SYNTHESES AND REACTIVITIES OF INDOLE AND INDOLYL COMPLEXES OF (CYMENE)RUTHENIUM(II)

The reaction of [(p-cymene)Ru(OTf)(2)](x) with a series of indoles has led to the synthesis of new Ru(II) indole complexes of the formula [(cymene)Ru(ind)](OTf)(2), where ind = indole (3a), 1-methylindole (3b), 2,3-dimethylindole (3c), and 2-methylindole (3d). Complex 3b has been characterized by an X-ray diffraction study. The complex crystallized in space group P2(1)/n with a = 16.180(3) Angstrom, b = 9.028(2) Angstrom, c = 18.827(4) Angstrom, beta = 109.54(2)degrees, V = 2591.7(9) Angstrom(3), and Z = 4. The structural study confirmed that the dication has a sandwich structure with parallel eta(6)-cymene and eta(6)-1-methylindole ligands. Complexes 3a, c, and d can be deprotonated at the indole nitrogen to form monocations [(cymene)Ru(indolyl)]OTf, 4a for indolyl, 4c for 2,3-dimethylindolyl, and 4d for 2-methylindolyl. The aqueous pK(a) values for the indole ligands in 3a, c, and d have been determined from titration data to be 7.71, 8.15, and 8.02, respectively. A tetraphenylborate salt of an indolyl derivative, [(cymene)-Ru(2,3-dimethylindolyl)]BPh(4), was obtained as a single crystal. The complex crystallized in space group C2/c with a = 40.050(14) Angstrom, b = 11.049(4) Angstrom, c = 16.778(6) Angstrom, beta = 109.70(3)degrees, and Z = 8. A preliminary X-ray diffraction study confirmed a sandwich structure with the indolyl ligand coordinated through the carbocyclic ring in an eta(6)-bonding mode. Complex 4c reacted with PdCl(2)PPh(3)(CH3CN) to form a heteronuclear complex, [(cymene)Ru(2,3-dimethylindolyl)PdCl(2)PPh(3)]OTf (5), in which the indolyl ligand undergoes eta(6)-coordination to ruthenium and eta(1)-N-coordination to Pd. The reaction of 4c with [CuOTf](2) . C6H6 led to the formation of a trinuclear product {[(cymene)Ru(2,3-dimethylindolyl)]Cu-2}(OTf)(3) (6), in which the copper ion is proposed to coordinate to two indolyl nitrogens. Reactions of 3, 4, and 6 with nucleophiles have been compared. Although the reactions of 3 and 4 gave complex mixtures of products, the reaction of 6 with LiAl(O-t-Bu)(3)H at -78 degrees C resulted in the clean formation of a single isomer, formulated as {[(cymene)Ru(2,3-dimethylindolyl-H-2)]Cu-2}(OTf) (7a). The latter is proposed to result from hydride addition to C4 in each indolyl ligand of 6.