DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 667–675 667 Complexes of new chiral terpyridyl ligands. Synthesis and characterization of their ruthenium(II) and rhodium(III) complexes Marco Ziegler,a Véronique Monney,a Helen Stoeckli-Evans,b Alex Von Zelewsky,*a Isabelle Sasaki,c Gilles Dupic,c Jean-Claude Daran c and Gilbert G. A. Balavoine *c a Institut de Chimie Inorganique et Analytique, Université de Fribourg, Pérolles, CH-1700 Fribourg, Switzerland b Institut de Chimie, Université de Neuchâtel, Av.Bellevaux 51, CH-2000 Neuchâtel, Switzerland c Laboratoire de Chimie de Coordination, CNRS, 205 route de Narbonne, F-31077 Toulouse, France Received 6th January 1999, Accepted 12th January 1999 Enantiomerically pure, chiral terpyridyl-type ligands L1 (‘dipineno’-[5,6:50,60]-fused 2,29:69,20-terpyridine) and L2 (‘dipineno’-[4,5:40,50]-fused 2,29:69,20-terpyridine) have been synthesized in high yields starting from 2,6- diacetylpyridine and enantiopure a-pinene.Complexes of L1 and L2 with RhIII and RuII have been prepared and studied spectroscopically. The complexes [Ru(L)2][PF6]2 (L = L1 or L2) were obtained in high yields using microwave heating in ethylene glycol as solvent. The rhodium(III) and ruthenium(II) complexes of L1 and L2 have a helically distorted terpyridyl moiety, as shown by the considerable optical activity in the ligand centered and metal to ligand charge transfer transitions. Crystal structures of [Rh(L1)Cl3] and [Ru(L1)Cl3] show a considerable out of plane distortion of the terpyridyl moiety, whereas free L2 and [Ru(trpy)(L2)][PF6]2 have a more planar arrangement of the pyridyl units. Introduction Substituted 2,29:69,20-terpyridines are promising building blocks for supramolecular systems 1 and there is great interest in their co-ordination with transition metals,2–7 mainly due to their interesting photophysical properties 8,9 and potential pharmaceutical applications.10,11 We report here the synthesis and characterization of “chiralized” ‘pineno’-fused terpyridyl ligands L1(1) and L1(2) (L1 = ‘dipineno’-[5,6:50,60]-fused 2,29:69,20-terpyridine) and L2(1) and L2(2) (L2 = ‘dipineno’- [4,5:40,50]-fused 2,29:69,20-terpyridine) and their ruthenium(II) complexes, which have predetermined helical twist.† Predetermination of the chirality of metal complexes using chiral ligands is of current interest and has been achieved in our group for bis- and tris-diimine complexes,13–15 and extended to quaterpyridines 16 using our concept.With C2-symmetrical, chiral terpyridyl ligands like L1 or L2 three diVerent stereoisomers are possible in an octahedral mer arrangement: an enantiomeric pair with D2 symmetry and an achiral, S4-symmetrical diastereomer (Scheme 1). In the D2- symmetrical, octahedral complexes a helical twist is induced by the non-planarity of the ligand. The S4-symmetrical complex is an example of a “narcissistic coupling” 17a between two enantiomers giving a meso achiral complex.From a purely geometrical point of view it is also possible to divide such an achiral S4-symmetrical complex by the “coupe du roi” 17b,c into two homochiral halves, cutting through the metal and the central pyridyl moiety of each ligand, which is, however, impossible in a real molecule. † The designation L1(1) refers to the enantiomer obtained from (1)- a-pinene, L1(2) from (2)-a-pinene, L2(1) from (1)-myrtenal and L2(2) from (2)-myrtenal.The locants 5,6 : 50,60 refer to the numbering of the 2,29:69,20-terpyridyl moiety and indicate the fusion sites with the ‘pinene’ moiety. This numbering scheme was introduced for related ligands.12 L1=2,6-Bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin- 2-yl)pyridine, L2 = 2,6-bis(7,7-dimethyl-5,6,7,8-tetrahydro- 6,8-methanoisoquinolin-3-yl)pyridine. Experimental Synthetic methods The enantiomerically pure ligands L1 and L2 have been obtained in an analogous preparation to the “CHIRAGEN” ligand system 15 according to Scheme 2.Complexes were synthesized according to Scheme 3; [Ru(trpy)Cl3] was prepared following literature methods.18,19 Preparations (1S)-(2)-Pinocarvone (6,6-dimethyl-2-methylenebicyclo- [3.1.1]heptan-3-one) I. Following the literature procedure,20 compound I was obtained in 85–100% yields from (1R)-(1)-apinene [enantiomeric excess, e.e.: 98%. a (589 nm, 21 8C) = 50.78] as starting material.(1R)-(1)-Pinocarvone II was obtained Scheme 1 Possible arrangements of octahedral complexes with chiral terpyridyl type ligands.668 J. Chem. Soc., Dalton Trans., 1999, 667–675 from (1S)-(2)-a-pinene [e.e.: 98%. a (589 nm, 21 8C) = 250.18] using the same procedure. (1S)-(1)-Myrtenal (6,6-dimethylbicyclo[3.1.1]hept-2-ene-2- carbaldehyde) III. This was obtained in 32% yield from (1R)- (1)-a-pinene after silica gel chromatography using ethyl acetate–hexane (10 : 90) as the eluent following a literature procedure.21 The pure product was characterized by 1H NMR.(1R)-(2)-Myrtenal is commercially available. 2,6-Bis(pyridinioacetyl)pyridine diiodide IV. To a solution of 3.27 g (20 mmol) of 2,6-diacetylpyridine (Fluka purum) in 15 mL of dry pyridine was added a solution of 10.45 g (41 mmol) of sublimated iodine in 15 mL of dry pyridine. The mixture was heated at 100 8C for 3 h and after cooling, the precipitate is filtered oV, rinsed once with pyridine and dried.Recrystallization from 95% ethanol yielded 9.71 g of a beige powder (91%). 1H NMR (DMSO-d6): d 9.12 [d, 4 H, H(10), 3J(H10H11) = 5.7]; 8.79 [dd, 2 H, H(12), 3J(H12H11) = 7.8]; 8.44 [s, 3 H, H(4), H(5)]; 8.34 [dd, 4 H, H(11), 3J(H11H12) = 7.8, 3J(H11H10) = 5.7 Hz] and 6.71 [s, 4 H, H(8)]. MS(EI): m/z 446 (M1 2 I2 ); 318 (M1 2 2I2 2 H1) and 240 (M1 2 2I2 2 py) (Found: C, 38.08; H, 2.88; N, 6.92. Calc. for C19H17I2N3O2 1 H2O: C, 38.60; H, 3.2; N, 7.10%) Crystal data: C19H17I2N3O2], M = 826.96, orthorhombic, space group Pbca, a = 11.253(4), b = 16.741(4), c = 25.941(7) Å, U = 4887(3) Å3, Z = 8, Dc = 2.249 g cm23, T = 293(2) K, 4687 reflections measured, 3387 unique (Rint = 0.0332) of which all were used in all calculations; final wR(F ) 0.0402, goodness of fit 1.020. L1(2).Compound II (9.0 g, 0.060 mol) 2, 17.2 g (0.030 mol) of IV, and 9.24 g ammonium acetate (0.120 mol, Merck p.a.) were dissolved in 100 mL glacial acetic acid, refluxed overnight, Scheme 2 (i) 1O2, Acetic anhydride, DMAP, [(4-dimethylamino)- pyridine] CH2Cl2, TPP, (5,10,15,20-tetra phenyl porphyrin) 20 8C, 8 h;20 (ii) SeO2, t-BuOOH, CH2Cl2, 35 8C, 48 h;21 (iii) I2/py; (iv) ammonium acetate, acetic acid, 125 8C, 12 h; (v) ammonium acetate, acetic acid, formamide, 100 8C, 12 h.Scheme 3 (i) EtOH–water, 2–12 h, 80 8C; (ii) CH2OHCH2OH, 4 min, microwave heating, 375 W. and 100 mL water added to the ice cold solution. The solution was extracted four times with 150 mL diethyl ether.The extracts were combined and washed first with 70 mL water, then four times with saturated NaHCO3 solution and finally with saturated NaCl. After drying over MgSO4 and filtration over active carbon the product slowly crystallized by evaporation of the solvent (8.84 g, 70%). The compound L1(1) was prepared similarly in 62% yield. 1H NMR (CDCl3): d 8.37 [d, 2 H, H(12), 3J(H12H11) = 7.9]; 8.28 [d, 2 H, H(3), H(5), 3J(H3H4) = 7.7]; 7.88 [dd, 1 H, H(4), 3J(H4H3) = 7.8]; 7.34 [d, 2 H, H(11), 3J(H11H12) = 7.8]; 3.20 [d, 4 H, H(13a/13b), 3J(H13H14) = 2.6]; 2.81 [dd, 2 H, H(16), 3J(H16H15b) = 5.6, 4J16,14 = 5.6]; 2.70 [dd, 2 H, H(15b), 3J(H15bH14) = 5.6, 3J(H15bH16) = 5.6, 2J15b,15a = 9.6]; 2.40 [m sept, 2 H, H(14)]; 1.41 [s, 6 H, H(19)]; 1.31 [d, 2 H, H(15a), 2J15a,15b = 9.6]; and 0.68 [s, 6 H, H(18)]. 13C-{1H} NMR (CDCl3): d 156.3, 153.8, 142.2, 137.6, 133.7, 120.1, 177.9, 46.6, 40.3, 39.6, 36.7, 32.0, 26.1 and 21.3 (Found: C, 81.97; H, 7.59; N, 9.73.Calc. for C29H31N3: C, 82.62; H, 7.41; N, 9.97%). MS(EI): m/z 421 (100, M1); 406 (38, M1 2 CH3); 380 (46, M1 2 H2C = C1–CH3); 334 (26); 167 (61); 128 (20); 77 (22); and 43 (73%). a (330 nm) = 280 8C, a (370) = 265 8C [20 8C, c = 8 × 1025 M (1.68 mg in 50 mL acetonitrile)]. L2(1). To a solution of 2.89 g (5.03 mmol) of compound IV in formamide were added 1.66 g (21.5 mmol) of ammonium acetate and 1.52 g (10.1 mmol) of III. Heating at 80 8C was maintained overnight.The precipitate was filtered oV, rinsed with water and dried. It could be used without purification for the synthesis of the complexes or recrystallized from ethyl acetate (yield = 36%). Compound L2(2) was prepared similarly from (1R)-(2)-myrtenal in 64% yield. 1H NMR (CDCl3): d 8.37 (s, 2 H), 8.34 (d, 2 H, 3J = 7.8), 8.21 (s, 2 H), 7.90 (t, 1 H, 3J = 7.7), 3.11 (d, 4 H, 3J = 2.7), 2.88 (dd, 1 H, 3J = 5.5, 4J = 5.5), 2.68 (ddd, 2 H, 2J = 9.5, 3J = 5.7, 5.4), 2.34 (m sept, 2 H), 1.42 (s, 6 H), 1.25 (d, 2 H, 2J = 9.5 Hz) and 0.67 (s, 6 H). 13C-{1H} NMR (CDCl3): d 155.82, 154.63, 145.49, 145.30, 142.92, 137.70, 120.46, 120.36, 44.51, 40.12, 39.25, 33.03, 31.83, 26.01 and 21.38. IR (KBr): 2923m, 1709 (s), 1554m, 1455m and 1385m (Found: C, 82.72; H, 7.50; N, 9.88. Calc. for C29H31N3: C, 82.62; H, 7.41; N, 9.97%). MS (DCI, NH3): m/z = 422 [M 1 H]1. a (589 nm, 20 8C, 9.6 mg in 2 mL of CHCl3) = 1163.58. [Ru(trpy)2][PF6]2 1. In a 100 mL round flask, 117 mg (0.5 mmol) trpy (Fluka, purum) and 65.5 mg RuCl3?3H2O (0.25 mmol) were suspended in 4 mL ethylene glycol (Fluka, purum) and refluxed for 4 min in a microwave oven (325 W).The salt NH4PF6 (1.0 g) in 25 mL water was added to the orange-brown solution, the precipitate collected in a Buchner funnel, washed with water and a little diethyl ether and recrystallized from acetonitrile–diethyl ether. Yield: 190.5 mg (89%). 1H NMR (CD3CN): d 8.73 [d, 4 H, H(3), 3J(H3H4) = 8.1]; 8.47 [d, 4 H, H(12), 3J(H12H11) = 8.5]; 8.39 [dd, 2 H, H(4), 3J(H4H3) = 8.0]; 7.90 [td, 4 H, H(11), 3J(H11H12) = 7.8, 4J(H11H9) = 1.5]; 7.32 [d, 4 H, H(9), 3J(H9H10) = 5.2]; 7.14 [ddd, 4 H, H(10), 3J(H10H11) = 7.8, 3J(H10H9) = 5.6, 4J(H10H12) = 1.4 Hz].MS(EI): m/z 713 (15, M1 2 PF6); 567 (22, M1 2 2 PF6); 334 (20); 234 (100); and 154 (100%). DC: silica gel; DMF: 8; H2O: 5 EtOH: 3; NaCl: 0.3 M; NH4Cl: 0.2 M; Rf = 0.58.J. Chem. Soc., Dalton Trans., 1999, 667–675 669 [Ru(L1)(2)Cl3 2.The compound L1(2) (84.3 mg, 0.2 mmol) and 48.6 mg RuCl3?3H2O (0.2 mmol) were suspended in 10 mL 1-butanol (Fluka, puriss.) and kept under constant reflux for 12 h. The greenish powder was filtered oV and washed with a little diethyl ether. Drying to constant weight yielded 115 mg of a green-brownish powder (92%). The substance was paramagnetic and contained some [Ru(L1(2))2]Cl2. Recrystallization from acetone yielded small, needle like crystals of 2. Diluted solutions of it in a number of polar solvents (EtOH, DMF, DMSO) all contained dissociated RuIII and free L1(2) as seen from the precipitation of the latter after slow evaporation and from spectroscopic data.MS(EI): m/z 593 (32, M1 2 Cl); 557 (28, M1 2 2 Cl); and 518 (100, M1 2 3 Cl). [Rh(L1(2))Cl3 3. In a 100 mL round flask, 1.60 g (3.80 mmol) L1(2) and 1.00 g RhCl3?3H20 were refluxed for 4 h in 30 mL ethanol. The orange-red precipitate was filtered oV, washed with a little ethanol and recrystallized from dichloromethane– diethyl ether (153 mg, 94%). The complex [Rh(L1(1))Cl3] 4 was obtained similarly from L1(1) in 87% yield. 1H NMR (CDCl3): d 8.03 [s, 3 H, H(3), H(4), (H5)]; 7.83 [d, 2 H, H(12), 3J(H12H11) = 7.8]; 7.44 [d, 2 H, H(11), 3J(H11H12) = 7.8]; 4.46 [m large, 4 H, H(13)]; 2.82 [dd, 2 H, H(16), 3J(H16H15b) = 5.7, 4J(H16H14) = 5.7]; 2.61 [dd, 2 H, H(15b), 3J(H15bH14) = 5.7, 3J(H15bH16) = 5.7, 2J(H15bH15a) = 9.9]); 2.47 [m sept, 2 H, H(14)]; 1.38 [s, 6 H, H(19)]; 1.28 [d, 2 H, H(15a), 2J(H15aH15b) = 9.9 Hz]; and 0.68 [s, 6 H, H(18)].MS(FAB): m/z 594 (100); 595 (34); 596 (69); 597 (22); 598 (14); 599(4) (M1 2 Cl); 559 (100); 560 (34); 561 (37); 562 (11); and 563 (1%) (M1 2 2 Cl). UV-VIS (CH2Cl2, c = 2.00 × 1025 M): l/nm (e/M21 cm21) 242 (42570); 276 (sh, 17000); 312 (21900); 354 (18000) and 376 (sh, 7600). a [404.6 nm, 20 8C, c = 2.00 × 1025 M (0.630 mg in 50 mL dichloromethane] = 112508. [Ru(trpy)(L1(2)][PF6]2 5.The complex [Ru(trpy)Cl3] (147 mg, 0.33 mmol) and 140 mg (0.33 mmol) L1(2) were refluxed in 15 mL ethylene glycol under vigorous stirring for 1 h. The solvent was distilled oV and the black residue dissolved in 100 mL water. After removal of unreacted complex by filtration the product was precipitated upon addition of 0.78 g NH4PF6 and filtered oV. Washing twice with 10 mL CH2Cl2 and once with 10 mL and drying to constant weight yielded 235 mg of an orange powder (67%).Recrystallization from a variety of solvents yielded needle like intense red crystals of 5 that were, however, unsuitable for X-ray measurements. 1H NMR (CD3CN): d 8.71 [d, 2 H, H(3), 3J(H3H4) = 8.2]; 8.63 [d, 2 H, H(39), 3J(H39H49) = 8.2]; 8.48 [ddd, 2 H, H(129), 3J(H129H119) = 8.1, 4J(H129H109) = 0.8, 5J129,99 = 0.6]; 8.39 [t, 1 H, H(49), 3J(H49H39) = 7.9]; 8.34 [t, 1 H, H(4), 3J(H4H3) = 7.9]; 8.24 [d, 2 H, H(12), 3J(H12H11) = 8.0]; 7.93 [td, 2 H, H(119), 3J(H119H109) = 7.9, 4J(H119H99) = 1.5]; 7.58 [d, 2 H, H(99), 3J(H99H109) = 5.8]; 7.43 [d, 2 H, H(11), 3J(H11H12) = 8.0]; 7.27 [ddd, 4 H, H(109), 3J(H109H119) = 7.9, 3J(H109H99) = 5.7, 4J(H109H129) = 1.4]; 2.63 [t, 2 H, H(16), 3J(H16H15b) = 5.7, 4J(H16H14) = 5.7]; 2.31 [ddd, 2 H, H(15b), 2J(H15bH15a) = 9.6, 3J(H15bH14) = 5.3, 3J(H15bH16) = 5.4]; 1.79 [dd, 2 H, H(13b), 2J(H13bH13a) = 16.7, 4J(H13bH14) = 2.9]; 1.71 [m, 2 H, H(14)]; 1.67 [dd, 2 H, H(13a), 2J(H13aH13b) = 16.4, 4J(H13bH14) = 3.0]; 1.13 [s, 6 H, H(19)]; [0.70 (d, 2 H, H(15a), 2J(H15aH15b) = 9.9 Hz]; and 20.14 [s, 6 H, H(18)]. NOE (300 MHz, acetonitrile): d 2.63 (1.9 {1.13}); 2.31 (0.6 {1.71}, 2.61 {1.13}); 1.71 (1.6 {1.13}); 1.13 (0.8 {1.71}); 0.70 (1.0 {1.71}; 20.14 (2.7 {1.13}, 2.0% {1.71}).MS(EI): m/z 902 (20, M1 2 PF6); 756 (38, M1 2 2 PF6); 422 (80); 334 (32); 154 (100); and 136 (91%). a (404.6 nm) = 5208, a (365 nm) = 110008 [20 8C, c = 1.017 × 1024 M (5.32 mg in 50 mL acetonitrile)]. DC: silica gel; DMF: 8; H2O: 5 EtOH: 3; NaCl: 0.3; NH4Cl: 0.2; Rf = 0.72.[Ru(L1(2))2][(PF6]2 6. In a 50 mL round flask, 32.8 mg (0.125 mmol) RuCl3?3H2O and 105.4 mg (0.25 mmol) L1(2) were suspended in 3 mL ethylene glycol (Fluka, purum) and refluxed for 4 min in a microwave oven (325 W). The salt NH4PF6 (0.5 g) in 20 mL water was added to the deep red, brownish solution, the precipitate collected in a Buchner funnel, washed with water and a little diethyl ether and recrystallized from acetonitrile–diethyl ether (153 mg, 99%).In another attempt under the same reaction conditions, 53.4 mg (95%) of [Ru((L1(1))2][BPh4]2 were obtained after recrystallization from acetone–pentane starting with 29.9 mg L1(1) and precipitation with NaBPh4. 1H NMR (CD3CN): d 8.61 [d, 2 H, H(3), H(5), 3J(H3H4) = 7.7]; 8.32 [dd, 1 H, H(4), 3J(H4H3) = 7.8]; 8.25 [d, 2 H, H(12), 3J(H12H11) = 7.9]; 7.46 [d, 2 H, H(11), 3J(H11H12) = 7.8]; 2.69 [dd, 2 H, H(16), 3J(H16H15b) = 5.2, 4J(H16H14) = 5.2]; 2.34 [ddd, 2 H, H(15b), 3J(H15bH14) = 5.6, 3J(H15bH16) = 5.6, 2J(H15bH15a) = 9.6]; 2.01 [d, 4 H, H(13a/13b), 3J(H13H14) = 2.1]; 1.78 [m sept, 2 H, H(14)]; 1.16 [s, 6 H, H(19)]; 0.84 [d, 2 H, H(15a), 2J(H15aH15b) = 9.8 Hz];and 20.14 [s, 6 H, H(18)].NOE (300 MHz, acetonitrile): d 8.61 (25.4 {8.25}, 1.2 {2.01}); 8.25 (0.7 {2.01}); 7.46 (9.4 {8.25}, 12.2 {2.69}, 0.5 {2.01}); 2.34 (1.0 {2.69}); 1.16 (3.6 {2.69}); 0.84 (1.0 {2.69}, 1.6 {2.01}); and 20.14 (0.8 {2.69}, 3.5% {2.01}).MS(EI): m/z 1090 (42, M1 2 PF6); 944 (79, M1 2 2 PF6); 518 (42); 472 (50); 154 (100); 136 (>100%). a (404.6 nm) = 114308, a (365 nm) = 125808 [20 8C, c = 7.29 × 1025 M (4.50 mg in 50 mL acetonitrile)]. DC: silica gel; DMF: 8; H2O: 5 EtOH: 3; NaCl: 0.3; NH4Cl: 0.2; Rf = 0.80. [Ru(trpy)(L2(1))]Cl2 7. The complex [Ru(trpy)Cl3] (74 mg) and 70 mg of L2(1) were refluxed in 20 mL of EtOH–water (1 : 1) for 1 d. The solvent was evaporated and the dark residue dissolved in 2 mL of 95% ethanol.After filtration of insoluble material the filtrate was purified by chromatography on a Sephadex LH20 column. The complex was eluted with 95% EtOH and after evaporation of the solvent the product was recovered as an red-orange powder (yield: 66%). The complex [Ru(trpy)(L2(2))]Cl2 8 has been obtained similarly in 76% yield. 1H NMR (CD3OD): d 8.96 (d, 2 H, 3J = 8.1), 8.88 (d, 2 H, 3J = 8.1), 8.72 (d, 2 H, 3J = 8.1), 8.55 (s, 2 H), 8.46 (t, 2 H, 3J = 8.1), 8.01 (dt, 2 H, 3J = 7.9, 4J = 1.4), 7.49 (dd, 2 H, 3J = 5.4, 4J = 0.6), 7.30 (dt, 2 H, 3J = 6.2, 4J = 1.1), 6.92 (s, 2 H), 3.21 (d, 4 H, 3J = 2.3), 2.62 (m, 2 H), 2.56 (dd, 2 H, 3J = 5.6, 4J = 5.6), 2.28 (m, 2 H), 1.29 (s, 6 H), 0.98 (d, 2 H, 3J = 8.9 Hz) and 0.38 (s, 6 H). 13C-{1H} NMR (CD3OD): d 159.93, 157.80, 157.24, 157.05, 153.32, 149.75, 149.53, 148.31, 139.40, 137.53, 137.14, 129.09, 125.97, 125.55, 125.27, 124.18, 45.82, 41.03, 39.91, 34.19, 31.98, 26.10 and 21.50. FAB (3-nitrobenzyl alcohol): m/z = 791, [M 2 Cl]1; and 756, [M 2 2 Cl]1 (Found: C, 55.46; H, 5.78; N, 8.85.Calc. for C44H42Cl2N6Ru 1 7 H2O: C, 55.46; H, 5.88; N, 8.82%). a (589 nm, 20 8C, 0.146 mg in 2 mL of EtOH) = 12748. [Ru(trpy)(L2(2))][PF6]2 8a was prepared for X-ray analysis. [Ru(L2(1))2]Cl2 9. To 30 mg (0.14 mmol) of RuCl3?3H2O in 20 mL of EtOH–water (1 : 1) were added 130 mg (0.31 mmol) of L2(1) and refluxed for 1 d. After evaporation of the solvent the mixture was purified on Sephadex LH20 as described.The complex [Ru(L1(2))2]Cl2 10 was prepared similarly from L2(2) in 56% yield. Quantitative yields were obtained by microwave heating (4 min, 375 W) in ethylene glycol using the same procedure as for [Ru(L1)2][PF6]2. 1H NMR (CD3OD): d 8.85 (d, 4 H, 3J = 8.1), 8.52 (s, 4 H), 8.41 (t, 2 H, 3J = 8.2), 6.91 (s, 4 H), 3.21 (d, 8 H), 2.64 (m, 4 H), 2.56 (dd, 4 H, 3J = 5.6, 4J = 5.6), 2.29 (m, 4 H), 1.30 (s, 12 H), 1.23 (d, 4 H, 3J = 9.6 Hz) and 0.29 (s, 12 H). 13C-{1H} NMR (CD3OD): d 157.83, 157.13, 149.37, 149.29, 148.08, 137.01, 125.40, 124.14, 41.07, 39.94, 34.19, 31.89, 26.04 and 21.44. FAB (3-nitrobenzyl alcohol): m/z = 979, [M 2 Cl]1; and 944 [M 2 2 Cl]1 (Found: C, 60.66; H, 6.87; N, 7.14. Calc. for C58H62Cl2N6Ru 1 7 H2O: C, 61.05; H,670 J. Chem. Soc., Dalton Trans., 1999, 667–675 Table 1 Shifts of protons of the unsubstituted trpy unit upon complexation in [Ru(trpy)2]21 and in [Ru(trpy)(L1(2))]21. The solvent for the complexes is CD3CN.For free trpy CDCl3 was used as solvent trpy [Ru(trpy)2]21 Dd [Ru(trpy)(L1)]21 Dd 39 8.44 8.73 10.29 8.63 10.19 49 7.94 8.39 10.45 8.39 10.45 99 8.68 7.32 21.36 7.58 21.10 109 7.31 7.14 20.17 7.27 20.04 119 7.84 7.90 10.06 7.93 10.09 129 8.60 8.47 20.13 8.48 20.12 6.66; N, 7.37%). a (589 nm, 20 8C, 0.226 mg in 2 mL of EtOH) = 15048. [Ru(L1(2))(L1(1))][PF6]2 11. This was obtained from [Ru(L1(2))Cl3] by adding L1(1) in equimolar amounts using ethylene glycol and microwave heating. However, the product was obtained as a statistical mixture of [Ru(L1(2))2][PF6]2, [Ru(L1(1))2][PF6]2 and [Ru(L1(2)(L1(1))][PF6]2 (1:1:2).Other solvents with milder conditions (refluxing in EtOH–water) always led to the statistical mixture. Separation of the diastereomers was unsuccessful. 1H NMR (CD3CN): d 8.61 [d, 2 H, H(3)]; 8.31 [dd, 1 H, H(4)]; 8.26 [d, 2 H, H(12)]; 7.48 [d, 2 H, H(11)]; 2.69 [dd, 2 H, H(16)]; 2.35 [ddd, 2 H, H(15b)]; 2.01 [d, 4 H, H(13a/13b)]; 1.78 [m sept, 2 H, H(14)]; 1.15 [s, 6 H, H(19)]; 0.61 [d, 2 H, H(15a)]; and 20.01 [s, 6 H, H(18)].X-Ray crystallography Details of the crystal parameters, data collection and refinement are given in Table 6. The structures were solved by direct methods and refined by the full-matrix least-squares method on all F data, except for [Rh(L1(2))Cl3] which was refined on all F 2 with an extinction correction to all Fc data. No absorption corrections were applied for [Ru(L1(2))Cl3] and [Ru(trpy)- (L2(2))][PF6]2 For [Rh(L1(2))Cl3] no suitable y scans could be measured, and only one equivalent of data was obtained.With m = 1.02 mm21 and a reasonably low residual electron density (1.162/21.011 e A3) no absorption correction was applied. All crystals were stable during the measurements. The H atoms were located on Fourier diVerence maps, but introduced in idealized positions [d(CH) = 0.96 Å] and their atomic coordinates recalculated after each cycle.They were given isotropic thermal parameters 20% higher than those of the carbon to which they are attached. The absolute configurations for all resolved compounds were examined by refining Flack’s parameter x. The absolute configuration cannot be determined reliably for L2(2), whereas for all other compounds the x value is in accord with the absolute configuration expected from the synthetic route. CCDC reference number 186/1310. See http://www.rsc.org/suppdata/dt/1999/667/ for crystallographic files in .cif format. Apparatus and chemicals used For the synthesis of reactants solvents of Fluka purum grade quality were used without further treatment.For spectroscopic purposes, acetonitrile from Aldrich (puriss. for spectroscopy) was used. The compound RuCl3?3H2O (Johnson Matthey) was used as ruthenium source. The NMR spectra were recorded using Bruker AM-250 (250 MHz), Varian Gemini300 (300 MHz) and Bruker DRX500 (500 MHz) spectrometers. The chemical shift values are reported relative to tetramethylsilane.The 2-D COSY and heteronuclear correlation (HETCOR) spectra as well as NOE were obtained according to standard procedures, MS (FAB) spectra on a VG Instruments 7070E spectrometer or with a quadripolar Nermag R10-10H instrument (3-nitrobenzyl alcohol matrix). Elemental analyses were performed by LCC (Laboratoire de Chimie de Coordination) Microanalytical Service. The UV-VIS absorption was determined using a Perkin-Elmer Lambda 5 spectrophotometer with 1 cm quartz cells.Column chromatography purification was performed with 70–200 mm Silica gel or on Sephadex LH20 (Pharmacia). For thin layer chromatography silica gel plates (Merck 60 F254) were used. Optical rotations were measured on a Perkin-Elmer polarimeter 241. The CD spectra were measured on a Dichrograph Mark 5 from Yobin Ivon in a 1 cm quartz cell. Crystal structures were measured on Stoe IPDS and on Stoe-Siemens four-circle AED-2 diVractometers (graphite-monochromated Mo-Ka radiation).Results and discussion Synthesis The Kröhnke condensation 22 of chiral b-unsaturated ketones or aldehydes opens an eYcient way to chiral terpyridines and their metal complexes. Microwave heating aVorded quantitatively bis(terpyridyl)ruthenium(II) complexes of high purity, with typical heating times of only 2–4 min. This procedure shows great advantages over previously reported synthetic methods for the preparation of such complexes in boiling aqueous ethanol.23–25 As an example, for the preparation of [Ru(trpy)2][PF6]2 the yield decreased from 86 (ethylene glycol, 4 min, 375 W) to 65 (ethanol, 3 h) or 21% (DMF, 3 h).It is known that pineno-fused bipyridines can be linked stereoselectively 12,27 by formally substituting H(13). Methylation of L1(2) yields only one diastereoisomer. Ligands of this type are presently being studied and will be reported elsewhere. NMR Table 1 shows relevant protons of the trpy unit with their chemical shifts for the ‘free’ and complexed ligand in [Ru(trpy)2]21 and in [Ru(trpy)(L1(2))]21.The chemical shift of certain protons is highly diagnostic for their environment. In [Ru(trpy)2]21 the proton 99 lies above the plane of the central pyridine ring of the other orthogonal ligand and is thus shifted upfield. In [Ru(trpy)(L1(2))]21 the shielding is less eYcient, which may indicate that proton 99 is pushed away from the face of the opposing central pyridine ring, probably due to the Fig. 1 The NMR signals of a statistical mixture of D2 and S4 symmetric [Ru(L1)2][PF6]2 for the aliphatic protons 15a and 18.J. Chem. Soc., Dalton Trans., 1999, 667–675 671 Table 2 Shifts of protons of free L1(2) as compared with those of [Ru(L1(2))2]21, [Ru(trpy)(L1(2))]21 and [Ru(L1(2)(L1(1))]21; CD3CN was used as solvent L1(2) [Ru(trpy)(L1(2))]21 Dd [Ru(L1(2))2]21 Dd [Ru(L1(2)(L1(1))]21 Dd 3 8.28 8.71 10.43 8.61 10.33 8.61 10.33 4 7.88 8.34 10.46 8.32 10.44 8.31 10.43 13a/b 3.20 1.73 21.47 2.01 21.15 2.01 21.15 14 2.40 1.71 20.69 1.78 20.62 1.78 20.62 15a 1.31 0.70 20.61 0.84 20.57 0.61 20.70 15b 2.70 2.31 20.39 2.34 20.36 2.35 20.35 16 2.81 2.63 20.18 2.69 20.12 2.69 20.12 18 0.68 20.14 20.82 20.14 20.82 20.01 20.69 19 1.41 1.13 20.28 1.16 20.25 1.15 20.26 crowding of the pinene groups of the other ligand.The protons 39 and 49 are slightly shifted downfield upon complexation due to their position in the deshielding plane of the two terminal pyridine rings of the orthogonal ligand.The protons 13a/b, 14, 15a/b, 18 and 19 of L1(2) lie above the plane of the central aromatic pyridine ring and are therefore considerably shifted upfield (Table 2, Fig. 1). In a 1 : 1 complex the protons 13a/b, 15a/b and 19, however, would not be so much shifted as compared to those of the 2 : 1 complex. This is clearly the case for [Rh(L1(2))Cl3]. For the complex [Ru(trpy)(L2(1))]21 the chemical shifts of the aliphatic protons of L2 are much closer to those of free L2 and the upfield shift is less pronounced due to the fact that the pinene group will not come close to the deshielding plane of the orthogonal pyridyl moiety. Electronic spectra The electronic spectra of all complexes (Figs. 2–5, Table 4) are characterized by intense absorptions between 200 and 380 nm attributed to p æÆ p* transitions associated with the aromatic rings of the ligand. Metal to ligand charge transfer (MLCT) Fig. 2 Ligand centered absorption of trpy (a), L1(2) (b), [Ru(trpy)(L1(2))]21 (c), [Ru(trpy)2]21 (d), and [Ru(L1(2))2]21 (e) in acetonitrile (1 × 1025 M). Fig. 3 The CD-spectra of trpy (a), L1(2) (b), [Ru(trpy)(L1(2))]21 (c) and [Ru(L1(2))2]21 (d) in acetonitrile (1 × 1025 M). transitions are observed for the ruthenium complexes at around 450 nm. The absorption spectra of L1(2), [Ru(trpy)2]21, [Ru(trpy)(L1(2))]21 and [Ru(L1(2))2]21 (Fig. 2) show components in the ligand centered absorptions which can be attributed to short and long axis polarized p æÆ p* transitions.For L1(2) C2 symmetry, the long axis transition transforms as A, the short axis transition as B, in trpy as A1 and B1, respectively. ZINDO Calculations (INDO/1 parameterization,27 active space for singlet/triplet CI within 38 orbitals lying below and above the HOMO/LUMO pair) indicate that the lowest lying Fig. 4 The CD spectra of [Ru(L1(1))2]21 (a) and [Ru(L1(2))2]21 (b) in acetonitrile (1 × 1025 M) and of [Ru(trpy)(L2(1))]21 (c) and [Ru(trpy)(L2(2))]21 (d) in Tris buVer.Fig. 5 Absorption (a,b) and circular dichroism spectra (c,d) of the MLCT transition of [Ru(trpy)(L1(2))]21 (dashed line) and [Ru(L1(2))2]21 (full line) in acetonitrile (2 × 1024 M).672 J. Chem. Soc., Dalton Trans., 1999, 667–675 Table 3 Calculated versus experimental transitions for trpy and L1(2). The main single determinants after CI are listed in brackets Trpy L1(2) Short-axis polarized Long-axis polarized Long-axis polarized Calc.(l/nm, f a) 215 (0.32) |1A1;a2(p) æÆ a2(p*)Ò 274 (0.29) |1B1;a2(p) æÆ b2(p*)Ò Measured (l/nm, e/M21 cm21) 236 (38400) 260 (20200) Calc. (l/nm, f a) 297 (0.52) |1A1;a2(p) æÆ a2(p*)Ò 266 (0.58) |1B1;b2(p) æÆ a2(p*)Ò 315 (0.45) |1B1;a2(p) æÆ b2(p*)Ò Measured (l/nm, e/M21 cm21) 289 (sh) 300 (55000) 278 (45000) 258 (34000) 296 (52000) 318 (sh) a f is oscillator strength. Table 4 Possible MLCT and LC transitions in for a D2d symmetrical d6 complex [Ru(trpy)2]21 MLCT LC Transitions b2 æÆ b1 b2 æÆ e b2 æÆ a2 a2 æÆ e a2 æÆ b1 a2 æÆ a2 b1 æÆ e b1 æÆ b1 Corresponding states A1 æÆ A2 A1 æÆ E A1 æÆ B1 A1 æÆ E A1 æÆ B2 A1 æÆ A1 A1 æÆ E A1 æÆ A1 Transitions e æÆ b1 e æÆ e e æÆ a2 b1 æÆ a2 e æÆ e e æÆ b1 e æÆ a2 Corresponding states A1 æÆ E A1 æÆ A1, A2, B1, B2 A1 æÆ E A1 æÆ B2 A1 æÆ A1, A2, B1, B2 A1 æÆ E A1 æÆ E p æÆ p* transitions [260 nm for trpy, 296 nm for L1(2)] are long axis polarized (Table 3).The corresponding MO scheme of [Ru(trpy)2]21 is depicted in Fig. 6.For all metal complexes the LC transitions are shifted to lower energy as compared to those of ‘free;’ ligand due the positive charge of the central metal, which increases the energy of the lowest p orbital of the ligand. This behavior was also observed for complexes of the tris-(bipyridyl) type.28 The MLCT transitions carry large intensities if the electron flow is parallel to the electric dipole moment.29 The electron flow during a MLCT transition is directed along the S4 axis (z axis) which transforms as B2.Therefore, the most intense MLCT transition is attributed to |1B2;e(dxy,dyz) æÆ e(p*)Ò.30,31 Emission properties have not been investigated in detail. At room temperature no emission is detectable as the excited state lifetimes of ruthenium(II) bis(terpyridyl) complexes are expected to be very short, i.e. for [Ru(trpy)2]21 t = 250 ps in water.32 CD Spectra Cotton eVects can be conveniently classified into three types by considering the symmetry properties and the nature of the Fig. 6 Qualitative MO scheme of [Ru(trpy)2]21 (D2d) and trpy (C2v). chromophores and their transitions: (I) from inherently achiral chromophores which are asymmetrically perturbed; (II) from inherently chiral chromophores; (III) due to dipole–dipole interactions between more than two chromophores, the orbitals of which do not mutually overlap. The amplitudes of Cotton eVects of type I are usually very small.Free L1 or L2 is such a case where a chiral substituent imposes a dissymmetric environment. The CD spectrum of L1(2) [Fig. 3(a)] is similar to those of (1)-a-pinene and other pyridines with pinene groups attached.12 However in the case of the reported complexes with L1, stronger CD in the LC absorptions indicates that eVects of type II or III must be present (Fig. 3). All enantiomeric pairs show mirror image CD as exemplified in Fig. 4. As crystal structure analyses of [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] show (Fig. 7), a helical distortion of the ligand p system occurs upon complexation, which is less pronounced in the complex [Ru(trpy)(L2(2))][PF6]. (Fig. 8). In free L1 the pyridyl moieties have a low energy barrier for rotation around the 2,29 and 29,60 bonds, whereas upon complexation rotation is excluded and the ligand is forced to take a helically distorted geometry. As a result of this helicity, all MLCT transitions show significant CD, which would not be present if the two ligand p systems were planar and strictly perpendicular (even though with chiral substituents) to each other.The sign of the CD bands of MLCT transitions can be derived from symmetry consideration of the orbitals involved. The condition to observe for rotational strength is ·a|m Æ|bÒ·a|mÆ |bÒ � 0. The z-axis directed MLCT transition in D2d |1B2;e(dxy,dyz) æÆ e(p*)Ò that carries most intensity becomes |1B1;b(dxy,yz) æÆ b(p*)Ò in D2 and |1A;b(dxy,yz) æÆ b(p*)Ò in C2, respectively, and in both cases transforms as Rz.Therefore these transitions also have non-zero rotational strengths. The sign of the CD of z-axis polarized transitions being only a function of the helicity of the p orbital involved, one finds that a left handed helical arrangement as in the crystal structure of [Ru(L1(2))Cl3] (Fig. 7) leads to a left handed charge displacement corresponding to a negative CD. This is observed for the strongest MLCT transitions of these complexes, which are therefore tentatively assigned to |1B1;b((dxz,yz) æÆ b(p*)Ò (Fig. 5). The CD activity in the LC transitions of bis(terpyridyl) complexes (Fig. 3) mainly arise from exciton coupling 33 between two intraligand transitions or between two diVerent terpyridyl ligands which have nonorthogonal transition dipole moments d to the out of plane distortion of the terpyridyl moiety. From the CD and UV-VISJ. Chem. Soc., Dalton Trans., 1999, 667–675 673 spectra the exciton splitting is determined to be around 1000 cm21 for the long axis polarized transition at around 315 nm (Fig. 3) of [Ru(L2)2]21. The observed Cotton eVect is consistent with a ligand geometry as found in [Ru(L1(1))Cl3] (Fig. 7). As the terpyridyl ligand L2 is somewhat less distorted in the ruthenium complexes than is the ligand L1, CD values recorded for [Ru(L2)2]21 and [Ru(trpy)(L2)]21 (Fig. 4) are smaller than those of [Ru(L1)2]21 and [Ru(trpy)(L1)]21. Therefore, we conclude that the transitions observed are due to the intrinsic helical arrangement of the ligand fixed at a metal center.Cyclic voltammetry In comparison to [Ru(trpy)2]21, the oxidation potentials of [Ru(trpy)(L1(2))]21 and [Ru(L1(2))2]21 are slightly increased Fig. 7 Molecular views of [Ru(L1(2))Cl3] (with hydrogens) and [Rh(L1(2))Cl3] (without hydrogens) with 50% probability thermal ellipsoids depicted. (Table 5). It is also evident that the first reduction in [Ru(trpy)(L1(2))]21 occurs in the trpy moiety since its reduction potential is equivalent to that of [Ru(trpy)2]21.The ligand L1(2) is a slightly weaker p* acceptor with respect to trpy and it has therefore a slightly lower reduction potential. Crystallographic data Selected bond lengths, angles and dihedral angles of [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] are given in Table 7, lengths and angles of [Ru(trpy)(L2(2))][PF6]2 in Table 8. The molecular structures of [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] are shown in Fig. 7. The helical out of plane distortion of the terpyridyl moiety is evident. The twisting angle between the two distant pyridine rings is 32 and 318 for the two complexes and the absolute configuration of these two rings can be denoted as L using the IUPAC designation for a pair of skew lines. The molecular structures of L2(2) and [Ru(trpy)(L2(2))]Cl2 with the atom numbering schemes are shown in Fig. 8. That of L2(2) possesses a twofold axis relating two asymmetric units through N(1) and C(3).The main part of the molecule is planar with the largest deviation being 0.168 Å at N(1). Only the C atoms of the pinene fragment are out of the plane with C(11) and C(13) being away from it by 1.13 and 21.10 Å. The cation [Ru(trpy)(L2(2))]21 adopts a six-coordinate geometry with a mer conformation of the two terpyridyl ligands which make a dihedral angle of 95.28. The distances between Ru and the central N(1) or N(4) atoms, 1.982(6) and 1.957(6) Å respectively, are significantly shorter than the values observed for the other Ru–N bonds, 2.065 Å (mean), and are comparable with the distances in [Ru- (L1(2))Cl3].Conclusion Mono- or bis- 2,29;69,60-terpyridyl complexes of octahedral co-ordination centers have often been considered to be valuable alternatives to bis- or tris-diimine complexes, because the problem of chirality, leading to isomeric mixtures in synthesis, can be avoided.This is due to the fact that terpyridyl ligands can co-ordinate exclusively in a meridional way in an Table 5 Electrochemical data for [Ru(trpy)2]21, [Ru(trpy)(L1(2))]21 and [Ru(L1(2))2]21 Complex [Ru(trpy)2]21 [Ru(trpy)(L1(2))]21 [Ru(L1(2))2]21 E0/V 1.28 (0.09) 1.31 (0.10) 1.34 (0.10) E1/DE 21.27 (0.08) 21.26 (0.08) 21.37 (0.08) E2/V 21.52 (0.10) 21.64 (0.10) 21.67 (0.10) Ia/Ic 0.98 0.95 0.85 Fig. 8 Molecular views of L2(2) and [Ru(trpy)(L2(2))][PF6]2 with 30% probability thermal ellipsoids depicted.674 J.Chem. Soc., Dalton Trans., 1999, 667–675 Table 6 Crystallographic data of L2(2), [Ru(trpy)(L2(2))][PF6]2 8a, [Ru(L1(2))Cl3] 2 and [Rh(L1(2))Cl3] 3 Molecular formula Molecular weight Crystal system Space group a/Å b/Å c/Å V/Å3 ZT /K m/mm21 No. reflections measured No. unique reflections Rint Flack’s parameter Final R values Goodness of fit L2(2) C29H31N3 421.63 Orthorhombic P21221 6.5893(9) 9.080(1) 19.494(4) 1167.0(2) 2 293(2) 0.066 7285 1783 0.032 R(F) = 0.0363 wR(F) = 0.0317 1.054 8a C44H42F12N6P2Ru 1045.91 Orthorhombic P212121 9.508(1) 12.745(2) 37.781(4) 4578(1) 4 293(2) 0.489 16335 4800 0.059 0.03(5) R(F) = 0.0440 wR(F = 0.0499 1.130 2 C32H37Cl3N3ORu 687.10 Orthorhombic P212121 7.9867(7) 15.6250(13) 25.199(2) 3144.6(4) 4 180(2) 0.77 20175 4945 0.0431 20.03(4) R(F) = 0.0217 wR(F) = 0.0244 1.063 3 C29H31Cl3N3Rh 630.85 Orthorhombic P212121 7.9810(10) 15.571(2) 24.630(2) 3060.8(6) 4 193(2) 1.02 3075 3072 0 20.05(5) R(F2) = 0.0396 wR(F 2) = 0.1020 1.101 octahedral complex.Monoterpyridyl complexes therefore have inherently C2V symmetry, bis(terpyridyl) complexes D2d, both achiral symmetry groups. The chiral terpyridyl ligands that are introduced here reduce these symmetries to C2 and D2, respectively (at least for the bis-homochiral terpyridine complex). Since the synthesis of the chiral terpyridyl ligands, derived from that of the earlier published and very versatile method for bipyridine derivatives, yields enantiopure material from natural products, the problem of isomeric mixtures does not occur any more, even though the resulting complexes are chiral.This fact adds a new dimension to the chemistry of octahedral complexes with terpyridyl ligands. For chiral structures, additional spectroscopic information is available from CD spectra. There is also a possibility to study interactions of such complexes with other chiral structures and finally there might be the possibility to build up relatively large linear structures that have a “chiral twist”.The introduction of the chiralized terpyridyl ligands, opens up the already quite varied chemistry of terpyridyl Table 7 Selected bond lengths (Å), angles and angles between the planes of the pyridyl moieties (8) for [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] where P2 and P3 denote the outer pyridine ring with N(2) and N(3) respectively, P1 the central pyridine ring with N(1) M–Cl(1) M–Cl(2) M–Cl(3) M–N(1) M–N(2) M–N(3) Cl(1)–M–Cl(2) Cl(1)–M–Cl(3) Cl(1)–M–N(1) Cl(1)–M–N(2) Cl–M–N(3) Cl(2)–M–Cl(3) Cl(2)–M–N(1) Cl(2)–M–N(2) Cl(2)–M–N(3) Cl(3)–M–N(1) Cl(3)–M–N(2) Cl(3)–M–N(3) N(1)–M–N(2) N(1)–M–N(3) N(2)–M–N(3) P1/P2 P1/P3 P2/P3 [Ru(L1(2))Cl3] 2.3729(14) 2.3331(16) 2.3365(16) 1.942(5) 2.110(5) 2.111(5) 91.09(6) 92.00(6) 179.66(16) 99.89(14) 100.03(15) 176.82(6) 88.74(16) 89.86(14) 88.97(14) 88.17(16) 90.30(14) 89.80(14) 79.82(21) 80.25(21) 160.07(20) 14.9(3) 18.8(3) 32.0(3) [Ru(L1(2))Cl3] 2.3794(6) 2.3322(7) 2.3504(7) 1.967(2) 2.147(2) 2.139(2) 93.04(2) 92.29(2) 179.70(6) 100.78(6) 100.37(6) 174.66(3) 86.85(6) 89.64(6) 89.05(6) 87.82(6) 89.14(6) 90.21(6) 79.51(9) 79.34(9) 158.85(8) 18.85(13) 13.08(13) 30.72(13) complexes using these ligands which introduce a well defined chiral element.Acknowledgements We thank Dominique Suhr for assistance in the synthesis of ligand L1(1), Dr Catherine Verchère-Béaur for measuring CD spectra of [Ru(trpy)(L2)]Cl2, Professor Peter Belser for advice concerning the synthesis of ruthenium complexes, and Professor R.Chauvin for fruitful discussion. The Swiss National Science Foundation and the Centre National de la Recherche Scientifique are acknowledged for financial support. References 1 J.-P. Collin, P. Gavina, V. Heitz and J.-P. Sauvage, Eur. J. Inorg. Chem., 1998, 1, 1. 2 E. C. Constable and A. W. C. Thompson, J. Chem. Soc., Dalton Trans., 1992, 2947. 3 J. P. Collin, S.Guillerez, J. P. Sauvage, F. Barigelletti, L. D. Cola, L. Flamigni and V. Balzani, Inorg. Chem., 1991, 30, 4230. 4 B. J. Coe, D. W. Thomson, C. T. Culbertson, J. R. Schoonover and T. J. Meyer, Inorg. Chem., 1995, 34, 3385. 5 D. J. Cardenas, P. Gavina and J. P. Sauvage, Chem. Commun., 1996, 1915. 6 G. S. Hanan, C. R. Arana, J. M. Lehn, G. Baum and D. Fenske, Chem. Eur. J., 1996, 2, 1292. 7 L. M. Scolaro, A. Romeo and A. Terracina, Chem. Commun., 1997, 1451. 8 V. Grosshenny, A.Harriman, M. Hissler and R. Ziessel, Platinum Metals Rev., 1996, 40, 72. 9 F. Barigelletti, L. Flamigni, V. Balzani, J.-P. Collin, J.-P. Sauvage and A. Sour, New J. Chem., 1995, 19, 793. 10 H. M. Brothers and N. M. Kostic, Inorg. Chem., 1988, 27, 1761. Table 8 Interatomic distances (Å) and angles (8) for [Ru(trpy)- (L2(2))][PF6]2 Ru(1)–N(1) Ru(1)–N(2) Ru(1)–N(3) N(1)–Ru(1)–N(2) N(1)–Ru(1)–N(3) N(2)–Ru(1)–N(3) N(1)–Ru(1)–N(4) N(2)–Ru(1)–N(4) N(3)–Ru(1)–N(4) N(1)–Ru(1)–N(5) N(2)–Ru(1)–N(5) 1.982(6) 2.066(6) 2.064(6) 78.7(3) 79.7(3) 158.4(3) 177.5(3) 103.9(3) 97.7(2) 101.0(3) 89.4(2) Ru(1)–N(4) Ru(1)–N(5) Ru(1)–N(6) N(3)–Ru(1)–N(5) N(4)–Ru(1)–N(5) N(1)–Ru(1)–N(6) N(2)–Ru(1)–N(6) N(3)–Ru(1)–N(6) N(4)–Ru(1)–N(6) N(5)–Ru(1)–N(6) 1.957(6) 2.073(7) 2.057(6) 95.5(2) 79.0(3) 101.0(3) 92.9(2) 90.3(3) 79.0(3) 157.9(3)J. Chem.Soc., Dalton Trans., 1999, 667–675 675 11 H. Shirai, K. Hanabusa, Y. Takahashi, F. Mizobe and K. Hanada, PCT Int. Appl., WO 94 14440 (Cl. A61K31/44), 7 July 1994, JP Appl. 92/348, 684, 28 Dec 1992, (Chem. Abstr., 121: 195935f). 12 N. C. Fletcher, F. R. Keene, M. Ziegler, H. Stoeckli-Evans, H. Viebrock and A. Von Zelewsky, Helv. Chim. Acta, 1996, 79, 1192. 13 H. Mürner, P. Belser and A. Von Zelewsky, J. Am. Chem. Soc., 1996, 118, 7989. 14 H. Mürner, G. Hopfgartner and A. Von Zelewsky, Inorg. Chim. Acta, 1998, 271, 36. 15 P. Hayoz, A. Von Zelewsky and H. Stoeckli-Evans, J. Am. Chem. Soc., 1993, 115, 5111. 16 E. C. Constable, T. Kulke, M. Neuburger and M. Zehnder, Chem. Commun., 1997, 489. 17 (a) R. Glaser, Chirality, 1993, 5, 272; (b) A. Horeau, personal communication and Collège de France lectures; (c) K. Mislow, Bull. Soc. Chim. Fr., 1994, 131, 534. 18 B. P. Sullivan, J. M. Calvert and T. J. Meyer, Inorg. Chem., 1980, 19, 1404. 19 E. C. Constable, J. Chem. Soc., Dalton Trans., 1985, 2687. 20 E. D. Mihelich and D. J. EickhoV, J. Org. Chem., 1983, 48, 4135. 21 R. K. De Richter, M. Bonato, M. Follet and K. Jean-Marc, J. Org. Chem., 1990, 55, 2855. 22 F. Kröhnke, Synthesis, 1976, 1. 23 D. Rose and G. Wilkinson, J. Chem. Soc., A., 1970, 1791. 24 T. J. Meyer and J. N. Braddock, J. Am. Chem. Soc., 1973, 95, 3158. 25 M. L. Stone and G. A. Crosby, Chem. Phys. Lett., 1981, 79, 169. 26 P. Hayoz and A. Von Zelewsky, Tetrahedron Lett., 1992, 33, 5165. 27 W. P. Anderson, T. R. Cundari, R. S. Drago and M. C. Zerner, Inorg. Chem., 1990, 29, 1. 28 I. Hanazaki and S. Nagakura, Inorg. Chem., 1969, 8, 648. 29 P. Day and N. J. Sanders, J. Chem. Soc. A, 1967, 1536. 30 C. Daul, C. W. Schlaepfer, A. Goursot, E. Penigault and J. Weber, Chem. Phys. Lett., 1981, 78, 304. 31 C. Daul and J. Weber, Chem. Phys. Lett., 1981, 77, 593. 32 J. R. Winkler, T. L. Netzel, C. Creutz and N. J. Sutin, J. Am. Chem. Soc., 1987, 109, 2381. 33 M. Ziegler and A. Von Zelewsky, Chem. Coord. Rev., 1998, in the press. Paper 9/00194H