Carbon−Oxygen Bond Formation at Metal(IV) Centers: Reactivity of Palladium(II) and Platinum(II) Complexes of the [2,6-(Dimethylaminomethyl)phenyl-N,C,N]-(Pincer) Ligand toward Iodomethane and Dibenzoyl Peroxide; Structural Studies of M(II) and M(IV) Complexes

Abstract

The presence of the [2,6-(dimethylaminomethyl)phenyl-N,C,N]- (pincer) ligand (NCN) in platinum(II) complexes has been used to generate stable organoplatinum(IV) complexes that model possible intermediates and reactivity in metal-catalyzed C−O bond formation processes. The complexes M(O2CPh)(NCN) [M = Pd (1), Pt (2)] were obtained by metathesis reactions from the chloro analogues, and although 1 does not react with dibenzoyl peroxide, 2 does so to form Pt(O2CPh)3(NCN) (3) as a model intermediate for the acetoxylation of arenes by acetic acid in the presence of palladium(II) acetate and an oxidizing agent. The complex Pt(O2CPh)(NCN) (2) reacts with iodomethane in a complex manner to form PtI(NCN) (6) and cis-Pt(O2CPh)2Me(NCN) (7). Complex 7 decomposes to form Pt(O2CPh)(NCN) (2) and MeO2CPh, probably via benzoate dissociation followed by nucleophilic attack by the benzoate ion at the PtIV-Me carbon atom. The Pd(II) analogue Pd(O2CPh)(NCN) (1) reacts with MeI to give PdI(NCN) (8) and MeO2CPh, for which the potential intermediacy of Pd(IV) species could not confirmed by 1H NMR spectroscopy. The complex PtTol(NCN) (4) (Tol = 4-tolyl) reacts with (PhCO2)2 to form cis-Pt(O2CPh)2Tol(NCN) (5), but, unlike the PtIVMe analogue 7, the PtIVTol complex 5 does not undergo facile C−O bond formation. X-ray structural studies of the isostructural square-planar complexes M(O2CPh)(NCN) (1, 2) and of the octahedral Pt(IV) complexes as solvates 3·1/2Me2CO, 5·Me2CO, and 7·Me2CO·H2O are reported. Complexes 5 and 7 have cis-PtC2 and cis-Pt(O2CPh)2 configurations.