenium cluster is mentioned in Deeming’s review of 1995.1 In this paper we describe the synthesis and structure of the tris(tricyclohexylphosphine)-substituted derivative [Ru3(CO)9- (PCy3)3] 1 and the highly electron-deficient (44e) triruthenium cluster [Ru3H2(CO)6(PCy3)3] 2, both accessible from Na[Ru3H- (CO)11] and PCy3.The reaction of Na[Ru3H(CO)11], easily accessible from [Ru3(CO)12] and Na[BH4],9 with tricyclohexylphosphine (1 : 5) in methanol leads, upon heating for 1 h at 80 8C in a closed reactor (pressure Schlenk tube), to the tri-substituted derivative [Ru3(CO)9(PCy3)3] 1, which precipitates from the reaction solution as a purple microcrystalline solid in 55% yield. Cluster 1 can be recrystallised from dichloromethane–methanol to give Ru Ru Ru OC PCy3 OC CO PCy3 OC C O C O OC OC Cy3P C O Ru H OC OC Ru Ru H Cy3P OC PCy3 CO CO PCy3 CO 1 2 dark red, air-stable, cube-like crystals which contain two water molecules of crystallisation (source: methanol).† The single crystal X-ray structure analysis ‡ of 1 (Fig. 1) reveals a triruthenium framework with the three phosphine ligands occupying equatorial positions at the three ruthenium atoms. The molecule has a perfect C3 symmetry.The nine carbonyl ligands are all terminal, six occupying the two axial positions of the Ru atoms, while the other three are alternating with the phosphine ligands in one of the two equatorial positions of each ruthenium atom. The Ru]CO(eq) distances of 1.876(7) Å are distinctly shorter than the Ru]CO(ax) distances [1.924(7) and 1.931(7) Å]. This is in keeping with the findings in the known cluster [Ru3(CO)9(PMe3)3],10 the Ru]P distances, however, are considerably longer in 1 [2.414(2) Å] than in the methyl derivative [2.330 Å (average)],10 reflecting the bulkiness of the cyclohexyl substituents.The Ru]Ru bonds in 1 [2.9396(8) Å] are also elongated with respect to those in [Ru3(CO)9(PMe3)3] [2.860(1), 2.862(1), 2.854(1) Å] 10 and in [Ru3(CO)12] [2.852(1), 2.851(1), Fig. 1 Molecular structure of [Ru3(CO)9(PCy3)3] 1 showing the atom numbering scheme; H atoms have been omitted for clarity. Selected bond lengths (Å) and angles (8): Ru(1)]Ru(2) 2.9396(8), Ru(1)]Ru(3) 2.9396(8), Ru(2)]Ru(3) 2.9396(8), Ru(1)]P(1) 2.414(2), Ru(1)]C(2) 1.876(7), Ru(1)]C(1) 1.924(7), Ru(1)]C(3) 1.931(7); Ru(3)]Ru(1)]P(1) 111.21(5), P(1)]Ru(1)]C(2) 98.3(2), P(1)]Ru(1)]C(1) 92.1(2), P(1)] Ru(1)]C(3) 90.3(2), Ru(1)]Ru(2)]Ru(3) 60.0, C(4)]P(1)]C(10) 101.4(3), C(10)]P(1)]C(16) 102.5(3) † Spectroscopic data for cluster 1.IR(CH2Cl2): n(CO) 1959vs, 1949vs cm21; 1H NMR (CDCl3): d 1.29–2.04 (m, C6H11); 31P NMR (CDCl3): d 47.3 (s, PCy3); FAB-MS: m/z 1397 (1395 related to 101Ru) (Found: C, 52.64; H, 7.0.Calc. for C63H99O9P3Ru3?2H2O: C, 52.82; H, 7.25%). ‡ Crystal data for cluster 1. C63H99O9P3Ru3?2H2O, M 1474.52, cubic space group Pa3� , a = 24.1347(12) Å, U = 14 058.1(12) Å3, T = 223(2) K, Z = 8, m(Mo-Ka) = 0.802 mm21. 4156 Reflections collected. Disordered molecules of dichloromethane and water were found in the crystal structure. Refinement converged at R1 = 0.0577 and wR2 = 0.1346 for 3224 data with I > 2s(I), and R1 = 0.0837 and wR2 = 0.1536 for all 4156 unique data.516 J. Chem.Soc., Dalton Trans., 1998, Pages 515–516 2.860(1) Å].11 The molecule 1 has almost D3h symmetry, the three phosphorus atoms being almost in the plane of the three ruthenium atoms (maximum distance between P and the Ru3 plane 0.20 Å) and the torsion angles C(axial)]Ru]Ru]C(axial) being less than 108. If Na[Ru3H(CO)11] is reacted with PCy3 (1 : 5) in methanol in an open reactor for 1 h under reflux (80 8C bath temperature), the reaction yields (instead of 1) the dihydro cluster [Ru3H2- (CO)6(PCy3)3] 2.The product precipitates directly from the reaction solution as a purple powder (60% yield). It can be recrystallised from dichloromethane–methanol to give dark red, block-shaped crystals which, in contrast to 1, are airsensitive. The 1H NMR spectrum of 2 shows two signals in the region of m3-hydrides, both showing a homo-spin coupling with the other hydride ligand and two hetero-spin couplings with the two types of phosphorus atoms (two trans and one cis, or one trans and two cis).§ The single-crystal X-ray structure analysis ¶ of 2 (Fig. 2) shows Fig. 2 Molecular structure of [Ru3H2(CO)6(PCy3)3] 2 showing the atom numbering scheme; H atoms on carbon have been omitted for clarity. Selected bond lengths (Å): Ru(1)]Ru(2) 2.6702(6), Ru(1)]Ru(3) 2.7180(7), Ru(2)]Ru(3) 2.6931(7), Ru(1)]P(1) 2.332(2), Ru(2)]P(3) 2.336(2), Ru(3)]P(2) 2.344(2), Ru(1)]H(1) 1.94, Ru(1)]H(2) 1.61, Ru(2)]H(1) 2.04, Ru(2)]H(2) 1.94, Ru(3)]H(1) 1.93, Ru(3)]H(2) 1.85, Ru(1)]C(4) 1.834(7), Ru(2)]C(6) 1.834(7), Ru(3)]C(5) 1.825(8), Ru(1)]C(1) 2.134(7), Ru(1)]C(3) 2.154(6), Ru(2)]C(3) 2.129(6), Ru(2)]C(2) 2.107(7), Ru(3)]C(2) 2.147(5), Ru(3)]C(1) 2.161(6) § Spectroscopic data for cluster 2.IR(CH2Cl2): n(CO) 2027vw, 1949m, 1917vs, 1871w, 1855w, 1819vs, 1757w cm21; 1H NMR (CDCl3): d 1.27– 2.30 (99 H, m, C6H11), 219.46 [1 H, dtd, J (H2]P3) = 28.3, J(H2]P1,P2) = 5.3, J(H1]H2) = 2.2, m3-H2], 221.02 [1 H, tdd, J(H1]P1,P2) = 26.4, J(H1]P3) = 5.4, J(H1]H2) = 2.1 Hz, m3-H1]; 31P-{1H} NMR (CDCl3): d 74.8 (s, 1 P), 71.3 (s, 2 P), no coupling observed; FABMS: m/z 1313 (based on 101Ru) (Found: C, 53.63; H, 7.45. Calc.for C60H101O6P3Ru3?2H2O: C, 53.36; H, 7.84%). ¶ Crystal data for cluster 2. C60H101O6P3Ru3?2H2O, M 1314.53, monoclinic, space group P21/n, a = 10.561(1), b = 36.649(2), c = 15.957(1) Å, b = 96.32(1)8, U = 6138.4(8) Å3, T = 223(2) K, Z = 4, m(Mo-Ka) = 0.854 mm21. 38 984 Reflections were collected. The cyclohexyl ring C(31)]C(36) was found to be disordered. Two positions for atoms C(33) and C(36) (the head and the foot of the chair conformation) were refined with occupancy 0.5 each. Refinement converged at R1 0.049 and wR2 = 0.090 for 6231 data with I > 2s(I ), and R1 = 0.104 and wR2 = 0.103 for all 11 651 unique data. CCDC reference number 186/ 846. See http://www.rsc.org/suppdata/dt/1998/515/ for crystallographic files in .cif format.a Ru3 skeleton bearing two m3-hydrido caps, one on either side of the triangle. The three Ru]Ru bonds are bridged by three m2-carbonyl ligands, being almost in the plane of the metal triangle. The three terminal carbonyl ligands as well as the three phosphine ligands are co-ordinated to the three Ru atoms, above and below the metal plane. Complex 2 is, to our knowledge, the only Ru3 cluster known presenting an electron count of 44.Trinuclear clusters with 44e have been reporting so far only for d8 metals: [Pd3(SO2)2(ButNC)5],12 [Pt3(CO)3(PCy3)3] 13 and [FePt2(CO)5{P(OPh)3}3].14 In accordance with this high electron deficiency, the Ru]Ru bonds in 2 are found to be rather short [2.6702(6), 2.6931(7) and 2.7180(7) Å] with respect to the typical Ru]Ru single bonds [2.9396(8) Å] in 1. In addition, the Ru]P bonds in 2 [2.332(2), 2.336(2) and 2.344(2) Å] are also shorter than in 1 [2.414(2) Å]. The two capping hydride ligands are slightly unsymmetrically co-ordinated, H(2) is also closer to the Ru3 triangle than H(1), reflecting the different environments [one PCy3 and two CO ligands surrounding H(2), two PCy3 and one CO ligands surrounding H(1)].Owing to the high degree of unsaturation (4e with respect to the EAN rule) cluster 2 is expected to be a highly reactive species. A study on the reactivity of 2 towards CO and other simple molecules is in progress. References 1 A. J. Deeming, in Comprehensive Organometallic Chemistry II, eds.E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol. 7, ch. 12. 2 M. I. Bruce, G. Shaw and F. G. A. Stone, J. Chem. Soc., Dalton Trans., 1972, 2094. 3 B. F. G. Johnson, J. Lewis and D. Pippard, J. Organomet. Chem., 1978, 160, 263; J. Chem. Soc., Dalton Trans., 1981, 407. 4 (a) M. I. Bruce, D. C. Kehoe, J. G. Matisons, B. K. Nicholson, P. H. Riegger and M. L. Williams, J. Chem. Soc., Chem. Commun., 1982, 442; (b) M.I. Bruce, J. G. Matisons and B. K. Nicholson, J. Organomet. Chem., 1983, 247, 321. 5 C. E. Kampe, N. M. Boag, C. B. Knobler and H. D. Kaesz, Inorg. Chem., 1984, 23, 1390; G. Lavigne and H. D. Kaesz, J. Am. Chem. Soc., 1984, 106, 4647. 6 (a) H. C. Böttcher, G. Rheinwald, H. Stoeckli-Evans and G. Süss- Fink, J. Organomet. Chem., 1994, 469, 163; (b) H. C. Böttcher, H. Thönnessen, P. G. Jones and R. Schmutzler, J. Organomet. Chem., 1996, 520, 15. 7 G. Süss-Fink, G. Rheinwald and H. Stoeckli-Evans, Inorg. Chem., 1996, 35, 3081. 8 N. E. Leadbeater, J. Lewis and P. R. Raithby, J. Organomet. Chem., 1997, 543, 251. 9 B. F. G. Johnson, J. Lewis, P. R. Raithby and G. Süss-Fink, J. Chem. Soc., Dalton Trans., 1979, 1356; G. Süss-Fink, Inorg. Synth., 1986, 24, 168. 10 M. I. Bruce, M. J. Liddell, O. bin Shawkataly, C. A. Hughes, B. W. Skelton and A. H. White, J. Organomet. Chem., 1988, 347, 207. 11 M. R. Churchill, F. J. Hollander and J. P. Hutchinson, Inorg. Chem., 1977, 16, 2655. 12 R. J. Haines, N. D. C. T. Steen and R. B. English, J. Organomet. Chem., 1981, 209, C34; J. Chem. Soc., Dalton Trans., 1984, 515. 13 S. Otsuka, Y. Tatsuno, M. Miki, T. Aoki, M. Matsumoto, H. Yoshioka and K. Nakatsu, J. Chem. Soc., Chem. Commun., 1973, 445. 14 A. Albinati, G. Cartuan and A. Musco, Inorg. Chim. Acta, 1977, 22, L31. Received 7th November 1997; Communication 7/08037I