Strained Ruthenium Complexes Bearing Tridentate Guanidine‐Derived Ligands

The dimer [{(η 6 ‐ p ‐cymene)RuCl} 2 ( μ ‐Cl) 2 ] (cymene=MeC 6 H 4 i Pr) reacts with N , N′ ‐bis( p ‐tolyl)‐ N′′ ‐(2‐pyridinylmethyl)guanidine ( H 2 L1 ) and N , N′ ‐bis( p ‐tolyl)‐ N′′ ‐(2‐diphenylphosphanoethyl)guanidine ( H 2 L2 ), in the presence of NaSbF 6 , giving rise to chlorido compounds of formula [(η 6 ‐ p ‐cymene)RuCl( H 2 L )][SbF 6 ] ( H 2 L = H 2 L1 ( 1 ), H 2 L2 ( 2 )) in which the guanidine ligand adopts a κ 2 chelate coordination mode. The related ligand ( S )‐ N , N′ ‐bis( p ‐tolyl)‐ N′′ ‐(1‐isopropyl, 2‐diphenylphosphano ethyl)guanidine ( H 2 L3 ) affords mixtures of the corresponding chlorido compound [(η 6 ‐ p ‐cymene)RuCl( H 2 L3 )][SbF 6 ] ( 3 ) together with the complexes [(η 6 ‐ p ‐cymene)RuCl 2 ( H 3 L3 )][SbF 6 ] ( 4 ) and [(η 6 ‐ p ‐cymene)Ru(κ 3 N , N′ , P‐ HL3 )][SbF 6 ] ( 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 AgSbF 6 rendering the cationic aqua‐complexes [(η 6 ‐ p ‐cymene)Ru( H 2 L )(OH 2 )][SbF 6 ] 2 ( H 2 L = H 2 L1 ( 5 ), H 2 L2 ( 6 ), H 2 L3 ( 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 NaHCO 3 renders the complexes [(η 6 ‐ p ‐cymene)Ru(κ 3 N , N′ , N′′ ‐ HL1 )][SbF 6 ] ( 8 ) and [(η 6 ‐ p ‐cymene)Ru(κ 3 N , N′ , P‐ HL )][SbF 6 ] ( HL = HL2 ( 9 ), HL3 ( 10 )), respectively, in which the HL ligand adopts a fac κ 3 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.