Strained Ruthenium Complexes Bearing Tridentate Guanidine-Derived Ligands

The dimer {(η⁶-p-cymene)RuCl}₂(μ-Cl)₂] (cymene=MeC₆H₄ⁱPr) reacts with N,N′-bis(p-tolyl)-N′′-(2-pyridinylmethyl)guanidine ( H₂L1 ) and N,N′-bis(p-tolyl)-N′′-(2-diphenylphosphanoethyl)guanidine ( H₂L2 ), in the presence of NaSbF₆, giving rise to chlorido compounds of formula (η⁶-p-cymene)RuCl( H₂L )]SbF₆] ( H₂L = H₂L1 ( 1 ), H₂L2 ( 2 )) in which the guanidine ligand adopts a κ² chelate coordination mode. The related ligand (S)-N,N′-bis(p-tolyl)-N′′-(1-isopropyl, 2-diphenylphosphano ethyl)guanidine ( H₂L3 ) affords mixtures of the corresponding chlorido compound (η⁶-p-cymene)RuCl( H₂L3 )]SbF₆] ( 3 ) together with the complexes (η⁶-p-cymene)RuCl₂( H₃L3 )]SbF₆] ( 4 ) and (η⁶-p-cymene)Ru(κ³N,N′,P- HL3 )]SbF₆] ( 10 ) which contain phosphano-guanidinium and phosphano-guanidinate ions acting as monodentate and tridentate ligand, respectively. Compounds 1 , 2 and mixture of 3 / 4 / 10 react with AgSbF₆ rendering the cationic aqua-complexes (η⁶-p-cymene)Ru( H₂L )(OH₂)]SbF₆]₂ ( H₂L = H₂L1 ( 5 ), H₂L2 ( 6 ), H₂L3 ( 7 )). These aqua-complexes exhibit a temperature-dependent fluxional process in solution. Experimental NMR studies and DFT theoretical calculations on complex 6 suggest that the process involves the exchange between two rotamers around one of the C?N guanidine bonds. Treatment of 5 – 7 with NaHCO₃ renders the complexes (η⁶-p-cymene)Ru(κ³N,N′,N′′- HL1 )]SbF₆] ( 8 ) and (η⁶-p-cymene)Ru(κ³N,N′,P- HL )]SbF₆] ( HL = HL2 ( 9 ), HL3 ( 10 )), respectively, in which the HL ligand adopts a fac κ³ coordination mode. The new complexes have been characterized by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1 , 2 , 5 , 9 and 10 , by X-ray diffractometric methods.