Chemistry of a new family of aryl ruthenium species incorporating α-diimine chelation and a pendant imine-phenol function

Abstract

The reaction of excess 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) with Ru(η²-RL)(PPh₃)₂(CO)Cl (1) has respectively furnished [Ru(η¹-RL)(PPh₃)₂(CO)(bpy)](PF₆) (2) and [Ru(η1-RL)(PPh₃)₂(CO)(phen)](PF₆) (3) in very good yield (η²-RL is C₆H₂O-2-CHNHC₆H₄R(p)-3-Me-5, η¹-RL is C₆H₂OH-2-CHNC₆H₄R(p)-3-Me-5 and R is H, Me, MeO, Cl). The chelation of bpy/phen is attended with the cleavage of Ru---O and Ru---Cl bonds and iminium-phenolato→imine-phenol prototropic shift. The carbon monoxide ligand is located syn to the phenolic oxygen in 2 and 3 as opposed anti in 1. The crystal and molecular structures of [Ru(η¹-HL)(PPh₃)₂(CO)(bpy)](PF₆)·CH₂Cl₂ (2(H)·CH₂Cl₂) and [Ru(η¹-ClL)(PPh₃)₂(CO)(phen)](PF6)·H₂O (3(Cl)·H₂O) are reported. In the lattice of 3(Cl)·H₂O, the water molecules form dimers (OO, 2.617(8) A). In the hydrogen bonded imine-phenol function the NO distance is 2.550(9) Å in 2(H)·CH₂Cl₂ and 2.581(7) Å in 3(Cl)·H₂O. The Rubpy fragment in 2(H)·CH₂Cl₂ along with the CO ligand and the metallated carbon atom define an equitorial plane from which the metallated aldimine fragment (pendant Ph excluded) is rotated by 39.1° due to interligand repulsion and the two Ru---P distances (2.384(3) and 2.456(3) Å) become significantly different. The repulsion also counteracts the trans influence of the metallated carbanionic site, the Ru---N bond trans to the site being shorter. The behaviour of 3(Cl)·H₂O is similar. In dichloromethane solution 2 and 3 display a quasireversible Ru^III/Ru^II cyclic voltammetric response with E_1/2 in the range 0.75-0.85 V versus SCE. The CO stretch in 2 and 3 is 30-40 cm^-1 higher than that in 1 due to the presence of dπ(Ru)-pπ(bpy/phen) back-bonding. The corresponding MLCT absorption (λ_max, ~470 nm) gives rise to fluorescence (λ_max, ~540 nm). The reaction of 2-(2-pyridyl)benzthiazole (pbt) with 1 has furnished [Ru(η¹-RL)(PPh₃)₂(CO)(pbt)](PF₆) (8) in which pbt is (N,N) chelated. The properties of 8 are generally similar to those of 2 and 3.