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)2 Ce} 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 Ph2 CO gave the Ce-bound product of C-C coupling, - N(SiMe3 )SiMe2 CH2 -CPh2 O- , through the C-H bond activation of a SiMe3 group. 31 P NMR spectroscopy was used to estimate the presence of a vacant coordination position at the cerium ion in the CeIII -PNP complexes by the examination of the δ(31 P) shift recorded both in non-polar (C6 D6 ) and polar ([D8 ]THF) solvents. Moreover, 31 P NMR spectroscopy was also found to be a useful tool for the estimation of the Ce-P bond distances in {(PNP)CeIII } and {(PNP)2 CeIII } systems. Electrochemical and computational studies for 1 and its lanthanum analogue containing a redox-innocent metal center revealed the stabilization of the CeIII oxidation state by the PNP ligand.