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.