Half-Sandwich Complexes Of Osmium Containing Guanidine-Derived Ligands

Pyridinyl- and phosphano-guanidino complexes of formula [(eta(6)-p-cymene)OsCl(H2L)](SIDF6] (cymene = MeC(6)H(4)iPr; H2L = N,N'-bis(p-Tolyl)-N ''-(2-pyridinylmethyl)guanidine, H(2)L1 (1) and N,N'-bis(p-Tolyl)-N ''(2-diphenylphosphanoethyl)guanidine, H(2)L2 (2)) have been prepared from the dimer ({(eta(6)-p-cymene) OsCl)(2) (mu-Cl)(2)] and H2L in the presence of NaSbF6. Treatment of complex 2 with HCl renders the phosphano-guanidinium complex [(eta(6)-p-cymene)OsCl2 (H3L2)][SbF6] (3). Compounds 1 and 2 react with AgSbF6 rendering the cationic aqua complexes [(eta(6)-p-cymene)Os(H2U(OH2)][SbF6](2) (H2L = H(2)L1 (4), H(2)L2 (5)). Addition of monodentate ligands L to compound 4 affords complexes of formula [(eta(6)-p-cymene)Os(H(2)L1)L][SbF6](2) (L = py (6), 4-(NHMe)py (7), CO (8), P(OMe)(3) (9)). Treatment of complexes 4 and 5 with NaHCO3 renders the monocationic complexes ((eta(6) -p-cymene)Os(kappa N-3,N',N ''-HL1)][SbF6] (10) and [(eta(6)-p-cymene)Os(kappa N-3,N'-HL2)][SbF6] (11), respectively, in which the HL ligand adopts a fac-kappa(3) coordination mode. The new complexes have been characterised by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1-4, 6, 8, and 11, by X-ray diffractometric methods. The phosphano-guanidino complexes 2 and 5 exhibit a temperature dependent fluxional process in solution. The new 18 electron complexes 1, 2, 6, and 8-10 are active catalysts for the Friedel-Crafts reaction between trans-beta-nitrostyrene and N-methyl-2- methylindole. Conversions greater than 90% were obtained. Proton NMR studies support a mechanism involving the Bronsted-acid activation of trans-beta-nitrostyrene through the NH functionalities of the coordinated guanidine ligands.