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

The formation of ruthenium amidophosphine complexes was accomplished by the addition
of [P2N2]Li2(Diox) (where P2N2 is PhP(CH2SiMe2NSiMe2CH2)2PPh and Diox is 1,4-dioxane)
to [RuCl2(cod)]x to generate [P2N2]Ru(cod), or to RuCl2(PPh3)3 to generate [P2NNH]Ru(C6H4PPh2). In the former complex, the Ru(II) center is in an octahedral environment perched
above the P2N2 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]Li2(THF)2 (where NPN is PhP(CH2SiMe2NPh)2) with [RuCl2(cod)]x results in the formation of two diastereomeric complexes of the formula [NPNH]Ru(η3:η2-C8H11), 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(SiMe3)2 generates a series of ruthenate complexes
of the formula [M(THF)]([NPN]Ru(η3:η2-C8H11)), where M = Li or Na. Addition of Me3SiCl
results in the formation of new diastereomers that contain silylated dangling arms, and
these diastereomers do not interconvert.