Intramolecular C−H and N−H Transfer by Ruthenium(II) Amidophosphine Complexes

Abstract

The formation of ruthenium amidophosphine complexes was accomplished by the addition of [P 2 N 2 ]Li 2 (Diox) (where P 2 N 2 is PhP(CH2SiMe2NSiMe2CH2)2PPh and Diox is 1,4-dioxane) to [RuCl 2 (cod)] x to generate [P 2 N 2 ]Ru(cod), or to RuCl 2 (PPh 3 ) 3 to generate [P 2 NNH]Ru(C 6 H 4 -PPh 2 ). In the former complex, the Ru(II) center is in an octahedral environment perched above the P 2 N 2 macrocycle having two formally anionic amido donors; in the latter complex, there is only one amido ligand with the other as an amine donor where the proton originates from the cyclometalated triphenylphosphine group. Reaction of the tridentate amidophosphine ligand precursor [NPN]Li 2 (THF) 2 (where NPN is PhP(CH 2 SiMe 2 NPh) 2 ) with [RuCl 2 -(cod)] x results in the formation of two diastereomeric complexes of the formula [NPNH]Ru(η 3 : η 2 -C 8 H 1 1 ), wherein the cyclooctadiene ligand has been deprotonated by the ancillary ligand to generate a cyclooctadienyl unit. These Ru(II) complexes are five-coordinate with a bidentate PN ligand and a dangling amine unit. The diastereomers are in equilibrium, as shown by variable-temperature NMR studies. The fluxional process that interconverts diastereomers involves proton transfer from the dangling amine arm to the amido unit, a process that equilibrates the two ends of the tridentate NPN ligand on the chemical time scale. Deprotonation of the amine arm by MN(SiMe 3 ) 2 generates a series of ruthenate complexes of the formula [M(THF)]([NPN]Ru(η 3 :η 2 -C 8 H 1 1 )), where M = Li or Na. Addition of Me 3 SiCl results in the formation of new diastereomers that contain silylated dangling arms, and these diastereomers do not interconvert.