16- and 18-Electron Ruthenium(II) Complexes of the Neutral, Potentially Tridentate Triamine Ligand 2,6-[Bis(dimethylamino)methyl]pyridine (NN‘N)

The potentially tridentate coordinating ligands NN ‘ N (2,6-bis[(dimethylamino)methyl]pyridine) and PNP (2,6-bis[(diphenylphosphino)methyl]pyridine) react with [RuCl 2 (PPh 3 ) 3 ] to give [ mer, trans -RuCl 2 ( NN ‘ N )(PPh 3 )] ( 1 ) and [ mer, trans -RuCl 2 ( PNP )(PPh 3 )] ( 2 ), respectively. Complex 1 functions as a starting material for a variety of Ru[ NN ‘ N ] complexes. It reacts with either 1 or 2 equiv of AgOTf (OTf - = SO 3 CF 3 - ) to yield monocationic [RuCl( NN ‘ N )(PPh 3 )]OTf ( 3 ) and [RuOTf( NN ‘ N )(PPh 3 )]OTf ( 4 ), respectively. The molecular structure of 4 shows a pentacoordinated ruthenium(II) center with a square-pyramidal environment. The reaction of 1 with either 1 or 2 equiv of AgOTf in the presence of MeCN results in the formation of the six-coordinate mono- or dicationic complexes [ mer -RuCl(MeCN)( NN ‘ N )(PPh 3 )]X ( 6a ) (X = OTf - ) and [ mer, trans -Ru(MeCN) 2 ( NN ‘ N )(PPh 3 )](OTf) 2 ( 7 ), respectively. At 55 °C in acetonitrile, 1 converts quantitatively into 6b (X = Cl - ) which is isostructural with 6a . Reaction of polymeric [RuCl 2 (nbd)] n (nbd = 2,5-norbornadiene) with NN ‘ N under a nitrogen atmosphere leads to the formation of neutral, dinitrogen-bridged dimeric [(μ-N 2 )( mer, trans -RuCl 2 { NN ‘ N }) 2 ] ( 8 ). The dinitrogen ligand is readily replaced when 8 is treated with CO, giving the neutral complex [ mer, trans -RuCl 2 (CO)( NN ‘ N )] ( 9 ). The 16-electron complex 3 reacts with CO giving [ mer, cis -RuCl(CO) 2 ( NN ‘ N )]OTf ( 10 ), involving the formation of [RuCl(CO)( NN ‘ N )(PPh 3 )]OTf ( 11 ), followed by substitution of PPh 3 by a second CO molecule. This stepwise mechanism was confirmed by the isolation of 11 . The 16-electron complex 4 reacts with CO under the formation of monocationic [ mer -RuOTf(CO)( NN ‘ N )(PPh 3 )]OTf ( 12 ) and a number of unidentified complexes. In the presence of ethyl alcohol, 4 reacts with CO to give monocationic [ mer -RuOTf(CO)( NN ‘ N )(HOEt)]OTf ( 13 ). The X-ray crystal structures of 1, 4, 6a, 8, 11, and 13 are reported in abbreviated form.