Half-sandwich complexes of osmium containing guanidine-derived ligands

Pyridinyl- and phosphano-guanidino complexes of formula [(η 6 - p -cymene)OsCl( H 2 L )][SbF 6 ] (cymene = MeC 6 H 4 iPr; H 2 L = 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 [{(η 6 - p -cymene)OsCl} 2 (μ-Cl) 2 ] and H 2 L in the presence of NaSbF 6 . Treatment of complex 2 with HCl renders the phosphano-guanidinium complex [(η 6 - p -cymene)OsCl 2 ( H 3 L 2 )][SbF 6 ] ( 3 ). Compounds 1 and 2 react with AgSbF 6 rendering the cationic aqua complexes [(η 6 - p -cymene)Os( H 2 L )(OH 2 )][SbF 6 ] 2 ( H 2 L = H 2 L1 ( 4 ), H 2 L2 ( 5 )). Addition of monodentate ligands L to compound 4 affords complexes of formula [(η 6 - p -cymene)Os( H 2 L1 ) L ][SbF 6 ] 2 ( L = py ( 6 ), 4-(NHMe)py ( 7 ), CO ( 8 ), P(OMe) 3 ( 9 )). Treatment of complexes 4 and 5 with NaHCO 3 renders the monocationic complexes [(η 6 - p -cymene)Os(κ 3 N , N ′, N ′′- HL1 )][SbF 6 ] ( 10 ) and [(η 6 - p -cymene)Os(κ 3 N , N ′, P - HL2 )][SbF 6 ] ( 11 ), respectively, in which the HL ligand adopts a fac -κ 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 -β-nitrostyrene and N -methyl-2-methylindole. Conversions greater than 90% were obtained. Proton NMR studies support a mechanism involving the Brønsted-acid activation of trans -β-nitrostyrene through the NH functionalities of the coordinated guanidine ligands. The osmium chemistry of guanidine derivatives is explored. The resulting complexes are active Brønsted-acid catalysts for the Friedel-Crafts reaction.