Structure, Electronics and Reactivity of Ce(PNP) Complexes.

Synthetic methods for the coordination of the monoanionic bis[2-(diisopropylphosphino)-4-methylphenyl]amido (PNP) ligand framework to the cerium(III) cation have been developed and applied for the isolation of a series of {(PNP)Ce} and {(PNP)₂Ce} type complexes. The structures of the complexes were studied by X-ray diffraction and multinuclear NMR spectroscopy. We found that the cerium(III) ion can induce the elimination of one of the iPr groups at phosphorus to yield a new dianionic PNP tridentate framework (PNP^{- iPr}) featuring a phosphido-donor functionality, which is bound to the cerium ion with the shortest known Ce−P bond of 2.7884(14) Å for molecular compounds. The reaction of the complex [(PNP)Ce{N(SiMe₃)₂}₂] ( 1) with Ph₂CO gave the Ce-bound product of C−C coupling, ^-N(SiMe₃)SiMe₂CH₂-CPh₂O⁻, through the C−H bond activation of a SiMe₃ group. ³¹P NMR spectroscopy was used to estimate the presence of a vacant coordination position at the cerium ion in the Ce^III-PNP complexes by the examination of the δ(³¹P) shift recorded both in non-polar (C₆D₆) and polar ([D₈]THF) solvents. Moreover, ³¹P NMR spectroscopy was also found to be a useful tool for the estimation of the Ce−P bond distances in {(PNP)Ce^III} and {(PNP)₂Ce^III} systems. Electrochemical and computational studies for 1 and its lanthanum analogue containing a redox-innocent metal center revealed the stabilization of the Ce^III oxidation state by the PNP ligand. [ABSTRACT FROM AUTHOR]